Regulation Of Lipid Homeostasis By The Zinc Finger Protein ZBTB20

With the accumulation of material wealth,metabolic syndrome including non-alcoholic fatty liver disease(NAFLD),diabetes,hyperlipidemia,and atherosclerosis become prevalent.Epidemiological surveys show that NAFLD become epidemic,and 20~30% people have variable degrees of steatosis.NAFLD are not only closely related with the progression of liver diseases such as hepatic fibrosis,cirrhosis,and hepatocellular carcinoma,but also possess similar pathophysiological mechanisms like hyperlipidemia.Clinical studies indicate that the progression of NAFLD has positive association with the development of metabolic syndrome such as hypertension,hyperlipidemia,diabetes,and atherosclerosis.The liver,as an important organ for lipid metabolism,participates in the regulation of lipid homeostasis.Given the prevalence of NAFLD and the close relationship between NAFLD and metabolic syndrome,the studies on the pathogenesis of NAFLD seem urgent.Recent studies have found that the increased rate of hepatic de novo lipogenesis leads to NAFLD.Transcriptional factor,carbohydrate related element binding protein(ChREBP),regulates glycolytic and lipogenic gene expression to mediate the rate of lipogenesis,which plays an important role in the metabolism of NAFLD.Although the role of ChREBP in metabolism has been studied,little is known about how the expression of ChREBP may be regulated.At the same time,the liver is involved in the maintenance of plasma lipid homeostasis through three pathways: lipid secretion,lipid uptake,and plasma lipolysis.Plasma lipid is a complex process including mutiple steps,while the procedure of lipid lipolysis is seen as the central part.Considering the indispensible role of lipoprotein lipase(LPL)in plasma lipolysis,LPL has been studied for several decades.Therefore,the structure and function of LPL has been investigated and its role in high expression tissues such as adipoctyes and heart,has been revealed too.However,the function of LPL in liver,the low expression tissue,remains to be discovered.My teacher has been studying on the function of zinc finger protein ZBTB20 in development and metabolism since 2001.Our previous study about liver-specific ZBTB20 knockout mice(LZB20KO)has showed that the LZB20 KO mice displayed decreased liver triglycerides,hypolipemia,decreased lipogenic rate and impaired hepatic lipid secretion.Target gene analysis revealed that liver ChREBP and the expression of its downstream DNL-related genes were low,suggesting that ZBTB20 might regulate lipid metabolism via ChREBP.My ph.d project established a adult-induced ZBTB20 knockout(Al-ZB20KO)mouse model via MX1-Cre.I further study the molecular mechanisms about how ZBTB20 regulates liver and plasma lipid metabolism in LZB20 KO mice,and then verify the role of ZBTB20 in maintaining lipid homeostasis in Al-ZB20 KO mice,.My results mainly consist of following parts:?.Regulation of hepatic lipogeneis by ZBTB20: The previous research suggested that ZBTB20 is likely to regulate hepatic lipogenesis via ChREBP.We performed adonovirues-mediated rescue experiments to explore the relationships among ZBTB20,ChREBP and lipogenic related genes.The data showed that ZBTB20 overexpression failed to rescue decreased liver triglyceride contents and DNL related gene expression in the absent of ChREBP,while ZBTB20 is not required for ChREBP-mediated lipogenic genes expression,suggesting that ZBTB20 may regulate hepatic de novo lipogenesis partially through ChREBP-dependent pathway.In order to clarify the molecular mechanism between ZBTB20 and ChREBP,we used classical transcriptional methods to find that ZBTB20 could transcriptionally activate ChREBP-? promoter,and ChREBP-? further activates downstream DNL-related target gene expression?.Regulation of plasma lipolysis by ZBTB20:LPL is the key enzyme in plasma lipolysis,the central part of lipid metabolism.Based on previous studies,we systematically verified the reduced plasma lipid levels in LZB20 KO mice,and the enhanced plasma lipid clearing ability was caused by increased plasma LPL activity,which was mainly due to the overexpression of liver LPL.At the same time,the result of immunofluorescence showed that Liver LPL protein was highly expressed.In order to clarify the role of hepatic LPL in LZB20 KO mice,we estabalished hepatic ZBTB20,LPL double gene knockout(LDKO)mice.No significant difference in plasma triglyceride contents between control and LDKO mice was found,suggesting that the overexpression of hepatic LPL in LZB20 KO is mainly involved in the regulation of plasma triglyceride metabolism.The results of ChIP and electrophoretic mobility shift assay suggest that ZBTB20 could bind hepatic LPL promoter directly.In Luciferase experiments,the evidence that ZBTB20 might transcriptionally inhibit the expression of hepatic LPLpromoter was observed.Taken together,ZBTB20 could bind and inhibit hepatic LPL expression.?.Regulation of lipid homeostasis by ZBTB20 : In order to eliminate the developmental effects on lipid metabolism,we constructed liver ZBTB20 inducible knockout mice using Mx1-Cre(Al-ZB20KO).Phenotypical analyses revealed decreased liver triglyceride and decreased plasma lipid contents.Target gene analyses showed decreased hepatic glycolytic and lipogenic gene expression,including ChREBP,Pklr,Fasn,Elovl6,Scd1.Meanwhile,enhanced hepatic LPL in Al-ZB20 KO mice was observed.The consequences are consistent with the results of LZB20 KO mice,indicating that ZBTB20 is truly involved in the regulation of systematic lipid homeostasis.Therefore,we come to our conclusion that ZBTB20 regulates hepatic lipid metabolism partially through activating ChREBP-dependent pathway,affacting the process of NAFLD,and ZBTB20 regulates plasma lipolysis through repressing the transcription of hepatic LPL,influencing plasma lipid contents.To sum up,ZBTB20 is indispensible in maintaining lipid homeostasis.The mechanical studies about ZBTB20 may acquire new knowledge about lipid metabolism and related metabolic syndrome,and provide new ideas for clinical treatments.Meanwhile,ZBTB20 is highly potential to become a pharmaceutical target for NAFLD and hyperlipidemia.