Differences in the Circuitry-Based Association of Copy Numbers and Gene Expression Between the Hippocampi of Patients With Schizophrenia and the Hippocampi of Patients With Bipolar Disorder
ABSTRACT GAD67 regulation involves a network of genes implicated in schizophrenia and bipolar disorder. We have studied the copy number intensities of these genes in specific hippocampal subregions to clarify whether abnormalities of genomic integrity covary with gene expression in a circuitry-based manner.
To compare the copy number intensities of genes associated with GAD67 regulation in the stratum oriens of sectors CA3/2 and CA1 in patients with schizophrenia, patients with bipolar disorder, and healthy controls.
Samples of sectors CA3/2 and CA1 were obtained from patients with schizophrenia, patients with bipolar disorder, and healthy controls. Genomic integrity was analyzed using microarrays, and the copy number intensities identified were correlated with the gene expression profile from a subset of these cases previously reported.
Harvard Brain Tissue Resource Center at McLean Hospital, Belmont, Massachusetts.
A total of 15 patients with schizophrenia, 15 patients with bipolar disorder, and 15 healthy controls.
The copy number intensities for 28 target genes were individually examined using single-nucleotide polymorphism microarrays and correlated with homologous messenger RNA (mRNA) fold changes.
The copy number intensities examined using both microarrays and quantitative real-time polymerase chain reaction for the GAD67 gene were significantly decreased in sector CA3/2 of patients with schizophrenia and patients with bipolar disorder. Other genes associated with GAD67 regulation also showed changes in copy number intensities, and these changes were similar in magnitude and direction to those previously reported for mRNA fold changes in sector CA3/2 but not sector CA1. Moreover, the copy number intensities and mRNA fold changes were significantly correlated for both patients with schizophrenia (r=0.649; P=.0003) and patients with bipolar disorder (r=0.772; P=.0002) in sector CA3/2 but not in sector CA1.
Insertions and deletions of genomic DNA in γ-aminobutyric acid cells at a key locus of the hippocampal circuit are reflected in transcriptional changes in GAD67 regulation that are circuitry-based and diagnosis-specific.
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ABSTRACT: Reduced hippocampal volume in schizophrenia is a well-replicated finding. New imaging techniques allow delineation of hippocampal subfield volumes. Studies including predominantly chronic patients demonstrate differences between subfields in sensitivity to illness, and in associations with clinical features. We carried out a cross-sectional and longitudinal study of first episode, sub-chronic, and chronic patients, using an imaging strategy that allows for the assessment of multiple hippocampal subfields. Hippocampal subfield volumes were measured in 34 patients with schizophrenia (19 first episode, 6 sub-chronic, 9 chronic) and 15 healthy comparison participants. A subset of 10 first episode and 12 healthy participants were rescanned after six months. Total left hippocampal volume was smaller in sub-chronic (p = 0.04, effect size 1.12) and chronic (p = 0.009, effect size 1.42) patients compared with healthy volunteers. The CA2-3 subfield volume of chronic patients was significantly decreased (p = 0.009, effect size 1.42) compared to healthy volunteers. The CA4-DG volume was significantly reduced in all three patient groups compared to healthy group (all p < 0.005). The two affected subfield volumes were inversely correlated with severity of negative symptoms (p < 0.05). There was a small, but statistically significant decline in left CA4-DG volume over the first six months of illness (p = 0.01). Imaging strategies defining the subfields of the hippocampus may be informative in linking symptoms and structural abnormalities, and in understanding more about progression during the early phases of illness in schizophrenia.PLoS ONE 02/2015; 10(2):e0117785. DOI:10.1371/journal.pone.0117785 · 3.53 Impact Factor
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ABSTRACT: Expression of GAD1 GABA synthesis enzyme is highly regulated by neuronal activity and reaches mature levels in the prefrontal cortex not before adolescence. A significant portion of cases diagnosed with schizophrenia show deficits in GAD1 RNA and protein levels in multiple areas of adult cerebral cortex, possibly reflecting molecular or cellular defects in subtypes of GABAergic interneurons essential for network synchronization and cognition. Here, we review 20 years of progress towards a better understanding of disease-related regulation of GAD1 gene expression. For example, deficits in cortical GAD1 RNA in some cases of schizophrenia are associated with changes in the epigenetic architecture of the promoter, affecting DNA methylation patterns and nucleosomal his-tone modifications. These localized chromatin defects at the 5′ end of GAD1 are superimposed by disordered locus-specific chromosomal conformations, including weakening of long-range promoter-enhancer loopings and physical disconnection of GAD1 core promoter sequences from cis-regulatory elements positioned 50 kilo-bases further upstream. Studies on the 3-dimensional architecture of the GAD1 locus in neurons, including devel-opmentally regulated higher order chromatin compromised by the disease process, together with exploration of locus-specific epigenetic interventions in animal models, could pave the way for future treatments of psychosis and schizophrenia. © 2014 Elsevier B.V. All rights reserved. 1. GABAergic dysfunction in schizophrenia — a brief chronology Schizophrenia (SCZ) — a major psychiatric disorder with symptoms of delusions, hallucinations disorganized thought and affect, social with-drawal and apathy — lacks unifying neuropathology (Dorph-Petersen and Lewis, 2011; Catts et al., 2013), or narrowly defined genetic risk architectures and disease etiologies (Rodriguez-Murillo et al., 2012; Andreassen et al., 2014). Yet, clinical and translational research con-ducted over the last 40 years is beginning to identify major building blocks within the complex pathophysiology of SCZ. As highlighted in the various articles in this Special Issue of Schizophrenia Research, one such building block is the inhibitory GABAergic circuitry in the cerebral cortex. While the primary focus of our review will be on the transcrip-tional dysregulation of the glutamic acid decarboxylase 1 (GAD1) gene, encoding the 67 KDa GABA synthesis enzyme, we will begin with a brief synopsis of past studies in pursuit of the 'GABAergic hypothesis of SCZ', which proposes that GABAergic systems could play a key role in the pathophysiology of SCZ. This idea is not new. Thus, 25 years after the first reports described the relatively large amounts of GABA and high levels of glutamic acid decarboxylase (GAD) in the brain (Roberts and Frankel, 1950, 1951), the role of inhibitory inputs to midbrain dopaminergic neurons was hypothesized to be the key mechanism responsible for excessive and dysregulated dopaminergic activity in psychosis (Stevens et al., 1974; Smythies et al., 1975). While it was quickly recognized that a generalized deficit in GABA sig-naling is not a characteristic of SCZ — as the symptoms of psychosis remained unresponsive to GABA agonists in early clinical trials (Tamminga et al., 1978) — the idea of region-specific dysfunctions of GABA systems nonetheless continued, up to the present day, to main-tain significant traction and in fact, emerged as one of the most popular hypotheses in SCZ research. For example, several studies reported a decrease in GABA levels and GAD activity in the medial temporal lobe, thalamus and ventral striatum of the SCZ postmortem brain (Bird et al., 1977; Perry et al., 1979; Spokes et al., 1980) albeit other investiga-tors reported negative findings (Cross et al., 1979). There were also re-ports on low GABA levels in the cerebrospinal fluid in at least a subset of patients diagnosed with SCZ (Lichtshtein et al., 1978; van Kammen et al., 1982). Following these early studies on GABA and GAD quantifica-tions in the schizophrenic brain, several papers explored alterations in the inhibitory system in the context of abnormal circuitry. This type of work was mainly focused on the cerebral cortex and hippocampus, starting with Benes' model proposing excessive excitatory and insuffi-cient inhibitory signaling in the upper layers of the cerebral cortex due to a possible loss of GABAergic neurons and/or supranormal numbers or densities of glutamatergic afferent input into the same cortical layers (Benes et al., 1992a,b). There is also an ongoing discussion if and how decreased expression of GABAergic marker genes in the cerebral cortex Schizophrenia Research xxx (2014) xxx–xxx ⁎ Corresponding author.Schizophrenia Research 10/2014; DOI:10.1016/j.schres.2014.10.020 · 4.43 Impact Factor
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ABSTRACT: Schizophrenia (SCZ) and bipolar disorder (BPD) are severe mental disorders with high heritability. Clinicians have long noticed the similarities of clinic symptoms between these disorders. In recent years, accumulating evidence indicates some shared genetic liabilities. However, what is shared remains elusive. In this study, we conducted whole transcriptome analysis of post-mortem brain tissues (cingulate cortex) from SCZ, BPD and control subjects, and identified differentially expressed genes in these disorders. We found 105 and 153 genes differentially expressed in SCZ and BPD, respectively. By comparing the t-test scores, we found that many of the genes differentially expressed in SCZ and BPD are concordant in their expression level (q⩽0.01, 53 genes; q⩽0.05, 213 genes; q⩽0.1, 885 genes). Using genome-wide association data from the Psychiatric Genomics Consortium, we found that these differentially and concordantly expressed genes were enriched in association signals for both SCZ (P<10(-7)) and BPD (P=0.029). To our knowledge, this is the first time that a substantially large number of genes show concordant expression and association for both SCZ and BPD. Pathway analyses of these genes indicated that they are involved in the lysosome, Fc gamma receptor-mediated phagocytosis, regulation of actin cytoskeleton pathways, along with several cancer pathways. Functional analyses of these genes revealed an interconnected pathway network centered on lysosomal function and the regulation of actin cytoskeleton. These pathways and their interacting network were principally confirmed by an independent transcriptome sequencing data set of the hippocampus. Dysregulation of lysosomal function and cytoskeleton remodeling has direct impacts on endocytosis, phagocytosis, exocytosis, vesicle trafficking, neuronal maturation and migration, neurite outgrowth and synaptic density and plasticity, and different aspects of these processes have been implicated in SCZ and BPD.Molecular Psychiatry advance online publication, 12 August 2014; doi:10.1038/mp.2014.82.Molecular Psychiatry 08/2014; DOI:10.1038/mp.2014.82 · 15.15 Impact Factor