子宮內膜異位症乃指子宮內膜組織生長於子宮腔外的環境，是生殖年齡婦女中很常見的婦科疾病之一。先前的研究結果已知子宮內膜異位組織在腹腔中面臨的缺氧因素在其血管新生的病程發展中扮演著重要的角色。然而缺氧在子宮內膜異位症中的致病機制，仍然有許多未知的部分尚待釐清。我們發現在子宮內膜異位症中，新穎的血管新生因子血管生成素，能夠被缺氧誘導增加其表達。然而利用生物資訊分析，血管生成素的啟動子並沒有缺氧反應元件。我們進一步針對血管生成素啟動子的潛在轉錄因子結合位點分析，顯示其可能受到雞卵蛋白上游啟動子轉錄因子-II調控。先前的研究指出雞卵蛋白游啟動子轉錄因子-II參與調控許多子宮內膜異位症的病理機轉，而其表現量減少的現象被認為是促進子宮內膜異位症病程發展的重要因素之一。因此，我們假設在子宮內膜異位症中，缺氧誘導血管生成素的表現量增加是透過抑制雞卵蛋白上游啟動子轉錄因子-II表達。我們以微小干擾核糖核酸抑制雞卵蛋白上游啟動子轉錄因子-II的表現，能夠誘導血管生成素的表現量增加，同時過度表現雞卵蛋白上游啟動子轉錄因子-II降低血管生成素的表現。缺氧或者使用模擬缺氧化合物的處理下能夠抑制雞卵蛋白上游啟動子轉錄因子-II的表達，同時增加血管生成素的表現量。在缺氧處理下，藉由過度表現的方式恢復雞卵蛋白上游啟動子轉錄因子-II的表現水平，能夠減少由缺氧誘導增加的血管生成素表現量，顯示雞卵蛋白上游啟動子轉錄因子-II的減少對於缺氧誘導血管生成素相當重要。我們進一步釐清血管生成素增加的現象是由於雞卵蛋白上游啟動子轉錄因子-II減少結合在血管新生素啟動子，進而促進血管生成素啟動子的活性。抑制雞卵蛋白上游啟動子轉錄因子-II誘導增加的血管生成素能夠分泌到細胞外，並促進形成血管網絡的能力；然而在抑制血管生成素的表現後能夠阻斷增加的血管網絡形成現象。在過度表現的雞卵蛋白上游啟動子轉錄因子-II的情況下，能夠導致缺氧誘導的血管生成素表現量的減少，進而導致由缺氧促進人類臍靜脈內皮細胞形成血管網絡能力的減低，顯示血管生成素在由缺氧介導的血管新生進程中扮演相當重要的促進角色。綜合以上，我們的研究結果指出一個新穎的血管新生因子—血管生成素—受到缺氧抑制雞卵蛋白上游啟動子轉錄因子-II的機制調控，導致血管新生的現象，進而促進子宮內膜異位組織的發展。

Endometriosis, characterized as the presence of endometrial tissues outside the uterus, is one of the most common gynecological diseases in women of reproductive age. Hypoxia plays important roles in promoting angiogenesis during the development of endometriosis. However, the underlying mechanism remains largely unknown. Herein, we identified angiogenin (ANG), a novel angiogenic factor, is increased under hypoxia in endometriosis. Since there is no hypoxia responsive element in the ANG promoter region, we analyzed the potential transcription factor binding site in the promoter region of ANG and identified potential binding sites for chicken ovalbumin upstream promoter transcription factor II (COUP-TFII). Downregulation of COUP-TFII is important for pathogenesis of endometriosis. Thus, we hypothesized that hypoxia regulates ANG expression via suppression of COUP-TFII in endometriosis. Knockdown of COUP-TFII in eutopic endometrial stromal cells increased ANG expression. Treatment of eutopic endometrial stromal cells with hypoxia decreased COUP-TFII expression and concomitantly induced ANG expression. In contrast, overexpression of COUP-TFII under hypoxia significantly reduced hypoxia-induced ANG expression. Chromatin immunoprecipitation-qPCR analysis revealed that binding of COUP-TFII to ANG promoter region was significantly reduced under hypoxia. Treatment with hypoxia or knockdown of COUP-TFII increased ANG promoter activity. Treatment of human umbilical vein endothelial cells with conditioned media collected from stromal cells with COUP-TFII knockdown significantly promoted tube formation. In contrast, the COUP-TFII knockdown-induced angiogenic capacity was abolished by simultaneously knocking down of ANG. Taken together, our results demonstrated that ANG involves in the angiogenesis of endometriosis through hypoxia-mediated loss-of-COUP-TFII expression and suggest ANG may be a novel therapeutic target for treatment of endometriosis.

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