title: The induction of microRNA targeting IRS-1 is involved in the development of insulin resistance under conditions of mitochondrial dysfunction in hepatocytes.
abstract: BACKGROUND
  Mitochondrial dysfunction induces insulin resistance in myocytes via a reduction of insulin receptor substrate-1 (IRS-1) expression. However, the effect of mitochondrial dysfunction on insulin sensitivity is not understood well in hepatocytes. Although research has implicated the translational repression of target genes by endogenous non-coding microRNAs (miRNA) in the pathogenesis of various diseases, the identity and role of the miRNAs that are involved in the development of insulin resistance also remain largely unknown.
  
  
  METHODS
  To determine whether mitochondrial dysfunction induced by genetic or metabolic inhibition causes insulin resistance in hepatocytes, we analyzed the expression and insulin-stimulated phosphorylation of insulin signaling intermediates in SK-Hep1 hepatocytes. We used qRT-PCR to measure cellular levels of selected miRNAs that are thought to target IRS-1 3' untranslated regions (3'UTR). Using overexpression of miR-126, we determined whether IRS-1-targeting miRNA causes insulin resistance in hepatocytes.
  
  
  RESULTS
  Mitochondrial dysfunction resulting from genetic (mitochondrial DNA depletion) or metabolic inhibition (Rotenone or Antimycin A) induced insulin resistance in hepatocytes via a reduction in the expression of IRS-1 protein. In addition, we observed a significant up-regulation of several miRNAs presumed to target IRS-1 3'UTR in hepatocytes with mitochondrial dysfunction. Using reporter gene assay we confirmed that miR-126 directly targeted to IRS-1 3'UTR. Furthermore, the overexpression of miR-126 in hepatocytes caused a substantial reduction in IRS-1 protein expression, and a consequent impairment in insulin signaling.
  
  
  CONCLUSIONS
  We demonstrated that miR-126 was actively involved in the development of insulin resistance induced by mitochondrial dysfunction. These data provide novel insights into the molecular basis of insulin resistance, and implicate miRNA in the development of metabolic disease.
authors.affiliation: Department of Biochemistry, Dongguk University College of Medicine, Kyungju, Korea.
authors.forename: Hyun Su
authors.initials: HS
authors.lastname: Ryu
authors.forename: Seung-Yoon
authors.initials: SY
authors.lastname: Park
authors.forename: Duan
authors.initials: D
authors.lastname: Ma
authors.forename: Jin
authors.initials: J
authors.lastname: Zhang
authors.forename: Wan
authors.initials: W
authors.lastname: Lee
mesh_terms: D020413:3' Untranslated Regions / Q000235:genetics; D001483:Base Sequence; D004272:DNA, Mitochondrial / Q000235:genetics; D004996:Ethidium / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology*; D006801:Humans; D055504:Insulin Receptor Substrate Proteins / Q000235:genetics / Q000378:metabolism*; D007333:Insulin Resistance / Q000235:genetics*; D035683:MicroRNAs / Q000235:genetics / Q000378:metabolism*; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism / Q000473:pathology*; D008969:Molecular Sequence Data; D011485:Protein Binding / Q000187:drug effects; D015398:Signal Transduction / Q000187:drug effects; D014158:Transcription, Genetic / Q000187:drug effects
chemical_list: D020413:3' Untranslated Regions; D004272:DNA, Mitochondrial; D055504:Insulin Receptor Substrate Proteins; C527111:MIRN126 microRNA, human; D035683:MicroRNAs; D004996:Ethidium