Senescence-associated cell death of human endothelial cells: the role of oxidative stress.

Replicative senescence of human endothelial cells was analyzed, using primary endothelial cells from the human umbilical vein endothelial cells (HUVEC) as an experimental model system. We had shown before that senescent HUVEC arrest in the G1 phase of the cell cycle and that a subpopulation of the senescent cells undergoes cell death. We now demonstrate that cell death occurs by apoptosis, characterized by activation of caspase 3. Using the redox-sensitive dye dihydrorhodamine 123, a significant accumulation of reactive oxygen species is detected in senescent but not young endothelial cells. To determine if increased oxidative stress may contribute to the senescent phenotype, cells were treated with tert-butyl hydroperoxide (tBHP), which is known to increase oxidative stress by decreasing the intracellular glutathione levels. We show here that mild tBHP stress induces a phenotype of premature senescence in a subpopulation of the treated cells, which closely resembles the phenotype of naturally senescent HUVEC, including growth arrest, senescence-associated beta-gal activity, and apoptotic cell death. These results establish a model of premature senescence for human endothelial cells, which will be suitable to analyze mechanisms of age-associated cell death.