Anopheles stephensi p38 MAPK signaling regulates innate immunity and bioenergetics during Plasmodium falciparum infection.
BACKGROUND
Fruit flies and mammals protect themselves against infection by mounting immune and metabolic responses that must be balanced against the metabolic needs of the pathogens. In this context, p38 mitogen-activated protein kinase (MAPK)-dependent signaling is critical to regulating both innate immunity and metabolism during infection. Accordingly, we asked to what extent the Asian malaria mosquito Anopheles stephensi utilizes p38 MAPK signaling during infection with the human malaria parasite Plasmodium falciparum.


METHODS
A. stephensi p38 MAPK (AsP38 MAPK) was identified and patterns of signaling in vitro and in vivo (midgut) were analyzed using phospho-specific antibodies and small molecule inhibitors. Functional effects of AsP38 MAPK inhibition were assessed using P. falciparum infection, quantitative real-time PCR, assays for reactive oxygen species and survivorship under oxidative stress, proteomics, and biochemical analyses.


RESULTS
The genome of A. stephensi encodes a single p38 MAPK that is activated in the midgut in response to parasite infection. Inhibition of AsP38 MAPK signaling significantly reduced P. falciparum sporogonic development. This phenotype was associated with AsP38 MAPK regulation of mitochondrial physiology and stress responses in the midgut epithelium, a tissue critical for parasite development. Specifically, inhibition of AsP38 MAPK resulted in reduction in mosquito protein synthesis machinery, a shift in glucose metabolism, reduced mitochondrial metabolism, enhanced production of mitochondrial reactive oxygen species, induction of an array of anti-parasite effector genes, and decreased resistance to oxidative stress-mediated damage. Hence, P. falciparum-induced activation of AsP38 MAPK in the midgut facilitates parasite infection through a combination of reduced anti-parasite immune defenses and enhanced host protein synthesis and bioenergetics to minimize the impact of infection on the host and to maximize parasite survival, and ultimately, transmission.


CONCLUSIONS
These observations suggest that, as in mammals, innate immunity and mitochondrial responses are integrated in mosquitoes and that AsP38 MAPK-dependent signaling facilitates mosquito survival during parasite infection, a fact that may attest to the relatively longer evolutionary relationship of these parasites with their invertebrate compared to their vertebrate hosts. On a practical level, improved understanding of the balances and trade-offs between resistance and metabolism could be leveraged to generate fit, resistant mosquitoes for malaria control.
Department of Medical Microbiology and Immunology, School of Medicine, University of California Davis, 3437 Tupper Hall, One Shields Avenue, Davis, CA, 95616, USA. bwangucd@gmail.com.
Bo
B
Wang
Department of Medical Microbiology and Immunology, School of Medicine, University of California Davis, 3437 Tupper Hall, One Shields Avenue, Davis, CA, 95616, USA. npakpour@ucdavis.edu.
Nazzy
N
Pakpour
Department of Molecular Biosciences, School of Veterinary Medicine, University of California Davis, Davis, CA, USA. enapoli@ucdavis.edu.
Eleonora
E
Napoli
Department of Medical Microbiology and Immunology, School of Medicine, University of California Davis, 3437 Tupper Hall, One Shields Avenue, Davis, CA, 95616, USA. drexlera@who.int.
Anna
A
Drexler
Department of Medical Microbiology and Immunology, School of Medicine, University of California Davis, 3437 Tupper Hall, One Shields Avenue, Davis, CA, 95616, USA. ekglennon@ucdavis.edu.
Elizabeth K K
EK
Glennon
Department of Medical Microbiology and Immunology, School of Medicine, University of California Davis, 3437 Tupper Hall, One Shields Avenue, Davis, CA, 95616, USA. fvetwsp@ku.ac.th.
Win
W
Surachetpong
Department of Medical Microbiology and Immunology, School of Medicine, University of California Davis, 3437 Tupper Hall, One Shields Avenue, Davis, CA, 95616, USA. kcheung@ucdavis.edu.
Kong
K
Cheung
Department of Medical Microbiology and Immunology, School of Medicine, University of California Davis, 3437 Tupper Hall, One Shields Avenue, Davis, CA, 95616, USA. apaguirre@ucdavis.edu.
Alejandro
A
Aguirre
Department of Medical Microbiology and Immunology, School of Medicine, University of California Davis, 3437 Tupper Hall, One Shields Avenue, Davis, CA, 95616, USA. jmklyver@ucdavis.edu.
John M
JM
Klyver
Department of Entomology and Nematology, University of California Davis, Davis, CA, USA. eelewis@ucdavis.edu.
Edwin E
EE
Lewis
Genome and Biomedical Sciences Center, University of California Davis, Davis, CA, USA. raeigen@yahoo.com.
Richard
R
Eigenheer
Genome and Biomedical Sciences Center, University of California Davis, Davis, CA, USA. bsphinney@ucdavis.edu.
Brett S
BS
Phinney
Department of Molecular Biosciences, School of Veterinary Medicine, University of California Davis, Davis, CA, USA. cgiulivi@ucdavis.edu.|Medical Investigations of Neurodevelopmental Disorders (MIND) Institute, University of California Davis, Davis, CA, USA. cgiulivi@ucdavis.edu.
Cecilia
C
Giulivi
Department of Medical Microbiology and Immunology, School of Medicine, University of California Davis, 3437 Tupper Hall, One Shields Avenue, Davis, CA, 95616, USA. sluckhart@ucdavis.edu.
Shirley
S
Luckhart
D000818:Animals; D000852:Anopheles / Q000276:immunology* / Q000378:metabolism; D004734:Energy Metabolism; D020869:Gene Expression Profiling; D007113:Immunity, Innate; D018384:Oxidative Stress; D010963:Plasmodium falciparum / Q000276:immunology*; D020543:Proteome / Q000032:analysis; D017382:Reactive Oxygen Species / Q000032:analysis; D060888:Real-Time Polymerase Chain Reaction; D015398:Signal Transduction; D016019:Survival Analysis; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism*
D020543:Proteome; D017382:Reactive Oxygen Species; D048051:p38 Mitogen-Activated Protein Kinases