Mechanisms of beta cell death in diabetes: a minor role for CD95

Oxidative Stress-Responsive Apoptosis Inducing Protein (ORAIP) Plays a Critical Role in High Glucose-Induced Apoptosis in Rat Cardiac Myocytes and Murine Pancreatic β-Cells

We previously identified a novel apoptosis-inducing humoral factor in the conditioned medium of hypoxic/reoxygenated-cardiac myocytes. We named this novel post-translationally-modified secreted-form of eukaryotic translation initiation factor 5A Oxidative stress-Responsive Apoptosis-Inducing Protein (ORAIP). We confirmed that myocardial ischemia/reperfusion markedly increased plasma ORAIP levels and rat myocardial ischemia/reperfusion injury was clearly suppressed by neutralizing anti-ORAIP monoclonal antibodies (mAbs) in vivo. In this study, to investigate the mechanism of cell injury of cardiac myocytes and pancreatic β-cells involved in diabetes mellitus (DM), we analyzed plasma ORAIP levels in DM model rats and the role of ORAIP in high glucose-induced apoptosis of cardiac myocytes in vitro. We also examined whether recombinant-ORAIP induces apoptosis in pancreatic β-cells. Plasma ORAIP levels in DM rats during diabetic phase were about 18 times elevated as compared with non-diabetic phase. High glucose induced massive apoptosis in cardiac myocytes (66.2 ± 2.2%), which was 78% suppressed by neutralizing anti-ORAIP mAb in vitro. Furthermore, recombinant-ORAIP clearly induced apoptosis in pancreatic β-cells in vitro. These findings strongly suggested that ORAIP plays a pivotal role in hyperglycemia-induced myocardial injury and pancreatic β-cell injury in DM. ORAIP will be a biomarker and a critical therapeutic target for cardiac injury and progression of DM itself.

Expansion of FasL-Expressing CD5+ B Cells in Type 1 Diabetes Patients

Fas ligand drives insulitis in the non-obese diabetic mouse model of type 1 diabetes (T1D) and negatively regulates IL-10-producing (IL-10^pos) CD5⁺ B cells in pancreata. Relevance of these phenomena to the human disease is poorly understood. Here, using splenocytes from T1D, autoantibody (Ab⁺), and non-diabetic (ND) human subjects, we show that a subpopulation of CD5⁺ B cells that is characterized by expression of FasL (FasL^hiCD5⁺) was significantly elevated in T1D subjects, many of whom had significantly reduced frequency of IL-10^posCD5⁺ B cells compared to Ab⁺ subjects. The majority of FasL^hiCD5⁺ B cells did not produce cytokines and were more highly resistant to activation-induced cell death than their IL-10^posCD5⁺ counterparts. These results associate expansion of FasL-expressing CD5⁺ B cells with T1D and lay the groundwork for future mechanistic studies to understand specific role in disease pathogenesis.

Autoreactive T cells induce necrosis and not BCL-2-regulated or death receptor-mediated apoptosis or RIPK3-dependent necroptosis of transplanted islets in a mouse model of type 1 diabetes

AIMS/HYPOTHESIS

Type 1 diabetes results from T cell-mediated destruction of pancreatic beta cells. The mechanisms of beta cell destruction in vivo, however, remain unclear. We aimed to test the relative roles of the main cell death pathways: apoptosis, necrosis and necroptosis, in beta cell death in the development of CD4(+) T cell-mediated autoimmune diabetes.

METHODS

We altered expression levels of critical cell death proteins in mouse islets and tested their ability to survive CD4(+) T cell-mediated attack using an in vivo graft model.

RESULTS

Loss of the B cell leukaemia/lymphoma 2 (BCL-2) homology domain 3-only proteins BIM, PUMA or BID did not protect beta cells from this death. Overexpression of the anti-apoptotic protein BCL-2 or combined deficiency of the pro-apoptotic multi-BCL2 homology domain proteins BAX and BAK also failed to prevent beta cell destruction. Furthermore, loss of function of the death receptor Fas or its essential downstream signalling molecule Fas-associated death domain (FADD) in islets was also not protective. Using electron microscopy we observed that dying beta cells showed features of necrosis. However, islets deficient in receptor-interacting serine/threonine protein kinase 3 (RIPK3), a critical initiator of necroptosis, were still normally susceptible to CD4(+) T cell-mediated destruction. Remarkably, simultaneous inhibition of apoptosis and necroptosis by combining loss of RIPK3 and overexpression of BCL-2 in islets did not protect them against immune attack either.

CONCLUSIONS/INTERPRETATION

Collectively, our data indicate that beta cells die by necrosis in autoimmune diabetes and that the programmed cell death pathways apoptosis and necroptosis are both dispensable for this process.

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.

Induction of rapid T cell death and phagocytic activity by Fas-deficient lpr macrophages

Peripheral T cells are maintained by the apoptosis of activated T cells through the Fas-Fas ligand system. Although it is well known that normal T cells fail to survive in the Fas-deficient immune condition, the molecular mechanism for the phenomenon has yet to be elucidated. In this study, we demonstrate that rapid cell death and clearance of normal T cells were induced by Fas-deficient lpr macrophages. Transfer of normal T cells into lpr mice revealed that Fas expression on donor T cells was promptly enhanced through the IFN-γ/IFN-γR. In addition, Fas ligand expression and phagocytic activity of lpr macrophages were promoted through increased NF-κB activation. Controlling Fas expression on macrophages plays an essential role in maintaining T cell homeostasis in the peripheral immune system. Our data suggest a critical implication to the therapeutic strategies such as transplantation and immunotherapy for immune disorder or autoimmunity related to abnormal Fas expression.

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.

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.

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.

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.

The many roles of FAS receptor signaling in the immune system

FAS belongs to the subgroup of the tumor necrosis factor receptor (TNF-R) family that contains an intracellular "death domain" and triggers apoptosis. Its physiological ligand FASL is a member of the TNF cytokine family. Studies with mutant mice and cells from human patients have shown that FAS plays critical roles in the immune system, including the killing of pathogen-infected cells and the death of obsolete and potentially dangerous lymphocytes. Fas thereby functions as a guardian against autoimmunity and tumor development. FAS triggers apoptosis through FADD-mediated recruitment and activation of caspase-8. In certain cells such as hepatocytes, albeit not lymphocytes, FAS-induced apoptosis requires amplification through proteolytic activation of the proapoptotic BCL-2 family member BID. Curiously, several components of the FAS signaling machinery have been implicated in nonapoptotic processes, including cellular activation, differentiation, and proliferation. This review describes current understanding of Fas-induced apoptosis signaling and proposes experimental strategies for future advances.

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.

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.

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.

NF-kappa B prevents beta cell death and autoimmune diabetes in NOD mice

Whereas NF-kappaB has potent antiapoptotic function in most cell types, it was reported that in pancreatic beta cells it serves a proapoptotic function and may contribute to the pathogenesis of autoimmune type 1 diabetes. To investigate the role of beta cell NF-kappaB in autoimmune diabetes, we produced transgenic mice expressing a nondegradable form of IkappaBalpha in pancreatic beta cells (RIP-mIkappaBalpha mice). beta cells of these mice were more susceptible to killing by TNF-alpha plus IFN-gamma but more resistant to IL-1beta plus IFN-gamma than normal beta cells. Similar results were obtained with beta cells lacking IkappaB kinase beta, a protein kinase required for NF-kappaB activation. Inhibition of beta cell NF-kappaB accelerated the development of autoimmune diabetes in nonobese diabetic mice but had no effect on glucose tolerance or serum insulin in C57BL/6 mice, precluding a nonphysiological effect of transgene expression. Development of diabetes after transfer of diabetogenic CD4(+) T cells was accelerated in RIP-mIkappaBalpha/nonobese diabetic mice and was abrogated by anti-TNF therapy. These results suggest that under conditions that resemble autoimmune type 1 diabetes, the dominant effect of NF-kappaB is prevention of TNF-induced apoptosis. This differs from the proapoptotic function of NF-kappaB in IL-1beta-stimulated beta cells.

Resistance of the target islet tissue to autoimmune destruction contributes to genetic susceptibility in Type 1 diabetes

Type 1 diabetes occurs when self-reactive T lymphocytes destroy the insulin-producing islet beta cells of the pancreas. The defects causing this disease have often been assumed to occur exclusively in the immune system. We present evidence that genetic variation at the Idd9 diabetes susceptibility locus determines the resilience of the targets of autoimmunity, the islets, to destruction. Susceptible islets exhibit hyper-responsiveness to inflammatory cytokines resulting in enhanced cell death and increased expression of the death receptor Fas. Fas upregulation in beta cells is mediated by TNFR2, and colocalization of TNFR2 with the adaptor TRAF2 in NOD beta cells is altered. TNFR2 lies within the candidate Idd9 interval and the diabetes-associated variant contains a mutation adjacent to the TRAF2 binding site. A component of diabetes susceptibility may therefore be determined by the target of the autoimmune response, and protective TNFR2 signaling in islets inhibit early cytokine-induced damage required for the development of destructive autoimmunity.

REVIEWERS

This article was reviewed by Matthiasvon Herrath, HaraldVon Boehmer, and Ciriaco Piccirillo (nominated by Ethan Shevach).

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.

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.

A critical role for granzyme B, in addition to perforin and TNFalpha, in alloreactive CTL-induced mouse pancreatic beta cell death

BACKGROUND

The precise effector mechanisms and molecular mediators used by alloreactive cytotoxic T lymphocytes to kill transplanted pancreatic beta cells are poorly defined. We have used mouse (H2b-anti-d) CTLs raised in strains deficient in various key cytotoxic effector molecules to assess the importance of the various signaling pathways mobilized to kill primary mouse pancreatic islet cells, the beta cell line NIT-1, and NIT-1 cells overexpressing dominant-negative FADD and Bcl-2.

METHODS

Death of target cells was assessed using 51Cr release assays.

RESULTS

In short-term assays (<5 hours) beta cell death did not require a functional FasL/Fas pathway, and was not inhibited by Bcl-2. However, the absence of either perforin or granzyme B resulted in cell survival. By contrast, a crucial role for granzyme B was not seen when hematopoietic P815 cells were used as targets, indicating differential regulation of apoptosis. Interestingly, coincubation with CTL for 24 hours revealed an additional but less potent "late phase" of beta cell death that did not require perforin. This delayed death was blocked by dominant-negative FADD, but not by Bcl-2, and was likely to be due to TNFalpha secretion.

CONCLUSIONS

This study suggests that strategies to protect beta cells from allogeneic CTL attack will need to inhibit the perforin/granzyme and probably also the TNFalpha pathway. As there are no known pharmacological approaches to blocking perforin, therapeutic approaches based on overexpressing both dominant negative FADD and an inhibitor of granzyme B may hold promise in prolonging beta cell survival in the allogeneic setting.

Efficient delivery of siRNA into cytokine-stimulated insulinoma cells silences Fas expression and inhibits Fas-mediated apoptosis

Fas/FasL interactions have been proposed as a potentially important mechanism mediating beta-cell death in type 1 diabetes. Recent investigations suggest RNA interference, afforded by small interfering RNAs (siRNA), can provide specific and robust gene silencing in mammalian cells. The current study attempted to investigate the effects of silencing Fas expression with siRNA on Fas-mediated apoptosis in mouse insulinoma cells following cytokine incubation. Our results indicate that siRNA is capable of rapid inhibition of cytokine-induced Fas mRNA production and cell surface Fas protein. A complete suppression of the total Fas protein was only observed after prolonged incubation with siRNA, suggesting a slow turn-over of Fas protein. Moreover, siRNA significantly inhibited Fas-mediated beta-cell apoptosis assessed by Caspase-3 and terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling assays, the extent of which positively correlated with the level of cell surface Fas. These observations provide additional evidence supporting a role for the Fas-mediated pathway in beta-cell destruction, and suggest that siRNA targeting Fas may be of therapeutic value in preventing type 1 diabetes and improving islet cell viability in transplantation.

Assay for high glucose-mediated islet cell sensitization to apoptosis induced by streptozotocin and cytokines

Pancreatic beta-cell apoptosis is known to participate in the beta-cell destruction process that occurs in diabetes. It has been described that high glucose level induces a hyperfunctional status which could provoke apoptosis. This phenomenon is known as glucotoxicity and has been proposed that it can play a role in type 1 diabetes mellitus pathogenesis. In this study we develop an experimental design to sensitize pancreatic islet cells by high glucose to streptozotocin (STZ) and proinflammatory cytokines [interleukin (IL)-1beta, tumor necrosis factor (TNF)-alpha and interferon (IFN)-gamma]-induced apoptosis. This method is appropriate for subsequent quantification of apoptotic islet cells stained with Tdt-mediated dUTP Nick-End Labeling (TUNEL) and protein expression assays by Western Blotting (WB).

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.

Fas ligand is required for resolution of granulomatous experimental autoimmune thyroiditis

We previously suggested that CD8(+) T cells promoted resolution of granulomatous experimental autoimmune thyroiditis (G-EAT) at least in part through regulation of Fas ligand (FasL) expression on thyroid epithelial cells. To directly evaluate the role of the Fas pathway in G-EAT resolution, Fas- and FasL-deficient mice on the NOD.H-2h4 background were used as recipients of activated G-EAT effector cells. When MTg-primed wild-type (WT) donor splenocytes were activated and transferred to WT recipients, thyroid lesions reached maximal severity on day 20 and resolved on day 50. Fas, FasL, and FLIP were up-regulated, and many apoptotic inflammatory cells were detected in recipient thyroids on day 20. Fas was predominantly expressed by inflammatory cells, and FasL and FLIP were mainly expressed by thyroid epithelial cells. After depletion of CD8(+) T cells, G-EAT resolution was delayed, FLIP and FasL were predominantly expressed by inflammatory cells, and few inflammatory cells were apoptotic. When WT donor splenocytes were transferred to gld recipients, disease severity on day 20 was similar to that in WT recipients, but resolution was delayed. As in CD8-depleted WT recipients, there were few apoptotic inflammatory cells, and FLIP and FasL were expressed primarily by inflammatory cells. These results indicated that the expression of functional FasL in recipient mice was critical for G-EAT resolution. WT cells induced minimal disease in lpr recipients. This was presumably because donor cells were eliminated by the increased FasL on lpr recipient cells, because donor cells were not eliminated, and the mice developed G-EAT if lpr recipients were given anti-FasL mAb.

Expression of Fas but not Fas ligand on fetal pig beta cells

BACKGROUND

The aim of this study was to determine whether fetal pig insulin-producing cells, a potential source of transplantable tissue for the treatment of type 1 diabetes, are affected by the Fas-FasL interaction, one of the cytotoxic pathways involved in T-cell-mediated autoimmune destruction of pancreatic beta cells.

METHODS

Expression of Fas/FasL on fetal pig beta cells was assessed by immunohistochemistry, flow cytometry, Western blot, and RT-PCR. Apoptosis of fetal pig beta cells induced by soluble FasL (sFasL) or anti-Fas antibody (APO-1) was detected by flow cytometry using PI. Expression of FLIP on fetal pig pancreatic tissue was detected by immunofluorescent staining and Western blot.

RESULTS

Fas was expressed on fetal pig pancreatic cells, both beta and non-beta cells, and the level of expression could be upregulated by exposure to human interleukin-1beta (IL1beta) 2000 pg/ml for 24 h. In contrast, FasL was not detected on fetal pig pancreatic cells but could be induced on both beta and non-beta cells when the cells were treated with IL1beta. Fas persisted on fetal pig beta cells transplanted as islet-like cell clusters into severe combined immunodeficient mice, with expression of this antigen at all times examined, 1 day, 2, 3 and 4 weeks. FasL was absent. Despite the presence of Fas on fetal pig beta cells, addition of sFasL or anti-Fas antibody failed to induce apoptosis of the fetal pig beta cells. In contrast, pig lymphocytes, which express Fas, were destroyed by addition of both sFasL and APO-1. A possible reason for this is the expression on the fetal pig pancreatic cells of FLIP, an inhibitor of Fas-induced apoptosis.

CONCLUSIONS

Fetal pig beta cells are resistant to Fas-FasL destruction. Our data imply that fetal pig beta cells transplanted into humans with type 1 diabetes may not be destroyed by activated T cells through the Fas-FasL-mediated pathway.

Fas deficiency prevents type 1 diabetes by inducing hyporesponsiveness in islet beta-cell-reactive T-cells

Type 1 diabetes is an autoimmune disease wherein autoreactive T-cells promote the specific destruction of pancreatic islet beta-cells. Evidence for a crucial role for Fas/FasL interactions in this destruction has been highly controversial because of the pleiotropic effects of Fas deficiency on the lymphoid and other systems. Fas-deficient mice are protected from spontaneous development of diabetes not because Fas has a role in the destruction of beta-cells, but rather because insulitis is abrogated. Fas may somehow be involved in the series of events provoking insulitis; for example, it may play a role in the physiological wave of beta-cell death believed to result in the export of pancreatic antigens to the pancreatic lymph nodes and, thereby, to circulating, naive, diabetogenic T-cells for the first time. To explore the implication of Fas in these events, we crossed the lpr mutation into the BDC2.5 model of type 1 diabetes to make it easier to monitor direct effects on the pathogenic specificity. We demonstrated that BDC2.5/NOD(lpr/lpr) mice have qualitatively and quantitatively less aggressive insulitis than do BDC2.5/NOD mice. In vitro proliferation assays showed that BDC2.5/NOD(lpr/lpr) splenocytes proliferated less vigorously than those from control mice in the presence of islet extracts, which reflects their inability to produce interleukin-2, resulting in weaker pathogenicity.

Death effectors of beta-cell apoptosis in type 1 diabetes

While it is generally agreed that apoptosis of pancreatic beta-cells is the most important and final step in the progression of type 1 diabetes without which clinical diabetes does not develop, it has not been elucidated which molecule(s) are the real culprit(s) in type 1 diabetes. Perforin, FasL, TNFalpha, IL-1, IFNgamma, and NO have been claimed as the effector molecules; however, they, as a single agent, might explain only part of beta-cell death in type 1 diabetes. While FasL was initially considered as a strong candidate for the most important death effector, following experiments cast doubt on such a hypothesis. Combinations or synergism between IFNgamma and TNFalpha or IL-1beta are being revisited as the death effectors, and molecular mechanism explaining such a synergism was addressed in several recent papers. The role of NF-kappaB for pancreatic beta-cell death in type 1 diabetes is also controversial. While NF-kappaB plays anti-apoptotic roles in most other death models, its role in type 1 diabetes might be different probably due to the involvement of multiple cytokines at different stages of the disease progression and the peculiarity of pancreatic beta-cells. Recent papers also suggested a role for Ca2+ in cytokine-mediated pancreatic beta-cell death. Such participation of Ca2+ in beta-cell death appears to have a close relevance to the mitochondrial events or ER stress that constitutes an important part of cell death machinery recently identified.

Role of calcium in pancreatic islet cell death by IFN-gamma/TNF-alpha

We studied the intracellular events associated with pancreatic beta cell apoptosis by IFN-gamma/TNF-alpha synergism. IFN-gamma/TNF-alpha treatment of MIN6N8 insulinoma cells increased the amplitude of high voltage-activated Ca(2+) currents, while treatment with IFN-gamma or TNF-alpha alone did not. Cytosolic Ca(2+) concentration ([Ca(2+)](c)) was also increased by IFN-gamma/TNF-alpha treatment. Blockade of L-type Ca(2+) channel by nifedipine abrogated death of insulinoma cells by IFN-gamma/TNF-alpha. Diazoxide that attenuates voltage-activated Ca(2+) currents inhibited MIN6N8 cell death by IFN-gamma/TNF-alpha, while glibenclamide that accentuates voltage-activated Ca(2+) currents augmented insulinoma cell death. A protein kinase C inhibitor attenuated MIN6N8 cell death and the increase in [Ca(2+)](c) by IFN-gamma/TNF-alpha. Following the increase in [Ca(2+)](c), calpain was activated, and calpain inhibitors decreased insulinoma cell death by IFN-gamma/TNF-alpha. As a downstream of calpain, calcineurin was activated and the inhibition of calcineurin activation by FK506 diminished insulinoma cell death by IFN-gamma/TNF-alpha. BAD phosphorylation was decreased by IFN-gamma/TNF-alpha because of the increased calcineurin activity, which was reversed by FK506. IFN-gamma/TNF-alpha induced cytochrome c translocation from mitochondria to cytoplasm and activation of caspase-9. Effector caspases such as caspase-3 or -7 were also activated by IFN-gamma/TNF-alpha treatment. These results indicate that IFN-gamma/TNF-alpha synergism induces pancreatic beta cell apoptosis by Ca(2+) channel activation followed by downstream intracellular events such as mitochondrial events and caspase activation and also suggest the therapeutic potential of Ca(2+) modulation in type 1 diabetes.

Transgenic expression of decoy receptor 3 protects islets from spontaneous and chemical-induced autoimmune destruction in nonobese diabetic mice

Decoy receptor 3 (DCR3) halts both Fas ligand– and LIGHT-induced cell deaths, which are required for pancreatic β cell damage in autoimmune diabetes. To directly investigate the therapeutic potential of DCR3 in preventing this disease, we generated transgenic nonobese diabetic mice, which overexpressed DCR3 in β cells. Transgenic DCR3 protected mice from autoimmune and cyclophosphamide-induced diabetes in a dose-dependent manner and significantly reduced the severity of insulitis. Local expression of the transgene did not alter the diabetogenic properties of systemic lymphocytes or the development of T helper 1 or T regulatory cells. The transgenic islets had a higher transplantation success rate and survived for longer than wild-type islets. We have demonstrated for the first time that the immune-evasion function of DCR3 inhibits autoimmunity and that genetic manipulation of grafts may improve the success and survival of islet transplants.

Tumor necrosis factor alpha is not implicated in the genesis of experimental autoimmune gastritis

Experimental autoimmune gastritis (EAG) characterised by mononuclear cell infiltrate, parietal and zymogenic cell destruction and circulating autoantibodies to gastric H(+)/K(+)ATPase is an animal model for human autoimmune gastritis, that leads to pernicious anaemia. We have previously shown that Fas has a role in initiating damage to target cells in EAG. Here we used three strategies to examine the role of TNFalpha in this disease. We administered neutralising anti-TNFalpha antibody either as a single injection or as twice weekly injections for 8 weeks to mice subjected to neonatal thymectomy-induced EAG. To address the role of apoptotic signals through TNFR1, TNFR1 deficient mice were either neonatally thymectomised or crossed to PC-GMCSF transgenic mice that spontaneously develop EAG. Neonatally thymectomised mice treated with anti-TNFalpha antibody developed destructive gastritis and autoantibodies to gastric H(+)/K(+)ATPase similar to control mice. Following either neonatal thymectomy or crossing to PC-GMCSF transgenic mice, TNFR1 deficient mice developed autoantibody-positive destructive gastritis at similar frequency compared with wild type and heterozygous littermates. Our observations that neutralisation of TNFalpha and absence of TNFR1 has no discernible effect on development of EAG suggest that TNFalpha is not required for mucosal cell damage or development of autoimmune gastritis. While blocking TNFalpha activity has therapeutic benefit in certain autoimmune diseases, this is not the case for EAG.

IL-1 receptor deficiency slows progression to diabetes in the NOD mouse

Proinflammatory cytokines are believed to be important in pancreatic beta-cell destruction in the development of type 1 diabetes. They act by upregulation of genes including Fas and inducible nitric oxide synthase (iNOS), which have both been shown to lead to beta-cell death in vitro. We used mice deficient in the interleukin (IL)-1 receptor (IL-1R) to assess the contribution of IL-1 to different models of diabetes. IL-1R-deficient islets were protected from the damaging effects of tumor necrosis factor (TNF) and interferon (IFN)-gamma in vitro, and beta-cell expression of iNOS was reduced, suggesting that IL-1 mediates the induction of iNOS by TNF and IFN-gamma. IL-1 action was not required for induction of class I major histocompatibility complex or Fas by TNF and IFN-gamma. IL-1R-deficient nonobese diabetic (NOD) mice developed diabetes significantly slower than wild-type mice. IL-1R deficiency did not affect diabetes in 8.3 TCR transgenic NOD mice but prolonged the time to diabetes in BDC2.5 TCR transgenic NOD mice. We conclude that IL-1R deficiency slows progression to diabetes in NOD mice but on its own does not prevent diabetes.

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

In type 1 diabetes, autoimmune T cells cause destruction of pancreatic β cells by largely unknown mechanism. Previous analyses have shown that β cell destruction is delayed but can occur in perforin-deficient nonobese diabetic (NOD) mice and that Fas-deficient NOD mice do not develop diabetes. However, because of possible pleiotropic functions of Fas, it was not clear whether the Fas receptor was an essential mediator of β cell death in type 1 diabetes. To directly test this hypothesis, we have generated a β cell–specific knockout of the Fas gene in a transgenic model of type 1 autoimmune diabetes in which CD4⁺ T cells with a transgenic TCR specific for influenza hemagglutinin (HA) are causing diabetes in mice that express HA under control of the rat insulin promoter. Here we show that the Fas-deficient mice develop autoimmune diabetes with slightly accelerated kinetics indicating that Fas-dependent apoptosis of β cells is a dispensable mode of cell death in this disease.

Dissecting autoimmune diabetes through genetic manipulation of non-obese diabetic mice

Type 1 diabetes results from a genetically and immunologically complex autoimmune process that is specifically directed against the pancreatic beta cells. Non-obese diabetic mice spontaneously develop a form of autoimmune diabetes closely resembling the disease in humans. This happens because, like human diabetic patients, non-obese diabetic mice have an unfortunate combination of apparently normal alleles at numerous loci associated with Type 1 diabetes. In isolation, each of these allelic variants affords a small degree of susceptibility to diabetes. In combination, however, they set in motion a series of immunological events that lead to islet inflammation and overt diabetes. Type 1 diabetes is associated with defects in self-tolerance and immunoregulation. It involves presentation of beta cell antigens to autoreactive T lymphocytes by professional antigen-presenting cells, the recruitment of antigen-activated T cells into pancreatic islets, and the differentiation of these antigen-activated lymphocytes into beta cell killers. Understanding the precise sequence of events in the pathogenesis of Type 1 diabetes has been, and remains, a challenging task. Much of our understanding of the immunology of the disease stems from studies of genetically engineered, non-obese diabetic mice. These mice provide reductionist systems, with which the contribution of individual cellular elements, molecules or genes to the disease process can be dissected. This review focuses on the lessons that have been learned through studies of these mice.

Fas is detectable on beta cells in accelerated, but not spontaneous, diabetes in nonobese diabetic mice

Fas (CD95) is a potential mechanism of pancreatic beta cell death in type 1 diabetes. beta cells do not constitutively express Fas but it is induced by cytokines. The hypothesis of this study is that Fas expression should be measurable on beta cells for them to be killed by this mechanism. We have previously reported that up to 5% of beta cells isolated from nonobese diabetic (NOD) mice are positive for Fas expression by flow cytometry using autofluorescence to identify beta cells. We have now found that these are not beta cells but contaminating dendritic cells, macrophages, and B lymphocytes. In contrast beta cells isolated from NODscid mice that are recipients of T lymphocytes from diabetic NOD mice express Fas 18-25 days after adoptive transfer but before development of diabetes. Fas expression on beta cells was also observed in BDC2.5, 8.3, and 4.1 TCR-transgenic models of diabetes in which diabetes occurs more rapidly than in unmodified NOD mice. In conclusion, Fas is observed on beta cells in models of diabetes in which rapid beta cell destruction occurs. Its expression is likely to reflect differences in the intraislet cytokine environment compared with the spontaneous model and may indicate a role for this pathway in beta cell destruction in rapidly progressive models.

Contribution of Fas to diabetes development

Fas (Tnfrsf6, Apo-1, CD95) is a death receptor involved in apoptosis induced in many cell types. Fas have been shown to be expressed by insulin-producing beta cells in mice and humans. However, the importance of Fas in the development of autoimmune diabetes remains controversial. To further evaluate the importance of Fas in pathogenesis of diabetes, we generated NOD mice (nonobese diabetic mice developing spontaneous autoimmune diabetes) with beta cell-specific expression of a dominant-negative point mutation in a death domain of Fas, known as lpr(cg) or Fas(cg). Spontaneous diabetes was significantly delayed in NOD mice expressing Fas(cg), and the effect depended on the expression level of the transgene. However, Fas(cg)-bearing mice were still sensitive to diabetes transferred by splenocytes from overtly diabetic NOD mice. At the same time, Fas(cg) expression did neutralize the accelerating effect of transgenic Fas-ligand expressed by the same beta cells. Thus, both Fas-dependent and -independent mechanisms are involved in beta cell destruction, but interference with the Fas pathway early in disease development may retard or prevent diabetes progression.

Fas/CD95 is required for gastric mucosal damage in autoimmune gastritis

BACKGROUND & AIMS

Experimental autoimmune gastritis (EAG), characterized by a gastric mononuclear cell infiltrate, mucosal cell damage, and autoantibodies to parietal cell-associated H(+)/K(+) adenosine triphosphatase, is a model for human autoimmune gastritis that leads to pernicious anemia. Previous in vitro studies have implicated Fas/CD95 in initiating damage to gastric mucosal cells in humans and an animal model of autoimmune gastritis. Here we used 2 in vivo animal models to examine the role of Fas in the development of mucosal cell damage in autoimmune gastritis.

METHODS

We initiated EAG in BALB/cCrSlc mice by neonatal thymectomy and examined for Fas expression in the gastric mucosa by immunohistochemistry. To address the in vivo relevance of Fas in mucosal injury, we examined the stomachs and sera of BALB/cCrSlc lpr/lpr mice subjected to neonatal thymectomy and BALB/cCrSlc nu/nu lpr/lpr mice transferred with lymphocytes from gastritic BALB/cCrSlc mice.

RESULTS

Fas expression was up-reguiated in parietal cells of mice with EAG. Neonatally thymectomized lpr/lpr mice were resistant to developing destructive gastritis compared with heterozygous and wild-type littermates. Nu/nu Fas-sufficient mice transferred with lymphocytes from thymectomized lpr/lpr mice developed destructive gastritis. Nu/nu lpr/lpr mice transferred with lymphocytes from gastritic mice developed a nondestructive gastritis.

CONCLUSIONS

The observations that Fas is up-regulated in gastric parietal cells of mice with EAG and that Fas-deficient mice are resistant to development of destructive gastritis provide compelling evidence that Fas is required in vivo for development of gastric mucosal cell damage in autoimmune gastritis.

Fas/Fas ligand interactions play an essential role in the initiation of murine autoimmune diabetes

Apoptosis via Fas/Fas ligand (FasL) interactions has been proposed to be a major T-cell-mediated effector mechanism in autoimmune diabetes. To elucidate the role of Fas/FasL interactions in NOD diabetes, the effects of neutralizing anti-FasL antibody on autoimmune responses were evaluated. Islet-specific CD8(+) and CD4(+) T-cells expressed FasL upon activation and mediated FasL-dependent cytotoxicity against Fas-expressing target cells in vitro, although their cytotoxicity against islet cells was not blocked by anti-FasL antibody. Moreover, administration of anti-FasL antibody failed to inhibit diabetes in vivo in the CD8(+) T-cell adoptive transfer model. On the other hand, blockade of Fas/FasL interactions significantly inhibited CD4(+) T-cell-dependent diabetes in adoptive transfer models. These results suggest a substantial contribution of Fas/FasL interactions to CD4(+), but not CD8(+), T-cell-mediated destruction of pancreatic beta-cells. When anti-FasL antibody was administered to NOD mice between 5 and 15 weeks of age, the onset of diabetes was slightly delayed but the incidence was not decreased. However, administration of anti-FasL antibody at 2-4 weeks of age completely prevented insulitis and diabetes. These results suggest that Fas/FasL interactions contribute to CD4(+) T-cell-mediated beta-cell destruction and play an essential role in the initiation of autoimmune NOD diabetes.

Fas and Fas ligand immunolocalization in pancreatic islets of NOD mice during spontaneous and cyclophosphamide-accelerated diabetes

During insulin-dependent diabetes mellitus, immune cells which infiltrate pancreatic islets mediate beta cell destruction over a prolonged asymptomatic prediabetic period. The molecular mechanisms of beta cell death in vivo remain unresolved. At least two major molecular processes of destruction have been proposed. One involves the Fas-FasL (Fas-Fas ligand) system and the other, the perforin pathway. Here, dual-label immunohistochemistry was employed to examine the intra-islet expression, distribution and cellular sources of Fas and FasL in the NOD mouse, during spontaneous diabetes (days 21, 40 and 90) and following acceleration of diabetes with cyclophosphamide (days 0, 4, 7, 11 and 14 after cyclophosphamide administration). The expression of the proteins was correlated with advancing disease. FasL was expressed constitutively in most beta cells but not in glucagon or somatostatin cells or islet inflammatory cells and paralleled the loss of insulin immunolabelling with advancing disease. It was also expressed in beta cells of non-diabetes prone CD-1 and C57BL/6 mice from a young age (day 21). Strong immunolabelling for Fas was first observed in extra-islet macrophages and those close to the islet in NOD and non-diabetes-prone mice. During spontaneous and cyclophosphamide diabetes, it was observed in a higher proportion of islet infiltrating macrophages than CD4 and CD8 T cells, concomitant with advancing insulitis. In cyclophosphamide-treated mice, the proportion of Fas-positive intra-islet CD4 and CD8 T cells at day 14 (with and without diabetes) was considerably higher than at days 0, 4, 7 and 11. At days 11 and 14, a proportion of Fas-positive intra-islet macrophages co-expressed interleukin-1beta and inducible nitric oxide synthase. Fas was not detectable in beta cells and other islet endocrine cells during spontaneous and cyclophosphamide induced diabetes. Our results show constitutive expression of FasL in beta cells in the NOD mouse and predominant expression of Fas in intra-islet macrophages and to a lesser extent in T cells prior to diabetes onset. Interleukin-1beta in intra-islet macrophages may induce Fas and inducible nitric oxide synthase expression in an autocrine and paracrine manner and mediate beta cell destruction or even death of some macrophages and T cells. However, other mechanisms of beta cell destruction during spontaneous and cyclophosphamide-accelerated diabetes and independent of Fas-FasL, require examination.

beta-Cell death during progression to diabetes

The hallmark of type 1 diabetes is specific destruction of pancreatic islet beta-cells. Apoptosis of beta-cells may be crucial at several points during disease progression, initiating leukocyte invasion of the islets and terminating the production of insulin in islet cells. beta-Cell apoptosis may also be involved in the occasional evolution of type 2 into type 1 diabetes.

Effector lymphocytes in autoimmunity

Autoimmune diseases result from complex interactions among different T- and B-lymphocyte subpopulations that target a rapidly growing number of autoantigens on different cell types. The etiology of most spontaneous autoimmune disorders, and both the kinetics and hierarchy of the underlying autoimmune responses are poorly understood. However, important advances have been made in recent years in our understanding of how autoreactive lymphocytes cause tissue damage, including the discovery that granzyme B binds to a cell surface receptor on target cells. This review is an attempt to summarize recent developments in this area.

A tripartite anoikis-like mechanism causes early isolated islet apoptosis

BACKGROUND

This study examines the mechanisms of early isolated islet apoptosis (II-APO) and loss of functional islet mass.

METHODS

Rhesus islets were isolated for transplantation, and an aliquot was used for in vitro molecular studies of II-APO. These studies used Western blotting to examine caspase activation and perinuclear envelope protein cleavage that are associated with II-APO and used immunofluorescence analysis of Annexin V and mitochondrial permeability index to examine spontaneous and tripartite anoikis-like (TRAIL) mechanism--induced II-APO.

RESULTS

Caspase 6 was prominently activated in association with spontaneous II-APO, which occurred after overnight culture. In contrast, caspase 7, 8, and 9 were not activated. Cleavage of focal adhesion kinase and Lamin, substrates of caspase 6, was also evident in spontaneous II-APO. II-APO was exaggerated by the addition of the TRAIL mechanism. The TRAIL mechanism--induced II-APO was blocked by the caspase 6 inhibitor, VEID, and by the soluble fusion proteins, DR4 or DR5, which act as decoy receptors. In vivo studies in diabetic severe combined immunodeficiency disease mice showed that rhesus islets were cytoprotected by either ex vivo gene transfer of Bcl-2 or treatment of the isolated islet with VEID.

CONCLUSIONS

These studies suggest 3 major mechanisms involved in II-APO: caspase 6 activation, a TRAIL-induced apoptosis pathway, and the mitochondrial-associated apoptosis pathway. Inhibition of these II-APO pathways may improve isolated islet survival and reduce functional islet mass loss, which compromises the stable reversal of diabetes.