Comparison of mRNA contents of interleukin-1 beta and nitric oxide synthase in pancreatic islets isolated from female and male nonobese diabetic mice

Identification of the inflammasome Nlrp1b as the candidate gene conferring diabetes risk at the Idd4.1 locus in the nonobese diabetic mouse

Type 1 diabetes in the NOD mouse model has been linked to >30 insulin-dependent diabetes (Idd) susceptibility loci. Idd4 on chromosome 11 consists of two subloci, Idd4.1 and Idd4.2. Using congenic analysis of alleles in NOD and NOD-resistant (NOR) mice, we previously defined Idd4.1 as an interval containing >50 genes that controlled expression of genes in the type 1 IFN pathway. In this study, we report refined mapping of Idd4.1 to a 1.1-Mb chromosomal region and provide genomic sequence analysis and mechanistic evidence supporting its role in innate immune regulation of islet-directed autoimmunity. Genetic variation at Idd4.1 was mediated by radiation-sensitive hematopoietic cells, and type 1 diabetes protection conferred by the NOR allele was abrogated in mice treated with exogenous type 1 IFN-β. Next generation sequence analysis of the full Idd4.1 genomic interval in NOD and NOR strains supported Nlrp1b as a strong candidate gene for Idd4.1. Nlrp1b belongs to the Nod-like receptor (NLR) gene family and contributes to inflammasome assembly, caspase-1 recruitment, and release of IL-1β. The Nlrp1b of NOR was expressed as an alternative spliced isoform that skips exon 9, resulting in a premature stop codon predicted to encode a truncated protein. Functional analysis of the truncated NOR Nlrp1b protein demonstrated that it was unable to recruit caspase-1 and process IL-1β. Our data suggest that Idd4.1-dependent protection from islet autoimmunity is mediated by differences in type 1 IFN- and IL-1β-dependent immune responses resulting from genetic variation in Nlrp1b.

IL-1β-Induced Mesenchymal Stem Cell Migration Involves MLCK Activation via PKC Signaling

Mesenchymal stem cells (MSCs) migrate via the bloodstream to sites of injury, possibly attracted by inflammatory cytokines. Although many cytokines can induce stem cell migration, the underlying mechanism is not fully understood. We found that tail vein-injected MSCs migrate to the pancreas in nonobese diabetic (NOD) mice. An ELISA assay revealed that hyperglycemic NOD mice have higher pancreatic levels of interleukin-1β (IL-1β) than normal NOD mice and that IL-1β stimulates MSC migration in a Transwell assay and electric cell-substrate impedance sensing system. Microarray analysis showed that myosin light chain kinase (MLCK) is involved in IL-1β-induced MSC migration, while Western blots showed that IL-1β stimulates MLCK expression and activation and that MLCK-siRNA transfection reduces MSC migration. Kinase inhibitors, chromatin immunoprecipitation, and a knockdown study revealed that IL-1β-induced MLCK expression is regulated by the PKCδ/NF-κB signaling pathway, and a kinase inhibitor study revealed that IL-1β-induced MLCK activation occurs via the PKCα/MEK/ERK signaling pathway. These results show that IL-1β released from the pancreas of hyperglycemic NOD mice induces MSC migration and that this is dependent on MLCK expression via the PKCδ/NF-κB pathway and on MLCK activation via the PKCα/MEK/ERK signaling cascade. This study increases our understanding of the mechanisms by which MSCs home to injury sites.

Aire deficiency causes increased susceptibility to streptozotocin-induced murine type 1 diabetes

Aire-deficient mice are a model of the human monogenic disorder autoimmune polyendocrine syndrome type I (APS I) characterized by a progressive autoimmune destruction of multiple endocrine glands such as the adrenal cortex, the parathyroids and the beta-cells of the pancreas. The disease is caused by mutations in the autoimmune regulator (AIRE) gene, a putative transcription factor expressed in thymic medullary epithelial cells and in antigen-presenting cells of the myeloid lineage in peripheral lymphoid organs. As Aire(-/-) mice do not spontaneously develop endocrinopathies, we wanted to evaluate the autoimmune multiple low-dose streptozotocin (MLDSTZ) diabetes model in Aire(-/-) mice. Surprisingly, Aire heterozygote mice were most susceptible to MLDSTZ-induced diabetes, whereas Aire(-/-) mice displayed an intermediate sensitivity to diabetes. Furthermore, Aire(-/-) macrophages produced higher levels of TNF-alpha and lower levels of IL-10 following streptozotocin stimulation, and Aire(-/-) mice developed a higher frequency of islet cells autoantibodies as a sign of increased activation. However, the number of islet infiltrating F4/80(+) Aire(-/-) macrophages was significantly decreased which was attributed to an increased susceptibility to streptozotocin cytotoxicity of Aire(-/-) macrophages. In conclusion, Aire(-/-) macrophages display an increased activation after STZ stimuli, but suffer from increased susceptibility to STZ cytotoxicity. These results support an important function of Aire in the control of peripheral tolerance through myeloid antigen-presenting cells.

Unraveling the Pathogenesis of Type 1 Diabetes with Proteomics: Present And Future Directions

Type 1 diabetes (T1D) is the result of selective destruction of the insulin-producing beta-cells in the pancreatic islets of Langerhans. T1D is due to a complex interplay between the beta-cell, the immune system, and the environment in genetically susceptible individuals. The initiating mechanism(s) behind the development of T1D are largely unknown, and no genes or proteins are specific for most T1D cases. Different pro-apoptotic cytokines, IL-1 beta in particular, are present in the islets during beta-cell destruction and are able to modulate beta-cell function and induce beta-cell death. In beta-cells exposed to IL-1 beta, a race between destructive and protective events are initiated and in susceptible individuals the deleterious events prevail. Proteins are involved in most cellular processes, and it is thus expected that their cumulative expression profile reflects the specific activity of cells. Proteomics may be useful in describing the protein expression profile and thus the diabetic phenotype. Relatively few studies using proteomics technologies to investigate the T1D pathogenesis have been published to date despite the defined target organ, the beta-cell. Proteomics has been applied in studies of differentiating beta-cells, cytokine exposed islets, dietary manipulated islets, and in transplanted islets. Although that the studies have revealed a complex and detailed picture of the protein expression profiles many functional implications remain to be answered. In conclusion, a rather detailed picture of protein expression in beta-cell lines, islets, and transplanted islets both in vitro and in vivo have been described. The data indicate that the beta-cell is an active participant in its own destruction during diabetes development. No single protein alone seems to be responsible for the development of diabetes. Rather the cumulative pattern of changes seems to be what favors a transition from dynamic stability in the unperturbed beta-cell to dynamic instability and eventually to beta-cell destruction.

IL-1 receptor deficiency slows progression to diabetes in the NOD mouse

Proinflammatory cytokines are believed to be important in pancreatic beta-cell destruction in the development of type 1 diabetes. They act by upregulation of genes including Fas and inducible nitric oxide synthase (iNOS), which have both been shown to lead to beta-cell death in vitro. We used mice deficient in the interleukin (IL)-1 receptor (IL-1R) to assess the contribution of IL-1 to different models of diabetes. IL-1R-deficient islets were protected from the damaging effects of tumor necrosis factor (TNF) and interferon (IFN)-gamma in vitro, and beta-cell expression of iNOS was reduced, suggesting that IL-1 mediates the induction of iNOS by TNF and IFN-gamma. IL-1 action was not required for induction of class I major histocompatibility complex or Fas by TNF and IFN-gamma. IL-1R-deficient nonobese diabetic (NOD) mice developed diabetes significantly slower than wild-type mice. IL-1R deficiency did not affect diabetes in 8.3 TCR transgenic NOD mice but prolonged the time to diabetes in BDC2.5 TCR transgenic NOD mice. We conclude that IL-1R deficiency slows progression to diabetes in NOD mice but on its own does not prevent diabetes.

Fas is detectable on beta cells in accelerated, but not spontaneous, diabetes in nonobese diabetic mice

Fas (CD95) is a potential mechanism of pancreatic beta cell death in type 1 diabetes. beta cells do not constitutively express Fas but it is induced by cytokines. The hypothesis of this study is that Fas expression should be measurable on beta cells for them to be killed by this mechanism. We have previously reported that up to 5% of beta cells isolated from nonobese diabetic (NOD) mice are positive for Fas expression by flow cytometry using autofluorescence to identify beta cells. We have now found that these are not beta cells but contaminating dendritic cells, macrophages, and B lymphocytes. In contrast beta cells isolated from NODscid mice that are recipients of T lymphocytes from diabetic NOD mice express Fas 18-25 days after adoptive transfer but before development of diabetes. Fas expression on beta cells was also observed in BDC2.5, 8.3, and 4.1 TCR-transgenic models of diabetes in which diabetes occurs more rapidly than in unmodified NOD mice. In conclusion, Fas is observed on beta cells in models of diabetes in which rapid beta cell destruction occurs. Its expression is likely to reflect differences in the intraislet cytokine environment compared with the spontaneous model and may indicate a role for this pathway in beta cell destruction in rapidly progressive models.

Strain dependent rat iNOS promoter activity--correlation to identified WT1 transcription factor binding site

The free radical nitric oxide (NO) has been implicated in cytokine mediated destruction of rat beta-cells in islets of Langerhans. Cytokine mediated NO production is associated with increased expression of the inducible nitric oxide synthase (iNOS). We have previously shown a strain dependent difference between Wistar Kyoto (WKY) and Brown Norway (BN) rats of IL-1beta mediated destruction of islets of Langerhans to be related to expression levels of iNOS and NO production. The aim of the present study was to clone and screen the iNOS gene promoter region from WKY and BN rats for polymorphisms and to functionally test such nucleotide differences. Within the total 2077 bp sequenced from both rat strains we identified three polymorphisms in two separate areas: (i) a GT-repeat polymorphism linked to (ii) a C/T polymorphisms, leading to a WT1 binding site approximately 1650bp upstream the BN iNOS promoter and (iii) a G/A SNP in exon 1. Apart from these polymorphisms the homology between all published rat iNOS sequences including the presently described are about 96%. Promoter activity was detected for both genes in a luciferase assay followed cloning of 2012 bp fragments and transient transfection into RIN cells. For both strains IL-1beta induced dose-dependent activity and strain dependent iNOS promoter activity was demonstrated when WT1 was co-expressed. To our knowledge, this is the first demonstration of functional WT1/iNOS promoter interaction. We conclude that the iNOS promoter is strain-dependently regulated which may relate to quantitatively as well as qualitatively strain dependent differences in transcription factor expression, in this study exemplified by WT1.

Role of nitric oxide synthase isoforms in glucose-stimulated insulin release

The role of islet constitutive nitric oxide synthase (cNOS) in insulin-releasing mechanisms is controversial. By measuring enzyme activities and protein expression of NOS isoforms [i.e., cNOS and inducible NOS (iNOS)] in islets of Langerhans cells in relation to insulin secretion, we show that glucose dose-dependently stimulates islet activities of both cNOS and iNOS, that cNOS-derived nitric oxide (NO) strongly inhibits glucose-stimulated insulin release, and that short-term hyperglycemia in mice induces islet iNOS activity. Moreover, addition of NO gas or an NO donor inhibited glucose-stimulated insulin release, and different NOS inhibitors effected a potentiation. These effects were evident also in K+-depolarized islets in the presence of the ATP-sensitive K+ channel opener diazoxide. Furthermore, our results emphasize the necessity of measuring islet NOS activity when using NOS inhibitors, because certain concentrations of certain NOS inhibitors might unexpectedly stimulate islet NO production. This is shown by the observation that 0.5 mmol/l of the NOS inhibitor N(G)-monomethyl-L-arginine (L-NMMA) stimulated cNOS activity in parallel with an inhibition of the first phase of glucose-stimulated insulin release in perifused rats islets, whereas 5.0 mmol/l of L-NMMA markedly suppressed cNOS activity concomitant with a great potentiation of the insulin secretory response. The data strongly suggest, but do not definitely prove, that glucose indeed has the ability to stimulate both cNOS and iNOS in the islets and that NO might serve as a negative feedback inhibitor of glucose-stimulated insulin release. The results also suggest that hyperglycemia-evoked islet NOS activity might be one of multiple factors involved in the impairment of glucose-stimulated insulin release in type II diabetes mellitus.

Immunoexpression of interleukin-1beta in pancreatic islets of NOD mice during cyclophosphamide-accelerated diabetes: co-localization in macrophages and endocrine cells and its attenuation with oral nicotinamide

During insulin-dependent diabetes mellitus, islet invading immune cells destroy beta cells over a prolonged asymptomatic pre-diabetic period. Cytokines synthesised and secreted by specific immune cells within the islet infiltrate may be crucial effectors of beta cell destruction or protection during the disease. Interleukin-1beta may be a key cytokine which may act in concert with other cytokines in initiating and/or promoting beta cell destruction. We have examined this hypothesis in NOD mice by assessing the intra-islet expression and co-localization of interleukin-1beta at different time-points following cyclophosphamide administration. We have also tested the effects of long-term oral nicotinamide given to NOD mice in suppressing intra-islet expression of the cytokine in this accelerated model. Cyclophosphamide was administered to day 95 female NOD mice. Pancreatic tissues were examined by dual-label confocal immunofluorescence microscopy for the expression and co-localization of interleukin-1beta at days 0, 4, 7, 11 and at onset of diabetes (day 14). Diabetes developed in 7/11 mice 14 days after administration of cyclophosphamide while nicotinamide completely prevented the disease. At day 0, interleukin-1beta immunolabelling was observed in selective intra-islet macrophages, several somatostatin cells and in a few beta cells. However, at day 4, it was seen mostly in somatostatin and some beta cells. At day 7, an increasing number of interleukin-1beta cells were observed within the islets and co-localized to several somatostatin cells, beta cells and macrophages. The mean number of intra-islet interleukin-1beta cells reached a peak at day 11 and was significantly higher than at day 7 (p = 0.05) and at day 14 (onset of diabetes; p = 0.03). At day 11, interleukin-1beta immunolabelling was also present in selective macrophages which co-expressed inducible nitric oxide synthase. At onset of diabetes, some macrophages, residual beta cells and somatostatin cells showed immunolabelling for the cytokine. Exposure of NOD mice to oral nicotinamide was associated with a considerably reduced expression of interleukin-1beta cells within the islet at day 11 (p = 0.002). We conclude that cylophosphamide treatment enhances the expression of interleukin-1beta in selective macrophages, somatostatin and beta cells during the course of the disease. Its expression reaches a maximum immediately prior to onset of diabetes. Interleukin-1beta present in intra-islet macrophages, somatostatin and beta cells may influence its expression by autocrine and paracrine means. Interleukin-1beta expression within islet macrophages may also up-regulate inducible nitric oxide synthase within the same macrophage or adjacent macrophage populations. These intra-islet molecular events may corroborate with other local cytotoxic processes leading to beta cell destruction. Oral nicotinamide may attenuate intra-islet expression of interleukin-1beta and thus inducible nitric oxide synthase during prevention of Type 1 diabetes in this animal model. The expression of interleukin-1beta in specific islet endocrine cell-types shown in this study requires further investigation.

Cytokine-induced functional suppression of microencapsulated rat pancreatic islets in vitro

BACKGROUND

It is likely that inflammatory cytokines are released near microencapsulated islets in vivo.

METHODS

Rates of insulin release or glucose oxidation were measured after culture of microencapsulated rat islets with interleukin (IL)-1beta and tumor necrosis factor-(TNF-alpha). Their ability to recover from IL-1beta-induced suppression was also investigated.

RESULTS

Microencapsulated islets were suppressed after exposure to IL-1beta, which was potentiated by TNF-alpha. After exposure to lower IL-1beta concentrations, microencapsulated islets had similar oxidation rates as corresponding controls. At higher concentrations, microencapsulated islets were more suppressed than nonencapsulated islets. Microencapsulated and control islets were able to recover from suppression after exposure to 2.5 U/ml of IL-1beta.

CONCLUSIONS

Microencapsulation using the present alginate/poly-L-lysine/alginate capsules does not protect islets against the detrimental effects of IL-1beta and TNF-alpha. Indeed, microencapsulated islets seem to be more susceptible to suppression at higher concentrations of IL-1beta. However, after exposure to a lower concentration of IL-1beta, microencapsulated islets can recover.

COX-2 inhibition prevents insulin-dependent diabetes in low-dose streptozotocin-treated mice

Insulin-dependent diabetes mellitus (IDDM) is an autoimmune disease believed to be caused by an inflammatory process in the pancreas leading to selective destruction of the beta cells. Inducible cyclooxygenase (COX-2) is expressed under inflammatory conditions and its product prostaglandin E(2) (PGE(2)) is an important inflammation mediator. We report here that administration of the selective COX-2 inhibitor NS-398 prevents the onset of diabetes in mice brought on by multiple low-doses of streptozotocin (STZ). Histological observations indicated that STZ-mediated destruction of beta cells was prevented by NS-398 treatment. Delayed (day 3) administration of NS-398 was also protective in this model. No protective effect was observed when NS-398 was administered prior to a high, toxic dose of STZ. These results demonstrate the critical importance of COX-2 activity in autoimmune destruction of beta cells, and point to the fact that COX-2 inhibition can potentially develop into a preventive therapy against IDDM.

Beta cell destruction in the development of autoimmune diabetes in the non-obese diabetic (NOD) mouse

In the non-obese diabetic (NOD) mouse model of Type 1 (insulin-dependent) diabetes, evidence suggests that pancreatic beta cells are destroyed in part by apoptotic mechanisms. The precise mechanisms of beta cell destruction leading to diabetes remain unclear. The NOD mouse has been studied to gain insight into the cellular and molecular mediators of beta cell death, which are discussed in this review. Perforin, secreted by CD8(+) T cells, remains one of the only molecules confirmed to be implicated in beta cell death in the NOD mouse. There are many other molecules, including Fas ligand and cytokines such as interferon-gamma, interleukin-1 and tumor necrosis factor-alpha, which may lead to beta cell destruction either directly or indirectly via regulation of toxic molecules such as nitric oxide. As beta cell death can occur in the absence of perforin, these other factors, in addition to other as yet unidentified factors, may be important in the development of diabetes. Effective protection of NOD mice from beta cell destruction may therefore require inhibition of multiple effector mechanisms.

Liposome-mediated transfer of IL-1 receptor antagonist gene to dispersed islet cells does not prevent recurrence of disease in syngeneically transplanted NOD mice

IL-1beta is cytotoxic to pancreatic beta-cells in vitro but its role in the vicinity of beta-cells in vivo is unknown. We explored whether liposome-mediated transfer of the interleukin 1 receptor antagonist (IL-1ra) gene to islet cells might prevent recurrence of disease in syngeneically transplanted non-obese diabetic (NOD) mice. NOD mouse islet cells were transfected using liposome-mediated gene transfer with a human IL-1ra cDNA construct and transplanted two days later to prediabetic NOD mice. Graft infiltration and destruction were monitored three, five and eight days posttransplantation by histology and determination of insulin and cytokine content. IL-1ra gene transfer resulted in transient expression of IL-1ra protein in islet cells in vitro as assessed by ELISA and of IL-1ra mRNA in transplanted islets as revealed by RT-PCR. However, both control and IL-1ra transfected NOD grafts exhibited massive infiltration and loss of insulin-positive cells, paralleled by a decreased insulin content. Increased IL-1ra expression did not clearly affect other cytokine profiles (IL-1beta, IFN-gamma, IL-2), except for an increase of IL-10 on day eight. In conclusion, liposome-mediated IL-1ra gene transfer to mouse islet cells results in transient expression of IL-1ra which is, however, insufficient to confer resistance to destruction of grafted insulin-producing cells in the NOD mouse.

Temporal relationship between immune cell influx and the expression of inducible nitric oxide synthase, interleukin-4 and interferon-gamma in pancreatic islets of NOD mice following adoptive transfer of diabetic spleen cells

Beta cell destruction in NOD mice can be accelerated by adoptive transfer of diabetic spleen cells into irradiated adult NOD mice. Here mice receiving diabetic spleen cells were examined at days 0, 7, 14, 21 and at onset of diabetes for the resulting insulitis and the number of intra-islet CD4 and CD8 cells and macrophages. The progression of insulitis and the number of intra-islet CD4 and CD8 cells and macrophages were correlated with the expression and co-localization of inducible nitric oxide synthase, interferon-gamma and interleukin-4 by dual-label light and confocal immunofluorescence microscopy. Diabetes developed in 7/8 mice by 27 days following cell transfer. The insulitis score increased slightly by day 7 but rose sharply at day 14 (p = 0.001) and was maintained until diabetes. The mean number of intra-islet CD4 and CD8 cells and macrophages showed a similar trend to the insulitis scores and were present in almost equal numbers within the islets. Immunolabelling for inducible nitric oxide synthase was observed at day 7 in only some cells of a few islets but increased sharply from day 14. It was restricted to islets with insulitis and was co-localized in selective macrophages. Weak intra-islet interleukin-4 labelling was observed at days 7 and 14 but became more pronounced at day 21 and at onset of diabetes, being present in selective CD4 cells. Intra-islet labelling for interferon-gamma was first observed at day 21, but became more intense at onset of diabetes and was co-localized in a proportion of macrophages. Both cytokines were expressed in islets with advanced insulitis. Interferon-gamma staining was also observed within endothelial cells located in the exocrine pancreas. We conclude that transfer of diabetic spleen cells results in a rapid influx of CD4 and CD8 cells and macrophages within the pancreas of recipient mice. During the period of heightened insulitis, selective immune cells begin to express inducible nitric oxide synthase and the opposing cytokines, interferon-gamma and interleukin-4. Expression of these molecules becomes more pronounced immediately prior to and during the onset of diabetes.

Effect of cyclosporin-A on the blood--retinal barrier permeability in streptozotocin-induced diabetes

BACKGROUND

Our previous results showed that in retinas from streptozotocin (STZ)-induced diabetic rats there is an increased level of interleukin-1beta (IL-1beta). This cytokine may be involved in the expression of the inducible isoform of the nitric oxide synthase (iNOS), with consequent synthesis of large amounts of NO and blood-retinal barrier (BRB) breakdown.

AIMS

The aim of this work was to examine whether the administration of cyclosporin-A (Cs-A) to STZ-induced diabetic rats inhibits the synthesis of IL-1beta and the expression of the inducible proteins, iNOS and cyclo-oxygenase-2 (COX-2) in retinal cells, and whether the activity of these proteins contribute to BRB breakdown.

METHODS

The level of IL-1beta was evaluated by ELISA and the NO production by L-[3H]-citrulline formation. Expression of iNOS and COX-2 proteins was determined by two methods, western blot and immunohistochemistry. The permeability of the BRB was assessed by quantification of the vitreous protein.

RESULTS AND DISCUSSION

Our results indicated that the levels of IL-1beta and NO in retinas from Cs-A-treated diabetic rats are significantly reduced, as compared to that in non-treated diabetic rats. The treatment of diabetic rats with Cs-A also significantly inhibited the expression of the inducible proteins, iNOS and COX-2. The evaluation of the vitreous protein content revealed that Cs-A also reduces the BRB permeability. Taken together, these results suggest that the increased production of the inflammatory mediators, IL-1beta and NO, in diabetes may affect the BRB permeability and therefore contribute to the development of diabetic retinopathy.

Novel experimental strategies to prevent the development of type 1 diabetes mellitus

Type 1 diabetes is an autoimmune disease leading to extensive destruction of the pancreatic beta-cells. Our research focusses on the role of beta-cells during the course of the disease, aiming at finding novel strategies to enhance beta-cell resistance against the cytotoxic damage inflicted by the immune system. Special attention has been paid to the possibility that cytokines released by the immune cells infiltrating the pancreatic islets can directly suppress and kill beta-cells. Certain cytokines (interleukin-1beta, tumor necrosis factor-alpha and interferon-gamma) either alone or in combination, are able to activate signal transduction pathways in beta-cells leading to transcription factor activation and de novo gene expression. In this context, it has been found that induction of inducible nitric oxide synthase mediates an elevated production of nitric oxide, which impairs mitochondrial function and causes DNA damage eventually leading to apoptosis and necrosis. However, other induced proteins SUCH AS heat shock protein 70 and superoxide dismutase may reflect a defense reaction elicited in the beta-cells by the cytokines. Our strategy is to further seek for proteins involved in both destruction and protection of beta-cells. Based on this knowledge, we plan to apply gene therapeutic approaches to increase expression of protective genes in beta-cells. If this is feasible we will then evaluate the function and survival of such modified beta-cells in animal models of type 1 diabetes such as the NOD mouse. The long-term goal for this research line is to find novel approaches to influence beta-cell resistance in humans at risk of developing type 1 diabetes.

L-arginine transport in retinas from streptozotocin diabetic rats: correlation with the level of IL-1 beta and NO synthase activity

Several evidences suggest that the pro-inflammatory cytokines IL-1 beta and the radical NO are implicated as effectors molecules in the pancreatic beta-cells dysfunction; an event preceding the pathogenesis of diabetes. IL-1 beta induces the expression of the inducible isoform of NO synthase (iNOS), which use L-arginine as substrate to overproduce NO. However, it is not known whether these events may participate in the development of diabetic retinopathy, which is the main cause of blindness. In this work, we found an increased level of IL-1 beta in retinas from streptozotocin-induced (STZ) diabetic rats. We also observed that the activity of the NO synthase (NOS) and the L-arginine uptake are enhanced in retinas from STZ-induced diabetic rats as compared to retinas from control rats. We found that the uptake of L-arginine in retinas from control and diabetic rats occurs through a transporter resembling the Y + system, i.e. it is saturable, not affected over the pH range 6.5 to 7.4, and is independent of the extracellular Na+. Nevertheless, the L-arginine transport in retinas from diabetic rats occurs through a carrier with lower affinity (K(m) = 25 microM) and higher capacity (Vmax = 295 +/- 22.4 pmol L-arginine/mg protein) than in retinas from control rats (K(m) = 5 microM and Vmax = 158 +/- 12.8 pmol L-arginine/mg protein) which is correlated with the increased NOS activity and consequent depletion of the intracellular pool of L-arginine.

Nitric oxide mediates IL-1beta stimulation of heat shock protein but not IL-1beta inhibition of glutamic acid decarboxylase

Interleukin-1beta (IL-1beta) has been implicated to play an important role in the autoimmune beta cell lesion of insulin-dependent diabetes mellitus (IDDM) because of its inhibition of insulin secretion, direct islet cytotoxicity and alteration of islet cell antigen expression. We have previously demonstrated that IL-1beta inhibits glutamic acid decarboxylase-65 (GAD-65) and increases heat shock protein-70 (HSP-70) expression in islet cells. IL-1beta stimulates the inducible form of nitric oxide (NO) synthase and the resultant increased NO mediates many of IL-1beta's effects. In this study we investigated the role of the NO pathway in mediating the effects of IL-1beta on GAD-65 and HSP-70 expression and on insulin secretion. Islets isolated from Sprague-Dawley rats were cultured with IL-1beta and aminoguanidine (AG), an inhibitor of inducible NO synthase, individually and in combination for 24 h. Accumulated nitrite production, insulin release and islet expression of GAD-65 and HSP-70 were measured. We found that (1) IL-1beta at 10 U/ml increased nitrite production, inhibited insulin release, increased HSP-70 expression and decreased GAD-65 expression. (2) AG alone at 1 mM/ml had no effect on nitrite production, insulin release, GAD-65 and HSP-70 expression. (3) In combination, AG completely blocked IL-1beta increased nitrite production, reversed IL-1beta inhibited insulin release by approximately 50%, completely reversed IL-1beta increased HSP-70 expression, but did not reverse IL-1beta inhibited GAD-65 expression. Our findings indicate that the effect of IL-1beta on HSP-70 expression is mediated by NO production, whereas a NO-independent pathway is involved in the effect of IL-1beta on GAD-65 expression and insulin secretion.

Evidence That β Cell Death in the Nonobese Diabetic Mouse Is Fas Independent

Recent studies suggest that Fas expression on pancreatic β cells may be important in the development of autoimmune diabetes in the nonobese diabetic (NOD) mouse. To address this, pancreatic islets from NOD mice were analyzed by flow cytometry to directly identify which cells express Fas and Fas ligand (FasL) ex vivo and after in vitro culture with cytokines. Fas expression was not detected on β cells isolated from young (35 days) NOD mice. In vitro, incubation of NOD mouse islets with both IL-1 and IFN-γ was required to achieve sufficient Fas expression and sensitivity for islets to be susceptible to lysis by soluble FasL. In islets isolated from older (≥125 days) NOD mice, Fas expression was detected on a limited number of β cells (1–5%). FasL was not detected on β cells from either NOD or Fas-deficient MRLlpr/lpr islets. Also, both NOD and MRLlpr/lpr islets were equally susceptible to cytokine-induced cell death. This eliminates the possibility that cytokine-treated murine islet cells commit “suicide” due to simultaneous expression of Fas and FasL. Last, we show that NO is not required for cytokine-induced Fas expression and Fas-mediated apoptosis of islet cells. These findings indicate that β cells can be killed by Fas-dependent cytotoxicity; however, our results raise further doubts about the clinical significance of Fas-mediated β cell destruction because few Fas-positive cells were isolated immediately before the development of diabetes.

Pancreatic islet blood perfusion in the nonobese diabetic mouse: diabetes-prone female mice exhibit a higher blood flow compared with male mice in the prediabetic phase

The present study tested the hypothesis that changes in pancreatic islet blood flow correlate with the difference in diabetes incidence between male and female nonobese diabetic (NOD) mice. The blood flows were determined by a microsphere technique. In animals aged 10 and 14 weeks, the islet blood perfusion was 3-fold higher in female NOD mice compared with that in either age-matched male NOD mice or age- and sex-matched control ICR mice. At 5 weeks of age islet blood flow was similar in all groups. No differences between male and female NOD mice in whole pancreatic, duodenal, ileal, or colonic blood flows were observed at any time point. Administration of a bolus dose of aminoguanidine (a blocker of inducible nitric oxide synthase) to 10-week-old animals selectively and markedly decreased islet blood flow in female NOD mice, whereas islet blood flow in ICR mice and male NOD mice remained unaffected. Aminoguanidine did not affect mean arterial blood pressure or whole pancreatic blood flow in any of the groups. Injection of N(G)-methyl-L-arginine, an unspecific inhibitor of both constitutive and inducible nitric oxide synthase, markedly decreased whole pancreatic and islet blood flow to the same level in both male and female NOD mice. These combined findings suggest that diabetes-prone female NOD mice have an increased islet blood flow, which is mediated by an excessive production of nitric oxide formed by inducible nitric oxide synthase. The islet blood hyperperfusion may augment homing to the pancreatic islets of inflammatory cells and soluble factors involved in beta-cell destruction during the development of insulin-dependent diabetes mellitus in this animal model. The presently observed gender difference in the blood flow response could, therefore, at least partially explain why female NOD mice are more prone to develop hyperglycemia than the males.

Cellular and molecular mechanisms for the initiation and progression of beta cell destruction resulting from the collaboration between macrophages and T cells

Insulin-dependent diabetes mellitus (IDDM) is caused by the progressive autoimmune destruction of insulin-producing pancreatic beta cells. Although the pathogenesis of autoimmune IDDM has been extensively studied, the precise mechanisms involved in the initiation and progression of beta cell destruction remain unclear. Animal models used in the study of IDDM, such as the BioBreeding (BB) rat and the nonobese diabetic (NOD) mouse, have greatly enhanced our understanding of the pathogenic mechanisms involved in this disease. In these animals, macrophages and/or dendritic cells are the first cell types to infiltrate the pancreatic islets. Macrophages must be involved in the pathogenesis of IDDM early on, since inactivation of macrophages results in the near-complete prevention of insulitis and diabetes in both NOD mice and BB rats. The presentation of beta cell-specific autoantigens by macrophages and/or dendritic cells to CD4+ T helper cells, in association with MHC class II molecules, is considered the initial step in the development of autoimmune IDDM. The activated macrophages secrete IL-12, which stimulates Th1 type CD4+ T cells. The CD4+ T cells secrete IFN-gamma and IL-2. IFN-gamma activates other resting macrophages, which, in turn, release cytokines, such as IL-1beta, TNF-alpha, and free radicals, which are toxic to beta cells. During this process, IL-2 and other cytokines induce the migration of CD8+ peripheral T cells to the inflamed islets, perhaps by inducing the expression of a specific homing receptor. The precytotoxic CD8+ T cells that bear beta cell-specific autoantigen receptors differentiate into cytotoxic effector T cells upon recognition of the beta cell-specific peptide bound to MHC class I molecules in the presence of beta cell-specific CD4+ T helper cells. The cytotoxic CD8+ T cells then effect beta cell damage by releasing perforin and granzyme, and by Fas-mediated apoptosis. In this way, macrophages, CD4+ T cells, and CD8+ T cells synergistically destroy beta cells, resulting in the onset of autoimmune IDDM.

Characterization of the changing lymphocyte populations and cytokine expression in the exocrine tissues of autoimmune NOD mice

NOD mice develop chronic lymphocytic invasion of the pancreas, submandibular, and lacrimal glands leading to loss of insulin secretion, salivary flow, and tear production. In this study, we have used flow cytometric analyses and RT-PCR to track glandular lymphocyte populations and cytokine expression spanning the initiation of autoimmune infiltration through the development of widespread autoimmune destruction of the salivary and lacrimal glands of NOD mice. Results demonstrate a predominance of CD4+ to CD8+ lymphocytes and a similar predominance of T-cells versus B-cells in both the submandibular and lacrimal gland infiltrates. A temporal increase in memory (CD3+CD45RBlo) T-cells was also detected; however, naive (CD3+CD45RBhi) T-cell populations as well as a CD3+, CD4-/CD8- double negative population were also present. In addition, a skewing of the TCR Vbeta repertoire toward Vbeta6+ and Vbeta8+ lymphocytes was evident in both glandular infiltrates. Analyses of cytokine mRNA expression in the submandibular glands demonstrated an increase between 12 and 16 wk of age of several proinflammatory cytokines including IL-1beta, IL-6, IL-7, IL-10, IFNgamma, TNFalpha, and inducible Nitric Oxide Synthase (iNOS). IL-4 synthesis was notably absent in both tissues. Cytokine mRNA transcripts detected in lacrimal tissue were similar to those seen in the submandibular glands but appeared both earlier and more intensely. These findings depict the progressive development of autoimmune exocrinopathy and can be used as a foundation to explore the similarities and potential differences in the immunopathogenic lesions of several distinct tissues within the same host.

Inducible nitric oxide synthase in pancreatic islets of the non-obese diabetic mouse: a light and confocal microscopical study of its ontogeny, co-localization and up-regulation following cytokine administration

Nitric oxide has been shown to mediate beta-cell destruction in rodent islets exposed to interleukin 1 beta in culture. The inhibitory effect is potentiated by tumour necrosis factor-alpha and interferon-gamma. Cytokine stimulation leads to gene transcription and translation of inducible nitric oxide synthase, the biosynthetic enzyme of nitric oxide. In the non-obese diabetic mouse, progressive invasion of pancreatic islets by immune cells may lead to local production of inflammatory cytokines, resulting in inducible nitric oxide synthase expression within the islets. In this study, the ontogeny of this enzyme and its cellular expression were examined in pancreatic sections of female non-obese diabetic mice by double-label immunofluorescence. Light and confocal microscopy were employed to study the up-regulation, co-localization and immunocytoplasmic distribution of the enzyme in female non-obese, diabetic and Swiss mice following cytokine treatment. From day 40 to day 220 a small number of beta-cells and a proportion of macrophages, usually in peri-islet and exocrine areas, expressed the enzyme. At onset of diabetes, an increasing number of macrophages within and surrounding the islets were positive for the enzyme. Treatment of day 60 female non-obese diabetic mice with interleukin 1 beta alone and in combination with tumour necrosis factor-alpha and/or interferon-gamma resulted in a significant influx of macrophages into the pancreas, while this was lower in female Swiss mice treated similarly. Cytokine administration led to intense but sometimes eccentric immunocytoplasmic labelling for the enzyme in a considerable proportion of macrophages and beta-cells. Macrophages positive for inducible nitric oxide synthase were located in peri- and intra-islet areas, being distal and adjacent to enzyme-positive and negative beta-cells. Treatment with tumour necrosis factor-alpha and/or interferon-gamma did not lead to enzyme up-regulation. These results show that in the non-obese diabetic mouse there is low and sustained expression of islet inducible nitric oxide synthase in the prediabetic period, which is followed by an increase around onset. However, treatment of female non-obese diabetic and Swiss mice with interleukin-1 beta, alone or together with tumour necrosis factor-alpha and/or interferon-gamma leads to a marked expression of this enzyme within macrophages and beta-cells.

Insulin-like growth factor-1 (IGF-1) protects NOD mice from insulitis and diabetes

To evaluate the effect of IGF-1 on the autoimmune process of beta cell destruction, permissive non-obese diabetic (NOD) recipients were adoptively transferred with 7 x 10(6) autoreactive T cells from diabetic NOD mice and were administered subcutaneously 10 micrograms rhIGF-1, twice daily for 3 weeks. Administration of rhIGF-1 reduced the final incidence of successful transfers of diabetes observed in only 6/24 mice (25%) versus 12/21 (57%) in control mice. A marked reduction of insulitis during histological analysis of pancreatic glands was also observed. Mice treated with rhIGF-1 had a higher percentage of intact islets (48.6 +/- 12% versus 1.6 +/- 1.1%, P = 0.001) and a lower percentage of infiltrated islets. Islets from rhIGF-1-treated mice had a more intense insulin staining reflecting a higher beta cell mass, but no difference was observed in the amount of insulin content of pancreatic extracts and in the amounts of mRNA transcripts for proinsulin. No difference was also observed in the titres of three islet cell antibody (ICA)-positive sera and in the pattern of A2B5 staining. Some mice developed diabetes and severe islet cell infiltration despite rhIGF-1, thus indicating that some committed T cells were still able to invade the islets and cause beta cell destruction. The percentages of CD4+ and CD8+ T cells in the spleen of experimental mice were similar. To evaluate the effects of rhIGF-1 on cell trafficking in recipient mice, T cells from diabetic NOD Thy-1,2 mice injected into congenic NOD-N Thy-1,1 mice were monitored 3 weeks after adoptive cell transfer. The percentage of Thy-1,2+ T cells was significantly reduced in the spleen (10.8 +/- 1.3% versus 17.2 +/- 3.9%, P = 0.004) of rhIGF-1 treated mice in contrast to the thymus (68.4 +/- 7.9% versus 72.87 +/- 6.2%, P = 0.306), suggesting that rhIGF-1 could influence T cell trafficking to the lymphoid organs. The findings that rhIGF-1 has protective effects in autoimmune diabetes opens new perspectives for future experiments as well as for preventive strategies in human type I diabetes.

Effects of prolonged exposure in vitro to interferon-gamma and tumour necrosis factor-alpha on nitric oxide and insulin production of rat pancreatic islets

It has been postulated that cytokines may mediate the beta-cell destructive process causing insulin-dependent diabetes mellitus. The aim of this investigation was to study cytokine effects on pancreatic islet functions in vitro. For this purpose 5-7 days precultured (medium RPMI 1640 +/- 10% fetal calf serum) rat pancreatic islets were exposed for another 48 h to either culture medium alone or with addition of rat interferon-gamma (IFN-gamma; 1000 U/ml), or human tumor necrosis factor-alpha (TNF-alpha; 1000 U/ml) or a combination of the cytokines. After the culture period the islets were subjected to short-term experiments in the absence of cytokines. Neither the DNA nor the insulin content of the islets were affected by the cytokines alone or by the combination. The combination IFN-gamma + TNF-alpha caused a 5-fold increase in the medium nitrite accumulation, indicating induction of nitric oxide formation. It was found that IFN-gamma reduced medium insulin accumulation and basal insulin secretion at 1.7 mM glucose, without affecting the medium nitrite level. On the other hand, the islet glucose oxidation rate at 16.7 mM glucose and the insulin secretory response to 16.7 mM glucose was normal or even increased when examined after 48 h. TNF-alpha alone had no significant effects. In conclusion, a combination of the cytokines can induce nitric oxide formation and inhibition of insulin production in rat pancreatic islets. However, this effect appears not to be sustained. Moreover, IFN-gamma alone seems to induce changes not related to nitric oxide.