Partial nephrogenic diabetes insipidus caused by a novel AQP2 variation impairing trafficking of the aquaporin-2 water channel. Issue 1 (December 2015)

• Record Type: Journal Article
• Authors: Dollerup, Pia; Thomsen, Troels; Nejsum, Lene; Færch, Mia; Österbrand, Martin; Gregersen, Niels; Rittig, Søren; Christensen, Jane; Corydon, Thomas
• Is Part Of: BMC nephrology. Volume 16:Issue 1(2015)
• Page Start: 1
• Page End: 12
• Publication Date: 2015-12
• Subjects: Aquaporin 2 -- Diabetes insipidus -- Congenital nephrogenic diabetes insipidus -- Lentivirus -- Cellular trafficking -- Intracellular localization; Kidneys -- Diseases -- Periodicals; 616.61005
• DOI: 10.1186/s12882-015-0213-3
• Languages: English
• ISSNs: 1471-2369

Abstract

Abstract Background Autosomal dominant inheritance of congenital nephrogenic diabetes insipidus (CNDI) is rare and usually caused by variations in theAQP2 gene. We have investigated the genetic and molecular background underlying symptoms of diabetes insipidus (DI) in a Swedish family with autosomal dominant inheritance of the condition. Methods The proband and her father were subjected to water deprivation testing and direct DNA sequencing of the coding regions of theAQP2 andAVP genes. Madin-Darby canine kidney (MDCK) cells stably expressing AQP2 variant proteins were generated by lentiviral gene delivery. Localization of AQP2 variant proteins in the cells under stimulated and unstimulated conditions was analyzed by means of immunostaining and confocal laser scanning microscopy. Intracellular trafficking of AQP2 variant proteins was studied using transient expression of mutant dynamin2-K44A-GFP protein and AQP2 variant protein phosphorylation levels were assessed by Western blotting analysis. Results Clinical and genetic data suggest that the proband and her father suffer from partial nephrogenic DI due to a variation (g.4807C > T) in theAQP2 gene. The variation results in substitution of arginine-254 to tryptophan (p.R254W) in AQP2. Analysis of MDCK cells stably expressing AQP2 variant proteins revealed disabled phosphorylation, impaired trafficking and intracellular accumulation of AQP2-R254W protein. Notably, blocking of the endocytic pathway demonstrated impairment of AQP2-R254W to reach the cell surface. Conclusions Partial CNDI in the Swedish family is caused by anAQP2 variation that seems to disable the encoded AQP2-R254W protein to reach the subapical vesicle population as well as impairing its phosphorylation at S256. The AQP2-R254W protein is thus unable to reach the plasma membrane to facilitate AVP mediated urine concentration.