Decoding the Signaling of a GPCR Heteromeric Complex Reveals a Unifying Mechanism of Action of Antipsychotic Drugs

Department of Structural and Chemical Biology, Mount Sinai School of Medicine, New York, NY 10029, USA.
Cell (Impact Factor: 32.24). 11/2011; 147(5):1011-23. DOI: 10.1016/j.cell.2011.09.055
Source: PubMed


Atypical antipsychotic drugs, such as clozapine and risperidone, have a high affinity for the serotonin 5-HT(2A) G protein-coupled receptor (GPCR), the 2AR, which signals via a G(q) heterotrimeric G protein. The closely related non-antipsychotic drugs, such as ritanserin and methysergide, also block 2AR function, but they lack comparable neuropsychological effects. Why some but not all 2AR inhibitors exhibit antipsychotic properties remains unresolved. We now show that a heteromeric complex between the 2AR and the G(i)-linked GPCR, metabotropic glutamate 2 receptor (mGluR2), integrates ligand input, modulating signaling output and behavioral changes. Serotonergic and glutamatergic drugs bind the mGluR2/2AR heterocomplex, which then balances Gi- and Gq-dependent signaling. We find that the mGluR2/2AR-mediated changes in Gi and Gq activity predict the psychoactive behavioral effects of a variety of pharmocological compounds. These observations provide mechanistic insight into antipsychotic action that may advance therapeutic strategies for disorders including schizophrenia and dementia.

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    • "However, a recent study provides both in vitro and in vivo evidence for a lack of interaction with dopamine D2 receptors by the mGlu2/3 receptor agonists LY354740 and LY379268 (Fell et al., 2009). Interestingly, a direct 5-HT2AR– mGluR2 interaction between the receptor complex seems to be involved in the altered cortical processes of SZ, providing a promising target for the treatment of psychosis (Fribourg et al., 2011; Gonzalez- Maeso et al., 2008). Further, glutamate and GABA are the major excitatory and inhibitory neurotransmitters that are critical for normal neuronal signaling. "
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    ABSTRACT: Group II metabotropic glutamate receptor (mGluR2/3) agonists once showed promise as non-dopaminergic antipsychotic drugs because of their efficacy in alleviating symptoms of schizophrenia (SZ) in both animal models and human patients. However, the recent failure of Phase III clinical trials dealt a huge blow to the scientific community and the aftershock of the setback in mGluR2/3 research can be felt everywhere from grant support and laboratory studies to paper publication. An immediate question raised is whether mGluR2/3 is still a promising therapeutic target for schizophrenia. Answering this question is not easy, but apparently a new strategy is needed. This article provides a focused review of literature on the study of mGluR2/3 agonists, especially on mGluR2/3 agonists' mechanism of action and efficacy in both normal conditions and animal models of SZ, as well as clinical studies in human patients with the disease. We argue that the cellular and molecular actions of mGluR2/3 agonists, the distinct roles between mGluR2 and mGluR3, as well as their effects on different stages of the disease and different subpopulations of patients, remain incompletely studied. Until the mechanisms associated with mGluR2/3 are clearly elucidated and all treatment options are tested, it would be a great mistake to terminate the study of mGluR2/3 as a therapeutic target for schizophrenia. This review will thus shed light on the comprehensive features of the translational potential mGluR2/3 agonists as well as the need for further research into the more selective activation of mGluR2. Copyright © 2015. Published by Elsevier Inc.
    Full-text · Article · Feb 2015 · Progress in Neuro-Psychopharmacology and Biological Psychiatry
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    • "Moreover, both selective mGlu 2/3 -R agonists and antagonists have shown antidepressant effects in animal models of depression (Chaki et al., 2013). 5-HT 2A -R and mGlu 2 -R form a functional receptor heterocomplex (Gonz alez-Maeso et al., 2008; Fribourg et al., 2011). Evidence of a ligand binding interaction (Moreno et al., 2012) and a transcriptional cross-regulation (Kurita et al., 2012) between 5- HT 2A -R and mGlu 2 -R has been demonstrated in human brain. "
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    ABSTRACT: Several studies have demonstrated alterations in serotonin 5-HT2A (5-HT2AR) and glutamate metabotropic mGlu2 (mGlu2R) receptors in depression, but never in the same sample population. Recently it has been shown that both receptors form a functional receptor heterocomplex that is altered in schizophrenia. The present study evaluates the gene expression and protein density of 5-HT2AR and mGlu2/3R in the postmortem prefrontal cortex of subjects with major depressive disorder (n=14) compared with control subjects (n=14) in a paired design. No significant differences between subjects with depression and controls in the relative mRNA levels of the genes HTR2A, GRM2 and GRM3 were observed. The 5-HT2AR density evaluated by [(3)H]ketanserin binding was significantly lower in antidepressant-treated subjects (Bmax=313±17 fmol/mg protein; p<0.05) compared to controls (Bmax=360±12 fmol/mg protein) but not in antidepressant-free subjects (Bmax=394±16 fmol/mg protein; p>0.05). In rats, chronic treatment with citalopram (10 mg/kg/day) and mirtazapine (5 mg/kg/day) decreased mRNA expression and 5-HT2AR density whereas reboxetine (20 mg/kg/day) modified only mRNA expression. The mGlu2/3R density evaluated by [(3)H]LY341495 binding was not significantly different between depression and control subjects. The present results demonstrate no changes in expression and density of both 5-HT2AR and mGlu2/3R in the postmortem prefrontal cortex of subjects with major depressive disorder under basal conditions. However, antidepressant treatment induces a decrease in 5-HT2AR density. This finding suggests that 5-HT2AR down-regulation may be a mechanism for antidepressant effect.
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    • "Dopamine D2 receptor blockade is a shared feature of these widely used drugs, but it does not appear to be their sole mechanism of action (Grunder et al., 2009; Meltzer, 2013). Other targets likely to be relevant for the therapeutic effects of antipsychotics include cholinergic receptors (Ibrahim and Tamminga, 2011), glutamate and serotonin receptors (Fribourg et al., 2011; Fell et al., 2012; de Bartolomeis et al., 2013), and α-1 noradrenergic receptors (Cohen and Lipinski, 1986; Ma et al., 2006). These examples are not meant to be exhaustive, but are listed here to illustrate the point that antipsychotics are multi-target drugs (Roth et al., 2004) with additional molecular mechanisms yet to be elucidated. "
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