Signaling of hypoxia‐induced autonomous proliferation of endothelial cells

Abstract

Endothelial cells exhibit an autonomous proliferative response to hypoxia, independent of paracrine effectors. In cultured endothelial cells of porcine aorta, we analyzed the signaling and compared hypoxia with mitochondrial inhibition by rotenone. Particularly, roles of the mitogen‐activated protein kinase (MAPK) kinase (MEK)/MAPK pathway and cytosolic Ca 2+ were studied. Hypoxia resulted in increased proliferation by 65±2%. Hypoxia induced transient activation of p42 MAPK (phosphorylation rose from 11±5 to 51±7%), followed by translocation of p42 MAPK into the nucleus. The proliferative response was diminished after inhibition of the MEK/MAPK pathway by PD 98059 (20 μM) or UO 126 (10 μM) but not sensitive to 8‐phenyl‐theophillin (10 μM), an adenosine receptor blocker, nor to a neutralizing antibody for vascular endothelial growth factor (VEGF). Inhibition of intracellular Ca 2+ release, capacitive Ca 2+ influx, or removal of extracellular Ca 2+ prevented hypoxic Ca 2+ overload and the proliferative response. Suppression of cytosolic Ca 2+ rise did not interfere with activation of p42 MAPK but abolished its nuclear translocation. Effects of hypoxia were mimicked by rotenone (10 μM). Transient hypoxic inhibition of mitochondria induces a proliferative endothelial response mediated through Ca 2+ ‐independent activation and Ca 2+ ‐dependent nuclear translocation of p42 MAPK. This proliferative response is independent of adenosine or VEGF.