Excess PrP inhibits muscle cell differentiation via miRNA-enhanced liquid-liquid phase separation implicated in myopathy.

The cellular prion protein (PrP) is required for skeletal muscle function. Here, we report that a higher level of PrP accumulates in the cytoplasm of the skeletal muscle of six myopathy patients compared to controls. PrP inhibits skeletal muscle cell autophagy, and blocks myoblast differentiation. PrP selectively binds to a subset of miRNAs during myoblast differentiation, and the colocalization of PrP and miR-214-3p was observed in the skeletal muscle of six myopathy patients with excessive PrP. We demonstrate that PrP is overexpressed in skeletal muscle cells under pathological conditions, inhibits muscle cell differentiation by physically interacting with a subset of miRNAs, and selectively recruits these miRNAs into its phase-separated condensate in living myoblasts, which in turn enhances liquid-liquid phase separation of PrP, promotes pathological aggregation of PrP, and results in the inhibition of autophagy-related protein 5-dependent autophagy and muscle bundle formation in myopathy patients characterized by incomplete muscle regeneration.