Altered ratios of alternatively spliced long and short gamma2 subunit mRNAs of the gamma-amino butyrate type A receptor in prefrontal cortex of schizophrenics

Proteomic signatures of schizophrenia-sourced iPSC-derived neural cells and brain organoids are similar to patients' postmortem brains

BACKGROUND

Schizophrenia is a complex and severe neuropsychiatric disorder, with a wide range of debilitating symptoms. Several aspects of its multifactorial complexity are still unknown, and some are accepted to be an early developmental deficiency with a more specifically neurodevelopmental origin. Understanding the timepoints of disturbances during neural cell differentiation processes could lead to an insight into the development of the disorder. In this context, human brain organoids and neural cells differentiated from patient-derived induced pluripotent stem cells are of great interest as a model to study the developmental origins of the disease.

RESULTS

Here we evaluated the differential expression of proteins of schizophrenia patient-derived neural progenitors (NPCs), early neurons, and brain organoids in comparison to healthy individuals. Using bottom-up shotgun proteomics with a label-free approach for quantitative analysis, we found multiple dysregulated proteins since NPCs, modified, and disrupted the 21DIV neuronal differentiation, and cerebral organoids. Our experimental methods have shown impairments in pathways never before found in patient-derived induced pluripotent stem cells studies, such as spliceosomes and amino acid metabolism; but also, those such as axonal guidance and synaptogenesis, in line with postmortem tissue studies of schizophrenia patients.

CONCLUSION

In conclusion, here we provide comprehensive, large-scale, protein-level data of different neural cell models that may uncover early events in brain development, underlying several of the mechanisms within the origins of schizophrenia.

A comprehensive atlas of fetal splicing patterns in the brain of adult myotonic dystrophy type 1 patients

In patients with myotonic dystrophy type 1 (DM1), dysregulation of RNA-binding proteins like MBNL and CELF1 leads to alternative splicing of exons and is thought to induce a return to fetal splicing patterns in adult tissues, including the central nervous system (CNS). To comprehensively evaluate this, we created an atlas of developmentally regulated splicing patterns in the frontal cortex of healthy individuals and DM1 patients, by combining RNA-seq data from BrainSpan, GTEx and DM1 patients. Thirty-four splice events displayed an inclusion pattern in DM1 patients that is typical for the fetal situation in healthy individuals. The regulation of DM1-relevant splicing patterns could partly be explained by changes in mRNA expression of the splice regulators MBNL1, MBNL2 and CELF1. On the contrary, interindividual differences in splicing patterns between healthy adults could not be explained by differential expression of these splice regulators. Our findings lend transcriptome-wide evidence to the previously noted shift to fetal splicing patterns in the adult DM1 brain as a consequence of an imbalance in antagonistic MBNL and CELF1 activities. Our atlas serves as a solid foundation for further study and understanding of the cognitive phenotype in patients.

GABRB2, a key player in neuropsychiatric disorders and beyond

The GABA receptors represent the main inhibitory system in the central nervous system that ensure synaptogenesis, neurogenesis, and the regulation of neuronal plasticity and learning. GABAA receptors are pentameric in structure and belong to the Cys-loop superfamily. The GABRB2 gene, located on chromosome 5q34, encodes the β2 subunit that combines with the α and γ subunits to form the major subtype of GABAA receptors, which account for 43% of all GABAA receptors in the mammalian brain. Each subunit probably consists of an extracellular N-terminal domain, four membrane-spanning segments, a large intracellular loop between TM3 and TM4, and an extracellular C-terminal domain. Alternative splicing of the RNA transcript of the GABRB2 gene gives rise at least to four long and short isoforms with dissimilar electrophysiological properties. Furthermore, GABRB2 is imprinted and subjected to epigenetic regulation and positive selection. It has been associated with schizophrenia first in Han Chinese, and subsequently validated in other populations. Gabrb2 knockout mice also exhibited schizophrenia-like behavior and neuroinflammation that were ameliorated by the antipsychotic drug risperidone. GABRB2 was also associated with other neuropsychiatric disorders including bipolar disorder, epilepsy, autism spectrum disorder, Alzheimer's disease, frontotemporal dementia, substance dependence, depression, internet gaming disorder, and premenstrual dysphoric disorder. Recently, it has been postulated that GABRB2 might be a potential marker for different cancer types. As GABRB2 has a pivotal role in the central nervous system and is increasingly recognized to contribute to human diseases, further understanding of its structure and function may expedite the generation of new therapeutic approaches.

Exploring the impact of adolescent exposure to cannabinoids and nicotine on psychiatric risk: insights from translational animal models

Adolescence represents a highly sensitive period of mammalian neurodevelopment wherein critical synaptic and structural changes are taking place in brain regions involved in cognition, self-regulation and emotional processing. Importantly, neural circuits such as the mesocorticolimbic pathway, comprising the prefrontal cortex, sub-cortical mesolimbic dopamine system and their associated input/output centres, are particularly vulnerable to drug-related insults. Human adolescence represents a life-period wherein many individuals first begin to experiment with recreational drugs such as nicotine and cannabis, both of which are known to profoundly modulate neurochemical signalling within the mesocorticolimbic pathway and to influence both long-term and acute neuropsychiatric symptoms. While a vast body of epidemiological clinical research has highlighted the effects of adolescent exposure to drugs such as nicotine and cannabis on the developing adolescent brain, many of these studies are limited to correlative analyses and rely on retrospective self-reports from subjects, making causal interpretations difficult to discern. The use of pre-clinical animal studies can avoid these issues by allowing for precise temporal and dose-related experimental control over drug exposure during adolescence. In addition, such animal-based research has the added advantage of allowing for in-depth molecular, pharmacological, genetic and neuronal analyses of how recreational drug exposure may set up the brain for neuropsychiatric risk. This review will explore some of the advantages and disadvantages of these models, with a focus on the common, divergent and synergistic effects of adolescent nicotine and cannabis exposure on neuropsychiatric risk.

Looking for Novelty in an "Old" Receptor: Recent Advances Toward Our Understanding of GABAARs and Their Implications in Receptor Pharmacology

Diverse populations of GABA_A receptors (GABA_ARs) throughout the brain mediate fast inhibitory transmission and are modulated by various endogenous ligands and therapeutic drugs. Deficits in GABA_AR signaling underlie the pathophysiology behind neurological and neuropsychiatric disorders such as epilepsy, anxiety, and depression. Pharmacological intervention for these disorders relies on several drug classes that target GABA_ARs, such as benzodiazepines and more recently neurosteroids. It has been widely demonstrated that subunit composition and receptor stoichiometry impact the biophysical and pharmacological properties of GABA_ARs. However, current GABA_AR-targeting drugs have limited subunit selectivity and produce their therapeutic effects concomitantly with undesired side effects. Therefore, there is still a need to develop more selective GABA_AR pharmaceuticals, as well as evaluate the potential for developing next-generation drugs that can target accessory proteins associated with native GABA_ARs. In this review, we briefly discuss the effects of benzodiazepines and neurosteroids on GABA_ARs, their use as therapeutics, and some of the pitfalls associated with their adverse side effects. We also discuss recent advances toward understanding the structure, function, and pharmacology of GABA_ARs with a focus on benzodiazepines and neurosteroids, as well as newly identified transmembrane proteins that modulate GABA_ARs.

Frequency-dependent gating of feedforward inhibition in thalamofrontal synapses

Thalamic recruitment of feedforward inhibition is known to enhance the fidelity of the receptive field by limiting the temporal window during which cortical neurons integrate excitatory inputs. Feedforward inhibition driven by the mediodorsal nucleus of the thalamus (MD) has been previously observed, but its physiological function and regulation remain unknown. Accumulating evidence suggests that elevated neuronal activity in the prefrontal cortex is required for the short-term storage of information. Furthermore, the elevated neuronal activity is supported by the reciprocal connectivity between the MD and the medial prefrontal cortex (mPFC). Therefore, detailed knowledge about the synaptic connections during high-frequency activity is critical for understanding the mechanism of short-term memory. In this study, we examined how feedforward inhibition of thalamofrontal connectivity is modulated by activity frequency. We observed greater short-term synaptic depression during disynaptic inhibition than in thalamic excitatory synapses during high-frequency activities. The strength of feedforward inhibition became weaker as the stimulation continued, which, in turn, enhanced the range of firing jitter in a frequency-dependent manner. We postulated that this phenomenon was primarily due to the increased failure rate of evoking action potentials in parvalbumin-expressing inhibitory neurons. These findings suggest that the MD-mPFC pathway is dynamically regulated by an excitatory-inhibitory balance in an activity-dependent manner. During low-frequency activities, excessive excitations are inhibited, and firing is restricted to a limited temporal range by the strong feedforward inhibition. However, during high-frequency activities, such as during short-term memory, the activity can be transferred in a broader temporal range due to the decreased feedforward inhibition.

Identification and Analysis of Micro-Exon Genes in the Rice Genome

Micro-exons are a kind of exons with lengths no more than 51 nucleotides. They are generally ignored in genome annotation due to the short length, whereas recent studies indicate that they have special splicing properties and important functions. Considering that there has been no genome-wide study of micro-exons in plants up to now, we screened and analyzed genes containing micro-exons in two indica rice varieties in this study. According to the annotation of Zhenshan 97 (ZS97) and Minghui 63 (MH63), ~23% of genes possess micro-exons. We then identified micro-exons from RNA-seq data and found that >65% micro-exons had been annotated and most of novel micro-exons were located in gene regions. About 60% micro-exons were constitutively spliced, and the others were alternatively spliced in different tissues. Besides, we observed that approximately 54% of genes harboring micro-exons tended to be ancient genes, and 13% were Oryza genus-specific. Micro-exon genes were highly conserved in Oryza genus with consistent domains. In particular, the predicted protein structures showed that alternative splicing of in-frame micro-exons led to a local structural recombination, which might affect some core structure of domains, and alternative splicing of frame-shifting micro-exons usually resulted in premature termination of translation by introducing a stop codon or missing functional domains. Overall, our study provided the genome-wide distribution, evolutionary conservation, and potential functions of micro-exons in rice.

γ2 GABAAR Trafficking and the Consequences of Human Genetic Variation

GABA type A receptors (GABA_ARs) mediate the majority of fast inhibitory neurotransmission in the central nervous system (CNS). Most prevalent as heteropentamers composed of two α, two β, and a γ2 subunit, these ligand-gated ionotropic chloride channels are capable of extensive genetic diversity (α1-6, β1-3, γ1-3, δ, 𝜀, 𝜃, π, ρ1-3). Part of this selective GABA_AR assembly arises from the critical role for γ2 in maintaining synaptic receptor localization and function. Accordingly, mutations in this subunit account for over half of the known epilepsy-associated genetic anomalies identified in GABA_ARs. Fundamental structure-function studies and cellular pathology investigations have revealed dynamic GABA_AR trafficking and synaptic scaffolding as critical regulators of GABAergic inhibition. Here, we introduce in vitro and in vivo findings regarding the specific role of the γ2 subunit in receptor trafficking. We then examine γ2 subunit human genetic variation and assess disease related phenotypes and the potential role of altered GABA_AR trafficking. Finally, we discuss new-age imaging techniques and their potential to provide novel insight into critical regulatory mechanisms of GABA_AR function.

Precise temporal regulation of alternative splicing during neural development

Alternative splicing (AS) is one crucial step of gene expression that must be tightly regulated during neurodevelopment. However, the precise timing of developmental splicing switches and the underlying regulatory mechanisms are poorly understood. Here we systematically analyze the temporal regulation of AS in a large number of transcriptome profiles of developing mouse cortices, in vivo purified neuronal subtypes, and neurons differentiated in vitro. Our analysis reveals early-switch and late-switch exons in genes with distinct functions, and these switches accurately define neuronal maturation stages. Integrative modeling suggests that these switches are under direct and combinatorial regulation by distinct sets of neuronal RNA-binding proteins including Nova, Rbfox, Mbnl, and Ptbp. Surprisingly, various neuronal subtypes in the sensory systems lack Nova and/or Rbfox expression. These neurons retain the "immature" splicing program in early-switch exons, affecting numerous synaptic genes. These results provide new insights into the organization and regulation of the neurodevelopmental transcriptome.

Effects of Adolescent THC Exposure on the Prefrontal GABAergic System: Implications for Schizophrenia-Related Psychopathology

Marijuana is the most commonly used drug of abuse among adolescents. Considerable clinical evidence supports the hypothesis that adolescent neurodevelopmental exposure to high levels of the principal psychoactive component in marijuana, -delta-9-tetrahydrocanabinol (THC), is associated with a high risk of developing psychiatric diseases, such as schizophrenia later in life. This marijuana-associated risk is believed to be related to increasing levels of THC found within commonly used marijuana strains. Adolescence is a highly vulnerable period for the development of the brain, where the inhibitory GABAergic system plays a pivotal role in the maturation of regulatory control mechanisms in the central nervous system (CNS). Specifically, adolescent neurodevelopment represents a critical period wherein regulatory connectivity between higher-order cortical regions and sub-cortical emotional processing circuits such as the mesolimbic dopamine (DA) system is established. Emerging preclinical evidence demonstrates that adolescent exposure to THC selectively targets schizophrenia-related molecular and neuropharmacological signaling pathways in both cortical and sub-cortical regions, including the prefrontal cortex (PFC) and mesolimbic DA pathway, comprising the ventral tegmental area (VTA) and nucleus accumbens (NAc). Prefrontal cortical GABAergic hypofunction is a key feature of schizophrenia-like neuropsychopathology. This GABAergic hypofunction may lead to the loss of control of the PFC to regulate proper sub-cortical DA neurotransmission, thereby leading to schizophrenia-like symptoms. This review summarizes preclinical evidence demonstrating that reduced prefrontal cortical GABAergic neurotransmission has a critical role in the sub-cortical DAergic dysregulation and schizophrenia-like behaviors observed following adolescent THC exposure.

Adolescent THC Exposure Causes Enduring Prefrontal Cortical Disruption of GABAergic Inhibition and Dysregulation of Sub-Cortical Dopamine Function

Chronic adolescent marijuana use has been linked to the later development of psychiatric diseases such as schizophrenia. GABAergic hypofunction in the prefrontal cortex (PFC) is a cardinal pathological feature of schizophrenia and may be a mechanism by which the PFC loses its ability to regulate sub-cortical dopamine (DA) resulting in schizophrenia-like neuropsychopathology. In the present study, we exposed adolescent rats to Δ-9-tetra-hydrocannabinol (THC), the psychoactive component in marijuana. At adulthood, we characterized the functionality of PFC GABAergic neurotransmission and its regulation of sub-cortical DA function using molecular, behavioral and in-vivo electrophysiological analyses. Our findings revealed a persistent attenuation of PFC GABAergic function combined with a hyperactive neuronal state in PFC neurons and associated disruptions in cortical gamma oscillatory activity. These PFC abnormalities were accompanied by hyperactive DAergic neuronal activity in the ventral tegmental area (VTA) and behavioral and cognitive abnormalities similar to those observed in psychiatric disorders. Remarkably, these neuronal and behavioral effects were reversed by pharmacological activation of GABA_A receptors in the PFC. Together, these results identify a mechanistic link between dysregulated frontal cortical GABAergic inhibition and sub-cortical DAergic dysregulation, characteristic of well-established neuropsychiatric endophenotypes.

The Nuclear Proteome of White and Gray Matter from Schizophrenia Postmortem Brains

Schizophrenia (SCZ) is a serious neuropsychiatric disorder that manifests through several symptoms from early adulthood. Numerous studies over the last decades have led to significant advances in increasing our understanding of the factors involved in SCZ. For example, mass spectrometry-based proteomic analysis has provided important insights by uncovering protein dysfunctions inherent to SCZ. Here, we present a comprehensive analysis of the nuclear proteome of postmortem brain tissues from corpus callosum (CC) and anterior temporal lobe (ATL). We show an overview of the role of deregulated nuclear proteins in these two main regions of the brain: the first, mostly composed of glial cells and axons of neurons, and the second, represented mainly by neuronal cell bodies. These samples were collected from SCZ patients in an attempt to characterize the role of the nucleus in the disease process. With the ATL nucleus enrichment, we found 224 proteins present at different levels, and 76 of these were nuclear proteins. In the CC analysis, we identified 119 present at different levels, and 24 of these were nuclear proteins. The differentially expressed nuclear proteins of ATL are mainly associated with the spliceosome, whereas those of the CC region are associated with calcium/calmodulin signaling.

Microexons: discovery, regulation, and function

The importance of RNA splicing in numerous cellular processes is well established. However, an underappreciated aspect is the ability of the spliceosome to recognize a set of very small (3-30 nucleotide, 1-10 amino acid) exons named microexons. Despite their small size, microexons and their regulation through alternative splicing have now been shown to play critical roles in protein and system function. Here we review the discovery of microexons over time and the mechanisms by which their splicing is regulated, including recent progress made through deep RNA sequencing. We also discuss the functional role of microexons in biology and disease. WIREs RNA 2017, 8:e1418. doi: 10.1002/wrna.1418 For further resources related to this article, please visit the WIREs website.

GABAergic Mechanisms in Schizophrenia: Linking Postmortem and In Vivo Studies

Schizophrenia is a psychiatric disorder characterized by hallucinations, delusions, disorganized thinking, and impairments in cognitive functioning. Evidence from postmortem studies suggests that alterations in cortical γ-aminobutyric acid (GABAergic) neurons contribute to the clinical features of schizophrenia. In vivo measurement of brain GABA levels using magnetic resonance spectroscopy (MRS) offers the possibility to provide more insight into the relationship between problems in GABAergic neurotransmission and clinical symptoms of schizophrenia patients. This study reviews and links alterations in the GABA system in postmortem studies, animal models, and human studies in schizophrenia. Converging evidence implicates alterations in both presynaptic and postsynaptic components of GABAergic neurotransmission in schizophrenia, and GABA may thus play an important role in the pathophysiology of schizophrenia. MRS studies can provide direct insight into the GABAergic mechanisms underlying the development of schizophrenia as well as changes during its course.

Impaired GABAergic inhibition in the hippocampus of Fmr1 knockout mice

Many clinical and molecular features of the fragile X syndrome, a common form of intellectual disability and autism, can be modeled by deletion of the Fmr1 protein (Fmrp) in mice. Previous studies showed a decreased expression of several components of the GABAergic system in Fmr1 knockout mice. Here, we used this mouse model to investigate the functional consequences of Fmrp deletion on hippocampal GABAergic inhibition in the CA1-region of the hippocampus. Whole-cell patch-clamp recordings demonstrated a significantly reduced amplitude of evoked inhibitory postsynaptic currents (eIPSCs) and a decrease in the amplitude and frequency of spontaneous IPSCs. In addition, miniature IPSCs were reduced in amplitude and frequency and decayed significantly slower than mIPSCs in controls. Quantitative real-time PCR revealed a significantly lower expression of α2, β1 and δ GABA_A receptor subunits in the hippocampus of the juvenile mice (P22) compared to wild-type littermates. Correspondingly, we found also at the protein level reduced amounts of α2, β1 and δ subunits in Fmr1 knockout mice. Overall, these results demonstrate that the reduction in several components of the GABAergic system is already present at young age and that this reduction results in measurable abnormalities on GABA_A receptor-mediated phasic inhibition. These abnormalities might contribute to the behavioral and cognitive deficits of this fragile X mouse model.

Nonfunctional Glial Proteins in Tripartite Synapses: A Pathophysiological Model of Schizophrenia

A model for the pathophysiology of schizophrenia is proposed that focuses on an unbalance of transmission in tripartite synapses. Synaptically associated astrocytes should be viewed as integral modulatory elements of tripartite synapses consisting of the presynapse, the postsynapse, and the glial element. Astrocytes may secrete glial binding protein into the synaptic cleft, thus binding free neurotransmitters and thereby reducing the levels of neurotransmitters available for stimulating the postsynapse. Astrocytes also have membrane-bound receptors for neurotransmitters, and when these bind neurotransmitters, the astrocytes upregulate the amount of binding protein secreted into the synapse, resulting in a negative feedback to the presynaptic terminal. The hypothesis presented here is that glia lose their negative feedback function due to loss of function mutations in the genes encoding the binding proteins and glial receptors. The mutations generate proteins that cannot be occupied by their cognate substances of the neuronal system, primarily neurotransmitters. Therefore, the glial-neuronal interaction in tripartite synapses affected becomes totally unbalanced, and the glia lose their inhibitory or boundary-setting function. As a result, neural flux is unconstrained by normal glial boundaries, also the flux of thought on the phenomenological level. Schizophrenia may be caused by the inability to delimit conceptual boundaries.

Traditional knowledge and formulations of medicinal plants used by the traditional medical practitioners of bangladesh to treat schizophrenia like psychosis

Schizophrenia is a subtle disorder of brain development and plasticity; it affects the most basic human processes of perception, emotion, and judgment. In Bangladesh the traditional medical practitioners of rural and remote areas characterized the schizophrenia as an insanity or a mental problem due to possession by ghosts or evil spirits and they have used various plant species' to treat such symptoms. The aim of the present study was to conduct an ethnomedicinal plant survey and documentation of the formulations of different plant parts used by the traditional medical practitioners of Rangamati district of Bangladesh for the treatment of schizophrenia like psychosis. It was observed that the traditional medical practitioners used a total of 15 plant species to make 14 formulations. The plants were divided into 13 families, used for treatment of schizophrenia and accompanying symptoms like hallucination, depression, oversleeping or insomnia, deterioration of personal hygiene, forgetfulness, and fear due to evil spirits like genies or ghost. A search of the relevant scientific literatures showed that a number of plants used by the medicinal practitioners have been scientifically validated in their uses and traditional medicinal knowledge has been a means towards the discovery of many modern medicines. Moreover, the antipsychotic drug reserpine, isolated from the dried root of Rauvolfia serpentina species, revolutionized the treatment of schizophrenia. So it is very much possible that formulations of the practitioner, when examined scientifically in their entireties, can form discovery of lead compounds which can be used as safe and effective antipsychotic drug to treat schizophrenia.

Increases in [3H]muscimol and [3H]flumazenil binding in the dorsolateral prefrontal cortex in schizophrenia are linked to α4 and γ2S mRNA levels respectively

Background

GABA_A receptors (GABA_AR) are composed of several subunits that determine sensitivity to drugs, synaptic localisation and function. Recent studies suggest that agonists targeting selective GABA_AR subunits may have therapeutic value against the cognitive impairments observed in schizophrenia. In this study, we determined whether GABA_AR binding deficits exist in the dorsolateral prefrontal cortex (DLPFC) of people with schizophrenia and tested if changes in GABA_AR binding are related to the changes in subunit mRNAs. The GABA orthosteric and the benzodiazepine allosteric binding sites were assessed autoradiographically using [³H]Muscimol and [³H]Flumazenil, respectively, in a large cohort of individuals with schizophrenia (n = 37) and their matched controls (n = 37). We measured, using qPCR, mRNA of β (β1, β2, β3), γ (γ1, γ2, γ2S for short and γ2L for long isoform, γ3) and δ subunits and used our previous measurements of GABA_AR α subunit mRNAs in order to relate mRNAs and binding through correlation and regression analysis.

Results

Significant increases in both [³H]Muscimol (p = 0.016) and [³H]Flumazenil (p = 0.012) binding were found in the DLPFC of schizophrenia patients. Expression levels of mRNA subunits measured did not show any significant difference in schizophrenia compared to controls. Regression analysis revealed that in schizophrenia, the [³H]Muscimol binding variance was most related to α4 mRNA levels and the [³H]Flumazenil binding variance was most related to γ2S subunit mRNA levels. [³H]Muscimol and [³H]Flumazenil binding were not affected by the lifetime anti-psychotics dose (chlorpromazine equivalent).

Conclusions

We report parallel increases in orthosteric and allosteric GABA_AR binding sites in the DLPFC in schizophrenia that may be related to a “shift” in subunit composition towards α4 and γ2S respectively, which may compromise normal GABAergic modulation and function. Our results may have implications for the development of treatment strategies that target specific GABA_AR receptor subunits.

Pathophysiological aspects of diversity in neuronal inhibition: a new benzodiazepine pharmacology

Inhibitory interneurons in the brain provide the balance to excitatory signaling. On the basis of brain imaging and human genetics, a deficit in GABAergic inhibition (GABA, γ-aminobuiyric acid) has been identified as contributing to the pathophysiology of anxiety disorders, epilepsy, and schizophrenia. Therapeutically, GABA_A receptors play a major role as targets for benzodiazepine drugs. The therapeutic relevance of the multitude of structurally diverse GABA_A receptor subtypes has only recently been identified. α₁-GABA_A receptors were found to mediate sedation, anterograde amnesia, and part of the seizure protection of these drugs, whereas α₂-GABA_A receptors, but not α₃-GABA_A receptors, mediate anxiolysis. Rational drug targeting to specific receptor subtypes has now become possible. Only restricted neuronal networks will be modulated by the upcoming subtype-selective drugs. For instance, anxiolytics devoid of drowsiness and sedation promise more sophisticated interventions in anxiety disorders. A new pharmacology of the benzodiazepine site is on the horizon.

Emerging roles of the spliceosomal machinery in myelodysplastic syndromes and other hematological disorders

In humans, the majority of all protein-coding transcripts contain introns that are removed by mRNA splicing carried out by spliceosomes. Mutations in the spliceosome machinery have recently been identified using whole-exome/genome technologies in myelodysplastic syndromes (MDS) and in other hematological disorders. Alterations in splicing factor 3 subunit b1 (SF3b1) were the first spliceosomal mutations described, immediately followed by identification of other splicing factor mutations, including U2 small nuclear RNA auxillary factor 1 (U2AF1) and serine arginine-rich splicing factor 2 (SRSF2). SF3b1/U2AF1/SRSF2 mutations occur at varying frequencies in different disease subtypes, each contributing to differences in survival outcomes. However, the exact functional consequences of these spliceosomal mutations in the pathogenesis of MDS and other hematological malignancies remain largely unknown and subject to intense investigation. For SF3b1, a gain of function mutation may offer the promise of new targeted therapies for diseases that carry this molecular abnormality that can potentially lead to cure. This review aims to provide a comprehensive overview of the emerging role of the spliceosome machinery in the biology of MDS/hematological disorders with an emphasis on the functional consequences of mutations, their clinical significance, and perspectives on how they may influence our understanding and management of diseases affected by these mutations.

Proteogenomic analysis of Mycobacterium tuberculosis by high resolution mass spectrometry

Mass spectrometric sequencing of low abundance, integral membrane proteins, particularly the transmembrane domains, presents challenges that span the multiple phases of sample preparation including solubilization, purification, enzymatic digestion, peptide extraction, and chromatographic separation. We describe a method through which we have obtained high peptide coverage for 12 γ-aminobutyric acid type A receptor (GABA_A receptor) subunits from 2 picomoles of affinity-purified GABA_A receptors from rat brain neocortex. Focusing on the α₁ subunit, we identified peptides covering 96% of the protein sequence from fragmentation spectra (MS2) using a database searching algorithm and deduced 80% of the amino acid residues in the protein from de novo sequencing of Orbitrap spectra. The workflow combined microscale membrane protein solubilization, protein delipidation, in-solution multi-enzyme digestion, multiple stationary phases for peptide extraction, and acquisition of high-resolution full scan and fragmentation spectra. For de novo sequencing of peptides containing the transmembrane domains, timed digestions with chymotrypsin were utilized to generate peptides with overlapping sequences that were then recovered by sequential solid phase extraction using a C4 followed by a porous graphitic carbon stationary phase. The specificity of peptide identifications and amino acid residue sequences was increased by high mass accuracy and charge state assignment to parent and fragment ions. Analysis of three separate brain samples demonstrated that 78% of the sequence of the α₁ subunit was observed in all three replicates with an additional 13% covered in two of the three replicates, indicating a high degree of sequence coverage reproducibility. Label-free quantitative analysis was applied to the three replicates to determine the relative abundances of 11 γ-aminobutyric acid type A receptor subunits. The deep sequence MS data also revealed two N-glycosylation sites on the α₁ subunit, confirmed two splice variants of the γ₂ subunit (γ_2L and γ_2S) and resolved a database discrepancy in the sequence of the α₅ subunit.

Dysfunctional gene splicing as a potential contributor to neuropsychiatric disorders

Alternative pre-mRNA splicing is a major mechanism by which the proteomic diversity of eukaryotic genomes is amplified. Much akin to neuropsychiatric disorders themselves, alternative splicing events can be influenced by genetic, developmental, and environmental factors. Here, we review the evidence that abnormalities of splicing may contribute to the liability toward these disorders. First, we introduce the phenomenon of alternative splicing and describe the processes involved in its regulation. We then review the evidence for specific splicing abnormalities in a wide range of neuropsychiatric disorders, including psychotic disorders (schizophrenia), affective disorders (bipolar disorder and major depressive disorder), suicide, substance abuse disorders (cocaine abuse and alcoholism), and neurodevelopmental disorders (autism). Next, we provide a theoretical reworking of the concept of "gene-focused" epidemiologic and neurobiologic investigations. Lastly, we suggest potentially fruitful lines for future research that should illuminate the nature, extent, causes, and consequences of alternative splicing abnormalities in neuropsychiatric disorders.

Insights into the neurodevelopmental origin of schizophrenia from postmortem studies of prefrontal cortical circuitry

The hypothesis that schizophrenia results from a developmental, as opposed to a degenerative, process affecting the connectivity and network plasticity of the cerebral cortex is supported by findings from morphological and molecular postmortem studies. Specifically, abnormalities in the expression of protein markers of GABA neurotransmission and the lamina- and circuit-specificity of these changes in the cortex in schizophrenia, in concert with knowledge of their developmental trajectories, offer crucial insight into the vulnerability of specific cortical networks to environmental insults during different periods of development. These findings reveal potential targets for therapeutic interventions to improve cognitive function in individuals with schizophrenia, and provide guidance for future preventive strategies to preserve cortical neurotransmission in at-risk individuals.

The effects of midazolam and sevoflurane on the GABA(A) receptors with alternatively spliced variants of the γ2 subunit

Background

Emergence agitation after sevoflurane anesthesia in children can be prevented by midazolam. Alternative splicing of the GABA_A receptor changes with age. Therefore, we hypothesized that alternative splicing of the γ2 subunit affects the GABA current when applying sevoflurane and midazolam.

Methods

We performed the whole-cell patch clamp technique on human embryonic kidney 293 cells that were transfected with α1β2γ2L or α1β2γ2S. The concentration-response relations were recorded for midazolam and sevoflurane, and the co-application responses were measured at concentrations of 1.5 nM, 15 nM and 300 nM of midazolam and 0.5%, 2.0% and 4.0% of sevoflurane. Each GABA current was compared with that produced by 5 µM of GABA.

Results

The concentration-response relationships for midazolam and sevoflurane were dose-dependent without any differences between the α1β2γ2L and α1β2γ2S subtypes. 1.5 nM and 15 nM of midazolam did not significantly enhance the current after treatment with 0.5% sevoflurane for both subtypes. The current after treatment with 2.0% sevoflurane was enhanced by 1.5 nM midazolam for the α1β2γ2S subtype, but not for the α1β2γ2L subtype. In the case of 2.0% sevoflurane with 15 nM of midazolam, and 4.0% sevoflurane with 300 nM of midazolam, the GABA currents were significantly enhanced for both subtypes.

Conclusions

These results show that the difference in the γ2 subunit cannot explain the emergence agitation after sevoflurane anesthesia in children in vitro. This suggests that co-application of sevoflurane and midazolam enhances the GABA current according to the alternative splicing of the γ2 subunit and the concentration of both drugs.

The inhibitory GABA system as a therapeutic target for cognitive symptoms in schizophrenia: investigational agents in the pipeline

IMPORTANCE OF THE FIELD

Cognitive impairments associated with schizophrenia include neuropsychological deficits in attention, working memory, learning and executive function. Because these cognitive deficits precede the onset of psychosis, are present in non-affected relatives and constitute the best predictor of functional outcome, they are a cardinal clinical feature in schizophrenia. Currently, no effective treatment for the cognitive symptoms in schizophrenia exists.

AREAS COVERED IN THIS REVIEW

There is evidence that the inhibitory GABA system is affected in schizophrenia, suggesting that cognitive impairments associated with schizophrenia may be effectively treated by drugs that modulate the GABA(A) receptor. However, classical benzodiazepines produce cognitive impairments and are associated with numerous side effects. The recent development of compounds with selective efficacy for different α subunits at the benzodiazepine site of the GABA(A) receptor has renewed interest for the therapeutic potential of GABAergic drugs.

WHAT THE READER WILL GAIN

This review summarizes the involvement of the inhibitory GABA system in the cognitive abnormalities of schizophrenia and discusses putative (selective) GABAergic cognition-enhancing drugs for schizophrenia.

TAKE HOME MESSAGE

If cognitive abnormalities in schizophrenic individuals are the result of GABAergic dysfunction, selectively modulating the GABA system could comprise a promising therapeutic intervention for cognitive symptoms in schizophrenia.

Effects of benzodiazepine treatment on cortical GABA(A) and muscarinic receptors: studies in schizophrenia and rats

Changes in cortical γ-aminobutyric acid A (GABA(A)) receptors and muscarinic receptors have been reported in schizophrenia, a disorder treated with antipsychotic drugs and benzodiazepines. As there is a reported functional relationship between the GABAergic and cholinergic systems in the human central nervous system we have investigated whether there are changes in the GABA(A) and muscarinic receptors in the cortex of subjects from APD-treated subjects with schizophrenia and whether changes were different in subjects who had also received benzodiazepine treatment. We failed to show any strong correlations between changes in GABA(A) and muscarinic receptors in the CNS of subjects with schizophrenia. We showed that subjects with schizophrenia treated with benzodiazepines had lower levels of muscarinic receptors; which was not the case in rats treated with APDs, benzodiazepines or a combination of both drugs. Further, the benzodiazepine binding site, but not the muscimol binding site, was decreased in the parietal cortex of subjects with schizophrenia independent of benzodiazepine status at death. These data would therefore support our previously stated hypotheses that changes in the cortical cholinergic and GABAergic systems are involved in the pathophysiology of schizophrenia.

Lamina-specific alterations in cortical GABA(A) receptor subunit expression in schizophrenia

Dysfunction of the dorsolateral prefrontal cortex (DLPFC) in schizophrenia is associated with lamina-specific alterations in particular subpopulations of interneurons. In pyramidal cells, postsynaptic γ-aminobutyric acid (GABA(A)) receptors containing different α subunits are inserted preferentially in distinct subcellular locations targeted by inputs from specific interneuron subpopulations. We used in situ hybridization to quantify the laminar expression of α1, α2, α3, and α5 subunit, and of β1-3 subunit, mRNAs in the DLFPC of schizophrenia, and matched normal comparison subjects. In subjects with schizophrenia, mean GABA(A) α1 mRNA expression was 17% lower in layers 3 and 4, α2 expression was 14% higher in layer 2, α5 expression was 15% lower in layer 4, and α3 expression did not differ relative to comparison subjects. The mRNA expression of β2, which preferentially assembles with α1 subunits, was also 20% lower in layers 3 and 4, whereas β1 and β3 mRNA levels were not altered in schizophrenia. These expression differences were not attributable to medication effects or other potential confounds. These findings suggest that GABA neurotransmission in the DLPFC is altered at the postsynaptic level in a receptor subunit- and layer-specific manner in subjects with schizophrenia and support the hypothesis that GABA neurotransmission in this illness is predominantly impaired in certain cortical microcircuits.

Developmental co-regulation of the beta and gamma GABAA receptor subunits with distinct alpha subunits in the human dorsolateral prefrontal cortex

The GABA(A) receptor (GABA(A)R) is a pentameric chloride ion channel that mediates neuronal inhibition and is commonly comprised of 2alpha, 2beta and 1gamma subunits. These subunits have distinct characteristics that critically impact receptor function. In this study, we sought to determine if developmental expression of the beta and gamma subunit mRNAs in the prefrontal cortex would show complementary or opposing patterns of change as compared to the alpha subunits. Certain GABA(A)R subunit genes are arranged in tandem on the chromosome, and we hypothesized that genomic proximity would lead to co-regulation during development. The mRNA expression of the 3beta and 3gamma subunits was measured in the human dorsolateral prefrontal cortex of 68 individuals aged neonate to adult, using microarray with qPCR validation. Changes between age groups were identified through ANOVA, linear regression and post hoc Fisher LSD tests while a principal component analysis was used to establish co-regulation of GABA(A)R genes. beta1, gamma1 and gamma3 subunits decreased in expression with age whereas gamma2 increased. beta2 showed dynamic regulation with early increases plateauing across childhood and adolescence before decreasing in adulthood while beta3 levels remained relatively constant. Using published alpha subunit data we identified two principal components labeled 'Decreasing' (alpha2, alpha5, beta1, gamma1 and gamma3) and 'Dynamic' (alpha1, alpha4, beta2 and gamma2) responsible for 84% of the variation in GABA(A)R subunit development. This grouping is generally consistent with the chromosomal localization of subunits, lending credence to regional transcriptional control mechanisms. In addition, understanding developmental changes in GABA(A)R subunits could foster better pediatric pharmaceutical treatments.

The short splice variant of the gamma 2 subunit acts as an external modulator of GABA(A) receptor function

GABA(A) receptors (GABA(A)Rs) regulate the majority of fast inhibition in the mammalian brain and are the target for multiple drug types, including sleep aids, anti-anxiety medication, anesthetics, alcohol, and neurosteroids. A variety of subunits, including the highly distributed gamma2, allow for pharmacologic and kinetic differences in particular brain regions. The two common splice variants gamma2S (short) and gamma2L (long) show different patterns of regional distribution both in adult brain and during the course of development, but show few notable differences when incorporated into pentameric receptors. However, results presented here show that the gamma2S variant can strongly affect both GABA(A)R pharmacology and kinetics by acting as an external modulator of fully formed receptors. Mutation of one serine residue can confer gamma2S-like properties to gamma2L subunits, and addition of a modified gamma2 N-terminal polypeptide to the cell surface recapitulates the pharmacological effect. Thus, rather than incorporation of a separate accessory protein as with voltage-gated channels, this is an example of an ion channel using a common subunit for dual purposes. The modified receptor properties conferred by accessory gamma2S have implications for understanding GABA(A)R pharmacology, receptor kinetics, stoichiometry, GABAergic signaling in the brain during development, and altered function in disease states such as epilepsy.

Genetic disruption of the autism spectrum disorder risk gene PLAUR induces GABAA receptor subunit changes

Disruption of the GABAergic system has been implicated in multiple developmental disorders, including epilepsy, autism spectrum disorder and schizophrenia. The human gene encoding uPAR (PLAUR) has been shown recently to be associated with the risk of autism. The uPAR(-/-) mouse exhibits a regionally-selective reduction in GABAergic interneurons in frontal and parietal regions of the cerebral cortex as well as in the CA1 and dentate gyrus subfields of the hippocampus. Behaviorally, these mice exhibit increased sensitivity to pharmacologically-induced seizures, heightened anxiety, and atypical social behavior. Here, we explore potential alterations in GABAergic circuitry that may occur in the context of altered interneuron development. Analysis of gene expression for 13 GABA(A) receptor subunits using quantitative real-time polymerase chain reaction (PCR) indicates seven subunit mRNAs (alpha(1), alpha(2), alpha(3), beta(2), beta(3), gamma(2S) and gamma(2L)) of interest. Semi-quantitative in situ hybridization analysis focusing on these subunit mRNAs reveals a complex pattern of potential gene regulatory adaptations. The levels of alpha(2) subunit mRNAs increase in frontal cortex, CA1 and CA3, while those of alpha3 decrease in frontal cortex and CA1. In contrast, alpha(1) subunit mRNAs are unaltered in any region examined. beta(2) subunit mRNAs are increased in frontal cortex whereas beta(3) subunit mRNAs are decreased in parietal cortex. Finally, gamma(2S) subunit mRNAs are increased in parietal cortex while gamma(2L) subunit mRNAs are increased in the dentate gyrus, potentially altering the gamma(2S):gamma(2L) ratio in these two regions. For all subunits, no changes were observed in forebrain regions where GABAergic interneuron numbers are normal. We propose that disrupted differentiation of GABAergic neurons specifically in frontal and parietal cortices leads to regionally-selective alterations in local circuitry and subsequent adaptive changes in receptor subunit composition. Future electrophysiological studies will be useful in determining how alterations in network activity in the cortex and hippocampus relate to the observed behavioral phenotype.

Association study of the gamma-aminobutyric acid type a receptor gamma2 subunit gene with schizophrenia

Schizophrenia (SCZ) is a severe neuropsychiatric disorder with a strong genetic basis. We analyzed eight GABRG2 and one DRD5 tag single-nucleotide polymorphisms for association with SCZ in 109 small nuclear families and 229 independent SCZ case-control pairs. The marker rs183294 in the 5' region of GABRG2 was found to be associated with SCZ in both samples with the C allele over-represented in SCZ cases and over-transmitted in SCZ families (combined z=9.18; p<1 x 10(-3)). Taken together, the results of the present study suggest that GABRG2 may be involved in SCZ susceptibility, but further studies are required.

Alternatively Spliced Genes as Biomarkers for Schizophrenia, Bipolar Disorder and Psychosis: A Blood-Based Spliceome-Profiling Exploratory Study

OBJECTIVE: Transcriptomic biomarkers of psychiatric diseases obtained from a query of peripheral tissues that are clinically accessible (e.g., blood cells instead of post-mortem brain tissue) have substantial practical appeal to discern the molecular subtypes of common complex diseases such as major psychosis. To this end, spliceome-profiling is a new methodological approach that has considerable conceptual relevance for discovery and clinical translation of novel biomarkers for psychiatric illnesses. Advances in microarray technology now allow for improved sensitivity in measuring the transcriptome while simultaneously querying the "exome" (all exons) and "spliceome" (all alternatively spliced variants). The present study aimed to evaluate the feasibility of spliceome-profiling to discern transcriptomic biomarkers of psychosis. METHODS: We measured exome and spliceome expression in peripheral blood mononuclear cells from 13 schizophrenia patients, nine bipolar disorder patients, and eight healthy control subjects. Each diagnostic group was compared to each other, and the combined group of bipolar disorder and schizophrenia patients was also compared to the control group. Furthermore, we compared subjects with a history of psychosis to subjects without such history. RESULTS: After applying Bonferroni corrections for the 21,866 full-length gene transcripts analyzed, we found significant interactions between diagnostic group and exon identity, consistent with group differences in rates or types of alternative splicing. Relative to the control group, 18 genes in the bipolar disorder group, eight genes in the schizophrenia group, and 15 genes in the combined bipolar disorder and schizophrenia group appeared differentially spliced. Importantly, thirty-three genes showed differential splicing patterns between the bipolar disorder and schizophrenia groups. More frequent exon inclusion and/or over-expression was observed in psychosis. Finally, these observations are reconciled with an analysis of the ontologies, the pathways and the protein domains significantly over-represented among the alternatively spliced genes, several of which support prior discoveries. CONCLUSIONS: To our knowledge, this is the first blood-based spliceome-profiling study of schizophrenia and bipolar disorder to be reported. The battery of alternatively spliced genes and exons identified in this discovery-oriented exploratory study, if replicated, may have potential utility to discern the molecular subtypes of psychosis. Spliceome-profiling, as a new methodological approach in transcriptomics, warrants further work to evaluate its utility in personalized medicine. Potentially, this approach could also permit the future development of tissue-sampling methodologies in a form that is more acceptable to patients and thereby allow monitoring of dynamic and time-dependent plasticity in disease severity and response to therapeutic interventions in clinical psychiatry.

Resolving deconvolution ambiguity in gene alternative splicing

Background

For many gene structures it is impossible to resolve intensity data uniquely to establish abundances of splice variants. This was empirically noted by Wang et al. in which it was called a "degeneracy problem". The ambiguity results from an ill-posed problem where additional information is needed in order to obtain an unique answer in splice variant deconvolution.

Results

In this paper, we analyze the situations under which the problem occurs and perform a rigorous mathematical study which gives necessary and sufficient conditions on how many and what type of constraints are needed to resolve all ambiguity. This analysis is generally applicable to matrix models of splice variants. We explore the proposal that probe sequence information may provide sufficient additional constraints to resolve real-world instances. However, probe behavior cannot be predicted with sufficient accuracy by any existing probe sequence model, and so we present a Bayesian framework for estimating variant abundances by incorporating the prediction uncertainty from the micro-model of probe responsiveness into the macro-model of probe intensities.

Conclusion

The matrix analysis of constraints provides a tool for detecting real-world instances in which additional constraints may be necessary to resolve splice variants. While purely mathematical constraints can be stated without error, real-world constraints may themselves be poorly resolved. Our Bayesian framework provides a generic solution to the problem of uniquely estimating transcript abundances given additional constraints that themselves may be uncertain, such as regression fit to probe sequence models. We demonstrate the efficacy of it by extensive simulations as well as various biological data.

GABA(A) receptors and their associated proteins: implications in the etiology and treatment of schizophrenia and related disorders

Gamma-aminobutyric acid type A (GABA(A)) receptors play an important role in mediating fast synaptic inhibition in the brain. They are ubiquitously expressed in the CNS and also represent a major site of action for clinically relevant drugs. Recent technological advances have greatly clarified the molecular and cellular roles played by distinct GABA(A) receptor subunit classes and isoforms in normal brain function. At the same time, postmortem and genetic studies have linked neuropsychiatric disorders including schizophrenia and bipolar disorder with GABAergic neurotransmission and various specific GABA(A) receptor subunits, while evidence implicating GABA(A)R-associated proteins is beginning to emerge. In this review we discuss the mounting genetic, molecular, and cellular evidence pointing toward a role for GABA(A) receptor heterogeneity in both schizophrenia etiology and therapeutic development. Finally, we speculate on the relationship between schizophrenia-related disorders and selected GABA(A) receptor associated proteins, key regulators of GABA(A) receptor trafficking, targeting, clustering, and anchoring that often carry out these functions in a subtype-specific manner.

Cell and receptor type-specific alterations in markers of GABA neurotransmission in the prefrontal cortex of subjects with schizophrenia

Impairments in cognitive control, such as those involved in working memory, are associated with dysfunction of the dorsolateral prefrontal cortex (DLPFC) in individuals with schizophrenia. This dysfunction appears to result, at least in part, from abnormalities in GABA-mediated neurotransmission. In this paper, we review recent findings indicating that the altered DLPFC circuitry in subjects with schizophrenia reflects changes in the expression of genes that encode selective presynaptic and postsynaptic components of GABA neurotransmission. Specifically, using a combination of methods, we found that subjects with schizophrenia exhibited expression deficits in GABA-related transcripts encoding presynaptic regulators of GABA neurotransmission, neuropeptide markers of specific subpopulations of GABA neurons, and certain subunits of the GABA(A) receptor. In particular, alterations in the expression of the neuropeptide somatostatin suggested that GABA neurotransmission is impaired in the Martinotti subset of GABA neurons that target the dendrites of pyramidal cells. In contrast, none of the GABA-related transcripts assessed to date were altered in the DLPFC of monkeys chronically exposed to antipsychotic medications, suggesting that the effects observed in the human studies reflect the disease process and not its treatment. In concert with previous findings, these data suggest that working memory dysfunction in schizophrenia may be attributable to altered GABA neurotransmission in specific DLPFC microcircuits.

Dopamine D4 Receptors Regulate GABAA Receptor Trafficking via an Actin/Cofilin/Myosin-dependent Mechanism

The GABA(A) receptor-mediated inhibitory transmission in prefrontal cortex (PFC) is implicated in cognitive processes such as working memory. Our previous study has found that GABA(A)R current is subject to the regulation of dopamine D(4) receptors, a PFC-enriched neuromodulator critically involved in various mental disorders associated with PFC dysfunction. In this study, we have investigated the cellular mechanism underlying D(4) modulation of GABA(A)Rs. We found that the density of surface clusters of GABA(A)R beta2/3 subunits was reduced by D(4), suggesting that the D(4) reduction of GABA(A)R current is associated with a decrease in functional GABA(A)Rs at the plasma membrane. Moreover, the D(4) reduction of GABA(A)R current was blocked by the actin stabilizer phalloidin and was occluded by the actin destabilizer latrunculin, suggesting that D(4) regulates GABA(A)R trafficking via an actin-dependent mechanism. Cofilin, a major actin depolymerizing factor whose activity is strongly increased by dephosphorylation at Ser(3), provides the possible link between D(4) signaling and the actin dynamics. Because myosin motor proteins are important for the transport of vesicles along actin filaments, we also tested the potential involvement of myosin in D(4) regulation of GABA(A)R trafficking. We found that dialysis with a myosin peptide, which competes with endogenous myosin proteins for actin-binding sites, prevented the D(4) reduction of GABA(A)R current. These results suggest that D(4) receptor activation increases cofilin activity presumably via its dephosphorylation, resulting in actin depolymerization, thus causing a decrease in the myosin-based transport of GABA(A)R clusters to the surface.

Alterations in GABA-related transcriptome in the dorsolateral prefrontal cortex of subjects with schizophrenia

In subjects with schizophrenia, impairments in working memory are associated with dysfunction of the dorsolateral prefrontal cortex (DLPFC). This dysfunction appears to be due, at least in part, to abnormalities in gamma-aminobutyric acid (GABA)-mediated inhibitory circuitry. To test the hypothesis that altered GABA-mediated circuitry in the DLPFC of subjects with schizophrenia reflects expression changes of genes that encode selective presynaptic and postsynaptic components of GABA neurotransmission, we conducted a systematic expression analysis of GABA-related transcripts in the DLPFC of 14 pairs of schizophrenia and age-, sex- and post-mortem interval-matched control subjects using a customized DNA microarray with enhanced sensitivity and specificity. Subjects with schizophrenia exhibited expression deficits in GABA-related transcripts encoding (1) presynaptic regulators of GABA neurotransmission (67 kDa isoform of glutamic acid decarboxylase (GAD(67)) and GABA transporter 1), (2) neuropeptides (somatostatin (SST), neuropeptide Y (NPY) and cholecystokinin (CCK)) and (3) GABA(A) receptor subunits (alpha1, alpha4, beta3, gamma2 and delta). Real-time qPCR and/or in situ hybridization confirmed the deficits for six representative transcripts tested in the same pairs and in an extended cohort, respectively. In contrast, GAD(67), SST and alpha1 subunit mRNA levels, as assessed by in situ hybridization, were not altered in the DLPFC of monkeys chronically exposed to antipsychotic medications. These findings suggest that schizophrenia is associated with alterations in inhibitory inputs from SST/NPY-containing and CCK-containing subpopulations of GABA neurons and in the signaling via certain GABA(A) receptors that mediate synaptic (phasic) or extrasynaptic (tonic) inhibition. In concert with previous findings, these data suggest that working memory dysfunction in schizophrenia is mediated by altered GABA neurotransmission in certain DLPFC microcircuits.

The relevance of neuroactive steroids in schizophrenia, depression, and anxiety disorders

1. Neuroactive steroids are steroid hormones that exert rapid, nongenomic effects at ligand-gated ion channels. There is increasing awareness of the possible role of these steroids in the pathology and manifestation of symptoms of psychiatric disorders. The aim of this paper is to review the current knowledge of neuroactive steroid functioning in the central nervous system, and to assess the role of neuroactive steroids in the pathophysiology and treatment of symptoms of schizophrenia, depression, and anxiety disorders. Particular emphasis will be placed on GABAA receptor modulation, given the extensive knowledge of the interactions between this receptor complex, neuroactive steroids, and psychiatric illness. 2. A brief description of neuroactive steroid metabolism is followed by a discussion of the interactions of neuroactive steroids with acute and chronic stress and the HPA axis. Preclinical and clinical studies related to psychiatric disorders that have been conducted on neuroactive steroids are also described. 3. Plasma concentrations of some neuroactive steroids are altered in individuals suffering from schizophrenia, depression, or anxiety disorders compared to values in healthy controls. Some drugs used to treat these disorders have been reported to alter plasma and brain concentrations in clinical and preclinical studies, respectively. 4. Further research is warranted into the role of neuroactive steroids in the pathophysiology of psychiatric illnesses and the possible role of these steroids in the successful treatment of these disorders.

GABAA receptors in central nervous system disease: anxiety, epilepsy, and insomnia

Brain function is based on an exquisite balance between excitatory and inhibitory neurotransmission. GABAergic neurons provide the major inhibitory control. By controlling spike timing and sculpting neuronal rhythms they play a key role in regulating behavior. GABAergic neurons are highly diverse and operate with a corresponding diversity of GABAA receptor subtypes. In this article, the contribution of GABAA receptor deficits to central nervous system disorders, in particular anxiety disorders, epilepsy, schizophrenia and insomnia, is reviewed.

Two isoforms of GABA(A) receptor beta2 subunit with different electrophysiological properties: Differential expression and genotypical correlations in schizophrenia

Single nucleotide polymorphisms in type A gamma-aminobutyric acid (GABA(A)) receptor beta2 subunit gene (GABRB2) were found to be associated with schizophrenia in Chinese, German, Japanese and Portuguese. To explore potential functional consequences of these DNA sequence polymorphisms, this study examined the expression and electrophysiological properties of two alternatively spliced products of GABRB2 along with genotypical disease association analysis. Real-time quantitative polymerase chain reaction, performed with a cohort of 31 schizophrenics and 31 controls of US population, showed 21.7% reduction in the expression of the long isoform beta(2L), 13.4% in the short isoform beta(2S) and 15.8% in the sum of the two isoforms beta(2T) in postmortem schizophrenic brain. Furthermore, two independent mRNA quantitation methods showed that the relative expression of the long over the short isoforms was significantly decreased, suggesting the occurrence of altered splicing, in schizophrenia. In male schizophrenics, the heterozygous genotypes of rs1876071 (T/C) and rs1876072 (A/G) were correlated with reduced expression of beta(2L), beta(2S) and beta(2T), and the heterozygous of rs2546620 (A/G) and homozygous-minor of rs1876071 (C/C) and rs1876072 (G/G) were correlated with reduced expression of beta(2T). Significant correlations of expression levels with different alleles and haplotypes were also indicated by quantitative trait analysis. Recombinant GABA(A) receptors expressed in HEK293 human cells containing beta(2L) underwent a steeper current rundown upon repetitive GABA activation than receptors containing beta(2S). The results thus revealed genotype-dependent expression of the alternatively spliced isoforms of GABA(A) receptor beta2 subunit, giving rise to electrophysiological consequences that could play an important role in the pathogenesis mechanism of schizophrenia.

Differential effects of antidepressants on dexamethasone-induced nuclear translocation and expression of glucocorticoid receptor

The glucocorticoid receptor (GR) is a key regulator of the hypothalamic-pituitary-adrenal (HPA) axis. Mood disorder patients often exhibit abnormalities in this axis. Although the clinical benefit of antidepressants is associated with the normalization of the disturbed HPA activity by enhanced negative feedback of the HPA axis, the precise mechanism remains unknown. In order to examine the effect of antidepressants on the translocation of GR into the nucleus, we performed time-lapse observation on SY5Y cells that had been transiently transfected with plasmids expressing the green fluorescence protein (GFP)-tagged GRalpha. Clomipramine and desipramine facilitated dexamethasone (Dex)-induced GFP-GRalpha nuclear translocation. Coincubation of verapamil, an inhibitor of membrane steroid transporters, showed little or no additive effect on GFP-GRalpha nuclear translocation induced by both Dex and clomipramine. In the absence of Dex, antidepressants did not induce the translocation of GFP-GRalpha into the nucleus. Using real-time PCR, we examined the effect of antidepressants on splicing isoform of GR, GRalpha, and GRbeta in SY5Y and Jurkat cells. Incubation with paroxetine and desipramine for 48 h and 7 days increased GRalpha expression, whereas the expression of GRbeta remained stable. Antidepressants did not alter the expression of SRp30c that is associated with alternative splicing of GR transcript. Thus, antidepressants exert differential effects on the translocation and expression of GR to enhance GR signaling.

Genetics of intelligence

This article provides an overview of the biometric and molecular genetic studies of human psychometric intelligence. In the biometric research, special attention is given to the environmental and genetic contributions to specific and general cognitive ability differences, and how these differ from early childhood to old age. Special mention is also made of multivariate studies that examine the genetic correlation between intelligence test scores and their correlates such as processing speed, birth weight and brain size. After an overview of candidate gene associations with intelligence test scores, there is a discussion of whole-genome linkage and association studies, the first of which have only recently appeared.

Analysis of GABRB2 association with schizophrenia in German population with DNA sequencing and one-label extension method for SNP genotyping

OBJECTIVES

Schizophrenia (SCZ) is a complex mental disease that affects approximately 1% of the population. In this study, six SNPs in GABRB2 were genotyped for a case-control association study with the cycloid psychosis subtype of SCZ in the German population using two methods for SNP genotyping.

DESIGN AND METHODS

The SNPs were genotyped by direct DNA sequencing, as well as a novel one-label extension method. The results were analyzed for association with SCZ.

RESULTS AND CONCLUSIONS

Significant association was found for SNPs rs1816071 and rs1816072 with SCZ susceptibility. This is consistent with our previous finding of association of SNPs in GABRB2 with SCZ susceptibility in Han Chinese. There was a total agreement between the genotyping results from one-label extensions and the results of direct DNA sequencing, thus validating the accuracy of the one-label extension method of SNP genotyping.

Pre-mRNA Missplicing as a Cause of Human Disease

Regulated alternative splice site selection emerges as one of the most important mechanisms to control the expression of genetic information in humans. It is therefore not surprising that a growing number of diseases are either associated with or caused by changes in alternative splicing. These diseases can be caused by mutation in regulatory sequences of the pre-mRNA or by changes in the concentration of trans-acting factors. The pathological expression of mRNA isoforms can be treated by transferring nucleic acids derivatives into cells that interfere with sequence elements on the pre-mRNA, which results in the desired splice site selection. Recently, a growing number of low molecular weight drugs have been discovered that influence splice site selection in vivo. These findings prove the principle that diseases caused by missplicing events could eventually be cured.

Genome-wide scan of IQ finds significant linkage to a quantitative trait locus on 2q

A genome-wide linkage scan of 795 microsatellite markers (761 autosomal, 34 X chromosome) was performed on Multidimensional Aptitude Battery subtests and verbal, performance and full scale scores, the WAIS-R Digit Symbol subtest, and two word-recognition tests (Schonell Graded Word Reading Test, Cambridge Contextual Reading Test) highly predictive of IQ. The sample included 361 families comprising 2-5 siblings who ranged in age from 15.7 to 22.2 years; genotype, but not phenotype, data were available for 81% of parents. A variance components analysis which controlled for age and sex effects showed significant linkage for the Cambridge reading test and performance IQ to the same region on chromosome 2, with respective LOD scores of 4.15 and 3.68. Suggestive linkage (LOD score>2.2) for various measures was further supported on chromosomes 6, 7, 11, 14, 21 and 22. Where location of linkage peaks converged for IQ subtests within the same scale, the overall scale score provided increased evidence for linkage to that region over any individual subtest. Association studies of candidate genes, particularly those involved in neural transmission and development, will be directed to genes located under the linkage peaks identified in this study.

Genetic investigation of chromosome 5q GABAA receptor subunit genes in schizophrenia

We previously performed a genome-wide linkage scan in Portuguese schizophrenia families that identified a risk locus on chromosome 5q31-q35. This finding was supported by meta-analysis of 20 other schizophrenia genome-wide scans that identified 5q23.2-q34 as the second most compelling susceptibility locus in the genome. In the present report, we took a two-stage candidate gene association approach to investigate a group of gamma-aminobutyric acid (GABA) A receptor subunit genes (GABRA1, GABRA6, GABRB2, GABRG2, and GABRP) within our linkage peak. These genes are plausible candidates based on prior evidence for GABA system involvement in schizophrenia. In the first stage, associations were detected in a Portuguese patient sample with single nucleotide polymorphisms (SNPs) and haplotypes in GABRA1 (P=0.00062-0.048), GABRP (P=0.0024-0.042), and GABRA6 (P=0.0065-0.0088). The GABRA1 and GABRP findings were replicated in the second stage in an independent German family-based sample (P=0.0015-0.043). Supportive evidence for association was also obtained for a previously reported GABRB2 risk haplotype. Exploratory analyses of the effects of associated GABRA1 haplotypes on transcript levels found altered expression of GABRA6 and coexpressed genes of GABRA1 and GABRB2. Comparison of transcript levels in schizophrenia patients and unaffected siblings found lower patient expression of GABRA6 and coexpressed genes of GABRA1. Interestingly, the GABRA1 coexpressed genes include synaptic and vesicle-associated genes previously found altered in schizophrenia prefrontal cortex. Taken together, these results support the involvement of the chromosome 5q GABAA receptor gene cluster in schizophrenia, and suggest that schizophrenia-associated haplotypes may alter expression of GABA-related genes.

Altered cortical glutamatergic and GABAergic signal transmission with glial involvement in depression

Abnormalities in L-glutamic acid (glutamate) and GABA signal transmission have been postulated to play a role in depression, but little is known about the underlying molecular determinants and neural mechanisms. Microarray analysis of specific areas of cerebral cortex from individuals who had suffered from major depressive disorder demonstrated significant down-regulation of SLC1A2 and SLC1A3, two key members of the glutamate/neutral amino acid transporter protein family, SLC1. Similarly, expression of L-glutamate-ammonia ligase, the enzyme that converts glutamate to nontoxic glutamine was significantly decreased. Together, these changes could elevate levels of extracellular glutamate considerably, which is potentially neurotoxic and can affect the efficiency of glutamate signaling. The astroglial distribution of the two glutamate transporters and L-glutamate-ammonia ligase strongly links glia to the pathophysiology of depression and challenges the conventional notion that depression is solely a neuronal disorder. The same cortical areas displayed concomitant up-regulation of several glutamate and GABA(A) receptor subunits, of which GABA(A)alpha1 and GABA(A)beta3 showed selectivity for individuals who had died by suicide, indicating their potential utility as biomarkers of suicidality. These findings point to previously undiscovered molecular underpinnings of the pathophysiology of major depression and offer potentially new pharmacological targets for treating depression.

Haplotype association between GABAA receptor gamma2 subunit gene (GABRG2) and methamphetamine use disorder

Psychostimulant use disorder and schizophrenia have a substantial genetic basis. Evidence from human and animal studies on the involvement of the gamma-aminobutyric acid (GABA) system in methamphetamine (METH) use disorder and schizophrenia is mounting. As we tested for the association of the human GABA(A) receptor gamma 2 subunit gene (GABRG2) with each diagnostic group, we used a case-control design with a set of 178 subjects with METH use disorder, 288 schizophrenics and 288 controls. First, we screened 96 controls and identified six SNPs in GABRG2, three of whom we newly reported. Next, we selected two SNPs, 315C>T and 1128+99C>A, as representatives of the linkage disequilibrium blocks for further case-control association analysis. Although no associations were found in either allelic or genotypic frequencies, we detected a haplotypic association in GABRG2 with METH use disorder, but not with schizophrenia. This finding partly replicates a recent case-control study of GABRG2 in METH use disorder, and thus indicates that GABRG2 may be one of the susceptibility genes of METH use disorder.