热卡限制对非酒精性脂肪肝病大鼠肝脏SIRT1表达的影响

目的研究热卡限制（CR）在非酒精性脂肪肝病（NAFLD）治疗中的分子作用机制。方法25只雄性Wistar大鼠分为2组,一组给予正常普通饲料喂养（NC组,7只）,一组给予高脂饲料喂养（HFM组,18只）。喂养2个月后,再将HFM组大鼠随机分为继续高脂饲料喂养组（HF组,9只）和60％热卡限制喂养组（CR组,9只）。1个月后将大鼠处死,观察大鼠体重、内脏脂肪含量、空腹血糖、空腹胰岛素及血脂的改变,电镜下观察各组大鼠肝脏超微结构变化,应用RT-PCR方法检测长寿基因SIRT1mRNA的表达,Westerm印迹法检测SIRT1的蛋白表达。结果HF组大鼠发生明显NAFLD,与正常对照组比较,大鼠内脏脂肪含量（15．1g±4．1g vs 9．0g±0．4g）、血脂（总胆固醇2．61mmol／L±0．29mmol／L vs 1．41mmol／L±0．28mmol／L;甘油三酯1．35mmol／L±0．21mmol／L vs 0．67mmol／L±0．10mmol／L）、血糖（6．2mmol／L±1．46mmol／L vs 4．4mmol／L±0．57mmol／L）,血胰岛素水平（29．22mU／L ± 7．28mU／L vs 13．09mU／L±1．18mU／L）明显增高,其肝脏超微结构亦发生明显异常,SIRTl表达在转录和翻译水平均低于正常组显著（P〈0．01）。相比较HF组,限制热卡后的CR组大鼠体重明显下降,内脏脂肪含量、血脂、血糖、血胰岛素水平显著降低,SIRT1的表达明显增加（P〈0．01）,同时肝细胞的超微病理改变亦显著改善。结论CR对大鼠NAFLD具有显著的逆转效应,其导致的肝脏SIRT1表达增加可能是改善NAFLD的重要分子作用机制。

Effects of calorie restriction on SIRT1 expression in liver of nonalcoholic fatty liver disease: experiment with rats

OBJECTIVE: To investigate the molecular mechanisms of calorie restriction (CR) in treatment of nonalcoholic fatty liver disease (NAFLD). METHODS: 25 male Wistar rats were randomly divided into 2 groups: normal control group (NC, n = 7) fed with regular diet and high fat diet-NAFLD model group (HFM, n = 18) fed with high-fat diet. Two months later, the rats in Group HFM were further divided into 2 subgroups: continuous high-fat feeding group (HF, n = 9) and normal diet feeding with 60% calorie restriction group (CR, n = 9). The rats were sacrificed after 1 month calorie restriction. By the end of experiment, body weight (BW), visceral fat mass (VF), fasting plasma glucose (FPG), fasting serum insulin (FINS), blood lipids (BL), including total cholesterol (TC) and triglyceride (TG), and hepatoultrastructure changes were examined to evaluate the effect of different feeding protocols on the experimental animals. The mRNA expression of the longevity gene SIRT1 in the liver was detected by RT-PCR. Western blot analysis was performed to determine the expression of SIRT1 protein in each group. RESULTS: Electron microscopy showed that the rats in group HF displayed obviously abnormal hepatoultrastructure, and the ultramicropathology changes of liver cell were improved obviously in Group CR. The VF, FINS, FPG, TC, and TG of the Group HF were 15.1 g +/- 4.1 g, 29.22 mU/L +/- 7.28 mU/L, 6.2 mmol/L +/- 1.46 mmol/L, 2.61 mmol/L +/- 0.29 mmol/L, and 1.35 mmol/L +/- 0.21 mmol/L respectively, all significantly higher than those in Group NC (9.0 g +/- 0.4 g, 13.09 mU/L +/- 1.18 mU/L, 4.4 mmol/L +/- 0.57 mmol/L, 1.41 mmol/L +/- 0.28 mmol/L, and 0.67 mmol/L +/- 0.10 mmol/L respectively, all P < 0.01). The mRNA expression of SIRT1 in the liver of Group HF was significantly lower than that of Group NC (P < 0.05), and the mRNA expression of SIRT1 in the liver of Group CR was significantly higher than those of Group HF and Group NC (both P < 0.01). The protein expression of SIRT1 of Group HF was significantly lower than that of Group NC (P < 0.01), and that of Group CR was significantly higher than that of Group HF, however, still significantly lower than that of Group NC (both P < 0.01). The BW and VF, FINS, FPG, TC, and TG of Group CR were all significantly lower than those of Group HF (all P < 0.01). CONCLUSION: CR can reverse NAFLD significantly. The increased expression of SIRT1 in liver induced by CR may be an important molecular mechanism involved in the improvement of NAFLD by CR.