High-fat diet causes dysregulation of ovarian endothelin-2 expression across the estrous cycle

Abstract

We have previously shown that high-fat diet (HFD) feeding in female mice leads to abnormal estrous cyclicity, subfertility, and aberrant ovarian expression of genes important in ovulatory function, regardless of obese phenotype1,2. We found that a gene critical to normal ovulation, endothelin-2 (Edn2), is significantly downregulated in animals exposed to HFD. Edn2’s ovarian expression increases sharply right before ovulation. However, it is unknown how Edn2 is expressed in the ovary across the estrous cycle and how that expression is impacted by HFD. We aimed to evaluate ovarian Edn2 expression throughout the estrous cycle in HFD exposed mice and compare it with chow fed controls. Prospective laboratory animal study. 5-week-old C57Bl/6J mice were fed a standard chow or 60% HFD for 10 weeks. Estrous cyclicity was evaluated daily for the last two weeks of feeding and ovaries were collected in each of the four estrous cycle stages (N = 9/group/stage). T-test and chi-square tests were used for statistical analysis, as appropriate. After 10 weeks of diet, HFD mice weighed more than chow controls (28.8 ± 0.7g, 21.1 ± 0.2g p < 0.0001). HFD mice also had a higher prevalence of abnormal estrous cycles compared to chow controls (58.3% and 21.6% p = 0.0018). In chow controls, Edn2 was expressed as expected with basal levels during diestrus and proestrus, increased 11.6-fold during estrus, and decreased back to basal levels during metestrus. In the HFD mice, Edn2 was dysregulated across the entire estrous cycle (table 1), and when Edn2 expression was examined across all cycle stages in HFD mice, there was no characteristic peak of Edn2 expression in estrus with the lowest levels of Edn2 observed. Endothelin converting enzyme (Ece, cleaves Edn2 pre-peptide to active form) transcript expression levels were found to be uniformly upregulated in the HFD exposed mice across all stages of the estrous cycle (table 1).Tabled 1Estrous StageEdn2 Ovarian ExpressionEce Ovarian ExpressionHFD Compared to Chow Controls (fold change)p-valueHFD Compared to Chow Controls (fold change)p-valueDiestrus6.20.0136.6<0.0001Proestrus10.90.0394.20.0002Estrus-6.250.267.9<0.0001Metestrus-4.760.216.10.0002 Open table in a new tab Our data suggest that Edn2 and its post-translational regulation is dysregulated across the estrous cycle in HFD-fed mice. Work is currently underway to examine ovarian protein Edn2 levels across the estrous cycle to confirm our gene expression data. Future research should investigate mechanisms behind dysregulated Edn2 expression with HFD feeding. Collectively, this work will allow us to better understand how HFD leads to ovulatory dysfunction and to develop strategies targeting HFD-induced ovulation defects.