A biphasic role of nuclear transcription factor (NF)-κB in the islet β-cell apoptosis induced by interleukin (IL)-1β

Stress-induced pseudokinase TRB3 augments IL1β signaling by interacting with Flightless homolog 1

Interleukin-1β is one of the most potent inducers of beta cell inflammation in the lead-up to type 1 diabetes. We have previously reported that IL1β-stimulated pancreatic islets from mice with genetic ablation of stress-induced pseudokinase TRB3(TRB3KO) show attenuated activation kinetics for the MAP3K MLK3 and JNK stress kinases. However, JNK signaling constitutes only a portion of the cytokine-induced inflammatory response. Here we report that TRB3KO islets also show a decrease in amplitude and duration of IL1β-induced phosphorylation of TAK1 and IKK, kinases that drive the potent NF-κB proinflammatory signaling pathway. We observed that TRB3KO islets display decreased cytokine-induced beta cell death, preceded by a decrease in select downstream NF-κB targets, including iNOS/NOS2 (inducible nitric oxide synthase), a mediator of beta cell dysfunction and death. Thus, loss of TRB3 attenuates both pathways required for a cytokine-inducible, proapoptotic response in beta cells. In order to better understand the molecular basis of TRB3-enhanced, post-receptor IL1β signaling, we interrogated the TRB3 interactome using coimmunoprecipitation followed by mass spectrometry to identify immunomodulatory protein Flightless homolog 1 (Fli1) as a novel, TRB3-interacting protein. We show that TRB3 binds and disrupts Fli1-dependent sequestration of MyD88, thereby increasing availability of this most proximal adaptor required for IL1β receptor-dependent signaling. Fli1 sequesters MyD88 in a multiprotein complex resulting in a brake on the assembly of downstream signaling complexes. By interacting with Fli1, we propose that TRB3 lifts the brake on IL1β signaling to augment the proinflammatory response in beta cells.

Biologics and atherosclerotic cardiovascular risk in rheumatoid arthritis: a review of evidence and mechanistic insights

Introduction: Cardiovascular disease is a leading comorbidity in rheumatoid arthritis. Timely introduction of biologic therapies in a treat-to-target approach has optimized disease-related outcomes and attenuated accrual of comorbidities, including cardiovascular risk.Areas covered: A literature search in MEDLINE (via PubMed) was performed between January 2009 and November 2020. This manuscript explores recent developments in atherosclerotic cardiovascular risk in RA compared with non-RA individuals; it synopsizes differences in vascular function and inflammation, prevalence, burden, vulnerability, and progression of atherosclerotic plaque and their underlying cellular and molecular mechanisms. Finally, it reviews the recent literature on cardioprotective benefits of biologics and draws mechanistic links with inhibition of new plaque formation, stabilization of high-risk lesions and improvement in endothelial function, arterial stiffness, lipid metabolism, and traditional cardiac risk factors.Expert opinion: Increasing evidence points to a solid cardioprotective influence of earlier, longer, and ongoing use of biologic treatments in RA. Nevertheless, the precise mechanistic effects of plaque progression and remodeling, vascular stiffness, endothelial dysfunction, lipid metabolism, and traditional cardiac risk factors are less rigorously characterized.

Relationship Between Inflammation and Metabolism in Patients With Newly Presenting Rheumatoid Arthritis

Background

Systemic inflammation in rheumatoid arthritis (RA) is associated with metabolic changes. We used nuclear magnetic resonance (NMR) spectroscopy-based metabolomics to assess the relationship between an objective measure of systemic inflammation [C-reactive protein (CRP)] and both the serum and urinary metabolome in patients with newly presenting RA.

Methods

Serum (n=126) and urine (n=83) samples were collected at initial presentation from disease modifying anti-rheumatic drug naïve RA patients for metabolomic profile assessment using 1-dimensional ¹H-NMR spectroscopy. Metabolomics data were analysed using partial least square regression (PLS-R) and orthogonal projections to latent structure discriminant analysis (OPLS-DA) with cross validation.

Results

Using PLS-R analysis, a relationship between the level of inflammation, as assessed by CRP, and the serum (p=0.001) and urinary (p<0.001) metabolome was detectable. Likewise, following categorisation of CRP into tertiles, patients in the lowest CRP tertile and the highest CRP tertile were statistically discriminated using OPLS-DA analysis of both serum (p=0.033) and urinary (p<0.001) metabolome. The most highly weighted metabolites for these models included glucose, amino acids, lactate, and citrate. These findings suggest increased glycolysis, perturbation in the citrate cycle, oxidative stress, protein catabolism and increased urea cycle activity are key characteristics of newly presenting RA patients with elevated CRP.

Conclusions

This study consolidates our understanding of a previously identified relationship between serum metabolite profile and inflammation and provides novel evidence that there is a relationship between urinary metabolite profile and inflammation as measured by CRP. Identification of these metabolic perturbations provides insights into the pathogenesis of RA and may help in the identification of therapeutic targets.

Functional cytochrome P450 1A enzymes are induced in mouse and human islets following pollutant exposure

AIMS/HYPOTHESIS

Exposure to environmental pollution has been consistently linked to diabetes incidence in humans, but the potential causative mechanisms remain unclear. Given the critical role of regulated insulin secretion in maintaining glucose homeostasis, environmental chemicals that reach the endocrine pancreas and cause beta cell injury are of particular concern. We propose that cytochrome P450 (CYP) enzymes, which are involved in metabolising xenobiotics, could serve as a useful biomarker for direct exposure of islets to pollutants. Moreover, functional CYP enzymes in islets could also impact beta cell physiology. The aim of this study was to determine whether CYP1A enzymes are activated in islets following direct or systemic exposure to environmental pollutants.

METHODS

Immortalised liver (HepG2) and rodent pancreatic endocrine cell lines (MIN6, βTC-6, INS1, α-TC1, α-TC3), as well as human islets, were treated in vitro with known CYP1A inducers 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and 3-methylcholanthrene (3-MC). In addition, mice were injected with either a single high dose of TCDD or multiple low doses of TCDD in vivo, and islets were isolated 1, 7 or 14 days later.

RESULTS

CYP1A enzymes were not activated in any of the immortalised beta or alpha cell lines tested. However, both 3-MC and TCDD potently induced CYP1A1 gene expression and modestly increased CYP1A1 enzyme activity in human islets after 48 h. The induction of CYP1A1 in human islets by TCDD was prevented by cotreatment with a cytokine mixture. After a systemic single high-dose TCDD injection, CYP1A1 enzyme activity was induced in mouse islets ~2-fold, ~40-fold and ~80-fold compared with controls after 1, 7 and 14 days, respectively, in vivo. Multiple low-dose TCDD exposure in vivo also caused significant upregulation of Cyp1a1 in mouse islets. Direct TCDD exposure to human and mouse islets in vitro resulted in suppressed glucose-induced insulin secretion. A single high-dose TCDD injection resulted in lower plasma insulin levels, as well as a pronounced increase in beta cell death.

CONCLUSIONS/INTERPRETATION

Transient exposure to TCDD results in long-term upregulation of CYP1A1 enzyme activity in islets. This provides evidence for direct exposure of islets to lipophilic pollutants in vivo and may have implications for islet physiology.

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

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

The human serum protein C4b-binding protein inhibits pancreatic IAPP-induced inflammasome activation

AIMS/HYPOTHESIS

Inflammasome activation and subsequent IL-1β production is a driver of islet pathology in type 2 diabetes. Oligomers, but not mature amyloid fibrils, of human islet amyloid polypeptide (IAPP), which is co-secreted with insulin, trigger NOD-like receptor pyrin domain containing-3 (NLRP3) inflammasome activation. C4b-binding protein (C4BP), present in serum, binds to IAPP and affects transition of IAPP monomers and oligomers to amyloid fibrils. We therefore hypothesised that C4BP inhibits IAPP-mediated inflammasome activation and IL-1β production.

METHODS

Macrophages were exposed to IAPP in the presence or absence of plasma-purified human C4BP, and inflammasome activation was assessed by IL-1β secretion as detected by ELISA and reporter cell lines. IAPP fibrillation was assessed by thioflavin T assay. Uptake of IAPP-C4BP complexes and their effects on phagolysosomal stability were assessed by flow cytometry and confocal microscopy. The effect of C4BP regulation of IAPP-mediated inflammasome activation on beta cell function was assessed using a clonal rat beta cell line. Immunohistochemistry was used to examine the association of IAPP amyloid deposits and macrophage infiltration in isolated human and mouse pancreatic islets, and expression of C4BP from isolated human pancreatic islets was assessed by quantitative PCR, immunohistochemistry and western blot.

RESULTS

C4BP significantly inhibited IAPP-mediated IL-1β secretion from primed macrophages at physiological concentrations in a dose-dependent manner. C4BP bound to and was internalised together with IAPP. C4BP did not affect IAPP uptake into phagolysosomal compartments, although it did inhibit its formation into amyloid fibrils. The loss of macrophage phagolysosomal integrity induced by IAPP incubation was inhibited by co-incubation with C4BP. Supernatant fractions from macrophages activated with IAPP inhibited both insulin secretion and viability of clonal beta cells in an IL-1β-dependent manner but the presence of C4BP during macrophage IAPP incubation rescued beta cell function and viability. In human and mouse islets, the presence of amyloid deposits correlated with higher numbers of infiltrating macrophages. Isolated human islets expressed and secreted C4BP, which increased with addition of IL-1β.

CONCLUSIONS/INTERPRETATION

IAPP deposition is associated with inflammatory cell infiltrates in pancreatic islets. C4BP blocks IAPP-induced inflammasome activation by preventing the loss of macrophage phagolysosomal integrity required for NLRP3 activation. The consequence of this is the preservation of beta cell function and viability. C4BP is secreted directly from human pancreatic islets and this increases in response to inflammatory cytokines. We therefore propose that C4BP acts as an extracellular chaperone protein that limits the proinflammatory effects of IAPP.

Abnormal Glucose Metabolism in Rheumatoid Arthritis

The incidence of abnormal glucose metabolism in patients with rheumatoid arthritis was considerably higher than the general population. The persistent systemic inflammatory state in rheumatoid arthritis might be associated with the glucose metabolism dysfunction. In this context, insulin resistance, islet β cell apoptosis, inflammatory cytokines, and other aspects which were linked with abnormal glucose metabolism in rheumatoid arthritis were reviewed. This review will be helpful in understanding the abnormal glucose metabolism mechanism in patients with rheumatoid arthritis and might be conducive to finding an effective treatment.

Short term exposure of beta cells to low concentrations of interleukin-1β improves insulin secretion through focal adhesion and actin remodeling and regulation of gene expression

Type 2 diabetes involves defective insulin secretion with islet inflammation governed in part by IL-1β. Prolonged exposure of islets to high concentrations of IL-1β (>24 h, 20 ng/ml) impairs beta cell function and survival. Conversely, exposure to lower concentrations of IL-1β for >24 h improves these same parameters. The impact on insulin secretion of shorter exposure times to IL-1β and the underlying molecular mechanisms are poorly understood and were the focus of this study. Treatment of rat primary beta cells, as well as rat or human whole islets, with 0.1 ng/ml IL-1β for 2 h increased glucose-stimulated (but not basal) insulin secretion, whereas 20 ng/ml was without effect. Similar differential effects of IL-1β depending on concentration were observed after 15 min of KCl stimulation but were prevented by diazoxide. Studies on sorted rat beta cells indicated that the enhancement of stimulated secretion by 0.1 ng/ml IL-1β was mediated by the NF-κB pathway and c-JUN/JNK pathway acting in parallel to elicit focal adhesion remodeling and the phosphorylation of paxillin independently of upstream regulation by focal adhesion kinase. Because the beneficial effect of IL-1β was dependent in part upon transcription, gene expression was analyzed by RNAseq. There were 18 genes regulated uniquely by 0.1 but not 20 ng/ml IL-1β, which are mostly involved in transcription and apoptosis. These results indicate that 2 h of exposure of beta cells to a low but not a high concentration of IL-1β enhances glucose-stimulated insulin secretion through focal adhesion and actin remodeling, as well as modulation of gene expression.

Pancreatic beta cells are highly susceptible to oxidative and ER stresses during the development of diabetes

The complex interplay of many cell types and the temporal heterogeneity of pancreatic islet composition obscure the direct role of resident alpha and beta cells in the development of Type 1 diabetes. Therefore, in addition to studying islets isolated from non-obese diabetic mice, we analyzed homogeneous cell populations of murine alpha (αTC-1) and beta (NIT-1) cell lines to understand the role and differential survival of these two predominant islet cell populations. A total of 56 proteins in NIT-1 cells and 50 in αTC-1 cells were differentially expressed when exposed to proinflammatory cytokines. The major difference in the protein expression between cytokine-treated NIT-1 and αTC-1 cells was free radical scavenging enzymes. A similar observation was made in cytokine-treated whole islets, where a comprehensive analysis of subcellular fractions revealed that 438 unique proteins were differentially expressed under inflammatory conditions. Our data indicate that beta cells are relatively susceptible to ER and oxidative stress and reveal key pathways that are dysregulated in beta cells during cytokine exposure. Additionally, in the islets, inflammation also leads to enhanced antigen presentation, which completes a three-way insult on beta cells, rendering them targets of infiltrating T lymphocytes.

Sustained NF-κB activation and inhibition in β-cells have minimal effects on function and islet transplant outcomes

The activation of the transcription factor NF-κB leads to changes in expression of many genes in pancreatic β-cells. However, the role of NF-κB activation in islet transplantation has not been fully elucidated. The aim of the present study was to investigate whether the state of NF-κB activation would influence the outcome of islet transplantation. Transgenic mice expressing a dominant active IKKβ (constitutively active) or a non-degradable form of IκBα (constitutive inhibition) under control of the rat insulin promoter were generated. Islets from these mice were transplanted into streptozotocin diabetic mice in suboptimal numbers. Further, the effects of salicylate (an inhibitor of NF-κB) treatment of normal islets prior to transplantation, and the effects of salicylate administration to mice prior to and after islet implantation were evaluated. Transplantation outcomes were not affected using islets expressing a non-degradable form of IκBα when compared to wild type controls. However, the transplantation outcomes using islets isolated from mice expressing a constitutively active mutant of NF-κB were marginally worse, although no aberrations of islet function in vitro could be detected. Salicylate treatment of normal islets or mice had no effect on transplantation outcome. The current study draws attention to the complexities of NF-κB in pancreatic beta cells by suggesting that they can adapt with normal or near normal function to both chronic activation and inhibition of this important transcription factor.

The mechanisms linking adiposopathy to type 2 diabetes

Obesity is defined as excessive accumulation of body fat in proportion to body size. When obesity occurs, the functions of adipose tissue may be deregulated, which is termed as adiposopathy. Adiposopathy is an independent risk factor for many diseases, including diabetes and cardiovascular diseases. In overweight or obese subjects with adiposopathy, hyperlipidemia exerts lipotoxicity in pancreatic islet and liver and induces pancreatic β cell dysfunction and liver insulin resistance, which are the decisive factors causing type 2 diabetes. Moreover, adipokines have been shown to play important roles in the regulation of glucose homeostasis. When adiposopathy occurs, abnormal changes in the serum adipokine profile correlate with the development and progression of pancreatic β cell dysfunction and insulin resistance in peripheral tissue. The current paper briefly discusses the latest findings regarding the effects of adiposopathy-related lipotoxicity and cytokine toxicity on the development of type 2 diabetes.

Resveratrol prevents interleukin-1β-induced dysfunction of pancreatic β-cells

Objective

Interleukin-1β (IL-1β) plays an important role in the development of type 1 and type 2 diabetes mellitus. Resveratrol, a polyphenol, is known to have a wide range of pharmacological properties in vitro. In this research, we examined the effects of resveratrol on IL-1β-induced β-cell dysfunction.

Methods

We first evaluated the effect of resveratrol on nitric oxide (NO) formation in RINm5F cells stimulated with IL-1β using the Griess method. Next, we performed transient transfection and reporter assays to measure the transcriptional activity of peroxisome proliferator-activated receptor-γ (PPAR-γ). We also used Western blotting analysis to assess the effect of resveratrol on inducible nitric oxide synthase (iNOS) expression and nuclear factor-κB (NF-κB) translocation to the nuclei in cells treated with IL-1β. In addition, we assessed the transcriptional activity of NF-κB using an electrophoretic mobility shift assay (EMSA). Finally, we evaluated the effect of resveratrol on IL-1β–induced inhibition of glucose-stimulated insulin secretion in freshly isolated rat pancreatic islets.

Results

Resveratrol significantly suppressed IL-1β-induced NO production, a finding that correlated well with reduced levels of iNOS mRNA and protein. The molecular mechanism by which resveratrol inhibited iNOS gene expression appeared to involve increased PPAR-γ activity, which resulted in the inhibition of NF-κB activation. Further analysis showed that resveratrol could prevent IL-1β-induced inhibition of glucose-stimulated insulin secretion in rat islets.

Conclusion

In this study, we demonstrated that resveratrol could protect against pancreatic β-cell dysfunction caused by IL-1β.

Transcriptional and translational regulation of cytokine signaling in inflammatory β-cell dysfunction and apoptosis

Disease is conventionally viewed as the chaotic inappropriate outcome of deranged tissue function resulting from aberrancies in cellular processes. Yet the patho-biology of cellular dysfunction and death encompasses a coordinated network no less sophisticated and regulated than maintenance of homeostatic balance. Cellular demise is far from passive subordination to stress but requires controlled coordination of energy-requiring activities including gene transcription and protein translation that determine the graded transition between defensive mechanisms, cell cycle regulation, dedifferentiation and ultimately to the activation of death programmes. In fact, most stressors stimulate both homeostasis and regeneration on one hand and impairment and destruction on the other, depending on the ambient circumstances. Here we illustrate this bimodal ambiguity in cell response by reviewing recent progress in our understanding of how the pancreatic β cell copes with inflammatory stress by changing gene transcription and protein translation by the differential and interconnected action of reactive oxygen and nitric oxide species, microRNAs and posttranslational protein modifications.

Formononetin attenuates IL-1β-induced apoptosis and NF-κB activation in INS-1 cells

Several studies suggest that the inflammation plays a role in the pathogenesis of some glucose disorders in adults. Exposure of pancreatic β-cells to cytokines, such as interleukin-1β (IL-1β), is thought to contribute to β-cell apoptosis. One important event triggered by IL-1β is induction of nitric oxide synthase (iNOS), an enzyme that catalyzes intracellular generation of the cytotoxic free radical NO. Recent work have suggested that formononetin, as an O-methylated isoflavone found in a number of plants and herbs like Astragalus membranaceus, inhibited some pro-inflammatory cytokine production in macrophages. However, the roles of formononetin in pancreatic beta cells have not been fully established. The aim of the present study was to assess possible in vitro effects of formononetin on cell apoptosis induced by IL-1β in the rat insulinoma cell line, INS-1. Our results demonstrate that formononetin significantly prevents IL-1β-increased INS-1 cell death and blocks cytokine-induced apoptotic signaling (the reduction of Bax/Bcl-2 ratio and caspase-3 activity). Formononetin also inhibited the activation of nuclear factor-kappaB (NF-κB), which is a significant transcription factor for iNOS, so as to decease nitric oxide (NO) formation in a dose dependent manner in vitro. Our observations indicated that formononetin could protect against pancreatic β-cell apoptosis caused by IL-1β and therefore could be used in the future as a new drug improving diabetes mellitus.

Gene expression changes in human islets exposed to type 1 diabetic serum

A major obstacle to the success of islet cell transplantation as a standard treatment for labile type 1 diabetes mellitus is the immediate loss of up to 70% of the transplanted islet mass. Activation of the complement cascade and coagulation factors has been implicated in initiating the destruction of the islet graft. In this study, we analyzed the gene expression changes in islet cells following exposure to type 1 diabetes mellitus serum (T1DM). Isolated human pancreatic islet cells were cultured for 2 d to stabilize islet cell gene expression. Cultured islets were divided into three groups for treatment as follows: group 1 was treated with autologous donor serum, while groups two and three were treated with sera from ABO-matched allogeneic donors or autoantibody positive type 1 diabetic patient, respectively. Complement was detected using anti-C3 FITC and CH50 assay. Islet gene expression was analyzed using Illumina micro-array technology. Results were confirmed using real-time PCR. Immunofluorescent imaging demonstrated complement deposition only in the T1DM condition. Gene array and class prediction analysis generated a list of 50 genes that were able to predict the effect of T1DM serum on islets. Quantitative PCR corroborated microarray results. Both techniques demonstrated upregulation of MMP9 (243%), IL-1β (255%), IL-11 (220%), IL-12A (132%), RAD (343%) and a concomitant downregulation of IL-1RN (64%) in islets treated with T1DM serum. Islets treated with T1DM serum overexpressed genes associated with angiogenesis while decreasing transcription of genes that protect islets from inflammatory cytokines and reactive oxygen species.

The central role of calcium in the effects of cytokines on beta-cell function: implications for type 1 and type 2 diabetes

The appropriate regulation of intracellular calcium is a requirement for proper cell function and survival. This review focuses on the effects of proinflammatory cytokines on calcium regulation in the insulin-producing pancreatic beta-cell and how normal stimulus-secretion coupling, organelle function, and overall beta-cell viability are impacted. Proinflammatory cytokines are increasingly thought to contribute to beta-cell dysfunction not only in type 1 diabetes (T1D), but also in the progression of type 2 diabetes (T2D). Cytokine-induced disruptions in calcium handling result in reduced insulin release in response to glucose stimulation. Cytokines can alter intracellular calcium levels by depleting calcium from the endoplasmic reticulum (ER) and by increasing calcium influx from the extracellular space. Depleting ER calcium leads to protein misfolding and activation of the ER stress response. Disrupting intracellular calcium may also affect organelles, including the mitochondria and the nucleus. As a chronic condition, cytokine-induced calcium disruptions may lead to beta-cell death in T1D and T2D, although possible protective effects are also discussed. Calcium is thus central to both normal and pathological cell processes. Because the tight regulation of intracellular calcium is crucial to homeostasis, measuring the dynamics of calcium may serve as a good indicator of overall beta-cell function.

In vivo islet protection by a nuclear import inhibitor in a mouse model of type 1 diabetes

Background

Insulin-dependent Type 1 diabetes (T1D) is a devastating autoimmune disease that destroys beta cells within the pancreatic islets and afflicts over 10 million people worldwide. These patients face life-long risks for blindness, cardiovascular and renal diseases, and complications of insulin treatment. New therapies that protect islets from autoimmune destruction and allow continuing insulin production are needed. Increasing evidence regarding the pathomechanism of T1D indicates that islets are destroyed by the relentless attack by autoreactive immune cells evolving from an aberrant action of the innate, in addition to adaptive, immune system that produces islet-toxic cytokines, chemokines, and other effectors of islet inflammation. We tested the hypothesis that targeting nuclear import of stress-responsive transcription factors evoked by agonist-stimulated innate and adaptive immunity receptors would protect islets from autoimmune destruction.

Principal Findings

Here we show that a first-in-class inhibitor of nuclear import, cSN50 peptide, affords in vivo islet protection following a 2-day course of intense treatment in NOD mice, which resulted in a diabetes-free state for one year without apparent toxicity. This nuclear import inhibitor precipitously reduces the accumulation of islet-destructive autoreactive lymphocytes while enhancing activation-induced cell death of T and B lymphocytes derived from autoimmune diabetes-prone, non-obese diabetic (NOD) mice that develop T1D. Moreover, in this widely used model of human T1D we noted attenuation of pro-inflammatory cytokine and chemokine production in immune cells.

Conclusions

These results indicate that a novel form of immunotherapy that targets nuclear import can arrest inflammation-driven destruction of insulin-producing beta cells at the site of autoimmune attack within pancreatic islets during the progression of T1D.

Feline pancreatic islet-like clusters and insulin producing cells express functional Toll-like receptors (TLRs)

Toll-like receptors (TLRs) are cellular receptors that recognize molecules derived from pathogens, endogenous molecules generated after cellular stress, and free fatty acids. TLR activation leads to a proinflammatory reaction that is fundamental in the initiation of an innate immune response and subsequent adaptive responses but also can damage tissues. TLRs are not only expressed within the immune system, but also in most other organ systems including the pancreas. TLR4 is expressed in pancreatic β-cells of rodents and humans and its stimulation affects insulin secretion in response to glucose. A low-grade inflammation is often associated with disturbed performance of β-cells and insulin resistance, the cardinal metabolic event of type-2 diabetes. Feline diabetes mellitus shares many similarities with type-2 diabetes in humans. Our objective was to elucidate the role of TLRs in feline pancreatic islets and islet-like clusters (ILC) that consist of islets with their adjacent tissue. We tested whether TLRs are triggered by their agonists and lead to the expression of inflammatory cytokines. We confirmed the expression of all known feline TLRs in pancreas and ILC. Furthermore, stimulation with TLR agonists increased IL-6 mRNA and protein content and the expression of other proinflammatory cytokines indicating a clear proinflammatory response. The reactivity to TLR ligands was stronger in β-cell enriched populations obtained after sorting by FACS indicating that inflammatory stimuli can also be generated within β-cells. We conclude that the microenvironment of feline β-cells harbor the potential for inflammatory reactions, that can be initiated by molecules released from bacteria or viruses or other molecules recognized by TLRs. Therefore infections associated with bacteriemia and viremia can induce inflammation in islets and damage the endocrine pancreatic tissue.

Cytokines in the Progression of Pancreatic β-Cell Dysfunction

The dysfunction of pancreatic β-cell and the reduction in β-cell mass are the decisive events in the progression of type 2 diabetes. There is increasing evidence that cytokines play important roles in the procedure of β-cell failure. Cytokines, such as IL-1β, IFN-γ, TNF-α, leptin, resistin, adiponectin, and visfatin, have been shown to diversely regulate pancreatic β-cell function. Recently, islet-derived cytokine PANcreatic DERived factor (PANDER or FAM3B) has also been demonstrated to be a regulator of islet β-cell function. The change in cytokine profile in islet and plasma is associated with pancreatic β-cell dysfunction and apoptosis. In this paper, we summarize and discuss the recent studies on the effects of certain important cytokines on pancreatic β-cell function. The imbalance in deleterious and protective cytokines plays pivotal roles in the development and progression of pancreatic β-cell dysfunction under insulin-resistant conditions.

Diabetes mellitus and apoptosis: inflammatory cells

Since the early observation that similarities between thyroiditis and insulitis existed, the important role played by inflammation in the development of diabetes has been appreciated. More recently, experiments have shown that inflammation also plays a prominent role in the development of target organ damage arising as complications, with both elements of the innate and the adaptive immune system being involved, and that cytokines contributing to local tissue damage may arise from both infiltrating and resident cells. This review will discuss the experimental evidence that shows that inflammatory cell-mediated apoptosis contributes to target organ damage, from beta cell destruction to both micro- and macro-vascular disease complications, and also how alterations in leukocyte turnover affects immune function.

Effects of DHMEQ, a novel nuclear factor-kappab inhibitor, on beta cell dysfunction in INS-1 cells

AIMS

Recent studies suggest that nuclear factor-kappaB (NF-kappaB) activation has an important role in leading to beta cell dysfunction in both type 1 and type 2 diabetes. In this study we tested this hypothesis by investigating the effects of dehydroxymethylepoxyquinomicin (DHMEQ), a novel NF-kappaB inhibitor, on tumor necrosis factor-alpha (TNF-alpha)-induced beta cell dysfunction.

METHODS

INS-1 cells were incubated with TNF- alpha and with or without DHMEQ for 24 hours. Glucose-stimulated insulin secretion, cell viability, mRNA expression and NF-kappaB activation were investigated.

RESULTS

DHMEQ suppressed TNF-alpha-induced NF-kappaB activation and partially ameliorated glucose-stimulated insulin secretion in a dose-dependent manner. DHMEQ also partially ameliorated decreased cell viability and insulin mRNA level induced by TNF-alpha.

CONCLUSION

DHMEQ suppressed NF-kappaB activation and ameliorated beta cell dysfunction induced by TNF- alpha. Inhibition of activated NF-kappaB in beta cells may be important to ameliorate beta cell dysfunction in diabetes.

Role of uncoupling protein UCP2 in cell-mediated immunity: how macrophage-mediated insulitis is accelerated in a model of autoimmune diabetes

Infiltration of inflammatory cells into pancreatic islets of Langerhans and selective destruction of insulin-secreting beta-cells are characteristics of type 1 diabetes. Uncoupling protein 2 (UCP2) is a mitochondrial protein expressed in immune cells. UCP2 controls macrophage activation by modulating the production of mitochondrial reactive oxygen species (ROS) and MAPK signaling. We investigated the role of UCP2 on immune cell activity in type 1 diabetes in Ucp2-deficient mice. Using the model of multiple low-dose streptozotocin (STZ)-induced diabetes, we found that autoimmune diabetes was strongly accelerated in Ucp2-KO mice, compared with Ucp2-WT mice with increased intraislet lymphocytic infiltration. Macrophages from STZ-treated Ucp2-KO mice had increased IL-1beta and nitric oxide (NO) production, compared with WT macrophages. Moreover, more macrophages were recruited in islets of STZ-treated Ucp2-KO mice, compared with Ucp2-WT mice. This finding also was accompanied by increased NO/ROS-induced damage. Altogether, our data show that inflammation is stronger in Ucp2-KO mice and islets, leading to the exacerbated disease in these mice. Our results highlight the mitochondrial protein UCP2 as a new player in autoimmune diabetes.

The c-Jun N-terminal kinase JNK participates in cytokine- and isolation stress-induced rat pancreatic islet apoptosis

AIMS/HYPOTHESIS

The protocols used for the preparation of human pancreatic islets immediately induce a sustained and massive activation of the c-Jun-N-terminal kinase (JNK). JNK, which participates in apoptosis of insulin-secreting cells, is activated by mechanical stresses, as well as by exposure to pro-inflammatory cytokines. Here, we investigated whether the delivery of a protease-resistant JNK inhibitory peptide (D-JNKI) through a protein transduction system during pancreatic digestion might impair JNK signalling throughout the transplantation procedure.

METHODS

Rat pancreases were treated with D-JNKI through the pancreatic duct and cells then isolated by enzymatic digestion. Protein extracts were prepared to determine JNK activity by kinase assays and total RNA was extracted to measure gene expressions by a Light-Cycler technique. Cell apoptosis rate was determined by terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL) assay and by scoring cells displaying pycnotic nuclei.

RESULTS

Our data establish that the peptide transduction system used here efficiently transfects islets, allowing for stable in vivo (up to 2 days) transfection of human islets transplanted under the kidney capsule. Further, D-JNKI decreases intracellular JNK signalling during isolation and following cytokine exposure in both human and rat islets, as measured by kinase assays and reduced c-fos expression; D-JNKI also confers protection against apoptosis induced during the rat islet preparation and subsequent to IL-1beta exposure.

CONCLUSIONS/INTERPRETATION

JNK signalling participates in islet isolation- and IL-1beta-induced apoptosis in rat islets. Furthermore, the system we used might be more generally applicable for the persistent blockage (several days) of pro-apoptotic pathways in the transplanted islets; this days-long protection might potentially be an absolute prerequisite to help transplanted islets better survive the first wave of the non-specific inflammatory attack.

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.

Effects of a vitamin D3 analog on diabetes in the bio breeding (BB) rat

Non-hypercalcemic analogs of vitamin D(3) modulate the immune response through antigen-presenting cells (APCs) and activated T-cells. A large population-base case-control showed that vitamin D(3) intake significantly decreases the risk of type 1 diabetes development. The aim of this study was, therefore, to observe the in vivo effects of a vitamin D(3) analog administered to Bio Breeding (BB) rats. 1,25-Dihydroxy-16,23Z-diene-26,27-hexafluoro-19-nor vitamin D(3) (BXL-219, formerly Ro 26-2198) (BioXell, Milan, Italy) was administered in vivo to BB rats from days 42 to 110 of life at 0.2 microg/Kg BW. Control animals received only vehicle (olive oil, 4.8 microl/100 g BW). The animals of these two groups were subjected to insulin treatment as they became diabetic. Insulin (Humulin, 28.6 UI/day) was administered irrespective of diabetes occurrence to another group of rats for comparison. Blood glucose, insulin levels, glycosuria, degree of islet infiltration, and the expression of some antigens were observed. Results showed that the vitamin D(3) analog reduced diabetes incidence, although limitedly, in BB rats while administration of oral insulin increased diabetes incidence. In addition, the vitamin D(3) analog did not stimulate an enhancement in the expression of CD4 and CD25 in BB rats as it does in NOD mice, which may explain the failure of this as well as other antidiabetic treatments in the BB animal model of type 1 diabetes.

MnSOD mimic compounds can counteract mechanical stress and islet β cell apoptosis, although at appropriate concentration ranges

Pancreatic islets are commonly isolated for research and transplantation without taking into consideration that they undergo mechanical or chemical stress during this process. In order to counteract both types of injuries, the compound AEOL10150, a novel MnSOD mimic, was added during isolation of islet at concentrations ranging from 18 to 100 microM. Mechanical or chemical stress-related pro-apoptotic signals were then studied. We demonstrate that this MnSOD mimic diminishes the negative effects of mechanical stress by blocking insulin impairment, production of non-specific islet beta-cell proteins, transcription of iNOS and FAS, activation of caspase-3 and -9 and, ultimately, apoptosis. Moreover, the effects of the MnSOD mimic on isolated islets were greatly influenced by dosage: the best dose able to fully counteract mechanical stress was found to be 100 microM; doses > or =150 microM were themselves highly toxic for islet cells. On the other hand, rIL-1beta-induced chemical stress is rather complex, and there was no protection in this scenario. Therefore, contrarily to what has been previously reported, MnSOD mimic administration is only capable of counteracting mechanical stress, and not cytokine-induced cytotoxicity, and that this drug acts within a limited concentration range.

Avenues for immunomodulation and graft protection by gene therapy in transplantation

Organ transplantation represents the only definitive therapy for many causes of end-organ failure. However, the universal success of this therapy is limited by chronic allograft rejection, the side effects of chronic immunosuppressive therapy, and a severe shortage of donor organs. Presently, the success of solid-organ transplantation depends on the continuous administration of toxic and nonspecific immunosuppressive agents, therapies that present risks for opportunistic infection, malignancy, and a variety of agent-specific side effects. To promote the use of transplantation with limited risk of long-term sequelae, three dominant research challenges emerge: (i) elimination of the need for exogenous immunosuppression by immunological tolerance induction; (ii) prevention of chronic rejection/graft dysfunction; and (iii) expansion of available organs for transplantation. Gene therapy may provide significant advances and solutions in each of these areas. Rejection of the graft in the immediate post-transplant period has been attacked through the transfer of immunomodulatory molecules in addition to tolerance inducing approaches. Chronic graft rejection may be similarly addressed through permanent tolerance induction or alternatively through the introduction of molecules to resist chronic graft damage. Genetic manipulation of stem cells may ultimately produce transgenic animals to serve as tissue donors to overcome the limited donor organ supply. This review will highlight ongoing developments in the translation of gene therapy approaches to the challenges inherent in transplantation.

Intracellular degradation of insulin and crinophagy are maintained by nitric oxide and cyclo-oxygenase 2 activity in isolated pancreatic islets

BACKGROUND INFORMATION

Pancreatic beta-cells require an optimal insulin content to allow instantaneous secretion of insulin. This is maintained by insulin biosynthesis and intracellular degradation of insulin. Degradation may be effected by crinophagy, i.e. the fusion of secretory granules with lysosomes. IL-1beta (interleukin 1beta) induces distinct changes of beta-cell lysosomes. To study the mechanisms for intracellular insulin degradation and crinophagy, isolated mouse pancreatic islets were exposed to IL-1beta and known pathways for IL-1beta actions were blocked. Intracellular insulin degradation was determined by following the fate of radioactively labelled insulin. Crinophagy was studied by ultrastructural analysis. The effects of blocking pathways for IL-1beta were monitored by measurements of nitrite and PGE(2) (prostaglandin E(2)).

RESULTS

IL-1beta caused an enhancement of islet intracellular insulin degradation and an increase in the lysosomal incorporation of beta-cell secretory granules. The effects of IL-1beta were abolished by aminoguanidine, a selective inhibitor of inducible NOS (nitric oxide synthase), or by rofecoxib, a specific inhibitor of COX-2 (cyclo-oxygenase 2). In the absence of IL-1beta, nitroarginine, which is a selective inhibitor of constitutive NOS, caused a decrease in intracellular degradation of insulin in parallel with a decreased production of NO and PGE(2) by the islets.

CONCLUSIONS

The correlation between the enhanced intracellular insulin degradation and lysosomal changes caused by IL-1beta suggests that insulin degradation may be effected by crinophagy. Under physiological conditions, significant beta-cell degradation of insulin may depend on the activity of COX-2, possibly stimulated by endogenous NO.

An early but intense cytokine production within the islets may be predictive for type 1 diabetes occurrence in the Bio Breeding (BB) rat

The Bio Breeding (BB) rat is a useful animal model of type 1 autoimmune diabetes. The aim of this study was to observe and follow the cytokine and antigenic expressions within the islets of Langerhans in young non-diabetic, in pre-diabetic hyperglycemic, and in overtly diabetic animals. BB rats were therefore checked at day 21 up to day 90 of life for blood glucose, insulin levels, degree of islet infiltration, expression of proinflammatory and protective cytokines and antibodies including CD4, CD8, CD25, LFA-1, and ICAM-1. Animals were treated with insulin as they became diabetic. We found that islets of non-diabetic BB rats became positive to both IL-1beta and IL-4 very early on, confirming a local but intense production of both cytokines within the islets during the initial non-diabetic period. In addition, we observed that the production of these interleukins together with the expression levels of CD4 and CD25 are events predictive for type 1 diabetes onset in non-diabetic BB rats, as for non-obese diabetic (NOD) mice. In particular, the production of IL-1beta and IL-4 during the non-diabetic period together with the lack of enhancement of CD4 and CD25, indicating selective recruitment of activated T cells, may explain the failure of anti-diabetic treatments in this animal model of type 1 diabetes.

NF-kappaB-dependent production of nitric oxide by astrocytes mediates apoptosis in differentiated PC12 neurons following exposure to manganese and cytokines

Neuronal injury in manganism is accompanied by activation of astroglia within the basal ganglia that is thought to increase production of inflammatory mediators such as nitric oxide (NO). The present studies postulated that astroglial-derived NO mediates neuronal apoptosis induced by manganese (Mn) and pro-inflammatory cytokines. Pheochromocytoma (PC12) cells differentiated with nerve growth factor (NGF) were co-cultured with primary astrocytes and exposed to Mn and tumor necrosis factor-alpha (TNF-alpha) plus interferon-gamma (IFN-gamma). Mn enhanced cytokine-induced expression of inducible nitric oxide synthase (NOS2, EC 1.14.13.39) and production of NO in astrocytes that correlated with apoptosis in co-cultured neurons, as determined by caspase activity, terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling (TUNEL), and nuclear morphology. Apoptosis in PC12 neurons required the presence of astrocytes and was blocked by overexpression of a phosphorylation-deficient mutant of IkappaBalpha (S32/36A) in astrocytes that prevented induction of NOS2. Pharmacologic inhibition of NOS2 with (+/-)-2-amino-5,6-dihydro-6-methyl-4H-1,3-thiazine (AMT) significantly reduced neuronal apoptosis, and the addition of low concentrations of the NO donor, S-nitroso-N-acetylpenicillamine (SNAP), to neurons cultured without astrocytes was sufficient to recover the apoptotic phenotype following exposure to Mn and TNF-alpha/IFN-gamma. It is concluded that Mn- and cytokine-dependent apoptosis in PC12 neurons requires astroglial-derived NO and NF-kappaB-dependent expression of NOS2.

Role of histone and transcription factor acetylation in diabetes pathogenesis

Globally, diabetes (and, in particular, type 2 diabetes) represents a major challenge to world health. Currently in the United States, the costs of treating diabetes and its associated complications exceed 100 billion US dollars annually, and this figure is expected to soar in the near future. Despite decades of intense research efforts, the genetic basis of the events involved in the pathogenesis of diabetes is still poorly understood. Diabetes is a complex multigenic syndrome primarily due to beta-cell dysfunction associated with a variable degree of insulin resistance. Recent advances have led to exciting new developments with regard to our understanding of the mechanisms that regulate insulin transcription. These include data that implicate chromatin as a critical regulator of this event. The 'Histone Code' is a widely accepted hypothesis, whereby sequential modifications to the histones in chromatin lead to regulated transcription of genes. One of the modifications used in the histone code is acetylation. This is probably the best characterized modification of histones, which is carried out under the control of histone acetyltransferases (HATs) and histone deacetylases (HDACs). These enzymes also regulate the activity of a number of transcription factors through acetylation. Increasing evidence links possible dysregulation of these mechanisms in the pathogenesis of diabetes, with important therapeutic implications.

Activation of NF-kappaB by extracellular matrix is involved in spreading and glucose-stimulated insulin secretion of pancreatic beta cells

Laminin-5-rich extracellular matrix derived from 804G cells (804G-ECM) engages beta1 integrins to induce spreading, improve glucose-stimulated insulin secretion (GSIS), and increase survival of pancreatic beta cells. The present study examines whether 804G-ECM activates the transcriptional activity of NF-kappaB and the involvement of NF-kappaB in those effects of 804G-ECM on pancreatic beta cells. 804G-ECM induces nuclear translocation and the DNA binding activity of the p65 subunit of NF-kappaB. 804G-ECM-induced nuclear translocation of NF-kappaB was weak as compared with that induced by interleukin-1beta. Transient 804G-ECM-induced DNA binding activity of NF-kappaB (peak at 2 h) and overexpression of NF-kappaB target genes IkappaB alpha and NF-kappaB1(p105) (peak at 4 h) were observed. When NF-kappaB was inhibited by an inhibitor of IkappaB alpha phosphorylation (Bay 11-7082) or by a recombinant adenovirus expressing the nonphosphorylatable form of IkappaB alpha, 804G-ECM-induced cell spreading and actin cytoskeleton organization were reduced. GSIS from cells on 804G-ECM was inhibited 5-fold, whereas cell survival was not affected. In summary, the results indicate that 804G-ECM induces a transient and moderate NF-kappaB activity. This study shows for the first time that ECM-induced NF-kappaB activity is necessary in maintaining GSIS, although it does not affect survival of pancreatic beta cells. The effects of ECM-induced NF-kappaB activity contrast with the deleterious effects of cytokine-induced NF-kappaB activity. It is proposed that transient and moderate NF-kappaB activity is essential for proper function of the pancreatic beta cell.