Regulating mosquito lifespan and immunity through insulin / IGF-like signaling in the midgut

Malaria, caused by protozoan parasites of the genus Plasmodium, kills nearly one million people annually. With rising drug and insecticide resistance, there is an urgent need to develop novel malarial control strategies, including the use of genetically modified mosquitoes. The IIS pathway is highly conserved and can regulate lifespan, metabolism, immunity and pathogen resistance. In this body of work, we demonstrate that IIS in the midgut can be manipulated genetically and via ingested insulin-like growth factor 1 (IGF1) to regulate A. stephensi immunity and fitness, resulting in both short and long-lived mosquitoes that can resist P. falciparum infection. We first show that transgenically increasing Akt, a key IIS nexus molecule, disrupts parasite development and concurrently reduces the duration that mosquitoes are infective to humans. Specifically, we find that increased Akt signaling in the midgut of A. stephensi completely blocks parasite infection and leads to an 18-20% reduction in average mosquito lifespan. Next, we show that ingested IGF1, a human insulin-like peptide that is functionally linked with lifespan and immunity, activates IIS in the A. stephensi midgut and reduces P. falciparum development by >20%. We also show that at low doses, IGF1 extends the average mosquito lifespan by 23%, and this was linked to a distinct pattern of IIS signal protein activation. Finally, we demonstrate that IGF1 mediated anti-parasite resistance is due to a rise in midgut reactive oxygen and nitrogen species (RNOS). Inhibiting RNOS by co-feeding the nitric-oxide synthase inhibitor L-NAME with IGF1 rescues parasite infection. Further, we link lifespan extension in low-dose IGF1 treated mosquitoes with control of RNOS induced damage in the midgut via dose-specific initiation of JNK and insulin/IGF signaling. Hence, in this body of work, we demonstrate that in A. stephensi, the IIS pathway, central to control of lifespan, immunity and metabolism, can be manipulated genetically and by the addition of human IGF1. We provide evidence that human IGF1 can fine tune IIS and processes controlling midgut epithelial homeostasis, to enhance lifespan and increase anti-parasite resistance. We reveal the importance of IIS controlled redox pathways in regulating A. stephensi midgut integrity and we demonstrate that IIS can be harnessed for the transgenic control of malaria. Taken together, these studies enhance our understanding of insulin/IGF1 signaling in the mosquito midgut and the ways in which this pathway can be leveraged to generate fit, resistant mosquitoes for malaria transmission control.