Human neutrophil alpha‐defensins induce formation of fibrinogen and thrombospondin‐1 amyloid‐like structures and activate platelets via glycoprotein IIb/IIIa

Abstract

Summary. Background: Human neutrophil α‐defensins (HNPs) are important constituents of the innate immune system. Beyond their antimicrobial properties, HNPs also have pro‐inflammatory features. While HNPs in plasma from healthy individuals are barely detectable, their level is strongly elevated in septic plasma and plasma from patients with acute coronary syndromes. Objectives: As thrombosis and inflammation are intertwined processes and activation of human polymorphonuclear leukocytes (PMNL) and subsequent degranulation is associated with full activation of surrounding platelets, we studied the effect of HNPs on platelet function. Methods: The effect of HNPs on platelet activation parameters and apoptosis was investigated via aggregometry, flow cytometry, confocal microscopy and the ELISA technique. Results: It was found that HNPs activate platelets in pathophysiologically relevant doses, inducing fibrinogen and thrombospondin‐1 binding, aggregation, granule secretion, sCD40L shedding, and procoagulant activity. HNPs bound directly to the platelet membrane, induced membrane pore formation, microparticle formation, mitochondrial membrane depolarization and caspase‐3‐activity. Confocal microscopy revealed the HNP‐induced formation of polymeric fibrinogen and thrombospondin‐1 amyloid‐like structures, which bound microorganisms. Platelets adhered to these structures and formed aggregates. Blocking of glycoprotein IIb/IIIa (GPIIb/IIIa) markedly inhibited HNP‐induced platelet activation. In addition, heparin, heparinoid, serpins and α2‐macroglobulin, which all bind to HNPs, blocked HNP‐1‐induced platelet activation in contrast to direct thrombin inhibitors such as hirudin. Conclusions: HNPs activate platelets and induce platelet apoptosis by formation of amyloid‐like proteins. As these structures entrapped bacteria and fungi, they might reflect an additional function of HNPs in host defense. The described mechanism links again thrombosis and infection.

Human neutrophil peptides inhibit cleavage of von Willebrand factor by ADAMTS13: a potential link of inflammation to TTP

“…31 However, HNPs can also exert adverse effects on the host as they promote platelet aggregation, 16 cause endothelial dysfunction, 32 inhibit fibrinolysis, 17 and For personal use only. on May 12, 2018.…”

“…16 This results in secretion of platelet granule contents, shedding of soluble CD40 ligand, and expression of platelet surface procoagulant activity. 16 Furthermore, HNPs can modulate the binding of tissue plasminogen activator and plasminogen to fibrin and endothelial cells, which inhibits fibrinolysis.…”

“…16 This results in secretion of platelet granule contents, shedding of soluble CD40 ligand, and expression of platelet surface procoagulant activity. 16 Furthermore, HNPs can modulate the binding of tissue plasminogen activator and plasminogen to fibrin and endothelial cells, which inhibits fibrinolysis. 17 Together, these results indicate that HNPs may be a family of potent proinflammatory and prothrombotic peptides that not only contributes to host defense against microbial invasion, but also promotes clinically significant microvascular thrombosis in settings such as TTP where circulating ADAMTS13 is already limited.…”

“…HNPs activate platelets by enhancing the interactions between platelets and fibrinogen or thrombospondin-1 leading to aggregation, secretion of granule contents, shedding of soluble CD40L, and the expression of platelet surface procoagulant activity. 16 In addition, HNPs may inhibit fibrinolysis by modulating the binding of tissue plasminogen activator and plasminogen to fibrin and endothelial cells. 17 The resultant localized microvascular thrombosis may be an integral component in host defense, but might also lead to infection/inflammation-associated microvascular thrombosis in settings where plasma ADAMTS13 levels are extremely low as in the cases of TTP.…”

Resolving Thromboinflammation in the Brain After Ischemic Stroke?

“…8 Neutrophil-platelet interactions are in fact likely to emerge as key players in stroke pathophysiology. Platelets promote the formation of neutrophil extracellular traps (NETs).…”