Effects Of Fibronectin/Integrin ? Signaling On Short-term High Fat Diet Induced Hepatic Steatosis And Its Underlying Mechanism

Backgroud Nonalcoholic fatty liver disease(NAFLD)is a clinic-pathological syndrome of diffuse hepatocelluer fat deposition due to causes other than excessive alcohol use or any other definite liver-impairment factors.The pathological syndrome includes four stages: nonalcoholic fatty liver(NAFL),nonalcoholic steatohepatitis(NASH),nonalcoholic hepatic fibrosis,and nonalcoholic liver cirrhosis.NAFL can progress to nonalcoholic hepatic fibrosis,which an is early stage lesion of liver cirrhosis.The impairment in liver function will occur as it progresses to the stage of liver cirrhosis.Fibronectin(FN)is a high-molecular weight glycoprotein of extracellular matrix that binds to membrane-spanning cell adhesion receptor proteins called integrins.FN plays an important role in many physiological and pathological processes,for instance liver fibrosis.Integrins are cell adhesion receptors and play important roles during developmental and pathological processes.The integrin family is composed of 24 ?? heterodimeric members that not only mediate the attachment of cells to the extracellular matrix(ECM)but also take part in specialized cell-cell interactions.Although there are many studies focused on FN and integrins,their roles in liver lipid metabolism had rarely been studied.Objective This study is to investigate the effects of fibronectin / integrin ? on short-term high fat diet(HFD)induced hepatic steatosis and its underlying mechanism.Methods 1.Male C57BL/6 mice were treated with HFD and HFD combined with ATN161,an inhibitor of integrin ?.Hepatic steatosis was demonstrated by Oil Red O staining of frozen liver sections.Liver lipids were extracted and the content of lipids in liver were determined.Serum triglyceride(TG),serum cholesterol(CHO)and serum low density lipoprotein cholesterol(LDL-C)were also detected.Intraperitoneal glucose tolerance test(IPGTT)was done to demonstrate insulin sensitivity of mice.The expression of lipid metabolism genes of liver tissues were detected with real-time quantitative polymerase chain reaction detecting system (q PCR).The protein levels of peroxisome proliferator-activated receptor ?(PPAR?)and stearic acyl coenzyme A desaturase(SCD1)were detected with Western blot.Results 1.HFD increased hepatic lipid accumulation.Compared with control group,the level of liver TG and plasma CHO,LDL-C were higher in HFD group.The mice in HFD group had higher expression of fibronectin(FN)and ?-smooth muscle actin(?-SMA).2.Short-term HFD+ATN161 treatment significantly down-regulated the expression of ?-SMA.However,hepatic lipid accumulation and the expression of key enzymes in lipogenesis(FAS and SCD1)and lipid uptake(CD36,and FATP1)were up-regulated in mice liver from HFD+ATN161 group.The up-regulated genes were target genes of PPAR?,which was also up-regulated.The protein levels of PPAR? and SCD1 were also increased.3.FN could inhibit the expression of lipogenic genes in Hep G2 cells.While the effects of inhibition could be blocked by ATN161.The expression of key genes involved in lipogenesis(CHREBP,SREBP1,ACC and SCD1)were significantly down-regulated in FN group,where as they were up-regulated approximately to the level of that in control group after ATN161 treatment.Conclusion 1.In short-term HFD-induced early stage of NAFL,hepatic fibrotic signaling pathway was activated other than hepatic lipid accumulation or insulin resistence.2.Inhibition of FN / Integrin ? signaling pathway with ATN161 could block short-term HFD-induced hepatic fibrotic signaling pathway at the expense of increasing hepatic lipid accumulation in HFD-induced early hepatic steatosis mice model by activating PPAR?.