The JAK-STAT Pathway Controls Plasmodium vivax Load in Early Stages of Anopheles aquasalis Infection

Ana C Bahia,Claudia M Ríos-Velásquez,Helena R C Araújo,Alessandra S Orfanó,Paulo F P Pimenta,Antonio J Tempone,Wanderli P Tadei,Nágila F C Secundino,Yara M Traub-Csekö,Marina S Kubota,Yeon S Han,Bruno A M Guedes,Carolina Barillas-Mury,Ken E Olson

doi:10.1371/journal.pntd.0001317

Abstract

Malaria affects 300 million people worldwide every year and 450,000 in Brazil. In coastal areas of Brazil, the main malaria vector is Anopheles aquasalis, and Plasmodium vivax is responsible for the majority of malaria cases in the Americas. Insects possess a powerful immune system to combat infections. Three pathways control the insect immune response: Toll, IMD, and JAK-STAT. Here we analyze the immune role of the A. aquasalis JAK-STAT pathway after P. vivax infection. Three genes, the transcription factor Signal Transducers and Activators of Transcription (STAT), the regulatory Protein Inhibitors of Activated STAT (PIAS) and the Nitric Oxide Synthase enzyme (NOS) were characterized. Expression of STAT and PIAS was higher in males than females and in eggs and first instar larvae when compared to larvae and pupae. RNA levels for STAT and PIAS increased 24 and 36 hours (h) after P. vivax challenge. NOS transcription increased 36 h post infection (hpi) while this protein was already detected in some midgut epithelial cells 24 hpi. Imunocytochemistry experiments using specific antibodies showed that in non-infected insects STAT and PIAS were found mostly in the fat body, while in infected mosquitoes the proteins were found in other body tissues. The knockdown of STAT by RNAi increased the number of oocysts in the midgut of A. aquasalis. This is the first clear evidence for the involvement of a specific immune pathway in the interaction of the Brazilian malaria vector A. aquasalis with P. vivax, delineating a potential target for the future development of disease controlling strategies.

Highlights

Malaria is one of the most important vector-borne diseases, affecting 300 million people worldwide every year and 22 countries in America
In mosquitoes it was demonstrated that the Imd pathway prevents the development of Plasmodium falciparum in Anopheles gambiae, Anopheles stephensi and Anopheles albimanus while the Toll pathway is most efficient in A. gambiae against Plasmodium berghei [2,3]
Malaria is endemic in 22 countries in the Americas where the Anopheles aquasalis mosquito is an important malaria vector and the Plasmodium vivax parasite is responsible for most malaria cases

Summary

Introduction

Malaria is one of the most important vector-borne diseases, affecting 300 million people worldwide every year and 22 countries in America. The lack of effective vaccines, the development of drug resistance in Plasmodium parasites and of insecticide resistance in mosquitoes, have prevented the successful control of human malaria in many tropical regions. Understanding the biology of the Plasmodium-mosquito vector interaction is important to identify potential targets for the development of novel malaria control strategies to disrupt the parasite life cycle in the insect vectors and prevent disease transmission to humans. Genetic studies in Drosophila identified three major signaling pathways that regulate expression of immune effector genes: TOLL, Immune deficiency (IMD), Janus Kinase and Signal Transducer and Activator of Transcription (JAK-STAT) pathways [5]. In mosquitoes it was demonstrated that the Imd pathway prevents the development of Plasmodium falciparum in Anopheles gambiae, Anopheles stephensi and Anopheles albimanus while the Toll pathway is most efficient in A. gambiae against Plasmodium berghei [2,3]

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