DMOG attenuates steroid-associated endothelial progenitor cell impairment and osteonecrosis of the femoral head via regulating HIF-1α signaling pathway in rabbit

Abstract Background: Steroid-associated osteonecrosis of the femoral head (SONFH), generally caused by chronic or/and high-dose use of Glucocorticoids (GCs), has long been puzzling mankind for a long time as the most essential etiology for non-traumatic ONFH. Hypoxia inducible factor-1α (HIF-1α) is an essential transcription factor that plays a significant role in maintaining bone homeostasis. By repressing prolyl hydroxylase domain (PHD) enzymic activity, Dimethyloxalylglycine (DMOG) was reported to inhibit the transcription and activation of HIF-1α. Recently, the impairment and dysfunction of endothelium has been closely related to the pathogenesis of SONFH. Our previous studies have shown the compromised number and function of endothelial progenitor cells (EPCs) which are the major source of restoring the endothelium during reendothelialization in SONFH patients. Nevertheless, whether activated HIF-1α by DMOG could alleviate GCs-related damaged biological function of EPCs remains unclear.Methods: We investigated that regulating HIF-1α signaling pathway of EPCs could be the therapeutic target for SONFH in vitro and vivo. Western blot analysis was used to assess protein expression. Transwell, tube formation, senescence-associated β-galactosidase and ELISA assays were carried out in vitro. SONFH was induced by methylprednisolone combined with lipopolysaccharide in rabbits. Histological staining of sections were conducted to evaluate the expression of HIF-1α which is of significance for osteogenesis and angiogenesis. Immunohistochemical staining of local femoral head slices and flow cytometry analysis of peripheral blood were used to quantify the number of EPCs.Results: High dose of GCs remarkably inhibited HIF-1α expression and subsequently compromised the bioactivity in EPCs. DMOG treatment was able to reverse the impairment effects in a concentration-dependent manner in vitro, while inhibition of HIF-1α by KC7F2 essentially attenuated these outcomes. Our in vivo experiments also showed that DMOG obviously increased blood supply and alleviated osteonecrosis owing to the increased HIF-1α expression of EPCs. Conclusion: The importance of HIF-1α to the regulation of EPCs is emphasized due to its reendothelialization in SONFH. Our results indicated that DMOG not only promoted the activation of HIF-1α signaling pathway in EPCs, but also boosted endogenous EPCs targeting and homing to damaged endothelium beneficial to reendothelialization in femoral head.