Insulin Signaling Induces AKR1C3 to Promote Lipid Overload through FASN in SGBS Cells, as a Model of PCOS Adipocytes

Abstract

Polycystic ovary syndrome (PCOS) is the most common endocrinopathy in women of reproductive age, affecting 8‐13% of women. The characteristic androgen excess (AE) of PCOS is believed to promote comorbidities, such as obesity and type 2 diabetes. AE correlates with insulin resistance (IR) in these women and may be the driving factor for lipid overload. Aldo‐keto reductase family 1 member C3 (AKR1C3) is induced by insulin in PCOS adipocytes and may be central in driving the AE of PCOS. AKR1C3 predominantly catalyzes formation of androgens such as testosterone and 5α‐dihydrotestosterone in peripheral tissues, which are potent agonists for the androgen receptor (AR) and upregulate de novo lipogenesis. Fatty acid synthase (FASN) is induced by androgens and may be responsible for an altered lipid profile in mature adipocytes. Nuclear factor erythroid 2‐related factor 2 (NRF2) is a known transcription factor for AKR1C3 and is regulated by insulin. AKR1C3 overexpression in adipocytes by insulin activation of NRF2 could increase androgen receptor signaling and promote de novo lipogenesis. The resulting lipid overflow could exacerbate insulin resistance through a feedforward mechanism and potentiate the cardio‐metabolic risk seen in PCOS. We hypothesize that insulin signaling induces AKR1C3 to promote lipid overload through FASN in PCOS adipocytes. Using differentiated human Simpson‐Golabi‐Behmel Syndrome (SGBS) adipocytes as a model for PCOS adipocytes, we have confirmed that AKR1C3 is induced >600 fold by insulin. Using pharmacological inhibition, we found that the insulin induction of AKR1C3 and FASN is dependent on PI3K/AKT/mTOR measured by RT‐qPCR and immunoblot. Using NRF2 siRNA and ML‐385, a NRF2 inhibitor, we have determined that AKR1C3 and FASN induction are NRF2 dependent, indicating NRF2 may be one transcription factor that binds to the AKR1C3 promotor region in adipocytes. We also determined that FASN induction is both AKR1C3 and AR dependent using pharmacological inhibition/antagonism and siRNA, where its effect was measured by RT‐qPCR and immunoblot. Pharmacological inhibition with NRF2 or AKR1C3 inhibitors additionally downregulated de novo lipogenesis measured by Oil Red O staining, which is a phenotypic readout for FASN activity. These studies elucidate the signaling mechanism by which AKR1C3 and FASN are induced by insulin in adipocytes. We conclude that upregulation of AKR1C3 may promote lipid overload in PCOS adipocytes by induction of FASN, and that AKR1C3 is a possible therapeutic target to prevent the risk of cardio‐metabolic disease in PCOS women.