Nuclear factor-kappaB represses hypoxia-induced mitochondrial defects and cell death of ventricular myocytes.
BACKGROUND
Oxygen deprivation for prolonged periods of time provokes cardiac cell death and ventricular dysfunction. Preventing inappropriate cardiac cell death in patients with ischemic heart disease would be of significant therapeutic value as a means to improve ventricular performance. In the present study, we wished to ascertain whether activation of the cellular factor nuclear factor (NF)-kappaB suppresses mitochondrial defects and cell death of ventricular myocytes during hypoxic injury.


RESULTS
In contrast to normoxic control cells, ventricular myocytes subjected to hypoxia displayed a 9.1-fold increase (P<0.05) in cell death, as determined by Hoechst 33258 nuclear staining and vital dyes. Mitochondrial defects consistent with permeability transition pore opening, loss of mitochondrial membrane potential (DeltaPsim), and Smac release were observed in cells subjected to hypoxia. An increase in postmitochondrial caspase 9 and caspase 3 activity was observed in hypoxic myocytes. Adenovirus-mediated delivery of wild-type IKKbeta (IKKbetawt) resulted in a significant increase in NF-kappaB-dependent DNA binding and gene transcription in ventricular myocytes. Interestingly, subcellular fractionation of myocytes revealed that the p65 subunit of NF-kappaB was localized to mitochondria. Hypoxia-induced mitochondrial defects and cell death were suppressed in cells expressing IKKbetawt but not in cells expressing the kinase-defective IKKbeta mutant.


CONCLUSIONS
To the best of our knowledge, the data provide the first direct evidence that activation of the NF-kappaB signaling pathways is sufficient to suppress cell death of ventricular myocytes during hypoxia. Moreover, our data further suggest that NF-kappaB averts cell death through a mechanism that prevents perturbations to the mitochondrion during hypoxic injury.
Regula
Kelly M
KM
Institute of Cardiovascular Sciences, St Boniface General Hospital Research Centre, Department of Physiology, Faculty of Medicine University of Manitoba, Winnipeg, Manitoba, Canada.
Baetz
Delphine
D
Kirshenbaum
Lorrie A
LA
D000818:Animals; D017209:Apoptosis; D053148:Caspase 3; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism; D015687:Cell Hypoxia; D002467:Cell Nucleus / Q000737:chemistry; D002478:Cells, Cultured; D004247:DNA / Q000378:metabolism; D005786:Gene Expression Regulation / Q000502:physiology; D006352:Heart Ventricles / Q000166:cytology; D051550:I-kappa B Kinase; D020672:I-kappa B Proteins / Q000378:metabolism; D007425:Intracellular Membranes / Q000502:physiology; D007473:Ion Channels / Q000378:metabolism; D008564:Membrane Potentials / Q000502:physiology; D008929:Mitochondria, Heart / Q000378:metabolism* / Q000473:pathology; D033681:Mitochondrial Membrane Transport Proteins; D000083162:Mitochondrial Permeability Transition Pore; D032383:Myocytes, Cardiac / Q000378:metabolism*; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000502:physiology*; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011993:Recombinant Fusion Proteins / Q000502:physiology; D015398:Signal Transduction; D014158:Transcription, Genetic / Q000502:physiology; D014161:Transduction, Genetic
D020672:I-kappa B Proteins; D007473:Ion Channels; D033681:Mitochondrial Membrane Transport Proteins; D000083162:Mitochondrial Permeability Transition Pore; D016328:NF-kappa B; C000606206:Nfkbia protein, rat; D011993:Recombinant Fusion Proteins; D000072000:NF-KappaB Inhibitor alpha; D004247:DNA; D017346:Protein Serine-Threonine Kinases; D051550:I-kappa B Kinase; C505410:Casp3 protein, rat; C506435:Casp9 protein, rat; D053148:Caspase 3; D053453:Caspase 9; D020169:Caspases