|
In contrast to prolonged hypoxia (>12 hours), which induces apoptosis of endothelial cells in culture as well as in the intact coronary vascular system, transient hypoxia (1 to 2h) can protect endothelial cells against apoptosis. Here the anti-apoptotic mechanism of transient hypoxia was analysed in cultured human umbilical vein endothelial cells. Apoptosis was induced by either serum starvation or TNFα stimulation (4 ng/ml) for 24 hours. Afterwards cells were exposed to normoxia (2h) or hypoxia (2h; pO2<1 mmHg) followed by reoxygenation (24h; pO2=120 mmHg). Cell number and apoptosis (FACS analysis) as well as activation of ERK 1/2 (Western blot) and NADPH oxidase (Video-Imaging) were analysed. Under normoxia serum starvation reduced cell number to 47,7±4% (n=6; P<0.05; for all further parameter). Within this population 52.3±6% of the cells were apoptotic. In contrast, transient hypoxia reduced cell number to only 74,1±8%, and decreased apoptosis to 25.9±1.5% of the surviving cell population. Transient hypoxia had similar effects on TNFα-induced apoptosis. With the onset of hypoxia ERK1/2 and NADPH oxidase were activated. Inhibition of ERK 1/2 or NADPH oxidase by antisense oligonucleotides against ERK 1/2 or p22phox subunit of NADPH oxidase abolished the anti-apoptotic effect of transient hypoxia. Conclusion: These data indicate, that endothelial cells possess an endogenous mechanism, which protects them against apoptotic cell death. This anti-apoptotic effect is caused by hypoxia-induced signal cascades, which include activation of NADPH oxidase and the MEK/ERK pathway.
|
J. Vasc. Biol. 42, Sup:2 (2005) pp90-91