Anti-diuretic activity of a CAPA neuropeptide can compromiseDrosophilachill tolerance

Abstract

For insects, chilling injuries that occur in the absence of freezing are often related to a systemic loss of ion and water balance that leads to extracellular hyperkalemia, cell depolarization and the triggering of apoptotic signalling cascades. The ability of insect ionoregulatory organs (e.g. the Malpighian tubules) to maintain ion balance in the cold has been linked to improved chill tolerance, and many neuroendocrine factors are known to influence ion transport rates of these organs. Injection of micromolar doses of CAPA (an insect neuropeptide) have been previously demonstrated to improve cold tolerance, but the mechanisms through which it impacts chill tolerance are unclear, and low doses of CAPA have been previously demonstrated to cause anti-diuresis in insects, including dipterans. Here, we provide evidence that low (femtomolar) and high (micromolar) doses of CAPA impair and improve chill tolerance, respectively, via two different effects on Malpighian tubule ion and water transport. While low doses of CAPA are anti-diuretic, reduce tubule K clearance rates and reduce chill tolerance, high doses facilitate K clearance from the haemolymph and increase chill tolerance. By quantifying CAPA peptide levels in the central nervous system, we estimated the maximum achievable hormonal titres of CAPA and found further evidence that CAPA may function as an anti-diuretic hormone in We provide the first evidence of a neuropeptide that can negatively affect cold tolerance in an insect and further evidence of CAPA functioning as an anti-diuretic peptide in this ubiquitous insect model.

Specialized stellate cells offer a privileged route for rapid water flux in Drosophila renal tubule

“…In Drosophila, the renal tubule has 2 major cell types (4)(5)(6); the mitochondria-rich principal cell actively transports protons via an apical, plasma membrane vacuolar H + -ATPase (V-ATPase) (7), setting up a gradient which is exchanged primarily for potassium (8,9), which enters the cell basolaterally through the combined activity of Na + , K + -ATPase (10), inward rectifier potassium channels (11)(12)(13) and potassium cotransports (14)(15)(16). The smaller stellate cell (17,18) provides a route for hormone-stimulated (19)(20)(21)(22) chloride conductance through a basolateral ClC-a chloride channel (23), partnered with secCl, an apical cys-loop chloride channel (24), to balance the lumen-positive charge, and so effect a net movement of salt. Aquaporins (AQPs; the water transporting major intrinsic proteins [MIPs]) are known to be highly expressed in insect tubules (25)(26)(27)(28)(29), and global knockdown of an AQP in the Aedes mosquito (30)(31)(32), or in the beetle Tribolium (33), impacts water loss.…”

An anti-diuretic hormone receptor in the human disease vector,Aedes aegypti: identification, expression analysis and functional deorphanization

“…However, countless studies in diverse insect species have established that ADHs can also act on the MTs to reduce primary urine secretion 31, 36–38,40,77 . CAPA neuropeptides have been demonstrated to display potent anti-diuretic effects in a variety of insects 38,39,42,78 , including A. aegypti mosquitoes 36,37 , while they have been shown to function as DHs and ADHs in D. melanogaster 40,79–81 .…”

“…Interestingly, the inhibition of both DH 31 - and 5-HT stimulated diuresis by Aedae CAPA-1 and cGMP were sensitive to the PKG inhibitor, KT5823, which indicates that while some differences in signalling associated with inhibition of different diuretic hormones may occur, these inhibitory pathways likely converge and involve cGMP activating protein kinase G. Taken together, the findings in this study provide definitive evidence that CAPA peptides are anti-diuretic hormones in the mosquito A. aegypti , which inhibit fluid secretion of adult mosquito MTs through a signalling cascade involving the NOS/cGMP/PKG pathway. Further studies are necessary in mosquitoes as well as other insects to elucidate the differential regulation by DHs and ADHs given ample data supporting that cGMP and related effectors can be both stimulatory 44,79,99,101 and inhibitory 31,32, 36–37,43,81,102 in their control on insect MTs. In conclusion, we have established an anti-diuretic hormone system in the adult mosquito A. aegypti providing evidence of a neural-renal axis whereby the neuropeptidergic anti-diuretic hormone is released by the abdominal segmental neurohaemal organs and subsequently targets their cognate receptor expressed within the principal cells of the MTs to counteract the activity of a subset of mosquito diuretic hormones.…”

Dissecting cause from consequence: a systematic approach to thermal limits

“…At the muscles, this time-and temperature-dependent hyperkalaemia causes cell depolarization, triggering Ca 2+ influx and initiating necrotic and/or apoptotic cell death (Andersen et al, 2017;Bayley et al, 2018;MacMillan et al, 2015a), which probably drives a feed-forward loop of further K + release from cells, further cell depolarization and further cell death (MacMillan et al, 2015b). In this framework, a chain of causation is emphasized and has, in some cases, been tested through manipulative experiments (Andersen et al, 2017;Bayley et al, 2018;MacMillan et al, 2015aMacMillan et al, , 2018. However, the majority of this work has been completed by a limited group of researchers focused mainly on low temperatures, and this model thus remains to be more widely tested.…”

“…Thus, at the organ system level, determining the causes of failure requires experiments that manipulate the function of the system in question while observing the effects in vitro, and reconciling these observations with parallel studies at the whole-organism level (e.g. MacMillan et al, 2018). When strong evidence for a relationship is found in this manner, molecular biology and genetics offer powerful tools for testing cause and effect (i.e.…”