| Background:Homocysteine(Hcy) is a intermediate metabolite of methionine, patients with severe hyperhomocysteinemia exhibit a wide range of clinical manifestations, including atherosclerosis, mental retardation, osteoporosis, and hepatic steatosis or "fatty liver" Hyperhomocysteinemia is a common, independent risk factor for cardiovascular disease, in recent years; there have been many reports on this aspect. However, the molecular mechanism of Hcy-induced changes in non-alcoholic fatty liver disease (NAFLD) is unclear. In the present study, we used a high methionine diet-induced hyperhomocysteinemia mouse model to explore the effects of Hcy on lipids metabolism in the liver and the possible mechanism.Methods:Twenty healthy 4 weeks old male C57BL/6J mice were chosen and assigned to two groups respectively. After two-week acclimation, animals in control group (CT) were fed with standard chow and those of high methionine diet group (MET) were fed with chow diet supplemented with 2% methionine for 16 weeks. Body weights were monitored every week. The samples of blood and liver tissue were collected after animals sacrificing. Liver morphologic analyses were performed by H.E staining. Serum AST, ALT, and other lipids profile were determined by automatic biochemical analyzing system. Plasma homocysteine was determined using ELISA tool kit. The mRNA expression levels of homocysteine metabolism relating enzyme genes were determined by quantitative Real-time PCR. The expression level of GRP78/BIP、 p-PERK、p-eIF2a and n-SREBP-1c were determined using Western blotting. Oil red O staining was performed to assess the lipids deposition in primary hepatocytes. The mRNA expression levels of lipid metabolism relating enzyme genes and endoplasmic reticulum stress were determined by quantitative Real-time PCR. The expression level of GRP78/BIP、 p-PERK and p-eIF2a were determined using western blotting.Results:Animals in MET group had higher liver/body weight ratio and epididymal fat/body weight ratio compared with control group, without significant deference of body weight gaining between two groups. Histological observation suggested there was macrovesicular steatosis in MET group. Methionine diet elevated plasma homocysteine level, TG and AST compared with control group. Plasma HDL level were significantly reduced in MET group. There were no significant difference of serum ALT、LDL and TC levels between two groups. Compared with CT group, the CBS mRNA levels in MET group were reduced significantly. Expression level of GRP78/Bip、activated form of PERK (p-PERK)、 activated form of eIF2a (p-eIF2a) and mature form of SREBP-1c (n-SREBP-lc) was higher than that of control. The result of oil red O staining suggested high homocysteine treatment led to obvious lipids deposition in primary hepatocytes, and PBA pretreatment could ameliorate the lipid accumulation. Compared with control group, the GRP78、CHOP、 FAS、ACC1α and HMG-CoA r mRNA levels in Hcy group and TM group were elevated significantly. PBA pretreatment could reduce GRP78、FAS and ACC1αmRNA levels. However, the mRNA expression levels of primary hepatocytes CHOP and HMG-CoA r in PBA pretreatment group were not significantly changed compared with Hcy group. The result of western blotting suggested high homocysteine and TM led to significantly increased levels of GRP78/BIP、p-PERK and p-eIF2a protein, and the above three indicators were significantly reduced in PBA pretreatment group in comparison with Hcy group.Conclusions:High methionine intake may result in fatty liver, which is associated with moderate hyperhomocysteinemia. These results indicate that homocysteine-induced ER stress leads to the transcriptional activation of genes responsible for lipogenesis that likely contribute to hepatic steatosis in hyperhomocysteinemia. Through increasing the expression level of n-SREBP-lc, a key transcription factor, elevated homocysteine may take effects on the process of lipogenesis, oxidation and secretion in the liver. |
PDF Full Text Request