Functional Characterisation and cAMP-Mediated Rescue of a Novel Truncating AVPR2 Mutation Causing Nephrogenic Diabetes Insipidus.

Abstract

Vasopressin plays a central endocrine role in water homeostasis by activating the AVPR2 receptor in renal collecting duct cells. Mutations in AVPR2 are a leading cause of X-linked nephrogenic diabetes insipidus (NDI), a disorder marked by renal insensitivity to vasopressin, leading to polyuria, polydipsia, and hypernatremia. We identified a novel truncating AVPR2 mutation (c.570dup; D191*) in a pediatric patient with NDI and investigated its molecular and functional consequences using a renal epithelial cell model (mIMCD-3). The D191* mutant exhibited marked reduction in total and surface receptor expression due to intracellular retention and rapid proteasomal degradation. Functional assays revealed that dDAVP stimulation failed to elicit cAMP production or activate downstream signalling targets, including CREB and ERK1/2, in cells expressing the mutant receptor. Aquaporin-2 (AQP2) membrane translocation, essential for water reabsorption, was also impaired. Notably, treatment with Forskolin or 8-bromo-cAMP restored cAMP levels, reactivated downstream signalling, and rescued AQP2 localisation to the apical membrane, independent of AVPR2 activation. These findings uncover the pathophysiological mechanism by which D191* impairs vasopressin signalling and suggest that bypassing the receptor via direct cAMP pathway activation offers a promising therapeutic strategy for NDI. This study highlights the endocrine relevance of precision molecular diagnostics and supports functional rescue approaches for receptor-based disorders.