Metformin Ameliorates Uterine Defects in a Rat Model of Polycystic Ovary Syndrome

Abstract

Adult rats treated concomitantly with insulin and human chorionic gonadotropin exhibit endocrine, metabolic, and reproductive abnormalities that are very similar to those observed in polycystic ovary syndrome (PCOS) patients. In this study, we used this rat model to assess the effects of metformin on PCOS-related uterine dysfunction. In addition to reducing androgen levels, improving insulin sensitivity, and correcting the reproductive cycle, metformin treatment induced morphological changes in the PCOS-like uterus. At the molecular and cellular levels, metformin normalized the androgen receptor-mediated transcriptional program and restored epithelial–stromal interactions. In contrast to glucose transport, uterine inflammatory gene expression was suppressed through the PI3K–Akt–NFκB network, but without affecting apoptosis. These effects appeared to be independent of AMPK subunit and autophagy-related protein regulation. We found that when metformin treatment partially restored implantation, several implantation-related genes were normalized in the PCOS-like rat uterus. These results improve our understanding of how metformin rescues the disruption of the implantation process due to the uterine defects that result from hyperandrogenism and insulin resistance. Our data provide insights into the molecular and functional clues that might help explain, at least in part, the potential therapeutic options of metformin in PCOS patients with uterine dysfunction.

Uterine progesterone signaling is a target for metformin therapy in PCOS-like rats

“…For treatment, metformin was dissolved in saline and given as a daily oral dose of 500 mg/kg by a cannula. The treatment time and tissue collection are described in our previous study 28 . Experiment 2: Rats were randomly divided into control (saline treatment, n = 21) and experimental (PCOS-like, n = 15) groups and treated as described in Experiment 1 (Supplemental Fig.…”

“…To identify the implantation sites, rats were injected intravenously with a Chicago Blue B dye solution (1% in saline) and sacrificed 10 min later. Uteri were dissected and assessed for clearly delineated blue bands as evidence of early implantation sites as described previously 28 . Experiment 3: Rats were divided into control (saline treatment, n = 9) and experimental (PCOS-like, n = 39) groups and treated as described in the Experiment 1.…”

“…Uterine tissues were fixed in 10% formalin, embedded in paraffin, and sectioned for hematoxylin and eosin staining according to standard procedures. Immunohistochemistry and immunofluorescence were performed according to previously described methods 28,29 . The endogenous peroxidase and nonspecific binding were removed by incubation with 3% H 2 O 2 for 10 min and with 10% normal goat serum for 1 h at room temperature.…”

“…To date, several PCOS-like animal models have been developed to mimic the disease's clinical characteristics and to allow studies of pharmacological effects on specific tissues and biological processes 27 . Our recent studies using a PCOS-like rat model found that chronic treatment with metformin has significant anti-androgenic and antiinflammatory impacts in the uterus 28 . Given the central role of P4 signaling in uterine implantation 6,16 and the ability of metformin to rescue implantation failure in some PCOSlike rats by modulating the expression of multiple implantation-related genes in the uterus in vivo 28 , we speculated that the beneficial effects of metformin might be mechanistically linked to the uterine P4 signaling pathway under pathological conditions such as PCOS.…”

“…Our recent studies using a PCOS-like rat model found that chronic treatment with metformin has significant anti-androgenic and antiinflammatory impacts in the uterus 28 . Given the central role of P4 signaling in uterine implantation 6,16 and the ability of metformin to rescue implantation failure in some PCOSlike rats by modulating the expression of multiple implantation-related genes in the uterus in vivo 28 , we speculated that the beneficial effects of metformin might be mechanistically linked to the uterine P4 signaling pathway under pathological conditions such as PCOS. To address this hypothesis, we analyzed PCOS-associated PGR isoform expression and the MAPK signaling network in human and rat uterine tissues.…”