P53 and Parkin co-regulate mitophagy in bone marrow mesenchymal stem cells to promote the repair of early steroid-induced osteonecrosis of the femoral head.

Survival and stemness of bone marrow mesenchymal stem cells (BMSCs) in osteonecrotic areas are especially important in the treatment of early steroid-induced osteonecrosis of the femoral head (ONFH). We had previously used BMSCs to repair early steroid-induced ONFH, but the transplanted BMSCs underwent a great deal of stress-induced apoptosis and aging in the oxidative-stress (OS) microenvironment of the femoral-head necrotic area, which limited their efficacy. Our subsequent studies have shown that under OS, massive accumulation of damaged mitochondria in cells is an important factor leading to stress-induced apoptosis and senescence of BMSCs. The main reason for this accumulation is that OS leads to upregulation of protein 53 (P53), which inhibits mitochondrial translocation of Parkin and activation of Parkin's E3 ubiquitin ligase, which decreases the level of mitophagy and leads to failure of cells to effectively remove damaged mitochondria. However, P53 downregulation can effectively reverse this process. Therefore, we upregulated Parkin and downregulated P53 in BMSCs. We found that this significantly enhanced mitophagy in BMSCs, decreased the accumulation of damaged mitochondria in cells, effectively resisted stress-induced BMSCs apoptosis and senescence, and improved the effect of BMSCs transplantation on early steroid-induced ONFH.