Nitric oxide produced by periostial hemocytes modulates the bacterial infection induced reduction of the mosquito heart rate

Abstract

The circulatory and immune systems of mosquitoes are functionally integrated. An infection induces the migration of hemocytes to the dorsal vessel, and specifically, to the regions surrounding the ostia of the heart. These periostial hemocytes phagocytose pathogens in the areas of the hemocoel that experience the highest hemolymph flow. Here, we investigated whether a bacterial infection affects cardiac rhythmicity in the African malaria mosquito, Anopheles gambiae. We discovered that infection with Escherichia coli, Staphylococcus aureus and Staphylococcus epidermidis, but not Micrococcus luteus, reduces the mosquito heart rate and alters the proportional directionality of heart contractions. Infection does not alter the expression of genes encoding crustacean cardioactive peptide (CCAP), FMRFamide, corazonin, neuropeptide F or short neuropeptide F, indicating that they do not drive the cardiac phenotype. Infection upregulates the transcription of two superoxide dismutase (SOD) genes, catalase and a glutathione peroxidase, but dramatically induces upregulation of nitric oxide synthase (NOS) in both the heart and hemocytes. Within the heart, nitric oxide synthase is produced by periostial hemocytes, and chemically inhibiting the production of nitric oxide using l-NAME reverses the infection-induced cardiac phenotype. Finally, infection induces the upregulation of two lysozyme genes in the heart and other tissues, and treating mosquitoes with lysozyme reduces the heart rate in a manner reminiscent of the infection phenotype. These data demonstrate an exciting new facet of the integration between the immune and circulatory systems of insects, whereby a hemocyte-produced factor with immune activity, namely nitric oxide, modulates heart physiology.

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

“…The heart of dsbla(Ap R ) uninfected mosquitoes contracted at 1.89 Hz, and infection for 4 h decreased the heart contraction rate by 8.4% (Figure 3A). Again, this infection-induced decrease in the heart rate is similar to what we have previously observed following infection with bacteria [27], and it is also similar to what we observed here at 24 h following treatment (Figure 2). Similar to dsbla(Ap R ) mosquitoes, infection decreased the heart rate of dsTGase1 mosquitoes by 6.3%.…”

Trained Immunity in Anopheles gambiae: Antibacterial Immunity Is Enhanced by Priming via Sugar Meal Supplemented With a Single Gut Symbiotic Bacterial Strain

“…However, once being introduced into hemocoel by injection with approximately 100 CFU per mosquito, both strains cause acute virulent infections (Figure 2), and none of the challenged mosquitoes survived beyond 3 days. Escherichia coli has been widely used as a representative of Gram-negative bacteria for studying antibacterial immunity in mosquitoes (Moita et al, 2006;Nakhleh et al, 2017;Das De et al, 2018;Brown et al, 2019;Reyes Ruiz et al, 2019;Estevez-Lao et al, 2020;Powers et al, 2020). According to the literature, E. coli causes a chronic infection in the hemocoel.…”

NO Synthesis in Immune-Challenged Locust Hemocytes and Potential Signaling to the CNS

“…In the fly Chrysomya megacephala, nitrate levels peaked 24 h after inoculation with yeast [ 32 ], and even in murine microglia cells, the highest nitrite levels indicative of NO synthesis were shown in response to LPS after 24 h [ 86 ]. In the mosquito, Anopheles gambiae , elevated NO synthesis [ 35 ] could at least partially be assigned to elevated NOS expression [ 33 , 44 ].…”

“…The synthetic activity of the induced NOS has been shown as Ca 2+ -dependent [ 30 , 32 , 33 , 34 ]. Elevated NO levels due to infection or immune stimulants were detected by the Griess reaction, for instance in Anopheles gambiae , Anopheles stephensi , Drosophila melanogaster , the flesh fly Sarcophaga argyrostoma or the moths Mythimna separata and Galleria mellonella [ 33 , 35 , 36 , 37 , 38 , 39 , 40 , 41 ]. Elevated NOS expression was shown by NADPH diaphorase activity [ 32 , 40 , 42 ], NOS-antibodies [ 33 , 42 , 43 ], or NOS mRNA levels [ 37 , 44 , 45 ]).…”