Anopheles stephensi p38 MAPK signaling regulates innate immunity and bioenergetics during Plasmodium falciparum infection

Abstract

BackgroundFruit 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.MethodsA. 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.ResultsThe 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.ConclusionsThese 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.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-015-1016-x) contains supplementary material, which is available to authorized users.

Anopheles gambiae: Metabolomic Profiles in Sugar‐Fed, Blood‐Fed, and Plasmodium falciparum‐Infected Midgut

“…In the Luckhart lab, the procedures for culture of P. falciparum strain NF54 MCB and mosquito infection were described previously [18]. The infection rate for each replicate mosquito cohort was determined by counting P. falciparum oocysts in the midgut of a sample of mosquitoes at day 10 after infection.…”

Host–pathogen interactions in malaria: cross-kingdom signaling and mitochondrial regulation

“…This pathology can be reduced, increasing mouse survivorship, through treatment of parasite-infected mice with SMIs that block p38 MAPK, PKC or JNK signaling [60• and 61]. Together with our data from the mosquito host [56], these observations suggest that protein kinase SMIs could be leveraged for drug treatment to reduce disease pathology in humans and to block parasite transmission in mosquitoes that feed on treated patients.…”

“…Consequences of increased p38 MAPK activation in response to P. falciparum include endothelial dysfunction, heightened TLR2 responsiveness, elevated plasma lysozyme levels, and overproduction of inflammatory cytokines [52, 53, 54• and 55]. In A. stephensi, P. falciparum infection rapidly activates p38 MAPK signaling in the mosquito midgut, which precipitates decreased transcription of a variety of NF-κB-dependent innate immune genes [56]. Conversely, delivery of small molecule inhibitors (SMIs) of p38 MAPK via the bloodmeal significantly enhances immune gene expression and reduces P. falciparum development in A. stephensi 56].…”

“…In A. stephensi, P. falciparum infection rapidly activates p38 MAPK signaling in the mosquito midgut, which precipitates decreased transcription of a variety of NF-κB-dependent innate immune genes [56]. Conversely, delivery of small molecule inhibitors (SMIs) of p38 MAPK via the bloodmeal significantly enhances immune gene expression and reduces P. falciparum development in A. stephensi 56]. While p38 MAPK-dependent signaling increases parasite burden in the mosquito host, resulting pathology from this burden appears to be offset by p38 MAPK-enhanced host survival during infection [56], a situation that may attest to the relatively longer evolutionary relationship of malaria parasites with their invertebrate hosts.…”

“…Conversely, delivery of small molecule inhibitors (SMIs) of p38 MAPK via the bloodmeal significantly enhances immune gene expression and reduces P. falciparum development in A. stephensi 56]. While p38 MAPK-dependent signaling increases parasite burden in the mosquito host, resulting pathology from this burden appears to be offset by p38 MAPK-enhanced host survival during infection [56], a situation that may attest to the relatively longer evolutionary relationship of malaria parasites with their invertebrate hosts. Collectively, these observations suggest that therapeutic use of p38 MAPK inhibitors could reduce disease pathology in human hosts and reduce parasite development and transmission by mosquitoes that feed on treated patients 1 .…”