Introduction-Thrombin or tryptase cleavage of protease-activated receptors (PAR) on human coronary artery endothelial cells (HCAEC) results in activation of a membrane-associated, calciumindependent phospholipase A 2 (iPLA 2 ) that selectively hydrolyzes plasmalogen phospholipids. Atherosclerotic plaque rupture results in a coronary ischemic event in which HCAEC in the ischemic area would be exposed to increased thrombin concentrations in addition to tryptase released by activated mast cells present in the plaque.
CD133+ cells can be utilized as a mast cell precursor population. The transendothelial migration is facilitated by the presence of tryptase and may utilize the PAF/PTAFR interaction in a manner similar to that involved in neutrophil transmigration. Following transmigration, a subset of these progenitor cells may mature into mast cells in the subendothelial space and play a role in propagation of the inflammatory process in atherosclerosis.
We demonstrated previously that thrombin stimulation of human coronary artery endothelial cells (HCAEC) results in release of choline lysophospholipids [lysophosphatidylcholine (lysoPtdCho) and lysoplasmenylcholine (lysoPlsCho)]. These amphiphilic metabolites have been implicated in arrhythmogenesis following the onset of myocardial ischemia, but studies examining their direct effects on the vasculature remain limited. We and others have shown that thrombin and lysoPtdCho can increase cell surface adhesion molecules and adherence of circulating inflammatory cells to the endothelium. This study supports our hypothesis that these changes may be mediated, at least in part, by lysoPlsCho, thus implicating this metabolite as an inflammatory mediator in the coronary vasculature and a modulator of the progression of atherosclerosis. Apical stimulation of HCAEC with thrombin resulted in the production and release of choline lysophospholipids from the apical surface of the HCAEC monolayer. Basolateral stimulation had no effect on choline lysophospholipid production or release from either the apical or basolateral surface of the HCAEC monolayer. Incubation of HCAEC with lysoPlsCho or lysoPtdCho resulted in similar increases in HCAEC surface expression of P-selectin and E-selectin. Furthermore, lysoPlsCho increased cell surface expression of P-selectin, E-selectin, vascular cell adhesion molecule-1, and intercellular adhesion molecule-1 with a time course similar to that of thrombin stimulation. Increased presence of cell surface adhesion molecules may contribute to the significant increase in adherence of neutrophils to either thrombin- or lysoPlsCho-stimulated HCAEC. These results demonstrate that the presence of thrombin at sites of vascular injury in the coronary circulation, resulting in increased choline lysophospholipid release from the HCAEC apical surface, has the potential to propagate vascular inflammation by upregulation of adhesion molecules and recruitment of circulating inflammatory cells to the endothelium.
Transmigration of hematopoietic progenitor cells across the vascular endothelium and subsequent maturation in the tissue helps to maintain the pool of resident mast cells. We determined the potential of CD133+ cells isolated from umbilical cord blood to migrate across an endothelial cell monolayer. CD133+ cells possess mRNA for several adhesion molecules that are critical in the process of neutrophil transmigration. Stem cell factor & its receptor CD117 are required for homing & differentiation of mast cells in the tissue. We detected the presence of CD34, CD117, CD29, & CD18 on the surface of CD133+ cells using flow cytometry. Tryptase stimulation leads to increased endothelial cell platelet activating factor (PAF) production that may facilitate the interaction between the endothelium & the PAF receptor (PTAFR) on circulating CD133+ cells. Treatment with the PTAFR antagonist CV3988 significantly reduced the percentage of transmigrating CD133+ cells across a tryptase stimulated endothelial monolayer. This suggests that CD133+ cell migration depends on the PAF/PTAFR interaction in a manner similar to that involved in neutrophil transmigration. Following transmigration there is the potential for a subset of these cells, in the presence of SCF & IL‐6, to mature into tissue mast cells.This work was supported by AHA Heartland Affiliate Grant # 0610118Z.
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