Mechanism of hepatocyte regeneration inhibition in rats with liver fibrosis induced by lipogenic methionine-choline- deficient diet

Abstract

To obtain the evidence of fibrotic resolution in fatty liver by changing the diet and to clarify the mechanism of hepatocyte proliferation inhibition in rat with fatty liver fibrosis. (1) Nonalcoholic steatohepatitis with advanced fibrosis was induced in rats by giving them a methionine-choline-deficient diet (MCDD) for 10 weeks (group M). A methionine-choline-control diet (MCCD) instead of MCDD was given for the last 2 weeks to the experimental group (group R). (2) Fibrosis and inflammation were determined by tissue staining. The activation of hepatic stellate cells and Kupffer cells were determined by immunostaining, immunoblot or quantitative RT-PCR respectively. (3) Hepatocytic apoptosis and proliferation were determined by TUNEL and BrdU staining respectively. Expressions of IL-6, STAT3, JNK-1, c-Jun, p21, C/EBPalpha, HNF6 and HGF-alpha were evaluated by quantitative RT-PCR and immunoblot to clarify the mechanism of hepatocytic proliferation inhibition. (1) Changing the diet from MCDD to MCCD triggered the reduction of fat in hepatocytes and a decrease in inflammatory response. (2) The regression of fibrosis was accompanied by the disappearance of activated stellate cells and macrophages. (3) Compared with control group (group C), hepatocytic apoptotic number increased significantly in group M (68 +/- 16 vs 40 +/- 8, P < 0.05) and the ratio of hepatocytic proliferation/apoptosis decreased markedly in group M (0.10 +/- 0.03 vs 0.19 +/- 0.03, P < 0.01); compared to group M, hepatocytic apoptotic number decreased significantly in group R (48 +/- 6, P < 0.05) and hepatocytic proliferation number and the ratio of hepatocytic proliferation/apoptosis increased markedly in group R (17.2 +/- 4.4 vs 7.5 +/- 3.0, 0.41 +/- 0.09 vs 0.10 +/- 0.03 respectively, P < 0.01). (4) Compared with group C, the mRNA level of IL-6, JNK-1, c-Jun, C/EBPalpha, p21 and HNF6 mRNA decreased significantly (0.34 +/- 0.18 vs 1.33 +/- 0.44, 0.41 +/- 0.11 vs 0.83 +/- 0.26, 0.19 +/- 0.03 vs 1.53 +/- 1.2, 1.94 +/- 0.64 vs 4.51 +/- 1.15, 0.34 +/- 0.20 vs 1.30 +/- 0.75, 0.47 +/- 0.21 vs 0.92 +/- 0.16 respectively, P < 0.05 or P < 0.01), and protein level of IL-6, STAT3, JNK-1, c-Jun, C/EBPalpha, P21 and HNF6 also decreased significantly in liver fibrotic stage (P < 0.05 or P < 0.01) while only IL-6, JNK-1 and p21 recovered immediately after a changed diet from MCDD to MCCD (P < 0.05 or P < 0.01). Food intake is a very important factor for controlling the fatty status and pathology of liver. Hepatocytic proliferation inhibition is associated with the arrested G(0)-S phasic transition in fatty liver fibrosis and the up-regulated expression of IL-6, JNK-1 and p21. These factors play a very important role in the recovery of fatty liver fibrosis.