IMMpress Magazine: The Power of Mitochondria (Volume 11 Issue 2)

IMMpress Magazine Magazine of the Department of Immunology, University of Toronto

2023 | vol.11 no.2

Mitochondria-induced inflammation: the dark side of a cell's "powerhouse" Uncovering the secrets of mitochondria: the road to an anti-aging remedy Mitochondrial replacement therapy modifying in-vitro fertilization to combat mitochondrial disease

ISSN 2291-2398

9 772291 239001

HeLa cells stained with MitoSpy™️ Orange (yellow), fixed and permeabilized with 4% PFA and 0.1% Triton X-100 followed by staining with Cytochrome C Alexa Fluor®️ 647 (red) and DAPI (blue).

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IMMpress

About the Cover Small but mighty, mitochondria are double-membraned organelles that generate energy for our cells and power biological processes that keep us alive.

These potent bodies of energy received its famous name “powerhouse of the cell” in 1857 for their essential role in keeping our cells alive. Near the end of the century, another “powerhouse” was being discovered — the use of neon lights to generate light.

Drawing parallels between the two powerhouses — mitochondria and neon lights — the cover of this issue depicts mitochondria as a set of neon lights. Morphologically, the winding folds of the mitochondria are reminiscent of the bends of neon light tubes. Similar to the way neon lights illuminate the night life in busy metropolitan cities, mitochondria produce energy for cells to connect different processes for life. Both symbolizing the essence of life, their means of vitality are both rooted in the flow of electrons. As one can imagine the darkness in the absence of light, one can similarly imagine the immense power mitochondria hold should they malfunction.

Design notes In this issue, our designers used a wide range of colours to convey the many facets of mitochondria. From the use of photographs to illustrations, our talented team beautifully conveyed the complexity that is mitochondria. If there were creativity cells in our bodies, then our designers must have an abundance of mitochondria in those cells! With that, we would like to thank all of our designers for their beautiful contributions this issue.

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Copyright © 2013 IMMpress Magazine. All rights reserved.

Reproduction without permission is prohibited.

IMMpress Magazine is a student-run initiative. Any opinions expressed by the author(s) do not necessarily reflect the opinions, views or policies of the Department of Immunology or the University of Toronto.

EDITORS-IN-CHIEF James Pollock Karen Yeung DESIGN DIRECTOR Kitty Liu SOCIAL MEDIA COORDINATOR Tianning Yu SENIOR EDITORS Baweleta Isho Manjula Kamath Meghan Kates Steve Lee James Pollock Siu Ling Tai Deeva Uthayakumar Matthew Wong Karen Yeung Evey Zheng DESIGN ASSISTANTS Jennifer Ahn Philip Barbulescu Baweleta Isho Meggie Kuypers Kitty Liu Louis Ngai Deeva Uthayakumar Karen Yeung Tianning Yu Evey Zheng CONTENT CONTRIBUTORS Jennifer Ahn Rebecca Chau Baweleta Isho Manjula Kamath Meghan Kates Steve Lee Jinny Tsang Boyan Tsankov Alara Tuncer Sila Usta Deeva Uthayakumar Karen Yeung Evey Zheng FOUNDING EDITORS Yuriy Baglaenko Charles Tran

O

ne of the holy grails of medicine is a cure for aging, and it has been the inspiration of many myths and legends, such as the Elixir of Life, the Philosopher’s Stone, or the Fountain of Youth. Although lifespan can vary, aging is an inevitable outcome of virtually all animals. As we start to develop a better understanding of the underlying biological processes that contribute to aging, the quest for an anti-aging remedy becomes less of a myth and more of a reality.

can also impair the structural integrity of the cell. The release of ROS and cell debris following cell death into the extracellular space within a given tissue could also trigger inflammation. All in all, these processes result in a loss of efficiency in cell metabolism and cell death due to oxidative stress. The mitochondrial theory of aging, therefore, proposes that the accumulation of damaged biomolecules and subsequent mitochondria dysfunction leading to cell death, drives aging.

linked to visible signs of aging, such as grey hair and wrinkle formation.

Healthy mitochondria play an important role in providing energy to cells for tissue regeneration, which becomes less efficient with age, making elderly individuals more prone to injury and muscle weakening. In the semitendinosus muscle of elderly individuals, there is an increase in mitochondrial factors that induce cell death, which could explain the decline in functionality and muscle volume with age.

While it may be easy to believe how this elaborate tale of mitochondrial dysfunction, ROS release, and cell death could lead to aging, does this theory have any weight? How do we connect

As regular mitochondrial function becomes compromised, cells attempt to recycle these faulty mitochondria into healthy ones, a process that becomes less efficient with age. While healthy mitochondria may not be the only component required to extend lifespan, many of our long-lived animal counterparts, such as the bivalve mollusc, Arctica Icelandica, that can live >500 years, have extremely efficient mitochondria that produce limited toxic by-products. Can restoring mitochondrial function in humans be a possible remedy for aging?

CONTENTS VOL 11. NO 2. [2023] One of the most prominent theories of aging revolves around mitochondria, the main energy producers of cells. Each cell in our body possesses hundreds of these intracellular structures, which facilitate the reaction between carbohydrates and oxygen to produce ATP, the main energy molecule of the cell. They are also essential for helping the cell digest other nutrients, such as amino acids and lipids, and can act as a switch to initiate cell death. The mitochondrial theory of aging, therefore, proposes that a decline in mitochondrial function is one of the causal factors of aging.

10

AND THE F LIFE

8

concert to perform all the basic processes of energy production called mitochonary for these small cells to maintain the ar organisms carry mitochondria within arya, meaning “true nucleus”. Life before -celled organisms from the domains of e to this day. How do eukaryotes fit into ria come in?

ournal of Theoretical Biology, it is now bacteria that were acquired by a pre-euquisition of the endosymbiont bacteria by co-evolution of both species, leading to hylogenetic analyses currently place the the alphaproteobacteria family, and the ea. However, the exact nature of the first remains

BACTERIA

12

Peptidoglycan cell wall No histones

romosome

Uncovering the secrets of mitochondria The road to anti-aging remedy Mitochondrial replacement therapy Modifying in-vitro fertilization to combat mitochondrial disease

8 Mitochondria and the complexity of life 16 See a need, fill a need: an alumni interview with Dr. Sam Saibil 17 What’s in a name? Monkeypox to mpox — What’s the real aim?

28

• Nucleus Endomembrane system • Linear chromosome • Sex/meiosis • Mitochondria!

•

14

Popular health trends, such as caloric restriction and daily While most of a cell’s genetic physical activity, are emerging as information is stored within the efficient strategies to slow down nucleus as DNA, the mitochonmitochondrial aging and delay dria also harbour some DNA of The bivalve mollusc, Arctica Icelandica age-related dysfunction through their own, termed mitochonBACTERIA EUKARYA ARCHAEA efficiently processing oxygen to drial DNA (mtDNA). This mtDNA en- the dots between mitochondrial dysfunc- avoid ROS production. In addition, the codes a small number of the cellular ma- tion and the overall declining health seen health benefits of red wine can be attribchinery required for the mitochondria to in aging individuals? Indeed, mitochon- uted to the natural compound resveraperform some of their metabolic func- dria are theorized to play a role in many trol, which can improve mitochondrial tions. With age, mtDNA becomes in- age-associated diseases and other aspects numbers and function, and has been hercreasingly prone to mutations, and the of human health that develop with age. alded as possessing “anti-aging” properMitochondria, oftenFor referred Another exciting tool is the deresulting machinery produced using this example,toageasis our a riskcells' factor powerhouses, for both ties. contain theiroxygen own atherosclerosis, unique DNA known as mitochondrial velopment of base editors DNA is less efficient at coupling which involves the DNA (mtDNA).

Mutations infats mtDNA can trigger for mtDNA editing.

Base metabolism with ATP synthesis, leading buildup of and cholesterol alongsevere the disAll inadapted all, our knowledge of the bioto the production orders of toxiclike oxygen by- artery Myopathy walls leading to inflammation, logical of aging is improving, Mitochondrial (marked by muscle dys- mechanism editors are advanced molecular machines MITOCHONDRIA-EARLY HYPOTHESIS: products, called function) “reactive and oxygen osteoarthritis, ismitochondria characteras reflected thesedirectly lifestyle convert trends. The Thewhich acquisition of pre-dates modern eukaryotic Leber'sand Hereditary Optic Neuropathy (marked thatincan one DNA base into anAn example is the “Hydrogen Hypothesis”, which species” or ROS. These ROS, in turn, can ized by the wear features. and tear of cartilage progress we have made in our underthatthese the original proto-mitochondrion wasother an by sudden vision loss). Despite their proposes rarity, diseases lack without requiring double-stranded DNA breaks. For alphaproteobacteria could ferment orstanding respire depending further promote DNA mutations both cells in joint tissues.

In boththatdiseases, thus far offers hope that a remon oxygen availability, and the archaeal host was an anaerobe existingand cures.

However, addressing rare diseases poses addimitochondrial these sophisticated molecular artisans within the mitochondria in other mtDNA mutationsthat were associated aging might indeedDNA, be something could not tolerate oxygen.with Under lowedy oxygenfor conditions, the alphaproteobacteria would produce nutrients (hydrogen) to tional in treatment development due to limited retranscend the conventional boundaries; specific mutations parts of the cell, as well challenges as react with disease severity, suggesting that mitothat exists the host as a byproduct of fermentation.

Under high oxygenoutside of the realm of science conditions, the alphaproteobacteria would remove oxygen other cell components like small proteins and chondrial dysfunction and excess ROS fiction, and the secrets of misearch, patient populations, diversity among cases, and canunlocking be corrected, or even introduced, with high precision. By harmful to the host by respiring. lipids in a chemical process disinterest. known as production may be contributingintomitochoncell tochondria biologythese may lie at the heart scientists can target and modify industry Yet, recent advancements utilizing base editors, • oxidation.

Ester-linked The buildup of ROS can di- loss and inflammation. of this fabled cure. drial DNA editing show promise. individual bases within the mtDNA with high precision, membrane rectly lipids damage mitochondrial and other paving the way for more accurate genetic interventions and cellular proteins, as oxidized metabolic In addition to disease outcomes, miDifferent to nuclear DNA—multiple copies of mtDNA for research and potential therapeutic proteins lose efficiency.

Lipid oxidation tochondrial dysfunction has also been can opening -new Deevaavenues Uthayakumar HYPOTHESIS: coexist within a single cell, resultingMITOCHONDRIA-LATER in a phenomenon called interventions in mitochondrial diseases.

24

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DNA replication, transcription, translation machinery

20 Trained Immunity? What’s that?!

The original archaeon host already exhibited most eukaryotic

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Mitochondria-induced inflammation The dark side of a cell’s “powerhouse”

Advancements in Mitochondrial DNA EDITING: A Gateway to Curing Incurable25 Diseases

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nucleus • l size lular fission reproduc-

› FEATURE ON [ISSUE]

AR UK

22 The mitochondria — the powerhouse against infectious diseases

featuresmutated prior to acquiring the mitochondria. heteroplasmy, where both normal and versions co-After being engulfed, the alphaproteobacteria escaped the digestion machinery to coexist with harmonious its host in the cytosol, eventually While the prospect of mitochondrial DNA (mtDNA) edithabitate. While serenity reigns supreme with the ceding all autonomy to its host and becoming an energy production center. outnumber the interplay, discord strikes when the insurgents ing holds immense promise for treating severe diseases associ24 Advancements in mitochondrial DNA virtuoso, heralding a crescendo of disease symptoms. ated with mtDNA mutations, several formidable challenges editing: A gateway must be addressed to ensure its safe and effective implementa- to curing incurable Conquering the elusive mtDNA has so far proven to be a tion. One major concern is the potential for off-target effects diseases technically arduous feat for researchers, due to the formidable during the editing process. Precise delivery of editing tools double mitochondrial membrane posing a daunting into the mitochondria is hampered by the double mitochonfortress against efforts of genetic manipulation. drial membrane, demanding the of effective tar- help our 25development How does exercise However, in the past two decades, significant geting strategies. Ensuring high specificity and accuracy in mitochondria? progress has been made in mitochondrial ge- editing mtDNA sequences is critical to avoid introducing unnetics. Scientists have discovered a way to intended mutations or adverse consequences. Ethical considmodify mtDNA using specialized pro- erations surrounding germ-line editing warrant careful conRedoxformedicine — the double edged teins, such as mitochondria-tar- templation, as it could have 26 implications future generageted nucleases, acting as molecu- tions. Additionally, the long-term safety and of stability of edited sword oxidants lar scissors to precisely cut and mtDNA remain uncertain, necessitating further research to remove mutated sequences. By assess potential risks. Despite these challenges, ongoing redoing so, they can restore the search and collaboration offer hope in overcoming ob- Annual Meeting CSI 2023 —these 35th 28 balance between healthy stacles and unlocking the transformative potential of mtDNA and mutated mtDNA, po- editing in mitigating mitochondrial diseases. tentially mitigating the ef30 Who is mitochondrial Eve — the fects of mitochondrial It is also crucial to recognize that mitochondrial diseases mother of all humans? diseases. This success can manifest with various symptoms and severity levels, condemonstrated in labora- tingent on the specific mtDNA mutations and their distributory trials and animal tion in the body. Since mitochondrial DNA is inherited from Mitochondria: bounded by membrane, 31 models ignites a ray of the mother, these disorders can be passed down maternally.

As hope for future thera- research continues to advance, our understanding of mito- impact but of unbounded peutic applications in chondrial diseases and potential treatments may improve, ofhumans. fering hope for affected individuals and their families.

30 31

- Alara Tuncer

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LETTER FROM THE

EDITORS

In order of left to right: James Pollock (Co-Editor-in-Chief), Kitty Liu (Design Director), Karen Yeung (Co-Editor-in-Chief), and Tianning Yu (Social Media Coordinator)

In this fast-paced world, how our bodies produce energy (and how we can produce more) is on many people’s minds. Much of this conversation surrounds diet, exercise, sleep, and other macro factors. In this issue of IMMpress Magazine, we explore human energy at the microscopic level by investigating the powerhouse of the cell: the mitochondria.

These tiny organelles keep our bodies moving through an elegant biochemical process. Beyond energy production, however, in this issue we are reminded of the many ways that mitochondria influence our overall health.

We begin with an infographic about the origins of mitochondria and their evolutionary journey (p9). We follow this with an article that details the role of mitochondria in trained immunity (p10). Next, we delve into some of the applications of mitochondrial research: the use of mitochondrial replacement therapy during in-vitro fertilization (p12), the search for an ancient ancestor, the Mitochondrial Eve (p30), and the relationship between exercise and mitochondrial health (p25). For insight on current mitochondrial research we interviewed UofT alumni Dr. Sam Saibil about his work on T cell metabolism.

But what happens when the powerhouse of the cell goes dark? We explore the systemic consequences of mitochondrial dysfunction (p14) with a closer look at the mitochondrial theory of aging (p20). In severe cases, mitochondrial dysfunction can increase infectious (p22) and genetic (p24) disease susceptibility. But not all is lost! Mitochondrial activity is a doubleedged sword with positive effects as well, which we discuss in an article on redox medicine (p26). The chaotic nature of mitochondria is further detailed in our review of the book Power, Sex, and Suicide by evolutionary biochemist Nick Lane (p31).

Finally, we recap the 35th annual Canadian Society for Immunology (CSI) meeting held this year in Orford, Quebec (p28), and congratulate the IMM250 IMMpress Prize winner, Rebecca Yik-Ming Chau, who describes the power of nomenclature in fuelling prejudice and reconciliation (p18).

Many thanks to our fantastic team of writers, editors, and designers for assembling yet another thought-provoking issue of IMMpress. As the next academic year begins, we’d like to welcome all the new students who’ve joined the Department of Immunology this year! Lastly, we hope our readers enjoy this issue and as always, stay safe and healthy!

James Pollock

Karen Yeung IMMpress Vol. 11 No. 2 2023

5

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LETTER

FROM THE CHAIR

Over the past 10 years, IMMpress Magazine has delivered remarkable features, timely analysis of critical topics, stunning infographics, and insightful articles. The current issue continues this IMMpeccable track record. This issue of IMMpress is truly a powerful one, as it delves into the heart of cellular energy production, the mighty mitochondrion.

As this is my last Chair’s Letter, I want to underscore my profound thanks and admiration to the IMMpress editorial teams, past and current. They have brought vision and dedication, creating an outstanding publication, which provides us with an important venue with which to communicate and share ideas with our broader community. This is a great example of how truly exceptional UofT Immunology graduate students are, and how fortunate we are as an academic unit to have them with us. Their creativity reassures me that the future of our field will be a bright one.

In terms of prospects for the future, you will be hearing from Prof. Jen Gommerman in the upcoming issues, as she becomes our next Chair on October 1, 2023. I am sure that Jen will share her goals for the Department of Immunology and provide us with her vision as we look ahead to the next 5 to 10 years, with a view that what lies ahead will be even better than our first forty, since the establishment of the Department in 1984.

Serving as Chair of the Department of Immunology since 2012 has been a wonderful experience, and I am endlessly grateful to all that made that journey so rewarding and productive. For now, towel in hand, I leave you with the parting remarks from The Hitchhiker’s Guide to the Galaxy by Douglas Adams. Don’t panic… and… So long, and Thanks for all the fish!

Juan Carlos Zúñiga-Pflücker, PhD Professor and Chair Department of Immunology IMMpress Vol. 11 No. 2 2023

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MITOCHONDRIA AND THE COMPLEXITY OF LIFE

BACTERIA

Our bodies are made up of trillions of cells that work in concert to perform all the basic processes required for life. Inside each cell are veritable factories of energy production called mitochondria, which help support the energy expenditure necessary for these small cells to maintain the much larger organism as a whole. In fact, all multicellular organisms carry mitochondria within their cells, falling under the domain of life known as Eukarya, meaning “true nucleus”. Life before the emergence of eukaryotes was dominated by single-celled organisms from the domains of Archaea and Bacteria, which remain major groups of life to this day. How do eukaryotes fit into the family tree of life on Earth, and where do mitochondria come in?

Popularized by Lyn Margulis’ 1967 article in the Journal of Theoretical Biology, it is now well-accepted that mitochondria were once free-living bacteria that were acquired by a pre-eukaryotic archaeal cell in an endosymbiotic event. The acquisition of the endosymbiont bacteria by the host archaea provided advantages that spurred the co-evolution of both species, leading to an inseparable integration to form the eukaryotic cell. Phylogenetic analyses currently place the original bacterial endosymbiont as a close relative to the alphaproteobacteria family, and the original host as potentially related to the Asgard archaea. However, the exact nature of the first two partners that gave rise to complex multicellular life remains a mystery lost to time.

BACTERIA

•

Use host metabolites for nutrients Potential protection from the environment

Closest archaeal host relative: Asgard archaea • •

No nucleus • • Small size • Unicellular • Binary fission (asexual reproduction) • Circular chromosome • Ribsosome

• •

HA EA

8 IMMpress Vol. 11 No. 2 2023

•

ARC

•

Endosymbiont may have removed toxic oxygen Provide metabolites for nutrients Eventually provided energy in the form of ATP

Peptidoglycan cell wall No histones

•

Ester-linked membrane lipids

•

Nucleus • Endomembrane system • Linear chromosome • Sex/meiosis • Mitochondria!

Ether-linked membrane lipids Metabolic enzymes

E

•

•

•

DNA replication, transcription, translation machinery

Y R A UK

A

Closest mitochondria relative: Alphaproteobacterial

EUKARYA

ARCHAEA

MITOCHONDRIA-EARLY HYPOTHESIS:

The acquisition of mitochondria pre-dates modern eukaryotic features. An example is the “Hydrogen Hypothesis”, which proposes that the original proto-mitochondrion was an alphaproteobacteria that could ferment or respire depending on oxygen availability, and the archaeal host was an anaerobe that could not tolerate oxygen. Under low oxygen conditions, the alphaproteobacteria would produce nutrients (hydrogen) to the host as a byproduct of fermentation. Under high oxygen conditions, the alphaproteobacteria would remove oxygen harmful to the host by respiring.

MITOCHONDRIA-LATER HYPOTHESIS:

The original archaeon host already exhibited most eukaryotic features prior to acquiring the mitochondria. After being engulfed, the alphaproteobacteria escaped the digestion machinery to coexist with its host in the cytosol, eventually ceding all autonomy to its host and becoming an energy production center.

- Karen Yeung

IMMpress Vol. 11 No. 2 2023

9

Mitochondria-induced inflammation: the dark side T of a cell's

"powerhouse"

he word “immunity” conjures up an image of our body fighting against infections. We picture our immune cells heroically battling against foreign, unwanted substances – viruses and bacteria – that have breached our barriers and invaded our anatomical space. Most of us love the classic tale of “good” versus “bad”. But what about the more twisted, exciting tale of “good-turned-bad”? Some systems designed to ensure our body’s survival can become dysfunctional and trigger an unnecessary immune response against the body’s own cells.

One of such essential systems are the mitochondria – organelles or structures inside each cell that generate chemical energy required to fuel cellular processes. The mitochondria use the tricarboxylic acid (TCA) cycle and electron transport chain to convert nutrients into adenosine triphosphate (ATP) molecules. Energy or ATP production is undeniably their most well-known function; however, the mitochondria carry out multiple other tasks to maintain cell survival. Mitochondrial products are used to make amino acids, nucleotides, and lipids – the building blocks of proteins, DNA, and cell membranes, respectively. For example, citrate and alpha ketoglutarate are both TCA cycle metabolites produced by the mitochondria.

In addition to participating in the TCA cycle, citrate is involved in synthesizing fatty acids and cholesterol while alpha ketoglutarate is converted to glutamate – the precursor to amino acids glutamine, alanine, and aspartate.

The responsibilities of mitochondria extend far beyond energy production or the synthesis of essential molecules.

Mitochondria can indirectly induce inflammation, alerting the immune system of infections and setting it to “attack” mode. Upon infection, a cell usually dies and bursts open, releasing its contents for adjacent

10 IMMpress Vol. 11 No. 2 2023

pathway and promote an inflammatory attack against the body’s own tissues. Similarly, chronic bronchitis – an inflammatory lung disease that restricts air flow – is also associated with high levels of mtDNA, ROS, and general mitochondrial dysfunction in the lungs. cells to recognize and receive danger signals. The most common danger signal is the mitochondrial product, ATP. Once released from the host cell, it binds to corresponding proteins on the surface of nearby immune cells and activates their inflammatory programming.

However, inflammatory responses that occur in absence of infections are far from benign as these “attacks” are directed against our own cells. Unwarranted and self-harming inflammatory responses can be initiated by mitochondria-gone-rogue. For instance, dysfunctional mitochondria can release high levels of reactive oxygen species (ROS), the natural by-product of ATP production. Excessive ROS is toxic to cells as it damages DNA, proteins, and lipids. It can also trigger the formation of inflammasomes, large multi-protein structures that signals an inflammatory cellular program.

Additionally, dysfunctional mitochondria release their DNA. Mitochondrial DNA (mtDNA) is different from DNA found in the nucleus and it is normally contained within the organelle to produce necessary mitochondrial proteins.

However, once released out of its designated environment, mtDNA can trigger a pathway called “cGAS-STING”. The cGAS-STING pathway is designed to sense foreign (usually viral) DNA that enters cells. Thus, mtDNA is inappropriately recognized as “foreign” by the cGAS-STING pathway, which again activates immune responses.

Ultimately, mitochondria-induced inflammation can have detrimental effects on our overall health. For example, mitochondrial dysfunction has been associated with systemic lupus erythematosus (SLE). SLE is an autoimmune disease that results in fever, joint pains, skin rashes, and damage to internal organs including brain, lungs, and kidneys. Studies have shown that patients with SLE have increased amounts of mtDNA in circulation, which activate the cGAS-STING

How can the mitochondria – an essential part of our cellular system – become so dangerous? In other words, what causes these mitochondria to become inflammatory? Naturally, there are mechanisms in place to prevent mitochondria-induced inflammation. For instance, dysfunctional or damaged mitochondria are eliminated from cells by a process called “mitophagy”. A similar process called “autophagy” can remove inflammasomes induced by mitochondrial ROS. Alternatively, cells that contain dysfunctional mitochondria undergo programmed cell death or apoptosis. This process involves permeabilization of the outer mitochondrial membrane, which releases mitochondrial molecules called cytochrome c. The rapid accumulation of cytochrome c in the cytoplasm initiates a cascade of events that lead to the death of a cell with inflammatory potential.

As soon as these safeguarding mechanisms are out of order, the mitochondria can easily trigger unwanted inflammation. In fact, patients with SLE have an excess of circulating mtDNA due to defects in mitophagy. Similarly, patients with Crohn’s disease – a chronic inflammatory disease of the digestive tract – have mutations in genes that regulate autophagy. These mutations result in faulty autophagy machineries, leading to the accumulation of dysfunctional mitochondria and mitochondria-induced inflammation.

Mitochondria are indeed necessary for the proper functioning of our cells. They supply not only energy but also materials to build fundamental cellular components. Yet, when rendered dysfunctional or mechanisms that remove defunct organelles go awry, the mitochondria can be a source of disease-causing inflammation. These complex and contradictory features, the good and the bad, make this organelle so much more than a “powerhouse of a cell”.

- Jennifer Ahn IMMpress Vol. 11 No. 2 2023

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12 IMMpress Vol. 11 No. 2 2023

O

ne of the holy grails of medicine is a cure for aging, and it has been the inspiration of many myths and legends, such as the Elixir of Life, the Philosopher’s Stone, and the Fountain of Youth. Although lifespan can vary, aging is an inevitable outcome of virtually all animals. As we start to develop a better understanding of the underlying biological processes that contribute to aging, the quest for an anti-aging remedy becomes less of a myth and more of a reality.

One of the most prominent theories of aging revolves around mitochondria, the main energy producers of cells. Each cell in our body possesses hundreds of these intracellular structures, which facilitate the reaction between carbohydrates and oxygen to produce ATP, the main energy molecule of the cell. They are also essential for helping the cell digest other nutrients, such as amino acids and lipids, and can act as a switch to initiate cell death. The mitochondrial theory of aging, therefore, proposes that a decline in mitochondrial function is one of the causal factors of aging.

can also impair the structural integrity of the cell. The release of ROS and cell debris following cell death into the extracellular space within a given tissue could also trigger inflammation. All in all, these processes result in a loss of efficiency in cell metabolism and cell death due to oxidative stress. The mitochondrial theory of aging, therefore, proposes that the accumulation of damaged biomolecules and subsequent mitochondria dysfunction leading to cell death, drives aging.

linked to visible signs of aging, such as grey hair and wrinkle formation.

Healthy mitochondria play an important role in providing energy to cells for tissue regeneration, which becomes less efficient with age, making elderly individuals more prone to injury and muscle weakening. In the semitendinosus muscle of elderly individuals, there is an increase in mitochondrial factors that induce cell death, which could explain the decline in functionality and muscle volume with age.

While it may be easy to believe how this elaborate tale of mitochondrial dysfunction, ROS release, and cell death could lead to aging, does this theory have any weight? How do we connect

As regular mitochondrial function becomes compromised, cells attempt to recycle these faulty mitochondria into healthy ones, a process that becomes less efficient with age. While healthy mitochondria may not be the only component required to extend lifespan, many of our long-lived animal counterparts, such as the bivalve mollusc, Arctica Icelandica, that can live >500 years, have extremely efficient mitochondria that produce limited toxic by-products. Can restoring mitochondrial function in humans be a possible remedy for aging?

While most of a cell’s genetic information is stored within the nucleus as DNA, the mitochondria also harbour some DNA of The bivalve mollusc, Arctica Icelandica their own, termed mitochondrial DNA (mtDNA). This mtDNA en- the dots between mitochondrial dysfunccodes a small number of the cellular ma- tion and the overall declining health seen chinery required for the mitochondria to in aging individuals? Indeed, mitochonperform some of their metabolic func- dria are theorized to play a role in many tions. With age, mtDNA becomes in- age-associated diseases and other aspects creasingly prone to mutations, and the of human health that develop with age. resulting machinery produced using this For example, age is a risk factor for both DNA is less efficient at coupling oxygen atherosclerosis, which involves the metabolism with ATP synthesis, leading buildup of fats and cholesterol along the to the production of toxic oxygen by- artery walls leading to inflammation, products, called “reactive oxygen and osteoarthritis, which is characterspecies” or ROS. These ROS, in turn, can ized by the wear and tear of cartilage further promote DNA mutations both cells in joint tissues. In both diseases, within the mitochondria and in other mtDNA mutations were associated with parts of the cell, as well as react with disease severity, suggesting that mitoother cell components like proteins and chondrial dysfunction and excess ROS lipids in a chemical process known as production may be contributing to cell oxidation. The buildup of ROS can di- loss and inflammation. rectly damage mitochondrial and other cellular proteins, as oxidized metabolic In addition to disease outcomes, miproteins lose efficiency. Lipid oxidation tochondrial dysfunction has also been

Popular health trends, such as caloric restriction and daily physical activity, are emerging as efficient strategies to slow down mitochondrial aging and delay age-related dysfunction through efficiently processing oxygen to avoid ROS production. In addition, the health benefits of red wine can be attributed to the natural compound resveratrol, which can improve mitochondrial numbers and function, and has been heralded as possessing “anti-aging” properties.

All in all, our knowledge of the biological mechanism of aging is improving, as reflected in these lifestyle trends. The progress we have made in our understanding thus far offers hope that a remedy for aging might indeed be something that exists outside of the realm of science fiction, and unlocking the secrets of mitochondria biology may lie at the heart of this fabled cure.

- Deeva Uthayakumar IMMpress Vol. 11 No. 2 2023

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Mitochondrial replacement therapy: modifying in-vitro fertilization to combat mitochondrial disease

Mito chrond ri a l re pl a ce m e nt thera py ( M RT ) , of ten refer red to a s “ 3 - pers on inv i tro fertilizat i o n ( I V F ) ,” i s a te c h nol og y t hat com bi nes t he m i toc hond r ial D N A (mtDNA) o f a do no r w i t h the n ucl ea r DN A of a coupl e i n a n em b r yo t hat is carried to term. T hi s te ch no l o gy ha s been p rop os ed to prevent t he t ra ns m i s s ion of maternally tra nsm i tte d m i to cho nd r i a l d i s ea s e. M i toc hondr i a l di s ea s es a re of ten caused by ge neti c m utati o ns affec t i ng bot h a dul t s a nd c hi l d ren, t hat can lead to diseases a cro ss m ul t i p l e o rga n s a n d have no c ure. W hi l e st rateg i es ex ist to prevent the ve rti ca l t ra nsm i ssi o n of m u tated mt DN A , s u c h a s a dopt i on , or eg g and e mbr yo do nat i o n, t he l a ck o f a ge neti c l i nk does pos e a probl em for s om e couples l ooking to have chi l dre n . I n t hi s a r t i c l e, we w i l l di s c us s t he h i stor y behi n d MRT, its s uccesses and so m e et hi ca l co nce r n s a n d cont rovers i es t h at have a r i s en s inc e its i nc ept i on.

T

he research that went into the modern processes of MRT began as early as the 1980s when Dr. Jacques Cohen and others used cytoplasmic transfer to assist in reproduction. Cytoplasmic transfer is a process in which a small amount of cytoplasm from a healthy donor’s oocyte is transferred to an oocyte from a person experiencing fertility issues. The first baby was born from this technique in 1997. Prior to regulation of this technique by the USA’s Food and Drug Administration in 2002, Cohen’s clinic used this technique for the conception and birth of 13 children. Since then, the promising research has led to the birth of 30-50 children worldwide (as of 2016). In 2009, two research teams published studies on mitochondrial donation that progressed the technology further. In 2010, Craven et al. conducted human trials with oocytes that yielded a carryover rate of only 2% mutated mtDNA. In 2015, the UK passed the Human Fertilization and Embryology (Mitochondrial Donation) Regulations making mtDNA donation legal under rare cases where a couple is at a higher risk of transmitting mitochondrial disease to their children. Since then, this technique has seen to the births of several children, including fewer than five children in the UK as of April 2023. While this procedure has been used and/ or approved in some countries (Greece, Ukraine, Australia, Mexico), it is still restricted in many countries including Canada and the USA.

In all these techniques, donor refers to a person with healthy mitochondria, and recipient refers to a person with mutated mtDNA that is trying to conceive a child.

In spindle transfer, the spindle-chromosome complex that contains the genetic material from the recipient is removed from an egg during cell division. This spindle-chromosome complex is inserted into a donor oocyte with the nucleus removed. This egg is fertilized and investigated for genetic mutations, particularly in the mtDNA, prior to implantation in the recipient.

In pronuclear transfer, an oocyte is removed from the recipient and donor. Both oocytes are fertilized with sperm from the same person. All pronuclei (nucleus from sperm or egg cells) are removed from each fertilized egg prior to the fusing, and the pronuclei from the recipient is transferred into the fertilized egg from the donor. Like in the spindle transfer procedure, the egg is investigated for genetic mutations prior to implantation.

The final technique is the newest and is called polar body transfer. A polar body is a small cell with very little cytoplasm that is created when an egg cell divides. In polar body transfer, a polar body from the recipient is used in its entirety instead of nuclear material from the recipient’s egg as in the other methods.

This is a promising technique as polar bodies have very Methods of MRT few mitochondria, thereby reducing the risk of transmitting The historical method of cytoplasmic transfer is no longer recipient mitochondria compared to maternal spindle transfer used in modern procedures of MRT. Rather three main methand pronuclear transfer which have small carryover of recipods exist: maternal spindle transfer, pronuclear transfer, and ient mitochondria.

Despite this, polar body transfer requires more recently, polar body transfer. further research to increase reproducibility and replication.

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Benefits of MRT

Several benefits exist for the use of MRT for IVF. First and most importantly, it is a strategy to allow couples to birth a biologically related child that does not have mitochondrial disease. In addition to the reduction in mitochondrial disease transmission, MRT may provide benefits for age-related infertility, where traditional IVF is unsuccessful. Despite these benefits, there has not been sufficient research to suggest that mitochondrial disease transmission can be lowered or avoided altogether by MRT, although preliminary research in animals may provide some insight into this in the future.

Scientific and Ethical Concerns of MRT

Although MRT can provide some families the benefit of having biological children without transmitting mitochondrial disease, there are some scientific and ethical concerns about the procedure.

Reversal is cited as the main concern in MRT and involves carried-over mitochondria increasing over time, ultimately replacing donor mitochondria in cells. In a study by Costa-Borges et al., 1 out of 6 children born from MRT exhibited reversal, where 30-60% of mitochondria were inherited from the recipient despite a carryover rate of only 1% from the recipient egg. While the child studied did not have any risk for a mitochondrial disease, this is not always the case. This carryover rate may mean that MRT might not be successful in limiting mitochondrial disease in the offspring of individuals with mitochondrial mutations. One possibility to explain this may be that genetic factors from the recipient increase the efficiency of replication for their own mitochondria, compared to that from the donor. It may be necessary to find similarities in mitochondrial DNA between recipient and donor to reduce the risk of reversal.

Harms to egg providers with healthy mitochondria: Although egg donation is voluntary, it is not without its physical and psychological risks. Donors are required to undergo several interviews, screens, as well as hormonal stimulation and egg retrievals with no “benefit” of having a child. These hormonal treatments can cause acute physical pain (cramping, nausea, vomiting).

Also, they can potentially cause longterm effects including but not limited to risk of cancer and decreased fertility.

The ethics of egg donation comes into play when considering the financial aspect of egg donation, where economically disadvantaged people may become targets for this process.

Harms to offspring: MRT still remains experimental, and as a result, long-term safety and efficacy must be investigated further. At this moment, there is no information on the impact that mixing genetic material and mtDNA may have on future progeny.

Although there is always risk in new technologies, thereby necessitating the need for clinical trials, it is necessary to assess the technique in preclinical trials rather than foregoing these processes by conducting the procedures in countries without regulations against the technique. This introduces further ethical concerns into medical tourism.

Conclusions

Overall, MRT provides a rewarding solution for people who would like to have biologically related offspring without risking the transmission of mitochondrial disease. However, scientific and ethical concerns subject this technology to further scrutiny prior to its popularization. Ultimately, national health organizations must continue to objectively analyze the research into MRT and its future use.

- Baweleta Isho

In addition to scientific concerns, ethical concerns have been raised regarding the use or MRT. These ethical concerns encompass various categories that can include harms to egg providers and harms to potential offspring.

IMMpress Vol. 11 No. 2 2023

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“E

very day in clinic, even with the best therapies, we see patients still not doing well. That is where we need to be looking,” said Dr. Sam Saibil, medical oncologist at Princess Margaret Cancer Centre, and an Assistant Professor in the Department of Immunology, University of Toronto. He uses this perspective to identify where there is the greatest need, so he can design his research to fill that need.

I sat down with Sam recently to get his perspective on the intersection between metabolism, mitochondria, immunology and clinical interests. Sam completed the PhD portion of his training in Dr. Pam Ohashi’s lab in 2009. This was done in the midst of his medical training from which he graduated the subsequent year.

Decision making When asked about how he decided that he wanted to become an MD/PhD, Sam commented that, “Everything in life is [about] who you meet, who you are lucky enough to encounter.” Sam has several medical doctors in his family, so growing up he was quite familiar with, and interested in, the profession. However, it was not until his undergrad that he encountered the realm of research during a summer position in Dr. Robert Kerbel’s lab, at Sunnybrook Research Institute. This experience got him excited about research and led him to where he is today. Sam found a program that would allow him to pursue both avenues of interest.

Pathway to metabolism and mitochondria research In the midst of his clinical training, Sam had an opening that allowed him to come back to the Ohashi lab as a post-doctoral fellow. At this time, Pam Ohashi and her lab were involved in a project using tumour-infiltrating lymphocytes (TILs) to treat cancer patients. Sam was interested in the translational application of this project and was excited to come back to the research side. However, not only did he become involved in translational research, but it was during this part of his training that he started to get involved in mitochondria and immunometabolism research.

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See a need, Fill a need: An Alumni Interview with Dr. Sam Saibil After his time away on the clinical side, Sam needed to get himself re-immersed in the science. He had the opportunity to attend an immunology conference in San Francisco. Sam mentioned that the cell therapy field was focused on memory T cells for their increased persistence in vivo as a way of improving tumour treatment. Particularly, Sam noted that he attended a talk

by Erika Pearce, a scientist responsible for several seminal papers in the T cell immunometabolism field. She discussed the metabolic programming underpinning memory T cell immunity. Refreshed, Sam came back to the Ohashi lab with an interest in pursuing immunometabolism. He worked extensively with then immunology graduate student Michael St. Paul. Their research sought to understand metabolic manipulations that can improve adoptive cell therapy and improve the persistence and function of T cells. The rest, as they say, is history, or at least several highly published papers.

Current research and future research

Advice for students I asked Sam if he had any wisdom for current PhD students, and especially those interested in clinical translation. He said that if you are interested in getting into the clinical side of research, you should start by reading the clinical literature and gaining an understanding of how research projects get into the clinic. This can provide perspective for designing research questions and projects, particularly with an understanding of the huge differences in timelines between the two worlds.

To improve science and the outcomes for patients, Sam noted that, “It’s cliché, but it takes a village. Big teams are important.” To get the best outcomes, it is necessary to bring both basic scientists and clinicians together to solve relevant problems. If you can speak both languages, you become more valuable to the process.

- Meghan Kates

Sam now uses all his training and perspective gained from working in the clinic to inform his research interests. In the last few years, Sam has started supervising students of his own, including myself. His lab focuses on ways of manipulating metabolism and mitochondria of T cells to improve adoptive cell therapy and therefore improve patient outcomes.

When asked where he wants to see the future of the field, Sam said that we need to get the field into the clinic. He stated that although there are a lot of people with great ideas in the immunometabolism field, there has been little to no success in the clinic.

In fact, the latest trial in melanoma failed miserably.

At this point, our conversation side tracked to talk about our own projects trying to bridge the gap between basic immunometabolism research and clinical trials. Developing a compound or intervention that could be applied to T cells ex vivo to improve their persistence and function in the tumour would be an excellent breakthrough that could help improve patient outcomes. There are many labs trying to find the answer. So, we will keep that information proprietary for now. Stay tuned to the literature for further updates.

IMMpress Vol. 11 No. 2 2023

17

WHAT’S IN A NAME?

– WHAT’S THE

T

he Edmonton Eskimos became the Edmonton Elks, and Confederation Bridge may soon be Epekwitk Crossing. With the fight for social justice that has emerged following George Floyd’s murder at the hands of police officers in Minneapolis come calls to rename schools, streets, and institutions reflecting racist, sexist, or otherwise problematic historical figures and ideologies to reflect current standards and beliefs. This decision seems a straightforward one, as the honouring of an individual in such a manner indicates to some extent, a validation of their actions. However, many worry that treating such action as the end-all-be-all, without further examination of the continued struggles and difficulties faced by minority populations, is nothing more than a novel way for governments and organizations to free themselves of culpability for these issues and skirt any acknowledgement of the injustices still prevalent in modern society. While not nearly as wrought with controversy as the idea of renaming Toronto’s iconic Dundas St — Scottish politician Henry Dundas, its namesake, was staunchly opposed to the abolition of the transatlantic slave trade, the World Health Organization (WHO) decision to rename the decades-old disease formerly known as “monkeypox” to “mpox” following the 2022 outbreak brings to mind many of the same concerns as these more contentious name changes.

The Heart of the “Monkey” Mpox is a smallpox-like virus transmitted from animals to humans and was initially named for an outbreak amongst lab monkeys in Copenhagen in 1958, though its true animal reservoir is suspected to be small rodents. It has long been endemic (regularly occurring in a relatively controlled manner) to Central and West Africa. In humans, mpox is characterized by a rash and flu-like symptoms, generally appearing within three weeks of exposure. Prior to the 2022 spread of mpox to non-endemic countries such as the United Kingdom, Portugal, Italy, Canada, and the United States of America, occurrence of the disease was rare, and could typically be traced back to close contact with open sores or blisters from infected travelers or transported animals. However, the majority of cases of mpox in non-endemic areas for the current international outbreak have no established connections to travel from endemic areas, and occur in gay or bisexual men who have sex with men (gbMSM).

The removal of the word “monkey” from the name of the disease aims primarily to combat the racist connotations the word carries, given the virus’ endemic nature in several African countries, and concurrently to correct the insinuation that monkeys are the animal reservoir for the virus. Addition18 IMMpress Vol. 11 No. 2 2023

ally, there is hope that a bland name will reduce the stigma associated with having the disease and avoid discrimination towards the 2SLGBTQI+ community, as was witnessed with the HIV/AIDS epidemic. However, the current mpox outbreak can be arguably traced back to a general neglect within Western medicine of the health of marginalized individuals, such as members of the 2SLGBTQI+ community, and those living in regions considered “far from home,” namely Black Africans. Simultaneously, these individuals are forced to bear a significant portion of the blame for the spread of the disease through biased reporting in Western media outlets.

Therefore, this renaming is a crucial first step, but is by no means a definitive solution to the inequalities associated with mpox.

In a Land “Far, Far, Away” Historical research regarding mpox has been relegated to the category of tropical diseases, which receive less funding and attention than those considered to have a large impact on Western society. Despite the inevitable spread of mpox to Europe and America through travel, there remain an unacceptable number of questions regarding the virus’ epidemiology, diagnosis, and virology. Over the years since the first human instance of mpox, Africa has reported dozens of outbreaks and case numbers in the tens of thousands, all of which have failed to raise alarm outside the continent.

The recurrent surges of human mpox in Africa could likely have been arrested if not for the unequal access to vaccines and health care resources faced by those living in the Global South. Meanwhile, a 2003 mpox outbreak in the United States was expeditiously traced back to a shipment of prairie dogs housed next to infected giant pouched rats from Ghana.

A ban on the importation of African rodents rapidly followed and the disease was quickly controlled, and subsequently forgotten, with no further efforts made to combat the disease in Africa.

Dr. Dimie Ogoina — the Nigerian physician responsible for the 2017 identification of the first known case of an mpox outbreak in Nigeria (the first case in the country for 38 years), and the first known case of the international mpox outbreak — was summarily told not to worry when he raised alarms that the virus had changed and was now spreading between humans, often through sexual contact. In the intervening five years since Dr. Ogoina’s discovery, international governing bodies could have taken steps to prevent the virus from spreading, not only throughout Nigeria, but to other

MONKEYPOX TO MPOX

REAL AIM?

countries, as we have seen happen over the last year. However, definitive action transpired only when the disease began to affect citizens in Europe and North America. Vaccination efforts for at-risk populations were swiftly mobilized in these continents, leaving Nigerians (and Africa for that matter) in the dust.

Since the outbreak, Western media outlets such as The Independent and CNBC have sensationalized the disease, whether intentionally or not, as an African disease, through the use of imagery depicting mpox blisters on Black skin, even when referring to the spread of the disease amongst their own country’s primarily white population. Propagating the message that Africa is undeveloped and to blame for the current mpox outbreak is overtly damaging to already underserved populations. Such an approach overshadows more important news, such as the root causes for the current outbreak, and is counterproductive to the overall goal of curbing the disease’s spread.

The Here and Now Current measures to address the spread of mpox are wrought with worry on how to increase awareness without also increasing the stigma and discrimination faced by GBMSM individuals, those currently at the highest risk for mpox infection. Mpox is known to be prevalent in GBMSM communities — a result of coincidence, owing to rapid spread at Pride events in Europe. In addition, its known methods of transmission — close contact with respiratory secretions, skin lesions, and recently contaminated objects, goes hand in hand with sexual intercourse. Public health institutions are reluctant to directly address this, fearful of providing fuel for homophobes or further traumatizing GBMSM. In this instance, the singular fixation on avoiding stigma has backfired, gravely undermining community-based efforts to increase awareness. Shuttering gay establishments and discouraging attendance of 2SLGBTQI+ events will not stop the transmission of the disease. Rather, we must increase awareness of its presentation and encourage self-examination for symptoms to prevent transmission by infected individuals. Reducing stigma towards GBMSM individuals does not begin and end with a name change; more research is needed to explore the impact of mpox-related attitudes on individuals’ willingness to seek out testing for a suspected mpox infection.

It is crucial for public health bodies to explicitly acknowledge the link between the current mpox outbreaks and GBMSM communities — not only to ensure adequate education, but also to address the increased risk of mpox infec-

tion faced by people with advanced HIV infection, many of whom in the current outbreak are GBMSM. Rather than the typical pimple or blister-like lesions found in mpox-infected individuals, those with a low CD4 cell (infection-fighting white blood cell) count who are HIV positive experience large flesh-eating patches with the potential of causing secondary infections in the lungs and other organs. While the overall mortality rate of mpox in the current outbreak is less than 0.1%, a study conducted in Mexico found that of 179 mpox-infected patients with a CD4 cell count of fewer than 200 cells per microliter (500 being the typical amount), 27 died, a 150-fold increase from the norm.

Since the onset of the outbreak, advances have been made in the treatment and prevention of mpox. While there is currently no specific treatment for mpox, antivirals developed for the treatment of smallpox are being used to treat severe mpox infections. Additionally, the 2-dose JYNNEOS vaccine is approved for protection against mpox and smallpox infections, and is safe for immunodeficient individuals such as those who are HIV positive. However, similar to the need to prioritize additional resources for African communities, it is essential to ensure the appropriate distribution of treatment and preventative vaccines in 2SLGBTQI+ communities, especially those in less affluent countries.

A Fairy Tale Ending?

The rebranding of Ryerson University as Toronto Metropolitan University does not negate the egregious involvement of Egerton Ryerson in the Canadian residential school system, nor the system’s continued traumatic impact on Indigenous communities in the present. Likewise, removing five letters from the name “monkeypox” will not miraculously cure the systemic injustices responsible for the current outbreak, nor will it alleviate the continued stigmatization of at-risk communities. HIV/AIDS, MRSA, and COVID-19 — in each of these instances, despite leveraging scientific nomenclature, vulnerable groups still became the target of misplaced blame and misconstrued responses. Therefore, this name change must serve as a springboard to explore the factors and determinants that have led to the perpetuation of mpox in African countries and the relative inaction on the research and intervention fronts that precipitated its eventual spread to non-endemic regions. Concurrently, informed and thoughtful care must be taken to ensure that GBMSM populations are not scapegoated for the outbreak’s continuation, and that all at-risk communities have access to the requisite education and clinical treatments to effectively navigate mpox.

- Rebecca Yik-Ming Chau IMMpress Vol. 11 No. 2 2023

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Trained Immunity What’s that?!

THE INNATE AND ADAPTIVE IMMUNE SYSTEM Our immune system is broadly divided into two separate “arms” that communicate with each other to protect us from infections. These two factions are termed the innate and adaptive immune systems. The innate immune system is evolutionarily more ancient than its adaptive counterpart. It acts as a broad first-line of defense when we get infected with pathogens (think viruses, bacteria, and fungi). For example, a particular innate immune cell, termed a macrophage, can “eat” whole bacteria when it encounters them. If the innate immune system is unable to clear the infection, it coordinates with the adaptive immune system to recruit reinforcements. Adaptive immunity (T and B cells) is more specialized than its innate counterpart, and therefore can mount highly specific responses, such as antibody production, against particular structures present on a given pathogen. Due to their highly specific nature, adaptive immune responses are often sufficient to clear an infection. Even after an infection is cleared, a small portion of pathogen-specific B and T cells remain in our bodies as memory cells to protect us from another infection.

munity and has received a lot of interest by scientists over the past few years. Importantly, in certain situations, innate immune memory may be even “better” than memory by adaptive immune cells, due to its ability to protect us from a wider array of infections. This is especially true for the BCG vaccine, whose ability to reduce infant mortality worldwide cannot be explained solely by its tuberculosis-specific protective effects.

MITOCHONDRIA TCA CYCLE

METABOLITES

WHAT IS IMMUNE MEMORY? Now what happens when we encounter the same infection again? Say we were vaccinated against tuberculosis with the BCG (or “Bacille Calmette-Guerin”) vaccine, then how would our immune system respond when we potentially encounter the causative bacteria of tuberculosis? Scientists previously thought that only the memory B and T cells will “remember” the 1st infection and will protect us when we get infected again. This is the principle behind how vaccines work; we have been mildly “infected” during a tuberculosis vaccination, and when we encounter the Mycobacterium tuberculosis bacterium later in our life, the memory B and T cells respond against it quickly, thereby protecting us from getting sick.

However, over the past years, scientists have learned that innate immune cells (remember the 1st line defenders?) can also remember previous infections. If you are surprised at this, you are not alone – scientists were too! This new discovery of memory by innate immune cells has been coined trained im20 IMMpress Vol. 11 No. 2 2023

DNA MODIFICATIONS

EPIGENETIC REPROGRAMMING

HOW DOES TRAINED IMMUNITY WORK? Although innate immune cells can remember previous foreign agents, the way they protect us during subsequent infections is fundamentally different than the protection provided by adaptive immune cells. For example, particular components on bacterial or fungal cell walls can “reprogram” innate immune cells to broadly protect us against different bacterial, fungal or even viral infections! In fact, recent experiments have shown that immunization with the tuberculosis vaccine, BCG, may be able to protect humans against Yellow Fever Virus.

How do innate immune cells become “reprogrammed” during an initial infection to mount protection against subsequent infections? This is a complicated question with an even more complicated answer that will take us on a journey into cellular epigenetics and metabolism. Do not worry – I will try to replace those horrid flashbacks of high school exams involving these terms with more positive imagery.

Epigenetics: The “nurture” part of nature vs. nurture. All living beings have a “nature” encoded into every cell of their organism in the form of DNA. Various environmental stimuli can control a cell’s ability to read DNA and are thereby able to turn genes, which encode cellular components, “on” or “off”. This is achieved through modifying DNA around these genes to alter their accessibility by cellular machinery, which rely on reading this genetic code to synthesize proteins. These DNA modifications in response to environmental stimuli are called epigenetic modifications. Innate immune training relies on such epigenetic modifications or colloquially, “reprogramming”. For example, BCG vaccination induces broad-scale epigenetic changes in innate immune cells, which causes them to secrete greater levels of protective proteins, or cytokines, upon subsequent challenge with viral, fungal, or bacterial agents.

What then causes epigenetic changes in innate immune cells following primary challenge? It turns out that cellular

metabolism – the pathways that serve to provide a cell with sufficient energy for survival and growth – can cause some of these changes. Recently, intermediate molecules in various metabolic pathways, termed metabolites, have received a lot of attention for their regulation of immune cell functionality.

Indeed, specific metabolites can induce epigenetic reprogramming in innate immune cells that allow for their memory formation during infection. For example, when innate immune cells are “trained” by exposure to a fungal cell wall component, they switch from a more energy-efficient form of metabolism, oxidative phosphorylation, to glycolysis, which is not as energetically favorable. Why would they do this? 1) Glycolysis allows a cell to have more “building blocks” to make the necessary proteins for immune defense and expansion, and 2) the metabolites produced by glycolysis can act in concert with specific proteins that enable the epigenetic modifications required for innate immune training. To put it more simply, during a 1st infection, the cells of our innate immune system switch their metabolism toward construction of defense proteins and epigenetic reprogramming, for improved efficacy during a 2nd infection.

It turns out that mitochondria are primary drivers of the metabolic changes innate immune cells undergo during training. During innate immune training by bacterial or fungal cell wall components, there is a repurposing of the citric acid (TCA) cycle within mitochondria. The TCA cycle is an important source of NADH, which are energy storage molecules that can later be used by the mitochondrial electron transport chain (ETC) to produce ATP, the main source of energy for the cell. As a factory that pumps out ATP, mitochondria are often, and aptly, termed the “powerhouse of the cell”. In addition to ATP through the TCA cycle, mitochondria are also paramount in providing other key metabolites for cell function and growth. One of these TCA intermediates, fumarate, drives epigenetic reprogramming of innate immune cells to fuel production of inflammatory defense molecules, highlighting mitochondria as an important player in trained immunity.

As it turns out, the adage “the mitochondria are the powerhouse of the cell” might be an understatement for our innate immune system.

- Boyan Tsankov

YOU AGAIN!

INNATE IMMUNE CELL

PATHOGEN Figures created with BioRender.com IMMpress Vol. 11 No. 2 2023

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the MITOC THE POWERHOUSE AGAINST INFECTIOUS DISEASES

M

itochondria are not just the powerhouse of the cell. Known for their role in energy production and metabolism, they also play a significant role in the immune system. While oxidative phosphorylation is the primary pathway of energy production in higher organisms, this process is oxygen-demanding and relatively slow under stressful conditions. Therefore, mitochondria can switch to glycolysis, a rapid energy-production method independent of oxygen supply. External stressors, like pathogen-specific metabolites, can also alter mitochondrial metabolism to favour pathogen survival and replication.

at the cellular level. They can transition from a catabolic, energy-producing phase to an anabolic phase to maximize the use of metabolites for both adenosine triphosphate (ATP) production (the cellular form of energy) and cellular homeostasis. Additionally, mitochondria generate reactive oxygen species (ROS) that activate inflammatory pathways within the cell to bolster protection against intracellular pathogens. ROS also activates essential immune cell subsets such as macrophages and T cells to control and clear extracellular pathogens. This article will explore the intricate interplay between mitochondrial metabolism and various bacterial and viral infections.

Notably, mitochondria can facilitate immune responses

MITOCHONDRIA AND BACTERIAL INFECTIONS

L

egionnaire’s disease, a severe and potentially fatal bacterial pneumonia, is caused by Legionella pneumophila, an intracellular bacterium. Upon entry into human lung macrophages, L. pneumophila injects pathogenic proteins into the cell to initiate bacterial replication. This interaction has piqued great interest in better understanding Legionella infections since macrophages activation are largely influenced by mitochondrial metabolic responses. In 1983 L. pneumophila was observed to form Legionella-containing vacuoles (LCVs) upon entry into macrophages and later associate with the mitochondria. Recent studies have shed further light on how LCVs can cause mitochondrial fragmentation, an indicator of cell death. Mitochondrial fragmentation renders cells more susceptible to stressors and increases ROS production, where uncontrolled ROS output and oxidative stress can also induce cell death.

Despite this, L. pneumophila did not induce other markers of cell death. Further analyses of macrophages’ metabolic rate after L. pneumophila infection revealed a shift from oxidative phosphorylation to glycolysis, a less sustainable option for long-term cell survival and energy production.

One bacterial metabolite, which is injected

22 IMMpress Vol. 11 No. 2 2023

LEGIONNAIRE’S DISEASE

into cells upon macrophage entry, Ceg3, may interfere with a component of the oxidative phosphorylation pathway, potentially impacting ATP output and subsequent cellular function.

Metabolic alterations that may favor glycolysis over oxidative phosphorylation resemble the Warburg effect observed in cancer cells, which allows for uncontrolled and deleterious cell division. Understanding the intricacies of this relationship between L. pneumophila infection and mitochondrial involvement provides valuable insights into the mechanisms of Legionnaire’s disease and potential avenues for therapeutic interventions.

H ON DR I A MITOCHONDRIA AND VIRAL INFECTIONS

L

ong COVID, or post-acute COVID-19 syndrome, is a condition characterized by long-term symptoms appearing after the resolution of a SARS-CoV-2 infection and affects 10% of all infected individuals. The severity of the initial infection is closely tied to the risk of developing long COVID and profoundly impacts the quality of life. Metabolic perturbations, particularly involving iron deposition and mitochondrial association in the liver, are strongly linked to the severity of SARS-CoV-2 disease. Elevated iron levels can lead to tissue damage, and disruptions in mitochondrial oxidative phosphorylation can also disrupt iron metabolism, leading to tissue inflammation in a positive feedback manner.

Aside from external metabolites that serve as an indicator of COVID-19 illness severity, the mitochondrial DNA (mtDNA), a unique set of DNA within the mitochondria which governs metabolic function independently of the cell’s nuclear DNA, may serve as a biomarker for the organism’s ability to fight against infections and diseases. High levels of circulating mtDNA in the blood are associated with inflammation and linked to the severity of the initial SARS-CoV-2 infection. Tissue damage during SARS-CoV-2 infections, may increase oxidative stress, alter mtDNA, and decrease oxidative phosphorylation efficiency, thereby reducing metabolic capacity. Additionally, viral infections can lead to the expulsion of damaged mtDNA from cells, suggesting that

LONG COVID

individuals with lower mitochondrial reserves may be more susceptible to long COVID. Host cells can also modulate metabolism to fight against SARS-CoV-2. For instance, manipulating iron metabolism and metabolite consumption via mitochondrial remodelling may be a form of starvation to slow viral replication. Metabolites like succinate, found within oxidative phosphorylation pathways, also play important roles in inflammation, immunomodulation, and anti-viral activity. During hypoxic conditions caused by lung infections, alterations in oxidative phosphorylation lead to succinate buildup, causing generation of excess ROS within the mitochondria. This suggests the importance of mitochondrial health for viral resistance, but also its tolerance against oxidative stress and ability to consume high levels of ROS. Similar to L. pneumophila infections, SARS-CoV-2 viral proteins can inhibit components of oxidative phosphorylation, disrupt ATP output, enhance mitochondrial fragmentation, and induce cell death. These mitochondrial perturbations suggest a shift towards glycolysis, indicating that SARS-CoV-2 infections may heighten the risk of cancer.

Altogether, severe COVID-19 infections may be associated with lung injuries due to mitochondrial damage, but it remains elusive what proportion of these effects are caused by host versus viral effects.

CONCLUSIONS From Legionella bacterial infections to SARS-CoV-2 and post-acute COVID-19 syndrome, mitochondria play crucial roles in shaping disease outcomes. Pathogens can dynamically interact with mitochondria, potentially induce fragmentation, and compromise cellular metabolism. Understanding of how mitochondrial disease impacts immunity has led to hypotheses of treatments options, like transferring healthy stem cells to “donate” mitochondria to host cells garnering the virus and damaged mitochondria. Continued research in the field of mitochondria is encouraged to foster the development of targeted therapeutic approaches.

- Jinny Tsang IMMpress Vol. 11 No. 2 2023

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Advancements in Mitochondrial DNA EDITING: A Gateway to Curing Incurable Diseases Mitochondria, often referred to as our cells' powerhouses, contain their own unique DNA known as mitochondrial DNA (mtDNA). Mutations in mtDNA can trigger severe disorders like Mitochondrial Myopathy (marked by muscle dysfunction) and Leber's Hereditary Optic Neuropathy (marked by sudden vision loss). Despite their rarity, these diseases lack existing cures. However, addressing rare diseases poses additional challenges in treatment development due to limited research, small patient populations, diversity among cases, and industry disinterest. Yet, recent advancements in mitochondrial DNA editing show promise.

Different to nuclear DNA—multiple copies of mtDNA can coexist within a single cell, resulting in a phenomenon called heteroplasmy, where both normal and mutated versions cohabitate. While serenity reigns supreme with the harmonious interplay, discord strikes when the insurgents outnumber the virtuoso, heralding a crescendo of disease symptoms.

Conquering the elusive mtDNA has so far proven to be a technically arduous feat for researchers, due to the formidable double mitochondrial membrane posing a daunting fortress against efforts of genetic manipulation.

However, in the past two decades, significant progress has been made in mitochondrial genetics. Scientists have discovered a way to modify mtDNA using specialized proteins, such as mitochondria-targeted nucleases, acting as molecular scissors to precisely cut and remove mutated sequences. By doing so, they can restore the balance between healthy and mutated mtDNA, potentially mitigating the effects of mitochondrial diseases. This success demonstrated in laboratory trials and animal models ignites a ray of hope for future therapeutic applications in humans.

Another exciting tool is the development of base editors adapted for mtDNA editing.

Base editors are advanced molecular machines that can directly convert one DNA base into another without requiring double-stranded DNA breaks. For mitochondrial DNA, these sophisticated molecular artisans transcend the conventional boundaries; specific mutations can be corrected, or even introduced, with high precision. By utilizing these base editors, scientists can target and modify individual bases within the mtDNA with high precision, paving the way for more accurate genetic interventions and opening new avenues for research and potential therapeutic interventions in mitochondrial diseases.

While the prospect of mitochondrial DNA (mtDNA) editing holds immense promise for treating severe diseases associated with mtDNA mutations, several formidable challenges must be addressed to ensure its safe and effective implementation. One major concern is the potential for off-target effects during the editing process. Precise delivery of editing tools into the mitochondria is hampered by the double mitochondrial membrane, demanding the development of effective targeting strategies. Ensuring high specificity and accuracy in editing mtDNA sequences is critical to avoid introducing unintended mutations or adverse consequences. Ethical considerations surrounding germ-line editing warrant careful contemplation, as it could have implications for future generations. Additionally, the long-term safety and stability of edited mtDNA remain uncertain, necessitating further research to assess potential risks. Despite these challenges, ongoing research and collaboration offer hope in overcoming these obstacles and unlocking the transformative potential of mtDNA editing in mitigating mitochondrial diseases.

It is also crucial to recognize that mitochondrial diseases can manifest with various symptoms and severity levels, contingent on the specific mtDNA mutations and their distribution in the body. Since mitochondrial DNA is inherited from the mother, these disorders can be passed down maternally. As research continues to advance, our understanding of mitochondrial diseases and potential treatments may improve, offering hope for affected individuals and their families.

- Alara Tuncer

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How does exercise help our mitochondria?

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he current world marathon record is set by Eilud Kipchoge, a Kenyan marathoner who finished a full 42.195 km in only 2:01:09 in the 2022 Berlin Marathon. I, on the other hand, who follows a stereotypical sedentary lifestyle, probably would go less than 10 kms within the same time and would already be exhausted.

For a long time, researchers have wondered what is responsible for such dramatic differences in the physical abilities of elite athletes and ordinary people. The first clue, of course, was the difference in muscle compositions. In 1945, it was experimentally established that exercise and training induce biochemical differences in skeletal muscles. Soon after in 1967, science pin-pointed that exercise could also affect mitochondrial respiration in skeletal muscles. Mitochondria have two membranes. The inner membrane surrounds a partition called cristae. Earlier studies showed no evidence of plasticity in the physical structure of cristae upon exercise.

Therefore, it had been long assumed that exercise affects the plasticity of mitochondria, and not of the cristae, towards an increase in the mitochondrial volume and respiration.

In general, density of cristae predicted the maximal oxygen uptake better than the overall volume of mitochondria.

All these results suggest that it is the cristae within our mitochondria that have a certain plasticity that appears to correlate with exercise and the activity levels in our lifestyle.

Exercise impacts not only the structure of mitochondrial cristae, but also the overall health of mitochondria. This is measured by how effectively mitochondria maintain or re-establish metabolic homeostasis upon changes in metabolic needs. The importance of mitochondrial health is highlighted over the course of aging. Sarcopenia, progressive decrease in muscle mass, is a hallmark of aging responsible for various health implications for the elderly population. Dysfunctional mitochondria, such as those with fragmented morphology or mutations in the mtDNA, are significant contributors to sarcopenia. It is important to note that the mitochondrial functions of elderly people who exercise regularly are similar to those from younger counterparts, suggesting that exercise is key in preserving mitochondrial health over the process of aging.

Mitochondrial Health

This assumption was questioned in a more recent study by a group of Danish and Swedish scientists. They recruited volNearly 1.5% of all medical publications are related to unteers who were either 1) obese with a sedentary lifestyle, mitochondria. This is far higher than any other organelles 2) recreationally active, or 3) elite including the nucleus in the second athletes. All of them donated their place at around 1%. Further, the inGrowth & Adulthood Aging leg muscle biopsy samples before terest in mitochondria has only been Development and after participating in a short increasing since 1980. While the role 10-week exercise schedule. Interestof mitochondria has been and coningly, the surface area of the cristae tinues to be highlighted in various asPh y Ac sical of athletes was 150% greater than pects of health and disease, exercise tive ly those of obese sedentary individuremains the most potent behavioral als. Also, the density of cristae sigtherapeutic approach for enhancing Se den nificantly increased in recreationally mitochondrial health and overall intar y active participants after exercise. dividual longevity.

Age - Steve Lee IMMpress Vol. 11 No. 2 2023

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REDOX MEDICINE THE DOUBLE-EDGED SWORD OF OXIDANTS

Y

ou may have read the packaging on an item at the grocery store and seen the words “High in Antioxidants” shining out. Antioxidants must be important then – why else advertise it? If antioxidants are good, then oxidants must be the opposite. So, what’s the deal with oxidation?

The biology of oxidants is a topic of interest in many subspecialities of science – ranging from free radical chemistry to cancer biology. In order to understand these molecules, it is important to establish some terminology:

Oxidation: Loss of electron Reduction: Gain of electron Oxidizing agent or oxidant: Gains the electron, is reduced Reducing agent or antioxidant: Loses the electron, is oxidized Now that we’ve clarified some terms, we can look at oxidants on a physiological level. Oxidants are formed from biological process including during normal metabolism. In the mitochondria, oxidative phosphorylation is the transfer of electrons in a baton-relay race that ends with the final electron acceptor, (the final oxidant), H2O. Normal chemical kinetics sometimes result in H2O being further reduced into reactive oxygen species (ROS) such as superoxide (O2-) or hydrogen peroxide (H2O2), the former of which is also a free radical. ROS can continue to propagate and become free radicals that interact with and modify lipids, proteins and most dangerously, DNA. While there are homeostatic counter molecules, antioxidants, there are instances where the levels of oxidants greatly exceed those of antioxidants and results in a state of biological oxidative stress. The effect of oxidative stress is oxidative damage to the essential macromolecules.

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Oxidative damage can have beneficial uses and detrimental effects. During immune responses against virus-infected cells or bacteria, phagocytes cells engulf pathogens into a phagocytic vacuole where they are met with a oxidative burst, an onslaught of peroxides, superoxides and other oxidants meant to destroy the pathogen. In this scenario, cells have harnessed the destructive power of oxidants in a controlled and contained manner as an immune line of defense.

In contrast, the unchecked accumulation of oxidant species can lead to devastating damage. This can occur in a number of ways:

1

2

3

External sources of oxidants: The most notable exogenous source of oxidants is cigarette smoke, which introduces considerable oxidative stress and damage to DNA. Dysregulation of homeostatic checks: When enzymes that control oxidant levels develop mutations, the delicate oxidant and antioxidant balance can be skewed towards a pro-oxidant state.

Antioxidant deficiency: Without the counter-defense of antioxidant molecules and the enzymes that generate them, ROS propagation can go forward unchecked.

A pro-oxidant state has trickle-down effects that are implicated in a multitude of illnesses including cardiovascular, neurological, respiratory, and ocular diseases as well as multi-organ cancers. A simple example of disease development is in atherosclerosis where oxidation of lipids in a process called lipid peroxidation contributes to plaque formation.

Thus emerges the field of redox medicine, which aims to harness and reinforce the antioxidant defense system.

ta Die

THE SHARP EDGE THE OTHER EDGE

r y A n t i ox i d a

nts

Dietary antioxidants such as vitamin C from fruits and green vegetables, vitamin E from whole grains and nuts, beta-carotene from squash and carrots and lycopene from tomatoes can neutralize oxidative stress.

These same powerful antioxidants can overshoot their effects and lead to the propagation of metal ion radicals, which can circle back to the pro-oxidative state. In addition, certain antioxidants, such as lycopene from tomatoes, can have negative effects in excess.

E xe r c i s e

THE SHARP EDGE THE OTHER EDGE

IN CANCER Based on our understanding of oxidative stress, it should be no surprise that oxidative damage can contribute to cancer pathology. DNA damage that accumulates, is transcribed, and then translated leads to aberrant macromolecules that affect signalling and physiology. It then follows that pharmaceutically moving the balance towards an antioxidant state can be useful. Targeting enzymes that generate oxidants or enhancing the antioxidant systems is the mantra of many therapeutics.

Conversely, some cells known as cancer stem cells, are known to have lower levels of ROS, thus making them resis-

While moderate exercise is known to produce oxidants, these levels are usually low enough to be scavenged by homeostatic means. In fact, exercise-induced pro-oxidant production can trigger a stronger antioxidant defense than immediately required, thus keeping the entire system armed and ready.

Deleterious effects arise when exercise is overly exhaustive and combined with a diet enriched in fats and carbohydrates and limited in antioxidant nutrients. The sum of excess oxidants and excess targets for oxidation leads to a state of oxidative stress. Recall the atherosclerosis plaques?

tant to antioxidant treatment. In fact, in some instances, lower levels of ROS act a protection against peroxide induced apoptosis. In this way, cancer cells mask themselves using the other side of the redox equation.

This double edge sword is a prime example of a core principle in chemistry, biology, and health; the need for moderation and a middle-ground. The struggle to establish it is evident in the need for physiological homeostasis and accepting trade-offs in medicine. It is no surprise then, that the maintaining the equilibrium of the redox equation is a delicate a balancing act.

- Sila Usta IMMpress Vol. 11 No. 2 2023

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Canadian Society for Immunology 2023 35th Annual Meeting

F

rom June 6-9, immunologists across the country gathered in the charming Eastern township of Orford, Quebec for the 35th annual meeting of the Canadian Society for Immunology (CSI) at the Hôtel Chéribourg. While the rainy weather dissuaded most from exploring the scenic trails around the conference site, the beautiful scenery nonetheless acted as a welcoming backdrop to four days of exciting immunology and networking with our colleagues from coast-to-coast.

KEYNOTE CSI 2023 opened with a keynote address delivered by Dr Luke O’Neill (Trinity College Dublin), showcasing how lessons learned from rare human diseases can help us better understand the underlying immunology for broader therapeutic applications. Thematic to this issue of IMMpress Magazine, the unifying concept of this address was how mitochondrial dysfunction underpins many flavours of inflammatory and autoimmune diseases. Poised at the intersection of biochemistry and immunology, Dr O’Neill spoke on the role of two Krebs’ cycle intermediates, itaconate and fumarate – molecules generated in the mitochondria during the process of metabolic respiration – in both metabolism and modulating the immune response. Macrophages stimulated by lipopolysaccharides (LPS), a major bacterial toxin, upregulate both itaconate and fumarate. Dr O’Neill and his team demonstrated that itaconate and related derivatives inhibit proteins involved in inflammatory pathways such as NLRP3 and JAK1, leading to anti-inflammatory and anti-microbial effects. On the other hand, fumarate accumulation, which occurs through fumarate hydrogenase inhibition, drives type I interferon release via mitochondrial stress and induced inflammatory responses. Interestingly, fumarate dehydrogenase has been found to be repressed in lupus patients, implying a role for metabolic dysregulation in certain autoinflammatory diseases. The stories of these two metabolites emphasized the untapped potential of immunometabolites as both therapeutic targets and agents across a spectrum of immune-mediated diseases.

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PERSONALIZED IMMUNITY The first symposium explored how different biological aspects can be considered to tailor therapies for effective clinical outcomes. Dr Ivona Aksentijevich (National Human Genome Research Institute) discussed how patient stratification by molecular diagnosis is critical in informing targeted therapies, particularly in cases of autoinflammatory diseases.

Next, Dr Keke Fairfax (University of Utah) spoke on how helminth infection by Schistosoma mansoni can interact with biological sex to modulate the risk of developing metabolic syndromes, conferring protection against atherosclerosis, obesity, and diabetes in male, but not female, mice. Dr Naoto Hirano (University of Toronto) then brought us to the other end of the spectrum of personalized medicine, introducing the generation of an HLA-agnostic chimeric antigen receptor (CAR) T cell therapy against the tumour antigen WT1 that can bypass the issue of cell therapy-patient HLA class II incompatibility. Dr Channakeshava Umeshappa (Dalhousie University) described a novel peptide-MHCII nanomedicine strategy that induces the differentiation of a novel regulator Maf+LiNKTR1 invariant natural killer T cell population that may represent a potential therapy in autoimmune liver diseases. Concluding the first symposium, Dr Marc Horwitz (University of British Columbia) demonstrated that latent chronic Epstein-Barr virus infection can drive increased susceptibility and severity of multiple sclerosis (MS) in mice, and discussed how this approach can be adapted using human immune cells to create personalized preclinical models of MS for therapeutic testing.

MECHANOSENSING Kicking off the second full conference day was a series of talks on how cell migration can influence immune function. Dr Morgan Huse (Memorial Sloan Kettering Cancer Center) showed how biophysical characteristics like plasma membrane abundance link the processes of phagocytosis and migration, providing evidence that deficiencies in the G protein subunit Gβ4 lead to altered patterns of chemotaxis and phagocytosis in myeloid cells. Moving towards the field of cancer immunology, Dr Valerie Weaver (University of California, San Francisco) described how fibrosis and stiffening of the tissue in breast cancer can be sensed by tumour cells to drive the epithelial-mesenchymal transition (EMT) and promote tumour metastasis. Dr Pablo Vargas (French Institute of Health and Medical Research) brought with him astonishing videos of various immune cells in motion as they maneuver through micro-fabricated obstacles and confined spaces reminiscent of the anatomical landscapes they scale daily while patrolling our tissues. Dr Judith Mandl (McGill University), the co-chair of this symposium, then took the stage to discuss how mechano-sensing of the tissue environment can act as a cue for tissue-resident memory T cell differentiation, initiated through changes in cellular cytoskeletal components such as F-actin. Rounding out the second symposium was Dr Spencer Freeman (University of Toronto), who spoke on how internal mechanical stresses within macrophages during fluid handling can translate into inflammatory responses.

THROMBOINFLAMMATION The last symposium brought focus to an oft-overlooked cell type that straddles the fields of immunology and hematology – platelets. Dr Bryan Heit (University of Western Ontario) shared his observations on the potential link between platelet activation and increased thrombotic events in patients infected with influenza A virus, which may be driven by the elevated levels of platelet-derived microvesicles enriched with transmembrane tissue factor in the serum of these patients.

Continuing the discussion on the role of platelets in respiratory infections, Dr Milka Koupenova (University of Massachusetts Medical School) explained how platelets can initiate innate immune responses against respiratory viruses such as influenza and SARS-CoV-2 by internalizing the virus and activating immune cells via complement and exosome release.

Despite the ability of platelets to initiate an inflammatory response, Dr Julie Rayes (University of Birmingham) spoke about how the immune functions of platelets are resistant to classic anti-platelet therapies in the context of inflammation, highlighting neutrophils as a central regulator for platelet activation through the release of danger-associated molecular patterns (DAMPs) that promote thrombosis and further leukocyte recruitment and activation. Dr Genevieve Pepin (Université du Québec à Montréal) took a step back to examine platelet development, which could provide clues to how platelet-intrinsic mechanisms through the cGAS/STING pathway may drive thromboinflammation. As the final symposium speaker for this year’s meeting, Dr Patricia Liaw (McMaster University) described how neutrophils activate coagulation through NETosis – the release of DNA to trap and contain

extracellular pathogens – in sepsis patients. Tying in themes from the first symposium on personalized immunity, Dr Liaw highlighted two biomarkers, the levels of circulating DNA and coagulant protein C, in stratifying sepsis patients for treatment based on the pathological contribution of neutrophils versus thrombosis.

AWARDS AND ACKNOWLEDGEMENTS Our congratulations to Dr Zhou Xing (McMaster University), the recipient of this year’s Bernhard Cinader Award. He shared with us his work on the effectiveness of inhaled vaccines in boosting the local respiratory immune response following a primary intramuscular vaccine, such as in the case of tuberculosis and COVID-19. Dr Xing highlighted the ability of this vaccine strategy in inducing a tripartite immune protection involving T cells, B cells, and lung macrophages, and provided two examples of such vaccines developed by his lab currently in clinical trials. He left us with some insights as a “solitary scientist” amidst the academic social scene, encouraging introverts among the room to

“unleash the quiet power in an ever louder scientific world.”

Other awardees of the year included Dr Kelly McNagny (University of British Columbia), recipient of the Investigator Award, and Dr Daniela Quail (McGill University), recipient of the New Investigator Award. A warm round of congratulations also goes out to all travel and poster award winners.

We were saddened this past year to have lost two long-standing members of the CSI community, Dr John Bienenstock (McMaster University) and Dr James Carlyle (University of Toronto), and in memoriam speeches were prepared by friends and colleagues to honour their contributions.

The CSI 2023 meeting would not be made possible without the generous support from an impressive list of sponsors: BioLegend (Champion Sponsor), 10X Genomics, Miltenyi Biotec, Thermo Fisher, Cytek Biosciences, Sony Biotechnology, CIHR, Clinical Immunology Network – Canada, Biogen Canada, Université Laval, Cedarlane Laboratories, Centre de recherche de l’Hôpital Maisonneuve-Rosemont, CHU Ste-Justine, CIHR – Institute of Infection and Immunity, Université de Sherbrooke, Leinco Tevchnologies, Paraza Pharma, Centre for Research of the CHUS, and Université du Québec à Trois-Rivières.

Last but not least, we thank the local organizing committee, the Trainee Engagement Committee, and staff for their tremendous work in putting together a packed schedule of talks, workshops, and trainee events: Dr Manu Rangachari (Chair - Université Laval), Dr Hélène Decaluwe (CHU Ste-Justine), Dr Momar Ndao (McGill University), Dr Martin Pelletier (Université Laval), Dr Geneviève Pépin (Université de Quebec à Trois-Rivières), and Dr Lee-Hwa Tai (Université Sherbrooke). Congratulations on a successful conference, and we look forward to seeing everyone again next year in Banff, Alberta for the 36th CSI meeting!

- Karen Yeung IMMpress Vol. 11 No. 2 2023

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Who is Mitochondrial Eve the mother of all humans?

T

he blueprint of our body lies within our DNA – the genetic material we inherit from our parents. It is common knowledge that equal parts of this DNA come from our mother and father. A single strand of someone’s DNA can not only be used to determine their biological parents but can also point to their ancestry. This is called ancestry tracing.

Many platforms, such as “ancestry.com” and “23andMe”, have made genomic DNA analysis available and accessible, helping determine your genetic predisposition to diseases as well as your carrier status for certain genetic diseases. They can also help quench your general curiosity regarding your ancestral history. However, the latter may not be accurate as they claim, as analyzing genetic information over an exceptionally large number of generations can be very challenging. Since each child has two parents, the amount of data doubles every generation you include in the analysis. For example, you have two parents, four grandparents, eight great-grandparents and so on. For this reason, ancestry tracing becomes quite tedious and leads to an excess of information when you are trying to look at hundreds and thousands of generations, which ultimately leads to inaccuracy and inconclusive results.

This is where people have turned to a special type of maternal ancestry tracing that is simpler yet informative, the mitochondrial DNA (mtDNA) tracing.

Contrary to conventional DNA tracing, which uses nuclear DNA information that is equal parts inherited from maternal and paternal DNA, mitochondria consist solely of genetic material derived from the mother.

Through mtDNA tracing, scientists like Allan Wilson have attempted to pinpoint the first human female by drawing a line through generations of mothers to our most recent common female ancestor – the Mitochondrial Eve. She is believed to have lived around 30 IMMpress Vol. 11 No. 2 2023

200,000 years ago in what’s now Africa.

Importantly, all currently living humans are descendants of her.

But is the Mitochondrial Eve truly the most recent common ancestor of the entire human race? Another group of scientists says no and thinks this is an overinterpretation of molecular evolution data. Soon after the proposal of the idea of mitochondrial Eve, F.J. Ayala, and others argued that such a retrospective method of looking at ancestral genes was not the best representation of the truth. They highlighted that it is crucial to acknowledge that Eve was not the only female of her time. There could be other female ancestors at this time; however, unlike Mitochondrial Eve, none have a direct matrilineal descent traceable to all humans living today.

This might be because being childless or only bearing sons stopped their maternal ancestry line in history. In addition, the amount of mtDNA that current humans have inherited from the Mitochondrial Eve is exceptionally minute, about 400,000th of the total DNA in a cell.

The rest of the DNA, namely nuclear DNA, can be from maternal and paternal lines; hence it includes other maternal ancestor genes. This makes it hard to pinpoint the first “real” common female

ancestor using mtDNA alone, as we might potentially carry more genes from females other than the identified Mitochondrial Eve. Moreover, the tree of evolution is not segmented.

Evidence has suggested continuous interbreeding between early human species like the Neanderthals and Denisovans, making it unrealistic to pinpoint the true female “human” ancestor.

Taken together, this evidence has raised some important questions – did Mitochondrial Eve truly exist? Or is she just a mythical creature conjured up by scientists who unknowingly oversimplified some very complex data? What do you think?

- Manjula Kamath

U

ndoubtedly, Power, Sex, Suicide is a book with a very punchy and eye-catching title. The title summarizes the critical message the author Nick Lane wants to convey: mitochondria are way more than just the powerhouse of the cell.

Currently a professor of Evolution Biochemistry at University College London, Lane has dedicated his career to mitochondrial and evolution research.

In this book, he lays out his knowledge of mitochondria—impressively extensive, in a light-hearted tone. Going in prepared to have a hard 500-pagegrind, I was pleasantly surprised at how story-like Lane presented the information and concepts. Lane walks us through the basics of mitochondria biology and functions, then outlines the current debates in mitochondrial research – their critical roles in eukaryotic cell evolution, the development of sex, and the mechanisms behind aging.

I found the section on aging most exciting and thought-provoking. Lane goes through front-running theories of mitochondria-induced aging from different schools of thought. By comparing relatively long-lived birds to relatively short-lived humans, Lane leads the audience in discussing why humans age and age faster. Lane touches upon the very popular and advertised anti-aging class of products, antioxidants, which claim to target oxidative products of mitochondria, as oxidative stress has been shown to be related to mitochondria-mediated aging. Lane argues that simply targeting mitochondrial products is an unviable and, in fact, dangerous solution to counter aging, as these molecules are integral in normal cell signalling and development. He also discusses a new perspective in understanding aging: long-lived birds have a relatively higher energy “spare capacity” for strenuous activities like flying.

He proposes that perhaps the “cure of aging” lies within increased mitochondrial numbers and the mitochondrial ability to regulate oxidative products.

This was undoubtedly a brand-new route to be considered in tackling aging issues.

Mitochondria: bounded by a membrane, but of unbounded impact a book review

Power, Sex, Suicide: Mitochondria and the meaning of life

By Nick Lane Oxford University Press, 2nd edition, 2018

Despite these assertions, I don’t find this argument convincing and believe more questions must be answered. For instance, since mitochondria evidently possess their own DNA, as they undergo uniparental inheritance, the chances of correcting mitochondrial mutations or creating genetic variation seem limited. How do cells correct these accumulating mutation burdens or enable mitochondria to adapt to changing external factors? In addition, it is puzzling why eukaryotic cells did not evolve to allow for mitochondrial DNA recombination, which would generate only one type of mitochondria, thereby minimizing the compatibility risks, similar to inheritance from only one parent.

Lane also proposes that mitochondria drive the establishment and derivation of sex - specifically, the existence of only two, but not more or less, biological sexes. I am, on the other hand, more dubious about this section of the book. As mutations and damages naturally occur in nuclear DNA, cells may become less fit for survival when mutations accumulate. Lane argues that “selfish” mitochondria drive their less fit cell “host” into fusing with another cell to strive for a better chance for survival. Through this process, two cells fuse and recombine to produce a healthier set of nuclear DNA. However, this may also lead to incompatibility between mitochondria from different cell sources. To avoid this conflict, it is more practical to consistently include mitochondria from only one source or parent, ultimately giving rise to the existence of two sexes - one being mitochondria-contributing and one not.

Although Lane tailors the content of the book to a vast, non-scientific background audience, readers without a biology background might find it challenging to get through the minutiae of the book. I appreciate that Lane not only presents the theories he believes in but also contradicting views, unravelling the history of discovery and key experiments. He often delivers thought-provoking questions to transition into different topics or discuss un-deciphered mysteries in a particular area. This type of narration provides the audience with not just dense facts, but also creates a fun story by taking the audience through the journey that the biology field took to unlock the hidden secrets of mitochondria. This book is worth a read for anyone interested in mitochondria and evolution.

- Evey Zheng

IMMpress Vol. 11 No. 2 2023

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Department of Immunology University of Toronto 1 King’s College Circle Toronto, ON M5S 1A8 Canada

King's College Circle showing the campus, library, and medical building with city in the distance.

(1903-1913)

Photo Credits: University of Toronto Archives.