Fructose-induced perturbation in cellular proteostasis via RPS6KB1 promotes hepatic steatosis

Abstract

Dietary fructose intake through increased consumption of refined sugar induces hepatic de novo lipogenesis (DNL), a major contributor to hepatic steatosis in NAFLD, however, it's mechanism is not completely understood. Using HepG2 cells, we show that fructose induced DNL involves ribosomal protein S6 kinase B1 (RPS6KB1) driven augmentation of hepatic protein synthesis. This consequently results in endoplasmic reticulum (ER)-stress induced expression of pro-lipogenic gene, fatty acid synthase (FASN). Additionally, the inhibition of fructose induced protein synthesis by either cycloheximide (CHX) or an RPS6KB1 inhibitor significantly reduced both ER-stress and FASN expression. Additionally, corroborating with our in vitro results, the analysis of human NAFLD transcriptomic datasets showed significant upregulation of protein synthesis pathways in the liver of patients with hepatic steatosis, thus linking protein synthesis to lipid accumulation during the early stages of NAFLD. Our results, therefore, demonstrate that RPS6KB1 driven "translation overdrive" coupled with ER-stress contributes to lipogenic gene transcription, and propose RPS6KB1 inhibition as a therapeutic strategy to counter fructose induced hepatic steatosis in NAFLD.

Keywords: De novo lipogenesis; ER-stress; Fructose; Hepatic steatosis; NAFLD; Protein synthesis; RPS6KB1.