Myogenic IL-6 Mediates Myofiber Type Transition in Porcine Skeletal Muscle Satellite Cells via the STAT3/myh7 Pathway

Myofiber type determines pork quality, with type I fibers conferring superior traits via myosin heavy chain 7 (Myh7). As a crucial myokine, interleukin-6 (IL-6) plays important roles in skeletal muscle development, whether it participates in myh7 transcription and type I myofiber differentiation remains unclear. To address this, we compared Putian (adipose-type) and DLY (lean-type) pigs through in vivo myofiber typing and in vitro satellite cell (SC) cultures, supplemented by ChIP-PCR and dual-luciferase reporter assays to investigate molecular mechanisms. Our results showed that Putian pigs exhibited significantly higher proportions of type I myofibers, myh7 mRNA and Myh7 protein expression, and IL-6 levels than DLY pigs. In vitro, IL-6 treatment promoted SC differentiation toward type I myofibers. Mechanistically, STAT3 bound directly to the myh7 promoter in a phosphorylation-dependent manner to enhance its transcription, as confirmed by ChIP-PCR and dual-luciferase reporter assays. STAT3 was required for IL-6-induced myh7 upregulation, and STAT3 inhibition abrogated this effect. Collectively, these findings demonstrate that muscle-derived IL-6 promotes type I myofiber differentiation by activating STAT3 phosphorylation and myh7 transcription, providing a candidate target for improving pork quality through selective breeding or nutritional intervention.