Endothelin-1 promotes human germinal vesicle-stage oocyte maturation by downregulating connexin-26 expression in cumulus cells

• Published in: Molecular human reproduction 2018-01, Vol.24 (1), p.27-36
• Main Authors: Cui, Long, Shen, Jiajie, Fang, Li, Mao, Xiaodan, Wang, Hanzhi, Ye, Yinghui
• Format: Article
• Language: English
• Subjects: Connexin 26 - metabolism; Cumulus Cells - metabolism; Endothelin-1 - metabolism; Female; Humans; In Vitro Oocyte Maturation Techniques; Meiosis - genetics; Meiosis - physiology; Oocytes - metabolism; Oogenesis - genetics; Oogenesis - physiology; Receptor, Endothelin B - genetics; Receptor, Endothelin B - metabolism
• ISSN: 1360-9947; 1460-2407; 1460-2407
• DOI: 10.1093/molehr/gax058

Abstract STUDY QUESTION Does endothelin-1 (ET-1) promote human oocyte maturation and by what mechanism? SUMMARY ANSWER Addition of ET-1 to the medium in which human germinal vesicle (GV)-stage immature oocytes are cultured enhances the GV breakdown (GVBD) rate; the resumption of meiosis may be initiated by ET-1 downregulating the expression of connexin-26 (Cx26) in cumulus cells via endothelin receptor type B (ETRB), leading to decreased cAMP levels in the oocyte. WHAT IS KNOWN ALREADY The paracrine factor ET-1 is secreted by ovarian somatic cells in pre-ovulatory follicles and regulates oocyte maturation in mice. Connexins, or gap junction proteins, form intercellular membrane channels that play important roles in the resumption of meiosis. STUDY DESIGN, SIZE, DURATION This laboratory study was conducted over a 1-year period. The effects of ET-1 on meiotic resumption were evaluated in human GV-stage cumulus-oocyte complexes (COCs; 70 oocytes/group). The transcriptome profiles of ET-1-treated or untreated cumulus cells were compared to explore the possible mechanisms by which ET-1 may regulate oocyte maturation. PARTICIPANTS/MATERIALS, SETTING, METHODS The ET-1, ETRA and ETRB expression levels in human cumulus cells from oocytes at different stages of maturation were evaluated using real-time quantitative PCR. Human GV-stage COCs collected from patients undergoing IVF at a university-affiliated infertility centre were cultured with or without ET-1, and cumulus cells were subsequently denuded using hyaluronidase and cultured in α-MEM. A GeneChip® Human Transcriptome Array was applied to explore differences in the whole-genome transcriptome profiles of cumulus cells treated with or without ET-1. Real-time quantitative PCR and Western blotting were used respectively to examine Cx26 mRNA and protein levels in cumulus cells. Changes in cAMP levels in both oocytes and cumulus cells after ET-1 treatment were measured using an enzyme-linked immunosorbent assay. MAIN RESULTS AND THE ROLE OF CHANCE Cumulus cells from MII-stage oocytes exhibited upregulated ET-1 expression, compared to those from GV-stage oocytes. The addition of ET-1 to the culture medium enhanced the GVBD rate of cumulus cell-enclosed human oocytes. Whole-genome transcriptome microarray analyses revealed significantly downregulated Cx26 expression in cumulus cells after ET-1 treatment, and this action was blocked by an ETRB antagonist. The involvement of Cx26 was further supported by the finding th