Silent information regulator 1 inhibition induces lipid metabolism disorders of hepatocytes and enhances hepatitis C virus replication.

AIM: Hepatic steatosis is an important histopathological feature of chronic hepatitis C virus (HCV) infection. Silent information regulator 1 (SIRT1) plays key role in regulation of hepatic lipid metabolism. We investigated the possible effect of HCV replication on lipid metabolism of hepatocytes and expression of SIRT1 using Huh-7.5 cells harboring HCV replicon.

METHODS: The level of reactive oxygen species (ROS) and malondialdehyde (MDA), the activity of superoxide dismutase (SOD), and the value of nicotinamide adenine dinucleotide (NAD(+) )/NADH was detected. The level of triacylglycerol (TG), total cholesterol (TC) and fatty acid β-oxidation rate was detected. The activity and expression levels of SIRT1 and expression of its downstream lipid-metabolism genes were measured.

RESULTS: In replicon cells, the level of ROS and MDA increased, SOD activity and the value of NAD(+) /NADH decreased, then the activity and expression level of mRNA and protein of SIRT1 reduced. Inhibition of SIRT1 decreased phosphorylation of forkhead box O1 (FoxO1), which not only upregulated SREBP-1c, FAS, ACC, SREBP-2, HMGR and HMGS genes and increased fatty acid synthesis; but also downregulated PPAR-α and CPT1A genes and decreased fatty acid β-oxidation. Interferon treatment restored aforementioned changes. SIRT1 activator improved lipid metabolism disorders by an increase in fatty acid β-oxidation and a decrease in TG and TC synthesis and inhibited HCV replication.

CONCLUSION: HCV replication decreasing NAD(+) /NADH ratio may downregulate the activity and the expression of SIRT1, then change the expression profile of lipid metabolism-related genes, thereby cause lipid metabolism disorders of hepatocytes and promote HCV replication. Treatment with SIRT1 activator ameliorates lipid metabolic disorders and inhibits HCV replication.