Impact of genetic and non-genetic factors in type 1 diabetes

An overview of type 2 diabetes and importance of vitamin D3-vitamin D receptor interaction in pancreatic β-cells

One significant health issue that plagues contemporary society is that of Type 2 diabetes (T2D). This disease is characterised by higher-than-average blood glucose levels as a result of a combination of insulin resistance and insufficient insulin secretions from the β-cells of pancreatic islets of Langerhans. Previous developmental research into the pancreas has identified how early precursor genes of pancreatic β-cells, such as Cpal, Ngn3, NeuroD, Ptf1a, and cMyc, play an essential role in the differentiation of these cells. Furthermore, β-cell molecular characterization has also revealed the specific role of β-cell-markers, such as Glut2, MafA, Ins1, Ins2, and Pdx1 in insulin expression. The expression of these genes appears to be suppressed in the T2D β-cells, along with the reappearance of the early endocrine marker genes. Glucose transporters transport glucose into β-cells, thereby controlling insulin release during hyperglycaemia. This stimulates glycolysis through rises in intracellular calcium (a process enhanced by vitamin D) (Norman et al., 1980), activating 2 of 4 proteinases. The rise in calcium activates half of pancreatic β-cell proinsulinases, thus releasing free insulin from granules. The synthesis of ATP from glucose by glycolysis, Krebs cycle and oxidative phosphorylation plays a role in insulin release. Some studies have found that the β-cells contain high levels of the vitamin D receptor; however, the role that this plays in maintaining the maturity of the β-cells remains unknown. Further research is required to develop a more in-depth understanding of the role VDR plays in β-cell function and the processes by which the beta cell function is preserved.

On the pathogenesis of insulin-dependent diabetes mellitus: the role of microbiota

Type 1 diabetes (T1D) is an autoimmune disorder characterized by the selective destruction of insulin-producing β cells as result of a complex interplay between genetic, stochastic and environmental factors in genetically susceptible individuals. An increasing amount of experimental data from animal models and humans has supported the role played by imbalanced gut microbiome in T1D pathogenesis. The commensal intestinal microbiota is fundamental for several physiologic mechanisms, including the establishment of immune homeostasis. Alterations in its composition have been correlated to changes in the gut immune system, including defective tolerance to food antigens, intestinal inflammation and enhanced gut permeability. Early findings reported differences in the intestinal microbiome of subjects affected by prediabetes or overt disease compared to healthy individuals. The present review focuses on microbiota-host homeostasis, its alterations, factors that influence microbiome composition and discusses their putative correlation with T1D development. Further studies are necessary to clarify the role played by microbiota modifications in the processes that cause enhanced permeability and the autoimmune mechanisms responsible for T1D onset.

A Critical Role for the Type I Interferon Receptor in Virus-Induced Autoimmune Diabetes in Rats

The pathogenesis of human type 1 diabetes, characterized by immune-mediated damage of insulin-producing β-cells of pancreatic islets, may involve viral infection. Essential components of the innate immune antiviral response, including type I interferon (IFN) and IFN receptor-mediated signaling pathways, are candidates for determining susceptibility to human type 1 diabetes. Numerous aspects of human type 1 diabetes pathogenesis are recapitulated in the LEW.1WR1 rat model. Diabetes can be induced in LEW.1WR1 weanling rats challenged with virus or with the viral mimetic polyinosinic:polycytidylic acid (poly I:C). We hypothesized that disrupting the cognate type I IFN receptor (type I IFN α/β receptor [IFNAR]) to interrupt IFN signaling would prevent or delay the development of virus-induced diabetes. We generated IFNAR1 subunit-deficient LEW.1WR1 rats using CRISPR-Cas9 (clustered regularly interspaced short palindromic repeats-associated protein 9) genome editing and confirmed functional disruption of the Ifnar1 gene. IFNAR1 deficiency significantly delayed the onset and frequency of diabetes and greatly reduced the intensity of insulitis after poly I:C treatment. The occurrence of Kilham rat virus-induced diabetes was also diminished in IFNAR1-deficient animals. These findings firmly establish that alterations in innate immunity influence the course of autoimmune diabetes and support the use of targeted strategies to limit or prevent the development of type 1 diabetes.

Understanding type 1 diabetes: etiology and models

Type 1 diabetes is a complex disease involving a combination of factors, such as genetic susceptibility, immunologic dysregulation and exposure to environmental triggers. Animal models serve an important function both in elucidating the pathophysiology and preliminary screening of antidiabetic molecules. Hence, the development of models for type 1 diabetes can be broadly divided into 3 categories, namely: identification of spontaneously developing type 1 diabetes mellitus strains, creating diabetes-prone species through gene transfer techniques and forced destruction of islet cells through chemical or surgical means. This review discusses the models used to study type 1 diabetes with special emphasis on genetics.

Risk factors and primary prevention trials for type 1 diabetes

Type 1 diabetes mellitus (T1DM) is a chronic autoimmune disease resulting in the designated immune destruction of insulin producing β-cells, usually diagnosed in youth, and associated with important psychological, familial, and social disorders. Once diagnosed, patients need lifelong insulin treatment and will experience multiple disease-associated complications. There is no cure for T1DM currently. The last decade has witnessed great progress in elucidating the causes and treatment of the disease based on numerous researches both in rodent models of spontaneous diabetes and in humans. This article summarises our current understanding of the pathogenesis of T1DM, the roles of the immune system, genes, environment and other factors in the continuing and rapid increase in T1DM incidence at younger ages in humans. In addition, we discuss the strategies for primary and secondary prevention trials of T1DM. The purpose of this review is to provide an overview of this disorder's pathogenesis, risk factors that cause the disease, as well as to bring forward an ideal approach to prevent and cure the disorder.

The incidence of type 1 diabetes mellitus among 15-34 years aged Lithuanian population: 18-year incidence study based on prospective databases

Background

The aim of this prospective study was to determine the incidence of type 1 diabetes mellitus in 15-34-year-aged Lithuanian males and females during 1991 - 2008

Methods

A contact system with general practitioners covering 100% of the 15-34-year-aged Lithuanian population was the primary data source. Reports from regional endocrinologists and statistical note-marks of State patient insurance fund served as secondary sources for case ascertainment.

Results

The average age-standardized incidence rate was 8.30 per 100,000 persons per year (95% Poisson distribution confidence interval [CI] 7.90-8.71) during 1991 - 2008 and was statistically significantly higher among males (10.44 per 100,000 persons per year, 95% CI 9.82-11.10) in comparison with females (6.10 per 100,000, 95% CI 5.62-6.62). Male/female rate ratio was 1.71 (95% CI 1.63-1.80). Results of the linear 1991 - 2008 regression model showed that the incidence of Type 1 diabetes in 15-34-year-aged males and females decreased slightly over the time (r = -0.215, p > 0.05).

Conclusions

Our data demonstrated the male predominance in primary incidence of type 1 diabetes mellitus in 15-34-year-aged population in Lithuania. The incidence of type 1 diabetes mellitus in 15-34-year-aged males and females decreased slightly during 1991-2008.

Virus-induced autoimmune diabetes in the LEW.1WR1 rat requires Iddm14 and a genetic locus proximal to the major histocompatibility complex

OBJECTIVE

To identify genes that confer susceptibility to autoimmune diabetes following viral infection in the LEW.1WR1 rat.

RESEARCH DESIGN AND METHODS

About 2% of LEW.1WR1 rats develop spontaneous autoimmune diabetes. Immunological perturbants including viral infection increase both the frequency and tempo of diabetes onset. To identify diabetes susceptibility genes (LEW.1WR1 x WF), F2 rats were infected with Kilham rat virus following brief pretreatment with polyinosinic:polycytidylic acid. This treatment induces diabetes in 100% of parental LEW.1WR1 rats and 0% of parental WF rats. Linkage to diabetes was analyzed by genome-wide scanning.

RESULTS

Among 182 F2 rats, 57 (31%) developed autoimmune diabetes after a mean latency of 16 days. All diabetic animals and approximately 20% of nondiabetic animals exhibited pancreatic insulitis. Genome-wide scanning revealed a requirement for the Iddm14 locus, long known to be required for diabetes in the BB rat. In addition, a new locus near the RT1 major histocompatibility complex (MHC) was found to be a major determinant of disease susceptibility. Interestingly, one gene linked to autoimmune diabetes in mouse and human, UBD, lies within this region.

CONCLUSIONS

The Iddm14 diabetes locus in the rat is a powerful determinant of disease penetrance in the LEW.1WR1 rat following viral infection. In addition, a locus near the MHC (Iddm37) conditions diabetes susceptibility in these animals. Other, as-yet-unidentified genes are required to convert latent susceptibility to overt diabetes. These data provide insight into the polygenic nature of autoimmune diabetes in the rat and the interplay of genetic and environmental factors underlying disease expression.

Closing the circle between the bedside and the bench: Toll-like receptors in models of virally induced diabetes

Animal models provide many strategies to unravel the complex interplay of genetic, immunologic, and environmental factors involved in the pathogenesis of type 1A (autoimmune) diabetes. Diabetes can be studied at multiple levels, and new technological advancements provide insights into the functioning of organelle and cellular structures. The role of innate immunity in the response to environmental pathogens has provided possible biochemical and molecular mechanisms which can explain certain clinical events in diabetes. These investigations may uncover new therapies and strategies to prevent type 1A diabetes.

Glucagon-like peptide-2 reduces intestinal permeability but does not modify the onset of type 1 diabetes in the nonobese diabetic mouse

The development of type 1 diabetes (T1D) has been linked to environmental factors and dietary components. Increasing evidence indicates that the integrity of the gut mucosa plays a role in the development of autoimmune diseases, and evidence from both preclinical and clinical studies demonstrates that increased leakiness of the intestinal epithelium precedes the development of type 1 diabetes. However, there is limited information on modulation of gut barrier function and its relationship to diabetes development. Here we show that the nonobese diabetic (NOD) mouse, a model of T1D, exhibits enhanced intestinal transcellular permeability before the development of autoimmune diabetes. Treatment of NOD mice with a glucagon-like peptide 2 (GLP-2) analog, synthetic human [Gly(2)] glucagon-like peptide-2 (h[Gly(2)]GLP-2, increased the length and weight of the small bowel and significantly improved jejunal transepithelial resistance. However, chronic administration of once daily h[Gly(2)]GLP-2 failed to delay or reverse the onset of T1D when treatment was initiated in young, normoglycemic female NOD mice. Furthermore, h[Gly(2)]GLP-2 administration had no significant effect on lymphocyte subpopulations in NOD mice. These findings demonstrate that h[Gly(2)]GLP-2-mediated enhancement of gut barrier function in normoglycemic NOD mice disease is not sufficient to prevent or delay the development of experimental T1D.

Infectious diseases and Type 1 diabetes in children

Type 1 diabetes (T1D) is an autoimmune disease triggered by environmental factors. Among those of infectious origin, viruses mostly associated to T1D are rubella virus, enteroviruses (Rotavirus, Coxackie B), Cytomegalovirus and mumps virus. The role of bacterial infections is still controversial, acting either as modulators or precipitating factors of an already started autoimmune process. Polymorphic genes of innate immunity, such as Toll-like receptors, nucleotide-binding oligomerization domain (NOD) 1 and NOD2 and mannose-binding lectin (MBL) genes, did not show a strict association with T1D onset, while protein tyrosine phosphatase (PTPN22), cytotoxic T-lymphocyte antigen (CTLA)4 and natural killer cells immunoglobulin-like receptor (KIR) genes appear to play an important role. However, the adaptive immune response genes (HLA) still provide the major contribution to T1D susceptibility. Here, we review the mechanism by which microorganisms might induce autoimmunity.

Gene-environment interactions in the development of complex disease phenotypes

The lack of knowledge about the earliest events in disease development is due to the multi-factorial nature of disease risk. This information gap is the consequence of the lack of appreciation for the fact that most diseases arise from the complex interactions between genes and the environment as a function of the age or stage of development of the individual. Whether an environmental exposure causes illness or not is dependent on the efficiency of the so-called “environmental response machinery” (i.e., the complex of metabolic pathways that can modulate response to environmental perturbations) that one has inherited. Thus, elucidating the causes of most chronic diseases will require an understanding of both the genetic and environmental contribution to their etiology. Unfortunately, the exploration of the relationship between genes and the environment has been hampered in the past by the limited knowledge of the human genome, and by the inclination of scientists to study disease development using experimental models that consider exposure to a single environmental agent. Rarely in the past were interactions between multiple genes or between genes and environmental agents considered in studies of human disease etiology. The most critical issue is how to relate exposure-disease association studies to pathways and mechanisms. To understand how genes and environmental factors interact to perturb biological pathways to cause injury or disease, scientists will need tools with the capacity to monitor the global expression of thousands of genes, proteins and metabolites simultaneously. The generation of such data in multiple species can be used to identify conserved and functionally significant genes and pathways involved in gene-environment interactions. Ultimately, it is this knowledge that will be used to guide agencies such as the U.S. Department of Health and Human Services in decisions regarding biomedical research funding and policy.

Newly weaned nonobese diabetic mice show heightened early diabetes sensitivity to multiple low doses of streptozotocin than nondiabetes-prone CD-1 mice: initial beta-cell damage a key trigger for type 1 diabetes?

OBJECTIVES

We determined if newly weaned female nonobese diabetic (NOD) mice show greater diabetes sensitivity to dose-adjusted regimens of multiple low doses of streptozotocin (Stz) than nondiabetes-prone CD-1 mice.

METHODS

Female NOD mice received 5 daily doses of Stz from day 21 (0, 5, 10, 15, 20, 30, and 40 mg/kg body weight) and CD-1 mice 20, 30, and 40 mg.

RESULTS

: Streptozotocin, at the 15-, 20-, 30-, and 40-mg dose, induced rapid diabetes in NOD mice. By day 100, 90% to 95% of NOD mice became diabetic after the 40- and 30-mg dose and 33% to 40% with the 15- and 20-mg dose. In comparison, only about 50% and 33% of CD-1 mice developed diabetes with the 40- and 30-mg dose, respectively, and 5.5% with the 20-mg dose. In NOD mice, the 20-mg dose also partially suppressed spontaneous diabetes. All diabetic mice displayed insulitis, variable immunostaining for insulin, and redistribution of glucagon and somatostatin cells. Glucose transporter-2 was markedly attenuated in selective beta cells.

CONCLUSIONS

Newly weaned female NOD mice show heightened early sensitivity to low doses of Stz than CD-1 mice. At diabetes, several beta cells remain and show variable immunostaining for insulin and an attenuated expression for glucose transporter-2. Specific low doses of Stz may also suppress spontaneous diabetes.

Sex-specific association of the human PTPN22 1858T-allele with type 1 diabetes

Type 1 diabetes (T1D) is a common organ-specific autoimmune disease of complex aetiology, involving the interaction of a large number of disease-associated genes. By comparison of a Danish population sample of 253 Caucasian children and adolescents with T1D and a control group consisted of 354 unrelated healthy blood donors, the present study provides evidence of an isolated association of the disease-associated PTPN22 1858T-allele with T1D to the female sex. Furthermore, the present data suggest that PTPN22 genotypes affect the age of onset in a sex-specific manner. The increased frequency of the risk allele and its association with age at onset in female T1D children and adolescents indicates that the genetic contribution to disease pathogenesis is more prominent in females in this population of Danish patients.

Epidemiology and genetic risk of type 1 diabetes among children in Aragon community, Spain

The incidence of type 1 diabetes in children from Aragon (a population of the North of Spain) is reported determining the relations between the onset of type 1 diabetes and gender, age at diagnosis, genetic risk (HLA class II genes) or climatology factors. The population at risk was all 0-14 year-old inhabitants. Patients were identified from five sources: hospitals, primary assistance, endocrinologists, diabetic associations and diabetes camps. The degree of ascertainment was 98.93%. HLA genetic study was performed. Annual incidence was 16.4 per 100,000 per year (95% CI: 14.7-18.2). This incidence was significantly higher in males than in females, 18.7 versus 14.2 (p<0.02), and increased with age. The haplotypes (DR3)-DQB1*0201/(DR4)-DQB1*0302 and (DR3)-DQB1*0201/(DR7)-DQB1*0202 conferred the highest risk of type 1 diabetes. A relative high incidence of type 1 diabetes mellitus has been demonstrated in the Northeast of Spain, and it does not support south-to-north incidence gradient in Europe. Haplotypes that conferred a higher risk of disease agree with those founded in other Caucasic populations.

PD-1 gene haplotype is associated with the development of type 1 diabetes mellitus in Japanese children

Interaction between Programmed cell death-1 (PD-1), a member of costimulatory molecules, and its receptors Programmed cell Death-1 Ligand 1 (PD-L1) and Programmed cell Death-1 Ligand 2 (PD-L2), play an important role in the negative regulation of immune reactions. It was shown that a polymorphism in a regulatory site of the PD-1 gene was associated with susceptibility to several autoimmune diseases in various ethnic groups, whereas the contribution of the PD-1 gene or its ligand genes to the onset of type 1 diabetes (T1D) mellitus in the Japanese population remains unknown. We first screened PD-1, PD-L1, and PD-L2 genes for polymorphisms in the Japanese population, and then investigated the frequencies of polymorphisms in patients with T1D mellitus in comparison with healthy controls. In total, we identified 26 polymorphic sites within these genes, and then 23 polymorphisms with minor allele frequencies greater than 5% were intensively analyzed for genotyping in the patients and the controls. As a result, allele and genotype frequencies of the polymorphism numbers 2, 3, 4, 5, 6, and 8 in the PD-1 gene were different to some extent between the patients and the controls with P < 0.05, which did not reach statistical significance after the correction of multiple comparisons. Allele or genotype frequencies of any SNPs in the PD-L1 or PD-L2 gene did not show differences between the patients and the controls. The frequencies of the estimated haplotypes, those of which consisted of polymorphism numbers 2, 3, 4, 5, 6, and 8 in the PD-1, were significantly different between the patients and the controls (P = 0.00095). The in vitro assessment for a transcription activity of each haplotype of the PD-1 gene by luciferase assay did not demonstrate a functional difference between the haplotypes. In conclusion, the genetic evaluation by association study demonstrated that the PD-1 gene was a predisposing gene to the development of T1D mellitus in the Japanese population.

LEW.1WR1 rats develop autoimmune diabetes spontaneously and in response to environmental perturbation

We describe a new rat model of autoimmune diabetes that arose in a major histocompatibility complex congenic LEW rat. Spontaneous diabetes in LEW.1WR1 rats (RT1(u/u/a)) occurs with a cumulative frequency of approximately 2% at a median age of 59 days. The disease is characterized by hyperglycemia, glycosuria, ketonuria, and polyuria. Both sexes are affected, and islets of acutely diabetic rats are devoid of beta-cells, whereas alpha- and delta-cell populations are spared. The peripheral lymphoid phenotype is normal, including the fraction of ART2(+) regulatory T-cells. We tested the hypothesis that the expression of diabetes would be increased by immunological perturbation of innate or adaptive immunity. Treatment of young rats with depleting anti-ART2.1 monoclonal antibody increased the frequency of diabetes to 50%. Treatment with the toll-like receptor 3 ligand polyinosinic:polycytidylic acid increased the frequency of diabetes to 100%. All diabetic rats exhibited end-stage islets. The LEW.1WR1 rat is also susceptible to collagen-induced arthritis but is free of spontaneous thyroiditis. The LEW.1WR1 rat provides a new model for studying autoimmune diabetes and arthritis in an animal with a genetic predisposition to both disorders that can be amplified by environmental perturbation.

Rat models of type 1 diabetes: genetics, environment, and autoimmunity

For many years, the vast amount of data gathered from analysis of nonobese diabetic (NOD) and congenic NOD mice has eclipsed interest in the rat for the study of type 1 diabetes. The study of rat models has continued, however, and recently there has been a reanimation of interest for several reasons. First, genetic analysis of the rat has accelerated. Ian4L1, cblb, and Iddm4 are now known to play major roles in rat autoimmunity. Second, rats are amenable to study the interactions of genetics and environment that may be critical for disease expression in humans. Environmental perturbants that predictably enhance the expression of rat autoimmune diabetes include viral infection, toll-like receptor ligation, and depletion of regulatory T cell populations. Finally, data generated in the rat have correctly predicted the outcome of several human diabetes prevention trials, notably the failure of nicotinamide and low dose parenteral and oral insulin therapies.

CTLA-4 gene polymorphisms and susceptibility to type 1 diabetes mellitus: a HuGE Review and meta-analysis

The authors performed a meta-analysis of 33 studies examining the association of type 1 diabetes mellitus with polymorphisms in the cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4) gene, including the A49G (29 comparisons), C(-318)T (three comparisons), and (AT)n microsatellite (six comparisons) polymorphisms. The studies included 5,637 cases of type 1 diabetes and 6,759 controls (4,775 and 5,829, respectively, for analysis of the A49G polymorphism). The random-effects odds ratio for the *G (Ala) allele versus the *A (Thr) allele was 1.45 (95% confidence interval (CI): 1.28, 1.65), with significant between-study heterogeneity (p < 0.001). The effect size tended to be higher in type 1 diabetes cases with age of onset <20 years (odds ratio (OR) = 1.61), and there was a significant association between the presence of glutamic acid decarboxylase-65 autoantibodies and the *G allele among type 1 diabetes cases (OR = 1.49). Larger studies showed more conservative results (p = 0.011). After exclusion of studies with fewer than 150 subjects and studies with significant deviation from Hardy-Weinberg equilibrium in the controls, the summary odds ratio was 1.40 (95% CI: 1.28, 1.54). Available data showed no strong association for the 106-base-pair allele of the microsatellite polymorphism (OR = 0.99, 95% CI: 0.64, 1.55) or the *T allele of the C(-318)T polymorphism (OR = 0.92, 95% CI: 0.45, 1.89). This meta-analysis demonstrates that the CTLA-4*G genotype is associated with type 1 diabetes.

Characteristics of childhood and adult-onset type 1 diabetes in a multi-ethnic population

OBJECTIVE

To compare patients with classic type 1 diabetes (T1D) diagnosed in childhood and adulthood regarding clinical presentation, GADA and HLA DR B1*03/04 prevalence in a multi-ethnic population.

METHODS

We studied 83 Brazilian patients with classic T1D divided in 2 groups: (1) diagnosed before 20 years old (n=42); (2) diagnosed at age 20 and up (n=41). All were interviewed and blood was sampled for GADA measurement and HLA DR B1 typing.

RESULTS

The study population comprised 52 women and 31 men, 52 white and 31 non-white individuals with mean age of 29.94 (+/-10.95) years and mean disease duration of 10.37 (+/-7.37) years. The mean age at onset in groups 1 and 2 were, respectively, 11.48 and 27.2 years old. There were no significant differences between groups regarding diabetic ketoacidosis at presentation. A longer symptomatic period preceding the diagnosis was observed in group 2 (p=0.039). The prevalence of GADA and HLA DR B1*03/04 was similar between groups. HLA DR B1*13 was significantly more common in the group 1 (p=0.024). GADA was more prevalent among patients with HLA DR B1*03 (p=0.02).

CONCLUSION

In this study, T1D diagnosed in adulthood was associated with longer symptomatic period preceding diagnosis and lower prevalence of HLA DR B1*13, but there were no differences regarding ketoacidosis as a form of disease presentation, GADA (+) or HLA DR B1* 03/04.

The rat diabetes susceptibility locus Iddm4 and at least one additional gene are required for autoimmune diabetes induced by viral infection

BBDR rats develop autoimmune diabetes only after challenge with environmental perturbants. These perturbants include polyinosinic:polycytidylic acid (poly I:C, a ligand of toll-like receptor 3), agents that deplete regulatory T-cell (Treg) populations, and a non-beta-cell cytopathic parvovirus (Kilham rat virus [KRV]). The dominant diabetes susceptibility locus Iddm4 is required for diabetes induced by treatment with poly I:C plus Treg depletion. Iddm4 is penetrant in congenic heterozygous rats on the resistant WF background and is 79% sensitive and 80% specific as a predictor of induced diabetes. Surprisingly, an analysis of 190 (BBDR x WF)F2 rats treated with KRV after brief exposure to poly I:C revealed that the BBDR-origin allele of Iddm4 is necessary but not entirely sufficient for diabetes expression. A genome scan identified a locus on chromosome 17, designated Iddm20, that is also required for susceptibility to diabetes after exposure to KRV and poly I:C (logarithm of odds score 3.7). These data suggest that the expression of autoimmune diabetes is a complex process that requires both major histocompatibility complex genes that confer susceptibility and additional genes such as Iddm4 and Iddm20 that operate only in the context of specific environmental perturbants, amplifying the immune response and the rate of disease progression.

TLR activation synergizes with Kilham rat virus infection to induce diabetes in BBDR rats

Virus infection is hypothesized to be an important environmental "trigger" of type 1 diabetes in humans. We used the BBDR rat model to investigate the relationship between viral infection and autoimmune diabetes. BBDR rats are diabetes-free in viral Ab-free housing, but the disease develops in approximately 30% of BBDR rats infected with Kilham rat virus (KRV) through a process that does not involve infection of pancreatic beta cells. Pretreatment with polyinosinic-polycytidylic (poly(I:C)), a ligand of TLR3, acts synergistically to induce diabetes in 100% of KRV-infected rats. The mechanisms by which KRV induces diabetes and TLR3 ligation facilitates this process are not clear. In this study, we demonstrate that activation of the innate immune system plays a crucial role in diabetes induction. We report that multiple TLR agonists synergize with KRV infection to induce diabetes in BBDR rats, as do heat-killed Escherichia coli or Staphylococcus aureus (natural TLR agonists). KRV infection increases serum IL-12 p40 in a strain-specific manner, and increases IL-12 p40, IFN-gamma-inducible protein-10, and IFN-gamma mRNA transcript levels, particularly in the pancreatic lymph nodes of BBDR rats. Infection with vaccinia virus or H-1 parvovirus induced less stimulation of the innate immune system and failed to induce diabetes in BBDR rats. Our results suggest that the degree to which the innate immune system is activated by TLRs is important for expression of virus-induced diabetes in genetically susceptible hosts.

Association of a putative regulatory polymorphism in the PD-1 gene with susceptibility to type 1 diabetes

The immunoreceptor programmed cell death-1 (PD-1) is reported to play an important role in the regulation of peripheral tolerance in rodents, and it was recently shown that a polymorphism in a regulatory site of the PD-1 gene is associated with susceptibility to the autoimmune disease systemic lupus erythematosus (SLE) in humans. We investigated the existence of single-nucleotide polymorphisms (SNPs) in the PD-1 gene in patients with type 1 diabetes in comparison with healthy control subjects, by analyzing 94 children and adolescents with type 1 diabetes diagnosed before their eighteenth birthday (male : female = 52 : 42) and 155 control subjects. Polymorphisms in the complete PD-1 gene (minus the large intron 1) were detected by sequencing. In total, we identified 14 SNPs, of which six have been previously described, including an intronic 7146G/A SNP. We found this polymorphism to be associated with the development of type 1 diabetes [found in 12.2% of diabetic individuals vs 6.8% in controls; odds ratio (OR) = 1.92]. The associated allele is previously shown to alter a transcription factor-binding site (RUNX1/AML1), and the results of this study suggest that this allele could act as an additional susceptibility allele to type 1 diabetes.

Laboratory tests in diagnosis and management of diabetes mellitus. Practical considerations

The clinical laboratory plays an essential role in both the diagnosis and therapeutic monitoring of diabetes mellitus. Here, a short review of the main laboratory parameters used in the monitoring of diabetes--glucose (including point-of-care testing), HbA1c and microalbuminuria--is presented. The impact of pre-analytical and analytical performance criteria on the clinical decision making process is discussed.

Fetal or neonatal low-glycotoxin environment prevents autoimmune diabetes in NOD mice

Advanced glycation end products (AGEs) are implicated in beta-cell oxidant stress. Diet-derived AGE (dAGE) are shown to contribute to end-organ toxicity attributed to diabetes. To assess the role of dAGE on type 1 diabetes, NOD mice were exposed to a high-AGE diet (H-AGE) and to a nutritionally similar diet with approximate fivefold-lower levels of N(epsilon)-carboxymethyllysine (CML) and methylglyoxal-derivatives (MG) (L-AGE). Suppression of serum CML and MG in L-AGE-fed mice was marked by suppression of diabetes (H-AGE mice >94% vs. L-AGE mice 33% in founder [F](0), 14% in F(1), and 13% in F(2) offspring, P < 0.006) and by a delay in disease onset (4-month lag). Survival for L-AGE mice was 76 vs. 0% after 44 weeks of H-AGE mice. Reduced insulitis in L-AGE versus H-AGE mice (P < 0.01) was marked by GAD- and insulin-unresponsive pancreatic interleukin (IL)-4-positive CD4+ cells compared with the GAD- and insulin-responsive interferon (IFN)-gamma-positive T-cells from H-AGE mice (P < 0.005). Splenocytes from L-AGE mice consisted of GAD- and insulin-responsive IL-10-positive CD4+ cells compared with the IFN-gamma-positive T-cells from H-AGE mice (P < 0.005). Therefore, high AGE intake may provide excess antigenic stimulus for T-cell-mediated diabetes or direct beta-cell injury in NOD mice; both processes are ameliorated by maternal or neonatal exposure to L-AGE nutrition.