Endocrine Abstracts

Diabetes insipidus is a disorder characterised by severe liquid-imbalance because of the inability to concentrate urine. Inactivating mutations in either arginine vasopressin receptor type 2 (AVPR2) or aquaporin 2 (AQP2) gene can cause congenital Nephrogenic diabetes insipidus (NDI). AVPR2 is a G protein-coupled receptor (GPCR) and is mainly expressed at the basolateral site of the kidneys collecting duct principal cells. Activation of this receptor by vasopressin is responsible for elevation of cAMP levels resulting in insertion of AQP2 water channels in the cell membrane of the collecting duct cells. In this study, four new mutations of AVPR2 gene (R68W, R67_G69del/G107W, V162A and T273M) were found in patients and were functionally analysed. For this purpose, all mutants were generated by a site-directed mutagenesis strategy. Both, total cellular expression and cell surface expression of mutant receptors were analysed in ELISA experiments. Also, cAMP accumulation and concentration response curves were determined for each mutant receptor. According to total ELISA results, all mutant receptors were synthesised comparable to WT receptor. However, cell surface expression was impaired for all mutants except of V162A. cAMP measurement for mutant and WT receptors revealed reduced Emax values for all mutants. For some mutants (R68W, R67_G69del/G107W and T273M) concentration response curves showed shifted EC50 values to higher vasopressin concentrations. In conclusion, we characterised four new AVPR2 mutations found in Turkish patients. Some mutations lead to shifted EC50 values by only one magnitude and treatment with higher amounts of AVP could be helpful for these patients to reduce high urine volumes and to restore kidney function.

Disclosure: This work was supported by the The Scientific and Technological Research Council of Turkey (Project Number: SBAG 112S513).