Beta cell cytoprotection using lentiviral vector-based iNOS-specific shRNA delivery

Early Treatment with Empagliflozin and GABA Improves β-Cell Mass and Glucose Tolerance in Streptozotocin-Treated Mice

While the autoimmune character of T1D (type 1 diabetes) is being challenged, it is currently recognized that inflammation plays a key role in its development. We hypothesized that glucotoxicity could contribute to β-cell mass destruction through participation in islet inflammation. We evaluated the potential of empagliflozin (EMPA) and GABA (gamma-aminobutyric acid) to protect β-cell mass against glucotoxicity and to increase β-cell mass after diagnosis of T1D. Empagliflozin is a SGLT2 (sodium-dependent glucose cotransporter) inhibitor which thereby blocks glucose recapture by the kidney and promotes glucose excretion in urine. GABA is an inhibitory neurotransmitter, which stimulates α-to-β cell transdifferentiation. In streptozotocin-treated mice, empagliflozin and/or GABA were delivered for a period of five days or three weeks. As compared to untreated T1D mice, EMPA-treated T1D mice had decreased FFA (free fatty acid) levels and improved glucose homeostasis. EMPA-treated T1D mice had higher islet density, with preserved architecture, compared to T1D mice, and EMPA-treated T1D mice also differed from T1D mice by the total absence of immune cell infiltration within islets. Islets from EMPA-treated mice were also less subjected to ER (endoplasmic reticulum) stress and inflammation, as shown by qPCR analysis. Glucose homeostasis parameters and islet area/pancreas area ratio improved, as compared to diabetic controls, when T1D mice were treated for three weeks with GABA and EMPA. T1D EMPA+GABA mice had higher glucagon levels than T1D mice, without modifications of glucagon area/islet area ratios. In conclusion, empagliflozin and GABA, used in monotherapy in streptozotocin-induced diabetic mice, have positive effects on β-cell mass preservation or proliferation through an indirect effect on islet cell inflammation and ER stress. Further research is mandatory to evaluate whether empagliflozin and GABA may be a potential therapeutic target for the protection of β-cell mass after new-onset T1D.

Inducible nitric-oxide synthase and nitric oxide donor decrease insulin receptor substrate-2 protein expression by promoting proteasome-dependent degradation in pancreatic beta-cells: involvement of glycogen synthase kinase-3beta

Insulin receptor substrate-2 (IRS-2) plays a critical role in the survival and function of pancreatic β-cells. Gene disruption of IRS-2 results in failure of the β-cell compensatory mechanism and diabetes. Nonetheless, the regulation of IRS-2 protein expression in β-cells remains largely unknown. Inducible nitric-oxide synthase (iNOS), a major mediator of inflammation, has been implicated in β-cell damage in type 1 and type 2 diabetes. The effects of iNOS on IRS-2 expression have not yet been investigated in β-cells. Here, we show that iNOS and NO donor decreased IRS-2 protein expression in INS-1/832 insulinoma cells and mouse islets, whereas IRS-2 mRNA levels were not altered. Interleukin-1β (IL-1β), alone or in combination with interferon-γ (IFN-γ), reduced IRS-2 protein expression in an iNOS-dependent manner without altering IRS-2 mRNA levels. Proteasome inhibitors, MG132 and lactacystin, blocked the NO donor-induced reduction in IRS-2 protein expression. Treatment with NO donor led to activation of glycogen synthase kinase-3β (GSK-3β) and c-Jun N-terminal kinase (JNK/SAPK) in β-cells. Inhibition of GSK-3β by pharmacological inhibitors or siRNA-mediated knockdown significantly prevented NO donor-induced reduction in IRS-2 expression in β-cells. In contrast, a JNK inhibitor, SP600125, did not effectively block reduced IRS-2 expression in NO donor-treated β-cells. These data indicate that iNOS-derived NO reduces IRS-2 expression by promoting protein degradation, at least in part, through a GSK-3β-dependent mechanism. Our findings suggest that iNOS-mediated decreased IRS-2 expression may contribute to the progression and/or exacerbation of β-cell failure in diabetes.

RNA interference for improving the outcome of islet transplantation

Islet transplantation has the potential to cure type 1 diabetes. Despite recent therapeutic success, it is still not common because a large number of transplanted islets get damaged by multiple challenges including instant blood mediated inflammatory reaction, hypoxia/reperfusion injury, inflammatory cytokines, and immune rejection. RNA interference (RNAi) is a novel strategy to selectively degrade target mRNA. The use of RNAi technologies to downregulate the expression of harmful genes has the potential to improve the outcome of islet transplantation. The aim of this review is to gain a thorough understanding of biological obstacles to islet transplantation and discuss how to overcome these barriers using different RNAi technologies. This eventually will help improve islet survival and function post transplantation. Chemically synthesized small interferring RNA (siRNA), vector based short hairpin RNA (shRNA), and their critical design elements (such as sequences, promoters, and backbone) are discussed. The application of combinatorial RNAi in islet transplantation is also discussed. Last but not the least, several delivery strategies for enhanced gene silencing are discussed, including chemical modification of siRNA, complex formation, bioconjugation, and viral vectors.

Silencing inducible nitric oxide synthase protects rat pancreatic islet

OBJECTIVE

To investigate the effect of inducible nitric oxide synthase (iNOS) RNA interference on cytokine-induced injury of pancreatic islet in rats.

MATERIALS AND METHODS

Islets from Wistar rats were cultured in vitro and then randomly divided into five groups: group A, islets were cultured exclusively; group B, islets were transfected with negative control siRNA; group C, islets were transfected with iNOS siRNA; group D, islets were transfected with iNOS siRNA and then treated with TNF-alpha+IL-1beta; group E, islets were treated with TNF-alpha+IL-1beta. The expression of iNOS, Bax and Fas was determined by RT-PCR and Western blot. The viability of islet was examined by AO/EB staining and function was examined by glucose-stimulated insulin secretion (GSIS) assay.

RESULTS

The expression of iNOS and the promoting apoptosis gene Bax and Fas were significantly up-regulated by the induction of IL-1beta and TNF-alpha. Thus they led to apoptosis increase and the insulin secretion index decrease (1.87+/-0.31 vs 3.83+/-1.40, P<0.01). Silencing iNOS by RNAi prevented the up-regulation of Bax and Fas induced by cytokine, thus reduced apoptosis of islets and recovered the insulin secretion index (3.43+/-0.24 vs 1.87+/-0.31, P<0.01).

CONCLUSION

The apoptosis from cytokines to islets mediated by iNOS could be suppressed by RNA interference, which favors the survival and function of islets.

Oxidative stress and beta-cell dysfunction

Diabetes mellitus type 1 and 2 (T1DM and T2DM) are complex multifactorial diseases. Loss of beta-cell function caused by reduced secretory capacity and enhanced apoptosis is a key event in the pathogenesis of both diabetes types. Oxidative stress induced by reactive oxygen and nitrogen species is critically involved in the impairment of beta-cell function during the development of diabetes. Because of their low antioxidant capacity, beta-cells are extremely sensitive towards oxidative stress. In beta-cells, important targets for an oxidant insult are cell metabolism and K(ATP) channels. The oxidant-evoked alterations of K(ATP) channel activity seem to be critical for oxidant-induced dysfunction because genetic ablation of K(ATP) channels attenuates the effects of oxidative stress on beta-cell function. Besides the effects on metabolism, interference of oxidants with mitochondria induces key events in apoptosis. Consequently, increasing antioxidant defence is a promising strategy to delay beta cell failure in (pre)-diabetic patients or during islet transplantation. Knock-out of K(ATP) channels has beneficial effects on oxidant-induced inhibition of insulin secretion and cell death. Interestingly, these effects can be mimicked by sulfonylureas that have been used in the treatment of T2DM for many years. Loss of functional K(ATP) channels leads to up-regulation of antioxidant enzymes, a process that depends on cytosolic Ca(2+). These observations are of great importance for clinical intervention because they show a possibility to protect beta-cells at an early stage before dramatic changes of the secretory capacity and loss of cell mass become manifest and lead to glucose intolerance or even overt diabetes.

Gene expression and silencing for improved islet transplantation

Islet transplantation has great potential as an effective means of treating type 1 diabetes. However, its successful application greatly depends on the rapid revascularization of islets and prevention from their apoptotic cell death. We co-expressed human vascular endothelial growth factor (hVEGF) and human interleukin-1 receptor antagonist (hIL-1Ra) after transduction of human islets with Adv-hVEGF-hIL-1Ra. Since hepatocyte growth factor (HGF) increases beta-cell proliferation and promotes revascularization of islets, we also constructed Adv-hHGF-hIL-1Ra. There was dose and time dependent expression of hVEGF and hIL-1Ra or hHGF and hIL-1Ra by islets, which led to decrease in caspase-3 activity and apoptosis induced by a cocktail of TNF-alpha, IL-1beta and IFN-gamma. Compared to non-treated islets, transduction of islets with these bipartite Adv vectors prior to transplantation under the kidney capsules of diabetic NOD-SCID mice reduced the blood glucose levels, and increased serum insulin and c-peptide levels. Immunohistochemical staining of the islet bearing kidney sections was positive for human insulin, growth factor (hVEGF or hHGF) and von Willebrand factor. Transduction with Adv-caspase-3-shRNA also prevented islets from cytokine induced apoptosis and improved islet transplantation. In conclusion, bipartite Adv vector efficiently co-expressed both growth factor and antiapoptotic genes or shRNA targeting pro-apoptotic genes, decreases apoptosis and improves the outcome of islet transplantation.

Cytokine-induced beta-cell apoptosis is NO-dependent, mitochondria-mediated and inhibited by BCL-XL

Pro-inflammatory cytokines are implicated as the main mediators of beta-cell death during type 1 diabetes but the exact mechanisms remain unknown. This study examined the effects of interleukin-1beta (IL-1beta), interferon-gamma (IFNgamma) and tumour necrosis factor alpha (TNFalpha) on a rat insulinoma cell line (RIN-r) in order to identify the core mechanism of cytokine-induced beta-cell death. Treatment of cells with a combination of IL-1beta and IFNgamma (IL-1beta/IFNgamma)induced apoptotic cell death. TNFalpha neither induced beta-cell death nor did it potentiate the effects of IL-1beta, IFNgamma or IL-1beta/IFNgamma . The cytotoxic effect of IL-1beta/IFNgamma was associated with the expression of inducible nitric oxide synthase (iNOS) and production of nitric oxide. Adenoviral-mediated expression of iNOS (AdiNOS) alone was sufficient to induce caspase activity and apoptosis. The broad range caspase inhibitor, Boc-D-fmk, blocked IL-1beta/IFNgamma -induced caspase activity, but not nitric oxide production nor cell death. However, pre-treatment with L-NIO, a NOS inhibitor, prevented nitric oxide production, caspase activity and reduced apoptosis. IL-1beta/IFNgamma -induced apoptosis was accompanied by loss of mitochondrial membrane potential, release of cytochrome c and cleavage of pro-caspase-9, -7 and -3. Transduction of cells with Ad-Bcl-X(L) blocked both iNOS and cytokine-mediated mitochondrial changes and subsequent apoptosis, downstream of nitric oxide. We conclude that cytokine-induced nitric oxide production is both essential and sufficient for caspase activation and beta-cell death, and have identified Bcl-X(L) as a potential target to combat beta-cell apoptosis.

Nitric oxide mediates the survival action of IGF-1 and insulin in pancreatic beta cells

Generation of low levels of nitric oxide (NO) contributes to beta cell survival in vitro. The purpose of this study was to explore the link between NO and the survival pathway triggered by insulin-like growth factor-1 (IGF-1) and insulin in insulin producing RINm5F cells and in pancreatic islets. Results show that exposure of cells to IGF-1/insulin protects against serum deprivation-induced apoptosis. This action is prevented with inhibitors of NO generation, PI3K and Akt. Moreover, transfection with the negative dominant form of the tyrosine kinase c-Src abrogates the effect of IGF-1 and insulin on DNA fragmentation. An increase in the expression level of NOS3 protein and in the enzyme activity is observed following exposure of serum-deprived RINm5F cells to IGF-1 and insulin. Phosphorylation of IRS-1, IRS-2 and to less extent IRS-3 takes place when serum-deprived RINm5F cells and rat pancreatic islets are exposed to either IGF-1, insulin, or diethylenetriamine nitric oxide adduct (DETA/NO). In human islets, IRS-1 and IRS-2 proteins are present and tyrosine phosphorylated upon exposure to IGF-1, insulin and DETA/NO. Both rat and human pancreatic islets undergo DNA fragmentation when cultured in serum-free medium and IGF-1, insulin and DETA/NO protect efficiently from this damage. We then conclude that generation of NO participates in the activation of survival pathways by IGF-1 and insulin in beta cells.

The Rational Design of β Cell Cytoprotective Gene Transfer Strategies: Targeting Deleterious iNOS Expression

Islet transplantation represents a promising therapeutic strategy for the treatment of type 1 diabetes mellitus (T1DM) [Hakim and Papalois (Ann Ital Chir 75:1-7, 2004); Jaeckel et al. (Internist (Berl) 45:1268-1280, 2004); Sutherland et al. (Transplant Proc 36:1697-1699, 2004)]. The insulin-secreting pancreatic beta cells of the islet allograft are, however, subject to recurrent immune-mediated damage. Principal among the molecular culprits involved in this destructive process is the proinflammatory cytokine IL-1beta. IL-1beta-induced beta cell destruction may be mediated by the generation of NO and/or ROS, although the relative importance of NO and ROS in this process remains unclear. This study broadly encompassed three arms of investigation: the first of these was geared toward the establishment of a robust in vitro cell system for the study of IL-1beta-induced pathophysiology; the second arm aimed to provide a comparative analysis of the gene transfer profiles of the three most commonly used gene transfer vehicles, namely plasmid vectors, adenoviral vectors, and lentiviral vectors, in the aforementioned cell system; the final arm aimed to screen an array of potentially cytoprotective gene transfer strategies incorporating the optimal gene transfer vectors. Briefly, we established an in vitro beta cell system that accurately reflected primary beta cell cytokine-induced pathophysiology. That is, IL-1beta exposure (100 U/ml) induced a time-dependent decrease in rat insulinoma (RIN) cell viability, which coincided with an induction in iNOS expression and nitrite accumulation. Gene transfer studies using plasmid, adenoviral, or lentiviral vectors underscored the superiority of viral vector-based gene transfer strategies for the manipulation of this beta cell line. Using these vectors, we provide evidence that NF-kappaB-based iNOS inhibition confers significant protection against IL-1beta-induced damage whereas antioxidant overexpression fails to provide protection. Conferred cytoprotection was associated with a suppression of iNOS expression and nitrite accumulation. From a therapeutic standpoint, gene transfer strategies employing efficient viral vectors to target iNOS activation may harbour therapeutic potential in preserving beta cell survival against proinflammatory cytokine exposure.