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Mechanical loading prevents the stimulating effect of IL-1β on osteocyte-modulated osteoclastogenesis.

All pubs - 18 hours 55 min ago

Mechanical loading prevents the stimulating effect of IL-1β on osteocyte-modulated osteoclastogenesis.

Biochem Biophys Res Commun. 2012 Mar 30;420(1):11-6

Authors: Kulkarni RN, Bakker AD, Everts V, Klein-Nulend J

Abstract
Inflammatory diseases such as rheumatoid arthritis are often accompanied by higher plasma and synovial fluid levels of interleukin-1β (IL-1β), and by increased bone resorption. Since osteocytes are known to regulate bone resorption in response to changes in mechanical stimuli, we investigated whether IL-1β affects osteocyte-modulated osteoclastogenesis in the presence or absence of mechanical loading of osteocytes. MLO-Y4 osteocytes were pre-incubated with IL-1β (0.1-1 ng/ml) for 24h. Cells were either or not subjected to mechanical loading by 1h pulsating fluid flow (PFF; 0.7 ± 0.3 Pa, 5 Hz) in the presence of IL-1β (0.1-1 ng/ml). Conditioned medium was collected after 1h PFF or static cultures. Subsequently mouse bone marrow cells were seeded on top of the IL-1β-treated osteocytes to determine osteoclastogenesis. Conditioned medium from mechanically loaded or static IL-1β-treated osteocytes was added to co-cultures of untreated osteocytes and mouse bone marrow cells. Gene expression of cysteine-rich protein 61 (CYR61/CCN1), receptor activator of nuclear factor kappa-B ligand (RANKL), and osteoprotegerin (OPG) by osteocytes was determined immediately after PFF. Incubation of osteocytes with IL-1β, as well as conditioned medium from static IL-1β-treated osteocytes increased the formation of osteoclasts. However, conditioned medium from mechanically loaded IL-1β-treated osteocytes prevented osteoclast formation. Incubation with IL-1β upregulated RANKL and downregulated OPG gene expression by static osteocytes. PFF upregulated CYR61, RANKL, and OPG gene expression by osteocytes. Our results suggest that IL-1β increases osteocyte-modulated osteoclastogenesis, and that mechanical loading of osteocytes may abolish IL-1β-induced osteoclastogenesis.

PMID: 22390927 [PubMed - indexed for MEDLINE]

Categories: Publications from Members of the BIIC

In Vivo Imaging of Endogenous Pancreatic β-Cell Mass in Healthy and Type 1 Diabetic Subjects Using 18F-Fluoropropyl-Dihydrotetrabenazine and PET.

All pubs - Wed, 05/16/2012 - 02:00

In Vivo Imaging of Endogenous Pancreatic β-Cell Mass in Healthy and Type 1 Diabetic Subjects Using 18F-Fluoropropyl-Dihydrotetrabenazine and PET.

J Nucl Med. 2012 May 9;

Authors: Normandin MD, Petersen KF, Ding YS, Lin SF, Naik S, Fowles K, Skovronsky DM, Herold KC, McCarthy TJ, Calle RA, Carson RE, Treadway JL, Cline GW

Abstract
The ability to noninvasively measure endogenous pancreatic β-cell mass (BCM) would accelerate research on the pathophysiology of diabetes and revolutionize the preclinical development of new treatments, the clinical assessment of therapeutic efficacy, and the early diagnosis and subsequent monitoring of disease progression. The vesicular monoamine transporter type 2 (VMAT2) is coexpressed with insulin in β-cells and represents a promising target for BCM imaging. METHODS: We evaluated the VMAT2 radiotracer (18)F-fluoropropyl-dihydrotetrabenazine ((18)F-FP-(+)-DTBZ, also known as (18)F-AV-133) for quantitative PET of BCM in healthy control subjects and patients with type 1 diabetes mellitus. Standardized uptake value was calculated as the net tracer uptake in the pancreas normalized by injected dose and body weight. Total volume of distribution, the equilibrium ratio of tracer concentration in tissue relative to plasma, was estimated by kinetic modeling with arterial input functions. Binding potential, the steady-state ratio of specific binding to nondisplaceable uptake, was calculated using the renal cortex as a reference tissue devoid of specific VMAT2 binding. RESULTS: Mean pancreatic standardized uptake value, total volume of distribution, and binding potential were reduced by 38%, 20%, and 40%, respectively, in type 1 diabetes mellitus. The radiotracer binding parameters correlated with insulin secretion capacity as determined by arginine-stimulus tests. Group differences and correlations with β-cell function were enhanced for total pancreas binding parameters that accounted for tracer binding density and organ volume. CONCLUSION: These findings demonstrate that quantitative evaluation of islet β-cell density and aggregate BCM can be performed clinically with (18)F-FP-(+)-DTBZ PET.

PMID: 22573821 [PubMed - as supplied by publisher]

Categories: Publications from Members of the BIIC

The appearance of pili annulati following alopecia areata.

All pubs - Wed, 05/16/2012 - 02:00

The appearance of pili annulati following alopecia areata.

Cutis. 2012 Mar;89(3):145-7

Authors: Cruz AP, Liang CA, Gray JP, Robinson-Bostom L, McDonald CJ

Abstract
Pili annulati is a rare autosomal-dominant hair shaft abnormality. It is characterized by alternating light and dark bands along the shaft due to air-filled cavities within the cortex of the hair shaft. Alopecia areata has been previously described as a common association with pili annulati, with improvement in alopecia areata coinciding with resolution of pili annulati. We report the case of a patient with a history of alopecia areata and alopecia universalis who developed the characteristic banded hair of pili annulati upon resolution of her alopecia areata. We provide direct microscopic examination of postregrowth hairs compared to normal and cross-polarized light microscopy.

PMID: 22530334 [PubMed - indexed for MEDLINE]

Categories: Publications from Members of the BIIC

Lipopolysaccharides Impair Insulin Gene Expression in Isolated Islets of Langerhans via Toll-Like Receptor-4 and NF-κB Signalling.

All pubs - Fri, 05/11/2012 - 02:00

Lipopolysaccharides Impair Insulin Gene Expression in Isolated Islets of Langerhans via Toll-Like Receptor-4 and NF-κB Signalling.

PLoS One. 2012;7(4):e36200

Authors: Amyot J, Semache M, Ferdaoussi M, Fontés G, Poitout V

Abstract
BACKGROUND: Type 2 diabetes is characterized by pancreatic β-cell dysfunction and is associated with low-grade inflammation. Recent observations suggest that the signalling cascade activated by lipopolysaccharides (LPS) binding to Toll-Like Receptor 4 (TLR4) exerts deleterious effects on pancreatic β-cell function; however, the molecular mechanisms of these effects are incompletely understood. In this study, we tested the hypothesis that LPS alters insulin gene expression via TLR4 and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) in islets.
METHODOLOGY/PRINCIPAL FINDINGS: A 24-h exposure of isolated human, rat and mouse islets of Langerhans to LPS dose-dependently reduced insulin gene expression. This was associated in mouse and rat islets with decreased mRNA expression of pancreas-duodenum homebox-1 (PDX-1) and mammalian homologue of avian MafA/l-Maf (MafA). Accordingly, LPS exposure also decreased glucose-induced insulin secretion. LPS repression of insulin, PDX-1 and MafA expression, as well as its inhibition of insulin secretion, were not observed in islets from TLR4-deficient mice. LPS inhibition of β-cell gene expression in rat islets was prevented by inhibition of the NF-κB pathway, but not the p38 mitogen-activated protein kinase (p38 MAPK) pathway.
CONCLUSIONS/SIGNIFICANCE: Our findings demonstrate that LPS inhibit β-cell gene expression in a TLR4-dependent manner and via NF-κB signaling in pancreatic islets, suggesting a novel mechanism by which the gut microbiota might affect pancreatic β-cell function.

PMID: 22558381 [PubMed - in process]

Categories: Publications from Members of the BIIC

NAD kinase (NADK) regulates the size of NADPH pool and insulin secretion in pancreatic beta cells.

All pubs - Sat, 05/05/2012 - 02:00

NAD kinase (NADK) regulates the size of NADPH pool and insulin secretion in pancreatic beta cells.

Am J Physiol Endocrinol Metab. 2012 May 1;

Authors: Gray JP, Alavian KN, Jonas EA, Heart EA

Abstract
NADPH is an important component of the antioxidant defense system and a proposed mediator in glucose-stimulated insulin secretion (GSIS) from pancreatic β-cells. An increase in the NADPH/NADP(+) ratio has been reported to occur within minutes following the rise in glucose concentration in β-cells. However, 30 minutes following the increase in glucose, the total NADPH pool also increases, through a mechanism not yet characterized. NAD-kinase (NADK) catalyzes the de novo formation of NADP(+) by phosphorylation of NAD(+). NAD kinases have been shown to be essential for redox regulation, oxidative stress defense, and survival in bacteria and yeast. However studies on NADK in eukaryotic cells are scarce and the function of this enzyme has not been described in β-cells. We employed INS-1 832/13 cells, an insulin secreting rat β-cell line, to investigate the role of NADK in β-cell metabolic pathways. Adenoviral-mediated over-expression of NADK resulted in a 2-3 fold increase of the total NADPH pool and NADPH/NADP+ ratio, suggesting that NADP+ formed by the NADK-catalyzed reaction is rapidly reduced to NADPH via cytosolic reductases. This increase in the NADPH pool was accompanied by an increase in GSIS in NADK over-expressing cells. Furthermore, NADK over-expression protected β-cells against oxidative damage by the redox cycling agent menadione, and reversed menadione-mediated inhibition of the GSIS. In parallel, knock down of NADK via shRNA exerted an opposite effect on all these parameters. These data suggest that NADK kinase regulates intracellular redox and affects insulin secretion and oxidative defense in the β-cell.

PMID: 22550069 [PubMed - as supplied by publisher]

Categories: Publications from Members of the BIIC

Reversal of muscle insulin resistance by weight reduction in young, lean, insulin-resistant offspring of parents with type 2 diabetes.

All pubs - Fri, 05/04/2012 - 02:00

Reversal of muscle insulin resistance by weight reduction in young, lean, insulin-resistant offspring of parents with type 2 diabetes.

Proc Natl Acad Sci U S A. 2012 Apr 30;

Authors: Petersen KF, Dufour S, Morino K, Yoo PS, Cline GW, Shulman GI

Abstract
To examine the role of intramyocellular lipid (IMCL) accumulation as well as circulating cytokines, branched-chain amino acids and acylcarnitines in the pathogenesis of muscle insulin resistance in healthy, young, lean insulin-resistant offspring of parents with type 2 diabetes (IR offspring), we measured these factors in plasma and used (1)H magnetic resonance spectroscopy to assess IMCL content and hyperinsulinemic-euglycemic clamps using [6,6-(2)H(2)] glucose to assess rates of insulin-stimulated peripheral glucose metabolism before and after weight reduction. Seven lean (body mass index < 25 kg/m(2)), young, sedentary IR offspring were studied before and after weight stabilization following a hypocaloric (1,200 Kcal) diet for ∼9 wks. This diet resulted in an average weight loss of 4.1 ± 0.6 kg (P < 0.0005), which was associated with an ∼30% reduction of IMCL from 1.1 ± 0.2% to 0.8 ± 0.1% (P = 0.045) and an ∼30% improvement in insulin-stimulated muscle glucose uptake [3.7 ± 0.3 vs. 4.8 ± 0.1 mg/(kg-min), P = 0.01]. This marked improvement in insulin-stimulated peripheral insulin responsiveness occurred independently of changes in plasma concentrations of TNF-α, IL-6, total adiponectin, C-reactive protein, acylcarnitines, and branched-chain amino acids. In conclusion, these data support the hypothesis that IMCL accumulation plays an important role in causing muscle insulin resistance in young, lean IR offspring, and that both are reversible with modest weight loss.

PMID: 22547801 [PubMed - as supplied by publisher]

Categories: Publications from Members of the BIIC

Distinct Functional Roles of the Two Terminal Halves of Eukaryotic Phosphofructokinase.

All pubs - Wed, 05/02/2012 - 02:00

Distinct Functional Roles of the Two Terminal Halves of Eukaryotic Phosphofructokinase.

Biochem J. 2012 Apr 25;

Authors: Martínez-Costa OH, Sánchez V, Lázaro A, Hernández ED, Tornheim K, Aragón JJ

Abstract
Eukaryotic phosphofructokinase, a key regulatory enzyme in glycolysis, has homologous N- and C-terminal domains thought to result from duplication, fusion, and divergence of an ancestral prokaryotic gene. It has been suggested that both the active site and the fructose 2,6-P2 allosteric site are formed by opposing N- and C-termini of subunits oriented antiparallel in a dimer. On the contrary, we show here that in fact the N-terminal halves form the active site, since expression of the N-terminal half of the enzymes from Dictyostelium discoideum and human muscle in phosphofructokinase-deficient yeast restored growth on glucose. However, the N-terminus alone was not stable in vitro. The C-terminus is not catalytic but is needed for stability of the enzyme, as is the connecting peptide that normally joins the two domains (here included in the N-terminus). Co-expression of homologous, but not heterologous, N- and C-termini yielded stable, fully active enzymes in vitro with sizes and kinetic properties similar to those of the wild type tetrameric enzymes. This indicates that the separately translated domains can fold sufficiently well to bind to each other, that such binding of complementary domains is stable and that the alignment is sufficiently accurate and tight as to preserve metabolite binding sites and allosteric interactions.

PMID: 22530721 [PubMed - as supplied by publisher]

Categories: Publications from Members of the BIIC

Glucose activates free fatty acid receptor 1 gene transcription via phosphatidylinositol-3-kinase-dependent O-GlcNAcylation of pancreas-duodenum homeobox-1.

All pubs - Thu, 04/26/2012 - 02:00

Glucose activates free fatty acid receptor 1 gene transcription via phosphatidylinositol-3-kinase-dependent O-GlcNAcylation of pancreas-duodenum homeobox-1.

Proc Natl Acad Sci U S A. 2012 Feb 14;109(7):2376-81

Authors: Kebede M, Ferdaoussi M, Mancini A, Alquier T, Kulkarni RN, Walker MD, Poitout V

Abstract
The G protein-coupled free fatty acid receptor-1 (FFA1/GPR40) plays a major role in the regulation of insulin secretion by fatty acids. GPR40 is considered a potential therapeutic target to enhance insulin secretion in type 2 diabetes; however, its mode of regulation is essentially unknown. The aims of this study were to test the hypothesis that glucose regulates GPR40 gene expression in pancreatic β-cells and to determine the mechanisms of this regulation. We observed that glucose stimulates GPR40 gene transcription in pancreatic β-cells via increased binding of pancreas-duodenum homeobox-1 (Pdx-1) to the A-box in the HR2 region of the GPR40 promoter. Mutation of the Pdx-1 binding site within the HR2 abolishes glucose activation of GPR40 promoter activity. The stimulation of GPR40 expression and Pdx-1 binding to the HR2 in response to glucose are mimicked by N-acetyl glucosamine, an intermediate of the hexosamine biosynthesis pathway, and involve PI3K-dependent O-GlcNAcylation of Pdx-1 in the nucleus. We demonstrate that O-GlcNAc transferase (OGT) interacts with the product of the PI3K reaction, phosphatidylinositol 3,4,5-trisphosphate (PIP(3)), in the nucleus. This interaction enables OGT to catalyze O-GlcNAcylation of nuclear proteins, including Pdx-1. We conclude that glucose stimulates GPR40 gene expression at the transcriptional level through Pdx-1 binding to the HR2 region and via a signaling cascade that involves an interaction between OGT and PIP(3) at the nuclear membrane. These observations reveal a unique mechanism by which glucose metabolism regulates the function of transcription factors in the nucleus to induce gene expression.

PMID: 22308370 [PubMed - indexed for MEDLINE]

Categories: Publications from Members of the BIIC

CT-PET weighted image fusion for separately scanned whole body rat.

All pubs - Fri, 04/20/2012 - 02:00

CT-PET weighted image fusion for separately scanned whole body rat.

Med Phys. 2012 Jan;39(1):533-42

Authors: Suh JW, Kwon OK, Scheinost D, Sinusas AJ, Cline GW, Papademetris X

Abstract
PURPOSE: The limited resolution and lack of spatial information in positron emission tomography (PET) images require the complementary anatomic information from the computed tomography (CT) and/or magnetic resonance imaging (MRI). Therefore, multimodality image fusion techniques such as PET/CT are critical in mapping the functional images to structural images and thus facilitate the interpretation of PET studies. In our experimental situation, the CT and PET images are acquired in separate scanners at different times and the inherent differences in the imaging protocols produce significant nonrigid changes between the two acquisitions in addition to dissimilar image characteristics. The registration conditions are also poor because CT images have artifacts due to the limitation of current scanning settings, while PET images are very blurry (in transmission-PET) and have vague anatomical structure boundaries (in emission-PET).
METHODS: The authors present a new method for whole body small animal multimodal registration. In particular, the authors register whole body rat CT image and PET images using a weighted demons algorithm. The authors use both the transmission-PET and the emission-PET images in the registration process emphasizing particular regions of the moving transmission-PET image using the emission-PET image. After a rigid transformation and a histogram matching between the CT and the transmission-PET images, the authors deformably register the transmission-PET image to the CT image with weights based on the intensity-normalized emission-PET image. For the deformable registration process, the authors develop a weighted demons registration method that can give preferences to particular regions of the input image using a weight image.
RESULTS: The authors validate the results with nine rat image sets using the M-Hausdorff distance (M-HD) similarity measure with different outlier-suppression parameters (OSP). In comparison with standard methods such as the regular demons and the normalized mutual information (NMI)-based nonrigid free-form deformation (FFD) registration, the proposed weighted demons registration method shows average M-HD errors: 3.99 ± 1.37 (OSP = 10), 5.04 ± 1.59 (OSP = 20) and 5.92 ± 1.61 (OSP = ∞) with statistical significance (p < 0.0003) respectively, while NMI-based nonrigid FFD has average M-HD errors: 5.74 ± 1.73 (OSP = 10), 7.40 ± 7.84 (OSP = 20) and 9.83 ± 4.13 (OSP = ∞), and the regular demons has average M-HD errors: 6.79 ± 0.83 (OSP = 10), 9.19 ± 2.39 (OSP = 20) and 11.63 ± 3.99 (OSP = ∞), respectively. In addition to M-HD comparisons, the visual comparisons on the faint-edged region between the CT and the aligned PET images also show the encouraging improvements over the other methods.
CONCLUSIONS: In the whole body multimodal registration between CT and PET images, the utilization of both the transmission-PET and the emission-PET images in the registration process by emphasizing particular regions of the transmission-PET image using an emission-PET image is effective. This method holds promise for other image fusion applications where multiple (more than two) input images should be registered into a single informative image.

PMID: 22225323 [PubMed - indexed for MEDLINE]

Categories: Publications from Members of the BIIC

Islets transplanted in immunoisolation devices: a review of the progress and the challenges that remain.

All pubs - Wed, 04/18/2012 - 02:00

Islets transplanted in immunoisolation devices: a review of the progress and the challenges that remain.

Endocr Rev. 2011 Dec;32(6):827-44

Authors: O'Sullivan ES, Vegas A, Anderson DG, Weir GC

Abstract
The concept of using an immunoisolation device to facilitate the transplantation of islets without the need for immunosuppression has been around for more than 50 yr. Significant progress has been made in developing suitable materials that satisfy the need for biocompatibility, durability, and permselectivity. However, the search is ongoing for a device that allows sufficient oxygen transfer while maintaining a barrier to immune cells and preventing rejection of the transplanted tissue. Separating the islets from the rich blood supply in the native pancreas takes its toll. The immunoisolated islets commonly suffer from hypoxia and necrosis, which in turn triggers a host immune response. Efforts have been made to improve the supply of nutrients by using proangiogenic factors to augment the development of a vascular supply in the transplant site, by using small islet cell aggregates to reduce the barrier to diffusion of oxygen, or by creating scaffolds that are in close proximity to a vascular network such as the omental blood supply. Even if these efforts are successful, the shortage of donor islet tissue available for transplantation remains a major problem. To this end, a search for a renewable source of insulin-producing cells is ongoing; whether these will come from adult or embryonic stem cells or xenogeneic sources remains to be seen. Herein we will review the above issues and chart the progress made with various immunoisolation devices in small and large animal models and the small number of clinical trials carried out to date.

PMID: 21951347 [PubMed - indexed for MEDLINE]

Categories: Publications from Members of the BIIC

Reactive oxygen species facilitate translocation of hormone sensitive lipase to the lipid droplet during lipolysis in human differentiated adipocytes.

All pubs - Tue, 04/17/2012 - 02:00

Reactive oxygen species facilitate translocation of hormone sensitive lipase to the lipid droplet during lipolysis in human differentiated adipocytes.

PLoS One. 2012;7(4):e34904

Authors: Krawczyk SA, Haller JF, Ferrante T, Zoeller RA, Corkey BE

Abstract
In obesity, there is an increase in reactive oxygen species (ROS) within adipose tissue caused by increases in inflammation and overnutrition. Hormone sensitive lipase (HSL) is part of the canonical lipolytic pathway and critical for complete lipolysis. This study hypothesizes that ROS is a signal that integrates regulation of lipolysis by targeting HSL. Experiments were performed with human differentiated adipocytes from the subcutaneous depot. Antioxidants were employed as a tool to decrease ROS, and it was found that scavenging ROS with diphenyliodonium, N-acetyl cysteine, or resveratrol decreased lipolysis in adipocytes. HSL phosphorylation of a key serine residue, Ser552, as well as translocation of this enzyme from the cytosol to the lipid droplet upon lipolytic stimulation were both abrogated by scavenging ROS. The phosphorylation status of other serine residues on HSL were not affected. These findings are significant because they document that ROS contributes to the physiological regulation of lipolysis via an effect on translocation. Such regulation could be useful in developing new obesity therapies.

PMID: 22493722 [PubMed - in process]

Categories: Publications from Members of the BIIC

Evolving insights regarding mechanisms for the inhibition of insulin release by norepinephrine and heterotrimeric G proteins.

All pubs - Tue, 04/17/2012 - 02:00

Evolving insights regarding mechanisms for the inhibition of insulin release by norepinephrine and heterotrimeric G proteins.

Am J Physiol Cell Physiol. 2012 Apr 4;

Authors: Straub SG, Sharp GW

Abstract
Norepinephrine has for many years been known to have three major effects on the pancreatic β-cell which lead to the inhibition of insulin release. These are activation of K(+) channels to hyperpolarize the cell and prevent the gating of voltage-dependent Ca(2+) channels that increase [Ca(2+)]i and trigger release; inhibition of adenylyl cyclases, thus preventing the augmentation of stimulated insulin release by cyclic AMP; and a "distal" effect that occurs downstream of increased [Ca(2+)]i to inhibit exocytosis. All three are mediated by the pertussis toxin (PTX)-sensitive heterotrimeric Gi and Go proteins. The distal inhibitory effect on exocytosis is now known to be due to the binding of G protein βγ subunits to the synaptosomal-associated protein of 25kDa (SNAP-25) on the soluble NSF attachment protein receptor (SNARE) complex. Recent studies have uncovered two more actions of norepinephrine on the β-cell, 1. Retardation of the refilling of the readily releasable granule pool after it has been discharged, an action that is mediated by Gα(i1) and/or Gα(i2), and 2. Inhibition of endocytosis that is mediated by Gz. Of importance also are new findings that Gα(o) regulates the number of docked granules in the β-cell, and that Gα(o2) maintains a tonic inhibitory influence on secretion. The latter provides another explanation as to why PTX, which blocks the effect of Gα(o2) was initially called "islet activating protein." Finally, there is clear evidence that overexpression of α(2A)-adrenergic receptors in β-cells can cause type 2 diabetes.

PMID: 22492651 [PubMed - as supplied by publisher]

Categories: Publications from Members of the BIIC

Altered insulin receptor signalling and β-cell cycle dynamics in type 2 diabetes mellitus.

All pubs - Tue, 04/17/2012 - 02:00

Altered insulin receptor signalling and β-cell cycle dynamics in type 2 diabetes mellitus.

PLoS One. 2011;6(11):e28050

Authors: Folli F, Okada T, Perego C, Gunton J, Liew CW, Akiyama M, D'Amico A, La Rosa S, Placidi C, Lupi R, Marchetti P, Sesti G, Hellerstein M, Perego L, Kulkarni RN

Abstract
Insulin resistance, reduced β-cell mass, and hyperglucagonemia are consistent features in type 2 diabetes mellitus (T2DM). We used pancreas and islets from humans with T2DM to examine the regulation of insulin signaling and cell-cycle control of islet cells. We observed reduced β-cell mass and increased α-cell mass in the Type 2 diabetic pancreas. Confocal microscopy, real-time PCR and western blotting analyses revealed increased expression of PCNA and down-regulation of p27-Kip1 and altered expression of insulin receptors, insulin receptor substrate-2 and phosphorylated BAD. To investigate the mechanisms underlying these findings, we examined a mouse model of insulin resistance in β-cells--which also exhibits reduced β-cell mass, the β-cell-specific insulin receptor knockout (βIRKO). Freshly isolated islets and β-cell lines derived from βIRKO mice exhibited poor cell-cycle progression, nuclear restriction of FoxO1 and reduced expression of cell-cycle proteins favoring growth arrest. Re-expression of insulin receptors in βIRKO β-cells reversed the defects and promoted cell cycle progression and proliferation implying a role for insulin-signaling in β-cell growth. These data provide evidence that human β- and α-cells can enter the cell-cycle, but proliferation of β-cells in T2DM fails due to G1-to-S phase arrest secondary to defective insulin signaling. Activation of insulin signaling, FoxO1 and proteins in β-cell-cycle progression are attractive therapeutic targets to enhance β-cell regeneration in the treatment of T2DM.

PMID: 22140505 [PubMed - indexed for MEDLINE]

Categories: Publications from Members of the BIIC

Enhanced GLP-1- and Sulfonylurea-Induced Insulin Secretion in Islets Lacking Leptin Signaling.

All pubs - Sun, 04/15/2012 - 02:00

Enhanced GLP-1- and Sulfonylurea-Induced Insulin Secretion in Islets Lacking Leptin Signaling.

Mol Endocrinol. 2012 Apr 3;

Authors: Morioka T, Dishinger JF, Reid KR, Liew CW, Zhang T, Inaba M, Kennedy RT, Kulkarni RN

Abstract
We have previously reported that the absence of leptin signaling in β-cells enhances glucose-stimulated insulin secretion and improves glucose tolerance in vivo. To investigate the relevance of β-cell leptin signaling in the context of postprandial or therapeutic insulin secretion, we examined the cross talk between leptin and glucagon-like peptide (GLP)-1 and sulfonylurea actions. Single and size-matched islets isolated from control or pancreas-specific leptin receptor knockout (pancreas-ObR-KO) mice were treated either with GLP-1 or with glibenclamide. Leptin suppressed GLP-1-stimulated intracellular Ca(2+) concentrations ([Ca(2+)](i)) increase that paralleled the decrease in insulin secretion in controls. In contrast, and as expected, the ObR-KO islets were nonresponsive to leptin, and instead, showed a 2.8-fold greater GLP-1-stimulated [Ca(2+)](i) increase and a 1.7-fold greater insulin secretion. Phosphorylation of cAMP-responsive element binding protein was enhanced, and phosphodiesterase enzymatic activity was suppressed in MIN6 β-cells with ObR knockdown compared with controls. The ObR-KO islets also showed significantly higher glibenclamide-induced insulin secretion compared with control islets, whereas [Ca(2+)](i) was similar to the controls. These data support enhanced insulinotropic effects of glucose, GLP-1, and sulfonylureas in the islets lacking leptin signaling with potential therapeutic implications.

PMID: 22474124 [PubMed - as supplied by publisher]

Categories: Publications from Members of the BIIC

Coordinated defects in hepatic long chain fatty acid metabolism and triglyceride accumulation contribute to insulin resistance in non-human primates.

All pubs - Sun, 04/15/2012 - 02:00

Coordinated defects in hepatic long chain fatty acid metabolism and triglyceride accumulation contribute to insulin resistance in non-human primates.

PLoS One. 2011;6(11):e27617

Authors: Kamath S, Chavez AO, Gastaldelli A, Casiraghi F, Halff GA, Abrahamian GA, Davalli AM, Bastarrachea RA, Comuzzie AG, Guardado-Mendoza R, Jimenez-Ceja LM, Mattern V, Paez AM, Ricotti A, Tejero ME, Higgins PB, Rodriguez-Sanchez IP, Tripathy D, DeFronzo RA, Dick EJ, Cline GW, Folli F

Abstract
UNLABELLED: Non-alcoholic fatty liver disease (NAFLD) is characterized by accumulation of triglycerides (TG) in hepatocytes, which may also trigger cirrhosis. The mechanisms of NAFLD are not fully understood, but insulin resistance has been proposed as a key determinant.
AIMS: To determine the TG content and long chain fatty acyl CoA composition profile in liver from obese non-diabetic insulin resistant (IR) and lean insulin sensitive (IS) baboons in relation with hepatic and peripheral insulin sensitivity.
METHODS: Twenty baboons with varying grades of adiposity were studied. Hepatic (liver) and peripheral (mainly muscle) insulin sensitivity was measured with a euglycemic clamp and QUICKI. Liver biopsies were performed at baseline for TG content and LCFA profile by mass spectrometry, and histological analysis. Findings were correlated with clinical and biochemical markers of adiposity and insulin resistance.
RESULTS: Obese IR baboons had elevated liver TG content compared to IS. Furthermore, the concentration of unsaturated (LC-UFA) was greater than saturated (LC-SFA) fatty acyl CoA in the liver. Interestingly, LC-FA UFA and SFA correlated with waist, BMI, insulin, NEFA, TG, QUICKI, but not M/I. Histological findings of NAFLD ranging from focal to diffuse hepatic steatosis were found in obese IR baboons.
CONCLUSION: Liver TG content is closely related with both hepatic and peripheral IR, whereas liver LC-UFA and LC-SFA are closely related only with hepatic IR in non-human primates. Mechanisms leading to the accumulation of TG, LC-UFA and an altered UFA: LC-SFA ratio may play an important role in the pathophysiology of fatty liver disease in humans.

PMID: 22125617 [PubMed - indexed for MEDLINE]

Categories: Publications from Members of the BIIC

Effects of Bixa orellana L. Seeds on Hyperlipidemia.

All pubs - Fri, 04/06/2012 - 02:00

Effects of Bixa orellana L. Seeds on Hyperlipidemia.

Phytother Res. 2012 Mar 26;

Authors: Ferreira JM, Sousa DF, Dantas MB, Fonseca SG, Menezes DB, Martins AM, de Queiroz MG

Abstract
Bixa orellana L., urucum, or urucu, a native tropical tree of Central and South American rain forests is used to treat various diseases in popular medicine. In Ceará, Northeast of Brazil, the seeds of urucum have been used for the treatment of high lipid blood levels. The present study investigated the effects of the aqueous extract from Bixa orellana seeds (AEBO) in mice with hyperlipidemia induced by tyloxapol, fructose and ethanol. In hyperlipidemia induced by Triton WR1339, 400 and 800 mg/kg AEBO reduced triglycerides (TG) serum levels at 24 h and 48 h. In the study of hypertriglyceridemia induced by fructose, AEBO in doses of 400 mg/kg and 800 mg/kg reduced TG levels by 48.2% and 48.7%, respectively. Finally, the ethanol experimental model with 400 mg/kg AEBO promoted a reduction of 33.6% of TG levels, while the 800 mg/kg concentration reduced hypertriglyceridemia in 62.2%. In conclusion, the aqueous extract of the seeds of Bixa orellana was capable of reversing the hypertriglyceridemia induced by Triton, fructose and ethanol, demonstrating a hypolipidemic effect. However, further studies are necessary to discover the precise mechanism of action. Copyright © 2012 John Wiley & Sons, Ltd.

PMID: 22451331 [PubMed - as supplied by publisher]

Categories: Publications from Members of the BIIC

ER Stress as a Trigger for β-Cell Dysfunction and Autoimmunity in Type 1 Diabetes.

All pubs - Fri, 04/06/2012 - 02:00

ER Stress as a Trigger for β-Cell Dysfunction and Autoimmunity in Type 1 Diabetes.

Diabetes. 2012 Apr;61(4):780-1

Authors: O'Sullivan-Murphy B, Urano F

PMID: 22442299 [PubMed - in process]

Categories: Publications from Members of the BIIC

Cannabinoids Induce Pancreatic β-Cell Death by Directly Inhibiting Insulin Receptor Activation.

All pubs - Mon, 04/02/2012 - 02:00

Cannabinoids Induce Pancreatic β-Cell Death by Directly Inhibiting Insulin Receptor Activation.

Sci Signal. 2012;5(216):ra23

Authors: Kim W, Lao Q, Shin YK, Carlson OD, Lee EK, Gorospe M, Kulkarni RN, Egan JM

Abstract
Cannabinoid 1 (CB1) receptors have been previously detected in pancreatic β cells, where they attenuate insulin action. We now report that CB1 receptors form a heteromeric complex with insulin receptors and the heterotrimeric guanosine triphosphate-binding protein α subunit Gα(i). Gα(i) inhibited the kinase activity of the insulin receptor in β cells by directly binding to the activation loop in the tyrosine kinase domain of the receptor. Consequently, phosphorylation of proapoptotic protein Bad was reduced and its apoptotic activity was stimulated, leading to β-cell death. Pharmacological blockade or genetic deficiency of CB1 receptors enhanced insulin receptor signaling after injury, leading to reduced blood glucose concentrations and activation of Bad, which increased β-cell survival. These findings provide direct evidence of physical and functional interactions between CB1 and insulin receptors and suggest a mechanism whereby peripherally acting CB1 receptor antagonists improve insulin action in insulin-sensitive tissues independent of the other metabolic effects of CB1 receptors.

PMID: 22434934 [PubMed - in process]

Categories: Publications from Members of the BIIC

Improvement of islet function in a bioartificial pancreas by enhanced oxygen supply and growth hormone releasing hormone agonist.

All pubs - Thu, 03/22/2012 - 02:00

Improvement of islet function in a bioartificial pancreas by enhanced oxygen supply and growth hormone releasing hormone agonist.

Proc Natl Acad Sci U S A. 2012 Mar 5;

Authors: Ludwig B, Rotem A, Schmid J, Weir GC, Colton CK, Brendel MD, Neufeld T, Block NL, Yavriyants K, Steffen A, Ludwig S, Chavakis T, Reichel A, Azarov D, Zimermann B, Maimon S, Balyura M, Rozenshtein T, Shabtay N, Vardi P, Bloch K, de Vos P, Schally AV, Bornstein SR, Barkai U

Abstract
Islet transplantation is a feasible therapeutic alternative for metabolically labile patients with type 1 diabetes. The primary therapeutic target is stable glycemic control and prevention of complications associated with diabetes by reconstitution of endogenous insulin secretion. However, critical shortage of donor organs, gradual loss in graft function over time, and chronic need for immunosuppression limit the indication for islet transplantation to a small group of patients. Here we present a promising approach to address these limitations by utilization of a macrochamber specially engineered for islet transplantation. The s.c. implantable device allows for controlled and adequate oxygen supply and provides immunological protection of donor islets against the host immune system. The minimally invasive implantable chamber normalized blood glucose in streptozotocin-induced diabetic rodents for up to 3 mo. Sufficient graft function depended on oxygen supply. Pretreatment with the growth hormone-releasing hormone (GHRH) agonist, JI-36, significantly enhanced graft function by improving glucose tolerance and increasing β-cell insulin reserve in rats thereby allowing for a reduction of the islet mass required for metabolic control. As a result of hypervascularization of the tissue surrounding the device, no relevant delay in insulin response to glucose changes has been observed. Consequently, this system opens up a fundamental strategy for therapy of diabetes and may provide a promising avenue for future approaches to xenotransplantation.

PMID: 22393012 [PubMed - as supplied by publisher]

Categories: Publications from Members of the BIIC

RNA-Binding Protein HuD Controls Insulin Translation.

All pubs - Thu, 03/22/2012 - 02:00

RNA-Binding Protein HuD Controls Insulin Translation.

Mol Cell. 2012 Feb 29;

Authors: Lee EK, Kim W, Tominaga K, Martindale JL, Yang X, Subaran SS, Carlson OD, Mercken EM, Kulkarni RN, Akamatsu W, Okano H, Perrone-Bizzozero NI, de Cabo R, Egan JM, Gorospe M

Abstract
Although expression of the mammalian RNA-binding protein HuD was considered to be restricted to neurons, we report that HuD is present in pancreatic β cells, where its levels are controlled by the insulin receptor pathway. We found that HuD associated with a 22-nucleotide segment of the 5' untranslated region (UTR) of preproinsulin (Ins2) mRNA. Modulating HuD abundance did not alter Ins2 mRNA levels, but HuD overexpression decreased Ins2 mRNA translation and insulin production, and conversely, HuD silencing enhanced Ins2 mRNA translation and insulin production. Following treatment with glucose, HuD rapidly dissociated from Ins2 mRNA and enabled insulin biosynthesis. Importantly, HuD-knockout mice displayed higher insulin levels in pancreatic islets, while HuD-overexpressing mice exhibited lower insulin levels in islets and in plasma. In sum, our results identify HuD as a pivotal regulator of insulin translation in pancreatic β cells.

PMID: 22387028 [PubMed - as supplied by publisher]

Categories: Publications from Members of the BIIC