Effect of antipsychotic drugs on group II metabotropic glutamate receptor expression and epigenetic control in postmortem brains of schizophrenia subjects

Antipsychotic-induced low availability of group II metabotropic glutamate receptors (including mGlu 2 R and mGlu 3 R) in brains of schizophrenia patients may explain the limited efficacy of mGlu 2/3 R ligands in clinical trials. Studies evaluating mGlu 2/3 R levels in well-designed, large postmortem brain cohorts are needed to address this issue. Postmortem samples from the dorsolateral prefrontal cortex of 96 schizophrenia subjects and matched controls were collected. Toxicological analyses identified cases who were (AP+) or were not (AP-) receiving antipsychotic treatment near the time of death. Protein and mRNA levels of mGlu 2 R and mGlu 3 R, as well as GRM2 and GRM3 promoter-attached histone posttranslational modifications, were quantified. Experimental animal models were used to compare with data obtained in human tissues. Compared to matched controls, schizophrenia cortical samples had lower mGlu 2 R protein amounts, regardless of antipsychotic medication. Downregulation of mGlu 3 R was observed in AP- schizophrenia subjects only. Greater predicted occupancy values of dopamine D 2 and serotonin 5HT 2A receptors correlated with higher density of mGlu 3 R, but not mGlu 2 R. Clozapine treatment and maternal immune activation in rodents mimicked the mGlu 2 R, but not mGlu 3 R regulation observed in schizophrenia brains. mGlu 2 R and mGlu 3 R mRNA levels, and the epigenetic control mechanisms did not parallel the alterations at the protein level, and in some groups correlated inversely. Insufficient cortical availability of mGlu 2 R and mGlu 3 R may be associated with schizophrenia. Antipsychotic treatment may normalize mGlu 3 R, but not mGlu 2 R protein levels. A model in which epigenetic feedback mechanisms controlling mGlu 3 R expression are activated to counterbalance mGluR loss of function is described.