MicroRNA-613 represses lipogenesis in HepG2 cells by downregulating LXRα

Background: MicroRNAs (miRNAs) emerge as new important regulators of lipid homeostasis by regulating corresponding genes. MiR-613 is a newly discovered microRNA, of which the biological function is unknown. A recent report has shown that miR-613 downregulates liver X receptor alpha (LXR alpha), a ligand-activated nuclear receptor playing an important role in the regulation of lipid metabolism. The purpose of this study is to explore the effect and the molecular basis of miR-613 on lipogenesis in HepG2 cells. Methods: HepG2 cells were transiently transfected with miR-613 mimic or control microRNA. Real time PCR, Western blot, Luciferase reporter assay and Oil Red O staining were employed to examine the expression of LXR alpha and its target genes involved in lipogenesis, binding site for miR-613 in 3'-untranslated region (3'-UTR) of LXR alpha mRNA and lipid droplet accumulation in the cells. Results: MiR-613 dramatically suppressed the expression of LXR alpha and its target genes including sterol-regulatory element binding protein 1c (SREBP-1c), fatty acid synthase (FAS), carbohydrate responsive element-binding protein (ChREBP) and acetyl-CoA carboxylase (ACC). Reporter assay showed that miR-613 directly bound to 3'-UTR of LXR alpha mRNA. Moreover, miR-613 significantly repressed LXR alpha-induced lipid droplet accumulation in HepG2 cells. Ectopic expression of LXR alpha without 3'-UTR markedly attenuated the miR-613-mediated downregulation of LXR alpha' s target genes and LXR alpha-induced lipid droplet accumulation. Conclusions: MiR-613 suppresses lipogenesis by directly targeting LXR alpha in HepG2 cells, suggesting that miR-613 may serve as a novel target for regulating lipid homeostasis.