Glucagon-like peptide-1 protects human islets against cytokine-mediated β-cell dysfunction and death: a proteomic study of the pathways involved

Liraglutide enhances insulin secretion and prolongs the remission period in adults with newly diagnosed type 1 diabetes (the NewLira study): A randomized, double-blind, placebo-controlled trial

AIM

To test the effect of the glucagon-like peptide-1 receptor agonist, liraglutide, on residual beta-cell function in adults with newly diagnosed type 1 diabetes.

MATERIALS AND METHODS

In a multicentre, double-blind, parallel-group trial, adults with newly diagnosed type 1 diabetes and stimulated C-peptide of more than 0.2 nmol/L were randomized (1:1) to 1.8-mg liraglutide (Victoza) or placebo once daily for 52 weeks with 6 weeks of follow-up with only insulin treatment. The primary endpoint was the between-group difference in C-peptide area under the curve (AUC) following a liquid mixed-meal test after 52 weeks of treatment.

RESULTS

Sixty-eight individuals were randomized. After 52 weeks, the 4-hour AUC C-peptide response was maintained with liraglutide, but decreased with placebo (P = .002). Six weeks after end-of-treatment, C-peptide AUCs were similar for liraglutide and placebo. The average required total daily insulin dose decreased from 0.30 to 0.23 units/kg/day with liraglutide, but increased from 0.29 to 0.43 units/kg/day in the placebo group at week 52 (P < .001). Time without the need for insulin treatment was observed in 13 versus two patients and lasted for 22 weeks (from 3 to 52 weeks) versus 6 weeks (from 4 to 8 weeks) on average for liraglutide and placebo, respectively. Patients treated with liraglutide had fewer episodes of hypoglycaemia compared with placebo-treated patients. The adverse events with liraglutide were predominantly gastrointestinal and transient.

CONCLUSIONS

Treatment with liraglutide improves residual beta-cell function and reduces the dose of insulin during the first year after diagnosis. Beta-cell function was similar at 6 weeks postliraglutide treatment.

Immunotherapy in type 1 diabetes: Novel pathway to the future ahead

Since the discovery of insulin over 100 years ago, the focus of research in the management of type 1 diabetes (T1D) has centered around glycemic control and management of complications rather than the prevention of autoimmune destruction of pancreatic β cells. Fortunately, in recent years, there has been significant advancement in immune-targeted pharmacotherapy to halt the natural progression of T1D. The immune-targeted intervention aims to alter the underlying pathogenesis of T1D by targeting different aspects of the immune system. The immunotherapy can either antagonize the immune mediators like T cells, B cells or cytokines (antibody-based therapy), or reinduce self-tolerance to pancreatic β cells (antigen-based therapy) or stem-cell treatment. Recently, the US Food and Drug Administration approved the first immunotherapy teplizumab to be used only in stage 2 of T1D. However, the window of opportunity to practically implement this approved molecule in the selected target population is limited. In this Editorial, we briefly discuss the various promising recent developments in the field of immunotherapy research in T1D. However, further studies of these newer therapeutic agents are needed to explore their true potential for prevention or cure of T1D.

Christensenella minuta, a new candidate next-generation probiotic: current evidence and future trajectories

Background

As the field of probiotic research continues to expand, new beneficial strains are being discovered. The Christensenellaceae family and its newly described member, Christensenella minuta, have been shown to offer great health benefits. We aimed to extensively review the existing literature on these microorganisms to highlight the advantages of their use as probiotics and address some of the most challenging aspects of their commercial production and potential solutions.

Methods

We applied a simple search algorithm using the key words "Christensenellaceae" and "Christensenella minuta" to find all articles reporting the biotherapeutic effects of these microorganisms. Only articles reporting evidence-based results were reviewed.

Results

The review showed that Christensenella minuta has demonstrated numerous beneficial properties and a wider range of uses than previously thought. Moreover, it has been shown to be oxygen-tolerant, which is an immense advantage in the manufacturing and production of Christensenella minuta-based biotherapeutics. The results suggest that Christensenellaceae and Christensenella munita specifically can play a crucial role in maintaining a healthy gut microbiome. Furthermore, Christensenellaceae have been associated with weight management. Preliminary studies suggest that this probiotic strain could have a positive impact on metabolic disorders like diabetes and obesity, as well as inflammatory bowel disease.

Conclusion

Christensenellaceae and Christensenella munita specifically offer immense health benefits and could be used in the management and therapy of a wide range of health conditions. In addition to the impressive biotherapeutic effect, Christensenella munita is oxygen-tolerant, which facilitates commercial production and storage.

Incretins beyond type 2 diabetes

Incretin-based therapies, in particular glucagon-like peptide-1 (GLP-1) receptor agonists, have been evaluated in other forms of diabetes, but randomised controlled trials are mainly limited to people living with type 1 diabetes. In this review we present the evidence issuing from these trials and discuss their clinical implications as well as the difficulties in interpreting the data. In type 1 diabetes, the addition of GLP-1 receptor agonists to intensive insulin therapy lowers weight and required insulin doses compared with placebo, but the effects on glucose control (HbA1c, risk of hypoglycaemia) are dependent on the different study protocols. Side effects are limited to the gastrointestinal complaints of nausea, vomiting and diarrhoea. We briefly discuss the potential for using GLP-1 receptor agonists as (adjunct) therapies in other forms of diabetes, where the evidence to date is scarce.

A peripherally restricted cannabinoid-1 receptor inverse agonist promotes insulin secretion and protects from cytokine toxicity in human pancreatic islets

The cannabinoid receptor CB1R is expressed in pancreatic β-cells; CB1R increased activity is associated with diabetes, obesity, cardiovascular disorders as well as decreased insulin secretion and insulin resistance. CB1R was shown to signal through G-protein coupling as well as β-arrestins in β-cells. Peripherally restricted CB1R inverse agonists purportedly have beneficial effects on insulin secretion in β-cells, without the unwanted effects in the central nervous system. Here we show that a peripherally restricted CB1R inverse agonist, MRI-1891, augments glucose stimulated insulin secretion in isolated human pancreatic islets and mouse islets. The insulin secretion enhancing effect of MRI-1891 is comparable to exendin-4, an analogue of the glucagon like peptide-1 (GLP1). Moreover, MRI-1891 treatment protects isolated human islet cells against cytokine-induced apoptosis, similar to exendin-4. Thus, MRI-1891, a new class of CB1R inverse agonist, may be considered a potential therapeutic for both type 1 and type 2 diabetes because of its ability to protect pancreatic β-cells from cytokine toxicity and to promote insulin secretion.

Gut Molecules in Cardiometabolic Diseases: The Mechanisms behind the Story

Atherosclerotic cardiovascular disease is the most common cause of morbidity and mortality worldwide. Diabetes mellitus increases cardiovascular risk. Heart failure and atrial fibrillation are associated comorbidities that share the main cardiovascular risk factors. The use of incretin-based therapies promoted the idea that activation of alternative signaling pathways is effective in reducing the risk of atherosclerosis and heart failure. Gut-derived molecules, gut hormones, and gut microbiota metabolites showed both positive and detrimental effects in cardiometabolic disorders. Although inflammation plays a key role in cardiometabolic disorders, additional intracellular signaling pathways are involved and could explain the observed effects. Revealing the involved molecular mechanisms could provide novel therapeutic strategies and a better understanding of the relationship between the gut, metabolic syndrome, and cardiovascular diseases.

New therapeutic approaches for type 1 diabetes: Disease-modifying therapies

It has been 100 years since the first successful clinical use of insulin, yet it remains the only treatment option for type 1 diabetes mellitus (T1DM) patients. Advances in diabetes care, such as insulin analogue therapies and new devices, including continuous glucose monitoring with continuous subcutaneous insulin infusion have improved the quality of life of patients but have no impact on the pathogenesis of the disease. They do not eliminate long-term complications and require several lifestyle sacrifices. A more ideal future therapy for T1DM, instead of supplementing the insufficient hormone production (a consequence of β-cell destruction), would also aim to stop or slow down the destructive autoimmune process. The discovery of the autoimmune nature of type 1 diabetes mellitus has presented several targets by which disease progression may be altered. The goal of disease-modifying therapies is to target autoimmune mechanisms and prevent β-cell destruction. T1DM patients with better β-cell function have better glycemic control, reduced incidence of long-term complications and hypoglycemic episodes. Unfortunately, at the time symptomatic T1DM is diagnosed, most of the insulin secreting β cells are usually lost. Therefore, to maximize the salvageable β-cell mass by disease-modifying therapies, detecting autoimmune markers in an early, optimally presymptomatic phase of T1DM is of great importance. Disease-modifying therapies, such as immuno- and regenerative therapies are expected to take a relevant place in diabetology. The aim of this article was to provide a brief insight into the pathogenesis and course of T1DM and present the current state of disease-modifying therapeutic interventions that may impact future diabetes treatment.

The Protective Action of Metformin against Pro-Inflammatory Cytokine-Induced Human Islet Cell Damage and the Mechanisms Involved

Metformin, a drug widely used in type 2 diabetes (T2D), has been shown to protect human β-cells exposed to gluco- and/or lipotoxic conditions and those in islets from T2D donors. We assessed whether metformin could relieve the human β-cell stress induced by pro-inflammatory cytokines (which mediate β-cells damage in type 1 diabetes, T1D) and investigated the underlying mechanisms using shotgun proteomics. Human islets were exposed to 50 U/mL interleukin-1β plus 1000 U/mL interferon-γ for 48 h, with or without 2.4 µg/mL metformin. Glucose-stimulated insulin secretion (GSIS) and caspase 3/7 activity were studied, and a shotgun label free proteomics analysis was performed. Metformin prevented the reduction of GSIS and the activation of caspase 3/7 induced by cytokines. Proteomics analysis identified more than 3000 proteins in human islets. Cytokines alone altered the expression of 244 proteins (145 up- and 99 down-regulated), while, in the presence of metformin, cytokine-exposure modified the expression of 231 proteins (128 up- and 103 downregulated). Among the proteins inversely regulated in the two conditions, we found proteins involved in vesicle motility, defense against oxidative stress (including peroxiredoxins), metabolism, protein synthesis, glycolysis and its regulation, and cytoskeletal proteins. Metformin inhibited pathways linked to inflammation, immune reactions, mammalian target of rapamycin (mTOR) signaling, and cell senescence. Some of the changes were confirmed by Western blot. Therefore, metformin prevented part of the deleterious actions of pro-inflammatory cytokines in human β-cells, which was accompanied by islet proteome modifications. This suggests that metformin, besides use in T2D, might be considered for β-cell protection in other types of diabetes, possibly including early T1D.

The molecular mechanism of vgf in appetite, lipids, and insulin regulation

Obesity is an indication of an imbalance between energy expenditure and food intake. It is a complicated disease of epidemic proportions as it involves many factors and organs. Sedentary lifestyles and overeating have caused a substantial rise in people with obesity and type 2 diabetes. Thus, the discovery of successful and sustainable therapies for these chronic illnesses is critical. However, the mechanisms of obesity and diabetes and the crosstalk between these diseases are still ambiguous. Numerous studies are being done to study these mechanisms, with updates made frequently. VGF peptide and its derivatives are anticipated to have a role in the development of obesity and diabetes. However, contradictory studies have produced conflicting findings on the function of VGF. Therefore, in this review, we attempt to clarify and explain the role of VGF peptides in the brain, pancreas, and adipose tissue in the development of obesity.

Current state of antigen-specific immunotherapy for type 1 diabetes

PURPOSE OF REVIEW

Update on antigen-specific immunotherapy (ASIT) in type 1 diabetes (T1D) with focus on deoxyribonucleic acid (DNA)-induced immunization and the current obstacles to further research and clinical realization.

RECENT FINDINGS

In T1D, immune system imbalances together with malfunctioning islet-specific processes cause autoreactive immune cells to destroy beta cells in the islets. ASIT may restore self-tolerance; however, the approach has yet to fully meet its promise and may require co-administration of antigen (preproinsulin) and suitable immune response modifiers.

SUMMARY

A self-tolerant immune system may be regained using ASIT where T effector cells are repressed and/or T regulatory cells are induced. Administration of exogenous antigens has been safe in T1D. Conversely, adequate and lasting beta cell preservation has yet to be tested in sufficiently large clinical trials in suitable patients and may require targeting of multiple parts of the immunopathophysiology using combination therapies. DNA-based induction of native antigen expression to ensure important posttranscriptional modifications and presentation to the immune system together with tolerance-enhancing immune response modifiers (i.e., cytokines) may be more efficacious than exogenous antigens given alone. Progress is limited mainly by the scarcity of validated biomarkers to track the effects of ASIT in T1D.

Mechanisms of Beta-Cell Apoptosis in Type 2 Diabetes-Prone Situations and Potential Protection by GLP-1-Based Therapies

Type 2 diabetes (T2D) is characterized by chronic hyperglycemia secondary to the decline of functional beta-cells and is usually accompanied by a reduced sensitivity to insulin. Whereas altered beta-cell function plays a key role in T2D onset, a decreased beta-cell mass was also reported to contribute to the pathophysiology of this metabolic disease. The decreased beta-cell mass in T2D is, at least in part, attributed to beta-cell apoptosis that is triggered by diabetogenic situations such as amyloid deposits, lipotoxicity and glucotoxicity. In this review, we discussed the molecular mechanisms involved in pancreatic beta-cell apoptosis under such diabetes-prone situations. Finally, we considered the molecular signaling pathways recruited by glucagon-like peptide-1-based therapies to potentially protect beta-cells from death under diabetogenic situations.

Anti-interleukin-21 antibody and liraglutide for the preservation of β-cell function in adults with recent-onset type 1 diabetes: a randomised, double-blind, placebo-controlled, phase 2 trial

BACKGROUND

Type 1 diabetes is characterised by progressive loss of functional β-cell mass, necessitating insulin treatment. We aimed to investigate the hypothesis that combining anti-interleukin (IL)-21 antibody (for low-grade and transient immunomodulation) with liraglutide (to improve β-cell function) could enable β-cell survival with a reduced risk of complications compared with traditional immunomodulation.

METHODS

This randomised, parallel-group, placebo-controlled, double-dummy, double-blind, phase 2 trial was done at 94 sites (university hospitals and medical centres) in 17 countries. Eligible participants were adults aged 18-45 years with recently diagnosed type 1 diabetes and residual β-cell function. Individuals with unstable type 1 diabetes (defined by an episode of severe diabetic ketoacidosis within 2 weeks of enrolment) or active or latent chronic infections were excluded. Participants were randomly assigned (1:1:1:1), with stratification by baseline stimulated peak C-peptide concentration (mixed-meal tolerance test [MMTT]), to the combination of anti-IL-21 and liraglutide, anti-IL-21 alone, liraglutide alone, or placebo, all as an adjunct to insulin. Investigators, participants, and funder personnel were masked throughout the treatment period. The primary outcome was the change in MMTT-stimulated C-peptide concentration at week 54 (end of treatment) relative to baseline, measured via the area under the concentration-time curve (AUC) over a 4 h period for the full analysis set (intention-to-treat population consisting of all participants who were randomly assigned). After treatment cessation, participants were followed up for an additional 26-week off-treatment observation period. This trial is registered with ClinicalTrials.gov, NCT02443155.

FINDINGS

Between Nov 10, 2015, and Feb 27, 2019, 553 adults were assessed for eligibility, of whom 308 were randomly assigned to receive either anti-IL-21 plus liraglutide, anti-IL-21, liraglutide, or placebo (77 assigned to each group). Compared with placebo (ratio to baseline 0·61, 39% decrease), the decrease in MMTT-stimulated C-peptide concentration from baseline to week 54 was significantly smaller with combination treatment (0·90, 10% decrease; estimated treatment ratio 1·48, 95% CI 1·16-1·89; p=0·0017), but not with anti-IL-21 alone (1·23, 0·97-1·57; p=0·093) or liraglutide alone (1·12, 0·87-1·42; p=0·38). Despite greater insulin use in the placebo group, the decrease in HbA_1c (a key secondary outcome) at week 54 was greater with all active treatments (-0·50 percentage points) than with placebo (-0·10 percentage points), although the differences versus placebo were not significant. The effects diminished upon treatment cessation. Changes in immune cell subsets across groups were transient and mild (<10% change over time). The most frequently reported adverse events included gastrointestinal disorders, in keeping with the known side-effect profile of liraglutide. The rate of hypoglycaemic events did not differ significantly between active treatment groups and placebo, with an exception of a lower rate in the liraglutide group than in the placebo group during the treatment period. No events of diabetic ketoacidosis were observed. One participant died while on liraglutide (considered unlikely to be related to trial treatment) in connection with three reported adverse events (hypoglycaemic coma, pneumonia, and brain oedema).

INTERPRETATION

The combination of anti-IL-21 and liraglutide could preserve β-cell function in recently diagnosed type 1 diabetes. The efficacy of this combination appears to be similar to that seen in trials of other disease-modifying interventions in type 1 diabetes, but with a seemingly better safety profile. Efficacy and safety should be further evaluated in a phase 3 trial programme.

FUNDING

Novo Nordisk.

Inflammation-Induced Citrullinated Glucose-Regulated Protein 78 Elicits Immune Responses in Human Type 1 Diabetes

The β-cell has become recognized as a central player in the pathogenesis of type 1 diabetes with the generation of neoantigens as potential triggers for breaking immune tolerance. We report that posttranslationally modified glucose-regulated protein 78 (GRP78) is a novel autoantigen in human type 1 diabetes. When human islets were exposed to inflammatory stress induced by interleukin-1β, tumor necrosis factor-α, and interferon-γ, arginine residue R510 within GRP78 was converted into citrulline, as evidenced by liquid chromatography-tandem mass spectrometry. This conversion, known as citrullination, led to the generation of neoepitopes, which effectively could be presented by HLA-DRB1*04:01 molecules. With the use of HLA-DRB1*04:01 tetramers and ELISA techniques, we demonstrate enhanced antigenicity of citrullinated GRP78 with significantly increased CD4+ T-cell responses and autoantibody titers in patients with type 1 diabetes compared with healthy control subjects. Of note, patients with type 1 diabetes had a predominantly higher percentage of central memory cells and a lower percentage of effector memory cells directed against citrullinated GRP78 compared with the native epitope. These results strongly suggest that citrullination of β-cell proteins, exemplified here by the citrullination of GRP78, contributes to loss of self-tolerance toward β-cells in human type 1 diabetes, indicating that β-cells actively participate in their own demise.

The progress and potential of proteomic biomarkers for type 1 diabetes in children

INTRODUCTION

Although it is possible to identify the genetic risk for type 1 diabetes (T1D), it is not possible to predict who will develop the disease. New biomarkers are needed that would help understand the mechanisms of disease onset and when to administer targeted therapies and interventions. Areas covered: An overview is presented of international study efforts towards understanding the cause of T1D, including the collection of several extensive temporal sample series that follow the development of T1D in at risk children. The results of the proteomics analysis of these materials are presented, which have included bodily fluids, such as serum or plasma and urine, as well as tissue samples from the pancreas. Expert commentary: Promising recent reports have indicated detection of early proteomic changes in the serum of patients prior to diagnosis, potentially providing new measures for risk assessment. Similarly, there has been evidence that post-translational modification (PTM) may result in the recognition of islet cell proteins as autoantigens; modified proteins could thus be used as targets for immunomodulation to overcome the threat of the autoimmune response.

Glucagon-like peptide-1 and cholecystokinin production and signaling in the pancreatic islet as an adaptive response to obesity

Precise control of blood glucose is dependent on adequate β‐cell mass and function. Thus, reductions in β‐cell mass and function lead to insufficient insulin production to meet demand, and result in diabetes. Recent evidence suggests that paracrine signaling in the islet might be important in obesity, and disruption of this signaling could play a role in the pathogenesis of diabetes. For example, we recently discovered a novel islet incretin axis where glucagon‐like peptide‐1 regulates β‐cell production of another classic gut hormone, cholecystokinin. This axis is stimulated by obesity, and plays a role in enhancing β‐cell survival. In the present review, we place our observations in the wider context of the literature on incretin regulation in the islet, and discuss the potential for therapeutic targeting of these pathways.

The skeleton in the closet: actin cytoskeletal remodeling in β-cell function

Over the last few decades, biomedical research has considered not only the function of single cells but also the importance of the physical environment within a whole tissue, including cell-cell and cell-extracellular matrix interactions. Cytoskeleton organization and focal adhesions are crucial sensors for cells that enable them to rapidly communicate with the physical extracellular environment in response to extracellular stimuli, ensuring proper function and adaptation. The involvement of the microtubular-microfilamentous cytoskeleton in secretion mechanisms was proposed almost 50 years ago, since when the evolution of ever more sensitive and sophisticated methods in microscopy and in cell and molecular biology have led us to become aware of the importance of cytoskeleton remodeling for cell shape regulation and its crucial link with signaling pathways leading to β-cell function. Emerging evidence suggests that dysfunction of cytoskeletal components or extracellular matrix modification influences a number of disorders through potential actin cytoskeleton disruption that could be involved in the initiation of multiple cellular functions. Perturbation of β-cell actin cytoskeleton remodeling could arise secondarily to islet inflammation and fibrosis, possibly accounting in part for impaired β-cell function in type 2 diabetes. This review focuses on the role of actin remodeling in insulin secretion mechanisms and its close relationship with focal adhesions and myosin II.

Brusatol inhibits the response of cultured beta-cells to pro-inflammatory cytokines in vitro

Brusatol is a natural terpenoid that is capable of inducing a variety of biological effects. We presently report that this substance dramatically improves beta-cell survival when exposed to pro-inflammatory cytokines (IL-1β and IFNγ) in vitro. This was observed in insulin producing rat (RIN-5AH), mouse (βTC6) and human (EndoC-βH1) beta-cell lines. Brusatol prevented beta-cell oxidative stress in response to cytokines and counteracted induction of iNOS on the protein level. Brusatol, however, block neither the cytokine-induced increase of iNOS mRNA, nor NF-κB activation, suggesting that inhibition of iNOS protein expression relies on posttranscriptional mechanism. This indicates that brusatol acts via a novel protective pathway, which may represent a more promising way of improving beta-cell function and survival.

The beta-cell in type 1 diabetes: What have we learned from proteomic studies?

Pancreatic beta-cells have a crucial role in the regulation of blood glucose homeostasis by the production and secretion of insulin. In type 1 diabetes (T1D), an autoimmune reaction against the beta-cells together with the presence of inflammatory cytokines and ROS in the islets leads to beta-cell dysfunction and death. This review gives an overview of proteomic studies that lead to better understanding of beta-cell functioning in T1D. Protein profiling of isolated islets and beta-cell lines in health and T1D contributed to the unraveling of pathways involved in cytokine-induced cell death. In addition, by studying the serological proteome of T1D patients, new biomarkers and beta-cell autoantigens were discovered, which may improve screening tests and follow-up of T1D development. Interestingly, an important role for PTMs was demonstrated in the generation of beta-cell autoantigens. To conclude, proteomic techniques are of indispensable value to improve the knowledge on beta-cell function in T1D and the search toward therapeutic targets.

Absence of glucagon and insulin action reveals a role for the GLP-1 receptor in endogenous glucose production

The absence of insulin results in oscillating hyperglycemia and ketoacidosis in type 1 diabetes. Remarkably, mice genetically deficient in the glucagon receptor (Gcgr) are refractory to the pathophysiological symptoms of insulin deficiency, and therefore, studies interrogating this unique model may uncover metabolic regulatory mechanisms that are independent of insulin. A significant feature of Gcgr-null mice is the high circulating concentrations of GLP-1. Hence, the objective of this report was to investigate potential noninsulinotropic roles of GLP-1 in mice where GCGR signaling is inactivated. For these studies, pancreatic β-cells were chemically destroyed by streptozotocin (STZ) in Gcgr(-/-):Glp-1r(-/-) mice and in Glp-1r(-/-) animals that were subsequently treated with a high-affinity GCGR antagonist antibody that recapitulates the physiological state of Gcgr ablation. Loss of GLP-1 action substantially worsened nonfasting glucose concentrations and glucose tolerance in mice deficient in, and undergoing pharmacological inhibition of, the GCGR. Further, lack of the Glp-1r in STZ-treated Gcgr(-/-) mice elevated rates of endogenous glucose production, likely accounting for the differences in glucose homeostasis. These results support the emerging hypothesis that non-β-cell actions of GLP-1 analogs may improve metabolic control in patients with insulinopenic diabetes.

Dipeptidyl peptidase-4 inhibitor, vildagliptin, inhibits pancreatic beta cell apoptosis in association with its effects suppressing endoplasmic reticulum stress in db/db mice

AIMS

Vildagliptin promotes beta cell survival by inhibiting cell apoptosis. It has been suggested that chronic ER (endoplasmic reticulum) stress triggers beta cell apoptosis. The objective of the study is to explore whether the pro-survival effect of vildagliptin is associated with attenuation of endoplasmic reticulum stress in islets of db/db mice.

METHODS

Vildagliptin was orally administered to db/db mice for 6 weeks, followed by evaluation of beta cell apoptosis by caspase3 activity and TUNEL staining method. Endoplasmic reticulum stress markers were determined with quantitative RT-PCR, immunohistochemistry and immunoblot analysis.

RESULTS

After 6 weeks of treatment, vildagliptin treatment increased plasma active GLP-1 levels (22.63±1.19 vs. 11.69±0.44, P<0.001), inhibited beta cell apoptosis as demonstrated by lower amounts of TUNEL staining nuclei (0.37±0.03 vs. 0.55±0.03, P<0.01) as well as decreased caspase3 activity (1.48±0.11 vs. 2.67±0.13, P<0.01) in islets of diabetic mice compared with untreated diabetic group. Further, vildagliptin treatment down-regulated several genes related to endoplasmic reticulum stress including TRIB3 (tribbles homolog 3) (15.9±0.4 vs. 33.3±1.7, ×10⁻³, P<0.001), ATF-4(activating transcription factor 4) (0.83±0.06 vs. 1.42±0.02, P<0.001) and CHOP(C/EBP homologous protein) (0.07±0.01 vs. 0.16±0.01, P<0.001).

CONCLUSIONS

Vildagliptin promoted beta cell survival in db/db mice in association with down-regulating markers of endoplasmic reticulum stress including TRIB3, ATF-4 as well as CHOP.

Citrullinated glucose-regulated protein 78 is an autoantigen in type 1 diabetes

Posttranslational modifications of self-proteins play a substantial role in the initiation or propagation of the autoimmune attack in several autoimmune diseases, but their contribution to type 1 diabetes is only recently emerging. In the current study, we demonstrate that inflammatory stress, induced by the cytokines interleukin-1β and interferon-γ, leads to citrullination of GRP78 in β-cells. This is coupled with translocation of this endoplasmic reticulum chaperone to the β-cell plasma membrane and subsequent secretion. Importantly, expression and activity of peptidylarginine deiminase 2, one of the five enzymes responsible for citrullination and a candidate gene for type 1 diabetes in mice, is increased in islets from diabetes-prone nonobese diabetic (NOD) mice. Finally, (pre)diabetic NOD mice have autoantibodies and effector T cells that react against citrullinated GRP78, indicating that inflammation-induced citrullination of GRP78 in β-cells generates a novel autoantigen in type 1 diabetes, opening new avenues for biomarker development and therapeutic intervention.

Glucagon-like peptide 1 protects INS-1E mitochondria against palmitate-mediated beta-cell dysfunction: a proteomic study

Proteomic analysis of the protein expression profiles of enriched mitochondrial preparations of rat INS-1E β cells treated with palmitate in the presence and in the absence of GLP-1.