Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0011849 (diabetes)
 277,896 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Glutamic acid decarboxylase (GAD) is a candidate target autoantigen involved in the pathogenesis of insulin-dependent diabetes mellitus (IDDM). The functional state of the beta cells has been suggested to play a pathogenic role in IDDM by altering beta-cell autoantigen expression. In this study, we investigated expression of GAD-65 and GAD-67 in isolated Sprague-Dawley rat islets cultured at different glucose concentrations. Using GAD isoform-specific antibodies in an immunoblot assay, we found that expression of both GAD-65 and GAD-67 in cultured islets was glucose dependent and that increased expression of both forms of GAD correlated with increased functional state of the beta cell. Our data indicate that the functional state of the beta cell influences islet cell expression of GAD. Thus, decreasing islet cell expression of GAD by suppressing beta cells activity may have a potential role in blunting the autoimmune destruction of pancreatic islet beta cells.
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PMID:Functional state of the beta cell affects expression of both forms of glutamic acid decarboxylase. 780 9

Glutamic acid decarboxylase antibodies (GADAbs) are being increasingly used in clinical and research programs for the prediction and classification of insulin-dependent diabetes mellitus (IDDM). A number of different assay formats for the measurement of GADAbs have been reported, but the degree of concordance between assays is unknown. In this study, GADAbs were measured on 16 coded sera in 34 assays to examine concordance between GADAb assays and establish the feasibility of an international GADAb standard of measurement unit. The 16 lyophilized coded samples consisted of sera from healthy control subjects (n = 2), IDDM patients (n = 3), a patient with polyendocrine autoimmunity (n = 1), and duplicate dilutions of plasmapheresis serum from a patient with stiff-man syndrome (SMS). A high level of concordance was found in the ranking of GADAb levels (P = 0.99, Friedman's test) in the samples. Thirteen (38%) assays could reproducibly distinguish dilutions of SMS serum and detect GADAbs in all IDDM and polyendocrine autoimmunity sera tested. Although assessed on only four samples, disease specificity was 100% in 29 assays. The majority of assays that immunoprecipitated radiolabeled GAD gave high results for sensitivity and specificity. Enzyme-linked immunosorbent assays and assays using immunofluorescence were generally less sensitive. Several assays, in particular those measuring GAD enzymatic activity immunoprecipitated in fluid phase from rat brain homogenate, showed a prozone-like phenomenon in the SMS dilution curve. Interpolation of results from a standard curve into workshop units resulted in relatively low scatter in samples with lower levels of GADAbs. Hence, the use of an international reference serum to enable comparison of results between laboratories appears feasible.(ABSTRACT TRUNCATED AT 250 WORDS)
Diabetes 1994 Aug
PMID:High level of concordance between assays for glutamic acid decarboxylase antibodies. The First International Glutamic Acid Decarboxylase Antibody Workshop. 803 93

Glutamic acid decarboxylase (GAD) is an autoantigen of the islet cell antibodies (ICAs) present in type I diabetes. GAD autoantibodies are also found in patients with stiffman syndrome and in certain ICA-positive individuals who rarely develop diabetes on long-term follow-up. This latter subset of ICA has been termed restricted or beta-cell-specific ICA because the antibodies react with only the beta-cells of the islet. By immunoprecipitation of recombinant GAD65 and GAD67 protein and protein fragments, 83% of sera from individuals with new-onset diabetes or prediabetes (n = 30) had GAD65 autoantibodies, but only 26% had GAD67 autoantibodies. In contrast, all restricted ICA sera (n = 6) had both GAD65 and GAD67 autoantibodies. In both types of sera, the binding of GAD67 autoantibodies could be blocked by preincubation of the serum with GAD65 and GAD67, but the binding of GAD65 autoantibodies could not be blocked by preincubation with GAD67. The titer of GAD65 autoantibodies was much higher in the restricted ICA sera (titer > 1:1,000) than in the sera from individuals with new-onset diabetes or prediabetes (titer < 1:100) and was reflected by the greater amount of GAD65 protein immunoprecipitated by restricted ICA sera (2.61 +/- 1.39 U) compared with sera from individuals with new-onset diabetes (0.51 +/- 0.34 U). The restricted ICA sera immunoprecipitated equimolar amounts of GAD65 protein fragments, suggesting a non-conformational or linear epitope; epitope mapping localized the major epitope region to amino acids 361-442 and a second minor epitope region to amino acids 1-195.(ABSTRACT TRUNCATED AT 250 WORDS)
Diabetes 1994 Aug
PMID:Identification of glutamic acid decarboxylase autoantibody heterogeneity and epitope regions in type I diabetes. 803 4

Glutamic acid decarboxylase (GAD) in pancreatic beta cells is an autoantigen in insulin-dependent diabetes (IDD). We measured immunity to GAD in 31 first-degree relatives of IDD patients judged to be at risk of developing IDD themselves because of the presence of islet-cell antibodies. We found that in most of the subjects GAD autoimmunity was either predominantly humoral or predominantly cellular. High concentrations of circulating autoantibodies that precipitate native GAD activity were associated with low proliferation of peripheral-blood T cells to recombinant GAD; conversely, low concentrations of autoantibody to GAD were associated with high T-cell proliferation to GAD. Although T-cell proliferation was measured in the presence of autologous serum, GAD autoantibodies did not have a blocking effect in vitro. This dichotomy of the immune response to GAD defined heterogeneity within at-risk relatives and could have prognostic importance. We postulate that, if GAD is a pathogenetic autoantigen, sensitisation to beta-cell GAD is more likely to lead to IDD when the immune response deviates towards the expansion of autoreactive T cells rather than towards generation of autoantibodies. This idea is consistent with evidence that beta-cell destruction is mediated by T cells and that high concentrations of GAD antibodies are associated with slower progression to clinical disease.
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PMID:Inverse relation between humoral and cellular immunity to glutamic acid decarboxylase in subjects at risk of insulin-dependent diabetes. 810 Sep 70

Glutamic acid decarboxylase (GAD) is considered as target antigen in pancreatic beta cell autoimmunity. Two isoforms of GAD (islet and brain GAD) were detected recently. In circulation of approximately 80% of recently detected patients with insulin-dependent diabetes mellitus (IDDM) autoantibodies to brain GAD (bGAD) have been demonstrated. To detect autoantibodies to bGAD blood sera of 48 children aged 1 to 14, 36 of these with newly diagnosed IDDM, 2 with impaired glucose tolerance (IGT), 10 healthy controls, were tested. Indirect immunofluorescent staining of rat cerebellum cryoslices was carried out. The results were assessed using fluorescent microscopy and processed by statistical methods. Autoantibodies to bGAD were found in 30 out of 36 patients with IDDM: 83.3 +/- 12.4% (p = 95%), in 1 with IGT, and in none of controls. The fact that all controls were antibody-negative proves a high specificity of this immunological marker of IDDM. Family history or a younger age by the moment of diabetes onset were conductive to a higher prevalence of autoantibodies to GAD, each of these factors being unrelated to the other.
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PMID:[Autoantibodies to glutamate decarboxylase in children with newly detected insulin-dependent diabetes mellitus]. 819 83

Glutamic acid decarboxylase (GAD) catalyzes synthesis of the inhibitory neurotransmitter gamma-amino butyric acid. Two homologous forms of GAD encoded by separate genes have been cloned from rat brain, with predicted protein sizes of 67 and 65 kilodaltons. GAD is present outside the brain, and pancreatic islet GAD is believed to be a target of autoimmunity in insulin-dependent diabetes mellitus. However, peripheral expression of the two GAD genes is incompletely characterized. We, therefore, investigated GAD expression in peripheral tissues, including pancreas, of mouse and rat. cDNAs encoding GAD 67 and GAD 65 were cloned from mouse brain and shown to be 95% homologous with the rat sequences. RNase protection assay using specific cRNA probes demonstrated expression of both GAD forms in freshly harvested pancreas and testis. Levels of both GAD mRNAs were greater in rat than mouse pancreas. GAD 67 mRNA was more abundant than GAD 65, and both were localized to islet beta-cells by in situ hybridization. In testis, both GAD mRNAs were localized to spermatocytes. Additionally, GAD 67, but not GAD 65, mRNA was detected in mouse and rat spleen and mouse liver. Thus, both GAD genes are expressed in peripheral tissues, with GAD 67 mRNA being more abundant under physiological conditions. 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.
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PMID:Localization and quantitation of expression of two glutamate decarboxylase genes in pancreatic beta-cells and other peripheral tissues of mouse and rat. 824 24

Glutamic acid decarboxylase (GAD) is the enzyme that synthesizes the neurotransmitter gamma-aminobutyric acid (GABA) in neurons and in pancreatic beta cells. It is a major target of autoimmunity in Stiff-Man syndrome (SMS), a rare neurological disease, and in insulin-dependent diabetes mellitus. The two GAD isoforms, GAD-65 and GAD-67, are the products of two different genes. GAD-67 and GAD-65 are very similar to each other in amino acid sequence and differ substantially only at their NH2-terminal region. We have investigated the reactivity of autoantibodies of 30 Stiff-Man syndrome patients to GAD. All patient sera contained antibodies that recognize strongly GAD-65, but also GAD-67, when tested by immunoprecipitation on brain extracts and by immunoprecipitation or immunocytochemistry on cells transfected with either the GAD-65 or the GAD-67 gene. When tested by Western blotting, all patient sera selectively recognized GAD-65. Western blot analysis of deletion mutants of GAD-65 demonstrated that autoantibodies are directed predominantly against two regions of the GAD-65 molecule. All SMS sera strongly recognized a fragment contained between amino acid 475 and the COOH terminus (amino acid 585). Within this region, amino acids 475-484 and 571-585 were required for reactivity. The requirement of these two discontinuous segments implies that the epitope is influenced by conformation. This reactivity is similar to that displayed by the monoclonal antibody GAD 6, suggesting the presence of a single immunodominant epitope (SMS-E1) in this region of GAD-65. In addition, most SMS sera recognized at least one epitope (SMS-E2) in the NH2-terminal domain of GAD-65 (amino acids 1-95). The demonstration in SMS patients of a strikingly homogeneous humoral autoimmune response against GAD and the identification of dominant autoreactive target regions may help to elucidate the molecular mechanisms of GAD processing and presentation involved in GAD autoimmunity. Moreover, the reactivity reported here of GAD autoantibodies in SMS partially differs from the reactivity of GAD autoantibodies in insulin-dependent diabetes mellitus, suggesting a link between the pattern of humoral autoimmunity and the clinical condition.
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PMID:Identification of a dominant epitope of glutamic acid decarboxylase (GAD-65) recognized by autoantibodies in stiff-man syndrome. 824 84

Culturing and comparing the discrete stages of tumorigenesis provide a route to defining important components of the cancer phenotype and, in addition, present the opportunity to establish cell cultures more representative of normal cells than the ultimate malignant cancer cells. Herein we report that preneoplastic foci in one multistep tumorigenesis pathway can be cultured in vitro and show that they preserve distinctive characteristics of the normal cells from which they arose, pancreatic beta cells. In the RIP1-Tag2 line of transgenic mice, which express the simian virus 40 T antigen in insulin-producing beta cells, pancreatic islets develop into vascularized tumors in a multistage pathway. We established conditions for reproducible derivation of beta-cell lines from individual hyperplastic islets that have not yet developed into solid tumors. Most of these cell lines, designated beta HC, release insulin at physiological concentrations of glucose. In contrast to tumor-derived lines (beta TC), which are not properly regulated, the ability of the beta HC lines to respond correctly to glucose correlated with maintenance of normally depressed levels of low-Km hexokinases. Glutamic acid decarboxylase (GAD), an early autoantigen in type I diabetes, was detected in most of the beta HC lines. The relative levels of the two forms of this enzyme (GAD65 and GAD67) varied significantly between the different cell lines, suggesting independent regulation. Class I major histocompatibility complex antigens were detected on the beta HC cells, and the levels of surface major histocompatibility complex expression correlated with their capacity to serve as targets in a cytotoxic T-cell killing assay. The beta HC lines will be of value for studies of beta-cell physiology, autoantigenicity, and tumor development. This work suggests the possibility of culturing preneoplastic stages of other cancers, both to address the mechanisms of transformation and to provide a source of cells that maintain important qualities of their normal progenitors.
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PMID:Pancreatic beta cells cultured from individual preneoplastic foci in a multistage tumorigenesis pathway: a potentially general technique for isolating physiologically representative cell lines. 839 34

Glutamic acid decarboxylase (GAD) catalyzes the synthesis of gamma-aminobutyric acid (GABA), which is known as a major inhibitory neurotransmitter in the central nervous system (CNS), but is also present outside the CNS. Recent studies showed that GAD is the major target of autoantibodies associated with the development of insulin-dependent diabetes mellitus and of the rare stiff man syndrome. Studies of GAD expression have demonstrated multiple transcripts, suggesting several isoforms of GAD. In this study, three different genes were mapped by in situ hybridization to both human and mouse chromosomes. The GAD1 gene was mapped to human chromosome 2q31 and to mouse chromosome 2D in a known region of conservation between human and mouse. GAD2, previously mapped to human chromosome 10p11.2-p12, was mapped to mouse chromosome 2A2-B, which identifies a new region of conservation between human and mouse chromosomes. A potential GAD3 transcript was mapped to human chromosome 22q13 and to mouse chromosome 15E in a known region of conservation between human and mouse. It is concluded that the GAD genes may form a family with as many as three related members.
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PMID:Mapping of glutamic acid decarboxylase (GAD) genes. 840 75

Glutamic acid decarboxylase (GAD) has been shown to be a target of autoantibodies in insulin-dependent diabetes (IDD). Two forms of GAD, with molecular weights of 67,000 and 65,000, have been cloned from separate genes. As pancreatic islet beta cell destruction DD is an autoimmune process mediated by T cells, we sought to determine if recombinant GAD67 was recognized by T cells in IDD subjects and particularly their first-degree relatives with islet cell antibodies known to be at risk for IDD. The central regions of human islet and brain GAD67 (amino acids 208-404) were cloned as fusion proteins with glutathione-S-transferase (GST). Proliferation of peripheral blood T cells in the presence of recombinant GAD67 was significantly higher in both at-risk relatives and recent-onset IDD subjects than in other autoimmune disease subjects and human histocompatibility leukocyte antigen (HLA)-matched healthy controls. Thus, 12 of 29 (41%) at-risk relatives and 11 of 29 (38%) recent-onset IDD subjects responded to GAD67, compared with 1 of 7 (14%) other autoimmune disease subjects and 1 of 23 (4%) HLA-matched controls. T cell responses to GST alone or to tetanus toxoid were not different between the groups. These findings demonstrate that GAD67 is a target autoantigen of T cells in IDD and suggest the possibility that GAD-reactive T cells may delineate asymptomatic subjects at increased risk for IDD.
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PMID:Glutamic acid decarboxylase 67-reactive T cells: a marker of insulin-dependent diabetes. 842 22


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