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McLoon LK, Christiansen SP, Ghose GM, Das VE, Mustari MJ. Improvement of Eye Alignment in Adult Strabismic Monkeys by Sustained IGF-1 Treatment. Invest Ophthalmol Vis Sci 2017; 57:6070-6078. [PMID: 27820875 PMCID: PMC5114034 DOI: 10.1167/iovs.16-19739] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Purpose The goal of this study was to determine if continuous application of insulin-like growth factor-1 (IGF-1) could improve eye alignment of adult strabismic nonhuman primates and to assess possible mechanisms of effect. Methods A continuous release pellet of IGF-1 was placed on one medial rectus muscle in two adult nonhuman primates (M1, M2) rendered exotropic by the alternating monocular occlusion method during the first months of life. Eye alignment and eye movements were recorded for 3 months, after which M1 was euthanized, and the lateral and medial rectus muscles were removed for morphometric analysis of fiber size, nerve, and neuromuscular density. Results Monkey 1 showed a 40% reduction in strabismus angle, a reduction of exotropia of approximately 11° to 14° after 3 months. Monkey 2 showed a 15% improvement, with a reduction of its exotropia by approximately 3°. The treated medial rectus muscle of M1 showed increased mean myofiber cross-sectional areas. Increases in myofiber size also were seen in the contralateral medial rectus and lateral rectus muscles. Similarly, nerve density increased in the contralateral medial rectus and yoked lateral rectus. Conclusions This study demonstrates that in adult nonhuman primates with a sensory-induced exotropia in infancy, continuous IGF-1 treatment improves eye alignment, resulting in muscle fiber enlargement and altered innervational density that includes the untreated muscles. This supports the view that there is sufficient plasticity in the adult ocular motor system to allow continuous IGF-1 treatment over months to produce improvement in eye alignment in early-onset strabismus.
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Affiliation(s)
- Linda K McLoon
- Department of Ophthalmology and Visual Neurosciences, University of Minnesota, Minneapolis, Minnesota, United States 2Department of Neuroscience, University of Minnesota, Minneapolis, Minnesota, United States
| | - Stephen P Christiansen
- Departments of Ophthalmology and Pediatrics, Boston University School of Medicine, Boston, Massachusetts, United States
| | - Geoffrey M Ghose
- Department of Neuroscience, University of Minnesota, Minneapolis, Minnesota, United States
| | - Vallabh E Das
- College of Optometry, University of Houston, Houston, Texas, United States
| | - Michael J Mustari
- Washington National Primate Center and Department of Ophthalmology, University of Washington, Seattle, Washington, United States
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Bryan MR, Bowman AB. Manganese and the Insulin-IGF Signaling Network in Huntington's Disease and Other Neurodegenerative Disorders. ADVANCES IN NEUROBIOLOGY 2017; 18:113-142. [PMID: 28889265 PMCID: PMC6559248 DOI: 10.1007/978-3-319-60189-2_6] [Citation(s) in RCA: 37] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Huntington's disease (HD) is an autosomal dominant neurodegenerative disease resulting in motor impairment and death in patients. Recently, several studies have demonstrated insulin or insulin-like growth factor (IGF) treatment in models of HD, resulting in potent amelioration of HD phenotypes via modulation of the PI3K/AKT/mTOR pathways. Administration of IGF and insulin can rescue microtubule transport, metabolic function, and autophagy defects, resulting in clearance of Huntingtin (HTT) aggregates, restoration of mitochondrial function, amelioration of motor abnormalities, and enhanced survival. Manganese (Mn) is an essential metal to all biological systems but, in excess, can be toxic. Interestingly, several studies have revealed the insulin-mimetic effects of Mn-demonstrating Mn can activate several of the same metabolic kinases and increase peripheral and neuronal insulin and IGF-1 levels in rodent models. Separate studies have shown mouse and human striatal neuroprogenitor cell (NPC) models exhibit a deficit in cellular Mn uptake, indicative of a Mn deficiency. Furthermore, evidence from the literature reveals a striking overlap between cellular consequences of Mn deficiency (i.e., impaired function of Mn-dependent enzymes) and known HD endophenotypes including excitotoxicity, increased reactive oxygen species (ROS) accumulation, and decreased mitochondrial function. Here we review published evidence supporting a hypothesis that (1) the potent effect of IGF or insulin treatment on HD models, (2) the insulin-mimetic effects of Mn, and (3) the newly discovered Mn-dependent perturbations in HD may all be functionally related. Together, this review will present the intriguing possibility that intricate regulatory cross-talk exists between Mn biology and/or toxicology and the insulin/IGF signaling pathways which may be deeply connected to HD pathology and, perhaps, other neurodegenerative diseases (NDDs) and other neuropathological conditions.
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Affiliation(s)
- Miles R Bryan
- Department of Neurology, Vanderbilt University Medical Center, Nashville, TN, 37232, USA.
- Vanderbilt Brain Institute, Vanderbilt University Medical Center, Nashville, TN, 37232, USA.
- Department of Pediatrics, Vanderbilt University Medical Center, Nashville, TN, 37232, USA.
| | - Aaron B Bowman
- Department of Neurology, Vanderbilt University Medical Center, Nashville, TN, 37232, USA
- Vanderbilt Brain Institute, Vanderbilt University Medical Center, Nashville, TN, 37232, USA
- Department of Pediatrics, Vanderbilt University Medical Center, Nashville, TN, 37232, USA
- Vanderbilt Center in Molecular Toxicology, Vanderbilt University Medical Center, Nashville, TN, 37232, USA
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Wolman MA, Jain RA, Marsden KC, Bell H, Skinner J, Hayer KE, Hogenesch JB, Granato M. A genome-wide screen identifies PAPP-AA-mediated IGFR signaling as a novel regulator of habituation learning. Neuron 2015; 85:1200-11. [PMID: 25754827 DOI: 10.1016/j.neuron.2015.02.025] [Citation(s) in RCA: 59] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2014] [Revised: 01/06/2015] [Accepted: 02/12/2015] [Indexed: 01/15/2023]
Abstract
Habituation represents a fundamental form of learning, yet the underlying molecular genetic mechanisms are not well defined. Here we report on a genome-wide genetic screen, coupled with whole-genome sequencing, that identified 14 zebrafish startle habituation mutants including mutants of the vertebrate-specific gene pregnancy-associated plasma protein-aa (pappaa). PAPP-AA encodes an extracellular metalloprotease known to increase IGF bioavailability, thereby enhancing IGF receptor signaling. We find that pappaa is expressed by startle circuit neurons, and expression of wild-type but not a metalloprotease-inactive version of pappaa restores habituation in pappaa mutants. Furthermore, acutely inhibiting IGF1R function in wild-type reduces habituation, while activation of IGF1R downstream effectors in pappaa mutants restores habituation, demonstrating that pappaa promotes learning by acutely and locally increasing IGF bioavailability. In sum, our results define the first functional gene set for habituation learning in a vertebrate and identify PAPPAA-regulated IGF signaling as a novel mechanism regulating habituation learning.
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Affiliation(s)
- Marc A Wolman
- Department of Cell and Developmental Biology, University of Pennsylvania Perelman School of Medicine, 1157 BRB II/III, 421 Curie Boulevard, Philadelphia, PA 19104, USA; Department of Zoology, University of Wisconsin; 213 Zoology Research Building, 1117 West Johnson Street, Madison, WI 53706, USA
| | - Roshan A Jain
- Department of Cell and Developmental Biology, University of Pennsylvania Perelman School of Medicine, 1157 BRB II/III, 421 Curie Boulevard, Philadelphia, PA 19104, USA
| | - Kurt C Marsden
- Department of Cell and Developmental Biology, University of Pennsylvania Perelman School of Medicine, 1157 BRB II/III, 421 Curie Boulevard, Philadelphia, PA 19104, USA
| | - Hannah Bell
- Department of Cell and Developmental Biology, University of Pennsylvania Perelman School of Medicine, 1157 BRB II/III, 421 Curie Boulevard, Philadelphia, PA 19104, USA
| | - Julianne Skinner
- Department of Cell and Developmental Biology, University of Pennsylvania Perelman School of Medicine, 1157 BRB II/III, 421 Curie Boulevard, Philadelphia, PA 19104, USA
| | - Katharina E Hayer
- Department of Systems Pharmacology and Translational Therapeutics, University of Pennsylvania Perelman School of Medicine, 829 BRB II/III, 421 Curie Boulevard, Philadelphia, PA 19104, USA
| | - John B Hogenesch
- Department of Systems Pharmacology and Translational Therapeutics, University of Pennsylvania Perelman School of Medicine, 829 BRB II/III, 421 Curie Boulevard, Philadelphia, PA 19104, USA
| | - Michael Granato
- Department of Cell and Developmental Biology, University of Pennsylvania Perelman School of Medicine, 1157 BRB II/III, 421 Curie Boulevard, Philadelphia, PA 19104, USA.
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Agis-Balboa RC, Fischer A. Generating new neurons to circumvent your fears: the role of IGF signaling. Cell Mol Life Sci 2014; 71:21-42. [PMID: 23543251 PMCID: PMC11113432 DOI: 10.1007/s00018-013-1316-2] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2012] [Revised: 02/12/2013] [Accepted: 03/04/2013] [Indexed: 12/13/2022]
Abstract
Extinction of fear memory is a particular form of cognitive function that is of special interest because of its involvement in the treatment of anxiety and mood disorders. Based on recent literature and our previous findings (EMBO J 30(19):4071-4083, 2011), we propose a new hypothesis that implies a tight relationship among IGF signaling, adult hippocampal neurogenesis and fear extinction. Our proposed model suggests that fear extinction-induced IGF2/IGFBP7 signaling promotes the survival of neurons at 2-4 weeks old that would participate in the discrimination between the original fear memory trace and the new safety memory generated during fear extinction. This is also called "pattern separation", or the ability to distinguish similar but different cues (e.g., context). To understand the molecular mechanisms underlying fear extinction is therefore of great clinical importance.
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Affiliation(s)
- R C Agis-Balboa
- Department of Psychiatry and Psychotherapy, University Medical Center Göttingen, Grisebach Str. 5, 37077, Göttingen, Germany,
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Mulcahy B, Holden-Dye L, O'Connor V. Pharmacological assays reveal age-related changes in synaptic transmission at the Caenorhabditis elegans neuromuscular junction that are modified by reduced insulin signalling. ACTA ACUST UNITED AC 2012; 216:492-501. [PMID: 23038730 DOI: 10.1242/jeb.068734] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Frailty is a feature of neuromuscular ageing. Here we provide insight into the relative contribution of pre- and postsynaptic dysfunction to neuromuscular ageing using the nematode Caenorhabditis elegans. Assays of C. elegans motility highlight a precipitous decline during ageing. We describe a novel deployment of pharmacological assays of C. elegans neuromuscular function to resolve pre- and postsynaptic dysfunction that underpin this decreased motility during ageing. The cholinergic agonist levamisole and the cholinesterase inhibitor aldicarb elicited whole worm contraction and allowed a direct comparison of neuromuscular integrity, from 1 to 16 days old: measurements could be made from aged worms that were otherwise almost completely immobile. The rapidity and magnitude of the drug-induced contraction provides a measure of neuromuscular signalling whilst the difference between levamisole and aldicarb highlights presynaptic effects. Presynaptic neuromuscular transmission increased between 1 and 5 days old in wild-type but not in the insulin/IGF1 receptor mutant daf-2 (e1370). Intriguingly, there was no evidence of a role for insulin-dependent effects in older worms. Notably in 16-day-old worms, which were virtually devoid of spontaneous movement, the maximal contraction produced by both drugs was unchanged. Taken together the data support a maturation of presynaptic function and/or upstream elements during early ageing that is lost after genetic reduction of insulin signalling. Furthermore, this experimental approach has demonstrated a counterintuitive phenomenon: in aged worms neuromuscular strength is maintained despite the absence of motility.
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Affiliation(s)
- Ben Mulcahy
- Centre for Biological Sciences, Life Sciences Building 85, University of Southampton, Southampton SO17 1BJ, UK.
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Fernandez AM, Torres-Alemán I. The many faces of insulin-like peptide signalling in the brain. Nat Rev Neurosci 2012; 13:225-39. [PMID: 22430016 DOI: 10.1038/nrn3209] [Citation(s) in RCA: 631] [Impact Index Per Article: 52.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Central and peripheral insulin-like peptides (ILPs), which include insulin, insulin-like growth factor 1 (IGF1) and IGF2, exert many effects in the brain. Through their actions on brain growth and differentiation, ILPs contribute to building circuitries that subserve metabolic and behavioural adaptation to internal and external cues of energy availability. In the adult brain each ILP has distinct effects, but together their actions ultimately regulate energy homeostasis - they affect nutrient sensing and regulate neuronal plasticity to modulate adaptive behaviours involved in food seeking, including high-level cognitive operations such as spatial memory. In essence, the multifaceted activity of ILPs in the brain may be viewed as a system organization involved in the control of energy allocation.
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Affiliation(s)
- Ana M Fernandez
- Cajal Institute, CSIC and Ciberned, Avenida Doctor Arce, 37, Madrid 28002, Spain
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Excitatory effect of the A2A adenosine receptor agonist CGS-21680 on spontaneous and K+-evoked acetylcholine release at the mouse neuromuscular junction. Neuroscience 2011; 172:164-76. [DOI: 10.1016/j.neuroscience.2010.10.015] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2010] [Revised: 09/25/2010] [Accepted: 10/05/2010] [Indexed: 11/18/2022]
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Kiryakova S, Söhnchen J, Grosheva M, Schuetz U, Marinova T, Dzhupanova R, Sinis N, Hübbers CU, Skouras E, Ankerne J, Fries JWU, Irintchev A, Dunlop SA, Angelov DN. Recovery of whisking function promoted by manual stimulation of the vibrissal muscles after facial nerve injury requires insulin-like growth factor 1 (IGF-1). Exp Neurol 2010; 222:226-34. [PMID: 20067789 DOI: 10.1016/j.expneurol.2009.12.031] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2009] [Accepted: 12/30/2009] [Indexed: 01/04/2023]
Abstract
Recently, we showed that manual stimulation (MS) of denervated vibrissal muscles enhanced functional recovery following facial nerve cut and suture (FFA) by reducing poly-innervation at the neuro-muscular junctions (NMJ). Although the cellular correlates of poly-innervation are established, with terminal Schwann cells (TSC) processes attracting axon sprouts to "bridge" adjacent NMJ, molecular correlates are poorly understood. Since quantitative RT-PCR revealed a rapid increase of IGF-1 mRNA in denervated muscles, we examined the effect of daily MS for 2 months after FFA in IGF-1(+/-) heterozygous mice; controls were wild-type (WT) littermates including intact animals. We quantified vibrissal motor performance and the percentage of NMJ bridged by S100-positive TSC. There were no differences between intact WT and IGF-1(+/-) mice for vibrissal whisking amplitude (48 degrees and 49 degrees ) or the percentage of bridged NMJ (0%). After FFA and handling alone (i.e. no MS) in WT animals, vibrissal whisking amplitude was reduced (60% lower than intact) and the percentage of bridged NMJ increased (42% more than intact). MS improved both the amplitude of vibrissal whisking (not significantly different from intact) and the percentage of bridged NMJ (12% more than intact). After FFA and handling in IGF-1(+/-) mice, the pattern was similar (whisking amplitude 57% lower than intact; proportion of bridged NMJ 42% more than intact). However, MS did not improve outcome (whisking amplitude 47% lower than intact; proportion of bridged NMJ 40% more than intact). We conclude that IGF-I is required to mediate the effects of MS on target muscle reinnervation and recovery of whisking function.
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Affiliation(s)
- S Kiryakova
- Department of Anatomy I, University of Cologne, D-50924 Cologne, Germany
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Liou JC, Kang KH, Chang LS, Ho SY. Mechanism of β-bungarotoxin in facilitating spontaneous transmitter release at neuromuscular synapse. Neuropharmacology 2006; 51:671-80. [PMID: 16806309 DOI: 10.1016/j.neuropharm.2006.05.016] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2005] [Revised: 05/12/2006] [Accepted: 05/15/2006] [Indexed: 10/24/2022]
Abstract
The mechanism of the action of beta-bungarotoxin (beta-BuTx) in the facilitation of spontaneous transmitter release at neuromuscular synapse was investigated in Xenopus cell culture using whole-cell patch clamp recording. Exposure of the culture to beta-BuTx dose-dependently enhances the frequency of spontaneous synaptic currents (SSCs). Buffering the rise of intracellular Ca2+ with BAPTA-AM hampered the facilitation of SSC frequency induced by beta-BuTx. The beta-BuTx-enhanced SSC frequency was reduced when the pharmacological Ca2+ -ATPase inhibitor thapsigargin was used to deplete intracellular Ca2+ store. Application of membrane-permeable inhibitors of inositol 1,4,5-trisphosphate (IP3) but not ryanodine receptors effectively occluded the increase of SSC frequency elicited by beta-BuTx. Treating cells with either wortmannin or LY294002, two structurally different inhibitors of phosphatidylinositol 3-kinase (PI3K) and with phospholipase C (PLC) inhibitor U73122, abolished the beta-BuTx-induced facilitation of synaptic transmission. The beta-BuTx-induced synaptic facilitation was completely abolished while there was presynaptic loading of the motoneuron with GDPbetaS, a non-hydrolyzable GDP analogue and inhibitor of G protein. Taken collectively, these results suggest that beta-BuTx elicits Ca2+ release from the IP3 sensitive intracellular Ca2+ stores of the presynaptic nerve terminal. This is done via PI3K/PLC signaling cascades and G protein activation, leading to an enhancement of spontaneous transmitter release.
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Affiliation(s)
- Jau-Cheng Liou
- Department of Biological Sciences, National Sun Yat-sen University, No 70, Lein-Hai Rd., Kaohsiung 804, Taiwan.
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Torres Aleman I. Role of Insulin-Like Growth Factors in Neuronal Plasticity and Neuroprotection. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2005; 567:243-58. [PMID: 16370142 DOI: 10.1007/0-387-26274-1_10] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
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Webber CA, Chen YY, Hehr CL, Johnston J, McFarlane S. Multiple signaling pathways regulate FGF-2-induced retinal ganglion cell neurite extension and growth cone guidance. Mol Cell Neurosci 2005; 30:37-47. [PMID: 15996482 DOI: 10.1016/j.mcn.2005.05.005] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2004] [Revised: 04/23/2005] [Accepted: 05/12/2005] [Indexed: 11/23/2022] Open
Abstract
Growth cones use cues in their environment in order to grow in a directed fashion to their targets. In Xenopus laevis, fibroblast growth factors (FGFs) participate in retinal ganglion cell (RGC) axon guidance in vivo and in vitro. The main intracellular signaling cascades known to act downstream of the FGF receptor include the mitogen-activated protein kinase (MAPK), phospholipase Cgamma (PLCgamma) and phosphotidylinositol 3-kinase (PI3K) pathways. We used pharmacological inhibitors to identify the signaling cascade(s) responsible for FGF-2-stimulated RGC axon extension and chemorepulsion. The MAPK, PI3K and PLCgamma pathways were blocked by U0126, LY249002 and U73122, respectively. D609 was used to test a role for the phosphotidylcholine-PLC (PC-PLC) pathway. We determined that the MAPK and two PLC pathways are required for FGF-2 to stimulate RGC neurite extension in vitro, but the response of axons to FGF-2 applied asymmetrically to the growth cone depended only on the PLC pathways.
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Affiliation(s)
- C A Webber
- Genes and Development Research Group, University of Calgary, 3330 Hospital Drive, NW, Calgary, AB, Canada T2N 4N1
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Liao YP, Ho SY, Liou JC. Non-genomic regulation of transmitter release by retinoic acid at developing motoneurons in Xenopus cell culture. J Cell Sci 2004; 117:2917-24. [PMID: 15161940 DOI: 10.1242/jcs.01153] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Although the long-term effects of all-trans retinoic acid (RA) on neuronal growth and differentiation have been intensively studied, nothing is known about its effect on synaptic transmission. Here we show that RA rapidly and specifically enhances the spontaneous acetylcholine release at developing neuromuscular synapses in Xenopus cell culture using whole-cell patch-clamp recording. Acute addition of RA dose-dependently and reversibly enhances the frequency of spontaneous synaptic currents (SSCs). Application of the lipophilic RA analogue all-trans retinol or RA metabolites produced by light-induced decomposition failed to provoke similar changes in SSC frequency, indicating the specificity of RA-induced facilitation of spontaneous transmitter release. Protein synthesis inhibitors anisomycin or cycloheximide had no effect on RA-induced SSC frequency facilitation. Treating cells with pan RA receptor (RAR) selective agonist or RARbeta-selective agonist, but not RARalpha-, RARgamma- or retinoid X receptor (RXR)-selective agonists, mimicked the action of RA. These results suggest that RA acts through the activation of RARbeta, to induce a rapid, non-genomic increase in the frequency of spontaneous transmitter release at developing neuromuscular synapses.
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Affiliation(s)
- Yi-Ping Liao
- Department of Biological Sciences, National Sun Yat-Sen University, Kaohsiung City 804, Taiwan
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Carro E, Torres-Aleman I. The role of insulin and insulin-like growth factor I in the molecular and cellular mechanisms underlying the pathology of Alzheimer's disease. Eur J Pharmacol 2004; 490:127-33. [PMID: 15094079 DOI: 10.1016/j.ejphar.2004.02.050] [Citation(s) in RCA: 201] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/27/2004] [Indexed: 11/26/2022]
Abstract
Cellular and molecular processes leading to abnormal accumulation of beta amyloid in the brain are slowly being uncovered. A potential involvement of insulin and insulin-like growth factor I (IGF-I) in this plausible pathogenic process in Alzheimer's disease has recently been proposed. Evidence favoring this idea stems from the ability of both hormones to stimulate beta amyloid release from neurons as well as by the stimulatory effect that IGF-I exerts on brain amyloid clearance. In addition, insulin and IGF-I levels are altered in Alzheimer's patients and, probably in close association to these changes, cell sensitivity towards insulin--and possibly also IGF-I--is decreased in these patients. We now review evidence that disturbed insulin/IGF-I signaling to brain cells, initiated at the level of the blood-brain barriers is probably instrumental in development of brain amyloidosis. Furthermore, insulin and IGF-I are potent neuroprotective factors and can regulate levels of phosphorylated tau, a major component of neurofibrillary tangles found in Alzheimer's brains. Therefore, a decrease in trophic support to neurons together with increased tau phosphorylation will follow loss of sensitivity towards insulin and IGF-I. Altogether, this supports the notion that a single pathogenic event, i.e., brain resistance to insulin/IGF-I, accounts for neuronal atrophy/death, tangle formation and brain amyloidosis typical of Alzheimer's pathology.
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Affiliation(s)
- Eva Carro
- Laboratory of Neuroendocrinology, Cajal Institute, CSIC, Avenida Doctor Arce 37, Madrid ES 28002, Spain
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