Contact analysis and performance evaluation of ring type traveling wave ultrasonic motors based on a surface contact model.

A surface contact model of ring type traveling wave ultrasonic motors is proposed in this paper in order to describe the circular three-dimensional contact and friction problem between the stator and rotor accurately. Differing from previous contact models of traveling wave ultrasonic motors, the flexibility of the rotor, which results in the irregular shape of contact area and inhomogeneous distribution of contact pressure along radial direction, is taken into account in the proposed model. The normal contact between the stator and rotor is analyzed with finite element method and the tangential force transmission on the contact surface is investigated with analytical method. The contact pressures and the tangential stresses on the contact surface are obtained. Mechanical performances of the motor are also studied based upon the proposed model. Finally, torque-speed curves of a prototype motor are measured and compared with the calculated results of the proposed model, and good agreements are obtained. In addition, the proposed surface contact model is compared with previous line contact models. It is found that the calculated results of the surface contact model are closer to measured results than those of line contact models. The comparison results verify the accuracy of the proposed surface contact model.

A Linear Ultrasonic Motor Based on Coupling Vibration Mode.

A coupled linear ultrasonic motor (LUSM) based on an eccentric constraint was proposed. Two pieces of oblique piezoelectric ceramics were arranged at each end of the elastomer, and the polarization direction of the ceramics was vertically upward. Using the tilting characteristics of the piezoelectric ceramics, the two ends of the fixed piezoelectric ceramics formed an eccentric restraint on the motor, providing conditions for the motor to generate coupled modes. When the elastomer of the motor generated the coupling vibration, the motion trajectories of the driving feet ends were oblique straight lines, and the oblique straight-line motion trajectories of the upper and lower driving feet ends were in opposite directions, driving the upper and lower sliders to run simultaneously. The stator parameters were optimized by using ANSYS to obtain larger amplitudes for the ends of the driving feet in both X and Z directions. The structure and operation principle of the motor are explained in detail. A prototype was fabricated to study the arrangement scheme with fixed constraints at the ends of the motor. The frequency-velocity characteristics, voltage-velocity characteristics, and mechanical characteristics of the motor were tested. The no-load speed and maximum output power were measured to be 45.9 mm/s and 3.24 mW.

Contact modeling and performance evaluation of ring type traveling wave ultrasonic motors considering stator teeth.

A contact model of ring type traveling wave ultrasonic motors is proposed in this paper in order to investigate the dynamic contact and friction drive mechanism between the stator and rotor. Differing from previous contact models of ring type traveling wave ultrasonic motors, the Dahl friction model is adopted and the stator teeth are taken into account in the proposed model. The normal stress, the tangential stress, and the torque-speed characteristics of the motor are evaluated in detail based on the proposed model. Finally, the torque-speed values of the prototype motor are measured and compared with the calculation ones. The results show that the calculation values are in good agreement with the experimental values, which validates the proposed model. Moreover, the proposed contact model is compared with previous contact models that adopt Coulomb friction law and meanwhile ignore stator teeth by assuming teeth surfaces to be continuous. The comparison results show that the proposed model is more accurate than previous models.

Reductive TCA cycle metabolism fuels glutamine- and glucose-stimulated insulin secretion.

Metabolic fuels regulate insulin secretion by generating second messengers that drive insulin granule exocytosis, but the biochemical pathways involved are incompletely understood. Here we demonstrate that stimulation of rat insulinoma cells or primary rat islets with glucose or glutamine + 2-aminobicyclo-(2,2,1)-heptane-2-carboxylic acid (Gln + BCH) induces reductive, "counter-clockwise" tricarboxylic acid (TCA) cycle flux of glutamine to citrate. Molecular or pharmacologic suppression of isocitrate dehydrogenase-2 (IDH2), which catalyzes reductive carboxylation of 2-ketoglutarate to isocitrate, results in impairment of glucose- and Gln + BCH-stimulated reductive TCA cycle flux, lowering of NADPH levels, and inhibition of insulin secretion. Pharmacologic suppression of IDH2 also inhibits insulin secretion in living mice. Reductive TCA cycle flux has been proposed as a mechanism for generation of biomass in cancer cells. Here we demonstrate that reductive TCA cycle flux also produces stimulus-secretion coupling factors that regulate insulin secretion, including in non-dividing cells.

Pancreatic, but not myeloid-cell, expression of interleukin-1alpha is required for maintenance of insulin secretion and whole body glucose homeostasis.

OBJECTIVE: The expression of the interleukin-1 receptor type I (IL-1R) is enriched in pancreatic islet ß-cells, signifying that ligands activating this pathway are important for the health and function of the insulin-secreting cell. Using isolated mouse, rat, and human islets, we identified the cytokine IL-1α as a highly inducible gene in response to IL-1R activation. In addition, IL-1α is elevated in mouse and rat models of obesity and Type 2 diabetes. Since less is known about the biology of IL-1α relative to IL-1ß in pancreatic tissue, our objective was to investigate the contribution of IL-1α to pancreatic ß-cell function and overall glucose homeostasis in vivo. METHODS: We generated a novel mouse line with conditional IL-1α alleles and subsequently produced mice with either pancreatic- or myeloid lineage-specific deletion of IL-1α. RESULTS: Using this in vivo approach, we discovered that pancreatic (IL-1αPdx1-/-), but not myeloid-cell, expression of IL-1α (IL-1αLysM-/-) was required for the maintenance of whole body glucose homeostasis in both male and female mice. Moreover, pancreatic deletion of IL-1α led to impaired glucose tolerance with no change in insulin sensitivity. This observation was consistent with our finding that glucose-stimulated insulin secretion was reduced in islets isolated from IL-1αPdx1-/- mice. Alternatively, IL-1αLysM-/- mice (male and female) did not have any detectable changes in glucose tolerance, respiratory quotient, physical activity, or food intake when compared with littermate controls. CONCLUSIONS: Taken together, we conclude that there is an important physiological role for pancreatic IL-1α to promote glucose homeostasis by supporting glucose-stimulated insulin secretion and islet ß-cell mass in vivo.

A single-modal linear ultrasonic motor based on multi vibration modes of PZT ceramics.

We have developed a single-modal linear motor which contains two kinds of PZT ceramics. The linear motor works by exciting the transverse vibration mode of the PZT ceramic on the upper surface of stator elastomer and the shear vibration mode of PZT ceramics at two ends simultaneously. The operation principle of the motor is analyzed in detail. And the rule of the driving foot amplitude varies with the size of the end protruding structure has been further researched by FEM analysis. The prototype is manufactured, and its operating characteristics are experimentally studied and analyzed. The no-load velocity and the maximum output force are tested to be 169.4 mm/s and 1.1 N, respectively. The results show that extra arrangement of PZT ceramics which works on shear vibration mode can efficiently improve the output of motor.

Identification of a small molecule that stimulates human ß-cell proliferation and insulin secretion, and protects against cytotoxic stress in rat insulinoma cells.

A key event in the development of both major forms of diabetes is the loss of functional pancreatic islet ß-cell mass. Strategies aimed at enhancing ß-cell regeneration have long been pursued, but methods for reliably inducing human ß-cell proliferation with full retention of key functions such as glucose-stimulated insulin secretion (GSIS) are still very limited. We have previously reported that overexpression of the homeobox transcription factor NKX6.1 stimulates ß-cell proliferation, while also enhancing GSIS and providing protection against ß-cell cytotoxicity through induction of the VGF prohormone. We developed an NKX6.1 pathway screen by stably transfecting 832/13 rat insulinoma cells with a VGF promoter-luciferase reporter construct, using the resultant cell line to screen a 630,000 compound chemical library. We isolated three compounds with consistent effects to stimulate human islet cell proliferation, but not expression of NKX6.1 or VGF, suggesting an alternative mechanism of action. Further studies of the most potent of these compounds, GNF-9228, revealed that it selectively activates human ß-cell relative to α-cell proliferation and has no effect on δ-cell replication. In addition, pre-treatment, but not short term exposure of human islets to GNF-9228 enhances GSIS. GNF-9228 also protects 832/13 insulinoma cells against ER stress- and inflammatory cytokine-induced cytotoxicity. GNF-9228 stimulates proliferation via a mechanism distinct from recently emergent DYRK1A inhibitors, as it is unaffected by DYRK1A overexpression and does not activate NFAT translocation. In conclusion, we have identified a small molecule with pleiotropic positive effects on islet biology, including stimulation of human ß-cell proliferation and insulin secretion, and protection against multiple agents of cytotoxic stress.

Pancreatic ß-Cell production of CXCR3 ligands precedes diabetes onset.

Type 1 diabetes mellitus (T1DM) results from immune cell-mediated reductions in function and mass of the insulin-producing ß-cells within the pancreatic islets. While the initial trigger(s) that initiates the autoimmune process is unknown, there is a leukocytic infiltration that precedes islet ß-cell death and dysfunction. Herein, we demonstrate that genes encoding the chemokines CXCL9, 10, and 11 are primary response genes in pancreatic ß-cells and are also elevated as part of the inflammatory response in mouse, rat, and human islets. We further established that STAT1 participates in the transcriptional control of these genes in response to the pro-inflammatory cytokines IL-1ß and IFN-γ. STAT1 is phosphorylated within five minutes after ß-cell exposure to IFN-γ, with subsequent occupancy at proximal and distal response elements within the Cxcl9 and Cxcl11 gene promoters. This increase in STAT1 binding is coupled to the rapid appearance of chemokine transcript. Moreover, circulating levels of chemokines that activate CXCR3 are elevated in non-obese diabetic (NOD) mice, consistent with clinical findings in human diabetes. We also report herein that mice with genetic deletion of CXCR3 (receptor for ligands CXCL9, 10, and 11) exhibit a delay in diabetes development after being injected with multiple low doses of streptozotocin. Therefore, we conclude that production of CXCL9, 10, and 11 from islet ß-cells controls leukocyte migration and activity into pancreatic tissue, which ultimately influences islet ß-cell mass and function. © 2016 BioFactors, 42(6):703-715, 2016.

Adenylosuccinate Is an Insulin Secretagogue Derived from Glucose-Induced Purine Metabolism.

Pancreatic islet failure, involving loss of glucose-stimulated insulin secretion (GSIS) from islet ß cells, heralds the onset of type 2 diabetes (T2D). To search for mediators of GSIS, we performed metabolomics profiling of the insulinoma cell line 832/13 and uncovered significant glucose-induced changes in purine pathway intermediates, including a decrease in inosine monophosphate (IMP) and an increase in adenylosuccinate (S-AMP), suggesting a regulatory role for the enzyme that links the two metabolites, adenylosuccinate synthase (ADSS). Inhibition of ADSS or a more proximal enzyme in the S-AMP biosynthesis pathway, adenylosuccinate lyase, lowers S-AMP levels and impairs GSIS. Addition of S-AMP to the interior of patch-clamped human ß cells amplifies exocytosis, an effect dependent upon expression of sentrin/SUMO-specific protease 1 (SENP1). S-AMP also overcomes the defect in glucose-induced exocytosis in ß cells from a human donor with T2D. S-AMP is, thus, an insulin secretagogue capable of reversing ß cell dysfunction in T2D.

IL-1ß reciprocally regulates chemokine and insulin secretion in pancreatic ß-cells via NF-κB.

Proinflammatory cytokines impact islet ß-cell mass and function by altering the transcriptional activity within pancreatic ß-cells, producing increases in intracellular nitric oxide abundance and the synthesis and secretion of immunomodulatory proteins such as chemokines. Herein, we report that IL-1ß, a major mediator of inflammatory responses associated with diabetes development, coordinately and reciprocally regulates chemokine and insulin secretion. We discovered that NF-κB controls the increase in chemokine transcription and secretion as well as the decrease in both insulin secretion and proliferation in response to IL-1ß. Nitric oxide production, which is markedly elevated in pancreatic ß-cells exposed to IL-1ß, is a negative regulator of both glucose-stimulated insulin secretion and glucose-induced increases in intracellular calcium levels. By contrast, the IL-1ß-mediated production of the chemokines CCL2 and CCL20 was not influenced by either nitric oxide levels or glucose concentration. Instead, the synthesis and secretion of CCL2 and CCL20 in response to IL-1ß were dependent on NF-κB transcriptional activity. We conclude that IL-1ß-induced transcriptional reprogramming via NF-κB reciprocally regulates chemokine and insulin secretion while also negatively regulating ß-cell proliferation. These findings are consistent with NF-κB as a major regulatory node controlling inflammation-associated alterations in islet ß-cell function and mass.

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

Type 1 and type 2 diabetes are ultimately characterized by depleted ß-cell mass. Characterization of the molecular pathways that control ß-cell proliferation could be harnessed to restore these cells. The homeobox ß-cell transcription factor Nkx6.1 induces ß-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 ß-cell proliferation as demonstrated by shRNA mediated knock down and pharmacological inhibition of AURKA kinase activity. AURKA preferentially induces DNA replication in ß-cells as measured by BrdU incorporation, and enhances the rate of histone H3 phosphorylation in primary ß-cells, demonstrating that AURKA induces the replicative and mitotic cell cycle phases in rat ß-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 ß-cell proliferation pathway.

Thiobenzothiazole-modified Hydrocortisones Display Anti-inflammatory Activity with Reduced Impact on Islet ß-Cell Function.

Glucocorticoids signal through the glucocorticoid receptor (GR) and are administered clinically for a variety of situations, including inflammatory disorders, specific cancers, rheumatoid arthritis, and organ/tissue transplantation. However, glucocorticoid therapy is also associated with additional complications, including steroid-induced diabetes. We hypothesized that modification of the steroid backbone is one strategy to enhance the therapeutic potential of GR activation. Toward this goal, two commercially unavailable, thiobenzothiazole-containing derivatives of hydrocortisone (termed MS4 and MS6) were examined using 832/13 rat insulinoma cells as well as rodent and human islets. We found that MS4 had transrepression properties but lacked transactivation ability, whereas MS6 retained both transactivation and transrepression activities. In addition, MS4 and MS6 both displayed anti-inflammatory activity. Furthermore, MS4 displayed reduced impact on islet ß-cell function in both rodent and human islets. Similar to dexamethasone, MS6 promoted adipocyte development in vitro, whereas MS4 did not. Moreover, neither MS4 nor MS6 activated the Pck1 (Pepck) gene in primary rat hepatocytes. We conclude that modification of the functional groups attached to the D-ring of the hydrocortisone steroid molecule produces compounds with altered structure-function GR agonist activity with decreased impact on insulin secretion and reduced adipogenic potential but with preservation of anti-inflammatory activity.

CCL20 is elevated during obesity and differentially regulated by NF-κB subunits in pancreatic ß-cells.

Enhanced leukocytic infiltration into pancreatic islets contributes to inflammation-based diminutions in functional ß-cell mass. Insulitis (aka islet inflammation), which can be present in both T1DM and T2DM, is one factor influencing pancreatic ß-cell death and dysfunction. IL-1ß, an inflammatory mediator in both T1DM and T2DM, acutely (within 1h) induced expression of the CCL20 gene in rat and human islets and clonal ß-cell lines. Transcriptional induction of CCL20 required the p65 subunit of NF-κB to replace the p50 subunit at two functional κB sites within the CCL20 proximal gene promoter. The NF-κB p50 subunit prevents CCL20 gene expression during unstimulated conditions and overexpression of p50 reduces CCL20, but enhances cyclooxygenase-2 (COX-2), transcript accumulation after exposure to IL-1ß. We also identified differential recruitment of specific co-activator molecules to the CCL20 gene promoter, when compared with the CCL2 and COX2 genes, revealing distinct transcriptional requirements for individual NF-κB responsive genes. Moreover, IL-1ß, TNF-α and IFN-γ individually increased the expression of CCR6, the receptor for CCL20, on the surface of human neutrophils. We further found that the chemokine CCL20 is elevated in serum from both genetically obese db/db mice and in C57BL6/J mice fed a high-fat diet. Taken together, these results are consistent with a possible activation of the CCL20-CCR6 axis in diseases with inflammatory components. Thus, interfering with this signaling pathway, either at the level of NF-κB-mediated chemokine production, or downstream receptor activation, could be a potential therapeutic target to offset inflammation-associated tissue dysfunction in obesity and diabetes.

Transcription of the gene encoding TNF-α is increased by IL-1ß in rat and human islets and ß-cell lines.

Synthesis and secretion of immunomodulatory proteins, such as cytokines and chemokines, controls the inflammatory response within pancreatic islets. When this inflammation does not resolve, destruction of pancreatic islet ß-cells leads to diabetes mellitus. Production of the soluble mediators of inflammation, such as TNF-α and IL-1ß, from resident and invading immune cells, as well as directly from islet ß-cells, is also associated with suboptimal islet transplantation outcomes. In this study, we found that IL-1ß induces rapid increases in TNF-α mRNA in rat and human islets and the 832/13 clonal ß-cell line. The surge in transcription of the TNF-α gene required the inhibitor of kappa B kinase beta (IκKß), the p65 subunit of the NF-κB and a signal-specific recruitment of RNA polymerase II to the gene promoter. Of note was the increased intracellular production of TNF-α protein in a manner consistent with mRNA accumulation in response to IL-1ß, but no detectable secretion of TNF-α into the media. Additionally, TNF-α specifically induces expression of CD11b, but not CD11c, on neutrophils, which could contribute to the inflammatory milieu and diabetes progression. We conclude that activation of the NF-κB pathway in pancreatic ß-cells leads to rapid intracellular production of the pro-inflammatory TNF-α protein through a combination of specific histone covalent modifications and NF-κB signaling pathways.

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

Loss of functional ß-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 ß-cell proliferation and enhances glucose-stimulated insulin secretion, but the pathway by which Nkx6.1 activates ß-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 ß-cell proliferation. Consistent with this finding, global knockout of Nr4a1 results in a decrease in ß-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 ß-cell proliferation, suggesting several unique targets for expansion of functional ß-cell mass.

NF-κB and STAT1 control CXCL1 and CXCL2 gene transcription.

Diabetes mellitus results from immune cell invasion into pancreatic islets of Langerhans, eventually leading to selective destruction of the insulin-producing ß-cells. How this process is initiated is not well understood. In this study, we investigated the regulation of the CXCL1 and CXCL2 genes, which encode proteins that promote migration of CXCR2(+) cells, such as neutrophils, toward secreting tissue. Herein, we found that IL-1ß markedly enhanced the expression of the CXCL1 and CXCL2 genes in rat islets and ß-cell lines, which resulted in increased secretion of each of these proteins. CXCL1 and CXCL2 also stimulated the expression of specific integrin proteins on the surface of human neutrophils. Mutation of a consensus NF-κB genomic sequence present in both gene promoters reduced the ability of IL-1ß to promote transcription. In addition, IL-1ß induced binding of the p65 and p50 subunits of NF-κB to these consensus κB regulatory elements as well as to additional κB sites located near the core promoter regions of each gene. Additionally, serine-phosphorylated STAT1 bound to the promoters of the CXCL1 and CXCL2 genes. We further found that IL-1ß induced specific posttranslational modifications to histone H3 in a time frame congruent with transcription factor binding and transcript accumulation. We conclude that IL-1ß-mediated regulation of the CXCL1 and CXCL2 genes in pancreatic ß-cells requires stimulus-induced changes in histone chemical modifications, recruitment of the NF-κB and STAT1 transcription factors to genomic regulatory sequences within the proximal gene promoters, and increases in phosphorylated forms of RNA polymerase II.

Regulation of iNOS gene transcription by IL-1ß and IFN-γ requires a coactivator exchange mechanism.

The proinflammatory cytokines IL-1ß and IFN-γ decrease functional islet ß-cell mass in part through the increased expression of specific genes, such as inducible nitric oxide synthase (iNOS). Dysregulated iNOS protein accumulation leads to overproduction of nitric oxide, which induces DNA damage, impairs ß-cell function, and ultimately diminishes cellular viability. However, the transcriptional mechanisms underlying cytokine-mediated expression of the iNOS gene are not completely understood. Herein, we demonstrated that individual mutations within the proximal and distal nuclear factor-κB sites impaired cytokine-mediated transcriptional activation. Surprisingly, mutating IFN-γ-activated site (GAS) elements in the iNOS gene promoter, which are classically responsive to IFN-γ, modulated transcriptional sensitivity to IL-1ß. Transcriptional sensitivity to IL-1ß was increased by generation of a consensus GAS element and decreased correspondingly with 1 or 2 nucleotide divergences from the consensus sequence. The nuclear factor-κB subunits p65 and p50 bound to the κB response elements in an IL-1ß-dependent manner. IL-1ß also promoted binding of serine-phosphorylated signal transducer and activator of transcription-1 (STAT1) (Ser727) but not tyrosine-phosphorylated STAT1 (Tyr701) to GAS elements. However, phosphorylation at Tyr701 was required for IFN-γ to potentiate the IL-1ß response. Furthermore, coactivator p300 and coactivator arginine methyltransferase were recruited to the iNOS gene promoter with concomitant displacement of the coactivator CREB-binding protein in cells exposed to IL-1ß. Moreover, these coordinated changes in factor recruitment were associated with alterations in acetylation, methylation, and phosphorylation of histone proteins. We conclude that p65 and STAT1 cooperate to control iNOS gene transcription in response to proinflammatory cytokines by a coactivator exchange mechanism. This increase in transcription is also associated with signal-specific chromatin remodeling that leads to RNA polymerase II recruitment and phosphorylation.

Synergistic expression of the CXCL10 gene in response to IL-1ß and IFN-γ involves NF-κB, phosphorylation of STAT1 at Tyr701, and acetylation of histones H3 and H4.

The CXCL10 gene encodes a peptide that chemoattracts a variety of leukocytes associated with type 1 and type 2 diabetes. The present study was undertaken to determine the molecular mechanisms required for expression of the CXCL10 gene in response to IL-1ß and IFN-γ using rat islets and ß cell lines. IL-1ß induced the expression of the CXCL10 gene and promoter activity, whereas the combination of IL-1ß plus IFN-γ was synergistic. Small interfering RNA-mediated suppression of NF-κB p65 markedly inhibited the ability of cytokines to induce the expression of the CXCL10 gene, whereas targeting STAT1 only diminished the synergy provided by IFN-γ. Furthermore, we found that a JAK1 inhibitor dose dependently reduced IFN-γ-controlled CXCL10 gene expression and promoter activity, concomitant with a decrease in STAT1 phosphorylation at Tyr(701). We further discovered that, although the Tyr(701) phosphorylation site is inducible (within 15 min of IFN-γ exposure), the Ser(727) site within STAT1 is constitutively phosphorylated. Thus, we generated single-mutant STAT1 Y701F and double-mutant STAT1 Y701F/S727A adenoviruses. Using these recombinant adenoviruses, we determined that overexpression of either the single- or double-mutant STAT1 decreased the IFN-γ-mediated potentiation of CXCL10 gene expression, promoter activity, and secretion of protein. Moreover, the Ser(727) phosphorylation was neither contingent on a functional Y701 site in ß cells nor was it required for cytokine-mediated expression of the CXCL10 gene. We conclude that the synergism of IL-1ß and IFN-γ to induce expression of the CXCL10 gene requires NF-κB, STAT1 phosphorylated at Tyr(701), recruitment of coactivators, and acetylation of histones H3 and H4.

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 ß-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 ß-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 ß-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.

Regulation of the CCL2 gene in pancreatic ß-cells by IL-1ß and glucocorticoids: role of MKP-1.

Release of pro-inflammatory cytokines from both resident and invading leukocytes within the pancreatic islets impacts the development of Type 1 diabetes mellitus. Synthesis and secretion of the chemokine CCL2 from pancreatic ß-cells in response to pro-inflammatory signaling pathways influences immune cell recruitment into the pancreatic islets. Therefore, we investigated the positive and negative regulatory components controlling expression of the CCL2 gene using isolated rat islets and INS-1-derived ß-cell lines. We discovered that activation of the CCL2 gene by IL-1ß required the p65 subunit of NF-κB and was dependent on genomic response elements located in the -3.6 kb region of the proximal gene promoter. CCL2 gene transcription in response to IL-1ß was blocked by pharmacological inhibition of the IKKß and p38 MAPK pathways. The IL-1ß-mediated increase in CCL2 secretion was also impaired by p38 MAPK inhibition and by glucocorticoids. Moreover, multiple synthetic glucocorticoids inhibited the IL-1ß-stimulated induction of the CCL2 gene. Induction of the MAP Kinase Phosphatase-1 (MKP-1) gene by glucocorticoids or by adenoviral-mediated overexpression decreased p38 MAPK phosphorylation, which diminished CCL2 gene expression, promoter activity, and release of CCL2 protein. We conclude that glucocorticoid-mediated repression of IL-1ß-induced CCL2 gene transcription and protein secretion occurs in part through the upregulation of the MKP-1 gene and subsequent deactivation of the p38 MAPK. Furthermore, the anti-inflammatory actions observed with MKP-1 overexpression were obtained without suppressing glucose-stimulated insulin secretion. Thus, MKP-1 is a possible target for anti-inflammatory therapeutic intervention with preservation of ß-cell function.