Hypoxia-induced exocytosis of endothelial cell Weibel-Palade bodies. A mechanism for rapid neutrophil recruitment after cardiac preservation.

Abstract

The period of hypoxia is an important priming event for the vascular dysfunction that accompanies reperfusion, with endothelial cells (ECs) and neutrophils (PMNs) playing a central role. We hypothesized that EC Weibel-Palade (WP) body exocytosis during the hypoxic/ischemic period during organ preservation permits brisk PMN recruitment into postischemic tissue, a process further amplified in an oxidant-rich milieu. Exposure of human umbilical vein ECs to a hypoxic environment (pO 2 ഠ 20 torr) stimulated release of von Willebrand factor (vWF), stored in EC WP bodies, as well as increased expression of the WP body-derived PMN adhesion molecule P-selectin at the EC surface. Increased binding of 111 In-labeled PMNs to hypoxic EC monolayers (compared with normoxic controls) was blocked with a blocking antibody to P-selectin, but was not affected by a nonblocking control antibody. Although increased P-selectin expression and vWF release were also noted during reoxygenation, hypoxia alone (even in the presence of antioxidants) was sufficient to increase WP body exocytosis. To determine the relevance of these observations to hypothermic cardiac preservation, during which the pO 2 within the cardiac vasculature declines to similarly low levels, experiments were performed in a rodent (rat and mouse) cardiac preservation/transplantation model. Immunodepletion of recipient PMNs or administration of a blocking anti-Pselectin antibody before transplantation resulted in reduced graft neutrophil infiltration and improved graft survival, compared with identically preserved hearts transplanted into control recipients. To establish the important role of endothelial P-selectin expression on the donor vasculature, murine cardiac transplants were performed using homozygous P-selectin deficient and wild-type control donor hearts flushed free of blood/platelets before preservation/transplantation. P-selectin-null hearts transplanted into wildtype recipients demonstrated a marked (13-fold) reduction in graft neutrophil infiltration and increased graft survival compared with wild-type hearts transplanted into wild-type recipients. To determine whether coronary endothelial WP exocytosis may occur during cardiac preservation in humans, the release of vWF into the coronary sinus (CS) was measured in 32 patients during open heart surgery. CS samples obtained at the start and conclusion of the ischemic period demonstrated an increase in CS vWF antigen (by ELISA) consisting of predominantly high molecular weight multimers (by immunoelectrophoresis). These data suggest that EC WP exocytosis occurs during hypothermic cardiac preservation, priming the vasculature to recruit PMNs rapidly during reperfusion. ( J. Clin. Invest. 1996. 97:493-500.)

Ischemia-Induced Exocytosis of Weibel-Palade Bodies Mobilizes Stem Cells

“…It has been shown that hypoxia per se activates exocytosis of WPB 14 (although UA levels were not determined), the event that may take place within the ischemic organ. Distant regulation of exocytosis of WPB can be accomplished, according to the data presented here, via release of the product of xanthine oxidase activation in the ischemic organ-UA.…”

Functional consequences of inhibiting exocytosis of Weibel-Palade bodies in acute renal ischemia

“…A list of compounds known to induce exocytosis of WPB is long and includes thrombin, histamine, peptido-leukotrienes, complement components, superoxide anion, VEGF, sphingosine-1-phosphate, ceramide, purine nucleotides, serotonin, vasopressin, and epinephrine (15, 21, 9). Notably, ischemia-reperfusion injury to various organs has been shown to release WPB (14,20).The possibility of exacerbated tissue injury and inflammation as a result of exocytosis of WPB has been explored in several studies. Matsushita et al (16) developed fusion polypeptides composed of a 22-amino acid N-ethyl-maleimidesensitive factor (a regulator of exocytosis) and a carrier peptide derived from the human immunodeficiency virus transactivating regulatory protein domain and demonstrated that inhibition of WPB exocytosis decreased leukocyte trafficking and peritonitis (7).…”

“…A list of compounds known to induce exocytosis of WPB is long and includes thrombin, histamine, peptido-leukotrienes, complement components, superoxide anion, VEGF, sphingosine-1-phosphate, ceramide, purine nucleotides, serotonin, vasopressin, and epinephrine (15, 21, 9). Notably, ischemia-reperfusion injury to various organs has been shown to release WPB (14,20).…”

Hypoxia/Hypoxemia-Induced Activation of the Procoagulant Pathways and the Pathogenesis of Ischemia-Associated Thrombosis

“…An example of this principle is the critical period during organ preservation, when hypoxemia and stasis prime the graft vasculature for damage during reperfusion. 15 Such tissue injury occurring as soon as blood flow to the graft is reestablished is limited by strategies to diminish preservation-induced vascular dysfunction with more optimal preservation solutions during the period of organ storage. Our brief review will focus on mechanisms through which hypoxemia promotes fibrin formation in vivo and the results of recent studies to elucidate the bases for such activation of the procoagulant pathway.…”