title: Toll-like receptor 4 signaling confers cardiac protection against ischemic injury via inducible nitric oxide synthase- and soluble guanylate cyclase-dependent mechanisms.
abstract: BACKGROUND
  Prior administration of a small dose of lipopolysaccharide confers a cardiac protection against ischemia-reperfusion injury. However, the signaling mechanisms that control the protection are incompletely understood. We tested the hypothesis that Toll-like receptor 4 (TLR4) mediates the ability of lipopolysaccharide to protect against cardiac ischemia-reperfusion injury through distinct intracellular pathways involving myeloid differentiation factor 88 (MyD88), TIR-domain-containing adaptor protein-inducing interferon-β-mediated transcription factor (Trif), inducible nitric oxide synthase (iNOS), and soluble guanylate cyclase (sGC).
  
  
  METHODS
  Wild-type mice and genetically modified mice, that is TLR4-deficient (TLR4(-def)), TLR2 knockout (TLR2(-/-)), MyD88(-/-), Trif(-/-), iNOS(-/-), and sGCα1(-/-), were treated with normal saline or 0.1 mg/kg lipopolysaccharide intraperitoneally. Twenty-four hours later, isolated hearts were perfused in a Langendorff apparatus and subsequently subjected to 30 min global ischemia and reperfusion for as long as 60 min. Left ventricular function and myocardial infarction sizes were examined.
  
  
  RESULTS
  Compared with saline-treated mice, lipopolysaccharide-treated mice had markedly improved left ventricular developed pressure and dP/dt(max) (P < 0.01) and reduced myocardial infarction sizes (37.2 ± 3.4% vs. 19.8 ± 4.9%, P < 0.01) after ischemia-reperfusion. The cardiac protective effect of lipopolysaccharide was abolished in the TLR4(-def) and MyD88(-/-) mice but remained intact in TLR2(-/-) or Trif(-/-) mice. iNOS(-/-) mice or wild-type mice treated with the iNOS inhibitor 1400W failed to respond to the TLR4-induced nitric oxide production and were not protected by the lipopolysaccharide preconditioning. Although sGCα(1)(-/-) mice had robust nitric oxide production in response to lipopolysaccharide, they were not protected by the TLR4-elicited cardiac protection.
  
  
  CONCLUSIONS
  TLR4 activation confers a potent cardiac protection against ischemia-reperfusion injury via a MyD88-dependent, but Trif-independent, mechanism. iNOS/sGC are essential for the TLR4-induced cardiac protection.
authors.affiliation: Anesthesia Center for Critical Care Research, Department of Anesthesia & Critical Care, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts 02114, USA.
authors.forename: E
authors.initials: E
authors.lastname: Wang
authors.forename: Yan
authors.initials: Y
authors.lastname: Feng
authors.forename: Ming
authors.initials: M
authors.lastname: Zhang
authors.forename: Lin
authors.initials: L
authors.lastname: Zou
authors.forename: Yan
authors.initials: Y
authors.lastname: Li
authors.forename: Emmanuel S
authors.initials: ES
authors.lastname: Buys
authors.forename: Peigen
authors.initials: P
authors.lastname: Huang
authors.forename: Peter
authors.initials: P
authors.lastname: Brouckaert
authors.forename: Wei
authors.initials: W
authors.lastname: Chao
mesh_terms: D033942:Adaptor Proteins, Vesicular Transport / Q000235:genetics / Q000502:physiology; D000818:Animals; D004452:Echocardiography; D004562:Electrocardiography / Q000187:drug effects; D006162:Guanylate Cyclase / Q000502:physiology*; D008070:Lipopolysaccharides / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D053594:Myeloid Differentiation Factor 88 / Q000235:genetics / Q000502:physiology; D009203:Myocardial Infarction / Q000473:pathology; D017202:Myocardial Ischemia / Q000517:prevention & control*; D015428:Myocardial Reperfusion Injury / Q000473:pathology; D009566:Nitrates / Q000097:blood; D052247:Nitric Oxide Synthase Type II / Q000235:genetics / Q000502:physiology*; D009573:Nitrites / Q000097:blood; D015398:Signal Transduction / Q000502:physiology*; D051197:Toll-Like Receptor 4 / Q000502:physiology*
chemical_list: D033942:Adaptor Proteins, Vesicular Transport; D008070:Lipopolysaccharides; C507779:MYD88 protein, human; D053594:Myeloid Differentiation Factor 88; D009566:Nitrates; D009573:Nitrites; C470409:TICAM1 protein, human; D051197:Toll-Like Receptor 4; D052247:Nitric Oxide Synthase Type II; D006162:Guanylate Cyclase