Taken together with our in vitro studies, which showed that ER stress inducers increased TGF-β1 expression in granulosa cells, the observations in the PCOS mouse model further suggest that ER stress activation in granulosa cells of PCOS patients induces ovarian fibrosis by upregulating TGF-β1 expression in granulosa cells. This evidence concerns the gene TGFB1 and polycystic ovary syndrome.