HYPOXIA ENHANCES STIMULUS-DEPENDENT INDUCTION OF E-SELECTIN ON AORTICENDOTHELIAL-CELLS

In many diseases, tissue hypoxia occurs in conjunction with other infl ammatory processes. Since previous studies have demonstrated a role fo r leukocytes in ischemia/reperfusion injury, we hypothesized that endo thelial hypoxia may ''superinduce'' expression of an important leukocy te adhesion molecule, E-selectin (ELAM-1, CD62E). Bovine aortic endoth elial monolayers were exposed to hypoxia in the presence or absence of tumor-necrosis factor alpha (TNF-alpha) or lipopolysaccharide (LPS). Cell surface E-selectin was quantititated by whole cell ELISA or by im munoprecipitation using polyclonal anti-E-selectin sera, Endothelial m RNA levels were assessed using ribonuclease protection assays. Hypoxia alone did not induce endothelial E-selectin expression. However, enha nced induction of E-selectin was observed with the combination of hypo xia and TNF-alpha (270% increase over normoxia and TNF-alpha) or hypox ia and LPS (190% increase over normoxia and LPS). These studies reveal ed that a mechanism for such enhancement may be hypoxia-elicited decre ments in endothelial intracellular levels of cAMP (<50% compared with normoxia). Addition of forskolin and isobutyl-methylxanthine during hy poxia resulted in reversal of cAMP decreases and a loss of enhanced E- selectin surface expression with the combination of TNF-alpha and hypo xia. We conclude that endothelial hypoxia may provide a novel signal f or superinduction of E-selectin during states of inflammation.