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

SIMPLE SUMMARY: The immune and circulatory systems of insects are functionally integrated. An infection induces the migration of immune cells called hemocytes to the surface of the heart, where they kill pathogens around valves called ostia. In mosquitoes, a transglutaminase inhibits the infection-induced aggregation of hemocytes on the heart. Here, we studied whether transglutaminases also modify the heart contraction rate. First, we confirmed that an infection decreases the mosquito heart rate. Then, we found that disrupting transglutaminase genes has infection-dependent effects on the heart rate. Silencing TGase1 does not affect heart physiology. However, silencing TGase2 eliminates the infection-induced decrease in the heart rate, and silencing TGase3 decreases the heart rate in uninfected mosquitoes but increases the heart rate in infected mosquitoes. These experiments identify new factors that affect heart physiology in mosquitoes. 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.