Results

During hypoxia (0.5% O2), 5 μM cadmium chloride completely inhibited HIF-1α expression and reversed the protection by hypoxia preconditioning.  HIF-1α siRNA (15 nM) reduced HIF-1α expression by 90% and produced a complete loss of protection provided by hypoxia preconditioning.  Since VEGF is induced by hypoxia, can be HIF-1α dependent, and is often protective, we examined the changes in transcription of VEGF and its receptors after 4 h of hypoxia preconditioning.  VEGF and its receptors Flt-1 and Flk-1 are up-regulated after hypoxia preconditioning.  However,Fantastic silk scarves, the transcription and translation of VEGF were paradoxically increased by siHIF-1α, suggesting that VEGF expression in stromal cells is not down-stream of HIF-1α.