Toll-like receptor 4 on islet beta cells senses expression changes in high-mobility group box 1 and contributes to the initiation of type 1 diabetes

Type 1 diabetes mellitus is caused by the autoimmune destruction of beta cells within the islets. In recent years, innate immunity has been proposed to play a key role in this process. High-mobility group box 1 (HMGB1), an inflammatory trigger in a number of autoimmune diseases, activates proinflammatory responses following its release from necrotic cells. Our aim was to determine the significance of HMGB1 in the natural history of diabetes in non-obese diabetic (NOD) mice. We observed that the rate of HMGB1 expression in the cytoplasm of islets was much greater in diabetic mice compared with non-diabetic mice. The majority of cells positively stained for toll-like receptor 4 (TLR4) were beta cells; few alpha cells were stained for TLR4. Thus, we examined the effects of anti-TLR4 antibodies on HMGB1 cell surface binding, which confirmed that HMGB1 interacts with TLR4 in isolated islets. Expression changes in HMGB1 and TLR4 were detected throughout the course of diabetes. Our findings indicate that TLR4 is the main receptor on beta cells and that HMGB1 may signal via TLR4 to selectively damage beta cells rather than alpha cells during the development of type 1 diabetes mellitus.

Mediators and mechanisms of pancreatic beta-cell death in type 1 diabetes

Type 1 diabetes mellitus (T1D) is characterized by severe insulin deficiency resulting from chronic and progressive destruction of pancreatic beta-cells by the immune system. The triggering of autoimmunity against the beta-cells is probably caused by environmental agent(s) acting in the context of a predisposing genetic background. Once activated, the immune cells invade the islets and mediate their deleterious effects on beta-cells via mechanisms such as Fas/FasL, perforin/granzyme, reactive oxygen and nitrogen species and pro-inflammatory cytokines. Binding of cytokines to their receptors on the beta-cells activates MAP-kinases and the transcription factors STAT-1 and NFkappa-B, provoking functional impairment, endoplasmic reticulum stress and ultimately apoptosis. This review discusses the potential mediators and mechanisms leading to beta-cell destruction in T1D.

O diabetes melito tipo 1 (DM1) tem como característica uma grave deficiência de insulina que resulta da destruição da célula-beta, crônica e progressiva, pelo sistema imune. O desencadeamento da autoimunidade contra a célula-beta é causado, provavelmente, por agentes ambientais que atuam quando existe predisposição genética. Uma vez ativadas, células imunes invadem as ilhotas, e os efeitos deletérios sobre as células-beta são mediados por mecanismos relacionados a Fas/FasL, perforina/granzima, espécies reativas de oxigênio e nitrogênio, e a citocinas pró-inflamatórias. A ligação de citocinas a seus receptores na célula-beta ativa MAP-quinase e fatores de transcrição STAT-1 e NFkapaB, provocando prejuízo funcional, estresse de retículo endoplasmático e, por fim, apoptose. Esta revisão discute os mecanismos e os mediadores potenciais que levam à destruição da célula-beta no DM1.

Frequency Of Pancreatic Beta-Cell Autoimmunity Markers In Patients With Autoimmune Thyroid Disease / Frecuencia de marcadores de autoinmunidad beta pancreática en pacientes con enfermedad tiroidea autoinmune

A total of 305 ambulatory patients recruited at the Division of Endocrinology, Hospital de Clínicas, University of Buenos Aires, with autoimmune thyroid disease (AITD) were studied to search for associations between autoimmune thyroid disease and presence of serum markers of autoimmune diabetes mellitus. Screening for markers of pancreatic beta-cell autoimmunity was performed by radioligand binding assays (RBA) as follows: autoantibodies to glutamic acid decarboxylase (GADA) and proinsulin (PAA) were determined in all sera, whereas autoantibodies to protein tyrosine phosphatase (IA-2A) and insulin (IAA) were additionally measured in 200 sera randomly selected from the total collection. In addition, every GADA positive serum among the remaining 105 sera was systematically tested for the presence of IA-2A and IAA. In the cohort of 305 AITD patients 22 (7.2%) were previously diagnosed as type 1, type 2 or insulin-requiring type 2 diabetics. Ten of these patients presented serum marker positivity specific for β-cell autoantigens and 12 were marker negative. On the other hand, considering the majority of non-diabetic AITD patients (n=283), β-cell marker positivity was detected in 17 individuals (6.0%). The prevalence of autoimmune diabetes markers was much higher in the studied population than in the general population utilized as a control group, and GADA was the most frequent marker.

Se investigó la asociación entre enfermedad tiroidea autoinmune y la presencia de marcadores séricos de diabetes mellitus en 305 pacientes ambulatorios con enfermedad tiroidea autoinmune reclutados en la División Endocrinología. La búsqueda de marcadores de autoinmunidad contra las células beta pancreáticas se realizó por la técnica de unión de radioligandos (RBA) como se detalla a continuación: se determinaron autoanticuerpos contra la decarboxilasa del ácido glutámico (GADA) y proinsulina (PAA) en todos los sueros, mientras que los anticuerpos contra la proteína tirosina fosfatasa (IA-2A) e insulina (IAA) fueron medidos en 200 de estos sueros tomados al azar de la colección total. Además, en los restantes 105 pacientes, la presencia de IA-2A y IAA fue evaluada en todos los sueros positivos para GADA. Del grupo de 305 pacientes con enfermedad tiroidea autoinmune 22 (7.2%) fueron diagnosticados previamente como diabéticos tipo 1, tipo 2 o tipo 2 insulino-requirientes. Diez de ellos presentaron positividad para marcadores específicos de autoantígenos de célula β, en tanto 12 fueron negativos. Por otra parte, en 17 de los 283 pacientes (6.0%) con enfermedad tiroidea autoimmune y sin diagnóstico previo de diabetes, se detectó positividad para marcadores de célula β. La prevalencia de marcadores de autoinmunidad asociados a diabetes fue mayor en la población estudiada que en la población general usada como grupo control, siendo GADA el marcador más frecuente.

[ presence of insulin catalytic antibodies in plasma of two type 2 diabetes patients]

Recent studies have reported the role of catalytic antibodies in the pathogenesis pattern of some diseases. Autoimmune reactions playing a role in some type 2 diabetic patients and the p- cell autoimmune markers were found to be present in some of these patients. The presence of such antibodies was assessed in the plasma of patients suffering from type 2diabetes. Antibodies in 3 diabetic patients and 7 non-diabetic control subjects were purified using protein-G sepharose affinity column chromatography and S-300 gel filtration methods; purity of the IgG antibodies was confirmed by SDS-PAGE and in western blot analysis and proteolytic activity of electrophoretically homogenous IgG antibodies was confirmed with zymogram analysis. The purified antibodies were incubated with insulin at 37°C for 6 days and the effect of antibodies on insulin degradation was assessed by Acetic Acid-Urea polyacrylamide gel electrophoresis. Insulin degradation effect was observed only in purified antibodies in the 2 diabetic patients and it was not seen in the 7 control subjects and the remaining diabetic patients. Our data revealed, for the first time, insulin degradation by isolated IgG from 2 diabetic patients. This finding may not only explain the insulin resistance observed in some diabetic patients, but may most likely propose also a new mechanism for occurrence of the disease

Genetic characteristics and beta-cell autoimmunity in T1DM children

T1DM is known to be polygenic disease that appears from the interaction of mutation in multiple genes including HLA. The autoimmune mediated destruction of pancreatic beta-cells is reflected by the presence of autoantibodies against prominent antigens in the pancreatic beta-cells. This study was designed to investigate the role of HLA-class I and class II antigens in the etiology of type 1 diabetes mellitus [T1DM] and also assessment of glutamic acid decarboxylase [GAD[65]] autoantibodies in the patients at the onset of the disease. Sixty T1DM patients who were newly onset of the disease [diagnosed less than five months] were selected. Eighty apparently healthy control subjects, matched with age, sex and ethnic backgrounds underwent the HLA-typing by lymphocytotoxicity assay. Finally 50 healthy individuals were selected randomly to undergo serological assessment of GAD[65] autoantibodies using IRMA method. At HLA-class I region, T1DM patients showed a significant increased frequency of antigen A9 [40.0 vs. 18.75%] and B8 [28.33 vs.8.75%] as compared to control subject. At HLA-class II region, DR3 and DR4 were significantly increased in patients [53.33 vs.26.25% and 50.0 vs. 12.5% respectively] as compared to controls. In addition to that, T1DM was significantly associated with DQ2 [33.33 vs.15%] and DQ3 [40.0 vs. 20%] antigens as compared to controls, suggesting that these haplotypes had a role in disease susceptibility, while the frequency of DR2 and DQ1 antigens were significantly lowered in patients compared to controls [6.66 vs. 25% and 6.66 vs. 22.5% respectively]. These molecules might had protective effect. Anti-GAD[65] autoantibodies were present in 50% of T1DM children especially in older ages and in females more than males. High proportion of GADA was found in the patients carrying HLA-DR3/DR4 heterozygous. In conclusion, susceptibility to T1DM is genetically controlled