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Havlicek S, Kohl Z, Mishra HK, Prots I, Eberhardt E, Denguir N, Wend H, Plötz S, Boyer L, Marchetto MCN, Aigner S, Sticht H, Groemer TW, Hehr U, Lampert A, Schlötzer-Schrehardt U, Winkler J, Gage FH, Winner B. Gene dosage-dependent rescue of HSP neurite defects in SPG4 patients' neurons. Hum Mol Genet 2013; 23:2527-41. [PMID: 24381312 PMCID: PMC3990156 DOI: 10.1093/hmg/ddt644] [Citation(s) in RCA: 91] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The hereditary spastic paraplegias (HSPs) are a heterogeneous group of motorneuron diseases characterized by progressive spasticity and paresis of the lower limbs. Mutations in Spastic Gait 4 (SPG4), encoding spastin, are the most frequent cause of HSP. To understand how mutations in SPG4 affect human neurons, we generated human induced pluripotent stem cells (hiPSCs) from fibroblasts of two patients carrying a c.1684C>T nonsense mutation and from two controls. These SPG4 and control hiPSCs were able to differentiate into neurons and glia at comparable efficiency. All known spastin isoforms were reduced in SPG4 neuronal cells. The complexity of SPG4 neurites was decreased, which was paralleled by an imbalance of axonal transport with less retrograde movement. Prominent neurite swellings with disrupted microtubules were present in SPG4 neurons at an ultrastructural level. While some of these swellings contain acetylated and detyrosinated tubulin, these tubulin modifications were unchanged in total cell lysates of SPG4 neurons. Upregulation of another microtubule-severing protein, p60 katanin, may partially compensate for microtubuli dynamics in SPG4 neurons. Overexpression of the M1 or M87 spastin isoforms restored neurite length, branching, numbers of primary neurites and reduced swellings in SPG4 neuronal cells. We conclude that neurite complexity and maintenance in HSP patient-derived neurons are critically sensitive to spastin gene dosage. Our data show that elevation of single spastin isoform levels is sufficient to restore neurite complexity and reduce neurite swellings in patient cells. Furthermore, our human model offers an ideal platform for pharmacological screenings with the goal to restore physiological spastin levels in SPG4 patients.
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Affiliation(s)
- Steven Havlicek
- IZKF Junior Research Group and BMBF Research Group Neuroscience, IZKF, Friedrich-Alexander University Erlangen-Nuernberg (FAU), Glückstr. 6, Erlangen 91054, Germany
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González C, Couve A. The axonal endoplasmic reticulum and protein trafficking: Cellular bootlegging south of the soma. Semin Cell Dev Biol 2013; 27:23-31. [PMID: 24361785 DOI: 10.1016/j.semcdb.2013.12.004] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2013] [Revised: 11/18/2013] [Accepted: 12/05/2013] [Indexed: 12/26/2022]
Abstract
Neurons are responsible for the generation and propagation of electrical impulses, which constitute the central mechanism of information transfer between the nervous system and internal or external environments. Neurons are large and polarized cells with dendrites and axons constituting their major functional domains. Axons are thin and extremely long specializations that mediate the conduction of these electrical impulses. Regulation of the axonal proteome is fundamental to generate and maintain neural function. Although classical mechanisms of protein transport have been around for decades, a variety newly identified mechanisms to control the abundance of axonal proteins have appeared in recent years. Here we briefly describe the classical models of axonal transport and compare them to the emerging concepts of axonal biosynthesis centered on the endoplasmic reticulum. We review the structure of the axonal endoplasmic reticulum, and its role in diffusion and trafficking of axonal proteins. We also analyze the contribution of other secretory organelles to axonal trafficking and evaluate the potential consequences of axonal endoplasmic reticulum malfunction in neuropathology.
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Affiliation(s)
- Carolina González
- Program of Physiology and Biophysics, Institute of Biomedical Sciences (ICBM) and Biomedical Neuroscience Institute (BNI), Faculty of Medicine, Universidad de Chile, Santiago, Chile
| | - Andrés Couve
- Program of Physiology and Biophysics, Institute of Biomedical Sciences (ICBM) and Biomedical Neuroscience Institute (BNI), Faculty of Medicine, Universidad de Chile, Santiago, Chile.
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Khundadze M, Kollmann K, Koch N, Biskup C, Nietzsche S, Zimmer G, Hennings JC, Huebner AK, Symmank J, Jahic A, Ilina EI, Karle K, Schöls L, Kessels M, Braulke T, Qualmann B, Kurth I, Beetz C, Hübner CA. A hereditary spastic paraplegia mouse model supports a role of ZFYVE26/SPASTIZIN for the endolysosomal system. PLoS Genet 2013; 9:e1003988. [PMID: 24367272 PMCID: PMC3868532 DOI: 10.1371/journal.pgen.1003988] [Citation(s) in RCA: 72] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2013] [Accepted: 10/14/2013] [Indexed: 12/26/2022] Open
Abstract
Hereditary spastic paraplegias (HSPs) are characterized by progressive weakness and spasticity of the legs because of the degeneration of cortical motoneuron axons. SPG15 is a recessively inherited HSP variant caused by mutations in the ZFYVE26 gene and is additionally characterized by cerebellar ataxia, mental decline, and progressive thinning of the corpus callosum. ZFYVE26 encodes the FYVE domain-containing protein ZFYVE26/SPASTIZIN, which has been suggested to be associated with the newly discovered adaptor protein 5 (AP5) complex. We show that Zfyve26 is broadly expressed in neurons, associates with intracellular vesicles immunopositive for the early endosomal marker EEA1, and co-fractionates with a component of the AP5 complex. As the function of ZFYVE26 in neurons was largely unknown, we disrupted Zfyve26 in mice. Zfyve26 knockout mice do not show developmental defects but develop late-onset spastic paraplegia with cerebellar ataxia confirming that SPG15 is caused by ZFYVE26 deficiency. The morphological analysis reveals axon degeneration and progressive loss of both cortical motoneurons and Purkinje cells in the cerebellum. Importantly, neuron loss is preceded by accumulation of large intraneuronal deposits of membrane-surrounded material, which co-stains with the lysosomal marker Lamp1. A density gradient analysis of brain lysates shows an increase of Lamp1-positive membrane compartments with higher densities in Zfyve26 knockout mice. Increased levels of lysosomal enzymes in brains of aged knockout mice further support an alteration of the lysosomal compartment upon disruption of Zfyve26. We propose that SPG15 is caused by an endolysosomal membrane trafficking defect, which results in endolysosomal dysfunction. This appears to be particularly relevant in neurons with highly specialized neurites such as cortical motoneurons and Purkinje cells. Hereditary spastic paraplegias (HSPs) are inherited disorders characterized by progressive weakness and spasticity of the legs. In HSP patients, nerve fibers connecting cortical motoneurons with spinal cord neurons are progressively lost. HSP subtype 15 (SPG15) is caused by mutations in ZFYVE26, and is characterized by additional cerebellar symptoms. We show that the Zfyve26 protein is broadly expressed in the brain. At the subcellular level Zfyve26 localizes to an intracellular compartment in the endocytic pathway from the plasma membrane to lysosomes, which is part of the degradative system of the cell. Closely resembling the human disease, mice deficient for Zfyve26 develop a progressive spastic gait disorder with cerebellar symptoms and degeneration of both neurons of the motor cortex and Purkinje cells in the cerebellum. Importantly, this degeneration is characterized by the intracellular accumulation of abnormal deposits, which stain positive for the lysosomal marker Lamp1. As Zfyve26 has been shown to interact with the newly identified adaptor complex AP5, which is supposed to be involved in cargo trafficking in the endolysosomal compartment, endolysosomal dysfunction may be caused by a targeting defect upon disruption of Zfyve26. As highly specialized neurons like cortical motoneurons and cerebellar Purkinje cells degenerate, these neurons appear to be particularly dependent on proper endolysosomal function.
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Affiliation(s)
- Mukhran Khundadze
- Institute of Human Genetics, Jena University Hospital, Friedrich-Schiller-University Jena, Jena, Germany
| | - Katrin Kollmann
- Department of Biochemistry, Children's Hospital, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Nicole Koch
- Institute of Biochemistry I, Jena University Hospital, Friedrich-Schiller-University Jena, Jena, Germany
| | - Christoph Biskup
- Department of Biomolecular Photonics, Jena University Hospital, Friedrich-Schiller-University Jena, Jena, Germany
| | - Sandor Nietzsche
- Electron Microscopy Center, Jena University Hospital, Friedrich-Schiller-University Jena, Jena, Germany
| | - Geraldine Zimmer
- Institute of Human Genetics, Jena University Hospital, Friedrich-Schiller-University Jena, Jena, Germany
| | - J. Christopher Hennings
- Institute of Human Genetics, Jena University Hospital, Friedrich-Schiller-University Jena, Jena, Germany
| | - Antje K. Huebner
- Institute of Human Genetics, Jena University Hospital, Friedrich-Schiller-University Jena, Jena, Germany
| | - Judit Symmank
- Institute of Human Genetics, Jena University Hospital, Friedrich-Schiller-University Jena, Jena, Germany
| | - Amir Jahic
- Institute of Clinical Chemistry, Jena University Hospital, Friedrich-Schiller-University Jena, Jena, Germany
| | - Elena I. Ilina
- Department of Neurology and Hertie-Institute for Clinical Brain Research, University of Tübingen, Tübingen, Germany
| | - Kathrin Karle
- Department of Neurology and Hertie-Institute for Clinical Brain Research, University of Tübingen, Tübingen, Germany
- German Center of Neurodegenerative Diseases (DZNE), Tübingen, Germany
| | - Ludger Schöls
- Department of Neurology and Hertie-Institute for Clinical Brain Research, University of Tübingen, Tübingen, Germany
- German Center of Neurodegenerative Diseases (DZNE), Tübingen, Germany
| | - Michael Kessels
- Institute of Biochemistry I, Jena University Hospital, Friedrich-Schiller-University Jena, Jena, Germany
| | - Thomas Braulke
- Department of Biochemistry, Children's Hospital, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Britta Qualmann
- Institute of Biochemistry I, Jena University Hospital, Friedrich-Schiller-University Jena, Jena, Germany
| | - Ingo Kurth
- Institute of Human Genetics, Jena University Hospital, Friedrich-Schiller-University Jena, Jena, Germany
| | - Christian Beetz
- Institute of Clinical Chemistry, Jena University Hospital, Friedrich-Schiller-University Jena, Jena, Germany
| | - Christian A. Hübner
- Institute of Human Genetics, Jena University Hospital, Friedrich-Schiller-University Jena, Jena, Germany
- * E-mail:
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Abstract
Autophagy is a major intracellular degradative process that delivers cytoplasmic materials to the lysosome for degradation. Since the discovery of autophagy-related (Atg) genes in the 1990s, there has been a proliferation of studies on the physiological and pathological roles of autophagy in a variety of autophagy knockout models. However, direct evidence of the connections between ATG gene dysfunction and human diseases has emerged only recently. There are an increasing number of reports showing that mutations in the ATG genes were identified in various human diseases such as neurodegenerative diseases, infectious diseases, and cancers. Here, we review the major advances in identification of mutations or polymorphisms of the ATG genes in human diseases. Current autophagy-modulating compounds in clinical trials are also summarized.
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205
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Dor T, Cinnamon Y, Raymond L, Shaag A, Bouslam N, Bouhouche A, Gaussen M, Meyer V, Durr A, Brice A, Benomar A, Stevanin G, Schuelke M, Edvardson S. KIF1C mutations in two families with hereditary spastic paraparesis and cerebellar dysfunction. J Med Genet 2013; 51:137-42. [PMID: 24319291 DOI: 10.1136/jmedgenet-2013-102012] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
BACKGROUND Hereditary spastic paraparesis (HSP) (syn. Hereditary spastic paraplegia, SPG) are a group of genetic disorders characterised by spasticity of the lower limbs due to pyramidal tract dysfunction. Nearly 60 disease loci have been identified, which include mutations in two genes (KIF5A and KIF1A) that encode motor proteins of the kinesin superfamily. Here we report a novel genetic defect in KIF1C of patients with spastic paraparesis and cerebellar dysfunction in two consanguineous families of Palestinian and Moroccan ancestry. METHODS AND RESULTS We performed autozygosity mapping in a Palestinian and classic linkage analysis in a Moroccan family and found a locus on chromosome 17 that had previously been associated with spastic ataxia type 2 (SPAX2, OMIM %611302). Whole-exome sequencing revealed two homozygous mutations in KIF1C that were absent among controls: a nonsense mutation (c.2191C>T, p.Arg731*) that segregated with the disease phenotype in the Palestinian kindred resulted in the entire absence of KIF1C protein from the patient's fibroblasts, and a missense variant (c.505C>T, p.Arg169Trp) affecting a conserved amino acid of the motor domain that was found in the Moroccan kindred. CONCLUSIONS Kinesin genes encode a family of cargo/motor proteins and are known to cause HSP if mutated. Here we identified nonsense and missense mutations in a further member of this protein family. The KIF1C mutation is associated with a HSP subtype (SPAX2/SAX2) that combines spastic paraplegia and weakness with cerebellar dysfunction.
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Affiliation(s)
- Talya Dor
- Department of Pediatrics, Neuropediatric Unit, Hadassah-Hebrew University Medical Center, Jerusalem, Israel
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206
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Liegel R, Handley M, Ronchetti A, Brown S, Langemeyer L, Linford A, Chang B, Morris-Rosendahl D, Carpanini S, Posmyk R, Harthill V, Sheridan E, Abdel-Salam G, Terhal P, Faravelli F, Accorsi P, Giordano L, Pinelli L, Hartmann B, Ebert A, Barr F, Aligianis I, Sidjanin D. Loss-of-function mutations in TBC1D20 cause cataracts and male infertility in blind sterile mice and Warburg micro syndrome in humans. Am J Hum Genet 2013; 93:1001-14. [PMID: 24239381 DOI: 10.1016/j.ajhg.2013.10.011] [Citation(s) in RCA: 93] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2013] [Revised: 09/20/2013] [Accepted: 10/11/2013] [Indexed: 12/22/2022] Open
Abstract
blind sterile (bs) is a spontaneous autosomal-recessive mouse mutation discovered more than 30 years ago. Phenotypically, bs mice exhibit nuclear cataracts and male infertility; genetic analyses assigned the bs locus to mouse chromosome 2. In this study, we first positionally cloned the bs locus and identified a putative causative mutation in the Tbc1d20 gene. Functional analysis established the mouse TBC1D20 protein as a GTPase-activating protein (GAP) for RAB1 and RAB2, and bs as a TBC1D20 loss-of-function mutation. Evaluation of bs mouse embryonic fibroblasts (mEFs) identified enlarged Golgi morphology and aberrant lipid droplet (LD) formation. Based on the function of TBC1D20 as a RABGAP and the bs cataract and testicular phenotypes, we hypothesized that mutations in TBC1D20 may contribute to Warburg micro syndrome (WARBM); WARBM constitutes a spectrum of disorders characterized by eye, brain, and endocrine abnormalities caused by mutations in RAB3GAP1, RAB3GAP2, and RAB18. Sequence analysis of a cohort of 77 families affected by WARBM identified five distinct TBC1D20 loss-of-function mutations, thereby establishing these mutations as causative of WARBM. Evaluation of human fibroblasts deficient in TBC1D20 function identified aberrant LDs similar to those identified in the bs mEFs. Additionally, our results show that human fibroblasts deficient in RAB18 and RAB3GAP1 function also exhibit aberrant LD formation. These findings collectively indicate that a defect in LD formation/metabolism may be a common cellular abnormality associated with WARBM, although it remains unclear whether abnormalities in LD metabolism are contributing to WARBM disease pathology.
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207
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Li S, Yang L, Selzer ME, Hu Y. Neuronal endoplasmic reticulum stress in axon injury and neurodegeneration. Ann Neurol 2013; 74:768-77. [PMID: 23955583 PMCID: PMC3963272 DOI: 10.1002/ana.24005] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2013] [Revised: 08/04/2013] [Accepted: 08/07/2013] [Indexed: 12/13/2022]
Abstract
Injuries to central nervous system axons result not only in Wallerian degeneration of the axon distal to the injury, but also in death or atrophy of the axotomized neurons, depending on injury location and neuron type. No method of permanently avoiding these changes has been found, despite extensive knowledge concerning mechanisms of secondary neuronal injury. The autonomous endoplasmic reticulum (ER) stress pathway in neurons has recently been implicated in retrograde neuronal degeneration. In addition to the emerging role of ER morphology in axon maintenance, we propose that ER stress is a common neuronal response to disturbances in axon integrity and a general mechanism for neurodegeneration. Thus, manipulation of the ER stress pathway could have important therapeutic implications for neuroprotection.
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Affiliation(s)
- Shaohua Li
- Shriners Hospitals Pediatric Research Center (Center for Neural Repair and Rehabilitation), Temple University School of Medicine, Philadelphia, PA, USA
- Department of Ophthalmology, Union Hospital, Tongji Medical College, Huazhong University of Science & Technology, Wuhan, China
| | - Liu Yang
- Shriners Hospitals Pediatric Research Center (Center for Neural Repair and Rehabilitation), Temple University School of Medicine, Philadelphia, PA, USA
| | - Michael E. Selzer
- Shriners Hospitals Pediatric Research Center (Center for Neural Repair and Rehabilitation), Temple University School of Medicine, Philadelphia, PA, USA
- Department of Neurology, Temple University School of Medicine, Philadelphia, PA, USA
| | - Yang Hu
- Shriners Hospitals Pediatric Research Center (Center for Neural Repair and Rehabilitation), Temple University School of Medicine, Philadelphia, PA, USA
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Chiurchiù V, Maccarrone M, Orlacchio A. The role of reticulons in neurodegenerative diseases. Neuromolecular Med 2013; 16:3-15. [PMID: 24218324 PMCID: PMC3918113 DOI: 10.1007/s12017-013-8271-9] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2013] [Accepted: 10/23/2013] [Indexed: 01/08/2023]
Abstract
Reticulons (RTNs) are a group of membrane-associated proteins mainly responsible for shaping the tubular endoplasmic reticulum network, membrane trafficking, inhibition of axonal growth, and apoptosis. These proteins share a common sequence feature, the reticulon homology domain, which consists of paired hydrophobic stretches that are believed to induce membrane curvature by acting as a wedge in bilayer membranes. RTNs are ubiquitously expressed in all tissues, but each RTN member exhibits a unique expression pattern that prefers certain tissues or even cell types. Recently, accumulated evidence has suggested additional and unexpected roles for RTNs, including those on DNA binding, autophagy, and several inflammatory-related functions. These manifold actions of RTNs account for their ever-growing recognition of their involvement in neurodegenerative diseases like Alzheimer's disease, amyotrophic lateral sclerosis, multiple sclerosis, as well as hereditary spastic paraplegia. This review summarizes the latest discoveries on RTNs in human pathophysiology, and the engagement of these in neurodegeneration, along with the implications of these findings for a better understanding of the molecular events triggered by RTNs and their potential exploitation as next-generation therapeutics.
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Affiliation(s)
- Valerio Chiurchiù
- Laboratorio di Neurochimica dei Lipidi, Centro Europeo di Ricerca sul Cervello (CERC) - Istituto di Ricovero e Cura a Carattere Scientifico (IRCCS) Santa Lucia, Rome, Italy
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209
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Goyal U, Blackstone C. Untangling the web: mechanisms underlying ER network formation. BIOCHIMICA ET BIOPHYSICA ACTA 2013; 1833:2492-8. [PMID: 23602970 PMCID: PMC3729797 DOI: 10.1016/j.bbamcr.2013.04.009] [Citation(s) in RCA: 121] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/29/2013] [Revised: 04/04/2013] [Accepted: 04/08/2013] [Indexed: 12/16/2022]
Abstract
The ER is a continuous membrane system consisting of the nuclear envelope, flat sheets often studded with ribosomes, and a polygonal network of highly-curved tubules extending throughout the cell. Although protein and lipid biosynthesis, protein modification, vesicular transport, Ca(2+)dynamics, and protein quality control have been investigated in great detail, mechanisms that generate the distinctive architecture of the ER have been uncovered only recently. Several protein families including the reticulons and REEPs/DP1/Yop1p harbor hydrophobic hairpin domains that shape high-curvature ER tubules and mediate intramembrane protein interactions. Members of the atlastin/RHD3/Sey1p family of dynamin-related GTPases interact with the ER-shaping proteins and mediate the formation of three-way junctions responsible for the polygonal structure of the tubular ER network, with Lunapark proteins acting antagonistically. Additional classes of tubular ER proteins including some REEPs and the M1 spastin ATPase interact with the microtubule cytoskeleton. Flat ER sheets possess a different complement of proteins such as p180, CLIMP-63 and kinectin implicated in shaping, cisternal stacking and cytoskeletal interactions. The ER is also in constant motion, and numerous signaling pathways as well as interactions among cytoskeletal elements, the plasma membrane, and organelles cooperate to position and shape the ER dynamically. Finally, many proteins involved in shaping the ER network are mutated in the most common forms of hereditary spastic paraplegia, indicating a particular importance for proper ER morphology and distribution in large, highly-polarized cells such as neurons. This article is part of a Special Issue entitled: Functional and structural diversity of endoplasmic reticulum.
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Affiliation(s)
- Uma Goyal
- Cell Biology Section, Neurogenetics Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA
| | - Craig Blackstone
- Cell Biology Section, Neurogenetics Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA
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Landouré G, Zhu PP, Lourenço CM, Johnson JO, Toro C, Bricceno KV, Rinaldi C, Meilleur KG, Sangaré M, Diallo O, Pierson TM, Ishiura H, Tsuji S, Hein N, Fink JK, Stoll M, Nicholson G, Gonzalez M, Speziani F, Dürr A, Stevanin G, Biesecker LG, Accardi J, Landis DMD, Gahl WA, Traynor BJ, Marques W, Züchner S, Blackstone C, Fischbeck KH, Burnett BG. Hereditary spastic paraplegia type 43 (SPG43) is caused by mutation in C19orf12. Hum Mutat 2013; 34:1357-60. [PMID: 23857908 PMCID: PMC3819934 DOI: 10.1002/humu.22378] [Citation(s) in RCA: 69] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2012] [Accepted: 06/30/2013] [Indexed: 12/14/2022]
Abstract
We report here the genetic basis for a form of progressive hereditary spastic paraplegia (SPG43) previously described in two Malian sisters. Exome sequencing revealed a homozygous missense variant (c.187G>C; p.Ala63Pro) in C19orf12, a gene recently implicated in neurodegeneration with brain iron accumulation (NBIA). The same mutation was subsequently also found in a Brazilian family with features of NBIA, and we identified another NBIA patient with a three-nucleotide deletion (c.197_199del; p.Gly66del). Haplotype analysis revealed that the p.Ala63Pro mutations have a common origin, but MRI scans showed no brain iron deposition in the Malian SPG43 subjects. Heterologous expression of these SPG43 and NBIA variants resulted in similar alterations in the subcellular distribution of C19orf12. The SPG43 and NBIA variants reported here as well as the most common C19orf12 missense mutation reported in NBIA patients are found within a highly conserved, extended hydrophobic domain in C19orf12, underscoring the functional importance of this domain.
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Affiliation(s)
- Guida Landouré
- Service de Neurologie, Centre Hospitalier Universitaire du Point “G”, Bamako, Mali
- Neurogenetics Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland
| | - Peng-Peng Zhu
- Neurogenetics Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland
| | - Charles M. Lourenço
- Department of Neuroscience and Behaviour Sciences, School of Medicine of Ribeirão Preto, University of Sao Polo, Brazil
| | - Janel O. Johnson
- Laboratory of Neurogenetics, National Institute on Aging, National Institutes of Health, Bethesda, Maryland
| | - Camilo Toro
- NIH Undiagnosed Diseases Program, NIH Common Fund, Office of the Director, National Institutes of Health, Bethesda, Maryland
| | - Katherine V. Bricceno
- Neurogenetics Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland
| | - Carlo Rinaldi
- Neurogenetics Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland
| | - Katherine G. Meilleur
- Tissue Injury Branch, National Institute of Nursing Research, National Institutes of Health, Bethesda, Maryland
| | - Modibo Sangaré
- Neurogenetics Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland
| | - Oumarou Diallo
- Neurogenetics Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland
| | - Tyler M. Pierson
- Neurogenetics Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland
- NIH Undiagnosed Diseases Program, NIH Common Fund, Office of the Director, National Institutes of Health, Bethesda, Maryland
| | - Hiroyuki Ishiura
- Department of Neurology, Graduate School of Medicine, University of Tokyo, Tokyo, Japan
| | - Shoji Tsuji
- Department of Neurology, Graduate School of Medicine, University of Tokyo, Tokyo, Japan
| | - Nichole Hein
- Department of Neurology, University of Michigan Medical School, Ann Arbor, Michigan
| | - John K. Fink
- Department of Neurology, University of Michigan Medical School, Ann Arbor, Michigan
- Geriatric Research Education and Clinical Center, Ann Arbor Veterans Affairs Medical Center, University of Michigan, Ann Arbor, Michigan
| | - Marion Stoll
- Northcott Neuroscience Laboratory, ANZAC Research Institute, University of Sydney, Sydney, Australia
| | - Garth Nicholson
- Northcott Neuroscience Laboratory, ANZAC Research Institute, University of Sydney, Sydney, Australia
| | - Michael Gonzalez
- Department of Human Genetics and John P. Hussman Institute for Human Genomics, University of Miami Miller School of Medicine, Miami, Florida
| | - Fiorella Speziani
- Department of Human Genetics and John P. Hussman Institute for Human Genomics, University of Miami Miller School of Medicine, Miami, Florida
| | - Alexandra Dürr
- AP-HP, Department of Genetics and Cytogenetics, Pitié-Salpêtrière Hospital, 75013 Paris, France
- Centre de Recherche de l'Institut du Cerveau et de la Moelle épinière, INSERM/UPMC UMRS975, CNRS UMR7225, Pitié-Salpêtrière Hospital, 75013 Paris, France
| | - Giovanni Stevanin
- AP-HP, Department of Genetics and Cytogenetics, Pitié-Salpêtrière Hospital, 75013 Paris, France
- Centre de Recherche de l'Institut du Cerveau et de la Moelle épinière, INSERM/UPMC UMRS975, CNRS UMR7225, Pitié-Salpêtrière Hospital, 75013 Paris, France
- Ecole Pratique des Hautes Etudes (EPHE), Paris, France
| | | | | | - John Accardi
- NIH Undiagnosed Diseases Program, NIH Common Fund, Office of the Director, National Institutes of Health, Bethesda, Maryland
| | - Dennis M. D. Landis
- NIH Undiagnosed Diseases Program, NIH Common Fund, Office of the Director, National Institutes of Health, Bethesda, Maryland
| | - William A. Gahl
- NIH Undiagnosed Diseases Program, NIH Common Fund, Office of the Director, National Institutes of Health, Bethesda, Maryland
| | - Bryan J. Traynor
- Laboratory of Neurogenetics, National Institute on Aging, National Institutes of Health, Bethesda, Maryland
| | - Wilson Marques
- Department of Neuroscience and Behaviour Sciences, School of Medicine of Ribeirão Preto, University of Sao Polo, Brazil
| | - Stephan Züchner
- Department of Human Genetics and John P. Hussman Institute for Human Genomics, University of Miami Miller School of Medicine, Miami, Florida
| | - Craig Blackstone
- Neurogenetics Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland
| | - Kenneth H. Fischbeck
- Neurogenetics Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland
| | - Barrington G. Burnett
- Neurogenetics Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland
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Beetz C, Koch N, Khundadze M, Zimmer G, Nietzsche S, Hertel N, Huebner AK, Mumtaz R, Schweizer M, Dirren E, Karle KN, Irintchev A, Alvarez V, Redies C, Westermann M, Kurth I, Deufel T, Kessels MM, Qualmann B, Hübner CA. A spastic paraplegia mouse model reveals REEP1-dependent ER shaping. J Clin Invest 2013; 123:4273-82. [PMID: 24051375 DOI: 10.1172/jci65665] [Citation(s) in RCA: 69] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2012] [Accepted: 07/03/2013] [Indexed: 11/17/2022] Open
Abstract
Axonopathies are a group of clinically diverse disorders characterized by the progressive degeneration of the axons of specific neurons. In hereditary spastic paraplegia (HSP), the axons of cortical motor neurons degenerate and cause a spastic movement disorder. HSP is linked to mutations in several loci known collectively as the spastic paraplegia genes (SPGs). We identified a heterozygous receptor accessory protein 1 (REEP1) exon 2 deletion in a patient suffering from the autosomal dominantly inherited HSP variant SPG31. We generated the corresponding mouse model to study the underlying cellular pathology. Mice with heterozygous deletion of exon 2 in Reep1 displayed a gait disorder closely resembling SPG31 in humans. Homozygous exon 2 deletion resulted in the complete loss of REEP1 and a more severe phenotype with earlier onset. At the molecular level, we demonstrated that REEP1 is a neuron-specific, membrane-binding, and membrane curvature-inducing protein that resides in the ER. We further show that Reep1 expression was prominent in cortical motor neurons. In REEP1-deficient mice, these neurons showed reduced complexity of the peripheral ER upon ultrastructural analysis. Our study connects proper neuronal ER architecture to long-term axon survival.
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212
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Protrudin binds atlastins and endoplasmic reticulum-shaping proteins and regulates network formation. Proc Natl Acad Sci U S A 2013; 110:14954-9. [PMID: 23969831 DOI: 10.1073/pnas.1307391110] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
Hereditary spastic paraplegias are inherited neurological disorders characterized by progressive lower-limb spasticity and weakness. Although more than 50 genetic loci are known [spastic gait (SPG)1 to -57], over half of hereditary spastic paraplegia cases are caused by pathogenic mutations in four genes encoding proteins that function in tubular endoplasmic reticulum (ER) network formation: atlastin-1 (SPG3A), spastin (SPG4), reticulon 2 (SPG12), and receptor expression-enhancing protein 1 (SPG31). Here, we show that the SPG33 protein protrudin contains hydrophobic, intramembrane hairpin domains, interacts with tubular ER proteins, and functions in ER morphogenesis by regulating the sheet-to-tubule balance and possibly the density of tubule interconnections. Protrudin also interacts with KIF5 and harbors a Rab-binding domain, a noncanonical FYVE (Fab-1, YGL023, Vps27, and EEA1) domain, and a two phenylalanines in an acidic tract (FFAT) domain and, thus, may also function in the distribution of ER tubules via ER contacts with the plasma membrane or other organelles.
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213
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Abstract
Shape changes and topological remodeling of membranes are essential for the identity of organelles and membrane trafficking. Although all cellular membranes have common features, membranes of different organelles create unique environments that support specialized biological functions. The endoplasmic reticulum (ER) is a prime example of this specialization, as its lipid bilayer forms an interconnected system of cisternae, vesicles, and tubules, providing a highly compartmentalized structure for a multitude of biochemical processes. A variety of peripheral and integral membrane proteins that facilitate membrane curvature generation, fission, and/or fusion have been identified over the past two decades. Among these, the dynamin-related proteins (DRPs) have emerged as key players. Here, we review recent advances in our functional and molecular understanding of fusion DRPs, exemplified by atlastin, an ER-resident DRP that controls ER structure, function, and signaling.
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Affiliation(s)
- James A McNew
- Department of Biochemistry and Cell Biology, Rice University, Houston, Texas 77005;
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214
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Klein CJ, Duan X, Shy ME. Inherited neuropathies: clinical overview and update. Muscle Nerve 2013; 48:604-22. [PMID: 23801417 DOI: 10.1002/mus.23775] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/31/2013] [Indexed: 11/06/2022]
Abstract
Inherited neuropathy is a group of common neurologic disorders with heterogeneous clinical presentations and genetic causes. Detailed neuromuscular evaluations, including nerve conduction studies, laboratory testing, and histopathologic examination, can assist in identification of the inherited component beyond family history. Genetic testing increasingly enables definitive diagnosis of specific inherited neuropathies. Diagnosis, however, is often complex, and neurologic disability may have both genetic and acquired components in individual patients. The decision of which genetic test to order or whether to order genetic tests is often complicated, and the strategies to maximize the value of testing are evolving. Apart from rare inherited metabolic neuropathies, treatment approaches remain largely supportive. We provide a clinical update of the various types of inherited neuropathies, their differential diagnoses, and distinguishing clinical features (where available). A framework is provided for clinical evaluations, including the inheritance assessment, electrophysiologic examinations, and specific genetic tests.
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Affiliation(s)
- Christopher J Klein
- Department of Neurology, Mayo Clinic, 200 First Street SW, Rochester, Minnesota, 55905, USA; Department of Medical Genetics, Mayo Clinic, Rochester, Minnesota, USA
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215
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Klemm RW, Norton JP, Cole RA, Li CS, Park SH, Crane MM, Li L, Jin D, Boye-Doe A, Liu TY, Shibata Y, Lu H, Rapoport TA, Farese RV, Blackstone C, Guo Y, Mak HY. A conserved role for atlastin GTPases in regulating lipid droplet size. Cell Rep 2013; 3:1465-75. [PMID: 23684613 DOI: 10.1016/j.celrep.2013.04.015] [Citation(s) in RCA: 112] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2012] [Revised: 02/19/2013] [Accepted: 04/17/2013] [Indexed: 12/22/2022] Open
Abstract
Lipid droplets (LDs) are the major fat storage organelles in eukaryotic cells, but how their size is regulated is unknown. Using genetic screens in C. elegans for LD morphology defects in intestinal cells, we found that mutations in atlastin, a GTPase required for homotypic fusion of endoplasmic reticulum (ER) membranes, cause not only ER morphology defects, but also a reduction in LD size. Similar results were obtained after depletion of atlastin or expression of a dominant-negative mutant, whereas overexpression of atlastin had the opposite effect. Atlastin depletion in Drosophila fat bodies also reduced LD size and decreased triglycerides in whole animals, sensitizing them to starvation. In mammalian cells, co-overexpression of atlastin-1 and REEP1, a paralog of the ER tubule-shaping protein DP1/REEP5, generates large LDs. The effect of atlastin-1 on LD size correlates with its activity to promote membrane fusion in vitro. Our results indicate that atlastin-mediated fusion of ER membranes is important for LD size regulation.
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Affiliation(s)
- Robin W Klemm
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA
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216
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Ryder PV, Vistein R, Gokhale A, Seaman MN, Puthenveedu MA, Faundez V. The WASH complex, an endosomal Arp2/3 activator, interacts with the Hermansky-Pudlak syndrome complex BLOC-1 and its cargo phosphatidylinositol-4-kinase type IIα. Mol Biol Cell 2013; 24:2269-84. [PMID: 23676666 PMCID: PMC3708732 DOI: 10.1091/mbc.e13-02-0088] [Citation(s) in RCA: 70] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
The WASH complex, an endosomal activator of the Arp2/3 complex involved in branched actin polymerization, is identified as a new factor in vesicle traffic mediated by the Hermansky–Pudlak syndrome complex BLOC-1. Vesicle biogenesis machinery components such as coat proteins can interact with the actin cytoskeleton for cargo sorting into multiple pathways. It is unknown, however, whether these interactions are a general requirement for the diverse endosome traffic routes. In this study, we identify actin cytoskeleton regulators as previously unrecognized interactors of complexes associated with the Hermansky–Pudlak syndrome. Two complexes mutated in the Hermansky–Pudlak syndrome, adaptor protein complex-3 and biogenesis of lysosome-related organelles complex-1 (BLOC-1), interact with and are regulated by the lipid kinase phosphatidylinositol-4-kinase type IIα (PI4KIIα). We therefore hypothesized that PI4KIIα interacts with novel regulators of these complexes. To test this hypothesis, we immunoaffinity purified PI4KIIα from isotope-labeled cell lysates to quantitatively identify interactors. Strikingly, PI4KIIα isolation preferentially coenriched proteins that regulate the actin cytoskeleton, including guanine exchange factors for Rho family GTPases such as RhoGEF1 and several subunits of the WASH complex. We biochemically confirmed several of these PI4KIIα interactions. Of importance, BLOC-1 complex, WASH complex, RhoGEF1, or PI4KIIα depletions altered the content and/or subcellular distribution of the BLOC-1–sensitive cargoes PI4KIIα, ATP7A, and VAMP7. We conclude that the Hermansky–Pudlak syndrome complex BLOC-1 and its cargo PI4KIIα interact with regulators of the actin cytoskeleton.
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Affiliation(s)
- P V Ryder
- Department of Cell Biology, Emory University, Atlanta, GA 30322, USA
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217
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Chen S, Novick P, Ferro-Novick S. ER structure and function. Curr Opin Cell Biol 2013; 25:428-33. [PMID: 23478217 DOI: 10.1016/j.ceb.2013.02.006] [Citation(s) in RCA: 139] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2013] [Accepted: 02/13/2013] [Indexed: 12/31/2022]
Abstract
The ER forms a contiguous structure of interconnected sheets and tubules that spreads from the nuclear envelope to the cell cortex. Through its attachment to the cytoskeleton, the ER undergoes dynamic rearrangements, such as tubule extension and movement. ER shaping proteins (reticulons and DP1/Yop1p) play key roles in generating and maintaining the unique reticular morphology of the ER. Atlastin and its yeast homologue, Sey1p, mediate homotypic ER membrane fusion, which leads to the formation of new three-way junctions within the polygonal network. At these junctions, the Lunapark protein, Lnp1p, works in conjunction with the reticulons, DP1/Yop1p, and in antagonism to atlastin/Sey1p to maintain the network in a dynamic equilibrium. Defects in ER morphology have been linked to certain neurological disorders.
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Affiliation(s)
- Shuliang Chen
- Department of Cellular and Molecular Medicine, Howard Hughes, Medical Institute, University of California at San Diego, La Jolla, CA 92093-0668, USA
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218
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Gonzalez M, Nampoothiri S, Kornblum C, Oteyza AC, Walter J, Konidari I, Hulme W, Speziani F, Schöls L, Züchner S, Schüle R. Mutations in phospholipase DDHD2 cause autosomal recessive hereditary spastic paraplegia (SPG54). Eur J Hum Genet 2013; 21:1214-8. [PMID: 23486545 DOI: 10.1038/ejhg.2013.29] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2012] [Revised: 01/18/2013] [Accepted: 01/22/2013] [Indexed: 11/09/2022] Open
Abstract
Hereditary spastic paraplegias (HSP) are a genetically heterogeneous group of disorders characterized by a distal axonopathy of the corticospinal tract motor neurons leading to progressive lower limb spasticity and weakness. Intracellular membrane trafficking, mitochondrial dysfunction and myelin formation are key functions involved in HSP pathogenesis. Only recently defects in metabolism of complex lipids have been implicated in a number of HSP subtypes. Mutations in the 23 known autosomal recessive HSP genes explain less than half of autosomal recessive HSP cases. To identify novel autosomal recessive HSP disease genes, exome sequencing was performed in 79 index cases with autosomal recessive forms of HSP. Resulting variants were filtered and intersected between families to allow identification of new disease genes. We identified two deleterious mutations in the phospholipase DDHD2 gene in two families with complicated HSP. The phenotype is characterized by early onset of spastic paraplegia, mental retardation, short stature and dysgenesis of the corpus callosum. Phospholipase DDHD2 is involved in intracellular membrane trafficking at the golgi/ endoplasmic reticulum interface and has been shown to possess phospholipase A1 activity in vitro. Discovery of DDHD2 mutations in HSP might therefore provide a link between two key pathogenic themes in HSP: membrane trafficking and lipid metabolism.
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Affiliation(s)
- Michael Gonzalez
- Hussman Institute for Human Genomics, University of Miami Miller School of Medicine, Miami, FL, USA
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219
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Kong XF, Bousfiha A, Rouissi A, Itan Y, Abhyankar A, Bryant V, Okada S, Ailal F, Bustamante J, Casanova JL, Hirst J, Boisson-Dupuis S. A novel homozygous p.R1105X mutation of the AP4E1 gene in twins with hereditary spastic paraplegia and mycobacterial disease. PLoS One 2013; 8:e58286. [PMID: 23472171 PMCID: PMC3589270 DOI: 10.1371/journal.pone.0058286] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2012] [Accepted: 02/01/2013] [Indexed: 12/22/2022] Open
Abstract
We report identical twins with intellectual disability, progressive spastic paraplegia and short stature, born to a consanguineous family. Intriguingly, both children presented with lymphadenitis caused by the live Bacillus Calmette-Guérin (BCG) vaccine. Two syndromes – hereditary spastic paraplegia (HSP) and mycobacterial disease – thus occurred simultaneously. Whole-exome sequencing (WES) revealed a homozygous nonsense mutation (p.R1105X) of the AP4E1 gene, which was confirmed by Sanger sequencing. The p.R1105X mutation has no effect on AP4E1 mRNA levels, but results in lower levels of AP-4ε protein and of the other components of the AP-4 complex, as shown by western blotting, immunoprecipitation and immunofluorescence. Thus, the C-terminal part of the AP-4ε subunit plays an important role in maintaining the integrity of the AP-4 complex. No abnormalities of the IL-12/IFN-γ axis or oxidative burst pathways were identified. In conclusion, we identified twins with autosomal recessive AP-4 deficiency associated with HSP and mycobacterial disease, suggesting that AP-4 may play important role in the neurological and immunological systems.
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Affiliation(s)
- Xiao-Fei Kong
- St. Giles Laboratory of Human Genetics of Infectious Diseases, Rockefeller Branch, The Rockefeller University, New York, New York, USA
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220
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Magnoni R, Palmfeldt J, Christensen JH, Sand M, Maltecca F, Corydon TJ, West M, Casari G, Bross P. Late onset motoneuron disorder caused by mitochondrial Hsp60 chaperone deficiency in mice. Neurobiol Dis 2013; 54:12-23. [PMID: 23466696 DOI: 10.1016/j.nbd.2013.02.012] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2012] [Revised: 01/29/2013] [Accepted: 02/22/2013] [Indexed: 01/07/2023] Open
Abstract
Cells rely on efficient protein quality control systems (PQCs) to maintain proper activity of mitochondrial proteins. As part of this system, the mitochondrial chaperone Hsp60 assists folding of matrix proteins and it is an essential protein in all organisms. Mutations in Hspd1, the gene encoding Hsp60, are associated with two human inherited diseases of the nervous system, a dominantly inherited form of spastic paraplegia (SPG13) and an autosomal recessively inherited white matter disorder termed MitCHAP60 disease. Although the connection between mitochondrial failure and neurodegeneration is well known in many neurodegenerative disorders, such as Huntington's disease, Parkinson's disease, and hereditary spastic paraplegia, the molecular basis of the neurodegeneration associated with these diseases is still ill-defined. Here, we investigate mice heterozygous for a knockout allele of the Hspd1 gene encoding Hsp60. Our results demonstrate that Hspd1 haploinsufficiency is sufficient to cause a late onset and slowly progressive deficit in motor functions in mice. We furthermore emphasize the crucial role of the Hsp60 chaperone in mitochondrial function by showing that the motor phenotype is associated with morphological changes of mitochondria, deficient ATP synthesis, and in particular, a defect in the assembly of the respiratory chain complex III in neuronal tissues. In the current study, we propose that our heterozygous Hsp60 mouse model is a valuable model system for the investigation of the link between mitochondrial dysfunction and neurodegeneration.
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Affiliation(s)
- Raffaella Magnoni
- Research Unit for Molecular Medicine, Department of Clinical Medicine, Health Aarhus University Hospital and Aarhus University, Aarhus, Denmark.
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221
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Abstract
SOLUTIONS TO THE MAJOR RIDDLES IN MOVEMENT DISORDERS ARE APPEARING AT A BREATHTAKING PACE: 1) loss-of-function mutations in PRRT2, which encodes a cell surface protein expressed in neurons, have been found in many patients with paroxysmal kinesigenic dyskinesias; 2) mutations in CIZ1, which encodes a protein involved in cell-cycle control at the G1-S checkpoint, have been identified in a small percentage of patients with cervical dystonia; and 3) finally, after many years of genetics and identification of more than 25 disease-associated genes, cellular studies related to the pathobiology of hereditary spastic paraplegia are converging on defects in modeling the endoplasmic reticulum and membrane trafficking. On the treatment front, the distinctive syndromes of faciobrachial dystonic seizures with anti-LRI1 antibodies and anti-N-methyl-d-aspartic acid encephalitis with orobuccolingual dyskinesias are becoming increasingly recognized by clinicians as imminently treatable conditions. Also on the treatment front, the first phase I trial of MRI-guided high-intensity focused ultrasound for essential tremor has been completed and intraoperative MRI is currently being used to place electrodes in the brains of patients with medically intractable dystonia. Definitive etiologies and efficacious treatments for non-Parkinson disease movement disorders are no longer wishful thinking.
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Affiliation(s)
- Mark S Ledoux
- Department of Neurology, University of Tennessee Health Science Center, Memphis
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222
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Oz-Levi D, Ben-Zeev B, Ruzzo EK, Hitomi Y, Gelman A, Pelak K, Anikster Y, Reznik-Wolf H, Bar-Joseph I, Olender T, Alkelai A, Weiss M, Ben-Asher E, Ge D, Shianna KV, Elazar Z, Goldstein DB, Pras E, Lancet D. Mutation in TECPR2 reveals a role for autophagy in hereditary spastic paraparesis. Am J Hum Genet 2012. [PMID: 23176824 DOI: 10.1016/j.ajhg.2012.09.015] [Citation(s) in RCA: 117] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
We studied five individuals from three Jewish Bukharian families affected by an apparently autosomal-recessive form of hereditary spastic paraparesis accompanied by severe intellectual disability, fluctuating central hypoventilation, gastresophageal reflux disease, wake apnea, areflexia, and unique dysmorphic features. Exome sequencing identified one homozygous variant shared among all affected individuals and absent in controls: a 1 bp frameshift TECPR2 deletion leading to a premature stop codon and predicting significant degradation of the protein. TECPR2 has been reported as a positive regulator of autophagy. We thus examined the autophagy-related fate of two key autophagic proteins, SQSTM1 (p62) and MAP1LC3B (LC3), in skin fibroblasts of an affected individual, as compared to a healthy control, and found that both protein levels were decreased and that there was a more pronounced decrease in the lipidated form of LC3 (LC3II). siRNA knockdown of TECPR2 showed similar changes, consistent with aberrant autophagy. Our results are strengthened by the fact that autophagy dysfunction has been implicated in a number of other neurodegenerative diseases. The discovered TECPR2 mutation implicates autophagy, a central intracellular mechanism, in spastic paraparesis.
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Affiliation(s)
- Danit Oz-Levi
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 76100, Israel.
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223
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Hirst J, Irving C, Borner GH. Adaptor Protein Complexes AP-4 and AP-5: New Players in Endosomal Trafficking and Progressive Spastic Paraplegia. Traffic 2012; 14:153-64. [DOI: 10.1111/tra.12028] [Citation(s) in RCA: 105] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2012] [Revised: 11/15/2012] [Accepted: 11/21/2012] [Indexed: 12/16/2022]
Affiliation(s)
- Jennifer Hirst
- Cambridge Institute for Medical Research; University of Cambridge; Wellcome Trust/MRC Building; Cambridge; CB2 0XY; UK
| | - Carol Irving
- MRC Centre for Developmental Neurobiology; King's College; London; SE1 1UL; UK
| | - Georg H.H. Borner
- Cambridge Institute for Medical Research; University of Cambridge; Wellcome Trust/MRC Building; Cambridge; CB2 0XY; UK
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224
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Lee S, Chang J, Renvoisé B, Tipirneni A, Yang S, Blackstone C. MITD1 is recruited to midbodies by ESCRT-III and participates in cytokinesis. Mol Biol Cell 2012; 23:4347-61. [PMID: 23015756 PMCID: PMC3496609 DOI: 10.1091/mbc.e12-04-0292] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The MITD1 is an largely uncharacterized MIT domain–containing protein. This protein localizes to the midbody, with its recruitment dependent on selective interactions with a number of ESCRT-III proteins. These interactions are required for proper abscission. Diverse cellular processes, including multivesicular body formation, cytokinesis, and viral budding, require the sequential functions of endosomal sorting complexes required for transport (ESCRTs) 0 to III. Of these multiprotein complexes, ESCRT-III in particular plays a key role in mediating membrane fission events by forming large, ring-like helical arrays. A number of proteins playing key effector roles, most notably the ATPase associated with diverse cellular activities protein VPS4, harbor present in microtubule-interacting and trafficking molecules (MIT) domains comprising asymmetric three-helical bundles, which interact with helical MIT-interacting motifs in ESCRT-III subunits. Here we assess comprehensively the ESCRT-III interactions of the MIT-domain family member MITD1 and identify strong interactions with charged multivesicular body protein 1B (CHMP1B), CHMP2A, and increased sodium tolerance-1 (IST1). We show that these ESCRT-III subunits are important for the recruitment of MITD1 to the midbody and that MITD1 participates in the abscission phase of cytokinesis. MITD1 also dimerizes through its C-terminal domain. Both types of interactions appear important for the role of MITD1 in negatively regulating the interaction of IST1 with VPS4. Because IST1 binding in turn regulates VPS4, MITD1 may function through downstream effects on the activity of VPS4, which plays a critical role in the processing and remodeling of ESCRT filaments in abscission.
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Affiliation(s)
- Seongju Lee
- Cell Biology Section, Neurogenetics Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA
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225
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Renvoisé B, Stadler J, Singh R, Bakowska JC, Blackstone C. Spg20-/- mice reveal multimodal functions for Troyer syndrome protein spartin in lipid droplet maintenance, cytokinesis and BMP signaling. Hum Mol Genet 2012; 21:3604-18. [PMID: 22619377 DOI: 10.1093/hmg/dds191] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Hereditary spastic paraplegias (HSPs; SPG1-48) are inherited neurological disorders characterized by lower extremity spasticity and weakness. Loss-of-function mutations in the SPG20 gene encoding spartin cause autosomal recessive Troyer syndrome (SPG20), which has additional features of short stature, cognitive deficits and distal amyotrophy. To identify cellular impairments underlying Troyer syndrome, we generated Spg20-/- mice, which exhibit progressive gait defects. Although gross central nervous system pathology appeared largely normal, cerebral cortical neurons cultured from neonatal Spg20-/- mice exhibited increased axon branching, a phenotype suppressed by reintroducing spartin and which required its interaction with the endosomal sorting complex required for transport (ESCRT)-III protein IST1. Analysis of the bone morphogenetic protein (BMP) signaling pathway in Spg20-/- embryonic fibroblasts indicated that Smad1/5 phosphorylation is modestly elevated, possibly due to alterations in BMP receptor trafficking. Cytokinesis was impaired in embryonic fibroblasts cultured from Spg20-/- mice, and binucleated chondrocytes were prominent in epiphyseal growth plates of bones in Spg20-/- mice, perhaps explaining the short stature of patients. Finally, adipose tissue from Spg20-/- female mice exhibited increased lipid droplet (LD) numbers and alterations in perilipin levels, supporting a role for spartin in LD maintenance. Taken together, our results support multimodal functions for spartin that provide important insights into HSP pathogenesis.
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Affiliation(s)
- Benoît Renvoisé
- Cell Biology Section, Neurogenetics Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA
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