Résumé
<p><b>OBJECTIVE</b>To study the role of apoptosis and the expression of apoptosis-related genes Fas ligand (FasL), Fas, caspase-3 and caspase-8 in an animal model of non-alcoholic steatohepatitis (NASH).</p><p><b>METHODS</b>An experimental progressive NASH model was established by feeding male C57BL6/J mice with a high fat, methionine-choline deficient (MCD-) diet for two days, five days, ten days, three weeks and eight weeks. Control mice were fed methionine-choline supplemented (MCD+) diet. Hepatic steatosis, inflammation and fibrosis were graded by examining their H and E stained liver sections. Hepatocyte apoptosis was detected by TUNEL assay. Expressions of mRNA and protein of FasL, Fas and caspase-8 were performed by quantitative real time RT-PCR and Western blot. Caspase-3 activity assay was conducted using ApoAlert caspase-3 assay kit.</p><p><b>RESULTS</b>In MCD- mice, minimal hepatic steatosis was observed at day 5, and by day 10, mild steatosis with inflammatory infiltration was found. Severe steatohepatitis was noted at week 3, and fibrosis at week 8. TUNEL assay showed that apoptotic index in MCD- group was higher than that in MCD+ group at week 3 (15.59%+/-4.87% vs 5.17%+/-3.19%, P less than 0.05) and at week 8 (11.29%+/-3.22% vs 5.41%+/-1.54%, P less than 0.05). Compared to MCD+ group, the expression of FasL was dramatically increased on day 10 and in week 3 in MCD- mice both at the mRNA and protein levels (P less than 0.05 and P less than 0.01). Expression of Fas mRNA was up-regulated in weeks 3 and 8 (P less than 0.01), and expression of Fas in protein level was higher at week 8 (P less than 0.01) in MCD- group. Expression of caspase-8 significantly increased at the mRNA level at week 3 and week 8 (P less than 0.01 and P less than 0.05 respectively) and at the protein level at week 8 (P less than 0.05) in MCD- group. In all of the time points except for day 5, caspase-3 activities were significantly more enhanced in MCD- group than that in MCD+ group (P less than 0.05).</p><p><b>CONCLUSIONS</b>In our experimental NASH model, hepatic apoptosis was frequently detected. Increased apoptosis was probably attributable to up-regulation of apoptosis-related genes, such as FasL/Fas system, and activation of the caspase pathway. These changes may provoke hepatic apoptosis and the development of inflammation and fibrosis.</p>