Suppression of COUP-TFII upregulates angiogenin and promotes angiogenesis in endometriosis

STUDY QUESTION: How does hypoxia-mediated downregulation of chicken ovalbumin upstream promoter-transcription factor II (COUP-TFII) promote angiogenesis in endometriosis? SUMMARY ANSWER: Suppression of COUP-TFII by hypoxia stimulates angiogenesis through induction of angiogenin (ANG). WHAT IS KNOWN ALREADY: The level of COUP-TFII is downregulated in endometriotic tissues, and downregulation of COUP-TFII contributes to the development of endometriosis. STUDY DESIGN, SIZE, DURATION: Twenty-seven patients of reproductive age with endometriosis were recruited in this study. Eutopic endometrial and ectopic endometriotic stromal cells were isolated, cultured and subjected to various treatments. PARTICIPANTS/MATERIALS, SETTING, METHODS: Microarray hybridization, quantitative RT-PCR, and Western blot were used to detect gene expression in normal and endometriotic samples. A luciferase reporter assay and chromatin immunoprecipitation in normoxia or hypoxia-treated primary cultures of human endometrial stromal cells were performed. Tube formation analysis was performed using primary human umbilical vein endothelial cells (HUVECs). MAIN RESULTS AND THE ROLE OF CHANCE: Protein level of COUP-TFII was downregulated by hypoxia (P < 0.05, normoxia versus hypoxia). Loss of COUP-TFII increased the angiogenic capacity of endometrial stromal cells (P < 0.05, COUP-TFII knockdown versus knockdown control). A novel COUP-TFII target gene, ANG, was identified through microarray analysis. Chromatin immunoprecipitation and promoter activity assays demonstrated that the ANG promoter was bound and suppressed by COUP-TFII (P < 0.05, COUP-TFII overexpression versus empty vector). The levels of ANG mRNA and protein were elevated in ectopic endometriotic stromal cells and negatively correlated with COUP-TFII (P < 0.05, endometrial versus endometriotic tissues/stromal cells). Both knockdown and forced-expression of COUP-TFII further demonstrated that ANG expression and ANG-mediated angiogenic activity were negatively regulated by COUP-TFII (P < 0.05, COUP-TFII knockdown versus knockdown control, and COUP-TFII overexpression versus empty vector). LIMITATIONS, REASONS FOR CAUTION: This study was conducted in primary human endometrial stromal cell cultures and HUVECs, therefore, may not fully reflect the situation in vivo. LARGE SCALE DATA: The raw data were submitted to Gene Expression Omnibus (GSE107469). WIDER IMPLICATIONS OF THE FINDINGS: This is the first study to highlight that the aberrant expression of ANG in endometriotic lesions is mediated by hypoxia-suppressed COUP-TFII expression, which reveals an as yet unidentified molecular pathogenesis of endometriosis.