Functional rescue of mutant Vasopressin V2 Receptors in Nephrogenic Diabetes Insipidus- From molecular cause to restored phenotype.

Item does not contain fulltextMutations in G protein-coupled receptors are the cause of many inheritable disorders, including X-linked Nephrogenic Diabebetes Insipidus (NDI). Patients suffering from NDI are unable to concentrate their urine in response to the antidiuretic hormone arginine-vaspressin (AVP), which increases the risk of dehydration in these patients. In this thesis, we describe the molecular causes that underlie X-linked NDI, which is due to mutations in the vasopressin V2 receptor (V2R). These mutations cause misfolding of the V2R, which leads to its entrapment in the endoplasmic reticulum (ER) as it fails the quality control standards of this organelle. However, in overexpression studies in COS cells, we found that several mutants were able to function on the molecular level, i.e. they are able to bind AVP and activate the stimulatory G protein. Since their intracellular retention prevents them to bind AVP at the cell surface, we set out to rescue the localization and/or the function of these receptor mutants in a polarized kidney cell line that mimics the kidney collecting duct. 1)We found that several chemical chaperones were able to rescue the cell surface localization of the V2R-V206D mutant, but not of eight other V2R mutants. 2)Cell-permeable antagonists (or ?pharmacological chaperones?) of the V2R were able to stabilize of 8 out of 9 V2R mutants in the ER and promote their trafficking to the cell surface, where they could be activated to different extents. This functional rescue was a balance between the ability of the antagonist to restore cell surface expression, and its subsequent displacement by AVP. 3)Cell-permeable agonists did not induce plasma membrane trafficking, but rescued their function by activating the mutant receptors inside the cell. Since cell-permeable agonists and antagonists are available for clinical use, or may become available in the near future, they are promising candidates to relieve NDI in patients.RU Radboud Universiteit Nijmegen, 06 december 2006Promotores : Knoers, N.V.A.M., Bindels, R.J.M. Co-promotor : Deen, P.M.T.169 p