Tachykinin Related Peptides

Introduction

In a number of invertebrates belonging to the mollusca, echiuridea, insecta and crustacea, peptides similar in sequence to members of the tachykinin family have been identified. These peptides have been designated tachykinin-related peptides (TRPs) and are characterized by the preserved C-terminal pentapeptide FX1GX2Ramide (X1 and X2 are variable residues). All invertebrate TRPs are myostimulatory on insect hindgut muscle, but also have a variety of additional actions: they can induce contractions in cockroach foregut and oviduct and in moth heart muscle, trigger a motor rhythm in the crab stomatogastric ganglion, depolarize or hyperpolarize identified interneurons of locust and the snail Helix and induce release of adipokinetic hormone from the locust corpora cardiaca.

Mechanism of action

Physiological roles of TRPs in vivo are not clear in insects. A few effects have, however, been demonstrated in vitro: TRPs stimulate the contractions of visceral and skeletal muscle, induce release of fatty motility hormone from locust corpora cardiaca, depolarize identified locust neurons and induce pheromone biosynthesis in the moth Bombyx mori. Actions of TRPs and tachykinins on cloned putative TRP receptors of Drosophila, a possible role of these in embryonic development.

Application of TRPs

In all examined species, and especially in mammals (the phylum more thoroughly studied), Tachykinins initiate a range of biological activities (both in the central nervous system and peripheral) that may vary significantly in strains of different species or even single species. The broad spectrum tachykinin antagonist spantide I can block the action of invertebrate TRPs and substance P in invertebrate models. This may suggest that the active conformation of the invertebrate TRPs and the mammalian tachykinins is similar. It appears that invertebrate TRPs are multifunctional peptides that may be involved in both developmental processes and in regulatory roles in the mature nervous system, certain glands and visceral muscle of different kinds. Diverse in vitro cell-based signal transduction experiments have been employed to study signal transduction induced by distinct TRPs. It would be fruitful in the future to extend these studies and to investigate whether these in vitro observations are also relevant for in vivo situations.

References

1. Henssen, A. G., Odersky, A., Szymansky, A., Seiler, M., Althoff, K., Beckers, A., ... & Struck, J. (2017). Targeting tachykinin receptors in neuroblastoma. Oncotarget, 8(1), 430.
2. Van Loy, T., Vandersmissen, H. P., Poels, J., Van Hiel, M. B., Verlinden, H., & Broeck, J. V. (2010). Tachykinin-related peptides and their receptors in invertebrates: a current view. Peptides, 31(3), 520-524.
   3. Satake, H. (2015). Tachykinin-Related Peptides. In Handbook of Hormones (pp. 364-e44B).