Inhibition of the PTBP1-PRKCZ axis activates autophagy to reprogram bone marrow mesenchymal stem cell fate commitment and ameliorate osteoporosis.

BACKGROUND/AIM: Osteoporosis is characterized by disrupted bone homeostasis while dysregulated autophagy contributes to impaired bone remodeling and bone loss. This study investigates the role of the RNA-binding protein polypyrimidine tract binding protein 1 (PTBP1) in osteoporosis progression through regulation of protein kinase C zeta (PRKCZ), and elucidates whether PTBP1 modulates the osteogenic-adipogenic fate commitment of bone marrow mesenchymal stem cells (BMSCs) via autophagy. METHODS: In vitro, BMSCs were subjected to lentiviral infection and/or autophagy inhibitor 3-methyladenine (3-MA) treatment to systematically evaluate autophagic activity and osteogenic and adipogenic differentiation. RNA immunoprecipitation coupled with quantitative polymerase chain reaction (RIP-qPCR) and RNA stability assays were performed to clarify the molecular regulatory relationship between PTBP1 and PRKCZ. The molecular regulatory relationship between PTBP1 and PRKCZ was verified. In vivo, a bilateral ovariectomy (OVX)-induced osteoporotic mouse model was established. Adeno-associated virus-mediated modulation of PTBP1 and PRKCZ expression was conducted. Osteogenic-adipogenic balance and bone mass were comprehensively assessed. RESULTS: Knockdown of PRKCZ markedly enhanced autophagic activity, promoted osteogenic differentiation, and suppressed adipogenic differentiation of BMSCs. These effects were reversed by 3-MA treatment. In OVX mice, PRKCZ expression was upregulated and was accompanied by impaired autophagy and osteogenic-adipogenic imbalance, whereas PRKCZ silencing substantially attenuated bone loss and reduced bone marrow adiposity. Mechanistically, PTBP1 increased PRKCZ expression by enhancing the stability of PRKCZ messenger RNA. Silencing PTBP1 activated autophagy via downregulation of PRKCZ, correcting the imbalance in BMSC fate commitment. CONCLUSION: Inhibition of the PTBP1-PRKCZ axis activates autophagy to reprogram the osteogenic-adipogenic differentiation balance of BMSCs, thereby mitigating osteoporosis.