651
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Song Y, Ori-McKenney KM, Zheng Y, Han C, Jan LY, Jan YN. Regeneration of Drosophila sensory neuron axons and dendrites is regulated by the Akt pathway involving Pten and microRNA bantam. Genes Dev 2012; 26:1612-25. [PMID: 22759636 DOI: 10.1101/gad.193243.112] [Citation(s) in RCA: 115] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Both cell-intrinsic and extrinsic pathways govern axon regeneration, but only a limited number of factors have been identified and it is not clear to what extent axon regeneration is evolutionarily conserved. Whether dendrites also regenerate is unknown. Here we report that, like the axons of mammalian sensory neurons, the axons of certain Drosophila dendritic arborization (da) neurons are capable of substantial regeneration in the periphery but not in the CNS, and activating the Akt pathway enhances axon regeneration in the CNS. Moreover, those da neurons capable of axon regeneration also display dendrite regeneration, which is cell type-specific, developmentally regulated, and associated with microtubule polarity reversal. Dendrite regeneration is restrained via inhibition of the Akt pathway in da neurons by the epithelial cell-derived microRNA bantam but is facilitated by cell-autonomous activation of the Akt pathway. Our study begins to reveal mechanisms for dendrite regeneration, which depends on both extrinsic and intrinsic factors, including the PTEN-Akt pathway that is also important for axon regeneration. We thus established an important new model system--the fly da neuron regeneration model that resembles the mammalian injury model--with which to study and gain novel insights into the regeneration machinery.
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Affiliation(s)
- Yuanquan Song
- Howard Hughes Medical Institute, Department of Physiology, Department of Biochemistry and Biophysics, University of California at San Francisco, San Francisco, California 94158, USA
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652
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Wang X, Hasan O, Arzeno A, Benowitz LI, Cafferty WBJ, Strittmatter SM. Axonal regeneration induced by blockade of glial inhibitors coupled with activation of intrinsic neuronal growth pathways. Exp Neurol 2012; 237:55-69. [PMID: 22728374 DOI: 10.1016/j.expneurol.2012.06.009] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2011] [Revised: 05/31/2012] [Accepted: 06/09/2012] [Indexed: 12/29/2022]
Abstract
Several pharmacological approaches to promote neural repair and recovery after CNS injury have been identified. Blockade of either astrocyte-derived chondroitin sulfate proteoglycans (CSPGs) or oligodendrocyte-derived NogoReceptor (NgR1) ligands reduces extrinsic inhibition of axonal growth, though combined blockade of these distinct pathways has not been tested. The intrinsic growth potential of adult mammalian neurons can be promoted by several pathways, including pre-conditioning injury for dorsal root ganglion (DRG) neurons and macrophage activation for retinal ganglion cells (RGCs). Singly, pharmacological interventions have restricted efficacy without foreign cells, mechanical scaffolds or viral gene therapy. Here, we examined combinations of pharmacological approaches and assessed the degree of axonal regeneration. After mouse optic nerve crush injury, NgR1-/- neurons regenerate RGC axons as extensively as do zymosan-injected, macrophage-activated WT mice. Synergistic enhancement of regeneration is achieved by combining these interventions in zymosan-injected NgR1-/- mice. In rats with a spinal dorsal column crush injury, a preconditioning peripheral sciatic nerve axotomy, or NgR1(310)ecto-Fc decoy protein treatment or ChondroitinaseABC (ChABC) treatment independently support similar degrees of regeneration by ascending primary afferent fibers into the vicinity of the injury site. Treatment with two of these three interventions does not significantly enhance the degree of axonal regeneration. In contrast, triple therapy combining NgR1 decoy, ChABC and preconditioning, allows axons to regenerate millimeters past the spinal cord injury site. The benefit of a pre-conditioning injury is most robust, but a peripheral nerve injury coincident with, or 3 days after, spinal cord injury also synergizes with NgR1 decoy and ChABC. Thus, maximal axonal regeneration and neural repair are achieved by combining independently effective pharmacological approaches.
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Affiliation(s)
- Xingxing Wang
- Cellular Neuroscience, Neurodegeneration and Repair Program, Yale University School of Medicine, New Haven, CT, USA
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653
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Ferreira LMR, Floriddia EM, Quadrato G, Di Giovanni S. Neural Regeneration: Lessons from Regenerating and Non-regenerating Systems. Mol Neurobiol 2012; 46:227-41. [DOI: 10.1007/s12035-012-8290-9] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2011] [Accepted: 06/07/2012] [Indexed: 12/22/2022]
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654
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Ferguson TA, Scherer SS. Neuronal cadherin (NCAD) increases sensory neurite formation and outgrowth on astrocytes. Neurosci Lett 2012; 522:108-12. [PMID: 22698587 DOI: 10.1016/j.neulet.2012.06.013] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2012] [Revised: 06/01/2012] [Accepted: 06/04/2012] [Indexed: 11/26/2022]
Abstract
We examined the neurite outgrowth of sensory neurons on astrocytes following the genetic deletion of N-cadherin (NCAD). Deletion abolished immunostaining for NCAD and the other classical cadherins, indicating that NCAD is likely the only classical cadherin expressed by astrocytes. Only 38% of neurons grown on NCAD-deficient astrocytes for 24 h produced neurites, as compared to 74% of neurons grown on NCAD-expressing astrocytes. Of the neurons that produced neurites, those grown on NCAD-deficient astrocytes had a mean total length of 378 μm, as compared to 1093 μm for neurons grown on NCAD-expressing astrocytes. Thus, the loss of NCAD greatly impairs the formation and extension neurites on astrocytes.
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Affiliation(s)
- Toby A Ferguson
- Department of Neurology, Temple University and Shriners Pediatric Research Center, Philadelphia, PA 19140, USA.
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655
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Tuszynski MH, Steward O. Concepts and methods for the study of axonal regeneration in the CNS. Neuron 2012; 74:777-91. [PMID: 22681683 PMCID: PMC3387806 DOI: 10.1016/j.neuron.2012.05.006] [Citation(s) in RCA: 227] [Impact Index Per Article: 18.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/11/2012] [Indexed: 12/22/2022]
Abstract
Progress in the field of axonal regeneration research has been like the process of axonal growth itself: there is steady progress toward reaching the target, but there are episodes of mistargeting, misguidance along false routes, and connections that must later be withdrawn. This primer will address issues in the study of axonal growth after central nervous system injury in an attempt to provide guidance toward the goal of progress in the field. We address definitions of axonal growth, sprouting and regeneration after injury, and the research tools to assess growth.
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Affiliation(s)
- Mark H Tuszynski
- Department of Neurosciences, University of California, San Diego, La Jolla, CA 92093-0662, USA.
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656
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Abstract
While ultimately, focus must be placed on experimentation using adult systems, vastly important clues to regeneration can be found in the study of the embryonic nervous system. In embryonic systems, axonal regeneration is successful before a critical period, and numerous advances have resulted from the study of isolated cells and tissues in vitro. Studies over many decades from the laboratory of Paul C. Letourneau have probed the cellular and molecular phenomena involved in axon outgrowth and guidance in the embryonic central and peripheral nervous system and have laid the framework for many current advances in regeneration research. Letourneau’s pioneering work related to growth cone behavior, guidance, and regeneration has resulted in considerable contributions toward our understanding not only of cellular mechanisms that underlie axon growth, but also of the specific areas of study that require attention to accomplish future breakthroughs. The present article summarizes some of the major contributions from Paul Letourneau and his team in the area of axonal regeneration.
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Affiliation(s)
- Diane M Snow
- Department of Anatomy and Neurobiology, Spinal Cord and Brain Injury Research Center, University of Kentucky, Lexington, Kentucky 40536, USA.
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657
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Ueno Y, Chopp M, Zhang L, Buller B, Liu Z, Lehman NL, Liu XS, Zhang Y, Roberts C, Zhang ZG. Axonal outgrowth and dendritic plasticity in the cortical peri-infarct area after experimental stroke. Stroke 2012; 43:2221-8. [PMID: 22618383 DOI: 10.1161/strokeaha.111.646224] [Citation(s) in RCA: 101] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
BACKGROUND AND PURPOSE Axonal remodeling is critical to brain repair after stroke. The present study investigated axonal outgrowth after stroke and the signaling pathways mediating axonal outgrowth in cortical neurons. METHODS Using a rodent model of middle cerebral artery occlusion, we examined high-molecular weight neurofilament (NFH) immunoreactive axons and myelin basic protein-positive oligodendrocytes in the peri-infarct area. In vitro, using cultured cortical neurons in a microfluidic chamber challenged by oxygen-glucose deprivation (OGD), we investigated mechanisms selectively regulating axonal outgrowth after OGD. RESULTS NFH(+) axons and MBP(+) oligodendrocytes substantially increased in the peri-infarct area during stroke recovery, concomitantly with an increase in dendrites and spines identified by Golgi-Cox staining. In vitro, cortical neurons subjected to OGD exhibited significant increases in axonal outgrowth and in phosphorylated NFH protein levels, concurrently with downregulation of phosphatase tensin homolog deleted on chromosome 10, activation of Akt, and inactivation of glycogen synthase kinase-3β in regenerated axons. Blockage of phosphoinositide 3-kinase with pharmacological inhibitors suppressed Akt activation and attenuated phosphorylation of glycogen synthase kinase-3β, which resulted in suppression of phosphorylated NFH and axonal outgrowth after OGD; whereas GSK-3 inhibitors augmented axonal regeneration and elevated phosphorylated NFH levels after OGD. CONCLUSIONS Stroke induces axonal outgrowth and myelination in rodent ischemic brain during stroke recovery, and the phosphoinositide 3-kinase/Akt/glycogen synthase kinase-3β signaling pathway mediates axonal regeneration of cortical neurons after OGD.
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Affiliation(s)
- Yuji Ueno
- Department of Neurology, Henry Ford Hospital, Detroit, MI 48202, USA
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658
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Lu Y, Chi JH. Seeing is believing--spinal chamber for spinal cord injury research. Neurosurgery 2012; 70:N19-20. [PMID: 22596008 DOI: 10.1227/01.neu.0000414946.48601.7b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
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659
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Specificity of peripheral nerve regeneration: interactions at the axon level. Prog Neurobiol 2012; 98:16-37. [PMID: 22609046 DOI: 10.1016/j.pneurobio.2012.05.005] [Citation(s) in RCA: 289] [Impact Index Per Article: 24.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2012] [Revised: 04/12/2012] [Accepted: 05/08/2012] [Indexed: 12/13/2022]
Abstract
Peripheral nerves injuries result in paralysis, anesthesia and lack of autonomic control of the affected body areas. After injury, axons distal to the lesion are disconnected from the neuronal body and degenerate, leading to denervation of the peripheral organs. Wallerian degeneration creates a microenvironment distal to the injury site that supports axonal regrowth, while the neuron body changes in phenotype to promote axonal regeneration. The significance of axonal regeneration is to replace the degenerated distal nerve segment, and achieve reinnervation of target organs and restitution of their functions. However, axonal regeneration does not always allows for adequate functional recovery, so that after a peripheral nerve injury, patients do not recover normal motor control and fine sensibility. The lack of specificity of nerve regeneration, in terms of motor and sensory axons regrowth, pathfinding and target reinnervation, is one the main shortcomings for recovery. Key factors for successful axonal regeneration include the intrinsic changes that neurons suffer to switch their transmitter state to a pro-regenerative state and the environment that the axons find distal to the lesion site. The molecular mechanisms implicated in axonal regeneration and pathfinding after injury are complex, and take into account the cross-talk between axons and glial cells, neurotrophic factors, extracellular matrix molecules and their receptors. The aim of this review is to look at those interactions, trying to understand if some of these molecular factors are specific for motor and sensory neuron growth, and provide the basic knowledge for potential strategies to enhance and guide axonal regeneration and reinnervation of adequate target organs.
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660
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Johnstone AL, Reierson GW, Smith RP, Goldberg JL, Lemmon VP, Bixby JL. A chemical genetic approach identifies piperazine antipsychotics as promoters of CNS neurite growth on inhibitory substrates. Mol Cell Neurosci 2012; 50:125-35. [PMID: 22561309 DOI: 10.1016/j.mcn.2012.04.008] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2012] [Revised: 03/23/2012] [Accepted: 04/20/2012] [Indexed: 01/22/2023] Open
Abstract
Injury to the central nervous system (CNS) can result in lifelong loss of function due in part to the regenerative failure of CNS neurons. Inhibitory proteins derived from myelin and the astroglial scar are major barriers for the successful regeneration of injured CNS neurons. Previously, we described the identification of a novel compound, F05, which promotes neurite growth from neurons challenged with inhibitory substrates in vitro, and promotes axonal regeneration in vivo (Usher et al., 2010). To identify additional regeneration-promoting compounds, we used F05-induced gene expression profiles to query the Broad Institute Connectivity Map, a gene expression database of cells treated with >1300 compounds. Despite no shared chemical similarity, F05-induced changes in gene expression were remarkably similar to those seen with a group of piperazine phenothiazine antipsychotics (PhAPs). In contrast to antipsychotics of other structural classes, PhAPs promoted neurite growth of CNS neurons challenged with two different glial derived inhibitory substrates. Our pharmacological studies suggest a mechanism whereby PhAPs promote growth through antagonism of calmodulin signaling, independent of dopamine receptor antagonism. These findings shed light on mechanisms underlying neurite-inhibitory signaling, and suggest that clinically approved antipsychotic compounds may be repurposed for use in CNS injured patients.
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Affiliation(s)
- Andrea L Johnstone
- The Miami Project to Cure Paralysis, University of Miami Miller School of Medicine, 1400 NW 12th Ave, Miami, FL 33136, USA
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661
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Joo NY, Knowles JC, Lee GS, Kim JW, Kim HW, Son YJ, Hyun JK. Effects of phosphate glass fiber-collagen scaffolds on functional recovery of completely transected rat spinal cords. Acta Biomater 2012; 8:1802-12. [PMID: 22326790 DOI: 10.1016/j.actbio.2012.01.026] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2011] [Revised: 01/20/2012] [Accepted: 01/22/2012] [Indexed: 12/12/2022]
Abstract
Phosphate-based glass fibers (PGFs), due to characteristics such as biodegradability and directionality, could be effective as spatial cues for axonal outgrowth following nerve injury. In the present study, PGF-containing cylindrical scaffolds of 1.8mm diameter and 3mm length were developed and implanted into the gap between the proximal and distal stumps following complete transection of rat spinal cords at T9. The PGF-free collagen scaffolds were implanted into the transected spinal cords of the control group. The open-field Basso, Beattie and Bresnahan locomotor scale revealed that the locomotor function of the experimental group was better than in the control group from 8 to 12 weeks after implantation, and urodynamic analysis revealed additional improvements in the experimental group in some parameters. Twelve weeks after implantation, some axon growth from the proximal and distal stumps to the scaffold was observed in the experimental group but not in the control group. Macrophages surrounded the injured thoracic spinal cord at 1 and 4 weeks after implantation; however, 6h after implantation, the pro-inflammatory cytokines did not differ between the control and experimental groups. Anterograde corticospinal tract (CST) tracing with biotinylated dextran amine showed that, in the experimental group, some CST outgrowths could reach the lumbar enlargement. By 12 weeks, the mRNA levels of brain-derived neurotrophic factor in the bladder had increased more in the experimental group than in the controls. We conclude that PGFs can have a beneficial effect on functional recovery following complete transection of the thoracic spinal cord in rats.
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662
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Targeting mTOR as a novel therapeutic strategy for traumatic CNS injuries. Drug Discov Today 2012; 17:861-8. [PMID: 22569182 DOI: 10.1016/j.drudis.2012.04.010] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2012] [Revised: 04/02/2012] [Accepted: 04/23/2012] [Indexed: 01/09/2023]
Abstract
The adult central nervous system (CNS) has a remarkable ability to repair itself. However, severe brain and spinal cord injuries (SCIs) cause lasting disability and there are only a few therapies that can prevent or restore function in such cases. In this review, we provide an overview of traumatic CNS injuries and discuss several emerging pharmacological options that have shown promise in preclinical and early clinical studies. We highlight therapies that modulate mammalian target of rapamycin (mTOR) signaling, a pathway that is well known for its roles in cell growth, metabolism and cancer. Interestingly, this pathway is also gaining newfound attention for its role in CNS repair and regeneration.
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663
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Christie KJ, Martinez JA, Zochodne DW. Disruption of E3 ligase NEDD4 in peripheral neurons interrupts axon outgrowth: Linkage to PTEN. Mol Cell Neurosci 2012; 50:179-92. [PMID: 22561198 DOI: 10.1016/j.mcn.2012.04.006] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2011] [Revised: 04/11/2012] [Accepted: 04/17/2012] [Indexed: 01/14/2023] Open
Abstract
Exploiting molecules and pathways important in developmental axon behaviour may offer new insights into regenerative behaviour of adult peripheral neurons after injury. In previous work, we have provided evidence that inhibition or knockdown of PTEN (phosphatase and tensin homolog deleted on chromosome ten) dramatically increases adult peripheral axon outgrowth, especially in preconditioned neurons (Christie et al., 2010). PTEN appears to operate as an endogenous brake to regeneration. Recent reports from Drinjakovic et al. (2010) have highlighted a role for the ubiquitin proteasome system (UPS) during neurite outgrowth in developing Xenopus retinal ganglion cells. Specifically, disruption of the UPS E3 ligase Nedd4 (neural precursor cell-expressed developmentally down-regulated protein 4) inhibited neurite branching through up-regulation of PTEN. We explored the potential role of Nedd4 in the peripheral neurons of adult rat dorsal root ganglia (DRG), particularly its impact on regenerative behaviour. Global inhibition of the UPS in vitro was associated with a severe decrease in neurite branching, both in preconditioned (injured) and control DRG sensory neurons. These involved neurons however maintained or qualitatively increased their PTEN expression, suggesting ongoing PTEN activity during UPS inhibition. Considering component's of UPS more specifically, Nedd4 co-localized with PTEN within sensory neurons in vivo and in vitro. Nedd4 also co-localized with PTEN and NF200 labelled regenerating axons at the injury site in the periphery following a 3 day sciatic nerve cut. A significant role for this unique co-expression was observed with fluorescently tagged siRNA inhibition of Nedd4, which decreased neurite outgrowth, an impact associated with greater expression of PTEN and that was completely reversed with application of a PTEN inhibitor. Overall, our results suggest an important role for Nedd4 regulation of PTEN in the response of peripheral neurons to injury. By degrading PTEN among other potential actions, Nedd4 supports axonal outgrowth whereas its inhibition facilitates PTEN inhibition of regeneration.
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Affiliation(s)
- Kimberly J Christie
- Department of Clinical Neurosciences and the Hotchkiss Brain Institute, University of Calgary, 168 HMRB, 3330 Hospital Dr. NW, Calgary, Canada AB T2N 4 N1
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664
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Krüppel-like Factor 7 engineered for transcriptional activation promotes axon regeneration in the adult corticospinal tract. Proc Natl Acad Sci U S A 2012; 109:7517-22. [PMID: 22529377 DOI: 10.1073/pnas.1120684109] [Citation(s) in RCA: 200] [Impact Index Per Article: 16.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Axon regeneration in the central nervous system normally fails, in part because of a developmental decline in the intrinsic ability of CNS projection neurons to extend axons. Members of the KLF family of transcription factors regulate regenerative potential in developing CNS neurons. Expression of one family member, KLF7, is down-regulated developmentally, and overexpression of KLF7 in cortical neurons in vitro promotes axonal growth. To circumvent difficulties in achieving high neuronal expression of exogenous KLF7, we created a chimera with the VP16 transactivation domain, which displayed enhanced neuronal expression compared with the native protein while maintaining transcriptional activation and growth promotion in vitro. Overexpression of VP16-KLF7 overcame the developmental loss of regenerative ability in cortical slice cultures. Adult corticospinal tract (CST) neurons failed to up-regulate KLF7 in response to axon injury, and overexpression of VP16-KLF7 in vivo promoted both sprouting and regenerative axon growth in the CST of adult mice. These findings identify a unique means of promoting CST axon regeneration in vivo by reengineering a developmentally down-regulated, growth-promoting transcription factor.
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665
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McCall J, Weidner N, Blesch A. Neurotrophic factors in combinatorial approaches for spinal cord regeneration. Cell Tissue Res 2012; 349:27-37. [PMID: 22526621 DOI: 10.1007/s00441-012-1388-6] [Citation(s) in RCA: 63] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2011] [Accepted: 02/23/2012] [Indexed: 01/09/2023]
Abstract
Axonal regeneration is inhibited by a plethora of different mechanisms in the adult central nervous system (CNS). While neurotrophic factors have been shown to stimulate axonal growth in numerous animal models of nervous system injury, a lack of suitable growth substrates, an insufficient activation of neuron-intrinsic regenerative programs, and extracellular inhibitors of regeneration limit the efficacy of neurotrophic factor delivery for anatomical and functional recovery after spinal cord injury. Thus, growth-stimulating factors will likely have to be combined with other treatment approaches to tap into the full potential of growth factor therapy for axonal regeneration. In addition, the temporal and spatial distribution of growth factors have to be tightly controlled to achieve biologically active concentrations, to allow for the chemotropic guidance of axons, and to prevent adverse effects related to the widespread distribution of neurotrophic factors. Here, we will review the rationale for combinatorial treatments in axonal regeneration and summarize some recent progress in promoting axonal regeneration in the injured CNS using such approaches.
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Affiliation(s)
- Julianne McCall
- Spinal Cord Injury Center, Heidelberg University Hospital, Schlierbacher Landstrasse 200 a, 69118 Heidelberg, Germany
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666
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Yang P, Wen H, Ou S, Cui J, Fan D. IL-6 promotes regeneration and functional recovery after cortical spinal tract injury by reactivating intrinsic growth program of neurons and enhancing synapse formation. Exp Neurol 2012; 236:19-27. [PMID: 22504113 DOI: 10.1016/j.expneurol.2012.03.019] [Citation(s) in RCA: 84] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2011] [Revised: 03/21/2012] [Accepted: 03/29/2012] [Indexed: 01/26/2023]
Abstract
Most neurons in adult mammalian central nervous system (CNS) fail to regenerate their axons after injury. Peripherally conditioned primary sensory neurons have an increased capacity to regenerate their central processes. Recent studies demonstrate that a conditioning lesion increased intrinsic growth capability is associated with the up-regulation of a group of growth-associated genes, one of the most established is interleukin-6 (IL-6). However, the cellular and molecular mechanisms by which IL-6 exerts its beneficial effect on axonal regeneration and functional recovery remain to be elucidated. The purpose of this study is to further investigate the molecular mechanisms of IL-6 in promoting regeneration and functional recovery after spinal cord injury (SCI). Here, we demonstrate that in vitro administration of IL-6 enhances neurite outgrowth of neurons on an inhibitory substrate myelin proteins, accompanied by increased expression of growth-associated genes GAP-43, SPRR1A and Arginase I. In vivo, intrathecal delivery of IL-6 for 7 days after cortical spinal tract injury induces synaptic rearrangements of sprouting axons and increases the expression of mTOR in neurons surrounding the lesion site, accompanied by improved functional recovery. In conclusion, our results show that IL-6 increases the expression of growth-associated genes and induces the expression of mTOR in lesion adjacent neurons, resulting in reactivating the intrinsic growth program of neurons to promote axonal regrowth and functional recovery after SCI.
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Affiliation(s)
- Ping Yang
- Department of Neurobiology, Chongqing Key Laboratory of Neurobiology, Third Military Medical University, Chongqing 400038, PR China.
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667
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Cabeza C, Figueroa A, Lazo OM, Galleguillos C, Pissani C, Klein A, Gonzalez-Billault C, Inestrosa NC, Alvarez AR, Zanlungo S, Bronfman FC. Cholinergic abnormalities, endosomal alterations and up-regulation of nerve growth factor signaling in Niemann-Pick type C disease. Mol Neurodegener 2012; 7:11. [PMID: 22458984 PMCID: PMC3395862 DOI: 10.1186/1750-1326-7-11] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2011] [Accepted: 03/29/2012] [Indexed: 12/21/2022] Open
Abstract
BACKGROUND Neurotrophins and their receptors regulate several aspects of the developing and mature nervous system, including neuronal morphology and survival. Neurotrophin receptors are active in signaling endosomes, which are organelles that propagate neurotrophin signaling along neuronal processes. Defects in the Npc1 gene are associated with the accumulation of cholesterol and lipids in late endosomes and lysosomes, leading to neurodegeneration and Niemann-Pick type C (NPC) disease. The aim of this work was to assess whether the endosomal and lysosomal alterations observed in NPC disease disrupt neurotrophin signaling. As models, we used i) NPC1-deficient mice to evaluate the central cholinergic septo-hippocampal pathway and its response to nerve growth factor (NGF) after axotomy and ii) PC12 cells treated with U18666A, a pharmacological cellular model of NPC, stimulated with NGF. RESULTS NPC1-deficient cholinergic cells respond to NGF after axotomy and exhibit increased levels of choline acetyl transferase (ChAT), whose gene is under the control of NGF signaling, compared to wild type cholinergic neurons. This finding was correlated with increased ChAT and phosphorylated Akt in basal forebrain homogenates. In addition, we found that cholinergic neurons from NPC1-deficient mice had disrupted neuronal morphology, suggesting early signs of neurodegeneration. Consistently, PC12 cells treated with U18666A presented a clear NPC cellular phenotype with a prominent endocytic dysfunction that includes an increased size of TrkA-containing endosomes and reduced recycling of the receptor. This result correlates with increased sensitivity to NGF, and, in particular, with up-regulation of the Akt and PLC-γ signaling pathways, increased neurite extension, increased phosphorylation of tau protein and cell death when PC12 cells are differentiated and treated with U18666A. CONCLUSIONS Our results suggest that the NPC cellular phenotype causes neuronal dysfunction through the abnormal up-regulation of survival pathways, which causes the perturbation of signaling cascades and anomalous phosphorylation of the cytoskeleton.
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Affiliation(s)
- Carolina Cabeza
- Physiology Department, Millennium Nucleus in Regenerative Biology, Faculty of Biological Sciences, Pontificia Universidad Católica de Chile, Santiago, Chile
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668
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Ueno M, Hayano Y, Nakagawa H, Yamashita T. Intraspinal rewiring of the corticospinal tract requires target-derived brain-derived neurotrophic factor and compensates lost function after brain injury. Brain 2012; 135:1253-67. [DOI: 10.1093/brain/aws053] [Citation(s) in RCA: 87] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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669
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Tonge DA, de Burgh HT, Docherty R, Humphries MJ, Craig SE, Pizzey J. Fibronectin supports neurite outgrowth and axonal regeneration of adult brain neurons in vitro. Brain Res 2012; 1453:8-16. [PMID: 22483961 PMCID: PMC3989037 DOI: 10.1016/j.brainres.2012.03.024] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2011] [Revised: 03/03/2012] [Accepted: 03/09/2012] [Indexed: 12/09/2022]
Abstract
The molecular basis of axonal regeneration of central nervous system (CNS) neurons remains to be fully elucidated. In part, this is due to the difficulty in maintaining CNS neurons in vitro. Here, we show that dissociated neurons from the cerebral cortex and hippocampus of adult mice may be maintained in culture for up to 9 days in defined medium without added growth factors. Outgrowth of neurites including axons was observed from both CNS sources and was significantly greater on plasma fibronectin than on other substrata such as laminin and merosin. Neurite outgrowth on fibronectin appears to be mediated by α5β1 integrin since a recombinant fibronectin fragment containing binding sites for this receptor was as effective as intact fibronectin in supporting neurite outgrowth. Conversely, function-blocking antibodies to α5 and β1 integrin sub-units inhibited neurite outgrowth on intact fibronectin. These results suggest that the axonal regeneration seen in in vivo studies using fibronectin-based matrices is due to the molecule itself and not a consequence of secondary events such as cellular infiltration. They also indicate the domains of fibronectin that may be responsible for eliciting this response.
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Affiliation(s)
- David A Tonge
- Wolfson-Centre for Age-Related Disease, King's College London, Hodgkin Building, Guy's Campus, London SE1 1UL, UK
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670
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Bradbury EJ. Re-wiring the spinal cord: introduction to the special issue on plasticity after spinal cord injury. Exp Neurol 2012; 235:1-4. [PMID: 22440889 DOI: 10.1016/j.expneurol.2012.03.004] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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671
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Jacques SJ, Ahmed Z, Forbes A, Douglas MR, Vigenswara V, Berry M, Logan A. AAV8(gfp) preferentially targets large diameter dorsal root ganglion neurones after both intra-dorsal root ganglion and intrathecal injection. Mol Cell Neurosci 2012; 49:464-74. [PMID: 22425560 DOI: 10.1016/j.mcn.2012.03.002] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2011] [Revised: 02/27/2012] [Accepted: 03/01/2012] [Indexed: 10/28/2022] Open
Abstract
Adeno-associated viral vectors (AAV) are increasingly used to deliver therapeutic genes to the central nervous system (CNS) where they promote transgene expression in post mitotic neurones for long periods with little or no toxicity. In adult rat dorsal root ganglia (DRG), we investigated the cellular tropism of AAV8 containing the green fluorescent protein gene (gfp) after either intra-lumbar DRG or intrathecal injection and showed that transduced DRG neurones (DRGN) expressed GFP irrespective of the delivery route, while non-neuronal cells were GFP(-). After intra-DRG delivery of AAV8(gfp), the mean DRGN transduction rate was 11%, while intrathecal delivery transduced a mean of 1.5% DRGN. After intra-DRG injection, 2% of small DRGN (<30 μm in diameter) were GFP(+) compared with 32% of large DRGN (>60 μm in diameter). Axons of transduced DRGN were also GFP(+); no intra-spinal neurones were transduced. A small number of contralateral DRGN were transduced after intra-DRG injection, suggesting that AAV8 may diffuse from injected DRG into the spinal canal. Microglia and astrocytes were highly ramified with increased GFAP(+) immunoreactivity (i.e. activated) in the neuropil around GFP(+) DRG axon projections within the cord after intra-DRG injection. This study showed that after both intra-DRG and intrathecal delivery, strong preferential AAV8 tropism exists for large DRGN unassociated with cell death, but GFP(+) axons projecting in the spinal cord induced local glial activation. These results open up opportunities for targeted delivery of therapeutics such as neurotrophic factors to the injured spinal cord.
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Affiliation(s)
- Steven J Jacques
- Neuropharmacology and Neurobiology Section, School of Clinical and Experimental Medicine, College of Medical and Dental Sciences, University of Birmingham, Birmingham B15 2TT, UK
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672
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Wang X, Duffy P, McGee AW, Hasan O, Gould G, Tu N, Harel NY, Huang Y, Carson RE, Weinzimmer D, Ropchan J, Benowitz LI, Cafferty WBJ, Strittmatter SM. Recovery from chronic spinal cord contusion after Nogo receptor intervention. Ann Neurol 2012; 70:805-21. [PMID: 22162062 DOI: 10.1002/ana.22527] [Citation(s) in RCA: 77] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
OBJECTIVE Several interventions promote axonal growth and functional recovery when initiated shortly after central nervous system injury, including blockade of myelin-derived inhibitors with soluble Nogo receptor (NgR1, RTN4R) decoy protein. We examined the efficacy of this intervention in the much more prevalent and refractory condition of chronic spinal cord injury. METHODS We eliminated the NgR1 pathway genetically in mice by conditional gene targeting starting 8 weeks after spinal hemisection injury and monitored locomotion in the open field and by video kinematics over the ensuing 4 months. In a separate pharmacological experiment, intrathecal NgR1 decoy protein administration was initiated 3 months after spinal cord contusion injury. Locomotion and raphespinal axon growth were assessed during 3 months of treatment between 4 and 6 months after contusion injury. RESULTS Conditional deletion of NgR1 in the chronic state results in gradual improvement of motor function accompanied by increased density of raphespinal axons in the caudal spinal cord. In chronic rat spinal contusion, NgR1 decoy treatment from 4 to 6 months after injury results in 29% (10 of 35) of rats recovering weight-bearing status compared to 0% (0 of 29) of control rats (p < 0.05). Open field Basso, Beattie, and Bresnahan locomotor scores showed a significant improvement in the NgR-treated group relative to the control group (p < 0.005, repeated measures analysis of variance). An increase in raphespinal axon density caudal to the injury is detected in NgR1 decoy-treated animals by immunohistology and by positron emission tomography using a serotonin reuptake ligand. INTERPRETATION Antagonizing myelin-derived inhibitors signaling with NgR1 decoy augments recovery from chronic spinal cord injury.
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Affiliation(s)
- Xingxing Wang
- Cellular Neuroscience, Neurodegeneration, and Repair Program, and Department of Neurology, Yale School of Medicine, New Haven, CT 06536-0812, USA
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673
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Liu CM, Hur EM, Zhou FQ. Coordinating Gene Expression and Axon Assembly to Control Axon Growth: Potential Role of GSK3 Signaling. Front Mol Neurosci 2012; 5:3. [PMID: 22347166 PMCID: PMC3272657 DOI: 10.3389/fnmol.2012.00003] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2011] [Accepted: 01/09/2012] [Indexed: 12/23/2022] Open
Abstract
Axon growth requires the coordinated regulation of gene expression in the neuronal soma, local protein translation in the axon, anterograde transport of synthesized raw materials along the axon, and assembly of cytoskeleton and membranes in the nerve growth cone. Glycogen synthase kinase 3 (GSK3) signaling has recently been shown to play key roles in the regulation of axonal transport and cytoskeletal assembly during axon growth. GSK3 signaling is also known to regulate gene expression via controlling the functions of many transcription factors, suggesting that GSK3 may be an important regulator of gene transcription supporting axon growth. We review signaling pathways that control local axon assembly at the growth cone and gene expression in the soma during developmental or regenerative axon growth and discuss the potential involvement of GSK3 signaling in these processes, with a particular focus on how GSK3 signaling modulates the function of axon growth-associated transcription factors.
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Affiliation(s)
- Chang-Mei Liu
- Department of Orthopaedic Surgery, The Johns Hopkins University School of Medicine Baltimore, MD, USA
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674
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Martin JH. Systems neurobiology of restorative neurology and future directions for repair of the damaged motor systems. Clin Neurol Neurosurg 2012; 114:515-23. [PMID: 22316612 DOI: 10.1016/j.clineuro.2012.01.011] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2011] [Accepted: 01/09/2012] [Indexed: 12/15/2022]
Abstract
Restoring movement control after central nervous system injury requires reconnecting the brain and spinal motoneurons, and doing so with sufficient precision and strength to enable robust voluntary muscle recruitment. Whereas the connection between the upper motoneuron in motor cortex and alpha-motoneurons was thought to be the only important connection for normal motor function in humans, we know that a multiplicity of motor circuits are recruited during normal motor control. Multiplicity of functionally important motor circuits points to the myriad possibilities of intervention that restorative neurology can turn to for repairing motor systems connections to recover movement control after injury. New motor systems repair strategies in animal models and humans are tapping into distributed motor control functions of the spinal cord; neural activity-based approaches, especially for corticospinal tract repair; and circuit-selective activation approaches. I focus on studies harnessing activity-based therapeutic approaches to promote sprouting of spared corticospinal tract axons after injury and redirecting potentially maladaptive plasticity. I discuss that we can see on the near horizon, many different strategies for repairing motor systems connections after injury.
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Affiliation(s)
- John H Martin
- Department of Physiology, Pharmacology, and Neuroscience, City College of the City University of New York, NY 10031, USA.
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675
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Haas C, Neuhuber B, Yamagami T, Rao M, Fischer I. Phenotypic analysis of astrocytes derived from glial restricted precursors and their impact on axon regeneration. Exp Neurol 2012; 233:717-32. [PMID: 22101004 PMCID: PMC3272137 DOI: 10.1016/j.expneurol.2011.11.002] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2011] [Revised: 10/12/2011] [Accepted: 11/01/2011] [Indexed: 12/16/2022]
Abstract
Although astrocytes are involved in the production of an inhibitory glial scar following injury, they are also capable of providing neuroprotection and supporting axonal growth. There is growing appreciation for a diverse and dynamic population of astrocytes, specified by a variety of glial precursors, whose function is regulated regionally and temporally. Consequently, the therapeutic application of glial precursors and astrocytes by effective transplantation protocols requires a better understanding of their phenotypic and functional properties and effective protocols for their preparation. We present a systematic analysis of astrocyte differentiation using multiple preparations of glial-restricted precursors (GRP), evaluating their morphological and phenotypic properties following treatment with fetal bovine serum (FBS), bone morphogenetic protein 4 (BMP-4), or ciliary neurotrophic factor (CNTF) in comparison to controls treated with basic fibroblast growth factor (bFGF), which maintains undifferentiated GRP. We found that treatments with FBS or BMP-4 generated similar profiles of highly differentiated astrocytes that were A2B5-/GFAP+. Treatment with FBS generated the most mature astrocytes, with a distinct and near-homogeneous morphology of fibroblast-like flat cells, whereas BMP-4 derived astrocytes had a stellate, but heterogeneous morphology. Treatment with CNTF induced differentiation of GRP to an intermediate state of GFAP+cells that maintained immature markers and had relatively long processes. Furthermore, astrocytes generated by BMP-4 or CNTF showed considerable experimental plasticity, and their morphology and phenotypes could be reversed with complementary treatments along a wide range of mature-immature states. Importantly, when GRP or GRP treated with BMP-4 or CNTF were transplanted acutely into a dorsal column lesion of the spinal cord, cells from all 3 groups survived and generated permissive astrocytes that supported axon growth and regeneration of host sensory axons into, but not out of the lesion. Our study underscores the dynamic nature of astrocytes prepared from GRP and their permissive properties, and suggest that future therapeutic applications in restoring connectivity following CNS injury are likely to require a combination of treatments.
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Affiliation(s)
| | | | - Takaya Yamagami
- Department of Neurobiology & Anatomy, Drexel University College of Medicine, 2900 Queen Lane, Philadelphia, PA, Life Technologies, Frederick, MD
| | | | - Itzhak Fischer
- Department of Neurobiology & Anatomy, Drexel University College of Medicine, 2900 Queen Lane, Philadelphia, PA, Life Technologies, Frederick, MD
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676
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Steward O, Popovich PG, Dietrich WD, Kleitman N. Replication and reproducibility in spinal cord injury research. Exp Neurol 2012; 233:597-605. [DOI: 10.1016/j.expneurol.2011.06.017] [Citation(s) in RCA: 142] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2011] [Accepted: 06/28/2011] [Indexed: 01/31/2023]
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677
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Lang C, Guo X, Kerschensteiner M, Bareyre FM. Single collateral reconstructions reveal distinct phases of corticospinal remodeling after spinal cord injury. PLoS One 2012; 7:e30461. [PMID: 22291960 PMCID: PMC3265484 DOI: 10.1371/journal.pone.0030461] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2011] [Accepted: 12/21/2011] [Indexed: 01/20/2023] Open
Abstract
Background Injuries to the spinal cord often result in severe functional deficits that, in case of incomplete injuries, can be partially compensated by axonal remodeling. The corticospinal tract (CST), for example, responds to a thoracic transection with the formation of an intraspinal detour circuit. The key step for the formation of the detour circuit is the sprouting of new CST collaterals in the cervical spinal cord that contact local interneurons. How individual collaterals are formed and refined over time is incompletely understood. Methodology/Principal Findings We traced the hindlimb corticospinal tract at different timepoints after lesion to show that cervical collateral formation is initiated in the first 10 days. These collaterals can then persist for at least 24 weeks. Interestingly, both major and minor CST components contribute to the formation of persistent CST collaterals. We then developed an approach to label single CST collaterals based on viral gene transfer of the Cre recombinase to a small number of cortical projection neurons in Thy1-STP-YFP or Thy1-Brainbow mice. Reconstruction and analysis of single collaterals for up to 12 weeks after lesion revealed that CST remodeling evolves in 3 phases. Collateral growth is initiated in the first 10 days after lesion. Between 10 days and 3–4 weeks after lesion elongated and highly branched collaterals form in the gray matter, the complexity of which depends on the CST component they originate from. Finally, between 3–4 weeks and 12 weeks after lesion the size of CST collaterals remains largely unchanged, while the pattern of their contacts onto interneurons matures. Conclusions/Significance This study provides a comprehensive anatomical analysis of CST reorganization after injury and reveals that CST remodeling occurs in distinct phases. Our results and techniques should facilitate future efforts to unravel the mechanisms that govern CST remodeling and to promote functional recovery after spinal cord injury.
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Affiliation(s)
- Claudia Lang
- Research Unit Therapy Development, Institute of Clinical Neuroimmunology, Ludwig-Maximilians-Universität München, Munich, Germany
| | - Xiaoli Guo
- Research Unit Therapy Development, Institute of Clinical Neuroimmunology, Ludwig-Maximilians-Universität München, Munich, Germany
| | - Martin Kerschensteiner
- Research Unit Therapy Development, Institute of Clinical Neuroimmunology, Ludwig-Maximilians-Universität München, Munich, Germany
- * E-mail: (FMB); (MK)
| | - Florence M. Bareyre
- Research Unit Therapy Development, Institute of Clinical Neuroimmunology, Ludwig-Maximilians-Universität München, Munich, Germany
- * E-mail: (FMB); (MK)
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678
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Role of mTOR in neuroprotection and axon regeneration after inflammatory stimulation. Neurobiol Dis 2012; 46:314-24. [PMID: 22273489 DOI: 10.1016/j.nbd.2012.01.004] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2011] [Revised: 01/03/2012] [Accepted: 01/09/2012] [Indexed: 11/23/2022] Open
Abstract
Mature retinal ganglion cells (RGCs) do not normally regenerate injured axons, but degenerate after axotomy. However, inflammatory stimulation (IS) enables RGCs to survive axotomy and regenerate axons in the injured optic nerve. Similar effects are achieved by the genetic deletion of phosphatase and tensin homolog (PTEN) and subsequent mammalian target of rapamycin (mTOR) activation. Here, we report that IS prevents the axotomy-induced decrease of mTOR activity in RGCs in a CNTF/LIF-dependent manner. Inactivation of mTOR significantly reduced the number of long axons regenerating in the optic nerve, but surprisingly, did not affect the initial switch of RGCs into the regenerative state, or the neuroprotective effects associated with IS. In vitro, inhibition of mTOR activity reduced regeneration on myelin or chondroitin sulfate proteoglycans (CSPGs), but not on a growth-permissive substrate. Thus, mTOR activity is not generally required for neuroprotection or switching mature neurons into an active regenerative state, but it is important for the maintenance of the axonal growth state and overcoming of inhibitory effects caused by myelin and CSPGs.
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679
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Axon degeneration in Parkinson's disease. Exp Neurol 2012; 246:72-83. [PMID: 22285449 DOI: 10.1016/j.expneurol.2012.01.011] [Citation(s) in RCA: 332] [Impact Index Per Article: 27.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2011] [Revised: 12/08/2011] [Accepted: 01/10/2012] [Indexed: 02/07/2023]
Abstract
Parkinson's disease (PD) is the most common neurodegenerative disease of the basal ganglia. Like other adult-onset neurodegenerative disorders, it is without a treatment that forestalls its chronic progression. Efforts to develop disease-modifying therapies to date have largely focused on the prevention of degeneration of the neuron soma, with the tacit assumption that such approaches will forestall axon degeneration as well. We herein propose that future efforts to develop neuroprotection for PD may benefit from a shift in focus to the distinct mechanisms that underlie axon degeneration. We review evidence from human post-mortem studies, functional neuroimaging, genetic causes of the disease and neurotoxin models that axon degeneration may be the earliest feature of the disease, and it may therefore be the most appropriate target for early intervention. In addition, we present evidence that the molecular mechanisms of degeneration of axons are separate and distinct from those of neuron soma. Progress is being made in understanding these mechanisms, and they provide possible new targets for therapeutic intervention. We also suggest that the potential for axon re-growth in the adult central nervous system has perhaps been underestimated, and it offers new avenues for neurorestoration. In conclusion, we propose that a new focus on the neurobiology of axons, their molecular pathways of degeneration and growth, will offer novel opportunities for neuroprotection and restoration in the treatment of PD and other neurodegenerative diseases.
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680
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Lerch JK, Kuo F, Motti D, Morris R, Bixby JL, Lemmon VP. Isoform diversity and regulation in peripheral and central neurons revealed through RNA-Seq. PLoS One 2012; 7:e30417. [PMID: 22272348 PMCID: PMC3260295 DOI: 10.1371/journal.pone.0030417] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2011] [Accepted: 12/15/2011] [Indexed: 11/19/2022] Open
Abstract
To fully understand cell type identity and function in the nervous system there is a need to understand neuronal gene expression at the level of isoform diversity. Here we applied Next Generation Sequencing of the transcriptome (RNA-Seq) to purified sensory neurons and cerebellar granular neurons (CGNs) grown on an axonal growth permissive substrate. The goal of the analysis was to uncover neuronal type specific isoforms as a prelude to understanding patterns of gene expression underlying their intrinsic growth abilities. Global gene expression patterns were comparable to those found for other cell types, in that a vast majority of genes were expressed at low abundance. Nearly 18% of gene loci produced more than one transcript. More than 8000 isoforms were differentially expressed, either to different degrees in different neuronal types or uniquely expressed in one or the other. Sensory neurons expressed a larger number of genes and gene isoforms than did CGNs. To begin to understand the mechanisms responsible for the differential gene/isoform expression we identified transcription factor binding sites present specifically in the upstream genomic sequences of differentially expressed isoforms, and analyzed the 3′ untranslated regions (3′ UTRs) for microRNA (miRNA) target sites. Our analysis defines isoform diversity for two neuronal types with diverse axon growth capabilities and begins to elucidate the complex transcriptional landscape in two neuronal populations.
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Affiliation(s)
- Jessica K. Lerch
- The Miami Project to Cure Paralysis, Miller School of Medicine, University of Miami, Miami, Florida, United States of America
| | - Frank Kuo
- The Miami Project to Cure Paralysis, Miller School of Medicine, University of Miami, Miami, Florida, United States of America
| | - Dario Motti
- The Miami Project to Cure Paralysis, Miller School of Medicine, University of Miami, Miami, Florida, United States of America
| | - Richard Morris
- The Miami Project to Cure Paralysis, Miller School of Medicine, University of Miami, Miami, Florida, United States of America
- The Hussman Institute for Human Genomics, Miller School of Medicine, University of Miami, Miami, Florida, United States of America
| | - John L. Bixby
- The Miami Project to Cure Paralysis, Miller School of Medicine, University of Miami, Miami, Florida, United States of America
- The Hussman Institute for Human Genomics, Miller School of Medicine, University of Miami, Miami, Florida, United States of America
- Department of Cellular and Molecular Pharmacology, Miller School of Medicine, University of Miami, Miami, Florida, United States of America
- * E-mail: (VPL); (JLB)
| | - Vance P. Lemmon
- The Miami Project to Cure Paralysis, Miller School of Medicine, University of Miami, Miami, Florida, United States of America
- Department of Neurological Surgery, Miller School of Medicine, University of Miami, Miami, Florida, United States of America
- * E-mail: (VPL); (JLB)
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681
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Abstract
In metazoans, TOR is an essential protein that functions as a master regulator of cellular growth and proliferation. Over the past decade, there has been an explosion of information about this critical master kinase, ranging from the composition of the TOR protein complex to its ability to act as an integrator of numerous extracellular signals. Unfortunately, this plethora of information has also raised numerous questions regarding TOR function. Currently, the prevailing view is that mammalian TOR (mTOR) exists in at least two molecular complexes, mTORC1 and mTORC2, which are largely defined by the presence of either RAPTOR or RICTOR. However, additional co-factors have been identified for each complex, and their importance in mediating mTOR signals has been incompletely elucidated. Similarly, there are differences in mTOR function that reflect the tissue of origin. In this review, we present an alternative view to mTOR complex formation and function, which envisions mTOR regulation and signal propagation as a reflection of cell type- and basal state-dependent conditions. The re-interpretation of mTOR biology in this framework may facilitate the design of therapies most likely to effectively inhibit this central regulator of cell behavior.
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Affiliation(s)
- Jason D Weber
- Department of Internal Medicine, Washington University School of Medicine, St. Louis, MO, USA
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682
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Systemic bisperoxovanadium activates Akt/mTOR, reduces autophagy, and enhances recovery following cervical spinal cord injury. PLoS One 2012; 7:e30012. [PMID: 22253859 PMCID: PMC3254642 DOI: 10.1371/journal.pone.0030012] [Citation(s) in RCA: 117] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2011] [Accepted: 12/11/2011] [Indexed: 12/29/2022] Open
Abstract
Secondary damage following primary spinal cord injury extends pathology beyond the site of initial trauma, and effective management is imperative for maximizing anatomical and functional recovery. Bisperoxovanadium compounds have proven neuroprotective effects in several central nervous system injury/disease models, however, no mechanism has been linked to such neuroprotection from bisperoxovanadium treatment following spinal trauma. The goal of this study was to assess acute bisperoxovanadium treatment effects on neuroprotection and functional recovery following cervical unilateral contusive spinal cord injury, and investigate a potential mechanism of the compound's action. Two experimental groups of rats were established to 1) assess twice-daily 7 day treatment of the compound, potassium bisperoxo (picolinato) vanadium, on long-term recovery of skilled forelimb activity using a novel food manipulation test, and neuroprotection 6 weeks following injury and 2) elucidate an acute mechanistic link for the action of the drug post-injury. Immunofluorescence and Western blotting were performed to assess cellular signaling 1 day following SCI, and histochemistry and forelimb functional analysis were utilized to assess neuroprotection and recovery 6 weeks after injury. Bisperoxovanadium promoted significant neuroprotection through reduced motorneuron death, increased tissue sparing, and minimized cavity formation in rats. Enhanced forelimb functional ability during a treat-eating assessment was also observed. Additionally, bisperoxovanadium significantly enhanced downstream Akt and mammalian target of rapamycin signaling and reduced autophagic activity, suggesting inhibition of the phosphatase and tensin homologue deleted on chromosome ten as a potential mechanism of bisperoxovanadium action following traumatic spinal cord injury. Overall, this study demonstrates the efficacy of a clinically applicable pharmacological therapy for rapid initiation of neuroprotection post-spinal cord injury, and sheds light on the signaling involved in its action.
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683
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Puttagunta R, Di Giovanni S. Retinoic acid signaling in axonal regeneration. Front Mol Neurosci 2012; 4:59. [PMID: 22287943 PMCID: PMC3249608 DOI: 10.3389/fnmol.2011.00059] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2011] [Accepted: 12/22/2011] [Indexed: 01/28/2023] Open
Abstract
Following an acute central nervous system (CNS) injury, axonal regeneration and functional recovery are extremely limited. This is due to an extrinsic inhibitory growth environment and the lack of intrinsic growth competence. Retinoic acid (RA) signaling, essential in developmental dorsoventral patterning and specification of spinal motor neurons, has been shown through its receptor, the transcription factor RA receptor β2 (RARβ2), to induce axonal regeneration following spinal cord injury (SCI). Recently, it has been shown that in dorsal root ganglion neurons (DRGs), cAMP levels were greatly increased by lentiviral RARβ2 expression and contributed to neurite outgrowth. Moreover, RARβagonists, in cerebellar granule neurons (CGN) and in the brain in vivo, induced phosphoinositide 3-kinase dependent phosphorylation of AKT that was involved in RARβ-dependent neurite outgrowth. More recently, RA-RARβpathways were shown to directly transcriptionally repress a member of the inhibitory Nogo receptor (NgR) complex, Lingo-1, under an axonal growth inhibitory environment in vitro as well as following spinal injury in vivo. This perspective focuses on these newly discovered molecular mechanisms and future directions in the field.
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Affiliation(s)
- Radhika Puttagunta
- Laboratory for Neuroregeneration and Repair, Center for Neurology, Hertie Institute for Clinical Brain Research, University of Tuebingen Tuebingen, Germany
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684
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Luo X, Park KK. Neuron-Intrinsic Inhibitors of Axon Regeneration. INTERNATIONAL REVIEW OF NEUROBIOLOGY 2012. [DOI: 10.1016/b978-0-12-398309-1.00008-1] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
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685
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Chew DJ, Fawcett JW, Andrews MR. The challenges of long-distance axon regeneration in the injured CNS. PROGRESS IN BRAIN RESEARCH 2012. [PMID: 23186719 DOI: 10.1016/b978-0-444-59544-7.00013-5] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Injury to the central nervous system (CNS) that results in long-tract axonal damage typically leads to permanent functional deficits in areas innervated at, and below, the level of the lesion. The initial ischemia, inflammation, and neurodegeneration are followed by a progressive generation of scar tissue, dieback of transected axons, and demyelination, creating an area inhibitory to regrowth and recovery. Two ways to combat this inhibition is to therapeutically target the extrinsic and intrinsic properties of the axon-scar environment. Scar tissue within and surrounding the lesion site can be broken down using an enzyme known as chondroitinase. Negative regulators of adult neuronal growth, such as Nogo, can be neutralized with antibodies. Both therapies greatly improve functional recovery in animal models. Alternatively, modifying the intrinsic growth properties of CNS neurons through gene therapy or pharmacotherapy has also shown promising axonal regeneration after injury. Despite these promising therapies, the main challenge of long-distance axon regeneration still remains; achieving a level of functional and organized connectivity below the level of the lesion that mimics the intact CNS.
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Affiliation(s)
- Daniel J Chew
- Centre for Brain Repair, University of Cambridge, Forvie Site, Robinson Way, Cambridge, UK
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686
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Eva R, Andrews MR, Franssen EHP, Fawcett JW. Intrinsic mechanisms regulating axon regeneration: an integrin perspective. INTERNATIONAL REVIEW OF NEUROBIOLOGY 2012; 106:75-104. [PMID: 23211460 DOI: 10.1016/b978-0-12-407178-0.00004-1] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Adult central nervous system (CNS) axons fail to regenerate after injury because of inhibitory factors in the surrounding environment and a low intrinsic regenerative capacity. Axons in the adult peripheral nervous system have a higher regenerative capacity, due in part to the presence of certain integrins-receptors for the extracellular matrix. Integrins are critical for axon growth during the development of the nervous system but are absent from some adult CNS axons. Here, we discuss the intrinsic mechanisms that regulate axon regeneration and examine the role of integrins. As correct localization is paramount to integrin function, we further discuss the mechanisms that regulate integrin traffic toward the axonal growth cone.
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Affiliation(s)
- Richard Eva
- Cambridge Centre for Brain Repair, Department of Clinical Neurosciences, University of Cambridge, Cambridge, United Kingdom
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687
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Hutson TH, Verhaagen J, Yáñez-Muñoz RJ, Moon LDF. Corticospinal tract transduction: a comparison of seven adeno-associated viral vector serotypes and a non-integrating lentiviral vector. Gene Ther 2012; 19:49-60. [PMID: 21562590 PMCID: PMC3160493 DOI: 10.1038/gt.2011.71] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2010] [Revised: 02/20/2011] [Accepted: 02/22/2011] [Indexed: 01/05/2023]
Abstract
The corticospinal tract (CST) is extensively used as a model system for assessing potential therapies to enhance neuronal regeneration and functional recovery following spinal cord injury (SCI). However, efficient transduction of the CST is challenging and remains to be optimised. Recombinant adeno-associated viral (AAV) vectors and integration-deficient lentiviral vectors are promising therapeutic delivery systems for gene therapy to the central nervous system (CNS). In the present study the cellular tropism and transduction efficiency of seven AAV vector serotypes (AAV1, 2, 3, 4, 5, 6, 8) and an integration-deficient lentiviral vector were assessed for their ability to transduce corticospinal neurons (CSNs) following intracortical injection. AAV1 was identified as the optimal serotype for transducing cortical and CSNs with green fluorescent protein (GFP) expression detectable in fibres projecting through the dorsal CST (dCST) of the cervical spinal cord. In contrast, AAV3 and AAV4 demonstrated a low efficacy for transducing CNS cells and AAV8 presented a potential tropism for oligodendrocytes. Furthermore, it was shown that neither AAV nor lentiviral vectors generate a significant microglial response. The identification of AAV1 as the optimal serotype for transducing CSNs should facilitate the design of future gene therapy strategies targeting the CST for the treatment of SCI.
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Affiliation(s)
- T H Hutson
- Neurorestoration Group, Wolfson Centre for Age-Related Diseases, King's College London, London, UK.
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688
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Yoon C, Tuszynski MH. Frontiers of spinal cord and spine repair: experimental approaches for repair of spinal cord injury. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2012; 760:1-15. [PMID: 23281510 DOI: 10.1007/978-1-4614-4090-1_1] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Regeneration of injured CNS neurons was once thought to be an unachievable goal. Most patients with significant damage to the spinal cord suffer from permanently impaired neurological function. A century of research, however, has led to an understanding of multiple factors that limit CNS regeneration and from this knowledge experimental strategies have emerged for enhancing CNS repair. Some of these approaches have undergone human translation. Nevertheless, translating experimental findings to human trials has been more challenging than anticipated. In this chapter, we will review the current state of knowledge regarding central axonal growth failure after injury, and approaches taken to enhance recovery after SCI.
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Affiliation(s)
- Choya Yoon
- Department of Neurosciences, University of California San Diego, La Jolla, California, USA.
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689
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Blackmore MG. Molecular control of axon growth: insights from comparative gene profiling and high-throughput screening. INTERNATIONAL REVIEW OF NEUROBIOLOGY 2012. [PMID: 23206595 DOI: 10.1016/b978-0-12-398309-1.00004-4] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Axon regeneration in the mammalian adult central nervous system (CNS) is limited by an intrinsically low capacity for axon growth in many CNS neurons. In contrast, embryonic, peripheral, and many nonmammalian neurons are capable of successful regeneration. Numerous studies have compared mammalian CNS neurons to their counterparts in regenerating systems in an effort to identify candidate genes that control regenerative ability. This review summarizes work using this comparative strategy and examines our current understanding of gene function in axon growth, highlighting the emergence of genome-wide expression profiling and high-throughput screening strategies to identify novel regulators of axon growth.
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Affiliation(s)
- Murray G Blackmore
- Department of Biomedical Sciences, Marquette University, Milwaukee, Wisconsin, USA.
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690
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Abstract
AbstractPTEN (phosphatase and tensin homologue deleted in chromosome 10) was first identified as a candidate tumour suppressor gene located on chromosome 10q23. It is considered as one of the most frequently mutated genes in human malignancies. Emerging evidence shows that the biological function of PTEN extends beyond its tumour suppressor activity. In the central nervous system PTEN is a crucial regulator of neuronal development, neuronal survival, axonal regeneration and synaptic plasticity. Furthermore, PTEN has been linked to the pathogenesis of neurodegenerative disorders such as Alzheimer’s disease, Parkinson’s disease and amyotrophic lateral sclerosis. Recently increased attention has been focused on PTEN as a potential target for the treatment of brain injury and neurodegeneration. In this review we discuss the essential functions of PTEN in the central nervous system and its involvement in neurodegeneration.
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691
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Ye T, Fu AK, Ip NY. Cyclin-Dependent Kinase 5 in Axon Growth and Regeneration. INTERNATIONAL REVIEW OF NEUROBIOLOGY 2012. [DOI: 10.1016/b978-0-12-398309-1.00006-8] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
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692
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Reier PJ, Lane MA, Hall ED, Teng YD, Howland DR. Translational spinal cord injury research: preclinical guidelines and challenges. HANDBOOK OF CLINICAL NEUROLOGY 2012; 109:411-33. [PMID: 23098728 PMCID: PMC4288927 DOI: 10.1016/b978-0-444-52137-8.00026-7] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Advances in the neurobiology of spinal cord injury (SCI) have prompted increasing attention to opportunities for moving experimental strategies towards clinical applications. Preclinical studies are the centerpiece of the translational process. A major challenge is to establish strategies for achieving optimal translational progression while minimizing potential repetition of previous disappointments associated with clinical trials. This chapter reviews and expands upon views pertaining to preclinical design reported in recently published opinion surveys. Subsequent discussion addresses other preclinical considerations more specifically related to current and potentially imminent cellular and pharmacological approaches to acute/subacute and chronic SCI. Lastly, a retrospective and prospective analysis examines how guidelines currently under discussion relate to select examples of past, current, and future clinical translations. Although achieving definition of the "perfect" preclinical scenario is difficult to envision, this review identifies therapeutic robustness and independent replication of promising experimental findings as absolutely critical prerequisites for clinical translation. Unfortunately, neither has been fully embraced thus far. Accordingly, this review challenges the notion "everything works in animals and nothing in humans", since more rigor must first be incorporated into the bench-to-bedside translational process by all concerned, whether in academia, clinical medicine, or corporate circles.
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Affiliation(s)
- Paul J Reier
- Department of Neuroscience, University of Florida College of Medicine, Gainesville, FL, USA.
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693
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Li Y, Li D, Ibrahim A, Raisman G. Repair involves all three surfaces of the glial cell. PROGRESS IN BRAIN RESEARCH 2012. [PMID: 23186716 DOI: 10.1016/b978-0-444-59544-7.00010-x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
We propose that severed adult CNS axons are intrinsically capable of regeneration and reestablishing lost functions and that the key to repair lies in reconfiguring the scarring response of the astrocytic network. Astrocytes are multifunctional cells with three distinct surfaces: a glia to glial surface, providing the junctions needed to incorporate the astrocytes into the network; a glia to mesodermal surface, at which astrocytes collaborate with the meningeal fibroblasts to maintain the protective covering of the CNS; and a glia to neuronal surface, which provides the routes along which axons travel. After injury, the astrocytes collaborate with the meningeal fibroblasts to form a scar, which provides the necessary defensive sealing of the opened surface of the CNS, but which also has the detrimental effect of closing off the pathways along which axons could regenerate. Incorporation of glial cells transplanted from the olfactory system into a CNS injury causes a re-arrangement of the scarred astrocyte/fibroblast complex so as to produce the alignment of the glia to neuronal surfaces needed to provide a pathway for the regeneration of severed axons. Olfactory ensheathing cells certainly have a direct stimulatory effect on axons, but without concomitant reorganization of the glial scar, this could not in itself lead to regeneration of severed axons to their targets.
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Affiliation(s)
- Ying Li
- Institute of Neurology, University College London, London, UK
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694
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Mo RH, Zaro JL, Shen WC. Comparison of cationic and amphipathic cell penetrating peptides for siRNA delivery and efficacy. Mol Pharm 2011; 9:299-309. [PMID: 22171592 DOI: 10.1021/mp200481g] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Cell penetrating peptides (CPPs) are short strands of arginine- and/or lysine-rich peptides (<30 amino acids) that use their cationic nature for efficient intracellular accumulation. CPPs have been used for small interfering RNA (siRNA) delivery by direct complexation with the siRNA anionic phosphate backbone. During this process, however, part of the CPP cationic charges are neutralized, and the resultant loss of free positive charges may substantially compromise CPP's internalization capabilities and eventually reduce siRNA delivery efficiency. The purpose of this study was to design a novel type of polyplex for siRNA delivery to overcome the CPP neutralization issue. This novel polyplex consists of three components: siRNA, 21mer oligolysine (K21) chemically modified to incorporate CPP conjugation sites (K21-PDP), and CPP delivery moiety. The siRNA was first neutralized by cationic charges of K21-PDP to form a polyplex. Then a cationic (hexaarginine, R6) or an amphipathic (model amphipathic peptide, MAP) CPP was conjugated to the polyplex. Agarose gel shift assays indicated that the siRNA could be released from the polyplex after K21-PDP degradation or polyplex dilution. Furthermore, the total intracellular internalization of these two CPP-polyplexes was studied. Compared with R6-polyplex, MAP-polyplex exhibited 170- and 600-fold greater uptake of fluorescently labeled siRNA at 1 and 6 h post-transfection, respectively. MAP-polyplex also exhibited comparable GFP silencing effects as Lipofectamine 2000 complex in Huh7.5 cells stably transfected to express GFP-light chain 3 protein, whereas R6-polyplex did not demonstrate significant silencing activity. Further studies indicated that the K21-PDP-siRNA polyplex formation and conjugation of MAP to the polyplex were essential for siRNA polyplex uptake and gene silencing. MAP-polyplex was also shown to be unaffected by the presence of 10% FBS during transfection. In addition, MAP-polyplex uptake was dependent on vesicle formation and fusion due to 70 and 54% loss of uptake at 4 and 16 °C, respectively, compared to incubation at 37 °C. Therefore, the amphipathic CPP is a more suitable carrier moiety for delivery of siRNA polyplex.
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Affiliation(s)
- Robert H Mo
- Department of Pharmacology and Pharmaceutical Sciences, University of Southern California School of Pharmacy, Los Angeles, California 90033, USA
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695
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Abstract
Axon regeneration is a fundamental problem facing neuroscientists and clinicians. Failure of axon regeneration is caused by both extrinsic and intrinsic mechanisms. New techniques to examine gene expression such as Next Generation Sequencing of the Transcriptome (RNA-Seq) drastically increase our knowledge of both gene expression complexity (RNA isoforms) and gene expression regulation. By utilizing RNA-Seq, gene expression can now be defined at the level of isoforms, an essential step for understanding the mechanisms governing cell identity, growth and ultimately cellular responses to injury and disease.
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Affiliation(s)
- Jessica K Lerch
- The Miami Project to Cure Paralysis, The University of Miami, Miami, FL, USA
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696
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Abstract
During development, axons are guided to their appropriate targets by a variety of guidance factors. On arriving at their synaptic targets, or while en route, axons form branches. Branches generated de novo from the main axon are termed collateral branches. The generation of axon collateral branches allows individual neurons to make contacts with multiple neurons within a target and with multiple targets. In the adult nervous system, the formation of axon collateral branches is associated with injury and disease states and may contribute to normally occurring plasticity. Collateral branches are initiated by actin filament– based axonal protrusions that subsequently become invaded by microtubules, thereby allowing the branch to mature and continue extending. This article reviews the current knowledge of the cellular mechanisms of the formation of axon collateral branches. The major conclusions of this review are (1) the mechanisms of axon extension and branching are not identical; (2) active suppression of protrusive activity along the axon negatively regulates branching; (3) the earliest steps in the formation of axon branches involve focal activation of signaling pathways within axons, which in turn drive the formation of actin-based protrusions; and (4) regulation of the microtubule array by microtubule-associated and severing proteins underlies the development of branches. Linking the activation of signaling pathways to specific proteins that directly regulate the axonal cytoskeleton underlying the formation of collateral branches remains a frontier in the field.
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Affiliation(s)
- Gianluca Gallo
- Department of Neurobiology and Anatomy, Drexel University College of Medicine, 2900 Queen Lane, Philadelphia, Pennsylvania 19129, USA.
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697
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Transforming growth factor α transforms astrocytes to a growth-supportive phenotype after spinal cord injury. J Neurosci 2011; 31:15173-87. [PMID: 22016551 DOI: 10.1523/jneurosci.3441-11.2011] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Astrocytes are both detrimental and beneficial for repair and recovery after spinal cord injury (SCI). These dynamic cells are primary contributors to the growth-inhibitory glial scar, yet they are also neuroprotective and can form growth-supportive bridges on which axons traverse. We have shown that intrathecal administration of transforming growth factor α (TGFα) to the contused mouse spinal cord can enhance astrocyte infiltration and axonal growth within the injury site, but the mechanisms of these effects are not well understood. The present studies demonstrate that the epidermal growth factor receptor (EGFR) is upregulated primarily by astrocytes and glial progenitors early after SCI. TGFα directly activates the EGFR on these cells in vitro, inducing their proliferation, migration, and transformation to a phenotype that supports robust neurite outgrowth. Overexpression of TGFα in vivo by intraparenchymal adeno-associated virus injection adjacent to the injury site enhances cell proliferation, alters astrocyte distribution, and facilitates increased axonal penetration at the rostral lesion border. To determine whether endogenous EGFR activation is required after injury, SCI was also performed on Velvet (C57BL/6J-Egfr(Vel)/J) mice, a mutant strain with defective EGFR activity. The affected mice exhibited malformed glial borders, larger lesions, and impaired recovery of function, indicating that intrinsic EGFR activation is necessary for neuroprotection and normal glial scar formation after SCI. By further stimulating precursor proliferation and modifying glial activation to promote a growth-permissive environment, controlled stimulation of EGFR at the lesion border may be considered in the context of future strategies to enhance endogenous cellular repair after injury.
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698
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Growing the growth cone: remodeling the cytoskeleton to promote axon regeneration. Trends Neurosci 2011; 35:164-74. [PMID: 22154154 DOI: 10.1016/j.tins.2011.11.002] [Citation(s) in RCA: 88] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2011] [Revised: 09/26/2011] [Accepted: 11/01/2011] [Indexed: 01/04/2023]
Abstract
Axon growth is driven by the movement of a growth cone, a specialized sensory motile structure located at the tip of a growing neurite. Although stalled retraction bulbs have long been recognized as hallmarks of regeneration failure, mechanisms that control the formation and migration of nerve endings are only beginning to be unraveled. Recent studies point to microtubules as key determinants for such processes, and emerging evidence suggests that regulators of actin and microtubule dynamics in the growth cone might serve as attractive targets for controlling both the speed and trajectory of regenerating axons. This review discusses the potential of and recent progress in direct modulation of the growth cone machinery as a novel strategy to promote axon regeneration in the nervous system after injury.
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699
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Sakagami K, Chen B, Nusinowitz S, Wu H, Yang XJ. PTEN regulates retinal interneuron morphogenesis and synaptic layer formation. Mol Cell Neurosci 2011; 49:171-83. [PMID: 22155156 DOI: 10.1016/j.mcn.2011.11.007] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2011] [Revised: 11/21/2011] [Accepted: 11/26/2011] [Indexed: 11/15/2022] Open
Abstract
The lipid phosphatase PTEN is a critical negative regulator of extracellular signal-induced PI3K activities, yet the roles of PTEN in the neural retina remain poorly understood. Here, we investigate the function of PTEN during retinal development. Deletion of Pten at the onset of neurogenesis in retinal progenitors results in the reduction of retinal ganglion cells and rod photoreceptors, but increased Müller glial genesis. In addition, PTEN deficiency leads to elevated phosphorylation of Akt, especially in the developing inner plexiform layer, where high levels of PTEN are normally expressed. In Pten mutant retinas, various subtypes of amacrine cells show severe dendritic overgrowth, causing specific expansion of the inner plexiform layer. However, the outer plexiform layer remains relatively undisturbed in the Pten deficient retina. Physiological analysis detects reduced rod function and augmented oscillatory potentials originating from amacrine cells in Pten mutants. Furthermore, deleting Pten or elevating Akt activity in individual amacrine cells is sufficient to disrupt dendritic arborization, indicating that Pten activity is required cell autonomously to control neuronal morphology. Moreover, inhibiting endogenous Akt activity attenuates inner plexiform layer formation in vitro. Together, these findings demonstrate that suppression of PI3K/Akt signaling by PTEN is crucial for proper neuronal differentiation and normal retinal network formation.
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Affiliation(s)
- Kiyo Sakagami
- Jules Stein Eye Institute, University of California, Los Angeles, CA 90095, USA
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700
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Abstract
STUDY DESIGN Review. OBJECTIVES To examine the state of research in central nervous system (CNS) regeneration and to suggest an alternative to the sterile research at the lesion site. SETTING Worldwide. METHODS A search of publications using 'PubMed' and a search of the historical literature relevant to CNS regeneration, biological models, the neurone theory, collateral sprouting, spinal shock and the central pattern generator. RESULTS There is no evidence for CNS regeneration. CONCLUSION A century of research focussed on the lesion site has been unproductive. An alternative field of research must be developed and the best candidate is the undamaged CNS.
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Affiliation(s)
- L S Illis
- Willow Pond House, Lymore Valley, Hampshire, UK.
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