Endoplasmic reticulum stress pathway gene expression is altered in the cumulus cells of PCOS patients undergoing IVF

Abstract

The endoplasmic reticulum (ER) stress pathway responds to accumulation of unfolded proteins in the ER by either restoring cellular homeostasis or mediating cell death. ER stress response is implicated in the pathogenesis of insulin resistance in type 2 diabetes and obesity. The expression of genes in the ER stress pathway is altered in granulosa cells of obese women1. Given the role of insulin resistance in polycystic ovary syndrome (PCOS), we sought to examine whether the expression of genes in the ER stress response pathway is also altered in the cumulus cells of women with PCOS undergoing IVF. Experimental. Cumulus cells were obtained from sixteen infertile couples undergoing IVF, eight with infertility secondary to PCOS and eight with male factor infertility. Total RNA was extracted from the cumulus cells and cDNA was synthesized by reverse transcription. Expression of five genes in the ER stress response pathway (ATF4, ATF6, CHOP, GRP78, and XBP1s) was assessed with quantitative real-time PCR. ER stress response gene RNA levels were normalized to GAPDH RNA levels, and relative gene expression was calculated by the ddCt method. Statistical analysis was performed with Student’s t-test. There was a 2.4-fold decrease in ATF4 expression (p=0.01) and a 2.0-fold increase in ATF6 expression (p=0.03) in cumulus cells of subjects with PCOS when compared to women undergoing IVF for male factor infertility. There were no significant differences in these subjects in the expression of CHOP, GRP78, or XBP1s. Of note, the two study groups had no significant differences in median age (30.5 in PCOS vs. 31.0 in male factor), BMI (25.4 kg/m2 vs. 24.4 kg/m2), or day 3 FSH level (5.26 mIU/mL vs. 5.46 mIU/mL). This study is the first to demonstrate altered expression of genes in the ER stress response pathway in cumulus cells of women with PCOS undergoing IVF. While ATF4 and ATF6 have parallel expression in many cellular contexts, prior in in vitro studies in goat granulosa cells revealed that sustained ER stress over time leads to increasing amounts of ATF6 expression but attenuation of ATF4 expression2. Thus, the concurrent upregulation of ATF6 and downregulation of ATF4 we observe in this study may reflect a sustained increase in ER stress in the cumulus cells of women with PCOS when compared to women undergoing IVF for male factor infertility. Future studies can investigate whether the ER stress response pathway mediates the ovarian dysfunction of PCOS.