Differences in intracellular calcium dynamics cause differences in α-granule secretion and phosphatidylserine expression in platelets adhering on glass and TiO2

Abstract

In this study, the activation of purified human platelets due to their adhesion on glass and TiO2 in the absence of extracellular calcium was investigated. Differences in α-granule secretion between platelets adhering on the two surfaces were detected by examining the expression and secretion of the α-granule markers P-selectin (CD62P) and β-thromboglobulin. Similarly, differences in the expression of phosphatidylserine (PS), and in the activation of the major integrin GPIIb/IIIa, on the surfaces of the adhering platelets, were also observed. While all of these activation markers were expressed in platelets adhering on glass, the surface markers were not expressed in platelets adhering on TiO2, and β-thromboglobulin secretion levels were substantially reduced. Differences in marker expression and secretion correlated with differences in the intracellular calcium dynamics. Calcium ionophore treatment triggered α-granule secretion and PS expression in TiO2-adhering platelets but had no effect on the activation of GPIIb/IIIa. These results demonstrate specificity in the way surfaces of artificial materials activate platelets, link differences in the intracellular calcium dynamics observed in the platelets adhering on the two surfaces to the differences in some of the platelet responses (α-granule secretion and PS expression), but also highlight the involvement of synergistic, calcium-independent pathways in platelet activation. The ability to control activation in surface-adhering platelets makes this an attractive model system for studying platelet signaling pathways and for tissue engineering applications.

Subpopulations in purified platelets adhering on glass

“…13,14 It adds to the growing body of evidence that artificial surfaces exhibit properties that are similar to those of classical platelet agonists, and that responses of platelets to different surfaces are different. 20,21,[23][24][25][26] Most likely, the surface-platelet signaling is mediated by the adsorbed proteins. 27,28 Properly studied, these phenomena offer a possibility to improve the control over the response of platelets to artificial surfaces.…”

“…29 The ability to independently regulate a-granule secretion must further be supposed to reconcile observations of CD62P expression heterogeneity in thrombi 19 and in the adhering platelets. 20,21 Where does this ability originate?…”

“…a-granule secretion heterogeneity was also observed in the adhering platelets. 20,21 These observations lead to an emerging hypothesis that different platelet subpopulations participate in these different processes. 15 The significance of this hypothesis to the clinicians is highlighted by the fact that whole-blood assays for detecting platelet subpopulations are beginning to emerge.…”

Preface: In Focus Issue on Blood–Biomaterial Interactions

“…In this context, the report of Cornelius et al 1 on the interaction of lipoproteins with bare and polyethylene glycol-modified polyurethane surfaces can be highlighted, as well as the two reports pointing to differences in plasma protein adsorption and activation at different surfaces. 2,9 Szott et al 2 and Gupta et al 3 also report differences in platelet activation between different surfaces. The two latter studies contribute to the growing body of evidence that platelet spreading may not be representative of other activation phenomena.…”

Toward a quantified, validated, and verifiable understanding of the Biointerface

“…Farrugia et al 8 reviewed the current and emerging materials and coatings being used in platelet storage as there is a current movement toward materials that will enable storage for over 7 days. Research from Szott et al 9 and Gupta et al 10 both highlighted the role that platelet attachment and spreading may have in moderating and even 11 The combination of chemical specificity with high spatial resolution for biological imaging is proving to be an asset, providing insight into metabolic processes and distinguishing disease states. For example, ToF-SIMS excels in detecting native lipids in tissue, and the method has been applied to imaging the distribution of amyloid-b, a biologically relevant peptide in Alzheimer's disease, advancing understanding of mechanisms of neurodegeneration.…”