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

Abstract

Transglutaminases are pleiotropic enzymes that in mosquitoes participate in the formation of the mating plug and the wound-induced antimalarial response. Moreover, one transglutaminase, TGase3, negatively regulates the infection-induced aggregation of hemocytes on the heart. Given that TGase3 is an inhibitor of periostial hemocyte aggregation, we used RNAi-based gene silencing followed by intravital video imaging to scrutinize whether any of the three transglutaminases encoded in the genome of the mosquito, Anopheles gambiae, play a role in modulating the heart rate of uninfected and infected mosquitoes. Initially, we confirmed that an infection decreases the heart rate. Then, we uncovered that silencing TGase1 does not impact heart physiology, but silencing TGase2 results in a constant heart rate regardless of infection status, eliminating the infection-induced decrease in the heart rate. Finally, silencing TGase3 decreases the heart rate in uninfected mosquitoes but increases the heart rate in infected mosquitoes. We conclude that TGase2 and TGase3 modulate heart physiology and demonstrate that factors not classically associated with insect circulatory physiology are involved in the functional integration of the immune and circulatory systems of mosquitoes.

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

“…The IMD pathway also induces the expression of the thioester containing protein TEP1 , which is involved in phagocytosis and periostial hemocyte aggregation (14). Moreover, transglutaminases are pleiotropic enzymes that in Drosophila inhibit the IMD pathway (38, 39), and a mosquito transglutaminase – TGase3 – negatively regulates periostial hemocyte aggregation and has infection-dependent effects on the heart rate (40, 41). Finally, the JNK pathway is associated with cell adhesion and phagocytosis by regulating the cytoskeleton (32, 42).…”

“…We recently tested whether transglutaminases are involved in periostial responses in A. gambiae , and found that TGase3 – but not TGase1 or TGase2 – negatively regulates periostial hemocyte aggregation during the early stages of infection and the sequestration of melanin by periostial hemocytes during the later stages of infection (40). Moreover, disrupting TGase2 and TGase3 has infection-dependent effects on the heart rate (41). Combined, these data further support our conclusion that the IMD pathway is a positive driver of heart-associated immune responses (Figure 6).…”

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

“…The IMD pathway also induces the expression of the thioester containing protein TEP1 , which is involved in phagocytosis and periostial haemocyte aggregation [14]. Moreover, transglutaminases are pleiotropic enzymes that in Drosophila inhibit the IMD pathway [38,39], and a mosquito transglutaminase— TGase3 —negatively regulates periostial haemocyte aggregation and has infection-dependent effects on the heart rate [40,41]. Finally, the JNK pathway is associated with cell adhesion and phagocytosis by regulating the cytoskeleton [32,42].…”

“…We recently tested whether transglutaminases are involved in periostial responses in A. gambiae , and found that TGase3 —but not TGase1 or TGase2 —negatively regulates periostial haemocyte aggregation during the early stages of infection and the sequestration of melanin by periostial haemocytes during the later stages of infection [40]. Moreover, disrupting TGase2 and TGase3 has infection-dependent effects on the heart rate [41]. Combined, these data further support our conclusion that the IMD pathway is a positive driver of heart-associated immune responses (figure 6).…”