• Yao Xiong, Yi Liu, Wenqian Xiong, Ling Zhang, Hengwei Liu, Yu Du, and Na Li.
• Department of Gynecology and Obstetrics, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430022, China.
• Hum. Reprod. 2016 Jun 1; 31 (6): 1327-38.

Study QuestionHow does hypoxia promote growth of lesions in the development of endometriosis?Summary AnswerHypoxia induces the epithelial-mesenchymal transition (EMT) of endometrial cells, resulting in changes in cellular characteristics, which may be a prerequisite for the establishment of endometriotic lesions.What Is Known AlreadyUp-regulated hypoxia-inducible factor 1α (HIF-1α) has recently been found in ectopic endometrial lesions. There is increasing evidence that EMT, in which epithelial cells acquire mesenchymal and migratory properties, may also play a role in the establishment of the disease. EMT induced by HIF-1α has been reported to play a role in the development of many tumor types.Study Design, Size, DurationWe investigated expression changes of N-cadherin, E-cadherin, β-catenin, HIF-1α and vimentin using immunohistochemistry in normal, eutopic and ectopic endometria. Endometrial tissues from 96 additional females without related pathology were collected, and these tissues were subjected to subsequent primary cell culture for further experiments.Participants/Materials, Setting, MethodsThe expression of N-cadherin, E-cadherin, β-catenin, HIF-1α and vimentin in 20 normal, 21 eutopic and 21 ectopic endometrial samples was assessed by immunohistochemistry. Human primary endometrial epithelial cells were isolated from 96 normal endometrial tissues. Times for hypoxia treatment for western blot analysis were 1, 2, 4 and 8 h, for transwell experiments was 48 h. Ishikawa cells were used instead of primary endometrial epithelial cells for transfection and part of the transwell experiments. The impact of hypoxia on invasion was evaluated by transwell assays. Overexpression and inhibition of HIF-1α were achieved by transfection of pG/CMV/HIF-1α/IRES/EGFP and MCS-shHIF-1α-EGFP-IRES plasmids separately. The effect of hypoxia, overexpression and knockdown of HIF-1α on hypoxia-induced changes of EMT markers and β-catenin were analyzed by western blot and reverse transcriptase polymerase chain reaction (RT-PCR).Main Results And The Role Of ChanceOverexpression of HIF-1α and changes associated with EMT were observed in normal, eutopic and ectopic endometrial tissues. Primary cultured human endometrial epithelial cells responded to hypoxia with classic EMT changes (fibroblastoid phenotype, increased expression of snail family zinc finger 1, β-catenin and mesenchymal markers, and decreased expression of E-cadherin) and increased invasiveness. The decreased invasiveness of Ishikawa cells by knockdown of HIF-1α was observed under hypoxic conditions. While up-regulation of HIF-1α induced changes characteristic of EMT, down-regulation of HIF-1α had the opposite effect. Statistical significance was defined as P < 0.05.Limitations, Reasons For CautionA weakness of this study is the relatively small sample size for immunohistochemistry. Ishikawa cells were used instead of primary endometrial epithelial cells for transfection and part of the transwell experiments.Wider Implications Of The FindingsHypoxia-stabilized HIF-1α may play an important role in the invasion of endometrial cells in ectopic endometrial lesions, and it may induce EMT in the development of endometriosis. HIF-1α may be a new and important target for the endometriosis treatment.Study Funding/Competing InterestsThis study was funded by the National Nature Science Foundation of China (grant number 81170545 and 81471439). The authors declare no competing interests.© The Author 2016. Published by Oxford University Press on behalf of the European Society of Human Reproduction and Embryology. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

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