The research team, led by Andriy Anishkin, Sangita Kachhap, and Sree V. Chintapalli across institutions including the University of Maryland and the Arkansas Children’s Nutrition Center, focused on two closely related metabolic cargo molecules. The first is palmitate, a sixteen-carbon saturated fatty acid that circulates abundantly in the bloodstream. The second is palmitoylcarnitine, the same fatty acyl chain but shuttled on a carnitine headgroup, the form in which long-chain fatty acids cross into mitochondria for beta-oxidation. Earlier work from the same group had shown that oxygenated myoglobin binds both molecules in a hydrophobic pocket near the heme, and that acylcarnitines actually grip the protein more tightly than free fatty acids do. What remained unknown was whether this bound cargo changes the protein’s behavior once it reaches the mitochondrial surface.

To answer that question, the team turned to molecular dynamics simulations, a technique that models every atom of a protein and membrane as they jiggle, rotate, and interact according to the laws of physics. They built two physiologically distinct models of the outer mitochondrial membrane. The first, an average-composition membrane, reflected the typical mixture of phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, and other headgroups found across the mitochondrial surface. The second, a contact-site membrane, was enriched in cardiolipin, a doubly charged phospholipid that clusters at specialized regions where the outer and inner mitochondrial membranes come into close apposition. Cardiolipin is best known as a signature lipid of the inner membrane, but its presence at contact sites makes those patches distinctly more negatively charged than the rest of the surface.

Into each membrane environment the researchers placed oxygenated myoglobin carrying either palmitate or palmitoylcarnitine, testing six different starting orientations of the protein so that no single docking pose would dominate the results. The simulation protocol unfolded in three stages. First, a weak steering force of roughly eleven piconewtons nudged each protein toward the membrane over forty nanoseconds, allowing thermal motion to rotate and reposition the complex so the final contact configuration depended little on the initial orientation. Then the external force was removed entirely, and each system relaxed for another forty nanoseconds to see whether the newly formed contacts would hold. Finally, a steered molecular dynamics phase pulled the protein away from the membrane at a constant velocity, recording the force required to break the association.

The results were striking in two ways. First, both lipid-bound forms of oxygenated myoglobin showed a clear preference for the cardiolipin-rich contact-site membrane over the average-composition membrane. The stability of the association, measured by how many protein-membrane atomic contacts survived the unrestrained relaxation phase, was 2.3-fold higher at the contact site for palmitate-bound myoglobin and 2.7-fold higher for palmitoylcarnitine-bound myoglobin. This mirrors the team’s earlier finding that unliganded oxygenated myoglobin also favors contact-site regions, and it suggests that cardiolipin’s negative charge acts as a general electrostatic beacon for the oxygen-carrying protein.

But the second result is what makes the new study stand out: the identity of the bound lipid changed everything about how the protein behaved at the membrane. Palmitate-bound myoglobin was ten to twenty percent more stable overall than its palmitoylcarnitine-bound counterpart, and when the researchers pulled the complexes off the membrane, palmitate-bound myoglobin required roughly twice the detachment force. At the contact-site membrane, the average detachment forces were 74.7 piconewtons for the palmitate complex versus 40.8 piconewtons for the palmitoylcarnitine complex. Lipid-specific contact analysis revealed why the two complexes behaved so differently: palmitate-bound myoglobin was strongly stabilized by cardiolipin, while palmitoylcarnitine-bound myoglobin leaned instead on phosphatidylethanolamine and phosphatidylinositol, with a smaller contribution from cardiolipin.

What makes this divergence remarkable is that the two cargo molecules share the identical sixteen-carbon palmitoyl chain. The only meaningful difference is the polar headgroup: palmitate carries a carboxylate, while palmitoylcarnitine carries the bulkier carnitine moiety. Yet that single chemical distinction was enough to rewire the entire network of protein-lipid contacts. Residue-level mapping showed that lysine-rich regions of the protein, particularly around helix F and the loop connecting helices C and D, dominated the membrane interactions, but the relative contributions of individual residues shifted depending on which lipid was bound. The authors emphasize that membrane stabilization was distributed across multiple residues and lipid species rather than concentrated at a single interaction site, pointing to a multicomponent, orientation-dependent mode of association.

The orientation result may prove to be the most consequential. In several palmitoylcarnitine-bound configurations, the heme crevice, the structural gateway through which oxygen enters and exits myoglobin, faced toward the membrane, whereas the more firmly anchored palmitate complex tended to adopt different membrane-facing poses. The researchers are careful to note that they did not directly simulate or measure oxygen release, so these orientation differences cannot yet be interpreted as evidence of faster or slower oxygen delivery. Still, the structural implications are tantalizing, because recent experimental work has shown that membrane contact itself perturbs the heme environment. A 2026 study in the Journal of the American Chemical Society reported that association with model liposomes roughly doubled the rate of oxygen dissociation from myoglobin, and complementary resonance Raman experiments showed that membrane-mimicking surfaces weaken the iron-oxygen bond. If the membrane is not just a docking site but an active participant in unloading oxygen, then the orientation of the heme crevice relative to the membrane surface becomes a potentially critical variable, and one that the bound metabolite appears to control.

The physiological context gives the finding real weight. Long-chain acylcarnitines accumulate in the blood and tissue when mitochondrial fatty acid oxidation falls behind substrate supply, a situation that arises during myocardial ischemia and in various metabolic disorders. Endurance exercise, fasting, and dietary fat intake all shift the balance between free fatty acids and acylcarnitine intermediates in muscle. The new simulations suggest that these metabolic fluctuations could change not just how much lipid-bound myoglobin sits at the mitochondrial surface, but in what configuration, potentially coupling oxygen delivery to the cell’s current fuel mix. The authors also point toward broader nutrient-sensing pathways such as mTORC1, which governs lipid metabolism and mitochondrial function, as a possible upstream regulator of the fatty acid and acylcarnitine pools that myoglobin encounters.

The study has clear limitations that the authors acknowledge candidly. Their membrane models contained only phospholipids, omitting the integral and peripheral proteins that crowd the real outer mitochondrial membrane, and the detachment forces measured under nonequilibrium pulling conditions cannot be read as equilibrium binding affinities. Oxygen release and lipid transfer were not directly measured, and the sampling, though broadened by six starting orientations per condition, represents a subset of the full conformational landscape. Even so, the central message is hard to escape: myoglobin’s metabolic cargo is not a passenger but a steering wheel. The same protein, carrying the same acyl chain, grips the mitochondrial surface with different strength, different lipid preferences, and different geometry depending on whether that chain arrives as a free fatty acid or a carnitine ester. Future experiments that directly measure oxygen release kinetics and lipid transfer from these complexes will determine whether this structural plasticity translates into a genuine regulatory mechanism, one that could tie the rhythm of cellular respiration to the shifting tides of fat metabolism in working muscle.

Subject of Research: How fatty acid and acylcarnitine binding modulates oxygenated myoglobin's interaction with the outer mitochondrial membrane

Article Title: Long-chain fatty acid- and acylcarnitine-bound oxygenated myoglobin interactions with outer mitochondrial membrane

Article References: Long-chain fatty acid- and acylcarnitine-bound oxygenated myoglobin interactions with outer mitochondrial membrane. (n.d.). https://doi.org/10.3389/fbinf.2026.1986755

Image Credits: AI Generated

DOI: 10.3389/fbinf.2026.1986755

Keywords: myoglobin, mitochondria, molecular dynamics, palmitate, palmitoylcarnitine, cardiolipin, outer mitochondrial membrane, oxygen transport, fatty acid metabolism, acylcarnitines, heme, simulations

To appreciate the significance of the discovery, it helps to understand how skeletal muscle is built. Muscle tissue is composed of bundles of fibers that come in distinct functional flavors. Fast-twitch fibers are tuned for quick, forceful bursts of effort but tire rapidly. Slow-twitch fibers are built for endurance and are packed with mitochondria, the organelles commonly described as the powerhouses of the cell. With age, muscle mitochondria work less efficiently, and yet the fiber population drifts toward the slow-twitch, mitochondria-dependent type. A similar shift occurs in many diseases that cause muscle wasting, which suggests that the phenomenon reflects a shared biological program rather than random wear and tear.

The Copenhagen-led team, working across more than 20 institutions and led by the NNF Center for Basic Metabolic Research at the University of Copenhagen together with the Center for Adipocyte Signaling at the University of Southern Denmark, focused their investigation on a fat molecule called cardiolipin. Cardiolipin occupies a singular position in cellular architecture: it is found essentially nowhere else in the cell but the inner membrane of mitochondria, where it is essential for maintaining that membrane’s characteristic folded structure, the cristae that give mitochondria their enormous effective surface area. Without adequate cardiolipin, mitochondria cannot produce sufficient energy, nor can they generate the metabolic signals and molecular building blocks that cells depend on to function.

When the researchers measured cardiolipin in muscle mitochondria from mice and humans, they found a consistent pattern: levels decline with both age and disease, and the mitochondria in cardiolipin-poor muscle appear distorted and unable to operate properly. That correlation alone, however, could not settle the question of causation. Declining cardiolipin might simply be a consequence of aging rather than a driver of the changes that accompany it. To distinguish between these possibilities, the team performed a decisive experiment in young mice, artificially lowering cardiolipin levels to mimic the drop seen naturally in aging. The result was striking: the young animals developed the same fast-to-slow-twitch fiber shift that occurs in aged mice and in aging humans, indicating that cardiolipin loss is sufficient to trigger the remodeling program on its own.

Even more consequential was what happened when the researchers partially restored cardiolipin. Bringing levels back to roughly two-thirds of normal was enough to begin reversing muscle wasting in the animals and to prevent their early deaths entirely. This partial-rescue result carries substantial therapeutic weight, because it suggests that a treatment does not need to fully normalize cardiolipin to deliver meaningful benefit. Senior author Zachary Gerhart-Hines, Associate Professor at the NNF Center for Basic Metabolic Research at the University of Copenhagen, emphasized this point in the announcement of the work, noting that even a partial recovery of cardiolipin was enough to bring the muscle back, and that the central question now is whether cardiolipin can be increased in aging muscle or whether the downstream pathway can be targeted to promote healthy adaptations.

But why would a muscle respond to mitochondrial damage by remodeling itself into a slower, more mitochondria-dependent fiber type? The answer the researchers uncovered reframes the entire phenomenon as a defense mechanism. As cardiolipin levels fall, the strained mitochondria generate far more reactive oxygen species, or ROS, the chemically reactive molecules that damage cellular components in excess. Yet ROS is not merely a destructive byproduct; it also functions as a signal. When the team used an antioxidant to mop up ROS in cardiolipin-depleted muscle cells, the shift toward slow-twitch fibers was blunted, demonstrating that the ROS signal is what initiates the remodeling program rather than an incidental side effect of it.

Tracing that signal to its destination, the researchers identified a protein called ERRγ, a nuclear receptor that acts as the switch driving the fiber-type transformation. ERRγ triggers muscle cells to remodel their mitochondria and convert from fast-twitch to slow-twitch identity. The causal role of the receptor was confirmed in the opposite direction: when the scientists blocked ERRγ in cultured muscle cells, the fiber switch was completely shut down. In other words, the entire adaptive program, from ROS sensing to mitochondrial remodeling to fiber-type conversion, runs through this single regulatory node, making it an unusually clean target for intervention.

The logic of the adaptation becomes clearer when one follows what the remodeled fibers do with sugar. Cardiolipin-deficient mice pulled much more glucose out of the bloodstream than expected, but not to burn it for energy. By tracing labeled sugar through the muscle, the researchers showed that the glucose was instead diverted into the manufacture of the cell’s own antioxidants, molecules that neutralize ROS and shield the stressed cell from further oxidative damage. The slow-twitch state, in this reading, is a metabolic bargain: the muscle trades raw power for biochemical protection. Fabian Finger, Assistant Professor at the University of Copenhagen and first and co-corresponding author of the study, described the switch as the muscle trading power for protection rather than failing, and cautioned that interfering with it can backfire. In a telling result, mice given antioxidants to clear ROS fared worse, not better, because the treatment suppressed a protective response the animals needed.

The translational implications are unusually concrete for basic mitochondrial biology. Cardiolipin is already a pharmacological target: the FDA recently granted accelerated approval to elamipretide, a drug proposed to stabilize cardiolipin, for the rare genetic disorder Barth syndrome. Whether that class of compounds can be repurposed or adapted for age-related muscle decline remains an open question, but the existence of an approved pathway demonstrates that the target is druggable. ERRγ offers a second point of entry. It belongs to the nuclear receptor family, a class of molecules targeted by roughly 10 to 15 percent of all FDA-approved small-molecule medications, and activators of ERRγ are already in preclinical development for other indications. The study was funded by the Novo Nordisk Foundation, the European Research Council, the Lundbeck Foundation and the US National Institutes of Health, among others, and the published work carries a disclosure that senior author Zachary Gerhart-Hines works in some capacity for Embark Laboratories ApS, a company developing therapeutics for diabetes and obesity.

Important caveats remain. The causal experiments were carried out in mice, and the human samples served only to confirm that cardiolipin also declines with age in people; whether the same ROS-driven, ERRγ-mediated switch operates identically in human muscle has yet to be demonstrated directly. Nor is it yet known whether raising cardiolipin in aging human muscle, or modulating ERRγ activity, would improve function without unintended metabolic consequences, particularly given the finding that blocking the pathway entirely shuts down what appears to be a protective program. Still, the study resolves a genuine paradox with a coherent mechanism: the fast-to-slow-twitch shift of aging is not the muscle surrendering to decay but a regulated trade of performance for resilience, governed by a lipid whose loss destabilizes mitochondria and a receptor that reorganizes the cell in response. If future work can safely tilt that trade back toward function, the hidden switch behind aging muscle may become one of the first points of genuine therapeutic control over a process long accepted as inevitable.

Subject of Research: The role of the mitochondrial lipid cardiolipin and the nuclear receptor ERRγ in driving age-related muscle fiber-type switching

Article Title: The hidden switch behind one of the biggest paradoxes in aging muscle

Article References: The hidden switch behind one of the biggest paradoxes in aging muscle. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: aging, muscle, mitochondria, cardiolipin, ERRγ, reactive oxygen species, muscle fibers, nuclear receptors, elamipretide, Nature Aging, sarcopenia, University of Copenhagen

The team, led by Wuming Wang of The Chinese University of Hong Kong together with colleagues including Haite Tang, Raina Liu, and Zhiqiang Xiong, induced differentiation of the H1 human embryonic stem cell line using sequential small-molecule modulation of WNT signaling, a standard protocol that recapitulates key steps of fetal cardiac development. They sampled cells at day zero, when the cells were still pluripotent stem cells; day three, when they had become mesoderm, the embryonic layer from which the heart arises; day six, when cardiac progenitor cells appeared; day ten, when immature cardiomyocytes emerged; and day thirty, when the cells had acquired mature features. Quality control was rigorous: by day ten, cardiac troponin T-positive cardiomyocytes made up 90 to 94 percent of the culture, and by day thirty, 88 to 95 percent of cells expressed MLC2v, a hallmark of ventricular lineage maturation.

To confirm that the day-thirty cells were genuinely mature, the researchers deployed multiple validation strategies. Confocal imaging revealed highly organized, parallel-aligned myofibrils with clear periodic striations corresponding to sarcomeric Z-lines, the repeating contractile units of heart muscle. The cells also displayed abundant, elongated mitochondria, consistent with the oxidative metabolism of adult cardiomyocytes. Microelectrode array recordings captured spontaneous extracellular spike patterns, demonstrating electromechanical competence. An induced pluripotent stem cell clone carrying an endogenous MYL2 fluorescent tag showed robust MLC2v signals in spontaneously beating cells. Together, these data established that the differentiation system reliably produced stage-specific, high-purity cardiomyocyte populations suitable for stage-resolved molecular profiling.

The lipidomic analysis itself was a technical tour de force. Using a low-input, trace lipidomics method adapted from protocols developed for early mammalian embryo studies, the team quantified 781 lipid species spanning 31 major lipid classes, each measured against a panel of stable isotope internal standards. Principal component analysis showed clean separation between developmental stages with tight clustering within groups, and a Shannon diversity index revealed that overall lipid diversity gradually declined as differentiation proceeded. The researchers then sorted every lipid subclass into four temporal patterns: monotonically decreasing, rising then falling, falling then rising, and monotonically increasing across the differentiation time course.

The earliest pattern was striking. Cardiolipins, the four-tailed phospholipids that populate the inner mitochondrial membrane, together with diacylglycerols, bis(monoacylglycero)phosphates, and simple glycosylceramides, all peaked at the pluripotent stem cell stage and declined thereafter. The authors propose that this abundance of relatively simple membrane lipids supports rapid membrane biogenesis and the maintenance of stem cell identity. Cardiolipin biology is particularly relevant to the heart: its biosynthesis is known to be essential for postnatal cardiomyocyte maturation, supporting the assembly of mitochondrial cristae and the accumulation of oxidative phosphorylation complexes. Notably, the cardiolipin acyl chains observed here shifted over time from shorter, monounsaturated species toward longer, more polyunsaturated forms containing C18:2, C20:3, and C20:4 fatty acids.

A second wave of remodeling occurred at the mesoderm and cardiac progenitor stages. Sphingolipids, sphingosine, acylcarnitines, cholesteryl esters, ether-linked phospholipids such as PE O plasmalogens, and lysophosphatidylethanolamines transiently enriched during this window before declining. Many sphingolipid species appeared in paired molecular forms differing only by hydroxylation status, with hydroxylated variants becoming enriched after differentiation onset, a signature of stage-associated remodeling of fatty acid hydroxylation. Acylcarnitines, which shuttle long-chain fatty acids into mitochondria for beta-oxidation, showed a chain-length-dependent split: short-chain species accumulated in mature cardiomyocytes, while longer-chain species peaked during the mesoderm and progenitor phases. The authors suggest these transient lipid enrichments may contribute to mesodermal fate transitions and progenitor state maintenance, though they emphasize that such interpretations remain correlative until tested by targeted metabolic perturbation.

The most sustained trend was a progressive accumulation of structurally complex lipids as cells matured. Fatty acids, phosphatidylethanolamines, phosphatidylinositols, phosphatidylcholines, lysophosphatidylcholines, lysophosphatidic acids, sphingomyelins, and the ganglioside GM3 all rose steadily, with longer-chain and more highly unsaturated species preferentially enriched in late-stage cells. Quantitative analysis showed that polyunsaturated lipids, those with more than two double bonds, rose markedly from the mesoderm stage onward, while mono- and diunsaturated lipids declined sharply. Among the 31 lipid classes, phosphatidylcholine displayed this pattern most prominently. The researchers hypothesize that this progressive polyunsaturation enhances membrane fluidity and dynamic responsiveness, accommodating the increasing contractile activity of late-stage cardiomyocytes, a testable idea they note will require direct biophysical measurements of membranes alongside functional assessments of contractility.

To connect the lipid data to gene regulation, the team integrated their RNA sequencing with previously published ATAC-seq chromatin accessibility data from cardiomyocyte differentiation. Motif scanning of regulatory regions around unsaturated fatty acid biosynthesis genes predicted a transcription factor network including SP1, KLF4, IRF1, IRF2, USF1, FOXO1, IRF4, and CREB1. Intersecting genes with progressively increasing chromatin accessibility against those with progressively increasing expression yielded 376 co-regulated genes, enriched for extracellular matrix organization, cell communication, and structural morphogenesis, indicating that late-stage epigenetic and transcriptional reprogramming ultimately drives the structural integration of myocardial tissue. Interestingly, promoter accessibility of lipid metabolic genes themselves peaked at the cardiac progenitor stage and then declined by day thirty, a pattern of transient epigenetic priming that led the team to hypothesize that maturing cells might become responsive to exogenous lipid supply.

That hypothesis was tested with phosphatidylcholine supplementation. Thirteen days of culture with 5 micromolar PC altered expression of electrophysiology genes in immature cardiomyocytes, including HCN4, a core heart rate modulator, and SCN5A, which encodes the cardiac sodium channel. In mature cardiomyocytes, PC supplementation moderately increased transcripts of GJA1, encoding gap junction proteins critical for electrical propagation, and MYL2, a maturity marker, while significantly downregulating the hypertrophy-associated genes NPPA and NPPB, changes confirmed at the protein level by immunofluorescence. Because physiological hypertrophy is a normal component of cardiomyocyte development, the authors interpret the reduced hypertrophy gene expression as a possible association between phospholipid availability and developmental state, with potential implications for hypertrophy-related cardiac disease. They caution, however, that only transcript and protein levels were assessed, and functional consequences for contractility, electrophysiology, and stress resistance remain to be determined.

The study is not without limitations, which the authors address candidly. The day-thirty cells, though structurally and electrophysiologically mature by in vitro standards, were grown in conventional two-dimensional monolayer culture and do not fully replicate adult cardiomyocytes in vivo. Lipidomics was performed on unsorted bulk cultures, leaving a small non-myocyte contribution, and the data represent relative molar fractions rather than absolute per-cell abundance. Only a male cell line was used, so sex-specific effects could not be evaluated. Still, by defining the dynamic lipidome of human cardiomyocyte differentiation and linking it to transcriptional and epigenetic programs, the work provides a framework for future efforts to mature stem cell-derived heart cells more efficiently, whether through fatty acid conditioning, three-dimensional culture, or precisely timed lipid supplementation, and may ultimately inform regenerative strategies for a disease burden that remains the leading cause of death worldwide.

Subject of Research: Lipid metabolism remodeling during human stem cell differentiation into cardiomyocytes

Article Title: Lipid metabolism remodeling in human cardiomyocyte differentiation and maturation

Article References: Tang, H., Liu, R., Xiong, Z., He, Q., Lu, G., Chan, W.-Y., & Wang, W. (2026). Lipid metabolism remodeling in human cardiomyocyte differentiation and maturation. iScience, 29(11), Article 117821. https://doi.org/10.1016/j.isci.2026.117821

Image Credits: AI Generated

DOI: 10.1016/j.isci.2026.117821

Keywords: cardiomyocytes, lipidomics, human embryonic stem cells, cardiac differentiation, phosphatidylcholine, cardiolipin, polyunsaturated lipids, multi-omics, ATAC-seq, heart regeneration, metabolic maturation, sphingolipids

The paradox that motivated the work is one that has puzzled muscle biologists for decades. Aging is well known to sap mitochondrial function, reducing the capacity of cells to generate energy through respiration. Yet at the same time, aging muscle becomes enriched in the very fiber types that are most dependent on mitochondria. Fast-twitch fibers, which rely on rapid glycolytic metabolism for bursts of force, selectively atrophy, while slow-twitch oxidative fibers persist. Something must be coordinating this shift, and whether failing mitochondria are merely a bystander or an active instigator has remained unresolved. The new research, led by Fabian Finger and Zachary Gerhart-Hines at the University of Copenhagen together with an international team, provides the strongest evidence yet that a single mitochondrial lipid sits near the top of that causal chain.

Cardiolipin is no ordinary fat. It is found almost exclusively in the inner mitochondrial membrane, where its four fatty acyl chains and distinctive shape confer the tight curvature that cristae, the energy-generating folds of the membrane, require. It stabilizes the respiratory supercomplexes that shuttle electrons through the electron transport chain, supports the enzymes of oxidative phosphorylation, and participates in virtually every aspect of mitochondrial architecture and function. Because cardiolipin is so central, its disruption has been implicated in conditions ranging from cardiomyopathy to neurodegeneration and Barth syndrome, a rare genetic disorder. All cardiolipin species originate from a single rate-limiting enzymatic reaction catalyzed by cardiolipin synthase 1, encoded by the gene Crls1, which made the enzyme an obvious point of attack for the researchers.

The team began by asking whether cardiolipin declines with age. Comparing young mice at nine weeks with mice at two years, they measured cardiolipin levels in both the oxidative soleus muscle and the glycolytic extensor digitorum longus, and found that total cardiolipin fell similarly in both muscle types. The gene most significantly reduced in aged muscle was Crls1 itself. Crucially, the same pattern appeared in human muscle biopsies: total cardiolipin declined in older participants aged 53 to 69 compared with young adults aged 22 to 35, along with significant shifts in the composition of individual cardiolipin species and reduced expression of cardiolipin synthesis genes. The conservation across species suggested that the loss of this lipid is a genuine signature of muscle aging rather than a rodent quirk.

To test whether the decline is a cause rather than a consequence of aging, the researchers genetically deleted Crls1 specifically in the skeletal muscle of young mice, creating a model they call MUCKO. The deletion reproduced a global reduction in cardiolipin across muscle types that closely mirrored the pattern seen in aged animals, even though cardiolipin represents less than two percent of the muscle phospholipidome. The consequences were dramatic. MUCKO mice failed to gain lean mass after weaning, and although oxidative muscle is naturally more cardiolipin-rich, it was the glycolytic EDL muscle that suffered the most severe atrophy. Transmission electron microscopy revealed disrupted cristae architecture in both muscle types, and respiratory supercomplex formation was uniformly diminished. When respiration was corrected for mitochondrial content, NADH-linked respiration, oxidative phosphorylation capacity, succinate-linked respiration and complex IV activity were all significantly reduced, confirming that cardiolipin loss cripples mitochondrial function across fiber types.

Yet the most surprising finding was not the damage but the adaptation. Despite losing respiratory capacity, the glycolytic EDL muscle of MUCKO mice dramatically increased its mitochondrial content, with citrate synthase activity and COX IV staining rising to levels resembling the oxidative soleus. Transcriptomic and proteomic profiling showed that EDL was undergoing a global fast-to-slow fiber-type switch: the most glycolytic type IIb fibers decreased while more oxidative IIa and IIx subtypes expanded. Individual fiber cross-sectional areas shrank, but the total number of fibers was unchanged, indicating that atrophy of existing fibers, not cell death, drove the tissue’s decline. In short, deleting one lipid-synthesizing enzyme in young muscle recapitulated a constellation of aging hallmarks on an accelerated timescale, establishing cardiolipin deficiency as a plausible causal driver of the aging phenotype.

The hunt for the molecular messenger connecting membrane to nucleus led to estrogen-related receptor gamma, or ERRγ, a nuclear receptor already known for its role in exercise-induced oxidative remodeling. In MUCKO muscle, Esrrg expression rose specifically in glycolytic EDL, mirroring the pattern of mitochondrial mass, and it was also elevated in aged mouse muscle. In cultured muscle cells, depleting Crls1 selectively increased the oxidative myosin heavy chain isoforms I and IIa, but this induction was completely blocked either by knocking down ERRγ with interfering RNA or by treating cells with the pharmacological antagonist GSK5182. Genome-wide, of the 773 genes significantly regulated by Crls1 loss, 626 proved dependent on ERRγ activity. The receptor also bound the promoter of myogenin, a master regulator of muscle differentiation, placing ERRγ upstream of MYOG in a signaling hierarchy that ultimately rewrites the muscle’s contractile machinery. This is retrograde communication in its purest form: a change in the lipid composition of the mitochondrial inner membrane is transduced into a transcriptional program that reshapes the entire fiber.

Why would aging muscle deliberately remodel itself this way? The answer, the researchers found, lies in antioxidant defense. Cardiolipin-deficient muscle showed elevated mitochondrial reactive oxygen species production and increased lipid peroxidation, along with a near-universal upregulation of ROS defense proteins. Proteomic and metabolomic analyses revealed that glucose entering these muscles was being rerouted away from complete glycolysis and into the pentose phosphate pathway, the hexosamine biosynthetic route, serine metabolism and the folate cycle, all of which generate the reducing power needed to neutralize oxidative stress. Isotopic tracing confirmed increased conversion of glucose to serine, and the muscles consumed markedly more glucose in vivo, making the mice strikingly glucose tolerant despite their mitochondrial dysfunction. When the researchers gave mice the antioxidant N-acetylcysteine for eight weeks, glucose uptake in the cardiolipin-deficient muscles was blunted, suggesting that ROS itself stimulates the sugar hunger that fuels these protective pathways.

Perhaps the most provocative result concerns reversibility. Using an inducible knockout model in adult mice, the team showed that stopping the genetic ablation allowed modest re-expression of Crls1, which raised cardiolipin levels from 27 percent to 67 percent of normal. That partial recovery was enough to initiate reversal of the dramatic weight loss and muscle atrophy, and it completely rescued the premature mortality that otherwise killed the knockout mice, apparently from diaphragm dysfunction. Even more counterintuitively, chronic antioxidant supplementation made things worse, lowering the sarcopenic index and further activating the stress response, presumably by starving the muscle of the glucose flux its defense pathways require. The findings reframe the fiber-type shift of aging not as degeneration alone but as an adaptive, ERRγ-driven survival strategy, one that cannot be patched by simply swallowing antioxidants. If future work confirms that boosting cardiolipin synthesis in aged muscle can restore youthful fiber composition, the humble mitochondrial fat may become an unexpected target in the quest for healthier aging.

Subject of Research: Role of the mitochondrial membrane lipid cardiolipin in driving age-related skeletal muscle fiber-type adaptations via estrogen-related receptor γ signaling

Article Title: Mitochondrial membrane lipid cardiolipin controls fiber-type adaptations in aging muscle via estrogen-related receptor γ

Article References: Finger, F., Frost, M., Watanabe, S., Ma, T., Kang, T., Biswas, D., Zapata-Perez, R., Anton, V., Dollet, L., Markussen, L. K., Senoo, N., Karavaeva, I., Basse, A. L., Dmytriyeva, O., TeSlaa, T., Havelund, J. F., Ehrlich, A. M., Moreno-Torres, M., Yonamine, C. Y., … Gerhart-Hines, Z. (2026). Mitochondrial membrane lipid cardiolipin controls fiber-type adaptations in aging muscle via estrogen-related receptor γ. Nature Aging. https://doi.org/10.1038/s43587-026-01227-7

Image Credits: AI Generated

DOI: 10.1038/s43587-026-01227-7

Keywords: cardiolipin, mitochondria, skeletal muscle, aging, sarcopenia, ERRγ, Crls1, fiber-type switching, mitonuclear signaling, reactive oxygen species, glucose metabolism, Nature Aging

The biological problem the researchers set out to tackle is well known to reproductive medicine. As women age, the quality of their oocytes deteriorates, driving up rates of miscarriage, chromosomal abnormalities, preterm birth and fetal growth restriction, and making women aged 35 to 39 more prone to infertility than any other age group. Oocyte quality hinges on two tightly coordinated processes: nuclear maturation, in which chromosomes separate during the resumption of meiosis, and cytoplasmic maturation, in which the egg stockpiles the messenger RNAs, proteins and substrates that fertilization and early embryonic development will demand. Aging disrupts the cytoplasmic arm of this program through mitochondrial dysfunction, disturbed calcium signaling, malformed smooth endoplasmic reticulum and cytoskeletal disarray.

Mitochondria sit at the center of that failure. The oocyte is one of the most energy-hungry cells in the body, relying on oxidative phosphorylation through the five complexes of the electron transport chain to power chromosome segregation, spindle migration and organelle repositioning. In aging oocytes, the respiratory capacity of each mitochondrion falls and the mitochondrial membrane potential drops, a shift typically accompanied by a surge in reactive oxygen species. That oxidative burst damages nuclear and mitochondrial DNA, destabilizes the meiotic spindle and can ultimately produce aneuploid eggs. Previous metabolic surveys of aging ovaries found depletion of NAD+, purines and pyrimidines alongside an accumulation of glycolysis substrates and glutamine, painting a consistent picture of failing mitochondrial metabolism.

Researchers have tried a succession of interventions to prop up the aging egg: the CD38 inhibitor 78c to raise NAD+ levels, rapamycin to restore protein homeostasis, melatonin to quench oxidative stress, spermidine to enhance mitophagy, and mitochondria-targeted antioxidants such as MitoQ and SkQ1, along with NAD+ boosters like nicotinamide mononucleotide and the electron carrier CoQ10. Each has shown promise, but low targeting efficiency and poor bioavailability have limited clinical translation. Elamipretide, a membrane-penetrating aromatic cationic tetrapeptide with the sequence Arg-Dmt-Lys-Phe-NH2, was attractive to the team precisely because it is small, water-soluble, resistant to peptidase degradation and stable in solution—properties that make it a plausible candidate for real-world clinical use.

The peptide’s mechanism is unusually specific. At physiological pH it carries three positive charges and accumulates in the inner mitochondrial membrane through electrostatic and hydrophobic interactions, where it binds with high affinity to cardiolipin, a signature phospholipid of that membrane. Cardiolipin is central to respiratory chain supercomplex assembly, membrane stability and energy transduction, but it is also vulnerable to oxidation under oxidative stress, which disrupts the membrane, saps electron transport efficiency and diminishes ATP output. By binding cardiolipin, elamipretide inhibits the peroxidase activity of cytochrome c, prevents cardiolipin oxidation and preserves the cristae architecture of the inner membrane, stabilizing energy production and cutting back the generation of reactive oxygen species.

To test whether these properties could rescue the aging ovary, the team treated 10-month-old mice—well past the mouse reproductive prime—with daily intraperitoneal injections at 3, 5 or 10 milligrams per kilogram. The 5 mg/kg dose proved optimal, and a seven-day course was the most effective duration, improving reproductive performance in 8-, 10- and 12-month-old animals with the strongest gains in the 10-month group. Ovarian sections showed a marked increase in high-quality dominant follicles, fertilization rates of aged oocytes rose substantially, and early embryonic development recovered: aged oocytes normally stall between the two-cell and four-cell stages after fertilization, but elamipretide effectively reversed that block. The benefit, however, was transient, lasting only about a month, which the authors note defines both the promise and the limits of the regimen.

Molecular profiling revealed an unexpected metabolic handle on the effect. Metabolomics of treated ovaries showed that elamipretide shifted the aged metabolome back toward a young-like profile, and pathway analysis singled out vitamin B6 metabolism as the most dramatically altered route. When the team supplemented aged oocytes directly, vitamin B6—but not the other strongly altered metabolites, L-acetylcarnitine and aminovaleric acid—fully reversed the age-associated decline in first polar body extrusion, the hallmark of successful nuclear maturation. Transcriptomics then pointed to the vascular endothelial growth factor pathway, whose age-elevated expression was normalized by the peptide. Blocking VEGF-A transcription with the inhibitor PTC299 reproduced many of elamipretide’s benefits in aged oocytes, restoring mitochondrial positioning, damping the ROS surge, repairing spindle defects and correcting chromosome misalignment, while PI3K/AKT inhibitors failed to do so—placing VEGF-A, acting downstream of vitamin B6 metabolism, at the heart of the mechanism.

Under the microscope, the cellular rescue was striking. Aged oocytes typically display aberrant spindles and scattered chromosomes, loss of γ-tubulin foci at the spindle poles, and reduced acetylation of tubulin, a marker of microtubule instability. Elamipretide restored all of these, along with the cytoplasmic actin network that aging disrupts, and it recovered the expression of ROCK1/2, proteins involved in actin assembly. Mitochondria, which drift away from the spindle and clump in the cytoplasm of aged eggs, returned to their proper peri-spindle domain; ATP levels normalized, mitochondrial DNA copy number partially rebounded, membrane potential rose and ROS fell. The peptide also repaired organelle systems beyond the mitochondria: Golgi markers Rab10 and GM130, endoplasmic reticulum positioning and the ER stress marker GRP78, lysosomal distribution and LC3-mediated autophagic flux all returned toward youthful patterns, indicating a coordinated restoration of cytoplasmic maturation.

Crucially, the findings were not confined to mice. In a randomized in vitro experiment approved under the Declaration of Helsinki, germinal vesicle oocytes from 39 patients undergoing intracytoplasmic sperm injection were cultured with or without 500 micromolar elamipretide. Among women aged 35 and older—three patients contributing 54 oocytes—the peptide improved maturation at both 24 and 48 hours and raised fertilization and cleavage rates after ICSI, with similar gains in younger women’s oocytes. In pigs, whose oocytes are a standard translational model, elamipretide at 1 millimolar rescued maturation in eggs subjected to hydrogen-peroxide-induced oxidative stress, restoring mitochondrial distribution, LC3 expression and apoptosis levels. The authors conclude that short-term elamipretide treatment reverses age-related oocyte decline through a vitamin B6–VEGF axis that jointly rescues nuclear and cytoplasmic maturation. Because the peptide has already advanced into human trials for cardiac and neuromuscular indications, the path from mouse ovary to fertility clinic may be shorter than for most laboratory discoveries—though the transient one-month window of benefit and the small human sample mean considerable work remains before any clinical application.

Subject of Research: Mitochondria-targeted peptide therapy for age-related decline in oocyte quality and female fertility

Article Title: Elamipretide Rejuvenates Oocyte Quality and Restores Female Fertility During Reproductive Aging

Article References: Zhang, H.-L., Wang, Y., Wang, C., Guo, X., Chen, H., Hou, Y.-X., Wu, X., Wu, Z.-J., Pan, W.-L., Ma, R.-J., Lu, P.-S., Shu, J., & Sun, S.-C. (2026). Elamipretide Rejuvenates Oocyte Quality and Restores Female Fertility During Reproductive Aging. Aging Cell, 25(10), Article e70749. https://doi.org/10.1111/acel.70749

Image Credits: AI Generated

DOI: 10.1111/acel.70749

Keywords: elamipretide, oocyte aging, female fertility, mitochondria, cardiolipin, vitamin B6, VEGF, oxidative stress, meiotic spindle, reproductive aging, in vitro maturation, Aging Cell

The research tackled a long-standing puzzle in vascular biology: why women fare disproportionately badly as they age. Although both sexes experience arterial stiffening and neurological decline with age, women show a higher incidence of cardiovascular disease and many neurological conditions after menopause compared with age-matched men. The link between arterial stiffness and mortality is nearly twice as strong in women as in men, and cognitive decline progresses more steeply in elderly females than in elderly males. Because aging-related vascular stiffening can alter the blood–brain barrier and brain function, the investigators reasoned that the earliest changes in the vessels of the neck—the carotid arteries and jugular veins—might be tightly coupled to biochemical remodeling inside the brain.

To capture that coupling, the team combined three complementary technologies in a single cohort of healthy female C57BL/6 mice. Ultrasound imaging, performed with a high-frequency transducer on a Vevo 3100 system, allowed them to measure vessel diameters and blood velocities in living animals, from which they calculated wall shear stress, circumferential cyclic strain, pulsatility index, and volumetric flow in the carotid artery. Histology then quantified the balance of elastin and collagen—the two structural proteins that determine whether an artery snaps back like a rubber band or behaves like a rigid pipe. Finally, two mass spectrometry approaches, liquid chromatography mass spectrometry and matrix-assisted laser desorption ionization mass spectrometry imaging, charted the lipid landscape of the carotid artery, jugular vein, and brain, mapping exactly where age-sensitive lipids reside in tissue.

The ultrasound results were unambiguous. Middle-aged females, at 52 weeks of age, showed a roughly 23.5 percent drop in average carotid velocity during systole compared with 12-week-old young females, and a 27.8 percent reduction in wall shear stress during systole, a difference that was highly statistically significant. Average volumetric flow, normalized to body weight, plummeted by about 55.2 percent with age. Because the reduction in shear stress was driven primarily by the decline in systolic velocity, the authors attribute it to age-related changes in vascular compliance and cardiac output. Circumferential cyclic strain and pulsatility index trended downward but did not reach statistical significance, while the jugular vein diameter grew about 11.6 percent larger in the older animals—evidence that even veins remodel with age.

Under the microscope, the structural counterpart of those functional losses came into focus. The elastin-to-collagen ratio in the carotid artery fell in middle-aged mice relative to young controls, a shift that reflects the fundamental biomechanics of aging arteries. Elastin fibers, which allow vessels to stretch and recoil, replenish at an extremely low rate throughout life; as they dwindle, stiffer collagen fibers accumulate in relative terms. A lower elastin-to-collagen ratio means diminished arterial compliance, limiting the vessel’s ability to dampen the pulsatile pressure generated by each heartbeat. When large arteries lose that damping capacity, the delicate microvasculature surrounding the brain is exposed to higher pulsatile energies than it can safely withstand, a mechanism that previous work has linked to damage of small vessels and the blood–brain barrier. Notably, the jugular vein showed the opposite trend, with a modest increase in its elastin-to-collagen ratio, suggesting that arteries and veins age along distinct structural trajectories.

The lipidomic data added a molecular dimension to this picture. In the brain, ten lipid headgroups—including hexosylceramides, phosphatidic acid, phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylinositol, phosphatidylserine, and sulfated hexosylceramides—decreased significantly with age, while N-acylethanolamines increased, possibly as a compensatory response to age-related stress or inflammation given their known neuroprotective roles. These reductions matter because the brain is among the most lipid-rich organs in the body. Phospholipids protect cells from damage, sphingolipids stabilize the myelin that insulates nerves, and low levels of these molecules can signal neuronal vulnerability. In the carotid artery, cardiolipins and lysophosphatidylethanolamines rose with age, changes the authors link to mitochondrial dysfunction and membrane remodeling within the vessel wall. A triglyceride species, TG 45:9, accumulated in the aged carotid—consistent with epidemiological evidence that triglycerides are the blood lipid most strongly associated with arterial stiffness—while the signaling lipid DG 55:10 declined, hinting at impaired endothelial responsiveness.

Perhaps the study’s most consequential technical insight came from comparing whole-brain and region-specific analyses. When the researchers ran an unsupervised principal component analysis on mass spectrometry imaging data from the entire brain, young and middle-aged animals overlapped almost completely, with only a faint suggestion of age-related variation. But when the same analysis was restricted to the hippocampus—the memory center known to be exquisitely sensitive to metabolic and mitochondrial stress—the two age groups separated cleanly, with minimal overlap. The dominant contributor to that separation was a cardiolipin-associated ion at mass-to-charge ratio 1489.73, which diminished in the middle-aged hippocampus. Cardiolipins are essential components of mitochondrial membranes, and their loss fits established models of mitochondrial dysfunction in brain aging. The lesson is methodological as much as biological: bulk analysis of the whole brain masks regional lipid remodeling that may drive cognitive decline, and imaging-based approaches can expose changes that homogenized tissue cannot.

Tying everything together, Pearson correlation analysis revealed moderate to strong associations—correlation coefficients exceeding 0.6 in magnitude—between vascular biomechanical measures such as wall shear stress and circumferential cyclic strain and specific lipid classes across tissues, including glycerolipids, phospholipids, and sphingolipids. The authors are careful to stress that these correlations do not establish causality, and because neuronal and glial endpoints were not directly measured, any link between vascular changes and downstream neurological consequences remains speculative. They also acknowledge limitations: the effect sizes were relatively small, the 52-week-old mice represent a middle-aged rather than truly aged cohort, and even careful use of anatomical landmarks could not eliminate all positional variability in imaging and biochemical sampling. More advanced aging or emerging pathology may be required to produce larger, more disruptive shifts in vascular metrics.

Even with those caveats, the study delivers a compelling integrated portrait of neurovascular aging in females. Declining blood flow, falling wall shear stress, stiffening arterial walls, and wholesale lipid remodeling in both vessel and brain appear together in otherwise healthy animals, well before overt disease. That timing matters: if neck vascular dysfunction genuinely precedes brain biochemical alteration, as related work from the same group suggests, the vasculature may offer an early warning system—and a potential intervention target—for the cognitive diseases that disproportionately afflict aging women. By establishing this baseline in disease-free mice, the team has laid groundwork for future mechanistic studies in models of neurodegeneration, and has underscored a point increasingly hard to ignore: brain aging cannot be understood without also understanding the blood vessels that feed it.

Subject of Research: The effects of aging on neck vascular function, vascular and brain lipid composition, and brain biochemistry in female mice.

Article Title: Impact of aging on neck vasculature and brain biochemistry in female mice

Article References: Jones, A. R., Jarrahi, A., Karpowich, K., Moody, E., Renner, L., Brown, L. P., Tressler, C. M., & Crouch, A. C. (2026). Impact of aging on neck vasculature and brain biochemistry in female mice. Physiological Reports, 14(17), Article e71059. https://doi.org/10.14814/phy2.71059

Image Credits: AI Generated

DOI: 10.14814/phy2.71059

Keywords: aging, carotid artery, wall shear stress, arterial stiffness, lipidomics, mass spectrometry imaging, hippocampus, cardiolipin, female mice, neurovascular, sphingolipids, brain biochemistry