An adenovirus vector for efficient RNA interference-mediated suppression of target genes in insulinoma cells and pancreatic islets of langerhans

Glucolipotoxic Stress-Induced Mig6 Desensitizes EGFR Signaling and Promotes Pancreatic Beta Cell Death

A loss of functional beta cell mass is a final etiological event in the development of frank type 2 diabetes (T2D). To preserve or expand beta cells and therefore treat/prevent T2D, growth factors have been considered therapeutically but have largely failed to achieve robust clinical success. The molecular mechanisms preventing the activation of mitogenic signaling pathways from maintaining functional beta cell mass during the development of T2D remain unknown. We speculated that endogenous negative effectors of mitogenic signaling cascades impede beta cell survival/expansion. Thus, we tested the hypothesis that a stress-inducible epidermal growth factor receptor (EGFR) inhibitor, mitogen-inducible gene 6 (Mig6), regulates beta cell fate in a T2D milieu. To this end, we determined that: (1) glucolipotoxicity (GLT) induces Mig6, thereby blunting EGFR signaling cascades, and (2) Mig6 mediates molecular events regulating beta cell survival/death. We discovered that GLT impairs EGFR activation, and Mig6 is elevated in human islets from T2D donors as well as GLT-treated rodent islets and 832/13 INS-1 beta cells. Mig6 is essential for GLT-induced EGFR desensitization, as Mig6 suppression rescued the GLT-impaired EGFR and ERK1/2 activation. Further, Mig6 mediated EGFR but not insulin-like growth factor-1 receptor nor hepatocyte growth factor receptor activity in beta cells. Finally, we identified that elevated Mig6 augmented beta cell apoptosis, as Mig6 suppression reduced apoptosis during GLT. In conclusion, we established that T2D and GLT induce Mig6 in beta cells; the elevated Mig6 desensitizes EGFR signaling and induces beta cell death, suggesting Mig6 could be a novel therapeutic target for T2D.

HCF-1 Regulates De Novo Lipogenesis through a Nutrient-Sensitive Complex with ChREBP

Carbohydrate response element binding protein (ChREBP) is a key transcriptional regulator of de novo lipogenesis (DNL) in response to carbohydrates and in hepatic steatosis. Mechanisms underlying nutrient modulation of ChREBP are under active investigation. Here we identify host cell factor 1 (HCF-1) as a previously unknown ChREBP-interacting protein that is enriched in liver biopsies of nonalcoholic steatohepatitis (NASH) patients. Biochemical and genetic studies show that HCF-1 is O-GlcNAcylated in response to glucose as a prerequisite for its binding to ChREBP and subsequent recruitment of OGT, ChREBP O-GlcNAcylation, and activation. The HCF-1:ChREBP complex resides at lipogenic gene promoters, where HCF-1 regulates H3K4 trimethylation to prime recruitment of the Jumonji C domain-containing histone demethylase PHF2 for epigenetic activation of these promoters. Overall, these findings define HCF-1's interaction with ChREBP as a previously unappreciated mechanism whereby glucose signals are both relayed to ChREBP and transmitted for epigenetic regulation of lipogenic genes.

Creation of versatile cloning platforms for transgene expression and dCas9-based epigenome editing

Genetic manipulation via transgene overexpression, RNAi, or Cas9-based methods is central to biomedical research. Unfortunately, use of these tools is often limited by vector options. We have created a modular platform (pMVP) that allows a gene of interest to be studied in the context of an array of promoters, epitope tags, conditional expression modalities, and fluorescent reporters, packaged in 35 custom destination vectors, including adenovirus, lentivirus, PiggyBac transposon, and Sleeping Beauty transposon, in aggregate >108,000 vector permutations. We also used pMVP to build an epigenetic engineering platform, pMAGIC, that packages multiple gRNAs and either Sa-dCas9 or x-dCas9(3.7) fused to one of five epigenetic modifiers. Importantly, via its compatibility with adenoviral vectors, pMAGIC uniquely enables use of dCas9/LSD1 fusions to interrogate enhancers within primary cells. To demonstrate this, we used pMAGIC to target Sa-dCas9/LSD1 and modify the epigenetic status of a conserved enhancer, resulting in altered expression of the homeobox transcription factor PDX1 and its target genes in pancreatic islets and insulinoma cells. In sum, the pMVP and pMAGIC systems empower researchers to rapidly generate purpose-built, customized vectors for manipulation of gene expression, including via targeted epigenetic modification of regulatory elements in a broad range of disease-relevant cell types.

β-Hydroxybutyrate improves β-cell mitochondrial function and survival

Pharmacological interventions aimed at improving outcomes in type 2 diabetes and achieving normoglycaemia, including insulin therapy, are increasingly common, despite the potential for substantial side effects. Carbohydrate-restricted diets that result in increased ketogenesis have effectively been used to improve insulin resistance, a fundamental feature of type 2 diabetes. In addition, limited evidence suggests that states of ketogenesis may also improve β-cell function in type 2 diabetics. Considering how little is known regarding the effects of ketones on β-cell function, we sought to determine the specific effects of β-Hydroxybutyrate (βHB) on pancreatic β-cell physiology and mitochondrial function. βHB treatment increased β-cell survival and proliferation, while also increasing mitochondrial mass, respiration and adenosine triphosphate (ATP) production. Despite these improvements, were unable to detect an increase in β-cell or islet insulin production and secretion. Collectively, these findings have two implications. Firstly, they indicate that β-cells have improved survival and proliferation in the midst of βHB, the circulating form of ketones. Secondly, insulin secretion does not appear to be directly related to apparent improvements in mitochondrial function and cellular proliferation.

Functional Analysis of Mouse G6pc1 Mutations Using a Novel In Situ Assay for Glucose-6-Phosphatase Activity and the Effect of Mutations in Conserved Human G6PC1/G6PC2 Amino Acids on G6PC2 Protein Expression

Elevated fasting blood glucose (FBG) has been associated with increased risk for development of type 2 diabetes. Single nucleotide polymorphisms (SNPs) in G6PC2 are the most important common determinants of variations in FBG in humans. Studies using G6pc2 knockout mice suggest that G6pc2 regulates the glucose sensitivity of insulin secretion. G6PC2 and the related G6PC1 and G6PC3 genes encode glucose-6-phosphatase catalytic subunits. This study describes a functional analysis of 22 non-synonymous G6PC2 SNPs, that alter amino acids that are conserved in human G6PC1, mouse G6pc1 and mouse G6pc2, with the goal of identifying variants that potentially affect G6PC2 activity/expression. Published data suggest strong conservation of catalytically important amino acids between all four proteins and the related G6PC3 isoform. Because human G6PC2 has very low glucose-6-phosphatase activity we used an indirect approach, examining the effect of these SNPs on mouse G6pc1 activity. Using a novel in situ functional assay for glucose-6-phosphatase activity we demonstrate that the amino acid changes associated with the human G6PC2 rs144254880 (Arg79Gln), rs149663725 (Gly114Arg) and rs2232326 (Ser324Pro) SNPs reduce mouse G6pc1 enzyme activity without affecting protein expression. The Arg79Gln variant alters an amino acid mutation of which, in G6PC1, has previously been shown to cause glycogen storage disease type 1a. We also demonstrate that the rs368382511 (Gly8Glu), rs138726309 (His177Tyr), rs2232323 (Tyr207Ser) rs374055555 (Arg293Trp), rs2232326 (Ser324Pro), rs137857125 (Pro313Leu) and rs2232327 (Pro340Leu) SNPs confer decreased G6PC2 protein expression. In summary, these studies identify multiple G6PC2 variants that have the potential to be associated with altered FBG in humans.

Mesenchymal stem cell and derived exosome as small RNA carrier and Immunomodulator to improve islet transplantation

Human bone marrow mesenchymal stem cells (hBMSCs) and their exosomes can suppress immune reaction and deliver small RNAs. Thus, they may improve islet transplantation by delivering small RNAs for promoting islet function and inhibiting immune rejection. Here, we proposed an hBMSC and its exosome-based therapy to overcome immune rejection and poor islet function, both of which hinder the success of islet transplantation. We found overexpressed siFas and anti-miR-375 in plasmid encoding shFas and anti-miR-375 transfected hBMSC-derived exosomes, which silenced Fas and miR-375 of human islets and improved their viability and function against inflammatory cytokines. This plasmid transfected hBMSCs downregulated Fas and miR-375 of human islets in a humanized NOD scid gamma (NSG) mouse model, whose immune reaction was inhibited by injecting hBMSC and peripheral blood mononuclear cell (PBMC) co-cultured exosomes. These exosomes suppressed immune reaction by inhibiting PBMC proliferation and enhancing regulatory T cell (Treg) function. Collectively, our studies elucidated the mechanisms of RNA delivery from hBMSCs to human islets and the immunosuppressive effect of hBMSC and peripheral blood mononuclear cell co-cultured exosomes for improving islet transplantation.

Cdk5r1 Overexpression Induces Primary β-Cell Proliferation

Decreased β-cell mass is a hallmark of type 1 and type 2 diabetes. Islet transplantation as a method of diabetes therapy is hampered by the paucity of transplant ready islets. Understanding the pathways controlling islet proliferation may be used to increase functional β-cell mass through transplantation or by enhanced growth of endogenous β-cells. We have shown that the transcription factor Nkx6.1 induces β-cell proliferation by upregulating the orphan nuclear hormone receptors Nr4a1 and Nr4a3. Using expression analysis to define Nkx6.1-independent mechanisms by which Nr4a1 and Nr4a3 induce β-cell proliferation, we demonstrated that cyclin-dependent kinase 5 regulatory subunit 1 (Cdk5r1) is upregulated by Nr4a1 and Nr4a3 but not by Nkx6.1. Overexpression of Cdk5r1 is sufficient to induce primary rat β-cell proliferation while maintaining glucose stimulated insulin secretion. Overexpression of Cdk5r1 in β-cells confers protection against apoptosis induced by etoposide and thapsigargin, but not camptothecin. The Cdk5 kinase complex inhibitor roscovitine blocks islet proliferation, suggesting that Cdk5r1 mediated β-cell proliferation is a kinase dependent event. Overexpression of Cdk5r1 results in pRb phosphorylation, which is inhibited by roscovitine treatment. These data demonstrate that activation of the Cdk5 kinase complex is sufficient to induce β-cell proliferation while maintaining glucose stimulated insulin secretion.

Aurora Kinase A is critical for the Nkx6.1 mediated β-cell proliferation pathway

Type 1 and type 2 diabetes are ultimately characterized by depleted β-cell mass. Characterization of the molecular pathways that control β-cell proliferation could be harnessed to restore these cells. The homeobox β-cell transcription factor Nkx6.1 induces β-cell proliferation by activating the orphan nuclear receptors Nr4a1 and Nr4a3. Here, we demonstrate that Nkx6.1 localizes to the promoter of the mitotic kinase AURKA (Aurora Kinase A) and induces its expression. Adenovirus mediated overexpression of AURKA is sufficient to induce proliferation in primary rat islets while maintaining glucose stimulated insulin secretion. Furthermore, AURKA is necessary for Nkx6.1 mediated β-cell proliferation as demonstrated by shRNA mediated knock down and pharmacological inhibition of AURKA kinase activity. AURKA preferentially induces DNA replication in β-cells as measured by BrdU incorporation, and enhances the rate of histone H3 phosphorylation in primary β-cells, demonstrating that AURKA induces the replicative and mitotic cell cycle phases in rat β-cells. Finally, overexpression of AURKA results in phosphorylation of the cell cycle regulator p53, which targets p53 for degradation and permits cell cycle progression. These studies define a pathway by which AURKA upregulation by Nkx6.1 results in phosphorylation and degradation of p53, thus removing a key inhibitory factor and permitting engagement of the β-cell proliferation pathway.

Pancreatic and duodenal homeobox protein 1 (Pdx-1) maintains endoplasmic reticulum calcium levels through transcriptional regulation of sarco-endoplasmic reticulum calcium ATPase 2b (SERCA2b) in the islet β cell

Although the pancreatic duodenal homeobox 1 (Pdx-1) transcription factor is known to play an indispensable role in β cell development and secretory function, recent data also implicate Pdx-1 in the maintenance of endoplasmic reticulum (ER) health. The sarco-endoplasmic reticulum Ca(2+) ATPase 2b (SERCA2b) pump maintains a steep Ca(2+) gradient between the cytosol and ER lumen. In models of diabetes, our data demonstrated loss of β cell Pdx-1 that occurs in parallel with altered SERCA2b expression, whereas in silico analysis of the SERCA2b promoter revealed multiple putative Pdx-1 binding sites. We hypothesized that Pdx-1 loss under inflammatory and diabetic conditions leads to decreased SERCA2b levels and activity with concomitant alterations in ER health. To test this, siRNA-mediated knockdown of Pdx-1 was performed in INS-1 cells. The results revealed reduced SERCA2b expression and decreased ER Ca(2+), which was measured using fluorescence lifetime imaging microscopy. Cotransfection of human Pdx-1 with a reporter fused to the human SERCA2 promoter increased luciferase activity 3- to 4-fold relative to an empty vector control, and direct binding of Pdx-1 to the proximal SERCA2 promoter was confirmed by chromatin immunoprecipitation. To determine whether restoration of SERCA2b could rescue ER stress induced by Pdx-1 loss, Pdx1(+/-) mice were fed a high-fat diet. Isolated islets demonstrated an increased spliced-to-total Xbp1 ratio, whereas SERCA2b overexpression reduced the Xbp1 ratio to that of wild-type controls. Together, these results identify SERCA2b as a novel transcriptional target of Pdx-1 and define a role for altered ER Ca(2+) regulation in Pdx-1-deficient states.

Nkx6.1 regulates islet β-cell proliferation via Nr4a1 and Nr4a3 nuclear receptors

Loss of functional β-cell mass is a hallmark of type 1 and type 2 diabetes, and methods for restoring these cells are needed. We have previously reported that overexpression of the homeodomain transcription factor NK6 homeobox 1 (Nkx6.1) in rat pancreatic islets induces β-cell proliferation and enhances glucose-stimulated insulin secretion, but the pathway by which Nkx6.1 activates β-cell expansion has not been defined. Here, we demonstrate that Nkx6.1 induces expression of the nuclear receptor subfamily 4, group A, members 1 and 3 (Nr4a1 and Nr4a3) orphan nuclear receptors, and that these factors are both necessary and sufficient for Nkx6.1-mediated β-cell proliferation. Consistent with this finding, global knockout of Nr4a1 results in a decrease in β-cell area in neonatal and young mice. Overexpression of Nkx6.1 and the Nr4a receptors results in increased expression of key cell cycle inducers E2F transcription factor 1 and cyclin E1. Furthermore, Nkx6.1 and Nr4a receptors induce components of the anaphase-promoting complex, including ubiquitin-conjugating enzyme E2C, resulting in degradation of the cell cycle inhibitor p21. These studies identify a unique bipartite pathway for activation of β-cell proliferation, suggesting several unique targets for expansion of functional β-cell mass.

Pdx-1 activates islet α- and β-cell proliferation via a mechanism regulated by transient receptor potential cation channels 3 and 6 and extracellular signal-regulated kinases 1 and 2

The homeodomain transcription factor Pdx-1 has important roles in pancreatic development and β-cell function and survival. In the present study, we demonstrate that adenovirus-mediated overexpression of Pdx-1 in rat or human islets also stimulates cell replication. Moreover, cooverexpression of Pdx-1 with another homeodomain transcription factor, Nkx6.1, has an additive effect on proliferation compared to either factor alone, implying discrete activating mechanisms. Consistent with this, Nkx6.1 stimulates mainly β-cell proliferation, whereas Pdx-1 stimulates both α- and β-cell proliferation. Furthermore, cyclins D1/D2 are upregulated by Pdx-1 but not by Nkx6.1, and inhibition of cdk4 blocks Pdx-1-stimulated but not Nkx6.1-stimulated islet cell proliferation. Genes regulated by Pdx-1 but not Nkx6.1 were identified by microarray analysis. Two members of the transient receptor potential cation (TRPC) channel family, TRPC3 and TRPC6, are upregulated by Pdx-1 overexpression, and small interfering RNA (siRNA)-mediated knockdown of TRPC3/6 or TRPC6 alone inhibits Pdx-1-induced but not Nkx6.1-induced islet cell proliferation. Pdx-1 also stimulates extracellular signal-regulated kinase 1 and 2 (ERK1/2) phosphorylation, an effect partially blocked by knockdown of TRPC3/6, and blockade of ERK1/2 activation with a MEK1/2 inhibitor partially impairs Pdx-1-stimulated proliferation. These studies define a pathway by which overexpression of Pdx-1 activates islet cell proliferation that is distinct from and additive to a pathway activated by Nkx6.1.

Control of voltage-gated potassium channel Kv2.2 expression by pyruvate-isocitrate cycling regulates glucose-stimulated insulin secretion

Recent studies have shown that the pyruvate-isocitrate cycling pathway, involving the mitochondrial citrate/isocitrate carrier and the cytosolic NADP-dependent isocitrate dehydrogenase (ICDc), is involved in control of glucose-stimulated insulin secretion (GSIS). Here we demonstrate that pyruvate-isocitrate cycling regulates expression of the voltage-gated potassium channel family member Kv2.2 in islet β-cells. siRNA-mediated suppression of ICDc, citrate/isocitrate carrier, or Kv2.2 expression impaired GSIS, and the effect of ICDc knockdown was rescued by re-expression of Kv2.2. Moreover, chronic exposure of β-cells to elevated fatty acids, which impairs GSIS, resulted in decreased expression of Kv2.2. Surprisingly, knockdown of ICDc or Kv2.2 increased rather than decreased outward K(+) current in the 832/13 β-cell line. Immunoprecipitation studies demonstrated interaction of Kv2.1 and Kv2.2, and co-overexpression of the two channels reduced outward K(+) current compared with overexpression of Kv2.1 alone. Also, siRNA-mediated knockdown of ICDc enhanced the suppressive effect of the Kv2.1-selective inhibitor stromatoxin1 on K(+) currents. Our data support a model in which a key function of the pyruvate-isocitrate cycle is to maintain levels of Kv2.2 expression sufficient to allow it to serve as a negative regulator of Kv channel activity.

Glucocorticoid-induced suppression of β-cell proliferation is mediated by Mig6

Glucocorticoids can cause steroid-induced diabetes or accelerate the progression to diabetes by creating systemic insulin resistance and decreasing functional β-cell mass, which is influenced by changes in β-cell function, growth, and death. The synthetic glucocorticoid agonist dexamethasone (Dex) is deleterious to functional β-cell mass by decreasing β-cell function, survival, and proliferation. However, the mechanism by which Dex decreases β-cell proliferation is unknown. Interestingly, Dex induces the transcription of an antiproliferative factor and negative regulator of epidermal growth factor receptor signaling, Mig6 (also known as gene 33, RALT, and Errfi1). We, therefore, hypothesized that Dex impairs β-cell proliferation by increasing the expression of Mig6 and thereby decreasing downstream signaling of epidermal growth factor receptor. We found that Dex induced Mig6 and decreased [(3)H]thymidine incorporation, an index of cellular replication, in mouse, rat, and human islets. Using adenovirally delivered small interfering RNA targeted to Mig6 in rat islets, we were able to limit the induction of Mig6 upon exposure to Dex, compared with islets treated with a control virus, and completely rescued the Dex-mediated impairment in replication. We demonstrated that both Dex and overexpression of Mig6 attenuated the phosphorylation of ERK1/2 and blocked the G(1)/S transition of the cell cycle. In conclusion, Mig6 functions as a molecular brake for β-cell proliferation during glucocorticoid treatment in β-cells, and thus, Mig6 may be a novel target for preventing glucocorticoid-induced impairments in functional β-cell mass.

Mitogen-inducible gene 6 triggers apoptosis and exacerbates ER stress-induced β-cell death

The increased insulin secretory burden placed on pancreatic β-cells during obesity and insulin resistance can ultimately lead to β-cell dysfunction and death and the development of type 2 diabetes. Mitogen-inducible gene 6 (Mig6) is a cellular stress-responsive protein that can negatively regulate the duration and intensity of epidermal growth factor receptor signaling and has been classically viewed as a molecular brake for proliferation. In this study, we used Mig6 heterozygous knockout mice (Mig6(+/-)) to study the role of Mig6 in regulating β-cell proliferation and survival. Surprisingly, the proliferation rate of Mig6(+/-) pancreatic islets was lower than wild-type islets despite having comparable β-cell mass and glucose tolerance. We thus speculated that Mig6 regulates cellular death. Using adenoviral vectors to overexpress or knockdown Mig6, we found that caspase 3 activation during apoptosis was dependent on the level of Mig6. Interestingly, Mig6 expression was induced during endoplasmic reticulum (ER) stress, and its protein levels were maintained throughout ER stress. Using polyribosomal profiling, we identified that Mig6 protein translation was maintained, whereas the global protein translation was inhibited during ER stress. In addition, Mig6 overexpression exacerbated ER stress-induced caspase 3 activation in vitro. In conclusion, Mig6 is transcriptionally up-regulated and resistant to global translational inhibition during stressed conditions in β-cells and mediates apoptosis in the form of caspase 3 activation. The sustained production of Mig6 protein exacerbates ER stress-induced β-cell death. Thus, preventing the induction, translation, and/or function of Mig6 is warranted for increasing β-cell survival.

The role of voltage-gated potassium channels Kv2.1 and Kv2.2 in the regulation of insulin and somatostatin release from pancreatic islets

The voltage-gated potassium channels Kv2.1 and Kv2.2 are highly expressed in pancreatic islets, yet their contribution to islet hormone secretion is not fully understood. Here we investigate the role of Kv2 channels in pancreatic islets using a combination of genetic and pharmacologic approaches. Pancreatic β-cells from Kv2.1(-/-) mice possess reduced Kv current and display greater glucose-stimulated insulin secretion (GSIS) relative to WT β-cells. Inhibition of Kv2.x channels with selective peptidyl [guangxitoxin-1E (GxTX-1E)] or small molecule (RY796) inhibitors enhances GSIS in isolated wild-type (WT) mouse and human islets, but not in islets from Kv2.1(-/-) mice. However, in WT mice neither inhibitor improved glucose tolerance in vivo. GxTX-1E and RY796 enhanced somatostatin release in isolated human and mouse islets and in situ perfused pancreata from WT and Kv2.1(-/-) mice. Kv2.2 silencing in mouse islets by adenovirus-small hairpin RNA (shRNA) specifically enhanced islet somatostatin, but not insulin, secretion. In mice lacking somatostatin receptor 5, GxTX-1E stimulated insulin secretion and improved glucose tolerance. Collectively, these data show that Kv2.1 regulates insulin secretion in β-cells and Kv2.2 modulates somatostatin release in δ-cells. Development of selective Kv2.1 inhibitors without cross inhibition of Kv2.2 may provide new avenues to promote GSIS for the treatment of type 2 diabetes.

Assessing replication and beta cell function in adenovirally-transduced isolated rodent islets

Glucose homeostasis is primarily controlled by the endocrine hormones insulin and glucagon, secreted from the pancreatic beta and alpha cells, respectively. Functional beta cell mass is determined by the anatomical beta cell mass as well as the ability of the beta cells to respond to a nutrient load. A loss of functional beta cell mass is central to both major forms of diabetes (1-3). Whereas the declining functional beta cell mass results from an autoimmune attack in type 1 diabetes, in type 2 diabetes, this decrement develops from both an inability of beta cells to secrete insulin appropriately and the destruction of beta cells from a cadre of mechanisms. Thus, efforts to restore functional beta cell mass are paramount to the better treatment of and potential cures for diabetes. Efforts are underway to identify molecular pathways that can be exploited to stimulate the replication and enhance the function of beta cells. Ideally, therapeutic targets would improve both beta cell growth and function. Perhaps more important though is to identify whether a strategy that stimulates beta cell growth comes at the cost of impairing beta cell function (such as with some oncogenes) and vice versa. By systematically suppressing or overexpressing the expression of target genes in isolated rat islets, one can identify potential therapeutic targets for increasing functional beta cell mass (4-6). Adenoviral vectors can be employed to efficiently overexpress or knockdown proteins in isolated rat islets (4,7-15). Here, we present a method to manipulate gene expression utilizing adenoviral transduction and assess islet replication and beta cell function in isolated rat islets (Figure 1). This method has been used previously to identify novel targets that modulate beta cell replication or function (5,6,8,9,16,17).

Prevalence of polyomaviruses and links with human diseases

The simian virus 40 and murine polyomaviruses were shown to be DNA tumor viruses in their natural hosts and/or heterologous experimental hosts in the mid-20th Century. The first two human polyomaviruses, the BK polyomavirus and JC polyomavirus, were discovered in 1971 and were shown to induce severe disease in immunocompromised patients, but their involvement in human cancers is still a matter for debate. The discovery of a polyomavirus associated with Merkel cell carcinoma (Merkel cell polyomavirus) in 2008 resulted in a renewed interest in the Polyomaviridae family, leading to the discovery of new human polyomaviruses. This review addresses the involvement of the nine human polyomaviruses and simian virus 40 in human diseases, with a particular focus on their prevalence and the humoral response directed against structural antigens in the general population and in subjects presenting specific diseases.

β cell protection by inhibition of iNOS through lentiviral vector-based strategies

Cytoprotective gene transfer to pancreatic islet β cell s may prove useful in preventing their destruction and prolonging islet graft survival after transplantation in patients with type 1 diabetes mellitus. A host of therapeutically relevant transgenes may potentially be incorporated into an appropriate gene delivery vehicle and used for islet modification. To examine this, we utilised a robust model of cytokine-induced β cell pathophysiology. Using this model, it is clear that antioxidant gene transfer confers no cytoprotective benefit. In contrast, we demonstrated that gene-based approaches to inhibit the activation of NF-κBNF-κB following cytokine exposure harbours therapeutic utility in preserving islet β cell viability in the face of cytokine toxicity. We identified that NF-κB-dependent induction of iNOSiNOS is a critical determinant of β cell fate following cytokine exposure. Having identified the pivotal role of iNOS activation in cytokine-induced β cell pathophysiology, lentiviral vectors may be used to efficiently deliver small interfering RNARNA molecules to confer efficient iNOS gene silencing. We have shown that lentiviral vector-based shRNA delivery holds significant promise in preserving β cell viability following cytotoxic cytokine exposure.

Differential and complementary effects of glucose and prolactin on islet DNA synthesis and gene expression

The mechanisms by which lactogenic hormones promote β-cell expansion remain poorly understood. Because prolactin (PRL) up-regulates β-cell glucose transporter 2, glucokinase, and pyruvate dehydrogenase activities, we reasoned that glucose availability might mediate or modulate the effects of PRL on β-cell mass. Here, we used male rat islets to show that PRL and glucose have differential but complementary effects on the expression of cell cyclins, cell cycle inhibitors, and various other genes known to regulate β-cell replication, including insulin receptor substrate 2, IGF-II, menin, forkhead box protein M1, tryptophan hydroxylase 1, and the PRL receptor. Differential effects on gene expression are associated with synergistic effects of glucose and PRL on islet DNA synthesis. The effects of PRL on gene expression are mirrored by β-cell overexpression of signal transducer and activator of transcription 5b and are opposed by dexamethasone. An ad-small interfering RNA specific for cyclin D2 attenuates markedly the effects of PRL on islet DNA synthesis. Our studies suggest a new paradigm for the control of β-cell mass and insulin production by hormones and nutrients. PRL up-regulates β-cell glucose uptake and utilization, whereas glucose increases islet PRL receptor expression and potentiates the effects of PRL on cell cycle gene expression and DNA synthesis. These findings suggest novel targets for prevention of neonatal glucose intolerance and gestational diabetes and may provide new insight into the pathogenesis of β-cell hyperplasia in obese subjects with insulin resistance.

Telomerase inhibition strategies by siRNAs against either hTR or hTERT in oral squamous cell carcinoma

Human telomerase RNA (hTR) and human telomerase reverse transcriptase (hTERT) are considered effective molecular targets for current anticancer therapy. In this study, we investigated the therapeutic effects of targeting hTR and hTERT individually or in combination by recombinant adenovirus-delivered small interfering RNA (siRNA) in oral squamous cell carcinoma (OSCC) Tca8113. Further, we screened the optimal strategy for RNA interference. Our results show that these different recombinant adenoviruses specifically reduced the levels of hTR mRNA, hTERT mRNA, hTERT protein and telomerase activity in Tca8113 cells. Moreover, they successfully inhibited xenograft tumor growth in nude mice. The potency of their antitumor activities was ranked as follows: anti-hTR >anti-hTR+anti-hTERT >anti-hTERT. Therefore, we demonstrated that the siRNA-expressing recombinant adenoviruses were an effective anticancer tool for treatment of OSCC. Furthermore, the anticancer effect of solely targeting hTR was more direct and efficient, compared with the effect of targeting hTR and hTERT in combination, or hTERT exclusively. The mechanism of this anticancer effect in OSCC was not only related to the inhibition of cell proliferation and the induction of cell apoptosis, but might also involve the inhibition of tumor angiogenesis.

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.

ATP-independent glucose stimulation of sphingosine kinase in rat pancreatic islets

Sphingosine kinase (SPHK) catalyzes sphingosine 1-phosphate production, promoting cell survival and reducing apoptosis in isolated rat pancreatic islets. Glucose, the primary islet beta-cell growth factor and insulin secretagogue, increased islet SPHK activity by 3- to 5-fold following acute (1 h) or prolonged (7 days) stimulation. Prolonged stimulation of islets with glucose induced SPHK1a and SPHK2 mRNA levels; there were no changes in SPHK protein expression. To isolate the metabolic effects of glucose on SPHK activation, islets were stimulated with glucose analogs or metabolites. 2-deoxy-D-glucose (2-DG), an analog phosphorylated by glucokinase but not an effective energy source, activated SPHK similarly to glucose. In contrast, 3-o-methylglucose (3-oMeG), which is transported but neither phosphorylated nor metabolized, did not increase islet SPHK activity. Glyceraldehyde and alpha-ketoisocaproic acid (KIC), metabolites that stimulate glycolysis and the citric acid cycle, respectively, did not activate islet SPHK. Moreover, inorganic phosphate blocked glucose-induced SPHK activation. A role for SPHK activity in beta-cell growth was confirmed when small interfering (si)SPHK2 RNA transfection reduced rat insulinoma INS-1e cell SPHK levels and activity and cell growth. Glucose induced an early and sustained increase in islet SPHK activity that was dependent on glucose phosphorylation, but independent of ATP generation or new protein biosynthesis. Glucose-supported beta-cell growth appears to be in part mediated by SPHK activity.

The mitochondrial 2-oxoglutarate carrier is part of a metabolic pathway that mediates glucose- and glutamine-stimulated insulin secretion

Glucose-stimulated insulin secretion from pancreatic islet beta-cells is dependent in part on pyruvate cycling through the pyruvate/isocitrate pathway, which generates cytosolic alpha-ketoglutarate, also known as 2-oxoglutarate (2OG). Here, we have investigated if mitochondrial transport of 2OG through the 2-oxoglutarate carrier (OGC) participates in control of nutrient-stimulated insulin secretion. Suppression of OGC in clonal pancreatic beta-cells (832/13 cells) and isolated rat islets by adenovirus-mediated delivery of small interfering RNA significantly decreased glucose-stimulated insulin secretion. OGC suppression also reduced insulin secretion in response to glutamine plus the glutamate dehydrogenase activator 2-amino-2-norbornane carboxylic acid. Nutrient-stimulated increases in glucose usage, glucose oxidation, glutamine oxidation, or ATP:ADP ratio were not affected by OGC knockdown, whereas suppression of OGC resulted in a significant decrease in the NADPH:NADP(+) ratio during stimulation with glucose but not glutamine + 2-amino-2-norbornane carboxylic acid. Finally, OGC suppression reduced insulin secretion in response to a membrane-permeant 2OG analog, dimethyl-2OG. These data reveal that the OGC is part of a mechanism of fuel-stimulated insulin secretion that is common to glucose, amino acid, and organic acid secretagogues, involving flux through the pyruvate/isocitrate cycling pathway. Although the components of this pathway must remain intact for appropriate stimulus-secretion coupling, production of NADPH does not appear to be the universal second messenger signal generated by these reactions.

Cholinergic augmentation of insulin release requires ankyrin-B

Parasympathetic stimulation of pancreatic islets augments glucose-stimulated insulin secretion by inducing inositol trisphosphate receptor (IP(3)R)-mediated calcium ion (Ca2+) release. Ankyrin-B binds to the IP(3)R and is enriched in pancreatic beta cells. We found that ankyrin-B-deficient islets displayed impaired potentiation of insulin secretion by the muscarinic agonist carbachol, blunted carbachol-mediated intracellular Ca2+ release, and reduced the abundance of IP3R. Ankyrin-B-haploinsufficient mice exhibited hyperglycemia after oral ingestion but not after intraperitoneal injection of glucose, consistent with impaired parasympathetic potentiation of glucose-stimulated insulin secretion. The R1788W mutation of ankyrin-B impaired its function in pancreatic islets and is associated with type 2 diabetes in Caucasians and Hispanics. Thus, defective glycemic regulation through loss of ankyrin-B-dependent stabilization of IP3R is a potential risk factor for type 2 diabetes.

Cooperative transcriptional regulation of the essential pancreatic islet gene NeuroD1 (beta2) by Nkx2.2 and neurogenin 3

Nkx2.2 and NeuroD1 are two critical regulators of pancreatic beta cell development. Nkx2.2 is a homeodomain transcription factor that is essential for islet cell type specification and mature beta cell function. NeuroD1 is a basic helix-loop-helix transcription factor that is critical for islet beta cell maturation and maintenance. Although both proteins influence beta cell development directly downstream of the endocrine progenitor factor, neurogenin3 (Ngn3), a connection between the two proteins in the regulation of beta cell fate and function has yet to be established. In this study, we demonstrate that Nkx2.2 transcriptional activity is required to facilitate the activation of NeuroD1 by Ngn3. Furthermore, Nkx2.2 is necessary to maintain high levels of NeuroD1 expression in developing mouse and zebrafish islets and in mature beta cells. Interestingly, Nkx2.2 regulates NeuroD1 through two independent promoter elements, one that is bound and activated directly by Nkx2.2 and one that appears to be regulated by Nkx2.2 through an indirect mechanism. Together, these findings suggest that Nkx2.2 coordinately activates NeuroD1 with Ngn3 within the endocrine progenitor cell and also plays a role in the maintenance of NeuroD1 expression to regulate beta cell function in the mature islet. Collectively, these findings further define the conserved regulatory networks involved in islet beta cell formation and function.

Long-term RNA interference and its application to hepatitis B virus

RNA interference (RNAi) is an ancient defensive mechanism in eukaryotes to control gene expressing and defend their genomes from foreign invaders. It refers to the phenomenon that double-stranded RNA results in the sequence-specific silencing of target gene expression. Although it was documented in a relatively short time ago, intensive research has facilitated making its mechanism clear. Researchers have found that it was a powerful tool for analyzing the functions of genes and treating tumors, infectious diseases and genetic abnormalities that are associated with a dominant gene defect. However, delivery in vivo, low blood stability and poor intracellular uptake present significant challenges for the development of RNAi reagents in clinical use. Thus, long-term inducible RNAi was designed. There are hundreds of millions of hepatitis B virus (HBV) carriers in the world at present, a portion of whom will lose their lives after several years due to chronic complications such as cirrhosis, hepatocellular carcinomas or both. Although a preventive vaccine is now available, the present therapeutic options for chronically infected patients are limited and of low efficiency. Admittedly, to date most RNAi experiments have been done in vitro, but it is hoped that they may be developed into a therapeutic strategy for HBV in the near future. In this article the principles and construction of long-term RNA are discussed. Its therapeutic potentiality and attention to the potential hazards will also outlined. We conclude that this ancient defensive mechanism can be recruited as a powerful weapon in the fight against HBV.

Relationship among brain and blood glucose levels and spontaneous and glucoprivic feeding

Although several studies implicate small declines in blood glucose levels as stimulus for spontaneous meal initiation, no mechanism is known for how these dips might initiate feeding. To assess the role of ventromedial hypothalamus (VMH) (arcuate plus ventromedial nucleus) glucosensing neurons as potential mediators of spontaneous and glucoprivic feeding, meal patterns were observed, and blood and VMH microdialysis fluid were sampled in 15 rats every 10 min for 3.5 h after dark onset and 2 h after insulin (5 U/kg, i.v.) infusion. Blood glucose levels declined by 11% beginning approximately 5 min before 65% of all spontaneous meals, with no fall in VMH levels. After insulin, blood and VMH glucose reached nadirs by 30-40 min, and the same rats ate 60% faster and spent 84% more time eating during the ensuing hypoglycemia. Although 83% of first hypoglycemic meals were preceded by 5 min dips in VMH (but not blood) glucose levels, neither blood nor VMH levels declined before second meals, suggesting that low glucose, rather than changing levels, was the stimulus for glucoprivic meals. Furthermore, altering VMH glucosensing by raising or lowering glucokinase (GK) activity failed to affect spontaneous feeding, body or adipose weights, or glucose tolerance. However, chronic depletion by 26-70% of VMH GK mRNA reduced glucoprivic feeding. Thus, although VMH glucosensing does not appear to be involved in either spontaneous feeding or long-term body-weight regulation, it does participate in glucoprivic feeding, similar to its role in the counter-regulatory neurohumoral responses to glucoprivation.

Caspase-3 gene silencing for inhibiting apoptosis in insulinoma cells and human islets

Although islet transplantation has great potential to treat type I diabetes, most islet grafts do not function due to the host immune rejection, nonspecific inflammatory response and poor revascularization. Since caspase-3 plays a crucial role in apoptosis of transplanted islet cells, we used chemically synthesized small interfering RNAs (siRNAs) to silence caspase-3 in insulinoma (INS-1E) cells and human islets, and then determined whether caspase-3 gene silencing can prevent these cells from cytokine-induced apoptosis. Transfection of INS-1E cells and islets with siRNAs reduced caspase-3 transcripts by 50-67% and 50%, respectively. Additionally, apoptosis in transfected insulinoma cells was markedly inhibited. Since gene silencing did not last beyond two days, we converted potent siRNA into shRNA and constructed replication deficient adenoviral (Adv) vectors encoding these shRNAs driven by a U6 or H1 promoter. Compared to chemically synthesized siRNA, Adv-caspase-3-shRNA efficiently transduced islets, showed relatively higher and prolonged levels of gene silencing beyond five days, with higher gene silencing with a U6 promoter, and protected islets from cytokine-induced apoptosis. Finally, return to normoglycemia was achieved at 1 day post-transplantation of Adv-caspase-3-shRNA transduced islets under the kidney capsules of streptozotocin induced nonobese diabetic-severe combined immunodeficiency (NOD-SCID) mice and maintained beyond two weeks. Blood glucose levels returned to > or = 325 mg/dL upon removal of the islet graft-bearing kidney at 32 days after transplantation, confirming that transplanted islets were functional.

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.

Methyltransferase Set7/9 maintains transcription and euchromatin structure at islet-enriched genes

OBJECTIVE

The activation of beta-cell genes, particularly of those encoding preproinsulin, requires an appropriate euchromatin (or "open") DNA template characterized by hypermethylation of Lys4 of histone H3. We hypothesized that this modification is maintained in islet beta-cells by the action of the histone methyltransferase Set7/9.

RESEARCH DESIGN AND METHODS

To identify the role of Set7/9, we characterized its expression pattern and gene regulation and studied its function using RNA interference in both cell lines and primary mouse islets.

RESULTS

Within the pancreas, Set7/9 protein shows striking specificity for islet cells, including alpha- and beta-cells, as well as occasional cells within ducts. Consistent with these findings, the Set7/9 gene promoter contained an islet-specific enhancer located between -5,768 and -6,030 base pairs (relative to the transcriptional start site) that exhibited Pdx1-responsive activation in beta-cells. To study Set7/9 function, we depleted insulinoma cells and primary mouse islets of Set7/9 protein using siRNA. Following siRNA treatment, we observed striking repression of genes involved in glucose-stimulated insulin secretion, including Ins1/2, Glut2, and MafA. These changes in transcription were accompanied by loss of dimethylated H3 Lys4 and RNA polymerase II recruitment, particularly at the Ins1/2 and Glut2 genes. Consistent with these data, depletion of Set7/9 in islets led to defects in glucose-stimulated Ca(2+) mobilization and insulin secretion.

CONCLUSIONS

We conclude that Set7/9 is required for normal beta-cell function, likely through the maintenance of euchromatin structure at genes necessary for glucose-stimulated insulin secretion.

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.

Small interfering RNA-mediated suppression of proislet amyloid polypeptide expression inhibits islet amyloid formation and enhances survival of human islets in culture

OBJECTIVE

Islet amyloid, formed by aggregation of the beta-cell peptide islet amyloid polypeptide (IAPP; amylin), is a pathological characteristic of pancreatic islets in type 2 diabetes. Toxic IAPP aggregates likely contribute to the progressive loss of beta-cells in this disease. We used cultured human islets as an ex vivo model of amyloid formation to investigate whether suppression of proIAPP expression would inhibit islet amyloid formation and enhance beta-cell survival and function.

RESEARCH DESIGN AND METHODS

Islets from cadaveric organ donors were transduced with a recombinant adenovirus expressing a short interfering RNA (siRNA) designed to suppress human proIAPP (Ad-hProIAPP-siRNA), cultured for 10 days, and then assessed for the presence of islet amyloid, beta-cell apoptosis, and beta-cell function.

RESULTS

Thioflavine S-positive amyloid deposits were clearly present after 10 days of culture. Transduction with Ad-hProIAPP-siRNA reduced proIAPP expression by 75% compared with nontransduced islets as assessed by Western blot analysis of islet lysates 4 days after transduction. siRNA-mediated inhibition of IAPP expression decreased islet amyloid area by 63% compared with nontransduced cultured islets. Cell death assessed by transferase-mediated dUTP nick-end labeling staining was decreased by 50% in transduced cultured human islets, associated with a significant increase in islet insulin content (control, 100 +/- 4 vs. +Ad-siRNA, 153 +/- 22%, P < 0.01) and glucose-stimulated insulin secretion (control, 222 +/- 33 vs. +Ad-siRNA, 285 +/- 21 percent basal, P < 0.05).

CONCLUSIONS

These findings demonstrate that inhibition of IAPP synthesis prevents amyloid formation and beta-cell death in cultured human islets. Inhibitors of IAPP synthesis may have therapeutic value in type 2 diabetes.

Silencing of cytosolic or mitochondrial isoforms of malic enzyme has no effect on glucose-stimulated insulin secretion from rodent islets

We have previously demonstrated a role for pyruvate cycling in glucose-stimulated insulin secretion (GSIS). Some of the possible pyruvate cycling pathways are completed by conversion of malate to pyruvate by malic enzyme. Using INS-1-derived 832/13 cells, it has recently been shown by other laboratories that NADP-dependent cytosolic malic enzyme (MEc), but not NAD-dependent mitochondrial malic enzyme (MEm), regulates GSIS. In the current study, we show that small interfering RNA-mediated suppression of either MEm or MEc results in decreased GSIS in both 832/13 cells and a new and more glucose- and incretin-responsive INS-1-derived cell line, 832/3. The effect of MEm to suppress GSIS in these cell lines was linked to a substantial decrease in cell growth, whereas MEc suppression resulted in decreased NADPH, shown previously to be correlated with GSIS. However, adenovirus-mediated delivery of small interfering RNAs specific to MEc and MEm to isolated rat islets, while leading to effective suppression of the targets transcripts, had no effect on GSIS. Furthermore, islets isolated from MEc-null MOD1(-/-) mice exhibit normal glucose- and potassium-stimulated insulin secretion. These results indicate that pyruvate-malate cycling does not control GSIS in primary rodent islets.

Ventromedial hypothalamic glucokinase is an important mediator of the counterregulatory response to insulin-induced hypoglycemia

OBJECTIVE

The counterregulatory response to insulin-induced hypoglycemia is mediated by the ventromedial hypothalamus (VMH), which contains specialized glucosensing neurons, many of which use glucokinase (GK) as the rate-limiting step in glucose's regulation of neuronal activity. Since conditions associated with increased VMH GK expression are associated with a blunted counterregulatory response, we tested the hypothesis that increasing VMH GK activity would similarly attenuate, while decreasing GK activity would enhance the counterregulatory response to insulin-induced hypoglycemia.

RESEARCH DESIGN AND METHODS

The counterregulatory response to insulin-induced hypoglycemia was evaluated in Sprague-Dawley rats after bilateral VMH injections of 1) a GK activator drug (compound A) to increase VMH GK activity, 2) low-dose alloxan (4 mug) to acutely inhibit GK activity, 3) high-dose alloxan (24 microg), or 4) an adenovirus expressing GK short hairpin RNA (shRNA) to chronically reduce GK expression and activity.

RESULTS

Compound A increased VMH GK activity sixfold in vitro and reduced the epinephrine, norepinephrine, and glucagon responses to insulin-induced hypoglycemia by 40-62% when injected into the VMH in vivo. On the other hand, acute and chronic reductions of VMH GK mRNA or activity had a lesser and more selective effect on increasing primarily the epinephrine response to insulin-induced hypoglycemia by 23-50%.

CONCLUSIONS

These studies suggest that VMH GK activity is an important regulator of the counterregulatory response to insulin-induced hypoglycemia and that a drug that specifically inhibited the rise in hypothalamic GK activity after insulin-induced hypoglycemia might improve the dampened counterregulatory response seen in tightly controlled diabetic subjects.

Chronic suppression of acetyl-CoA carboxylase 1 in beta-cells impairs insulin secretion via inhibition of glucose rather than lipid metabolism

Acetyl-CoA carboxylase 1 (ACC1) currently is being investigated as a target for treatment of obesity-associated dyslipidemia and insulin resistance. To investigate the effects of ACC1 inhibition on insulin secretion, three small interfering RNA (siRNA) duplexes targeting ACC1 (siACC1) were transfected into the INS-1-derived cell line, 832/13; the most efficacious duplex was also cloned into an adenovirus and used to transduce isolated rat islets. Delivery of the siACC1 duplexes decreased ACC1 mRNA by 60-80% in 832/13 cells and islets and enzyme activity by 46% compared with cells treated with a non-targeted siRNA. Delivery of siACC1 decreased glucose-stimulated insulin secretion (GSIS) by 70% in 832/13 cells and by 33% in islets. Surprisingly, siACC1 treatment decreased glucose oxidation by 49%, and the ATP:ADP ratio by 52%, accompanied by clear decreases in pyruvate cycling activity and tricarboxylic acid cycle intermediates. Exposure of siACC1-treated cells to the pyruvate cycling substrate dimethylmalate restored GSIS to normal without recovery of the depressed ATP:ADP ratio. In siACC1-treated cells, glucokinase protein levels were decreased by 25%, which correlated with a 36% decrease in glycogen synthesis and a 33% decrease in glycolytic flux. Furthermore, acute addition of the ACC1 inhibitor 5-(tetradecyloxy)-2-furoic acid (TOFA) to beta-cells suppressed [(14)C]glucose incorporation into lipids but had no effect on GSIS, whereas chronic TOFA administration suppressed GSIS and glucose metabolism. In sum, chronic, but not acute, suppression of ACC1 activity impairs GSIS via inhibition of glucose rather than lipid metabolism. These findings raise concerns about the use of ACC inhibitors for diabetes therapy.

Stimulation of human and rat islet beta-cell proliferation with retention of function by the homeodomain transcription factor Nkx6.1

The homeodomain transcription factor Nkx6.1 plays an important role in pancreatic islet beta-cell development, but its effects on adult beta-cell function, survival, and proliferation are not well understood. In the present study, we demonstrated that treatment of primary rat pancreatic islets with a cytomegalovirus promoter-driven recombinant adenovirus containing the Nkx6.1 cDNA (AdCMV-Nkx6.1) causes dramatic increases in [methyl-(3)H] thymidine and 5-bromo-2'-deoxyuridine (BrdU) incorporation and in the number of cells per islet relative to islets treated with a control adenovirus (AdCMV-betaGAL), whereas suppression of Nkx6.1 expression reduces thymidine incorporation. Immunocytochemical studies reveal that >80% of BrdU-positive cells in AdCMV-Nkx6.1-treated islets are beta cells. Microarray, real-time PCR, and immunoblot analyses reveal that overexpression of Nkx6.1 in rat islets causes concerted upregulation of a cadre of cell cycle control genes, including those encoding cyclins A, B, and E, and several regulatory kinases. Cyclin E is upregulated earlier than the other cyclins, and adenovirus-mediated overexpression of cyclin E is shown to be sufficient to activate islet cell proliferation. Moreover, chromatin immunoprecipitation assays demonstrate direct interaction of Nkx6.1 with the cyclin A2 and B1 genes. Overexpression of Nkx6.1 in rat islets caused a clear enhancement of glucose-stimulated insulin secretion (GSIS), whereas overexpression of Nkx6.1 in human islets caused an increase in the level of [(3)H]thymidine incorporation that was twice the control level, along with complete retention of GSIS. We conclude that Nkx6.1 is among the very rare factors capable of stimulating beta-cell replication with retention or enhancement of function, properties that may be exploitable for expansion of beta-cell mass in treatment of both major forms of diabetes.

Normal flux through ATP-citrate lyase or fatty acid synthase is not required for glucose-stimulated insulin secretion

It has been proposed that de novo synthesis of long-chain acyl-CoA (LC-CoA) is a signal for glucose-stimulated insulin secretion (GSIS). Key enzymes involved in synthesis of fatty acids from glucose include ATP-citrate lyase (CL) and fatty acid synthase (FAS). An inhibitor of CL, hydroxycitrate (HC), has been reported to inhibit insulin secretion in some laboratories but not in others. Here we show that high concentrations of NaCl created during preparation of HC by standard methods explain the inhibition of GSIS, and that removal of the excess NaCl prevents the effect. To further investigate the role of CL, two small interfering RNA adenoviruses (Ad-siCL2 and Ad-siCL3) were generated. Ad-siCL3 reduced CL mRNA levels by 92 +/- 6% and CL protein levels by 75 +/- 4% but did not affect GSIS in 832/13 cells compared with cells treated with a control adenovirus (Ad-siControl). Similar results were obtained with Ad-siCL2. Ad-siCL3-treated cells also exhibited a 52 +/- 7% reduction in cytosolic oxaloacetate, an 83 +/- 4% reduction in malonyl-CoA levels, and inhibition of [U-(14)C]glucose incorporation into lipid by 43 +/- 4%, all expected metabolic out-comes of CL suppression. Similarly, treatment of 832/13 cells with a recombinant adenovirus specific to FAS (Ad-siFAS) reduced FAS mRNA levels by 81 +/- 2% in 832/13 cells, resulting in a 59 +/- 4% decrease in [U-(14)C]glucose incorporation into lipid, without affecting GSIS. Finally, treatment of primary rat islets with Ad-siCL3 or Ad-siFAS reduced CL and FAS mRNA levels by 65 +/- 4% and 52 +/- 3%, respectively, but had no effect on GSIS relative to Ad-siControl-treated islets. These findings demonstrate that a normal rate of flux of glucose carbons through CL and FAS is not required for GSIS in insulinoma cell lines or rat islets.

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.

Inhibition of telomerase RNA (hTR) in cervical cancer by adenovirus-delivered siRNA

Small interfering RNA (siRNA) has become a powerful tool for selectively silencing gene expression in cultured mammalian cells. In this study, a 67-bp oligonucleotide encoding human telomerase RNA (hTR) was introduced into pSIREN, a shuttle vector for construction of recombinant adenovirus. Then the U6-RNA promoter and siRNA-encoding insert were cut out from the pSIREN and subcloned into pAdeno-X to construct the plasmid pAd-hTR. After the pAd-hTR was transfected into a mammalian cell line HEK-293, adenovirus carrying the hTR-targeting siRNA (Ad-hTR-siRNA) was obtained. We performed a series of experiments to demonstrate silencing of the telomerase mediated by Ad-hTR-siRNA in HeLa cells. Compared with control virus (Ad-NT-siRNA), Ad-hTR-siRNA significantly reduced both hTR mRNA level (by 70.21%) and telomerase activity (by 58.87%) in HeLa cells. Moreover, it induced apoptosis in HeLa cells. Treatment of subcutaneous tumor xenografted with Ad-hTR-siRNA could slow down tumor growth, at least partially due to the induction of apoptosis (P<0.05) in vivo. Taken together, our results demonstrated efficient and specific knockdown of telomerase in HeLa cell line by the hTR siRNA, and indicated the prospect of applying this siRNA expressing recombinant adenovirus system in cancer gene therapy.

CCAAT/enhancer-binding protein beta deletion reduces adiposity, hepatic steatosis, and diabetes in Lepr(db/db) mice

CCAAT/enhancer-binding protein beta (C/EBPbeta) plays a key role in initiation of adipogenesis in adipose tissue and gluconeogenesis in liver; however, the role of C/EBPbeta in hepatic lipogenesis remains undefined. Here we show that C/EBPbeta inactivation in Lepr(db/db) mice attenuates obesity, fatty liver, and diabetes. In addition to impaired adipogenesis, livers from C/EBPbeta(-/-) x Lepr(db/db) mice had dramatically decreased triglyceride content and reduced lipogenic enzyme activity. C/EBPbeta deletion in Lepr(db/db) mice down-regulated peroxisome proliferator-activated receptor gamma2 (PPARgamma2) and stearoyl-CoA desaturase-1 and up-regulated PPARalpha independent of SREBP1c. Conversely, C/EBPbeta overexpression in wild-type mice increased PPARgamma2 and stearoyl-CoA desaturase-1 mRNA and hepatic triglyceride content. In FAO cells, overexpression of the liver inhibiting form of C/EBPbeta or C/EBPbeta RNA interference attenuated palmitate-induced triglyceride accumulation and reduced PPARgamma2 and triglyceride levels in the liver in vivo. Leptin and the anti-diabetic drug metformin acutely down-regulated C/EBPbeta expression in hepatocytes, whereas fatty acids up-regulate C/EBPbeta expression. These data provide novel evidence linking C/EBPbeta expression to lipogenesis and energy balance with important implications for the treatment of obesity and fatty liver disease.

Anticancer activity of an adenoviral vector expressing short hairpin RNA against BK virus T-ag

The human polyomavirus BK (BKV) is oncogenic in rodents and induces malignant transformation of rodent cells in vitro. Although its role in human tumorigenesis is still debated, BKV represents an excellent model to evaluate molecularly targeted antineoplastic approaches. Here, we have tested whether stable suppression of the T antigen (T-ag) oncogene expression could inhibit the in vitro and in vivo malignant phenotype of BKV-transformed mouse cells. An adenovirus vector system that expresses small hairpin RNAs (shRNAs), which are converted into active small interfering RNAs (siRNA) molecules against the BKV T-ag, was developed. This vector was able to inhibit the expression of BKV T-ag through a highly efficient in vitro and in vivo delivery of the siRNA molecule. In addition, it allowed a stable expression of siRNA for a period of time sufficient to elicit a biological effect. Inhibition of T-ag expression results in reduction of the in vitro growth rate of BKV-transformed cells, which is, at least in part, caused by restoration of p53 activity and induction of apoptosis. In vivo studies proved that adenovirus vectors expressing anti-T-ag siRNA were able to suppress tumorigenicity of BKV-transformed cells. Moreover, adenovirus vector direct treatment of growing tumors resulted in a significant reduction of tumor growth. This study indicates that siRNAs delivery via a viral vector have a potential usefulness as in vivo anticancer tool against viral and cellular oncogenes.

Functional genomics of the beta-cell: short-chain 3-hydroxyacyl-coenzyme A dehydrogenase regulates insulin secretion independent of K+ currents

Recent advances in functional genomics afford the opportunity to interrogate the expression profiles of thousands of genes simultaneously and examine the function of these genes in a high-throughput manner. In this study, we describe a rational and efficient approach to identifying novel regulators of insulin secretion by the pancreatic beta-cell. Computational analysis of expression profiles of several mouse and cellular models of impaired insulin secretion identified 373 candidate genes involved in regulation of insulin secretion. Using RNA interference, we assessed the requirements of 10 of these candidates and identified four genes (40%) as being essential for normal insulin secretion. Among the genes identified was Hadhsc, which encodes short-chain 3-hydroxyacyl-coenzyme A dehydrogenase (SCHAD), an enzyme of mitochondrial beta-oxidation of fatty acids whose mutation results in congenital hyperinsulinism. RNA interference-mediated gene suppression of Hadhsc in insulinoma cells and primary rodent islets revealed enhanced basal but normal glucose-stimulated insulin secretion. This increase in basal insulin secretion was not attenuated by the opening of the KATP channel with diazoxide, suggesting that SCHAD regulates insulin secretion through a KATP channel-independent mechanism. Our results suggest a molecular explanation for the hyperinsulinemia hypoglycemic seen in patients with SCHAD deficiency.

The mitochondrial citrate/isocitrate carrier plays a regulatory role in glucose-stimulated insulin secretion

Glucose-stimulated insulin secretion (GSIS) is mediated in part by glucose metabolism-driven increases in ATP/ADP ratio, but by-products of mitochondrial glucose metabolism also play an important role. Here we investigate the role of the mitochondrial citrate/isocitrate carrier (CIC) in regulation of GSIS. Inhibition of CIC activity in INS-1-derived 832/13 cells or primary rat islets by the substrate analogue 1,2,3-benzenetricarboxylate (BTC) resulted in potent inhibition of GSIS, involving both first and second phase secretion. A recombinant adenovirus containing a CIC-specific siRNA (Ad-siCIC) dose-dependently reduced CIC expression in 832/13 cells and caused parallel inhibitory effects on citrate accumulation in the cytosol. Ad-siCIC treatment did not affect glucose utilization, glucose oxidation, or ATP/ADP ratio but did inhibit glucose incorporation into fatty acids and glucose-induced increases in NADPH/NADP+ ratio relative to cells treated with a control siRNA virus (Ad-siControl). Ad-siCIC also inhibited GSIS in 832/13 cells, whereas overexpression of CIC enhanced GSIS and raised cytosolic citrate levels. In normal rat islets, Ad-siCIC treatment also suppressed CIC mRNA levels and inhibited GSIS. We conclude that export of citrate and/or isocitrate from the mitochondria to the cytosol is an important step in control of GSIS.

FoxA2, Nkx2.2, and PDX-1 regulate islet beta-cell-specific mafA expression through conserved sequences located between base pairs -8118 and -7750 upstream from the transcription start site

The MafA transcription factor is both critical to islet beta-cell function and has a unique pancreatic cell-type-specific expression pattern. To localize the potential transcriptional regulatory region(s) involved in directing expression to the beta cell, areas of identity within the 5' flanking region of the mouse, human, and rat mafA genes were found between nucleotides -9389 and -9194, -8426 and -8293, -8118 and -7750, -6622 and -6441, -6217 and -6031, and -250 and +56 relative to the transcription start site. The identity between species was greater than 75%, with the highest found between bp -8118 and -7750 ( approximately 94%, termed region 3). Region 3 was the only upstream mammalian conserved region found in chicken mafA (88% identity). In addition, region 3 uniquely displayed beta-cell-specific activity in cell-line-based reporter assays. Important regulators of beta-cell formation and function, PDX-1, FoxA2, and Nkx2.2, were shown to specifically bind to region 3 in vivo using the chromatin immunoprecipitation assay. Mutational and functional analyses demonstrated that FoxA2 (bp -7943 to -7910), Nkx2.2 (bp -7771 to -7746), and PDX-1 (bp -8087 to -8063) mediated region 3 activation. Consistent with a role in transcription, small interfering RNA-mediated knockdown of PDX-1 led to decreased mafA mRNA production in INS-1-derived beta-cell lines (832/13 and 832/3), while MafA expression was undetected in the pancreatic epithelium of Nkx2.2 null animals. These results suggest that beta-cell-type-specific mafA transcription is principally controlled by region 3-acting transcription factors that are essential in the formation of functional beta cells.

A pyruvate cycling pathway involving cytosolic NADP-dependent isocitrate dehydrogenase regulates glucose-stimulated insulin secretion

Glucose-stimulated insulin secretion (GSIS) from pancreatic islet beta-cells is central to control of mammalian fuel homeostasis. Glucose metabolism mediates GSIS in part via ATP-regulated K+ (KATP) channels, but multiple lines of evidence suggest participation of other signals. Here we investigated the role of cytosolic NADP-dependent isocitrate dehydrogenase (ICDc) in control of GSIS in beta-cells. Delivery of small interfering RNAs specific for ICDc caused impairment of GSIS in two independent robustly glucose-responsive rat insulinoma (INS-1-derived) cell lines and in primary rat islets. Suppression of ICDc also attenuated the glucose-induced increments in pyruvate cycling activity and in NADPH levels, a predicted by-product of pyruvate cycling pathways, as well as the total cellular NADP(H) content. Metabolic profiling of eight organic acids in cell extracts revealed that suppression of ICDc caused increases in lactate production in both INS-1-derived cell lines and primary islets, consistent with the attenuation of pyruvate cycling, with no significant changes in other intermediates. Based on these studies, we propose that a pyruvate cycling pathway involving ICDc plays an important role in control of GSIS.

Compensatory responses to pyruvate carboxylase suppression in islet beta-cells. Preservation of glucose-stimulated insulin secretion

We have previously reported that glucose-stimulated insulin secretion (GSIS) is tightly correlated with pyruvate carboxylase (PC)-catalyzed anaplerotic flux into the tricarboxylic acid cycle and stimulation of pyruvate cycling activity. To further evaluate the role of PC in beta-cell function, we constructed a recombinant adenovirus containing a small interfering RNA (siRNA) specific to PC (Ad-siPC). Ad-siPC reduced PC mRNA levels by 83 and 64% and PC protein by 56 and 35% in INS-1-derived 832/13 cells and primary rat islets, respectively. Surprisingly, this manipulation did not impair GSIS in rat islets. In Ad-siPC-treated 832/13 cells, GSIS was slightly increased, whereas glycolytic rate and glucose oxidation were unaffected. Flux through PC at high glucose was decreased by only 20%, suggesting an increase in PC-specific activity. Acetyl carnitine, a surrogate for acetyl-CoA, an allosteric activator of PC, was increased by 36% in Ad-siPC-treated cells, suggesting a mechanism by which PC enzymatic activity is maintained with suppressed PC protein levels. In addition, the NADPH:NADP ratio, a proposed coupling factor for GSIS, was unaffected in Ad-siPC-treated cells. We conclude that beta-cells activate compensatory mechanisms in response to suppression of PC expression that prevent impairment of anaplerosis, pyruvate cycling, NAPDH production, and GSIS.

Efficient gene delivery to pancreatic islets with ultrasonic microbubble destruction technology

This study describes a method of gene delivery to pancreatic islets of adult, living animals by ultrasound targeted microbubble destruction (UTMD). The technique involves incorporation of plasmids into the phospholipid shell of gas-filled microbubbles, which are then infused into rats and destroyed within the pancreatic microcirculation with ultrasound. Specific delivery of genes to islet beta cells by UTMD was achieved by using a plasmid containing a rat insulin 1 promoter (RIP), and reporter gene expression was regulated appropriately by glucose in animals that received a RIP-luciferase plasmid. To demonstrate biological efficacy, we used UTMD to deliver RIP-human insulin and RIP-hexokinase I plasmids to islets of adult rats. Delivery of the former plasmid resulted in clear increases in circulating human C-peptide and decreased blood glucose levels, whereas delivery of the latter plasmid resulted in a clear increase in hexokinase I protein expression in islets, increased insulin levels in blood, and decreased circulating glucose levels. We conclude that UTMD allows relatively noninvasive delivery of genes to pancreatic islets with an efficiency sufficient to modulate beta cell function in adult animals.

Use of recombinant calpain-2 siRNA adenovirus to assess calpain-2 modulation of lung endothelial cell migration and proliferation

In this study, we developed an adenoviral vector harboring calpain-2 siRNA expression unit in which sense and anti-sense strands composing the siRNA duplex were connected by a loop and transcribed into a siRNA in porcine pulmonary artery endothelial cells (PAEC). We screened one efficient adenoviral vector Ad/si-m187 and found that Ad/si-m187 successfully exerted a gene knockdown effect on calpain-2 mRNA transcription and protein expression levels. The protein content of calpain-2 was reduced by 30%-80% in PAEC infected with Ad/si-m187 in comparison to a control adenoviral vector Ad/si-luc. The mRNA levels of calpain-2 were measured by real-time PCR and were decreased by 60%-100% and in a dose dependent manner. In correspondence to silencing calpain-2 gene expression, calpain-2 activity was decreased significantly. We further evaluated the role of calpain-2 in endothelial cell migration and proliferation. PAEC infected with Ad/si-m187 displayed impaired migration and cell proliferation in comparison to cells infected with control adenoviral vector (Ad/si-luc). These results indicate that adenoviral vector harboring calpain-2 siRNA expression unit is a valuable tool to study the biology of calpains and that calpain-2 plays an important role in lung endothelial cell migration and proliferation.