P-628 Prenatally androgenized PCOS-like mice present with dysregulated endometrium during window of implantation (WOI) and decidualization
Authors: Luyckx L , Virtanen N , Arffman R , Saarela U , Prunskaite-Hyyryläinen R , Vriens J , Piltonen T 
Published: June 2023

Abstract

Study question
How do prenatal androgenization and excessive body weight impact endometrial preparation for implantation?

Summary answer
Prenatal androgenization rather than excessive body weight causes abnormal uterine function and gene expression during artificially induced window of implantation and decidualization events in vivo.

What is known already
Polycystic ovary syndrome (PCOS) is a common endocrine disorder in women characterized by reproductive defects including irregular menstruation and pregnancy complications, but also by metabolic derangements such as obesity, insulin resistance and cardiovascular diseases. It is hypothesized that PCOS originates from prenatal androgenization (PNA), hence PNA mice models mimicking PCOS features have been generated. PNA has been shown to disrupt reproductive cycles, ovarian functioning and normal embryonic development; however, endometrial function in PNA mice is currently understudied. Therefore, this project aimed to study endometrial function during endometrial preparation for implantation in a PNA PCOS-like mouse model.

Study design, size, duration
Female PNA mice received a high-fat high-sugar (HFHS) diet to capture both reproductive and metabolic phenotypes of PCOS. Uteri were collected for histological and transcriptome analysis from 12-week-old ovariectomized PNA mice undergoing hormonal treatments to induce window of implantation (WOI) or decidualization states. Sample collection was done from minimum 6 animals per group from 4 different study groups depending on PNA status (PNA versus control) and diet (HFHS versus normal diet).

Participants/materials, setting, methods
PNA mice were generated by administrating 250 µg dihydrotestosterone daily to pregnant C57BL/6J dams during E16.5-E18.5. The female pups received a HFHS diet to induce obesity. Estrous cyclicity and anogenital distance were assessed to confirm PCOS phenotype. After ovariectomy, estrogen and progesterone injections were used to artificially induce WOI or decidualization states (intra-uterine injection of 25 µl oil was used for decidual trauma). The collected uteri were analyzed using RNA sequencing (RNAseq) and immunohistochemistry.

Main results and the role of chance
PNA mice showed increased anogenital distance and disrupted estrous cycles, confirming the PCOS-like phenotype. PNA, but not HFHS diet caused defective uterine luminal closure. PNA mice had altered gene expression during the WOI, including genes important for endometrial receptivity, genes associated with human PCOS, and genes related to reproduction failure. The HFHS diet induced a milder phenotype, i.e., enriched pathways related to mitochondrial functions, cell cycle and DNA damage response. Analysis of artificially decidualized uteri showed a severe morphological decidualization defect in PNA groups, as demonstrated by the reduced weights of the decidualized uterine horns, whereas HFHS diet did not have a significant additive effect. RNA sequencing data showed that PNA decidualized horns clustered together with non-decidualized control and PNA horns, irrespective of diet. Pathways enriched in PNA were associated with changes in extracellular matrix and ion homeostasis. HFHS diet with PNA further aggravated endometrial dysfunction, as shown by reduced prolactin expression, a classical marker for endometrial decidualization. Role of chance: while drastic effects of PNA on endometrial function are detectable, the sample size might be too small to detect more subtle morphological effects caused by the HFHS diet.

Limitations, reasons for caution
PNA mouse models display selective features of PCOS but cannot mirror the comprehensive PCOS phenotype due to the complexity and heterogeneity of the disorder. Nevertheless, this model provides insights into the impact of PNA and excessive body weight on endometrial physiology.

Wider implications of the findings
This in-dept investigation of PNA and overweight mice demonstrates the utility of the model for studying PCOS-related endometrial dysfunction and provides cues towards its pathophysiology. This report supports the hypothesis of prenatal androgen exposure as the major factor in the aetiology of PCOS-related subfertility, rather than metabolic status.

Trial registration number
not applicable