Beta-induced Cell Death Research Articles

Enterovirus-induced gene expression profile is critical for human pancreatic islet destruction

Virally induced inflammatory responses, beta cell destruction and release of beta cell autoantigens may lead to autoimmune reactions culminating in type 1 diabetes. Therefore, viral capability to induce beta cell death and the nature of virus-induced immune responses are among key determinants of diabetogenic viruses. We hypothesised that enterovirus infection induces a specific gene expression pattern that results in islet destruction and that such a host response pattern is not shared among all enterovirus infections but varies between virus strains. The changes in global gene expression and secreted cytokine profiles induced by lytic or benign enterovirus infections were studied in primary human pancreatic islet using DNA microarrays and viral strains either isolated at the clinical onset of type 1 diabetes or capable of causing a diabetes-like condition in mice. The expression of pro-inflammatory cytokine genes (IL-1-α, IL-1-β and TNF-α) that also mediate cytokine-induced beta cell dysfunction correlated with the lytic potential of a virus. Temporally increasing gene expression levels of double-stranded RNA recognition receptors, antiviral molecules, cytokines and chemokines were detected for all studied virus strains. Lytic coxsackievirus B5 (CBV-5)-DS infection also downregulated genes involved in glycolysis and insulin secretion. The results suggest a distinct, virus-strain-specific, gene expression pattern leading to pancreatic islet destruction and pro-inflammatory effects after enterovirus infection. However, neither viral replication nor cytotoxic cytokine production alone are sufficient to induce necrotic cell death. More likely the combined effect of these and possibly cellular energy depletion lie behind the enterovirus-induced necrosis of islets.

Interleukin‐6 treatment induces beta‐cell apoptosis via STAT‐3‐mediated nitric oxide production

Type 2 diabetes is characterized by progressive beta-cell failure and apoptosis is probably the main form of beta-cell death in this disease. It was reported that circulating levels of interleukin-6 are elevated in type 2 diabetic patients, but whether this is involved in the pathogenesis of type 2 diabetes is still debated. In this study, we examined whether interleukin-6 can induce beta-cell damage in vitro and elucidated its mechanisms. To examine the effect of interleukin-6 on beta cells, glucose-stimulated insulin secretion (GSIS) by enzyme immunoassay (EIA) method and cell apoptosis by propidium iodide and annexin-V staining were measured in a rat beta-cell line (INS-1 or INS-832/13) after treatment with interleukin-6. The expression of apoptosis-related molecules was measured using western blotting and nitric oxide (NO) production was measured using Griess assay. AG490 and N-monomethyl-L-arginine were used to inhibit Janus kinase-mediated signal transducers and activators of transcription signalling and NO production, respectively. Exposure (48 h) of INS-1 cells to 20 ng/mL interleukin-6 significantly decreased GSIS as well as cell viability. We found that sub-G1/G0 population was increased as compared with untreated cells and expression of cleaved caspase-3, cleaved poly(ADP-ribose) polymerase, phosphorylated p38 mitogen-activated protein kinase and phosphorylated nuclear factor-κB was increased in interleukin-6-treated INS-1 cells. Interleukin-6 increased the amount of early apoptotic cells; this increase was blocked by AG490 or N-monomethyl-L-arginine treatment. Moreover, NO production, which is known to induce apoptosis, was increased by interleukin-6 treatment but abrogated in AG490-treated cells. Our results show that exposure to interleukin-6 for 48 h can induce beta-cell death, in part via signal transducers and activators of transcription-3-mediated NO production.

MRNA of the pro-apoptotic gene BBC3 serves as a molecular marker for TNF-α-induced islet damage in humans

TNF-α plays important roles in the pathogenesis of type 1 and type 2 diabetes mellitus. In light of this, we examined the involvement of a pro-apoptotic gene, BBC3 (also known as PUMA), in TNF-α-mediated beta cell dysfunction and destruction in human islets. Human islets were exposed in vitro to TNF-α alone or in combination with IFN-γ. Gene expression was assessed by RT-PCR using a set of single islets. Protein abundance and cellular localisation of BBC3 were assessed by immunoblot and immunohistochemistry. A marginal number of islets were transplanted into diabetic NODscid mice to correlate in vivo islet function with BBC3 expression. BBC3 and IL8 mRNA were upregulated in TNF-α-stimulated islets in a dose-dependent manner and enhanced through addition of IFN-γ, but not upregulated by IFN-γ alone. Immunohistochemistry revealed that TNF-α in combination with IFN-γ upregulated basal BBC3 abundance in the cytoplasm of beta cells along with the perinuclear clustering of mitochondria partially co-localised with BBC3. TNF-α alone did not induce beta cell death, but did abrogate preproinsulin precursor mRNA synthesis in response to high glucose stimulation, which was inversely associated with upregulation of BBC3 mRNA expression by TNF-α. Higher BBC3 mRNA expression in islets correlated with decreased graft function in vivo. These results suggest that BBC3 mRNA can serve as a molecular marker to detect early TNF-α-induced beta cell stress and may help identify islet-protective compounds for the treatment of diabetes.

Regulation and function of the cytosolic viral RNA sensor RIG-I in pancreatic beta cells

Enteroviral infections are associated with type I diabetes. The mechanisms by which viruses or viral products such as double-stranded RNA (dsRNA) affect pancreatic beta cell function and survival remain unclear. We have shown that extracellular dsRNA induces beta cell death via Toll-like receptor-3 (TLR3) signaling whereas cytosolic dsRNA triggers the production of type I interferons and apoptosis via a TLR3-independent process. We presently examined expression of the intracellular viral RNA sensors, the RNA helicases RIG-I and MDA5, and documented the functionality of RIG-I in pancreatic beta cells. FACS-purified rat beta cells and islet cells from wild-type or TLR3 −/− mice were cultured with or without the RIG-I-specific ligand 5′-triphosphate single-stranded RNA (5′triP-ssRNA), the synthetic dsRNA polyI:C (PIC) or 5′OH-ssRNA (negative control); the RNA compounds were added in the medium or transfected in the cells using lipofectamine. RIG-I and MDA5 expression were determined by real-time RT-PCR. NF-κB and IFN-β promoter activation were studied in the presence or absence of a dominant-negative form of RIG-I (DN-RIG-I). Both extracellular (PICex) and intracellular (PICin) PIC increased expression of RIG-I and MDA5 in pancreatic beta cells. TLR3 deletion abolished PICex-induced up-regulation of the helicases in beta cells but not in dendritic cells. PICin-induced NF-κB and IFN-β promoter activation were prevented by the DN-RIG-I. The RIG-I-specific ligand 5′triP-ssRNA induced IFN-β promoter activation and beta cell apoptosis. Our results suggest that the RIG-I pathway is present and active in beta cells and could contribute to the induction of insulitis by viral RNA intermediates.

Signaling by IL-1β+IFN-γ and ER stress converge on DP5/Hrk activation: a novel mechanism for pancreatic β-cell apoptosis

Chronic inflammation and pro-inflammatory cytokines are important mediators of pancreatic beta-cell destruction in type 1 diabetes (T1D). We presently show that the cytokines IL-1beta+IFN-gamma and different ER stressors activate the Bcl-2 homology 3 (BH3)-only member death protein 5 (DP5)/harakiri (Hrk) resulting in beta-cell apoptosis. Chemical ER stress-induced DP5 upregulation is JNK/c-Jun-dependent. DP5 activation by cytokines also involves JNK/c-Jun phosphorylation and is antagonized by JunB. Interestingly, cytokine-inducted DP5 expression precedes ER stress: mitochondrial release of cytochrome c and ER stress are actually a consequence of enhanced DP5 activation by cytokine-mediated nitric oxide formation. Our findings show that DP5 is central for beta-cell apoptosis after different stimuli, and that it can act up- and downstream of ER stress. These observations contribute to solve two important questions, namely the mechanism by which IL-1beta+IFN-gamma induce beta-cell death and the nature of the downstream signals by which ER stress 'convinces' beta-cells to trigger apoptosis.

Interferon signalling in pancreatic beta cells

Type 1 diabetes results from apoptotic destruction of insulin-producing beta cells by a range of effector molecules produced by immune cells that infiltrate pancreatic islets. Interferons are found within the inflammatory infiltrate of islets during progression to type 1 diabetes. Interferons can promote the action of effector cells that induce beta cell death. They can also act directly on islet cells to induce gene expression, and together with other cytokines they can cause beta cell death. Because of their pleiotropic nature, it was proposed that this family of cytokines may be involved in type 1 diabetes development. In the non-obese diabetic mouse model, interventions have been made at multiple points in the signalling pathways of interferons. This review aims to construct a clear picture of the outcomes of these interventions to determine how interferons are involved in the pathogenesis of type 1 diabetes.

Fructus Corni suppresses hepatic gluconeogenesis related gene transcription, enhances glucose responsiveness of pancreatic beta-cells, and prevents toxin induced beta-cell death

Ethnopharmacological relevance Fructus Corni, the fruits of Cornus officinalis Sieb. et Zucc., is one important ingredient in Quei Fu Di Huang Wan, a Chinese herbal mixture. Aim of the Study In the present study, additional anti-diabetic actions of Fructus Corni on transcriptional regulation of hepatic gluconeogenesis or β-cell functions were investigated. Materials and methods Insulin mimetic action of Fructus Corni on dexamethasone and 8-bromo-cAMP induced phosphoenolpyruvate carboxykinase (PEPCK) expression in H4IIE cells was investigated. Besides, BRIN-BD11 cells were used to evaluate both insulinotropic and β-cell protective effect of Fructus Corni. Results Firstly, both methanol extract (CO-W-M) and fraction (CO-W-M2) had potent insulin mimic activity on PEPCK expression. Secondly, possibility of both loganin and ursolic acid as the responsible compounds was excluded. Moreover, indication of the existence of phenolic compounds in CO-W-M2 was noticed. In the presence of CO-W-M2, not only was the viability of BRIN-BD11 cells treated with alloxan, streptozotcin, or cytokine mix all significantly increased but also glucose-stimulated insulin secretion was potentiated. Conclusions The ability of CO-W-M2 to reduce gene expression for hepatic gluconeogenesis, to protect β-cell against toxic challenge, and to enhance insulin secretion strengthen the role of Fructus Corni in diabetes therapy.

Inhibition of histone deacetylases prevents cytokine-induced toxicity in beta cells

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.

Inverse and distinct modulation of tau‐dependent neurodegeneration by presenilin 1 and amyloid‐β in cultured cortical neurons: evidence that tau phosphorylation is the limiting factor in amyloid‐β‐induced cell death

Alzheimer's disease (AD) is characterized by massive neuron loss in distinct brain regions, extracellular accumulations of the amyloid precursor protein-fragment amyloid-beta (A beta) and intracellular tau fibrils containing hyperphosphorylated tau. Experimental evidence suggests a relation between presenilin (PS) mutations, A beta formation, and tau phosphorylation in triggering cell death; however, how A beta and PS affect tau-dependent degeneration is unknown. Using herpes simplex virus 1-mediated gene-transfer of fluorescent-tagged tau constructs in primary cortical neurons, we demonstrate that tau expression exerts a neurotoxic effect that is increased with a construct mimicking disease-like hyperphosphorylation [pseudohyperphosphorylated (PHP) tau]. Live imaging revealed that PHP tau expression is associated with increased perikarya suggesting the development of a 'ballooned' phenotype as a specific feature of tau-mediated cell death. Transgenic expression of PS1 suppressed tau-induced neurodegeneration. In contrast, A beta amplified degeneration in the presence of wt tau but not of PHP tau. The data indicate that PS1 and A beta inversely modulate tau-dependent neurodegeneration at distinct steps. They indicate that the mode by which PHP tau causes neurotoxicity is downstream of A beta and that tau phosphorylation is the limiting factor in A beta-induced cell death. Suppression of tau expression or inhibition of tau phosphorylation at disease-relevant sites may provide an effective therapeutic strategy to prevent neurodegeneration in Alzheimer's disease.

P35/Cyclin-dependent kinase 5 is required for protection against β-amyloid-induced cell death but not tau phosphorylation by ceramide

Ceramide is a bioactive sphingolipid that can prevent calpain activation and beta-amyloid (A beta) neurotoxicity in cortical neurons. Recent evidence supports A beta induction of a calpain-dependent cleavage of the cyclin-dependent kinase 5 (cdk5) regulatory protein p35 that contributes to tau hyperphosphorylation and neuronal death. Using cortical neurons isolated from wild-type and p35 knockout mice, we investigated whether ceramide required p35/cdk5 to protect against A beta-induced cell death and tau phosphorylation. Ceramide inhibited A beta-induced calpain activation and cdk5 activity in wild-type neurons and protected against neuronal death and tau hyperphosphorylation. Interestingly, A beta also increased cdk5 activity in p35-/- neurons, suggesting that the alternate cdk5 regulatory protein, p39, might mediate this effect. In p35 null neurons, ceramide blocked A beta-induced calpain activation but did not inhibit cdk5 activity or cell death. However, ceramide blocked tau hyperphosphorylation potentially via inhibition of glycogen synthase kinase-3beta. These data suggest that ceramide can regulate A beta cell toxicity in a p35/cdk5-dependent manner.

Interferon-γ potentiates endoplasmic reticulum stress-induced death by reducing pancreatic beta cell defence mechanisms

A tight control of endoplasmic reticulum homeostasis is crucial for beta cell function and survival. We recently described that IL-1beta plus IFN-gamma deplete endoplasmic reticulum Ca2+ stores in beta cells, leading to endoplasmic reticulum stress and apoptosis. IL-1beta alone induced endoplasmic reticulum stress but failed to induce beta cell death, while IFN-gamma alone neither caused endoplasmic reticulum stress nor induced beta cell death. This suggests that IFN-gamma aggravates endoplasmic reticulum stress induced by IL-1beta, eventually triggering apoptosis. Here we tested this hypothesis and the mechanisms involved, by investigating the effects of IFN-gamma on endoplasmic reticulum-stress-induced beta cell apoptosis caused by a specific blocker of the sarcoendoplasmic-reticulum pump Ca2+-ATPase (SERCA). INS-1E cells or beta cells were pretreated with IFN-gamma and then exposed to the SERCA blocker cyclopiazonic acid (CPA) for induction of endoplasmic reticulum stress. Cell death was evaluated by Hoechst 342 and propidium iodide staining. Expression of genes related to endoplasmic reticulum stress was determined by real-time RT-PCR, while activation of the endoplasmic reticulum stress response was determined by analysing X-box binding protein-1 (Xbp1) splicing and using a reporter construct containing five copies of the unfolded protein response element (UPRE). CPA induces endoplasmic reticulum stress and apoptosis in insulin-producing cells. Pretreatment with IFN-gamma decreased the basal level of spliced Xbp1 mRNA, the basal and CPA-induced activity of the UPRE reporter, and the mRNA expression of several endoplasmic reticulum chaperones (Bip, Grp94 and Orp 150) and Sec61a. Furthermore, CPA-induced Chop mRNA expression and beta cell apoptosis were potentiated in cells that had been pretreated with IFN-gamma. CPA-induced endoplasmic reticulum stress and apoptosis is enhanced in IFN-gamma-treated beta cells. These effects are mediated via downregulation of the expression of genes involved in beta cell defence against endoplasmic reticulum stress.

Interleukin-1 Stimulates β-Cell Necrosis and Release of the Immunological Adjuvant HMGB1

BackgroundThere are at least two phases of β-cell death during the development of autoimmune diabetes: an initiation event that results in the release of β-cell-specific antigens, and a second, antigen-driven event in which β-cell death is mediated by the actions of T lymphocytes. In this report, the mechanisms by which the macrophage-derived cytokine interleukin (IL)-1 induces β-cell death are examined. IL-1, known to inhibit glucose-induced insulin secretion by stimulating inducible nitric oxide synthase expression and increased production of nitric oxide by β-cells, also induces β-cell death.Methods and FindingsTo ascertain the mechanisms of cell death, the effects of IL-1 and known activators of apoptosis on β-cell viability were examined. While IL-1 stimulates β-cell DNA damage, this cytokine fails to activate caspase-3 or to induce phosphatidylserine (PS) externalization; however, apoptosis inducers activate caspase-3 and the externalization of PS on β-cells. In contrast, IL-1 stimulates the release of the immunological adjuvant high mobility group box 1 protein (HMGB1; a biochemical maker of necrosis) in a nitric oxide-dependent manner, while apoptosis inducers fail to stimulate HMGB1 release. The release of HMGB1 by β-cells treated with IL-1 is not sensitive to caspase-3 inhibition, while inhibition of this caspase attenuates β-cell death in response to known inducers of apoptosis.Patient SummaryBackgroundType 1 diabetes (also called autoimmune diabetes or juvenile diabetes) is an autoimmune disease. For unknown reasons, at some point in childhood or adolescence, the body's own immune system starts attacking and destroying the insulin-producing islet cells in the pancreas. Once the majority of islet cells are destroyed, patients can no longer produce insulin to regulate their blood sugar and must depend on strict diets and insulin injections. Scientists are trying to understand the early events during the development of the disease. There are two fundamentally different kinds of cell death in cells of higher animals and humans, called apoptosis and necrosis. Apoptosis (also called programmed cell death) is an organized, clean way in which cells die without spilling their contents and without causing an inflammatory immune response. They are simply gobbled up by other cells that serve as the body's garbage collectors. Necrosis, on the other hand, is a more messy process and one that does activate the immune system and cause local inflammation.Why Was This Study Done?The scientists who did this study are interested in the early stages of islet cell death. Specifically, they wanted to know whether islet cells during the early events of autoimmune diabetes die via apoptosis or necrosis. Earlier experiments to address this question had yielded no clear-cut results.What Did the Researchers Do and Find?All the experiments for this study were done in cultured cells in the laboratory. For the most part, the researchers used rodent islet cells, and then they confirmed the crucial finding in human islet cells. They grew the cells under conditions that resembled, to the best of their knowledge, the early stages of diabetes, which caused some of the cells to die. They then did a variety of tests to see whether that cell death was through apoptosis or necrosis, and the results showed that the latter was the case. They also identified some of the key factors involved in promoting and executing the necrosis process.What Does This Mean?One must always be careful to extrapolate from laboratory results like these. With this caveat, the results suggest that early in the development of diabetes cells die by necrosis, and they point to some of the key factors involved. These are important results that will inform future studies toward the goal of understanding autoimmune diabetes well enough to prevent or stop its development.Where Can I Find More Information Online?The following Web sites provide information on autoimmune diabetes.MedlinePlus pages on type 1 diabetes: http://www.nlm.nih.gov/medlineplus/ency/article/000305.htm Web site of the Juvenile Diabetes Research Foundation: http://www.jdrf.org/index.cfm?page_id=101982 Pages on type 1 diabetes from the Canadian Diabetes Association: http://www.diabetes.ca/Section_About/type1.asp Type 1 diabetes pages from the UK National Institute for Health and Clinical Excellence: http://www.nice.org.uk/page.aspx?o=213575 UK National Diabetes Information Clearinghouse: http://diabetes.niddk.nih.gov/index.htm American Diabetes Association Web site: http://www.diabetes.org ConclusionsThese findings indicate that IL-1 induces β-cell necrosis and support the hypothesis that macrophage-derived cytokines may participate in the initial stages of diabetes development by inducing β-cell death by a mechanism that promotes antigen release (necrosis) and islet inflammation (HMGB1 release).

Amyloid Beta Peptide-Induced Cerebral Neuronal Loss Is Mediated By Caspase-3 In Vivo

Amyloid beta peptide (A beta) is widely believed to play a central and etiological role in Alzheimer disease (AD). A beta has been shown to have cytotoxic effects in neural cells, although the mechanism by which it does this is still unclear. To examine the involvement of the apoptotic cascade in A beta-induced cell death, we used mice deficient in caspase-3 (CPP 32), a key protease in this cascade. We microinjected A beta(1-40) into hippocampal regions of the brains of adult mice because AD is an adult-onset disease. We found significant cellular loss in the hippocampal regions of wild-type mice and dramatic rescue of neuronal cell death in caspase-3-deficient mice, with a gene dosage effect. In addition to adult mice, we observed little A beta-induced death of cultured neurons prepared from fetal brains of caspase-3-deficient mice but did observe death of such neurons from wild-type mice. The difference in A beta-induced neuronal death between wild-type and caspase-3-deficient mice was highly significant, indicating that A beta-induced neuronal death is mediated in vivo as well as in vitro by the caspase-3 apoptotic cascade.

Mechanisms of coxsackievirus B5 mediated beta-cell death depend on the multiplicity of infection.

Coxsackievirus infections may trigger and accelerate pancreatic beta-cell death, leading to type I diabetes. Unrestricted coxsackievirus B5 replication in cultured beta-cells inoculated with high multiplicity leads to rapid lytic cell death. Evidence from other virus-host cell systems indicates that host cell responses to infection may depend on the multiplicity of infection (MOI). Thus, the aim of this study was to compare the mechanisms of beta-cell death during high versus low multiplicity of coxsackievirus B5 infection. Cultures of highly differentiated mouse insulinoma cells and primary adult human islets were infected with coxsackievirus B5 at multiplicities of >1,000 or <0.5 TCID50 per cell. The results of nuclear morphology and viability stainings, TUNEL staining and electrophoretic DNA fragmentation analysis showed high multiplicity infection to predominantly induce necrosis and transient apoptosis. In low multiplicity culture, however, necrosis was only moderately induced and apoptosis increased steadily with time. This was best demonstrated by a tenfold higher apoptosis/necrosis ratio than after high multiplicity inoculation. Expression of gamma-glutamyl cysteine synthetase increased in both infective cultures but the level of intracellular glutathione permanently depleted only at high multiplicity and recovered fully at low multiplicity. Thus, apoptosis represents an important mechanism of beta-cell death after low multiplicity of coxsackievirus B5 infection. This process is associated with maintenance of a physiological intracellular glutathione profile differing dramatically from the high multiplicity infection during which necrosis dominates and intracellular thiol balance deteriorates. These data suggest that the pattern and mechanisms of coxsackievirus B5 infection induced beta-cell death depend on the MOI.

An oestrogen membrane receptor participates in estradiol actions for the prevention of amyloid-beta peptide1-40-induced toxicity in septal-derived cholinergic SN56 cells.

Although oestrogen [17 beta-estradiol (E2)]-related neuroprotection has been demonstrated in different models, the involvement of non-classical oestrogen receptors (ERs) remains unexplored. Using the SN56 cholinergic cell line, we present evidence indicating that an ER associated with the plasma membrane participates in oestrogen-dependent inhibition of cell death induced by amyloid-beta peptide (A beta) toxicity. Similarly to E2 alone, a 15-min exposure to estradiol-horseradish peroxidase (E-HRP) significantly reduced A beta-induced cell death. This effect was decreased by the ER antagonist ICI 182,780 as well as by MC-20 antibody directed to a region neighbouring the ligand-binding domain of ER alpha. Using confocal microscopy on unpermeabilized SN56 cells exposed to MC-20 antibody, we identified a protein at the plasma membrane level. Western blot analysis of purified SN56 cell membrane fractions using MC-20 antibody revealed the presence of one band with the same electrophoretic mobility as intracellular ER alpha. Using conjugated forms of the steroid, E-HRP and E2 conjugated to bovine serum albumin-FITC, we demonstrated by confocal microscopy that SN56 cells contain surface binding sites for E2. Binding of both conjugates was blocked by pre-incubation with E2 and decreased by either ICI 182,780 or MC-20 antibody in a concentration-dependent manner. Thus, a membrane-related ER that shares some structural homologies with ER alpha may participate in oestrogen-mediated neuroprotection.

Transmembrane TNF and IFNγ Induce Caspase-independent Death of Primary Mouse Pancreatic Beta Cells

Tumor necrosis factor (TNF) is important in the pathogenesis of autoimmune diabetes. It has an important role in immunological and inflammatory processes, and has also been shown to induce apoptotic cell death. We have shown that TNF+IFN n induce islet cell death in vitro . TNF exists as a biologically active transmembrane molecule (tmTNF), which is then cleaved to form soluble TNF (sTNF). We reasoned that sTNF, which has been used in previous studies, may not represent TNF in its physiological form. We compared the contributions of caspase activation and nitric oxide production to beta cell death induced by either tmTNF or sTNF together with IFN n . CHO cells transfected with a mutated TNF were used as a source of tmTNF. Either sTNF or tmTNF, together with IFN n, induced caspase-dependent cell death of the NIT-1 insulinoma cell line, as measured by DNA fragmentation and a fluorogenic caspase 3 activation assay. TNF+IFN n did not induce caspase 3 activation in primary mouse islets. Instead, iNOS gene expression was induced and cell death which was partly NO-dependent occurred. We conclude that the role of TNF in the development of type 1 diabetes is likely to be the activation of gene expression and not apoptosis. It appears that both tmTNF and sTNF act by a similar mechanism to induce beta cell death.

Mechanisms of β-Cell Death in Response to Double-Stranded (ds) RNA and Interferon-γ: dsRNA-Dependent Protein Kinase Apoptosis and Nitric Oxide-Dependent Necrosis

Viral infection is one environmental factor that has been implicated as a precipitating event that may initiate beta-cell damage during the development of diabetes. This study examines the mechanisms by which the viral replicative intermediate, double-stranded (ds) RNA impairs beta-cell function and induces beta-cell death. The synthetic dsRNA molecule polyinosinic-polycytidylic acid (poly IC) stimulates beta-cell DNA damage and apoptosis without impairing islet secretory function. In contrast, the combination of poly IC and interferon (IFN)-gamma stimulates DNA damage, apoptosis, and necrosis of islet cells, and this damage is associated with the inhibition of glucose-stimulated insulin secretion. Nitric oxide mediates the inhibitory and destructive actions of poly IC + IFN-gamma on insulin secretion and islet cell necrosis. Inhibitors of nitric oxide synthase, aminoguanidine, and N(G)-monomethyl-L-arginine, attenuate poly IC + IFN-gamma-induced DNA damage to levels observed in response to poly IC alone, prevent islet cell necrosis, and prevent the inhibitory actions on glucose-stimulated insulin secretion. N(G)-monomethyl-L-arginine fails to prevent poly IC- and poly IC + IFN-gamma-induced islet cell apoptosis. PKR, the dsRNA-dependent protein kinase that mediates the antiviral response in infected cells, is required for poly IC- and poly IC + IFN-gamma-induced islet cell apoptosis, but not nitric oxide-mediated islet cell necrosis. Alone, poly IC fails to stimulate DNA damage in islets isolated from PKR-deficient mice; however, nitric oxide-dependent DNA damage induced by the combination of poly IC + IFN-gamma is not attenuated by the genetic absence of PKR. These findings indicate that dsRNA stimulates PKR-dependent islet cell apoptosis, an event that is associated with normal islet secretory function. In contrast, poly IC + IFN-gamma-induced inhibition of glucose-stimulated insulin secretion and islet cell necrosis are events that are mediated by islet production of nitric oxide. These findings suggest that at least one IFN-gamma-induced antiviral response (islet cell necrosis) is mediated through a PKR-independent pathway.

Role of spermine in amyloid ?-peptide-associated free radical-induced neurotoxicity

The polyamines, relatively low-molecular-weight aliphatic compounds, are the main inducers of eukaryotic cell growth and proliferation. Although polyamine requirements for cell growth are well defined, their role is still enigmatic. We have previously reported that amyloid beta-peptide (A beta), the main constituent of senile plaques in Alzheimer's disease (AD) brain, is toxic to neurons through a free radical-dependent oxidative stress mechanism and that A beta(1--42), the principal form of A beta in AD brain, causes an increase in polyamine metabolism manifested by up-regulated polyamine uptake and increased ornithine decarboxylase (ODC) activity. Both effects were prevented by the free radical scavenger vitamin E. Spermine has been reported to function directly as a free radical scavenger. In the current study, we aimed to address whether up-regulation of polyamine metabolism is a defense against, or a result of, A beta-induced oxidative stress by investigating the capability of spermine to quench A beta-associated free radicals in solution and to assert a protective function of spermine in neuronal culture against A beta. Pretreatment of cultured neurons with spermine prior to A beta exposure failed to prevent A beta-induced cell death. Indeed, A beta plus spermine added to cultured neurons was even more neurotoxic than either agent alone. Additionally, inhibition of the polyamine synthesis by difluoromethylornithine (DFMO) did not protect cells from A beta-induced free radical toxicity, and stimulation of the synthesis of putrescine and spermine by the aminopropyltransferase inhibitor S-adenosyl-1,8-diamino-thiooctane (AdoDATO), rather, further enhanced A beta-induced toxicity. Although spermine is capable of scavenging free radicals generated by A beta in solution as measured by electron paramagnetic resonance (EPR) spectroscopy, the up-regulated transport of exogenously added spermine together with A beta may lead to overaccumulation of a cellular spermine pool, with resulting enhanced neurotoxicity.

Autoimmune insulitis and diabetes in the absence of antigen-specific contact between T cells and islet beta-cells.

Autoimmune diabetes develops following recognition of organ-specific antigens by T cells. The disease begins with peri-islet infiltration by mononuclear cells, proceeds with insulitis and becomes manifest with destruction of insulin-producing islet beta-cells. T cells are necessary to induce insulitis and diabetes, but it is not clear by what mechanisms they can do so, i. e. whether the T cells need to make antigen-specific contact with the beta-cell or whether other interactions are sufficient to induce beta-cell death. In the present study we have constructed chimeric mice in which the bone marrow-derived antigen-presenting cells, but not the islet beta-cells, are capable of presenting antigen to monospecific T cells. We show that both insulitis as well as beta-cell destruction can proceed in the absence of islet beta-cell surface antigen recognition by T cells. Our results support the notion that diabetes can be caused by distinct effector mechanisms.

Transfection of human pancreatic islets with an anti-apoptotic gene (bcl-2) protects beta-cells from cytokine-induced destruction.

Apoptosis has been identified as a mechanism of pancreatic islet beta-cell death in autoimmune diabetes. Proinflammatory cytokines are candidate mediators of beta-cell death in autoimmune diabetes, and these cytokines can induce beta-cell death by apoptosis. In the present study, we examined whether transfection of human islet beta-cells with an anti-apoptotic gene, bcl-2, can prevent cytokine-induced beta-cell destruction. Human islet beta-cells were transfected by a replication-defective herpes simplex virus (HSV) amplicon vector that expressed the bcl-2 gene (HSVbcl-2) and, as a control, the same HSV vector that expressed a beta-galactosidase reporter gene (HSVlac). Two-color immunohistochemical staining revealed that 95+/-3% of beta-cells transfected with HSVbcl-2 expressed Bcl-2 protein compared with 14+/-3% of beta-cells transfected with HSVlac and 19+/-4% of nontransfected beta-cells. The bcl-2-transfected beta-cells were fully protected from impaired insulin secretion and destruction resulting from incubation for 5 days with the cytokine combination of interleukin (IL)-1beta, tumor necrosis factor (TNF)-alpha, and interferon (IFN)-gamma. In addition, the bcl-2-transfected islet cells were significantly protected from cytokine-induced lipid peroxidation and DNA fragmentation. These results demonstrate that cytokine-induced beta-cell dysfunction and death involve mechanisms subject to regulation by an anti-apoptotic protein, Bcl-2. Therefore, bcl-2 gene therapy has the potential to protect human beta-cells in pancreatic islets, or islet grafts, from immune-mediated damage in type 1 diabetes.