Identification and characterization of the promoter region of the GRM3 gene

Effect of metabotropic glutamate receptor-3 variants on prefrontal brain activity in schizophrenia: An imaging genetics study using multi-channel near-infrared spectroscopy

BACKGROUND

The glutamatergic system is essential for learning and memory through its crucial role in neural development and synaptic plasticity. Genes associated with the glutamatergic system, including metabotropic glutamate receptor (mGluR or GRM) genes, have been implicated in the pathophysiology of schizophrenia. Few studies, however, have investigated a relationship between polymorphism of glutamate-related genes and cortical function in vivo in patients with schizophrenia. We thus explored an association between genetic variations in GRM3 and brain activation driven by a cognitive task in the prefrontal cortex in patients with schizophrenia.

MATERIALS AND METHODS

Thirty-one outpatients with schizophrenia and 48 healthy controls participated in this study. We measured four candidate single nucleotide polymorphisms (rs274622, rs2299225, rs1468412, and rs6465084) of GRM3, and activity in the prefrontal and temporal cortices during a category version of a verbal fluency task, using a 52-channel near-infrared spectroscopy instrument.

RESULTS AND DISCUSSION

The rs274622 C carriers with schizophrenia were associated with significantly smaller prefrontal activation than patients with TT genotype. This between-genotype difference tended to be confined to the patient group. GRM3 polymorphisms are associated with prefrontal activation during cognitive task in schizophrenia.

Association of variants in DRD2 and GRM3 with motor and cognitive function in first-episode psychosis

Similar smooth pursuit eye tracking dysfunctions are present across psychotic disorders. They include pursuit initiation and maintenance deficits that implicate different functional brain systems. This candidate gene study examined psychosis-related genotypes regulating dopamine and glutamate neurotransmission in relation to these pursuit deficits. One hundred and thirty-eight untreated first-episode patients with a psychotic disorder were genotyped for four markers in DRD2 and four markers in GRM3. The magnitude of eye movement abnormality in patients was defined in relation to performance of matched healthy controls (N = 130). Eighty three patients were followed after 6 weeks of antipsychotic treatment. At baseline, patients with a -141C deletion in DRD2 rs1799732 had slower initiation eye velocity and longer pursuit latency than CC insertion carriers. Further, GRM3 rs274622_CC carriers had poorer pursuit maintenance than T-carriers. Antipsychotic treatment resulted in prolonged pursuit latency in DRD2 rs1799732_CC insertion carriers and a decline in pursuit maintenance in GRM3 rs6465084_GG carriers. The present study demonstrates for the first time that neurophysiological measures of motor and neurocognitive deficits in patients with psychotic disorders have different associations with genes regulating dopamine and glutamate systems, respectively. Alterations in striatal D2 receptor activity through the -141C Ins/Del polymorphism could contribute to pursuit initiation deficits in psychotic disorders. Alterations in GRM3 coding for the mGluR3 protein may impair pursuit maintenance by compromising higher perceptual and cognitive processes that depend on optimal glutamate signaling in corticocortical circuits. DRD2 and GRM3 genotypes also selectively modulated the severity of adverse motor and neurocognitive changes resulting from antipsychotic treatment.

Metabotropic glutamate receptor 3 is associated with heroin dependence but not depression or schizophrenia in a Chinese population

Metabotropic glutamate receptor subtype 3 (mGluR3, encoded by GRM3) plays important roles in the pathophysiology of schizophrenia, depression, and drug dependence. GRM3 polymorphisms were reported to be associated with prefrontal activity, cognitive shifting, and memory capability in healthy subjects, as well as susceptibility to schizophrenia and depression. The goal of this study was to replicate the association of GRM3 with schizophrenia and depression and to explore GRM3's potential association with heroin dependence (HD) in a Chinese population. Seventeen SNPs throughout the GRM3 gene were genotyped using MALDI-TOF within the MassARRAY system, and the allele and genotype distributions were compared between 619 healthy controls and 433 patients with schizophrenia, 409 patients with major depression, and 584 unrelated addicts. We found that GRM3 polymorphisms modulate the susceptibility to HD but do not significantly influence the risk for schizophrenia or depression. An increased risk of HD was significantly associated with the minor alleles of two GRM3 SNPs, including the T allele of rs274618 (Odds ratio (OR) = 1.631, 95% confidence interval (95%CI): 1.317-2.005), the T allele of rs274622 (OR = 1.652, 95% CI: 1.336-2.036), compared with the major alleles. The addicts carrying the minor allele of rs274618 or rs274622 had a shortened duration for transition from first use to dependence (DTFUD) in comparison to homozygote for major allele (P<0.0001 for each SNP using log rank test). Additionally, a 6-SNP haplotype within 5' region of the GRM3 including the minor alleles of the two aforementioned SNPs was significantly associated with an increased risk of HD (P = 0.00001, OR = 1.668, 95% CI: 1.335-2.084). Our data indicated that GRM3 polymorphisms do not contribute to genetic susceptibility to schizophrenia and depression, but they confer an increased risk of HD in a Chinese population.

Association between type-three metabotropic glutamate receptor gene (GRM3) variants and symptom presentation in treatment refractory schizophrenia

OBJECTIVE

Positive associations between polymorphisms in the type-three metabotropic glutamate receptor gene (GRM3) and the pathogenesis of schizophrenia as well as response to antipsychotic treatment have been reported. The objective of this study was to determine whether refractory psychiatric symptoms in antipsychotic non-responders are related to polymorphisms in GRM3.

METHODS

Ninety-five treatment refractory schizophrenia participants were enrolled. Prior to a medication switch, global psychopathology and negative symptoms were rated. These participants were genotyped for seven markers in GRM3. Genotype associations with symptoms were assessed.

RESULTS

Two markers in GRM3 (rs1989796 and rs1476455), were associated with the presence of refractory global symptoms as measured by the Brief Psychiatric Rating Scale (BPRS) Total scores. Participants with an rs1476455_CC genotype had significantly higher BPRS scores than A-carriers (55.1±10.4 vs. 48.3±9.2; F=7.6, p=0.0071). Additionally, participants with the rs1989796_CC genotype had significantly higher BPRS scores than T-carriers (50.1±5.7 vs. 55.8±10.5, F=7.1, p=0.0091). No evidence for significant associations with negative symptoms was observed.

CONCLUSIONS

Polymorphisms in the GRM3 gene may be associated with refractory global psychosis symptoms but not negative symptoms in persons with schizophrenia.

Transcriptional regulation of type-2 metabotropic glutamate receptors: an epigenetic path to novel treatments for chronic pain

Activation of metabotropic glutamate 2 (mGlu2) receptors inhibits pain transmission at the synapses between primary afferent fibers and neurons in the dorsal horn of the spinal cord. In addition, mGlu2 receptors are found in peripheral nociceptors, and in pain-regulatory centers of the brain stem and forebrain. mGlu2 receptor agonists produce analgesia in models of inflammatory and neuropathic pain, but their use is limited by the development of tolerance. A new therapeutic strategy could be based on the transcriptional regulation of mGlu2 receptors via the acetylation-promoted activation of the p65/RelA transcription factor. "Epigenetic" drugs that increase mGlu2 receptor expression, including l-acetylcarnitine and inhibitors of histone deacetylases, have a different analgesic profile with no tolerance to the therapeutic effect after repeated dosing.

The group II metabotropic glutamate receptor 3 (mGluR3, mGlu3, GRM3): expression, function and involvement in schizophrenia

Group II metabotropic glutamate receptors (mGluRs) comprise mGluR2 (mGlu2; encoded by GRM2) and mGluR3 (mGlu3; encoded by GRM3) and modulate glutamate neurotransmission and synaptic plasticity. Here we review the expression and function of mGluR3 and its involvement in schizophrenia. mGluR3 is expressed by glia and neurons in many brain regions and has a predominantly presynaptic distribution, consistent with its role as an inhibitory autoreceptor and heteroceptor. mGluR3 splice variants exist in human brain but are of unknown function. Differentiation of mGluR3 from mGluR2 has been problematic because of the lack of selective ligands and antibodies; the available data suggest particular roles for mGluR3 in long-term depression, in glial function and in neuroprotection. Some but not all studies find genetic association of GRM3 polymorphisms with psychosis, with the risk alleles also being associated with schizophrenia-related endophenotypes such as impaired cognition, cortical activation and glutamate markers. The dimeric form of mGluR3 may be reduced in the brain in schizophrenia. Finally, preclinical findings have made mGluR3 a putative therapeutic target, and now direct evidence for antipsychotic efficacy of a group II mGluR agonist has emerged from a randomised clinical trial in schizophrenia. Together these data implicate mGluR3 in aetiological, pathophysiological and pharmacotherapeutic aspects of the disorder.

Transcriptional activators and repressors for the neuron-specific expression of a metabotropic glutamate receptor

Metabotropic glutamate receptor 1 (mGlu1) has a discrete distribution in the central nervous system restricted to neurons. Its expression undergoes important changes during development and in response to physiological and pathological modifications. Here, we have determined the structure of the mGlu1 gene and demonstrated that mGlu1 transcription takes places at alternative first exons. Moreover, we have identified active promoter regions upstream from the two most expressed first exons by means of luciferase reporter gene assays performed in primary cerebellar granule neurons. Targeted mutations of active elements constituting the core promoter and electrophoretic mobility shift assays demonstrated that the factors thyroid transcription factor-1 and CCAAT/enhancer-binding proteins beta act synergistically to promote mGlu1 transcription. We have also elucidated the molecular bases for the neuron-specific expression of mGlu1 identifying a neural restrictive silencing element and a regulatory factor for X box element, which suppressed mGlu1 expression in nonneuronal cells. These results reveal the molecular bases for cell- and context-specific expression of an important glutamate receptor critically involved in synaptogenesis, neuronal differentiation, synaptic transmission, and plasticity.

Transcriptional regulation of metabotropic glutamate receptor 2/3 expression by the NF-kappaB pathway in primary dorsal root ganglia neurons: a possible mechanism for the analgesic effect of L-acetylcarnitine

L-acetylcarnitine (LAC), a drug utilized for the treatment of neuropathic pain in humans, has been shown to induce analgesia in rodents by up-regulating the expression of metabotropic glutamate receptor 2 (mGlu2) in dorsal root ganglia (DRG). We now report that LAC-induced upregulation of mGlu2 expression in DRG cultures involves transcriptional activation mediated by nuclear factor-kappaB (NF-kappaB). A single application of LAC (250 muM) to DRG cultures induced a transient increase in mGlu2 mRNA, which was observable after 1 hour and was no longer detectable after 1 to 4 days. In contrast, LAC treatment had no effect on mGlu3 mRNA expression. Pharmacological inhibition of NF-kappaB binding to DNA by caffeic acid phenethyl ester (CAPE) (2.5 microg/ml for 30 minutes) reduced the constitutive expression of mGlu2 and mGlu3 mRNA after 1-4 days and reduced the constitutive expression of mGlu2/3 protein at 4 days. This evidence combined with the expression of p65/RelA and c-Rel in DRG neurons indicated that expression of mGlu2 and mGlu3 is endogenously regulated by the NF-kappaB family of transcription factors. Consistent with this idea, the transient increase in mGlu2 mRNA induced by LAC after 1 hour was completely suppressed by CAPE. Furthermore, LAC induced an increase in the acetylation of p65/RelA, a process that enhances the transcriptional activity of p65/RelA. These results are consistent with the hypothesis that LAC selectively induces the expression of mGlu2 by acting as a donor of acetyl groups, thus enhancing the activity of the NF-kappaB family of transcription factors. Accordingly, we show that carnitine, which has no effect on pain thresholds, had no effect on p65/RelA acetylation and did not enhance mGlu2 expression. Taken together, these results demonstrate that expression of mGlu2 and mGlu3 mRNA is regulated by the NF-kappaB transcriptional machinery, and that agents that increase acetylation and activation of NF-kappaB transcription factors might induce analgesia via upregulation of mGlu2 in DRG neurons.

Gene structure of the human metabotropic glutamate receptor 5 and functional analysis of its multiple promoters in neuroblastoma and astroglioma cells

The metabotropic glutamate receptor 5 (mGluR5) has a discrete tissue expression mainly limited to neural cells. Expression of mGluR5 is developmentally regulated and undergoes dramatic changes in association with neuropathological disorders. We report the complete genomic structure of the mGluR5 gene, which is composed of 11 exons and encompasses approximately 563 kbp. Three clusters of multiple transcription initiation sites located on three distinct exons (IA, IB, and II), which undergo alternative splicing, have been identified. The 5'-flanking regions of these exons were isolated and, using a luciferase reporter gene assay, shown to possess active promoter elements in SKN-MC neuroblastoma and U178-MG astroglioma cells. Promoter IA was characterized by a CpG island; promoter IB contained a TATA box, and promoter II possessed three active Oct-1-binding sites. Preferential luciferase activity was observed in SKN-MC concomitant with differential DNA binding activity to several responsive elements, including CREB, Oct-1, C/EBP, and Brn-2. Exposure to growth factors produced enhanced expression of promoters IB and II in astroglioma cells and activation of NF-kappa B. These results suggest that alternative 5'-splicing and usage of multiple promoters may contribute regulatory mechanisms for tissue- and context-specific expression of the mGluR5 gene.