Effect And Mechanism Of Secretory Fibroblast Growth Factor 21 And 19/15 In Alcoholic Liver Disease

Alcohol abuse is one of the leading causes of chronic liver disease. Chronic alcoholic liver disease(ALD) may induce cumulative damage to the liver ranging from simple steatosis to steatohepatitis, liver fibrosis, liver cirrhosis and hepatocellular carcinoma. In China, ALD is one of the common liver diseases and a major cause of morbidity and mortality causing serious economic losses to society.Fibroblast growth factor(FGF) 19/15 and FGF21 comprise a subfamily that distinguishes it from typical FGFs and acts as endocrine hormones. FGF21 is produced by liver and other metabolic tissues, and FGF15/19 is only produced in the ileum. FGF21 and FGF15/19 are newly-discovered endocrine regulators in glyco- and lipid-metabolism. Recent studies showed that FGF21 and FGF15/19 play an important role in metabolic diseases. We sought to determine the role of FGF21 and FGF15/19 in ALD and to discern underlying mechanisms.Methods:1. Male FGF21 knockout(FGF21 KO) and control(WT) mice were divided into groups that were fed either the Lieber De Carli diet containing 5% alcohol or an isocaloric(control) diet for 4weeks. One group of WT mice exposed to alcohol received recombinant human FGF21(rh FGF21) for the last 5 days. Liver steatosis and inflammation were assessed. Hepatic genes and the products involved in in situ lipogenesis and fatty acid β-oxidation were analyzed.Primary mouse hepatocytes and AML-12 cells were incubated with metformin or rh FGF21 to analyze Sirt1-mediated signaling.2. Male FGF21 KO and WT mice were divided into groups that were fed either the Lieber De Carli diet containing 5% alcohol or an isocaloric(control) diet for 12 days. On the last day of experiment, mice were gavage with a single dose of alcohol(5g/Kg body weight) or isocaloric maltose dextrin. Mice were killed 6 hours later. One group of alcohol-exposed FGF21 KO mice were treated with recombinant human FGF21(KO+AF+rh FGF21) via intraperitoneal injection during the last 5 days. Serum catecholamine levels, epididymal white adipose tissue lipolysis and liver steatosis are investigated.3. In chronic alcohol exposure mouse model, the expression of ileal FGF15 and intestinal and hepatic expression of the genes involved in the bile acid metabolism were examined.4. Serum levels of FGF21 in alcoholic steatohepatitis and stable abstinent alcoholic cirrhosis patients were measured. Serum levels of FGF19, total bile acid(BA) and inflammation markers of subjects with alcoholic cirrhosis were measured.Result:1. Alcohol exposure increased circulating levels and hepatic expression of FGF21. FGF21 depletion exacerbated alcohol-induced hepatic steatosis and liver injury, which was associated with increased activation of genes involved in lipogenesis, mediated by SREBP1 c and decreased expression of genes involved in fatty acid β-oxidation mediated by PGC1α. Alcohol-induced hepatic Sirt1 decrease was more pronounced in the FGF21 KO mice than WT mice. FGF21 depletion significant increased activation of NFk B and the expression of inflammatory cytokines.rh FGF21 administration reduced alcohol-induced hepatic steatosis and inflammation in WT mice. In vitro studies showed that metformin-induced Sirt1 expression was attenuated in the FGF21 KO hepatocytes, and rh FGF21 treatment promoted Sirt1 nuclear translocation in AML-12 cells.2. Alcohol exposure causes adipose intracellular c AMP elevation and lipolytic enzymes activation, leading to FFA mobilization in both WT and FGF21 KO mice. However,alcohol-induced adipose tissue lipolysis and systemic elevation of catecholamine, which is known to be a major player in adipose lipolysis by binding to the β-adrenergic receptor, were markedly inhibited in FGF21 KO mice. Supplementation with rh FGF21 to alcohol-exposed FGF21 KO mice caused increased fat loss in parallel with an increase of circulating norepinephrine concentration. Furthermore, alcohol consumption-induced fatty liver is blunted in the KO mice, indicating an inhibition of fatty acid reverse transport from adipose to the liver in the KO mice.3. Chronic alcohol exposure induced liver steatosis and injury, and up-regulated genes responsible for FGF15 synthesis which is activated by BA in the ileum. Alcohol feeding decreased hepatic Cyp7A1 gene expression, which regulates hepatic BA synthesis.4. Mean serum FGF21 concentrations were significantly increased in alcoholic steatohepatitis subjects, but not in alcoholic cirrhosis patients. Mean serum FGF19 and total BA concentrations were significantly higher in alcoholic cirrhosis subjects than that in controls. There was a positive association between serum FGF19 and total BA levels in all alcoholic cirrhosis and control subjects. Serum levels of AST, M30 and M65 were also increased in alcoholic cirrhosis subjects compared to controls, which are positively associated with serum FGF19 and/or total BA concentrations.Conclusion:1. FGF21 levels are elevated in patients with fatty liver and inflammation, implying an interplay between hepatic fat content and FGF21 expression.2. Chronic alcohol exposure-induced FGF21 expression is a hepatic adaptive response to lipid dysregulation. But in chronic-binge alcohol exposure model, FGF21-KO mice are protected from alcohol-induced adipose tissue excess-lipolysis through a mechanism involving systemic catecholamine release.3. The elevation of serum FGF19 maybe negative feedback inhibition of BA synthesis.To our knowledge, this is the first study to elucidate the role of FGF21 and FGF15/19 in the alcohol-induced liver steatosis and injury. Developing strategies targeting FGF21 signaling is a novel treatment approach for alcoholic liver disease. FGF19 may serve as an additional marker for AC patients. Targeting FGF19 pathway may be useful in the design of novel strategies for treatment/prevention of alcoholic cirrhosis.