BMP9 Alleviates Iron Accumulation-Induced Osteoporosis via the USP10/FOXO1/GPX4 Axis.

Introduction: Ferroptosis induced by iron accumulation can disrupt the physiological functions of bone marrow mesenchymal stem cells (BMSCs). BMP9 is an effective osteogenic factor. However, the role of BMP9 and its molecular mechanisms in osteoporosis induced by iron accumulation remain unclear.

Objectives: This study aims to explore the role and mechanism of BMP9 in alleviating iron accumulation induced osteoporosis.

Methods: Clinical samples were collected to analyze the relationship between iron accumulation and osteoporosis. The effect of BMP9 on lipid peroxidation levels in BMSCs under iron accumulation conditions was assessed using C11-BODIPY staining, MitoSOX staining, MDA and SOD activity measurement. The osteogenic capacity of BMP9 in BMSCs under iron accumulation conditions was evaluated by measuring ALP activity and calcium nodule formation. The mechanisms of BMP9 in regulating BMSCs under iron accumulation conditions were explored through experiments including cycloheximide treatment, RT-PCR, Western blot, GST pull-down, ChIP, and CO-IP.

Results: It was observed in human samples that serum ferritin levels were negatively correlated with the bone mineral density of the lumbar spine and femoral neck. Meanwhile, ferroptosis is considered a key factor affecting bone health. Further research indicated that BMP9 could inhibit ferroptosis in cells and animal models with iron accumulation, while also improving oxidative stress and osteogenic capacity. In-depth investigation of its mechanism reveals that BMP9 promotes the expression of USP10, which removes the K48-linked ubiquitin chains on FOXO1, inhibiting its excessive ubiquitination in the cytoplasm. This stabilization allows FOXO1 to accumulate in the cytoplasm and eventually re-enter the nucleus. This process activated the expression of the key inhibitor of cell death, GPX4, enhancing the cell's antioxidant response, reducing ferroptosis-induced damage to BMSCs, and promoting their osteogenic differentiation.

Conclusion: This study reveals that BMP9 inhibits ferroptosis through the USP10/FOXO1/GPX4 axis, providing a new therapeutic strategy for osteoporosis caused by iron accumulation.