title: Farnesoid X receptor protects hepatocytes from injury by repressing miR-199a-3p, which increases levels of LKB1.
abstract: OBJECTIVE
  Hepatocyte injury occurs during liver fibrogenesis. MicroRNAs (miRNA) regulate some of these processes, and some are regulated by the farnesoid X receptor (FXR). We investigated the effect of repression of specific miRNAs by FXR in hepatocyte injury using fibrotic liver tissue from patients and hepatocytes.
  
  
  METHODS
  We used immunohistochemistry or real-time polymerase chain reaction to analyze proteins and miRNAs in human and mouse liver samples. HepG2 cells were transfected with pre-miRNA, antisense oligonucleotides, small interfering RNAs, the 3'-untranslated region of liver kinase B1 (LKB1) (STK11), or constructs for overexpression, and analyzed.
  
  
  RESULTS
  Liver tissue from patients with severe fibrosis had lower levels of FXR and greater amounts of hepatocyte death than samples from patients with mild disease. Levels of several miRNAs changed when FXR expression was disrupted in the liver; one of these, miR-199a-3p, was significantly up-regulated in patients with severe fibrosis. Activation of FXR by its ligand reduced the level of miR-199a-3p in HepG2 cells. LKB1 messenger RNA was identified as a target of miR-199a-3p, and its expression was reduced in human fibrotic liver tissue. Overexpression of FXR or incubation of cultured hepatocytes with the FXR ligand up-regulated LKB1; LKB1 was not induced in cells transfected with miR-199a-3p. Incubation of HepG2 cells with FXR ligand, or injection of the ligand into mice, protected hepatocytes from injury and increased levels of LKB1; levels of miR-199a-3p were reduced compared with cells that were not incubated with the FXR ligand. Activation of FXR reduced mitochondrial dysfunction and oxidative stress and increased hepatocyte survival.
  
  
  CONCLUSIONS
  In hepatocytes, FXR represses production of miR-199a-3p. In fibrotic livers of humans and mice, FXR expression is reduced, increasing levels of miR-199a-3p, which reduces levels of LKB1. FXR therefore protects hepatocytes from injury by repressing miR-199a-3p and thereby increasing levels of LKB1.
authors.affiliation: College of Pharmacy and Research Institute of Pharmaceutical Sciences, Seoul National University, Seoul, Korea.
authors.forename: Chan Gyu
authors.initials: CG
authors.lastname: Lee
authors.forename: Young Woo
authors.initials: YW
authors.lastname: Kim
authors.forename: Eun Hyun
authors.initials: EH
authors.lastname: Kim
authors.forename: Zhipeng
authors.initials: Z
authors.lastname: Meng
authors.forename: Wendong
authors.initials: W
authors.lastname: Huang
authors.forename: Se Jin
authors.initials: SJ
authors.lastname: Hwang
authors.forename: Sang Geon
authors.initials: SG
authors.lastname: Kim
mesh_terms: D000091162:AMP-Activated Protein Kinase Kinases; D055372:AMP-Activated Protein Kinases / Q000502:physiology; D019610:Cytoprotection; D056945:Hep G2 Cells; D022781:Hepatocytes / Q000378:metabolism*; D006801:Humans; D035683:MicroRNAs / Q000037:antagonists & inhibitors* / Q000502:physiology; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000502:physiology*; D012333:RNA, Messenger / Q000032:analysis; D018160:Receptors, Cytoplasmic and Nuclear / Q000502:physiology*; D012097:Repressor Proteins / Q000502:physiology*; D000099150:Receptor, Farnesoid X-Activated
chemical_list: D000091162:AMP-Activated Protein Kinase Kinases; D055372:AMP-Activated Protein Kinases; D035683:MicroRNAs; D017346:Protein Serine-Threonine Kinases; D012333:RNA, Messenger; D018160:Receptors, Cytoplasmic and Nuclear; D012097:Repressor Proteins; D000099150:Receptor, Farnesoid X-Activated; C531408:mirn199 microRNA, human; C109790:STK11 protein, human