Inhibition of collagen-induced platelet aggregation by anopheline antiplatelet protein, a saliva protein from a malaria vector mosquito

Abstract

During blood feeding, mosquitoes inject saliva containing a mixture of molecules that inactivate or inhibit various components of the hemostatic response to the bite injury as well as the inflammatory reactions produced by the bite, to facilitate the ingestion of blood. However, the molecular functions of the individual saliva components remain largely unknown. Here, we describe anopheline antiplatelet protein (AAPP) isolated from the saliva of Anopheles stephensi, a human malaria vector mosquito. AAPP exhibited a strong and specific inhibitory activity toward collagen-induced platelet aggregation. The inhibitory mechanism involves direct binding of AAPP to collagen, which blocks platelet adhesion to collagen and inhibits the subsequent increase in intracellular Ca(2+) concentration ([Ca(2+)]i). The binding of AAPP to collagen effectively blocked platelet adhesion via glycoprotein VI (GPVI) and integrin alpha(2)beta(1). Cell adhesion assay showed that AAPP inhibited the binding of GPVI to collagen type I and III without direct effect on GPVI. Moreover, intravenously administered recombinant AAPP strongly inhibited collagen-induced platelet aggregation ex vivo in rats. In summary, AAPP is a malaria vector mosquito-derived specific antagonist of receptors that mediate the adhesion of platelets to collagen. Our study may provide important insights for elucidating the effects of mosquito blood feeding against host hemostasis.

Inhibitors of Platelet Adhesion

“…An alternative approach to direct inhibition of GP VI or GP Ia/IIa to disrupt the platelet-collagen adhesive process has been recently reported, using a novel protein isolated from the saliva of the malaria vector mosquito Anopheles stephensi 63 (Table). In this study, the anopheline antiplatelet protein (AAPP) inhibited platelet adhesion in vitro along with ex vivo collagen-induced platelet aggregation in rats.…”

“…In this study, the anopheline antiplatelet protein (AAPP) inhibited platelet adhesion in vitro along with ex vivo collagen-induced platelet aggregation in rats. 63 The AAPP seems to inhibit platelet adhesion through a GP VIand GP Ia/IIa-independent mechanism by direct binding to collagen. 63 Additional investigation in the future will determine whether this agent or other potential inhibitors of collagen may be useful targets to inhibit platelet adhesion.…”

Neither Mosquito Saliva nor Immunity to Saliva Has a Detectable Effect on the Infectivity ofPlasmodiumSporozoites Injected into Mice

“…Mosquito saliva is known to enhance the ability of the mosquito to locate a blood source and to inhibit hemostasis by any of several mechanisms. These include injection of an anticoagulant factor (34), inhibition of platelet aggregation by salivary apyrase (29) or a salivary factor that inhibits collagen-induced platelet aggregation (43), inhibition of thrombin activity (14), and vasodilation of host blood vessels (30). Arthropod saliva has been shown to enhance the infectivity of several different pathogens introduced into hosts by arthropods; these include sandfly transmission of Leishmania, tick transmission of viruses and spirochetes, and mosquito transmission of viruses (for a review, see reference 36).…”

The Salivary Gland Transcriptome of the Eastern Tree Hole Mosquito,Ochlerotatus triseriatus

“…The multigene pattern has been observed previously for Aedes and Culex mosquitoes (Ribeiro et al 2004Arca et al 2007), whereas anophelines to date appear to have only one gene (Valenzuela et al 2003, Arca et al 2005, Calvo et al 2009b. One of the Aedes and one of the Anopheles proteins have been characterized as inhibitors of collagen-induced platelet aggregation by their strong interaction with collagen (Calvo et al 2007b, Yoshida et al 2008). …”