Endocrine Abstracts

Non-alcoholic fatty liver disease (NAFLD) is the hepatic manifestation of the metabolic syndrome. It represents a spectrum of disease, ranging from steatosis to non-alcoholic steatohepatitis, progressing to fibrosis, cirrhosis, and hepatocellular carcinoma. BAs, as well as their intermediary products (oxysterols), are metabolic modulators exerting their effects through activation of nuclear receptors (NRs), including the farnesoid-X- (FXR) and liver-X-receptors (LXR). Crucially, dysregulated BA synthesis has been associated with NAFLD. 3α-hydroxysteroid dehydrogenase type 1 (AKR1C4) is an enzyme exclusively expressed in the liver and plays an important role in BA synthesis. We hypothesised that AKR1C4 plays a crucial role in the pathogenesis of NAFLD. Genetic manipulation of AKR1C4 was performed in human Huh7 liver cells, and mRNA expression was determined by qPCR and RNA-sequencing. Serum and medium BA- and oxysterol concentrations were measured by LC-MS, and cholesterol levels by biochemical assays. Nuclear receptor activation was determined by luciferase assays. AKR1C4 expression and total BAs were increased in liver biopsies and serum samples from patients with advanced NAFLD, respectively. Supporting these data, data mining of genome-wide association studies (GWAS) identified protein-inactivating single nucleotide polymorphisms (SNPs) at the AKR1C4 locus associated with lower circulating triglyceride levels. In Huh7 cells, AKR1C4 knockdown reduced BA and oxysterol synthesis downstream decreasing LXR activation with no changes in total cholesterol, whilst RNA-sequencing analysis identified dysregulated pathways impacting upon a variety of cellular phenotypes, including cell cycle, lipid/carbohydrate metabolism, and insulin sensitivity. Complementing these data, mRNA expression analysis in AKR1C4-knockdown Huh7 cells revealed decreased expression of lipid and carbohydrate metabolism genes (SCD1, PEPCK, G6PC) and increased expression of insulin signalling genes (AKT1, IRS1). In conclusion, AKR1C4 is upregulated in advanced NAFLD, and AKR1C4 silencing improves BA homeostasis and metabolic gene expression profile in vitro. Taken together, these data suggest an as yet unexplored role of AKR1C4 in NAFLD.