Regulation of Lipid Metabolism Genes, Lipid Carrier Protein Lipophorin, and Its Receptor during Immune Challenge in the Mosquito Aedes aegypti

Abstract

In the mosquito Aedes aegypti, the expression of two fat body genes involved in lipid metabolism, a lipid carrier protein lipophorin (Lp) and its lipophorin receptor (LpRfb), was significantly increased after infections with Gram (؉) bacteria and fungi, but not with Gram (؊) bacteria. The expression of these genes was enhanced after the infection with Plasmodium gallinaceum. RNA interference (RNAi) knockdown of Lp strongly restricted the development of Plasmodium oocysts, reducing their number by 90%. In Vg-⌬REL1-A transgenic mosquitoes, with gain-of-function phenotype of Toll/REL1 immune pathway activated after blood feeding, both the Lp and LpRfb genes were overexpressed independently of septic injury. The same phenotype was observed in the mosquitoes with RNAi knockdown of Cactus, an IB inhibitor in the Toll/REL1 pathway. These results showed that, in the mosquito fat body, both Lp and LpRfb gene expression were regulated by the Toll/REL1 pathway during immune induction by pathogen and parasite infections. Indeed, the proximal region of the LpRfb promoter contained closely linked binding motifs for GATA and NF-B transcription factors. Transfection and in vivo RNAi knockdown experiments showed that the bindings of both GATA and NF-B transcription factors to the corresponding motif were required for the induction of the LpRfb gene. These findings suggest that lipid metabolism is involved in the mosquito systemic immune responses to pathogens and parasites. Lipophorin (Lp)2 is the major lipid carrier protein in insects. It delivers lipids to various organs via the hemolymph as a reusable shuttle, with no concomitant degradation of the protein matrix of the Lp particle. The fat body, which is an insect analog of vertebrate liver and adipose tissue combined, plays a key role in lipid metabolism by being the site of lipid storage and mobilization. The loading and unloading of lipids into and from fat body cells is accomplished by a shuttle mechanism involving Lp and a multiprotein complex called a lipid transfer particle. The lipophorin particle consists of three apolipoproteins: apolipoprotein I, apolipoprotein II, and apolipoprotein III (1-3). ApoLpI and apoLpII are encoded by a single gene (4 -6). Likewise, mosquito Aedes aegypti Lp consists of apoLpI and apoLpII, the mRNAs of which originate from a single large precursor RNA, indicating that they are encoded by the same gene. Aedes Lp protein level increases upon ingestion of a blood meal, when the mosquito needs an increased rate of lipid transport to developing oocytes. Lipophorin in the whole bodies reaches its maximal levels by 40 -48 h post-blood meal (PBM) when major events of egg yolk and lipid deposition have been completed. However, Lp mRNA and the rate of Lp synthesis in the fat body reach their maximal levels at 18 -20 h PBM (7, 8 -10).The intracellular uptake of Lp is mediated by its cognate lipophorin receptor (LpR), which belongs to the superfamily of low density lipoprotein receptors (LDLRs) (11-15). LpRs have been cloned from several insects, in...

Effect of Wolbachia on Replication of West Nile Virus in a Mosquito Cell Line and Adult Mosquitoes

“…In addition, GATA4 in conjunction with NF-B transcription factors were found to be required for induction of lipophorin receptor gene involved in A. aegypti systemic immune responses and lipid metabolism (32). In insects, lipophorin is the main lipid carrier protein transporting lipids to various tissues and is also involved in immune responses (32,33). It is not clear at this stage how upregulation of GATA4 by KUNmiR-1 or Wolbachia may facilitate WNV gRNA replication in mosquito cells, and this requires further investigation.…”

“…GATA4, specifically, is expressed after a blood meal and acts as a transcriptional activator of vitellogenin (vg), which is an important protein in vitellogenesis and egg development (31). In addition, GATA4 in conjunction with NF-B transcription factors were found to be required for induction of lipophorin receptor gene involved in A. aegypti systemic immune responses and lipid metabolism (32). In insects, lipophorin is the main lipid carrier protein transporting lipids to various tissues and is also involved in immune responses (32,33).…”

Quantitative Analysis of Replication and Tropisms of Dengue Virus Type 2 in Aedes albopictus

“…42 Pathogen infections can activate a lot of immune factors expressed in mosquito fat body. [43][44][45][46][47][48][49] Therefore, immune response may play an important role in the process of DENV infection in mosquito fat body. Our results indicated that DENV-2 infection in fat body may induce rapid immune response at early times post-infection that can suppress virus replication in low level and protect fat body and even other organs from damage.…”

Cell Signaling During Trypanosoma cruzi Development in Triatominae

“…Also, we have shown lipid uptake by the malaria parasite during its life cycle in the invertebrate host [49]. Molecular evidence for the role of Lp in malaria parasite development has been provided [50]. However, the direct uptake of Lp and lipids by malaria parasite stages while inside its vector are not available.…”