Abstract
Tachykinin-related peptides (TRPs) are important neuropeptides. Here we show that they affect the insect immune system, especially the cellular response. We also identify and predict the sequence and structure of the tachykinin-related peptide receptor (TRPR) and confirm the presence of expression of gene encoding TRPR on Tenebrio molitor haemocytes.After application of the Tenmo-TRP-7 in T. molitor the number of circulating haemocytes increased and the number of haemocytes participating in phagocytosis of latex beads decreased in a dose- and time-dependent fashion. Also, Tenmo-TRP-7 affects the adhesion ability of haemocytes. Six hours after injection of Tenmo-TRP-7, a decrease of haemocyte surface area was observed under both tested Tenmo-TRP-7 concentrations (10−7 and 10−5 M). The opposite effect was reported 24 h after injection, which indicates that the influence of Tenmo-TRP-7 on modulation of haemocyte behaviour differs at different stages of stress response. Tenmo-TRP-7 application also resulted in increased phenoloxidase activity 6 and 24 h after injection.The assessment of DNA integrity of haemocytes showed that the injection of Tenmo-TRP-7 at 10−7 M led to a decrease in DNA damage compared to control individuals. This effect was only visible 6 h after Tenmo-TRP-7 application. After 24 h, Tenmo-TRP-7 injection increased DNA damage.We also confirmed the expression of immune-related genes in nervous tissue of T. molitor. Transcripts for genes encoding receptors participating in pathogen recognition processes and antimicrobial peptides were detected in T. molitor brain, retrocerebral complex and ventral nerve cord. These results may indicate a role of the insect nervous system in pathogen recognition and modulation of immune response similar to vertebrates.Taken together, our results support the notion that tachykinin-related peptides probably play an important role in the regulation of the insect immune system. Moreover, some resemblances with action of tachykinin-related peptides and substance P showed that insects can be potential model organisms for analysis of hormonal regulation of conserved innate immune mechanisms.
Highlights
During a stress response many insect physiological systems coop erate to return to homeostasis (Adamo, 2014)
One of the most important questions was whether Tachykinin-related peptides (TRPs) can directly influence T. molitor haemocytes and shape their behaviour? The results of RT-PCR assay confirmed the presence of transcript for Tenmo-tachykinin-related peptide receptor (TRPR) gene on T. molitor haemocytes, which may suggest the presence of the receptors on the surface of these cells
Our results indicate an immunostatic effect of TRPs on insect haemocytes, which is more akin to effects of stress hormones in insects
Summary
During a stress response many insect physiological systems coop erate to return to homeostasis (Adamo, 2014). Recent research clearly showed that, similar to vertebrates, in insects stress responses are regulated by hormones, especially octopamine (OCT), a structural and functional homologue of norepinephrine, and adipokinetic hormones (AKHs) which in insects play a role similar to glucagon in mammals (Adamo, 2014; Chowanski et al, 2017). Both compounds regulate insect metabolism and immune system activity, and very often cause similar effects. Based on the knowledge about hormonal regulation during stress responses in
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