Study On The Role Of Peroxisome Proliferator Activated Receptor Gamma In The Pathogensis Of Nonalcoholic Steatohepatitis

Objective: Non-alcoholic steatohepatitis (NASH) is a liver disease characterized by steatosis and periportal and lobular inflammation. The diagnosis of nonalcoholic fatty liver disease (NAFLD) requires evidence of fatty changes in the liver in the absence of a history of excessive alcohol consumption. The histologic spectrum of NAFLD spans from generally benign, bland steatosis to steatosis with evidence of hepatocellular inflammation and damage (nonalcoholic steatohepatitis, or NASH), which may be complicated by progressive fibrosis and cirrhosis. Disease presentation ranges from asymptomatic elevated liver enzyme levels to cirrhosis with complications of liver failure and hepatocellular carcinoma. Although the mechanisms for fatty liver in primary NASH are not fully understood, there is growing evidence that insulin resistance can cause hepatic steatosis, which can trigger mitochondrial dysfunction, which plays an important role in the genesis of liver lesions. Peroxisome proliferator-activated receptor gamma (PPARγ) is a member of the nuclear hormone receptor superfamily of transcription factors, whose activities are regulated through the high affinity binding of small lipophilic ligands. Rosiglitazone have been developed as agonists that bind to the PPARγ. PPARγis expressed in liver and skeletal muscle. The role of PPARγin NASH has not been well addressed. In this study, experimental NASH models were established by feeding male C57BL6/J mice with high fat, choline-methionine deficiency diet, and use rosiglitazone as intervention group, Expression of PPARγand TNF-αwas analyzed by RT-PCR and Western blot. To investigate the expression and possible roles of PPARγin liver of mice with NASH, and to evaluate the role of rosiglitazone in treatment of NASH induced by high fat, choline-methionine deficiency diet.Methods: Fifteen healthy male C57BL6/J mice were randomly divided into 3 groups: mice fed with high fat, methionine and choline difficient diet (MCD); mice fed with methionine-choline supplemented diet and mice fed with MCD diet supplemented with rosiglitazone (50mg/kg/day) for 3 weeks. Serum activities of alanine aminotransferase (ALT) and triglyceride (TG) were detected. Hepatic steatosis, inflammation and fibrosis were graded by routine hematoxylin-eosin staining in liver sections. Expression of PPARγand TNF-αwas analyzed by RT-PCR and Western blot.Results: 1 The common behavior of mice: control mice were active, their hair were bright and weight increased gradually. Body weight of mice in model group and rosiglitazone group decreased remarkably, Body weight and liver weight in control group were high remarkably compared to that of model group and rosiglitazone group (25.20±1.10vs16.80±2.28vs17.60±0.89, 0.12±0.01vs0.07±0.01vs0.07±0.01, P<0.05). The liver index of control group were increased compared to rosiglitazone group (0.47±0.04vs0.37±0.07, p<0.05).2 The examination of biochemical markers of serum: The levels of serum ALT of mice: model group>rosiglitazone group> control group (211.00±12.73vs99.75±10.97vs48.33±11.59, P<0.01); The levels of serum TG of mice: model group>control group>rosiglitazone group (0.73±0.04vs 0.53±0.14vs0.33±0.07, P<0.01).3 Routine pathologic examinations: The liver histology is normal in control mice. However, moderate steatohepatitis was developed in mice fed with MCD diet, the hepatocytes presented modest to steatosis of with the inflammation of the interlobular areas. In addition to the macrovesicular steatosis mainly prominent in zone 3 near the central vein, large areas of mixed inflammatory infiltrate with lymphocyte and polymorphonuclear neutrophil necroinflammation can be seen throughout the hepatic lobule. Rosiglitazone supplement prevented steatohepatitis progression, in consistent with the liver histology.4 Both PPARγmRNA and protein were significantly increased regulated by rosiglitazone (0.72±0.01 vs 0.75±0.01 vs0.83±0.01, 0.49±0.01 vs 0.69±0.02 vs0.77±0.00, P<0.01).5 Both TNF-αmRNA and protein were significantly down regulated by rosiglitazone (1.11±0.01 vs 0.99±0.00 vs 0.91±0.00, 0.99±0.01 vs0.60±0.01 vs 0.47±0.01. P<0.01).Conclusion:1 The NASH model could be established successfully by feeding with high fat, choline-methionine deficiency diet for 3 weeks. And this model is consonant with the pathological features of human.2 The expression of PPARγand TNF-αchanged consistently in NASH model. We speculate the increased expression of PPARγmRNA and protein is a compensatory mechanism for the organism. TNF-αmight contribute to the development of steatohepatitis.3 PPAR-γagonist rosiglitazone ameliorated experimental steatohepatitis. The increased expression of PPARγmight down-regulated TNF-αexpression and provides new insight to treatment of steatohepatitis.