Role of p38 mitogen-activated protein kinase (p38 MAPK) in cytokine-induced rat islet cell apoptosis

A Supportive Role of Mesenchymal Stem Cells on Insulin-Producing Langerhans Islets with a Specific Emphasis on The Secretome

Type 1 Diabetes (T1D) is a chronic autoimmune disease characterized by a gradual destruction of insulin-producing β-cells in the endocrine pancreas due to innate and specific immune responses, leading to impaired glucose homeostasis. T1D patients usually require regular insulin injections after meals to maintain normal serum glucose levels. In severe cases, pancreas or Langerhans islet transplantation can assist in reaching a sufficient β-mass to normalize glucose homeostasis. The latter procedure is limited because of low donor availability, high islet loss, and immune rejection. There is still a need to develop new technologies to improve islet survival and implantation and to keep the islets functional. Mesenchymal stem cells (MSCs) are multipotent non-hematopoietic progenitor cells with high plasticity that can support human pancreatic islet function both in vitro and in vivo and islet co-transplantation with MSCs is more effective than islet transplantation alone in attenuating diabetes progression. The beneficial effect of MSCs on islet function is due to a combined effect on angiogenesis, suppression of immune responses, and secretion of growth factors essential for islet survival and function. In this review, various aspects of MSCs related to islet function and diabetes are described.

Effectiveness of Hydroalcoholic Seed Extract of Securigera securidaca on Pancreatic Local Renin-Angiotensin System and Its Alternative Pathway in Streptozotocin-Induced Diabetic Animal Model

Background

Available data suggest inhibition of the pancreatic local-renin-angiotensin system (RAS) reduces tissue complications of diabetes. The purpose of the present study was to investigate the effect of hydroalcoholic seed extract of Securigera securidaca (S. securidaca) (HESS) on the pancreatic local-RAS and its alternative pathway.

Methods

Three doses of HESS were orally administered to three groups of diabetic male Wistar rats, and the results were compared with both diabetic and healthy control groups. After 35 days of treatment, the groups were assessed for the levels of pancreatic local-RAS components, including renin, angiotensinogen, ACE, and Ang II, as well as ACE2 and Ang-(1-7) in the alternative pathway. The effect of herbal medicine treatment on tissue damage status was investigated by evaluating tissue levels of oxidative stress, proinflammatory and anti-inflammatory cytokines, and through histopathological examination of the pancreas.

Results

HESS showed a dose-dependent palliative effect on the tissue oxidative stress profile (P < 0.05) as well as the levels of pancreatic local-RAS components (P < 0.05), compared to diabetic control group. Considering the interrelationship between tissue oxidative stress and local-RAS activity, the moderating effect of HESS on this relationship could be attributed to the increase in total tissue antioxidant capacity (TAC) and pancreatic Ang-(1-7) concentration. Decrease in local-RAS activity was associated with decrease in the tissue levels of inflammatory cytokines (IL1, IL6, and TNFα) (P < 0.05) and increase in the levels of anti-inflammatory cytokine of IL-10 (P < 0.05). In addition, histological results were consistent with tissue biochemical results.

Conclusions

Due to the reduction of local pancreatic RAS activity as well as oxidative stress and proinflammatory cytokines following treatment with HESS, S. securidaca seed can be proposed as a suitable herbal supplement in the drug-treatment of diabetes.

The Prospective Application of Melatonin in Treating Epigenetic Dysfunctional Diseases

In the past, different human disorders were described by scientists from the perspective of either environmental factors or just by genetically related mechanisms. The rise in epigenetic studies and its modifications, i.e., heritable alterations in gene expression without changes in DNA sequences, have now been confirmed in diseases. Modifications namely, DNA methylation, posttranslational histone modifications, and non-coding RNAs have led to a better understanding of the coaction between epigenetic alterations and human pathologies. Melatonin is a widely-produced indoleamine regulator molecule that influences numerous biological functions within many cell types. Concerning its broad spectrum of actions, melatonin should be investigated much more for its contribution to the upstream and downstream mechanistic regulation of epigenetic modifications in diseases. It is, therefore, necessary to fill the existing gaps concerning corresponding processes associated with melatonin with the physiological abnormalities brought by epigenetic modifications. This review outlines the findings on melatonin’s action on epigenetic regulation in human diseases including neurodegenerative diseases, diabetes, cancer, and cardiovascular diseases. It summarizes the ability of melatonin to act on molecules such as proteins and RNAs which affect the development and progression of diseases.

Islet neogenesis associated protein (INGAP) protects pancreatic β cells from IL-1β and IFNγ-induced apoptosis

The goal of this study was to determine whether recombinant Islet NeoGenesis Associated Protein (rINGAP) and its active core, a pentadecapeptide INGAP104-118 (Ingap-p), protect β cells against cytokine-induced death. INGAP has been shown to induce islet neogenesis in diabetic animals, to stimulate β-cell proliferation and differentiation, and to improve islet survival and function. Importantly, Ingap-p has shown promising results in clinical trials for diabetes (phase I/II). However, the full potential of INGAP and its mechanisms of action remain poorly understood. Using rat insulinoma cells RINm5F and INS-1 treated with interleukin-1β (IL-1β) and interferon-gamma (IFN-γ), we demonstrate here that both rINGAP and Ingap-p inhibit apoptosis, Caspase-3 activation, inducible nitric oxide synthase (iNOS) expression and nitric oxide (NO) production, and explore the related signaling pathways. As expected, IL-1β induced nuclear factor kappa B (NF-κB), p38, and JNK signaling, whereas interferon-gamma (IFN-γ) activated the JAK2/STAT1 pathway and potentiated the IL-1β effects. Both rINGAP and Ingap-p decreased phosphorylation of IKKα/β, IkBα, and p65, although p65 nuclear translocation was not inhibited. rINGAP, used for further analysis, also inhibited STAT3, p38, and JNK activation. Interestingly, all inhibitory effects of rINGAP were observed for the cytokine cocktail, not IL-1β alone, and were roughly equal to reversing the potentiating effects of INFγ. Furthermore, rINGAP had no effect on IL-1β/NF-κB-induced gene expression (e.g., Ccl2, Sod2) but downregulated several IFNγ-stimulated (Irf1, Socs1, Socs3) or IFNγ-potentiated (Nos2) genes. This, however, was observed again only for the cytokine cocktail, not IFNγ alone, and rINGAP did not inhibit the IFNγ-induced JAK2/STAT1 activation. Together, these intriguing results suggest that INGAP does not target either IL-1β or IFNγ individually but rather inhibits the signaling crosstalk between the two, the exact mechanism of which remains to be investigated. In summary, our study characterizes the anti-inflammatory effects of INGAP, both protein and peptide, and suggests a new therapeutic utility for INGAP in the treatment of diabetes.

Protective Role of St. John's Wort and Its Components Hyperforin and Hypericin against Diabetes through Inhibition of Inflammatory Signaling: Evidence from In Vitro and In Vivo Studies

Diabetes mellitus is a very common chronic disease with progressively increasing prevalence. Besides the well-known autoimmune and inflammatory pathogenesis of type 1 diabetes, in many people, metabolic changes and inappropriate lifestyle favor a subtle chronic inflammatory state that contributes to development of insulin resistance and progressive loss of β-cell function and mass, eventually resulting in metabolic syndrome or overt type 2 diabetes. In this paper, we review the anti-inflammatory effects of the extract of Hypericum perforatum L. (St. John's wort, SJW) and its main active ingredients firstly in representative pathological situations on inflammatory basis and then in pancreatic β cells and in obese or diabetic animal models. The simultaneous and long-lasting inhibition of signal transducer and activator of transcription (STAT)-1, nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and mitogen-activated protein kinases (MAPKs)/c-jun N-terminal kinase (JNK) signaling pathways involved in pro-inflammatory cytokine-induced β-cell dysfunction/death and insulin resistance make SJW particularly suitable for both preventive and therapeutic use in metabolic diseases. Hindrance of inflammatory cytokine signaling is likely dependent on the hyperforin content of SJW extract, but recent data reveal that hypericin can also exert relevant protective effects, mediated by activation of the cyclic adenosine monophosphate (cAMP)/protein kinase cAMP-dependent (PKA)/adenosine monophosphate activated protein kinase (AMPK) pathway, against high-fat-diet-induced metabolic abnormalities. Actually, the mechanisms of action of the two main components of SJW appear complementary, strengthening the efficacy of the plant extract. Careful quantitative analysis of SJW components and suitable dosage, with monitoring of possible drug-drug interaction in a context of remarkable tolerability, are easily achievable pre-requisites for forthcoming clinical applications.

Regulation of c-Jun NH2-Terminal Kinase for Islet Transplantation

Islet transplantation has been demonstrated to provide superior glycemic control with reduced glucose lability and hypoglycemic events compared with standard insulin therapy. However, the insulin independence rate after islet transplantation from one donor pancreas has remained low. The low frequency of islet grafting is dependent on poor islet recovery from donors and early islet loss during the first hours following grafting. The reduction in islet mass during pancreas preservation, islet isolation, and islet transplantation leads to β-cell death by apoptosis and the prerecruitment of intracellular death signaling pathways, such as c-Jun NH₂-terminal kinase (JNK), which is one of the stress groups of mitogen-activated protein kinases (MAPKs). In this review, we show some of the most recent contributions to the advancement of knowledge of the JNK pathway and several possibilities for the treatment of diabetes using JNK inhibitors.

Therapeutic Delivery of miR-29b Enhances Radiosensitivity in Cervical Cancer

Radioresistant cervical cancer is likely to give rise to local recurrence, distant metastatic relapse, and decreased survival rates. Recent studies revealed microRNA mediated regulation of tumor aggressiveness and metastasis; however, whether specific microRNAs regulate tumor radioresistance and can be exploited as radiosensitizing agents remains unclear. Here, we find that miR-29b could promote radiosensitivity in radioresistant subpopulations of cervical cancer cells. Notably, therapeutic delivery of miR-29b mimics via R11-SSPEI nanoparticle, whose specificity has been proved by our previous studies, can sensitize the tumor to radiation in a xenograft model. Mechanistically, we reveal a novel function of miR-29b in regulating intracellular reactive oxygen species signaling and explore a potential application for its use in combination with therapies known to increase oxidative stress such as radiation. Moreover, miR-29b inhibits DNA damage repair by targeting phosphate and tension homology deleted on chromsome ten (PTEN), and overexpression of PTEN could partially rescue miR-29b-mediated homologous recombination (HR)-DNA damage repair and increase radiosensitivity. These findings identify miR-29b as a radiosensitizing microRNA and reveal a new therapeutic strategy for radioresistant tumors.

Inhibition of p38 mitogen-activated protein kinase exerts a hypoglycemic effect by improving β cell function via inhibition of β cell apoptosis in db/db mice

The p38 mitogen-activated protein kinase (MAPK) pathway is involved in endoplasmic reticulum stress (ERS) and inflammation, which may play an important role in the pathogenesis of type 2 diabetes (T2DM). This study aimed to investigate whether p38 MAPK contributes to the pathogenesis of T2DM. 6-week-old female db/db mice were randomly assigned to Dmo and Dmi groups, and C57 mice were assigned as controls. The Dmi group was gavaged with the p38 MAPK inhibitor SB203580 for 9 weeks, and the effects on β cell dysfunction and apoptosis were investigated. db/db mice showed higher food intake, body mass, fasting glucose, and plasma insulin levels than C57 mice. After SB203580 administration, blood glucose was significantly lower. HOMA β and HOMA IR were improved. Islet mRNA expression levels of the ERS markers were lower. P38 MAPK inhibition reduced blood glucose and improved β cell function, at least in part by reducing β cell apoptosis.

Proteasomal degradation of the histone acetyl transferase p300 contributes to beta-cell injury in a diabetes environment

In type 2 diabetes, amyloid oligomers, chronic hyperglycemia, lipotoxicity, and pro-inflammatory cytokines are detrimental to beta-cells, causing apoptosis and impaired insulin secretion. The histone acetyl transferase p300, involved in remodeling of chromatin structure by epigenetic mechanisms, is a key ubiquitous activator of the transcriptional machinery. In this study, we report that loss of p300 acetyl transferase activity and expression leads to beta-cell apoptosis, and most importantly, that stress situations known to be associated with diabetes alter p300 levels and functional integrity. We found that proteasomal degradation is the mechanism subserving p300 loss in beta-cells exposed to hyperglycemia or pro-inflammatory cytokines. We also report that melatonin, a hormone produced in the pineal gland and known to play key roles in beta-cell health, preserves p300 levels altered by these toxic conditions. Collectively, these data imply an important role for p300 in the pathophysiology of diabetes.

Spirulina Extract Enhanced a Protective Effect in Type 1 Diabetes by Anti-Apoptosis and Anti-ROS Production

Interest in the nutritional value and pharmacological activities of blue-green algae has gradually increased. Spirulina extracts show protective effects against apoptosis and inflammatory damage in various cell types. Here, we investigated the protective effects of extracts from Spirulina maxima in a cytokine-mediated type 1 diabetes model in vitro and in streptozotocin-induced diabetic Wistar rats in vivo. Interleukin-1β and interferon-gamma induced substantial cytotoxicity to RINm5F rat insulinoma cells, increasing nitric oxide (NO) production, nuclear factor-kappa B (NF-κB) activity, the expression of endoplasmic reticulum (ER) stress genes, and activation of mitogen-activated protein kinases and key genes related apoptosis. However, the cytotoxicity of cytokines was significantly attenuated by Spirulina extract, which effectively prevented NO production by inhibiting the synthesis of cytokine-activated NO synthase (iNOS), and apoptosis was suppressed. These results suggest that Spirulina extract might be effective to preserve the viability and function of pancreatic β-cells against cytotoxic conditions. Moreover, diabetic mice orally administered Spirulina extract showed decreased glucose levels, increased insulin, and improvement in liver enzyme markers. The antioxidant effect of Spirulina extract may be helpful in treating type 1 diabetes by enhancing the survival, and reducing or delaying cytokine-mediated β-cells destruction.

Kinase Signaling in Apoptosis Induced by Saturated Fatty Acids in Pancreatic β-Cells

Pancreatic β-cell failure and death is considered to be one of the main factors responsible for type 2 diabetes. It is caused by, in addition to hyperglycemia, chronic exposure to increased concentrations of fatty acids, mainly saturated fatty acids. Molecular mechanisms of apoptosis induction by saturated fatty acids in β-cells are not completely clear. It has been proposed that kinase signaling could be involved, particularly, c-Jun N-terminal kinase (JNK), protein kinase C (PKC), p38 mitogen-activated protein kinase (p38 MAPK), extracellular signal-regulated kinase (ERK), and Akt kinases and their pathways. In this review, we discuss these kinases and their signaling pathways with respect to their possible role in apoptosis induction by saturated fatty acids in pancreatic β-cells.

Inhibition of the MAP3 kinase Tpl2 protects rodent and human β-cells from apoptosis and dysfunction induced by cytokines and enhances anti-inflammatory actions of exendin-4

Proinflammatory cytokines exert cytotoxic effects on β-cells, and are involved in the pathogenesis of type I and type II diabetes and in the drastic loss of β-cells following islet transplantation. Cytokines induce apoptosis and alter the function of differentiated β-cells. Although the MAP3 kinase tumor progression locus 2 (Tpl2) is known to integrate signals from inflammatory stimuli in macrophages, fibroblasts and adipocytes, its role in β-cells is unknown. We demonstrate that Tpl2 is expressed in INS-1E β-cells, mouse and human islets, is activated and upregulated by cytokines and mediates ERK1/2, JNK and p38 activation. Tpl2 inhibition protects β-cells, mouse and human islets from cytokine-induced apoptosis and preserves glucose-induced insulin secretion in mouse and human islets exposed to cytokines. Moreover, Tpl2 inhibition does not affect survival or positive effects of glucose (i.e., ERK1/2 phosphorylation and basal insulin secretion). The protection against cytokine-induced β-cell apoptosis is strengthened when Tpl2 inhibition is combined with the glucagon-like peptide-1 (GLP-1) analog exendin-4 in INS-1E cells. Furthermore, when combined with exendin-4, Tpl2 inhibition prevents cytokine-induced death and dysfunction of human islets. This study proposes that Tpl2 inhibitors, used either alone or combined with a GLP-1 analog, represent potential novel and effective therapeutic strategies to protect diabetic β-cells.

Lonicera caerulea berry extract suppresses lipopolysaccharide-induced inflammation via Toll-like receptor and oxidative stress-associated mitogen-activated protein kinase signaling

The protective effects of Lonicera caerulea berry extract (LCBE) against hepatic inflammation and the underlying mechanisms were investigated in a rat model of lipopolysaccharide (LPS)-induced chronic liver inflammation.

Accelerated apoptotic death and in vivo turnover of erythrocytes in mice lacking functional mitogen- and stress-activated kinase MSK1/2

The mitogen- and stress-activated kinase MSK1/2 plays a decisive role in apoptosis. In analogy to apoptosis of nucleated cells, suicidal erythrocyte death called eryptosis is characterized by cell shrinkage and cell membrane scrambling leading to phosphatidylserine (PS) externalization. Here, we explored whether MSK1/2 participates in the regulation of eryptosis. To this end, erythrocytes were isolated from mice lacking functional MSK1/2 (msk^−/−) and corresponding wild-type mice (msk^+/+). Blood count, hematocrit, hemoglobin concentration and mean erythrocyte volume were similar in both msk^−/− and msk^+/+ mice, but reticulocyte count was significantly increased in msk^−/− mice. Cell membrane PS exposure was similar in untreated msk^−/− and msk^+/+ erythrocytes, but was enhanced by pathophysiological cell stressors ex vivo such as hyperosmotic shock or energy depletion to significantly higher levels in msk^−/− erythrocytes than in msk^+/+ erythrocytes. Cell shrinkage following hyperosmotic shock and energy depletion, as well as hemolysis following decrease of extracellular osmolarity was more pronounced in msk^−/− erythrocytes. The in vivo clearance of autologously-infused CFSE-labeled erythrocytes from circulating blood was faster in msk^−/− mice. The spleens from msk^−/− mice contained a significantly greater number of PS-exposing erythrocytes than spleens from msk^+/+ mice. The present observations point to accelerated eryptosis and subsequent clearance of erythrocytes leading to enhanced erythrocyte turnover in MSK1/2-deficient mice.

Tissue factor/factor VIIa signalling promotes cytokine-induced beta cell death and impairs glucose-stimulated insulin secretion from human pancreatic islets

AIMS/HYPOTHESIS

Patients diagnosed with type 1 or type 2 diabetes have elevated levels of coagulation factor VIIa (FVIIa) and its receptor tissue factor (TF) in their bloodstream. This may affect the fate of the beta cells. We aimed to study the effects of TF/FVIIa signalling on cytokine-induced beta cell death and islet function in vitro.

METHODS

Human pancreatic islets and MIN-6 beta cells were used to study TF mRNA and protein expression using real-time PCR, immunoblotting and flow cytometry. The effects of TF/FVIIa on cytokine-induced beta cell death were studied in MIN-6 cells and human pancreatic islets using cell-death ELISA and propidium iodide and cleaved caspase-3 staining. Effects of TF/FVIIa on the phosphorylation of p38, extracellular signal-regulated kinase and c-Jun N-terminal kinase (JNK) were investigated by immunoblotting. Glucose-stimulated insulin secretion (GSIS) from human islets was measured with an insulin ELISA.

RESULTS

A combination of the cytokines IL-1β, TNF-α and IFN-γ induced TF expression in human pancreatic islets and in beta cells. TF/FVIIa did not affect basal beta cell death but, independently of downstream coagulation activity, augmented beta cell death in response to cytokines. The effect of TF/FVIIa on cytokine-induced beta cell death was found to be dependent on the stress kinase JNK, since FVIIa addition potentiated cytokine-induced JNK activation and JNK inhibition abolished the effect of TF/FVIIa on cytokine-induced beta cell death. Moreover, TF/FVIIa signalling resulted in inhibition of GSIS from human pancreatic islets.

CONCLUSIONS/INTERPRETATION

These results indicate that TF/FVIIa signalling has a negative effect on beta cell function and promotes beta cell death in response to cytokines.

Role of the AMP kinase in cytokine-induced human EndoC-βH1 cell death

The aim of the present investigation was to delineate cytokine-induced signaling and death using the EndoC-βH1 cells as a model for primary human beta-cells. The cytokines IL-1β and IFN-γ induced a rapid and transient activation of NF-κB, STAT-1, ERK, JNK and eIF-2α signaling. The EndoC-βH1 cells died rapidly when exposed to IL-1β + IFN-γ, and this occurred also in the presence of the actinomycin D. Inhibition of NF-κB and STAT-1 did not protect against cell death, nor did the cytokines activate iNOS expression. Instead, cytokines promoted a rapid decrease in EndoC-βH1 cell respiration and ATP levels, and we observed protection by the AMPK activator AICAR against cytokine-induced cell death. It is concluded that EndoC-βH1 cell death can be prevented by AMPK activation, which suggests a role for ATP depletion in cytokine-induced human beta-cell death.

CRFR1 activation protects against cytokine-induced β-cell death

During the development of diabetes β-cells are exposed to elevated concentrations of proinflammatory cytokines, TNFα and IL1β, which in vitro induce β-cell death. The class B G-protein-coupled receptors (GPCRs): corticotropin-releasing factor receptor 1 (CRFR1) and CRFR2 are expressed in pancreatic islets. As downstream signaling by other class B GPCRs can protect against cytokine-induced β-cell apoptosis, we evaluated the protective potential of CRFR activation in β-cells in a pro-inflammatory setting. CRFR1/CRFR2 ligands activated AKT and CRFR1 signaling and reduced apoptosis in human islets. In rat and mouse insulin-secreting cell lines (INS-1 and MIN6), CRFR1 agonists upregulated insulin receptor substrate 2 (IRS2) expression, increased AKT activation, counteracted the cytokine-mediated decrease in BAD phosphorylation, and inhibited apoptosis. The anti-apoptotic signaling was dependent on prolonged exposure to corticotropin-releasing factor family peptides and followed PKA-mediated IRS2 upregulation. This indicates that CRFR signaling counteracts proinflammatory cytokine-mediated apoptotic pathways through upregulation of survival signaling in β-cells. Interestingly, CRFR signaling also counteracted basal apoptosis in both cultured INS-1 cells and intact human islets.

A critical role for CK2 in cytokine-induced activation of NFκB in pancreatic β cell death

This study aimed to assess the role of constitutive protein kinase CK2 in cytokine-induced activation of NFκB in pancreatic β cell death. The CK2 inhibitors DRB (5,6-dichloro-1-β-D-ribofuranosylbenzimidazole) (50 μM) and DMAT (2-dimethylamino-4,5,6,7-tetrabromo-1H-benzimidazole) (5 μM), which decreased CK2 activity by approx. 65 %, rescued INS-1E β cells and mouse islets from cytokine (IL-1β, TNF-α plus IFN-γ)-induced β cell death without affecting H2O2- or palmitate-induced β cell death. Western blot analysis revealed that while DRB or DMAT did not influence cytokine-induced IκBα degradation, they inhibited NFκB-dependent IκBα resynthesis, demonstrating that cytokine-induced NFκB activity is dependent on CK2. Both DRB and DMAT inhibited the constitutive phosphorylation of NFκB p65 at serine 529, while leaving cytokine-induced phosphorylations of NFκB p65 at serines 276 and 536 unaltered. In comparison, putative phosphorylation sites for CK2 on HDACs 1, 2, and 3 at serines 421/423, 394, and 424, respectively, which may stimulate NFκB transcriptional activity, were unchanged by cytokines and CK2 inhibitors. Whereas IL-1β and TNF-α stimulate IκBα degradation and NFκB activation, IFN-γ potentiates cytokine-induced β cell death through activation of STAT1. DRB and DMAT inhibited IFN-γ-stimulated phosphorylation of STAT1 at serine 727, while leaving IFN-γ-induced phosphorylation of STAT1 at tyrosine 701 unaffected. Inhibition of cytokine-induced β cell death by CK2 inhibitors was, however, not dependent on IFN-γ, and IFN-γ did not affect CK2-dependent IκBα turnover. In conclusion, it is suggested that cytokine-induced activation of NFκB in β cells is dependent on CK2 activity, which phosphorylates NFκB p65 at serine 529.

β-Cell responses to nitric oxide

Autoimmune diabetes is characterized by the selective destruction of insulin-secreting β-cells that occurs during an inflammatory reaction in and around pancreatic islets of Langerhans. Cytokines such as interleukin-1, released by activated immune cells, have been shown to inhibit insulin secretion from pancreatic β-cells and cause islet destruction. In response to cytokines, β-cells express inducible nitric oxide synthase and produce micromolar levels of the free radical nitric oxide. Nitric oxide inhibits the mitochondrial oxidation of glucose resulting in an impairment of insulin secretion. Nitric oxide is also responsible for cytokine-mediated DNA damage in β-cells. While nitric oxide mediates the inhibitory and toxic effects of cytokines, it also activates protective pathways that allow β-cells to recover from this damage. This review will focus on the dual role of nitric oxide as a mediator of cytokine-induced damage and the activator of repair mechanisms that protect β-cells from cytokine-mediated injury.

Mechanism of IL-1β modulation of intestinal epithelial barrier involves p38 kinase and activating transcription factor-2 activation

The defective intestinal epithelial tight junction (TJ) barrier has been postulated to be an important pathogenic factor contributing to intestinal inflammation. It has been shown that the proinflammatory cytokine IL-1β causes an increase in intestinal permeability; however, the signaling pathways and the molecular mechanisms involved remain unclear. The major purpose of this study was to investigate the role of the p38 kinase pathway and the molecular processes involved. In these studies, the in vitro intestinal epithelial model system (Caco-2 monolayers) was used to delineate the cellular and molecular mechanisms, and a complementary in vivo mouse model system (intestinal perfusion) was used to assess the in vivo relevance of the in vitro findings. Our data indicated that the IL-1β increase in Caco-2 TJ permeability correlated with an activation of p38 kinase. The activation of p38 kinase caused phosphorylation and activation of p38 kinase substrate, activating transcription factor (ATF)-2. The activated ATF-2 translocated to the nucleus where it attached to its binding motif on the myosin L chain kinase (MLCK) promoter region, leading to the activation of MLCK promoter activity and gene transcription. Small interfering RNA induced silencing of ATF-2, or mutation of the ATF-2 binding motif prevented the activation of MLCK promoter and MLCK mRNA transcription. Additionally, in vivo intestinal perfusion studies also indicated that the IL-1β increase in mouse intestinal permeability required p38 kinase-dependent activation of ATF-2. In conclusion, these studies show that the IL-1β-induced increase in intestinal TJ permeability in vitro and in vivo was regulated by p38 kinase activation of ATF-2 and by ATF-2 regulation of MLCK gene activity.

Is ARE/poly(U)-binding factor 1 (AUF1) a new player in cytokine-mediated beta cell apoptosis?

Type 1 diabetes is a chronic autoimmune disease involving the progressive loss of beta cell mass. Cytokines released by immune cells are early contributors to beta cell apoptosis. Thus, an understanding of the signal transduction mechanisms induced by cytokines in beta cells is necessary for the rational design of novel therapies to prevent or to cure this disease. Cytokine-mediated beta cell apoptosis is a complex phenomenon that includes activation of the transcription factors signal transducer and activator of transcription 1 and nuclear factor κB (NFκB), c-Jun N-terminal kinase, endoplasmic reticulum (ER) stress and the intrinsic mitochondrial apoptotic pathway. NFκB has both a pro-inflammatory and a pro-apoptotic role in beta cells. One of the mechanisms by which NFκB contributes to beta cell apoptosis is via activation of ER stress. The role for ER stress in beta cell apoptosis is not completely clarified but involves production of C/EBP homologous protein and activation of the intrinsic mitochondrial apoptotic pathway. In this issue of Diabetologia, Roggli et al (DOI 10.1007/s00125-011-2399-7) report on a new player in this elaborate response, the RNA-binding protein ARE/poly(U)-binding factor 1. This commentary discusses these findings and their relevance to the field.

Cryptotanshinone activates p38/JNK and inhibits Erk1/2 leading to caspase-independent cell death in tumor cells

Cryptotanshinone (CPT), a natural compound isolated from the plant Salvia miltiorrhiza Bunge, is a potential anticancer agent. However, the underlying mechanism is not well understood. Here, we show that CPT induced caspase-independent cell death in human tumor cells (Rh30, DU145, and MCF-7). Besides downregulating antiapoptotic protein expression of survivin and Mcl-1, CPT increased phosphorylation of p38 mitogen-activated protein kinase (MAPK) and c-jun N-terminal kinase (JNK), and inhibited phosphorylation of extracellular signal-regulated kinases 1/2 (Erk1/2). Inhibition of p38 with SB202190 or JNK with SP600125 attenuated CPT-induced cell death. Similarly, silencing p38 or c-Jun also in part prevented CPT-induced cell death. In contrast, expression of constitutively active mitogen-activated protein kinase kinase 1 (MKK1) conferred resistance to CPT inhibition of Erk1/2 phosphorylation and induction of cell death. Furthermore, we found that all of these were attributed to CPT induction of reactive oxygen species (ROS). This is evidenced by the findings that CPT induced ROS in a concentration- and time-dependent manner; CPT induction of ROS was inhibited by N-acetyl-L-cysteine (NAC), a ROS scavenger; and NAC attenuated CPT activation of p38/JNK, inhibition of Erk1/2, and induction of cell death. The results suggested that CPT induction of ROS activates p38/JNK and inhibits Erk1/2, leading to caspase-independent cell death in tumor cells.

Effects of Imatinib Mesylate (Gleevec) on human islet NF-kappaB activation and chemokine production in vitro

Purpose

Imatinib Mesylate (Gleevec) is a drug that potently counteracts diabetes both in humans and in animal models for human diabetes. We have previously reported that this compound in human pancreatic islets stimulates NF-κB signaling and islet cell survival. The aim of this study was to investigate control of NF-κB post-translational modifications exerted by Imatinib and whether any such effects are associated with altered islet gene expression and chemokine production in vitro.

Procedures

Human islets were either left untreated or treated with Imatinib for different timepoints. IκB-α and NF-κB p65 phosphorylation and methylation were assessed by immunoblot analysis. Islet gene expression was assessed using a commercial Pathway Finder microarray kit and RT-PCR. Islet chemokine production was determined by flow cytometric bead array analysis.

Findings

Human islet IκB-α and Ser276-p65 phosphorylation were increased by a 20 minute Imatinib exposure. Methylation of p65 at position Lys221 was increased after 60 min of Imatinib exposure and persisted for 3 hours. Microarray analysis of islets exposed to Imatinib for 4 hours revealed increased expression of the inflammatory genes IL-4R, TCF5, DR5, I-TRAF, I-CAM, HSP27 and IL-8. The islet release of IL-8 was augmented in islets cultured over night in the presence of Imatinib. Following 30 hours of Imatinib exposure, the cytokine-induced IκB-α and STAT1 phosphorylation was abolished and diminished, respectively. The cytokine-induced release of the chemokines MIG and IP10 was lower in islets exposed to Imatinib for 30 hours.

Conclusion

Imatinib by itself promotes a modest activation of NF-κB. However, a prolonged exposure of human islets to Imatinib is associated with a dampened response to cytokines. It is possible that Imatinib induces NF-κB preconditioning of islet cells leading to lowered cytokine sensitivity and a mitigated islet inflammation.

Modulation of IL-2 expression after uptake of hepatitis C virus non-enveloped capsid-like particles: the role of p38 kinase

Hepatitis C virus (HCV) has been shown to actively replicate in cells of the immune system, altering both their function and cytokine expression. Naked nucleocapsids have been reported in the serum of infected patients. We investigated interference of recombinant non-enveloped capsid-like particles with signaling pathways in T cells. HCV non-enveloped particles (HCVne) internalization was verified in Jurkat and Hut 78 T cells, as well as primary human peripheral blood and intrahepatic mononuclear cells. HCVne uptake leads to activation of the MAPKs-p38 signaling pathway. Using specific phosphoantibodies, signaling pathways inhibitors, and chemical agents, it was demonstrated that p38 activation in T cells correlated with IL-2 transcriptional activation and was accompanied by a parallel increase of IL-2 cytokine secretion. c-fos and egr-1, two transcription factors, essential for IL-2 promoter activity, were also found to be elevated. We propose that HCVne uptake by T lymphocytes results in increased MAPKs-p38 activity and IL-2 expression, thus altering the host immune response.

Knockouts of SOD1 and GPX1 exert different impacts on murine islet function and pancreatic integrity

Metabolic subtlety and clinical relevance of different forms of reactive oxygen species in diabetes remain unclear. Using single knockout of Cu,Zn-superoxide dismutase (SOD1(-/-)) or Se-glutathione peroxidase-1 (GPX1(-/-)) and their double-knockout (DKO) mouse models, we determined if elevating endogenously-derived superoxide and hydroperoxide exerted distinct impacts and mechanisms on body glucose homeostasis. Whereas the three knockout groups displayed decreased plasma insulin concentrations and islet β-cells mass, only SOD1(-/-) showed decreased body weight, increased blood glucose, and blocked glucose-stimulated insulin secretion. Null of SOD1 and GPX1 elevated respective islet superoxide and hydroperoxide production, and upregulated p53 phosphorylation. Knockout of SOD1 downregulated the foxhead box A2/pancreatic and duodenal homeobox 1 pathway in a superoxide-dependent fashion at epigenetic, mRNA, and protein levels in islets, but improved insulin signaling in liver and muscle. The SOD1(-/-) mice showed more apparent pancreatitis than the GPX1(-/-) mice that were more susceptible to the cerulein-induced amylase increase. Knockout of SOD1 impaired islet function, pancreas integrity, and body glucose homeostasis more than that of GPX1. Simultaneous ablation of both enzymes did not result in additive or aggravated metabolic outcomes.

Interleukin-targeted therapy for metabolic syndrome and type 2 diabetes

Interleukin-1β Interleukin-1β (IL-1β) is a key regulator of the body's inflammatory response and is produced after infection, injury, and an antigenic challenge. Cloned in 1984, the single polypeptide IL-1β has been shown to exert numerous biological effects. It plays a role in various diseases, including autoimmune diseases such as rheumatoid arthritis, inflammatory bowel diseases, and Type 1 diabetes, as well as in diseases associated with metabolic syndrome such as atherosclerosis, chronic heart failure, and Type 2 diabetes. The macrophage is the primary source of IL-1β, but epidermal, epithelial, lymphoid, and vascular tissues also synthesize IL-1. Recently, IL-1β production and secretion have also been reported from pancreatic islets. Insulin-producing β-cells β-cells within the pancreatic islets are specifically prone to IL-β-induced destruction and loss of function. Macrophage-derived IL-1β production in insulin-sensitive organs leads to the progression of inflammation inflammation and induction of insulin resistance in obesity. This chapter explains the mechanisms involved in the inflammatory response during diabetes progression with specific attention to the IL-1β signal effects influencing insulin action and insulin secretion insulin secretion . We highlight recent clinical studies, rodent and in vitro experiments with isolated islets using IL-1β as a potential target for the therapy of Type 2 diabetes.

Cyclic AMP stimulates Mrp2 translocation by activating p38{alpha} MAPK in hepatic cells

Cyclic AMP (cAMP) induces translocation of multidrug resistant protein 2 (Mrp2) to the canalicular membrane and activates p38 MAPK in rat hepatocytes. In this study, we tested the hypothesis that cAMP-induced Mrp2 translocation may be mediated via p38 MAPK. Studies were conducted in rat hepatocytes and in a human hepatoma cell line, HuH-7. In rat hepatocytes, cAMP increased Mrp2 translocation and p38 MAPK activity. These effects of cAMP were inhibited by SB203580, an inhibitor of p38 MAPK. Wortmannin, a specific inhibitor of phosphoinositide-3-kinase (PI3K), did not inhibit cAMP induced activation of p38 MAPK, indicating PI3K-independent activation of p38 MAPK by cAMP. To further define the role of p38 MAPK, molecular approaches were used to up- or downregulate p38 MAPK activity in HuH-7 cells using constitutively active (CA) and dominant-negative (DN) MAPK kinase 3 and 6 (MKK3/6). MKK3/6 are upstream kinases responsible for the activation of p38 MAPK. Cells transfected with CAMKK6 showed increased p38 MAPK activity and MRP2 translocation compared with empty vector. cAMP-induced activation of p38 MAPK was inhibited in cells transfected with DNMKK3/6 and DNMKK3, but not with DNMKK6. DNMKK3/6 and DNMKK3 also inhibited cAMP-induced MRP2 translocation. cAMP selectively activated p38alpha MAPK in HuH-7 cells. Knockdown of p38alpha MAPK by short heterodimer RNA resulted in decreased level of p38 MAPK and failure of cAMP to stimulate MRP2 translocation. Taken together, these results suggest that cAMP-induced MRP2 translocation in hepatic cells is mediated via PI3K-independent and MKK3-mediated activation of p38alpha MAPK.

12-Lipoxygenase Products Reduce Insulin Secretion and {beta}-Cell Viability in Human Islets

CONTEXT

Inflammation is increasingly recognized as an important contributing factor in diabetes mellitus. Lipoxygenases (LOs) produce active lipids that promote inflammatory damage by catalyzing the oxidation of linoleic and arachidonic acid, and LO is expressed in rodent and human islets. Little is known about the differential effect of the various hydroxyeicosatetraenoic acids (HETEs) that result from LO activity in human islets.

OBJECTIVE

We compared the effects of 12-LO products on human islet viability and function.

DESIGN

Human islets were treated with stable compounds derived from LOs: 12(S)-HETE, 15HETE, 12HPETE, and 12RHETE and then examined for insulin secretion and islet viability. The p38-MAPK (p38) and JNK stress-activated pathways were investigated as mechanisms of 12-LO-mediated islet inhibition in rodent and human islets.

RESULTS

Insulin secretion was consistently reduced by 12(S)-HETE and 12HPETE. 12(S)-HETE at 1 nm reduced viability activity by 32% measured by MTT assay and increased cell death by 50% at 100 nm in human islets. These effects were partially reversed with lisofylline, a small-molecule antiinflammatory compound that protects mitochondrial function. 12(S)-HETE increased phosphorylated p38-MAPK (pp38) protein activity in human islets. Injecting 12-LO siRNA into C57BL/6 mice reduced 12-LO and pp38-MAPK protein levels in mouse islets. The addition of proinflammatory cytokines increased pp38 levels in normal mouse islets but not in siRNA-treated islets.

CONCLUSIONS

These data suggest that 12(S)-HETE reduces insulin secretion and increases cell death in human islets. The 12-LO pathway is present in human islets, and expression is up-regulated by inflammatory cytokines. Reduction of 12-LO activity could thus provide a new therapeutic approach to protect human beta-cells from inflammatory injury.

Beta cell apoptosis in diabetes

Apoptosis of beta cells is a feature of both type 1 and type 2 diabetes as well as loss of islets after transplantation. In type 1 diabetes, beta cells are destroyed by immunological mechanisms. In type 2 diabetes abnormal levels of metabolic factors contribute to beta cell failure and subsequent apoptosis. Loss of beta cells after islet transplantation is due to many factors including the stress associated with islet isolation, primary graft non-function and allogeneic graft rejection. Irrespective of the exact mediators, highly conserved intracellular pathways of apoptosis are triggered. This review will outline the molecular mediators of beta cell apoptosis and the intracellular pathways activated.

JNK3 is abundant in insulin-secreting cells and protects against cytokine-induced apoptosis

AIMS/HYPOTHESIS

In insulin-secreting cells, activation of the c-Jun NH(2)-terminal kinase (JNK) pathway triggers apoptosis. Whereas JNK1 and JNK2 are ubiquitously produced, JNK3 has been described exclusively in neurons. This report aims to characterise the expression and role in apoptosis of the three JNK isoforms in insulin-secreting cells exposed to cytokines.

METHODS

Sections of human and mouse pancreases were used for immunohistochemistry studies with isoform-specific anti-JNK antibodies. Human, pig, mouse and rat pancreatic islets were isolated by enzymatic digestion and RNA or protein extracts were prepared. RNA and protein levels were determined by quantitative RT-PCR and western blotting respectively, using JNK-isoform-specific primers and isoform-specific antibodies; activities of the three JNK isoforms were determined by kinase assays following quantitative immunoprecipitation/depletion of JNK3. JNK silencing was performed with small interfering RNAs and apoptotic rates were determined in INS-1E cells by scoring cells displaying pycnotic nuclei.

RESULTS

JNK3 and JNK2 mRNAs are the predominant isoforms expressed in human pancreatic islets. JNK3 is nuclear while JNK2 is also cytoplasmic. In INS-1E cells, JNK3 knockdown increases c-Jun levels and caspase-3 cleavage and sensitises cells to cytokine-induced apoptosis; in contrast, JNK1 or JNK2 knockdown is protective.

CONCLUSIONS/INTERPRETATION

In insulin-secreting cells, JNK3 plays an active role in preserving pancreatic beta cell mass from cytokine attacks. The specific localisation of JNK3 in the nucleus, its recruitment by cytokines, and its effects on key transcription factors such as c-Jun, indicate that JNK3 is certainly an important player in the transcriptional control of genes expressed in insulin-secreting cells.

Aldosterone induces apoptosis in rat podocytes: role of PI3-K/Akt and p38MAPK signaling pathways

BACKGROUND

Podocytes play a critical role in the pathogenesis of glomerulosclerosis. Increasing evidence suggests that aldosterone (ALD) is involved in the initiation and progression of glomerular damage. It is, however, unknown whether there is a direct injurious effect of ALD on podocytes. Therefore, in the present study, we evaluated the effect of ALD on podocyte apoptosis and studied the role of phosphatidylinositol 3-kinase/Akt (PI3-K/Akt) and p38 mitogen-activated protein kinase (p38MAPK) signaling pathways in this process.

METHODS

Podocytes were incubated in media containing either buffer or increasing concentrations of ALD (10(-9) approximately 10(-5)M) for variable time periods. The cells were also treated with either wortmannin (inhibitor of PI3-K, 100 nM), SB202190 (SB20, inhibitor of p38MAPK, 10 microM) or buffer. All treatments were performed with or without ALD (10(-7)M) for 24 h. At the end of the incubation period, apoptosis was evaluated by cell nucleus staining and flow cytometric analyses. Activation of PI3-K/Akt and p38MAPK phosphorylation of cultured rat podocytes was evaluated by performing Akt kinase assay and Western blot, respectively.

RESULTS

Apoptosis of cultured rat podocytes was induced by ALD in a dose- and time-dependent manner. ALD inhibited the activity of PI3-K/Akt and increased the activation of p38MAPK. PI3-K/Akt activity was further inhibited by the addition of wortmannin to the cells in the presence of ALD. This was accompanied by a significant increase in apoptosis. ALD-induced p38MAPK phosphorylation and apoptosis were inhibited when the cells were pretreated with SB20. Furthermore, treatment with spironolactone not only attenuated the proapoptotic effect of ALD, but also significantly reversed its effects on PI3-K/Akt and p38MAPK signaling pathways.

CONCLUSION

ALD induces apoptosis in rat podocytes through inhibition of PI3-K/Akt and stimulation of p38 MAPK signaling pathways. Spironolactone attenuates ALD-induced podocyte apoptosis, thereby positioning this compound as a potential promising target of intervention in human renal damage.

IL-1beta receptor blockade protects islets against pro-inflammatory cytokine induced necrosis and apoptosis

Pro-inflammatory cytokines (PIC) impair islet viability and function by activating inflammatory pathways that induce both necrosis and apoptosis. The aim of this study was to utilize an in vitro rat islet model to evaluate the efficacy of a clinically approved IL-1 receptor antagonist (Anakinra) in blocking PIC induced islet impairment. Isolated rat islets were cultured for 48 h +/- PIC (IL-1beta, IFNgamma, and TNFalpha) and +/-IL-1ra then assayed for cellular integrity by flow cytometry, MAPK phosphorylation by proteome array, and gene expression by RT-PCR. Nitric oxide (NO) release into the culture media was measured by Griess reaction. Islet functional potency was tested by glucose stimulated insulin secretion (GSIS) and by transplantation into streptozotocin-induced diabetic NOD.scid mice. Rat islets cultured with PIC upregulated genes for NOS2a, COX2, IL6, IL1b, TNFa, and HMOX1. IL-1ra prevented the PIC induced upregulation of all of these genes except for TNFa. Inhibition of PIC induced iNOS by NG-monomethyl-L-arginine (NMMA) only blocked the increased expression of HMOX1. IL-1ra completely abrogated the effects of PIC with respect to NO production, necrosis, apoptosis, mitochondrial dysfunction, GSIS, and in vivo potency. IL-1ra was not effective at preventing the induction of necrosis or apoptosis by exogenous NO. These data demonstrate that Anakinra is an effective agent to inhibit the activation of IL-1beta dependent inflammatory pathways in cultured rat islets and support the extension of its application to human islets in vitro and potentially as a post transplant therapy.

Serum albumin protects from cytokine-induced pancreatic beta cell death by a phosphoinositide 3-kinase-dependent mechanism

The present study was undertaken to investigate the biological activity of serum albumin when pancreatic beta cells were challenged by cytokines and pro-apoptotic reactive oxygen species like H(2)O(2). Culture of mouse islets or INS-1E beta cells for 24 h in the presence of H(2)O(2) (25 micromol/l) increased cell death. This demise was prevented by serum albumin, dependent on its free sulfhydryl group, emphasizing that albumin may scavenge H(2)O(2) due to its antioxidant properties. Culture for 48 h with a cytokine mixture of IL-1beta (160 pg/ml), IFN-gamma (200 ng/ml), and TNF-alpha (2 ng/ml) revealed that albumin, also protected against cytokine-induced death of both mouse islets and INS-1E beta cells. This protective effect against cytokine-induced beta cell death was, however, not dependent on albumins free sulfhydryl group, but was inhibited by the phosphoinositide 3-kinase (PI3K) inhibitors LY294002 (25 micromol/l) and wortmannin (1 micromol/l), suggesting that albumin may rescue beta cells from cytokine-induced cell death by activation of PI3K. In accordance, albumin stimulated phosphorylation of Akt, a down-stream target for PI3K. In conclusion, it is suggested that albumin may be a survival factor for pancreatic beta cells through scavenging of reactive oxygen species and by PI3K-dependent activation of Akt.

T cells cooperate with palmitic acid in induction of beta cell apoptosis

Background

Diabetes is characterized by progressive failure of insulin producing beta cells. It is well known that both saturated fatty acids and various products of immune cells can contribute to the reduction of beta cell viability and functionality during diabetes pathogenesis. However, their joint action on beta cells has not been investigated, so far. Therefore, we explored the possibility that leukocytes and saturated fatty acids cooperate in beta cell destruction.

Results

Rat pancreatic islets or insulinoma cells (RIN) were co-cultivated with concanavalin A (ConA)-stimulated rat lymph node cells (LNC), or they were treated with cell-free supernatants (Sn) obtained from ConA-stimulated spleen cells or from activated CD3⁺ cells, in the absence or presence of palmitic acid (PA). ConA-stimulated LNC or Sn and PA cooperated in inducing caspase-3-dependent RIN cell apoptosis. The observed effect of PA and Sn on RIN cell viability was mediated by p38 mitogen-activated protein kinase (MAPK)-signaling and was achieved through auto-destructive nitric oxide (NO) production. The cooperative effect of Sn was mimicked with the combination of interleukin-1β, interleukin-2, interleukin-6, interleukin-17, interferon-γ and tumor necrosis factor-α.

Conclusion

These results imply that stimulated T cells produce cytokines that cooperate with saturated free fatty acids in beta cell destruction during diabetes pathogenesis.

MAPK kinase kinase-1 is essential for cytokine-induced c-Jun NH2-terminal kinase and nuclear factor-kappaB activation in human pancreatic islet cells

OBJECTIVE

The transcription factor nuclear factor-kappaB (NF-kappaB) and the mitogen-activated protein kinases (MAPKs) c-Jun NH(2)-terminal kinase (JNK) 1/2 are known to play decisive roles in cytokine-induced damage of rodent beta-cells. The upstream events by which these factors are activated in response to cytokines are, however, uncharacterized. The aim of the present investigation was to elucidate a putative role of the MAPK kinase kinase-1 (MEKK-1) in cytokine-induced signaling.

RESEARCH DESIGN AND METHODS

To establish a functional role of MEKK-1, the effects of transient MEKK-1 overexpression in betaTC-6 cells, achieved by lipofection and cell sorting, and MEKK-1 downregulation in betaTC-6 cells and human islet cells, achieved by diced-small interfering RNA treatment, were studied.

RESULTS

We observed that overexpression of wild-type MEKK-1, but not of a kinase dead MEKK-1 mutant, resulted in potentiation of cytokine-induced JNK activation, inhibitor of kappaB (IkappaB) degradation, and cell death. Downregulation of MEKK-1 in human islet cells provoked opposite effects, i.e., attenuation of cytokine-induced JNK and MKK4 activation, IkappaB stability, and a less pronounced NF-kappaB translocation. betaTC-6 cells with a downregulated MEKK-1 expression displayed also a weaker cytokine-induced iNOS expression and lower cell death rates. Also primary mouse islet cells with downregulated MEKK-1 expression were protected against cytokine-induced cell death.

CONCLUSIONS

MEKK-1 mediates cytokine-induced JNK- and NF-kappaB activation, and this event is necessary for iNOS expression and cell death.

Cytokines and beta-cell biology: from concept to clinical translation

The tale of cytokines and the beta-cell is a long story, starting with in vitro discovery in 1984, evolving via descriptive and phenomenological studies to detailed mapping of the signalling pathways, gene- and protein expression patterns, molecular and biochemical effector mechanisms to in vivo studies in spontaneously diabetic and transgenic animal models. Only very recently have steps been taken to translate the accumulating compelling preclinical data into clinical trials. The aim of this chapter is to present an overview of early and recent key observations from our own groups as well as other laboratories that serve to illuminate the road from concept to clinical translation.

MKK3 signalling plays an essential role in leukocyte-mediated pancreatic injury in the multiple low-dose streptozotocin model

In vitro studies have implicated activation of the p38 mitogen-activated protein kinase (MAPK) signalling pathway in cytokine-mediated pancreatic beta-cell injury. Activation of the p38 MAPK occurs through two different upstream kinases, mitogen-activated protein kinase kinase 3 (MKK3) and MKK6. This study examined the role of MKK3 signalling in an in vivo model of cytokine-dependent pancreatic injury induced by multiple low doses of streptozotocin (MLD-STZ). Groups of wild-type (WT) or Mkk3-/- C57BL/6J mice received 5 daily injections of STZ (40 mg/kg) and were killed on day 5, week 2 or week 4. MLD-STZ in WT mice exhibited two distinct phases of pancreatic damage: islet cell apoptosis (immunostaining for cleaved caspase-3) on day 5 in the absence of leukocyte infiltration, and this was followed by islet inflammation (leukocyte infiltration and cytokine production) and further islet cell apoptosis on day 14 resulting in a loss of insulin-producing beta-cells and an 80% incidence of hyperglycaemia. Mkk3-/- mice were not protected from the initial phase of STZ-induced islet cell apoptosis day 5. However, Mkk3-/- mice were completely protected from the induction of hyperglycaemia. This was attributed to inhibition of leukocyte infiltration, production of pro-inflammatory cytokines and islet cell apoptosis at day 14 of MLD-STZ. In vitro studies showed that cultured islets from Mkk3-/- and WT mice are equally susceptible to STZ and cytokine-induced apoptosis. In conclusion, MKK3 signalling plays an essential role in the development of islet inflammation leading to destruction of beta-cells and hyperglycaemia in MLD-STZ-induced pancreatic injury.

The role of nitric oxide and the unfolded protein response in cytokine-induced beta-cell death

OBJECTIVE

The unfolded protein response (UPR) is a conserved cellular response designed to alleviate damage and promote survival of cells experiencing stress; however, prolonged UPR activation can result in apoptotic cell death. The UPR, activated by cytokine-induced nitric oxide (NO) production, has been proposed to mediate beta-cell death in response to cytokines. In this study, the role of UPR activation in cytokine-induced beta-cell death was examined.

RESEARCH DESIGN AND METHODS

The effects of cytokine treatment of rat and human islets and RINm5F cells on UPR activation, NO production, and cell viability were examined using molecular and biochemical methodologies.

RESULTS

UPR activation correlates with beta-cell death in interleukin (IL)-1-treated rat islets. NO mediates both cytokine-induced UPR activation and beta-cell death as NO synthase inhibitors attenuate each of these IL-1-stimulated events. Importantly, cytokines and tunicamycin, a classical UPR activator, induce beta-cell death by different mechanisms. Cell death in response to the classical UPR activator is associated with a 2.5-fold increase in caspase-3 activity, while IL-1 fails to stimulate caspase-3 activity. In addition, cell death is enhanced by approximately 35% in tunicamycin-treated cells expressing an S51A eIF2 alpha mutant that cannot be phosphorylated or in cells lacking PERK (protein kinase regulated by RNA/endoplasmic reticulum-like kinase). In contrast, neither the absence of PERK nor the expression of the S51A eIF2 alpha mutant affects the levels of cytokine-induced death.

CONCLUSIONS

While cytokine-induced beta-cell death temporally correlates with UPR activation, the lack of caspase activity and the ability of NO to attenuate caspase activity suggest that prolonged UPR activation does not mediate cytokine-induced beta-cell death.

Transforming growth factor-beta-activated protein kinase 1-binding protein (TAB)-1alpha, but not TAB1beta, mediates cytokine-induced p38 mitogen-activated protein kinase phosphorylation and cell death in insulin-producing cells

Previous studies have indicated that the p38 MAPK participates in signaling events that lead to the death of the insulin-producing beta-cell. The aim of the present study was to elucidate the role of the TGF-beta-activated protein kinase 1-binding protein 1 (TAB1) in the cytokine-induced activation of p38. Levels of TAB1 mRNA and protein were analyzed by real-time PCR and immunoblotting, and TAB1 expression in mouse and human islet cells was down-regulated using lipofection of diced-small interfering RNA. TAB1 overexpression in beta-TC6 cells was achieved by transient transfections followed by fluorescence activated cell sorting. Phosphorylation of p38, c-Jun N-terminal kinase, and ERK was assessed by immunoblotting, and viability was determined using vital staining with bisbenzimide and propidium iodide. We observed that TAB1 is expressed in insulin-producing cells. Cytokine (IL-1beta + interferon-gamma)-stimulated p38 phosphorylation was significantly increased by TAB1alpha overexpression, but not TAB1beta overexpression, in beta-TC6 cells. The TAB1alpha-augmented p38 phosphorylation was paralleled by an increased cell death rate. Treatment of islet cells with diced-small interfering RNA specific for TAB1, but not for TGF-beta-activated kinase 1, resulted in lowered cytokine-induced p38 phosphorylation and protection against cell death. The cytokine-induced phosphorylation of c-Jun N-terminal kinase and ERK was not affected by changes in TAB1 levels. Finally, TAB1 phosphorylation was decreased by the p38 inhibitor SB203580. We conclude that TAB1alpha, but not TAB1beta, plays an important role in the activation of p38 in insulin-producing cells and therefore also in cytokine-induced beta-cell death.

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

AIMS/HYPOTHESIS

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

METHODS

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

RESULTS

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

CONCLUSIONS/INTERPRETATION

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

Transforming Growth Factor β Is a Critical Regulator of Adult Human Islet Plasticity

Tissue plasticity is well documented in the context of pancreatic regeneration and carcinogenesis, with recent reports implicating dedifferentiated islet cells both as endocrine progenitors and as the cell(s) of origin in pancreatic adenocarcinoma. Accordingly, it is noteworthy that accumulating evidence suggests that TGFβ signaling is essential to pancreatic endocrine development and maintenance, whereas its loss is associated with the progression to pancreatic adenocarcinoma. The aim of this study was to examine the role of TGFβ in an in vitro model of islet morphogenetic plasticity. Human islets were embedded in a collagen gel and cultured under conditions that induced transformation into duct-like epithelial structures (DLS). Addition of TGFβ caused a dose-dependent decrease in DLS formation. Although it was demonstrated that collagen-embedded islets secrete low levels of TGFβ, antibody-mediated neutralization of this endogenously released TGFβ improved DLS formation rates, suggesting local TGFβ concentrations may in fact be higher. Time course studies indicated that TGFβ signaling was associated with an increase in ERK and p38 MAPK phosphorylation, although inhibitor-based studies were consistent with an islet endocrine-stabilizing effect mediated by p38 alone. Localization of TGFβ signaling molecules suggested that the action of TGFβ is directly on the β-cell to inhibit apoptosis and thus stabilize endocrine phenotype.

Cytokine-induced osteoprotegerin expression protects pancreatic beta cells through p38 mitogen-activated protein kinase signalling against cell death

AIMS/HYPOTHESIS

Pro-inflammatory cytokines play a crucial role in immune-mediated beta cell destruction, an essential mechanism in the pathogenesis of type 1 diabetes mellitus. Microarray analysis recently identified osteoprotegerin (OPG; now known as tumour necrosis factor receptor superfamily, member 11b [TNFRSF11B]) as a cytokine-induced gene in beta cells. The aim of the present study was to characterise the functional role and signalling pathways of OPG that are involved in cytokine-induced beta cell death.

MATERIALS AND METHODS

As cellular models, the rat beta cell line INS-1E and human primary pancreatic islets were employed. The effects of IL-1beta and TNF-alpha on OPG expression were characterised by northern blot and immunoassay. The effect of OPG on beta cell survival was assessed by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Signalling pathways were evaluated by western blot analysis using antibodies against p38 mitogen-activated protein kinases (MAPK), c-Jun N-terminal kinase and extracellular signal-regulated kinase 1/2.

RESULTS

The INS-1E cell line and primary pancreatic islets expressed OPG mRNA and secreted OPG protein, both of which were enhanced by IL-1beta and TNF-alpha. Exposure to IL-1beta resulted in sustained phosphorylation of p38 MAPK in INS-1E cells and subsequent cell death. Administration of exogenous OPG prevented both IL-1beta-induced beta cell death and sustained p38 MAPK phosphorylation.

CONCLUSIONS/INTERPRETATION

Our data indicate that cytokine-induced production of OPG may protect beta cells from further damage. This protective effect is, at least in part, mediated through inhibition of p38 MAPK phosphorylation. Thus OPG is an autocrine or paracrine survival factor for beta cells.

Activation of c-Jun NH2-terminal kinase during islet isolation

Pancreatic islet transplantation has been remarkably improved by the Edmonton protocol; however, it is not easy to achieve insulin independence after islet transplantation from one donor pancreas. The islet isolation procedure itself destroys cellular and noncellular components of the pancreas that probably play a role in supporting islet survival. Further islet transplantation exposes cells to a variety of stressful stimuli such as proinflammatory cytokines. The reduction in islet mass immediately after isolation and transplantation implicates beta cell death by apoptosis and the prerecruitment of intracellular death signalling pathways. The c-Jun NH2-terminal kinases (JNKs) are classic stress-activated protein kinases and many cellular stresses have been shown to stimulate JNK activation. JNK in the pancreas is activated during brain death, pancreas procurement, and organ preservation, and its activity is progressively increased during the isolation procedure. Moreover, JNK activity in the transplanted liver after islet transplantation increases markedly within 24 hrs. Use of the JNK inhibitor in pancreas preservation, islet culture, and/or islet transplantation prevents islet apoptosis and improves islet graft function. These findings suggest that the control of JNK activation is important for pancreatic islet transplantation.

Role of TAB1 in nitric oxide-induced p38 activation in insulin-producing cells

The aim of present study was to elucidate the role of TAB1 in nitric oxide-induced activation of p38 MAPK. For this purpose we over-expressed TAB1 in insulin-producing β-TC6 cells. We observed in cells transiently over-expressing TAB1 that p38 activation was enhanced in response to DETA/NONOate. A lowering of TAB1 levels, using the siRNA technique, resulted in the opposite effect. The DETA/NONOate-induced cell death rate was increased in cells transiently overexpressing TAB1. In stable β-TC6 cell clones with very high TAB1 levels p38 phosphorylation was enhanced also at basal conditions. DETA/NONOate increased also the phosphorylation of JNK and ERK in β-TC6 cells, but these events were not affected by TAB1. Interestingly, the inhibitory effect of SB203580 on p38 phosphorylation was paralleled by a stimulatory effect on JNK phosphorylation and an inhibitory effect on ERK phosphorylation. In summary, we propose that TAB1 promotes nitric oxide-induced p38 autophosphorylation. In addition, nitric oxide-induced p38 activation seems to promote JNK inhibition and ERK activation, but this effect appears to not require TAB1. A better understanding of how the TAB1/p38 pathway promotes β-cell death in response to nitric oxide might help in the development of novel pharmacological approaches in the treatment of diabetes.

IL-1beta-induced pro-apoptotic signalling is facilitated by NCAM/FGF receptor signalling and inhibited by the C3d ligand in the INS-1E rat beta cell line

AIMS/HYPOTHESIS

IL-1beta released from immune cells induces beta cell pro-apoptotic signalling via mitogen-activated protein kinases (MAPKs) and nuclear factor-kappaB (NF-kappaB). In neurons, the neural cell adhesion molecule (NCAM) signals to several elements involved in IL-1beta-induced pro-apoptotic signalling in beta cells. Pancreatic beta cells express NCAM, but its biological effects in these cells are unclear. The aim of this study was to investigate whether there is cross-talk between NCAM signalling and cytokine-induced pro-apoptotic signalling.

MATERIALS AND METHODS

Western blotting was used to investigate levels of NCAM and inducible nitric oxide synthase, phosphorylation of Src and MAPKs, and cleavage of caspase-3. MAPK activity was investigated with an in vitro kinase assay. Apoptosis was detected by cleaved caspase-3 and a Cell Death Detection ELISA(plus) assay. NCAM-induced fibroblast growth factor receptor (FGFR) activation was investigated in NCAM(-/-) Trex293 cells where FGFR phosphorylation was measured by Western blotting after NCAM transfection.

RESULTS

Pre-exposure of INS-1E cells to the FGFR-inhibitor SU5402, but not to the Src-inhibitor PP2, dose-dependently inhibited IL-1beta-mediated MAPK activity. A synthetic peptide, C3d, reported to bind NCAM, did not activate MAPK or Akt as reported in neurons but inhibited IL-1beta-induced MAPK activity, thereby mimicking the effect of SU5402. Furthermore, C3d inhibited NCAM-induced FGFR phosphorylation and apoptosis induced by IL-1beta plus IFN-gamma, but did not affect IL-1beta-induced NF-kappaB signalling.

CONCLUSIONS/INTERPRETATION

We suggest that NCAM signalling through FGFR is required for efficient IL-1beta pro-apoptotic signalling by facilitating IL-1beta-induced MAPK activation downstream of the NF-kappaB-MAPK branching point. Further, these data identify a novel function of C3d as an inhibitor of NCAM-induced FGFR activity and of IL-1beta-induced MAPK activation in beta cells.

Activation of activating transcription factor 2 by p38 MAP kinase during apoptosis induced by human amylin in cultured pancreatic beta-cells

Amylin-mediated islet beta-cell death is implicated in diabetogenesis. We previously reported that fibrillogenic human amylin (hA) evokes beta-cell apoptosis through linked activation of Jun N-terminal kinase 1 (JNK 1) and a caspase cascade. Here we show that p38 kinase [p38 mitogen-activated protein (MAP) kinase] became activated by hA treatment of cultured beta-cells whereas extracellular signal-regulated kinase (ERK) did not; by contrast, nonfibrillogenic rat amylin (rA) altered neither. Pretreatment with the p38 kinase-inhibitor SB203580 decreased hA-induced apoptosis and caspase-3 activation by approximately 30%; as did combined SB203580 and JNK inhibitor I, by about 70%; and the combination of SB203580, the JNK inhibitor I and a caspase-8 inhibitor, by 100%. These findings demonstrate the requirement for concurrent activation of the p38 kinase, JNK and caspase-8 pathways. We further showed that hA elicits time-dependent activation of activating transcription factor 2 (ATF-2), which was largely suppressed by SB203580, indicating that this activation is catalyzed mainly by p38 kinase. Furthermore, hA-induced apoptosis was suppressed by specific antisense ATF-2, and increased phospho-ATF-2 (p-ATF-2) was associated with increased CRE (cAMP-response element) DNA binding and CRE-mediated transcriptional activity, as well as enhancement of c-jun promoter activation. We also detected changes in the phosphorylation status and composition of the CRE complex that may play important roles in regulation of distinct downstream target genes. These studies establish p38 MAP kinase-mediated activation of ATF-2 as a significant mechanism in hA-evoked beta-cell death, which may serve as a target for pharmaceutical intervention and effective suppression of beta-cell failure in type-2 diabetes.