Functional Characterization of the Obesity-Linked Variant of the β3-Adrenergic Receptor.

Esraa Haji,Shuja Shafi Malik,Saeed Al Mahri,Sameer Mohammad,Yumna Aloraij

doi:10.3390/ijms22115721

Abstract

Adrenergic receptor β3 (ADRβ3) is a member of the rhodopsin-like G protein-coupled receptor family. The binding of the ligand to ADRβ3 activates adenylate cyclase and increases cAMP in the cells. ADRβ3 is highly expressed in white and brown adipocytes and controls key regulatory pathways of lipid metabolism. Trp64Arg (W64R) polymorphism in the ADRβ3 is associated with the early development of type 2 diabetes mellitus, lower resting metabolic rate, abdominal obesity, and insulin resistance. It is unclear how the substitution of W64R affects the functioning of ADRβ3. This study was initiated to functionally characterize this obesity-linked variant of ADRβ3. We evaluated in detail the expression, subcellular distribution, and post-activation behavior of the WT and W64R ADRβ3 using single cell quantitative fluorescence microscopy. When expressed in HEK 293 cells, ADRβ3 shows a typical distribution displayed by other GPCRs with a predominant localization at the cell surface. Unlike adrenergic receptor β2 (ADRβ2), agonist-induced desensitization of ADRβ3 does not involve loss of cell surface expression. WT and W64R variant of ADRβ3 displayed comparable biochemical properties, and there was no significant impact of the substitution of tryptophan with arginine on the expression, cellular distribution, signaling, and post-activation behavior of ADRβ3. The obesity-linked W64R variant of ADRβ3 is indistinguishable from the WT ADRβ3 in terms of expression, cellular distribution, signaling, and post-activation behavior.

Highlights

WT and W64R HA-Adrenergic receptor β3 (ADRβ3) -GFP constructs were stably expressed in HEK 293 cells, and the effect of W64R mutation on the expression and subcellular distribution of ADRβ3 was assessed
We evaluated the extent of desensitization in cells expressing WT or W64R ADRβ3 and compared it with that of adrenergic receptor β2 (ADRβ2), a well-studied and closely related G-protein-coupled receptors (GPCRs)
Our results show that W64R mutation does not affect the expression or the subcellular distribution of ADRβ¬3

Summary

Introduction

Beta-adrenergic receptors (ADRβ) belong to the family of seven transmembrane receptors called G-protein-coupled receptors (GPCRs) [1,2,3]. They are expressed on the surface of several cell types and can bind epinephrine and norepinephrine as well as exogenously administered drugs, including beta-agonists and antagonists (‘beta-blockers’) [4,5,6,7,8]. ADRβ play a key role in several important processes including fat and glucose metabolism and alterations in myocardial metabolism, heart rate, and systolic and diastolic function [9,10,11,12,13,14]

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Conclusion