Effects of insulin on the decidualization of human endometrial stromal cells : in vitro studies

Abstract

Hyperinsulinemia is a known characteristic of obesity and polycystic ovary syndrome, two common clinical conditions associated with reproductive problems. However, the underlying mechanisms to reduced fertility are not fully elucidated, and the role of insulin in reproduction needs further investigation. Decidualization is an extensive post-ovulatory reorganization of the endometrial stromal compartment in preparation for a pregnancy. Defective decidualization has been associated with implantation failure and various pregnancy complications. The overall aim of this thesis was to study the effect of high insulin levels on different aspects of decidualization in vitro.

Study I aimed to examine the role of forkhead box O (FOXO) 1 in mediating the effect of insulin on decidualizing endometrial stromal cells (ESCs) and relate changes in decidual markers to cell morphology. We found that insulin downregulates the expression of FOXO1- target genes by nuclear export of FOXO1. However, despite significant suppression of these decidual markers, no significant changes in morphological transformation characteristic to decidualization were detected. Study II describes the role of insulin in the regulation of prokineticin (PROK) 1, a known regulator of placenta formation during the first trimester. We demonstrated a significant enhancement of PROK1 expression when ESCs were decidualized in the presence of insulin. Furthermore, PROK1 inhibited the migration of ESCs, and the migration and invasion of extravillous trophoblast cells. Study III aimed to elucidate the effect of high insulin levels on decidual solute carrier family 2 member 1 (SLC2A1), the most abundant glucose transporter in decidual ESCs, and glucose uptake. SLC2A1 mRNA and protein were suppressed by insulin. Furthermore, suppression in decidual cell glucose uptake was detected. Study IV investigated a potential interaction between insulin and androgens in the regulation of decidual gene expression, cell morphology and motility. We showed that the combination of insulin and dihydrotestosterone enhanced the expression of several decidual markers, increased decidual cell size and complexity, but at the same time inhibited the migration of decidual ESCs and invasion of trophoblast cells.

In summary, the results of this thesis suggest that high levels of insulin significantly modify several aspects of decidualization, including suppressing FOXO1 target genes and augmenting other decidual markers. Insulin also interacts with androgens in enhancing some decidual characteristics while inhibiting cell migration and trophoblast invasion. The overall effect seems to be a dysregulation of the process, which might have implications for the understanding of reproductive problems in conditions of hyperinsulinemia and hyperandrogenism.