Vascular endothelial growth factor (VEGF) plays a pivotal role in angiogenesis in ovaries, particularly during follicular development and ovulation. Interleukin-6 (IL-6) is one of the major pro-inflammatory factors that are involved in the angiogenesis process physiologically and pathologically. Previous studies have shown that 17β-estradiol (E2) stimulates VEGF expression by upregulating hypoxia-inducible factor 1α (HIF-1α) in many cell types, and the high level of E2 causes an inflammatory-like microenvironment before ovulation. However, whether IL-6 signaling is involved in E2-regulating VEGF expression in swine granulosa cells (GCs) is still unknown. In this study, we found the estrogen membrane receptor, G-protein-coupled estrogen receptor 1 (GPER), was expressed in swine GCs, and the expression level of GPER, HIF-1α, and VEGF increased with follicular development. In vitro study showed that E2, ICI182780, and GPER agonist (G1) promoted the expressions of HIF-1α and VEGF in swine GCs, while GPER antagonist (G15) inhibited the stimulating effect of E2 and G1. Meanwhile, G15 inhibited the stimulating effect of E2 and G1 on IL-6 mRNA expression and secretion. Furthermore, IL-6 antibody and AG490 (JAK2/STAT3 inhibitor) attenuated G1-induced HIF-1α and VEGF expression. In conclusion, this study revealed how estrogen-induced HIF-1α and VEGF expressions in swine GCs are mediated through GPER-derived IL-6 secretion leading to JAK2/STAT3 activation.
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