Long Non-coding RNA: Functional Study Of Lnc-217 In Regulating Hepatic Lipid Metabolism

Nonalcoholic fatty liver Disease(NAFLD)is a clinical pathological syndrome characterized by excess deposition of fat in liver due to factors other than alcohol and other definitive liver damages,including simple steatosis,nonalcoholic steatohepatitis,liver fibrosis and cirrhosis..It is closely associated with obesity,insulin resistance,type 2 diabetes and other metabolic syndrome.It has become one of the most common prevalent chronic liver diseases all over the world.However,the mechanism of pathogenesis of NAFLD is still unclear.The "two hits" hypothesis was developed to explain the pathogenesis of the NAFLD spectrum.The factors that metabolically promote the deposition of triacylglycerides(TAG)in the liver,including a high-fat diet,obesity,and insulin resistance,represent the "first hit" in the pathogenesis of NAFLD.Signaling process such as extracellular cytokines,adipokines,bacterial endotoxin,mitochondrial dysfunction,and/or endoplasmic reticulum(ER)stress provide the second hit for progression to NASH,activating inflammatory cascades and fibrogenesis.LncRNA is a functional RNA,transcribed by RNA polymerase II,which is larger than 200nt and does not have the ability to encode protein.It was once considered as a by-product of gene transcription.With the in-depth study of noncoded RNA,LncRNA has become an important regulatory factor,not only participates in biological processes such as cell development,proliferation and apoptosis,but also plays an important role in the development of cancer and other metabolic diseases.In recent years,the emerging evidences have shown that LncRNA is not only closely related to lipid metabolism but also for the development of NAFLD.Therefore,we performed RNAseq in the liver of HFD feeding for 4 weeks and bioinformatics analysis to identify differentially expressed LncRNAs.We found an unknown function LncRNA Inc-217.Lnc-217 expression level was increased significantly in the liver of high-fat-diet mice as well as in ob/ob and db/db mice.Using rapid-amplification of cDNA ends technology to amplify the full-length of this LncRNA,we proved that lnc-217 is located in chromosome 7 of mice,and could not be translated to produce protein.To investigate the role of lnc-217 in the development of NAFLD,we knockdown lnc-217 in liver of mice by tail vein injection with Ad-shlnc-217.The hepatic triglyceride level was significantly decreased in lnc-217 knockdown mice compared with mice injected with Ad-shcon,meanwhile,the blood triglyceride and free fatty acid level were significantly decreased in thoese mice.These results indicated that lnc-217 affect lipid metabolism,indeed.In addition,the lipogenic gene expression levels such as SREBP-1c?Fas?Acc were significantly decreased but expression level of genes involved in fatty acid oxidation pathway such as Ppara?Cpt-la were significantly increased in liver with knockdown of lnc-217.The results of in vitro studies in hepatocytes with knockdown lnc-217 were consistent with in vivo study.Collectively,we identified a new long noncoding RNA lnc-217 which was mainly located in the nucleus of the mouse liver.The expression level of lnc-217 were increased in the liver of high fat diet induced fatty liver and obese mice.Knockdown lnc-217 protected HFD induced triglyceride accumulation via increased hepatic fatty acid ?-oxidation and reduced fatty acid synthesis.Taken together,lnc-217 plays important role in the pathological process of NAFLD and investigate the mechanism of lnc-217 in regulating lipid metabolism in liver will provide a new insight for the novel therapeutic target development of NAFLD.