Molecular Mechanism And Effects Of Bile Acid Receptor Fxr On Dlk1 Expression

Liver cancer is characterized by high mortality and high morbidity.A variety of factors induce the development of liver cancer.Though it has been shown that many genes were involved in the process of liver cancer,the mechanisms still need to be investigated.Bile acids play important roles in liver regeneration,liver repaire and hepatocellular carcinoma.The appropriate concentration of bile acid was beneficial to the digestion of lipids and liver regeneration.The bile acid receptor Fxr was involved in the synthesis,transport and metabolism of bile acids.It maintained the bile acid balance,and prevented the toxic effects caused by high concentrations of bile acids.Several studies have indicated that Fxr was a tumor suppressor,but it is still unkown how Fxr represses the tumor growth.Dlk1 has been showed to promote malignant tumor progression and expected to be a diagnostic marker for early liver cancer.Since both Fxr and Dlk1 play an important roles in liver tumors,we hypothesized that there might be a regulatory relationship between Fxr and Dlk1.Our data demonstrated that Dlk1 was the downstream gene of Fxr and activation Fxr inhibited Dlk1 expression..The main research contents were as follows:1.The expression of Dlk1 was inhibited by Fxr in vitroBone marrow mesenchymal stem cells(BMSC)and human hepatocellular carcinoma cell line Huh7 were treated with Fxr-specific agonist GW4064 for 24 h.Expression of Dlk1 was significantly decreased in mRNA and protein level after GW4064 treatment.The data indicated that Fxr inhibited Dlk1 expression.2.Dlk1 promoter transcription activity was repressed by Fxr specific ligand GW4064Hep1-6 cells were transfected with the pGL3-Dlk1 promoter reporter plasmid.Cells were subsequently treated with GW4064 for 24 h.Dual luciferase reporter gene assay showed that the transcriptional activity of pGL3-Dlk1-promoter reporter plasmid was significantly repressed by GW4064 compared to the control group.3.Establied DDC liver injury modelC57/BL mice were fed standard rodent chow diet supplemented with 0.1% 3,5-diethoxycarbonyl-1,4-dihydro-2,4,6-trimethylpyridine(DDC)for 7 days to establish a model of liver injury.The ALT and AST levels were significantly elevated in serum.Inflammatory cell infiltration was revealed by HE staining in the liver portal area.4.Hepatic damage was alleviated by CDCA in DDC injured liver modelC57/BL mice were fed standard rodent chow diet supplemented with 0.1% DDC daily and were gavaged with 20 mg/kg/day CDCA simultaneously for 7 days.QRT-PCR showed that Bsep mRNA levels were increased,while Dlk1 was decreased in treatment group by Western Blot confirmed.At the same time,the ALT and AST levels were significantly reduced after intragastric administration with CDCA in serum.HE staining results also showed that liver inflammation was significantly alleviated after CDCA treatment.The expression of Dlk1 was suppressed by CDCA,which may be responsible for alleviating liver damage caused by DDC.