Fas ligand-mediated mechanisms are involved in autoimmune destruction of islet beta cells in non-obese diabetic mice

α1-antitrypsin increases interleukin-1 receptor antagonist production during pancreatic islet graft transplantation

Although islet transplantation for individuals with type 1 diabetes has been shown to yield superior blood glucose control, it remains inadequate for long-term control. This is partly due to islet injuries and stresses that can lead to beta cell loss. Inhibition of excess IL-1β activity might minimize islet injuries, thus preserving function. The IL-1 receptor antagonist (IL-1Ra), an endogenous inhibitor of IL-1β, protects islets from cytokine-induced necrosis and apoptosis. Therefore, an imbalance between IL-1β and IL-1Ra might influence the courses of allogeneic and autoimmune responses to islets. Our group previously demonstrated that the circulating serine-protease inhibitor human alpha-1-antitrypsin (hAAT), the levels of which increase in circulation during acute-phase immune responses, exhibits anti-inflammatory and islet-protective properties, as well as immunomodulatory activity. In the present study, we sought to determine whether the pancreatic islet allograft-protective activity of hAAT was mediated by IL-1Ra induction. Our results demonstrated that hAAT led to a 2.04-fold increase in IL-1Ra expression in stimulated macrophages and that hAAT-pre-treated islet grafts exhibited a 4.851-fold increase in IL-1Ra transcript levels, which were associated with a moderate inflammatory profile. Unexpectedly, islets that were isolated from IL-1Ra-knockout mice and pre-treated with hAAT before grafting into wild-type mice yielded an increase in intragraft IL-1Ra expression that was presumably derived from infiltrating host cells, albeit in the absence of hAAT treatment of the host. Indeed, hAAT-pre-treated islets generated hAAT-free conditioned medium that could induce IL-1Ra production in cultured macrophages. Finally, we demonstrated that hAAT promoted a distinct phosphorylation and nuclear translocation pattern for p65, a key transcription factor required for IL-1Ra expression.

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.

Role of the mitochondria in immune-mediated apoptotic death of the human pancreatic β cell line βLox5

Mitochondria are indispensable in the life and death of many types of eukaryotic cells. In pancreatic beta cells, mitochondria play an essential role in the secretion of insulin, a hormone that regulates blood glucose levels. Unregulated blood glucose is a hallmark symptom of diabetes. The onset of Type 1 diabetes is preceded by autoimmune-mediated destruction of beta cells. However, the exact role of mitochondria has not been assessed in beta cell death. In this study, we examine the role of mitochondria in both Fas- and proinflammatory cytokine-mediated destruction of the human beta cell line, βLox5. IFNγ primed βLox5 cells for apoptosis by elevating cell surface Fas. Consequently, βLox5 cells were killed by caspase-dependent apoptosis by agonistic activation of Fas, but only after priming with IFNγ. This beta cell line undergoes both apoptotic and necrotic cell death after incubation with the combination of the proinflammatory cytokines IFNγ and TNFα. Additionally, both caspase-dependent and -independent mechanisms that require proper mitochondrial function are involved. Mitochondrial contributions to βLox5 cell death were analyzed using mitochondrial DNA (mtDNA) depleted βLox5 cells, or βLox5 ρ⁰ cells. βLox5 ρ⁰ cells are not sensitive to IFNγ and TNFα killing, indicating a direct role for the mitochondria in cytokine-induced cell death of the parental cell line. However, βLox5 ρ⁰ cells are susceptible to Fas killing, implicating caspase-dependent extrinsic apoptotic death is the mechanism by which these human beta cells die after Fas ligation. These data support the hypothesis that immune mediators kill βLox5 cells by both mitochondrial-dependent intrinsic and caspase-dependent extrinsic pathways.

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

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

Beta cell apoptosis in diabetes

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

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.

Nuclear and Mitochondrial Interaction Involving mt-Nd2 Leads to Increased Mitochondrial Reactive Oxygen Species Production

NADH dehydrogenase subunit 2, encoded by the mtDNA, has been associated with resistance to autoimmune type I diabetes (T1D) in a case control study. Recently, we confirmed a role for the mouse ortholog of the protective allele (mt-Nd2(a)) in resistance to T1D using genetic analysis of outcrosses between T1D-resistant ALR and T1D-susceptible NOD mice. We sought to determine the mechanism of disease protection by elucidating whether mt-Nd2(a) affects basal mitochondrial function or mitochondrial function in the presence of oxidative stress. Two lines of reciprocal conplastic mouse strains were generated: one with ALR nuclear DNA and NOD mtDNA (ALR.mt(NOD)) and the reciprocal with NOD nuclear DNA and ALR mtDNA (NOD.mt(ALR)). Basal mitochondrial respiration, transmembrane potential, and electron transport system enzymatic activities showed no difference among the strains. However, ALR.mt(NOD) mitochondria supported by either complex I or complex II substrates produced significantly more reactive oxygen species when compared with both parental strains, NOD.mt(ALR) or C57BL/6 controls. Nitric oxide inhibited respiration to a similar extent for mitochondria from the five strains due to competitive antagonism with molecular oxygen at complex IV. Superoxide and hydrogen peroxide generated by xanthine oxidase did not significantly decrease complex I function. The protein nitrating agents peroxynitrite or nitrogen dioxide radicals significantly decreased complex I function but with no significant difference among the five strains. In summary, mt-Nd2(a) does not confer elevated resistance to oxidative stress; however, it plays a critical role in the control of the mitochondrial reactive oxygen species production.

Apoptosis in autoimmune diabetes: the fate of beta-cells in the cleft between life and death

Cytokine-induced beta-cell death is the end-stage event in the pathogenesis of autoimmune diabetes. Beside cytokines, several pro-apoptotic pathways mediated through nitric oxide, reactive oxygen species, glucose and Fas ligation can be involved, suggesting that programmed cell death (PCD) is a critical aspect in this process. The apoptotic program is activated by the utilization of the Fas/Fas-ligand (FasL) axis in the interrelation of T and beta-cells. Evidence for this mechanism arose from the finding that beta-cells in NOD mice could be protected from apoptosis by blocking the Fas-FasL pathway. Glucose is a regulator of Fas expression on human beta-cells and elevated glucose levels may contribute to accelerated beta-cell destruction by constitutively expressed FasL independently of the autoimmune reaction. It can thus be concluded that immunological, as well as metabolic, pathways may act in concert to cause beta-cell destruction. Much experimental work has been carried out to manipulate beta-cells in transgenic mice expressing apoptosis modulators in islets. For example, the transcription factor, nuclear factor-kappaB (NF-kappaB), promotes the expression of several beta-cell genes, including pro- and anti-apoptotic genes. The prevention of cytokine-induced gene expression of several NF-kappaB targets, such as inducible nitric oxide synthase, Fas, and manganese superoxide dismutase can prevent beta-cell death. Thus, modulating the expression of apoptotic mediators may significantly affect the end-stage outcome of autoimmune diabetes and could thus be a potential avenue for clinical therapy, even though currently existing findings remain exploratory due to the restrictions of transgenic mouse models.

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.

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.

Rapid destruction of encapsulated islet xenografts by NOD mice is CD4-dependent and facilitated by B-cells: innate immunity and autoimmunity do not play significant roles

BACKGROUND

Spontaneously diabetic NOD mice rapidly reject microencapsulated islet xenografts via an intense pericapsular inflammatory response.

METHODS

Tilapia (fish) islets were encapsulated in 1.5% alginate gel microspheres. Recipients in series 1 were spontaneously diabetic NOD mice and streptozotocin-diabetic nude, euthymic Balb/c, prediabetic NOD, and NOR (a recombinant congenic strain not prone to autoimmune diabetes) mice. Recipients in Series 2 were STZ-diabetic NOD, NOD-scid, NOD CD4 T-cell KO, NOD CD8 T-cell KO, and NOD B-cell KO mice.

RESULTS

In Series 1, encapsulated fish islet grafts uniformly survived long-term in nude mice but were rejected in Balb/c and, at a markedly accelerated rate, in spontaneously diabetic NOD, streptozotocin-diabetic NOD and NOR recipients. Histologically, intense inflammation (macrophages and eosinophils) surrounding the microcapsules was seen only in NOD and NOR recipients. In Series 2, encapsulated fish islets uniformly survived long-term in NOD-scid and NOD CD4 KO mice; graft survival was markedly prolonged in B-cell KO (P<0.001) but not CD8 KO mice.

CONCLUSIONS

The rapid rejection of alginate encapsulated islet xenografts by NOD mice is not solely a consequence of beta-cell directed autoimmunity nor is it merely a vigorous innate immune response. Graft rejection requires CD4 T-cells, is facilitated by B-cells, and does not require CD8 T-cells.

Fas ligand down-regulates cytokine-induced Fas receptor expression on insulinoma (NIT-1), but not islet cells, from autoimmune nonobese diabetic mice

In the pathogenesis of autoimmune type 1 diabetes, the apoptosis receptor Fas appears de novo on the surface of insulin-producing beta-cells. Fas expression is thought to be induced by proinflammatory cytokines, such as IL-1beta, interferon-gamma (IFNgamma), and TNFalpha, released by islet-infiltrating mononuclear cells. To determine whether beta-cells can modulate their sensitivity to apoptosis at the level of Fas, we investigated the effect of Fas ligand (FasL) on surface expression of Fas in NIT-1 insulinoma cells from nonobese diabetic (NOD) mice prone to autoimmune diabetes and islet cells from NOD and nonautoimmune BALB/c mice. In NIT-1 insulinoma cells, Fas expression induced by the cytokine combination IL-1beta and IFNgamma was reduced in the presence of FasL, whereas in islet cells Fas expression was unaffected by FasL. The effect of FasL on NIT-1 cells was evident during and after the induction of Fas expression by IL-1beta and IFNgamma. Thus, FasL down-regulates cytokine-induced Fas expression in NOD mouse-derived NIT-1 cells, but not in NOD or BALB/c mouse islets. The ability of NIT-1 cells to down-regulate Fas receptor in response to ligation is similar to that of a variety of tumor cells, which may use this mechanism to escape destruction by cytotoxic T cells. Islets apparently cannot protect themselves against FasL-induced apoptosis by down-regulating the Fas receptor. Understanding how NIT-1 insulinoma cells down-regulate Fas receptor in response to ligation by FasL has therapeutic implications for protecting normal beta-cells in autoimmune type 1 diabetes.

Virally induced inflammation triggers fratricide of Fas-ligand-expressing beta-cells

Tissue-specific expression of Fas-ligand (Fas-L) can provide immune privilege by inducing apoptosis of "invading" lymphocytes expressing Fas. However, accelerated diabetes has been reported in transgenic mice expressing Fas-L in islets (RIP-Fas-L) as a result of Fas-dependent fratricide of beta-cells after transfer of diabetogenic clones. Here we studied whether Fas-L could protect islets from autoaggressive CD8 lymphocytes in a transgenic model of virally induced diabetes (RIP-LCMV-NP transgenic mice), in which the autoaggressive response is directed to a viral nucleoprotein (NP) expressed as a transgene in beta-cells. Indeed, disease incidence after viral (lymphocytic choriomeningitis virus [LCMV]) infection was reduced by approximately 30%, which was associated with a decrease of autoaggressive CD8 NP-specific lymphocytes in islets and pancreatic draining lymph nodes. However, surprisingly, a high degree (50%) of diabetes was seen in mice that expressed only Fas-L but not the viral transgene (NP) in beta-cells after infection with LCMV. This was due to induction of Fas on beta-cells after LCMV infection of the pancreas, resulting in Fas/Fas-L-mediated fratricide. Thus, although Fas-L can lend some immune privilege to islet cells, local virus-induced inflammation will induce Fas on beta-cells, leading to their mutual destruction if Fas-L is present. Expression of Fas-L therefore might not be protective in situations in which viral inflammation can be expected, resulting in Fas induction on the targeted cell itself.

Vaccine therapies for the prevention of type 1 diabetes mellitus

Type 1 diabetes mellitus results from immune-mediated destruction of pancreatic beta-cells, leading to loss of insulin production. Strategies to prevent or reverse diabetes development include beta-cell protection, regeneration, or replacement. Recent advances in our understanding of the autoimmune process leading to diabetes has generated interest in the potential use of immunomodulatory agents that may collectively be termed vaccines, to prevent type 1 diabetes. Vaccines may work in various ways, including changing the immune response from a destructive (e.g. Th1) to a more benign (e.g. Th2) response, inducing antigen-specific regulatory T cells, deleting autoreactive T cells, or preventing immune cell interaction. To date, most diabetes vaccine development has been in animal models, with relatively few human trials having been completed. A major finding of animal models such as the non-obese diabetic (NOD) mouse is that they are extremely sensitive to diabetes protection, such that many interventions that protect mice are not successful in humans. This is particularly evident for human insulin tolerance studies, including the Diabetes Prevention Trial-1, where no human protection was seen from insulin despite positive NOD results. Further challenges are posed by the need to translate protective vaccine doses in mice to effective human doses. Despite such problems, some promising human vaccine data are beginning to emerge. Recent pilot studies have suggested a beneficial effect in recent-onset human type 1 diabetes from administration of nondepleting anti-CD3 antibodies or a peptide from heat shock protein 60. Given past experience, however, large multicenter, double-blind, controlled confirmatory studies are clearly required and longer term toxicity issues of drugs such as anti-CD3 need to be addressed.Diabetes vaccine development would benefit greatly from the development of reliable surrogate markers of immunoregulation. These would allow faster and more efficient screening of vaccine candidates, and would also assist in the translation of vaccine doses from animal to human studies. Unfortunately, research funding bodies desperate to find a cure are embarking on expensive clinical trials without first addressing important underlying issues such as animal-human dose translation and possible mechanisms of action. No doubt this is due to pressure from their constituency to rapidly find a cure, but unfortunately this approach may slow rather than speed the development of an effective vaccine cure. However, despite the significant hurdles that remain, vaccines remain one of the most promising strategies to prevent type 1 diabetes, with major advantages including convenience, safety, and long-lasting protection.

Autoimmune Diabetes in the NOD Mouse: An Essential Role of Fas-FasL Signaling in β Cell Apoptosis

Despite evidence that both Fas and FasL can be expressed in pancreatic islets, there has been considerable controversy regarding the potential role of Fas signaling in autoimmune beta cell death. Using the HIPFasL model, we have been able to demonstrate that, in the presence of an inflammatory infiltrate, FasL-expressing beta cells are exquisitely sensitive to Fas-mediated apoptosis and that this can be blocked by preventing FasL-Fas interaction. This points to a highly important role of Fas-FasL interaction in autoimmune beta cell death.

Developmentally regulated expression of Survivin in human pancreatic islets

Islet cell apoptosis plays a role in both normal development of the endocrine pancreas and in the pathogenesis of Type I and Type II diabetes. The molecular mechanisms regulating islet cell death and survival in both normal and pathological situations are still not completely elucidated. The inhibitor of apoptosis protein (IAP) Survivin has an anti-apoptotic function mediated by several mechanisms; these include inhibiting caspase 3 and caspase 7. Survivin expression has been reported in human fetal islets and it may play a role in pancreatic remodeling and islet homeostasis. However, there are no data concerning either its expression in neonate or adult islets or its expression in any specific subtype of islet cells. We identified Survivin expression by immunohistochemistry in alpha cells and beta islet cells of 5/5 fetal pancreases. In contrast, fetal delta cells failed to demonstrate any detectable level of Survivin expression. Survivin expression was subsequently lost in the beta cells but not the alpha cells of 5/5 newborns and 5/5 adult subjects. Neonatal and adult delta cells maintained the lack of Survivin expression seen in fetal islets. These data show that different subtypes of islet cells differ in their pattern of Survivin expression. Furthermore, expression of Survivin in the beta cells is developmentally regulated.

Pancreatic-derived factor (FAM3B), a novel islet cytokine, induces apoptosis of insulin-secreting beta-cells

PANDER (PANcreatic DERived factor, FAM3B), a newly discovered secreted cytokine, is specifically expressed at high levels in the islets of Langerhans of the endocrine pancreas. To evaluate the role of PANDER in beta-cell function, we investigated the effects of PANDER on rat, mouse, and human pancreatic islets; the beta-TC3 cell line; and the alpha-TC cell line. PANDER protein was present in alpha- and beta-cells of pancreatic islets, insulin-secreting beta-TC3 cells, and glucagon-secreting alpha-TC cells. PANDER induced islet cell death in rat and human islets. Culture of beta-TC3 cells with recombinant PANDER had a dose-dependent inhibitory effect on cell viability. This effect was also time-dependent. PANDER caused apoptosis of beta-cells as assessed by electron microscopy, annexin V fluorescent staining, and flow-cytometric terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling assay. PANDER did not affect cytosolic Ca(2+) levels or nitric oxide levels. However, PANDER activated caspase-3. Hence, PANDER may have a role in the process of pancreatic beta-cell apoptosis.

Mechanisms of accelerated immune-mediated diabetes resulting from islet beta cell expression of a Fas ligand transgene

Nonobese diabetic (NOD) mice transgenic for Fas ligand (FasL) on islet beta cells (HIPFasL mice) exhibit an accelerated diabetes distinct from the normal autoimmune diabetes of NOD mice. This study was undertaken to define the mechanism underlying accelerated diabetes development in HIPFasL mice. It was found that diabetes in HIPFasL mice is dependent on the NOD genetic background, as HIPFasL does not cause diabetes when crossed into other mice strains and is lymphocyte dependent, as it does not develop in HIPFasL(SCID) mice. Diabetes development in NOD(SCID) recipients of diabetic HIPFasL splenocytes is slower than when using splenocytes from diabetic NOD mice. Beta cells from HIPFasL mice are more susceptible to cytokine-induced apoptosis than wild-type NOD beta cells, and this can be blocked with anti-FasL Ab. HIPFasL islets are more rapidly destroyed than wild-type islets when transplanted into nondiabetic NOD mice. This confirms that FasL(+) islets do not obtain immune privilege, and instead NOD beta cells constitutively expressing FasL are more susceptible to apoptosis induced by Fas-FasL interaction. These findings are consistent with the accelerated diabetes of young HIPFasL mice being a different disease process from the autoimmune diabetes of wild-type NOD mice. The data support a mechanism by which cytokines produced by the insulitis lesion mediate up-regulation of beta cell Fas expression, resulting in suicide or fratricide of HIPFasL beta cells that overexpress FasL.

Human, nonhuman primate, and rat pancreatic islets express erythropoietin receptors

BACKGROUND

Erythropoietin (EPO) promotes survival in a variety of cells by mediating antiapoptotic signals through the EPO receptor (R). The authors examined pancreatic islets for the presence of EPO-R to determine whether these cells are protected by EPO from cytokine-induced apoptosis.

METHODS

Reverse-transcriptase polymerase chain reaction, immunohistology, and Western blots were used to establish the presence and localization of EPO-R on rat, nonhuman primate, and human islets. Islets were exposed to cytokines in the presence and absence of recombinant EPO and apoptosis was measured using a terminal deoxynucleotide transferase-mediated dUTP nick-end labeling assay followed by fluorescence-activated cell sorter analysis. Glucose stimulation indices were measured to assess the effect of EPO on islet function.

RESULTS

The presence of EPO-R was demonstrated on islets regardless of species. Recombinant EPO protected islets in culture from cytokine-induced apoptosis in a dose-dependent manner. Furthermore, the presence of EPO in the media does not adversely affect islet function.

CONCLUSIONS

This is the first demonstration that pancreatic islets express EPO-R and that EPO may prevent islet-cell apoptosis in culture. In vivo trials to evaluate the potential of long-term expression of EPO to augment islet survival in transplantation are underway.

Prospects for the prevention and reversal of type 1 diabetes mellitus

Type 1 (insulin-dependent) diabetes mellitus results from selective immune-mediated destruction of pancreatic islet beta cells. Strategies to prevent or reverse the development of diabetes can be divided into three groups, depending on whether they focus on beta-cell protection, regeneration or replacement. Prevention of immune beta-cell destruction involves either halting the immune attack directed against beta cells or making beta cells better able to withstand immune attack, for example, by making them resistant to free radical damage. The recent identification of beta-cell growth factors and development of stem cell technologies provides an alternative route to the reversal of diabetes, namely beta-cell regeneration. Interestingly, stem cell-derived islets appear to be less sensitive to recurrent immune destruction that is normally seen in response to islet transplantation. The last alternative is beta-cell replacement or substitution. This covers a wide range of interventions including human whole pancreas transplantation, xenotransplantation, genetically modified beta cells, mechanical insulin sensing and delivery devices, and the artificial pancreas. This review describes recent advances in each of these research areas and aims to provide clinicians with an idea of where and when an effective strategy to prevent or reverse diabetes development will become available.

Efficient transduction of pancreatic islets by feline immunodeficiency virus vectors1

BACKGROUND

Pancreatic islets transplanted into immunocompetent diabetic subjects are rapidly lost to apoptotic or lytic death or both. Genetic engineering of islets before transplantation with protective genes may enhance their posttransplantation survival. Accomplishing this goal requires the development of a safe, efficient vector for islet gene delivery.

METHODS

The ability of feline immunodeficiency virus (FIV) vectors to transfer a green fluorescent protein (GFP) gene to NIT-1 cells and primary islets was measured and compared with murine leukemia virus (MLV) and human immunodeficiency virus (HIV) vectors. Islets were examined using confocal microscopy to determine the extent and pattern of infection. Toxicity of the procedure was assessed via measurement of glucose stimulation indices and by reversion of diabetic mice using either FIV-infected or control islet transplants.

RESULTS

FIV effectively transduces islets with no untoward effect on the insulin secretion capacity of the beta cells. When FIV, HIV, and MLV GFP vectors were standardized to the same 293 cell titer and used to infect NIT-1 cells or whole islets, the FIV transduced equal or greater numbers of cells relative to the HIV vector and significantly more than the MLV vector. Islets transduced with FIV GFP were transplanted in a murine model for diabetes and were shown to revert diabetes and express GFP 4 weeks after transduction and 3 weeks after transplantation.

CONCLUSIONS

FIV transduction is a nontoxic and efficient method to genetically modify pancreatic islets and may prove promising for delivering genes to augment islet survival after transplantation.

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.

The role of Fas ligand in beta cell destruction in autoimmune diabetes of NOD mice

Fas ligand (FasL), a type 2 membrane protein belonging to the TNF family, plays an important role in the induction of cell death. Ligation of Fas receptors by FasL results in apoptosis of the Fas-expressing cell. Autoimmune diabetes results from beta cell destruction by islet-reactive T cells, a process that involves beta cell apoptosis. This raises the question of whether the FasL-Fas pathway plays a major role in beta cell death. To address this issue it is important to know whether beta cells express Fas and/or FasL and, if so, whether induction of these molecules leads to beta cell death. In fact, both Fas and FasL have been demonstrated to be expressed by beta cells in response to cytokine stimulation, although there remains an argument in the literature as to whether beta cells truly express FasL. This is largely because FasL expression has only been demonstrable by immunohistochemistry and not by flow cytometry. Transgenic NOD mice with beta cells expressing a FasL transgene develop an accelerated form of diabetes. We show here that beta cells from FasL transgenic NOD mice are more susceptible to cytokine-induced apoptosis than wild-type beta cells, consistent with the hypothesis that if beta cells express FasL then Fas-FasL interaction on the beta cell surface is able to mediate beta cell self-death in the absence of T cells. Interventions that block the Fas-FasL pathway may be useful, therefore, in the prevention or treatment of type 1 diabetes.

Cell surface trafficking of Fas in NIT-1 cells and dissection of surface and total Fas expression

The appearance of Fas receptor at the surface of pancreatic beta-cells affected by progressive insulitis strongly suggests that Fas-mediated beta-cell apoptosis plays an important role in the pathogenesis of type 1 diabetes. In support of this concept, the present study has shown that islet cells from NOD mice and the beta-cell line NIT-1 respond to the proinflammatory cytokines IL-1beta and IFN-gamma with Fas surface expression in a dose- and time-dependent manner. Moreover, the prevention of cytokine-induced surface Fas expression by actinomycin D, cycloheximide, and brefeldin A demonstrated that trafficking of Fas to the beta-cell surface requires RNA and protein synthesis and, in addition is critically dependent on intracellular protein transport. Compared with total cellular Fas protein, the amount of Fas at the cell surface was relatively small and indicated that Fas is preferentially expressed in cytoplasmic compartments of NIT-1 cells. It is concluded that inflammatory insults specifically induce translocation of Fas to the beta-cell surface and that interference with cell surface Fas expression is a new strategy to improve beta-cell survival in inflamed islets.

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.

Cytokine induction of Fas gene expression in insulin-producing cells requires the transcription factors NF-kappaB and C/EBP

Fas-mediated cell death may play a role in the autoimmune destruction of pancreatic beta-cells in type 1 diabetes. beta-Cells do not express Fas under physiological conditions, but Fas mRNA and protein are induced in cytokine-exposed mouse and human islets, rendering the beta-cells susceptible to Fas ligand-induced apoptosis. The aim of the present study was to investigate the molecular regulation of Fas by cytokines in rat beta-cells and in insulin-producing RINm5F cells. Fas mRNA expression was increased 15-fold in fluorescence-activated cell sorting-purified rat beta-cells exposed to interleukin (IL)-1beta, whereas gamma-interferon had no effect. Transfection experiments of rat Fas promoter-luciferase reporter constructs into purified rat beta-cells and RINm5F insulinoma cells identified an IL-1beta-responsive region between nucleotides -223 and -54. Inactivation of two adjacent NF-kappaB and C/EBP sites in this region abolished IL-1beta-induced Fas promoter activity in RINm5F cells. Binding of NF-kappaB and C/EBP factors to their respective sites was confirmed by gel shift assays. In cotransfection experiments, NF-kappaB p65 transactivated the Fas promoter. NF-kappaB p50 and C/EBPbeta overexpression had no effect by themselves on the Fas promoter activity, but when cotransfected with p65, each factor inhibited transactivation by p65. These results suggest a critical role for NF-kappaB and C/EBP factors in cytokine-regulation of Fas expression in insulin-producing cells.

Ethanol-induced apoptosis in mouse liver: Fas- and cytochrome c-mediated caspase-3 activation pathway

Hepatic apoptosis has been shown to occur in both experimental and clinical alcoholic liver disease, but the signaling pathway remains unknown. This study was undertaken to examine specifically the involvement of the upstream signals, Fas and cytochrome c, in alcohol-induced caspase-3 activation and apoptosis in the liver. Male FVB mice were administrated intragastrically a single dose of alcohol at 6 g/kg, which has been shown to represent binge drinking in humans. Hepatic apoptosis was detected by a terminal deoxynucleotidyl transferase dUTP nick-end labeling assay. Active form of caspase-3 was identified by immunoperoxidase staining and confirmed by immunogold labeling and was found to be in the cytosol and nucleus. Enzymic assay further confirmed caspase-3 activation and nucleus localization. Systemic administration of caspase-3 inhibitor, Ac-DEVD-FMK, inhibited caspase-3 activity and abrogated apoptosis. Elevation of cytosolic cytochrome c was found by immunoperoxidase staining, immunogold labeling, and Western blot. Increased Fas ligand expression was detected by immunoperoxidase staining. Intravenous administration of a neutralizing Fas ligand monoclonal antibody resulted in suppression of caspase-3 activation and attenuation of apoptosis, but did not inhibit mitochondrial cytochrome c release. The results thus demonstrate that Fas/Fas ligand system-mediated caspase-3 activation plays a central role in the ethanol-induced hepatic apoptosis.