Study On The Metabolic Function Of TETs In Liver

Background and aims:Glucose and fatty acids are the primary energy sources of the human body.The metabolism of glucose and fatty acids is often intertwined and regulated.Glucose can be converted to fatty acids and cholesterol through the de novo lipid biosynthesis pathway.Excess lipids are secreted in lipoproteins or stored in lipid droplets.Metabolites of glucose and lipids are dynamically transported between and within cells and then converted to other molecules in specific compartments.Disorders of glucose and lipid metabolism lead to severe diseases such as cardiovascular disease,diabetes,and fatty liver.The liver has a central role in regulating whole-body glucose and lipid metabolism during feeding and fasting.Energy requirements are met by coordinated control of carbohydrate and lipid fluxes into and out of the Kerb cycle,tightly regulated by insulin and glucagon.In mammals,5-methylcytosine（5m C）is the predominant form of DNA modification with essential roles in development and disease.Approximately 60-80%of Cp G sites in the mammalian genome are modified by 5m C.The main functions of5m C include mediating genomic imprinting,X chromosome inactivation,repression of transposable elements,and regulation of transcription.5m C is chemically and genetically stable.DNA methylation is closely related to liver metabolism.Hepatic downregulation of DNA demethylases（TETs）is extremely common in chronic liver disease,which results in genome-wide differences in 5-m C and 5-hm C levels,resulting in genome-wide transcriptional alterations.Alterations in gene expression caused by aberrant DNA methylation have been implicated in the pathogenesis of human diseases.However,the stimulatory factors of DNA methylation changes and the mechanisms that cause DNA methylation changes are unclear,and the role and function of demethylases in the liver have not been reported.Materials and methods:Based on TETsflox/flox mice,we used AAV-TBG-cre virus to carry out specific TETs knockout in the liver to observe DNA methylation change in the mouse liver.The changes in the body’s glucose and lipid metabolism and liver pathology,and liver fat and metabolites were observed and analyzed by differences in gene expression changes within the genome.Results:We used AAV8-TBG-cre and TETsf^lox/floxmice to establish liver-specific TETs knockout mice.AAV8-TBG-cre can significantly knock down the m RNA and protein levels of TETs in the liver.After TETs knockdown,the level of 5hm C in hepatocytes decreased,the expression of DNA damage markers increased,and hepatocytes compensated for the function of TETs through base excision repair（BER）to achieve demethylation.In addition,TETs knockout mice increased hepatic lipid accumulations,decreased fatty acid oxidation,increased hepatic inflammation-related expression,significantly decreased liver nucleotides and intermediates of fat metabolism,and changed the proportion of metabolites and lipids in the liver.In terms of glucose metabolism in the body,after short-term TETs knockout,the glucose utilization efficiency of the liver increases,but glycogen synthesis or storage is insufficient.Therefore,in the late stage of TETs knockout,along with the formation of large lipid droplets in the liver and an increase in inflammation,glucose tolerance（GTT）is worse than wild type.Conclusion:1.AAV8-TBG-Cre can effectively knock down TETs in the liver and decrease the level of 5hm C in the liver.2.TETs are key molecules to maintain the homeostasis of liver metabolism,especially lipid metabolism.3.TETs KO can destroy the stability of hepatocyte DNA.