Hypoxic stress simultaneously stimulates vascular endothelial growth factor via hypoxia-inducible factor-1α and inhibits stromal cell-derived factor-1 in human endometrial stromal cells

BACKGROUND: Hypoxia of the human endometrium is a physiologic event occurring during the perimenstrual period and the local stimulus for angiogenesis. The aim of this study was to investigate the effects of hypoxic stress on the regulation of vascular endothelial growth factor (VEGF) and stromal cell-derived factor-1 (SDF-1/CXCL12), and the potential role of hypoxia-inducible factor-1 alpha (HIF-1 alpha) in the endometrium. METHODS: Human endometrial stromal cells (ESCs, n = 22 samples) were studied in vitro. ESCs were cultured under hypoxic and normoxic conditions and treated with cobalt chloride (CoCl2; a hypoxia-mimicking agent) and/or echinomycin, a small-molecule inhibitor of HIF-1 alpha activity. The mRNA levels and production of VEGF and SDF-1 were assessed by real-time PCR and ELISA, respectively. The HIF-1 alpha protein levels were measured using western blot analysis. RESULTS: Hypoxia simultaneously induced the expression of mRNA and production of VEGF and attenuated the expression and production of SDF-1 from ESCs in a time-dependent manner. Similar changes were observed in the ESCs after stimulation with CoCl2 in a dose-dependent manner. CoCl2 significantly induced the expression of HIF-1 alpha protein, and its highest expression was observed at 6 h. Echinomycin inhibited hypoxia-induced VEGF production without affecting the HIF-1 alpha protein level and cell toxicity and had no effect on SDF-1 secretion (P < 0.01). CONCLUSIONS: Hypoxia simultaneously acts to increase VEGF via HIF-1 alpha and to decrease SDF-1 in a HIF-1 alpha-independent manner in ESCs. These results indicate a potential mechanism for the action of hypoxic conditions that could influence angiogenesis in the human endometrium.