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

## TL;DR

This study shows that the FRZB gene limits muscle growth in pigs by blocking Wnt signals, which could help improve meat production through selective breeding.

## Contribution

The study identifies FRZB as a negative regulator of myogenesis in pigs via the Wnt pathway, linking it to breed-specific muscle growth differences.

## Key findings

- FRZB expression is higher in slow-growing indigenous pigs compared to fast-growing commercial breeds.
- Reducing FRZB in muscle cells increases proliferation, migration, and formation of larger muscle fibers.
- FRZB silencing upregulates myogenic and fusion markers while promoting hypertrophy-related genes.

## Abstract

Skeletal muscle growth is the primary factor determining meat production in the pig industry. A gene called FRZB is known to affect bone development, but its specific role in muscle formation is not well understood. This study aimed to investigate how FRZB influences muscle growth and whether it contributes to the size differences between pig breeds. We compared slow-growing indigenous pigs with fast-growing commercial pigs and found that the slow-growing breeds had significantly higher levels of FRZB in their loin muscles during development. To understand its function, we reduced the levels of FRZB in muscle cells in the laboratory. We observed that cells with lower FRZB levels multiplied faster and formed larger, thicker muscle fibers. Our results suggest that FRZB acts like a natural “brake” on muscle growth by blocking specific growth signals. This research is valuable to society because it identifies a biological factor that limits meat yield. Understanding this mechanism could help animal breeders select pigs with better muscle growth traits, ultimately improving efficiency in meat production.

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.