Functional analysis of AQP2 mutants found in patients with diabetes insipidus


KARADUMAN T., Ozcan Turkmen M., Ozer E., ERGİN B., SAĞLAM B., ERDEM TUNÇDEMİR B., ...More

BIOLOGIA, vol.76, no.9, pp.2767-2776, 2021 (SCI-Expanded) identifier identifier

  • Publication Type: Article / Article
  • Volume: 76 Issue: 9
  • Publication Date: 2021
  • Doi Number: 10.1007/s11756-021-00807-9
  • Journal Name: BIOLOGIA
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus, Academic Search Premier, Animal Behavior Abstracts, Aquatic Science & Fisheries Abstracts (ASFA), BIOSIS, CAB Abstracts, Veterinary Science Database
  • Page Numbers: pp.2767-2776
  • Keywords: Diabetes insipidus, AQP2, Mutation, Functional analysis, AQUAPORIN-2 WATER CHANNEL, WILD-TYPE AQUAPORIN-2, MEMBRANE EXPRESSION, APICAL MEMBRANE, MUTATIONS, PHOSPHORYLATION, GENES, COTRANSPORTER, TRAFFICKING, RECEPTOR
  • Hacettepe University Affiliated: Yes

Abstract

Aquaporin-2 (AQP2) is a homotetrameric water channel responsible for the reabsorption of water in the main collecting duct cells of kidneys. Mutations in AQP2 gene induce nephrogenic diabetes insipidus (NDI), a pathogenic condition involving the maintenance of body water homeostasis, leading to excess urine production. Several hypotheses in the literature were confirmed by clinical and experimental observations regarding the role of these mutations in the pathogenesis of NDI. In this study, three mutations (A45T, R85X, and A147T) identified in NDI patients were analyzed using stably transfected Madin-Darby canine kidney (MDCK) cells and Xenopus laevis (X. laevis) oocyte expression system compared to the wt-AQP2. According to our study, the A45T-AQP2 protein is characterized by reduced half-life and targeting defects, therefore this mutant protein can be retained in the endoplasmic reticulum (ER). The mutation also causes the formation of a nonfunctional water channel. The R85X-AQP2 protein was not detected in immunoblot analysis, but the results of water permeability test data prove that this mutant protein cannot form a functional water channel. Despite its features such as partial false targeting and reduced half-life, A147T-AQP2 protein forms a semi-functional water channel. In a conclusion, studies on the intracellular functions of mutant water channels are important because these studies elucidate the mechanisms leading to disease phenotype and support development of pharmacological strategies related to pathological mechanisms.