Impact of paroxetine on proximal β-adrenergic receptor signaling

D-adrenergic receptors (beta AR) regulate numerous functions throughout the body, however G protein-coupled receptor kinase (GRK)-dependent desensitization of beta AR has long been recognized as a maladaptive process in the progression of various disease states. Thus, the development of small molecule inhibitors of GRKs for the study of these processes and as potential therapeutics has been at the forefront of recent research efforts. Via structural and biochemical analyses, the selective serotonin reuptake inhibitor (SSRI) paroxetine was identified as a GRK2 inhibitor that enhances PAR-dependent cardiomyocyte and cardiac contractility and reverses cardiac dysfunction and myocardial DAR expression in mouse models of heart failure. Despite these functional outcomes, consistent with diminished beta AR desensitization, the proximal PAR signaling mechanisms sensitive to paroxetine have not been reported. In this study, we aimed to determine whether paroxetine prevents classic beta AR desensitization-related signaling mechanisms at a molecular level. Therefore, via immunoblotting, radioligand binding, fluorescence resonance energy transfer (FRET) and microscopy assays, we have performed an assessment of the effect of paroxetine on proximal beta AR signaling responses. Indeed, paroxetine treatment inhibited ligand-induced beta 2AR phosphorylation in a concentration -dependent manner. Additionally, for both beta 1AR and beta 2AR, paroxetine decreased ligatid-induced beta arrestin2 recruitment and subsequent receptor internalization. Thus, paroxetine inhibits DAR desensitization mechanisms consistent with GRK2 inhibition and provides a useful pharmacological tool for studying these proximal GPCR signaling responses.