The Effect Of Farnesoid X Receptor On Liver Fatty Acid-binding Protein And The Mechanism

Background:Non-alcoholic fatty liver(NAFL) is a clinical pathological syndrome characterized as liver steatosis and lipoidosis in patients without excessive alcohol consumption,which fatty acid metabolic disorder is closely related with the occurrence and development of NAFL.L-FABP is a member of fatty acid-binding protein supfamily,which is highly expressed in liver and intestine, and regulates intracellular uptake,transportion, oxidation and esterification of fatty acid.In recent years,study shows that L-FABP-deficient mice can effectively resist fatty liver,thus doing research on L-FABP will be helpful to prevent and treat of fatty liver.The nuclear farnesoid X receptor plays an important role in glucose,cholesterol, triglyceride metabolism,and there is a closely link with the FXR deficiency and fatty liver.FXR and L-FABP both are mainly expressed in liver,both of them are related with NAFL,so the study on the effect of FXR on L-FABP will provide useful information with regarding to the physiological roles that FXR and L-FABP play in occurrence and development of NAFL,and may supply a potential drug target for prevention and cure of NAFL.Objectives:The present study investigated the effect of FXR on L-FABP expression and the mechanism by which FXR inhibits the expression of L-FABP.Methods:1.Hepatoblastoma HepG2 cells and hepatocyte L02 cells were treated with FXR agonists chenodesoxycholic acid(CDCA) or GW4064.L-FABP expression levels were detected by reverse transcription polymerase chain reaction(RT-PCR) and western blot after 24 hours.2.C57BL/6 mice were treated with FXR agonist CDCA with different concentration of 0mg/kg,10 mg/kg,50 mg/kg for seven days and the levels of L-FABP expression were detected by RT-PCR,western blot and immunohistochemistry. 3.Bioinfo- rmatics analysis indicated that there is a potential FXR binding site(DR9) in the L-FABP promoter region; The L-FABP 5'flanking region was amplied from genomic DNA of HepG2 cells to create two defferent 5'detetion constructs of the L-FABP promoter(-2984~+128) which includes DR9,and L-FABP promoter (-2172~+11) which doesn't include DR9,they were cloned into PGL3-Basic luciferase vector, Then transiently transfected into HepG2 cells with or without Vp-FXR by liposome.The activity of each plasmid would be detected after 24 hours.Results:1.After treated with CDCA or GW4064.The mRNA and protein levels of L-FABP decreased dramatically(P<0.05) in HepG2 cells and L02 cells. 2.In C57BL/6 mice FXR down-regulated the expression of L-FABP determined by RT-PCR,western blot and immunohistochemistry 3.Function assay showed that FXR could inhibit the activity of pGL-2984/+128 which includes DR9,but the activity of pGL-2172/+11 which doesn't include DR9 was not effected.Conclusions:It is demonstrated that FXR agonists can decrease L-FABP expression at the mRNA and protein levels in vitro or in vivo.So we identify that L-FABP maybe a novel FXR regulated gene in liver cells. Function assay showed that FXR regulated L-FABP expression might through DR9,but it's need further study to confirm this conclusion.The study on the effect of FXR on L-FABP expression will provide useful information with regarding to the physiological and pathological roles that FXR plays in fatty acid metabolism and NAFL,and suggests a new therapy.