The IMD and JNK pathways drive the functional integration of the immune and circulatory systems of mosquitoes

Abstract

The immune and circulatory systems of animals are functionally integrated. In mammals, the spleen and lymph nodes filter and destroy microbes circulating in the blood and lymph, respectively. In insects, immune cells that surround the heart valves (ostia), called periostial hemocytes, destroy pathogens in the areas of the body that experience the swiftest hemolymph (blood) flow. An infection recruits additional periostial hemocytes, amplifying heart-associated immune responses. Although the structural mechanics of periostial hemocyte aggregation have been defined, the genetic factors that regulate this process remain less understood. Here, we conducted RNAseq in the African malaria mosquito, Anopheles gambiae, and discovered that an infection upregulates multiple components of the IMD and JNK pathways in the heart with periostial hemocytes. This upregulation is greater in the heart with periostial hemocytes than in the circulating hemocytes or the entire abdomen. RNAi-based knockdown then showed that the IMD and JNK pathways drive periostial hemocyte aggregation and alter phagocytosis and melanization on the heart, thereby demonstrating how these pathways regulate the functional integration between the immune and circulatory systems. Understanding how insects fight infection lays the foundation for novel strategies that could protect beneficial insects and harm detrimental ones.

Silencing Transglutaminase Genes TGase2 and TGase3 Has Infection-Dependent Effects on the Heart Rate of the Mosquito Anopheles gambiae

“…The genome of D. melanogaster encodes one transglutaminase, and it is a negative regulator of the IMD pathway [9,10]. In mosquitoes, TGase3 is a negative regulator of periostial hemocyte aggregation [19], and because the IMD pathway is a positive regulator of periostial hemocyte aggregation [26], we hypothesized that TGase3 impacts periostial hemocyte aggregation by inhibiting the IMD pathway. The IMD pathway produces an array of antimicrobial peptides [52][53][54], and therefore, removing an inhibitor of the IMD pathway may increase antimicrobial peptide production.…”

“…Members of the thioester containing protein family (TEP) and nimrod protein family (NIM) influence periostial hemocyte aggregation [ 24 , 25 ]. Moreover, the IMD pathway and the interlinked JNK pathway—as tested via the RNAi-based silencing of the positive regulators rel2 , JNK1 and JNK3 , and the negative regulators caspar and puckered —drive periostial hemocyte aggregation [ 26 ]. An RNAseq analysis in that same study identified transglutaminases as being more highly expressed in the heart containing periostial hemocytes than in other tissues [ 26 ], and follow-up experiments confirmed that TGase3 —but not TGase1 or TGase2 —is a negative regulator of periostial hemocyte aggregation during the early stages of infection, presumably by inhibiting the IMD pathway [ 19 ].…”

The immune deficiency and c-Jun N-terminal kinase pathways drive the functional integration of the immune and circulatory systems of mosquitoes

“…The datasets generated and analysed during the current study are available in an accompanying electronic supplementary material dataset file [112].…”

The Role of Mosquito Hemocytes in Viral Infections

“…The gene encoding this protein is also upregulated in periosteal hemocytes of An. gambiae after a bacterial infection [ 86 ]. Even though this pathway plays important roles in both hemocyte biology and general antiviral responses, studies connecting these two areas are lacking.…”

“…gambiae [ 93 ]. In addition, the IMD and JNK pathways regulate periosteal aggregation, phagocytosis, and melanization associated with hemocytes, most probably by the regulation of TEP expression [ 86 ]. Recently, it was reported that in An.…”