Disease relevance of Gad2

• The expression of both GAD 67 and GAD 65 genes specifically in islet beta-cells indicates that both GAD forms are candidate autoantigens in rodent models of insulin-dependent diabetes mellitus [1].
• Human monoclonal autoantibodies and experimentally raised antibodies reacted with mouse GAD65 produced in a baculovirus expression system by Western blotting and immunoprecipitation and with GAD65 in mouse brain by immunohistochemistry but failed to detect GAD65 in mouse islets by the latter two methods [2].
• Similar to GAD67-deficient mice, the GAD65/67-deficient mice did not survive after birth because of cleft palate [3].
• Immune deviation of T-cell responses to the beta-cell autoantigen glutamate decarboxylase (GAD65), induced an active form of self-tolerance that was associated with an inhibition of disease progression in prediabetic mice and prolonged survival of syngeneic islet grafts in diabetic NOD mice [4].
• Additionally, the fact that autoimmune infiltration in GAD65 transgenic NOD mice remained largely restricted to the pancreas, indicates that the organ-specificity of autoimmune disease is dictated by tissue-specific factors in addition to those directing autoantigen expression [5].

Psychiatry related information on Gad2

• Targeted disruption of tPA release or its upstream regulation by glutamic acid decarboxylase (GAD65) prevented MD-induced spine loss that was pharmacologically rescued concomitant with critical period plasticity [6].
• Recently we have produced GAD65 -/- mice and demonstrated that lack of GAD65 does not change brain GABA contents or animal behavior, except for a slight increase in susceptibility to seizures [7].

High impact information on Gad2

• Short-term presynaptic dynamics reflected a synaptic reorganization in GAD65 knockout mice after chronic diazepam treatment [8].
• In mice of all ages lacking an isoform of GABA (gamma-aminobutyric acid) synthetic enzyme (GAD65), as well as in immature wild-type animals before the onset of their natural critical period, benzodiazepines selectively reduced a prolonged discharge phenotype to unmask plasticity [8].
• Furthermore, NOD mice receiving intrathymic injections of GAD65 exhibit markedly reduced T-cell proliferative responses to GAD and to the rest of the panel, in addition to remaining free of diabetes [9].
• Finally, GAD65 peptide treatment reduced insulitis and long-term IDDM incidence [10].
• We previously demonstrated that a spontaneous Th1 response against glutamate decarboxylase (GAD65) arises in NOD mice at four weeks in age and subsequently T cell autoimmunity spreads both intramolecularly and intermolecularly [10].

Chemical compound and disease context of Gad2

• The results suggest that GABA generated by either GAD65 or GAD67 is not critically involved in islet formation and that GAD65 expression is not an absolute requirement for development of autoimmune diabetes in the NOD mouse [11].

Biological context of Gad2

• Furthermore, at the low penetrance of diabetes in this backcross, GAD65-deficient mice developed disease at the same rate and incidence as wildtype mice [11].
• The smaller form of the autoantigen glutamic acid decarboxylase, GAD65 (formerly the 64,000 M(r) autoantigen), is a major target of humoral autoimmunity in type I diabetes [2].
• We here show that the dimerization region in GAD65 is distinct from the NH(2)-terminal membrane-anchoring region and that a membrane anchoring GAD65 subunit can indeed target a soluble subunit to membrane compartments by dimerization [12].
• However, freezing was reduced and flight and escape behavior were increased in GAD65-/- mice compared to their wild type and heterozygous littermates, while corticosterone levels and defecation rates did not differ between genotypes [13].
• GAD65 peptides displaying the human histocompatibility leukocyte antigen (HLA)-A*0201 binding motif have been synthesized [14].

Anatomical context of Gad2

• Yet GAD65 has been shown to be a target of very early autoimmune T-cell responses associated with beta-cell destruction in the non-obese diabetic (NOD) mouse model of Type 1 diabetes [11].
• Lack of either GAD65 or GAD67 did not effect the development of islet cells and the general morphology of islets [11].
• Furthermore, in GAD65-/- mouse brain, GAD67, which no longer partitions into the Triton X-114 detergent phase, still anchors to membranes at similar levels as in wild-type mice [12].
• No significant effects were observed with lymphocytes transduced with gad65 and sgad55 constructs at low m.o.i. By contrast, at high m.o.i., lymphocytes transduced with the sgad55 and seap constructs caused a decrease in insulitis and blood glucose levels and in insulitis alone, respectively [15].
• In contrast, only about half of GAD65 (which is found in synaptic terminals) exists as active holoenzyme [16].

Associations of Gad2 with chemical compounds

• Therefore, these results do not support the hypothesis of an involvement of Gad1 or Gad2 in the pathophysiology of acute ethanol withdrawal severity and the other ethanol related traits [17].
• The separate role of the two isoforms is unknown, but differences in saturation with cofactor and subcellular localization suggest that GAD65 may provide reserve pools of GABA for regulation of inhibitory neurotransmission [18].
• Additionally, GAD65-deficient mice have a diminished response to the anxiolytics diazepam and pentobarbital, both of which interact with GABA-A receptors in a GABA-dependent fashion to facilitate GABAergic neurotransmission [19].
• This effect was not observed for GAD65 or neuronal-specific enolase and was not replicated by glycine doses 2-fold greater than those of l-methionine [20].
• This partial cDNA shows 90% identity with mammalian GAD 65 and presents the Asn-Pro-His-Lys (NPHK) sequence corresponding to the pyridoxal-binding region of porcine DOPA decarboxylase or mammalian GAD [21].

Regulatory relationships of Gad2

• Immunization against GAD65 was not associated with substantial alterations in cytokine production by splenic lymphocytes stimulated with immunogenic GAD65 peptides [22].
• To investigate the differentiation of GABAergic interneurons of the olfactory bulb we used a transgenic mouse which expresses green fluorescent protein (GFP) under the control of the glutamic acid decarboxylase 65 kDa (GAD65) promoter [23].

Other interactions of Gad2

• GAD 67 mRNA was more abundant than GAD 65, and both were localized to islet beta-cells by in situ hybridization [1].
• Seizure susceptibility is dramatically increased in GAD65-/- mice backcrossed into a second genetic background, the nonobese diabetic (NOD/LtJ) strain of mice enabling electroencephalogram analysis of the seizures [18].
• These data suggest that GABA synthesized by GAD65 is important in the dynamic regulation of neural network excitability, implicate at least one modifier locus in the NOD/LtJ strain, and present GAD65-/- animals as a model of epilepsy involving GABA-ergic pathways [18].
• Using an RNase protection assay, both GAD 65 and GAD 67 mRNAs were detected in the rodent small intestine [24].
• NCAM-EC transgenic mice exhibited a striking reduction in synaptic puncta of GABAergic interneurons in the cingulate, frontal association cortex, and amygdala but not hippocampus, as shown by decreased immunolabeling of glutamic acid decarboxylase-65 (GAD65), GAD67, and GABA transporter 1 [25].

Analytical, diagnostic and therapeutic context of Gad2

• In addition, no significant GAD65 or GAD67 expression differences were detected in either drug-nai;ve or acute ethanol withdrawn animals by Western blot experiments [17].
• Moreover, double-labeling immunohistochemistry and confocal microscopy revealed selective colocalization of SPO and glutamate decarboxylase (GAD 65), a marker for gamma-aminobutyric acid (GABA)ergic terminals [26].
• Consistent with the induction of an active tolerance mechanism, splenic CD4+ (but not CD8+) T cells from GAD65 peptide-treated mice, inhibited the adoptive transfer of IDDM to NOD-scid/scid mice [10].
• We observed that a single intranasal administration of GAD65 peptides to 2-3-wk-old NOD mice induced high levels of IgG1 antibodies to GAD65 [10].
• However, reverse-transcription PCR and ELISA measurements of cytokine mRNA and protein levels showed that the GAD65-reactive T cells from both line 5 and line 12 mice produced higher levels of IL-4 and lower levels of IFN-gamma than similar T cells from standard NOD/Lt mice [27].

References