Pathophysiology of insulin resistance and steatosis in patients with chronic viral hepatitis

Chronic hepatitis due to any cause leads to cirrhosis and end-stage liver disease.A growing body of literature has also shown that fatty liver due to overweight or obesity is a leading cause of cirrhosis.Due to the obesity epidemic,fatty liver is now a significant problem in clinical practice.Steatosis has an impact on the acceleration of liver damage in patients with chronic hepatitis due to other causes.An association between hepatitis C virus (HCV) infection,steatosis and the onset of insulin resistance has been reported.Insulin resistance is one of the leading factors for severe fibrosis in chronic HCV infections.Moreover,hyperinsulinemia has a deleterious effect on the management of chronic HCV.Response to therapy is increased by decreasing insulin resistance by weight loss or the use of thiazolidenediones or metformin.The underlying mechanisms of this complex interaction are not fully understood.A direct cytopathic effect of HCV has been suggested.The genomic structure of HCV (suggesting that some viral sequences are involved in the intracellular accumulation of triglycerides),lipid metabolism,the molecular links between the HCV core protein and lipid droplets (the core protein of HCV and its transcriptional regulatory function which induce a triglyceride accumulation in hepatocytes) and increased neolipogenesis and inhibited fatty acid degradation in mitochondria have been investigated.

固醇调节元件结合蛋白1c激活大鼠Patatin样磷酯酶结构域蛋白3基因转录

目的探讨固醇调节元件结合蛋白1c（SREBP-1e）对Patatin样磷酯酶结构域蛋白3（PNPLA3）基因的转录调控作用。方法构建7周龄雄性体重匹配的禁食（24h）以及禁食后再喂食（48h）SD大鼠（自由饮食组3只，饥饿组3只，再喂食组4只）和高脂及小剂量链脲佐菌素诱导的2型糖尿病sD大鼠（正常对照组5只，2型糖尿病组6只）。用逆转录聚合酶链反应（RT—PCR）和Western blotting法检测各组大鼠肝脏组织中SREBP一1c和PAPM3的表达水平。将大鼠PⅣP翻3启动子5’端上游-1000bp序列分成3段，分别构建荧光素酶报告载体（R—PⅣPM3．1、R—PM似3—2、R—PNPL43—3），转染人正常肝细胞株L02，比较3个载体基础荧光素酶活性以及SREBP-1e过表达诱导的荧光素酶活性。分析上述实验中荧光素酶活性最高的PNPLA3启动子片段可能的SREBP-1c结合位点（SRE），分别构建野生型和SRE突变型报告载体，比较两个载体荧光素酶活性。多组定量资料比较用方差分析，两组定量资料比较用t检验。结果与自由饮食组相比，饥饿组大鼠肝脏SREBP—lc、PNPLA3和脂肪酸合成酶FAS基因表达均下降，再喂食组三者表达显著升高，差异均有统计学意义（F=114．14，334．11，754．20，均P〈0．05）。与正常对照组相比，2型糖尿病组SREBP-1e、PNPLA3基因（t=-18．39，-30．07，均P〈0．05）及蛋白表达（t=4．58，6．81，均P〈0．05）均显著增高。R—PNPLA3-1报告载体基础荧光素酶活性较对照升高51．13倍（t=-28．93，P〈0．05），R一删PM3—2和R—PNPLA3—3无基础荧光素酶活性；在L02细胞中，转染SREBP-1c表达质粒的R—PⅣPL43—1组荧光比值较转染空质粒的组升高2．63倍（t=-7．64，P〈0．05），而R—PⅣPM3．2组及R—PNPLA3—3组转染SREBP-1e表达质粒荧光比值较转染空质粒组均无变化；PNPLA3启动子-100～-911）p存在SRE，SRE突变的报告载体（MUT—R—PNPLA３—1）荧光比值较野生型（R—PNPLA３-1）降低40．80％（t=4．99，P〈0．05）。结论SREBP-1c通过PNPLA３基因启动子－100～－91bp激活大鼠PNPLA3基因转录。