Nuclear factor-kappaB represses hypoxia-induced mitochondrial defects and cell death of ventricular myocytes

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.

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.

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.