Comparative effects of aerobic exercise in early versus late middle age on skeletal muscle function and miRNA profiling in mice.

BACKGROUND: Skeletal muscle plasticity progressively declines from middle age onward, and exercise may partially mitigate this deterioration through microRNA (miRNA)-mediated regulatory networks. However, whether the timing of aerobic exercise initiation during middle age (early vs. late) differentially influences muscle function and miRNA expression profiles remains incompletely understood.

METHODS AND RESULTS: Male C57BL/6 mice were assigned to four groups: middle-aged control (MC, 12 months), old-aged control (MC18, 18 months), early exercise (PRE18, 12-15 months), and late exercise (POS18, 15-18 months). Gastrocnemius muscles were collected for miRNA sequencing and subsequent functional analyses. The MC18 group exhibited sarcopenic-like phenotypes, with 176 differentially expressed miRNAs (DEmiRNAs) identified relative to the MC group. Aerobic exercise was associated with attenuation of age-related muscle atrophy, with PRE18 showing comparatively more pronounced effects than POS18. miRNA sequencing identified 21 DEmiRNAs with reversed expression patterns in the PRE18 group, whereas only 2 such miRNAs were identified in the POS18 group. Bioinformatic analysis of predicted targets suggested that early-exercise-induced miRNAs may be involved in suppressing FOXO/ubiquitin-mediated proteolysis and restoring Wnt/cAMP signaling, whereas late-exercise-induced miRNAs appeared to have a limited capacity to restore Wnt signaling. miR-195a-5p_R+1, miR-298-5p_R-2, miR-671-5p_R+1 and miR-150-5p were identified as candidate hub miRNAs based on target enrichments within these pathways. Western blot analyses indicated that PRE18 was associated with elevated expression of Wnt‑related (β‑catenin) and cAMP‑related (CREB1, PGC‑1α) proteins, alongside reduced levels of atrophic markers (FOXO3A, FBXO32, and MuRF1). In contrast, POS18 primarily affected atrophic protein expression, with relatively modest influence on Wnt signaling components.

CONCLUSIONS: These preliminary findings collectively suggest that the sustained benefits of exercise initiated in early middle age might be partially attributable to exercise‑induced miRNAs dually targeting both regenerative and atrophic pathways. Conversely, late initiation appears to be predominantly linked to anti‑atrophic effects, with less impact on regenerative signaling. Together, these observations provide initial evidence for temporal epigenetic plasticity and suggest broader molecular advantages of earlier intervention, although further mechanistic studies are warranted.