Hepatitis B virus (HBV) has been implicated as a potential trigger of hepatic steatosis although molecular mechanisms involved in the pathogenesis of HBV-associated hepatic steatosis still remain elusive. Our prior work has revealed that the expression level of liver fatty acid binding protein 1 (FABP1), a key regulator of hepatic lipid metabolism, was elevated in HBV-producing hepatoma cells. In this study, the effects of HBV X protein (HBx) mediated FABP1 regulation on hepatic steatosis and the underlying mechanism were determined. mRNA and protein levels of FABP1 were measured by quantitative RT-PCR (qPCR) and Western blotting. HBx-mediated FABP1 regulation was evaluated by luciferase assay, coimmunoprecipitation, and chromatin immunoprecipitation. Hepatic lipid accumulation was measured by using Oil-Red-O staining and the triglyceride level. It was found that expression of FABP1 was increased in HBV-producing hepatoma cells, the sera of HBV-infected patients, and the sera and liver tissues of HBV-transgenic mice. IMPORTANCEAccumulating evidence from epidemiological and experimental studies has indicated that chronic HBV infection is associated with hepatic steatosis. However, the molecular mechanism underlying HBV-induced pathogenesis of hepatic steatosis still remains to be elucidated. In this study, we found that expression of liver fatty acid binding protein (FABP1) was dramatically increased in the sera of HBV-infected patients and in both sera and liver tissues of HBV-transgenic mice. Forced expression of HBx led to FABP1 upregulation, whereas knockdown of FABP1 remarkably diminished lipid accumulation in both in vitro and in vivo models. It is possible that HBx promotes hepatic lipid accumulation through upregulating FABP1 in the development of HBV-induced nonalcoholic fatty liver disease. Therefore, inhibition of FABP1 might have therapeutic value in steatosis-associated chronic HBV infection. H epatitis B virus (HBV) infection is a serious health problemworldwide, causing acute and chronic hepatitis, cirrhosis, and hepatocellular carcinoma (1). Emerging evidence from epidemiological and experimental studies suggests that chronic HBV infection, as well as HCV infection, is associated with hepatic steatosis (2, 3). The frequency of hepatic steatosis in subjects with a chronic HBV infection ranges from 27 to 51% (4). Furthermore, HBV X protein (HBx) is known to cause hepatic lipid deposition by inhibiting the secretion of apolipoprotein B (5). A previous report showed that the increased HBx expression can cause lipid accumulation in hepatocytes, likely mediated by sterol regulatory element binding protein 1 and peroxisome proliferator-activated receptor ␥ (PPAR␥) (4). The molecular mechanism by which HBV induces the pathogenesis of hepatic steatosis remains elusive. Using fluorescent two-dimensional difference gel electrophoresis and matrix-assisted laser desorption ionization-time of flight mass spectrometry analysis, we found that the protein level of liver fatty acid binding protein (L-FABP ...

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