Abstract 17418: Platelet-Mediated Inflammation - Toll-Like Receptor 2 Stimulation Potently Induces Serotonin Release
Introduction A central role for the innate immunity-mediating toll-like receptors (TLRs) in atherosclerosis has recently emerged. Platelets are involved in early and late stages of atherosclerosis. Furthermore, they execute innate immunity functions and stimulation of platelet TLR2 at high agonist concentrations induces platelet activation. We have previously shown that platelet serotonin induces activation of platelet tumor necrosis factor alpha converting enzyme (TACE), resulting in shedding of the adhesion molecule glycoprotein (GP)Ibalpha. We hypothesized that platelet immunological stimulation via TLR2 regulates serotonin release.
Methods Platelet TLR2 was stimulated by incubation of human platelets with the TLR2 agonist Pam3CSK4 and compared to platelet activation by adenosine diphosphate (ADP, 20μM), thrombin receptor activating peptide (TRAP, 30μM), and phenylmaleinine phenylmaleic anhydride (PMA, 75nM). Expression of surface markers was quantified by flow cytometry. Release of serotonin from dense granules into the supernatant was measured by high-sensitivity ELISA.
Results Incubation of platelets in the presence but not absence of plasma with Pam3CSK4 resulted in a dose-dependent increase of the surface expression of P-selectin and activated GPIIb/IIIa (up to 10-fold increase after incubation with 10-100μg/ml Pam3CSK4, p<0.01, n=8). High-dose Pam3CSK4 also induced shedding of the TACE substrate GPIbalpha (50% decrease with 50μg/ml Pam3CSK4, p10μg/ml Pam3CSK4. Serotonin release was triggered by TLR2 stimulation with higher potency: doses of Pam3CSK4 (0.1-1μg/ml) that did not change P-selectin, activated GPIIb/IIIa, or GPIbalpha induced a significant increase of serotonin in the supernatant (p<0.01, n=8).
Conclusion We report here that platelet TLR2 stimulation induces serotonin release much more potently than regular, "hemostatic" platelet activation. This mechanism may constitute a novel innate immune function of platelets via selective release of the immuno-modulator serotonin.
- © 2012 by American Heart Association, Inc.