Disruption of the gamma-interferon signaling pathway at the level of signal transducer and activator of transcription-1 prevents immune destruction of beta-cells

Pancreatic Islet Cells Response to IFNγ Relies on Their Spatial Location within an Islet

Type 1 diabetes (T1D) is an auto-immune disease characterized by the progressive destruction of insulin-producing pancreatic beta cells. While beta cells are the target of the immune attack, the other islet endocrine cells, namely the alpha and delta cells, can also be affected by the inflammatory milieu. Here, using a flow cytometry-based strategy, we compared the impact of IFNγ, one of the main cytokines involved in T1D, on the three endocrine cell subsets isolated from C57BL/6 mouse islets. RNA-seq analyses revealed that alpha and delta cells exposed in vitro to IFNγ display a transcriptomic profile very similar to that of beta cells, with an increased expression of inflammation key genes such as MHC class I molecules, the CXCL10 chemokine and the programmed death-ligand 1 (PD-L1), three hallmarks of IFNγ signaling. Interestingly, at low IFNγ concentration, we observed two beta cell populations (responders and non-responders) based on PD-L1 protein expression. Our data indicate that this differential sensitivity relies on the location of the cells within the islet rather than on the existence of two different beta cells subsets. The same findings were corroborated by the in vivo analysis of pancreatic islets from the non-obese diabetic mouse model of T1D, showing more intense PD-L1 staining on endocrine cells close to immune infiltrate. Collectively, our work demonstrates that alpha and delta cells are as sensitive as beta cells to IFNγ, and suggests a gradual diffusion of the cytokine into an islet. These observations provide novel insights into the in situ inflammatory processes occurring in T1D progression.

Immediate-release tofacitinib reduces insulin resistance in non-diabetic active rheumatoid arthritis patients: A single-center retrospective study

BACKGROUND

An increased risk of insulin resistance (IR) has been identified in rheumatoid arthritis (RA), a chronic inflammatory disorder with elevated levels of pathogenic cytokines. Biologics targeting proinflammatory cytokines can control the disease and improve insulin sensitivity in RA. Although Janus kinase (JAK) signaling can regulate cytokine receptors and participate in RA pathogenesis, it remains to be elucidated whether there is a reduction of IR in such patients under JAK inhibitor (JAKi) therapy.

AIM

To study the effect of JAKi treatment on the reduction of IR in RA patients with active disease.

METHODS

A retrospective study was carried out from April 1, 2017 to March 31, 2021 in a population of non-diabetic patients with active RA who were undergoing tofacitinib (TOF) therapy with 5 mg twice-daily immediate-release formulation.

RESULTS

Fifty-six RA patients, aged 30 years to 75 years (mean ± SD: 52.3 ± 11.1) with disease activity score 28 values ranging from 4.54 to 7.37 (5.82 ± 0.74), were classified into high-IR (> 2.0) and low-IR (≤ 2.0) groups based on their baseline homeostatic model assessment (HOMA)-IR levels. They had no previous exposure to JAKi, and received TOF therapy for no less than 6 mo. In 30 patients who were naïve to biologics, after a 24-week therapeutic period, the high-IR group showed reduced HOMA-IR levels (3.331 ± 1.036 vs 2.292 ± 0.707, P < 0.001). In another 26 patients who were exposed to tumor necrosis factor-α or interleukin-6 blockers, the high-IR group, despite having achieved a decrease but with lower magnitude than in naïve patients, showed reduced HOMA-IR levels (2.924 ± 0.790 vs 2.545 ± 1.080, P = 0.018).

CONCLUSION

In this retrospective study, reduced IR was achieved in non-diabetic active RA patients following 24 wk of TOF therapy.

Emerging diabetes therapies: Bringing back the β-cells

BACKGROUND

Stem cell therapies are finally coming of age as a viable alternative to pancreatic islet transplantation for the treatment of insulin-dependent diabetes. Several clinical trials using human embryonic stem cell (hESC)-derived β-like cells are currently underway, with encouraging preliminary results. Remaining challenges notwithstanding, these strategies are widely expected to reduce our reliance on human isolated islets for transplantation procedures, making cell therapies available to millions of diabetic patients. At the same time, advances in our understanding of pancreatic cell plasticity and the molecular mechanisms behind β-cell replication and regeneration have spawned a multitude of translational efforts aimed at inducing β-cell replenishment in situ through pharmacological means, thus circumventing the need for transplantation.

SCOPE OF REVIEW

We discuss here the current state of the art in hESC transplantation, as well as the parallel quest to discover agents capable of either preserving the residual mass of β-cells or inducing their proliferation, transdifferentiation or differentiation from progenitor cells.

MAJOR CONCLUSIONS

Stem cell-based replacement therapies in the mold of islet transplantation are already around the corner, but a permanent cure for type 1 diabetes will likely require the endogenous regeneration of β-cells aided by interventions to restore the immune balance. The promise of current research avenues and a strong pipeline of clinical trials designed to tackle these challenges bode well for the realization of this goal.

Small-molecule discovery in the pancreatic beta cell

The pancreatic beta cell is the only cell type in the body responsible for insulin secretion, and thus plays a unique role in the control of glucose homeostasis. The loss of beta-cell mass and function plays an important role in both type 1 and type 2 diabetes. Thus, using chemical biology to identify small molecules targeting the beta cell could be an important component to developing future therapeutics for diabetes. This strategy provides an attractive path toward increasing beta-cell numbers in vivo. A regenerative strategy involves enhancing proliferation, differentiation, or neogenesis. On the other hand, protecting beta cells from cell death, or improving maturity and function, could preserve beta-cell mass. Here, we discuss the current state of chemical matter available to study beta-cell regeneration, and how they were discovered.

PTPN2 Regulates the Interferon Signaling and Endoplasmic Reticulum Stress Response in Pancreatic β-Cells in Autoimmune Diabetes

Type 1 diabetes (T1D) results from autoimmune destruction of β-cells in the pancreas. Protein tyrosine phosphatases (PTPs) are candidate genes for T1D and play a key role in autoimmune disease development and β-cell dysfunction. Here, we assessed the global protein and individual PTP profiles in the pancreas from nonobese mice with early-onset diabetes (NOD) mice treated with an anti-CD3 monoclonal antibody and interleukin-1 receptor antagonist. The treatment reversed hyperglycemia, and we observed enhanced expression of PTPN2, a PTP family member and T1D candidate gene, and endoplasmic reticulum (ER) chaperones in the pancreatic islets. To address the functional role of PTPN2 in β-cells, we generated PTPN2-deficient human stem cell-derived β-like and EndoC-βH1 cells. Mechanistically, we demonstrated that PTPN2 inactivation in β-cells exacerbates type I and type II interferon signaling networks and the potential progression toward autoimmunity. Moreover, we established the capacity of PTPN2 to positively modulate the Ca2+-dependent unfolded protein response and ER stress outcome in β-cells. Adenovirus-induced overexpression of PTPN2 partially protected from ER stress-induced β-cell death. Our results postulate PTPN2 as a key protective factor in β-cells during inflammation and ER stress in autoimmune diabetes.

Puerarin Inhibits the PERK-eIF2[Formula: see text]-ATF4-CHOP Pathway through Inactivating JAK2/STAT3 Signal in Pancreatic beta-Cells

Type 1 diabetes (T1D) is an autoimmune and inflammatory disease with excessive loss of pancreatic islet [Formula: see text]-cells. Accumulating evidence indicated that endoplasmic reticulum (ER) stress played a critical role in [Formula: see text]-cells loss, leading to T1D. Therefore, promoting the survival of pancreatic [Formula: see text]cells would be beneficial for patients with T1D. Puerarin is a natural isoflavone that has been demonstrated to be able to decrease blood glucose in patients with T1D. However, it remains unknown whether puerarin improves ER stress to prevent [Formula: see text]-cells from apoptosis. Here, we sought to investigate the role of puerarin in ER stress-associated apoptosis and explore its underlying mechanism in the mouse insulinoma cell line (MIN6). Flow cytometry and cell counting kit-8 (CCK8) experiments showed that puerarin caused a significant increase in the viability of MIN6 cells injured by H₂O₂. Furthermore, the protein kinase R-like ER kinase (PERK) signal pathway, a critical branch of ER stress response, was found to be involved in this process. Puerarin inhibited the phosphorylation of PERK, subsequently suppressed the phosphorylation of eukaryotic initiation factor 2[Formula: see text] (eIF2[Formula: see text], then decreased the activating transcription factor 4 (ATF4) and C/EBP homologous protein (CHOP) expression, ultimately attenuating ER stress to prevent MIN6 cells from apoptosis. In addition, puerarin inhibited the activation of Janus kinase 2 (JAK2)/signal transducer and activators of transcription 3 (STAT3), which suppressed the PERK signal cascade with decreased ATF4 and CHOP levels. Taken together, our results firstly demonstrated that puerarin could prevent MIN6 cells from apoptosis at least in part by inhibiting the PERK-eIF2[Formula: see text]-ATF4-CHOP axis under ER stress conditions, which might be mediated by inactivation of the JAK2/STAT3 signal pathway. Therefore, investigating the mechanism underlying the effects of puerarin might highlight the potential roles of puerarin developing into an antidiabetic drug.

Role of interferons in diabetic retinopathy

Diabetic retinopathy (DR) is one of the major causes of visual impairment and irreversible blindness in developed regions. Aside from abnormal angiogenesis, inflammation is the most specific and might be the initiating factor of DR. As a key participant in inflammation, interferon-gamma (IFN-γ) can be detected in different parts of the eye and is responsible for the breakdown of the blood-retina barrier and activation of inflammatory cells and other cytokines, which accelerate neovascularization and neuroglial degeneration. In addition, IFN-γ is involved in other vascular complications of diabetes mellitus and angiogenesis-dependent diseases, such as diabetic nephropathy, cerebral microbleeds, and age-related macular degeneration. Traditional treatments, such as anti-vascular endothelial growth factor agents, vitrectomy, and laser photocoagulation therapy, are more effective for angiogenesis and not tolerable for every patient. Many ongoing clinical trials are exploring effective drugs that target inflammation. For instance, IFN-α acts against viruses and angiogenesis and is commonly used to treat malignant tumors. Moreover, IFN-α has been shown to contribute to alleviating the progression of DR and other ocular diseases. In this review, we emphasize the roles that IFNs play in the pathogenesis of DR and discuss potential clinical applications of IFNs in DR, such as diagnosis, prognosis, and therapeutic treatment.

SKAP2, a Candidate Gene for Type 1 Diabetes, Regulates β-Cell Apoptosis and Glycemic Control in Newly Diagnosed Patients

The single nucleotide polymorphism rs7804356 located in the Src kinase-associated phosphoprotein 2 (SKAP2) gene is associated with type 1 diabetes (T1D), suggesting SKAP2 as a causal candidate gene. The objective of the study was to investigate if SKAP2 has a functional role in the β-cells in relation to T1D. In a cohort of children with newly diagnosed T1D, rs7804356 predicted glycemic control and residual β-cell function during the 1st year after diagnosis. In INS-1E cells and rat and human islets, proinflammatory cytokines reduced the content of SKAP2. Functional studies revealed that knockdown of SKAP2 aggravated cytokine-induced apoptosis in INS-1E cells and primary rat β-cells, suggesting an antiapoptotic function of SKAP2. In support of this, overexpression of SKAP2 afforded protection against cytokine-induced apoptosis, which correlated with reduced nuclear content of S536-phosphorylated nuclear factor-κB (NF-κB) subunit p65, lower nitric oxide production, and diminished CHOP expression indicative of decreased endoplasmic reticulum stress. Knockdown of CHOP partially counteracted the increase in cytokine-induced apoptosis caused by SKAP2 knockdown. In conclusion, our results suggest that SKAP2 controls β-cell sensitivity to cytokines possibly by affecting the NF-κB-inducible nitric oxide synthase-endoplasmic reticulum stress pathway.

Good Cop, Bad Cop: The Opposing Effects of Macrophage Activation State on Maintaining or Damaging Functional β-Cell Mass

Loss of functional β-cell mass is a hallmark of Type 1 and Type 2 Diabetes. Macrophages play an integral role in the maintenance or destruction of pancreatic β-cells. The effect of the macrophage β-cell interaction is dependent on the activation state of the macrophage. Macrophages can be activated across a spectrum, from pro-inflammatory to anti-inflammatory and tissue remodeling. The factors secreted by these differentially activated macrophages and their effect on β-cells define the effect on functional β-cell mass. In this review, the spectrum of macrophage activation is discussed, as are the positive and negative effects on β-cell survival, expansion, and function as well as the defined factors released from macrophages that impinge on functional β-cell mass.

Advances in Knowledge of Candidate Genes Acting at the Beta-Cell Level in the Pathogenesis of T1DM

T1DM (type 1 diabetes mellitus), which results from the irreversible elimination of beta-cells mediated by autoreactive T cells, is defined as an autoimmune disease. It is widely accepted that T1DM is caused by a combination of genetic and environmental factors, but the precise underlying molecular mechanisms are still unknown. To date, more than 50 genetic risk regions contributing to the pathogenesis of T1DM have been identified by GWAS (genome-wide association studies). Notably, more than 60% of the identified candidate genes are expressed in islets and beta-cells, which makes it plausible that these genes act at the beta-cell level and play a key role in the pathogenesis of T1DM. In this review, we focus on the current status of candidate genes that act at the beta-cell level by regulating the innate immune response and antiviral activity, affecting susceptibility to proapoptotic stimuli and influencing the pancreatic beta-cell phenotype.

Boosting to Amplify Signal with Isobaric Labeling (BASIL) Strategy for Comprehensive Quantitative Phosphoproteomic Characterization of Small Populations of Cells

Comprehensive phosphoproteomic analysis of small populations of cells remains a daunting task due primarily to the insufficient MS signal intensity from low concentrations of enriched phosphopeptides. Isobaric labeling has a unique multiplexing feature where the "total" peptide signal from all channels (or samples) triggers MS/MS fragmentation for peptide identification, while the reporter ions provide quantitative information. In light of this feature, we tested the concept of using a "boosting" sample (e.g., a biological sample mimicking the study samples but available in a much larger quantity) in multiplexed analysis to enable sensitive and comprehensive quantitative phosphoproteomic measurements with <100 000 cells. This simple boosting to amplify signal with isobaric labeling (BASIL) strategy increased the overall number of quantifiable phosphorylation sites more than 4-fold. Good reproducibility in quantification was demonstrated with a median CV of 15.3% and Pearson correlation coefficient of 0.95 from biological replicates. A proof-of-concept experiment demonstrated the ability of BASIL to distinguish acute myeloid leukemia cells based on the phosphoproteome data. Moreover, in a pilot application, this strategy enabled quantitative analysis of over 20 000 phosphorylation sites from human pancreatic islets treated with interleukin-1β and interferon-γ. Together, this signal boosting strategy provides an attractive solution for comprehensive and quantitative phosphoproteome profiling of relatively small populations of cells where traditional phosphoproteomic workflows lack sufficient sensitivity.

The Association between Depression and Type 1 Diabetes Mellitus: Inflammatory Cytokines as Ferrymen in between?

The depression incidence is much higher in patients with diabetes mellitus (DM), and the majority of these cases remain under-diagnosed. Type 1 diabetes mellitus (T1D) is now widely thought to be an organ-specific autoimmune disease. As a chronic autoimmune condition, T1D is characterized by T cell-mediated selective loss of insulin-producing β-cells. The age of onset of T1D is earlier than T2D, and T1D patients have an increased vulnerability to depression due to its diagnosis and treatment burden occurring in a period when the individuals are young. The literature has suggested that inflammatory cytokines play a wide role in both diseases. In this review, the mechanisms behind the initiation and propagation of the autoimmune response in T1D and depression are analyzed, and the contribution of cytokines to both conditions is discussed. This review outlines the immunological mechanism of T1D and depression, with a particular emphasis on the role of tumor necrosis factor-α (TNF-α), IL-1β, and interferon-γ (IFN-γ) cytokines and their signaling pathways. The purpose of this review is to highlight the possible pathways of the cytokines shared by these two diseases via deciphering their cytokine cascades. They may provide a basic groundwork for future study of the possible mechanism that links these two diseases and to develop new compounds that target the same pathway but can conquer two diseases.

JAK/STAT - Emerging Players in Metabolism

The Janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathway is crucial for transducing signals from a variety of metabolically relevant hormones and cytokines including growth hormone, leptin, erythropoietin, IL4, IL6 and IFNγ. A growing body of evidence suggests that this pathway is dysregulated in the context of obesity and metabolic disease. Recent development of animal models has been instrumental in identifying the role of JAK/STAT signaling in the peripheral metabolic organs including adipose, liver, muscle, pancreas, and the immune system. In this review we summarize current knowledge about the function of JAK/STAT proteins in the regulation of metabolism, and highlight new potential therapeutic targets for the treatment of obesity and diabetes.

Persistence of STAT-1 inhibition and induction of cytokine resistance in pancreatic β cells treated with St John's wort and its component hyperforin

OBJECTIVES

St John's wort extract (SJW) and its component hyperforin (HPF) were shown to potently inhibit cytokine-induced STAT-1 and NF-κB activation in pancreatic β cells and protect them against injury. This study aimed at exploring the time course of STAT-1 inhibition afforded by these natural compounds in the β-cell line INS-1E.

METHODS

INS-1E cells were pre-incubated with SJW extract (2-5 μg/ml) or HPF (0.5-2 μm) and then exposed to a cytokine mixture. In some experiments, these compounds were added after or removed before cytokine exposure. STAT-1 activation was assessed by electrophoretic mobility shift assay, apoptosis by caspase-3 activity assay, mRNA gene expression by RT-qPCR.

KEY FINDINGS

Pre-incubation with SJW/HPF for 1-2 h exerted a remarkable STAT-1 downregulation, which was maintained upon removal of the compounds before early or delayed cytokine addition. When the protective compounds were added after cell exposure to cytokines, between 15 and 90 min, STAT-1 inhibition also occurred at a progressively decreasing extent. Upon 24-h incubation, SJW and HPF counteracted cytokine-induced β-cell dysfunction, apoptosis and target gene expression.

CONCLUSIONS

SJW and HPF confer to β cells a state of 'cytokine resistance', which can be elicited both before and after cytokine exposure and safeguards these cells from deleterious cytokine effects.

Cell Loss during Pseudoislet Formation Hampers Profound Improvements in Islet Lentiviral Transduction Efficacy for Transplantation Purposes

Islet transplantation is a promising treatment in type 1 diabetes, but the need for chronic immunosuppression is a major hurdle to broad applicability. Ex vivo introduction of agents by lentiviral vectors—improving β-cell resistance against immune attack—is an attractive path to pursue. The aim of this study was to investigate whether dissociation of islets to single cells prior to viral infection and reaggregation before transplantation would improve viral transduction efficacy without cytotoxicity. This procedure improved transduction efficacy with a LV-pWPT-CMV-EGFP construct from 11.2 ± 4.1% at MOI 50 in whole islets to 80.0 ± 2.8% at MOI 5. Viability (as measured by Hoechst/PI) and functionality (as measured by glucose challenge) remained high. After transplantation, the transfected pseudoislet aggregates remained EGFP positive for more than 90 days and the expression of EGFP colocalized primarily with the insulin-positive β-cells. No increased vulnerability to immune attack was observed in vitro or in vivo. These data demonstrate that dispersion of islets prior to lentiviral transfection and reaggregation prior to transplantation is a highly efficient way to introduce genes of interest into islets for transplantation purposes in vitro and in vivo, but the amount of β-cells needed for normalization of glycemia was more than eightfold higher when using dispersed cell aggregates versus unmanipulated islets. The high price to pay to reach stable and strong transgene expression in islet cells is certainly an important cell loss.

Pannexin-2-deficiency sensitizes pancreatic β-cells to cytokine-induced apoptosis in vitro and impairs glucose tolerance in vivo

Pannexins (Panx's) are membrane proteins involved in a variety of biological processes, including cell death signaling and immune functions. The role and functions of Panx's in pancreatic β-cells remain to be clarified. Here, we show Panx1 and Panx2 expression in isolated islets, primary β-cells, and β-cell lines. The expression of Panx2, but not Panx1, was downregulated by interleukin-1β (IL-1β) plus interferon-γ (IFNγ), two pro-inflammatory cytokines suggested to contribute to β-cell demise in type 1 diabetes (T1D). siRNA-mediated knockdown (KD) of Panx2 aggravated cytokine-induced apoptosis in rat INS-1E cells and primary rat β-cells, suggesting anti-apoptotic properties of Panx2. An anti-apoptotic function of Panx2 was confirmed in isolated islets from Panx2^-/- mice and in human EndoC-βH1 cells. Panx2 KD was associated with increased cytokine-induced activation of STAT3 and higher expression of inducible nitric oxide synthase (iNOS). Glucose-stimulated insulin release was impaired in Panx2^-/- islets, and Panx2^-/- mice subjected to multiple low-dose Streptozotocin (MLDS) treatment, a model of T1D, developed more severe diabetes compared to wild type mice. These data suggest that Panx2 is an important regulator of the insulin secretory capacity and apoptosis in pancreatic β-cells.

Dual genetic absence of STAT6 and IL-10 does not abrogate anti-hyperglycemic effects of Schistosoma mansoni in streptozotocin-treated diabetic mice

Schistosoma mansoni (Sm) is known to exert protective effects against various allergic and autoimmune disorders. It has been reported that this parasite protects NOD mice from spontaneous type 1 diabetes (T1D) and ameliorates streptozotocin (STZ)-induced T1D in wild-type mice. Here, we tried to clarify the anti-diabetic mechanisms of Sm in the latter model. Sm infection partially prevented the degradation of pancreatic islets and hyperglycemia in multiple low-dose (MLD) STZ-treated mice. Neither Treg cell depletion nor genetic absences of IL-10 and/or STAT6 abrogated the anti-hyperglycemic effects of Sm. Among M2 macrophage markers, Arg-1 and Ym1, but not Retnla, remained up-regulated in the pancreatic lymph nodes and in the spleens of STAT6/IL-10 double deficient (DKO) mice. Collectively, it is suggested that Sm exerts anti-diabetic effects on this experimental T1D model via Treg/IL-4/IL-13/IL-10-independent mechanisms. Augmented expressions of Arg-1 and Ym1 in the lymphoid organs adjacent to pancreas may be relevant to the anti-diabetic effects of Sm.

Estrogen-regulated STAT1 activation promotes TLR8 expression to facilitate signaling via microRNA-21 in systemic lupus erythematosus

Recent studies implicate innate immunity to systemic lupus erythematosus (SLE) pathogenesis. Toll-like receptor (TLR)8 is estrogen-regulated and binds viral ssRNA to stimulate innate immune responses, but recent work indicates that microRNA (miR)-21 within extracellular vesicles (EVs) can also trigger this receptor. Our objective was to examine TLR8 expression/activation to better understand sex-biased responses involving TLR8 in SLE. Our data identify an estrogen response element that promotes STAT1 expression and demonstrate STAT1-dependent transcriptional activation of TLR8 with estrogen stimulation. In lieu of viral ssRNA activation, we explored EV-encapsulated miR-21 as an endogenous ligand and observed induction of both TLR8 and cytokine expression in vitro. Moreover, extracellular miR detection was found predominantly within EVs. Thus, just as a cytokine or chemokine, EV-encapsulated miR-21 can act as an inflammatory signaling molecule, or miRokine, by virtue of being an endogenous ligand of TLR8. Collectively, our data elucidates a novel innate inflammatory pathway in SLE.

Cytokines and Pancreatic β-Cell Apoptosis

The discovery 30 years ago that inflammatory cytokines cause a concentration, activity, and time-dependent bimodal response in pancreatic β-cell function and viability has been a game-changer in the fields of research directed at understanding inflammatory regulation of β-cell function and survival and the causes of β-cell failure and destruction in diabetes. Having until then been confined to the use of pathophysiologically irrelevant β-cell toxic chemicals as a model of β-cell death, researchers could now mimic endocrine and paracrine effects of the cytokine response in vitro by titrating concentrations in the low to the high picomolar-femtomolar range and vary exposure time for up to 14-16h to reproduce the acute regulatory effects of systemic inflammation on β-cell secretory responses, with a shift to inhibition at high picomolar concentrations or more than 16h of exposure to illustrate adverse effects of local, chronic islet inflammation. Since then, numerous studies have clarified how these bimodal responses depend on discrete signaling pathways. Most interest has been devoted to the proapoptotic response dependent upon mainly nuclear factor κ B and mitogen-activated protein kinase activation, leading to gene expressional changes, endoplasmic reticulum stress, and triggering of mitochondrial dysfunction. Preclinical studies have shown preventive effects of cytokine antagonism in animal models of diabetes, and clinical trials demonstrating proof of concept are emerging. The full clinical potential of anticytokine therapies has yet to be shown by testing the incremental effects of appropriate dosing, timing, and combinations of treatments. Due to the considerable translational importance of enhancing the precision, specificity, and safety of antiinflammatory treatments of diabetes, we review here the cellular, preclinical, and clinical evidence of which of the death pathways recently proposed in the Nomenclature Committee on Cell Death 2012 Recommendations are activated by inflammatory cytokines in the pancreatic β-cell to guide the identification of antidiabetic targets. Although there are still scarce human data, the cellular and preclinical studies point to the caspase-dependent intrinsic apoptosis pathway as the prime effector of inflammatory β-cell apoptosis.

Genetic predisposition for beta cell fragility underlies type 1 and type 2 diabetes

Type 1 (T1D) and type 2 (T2D) diabetes share pathophysiological characteristics, yet mechanistic links have remained elusive. T1D results from autoimmune destruction of pancreatic beta cells, whereas beta cell failure in T2D is delayed and progressive. Here we find a new genetic component of diabetes susceptibility in T1D non-obese diabetic (NOD) mice, identifying immune-independent beta cell fragility. Genetic variation in Xrcc4 and Glis3 alters the response of NOD beta cells to unfolded protein stress, enhancing the apoptotic and senescent fates. The same transcriptional relationships were observed in human islets, demonstrating the role of beta cell fragility in genetic predisposition to diabetes.

TRAF2 mediates JNK and STAT3 activation in response to IL-1β and IFNγ and facilitates apoptotic death of insulin-producing β-cells

Interleukin-1β (IL-1β) and interferon-γ (IFNγ) contribute to type 1 diabetes (T1D) by inducing β-cell death. Tumor necrosis factor (TNF) receptor-associated factor (TRAF) proteins are adaptors that transduce signaling from a variety of membrane receptors including cytokine receptors. We show here that IL-1β and IFNγ upregulate the expression of TRAF2 in insulin-producing INS-1E cells and isolated rat pancreatic islets. siRNA-mediated knockdown (KD) of TRAF2 in INS-1E cells reduced IL-1β-induced phosphorylation of JNK1/2, but not of p38 or ERK1/2 mitogen-activated protein kinases. TRAF2 KD did not modulate NFκB activation by cytokines, but reduced cytokine-induced inducible nitric oxide synthase (iNOS) promotor activity and expression. We further observed that IFNγ-stimulated phosphorylation of STAT3 required TRAF2. KD of TRAF2 or STAT3 reduced cytokine-induced caspase 3/7 activation, but, intriguingly, potentiated cytokine-mediated loss of plasma membrane integrity and augmented the number of propidium iodide-positive cells. Finally, we found that TRAF2 KD increased cytokine-induced production of reactive oxygen species (ROS). In summary, our data suggest that TRAF2 is an important mediator of IL-1β and IFNγ signaling in pancreatic β-cells.

The microRNA-29 Family Dictates the Balance Between Homeostatic and Pathological Glucose Handling in Diabetes and Obesity

The microRNA-29 (miR-29) family is among the most abundantly expressed microRNA in the pancreas and liver. Here, we investigated the function of miR-29 in glucose regulation using miR-29a/b-1 (miR-29a)-deficient mice and newly generated miR-29b-2/c (miR-29c)-deficient mice. We observed multiple independent functions of the miR-29 family, which can be segregated into a hierarchical physiologic regulation of glucose handling. miR-29a, and not miR-29c, was observed to be a positive regulator of insulin secretion in vivo, with dysregulation of the exocytotic machinery sensitizing β-cells to overt diabetes after unfolded protein stress. By contrast, in the liver both miR-29a and miR-29c were important negative regulators of insulin signaling via phosphatidylinositol 3-kinase regulation. Global or hepatic insufficiency of miR-29 potently inhibited obesity and prevented the onset of diet-induced insulin resistance. These results demonstrate strong regulatory functions for the miR-29 family in obesity and diabetes, culminating in a hierarchical and dose-dependent effect on premature lethality.

Heterozygous inactivation of plasma membrane Ca(2+)-ATPase in mice increases glucose-induced insulin release and beta cell proliferation, mass and viability

AIMS/HYPOTHESIS

Calcium plays an important role in the process of glucose-induced insulin release in pancreatic beta cells. These cells are equipped with a double system responsible for Ca(2+) extrusion--the Na/Ca exchanger (NCX) and the plasma membrane Ca(2+)-ATPase (PMCA). We have shown that heterozygous inactivation of NCX1 in mice increased glucose-induced insulin release and stimulated beta cell proliferation and mass. In the present study, we examined the effects of heterozygous inactivation of the PMCA on beta cell function.

METHODS

Biological and morphological methods (Ca(2+) imaging, Ca(2+) uptake, glucose metabolism, insulin release and immunohistochemistry) were used to assess beta cell function and proliferation in Pmca2 (also known as Atp2b2) heterozygous mice and control littermates ex vivo. Blood glucose and insulin levels were also measured to assess glucose metabolism in vivo.

RESULTS

Pmca (isoform 2) heterozygous inactivation increased intracellular Ca(2+) stores and glucose-induced insulin release. Moreover, increased beta cell proliferation, mass, viability and islet size were observed in Pmca2 heterozygous mice. However, no differences in beta cell glucose metabolism, proinsulin immunostaining and insulin content were observed.

CONCLUSIONS/INTERPRETATION

The present data indicates that inhibition of Ca(2+) extrusion from the beta cell and its subsequent intracellular accumulation stimulates beta cell function, proliferation and mass. This is in agreement with our previous results observed in mice displaying heterozygous inactivation of NCX, and indicates that inhibition of Ca(2+) extrusion mechanisms by small molecules in beta cells may represent a new approach in the treatment of type 1 and type 2 diabetes.

Inactivation of Protein Tyrosine Phosphatases Enhances Interferon Signaling in Pancreatic Islets

Type 1 diabetes (T1D) is the result of an autoimmune assault against the insulin-producing pancreatic β-cells, where chronic local inflammation (insulitis) leads to β-cell destruction. T cells and macrophages infiltrate into islets early in T1D pathogenesis. These immune cells secrete cytokines that lead to the production of reactive oxygen species (ROS) and T-cell invasion and activation. Cytokine-signaling pathways are very tightly regulated by protein tyrosine phosphatases (PTPs) to prevent excessive activation. Here, we demonstrate that pancreata from NOD mice with islet infiltration have enhanced oxidation/inactivation of PTPs and STAT1 signaling compared with NOD mice that do not have insulitis. Inactivation of PTPs with sodium orthovanadate in human and rodent islets and β-cells leads to increased activation of interferon signaling and chemokine production mediated by STAT1 phosphorylation. Furthermore, this exacerbated STAT1 activation-induced cell death in islets was prevented by overexpression of the suppressor of cytokine signaling-1 or inactivation of the BH3-only protein Bim. Together our data provide a mechanism by which PTP inactivation induces signaling in pancreatic islets that results in increased expression of inflammatory genes and exacerbated insulitis.

Transcriptional regulation of chemokine genes: a link to pancreatic islet inflammation?

Enhanced expression of chemotactic cytokines (aka chemokines) within pancreatic islets likely contributes to islet inflammation by regulating the recruitment and activation of various leukocyte populations, including macrophages, neutrophils, and T-lymphocytes. Because of the powerful actions of these chemokines, precise transcriptional control is required. In this review, we highlight what is known about the signals and mechanisms that govern the transcription of genes encoding specific chemokine proteins in pancreatic islet β-cells, which include contributions from the NF-κB and STAT1 pathways. We further discuss increased chemokine expression in pancreatic islets during autoimmune-mediated and obesity-related development of diabetes.

A combined "omics" approach identifies N-Myc interactor as a novel cytokine-induced regulator of IRE1 protein and c-Jun N-terminal kinase in pancreatic beta cells

Type 1 diabetes is an autoimmune disease with a strong inflammatory component. The cytokines interleukin-1β and interferon-γ contribute to beta cell apoptosis in type 1 diabetes. These cytokines induce endoplasmic reticulum stress and the unfolded protein response (UPR), contributing to the loss of beta cells. IRE1α, one of the UPR mediators, triggers insulin degradation and inflammation in beta cells and is critical for the transition from "physiological" to "pathological" UPR. The mechanisms regulating inositol-requiring protein 1α (IRE1α) activation and its signaling for beta cell "adaptation," "stress response," or "apoptosis" remain to be clarified. To address these questions, we combined mammalian protein-protein interaction trap-based IRE1α interactome and functional genomic analysis of human and rodent beta cells exposed to pro-inflammatory cytokines to identify novel cytokine-induced regulators of IRE1α. Based on this approach, we identified N-Myc interactor (NMI) as an IRE1α-interacting/modulator protein in rodent and human pancreatic beta cells. An increased expression of NMI was detected in islets from nonobese diabetic mice with insulitis and in rodent or human beta cells exposed in vitro to the pro-inflammatory cytokines interleukin-1β and interferon-γ. Detailed mechanistic studies demonstrated that NMI negatively modulates IRE1α-dependent activation of JNK and apoptosis in rodent and human pancreatic beta cells. In conclusion, by using a combined omics approach, we identified NMI induction as a novel negative feedback mechanism that decreases IRE1α-dependent activation of JNK and apoptosis in cytokine-exposed beta cells

Protein tyrosine phosphatases: molecular switches in metabolism and diabetes

Protein tyrosine phosphatases (PTPs) are a large family of enzymes that generally oppose the actions of protein tyrosine kinases (PTKs). Genetic polymorphisms for particular PTPs are associated with altered risk of both type 1 diabetes (T1D) and type 2 diabetes (T2D). Moreover, recent evidence suggests that PTPs play crucial roles in metabolism. They can act as regulators of liver homeostasis, food intake, or immune-mediated pancreatic b cell death. In this review we describe the mechanisms by which different members of the non-receptor PTP (PTPN) family influence metabolic physiology. This 'metabolic job' of PTPs is discussed in depth and the role of these proteins in different cell types compared. Understanding the pathways regulated by PTPs will provide novel therapeutic strategies for the treatment of diabetes.

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.

Role and mechanism of pancreatic β-cell death in diabetes: The emerging role of autophagy

Pancreatic β‐cell failure resulting from decreased β‐cell mass or dysfunction is the ultimate step towards most types of diabetes. Even if insulin resistance exists, diabetes does not develop unless pancreatic β‐cell function or its adaptation is compromised. Classically, two types of cell death (apoptosis and necrosis) have been studied in the diabetes field. Recently, a third type of cell death (autophagy, sometimes called type 2 programmed cell death in comparison with apoptosis, type 1 programmed cell death) and its pathophysiological role have been recognized and are being investigated. In the present review, we will discuss the role of various types of cell death in the development of type 1 and type 2 diabetes. Specifically, we will briefly cover recent progress regarding the role of autophagy in diabetes, which is becoming a hot topic in diabetes and metabolism. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2010.0054.x, 2010)

IL-17A increases the expression of proinflammatory chemokines in human pancreatic islets

AIMS/HYPOTHESIS

Cytotoxic T cells and macrophages contribute to beta cell destruction in type 1 diabetes at least in part through the production of cytokines such as IL-1β, IFN-γ and TNF-α. We have recently shown the IL-17 pathway to be activated in circulating T cells and pancreatic islets of type 1 diabetes patients. Here, we studied whether IL-17A upregulates the production of chemokines by human pancreatic islets, thus contributing to the build-up of insulitis.

METHODS

Human islets (from 18 donors), INS-1E cells and islets from wild-type and Stat1 knockout mice were studied. Dispersed islet cells were left untreated, or were treated with IL-17A alone or together with IL-1β+IFN-γ or TNF-α+IFN-γ. RNA interference was used to knock down signal transducer and activator of transcription 1 (STAT1). Chemokine expression was assessed by quantitative RT-PCR, ELISA and histology. Cell viability was evaluated with nuclear dyes.

RESULTS

IL-17A augmented IL-1β+IFN-γ- and TNF-α+IFN-γ-induced chemokine mRNA and protein expression, and apoptosis in human islets. Beta cells were at least in part the source of chemokine production. Knockdown of STAT1 in human islets prevented cytokine- or IL-17A+cytokine-induced apoptosis and the expression of particular chemokines, e.g. chemokine (C-X-C motif) ligands 9 and 10. Similar observations were made in islets isolated from Stat1 knockout mice.

CONCLUSIONS/INTERPRETATION

Our findings indicate that IL-17A exacerbates proinflammatory chemokine expression and secretion by human islets exposed to cytokines. This suggests that IL-17A contributes to the pathogenesis of type 1 diabetes by two mechanisms, namely the exacerbation of beta cell apoptosis and increased local production of chemokines, thus potentially aggravating insulitis.

St. John's wort extract and hyperforin protect rat and human pancreatic islets against cytokine toxicity

The extract of Hypericum perforatum (St. John's wort, SJW) and its component hyperforin (HPF) were previously shown to inhibit cytokine-induced activation of signal transducer and activator of transcription-1 and nuclear factor κB and prevent apoptosis in a cultured β-cell line. Objective of this study was to assess the protection exerted by SJW and HPF on isolated rat and human islets exposed to cytokines in vitro. Functional, ultrastructural, biomolecular and cell death evaluation studies were performed. In both rat and human islets, SJW and HPF counteracted cytokine-induced functional impairment and down-regulated mRNA expression of pro-inflammatory target genes, such as iNOS, CXCL9, CXCL10, COX2. Cytokine-induced NO production from cultured islets, evaluated by nitrites measurement in the medium, was significantly reduced in the presence of the vegetal compounds. Noteworthy, the increase in apoptosis and necrosis following 48-h exposure to cytokines was fully prevented by SJW and partially by HPF. Ultrastructural morphometric analysis in human islets exposed to cytokines for 20 h showed that SJW or HPF avoided early β-cell damage (e.g., mitochondrial alterations and loss of insulin granules). In conclusion, SJW compounds protect rat and human islets against cytokine effects by counteracting key mechanisms of cytokine-mediated β-cell injury and represent promising pharmacological tools for prevention or limitation of β-cell dysfunction and loss in type 1 diabetes.

The efficacy of SPA0355 in protecting β cells in isolated pancreatic islets and in a murine experimental model of type 1 diabetes

Cytokines activate several inflammatory signals that mediate β-cell destruction. We recently determined that SPA0355 is a strong anti-inflammatory compound, thus reporting its efficacy in protecting β cells from various insults. The effects of SPA0355 on β-cell survival were studied in RINm5F cells and primary islets. The protective effects of this compound on the development of type 1 diabetes were evaluated in non-obese diabetic (NOD) mice. SPA0355 completely prevented cytokine-induced nitric oxide synthase (iNOS) expression and cytotoxicity in RINm5F cells and isolated islets. The molecular mechanism of SPA0355 inhibition of iNOS expression involves the inhibition of nuclear factor κB and Janus kinase signal transducer and activator of transcription pathways. The protective effects of SPA0355 against cytokine toxicity were further demonstrated by normal insulin secretion and absence of apoptosis of cytokine-treated islets. In experiments with NOD mice, the occurrence of diabetes was efficiently reduced when the mice were treated with SPA0355. Therefore, SPA0355 might be a valuable treatment option that delays the destruction of pancreatic β cells in type 1 diabetes.

Role of pancreatic β-cell death and inflammation in diabetes

Apoptosis of pancreatic β-cells is the final step in the development of type 1 diabetes (T1D), leading to critically diminished β-cell mass and contributing to the onset of hyperglycaemia. The spontaneous apoptosis of pancreatic β-cells during pancreas ontogeny also induces cell death-associated inflammation, stimulates antigen-presenting cells and sensitizes naïve diabetogenic T cells. The role of pancreatic β-cell death in type 2 diabetes (T2D) is less clear. In the preclinical period of T2D, hyperinsulinaemia and β-cell hyperplasia develop to compensate for insulin resistance, which is clearly seen in animal models of T2D. For the development of overt T2D, relative insulin deficiency is critical in addition to insulin resistance. Insulin deficiency could be due to β-cell dysfunction and/or decreased β-cell mass. Pancreatic β-cell apoptosis due to lipid injury (lipoapoptosis), endoplasmic reticulum (ER) stress or JNK activation could contribute to the decreased β-cell mass in T2D. Activation of inflammasomes by lipid injury, ER stress, human islet amyloid polypeptide, hyperglycaemia or autophagy insufficiency could also lead to β-cell death or dysfunction. Thus, β-cell death and cell death-associated inflammation through innate immune receptors could be important in both T1D and T2D.

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

Glucagon-like peptide-1 (GLP-1) has been shown to protect pancreatic β-cells against cytokine-induced dysfunction and destruction. The mechanisms through which GLP-1 exerts its effects are complex and still poorly understood. The aim of this study was to analyze the protein expression profiles of human islets of Langerhans treated with cytokines (IL-1β and IFN-γ) in the presence or absence of GLP-1 by 2D difference gel electrophoresis and subsequent protein interaction network analysis to understand the molecular pathways involved in GLP-1-mediated β-cell protection. Co-incubation of cytokine-treated human islets with GLP-1 resulted in a marked protection of β-cells against cytokine-induced apoptosis and significantly attenuated cytokine-mediated inhibition of glucose-stimulated insulin secretion. The cytoprotective effects of GLP-1 coincided with substantial alterations in the protein expression profile of cytokine-treated human islets, illustrating a counteracting effect on proteins from different functional classes such as actin cytoskeleton, chaperones, metabolic proteins, and islet regenerating proteins. In summary, GLP-1 alters in an integrated manner protein networks in cytokine-exposed human islets while protecting them against cytokine-mediated cell death and dysfunction. These data illustrate the beneficial effects of GLP-1 on human islets under immune attack, leading to a better understanding of the underlying mechanisms involved, a prerequisite for improving therapies for diabetic patients.

Pam3CSK(4) enhanced beta cell loss and diabetogenesis: the roles of IFN-gamma and IL-17

Toll like receptors are primary sensors of both innate and adaptive immune systems. They activate APCs and influence T-cell function in inflammatory autoimmune response. Studies have shown that TLR manipulation may lead to either tolerance or trigger autoimmunity. Using diabetogenic and subdiabetogenic multiple low doses of streptozotocin, we demonstrate here that Pam3 CYS-CK4 a TLR-2 agonist, enhances and promotes diabetes in C57BL/6 male mice following increased apoptosis of β islet cells. FACS analysis of isolated pancreatic lymph node cells revealed significant increased number of macrophages, dendritic cells, CD4(+) TNF-α(+), CD4(+) IFN-γ(+) and most significantly, CD4(+) IL-17(+) and reduced number of CD25(+)Fox p3(+) T cells after Pam3CSK4 treatment. Genetic deletion of IFN-γ prevents whereas deletion of IL-17 reduced severity of Pam3CSK4-induced enhancement of diabetes. TLR-2 agonist-enhanced diabetogenesis is also influenced by enhanced influx of antigen presenting cells and suppression of regulatory T cell activity.

Prevention of type 1 diabetes through infection with an intestinal nematode parasite requires IL-10 in the absence of a Th2-type response

Helminth infection can prevent type 1 diabetes (T1D); however, the regulatory mechanisms inhibiting disease remain largely undefined. In these studies, nonobese diabetic (NOD) IL-4(-/-) mice were infected with the strictly enteric nematode parasite, Heligmosomoides polygyrus. Short-term infection, 5-7 weeks of age, inhibited T1D onset, as late as 40 weeks of age. CD4(+) T-cell STAT6 phosphorylation was inhibited, while suppressed signal transducer and activator of transcription 1 phosphorylation was sustained, as were increases in FOXP3(-), CD4(+) T-cell interleukin (IL)-10 production. Blockade of IL-10 signaling in NOD-IL-4(-/-), but not in NOD, mice during this short interval abrogated protective effects resulting in pancreatic β-cell destruction and ultimately T1D. Transfer of CD4(+) T cells from H. polygyrus (Hp)-inoculated NOD IL-4(-/-) mice to NOD mice blocked the onset of T1D. These studies indicate that Hp infection induces non-T-regulatory cells to produce IL-10 independently of STAT6 signaling and that in this Th2-deficient environment IL-10 is essential for T1D inhibition.

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.

Ciliary neurotrophic factor protects mice against streptozotocin-induced type 1 diabetes through SOCS3: the role of STAT1/STAT3 ratio in β-cell death

Type 1 diabetes is characterized by a loss of islet β-cells. Ciliary neurotrophic factor (CNTF) protects pancreatic islets against cytokine-induced apoptosis. For this reason, we assessed whether CNTF protects mice against streptozotocin-induced diabetes (a model of type 1 diabetes) and the mechanism for this protection. WT and SOCS3 knockdown C57BL6 mice were treated for 5 days with citrate buffer or 0.1 mg/kg CNTF before receiving 80 mg/kg streptozotocin. Glycemia in non-fasted mice was measured weekly from days 0-28 after streptozotocin administration. Diabetes was defined as a blood glucose > 11.2 mmol/liter. Wild-type (WT) and SOCS3 knockdown MIN6 cells were cultured with CNTF, IL1β, or both. CNTF reduced diabetes incidence and islet apoptosis in WT but not in SOCS3kd mice. Likewise, CNTF inhibited apoptosis in WT but not in SOCS3kd MIN6 cells. CNTF increased STAT3 phosphorylation in WT and SOCS3kd mice and MIN6 cells but reduced STAT1 phosphorylation only in WT mice, in contrast to streptozotocin and IL1β. Moreover, CNTF reduced NFκB activation and required down-regulation of inducible NO synthase expression to exert its protective effects. In conclusion, CNTF protects mice against streptozotocin-induced diabetes by increasing pancreatic islet survival, and this protection depends on SOCS3. In addition, SOCS3 expression and β-cell fate are dependent on STAT1/STAT3 ratio.

Use of RNA interference to investigate cytokine signal transduction in pancreatic beta cells

Type 1 diabetes (T1D) is a chronic autoimmune disease characterized by immune infiltration of the pancreatic islets resulting in an inflammatory reaction named insulitis and subsequent beta cell apoptosis. During the course of insulitis beta cell death is probably caused by direct contact with activated macrophages and T-cells, and/or exposure to soluble mediators secreted by these cells, including cytokines, nitric oxide, and free oxygen radicals. In vitro exposure of beta cells to the cytokines interleukin(IL)-1β + interferon(IFN)-γ or to tumor necrosis factor(TNF)-α + IFN-γ induces beta cell dysfunction and ultimately apoptosis. The transcription factors NF-κB and STAT1 are key regulators of cytokine-induced beta cell death. However, little is known about the gene networks regulated by these (or other) transcription factors that trigger beta cell apoptosis. The recent development of RNA interference (RNAi) technology offers a unique opportunity to decipher the cytokine-activated molecular pathways responsible for beta cell death. Use of RNAi has been hampered by technical difficulties in transfecting primary beta cells, but in recent years we have succeeded in developing reliable and reproducible protocols for RNAi in beta cells. This chapter details the methods and settings used to achieve efficient and nontoxic transfection of small interfering RNA in immortal and primary beta cells.

Cytokines tumor necrosis factor-α and interferon-γ induce pancreatic β-cell apoptosis through STAT1-mediated Bim protein activation

Type 1 diabetes is characterized by local inflammation (insulitis) in the pancreatic islets causing β-cell loss. The mitochondrial pathway of apoptosis is regulated by the balance and interaction between Bcl-2 members. Here we clarify the molecular mechanism of β-cell death triggered by the pro-inflammatory cytokines tumor necrosis factor (TNF)-α and interferon (IFN)-γ. The combination of TNF-α + IFN-γ induced DP5, p53 up-regulated modulator of apoptosis (PUMA), and Bim expression in human islets and rodent β-cells. DP5 and PUMA inactivation by RNA interference partially protected against TNF-α + IFN-γ-induced β-cell apoptosis. DP5 knock-out mice had increased β-cell area, and isolated islets from these mice were resistant to cytokine exposure. Bim expression was transcriptionally regulated by STAT1, and its activation triggered cleavage of caspases. Silencing of Bim protected rodent and human β-cells to a large extent against TNF-α + IFN-γ, indicating a major role of this BH3-only activator protein in the mechanism of apoptosis. Our data support a highly regulated and context-dependent modulation of specific Bcl-2 members controlling the mitochondrial pathway of β-cell apoptosis during insulitis.

Differential regulation of adaptive and apoptotic unfolded protein response signalling by cytokine-induced nitric oxide production in mouse pancreatic beta cells

AIMS/HYPOTHESIS

Pro-inflammatory cytokines such as IL-1β, IFN-γ and TNF-α may contribute to pancreatic beta cell destruction in type 1 diabetes. A mechanism requiring nitric oxide, which is generated by inducible nitric oxide synthase (iNOS), in cytokine-induced endoplasmic reticulum (ER) stress and apoptosis has been proposed. Here, we tested the role of nitric oxide in cytokine-induced ER stress and the subsequent unfolded protein response (UPR) in beta cells.

METHODS

Isolated islets from wild-type and iNos (also known as Nos2) knockout (iNos ( -/- )) mice, and MIN6 beta cells were incubated with IL-1β, IFN-γ and TNF-α for 24-48 h. N (G)-methyl-L: -arginine was used to inhibit nitric oxide production in MIN6 cells. Protein levels and gene expression were assessed by western blot and real-time RT-PCR.

RESULTS

In islets and MIN6 cells, inhibition of nitric oxide production had no effect on the generation of ER stress by cytokines, as evidenced by downregulation of Serca2b (also known as Atp2a2) mRNA and increased phosphorylation of PKR-like ER kinase, Jun N-terminal kinase (JNK) and eukaryotic translation initiation factor 2 α subunit. However, nitric oxide regulated the pattern of UPR signalling, which delineates the cellular decision to adapt to ER stress or to undergo apoptosis. Inhibition of nitric oxide production led to reduced expression of pro-apoptotic UPR markers, Chop (also known as Ddit3), Atf3 and Trib3. In contrast, adaptive UPR markers (chaperones, foldases and degradation enhancers) were increased. Further analysis of mouse islets showed that cytokine-induced Chop and Atf3 expression was also dependent on JNK activity.

CONCLUSIONS/INTERPRETATION

The mechanism by which cytokines induce ER stress in mouse beta cells is independent of nitric oxide production. However, nitric oxide may regulate the switch between adaptive and apoptotic UPR signalling.

Histone deacetylase (HDAC) inhibition as a novel treatment for diabetes mellitus

Both common forms of diabetes have an inflammatory pathogenesis in which immune and metabolic factors converge on interleukin-1β as a key mediator of insulin resistance and β-cell failure. In addition to improving insulin resistance and preventing β-cell inflammatory damage, there is evidence of genetic association between diabetes and histone deacetylases (HDACs); and HDAC inhibitors (HDACi) promote β-cell development, proliferation, differentiation and function and positively affect late diabetic microvascular complications. Here we review this evidence and propose that there is a strong rationale for preclinical studies and clinical trials with the aim of testing the utility of HDACi as a novel therapy for diabetes.

Overexpression of peroxiredoxin 4 protects against high-dose streptozotocin-induced diabetes by suppressing oxidative stress and cytokines in transgenic mice

Peroxiredoxin 4 (PRDX4) is one of a newly discovered family of antioxidative proteins. We generated human PRDX4 (hPRDX4) transgenic (Tg) mice, displaying a high level of hPRDX4 expression in the pancreatic islets, and then focused on the functions of PRDX4 in a type 1 diabetes mellitus (T1DM) model using a single high dose of streptozotocin (SHDS). After SHDS-injection, Tg mice showed significantly less hyperglycemia and hypoinsulinemia and a much faster response on glucose tolerance test than wild-type (WT) mice. Morphologic and immunohistochemical observation revealed that the pancreatic islet areas of Tg mice were larger along with less CD3-positive lymphocyte infiltration compared with WT mice. Upon comparison between these two mouse models, β-cell apoptosis was also repressed, and reversely, β-cell proliferation was enhanced in Tg mice. Real-time RT-PCR demonstrated that the expression of many inflammatory-related molecules and their receptors and transcription factors were significantly downregulated in Tg mice. These data indicate that PRDX4 can protect pancreatic islet β-cells against injury caused by SHDS-induced insulitis, which strongly suggests that oxidative stress plays an essential role in SHDS-induced diabetes. This study, for the first time, implicates that PRDX4 has a pivotal protective function against diabetes progression in this T1DM model.

STAT1 is a master regulator of pancreatic {beta}-cell apoptosis and islet inflammation

Cytokines produced by islet-infiltrating immune cells induce β-cell apoptosis in type 1 diabetes. The IFN-γ-regulated transcription factors STAT1/IRF-1 have apparently divergent effects on β-cells. Thus, STAT1 promotes apoptosis and inflammation, whereas IRF-1 down-regulates inflammatory mediators. To understand the molecular basis for these differential outcomes within a single signal transduction pathway, we presently characterized the gene networks regulated by STAT1 and IRF-1 in β-cells. This was done by using siRNA approaches coupled to microarray analysis of insulin-producing cells exposed or not to IL-1β and IFN-γ. Relevant microarray findings were further studied in INS-1E cells and primary rat β-cells. STAT1, but not IRF-1, mediates the cytokine-induced loss of the differentiated β-cell phenotype, as indicated by decreased insulin, Pdx1, MafA, and Glut2. Furthermore, STAT1 regulates cytokine-induced apoptosis via up-regulation of the proapoptotic protein DP5. STAT1 and IRF-1 have opposite effects on cytokine-induced chemokine production, with IRF-1 exerting negative feedback inhibition on STAT1 and downstream chemokine expression. The present study elucidates the transcriptional networks through which the IFN-γ/STAT1/IRF-1 axis controls β-cell function/differentiation, demise, and islet inflammation.

The induction of STAT1 gene by activating transcription factor 3 contributes to pancreatic beta-cell apoptosis and its dysfunction in streptozotocin-treated mice

It is well established that the IFN-gamma/STAT1 pathway plays an important role in the pancreatic beta-cell apoptosis that is observed in STZ-induced type 1 diabetes; however, the upstream regulatory proteins involved have not been understood. Here, we investigated whether activating transcription factor 3 (ATF3) affects STAT1-mediated beta-cell dysfunction and apoptosis in streptozotocin-treated mice. To this, STZ (80 mg/kg, i.p.) was administered to wild-type and STAT1(-/-) or IFN-gamma(-/-) mice for 5 days and the mice were euthanized after 14 days. STZ-induced beta-cell dysfunction and apoptosis were associated with increased STAT1/IRF-1 and ATF3 expression and were correlated with elevated IFN-gamma levels. Genetic depletion using IFN-gamma(-/-) or STAT1(-/-) mice strongly inhibited the reduction of islet cell mass or insulin synthesis/secretion and the increase of beta-cell apoptosis observed in STZ-treated wild-type mice. ATF3 overexpression, especially the C-terminal domain, strongly enhanced beta-cell dysfunction and apoptosis by enhancing STAT1 activation and its accumulation, which were abolished with an ATF3-specific siRNA or C-terminal-deleted ATF3. The STZ induction of ATF3 was completely depleted in IFN-gamma(-/-) mice, but not in STAT1(-/-) mice. Furthermore, STAT1 did not affect ATF3 expression, but STAT1 depletion or its inactivation inhibited STZ-induced ATF3 nuclear translocation and beta-cell apoptosis. Interestingly, ATF3 also increased STAT1 transcription by directly binding to a putative binding region (-116 to -96 bp) in the STAT1 promoter. Our results suggest that ATF3 functions as a potent upstream regulator of STAT1 and ATF3 may play a role in STZ-induced beta-cell dysfunction by enhancing the steady state abundance of STAT1.

MDA5 and PTPN2, two candidate genes for type 1 diabetes, modify pancreatic beta-cell responses to the viral by-product double-stranded RNA

β-Cell destruction in type 1 diabetes (T1D) is at least in part consequence of a ‘dialog’ between β-cells and immune system. This dialog may be affected by the individual's genetic background. We presently evaluated whether modulation of MDA5 and PTPN2, two candidate genes for T1D, affects β-cell responses to double-stranded RNA (dsRNA), a by-product of viral replication. These genes were selected following comparison between known candidate genes for T1D and genes expressed in pancreatic β-cells, as identified in previous array analysis. INS-1E cells and primary fluorescence-activated cell sorting-purified rat β-cells were transfected with small interference RNAs (siRNAs) targeting MDA5 or PTPN2 and subsequently exposed to intracellular synthetic dsRNA (polyinosinic–polycitidilic acid—PIC). Real-time RT–PCR, western blot and viability assays were performed to characterize gene/protein expression and viability. PIC increased MDA5 and PTPN2 mRNA expression, which was inhibited by the specific siRNAs. PIC triggered apoptosis in INS-1E and primary β-cells and this was augmented by PTPN2 knockdown (KD), although inhibition of MDA5 did not modify PIC-induced apoptosis. In contrast, MDA5 silencing decreased PIC-induced cytokine and chemokine expression, although inhibition of PTPN2 induced minor or no changes in these inflammatory mediators. These findings indicate that changes in MDA5 and PTPN2 expression modify β-cell responses to dsRNA. MDA5 regulates inflammatory signals, whereas PTPN2 may function as a defence mechanism against pro-apoptotic signals generated by dsRNA. These two candidate genes for T1D may thus modulate β-cell apoptosis and/or local release of inflammatory mediators in the course of a viral infection by acting, at least in part, at the pancreatic β-cell level.