Department of Animal Genetic, Breeding and Reproduction Science, College of Animal Science and Technology, Nanjing Agricultural University, Nanjing, China.
J Cell Physiol. 2024 Feb;239(2):e31162. doi: 10.1002/jcp.31162. Epub 2023 Nov 22.
The developmental fate of ovarian follicles is primarily determined by the survival status (proliferation or apoptosis) of granulosa cells (GCs). Owing to the avascular environment within follicles, GCs are believed to live in a hypoxic niche. Follicle-stimulating hormone (FSH) has been reported to improve GCs survival by governing hypoxia-inducible factor-1α (HIF-1α)-dependent hypoxia response, but the underlying mechanisms remain poorly understood. Growth arrest-specific gene 6 (GAS6) is a secreted ligand of tyrosine kinase receptors, and has been documented to facilitate tumor growth. Here, we showed that the level of GAS6 was markedly increased in mouse ovarian GCs after the injection of FSH. Specifically, FSH-induced GAS6 expression was accompanied by HIF-1α accumulation under conditions of hypoxia both in vivo and in vitro, whereas inhibition of HIF-1α with small interfering RNAs/antagonist repressed both expression and secretion of GAS6. As such, Luciferase reporter assay and chromatin immunoprecipitation assay showed that HIF-1α directly bound to a hypoxia response element site within the Gas6 promoter and contributed to the regulation of GAS6 expression in response to FSH. Notably, blockage of GAS6 and/or its receptor Axl abrogated the pro-survival effects of FSH under hypoxia. Moreover, phosphorylation of Axl by GAS6 is required for FSH-mediated Akt activation and the resultant pro-survival phenotypes. Finally, the in vitro findings were verified in vivo, which showed that FSH-induced proliferative and antiapoptotic effects in ovarian GCs were diminished after blocking GAS6/Axl using HIF-1α antagonist. These findings highlight a novel function of FSH in preserving GCs viability against hypoxic stress by activating the HIF-1a-GAS6-Axl-Akt pathway.
卵泡的发育命运主要取决于颗粒细胞（GCs）的存活状态（增殖或凋亡）。由于卵泡内的血管环境，GCs被认为生活在缺氧环境中。卵泡刺激素（FSH）通过调节缺氧诱导因子-1α（HIF-1α）依赖性缺氧反应，已被报道可改善 GCs 的存活，但潜在机制仍知之甚少。生长停滞特异性基因 6（GAS6）是一种酪氨酸激酶受体的分泌配体，已被证明可促进肿瘤生长。在这里，我们发现在 FSH 注射后，小鼠卵巢 GCs 中的 GAS6 水平显着增加。具体而言，在体内和体外缺氧条件下，FSH 诱导的 GAS6 表达伴随着 HIF-1α 的积累，而用小干扰 RNA/拮抗剂抑制 HIF-1α 则抑制了 GAS6 的表达和分泌。因此，荧光素酶报告基因检测和染色质免疫沉淀检测表明，HIF-1α 直接结合 GAS6 启动子内的缺氧反应元件位点，并有助于 FSH 对 GAS6 表达的调节。值得注意的是，阻断 GAS6 和/或其受体 Axl 可消除缺氧下 FSH 的促生存作用。此外，GAS6 对 Axl 的磷酸化是 FSH 介导的 Akt 激活和由此产生的促生存表型所必需的。最后，在体内验证了体外发现，表明使用 HIF-1α 拮抗剂阻断 GAS6/Axl 后，FSH 在卵巢 GCs 中诱导的增殖和抗凋亡作用减弱。这些发现强调了 FSH 通过激活 HIF-1a-GAS6-Axl-Akt 通路来维持 GCs 对缺氧应激的存活能力的新功能。
