The roles of CLEC18 in liver fibrosis and steatohepatitis

• Main Authors: Yi Cheng, 程奕
• Other Authors: Wan-Wan Lin
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/x57yzf

碩士 === 國立臺灣大學 === 藥理學研究所 === 106 === CLEC18 family is a novel polymorphic C-type lectin (CLEC) containing the conserved C-type lectin-like domain (CTLD) and the sperm-coating protein (SCP)/Tpx-1/Ag5/PR-1/Sc7 (TAPS) domain, also known as the cysteine-rich secretory proteins/antigen 5/pathogenesis-related 1 proteins (CAP) domain. In general, CTLD and SCP domain recognize glycans and lipids/sterols, respectively, and exert the ligand binding functions of CLRs. Human C-type lectin 18 (clec18) gene cluster contains clec18a, clec18b and clec18c three loci and is located in human chromosome 16q22. Structurally CLEC18A contains three amino acid residues distinct from CLEC18A-1: Val(118)→Ala(118) and Thr(151)→Met(151) in SCP domain and Ser(339)→Arg(339) in CTLD. Unlike human CLEC18A which is ubiquitously expressed, mouse CELC18A is only expressed in the brain, heart, and kidney. Until now the biological functions of CLEC18s are not investigated until a recent study demonstrated that the S339R339 mutation in CTLD leads to the differential binding affinities of CLEC18A/A-1 to various types of glycans. Since liver fibrosis and steatohepatitis are two major causes of the hepatocellular carcinoma development, here we used hCLEC18A knock-in (KI) and hCLEC18A-1 KI mice to evaluate the roles of CLEC18 in liver fibrosis and steatohepatitis. In the first part of this thesis, we applied the bile duct ligation (BDL) surgery to evaluate the roles of CLEC18A/18A-1 in liver fibrosis. We found that CLEC18A KI and CLEC18A-1 KI ameliorated BDL-induced liver fibrosis (i.e. collagen deposition and bile duct hyperplasia), clinical manifestation (i.e. increased serum levels of cholesterol, AST, ALT, and bilirubin), and mice death. In the liver lysates of operated mice, protein and/or gene expressions of fibrosis markers -SMA, collagen 1A1, periostin, CTGF, vimentin, elastin and PDGFR were alleviated in CLEC18A/18A-1 KI mice compared with WT mice. In addition, silence of the CLEC18A in human LX2 hepatic stellate cell (HSC) line resulted in more severe PDGF-BB- and TGF-induced HSC activation, including cell migration and fibrosis markers expressions. In the second part of this thesis, we utilized both methionine choline-deficient (MCD) and high fat diet (HFD) models to elucidate the roles of CLEC18A/18A-1 in hepatosteatosis. In normal diet situation, the CLEC18A-1 KI mice exhibited lower serum T-Cho, TG, and LDL level compared with WT mice. After the MCD treatment, CLEC18A-1 KI but not CLEC18A KI mice exhibited more severe MCD-induced fatty change score in liver. In addition, CLEC18A-1 KI induced higher expressions of lipogenic hepatic nuclear receptor ChREBP, its target gene MTTP and ER lipogenic enzymes HMGCR and SOAT. Except for the MCD treatment, CLEC18A-1 KI mice exhibited more severe microvascular fatty changes in livers after HFD treatment. Furthermore, increased insulin resistance and glucose intolerance as well as decreased expression of lipolytic PPAR gene expression in liver were found in CLEC18A-1 KI mice after HFD treatment. In conclusion, CLEC18A and CLEC18A-1 play protective roles in the progression of liver fibrosis, which might result from the inhibition of PDGF- and TGF-induced HSC activation. Nevertheless, CLEC18A-1 might also exhibit a more significant action than CLEC18A in the development of liver steatosis.