The Role Of Endothelial Progenitor Cell In The Pathogenesis And Treatment Of Avascular Necrosis Of The Femoral Head

Objective:Once non-traumatic avascular necrosis of the femoral head (ANFH) happened, vascular impairment and feeble collateral circulation are followed by poor outcomes. Circulating endothelial progenitor cells (EPCs) may substantially contribute to vascular homeostasis such as vascular repair and new blood vessel growth. We investigated whether abnormalities in EPCs levels and functions are present in ANFH patients.Methods:54 ANFH patients were enrolled, including steroid-induced (n=21), alcohol-induced (n=15) and idiopathic ANFH (n=18), and 30 healthy subjects as control (HC).The numbers of circulation EPCs were determined by fluorescence-activated cell-sorting (FACS) analysis. EPCs cultured from peripheral blood mononuclear cells on fibronectin to induce the expression of receptors for acetylated low-density lipoprotein and ulex-lectin. EPCs colony-forming units (CFUs) were observed from 54 patients and 30 healthy controls. Migratory capacity to chemo-attractants (vascular endothelial growth factor),cellular senescence levels and in vitro angiogenesis ability were assessed in age-matched subjects (n=10 per group).Results:Mean numbers of circulating EPC were 1460±265 cells/ml in HC,545±177 in ANFH, (P<0.001). Mean numbers of CFUs were 26.2±6.2 in HC,19.6±7.7 in ANFH,(P<0.001). Although there were not significant differences in circulating EPC and CFUs among the steroid-induced, alcohol-induced or idiopathic three groups, all these risk factors contributed to the decreased circulating EPCs numbers and CFUs. In addition, EPCs from ANFH patients showed reduced migratory capacity and increased cellular senescence compared with EPCs from normal subjects, furthermore the ability of angiogenesis in vitro was also impaired.Conclusion:Circulating endothelial progenitor cells (EPCs) numbers and functions are reduced in ANFH patients, suggesting that risk factors of ANFH may alter EPCs biology in angiogenesis and vascular repair. Objective:Hypoxia inducible factor-1α(HIF-1α) is a key determinant of oxygen-dependent gene regulation in angiogenesis. HIF-1αover expression may be beneficial in endothelial progenitor cells (EPCs) therapy of hypoxia-induced pathophysiological processes, such as avascular necrosis of the femoral head (ANFH). We will investigate the effects of HIF-1αon the proliferation, migration and angiogenesis of bone marrow-derived EPCs.Methods:Bone marrow EPCs were collected from rabbits, HIF-1αwas activated in the EPCs with the prolylhydroxylase inhibitor dimethyloxalylglycine (DMOG) with various concentrations(0μM,50μM,100μM,200μM,500μM,1000μM).MTT test, CFU assay were employed. The levels of HIF-1αprotein and its phosphorylation were detected by WesternBlot analysis. Nitric oxide (NO) production and were evaluated by a colorimetric assay based on Griess reaction. VEGF and SDF-1 were evaluated by Elisa. Migratory capacity to chemo-attractants (vascular endothelial growth factor),cellular senescence levels and in vitro angiogenesis ability were assessed.Results:The activator DMOG of HIF-1αhad an obvious facilitative effect on the proliferation of EPCs in a dose-dependent fashion, and DMOG contributed to the levels of HIF-1αprotein in a time-dependent pattern. DMOG could substantially improve the secretion of NO. VEGF and SDF-1, which could be neutralized by HIF-1αantibody. Beside this, DOMG ameliorated the Migratory functions and angiogenesis ability of EPCs, and significantly protected EPCs from cellular senescence.Conclusion:In vitro, DMOG can activate HIF-1αin EPCs and act on EPCs to improve proliferation,migration capacities and angiogenesis ability. The possible mechanism is that DMOG can stimulate HIF-1αand subsequently increase NO product and the secretion of VEGF and SDF-1. Objective:Hypoxia inducible factor-1α(HIF-1α) is a key determinant of oxygen-dependent gene regulation in angiogenesis. HIF-1αover expression may be beneficial in endothelial progenitor cells (EPCs) therapy of hypoxia-induced pathophysiological processes, such as avascular necrosis of the femoral head (ANFH). We will investigate the role of Endothelial Progenitor Cells in the treatment of hypoxia inducible factor-1alpha activator on the steroid-associated osteonecrosis in rabbits.Methods:Steroid-associated Osteonecrosis was induced by low-dose lipopolysaccharide and subsequent with high-dose methylprednisolone. Rabbits in the treatment group were subjected to intramuscular injections of DMOG at a dose of 20mg/kg per interval day for a week; and the control groups were given saline. Blood samples were collected before the rabbits sacrificed. Then bilateral femora were harvested and processed to tissue sections for immunohistochemical, histologic and histomorphometric analysis. The circulating EPCs were detected by Flow cytometric analyse.Results:The HIF-1αactivator DMOG ameliorates the steroid-associated osteonecrosis in rabbits. Quantitative analysis showed that new vessel and vessel density in the treatment group was signifantly improved than the control groups (14.7±4.1 VS 5.8±2.3, P<0.001). The histologic and histomorphometric analysis revealed that the new bone volume was significantly higher in the DMOG group than in control group(5.86±1.24 VS 2.71±0.93, P<0.05). The DMOG activated differently the HIF-1αof the marrow cells around the osteonecrosis. The circulating EPCs and the marrow progenitor cells were substantially boosted by DMOG.Conclusion:In vivo, DMOG can activate HIF-1αin marrow cells and act on EPCs to mobilizaion,releasing,migration to area of necrosis, thus contributed to angiogenesis and new bone formation. The EPCs played central role in the HIF-1αactivator ameliorates the steroid-associated osteonecrosis in rabbits by new vessel formation.