Upregulation of Aryl Hydrocarbon Receptor in Granulosa Cells by Endoplasmic Reticulum Stress Contributes to the PCOS Pathophysiology

Studies have demonstrated that endocrine disrupting chemicals (EDC) are involved in the pathophysiology of PCOS, and aryl hydrocarbon receptor (AHR) mediates the cellular effect of EDC by inducing xenobiotic metabolizing enzymes including cytochrome P450 1B1 (CYP1B1). However, recent studies suggest the novel role of AHR in various diseases, including obesity and cancer progression, independent from the EDC metabolism. We previously demonstrated that endoplasmic reticulum (ER) stress, a newly recognized local factor, contributes to PCOS pathology by affecting diverse functions of granulosa cells. We hypothesized that ER stress induces the expression of AHR and activates its downstream signaling in granulosa cells, irrespective of the presence of EDCs, thereby promoting PCOS pathogenesis. At first, we determined the upregulation of AHR, AHR nuclear translocator (ARNT), and AHR target gene cytochrome P450 1B1 (CYP1B1) in the granulosa cells of PCOS patients and model mice by immunohistochemical staining and qPCR. We examined CYP1B1 as a representative AHR target gene. Treatment of cultured human granulosa-lutein cells (GLCs) with tunicamycin (ER stress inducer) upregulated the expression of AHR, ARNT and CYP1B1. Knockdown of AHR decreased the tunicamycin-induced expression and activity of CYP1B1, suggesting the intermediary role of AHR in upregulation of AHR activity by ER stress. To confirm the role of AHR in vivo, we administered the AHR antagonist CH223191 to PCOS model mice. The administration of the antagonist restored estrous cycling and decreased the number of atretic antral follicles, concomitant with downregulation of AHR and CYP1B1 in granulosa cells. Taken together, this study indicates that AHR and downstream signaling are activated by ER stress in GLCs of PCOS. Moreover, downregulation of local AHR expression and activation restores a normal reproductive phenotype in a PCOS mouse model. Our findings demonstrate that AHR activated by ER stress in the follicular microenvironment contributes to PCOS pathology, and that AHR represents a novel therapeutic target for PCOS.