MiR-451a attenuates hepatic steatosis and hepatitis C virus replication by targeting glycerol kinase.

Background: Lipotoxicity is one of the causes for the progression of fatty liver in chronic hepatitis (CH) towards end-stage liver diseases. The role of miRNAs in the signalling pathways of lipid metabolism has been studied, but their direct targets in this pathway have not been identified yet. Here, we have characterized a downregulated miRNA in CH namely miR-451a, which has a direct impact on the lipid metabolism pathway.

Methods: Liver tissue samples and blood were collected from CHC/CHB patients and normal individuals. Huh7 and SNU449 cell lines were used for in vitro assays. Expressions of miRNA/mRNAs and proteins were confirmed by qRT-PCR and immuno-blot analysis. Oil Red O staining, Colorimetric, and Fluorometric assay kit were used to quantify triglyceride (TG) and cholesterol from tissue and serum, respectively. Target prediction and pathway analysis were performed using Targetscan, miRWalk, and DAVID respectively. 3'UTR-Luciferase assay and Co-immuno-precipitation were conducted to determine direct interaction between miRNA-mRNA and protein-protein, respectively. Unpaired two-tailed Student's t-test and Mann-Whitney test were employed as required using GraphPad prism. P < 0.05 was considered as significant.

Results: The miRNA, miR-451a was selected as one of the downregulated miRNAs in progressive liver disease stages of CHC and CHB. Target identification and pathway analysis of this miRNA revealed that lipid metabolism pathway gene, glycerol kinase (GK), could be the target of this miRNA. Subsequent 3'UTR Luciferase assay and immuno-blot analysis confirmed the binding of miR-451a to GK. Though both hepatitis viruses, HCV and HBV, could alter the lipid metabolism pathways, intracellular TG and cholesterol content were observed to be significantly higher upon HCV infection only. It also suppressed the expression of miR-451a, resulting in overshooting of GK expression. GK interacted positively with the transcription factor SREBP1, which led to overexpression of Fatty acid synthase, Acetyl- CoA Carboxylase, and Stearoyl-CoA desaturase. As a result, intracellular fatty acids, TG, and cholesterol synthesis and accumulation heightened but trafficking dropped, resulting in hypo-cholesterolemia in blood. While, restoration of miR-451a impeded lipid accumulation, reduced steatohepatitis and suppressed HCV replication as well.

Conclusion: These findings suggest that the alteration in the hepatic lipid profile upon HCV/HBV infection is attributed to the downregulation of miR-451a, which has the potential to restrict the expression of GK and SREBP1 in the TG biosynthesis pathway, implying that supplementation of miR-451a may be a potential therapeutic strategy for impeding CHC.