Mechanisms of hypoxia-induced endothelial cell death - Role of p53 in apoptosis

Endothelial cell death may contribute to tissue injury from ischemia, Littl e is known, however, about the characteristics of endothelial cell death in response to hypoxia. Using an in vitro model, we found that human umbilica l vein endothelial cells were resistant to hypoxia-induced cell death with only a 2% reduction in viability at 24 h and 45% reduction in viability at 48 h. Overexpression of a mutant, I kappa B alpha, via adenoviral vector di d not potentiate cell death in hypoxia, indicating that nuclear factor-kapp a B activation was not involved in cytoprotection. Cell death in hypoxia wa s determined to be apoptotic by 3' labeling of DNA using terminal deoxynucl eotidyl transferase staining and reversibility of cell death with a caspase inhibitor. Exposure of endothelial cells to hypoxia did not alter levels o f proapoptotic and antiapoptotic Bcl-2 family members Bar and Bcl-X-L by im munoblot analysis. In contrast, changes in p53 protein levels correlated wi th the induction of apoptosis in hypoxic endothelial cells. Inhibition of t he proteasome increased p53 protein levels and accelerated cell death in hy poxia. Overexpression of p53 by adenoviral transduction was sufficient to i nitiate apoptosis of normoxic endothelial cells. These data provide a frame work for the study of factors regulating endothelial cell survival and deat h in hypoxia.