Porcine FRZB (sFRP3) Negatively Regulates Myogenesis via the Wnt Signaling Pathway

Secreted frizzled-related protein 3 (sFRP3/FRZB) is a soluble Wnt antagonist with established roles in skeletal development, however, its specific function in myogenesis remains underexplored. This study investigated the regulatory role of FRZB in muscle development, hypothesizing that it contributes to breed-specific growth differences in pigs. We examined FRZB expression in fetal tissues of slow-growing (Tibetan and Wujin) and fast-growing (Large White) pigs, and assessed its function in C2C12 myoblasts via siRNA-mediated knockdown. FRZB was widely expressed across porcine fetal tissues, with significantly higher abundance in the longissimus dorsi of slow-growing breeds. In vitro, FRZB silencing significantly enhanced myoblast proliferation and migration. Furthermore, knockdown accelerated differentiation and promoted the formation of longer, thicker multinucleated myotubes, accompanied by the upregulation of myogenic (MyoD, MyoG, MyHC) and fusion (β1-integrin, Myomaker) markers. Transcriptional profiling revealed a shift toward hypertrophy (Fst and Nog upregulation) and away from atrophy (Atrogin1 downregulation). These findings identify FRZB as a negative regulator of myogenesis via the Wnt signaling pathway. The elevated expression in indigenous breeds suggests FRZB may impose a molecular constraint on muscle development, highlighting its potential as a candidate gene for regulating carcass traits.