MON-230 Androgen-Induced Disruption of the Biological Clock: The Link between PCOS and NAFLD

Abstract

In women, excess androgen causes polycystic ovarian syndrome (PCOS), a common fertility disorder with comorbid metabolic dysfunction. A growing body of evidence show that non-alcoholic fatty liver disease (NAFLD) rates are elevated in PCOS women, with higher risk of developing more severe forms of NAFLD. PCOS is a complex condition encompassing insulin resistance, androgen excess and obesity and it is believed that the development of NAFLD in PCOS is a cumulative effect of all these conditions. However, recent studies in PCOS women and in mouse models show that NAFLD occurs independent of weight and metabolic features associated with PCOS. Since hyperandrogenism is a key feature of PCOS, we hypothesized that high androgen level directly modulates liver metabolism and contributes to the development of NAFLD in PCOS conditions. Using a well-established PCOS mouse model involving subcutaneous implantation of 90-day continuous-release DHT pellet, we found that chronic high level of androgen significantly increases fatty acid and triglyceride levels in the liver. Furthermore, we have performed a RNA-seq study to identify differentially expressed genes in female mouse liver with respect to high androgen. Results show that there were 787 differentially regulated genes among DHT pellet vs placebo livers out of which 361 genes were upregulated and 426 genes were downregulated. Furthermore, 236 genes were metabolic genes amongst which 103 were upregulated and 133 were downregulated. Surprisingly, we found that about 23 circadian genes were also differentially regulated in the DHT pellet livers. The circadian timing system is a key regulator of cyclic expression of different metabolic enzymes and factors, and perturbations of the clock mechanism causes liver dysfunction. In fact, we found that in vitro androgen treatment of liver tissue explants disrupts the timing system. Next, we wanted to find how androgens may regulate the circadian clock. We recently reported that androgens inhibit the expression of a histone methyltransferase, Ezh2, that promotes histone H3 lysine 27 trimethylation (H3K27me3), a gene silencing mark. Androgens induce the expression of miR101 that targets Ezh2 expression. Consequently, we found that androgen treatment significantly increase miR101 expression while lowers H3K27me3 levels and Ezh2 expression in the liver, in vitro and in vivo. Moreover, ChIP studies revealed significant lower H3K27me3 mark on the promoter of circadian clock genes. Intriguingly, Ezh2 is a known critical regulator of liver metabolism and Ezh2 down-regulation exacerbates lipid accumulation causing NAFLD. Therefore, we propose that in the liver, high levels of androgens modulate the circadian clock through inhibiting Ezh2 expression and lowering the H3K27me3 mark that causes irregular patterns of metabolic gene expression leading to disrupted liver metabolism and development of NAFLD.