Elucidating the Anti‐Diuretic Hormone Signalling System of CAPA Neuropeptides in the Disease Vector Mosquito, Aedes aegypti
Authors: Sajadi Farwa , Paluzzi Jean-Paul 
Published: April 2020

Blood‐feeding insects, including female Aedes aegypti mosquitoes, face the challenge of excess water and ion intake after a blood meal. To cope with this, insects have a highly active excretory system that includes the Malpighian ‘renal’ tubules (MTs), which are under rigorous control by several neuroendocrine factors. While endocrine regulation has been extensively studied in insects, most research has focused on the effects of diuretic hormones with limited study on anti‐diuretic hormones. Insect CAPA neuropeptides are produced in the central nervous system and are evolutionarily related to the vertebrate neuromedinU peptides. While CAPA peptides elicit distinct responses in different insect species, their activity on stimulated MTs in the adult A. aegypti remained unknown. Given the CAPA receptor is highly enriched in insect MTs, the objectives of this study were to examine the effects of a CAPA peptide on adult female MTs stimulated with various diuretic factors.

The effect of endocrine factors on fluid secretion rate was measured using an in vitro bioassay where CAPA was found to inhibit secretion of MTs stimulated by select diuretic factors, 5‐HT and DH31, while having no effect on other diuretic factors, including kinin‐related and corticotropin releasing factor‐related (CRF) peptides. Although CAPA elicits strong anti‐diuretic activity, it does not influence the relative proportions of cations transported by adult MTs, thus maintaining the kaliuretic activity of 5‐HT and the natriuretic activity of DH31. Notably, the inhibitory effect of CAPA was abolished by knocking down the receptor using RNAi, verifying its critical role in anti‐diuresis. To investigate the signalling cascade mediating this anti‐diuretic effect, the second messenger cGMP was tested on adult MTs revealing that both 5‐HT and DH31–stimulated secretion is strongly inhibited by cGMP, similar to effects seen with CAPA. Pharmacological inhibition of PKG/NOS signalling abolishes the anti‐diuretic activity of CAPA, confirming the role of cGMP/PKG/NOS in the CAPA signalling pathway. Furthermore, MTs treated with bafilomycin, a V‐type H+‐ATPase inhibitor, was found to inhibit fluid secretion stimulated by 5‐HT and DH31, while having no inhibitory action on CRF‐stimulated MTs. Additionally, alkalization of the secreted fluid in response to CAPA suggests inhibition of the apical V‐type H+‐ATPase, which may lead to constrained entry of cations (Na+and K+) across the apical membrane of the MTs.

A. aegypti mosquitoes are vectors of a variety of pathogens leading to diseases including Dengue fever and Zika virus. In this study, the importance of hormonal regulation of the MTs is demonstrated, analyzing the importance of both diuretic and anti‐diuretic hormones. Given the central importance of the MTs in insect biology, these insights will be useful considering the need to develop novel strategies or compounds which more specifically and efficiently reduce the burden of insect disease vectors.

Support or Funding Information

Supported by an NSERC Discovery Grant (JPP), Petro Canada Young Innovator Award (JPP), Ontario Ministry of Research & Innovation Early Researcher Award (JPP), NSERC Canada Graduate Scholarship (FS), Vernon Oliver Stong Graduate Scholarship in Science (FS), and The Carswell Scholarships in the Faculty of Science (FS)