Regulation Of Hepatokine Fetuin B On Glucose And Lipid Metabolism In Obesity And Its Activation Mechanism

Objective:Currently,1.1 billion adults worldwide are overweight or obese,and its incidence is increasing year by year.Obesity has become the most obvious but most easily ignored public health problem.With the deepening of obesity research,metabolically healthy obesity has attracted more and more attention,and the phased of metabolically healthy obesity was realized.Therefore,to explore the key molecules that induce metabolic disorders in obesity is great significance for the classification diagnosis,refinement treatment and delay or even reverse of metabolic disorders.Fetuin B is a hepatokine closely related to energy metabolism.Its expression is significantly increased in metabolic diseases such as obesity,diabetes,and non-alcoholic fatty liver disease.The previous study of our group found that the serum Fetuin B level of patients with metabolic syndrome was significantly higher than that of patients without metabolic syndrome in central obese people.Further analysis showed that serum Fetuin B level was closely related to blood glucose and blood lipid which is two key components of metabolic syndrome.Therefore,in this study,the induction effect of hepatokine Fetuin B on obesity-related glucose and lipid metabolism disorders was explored,and the molecular mechanism of obesity-induced increased liver Fetuin B expression was also clarified in obese mice models.Methods:To explore the function of Fetuin B,we fed C57BL/6 mice with high-fat diet for 20 weeks to establish obese mouse models,and the level of Fetuin B in liver and serum were detected.Besides,Fetuin B level of obese mice was knocked down by injection of Adenoassociated virus(AAV)through the tail vein,and metabolic phenotypes were detected after a high-fat diet and intravenous injection of AAV for 20 weeks.The mice were weighed every week,and multiple time points were selected to identify knockdown efficiency and detect metabolic phenotype.Euthanasia was performed at 5 and 20 weeks,and tissue studies were performed.Metabolic phenotype monitoring included body component analysis,fasting blood glucose test,glucose tolerance test,insulin sensitivity test,pyruvate tolerance test,blood lipid test,intrahepatic triglyceride content test,tissue oil red and HE staining,and energy metabolism test.Proteins and genes involved in the metabolic process were detected with Western blot and quantitative real-time PCR.In the study of Fetuin B regulation,the physical examination and the laboratory test data of the central obese population were analyzed.And the results of the population were verified in the high-fat diet-induced obesity mouse model and the db/db and ob/ob mouse model.Then the molecular mechanism of Fetuin B transcriptional regulation was explored in mouse primary hepatocytes cells and mouse AML 12 cells.Finally,mediation analysis was applied to investigate the physiological significance of the increased expression of Fetuin B in obese.The relative experimental method included enzyme linked immunosorbent assay,western blot,real-time quantitative PCR,dual luciferase reporter assay and chromatin immunoprecipitation assay.Results:The in vivo result showed that the glucose and lipid metabolism disorders were closely related to the level of Fetuin B.It mainly includes:(1)Although the Fetuin B knockdown did not affect the weight gain induced by high-fat diet,it could reduce the body fat rate in early stage of obesity.(2)Fetuin B may promote abnormal glucose metabolism in obesity.Fetuin B knockdown significantly and consistently reduced fasting blood glucose levels,alleviated the impaired glucose tolerance,improved the systemic insulin sensitivity,and reduced insulin resistance in obese mice.(3)Meanwhile,Fetuin B is involved in obesityinduced fatty acid metabolism disorders.Knockdown Fetuin B may reduce serum total cholesterol and low-density lipoprotein levels in obese mice induced by high-fat diet.The intrahepatic triglyceride content was decreased and steatosis was alleviated.In primary hepatocytes,Fetuin B may be involved in palmitic acid-induced hepatic lipid accumulation.On the other hand,we mainly explored the upstream regulation mechanism of Fetuin B under the condition of obesity.The results showed that there was a significant correlation between serum leptin and Fetuin B in obese people and mouse models.And the transcriptional regulation of leptin pathway on hepatokine Fetuin B was confirmed in vitro,which may be related to insulin resistance induced by Fetuin B.Specifically,in the case of obesity,adipose tissue continuously expanded and increased the synthesis and secretion of leptin.Leptin may activate Jak/Stat3 pathway in the liver by binding to the leptin receptor on the hepatic surface.Then the phosphorylated Stat3 directly binds to the Fetuin B promoter to realize the transcriptional regulation of Fetuin B.At the same time,free fatty acids may also activate the leptin pathway by directly inducing the leptin receptor transcription in liver,and then induce the expression of Fetuin B.Finally,combined with population data,the mediation effect of Fetuin B on the relationship between leptin and insulin resistance in obese people was analyzed.And we found that Fetuin B had a significant mediating effect on the relationship between the leptin and the insulin resistance.Conclusions:Based on the above results,we found that Fetuin B may induce glucose and lipid metabolism disorder independent of body weight and body composition.At the same time,the leptin signaling pathway may promote insulin resistance under obesity by inducing the transcription of Fetuin B.This research comprehensively explored the effects of Fetuin B protein on glucose and lipid metabolism disorders in obesity mouse induced by high fat diet,and preliminarily explored the possible mechanisms involved.In addition,targeting Fetuin B may provide a deeper understanding of the role of leptin signaling in liver.In this study,we explored the possibility of Fetuin B as a predictive marker of metabolic typing and metabolic prognosis in obese,and revealed a new interaction mode between adipose tissue and liver tissue in the context of obesity.This study may prove a new perspective for the prediction of metabolic outcomes and clinical intervention in obese patients.