bluuebunny/crossref_metadata_2025 huggingface dataset:
Neuromuscular Development in the Absence of Programmed Cell Death: Phenotypic Alteration of Motoneurons and Muscle
Authors: Buss Robert R. , Gould Thomas W. , Ma Jianjun , Vinsant Sharon , Prevette David , Winseck Adam , Toops Kimberly A. , Hammarback James A. , Smith Thomas L. , Oppenheim Ronald W.
Published: December 2006

The widespread, massive loss of developing neurons in the central and peripheral nervous system of birds and mammals is generally considered to be an evolutionary adaptation. However, until recently, models for testing both the immediate and long-term consequences of preventing this normal cell loss have not been available. We have taken advantage of several methods for preventing neuronal deathin vivoto ask whether rescued neurons [e.g., motoneurons (MNs)] differentiate normally and become functionally incorporated into the nervous system. Although many aspects of MN differentiation occurred normally after the prevention of cell death (including the expression of several motoneuron-specific markers, axon projections into the ventral root and peripheral nerves, ultrastructure, dendritic arborization, and afferent axosomatic synapses), other features of the neuromuscular system (MNs and muscle) were abnormal. The cell bodies and axons of MNs were smaller than normal, many MN axons failed to become myelinated or to form functional synaptic contacts with target muscles, and a subpopulation of rescued cells were transformed from α- to γ-like MNs. Additionally, after the rescue of MNs in myogenin glial cell line-derived neurotrophic factor (MyoGDNF) transgenic mice, myofiber differentiation of extrafusal skeletal muscle was transformed and muscle physiology and motor behaviors were abnormal. In contrast, extrafusal myofiber phenotype, muscle physiology, and (except for muscle strength tests) motor behaviors were all normal after the rescue of MNs by genetic deletion of the proapoptotic geneBax. However, there was an increase in intrafusal muscle fibers (spindles) inBaxknock-out versus both wild-type andMyoGDNFmice. Together, these data indicate that after the prevention of MN death, the neuromuscular system becomes transformed in novel ways to compensate for the presence of the thousands of excess cells.
Forebrain Adenosine A2AReceptors Contribute to l-3,4-Dihydroxyphenylalanine-Induced Dyskinesia in Hemiparkinsonian Mice
Authors: Xiao Danqing , Bastia Elena , Xu Yue-Hang , Benn Caroline L. , Cha Jang-Ho J. , Peterson Tracy S. , Chen Jiang-Fan , Schwarzschild Michael A.
Published: December 2006

Adenosine A2Areceptor antagonists provide a promising nondopaminergic approach to the treatment of Parkinson's disease (PD). Initial clinical trials of A2Aantagonists targeted PD patients who had already developed treatment complications known asl-3,4-dihydroxyphenylalanine (l-DOPA)-induced dyskinesia (LID) in an effort to improve symptoms while reducing existing LID. The goal of this study is to explore the effect of A2Aantagonists and targeted A2Areceptor depletion on the actual development of sensitized responses tol-DOPA in mouse models of LID in PD. Hemiparkinsonian mice (unilaterally lesioned with 6-OHDA) were treated daily for 3 weeks with a low dose ofl-DOPA (2 mg/kg) preceded by a low dose of selective A2Aantagonist (KW-6002 [(E)-1,3-diethyl-8-(3,4-dimethoxystyryl)-7-methyl-3,7-dihydro-1H-purine-2,6-dione] at 0.03 or 0.3 mg/kg, or SCH58261 [5-amino-7-(2-phenylethyl)-2-(2-furyl)-pyrazolo[4,3-e]-1,2,4-triazolo[1,5-c]pyrimidine] at 0.03 mg/kg) or vehicle intraperitoneally. In control mice, contralateral rotational responses to dailyl-DOPA gradually increased over the initial week before reaching a persistent maximum. Both A2Aantagonists inhibited the development of sensitized contralateral turning, with KW-6002 pretreatment reducing the sensitized rotational responses by up to threefold. The development of abnormal involuntary movements (a measure of LID) as well as rotational responses was attenuated by the postnatal depletion of forebrain A2Areceptors in conditional (Cre/loxPsystem) knock-out mice. These pharmacological and genetic data provide evidence that striatal A2Areceptors play an important role in the neuroplasticity underlying behavioral sensitization tol-DOPA, supporting consideration of early adjunctive therapy with an A2Aantagonist to reduce the risk of LID in PD.
Metabotropic Glutamate Receptors Differentially Regulate GABAergic Inhibition in Thalamus
Authors: Govindaiah G. , Cox Charles L.
Published: December 2006

Thalamic interneurons and thalamic reticular nucleus (TRN) neurons provide inhibitory innervation of thalamocortical cells that significantly influence thalamic gating. The local interneurons in the dorsal lateral geniculate nucleus (dLGN) give rise to two distinct synaptic outputs: classical axonal and dendrodendritic. Activation of metabotropic glutamate receptors (mGluRs) by agonists or optic tract stimulation increases the output of these presynaptic dendrites leading to increased inhibition of thalamocortical neurons. The present study was aimed to evaluate the actions of specific mGluRs on inhibitory GABA-mediated signaling. We found that the group I mGluR (mGluR1,5) agonist (RS)-3,5-dihydroxyphenylglycine (DHPG) or optic tract stimulation produced a robust increase in spontaneous IPSCs (sIPSCs) in thalamocortical neurons that was attenuated by the selective mGluR5antagonist 2-methyl-6-(phenylethynyl)pyridine hydrochloride (MPEP). In contrast, the group II mGluR (mGluR2,3) agonists (2R, 4R)-4-aminopyrrolidine-2,4-dicarboxylate (APDC) or (2S,2′R,3′R)-2-(2′3′-dicarboxycyclopropyl)glycine (DCG-IV) suppressed the frequency of sIPSCs. In addition, mGluR1,5agonist DHPG produced depolarizations and mGluR2/3agonists APDC or L-CCG-I [(2S,1′S,2′S)-2-(carboxycyclopropyl)glycine] produced hyperpolarizations in dLGN interneurons. Furthermore, the enhanced sIPSC activity by optic tract stimulation was reduced when paired with corticothalamic fiber stimulation. The present data indicate that activation of specific mGluR subtypes differentially regulates inhibitory activity via different synaptic pathways. Our results suggest that activation of specific mGluR subtypes can upregulate or downregulate inhibitory activity in thalamic relay neurons, and these actions likely shape excitatory synaptic integration and thus regulate information transfer through thalamocortical circuits.
Extracellular Hippocampal Acetylcholine Level Controls Amygdala Function and Promotes Adaptive Conditioned Emotional Response
Authors: Calandreau Ludovic , Trifilieff Pierre , Mons Nicole , Costes Laurence , Marien Marc , Marighetto Aline , Micheau Jacques , Jaffard Robert , Desmedt Aline
Published: December 2006

Ample data indicate that tone and contextual fear conditioning differentially require the amygdala and the hippocampus. However, mechanisms subserving the adaptive selection among environmental stimuli (discrete tone vs context) of those that best predict an aversive event are still elusive. Because the hippocampal cholinergic neurotransmission is thought to play a critical role in the coordination between different memory systems leading to the selection of appropriate behavioral strategies, we hypothesized that this cholinergic signal may control the competing acquisition of amygdala-mediated tone and contextual conditioning. Using pavlovian fear conditioning in mice, we first show a higher level of hippocampal acetylcholine release and a specific pattern of extracellular signal-regulated kinase 1/2 (ERK1/2) activation within the lateral (LA) and basolateral (BLA) amygdala under conditions in which the context is a better predictor than a discrete tone stimulus. Second, we demonstrate that levels of hippocampal cholinergic neurotransmission are causally related to the patterns of ERK1/2 activation in amygdala nuclei and actually determine the selection among the context or the simple tone the stimulus that best predicts the aversive event. Specifically, decreasing the hippocampal cholinergic signal not only impaired contextual conditioning but also mimicked conditioning to the discrete tone, both in terms of the behavioral outcome and the LA/BLA ERK1/2 activation pattern. Conversely, increasing this cholinergic signal not only disrupted tone conditioning but also promoted contextual fear conditioning. Hence, these findings highlight that hippocampal cholinergic neurotransmission controls amygdala function, thereby leading to the selection of relevant emotional information.
Bidirectional Activity-Dependent Regulation of Neuronal Ion Channel Phosphorylation
Authors: Misonou Hiroaki , Menegola Milena , Mohapatra Durga P. , Guy Lauren K. , Park Kang-Sik , Trimmer James S.
Published: December 2006

Activity-dependent dephosphorylation of neuronal Kv2.1 channels yields hyperpolarizing shifts in their voltage-dependent activation and homoeostatic suppression of neuronal excitability. We recently identified 16 phosphorylation sites that modulate Kv2.1 function. Here, we show that in mammalian neurons, compared with other regulated sites, such as serine (S)563, phosphorylation at S603 is supersensitive to calcineurin-mediated dephosphorylation in response to kainate-induced seizuresin vivo, and brief glutamate stimulation of cultured hippocampal neurons.In vitrocalcineurin digestion shows that supersensitivity of S603 dephosphorylation is an inherent property of Kv2.1. Conversely, suppression of neuronal activity by anestheticin vivocauses hyperphosphorylation at S603 but not S563. Distinct regulation of individual phosphorylation sites allows for graded and bidirectional homeostatic regulation of Kv2.1 function. S603 phosphorylation represents a sensitive bidirectional biosensor of neuronal activity.
Deficits in Synaptic Transmission and Learning in Amyloid Precursor Protein (APP) Transgenic Mice Require C-Terminal Cleavage of APP
Authors: Saganich Michael J. , Schroeder Brock E. , Galvan Veronica , Bredesen Dale E. , Koo Edward H. , Heinemann Stephen F.
Published: December 2006

Synaptic dysfunction has been shown to be one of the earliest correlates of disease progression in animal models of Alzheimer's disease. Amyloid-β protein (Aβ) is thought to play an important role in disease-related synaptic dysfunction, but the mechanism by which Aβ leads to synaptic dysfunction is not understood. Here we describe evidence that cleavage of APP in the C terminus may be necessary for the deficits present in APP transgenic mice. In APP transgenic mice with a mutated cleavage site at amino acid 664, normal synaptic transmission, synaptic plasticity, and learning were maintained despite the presence of elevated levels of APP, Aβ42, and even plaque accumulation. These results indicate that cleavage of APP may play a critical role in the development of synaptic and behavioral dysfunction in APP transgenic mice.
The Endurance and Selectivity of Spatial Patterns of Long-Term Potentiation/Depression in Dendrites under Homeostatic Synaptic Plasticity
Authors: Rabinowitch Ithai , Segev Idan
Published: December 2006

We investigated analytically and numerically the interplay between two opposing forms of synaptic plasticity: positive-feedback, long-term potentiation/depression (LTP/LTD), and negative-feedback, homeostatic synaptic plasticity (HSP). A detailed model of a CA1 pyramidal neuron, with numerous HSP-modifiable dendritic synapses, demonstrates that HSP may have an important role in selecting which spatial patterns of LTP/LTD are to last. Several measures are developed for predicting the net residual potentiation/depression after HSP from the initial spatial pattern of LTP/LTD. Under a local dendritic HSP mechanism, sparse patterns of LTP/LTD, which we show, using information theoretical tools, to have a significant impact on the output of the postsynaptic neuron, will persist. In contrast, spatially clustered patterns with a smaller impact on the output will diminish. A global somatic HSP mechanism, conversely, will favor distally occurring LTP/LTDs over proximal ones. Despite the negative-feedback nature of HSP, under both local and global HSP, numerous synaptic potentiations/depressions can persist. These experimentally testable results imply that HSP could be significantly involved in shaping the spatial distribution of synaptic weights in the dendrites and not just normalizing it, as is currently believed.
Single-Cell Characterization of Retrograde Signaling by Brain-Derived Neurotrophic Factor
Authors: Magby Jason P. , Bi Caixia , Chen Zhe-Yu , Lee Francis S. , Plummer Mark R.
Published: December 2006

Brain-derived neurotrophic factor (BDNF) is a key regulator of hippocampal synaptic plasticity in the developing and adult nervous system. It can be released from pyramidal neuron dendrites in an activity-dependent manner and has therefore been suggested to serve as a signal that provides the retrograde intercellular communication necessary for Hebbian plasticity and hippocampal-dependent learning. Although much has been learned about BDNF function by field stimulation of hippocampal neurons, it is not known whether moderate action potential-independent depolarization of single cells is capable of releasing sufficient BDNF to influence transmission at individual synapses. In this study, we show directly at the single-cell level that such modulation can occur. By using K-252a, anti-BDNF antibody, and interruption of regulated release, we confirm a model in which postsynaptic depolarization elicits calcium-dependent release of BDNF that diffuses retrogradely and enhances presynaptic transmitter release.
Upregulation of the Neuron-Specific K+/Cl−Cotransporter Expression by Transcription Factor Early Growth Response 4
Authors: Uvarov Pavel , Ludwig Anastasia , Markkanen Marika , Rivera Claudio , Airaksinen Matti S.
Published: December 2006

The expression of the neuron-specific K+/Cl−cotransporter (KCC2) is restricted to the CNS and is strongly upregulated during neuronal maturation, yielding a low intracellular chloride concentration that is required for fast synaptic inhibition in adult neurons. To elucidate the mechanisms of KCC2 gene regulation, we analyzed the KCC2 (aliasSlc12a5) promoter and proximal intron-1 regions and revealed 10 candidate transcription factor binding sites that are highly conserved in mammalian KCC2 genes. Here we focus on one of these factors, early growth response 4 (Egr4), which shows a similar developmental upregulation in CNS neurons as KCC2. KCC2 luciferase reporter constructs containing the Egr4 site (Egr4KCC2) were strongly induced by Egr4 overexpression in neuro-2a neuroblastoma cells and in cultured neurons. Egr4-mediated induction was decreased significantly by point-mutating the Egr4KCC2. Insertion of Egr4KCC2into the KCC2 basal promoter in the endogenous reverse, but not in the opposite, orientation reestablished Egr4-mediated induction. Electrophoretic mobility shift assay confirmed specific Egr4 binding to Egr4KCC2. Interference RNA-mediated knock-down of Egr4 and a dominant-negative isoform of Egr4 significantly inhibited KCC2 reporter induction and endogenous KCC2 expression in cultured neurons. Together, the results indicate an important role for Egr4 in the developmental upregulation of KCC2 gene expression.
Exendin-4 Potently Decreases Ghrelin Levels in Fasting Rats
Authors: Pérez-Tilve Diego , González-Matías Lucas , Alvarez-Crespo Mayte , Leiras Roberto , Tovar Sulay , Diéguez Carlos , Mallo Federico
Published: December 2006

Ghrelin is a potent orexigenic and adipogenic hormone that strongly influences fat deposition and the generation of hunger in obesity. Indeed, hyperghrelinemia appears to promote an increase in food intake as seen in Prader-Willi Syndrome (PWS). Exendin (Ex)-4 is an agonist of the glucagon-like peptide (GLP)-1 receptor (GLP-1r) that has anorexigenic and fat-reducing properties. Here, we report that Ex-4 reduces the levels of ghrelin by up to 74% in fasted rats. These effects are dose dependent and long lasting (up to 8 h), and they can be detected after both central and peripheral administration of Ex-4. Suppression of ghrelin was neither mimicked by GLP-1(7–36)-NH2 nor blocked by the GLP-1r antagonist Ex-(9–39). Moreover, it was independent of the levels of leptin and insulin. The decrease in ghrelin levels induced by Ex-4 may explain the reduced food intake in fasted rats, justifying the more potent anorexigenic effects of Ex-4 when compared with GLP-1. As well as the potential benefits of Ex-4 in type 2 diabetes, the potent effects of Ex-4 on ghrelin make it tempting to speculate that Ex-4 could offer a therapeutic option for PWS and other syndromes characterized by substantial amounts of circulating ghrelin.
Involvement of Apolipoprotein E in Excess Fat Accumulation and Insulin Resistance
Authors: Gao Junhong , Katagiri Hideki , Ishigaki Yasushi , Yamada Tetsuya , Ogihara Takehide , Imai Junta , Uno Kenji , Hasegawa Yutaka , Kanzaki Makoto , Yamamoto Tokuo T. , Ishibashi Shun , Oka Yoshitomo
Published: December 2006

Although apolipoprotein E (apoE) is well known to play a major role in lipid metabolism, its role in glucose and energy homeostasis remains unclear. Herein, we established apoE-deficient genetically obese Ay (apoE−/−;Ay/+) mice. ApoE deficiency in Ay mice prevented the development of obesity, with decreased fat accumulation in the liver and adipose tissues. ApoE−/−;Ay/+ mice exhibited better glucose tolerance than apoE+/+;Ay/+ mice. Insulin tolerance testing and hyperinsulinemic-euglycemic clamp study revealed marked improvement of insulin sensitivity, despite increased plasma free fatty acid levels. These metabolic phenotypes were reversed by adenoviral replenishment of apoE protein, indicating circulating apoE to be involved in increased adiposity and obesity-related metabolic disorders. Uptake of apoE-lacking VLDL into the liver and adipocytes was markedly inhibited, but adipocytes in apoE−/−;Ay/+ mice exhibited normal differentiation, suggesting that apoE-dependent VLDL transport is involved in the development of obesity, i.e., surplus fat accumulation. Interestingly, apoE−/−;Ay/+ mice exhibited decreased food intake and increased energy expenditure. Pair-feeding experiments indicate these phenomena to both contribute to the obesity-resistant phenotypes associated with apoE deficiency. Thus, apoE is involved in maintaining energy homeostasis. ApoE-dependent excess fat accumulation is a promising therapeutic target for the metabolic syndrome.
Attenuation of Angiotensin II Signaling Recouples eNOS and Inhibits Nonendothelial NOX Activity in Diabetic Mice
Authors: Oak Jeong-Ho , Cai Hua
Published: December 2006

Angiotensin II (Ang II) levels are increased in patients with diabetes, but mechanisms underlying its contribution to diabetic vascular diseases are incompletely understood. We recently reported that in aortic endothelial cells, Ang II induces endothelial nitric oxide synthase (eNOS) uncoupling to produce superoxide (O2·−) rather than nitric oxide (NO·), upon loss of the tetrahydrobiopterin (H4B) salvage enzyme dihydrofolate reductase (DHFR). Here, we found that streptozotocin-induced diabetic mice had a marked increase in aortic O2·− production, which was inhibited by N-nitro-l-arginine methyl ester hydrochloride, indicating uncoupling of eNOS. Ang II receptor type 1 blocker candesartan or ACE inhibitor captopril markedly attenuated eNOS-derived O2·− and hydrogen peroxide production while augmenting NO· bioavailability in diabetic aortas, implicating recoupling of eNOS. O2·− and NO· production were characteristically and quantitatively measured by electron spin resonance. DHFR expression was decreased in diabetic aortas but significantly restored by candesartan or captopril. Either also improved vascular H4B content and endothelium-dependent vasorelaxation in diabetes. Rac1-dependent NAD(P)H oxidase (NOX) activity was more than doubled in the endothelium-denuded diabetic aortas but was attenuated by candesartan or captopril, indicating that NOX remains active in nonendothelial vascular tissues, although uncoupled eNOS is responsible for endothelial production of O2·−. These data demonstrate a novel role of Ang II in diabetic uncoupling of eNOS and that Ang II–targeted therapy improves endothelial function via the novel mechanism of recoupling eNOS. Dual effectiveness on uncoupled eNOS and NOX may explain the high efficacy of Ang II antagonists in restoring endothelial function.
Mice With a Deletion in the Gene for CCAAT/Enhancer-Binding Protein β Are Protected Against Diet-Induced Obesity
Authors: Millward Carrie A. , Heaney Jason D. , Sinasac David S. , Chu Eric C. , Bederman Ilya R. , Gilge Danielle A. , Previs Stephen F. , Croniger Colleen M.
Published: December 2006

The CCAAT/enhancer-binding protein β (C/EBPβ) is required for adipocyte differentiation and maturation. We have studied the role of the transcription factor, C/EBPβ, in the development of diet-induced obesity. Mice with a deletion in the gene for C/EBPβ (C/EBPβ−/−) and wild-type mice were fed a high-fat diet (60% fat) for 12 weeks. The C/EBPβ−/− mice lost body fat, whereas the wild-type mice increased their total body fat on a high-fat diet. The C/EBPβ−/− mice had lower levels of blood triglycerides, free fatty acids, cholesterol, and hepatic triglyceride accumulation compared with the wild-type mice, thus protecting them from diet-induced obesity and fatty liver on a high-fat diet. Deletion of C/EBPβ gene resulted in greatly reducing hepatic lipogenic genes, acetyl CoA carboxylase, and fatty acid synthase and increasing the expression of β-oxidation genes in the brown adipose tissue. CO2 production was significantly higher in the C/EBPβ−/− mice as was the level of uncoupling protein (UCP)-1 and UCP-3 in the muscle. In conclusion, the transcription factor C/EBPβ is an important regulator in controlling lipid metabolism and in the development of diet-induced obesity.
Inhibition of Caspase-1/Interleukin-1β Signaling Prevents Degeneration of Retinal Capillaries in Diabetes and Galactosemia
Authors: Vincent Jason A. , Mohr Susanne
Published: December 2006

The proinflammatory cytokine, interleukin (IL)-1β, is known to induce vascular dysfunction and cell death. We investigated the role of IL-1β and caspase-1 (the enzyme that produces it) in diabetes-induced degeneration of retinal capillaries. Caspase-1 activity is increased in retinas of diabetic and galactosemic mice and diabetic patients. First, we investigated the effect of agents known to inhibit caspase-1 (minocycline and tetracycline) on IL-1β production and retinal capillary degeneration in diabetic and galactose-fed mice. Second, we examined the effect of genetic deletion of the IL-1β receptor on diabetes-induced caspase activities and retinal capillary degeneration. Diabetic and galactose-fed mice were injected intraperitoneally with minocycline or tetracycline (5 mg/kg). At 2 months of diabetes, minocycline inhibited hyperglycemia-induced caspase-1 activity and IL-1β production in the retina. Long-term administration of minocycline prevented retinal capillary degeneration in diabetic (6 months) and galactose-fed (13 months) mice. Tetracycline inhibited hyperglycemia-induced caspase-1 activity in vitro but not in vivo. Mice deficient in the IL-1β receptor were protected from diabetes-induced caspase activation and retinal pathology at 7 months of diabetes. These results indicate that the caspase-1/IL-1β signaling pathway plays an important role in diabetes-induced retinal pathology, and its inhibition might represent a new strategy to inhibit capillary degeneration in diabetic retinopathy.
Role for Mitochondrial Reactive Oxygen Species in Brain Lipid Sensing
Authors: Benani Alexandre , Troy Stéphanie , Carmona Maria Carmen , Fioramonti Xavier , Lorsignol Anne , Leloup Corinne , Casteilla Louis , Pénicaud Luc
Published: December 2006

The ability for the brain to sense peripheral fuel availability is mainly accomplished within the hypothalamus, which detects ongoing systemic nutrients and adjusts food intake and peripheral metabolism as needed. Here, we hypothesized that mitochondrial reactive oxygen species (ROS) could trigger sensing of nutrients within the hypothalamus. For this purpose, we induced acute hypertriglyceridemia in rats and examined the function of mitochondria in the hypothalamus. Hypertriglyceridemia led to a rapid increase in the mitochondrial respiration in the ventral hypothalamus together with a transient production of ROS. Cerebral inhibition of fatty acids–CoA mitochondrial uptake prevented the hypertriglyceridemia-stimulated ROS production, indicating that ROS derived from mitochondrial metabolism. The hypertriglyceridemia-stimulated ROS production was associated with change in the intracellular redox state without any noxious cytotoxic effects, suggesting that ROS function acutely as signaling molecules. Moreover, cerebral inhibition of hypertriglyceridemia-stimulated ROS production fully abolished the satiety related to the hypertriglyceridemia, suggesting that hypothalamic ROS production was required to restrain food intake during hypertriglyceridemia. Finally, we found that fasting disrupted the hypertriglyceridemia-stimulated ROS production, indicating that the redox mechanism of brain nutrient sensing could be modulated under physiological conditions. Altogether, these findings support the role of mitochondrial ROS as molecular actors implied in brain nutrient sensing.
Screening of 134 Single Nucleotide Polymorphisms (SNPs) Previously Associated With Type 2 Diabetes Replicates Association With 12 SNPs in Nine Genes
Authors: Willer Cristen J. , Bonnycastle Lori L. , Conneely Karen N. , Duren William L. , Jackson Anne U. , Scott Laura J. , Narisu Narisu , Chines Peter S. , Skol Andrew , Stringham Heather M. , Petrie John , Erdos Michael R. , Swift Amy J. , Enloe Sareena T. , Sprau Andrew G. , Smith Eboni , Tong Maurine , Doheny Kimberly F. , Pugh Elizabeth W. , Watanabe Richard M. , Buchanan Thomas A. , Valle Timo T. , Bergman Richard N. , Tuomilehto Jaakko , Mohlke Karen L. , Collins Francis S. , Boehnke Michael
Published: December 2006

More than 120 published reports have described associations between single nucleotide polymorphisms (SNPs) and type 2 diabetes. However, multiple studies of the same variant have often been discordant. From a literature search, we identified previously reported type 2 diabetes–associated SNPs. We initially genotyped 134 SNPs on 786 index case subjects from type 2 diabetes families and 617 control subjects with normal glucose tolerance from Finland and excluded from analysis 20 SNPs in strong linkage disequilibrium (r2 > 0.8) with another typed SNP. Of the 114 SNPs examined, we followed up the 20 most significant SNPs (P < 0.10) on an additional 384 case subjects and 366 control subjects from a population-based study in Finland. In the combined data, we replicated association (P < 0.05) for 12 SNPs: PPARG Pro12Ala and His447, KCNJ11 Glu23Lys and rs5210, TNF −857, SLC2A2 Ile110Thr, HNF1A/TCF1 rs2701175 and GE117881_360, PCK1 −232, NEUROD1 Thr45Ala, IL6 −598, and ENPP1 Lys121Gln. The replication of 12 SNPs of 114 tested was significantly greater than expected by chance under the null hypothesis of no association (P = 0.012). We observed that SNPs from genes that had three or more previous reports of association were significantly more likely to be replicated in our sample (P = 0.03), although we also replicated 4 of 58 SNPs from genes that had only one previous report of association.
Common Genetic Variations in CCK, Leptin, and Leptin Receptor Genes Are Associated With Specific Human Eating Patterns
Authors: de Krom Mariken , van der Schouw Yvonne T. , Hendriks Judith , Ophoff Roel A. , van Gils Carla H. , Stolk Ronald P. , Grobbee Diederick E. , Adan Roger
Published: December 2006

Obesity has a heritable component; however, the heterogeneity of obesity complicates dissection of its genetic background. In this study, we therefore focused on eating patterns as specific traits within obesity. These traits have a heritable component; genes associated with a specific eating pattern have not yet been reported at the population level. In this study, we determined whether genetic variations in cholecystokinin (CCK) and leptin genes underlie specific eating patterns. We selected obese individuals showing extreme snacking behavior or use of excessive portion sizes from a large population-based sample (n = 17,357) from the Prospect-EPIC (European Prospective Study into Cancer and Nutrition) study. Using allele-specific PCRs, we tested several single nucleotide polymorphisms in the candidate genes and performed haplotype analysis. Obese carriers of common allelic variations in leptin or the leptin receptor gene had an increased risk to display extreme snacking behavior. In contrast, obese carriers of common allelic variations in CCK had an increased risk to eating increased meal sizes. In conclusion, we identified common allelic variants specifically associated with distinctly different eating patterns, namely extreme snacking behavior or excessive portion size.
Combined Use of Rosiglitazone and Fenofibrate in Patients With Type 2 Diabetes
Authors: Boden Guenther , Homko Carol , Mozzoli Maria , Zhang Meijuan , Kresge Karen , Cheung Peter
Published: December 2006

Elevated plasma free fatty acid (FFA) levels are responsible for much of the insulin resistance in obese patients with type 2 diabetes. To lower plasma FFA levels effectively and long term, we have treated eight obese patients with type 2 diabetes for 2 months with placebo followed by 2 months of treatment with a combination of rosiglitazone (RGZ) (8 mg/day) and fenofibrate (FFB) (160 mg/day) in a single-blind placebo-controlled study design. Compared with placebo, RGZ/FFB lowered mean 24-h plasma FFA levels 30% (P < 0.03) and mean 24-h glucose levels 23% (P < 0.03) and increased insulin-stimulated glucose uptake (glucose rate of disappearance [GRd], determined using euglycemic-hyperinsulinemic clamp) 442% (P < 0.01), oral glucose tolerance (area under the curve for 3-h oral glucose tolerance test) 28% (P < 0.05), and plasma adiponectin levels 218% (P < 0.01). These RGZ/FFB results were compared with results obtained in five patients treated with RGZ alone. RGZ/FFB prevented the fluid retention usually associated with RGZ (−1.6 vs. 5.6%, P < 0.05), lowered fasting plasma FFA more effectively than RGZ alone (−22 vs. 5%, P < 0.05), and tended to be more effective than RGZ alone in lowering A1C (−0.9 vs. −0.4%) and triglyceride levels (−38 vs. −5%) and increasing GRd (442 vs. 330%). We conclude that RGZ/FFB is a promising new therapy for type 2 diabetes that lowers plasma FFA more than RGZ alone and in contrast to RGZ does not cause water retention and weight gain.
The Role of Arachidonic Acid and Its Metabolites in Insulin Secretion From Human Islets of Langerhans
Authors: Persaud Shanta J. , Muller Dany , Belin Véronique D. , Kitsou-Mylona Isidora , Asare-Anane Henry , Papadimitriou Alexandros , Burns Chris J. , Huang Guo Cai , Amiel Stephanie A. , Jones Peter M.
Published: December 2006

The roles played by arachidonic acid and its cyclooxygenase (COX)-generated and lipoxygenase (LOX)-generated metabolites have been studied using rodent islets and insulin-secreting cell lines, but very little is known about COX and LOX isoform expression and the effects of modulation of arachidonic acid generation and metabolism in human islets. We have used RT-PCR to identify mRNAs for cytosolic phospholipase A2 (cPLA2), COX-1, COX-2, 5-LOX, and 12-LOX in isolated human islets. COX-3 and 15-LOX were not expressed by human islets. Perifusion experiments with human islets indicated that PLA2 inhibition inhibited glucose-stimulated insulin secretion, whereas inhibitors of COX-2 and 12-LOX enzymes enhanced basal insulin secretion and also secretory responses induced by 20 mmol/l glucose or by 50 μmol/l arachidonic acid. Inhibition of COX-1 with 100 μmol/l acetaminophen did not significantly affect glucose-stimulated insulin secretion. These data indicate that the stimulation of insulin secretion from human islets in response to arachidonic acid does not require its metabolism through COX-2 and 5-/12-LOX pathways. The products of COX-2 and LOX activities have been implicated in cytokine-mediated damage of β-cells, so selective inhibitors of these enzymes would be expected to have a dual protective role in diabetes: they would minimize β-cell dysfunction while maintaining insulin secretion through enhancing endogenous arachidonic acid levels.
Altered Natural Killer Cells in Type 1 Diabetic Patients
Authors: Rodacki Melanie , Svoren Britta , Butty Vincent , Besse Whitney , Laffel Lori , Benoist Christophe , Mathis Diane
Published: December 2006

Evidence from animal models suggests that natural killer (NK) cells can be important players in the development of type 1 diabetes, although data in humans are still sparse. We studied the frequency and activation state of blood NK cells at different stages of human type 1 diabetes, and whether genetic or phenotypic NK cell peculiarities could be associated with an early onset of diabetes. The onset period is marked by a slight reduction in blood NK cells, but these are unusually activated in some patients (γ-interferon expression). This activation status does not correlate, however, with a particularly young age at onset. In contrast, NK cells in patients with long-standing type 1 diabetes had a markedly lower expression of p30/p46 NK-activating receptor molecules compared with those of control subjects. A slightly decreased expression of NKG2D in all type 1 diabetic patients relative to control subjects was observed, independent of the duration of disease, parallel to prior observations in the NOD mouse. Finally, type 1 diabetic patients had an increased frequency of KIR gene haplotypes that include the activating KIR2DS3 gene, with a genetic interaction between the KIR and HLA complexes. The reduced activation of NK cells in individuals with long-standing type 1 diabetes would seem to be a consequence rather than a cause, but other peculiarities may relate to type 1 diabetes pathogenesis.
Tissue-Specific Deletion of the Retinoblastoma Protein in the Pancreatic β-Cell Has Limited Effects on β-Cell Replication, Mass, and Function
Authors: Vasavada Rupangi C. , Cozar-Castellano Irene , Sipula Darinka , Stewart Andrew F.
Published: December 2006

Animal studies show that G1/S regulatory molecules (D-cyclins, cdk-4, p18, p21, p27) are critical for normal regulation of β-cell proliferation, mass, and function. The retinoblastoma protein, pRb, is positioned at the very end of a cascade of these regulatory proteins and is considered the final checkpoint molecule that maintains β-cell cycle arrest. Logically, removal of pRb from the β-cell should result in unrestrained β-cell replication, increased β-cell mass, and insulin-mediated hypoglycemia. Because global loss of both pRb alleles is embryonic lethal, this hypothesis has not been tested in β-cells. We developed two types of conditional knockout (CKO) mice in which both alleles of the pRb gene were inactivated specifically in β-cells. Surprisingly, although the pRb gene was efficiently recombined in β-cells of both CKO models, changes in β-cell mass, β-cell replication rates, insulin concentrations, and blood glucose levels were limited or absent. Other pRb family members, p107 and p130, were not substantially upregulated. In contrast to dogma, the pRb protein is not essential to maintain cell cycle arrest in the pancreatic β-cell. This may reflect fundamental inaccuracies in models of β-cell cycle control or complementation for pRb by undefined proteins.
Induction of Indoleamine 2,3-Dioxygenase by Interferon-γ in Human Islets
Authors: Sarkar Suparna A. , Wong Randall , Hackl Seija I. , Moua Ong , Gill Ronald G. , Wiseman Alexander , Davidson Howard W. , Hutton John C.
Published: December 2006

Indoleamine 2,3-dioxygenase (IDO) catalyzes the initial, rate-limiting step of tryptophan (Trp) catabolism along the kynurenine (KYN) pathway, and its induction in cells of the immune system in response to cytokines has been implicated in the regulation of antigen presentation and responses to cell-mediated immune attack. Microarray and quantitative PCR analyses of isolated human islets incubated with interferon (IFN)-γ for 24 h revealed increased expression of IDO mRNA (>139-fold) and Trp-tRNA synthase (WARS) (>17-fold) along with 975 other transcripts more than threefold, notably the downstream effectors janus kinase (JAK)2, signal transducer and activator of transcription (STAT)1, IFN-γ regulatory factor-1, and several chemokines (CXCL9/MIG, CXCL10/IP10, CXCL11/1-TAC, CCL2, and CCL5/RANTES) and their receptors. IDO protein expression was upregulated in IFN-γ–treated islets and accompanied by increased intracellular IDO enzyme activity and the release of KYN into the media. The response to IFN-γ was countered by interleukin-4 and 1α-methyl Trp. Immunohistochemical localization showed IDO to be induced in cells of both endocrine, including pancreatic duodenal homeobox 1–positive β-cells, and nonendocrine origin. We postulate that in the short term, IDO activation may protect islets from cytotoxic damage, although chronic exposure to various Trp metabolites could equally lead to β-cell attrition.
Vascular Reactivity in Arterioles From Normal and Alloxan-Diabetic Mice
Authors: Lai En Yin , Jansson Leif , Patzak Andreas , Persson A. Erik G.
Published: December 2006

Pancreatic islets possess an autonomous mechanism of blood flow regulation, independent of that of the exocrine pancreas. To study islet vascular regulation without confounding effects of the exocrine blood vessels, we have developed a technique enabling us to isolate single pancreatic islets and then to perfuse them using their endogenous vasculature for distribution of the medium. This made it possible to directly study the vascular reactivity of islet arterioles to different substances. We confirmed that control of islet blood flow is mainly located at the precapillary level. As expected, administration of angiotensin II and l-nitro-arginine methyl ester contracted islet arterioles, whereas nitric oxide and adenosine dilated them. d-glucose, the main insulin secretagogue, had a selective dilating effect on smooth muscle in islet arterioles but not in glomerular afferent arterioles. The response to glucose was amplified in islet arterioles from diabetic animals, indicating enhanced islet blood perfusion in diabetes. This newly developed technique for perfusing isolated pancreatic islets will provide new insights into islet perfusion control and its possible contributions to the pathogenesis of type 2 diabetes.
Genotype-by-Sex Interaction on Fasting Insulin Concentration
Authors: North Kari E. , Franceschini Nora , Borecki Ingrid B. , Gu C. Charles , Heiss Gerardo , Province Michael A. , Arnett Donna K. , Lewis Cora E. , Miller Michael B. , Myers Richard H. , Hunt Steven C. , Freedman Barry I.
Published: December 2006

Recent studies have demonstrated the importance of sex effects on the underlying genetic architecture of insulin-related traits. To explore sex-specific genetic effects on fasting insulin, we tested for genotype-by-sex interaction and conducted linkage analysis of fasting insulin in Hypertension Genetic Epidemiology Network families. Hypertensive siblings and their first-degree relatives were recruited from five field centers. We performed a genome scan for quantitative trait loci influencing fasting insulin among 1,505 European Americans and 1,616 African Americans without diabetes. Sex-stratified linear regression models, adjusted for race, center, and age, were explored. The Mammalian Genotyping Service typed 391 microsatellite markers, spaced roughly 9 cM. Variance component linkage analysis was performed in SOLAR using ethnic-specific marker allele frequencies and multipoint IBDs calculated in MERLIN. We detected a quantitative trait locus influencing fasting insulin in female subjects (logarithm of odds [LOD] = 3.4) on chromosome 2 at 95 cM (between GATA69E12 and GATA71G04) but not in male subjects (LOD = 0.0, P for interaction = 0.007). This sex-specific signal at 2p13.2 was detected in both European-American (LOD = 2.1) and African-American (LOD = 1.2) female subjects. Our findings overlap with several other linkage reports of insulin-related traits and demonstrate the importance of considering complex context-dependent interactions in the search for insulin-related genes.
Modulating Protective and Pathogenic CD4+ Subsets via CD137 in Type 1 Diabetes
Authors: Irie Junichiro , Wu Yuehong , Kachapati Kritika , Mittler Robert S. , Ridgway William M.
Published: December 2006

CD137 (TNFRSF9) is an activation-inducible T-cell costimulatory molecule and a member of the tumor necrosis factor (TNF) receptor superfamily. Cd137 is also a candidate gene (in the Idd9.3 interval) for autoimmune diabetes in NOD mice. Here, we demonstrate that anti-CD137 treatment protects NOD mice from diabetes. Anti-CD137–treated mice are not protected from insulitis and still harbor pathogenic T-cells, as demonstrated by transfer studies. Transfer of CD4+, but not CD8+, cells from anti-CD137–treated pre-diabetic NOD mice into NOD-scid mice delayed diabetes onset. Anti-CD137 treatment significantly increased the number of CD4+CD25+ cells, which demonstrated intracellular Foxp3 expression and in vitro suppressive activity. The CD4+CD25+ cell subset from anti-CD137–treated mice transferred complete protection from diabetes, whereas the CD4+CD25− cell subset offered no significant protection. Anti-CD137 treatment of NOD-scid recipients of diabetic spleen cells, however, hastened the onset of disease, showing that the effect of anti-CD137 treatment depends on the balance of pathogenic and protective cells. These results support a critical role for CD137 acting in the early phase of autoimmune diabetes to enhance regulatory cell production. Disease-associated CD137 alleles are likely ineffectual at stimulating a regulatory T-cell population sufficient to prevent disease.
Preferential Uptake of Dietary Fatty Acids in Adipose Tissue and Muscle in the Postprandial Period
Authors: Bickerton Alex S.T. , Roberts Rachel , Fielding Barbara A. , Hodson Leanne , Blaak Ellen E. , Wagenmakers Anton J.M. , Gilbert Marjorie , Karpe Fredrik , Frayn Keith N.
Published: December 2006

Despite consistent evidence that abnormalities of fatty acid delivery and storage underlie the metabolic defects of insulin resistance, physiological pathways by which fat is stored in adipose tissue and skeletal muscle are not clear. We used a combination of stable isotope labeling and arteriovenous difference measurements to elucidate pathways of postprandial fat deposition in adipose tissue and skeletal muscle in healthy humans. A test meal containing [U-13C]palmitate was combined with intravenous infusion of [2H2]palmitate to label plasma fatty acids and VLDL-triglyceride. Both dietary (chylomicron) and VLDL-triglyceride were cleared across adipose tissue and muscle, though with greater fractional extraction of the chylomicron-triglyceride. In adipose tissue there was significant uptake of plasma nonesterified fatty acids (NEFAs) in the postprandial but not the fasting state. However, this was minor in comparison with chylomicron-triglyceride fatty acids. We modeled the fate of fatty acids released by lipoprotein lipase (LPL). There was clear preferential uptake of these fatty acids compared with plasma NEFAs. In muscle, there was unexpected evidence for release of LPL-derived fatty acids into the plasma. With this integrative physiological approach, we have revealed hidden complexities in pathways of fatty acid uptake in adipose tissue and skeletal muscle.
Genetic Control of Alternative Splicing in theTAP2Gene
Authors: Qu Hui-Qi , Lu Yang , Marchand Luc , Bacot François , Fréchette Rosalie , Tessier Marie-Catherine , Montpetit Alexandre , Polychronakos Constantin
Published: December 2006

The transporter 2, ATP-binding cassette, subfamily B (TAP2) is involved in the transport of antigenic peptides to HLA molecules. Coding TAP2 polymorphisms shows a strong association with type 1 diabetes, but it is not clear whether this association may be entirely due to linkage disequilibrium with HLA DR and DQ. Functionally, rat Tap2 nonsynonymous single-nucleotide polymorphisms (nsSNPs) confer differential selectivity for antigenic peptides, but this was not shown to be the case for human TAP2 nsSNPs. In the human, differential peptide selectivity is rather conferred by two splicing isoforms with alternative carboxy terminals. Here, we tested the hypothesis that alleles at the coding SNPs favor different splicing isoforms, thus determining peptide selectivity indirectly. This may be the basis for independent contribution to the type 1 diabetes association. In RNA from heterozygous lymphoblastoid lines, we measured the relative abundance of each SNP haplotype in each isoform. In isoform NM_000544, the G (Ala) allele at 665 Thr>Ala (rs241447) is more than twice as abundant as A (Thr) (GA = 2.2 ± 0.4, P = 1.5 × 10−4), while isoform NM_018833 is derived almost exclusively from chromosomes carrying A (AG = 18.1 ± 5.6, P = 2.04 × 10−7). In 889 Canadian children with type 1 diabetes, differential transmission of parental TAP2 alleles persisted (P = 0.011) when analysis was confined to chromosomes carrying only DQ*02 alleles, which mark a conserved DR-DQ haplotype, thus eliminating most of the variation at DR-DQ. Thus, we present evidence of TAP2 association with type 1 diabetes that is independent of HLA DR-DQ and describe a plausible functional mechanism based on allele dependence of splicing into isoforms known to have differential peptide selectivities.
The Effect of Borderline Diabetes on the Risk of Dementia and Alzheimer’s Disease
Authors: Xu Weili , Qiu Chengxuan , Winblad Bengt , Fratiglioni Laura
Published: December 2006

To verify the hypothesis that borderline diabetes may increase the risk of dementia and Alzheimer’s disease, a community-based cohort of 1,173 dementia- and diabetes-free individuals aged ≥75 years was longitudinally examined three times to detect patients with dementia and Alzheimer’s disease (Diagnostic and Statistical Manual of Mental Disorders, Revised Third Edition criteria). Borderline diabetes was defined as a random plasma glucose level of 7.8–11.0 mmol/l. Data were analyzed using Cox proportional hazards models. During the 9-year follow-up, 397 subjects developed dementia, including 307 Alzheimer’s cases. At baseline, 47 subjects were identified with borderline diabetes. Borderline diabetes was associated with adjusted hazard ratios (95% CIs) of 1.67 (1.04–2.67) for dementia and 1.77 (1.06–2.97) for Alzheimer’s disease; the significant associations were present after additional adjustment for future development of diabetes. Stratified analysis suggested a significant association between borderline diabetes and Alzheimer’s disease only among noncarriers of APOE ε4 allele. There was an interaction between borderline diabetes and severe systolic hypertension on the risk of Alzheimer’s disease (P = 0.04). We conclude that borderline diabetes is associated with increased risks of dementia and Alzheimer’s disease; the risk effect is independent of the future development of diabetes. Borderline diabetes may interact with severe systolic hypertension to multiply the risk of Alzheimer’s disease.