Plasmodium falciparum infection induces expression of a mosquito salivary protein (Agaphelin) that targets neutrophil function and inhibits thrombosis without impairing hemostasis.
PLoS Pathog 2014;
10:e1004338. [PMID:
25211214 PMCID:
PMC4161438 DOI:
10.1371/journal.ppat.1004338]
[Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2014] [Accepted: 07/02/2014] [Indexed: 01/05/2023] Open
Abstract
Background
Invasion of mosquito salivary glands (SGs) by Plasmodium falciparum sporozoites is an essential step in the malaria life cycle. How infection modulates gene expression, and affects hematophagy remains unclear.
Principal Findings
Using Affimetrix chip microarray, we found that at least 43 genes are differentially expressed in the glands of Plasmodium falciparum-infected Anopheles gambiae mosquitoes. Among the upregulated genes, one codes for Agaphelin, a 58-amino acid protein containing a single Kazal domain with a Leu in the P1 position. Agaphelin displays high homology to orthologs present in Aedes sp and Culex sp salivary glands, indicating an evolutionarily expanded family. Kinetics and surface plasmon resonance experiments determined that chemically synthesized Agaphelin behaves as a slow and tight inhibitor of neutrophil elastase (KD∼10 nM), but does not affect other enzymes, nor promotes vasodilation, or exhibit antimicrobial activity. TAXIscan chamber assay revealed that Agaphelin inhibits neutrophil chemotaxis toward fMLP, affecting several parameter associated with cell migration. In addition, Agaphelin reduces paw edema formation and accumulation of tissue myeloperoxidase triggered by injection of carrageenan in mice. Agaphelin also blocks elastase/cathepsin-mediated platelet aggregation, abrogates elastase-mediated cleavage of tissue factor pathway inhibitor, and attenuates neutrophil-induced coagulation. Notably, Agaphelin inhibits neutrophil extracellular traps (NETs) formation and prevents FeCl3-induced arterial thrombosis, without impairing hemostasis.
Conclusions
Blockade of neutrophil elastase emerges as a novel antihemostatic mechanism in hematophagy; it also supports the notion that neutrophils and the innate immune response are targets for antithrombotic therapy. In addition, Agaphelin is the first antihemostatic whose expression is induced by Plasmodium sp infection. These results suggest that an important interplay takes place in parasite-vector-host interactions.
Malaria is transmitted by Plasmodium falciparum-infected Anopheles gambiae mosquitoes. Salivary gland contributes to the development of the parasite by creating a favorable environment for the infection and facilitating blood feeding and reproduction of the vector. However, the molecular mechanism by which the vector salivary gland modulates parasite/host interactions is not understood. We discovered that infection of the mosquito salivary gland upregulates several genes; among them, one codes for a protease inhibitor named Agaphelin. Notably, Agaphelin was found to exhibit multiple antihemostatic functions by targeting elastase. As a result, it inhibits platelet function which is required for blood to clot, and it prevents cleavage of TFPI, an anticoagulant that has recently been found to play a crucial role in thrombus formation in vivo. Agaphelin also attenuates neutrophils chemotaxis and the release of Neutrophil Extracellular Traps. These results provide evidence that neutrophils serve as a link between coagulation and the innate immune response. Agaphelin also exhibits anti-inflammatory and antithrombotic effects in vivo. Furthermore, Agaphelin did not promote bleeding, suggesting that targeting neutrophil exhibits potential therapeutic value. Altogether, these results highlight that the interplay between parasite, vector and host is a dynamic process that contributes and sustains the interface among Plasmodium, Anopheles and humans.
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