Reactive Oxygen Species-Dependent Cell Signaling Regulates the Mosquito Immune Response to Plasmodium falciparum

Department of Medical Microbiology and Immunology, University of California, Davis, Davis, California 95616, USA.
Antioxidants & Redox Signaling (Impact Factor: 7.41). 03/2011; 14(6):943-55. DOI: 10.1089/ars.2010.3401
Source: PubMed


Reactive oxygen species (ROS) have been implicated in direct killing of pathogens, increased tissue damage, and regulation of immune signaling pathways in mammalian cells. Available research suggests that analogous phenomena affect the establishment of Plasmodium infection in Anopheles mosquitoes. We have previously shown that provision of human insulin in a blood meal leads to increased ROS levels in Anopheles stephensi. Here, we demonstrate that provision of human insulin significantly increased parasite development in the same mosquito host in a manner that was not consistent with ROS-induced parasite killing or parasite escape through damaged tissue. Rather, our studies demonstrate that ROS are important mediators of both the mitogen-activated protein kinase and phosphatidylinositol 3-kinase/Akt signaling branches of the mosquito insulin signaling cascade. Further, ROS alone can directly activate these signaling pathways and this activation is growth factor specific. Our data, therefore, highlight a novel role for ROS as signaling mediators in the mosquito innate immune response to Plasmodium parasites.

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Available from: Kong Wai Cheung, May 21, 2014
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    • "The MEK-ERK signaling module plays a central role in the regulation of malaria parasite development in Anopheles stephensi, the Indian malaria mosquito [19-22]. In particular, human transforming growth factor-beta1 (TGF-β1) ingested with a P. falciparum-infected blood meal induces ERK activation in the midgut [20-22]. The provision of small molecule inhibitors of MEK in the blood meal reproducibly reduced ERK activation in the A. stephensi midgut and enhanced nitric oxide synthase (NOS) transcription within 24 h after infection, resulting in the production of inflammatory levels of reactive oxygen and nitrogen species in the midgut lumen [23] that are directly toxic to P. falciparum[24] and leading to significant reductions in oocyst numbers on the midgut epithelium [21]. "
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    ABSTRACT: Background Susceptibility to Plasmodium infection in Anopheles gambiae has been proposed to result from naturally occurring polymorphisms that alter the strength of endogenous innate defenses. Despite the fact that some of these mutations are known to introduce non-synonymous substitutions in coding sequences, these mutations have largely been used to rationalize knockdown of associated target proteins to query the effects on parasite development in the mosquito host. Here, we assay the effects of engineered mutations on an immune signaling protein target that is known to control parasite sporogonic development. By this proof-of-principle work, we have established that naturally occurring mutations can be queried for their effects on mosquito protein function and on parasite development and that this important signaling pathway can be genetically manipulated to enhance mosquito resistance. Methods We introduced SNPs into the A. gambiae MAPK kinase MEK to alter key residues in the N-terminal docking site (D-site), thus interfering with its ability to interact with the downstream kinase target ERK. ERK phosphorylation levels in vitro and in vivo were evaluated to confirm the effects of MEK D-site mutations. In addition, overexpression of various MEK D-site alleles was used to assess P. berghei infection in A. gambiae. Results The MEK D-site contains conserved lysine residues predicted to mediate protein-protein interaction with ERK. As anticipated, each of the D-site mutations (K3M, K6M) suppressed ERK phosphorylation and this inhibition was significant when both mutations were present. Tissue-targeted overexpression of alleles encoding MEK D-site polymorphisms resulted in reduced ERK phosphorylation in the midgut of A. gambiae. Furthermore, as expected, inhibition of MEK-ERK signaling due to D-site mutations resulted in reduction in P. berghei development relative to infection in the presence of overexpressed catalytically active MEK. Conclusion MEK-ERK signaling in A. gambiae, as in model organisms and humans, depends on the integrity of conserved key residues within the MEK D-site. Disruption of signal transmission via engineered SNPs provides a purposeful proof-of-principle model for the study of naturally occurring mutations that may be associated with mosquito resistance to parasite infection as well as an alternative genetic basis for manipulation of this important immune signaling pathway.
    Parasites & Vectors 06/2014; 7(1):287. DOI:10.1186/1756-3305-7-287 · 3.43 Impact Factor
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    • "ested blood meal also affect mosquito immune function ( Pakpour et al . 2013 ) . TGF - ß1 and insulin in the ingested blood are believed to activate insulin / insu - insulin / insu - insu - lin growth factor 1 ( IGF1 ) signalling ( IIS ) and MAPK signalling cascades in the mosquito thus increasing mos - quito susceptibility to parasite infection ( Surachetpong et al . 2009 , 2011 , Pakpour et al . 2012 ) . In contrast , another blood component , human IGF1 , reduces malaria parasite infection ( Drexler et al . 2013 ) . It appears that a number of factors contribute to IIS and MAPK signalling and that this delicate balance determines Plasmodium devel - opmental success in the mosquito host . However , there is mu"
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    ABSTRACT: Nearly one million people are killed every year by the malaria parasite Plasmodium. Although the disease-causing forms of the parasite exist only in the human blood, mosquitoes of the genus Anopheles are the obligate vector for transmission. Here, we review the parasite life cycle in the vector and highlight the human and mosquito contributions that limit malaria parasite development in the mosquito host. We address parasite killing in its mosquito host and bottlenecks in parasite numbers that might guide intervention strategies to prevent transmission.
    Memórias do Instituto Oswaldo Cruz 04/2014; DOI:10.1590/0074-0276140597 · 1.59 Impact Factor
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    • "Knock down experiments in adult female A. gambiae mosquitoes have indicated that JNK regulates the expression of H2O2 detoxifying enzymes and promotes survival during chronic oxidative stress [43]. It was recently demonstrated that H2O2 challenge causes phosphorylation of p38 in A. gambiae 4a3B cells [44] and FOXO (Akt- mediated) in A. stephensi ASE cells [45]. Inactivation of FOXO through the PI3K/Akt signal cascade could in turn also potentially increase oxidative stress [45]. "
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    ABSTRACT: Despite efficient vector transmission, Plasmodium parasites suffer great bottlenecks during their developmental stages within Anopheles mosquitoes. The outcome depends on a complex three-way interaction between host, parasite and gut bacteria. Although considerable progress has been made recently in deciphering Anopheles effector responses, little is currently known regarding the underlying microbial immune elicitors. An interesting candidate in this sense is the pathogen-derived prenyl pyrophosphate and designated phosphoantigen (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate (HMBPP), found in Plasmodium and most eubacteria but not in higher eukaryotes. HMBPP is the most potent stimulant known of human Vγ9Vδ2 T cells, a unique lymphocyte subset that expands during several infections including malaria. In this study, we show that Vγ9Vδ2 T cells proliferate when stimulated with supernatants from intraerythrocytic stages of Plasmodium falciparum cultures, suggesting that biologically relevant doses of phosphoantigens are excreted by the parasite. Next, we used Anopheles gambiae to investigate the immune- and redox- stimulating effects of HMBPP. We demonstrate a potent activation in vitro of all but one of the signaling pathways earlier implicated in the human Vγ9Vδ2 T cell response, as p38, JNK and PI3K/Akt but not ERK were activated in the A. gambiae 4a3B cell line. Additionally, both HMBPP and the downstream endogenous metabolite isopentenyl pyrophosphate displayed antioxidant effects by promoting cellular tolerance to hydrogen peroxide challenge. When provided in the mosquito blood meal, HMBPP induced temporal changes in the expression of several immune genes. In contrast to meso-diaminopimelic acid containing peptidoglycan, HMBPP induced expression of dual oxidase and nitric oxide synthase, two key determinants of Plasmodium infection. Furthermore, temporal fluctuations in midgut bacterial numbers were observed. The multifaceted effects observed in this study indicates that HMBPP is an important elicitor in common for both Plasmodium and gut bacteria in the mosquito.
    PLoS ONE 08/2013; 8(8):e73868. DOI:10.1371/journal.pone.0073868 · 3.23 Impact Factor
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