Abstract 19719: Lpa5 Lysophosphatidate Receptor Mediates Megakaryocyte Shape Change Induced by Human Atherosclerotic Plaques
Background: Oxidative processes and vascular inflammation underlying atherosclerosis lead to an accumulation of lysophosphatidic acid (LPA) in the atheromatous intima. In human atherosclerotic plaques, LPA molecules of high platelet-activating potency have been identified that mediate the initial platelet response — shape change — by the plaque lipid-rich core, and induce synergistically with other platelet stimuli aggregation. Moreover, LPA at concentrations approaching those found in vivo triggers platelet aggregation in whole blood. After rupture of lipid-rich atherosclerotic plaques, LPA exposed to circulating platelets might contribute to arterial thrombus formation. Human platelets express mRNA for seven G protein-coupled LPA receptors (LPA1-7) that derive from megakaryocytes. The functional platelet LPA receptor(s) is (are) not known. LPA does not stimulate murine platelets making studies in mice pointless.
Objective: The aim of our study was to identify the functional LPA receptor(s) in human platelets by silencing the individual LPA1-7 receptors in megakaryocytes.
Methods and Results: We studied two human megakaryocytic (MK) cell lines (Meg-01, Dami) that showed a rapid, Rho-kinase mediated shape change similar to that of human platelets upon exposure to LPA. Quantitative RT-PCR analysis of LPA receptor expression showed mRNA for LPA1-7 in both cell lines; LPA4–5 were the most abundant receptor transcripts. In both Meg-01 and Dami cells, the rank order of activation by LPA species was similar to that found in platelets: alkyl-LPA 18:1 > alkyl-LPA 16:0 > acyl-LPA 18:1 >> alkyl-LPA 18:0. Knock-down of individual LPA receptors by siRNA showed that LPA-mediated shape change was inhibited in LPA5 -silenced MK cells, but not in LPA1-4,6,7 silenced cells. Importantly, we found that human atherosclerotic plaque and lipid-rich core induced shape change of Dami cells, and that this effect was inhibited after LPA5 silencing.
Conclusions: Our findings indicate that the LPA5 receptor mediates LPA-induced shape change of megakaryocytic cells and strongly support its involvement in lipid-rich atherosclerotic plaque mediated platelet activation. This receptor could be an attractive novel target for antithrombotic therapy.
- © 2010 by American Heart Association, Inc.