Janette Allison

Induction of Autoimmune Diabetes by Oral Administration of Autoantigen

An antigen administered orally can induce immunological tolerance to a subsequent challenge with the same antigen. Evidence has been provided for the efficacy of this approach in the treatment of human autoimmune diseases such as rheumatoid arthritis and multiple sclerosis. However, oral administration of autoantigen in mice was found to induce a cytotoxic T lymphocyte response that could lead to the onset of autoimmune diabetes. Thus, feeding autoantigen can cause autoimmunity, which suggests that caution should be used when applying this approach to the treatment of human autoimmune diseases.

Transgenic Expression of Mouse Proinsulin II Prevents Diabetes in Nonobese Diabetic Mice

IDDM in humans and in nonobese diabetic (NOD) mice is a T-cell–dependent autoimmune disease in which the β-cells of the pancreatic islets are destroyed. Several putative β-cell autoantigens have been identified, but insulin and its precursor, proinsulin, are the only ones that are β-cell specific. (Pro)insulin may be a key autoantigen in IDDM. To address the role of proinsulin in the development of IDDM, we generated NOD mice transgenic for the mouse proinsulin II gene driven off a major histocompatibility complex (MHC) class II promoter to direct expression of the transgene to MHC class II bearing cells, including those in the thymus, with the aim of deleting proinsulin-reactive T-cells. The mononuclear cell infiltration of the islets (insulitis) is almost completely absent, and diabetes is prevented in these transgenic NOD mice. The mononuclear cell infiltration of the salivary glands (sialitis) and immune responses to ovalbumin (OVA) are not altered, indicating that the protective effect of the transgene is specific for islet pathology and not due to general immunosuppression. We conclude that autoimmunity to proinsulin plays a pivotal role in the development of IDDM.

Glucose induces pancreatic islet cell apoptosis that requires the BH3-only proteins Bim and Puma and multi-BH domain protein Bax

OBJECTIVE High concentrations of circulating glucose are believed to contribute to defective insulin secretion and β-cell function in diabetes and at least some of this effect appears to be caused by glucose-induced β-cell apoptosis. In mammalian cells, apoptotic cell death is controlled by the interplay of proapoptotic and antiapoptotic members of the Bcl-2 family. We investigated the apoptotic pathway induced in mouse pancreatic islet cells after exposure to high concentrations of the reducing sugars ribose and glucose as a model of β-cell death due to long-term metabolic stress. RESEARCH DESIGN AND METHODS Islets isolated from mice lacking molecules implicated in cell death pathways were exposed to high concentrations of glucose or ribose. Apoptosis was measured by analysis of DNA fragmentation and release of mitochondrial cytochrome c. RESULTS Deficiency of interleukin-1 receptors or Fas did not diminish apoptosis, making involvement of inflammatory cytokine receptor or death receptor signaling in glucose-induced apoptosis unlikely. In contrast, overexpression of the prosurvival protein Bcl-2 or deficiency of the apoptosis initiating BH3-only proteins Bim or Puma, or the downstream apoptosis effector Bax, markedly reduced glucose- or ribose-induced killing of islets. Loss of other BH3-only proteins Bid or Noxa, or the Bax-related effector Bak, had no impact on glucose-induced apoptosis. CONCLUSIONS These results implicate the Bcl-2 regulated apoptotic pathway in glucose-induced islet cell killing and indicate points in the pathway at which interventional strategies can be designed.

Induction of peripheral CD8+ T-cell tolerance by cross-presentation of self antigens

Summary: There is now convincing evidence that CD8+ T cells can be activated by professional antigen‐presenting ceils which present antigens derived from non‐lymphoid tissues in association with MHC class I molecules in the draining lymph nodes. This mechanism, referred to as cross‐presentation, enables the immune system to respond to those microorganisms that infect only non‐lymphoid tissues. Consistent with this view, cross‐presentation was found to focus on antigens expressed in high concentrations and those released from dying cells, which can be expected to result from viral infections. Recent evidence, however, demonstrates that high dose self antigens can be cross‐presented constitutively, resulting m the activation of autoreactive CD8+ T cells. This does not lead to auto‐immunity under physiologic conditions, but to CD95‐mediated deletion of the T cells. Cross‐presentation can thus engage a well‐defined pathway of antigen‐induced T‐cell death and purge the immune system of autoreactive CD8+ T cells. Low dose self antigens are not cross‐presented and are consequently ignored. The immune system therefore uses two strategies to avoid CD8+ T‐cell‐mediated autoimmunity in the periphery: deletion of autoreactive CD8+ T cells responding to high dose self antigens and ignorance of self antigens expressed at low concentrations.

Proapoptotic BH3-Only Protein Bid Is Essential For Death Receptor–Induced Apoptosis of Pancreatic β-Cells

OBJECTIVE—Apoptosis of pancreatic β-cells is critical in both diabetes development and failure of islet transplantation. The role in these processes of pro- and antiapoptotic Bcl-2 family proteins, which regulate apoptosis by controlling mitochondrial integrity, remains poorly understood. We investigated the role of the BH3-only protein Bid and the multi-BH domain proapoptotic Bax and Bak, as well as prosurvival Bcl-2, in β-cell apoptosis. RESEARCH DESIGN AND METHODS—We isolated islets from mice lacking Bid, Bax, or Bak and those overexpressing Bcl-2 and exposed them to Fas ligand, tumor necrosis factor (TNF)-α, and proinflammatory cytokines or cytotoxic stimuli that activate the mitochondrial apoptotic pathway (staurosporine, etoposide, γ-radiation, tunicamycin, and thapsigargin). Nuclear fragmentation was measured by flow cytometry. RESULTS—Development and function of islets were not affected by loss of Bid, and Bid-deficient islets were as susceptible as wild-type islets to cytotoxic stimuli that cause apoptosis via the mitochondrial pathway. In contrast, Bid-deficient islets and those overexpressing antiapoptotic Bcl-2 were protected from Fas ligand–induced apoptosis. Bid-deficient islets were also resistant to apoptosis induced by TNF-α plus cycloheximide and were partially resistant to proinflammatory cytokine-induced death. Loss of the multi-BH domain proapoptotic Bax or Bak protected islets partially from death receptor–induced apoptosis. CONCLUSIONS—These results demonstrate that Bid is essential for death receptor–induced apoptosis of islets, similar to its demonstrated role in hepatocytes. This indicates that blocking Bid activity may be useful for protection of islets from immune-mediated attack and possibly also in other pathological states in which β-cells are destroyed.

The Beta Cell in Autoimmune Diabetes: Many Mechanisms and Pathways of Loss

Death of pancreatic beta cells is the final step in the pathogenesis of type 1 diabetes before it becomes clinically apparent. Applying recent basic research about how cells die to the clinical problem of diabetes is a current opportunity and challenge. To date, perforin is the only factor definitely implicated in beta-cell killing in the non-obese diabetic (NOD) mouse model, although some perforin-deficient NOD mice develop diabetes. Our results suggest that other factors that cause beta-cell death remain to be identified.

Apoptosis and beta-cell destruction in pancreatic islets of NOD mice with spontaneous and cyclophosphamide-accelerated diabetes

Summary Autoimmune-mediated destruction of pancreatic islet beta cells leads to insulin-dependent diabetes in non-obese diabetic (NOD) mice. Although both direct cytotoxic T cell- and indirect cytokine-, nitric oxide- or free radical-mediated mechanisms induce beta-cell apoptosis in vitro, beta-cell death in vivo in spontaneous autoimmune diabetes is not well-characterized. Furthermore, whether beta cells die gradually, or rapidly in the late pre-clinical stage, is a question of current interest. To investigate beta-cell death in vivo, we measured the frequency and intra-islet localisation of apoptosis, defined as DNA strand breaks by the terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling (TUNEL) technique, during spontaneous and cyclophosphamide-accelerated diabetes in NOD mice. In spontaneous diabetes, the frequency of apoptosis in islets correlated with the progression of beta-cell destruction with age. Although apoptosis was detected at low frequency within the reduced insulin-positive islet area of pre-diabetic mice at 90 days of age, it was rarely co-localised to beta cells. After acceleration of beta-cell destruction with cyclophosphamide, the frequency of apoptosis reached maximum at 12 days, at which time 3.2 % of apoptotic cells were beta cells. Apoptosis was most frequent in the insulin-negative islet area comprised of mononuclear cell infiltrate and was localized to CD8+ T cells. The rarity of detectable apoptotic beta cells in spontaneous pre-diabetic mice with pronounced insulitis and reduced insulin-positive islet areas most likely reflects the rapid clearance of apoptotic beta cells. Our findings are more consistent with gradual destruction of non-renewable beta-cells in spontaneous diabetes, than with their rapid, accelerated destruction (as after cyclophosphamide) in the late pre-clinical stage. [Diabetologia (1998) 41: 1381–1388]

Rotavirus Infection Accelerates Type 1 Diabetes in Mice with Established Insulitis

ABSTRACT Infection modulates type 1 diabetes, a common autoimmune disease characterized by the destruction of insulin-producing islet β cells in the pancreas. Childhood rotavirus infections have been associated with exacerbations in islet autoimmunity. Nonobese diabetic (NOD) mice develop lymphocytic islet infiltration (insulitis) and then clinical diabetes, whereas NOD8.3 TCR mice, transgenic for a T-cell receptor (TCR) specific for an important islet autoantigen, show more rapid diabetes onset. Oral infection of infant NOD mice with the monkey rotavirus strain RRV delays diabetes development. Here, the effect of RRV infection on diabetes development once insulitis is established was determined. NOD and NOD8.3 TCR mice were inoculated with RRV aged ≥12 and 5 weeks, respectively. Diabetes onset was significantly accelerated in both models (P < 0.024), although RRV infection was asymptomatic and confined to the intestine. The degree of diabetes acceleration was related to the serum antibody titer to RRV. RRV-infected NOD mice showed a possible trend toward increased insulitis development. Infected males showed increased CD8+ T-cell proportions in islets. Levels of β-cell major histocompatibility complex class I expression and islet tumor necrosis factor alpha mRNA were elevated in at least one model. NOD mouse exposure to mouse rotavirus in a natural experiment also accelerated diabetes. Thus, rotavirus infection after β-cell autoimmunity is established affects insulitis and exacerbates diabetes. A possible mechanism involves increased exposure of β cells to immune recognition and activation of autoreactive T cells by proinflammatory cytokines. The timing of infection relative to mouse age and degree of insulitis determines whether diabetes onset is delayed, unaltered, or accelerated.

Targeted insertion of a lacZ reporter gene into the mouse Cer1 locus reveals complex and dynamic expression during embryogenesis.

Summary: The mouse Cer1 (mCer1, Cer‐l, Cerr1) gene encodes one member of a family of cytokines structurally and functionally related to the Xenopus head‐inducing factor, Cerberus (xCer). We generated a mouse line in which the Cer1 gene was inactivated by replacing the first coding exon with a lacZ reporter gene. Mice homozygous for this allele (Cer1lacZ) showed no apparent perturbation of embryogenesis or later development. However, the lacZ reporter revealed a number of hitherto uncharacterised sites of Cer1 expression in late fetal and adult tissues. Preliminary analysis suggests that Cer1 is not essential for their morphogenesis, differentiation, or homeostasis. genesis 26:259–264, 2000.

Transgenic Expression of Dominant-Negative Fas-Associated Death Domain Protein in β Cells Protects against Fas Ligand-Induced Apoptosis and Reduces Spontaneous Diabetes in Nonobese Diabetic Mice

In type 1 diabetes, many effector mechanisms damage the β cell, a key one being perforin/granzyme B production by CD8+ T cells. The death receptor pathway has also been implicated in β cell death, and we have therefore generated NOD mice that express a dominant-negative form of the Fas-associated death domain protein (FADD) adaptor to block death receptor signaling in β cells. Islets developed normally in these animals, indicating that FADD is not necessary for β cell development as it is for vasculogenesis. β cells from the transgenic mice were resistant to killing via the Fas pathway in vitro. In vivo, a reduced incidence of diabetes was found in mice with higher levels of dominant-negative FADD expression. This molecule also blocked signals from the IL-1R in culture, protecting isolated islets from the toxic effects of cytokines and also marginally reducing the levels of Fas up-regulation. These data support a role for death receptors in β cell destruction in NOD mice, but blocking the perforin/granzyme pathway would also be necessary for dominant-negative FADD to have a beneficial clinical effect.