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

Adrenergic receptor β (ADRβ) is a member of the rhodopsin-like G protein-coupled receptor family. The binding of the ligand to ADRβ activates adenylate cyclase and increases cAMP in the cells. ADRβ is highly expressed in white and brown adipocytes and controls key regulatory pathways of lipid metabolism. Trp64Arg (W64R) polymorphism in the ADRβ 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 ADRβ. This study was initiated to functionally characterize this obesity-linked variant of ADRβ. We evaluated in detail the expression, subcellular distribution, and post-activation behavior of the WT and W64R ADRβ using single cell quantitative fluorescence microscopy. When expressed in HEK 293 cells, ADRβ shows a typical distribution displayed by other GPCRs with a predominant localization at the cell surface. Unlike adrenergic receptor β (ADRβ), agonist-induced desensitization of ADRβ does not involve loss of cell surface expression. WT and W64R variant of ADRβ 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 ADRβ. The obesity-linked W64R variant of ADRβ is indistinguishable from the WT ADRβ in terms of expression, cellular distribution, signaling, and post-activation behavior.