Single platelets seal neutrophil-induced vascular breaches via GPVI during immune-complex–mediated inflammation in mice

Abstract

Key Points• GPVI-dependent platelet binding and activation contribute to seal neutrophilinduced vascular damage in IC-mediated inflammation.• Inflammation represents an uncommon hemostatic situation in which adhesion and activation of single platelets prevent bleeding.Platelets protect vascular integrity during inflammation. Recent evidence suggests that this action is independent of thrombus formation and requires the engagement of glycoprotein VI (GPVI), but it remains unclear how platelets prevent inflammatory bleeding. We investigated whether platelets and GPVI act primarily by preventing detrimental effects of neutrophils using models of immune complex (IC)-mediated inflammation in mice immunodepleted in platelets and/or neutrophils or deficient in GPVI. Depletion of neutrophils prevented bleeding in thrombocytopenic and GPVI 2/2 mice during IC-mediated dermatitis. GPVI deficiency did not modify neutrophil recruitment, which was reduced by thrombocytopenia. Neutrophil cytotoxic activities were reduced in thrombocytopenic and GPVI 2/2 mice during IC-mediated inflammation. Intravital microscopy revealed that in this setting, intravascular binding sites for platelets were exposed by neutrophils, and GPVI supported the recruitment of individual platelets to these spots. Furthermore, the platelet secretory response accompanying IC-mediated inflammation was partly mediated by GPVI, and blocking of GPVI signaling impaired the vasculoprotective action of platelets. Together, our results show that GPVI plays a dual role in inflammation by enhancing neutrophil-damaging activities while supporting the activation and hemostatic adhesion of single platelets to neutrophil-induced vascular breaches. (Blood. 2015;126(8):1017-1026

Tetraspanin Tspan9 regulates platelet collagen receptor GPVI lateral diffusion and activation

“…Platelet GPVI is established as the major platelet-activating collagen receptor [1–4], but also binds laminin [5] and fibrin [6, 7]. GPVI has only a minor role in haemostasis, but is important in arterial thrombosis, ischaemic stroke and maintaining vascular integrity during inflammation [8, 9]. The GPVI signalling pathway is well characterised and is initiated by phosphorylation of immunoreceptor tyrosine-based activation motifs (ITAMs) in the FcRγ chain dimer that is associated with GPVI [1, 4].…”

Soluble GPVI is elevated in injured patients: shedding is mediated by fibrin activation of GPVI

“…GPVI is critical for the maintenance of vessel wall integrity in inflammation 19 by inhibiting neutrophil-induced vascular damage. 20,21 GPVI levels are stable on circulating platelets, but GPVI undergoes rapid metalloproteolytic cleavage, and in some cases internalization, on activation. [22][23][24][25] GPVI shedding is induced by GPVI ligands including collagen, collagen-related peptide (CRP), and venom toxins, 23,24,26,27 and by engagement of other platelet ITAM receptors FcgRIIA and CLEC-2.…”

Platelets at the vascular interface

“…Interestingly, recent studies suggest that platelet GTPase signaling is much less important in situations where vascular lesions are very small. At sites of inflammation, single platelets plug holes in the vascular lining (Figure 1B)[63], tiny lesions induced by transmigrating inflammatory cells[64]. Without platelets (severe thrombocytopenia), these vessels become leaky for RBCs, causing hemorrhage in the affected areas[62].…”