The Contribution of Neutrophils and NETs to the Development of Type 1 Diabetes

Type 2 diabetes (T2D) is predicted to affect one in three Americans by the year 2050 and is a leading cause of blindness, end stage renal failure and loss of limb with associated costs exceeding $180 billion/year. Insulin resistance in liver and skeletal muscle are major factors in the pathogenesis of T2D, with a strong relationship between ectopic lipid content in liver and skeletal muscle with insulin resistance and T2D in both humans and rodent models of NAFLD and T2D (Shulman, J. Clin. Invest. 2000; 106:171-6, Samuel and Shulman, Cell 2012; 148:852-71). Evidence in support of the key role of ectopic lipid in the pathogenesis of hepatic insulin resistance and T2D in humans comes from studies where we (Petersen et al., Diabetes 2005; 54:603-608) and others (Lim et al., Diabetologia 2011, 54:2506-2514) have shown that modest weight loss (~8 kg) resulted in large (~80%) reductions in liver triglyceride content, which were associated with normalization of fasting plasma glucose concentrations, hepatic glucose production and hepatic insulin sensitivity. Thus we hypothesized that reversal of non-alcoholic fatty liver disease (NAFLD), by promoting mild mitochondrial uncoupling would reverse insulin resistance and diabetes in rat models of NAFLD and T2D. Previous studies by our group had found that treating high fat fed rats with 2,4-dinitrophenol (DNP), a well established mitochondrial protonophore, would lead to mitochondrial energy uncoupling leading to reductions in liver triacylglycerol (TAG) and DAG content, decreased PKCe activation and decreased hepatic insulin resistance (Samuel et al., J. Biol. Chem. 2004; 279:32345-53). DNP uncouples mitochondrial glucose and fat oxidation from ATP production by shuttling protons across the mitochondrial membrane resulting in increased mitochondrial energy consumption, but can be fatally toxic due to its on-target side effect of hyperthermia. We hypothesized that we could markedly increase the therapeutic window of DNP by targeting it to the liver. We therefore generated several derivatives of DNP, which would be preferentially metabolized by the cytochrome P-450 system in the liver to the active protonophore, DNP, and screened them in isolated hepatocytes for their ability to promote increased oxygen consumption. From this screen we identified DNP-methyl ether (DNPME), which raised oxygen consumption rates with similar potencies to DNP. As predicted, the ratio of toxic to effective dose was 50-fold greater for DNPME than DNP, without any evidence of hyperthermia or renal or hepatic toxicity in rats treated for 6 weeks with DNPME. This therapeutic index also compares favorably with other drugs that are in common use such as acetaminophen, which has a LD50/ED50 of 13. Given the markedly increased therapeutic window for DNPME versus DNP we then examined whether DNPME would reverse insulin resistance, hepatic steatosis and diabetes in the rat. Despite identical body weights at the time of study, DNPME-treated rats had lower fasting plasma glucose, insulin, and triglyceride concentrations; improved glucose tolerance; and increased hepatic and peripheral insulin sensitivity. These improvements in liver and muscle insulin responsiveness were associated with reductions in liver and muscle TAG and DAG content as well as decreases in PKC activity in liver and skeletal muscle. In contrast there were no changes in tissue ceramide content or inflammatory markers with DNPME treatment, disassociating these factors from reversal of insulin resistance and diabetes in these animals. Given the surprising effect of DNPME to increase peripheral insulin sensitivity we examined the effects of DNPME on hepatic VLDL production and found that DNPME treatment resulted in a ~50% reduction in hepatic VLDL export, consistent with DNPME induced reductions in plasma triglyceride concentrations. In addition we observed that DNPME treatment caused a 60% increase in hepatic tricarboxylic acid (TCA) cycle flux whereas there were no observable effects of DNPME treatment on relative rates of mitochondrial fatty acid/TCA cycle flux in heart, skeletal muscle, brain, or kidney. Taken together these data imply that DNPME treatment promotes increased hepatic mitochondrial oxidation rates resulting in lower hepatic TAG and DAG content and reduced VLDL production resulting in decreased plasma triglyceride concentrations and decreased muscle TAG and DAG content (Figure). Because DNPME treatment promoted regression of NAFLD and insulin resistance in high fat fed rat models of NAFLD, we next examined whether DNPME would also be effective in two rat models of T2D. DNPME treatment led to a reduction in fasting plasma glucose, insulin, and triglyceride concentrations, improved glucose tolerance and reduced hepatic and peripheral muscle lipid content without any indication of hepatic or renal toxicity in both rat models, highlighting its potential for use as a therapeutic agent in patients with T2D. In summary these data demonstrate that by promoting a relatively small increase in hepatic mitochondrial uncoupling, DNPME can safely reverse hepatic steatosis, hypertriglyceridemia and insulin resistance in a rat model of NAFLD without inducing hyperthermia or associated systemic toxicities. In addition we also found that DNPME reduces fasting plasma glucose and insulin concentrations and improves glucose tolerance in two rat models of T2D. Taken together these data demonstrate the potential feasibility of disassociating the toxicity of DNP from its efficacy by altering the pharmacokinetics of DNP metabolism to treat the related epidemics of NAFLD, metabolic syndrome and type 2 diabetes. Figure 1 Mechanism by which DNPME reverses liver and muscle insulin resistance.

Increased formation of neutrophil extracellular traps (NETs) is associated with gut leakage in type 1 diabetes (T1D). To explore the mechanism of how enteropathy exacerbated by NETs triggers pancreatic autoimmunity in T1D, we carried out a correlation analysis for NET formation with gut barrier functions and autoimmunity in nonobese diabetic (NOD) mice. Inducing chronic colitis or knocking out of peptidyl arginine deiminase type 4 (PAD4) in NOD mice were used to further study the effect of NET formation on the progression of T1D. Microbial alterations in Deferribacteres and Proteobacteria, along with the loss of gut barrier function, were found to be associated with increased endotoxin and abnormal formation of NETs in NOD mice. Both DSS-induced colitis and knockout of PAD4 in NOD mice indicated that PAD4-dependent NET formation was involved in the aggravation of gut barrier dysfunction, the production of autoantibodies, and the activation of enteric autoimmune T cells, which then migrated to pancreatic lymph nodes (PLNs) and caused self-damage. The current study thus provides evidence that PAD4-dependent NET formation is engaged in leaky gut triggering pancreatic autoimmunity and suggests that either degradation of NETs or inhibition of NET formation may be helpful for innovative therapeutic interventions in T1D.

Type 1 diabetes (T1D) is an autoimmune disease in which insulin-producing beta cells in pancreatic islets are progressively destroyed. Clinical trials of immunotherapies in recently diagnosed T1D patients have only transiently and partially impacted the disease course, suggesting that other approaches are required. Our previous studies have demonstrated that heparan sulfate (HS), a glycosaminoglycan conventionally expressed in extracellular matrix, is present at high levels inside normal mouse beta cells. Intracellular HS was shown to be critical for beta cell survival and protection from oxidative damage. T1D development in Non-Obese Diabetic (NOD) mice correlated with loss of islet HS and was prevented by inhibiting HS degradation by the endoglycosidase, heparanase. In this study we investigated the distribution of HS and heparan sulfate proteoglycan (HSPG) core proteins in normal human islets, a role for HS in human beta cell viability and the clinical relevance of intra-islet HS and HSPG levels, compared to insulin, in human T1D. In normal human islets, HS (identified by 10E4 mAb) co-localized with insulin but not glucagon and correlated with the HSPG core proteins for collagen type XVIII (Col18) and syndecan-1 (Sdc1). Insulin-positive islets of T1D pancreases showed significant loss of HS, Col18 and Sdc1 and heparanase was strongly expressed by islet-infiltrating leukocytes. Human beta cells cultured with HS mimetics showed significantly improved survival and protection against hydrogen peroxide-induced death, suggesting that loss of HS could contribute to beta cell death in T1D. We conclude that HS depletion in beta cells, possibly due to heparanase produced by insulitis leukocytes, may function as an important mechanism in the pathogenesis of human T1D. Our findings raise the possibility that intervention therapy with dual activity HS replacers/heparanase inhibitors could help to protect the residual beta cell mass in patients recently diagnosed with T1D.

In animal models autoreactive CD8(+) T cells are crucial in the development of type 1 diabetes (T1D); however, their role in human T1D is still not known. To address the role of CD81 T cells we performed a pilot study by investigating CD8(+) T cell-mediated cytokine secretion after in vitro stimulation with 94 preproinsulin (PPI) peptides. We were able to show that CD8(+) T cells contribute to a strong IFNgamma reactivity against PPI in human T1D. Further investigations defining epitope specificity, cytokine secretion, and cytotoxic capacity are important to clarify their role in T1D development.

The generation of post-translational modifications (PTMs) in human proteins is a physiological process leading to structural and immunologic variety in proteins, with potentially altered biological functions. PTMs often arise through normal responses to cellular stress, including general oxidative changes in the tissue microenvironment and intracellular stress to the endoplasmic reticulum or immune-mediated inflammatory stresses. Many studies have now illustrated the presence of ‘neoepitopes’ consisting of PTM self-proteins that induce robust autoimmune responses. These pathways of inflammatory neoepitope generation are commonly observed in many autoimmune diseases including systemic lupus erythematosus, rheumatoid arthritis, multiple sclerosis, and type 1 diabetes (T1D), among others. This review will focus on one specific PTM to self-proteins known as citrullination. Citrullination is mediated by calcium-dependent peptidylarginine deiminase (PAD) enzymes, which catalyze deimination, the conversion of arginine into the non-classical amino acid citrulline. PADs and citrullinated peptides have been associated with different autoimmune diseases, notably with a prominent role in the diagnosis and pathology of rheumatoid arthritis. More recently, an important role for PADs and citrullinated self-proteins has emerged in T1D. In this review we will provide a comprehensive overview on the pathogenic role for PADs and citrullination in inflammation and autoimmunity, with specific focus on evidence for their role in T1D. The general role of PADs in epigenetic and transcriptional processes, as well as their crucial role in histone citrullination, neutrophil biology and neutrophil extracellular trap (NET) formation will be discussed. The latter is important in view of increasing evidence for a role of neutrophils and NETosis in the pathogenesis of T1D. Further, we will discuss the underlying processes leading to citrullination, the genetic susceptibility factors for increased recognition of citrullinated epitopes by T1D HLA-susceptibility types and provide an overview of reported autoreactive responses against citrullinated epitopes, both of T cells and autoantibodies in T1D patients. Finally, we will discuss recent observations obtained in NOD mice, pointing to prevention of diabetes development through PAD inhibition, and the potential role of PAD inhibitors as novel therapeutic strategy in autoimmunity and in T1D in particular.

Type 1 diabetes (T1D) is an autoimmune disorder with unambiguous involvement of both innate and adaptive immune mechanisms in the destruction of pancreatic beta cells. Recent evidence demonstrated that neutrophils infiltrate the pancreas prior to disease onset and therein extrude neutrophil extracellular traps (NETs), web-like structures of DNA and nuclear proteins with a strong pro-inflammatory biologic activity. Our previous work showed that T1D NETs activate dendritic cells, which consequently induce IFNγ-producing Th1 lymphocytes. The aim of this study was to assess direct ex vivo biomarkers of NETosis in the serum of recent onset and long-term pediatric T1D patients, their first-degree relatives and healthy controls. To this end we evaluated serum levels of myeloperoxidase (MPO), neutrophil elastase (NE), proteinase 3 (PR3), protein arginine deiminase 4 (PAD4), LL37 and cell-free DNA-histone complexes in sex- and age-matched cohorts of T1D first-degree relatives, recent-onset T1D patients, and in patients 12 months after clinical manifestation of the disease. Our data shows that disease onset is accompanied by peripheral neutrophilia and significant elevation of MPO, NE, PR3, PAD4 and cell-free DNA-histone complexes. Most biomarkers subsequently decrease but do not always normalize in long-term patients. First-degree relatives displayed an intermediate phenotype, except for remarkably high levels of LL37. Together, this report provides evidence for the presence of ongoing NETosis in pediatric patients with T1D at time of clinical manifestation of the disease, which partly subsides in subsequent years.

The role of the innate immune system in destruction of pancreatic beta cells in NOD mice and humans with type I diabetes

Expressions of TLR7, 8, 9 mRNA, COX-2 mRNA, and mPGES-1 mRNA in local endometriosis lesions

Type 1 diabetes (T1D) results from autoimmune destruction of insulin-producing beta cells in pancreatic islets. The degradation of the glycosaminoglycan heparan sulfate (HS) by the endo-β-D-glycosidase heparanase plays a critical role in multiple stages of the disease process. Heparanase aids (i) migration of inflammatory leukocytes from the vasculature to the islets, (ii) intra-islet invasion by insulitis leukocytes, and (iii) selective destruction of beta cells. These disease stages are marked by the solubilization of HS in the subendothelial basement membrane (BM), HS breakdown in the peri-islet BM, and the degradation of HS inside beta cells, respectively. Significantly, healthy islet beta cells are enriched in highly sulfated HS which is essential for their viability, protection from damage by reactive oxygen species (ROS), beta cell function and differentiation. Consequently, mouse and human beta cells but not glucagon-producing alpha cells (which contain less-sulfated HS) are exquisitely vulnerable to heparanase-mediated damage. In vitro, the death of HS-depleted mouse and human beta cells can be prevented by HS replacement using highly sulfated HS mimetics or analogues. T1D progression in NOD mice and recent-onset T1D in humans correlate with increased expression of heparanase by circulating leukocytes of myeloid origin and heparanase-expressing insulitis leukocytes. Treatment of NOD mice with the heparanase inhibitor and HS replacer, PI-88, significantly reduced T1D incidence by 50%, impaired the development of insulitis and preserved beta cell HS. These outcomes identified heparanase as a novel destructive tool in T1D, distinct from the conventional cytotoxic and apoptosis-inducing mechanisms of autoreactive T cells. In contrast to exogenous catalytically active heparanase, endogenous heparanase may function in HS homeostasis, gene expression and insulin secretion in normal beta cells and immune gene expression in leukocytes. In established diabetes, the interplay between hyperglycemia, local inflammatory cells (e.g. macrophages) and heparanase contributes to secondary micro- and macro-vascular disease. We have identified dual activity heparanase inhibitors/HS replacers as a novel class of therapeutic for preventing T1D progression and potentially for mitigating secondary vascular disease that develops with long-term T1D.

Platelet-neutrophil aggregates (PNAs) facilitate neutrophil activation and migration and could underpin the recruitment of neutrophils to the pancreas during type 1 diabetes (T1D) pathogenesis. PNAs, measured by flow cytometry, were significantly elevated in the circulation of autoantibody-positive (Aab+) children and new-onset T1D children, as well as in pre-T1D (at 4 weeks and 10–12 weeks) and T1D-onset NOD mice, compared with relevant controls, and PNAs were characterized by activated P-selectin+ platelets. PNAs were similarly increased in pre-T1D and T1D-onset NOD isolated islets/insulitis, and immunofluorescence staining revealed increased islet-associated neutrophil extracellular trap (NET) products (myeloperoxidase [MPO] and citrullinated histones [CitH3]) in NOD pancreata. In vitro, cell-free histones and NETs induced islet cell damage, which was prevented by the small polyanionic drug methyl cellobiose sulfate (mCBS) that binds to histones and neutralizes their pathological effects. Elevated circulating PNAs could, therefore, act as an innate immune and pathogenic biomarker of T1D autoimmunity. Platelet hyperreactivity within PNAs appears to represent a previously unrecognized hematological abnormality that precedes T1D onset. In summary, PNAs could contribute to the pathogenesis of T1D and potentially function as a pre-T1D diagnostic.

After completing this article, readers should be able to: 1. Outline the current concepts of the pathogenesis of type 1 diabetes (T1D) with regard to dietary triggers and genetic susceptibility. 2. Discuss the evidence, both epidemiologic and that derived from studies of animal models, that supports the association between infant feeding practices and T1D. 3. Describe the roles for intestinal immunity and permeability in supporting the hypothetical model of cow milk protein mediation of T1D autoimmunity. 4. Delineate the goals and rationale for prospective clinical trials evaluating neonatal nutrition and the development of T1D. 5. List the putative dietary modulators of T1D. Type 1 diabetes (T1D), a disease that has unacceptably high morbidity and mortality, is increasing in incidence, prompting the redoubling of efforts toward its prevention. Progress toward prevention and cure relies on elucidation of the disease’s pathogenesis, which, to date, has remained poorly defined. The defining features of T1D, insulin deficiency and hyperglycemia, result from an immune-mediated destruction of insulin-secreting beta cells in the pancreatic islets. The loss of beta cell mass is believed to be gradual for most individuals, accounting for the sometimes prolonged asymptomatic periods of autoimmunity preceding overt diabetes (Fig. 1). Indeed, the chronic autoimmune nature of the disease is well established, as is the genetic predisposition. Specific associations with molecules of the human lymphocyte antigen (HLA) define both susceptibility to and protection from T1D. However, T1D is a polygenic disorder with more than 20 loci associated with susceptibility or resistance to the disease, of which the HLA may account for less than 50% of the genetic predisposition. Genetics clearly comprises a major component of the development of T1D, but the interaction between the environment and the immune system abnormalities is believed to weigh heavily in disease development. Indeed, trends in T1D incidence, both geographic and temporal, suggest a strong …

The Review of Diabetic Studies,2005,2,4,187-189.DOI:10.1900/RDS.2005.2.187Published:February 2006Type:CommentaryAuthors:Damien Bresson, and Matthias von Herrath Author(s) affiliations:Damien Bresson and Matthias von Herrath La Jolla Institute for Allergy and Immunology, Department of Developmental Immunology 3, 10355 Science Center Drive, San Diego, California 92121, USA. Abstract:The article by Drs. Chatenoud and Bach [1] is in many aspects sophisticated as well as surging. It summarizes the latest findings on immunotherapy of type 1 diabetes (T1D) regarding the application of CD3 antibodies by scrutinizing four prevailing concepts that could mislead the further development of such therapies. Inasmuch these concepts, i.e. antigenspecific therapies, initiation of immunotherapy before diabetes onset, combining several agents and, finally, caution regarding the generalization of results obtained from NOD mice, still remain burning issues in diabetes research, the article contributes valuably to the path of finding the optimal intervention strategy. The authors present criticism to the four concepts and take a clear stand of the promise of antigen-nonspecific immunotherapy in the establishment of long-term remission. Insofar, the article inspires to a more intensive discussion to include aspects that could be able to enrich the discussion on these critical concepts. Firstly, it is noticeable that the outcomes of several investigations do not confirm the role of anti-CD3 alone as a cure for T1D in humans [2-4]. If we act on this assumption, then either additional therapies and combinations will be needed or another holistic approach to cure the disease must be taken into consideration. Another critical issue in anti-CD3 therapy is the dose of administration. The dose that is currently being used in clinical trials is probably close to the maximum that can be ethically given. This is because of the initial cytokine release syndrome and the transient EBV reactivation that occurs in many patients due to the systemically immunosuppressive properties of anti- CD3 [5-8]. In order to avoid high doses, more frequent administrations of anti-CD3 or administration during the prediabetic phase could be beneficial, although we do not know whether this strategy will be safe. In this regard, we may consider why the NOD animal model could be misleading. Although anti-CD3 did not completely protect from diabetes when given to prediabetic NOD mice, it did in other diabetes models, such as the streptozotocin-treated CD1 mice [9] and the rat insulin promoter-lymphocytic choriomeningitis virus (RIPLCMV) model [10]. Therefore, maybe due to its multiple immune defects, the NOD mouse might not accurately reflect the immune status of the average prediabetic patient. Keywords:NilView:PDF (174.19 KB)

Overt autoantibodies to the smaller isoform of glutamate decarboxylase (GAD65Ab) are a characteristic in patients with Type 1 diabetes (T1D). Anti-idiotypic antibodies (anti-Id) directed to GAD65Ab effectively prevent the binding of GAD65 to GAD65Ab in healthy individuals. Levels of GAD65Ab-specific anti-Id are significantly lower in patients with T1D, leading to overt GAD65Ab in these patients. To determine the possible protective role of GAD65Ab-specific anti-Id in T1D pathogenesis, we developed the monoclonal anti-Id MAb 8E6G4 specifically targeting human monoclonal GAD65Ab b96.11. MAb 8E6G4 was demonstrated as a specific anti-Id directed to the antigen binding site of b96.11. MAb 8E6G4 recognized human antibodies in sera from healthy individuals, T2D patients, and T1D patients as established by ELISA. We confirmed these MAb 8E6G4-bound human antibodies to contain GAD65Ab by testing the eluted antibodies for binding to GAD65 in radioligand binding assays. These findings confirm that GAD65Ab are present in sera of individuals, who test GAD65Ab-negative in conventional detection assays. To test our hypothesis that GAD65Ab-specific anti-Id have an immune modulatory role in T1D, we injected young Non Obese Diabetic (NOD) mice with MAb 8E6G4. The animals were carefully monitored for development of T1D for 40 weeks. Infiltration of pancreatic islets by mononuclear cells (insulitis) was determined to establish the extent of an autoimmune attack on the pancreatic islets. Administration of MAb 8E6G4 significantly reduced the cumulative incidence rate of T1D and delayed the time of onset. Insulitis was significantly less severe in animals that received MAb 8E6G4 as compared to control animals. These results support our hypothesis that anti-Id specific to GAD65Ab have a protective role in T1D.

B cells and type 1 diabetes …in mice and men

Immune Checkpoint Inhibitors (ICI) Promote Neutrophil-Platelet Aggregate and NET Formation in Tumor-Bearing Mice