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

Secreted frizzled-related protein 3 (sFRP3/<i>FRZB</i>) 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 <i>FRZB</i> in muscle development, hypothesizing that it contributes to breed-specific growth differences in pigs. We examined <i>FRZB</i> 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. <i>FRZB</i> was widely expressed across porcine fetal tissues, with significantly higher abundance in the longissimus dorsi of slow-growing breeds. In vitro, <i>FRZB</i> 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 (<i>MyoD</i>, <i>MyoG</i>, <i>MyHC</i>) and fusion (<i>β1-integrin</i>, <i>Myomaker</i>) markers. Transcriptional profiling revealed a shift toward hypertrophy (<i>Fst</i> and <i>Nog</i> upregulation) and away from atrophy (<i>Atrogin1</i> downregulation). These findings identify <i>FRZB</i> as a negative regulator of myogenesis via the Wnt signaling pathway. The elevated expression in indigenous breeds suggests <i>FRZB</i> may impose a molecular constraint on muscle development, highlighting its potential as a candidate gene for regulating carcass traits.