Functional characterization and cAMP-mediated rescue of a novel truncating AVPR2 mutation causing nephrogenic diabetes insipidus.

Vasopressin plays a central endocrine role in water homeostasis by activating the arginine vasopressin receptor 2 (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. The D191* mutant exhibited marked reduction in total and surface receptor expression due to intracellular retention and rapid proteasomal degradation. Functional assays revealed that 1-deamino-8-d-arginine vasopressin (dDAVP) stimulation failed to elicit cAMP production or activate downstream signaling 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 signaling, and rescued AQP2 localization to the apical membrane, independent of AVPR2 activation. These findings uncover the pathophysiological mechanism by which D191* impairs vasopressin signaling 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.NEW & NOTEWORTHY This study identifies and functionally characterizes a previously unreported truncating AVPR2 mutation (c.570dup; p.D191*) causing congenital nephrogenic diabetes insipidus. Using renal epithelial cell models, the authors show that D191* leads to receptor misfolding, proteasomal degradation, absent cAMP signaling, and failure of aquaporin-2 trafficking. Remarkably, forskolin and 8-bromo-cAMP bypass the defective receptor to restore downstream signaling and water channel localization, highlighting a potential therapeutic strategy of receptor-independent cAMP activation for AVPR2-null nephrogenic diabetes insipidus.