Beta cell apoptosis in T cell-mediated autoimmune diabetes

CD3 monoclonal antibodies: a first step towards operational immune tolerance in the clinic

Type 1 diabetes (T1D) is a prototypic organ-specific autoimmune disease resulting from the selective destruction of insulin-secreting β-cells within the pancreatic islets of Langerhans. It is caused by an immune-mediated inflammation, involving autoreactive CD4⁺ and CD8⁺ T lymphocytes that infiltrate the islets and initiate insulitis. The use of exogenous insulin is the current standard treatment. However, in spite of significant advances, this therapy is still associated with major constraints, including risk of hypoglycemia and severe degenerative complications. As T1D mainly affects children and young adults, any candidate immune therapy must be safe, and it must avoid a sustained depression of immune responses with all its attendant problems of recurrent infection and drug toxicity. In this context, inducing or restoring immune tolerance to target autoantigens would be the ideal approach. We refer to immune tolerance here as the selective damping of the damaging autoimmune response following a short treatment, while keeping intact the capacity of the host to respond normally to exogenous antigens. The therapeutic approach we discuss in this article originates from attempts to induce tolerance both to soluble antigens and tissue antigens (i.e. alloantigens and autoantigens) by using biological agents that selectively interfere with lymphocyte activation, namely polyclonal and monoclonal anti-T cell antibodies. The challenged dogma was that, in an adult-primed immune system, it was not possible to restore self-tolerance therapeutically without the use of exogenous autoantigen administration. The reality has been that, in diabetes, endogenous host autoantigen can fulfill this role because a significant amount of functioning β-cells remains, even at the time of established hyperglycemia. Experimental results obtained in the 1990s showed that a short-term CD3 antibody treatment in recently diagnosed diabetic non-obese diabetic (NOD) mice induced permanent remission of the disease by restoring self-tolerance. Based on these findings, phase I, II, and III trials were conducted using two distinct humanized Fc-mutated antibodies to human CD3, namely ChAglyCD3 (otelixizumab) and OKT3γ1 Ala-Ala (teplizumab). Overall, when dosing was adequate, the results demonstrated that CD3 antibodies preserved β-cell function very efficiently, maintaining significantly high levels of endogenous insulin secretion in treated patients for up to 24 months after treatment. These data provided the first proof of concept for a long-term therapeutic effect in T1D following a short course administration of a therapeutic agent. Our aim is to review these data and to discuss them in the context of the pitfalls linked to pharmaceutical development, especially in the context of pediatric patients, as in autoimmune diabetes.

Specific silencing of the REST target genes in insulin-secreting cells uncovers their participation in beta cell survival

The absence of the transcriptional repressor RE-1 Silencing Transcription Factor (REST) in insulin-secreting beta cells is a major cue for the specific expression of a large number of genes. These REST target genes were largely ascribed to a function of neurotransmission in a neuronal context, whereas their role in pancreatic beta cells has been poorly explored. To identify their functional significance, we have generated transgenic mice expressing REST in beta cells (RIP-REST mice), and previously discovered that REST target genes are essential to insulin exocytosis. Herein we characterized a novel line of RIP-REST mice featuring diabetes. In diabetic RIP-REST mice, high levels of REST were associated with postnatal beta cell apoptosis, which resulted in gradual beta cell loss and sustained hyperglycemia in adults. Moreover, adenoviral REST transduction in INS-1E cells led to increased cell death under control conditions, and sensitized cells to death induced by cytokines. Screening for REST target genes identified several anti-apoptotic genes bearing the binding motif RE-1 that were downregulated upon REST expression in INS-1E cells, including Gjd2, Mapk8ip1, Irs2, Ptprn, and Cdk5r2. Decreased levels of Cdk5r2 in beta cells of RIP-REST mice further confirmed that it is controlled by REST, in vivo. Using siRNA-mediated knock-down in INS-1E cells, we showed that Cdk5r2 protects beta cells against cytokines and palmitate-induced apoptosis. Together, these data document that a set of REST target genes, including Cdk5r2, is important for beta cell survival.

TOSO promotes β-cell proliferation and protects from apoptosis

Decreased β-cell mass reflects a shift from quiescence/proliferation into apoptosis, it plays a crucial role in the pathophysiology of diabetes. A major attempt to restore β-cell mass and normoglycemia is to improve β-cell survival. Here we show that switching off the Fas pathway using Fas apoptotic inhibitory protein (Faim/TOSO), which regulates apoptosis upstream of caspase 8, blocked β-cell apoptosis and increased proliferation in human islets. TOSO was clearly expressed in pancreatic β-cells and down-regulated in T2DM. TOSO expression correlated with β-cell turnover; at conditions of improved survival, TOSO was induced. In contrast, TOSO downregulation induced β-cell apoptosis. Although TOSO overexpression resulted in a 3-fold induction of proliferation, proliferating β-cells showed a very limited capacity to undergo multiple rounds of replication. Our data suggest that TOSO is an important regulator of β-cell turnover and switches β-cell apoptosis into proliferation.

Apoptosis of human islet cells by cytokines

FasL, perforin, TNFα, IL-1 and NO have been considered as effector molecule(s) leading to β-cell death in autoimmune diabetes. However, the real culprit(s) of β-cell destruction have long been elusive despite intense investigation. Previously we have suggested IFNγ/TNFα synergism as the final effector molecules in autoimmune diabetes of NOD mice. A combination of IFNγ and TNFα but neither cytokine alone, induced classical caspase-dependent apoptosis in murine insulinoma and pancreatic islet cells. IFNγ treatment conferred susceptibility to TNFα-induced apoptosis on otherwise resistant murine insulinoma cells by STAT1 activation followed by IRF-1 induction. Here we report that IFNγ/TNFα synergism induces apoptosis of human pancreatic islet cells. We also observed STAT1 activation followed by IRF-1 induction by IFNγ treatment in human islet cells. Taken together, we suggest that IFNγ/TNFα synergism could be involved in human islet cell death in type 1 diabetes, similar to murine type 1 diabetes.

Induction of protective genes leads to islet survival and function

Islet transplantation is the most valid approach to the treatment of type 1 diabetes. However, the function of transplanted islets is often compromised since a large number of β cells undergo apoptosis induced by stress and the immune rejection response elicited by the recipient after transplantation. Conventional treatment for islet transplantation is to administer immunosuppressive drugs to the recipient to suppress the immune rejection response mounted against transplanted islets. Induction of protective genes in the recipient (e.g., heme oxygenase-1 (HO-1), A20/tumor necrosis factor alpha inducible protein3 (tnfaip3), biliverdin reductase (BVR), Bcl2, and others) or administration of one or more of the products of HO-1 to the donor, the islets themselves, and/or the recipient offers an alternative or synergistic approach to improve islet graft survival and function. In this perspective, we summarize studies describing the protective effects of these genes on islet survival and function in rodent allogeneic and xenogeneic transplantation models and the prevention of onset of diabetes, with emphasis on HO-1, A20, and BVR. Such approaches are also appealing to islet autotransplantation in patients with chronic pancreatitis after total pancreatectomy, a procedure that currently only leads to 1/3 of transplanted patients being diabetes-free.

Intracellular pathways of pancreatic β-cell apoptosis in type 1 diabetes

BACKGROUND

Apoptosis of β cells is a feature of type 1 diabetes. It is also increasingly recognized in type 2 diabetes and islet graft rejection.

METHODS

We have studied the intracellular pathways that regulate β-cell apoptosis in type 1 and 2 diabetes. We have examined the role of Bid, a pro-apoptotic member of the Bcl-2 family, using islets from mice deficient in Bid. We also studied the Bcl-2 family molecules involved in killing by using high concentrations of reducing sugars such as glucose or ribose.

RESULTS

We found that Bid-deficient islets are protected from recombinant human perforin and granzyme B, as well as from Fas-mediated killing. This makes Bid a target for protection of β cells from multiple insults relevant to type 1 diabetes. In contrast to granzyme B and death receptor signalling, we found that islets lacking Bim or Puma were protected from glucose toxicity.

CONCLUSIONS

Our data indicate that different stimuli activate different initiator molecules in the Bcl-2-regulated pathway in β cells.

Insulinoma-released exosomes or microparticles are immunostimulatory and can activate autoreactive T cells spontaneously developed in nonobese diabetic mice

Exosomes (EXO) are secreted intracellular microparticles that can trigger inflammation and induce Ag-specific immune responses. To test possible roles of EXO in autoimmunity, we isolated small microparticles, mainly EXO, from mouse insulinoma and examined their activities to stimulate the autoimmune responses in NOD mice, a model for human type 1 diabetes. We demonstrate that the EXO contains strong innate stimuli and expresses candidate diabetes autoantigens. They can induce secretion of inflammatory cytokines through a MyD88-dependent pathway, and activate purified APC and result in T cell proliferation. To address whether EXO or the secreted microparticles are possible autoimmune targets causing islet-specific inflammation, we monitored the T cell responses spontaneously developed in prediabetic NOD mice for their reactivity to the EXO, and compared this reactivity between diabetes-susceptible and -resistant congenic mouse strains. We found that older NOD females, which have advanced islet destruction, accumulated more EXO-reactive, IFN-γ-producing lymphocytes than younger females or age-matched males, and that pancreatic lymph nodes from the prediabetic NOD, but not from the resistant mice, were also enriched with EXO-reactive Th1 cells. In vivo, immunization with the EXO accelerates insulitis development in nonobese diabetes-resistant mice. Thus, EXO or small microparticles can be recognized by the diabetes-associated autoreactive T cells, supporting that EXO might be a possible autoimmune target and/or insulitis trigger in NOD or congenic mouse strains.

The microRNA-21-PDCD4 axis prevents type 1 diabetes by blocking pancreatic beta cell death

Death of pancreatic β cells is a pathological hallmark of type 1 diabetes (T1D). However, the molecular mechanisms of β cell death and its regulation are poorly understood. Here we describe a unique regulatory pathway of β cell death that comprises microRNA-21, its target tumor suppressor PDCD4, and its upstream transcriptional activator nuclear factor-κB (NF-κB). In pancreatic β cells, c-Rel and p65 of the NF-κB family activated the mir21 gene promoter and increased miR-21 RNA levels; miR-21 in turn decreased the level of PDCD4, which is able to induce cell death through the Bax family of apoptotic proteins. Consequently, PDCD4 deficiency in pancreatic β cells renders them resistant to death, and PDCD4 deficiency in NOD or C57BL/6 mice conferred resistance to spontaneous diabetes and diabetes induced by autoimmune T cells or the β cell toxin streptozotocin (STZ). Thus, the NF-κB-microRNA-21-PDCD4 axis plays a crucial role in T1D and represents a unique therapeutic target for treating the disease.

Suppressive effects of continuous low-dose-rate γ irradiation on diabetic nephropathy in type II diabetes mellitus model mice

It has been proposed that the development of diabetic nephropathy is caused in large part by oxidative stress. We previously showed that continuous exposure of mice to low-dose-rate γ radiation enhances antioxidant activity. Here, we studied the ameliorative effect of continuous whole-body irradiation with low-dose-rate γ rays on diabetic nephropathy. Ten-week-old female db/db mice, an experimental model for type II diabetes, were irradiated with low-dose-rate γ rays from 10 weeks of age throughout their lives. Nephropathy was studied by histological observation and biochemical analysis of serum and urine. Antioxidant activities in kidneys were determined biochemically. Continuous low-dose-rate γ radiation significantly increases life span in db/db mice. Three of 24 irradiated mice were free of glucosuria after 80 weeks of irradiation. Histological studies of kidney suggest that low-dose irradiation increases the number of normal capillaries in glomeruli. Antioxidant activities of superoxide dismutase, catalase and glutathione are significantly increased in kidneys of irradiated db/db mice. Continuous low-dose-rate γ irradiation ameliorates diabetic nephropathy and increases life span in db/db mice through the activation of renal antioxidants. These findings have noteworthy implications for radiation risk estimation of non-cancer diseases as well as for the clinical application of low-dose-rate γ radiation for diabetes treatment.

Breaking T cell tolerance to beta cell antigens by merocytic dendritic cells

In type 1 diabetes (T1D), a break in central and peripheral tolerance results in antigen-specific T cells destroying insulin-producing, pancreatic beta cells. Herein, we discuss the critical sub-population of dendritic cells responsible for mediating both the cross-presentation of islet antigen to CD8(+) T cells and the direct presentation of beta cell antigen to CD4(+) T cells. These cells, termed merocytic dendritic cells (mcDC), are more numerous in non-obese diabetic (NOD), and antigen-loaded mcDC rescue CD8(+) T cells from peripheral anergy and deletion, and stimulate islet-reactive CD4(+) T cells. When purified from the pancreatic lymph nodes of overtly diabetic NOD mice, mcDC can break peripheral T cell tolerance to beta cell antigens in vivo and induce rapid onset T cell-mediated T1D in young NOD mouse. Thus, the mcDC subset appears to represent the long-sought critical antigen-presenting cell responsible for breaking peripheral tolerance to beta cell antigen in vivo.

Oxidative stress and redox modulation potential in type 1 diabetes

Redox reactions are imperative to preserving cellular metabolism yet must be strictly regulated. Imbalances between reactive oxygen species (ROS) and antioxidants can initiate oxidative stress, which without proper resolve, can manifest into disease. In type 1 diabetes (T1D), T-cell-mediated autoimmune destruction of pancreatic β-cells is secondary to the primary invasion of macrophages and dendritic cells (DCs) into the islets. Macrophages/DCs, however, are activated by intercellular ROS from resident pancreatic phagocytes and intracellular ROS formed after receptor-ligand interactions via redox-dependent transcription factors such as NF-κB. Activated macrophages/DCs ferry β-cell antigens specifically to pancreatic lymph nodes, where they trigger reactive T cells through synapse formation and secretion of proinflammatory cytokines and more ROS. ROS generation, therefore, is pivotal in formulating both innate and adaptive immune responses accountable for islet cell autoimmunity. The importance of ROS/oxidative stress as well as potential for redox modulation in the context of T1D will be discussed.

Investigating the role of T-cell avidity and killing efficacy in relation to type 1 diabetes prediction

During the progression of the clinical onset of Type 1 Diabetes (T1D), high-risk individuals exhibit multiple islet autoantibodies and high-avidity T cells which progressively destroy beta cells causing overt T1D. In particular, novel autoantibodies, such as those against IA-2 epitopes (aa1-577), had a predictive rate of 100% in a 10-year follow up (rapid progressors), unlike conventional autoantibodies that required 15 years of follow up for a 74% predictive rate (slow progressors). The discrepancy between these two groups is thought to be associated with T-cell avidity, including CD8 and/or CD4 T cells. For this purpose, we build a series of mathematical models incorporating first one clone then multiple clones of islet-specific and pathogenic CD8 and/or CD4 T cells, together with B lymphocytes, to investigate the interaction of T-cell avidity with autoantibodies in predicting disease onset. These models are instrumental in examining several experimental observations associated with T-cell avidity, including the phenomenon of avidity maturation (increased average T-cell avidity over time), based on intra- and cross-clonal competition between T cells in high-risk human subjects. The model shows that the level and persistence of autoantibodies depends not only on the avidity of T cells, but also on the killing efficacy of these cells. Quantification and modeling of autoreactive T-cell avidities can thus determine the level of risk associated with each type of autoantibodies and the timing of T1D disease onset in individuals that have been tested positive for these autoantibodies. Such studies may lead to early diagnosis of the disease in high-risk individuals and thus potentially serve as a means of staging patients for clinical trials of preventive or interventional therapies far before disease onset.

In vivo diabetogenic action of CD4+ T lymphocytes requires Fas expression and is independent of IL-1 and IL-18

CD4(+) T lymphocytes are required to induce spontaneous autoimmune diabetes in the NOD mouse. Since pancreatic β cells upregulate Fas expression upon exposure to pro-inflammatory cytokines, we studied whether the diabetogenic action of CD4(+) T lymphocytes depends on Fas expression on target cells. We assayed the diabetogenic capacity of NOD spleen CD4(+) T lymphocytes when adoptively transferred into a NOD mouse model combining: (i) Fas-deficiency, (ii) FasL-deficiency, and (iii) SCID mutation. We found that CD4(+) T lymphocytes require Fas expression in the recipients' target cells to induce diabetes. IL-1β has been described as a key cytokine involved in Fas upregulation on mouse β cells. We addressed whether CD4(+) T cells require IL-1β to induce diabetes. We also studied spontaneous diabetes onset in NOD/IL-1 converting enzyme-deficient mice, in NOD/IL-1β-deficient mice, and CD4(+) T-cell adoptively transferred diabetes into NOD/SCID IL-1β-deficient mice. Neither IL-1β nor IL-18 are required for either spontaneous or CD4(+) T-cell adoptively transferred diabetes. We conclude that CD4(+) T-cell-mediated β-cell damage in autoimmune diabetes depends on Fas expression, but not on IL-1β unveiling the existing redundancy regarding the cytokines involved in Fas upregulation on NOD β cells in vivo.

Interleukin-21 is critically required in autoimmune and allogeneic responses to islet tissue in murine models

OBJECTIVE

Type 1 diabetes is an incurable chronic autoimmune disease. Although transplantation of pancreatic islets may serve as a surrogate source of insulin, recipients are subjected to a life of immunosuppression. Interleukin (IL)-21 is necessary for type 1 diabetes in NOD mice. We examined the efficacy of an IL-21-targeted therapy on prevention of diabetes in NOD mice, in combination with syngeneic islet transplantation. In addition, we assessed the role of IL-21 responsiveness in islet allograft rejection in mouse animal models.

RESEARCH DESIGN AND METHODS

NOD mice were treated with IL-21R/Fc, an IL-21-neutralizing chimeric protein. This procedure was combined with syngeneic islet transplantation to treat diabetic NOD mice. Survival of allogeneic islet grafts in IL-21R-deficient mice was also assessed.

RESULTS

Evidence is provided that IL-21 is continually required by the autoimmune infiltrate, such that insulitis was reduced and reversed and diabetes inhibited by neutralization of IL-21 at a late preclinical stage. Recovery from autoimmune diabetes was achieved by combining neutralization of IL-21 with islet transplantation. Furthermore, IL-21-responsiveness by CD8+ T-cells was sufficient to mediate islet allograft rejection.

CONCLUSIONS

Neutralization of IL-21 in NOD mice can inhibit diabetes, and when paired with islet transplantation, this therapeutic approach restored normoglycemia. The influence of IL-21 on a graft-mounted immune response was robust, since the absence of IL-21 signaling prevented islet allograft rejection. These findings suggest that therapeutic manipulation of IL-21 may serve as a suitable treatment for patients with type 1 diabetes.

Disruption of hepatocyte growth factor/c-Met signaling enhances pancreatic beta-cell death and accelerates the onset of diabetes

OBJECTIVE

To determine the role of hepatocyte growth factor (HGF)/c-Met on β-cell survival in diabetogenic conditions in vivo and in response to cytokines in vitro.

RESEARCH DESIGN AND METHODS

We generated pancreas-specific c-Met-null (PancMet KO) mice and characterized their response to diabetes induced by multiple low-dose streptozotocin (MLDS) administration. We also analyzed the effect of HGF/c-Met signaling in vitro on cytokine-induced β-cell death in mouse and human islets, specifically examining the role of nuclear factor (NF)-κB.

RESULTS

Islets exposed in vitro to cytokines or from MLDS-treated mice displayed significantly increased HGF and c-Met levels, suggesting a potential role for HGF/c-Met in β-cell survival against diabetogenic agents. Adult PancMet KO mice displayed normal glucose and β-cell homeostasis, indicating that pancreatic c-Met loss is not detrimental for β-cell growth and function under basal conditions. However, PancMet KO mice were more susceptible to MLDS-induced diabetes. They displayed higher blood glucose levels, marked hypoinsulinemia, and reduced β-cell mass compared with wild-type littermates. PancMet KO mice showed enhanced intraislet infiltration, islet nitric oxide (NO) and chemokine production, and β-cell apoptosis. c-Met-null β-cells were more sensitive to cytokine-induced cell death in vitro, an effect mediated by NF-κB activation and NO production. Conversely, HGF treatment decreased p65/NF-κB activation and fully protected mouse and, more important, human β-cells against cytokines.

CONCLUSIONS

These results show that HGF/c-Met is critical for β-cell survival by attenuating NF-κB signaling and suggest that activation of the HGF/c-Met signaling pathway represents a novel strategy for enhancing β-cell protection.

On how monospecific memory-like autoregulatory CD8+ T cells can blunt diabetogenic autoimmunity: a computational approach

We have recently shown that during progression to autoimmune diabetes in NOD mice, memory autoreactive regulatory CD8(+) T cells arising from low-avidity precursors can be expanded to therapeutic levels using nanoparticles coated with disease-relevant peptide-major histocompatibility complexes (pMHCs). Here we examine the dynamics of memory autoregulatory CD8(+) T cells specific for islet-specific glucose-6-phosphatase catalytic subunit-related protein(206-214), a prevalent β cell autoantigen; their high-avidity counterparts (dominant effectors); and all other autoreactive non-islet-specific glucose-6-phosphatase catalytic subunit-related protein(206-214)-specific CD8(+) T cell specificities (subdominant effectors) in response to pMHC-coated nanoparticle (pMHC-nanoparticle) therapy. We combine experimental data with mathematical modeling to investigate the clonal competition dynamics of these T cell pools. To mimic the response diversity observed in NOD mice, we simulated many individual mice, using a wide range of parameters, and averaged the results as done experimentally. We find that under certain circumstances, pMHC-nanoparticle-induced expansion of autoregulatory CD8(+) T cells can effectively suppress the expansion of dominant and subdominant effectors simultaneously but, in some few cases, can lead to the substitution (or switching) of one effector population by another. The model supports the idea that disease suppression is based on the elimination of autoantigen-loaded APCs by the expanded autoregulatory CD8(+) T cells. The model also predicts that treatment strategies that operate by selectively inhibiting autoantigen-loaded APCs, such as the pMHC-nanoparticle approach, have the highest promise to blunt polyclonal, multiantigen-specific autoimmune responses in vivo without impairing systemic immunity.

Cutting edge: merocytic dendritic cells break T cell tolerance to beta cell antigens in nonobese diabetic mouse diabetes

In type 1 diabetes, the breach of central and peripheral tolerance results in autoreactive T cells that destroy insulin-producing, pancreatic beta cells. In this study, we identify a critical subpopulation of dendritic cells responsible for mediating both the cross-presentation of islet Ags to CD8(+) T cells and the direct presentation of beta cell Ags to CD4(+) T cells. These cells, termed merocytic dendritic cells (mcDCs), are more numerous in the NOD mouse and, when Ag-loaded, rescue CD8(+) T cells from peripheral anergy and deletion while stimulating islet-reactive CD4(+) T cells. When purified from the pancreatic lymph nodes of overtly diabetic NOD mice, mcDCs break peripheral T cell tolerance to beta cells in vivo and induce rapid onset type 1 diabetes in the young NOD mouse. Thus, the mcDC subset appears to represent the long-sought APC responsible for breaking peripheral tolerance to beta cell Ags in vivo.

The pathogenicity of self-antigen decreases at high levels of autoantigenicity: a computational approach

Recent experimental evidence suggests that antigenic stability facilitates antigen shuttling from target tissue to dendritic cells (DCs), enabling cross-priming of naive T cells. On the other hand, antigenic stability affects the efficiency of peptide-MHC (p-MHC) complex formation, altering a target cell's susceptibility to killing by the resulting CTLs. Using a mathematical model, we show how antigenic stability and p-MHC production efficiency interplay in autoantigenicity and pathogenic potential of target cell proteins in autoimmune disease. We consider protein allocated to both rapidly degraded versus stable functional pools [fractions f, 1 - f], contributing, with relative efficiency eta, to p-MHC presentation on a target cell, as well as to cross-presentation on a DC; we analyze the combined effect of these parameters. Our results suggest that autoantigenicity and pathogenicity (ability to elicit T cell activation versus target cell lysis) are not equivalent and that pathogenicity peaks at low to moderate levels of autoantigenicity.

Emerging roles for B lymphocytes in Type 1 diabetes

Self-reactive B lymphocytes play two main pathological roles in autoimmune diseases: as secretors of autoantibodies and as specialized antigen-presenting cells that present self-components to autoreactive T lymphocytes. In recognition of these roles, recent clinical trials have utilized B-lymphocyte-depleting monoclonal antibodies to treat various autoimmune diseases, with encouraging results in those where humoral autoimmunity is clearly important. Surprisingly, recent results in animal models suggest that B-lymphocyte depletion may also be effective in the treatment of T-lymphocyte-mediated autoimmune diseases, such as Type 1 diabetes (T1D). This article reviews the experimental evidence that has uncovered pathogenic as well as regulatory roles for B lymphocytes in the prodrome of T1D and how this information is being used to develop novel therapeutic strategies to treat the disease.

Non-viral systemic delivery of Fas siRNA suppresses cyclophosphamide-induced diabetes in NOD mice

A membrane receptor, Fas (CD95), and its ligand FasL have been considered as key players in diabetes pathogenesis. They are known to mediate interactions between beta cells and cytotoxic T cells, which results in apoptotic cell death. We hypothesized that the interruption of Fas-FasL interactions by suppressing Fas expression in beta cells would affect the development of diabetes. The effect of Fas-silencing siRNA (Fas siRNA) on diabetes development was evaluated in a cyclophosphamide (CY)-accelerated diabetes animal model after intravenous administration using a polymeric carrier, polyethylenimine (PEI). The systemic non-viral delivery of Fas siRNA showed significant delay in diabetes incidence up to 40 days, while the control mice treated with naked Fas siRNA, scrambled dsRNA, or PBS were afflicted with diabetes within 20 days. The retardation of diabetes incidence after the treatment of Fas siRNA may be due to the delayed progression of the pancreatic insulitis. In this study, the potential use of a non-viral carrier based siRNA gene therapy for the prevention of type-1 diabetes is demonstrated.

Beta cell apoptosis in diabetes

Apoptosis of beta cells is a feature of both type 1 and type 2 diabetes as well as loss of islets after transplantation. In type 1 diabetes, beta cells are destroyed by immunological mechanisms. In type 2 diabetes abnormal levels of metabolic factors contribute to beta cell failure and subsequent apoptosis. Loss of beta cells after islet transplantation is due to many factors including the stress associated with islet isolation, primary graft non-function and allogeneic graft rejection. Irrespective of the exact mediators, highly conserved intracellular pathways of apoptosis are triggered. This review will outline the molecular mediators of beta cell apoptosis and the intracellular pathways activated.

Mitochondria mediated cell death in diabetes

Mitochondrial dysfunction plays a role in the pathogenesis of a wide range of diseases that involve disordered cellular fuel metabolism and survival/death pathways, including neurodegenerative diseases, cancer and diabetes. Cytokine, virus recognition and cellular stress pathways converging on mitochondria cause apoptotic and/or necrotic cell death of beta-cells in type-1 diabetes. Moreover, since mitochondria generate crucial metabolic signals for glucose stimulated insulin secretion (GSIS), mitochondrial dysfunction underlies both the functional derangement of GSIS and (over-nutrition) stress-induced apoptotic/necrotic beta-cell death, hallmarks of type-2 diabetes. The apparently distinct mechanisms governing beta-cell life/death decisions during the development of diabetes provide a remarkable example where remote metabolic, immune and stress signalling meet with mitochondria mediated apoptotic/necrotic death pathways to determine the fate of the beta-cell. We summarize the main findings supporting such a pivotal role of mitochondria in beta-cell death in the context of current trends in diabetes research.

The ToI-beta transgenic mouse: a model to study the specific role of NF-kappaB in beta-cells

Type 1 diabetes is characterized by the infiltration of inflammatory cells into pancreatic islets of Langerhans, followed by the selective and progressive destruction of insulin-secreting beta-cells. Islet infiltrating leukocytes secrete cytokines including IL-1beta and IFN-gamma, which contribute to beta-cell death. In vitro evidence suggests that cytokine-induced activation of the transcription factor NF-kappaB is an important component of the signal triggering beta-cell apoptosis. To study the role of NF-kappaB in vivo we generated a transgenic mouse line expressing a degradation-resistant NF-kappaB protein inhibitor (DeltaNIkappaBalpha) and the luciferase gene, acting specifically in beta-cells, in an inducible and reversible manner, by using the tet-on regulation system. Using this new mouse model, termed the ToI-beta mouse (for Tet-Ondelta I kappaB in beta-cells) we have previously shown in vitro, that islets expressing the DeltaNIkappaBalpha protein were resistant to the deleterious effects of IL-1beta and IFN-gamma, as assessed by reduced NO production and beta-cell apoptosis. In vivo, a nearly complete protection against multiple low dose streptozocin-induced diabetes was observed, with reduced intra-islet lymphocytic infiltration. In the present study we demonstrate the tight regulated and reversible expression of the DeltaNIkappaBalpha transgene in the ToI-beta mouse model as well as the effect of its overexpression on glucose metabolism and insulin secretion. The results show a lack of effect of transgene induction on both in vivo glucose tolerance tests and in vitro islet insulin secretion and content. Furthermore, to prove the tight control of induction in the model, luciferase mediated light emission was only detected at constant levels in Dox-treated double transgenic mice or islets as well as in a model of islet transplantation. Upon removal of the inducing stimulus, complete reversal of both NF-kappaB inhibition and luciferase activity were observed. Together, our results show the ToI-beta mouse model to be a highly controlled and very accurate model for examining pancreatic beta-cell-specific temporal inhibition of NF-kappaB.

Therapy of experimental type 1 diabetes by isolated Sertoli cell xenografts alone

Type I diabetes mellitus is caused by autoimmune destruction of pancreatic β cells, and effective treatment of the disease might require rescuing β cell function in a context of reinstalled immune tolerance. Sertoli cells (SCs) are found in the testes, where their main task is to provide local immunological protection and nourishment to developing germ cells. SCs engraft, self-protect, and coprotect allogeneic and xenogeneic grafts from immune destruction in different experimental settings. SCs have also been successfully implanted into the central nervous system to create a regulatory environment to the surrounding tissue which is trophic and counter-inflammatory. We report that isolated neonatal porcine SC, administered alone in highly biocompatible microcapsules, led to diabetes prevention and reversion in the respective 88 and 81% of overtly diabetic (nonobese diabetic [NOD]) mice, with no need for additional β cell or insulin therapy. The effect was associated with restoration of systemic immune tolerance and detection of functional pancreatic islets that consisted of glucose-responsive and insulin-secreting cells. Curative effects by SC were strictly dependent on efficient tryptophan metabolism in the xenografts, leading to TGF-β–dependent emergence of autoantigen-specific regulatory T cells and recovery of β cell function in the diabetic recipients.

Regulatory T cells enter the pancreas during suppression of type 1 diabetes and inhibit effector T cells and macrophages in a TGF-beta-dependent manner

Treg can suppress autoimmune diseases such as type 1 diabetes, but their in vivo activity during suppression remains poorly characterized. In type 1 diabetes, Treg activity has been demonstrated in the pancreatic lymph node, but little has been studied in the pancreas, the site of autoimmune islet destruction. In this study we induced islet-specific Treg from the BDC-6.9 TCR transgenic mouse by activation of T cells in the presence of TGF-beta. These Treg can suppress spontaneous diabetes as well as transfer of diabetes into NOD.scid mice by diabetic NOD spleen cells or activated BDC-2.5 TCR transgenic Th1 effector T cells. In the latter transfer model, we observed infiltration of the pancreas by both effector T cells and Treg, suggesting that Treg are active in the inflammatory site and are not just restricted to the draining lymph node. Within the pancreas, we demonstrate that Treg transfer causes a reduction in the number of effector Th1 T cells and macrophages, and also inhibits effector T-cell cytokine and chemokine production. Although we found no role for TGF-beta in vitro, transfection of effector T cells with a dominant-negative TGF-beta receptor demonstrated that in vivo suppression of diabetes by TGF-beta-induced Treg is TGF-beta-dependent.

Parameters influencing antigen-specific immunotherapy for Type 1 diabetes

Type 1 diabetes (T1D) is a T cell-mediated autoimmune disease in which the insulin producing beta cells are destroyed. Antigen-based immunotherapy provides an approach to selectively tolerize pathogenic beta cell-specific T cells, while leaving the remainder of the immune system intact. In this article, we discuss our group's experience in defining the parameters that impact the efficacy of beta cell antigen "vaccination" for the prevention and treatment of T1D.

CXCL10 impairs beta cell function and viability in diabetes through TLR4 signaling

In type 1 and type 2 diabetes (T1/T2DM), beta cell destruction by apoptosis results in decreased beta cell mass and progression of the disease. In this study, we found that the interferon gamma-inducible protein 10 plays an important role in triggering beta cell destruction. Islets isolated from patients with T2DM secreted CXCL10 and contained 33.5-fold more CXCL10 mRNA than islets from control patients. Pancreatic sections from obese nondiabetic individuals and patients with T2DM and T1DM expressed CXCL10 in beta cells. Treatment of human islets with CXCL10 decreased beta cell viability, impaired insulin secretion, and decreased insulin mRNA. CXCL10 induced sustained activation of Akt, JNK, and cleavage of p21-activated protein kinase 2 (PAK-2), switching Akt signals from proliferation to apoptosis. These effects were not mediated by the commonly known CXCL10 receptor CXCR3 but through TLR4. Our data suggest CXCL10 as a binding partner for TLR4 and as a signal toward beta cell failure in diabetes.

Intracellular versus extracellular granzyme B in immunity and disease: challenging the dogma

The cytotoxic granzyme B (GrB)/perforin pathway has been traditionally viewed as a primary mechanism that is used by cytotoxic lymphocytes to eliminate allogeneic, virally infected and/or transformed cells. Although originally proposed to have intracellular and extracellular functions, upon the discovery that perforin, in combination with GrB, could induce apoptosis, other potential functions for this protease were, for the most part, disregarded. As there are 5 granzymes in humans and 11 granzymes in mice, many studies used perforin knockout mice as an initial screen to evaluate the role of granzymes in disease. However, in recent years, emerging clinical and biochemical evidence has shown that the latter approach may have overlooked a critical perforin-independent, pathogenic role for these proteases in disease. This review focuses on GrB, the most characterized of the granzyme family, in disease. Long known to be a pro-apoptotic protease expressed by cytotoxic lymphocytes and natural killer cells, it is now accepted that GrB can be expressed in other cell types of immune and nonimmune origin. To the latter, an emerging immune-independent role for GrB has been forwarded due to recent discoveries that GrB may be expressed in nonimmune cells such as smooth muscle cells, keratinocytes, and chondrocytes in certain disease states. Given that GrB retains its activity in the blood, can cleave extracellular matrix, and its levels are often elevated in chronic inflammatory diseases, this protease may be an important contributor to certain pathologies. The implications of sustained elevations of intracellular and extracellular GrB in chronic vascular, dermatological, and neurological diseases, among others, are developing. This review examines, for the first time, the multiple roles of GrB in disease pathogenesis.

The role of low avidity T cells in the protection against type 1 diabetes: a modeling investigation

Cytotoxic T lymphocytes (CTLs) play a dominant role in the pathogenesis of autoimmune diabetes, commonly denoted Type 1 Diabetes (T1D). These CTLs (notably CD8(+) T cells) recognize and kill insulin-secreting pancreatic beta cells, reducing their number by approximately 90%. The resulting reduction of insulin secretion causes the defective regulation of glucose metabolism, leading to the characteristic symptoms of diabetes. Recognition of beta cells as targets by CTLs depends on the interactions between MHC-peptide complexes on the surface of beta cells and receptors (TCRs) on T cells. Those CTLs with high affinity TCRs (also called high avidity T cells) cause most of the harm, while those with low affinity TCRs (also called low avidity T cells) play a more mysterious role. Recent experimental evidence suggests that low avidity T cells accumulate as memory T cells during the disease and may be protective in NOD mice (a strain prone to developing T1D), delaying disease progression. It has been hypothesized that such low avidity T cells afford disease protection either by crowding the islets of Langerhans, where beta cells reside, or by killing antigen presenting cells (APCs). In this paper, we explore the hypothesized mechanisms for this protective effect in the context of a series of models for (1) the interactions of low and high avidity T cells, (2) the effect of APCs and (3) the feedback from beta cell killing to autoantigen-induced T cell proliferation. We analyze properties of these models, noting consistency of predictions with observed behaviour. We then use the models to examine the influence of various treatment strategies on the progression of the disease. The model reveals that progressive accumulation of memory low avidity autoreactive T cells during disease progression makes treatments aimed at expanding these protective T cell types more effective close to, or at the onset of clinical disease. It also provides evidence for the hypothesis that low avidity T cells kill APCs (rather than the alternate hypothesis that they crowd the islets).

CD28/CD154 blockade prevents autoimmune diabetes by inducing nondeletional tolerance after effector t-cell inhibition and regulatory T-cell expansion

OBJECTIVE

Blocking T-cell signaling is an effective means to prevent autoimmunity and allograft rejection in many animal models, yet the clinical translation of many of these approaches has not resulted in the success witnessed in experimental systems. Improved understanding of these approaches may assist in developing safe and effective means to treat disorders such as autoimmune diabetes.

RESEARCH DESIGN AND METHODS

We studied the effect of anti-CD154 and CTLA4-Ig on diabetes development, and the requirements to induce tolerance in nod.scid mice after transfer of transgenic beta-cell reactive BDC2.5.NOD T-cells.

RESULTS

Nod.scid recipients of diabetogenic BDC2.5.NOD cells were protected indefinitely from diabetes by a short course of combined costimulation blockade, despite the continued diabetogenic potential of their T-cells. The presence of pathogenic T-cells in the absence of disease indicates peripheral immune tolerance. T-cell maturation occurred in protected recipients, yet costimulation blockade temporarily blunted early T-cell proliferation in draining pancreatic nodes. Tolerance required preexisting regulatory T-cells (Tregs), and protected recipients had greater numbers of Tregs than diabetic recipients. Diabetes protection was successful in the presence of homeostatic expansion and high T-cell precursor frequency, both obstacles to tolerance induction in other models of antigen-specific immunity.

CONCLUSIONS

Immunotherapies that selectively suppress effector T-cells while permitting the development of natural regulatory mechanisms may have a unique role in establishing targeted long-standing immune protection and peripheral tolerance. Understanding the mechanism of these approaches may assist in the design and use of therapies for human conditions, such as type 1 diabetes.

Molecular mechanisms of death ligand-mediated immune modulation: a gene therapy model to prolong islet survival in type 1 diabetes

Type 1 diabetes results from the T cell-mediated destruction of pancreatic beta cells. Islet transplantation has recently become a potential therapeutic approach for patients with type 1 diabetes. However, islet-graft failure appears to be a challenging issue to overcome. Thus, complementary gene therapy strategies are needed to improve the islet-graft survival following transplantation. Immune modulation through gene therapy represents a novel way of attacking cytotoxic T cells targeting pancreatic islets. Various death ligands of the TNF family such as FasL, TNF, and TNF-Related Apoptosis-Inducing Ligand (TRAIL) have been studied for this purpose. The over-expression of TNF or FasL in pancreatic islets exacerbates the onset of type 1 diabetes generating lymphocyte infiltrates responsible for the inflammation. Conversely, the lack of TRAIL expression results in higher degree of islet inflammation in the pancreas. In addition, blocking of TRAIL function using soluble TRAIL receptors facilitates the onset of diabetes. These results suggested that contrary to what was observed with TNF or FasL, adenovirus mediated TRAIL gene delivery into pancreatic islets is expected to be therapeutically beneficial in the setting of experimental models of type 1 diabetes. In conclusion; this study mainly reveals the fundamental principles of death ligand-mediated immune evasion in diabetes mellitus.

Low-dose radiation and its clinical implications: diabetes

Induction of hormesis and adaptive response by low-dose radiation (LDR) has been extensively indicated. Adaptive response induced by LDR was not only resistant to damage caused by a subsequently high-dose radiation, but also cross-resistant to other non-radiation challenges, such as chemicals. Mechanisms by which LDR induces the preventive effect on radiation- or chemical-induced tissue damage include induced or up-regulated expression of protective proteins, such as heat shock proteins and antioxidants. Since oxidative damage to tissues is a major pathogenesis of many human diseases including diabetes, this review will summarize the available data with an emphasis of the preventive effect of LDR on the development of diabetes and the therapeutic effect of LDR on diabetic cardiovascular complications. The available data indicated that pre-exposure of mice to LDR reduced the incidence of alloxan-induced diabetes, and also delayed the onset of hyperglycaemia in diabetes-prone non-obese diabetic mice. Experiments with animals indicated the effectively therapeutic effect of low-intensity or power laser (LIL or LPL) radiation on skin wound healing, which has stimulated clinical use of LIL to cure skin ulcer in diabetic patients. Mechanisms by which LDR prevents diabetes, though are unclear now, may include the induction of pancreatic antioxidants to prevent beta cell from oxidative damage and immunomodulation to preserve pancreatic function. For LIL therapeutic effect on diabetic wound healing, mechanisms may include its antioxidant action, immunomodulation, cell proliferation stimulation as well as improvement of systemic and wound-regional microcirculation. Therefore, although only a few studies indicating LDR prevention of the development of diabetes, many studies have demonstrated LDR, specifically LIL, therapeutic effectiveness of diabetic wound healing. These preliminary results are really encouraging for us to further pursue the clinical implication of LDT to diabetes-related areas.

Cytotoxic T-lymphocyte-mediated killing of human pancreatic islet cells in vitro

Cytotoxic T lymphocytes (CTL) are believed to play an essential role in beta-cell destruction leading to development of type 1 diabetes and allogeneic islet graft failure. We aimed to identify the mechanisms used by CTL to kill human beta cells. CTL clones that recognize epitopes from influenza virus and Epstein-Barr virus restricted by human leukocyte antigen (HLA)-A0201 and -B0801, respectively, were used to investigate the susceptibility of human beta cells to CTL. In a short-term (5-hour) assay, CTL killed human islet cells of the appropriate major histocompatibility complex (MHC) class I type that had been pulsed with viral peptides. Killing was increased by pretreating islets with interferon gamma that increases MHC class I on target cells. Killing was abolished by incubation of CTL with the perforin inhibitor concanamycin A. The Fas pathway did not contribute to killing because blocking with neutralizing anti-Fas ligand antibody did not significantly reduce beta-cell killing. In conclusion, we report a novel way of investigating the interaction between CTL and human islets. Human islets were rapidly killed in vitro by MHC class I-restricted CTL predominantly by the granule exocytosis pathway.

Role of NF-κB in β-cell death

Apoptotic β-cell death appears to be central to the pathogenesis of Type 1 diabetes mellitus and in islet graft rejection. The β-cell destruction is partially mediated by cytokines, such as IL-1β (interleukin 1β), TNFα (tumour necrosis factor α) and IFN-γ (interferon γ). IL-1β and TNFα mediate activation of the transcription factor NF-κB (nuclear factor κB) pathway. Use of a degradation-resistant NF-κB protein inhibitor (ΔNIκBα), specifically expressed in β-cells, significantly reduced IL-1β+IFN-γ-induced apoptosis. Moreover, in vivo, it protected against multiple low-dose streptozocin-induced diabetes, with reduced intra-islet lymphocytic infiltration. Thus β-cell-specific activation of NF-κB is a key event in the progressive loss of β-cells in diabetes. Inhibition of this process could be a potential effective strategy for β-cell protection.

The antiinflammatory cytokine interleukin-1 receptor antagonist protects from high-fat diet-induced hyperglycemia

Subclinical inflammation is a recently discovered phenomenon in type 2 diabetes. Elevated cytokines impair beta-cell function and survival. A recent clinical trial shows that blocking IL-1beta signaling by IL-1 receptor antagonist (IL-1Ra) improves beta-cell secretory function in patients with type 2 diabetes. In the present study, we provide further mechanisms of the protective role of IL-1Ra on the beta-cell. IL-1Ra prevented diabetes in vivo in C57BL/6J mice fed a high-fat/high-sucrose diet (HFD) for 12 wk; it improved glucose tolerance and insulin secretion. High-fat diet treatment increased serum levels of free fatty acids and of the adipokines resistin and leptin, which were reduced by IL-1Ra treatment. In addition, IL-1Ra counteracted adiponectin levels, which were decreased by high-fat feeding. Studies on isolated islets revealed that IL-1Ra specifically acted on the beta-cell. IL-1Ra protected islets from HFD treated animals from beta-cell apoptosis, induced beta-cell proliferation, and improved glucose-stimulated insulin secretion. Insulin mRNA was reduced in islets from mice fed a HFD but normalized in the IL-1Ra group. Our results show that IL-1Ra improves beta-cell survival and function, and support the potential role for IL-1Ra in the treatment of diabetes.

Macrophage migration inhibitory factor (MIF) is necessary for progression of autoimmune diabetes mellitus

Macrophage migration inhibitory factor (MIF) is a proinflammatory cytokine of the innate immune system that plays a major role in the induction of immunoinflammatory responses. To examine the role of endogenous MIF in the pathogenesis of type 1 diabetes (TID) we evaluated the effects of administration of neutralizing anti-MIF antibodies to NOD mice with accelerated forms of diabetes induced by injection of cyclophosphamide or by transfer of diabetogenic spleen cells. Both accelerated forms of diabetes were markedly reduced by anti-MIF antibody. Furthermore, MIF-deficient (MIF(-/-)) mice were less susceptible to the induction of immunoinflammatory diabetes, insulitis and apoptosis within the endocrine pancreas by multiple low doses of streptozotocin (MLD-STZ) than genetically matched wild type (WT) mice. MIF deficiency resulted in lower proliferation and lymphocyte adhesion, as well as reduced production from the spleens and peritoneal cells of a variety of inflammatory mediators typically associated with development of the disease including IL-12, IL-23, TNF-alpha, and IL-1beta. Furthermore, MIF deletion affected the production of IL-18, TNF-alpha, IL-1beta, and iNOS in the islets of Langerhans. These data, along with the higher expression of IL-4 and TGF-beta observed in the periphery and in the pancreas of MLD-STZ-challenged MIF(-/-) mice as compared to WT controls suggest that MIF deficiency has induced an immune deviation towards protective type 2/3 response. These results suggest that MIF participates in T1D by controlling the functional activity of monocytes/macrophages and T cells and modulating their secretory capacity of pro- and anti-inflammatory molecules.

Neuron-specific enolase antibodies in patients with sudden acquired retinal degeneration syndrome

Sudden acquired retinal degeneration syndrome (SARDS) is a disease characterised by sudden and bilateral vision loss of dogs. Previous studies failed to identify the underlying cause [Mattson, A., Roberts, S.M., Isherwood, J.M.E., 1992. Clinical features suggesting hyperadrenocorticism associated with sudden acquired retinal degeneration syndrome in a dog. J. Am. Anim. Hosp. Assoc. 28, 199-202; Van der Woerdt, A., Nasisse, M.P., Davidson, M.G., 1991. Sudden acquired retinal degeneration in the dog: clinical and laboratory findings in 36 cases. Prog. Vet. Comp. Ophthamol. 1, 11-18] and earlier investigations about the occurrence of anti-retinal antibodies in SARDS patients showed inconsistent results. To provide a novel approach to those findings we designed a more detailed study. Autoantibodies of SARDS patients and normal controls were tested against the purified autoantigens S-antigen and cellular retinaldehyde binding protein (CRALBP) that play a role in human autoimmune uveitis. Next we tested the autoantibody binding pattern to whole retinal lysate. No difference in the incidence of autoantibodies could be found between SARDS patients and healthy controls while testing the well-known autoantigens S-antigen and CRALBP. Potential novel, yet unknown autoantigens were identified by a screening test using the retinal proteome as an autoantigenic source. In SARDS patients and normal controls, several retinal proteins were bound by IgG antibodies, but one band was strongly marked by SARDS patients. That band was excised, subjected to mass spectrometry (matrix-assisted laser desorption/ionisation-time of flight (MALDI-TOF/TOF)) and identified as neuron-specific enolase. Binding of the IgG autoantibodies of SARDS-affected dogs to this protein was verified using purified NSE, revealing 25% of NSE autoantibody-positive SARDS patients and 0% of negative controls. Our findings indicate that at least some dogs with SARDS have autoantibodies against NSE, although it is unclear whether these play a causative role in SARDS or whether they are the result of retinal destruction by another mechanism.

Pharmacological and clinical aspects of heme oxygenase

This review is intended to stimulate interest in the effect of increased expression of heme oxygenase-1 (HO-1) protein and increased levels of HO activity on normal and pathological states. The HO system includes the heme catabolic pathway, comprising HO and biliverdin reductase, and the products of heme degradation, carbon monoxide (CO), iron, and biliverdin/bilirubin. The role of the HO system in diabetes, inflammation, heart disease, hypertension, neurological disorders, transplantation, endotoxemia and other pathologies is a burgeoning area of research. This review focuses on the clinical potential of increased levels of HO-1 protein and HO activity to ameliorate tissue injury. The use of pharmacological and genetic probes to manipulate HO, leading to new insights into the complex relationship of the HO system with biological and pathological phenomena under investigation, is reviewed. This information is critical in both drug development and the implementation of clinical approaches to moderate and to alleviate the numerous chronic disorders in humans affected by perturbations in the HO system.

The Countervailing Actions of Myeloid and Plasmacytoid Dendritic Cells Control Autoimmune Diabetes in the Nonobese Diabetic Mouse

Islet Ag-specific CD4(+) T cells receive antigenic stimulation from MHC class II-expressing APCs. Herein, we delineate the direct in vivo necessity for distinct subsets of macrophages and dendritic cells (DC) in type 1 diabetes mellitus of the NOD mouse by using diphtheria toxin-mediated cell ablation. The ablation of macrophages had no impact on islet Ag presentation or on the induction of insulitis or diabetes in either transfer or spontaneous models. However, the ablation of CD11b(+)CD11c(+) DC led to the loss of T cell activation, insulitis, and diabetes mediated by CD4(+) T cells. When the specific myeloid DC subset was "added-back" to mice lacking total DC, insulitis and diabetes were restored. Interestingly, when NOD mice were allowed to progress to the insulitis phase, the ablation of DC led to accelerated insulitis. This accelerated insulitis was mediated by the loss of plasmacytoid DC (pDC). When pDC were returned to depleted mice, the localized regulation of insulitis was restored. The loss of pDC in the pancreas itself was accompanied by the localized loss of IDO and the acceleration of insulitis. Thus, CD11c(+)CD11b(+) DC and pDC have countervailing actions in NOD diabetes, with myeloid DC providing critical antigenic stimulation to naive CD4(+) T cells and pDC providing regulatory control of CD4(+) T cell function in the target tissue.

Essential role for signal transducer and activator of transcription-1 in pancreatic beta-cell death and autoimmune type 1 diabetes of nonobese diabetic mice

OBJECTIVE

We have reported important roles for signal transducer and activator of transcription-1 (STAT1) in pancreatic beta-cell death by cytokines in vitro. However, in vivo evidence supporting the role for STAT1 in natural type 1 diabetes has not been reported. We studied whether STAT1 plays an important role in the development of natural type 1 diabetes.

RESEARCH DESIGN AND METHODS

We produced nonobese diabetic (NOD)/STAT1(-/-) mice by backcrossing and studied the in vivo role of STAT1 in beta-cell death and type 1 diabetes.

RESULTS

STAT1(-/-) islet cells were resistant to death by interferon (IFN)-gamma/tumor necrosis factor (TNF)-alpha or IFN-gamma/interleukin (IL)-1 beta combination. Cytochrome c translocation by IFN-gamma/TNF-alpha was abrogated in STAT1(-/-) islet cells. The induction of X-linked inhibitor of apoptosis protein by TNF-alpha was inhibited by IFN-gamma in STAT1(+/-) islet cells but not in STAT1(-/-) islet cells. Inducible nitric oxide (NO) synthase induction and NO production by IFN-gamma/IL-1 beta were impaired in STAT1(-/-) islet cells. Strikingly, diabetes and insulitis were completely abrogated in NOD/STAT1(-/-) mice. Development of diabetes after CD4(+) diabetogenic T-cell transfer was inhibited in those mice. STAT1(-/-) neonatal pancreata were not destroyed when grafted into diabetic NOD/BDC2.5 mice that developed CD4(+) T-cell-dependent islet cell death. In NOD/STAT1(-/-) mice, autoreactive T-cell priming was not impaired, but Th1 differentiation was impaired. A janus kinase (JAK) 2 inhibitor upstream of STAT1 attenuated islet cell death by IFN-gamma/TNF-alpha or IFN-gamma/IL-1 beta and delayed diabetes onset in NOD/BDC2.5-SCID mice.

CONCLUSIONS

These data demonstrate a critical role for STAT1 in beta-cell death, T-cell immunoregulation, and type 1 diabetes in vivo and suggest potential therapeutic values of STAT1 or JAK inhibitors in the treatment/prevention of type 1 diabetes.

Human chorionic gonadotropin is an immune modulator and can prevent autoimmune diabetes in NOD mice

AIMS/HYPOTHESIS

Expression of T helper (Th)1 cytokine mRNA in pregnant women is known to be inversely correlated with serum human chorionic gonadotropin (hCG). Type 1 diabetes is a Th1-mediated autoimmune disease, in which intervention at an early stage of the autoimmune process can prevent disease progression. We hypothesised that immune modulation by treating young NOD mice with hCG may prevent diabetes.

METHODS

Female NOD mice were treated with hCG or recombinant hCG from 3 to 15 weeks of age and the incidence of diabetes and development of insulitis was determined. CD4(+) and CD8(+) T cell populations, T cell proliferation, cytokine production and CD4(+)CD25(+) regulatory T cells were examined and adoptive transfer experiments were performed.

RESULTS

Both purified and recombinant hCG prevented development of diabetes in NOD mice. hCG decreased the proportion and number of CD4(+) and CD8(+) T cells and inhibited T cell proliferative responses against beta cell antigens. hCG treatment suppressed IFN-gamma production, but increased IL-10 and TGF-beta production in splenocytes stimulated with anti-CD3 antibody. hCG treatment also suppressed TNF-alpha production in splenocytes stimulated with lipopolysaccharide. Furthermore, hCG treatment increased the CD4(+)CD25(+)/CD4(+) T cell ratio in spleen and pancreatic lymph nodes. Depletion of CD4(+)CD25(+) T cells from splenocytes of hCG-treated NOD mice abolished their preventive effect on diabetes transfer.

CONCLUSIONS/INTERPRETATION

We conclude that hCG has an immunomodulatory effect by downregulating effector cells, including Th1 cells, CD8(+) T cells and macrophages, and increasing the CD4(+)CD25(+)/CD4(+) T cell ratio, thus preventing autoimmune diabetes in NOD mice.

Continuous stimulation of human glucagon-like peptide-1 (7-36) amide in a mouse model (NOD) delays onset of autoimmune type 1 diabetes

AIMS/HYPOTHESIS

We examined the effect of glucagon-like peptide-1 (GLP-1) on the development of diabetes and islet morphology in NOD mice by administering GLP-1 to prediabetic mice.

METHODS

Eight-week-old female NOD mice were infused subcutaneously with human GLP-1 via a mini-osmotic pump for 4 or 8 weeks. In mice treated with GLP-1 for 4 weeks, blood glucose levels and body weight were measured. An intraperitoneal glucose tolerance test (IPGTT) and evaluation of insulitis score were also performed. Beta cell area, proliferation, apoptosis, neogenesis from ducts and subcellular localisation of forkhead box O1 (FOXO1) were examined by histomorphometrical, BrdU-labelling, TUNEL, insulin/cytokeratin and FOXO1/insulin double-immunostaining methods, respectively.

RESULTS

Mice treated with human GLP-1 for 4 weeks had lower blood glucose levels until 2 weeks after completion of treatment, showing improved IPGTT data and insulitis score. This effect continued even after cessation of the treatment. In addition to the increase of beta cell neogenesis, BrdU labelling index was elevated (0.24 vs 0.13%, p < 0.001), while apoptosis was suppressed by 54.2% (p < 0.001) in beta cells. Beta cell area was increased in parallel with the translocation of FOXO1 from the nucleus to the cytoplasm. The onset of diabetes was delayed in mice treated with GLP-1 for 4 weeks, while mice treated with GLP-1 for 8 weeks did not develop diabetes by age 21 weeks compared with a 60% diabetes incidence in control mice at this age.

CONCLUSIONS/INTERPRETATION

Continuous infusion of human GLP-1 to prediabetic NOD mice not only induces beta cell proliferation and neogenesis, but also suppresses beta cell apoptosis and delays the onset of type 1 diabetes.

TCR-based lineage tracing: no evidence for conversion of conventional into regulatory T cells in response to a natural self-antigen in pancreatic islets

Foxp3-expressing regulatory T (T reg) cells derive primarily from selection in the thymus. Yet conversion of mature conventional CD4⁺ T (T conv) cell lymphocytes can be achieved in several conditions, such as transforming growth factor β treatment, homeostatic expansion, or chronic exposure to low-dose antigen. Such conversion might provide a means to generate peripheral tolerance by “converting” potentially damaging T cells that react to self-antigens. We tested this hypothesis in mice transgenic for the BDC2.5 T cell receptor (TCR), which is representative of a diabetogenic specificity that is naturally present in NOD mice and reactive against a pancreatic self-antigen. In the thymus, before any exposure to antigen, clonotype-positive T reg and T conv cells express a second TCRα chain derived from endogenous loci. High-throughput single-cell sequencing of secondary TCRs of the Vα2 family showed their joining CDR3α regions to be very different in T reg and T conv cell thymocytes. These specific CDR3α motifs, thus, provided a “tag” with which to test the actual impact of T conv to T reg cell conversion in response to peripheral self-antigen; should the autoreactive clonotypic TCR induce T conv to T reg cell conversion upon encounter of cognate antigen in the pancreas or draining lymph node, one would expect to detect tag CDR3α motifs from T conv cells in the T reg cell populations. Sequencing large numbers of peripheral BDC⁺Vα2⁺ cells showed that little to no conversion occurs in response to this pancreatic autoantigen.

Interdiction of the diabetic state in NOD mice by sustained induction of heme oxygenase: possible role of carbon monoxide and bilirubin

The aims of the present study were to assess whether sustained HO-1 expression could moderate or prevent diabetes in an animal model of the disease and, if so, to examine the possible mechanisms involved. Our results showed that HO-1 expression and HO activity were upregulated in the pancreas of non-obese diabetic (NOD) mice by the weekly administration of cobalt protoporphyrin (CoPP). Blood glucose levels in CoPPtreated mice decreased to normal, but continuously increased in untreated controls. Beta-cell numbers were preserved in the islets of CoPP-treated mice, whereas no beta cells were found in untreated diabetic mice. The number of CD11c(+) dendritic cells was significantly decreased in the pancreas of CoPP-treated NOD mice, but this effect was reversed by the inhibition of HO activity. Increased levels of HO-1 produced a new pancreatic phenotype, as reflected by increases in phosphorylated AKT, BcL-xL and RSK levels, and decreases in O(2)- and 3-NT levels. These novel findings provide a link between the increase in HO-1 activity, with its concurrent enhanced production of carbon monoxide (CO) and bilirubin, a decrease in infiltrated CD11c(+) dendritic cells and an increase in anti-apoptotic proteins, including RSK and BcL-xL, in the interdiction of the diabetic state.

Amelioration of type II diabetes in db/db mice by continuous low-dose-rate gamma irradiation

Low-dose-rate radiation modulates various biological responses including carcinogenesis, immunological responses and diabetes. We found that continuous irradiation with low-dose-rate gamma rays ameliorated type II diabetes in db/db mice, diabetic mice that lack leptin receptors. Whole-body exposure of db/db mice to low dose-rate gamma radiation improved glucose clearance without affecting the response to insulin. Histological studies suggested that degeneration of pancreatic islets was significantly suppressed by the radiation. Insulin secretion in response to glucose loading was increased significantly in the irradiated mice. These results suggest that low-dose-rate gamma radiation ameliorates type II diabetes by maintaining insulin secretion, which gradually decreases during the progression of diabetes due to degeneration of pancreatic islets. We also inferred that protection from oxidative damage is involved in the anti-diabetic effect of low-dose-rate gamma rays because expression and activity of pancreatic superoxide dismutase were significantly elevated by low-dose-rate gamma radiation.

Diets rich in polyphenols and vitamin A inhibit the development of type I autoimmune diabetes in nonobese diabetic mice

Type I juvenile diabetes mellitus is characterized by the infiltration of activated T lymphocytes and monocytes into the islets of Langerhans of the pancreas, resulting in inflammation and progressive destruction of the insulin-producing beta cells. We hypothesized that feeding nonobese diabetic (NOD) mice diets rich in polyphenols or vitamin A, both known modulators of immune function, would decrease the autoimmune inflammatory process associated with type I diabetes. NOD mice were fed a control diet (C) and diets containing either 1% freeze-dried grape powder (GP) or 250 IU vitamin A/g (VA; 0.262 micromol retinyl acetate/g) of food. Mice were considered diabetic and killed when blood glucose reached 13.9 mmol/L or greater. By approximately 7 mo of age, 71% of C mice progressed to diabetes. Incidence of diabetes was reduced to 33% (P < 0.05) and 25% (P < 0.05) in mice receiving 1% dietary grape powder and VA, respectively. Splenocytes from mice receiving both GP and VA had lower TNF-alpha production after LPS stimulation than C mice (P < 0.05). Histological analysis of pancreatic tissue showed a significant reduction in the severity of insulitis in the mice receiving GP and VA compared with C mice. These data suggest that diets rich in polyphenols or vitamin A have protective effects against autoimmune inflammatory attack of the islet beta cells and have the potential to reduce the onset and pathogenesis of autoimmune diabetes.