1
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Ding EA, Kumar S. Neurofilament Biophysics: From Structure to Biomechanics. Mol Biol Cell 2024; 35:re1. [PMID: 38598299 PMCID: PMC11151108 DOI: 10.1091/mbc.e23-11-0438] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2024] [Revised: 03/25/2024] [Accepted: 04/04/2024] [Indexed: 04/12/2024] Open
Abstract
Neurofilaments (NFs) are multisubunit, neuron-specific intermediate filaments consisting of a 10-nm diameter filament "core" surrounded by a layer of long intrinsically disordered protein (IDP) "tails." NFs are thought to regulate axonal caliber during development and then stabilize the mature axon, with NF subunit misregulation, mutation, and aggregation featuring prominently in multiple neurological diseases. The field's understanding of NF structure, mechanics, and function has been deeply informed by a rich variety of biochemical, cell biological, and mouse genetic studies spanning more than four decades. These studies have contributed much to our collective understanding of NF function in axonal physiology and disease. In recent years, however, there has been a resurgence of interest in NF subunit proteins in two new contexts: as potential blood- and cerebrospinal fluid-based biomarkers of neuronal damage, and as model IDPs with intriguing properties. Here, we review established principles and more recent discoveries in NF structure and function. Where possible, we place these findings in the context of biophysics of NF assembly, interaction, and contributions to axonal mechanics.
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Affiliation(s)
- Erika A. Ding
- Department of Chemical and Biomolecular Engineering, University of California, Berkeley, Berkeley, CA 94720
| | - Sanjay Kumar
- Department of Chemical and Biomolecular Engineering, University of California, Berkeley, Berkeley, CA 94720
- Department of Bioengineering, University of California, Berkeley, Berkeley, CA 94720
- Department of Bioengineering and Therapeutic Sciences, University of California, San Francisco, San Francisco, CA 94158
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2
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López-Erauskin J, Bravo-Hernandez M, Presa M, Baughn MW, Melamed Z, Beccari MS, Agra de Almeida Quadros AR, Arnold-Garcia O, Zuberi A, Ling K, Platoshyn O, Niño-Jara E, Ndayambaje IS, McAlonis-Downes M, Cabrera L, Artates JW, Ryan J, Hermann A, Ravits J, Bennett CF, Jafar-Nejad P, Rigo F, Marsala M, Lutz CM, Cleveland DW, Lagier-Tourenne C. Stathmin-2 loss leads to neurofilament-dependent axonal collapse driving motor and sensory denervation. Nat Neurosci 2024; 27:34-47. [PMID: 37996528 PMCID: PMC10842032 DOI: 10.1038/s41593-023-01496-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2022] [Accepted: 10/16/2023] [Indexed: 11/25/2023]
Abstract
The mRNA transcript of the human STMN2 gene, encoding for stathmin-2 protein (also called SCG10), is profoundly impacted by TAR DNA-binding protein 43 (TDP-43) loss of function. The latter is a hallmark of several neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS). Using a combination of approaches, including transient antisense oligonucleotide-mediated suppression, sustained shRNA-induced depletion in aging mice, and germline deletion, we show that stathmin-2 has an important role in the establishment and maintenance of neurofilament-dependent axoplasmic organization that is critical for preserving the caliber and conduction velocity of myelinated large-diameter axons. Persistent stathmin-2 loss in adult mice results in pathologies found in ALS, including reduced interneurofilament spacing, axonal caliber collapse that drives tearing within outer myelin layers, diminished conduction velocity, progressive motor and sensory deficits, and muscle denervation. These findings reinforce restoration of stathmin-2 as an attractive therapeutic approach for ALS and other TDP-43-dependent neurodegenerative diseases.
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Affiliation(s)
- Jone López-Erauskin
- Ludwig Institute and Department of Cellular and Molecular Medicine, University of California at San Diego, La Jolla, CA, USA
| | - Mariana Bravo-Hernandez
- Department of Anesthesiology and Stem Cell Program and Institute for Genomic Medicine, University of California at San Diego, La Jolla, CA, USA
- Ionis Pharmaceuticals Inc., Carlsbad, CA, USA
| | | | - Michael W Baughn
- Ludwig Institute and Department of Cellular and Molecular Medicine, University of California at San Diego, La Jolla, CA, USA
| | - Ze'ev Melamed
- Ludwig Institute and Department of Cellular and Molecular Medicine, University of California at San Diego, La Jolla, CA, USA
- Department of Medical Neurobiology, Faculty of Medicine, The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Melinda S Beccari
- Ludwig Institute and Department of Cellular and Molecular Medicine, University of California at San Diego, La Jolla, CA, USA
| | - Ana Rita Agra de Almeida Quadros
- Department of Neurology, The Sean M. Healey and AMG Center for ALS, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA
- Broad Institute of Harvard and MIT, Cambridge, MA, USA
| | - Olatz Arnold-Garcia
- Ludwig Institute and Department of Cellular and Molecular Medicine, University of California at San Diego, La Jolla, CA, USA
- Department of Neurosciences, Biodonostia Health Research Institute, San Sebastián, Spain
- CIBERNED, ISCIII (CIBER, Carlos III Institute, Spanish Ministry of Sciences and Innovation), Madrid, Spain
| | | | - Karen Ling
- Ionis Pharmaceuticals Inc., Carlsbad, CA, USA
| | - Oleksandr Platoshyn
- Department of Anesthesiology and Stem Cell Program and Institute for Genomic Medicine, University of California at San Diego, La Jolla, CA, USA
| | - Elkin Niño-Jara
- Department of Anesthesiology and Stem Cell Program and Institute for Genomic Medicine, University of California at San Diego, La Jolla, CA, USA
| | - I Sandra Ndayambaje
- Department of Neurology, The Sean M. Healey and AMG Center for ALS, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA
| | - Melissa McAlonis-Downes
- Ludwig Institute and Department of Cellular and Molecular Medicine, University of California at San Diego, La Jolla, CA, USA
| | - Larissa Cabrera
- Ludwig Institute and Department of Cellular and Molecular Medicine, University of California at San Diego, La Jolla, CA, USA
| | - Jonathan W Artates
- Ludwig Institute and Department of Cellular and Molecular Medicine, University of California at San Diego, La Jolla, CA, USA
| | | | - Anita Hermann
- Department of Neurosciences, School of Medicine, University of California at San Diego, La Jolla, CA, USA
| | - John Ravits
- Department of Neurosciences, School of Medicine, University of California at San Diego, La Jolla, CA, USA
| | | | | | - Frank Rigo
- Ionis Pharmaceuticals Inc., Carlsbad, CA, USA
| | - Martin Marsala
- Department of Anesthesiology and Stem Cell Program and Institute for Genomic Medicine, University of California at San Diego, La Jolla, CA, USA
| | | | - Don W Cleveland
- Ludwig Institute and Department of Cellular and Molecular Medicine, University of California at San Diego, La Jolla, CA, USA.
| | - Clotilde Lagier-Tourenne
- Department of Neurology, The Sean M. Healey and AMG Center for ALS, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA.
- Broad Institute of Harvard and MIT, Cambridge, MA, USA.
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3
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Kotaich F, Caillol D, Bomont P. Neurofilaments in health and Charcot-Marie-Tooth disease. Front Cell Dev Biol 2023; 11:1275155. [PMID: 38164457 PMCID: PMC10758125 DOI: 10.3389/fcell.2023.1275155] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2023] [Accepted: 10/02/2023] [Indexed: 01/03/2024] Open
Abstract
Neurofilaments (NFs) are the most abundant component of mature neurons, that interconnect with actin and microtubules to form the cytoskeleton. Specifically expressed in the nervous system, NFs present the particularity within the Intermediate Filament family of being formed by four subunits, the neurofilament light (NF-L), medium (NF-M), heavy (NF-H) proteins and α-internexin or peripherin. Here, we review the current knowledge on NF proteins and neurofilaments, from their domain structures and their model of assembly to the dynamics of their transport and degradation along the axon. The formation of the filament and its behaviour are regulated by various determinants, including post-transcriptional (miRNA and RBP proteins) and post-translational (phosphorylation and ubiquitination) modifiers. Altogether, the complex set of modifications enable the neuron to establish a stable but elastic NF array constituting the structural scaffold of the axon, while permitting the local expression of NF proteins and providing the dynamics necessary to fulfil local demands and respond to stimuli and injury. Thus, in addition to their roles in mechano-resistance, radial axonal outgrowth and nerve conduction, NFs control microtubule dynamics, organelle distribution and neurotransmission at the synapse. We discuss how the studies of neurodegenerative diseases with NF aggregation shed light on the biology of NFs. In particular, the NEFL and NEFH genes are mutated in Charcot-Marie-Tooth (CMT) disease, the most common inherited neurological disorder of the peripheral nervous system. The clinical features of the CMT forms (axonal CMT2E, CMT2CC; demyelinating CMT1F; intermediate I-CMT) with symptoms affecting the central nervous system (CNS) will allow us to further investigate the physiological roles of NFs in the brain. Thus, NF-CMT mouse models exhibit various degrees of sensory-motor deficits associated with CNS symptoms. Cellular systems brought findings regarding the dominant effect of NF-L mutants on NF aggregation and transport, although these have been recently challenged. Neurofilament detection without NF-L in recessive CMT is puzzling, calling for a re-examination of the current model in which NF-L is indispensable for NF assembly. Overall, we discuss how the fundamental and translational fields are feeding each-other to increase but also challenge our knowledge of NF biology, and to develop therapeutic avenues for CMT and neurodegenerative diseases with NF aggregation.
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Affiliation(s)
| | | | - Pascale Bomont
- ERC team, NeuroMyoGene Institute-Pathophysiology and Genetics of Neuron and Muscle, Inserm U1315, CNRS UMR5261, University of Lyon 1, Lyon, France
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4
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Zhulina EB, Borisov OV. Cylindrical brushes with ionized side chains: Scaling theory revisited. SOFT MATTER 2023; 19:8440-8452. [PMID: 37881868 DOI: 10.1039/d3sm00727h] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2023]
Abstract
We revisit the classic scaling model of a cylindrical polyelectrolyte (PE) brush focusing on molecular brushes with stiff backbones and dispersions of polymer-decorated nanorods. Based on the blob representation we demonstrate that similarly to the case of planar PE brushes, separation of intra- and intermolecular repulsions between charges leads to novel scaling regimes for cylindrical PE brushes in salt-added solution and a sharper decrease in its thickness versus salt concentration dependence. These theoretical predictions may inspire further comprehensive experimental research and computer simulations of synthetic and biopolyelectrolyte cylindrical brushes.
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Affiliation(s)
- Ekaterina B Zhulina
- Institute of Macromolecular Compounds of the Russian Academy of Sciences, St. Petersburg, Russia.
| | - Oleg V Borisov
- Institute of Macromolecular Compounds of the Russian Academy of Sciences, St. Petersburg, Russia.
- Institut des Sciences Analytiques et de Physico-Chimie pour l'Environnement et les Matériaux, UMR 5254 CNRS UPPA, Pau, France
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5
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Uchida A, Peng J, Brown A. Regulation of neurofilament length and transport by a dynamic cycle of phospho-dependent polymer severing and annealing. Mol Biol Cell 2023; 34:ar68. [PMID: 36989035 PMCID: PMC10295484 DOI: 10.1091/mbc.e23-01-0024] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2023] [Revised: 03/17/2023] [Accepted: 03/22/2023] [Indexed: 03/30/2023] Open
Abstract
Neurofilaments are cargoes of axonal transport which are unique among known intracellular cargoes in that they are long, flexible protein polymers. These polymers are transported into axons, where they accumulate in large numbers to drive the expansion of axon caliber, which is an important determinant of axonal conduction velocity. We reported previously that neurofilaments can be lengthened by joining ends, called end-to-end annealing, and that they can be shortened by severing. Here, we show that neurofilament annealing and severing are robust and quantifiable phenomena in cultured neurons that act antagonistically to regulate neurofilament length. We show that this in turn regulates neurofilament transport and that severing is regulated by N-terminal phosphorylation of the neurofilament subunit proteins. We propose that focal destabilization of intermediate filaments by site-directed phosphorylation may be a general enzymatic mechanism for severing these cytoskeletal polymers, providing a mechanism to regulate the transport and accumulation of neurofilaments in axons.
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Affiliation(s)
- Atsuko Uchida
- Department of Neuroscience, Ohio State University, Columbus, OH 43210
| | - Juan Peng
- Center for Biostatistics and Department of Biomedical Informatics, Ohio State University, Columbus, OH 43210
| | - Anthony Brown
- Department of Neuroscience, Ohio State University, Columbus, OH 43210
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6
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Rao MV, Darji S, Stavrides PH, Goulbourne CN, Kumar A, Yang DS, Yoo L, Peddy J, Lee JH, Yuan A, Nixon RA. Autophagy is a novel pathway for neurofilament protein degradation in vivo. Autophagy 2023; 19:1277-1292. [PMID: 36131358 PMCID: PMC10012948 DOI: 10.1080/15548627.2022.2124500] [Citation(s) in RCA: 9] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022] Open
Abstract
How macroautophagy/autophagy influences neurofilament (NF) proteins in neurons, a frequent target in neurodegenerative diseases and injury, is not known. NFs in axons have exceptionally long half-lives in vivo enabling formation of large stable supporting networks, but they can be rapidly degraded during Wallerian degeneration initiated by a limited calpain cleavage. Here, we identify autophagy as a previously unrecognized pathway for NF subunit protein degradation that modulates constitutive and inducible NF turnover in vivo. Levels of NEFL/NF-L, NEFM/NF-M, and NEFH/NF-H subunits rise substantially in neuroblastoma (N2a) cells after blocking autophagy either with the phosphatidylinositol 3-kinase (PtdIns3K) inhibitor 3-methyladenine (3-MA), by depleting ATG5 expression with shRNA, or by using both treatments. In contrast, activating autophagy with rapamycin significantly lowers NF levels in N2a cells. In the mouse brain, NF subunit levels increase in vivo after intracerebroventricular infusion of 3-MA. Furthermore, using tomographic confocal microscopy, immunoelectron microscopy, and biochemical fractionation, we demonstrate the presence of NF proteins intra-lumenally within autophagosomes (APs), autolysosomes (ALs), and lysosomes (LYs). Our findings establish a prominent role for autophagy in NF proteolysis. Autophagy may regulate axon cytoskeleton size and responses of the NF cytoskeleton to injury and disease.
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Affiliation(s)
- Mala V Rao
- Center for Dementia Research, Nathan Kline Institute, Orangeburg, NY, USA.,Department of Psychiatry, New York University Langone Medical Center, New York, NY, USA
| | - Sandipkumar Darji
- Center for Dementia Research, Nathan Kline Institute, Orangeburg, NY, USA
| | - Philip H Stavrides
- Center for Dementia Research, Nathan Kline Institute, Orangeburg, NY, USA
| | - Chris N Goulbourne
- Center for Dementia Research, Nathan Kline Institute, Orangeburg, NY, USA
| | - Asok Kumar
- Center for Dementia Research, Nathan Kline Institute, Orangeburg, NY, USA
| | - Dun-Sheng Yang
- Center for Dementia Research, Nathan Kline Institute, Orangeburg, NY, USA.,Department of Psychiatry, New York University Langone Medical Center, New York, NY, USA
| | - Lang Yoo
- Center for Dementia Research, Nathan Kline Institute, Orangeburg, NY, USA
| | - James Peddy
- Center for Dementia Research, Nathan Kline Institute, Orangeburg, NY, USA.,Department of Psychiatry, New York University Langone Medical Center, New York, NY, USA
| | - Ju-Hyun Lee
- Center for Dementia Research, Nathan Kline Institute, Orangeburg, NY, USA.,Department of Psychiatry, New York University Langone Medical Center, New York, NY, USA
| | - Aidong Yuan
- Center for Dementia Research, Nathan Kline Institute, Orangeburg, NY, USA
| | - Ralph A Nixon
- Center for Dementia Research, Nathan Kline Institute, Orangeburg, NY, USA.,Department of Psychiatry, New York University Langone Medical Center, New York, NY, USA.,Cell Biology, NewYork University Langone Medical Center, NY, USA.,NYU Neuroscience Institute, New York University, New York, NY, USA
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7
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Wiche G. Plectin-Mediated Intermediate Filament Functions: Why Isoforms Matter. Cells 2021; 10:cells10082154. [PMID: 34440923 PMCID: PMC8391331 DOI: 10.3390/cells10082154] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2021] [Revised: 08/13/2021] [Accepted: 08/17/2021] [Indexed: 11/26/2022] Open
Abstract
This essay focuses on the role of plectin and its various isoforms in mediating intermediate filament (IF) network functions. It is based on previous studies that provided comprehensive evidence for a concept where plectin acts as an IF recruiter, and plectin-mediated IF networking and anchoring are key elements in IF function execution. Here, plectin’s global role as modulator of IF functionality is viewed from different perspectives, including the mechanical stabilization of IF networks and their docking platforms, contribution to cellular viscoelasticity and mechanotransduction, compartmentalization and control of the actomyosin machinery, connections to the microtubule system, and mechanisms and specificity of isoform targeting. Arguments for IF networks and plectin acting as mutually dependent partners are also given. Lastly, a working model is presented that describes a unifying mechanism underlying how plectin–IF networks mechanically control and propagate actomyosin-generated forces, affect microtubule dynamics, and contribute to mechanotransduction.
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Affiliation(s)
- Gerhard Wiche
- Max Perutz Laboratories, Department of Biochemistry and Cell Biology, University of Vienna, 1030 Vienna, Austria
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8
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Jia Z, Li Y. A possible mechanism for neurofilament slowing down in myelinated axon: Phosphorylation-induced variation of NF kinetics. PLoS One 2021; 16:e0247656. [PMID: 33711034 PMCID: PMC7954336 DOI: 10.1371/journal.pone.0247656] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2020] [Accepted: 02/10/2021] [Indexed: 11/18/2022] Open
Abstract
Neurofilaments(NFs) are the most abundant intermediate filaments that make up the inner volume of axon, with possible phosphorylation on their side arms, and their slow axonal transport by molecular motors along microtubule tracks in a “stop-and-go” manner with rapid, intermittent and bidirectional motion. The kinetics of NFs and morphology of axon are dramatically different between myelinate internode and unmyelinated node of Ranvier. The NFs in the node transport as 7.6 times faster as in the internode, and the distribution of NFs population in the internode is 7.6 folds as much as in the node of Ranvier. We hypothesize that the phosphorylation of NFs could reduce the on-track rate and slow down their transport velocity in the internode. By modifying the ‘6-state’ model with (a) an extra phosphorylation kinetics to each six state and (b) construction a new ‘8-state’ model in which NFs at off-track can be phosphorylated and have smaller on-track rate, our model and simulation demonstrate that the phosphorylation-induced decrease of on-track rate could slow down the NFs average velocity and increase the axonal caliber. The degree of phosphorylation may indicate the extent of velocity reduction. The Continuity equation used in our paper predicts that the ratio of NFs population is inverse proportional to the ratios of average velocity of NFs between node of Ranvier and internode. We speculate that the myelination of axon could increase the level of phosphorylation of NF side arms, and decrease the possibility of NFs to get on-track of microtubules, therefore slow down their transport velocity. In summary, our work provides a potential mechanism for understanding the phosphorylation kinetics of NFs in regulating their transport and morphology of axon in myelinated axons, and the different kinetics of NFs between node and internode.
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Affiliation(s)
- Zelin Jia
- School of Systems Science, Beijing Normal University, Beijing, China
| | - Yinyun Li
- School of Systems Science, Beijing Normal University, Beijing, China
- * E-mail:
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9
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Prokop A. Cytoskeletal organization of axons in vertebrates and invertebrates. J Cell Biol 2020; 219:e201912081. [PMID: 32369543 PMCID: PMC7337489 DOI: 10.1083/jcb.201912081] [Citation(s) in RCA: 30] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2019] [Revised: 04/13/2020] [Accepted: 04/14/2020] [Indexed: 12/11/2022] Open
Abstract
The maintenance of axons for the lifetime of an organism requires an axonal cytoskeleton that is robust but also flexible to adapt to mechanical challenges and to support plastic changes of axon morphology. Furthermore, cytoskeletal organization has to adapt to axons of dramatically different dimensions, and to their compartment-specific requirements in the axon initial segment, in the axon shaft, at synapses or in growth cones. To understand how the cytoskeleton caters to these different demands, this review summarizes five decades of electron microscopic studies. It focuses on the organization of microtubules and neurofilaments in axon shafts in both vertebrate and invertebrate neurons, as well as the axon initial segments of vertebrate motor- and interneurons. Findings from these ultrastructural studies are being interpreted here on the basis of our contemporary molecular understanding. They strongly suggest that axon architecture in animals as diverse as arthropods and vertebrates is dependent on loosely cross-linked bundles of microtubules running all along axons, with only minor roles played by neurofilaments.
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Affiliation(s)
- Andreas Prokop
- School of Biology, Faculty of Biology, Medicine and Health, Manchester Academic Health Science Centre, The University of Manchester, Manchester, UK
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10
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Bott CJ, Winckler B. Intermediate filaments in developing neurons: Beyond structure. Cytoskeleton (Hoboken) 2020; 77:110-128. [PMID: 31970897 DOI: 10.1002/cm.21597] [Citation(s) in RCA: 37] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2019] [Revised: 01/06/2020] [Accepted: 01/08/2020] [Indexed: 12/20/2022]
Abstract
Neuronal development relies on a highly choreographed progression of dynamic cellular processes by which newborn neurons migrate, extend axons and dendrites, innervate their targets, and make functional synapses. Many of these dynamic processes require coordinated changes in morphology, powered by the cell's cytoskeleton. Intermediate filaments (IFs) are the third major cytoskeletal elements in vertebrate cells, but are rarely considered when it comes to understanding axon and dendrite growth, pathfinding and synapse formation. In this review, we first introduce the many new and exciting concepts of IF function, discovered mostly in non-neuronal cells. These roles include dynamic rearrangements, crosstalk with microtubules and actin filaments, mechano-sensing and -transduction, and regulation of signaling cascades. We then discuss the understudied roles of neuronally expressed IFs, with a particular focus on IFs expressed during development, such as nestin, vimentin and α-internexin. Lastly, we illustrate how signaling modulation by the unconventional IF nestin shapes neuronal morphogenesis in unexpected and novel ways. Even though the first IF knockout mice were made over 20 years ago, the study of the cell biological functions of IFs in the brain still has much room for exciting new discoveries.
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Affiliation(s)
- Christopher J Bott
- Department of Cell Biology, University of Virginia, Charlottesville, Virginia
| | - Bettina Winckler
- Department of Cell Biology, University of Virginia, Charlottesville, Virginia
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11
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Didonna A, Opal P. The role of neurofilament aggregation in neurodegeneration: lessons from rare inherited neurological disorders. Mol Neurodegener 2019; 14:19. [PMID: 31097008 PMCID: PMC6524292 DOI: 10.1186/s13024-019-0318-4] [Citation(s) in RCA: 71] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2018] [Accepted: 04/26/2019] [Indexed: 12/13/2022] Open
Abstract
Many neurodegenerative disorders, including Parkinson's, Alzheimer's, and amyotrophic lateral sclerosis, are well known to involve the accumulation of disease-specific proteins. Less well known are the accumulations of another set of proteins, neuronal intermediate filaments (NFs), which have been observed in these diseases for decades. NFs belong to the family of cytoskeletal intermediate filament proteins (IFs) that give cells their shape; they determine axonal caliber, which controls signal conduction; and they regulate the transport of synaptic vesicles and modulate synaptic plasticity by binding to neurotransmitter receptors. In the last two decades, a number of rare disorders caused by mutations in genes that encode NFs or regulate their metabolism have been discovered. These less prevalent disorders are providing novel insights into the role of NF aggregation in the more common neurological disorders.
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Affiliation(s)
- Alessandro Didonna
- Department of Neurology and Weill Institute for Neurosciences, University of California at San Francisco, San Francisco, CA, 94158, USA
| | - Puneet Opal
- Davee Department of Neurology, Northwestern University Feinberg School of Medicine, Chicago, IL, 60611, USA. .,Department of Cell and Molecular Biology, Northwestern University Feinberg School of Medicine, Chicago, IL, 60611, USA.
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12
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Liao ML, Peng WH, Kan D, Chien CL. Distribution patterns of the zebrafish neuronal intermediate filaments inaa and inab. J Neurosci Res 2018; 97:202-214. [PMID: 30387501 DOI: 10.1002/jnr.24347] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2018] [Revised: 09/27/2018] [Accepted: 10/03/2018] [Indexed: 01/27/2023]
Abstract
It has been reported that the neuronal intermediate filament (IF) α-internexin may plays a role in the formation of the neuronal cytoskeleton during mammalian development. From a phylogenetic viewpoint, zebrafish express inaa and inab as homologs of mammalian α-internexin. However, the distribution patterns of the inaa and inab proteins throughout zebrafish development have not been well-characterized. We generated antibodies specific for zebrafish inaa and inab and analyzed the distribution of these two proteins in developing zebrafish. Inaa was identified in the major subdivisions of embryonic and larval brains as early as 1 day postfertilization (dpf), including the telencephalon, optic tectum, and cerebellum, and inab was also detected in the same regions from 3 dpf to the adult stage. Moreover, we demonstrated for the first time that inaa was distinctively expressed in the photoreceptor-like cells of the pineal gland, where inab was sparsely detected. Besides, the expression of inaa in male adult fish was found to be stable under different photoperiod conditions. Thus, we suggest that inaa is one of useful markers for studies of zebrafish cone photoreceptors not only in the retina but also in the pineal gland. In conclusion, we report that the distribution patterns of inaa and inab are phylogenetically conserved in the telencephalon, optic tectum, and cerebellum. Moreover, inaa and inab had different expression patterns in the pineal gland and retina during zebrafish development. Both inaa and inab are neuronal IFs and their functional roles may be different in various aspects of zebrafish neuronal development.
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Affiliation(s)
- Meng-Lin Liao
- Department of Anatomy and Cell Biology, College of Medicine, National Taiwan University, Taipei, Taiwan
| | - Wei-Hau Peng
- Department of Anatomy and Cell Biology, College of Medicine, National Taiwan University, Taipei, Taiwan.,School of Medicine for International Student, College of Medicine, I-Shou University (Yanchao Campus), Kaohsiung, Taiwan
| | - Daphne Kan
- Center of Genomic Medicine, National Taiwan University, Taipei, Taiwan
| | - Chung-Liang Chien
- Department of Anatomy and Cell Biology, College of Medicine, National Taiwan University, Taipei, Taiwan.,Center of Genomic Medicine, National Taiwan University, Taipei, Taiwan
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13
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Villalón E, Barry DM, Byers N, Frizzi K, Jones MR, Landayan DS, Dale JM, Downer NL, Calcutt NA, Garcia ML. Internode length is reduced during myelination and remyelination by neurofilament medium phosphorylation in motor axons. Exp Neurol 2018; 306:158-168. [PMID: 29772247 PMCID: PMC5994378 DOI: 10.1016/j.expneurol.2018.05.009] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2017] [Revised: 05/03/2018] [Accepted: 05/09/2018] [Indexed: 01/04/2023]
Abstract
The distance between nodes of Ranvier, referred to as internode length, positively correlates with axon diameter, and is optimized during development to ensure maximal neuronal conduction velocity. Following myelin loss, internode length is reestablished through remyelination. However, remyelination results in short internode lengths and reduced conduction rates. We analyzed the potential role of neurofilament phosphorylation in regulating internode length during remyelination and myelination. Following ethidium bromide induced demyelination, levels of neurofilament medium (NF-M) and heavy (NF-H) phosphorylation were unaffected. Preventing NF-M lysine-serine-proline (KSP) repeat phosphorylation increased internode length by 30% after remyelination. To further analyze the role of NF-M phosphorylation in regulating internode length, gene replacement was used to produce mice in which all KSP serine residues were replaced with glutamate to mimic constitutive phosphorylation. Mimicking constitutive KSP phosphorylation reduced internode length by 16% during myelination and motor nerve conduction velocity by ~27% without altering sensory nerve structure or function. Our results suggest that NF-M KSP phosphorylation is part of a cooperative mechanism between axons and Schwann cells that together determine internode length, and suggest motor and sensory axons utilize different mechanisms to establish internode length.
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Affiliation(s)
- Eric Villalón
- Department of Biological Sciences, University of Missouri, Columbia, MO 65211, United States; C.S. Bond Life Sciences Center, University of Missouri, Columbia, MO 65211, United States
| | - Devin M Barry
- Department of Anesthesiology, Center for the Study of Itch, Washington University School of Medicine, St. Louis, MO 63110, United States
| | - Nathan Byers
- Department of Biomedical Sciences, Colorado State University, Fort Collins, CO 80523, United States
| | - Katie Frizzi
- Department of Pathology, University of California San Diego, La Jolla, CA 92093, United States
| | - Maria R Jones
- Department of Biological Sciences, University of Missouri, Columbia, MO 65211, United States; C.S. Bond Life Sciences Center, University of Missouri, Columbia, MO 65211, United States
| | - Dan S Landayan
- Department of Quantitative and Systems Biology, University of California Merced, Merced, CA 95343, United States
| | - Jeffrey M Dale
- Department of Biological Sciences, University of Missouri, Columbia, MO 65211, United States; C.S. Bond Life Sciences Center, University of Missouri, Columbia, MO 65211, United States
| | - Natalie L Downer
- Department of Biological Science, Moberly Area Community College, Moberly, MO 65270, United States
| | - Nigel A Calcutt
- Department of Pathology, University of California San Diego, La Jolla, CA 92093, United States
| | - Michael L Garcia
- Department of Biological Sciences, University of Missouri, Columbia, MO 65211, United States; C.S. Bond Life Sciences Center, University of Missouri, Columbia, MO 65211, United States.
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Induction of morphological and functional differentiation of human neuroblastoma cells by miR-124. J Biosci 2018; 42:555-563. [PMID: 29229874 DOI: 10.1007/s12038-017-9714-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Neuroblastoma is the most common extracranial solid tumour in children, and differentiation is considered its most appropriate therapy. In this work, we studied effects of miR-124 overexpression on differentiation in M17 cell line as a model of neuroblastoma cancer. Influence of miR-124 overexpression on differentiation in M17 cells was studied. M17 cells were infected with lentivirus that contained miR-124 precursor sequence and followed for 2 weeks to differentiate. Ectopic expression of miR-124 in M17 cells changed the shape of spherical undifferentiated cells to cells with extended neurites that formed neuronal networks. Overexpression of MiR-124 respectively increased the expression level of markers of β-Tubulin III, MAP2, SYN, NF-M and Nestin by 16-, 5-, 4-, 2.3- and 2-folds at the messenger RNA level. MiR-124 overexpression also increased the protein levels of β-Tubulin III and MAP2. Moreover, exogenous expression of miR-124 significantly increased the intracellular calcium in differentiated M17 cells. Since miR-124 is naturally expressed in neuronal cells and is downregulated in neuroblastoma cancer cells, differentiation with this type of microRNA can be a novel treatment for neuroblastoma cancer.
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Lancaster E, Li J, Hanania T, Liem R, Scheideler MA, Scherer SS. Myelinated axons fail to develop properly in a genetically authentic mouse model of Charcot-Marie-Tooth disease type 2E. Exp Neurol 2018; 308:13-25. [PMID: 29940160 DOI: 10.1016/j.expneurol.2018.06.010] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2018] [Revised: 06/14/2018] [Accepted: 06/19/2018] [Indexed: 11/25/2022]
Abstract
We have analyzed a mouse model of Charcot-Marie-Tooth disease 2E (CMT2E) harboring a heterozygous p.Asn98Ser (p.N98S) Nefl mutation, whose human counterpart results in a severe, early-onset neuropathy. Behavioral, electrophysiological, and pathological analyses were done on separate cohorts of NeflN98S/+ mutant mice and their wild type Nefl+/+ littermates between 8 and 48 weeks of age. The motor performance of NeflN98S/+ mice, as evidenced by altered balance and gait measures, was impaired at every age examined (from 6 to 25 weeks of age). At all times examined, myelinated axons were smaller and contained markedly fewer neurofilaments in NeflN98S/+ mice, in all examined aspects of the PNS, from the nerve roots to the distal ends of the sciatic and caudal nerves. Similarly, the myelinated axons in the various tracts of the spinal cord and in the optic nerves were smaller and contained fewer neurofilaments in mutant mice. The myelinated axons in both the PNS and the CNS of mutant mice had relatively thicker myelin sheaths. The amplitude and the nerve conduction velocity of the caudal nerves were reduced in proportion with the diminished sizes of myelinated axons. Conspicuous aggregations of neurofilaments were only seen in primary sensory and motor neurons, and were largely confined to the cell bodies and proximal axons. There was evidence of axonal degeneration and regeneration of myelinated axons, mostly in distal nerves. In summary, the p.N98S mutation causes a profound reduction of neurofilaments in the myelinated axons of the PNS and CNS, resulting in substantially reduced axonal diameters, particularly of large myelinated axons, and distal axon loss in the PNS.
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Affiliation(s)
- Eunjoo Lancaster
- Department of Neurology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, United States
| | - Jian Li
- Department of Neurology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, United States
| | - Taleen Hanania
- Psychogenics Inc 215 College Road Paramus, NJ 07652, United States
| | - Ronald Liem
- Department of Pathology, Columbia University College of Physicians & Surgeons, New York, NY 10032, United States
| | | | - Steven S Scherer
- Department of Neurology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, United States.
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Yuan A, Rao MV, Veeranna, Nixon RA. Neurofilaments and Neurofilament Proteins in Health and Disease. Cold Spring Harb Perspect Biol 2017; 9:9/4/a018309. [PMID: 28373358 DOI: 10.1101/cshperspect.a018309] [Citation(s) in RCA: 419] [Impact Index Per Article: 59.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
SUMMARYNeurofilaments (NFs) are unique among tissue-specific classes of intermediate filaments (IFs) in being heteropolymers composed of four subunits (NF-L [neurofilament light]; NF-M [neurofilament middle]; NF-H [neurofilament heavy]; and α-internexin or peripherin), each having different domain structures and functions. Here, we review how NFs provide structural support for the highly asymmetric geometries of neurons and, especially, for the marked radial expansion of myelinated axons crucial for effective nerve conduction velocity. NFs in axons extensively cross-bridge and interconnect with other non-IF components of the cytoskeleton, including microtubules, actin filaments, and other fibrous cytoskeletal elements, to establish a regionally specialized network that undergoes exceptionally slow local turnover and serves as a docking platform to organize other organelles and proteins. We also discuss how a small pool of oligomeric and short filamentous precursors in the slow phase of axonal transport maintains this network. A complex pattern of phosphorylation and dephosphorylation events on each subunit modulates filament assembly, turnover, and organization within the axonal cytoskeleton. Multiple factors, and especially turnover rate, determine the size of the network, which can vary substantially along the axon. NF gene mutations cause several neuroaxonal disorders characterized by disrupted subunit assembly and NF aggregation. Additional NF alterations are associated with varied neuropsychiatric disorders. New evidence that subunits of NFs exist within postsynaptic terminal boutons and influence neurotransmission suggests how NF proteins might contribute to normal synaptic function and neuropsychiatric disease states.
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Affiliation(s)
- Aidong Yuan
- Center for Dementia Research, Nathan Kline Institute, Orangeburg, New York 10962.,Department of Psychiatry, New York University School of Medicine, New York, New York 10016
| | - Mala V Rao
- Center for Dementia Research, Nathan Kline Institute, Orangeburg, New York 10962.,Department of Psychiatry, New York University School of Medicine, New York, New York 10016
| | - Veeranna
- Center for Dementia Research, Nathan Kline Institute, Orangeburg, New York 10962.,Department of Psychiatry, New York University School of Medicine, New York, New York 10016
| | - Ralph A Nixon
- Center for Dementia Research, Nathan Kline Institute, Orangeburg, New York 10962.,Department of Psychiatry, New York University School of Medicine, New York, New York 10016.,Cell Biology, New York University School of Medicine, New York, New York 10016
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18
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Liao ML, Peng WH, Kan D, Chien CL. Developmental pattern of the neuronal intermediate filament inaa in the zebrafish retina. J Comp Neurol 2016; 524:3810-3826. [PMID: 27159642 DOI: 10.1002/cne.24033] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2016] [Revised: 04/28/2015] [Accepted: 04/29/2016] [Indexed: 12/17/2022]
Abstract
α-Internexin is a member of the neuronal intermediate filament (nIF) protein family, which also includes peripherin and neurofilament (NF) triplet proteins. Previous studies found that expression of α-internexin precedes that of the NF triplet proteins in mammals and suggested that α-internexin plays a key role in the neuronal cytoskeleton network during development. In this study, we aimed to analyze the expression patterns and function of internexin neuronal intermediate filament protein-alpha a (inaa), the encoding gene of which is a homolog of the mammalian α-internexin, during retinal development in zebrafish. Via in vitro and in vivo studies, we demonstrated that zebrafish inaa is an α-internexin homolog that shares characteristics with nIFs. An immunohistochemical analysis of zebrafish revealed that inaa was distributed dynamically in the developing retina. It was widely localized in retinal neuroepithelial cells at 1 day postfertilization (dpf), and was mainly found in the ganglion cell layer (GCL) and inner part of the inner nuclear layer (INL) from 3-9 dpf; after 14 dpf, it was restricted to the outer nuclear layer (ONL). Moreover, we demonstrated for the first time that inaa acted distinctively from the cytoskeletal scaffold of zebrafish cone photoreceptors during development. In conclusion, we demonstrated the morphological features of a novel nIF, inaa, and illustrated its developmental expression pattern in the zebrafish retina. J. Comp. Neurol. 524:3810-3826, 2016. © 2016 Wiley Periodicals, Inc.
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Affiliation(s)
- Meng-Lin Liao
- Department of Anatomy and Cell Biology, College of Medicine; National Taiwan University; Taipei Taiwan
| | - Wei-Hau Peng
- Department of Anatomy and Cell Biology, College of Medicine; National Taiwan University; Taipei Taiwan
| | - Daphne Kan
- Center of Genomic Medicine; National Taiwan University; Taipei Taiwan
| | - Chung-Liang Chien
- Department of Anatomy and Cell Biology, College of Medicine; National Taiwan University; Taipei Taiwan
- Center of Genomic Medicine; National Taiwan University; Taipei Taiwan
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19
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Yuan A, Nixon RA. Specialized roles of neurofilament proteins in synapses: Relevance to neuropsychiatric disorders. Brain Res Bull 2016; 126:334-346. [PMID: 27609296 PMCID: PMC5079776 DOI: 10.1016/j.brainresbull.2016.09.002] [Citation(s) in RCA: 53] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2016] [Revised: 09/02/2016] [Accepted: 09/03/2016] [Indexed: 01/05/2023]
Abstract
Neurofilaments are uniquely complex among classes of intermediate filaments in being composed of four subunits (NFL, NFM, NFH and alpha-internexin in the CNS) that differ in structure, regulation, and function. Although neurofilaments have been traditionally viewed as axonal structural components, recent evidence has revealed that distinctive assemblies of neurofilament subunits are integral components of synapses, especially at postsynaptic sites. Within the synaptic compartment, the individual subunits differentially modulate neurotransmission and behavior through interactions with specific neurotransmitter receptors. These newly uncovered functions suggest that alterations of neurofilament proteins not only underlie axonopathy in various neurological disorders but also may play vital roles in cognition and neuropsychiatric diseases. Here, we review evidence that synaptic neurofilament proteins are a sizable population in the CNS and we advance the concept that changes in the levels or post-translational modification of individual NF subunits contribute to synaptic and behavioral dysfunction in certain neuropsychiatric conditions.
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Affiliation(s)
- Aidong Yuan
- Center for Dementia Research, Nathan Kline Institute, Orangeburg, New York, 10962, United States; Departments of Psychiatry, New York University School of Medicine, New York, NY, 10016, United States.
| | - Ralph A Nixon
- Center for Dementia Research, Nathan Kline Institute, Orangeburg, New York, 10962, United States; Departments of Psychiatry, New York University School of Medicine, New York, NY, 10016, United States; Department of Cell Biology, New York University School of Medicine, New York, NY, 10016, United States.
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20
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Intermediate Filaments as Organizers of Cellular Space: How They Affect Mitochondrial Structure and Function. Cells 2016; 5:cells5030030. [PMID: 27399781 PMCID: PMC5040972 DOI: 10.3390/cells5030030] [Citation(s) in RCA: 49] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2016] [Revised: 06/24/2016] [Accepted: 06/30/2016] [Indexed: 12/17/2022] Open
Abstract
Intermediate filaments together with actin filaments and microtubules form the cytoskeleton, which is a complex and highly dynamic 3D network. Intermediate filaments are the major mechanical stress protectors but also affect cell growth, differentiation, signal transduction, and migration. Using intermediate filament-mitochondrial crosstalk as a prominent example, this review emphasizes the importance of intermediate filaments as crucial organizers of cytoplasmic space to support these functions. We summarize observations in different mammalian cell types which demonstrate how intermediate filaments influence mitochondrial morphology, subcellular localization, and function through direct and indirect interactions and how perturbations of these interactions may lead to human diseases.
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Jones MR, Villalón E, Garcia ML. Genetic Manipulation of Neurofilament Protein Phosphorylation. Methods Enzymol 2015; 568:461-76. [PMID: 26795480 DOI: 10.1016/bs.mie.2015.07.027] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Neurofilament biology is important to understanding structural properties of axons, such as establishment of axonal diameter by radial growth. In order to study the function of neurofilaments, a series of genetically modified mice have been generated. Here, we describe a brief history of genetic modifications used to study neurofilaments, as well as an overview of the steps required to generate a gene-targeted mouse. In addition, we describe steps utilized to analyze neurofilament phosphorylation status using immunoblotting. Taken together, these provide comprehensive analysis of neurofilament function in vivo, which can be applied to many systems.
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Affiliation(s)
- Maria R Jones
- Department of Biological Sciences, University of Missouri, Columbia, Missouri, USA; C.S. Bond Life Sciences Center, University of Missouri, Columbia, Missouri, USA
| | - Eric Villalón
- Department of Biological Sciences, University of Missouri, Columbia, Missouri, USA; C.S. Bond Life Sciences Center, University of Missouri, Columbia, Missouri, USA
| | - Michael L Garcia
- Department of Biological Sciences, University of Missouri, Columbia, Missouri, USA; C.S. Bond Life Sciences Center, University of Missouri, Columbia, Missouri, USA.
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22
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Kornreich M, Malka-Gibor E, Laser-Azogui A, Doron O, Herrmann H, Beck R. Composite bottlebrush mechanics: α-internexin fine-tunes neurofilament network properties. SOFT MATTER 2015; 11:5839-5849. [PMID: 26100609 DOI: 10.1039/c5sm00662g] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Neuronal cytoplasmic intermediate filaments are principal structural and mechanical elements of the axon. Their expression during embryonic development follows a differential pattern, while their unregulated expression is correlated to neurodegenerative diseases. The largest neurofilament proteins of medium (NF-M) and high molecular weight (NF-H) were shown to modulate the axonal architecture and inter-filament spacing. However, the individual roles of the remaining α-internexin (α-Inx) and neurofilament of low molecular weight (NF-L) proteins in composite filaments remained elusive. In contrast to previous predictions, we show that when co-assembled with NF-M, the shortest and the least charged α-Inx protein increases inter-filament spacing. These findings suggest a novel structural explanation for the expression pattern of neurofilament proteins during embryonic development. We explain our results by an analysis of ionic cross-links between the disordered polyampholytic C-terminal tails and suggest that a collapsed conformation of the α-Inx tail domain interferes with tail cross-linking near the filament backbone.
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Affiliation(s)
- M Kornreich
- The Raymond and Beverly Sackler School of Physics and Astronomy, Tel-Aviv University, 69978 Tel Aviv, Israel.
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23
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Yuan A, Hassinger L, Rao MV, Julien JP, Miller CCJ, Nixon RA. Dissociation of Axonal Neurofilament Content from Its Transport Rate. PLoS One 2015. [PMID: 26208164 PMCID: PMC4514674 DOI: 10.1371/journal.pone.0133848] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The axonal cytoskeleton of neurofilament (NF) is a long-lived network of fibrous elements believed to be a stationary structure maintained by a small pool of transported cytoskeletal precursors. Accordingly, it may be predicted that NF content in axons can vary independently from the transport rate of NF. In the present report, we confirm this prediction by showing that human NFH transgenic mice and transgenic mice expressing human NFL Ser55 (Asp) develop nearly identical abnormal patterns of NF accumulation and distribution in association with opposite changes in NF slow transport rates. We also show that the rate of NF transport in wild-type mice remains constant along a length of the optic axon where NF content varies 3-fold. Moreover, knockout mice lacking NFH develop even more extreme (6-fold) proximal to distal variation in NF number, which is associated with a normal wild-type rate of NF transport. The independence of regional NF content and NF transport is consistent with previous evidence suggesting that the rate of incorporation of transported NF precursors into a metabolically stable stationary cytoskeletal network is the major determinant of axonal NF content, enabling the generation of the striking local variations in NF number seen along axons.
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Affiliation(s)
- Aidong Yuan
- Center for Dementia Research, Nathan Kline Institute, Orangeburg, New York, United States of America
- Department of Psychiatry, New York University School of Medicine, New York, New York, United States of America
- * E-mail: (AY); (RAN)
| | - Linda Hassinger
- Department of Psychiatry, McLean Hospital, Harvard Medical School, Belmont, Massachusetts, United States of America
| | - Mala V. Rao
- Center for Dementia Research, Nathan Kline Institute, Orangeburg, New York, United States of America
- Department of Psychiatry, New York University School of Medicine, New York, New York, United States of America
| | - Jean-Pierre Julien
- Centre de Recherche du Centre Hospitalier de l'Université Laval, Département d'anatomie et physiologie de l'Université Laval, Québec, Canada
| | - Christopher C. J. Miller
- Department of Neuroscience, Institute of Psychiatry, Kings College London, London, United Kingdom
- Clinical Neurosciences, Institute of Psychiatry, Kings College London, London, United Kingdom
| | - Ralph A. Nixon
- Center for Dementia Research, Nathan Kline Institute, Orangeburg, New York, United States of America
- Department of Psychiatry, New York University School of Medicine, New York, New York, United States of America
- Department of Cell Biology, New York University School of Medicine, New York, New York, United States of America
- * E-mail: (AY); (RAN)
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Gentil BJ, Tibshirani M, Durham HD. Neurofilament dynamics and involvement in neurological disorders. Cell Tissue Res 2015; 360:609-20. [PMID: 25567110 DOI: 10.1007/s00441-014-2082-7] [Citation(s) in RCA: 66] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2014] [Accepted: 11/19/2014] [Indexed: 12/21/2022]
Abstract
Neurons are extremely polarised cells in which the cytoskeleton, composed of microtubules, microfilaments and neurofilaments, plays a crucial role in maintaining structure and function. Neurofilaments, the 10-nm intermediate filaments of neurons, provide structure and mechanoresistance but also provide a scaffolding for the organization of the nucleus and organelles such as mitochondria and ER. Disruption of neurofilament organization and expression or metabolism of neurofilament proteins is characteristic of certain neurological syndromes including Amyotrophic Lateral Sclerosis, Charcot-Marie-Tooth sensorimotor neuropathies and Giant Axonal Neuropathy. Microfluorometric live imaging techniques have been instrumental in revealing the dynamics of neurofilament assembly and transport and their functions in organizing intracellular organelle networks. The insolubility of neurofilament proteins has limited identifying interactors by conventional biochemical techniques but yeast two-hybrid experiments have revealed new roles for oligomeric, nonfilamentous structures including vesicular trafficking. Although having long half-lives, new evidence points to degradation of subunits by the ubiquitin-proteasome system as a mechanism of normal turnover. Although certain E3-ligases ubiquitinating neurofilament proteins have been identified, the overall process of neurofilament degradation is not well understood. We review these mechanisms of neurofilament homeostasis and abnormalities in motor neuron and peripheral nerve disorders. Much remains to discover about the disruption of processes that leads to their pathological aggregation and accumulation and the relevance to pathogenesis. Understanding these mechanisms is crucial for identifying novel therapeutic strategies.
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Affiliation(s)
- Benoit J Gentil
- Department of Neurology/Neurosurgery and Montreal Neurological Institute, McGill University, Montreal, QC, H3A 2B4, Canada,
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25
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Snider NT, Omary MB. Post-translational modifications of intermediate filament proteins: mechanisms and functions. Nat Rev Mol Cell Biol 2014; 15:163-77. [PMID: 24556839 PMCID: PMC4079540 DOI: 10.1038/nrm3753] [Citation(s) in RCA: 370] [Impact Index Per Article: 37.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Intermediate filaments (IFs) are cytoskeletal and nucleoskeletal structures that provide mechanical and stress-coping resilience to cells, contribute to subcellular and tissue-specific biological functions, and facilitate intracellular communication. IFs, including nuclear lamins and those in the cytoplasm (keratins, vimentin, desmin, neurofilaments and glial fibrillary acidic protein, among others), are functionally regulated by post-translational modifications (PTMs). Proteomic advances highlight the enormous complexity and regulatory potential of IF protein PTMs, which include phosphorylation, glycosylation, sumoylation, acetylation and prenylation, with novel modifications becoming increasingly appreciated. Future studies will need to characterize their on-off mechanisms, crosstalk and utility as biomarkers and targets for diseases involving the IF cytoskeleton.
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Affiliation(s)
- Natasha T. Snider
- Department of Molecular and Integrative Physiology, University of Michigan Medical School, Ann Arbor, Michigan
| | - M. Bishr Omary
- Department of Molecular and Integrative Physiology, University of Michigan Medical School, Ann Arbor, Michigan
- Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, Michigan
- VA Ann Arbor Healthcare System, Ann Arbor, Michigan
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26
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Affiliation(s)
- Aidong Yuan
- Center for Dementia Research, Nathan Kline Institute, Orangeburg, New York, NY 10962, USA.
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27
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28
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Holmgren A, Bouhy D, Timmerman V. Neurofilament phosphorylation and their proline-directed kinases in health and disease. J Peripher Nerv Syst 2012; 17:365-76. [DOI: 10.1111/j.1529-8027.2012.00434.x] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
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29
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Rao MV, Yuan A, Campbell J, Kumar A, Nixon RA. The C-terminal domains of NF-H and NF-M subunits maintain axonal neurofilament content by blocking turnover of the stationary neurofilament network. PLoS One 2012; 7:e44320. [PMID: 23028520 PMCID: PMC3448626 DOI: 10.1371/journal.pone.0044320] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2012] [Accepted: 08/01/2012] [Indexed: 02/03/2023] Open
Abstract
Newly synthesized neurofilaments or protofilaments are incorporated into a highly stable stationary cytoskeleton network as they are transported along axons. Although the heavily phosphorylated carboxyl-terminal tail domains of the heavy and medium neurofilament (NF) subunits have been proposed to contribute to this process and particularly to stability of this structure, their function is still obscure. Here we show in NF-H/M tail deletion [NF-(H/M)(tailΔ)] mice that the deletion of both of these domains selectively lowers NF levels 3-6 fold along optic axons without altering either rates of subunit synthesis or the rate of slow axonal transport of NF. Pulse labeling studies carried out over 90 days revealed a significantly faster rate of disappearance of NF from the stationary NF network of optic axons in NF-(H/M)(tailΔ) mice. Faster NF disappearance was accompanied by elevated levels of NF-L proteolytic fragments in NF-(H/M)(tailΔ) axons. We conclude that NF-H and NF-M C-terminal domains do not normally regulate NF transport rates as previously proposed, but instead increase the proteolytic resistance of NF, thereby stabilizing the stationary neurofilament cytoskeleton along axons.
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Affiliation(s)
- Mala V Rao
- Center for Dementia Research, Nathan Kline Institute, Orangeburg, New York, United States of America.
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30
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Wakeling EN, Joussemet B, Costiou P, Fanuel D, Moullier P, Barkats M, Fyfe JC. Failure of lower motor neuron radial outgrowth precedes retrograde degeneration in a feline model of spinal muscular atrophy. J Comp Neurol 2012; 520:1737-50. [PMID: 22120001 DOI: 10.1002/cne.23010] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Feline spinal muscular atrophy (SMA) is a fully penetrant, autosomal recessive lower motor neuron disease in domestic cats that clinically resembles human SMA Type III. A whole genome linkage scan identified a ∼140-kb deletion that abrogates expression of LIX1, a novel SMA candidate gene of unknown function. To characterize the progression of feline SMA, we assessed pathological changes in muscle and spinal cord from 3 days of age to beyond onset of clinical signs. Electromyographic (EMG) analysis indicating denervation occurred between 10 and 12 weeks, with the first neurological signs occurring at the same time. Compound motor action potential (CMAP) amplitudes were significantly reduced in the soleus and extensor carpi radialis muscles at 8-11 weeks. Quadriceps femoris muscle fibers from affected cats appeared smaller at 10 weeks; by 12 weeks atrophic fibers were more prevalent than in age-matched controls. In affected cats, significant loss of L5 ventral root axons was observed at 12 weeks. By 21 weeks of age, affected cats had 40% fewer L5 motor axons than normal. There was no significant difference in total L5 soma number, even at 21 weeks; thus degeneration begins distal to the cell body and proceeds retrogradely. Morphometric analysis of L5 ventral roots and horns revealed that 4 weeks prior to axon loss, motor axons in affected cats failed to undergo radial enlargement, suggesting a role for the putative disease gene LIX1 in radial growth of axons.
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Affiliation(s)
- Erin N Wakeling
- Genetics Program, Michigan State University East Lansing, Michigan 48824, USA.
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Barry DM, Stevenson W, Bober BG, Wiese PJ, Dale JM, Barry GS, Byers NS, Strope JD, Chang R, Schulz DJ, Shah S, Calcutt NA, Gebremichael Y, Garcia ML. Expansion of neurofilament medium C terminus increases axonal diameter independent of increases in conduction velocity or myelin thickness. J Neurosci 2012; 32:6209-19. [PMID: 22553027 PMCID: PMC3363292 DOI: 10.1523/jneurosci.0647-12.2012] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2012] [Revised: 03/13/2012] [Accepted: 03/17/2012] [Indexed: 12/30/2022] Open
Abstract
Maturation of the peripheral nervous system requires specification of axonal diameter, which, in turn, has a significant influence on nerve conduction velocity. Radial axonal growth initiates with myelination, and is dependent upon the C terminus of neurofilament medium (NF-M). Molecular phylogenetic analysis in mammals suggested that expanded NF-M C termini correlated with larger-diameter axons. We used gene targeting and computational modeling to test this new hypothesis. Increasing the length of NF-M C terminus in mice increased diameter of motor axons without altering neurofilament subunit stoichiometry. Computational modeling predicted that an expanded NF-M C terminus extended farther from the neurofilament core independent of lysine-serine-proline (KSP) phosphorylation. However, expansion of NF-M C terminus did not affect the distance between adjacent neurofilaments. Increased axonal diameter did not increase conduction velocity, possibly due to a failure to increase myelin thickness by the same proportion. Failure of myelin to compensate for larger axonal diameters suggested a lack of plasticity during the processes of myelination and radial axonal growth.
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Affiliation(s)
- Devin M. Barry
- Department of Biological Sciences and
- C.S. Bond Life Sciences Center, University of Missouri, Columbia, Missouri 65211
| | - William Stevenson
- Department of Biomedical Engineering, Wayne State University, Detroit, Michigan 48201
| | | | | | - Jeffrey M. Dale
- Department of Biological Sciences and
- C.S. Bond Life Sciences Center, University of Missouri, Columbia, Missouri 65211
| | - Garet S. Barry
- Department of Biological Sciences and
- C.S. Bond Life Sciences Center, University of Missouri, Columbia, Missouri 65211
| | - Nathan S. Byers
- Department of Biological Sciences and
- C.S. Bond Life Sciences Center, University of Missouri, Columbia, Missouri 65211
| | - Jonathan D. Strope
- Department of Biological Sciences and
- C.S. Bond Life Sciences Center, University of Missouri, Columbia, Missouri 65211
| | - Rakwoo Chang
- Department of Chemistry, Kwangwoon University, Seoul 139-701, Republic of Korea
| | | | | | - Nigel A. Calcutt
- Pathology, University of California, San Diego, La Jolla, California 92093, and
| | | | - Michael L. Garcia
- Department of Biological Sciences and
- C.S. Bond Life Sciences Center, University of Missouri, Columbia, Missouri 65211
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32
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Neurofilament Phosphorylation during Development and Disease: Which Came First, the Phosphorylation or the Accumulation? JOURNAL OF AMINO ACIDS 2012; 2012:382107. [PMID: 22570767 PMCID: PMC3337605 DOI: 10.1155/2012/382107] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/17/2011] [Accepted: 01/31/2012] [Indexed: 11/17/2022]
Abstract
Posttranslational modification of proteins is a ubiquitous cellular mechanism for regulating protein function. Some of the most heavily modified neuronal proteins are cytoskeletal proteins of long myelinated axons referred to as neurofilaments (NFs). NFs are type IV intermediate filaments (IFs) that can be composed of four subunits, neurofilament heavy (NF-H), neurofilament medium (NF-M), neurofilament light (NF-L), and α-internexin. Within wild type axons, NFs are responsible for mediating radial growth, a process that determines axonal diameter. NFs are phosphorylated on highly conserved lysine-serine-proline (KSP) repeats located along the C-termini of both NF-M and NF-H within myelinated axonal regions. Phosphorylation is thought to regulate aspects of NF transport and function. However, a key pathological hallmark of several neurodegenerative diseases is ectopic accumulation and phosphorylation of NFs. The goal of this review is to provide an overview of the posttranslational modifications that occur in both normal and diseased axons. We review evidence that challenges the role of KSP phosphorylation as essential for radial growth and suggests an alternative role for NF phosphorylation in myelinated axons. Furthermore, we demonstrate that regulation of NF phosphorylation dynamics may be essential to avoiding NF accumulations.
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LEERMAKERS FAM, ZHULINA EB. SELF-CONSISTENT FIELD MODELING OF THE NEUROFILAMENT NETWORK. ACTA ACUST UNITED AC 2011. [DOI: 10.1142/s179304800800085x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
We have investigated, on a self-consistent field level, the equilibrium structure of the neurofilament network formed by the NF -H, NF -M and NF -L proteins, using the one-gradient version of the numerical model of Scheutjens and Fleer. We demonstrate a reticulation of NFs in parallel bundles that occurs due to hydrophobic attractions between apolar aminoacid residues in the terminal parts of the M- and H-tails. We elaborate on the feasibility that the stability of the NF network can be enhanced by specific interactions between the projection domains, possibly induced by accessary proteins. We demonstrate that the phosphorylation of KSP repeats in the M- and H-tails promotes the cross-bridging between the NFs and therefore helps form the NF network.
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Affiliation(s)
- F. A. M. LEERMAKERS
- Laboratory of Physical Chemistry and Colloid Science, Wageningen University, Dreijenplein 6, 6307 HB Wageningen, The Netherlands
| | - E. B. ZHULINA
- Institute of Macromolecular Compounds of the Russian Academy of Sciences, 199004 St. Petersburg, Russia
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34
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Shea TB, Lee S. Neurofilament phosphorylation regulates axonal transport by an indirect mechanism: a merging of opposing hypotheses. Cytoskeleton (Hoboken) 2011; 68:589-95. [PMID: 21990272 DOI: 10.1002/cm.20535] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2011] [Accepted: 09/22/2011] [Indexed: 01/22/2023]
Abstract
Neurofilaments (NFs) are among the most abundant constituents of the axonal cytoskeleton. NFs consist of four subunits, termed NF-H, NF-M and NF-L, corresponding to heavy, medium and light in reference to their molecular mass and α-internexin. Phosphorylation of the C-terminal "sidearms" of NF-H and NF-M regulates the ability of NFs to form a cytoskeletal lattice that supports the mature axon. C-terminal phosphorylation events have classically been considered to regulate NF axonal transport. By contrast, studies demonstrating that NF axonal transport was not accelerated following sidearm deletion provided evidence that phosphorylation does not regulate NF transport. Herein, we demonstrate how comparison of transport and distribution of differentially phosphorylated NFs along axons identify common ground between these hypotheses and may resolve this controversy.
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Affiliation(s)
- Thomas B Shea
- Department of Biological Sciences, Center for Cellular Neurobiology and Neurodegeneration Research, University of Massachusetts-Lowell, Lowell, Massachusetts 01854, USA.
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35
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Pundir AS, Hameed LS, Dikshit PC, Kumar P, Mohan S, Radotra B, Shankar SK, Mahadevan A, Iyengar S. Expression of medium and heavy chain neurofilaments in the developing human auditory cortex. Brain Struct Funct 2011; 217:303-21. [DOI: 10.1007/s00429-011-0352-7] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2011] [Accepted: 09/21/2011] [Indexed: 12/31/2022]
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36
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Szaro BG, Strong MJ. Regulation of Cytoskeletal Composition in Neurons: Transcriptional and Post-transcriptional Control in Development, Regeneration, and Disease. ADVANCES IN NEUROBIOLOGY 2011. [DOI: 10.1007/978-1-4419-6787-9_24] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/12/2023]
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37
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Stevenson W, Chang R, Gebremichael Y. Phosphorylation-mediated conformational changes in the mouse neurofilament architecture: insight from a neurofilament brush model. J Mol Biol 2010; 405:1101-18. [PMID: 21134382 DOI: 10.1016/j.jmb.2010.11.022] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2010] [Revised: 11/08/2010] [Accepted: 11/11/2010] [Indexed: 11/24/2022]
Abstract
Neurofilaments (NFs) are important cytoskeletal filaments that consist of long flexible C-terminal tails that are abundant with charges. The tails attain additional negative charges through serine phosphorylation of Lys-Ser-Pro (KSP) repeat motifs that are particularly found in neurofilament heavy (NF-H) and neurofilament medium (NF-M) proteins. These side-arm protrusions mediate the interaction between neighboring filaments and maintain axonal diameter. However, the precise role of NF proteins and their phosphorylation in regulating interfilament distances and axonal diameter still remains unclear. In this regard, a recent gene replacement study revealed that the phosphorylation of mouse NF-M KSP repeats does not affect axonal cytoarchitecture, challenging the conventional viewpoint on the role of NF phosphorylation. To better understand the effect of phosphorylation, particularly NF-M phosphorylation, we applied a computational method to reveal phosphorylation-mediated conformational changes in mouse NF architecture. We employed a three-dimensional sequence-based coarse-grained NF brush model to perform Monte Carlo simulations of mouse NF by using the sequence and stoichiometry of mouse NF proteins. Our result shows that the phosphorylation of mouse NF-M does not change the radial extension of NF-M side arms under a salt-free condition and in ionic solution, highlighting a structural factor that supports the notion that NF-M KSP phosphorylation has no effect on the axonal diameter of mouse. On the other hand, significant phosphorylation-mediated conformational changes were found in NF-H side arms under the salt-free condition, while the changes in ionic solution are not significant. However, NF-H side arms are found at the periphery of mouse NF architecture, implying a role in linking neighboring filaments.
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Affiliation(s)
- William Stevenson
- Department of Biomedical Engineering, Wayne State University, Detroit, MI 48201, USA
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38
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Lee S, Sunil N, Shea TB. C-terminal neurofilament phosphorylation fosters neurofilament-neurofilament associations that compete with axonal transport. Cytoskeleton (Hoboken) 2010; 68:8-17. [PMID: 20862740 DOI: 10.1002/cm.20488] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2010] [Accepted: 09/16/2010] [Indexed: 12/20/2022]
Abstract
Neurofilaments (NFs) associate with each other and with other cytoskeletal elements to form a lattice that supports the mature axon. Phosphorylation contributes to formation of this structure by fostering cation-dependent interactions among NF sidearms. By inducing NF bundling, phosphorylation impedes their axonal transport. To examine the impact of the known NF kinase cdk5 on these phenomena, transfected cells with constructs expressing GFP-tagged NF-H sidearms (lacking the rod domain to preclude assembly) with and without site-directed mutagenesis of 7 cdk5 consensus sites, and monitored the impact on NF transport and association with the axonal NF bundle. These mutations did not alter transport but pseudo-phosphorylated mutants displayed a greater association with axonal NF bundles. By contrast, these same mutations in full-length NF-H altered NF transport as well as bundling. Since isolated sidearms cannot assemble, they can only interact with NFs via a single sidearm-sidearm interaction, while assembled NFs can form multiple such interactions. These finding suggest that individual sidearm-sidearm interactions are dynamic and do not persist long enough to slow NF transport, and that bundle formation and maintenance depends upon both the long half-life of NF polymers and the establishment of multiple phosphorylation-dependent sidearm-mediated interactions among NFs.
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Affiliation(s)
- Sangmook Lee
- Department of Biological Sciences, Center for Cellular Neurobiology and Neurodegeneration Research, University of Massachusetts, Lowell, Massachusetts 01854, USA
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39
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Vavlitou N, Sargiannidou I, Markoullis K, Kyriacou K, Scherer SS, Kleopa KA. Axonal pathology precedes demyelination in a mouse model of X-linked demyelinating/type I Charcot-Marie Tooth neuropathy. J Neuropathol Exp Neurol 2010; 69:945-58. [PMID: 20720503 PMCID: PMC3034224 DOI: 10.1097/nen.0b013e3181efa658] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
The X-linked demyelinating/type I Charcot-Marie-Tooth neuropathy (CMT1X) is an inherited peripheral neuropathy caused by mutations in GJB1, the gene that encodes the gap junction protein connexin32. Connexin32 is expressed by myelinating Schwann cells and forms gap junctions in noncompact myelin areas, but axonal involvement is more prominent in X-linked compared with other forms of demyelinating Charcot-Marie-Tooth disease. To clarify the cellular and molecular mechanisms of axonal pathology in CMT1X, we studied Gjb1-null mice at early stages (i.e. 2-4 months old) of the neuropathy, when there is minimal or no demyelination. The diameters of large myelinated axons were progressively reduced in Gjb1-null mice compared with those in wild-type littermates. Furthermore, neurofilaments were relatively more dephosphorylated and more densely packed starting at 2 months of age. Increased expression of β-amyloid precursor protein, a marker of axonal damage, was also detected in Gjb1-null nerves. Finally, fast axonal transport, assayed by sciatic nerve ligation experiments, was slower in distal axons of Gjb1-null versus wild-type animals with reduced accumulation of synaptic vesicle-associated proteins. These findings demonstrate that axonal abnormalities including impaired cytoskeletal organization and defects in axonal transport precede demyelination in this mouse model of CMT1X.
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Affiliation(s)
- Natalie Vavlitou
- Neuroscience Laboratory and Neurology Clinics, The Cyprus Institute of Neurology and Genetics, Nicosia, Cyprus
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40
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Zhulina EB, Leermakers FAM. The polymer brush model of neurofilament projections: effect of protein composition. Biophys J 2010; 98:462-9. [PMID: 20141760 DOI: 10.1016/j.bpj.2009.10.033] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2009] [Revised: 10/20/2009] [Accepted: 10/21/2009] [Indexed: 01/11/2023] Open
Abstract
Applying self-consistent field theory, we consider a coarse-grained model for the polymerlike projections of neurofilament (NF) proteins that form a brush structure around neurofilaments. We focus on effects of molecular composition, which is the relative occurrence of NF-H, NF-M, and NF-L proteins, on the organization of NF projection domains. We consider NF brushes with selectively truncated projections, and with a varied ratio L:H:M of constituent tails. Our conclusion is that the NF brush structure is remarkably tolerant with respect to the variation in M and H chains. Results compare favorably with experimental data on model animals, provided that due attention is paid on the level of phosphorylation of the KSP repeats.
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Affiliation(s)
- E B Zhulina
- Institute of Macromolecular Compounds of the Russian Academy of Sciences, St. Petersburg, Russia
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41
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Leermakers FAM, Zhulina EB. How the projection domains of NF-L and alpha-internexin determine the conformations of NF-M and NF-H in neurofilaments. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2010; 39:1323-34. [PMID: 20213320 DOI: 10.1007/s00249-010-0585-z] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/18/2009] [Revised: 01/25/2010] [Accepted: 02/08/2010] [Indexed: 02/06/2023]
Abstract
Making use of a numerical self-consistent field method and polymer brush concepts, we model the solvated corona of neurofilaments (NF) composed of projection domains (unstructured tails) of constituent proteins. Projections are modeled with amino acid resolution. We focus on the importance of the two shortest ones (alpha-internexin and NF-L) in regulating the conformations of the two longer ones (NF-M and NF-H) in an isolated NF. We take the wild-type NF with no alpha-internexin as the reference, for which the phosphorylation-induced translocation of M- and H-tails has been examined previously. We demonstrate that a subbrush of L-tails creates an electrostatic potential profile with an approximately parabolic shape. An experimentally relevant (2:1) ratio of L- to alpha-projections reduces the charge density of the L subbrush and shifts the translocation transition of the H-tails to slightly higher degrees of phosphorylation. Replacing all L-tails by alpha-projections destroys the substructure of the NF corona and this alters the NF response to the phosphorylation of long tails.
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42
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Barry DM, Carpenter C, Yager C, Golik B, Barry KJ, Shen H, Mikse O, Eggert LS, Schulz DJ, Garcia ML. Variation of the neurofilament medium KSP repeat sub-domain across mammalian species: implications for altering axonal structure. ACTA ACUST UNITED AC 2010; 213:128-36. [PMID: 20008369 DOI: 10.1242/jeb.033787] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The evolution of larger mammals resulted in a corresponding increase in peripheral nerve length. To ensure optimal nervous system functionality and survival, nerve conduction velocities were likely to have increased to maintain the rate of signal propagation. Increases of conduction velocities may have required alterations in one of the two predominant properties that affect the speed of neuronal transmission: myelination or axonal diameter. A plausible mechanism to explain faster conduction velocities was a concomitant increase in axonal diameter with evolving axonal length. The carboxy terminal tail domain of the neurofilament medium subunit is a determinant of axonal diameter in large caliber myelinated axons. Sequence analysis of mammalian orthologs indicates that the neurofilament medium carboxy terminal tail contains a variable lysine-serine-proline (KSP) repeat sub-domain flanked by two highly conserved sub-domains. The number of KSP repeats within this region of neurofilament medium varies among species. Interestingly, the number of repeats does not change within a species, suggesting that selective pressure conserved the number of repeats within a species. Mapping KSP repeat numbers onto consensus phylogenetic trees reveals independent KSP expansion events across several mammalian clades. Linear regression analyses identified three subsets of mammals, one of which shows a positive correlation in the number of repeats with head-body length. For this subset of mammals, we hypothesize that variations in the number of KSP repeats within neurofilament medium carboxy terminal tail may have contributed to an increase in axonal caliber, increasing nerve conduction velocity as larger mammals evolved.
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Affiliation(s)
- D M Barry
- Department of Biological Sciences, University of Missouri, Columbia, Columbia, MO 65211, USA
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43
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Fuchs P, Zörer M, Reipert S, Rezniczek GA, Propst F, Walko G, Fischer I, Bauer J, Leschnik MW, Lüscher B, Thalhammer JG, Lassmann H, Wiche G. Targeted inactivation of a developmentally regulated neural plectin isoform (plectin 1c) in mice leads to reduced motor nerve conduction velocity. J Biol Chem 2009; 284:26502-9. [PMID: 19625254 PMCID: PMC2785338 DOI: 10.1074/jbc.m109.018150] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2009] [Revised: 07/08/2009] [Indexed: 12/27/2022] Open
Abstract
Cytolinker proteins stabilize cells mechanically, regulate cytoskeleton dynamics, and provide scaffolds for signaling molecules. For plectin, the prototype of these proteins, an unusual diversity of isoforms has been reported, which show distinct expression patterns, subcellular localizations, and functions. Plectin has been shown to have important functions in skin and muscle, but little is known about its role in neural cells. To address this issue, we generated two knock-out mouse lines, one which was selectively lacking plectin 1c (P1c), the major isoform expressed in neural cells, and another in which plectin was conditionally deleted in neuronal precursor cells. Using isoform-specific antibodies, we found P1c to be expressed late in development and to associate with postsynaptic dendrites of central nervous system neurons, motorneurons of spinal cord, sciatic nerve axons, and Schwann cells. Motor nerve conduction velocity was found significantly reduced in sciatic nerve from P1c-deficient as well as from conditional knock-out mice. This defect was traceable to an increased number of motor nerve fibers with small cross-sectional areas; the thicknesses of axons and of myelin sheaths were unaffected. This is the first report demonstrating an important role of plectin in a major nerve function.
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Affiliation(s)
- Peter Fuchs
- From the Department of Biochemistry and Cell Biology, Max F. Perutz Laboratories, University of Vienna, Dr. Bohr-Gasse 9, 1030 Vienna, Austria
| | - Michael Zörer
- From the Department of Biochemistry and Cell Biology, Max F. Perutz Laboratories, University of Vienna, Dr. Bohr-Gasse 9, 1030 Vienna, Austria
| | - Siegfried Reipert
- From the Department of Biochemistry and Cell Biology, Max F. Perutz Laboratories, University of Vienna, Dr. Bohr-Gasse 9, 1030 Vienna, Austria
| | - Günther A. Rezniczek
- From the Department of Biochemistry and Cell Biology, Max F. Perutz Laboratories, University of Vienna, Dr. Bohr-Gasse 9, 1030 Vienna, Austria
| | - Friedrich Propst
- From the Department of Biochemistry and Cell Biology, Max F. Perutz Laboratories, University of Vienna, Dr. Bohr-Gasse 9, 1030 Vienna, Austria
| | - Gernot Walko
- From the Department of Biochemistry and Cell Biology, Max F. Perutz Laboratories, University of Vienna, Dr. Bohr-Gasse 9, 1030 Vienna, Austria
| | - Irmgard Fischer
- From the Department of Biochemistry and Cell Biology, Max F. Perutz Laboratories, University of Vienna, Dr. Bohr-Gasse 9, 1030 Vienna, Austria
| | - Jan Bauer
- the Department of Neuroimmunology, Center for Brain Research, Medical University of Vienna, 1090 Vienna, Austria
| | - Michael W. Leschnik
- the Clinic for Internal Medicine and Infectious Diseases, University of Veterinary Medicine Vienna, 1210 Vienna, Austria, and
| | - Bernhard Lüscher
- the Division of Biochemistry and Molecular Biology, Medical Faculty of the Rheinisch-Westfaelische Technische Hochschule Aachen University, 52074 Aachen, Germany
| | - Johann G. Thalhammer
- the Clinic for Internal Medicine and Infectious Diseases, University of Veterinary Medicine Vienna, 1210 Vienna, Austria, and
| | - Hans Lassmann
- the Department of Neuroimmunology, Center for Brain Research, Medical University of Vienna, 1090 Vienna, Austria
| | - Gerhard Wiche
- From the Department of Biochemistry and Cell Biology, Max F. Perutz Laboratories, University of Vienna, Dr. Bohr-Gasse 9, 1030 Vienna, Austria
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44
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Abstract
Neurofilaments assemble from three intermediate-filament proteins, contribute to the radial growth of axons, and are exceptionally stable. Microtubules are dynamic structures that assemble from tubulin dimers to support intracellular transport of molecules and organelles. We show here that neurofilaments, and other intermediate-filament proteins, contain motifs in their N-terminal domains that bind unassembled tubulin. Peptides containing such motifs inhibit the in vitro polymerization of microtubules and can be taken up by cultured cells in which they disrupt microtubules leading to altered cell shapes and an arrest of division. In transgenic mice in which neurofilaments are withheld from the axonal compartment, axonal tubulin accumulation is normal but microtubules assemble in excessive numbers. These observations suggest a model in which axonal neurofilaments modulate local microtubule assembly. This capacity also suggests novel mechanisms through which inherited or acquired disruptions in intermediate filaments might contribute to pathogenesis in multiple conditions.
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45
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Kushkuley J, Chan WKH, Lee S, Eyer J, Leterrier JF, Letournel F, Shea TB. Neurofilament cross-bridging competes with kinesin-dependent association of neurofilaments with microtubules. J Cell Sci 2009; 122:3579-86. [PMID: 19737816 DOI: 10.1242/jcs.051318] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
The phosphorylation of neurofilaments (NFs) has long been considered to regulate their axonal transport rate and in doing so to provide stability to mature axons. Axons contain a centrally situated ;bundle' of closely opposed phospho-NFs that display a high degree of NF-NF associations and phospho-epitopes, surrounded by less phosphorylated ;individual' NFs that are often associated with kinesin and microtubules (MTs). Bundled NFs transport substantially slower than the surrounding individual NFs and might represent a resident population that stabilizes axons and undergoes replacement by individual NFs. To examine this possibility, fractions enriched in bundled NFs and individual NFs were generated from mice and NB2a/d1 cells by sedimentation of cytoskeletons over a sucrose cushion. More kinesin was recovered within individual versus bundled NF fractions. Individual but not bundled NFs aligned with purified MTs under cell-free conditions. The percentage of NFs that aligned with MTs was increased by the addition of kinesin, and inhibited by anti-kinesin antibodies. Bundles dissociated following incubation with EGTA or alkaline phosphatase, generating individual NFs that retained or were depleted of phospho-epitopes, respectively. These dissociated NFs aligned with MTs at a level identical to those originally isolated as individual NFs regardless of phosphorylation state. EGTA-mediated dissociation of bundles was prevented and reversed by excess Ca(2+), whereas individual NFs did not associate in the presence of excess Ca(2+). These findings confirm that bundling competes with NF-MT association, and provide a mechanism by which C-terminal NF phosphorylation might indirectly contribute to the observed slowing in axonal transport of phospho-NFs.
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Affiliation(s)
- Jacob Kushkuley
- Center for Cellular Neurobiology and Neurodegeneration Research, Departments of Biological Sciences and Biochemistry, University of Massachusetts Lowell, Lowell, MA 01854, USA
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46
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Abstract
Neuron connectivity and correct neural function largely depend on axonal integrity. Neurofilaments (NFs) constitute the main cytoskeletal network maintaining the structural integrity of neurons and exhibit dynamic changes during axonal and dendritic growth. However, the mechanisms underlying axonal development and maintenance remain poorly understood. Here, we identify that multisynthetase complex p43 (MSC p43) is essential for NF assembly and axon maintenance. The MSC p43 protein was predominantly expressed in central neurons and interacted with NF light subunit in vivo. Mice lacking MSC p43 exhibited axon degeneration in motor neurons, defective neuromuscular junctions, muscular atrophy, and motor dysfunction. Furthermore, MSC p43 depletion in mice caused disorganization of the axonal NF network. Mechanistically, MSC p43 is required for maintaining normal phosphorylation levels of NFs. Thus, MSC p43 is indispensable in maintaining axonal integrity. Its dysfunction may underlie the NF disorganization and axon degeneration associated with motor neuron degenerative diseases.
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47
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Liem RKH, Messing A. Dysfunctions of neuronal and glial intermediate filaments in disease. J Clin Invest 2009; 119:1814-24. [PMID: 19587456 DOI: 10.1172/jci38003] [Citation(s) in RCA: 105] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
Intermediate filaments (IFs) are abundant structures found in most eukaryotic cells, including those in the nervous system. In the CNS, the primary components of neuronal IFs are alpha-internexin and the neurofilament triplet proteins. In the peripheral nervous system, a fifth neuronal IF protein known as peripherin is also present. IFs in astrocytes are primarily composed of glial fibrillary acidic protein (GFAP), although vimentin is also expressed in immature astrocytes and some mature astrocytes. In this Review, we focus on the IFs of glial cells (primarily GFAP) and neurons as well as their relationship to different neurodegenerative diseases.
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Affiliation(s)
- Ronald K H Liem
- Department of Pathology and Cell Biology, Taub Institute for Research on Alzheimer's Disease and the Aging Brain, Columbia University College of Physicians and Surgeons, New York, NY, USA.
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48
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Structural properties of neurofilament sidearms: sequence-based modeling of neurofilament architecture. J Mol Biol 2009; 391:648-60. [PMID: 19559031 DOI: 10.1016/j.jmb.2009.06.045] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2009] [Revised: 06/15/2009] [Accepted: 06/17/2009] [Indexed: 11/24/2022]
Abstract
Neurofilaments (NFs) are essential cytoskeletal filaments that impart mechanical integrity to nerve cells. They are assembled from three distinct molecular mass proteins that bind to each other to form a 10-nm-diameter filamentous rod with sidearm extensions. The sidearms are considered to play a critical role in modulating interfilament spacing and axonal caliber. However, the precise mechanism by which NF protrusions regulate axonal diameter remains to be well understood. In particular, the role played by individual NF protrusions in specifying interfilament distances is yet to be established. To gain insight into the role of individual proteins, we investigated the structural organization of NF architecture under different phosphorylation conditions. To this end, a physically motivated sequence-based coarse-grain model of NF brush has been developed based on the three-dimensional architecture of NFs. The model incorporates the charge distribution of sidearms, including charges from the phosphorylation sites corresponding to Lys-Ser-Pro repeat motifs. The model also incorporates the proper grafting of the real NF sidearms based on the stoichiometry of the three subunits. The equilibrium structure of the NF brush is then investigated under different phosphorylation conditions. The phosphorylation of NF modifies the structural organization of sidearms. Upon phosphorylation, a dramatic change involving a transformation from a compact conformation to an extended conformation is found in the heavy NF (NF-H) protein. However, in spite of extensive phosphorylation sites present in the NF-H subunit, the tails of the medium NF subunit are found to be more extended than the NF-H sidearms. This supports the notion that medium NF protrusions are critical in regulating NF spacings and, hence, axonal caliber.
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Marked calpastatin (CAST) depletion in Alzheimer's disease accelerates cytoskeleton disruption and neurodegeneration: neuroprotection by CAST overexpression. J Neurosci 2009; 28:12241-54. [PMID: 19020018 DOI: 10.1523/jneurosci.4119-08.2008] [Citation(s) in RCA: 82] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Increased activity of calpains is implicated in synaptic dysfunction and neurodegeneration in Alzheimer's disease (AD). The molecular mechanisms responsible for increased calpain activity in AD are not known. Here, we demonstrate that disease progression is propelled by a marked depletion of the endogenous calpain inhibitor, calpastatin (CAST), from AD neurons, which is mediated by caspase-1, caspase-3, and calpains. Initial CAST depletion focally along dendrites coincides topographically with calpain II and ERK 1/2 activation, tau cleavage by caspase-3, and tau and neurofilament hyperphosphorylation. These same changes, together with cytoskeletal proteolysis and neuronal cell death, accompany CAST depletion after intrahippocampal kainic acid administration to mice, and are substantially reduced in mice overexpressing human CAST. Moreover, CAST reduction by shRNA in neuronal cells causes calpain-mediated death at levels of calcium-induced injury that are sublethal to cells normally expressing CAST. Our results strongly support a novel hypothesis that CAST depletion by multiple abnormally activated proteases accelerates calpain dysregulation in AD leading to cytoskeleton disruption and neurodegeneration. CAST mimetics may, therefore, be neuroprotective in AD.
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Myosin Va increases the efficiency of neurofilament transport by decreasing the duration of long-term pauses. J Neurosci 2009; 29:6625-34. [PMID: 19458233 DOI: 10.1523/jneurosci.3829-08.2009] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
We investigated the axonal transport of neurofilaments in cultured neurons from two different strains of dilute lethal mice, which lack myosin Va. To analyze the motile behavior, we tracked the movement of green fluorescent protein (GFP)-tagged neurofilaments through naturally occurring gaps in the axonal neurofilament array of cultured superior cervical ganglion neurons from DLS/LeJ dilute lethal mice. Compared with wild-type controls, we observed no statistically significant difference in velocity or frequency of movement. To analyze the pausing behavior, we used a fluorescence photoactivation pulse-escape technique to measure the rate of departure of PAGFP (photoactivatable GFP)-tagged neurofilaments from photoactivated axonal segments in cultured dorsal root ganglion neurons from DLS/LeJ and dl20J dilute lethal mice. Compared with wild-type controls, we observed a 48% increase in the mean time for neurofilaments to depart the activated regions in neurons from DLS/LeJ mice (p < 0.001) and a 169% increase in neurons from dl20J mice (p < 0.0001). These data indicate that neurofilaments pause for more prolonged periods in the absence of myosin Va. We hypothesize that myosin Va is a short-range motor for neurofilaments and that it can function to enhance the efficiency of neurofilament transport in axons by delivering neurofilaments to their microtubule tracks, thereby reducing the duration of prolonged off-track pauses.
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