We deposited deeply Ag-doped REBa 2 Cu 3 O 7-x (REBCO) films of 0.5-2.0 μm thick by hot-wall pulsed laser deposition (PLD) method on 12 mm wide and 50 μm thick Hastelloy tapes with ion beam assisted ...deposition (IBAD) templates. Ag protection layer of 2.0 μm thick were deposited on them by sputtering. Lap or bridge joints of those tapes were made just by soldering. The joint resistances were measured by DC four-probe method at 77 K and by the loop current attenuation method at 4.2 K. Microscopic structures were evaluated by the scanning electron microscope (SEM). Metal Ag particles were clearly dispersed at REBCO surface. The joint resistances were measured as 0.9-1.8 × 10 −12 Ωm 2 at 77 K, and 1.6-4.8 × 10 −13 Ωm 2 at 4.2 K. Double layer structure of a thin Ag-doped REBCO film on a high- I c 2.5 μm thick REBCO film had also a low joint resistance without spoiling high- I c properties. The results indicate a possibility to make low joint resistance of 10 −12 Ω just by soldering of commercial REBCO coated conductors.
Wolfram syndrome is an autosomal recessive disorder characterised by childhood diabetes mellitus, optic atrophy and severe neurodegeneration, resulting in premature death. The aim of this study was ...to investigate the mechanisms responsible for the phenotype of carbohydrate intolerance and loss of pancreatic beta cells in this disorder.
To study the role of the Wolfram gene (Wfs1) in beta cells, we developed a mouse model with conditional deletion of Wfs1 in beta cells by crossing floxed Wfs1 exon 8 animals with mice expressing Cre recombinase under the control of a rat insulin promoter (RIP2-Cre). Complementary experiments using RNA interference of Wfs1 expression were performed in mouse insulinoma (MIN6) cell lines (WfsKD).
Male knockout mice (betaWfs(-/-)) began developing variable and progressive glucose intolerance and concomitant insulin deficiency, compared with littermate controls, by 12 weeks of age. Analysis of islets from betaWfs(-/-) mice revealed a reduction in beta cell mass, enhanced apoptosis, elevation of a marker of endoplasmic reticulum stress (immunoglobulin heavy chain-binding protein BiP), and dilated endoplasmic reticulum with decreased secretory granules by electron microscopy. WfsKD cell lines had significantly increased apoptosis and elevated expression of the genes encoding BiP and C/EBP-homologous protein (CHOP), two markers of endoplasmic reticulum stress.
These results indicate that (1) lack of expression of Wfs1 in beta cells was sufficient to result in the diabetes mellitus phenotype; (2) beta cell death occurred by an accelerated process of apoptosis; and (3) lack of Wfs1 was associated with dilated endoplasmic reticulum and increased markers of endoplasmic reticulum stress, which appears to be a significant contributor to the reduction in beta cell survival.
Aims/hypothesis
We investigated changes in the expression of genes involved in beta cell function and proliferation in mouse islets stimulated with glucokinase activator (GKA) in order to elucidate ...the mechanisms by which GKA stimulates beta cell function and proliferation.
Methods
Islets isolated from mice were used to investigate changes in the expression of genes related to beta cell function and proliferation stimulated by GKA. In addition,
Irs2
knockout (
Irs2
−/−
) mice on a high-fat diet or a high-fat diet containing GKA were used to investigate the effects of GKA on beta cell proliferation in vivo.
Results
In wild-type mice,
Irs2
and
Pdx1
expression was increased by GKA. In
Irs2
−/−
mice, GKA administration increased the glucose-stimulated secretion of insulin and
Pdx1
expression, but not beta cell proliferation. It was particularly noteworthy that oxidative stress inhibited the upregulation of the
Irs2
and
Pdx1
genes induced by GKA. Moreover, whereas neither GKA alone nor exendin-4 alone upregulated the expression of
Irs2
and
Pdx1
in the islets of
db
/
db
mice, prior administration of exendin-4 to the mice caused GKA to increase the expression of these genes.
Conclusions/interpretation
GKA-stimulated IRS2 production affected beta cell proliferation but not beta cell function. Oxidative stress diminished the effects of GKA on the changes in expression of genes involved in beta cell function and proliferation. A combination of GKA and an incretin-related agent might therefore be effective in therapy.
Aims/hypothesis
Insufficient insulin secretion and reduced pancreatic beta cell mass are hallmarks of type 2 diabetes. Here, we focused on a family of serine-threonine kinases known as ...homeodomain-interacting protein kinases (HIPKs). HIPKs are implicated in the modulation of Wnt signalling, which plays a crucial role in transcriptional activity, and in pancreas development and maintenance. The aim of the present study was to characterise the role of HIPKs in glucose metabolism.
Methods
We used RNA interference to characterise the role of HIPKs in regulating insulin secretion and transcription activity. We conducted RT-PCR and western blot analyses to analyse the expression and abundance of HIPK genes and proteins in the islets of high-fat diet-fed mice. Glucose-induced insulin secretion and beta cell proliferation were measured in islets from
Hipk3
−/−
mice, which have impaired glucose tolerance owing to an insulin secretion deficiency. The abundance of pancreatic duodenal homeobox (PDX)-1 and glycogen synthase kinase (GSK)-3β phosphorylation in
Hipk3
−/−
islets was determined by immunohistology and western blot analyses.
Results
We found that HIPKs regulate insulin secretion and transcription activity.
Hipk3
expression was most significantly increased in the islets of high-fat diet-fed mice. Furthermore, glucose-induced insulin secretion and beta cell proliferation were decreased in the islets of
Hipk3
−/−
mice. Levels of PDX1 and GSK-3β phosphorylation were significantly decreased in
Hipk3
−/−
islets.
Conclusions/interpretation
Depletion of HIPK3 impairs insulin secretion and glucose tolerance. Decreased levels of HIPK3 may play a substantial role in the pathogenesis of type 2 diabetes.
The Wnt signaling pathway is essential for embryonic development and carcinogenesis. Upon Wnt stimulation, β-catenin is stabilized and associates with T-cell factor or lymphoid enhancing factor, ...thereby activating transcription of target genes. In the absence of Wnt stimulation, the level of β-catenin is reduced via glycogen synthase kinase (GSK)-3β-mediated phosphorylation and subsequent proteasome-dependent degradation. Here, we report the identification of Ajuba as a negative regulator of the Wnt signaling pathway. Ajuba is a member of LIM domain-containing proteins that contribute to cell fate determination and regulate cell proliferation and differentiation. We found that enforced expression of Ajuba destabilized β-catenin and suppressed target gene expression. Ajuba promoted GSK-3β-mediated phosphorylation of β-catenin by reinforcing the association between β-catenin and GSK-3β. Furthermore, Wnt stimulation induced both accumulation of β-catenin and destabilization of Ajuba. Our findings suggest that Ajuba is important for regulation of the Wnt signaling pathway.
The cell adhesion molecule E-cadherin mediates the compaction process of mouse preimplantation embryos and is important for the maintenance and function of epithelial cell layers. To determine ...precisely the role of E-cadherin in epithelial biogenesis we monitored the developmental potential of embryos homozygously negative for E-cadherin that were derived from E-cadherin heterozygous transgenic mice. The homozygous negative embryos died around the time of implantation, although they did undergo compaction like their litter-mate controls, largely due to the presence of residual maternal E-cadherin. At the blastocyst stage, E-cadherin-negative embryos failed to form a trophectodermal epithelium or a blastocyst cavity. These results demonstrate the pivotal role of E-cadherin in one of the most basic morphogenetic events in the development of multicellular organisms, the biogenesis of an epithelium.
Molecular analysis of the cadherin-catenin complex elucidated the central role of beta-catenin in this adhesion complex, as it binds to the cytoplasmic domain of E-cadherin and to alpha-catenin. ...beta-Catenin may also function in signalling pathways, given its homology to the gene product of the Drosophila segment polarity gene armadillo, which is known to be involved in the wingless signalling cascade. To study the function of beta-catenin during mouse development, gene knock-out experiments were performed in embryonic stem cells and transgenic mice were generated. beta-Catenin null-mutant embryos formed blastocysts, implanted and developed into egg-cylinder-stage embryos. At day 7 post coitum, the development of the embryonic ectoderm was affected in mutant embryos. Cells detached from the ectodermal cell layer and were dispersed into the proamniotic cavity. No mesoderm formation was observed in mutant embryos. The development of extraembryonic structures appeared less dramatically or not at all affected. Our results demonstrate that, although beta-catenin is expressed rather ubiquitously, it is specifically required in the ectodermal cell layer.
In type 2 diabetes, there is a defect in the regulation of functional β-cell mass to overcome high-fat (HF) diet-induced insulin resistance. Many signals and pathways have been implicated in β-cell ...function, proliferation and apoptosis. The co-ordinated regulation of functional β-cell mass by insulin signalling and glucose metabolism under HF diet-induced insulin-resistant conditions is discussed in this article. Insulin receptor substrate (IRS)-2 is one of the two major substrates for the insulin signalling. Interestingly, IRS-2 is involved in the regulation of β-cell proliferation, as has been demonstrated using knockout mice models. On the other hand, in an animal model for human type 2 diabetes with impaired insulin secretion because of insufficiency of glucose metabolism, decreased β-cell proliferation was observed in mice with β-cell-specific glucokinase haploinsufficiency (Gck⁺/⁻) fed a HF diet without upregulation of IRS-2 in β-cells, which was reversed by overexpression of IRS-2 in β-cells. As to the mechanism underlying the upregulation of IRS-2 in β-cells, glucose metabolism plays an important role independently of insulin, and phosphorylation of cAMP response element-binding protein triggered by calcium-dependent signalling is the critical pathway. Downstream from insulin signalling via IRS-2 in β-cells, a reduction in FoxO1 nuclear exclusion contributes to the insufficient proliferative response of β-cells to insulin resistance. These findings suggest that IRS-2 is critical for β-cell hyperplasia in response to HF diet-induced insulin resistance.
We fabricated and examined the operation of graphene-based superconducting interference device (SQUID) consisting of two superconductor-single layer graphene-superconductor junctions connected in ...parallel on a superconducting loop made of aluminum. Current-voltage characteristic of the device exhibits supercurrent flowing through SGS junctions. Mean switching current can be modulated with the applied magnetic field periodically. Deduced oscillation period coincides well with that estimated from the device geometry, suggesting that our device works as a graphene-based SQUID.
PDF
