Proline-driven metabolic reprogramming promotes skeletal muscle hypertrophy and oxidative myofiber specification in porcine offspring: a stage-optimized maternal nutritional intervention.

BACKGROUND: While maternal proline (Pro) supplementation has demonstrated efficacy in enhancing placental angiogenesis and farrowing efficiency in swine, its regulatory role in fetal skeletal muscle ontogeny remains undefined. This study systematically evaluated the temporal-specific impacts of dietary Pro supplementation during critical phases of fetal myogenesis (encompassing primary myofiber formation and secondary myofiber hyperplasia) on offspring muscle development. A total of 120 sows with similar farrowing schedules were assigned to three groups: CON (basal diet), ST-Pro (0.5% Pro supplementation during secondary myofiber formation period, from d 60 gestation to farrowing), LT-Pro (0.5% Pro supplementation spanning primary and secondary myofiber formation period: from d 20 gestation to farrowing). RESULTS: LT-Pro group significantly increased the longissimus dorsi (LD) muscle mass per unit body weight in newborn piglets compared to CON group (P < 0.05), while no such effect was observed in the ST-Pro group. Metabolomic profiling revealed elevated Pro, lysine, and tryptophan levels in the LD muscle of LT-Pro group piglets, accompanied by reduced branched-chain amino acids (BCAAs; leucine, isoleucine, and valine) in both serum and muscle (P < 0.05). Histological analysis demonstrated a 45.74% increase in myofiber cross-sectional area in the LT-Pro group (P < 0.05). At the molecular level, LT-Pro group piglets exhibited upregulated mRNA expression levels of myogenic regulatory genes (MYOD1, MYF6) and the cell cycle accelerator CCND1 (P < 0.05), coupled with activation of the STAT3 signaling pathway (phosphorylated STAT3 protein increased by 2.53-fold, P < 0.01). Furthermore, Pro supplementation enhanced oxidative metabolism, evidenced by elevated mitochondrial biogenesis markers (the mRNA expression levels of PPARGC1A, OPA1, and SQSTM1) and a 61.58% increase in succinate dehydrogenase activity (P < 0.05). Notably, LT-Pro group piglets showed a selective shift toward slow-twitch oxidative fibers, with both MyHC1 mRNA and protein expression levels significantly upregulated (P < 0.05), while the mRNA expression levels of MyHCIIb showed no significant change. CONCLUSIONS: This study identified the primary fiber formation period as a critical window. Supplementation with Pro during G20-114 reprogrammed offspring skeletal muscle development through STAT3-CCND1-mediated myoblast proliferation, enhanced mitochondrial bioenergetics, and oxidative fiber specification. However, no such effects were observed during G60-114. These findings propose maternal Pro intervention as a novel strategy to enhance muscle yield and metabolic efficiency in swine production, with potential applications for improving meat quality traits linked to oxidative muscle phenotypes.