(355) Endocrine Disruption in Obese Mothers Accelerates Follicular Depletion and Impairs Oocyte Quality

Obesity is associated with profound endocrine changes, often characterised by hyperleptinemia, hyperinsulinemia, and hyperestrogenism leading to ovarian dysfunction and infertility. Traditional mouse models often fail to fully recapitulate such hormonal changes without inducing severe obesity or diabetes. The db/+ mouse, with partial leptin receptor deficiency and a lean hyperleptinemic phenotype, offers a physiologically relevant system to investigate the effects of altered hormonal profile observed in obese mothers on ovarian function and follicular dynamics, independent of obesity. The aim of this study was to investigate the direct impact of increased systemic leptin, insulin, and oestradiol on ovarian function, follicular recruitment, and oocyte quality. Heterozygous B6.BKS(D)-Leprdb/J (db/+) mice were compared to the control group, female C57BL/6J (B6) mice. Ovaries were collected from mice at postnatal day 7 and young adult females (10-12 weeks old). Body composition and adiposity index were assessed using nuclear magnetic resonance, and plasma hormone levels (leptin, insulin, oestradiol, progesterone and anti-mullerian hormone-Amh) by ELISA assays. Glucose and insulin tolerance tests were performed to evaluate glucose metabolism. Ovarian function was assessed after histological analysis and follicle count, or real time-qPCR and western blotting analysis. Germinal vesicle oocytes were collected for single-cell RNA sequencing. In vitro fertilisation (IVF) was performed to assess fertilisation and blastocyst development rates. Finally, pregnancy outcomes were assessed by litter size, and foetal-placental growth measurements on gestational day 18.5 Heterozygous db/+ females exhibited moderate gain in body weight (23.14 ± 1.49 gm vs 18.93 ± 087, p< 0.001) and systemic hyperleptinemia (p < 0.001), hyperestrogenism (p < 0.01), and hyperinsulinemia (p < 0.01) while maintaining insulin sensitivity and glucose metabolism. Reproductive cyclicity was altered, with increased incidence of oestrus (p < 0.05) and reduction of dioestrus (p < 0.001) and proestrus stages (p < 0.05).  The ovaries of db/+ mice presented increased mRNA levels of Fshr (p < 0.01), Cyp19a1 (p < 0.01), and the oestrogen receptors Era and Erb (p < 0.01). Ovarian mRNA transcription of progesterone receptors (Pgr a+b) was decreased in db/+ mice, followed by low progesterone systemic levels (p < 0.01). Genes regulating angiogenesis, such as Vegf, Nos3, Cox2 were also downregulated in db/+ ovaries (p < 0.05). Furthermore, follicular activation at P7 was marked by decreased mRNA transcription of Foxo3a, Nobox, and Lhx8 (p < 0.05). This was associated with reduced antral follicle count (p < 0.05) and metaphase-II oocyte count (p < 0.05), in adult mice. The plasma levels of Amh and Amh mRNA transcription (p < 0.01) was also decreased in the ovaries of adult db/+ females. The scRNA-seq analysis revealed 644 differentially expressed genes (DEGs) after DESeq (p-adjusted < 0.01, |log2FC| >1). Gene Ontology (GO) showed increased oxidative phosphorylation. Furthermore, after IVF, we observed compromised blastocyst development ( < 0.05), and reduced litter size (p < 0.01) in db/+ females. Hence, the endocrine milieu commonly observed in obese mothers, in association with ovarian leptin resistance, promotes accelerated follicular recruitment, premature follicle exhaustion, and decreased fertility. Increased oestradiol and decreased ObRb activation in the ovary suppress Foxo3a, triggering primordial to primary follicle transition. Furthermore, transcriptomic analysis of GV oocytes revealed profound metabolic changes, with impaired glycolysis and heightened oxidative phosphorylation. These disruptions may compromise zygote viability and blastocyst formation, which was corroborated by low litter size. Together, these findings highlight how obesity-induced hormonal imbalance disrupts ovarian function, compromising oocyte quality and reproductive outcomes.Work supported by Polish National Centre for Science (No. 2019/34/E/NZ4/00349) grant, awarded to A.M.G.