Sex differences in muscle protein expression and DNA methylation in response to exercise training

BackgroundExercise training elicits changes in muscle physiology, epigenomics, transcriptomics, and proteomics, with males and females exhibiting differing physiological responses to exercise training. However, the molecular mechanisms contributing to the differing adaptations between the sexes are poorly understood.MethodsWe performed a meta-analysis for sex differences in skeletal muscle DNA methylation following an endurance training intervention (Gene SMART cohort and E-MTAB-11282 cohort). We investigated for sex differences in the skeletal muscle proteome following an endurance training intervention (Gene SMART cohort). Lastly, we investigated whether the methylome and proteome are associated with baseline cardiorespiratory fitness (maximal oxygen consumption; VO2max) in a sex-specific manner.ResultsHere, we investigated for the first time, DNA methylome and proteome sex differences in response to exercise training in human skeletal muscle (n = 78; 50 males, 28 females). We identified 92 DNA methylation sites (CpGs) associated with exercise training; however, no CpGs changed in a sex-dependent manner. In contrast, we identified 189 proteins that are differentially expressed between the sexes following training, with 82 proteins differentially expressed between the sexes at baseline. Proteins showing the most robust sex-specific response to exercise include SIRT3, MRPL41, and MBP. Irrespective of sex, cardiorespiratory fitness was associated with robust methylome changes (19,257 CpGs) and no proteomic changes. We did not observe sex differences in the association between cardiorespiratory fitness and the DNA methylome. Integrative multi-omic analysis identified sex-specific mitochondrial metabolism pathways associated with exercise responses. Lastly, exercise training and cardiorespiratory fitness shifted the DNA methylomes to be more similar between the sexes.ConclusionsWe identified sex differences in protein expression changes, but not DNA methylation changes, following an endurance exercise training intervention; whereas we identified no sex differences in the DNA methylome or proteome response to lifelong training. Given the delicate interaction between sex and training as well as the limitations of the current study, more studies are required to elucidate whether there is a sex-specific training effect on the DNA methylome. We found that genes involved in mitochondrial metabolism pathways are differentially modulated between the sexes following endurance exercise training. These results shed light on sex differences in molecular adaptations to exercise training in skeletal muscle. The skeletal muscle proteome displayed robust sex differences at baseline.The skeletal muscle proteome responded to 4 weeks of endurance training in a sex-specific manner.The skeletal muscle DNA methylome responded to 4 and 8 weeks of endurance training similarly between males and females.O2max levels, an indicator of cardiorespiratory fitness and lifelong training, displayed a strong, universal signature on the muscle methylome, but not on the muscle proteome; both in a sex-invariable manner.VBoth endurance training and cardiorespiratory fitness shifted the DNA methylomes to be more similar between the sexes. Exercise provides health benefits to every organ of the body, with specific genes and proteins changing in response to exercise. Males and females have distinct physiology which influences the body's responds to exercise. However, it is largely unknown whether males and females respond differently to exercise on a molecular level. To function effectively, our muscles need specific proteins whose expression is regulated by a process called epigenetics. Epigenetics refers to modifications to our DNA that occur as a result of various environmental factors, such as exercise. We investigated sex differences in two aspects of molecular response to exercise: epigenetics and protein expression. We discovered that few weeks-long exercise programmes led to significant changes in protein expression but minimal changes in epigenetics. The proteins changed after exercise differed between the sexes and were involved in metabolism. This indicates that exercise has an immediate impact on muscle proteins in a sex-specific manner, but perhaps changes in epigenetics are slower. We then wondered whether a longer period of exercise would illicit sex-specific changes in epigenetics and protein expression. We showed that fitter individuals exhibited epigenetic differences compared to less fit individuals, while protein expression remained unchanged. Fit males and females showed similar epigenetic changes compared to their unfit counterparts. This suggests that lifelong training shifts the muscle epigenetic patterns in a similar manner in both males and females. Our findings emphasise the importance of lifelong fitness for stimulating epigenetic remodelling in muscle, as well as the importance of taking sex differences into consideration.