G protein-coupled receptors (GPCRs) are the targets of many drugs used in clinical practice because G proteins mediate a plethora of physiological functions. Recently, heteromeric GPCR complexes have become attractive targets in drug development since they exhibit distinct pharmacology and cell-specific localization from their respective protomers. Yet, the effect of heteromerization on the pharmacology and signaling of many GPCRs remains unknown. We have undertaken the task to examine the effect of heteromerization on the Gs signaling through the adenosine 2A receptor (A2AR) and Gi signaling through the dopamine receptor type 2 (D2R). Signaling through the A2AR-D2R heteromeric complex is of great interest as this heteromer is a potential pharmacological target for pathologies associated with dysfunctional dopaminergic signaling, such as Parkinson's disease. A2AR antagonists have been explored as therapeutics for Parkinson's disease because the A2AR allosterically inhibits signaling through the D2R. Therefore, we hypothesize that combining D2R full agonists with A2AR antagonists will maximize dopaminergic Gi signaling through the heteromer and will be more efficacious in treating Parkinson's disease than current therapeutics targeting just the D2R. To test this hypothesis, we have developed specific aims to characterize the potency and efficacy of various D2R and A2AR ligands on heteromeric signaling. In order to analyze A2AR-D2R heterocomplex cross signaling, we are using electrophysiological assays with heterologously expressed channels serving as reporters for GPCR signaling. Once we have characterized Gs and Gi signaling through the A2AR-D2R heteromer in our heterologous expression system, we will validate the results in native cells to ensure physiological relevance. To corroborate our findings, we will use in vitro [35S]GTP?S binding in primary neurons and in vivo microdialysis studies in rats. Characterization of the signaling pathway through the A2AR-D2R heteromer will provide insight into what ligands optimize dopaminergic signaling through the D2R leading to the development of novel therapeutics for Parkinson's disease.

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Heteromeric A2AR-D2R interactions play a critical role in dopaminergic neuronal excitability in the striatum making these receptors suitable targets for antiparkinsonian therapeutics. We hypothesize that combining D2R ligands with A2AR ligands targeting the heteromer will be more efficacious in optimizing dopaminergic signaling than current therapeutics targeting the D2R alone. In order to test this hypothesis, we have developed specific aims to characterize the potency and efficacy of various D2R and A2AR ligands on heteromeric signaling aiming to develop a novel Parkinson's disease treatment.

National Institute of Health (NIH)
National Institute of Neurological Disorders and Stroke (NINDS)
Predoctoral Individual National Research Service Award (F31)
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Special Emphasis Panel (ZRG1)
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Sieber, Beth-Anne
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Virginia Commonwealth University
Schools of Medicine
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Hatcher-Solis, Candice; Fribourg, Miguel; Spyridaki, Katerina et al. (2014) G protein-coupled receptor signaling to Kir channels in Xenopus oocytes. Curr Pharm Biotechnol 15:987-95