In vitro senescence occurring in normal human endothelial cells can be rescued by ectopic telomerase activity

Telomerase activation is a means to delay in vitro replicative senescence in human cells via telomere maintainence; however, this enzymatic activity is virtually absent in almost all normal somatic cells. As a result, cell senesce, leading to an eventual loss of graft function. Aging allografts, either due to cell injury related to transplantation and/or the use of organs from older donors, pose a threat to the long-term survival of a graft as constitutive cells of an aging organ have a much reduced ability to thrive after transplantation. In our study, human endothelial cells were found to undergo replicative senescence in culture with an increase in the percentage of senescent cells (beta-gal staining at pH 6) and a decrease in both the fraction of S-phase cycling cells and the proliferative index measured using CFDA-SE dye. Aging endothelial cells also demonstrated slow rates of proliferation and migration compared to younger cells. Unlike control cells that were transfected with an irrelevant gene vector, telomerase-transfected endothelial cells recovered rapidly after media replacement in cultures that had been serum starved for 2 weeks. Telomerase-transfected cells also retained a high proliferative index comparable to young cells as opposed to untransfected control cells. This young phenotype provided by telomerase expression through restoration of the telomeres may help to increase the longevity of organ transplants.