Hypoxia-Induced Endothelial Apoptosis Through Nuclear Factor-κB (NF-κB)–Mediated bcl-2 Suppression

Abstract

Abstract —The transcription factor nuclear factor-κB (NF-κB) plays a pivotal role in the coordinated transactivation of cytokine and adhesion molecule genes involved in endothelial activation. Although recent reports have documented the contribution of NF-κB to apoptosis, it is still controversial. Especially, the role of NF-κB in endothelial apoptosis is largely unknown. Hypoxia significantly induced human aortic endothelial cell death and apoptosis in a time-dependent manner ( P <0.01), accompanied by NF-κB activation. Decrease in total cell number and increase in apoptotic cells induced by hypoxia were significantly attenuated by NF-κB decoy, but not by scrambled decoy, oligodeoxynucleotides (ODNs) ( P <0.01). Increase in DNA fragmentation induced by hypoxia was also significantly inhibited by NF-κB decoy ODNs as compared with scrambled decoy ODNs ( P <0.01). Moreover, transfection of NF-κB decoy ODNs resulted in a significant decrease in caspase-3–like activity, which is a common pathway for apoptosis, compared with scrambled decoy ODNs. Importantly, transfection of NF-κB decoy ODNs significantly increased protein of bcl-2, an inhibitor of apoptosis, and did not alter bax, a promoter of apoptosis, thereby resulting in a significant increase in the ratio of bcl-2 to bax ( P <0.01). bcl-2 mRNA was also decreased by hypoxia, whereas transfection of NF-κB decoy ODNs significantly attenuated decrease in bcl-2 mRNA. These results demonstrate that activation of NF-κB by hypoxia induced endothelial apoptosis in a bcl-2–dependent manner. The importance of NF-κB in endothelial apoptosis was confirmed by the observation that pyrrolidine dithiocarbamate, a potent NF-κB inhibitor, prevented endothelial apoptosis, caspase 3–like activity, and bcl-2 downregulation induced by hypoxia. To test this hypothesis in vivo, we transfected NF-κB decoy ODNs into rat intact carotid artery after reperfusion injury. Reperfusion injury was associated with a significant increase in endothelial apoptosis at 24 hours, whereas NF-κB decoy ODN treatment markedly decreased terminal deoxynucleotidyltransferase–mediated dUTP nick end labeling (TUNEL)–positive endothelial cells at 24 hours after reperfusion ( P <0.01). Here, using synthetic double-stranded DNA with high affinity for NF-κB as a decoy approach, we demonstrated that activation of NF-κB by hypoxia caused aortic endothelial cell death and apoptosis through the suppression of bcl-2. NF-κB–mediated endothelial apoptosis induced by hypoxia may be involved in the pathogenesis of endothelial dysfunction observed in cardiovascular ischemic diseases.