Endothelial cells maintain a reduced redox environment even as mitochondrial function declines

Abstract

. Endothelial cells maintain a reduced redox environment even as mitochondrial function declines. Am J Physiol Cell Physiol 283: C1675-C1686, 2002. First published August 22, 2002 10.1152/ajpcell.00092.2002 are an endothelial model of replicative senescence. Oxidative stress, possibly due to dysfunctional mitochondria, is believed to play a key role in replicative senescence and atherosclerosis, an age-related vascular disease. In this study, we determined the effect of cell division on genomic instability, mitochondrial function, and redox status in HUVECs that were able to replicate for ϳ60 cumulative population doublings (CPD). After 20 CPD, the nuclear genome deteriorated and the protein content of the cell population increased. This indicated an increase in cell size, which was accompanied by an increase in oxygen consumption, ATP production, and mitochondrial genome copy number and ϳ10% increase in mitochondrial mass. The antioxidant capacity increased, as seen by an increase in reduced glutathione, glutathione peroxidase, GSSG reductase, and glucose-6-phosphate dehydrogenase. However, by CPD 52, the latter two enzymes decreased, as well as the ratio of mitochondrial-to-nuclear genome copies, the mitochondrial mass, and the oxygen consumption per milligram of protein. Our results signify that HUVECs maintain a highly reducing (GSH) environment as they replicate despite genomic instability and loss of mitochondrial function. replicative senescence; glutathione; cell size changes; genomic instability; human umbilical vein endothelial cells HUMAN UMBILICAL VEIN ENDOTHELIAL CELLS (HUVECs) replicate a finite number of times in culture and are an endothelial model of replicative senescence. Reactive oxygen species (ROS) and oxidative damage to DNA (24), protein (7), and lipid (45) increase with age and have been implicated in aging and replicative senescence (19,48). Oxidative stress has also been implicated in atherosclerosis, an age-related vascular disease, and homocysteine, a contributing factor to atherosclerosis that induces oxidative stress, accelerates endothelial senescence in culture (52). Atherosclerosis is hypothesized to be the result of a "response to injury" of the endothelium. The endothelium must constantly respond to changes in the vascular environment and experiences frequent insults from mechanical, hemodynamic, and inflammatory stresses, all of which enhance oxygen free radical production. In response to injury, endothelial cells must replicate to repair blood vessels. Telomere length is shorter in endothelial cells derived from vessels where there is greater hemodynamic stress, and presumably more endothelial cell replication to repair injury, than in cells isolated from areas of lower stress (10). Injury induced by balloon catheter denudation of rabbit carotid arteries has been shown to result in the accumulation of senescent endothelial cells (18). Studies of the endothelium at atherosclerotic lesions (9, 50) and in vessels from elderly people (30, 50) have detected multinucleated cells ...

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