Insulin, IGF and Insulin Signaling: effects on Anopheles lifespan and immunity

摘要

Abstract Increased drug and pesticide resistance has rendered many control programs for mosquito-borne diseases useless, resulting in an urgent need for new control strategies. Since malaria parasites must develop for up to two weeks in the mosquito there is opportunity to disrupt this development by enhancing mosquito innate immunity or shortening the mosquito's lifespan. The insulin/IGF-1 signaling cascade (ISC) has been shown to regulate both innate immunity and lifespan in invertebrates, and could be manipulated to reduce vector competence of mosquitoes. Based on our preliminary data, exogenous insulin and IGF-1 in the bloodmeal may also play major roles in the midgut and other tissues. To test these hypotheses, we will first determine whether exogenous human insulin and IGF-1 can stimulate the ISC in the midgut and other tissues, such as the fat body, in the mosquito Anopheles stephensi. We will also test the impact of these factors on oxidative stress and NO production, key components of aging, innate immunity, and signaling. Next we will engineer An. stephensi mosquitoes to express active forms of two ISC proteins, Akt and PTEN, in the midgut after a bloodmeal. Because AKT activates the midgut ISC and PTEN has the opposite effect, we will be able to answer three questions. 1) Does the midgut ISC regulate oxidative stress and in turn aging? 2) Does the midgut ISC affect signaling in other tissues? 3) Do changes to the ISC affect Plasmodium falciparum development? Finally, we will examine the impact of physiological levels of exogenous human insulin and IGF- 1 on the transgenic mosquitoes described above. Insulin levels in human blood can vary by as much as 10-fold after a meal and during malaria parasite infection. By understanding and taking into account the effects of this naturally occurring variation in human bloodmeals we can better predict the efficacy of Akt and PTEN overexpression on critical variables (e.g., lifespan and immunity) of vector competence. In summary, our proposed work will test both basic and applied hypotheses regarding the ISC and its impacts on mosquito physiology and vector competence that were conceptualized for Caenorhabditis elegans, Drosophila melanogaster and mammals. In addition, our work offers a different approach to the transgenic modification of mosquitoes to limit their vectorial capacity. Relevance: Many mosquito-borne disease agents, including malaria parasites, dengue virus, and West Nile virus, must develop in mosquitoes for extended periods before being transmitted to humans. We hope to enhance innate immunity and/or reduce average lifespan of a model mosquito below this development period so that transmission of malaria parasites is reduced or eliminated.