Elevated expression of leptin in endometriotic tissue results in an increase in stromal cell proliferation and may contribute to the development of endometriosis. However, the underlying mechanism responsible for aberrant expression of leptin is not known. We hypothesize that aberrant expression of leptin in endometriotic stroma may be regulated by increased levels of hypoxia-inducible factor-1 (HIF-1), the master transcription factor that controls gene expression in response to hypoxia. Herein we show that the mRNA and protein levels of HIF-1 were greater in ectopic endometriotic tissue compared with its eutopic counterpart. Exposure of eutopic endometrial stromal cells under hypoxic conditions or treated with desferrioxamine (DFO, chemical hypoxia) resulted in a time-dependent increase in leptin gene expression. A promoter activity assay demonstrated that HIF-1 induced leptin promoter activity after DFO treatment. Chromatin immunoprecipitation assay further demonstrated that binding of HIF-1 to leptin promoter was evident after DFO treatment. Finally, depletion of HIF-1 by short interference RNA abolished leptin expression in ectopic endometriotic stromal cells. Taken together, our data demonstrate that aberrant expression of leptin in ectopic endometriotic stromal cells is induced, at least in part, by an elevated level of HIF-1 in these cells, providing new insights into the etiology of endometriosis.
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