Excess PrPC Inhibits Muscle Cell Differentiation Via Mirna-Enhanced Liquid–liquid Phase Separation Implicated in Myopathy

The cellular prion protein (PrPC), a glycoprotein existing in membrane-bound and cytoplasmic forms, has functional importance in skeletal muscle, but the mechanism behind the phenomenon remains poorly understood. Here we report that PrPC is overexpressed and located in the cytoplasm of the skeletal muscle of six myopathy patients; cytoplasmic PrPC strongly inhibits skeletal muscle cell autophagy and blocks myoblast differentiation. PrPC selectively binds to a subset of miRNAs during myoblast differentiation, and the co-localization of PrPC with miR-214-3p was clearly observed in the skeletal muscle of six myopathy patients but not in that of four age-matched controls. We demonstrate that PrPC is overexpressed in skeletal muscle cells under pathological conditions and inhibits muscle cell differentiation via physically interacting with a subset of miRNAs to significantly inhibit autophagy-related protein 5-dependent autophagy, and selectively recruits these miRNAs into phase-separated condensates in living myoblasts, which in turn greatly enhances liquid–liquid phase separation (LLPS) of PrPC and results in the subsequent PrP aggregation and muscle bundle formation in myopathy patients characterized by incomplete muscle regeneration. Our findings show how excess PrPC can inhibit muscle cell differentiation via miRNA-enhanced LLPS implicated in myopathy. ### Competing Interest Statement The authors have declared no competing interest.