The immune-mediated elimination of pancreatic beta cells in type 1 diabetes involves release of cytotoxic cytokines such as IL-1beta and IFNgamma, which induce beta cell death in vitro by mechanisms ...that are both dependent and independent of nitric oxide (NO). Nuclear factor kappa B (NFkappaB) is a critical signalling molecule in inflammation and is required for expression of the gene encoding inducible NO synthase (iNOS) and of pro-apoptotic genes. NFkappaB has recently been shown to associate with chromatin-modifying enzymes histone acetyltransferases and histone deacetylases (HDAC), and positive effects of HDAC inhibition have been obtained in several inflammatory diseases. Thus, the aim of this study was to investigate whether HDAC inhibition protects beta cells against cytokine-induced toxicity.
The beta cell line, INS-1, or intact rat islets were precultured with HDAC inhibitors suberoylanilide hydroxamic acid or trichostatin A in the absence or presence of IL-1beta and IFNgamma. Effects on insulin secretion and NO formation were measured by ELISA and Griess reagent, respectively. iNOS levels and NFkappaB activity were measured by immunoblotting and by immunoblotting combined with electrophoretic mobility shift assay, respectively. Viability was analysed by 3-(4,5-dimethyldiazol-2-yl)-2,5-diphenyl-tetrazolium bromide and apoptosis by terminal deoxynucleotidyl transferase mediated dUTP nick end labeling (TUNEL) assay and histone-DNA complex ELISA.
HDAC inhibition reduced cytokine-mediated decrease in insulin secretion and increase in iNOS levels, NO formation and apoptosis. IL-1beta induced a bi-phasic phosphorylation of inhibitor protein kappa Balpha (IkappaBalpha) with the 2nd peak being sensitive to HDAC inhibition. No effect was seen on IkappaBalpha degradation and NFkappaB DNA binding.
HDAC inhibition prevents cytokine-induced beta cell apoptosis and impaired beta cell function associated with a downregulation of NFkappaB transactivating activity.
With the worldwide increase in diabetes prevalence there is a pressing unmet need for novel antidiabetic therapies. Insufficient insulin production due to impaired β‐cell function and apoptotic ...reduction of β‐cell mass is a common denominator in the pathogenesis of diabetes. Current treatments are directed at improving insulin sensitivity, and stimulating insulin secretion or replacing the hormone, but do not target progressive apoptotic β‐cell loss. Here we review the current development of small‐molecule inhibitors designed to rescue β‐cells from apoptosis. Several distinct classes of small molecules have been identified that protect β‐cells from inflammatory, oxidative and/or metabolically induced apoptosis. Although none of these have yet reached the clinic, β‐cell protective small molecules alone or in combination with current therapies provide exciting opportunities for the development of novel treatments for diabetes.
The haemoglobin glycation index (HGI) has been proposed as a marker of interindividual differences in haemoglobin glycosylation. Previous studies have shown a relationship between high HGI and risk ...of cardiovascular disease (CVD) in patients with diabetes. However, no studies have investigated the role of previous CVD in this association.
The study cohort comprised patients with type 2 diabetes mellitus (T2DM; n=1910) included in the Second Manifestations of Arterial Disease (SMART) study. The relationship between either HGI or HbA1c and a composite of cardiovascular events as the primary outcome, and mortality, cardiovascular mortality, myocardial infarction and stroke as secondary outcomes, was investigated using Cox proportional-hazards models. Similar analyses were performed after stratification according to previous CVD.
A 1-unit higher HGI was associated with a 29% greater risk of a composite of cardiovascular events (HR: 1.29, 95% CI: 1.06–1.57) in patients without previous CVD, whereas no such relationship was seen in patients with previous CVD (HR: 0.96, 95% CI: 0.86–1.08). The direction and magnitude of the hazard ratios (HRs) of HGI and HbA1c in relation to outcomes were similar. Additional adjustment for HbA1c in the association between HGI and outcomes lowered the HRs.
Similar to HbA1c, higher HGI is related to higher risk of cardiovascular events in patients with T2DM without CVD. As HbA1c has proved to be a comparable risk factor, and obtaining and interpreting the HGI is complicated, any additional benefit of applying the HGI in clinical settings is likely to be limited.
Aims/hypothesis
Histone deacetylases (HDACs) are promising pharmacological targets in cancer and autoimmune diseases. All 11 classical HDACs (HDAC1–11) are found in the pancreatic beta cell, and HDAC ...inhibitors (HDACi) protect beta cells from inflammatory insults. We investigated which HDACs mediate inflammatory beta cell damage and how the islet content of these HDACs is regulated in recent-onset type 1 diabetes.
Methods
The rat beta cell line INS-1 and dispersed primary islets from rats, either wild type or HDAC1–3 deficient, were exposed to cytokines and HDACi. Molecular mechanisms were investigated using real-time PCR, chromatin immunoprecipitation and ELISA assays. Pancreases from healthy children and children with type 1 diabetes were assessed using immunohistochemistry and immunofluorescence.
Results
Screening of 19 compounds with different HDAC selectivity revealed that inhibitors of HDAC1, -2 and -3 rescued INS-1 cells from inflammatory damage. Small hairpin RNAs against HDAC1 and -3, but not HDAC2, reduced pro-inflammatory cytokine-induced beta cell apoptosis in INS-1 and primary rat islets. The protective properties of specific HDAC knock-down correlated with attenuated cytokine-induced
iNos
expression but not with altered expression of the pro-inflammatory mediators
Il1α
,
Il1β
,
Tnfα
or
Cxcl2
. HDAC3 knock-down reduced nuclear factor κB binding to the
iNos
promoter and HDAC1 knock-down restored insulin secretion. In pancreatic sections from children with type 1 diabetes of recent onset, HDAC1 was upregulated in beta cells whereas HDAC2 and -3 were downregulated in comparison with five paediatric controls.
Conclusions/interpretation
These data demonstrate non-redundant functions of islet class I HDACs and suggest that targeting HDAC1 and HDAC3 would provide optimal protection of beta cell mass and function in clinical islet transplantation and recent-onset type 1 diabetic patients.
ObjectiveBody weight-related insulin resistance probably plays a role in progression to type 1 diabetes, but has an uncertain impact following diagnosis. In this study, we investigated whether BMI ...measured at diagnosis was an independent predictor of C-peptide decline 1-year post-diagnosis.DesignMulticentre longitudinal study carried out at diagnosis and up to 1-year follow-up.MethodsData on C-peptide were collected from seven diabetes centres in Europe. Patients were grouped according to age at diagnosis (<5 years, n=126; >5 years <10 years, n=295; >10 years <18 years, n=421; >18 years, n=410). Linear regression was used to investigate whether BMI was an independent predictor of change in fasting C-peptide over 1 year. Models were additionally adjusted for baseline insulin dose and HbA1c.ResultsIn individuals diagnosed between 0 and 5 years, 5 and 10 years and those diagnosed >18 years, we found no association between BMI and C-peptide decline. In patients aged 10–18 years, higher BMI at baseline was associated with a greater decline in fasting C-peptide over 1 year with a decrease (β 95% CI; P value) of 0.025 (0.010, 0.041) nM/kg per m2 higher baseline BMI (P=0.001). This association remained significant after adjusting for gender and differences in HbA1c and insulin dose (β=0.026, 95% CI=0.0097, 0.042; P=0.002).ConclusionsThese observations indicate that increased body weight and increased insulin demand are associated with more rapid disease progression after diagnosis of type 1 diabetes in an age group 10–18 years. This should be considered in studies of β-cell function in type 1 diabetes.
Pro-inflammatory cytokines cause beta cell secretory dysfunction and apoptosis--a process implicated in the pathogenesis of type 1 diabetes. Cytokines induce the expression of inducible nitric oxide ...(NO) synthase (iNOS) leading to NO production. NO contributes to cytokine-induced apoptosis, but the underlying mechanisms are unclear. The aim of this study was to investigate whether NO modulates signalling via mitogen-activated protein kinases (MAPKs) and Akt.
MAPK activities in INS-1 cells and isolated islets were determined by immunoblotting and in vitro kinase assay. Apoptosis was determined by ELISA measurement of histone-DNA complexes present in cytoplasm.
Apoptosis in INS-1 cells induced by IL-1beta plus IFNgamma was dependent on NO production as demonstrated by the use of the NOS blocker NG-methyl-L-arginine. Accordingly, an NO donor (S-nitroso-N-acetyl-D, L-penicillamine, SNAP) dose-dependently caused apoptosis in INS-1 cells. SNAP activated c-Jun N-terminal kinase (JNK) and p38 MAPK, but suppressed the activity of extracellular signal-regulated kinase MAPK. In rat islets, NOS inhibition decreased JNK and p38 activities induced by a 6-h exposure to IL-1beta. Likewise, IL-1beta-induced JNK and p38 activities were lower in iNOS(-/-) mouse islets than in wild-type islets. In human islets, SNAP potentiated IL-1beta-induced JNK activation. The constitutive level of active, Ser473-phosphorylated Akt in INS-1 cells was suppressed by SNAP. IGF-I activated Akt and protected against SNAP-induced apoptosis. The anti-apoptotic effect of IGF-I was not associated with reduced JNK activation.
We suggest that NO contributes to cytokine-induced apoptosis via potentiation of JNK activity and suppression of Akt.
Aims/hypothesis Cytokine-induced beta cell toxicity is abrogated by non-selective inhibitors of lysine deacetylases (KDACs). The KDAC family consists of 11 members, namely histone deacetylases HDAC1 ...to HDAC11, but it is not known which KDAC members play a role in cytokine-mediated beta cell death. The aim of the present study was to examine the KDAC gene expression profile of the beta cell and to investigate whether KDAC expression is regulated by cytokines. In addition, the protective effect of the non-selective KDAC inhibitor ITF2357 and interdependent regulation of four selected KDACs were investigated. Methods The beta cell line INS-1 and intact rat and human islets were exposed to cytokines with or without ITF2357. Expression of mRNA was assessed by real-time PCR and selected targets validated at the protein level by immunoblotting. Effects on cytokine-induced toxicity were investigated by in vitro assays. Results Hdac1 to Hdac11 were expressed and differentially regulated by cytokines in INS-1 cells and rat islets. HDAC1, -2, -6 and -11 were found to be expressed and regulated by cytokines in human islets. ITF2357 protected against cytokine-induced beta cell apoptosis and counteracted cytokine-induced attenuation of basal insulin secretion. In addition, cytokine-induced regulation of Hdac2 and Hdac6, but not Hdac1 and Hdac11, was reduced by KDAC inhibition. Conclusions/interpretation All classical KDAC genes are expressed by beta cells and differentially regulated by cytokines. Based on the relative expression levels and degree of regulation by cytokines, we propose that HDAC1, -2, -6 and -11 are of particular importance for beta cell function. These observations may help in the design of specific KDAC inhibitors to prevent beta cell destruction in situ and in islet grafts.
The c-Jun amino-terminal kinase pathway is preferentially activated by interleukin-1 and controls apoptosis in differentiating
pancreatic beta-cells.
A Ammendrup ,
A Maillard ,
K Nielsen ,
N Aabenhus ...Andersen ,
P Serup ,
O Dragsbaek Madsen ,
T Mandrup-Poulsen and
C Bonny
Steno Diabetes Center and Hagedorn Research Institute, Gentofte, Denmark.
Abstract
To characterize the differentiation events that selectively target insulin-producing cells to interleukin (IL)-1beta-induced
apoptosis, we studied IL-1beta signaling via mitogen-activated protein kinase (MAPK) and stress-activated protein kinase in
2 pancreatic endocrine cell lines. We studied the glucagon-secreting AN-glu cell line and the insulin and the islet amyloid
polypeptide-producing beta-cell line (AN-ins cells), which is derived by stable transfection of AN-glu cells with the transcription
factor pancreatic duodenal homeobox factor-1. AN-ins cells were more sensitive to the cytotoxic action of IL-1beta. This increased
sensitivity was not associated with a more pronounced IL-l-induced nitric oxide production in AN-ins cells, but it correlated
with a more marked activation of the 3 MAPKs extracellular signal-regulated kinases (ERKs)-1/2, c-Jun NH2-terminal kinase
(JNK), and p38 MAPK (p38). This led to increased phosphorylation of the transcription factors c-Jun, Elk-1, and ATF2 and of
heat shock protein 25. Inhibition of ERK-1/2 and p38 did not prevent but aggravated IL-1beta-induced cell death. In contrast,
inhibition of JNK by transfection with the dominant negative inhibitor of the JNK-binding domain prevented apoptosis in both
cell types. Cell death could be elicited by overexpressing the catalytic domain of MAPK kinase kinase 1, a specific activator
of JNK and nuclear factor-kappaB, which does not recruit ERK-1/2 or p38. Coactivation of ERK-1/2 with JNK did not prevent
apoptosis. In conclusion, increased MAPK signaling in response to IL-1beta may represent a novel molecular marker of beta-cell
differentiation. JNK inhibition represents an effective means of preventing IL-1beta-activated beta-cell destruction.
Inflammatory mechanisms play a key role in the pathogenesis of type 1 diabetes. Individuals who progress to type 2 diabetes display features of low-grade inflammation years in advance of disease ...onset. This low-grade inflammation has been proposed to be involved in the pathogenetic processes causing type 2 diabetes. Mediators of inflammation such as tumor necrosis factor-alpha, interleukin (IL)-1beta, the IL-6 family of cytokines, IL-18, and certain chemokines have been proposed to be involved in the events causing both forms of diabetes. IL-6 has in addition to its immunoregulatory actions been proposed to affect glucose homeostasis and metabolism directly and indirectly by action on skeletal muscle cells, adipocytes, hepatocytes, pancreatic beta-cells, and neuroendocrine cells. Here we argue that IL-6 action-in part regulated by variance in the IL-6 and IL-6alpha receptor genes-contributes to, but is probably neither necessary nor sufficient for, the development of both type 1 and type 2 diabetes. Thus, the two types of diabetes are also in this respect less apart than apparent. However, the mechanisms are not clear, and we therefore propose future directions for studies in this field.
The past decade has provided exciting insights into a novel class of central (small) RNA molecules intimately involved in gene regulation. Only a small percentage of our DNA is translated into ...proteins by mRNA, yet 80% or more of the DNA is transcribed into RNA, and this RNA has been found to encompass various classes of novel regulatory RNAs, including, e.g., microRNAs. It is well known that DNA is constantly oxidized and repaired by complex genome maintenance mechanisms. Analogously, RNA also undergoes significant oxidation, and there are now convincing data suggesting that oxidation, and the consequent loss of integrity of RNA, is a mechanism for disease development. Oxidized RNA is found in a large variety of diseases, and interest has been especially devoted to degenerative brain diseases such as Alzheimer disease, in which up to 50–70% of specific mRNA molecules are reported oxidized, whereas other RNA molecules show virtually no oxidation. The iron-storage disease hemochromatosis exhibits the most prominent general increase in RNA oxidation ever observed. Oxidation of RNA primarily leads to strand breaks and to oxidative base modifications. Oxidized mRNA is recognized by the ribosomes, but the oxidation results in ribosomal stalling and dysfunction, followed by decreased levels of functional protein as well as the production of truncated proteins that do not undergo proper folding and may result in protein aggregation within the cell. Ribosomal dysfunction may also signal apoptosis by p53-independent pathways. There are very few reports on interventions that reduce RNA oxidation, one interesting observation being a reduction in RNA oxidation by ingestion of raw olive oil. High urinary excretion of 8-oxo-guanosine, a biomarker for RNA oxidation, is highly predictive of death in newly diagnosed type 2 diabetics; this demonstrates the clinical relevance of RNA oxidation. Taken collectively the available data suggest that RNA oxidation is a contributing factor in several diseases such as diabetes, hemochromatosis, heart failure, and β-cell destruction. The mechanism involves free iron and hydrogen peroxide from mitochondrial dysfunction that together lead to RNA oxidation that in turn gives rise to truncated proteins that may cause aggregation. Thus RNA oxidation may well be an important novel contributing mechanism for several diseases.
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► RNA oxidation is more abundant than DNA oxidation. ► High levels of oxidized RNA are found in degenerative brain diseases. ► General RNA oxidation is measured by 8-oxoGuo excretion into urine. ► General RNA oxidation predicts death in type 2 diabetes. ► RNA may be a novel and important mechanism of diseases such as diabetes, degenerative brain diseases, and hemochromatosis.
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