Pbk positively regulates myoblast differentiation and muscle regeneration via enhancing AMPK/ULK1 mediated myogenic autophagy.

BACKGROUND: The activity of normal myoblasts is essential for the regeneration of skeletal muscle following injury. Nevertheless, the intrinsic mechanisms governing myoblast functions and muscle regeneration remain inadequately elucidated. PDZ binding kinase (Pbk) is a serine-threonine kinase that plays critical roles in various cellular functions and pathologies. However, its role in skeletal muscle remains largely unexplored. In this study, we have identified Pbk as a novel positive regulator of myoblast functions in vitro and muscle regeneration in vivo. METHODS: Herein, We analyzed the effects of Pbk on myoblast function and muscle regeneration through in vitro and in vivo experiments. In vivo, we analyzed the effects of Pbk on skeletal muscle regeneration through bioinformatic analysis combined with a mouse skeletal muscle injury model. In vitro, we analyzed the effects of Pbk knockdown or overexpression on myoblast proliferation, survival, and differentiation through lentivirus-mediated cell infection. Also, we further studied the molecular mechanisms by which Pbk affects myoblast differentiation and muscle regeneration combined with the molecular biology and biochemistry, and drug rescue approaches. RESULTS: In vitro experiments demonstrated that knockdown of Pbk results in impaired cell proliferation and accelerated apoptosis of myoblasts. Unlike proliferating myoblasts, Pbk is upregulated and restricted from translocating from the cytoplasm to the nucleus during myoblast differentiation. Notably, the positive effect of Pbk on myoblast differentiation and fusion is contingent upon its kinase activity. Mechanistic investigations revealed that Pbk facilitates myogenic autophagy by enhancing AMPK-mediated phosphorylation of ULK1, which ultimately contributes to myogenic differentiation and fusion. In vivo, we observed that Pbk is upregulated in embryonic myosin heavy chain (eMyHC) positive regenerative myofibers in muscle specimens from patients with Duchenne muscular dystrophy (DMD) and immune-mediated necrotizing myopathy (IMNM). Furthermore, in a murine model of skeletal muscle injury, Pbk knockdown hinders the regeneration of myofibers. CONCLUSIONS: Collectively, our findings suggest that Pbk plays a positive regulatory role in myoblast differentiation and muscle regeneration by modulating AMPK/ULK1-mediated autophagy signaling. This pathway may represent a novel target for the manipulation of myoblast functions and the development of myoblast-based therapies for skeletal muscle injuries.