title: Endoplasmic Reticulum Stress in Hepatic Stellate Cells Promotes Liver Fibrosis via PERK-Mediated Degradation of HNRNPA1 and Up-regulation of SMAD2.
abstract: OBJECTIVE
  Endoplasmic reticulum (ER) stress has been implicated in a variety of diseases. Hepatic stellate cells (HSCs) contribute to the development of liver fibrosis. Information on the link between ER stress and HSC activation is scarce. We investigated the effects of ER stress in HSCs on the progression of liver fibrosis and the regulation of this process in cells and mice.
  
  
  METHODS
  Proteins and messenger RNAs were measured in 2 sets of liver samples (n = 25 and n = 44) collected from patients with chronic hepatitis C virus infection and/or fibrosis. ER stress was induced in cells and mice using chemical agents. Lentiviral vectors were constructed to express glucose-regulated protein 78 (GRP78; also known as HSPA5) or heterogeneous nuclear ribonucleoprotein A1 (HNRNPA1) from the α-smooth muscle actin promoter and injected into C57BL/6 mice for HSC-specific gene expression. Liver tissues and HSCs were collected from mice or rats and analyzed using immunoblottings and quantitative reverse-transcription polymerase chain reaction. LX-2 cells were transfected with small interfering RNAs, microRNA mimics, or overexpression vectors.
  
  
  RESULTS
  Hepatic ER stress was much higher in liver tissues from patients with severe vs mild fibrosis. ER stress induced fibrogenic genes in HSCs. Targeted lentiviral delivery of glucose-regulated protein 78 to HSCs in mice reduced fiber accumulation in liver. Levels of SMAD2, but not SMAD3, were increased in fibrotic liver tissues from patients or mice exposed to ER stress; small interfering RNA-mediated knockdown of SMAD2 reduced ER stress-mediated activation of HSCs. In rat HSCs, ER stress increased levels of SMAD2 messenger RNA by decreasing levels of microRNA 18a (MIR18A), an inhibitor of SMAD2 expression, rather than transactivating the SMAD2 gene. ER stress-activated PKR-like endoplasmic reticulum kinase, also known as EIF2AK3 (PERK) phosphorylated HNRNPA1, a protein required for the maturational processing of primary MIR18A, at Thr51, accelerating its degradation. Overexpression of HNRNPA1 (or its T51A mutant) in HSCs of mice inhibited liver fibrosis. Severe fibrotic liver tissues from patients had increased levels of phosphorylated PERK and reduced levels of HNRNPA1 in HSCs, compared with mild fibrotic liver tissues.
  
  
  CONCLUSIONS
  ER stress in HSCs promotes liver fibrosis by inducing overexpression of SMAD2, via dysregulation of MIR18A; this dysregulation is mediated by PERK phosphorylation and destabilization of HNRNPA1.
authors.affiliation: College of Pharmacy and Research Institute of Pharmaceutical Sciences, Seoul National University, Seoul, Korea.
authors.forename: Ja Hyun
authors.initials: JH
authors.lastname: Koo
authors.affiliation: College of Pharmacy and Research Institute of Pharmaceutical Sciences, Seoul National University, Seoul, Korea.
authors.forename: Hyo Ju
authors.initials: HJ
authors.lastname: Lee
authors.affiliation: Department of Internal Medicine, Seoul Metropolitan Government Seoul National University Boramae Medical Center, Seoul, Korea.
authors.forename: Won
authors.initials: W
authors.lastname: Kim
authors.affiliation: College of Pharmacy and Research Institute of Pharmaceutical Sciences, Seoul National University, Seoul, Korea. Electronic address: sgk@snu.ac.kr.
authors.forename: Sang Geon
authors.initials: SG
authors.lastname: Kim
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000235:genetics; D002478:Cells, Cultured; D004195:Disease Models, Animal; D000091342:Endoplasmic Reticulum Chaperone BiP; D059865:Endoplasmic Reticulum Stress / Q000235:genetics*; D055166:Hepatic Stellate Cells / Q000378:metabolism; D000076245:Heterogeneous Nuclear Ribonucleoprotein A1; D034481:Heterogeneous-Nuclear Ribonucleoprotein Group A-B / Q000378:metabolism; D006801:Humans; D008103:Liver Cirrhosis / Q000378:metabolism / Q000473:pathology* / Q000503:physiopathology; D051379:Mice; D008810:Mice, Inbred C57BL; D010766:Phosphorylation / Q000235:genetics; D051381:Rats; D012680:Sensitivity and Specificity; D051899:Smad2 Protein / Q000235:genetics*; D014415:Tunicamycin / Q000494:pharmacology; D015854:Up-Regulation; D019892:eIF-2 Kinase / Q000378:metabolism*
chemical_list: D000091342:Endoplasmic Reticulum Chaperone BiP; D000076245:Heterogeneous Nuclear Ribonucleoprotein A1; D034481:Heterogeneous-Nuclear Ribonucleoprotein Group A-B; D051899:Smad2 Protein; D014415:Tunicamycin; D019892:eIF-2 Kinase; C000717247:HSPA5 protein, human; C000619657:Hnrnpa1 protein, mouse; C000619658:Hnrnpa1 protein, rat; C000717248:Hspa5 protein, mouse; C497783:Smad2 protein, mouse; C000619656:hnRNPA1 protein, human
keywords: ER Stress; HSC Activation; miR-18a