Overexpression of phosphatase and tensin homolog improves fitness and decreases Plasmodium falciparum development in Anopheles stephensi

Abstract

The insulin/insulin-like growth factor signaling (IIS) cascade is highly conserved and regulates diverse physiological processes such as metabolism, lifespan, reproduction and immunity. Transgenic overexpression of Akt, a critical regulator of IIS, was previously shown to shorten mosquito lifespan and increase resistance to the human malaria parasite Plasmodium falciparum. To further understand how IIS controls mosquito physiology and resistance to malaria parasite infection, we overexpressed an inhibitor of IIS, phosphatase and tensin homolog (PTEN), in the Anopheles stephensi midgut. PTEN overexpression inhibited phosphorylation of the IIS protein FOXO, an expected target for PTEN, in the midgut of A. stephensi. Further, PTEN overexpression extended mosquito lifespan and increased resistance to P. falciparum development. The reduction in parasite development did not appear to be due to alterations in an innate immune response, but rather was associated with increased expression of genes regulating autophagy and stem cell maintenance in the midgut and with enhanced midgut barrier integrity. In light of previous success in genetically targeting the IIS pathway to alter mosquito lifespan and malaria parasite transmission, these data confirm that multiple strategies to genetically manipulate IIS can be leveraged to generate fit, resistant mosquitoes for malaria control.

Plasmodium falciparum suppresses the host immune response by inducing the synthesis of insulin-like peptides (ILPs) in the mosquito Anopheles stephensi

“…To test these hypotheses, we utilized two approaches established in our previous studies for inhibition of MEK/ERK and PI3K/Akt signaling. We used the MEK inhibitors PD98059 and U0126 (Surachepong et al, 2009) and the PI3K inhibitor wortmannin (Lim et al, 2005; Pakpour et al, 2012) as well as overexpression of A. stephensi phosphatase and tensin homolog (PTEN, Hauck et al, 2013), the endogenous inhibitor of PI3K/Akt signaling, to query regulation of inducible and baseline AsILP expression, respectively. Pre-treatment of ASE cells with PD98059 for 1 hour prior to stimulation, prevented Pf Ps-induced ERK phosphorylation (Fig.…”

“…In the mosquito midgut, ingested Plasmodium gametocytes undergo a series of developmental changes in the context of robust immune responses that contribute to marked losses in parasite numbers (Clayton et al, 2014; Yassine et al, 2010). This process is regulated in part by insulin/insulin-like growth factor signaling (IIS) and mitogen-activated protein kinase (MAPK) pathways (Corby-Harris et al, 2010; Drexler et al, 2013; Drexler et al, 2014; Hauck et al, 2013; Horton et al, 2010; Luckhart et al, 2013; Pakpour et al, 2012; Surachetpong et al, 2009; Surachetpong et al, 2010). …”

Supplementation with Abscisic Acid Reduces Malaria Disease Severity and Parasite Transmission

“…stephensi nitric oxide synthase (AsNOS), defensin, LRIM, TEP1, and APL1 were as previously described. 28,29 For gene expression analysis of mouse liver and spleen, organs were flash frozen after necropsy and stored at −80°C before RNA was extracted in TriZOL and cDNA synthesized. Real-time polymerase chain reaction was performed using TaqMan ® Gene Expression Assays for mouse NOS2, PPARγ, and β-actin (Applied Biosystems) with volumes and cycling conditions as previously described.…”

Effects of ingested vertebrate-derived factors on insect immune responses

“…Indeed, exogenous insulin from vertebrate blood activates IIS in mosquitoes [26, 27] and tsetse flies [34]. In anopheline mosquitoes, physiological levels of insulin (170 pM) can significantly increase P. falciparum oocyst development [26–28], and control of malaria parasite infection requires at least three IIS proteins (ERK [35], Akt/PKB [36••, 37], PTEN [38]). In humans, IIS modifies innate immune responses through the regulation of NF-κB transcription factors [39].…”