ABCA12 regulates insulin secretion from ß-cells.

Dysregulation of lipid homeostasis is intimately associated with defects in insulin secretion, a key feature of type 2 diabetes. Here, we explore the role of the putative lipid transporter ABCA12 in regulating insulin secretion from ß-cells. Mice with ß-cell-specific deletion of Abca12 display impaired glucose-stimulated insulin secretion and eventual islet inflammation and ß-cell death. ABCA12's action in the pancreas is independent of changes in the abundance of two other cholesterol transporters, ABCA1 and ABCG1, or of changes in cellular cholesterol or ceramide content. Instead, loss of ABCA12 results in defects in the genesis and fusion of insulin secretory granules and increases in the abundance of lipid rafts at the cell membrane. These changes are associated with dysregulation of the small GTPase CDC42 and with decreased actin polymerisation. Our findings establish a new, pleiotropic role for ABCA12 in regulating pancreatic lipid homeostasis and insulin secretion.

Deficiency of the innate immune adaptor STING promotes autoreactive T cell expansion in NOD mice.

AIMS/HYPOTHESIS: Stimulator of IFN genes (STING) is a central hub for cytosolic nucleic acid sensing and its activation results in upregulation of type I IFN production in innate immune cells. A type I IFN gene signature seen before the onset of type 1 diabetes has been suggested as a driver of disease initiation both in humans and in the NOD mouse model. A possible source of type I IFN is through activation of the STING pathway. Recent studies suggest that STING also has antiproliferative and proapoptotic functions in T cells that are independent of IFN. To investigate whether STING is involved in autoimmune diabetes, we examined the impact of genetic deletion of STING in NOD mice. METHODS: CRISPR/Cas9 gene editing was used to generate STING-deficient NOD mice. Quantitative real-time PCR was used to assess the level of type I IFN-regulated genes in islets from wild-type and STING-deficient NOD mice. The number of islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP)206-214-specific CD8+ T cells was determined by magnetic bead-based MHC tetramer enrichment and flow cytometry. The incidence of spontaneous diabetes and diabetes after adoptive transfer of T cells was determined. RESULTS: STING deficiency partially attenuated the type I IFN gene signature in islets but did not suppress insulitis. STING-deficient NOD mice accumulated an increased number of IGRP206-214-specific CD8+ T cells (2878 ± 642 cells in NOD.STING-/- mice and 728.8 ± 196 cells in wild-type NOD mice) in peripheral lymphoid tissue, associated with a higher incidence of spontaneous diabetes (95.5% in NOD.STING-/- mice and 86.2% in wild-type NOD mice). Splenocytes from STING-deficient mice rapidly induced diabetes after adoptive transfer into irradiated NOD recipients (median survival 75 days for NOD recipients of NOD.STING-/- mouse splenocytes and 121 days for NOD recipients of NOD mouse splenocytes). CONCLUSIONS/INTERPRETATION: Data suggest that sensing of endogenous nucleic acids through the STING pathway may be partially responsible for the type I IFN gene signature but not autoimmunity in NOD mice. Our results show that the STING pathway may play an unexpected intrinsic role in suppressing the number of diabetogenic T cells.

Perforin facilitates beta cell killing and regulates autoreactive CD8+ T-cell responses to antigen in mouse models of type 1 diabetes.

In type 1 diabetes, cytotoxic CD8(+) T lymphocytes (CTLs) directly interact with pancreatic beta cells through major histocompatibility complex class I. An immune synapse facilitates delivery of cytotoxic granules, comprised mainly of granzymes and perforin. Perforin deficiency protects the majority of non-obese diabetic (NOD) mice from autoimmune diabetes. Intriguingly perforin deficiency does not prevent diabetes in CD8(+) T-cell receptor transgenic NOD8.3 mice. We therefore investigated the importance of perforin-dependent killing via CTL-beta cell contact in autoimmune diabetes. Perforin-deficient CTL from NOD mice or from NOD8.3 mice were significantly less efficient at adoptive transfer of autoimmune diabetes into NODRag1(-/-) mice, confirming that perforin is essential to facilitate beta cell destruction. However, increasing the number of transferred in vitro-activated perforin-deficient 8.3 T cells reversed the phenotype and resulted in diabetes. Perforin-deficient NOD8.3 T cells were present in increased proportion in islets, and proliferated more in response to antigen in vivo indicating that perforin may regulate the activation of CTLs, possibly by controlling cytokine production. This was confirmed when we examined the requirement for direct interaction between beta cells and CD8(+) T cells in NOD8.3 mice, in which beta cells specifically lack major histocompatibility complex (MHC) class I through conditional deletion of ß2-microglobulin. Although diabetes was significantly reduced, 40% of these mice developed diabetes, indicating that NOD8.3 T cells can kill beta cells in the absence of direct interaction. Our data indicate that although perforin delivery is the main mechanism that CTL use to destroy beta cells, they can employ alternative mechanisms to induce diabetes in a perforin-independent manner.

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.

Intra-islet proliferation of cytotoxic T lymphocytes contributes to insulitis progression.

Infiltration of pancreatic islets by immune cells, termed insulitis, increases progressively once it begins and leads to clinical type 1 diabetes. But even after diagnosis some islets remain unaffected and infiltration is patchy rather than uniform. Traffic of autoreactive T cells into the pancreas is likely to contribute to insulitis progression but it could also depend on T-cell proliferation within islets. This study utilizes transgenic NOD mice to assess the relative contributions of these two mechanisms. Progression of insulitis in NOD8.3 TCR transgenic mice was mildly reduced by inhibition of T-cell migration with the drug FTY720. In FTY720-treated mice, reduced beta cell MHC class I expression prevented progression of insulitis both within affected islets and to previously unaffected islets. CTL proliferation was significantly reduced in islets with reduced or absent beta cell expression of MHC class I protein. This indicates that intra-islet proliferation, apparently dependent on beta cell antigen presentation, in addition to recruitment, is a significant factor in progression of insulitis.

Autoreactive cytotoxic T lymphocytes acquire higher expression of cytotoxic effector markers in the islets of NOD mice after priming in pancreatic lymph nodes.

Cytotoxic T lymphocytes (CTLs) that cause type 1 diabetes are activated in draining lymph nodes and become concentrated as fully active CTLs in inflamed pancreatic islets. It is unclear whether CTL function is driven by signals received in the lymph node or also in the inflamed tissue. We studied whether the development of cytotoxicity requires further activation in islets. Autoreactive CTLs found in the islets of diabetes-prone NOD mice had acquired much higher expression of the cytotoxic effector markers granzyme B, interferon γ, and CD107a than had those in the pancreatic lymph node (PLN). Increased expression seemed to result from stimulation in the islet itself. T cells held up from migrating from the PLN by administration of the sphingosine-1-phosphate agonist FTY720 did not increase expression of cytotoxic molecules in the PLN. Stimulation did not require antigen presentation or cytokine secretion by the target ß cells because it was not affected by the absence of class I major histocompatibility complex expression or by the overexpression of suppressor of cytokine signaling-1. Activation of CD40-expressing cells stimulated increased CTL function and ß-cell destruction, suggesting that signals derived from CD40-expressing cells promote the acquisition of cytotoxicity in the islet environment. These data provide in vivo evidence that stimulation of cytotoxic effector molecule expression occurs in inflamed islets and is independent of ß cells.

Diabetes induced by checkpoint inhibition in nonobese diabetic mice can be prevented or reversed by a JAK1/JAK2 inhibitor.

Objectives: Immune checkpoint inhibitors have achieved clinical success in cancer treatment, but this treatment causes immune-related adverse events, including type 1 diabetes (T1D). Our aim was to test whether a JAK1/JAK2 inhibitor, effective at treating spontaneous autoimmune diabetes in nonobese diabetic (NOD) mice, can prevent diabetes secondary to PD-L1 blockade. Methods: Anti-PD-L1 antibody was injected into NOD mice to induce diabetes, and JAK1/JAK2 inhibitor LN3103801 was administered by oral gavage to prevent diabetes. Flow cytometry was used to study T cells and beta cells. Mesothelioma cells were inoculated into BALB/c mice to induce a transplantable tumour model. Results: Anti-PD-L1-induced diabetes was associated with increased immune cell infiltration in the islets and upregulated MHC class I on islet cells. Anti-PD-L1 administration significantly increased islet T cell proliferation and islet-specific CD8+ T cell numbers in peripheral lymphoid organs. JAK1/JAK2 inhibitor treatment blocked IFNγ-mediated MHC class I upregulation on beta cells and T cell proliferation mediated by cytokines that use the common γ chain receptor. As a result, anti-PD-L1-induced diabetes was prevented by JAK1/JAK2 inhibitor administered before or after checkpoint inhibitor therapy. Diabetes was also reversed when the JAK1/JAK2 inhibitor was administered after the onset of anti-PD-L1-induced hyperglycaemia. Furthermore, JAK1/JAK2 inhibitor intervention after checkpoint inhibitors did not reverse or abrogate the antitumour effects in a transplantable tumour model. Conclusion: A JAK1/JAK2 inhibitor can prevent and reverse anti-PD-L1-induced diabetes by blocking IFNγ and γc cytokine activities. Our study provides preclinical validation of JAK1/JAK2 inhibitor use in checkpoint inhibitor-induced diabetes.

Neuropeptide Y1 receptor antagonism protects ß-cells and improves glycemic control in type 2 diabetes.

OBJECTIVES: Loss of functional ß-cell mass is a key factor contributing to poor glycemic control in advanced type 2 diabetes (T2D). We have previously reported that the inhibition of the neuropeptide Y1 receptor improves the islet transplantation outcome in type 1 diabetes (T1D). The aim of this study was to identify the pathophysiological role of the neuropeptide Y (NPY) system in human T2D and further evaluate the therapeutic potential of using the Y1 receptor antagonist BIBO3304 to improve ß-cell function and survival in T2D. METHODS: The gene expression of the NPY system in human islets from nondiabetic subjects and subjects with T2D was determined and correlated with the stimulation index. The glucose-lowering and ß-cell-protective effects of BIBO3304, a selective orally bioavailable Y1 receptor antagonist, in high-fat diet (HFD)/multiple low-dose streptozotocin (STZ)-induced and genetically obese (db/db) T2D mouse models were assessed. RESULTS: In this study, we identified a more than 2-fold increase in NPY1R and its ligand, NPY mRNA expression in human islets from subjects with T2D, which was significantly associated with reduced insulin secretion. Consistently, the pharmacological inhibition of Y1 receptors by BIBO3304 significantly protected ß cells from dysfunction and death under multiple diabetogenic conditions in islets. In a preclinical study, we demonstrated that the inhibition of Y1 receptors by BIBO3304 led to reduced adiposity and enhanced insulin action in the skeletal muscle. Importantly, the Y1 receptor antagonist BIBO3304 treatment also improved ß-cell function and preserved functional ß-cell mass, thereby resulting in better glycemic control in both HFD/multiple low-dose STZ-induced and db/db T2D mice. CONCLUSIONS: Our results revealed a novel causal link between increased islet NPY-Y1 receptor gene expression and ß-cell dysfunction and failure in human T2D, contributing to the understanding of the pathophysiology of T2D. Furthermore, our results demonstrate that the inhibition of the Y1 receptor by BIBO3304 represents a potential ß-cell-protective therapy for improving functional ß-cell mass and glycemic control in T2D.

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.

Liver-specific suppressor of cytokine signaling-3 deletion in mice enhances hepatic insulin sensitivity and lipogenesis resulting in fatty liver and obesity.

UNLABELLED: Obesity is associated with chronic inflammation and contributes to the development of insulin resistance and nonalcoholic fatty liver disease. The suppressor of cytokine signaling-3 (SOCS3) protein is increased in inflammation and is thought to contribute to the pathogenesis of insulin resistance by inhibiting insulin and leptin signaling. Therefore, we studied the metabolic effects of liver-specific SOCS3 deletion in vivo. We fed wild-type (WT) and liver-specific SOCS3 knockout (SOCS3 LKO) mice either a control diet or a high-fat diet (HFD) for 6 weeks and examined their metabolic phenotype. We isolated hepatocytes from WT and SOCS3 LKO mice and examined the effects of tumor necrosis factor α and insulin on Akt phosphorylation and fatty acid metabolism and lipogenic gene expression. Hepatocytes from control-fed SOCS3 LKO mice were protected from developing tumor necrosis factor α-induced insulin resistance but also had increased lipogenesis and expression of sterol response element-binding protein-1c target genes. Lean SOCS3 LKO mice fed a control diet had enhanced hepatic insulin sensitivity; however, when fed an HFD, SOCS3 LKO mice had increased liver fat, inflammation, and whole-body insulin resistance. SOCS3 LKO mice fed an HFD also had elevated hypothalamic SOCS3 and fatty acid synthase expression and developed greater obesity due to increased food intake and reduced energy expenditure. CONCLUSION: Deletion of SOCS3 in the liver increases liver insulin sensitivity in mice fed a control diet but paradoxically promotes lipogenesis, leading to the development of nonalcoholic fatty liver disease, inflammation, and obesity.

IL-17F induces inflammation, dysfunction and cell death in mouse islets.

Type 17 immune responses, typified by the production of the cytokines IL-17A and IL-17F, have been implicated in the development of type 1 diabetes in animal models and human patients, however the underlying pathogenic mechanisms have not been clearly elucidated. While previous studies show that IL-17A enhances inflammatory gene expression and cell death in mouse ß-cells and human islets, the function of IL-17F in pancreatic ß-cells is completely untested to date. Here we show that IL-17F exhibits potent pathogenic effects in mouse ß-cell lines and islets. IL-17F signals via the IL-17RA and -RC subunits in ß-cells and in combination with other inflammatory cytokines induces expression of chemokine transcripts, suppresses the expression of ß-cell identity genes and impairs glucose stimulated insulin secretion. Further IL-17F induces cell death in primary mouse islets. This occurs via Jnk, p38 and NF-κB dependent induction of Nos2 and is completely ablated in the presence of an inducible nitric oxide synthase (iNOS) inhibitor. Together these data indicate that IL-17F possesses similar pathogenic activities to IL-17A in mouse ß-cell lines and islets and is likely to be a type 17 associated pathogenic factor in type 1 diabetes.

The JAK1 Selective Inhibitor ABT 317 Blocks Signaling Through Interferon-γ and Common γ Chain Cytokine Receptors to Reverse Autoimmune Diabetes in NOD Mice.

Cytokines that signal through the JAK-STAT pathway, such as interferon-γ (IFN-γ) and common γ chain cytokines, contribute to the destruction of insulin-secreting ß cells by CD8+ T cells in type 1 diabetes (T1D). We previously showed that JAK1/JAK2 inhibitors reversed autoimmune insulitis in non-obese diabetic (NOD) mice and also blocked IFN-γ mediated MHC class I upregulation on ß cells. Blocking interferons on their own does not prevent diabetes in knockout NOD mice, so we tested whether JAK inhibitor action on signaling downstream of common γ chain cytokines, including IL-2, IL-7 IL-15, and IL-21, may also affect the progression of diabetes in NOD mice. Common γ chain cytokines activate JAK1 and JAK3 to regulate T cell proliferation. We used a JAK1-selective inhibitor, ABT 317, to better understand the specific role of JAK1 signaling in autoimmune diabetes. ABT 317 reduced IL-21, IL-2, IL-15 and IL-7 signaling in T cells and IFN-γ signaling in ß cells, but ABT 317 did not affect GM-CSF signaling in granulocytes. When given in vivo to NOD mice, ABT 317 reduced CD8+ T cell proliferation as well as the number of KLRG+ effector and CD44hiCD62Llo effector memory CD8+ T cells in spleen. ABT 317 also prevented MHC class I upregulation on ß cells. Newly diagnosed diabetes was reversed in 94% NOD mice treated twice daily with ABT 317 while still on treatment at 40 days and 44% remained normoglycemic after a further 60 days from discontinuing the drug. Our results indicate that ABT 317 blocks common γ chain cytokines in lymphocytes and interferons in lymphocytes and ß cells and are thus more effective against diabetes pathogenesis than IFN-γ receptor deficiency alone. Our studies suggest use of this class of drug for the treatment of type 1 diabetes.

Soluble FAS ligand is not required for pancreatic islet inflammation or beta-cell destruction in non-obese diabetic mice.

CD8+ T cells play a central role in beta-cell destruction in type 1 diabetes. CD8+ T cells use two main effector pathways to kill target cells, perforin plus granzymes and FAS ligand (FASL). We and others have established that in non-obese diabetic (NOD) mice, perforin is the dominant effector molecule by which autoreactive CD8+ T cells kill beta cells. However, blocking FASL pharmacologically was shown to protect NOD mice from diabetes, indicating that FASL may have some role. FASL can engage with its receptor FAS on target cells either as membrane bound or soluble FASL. It has been shown that membrane-bound FASL is required to stimulate FAS-induced apoptosis in target cells, whereas excessive soluble FASL can induce NF-κB-dependent gene expression and inflammation. Because islet inflammation is a feature of autoimmune diabetes, we tested whether soluble FASL could be important in disease pathogenesis independent of its cell death function. We generated NOD mice deficient in soluble FASL, while maintaining expression of membrane-bound FASL due to a mutation in the FASL sequence required for cleavage by metalloproteinase. NOD mice lacking soluble FASL had normal numbers of lymphocytes in their spleen and thymus. Soluble FASL deficient NOD mice had similar islet inflammation as wild-type NOD mice and were not protected from diabetes. Our data indicate that soluble FASL is not required in development of autoimmune diabetes.

IL-21 regulates SOCS1 expression in autoreactive CD8+ T cells but is not required for acquisition of CTL activity in the islets of non-obese diabetic mice.

In type 1 diabetes, maturation of activated autoreactive CD8+ T cells to fully armed effector cytotoxic T lymphocytes (CTL) occurs within the islet. At present the signals required for the maturation process are poorly defined. Cytokines could potentially provide the necessary "third signal" required to generate fully mature CTL capable of killing insulin-producing ß-cells. To determine whether autoreactive CTL within islets respond to cytokines we generated non-obese diabetic (NOD) mice with a reporter for cytokine signalling. These mice express a reporter gene, hCD4, under the control of the endogenous regulatory elements for suppressor of cytokine signalling (SOCS)1, which is itself regulated by pro-inflammatory cytokines. In NOD mice, the hCD4 reporter was expressed in infiltrated islets and the expression level was positively correlated with the frequency of infiltrating CD45+ cells. SOCS1 reporter expression was induced in transferred ß-cell-specific CD8+ 8.3T cells upon migration from pancreatic draining lymph nodes into islets. To determine which cytokines induced SOCS1 promoter activity in islets, we examined hCD4 reporter expression and CTL maturation in the absence of the cytokine receptors IFNAR1 or IL-21R. We show that IFNAR1 deficiency does not confer protection from diabetes in 8.3 TCR transgenic mice, nor is IFNAR1 signalling required for SOCS1 reporter upregulation or CTL maturation in islets. In contrast, IL-21R-deficient 8.3 mice have reduced diabetes incidence and reduced SOCS1 reporter activity in islet CTLs. However IL-21R deficiency did not affect islet CD8+ T cell proliferation or expression of granzyme B or IFNγ. Together these data indicate that autoreactive CD8+ T cells respond to IL-21 and not type I IFNs in the islets of NOD mice, but neither IFNAR1 nor IL-21R are required for islet intrinsic CTL maturation.

Repurposed JAK1/JAK2 Inhibitor Reverses Established Autoimmune Insulitis in NOD Mice.

Recent advances in immunotherapeutics have not yet changed the routine management of autoimmune type 1 diabetes. There is an opportunity to repurpose therapeutics used to treat other diseases to treat type 1 diabetes, especially when there is evidence for overlapping mechanisms. Janus kinase (JAK) 1/JAK2 inhibitors are in development or clinical use for indications including rheumatoid arthritis. There is good evidence for activation of the JAK1/JAK2 and signal transducer and activator of transcription (STAT) 1 pathway in human type 1 diabetes and in mouse models, especially in ß-cells. We tested the hypothesis that using these drugs to block the JAK-STAT pathway would prevent autoimmune diabetes. The JAK1/JAK2 inhibitor AZD1480 blocked the effect of cytokines on mouse and human ß-cells by inhibiting MHC class I upregulation. This prevented the direct interaction between CD8+ T cells and ß-cells, and reduced immune cell infiltration into islets. NOD mice treated with AZD1480 were protected from autoimmune diabetes, and diabetes was reversed in newly diagnosed NOD mice. This provides mechanistic groundwork for repurposing clinically approved JAK1/JAK2 inhibitors for type 1 diabetes.

Granzyme A Deficiency Breaks Immune Tolerance and Promotes Autoimmune Diabetes Through a Type I Interferon-Dependent Pathway.

Granzyme A is a protease implicated in the degradation of intracellular DNA. Nucleotide complexes are known triggers of systemic autoimmunity, but a role in organ-specific autoimmune disease has not been demonstrated. To investigate whether such a mechanism could be an endogenous trigger for autoimmunity, we examined the impact of granzyme A deficiency in the NOD mouse model of autoimmune diabetes. Granzyme A deficiency resulted in an increased incidence in diabetes associated with accumulation of ssDNA in immune cells and induction of an interferon response in pancreatic islets. Central tolerance to proinsulin in transgenic NOD mice was broken on a granzyme A-deficient background. We have identified a novel endogenous trigger for autoimmune diabetes and an in vivo role for granzyme A in maintaining immune tolerance.

Activation of the NLRP3 inflammasome complex is not required for stress-induced death of pancreatic islets.

Loss of pancreatic beta cells is a feature of type-2 diabetes. High glucose concentrations induce endoplasmic reticulum (ER) and oxidative stress-mediated apoptosis of islet cells in vitro. ER stress, oxidative stress and high glucose concentrations may also activate the NLRP3 inflammasome leading to interleukin (IL)-1ß production and caspase-1 dependent pyroptosis. However, whether IL-1ß or intrinsic NLRP3 inflammasome activation contributes to beta cell death is controversial. This possibility was examined in mouse islets. Exposure of islets lacking functional NLRP3 or caspase-1 to H2O2, rotenone or thapsigargin induced similar cell death as in wild-type islets. This suggests that oxidative or ER stress do not cause inflammasome-mediated cell death. Similarly, deficiency of NLRP3 inflammasome components did not provide any protection from glucose, ribose or gluco-lipotoxicity. Finally, genetic activation of NLRP3 specifically in beta cells did not increase IL-1ß production or cell death, even in response to glucolipotoxicity. Overall, our results show that glucose-, ER stress- or oxidative stress-induced cell death in islet cells is not dependent on intrinsic activation of the NLRP3 inflammasome.

Deficiency in type I interferon signaling prevents the early interferon-induced gene signature in pancreatic islets but not type 1 diabetes in NOD mice.

Type I interferons (IFNs) have been implicated in the initiation of islet autoimmunity and development of type 1 diabetes. To directly test their involvement, we generated NOD mice deficient in type I IFN receptors (NOD.IFNAR1(-/-)). Expression of the type I IFN-induced genes Mx1, Isg15, Ifit1, Oas1a, and Cxcr4 was detectable in NOD islets as early as 1 week of age. Of these five genes, expression of Isg15, Ifit1, Oas1a, and Mx1 peaked at 3-4 weeks of age, corresponding with an increase in Ifnα mRNA, declined at 5-6 weeks of age, and increased again at 10-14 weeks of age. Increased IFN-induced gene expression was ablated in NOD.IFNAR1(-/-) islets. Loss of Toll-like receptor 2 (TLR2) resulted in reduced islet expression of Mx1 at 2 weeks of age, but TLR2 or TLR9 deficiency did not change the expression of other IFN-induced genes in islets compared with wild-type NOD islets. We observed increased ß-cell major histocompatibility complex class I expression with age in NOD and NOD.IFNAR1(-/-) mice. NOD.IFNAR1(-/-) mice developed insulitis and diabetes at a similar rate to NOD controls. These results indicate type I IFN is produced within islets in young mice but is not essential for the initiation and progression of diabetes in NOD mice.

The protective effects of CD39 overexpression in multiple low-dose streptozotocin-induced diabetes in mice.

Islet allograft survival limits the long-term success of islet transplantation as a potential curative therapy for type 1 diabetes. A number of factors compromise islet survival, including recurrent diabetes. We investigated whether CD39, an ectonucleotidase that promotes the generation of extracellular adenosine, would mitigate diabetes in the T cell-mediated multiple low-dose streptozotocin (MLDS) model. Mice null for CD39 (CD39KO), wild-type mice (WT), and mice overexpressing CD39 (CD39TG) were subjected to MLDS. Adoptive transfer experiments were performed to delineate the efficacy of tissue-restricted overexpression of CD39. The role of adenosine signaling was examined using mutant mice and pharmacological inhibition. The susceptibility to MLDS-induced diabetes was influenced by the level of expression of CD39. CD39KO mice developed diabetes more rapidly and with higher frequency than WT mice. In contrast, CD39TG mice were protected. CD39 overexpression conferred protection through the activation of adenosine 2A receptor and adenosine 2B receptor. Adoptive transfer experiments indicated that tissue-restricted overexpression of CD39 conferred robust protection, suggesting that this may be a useful strategy to protect islet grafts from T cell-mediated injury.

Complete diabetes protection despite delayed thymic tolerance in NOD8.3 TCR transgenic mice due to antigen-induced extrathymic deletion of T cells.

Prevention of autoimmunity requires the elimination of self-reactive T cells during their development in the thymus and maturation in the periphery. Transgenic NOD mice that overexpress islet-specific glucose 6 phosphatase catalytic subunit-related protein (IGRP) in antigen-presenting cells (NOD-IGRP mice) have no IGRP-specific T cells. To study the relative contribution of central and peripheral tolerance mechanisms to deletion of antigen-specific T cells, we crossed NOD-IGRP mice to highly diabetogenic IGRP206-214 T-cell receptor transgenic mice (NOD8.3 mice) and studied the frequency and function of IGRP-specific T cells in the thymus and periphery. Peripheral tolerance was extremely efficient and completely protected NOD-IGRP/NOD8.3 mice from diabetes. Peripheral tolerance was characterized by activation of T cells in peripheral lymphoid tissue where IGRP was expressed followed by activation-induced cell death. Thymectomy showed that thymic output of IGRP-specific transgenic T cells compensated for peripheral deletion to maintain peripheral T-cell numbers. Central tolerance was undetectable until 10 weeks and complete by 15 weeks. These in vivo data indicate that peripheral tolerance alone can protect NOD8.3 mice from autoimmune diabetes and that profound changes in T-cell repertoire can follow subtle changes in thymic antigen presentation.