Platelet endothelial cell adhesion molecule-1 is a negative regulator of platelet-collagen interactions

Abstract

The functional importance of platelet endothelial cell adhesion molecule-1 (PECAM-1/CD31) in platelets is unclear. Because PECAM-1 represents a newly assigned immunoglobulin-ITIM superfamily member expressed on the surface of platelets, it was hypothesized that it may play an important regulatory role in modulating ITAM-bearing receptors such as collagen (GP)VI receptor and Fc␥RIIA. To examine the functional role of PECAM-1 in regulating platelet-collagen interactions, 2 different approaches were applied using recombinant human PECAM-1-immunoglobulin chimeras and platelets derived from PECAM-1-deficient mice. Stimulation of platelets by collagen-, (GP)VI-selective agonist, collagen-related peptide (CRP)-, and PECAM-1-immunoglobulin chimera induced tyrosine phosphorylation of PECAM-1 in a time-and dose-dependent manner. Activation of PECAM-1 directly through the addition of soluble wild-type PECAM-1-immunoglobulin chimera, but not mutant K89A PECAM-1-immunoglobulin chimera that prevents homophilic binding, was found to inhibit collagen-and CRP-induced platelet aggregation. PECAM-1-deficient platelets displayed enhanced platelet aggregation and secretion responses on stimulation with collagen and CRP, though the response to thrombin was unaffected. Under conditions of flow, human platelet thrombus formation on a collagen matrix was reduced in a dose-dependent manner by human PECAM-1-immunoglobulin chimera. Platelets derived from PECAM-1-deficient mice form larger thrombi when perfused over a collagen matrix under flow at a shear rate of 1800 seconds ؊1 compared to wild-type mice. Collectively, these results indicate that PECAM-1 serves as a physiological negative regulator of platelet-collagen interactions that may function to negatively limit growth of platelet thrombi on collagen surfaces.

RhoA Sustains Integrin αIIbβ3Adhesion Contacts under High Shear

“…Findings similar to c7E3 Fab were observed with another potent integrin ␣ IIb ␤ 3 antagonist, aggrastat (data not shown). These findings suggest that RGDS peptide may not completely block ligand binding to integrin ␣ IIb ␤ 3 , a finding consistent with previous reports (31).…”

CEACAM1 negatively regulates platelet-collagen interactions and thrombus growth in vitro and in vivo

“…1,2 The subtle phenotype was most evident at concentrations of collagen at 1 g/mL but was not so evident at higher concentrations of collagen 10 to 30 g/mL. This was also the case using CRP as the GPVI-selective agonist.…”

“…At 5 to 10 g/mL CRP, wild-type and pecam-1 Ϫ/Ϫ platelets were less hyperresponsive. 1,2 Platelets from ceacam1 Ϫ/Ϫ mice exhibited increased adhesion on type I fibrillar collagen but not fibrinogen. This hyperresponsive adhesion phenotype of ceacam1 Ϫ/Ϫ platelets on type I fibrillar collagen was evident at all time points.…”

“…1,2 However, based on several studies, it would appear that platelets contain multiple Ig-ITIM superfamily members that are likely to have a modulatory role in regulating platelet-collagen interactions. Several reports suggest that platelets contain other Ig-ITIM superfamily members, including G6B and TREM (triggering receptors expressed on myeloid cells)-like transcript-1 (TLT-1), that may attenuate platelet function.…”

“…These include prostacylin and nitric oxide released from endothelium and the immunoglobulin (Ig)-immunoreceptor tyrosine-based inhibitory motif (ITIM) superfamily member, platelet endothelial cell adhesion molecule-1 (PECAM-1) that serves an autoregulatory role when platelets come into contact with each other after exposure to collagen. [1][2][3][4] Given the importance of collagen in promoting platelet adhesion and thrombus formation, particularly involving glycoprotein VI (GPVI)/Fc receptor (FcR)-␥-chain signaling, it is essential that natural inhibitors that contribute to autoregulatory mechanisms that modulate signaling between collagen and the GPVI/FcR␥ chain are characterized in platelets.…”