Endothelin-B receptor-mediated suppression of endothelial apoptosis

Endothelin (ET)-1 is an endothelium-derived vasoconstrictor as well as a mitogen. We have recently described a novel role of ET-1 as a survival factor for rat endothelial cells from serum deprivation-induced apoptosis. The present study was designed to determine which receptor subtype (ETA or ETB) is responsible for and what intracellular mediators are involved in endothelial apoptosis. Apoptotic cell death was evaluated by nucleosomal ladders on agarose gel electrophoresis and immunohistochemical study using anti-single-stranded DNA antiserum. ET-1 and an ETB receptor agonist suppressed endothelial apoptosis, whose effects were abrogated by an ETB receptor antagonist but not by an ETA receptor antagonist. Addition of an ETB receptor antagonist or nonselective ETA/B receptor antagonists, but not an ETA receptor antagonist, enhanced the apoptotic events caused by serum deprivation, suggesting an autocrine/paracrine role of endogenous ET-1 in protecting against endothelial apoptosis. The effect of ET-1 in suppressing apoptosis was unaffected by any of the following reagents: a phospholipase C inhibitor (U73122), a tyrosine kinase inhibitor (ST638), an MEK inhibitor (PD98059), a phosphatidylinositol-3 kinase inhibitors (wortmannin, LY294002). Taken together, these results confirm a role for ET-1 as an autocrine/paracrine survival factor for rat endothelial cells, in which neither phospholipase C, tyrosine kinase, MAP kinase, nor phosphatidylinositol-3 kinase is involved in mediating the antiapoptotic effect of ET-1.