Sex differences in resting skeletal muscle and the acute and long-term response to endurance exercise in individuals with overweight and obesity.

Objectives: Endurance exercise reduces the risk of metabolic diseases by improving skeletal muscle metabolism, particularly in individuals with overweight and obesity. As biological sex impacts glucose and fatty acid handling in skeletal muscle, we hypothesized sex differences at the transcriptomic and proteomic level in the acute response to exercise and after an 8-week exercise intervention.

Methods: We analyzed skeletal muscle biopsies from 25 sedentary subjects (16f/9 m) with overweight and obesity using transcriptomics and proteomics at baseline, after acute exercise, and following an 8-week endurance training program. Regulation of sex-specific differences was studied in primary myotubes from the donors.

Results: At baseline, differentially methylated CpG-sites potentially explain up to 59% of transcriptomic and 67% of proteomic sex differences. Differences were dominated by higher abundance of fast-twitch fiber type proteins, and transcripts and proteins regulating glycogen degradation and glycolysis in males. Females showed higher abundance of proteins regulating fatty acid uptake and storage. Acute exercise induced stress-responsive transcripts and serum myoglobin predominantly in males. Both sexes adapted to 8-week endurance training by upregulating mitochondrial proteins involved in TCA cycle, oxidative phosphorylation, and β-oxidation. Training equalized fast-twitch fiber type protein levels, mainly by reducing them in males. In vivo sex differences in autosomal genes were poorly retained in myotubes but partially restored by sex hormone treatment.

Conclusions: Our findings highlight sex-specific molecular signatures that reflect known differences in glucose and lipid metabolism between female and male skeletal muscle. After just 8 weeks of endurance training, these sex differences were attenuated, suggesting a convergence towards a shared beneficial adaptation at the molecular level.