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This Article Full Text Full Text (PDF) All Versions of this Article: 297/2/F489    most recent 90589.2008v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Guyon, C. Articles by Bichet, D. G. PubMed PubMed Citation Articles by Guyon, C. Articles by Bichet, D. G.

Characterization of D150E and G196D aquaporin-2 mutations responsible for nephrogenic diabetes insipidus: importance of a mild phenotype

¹Groupe d'Étude des Protéines Membranaires (GÉPROM), Département de Physiologie, Université de Montréal; ²Centre de Recherche, Hôpital du Sacré-Cœur de Montréal, Montréal, Québec, Canada; ³Hospital Infantil Universitario Virgin del Rocio, qaUnidad de Nephrologia Infantil, Seville, Spain; and ⁴Institute of Pediatric Endocrinology, Endocrinology Research Center, Moscow, Russia

Submitted 3 October 2008 ; accepted in final form 14 May 2009

Aquaporin-2 (AQP2) is a water channel responsible for the final water reabsorption in renal collecting ducts. Alterations in AQP2 function induce nephrogenic diabetes insipidus (NDI), a condition characterized by severe polyuria and polydipsia. Three patients affected with severe NDI, who were compound heterozygous for the AQP2 mutations D150E and G196D, are presented here along with a mildly affected D150E homozygous patient from another family. Using Xenopus oocytes as an expression system, these two mutations (G196D and D150E) were compared with the wild-type protein (AQP2-wt) for functional activity (water flux analysis), protein maturation, and plasma membrane targeting. AQP2-wt induces a major increase in water permeability (P_f = 47.4 ± 12.2 x 10^–4 cm/s) whereas D150E displays intermediate P_f values (P_f = 12.5 ± 3.0 x 10^–4 cm/s) and G196D presents no specific water flux, similar to controls (P_f = 2.1 ± 0.8 x 10^–4 cm/s and 2.2 ± 0.7 x 10^–4 cm/s, respectively). Western blot and immunocytochemical evaluations show protein targeting that parallels activity levels with AQP2-wt adequately targeted to the plasma membrane, partial targeting for D150E, and complete sequestration of G196D within intracellular compartments. When coinjecting AQP2-wt with mutants, no (AQP2-wt + D150E) or partial (AQP2-wt + G196D) reduction of water flux were observed compared with AQP2-wt alone, whereas complete loss of function was found when both mutants were coinjected. These results essentially recapitulate the clinical profiles of the family members, showing a typical dominant negative effect when G196D is coinjected with either AQP2-wt or D150E but not between AQP2-wt and D150E mutant.

functional expression; Xenopus oocyte; water channel