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Anopheles Imd pathway factors and effectors in infection intensity-dependent anti-Plasmodium action.

Garver LS, Bahia AC, Das S, Souza-Neto JA, Shiao J, Dong Y, Dimopoulos G - PLoS Pathog. (2012)

Bottom Line: Silencing the expression of caspar, a negative regulator of the Imd pathway, or over-expressing rel2, an Imd pathway-controlled NFkappaB transcription factor, confers a resistant phenotype on A. gambiae mosquitoes that involves an array of immune effector genes.We further demonstrated that caspar silencing alone is sufficient to induce a robust anti-P. falciparum response even in the relative absence of resident gut microbiota.Finally, we established the relevance of the Imd pathway components and regulated effectors TEP1, APL1, and LRIM1 in parasite infection intensity-dependent defense, thereby shedding light on the relevance of laboratory versus natural infection intensity models.

View Article: PubMed Central - PubMed

Affiliation: W. Harry Feinstone Department of Molecular Microbiology and Immunology, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, Maryland, United States of America.

ABSTRACT
The Anopheles gambiae immune response against Plasmodium falciparum, an etiological agent of human malaria, has been identified as a source of potential anti-Plasmodium genes and mechanisms to be exploited in efforts to control the malaria transmission cycle. One such mechanism is the Imd pathway, a conserved immune signaling pathway that has potent anti-P. falciparum activity. Silencing the expression of caspar, a negative regulator of the Imd pathway, or over-expressing rel2, an Imd pathway-controlled NFkappaB transcription factor, confers a resistant phenotype on A. gambiae mosquitoes that involves an array of immune effector genes. However, unexplored features of this powerful mechanism that may be essential for the implementation of a malaria control strategy still remain. Using RNA interference to singly or dually silence caspar and other components of the Imd pathway, we have identified genes participating in the anti-Plasmodium signaling module regulated by Caspar, each of which represents a potential target to achieve over-activation of the pathway. We also determined that the Imd pathway is most potent against the parasite's ookinete stage, yet also has reasonable activity against early oocysts and lesser activity against late oocysts. We further demonstrated that caspar silencing alone is sufficient to induce a robust anti-P. falciparum response even in the relative absence of resident gut microbiota. Finally, we established the relevance of the Imd pathway components and regulated effectors TEP1, APL1, and LRIM1 in parasite infection intensity-dependent defense, thereby shedding light on the relevance of laboratory versus natural infection intensity models. Our results highlight the physiological considerations that are integral to a thoughtful implementation of Imd pathway manipulation in A. gambiae as part of an effort to limit the malaria transmission cycle, and they reveal a variety of previously unrecognized nuances in the Imd-directed immune response against P. falciparum.

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Anopheles Imd pathway model.Components of the Imd pathway explored in this study or others are represented by different colored shapes. Black arrows or lines indicate known interactions or translocations. Gray arrows indicate potential interactions based on D. melanogaster studies. The gray bracketed area indicates the molecules possibly involved in other responses, but not the responses against P. falciparum. Numbers and arrows within colored blocks indicate the -fold change in P. falciparum infection that results when the corresponding pathway member is silenced. The list of genes inside the nucleus portion of the diagram shows those known to be active against Plasmodium and whose expression has been shown by our studies to be REL2-regulated.
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ppat-1002737-g001: Anopheles Imd pathway model.Components of the Imd pathway explored in this study or others are represented by different colored shapes. Black arrows or lines indicate known interactions or translocations. Gray arrows indicate potential interactions based on D. melanogaster studies. The gray bracketed area indicates the molecules possibly involved in other responses, but not the responses against P. falciparum. Numbers and arrows within colored blocks indicate the -fold change in P. falciparum infection that results when the corresponding pathway member is silenced. The list of genes inside the nucleus portion of the diagram shows those known to be active against Plasmodium and whose expression has been shown by our studies to be REL2-regulated.

Mentions: We first addressed the contribution of specific Imd pathway components in the anti-Plasmodium defense. Existing data have implicated the negative regulator Caspar, the transcription factor REL2, and the pattern recognition receptor PGRP-LC in the defense against malaria so we concentrated our efforts on the Imd pathway components known in Drosophila to interact with or between these components and that have a clear 1-to-1 ortholog in Anopheles (Figure 1), though Anopheles immune signaling pathways do not necessarily mimic those in Drosophila. As examples, mosquitoes do not have an ortholog of Dif, one of the transcription factors downstream of the Toll pathway in Drosophila[11], Anopheles possesses two functional isoforms of REL2, while flies have only one [12] and TAB2 does not have a reliable ortholog in A. gambiae. We specifically sought to identify the range of Imd pathway genes that have an impact on P. falciparum infection, so we assessed the contribution of each potential pathway member to both the natural (infection only) and the artificially enhanced (infection plus caspar silencing) immune response against P. falciparum.


Anopheles Imd pathway factors and effectors in infection intensity-dependent anti-Plasmodium action.

Garver LS, Bahia AC, Das S, Souza-Neto JA, Shiao J, Dong Y, Dimopoulos G - PLoS Pathog. (2012)

Anopheles Imd pathway model.Components of the Imd pathway explored in this study or others are represented by different colored shapes. Black arrows or lines indicate known interactions or translocations. Gray arrows indicate potential interactions based on D. melanogaster studies. The gray bracketed area indicates the molecules possibly involved in other responses, but not the responses against P. falciparum. Numbers and arrows within colored blocks indicate the -fold change in P. falciparum infection that results when the corresponding pathway member is silenced. The list of genes inside the nucleus portion of the diagram shows those known to be active against Plasmodium and whose expression has been shown by our studies to be REL2-regulated.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3369948&req=5

ppat-1002737-g001: Anopheles Imd pathway model.Components of the Imd pathway explored in this study or others are represented by different colored shapes. Black arrows or lines indicate known interactions or translocations. Gray arrows indicate potential interactions based on D. melanogaster studies. The gray bracketed area indicates the molecules possibly involved in other responses, but not the responses against P. falciparum. Numbers and arrows within colored blocks indicate the -fold change in P. falciparum infection that results when the corresponding pathway member is silenced. The list of genes inside the nucleus portion of the diagram shows those known to be active against Plasmodium and whose expression has been shown by our studies to be REL2-regulated.
Mentions: We first addressed the contribution of specific Imd pathway components in the anti-Plasmodium defense. Existing data have implicated the negative regulator Caspar, the transcription factor REL2, and the pattern recognition receptor PGRP-LC in the defense against malaria so we concentrated our efforts on the Imd pathway components known in Drosophila to interact with or between these components and that have a clear 1-to-1 ortholog in Anopheles (Figure 1), though Anopheles immune signaling pathways do not necessarily mimic those in Drosophila. As examples, mosquitoes do not have an ortholog of Dif, one of the transcription factors downstream of the Toll pathway in Drosophila[11], Anopheles possesses two functional isoforms of REL2, while flies have only one [12] and TAB2 does not have a reliable ortholog in A. gambiae. We specifically sought to identify the range of Imd pathway genes that have an impact on P. falciparum infection, so we assessed the contribution of each potential pathway member to both the natural (infection only) and the artificially enhanced (infection plus caspar silencing) immune response against P. falciparum.

Bottom Line: Silencing the expression of caspar, a negative regulator of the Imd pathway, or over-expressing rel2, an Imd pathway-controlled NFkappaB transcription factor, confers a resistant phenotype on A. gambiae mosquitoes that involves an array of immune effector genes.We further demonstrated that caspar silencing alone is sufficient to induce a robust anti-P. falciparum response even in the relative absence of resident gut microbiota.Finally, we established the relevance of the Imd pathway components and regulated effectors TEP1, APL1, and LRIM1 in parasite infection intensity-dependent defense, thereby shedding light on the relevance of laboratory versus natural infection intensity models.

View Article: PubMed Central - PubMed

Affiliation: W. Harry Feinstone Department of Molecular Microbiology and Immunology, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, Maryland, United States of America.

ABSTRACT
The Anopheles gambiae immune response against Plasmodium falciparum, an etiological agent of human malaria, has been identified as a source of potential anti-Plasmodium genes and mechanisms to be exploited in efforts to control the malaria transmission cycle. One such mechanism is the Imd pathway, a conserved immune signaling pathway that has potent anti-P. falciparum activity. Silencing the expression of caspar, a negative regulator of the Imd pathway, or over-expressing rel2, an Imd pathway-controlled NFkappaB transcription factor, confers a resistant phenotype on A. gambiae mosquitoes that involves an array of immune effector genes. However, unexplored features of this powerful mechanism that may be essential for the implementation of a malaria control strategy still remain. Using RNA interference to singly or dually silence caspar and other components of the Imd pathway, we have identified genes participating in the anti-Plasmodium signaling module regulated by Caspar, each of which represents a potential target to achieve over-activation of the pathway. We also determined that the Imd pathway is most potent against the parasite's ookinete stage, yet also has reasonable activity against early oocysts and lesser activity against late oocysts. We further demonstrated that caspar silencing alone is sufficient to induce a robust anti-P. falciparum response even in the relative absence of resident gut microbiota. Finally, we established the relevance of the Imd pathway components and regulated effectors TEP1, APL1, and LRIM1 in parasite infection intensity-dependent defense, thereby shedding light on the relevance of laboratory versus natural infection intensity models. Our results highlight the physiological considerations that are integral to a thoughtful implementation of Imd pathway manipulation in A. gambiae as part of an effort to limit the malaria transmission cycle, and they reveal a variety of previously unrecognized nuances in the Imd-directed immune response against P. falciparum.

Show MeSH
Related in: MedlinePlus