| 1 | Biol. Psychiatry 2005 Jun 57: 1493-503 |
|---|---|
| PMID | 15953485 |
| Title | Identification of multiple serine racemase (SRR) mRNA isoforms and genetic analyses of SRR and DAO in schizophrenia and D-serine levels. |
| Abstract | We previously reported a reduction in serum levels of D-serine, an endogenous co-agonist of the N-methyl-D-aspartate (NMDA) receptor, in schizophrenia, supporting the hypofunction hypothesis of NMDA neurotransmission in schizophrenia. In this study, we examined the genetic roles of serine racemase (SRR), an enzyme catalyzing the formation of D-serine from L-serine, and D-amino-acid oxidase (DAO) in the susceptibility to schizophrenia and the regulation of serum D-serine levels. We determined the complete cDNA and genomic structures of SRR and performed mutation screening. Single nucleotide polymorphisms (SNPs) in SRR and DAO were tested for their association with schizophrenia in both case-control and family-based designs and for correlation with serum levels of D-serine. Genomic analyses revealed that human brain SRR transcripts consist of four isoforms with one major species, which were derived from alternative use of various 5' end exons. Genetic association analyses showed no significant association between SRR/DAO and schizophrenia. We replicated the decreased serum D-serine levels in schizophrenia in the sample set, but D-serine levels did not correlate with SRR/DAO genotypes. The SRR/DAO are not likely to be major genetic determinants in the development of schizophrenia or control of serum D-serine levels. |
| SCZ Keywords | schizophrenia, schizophrenic, schizophrenics |
| 2 | Psychiatr. Genet. 2007 Apr 17: 125 |
| PMID | 17413455 |
| Title | No association between the serine racemase gene (SRR) and schizophrenia in a German case-control sample. |
| Abstract | -1 |
| SCZ Keywords | schizophrenia, schizophrenic, schizophrenics |
| 3 | Biol. Psychiatry 2007 May 61: 1200-3 |
| PMID | 17067558 |
| Title | A genetic variant of the serine racemase gene is associated with schizophrenia. |
| Abstract | Serine racemase (SRR) is a brain-enriched enzyme that converts L-serine to D-serine, which acts as an endogenous ligand of N-methyl D-aspartate (NMDA) receptors. Dysfunction of SRR may reduce the function of NMDA receptors and susceptibility to schizophrenia. We genotyped three single-nucleotide polymorphisms (SNPs) of the 5' region of the SRR gene in 525 patients with schizophrenia and 524 healthy controls. Effects of SNPs on the promoter activity and on serum levels of total and D-serine were examined. We found a significant excess of the IVS1a+465C allele of the SRR gene in schizophrenia, especially in the paranoid subtype (p = .0028). A reporter assay showed that the IVS1a+465C allele had 60% lower promoter activity than did the IVS1a+465G allele. The IVS1a+465C allele of the SRR gene, which reduces expression of the gene, is a risk factor for schizophrenia, especially the paranoid subtype. |
| SCZ Keywords | schizophrenia, schizophrenic, schizophrenics |
| 4 | Hum. Mol. Genet. 2009 Sep 18: 3227-43 |
| PMID | 19483194 |
| Title | Serine racemase is associated with schizophrenia susceptibility in humans and in a mouse model. |
| Abstract | Abnormal N-methyl-d-aspartate receptor (NMDAR) function has been implicated in the pathophysiology of schizophrenia. d-serine is an important NMDAR modulator, and to elucidate the role of the d-serine synthesis enzyme serine racemase (SRR) in schizophrenia, we identified and characterized mice with an ENU-induced mutation that results in a complete loss of SRR activity and dramatically reduced d-serine levels. Mutant mice displayed behaviors relevant to schizophrenia, including impairments in prepulse inhibition, sociability and spatial discrimination. Behavioral deficits were exacerbated by an NMDAR antagonist and ameliorated by d-serine or the atypical antipsychotic clozapine. Expression profiling revealed that the SRR mutation influenced several genes that have been linked to schizophrenia and cognitive ability. Transcript levels altered by the SRR mutation were also normalized by d-serine or clozapine treatment. Furthermore, analysis of SRR genetic variants in humans identified a robust association with schizophrenia. This study demonstrates that aberrant SRR function and diminished d-serine may contribute to schizophrenia pathogenesis. |
| SCZ Keywords | schizophrenia, schizophrenic, schizophrenics |
| 5 | Prog. Neuropsychopharmacol. Biol. Psychiatry 2009 Apr 33: 511-8 |
| PMID | 19223009 |
| Title | Association analysis of glycine- and serine-related genes in a Japanese population of patients with schizophrenia. |
| Abstract | Differences in the levels of the glutamate-related amino acids glycine and serine in brain/plasma between schizophrenic patients and normal subjects and changes in the plasma concentrations of these amino acids according to the clinical course have been reported. It has been hypothesized that glycine and serine metabolism may be altered in schizophrenia. In fact, some genes related to the metabolism of these amino acids have been suggested to be candidate genes for schizophrenia. Thus, we performed a genomic case-control analysis of amino acid metabolism-related genes in Japanese patients with schizophrenia. Case-control genetic association analysis of PHGDH, SHMT1, SRR, and DAO was performed. In addition, the effect of the various genotypes resulting from these four genes on changes in plasma amino acid levels in schizophrenia was assessed. The genetic case-control analysis showed that no individual single-nucleotide polymorphism (SNP) in any of the four genes was associated with schizophrenia; only the two (rs3918347-rs4964770, P=0.0009) and three (rs3825251-rs3918347-rs4964770, P=0.002) SNP-based haplotype analysis of the DAO gene showed an association with schizophrenia even after correction for multiple testing. None of the genotypes studied was associated with changes in the plasma glycine and l- and d-serine levels during the schizophrenic clinical course. The DAO gene may be a susceptibility locus for schizophrenia. |
| SCZ Keywords | schizophrenia, schizophrenic, schizophrenics |
| 6 | Prog. Neuropsychopharmacol. Biol. Psychiatry 2009 Apr 33: 511-8 |
| PMID | 19223009 |
| Title | Association analysis of glycine- and serine-related genes in a Japanese population of patients with schizophrenia. |
| Abstract | Differences in the levels of the glutamate-related amino acids glycine and serine in brain/plasma between schizophrenic patients and normal subjects and changes in the plasma concentrations of these amino acids according to the clinical course have been reported. It has been hypothesized that glycine and serine metabolism may be altered in schizophrenia. In fact, some genes related to the metabolism of these amino acids have been suggested to be candidate genes for schizophrenia. Thus, we performed a genomic case-control analysis of amino acid metabolism-related genes in Japanese patients with schizophrenia. Case-control genetic association analysis of PHGDH, SHMT1, SRR, and DAO was performed. In addition, the effect of the various genotypes resulting from these four genes on changes in plasma amino acid levels in schizophrenia was assessed. The genetic case-control analysis showed that no individual single-nucleotide polymorphism (SNP) in any of the four genes was associated with schizophrenia; only the two (rs3918347-rs4964770, P=0.0009) and three (rs3825251-rs3918347-rs4964770, P=0.002) SNP-based haplotype analysis of the DAO gene showed an association with schizophrenia even after correction for multiple testing. None of the genotypes studied was associated with changes in the plasma glycine and l- and d-serine levels during the schizophrenic clinical course. The DAO gene may be a susceptibility locus for schizophrenia. |
| SCZ Keywords | schizophrenia, schizophrenic, schizophrenics |
| 7 | Nihon Shinkei Seishin Yakurigaku Zasshi 2010 Nov 30: 197-200 |
| PMID | 21226315 |
| Title | [Analysis of mouse strain-dependent prepulse inhibition points to a role for Shmt1 (SHMT1) in mice and in schizophrenia]. |
| Abstract | Deficits in prepulse inhibition (PPI) are thought to be a biological trait of mental illnesses, including schizophrenia. It is known that the N-methyl-D-aspartate type glutamate (NMDA) receptor function affects PPI integrity and D-serine and glycine are typical endogenous co-agonists for the receptor. In parallel, we re-visited our prior quantitative trait loci (QTL) analysis study that examined C57BL/6 (B6) mice with high PPI and C3H/He (C3) with low PPI, and noticed that the genes encoding enzymes responsible for the productions of D-serine (serine racemase: SRR) and glycine (serine hydroxymethyltransferase 1: Shmt1) map to the chromosome 11 QTL. Therefore, we set out to examine whether brain interstitial fluid (ISF) levels of the two amino acids are different between the two mouse strains, using in vivo microdialysis. Recovery of D-serine and glycine from the dialysate of the frontal cortex was higher in B6 mice, which performed better in PPI, compared to C3 mice. Next, we analyzed the two genes, SRR and Shmt1. We then identified promoter polymorphisms in Shmt1 which elicit lower transcriptional activity in B6 compared to C3 mice. Human studies revealed higher expression levels of SHMT1 in the frontal cortex of postmortem brains from schizophrenics compared to controls, but no changes in SRR levels. In addition, genetic analysis detected a nominal association between SHMT1 and schizophrenia. These results suggest that Shmt1 (SHMT1) is one of the genetic components regulating PPI in mice and is relevant to schizophrenia susceptibility in humans. |
| SCZ Keywords | schizophrenia, schizophrenic, schizophrenics |
| 8 | Schizophr. Res. 2010 Jul 120: 236-7 |
| PMID | 20385472 |
| Title | Elevated PICK1 mRNA in schizophrenia increased SRR mRNA in suicide. |
| Abstract | -1 |
| SCZ Keywords | schizophrenia, schizophrenic, schizophrenics |
| 9 | Nihon Shinkei Seishin Yakurigaku Zasshi 2010 Nov 30: 197-200 |
| PMID | 21226315 |
| Title | [Analysis of mouse strain-dependent prepulse inhibition points to a role for Shmt1 (SHMT1) in mice and in schizophrenia]. |
| Abstract | Deficits in prepulse inhibition (PPI) are thought to be a biological trait of mental illnesses, including schizophrenia. It is known that the N-methyl-D-aspartate type glutamate (NMDA) receptor function affects PPI integrity and D-serine and glycine are typical endogenous co-agonists for the receptor. In parallel, we re-visited our prior quantitative trait loci (QTL) analysis study that examined C57BL/6 (B6) mice with high PPI and C3H/He (C3) with low PPI, and noticed that the genes encoding enzymes responsible for the productions of D-serine (serine racemase: SRR) and glycine (serine hydroxymethyltransferase 1: Shmt1) map to the chromosome 11 QTL. Therefore, we set out to examine whether brain interstitial fluid (ISF) levels of the two amino acids are different between the two mouse strains, using in vivo microdialysis. Recovery of D-serine and glycine from the dialysate of the frontal cortex was higher in B6 mice, which performed better in PPI, compared to C3 mice. Next, we analyzed the two genes, SRR and Shmt1. We then identified promoter polymorphisms in Shmt1 which elicit lower transcriptional activity in B6 compared to C3 mice. Human studies revealed higher expression levels of SHMT1 in the frontal cortex of postmortem brains from schizophrenics compared to controls, but no changes in SRR levels. In addition, genetic analysis detected a nominal association between SHMT1 and schizophrenia. These results suggest that Shmt1 (SHMT1) is one of the genetic components regulating PPI in mice and is relevant to schizophrenia susceptibility in humans. |
| SCZ Keywords | schizophrenia, schizophrenic, schizophrenics |
| 10 | J. Neurochem. 2010 Dec 115: 1374-85 |
| PMID | 20977478 |
| Title | Analysis of strain-dependent prepulse inhibition points to a role for Shmt1 (SHMT1) in mice and in schizophrenia. |
| Abstract | Deficits in prepulse inhibition (PPI) are known in mental illnesses, including schizophrenia. NMDA receptor function affects PPI integrity and D-serine and glycine are endogenous co-agonists for the receptor. Our previous quantitative trait loci analysis using C57BL/6 (B6) mice with better PPI performance and C3H/He (C3) with lower PPI score, shows that genes for both D-serine synthesizing enzyme and enzyme for reversible conversion between glycine and L-serine (SRR and Shmt1, respectively) are located in the same PPI-quantitative trait loci peak. Therefore, we set out to determine which gene is likely to explain the PPI difference and whether the gene is potentially relevant to schizophrenia. We first examined brain interstitial fluid levels of the two amino acids using microdialysis. Recovery of D-serine and glycine from the dialysate was higher in B6, compared to C3. Next, we analyzed expression levels and genetic polymorphisms of the two genes. There were promoter polymorphisms in Shmt1, which elicit lower transcriptional activity in B6 compared to C3 conforming to the results of brain expression levels, but no functional genetic variants in SRR. Finally, we evaluated expression levels of the two genes in the postmortem brains of schizophrenia and genetic associations with the disease. The SHMT1 levels were higher in schizophrenic brains compared to controls, but no changes in SRR levels. We detected a nominal association between SHMT1 and schizophrenia. These results suggest that Shmt1 (SHMT1), but not SRR, is likely to be one of the genetic components regulating PPI in mice and possibly relevant to schizophrenia. |
| SCZ Keywords | schizophrenia, schizophrenic, schizophrenics |
| 11 | J. Neurochem. 2010 Dec 115: 1374-85 |
| PMID | 20977478 |
| Title | Analysis of strain-dependent prepulse inhibition points to a role for Shmt1 (SHMT1) in mice and in schizophrenia. |
| Abstract | Deficits in prepulse inhibition (PPI) are known in mental illnesses, including schizophrenia. NMDA receptor function affects PPI integrity and D-serine and glycine are endogenous co-agonists for the receptor. Our previous quantitative trait loci analysis using C57BL/6 (B6) mice with better PPI performance and C3H/He (C3) with lower PPI score, shows that genes for both D-serine synthesizing enzyme and enzyme for reversible conversion between glycine and L-serine (SRR and Shmt1, respectively) are located in the same PPI-quantitative trait loci peak. Therefore, we set out to determine which gene is likely to explain the PPI difference and whether the gene is potentially relevant to schizophrenia. We first examined brain interstitial fluid levels of the two amino acids using microdialysis. Recovery of D-serine and glycine from the dialysate was higher in B6, compared to C3. Next, we analyzed expression levels and genetic polymorphisms of the two genes. There were promoter polymorphisms in Shmt1, which elicit lower transcriptional activity in B6 compared to C3 conforming to the results of brain expression levels, but no functional genetic variants in SRR. Finally, we evaluated expression levels of the two genes in the postmortem brains of schizophrenia and genetic associations with the disease. The SHMT1 levels were higher in schizophrenic brains compared to controls, but no changes in SRR levels. We detected a nominal association between SHMT1 and schizophrenia. These results suggest that Shmt1 (SHMT1), but not SRR, is likely to be one of the genetic components regulating PPI in mice and possibly relevant to schizophrenia. |
| SCZ Keywords | schizophrenia, schizophrenic, schizophrenics |
| 12 | J. Neurosci. Res. 2010 Jun 88: 1829-40 |
| PMID | 20091774 |
| Title | D-Serine metabolism in C6 glioma cells: Involvement of alanine-serine-cysteine transporter (ASCT2) and serine racemase (SRR) but not D-amino acid oxidase (DAO). |
| Abstract | D-serine is an endogenous N-methyl-D-aspartate (NMDA) receptor coagonist. It is synthesized from L-serine by serine racemase (SRR), but many aspects of its metabolism remain unclear, especially in the forebrain, which lacks active D-amino acid oxidase (DAO), the major D-serine degradative enzyme. Candidate mechanisms include SRR operating in alpha,beta-eliminase mode (converting D-serine to pyruvate) and regulation by serine transport, in which the alanine-serine-cysteine transporter ASCT2 is implicated. Here we report studies in C6 glioma cells, which "simulate" the forebrain, in that the cells express SRR and ASCT2 but lack DAO activity. We measured D-serine, ASCT2, SRR, and DAO expression and DAO activity in two situations: after incubation of cells for 48 hr with serine isomers and after increased or decreased SRR expression by transfection and RNA interference, respectively. Incubation with serine enantiomers decreased [(3)H]D-serine uptake and ASCT2 mRNA and increased SRR immunoreactivity but did not alter DAO immunoreactivity, and DAO activity remained undetectable. SRR overexpression increased D-serine and pyruvate and decreased [(3)H]D-serine uptake and ASCT2 mRNA but did not affect DAO. SRR knockdown did not alter any of the parameters. Our data suggest that D-serine transport mediated by ASCT2 contributes prominently to D-serine homeostasis when DAO activity is absent. The factors regulating D-serine are important for understanding normal NMDA receptor function and because D-serine, along with DAO and SRR, is implicated in the pathogenesis and treatment of schizophrenia. |
| SCZ Keywords | schizophrenia, schizophrenic, schizophrenics |
| 13 | Neuropharmacology 2012 Mar 62: 1484-503 |
| PMID | 21295046 |
| Title | Contributions of the D-serine pathway to schizophrenia. |
| Abstract | The glutamate neurotransmitter system is one of the major candidate pathways for the pathophysiology of schizophrenia, and increased understanding of the pharmacology, molecular biology and biochemistry of this system may lead to novel treatments. Glutamatergic hypofunction, particularly at the NMDA receptor, has been hypothesized to underlie many of the symptoms of schizophrenia, including psychosis, negative symptoms and cognitive impairment. This review will focus on D-serine, a co-agonist at the NMDA receptor that in combination with glutamate, is required for full activation of this ion channel receptor. Evidence implicating D-serine, NMDA receptors and related molecules, such as D-amino acid oxidase (DAO), G72 and serine racemase (SRR), in the etiology or pathophysiology of schizophrenia is discussed, including knowledge gained from mouse models with altered D-serine pathway genes and from preliminary clinical trials with D-serine itself or compounds modulating the D-serine pathway. Abnormalities in D-serine availability may underlie glutamatergic dysfunction in schizophrenia, and the development of new treatments acting through the D-serine pathway may significantly improve outcomes for many schizophrenia patients. |
| SCZ Keywords | schizophrenia, schizophrenic, schizophrenics |
| 14 | Transl Psychiatry 2012 -1 2: e113 |
| PMID | 22832957 |
| Title | Association between SNPs and gene expression in multiple regions of the human brain. |
| Abstract | Identifying the genetic cis associations between DNA variants (single-nucleotide polymorphisms (SNPs)) and gene expression in brain tissue may be a promising approach to find functionally relevant pathways that contribute to the etiology of psychiatric disorders. In this study, we examined the association between genetic variations and gene expression in prefrontal cortex, hippocampus, temporal cortex, thalamus and cerebellum in subjects with psychiatric disorders and in normal controls. We identified cis associations between 648 transcripts and 6725 SNPs in the various brain regions. Several SNPs showed brain regional-specific associations. The expression level of only one gene, PDE4DIP, was associated with a SNP, rs12124527, in all the brain regions tested here. From our data, we generated a list of brain cis expression quantitative trait loci (eQTL) genes that we compared with a list of schizophrenia candidate genes downloaded from the schizophrenia Forum (SZgene) database (http://www.szgene.org/). Of the SZgene candidate genes, we found that the expression levels of four genes, HTR2A, PLXNA2, SRR and TCF4, were significantly associated with cis SNPs in at least one brain region tested. One gene, SRR, was also involved in a coexpression module that we found to be associated with disease status. In addition, a substantial number of cis eQTL genes were also involved in the module, suggesting eQTL analysis of brain tissue may identify more reliable susceptibility genes for schizophrenia than case-control genetic association analyses. In an attempt to facilitate the identification of genetic variations that may underlie the etiology of major psychiatric disorders, we have integrated the brain eQTL results into a public and online database, Stanley Neuropathology Consortium Integrative Database (SNCID; http://sncid.stanleyresearch.org). |
| SCZ Keywords | schizophrenia, schizophrenic, schizophrenics |
| 15 | PLoS ONE 2013 -1 8: e62438 |
| PMID | 23630632 |
| Title | Neonatal disruption of serine racemase causes schizophrenia-like behavioral abnormalities in adulthood: clinical rescue by d-serine. |
| Abstract | D-Serine, an endogenous co-agonist of the N-methyl-D-aspartate (NMDA) receptor, is synthesized from L-serine by serine racemase (SRR). Given the role of D-serine in both neurodevelopment and the pathophysiology of schizophrenia, we examined whether neonatal disruption of D-serine synthesis by SRR inhibition could induce behavioral abnormalities relevant to schizophrenia, in later life. Neonatal mice (7-9 days) were injected with vehicle or phenazine methosulfate (Met-Phen: 3 mg/kg/day), an SRR inhibitor. Behavioral evaluations, such as spontaneous locomotion, novel object recognition test (NORT), and prepulse inhibition (PPI) were performed at juvenile (5-6 weeks old) and adult (10-12 weeks old) stages. In addition, we tested the effects of D-serine on PPI deficits in adult mice after neonatal Met-Phen exposure. Finally, we assessed whether D-serine could prevent the onset of schizophrenia-like behavior in these mice. Neonatal Met-Phen treatment reduced D-serine levels in the brain, 24 hours after the final dose. Additionally, this treatment caused behavioral abnormalities relevant to prodromal symptoms in juveniles and to schizophrenia in adults. A single dose of D-serine improved PPI deficits in adult mice. Interestingly, chronic administration of D-serine (900 mg/kg/day from P35 to P70) significantly prevented the onset of PPI deficits after neonatal Met-Phen exposure. This study shows that disruption of D-serine synthesis during developmental stages leads to behavioral abnormalities relevant to prodromal symptoms and schizophrenia, in later life. Furthermore, early pharmacological intervention with D-serine may prevent the onset of psychosis in adult. |
| SCZ Keywords | schizophrenia, schizophrenic, schizophrenics |
| 16 | Mol. Psychiatry 2015 Dec 20: 1557-64 |
| PMID | 25666758 |
| Title | Genome-wide association study of NMDA receptor coagonists in human cerebrospinal fluid and plasma. |
| Abstract | The N-methyl-D-aspartate receptor (NMDAR) coagonists glycine, D-serine and L-proline play crucial roles in NMDAR-dependent neurotransmission and are associated with a range of neuropsychiatric disorders. We conducted the first genome-wide association study of concentrations of these coagonists and their enantiomers in plasma and cerebrospinal fluid (CSF) of human subjects from the general population (N=414). Genetic variants at chromosome 22q11.2, located in and near PRODH (proline dehydrogenase), were associated with L-proline in plasma (?=0.29; P=6.38 × 10(-10)). The missense variant rs17279437 in the proline transporter SLC6A20 was associated with L-proline in CSF (?=0.28; P=9.68 × 10(-9)). Suggestive evidence of association was found for the D-serine plasma-CSF ratio at the D-amino-acid oxidase (DAO) gene (?=-0.28; P=9.08 × 10(-8)), whereas a variant in SRR (that encodes serine racemase and is associated with schizophrenia) constituted the most strongly associated locus for the L-serine to D-serine ratio in CSF. All these genes are highly expressed in rodent meninges and choroid plexus, anatomical regions relevant to CSF physiology. The enzymes and transporters they encode may be targeted to further construe the nature of NMDAR coagonist involvement in NMDAR gating. Furthermore, the highlighted genetic variants may be followed up in clinical populations, for example, schizophrenia and 22q11 deletion syndrome. Overall, this targeted metabolomics approach furthers the understanding of NMDAR coagonist concentration variability and sets the stage for non-targeted CSF metabolomics projects. |
| SCZ Keywords | schizophrenia, schizophrenic, schizophrenics |