Tissue hypoxia (H), common to many cardiopulmonary/vascular disorders, affects vascular homeostasis by modulating central properties of endothelial cells (ECs) and smooth muscle cells (SMCs). In ECs: P-selectin is translocated to the cell surface; von Willebrand factor is released; cytokines, such as Interleukins (ILs)-1, -6, and -8, are produced; permeability of th EC monolayer increases in parallel with a decline in intracellular cAMP levels; thrombogenicity increases; and nitric oxide levels are reduced. In SMCs, cAMP levels fall, potentially promoting vasoconstriction. Effects of acute H on EC/SMC properties, as well as their consequences for vascular function, are observed in cardiac and pulmonary grafts after prolonged preservation, in which increased permeability, vasoconstriction, leukocyte (PMN) infiltration and thrombus formation contribute to graft failure. We have shown that by addition of cAMP and NO/cGMP agonists to cardiac preservation solutions, these vascular homeostatic properties are maintained, thereby enhancing successful function of the graft. In pilot work, we have developed a reproducible rat model of orthotopic lung transplantation, and have similarly found that maintenance of vascular homeostatic properties within the graft is essential for graft function/survival. Based on these finding, we hypothesize that H primes ECs and SMCs for subsequent vascular dysfunction, by enhancing PMN-EC interactions, inducing cytokine production, and perturbing cAMP/cGMP messenger pathways.
Our specific aims are; (1) to determine mechanisms underlying hypoxic modulation of increased PMN-EC interactions, and suppression of intracellular second messenger cyclic nucleotide levels: and (2) to use insights from these in vitro studies to develop an improved strategy for lung preservation, where regimens for optimal organ storage are still emerging, and rapid vasoconstriction and oxidant stress are well documented. We propose to enhance lung preservation by utilizing cAMP and NO/cGMP agonists, and other interventions targeted to the vasculature, such as blocking antibodies to cell adhesion molecules. The long-term goal of these studies is to understand the contribution of H-induced perturbation of ECs/SMCs to the pathogenesis of a variety of disorders, ranging from vascular dysfunction accompanying organ preservation to atherosclerosis, in order to design more effective preventive and therapeutic strategies.
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