Effective destruction of Fas-deficient insulin-producing beta cells in type 1 diabetes

RIPK1 is dispensable for cell death regulation in β-cells during hyperglycemia

OBJECTIVE

Receptor-interacting protein kinase 1 (RIPK1) orchestrates the decision between cell survival and cell death in response to tumor necrosis factor (TNF) and other cytokines. Whereas the scaffolding function of RIPK1 is crucial to prevent TNF-induced apoptosis and necroptosis, its kinase activity is required for necroptosis and partially for apoptosis. Although TNF is a proinflammatory cytokine associated with β-cell loss in diabetes, the mechanism by which TNF induces β-cell demise remains unclear.

METHODS

Here, we dissected the contribution of RIPK1 scaffold versus kinase functions to β-cell death regulation using mice lacking RIPK1 specifically in β-cells (Ripk1β-KO mice) or expressing a kinase-dead version of RIPK1 (Ripk1D138N mice), respectively. These mice were challenged with streptozotocin, a model of autoimmune diabetes. Moreover, Ripk1β-KO mice were further challenged with a high-fat diet to induce hyperglycemia. For mechanistic studies, pancreatic islets were subjected to various killing and sensitising agents.

RESULTS

Inhibition of RIPK1 kinase activity (Ripk1D138N mice) did not affect the onset and progression of hyperglycemia in a type 1 diabetes model. Moreover, the absence of RIPK1 expression in β-cells did not affect normoglycemia under basal conditions or hyperglycemia under diabetic challenges. Ex vivo, primary pancreatic islets are not sensitised to TNF-induced apoptosis and necroptosis in the absence of RIPK1. Intriguingly, we found that pancreatic islets display high levels of the antiapoptotic cellular FLICE-inhibitory protein (cFLIP) and low levels of apoptosis (Caspase-8) and necroptosis (RIPK3) components. Cycloheximide treatment, which led to a reduction in cFLIP levels, rendered primary islets sensitive to TNF-induced cell death which was fully blocked by caspase inhibition.

CONCLUSIONS

Unlike in many other cell types (e.g., epithelial, and immune), RIPK1 is not required for cell death regulation in β-cells under physiological conditions or diabetic challenges. Moreover, in vivo and in vitro evidence suggest that pancreatic β-cells do not undergo necroptosis but mainly caspase-dependent death in response to TNF. Last, our results show that β-cells have a distinct mode of regulation of TNF-cytotoxicity that is independent of RIPK1 and that may be highly dependent on cFLIP.

Association of the apoptotic markers Apo1/Fas and cCK-18 and the adhesion molecule ICAM-1 with Type 1 diabetes mellitus in children and adolescents

BACKGROUND

Type 1 diabetes mellitus (T1DM) is characterized by immune and metabolic dysregulation. Apo1/Fas is implicated in maintaining homeostasis of the immune system. Cytokeratin-18 (cCK-18) is a predictive marker of liver disorders in T2DM. Intercellular adhesion molecule-1 (ICAM-1) is considered to increase susceptibility to diabetes mellitus. All three markers are associated with endothelial function, apoptosis and diabetes-related complications. The possible role of Apo1/Fas, cCK-18 and ICAM-1 was investigated in children and adolescents with T1DM.

METHOD

Forty-nine (49) children and adolescents with T1DM and 49 controls were included in the study. Somatometric measurements were obtained and the Body Mass Index (BMI) of the participants was calculated. Biochemical parameters were measured by standard laboratory methods and Apo1/Fas, cCK-18 and ICAM-1 were measured using appropriate ELISA kits. The statistical analysis was performed using the IBM SPSS Statistics 23 program.

RESULTS

Apo1/Fas (p = 0.001), cCK-18 (p < 0.001) and ICAM-1 (p < 0.001) were higher in patients with T1DM compared to the controls. Apo1Fas was negatively correlated with glucose (p = 0.042), uric acid (p = 0.026), creatinine (p = 0.022), total cholesterol (p = 0.023) and LDL (p = 0.005) in the controls. In children and adolescents with T1DM, Apo1/Fas was positively correlated with total cholesterol (p = 0.013) and LDL (p = 0.003). ICAM-1 was negatively correlated with creatinine (p = 0.019) in the controls, whereas in patients with T1DM it was negatively correlated with HbA1c (p = 0.05).

CONCLUSIONS

Apo1/Fas, cCK-18 and ICAM-1 may be useful as serological markers for immune and metabolic dysregulation in children and adolescents with T1DM. Also, Apo1/Fas may have a protective role against metabolic complications in healthy children.

A Composite Biomarker Signature of Type 1 Diabetes Risk Identified via Augmentation of Parallel Multi-Omics Data from a Small Cohort

Background

Biomarkers of early pathogenesis of type 1 diabetes (T1D) are crucial to enable effective prevention measures in at-risk populations before significant damage occurs to their insulin producing beta-cell mass. We recently introduced the concept of integrated parallel multi-omics and employed a novel data augmentation approach which identified promising candidate biomarkers from a small cohort of high-risk T1D subjects. We now validate selected biomarkers to generate a potential composite signature of T1D risk.

Methods

Twelve candidate biomarkers, which were identified in the augmented data and selected based on their fold-change relative to healthy controls and cross-reference to proteomics data previously obtained in the expansive TEDDY and DAISY cohorts, were measured in the original samples by ELISA.

Results

All 12 biomarkers had established connections with lipid/lipoprotein metabolism, immune function, inflammation, and diabetes, but only 7 were found to be markedly changed in the high-risk subjects compared to the healthy controls: ApoC1 and PON1 were reduced while CETP, CD36, FGFR1, IGHM, PCSK9, SOD1, and VCAM1 were elevated.

Conclusions

Results further highlight the promise of our data augmentation approach in unmasking important patterns and pathologically significant features in parallel multi-omics datasets obtained from small sample cohorts to facilitate the identification of promising candidate T1D biomarkers for downstream validation. They also support the potential utility of a composite biomarker signature of T1D risk characterized by the changes in the above markers.

SAM protects against alveolar septal cell apoptosis in autoimmune emphysema rats

BACKGROUND

Hypomethylation of the perforin gene promoter in CD4 + T cells, inflammation and oxidative stress, might be involved in alveolar septal cell apoptosis associated with emphysema in rats. This study aimed to investigate the effects of S-adenosylmethionine (SAM) on this kind of apoptosis in rats with autoimmune emphysema.

METHODS

Twenty-four rats were randomly divided into three groups: a normal control group, a model group, and a SAM group. Pathological changes in lung tissues were observed, and the mean linear intercept (MLI) and mean alveolar number (MAN) were measured. The levels of anti-endothelial cell antibodies (AECA) in serum, alveolar septal cell apoptosis, perforin gene promotor methylation in CD4 + T cells in the spleen, and the levels of cytokines, malondialdehyde (MDA), and glutathione (GSH) and the activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) in bronchoalveolar lavage fluid (BALF) were investigated.

RESULTS

The MLI, apoptosis index (AI) of alveolar septal cells, levels of AECA in serum, and levels of tumour necrosis factor-α (TNF-α), matrix metalloproteinase-9 (MMP-9) and MDA in BALF were increased, while the MAN, methylation levels, and the activities of GSH, SOD and GSH-Px in BALF were decreased in the model group compared with those in the normal control group and the SAM group (all P < 0.05). The levels of interleukin-8 (IL-8) in BALF were greater in the model group than in the normal control group (P < 0.05).

CONCLUSIONS

SAM protects against alveolar septal cell apoptosis, airway inflammation and oxidative stress in rats with autoimmune emphysema possibly by partly reversing the hypomethylation of the perforin gene promoter in CD4 + T cells.

Exploring Computational Data Amplification and Imputation for the Discovery of Type 1 Diabetes (T1D) Biomarkers from Limited Human Datasets

BACKGROUND

Type 1 diabetes (T1D) is a devastating disease with serious health complications. Early T1D biomarkers that could enable timely detection and prevention before the onset of clinical symptoms are paramount but currently unavailable. Despite their promise, omics approaches have so far failed to deliver such biomarkers, likely due to the fragmented nature of information obtained through the single omics approach. We recently demonstrated the utility of parallel multi-omics for the identification of T1D biomarker signatures. Our studies also identified challenges.

METHODS

Here, we evaluated a novel computational approach of data imputation and amplification as one way to overcome challenges associated with the relatively small number of subjects in these studies.

RESULTS

Using proprietary algorithms, we amplified our quadra-omics (proteomics, metabolomics, lipidomics, and transcriptomics) dataset from nine subjects a thousand-fold and analyzed the data using Ingenuity Pathway Analysis (IPA) software to assess the change in its analytical capabilities and biomarker prediction power in the amplified datasets compared to the original. These studies showed the ability to identify an increased number of T1D-relevant pathways and biomarkers in such computationally amplified datasets, especially, at imputation ratios close to the "golden ratio" of 38.2%:61.8%. Specifically, the Canonical Pathway and Diseases and Functions modules identified higher numbers of inflammatory pathways and functions relevant to autoimmune T1D, including novel ones not identified in the original data. The Biomarker Prediction module also predicted in the amplified data several unique biomarker candidates with direct links to T1D pathogenesis.

CONCLUSIONS

These preliminary findings indicate that such large-scale data imputation and amplification approaches are useful in facilitating the discovery of candidate integrated biomarker signatures of T1D or other diseases by increasing the predictive range of existing data mining tools, especially when the size of the input data is inherently limited.

Neutralization Versus Reinforcement of Proinflammatory Cytokines to Arrest Autoimmunity in Type 1 Diabetes

As physiological pathways of intercellular communication produced by all cells, cytokines are involved in the pathogenesis of inflammatory insulitis as well as pivotal mediators of immune homeostasis. Proinflammatory cytokines including interleukins, interferons, transforming growth factor-β, tumor necrosis factor-α, and nitric oxide promote destructive insulitis in type 1 diabetes through amplification of the autoimmune reaction, direct toxicity to β-cells, and sensitization of islets to apoptosis. The concept that neutralization of cytokines may be of therapeutic benefit has been tested in few clinical studies, which fell short of inducing sustained remission or achieving disease arrest. Therapeutic failure is explained by the redundant activities of individual cytokines and their combinations, which are rather dispensable in the process of destructive insulitis because other cytolytic pathways efficiently compensate their deficiency. Proinflammatory cytokines are less redundant in regulation of the inflammatory reaction, displaying protective effects through restriction of effector cell activity, reinforcement of suppressor cell function, and participation in islet recovery from injury. Our analysis suggests that the role of cytokines in immune homeostasis overrides their contribution to β-cell death and may be used as potent immunomodulatory agents for therapeutic purposes rather than neutralized.

CHOP Deficiency Ameliorates ERK5 Inhibition-Mediated Exacerbation of Streptozotocin-Induced Hyperglycemia and Pancreatic β-Cell Apoptosis

Streptozotocin (STZ)-induced murine models of type 1 diabetes have been used to examine ER stress during pancreatic β-cell apoptosis, as this ER stress plays important roles in the pathogenesis and development of the disease. However, the mechanisms linking type 1 diabetes to the ER stress-modulating anti-diabetic signaling pathway remain to be addressed, though it was recently established that ERK5 (Extracellular-signal-regulated kinase 5) contributes to the pathogeneses of diabetic complications. This study was undertaken to explore the mechanism whereby ERK5 inhibition instigates pancreatic β-cell apoptosis via an ER stress-dependent signaling pathway. STZ-induced diabetic WT and CHOP deficient mice were i.p. injected every 2 days for 6 days under BIX02189 (a specific ERK5 inhibitor) treatment in order to evaluate the role of ERK5. Hyperglycemia was exacerbated by co-treating C57BL/6J mice with STZ and BIX02189 as compared with mice administered with STZ alone. In addition, immunoblotting data revealed that ERK5 inhibition activated the unfolded protein response pathway accompanying apoptotic events, such as, PARP-1 and caspase-3 cleavage. Interestingly, ERK5 inhibition-induced exacerbation of pancreatic β-cell apoptosis was inhibited in CHOP deficient mice. Moreover, transduction of adenovirus encoding an active mutant form of MEK5α, an upstream kinase of ERK5, inhibited STZ-induced unfolded protein responses and β-cell apoptosis. These results suggest that ERK5 protects against STZ-induced pancreatic β-cell apoptosis and hyperglycemia by interrupting the ER stress-mediated apoptotic pathway.

Emerging roles for A20 in islet biology and pathology

A20 is most characteristically described in terms relating to inflammation and inflammatory pathologies. The emerging understanding of inflammation in the etiology of diabetes mellitus lays the framework for considering a central role for A20 in this disease process. Diabetes mellitus is considered a major health issue, and describes a group of common metabolic disorders pathophysiologically characterized by hyperglycemia. Within islets of Langherhans, the endocrine powerhouse of the pancreas, are the insulin-producing pancreatic beta-cells. Loss of beta-cell mass and function to inflammation and apoptosis is a major contributing factor to diabetes. Consequently, restoring functional beta-cell mass via transplantation represents a therapeutic option for diabetes. Unfortunately, transplanted islets also suffers from loss of beta-cell function and mass fueled by a multifactorial inflammatory cycle triggered by islet isolation prior to transplantation, the ischemic environment at transplantation as well as allogeneic or recurrent auto-immune responses. Activation of the transcription factor NF-kappaB is a central mediator of inflammatory mediated beta-cell dysfunction and loss. Accordingly, a plethora of strategies to block NF-kappaB activation in islets and hence limit beta-cell loss have been explored, with mixed success. We propose that the relatively poor efficacy of NF-kappaB blockade in beta-cells is due to concommittant loss of the important, NF-kappaB regulated anti-apoptotic and anti-inflammatory protein A20. A20 has been identified as a beta-cell expressed gene, raising questions about its role in beta-cell development and function, and in beta-cell related pathologies. Involvement of apoptosis, inflammation and NF-kappaB activation as beta-cell factors contributing to the pathophysiology of diabetes, coupled with the knowledge that beta-cells express the A20 gene, implies an important role for A20 in both normal beta-cell biology as well as beta-cell related pathology. Genome wide association studies (GWAS) linking single nucleotide polymorphisms in the A20 gene with the occurrence of diabetes and its complications support this hypothesis. In this chapter we review data supporting the role of A20 in beta-cell health and disease. Furthermore, by way of their specialized function in metabolism, pancreatic beta-cells also provide opportunities to explore the biology of A20 in scenarios beyond inflammation.

Role of pancreatic β-cell death and inflammation in diabetes

Apoptosis of pancreatic β-cells is the final step in the development of type 1 diabetes (T1D), leading to critically diminished β-cell mass and contributing to the onset of hyperglycaemia. The spontaneous apoptosis of pancreatic β-cells during pancreas ontogeny also induces cell death-associated inflammation, stimulates antigen-presenting cells and sensitizes naïve diabetogenic T cells. The role of pancreatic β-cell death in type 2 diabetes (T2D) is less clear. In the preclinical period of T2D, hyperinsulinaemia and β-cell hyperplasia develop to compensate for insulin resistance, which is clearly seen in animal models of T2D. For the development of overt T2D, relative insulin deficiency is critical in addition to insulin resistance. Insulin deficiency could be due to β-cell dysfunction and/or decreased β-cell mass. Pancreatic β-cell apoptosis due to lipid injury (lipoapoptosis), endoplasmic reticulum (ER) stress or JNK activation could contribute to the decreased β-cell mass in T2D. Activation of inflammasomes by lipid injury, ER stress, human islet amyloid polypeptide, hyperglycaemia or autophagy insufficiency could also lead to β-cell death or dysfunction. Thus, β-cell death and cell death-associated inflammation through innate immune receptors could be important in both T1D and T2D.

Genetically engineered human islets protected from CD8-mediated autoimmune destruction in vivo

Islet transplantation is a promising therapy for type 1 diabetes, but graft function and survival are compromised by recurrent islet autoimmunity. Immunoprotection of islets will be required to improve clinical outcome. We engineered human β cells to express herpesvirus-encoded immune-evasion proteins, "immunevasins." The capacity of immunevasins to protect β cells from autoreactive T-cell killing was evaluated in vitro and in vivo in humanized mice. Lentiviral vectors were used for efficient genetic modification of primary human β cells without impairing their function. Using a novel β-cell-specific reporter gene assay, we show that autoreactive cytotoxic CD8(+) T-cell clones isolated from patients with recent onset diabetes selectively destroyed human β cells, and that coexpression of the human cytomegalovirus-encoded US2 protein and serine proteinase inhibitor 9 offers highly efficient protection in vitro. Moreover, coimplantation of these genetically modified pseudoislets with β-cell-specific cytotoxic T cells into immunodeficient mice achieves preserved human insulin production and C-peptide secretion. Collectively, our data provide proof of concept that human β cells can be efficiently genetically modified to provide protection from killing mediated by autoreactive T cells and retain their function in vitro and in vivo.

Foxp3(+) regulatory T cells in mouse models of type 1 diabetes

Studies on human type 1 diabetes (T1D) are facilitated by the availability of animal models such as nonobese diabetic (NOD) mice that spontaneously develop autoimmune diabetes, as well as a variety of genetically engineered mouse models with reduced genetic and pathogenic complexity, as compared to the spontaneous NOD model. In recent years, increasing evidence has implicated CD4(+)CD25(+) regulatory T (Treg) cells expressing the transcription factor Foxp3 in both the breakdown of self-tolerance and the restoration of immune homeostasis in T1D. In this paper, we provide an overview of currently available mouse models to study the role of Foxp3(+) Treg cells in the control of destructive β cell autoimmunity, including a novel NOD model that allows specific and temporally controlled deletion of Foxp3(+) Treg cells.

Pathogenic mechanisms in type 1 diabetes: the islet is both target and driver of disease

Recent advances in our understanding of the pathogenesis of type 1 diabetes have occurred in all steps of the disease. This review outlines the pathogenic mechanisms utilized by the immune system to mediate destruction of the pancreatic beta-cells. The autoimmune response against beta-cells appears to begin in the pancreatic lymph node where T cells, which have escaped negative selection in the thymus, first meet beta-cell antigens presented by dendritic cells. Proinsulin is an important antigen in early diabetes. T cells migrate to the islets via the circulation and establish insulitis initially around the islets. T cells within insulitis are specific for islet antigens rather than bystanders. Pathogenic CD4⁺ T cells may recognize peptides from proinsulin which are produced locally within the islet. CD8⁺ T cells differentiate into effector T cells in islets and then kill beta-cells, primarily via the perforin-granzyme pathway. Cytokines do not appear to be important cytotoxic molecules in vivo. Maturation of the immune response within the islet is now understood to contribute to diabetes, and highlights the islet as both driver and target of the disease. The majority of our knowledge of these pathogenic processes is derived from the NOD mouse model, although some processes are mirrored in the human disease. However, more work is required to translate the data from the NOD mouse to our understanding of human diabetes pathogenesis. New technology, especially MHC tetramers and modern imaging, will enhance our understanding of the pathogenic mechanisms.

Cytotoxic mechanisms employed by mouse T cells to destroy pancreatic β-cells

Several cytotoxic mechanisms have been attributed to T cells participating in β-cell death in type 1 diabetes. However, sensitivity of β-cells to these mechanisms in vitro and in vivo is likely to be different. Moreover, CD4⁺ and CD8⁺ T cells may use distinct mechanisms to cause β-cell demise that possibly involve activation of third-party cytotoxic cells. We used the transfer of genetically modified diabetogenic T cells into normal, mutant, and bone marrow chimeric recipients to test the contribution of major cytotoxic mechanisms in β-cell death. We found that 1) the killing of β-cells by CD4⁺ T cells required activation of the recipient's own cytotoxic cells via tumor necrosis factor-α (TNF-α); 2) CD8⁺ T-cell cytotoxic mechanisms destroying β-cells were limited to perforin and Fas ligand, as double knockouts of these molecules abrogated the ability of T cells to cause diabetes; and 3) individual CD8⁺ T-cell clones chose their cytotoxic weaponry by a yet unknown mechanism and destroyed their targets via either Fas-independent or Fas-dependent (~40% of clones) pathways. Fas-dependent destruction was assisted by TNF-α.

The potential of Fas ligand (apoptosis-inducing molecule) as an unconventional therapeutic target in type 1 diabetes

The development of type 1 diabetes (T1D) is driven by autoreactive T cells that attack and destroy the insulin-producing β-cells in pancreatic islets, forcing patients to take multiple daily insulin injections. Insulin therapy, however, is not a cure and diabetic patients often develop serious long-term microvascular and cardiovascular complications. Therefore, intensive efforts are being directed toward developing safe immunotherapy for the disease that does not impair host defense and preserves β-cells, leading to better glycemic control than exogenous insulin therapy. Engineering therapies that differentially cripple or tolerate autoreactive diabetogenic T cells while sparing protective T cells necessary for maintaining a competent immune system has proven challenging. Instead, recent efforts have focused on modulating or resetting the immune system through global but transient deletion of T cells or B cells using anti-CD3 or anti-CD20 mAb, respectively. However, phase III clinical trials have shown promising but modest efficacy so far with these approaches. Therefore, there is a need to identify novel biological targets that do not fit the classic properties of being involved in adaptive immune cell activation. In this prospective, we provide preclinical evidence that targeting Fas ligand (FasL) may provide a unique opportunity to prevent or cure T1D and perhaps other organ-specific autoimmune diseases without causing immune suppression. Unlike conventional targets that are involved in T and B lymphocyte activation (such as CD3 and CD20, respectively), FasL is an apoptosis-inducing surface molecule that triggers cell death by binding to Fas (also known as CD95 Apo-1). Therefore, targeting FasL is not expected to cause immune suppression, the Achilles Heel of conventional approaches. We will discuss the hypothesis that targeting FasL has unique benefits that are not offered by current immunomodulatory approaches.

Requirement of myeloid cell-specific Fas expression for prevention of systemic autoimmunity in mice

OBJECTIVE

The death receptor Fas is a critical mediator of the extrinsic apoptotic pathway, and its role in mediating lymphoproliferation has been extensively examined. The present study was undertaken to investigate the impact of myeloid cell-specific loss of Fas.

METHODS

Mice with Fas flanked by loxP sites (Fas(flox/flox) ) were crossed with mice expressing Cre under control of the murine lysozyme M gene promoter (Cre(LysM) ), which functions in mature lysozyme-expressing cells of the myelomonocytic lineage. The genotype for Cre(LysM) Fas(flox/flox) mice was verified by polymerase chain reaction and flow cytometric analysis. Flow cytometric analysis was also used to characterize myeloid, dendritic, and lymphoid cell distribution and activation in bone marrow, blood, and spleen. Luminex-based assays and enzyme-linked immunosorbent assays were used to measure serum cytokine/chemokine and immunoglobulin levels. Renal damage or dysfunction was examined by immunohistochemical and immunofluorescence analysis.

RESULTS

Cre(LysM) Fas(flox/flox) mice exhibited a systemic lupus erythematosus (SLE)-like disease that included leukocytosis, splenomegaly, hypergammaglobulinemia, antinuclear autoantibody and proinflammatory cytokine production, and glomerulonephritis. Loss of Fas in myeloid cells increased levels of both Gr-1(low) and Gr-1(intermediate) blood monocytes and splenic macrophages and, in a paracrine manner, incited activation of conventional dendritic cells and lymphocytes in Cre(LysM) Fas(flox/flox) mice.

CONCLUSION

Taken together, these results suggest that loss of Fas in myeloid cells is sufficient to induce inflammatory phenotypes in mice, reminiscent of an SLE-like disease. Thus, Fas in myeloid cells may be considered a suppressor of systemic autoimmunity.

The pro-apoptotic BH3-only protein Bid is dispensable for development of insulitis and diabetes in the non-obese diabetic mouse

Type 1 diabetes is caused by death of insulin-producing pancreatic beta cells. Beta-cell apoptosis induced by FasL may be important in type 1 diabetes in humans and in the non-obese diabetic (NOD) mouse model. Deficiency of the pro-apoptotic BH3-only molecule Bid protects beta cells from FasL-induced apoptosis in vitro. We aimed to test the requirement for Bid, and the significance of Bid-dependent FasL-induced beta-cell apoptosis in type 1 diabetes. We backcrossed Bid-deficient mice, produced by homologous recombination and thus without transgene overexpression, onto a NOD genetic background. Genome-wide single nucleotide polymorphism analysis demonstrated that diabetes-related genetic regions were NOD genotype. Transferred beta cell antigen-specific CD8+ T cells proliferated normally in the pancreatic lymph nodes of Bid-deficient mice. Moreover, Bid-deficient NOD mice developed type 1 diabetes and insulitis similarly to wild-type NOD mice. Our data indicate that beta-cell apoptosis in type 1 diabetes can proceed without Fas-induced killing mediated by the BH3-only protein Bid.

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.

Inhibition of Fas ligand in NOD mice unmasks a protective role for IL-10 against insulitis development

Type 1 diabetes mellitus (T1D) is an autoimmune disease caused by the destruction of pancreatic insulin-producing β cells by autoreactive T cells early in life. Despite daily insulin injections, patients typically develop cardiovascular and other complications; and intensive efforts are being directed toward identifying therapeutic targets to prevent the disease without directly impinging on the host defense. Fas ligand (FasL) is one potential target. Fas-FasL interactions primarily regulate T-cell homeostasis, not activation. Nevertheless, spontaneous gene mutation of Fas (called lpr mutation) or FasL (called the gld mutation) prevents autoimmune diabetes in nonobese diabetic (NOD) mice, the widely used model for T1D. Furthermore, although homozygous gld mutations cause age-dependent lymphoproliferation, limiting the gld mutation to one allele (NOD-gld/+) or treating NOD-wild-type mice with FasL-neutralizing monoclonal antibody completely prevents the disease development without causing lymphoproliferation or immune suppression. Herein, we show that the heterozygous gld mutation inhibits the accumulation of diabetogenic T cells in the pancreas, without interfering with their proliferation and expansion in the draining pancreatic lymph nodes. Pancreata from NOD-gld/+ mice contained B cells that expressed CD5 and produced IL-10, which was critical for maintenance of the disease resistance because its neutralization with an IL-10 receptor-blocking monoclonal antibody allowed accumulation of CD4 T cells in the pancreas and led to insulitis development. The results provide novel insights into the pathogenesis of T1D that could have important therapeutic implications.

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.

Immunotherapeutic targets in estrogen deficiency-dependent Sjögren's syndrome-related manifestations

Although a number of autoimmune diseases are known to develop in postmenopausal women, the mechanisms by which estrogen deficiency influences autoimmunity remain unclear. Previously, we found that tissue-specific apoptosis in the exocrine glands in estrogen-deficient mice may contribute to the development of autoimmune exocrinopathy. We found that RbAp48 overexpression induces p53-mediated apoptosis in the exocrine glands depending on estrogen deficiency. RbAp48-inducible transfectants result in rapid apoptosis with p53 phosphorylation (Ser9), and alpha-fodrin cleavage. Indeed, transgenic expression of the RbAp48 gene induced apoptosis in the exocrine glands, resulting in the development of autoimmune exocrinopathy resembling Sjögren's syndrome (SS). CD4(+) T-cell-mediated autoimmune lesions were aggravated with age, in association with production of autoantibodies against SS-A, SS-B and alpha-fodrin. These findings demonstrated that estrogen deficiency initiates tissue-specific apoptosis in the exocrine gland cells through RbAp48 overexpression and exerts a possible gender-based risk of autoimmune exocrinopathy in postmenopausal women. Thus, these data indicate RbAp48 to be a novel immunotherapeutic target for preventing epithelial cell apoptosis and the development of gender-based autoimmune exocrinopathy.

Dendritic cells recruit T cell exosomes via exosomal LFA-1 leading to inhibition of CD8+ CTL responses through downregulation of peptide/MHC class I and Fas ligand-mediated cytotoxicity

Active T cells release bioactive exosomes (EXOs). However, its potential modulation in immune responses is elusive. In this study, we in vitro generated active OVA-specific CD8(+) T cells by cultivation of OVA-pulsed dendritic cells (DC(OVA)) with naive CD8(+) T cells derived from OVA-specific TCR transgenic OTI mice and purified EXOs from CD8(+) T cell culture supernatant by differential ultracentrifugation. We then investigated the suppressive effect of T cell EXOs on DC(OVA)-mediated CD8(+) CTL responses and antitumor immunity. We found that DC(OVA) uptake OTI T cell EXOs expressing OVA-specific TCRs and Fas ligand via peptide/MHC Ag I-TCR and CD54-LFA-1 interactions leading to downregulation of peptide/MHC Ag I expression and induction of apoptosis of DC(OVA) via Fas/Fas ligand pathway. We demonstrated that OVA-specific OTI T cell EXOs, but not lymphocytic choriomeningitis virus-specific TCR transgenic mouse CD8(+) T cell EXOs, can inhibit DC(OVA)-stimulated CD8(+) CTL responses and antitumor immunity against OVA-expressing B16 melanoma. In addition, these T cell EXOs can also inhibit DC(OVA)-mediated CD8(+) CTL-induced diabetes in transgenic rat insulin promoter-mOVA mice. Interestingly, the anti-LFA-1 Ab treatment significantly reduces T cell EXO-induced inhibition of CD8(+) CTL responses in both antitumor immunity and autoimmunity. EXOs released from T cell hybridoma RF3370 cells expressing OTI CD8(+) TCRs have a similar inhibitory effect as T cell EXOs in DC(OVA)-stimulated CTL responses and antitumor immunity. Therefore, our data indicate that Ag-specific CD8(+) T cells can modulate immune responses via T cell-released EXOs, and T cell EXOs may be useful for treatment of autoimmune diseases.

Analysis of gene profile, steady state proliferation and apoptosis of double-negative T cells in the periphery and gut epithelium provides new insights into the biological functions of the Fas pathway

Considerable progress has been made in understanding the Fas pathway at the molecular and cellular levels, but fundamental questions about the overall biological role of the Fas pathway remain unresolved. A major question is why lymphoproliferation caused by the lpr mutation of Fas and gld mutation of FasL ligand (FasL) is dominated by CD4(-) and CD8(-) double-negative alphabeta T cells (DN T cells) that are otherwise rare components of the peripheral T cell repertoire. A second unresolved question is why inactivation of the Fas pathway prevents organ-specific autoimmunity (including as type 1 diabetes and multiple sclerosis) while causing systemic lymphoproliferation? Understanding the mechanisms of these processes could uncover important aspects of the biological role of the Fas pathway and could have significant therapeutic implications. For example, revealing the basis of how inactivation of the Fas pathway prevents organ-specific autoimmunity could lead to new immunotherapeutic strategies to promote self tolerance without causing immunosuppression, as the Fas pathway is not essential for T cell activation. Here we discuss recent and new findings from my laboratory that address these questions. On the basis of these findings, we propose a new role for the Fas pathway in sequestration of DN T cells within the gut epithelium.

Perforin: more than just a pore-forming protein

Cellular apoptosis induced by T cells is mainly mediated by two pathways. One, granule exocytosis utilizes perforin/granzymes. The other involves signaling through death receptors of the TNF-alpha R super-family, especially FasL. Perforin plays a central role in apoptosis induced by granzymes. However, the mechanisms of perforin-mediated cytotoxicity are still not elucidated completely. Perforin is not only a pore-forming protein, but also performs multiple biological functions or perforin performs one biological function (cytolysis), but has multiple biological implications in the cellular immune responses, including regulation of proliferation of CD8+ CTLs.

Executioners of apoptosis in pancreatic {beta}-cells: not just for cell death

Pancreatic beta-cell mass is dynamic and is regulated by beta-cell proliferation, neogenesis, and apoptosis. Under physiological conditions, apoptosis is tightly regulated with a slow, net rise in beta-cell mass over time. Excessive beta-cell apoptosis is an important contributor to both type 1 and type 2 diabetes development. Therefore, much effort has been given recently to better understand the mechanisms of apoptosis that occur both during physiological homeostasis and during the course of both types of diabetes. Caspases are the executioners of apoptosis that ultimately result in cell suicide. In mammals, there are 14 caspases, of which many participate in the apoptotic pathways. Genetic mouse models have been important tools for elucidation of the specific apoptotic pathways that play an essential role in beta-cell apoptosis under physiological and pathological conditions. This review focuses on the diverse roles of each of the specific caspases and their regulators, unveiling both the classical apoptotic roles as well as emerging nonapoptotic roles.

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.

Deletion of Fas in the pancreatic beta-cells leads to enhanced insulin secretion

Fas/Fas ligand belongs to the tumor necrosis factor superfamily of receptors/ligands and is best known for its role in apoptosis. However, recent evidence supports its role in other cellular responses, including proliferation and survival. Although Fas has been implicated as an essential mediator of beta-cell death in the pathogenesis of type 1 diabetes, the essential role of Fas specifically in pancreatic beta-cells has been found to be controversial. Moreover, the role of Fas on beta-cell homeostasis and function is not clear. The objective of this study is to determine the role of Fas specifically in beta-cells under both physiological and diabetes models. Mice with Fas deletion specifically in the beta-cells were generated using the Cre-loxP system. Cre-mediated Fas deletion was under the control of the rat insulin promoter. Absence of Fas in beta-cells leads to complete protection against FasL-induced cell death. However, Fas is not essential in determining beta-cell mass or susceptibility to streptozotocin- or HFD-induced diabetes. Importantly, Fas deletion in beta-cells leads to increased p65 expression, enhanced glucose tolerance, and glucose-stimulated insulin secretion, with increased exocytosis as manifested by increased changes in membrane capacitance and increased expression of Syntaxin1A, VAMP2, and munc18a. Together, our study shows that Fas in the beta-cells indeed plays an essential role in the canonical death receptor-mediated apoptosis but is not essential in regulating beta-cell mass or diabetes development. However, beta-cell Fas is critical in the regulation of glucose homeostasis through regulation of the exocytosis machinery.

Active CD4+ helper T cells directly stimulate CD8+ cytotoxic T lymphocyte responses in wild-type and MHC II gene knockout C57BL/6 mice and transgenic RIP-mOVA mice expressing islet beta-cell ovalbumin antigen leading to diabetes

CD4+ helper T (Th) cells play crucial role in priming, expansion and survival of CD8+ cytotoxic T lymphocytes (CTLs). However, how CD4+ Th cell's help is delivered to CD8+ T cells in vivo is still unclear. We previously demonstrated that CD4+ Th cells can acquire ovalbumin (OVA) peptide/major histocompatibility complex (pMHC I) and costimulatory CD80 by OVA-pulsed DC (DC(OVA)) stimulation, and then stimulate OVA-specific CD8+ CTL responses in C57BL/6 mice. In this study, we further investigated CD4+ Th cell's effect on stimulation of CD8 CTL responses in major histocompatibility complex (MHC II) gene knockout (KO) mice and transgenic rat insulin promoter (RIP)-mOVA mice with moderate expression of self OVA by using CD4+ Th cells or Th cells with various gene deficiency. We demonstrated that the in vitro DC(OVA)-activated CD4+ Th cells (3 x 10(6) cells/mouse) can directly stimulate OVA-specific CD8+ T-cell responses in wild-type C57BL/6 mice and MHC II gene KO mice lacking CD4+ T cells. A large amount of CD4+ Th cells (12 x 10(6) cells/mouse) can even overcome OVA-specific immune tolerance in transgenic RIP-mOVA mice, leading to CD8+ CTL-mediated mouse pancreatic islet destruction and diabetes. The stimulatory effect of CD4+ Th cells is mediated by its IL-2 secretion and CD40L and CD80 costimulations, and is specifically delivered to OVA-specific CD8+ T cells in vivo via its acquired pMHC I complexes. Therefore, the above elucidated principles for CD4+ Th cells will have substantial implications in autoimmunity and antitumor immunity, and regulatory T-cell-dependent immune suppression.

Role of perforin-mediated cell apoptosis in murine models of infusion-induced bone marrow failure

OBJECTIVE

To investigate the role of perforin-mediated cell apoptosis in murine models of immune-mediated bone marrow (BM) failure.

MATERIALS AND METHODS

We compared C57BL/6J (B6) mice carrying a perforin gene deletion (Prf(-/-)) with wild-type (WT) controls for cellular composition in lymphohematopoietic tissues. Lymph node (LN) cells from Prf(-/-) mice were coincubated with BM cells from B10-H2(b)/LilMcdJ (C.B10) mice in an apoptosis assay in vitro. We then infused Prf(-/-) and WT B6 LN cells into sublethally irradiated C.B10 and CByB6F1 recipients with mismatches at the minor and major histocompatibility loci, respectively, in order to induce BM failure. Cellular composition was analyzed by flow cytometry.

RESULTS

Prf(-/-) mice showed normal lymphoid cell composition, but Prf(-/-) LN cells had reduced ability to induce C.B10 BM cell apoptosis in vitro. Infusion of 5 to 10 x 10(6) Prf(-/-) LN cells produced obvious BM failure in C.B10 and CByB6F1 recipients; pancytopenia and BM hypocellularity were only slightly less severe than those caused by infusion of 5 x 10(6) WT B6 LN cells. Infused Prf(-/-) LN cells showed less T-cell expansion, normal T-cell activation, and higher proportions of T cells expressing gamma-interferon, tissue necrosis factor-alpha, and Fas ligand CD178, in comparison to infused WT B6 LN cells. Fas expression was equally high in residual BM cells in recipient of both Prf(-/-) and B6 LN cells.

CONCLUSION

Perforin deficiency alters T-cell expansion but upregulates T-cell Fas ligand expression. Perforin-mediated cell death appears to play a minor role in mouse models of immune-mediated BM failure.

Peculiar subcellular localization of Fas antigen in human and mouse spermatozoa

The highly polarized structure and function of mammalian spermatozoa dictate that these cells compartmentalize specific metabolic and signaling pathways to regions where they are needed. Fas was initially identified as membrane receptor for pro-apoptotic signals, has been recently recognized as a molecule with pleiotropic functions. In this article, we provide evidence of a peculiar Fas localization: it is closely associated to the perinucleus, mainly at the level of the inner acrosomal membrane, as well as in the inner compartment of mitochondria. Immunoelectron microscopy and Western blot analysis indicated that intracellular Fas was associated with mitochondria in mouse epididymal spermatozoa. Accordingly, also in human ejaculated sperm, immunofluorescence analysis showed Fas localized in the middle piece of sperm flagellum where mitochondria are grouped. The potential functional implications of these findings are discussed.

In vivo effects of cytokines on pancreatic beta-cells in models of type I diabetes dependent on CD4(+) T lymphocytes

CD4(+) T cells can actively kill beta-cells in type I diabetes as well as help CD8(+) T cells become cytolytic. Cytokines have the potential to kill beta-cells, or upregulate Fas on beta-cells, and increase their susceptibility to FasL. We investigated the direct effects of cytokines on beta-cells in perforin-deficient non-obese diabetic (NOD) mice and NOD4.1 TCR transgenic mice, two models in which CD8(+) T cells play a less dominant role. Inhibiting the effects of cytokines by the overexpression of suppressor of cytokine signalling-1 (SOCS1) in beta-cells did not reduce diabetes or insulitis in perforin-deficient NOD, NOD4.1 or interleukin (IL)-1 receptor-deficient NOD4.1 mice. SOCS1 overexpression prevented Fas upregulation on NOD4.1 beta-cells, but did not prevent islet destruction because SOCS1 transgenic islets were killed when grafted into NOD4.1.scid mice. Likewise, Fas-deficient NOD.lpr islets were destroyed in NOD4.1 mice. Although blocking the effects of interferon (IFN)gamma on beta-cells did not affect diabetes in NOD4.1 mice, global deficiency of IFNgammaR2 reduced diabetes and insulitis, suggesting that IFNgamma is involved in CD4(+) T-cell activation or migration. Our data show that beta-cells under attack by CD4(+) T cells are not destroyed by the effects of cytokines including IFNgamma and IL-1 or Fas-dependent cytotoxicity.

Expression of the retinoblastoma protein RbAp48 in exocrine glands leads to Sjögren's syndrome-like autoimmune exocrinopathy

Although several autoimmune diseases are known to develop in postmenopausal women, the mechanisms by which estrogen deficiency influences autoimmunity remain unclear. Recently, we found that retinoblastoma-associated protein 48 (RbAp48) induces tissue-specific apoptosis in the exocrine glands depending on the level of estrogen deficiency. In this study, we report that transgenic (Tg) expression of RbAp48 resulted in the development of autoimmune exocrinopathy resembling Sjögren's syndrome. CD4(+) T cell-mediated autoimmune lesions were aggravated with age, in association with autoantibody productions. Surprisingly, we obtained evidence that salivary and lacrimal epithelial cells can produce interferon-gamma (IFN-gamma) in addition to interleukin-18, which activates IFN regulatory factor-1 and class II transactivator. Indeed, autoimmune lesions in Rag2(-/-) mice were induced by the adoptive transfer of lymph node T cells from RbAp48-Tg mice. These results indicate a novel immunocompetent role of epithelial cells that can produce IFN-gamma, resulting in loss of local tolerance before developing gender-based autoimmunity.

Mouse vanin-1 is cytoprotective for islet beta cells and regulates the development of type 1 diabetes

AIMS/HYPOTHESIS

Islet cell death is a key initiating and perpetuating event in type 1 diabetes and involves both immune-mediated and endogenous mechanisms. The epithelial pantetheinase vanin-1 is proinflammatory and cytoprotective via cysteamine release in some tissues. We investigated the impact of a vanin-1 deficiency on islet death and type 1 diabetes incidence.

METHODS

Vanin-1-deficient mice were produced and tested in drug-induced and autoimmune diabetes models. The contribution of vanin-1 to islet survival versus immune responses was evaluated using lymphocyte transfer and islet culture experiments.

RESULTS

The vanin-1/cysteamine pathway contributes to the protection of islet beta cells from streptozotocin-induced death in vitro and in vivo. Furthermore, vanin-1-deficient NOD mice showed a significant aggravation of diabetes, which depended upon loss of vanin-1 expression by host tissues. This increased islet fragility was accompanied by greater CD4+ insulitis without impairment of regulatory cells. Addition of cystamine, the product of pantetheinase activity, protected islets in vitro and compensated for vanin-1 deficiency in vivo.

CONCLUSIONS/INTERPRETATION

This study unravels a major cytoprotective role of cysteamine for islet cells and suggests that modulation of pantetheinase activity may offer alternative strategies to maintain islet cell homeostasis.

Distinct local immunogenic stimuli dictate differential requirements for CD4+ and CD8+ T cell subsets in the pathogenesis of spontaneous autoimmune diabetes

The strong MHC class II association in human as well as murine Type 1 diabetes (T1D) suggests a central role for CD4+T cells in the disease pathogenesis. Nonetheless, CD8+T cells also play a role in the pathogenic process. We describe how CD4+ or CD8+T cells can contribute differentially to the pathogenesis of T1D using the HLA-DQ8 transgenic mouse models. HLA-DQ8 transgenic mice expressing the costimulatory molecule, B7.1 (RIP.B7.1), or the proinflammatory cytokine, TNF-alpha (RIP.TNF) or both (RIP.B7.RIP.TNF) under the control of rat insulin promoter (RIP) were used. Our observations indicate that in the RIP-B7 model, CD4+T cells were absolutely required for diabetes to occur. However, when CD8+ T cells were also present, the incidence of diabetes increased. On the other hand, in the RIP-TNF model, CD8+T cells were absolutely required for diabetes to occur. Interestingly, when CD4+T cells were also present, the incidence of diabetes decreased. In the RIP-B7.RIP-TNF double transgenic mouse model, either CD4+ or CD8+T cells were sufficient to precipitate diabetes in 100% of the animals. Thus, the relative roles of CD4+ or CD8+T cells in the pathogenesis of T1D are possibly determined by the local inflammatory stimuli.

The vicious cycle of apoptotic beta-cell death in type 1 diabetes

Autoimmune insulitis, the cause of type 1 diabetes, evolves through several discrete stages that culminate in beta-cell death. In the first stage, antigenic epitopes of B-cell-specific peptides are processed by antigen presenting cells in local lymph nodes, and auto-reactive lymphocyte clones are propagated. Subsequently, cell-mediated and direct cytokine-mediated reactions are generated against the beta-cells, and the beta-cells are sensitized to apoptosis. Ironically, the beta-cells themselves contribute some of the cytokines and chemokines that provoke the immune reaction within the islets. Once this vicious cycle of autoimmunity is fully developed, the fate of the beta-cells in the islets is sealed, and clinical diabetes inevitably ensues. Differences in various aspects of these concurrent events appear to underlie the significant discrepancies in experimental data observed in experimental models that simulate autoimmune insulitis.

Protection from autoimmune diabetes and T-cell lymphoproliferation induced by FasL mutation are differentially regulated and can be uncoupled pharmacologically

Spontaneous mutation of Fas (lpr) or FasL (gld) completely protects nonobese diabetic mice from autoimmune diabetes but also causes massive double-negative T-cell lymphoproliferation. In this study, we used bone marrow chimeras and adoptive transfer analysis to investigate further the role of FasL in the pathogenesis of autoimmune diabetes and to determine whether gld-induced tolerance and double-negative T-cell lymphoproliferation can be uncoupled from each other. We show that FasL expressed on hematopoietic and nonhematopoietic compartments plays nonredundant roles in the pathogenesis of autoimmune diabetes. Mutation of FasL in either compartment interferes with the autoimmune process and prevents onset of diabetes, but FasL expressed in the hematopoietic compartment is the dominant regulator of T-cell homeostasis. Furthermore, pathogenesis of diabetes is dependent on normal FasL expression in both compartments, whereas only minimal FasL function is required to maintain T-cell homeostasis. Consequently, partial disruption of FasL protects from autoimmune diabetes without causing T-cell lymphoproliferation. This is demonstrated genetically in nonobese diabetic-gld/+ mice and pharmacologically by using FasL-neutralizing antibody. These results have important implications for understanding the role of the Fas pathway in pathogenesis of autoimmune diseases and for designing novel FasL-modulating therapies.

The CD95 receptor: apoptosis revisited

CD95 is the quintessential death receptor and, when it is bound by ligand, cells undergo apoptosis. Recent evidence suggests, however, that CD95 mediates not only apoptosis but also diverse nonapoptotic functions depending on the tissue and the conditions.

Cytotoxic T-cells from T-cell receptor transgenic NOD8.3 mice destroy beta-cells via the perforin and Fas pathways

Cytotoxic T-cells are the major mediators of beta-cell destruction in type 1 diabetes, but the molecular mechanisms are not definitively established. We have examined the contribution of perforin and Fas ligand to beta-cell destruction using islet-specific CD8(+) T-cells from T-cell receptor transgenic NOD8.3 mice. NOD8.3 T-cells killed Fas-deficient islets in vitro and in vivo. Perforin-deficient NOD8.3 T-cells were able to destroy wild-type but not Fas-deficient islets in vitro. These results imply that NOD8.3 T-cells use both pathways and that Fas is required for beta-cell killing only when perforin is missing. Consistent with this theory, transgenic NOD8.3 mice with beta-cells that do not respond to Fas ligation were not protected from diabetes. We next investigated the mechanism of protection provided by overexpression of suppressor of cytokine signaling-1 (SOCS-1) in beta-cells of NOD8.3 mice. SOCS-1 islets remained intact when grafted into NOD8.3 mice and were less efficiently killed in vitro. However, addition of exogenous peptide rendered SOCS-1 islets susceptible to 8.3 T-cell-mediated lysis. Therefore, NOD8.3 T-cells use both perforin and Fas pathways to kill beta-cells and the surprising blockade of NOD8.3 T-cell-mediated beta-cell death by SOCS-1 overexpression may be due in part to reduced target cell recognition.

Perforin and Fas induced by IFNgamma and TNFalpha mediate beta cell death by OT-I CTL

Direct interaction between auto-reactive CTL and specific peptide-MHC class I complexes on pancreatic beta cells is critical in mediating beta cell destruction in type I diabetes. We used mice with genetic modifications in three major pathways used by CTL, perforin, Fas and pro-inflammatory cytokines to assess the relative contribution of these mechanisms to beta cell death. In vitro-activated ovalbumin (OVA)-specific CTL, from OT-I TCR-transgenic mice, specifically killed transgenic beta cells expressing OVA (from RIP-mOVA mice) in a 16-h cytotoxicity assay. Perforin-deficient CTL had a reduced ability to kill OVA-expressing islets in vitro (22.1 +/- 3.8%) compared with wild-type CTL (71.4 +/- 4.6%). Fas-deficient islets were only slightly protected from wild-type CTL but were completely protected from the residual killing observed with perforin-deficient CTL. Residual cytotoxicity in perforin-deficient CTL was also prevented by overexpression of SOCS-1, which blocks multiple cytokine signaling pathways. It was also prevented by pre-incubation with anti-tumor necrosis factor-alpha (anti-TNFalpha) antibody or by blocking IFNgamma responsiveness through expressing a dominant negative IFNgamma receptor. Perforin-deficient CTL produced IFNgamma and TNFalpha that was shown to directly induce islet Fas expression during the assays. This suggests that Fas-deficiency, SOCS-1 overexpression and blockade of IFNgamma and TNFalpha all protect beta cells from residual cytotoxicity of perforin-deficient CTL by blocking Fas upregulation. These findings indicate that wild-type CTL destroy antigen-expressing islets via a perforin-dependent mechanism. However, in the absence of perforin, the Fas/FasL pathway provides an alternative mechanism dependent on islet cell Fas upregulation by cytokines IFNgamma and TNFalpha.

Novel role for RbAp48 in tissue-specific, estrogen deficiency-dependent apoptosis in the exocrine glands

Although tissue-specific apoptosis in the exocrine glands in estrogen-deficient mice may contribute to the development of autoimmune exocrinopathy, the molecular mechanism responsible for tissue-specific apoptosis remains obscure. Here we show that RbAp48 overexpression induces p53-mediated apoptosis in the exocrine glands caused by estrogen deficiency. RbAp48-inducible transfectant results in rapid apoptosis with p53 phosphorylation (Ser9) and alpha-fodrin cleavage. Reducing the expression of RbAp48 through small interfering RNA inhibits the apoptosis. Prominent RbAp48 expression with apoptosis was observed in the exocrine glands of C57BL/6 ovariectomized (OVX) mice but not in OVX estrogen receptor alpha(-/-), p53(-/-), and E2F-1(-/-) mice. Indeed, transgenic expression of the RbAp48 gene induced apoptosis in the exocrine glands but not in other organs. These findings indicate that estrogen deficiency initiates p53-mediated apoptosis in the exocrine gland cells through RbAp48 overexpression and exerts a possible gender-based risk of autoimmune exocrinopathy in postmenopausal women.

The dual role of Fas-ligand as an injury effector and defense strategy in diabetes and islet transplantation

The exact process that leads to the eruption of autoimmune reactions against beta cells and the evolution of diabetes is not fully understood. Macrophages and T cells may launch an initial immune reaction against the pancreatic islets of Langerhans, provoking inflammation and destructive insulitis. The information on the molecular mechanisms of the emergence of beta cell injury is controversial and points to possibly important roles for the perforin-granzyme, Fas-Fas-ligand (FasL) and tumor-necrosis-factor-mediated apoptotic pathways. FasL has several unique features that make it a potentially ideal immunomodulatory tool. Most important, FasL is selectively toxic to cytotoxic T cells and less harmful to regulatory T cells. This review discusses the intrinsic sensitivity of beta cells to FasL-mediated apoptosis, the conditions that underlie this beta cell sensitivity, and the feasibility of using FasL to arrest autoimmunity and prevent islet allograft rejection. In both the autoimmune and transplant settings, it is imperative to progress from the administration of nonspecific immunosuppressive therapy to the concept of beta-cell-specific immunomodulation. FasL evolves as a prime candidate for antigen-specific immunomodulation.

Autoimmune destruction of pancreatic beta cells

Type 1 diabetes results from the destruction of insulin-producing pancreatic beta cells by a beta cell-specific autoimmune process. Beta cell autoantigens, macrophages, dendritic cells, B lymphocytes, and T lymphocytes have been shown to be involved in the pathogenesis of autoimmune diabetes. Beta cell autoantigens are thought to be released from beta cells by cellular turnover or damage and are processed and presented to T helper cells by antigen-presenting cells. Macrophages and dendritic cells are the first cell types to infiltrate the pancreatic islets. Naive CD4+ T cells that circulate in the blood and lymphoid organs, including the pancreatic lymph nodes, may recognize major histocompatibility complex and beta cell peptides presented by dendritic cells and macrophages in the islets. These CD4+ T cells can be activated by interleukin (IL)-12 released from macrophages and dendritic cells. While this process takes place, beta cell antigen-specific CD8+ T cells are activated by IL-2 produced by the activated TH1 CD4+ T cells, differentiate into cytotoxic T cells and are recruited into the pancreatic islets. These activated TH1 CD4+ T cells and CD8+ cytotoxic T cells are involved in the destruction of beta cells. In addition, beta cells can also be damaged by granzymes and perforin released from CD8+ cytotoxic T cells and by soluble mediators such as cytokines and reactive oxygen molecules released from activated macrophages in the islets. Thus, activated macrophages, TH1 CD4+ T cells, and beta cell-cytotoxic CD8+ T cells act synergistically to destroy beta cells, resulting in autoimmune type 1 diabetes.

Targeted expression of the anti-apoptotic gene CrmA to NOD pancreatic islets protects from autoimmune diabetes

The activation of apoptosis is a critical mechanism by which pancreatic beta cells are destroyed in type 1 diabetes (T1DM). Strategies aimed at interfering with the apoptotic pathways could therefore be of potential therapeutic value. To this end, we generated NOD transgenic mice with targeted expression of the anti-apoptotic gene Cytokine response modifier A (CrmA) to pancreatic beta cells using the rat insulin promoter and the reverse tetracycline transactivator to express CrmA in a temporally controlled manner. Two lines of transgenic mice were studied whose expression of CrmA occurred only after feeding doxycycline food. Islet expression of CrmA partially protected pancreatic beta cells from the cytokine-mediated cytotoxicity in vitro and reduced modestly the spontaneous development of diabetes in NOD mice in vivo. In addition, beta cells from NOD CrmA mice were significantly protected from the destruction by diabetogenic T cells after adoptive transfer. More strikingly, NODCrmA mice were significantly resistant to the diabetogenic activity of a potent insulin-specific CD8 T-cell clone. Since these adoptive transfer models mainly represent the effector phase rather than the initiation phase of autoimmune diabetes, our data suggest that the latter is more sensitive to CrmA protection. We conclude that anti-apoptotic genes such as CrmA might be potential candidates to enhance islet graft survival in T1DM.

Transplanted islets from lpr mice are resistant to autoimmune destruction in a model of streptozotocin-induced type I diabetes

The mechanism by which beta-cells die during autoimmune diabetes has remained a subject of intense investigation. The loss of beta-cells in the disease is T cell mediated and thought to result from a number of different insults including apoptosis induction through the death receptor CD95. However, the role of CD95 in autoimmune diabetes, studied primarily in the non-obese diabetic (NOD) mouse model, has been controversial. We have used an alternative model of autoimmune diabetes triggered by repeated low doses of streptozotocin. In this model, islet grafts from C3H mice that carry the lpr mutation, and therefore lack the ability to undergo apoptosis through CD95-CD95L interaction, were completely protected when grafted in autoimmune diabetic mice despite periinsulitis (infiltration of T cells) which however did not progress to islet destruction. In contrast wild-type grafts were rapidly eliminated in autoimmune recipients. Our data provide strong support for a major role of CD95 in the destruction of islets in autoimmune mice.

Transgenic expression of dominant-negative Fas-associated death domain protein in beta cells protects against Fas ligand-induced apoptosis and reduces spontaneous diabetes in nonobese diabetic mice

In type 1 diabetes, many effector mechanisms damage the beta cell, a key one being perforin/granzyme B production by CD8(+) T cells. The death receptor pathway has also been implicated in beta 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 beta cells. Islets developed normally in these animals, indicating that FADD is not necessary for beta cell development as it is for vasculogenesis. beta 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 beta 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.

The intriguing biology of the tumour necrosis factor/tumour necrosis factor receptor superfamily: players, rules and the games

The members of the tumour necrosis factor (TNF)/tumour necrosis factor receptor (TNFR) superfamily are critically involved in the maintenance of homeostasis of the immune system. The biological functions of this system encompass beneficial and protective effects in inflammation and host defence as well as a crucial role in organogenesis. At the same time, members of this superfamily are responsible for host damaging effects in sepsis, cachexia, and autoimmune diseases. This review summarizes recent progress in the immunobiology of the TNF/TNFR superfamily focusing on results obtained from animal studies using gene targeted mice. The different modes of signalling pathways affecting cell proliferation, survival, differentiation, apoptosis, and immune organ development as well as host defence are reviewed. Molecular and cellular mechanisms that demonstrate a therapeutic potential by targeting individual receptors or ligands for the treatment of chronic inflammatory or autoimmune diseases are discussed.