Do Second Messengers of Neuroendocrine Factors Alter Aquaporin Expression in Malpighian tubules of the Mosquito, Aedes aegypti?

Abstract

The mosquito Aedes aegypti is considered one of the most dangerous disease vectors because it can transmit several arboviral diseases including Dengue, Chikungunya, Zika virus, and yellow fever. The larvae are aquatic typically inhabiting hypotonic freshwater whereas the adults are terrestrial. Hence, the larvae are usually faced with the osmoregulatory challenge of eliminating excess water from body fluids while adults usually conserve water, that is, with the exception of females when they take a blood meal, at which time they too need to eliminate excess water. Osmoregulation is accomplished, in part by regulating water flux across epithelia of organs such as the midgut, Malpighian tubules (MTs), hindgut and, in the case of larvae, the anal papillae. The MTs with the hindgut are functionally analogous to the renal tubes of mammalian kidneys where urine is produced; however, the mechanisms of urine production are different. In MTs, urine production is accomplished by ion secretion driven by an apical V‐type H+‐ATPase and water is obliged to follow by osmosis. There is a plethora of literature which describes the regulation of MTs fluid secretion in insects but these studies mostly describe effects on ion transport. Little is known about the regulation of water transport across the epithelium of the MTs. The mosquito, A. aegypti, possesses six aquaporin (water transporter) genes designated AaAQP1 through 6, which are expressed in the MTs and transcript abundance is affected by blood feeding in adult females. Furthermore, AaAQP5 mediates water flux across larval MTs whereas AaAQP1 is expressed in tracheolar cells of adult MTs. In this study we have begun to examine if and how known second messengers of neuroendocrine factors influence AaAQP protein expression in the MTs of A. aegypti with western blots. Thus far we have found that in MTs of larvae incubated with cAMP, AaAQP1 protein expression is higher than unstimulated controls but AaAQP4 levels are unaffected while both AaAQP1 and AaAQP5 expression is not affected by cGMP also in comparison to unstimulated controls. In larvae and adult mosquitoes, cAMP is a second messenger of diuretic hormones that stimulate urine production whereas cGMP is the second messenger of anti‐diuretic hormones, including CAPA peptides, which inhibit fluid secretion at physiological doses. In heterologous expression systems, AaAQP1 and AaAQP5 transport water whereas AaAQP4 is an entomoglyceroporin which transports solutes like trehalose preferentially over water. We conclude that stimulatory hormones of MTs facilitate fluid secretion at least in part by increasing the basal expression of AaAQP1 and that inhibitory hormones may not affect basal AaAQP expression; however, effects of these factors on stimulated MTs and on the expression of the other AaAQP genes is the subject of continuing work.Support or Funding InformationNSERC‐Discovery RGPIN‐2018‐05841