Abstract: ：Objective To observe the expression of Toll-like receptor 4 (TLR4) gene and its methylation level in liver of non-alcoholic steatohepatitis (NASH) model rats, and explore the correlation between the two in the pathogenesis of NASH. Methods Twenty rats were randomly divided into normal group and model group,with 10 rats in each group. Rats in the normal group and the model group were fed with ordinary diet and high-fat and high-sugar diet. Rats were sacrificed after 24 weeks. The body weight and liver weight of the rats were measured. The serum samples and liver tissues were collected under low temperature conditions. The morphological staining was used to observe morphological changes,steatosis and inflammatory cell infiltration of hepatocytes. The serum levels of alanine aminotransferase (ALT), aspartic aminotransferase (AST),triglyceride (TG) and total cholesterol (TC) were detected by ELISA.The expression of CD68 protein in liver was detected by immunohistochemistry. The expression of TLR4 protein in liver was detected by Western blot assay. Real-time fluorescence quantitative PCR was used to detect the mRNA content of TLR4 in liver. Methylation of TLR4 gene in liver was detected by bisulfite sequencing PCR (BSP). Results Compared with the normal group，the volume of liver cells became larger, a large number of fat vacuoles appeared, and inflammatory cell infiltration was obvious; The liver index increased in the model group, the serum levels of AST,ALT,TG and TC increased significantly (P＜0.01). The expressions of TLR4 and CD68 protein increased significantly (P＜0.01). The mRNA content of TLR4 gene increased obviously (P＜0.01)， and its methylation level decreased (P＜0.01). Conclusion The expression of TLR4 gene is negatively correlated with its methylation level in the liver of NASH model rats. The reduction of TLR4 gene methylation level plays an important role in the pathogenesis of NASH.

Key words: non-alcoholic fatty liver disease, Toll-like receptor 4, DNA methylation, nonalcoholic steatohepatitis