Sex Differences in Mitochondrial Function in Aging Mouse Skeletal Muscle

Sex differences in lifespan and age-associated phenotypes are pervasive across species, yet the mechanisms remain poorly understood. Mitochondrial dysfunction is a major hallmark of aging, but whether skeletal muscle mitochondria age along sex specific trajectories remains incompletely defined. Here, we profiled mitochondrial bioenergetics and DNA integrity in flexor digitorum brevis (FDB) muscle from young (3–4 months) and aged (20–24 months) male and female C57BL/6 mice.

We quantified cellular respiration in intact myofibers, measured mitochondrial DNA (mtDNA) copy number, and assessed expression of genes involved in mitochondrial dynamics, electron transport chain (ETC) function, and mtDNA maintenance. Cellular respiration differed by sex at baseline and changed with age in a sex dependent manner. Aged females exhibited a lower basal and ATP-linked respiration than aged males. In contrast, spare respiratory capacity increased in aged females relative to aged males, consistent with age- and sex-specific remodeling of the bioenergetic reserve. mtDNA copy number increased with age in both sexes, with a greater increase in mtDNA content in aged males. Gene expression analyses revealed age- and/or sex-dependent changes, including lower Pink1 expression in females compared to males, an age-related increase in the mtDNA maintenance gene Polg2 only in males, though most genes were not significantly different. As an exploratory systemic readout, we additionally assessed DNA damage responsiveness in whole-blood leukocytes using the alkaline comet assay following oxidative challenge; young females exhibited greater induced DNA damage than young males.

Together, these data define sex- and age-associated mitochondrial remodeling in FDB and provide an initial assessment of sex-dependent inducible DNA damage responses in blood, underscoring the importance of sex as a biological variable in studies of aging.

Included Data:
qPCR file for Mitochondrial Genomic DNA: Graphpad file of the average qPCR results for the genomic mitochondrial DNA genes, excel files with the raw CT values and calculations
OCR file: Graphpad Prism file of the average oxygen consumption rate, Graphpad Prism file for the OCR trace graphs
Gene expression qPCR file: File with Graphpad Prism file of the average qPCR results for the gene expression, excel files with the raw CT values and calculations
Comet assay data file: Comet images, excel file of the number of comets counted per mouse per condition, graphpad file of the average comet assay data