title: Plasmodium falciparum suppresses the host immune response by inducing the synthesis of insulin-like peptides (ILPs) in the mosquito Anopheles stephensi.
abstract: The insulin-like peptides (ILPs) and their respective signaling and regulatory pathways are highly conserved across phyla. In invertebrates, ILPs regulate diverse physiological processes, including metabolism, reproduction, behavior, and immunity. We previously reported that blood feeding alone induced minimal changes in ILP expression in Anopheles stephensi. However, ingestion of a blood meal containing human insulin or Plasmodium falciparum, which can mimic insulin signaling, leads to significant increases in ILP expression in the head and midgut, suggesting a potential role for AsILPs in the regulation of P. falciparum sporogonic development. Here, we show that soluble P. falciparum products, but not LPS or zymosan, directly induced AsILP expression in immortalized A. stephensi cells in vitro. Further, AsILP expression is dependent on signaling by the mitogen-activated protein kinase kinase/extracellular signal-regulated kinase (MEK/ERK) and phosphatidylinositol 3'-kinase (PI3K)/Akt branches of the insulin/insulin-like growth factor signaling (IIS) pathway. Inhibition of P. falciparum-induced ILPs in vivo decreased parasite development through kinetically distinct effects on mosquito innate immune responses. Specifically, knockdown of AsILP4 induced early expression of immune effector genes (1-6 h after infection), a pattern associated with significantly reduced parasite abundance prior to invasion of the midgut epithelium. In contrast, knockdown of AsILP3 increased later expression of the same genes (24 h after infection), a pattern that was associated with significantly reduced oocyst development. These data suggest that P. falciparum parasites alter the expression of mosquito AsILPs to dampen the immune response and facilitate their development in the mosquito vector.
authors.affiliation: Department of Medical Microbiology and Immunology, 3437 Tupper Hall, One Shields Avenue, School of Medicine, University of California, Davis, CA 95616, USA. Electronic address: jepietri@ucdavis.edu.
authors.forename: Jose E
authors.initials: JE
authors.lastname: Pietri
authors.affiliation: Department of Medical Microbiology and Immunology, 3437 Tupper Hall, One Shields Avenue, School of Medicine, University of California, Davis, CA 95616, USA. Electronic address: ejpietri@ucdavis.edu.
authors.forename: Eduardo J
authors.initials: EJ
authors.lastname: Pietri
authors.affiliation: Department of Medical Microbiology and Immunology, 3437 Tupper Hall, One Shields Avenue, School of Medicine, University of California, Davis, CA 95616, USA. Electronic address: rapotts@ucdavis.edu.
authors.forename: Rashaun
authors.initials: R
authors.lastname: Potts
authors.affiliation: Department of Entomology, 410 Forbes, College of Agriculture and Life Sciences, University of Arizona, Tucson, AZ 85721, USA. Electronic address: mriehle@ag.arizona.edu.
authors.forename: Michael A
authors.initials: MA
authors.lastname: Riehle
authors.affiliation: Department of Medical Microbiology and Immunology, 3437 Tupper Hall, One Shields Avenue, School of Medicine, University of California, Davis, CA 95616, USA. Electronic address: sluckhart@ucdavis.edu.
authors.forename: Shirley
authors.initials: S
authors.lastname: Luckhart
mesh_terms: D000818:Animals; D000852:Anopheles / Q000276:immunology* / Q000469:parasitology*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D007301:Insect Hormones / Q000235:genetics*; D019476:Insect Proteins / Q000096:biosynthesis / Q000235:genetics; D007328:Insulin / Q000031:analogs & derivatives; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics; D020935:MAP Kinase Signaling System / Q000276:immunology; D016778:Malaria, Falciparum / Q000276:immunology / Q000469:parasitology; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D036361:Peptide Hormones / Q000235:genetics*; D058539:Phosphatidylinositol 3-Kinase / Q000378:metabolism; D010963:Plasmodium falciparum / Q000276:immunology*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D013002:Somatomedins / Q000378:metabolism
chemical_list: D007301:Insect Hormones; D019476:Insect Proteins; D007328:Insulin; D036341:Intercellular Signaling Peptides and Proteins; D036361:Peptide Hormones; D013002:Somatomedins; D058539:Phosphatidylinositol 3-Kinase; D051057:Proto-Oncogene Proteins c-akt; D048049:Extracellular Signal-Regulated MAP Kinases; D020929:Mitogen-Activated Protein Kinase Kinases
keywords: Anopheles; Immunity; Insulin; Insulin-like peptide; Malaria; Mosquito; NF-κB; Plasmodium