Metabotropic glutamate type 5, dopamine D₂ and adenosine A_2a receptors form higher‐order oligomers in living cells

Abstract

G protein-coupled receptors are known to form homo- and heteromers at the plasma membrane, but the stoichiometry of these receptor oligomers are relatively unknown. Here, by using bimolecular fluorescence complementation, we visualized for the first time the occurrence of heterodimers of metabotropic glutamate mGlu5 receptors (mGlu5R) and dopamine D2 receptors (D2R) in living cells. Furthermore, the combination of bimolecular fluorescence complementation and bioluminescence resonance energy transfer techniques, as well as the sequential resonance energy transfer (SRET) technique, allowed us to detect the occurrence receptor oligomers containing more than two protomers, mGlu5R, D2R and adenosine A2A receptor (A2AR). Interestingly, by using high-resolution immunoelectron microscopy we could confirm that the three receptors co-distribute within the extrasynaptic plasma membrane of the same dendritic spines of asymmetrical, putative glutamatergic, striatal synapses. Also, co-immunoprecipitation experiments in native tissue demonstrated the existence of an association of mGlu5R, D2R and A2AR in rat striatum homogenates. Overall, these results provide new insights into the molecular composition of G protein-coupled receptor oligomers in general and the mGlu5R/D2R/A2AR oligomer in particular, a receptor oligomer that might constitute an important target for the treatment of some neuropsychiatric disorders.

Heteromeric Dopamine Receptor Signaling Complexes: Emerging Neurobiology and Disease Relevance

“…However, given the identification of neurons that coexpress the D1R and D2R in both the direct and indirect pathways, the expression of A1-D1-D2 or D1-D2-A2 heteromers in these neurons is a possibility, an intriguing prospect given that the sites of interaction between the D2R and D1R or A2R have been reported and are distinct (Ciruela et al, 2004;O'Dowd et al, 2012). Heterotrimeric receptor complexes involving dopamine receptors have already been identified, including the higher-order adenosine-dopamine receptor heteromer, the A2-D2-mGlu5 heteromer (Cabello et al, 2009), which has been suggested as a therapeutic target for schizophrenia by counteracting exaggerated D2R signaling in the ventral striatopallidal pathway (Fuxe et al, 2010).…”

G-protein-coupled receptor heteromer dynamics

“…The capacity of GPCR heterodimers to modulate receptor function leads to the concept that dysregulation of receptor heterodimer expression and function might be implicated in several diseases (Prinster et al, 2005;Dalrymple et al, 2008;Rozenfeld and Devi, 2010). Recent studies show that A 2A R, D 2 R and mGlu 5 R form a receptor heterocomplex in the striatal spine module (Cabello et al, 2009), a site that has a crucial role in controlling motor activity, motor learning and some forms of associative and visual learning. Imbalance of these activities caused by a gradual and progressive loss of dopaminergic neurons, which are implicated in glutamatergic, dopaminergic and adenosinergic neurotransmission, is thought to be one of the crucial determinants of Parkinson's disease.…”

Metabotropic Receptors for Glutamate and GABA

“…Additionally, are postulated to not only be co-expressed, but also to form hetero-oligomers in striatal neurons and in heterologous cells systems (Ferre et al, 2002). Recently, Cabello et al (2009) demonstrated that mGlu 5 , dopamine D 2 and adenosines A 2A receptors are localised within the same dendritic spines in glutamatergic striatal synapses, which led them to hypothesise that there may be hetero-oligomeric triplets of A 2A , mGlu 5 and D 2 receptors; this association was then investigated through the employment of various fluorescence techniques. Their data supported the formation of heterooligomers containing all three receptors and thus allosterically interacting with one another to influence either efficacy or affinity or both.…”

“…Indeed, antagonists of both mGlu 5 and A 2A display anti-parkinsonian effects, while the dopamine D 2 receptor is the target of L-DOPA, which is used to treat parkinsonian symptoms. It has been suggested that these three receptors may act in concert in pairs or as a triplet via signalling cross-talk or otherwise, to influence the striatal function in motor coordination (Agnati et al, 2003;Cabello et al, 2009). Indeed, this cross-regulation was observed in vivo, where mGlu 5 antagonist-induced motor effects were augmented by A 2A receptor antagonists; and conversely these effects were diminished in A 2A -D 2 receptor double knock-out mice (Kachroo et al, 2005).…”