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Maor G, Dubreuil RR, Feany MB. α-synuclein promotes neuronal dysfunction and death by disrupting the binding of ankyrin to ß-spectrin. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.06.02.543481. [PMID: 37333277 PMCID: PMC10274672 DOI: 10.1101/2023.06.02.543481] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/20/2023]
Abstract
α-synuclein plays a key role in the pathogenesis of Parkinson's disease and related disorders, but critical interacting partners and molecular mechanisms mediating neurotoxicity are incompletely understood. We show that α-synuclein binds directly to ß-spectrin. Using males and females in a Drosophila model of α-synuclein-related disorders we demonstrate that ß-spectrin is critical for α-synuclein neurotoxicity. Further, the ankyrin binding domain of ß-spectrin is required for α-synuclein binding and neurotoxicity. A key plasma membrane target of ankyrin, Na+/K+ ATPase, is mislocalized when human α-synuclein is expressed in Drosophila. Accordingly, membrane potential is depolarized in α-synuclein transgenic fly brains. We examine the same pathway in human neurons and find that Parkinson's disease patient-derived neurons with a triplication of the α-synuclein locus show disruption of the spectrin cytoskeleton, mislocalization of ankyrin and Na+/K+ ATPase, and membrane potential depolarization. Our findings define a specific molecular mechanism by which elevated levels of α-synuclein in Parkinson's disease and related α-synucleinopathies leads to neuronal dysfunction and death.
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Affiliation(s)
- Gali Maor
- Department of Pathology, Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA
| | - Ronald R. Dubreuil
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, Illinois 60607
| | - Mel B. Feany
- Department of Pathology, Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA
- Aligning Science Across Parkinson’s (ASAP) Collaborative Research Network, Chevy Chase, MD, 20815
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2
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Maor G, Dubreuil RR, Feany MB. α-Synuclein Promotes Neuronal Dysfunction and Death by Disrupting the Binding of Ankyrin to β-Spectrin. J Neurosci 2023; 43:1614-1626. [PMID: 36653193 PMCID: PMC10008058 DOI: 10.1523/jneurosci.1922-22.2022] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2022] [Revised: 11/30/2022] [Accepted: 12/08/2022] [Indexed: 01/20/2023] Open
Abstract
α-Synuclein plays a key role in the pathogenesis of Parkinson's disease and related disorders, but critical interacting partners and molecular mechanisms mediating neurotoxicity are incompletely understood. We show that α-synuclein binds directly to β-spectrin. Using males and females in a Drosophila model of α-synuclein-related disorders, we demonstrate that β-spectrin is critical for α-synuclein neurotoxicity. Further, the ankyrin binding domain of β-spectrin is required for α-synuclein binding and neurotoxicity. A key plasma membrane target of ankyrin, Na+/K+ ATPase, is mislocalized when human α-synuclein is expressed in Drosophila Accordingly, membrane potential is depolarized in α-synuclein transgenic fly brains. We examine the same pathway in human neurons and find that Parkinson's disease patient-derived neurons with a triplication of the α-synuclein locus show disruption of the spectrin cytoskeleton, mislocalization of ankyrin and Na+/K+ ATPase, and membrane potential depolarization. Our findings define a specific molecular mechanism by which elevated levels of α-synuclein in Parkinson's disease and related α-synucleinopathies lead to neuronal dysfunction and death.SIGNIFICANCE STATEMENT The small synaptic vesicle associate protein α-synuclein plays a critical role in the pathogenesis of Parkinson's disease and related disorders, but the disease-relevant binding partners of α-synuclein and proximate pathways critical for neurotoxicity require further definition. We show that α-synuclein binds directly to β-spectrin, a key cytoskeletal protein required for localization of plasma membrane proteins and maintenance of neuronal viability. Binding of α-synuclein to β-spectrin alters the organization of the spectrin-ankyrin complex, which is critical for localization and function of integral membrane proteins, including Na+/K+ ATPase. These finding outline a previously undescribed mechanism of α-synuclein neurotoxicity and thus suggest potential new therapeutic approaches in Parkinson's disease and related disorders.
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Affiliation(s)
- Gali Maor
- Department of Pathology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115
| | - Ronald R Dubreuil
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, Illinois 60607
| | - Mel B Feany
- Department of Pathology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115
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Deng H, Yang L, Wen P, Lei H, Blount P, Pan D. Spectrin couples cell shape, cortical tension, and Hippo signaling in retinal epithelial morphogenesis. J Cell Biol 2020; 219:133846. [PMID: 32328630 PMCID: PMC7147103 DOI: 10.1083/jcb.201907018] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2019] [Revised: 11/26/2019] [Accepted: 01/17/2020] [Indexed: 01/05/2023] Open
Abstract
Although extracellular force has a profound effect on cell shape, cytoskeleton tension, and cell proliferation through the Hippo signaling effector Yki/YAP/TAZ, how intracellular force regulates these processes remains poorly understood. Here, we report an essential role for spectrin in specifying cell shape by transmitting intracellular actomyosin force to cell membrane. While activation of myosin II in Drosophila melanogaster pupal retina leads to increased cortical tension, apical constriction, and Yki-mediated hyperplasia, spectrin mutant cells, despite showing myosin II activation and Yki-mediated hyperplasia, paradoxically display decreased cortical tension and expanded apical area. Mechanistically, we show that spectrin is required for tethering cortical F-actin to cell membrane domains outside the adherens junctions (AJs). Thus, in the absence of spectrin, the weakened attachment of cortical F-actin to plasma membrane results in a failure to transmit actomyosin force to cell membrane, causing an expansion of apical surfaces. These results uncover an essential mechanism that couples cell shape, cortical tension, and Hippo signaling and highlight the importance of non–AJ membrane domains in dictating cell shape in tissue morphogenesis.
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Affiliation(s)
- Hua Deng
- Department of Physiology, Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, TX
| | - Limin Yang
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, TX
| | - Pei Wen
- Department of Physiology, Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, TX
| | - Huiyan Lei
- Department of Physiology, Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, TX
| | - Paul Blount
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, TX
| | - Duojia Pan
- Department of Physiology, Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, TX
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Luo G, Zhao L, Xu X, Qin Y, Huang L, Su Y, Zheng W, Yan Q. Integrated dual RNA-seq and dual iTRAQ of infected tissue reveals the functions of a diguanylate cyclase gene of Pseudomonas plecoglossicida in host-pathogen interactions with Epinephelus coioides. FISH & SHELLFISH IMMUNOLOGY 2019; 95:481-490. [PMID: 31698069 DOI: 10.1016/j.fsi.2019.11.008] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/05/2019] [Revised: 10/30/2019] [Accepted: 11/02/2019] [Indexed: 06/10/2023]
Abstract
The interactions between host and pathogen is exceedingly complex, which involves alterations at multiple molecular layers. However, research to simultaneously monitor the alterations of transcriptome and proteome between a bacterial pathogen and aquatic animal host through integrated dual RNA-seq and dual iTRAQ of tissue during infection is currently lacking. The important role of a diguanylate cyclase gene (L321_RS15240) in pathogenicity of Pseudomonas plecoglossicida against Epinephelus coioides was suggested by previous dual RNA-seq of our lab. Then L321_RS15240-RNAi strains of P. plecoglossicida were constructed with pCM130/tac, and the mutant with the best silencing effect was selected for follow-up study. The RNAi of L321_RS15240 resulted in a significant decrease in bacterial virulence of P. plecoglossicida. The E. coioides spleens infected by wild type strain or L321_RS15240-RNAi strain of P. plecoglossicida were subjected to dual RNA-seq and dual iTRAQ, respectively. The results showed that: RNAi of L321_RS15240 led to 1)alterations of host transcriptome associated with complement and coagulation cascades, ribosome, arginine and proline metabolism, and oxidative phosphorylation; 2)high expression of host proteins which related to phagosome and metabolism responses (metabolism of glutathione, amino sugar and nucleotide sugar); 3)the highly differentially expression of host lncRNAs and miRNAs. The differentially expressed proteins and mRNAs of pathogen were different after infection, but the functions of these proteins and mRNAs were mainly related to metabolism and virulence. This study provides a new insight to comprehensively understand the gene functions of pathogens and hosts at multiple molecular layers during in vivo infection.
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Affiliation(s)
- Gang Luo
- Fisheries College, Jimei University, Xiamen, Fujian, 361021, PR China; Hubei Key Laboratory of Cell Homeostasis, College of Life Sciences, Wuhan University, Wuhan, Hubei, 430072, PR China
| | - Lingmin Zhao
- Fisheries College, Jimei University, Xiamen, Fujian, 361021, PR China
| | - Xiaojin Xu
- Fisheries College, Jimei University, Xiamen, Fujian, 361021, PR China
| | - Yingxue Qin
- Fisheries College, Jimei University, Xiamen, Fujian, 361021, PR China
| | - Lixing Huang
- Fisheries College, Jimei University, Xiamen, Fujian, 361021, PR China
| | - Yongquan Su
- State Key Laboratory of Large Yellow Croaker Breeding, Ningde, Fujian, 352000, PR China
| | - Weiqiang Zheng
- State Key Laboratory of Large Yellow Croaker Breeding, Ningde, Fujian, 352000, PR China
| | - Qingpi Yan
- Fisheries College, Jimei University, Xiamen, Fujian, 361021, PR China; State Key Laboratory of Large Yellow Croaker Breeding, Ningde, Fujian, 352000, PR China.
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5
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Ugrankar R, Bowerman J, Hariri H, Chandra M, Chen K, Bossanyi MF, Datta S, Rogers S, Eckert KM, Vale G, Victoria A, Fresquez J, McDonald JG, Jean S, Collins BM, Henne WM. Drosophila Snazarus Regulates a Lipid Droplet Population at Plasma Membrane-Droplet Contacts in Adipocytes. Dev Cell 2019; 50:557-572.e5. [PMID: 31422916 PMCID: PMC7446143 DOI: 10.1016/j.devcel.2019.07.021] [Citation(s) in RCA: 33] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2018] [Revised: 04/22/2019] [Accepted: 07/17/2019] [Indexed: 01/22/2023]
Abstract
Adipocytes store nutrients as lipid droplets (LDs), but how they organize their LD stores to balance lipid uptake, storage, and mobilization remains poorly understood. Here, using Drosophila fat body (FB) adipocytes, we characterize spatially distinct LD populations that are maintained by different lipid pools. We identify peripheral LDs (pLDs) that make close contact with the plasma membrane (PM) and are maintained by lipophorin-dependent lipid trafficking. pLDs are distinct from larger cytoplasmic medial LDs (mLDs), which are maintained by FASN1-dependent de novo lipogenesis. We find that sorting nexin CG1514 or Snazarus (Snz) associates with pLDs and regulates LD homeostasis at ER-PM contact sites. Loss of SNZ perturbs pLD organization, whereas Snz over-expression drives LD expansion, triacylglyceride production, starvation resistance, and lifespan extension through a DESAT1-dependent pathway. We propose that Drosophila adipocytes maintain spatially distinct LD populations and identify Snz as a regulator of LD organization and inter-organelle crosstalk.
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Affiliation(s)
- Rupali Ugrankar
- Department of Cell Biology, UT Southwestern Medical Center, 6000 Harry Hines Boulevard, Dallas, TX 75390, USA
| | - Jade Bowerman
- Department of Cell Biology, UT Southwestern Medical Center, 6000 Harry Hines Boulevard, Dallas, TX 75390, USA
| | - Hanaa Hariri
- Department of Cell Biology, UT Southwestern Medical Center, 6000 Harry Hines Boulevard, Dallas, TX 75390, USA
| | - Mintu Chandra
- Institute for Molecular Bioscience, the University of Queensland, St. Lucia, QLD 4072, Australia
| | - Kevin Chen
- Institute for Molecular Bioscience, the University of Queensland, St. Lucia, QLD 4072, Australia
| | - Marie-France Bossanyi
- Department of Anatomy and Cell Biology, University of Sherbrooke, 2500 Boulevard de l'Universite, Sherbrooke, QC J1K 2R1, Canada
| | - Sanchari Datta
- Department of Cell Biology, UT Southwestern Medical Center, 6000 Harry Hines Boulevard, Dallas, TX 75390, USA
| | - Sean Rogers
- Department of Cell Biology, UT Southwestern Medical Center, 6000 Harry Hines Boulevard, Dallas, TX 75390, USA
| | - Kaitlyn M Eckert
- Center for Human Nutrition, UT Southwestern Medical Center, Dallas, TX 75390, USA
| | - Gonçalo Vale
- Center for Human Nutrition, UT Southwestern Medical Center, Dallas, TX 75390, USA
| | - Alexia Victoria
- Department of Cell Biology, UT Southwestern Medical Center, 6000 Harry Hines Boulevard, Dallas, TX 75390, USA
| | | | - Jeffrey G McDonald
- Center for Human Nutrition, UT Southwestern Medical Center, Dallas, TX 75390, USA; Department of Molecular Genetics, UT Southwestern Medical Center, Dallas, TX 75390, USA
| | - Steve Jean
- Department of Anatomy and Cell Biology, University of Sherbrooke, 2500 Boulevard de l'Universite, Sherbrooke, QC J1K 2R1, Canada
| | - Brett M Collins
- Institute for Molecular Bioscience, the University of Queensland, St. Lucia, QLD 4072, Australia
| | - W Mike Henne
- Department of Cell Biology, UT Southwestern Medical Center, 6000 Harry Hines Boulevard, Dallas, TX 75390, USA.
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Higham JP, Malik BR, Buhl E, Dawson JM, Ogier AS, Lunnon K, Hodge JJL. Alzheimer's Disease Associated Genes Ankyrin and Tau Cause Shortened Lifespan and Memory Loss in Drosophila. Front Cell Neurosci 2019; 13:260. [PMID: 31244615 PMCID: PMC6581016 DOI: 10.3389/fncel.2019.00260] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2019] [Accepted: 05/23/2019] [Indexed: 12/21/2022] Open
Abstract
Alzheimer's disease (AD) is the most common form of dementia and is characterized by intracellular neurofibrillary tangles of hyperphosphorylated Tau, including the 0N4R isoform and accumulation of extracellular amyloid beta (Aβ) plaques. However, less than 5% of AD cases are familial, with many additional risk factors contributing to AD including aging, lifestyle, the environment and epigenetics. Recent epigenome-wide association studies (EWAS) of AD have identified a number of loci that are differentially methylated in the AD cortex. Indeed, hypermethylation and reduced expression of the Ankyrin 1 (ANK1) gene in AD has been reported in the cortex in numerous different post-mortem brain cohorts. Little is known about the normal function of ANK1 in the healthy brain, nor the role it may play in AD. We have generated Drosophila models to allow us to functionally characterize Drosophila Ank2, the ortholog of human ANK1 and to determine its interaction with human Tau and Aβ. We show expression of human Tau 0N4R or the oligomerizing Aβ 42 amino acid peptide caused shortened lifespan, degeneration, disrupted movement, memory loss, and decreased excitability of memory neurons with co-expression tending to make the pathology worse. We find that Drosophila with reduced neuronal Ank2 expression have shortened lifespan, reduced locomotion, reduced memory and reduced neuronal excitability similar to flies overexpressing either human Tau 0N4R or Aβ42. Therefore, we show that the mis-expression of Ank2 can drive disease relevant processes and phenocopy some features of AD. Therefore, we propose targeting human ANK1 may have therapeutic potential. This represents the first study to characterize an AD-relevant gene nominated from EWAS.
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Affiliation(s)
- James P. Higham
- School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, United Kingdom
| | - Bilal R. Malik
- School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, United Kingdom
| | - Edgar Buhl
- School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, United Kingdom
| | - Jennifer M. Dawson
- School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, United Kingdom
| | - Anna S. Ogier
- School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, United Kingdom
| | - Katie Lunnon
- University of Exeter Medical School, University of Exeter, Exeter, United Kingdom
| | - James J. L. Hodge
- School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, United Kingdom
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Duan R, Kim JH, Shilagardi K, Schiffhauer ES, Lee DM, Son S, Li S, Thomas C, Luo T, Fletcher DA, Robinson DN, Chen EH. Spectrin is a mechanoresponsive protein shaping fusogenic synapse architecture during myoblast fusion. Nat Cell Biol 2018; 20:688-698. [PMID: 29802406 PMCID: PMC6397639 DOI: 10.1038/s41556-018-0106-3] [Citation(s) in RCA: 31] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2017] [Accepted: 04/18/2018] [Indexed: 12/24/2022]
Abstract
Spectrin is a membrane skeletal protein best known for its structural role in maintaining cell shape and protecting cells from mechanical damage. Here, we report that α/βH-spectrin (βH is also called karst) dynamically accumulates and dissolves at the fusogenic synapse between fusing Drosophila muscle cells, where an attacking fusion partner invades its receiving partner with actin-propelled protrusions to promote cell fusion. Using genetics, cell biology, biophysics and mathematical modelling, we demonstrate that spectrin exhibits a mechanosensitive accumulation in response to shear deformation, which is highly elevated at the fusogenic synapse. The transiently accumulated spectrin network functions as a cellular fence to restrict the diffusion of cell-adhesion molecules and a cellular sieve to constrict the invasive protrusions, thereby increasing the mechanical tension of the fusogenic synapse to promote cell membrane fusion. Our study reveals a function of spectrin as a mechanoresponsive protein and has general implications for understanding spectrin function in dynamic cellular processes.
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Affiliation(s)
- Rui Duan
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, MD, USA
- Laboratory of Regenerative Medicine in Sports Science, School of Sports Science, South China Normal University, Guangzhou, China
| | - Ji Hoon Kim
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Khurts Shilagardi
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Eric S Schiffhauer
- Department of Cell Biology, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Donghoon M Lee
- Department of Molecular Biology, UT Southwestern Medical Center, Dallas, TX, USA
| | - Sungmin Son
- Department of Bioengineering, University of California, Berkeley, Berkeley, CA, USA
| | - Shuo Li
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Claire Thomas
- Departments of Biology and of Biochemistry and Molecular Biology, Penn State University, University Park, PA, USA
| | - Tianzhi Luo
- Department of Modern Mechanics, University of Science and Technology of China, Hefei, China
| | - Daniel A Fletcher
- Department of Bioengineering, University of California, Berkeley, Berkeley, CA, USA
| | - Douglas N Robinson
- Department of Cell Biology, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Elizabeth H Chen
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, MD, USA.
- Department of Molecular Biology, UT Southwestern Medical Center, Dallas, TX, USA.
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β-III-spectrin spinocerebellar ataxia type 5 mutation reveals a dominant cytoskeletal mechanism that underlies dendritic arborization. Proc Natl Acad Sci U S A 2017; 114:E9376-E9385. [PMID: 29078305 DOI: 10.1073/pnas.1707108114] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
A spinocerebellar ataxia type 5 (SCA5) L253P mutation in the actin-binding domain (ABD) of β-III-spectrin causes high-affinity actin binding and decreased thermal stability in vitro. Here we show in mammalian cells, at physiological temperature, that the mutant ABD retains high-affinity actin binding. Significantly, we provide evidence that the mutation alters the mobility and recruitment of β-III-spectrin in mammalian cells, pointing to a potential disease mechanism. To explore this mechanism, we developed a Drosophila SCA5 model in which an equivalent mutant Drosophila β-spectrin is expressed in neurons that extend complex dendritic arbors, such as Purkinje cells, targeted in SCA5 pathogenesis. The mutation causes a proximal shift in arborization coincident with decreased β-spectrin localization in distal dendrites. We show that SCA5 β-spectrin dominantly mislocalizes α-spectrin and ankyrin-2, components of the endogenous spectrin cytoskeleton. Our data suggest that high-affinity actin binding by SCA5 β-spectrin interferes with spectrin-actin cytoskeleton dynamics, leading to a loss of a cytoskeletal mechanism in distal dendrites required for dendrite stabilization and arbor outgrowth.
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9
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βIII Spectrin Is Necessary for Formation of the Constricted Neck of Dendritic Spines and Regulation of Synaptic Activity in Neurons. J Neurosci 2017; 37:6442-6459. [PMID: 28576936 DOI: 10.1523/jneurosci.3520-16.2017] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2016] [Revised: 04/19/2017] [Accepted: 05/19/2017] [Indexed: 01/08/2023] Open
Abstract
Dendritic spines are postsynaptic structures in neurons often having a mushroom-like shape. Physiological significance and cytoskeletal mechanisms that maintain this shape are poorly understood. The spectrin-based membrane skeleton maintains the biconcave shape of erythrocytes, but whether spectrins also determine the shape of nonerythroid cells is less clear. We show that βIII spectrin in hippocampal and cortical neurons from rodent embryos of both sexes is distributed throughout the somatodendritic compartment but is particularly enriched in the neck and base of dendritic spines and largely absent from spine heads. Electron microscopy revealed that βIII spectrin forms a detergent-resistant cytoskeletal network at these sites. Knockdown of βIII spectrin results in a significant decrease in the density of dendritic spines. Surprisingly, the density of presynaptic terminals is not affected by βIII spectrin knockdown. However, instead of making normal spiny synapses, the presynaptic structures in βIII spectrin-depleted neurons make shaft synapses that exhibit increased amplitudes of miniature EPSCs indicative of excessive postsynaptic excitation. Thus, βIII spectrin is necessary for formation of the constricted shape of the spine neck, which in turn controls communication between the synapse and the parent dendrite to prevent excessive excitation. Notably, mutations of SPTNB2 encoding βIII spectrin are associated with neurodegenerative syndromes, spinocerebellar ataxia Type 5, and spectrin-associated autosomal recessive cerebellar ataxia Type 1, but molecular mechanisms linking βIII spectrin functions to neuronal pathologies remain unresolved. Our data suggest that spinocerebellar ataxia Type 5 and spectrin-associated autosomal recessive cerebellar ataxia Type 1 pathology likely arises from poorly controlled synaptic activity that leads to excitotoxicity and neurodegeneration.SIGNIFICANCE STATEMENT Dendritic spines are small protrusions from neuronal dendrites that make synapses with axons of other neurons in the brain. Dendritic spines usually have a mushroom-like shape, which is essential for brain functions, because aberrant spine morphology is associated with many neuropsychiatric disorders. The bulbous head of a mushroom-shaped spine makes the synapse, whereas the narrow neck transmits the incoming signals to the dendrite and supposedly controls the signal propagation. We show that a cytoskeletal protein βIII spectrin plays a key role for the formation of narrow spine necks. In the absence of βIII spectrin, dendritic spines collapse onto dendrites. As a result, synaptic strength exceeds acceptable levels and damages neurons, explaining pathology of human syndromes caused by βIII spectrin mutations.
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Khanna MR, Mattie FJ, Browder KC, Radyk MD, Crilly SE, Bakerink KJ, Harper SL, Speicher DW, Thomas GH. Spectrin tetramer formation is not required for viable development in Drosophila. J Biol Chem 2014; 290:706-15. [PMID: 25381248 DOI: 10.1074/jbc.m114.615427] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
The dominant paradigm for spectrin function is that (αβ)2-spectrin tetramers or higher order oligomers form membrane-associated two-dimensional networks in association with F-actin to reinforce the plasma membrane. Tetramerization is an essential event in such structures. We characterize the tetramerization interaction between α-spectrin and β-spectrins in Drosophila. Wild-type α-spectrin binds to both β- and βH-chains with high affinity, resembling other non-erythroid spectrins. However, α-spec(R22S), a tetramerization site mutant homologous to the pathological α-spec(R28S) allele in humans, eliminates detectable binding to β-spectrin and reduces binding to βH-spectrin ∼1000-fold. Even though spectrins are essential proteins, α-spectrin(R22S) rescues α-spectrin mutants to adulthood with only minor phenotypes indicating that tetramerization, and thus conventional network formation, is not the essential function of non-erythroid spectrin. Our data provide the first rigorous test for the general requirement for tetramer-based non-erythroid spectrin networks throughout an organism and find that they have very limited roles, in direct contrast to the current paradigm.
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Affiliation(s)
- Mansi R Khanna
- From the Department of Biology and the Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802 and
| | - Floyd J Mattie
- From the Department of Biology and the Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802 and
| | - Kristen C Browder
- From the Department of Biology and the Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802 and
| | - Megan D Radyk
- From the Department of Biology and the Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802 and
| | - Stephanie E Crilly
- From the Department of Biology and the Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802 and
| | - Katelyn J Bakerink
- From the Department of Biology and the Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802 and
| | - Sandra L Harper
- the Systems Biology Division, The Wistar Institute, Philadelphia, Pennsylvania 19104
| | - David W Speicher
- the Systems Biology Division, The Wistar Institute, Philadelphia, Pennsylvania 19104
| | - Graham H Thomas
- From the Department of Biology and the Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802 and
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11
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He M, Abdi KM, Bennett V. Ankyrin-G palmitoylation and βII-spectrin binding to phosphoinositide lipids drive lateral membrane assembly. J Cell Biol 2014; 206:273-88. [PMID: 25049274 PMCID: PMC4107783 DOI: 10.1083/jcb.201401016] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2014] [Accepted: 06/17/2014] [Indexed: 12/22/2022] Open
Abstract
Ankyrin-G and βII-spectrin colocalize at sites of cell-cell contact in columnar epithelial cells and promote lateral membrane assembly. This study identifies two critical inputs from lipids that together provide a rationale for how ankyrin-G and βII-spectrin selectively localize to Madin-Darby canine kidney (MDCK) cell lateral membranes. We identify aspartate-histidine-histidine-cysteine 5/8 (DHHC5/8) as ankyrin-G palmitoyltransferases required for ankyrin-G lateral membrane localization and for assembly of lateral membranes. We also find that βII-spectrin functions as a coincidence detector that requires recognition of both ankyrin-G and phosphoinositide lipids for its lateral membrane localization. DHHC5/8 and βII-spectrin colocalize with ankyrin-G in micrometer-scale subdomains within the lateral membrane that are likely sites for palmitoylation of ankyrin-G. Loss of either DHHC5/8 or ankyrin-G-βII-spectrin interaction or βII-spectrin-phosphoinositide recognition through its pleckstrin homology domain all result in failure to build the lateral membrane. In summary, we identify a functional network connecting palmitoyltransferases DHHC5/8 with ankyrin-G, ankyrin-G with βII-spectrin, and βII-spectrin with phosphoinositides that is required for the columnar morphology of MDCK epithelial cells.
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Affiliation(s)
- Meng He
- Department of Pharmacology and Cancer Biology, Department of Cell Biology, Department of Biochemistry, and Department of Neurobiology, Duke University Medical Center, Durham, NC 27710
| | - Khadar M Abdi
- Department of Pharmacology and Cancer Biology, Department of Cell Biology, Department of Biochemistry, and Department of Neurobiology, Duke University Medical Center, Durham, NC 27710
| | - Vann Bennett
- Department of Pharmacology and Cancer Biology, Department of Cell Biology, Department of Biochemistry, and Department of Neurobiology, Duke University Medical Center, Durham, NC 27710Department of Pharmacology and Cancer Biology, Department of Cell Biology, Department of Biochemistry, and Department of Neurobiology, Duke University Medical Center, Durham, NC 27710 Howard Hughes Medical Institute, Durham, NC 27710
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Genetic studies of spectrin in the larval fat body of Drosophila melanogaster: evidence for a novel lipid uptake apparatus. Genetics 2013; 195:871-81. [PMID: 24037266 DOI: 10.1534/genetics.113.155192] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Spectrin cytoskeleton defects produce a host of phenotypes affecting the plasma membrane, cell polarity, and secretory membrane traffic. However, many of the underlying molecular mechanisms remain unexplained by prevailing models. Here we used the larval fat body of Drosophila melanogaster as a genetic model system to further elucidate mechanisms of αβ-spectrin function. The results provide unexpected new insights into spectrin function as well as mechanisms of dietary fat uptake and storage. We show that loss of α- or β-spectrin in the fat body eliminated a population of small cortical lipid droplets and altered plasma membrane architecture, but did not affect viability of the organism. We present a novel model in which αβ-spectrin directly couples lipid uptake at the plasma membrane to lipid droplet growth in the cytoplasm. In contrast, strong overexpression of β-spectrin caused fat body atrophy and larval lethality. Overexpression of β-spectrin also perturbed transport of dietary fat from the midgut to the fat body. This hypermorphic phenotype appears to be the result of blocking secretion of the lipid carrier lipophorin from fat cells. However, this midgut phenotype was never seen with spectrin loss of function, suggesting that spectrin is not normally required for lipophorin secretion or function. The β-spectrin hypermorphic phenotype was ameliorated by co-overexpression of α-spectrin. Based on the overexpression results here, we propose that β-spectrin family members may be prone to hypermorphic effects (including effects on secretion) if their activity is not properly regulated.
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