Functional characterization of AVPR2 mutants found in Turkish patients with nephrogenic diabetes insipidus.

Beril Erdem,Angela Schulz,Torsten Schöneberg,Emel Saglar,Hatice Mergen,Ferhat Deniz

doi:10.1530/ec-17-0236

Beril Erdem, Angela Schulz + Show 4 more

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https://doi.org/10.1530/ec-17-0236

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Journal: Endocrine connections	Publication Date: Nov 8, 2017
Citations: 5	License type: CC BY 4.0

Affiliation: Hacettepe University, Leipzig University

Abstract

Diabetes insipidus is a rare disorder characterized by an impairment in water balance because of the inability to concentrate urine. While central diabetes insipidus is caused by mutations in the AVP, the reason for genetically determined nephrogenic diabetes insipidus can be mutations in AQP2 or AVPR2. After release of AVP from posterior pituitary into blood stream, it binds to AVPR2, which is one of the receptors for AVP and is mainly expressed in principal cells of collecting ducts of kidney. Receptor activation increases cAMP levels in principal cells, resulting in the incorporation of AQP2 into the membrane, finally increasing water reabsorption. This pathway can be altered by mutations in AVPR2 causing nephrogenic diabetes insipidus. In this study, we functionally characterize four mutations (R68W, ΔR67-G69/G107W, V162A and T273M) in AVPR2, which were found in Turkish patients. Upon AVP stimulation, R68W, ΔR67-G69/G107W and T273M showed a significantly reduced maximum in cAMP response compared to wild-type receptor. All mutant receptor proteins were expressed at the protein level; however, R68W, ΔR67-G69/G107W and T273M were partially retained in the cellular interior. Immunofluorescence studies showed that these mutant receptors were trapped in ER and Golgi apparatus. The function of V162A was indistinguishable from the indicating other defects causing disease. The results are important for understanding the influence of mutations on receptor function and cellular trafficking. Therefore, characterization of these mutations provides useful information for further studies addressing treatment of intracellularly trapped receptors with cell-permeable antagonists to restore receptor function in patients with nephrogenic diabetes insipidus.

Highlights

Water homeostasis of the body is rigidly controlled by several mechanisms
Four different mutations were introduced into pLV2R with a PCR-based site-directed mutagenesis and restriction fragment replacement method (R68W, ΔR67-G69/G107W, V162A and T273M)
For R68W and T273M, we found only ~28% cell surface expression compared to the WT arginine vasopressin type 2 receptor (AVPR2)

Summary

Introduction

Water homeostasis of the body is rigidly controlled by several mechanisms. Various sensor systems such as endothelial baroreceptors and hypothalamic osmoreceptors, which detect reduced blood volume (hypovolemia) and increased blood electrolyte concentration (hypernatremia), respectively, are capable to sense changes in water balance and serum osmolality. Reduction in blood volume or increase in blood electrolyte concentration induces the release of arginine vasopressin (AVP) from the posterior pituitary gland. AVP is transported to the kidneys via the bloodstream and binds to one of its receptors, the arginine vasopressin type 2 receptor (AVPR2). The hormone–receptor complex initiates the activation of the Gs protein resulting in the activation of the adenylyl cyclase and an increase of the intracellular cyclic AMP (cAMP) concentration.

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