title: Extracellular heat shock protein 70 induces cardiomyocyte inflammation and contractile dysfunction via TLR2.
abstract: BACKGROUND
  Toll-like receptors (TLRs) are expressed on cardiomyocytes and recognize pathogen-associated molecular patterns. Whether endogenous molecules produced by tissue injury (damage associated molecular patterns, DAMPs) can induce cardiomyocyte inflammation via TLR signalling pathways and/or reduce cardiomyocyte contractility is unknown.
  
  
  RESULTS
  Primary cardiomyocytes isolated from nuclear factor κ B (NFκB)-luciferase knock-in mice were used to assess NFκB signalling. DAMPs, HSP60, HSP70 and HMGB1, increased NFκB transcriptional activity compared to controls. HSP70 stood out compared to other DAMPs and even lipopolysaccharide (LPS). Subsequent experiments focused on HSP70. Cardiomyocytes exposed to HSP70 had a 58% decrease in contractility without a decrease in calcium flux. Exposure of cultured HL-1 cardiomyocytes to HSP70 resulted in increased expression of intercellular adhesion molecule 1 (ICAM-1), interleukin 6 (IL-6) and keratinocyte-derived chemokine (KC) compared to controls. Knock-out mice for TLR2, TLR4 and MyD88, plus background strain controls (C57BL/6) were used to assess induction of cardiomyocyte inflammation by HSP70. The cardiomyocyte expression of ICAM-1 induced by HSP70 was significantly reduced in TLR2 and MyD88 knock-out mice but not TLR4 knock-out mice; implicating the TLR2 signalling pathway. Furthermore, blocking antibodies to TLR2 were able to abrogate HSP70-induced contractile dysfunction and cell death.
  
  
  CONCLUSIONS
  Extracellular HSP70 acting via TLR2 and its obligate downstream adaptor molecule, MyD88, activate NFκB. This causes cardiomyocyte inflammation and decreased contractility.
authors.affiliation: Critical Care Research Laboratories, Heart+Lung Institute at St. Paul's Hospital, University of British Columbia, Canada.
authors.forename: Sumeet
authors.initials: S
authors.lastname: Mathur
authors.forename: Keith R
authors.initials: KR
authors.lastname: Walley
authors.forename: Yingjin
authors.initials: Y
authors.lastname: Wang
authors.forename: Toonchai
authors.initials: T
authors.lastname: Indrambarya
authors.forename: John H
authors.initials: JH
authors.lastname: Boyd
mesh_terms: D000818:Animals; D018840:HSP70 Heat-Shock Proteins / Q000502:physiology*; D018799:Intercellular Adhesion Molecule-1 / Q000235:genetics; D051379:Mice; D018345:Mice, Knockout; D053594:Myeloid Differentiation Factor 88 / Q000378:metabolism; D009200:Myocardial Contraction; D032383:Myocytes, Cardiac / Q000473:pathology*; D016328:NF-kappa B / Q000378:metabolism; D015398:Signal Transduction; D051195:Toll-Like Receptor 2 / Q000378:metabolism / Q000502:physiology*; D015533:Transcriptional Activation
chemical_list: D018840:HSP70 Heat-Shock Proteins; C507780:Myd88 protein, mouse; D053594:Myeloid Differentiation Factor 88; D016328:NF-kappa B; C493486:Tlr2 protein, mouse; D051195:Toll-Like Receptor 2; D018799:Intercellular Adhesion Molecule-1