title: Pharmacological preconditioning with tumor necrosis factor-alpha activates signal transducer and activator of transcription-3 at reperfusion without involving classic prosurvival kinases (Akt and extracellular signal-regulated kinase).
abstract: BACKGROUND
  We previously reported that tumor necrosis-factor-alpha (TNF-alpha) can mimic classic ischemic preconditioning (IPC) in a dose- and time-dependent manner. Because TNF-alpha activates the signal transducer and activator of transcription-3 (STAT-3), we hypothesized that TNF-alpha-induced preconditioning requires phosphorylation of STAT-3 rather than involving the classic prosurvival kinases, Akt and extracellular signal-regulated kinase (Erk) 1/2, during early reperfusion.
  
  
  RESULTS
  Isolated, ischemic/reperfused rat hearts were preconditioned by either IPC or low-dose TNF-alpha (0.5 ng/mL). Western blot analysis confirmed that IPC phosphorylated Akt and Erk 1/2 after 5 minutes of reperfusion (Akt increased by 34+/-6% and Erk, by 105+/-28% versus control; P<0.01). Phosphatidylinositol 3-kinase/Akt inhibition (wortmannin) or mitogen-activated protein kinase-Erk 1/2 kinase inhibition (PD-98059) during early reperfusion abolished the infarct-sparing effect of IPC. In contrast, TNF-alpha preconditioning did not phosphorylate these kinases (Akt increased by 7+/-7% and Erk, by 17+/-14% versus control; P=NS). Neither wortmannin nor PD-98059 inhibited TNF-alpha-mediated cardioprotection. However, TNF-alpha and IPC both phosphorylated STAT-3 and the proapoptotic protein Bcl-2 antagonist of cell death (BAD) (STAT-3 increased by 58+/-17% with TNF-alpha or by 68+/-12% with IPC; BAD increased by 75+/-8% with TNF-alpha or by 205+/-20% with IPC; P<0.01 versus control), thereby activating the former and inactivating the latter. The STAT-3 inhibitor AG 490 abolished cardioprotection and BAD phosphorylation with both preconditioning stimuli.
  
  
  CONCLUSIONS
  Activation of the classic prosurvival kinases (Akt and Erk 1/2) is not essential for TNF-alpha-induced preconditioning in the early reperfusion phase. We show the existence of an alternative protective pathway that involves STAT-3 activation specifically at reperfusion in response to both TNF-alpha and classic IPC. This novel prosurvival pathway may have potential therapeutic significance.
authors.affiliation: Department of Medicine, Hatter Institute for Cardiology Research, Cape Heart Centre, Faculty of Health Sciences, University of Cape Town, South Africa. Sandrine@capeheart.uct.ac.za
authors.forename: Sandrine
authors.initials: S
authors.lastname: Lecour
authors.forename: Naushaad
authors.initials: N
authors.lastname: Suleman
authors.forename: Graeme A
authors.initials: GA
authors.lastname: Deuchar
authors.forename: Sarin
authors.initials: S
authors.lastname: Somers
authors.forename: Lydia
authors.initials: L
authors.lastname: Lacerda
authors.forename: Barbara
authors.initials: B
authors.lastname: Huisamen
authors.forename: Lionel H
authors.initials: LH
authors.lastname: Opie
mesh_terms: D000818:Animals; D002316:Cardiotonic Agents / Q000494:pharmacology; D002470:Cell Survival; D066298:In Vitro Techniques; D019157:Ischemic Preconditioning, Myocardial / Q000379:methods*; D008297:Male; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D009203:Myocardial Infarction / Q000517:prevention & control; D015425:Myocardial Reperfusion; D010766:Phosphorylation / Q000187:drug effects; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D050796:STAT3 Transcription Factor / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology / Q000627:therapeutic use*
chemical_list: D002316:Cardiotonic Agents; D050796:STAT3 Transcription Factor; C494088:Stat3 protein, rat; D014409:Tumor Necrosis Factor-alpha; D051057:Proto-Oncogene Proteins c-akt; D048052:Mitogen-Activated Protein Kinase 3