Gene silencing in the endocrine pancreas mediated by short-interfering RNA

Insulin secretion deficits in a Prader-Willi syndrome β-cell model are associated with a concerted downregulation of multiple endoplasmic reticulum chaperones

Prader-Willi syndrome (PWS) is a multisystem disorder with neurobehavioral, metabolic, and hormonal phenotypes, caused by loss of expression of a paternally-expressed imprinted gene cluster. Prior evidence from a PWS mouse model identified abnormal pancreatic islet development with retention of aged insulin and deficient insulin secretion. To determine the collective roles of PWS genes in β-cell biology, we used genome-editing to generate isogenic, clonal INS-1 insulinoma lines having 3.16 Mb deletions of the silent, maternal- (control) and active, paternal-allele (PWS). PWS β-cells demonstrated a significant cell autonomous reduction in basal and glucose-stimulated insulin secretion. Further, proteomic analyses revealed reduced levels of cellular and secreted hormones, including all insulin peptides and amylin, concomitant with reduction of at least ten endoplasmic reticulum (ER) chaperones, including GRP78 and GRP94. Critically, differentially expressed genes identified by whole transcriptome studies included reductions in levels of mRNAs encoding these secreted peptides and the group of ER chaperones. In contrast to the dosage compensation previously seen for ER chaperones in Grp78 or Grp94 gene knockouts or knockdown, compensation is precluded by the stress-independent deficiency of ER chaperones in PWS β-cells. Consistent with reduced ER chaperones levels, PWS INS-1 β-cells are more sensitive to ER stress, leading to earlier activation of all three arms of the unfolded protein response. Combined, the findings suggest that a chronic shortage of ER chaperones in PWS β-cells leads to a deficiency of protein folding and/or delay in ER transit of insulin and other cargo. In summary, our results illuminate the pathophysiological basis of pancreatic β-cell hormone deficits in PWS, with evolutionary implications for the multigenic PWS-domain, and indicate that PWS-imprinted genes coordinate concerted regulation of ER chaperone biosynthesis and β-cell secretory pathway function.

Intracellular ATP Signaling Contributes to FAM3A-Induced PDX1 Upregulation in Pancreatic Beta Cells

FAM3A is a recently identified mitochondrial protein that stimulates pancreatic-duodenal homeobox 1 (PDX1) and insulin expressions by promoting ATP release in islet β cells. In this study, the role of intracellular ATP in FAM3A-induced PDX1 expression in pancreatic β cells was further examined. Acute FAM3A inhibition using siRNA transfection in mouse pancreatic islets significantly reduced PDX1 expression, impaired insulin secretion, and caused glucose intolerance in normal mice. In vitro , FAM3A overexpression elevated both intracellular and extracellular ATP contents and promoted PDX1 expression and insulin secretion. FAM3A-induced increase in cellular calcium (Ca ²⁺ ) levels, PDX1 expression, and insulin secretion, while these were significantly repressed by inhibitors of P2 receptors or the L-type Ca ²⁺ channels. FAM3A-induced PDX1 expression was abolished by a calmodulin inhibitor. Likewise, FAM3A-induced β-cell proliferation was also inhibited by a P2 receptor inhibitor and an L-type Ca ²⁺ channels inhibitor. Both intracellular and extracellular ATP contributed to FAM3A-induced PDX1 expression, insulin secretion, and proliferation of pancreatic β cells.

miRNAs: Nanomachines That Micromanage the Pathophysiology of Diabetes Mellitus

Diabetes mellitus (DM) refers to a combination of heterogeneous complex metabolic disorders that are associated with episodes of hyperglycemia and glucose intolerance occurring as a result of defects in insulin secretion, action, or both. The prevalence of DM is increasing at an alarming rate, and there exists a need to develop better therapeutics and prognostic markers for earlier detection and diagnosis. In this review, after giving a brief introduction of diabetes mellitus and microRNA (miRNA) biogenesis pathway, we first describe various in vitro and animal model systems that have been developed to study diabetes. Further, we elaborate on the significant roles played by miRNAs as regulators of gene expression in the context of development of diabetes and its secondary complications. The different approaches to quantify miRNAs and their potential to be used as therapeutic targets for alleviation of diabetes have also been discussed.

CARD9 gene silencing with siRNA protects rats against severe acute pancreatitis: CARD9-dependent NF-κB and P38MAPKs pathway

We previously reported the up‐regulation of caspase recruitment domain 9 (CARD9) expressions in severe acute pancreatitis (SAP) patients, but little is known about its regulation. In this study, small interfering RNA (siRNA) was used to reduce the levels of CARD9 expression in sodium taurocholate‐stimulated SAP rats. CARD9 was overexpressed in SAP rats, which correlated with the severity of pancreatitis. When compared to the untreated group, the cohort that received the siRNA treatment demonstrated a significant reduction in pancreatic injury, neutrophil infiltration, myeloperoxidase activity and pro‐inflammatory cytokines. Furthermore, siRNAs showed that the reduction of CARD9 in SAP rats down‐regulated the expression of NF‐κBp65 and P38MAPK which are involved in the transcription and release of a wide variety of inflammatory cytokines. These findings provide evidence that CARD9 is up‐regulated in SAP rats and acts as a potential therapeutic target for the treatment thereof. Blocking the activation of NF‐κB and P38MAPK via siRNA‐mediated gene knock‐down of CARD9 appears to reduce the inflammatory response in pancreatic tissue.

Neuronostatin acts via GPR107 to increase cAMP-independent PKA phosphorylation and proglucagon mRNA accumulation in pancreatic α-cells

Neuronostatin (NST) is a recently described peptide that is produced from the somatostatin preprohormone in pancreatic δ-cells. NST has been shown to increase glucagon secretion from primary rat pancreatic islets in low-glucose conditions. Here, we demonstrate that NST increases proglucagon message in α-cells and identify a potential mechanism for NST's cellular activities, including the phosphorylation of PKA following activation of the G protein-coupled receptor, GPR107. GPR107 is abundantly expressed in the pancreas, particularly, in rodent and human α-cells. Compromise of GPR107 in pancreatic α-cells results in failure of NST to increase PKA phosphorylation and proglucagon mRNA levels. We also demonstrate colocalization of GPR107 and NST on both mouse and human pancreatic α-cells. Taken together with our group's observation that NST infusion in conscious rats impairs glucose clearance in response to a glucose challenge and that plasma levels of the peptide are elevated in the fasted compared with the fed or fasted-refed state, these studies support the hypothesis that endogenous NST regulates islet cell function by interacting with GPR107 and initiating signaling in glucagon-producing α-cells.

Brain-selective kinase 2 (BRSK2) phosphorylation on PCTAIRE1 negatively regulates glucose-stimulated insulin secretion in pancreatic β-cells

Brain-selective kinase 2 (BRSK2) has been shown to play an essential role in neuronal polarization. In the present study, we show that BRSK2 is also abundantly expressed in pancreatic islets and MIN6 β-cell line. Yeast two-hybrid screening, GST fusion protein pull-down, and co-immunoprecipitation assays reveal that BRSK2 interacts with CDK-related protein kinase PCTAIRE1, a kinase involved in neurite outgrowth and neurotransmitter release. In MIN6 cells, BRSK2 co-localizes with PCTAIRE1 in the cytoplasm and phosphorylates one of its serine residues, Ser-12. Phosphorylation of PCTAIRE1 by BRSK2 reduces glucose-stimulated insulin secretion (GSIS) in MIN6 cells. Conversely, knockdown of BRSK2 by siRNA increases serum insulin levels in mice. Our results reveal a novel function of BRSK2 in the regulation of GSIS in β-cells via a PCTAIRE1-dependent mechanism and suggest that BRSK2 is an attractive target for developing novel diabetic drugs.

Inhibition of glucose-stimulated insulin secretion by KCNJ15, a newly identified susceptibility gene for type 2 diabetes

Potassium inwardly rectifying channel, subfamily J, member 15 (KCNJ15) is a type 2 diabetes-associated risk gene, and Kcnj15 overexpression suppresses insulin secretion in rat insulinoma (INS1) cells. The aim of the current study was to characterize the role of Kcnj15 by knockdown of this gene in vitro and in vivo. Human islet cells were used to determine the expression of KCNJ15. Expression of KCNJ15 mRNA in islets was higher in subjects with type 2 diabetes. In INS1 cells, Kcnj15 expression was induced by high glucose-containing medium. Regulation of Kcnj15 by glucose and its effect on insulin secretion were analyzed in INS1 cells and in normal mice and diabetic mice by the inactivation of Kcnj15 using small interfering RNA. Knockdown of Kcnj15 increased the insulin secretion in vitro and in vivo. KCNJ15 and Ca(2+)-sensing receptor (CsR) interact in the kidney. Binding of Kcnj15 with CsR was also detected in INS1 cells. In conclusion, downregulation of Kcnj15 leads to increased insulin secretion in vitro and in vivo. The mechanism to regulate insulin secretion involves KCNJ15 and CsR.

Brain-derived neurotrophic factor modulates N-methyl-D-aspartate receptor activation in a rat model of cancer-induced bone pain

Brain-derived neurotrophic factor (BDNF) released within the spinal cord induces phosphorylation of N-methyl-D-aspartate (NMDA) receptors on the spinal cord neurons. This process is necessary for maintaining pain hypersensitivity after nerve injury. However, little is known about the role of BDNF and NMDA receptors in cancer-induced bone pain (CIBP), whose features are unique. This study demonstrates a critical role of the BDNF-modulated NMDA subunit 1 (NR1) in the induction and maintenance of behavioral hypersensitivity in a rat model of CIBP, both in the spinal cord and in the dorsal root ganglia (DRG). We selectively suppressed BDNF expression by RNA interference (RNAi) using intrathecal administration of BDNF small interfering RNA (siRNA). Then, we assessed mechanical threshold and spontaneous pain in CIBP rats. Real-time PCR, Western blotting, and fluorescent immunohistochemical staining were used to detect BDNF or NR1 both in vivo and in vitro. BDNF and phospho-NR1 were expressed under CIBP experimental conditions, with expression levels peaking at day 6 (BDNF) or 9 (NR1). Intrathecal BDNF siRNA prevented CIBP at an early stage of tumor growth (days 4-6). However, at later stages (days 10-12), intrathecal BDNF siRNA only attenuated, but did not completely block, the established CIBP. BDNF-induced NMDA receptor activation in the spinal cord or DRG leads to central sensitization and behavioral hypersensitivity. Thus, BDNF might provide a targeting opportunity for alleviating CIBP.

Combined lentiviral and RNAi technologies for the delivery and permanent silencing of the hsp25 gene

Elevated heat shock protein 27 (Hsp27) expression has been found in a number of tumors, including breast, prostate, gastric, uterine, ovarian, head and neck, and tumor arising from the nervous system and urinary system, and determined to be a predictor of poor clinical outcome. Although the mechanism of action of Hsp27 has been well documented, there are currently no available inhibitors of Hsp27 in clinical trials. RNA interference (RNAi) has the potential to offer more specificity and flexibility than traditional drugs to silence gene expression. Not surprisingly, RNAi has become a major focus for biotechnology and pharmaceutical companies, which are now in the early stages of developing RNAi therapeutics, mostly based on short interfering RNA (siRNAs), to target viral infection, cancer, hypercholesterolemia, cardiovascular disease, macular degeneration, and neurodegenerative diseases. However, the critical issues associated with RNAi as a therapeutic are delivery, specificity, and stability of the RNAi reagents. To date, the delivery is currently considered the biggest hurdle, as the introduction of siRNAs systemically into body fluids can result in their degradation, off-target effects, and immune detection. In this chapter, we discuss a method of combined lentiviral and RNAi-based technology for the delivery and permanent silencing of the hsp25 gene.

Common variation in GPC5 is associated with acquired nephrotic syndrome

Severe proteinuria is a defining factor of nephrotic syndrome irrespective of the etiology. Investigation of congenital nephrotic syndrome has shown that dysfunction of glomerular epithelial cells (podocytes) plays a crucial role in this disease. Acquired nephrotic syndrome is also assumed to be associated with podocyte injury. Here we identify an association between variants in GPC5, encoding glypican-5, and acquired nephrotic syndrome through a genome-wide association study and replication analysis (P value under a recessive model (P(rec)) = 6.0 × 10(-11), odds ratio = 2.54). We show that GPC5 is expressed in podocytes and that the risk genotype is associated with higher expression. We further show that podocyte-specific knockdown and systemic short interfering RNA injection confers resistance to podocyte injury in mouse models of nephrosis. This study identifies GPC5 as a new susceptibility gene for nephrotic syndrome and implicates GPC5 as a promising therapeutic target for reducing podocyte vulnerability in glomerular disease.

Microtrial methods for translating gene-environment dynamics into preventive interventions

Genetically informed research on behavioral outcomes holds substantial promise for guiding efforts to enhance the efficacy and effectiveness of preventive interventions, but it also poses considerable challenges given the complexities of the dynamic interplay between genes and environment. This paper introduces a relatively uncommon research design, called microtrials, to provide a means of translating basic research findings into prevention trials, particularly through introducing genetic effects into prevention models. Microtrials are defined as randomized experiments testing the effects of relatively brief and focused environmental manipulations designed to suppress specific risk mechanisms or enhance specific protective mechanisms, but not to bring about full treatment or prevention effects in distal outcomes. Microtrial methods are described in detail, with discussion of their unique advantages for translating this knowledge base into prevention research. We end by raising several issues to consider when constructing genetically sensitive microtrials.

siRNA applications in nanomedicine

The ability to specifically silence genes using RNA interference (RNAi) has wide therapeutic applications for the treatment of disease or the augmentation of tissue formation. RNAi is the sequence-specific gene silencing mediated by a 21-25 nucleotide double-stranded small interfering RNA (siRNA) molecule. siRNAs are incorporated into the RNA-induced silencing complex (RISC), which mediates mRNA sequence-specific binding and cleavage. Although RNAi has the potential to be a powerful therapeutic drug, its delivery remains a major limitation. The generation of nanosized particles is being investigated to enhance the delivery of siRNA-based drugs. These nanoparticles are generally designed to overcome one or more of the barriers encountered by the siRNA when trafficked to the cytosol. In this review, we will discuss recent advances in the design of delivery strategies for siRNA, focusing our attention to those strategies that have had in vivo success or have introduced novel functionality that allowed enhanced intracellular trafficking and/or cellular targeting. First, we will discuss the different barriers that must be overcome for efficient siRNA delivery. Second, we will discuss the approaches for siRNA delivery by size including direct modification of siRNAs (less than 10 nm), self-assembled particles based on cationic polymers and cationic lipids (100-300 nm), neutral liposomes (<200 nm), and macroscale matrices that contain naked siRNA or siRNA loaded nanoparticles (>100 microm). Finally, we will briefly discuss recent in vivo therapeutic success.

Delivery systems for the direct application of siRNAs to induce RNA interference (RNAi) in vivo

RNA interference (RNAi) is a powerful method for specific gene silencing which may also lead to promising novel therapeutic strategies. It is mediated through small interfering RNAs (siRNAs) which sequence-specifically trigger the cleavage and subsequent degradation of their target mRNA. One critical factor is the ability to deliver intact siRNAs into target cells/organs in vivo. This review highlights the mechanism of RNAi and the guidelines for the design of optimal siRNAs. It gives an overview of studies based on the systemic or local application of naked siRNAs or the use of various nonviral siRNA delivery systems. One promising avenue is the the complexation of siRNAs with the polyethylenimine (PEI), which efficiently stabilizes siRNAs and, upon systemic administration, leads to the delivery of the intact siRNAs into different organs. The antitumorigenic effects of PEI/siRNA-mediated in vivo gene-targeting of tumor-relevant proteins like in mouse tumor xenograft models are described.

Role and therapeutic potential of microRNAs in diabetes

The discovery in mammalian cells of hundreds of small RNA molecules, called microRNAs, with the potential to modulate the expression of the majority of the protein-coding genes has revolutionized many areas of biomedical research, including the diabetes field. MicroRNAs function as translational repressors and are emerging as key regulators of most, if not all, physiological processes. Moreover, alterations in the level or function of microRNAs are associated with an increasing number of diseases. Here, we describe the mechanisms governing the biogenesis and activities of microRNAs. We present evidence for the involvement of microRNAs in diabetes mellitus, by outlining the contribution of these small RNA molecules in the control of pancreatic beta-cell functions and by reviewing recent studies reporting changes in microRNA expression in tissues isolated from diabetes animal models. MicroRNAs hold great potential as therapeutic targets. We describe the strategies developed for the delivery of molecules mimicking or blocking the function of these tiny regulators of gene expression in living animals. In addition, because changes in serum microRNA profiles have been shown to occur in association with different human diseases, we also discuss the potential use of microRNAs as blood biomarkers for prevention and management of 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.

Temporal silencing of an androgenic gland-specific insulin-like gene affecting phenotypical gender differences and spermatogenesis

Androgenic glands (AGs) of the freshwater prawn Macrobrachium rosenbergii were subjected to endocrine manipulation, causing them to hypertrophy. Transcripts from these glands were used in the construction of an AG cDNA subtractive library. Screening of the library revealed an AG-specific gene, termed the M. rosenbergii insulin-like AG (Mr-IAG) gene. The cDNA of this gene was then cloned and fully sequenced. The cysteine backbone of the predicted mature Mr-IAG peptide (B and A chains) showed high similarity to that of other crustacean AG-specific insulin-like peptides. In vivo silencing of the gene, by injecting the prawns with Mr-IAG double-stranded RNA, temporarily prevented the regeneration of male secondary sexual characteristics, accompanied by a lag in molt and a reduction in growth parameters, which are typically higher in males of the species. In terms of reproductive parameters, silencing of Mr-IAG led to the arrest of testicular spermatogenesis and of spermatophore development in the terminal ampullae of the sperm duct, accompanied by hypertrophy and hyperplasia of the AGs. This study constitutes the first report of the silencing of a gene expressed specifically in the AG, which caused a transient adverse effect on male phenotypical gender differences and spermatogenesis.

Multifunctional magnetic nanocarriers for image-tagged SiRNA delivery to intact pancreatic islets

BACKGROUND

With the ultimate hope of finding a cure for diabetes, researches are looking into altering the genetic profile of the beta cell as a way to manage metabolic dysregulation. One of the most powerful new approaches for the directed regulation of gene expression uses the phenomenon of RNA interference.

METHODS

Here, we establish the feasibility of a novel technology centered around multifunctional magnetic nanocarriers, which concurrently deliver siRNA to intact pancreatic islets and can be detected by magnetic resonance and optical imaging.

RESULTS

In the proof-of-principle studies described here, we demonstrate that, after in vitro incubation, magnetic nanoparticles carrying siRNA designed to target the model gene for enhanced green fluorescent protein are efficiently taken up by murine pancreatic islets, derived from egfp transgenic animals. This uptake can be visualized by magnetic resonance imaging and near-infrared fluorescence optical imaging and results in suppression of the target gene.

CONCLUSIONS

These results illustrate the value of our approach in overcoming the challenges associated with genetic modification of intact pancreatic islets in a clinically acceptable manner. Furthermore, an added advantage of our technology derives from the combined capability of our magnetic nanoparticles for siRNA delivery and magnetic labeling of pancreatic islets.

RNA processing and mRNA surveillance in monogenic diabetes

In the eukaryotic cell a number of molecular mechanisms exist to regulate the nature and quantity of transcripts intended for translation. For monogenic diabetes an understanding of these processes is aiding scientists and clinicians in studying and managing this disease. Knowledge of RNA processing and mRNA surveillance pathways is helping to explain disease mechanisms, form genotype-phenotype relationships, and identifying new regions within genes to screen for mutations. Furthermore, recent insights into the regulatory role of micro RNAs (miRNAs) and RNA editing in the pancreas suggests that these mechanisms may also be important in the progression to the diabetic state.

Small-interference RNA gene knockdown of pancreatitis-associated proteins in rat acute pancreatitis

OBJECTIVES

Pancreatitis-associated proteins (PAPs) are induced in acute pancreatitis and antisense-mediated gene knockdown of PAP decreased PAP gene expression and worsened pancreatitis. Here, we investigated the effect of a more stable inhibition of PAP using small-interference RNA gene knockdown in vitro and in an in vivo model of experimental pancreatitis.

METHODS

Pancreatitis-associated protein-specific siRNA was administered to AR42J cell cultures or rats induced with pancreatitis. Controls included administration of scrambled siRNA or vehicle alone. After 24 hours, cells and pancreata were harvested and assessed for PAP (PAP 1, PAP 2, PAP 3) gene expression and pancreatitis severity.

RESULTS

In vitro, PAP protein, and mRNA levels were reduced (PAP 1, 76%; PAP 2, 8%; PAP 3, 24%) in cells treated with PAP siRNA. In vivo, PAP 1, and PAP 3 expressions were reduced (PAP 1, 36%; PAP 3, 66%) in siRNA-treated rats; there was no difference in PAP 2 isoform mRNA expression and serum protein levels. Serum amylase and lipase levels decreased (> or =50%) after administration of siRNA; interleukin (IL) 1beta, IL-4, and IL-6 increased, whereas C-reactive protein and tumor necrosis factor-alpha decreased when compared with vehicle control. Administration of PAP siRNA correlated with worsening histopathology.

CONCLUSIONS

siRNA-mediated gene knockdown of PAP worsens pancreatitis. Differences in gene knockdown technology may provide different approaches to study gene function.

Genetic association meets RNA interference: large-scale genomic screens for causation and mechanism of complex diseases

While the genomic era offers great promise for biomedicine in general and for biomarker discovery in particular, it has yet to significantly impact drug target discovery. Meanwhile, despite improvements over the past 20 years in reducing attrition in clinical trials due to adverse drug responses, the pharmaceutical industry continues to be beset by the high rate of attrition of compounds in late-stage development, primarily due to the lack of drug efficacy. Clearly, even highly potent drugs with ideal safety and pharmacokinetic profiles will fail to survive clinical trials if the drug target itself is not a key point of intervention for most patients. Genetic association studies and RNA interference are two scaleable genomic approaches that together can address the quality as well as quantity of candidate drug targets. Human genetic information has long been used to identify 'molecular bottlenecks' that can highlight the importance of a gene or pathway at the clinical level. The recent availability of the human HapMap and of high-throughput genotyping platforms now enables more systematic genetic screens for novel, clinically-relevant drug targets. In addition, RNA interference can help dissect the molecular role of a candidate drug target in preclinical model systems in vitro and in vivo. Wider applicability of RNA interference methods will closely follow continued progress on efficient delivery into appropriate cell models and target tissues.

Hydrodynamic gene delivery: its principles and applications

Efficient and safe methods for delivering genetic materials into cells must be developed before the clinical potential of gene therapy can be fully realized. Recently, hydrodynamic gene delivery using a rapid injection of a relatively large volume of DNA solution has opened up a new avenue for gene therapy studies in vivo. This method is superior to the existing delivery systems because of its simplicity, efficiency, and versatility. Wide success in applying hydrodynamic principles to delivery of DNA, RNA, proteins, and synthetic compounds, into the cells in various tissues of small animals, has inspired the recent attempts at establishing a hydrodynamic procedure for clinical use. In this review, we provide an overview of the theory and practice of hydrodynamic gene delivery so as to aid researchers for the use of this method in their pre-clinical and translational gene therapy studies.

Effect of iNOS and NF-kappaB gene silencing on beta-cell survival and function

PURPOSE

Type I diabetes results from beta-cell death and dysfunction, induced by infiltration of immune cells and local production of inflammatory cytokines. Therefore, we investigated the effect of iNOS and NF-kappaB gene silencing on beta-cell survival and function.

METHODS

Rat insulinoma INS-1E cells were transfected with chemically synthesized siRNA after complex formation with Lipofectamine 2000. Cells were then treated with a cocktail of inflammatory cytokines (IL-1beta+ TNF-alpha+ IFN-alpha), and glucose stimulated-insulin response and viability were determined. iNOS and NF-kappaB gene expression was assessed at mRNA level by real time RT-PCR. The effect of gene silencing was also correlated with cytokine-induced NO production and apoptosis.

RESULTS

Transfection of INS-1E cells with siRNAs silenced iNOS and NF-kappaB gene expression and reduced NO production in a sequence-specific manner without causing significant loss of cell viability and function. However, the abrogation of NO production did not prevent INS-1E cells from cytokine-induced apoptosis, suggesting that this event may not be totally dependent on NO production.

CONCLUSION

The gene silencing approach presented here is capable of attenuating the effects of inflammatory cytokines, such as iNOS expression and NO production and it will help to identify new target genes to improve islet transplantation.

Applications of RNA interference: current state and prospects for siRNA-based strategies in vivo

Within the recent years, RNA interference (RNAi) has become an almost-standard method for in vitro knockdown of any target gene of interest. Now, one major focus is to further explore its potential in vivo, including the development of novel therapeutic strategies. From the mechanism, it becomes clear that small interfering RNAs (siRNAs) play a pivotal role in triggering RNAi. Thus, the efficient delivery of target gene-specific siRNAs is one major challenge in the establishment of therapeutic RNAi. Numerous studies, based on different modes of administration and various siRNA formulations and/or modifications, have already accumulated promising results. This applies to various animal models covering viral infections, cancer and multiple other diseases. Continuing efforts will lead to the development of efficient and “double-specific” drugs, comprising of siRNAs with high target gene specificity and of nanoparticles enhancing siRNA delivery and target organ specificity.

In vivo suppression of mafA mRNA with siRNA and analysis of the resulting alteration of the gene expression profile in mouse pancreas by the microarray method

Maf is a family of transcription factor proteins that is characterized by a typical bZip structure, and one of the large mafs, mafA is a strong transactivator of insulin. To explore the role of mafA in the pancreas, we modified the mafA mRNA level in vivo in mice by the RNA interference (siRNA) technique and analyzed the resulting alteration of the expressed gene profile with a microarray system. The mafA expression level in siRNA-treated mice was reduced approximately 60% compared with control-siRNA-treated animals. Microarray analysis revealed changes in the expression level of several genes in the siRNA-treated mice, with prominent down-regulated expression of the genes encoding insulin, glucagon, and adipocytokines, suggesting possible role of mafA in the pathophysiological states of impaired metabolic responses or inflammatory reactions.

Systemic siRNA delivery via hydrodynamic intravascular injection

The main barrier to the use of RNAi in mammalian systems is the difficulty in delivering siRNA or shRNA to the appropriate tissues. Although progress has been made in this area, many of the technologies developed require specialized expertise and reagents that are beyond the reach of most investigators. In contrast, the hydrodynamic injection technique is simple to perform and enables highly efficient delivery of naked, unmodified siRNA to a number of tissues, especially the liver. This review describes the development of the technique and explores the possible mechanisms that enable uptake of siRNA to biological effect. Examples of the use of hydrodynamic injection in animal models of disease and for the study of gene function are presented and discussed.

Current strategies and perspectives in insulin gene therapy for diabetes

Insulin gene therapy is an approach that might overcome the weakness of islet cell therapy owing to its vulnerability to autoimmune attack. There are several mandatory conditions for successful insulin gene therapy. Efficient insulin gene therapy should have an effective insulin gene delivery mechanism, a system of regulation of the insulin biosynthesis that responds to glucose within extremely narrow physiological limits, a system of insulin processing into its active form and a choice of appropriate target cells, which possess biochemical characteristics similar to β cells, but are not targets for β-cell-specific self-reactivity. In this article, advantages and disadvantages of non-β-cell types that are most likely to be used for generating surrogate insulin-producing β cells are compared. Current achievements in insulin gene therapy are critically evaluated and future challenges are discussed.

Therapeutic potential of RNAi in metabolic diseases

Over the past years RNA interference (RNAi) has exploded as a new approach to manipulate gene expression in mammalian systems. More recently, RNAi has acquired interest as a potential therapeutic strategy. This review focuses on the potential therapeutic use of RNAi for metabolic diseases, the current understanding of RNAi biology, and how RNAi has been utilized to study the role of different genes in the pathogenesis of diabetes and obesity. Also reviewed are the in vivo proof-of-principle experiments that provide the preclinical justification for the development of RNAi-based therapeutics for diabetes and the key challenges that currently limit its application in the clinical setting.