A cell kinetic analysis of human umbilical vein endothelial cells

Cultures of normal human cells 'age' and become senescent in vitro due to a continuously declining mitotic fraction. Although endothelial cells repres ent a tissue of major relevance in the development of age-related vascular disease, the rate at which these cells senesce has never been systematicall y measured in culture. Accordingly the population kinetics of human vascula r endothelial cells (HUVECs) serially passaged in vitro has been studied in order to determine (i) the rate of decline in the growth fraction; (ii) th e rate of increase of the senescent fraction and (iii) the relationship bet ween changes in these parameters and the baseline rate of apoptosis. Immuno cytochemical visualisation of the growth fraction using antisera to the pro liferation marker pKi67 showed a rate of decline in the growth fraction of 4.43 +/- 0.31% per population doubling. This was not accompanied by any cha nge in cell cycle time as assessed using time lapse video microscopy. The n umber of senescent cells within the population increased at a rate of 6.47 +/- 0.3% as assessed by senescence associated beta -galactosidase activity. The baseline rate of apoptosis as measured by TUNEL remained essentially u nchanged (0.31 +/- 0.07%) during this process. These data show (i) that sen escence and apoptosis are unrelated processes in HUVEC and (ii) that senesc ent cells rapidly and progressively accumulate in dividing populations of e ndothelial cells. The physiological relevance of these observations is disc ussed. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.