GABA Catabolism Research Articles

Enhanced accumulation of γ-aminobutyric acid by deletion of aminotransferase genes involved in γ-aminobutyric acid catabolism in engineered Halomonas elongata.

In this study, we were able to increase the yield of GABA by 1.5 times in the GABA-producing H. elongata ZN3 strain by deleting the gabT gene, which encodes GABA-AT, the initial enzyme of the GABA catabolic pathway. We also report the first in vivo evidence for GABA aminotransferase activity of an ectB-encoded DABA-AT, confirming a longstanding speculation based on the reported in vitro GABA-AT activity of DABA-AT. According to our findings, the DABA-AT enzyme can catalyze the initial step of GABA catabolism, in addition to its known function in ectoine biosynthesis. This creates a cycle that promotes adequate substrate flow between the two pathways, particularly during the early stages of high-salinity stress response when the expression of the ectB gene is upregulated.

Copper-Nanoparticle-Induced Neurotoxic Effect and Oxidative Stress in the Early Developmental Stage of Zebrafish (Danio rerio).

Copper nanoparticles (CuNPs) are extensively used in electronics, cosmetics, fungicides, and various other fields due to their distinctive qualities. However, this widespread usage can contribute to environmental contamination and heightened health risks for living organisms. Despite their prevalent use, the ecological impacts and biosafety of CuNPs remain inadequately understood. The present study aims to delve into the potential toxic effects of CuNPs on zebrafish (Danio rerio) embryos, focusing on multiple indexes such as embryonic development, neurotoxicity, oxidative stress, and inflammatory response. The results revealed a notable increase in the death rate and deformity rate, alongside varying degrees of decrease in hatching rate and heart rate following CuNPs exposure. Particularly, the frequency of spontaneous tail coiling significantly declined under exposure to CuNPs at concentrations of 500 µg/L. Furthermore, CuNPs exposure induced alterations in the transcriptional expression of GABA signaling pathway-related genes (gabra1, gad, abat, and gat1), indicating potential impacts on GABA synthesis, release, catabolism, recovery, and receptor binding. Additionally, CuNPs triggered oxidative stress, evidenced by disruption in superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) activities, along with elevated malondialdehyde (MDA) levels. This oxidative stress subsequently led to a proinflammatory cascade, as demonstrated by the increased transcriptional expression of inflammatory markers (il-1β, tnf-α, il-6, and il-8). Comparative analysis with copper ion (provided as CuCl2) exposure highlighted more significant changes in most indexes with CuCl2, indicating greater toxicity compared to CuNPs at equivalent concentrations. In conclusion, these findings provide valuable insights into the toxic effects of CuNPs on zebrafish embryo development and neurotransmitter conduction. Furthermore, they present technical methodologies for assessing environmental and health risks associated with CuNPs, contributing to a better understanding of their biosafety and ecological impact.

Epigenetic regulation of GABA catabolism in iPSC-derived neurons: The molecular links between FGF21 and histone methylation

ObjectiveFibroblast growth factor 21 (FGF21) analogs have been tested as potential therapeutics for substance use disorders. Prior research suggests that FGF21 administration might affect alcohol consumption and reward behaviors. Our recent report showed that plasma FGF21 levels were positively correlated with alcohol use in patients with alcohol use disorder (AUD). FGF21 has a short half-life (0.5–2 h) and crosses the blood–brain barrier. Therefore, we set out to identify molecular mechanisms for both the naïve form of FGF21 and a long-acting FGF21 molecule (PF-05231023) in induced pluripotent stem cell (iPSC)-derived forebrain neurons. MethodsWe performed RNA-seq in iPSC-derived forebrain neurons treated with naïve FGF21 or PF-05231023 at physiologically relevant concentrations. We obtained plasma levels of FGF21 and GABA from our previous AUD clinical trial (n = 442). We performed ELISA for FGF21 in both iPSC-derived forebrain neurons and forebrain organoids. We determined protein interactions using co-immunoprecipitation. Finally, we applied ChIP assays to confirm the occupancy of REST, EZH2 and H3K27me3 by FGF21 using iPSC-derived forebrain neurons with and without drug exposure. ResultsWe identified 4701 and 1956 differentially expressed genes in response to naïve FGF21 or PF-05231023, respectively (FDR < 0.05). Notably, 974 differentially expressed genes overlapped between treatment with naïve FGF21 and PF-05231023. REST was the most important upstream regulator of differentially expressed genes. The GABAergic synapse pathway was the most significant pathway identified using the overlapping genes. We also observed a significant positive correlation between plasma FGF21 and GABA concentrations in AUD patients. In parallel, FGF21 and PF-05231023 significantly induced GABA levels in iPSC-derived neurons. Finally, functional genomics studies showed a drug-dependent occupancy of REST, EZH2, and H3K27me3 in the promoter regions of genes involved in GABA catabolism which resulted in transcriptional repression. ConclusionsOur results highlight a significant role in the epigenetic regulation of genes involved in GABA catabolism related to FGF21 action.(The ClinicalTrials.gov Identifier: NCT00662571)

Gamma-Aminobutyric Acid Transaminase (GABA-T) Deficiency in a Consanguineous Saudi Family: A Case Report and Literature Review

AbstractGamma-aminobutyric acid transaminase (GABA-T) deficiency is a rare, autosomal recessive disorder caused by mutations in the 4-aminobutyrate aminotransferase (ABAT) gene, which encodes an enzyme involved in GABA catabolism. It is characterized by severe psychomotor retardation, early-onset epileptic encephalopathy, intractable seizures, hypotonia, hyperreflexia, movement disorder, hypersomnolence, and early childhood mortality. It is associated with elevated free GABA in cerebrospinal fluid (CSF), GABA-T deficiency in cultured lymphoblasts, hypomyelination on brain magnetic resonance imaging (MRI), and elevated GABA level in the basal ganglia on proton magnetic resonance spectroscopy (MRS). Only 14 cases have been published in the literature. A rare case of infantile epileptic encephalopathy caused by GABA-T deficiency resulting from a previously unreported homozygous missense mutation in the ABAT gene is described. Our findings add to the phenotypic, neuroradiological, and genetic spectrum of ABAT mutations.

Pseudomonas syringae pv. tomato infection of tomato plants is mediated by GABA and l-Pro chemoperception.

Foliar bacterial pathogens have to penetrate the plant tissue and access the interior of the apoplast in order to initiate the pathogenic phase. The entry process is driven by chemotaxis towards plant‐derived compounds in order to locate plant openings. However, information on plant signals recognized by bacterial chemoreceptors is scarce. Here, we show that the perception of GABA and l‐Pro, two abundant components of the tomato apoplast, through the PsPto‐PscC chemoreceptor drives the entry of Pseudomonas syringae pv. tomato into the tomato apoplast. The recognition of both compounds by PsPto‐PscC caused chemoattraction to both amino acids and participated in the regulation of GABA catabolism. Mutation of the PsPto‐PscC chemoreceptor caused a reduced chemotactic response towards these compounds which in turn impaired entry and reduced virulence in tomato plants. Interestingly, GABA and l‐Pro levels significantly increase in tomato plants upon pathogen infection and are involved in the regulation of the plant defence response. This is an example illustrating how bacteria respond to plant signals produced during the interaction as cues to access the plant apoplast and to ensure efficient infection.

Metabotropic glutamate receptor 5 upregulation of γ-aminobutyric acid transporter 3 expression ameliorates cognitive impairment after traumatic brain injury in mice

Traumatic brain injury (TBI) causes neurotransmitter disturbances contributing to neuronal cell death and neurological deficits. In humans, brain injuries impair γ-aminobutyric acid (GABA) uptake and ultimately result in cognitive impairment. GABA transporter 3 (GAT3) is a vital approach of GABA reuptake and catabolism. The contribution of GAT3 in TBI-induced cognitive impairment and its underlying mechanisms remain unknown, which were explored in the present study. Here, we found that expression of GAT3 was downregulated to increase GABA concentration in the mouse brain after TBI. And GAT3 was detected in neurons and astrocytes after TBI unexpectedly, instead of merely expressed on astrocytes in physiological states. Subsequently, activated metabotropic glutamate receptor 5 (mGluR5) reduced GABA content by elevating the expression levels of GAT3. Then, increased mGluR5 activity obviously improved cognitive impairment. Mechanistically, mGluR5 was activated to evidently induce the expression of p-ERK, CREB, and p-CREB after TBI. The inhibition of CREB decreased the expression of CREB, p-CREB, and GAT3 elevated by active mGluR5. However, the CREB inhibitor increased GABA content. Furthermore, Rab11a regulating GAT3 trafficking by endocytosis was elevated after TBI. And Rab11a downregulated by active mGluR5 was reversed by CREB inhibitor. In summary our findings elucidated that activated mGluR5 ameliorated cognitive function by upregulating GAT3 in TBI. And mGluR5 possibly regulated GAT3 by ERK/CREB/Rab11a pathway. GAT3 could serve as a potential target for TBI cognitive treatment.

Understanding the Molecular Mechanisms of Succinic Semialdehyde Dehydrogenase Deficiency (SSADHD): Towards the Development of SSADH-Targeted Medicine.

Succinic semialdehyde dehydrogenase deficiency (SSADHD) is a rare genetic disorder caused by inefficient metabolic breakdown of the major inhibitory neurotransmitter, γ-aminobutyric acid (GABA). Pathologic brain accumulation of GABA and γ-hydroxybutyrate (GHB), a neuroactive by-product of GABA catabolism, leads to a multitude of molecular abnormalities beginning in early life, culminating in multifaceted clinical presentations including delayed psychomotor development, intellectual disability, hypotonia, and ataxia. Paradoxically, over half of patients with SSADHD also develop epilepsy and face a significant risk of sudden unexpected death in epilepsy (SUDEP). Here, we review some of the relevant molecular mechanisms through which impaired synaptic inhibition, astrocytic malfunctions and myelin defects might contribute to the complex SSADHD phenotype. We also discuss the gaps in knowledge that need to be addressed for the implementation of successful gene and enzyme replacement SSADHD therapies. We conclude with a description of a novel SSADHD mouse model that enables ‘on-demand’ SSADH restoration, allowing proof-of-concept studies to fine-tune SSADH restoration in preparation for eventual human trials.

Early vigabatrin augmenting GABA-ergic pathways in post-anoxic status epilepticus (VIGAB-STAT) phase IIa clinical trial study protocol

BackgroundNearly one in three unconscious cardiac arrest survivors experience post-anoxic status epilepticus (PASE). Historically, PASE has been deemed untreatable resulting in its exclusion from status epilepticus clinical trials. However, emerging reports of survivors achieving functional independence following early and aggressive treatment of PASE challenged this widespread therapeutic nihilism. In the absence of proven therapies specific to PASE, standard of care treatment leans on general management strategies for status epilepticus. Vigabatrin—an approved therapy for refractory focal-onset seizures in adults—inhibits the enzyme responsible for GABA catabolism, increases brain GABA levels and may act synergistically with anesthetic agents to abort seizures. Our central hypothesis is that early inhibition of GABA breakdown is possible in the post-cardiac arrest period and may be an effective adjunctive treatment in PASE.MethodsThis is a phase IIa, single-center, open-label, pilot clinical trial with blinded outcome assessment, of a single dose of vigabatrin in 12 consecutive PASE subjects. Subjects will receive a single loading dose of 4500 mg of vigabatrin (or dose adjusted in moderate and severe renal impairment) via enteric tube within 48 h of PASE onset. Vigabatrin levels will be monitored at 0- (baseline), 0.5-, 1-, 2-, 3-, 6-, 12-, 24-, 48-, 72- and 168-h (7 days) post-vigabatrin. Serum biomarkers of neuronal injury will be measured at 0-, 24-, 48-, 72- and 96-h post-vigabatrin. The primary feasibility endpoint is the proportion of enrolled subjects among identified eligible subjects receiving vigabatrin within 48 h of PASE onset. The primary pharmacokinetic endpoint is the measured vigabatrin level at 3 h post-administration. Descriptive statistics with rates and proportions will be obtained regarding feasibility outcomes, along with the noncompartmental method for pharmacokinetic analyses. The area under the vigabatrin concentration-time curve in plasma from zero to the time of the last quantifiable concentration (AUC0-tlqc) will be calculated to estimate dose-linear pharmacokinetics.PerspectiveVigabatrin demonstrates high potential for synergism with current standard of care therapies. Demonstration of the feasibility of vigabatrin administration and preliminary safety in PASE will pave the way for future efficacy and safety trials of this pharmacotherapeutic.Trial Registration NCT04772547.

Medulloblastoma uses GABA transaminase to survive in the cerebrospinal fluid microenvironment and promote leptomeningeal dissemination.

SUMMARYMedulloblastoma (MB) is a malignant pediatric brain tumor arising in the cerebellum. Although abnormal GABAergic receptor activation has been described in MB, studies have not yet elucidated the contribution of receptor-independent GABA metabolism to MB pathogenesis. We find primary MB tumors globally display decreased expression of GABA transaminase (ABAT), the protein responsible for GABA metabolism, compared with normal cerebellum. However, less aggressive WNT and SHH subtypes express higher ABAT levels compared with metastatic G3 and G4 tumors. We show that elevated ABAT expression results in increased GABA catabolism, decreased tumor cell proliferation, and induction of metabolic and histone characteristics mirroring GABAergic neurons. Our studies suggest ABAT expression fluctuates depending on metabolite changes in the tumor microenvironment, with nutrient-poor conditions upregulating ABAT expression. We find metastatic MB cells require ABAT to maintain viability in the metabolite-scarce cerebrospinal fluid by using GABA as an energy source substitute, thereby facilitating leptomeningeal metastasis formation.

A highly conserved mechanism for the detoxification and assimilation of the toxic phytoproduct L-azetidine-2-carboxylic acid in Aspergillus nidulans

Plants produce toxic secondary metabolites as defense mechanisms against phytopathogenic microorganisms and predators. L-azetidine-2-carboxylic acid (AZC), a toxic proline analogue produced by members of the Liliaceae and Agavaciae families, is part of such a mechanism. AZC causes a broad range of toxic, inflammatory and degenerative abnormalities in human and animal cells, while it is known that some microorganisms have evolved specialized strategies for AZC resistance. However, the mechanisms underlying these processes are poorly understood. Here, we identify a widespread mechanism for AZC resistance in fungi. We show that the filamentous ascomycete Aspergillus nidulans is able to not only resist AZC toxicity but also utilize it as a nitrogen source via GABA catabolism and the action of the AzhA hydrolase, a member of a large superfamily of detoxifying enzymes, the haloacid dehalogenase-like hydrolase (HAD) superfamily. This detoxification process is further assisted by the NgnA acetyltransferase, orthologue of Mpr1 of Saccharomyces cerevisiae. We additionally show that heterologous expression of AzhA protein can complement the AZC sensitivity of S. cerevisiae. Furthermore, a detailed phylogenetic analysis of AzhA homologues in Fungi, Archaea and Bacteria is provided. Overall, our results unravel a widespread mechanism for AZC resistance among microorganisms, including important human and plant pathogens.

Polymorphic Genetic Markers of the GABA Catabolism Pathway in Alzheimer’s Disease

The compilation of a list of genetic modifiers in Alzheimer's disease (AD) is an open research field. The GABAergic system is affected in several neurological disorders but its role in AD is largely understudied. As an explorative study, we considered variants in genes of GABA catabolism (ABAT, ALDH5A1, AKR7A2), and APOE in 300 Italian patients and 299 controls. We introduce a recent multivariate method to take into account the individual APOE genotype, thus controlling for the effect of the discrepant allele distributions in cases versus controls. We add a genotype-phenotype analysis based on age at onset and the Mini-Mental State Evaluation score. On the background of strongly divergent APOE allele distributions in AD versus controls, two genotypic interactions that represented a subtle but significant peculiarity of the AD cohort emerged. The first is between ABAT and APOE, and the second between some ALDH5A1 genotypes and APOE. Decreased SSADH activity is predicted in AD carriers of APOEɛ4, representing an additional suggestion for increased oxidative damage. We identified a difference between AD and controls, not in a shift of the allele frequencies at genes of the GABA catabolism pathway, but rather in gene interactions peculiar of the AD cohort. The emerging view is that of a multifactorial contribution to the disease, with a main risk factor (APOE), and additional contributions by the variants here considered. We consider genes of the GABA degradation pathway good candidates as modifiers of AD, contributing to energy impairment in AD brain.

γ-aminobutyric acid production by Kluyveromyces marxianus strains.

Kluyveromyces marxianus dairy strains were tested for γ-aminobutyric acid (GABA) production. The genes involved in GABA catabolism (UGA1 and UGA2) and anabolism (GAD1) were found in K. marxianus genome. Their relative expression was evaluated with primer designed ad hoc. Strains were grouped on the basis of GAD1 gene sequence. Representative strains for each group were tested for GABA production by high-performance liquid chromatography. All strains produced it at low levels. qRT-PCR showed the absence of a relation between GABA production and GAD1 gene expression. UGA1 and UGA2 genes were not upregulated and low amounts of succinic acid were detected. All strains released a low amount of GABA suggesting that probably it was stored within cells. The different behaviour of strains in terms of GABA and succinic acid production as well as gene expression highlighted the genetic and phenotypic biodiversity of this species. GABA production and genes involved in its catabolism and anabolism were described in a population of dairy K. marxianus for the first time. The variability observed in terms of genetic and phenotypic biodiversity is important especially to exploit this non-conventional yeast as microbial platform.

Metabolic Control of Immune-Competency by Odors in &lt;i&gt;Drosophila&lt;/i&gt;

Drosophila blood-progenitor cells generate an inflammatory cell-type termed lamellocyte, in response to parasitic wasp-infections. In this study we show that olfaction primes lamellocyte potential. Specifically, larval odor-detection mediated release of systemic γ-aminobutyric acid (GABA) from neurosecretory cells, is detected and internalized by blood progenitor-cells. GABA catabolism through the GABA-shunt pathway prevents Sima (HIFα) protein degradation. Sima is necessary and sufficient for lamellocyte induction. However, limited systemic GABA availability during development restricts blood-progenitor Sima levels and consequently their lamellocyte potential. Preconditioning Drosophila larvae in odor environments mimicking parasitoid-threatened conditions raises systemic GABA and blood-progenitor Sima levels. As a result, infection responses in these animals are rapid and efficient. Overall, this study explores the importance of sensory control of myeloid-immunity and unravels the adaptive influence of environmental odor-experience on myeloid-metabolism and priming innate-immune potential.

Succinic semialdehyde dehydrogenase deficiency: The combination of a novel ALDH5A1 gene mutation and a missense SNP strongly affects SSADH enzyme activity and stability

Succinic semialdehyde dehydrogenase deficiency (SSADHD) is a rare autosomal recessive metabolic disorder of GABA catabolism. SSADH is a mitochondrial homotetrameric enzyme encoded by ALDH5A1 gene. We report the molecular characterization of ALDH5A1 gene in an Italian SSADHD patient, showing heterozygosity for four missense mutations: c.526G>A (p.G176R), c.538C>T (p.H180Y), c.709G>T (p.A237S) and c.1267A>T (p.T423S), the latter never described so far. The patient inherited c.526A in cis with c.538T from the mother and c.709T in cis with c.1267T from the father. To explore the effects of the two allelic arrangements on SSADH activity and protein level, wild type, single or double mutated cDNA constructs were expressed in a cell system. The p.G176R change, alone or in combination with p.H180Y, causes the abolishment of enzyme activity. Western blot analysis showed a strongly reduced amount of the p.176R-p.180Y double mutant protein, suggesting increased degradation. Indeed, in silico analyses confirmed high instability of this mutant homotetramer. Enzyme activity relative to the other p.423S-p.237S double mutant is around 30% of wt. Further in silico analyses on all the possible combinations of mutant monomers suggest the lowest stability for the tetramer constituted by p.176R-p.180Y monomers and the highest stability for that constituted by p.237S-p.423S monomers. The present study shows that when a common SNP, associated with a slight reduction of SSADH activity, is inherited in cis with a mutation showing no consequences on the enzyme function, the activity is strongly affected. In conclusion, the peculiar arrangement of four missense mutations occurring in this patient is responsible for the SSADHD phenotype.

WORLDSymposium™ 2018 Introduction.

Succinic semialdehyde dehydrogenase deficiency (SSADHD) is a rare autosomal recessive metabolic disorder of GABA catabolism. SSADH is a mitochondrial homotetrameric enzyme encoded by ALDH5A1 gene. We report the molecular characterization of ALDH5A1 gene in an Italian SSADHD patient, showing heterozygosity for four missense mutations: c.526G>A (p.G176R), c.538C>T (p.H180Y), c.709G>T (p.A237S) and c.1267A>T (p.T423S), the latter never described so far. The patient inherited c.526A in cis with c.538T from the mother and c.709T in cis with c.1267T from the father. To explore the effects of the two allelic arrangements on SSADH activity and protein level, wild type, single or double mutated cDNA constructs were expressed in a cell system. The p.G176R change, alone or in combination with p.H180Y, causes the abolishment of enzyme activity. Western blot analysis showed a strongly reduced amount of the p.176R-p.180Y double mutant protein, suggesting increased degradation. Indeed, in silico analyses confirmed high instability of this mutant homotetramer. Enzyme activity relative to the other p.423S-p.237S double mutant is around 30% of wt. Further in silico analyses on all the possible combinations of mutant monomers suggest the lowest stability for the tetramer constituted by p.176R-p.180Y monomers and the highest stability for that constituted by p.237S-p.423S monomers. The present study shows that when a common SNP, associated with a slight reduction of SSADH activity, is inherited in cis with a mutation showing no consequences on the enzyme function, the activity is strongly affected. In conclusion, the peculiar arrangement of four missense mutations occurring in this patient is responsible for the SSADHD phenotype.

Odiparcil is a promising substrate reduction therapy in MPS VI murine model

Succinic semialdehyde dehydrogenase deficiency (SSADHD) is a rare autosomal recessive metabolic disorder of GABA catabolism. SSADH is a mitochondrial homotetrameric enzyme encoded by ALDH5A1 gene. We report the molecular characterization of ALDH5A1 gene in an Italian SSADHD patient, showing heterozygosity for four missense mutations: c.526G>A (p.G176R), c.538C>T (p.H180Y), c.709G>T (p.A237S) and c.1267A>T (p.T423S), the latter never described so far. The patient inherited c.526A in cis with c.538T from the mother and c.709T in cis with c.1267T from the father. To explore the effects of the two allelic arrangements on SSADH activity and protein level, wild type, single or double mutated cDNA constructs were expressed in a cell system. The p.G176R change, alone or in combination with p.H180Y, causes the abolishment of enzyme activity. Western blot analysis showed a strongly reduced amount of the p.176R-p.180Y double mutant protein, suggesting increased degradation. Indeed, in silico analyses confirmed high instability of this mutant homotetramer. Enzyme activity relative to the other p.423S-p.237S double mutant is around 30% of wt. Further in silico analyses on all the possible combinations of mutant monomers suggest the lowest stability for the tetramer constituted by p.176R-p.180Y monomers and the highest stability for that constituted by p.237S-p.423S monomers. The present study shows that when a common SNP, associated with a slight reduction of SSADH activity, is inherited in cis with a mutation showing no consequences on the enzyme function, the activity is strongly affected. In conclusion, the peculiar arrangement of four missense mutations occurring in this patient is responsible for the SSADHD phenotype.

Serial Magnetic Resonance Imaging and 1H-Magnetic Resonance Spectroscopy in GABA Transaminase Deficiency: A Case Report.

Gamma-aminobutyric acid transaminase (GABA-T) deficiency is a rare, autosomal recessive disorder characterized by severe psychomotor retardation, early-onset epileptic encephalopathy, intractable seizures, hypotonia, and hyperreflexia. The disease is caused by mutation in the 4-aminobutyrate aminotransferase (ABAT) gene, which encodes an enzyme involved in GABA catabolism. In this chapter, a 10-year follow-up of GABA-T deficiency in a rare case of a long-term survivor patient is discussed. The patient showed a progression of clinical phases with increasing age. In infancy, the patient developed psychomotor retardation and recurrent encephalopathic episodes associated with febrile illness. In early childhood, the patient presented with refractory involuntary and hyperkinetic movements and dystonic hypertonicity. In childhood, the patient gradually progressed into the chronic stable phase of the condition. Magnetic resonance imaging demonstrated high signal intensity on diffusion-weighted images involving the internal and external capsules and cerebral white matter in infancy which disappeared gradually by the age of 3years, and showed subsequently diffuse brain atrophy in childhood. Using proton magnetic resonance spectroscopy, GABA levels in the basal ganglia were shown to be markedly elevated at the age of 1-2years, and subsequently decreased with increasing age (toward 5years). These findings suggest that the encephalopathic episodes in infancy and clinical severity of involuntary and hyperkinetic movements may be correlated with levels of GABA in the basal ganglia. The high levels of GABA in the cerebrospinal fluid remained unaltered, whereas levels of GABA in the serum decreased during childhood. Further investigation of long-term clinical surveillance may improve the understanding of GABA-T deficiency.

Functional loss of GABA transaminase (GABA-T) expressed early leaf senescence under various stress conditions in Arabidopsis thaliana

GABA-transaminase (GABA-T) involved in carbon and nitrogen metabolism during the plant development process via GABA shunt and GABA-T mutant, which is defective in GABA catabolism, is ideal model to examine the role of GABA-T in plant development and leaf senescence of plant. We have characterized GABA transaminase knock out mutant pop2-1 that is transition and pop2-3 which is T-DNA insertion mutant of Arabidopsis thaliana during various stress conditions.The GABA-T knockout mutant plants displayed precocious leaf senescence, which was accompanied by the assays of physiological parameters of leaf senescence during various stress conditions. Furthermore, our physiological evidence indicates that pop2-1 and pop2-3 mutations rapidly decreased the efficiency of leaf photosynthesis, chlorophyll content, GABA content, GABA-T, and glutamate decarboxylase (GAD) activity and on the other hand increases membrane ion leakage, malondialdehyde (MDA) level in stress induced leaves. However, cell viability assay by trypan blue and insitu Hydrogen peroxidation assay by 3,3-diaminobenzidine (DAB) in stress induced leaves also display that pop2-1 and pop2-3 mutant leaves show oversensitivity in response to different stress conditions as compared to wild type. These results strongly indicate that the loss-of-function of GABA transaminase gene induces early leaf senescence in Arabidopsis thaliana during various stress conditions.

GABAergic regulation of cerebellar NG2 cell development is altered in perinatal white matter injury.

Diffuse white matter injury (DWMI), a leading cause of neurodevelopmental disabilities in preterm infants, is characterized by reduced oligodendrocyte formation. Oligodendrocyte precursor cells (NG2-cells) are exposed to various extrinsic regulatory signals, including the neurotransmitter GABA. We investigated GABAergic signaling to cerebellar white matter NG2-cells in a mouse model of DWMI (chronic neonatal hypoxia). We found that hypoxia caused a loss of GABAA receptor-mediated synaptic input to NG2-cells, extensive proliferation of these cells and delayed oligodendrocyte maturation, leading to dysmyelination. Treatment of control mice with a GABAA receptor antagonist or deletion of the chloride-accumulating transporter NKCC1 mimicked the effects of hypoxia. Conversely, blockade of GABA catabolism or GABA uptake reduced NG2-cell numbers and increased the formation of mature oligodendrocytes both in control and hypoxic mice. Our results indicate that GABAergic signaling regulates NG2-cell differentiation and proliferation in vivo, and suggest that its perturbation is a key factor in DWMI.

Transcriptional profiling of genes encoding GABA-transaminases in Brassica napus reveals their regulation by water deficit

In plants, GABA (γ-aminobutyric acid) accumulates in response to a wide range of environmental stresses. The metabolism of this non-protein amino acid occurs in two distinct cellular compartments: it is synthesized in the cytosol and degraded in mitochondria. Although many studies have reported its involvement in development, the role of stress-induced GABA accumulation remains unclear. The effects of GABA accumulation have been examined in plants defective in GABA catabolism. In Arabidopsis mutants deficient for GABA transaminase (GABA-T), the first step in GABA degradation, it was shown to be involved in salt stress tolerance. Here, we investigated GABA-T genes in the Brassicaceae crop species Brassica napus at the molecular structure and transcriptional levels. We show that several copies of GABA-T are ubiquitously expressed in many organs of oilseed rape. Analysis of BnaGABA-T promoters using the GUS reporter gene found no difference in localization between GABA-T family members. Additionally, we show that their expression profiles are modified during development and in response to water stress depending on leaf rank. The role of GABA-T regulation in water stressed B. napus plants is discussed.