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Mobilization of lipids in Aedes aegypti

Mobilization of lipids in Aedes aegypti

Woong Hee Cho

Biochemistry & Molecular Biology

Generally, mosquitoes feed on fruits and nectars of flowers. However, there are several species of mosquitoes -anautogenous mosquitoes- in which the female insect must feed a blood meal on a vertebrate host to produce eggs. For this reason anautogenous female mosquitoes are able to transmit diseases. These mosquitoes do not cause diseases; the parasites do. When non-infected female mosquito bites a person who already has dengue or Zika virus, the virus will also be passed on to the mosquito, and thus the mosquito carries the parasite. When the mosquito bites a heathy person, the person will likely be infected and it goes on. Female mosquitoes act as carriers (vectors) of various diseases such as malaria caused by plasmodium – a one-cell microorganism parasite-, Dengue and yellow fever caused by flavivirus. The main vector of Dengue, Yellow fever, Chikungunya, and Zika is Aedes aegypti. Mosquitoes have been traditionally controlled by use of chemical insecticides but new mechanisms of insecticide resistance are a serious concern. Alternative methods to control mosquito population are needed. To design new strategies to control mosquito population, first we need a detailed understanding of mosquito biology. In this context, we are studying the mechanisms of mobilization of fat (lipid) in the females of Aedes aegypti. Mobilization of fat reserves from the fat (adipose) tissue to the ovaries is a crucial step for egg maturation. Unlike most insects that mobilize lipids as diglycerides (DG), mosquitoes secrete TG into circulation (Ford and Van Heusden, 1994). In other words, the main lipid component of lipophorin-the lipid carrier in circulation- is triglycerides (TG) instead of diglycerides (DG) as the vast majority of insects. We proposed that the mobilization of lipids in mosquitoes take three steps: TG hydrolysis at the surface of the lipid droplets, TG re-synthesis (endoplasmic reticulum) and TG secretion (TG-lipophorin). We began the study of the second step of TG mobilization which involves TG-re-synthesis. Multiple proteins are involved in this process including the lipid droplet associated proteins PLIN1 and PLIN2 and the essential enzymes: monoacylglycerol acyltransferase (MGAT) and diacylglycerol acyltransferase (DGAT) (Soulages et al., 2014). MGAT re-synthesize MG back to DG whereas DG will also resynthesize to TG by DGAT. It is unknown why mosquitoes have different mechanism of lipid mobilization. It could be that mosquitoes have strong activities of MGAT and DGAT; thus resynthesizing MG and DG back to TG. If we could figure out the balance of DGAT and MGAT in mosquitoes, we will be able to know why mosquitoes transport lipids in the form of TG.