Elevated insulin levels compromise endometrial decidualization in mice with decrease in uterine apoptosis in early-stage pregnancy

Women with hyperinsulinism and insulin resistance have reduced fertility, but the underlying mechanism is still poorly understood. Aberrant endometrial decidualization in early pregnancy was linked to pregnancy complications. In this study, we aimed to test whether elevated insulin levels compromise decidualization in early-stage pregnancy. C57BL/6J mice in high insulin-exposed group were given a subcutaneous injection of recombinant insulin at a concentration of 0.05 IU daily. During decidualization in early pregnancy, serum levels of insulin, E2, P4, LH, FSH and blood glucose were significantly altered in mice treated with high insulin levels. The number of embryo implantation sites and endometrial decidual markers BMP2, ER, PR was significantly decreased by high insulin levels in vivo. Artificial decidual induction in primary mouse endometrial stromal cells and immortal human endometrial stromal cells line were all compromised after treated with 100 nmol/L insulin levels. All these results on flow cytometry, transmission electron microscopy and western blotting of Bax, Bcl2, cleaved Caspase3, cleaved PARP proteins level showed that decidual cells apoptosis was significantly decreased. Mitochondrial transmembrane potential also significantly increased by the influence of high insulin levels. PI3K and p-Akt were much higher after insulin exposure and the compromised decidualization by high insulin treatment was rescued by PI3K/Akt inhibitor LY294002 both in vitro and in vivo. In conclusion, we demonstrated that elevated insulin levels could compromise mice decidualization in early-stage pregnancy and PI3K/p-Akt-regulated apoptosis was essential for this role. It provides a clue for future investigation on compromised reproduction in women with hyperinsulinemia.