Regulation Of Lipid Metabolism And Insulin Sensitivity By Hepatic Zinc Finger Protein ZBTB20

Hepatic lipid metabolism disorder is a serious threat to human health, and has closerelationship with the occurrence and development of cardiovascular and cerebrovasculardiseases, diabetes, hypertension, obesity and metabolic syndrome and otherdiseases.With the improvement of living standards and changes of lifestyle, theincidence of these diseases increased year by year.ZBTB20is a member of zinc fingerprotein family containing BTB/POZ and C2H2domains.It has been suggested thatZBTB20plays a variety of important roles in multiple systems.We generated ZBTB20global knockout mice, and found that the ZBTB20global knockout mice have severedisorders of metabolism.The liver is the major site of carbohydrate metabolism andtriglyceride synthesis.To understand the tissue-specific role of ZBTB20in energyhomeostasis, we used Cre-loxP technology to generate mice with a liver-specificknockout of ZBTB20(LZB20KO). In this study, we show that zinc finger proteinZBTB20has an essential role in hepatic lipid metabolism.1．The phenotypic analysis of LZB20KO miceOur previous study show that ZBTB20null mice display severe metabolicdysfunction.The liver is the major site of carbohydrate metabolism and lipogenesis.Tostudy metabolic functions of ZBTB20in the liver, we generated liver-specific knockoutof ZBTB20(LZB20KO) by crossing the ZBTB20flox mice with mice that carry analbumin promoter driven Cre transgene.LZB20KO mice did not show any noticeablegross abnormalities, had normal body weight and liver mass.Plasma glucose levels inLZB20KO mice were normal in fasted states, but significantly decreased in the fed state.However, LZB20KO mice exhibited significantly lower levels of plasma triglyceride,cholesterol and free fatty acids, which suggests that ZBTB20played an important role inhepatic lipid metabolism. LZB20KO mice exhibited significant decrease in the rate offatty acid synthesis and cholesterol synthesis through3H-water. In addition, LZB20KOhad a significantly higher rate of triglyceride clearance and decreased serum LPLactivity.2． The regulatory role of ZBTB20in hepatic lipid metabolism and itsmechanismsThe liver plays an important role in fatty acid uptake, oxidation, synthesis, esterification and triglyceride transport. We found that ZBTB20regulate the expressionof LPL and a subset of glycoclastic and lipogenic genes. ZBTB20displayed significantbinding to LPL promoter and ChREBP-α promoter in the liver.In addition, ZBTB20directly binds to Scd1,Gpat and Dgat2promoter in the liver.3. Hepatic ZBTB20deficiency protects mice from high carbohydratediet-induced hepatic steatosisProlonged feeding of high-carbohydrate diets increase de novo lipid synthesis in theliver through induction of genes encoding lipogenic enzymes and induce the occurrenceof hepatic steatosis.The ablation of ZBTB20in liver might protect from highcarbohydrate diet-induced hepatic steatosis compared with wild-type mice. We fed the4-week-old wild-type and LZB20KO mice with a HCD for2months. the plasma TG andTC level of LZB20KO mice decreased significantly compared with WT mice underHCD. LZB20KO mice were protected from both HCD induced fatty liver. Hepaticsteatosis is known to be closely associated with insulin resistance.We found that targetedablation of hepatic ZBTB20led to improvement of insulin resistance.Glucose tolerancetest showed dramatically improved glucose tolerance in LZB20KO mice under HCD for2month. All these data indicated that ZBTB20has close relationship with the HCDinduced fatty liver and insulin resistance.4. The pathological role of hepatic ZBTB20in ob/ob miceWe have chosen to determine the role of ZBTB20in the pathophysiology of hepaticsteatosis using the ob/ob mouse model.The ob/ob mouse is commonly studied not onlyas a model of early onset of severe obesity and insulin resistance but also as an excellentmodel of fatty liver.Through RT-PCR and western blot, we found that the expression ofZBTB20is significantly increased in the liver of ob/ob mice indicated that ZBTB20hasclose relationship with the development of fatty liver of ob/ob mice.We created ob/ob liver-specific ZBTB20knockout (LZB20KO-ob/ob) mice, andobserved the lipid metabolism condition in LZB20KO-ob/ob mice.we found thatLZB20KO-ob/ob mice exhibited significantly lower plasma Triglyceride, the lipiddeposition was significantly decreased in the liver of LZB20KO-ob/ob mice. Targetedablation of hepatic ZBTB20in ob/ob mice led to improvement of insulin resistance ofob/ob mice. All these data indicated that ZBTB20has close relationship with thedevelopment of fatty liver and insulin resistance of ob/ob mice. In conclusion，we showed that the liver-specific ablation of ZBTB20resulted in theincreased expression of LPL and the down-regulation of ChREBP-α and its target genesexpression.Consequently，LZB20KO has lower rate of fatty acid synthesis and protectedfrom high-carbohydrate diet induced hepatic steatosis.Liver-specific inhibition ofZBTB20decreased the rate of hepatic lipogenesis and improved hepatic steatosis andinsulin resistance in obese ob/ob mice.These findings strongly suggest that in addition toregulating AFP transcription, ZBTB20plays an important role in the regulation ofhepatic lipid metabolism.