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

Insect CAPA neuropeptides, which are homologs of mammalian neuromedin U, have been described in various insect species and are known to influence ion and water balance by regulating the activity of the Malpighian ‘renal’ tubules (MTs). A number of diuretic hormones have been shown to increase primary fluid and ion secretion by the insect MTs and, in the adult female mosquito, a calcitonin-related peptide (DH) also known as mosquito natriuretic peptide, increases sodium secretion at the expense of potassium to remove the excess salt load acquired upon blood-feeding. An endogenous mosquito anti-diuretic hormone was recently described, having inhibitory activity against select diuretic factors and being particularly potent against DH-stimulated diuresis. In the present study, we have functionally deorphanized, both and , a mosquito anti-diuretic hormone receptor (ADHr). Expression analysis by quantitative PCR indicates the receptor is highly enriched in the MTs, and fluorescent hybridization confirms expression within principal cells. Characterization using a heterologous system demonstrated the receptor was highly sensitive to mosquito CAPA peptides. In adult females, ADHr transcript knockdown using RNAi led to the abolishment of CAPA-peptide induced anti-diuretic control of DH-stimulated MTs. The neuropeptidergic ligand is produced within a pair of neurosecretory cells in each of the six abdominal ganglia, whose axonal projections innervate the abdominal neurohaemal organs (known as the perivisceral organs), where these neurohormones are released into the open circulatory system of the insect. Furthermore, pharmacological inhibition of PKG/NOS signalling abolished the anti-diuretic activity of CAPA-1, which collectively confirms the role of cGMP/PKG/NOS in this anti-diuretic signalling pathway.