In a recent paper in Nature Communications, a research team led by Daria Mochly-Rosen of Stanford University discovered a small protein that facilitates the interactions of other proteins to maintain mitochondrial integrity and function during oxidative stress.
Mitochondria are unusual cell organelles. They have their own DNA and are involved in multiple key activities. Disruption of these activities contributes to many acute and chronic diseases. Mitochondria also have mechanisms, such as fission and fusion, to ensure they maintain their effectiveness. Fusion allows damaged mitochondria to be improved by adding functional components, and fission provides a way to either increase mitochondrial number and/or to eliminate those damaged beyond repair.
Mitochondrial fission is overactivated in times of oxidative stress. The mechanism was partially understood. During stress, this process begins when a protein in the outer mitochondrial membrane called fission protein 1 (Fis1) recruits a GTPase called Drp1 to the outer mitochondrial membrane. In yeast, this interaction is enough to initiate fission in both physiological and stress conditions, but not in humans.
Suman Pokhrel in the Mochly-Rosen lab sought to determine what was missing by using protein studies and genetically engineered cells. Her team discovered that a key cysteine amino acid in Fis1 (Cys41) was critical for the process. Cysteines are often important components of intermolecular associations because they can form disulfide bonds. During oxidative stress, this is just what happens. The two molecules of Fis1 bound together serve to induce excessive fission. Through further research, the team discovered a new drug called SP11 that selectively inhibits dimerization of Fis1 and thus inhibits excessive fission during stress.
The findings of the group, including the discovery of the pivotal role of Cys41 in dimerization, show how mitochondrial fragmentation can be selectively inhibited during oxidative stress. Furthermore, SP11 or other compounds that work like it might become a therapeutic for the treatment of many chronic diseases associated with mitochondrial fragmentation and dysfunction.
A discussion with Dr. Mochly-Rosen
MitoWorld: This is an interesting paper. Can you suggest what might be the next steps in this research?
Mochly-Rosen: We will continue the basic research to examine how Fis1 binds Drp1 and recruits it to the outer mitochondrial membrane. We also plan to continue developing therapeutics that inhibit Fis1 activation during stress. We will keep optimizing these molecules and evaluate their safety and effectiveness in animal models as part of our interest in translating our research to the clinic.
MitoWorld: Your results indicate that there is an extra step in humans compared to yeast. Do you have any speculation on why that extra step would have evolved?
Mochly-Rosen: Humans are multicellular, and their biology is far more complex than a single‑celled organism, such as yeast. As a result, multicellular creatures often evolve new machinery and more finely tuned regulatory mechanisms to carry out complex functions, and the divergence of Fis1 function is one example of that. One interesting observation is that genetically removing Fis1 causes death of mice during embryonic development, implying that Fis1 plays a critical role at embryonic stage. This suggests that in humans, Fis1 evolved to carry out an important role in embryonic development that yeast simply doesn’t need.
MitoWorld: The involvement of Cys41 is an “extra” step in human and other mammalians. However, that still begs the question of what signal initiates fusion. Do you know what the beginning step is yet?
Mochly-Rosen: Cys residues are sensitive to oxidative stress and their SH moiety in two Cys residues that are close enough to each other losses the proton (H) to generate an S-S bond between these adjacent residues, thus linking the two Fis1. The dimeric Fis 1 can now bind dimeric Drp1 to trigger mitochondrial fission. Thus, oxidative stress is required to activate this process, and by inhibiting the dimerization, the mitochondria are protected.
MitoWorld: This paper goes a long way to explain the mechanism for pathological fission. Is it too simple to hope that some aspects of this work would be helpful in unraveling the fusion process?
Mochly-Rosen: Mitochondrial fusion and fission are driven by distinct protein machinery within cells. Although mechanistic understanding of fission components alone doesn’t directly provide insights into understanding the fusion process, it helps reveal how these processes are balanced and suggests that dimerization of the components is the first step in their activation. Our research will examine this possibility.
MitoWorld: You have already done considerable work on possible therapeutic agents. Might it be a drug that uses the phenothiazine moiety and mimics SP11’s actions? Do you plan to follow up on your work in mice?
Mochly-Rosen: Our molecule, SP11, needs further development to improve its drug properties. We need to be sure the molecule is completely safe and sufficiently stable so it stays in the body long enough to exert its effect. Once we’ve optimized for safety and stability, we plan to test this new series of molecules in animal disease models.
MitoWorld: What caused you to become interested in mitochondria in the first place?
Mochly-Rosen: Way back, almost two decades ago, we looked at cells from rats with high blood pressure and noticed their mitochondria were a lot more broken up than usual. When we treated animals with neurodegenerative diseases with compounds that prevented that fragmentation, they got better. Since then, we’ve been interested in understanding this pathological mitochondrial fission and discovering chemical agents that block fragmentation. The more I’ve learned about mitochondria, the more fascinated I’ve become with these organelles. Today I believe that having healthy mitochondria is the key to healthy cells and thus to healthy organs and a healthy body. New medical interventions that target mitochondria won’t necessarily cure all diseases, but by reducing the burden on the cell, they can allow it to heal itself—and even other cells. I’ve been following the remarkable progress in mitochondrial research over the past few years, and I’m hopeful that discoveries in the field will translate into solutions that help patients.
Reference
Pokhrel S, Heo G, Mathews I, Yokoi S, Matsui T, Mitsutake A, Wakatsuki S, Mochly-Rosen D
(2025) A hidden cysteine in Fis1 targeted to prevent excessive mitochondrial fission and dysfunction under oxidative stress. Nat Commun 16: 4187.
In a paper1 published in Nature Metabolism, a research group at the University of Helsinki led by Pekka Katajisto, examined the effect of organelle age on cell fate determinations in tissues. Interestingly, they found that asymmetric cell divisions concentrate older mitochondria in stem cells that are more efficient in tissue renewal.
Specifically, the team sought to test the hypothesis that metabolism is a major factor in cell fate decisions and regeneration. They studied mouse intestinal stem cells (ISCs) that inhabit the crypts in the intestine where new intestinal epithelial cells are created to replace those normally worn out. They developed methods to isolate ISCs, based on the age of their mitochondria.
They were particularly interested in a subset of ISCs enriched with older mitochondria. While many other characteristics of this subset were similar to other ISCs, they did have some intriguing aspects. They form organoids more readily, which is consistent with their ability to reform their niche cells, thus leading to better resistance to damage by chemotherapy. They produce more a-ketoglutarate (aKG) that has many activities, including the ability to change epigenetics.
In summary, they found that in ISCs the aged mitochondria regulate cell fate. The findings suggest future treatment strategies that target the found metabolic mechanisms.
A Discussion with Dr. Katajisto
MitoWorld: What do you see as the next steps in your work? For example, you suggest that epigenetic changes (e.g., with aKG) might drive this process. Do you plan to look at that possibility?
Yes, we do already know that the process is dependent on epigenetic modifiers of the TET group of enzymes that hydroxymethylates methylated cytosines in the DNA. Interestingly, out of the relatively small set of genes with changes in this mark in ISC with old mitochondria, surprisingly many have been linked to processes related to regeneration or niche cell differentiation. We are currently probing if hydroxymethylation of these genes is crucial for the first steps of fate determination as ISCs become niche cells.
MitoWorld: Your paper suggests some fascinating possibilities. Can you speculate on the mechanism that allows the older mitochondria to be segregated during cell division? Is the relative success of cells with older mitochondria determined purely by energy needs?
The answer is that we don’t know yet. Somehow the cell must be able to recognize domains of the mitochondrial network based on their age as they enter mitosis. In our previous work2 using human asymmetrically dividing cell lines, we saw that older mitochondria localize closer to the nucleus. But how they are recognized and asymmetrically segregated in the cell we don’t yet know. We don’t think the intestinal stem cells with older mitochondria necessarily produce more energy in the form of ATP, as their morphology is not consistent with having higher oxidative phosphorylation capacity. However, again in our previous work3 we did see that older mitochondria in cultured cells have higher oxphos capacity. In the ISCs it seems to be instead the relative amount of the TCA intermediates aKG, succinate and 2-HG, which are crucial for the success of ISCs with old mitochondria in generating niche cells faster, and subsequently regenerate the epithelium.
MitoWorld: It has been hypothesized that aging began from the asymmetric division in bacteria. It is interesting that mitochondria, which derived from bacteria, have continued this practice in other settings. Is this as common a phenomenon as it might seem?
Katajisto: What a fascinating question. Although we have not looked into this it is quite possible that some of the mechanisms allowing of segregation of mitochondria of different age could be common to their bacterial ancestors, as are many other features of mitochondria. In any case, the discovery of seemingly separate sub-pools of mitochondria that are also selectively and asymmetrically segregated in cell divisions, raises interesting questions also for example on regulation of fission and fusion dynamics of mitochondria.
MitoWorld: The reprogramming of cells to iPSCs and other cell types has become routine in labs and showed the plasticity of cell fate commitments. Any thoughts on how mitochondrial aging and segregation fares in those protocols?
Katajisto: It is indeed interesting to look into this phenomenon in many iPSC-derived differentiations as introduction of our construct is relatively straightforward. However, the high amount of growth factors and inhibitors used in the in vitro differentiation protocols to force specification of certain lineages and cell fate may override naturally occurring subtle mechanisms, such as the metabolism imposed by age-selective mitochondrial segregation. We are currently looking for example into how mitochondrial age impacts the functional maturity of PSC derived pancreatic beta cells.
MitoWorld: This is an important finding for science. Can you see any treatment possibilities down the road? For example, might aKG supplementation be helpful? Or on a more speculative note, if the cell-to-cell transfer of mitochondria can be mastered, might those transfers be beneficial?
Katajisto: In our work, we found that giving aKG to old mice for 2 weeks before administration of the commonly used chemotherapeutic drug 5-FU promoted their recovery after the treatment known to cause severe side effects particularly in elderly patients. Thus, we think that aKG administration indeed has potential in chemoprotection, but we of course have to first test how aKG impacts the effectiveness of the drug against cancer. Mitochondrial transfer is another fascinating avenue, and it might well be that the differentiation potential or fitness of cells that are to be used for cellular therapy could be boosted with the transfer of the right kind of mitochondria. However, the effect from transferred mitochondria would probably be very transient, and so strategies targeting or mimicking the age-specific traits of mitochondrial metabolism by other means are likely going to be more practical.
Katajisto: MitoWorld: What drew you to the study mitochondria in the first place?
Originally,2 I set out to study if age-dependent segregation of organelles is a feature of mammalian asymmetrically dividing cells with the thought that stem cells might push the older, possibly damaged organelles, into the differentiating daughter cell to keep the stem cell pool healthy. Mitochondria3 and peroxisomes4 were found to be asymmetrically segregated between the differentiating and self-renewing daughter cells, but it turned out that old organelles were not damaged, just metabolically different. Thus, I started studying mitochondria because they were the most striking age-dependently segregated organelle in my original findings, using the human cell line, and it turned out that this was also taking place in tissue resident stem cells in mice.
References
1Andersson S, Bui H, Viitanen A, Borshagovski D, Salminen E, Kilpinen S, Gebhart A, Kuuluvainen E, Gopalakrishnan S, Peltokangas N, James M, Achim K, Jokitalo E, Auvinen P, Hietakangas V, Katajisto P (2025) Old mitochondria regulate niche renewal via α-ketoglutarate metabolism in stem cells. Nat Metab 7: 1344–1357.
2Katajisto P, Döhla J, Chaffer CL, Pentinmikko N, Marjanovic N, Iqbal S, Zoncu R, Chen W, Weinberg RA, Sabatini DM (2015) Asymmetric apportioning of aged mitochondria between daughter cells is required for stemness. Science 348: 340–343.
3Döhla, J., Kuuluvainen, E., Gebert, N. et al. (2022) Metabolic determination of cell fate through selective inheritance of mitochondria. Nat Cell Biol 24: 148–154.
4Bui, H., Andersson, S., Sola-Carvajal, A. et al. (2025) Glucose-6-phosphate-dehydrogenase on old peroxisomes maintains self-renewal of epithelial stem cells after asymmetric cell division. Nat Commun 16: 3932.
A paper1 recently published in Science explored the fascinating question of how the mitochondrial genome affects cellular function. The research work was carried out at the University Medical Center of Gottingen, led by Prof. Peter Rehling and Luis Daniel Cruz-Zaragoza (currently Professor at the Department of Biology, Université de Sherbrooke). Through a multi-institutional collaboration, the team developed a method to silence the translation of specific mitochondrial mRNAs selectively and used it to gain a deeper understanding of how mitochondria regulate translation.
Human mitochondria have their own small circular genome that encodes genes for essential proteins needed for oxidative phosphorylation. However, they are also involved in many other cellular functions, and most of the genes for those other functions are contained in the nuclear genome. The interactions of the two genomes are one of the most interesting open questions in biology today. Dissecting the translation of mitochondrial mRNAs has been challenging because standard methods (e.g., CRISPR) do not work inside mitochondria.
To overcome this challenge, the scientific team used synthetic peptide-morpholino chimeras to inhibit translation of specific mitochondrial genes. These synthetic molecules combine the phosphorodiamidate morpholino oligonucleotides directed against a specific mRNA with a mitochondrial targeting signal (or presequence). The chimeric molecules entered the mitochondria and blocked translation. By inhibiting the synthesis of each protein under different conditions, the researchers could ascertain the particular cellular response upon depletion.
With this study, the team identified proteins involved in the biogenesis and activity of the oxidative phosphorylation complexes. They also gained insights into how the cell deals with the loss of a key protein. Ultimately, the method can be applied to numerous other studies in mitochondrial biology.
Conversation with Dr. Cruz-Zaragoza
MitoWorld: Polymorpholino oligonucleotides are typically used as antisense oligonucleotides. Why did you decide to apply them for targeting the expression of mitochondrially encoded genes?
LDCZ: Close to 99% of proteins in the human mitochondria are encoded in the nuclear genome, translated in the cytosol, and imported into the mitochondria. Several genetic approaches are available to study and understand the function of this group of proteins, including CRISPR-Cas9, siRNA, epigenomic expression, and genomic integration. Those methods require the use of nucleic acids. Although transfecting nucleic acids into a cell is relatively straightforward, the same doesn’t apply to the mitochondria.
Mitochondria have two membranes: the outer mitochondrial membrane (OMM) and the inner mitochondrial membrane (IMM). The electron transport chain (ETC) is localized on the IMM. The activity of ETC generates a potential difference across the mitochondrial membrane, known as the mitochondrial membrane potential, making the IMM’s luminal side negatively charged. Therefore, it is no surprise that the introduction of nucleic acids into the mitochondria is highly inefficient, hindering efforts to apply genetic engineering to mitochondrial gene expression. Remarkably, researchers have developed several solutions based on proteins, such as base editors and mito-zinc finger protein nucleases.
We expected that non-charged oligonucleotides, such as phosphorodiamidate morpholino oligonucleotides, should be better imported into mitochondria. To target the morpholinos (MO) to the mitochondria, we initially fused the MO to a protein carrier via click chemistry, generating protein-MO chimeras. We applied this initial approach in isolated mitochondria.2
However, it did not escape our attention that a more versatile method was required for use in living cells. Therefore, building on our previous work, we optimized the chimera stability and efficiency by replacing the protein component with a mitochondrial targeting signal peptide.1
MitoWorld: What experiments do you have planned to extend this work?
LDCZ: It was thrilling to develop this expression-silencing project. For our recently published work, I had the opportunity to work with several talented graduate students. In addition, the collaborators who participated in our study are remarkable, combining expertise in proteomics (Bettina Warscheid’s group), microscopy (Stefan Jakob’s group), and transcriptomic data analysis (Michael Lidschreiber’s group). So, exciting work is in the making at University Medical Center of Gottingen.
I recently established my lab at the Université de Sherbrooke in Canada. As part of our research program, we will address the functional aspects of mitochondrial RNA life using the peptide-MO chimeras. We will follow an RNA-centered approach and examine how it correlates with the traditional protein-centered one. Luckily, Quebec, and Sherbrooke in particular, has an excellent group of scientists working in RNA biology as part of the RiboClub and the DNA to RNA Initiatives. Exciting times ahead!
MitoWorld: Were you able to link the loss of a specific protein to any human disease?
LDCZ: In our work, we explored the cellular response to challenges associated with the inhibition of subunits encoded in the mitochondrial genome. We have not yet made a direct comparison with mtDNA human disease models. However, it is an attractive problem that we, and other labs, will follow up on. One exciting aspect of our approach is the possibility of revealing and understanding, at the cellular level, the initial stages of defects in mitochondrial gene expression. In the field, researchers traditionally study patient-derived cells that have undergone long-term adaptation. However, silencing mitochondrial transcripts recapitulates the initial chronic depletion of proteins produced in the mitochondria, allowing us to examine how the cell responds and adapts to the challenge. In fact, one can study the onset of the disease in specialized cells, such as cardiomyocytes and hepatocytes. Therefore, this could be extended to other cell types, such as neurons and oocytes. This could contribute to the development of better therapies for mitochondrial diseases.
MitoWorld: Do you see any clinical or diagnostic applications for this methodology?
LDCZ: That is a great question. We can now tune the expression of specific genes encoded in mtDNA. This would allow for controlling the assembly rate of proteins with different genetic origins (nuclear and mtDNA) that form the respiratory complexes, which could be an avenue for treating disorders where the balance is lost. However, some aspects must be addressed before. The most important one is to show that the silencing approach is working in animal models.
MitoWorld: What drew you to mitochondria in the first place?
LDCZ: I have always been intrigued by the eukaryotic cell compartments. During my doctoral studies in Ralf Erdmann’s group at Ruhr-Universität Bochum, I investigated the peroxisome, focusing on its biogenesis mechanisms and function. I enjoyed it very much as part of the Marie Curie Initial Training Network PERFUME (PERoxisome, FUnction, MEtabolism). While attending conferences about protein targeting, I saw how exciting the research in mitochondria was. After finishing my PhD, I joined Prof. Rehling’s group to study mitochondrial protein import. Later, I became interested in working on mitochondrial gene expression. Combining my scientific interests in protein import and gene expression was central to devising the strategy of importing protein-MO chimeras to regulate mitochondrial gene expression.
References
1Cruz-Zaragoza LD, Dahal D, Koschel M, Boshnakovska A, Zheenbekova A, Yilmaz M, Morgenstern M, Dohrke JN, Bender J, Valpadashi A, Henningfeld KA, Oeljeklaus S, Kremer LS, Breuer M, Urbach O, Dennerlein S, Lidschreiber M, Jakobs S, Warscheid B, Rehling P (2025) Silencing mitochondrial gene expression in living cells. Science DOI: 10.1126/science.adr3498.
2Cruz-Zaragoza LD, Dennerlein S, Linden A, Yousefi R, Lavdovskaia E, Aich A, Falk RR, Gomkale R, Schöndorf T, Bohnsack MT, Ricarda Richter-Dennerlein R, Henning Urlaub H, Peter Rehling P (2021) An in vitro system to silence mitochondrial gene expression. Cell 184: 5824–5837.
A recent paper in Science Advances describes the findings of a research team led by Mondira Kundu, MD, PhD, at St. Jude Children’s Research Hospital. The study investigates how mitochondrial (mt) DNA mutations influence leukemia pathology. Unexpectedly, their research showed that a moderate burden of mtDNA mutations can enhance the development of leukemia. They also show that cancer can be re-initiated by inhibiting a specific enzyme in cells carrying a high burden of mtDNA mutations.
Cancers are highly energy dependent, with the mitochondria serving as the cell’s main energy producers. While most research into this connection has focused on mutations in nuclear DNA that affect mitochondrial function, Dr. Kundu’s team explored whether mutations directly in the mtDNA contribute to tumor development.
The researchers began with three lines of mice expressing a mutant exonuclease-inactive mitochondrial DNA polymerase (Polgmut) that lacks accurate proofreading ability. These lines possess either zero (Polgwt/wt), one (Polgwt/mut), or two (Polgmut/mut) copies of the mutated allele, resulting in a graded accumulation of mtDNA mutations. Hematopoietic progenitor cells (HPCs) were isolated from these mice and engineered to express NMyc, a member of the MYC family of transcription factors. Members of the MYC family are commonly dysregulated in many blood cancers, such as leukemia. By transplanting these HPCs into irradiated recipient mice, the team assessed the impact of different levels of mtDNA mutations on cellular metabolism and cancer development.
The findings were unexpected: while metabolism was reduced in mice with either heterozygous or homozygous mutant cells, mice with a moderate mutation load (Polgmut/wt) were more prone to tumor formation than those with a high mutation load (Polgmut/mut). Metabolic plasticity was affected by the number of mtDNA mutations and was critical to the tumorigenic potential of the HPCs. In essence, a moderate number of mutations makes cells more metabolically flexible and more carcinogenic, whereas extensive mutations diminish both their metabolic flexibility and cancerous potential.
Conversation with Dr. Kundu
MitoWorld. Your results are unexpected. Do you have any thoughts on why the partially damaged mitochondria would be beneficial to the cancer? Yes, it appears that partially damaged mitochondria create a unique metabolic environment that cancer cells can exploit. Moderate mitochondrial dysfunction may allow for metabolic reprogramming—enhancing glycolysis and other pathways that support rapid cell growth—without fully compromising energy production. This balance may give cancer cells a survival and growth advantage.
MitoWorld. Can you speculate on how the damaged mitochondria are able to increase their metabolic support for the tumors? Damaged mitochondria may trigger adaptive responses in cancer cells, activating alternative metabolic pathways and stress responses. For instance, partial mitochondrial dysfunction can increase the reliance on glycolysis (the Warburg effect) and other biosynthetic pathways, thereby supporting both energy needs and the synthesis of cellular building blocks required for proliferation. The cells remain metabolically flexible, which is crucial for tumor growth.
MitoWorld. You note both similar and different results with this mutation and different cancers. To what would you attribute those varying results? The impact of mtDNA mutations likely depends on the tissue context and the specific metabolic requirements of different cancers. Some tumors may be more resilient to mitochondrial dysfunction, while others are more dependent on intact mitochondrial metabolism. Additionally, the interplay between mtDNA mutations and nuclear gene mutations can vary, influencing how cells adapt metabolically and whether they become more or less tumorigenic.
MitoWorld. Your results show that inhibiting pyruvate dehydrogenase kinase improved the ability of the homozygous mutant to cause tumors. Does this observation have any therapeutic implications? While our findings are not immediately translatable to therapy, they do highlight the critical role of metabolic plasticity in leukemogenesis. The fact that inhibiting pyruvate dehydrogenase kinase (PDK) restored the proliferative capacity of homozygous mutant HPCs suggests that metabolic pathways can profoundly influence tumor development. This raises the possibility that targeting metabolic enzymes like PDK could one day be leveraged to modulate cancer cell growth, either by restricting the metabolic flexibility of cancer cells or by exploiting specific metabolic vulnerabilities. However, more research is needed, especially since the mutation burden in human leukemias typically comes from single mtDNA mutations, unlike the mouse model, where the burden comes from the cumulative effect of many mutations.
MitoWorld. What do you see as the next steps to follow up on this work? The next step is to introduce specific mtDNA mutations into primary cells and then add oncogenes. This will allow us to examine how individual mtDNA mutations—and their allele fractions—impact tumorigenesis. By better modeling the mutation patterns seen in human cancers, we can determine whether particular mtDNA mutations or metabolic states make cancer cells more susceptible to targeted metabolic therapies. Ultimately, this line of research could guide the development of new therapeutic strategies that exploit the metabolic dependencies created by mtDNA mutations in cancer cells.
MitoWorld. What attracted you to the study of mitochondria? As a hematopathologist, I have a strong interest in hematologic diseases, but my research has always spanned a variety of biological systems. My interest in mitochondria began during my postdoctoral fellowship in Craig Thompson’s lab, where I used red blood cell maturation as a model to study mitophagy—the process by which cells selectively remove damaged or superfluous mitochondria. That experience highlighted for me how central mitochondrial function and dysfunction are to cell biology and disease, including cancer. I am particularly intrigued by how cells sense and respond to mitochondrial dysfunction—especially when it’s caused by mtDNA mutations—and how these adaptive pathways can contribute to cancer development. Understanding the complex interplay between mitochondrial function and cellular responses not only deepens our knowledge of cancer biology but also points to new possibilities for therapeutic intervention.
Reference
Li-Harms X, Lu J, Fukuda Y, Lynch J, Sheth A, Pareek G, Kaminski MM, Ross HS, Wright CW, Smith AL, Wu H, Wang Y-D, Valentine M, Neale G, Vogel P, Pounds S, Schuetz JD, Ni M, Kundu M (2025) Somatic mtDNA mutation burden shapes metabolic plasticity in leukemogenesis. Science Advances 11(1): eads8489.
In a preprint article currently under review1, “Guardians of the mitochondria: Space mitochondria 2.0 systemic analysis reveals bioenergetic dysregulation across species,” a research team led by Afshin Beheshti (Director of Center for Space Biomedicine, Associate Director of the McGowan Institute for Regenerative Medicine, and Professor of Surgery and Computational and Systems Biology at the University of Pittsburgh) with co-senior author Chris Mason (WorldQuant Professor at Weill Cornell Medicine) explores the broad impacts of spaceflight on mitochondrial biology in humans and across a range of animal species to identify consistent effects of space exposure on the organelle and its influence on human health.
Astronauts returning to Earth after extended time in space suffer a number of stressors, including bone and muscle loss, cardiovascular and renal issues, circadian rhythm disruptions, potential long-term cancer risks, and ocular disorders. These health effects are thought to be caused by some combination of exposure to higher levels of radiation and reduced gravity. However, the exact mechanisms of how the conditions of space travel manifest in the physical symptoms in astronauts and other organisms are still unclear.
Previous work by Mason and Beheshti, including the “NASA Twins Study” and the “Space Omics and Medical Atlas,” measured biological characteristics in twin astronauts, Mark and Scott Kelly2 and then compared them to many additional cohorts and missions. The landmark Twins study tracked the astronauts over 340 days, while one flew on the international space station and the other remained on Earth. Surprisingly, the investigators identified mitochondrial respiration as one of the first and most important biological processes to be disrupted by spaceflight.
This new report aims to expand upon and generalize the prior findings by extracting mitochondrial function data from several studies of space exposure in a range of species, including humans (Guarnieri et al., in review). This large-scale, multi-institute study integrates an impressive collection of multi-omics data from humans, rodents, and other organisms before, during, and after returning from space. This rich dataset enables the authors to draw broader conclusions about how the mitochondria of people or animals will respond to spaceflight.
The authors show that effects of space exposure occur in a duration-dependent manner across species and tissues. More specifically, it causes accumulation of reactive oxygen species (ROS) and impairs mitochondrial oxidative phosphorylation (OxPhos), the series of enzymatic reactions that mitochondria use to extract the energy from the food we eat. Moreover, the cellular stress induced by ROS accumulation and OxPhos disruption causes the release of mitochondrial signals that trigger immune system abnormalities in astronauts and animals. Strikingly, the changes to OxPhos and immune activity are accompanied by epigenetic changes that influence mitochondrial gene expression and last for more than 14 weeks after astronauts return to Earth.
The severity of mitochondrial impairment was influenced by the genetic background of the animals exposed to the space environment. Mice with mutations leading to less robust mitochondrial antioxidant defenses against ROS experienced greater damage during space flight, suggesting certain biological pathways can be harnessed to stratify risk profiles and protect astronauts on future missions. To this end, the team tested if kaempferol, an antioxidant compound and stimulator of mitochondrial biogenesis, could reduce the damage from space exposure. Mice treated with kaempferol were protected from liver damage during spaceflight, and human liver organoids exposed to the compound in space lost less mass and retained their function, compared to their untreated counterparts.
This study differs from previous efforts in that it examines changes in mitochondrial biology in response to a range of space-exposure durations across species of animals. It emphasizes the need for and provides evidence of preventative measures and in-flight treatments that can protect astronauts from damage to their mitochondria during longer space missions. These methods and countermeasures will become more important as longer space flights are considered, and they may also shed light on Earth-bound disease mechanisms as well.
Discussion with Drs. Beheshti and Mason
MitoWorld: Space travel seems to affect multiple tissue and organ systems. Could you expand on the mechanisms underlying the effects on mitochondrial function? What work do you think should be done to better understand the conditions that lead to mitochondrial stress?
Beheshti: The two primary stressors in space that drive mitochondrial dysfunction are microgravity and space radiation. In our recent preprint, we highlight how the degree of mitochondrial disruption depends on the radiosensitivity of different tissues, suggesting that some tissues are more vulnerable than others. While both microgravity and radiation are likely to act synergistically, I believe radiation has a more pronounced and compounding impact on mitochondrial health. To better understand these mechanisms, we need studies that systematically compare the effects of microgravity and radiation, both independently and in combination. Additionally, ongoing research, including our own, is evaluating a range of mitochondrial-targeted supplements and therapies as potential countermeasures. I believe there’s strong potential to develop an optimized “mitochondrial cocktail,” a combination therapy tailored to protect against space-induced mitochondrial stress and, ultimately, safeguard astronaut health during long-duration missions.
MitoWorld: Different tissues seem to respond to space exposure in unique ways. Can you speculate on why our organs have different sensitivities to spaceflight? Furthermore, does the stress response to damage in one organ system feed forward to damage otherwise more resilient tissues?
Beheshti: As I mentioned earlier, different organs in the body have varying degrees of radiosensitivity, which helps explain why tissues respond differently to spaceflight. In our recent work, we outline how tissues, such as the spleen, skin, eyes, and immune-related organs, tend to be more radiosensitive, and denser tissues, such as muscle, bone, and brain, are generally more radioresistant. These differences have long been established in the field of radiation biology and translate well to the context of space radiation exposure. However, even the more resistant tissues are not immune. Given prolonged exposure to the space environment, we observed a widespread suppression of mitochondrial OxPhos across all tissues, including long-term effects after returning to Earth.
An important and often overlooked aspect is how damage in one organ system can propagate systemic stress. While we didn’t delve into this in the paper due to limited available data, the concept of a “bystander effect” from radiation biology is highly relevant here. This phenomenon describes how irradiated cells can transmit stress signals to neighboring non-irradiated cells, leading to secondary damage. Similar effects have been observed at the tissue level, suggesting that injury to more radiosensitive organs could exacerbate dysfunction in otherwise more resilient tissues. This kind of cascading, systemic stress response may play a significant role in how the body as a whole reacts to prolonged space exposure, and underscores the need for integrated, multi-organ studies to fully understand and mitigate these complex interactions.
Mason: Each organ system has distinct energetic requirements, and thus, we expect to see some heterogeneity in the response across tissues. Also, each organ ages at different rates, and so, this also is likely a function of mitochondrial function and complex biological interactions across multiple pathways and systems.
MitoWorld: Does mitochondrial morphology or dynamics change in the low-gravity conditions of spaceflight?
Beheshti: This is an important and still open question. At this time, we don’t have definitive data on how mitochondrial morphology or dynamics change under microgravity conditions, but it’s an area that absolutely warrants deeper investigation. In fact, we are currently conducting imaging experiments to address this very question, and we hope to provide new insights soon. Based on what we know about mitochondrial behavior under various stress conditions on Earth, I strongly suspect that mitochondrial morphology does change in microgravity. Disruptions in mitochondrial fission and fusion dynamics, alterations in cristae structure, and changes in network connectivity are all possible responses to the unique stresses of spaceflight. These changes could have significant downstream effects on energy production, redox balance, and apoptosis, ultimately impacting tissue health and resilience. Understanding these structural and functional adaptations will be key to developing targeted interventions to preserve mitochondrial health in space.
MitoWorld: It’s very interesting that the immune system is affected by mitochondrial stress induced by space flight and that epigenetic changes persist for weeks after astronauts return to Earth. Are returning astronauts more susceptible to infection after long-duration space missions, and does this pose a risk for infections threatening the viability of future space settlements and long-duration travel throughout the solar system?
Beheshti: Our findings suggest that mitochondrial dysfunction, particularly the long-term suppression of OXPHOS, plays a central role in disrupting immune function during and after spaceflight. This mitochondrial stress appears to impair the energy metabolism required for proper immune cell activation and response, leading to broader immune dysregulation. While our study highlights this link mechanistically, it raises the concern that astronauts may indeed be more susceptible to infections after long-duration missions. However, it’s important to note that direct evidence of increased infection rates in returning astronauts is still limited.
What is particularly concerning is that these mitochondrial and immune impairments persist for weeks after return to Earth, and are accompanied by sustained epigenetic changes. This suggests that the immune system does not immediately rebound post-flight, which could pose risks not only upon re-entry but also during extended missions, where access to medical intervention is limited. If such immune vulnerabilities are not properly mitigated, they could threaten the health of crew members and the overall viability of future deep space missions or permanent settlements.
Moving forward, more research is needed to directly measure susceptibility to infection post-flight and to identify reliable biomarkers that flag immune dysfunction early. We must also begin validating countermeasures, including mitochondrial-targeted therapies, that preserve or restore immune resilience in the space environment.
Mason: We don’t see longer risk of infection post-flight, but we and others do see a lot of viral activation in-flight, and changes in biological pathways related to immune function and activation.
MitoWorld: If astronauts, who are selected for being very physically fit and disciplined individuals, suffer ill health effects from long duration space travel, how would the physiological response to long-term spaceflight differ in a cross section of the population?
Beheshti: When it comes to mitochondrial dysfunction, I believe we would see similar core impacts across the general population, but the severity and resilience of the physiological response could vary widely, depending on baseline health, genetic predispositions, and other risk factors. Astronauts are among the most physically fit and medically screened individuals; yet, even they exhibit signs of mitochondrial stress, immune dysregulation, and other health effects during and after long-duration spaceflight. This suggests that members of the general population, who may have pre-existing conditions or less physiological reserve, could be even more vulnerable to the same stressors.
As Dr. Mason pointed out, the Inspiration4 mission, which was the first all-civilian crewed orbital mission, provided a glimpse into how non-career astronauts might respond to spaceflight. While it was a short-duration mission, it offered early indications that space-induced physiological changes are not limited to elite astronauts. If missions extend to months or years, as envisioned for Mars or deep-space travel, we can expect a wider range of biological responses and potentially more severe health challenges in a more diverse population.
This underscores the need for personalized countermeasures and comprehensive health monitoring tools that can accommodate a broader range of individuals. Future missions will likely include people of varied ages, health backgrounds, and genetic profiles. Understanding these differences and proactively developing adaptable therapies, particularly those targeting mitochondrial resilience, will be critical for the success and safety of long-duration human exploration throughout the solar system.
Mason: We saw that the Inspiration4 crew, which was an all-civilian crew, did just fine during a 3-day orbital mission, and so we are cautiously optimistic for future civilian crews. However, as noted above with the murine data and organ risk, the genetic background of the person and other medical factors should all be considered when assessing flight plans.
MitoWorld: This paper showed that an antioxidant and stimulator of mitochondrial biogenesis may have therapeutic benefit for astronauts. Are there any other pathways revealed by your work that you would like to target next to mitigate the damage from spaceflight?
Beheshti: Absolutely. While our study highlighted the therapeutic potential of compounds, such as kaempferol, an antioxidant and activator of mitochondrial biogenesis, our multi-omics analysis revealed additional pathways and molecular targets that warrant investigation as countermeasures. One key area involves the TCA cycle, which we found to be significantly disrupted across multiple tissues post-spaceflight, particularly at later recovery times. This dysfunction alters key metabolites, such as α-ketoglutarate and succinate, that compromise energy metabolism and act as epigenetic regulators, influencing long-term gene expression patterns.
We also observed suppression of mitochondrial protein import machinery (e.g., TOMM20, CHCHD4), MT-ribosome biogenesis, and Fe-S cluster biosynthesis—critical components for maintaining mitochondrial integrity. These are promising intervention points. Another major axis of dysfunction involves sustained activation of the HIF-1α/mTOR pathway, which shifts cellular metabolism from OXPHOS toward glycolysis in a maladaptive response to stress. Targeting this metabolic rewiring could help preserve energy efficiency and reduce cellular senescence.
Additionally, our work showed that mitochondrial damage leads to the release of DAMPs, such as mtDNA and mtdsRNA, which chronically activate innate immune responses (e.g., via cGAS-STING, NLRP3, and RIG-I/MDA5 pathways). This immune dysregulation could be addressed through strategies that reduce mtDAMP release or block downstream inflammatory cascades.
Beyond antioxidants, we’re also exploring:
- SOD2 mimetics (e.g., MnTBAP, EUK8) to reduce oxidative damage,
- MicroRNA-based therapeutics (targeting miR-16-5p, miR-125b-5p, and let-7a-5p),
- PGC1α activators, such as epicatechin or TFEB/NRF1 inducers, and
- regulators of mtDNA replication and repair, including POLG co-factors.
These approaches offer a systems-level path forward. We’re now working to identify synergistic combinations, a kind of “mitochondrial cocktail,” to simultaneously stabilize bioenergetics, dampen inflammation, and promote mitochondrial renewal. These countermeasures are critical for astronaut health during deep space missions and for understanding and treating age-related mitochondrial decline here on Earth.
MitoWorld: You examined an extraordinary number of systems in this paper. What might be the next steps to follow up on this study?
Beheshti: This study was an ambitious effort to map systemic mitochondrial dysfunction across species, but it’s just the beginning. The next logical step is to expand these investigations into additional models that more closely simulate the conditions of deep space, particularly with higher radiation doses and longer exposure durations. These environments will allow us to better assess how prolonged mitochondrial suppression impacts organ function, immune resilience, and aging-like phenotypes.
Equally important is advancing the development and testing of mitochondrial-targeted countermeasures. While our results with kaempferol are promising, a broader, more systematic approach is needed. This includes evaluating combinations of antioxidants, metabolic modulators, gene expression regulators, and mitochondrial biogenesis enhancers across multiple tissues and models. I believe we’re on the cusp of identifying an optimal therapeutic mitochondrial cocktail that could protect against the chronic stressors of spaceflight.
I also want to take this opportunity to invite the broader mitochondrial and space biology communities to join us. Collaboration will be essential to accelerate the development of effective interventions. This is an open call. If you’re working on relevant pathways or therapeutics, let’s connect and build a coordinated strategy to move this field forward together.
Finally, space provides a unique and accelerated model of mitochondrial disease. The dysfunctions we observed in astronauts mirror and, in some cases, intensify those seen in patients with mitochondrial disorders. If we can validate countermeasures that work under the extreme conditions of space, there’s a strong potential to translate those findings back to Earth and develop novel treatments for patients suffering from mitochondrial diseases and related chronic conditions.
Mason: Replication is the cornerstone of good science, and so we want to continue to test these models in future missions, other animal cohorts, and in other cellular contexts.
MitoWorld: Aging induces changes in mtDNA over time and causes changes in the ratio of healthy mtDNA to damaged mtDNA, known as heteroplasmy. Would it be wise in future studies to look at heteroplasmic shifts and if they are permanent or seem to rebound once astronauts return to Earth?
Beheshti: Yes, indeed it will be. We have plans to further explore this.
Mason: Yes, we have seen some evidence of this already from prior missions, and this is an exciting area for future study.
References
1Guarnieri JW, Maghsoudi Z, et al. Guardians of the mitochondria: Space mitochondria 2.0 systemic analysis reveals bioenergetic dysregulation across species. Cell In review.
http://dx.doi.org/10.2139/ssrn.5087025
2Garrett-Bakelman FE, Darshi M, Green SJ, Gur RC, Lin L, Macias BR, McKenna MJ, Meydan C, Mishra T, Nasrini J, Piening BD (2019) The NASA Twins Study: A multidimensional analysis of a year-long human spaceflight. Science 364(6436): eaau8650.
Preface:
If we consider that mitochondria are the power plants of the cell, it may come as no surprise that they house a complex array of molecular machines, fine-tuned to churn out copious amounts of energy. What is remarkable, however, is that the blueprints for this machinery are rolled up in two distinct genomes—one nuclear, the other mitochondrial. This dual-genome system presents both challenges and opportunities to the cell in its never-ending quest to produce energy and adapt to an ever-changing world.
Each day, we synthesize roughly our own body weight in adenosine triphosphate (ATP) molecules, the universal energy currency that powers nearly every biological function1. Mitochondria—abundant in virtually all human cells—are the primary source of this ATP, synthesizing it from the oxygen we breathe and the nutrients we consume. The molecular machines that perform this astonishing work, every moment of every day, are situated in the inner mitochondrial membrane (IMM) and are known as the respiratory complexes (RCs). Together, complexes I through IV create an electrochemical gradient of protons across the IMM; these protons subsequently pass through complex V, driving its rotary mechanism and catalyzing ATP synthesis.
For these RCs to function efficiently, nearly 100 protein subunits must assemble in the IMM—a feat made more complex by the need to coordinate expression across two separate genomes: the diploid nuclear genome and the numerous circular copies of mitochondrial (mt)DNA distributed throughout the dynamic mitochondrial network. Significant genetic mismatch between these genomes can result in mitonuclear incompatibility, disrupting OxPhos assembly and ATP production.
Although the molecular mechanism of OxPhos is coming into focus in increasingly granular detail, an ambitious new study—published in Cell Genomics, from the lab of José Antonio Enríquez—traces the fundamental role of evolution in shaping the RC subunits at both the population and individual levels2. Over the course of more than 6 years, the authors conducted detailed analyses of each of the OxPhos subunits, integrating comparative genomics, protein structural modeling, and rigorous statistical analysis to produce a comprehensive map of both the diversity and the evolutionary constraints operating within this critical energy-producing system.
Notably, examination of more than 2,500 genotypes in the 1000 Genomes Project revealed an unexpected plasticity in the extent to which individuals could assemble different versions of the OxPhos machinery, based on the inherent variability stemming from diploidy and heterozygosity (i.e., different versions of the same gene coming from maternal and paternal chromosomes). For example, over 90% of people analyzed in this study could assemble at least two configurations of complex I. In the cases of complexes IV and V, no individual could assemble only a single version of the molecular machines. Thus, contrary to prior assumptions, the OxPhos machinery is not a rigid structure but a dynamic ensemble, that assembles in multiple configurations, depending on an individual’s genetic makeup. Moreover, a systematic analysis of individual amino acid residues—encoded by mtDNA, X, or autosomal chromosomes—demonstrated that the mitochondrial genome, due to its elevated mutation rate, represents a key source of variation and adaptability in human populations.
To further probe the evolutionary dynamics of the OxPhos proteins, the authors developed a novel methodology, called ConScore, for evaluating the extent to which specific amino acid residues are conserved across evolution. How compatible OxPhos protein subunits may be with one another depends substantially on how well they fit together in the larger 3D macromolecular complexes. Therefore, interface residues (IFRs) represent key determinants of mitonuclear compatibility. While interface residues (IFRs) in nuclear-encoded subunits—particularly those encoded on autosomes—are highly conserved, those in mtDNA-encoded subunits are surprisingly variable. This increased plasticity likely reflects an evolutionary mechanism that facilitates compatibility between divergent nuclear and mitochondrial genomes, especially at heterologous binding sites.
Despite this flexibility observed in heterologous IFRs encoded by mtDNA, 65–75% of all OxPhos residues exhibit no variability. Moreover, for many OxPhos genes, one of the two alleles is preferentially expressed, a phenomenon known as allelic imbalance. This early developmental bias constrains which subunits are effectively produced, thereby limiting the potential variability at the protein level—even when multiple variants are present in the genome.
Overall, this study illuminates the evolutionary forces that shape the essential OxPhos machinery. It reveals how cells balance strict functional requirements with surprising structural plasticity—maintaining energy production while allowing adaptability through mechanisms like mtDNA variation, allelic imbalance, and isoform diversity. These findings deepen our understanding of mitochondrial biology and offer insights relevant to disease, aging, and speciation.
MitoWorld: Oxidative phosphorylation requires the coordinated assembly and activity of numerous protein subunits from the nuclear and mitochondrial genomes. What was the inspiration for your study, and what key gaps in knowledge did you aim to address at the outset?
Mito-nuclear incompatibilities are widely recognized not only as drivers of speciation but also as key contributors to mitochondrial diseases in humans. The goal of our study was to better understand the evolutionary trajectory of oxidative phosphorylation (OxPhos) from vertebrates to modern human populations at the finest possible resolution—down to individual amino acid residues. We focused on two main objectives. First, we aimed to identify evolutionary patterns among respiratory complexes or subunits, distinguishing them based on their coding genome or mode of inheritance (mtDNA-encoded, nuclear autosomal-encoded, or X-chromosome-linked). Second, we sought to refine the current understanding of functional constraint in human OxPhos proteins at the residue level, by comparing conservation patterns across nested phylogenetic scales: vertebrates, mammals, and primates. All analyses and interpretations were conducted with a strong emphasis on molecular 3D structures, which serve as the central framework of this work.
MitoWorld: From an evolutionary perspective, what key differences did you identify between the mitochondrial and nuclear genomes?
The behavior of these two genomes shows distinct variation in relation to the respiratory complexes, most notably in complexes I (CI) and IV (CIV). Our findings suggest that mitochondrial DNA (mtDNA) functions not only as an evolutionary driver, facilitating speciation, but also exhibits a continuous dynamic role. This supports the hypothesis that the capacity for change (defined by the mutational rate of mtDNA) is a conserved trait. At the population level, this capacity for change enables mtDNA to undergo selective sweeps that help to balance the heterozygosity in nuclear-encoded OxPhos subunits. The result is the emergence and maintenance of viable mitonuclear combinations that highlight a cooperative, co-evolutionary process between the two genomes.
MitoWorld: Your study integrated genomic analyses with structural data. How did bringing together information from these different disciplines enhance your overall understanding of the OxPhos system?
Genetics or genomics and structural biology, although developed and studied as independent branches of biology, are deeply interconnected. Genetic changes often gain biological and evolutionary significance when they manifest as phenotypic traits, particularly through alterations in proteins, whose function is closely tied to their 3D structure. Moreover, certain evolutionary trends can only be observed by examining their impact on protein structures, such as the differential evolutionary patterns in binding sites.
MitoWorld: You used extensive datasets like the 1000 Genomes Project and gnomAD v3. Were there any limitations or biases in these datasets that might affect how we interpret the variability and constraints you observed?
Certainly, these databases, while representing a significant effort to cover human variability, are far from a comprehensive picture of the human genetic diversity. Therefore, we complemented human variation data with comparative analyses across other phylogenetic groups, anchoring our interpretations in evolutionary conservation and maintaining a focus on human protein structures. This cross-species perspective allows us to broaden our understanding of the functional significance of specific residues by examining their tolerance to change.
MitoWorld: Throughout your analysis, what results did you find most unexpected, and how did they shift your view of the respiratory complexes?
One of our most surprising findings was the prominent role of heterozygosity as a critical source of individual genetic variability, supported by analysis from the 1,000 Genomes Project. In a biological system, such as OxPhos, which is governed by the interplay and coevolution of two separate genomes, this observation raised the fundamental question about how such variability is managed at the molecular level. This led us to investigate allelic imbalance as a possible mechanism. To delve deeper, we focused on a pronounced example (hybrids between subspecies). Our findings revealed that allelic imbalance serves not only as an evolutionary means to mitigate heterozygosity but also as an indicator of additional regulatory complexity. It directly impacts the precise coordination required for the expression and assembly of multi-component systems; mismatches in this process may predispose to disease. Another striking result was how strongly selective pressures shape the 3D landscape of functional constraints within OxPhos complexes. This 3D map reflects the intricate evolutionary pressures at play on protein structure and function at the residue level.
MitoWorld: To evaluate the extent to which individual amino acid residues of the respiratory complexes are conserved, you developed a methodology called ConScore. Can you explain how this works and why it can shed light on the impact of mutations in different regions of a protein?
ConScore measures how conserved a specific position in a protein is, helping us to understand how likely it is to tolerate mutations. It combines information from variations in humans and other species (using sequence alignments) to show which changes at that position are allowed by evolution.
MitoWorld: How do you think that ConScore could be leveraged to characterize the genetic underpinnings of different pathologies associated with OxPhos dysregulation, such as mitochondrial diseases, cancer, or neurodegeneration?
Benchmarking results suggest that the ConScore can be directly applied to variant prioritization. However, to realize its full clinical potential, we envision two complementary directions for future development. First, we aim to evaluate its applicability beyond OxPhos components, extending its use to proteins that interact with OxPhos pathways. Second, we propose incorporating ConScore as a feature within machine-learning models to develop a more refined tool for assessing the pathogenicity of mutations.
MitoWorld: Mitochondrial transplantation or transfer involves the incorporation of mitochondria through different strategies, such as injection, vesicular transport, or intercellular bridges. Your study highlights the importance of mitonuclear incompatibility. How can we potentially optimize the coordinated expression and function of the hundred or so OxPhos subunits in the context of potential therapies?
Our previous work already found that this may be a relevant issue from a clinical point of view (PMID: 35236094; PMID: 32832682; PMID: 31588014; PMID: 27383793). Here we developed and refined in silico models of the OxPhos respiratory complexes that can be used to investigate ConScore-guided sequence variations in nuclear and mtDNA-encoded OxPhos components to anticipate compatibility issues, supporting further research in this area.
MitoWorld: Your work suggests that the high mutation rate of mtDNA is not just a vulnerability but may be an adaptive feature. Do you think that mtDNA mutability itself has been selected for during evolution?
The answer is yes. The symbiosis that led to the origin of eukaryotic cells incorporated mtDNA from the very beginning. Therefore, the mutation rate of each chromosome, including the mtDNA, has been optimized for evolutive success. This idea was also suggested by Wallace in 2010. In our study, we observed that, compared to nuclear-encoded subunits, the variability in mtDNA-encoded subunits is higher between species (with some exceptions, depending on the respiratory complex) and within human populations. Moreover, interface residues in mtDNA-encoded subunits show greater variability than other regions of the same proteins, suggesting a relaxation of selective constraints that is maintained even among humans.
These patterns support the idea that mtDNA mutability should not be understood as a vulnerability, but rather an evolved feature that contributes to functional flexibility and adaptive potential, especially in the context of mito-nuclear coevolution. The increased mutation rate in mtDNA could allow more rapid exploration of sequence space, enabling compensatory adaptations in response to changes in nuclear-encoded partners or environmental pressures. While more evidence is needed to confirm whether mtDNA mutability itself has been directly selected for, our results are consistent with the hypothesis that this feature plays an adaptive role in fine-tuning oxidative phosphorylation and maintaining mito-nuclear compatibility.
MitoWorld: What are some big outstanding questions relating to how evolution molds the OxPhos machinery?
Well, a challenge to address is investigating the functional differences in the OxPhos system among phylogenetic groups and their adaptive significance across various ecosystems. This exploration should occur at the residue, protein, respiratory complex, and supercomplex level.
References:
1. Lane, Nick (2018) Power, Sex, Suicide: Mitochondria and the Meaning of Life. Oxford University Press, Oxford, UK.
2. Cabrera-Alarcón JL, Rosa-Moreno M, Sánchez-García L, Agustín PH, Jiménez-Gómez MC, Martínez F, Sánchez-Cabo F, Enríquez JA (2025) Structural diversity and evolutionary constraints of oxidative phosphorylation. Cell Genom. 100945. doi: 10.1016/j.xgen.2025.100945. Epub ahead of print. PMID: 40614727.
In a recent paper published in Nature Communications, a research team led by Nick Jones at Imperial College London explored the relationship between mutations in mitochondrial DNA and aging. More specifically, they examined “cryptic mutations” that are somatic mtDNA mutations unique to single cells in the sample.
The team accessed publicly available sequencing of the nuclear and mtDNAs of 140,000 individual cells from four mammalian species and seven tissues. Both DNA types show increased numbers of mutations with aging. As assumed, the increase in nuclear DNA mutations was linear. However the mtDNA showed a nonlinearity. In fact, the number of mutant genomes in a cell reached high levels around the time when the effects of aging are seen in humans. Although these results are surprising, they are also consistent with previous studies that show that mice with more rapid rates of mtDNA mutation age more rapidly.
They also noted that the rise of mtDNA mutations correlates with key aging manifestations, such as protein misfolding, endoplasmic reticulum stress, and markers of neurodegeneration.
Conversation with Dr. Alistair Green and Prof. Nick Jones
MitoWorld: These are intriguing results. Others have suggested that infusions of healthy mitochondria into cells would have therapeutic benefits. Might they also slow the aging process?
Jones: This could be a fertile direction to pursue, though there is not much evidence that large amounts of mtDNA are transferred into cells.
MitoWorld: Mitochondria are associated with many key cellular functions, but they have genes for little more than energy production. Can you speculate on the mechanism that links these mutations to aging? Could it be as simple as the loss of ability to produce energy, or is there more?
Green: Loss of energy production is definitely the leading order concern, but there are other mechanisms that could be at work. Mito-nuclear mismatch has been known to impair function, and we see a stress response in cells carrying cryptic mutations. If mutant mtDNA is released into the cytoplasm this could also be causing this stress response.
MitoWorld: Your results seem to correlate with caloric restriction as a mechanism to slow aging. Interestingly, that would seem to lower available energy levels. Can you comment on that seeming contradiction?
Green – While severe caloric restriction can lower energy levels, the opposite is true for mild restriction. Mitochondria can become more efficient and crucially for our model, cells can switch on mitochondrial biogenesis, increasing the number of mitochondria in cells. This increase in copy number is what our model predicts would slow the ageing we observe.
MitoWorld: Could there be some “cryptic” signaling between the mtDNA and nuclear DNA to account for this correlation?
Jones: Trying to establish just what is causing the correlation is definitely the focus of future work. Some signaling between nuclear DNA and mitochondrial DNA is definitely one avenue of investigation.
MitoWorld: Did you find any particular mtDNA mutation that seemed to stand out or were they more or less equally distributed?
Green: They are fairly evenly distributed across the genome, excepting the known mutational hotspot by the origin of replication. The lack of selection we see would support that cells have a hard time identifying mutations in any particular region that they might be less tolerant to.
MitoWorld: What do you see as the next steps in this research?
Jones: We would like to corroborate these effects in more proliferative cell types.
MitoWorld: How did a mathematician become interested in mitochondria?
Jones: There are multiple copies of mtDNA in a cell and the fluctuations in that number, and the number of mutations they contain, is quantifiable and presents tricky mathematical challenges. Simultaneously the products of this single quantifiable entity have wide-reaching cell physiological effects: this is thus a setting where bringing together stochastic modelling, inference, informatics and experimental design can yield transformative insights.
MitoWorld: Another recent paper reports on mtDNA mutations and aging (Wang, Z., Li, Z., Liu, H. et al. Mitochondrial clonal mosaicism encodes a biphasic molecular clock of aging. Nat Aging (2025). https://doi.org/10.1038/s43587-025-00890-6). Do you have any thoughts on that paper?
Jones: This recent interesting paper is based on using bulk-RNA seq — our paper first appeared on bioRxiv two years ago and is focused on single cells and thus gives a direct insight on the process at hand.
Reference
Green AP, Klimm F, Marshall AS, Leetmaa R, Aryaman J, Gomez-Duran A, Chinnery PF, Jones NS (2025) Cryptic mitochondrial DNA mutations coincide with mid-late life and are pathophysiologically informative in single cells across tissues and species. Nat Commun 16: 2250. https://doi.org/10.1038/s41467-025-57286-8
In a paper in Nature Communications, a multi-institution research team, led by Phillip West at The Jackson Laboratory, describes hyperactivity of the innate immune system in models of polymerase gamma (PolG)-related mitochondrial disease (VanPortfliet et al., 2025). This work advances understanding of how mitochondrial diseases impact the immune system and identifies potential therapeutic targets to limit immunopathology and other infection-associated complications.
Mitochondrial diseases (MtDs) are the most common inborn errors of metabolism. Although patients with MtD do not appear to have more viral and bacterial infections than others, emerging research suggests infections can result in more severe outcomes, including sepsis and death. The relationship of MtDs and inflammation has therefore become a topic of considerable interest in the research community. Mitochondrial dysfunction can activate the innate immune system, which responds with inflammation that, when unregulated, further damages mitochondrial activity.
In their paper, West’s team delved further into this problem. More specifically, they examined two mouse models that carry deleterious mutations in the PolG gene (PolgD257A and PolgR292C). They found that these mutations, which impact mitochondrial DNA (mtDNA) stability, result in chronic activation of the type I interferon (IFN-I) pathway in immune cells and tissues. Furthermore, they uncovered that IFN-I hyperactivates another immune sensor called caspase-11, which senses bacterial cell wall components and promotes inflammatory cell death in macrophages. This form of cell death, called pyroptosis, is critical for control of bacterial infections, but must be tightly regulated because it promotes the release of cytokines and other factors that lead to a strong inflammatory response. When innate immune cells from the PolG mutant mice were infected with bacteria, they underwent pyroptosis much more readily and caused a dramatic increase in inflammatory responses. This overactive innate immune response was also seen when PolG mutant mice were infected with bacteria.
Although these PolG mutant mice do not recapitulate all aspects of PolG-related MtDs, chronic activation of the innate immune system, increased inflammatory responses, and other symptoms are seen in MtDs in humans. Thus, this experimental system is an excellent model for studying innate immunity in MtDs.
A Conversation with Dr. West
MitoWorld: What caused you to become interested in mitochondria and MtDs?
West: I have been studying the interplay between mitochondria and the innate immune system since my PhD training at Yale. I somewhat stumbled into mitochondrial biology during my thesis research, but have been fascinated by these organelles ever since. As a postdoctoral fellow with Gerry Shadel, I found that mtDNA release is a potent trigger of interferon and inflammatory responses. As all of our early work was in cells, I wanted to translate our findings into animal models when I opened my own lab. We hypothesized that because MtDs have dysfunctional mitochondria and often exhibit mtDNA instability, there may be an unappreciated role for immune dysfunction in these diseases. We are addressing this hypothesis in mouse models of MtD, including the PolG mutants used in this paper, but are also striving to translate our results into understanding immune dysfunction in human MtDs.
MitoWorld: Under normal circumstances, the immune system is carefully regulated. Too little control is thought to allow cancers to grow. Too much results in autoimmune diseases. MtDs are yet another source of immune dysregulation. Do you have ideas about how to follow up your work in humans?
West: We are working collaboratively with Dr. Peter McGuire’s group at the NIH/NHGRI, who are also studying in immune dysregulation in MtDs. We were fortunate to be included on Peter’s recent study (Warren et al., 2023) that revealed interferon and inflammatory gene signatures in the white blood cells of patients with diverse MtDs. There was significant overlap in the immune signatures seen in patient cells and two of our mitochondria mutant mice, so we do feel our animal studies correlate with human data. Our goal now is to identify immunotherapeutics that may be used to restore proper immune function and limit infection-related complications in individuals with MtDs.
MitoWorld: It’s interesting that MtD patients are more susceptible to infections and have an enhanced innate immune response. During the Covid pandemic, any vaccination was thought to activate the innate immune system and protect (to a degree) against coronavirus infection. Is the MtD case, just another example of the immune system gone awry?
West: This is an interesting question. I think it is important to highlight that the immune phenotypes in MtDs will probably be diverse and not manifest in exactly the same ways. For example, those with Barth syndrome often have neutropenia, or to few neutrophils, and are susceptible to bacterial infections. In addition, Dr. Anu Suomalainen-Wartiovaara’s group recently reported reduced antiviral responses in patient samples and mice carrying the PolG MIRAS allele, suggesting that there may be dramatic differences in immune phenotypes even within PolG-related MtDs (Kang et al., 2024). Other MtDs may cause hyperactive innate immunity, whereas some may lead to problems with adaptive immunity (i.e., antibodies and T cells). We are early in these studies, and MtDs are rare diseases, making it often difficult to obtain large patient cohorts for study. However, we can rapidly advance the field by generating new, more relevant animal models of MtD and coupling these findings with data from human studies.
MitoWorld: MtDs manifest at different ages. Do you have any ideas about what might activate the immune system in an MtD?
West: We hypothesize that mitochondrial dysfunction in MtDs basally alters the tone of immune cells. This is likely due to small amounts of cytokines and other stimulatory factors being released constitutively. For example, we showed that the aberrant release of mtDNA and other nucleic acids triggers the innate immune system in the absence of infection. Metabolic alterations in MtDs can also profoundly impact immune cell development and function. In the context of infection, innate immune cells, such as macrophages, may mount an overactive response, and this can feed forward to damage mitochondria and trigger subsequent rounds of mtDNA release or elevate metabolic crisis.
MitoWorld: So many of the former mitochondrial genes are now part of the host genome. Could mutations in those genes cause similar problems in mitochondria?
West: Most of my lab’s work has focused on examining innate immune responses in mouse models where nuclear-encoded mitochondrial genes are missing or mutated. However, others are examining immune responses in patients and animal models with particular disease-relevant mtDNA mutations. For example, Dr. Martin Picard has shown that cells from patients carrying a single, large-scale mtDNA deletion have blunted inflammatory cytokine responses (Karen et al., 2022). In contrast, a mouse model carrying a heteroplasmic mtDNA mutation (m.5019A>G) mirroring that seen in humans exhibit a hyperinflammatory immune status characterized by elevated interferon (Marques et al., 2025). Therefore, mutations in nuclear and mtDNA encoded mitochondrial genes can impact the immune system.
MitoWorld: How do you plan to extend this research?
West: My lab and colleagues at JAX are working to expand the toolkit of mouse models for MtDs, and we are excited to send our new models into labs around the globe. I am quite hopeful that MitoWorld, the UMDF, the PolG Foundation, and other advocacy groups will better unite researchers examining immunological issues in animal models and patients with MtDs.
* Two hours after infection, macrophages were stained with antibodies and dyes to mark the cell membrane (white), mitochondria (green), the nucleus (blue), and Pseudomonas bacteria (magenta). Cells were then imaged on a confocal microscope. The macrophage at the bottom right is undergoing pyroptosis, an inflammatory cell death pathway resulting in nuclear condensation, membrane permeabilization, loss of mitochondria, and release of cytokines.
References
Kang Y, Hepojoki J, Sartori Maldonado R et al. (2024) Ancestral allele of DNA polymerase gamma modifies antiviral tolerance. Nature 628: 844–853.
Karan KR, Trumpff C, Cross M, Engelstad KM, Marsland AL, McGuire PJ, Hirano M, Picard M (2022) Leukocyte cytokine responses in adult patients with mitochondrial DNA defects. J Mol Med (Berl) 100: 963–971.
https://pmc.ncbi.nlm.nih.gov/articles/PMC9885136/ (PubMed Central)
https://link.springer.com/article/10.1007/s00109-022-02206-2 (behind paywall)
Marques E, Burr SP, Casey AM, Stopforth RJ, Yu CS, Turner K, Wolf DM, Dilucca M, Tyrrell VJ, Kramer R, Kanse YM. An inherited mtDNA mutation remodels inflammatory cytokine responses in macrophages and in vivo. bioRxiv 2025 Jan 5:2025-01.
https://www.biorxiv.org/content/10.1101/2025.01.05.631298v1
VanPortfliet JJ, Lei Y, Ramanathan M, Guerra Martinez C, Wong J, Stodola TJ, Hoffmann BR, Pflug K, Sitcheran R, Kneeland SC, Murray SA, McGuire PJ, Cannon CL, West AP (2025) Caspase-11 drives macrophage hyperinflammation in models of Polg-related mitochondrial disease. Nat Commun 16: 4640.
https://doi.org/10.1038/s41467-025-59907-8
Warren EB, Gordon-Lipkin EM, Cheung F et al. (2023) Inflammatory and interferon gene expression signatures in patients with mitochondrial disease. J Transl Med 21: 331. https://doi.org/10.1186/s12967-023-04180-w
In a review paper in Endocrine Reviews, Rachel Varughese and Shamima Rahman of University College London describe the effects of primary mitochondrial disease on the endocrine system and how these diseases can be diagnosed and treated.
Mitochondria provide the energy for the production and export of many cellular products. Mutations that affect mitochondrial function can disrupt the production of key molecules, including endocrine hormones. The result might be diabetes, growth hormone deficiency, adrenal insufficiency, hypogonadism, and parathyroid dysfunction. In fact, the authors suggest that the possibility of underlying mitochondrial dysfunction should be considered in all hormonal diseases. Thus, understanding how the mitochondria are involved in those diseases is critical.
Primary mitochondrial disorders (PMDs) are genetic disorders that affect the structure or function of the mitochondria. Because mitochondria are so intimately involved with multiple cellular functions, mitochondrial mutations can manifest in many disorders. The mutation can occur in either the nuclear or mitochondrial genome.
Varughese and Rahman provide an extensive review of how mitochondria can be damaged and of the diseases that can result. They conclude by noting that clinicians should be suspicious of a PMD for any patient who has an atypical presentation or seemingly unrelated comorbidities. The treatment of PMDs can be complex and quite different than the “normal” treatment for a particular endocrine manifestation.
A conversation with Rahman and Varughese
MitoWorld: Since there is no cure for PMDs right now, are clinicians left with treating the symptoms?
Rahman: Yes, symptomatic management is the mainstay of managing PMDs at present. This means being vigilant and monitoring for known complications of the disease and acting promptly with symptomatic measures when these complications arise.
MitoWorld: You seem to be suggesting that clinicians should be aware of multiple, possible unusual combinations of symptoms that might indicate a PMD. Are there key diseases other than diabetes that should raise suspicion?
Rahman. Table 6 in our paper gives several examples of combinations of symptoms that should arouse suspicion of an underlying PMD. For example, the combination of adrenal insufficiency or growth hormone deficiency with progressive external ophthalmoplegia, pigmentary retinopathy and heart block should alert the clinician to the possibility of Kearns-Sayre syndrome, while the combination of premature ovarian insufficiency and sensorineural hearing loss is suspicious of Perrault syndrome.
MitoWorld: What are the most promising treatments that you are aware of?
Rahman: Unfortunately, there are no disease-modifying therapies that are licensed for PMDs. Many treatments are in development at the preclinical stages, including pharmacological and genetic approaches. Currently, genetic approaches seem more promising as strategies to provide personalized tailored curative treatments, but are not yet available for PMDs, with the exception of Leber Hereditary Optic Neuropathy.
MitoWorld: What interested you in mitochondrial in the first place?
Rahman: I first began caring for patients with mitochondrial diseases as a junior doctor (paediatric trainee) in the early 1990s. Deeply moved by the challenges faced by affected patients and their families, I have devoted my career to improving the diagnosis and management of these conditions.
Varughese: I am a paediatric endocrinologist. As a paediatrician, I was drawn to endocrinology by the opportunity to make lasting impacts on children’s growth and development through targeted, evidence-based care. My interest in mitochondrial disease emerged from seeing its intricate interplay with multiple organ systems, including endocrine function. Writing this article was a way to bridge both interests, aiming to improve both early recognition of endocrine issues in affected children and the identification of underlying mitochondrial disease in patients with atypical constellations of symptoms.
Reference
Varughese R, Rahman S (2025) Endocrine dysfunction in primary mitochondrial diseases. Endocrine Reviews 46: 376–396.
Columbia University mitochondria researcher Martin Picard’s life changed in 2014 when he peered through a microscope in Douglas Wallace’s lab at the Children’s Hospital Philadelphia. He saw something that didn’t fit the textbook “powerhouse of the cell” picture. Mitochondria are tiny elongated and sometimes spherical energy-producing organelles. While many times thinner in diameter than a human hair, hundreds to thousands of mitochondria populate the interior of each human cell.
After 20 years of wonder, Picard’s personal and professional journey was picked up by Scientific American, which has just published his article, The Social Lives of Mitochondria: When These Energy-Giving Organelles Thrive, So Do We (Scientific American June 2025). The online version of the print article, viewed here, is entitled Mitochondria Are More Than Powerhouses—They’re the Motherboard of the Cell.
Picard writes, “Under the high-power microscope, mitochondria have many tiny generally horizontal “baffles”, called cristae, the site of ATP production, the cellular energy currency. Energy transformation within cristae involves the stripping of electrons from food and allows them to flow onto the oxygen we breathe”.
With hundreds to thousands of mitochondria bunched together, it is hard to know if they are acting in concert or as random lone operators. What Picard saw through the microscope, featured here and below was the alignment of the cristae between mitochondria. “The first physical evidence of non-molecular information exchange between mitochondria,” says Picard.
https://www.nature.com/articles/ncomms7259/figures/3
Since then, Picard and others have probed this mitochondrial behavior to the point that it appears mitochondria are operating communally or failing to do so. Different organs, researchers have found, have different types of mitochondria. “Mitochondria have a bacterial origin in evolution, and there is ample evidence from bacteria today that they do what is called “quorum sensing” where they signal and align to perform tasks a single bacterium or mitochondrion could not accomplish on its own,” Picard explains.
For more background and context, MitoWorld talked with Picard:
MitoWorld: Can you show us any microscopy or artistic renditions or video that shows the “social” nature of mitochondria?
Picard: The best video is this. Also this video showing cristae align between mitos changed my life. This picture shows mitochondria networking.
MitoWorld: What led to your thoughts about the social nature of mitochondria?
Picard: Everything in biology has somewhat of an interactive nature to it. And across the universe, everything is interconnected, from electrostatically attracted protons and electrons within atoms, to attracted social human beings, to planets attracted to each other by gravitational forces. Why would our biology be different? And could there be some kind of “social” behavior deep within our cells that led to our organs, bodies, and to our mind to becoming “social”. And it could have started with the endosymbiosis of mitochondria.
MitoWorld: Has this been on your mind for a while, how did you begin to verify the social conjecture?
Picard: Early work by David Chan on mitochondrial fusion. In 2012 I wrote a piece called “Mitochondria: Starving to Reach Quorum” that touched on their “social” nature, like bacteria that talk to each other to do “quorum sensing” and increase their virulence. Then in 2014, I saw cristae alignment between mitochondria. Since then, many labs have observed that, if you prevent mito-mito interactions (disrupt their social interactions), they go bad, as do the cells that house them too. My neuroscientist colleague Carmen Sandi and I detailed this in a paper in 2021.
MitoWorld: Help readers understand how important mitochondria are to the life of cells.
Picard: Without mitochondria, we would not exist. When they appeared in evolution, the result of a merger. This was the click—the beginning of a new phase of life. Somehow their presence allowed a type of multicellular life that wasn’t possible before. My hunch is that mitochondria provided the ability to process information: they made cells smarter and elevated their “social” behavior to a next level. With this, cells could come together into larger collectives, hold larger goals, and grow organisms that behave, think, and feel. This may all have been possible because the Mitochondrial Information Processing System (MIPS) became the “brain” of the cell.
MitoWorld: What are the behaviors of mitochondria that are “social”?
Picard: Mitochondria 1) communicate with each other and other organelles, 2) exhibit group formation, 3) are interdependent, 4) synchronize their behaviors, and 5) functionally specialize to accomplish specific functions.
MitoWorld: What are the health, medical and research avenues that open as a result of the mounting evidence of the social nature of mitochondria?
Picard: I think it’s time to see ourselves energetically. We are not just molecular machines. That mechanical, somewhat static view has been propagated for too long without seeing the wider energetic context. Understanding the “social” layer of biological organization makes it clear that there are biological processes and forces, including “goals” that cells and organisms have, that aren’t just the product of cogwheels. For example, the healing process is a completely untapped area of medicine and science that needs attention. I would suggest that, alongside our mitochondrial research, we need Healing Science, a new area of science that will map out how we manage to heal, every day. Charting this new territory of health and healing science has to be grounded in first principles. The interconnectedness of our biology, together with our fundamental energetic nature, are those first principles. Realizing that mitochondria are “social” is a step towards a more accurate view of how life works, and of what keeps us healthy day after day.