Accumulation of P-selectin in the lumen of irradiated blood vessels

Ionizing radiation induces the inflammatory response in part through leukoc yte binding to cell adhesion molecules that are expressed on the vascular e ndothelium. We studied the effects of X radiation on the pattern of immunoh istochemical staining of CD62P (P-selectin). P-selectin was localized withi n cytoplasmic granules in the untreated vascular endothelium, Immunohistoch emical staining of P-selectin was observed at the luminal surface of vascul ar endothelium within 1 h of irradiation, Increased P-selectin staining at the blood-tissue interface occurred primarily in pulmonary and intestinal b lood vessels. To determine whether localization of P-selectin at the vascul ar lumen occurs through exocytosis of endothelial cell stores in addition t o platelet aggregation, we removed the vascular endothelium from the circul ation and irradiated endothelial cells in vitro. In this system, we studied the mechanisms by which ionizing radiation induced translocation of P-sele ctin by using immunofluorescence of human umbilical vein endothelial cells (HUVEC) and confocal microscopy. Prior to irradiation, P-selectin is locali zed in cytoplasmic reservoirs of HUVEC. After irradiation of HUVEC, P-selec tin was translocated to the cell membrane, where it remained tethered. The lowest dose at which we could expect translocation of P-selectin to the cel l membrane was 2 Gy. To determine whether P-selectin in Weibel-Palade bodie s requires microtubule-dependent membrane transport, we added two microtubu le-depolymerizing agents, Colcemid and nocodazole. Microtubule-depolymerizi ng agents prevented radiation-induced translocation of P-selectin to the ce ll membrane. Thus P-selectin accumulates in irradiated blood vessels throug h both platelet aggregation and microtubule-dependent exocytosis of storage reservoirs within the vascular endothelium. (C) 1999 by Radiation Research Society.