Javier Gonzalez-Maeso - US grants

DESCRIPTION (provided by applicant): One of the guiding objectives of modern schizophrenia research is to build a bridge from molecular and cellular biology to the clinical symptoms of this psychotic mental disorder. Monoaminergic neurotransmitters have been the principal focus of schizophrenia research for many decades. Several approaches have also linked the neurotransmitter glutamate to the neurochemical alterations in patients with schizophrenia. Notably, clozapine and other atypical antipsychotics have high affinity for serotonin 5-HT2A receptors (2AR), and metabotropic glutamate receptors 2/3 (mGluR2/3) agonists have recently shown efficacy in treating schizophrenia. We identify a novel and unexpected functional brain 2AR/mGluR2 receptor complex that may unify the anti- serotonin and glutamatergic therapies of schizophrenia. Our results based on in vitro, animal models and postmortem human brain of schizophrenic subjects suggest that this 2AR/mGluR2 complex may be responsible for some psychotic symptoms in schizophrenia, and that it is the direct target of these two different classes of antipsychotic drugs. In order to understand the role of the 2AR/mGluR2 complex in brain function and to set the stage for future drug development we will pursue two aims. We will use in vitro studies in conjunction with cutting-edge computational approaches to investigate the molecular determinants at the interaction interface responsible for 2AR/mGluR2 complex stabilization and functional crosstalk. In cortical primary cultures and in vivo in mouse models we will study the neuronal signaling and behavior dependent on 2AR/mGluR2 complex function. Results of the proposed studies have the potential to provide a greater understanding of the structure and function of the 2AR/mGluR2 complex than is currently available for any G protein-coupled receptor heterocomplex, and may provide the basis for new pharmacological approaches to the treatment of schizophrenia. PUBLIC HEALTH RELEVANCE: Schizophrenia is a chronic, debilitating psychotic mental disorder that affects about one percent of the population in the U.S.A., and the seventh most costly medical illness to our society. We have discovered a new neuroreceptor complex that induces hallucinations in mouse, and is affected in schizophrenia brain. The characterization of the structure of the neuroreceptor will extend our understanding of the molecular basis of psychosis, and may provide a route to the development of new, more effective drugs for the treatment of schizophrenia.

DESCRIPTION (provided by applicant): Our final goal is to mechanistically characterize the essential role of the serotonin 5-HT2A (5HT2A) receptor and the metabotropic glutamate 2 (mGlu2) receptor as a G protein-coupled receptor (GPCR) heteromeric complex in regulating receptor trafficking, signaling, and antipsychotic-like behavior. The neurotransmitters serotonin and glutamate both have been the target of considerable attention regarding psychosis and antipsychotic drug development. Family A 5HT2A and family C mGlu2 are GPCRs that have been implicated in the pathophysiology and treatment of schizophrenia and other psychotic disorders. Atypical antipsychotic drugs, such as clozapine, olanzapine and risperidone, all have in common a high affinity for the 5HT2A receptor. Recent preclinical assays in rodents suggest that drugs that activate the mGlu2 receptor represent potential new antipsychotic medications. Our previous findings demonstrate that 5HT2A and mGlu2 maintain close molecular proximity in heterologous systems and in mouse frontal cortex. Using the combination of interdisciplinary approaches in vitro, in animal models and in postmortem human brain of schizophrenic subjects, we provide evidence that the 5HT2A-mGlu2 heteromeric receptor complex is necessary for the therapeutic responses induced by atypical and glutamate antipsychotic drugs, and is potentially involved in the altered cortical processes of schizophrenia. In order to provide a better understanding of the 5HT2A-mGlu2 complex in brain function, and the foundation for the development of more effective antipsychotic drugs, we propose to characterize the basic molecular mechanisms involved in its intracellular trafficking and signaling, as well as to investigate the antipsychotic-like behavioral responses that require expression of 5HT2A and mGlu2 as a GPCR heteromer in mouse. Our results are expected to extend our understanding of the molecular basis of psychosis, and may provide a route to the identification of new and more effective drugs for the treatment of schizophrenia and other psychiatric disorders.

Project Summary About 74% of schizophrenia patients discontinue use within 18 months of therapy due to either poor tolerability of incomplete efficacy. This underscores the need for novel and more effective therapeutic targets for schizophrenia treatment. Recent clinical studies suggested that the metabotropic glutamate 2/3 receptor (mGlu2/3) agonist LY2140023 had antipsychotic properties, providing a new alternative for the treatment of schizophrenia. Unfortunately, follow-up studies with LY2140023 showed either inconclusive results, or clinical outcomes that were not different from placebo. Our published data demonstrated that chronic treatment with atypical antipsychotics, such as with clozapine or risperidone, but not with typical antipsychotics, such as haloperidol, induces repressive histone modifications at the mGlu2 (Grm2) promoter in mouse and human frontal cortex. Remarkably, the translational significance of our preclinical findings has been validated by a recent post-hoc analysis: patients previously treated with typical antipsychotics responded to LY2140023, whereas the effects of LY2140023 in patients previously exposed to atypical antipsychotics did not differ from placebo. Our published and preliminary data also suggest that these repressive epigenetic modifications occurred through a signaling mechanism that requires a serotonin 5-HT2A receptor (5HT2A)-dependent enhancement of NF-?B transcriptional function via I?B?, which is followed by NF-?B-dependent up-regulation and increased binding of histone deacetylase 2 (HDAC2) to the mGlu2 promoter. We have focused our investigation on the potential role of HDAC2 as the basic molecular mechanism underlying down-regulation of mGlu2 expression after chronic antipsychotic drug treatment. Our results are expected to provide a route to the identification of new and more effective epigenetic drugs to improve the currently limited response to treatment with glutamate antipsychotics.

Major depressive disorder is a mental illness afflicting approximately 16% of the world population. Currently available interventions including monoamine-based pharmacotherapies require several weeks to months for beneficial effects to occur. In addition, these treatments are often accompanied by undesirable side effects. Therefore, there is an urgent need for better antidepressant medications, with a faster onset of action, which will also be effective in patients who do not respond to classical antidepressants. Recent clinical findings suggest that psilocybin ? a hallucinogenic serotonin 5-HT2A receptor (5-HT2AR) agonist, exerts fast-acting and long-lasting antidepressant actions in patients suffering from major depression. Despite these striking effects, a number of alterations in various mental domains, including sensory perception and thought processes, precludes the routine use of psilocybin and other hallucinogens in daily clinical practice. G protein-coupled receptors (GPCRs) are critical mediators of cell signaling. Although recognized as capable of activating G proteins in a monomeric form, numerous studies reveal their possible association into hetero-oligomers, enabling allosteric crosstalk between receptor protomers. We previously reported that 5-HT2AR and metabotropic glutamate receptor 2 (mGluR2) are able to interact physically to form a GPCR complex. Results from earlier versions of this R01 grant showed that at least part of the cellular signaling and psychosis-like behaviors induced by hallucinogenic 5- HT2AR agonists require expression of the 5-HT2AR-mGluR2 heteromer in the mouse frontal cortex. However, the ability of cortical 5-HT2AR-mGluR2 to affect behavioral states associated with depression upon hallucinogen administration remains to be elucidated. Similarly, as the functional importance of GPCR oligomerization remains controversial, additional studies related to basic structural and signaling properties of the 5-HT2AR-mGluR2 complex are needed. Our published data and the preliminary data presented here support our working hypothesis that inter-family GPCR heteromerization affects structure, sub-cellular localization and function of both 5-HT2AR and mGluR2 in living mammalian cells. Our data are also consonant with the hypothesis that a single dose of hallucinogenic 5-HT2AR agonists induces fast-acting and long-lasting effects on remission of behavioral states associated with depression, and that these therapeutic-related phenotypes require expression of 5-HT2AR and mGluR2 as a GPCR heteromer in the frontal cortex of mice. These data set the stage for a uniquely comprehensive analysis of the molecular mechanism underlying the antidepressant effects of hallucinogens, with the ultimate goal of developing safer, more effective, and non-hallucinogenic depression treatment strategies.