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Hart CC, Lee YI, Xie J, Gao G, Lin BL, Hammers DW, Sweeney HL. Potential limitations of microdystrophin gene therapy for Duchenne muscular dystrophy. JCI Insight 2024; 9:e165869. [PMID: 38713520 DOI: 10.1172/jci.insight.165869] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2022] [Accepted: 05/01/2024] [Indexed: 05/09/2024] Open
Abstract
Clinical trials delivering high doses of adeno-associated viruses (AAVs) expressing truncated dystrophin molecules (microdystrophins) are underway for Duchenne muscular dystrophy (DMD). We examined the efficiency and efficacy of this strategy with 4 microdystrophin constructs (3 in clinical trials and a variant of the largest clinical construct), in a severe mouse model of DMD, using AAV doses comparable with those in clinical trials. We achieved high levels of microdystrophin expression in striated muscles with cardiac expression approximately 10-fold higher than that observed in skeletal muscle. Significant, albeit incomplete, correction of skeletal muscle disease was observed. Surprisingly, a lethal acceleration of cardiac disease occurred with 2 of the microdystrophins. The detrimental cardiac effect appears to be caused by variable competition (dependent on microdystrophin design and expression level) between microdystrophin and utrophin at the cardiomyocyte membrane. There may also be a contribution from an overloading of protein degradation. The significance of these observations for patients currently being treated with AAV-microdystrophin therapies is unclear since the levels of expression being achieved in the DMD hearts are unknown. However, these findings suggest that microdystrophin treatments need to avoid excessively high levels of expression in the heart and that cardiac function should be carefully monitored in these patients.
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Affiliation(s)
- Cora C Hart
- Department of Pharmacology & Therapeutics and
- Myology Institute, University of Florida College of Medicine, Gainesville, Florida, USA
| | - Young Il Lee
- Department of Pharmacology & Therapeutics and
- Myology Institute, University of Florida College of Medicine, Gainesville, Florida, USA
| | - Jun Xie
- Horae Gene Therapy Center, University of Massachusetts Medical School, Worchester, Massachusetts, USA
| | - Guangping Gao
- Horae Gene Therapy Center, University of Massachusetts Medical School, Worchester, Massachusetts, USA
| | - Brian L Lin
- Department of Cell Biology, Neurobiology, and Anatomy & Department of Pediatrics, Medical College of Wisconsin, Milwaukee, Wisconsin, USA
| | - David W Hammers
- Department of Pharmacology & Therapeutics and
- Myology Institute, University of Florida College of Medicine, Gainesville, Florida, USA
| | - H Lee Sweeney
- Department of Pharmacology & Therapeutics and
- Myology Institute, University of Florida College of Medicine, Gainesville, Florida, USA
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Navarro-Martínez A, Vicente-García C, Carvajal JJ. NMJ-related diseases beyond the congenital myasthenic syndromes. Front Cell Dev Biol 2023; 11:1216726. [PMID: 37601107 PMCID: PMC10436495 DOI: 10.3389/fcell.2023.1216726] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2023] [Accepted: 07/21/2023] [Indexed: 08/22/2023] Open
Abstract
Neuromuscular junctions (NMJs) are a special type of chemical synapse that transmits electrical stimuli from motor neurons (MNs) to their innervating skeletal muscle to induce a motor response. They are an ideal model for the study of synapses, given their manageable size and easy accessibility. Alterations in their morphology or function lead to neuromuscular disorders, such as the congenital myasthenic syndromes, which are caused by mutations in proteins located in the NMJ. In this review, we highlight novel potential candidate genes that may cause or modify NMJs-related pathologies in humans by exploring the phenotypes of hundreds of mouse models available in the literature. We also underscore the fact that NMJs may differ between species, muscles or even sexes. Hence the importance of choosing a good model organism for the study of NMJ-related diseases: only taking into account the specific features of the mammalian NMJ, experimental results would be efficiently translated to the clinic.
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Affiliation(s)
| | - Cristina Vicente-García
- Centro Andaluz de Biología del Desarrollo, CSIC-UPO-JA, Universidad Pablo de Olavide, Sevilla, Spain
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Dong T, Zhao Y, Jin HF, Shen L, Lin Y, Si LL, Chen L, Liu JC. SNTA1-deficient human cardiomyocytes demonstrate hypertrophic phenotype and calcium handling disorder. Stem Cell Res Ther 2022; 13:288. [PMID: 35773684 PMCID: PMC9248201 DOI: 10.1186/s13287-022-02955-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2022] [Accepted: 05/07/2022] [Indexed: 11/13/2022] Open
Abstract
Background α-1-syntrophin (SNTA1), a protein encoded by SNTA1, is highly expressed in human cardiomyocytes. Mutations in SNTA1 are associated with arrhythmia and cardiomyopathy. Previous research on SNTA1 has been based on non-human cardiomyocytes. This study was designed to identify the phenotype of SNTA1-deficiency using human cardiomyocytes. Methods SNTA1 was knocked out in the H9 embryonic stem cell line using the CRISPR-Cas9 system. H9SNTA1KO cells were then induced to differentiate into cardiomyocytes using small molecule inhibitors. The phenotypic discrepancies associated with SNTA1-deficient cardiomyocytes were investigated. Results SNTA1 was truncated at the 149th amino acid position of PH1 domain by a stop codon (TGA) using the CRISPR-Cas9 system. SNTA1-deficiency did not affect the pluripotency of H9SNTA1KO, and they retain their in vitro ability to differentiate into cardiomyocytes. However, H9SNTA1KO derived cardiomyocytes exhibited hypertrophic phenotype, lower cardiac contractility, weak calcium transient intensity, and lower level of calcium in the sarcoplasmic reticulum. Early treatment of SNTA1-deficient cardiomyocytes with ranolazine improved the calcium transient intensity and cardiac contractility. Conclusion SNTA1-deficient cardiomyocytes can be used to research the etiology, pathogenesis, and potential therapies for myocardial diseases. The SNTA1-deficient cardiomyocyte model suggests that the maintenance of cardiac calcium homeostasis is a key target in the treatment of myocardial-related diseases. Supplementary Information The online version contains supplementary material available at 10.1186/s13287-022-02955-4.
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Affiliation(s)
- Tao Dong
- Basic Medicine School, Qiqihar Medical University, 333 Bukui Street, Qiqihar, 161006, Heilongjiang, China.
| | - Yan Zhao
- College of Life Science and Agroforestry, Qiqihar University, Qiqihar, 161006, Heilongjiang, China
| | - Hai-Feng Jin
- Basic Medicine School, Qiqihar Medical University, 333 Bukui Street, Qiqihar, 161006, Heilongjiang, China
| | - Lei Shen
- Basic Medicine School, Qiqihar Medical University, 333 Bukui Street, Qiqihar, 161006, Heilongjiang, China
| | - Yan Lin
- Basic Medicine School, Qiqihar Medical University, 333 Bukui Street, Qiqihar, 161006, Heilongjiang, China
| | - Long-Long Si
- CAS Key Laboratory of Quantitative Engineering Biology, Shenzhen Institute of Synthetic Biology, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen, 518055, China
| | - Li Chen
- CAS Key Laboratory of Quantitative Engineering Biology, Shenzhen Institute of Synthetic Biology, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen, 518055, China
| | - Ji-Cheng Liu
- Qiqihar Institute of Medical and Pharmaceutical Sciences, Qiqihar Medical University, 333 Bukui Street, Qiqihar, 161006, Heilongjiang, China.
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4
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Banks GB, Chamberlain JS, Odom GL. Microutrophin expression in dystrophic mice displays myofiber type differences in therapeutic effects. PLoS Genet 2020; 16:e1009179. [PMID: 33175853 PMCID: PMC7682874 DOI: 10.1371/journal.pgen.1009179] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2020] [Revised: 11/23/2020] [Accepted: 10/06/2020] [Indexed: 12/28/2022] Open
Abstract
Gene therapy approaches for DMD using recombinant adeno-associated viral (rAAV) vectors to deliver miniaturized (or micro) dystrophin genes to striated muscles have shown significant progress. However, concerns remain about the potential for immune responses against dystrophin in some patients. Utrophin, a developmental paralogue of dystrophin, may provide a viable treatment option. Here we examine the functional capacity of an rAAV-mediated microutrophin (μUtrn) therapy in the mdx4cv mouse model of DMD. We found that rAAV-μUtrn led to improvement in dystrophic histopathology & mostly restored the architecture of the neuromuscular and myotendinous junctions. Physiological studies of tibialis anterior muscles indicated peak force maintenance, with partial improvement of specific force. A fundamental question for μUtrn therapeutics is not only can it replace critical functions of dystrophin, but whether full-length utrophin impacts the therapeutic efficacy of the smaller, highly expressed μUtrn. As such, we found that μUtrn significantly reduced the spacing of the costameric lattice relative to full-length utrophin. Further, immunostaining suggested the improvement in dystrophic pathophysiology was largely influenced by favored correction of fast 2b fibers. However, unlike μUtrn, μdystrophin (μDys) expression did not show this fiber type preference. Interestingly, μUtrn was better able to protect 2a and 2d fibers in mdx:utrn-/- mice than in mdx4cv mice where the endogenous full-length utrophin was most prevalent. Altogether, these data are consistent with the role of steric hindrance between full-length utrophin & μUtrn within the sarcolemma. Understanding the stoichiometry of this effect may be important for predicting clinical efficacy.
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MESH Headings
- Animals
- Dependovirus/genetics
- Disease Models, Animal
- Dystrophin/genetics
- Gene Transfer Techniques
- Genetic Therapy/methods
- Genetic Vectors/genetics
- HEK293 Cells
- Humans
- Mice
- Mice, Inbred mdx
- Microscopy, Electron
- Muscle Contraction
- Muscle Fibers, Skeletal/cytology
- Muscle Fibers, Skeletal/pathology
- Muscle Fibers, Skeletal/ultrastructure
- Muscle, Skeletal
- Muscular Dystrophy, Duchenne/genetics
- Muscular Dystrophy, Duchenne/pathology
- Muscular Dystrophy, Duchenne/therapy
- Neuromuscular Junction/pathology
- Neuromuscular Junction/ultrastructure
- Sarcolemma/pathology
- Sarcolemma/ultrastructure
- Utrophin/genetics
- Utrophin/therapeutic use
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Affiliation(s)
- Glen B. Banks
- Department of Neurology, University of Washington, Seattle, Washington, United States of America
- Department of Medicine, University of Washington, Seattle, Washington, United States of America
- Wellstone Muscular Dystrophy Specialized Research Center, University of Washington, Seattle, Washington, United States of America
| | - Jeffrey S. Chamberlain
- Department of Neurology, University of Washington, Seattle, Washington, United States of America
- Department of Medicine, University of Washington, Seattle, Washington, United States of America
- Wellstone Muscular Dystrophy Specialized Research Center, University of Washington, Seattle, Washington, United States of America
- Department of BioChemistry, University of Washington, Seattle, Washington, United States of America
| | - Guy L. Odom
- Department of Neurology, University of Washington, Seattle, Washington, United States of America
- Department of Medicine, University of Washington, Seattle, Washington, United States of America
- Wellstone Muscular Dystrophy Specialized Research Center, University of Washington, Seattle, Washington, United States of America
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5
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Bhat HF, Mir SS, Dar KB, Bhat ZF, Shah RA, Ganai NA. ABC of multifaceted dystrophin glycoprotein complex (DGC). J Cell Physiol 2017; 233:5142-5159. [DOI: 10.1002/jcp.25982] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2017] [Accepted: 05/01/2017] [Indexed: 01/16/2023]
Affiliation(s)
- Hina F. Bhat
- Division of BiotechnologySher‐e‐Kashmir University of Agricultural Sciences and Technology of Kashmir SKUAST‐KShuhama, SrinagarJammu and KashmirIndia
| | - Saima S. Mir
- Department of BiotechnologyUniversity of KashmirHazratbal, SrinagarJammu and KashmirIndia
| | - Khalid B. Dar
- Department of BiochemistryUniversity of KashmirHazratbal, SrinagarJammu and KashmirIndia
| | - Zuhaib F. Bhat
- Division of Livestock Products and TechnologySher‐e‐Kashmir University of Agricultural Sciences and Technology of Jammu (SKUAST‐J), R.S. PoraJammuJammu and KashmirIndia
| | - Riaz A. Shah
- Division of BiotechnologySher‐e‐Kashmir University of Agricultural Sciences and Technology of Kashmir SKUAST‐KShuhama, SrinagarJammu and KashmirIndia
| | - Nazir A. Ganai
- Division of BiotechnologySher‐e‐Kashmir University of Agricultural Sciences and Technology of Kashmir SKUAST‐KShuhama, SrinagarJammu and KashmirIndia
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Chalkiadaki A, Igarashi M, Nasamu AS, Knezevic J, Guarente L. Muscle-specific SIRT1 gain-of-function increases slow-twitch fibers and ameliorates pathophysiology in a mouse model of duchenne muscular dystrophy. PLoS Genet 2014; 10:e1004490. [PMID: 25032964 PMCID: PMC4102452 DOI: 10.1371/journal.pgen.1004490] [Citation(s) in RCA: 91] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2013] [Accepted: 05/21/2014] [Indexed: 11/18/2022] Open
Abstract
SIRT1 is a metabolic sensor and regulator in various mammalian tissues and functions to counteract metabolic and age-related diseases. Here we generated and analyzed mice that express SIRT1 at high levels specifically in skeletal muscle. We show that SIRT1 transgenic muscle exhibits a fiber shift from fast-to-slow twitch, increased levels of PGC-1α, markers of oxidative metabolism and mitochondrial biogenesis, and decreased expression of the atrophy gene program. To examine whether increased activity of SIRT1 protects from muscular dystrophy, a muscle degenerative disease, we crossed SIRT1 muscle transgenic mice to mdx mice, a genetic model of Duchenne muscular dystrophy. SIRT1 overexpression in muscle reverses the phenotype of mdx mice, as determined by histology, creatine kinase release into the blood, and endurance in treadmill exercise. In addition, SIRT1 overexpression also results in increased levels of utrophin, a functional analogue of dystrophin, as well as increased expression of PGC-1α targets and neuromuscular junction genes. Based on these findings, we suggest that pharmacological interventions that activate SIRT1 in skeletal muscle might offer a new approach for treating muscle diseases.
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Affiliation(s)
- Angeliki Chalkiadaki
- Glenn Laboratory for the Science of Aging and Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States of America
| | - Masaki Igarashi
- Glenn Laboratory for the Science of Aging and Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States of America
| | - Armiyaw Sebastian Nasamu
- Glenn Laboratory for the Science of Aging and Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States of America
| | - Jovana Knezevic
- Glenn Laboratory for the Science of Aging and Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States of America
| | - Leonard Guarente
- Glenn Laboratory for the Science of Aging and Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States of America
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Altered acetylcholine release in the hippocampus of dystrophin-deficient mice. Neuroscience 2014; 269:173-83. [PMID: 24704431 DOI: 10.1016/j.neuroscience.2014.03.050] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2014] [Revised: 03/22/2014] [Accepted: 03/25/2014] [Indexed: 12/29/2022]
Abstract
Mild cognitive impairments have been described in one-third of patients with Duchenne muscle dystrophy (DMD). DMD is characterized by progressive and irreversible muscle degeneration caused by mutations in the dystrophin gene and lack of the protein expression. Previously, we have reported altered concentrations of α7- and β2-containing nicotinic acetylcholine receptors (nAChRs) in hippocampal membranes of dystrophic (mdx) mice. This suggests that alterations in the central cholinergic synapses are associated with dystrophin deficiency. In this study, we examined the release of acetylcholine (ACh) and the level of the vesicular ACh transporter (VAChT) using synaptosomes isolated from brain regions that normally have a high density of dystrophin (cortex, hippocampus and cerebellum), in control and mdx mice at 4 and 12months of age. ACh release evoked by nicotinic stimulation or K(+) depolarization was measured as the tritium outflow from superfused synaptosomes preloaded with [(3)H]-choline. The results showed that the evoked tritium release was Ca(2+)-dependent and mostly formed by [(3)H]-ACh. β2-containing nAChRs were involved in agonist-evoked [(3)H]-ACh release in control and mdx preparations. In hippocampal synaptosomes from 12-month-old mdx mice, nAChR-evoked [(3)H]-ACh release increased by 57% compared to age-matched controls. Moreover, there was a 98% increase in [(3)H]-ACh release compared to 4-month-old mdx mice. [(3)H]-ACh release evoked by K(+) depolarization was not altered, while the VAChT protein level was decreased (19%) compared to that of age-matched controls. In cortical and cerebellar preparations, there was no difference in nAChR-evoked [(3)H]-ACh release and VAChT levels between mdx and age-matched control groups. Our previous findings and the presynaptic alterations observed in the hippocampi of 12-month-old mdx mice indicate possible dysfunction of nicotinic cholinergic synapses associated with dystrophin deficiency. These changes may contribute to the cognitive and behavioral abnormalities described in dystrophic mice and patients with DMD.
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8
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Horiuchi N, Aihara N, Mizutani H, Kousaka S, Nagafuchi T, Ochiai M, Ochiai K, Kobayashi Y, Furuoka H, Asai T, Oishi K. Becker muscular dystrophy-like myopathy regarded as so-called "fatty muscular dystrophy" in a pig: a case report and its diagnostic method. J Vet Med Sci 2013; 76:243-8. [PMID: 24162004 PMCID: PMC3982806 DOI: 10.1292/jvms.13-0336] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
Abstract
We describe a case of human Becker muscular dystrophy (BMD)-like myopathy that was characterized by the declined stainability of dystrophin at sarcolemma in a pig and the immunostaining for dystrophin on the formalin-fixed, paraffin-embedded (FFPE) tissue. The present case was found in a meat inspection center. The pig looked appeared healthy at the ante-mortem inspection. Muscular abnormalities were detected after carcass dressing as pale, discolored skeletal muscles with prominent fat infiltrations and considered so-called “fatty muscular dystrophy”. Microscopic examination revealed following characteristics: diffused fat infiltration into the skeletal muscle and degeneration and regeneration of the remaining skeletal muscle fibers. Any lesions that were suspected of neurogenic atrophy, traumatic muscular degeneration, glycogen storage disease or other porcine muscular disorders were not observed. The immunostaining for dystrophin was conducted and confirmed to be applicable on FFPE porcine muscular tissues and revealed diminished stainability of dystrophin at the sarcolemma in the present case. Based on the histological observations and immunostaining results, the present case was diagnosed with BMD-like myopathy associated with dystrophin abnormality in a pig. Although the genetic properties were not clear, the present BMD-like myopathy implied the occurrence of dystrophinopathy in pigs. To the best of our knowledge, this is the first report of a natural case of myopathy associated with dystrophin abnormalities in a pig.
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Affiliation(s)
- Noriyuki Horiuchi
- Department of Basic Veterinary Medicine, Obihiro University of Agriculture and Veterinary Medicine, Inada, Obihiro, Hokkaido 080-8555, Japan
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9
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Bhat HF, Adams ME, Khanday FA. Syntrophin proteins as Santa Claus: role(s) in cell signal transduction. Cell Mol Life Sci 2013; 70:2533-54. [PMID: 23263165 PMCID: PMC11113789 DOI: 10.1007/s00018-012-1233-9] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2012] [Revised: 11/21/2012] [Accepted: 12/03/2012] [Indexed: 11/30/2022]
Abstract
Syntrophins are a family of cytoplasmic membrane-associated adaptor proteins, characterized by the presence of a unique domain organization comprised of a C-terminal syntrophin unique (SU) domain and an N-terminal pleckstrin homology (PH) domain that is split by insertion of a PDZ domain. Syntrophins have been recognized as an important component of many signaling events, and they seem to function more like the cell's own personal 'Santa Claus' that serves to 'gift' various signaling complexes with precise proteins that they 'wish for', and at the same time care enough for the spatial, temporal control of these signaling events, maintaining overall smooth functioning and general happiness of the cell. Syntrophins not only associate various ion channels and signaling proteins to the dystrophin-associated protein complex (DAPC), via a direct interaction with dystrophin protein but also serve as a link between the extracellular matrix and the intracellular downstream targets and cell cytoskeleton by interacting with F-actin. They play an important role in regulating the postsynaptic signal transduction, sarcolemmal localization of nNOS, EphA4 signaling at the neuromuscular junction, and G-protein mediated signaling. In our previous work, we reported a differential expression pattern of alpha-1-syntrophin (SNTA1) protein in esophageal and breast carcinomas. Implicated in several other pathologies, like cardiac dys-functioning, muscular dystrophies, diabetes, etc., these proteins provide a lot of scope for further studies. The present review focuses on the role of syntrophins in membrane targeting and regulation of cellular proteins, while highlighting their relevance in possible development and/or progression of pathologies including cancer which we have recently demonstrated.
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Affiliation(s)
- Hina F Bhat
- Department of Biotechnology, University of Kashmir, Srinagar, Jammu and Kashmir, India.
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10
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Carlson SS, Valdez G, Sanes JR. Presynaptic calcium channels and α3-integrins are complexed with synaptic cleft laminins, cytoskeletal elements and active zone components. J Neurochem 2010; 115:654-66. [PMID: 20731762 DOI: 10.1111/j.1471-4159.2010.06965.x] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
At chemical synapses, synaptic cleft components interact with elements of the nerve terminal membrane to promote differentiation and regulate function. Laminins containing the β2 subunit are key cleft components, and they act in part by binding the pore-forming subunit of a pre-synaptic voltage-gated calcium channel (Ca(v)α) (Nishimune et al. 2004). In this study, we identify Ca(v)α-associated intracellular proteins that may couple channel-anchoring to assembly or stabilization of neurotransmitter release sites called active zones. Using Ca(v)α-antibodies, we isolated a protein complex from Torpedo electric organ synapses, which resemble neuromuscular junctions but are easier to isolate in bulk. We identified 10 components of the complex: six cytoskeletal proteins (α2/β2 spectrins, plectin 1, AHNAK/desmoyokin, dystrophin, and myosin 1), two active zone components (bassoon and piccolo), synaptic laminin, and a calcium channel β subunit. Immunocytochemistry confirmed these proteins in electric organ synapses, and PCR analysis revealed their expression by developing mammalian motor neurons. Finally, we show that synaptic laminins also interact with pre-synaptic integrins containing the α3 subunit. Together with our previous finding that a distinct synaptic laminin interacts with SV2 on nerve terminals (Son et al. 2000), our results identify three paths by which synaptic cleft laminins can send developmentally important signals to nerve terminals.
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Affiliation(s)
- Steven S Carlson
- Department of Physiology and Biophysics, University of Washington, Seattle, Washington 98195, USA.
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11
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Banks GB, Chamberlain JS, Froehner SC. Truncated dystrophins can influence neuromuscular synapse structure. Mol Cell Neurosci 2009; 40:433-41. [PMID: 19171194 DOI: 10.1016/j.mcn.2008.12.011] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2008] [Revised: 12/12/2008] [Accepted: 12/16/2008] [Indexed: 11/18/2022] Open
Abstract
Duchenne muscular dystrophy (DMD) is characterized by muscle degeneration and structural defects in the neuromuscular synapse that are caused by mutations in dystrophin. Whether aberrant neuromuscular synapse structure is an indirect consequence of muscle degeneration or a direct result of loss of dystrophin function is not known. Rational design of truncated dystrophins has enabled the design of expression cassettes highly effective at preventing muscle degeneration in mouse models of DMD using gene therapy. Here we examined the functional capacity of a minidystrophin (minidysGFP) and a microdystrophin (microdystrophin(DeltaR4-R23)) transgene on the maturation and maintenance of neuromuscular junctions (NMJ) in mdx mice. We found that minidysGFP prevents fragmentation and the loss of postsynaptic folds at the NMJ. In contrast, microdystrophin (DeltaR4-R23) was unable to prevent synapse fragmentation in the limb muscles despite preventing muscle degeneration, although fragmentation was observed to temporally correlate with the formation of ringed fibers. Surprisingly, microdystrophin(DeltaR4-R23) increased the length of synaptic folds in the diaphragm muscles of mdx mice independent of muscle degeneration or the formation of ringed fibers. We also demonstrate that the number and depth of synaptic folds influences the density of voltage-gated sodium channels at the neuromuscular synapse in mdx, microdystrophin(DeltaR4-R23)/mdx and mdx:utrophin double knockout mice. Together, these data suggest that maintenance of the neuromuscular synapse is governed through its lateral association with the muscle cytoskeleton, and that dystrophin has a direct role in promoting the maturation of synaptic folds to allow more sodium channels into the junction.
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Affiliation(s)
- Glen B Banks
- Department of Neurology, Senator Paul D Wellstone Muscular Dystrophy Cooperative Research Center, University of Washington, Seattle, Washington 98195, USA.
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12
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Affiliation(s)
- Andrew G Engel
- Department of Neurology, Mayo Clinic, Rochester, MN, USA.
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13
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Ervasti JM, Sonnemann KJ. Biology of the striated muscle dystrophin-glycoprotein complex. INTERNATIONAL REVIEW OF CYTOLOGY 2008; 265:191-225. [PMID: 18275889 DOI: 10.1016/s0074-7696(07)65005-0] [Citation(s) in RCA: 110] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/04/2022]
Abstract
Since its first description in 1990, the dystrophin-glycoprotein complex has emerged as a critical nexus for human muscular dystrophies arising from defects in a variety of distinct genes. Studies in mammals widely support a primary role for the dystrophin-glycoprotein complex in mechanical stabilization of the plasma membrane in striated muscle and provide hints for secondary functions in organizing molecules involved in cellular signaling. Studies in model organisms confirm the importance of the dystrophin-glycoprotein complex for muscle cell viability and have provided new leads toward a full understanding of its secondary roles in muscle biology.
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Affiliation(s)
- James M Ervasti
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455, USA
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Hussein MR, Hamed SA, Mostafa MG, Abu-Dief EE, Kamel NF, Kandil MR. The effects of glucocorticoid therapy on the inflammatory and dendritic cells in muscular dystrophies. Int J Exp Pathol 2007; 87:451-61. [PMID: 17222213 PMCID: PMC2517389 DOI: 10.1111/j.1365-2613.2006.00470.x] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
Various clinical trials have documented the therapeutic benefit of glucocorticoids (GCs) in enhancing muscle strength and slowing disease progression of Duchenne and Becker muscular dystrophies (DMD/BMD). We hypothesized that GCs may have relevance to the differential anti-inflammatory effect on mononuclear inflammatory cells (MICs) and Dendritic cells (DCs) infiltrating the dystrophic muscles. In this prospective study, two muscle biopsies were obtained (before and after 6-month prednisone therapy) from 30 patients with dystrophies (DMD = 18; BMD = 6; and limb girdle muscular dystrophies (LGMD) = 6). MICs and DCs infiltrating the muscles were examined using mouse monoclonal antibodies and immunoperoxidase staining methods. Muscle strength was evaluated monthly by manual testing, motor ability and timed tests. Prednisone therapy was associated with: (i) functional improvement of overall motor disability, in upper limbs of DMD (P < 0.001) and BMD (P < 0.01) and lower limbs of DMD (P < 0.001) and BMD (P < 0.05); (ii) histological improvement such as fibre size variation (DMD, P < 0.01; BMD, P < 0.05), internalization of nuclei (DMD, P < 0.05), degeneration and necrosis (DMD and BMD, P < 0.01), regeneration (DMD, P < 0.001; BMD, P < 0.01) and endomysial connective tissue proliferation (DMD, P < 0.01; BMD, P < 0.05) and (iii) reduction of total MICs (P < 0.01) and DCs (P < 0.01). There was a positive correlation between the degree of improvement in overall motor disability and reduction of DCs numbers (In upper limbs; r = 0.638, P < 0.01 for DMD and r = 0.725, P < 0.01 for BMD, in Lower limbs; r = 0.547, P < 0.05 for DMD and r = 0.576, P < 0.05 for BMD). Such improvements and changes of MICs/DCs were absent in LGMD. In DMD/BMD, prednisone therapeutic effect was associated with reduced MICs and DCs numbers. Whether this therapeutic effect reflects targeting of the deleterious immune response produced by these cells mandates further investigations.
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15
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Yue Y, Liu M, Duan D. C-terminal-truncated microdystrophin recruits dystrobrevin and syntrophin to the dystrophin-associated glycoprotein complex and reduces muscular dystrophy in symptomatic utrophin/dystrophin double-knockout mice. Mol Ther 2006; 14:79-87. [PMID: 16563874 PMCID: PMC2581714 DOI: 10.1016/j.ymthe.2006.01.007] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2005] [Revised: 01/03/2006] [Accepted: 01/12/2006] [Indexed: 01/19/2023] Open
Abstract
C-terminal-truncated (DeltaC) microdystrophin is being developed for Duchenne muscular dystrophy gene therapy. Encouraging results have been achieved in the mdx mouse model. Unfortunately, mdx mice do not display the same phenotype as human patients. Evaluating DeltaC microdystrophin in a symptomatic model will be of significant relevance to human trials. Utrophin/dystrophin double-knockout (u-dko) mice were developed to model severe dystrophic changes in human patients. In this study we evaluated the therapeutic effect of the DeltaR4-R23/DeltaC microdystrophin gene (DeltaR4/DeltaC) after serotype-6 adeno-associated virus-mediated gene transfer in neonatal u-dko muscle. At 2 months after gene transfer, the percentage of centrally nucleated myofiber was reduced from 89.2 to 3.4% and muscle weight was normalized. Furthermore, we have demonstrated for the first time that DeltaC microdystrophin can eliminate interstitial fibrosis and macrophage infiltration and restore dystrobrevin and syntrophin to the dystrophin-associated glycoprotein complex. Interestingly neuronal nitric oxide synthase was not restored. The most impressive results were achieved in muscle force measurement. Neonatal gene therapy increased twitch- and tetanic-specific force. It also brought the response to eccentric contraction-induced injury to the normal range. In summary, our results suggest that the DeltaR4/DeltaC microgene holds great promise in preventing muscular dystrophy.
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Affiliation(s)
| | | | - Dongsheng Duan
- To whom correspondence and reprint requests should be addressed. Fax: +1 573 882 4287. E-mail:
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16
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Stocksley MA, Chakkalakal JV, Bradford A, Miura P, De Repentigny Y, Kothary R, Jasmin BJ. A 1.3 kb promoter fragment confers spatial and temporal expression of utrophin A mRNA in mouse skeletal muscle fibers. Neuromuscul Disord 2005; 15:437-49. [PMID: 15907291 DOI: 10.1016/j.nmd.2005.03.008] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2005] [Revised: 03/02/2005] [Accepted: 03/04/2005] [Indexed: 10/25/2022]
Abstract
Upregulation of utrophin in muscle is currently being examined as a potential therapy for Duchenne muscular dystrophy patients. In this context, we generated transgenic mice harboring a 1.3 kb human utrophin A promoter fragment driving expression of the lacZ gene. Characterization of reporter expression during postnatal muscle development revealed that the levels and localization of beta-galactosidase parallel expression of utrophin A transcripts. Moreover, we noted that the utrophin A promoter is more active in slow soleus muscles. Additionally, expression of the reporter gene was regulated during muscle regeneration in a manner similar to utrophin A transcripts. Together, these results show that the utrophin A promoter-lacZ construct mirrors expression of utrophin A mRNAs indicating that this utrophin A promoter fragment confers temporal and spatial patterns of expression in skeletal muscle. This transgenic mouse will be valuable as an in vivo model for developing and testing molecules aimed at increasing utrophin A expression.
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MESH Headings
- Animals
- Animals, Newborn
- Female
- Gene Expression
- Genes, Reporter
- Genetic Therapy
- Lac Operon
- Male
- Mice
- Mice, Inbred C57BL
- Mice, Transgenic
- Muscle Fibers, Fast-Twitch/physiology
- Muscle Fibers, Slow-Twitch/physiology
- Muscle, Skeletal/cytology
- Muscle, Skeletal/physiology
- Muscular Dystrophy, Duchenne/physiopathology
- Muscular Dystrophy, Duchenne/therapy
- Neuromuscular Junction/physiology
- Promoter Regions, Genetic/genetics
- RNA, Messenger/analysis
- Regeneration/physiology
- Utrophin/genetics
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Affiliation(s)
- Mark A Stocksley
- Department of Cellular and Molecular Medicine and Centre for Neuromuscular Disease, Faculty of Medicine, University of Ottawa, 451 Smyth Road, Ottawa, Ont., Canada K1H 8M5
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17
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Minatel E, Neto HS, Marques MJ. Acetylcholine receptor distribution and synapse elimination at the developing neuromuscular junction of mdx mice. Muscle Nerve 2003; 28:561-9. [PMID: 14571457 DOI: 10.1002/mus.10416] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The pattern of innervation of the vertebrate neuromuscular junction is established during early development, when junctions go from multiple to single innervation in the phenomenon of synapse elimination, suggesting that changes at the molecular level in the postsynaptic cell lead to the removal of nerve terminals. The mdx mouse is deficient in dystrophin and associated proteins that are part of the postsynaptic cytoskeleton. We used rhodamine-alpha-bungarotoxin and anti-neurofilament IgG-FITC to stain acetylcholine receptors and nerve terminals of the sternomastoid muscle during postnatal development in mdx and control C57BL/10 mice. Using fluorescence confocal microscopy, we observed that, 7 days after birth, 86.7% of the endplates of mdx mice were monoinnervated (n = 200) compared with 41.4% in control mice (n = 200). By the end of the second postnatal week, all endplates were innervated singly (100% mdx and 94.7% controls, n = 200 per group). These results show that dystrophic fibers achieve single innervation earlier, perhaps because dystrophin or a normal cytoskeletal complex is implicated in this phenomenon.
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Affiliation(s)
- Elaine Minatel
- Departamento de Anatomia, Instituto de Biologia, Universidade Estadual de Campinas (UNICAMP), Campinas, São Paulo 13083-970, Brazil
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18
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Ebert JG, Zelenka M, Gath I, Gödtel-Armbrust U, Förstermann U. Colocalization but differential regulation of neuronal NO synthase and nicotinic acetylcholine receptor in C2C12 myotubes. Am J Physiol Cell Physiol 2003; 284:C1065-72. [PMID: 12620898 DOI: 10.1152/ajpcell.00476.2002] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In mammalian skeletal muscle, neuronal-type nitric oxide synthase (nNOS) is found to be enriched at neuromuscular endplates. Here we demonstrate the colocalization of the nicotinic acetylcholine receptor (nAChR, stained with alpha-bungarotoxin) and nNOS (stained with a specific antibody) in murine C(2)C(12) myotubes. However, coimmunoprecipitation experiments demonstrated no evidence for a direct protein-protein association between the nAChR and nNOS in C(2)C(12) myotubes. An antibody to the alpha(1)-subunit of the nAChR did not coprecipitate nNOS, and an nNOS-specific antibody did not precipitate the alpha(1)-subunit of the nAChR. Treatment of mice with bacterial LPS downregulated the expression of nNOS in skeletal muscle, and treatment of C(2)C(12) cells with bacterial LPS and interferon-gamma markedly decreased nNOS mRNA and protein expression. In contrast, mRNA and protein of the nAChR (alpha-, gamma-, and epsilon-subunits) remained unchanged at the mRNA and protein levels. These data demonstrate that nNOS and the nAChR are colocalized in murine skeletal muscle and C(2)C(12) cells but differ in their expressional regulation.
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Affiliation(s)
- Jutta G Ebert
- Department of Pharmacology, Johannes Gutenberg University, D-55101 Mainz, Germany
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19
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Hosaka Y, Yokota T, Miyagoe-Suzuki Y, Yuasa K, Imamura M, Matsuda R, Ikemoto T, Kameya S, Takeda S. Alpha1-syntrophin-deficient skeletal muscle exhibits hypertrophy and aberrant formation of neuromuscular junctions during regeneration. J Cell Biol 2002; 158:1097-107. [PMID: 12221071 PMCID: PMC2173222 DOI: 10.1083/jcb.200204076] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Alpha1-syntrophin is a member of the family of dystrophin-associated proteins; it has been shown to recruit neuronal nitric oxide synthase and the water channel aquaporin-4 to the sarcolemma by its PSD-95/SAP-90, Discs-large, ZO-1 homologous domain. To examine the role of alpha1-syntrophin in muscle regeneration, we injected cardiotoxin into the tibialis anterior muscles of alpha1-syntrophin-null (alpha1syn-/-) mice. After the treatment, alpha1syn-/- muscles displayed remarkable hypertrophy and extensive fiber splitting compared with wild-type regenerating muscles, although the untreated muscles of the mutant mice showed no gross histological change. In the hypertrophied muscles of the mutant mice, the level of insulin-like growth factor-1 transcripts was highly elevated. Interestingly, in an early stage of the regeneration process, alpha1syn-/- mice showed remarkably deranged neuromuscular junctions (NMJs), accompanied by impaired ability to exercise. The contractile forces were reduced in alpha1syn-/- regenerating muscles. Our results suggest that the lack of alpha1-syntrophin might be responsible in part for the muscle hypertrophy, abnormal synapse formation at NMJs, and reduced force generation during regeneration of dystrophin-deficient muscle, all of which are typically observed in the early stages of Duchenne muscular dystrophy patients.
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Affiliation(s)
- Yukio Hosaka
- Department of Molecular Therapy, National Institute of Neuroscience, National Center of Neurology and Psychiatry, 4-1-1 Ogawa-higashi, Kodaira 187-8502, Tokyo, Japan
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20
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Biggar WD, Klamut HJ, Demacio PC, Stevens DJ, Ray PN. Duchenne muscular dystrophy: current knowledge, treatment, and future prospects. Clin Orthop Relat Res 2002:88-106. [PMID: 12151886 DOI: 10.1097/00003086-200208000-00012] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The cloning of the dystrophin gene has led to major advances in the understanding of the molecular genetic basis of Duchenne, Becker, and other muscular dystrophies associated with mutations in genes encoding members of the dystrophin-associated glycoprotein complex. The recent introduction of pharmaceutical agents such as prednisone has shown great promise in delaying the progression of Duchenne muscular dystrophy but there remains a need to develop more long-term therapeutic interventions. Knowledge of the nature of the dystrophin gene and the glycoprotein complex has led many researchers to think that somatic gene replacement represents the most promising approach to treatment. The potential use of this strategy has been shown in the mdx mouse model of Duchenne muscular dystrophy, where germ line gene transfer of either a full-length or a smaller Becker-type dystrophin minigene prevents necrosis and restores normal muscle function.
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Affiliation(s)
- W Douglas Biggar
- Bloorview MacMillan Children's Centre and Department of Paediatrics, University of Toronto, Ontario, Canada
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21
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Tews DS. Role of nitric oxide and nitric oxide synthases in experimental models of denervation and reinnervation. Microsc Res Tech 2001; 55:181-6. [PMID: 11747093 DOI: 10.1002/jemt.1169] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Nitric oxide (NO) is a short-living free molecule synthesized by three different isoforms of nitric oxide synthases (NOS)-neuronal NOS, endothelial NOS, and inducible NOS-associated with neuromuscular transmission, muscle contractility, mitochondrial respiration, and carbohydrate metabolism in skeletal muscle. Neuronal NOS is constitutively expressed at the muscle fiber sarcolemma linked to the dystrophin-glycoprotein complex and concentrated at the neuromuscular endplate. There is increasing evidence that altered expression of neuronal NOS plays a role in muscle fiber damage in neuromuscular diseases such as dystrophinopathies and denervating disorders. Although there have been some previous conflicting results on the neuronal NOS expression pattern in denervated muscle fibers, it is now well established that denervation is associated with a down-regulation and disappearance of sarcolemmal neuronal NOS at synaptic/extrasynaptic or both sites. As NO has been shown to induce collapse and growth arrest on neuronal growth cones, down-regulation of sarcolemmal neuronal NOS may contribute to axonal regeneration and attraction to muscle fibers aiming at the formation of new motor endplates providing reinnervation and reconstitution of NOS expression. As NO serves as a retrograde messenger, it may trigger structural downstream events responsible for neuromuscular synaptogenesis and preventing polyneural innervation. Nevertheless, decreased NO production in denervation reduces the cytoprotective scavenger function of NO for superoxide anions promoting oxidative stress that is likely to be involved in muscle fiber damage and death. However, the multifaced role of NOS and NO under physiological and pathological conditions remains poorly understood on the basis of the current knowledge.
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Affiliation(s)
- D S Tews
- Division of Neuropathology, Johannes Gutenberg-University Hospital, Langenbeckstrasse 1, D-55101 Mainz, Germany 2001.
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22
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Marchand S, Stetzkowski-Marden F, Cartaud J. Differential targeting of components of the dystrophin complex to the postsynaptic membrane. Eur J Neurosci 2001. [DOI: 10.1046/j.1460-9568.2001.01373.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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23
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Marchand S, Stetzkowski-Marden F, Cartaud J. Differential targeting of components of the dystrophin complex to the postsynaptic membrane. Eur J Neurosci 2001. [DOI: 10.1111/j.1460-9568.2001.01373.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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24
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Adams ME, Kramarcy N, Krall SP, Rossi SG, Rotundo RL, Sealock R, Froehner SC. Absence of alpha-syntrophin leads to structurally aberrant neuromuscular synapses deficient in utrophin. J Cell Biol 2000; 150:1385-98. [PMID: 10995443 PMCID: PMC2150701 DOI: 10.1083/jcb.150.6.1385] [Citation(s) in RCA: 190] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The syntrophins are a family of structurally related proteins that contain multiple protein interaction motifs. Syntrophins associate directly with dystrophin, the product of the Duchenne muscular dystrophy locus, and its homologues. We have generated alpha-syntrophin null mice by targeted gene disruption to test the function of this association. The alpha-Syn(-/)- mice show no evidence of myopathy, despite reduced levels of alpha-dystrobrevin-2. Neuronal nitric oxide synthase, a component of the dystrophin protein complex, is absent from the sarcolemma of the alpha-Syn(-/)- mice, even where other syntrophin isoforms are present. alpha-Syn(-/)- neuromuscular junctions have undetectable levels of postsynaptic utrophin and reduced levels of acetylcholine receptor and acetylcholinesterase. The mutant junctions have shallow nerve gutters, abnormal distributions of acetylcholine receptors, and postjunctional folds that are generally less organized and have fewer openings to the synaptic cleft than controls. Thus, alpha-syntrophin has an important role in synapse formation and in the organization of utrophin, acetylcholine receptor, and acetylcholinesterase at the neuromuscular synapse.
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Affiliation(s)
- M E Adams
- Department of Cell and Molecular Physiology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7545, USA
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25
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Knuesel I, Bornhauser BC, Zuellig RA, Heller F, Schaub MC, Fritschy JM. Differential expression of utrophin and dystrophin in CNS neurons: an in situ hybridization and immunohistochemical study. J Comp Neurol 2000; 422:594-611. [PMID: 10861528 DOI: 10.1002/1096-9861(20000710)422:4<594::aid-cne8>3.0.co;2-q] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The cellular distribution of utrophin, the autosomal homologue of dystrophin, was investigated in developing and adult rat and mouse brain by in situ hybridization and immunohistochemistry. Digoxigenin-labeled cRNA probes complementary to N-terminal, rod-domain, and C-terminal encoding sequences of utrophin were used to differentiate between full-length and short C-terminal isoforms. Largely overlapping distribution patterns were seen for the three probes in neurons of cerebral cortex, accessory olfactory bulb, and several sensory and motor brainstem nuclei as well as in blood vessels, pia mater, and choroid plexus. The C-terminal probe was detected in addition in the main olfactory bulb, striatum, thalamic reticular nucleus, and hypothalamus, suggesting a selective expression of G-utrophin in these neurons. Western blot analysis with isoform-specific antisera confirmed the expression of both full-length and G-utrophin in brain. Immunohistochemically, only full-length utrophin was detected in neurons, in close association with the plasma membrane. In addition, intense staining was seen in blood vessels, meninges, and choroid plexus, selectively localized in the basolateral membrane of immunopositive epithelial cells. The expression pattern of utrophin was already established at early postnatal stages and did not change thereafter. Double-labeling analysis revealed that utrophin and dystrophin are differentially expressed on the cellular and subcellular levels in juvenile and adult brain. Likewise, in mice lacking full-length dystrophin isoforms (mdx mice), no change in utrophin expression and distribution could be detected in brain, although utrophin was markedly up-regulated in muscle cells. These results suggest that utrophin and dystrophin are independently regulated and have distinct functional roles in CNS neurons.
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Affiliation(s)
- I Knuesel
- Institute of Pharmacology, University of Zurich, CH-8057 Zurich, Switzerland
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26
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Porter GA, Scher MG, Resneck WG, Porter NC, Fowler VM, Bloch RJ. Two populations of beta-spectrin in rat skeletal muscle. CELL MOTILITY AND THE CYTOSKELETON 2000; 37:7-19. [PMID: 9142435 DOI: 10.1002/(sici)1097-0169(1997)37:1<7::aid-cm2>3.0.co;2-7] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
We use immunoblotting, immunoprecipitation, and centrifugation in sucrose density gradients to show that the product of the erythrocyte beta-spectrin gene in rat skeletal muscle (muscle beta-spectrin) is present in two states, one associated with fodrin, and another that is not associated with any identifiable spectrin or fodrin subunit. Immunofluorescence studies indicate that a significant amount of beta-spectrin without alpha-fodrin is present in the myoplasm of some muscle fibers, and, more strikingly, at distinct regions of the sarcolemma. These results suggest that alpha-fodrin and muscle beta-spectrin associate in muscle in situ, but that some muscle beta-spectrin without a paired alpha-subunit forms distinct domains at the sarcolemma.
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Affiliation(s)
- G A Porter
- Department of Physiology, University of Maryland School of Medicine, Baltimore, USA
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27
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Cartaud J, Cartaud A, Kordeli E, Ludosky MA, Marchand S, Stetzkowski-Marden F. The torpedo electrocyte: a model system to study membrane-cytoskeleton interactions at the postsynaptic membrane. Microsc Res Tech 2000; 49:73-83. [PMID: 10757880 DOI: 10.1002/(sici)1097-0029(20000401)49:1<73::aid-jemt8>3.0.co;2-l] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Many aspects of the organization of the electromotor synapse of electric fish resemble the nerve-muscle junction. In particular, the postsynaptic membrane in both systems share most of their proteins. As a remarquable source of cholinergic synapses, the Torpedo electrocyte model has served to identify the most important components involved in synaptic transmission such as the nicotinic acetylcholine receptor and the enzyme acetylcholinesterase, as well as proteins associated with the subsynaptic cytoskeleton and the extracellular matrix involved in the assembly of the postsynaptic membrane, namely the 43-kDa protein-rapsyn, the dystrophin/utrophin complex, agrin, and others. This review encompasses some representative experiments that helped to clarify essential aspects of the supramolecular organization and assembly of the postsynaptic apparatus of cholinergic synapses.
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Affiliation(s)
- J Cartaud
- Biologie Cellulaire des Membranes, Institut Jacques Monod, UMR 9275, CNRS, Universités Paris 6 et Paris7, 75251 Paris Cedex 05, France.
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28
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Mitsui T, Kawajiri M, Kunishige M, Endo T, Akaike M, Aki K, Matsumoto T. Functional association between nicotinic acetylcholine receptor and sarcomeric proteins via actin and desmin filaments. J Cell Biochem 2000; 77:584-95. [PMID: 10771514 DOI: 10.1002/(sici)1097-4644(20000615)77:4<584::aid-jcb6>3.0.co;2-u] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
By affinity chromatography utilizing alpha-cobrotoxin from digitonin-solubilized fractions of rabbit skeletal muscle, we found that many proteins are associated with the nicotinic acetylcholine receptor (AChR). In addition to the proteins we previously reported to bind to AChR (including dystrophin-dystrophin-associated protein (DAP) complex, utrophin, rapsyn, and actin; Mitsui et al. [1996] Biochem. Biophys. Res. Commun.224:802-807), alpha-actinin, desmin, myosin, tropomyosin, troponin T, and titin are also identified to be associated with AChR. Alkaline treatment or Triton X-100 solubilization released dystrophin-DAP complex, utrophin, and rapsyn from the AChR fraction, while actin and desmin remained associated. These findings demonstrate that AChR is supported primarily by a submembranous organization of actin and desmin filaments, and is linked to sarcomeric proteins via these filaments. To further investigate whether the association has any functional role, we studied the effect of acetylcoline on ATPase activity of the AChR fraction. Acetylcholine (0.5-4 microM) significantly activated Mg(2+)-ATPase activity of digitonin-solubilized AChR fraction (P < 0.05). Furthermore, we found that desmin as well as actin activated myosin Mg(2+)-ATPase activity. From these findings, it is suggested that desmin and actin form a submembranous organization in the postsynaptic region, and function as mediators of excitation of AChR to the sarcomeric contraction system.
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Affiliation(s)
- T Mitsui
- First Department of Internal Medicine, School of Medicine, University of Tokushima, Tokushima 770-8503, Japan.
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29
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Abstract
Membrane skeletons, in particular the spectrin-based skeleton, are thought to participate in the organization of specialized membrane domains by restricting integral proteins to specific membrane sites. In the neuromuscular junction, discrete isoforms of spectrin and ankyrin, the peripheral protein that links spectrin to the membrane, colocalize with voltage-dependent sodium channels and N-CAM at the troughs of the postsynaptic membrane folds. Moreover, beta-spectrin, N-CAM, and sodium channels become clustered at the endplate during a period of time coincident with postsynaptic fold formation and synapse maturation. These observations suggest a role of the spectrin skeleton in directing and maintaining postsynaptic accumulations of sodium channels and N-CAM. In addition, the coexistence of spectrin and dystrophin at the troughs of the junctional folds raises the question of their respective functions in this membrane domain, where both cytoskeletal proteins have the potential to associate with sodium channels via ankyrin and syntrophin, respectively. Possible scenarios are discussed here with respect to accumulating evidence from studies of assembly of similar membrane domains in neurons.
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Affiliation(s)
- E Kordeli
- Biologie Cellulaire des Membranes, Institut Jacques Monod, CNRS, UMR 7592, Universités Paris 6/7, 75251 Paris-Cedex 05, France.
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30
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Kramarcy NR, Sealock R. Syntrophin isoforms at the neuromuscular junction: developmental time course and differential localization. Mol Cell Neurosci 2000; 15:262-74. [PMID: 10736203 DOI: 10.1006/mcne.1999.0823] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The syntrophins are a family of cytoplasmic adapter proteins that associate with dystrophin family proteins and have putative signaling and structural roles at the neuromuscular junction. We have localized the syntrophin family members within the rodent junction from birth to adulthood. Alpha-syntrophin is the only isoform on the postsynaptic membrane at birth. In the adult, it occurs on the crests of the junctional folds, with utrophin, and in the troughs, with dystrophin. Surprisingly, neuronal nitric oxide synthase (nNOS) does not accompany alpha-syntrophin onto the crests. Beta2-syntrophin, a junction-specific form, is not present at birth and occurs mainly in the troughs in the adult. Beta1-syntrophin is a sarcolemmal form at birth, not concentrated at the junction, and disappears entirely from most fibers by 6 weeks. In positive fibers, junctional beta1-syntrophin occurs exclusively in the troughs. These results suggest that the syntrophin isoforms have distinct functions at the junction and show that the known protein-protein associations of the syntrophins and nNOS in skeletal muscle are not sufficient to explain their localizations.
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Affiliation(s)
- N R Kramarcy
- Department of Cell and Molecular Physiology, University of North Carolina, Chapel Hill, North Carolina 27599, USA
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31
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Abstract
Since the identification of dystrophin as the causitive factor in Duchenne muscular dystrophy, there has been substantial progress in understanding the functions and interactions of this protein. Dystrophin has been shown to interact with a group of peripheral- and trans-membrane proteins known as the dystrophin-associated protein complex (DAPC) and mutations in some of the members of this complex have been shown to account for other forms of muscular dystrophy. This review summarizes the experiments using transgenic and knockout mouse models that have defined the roles of dystrophin, and the dystrophin-related protein utrophin at the skeletal muscle membrane and at the neuromuscular junction. These studies are presented in the context of other known interactions at the muscle membrane. Studies of the dystrophin-deficient mdx mouse have lead to a greater understanding of the human disease. Knockouts and transgenics of utrophin have shown this protein to be sufficient to functionally compensate for dystrophin. Dystrophin transgenic mice combined with the mdx mouse have been used to study the function of specific domains of the dystrophin protein. Together these animal models have led to a delineation of protein functions and localization patterns that will be useful for the generation of potential therapies for DMD.
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Affiliation(s)
- J A Rafael
- Department of Medical Biochemistry, The Ohio State University, College of Medicine, Columbus, Ohio 43210, USA.
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32
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Hoch W. Formation of the neuromuscular junction. Agrin and its unusual receptors. EUROPEAN JOURNAL OF BIOCHEMISTRY 1999; 265:1-10. [PMID: 10491152 DOI: 10.1046/j.1432-1327.1999.00765.x] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Synapses are essential relay stations for the transmission of information between neurones and other cells. An ordered and tightly regulated formation of these structures is crucial for the functioning of the nervous system. The induction of the intensively studied synapse between nerve and muscle is initiated by the binding of neurone-specific isoforms of the basal membrane protein agrin to receptors on the surface of myotubes. Agrin activates a receptor complex that includes the muscle-specific kinase and most likely additional, yet to be identified, components. Receptor activation leads to the aggregation of acetylcholine receptors (AChR) and other proteins of the postsynaptic apparatus. This activation process has unique features which distinguish it from other receptor tyrosine kinases. In particular, the autophosphorylation of the kinase domain, which usually induces the recruitment of adaptor and signalling molecules, is not sufficient for AChR aggregation. Apparently, interactions of the extracellular domain with unknown components are also required for this process. Agrin binds to a second protein complex on the muscle surface known as the dystrophin-associated glycoprotein complex. This binding forms one end of a molecular link between the extracellular matrix and the cytoskeleton. While many components of the machinery triggering postsynaptic differentiation have now been identified, our picture of the molecular pathway causing the redistribution of synaptic proteins is still incomplete.
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Affiliation(s)
- W Hoch
- Max-Planck-Institut für Entwicklungsbiologie, Abteilung Biochemie, Tübingen, Germany.
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33
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Enigk RE, Maimone MM. Differential expression and developmental regulation of a novel alpha-dystrobrevin isoform in muscle. Gene 1999; 238:479-88. [PMID: 10570976 DOI: 10.1016/s0378-1119(99)00358-3] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Alpha-dystrobrevin is a dystrophin-related protein expressed primarily in skeletal muscle, heart, lung and brain. In skeletal muscle, alpha-dystrobrevin is a component of the dystrophin-associated glycoprotein complex and is localized to the sarcolemma, presumably through interactions with dystrophin and utrophin. Alternative splicing of the alpha-dystrobrevin gene generates multiple isoforms which have been grouped into three major classes: alpha-DB1, alpha-DB2, and alpha-DB3. Various isoforms have been shown to interact with a variety of proteins; however, the physiological function of the alpha-dystrobrevins remains unknown. In the present study, we have cloned a novel alpha-dystrobrevin cDNA encoding a protein (referred to as alpha-DB2b) with a unique 11 amino acid C-terminal tail. Using RT PCR with primers specific to the new isoform, we have characterized its expression in skeletal muscle, heart, and brain, and in differentiating C2C12 muscle cells. We show that alpha-DB2b is expressed in skeletal muscle, heart and brain, and that exons 12 and 13 are alternatively spliced in alpha-DB2b to generate at least three splice variants. The major alpha-DB2b splice variant expressed in adult skeletal muscle and heart contains exons 12 and 13, while in adult brain, two alpha-DB2b splice variants are expressed at similar levels. This is consistent with the preferential expression of exons 12 and 13 in other alpha-dystrobrevin isoforms in skeletal muscle and heart. Similarly, in alpha-DB1 the first 21 nucleotides of exon 18 are preferentially expressed in skeletal muscle and heart relative to brain. We also show that the expression of alternatively spliced alpha-DB2b is developmentally regulated in muscle; during differentiation of C2C12 cells, alpha-DB2b expression switches from an isoform lacking exons 12 and 13 to one containing them. We demonstrate similar developmental upregulation of exons 12, 13, and 18 in alpha-DB1 and of exons 12 and 13 in alpha-DB2a. Finally, we show that alpha-DB2b protein is expressed in adult skeletal muscle, suggesting that it has a functional role in adult muscle. Together, these data suggest that alternatively spliced variants of the new alpha-dystrobrevin isoform, alpha-DB2b, are differentially expressed in various tissues and developmentally regulated during muscle cell differentiation in a fashion similar to that previously described for alpha-dystrobrevin isoforms.
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Affiliation(s)
- R E Enigk
- Department of Anatomy and Cell Biology, State University of New York Health Science Center, Syracuse 13210, USA
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34
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Abstract
Dystrophin is a cytoplasmic protein underlying the plasma membrane in normal skeletal muscle. Its absence leads to muscle degeneration as seen in Duchenne muscular dystrophy (DMD) and in mdx mice. One puzzling question in the study of dystrophinopathies is that in mdx muscles the neuromuscular junctions (NMJs) show little, if any, developmental defect, but morphological and functional abnormalities of NMJs are obvious after muscle damage and regeneration begin. This phenomenon leads us to hypothesize that dystrophin may be required for endplate maintenance and/or endplate remodeling in regenerating fibers. Here we show that the absence of dystrophin causes NMJ fragmentation in adult muscle fibers, and greatly reduces both spontaneous and agrin-induced acetylcholine receptor (AChR) clustering activities on cultured myotubes derived from satellite cells. The lower AChR clustering in mdx myotubes originates in the smaller size of each cluster and from a 72% reduction in the occurrence of large (> 10 micron 2) AChR clusters. Our results suggest dystrophin is involved in organizing small AChR clusters into large AChR aggregates during muscle regeneration, although it is not required for initiating the original AChR clustering activity.
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MESH Headings
- Age Factors
- Agrin/genetics
- Agrin/immunology
- Agrin/metabolism
- Animals
- Antibodies, Monoclonal/pharmacology
- CHO Cells
- Cricetinae
- Dystrophin/physiology
- Gene Expression/physiology
- Mice
- Mice, Inbred C57BL
- Mice, Inbred mdx
- Muscle Fibers, Skeletal/chemistry
- Muscle Fibers, Skeletal/cytology
- Muscle Fibers, Skeletal/metabolism
- Muscle, Skeletal/cytology
- Muscle, Skeletal/physiology
- Muscular Dystrophy, Animal/metabolism
- Muscular Dystrophy, Animal/pathology
- Neuromuscular Junction/chemistry
- Neuromuscular Junction/metabolism
- Neuromuscular Junction/pathology
- Receptors, Cholinergic/analysis
- Receptors, Cholinergic/metabolism
- Regeneration/physiology
- Transfection
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Affiliation(s)
- J Kong
- Department of Human Anatomy and Cell Science, University of Manitoba, Winnipeg, Canada
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35
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De la Porte S, Morin S, Koenig J. Characteristics of skeletal muscle in mdx mutant mice. INTERNATIONAL REVIEW OF CYTOLOGY 1999; 191:99-148. [PMID: 10343393 DOI: 10.1016/s0074-7696(08)60158-8] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
We review the extensive research conducted on the mdx mouse since 1987, when demonstration of the absence of dystrophin in mdx muscle led to X-chromosome-linked muscular dystrophy (mdx) being considered as a homolog of Duchenne muscular dystrophy. Certain results are contradictory. We consider most aspects of mdx skeletal muscle: (i) the distribution and roles of dystrophin, utrophin, and associated proteins; (ii) morphological characteristics of the skeletal muscle and hypotheses put forward to explain the regeneration characteristic of the mdx mouse; (iii) special features of the diaphragm; (iv) changes in basic fibroblast growth factor, ion flux, innervation, cytoskeleton, adhesive proteins, mastocytes, and metabolism; and (v) different lines of therapeutic research.
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Affiliation(s)
- S De la Porte
- Laboratoire de Neurobiologie Cellulaire et Moléculaire, CNRS UPR 9040, Gif sur Yvette, France
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36
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Williams MW, Bloch RJ. Differential distribution of dystrophin and beta-spectrin at the sarcolemma of fast twitch skeletal muscle fibers. J Muscle Res Cell Motil 1999; 20:383-93. [PMID: 10531619 DOI: 10.1023/a:1005512217552] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
We used double label immunofluorescence and confocal microscopy to examine the organization of beta-spectrin and dystrophin at the sarcolemma of fast twitch myofibers in the Extensor Digitorum Longus (EDL) of the rat. Both beta-spectrin and dystrophin are concentrated in costameres, a rectilinear sarcolemmal array composed of longitudinal strands and transverse elements overlying Z and M lines. In contrast, intercostameric regions, lying between these linear structures, contain significant levels of dystrophin but little detectable beta-spectrin. The dystrophin-associated proteins, syntrophin and beta-dystroglycan, are also concentrated at costameres but, like dystrophin, are present in intercostameric regions as well. Dystrophin is present at costameres and intercostameric regions in fast twitch muscles of the mouse but is absent from all regions of the sarcolemma in the mdx mouse, which lacks dystrophin. Areas of the sarcolemma near myonuclei also contain dystrophin without beta-spectrin, consistent with the idea that the distribution of dystrophin at the sarcolemma is not dependent on beta-spectrin. We conclude that dystrophin is present under all areas of the sarcolemma. The increased fragility of the sarcolemma in patients with Duchennes muscular dystrophy may be explained in part by the absence of dystrophin not only from costameres, but also from intercostameric regions.
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Affiliation(s)
- M W Williams
- Department of Physiology, School of Medicine, University of Maryland, Baltimore, USA
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37
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Kachinsky AM, Froehner SC, Milgram SL. A PDZ-containing scaffold related to the dystrophin complex at the basolateral membrane of epithelial cells. J Biophys Biochem Cytol 1999; 145:391-402. [PMID: 10209032 PMCID: PMC2133114 DOI: 10.1083/jcb.145.2.391] [Citation(s) in RCA: 88] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Membrane scaffolding complexes are key features of many cell types, serving as specialized links between the extracellular matrix and the actin cytoskeleton. An important scaffold in skeletal muscle is the dystrophin-associated protein complex. One of the proteins bound directly to dystrophin is syntrophin, a modular protein comprised entirely of interaction motifs, including PDZ (protein domain named for PSD-95, discs large, ZO-1) and pleckstrin homology (PH) domains. In skeletal muscle, the syntrophin PDZ domain recruits sodium channels and signaling molecules, such as neuronal nitric oxide synthase, to the dystrophin complex. In epithelia, we identified a variation of the dystrophin complex, in which syntrophin, and the dystrophin homologues, utrophin and dystrobrevin, are restricted to the basolateral membrane. We used exogenously expressed green fluorescent protein (GFP)-tagged fusion proteins to determine which domains of syntrophin are responsible for its polarized localization. GFP-tagged full-length syntrophin targeted to the basolateral membrane, but individual domains remained in the cytoplasm. In contrast, the second PH domain tandemly linked to a highly conserved, COOH-terminal region was sufficient for basolateral membrane targeting and association with utrophin. The results suggest an interaction between syntrophin and utrophin that leaves the PDZ domain of syntrophin available to recruit additional proteins to the epithelial basolateral membrane. The assembly of multiprotein signaling complexes at sites of membrane specialization may be a widespread function of dystrophin-related protein complexes.
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Affiliation(s)
- A M Kachinsky
- Department of Cell and Molecular Physiology and Curriculum in Neurobiology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7545, USA
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38
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Howard PL, Dally GY, Ditta SD, Austin RC, Worton RG, Klamut HJ, Ray PN. Dystrophin isoforms DP71 and DP427 have distinct roles in myogenic cells. Muscle Nerve 1999; 22:16-27. [PMID: 9883853 DOI: 10.1002/(sici)1097-4598(199901)22:1<16::aid-mus5>3.0.co;2-r] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Duchenne muscular dystrophy is caused by mutations in the dystrophin gene, a complex gene that generates a family of distinct isoforms. In immature muscle cells, two dystrophin isoforms are expressed, Dp427 and Dp71. To characterize the function of Dp71 in myogenesis, we have examined the expression of Dp71 in myogenic cells. The localization of Dp71 in these cells is distinct from the localization of Dp427. Whereas Dp427 localizes to focal adhesions and surface membrane during myogenesis, Dp71 localizes to stress fiberlike structures in myogenic cells. Biochemical fractionation of myogenic cells demonstrates that Dp71 cosediments with the actin bundles thus confirming this interaction. Furthermore, transfection of C2C12 myoblasts with constructs encoding Dp71 fused to green fluorescent protein targeted the protein to the actin microfilament bundles. These results demonstrate involvement of Dp71 with the actin cytoskeleton during myogenesis and suggest a role for Dp71 that is distinct from Dp427.
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Affiliation(s)
- P L Howard
- Department of Molecular and Medical Genetics, University of Toronto, Canada
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39
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Peters MF, Sadoulet-Puccio HM, Grady MR, Kramarcy NR, Kunkel LM, Sanes JR, Sealock R, Froehner SC. Differential membrane localization and intermolecular associations of alpha-dystrobrevin isoforms in skeletal muscle. J Cell Biol 1998; 142:1269-78. [PMID: 9732287 PMCID: PMC2149339 DOI: 10.1083/jcb.142.5.1269] [Citation(s) in RCA: 92] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/1998] [Revised: 07/08/1998] [Indexed: 11/22/2022] Open
Abstract
alpha-Dystrobrevin is both a dystrophin homologue and a component of the dystrophin protein complex. Alternative splicing yields five forms, of which two predominate in skeletal muscle: full-length alpha-dystrobrevin-1 (84 kD), and COOH-terminal truncated alpha-dystrobrevin-2 (65 kD). Using isoform-specific antibodies, we find that alpha-dystrobrevin-2 is localized on the sarcolemma and at the neuromuscular synapse, where, like dystrophin, it is most concentrated in the depths of the postjunctional folds. alpha-Dystrobrevin-2 preferentially copurifies with dystrophin from muscle extracts. In contrast, alpha-dystrobrevin-1 is more highly restricted to the synapse, like the dystrophin homologue utrophin, and preferentially copurifies with utrophin. In yeast two-hybrid experiments and coimmunoprecipitation of in vitro-translated proteins, alpha-dystrobrevin-2 binds dystrophin, whereas alpha-dystrobrevin-1 binds both dystrophin and utrophin. alpha-Dystrobrevin-2 was lost from the nonsynaptic sarcolemma of dystrophin-deficient mdx mice, but was retained on the perisynaptic sarcolemma even in mice lacking both utrophin and dystrophin. In contrast, alpha-dystrobrevin-1 remained synaptically localized in mdx and utrophin-negative muscle, but was absent in double mutants. Thus, the distinct distributions of alpha-dystrobrevin-1 and -2 can be partly explained by specific associations with utrophin and dystrophin, but other factors are also involved. These results show that alternative splicing confers distinct properties of association on the alpha-dystrobrevins.
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Affiliation(s)
- M F Peters
- Department of Cell and Molecular Physiology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7545, USA
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40
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Balasubramanian S, Fung ET, Huganir RL. Characterization of the tyrosine phosphorylation and distribution of dystrobrevin isoforms. FEBS Lett 1998; 432:133-40. [PMID: 9720911 DOI: 10.1016/s0014-5793(98)00804-7] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Dystrobrevin, a member of the dystrophin family of proteins, was initially identified as a major tyrosine phosphorylated synaptic protein in the electric organ of Torpedo californica. In this paper, we show that the major sites of tyrosine phosphorylation of Torpedo dystrobrevin are within its C-terminus, on Tyr-693 and Tyr-710. Cloning of the mammalian homologue of dystrobrevin has recently shown that this phosphotyrosine containing tail, or PYCT, is subject to alternative splicing. To compare the expression and distribution of PYCT- and PYCT+ splice variants, we generated antibodies against different regions of dystrobrevin. Here we show that the PYCT- isoform of 62 kDa is expressed at high levels in all tissues examined. In contrast, PYCT+ isoforms are expressed primarily in brain and muscle, where they are concentrated at synapses. Moreover, PYCT+ isoforms associate more tightly with the membrane and with syntrophin, another synaptically enriched protein. These results suggest that PYCT+ isoforms of dystrobrevin are specialized components of the dystroglycan complex which render the complex sensitive to regulation by tyrosine kinases.
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Affiliation(s)
- S Balasubramanian
- Howard Hughes Medical Institute, Johns Hopkins University School of Medicine, Department of Neuroscience, Baltimore, MD 21205-2185, USA
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41
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Bezakova G, Bloch RJ. The zinc finger domain of the 43-kDa receptor-associated protein, rapsyn: role in acetylcholine receptor clustering. Mol Cell Neurosci 1998; 11:274-88. [PMID: 9698394 DOI: 10.1006/mcne.1998.0688] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We injected rat myotubes with proteins and antibodies to assess the importance of the zinc finger (ZnF) domain of the 43-kDa receptor-associated protein, rapsyn, in clustering acetylcholine receptors (AChR). Injection of rat myotubes with a fusion protein containing the ZnF domain of rapsyn disrupted AChR clusters. Clusters were unaffected by a fusion protein containing a double mutant that does not bind zinc. Similar results were obtained with the purified wild type and mutant ZnF domains. The ZnF of HIV-1 nucleocapsid protein had no effect. AChR clusters were also disrupted in myotubes injected with antibodies to the ZnF domain, followed by injection of anti-antibodies. Injection of antibodies directed against a different rapsyn epitope or against the cytoplasmic domain of the AChR had no effect. In transfection experiments with HEK 293 cells, the ZnF domain failed to associate with membrane aggregates containing full-length rapsyn, AChR, or rapsyn and AChR together. We conclude that the ZnF domain of rapsyn provides a binding site essential for AChR clustering, but that this site is unlikely to be involved in high affinity binding of rapsyn to itself or to AChR.
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Affiliation(s)
- G Bezakova
- Department of Physiology, University of Maryland School of Medicine, 660 West Redwood Street, Baltimore, Maryland, 21201, USA
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42
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Axon withdrawal during synapse elimination at the neuromuscular junction is accompanied by disassembly of the postsynaptic specialization and withdrawal of Schwann cell processes. J Neurosci 1998. [PMID: 9634561 DOI: 10.1523/jneurosci.18-13-04953.1998] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Nerve terminal withdrawal is accompanied by a loss of acetylcholine receptors (AChRs) at corresponding postsynaptic sites during the process of synapse elimination at developing () and reinnervated adult () neuromuscular junctions. Aside from AChR and nerve terminal loss, however, the molecular and cellular alterations that occur at sites of elimination are unknown. To gain a better understanding of the cascade of events that leads to the disassembly of synaptic sites during the synapse elimination process, we surveyed the distribution of molecular elements of the postsynaptic specialization, the basal lamina, and supporting Schwann cells during the process of synapse elimination that occurs after reinnervation. In addition, quantitative techniques were used to determine the temporal order of disappearance of molecules that were lost relative to the loss of postsynaptic AChRs. We found that the dismantling of the postsynaptic specialization was inhomogeneous, with evidence of rapid dissolution of some aspects of the postsynaptic apparatus and slower loss of others. We also observed a loss of Schwann cell processes from sites of synapse elimination, with a time course similar to that seen for nerve terminal retraction. In contrast, all of the extracellular markers that we examined were lost slowly from sites of synapse loss. We therefore conclude that the synapse elimination process is synapse-wide, removing not only nerve terminals but also Schwann cells and many aspects of the postsynaptic apparatus. The disassembly occurs in a stereotyped sequence with some synaptic elements appearing much more stable than others.
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43
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Culican SM, Nelson CC, Lichtman JW. Axon withdrawal during synapse elimination at the neuromuscular junction is accompanied by disassembly of the postsynaptic specialization and withdrawal of Schwann cell processes. J Neurosci 1998; 18:4953-65. [PMID: 9634561 PMCID: PMC6792572] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Nerve terminal withdrawal is accompanied by a loss of acetylcholine receptors (AChRs) at corresponding postsynaptic sites during the process of synapse elimination at developing () and reinnervated adult () neuromuscular junctions. Aside from AChR and nerve terminal loss, however, the molecular and cellular alterations that occur at sites of elimination are unknown. To gain a better understanding of the cascade of events that leads to the disassembly of synaptic sites during the synapse elimination process, we surveyed the distribution of molecular elements of the postsynaptic specialization, the basal lamina, and supporting Schwann cells during the process of synapse elimination that occurs after reinnervation. In addition, quantitative techniques were used to determine the temporal order of disappearance of molecules that were lost relative to the loss of postsynaptic AChRs. We found that the dismantling of the postsynaptic specialization was inhomogeneous, with evidence of rapid dissolution of some aspects of the postsynaptic apparatus and slower loss of others. We also observed a loss of Schwann cell processes from sites of synapse elimination, with a time course similar to that seen for nerve terminal retraction. In contrast, all of the extracellular markers that we examined were lost slowly from sites of synapse loss. We therefore conclude that the synapse elimination process is synapse-wide, removing not only nerve terminals but also Schwann cells and many aspects of the postsynaptic apparatus. The disassembly occurs in a stereotyped sequence with some synaptic elements appearing much more stable than others.
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Affiliation(s)
- S M Culican
- Department of Anatomy and Neurobiology, Washington University School of Medicine, St Louis, MO 63110, USA
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44
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Abstract
Abnormal expression of the cytoskeletal protein dystrophin has deleterious consequences for skeletal muscle, cardiac muscle, and the central nervous system. A complete failure to express the protein produces Duchenne muscular dystrophy (DMD), in which there is extensive and progressive skeletal muscle necrosis, the development of a life-threatening dilated cardiomyopathy, and mild mental retardation. Dystrophin binds the F-actin cytoskeleton and is normally expressed in a complex of transmembrane proteins (the "dystrophin protein complex") that interact with external components of the basal lamina. One pathogenic model for DMD (the "structural hypothesis") suggests that this complex forms a structural bridge between the external basal lamina and the internal cytoskeleton and that the absence of dystrophin produces a defect in membrane structural support that renders skeletal muscle susceptible to plasmalemmal ruptures (or "tears") during the course of contractile activity. This review attempts to critically evaluate the structural hypothesis for DMD and presents an opposing model (the "channel aggregation model") that highlights the role of dystrophin in organizing the membrane cytoskeleton and the role of the cytoskeleton in aggregating ion channels and neurotransmitter receptors. Since ion channel aggregation is a process that is common across organ systems, the idea that channel function can be altered when aggregated ion channels interact with a dystrophic cytoskeleton has immediate implications for the expression of the dystrophinopathies in skeletal muscle, cardiac muscle, and the central nervous system.
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Affiliation(s)
- C G Carlson
- Department of Physiology, Kirksville College of Osteopathic Medicine, Missouri 63501, USA
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45
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Liberona JL, Powell JA, Shenoi S, Petherbridge L, Caviedes R, Jaimovich E. Differences in both inositol 1,4,5-trisphosphate mass and inositol 1,4,5-trisphosphate receptors between normal and dystrophic skeletal muscle cell lines. Muscle Nerve 1998; 21:902-9. [PMID: 9626250 DOI: 10.1002/(sici)1097-4598(199807)21:7<902::aid-mus8>3.0.co;2-a] [Citation(s) in RCA: 50] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Human normal (RCMH) and Duchenne muscular dystrophy (RCDMD) cell lines, as well as newly developed normal and dystrophic murine cell lines, were used for the study of both changes in inositol 1,4,5-trisphosphate (IP3) mass and IP3 binding to receptors. Basal levels of IP3 were increased two- to threefold in dystrophic human and murine cell lines compared to normal cell lines. Potassium depolarization induced a time-dependent IP3 rise in normal human cells and cells of the myogenic mouse cell line (129CB3), which returned to their basal levels after 60 s. However, in the human dystrophic cell line (RCDMD), IP3 levels remained high up to 200 s after potassium depolarization. Expression of IP3 receptors was studied measuring specific binding of 3H-IP3 in the murine cell lines (normal 129CB3 and dystrophic mdx XLT 4-2). All the cell lines bind 3H-IP3 with relatively high affinity (Kd: between 40 and 100 nmol/L). IP3 receptors are concentrated in the nuclear fraction, and their density is significantly higher in dystrophic cells compared to normal. These findings together with high basal levels of IP3 mass suggest a possible role for this system in the deficiency of intracellular calcium regulation in Duchenne muscular dystrophy.
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MESH Headings
- Actinin/analysis
- Animals
- Calcium Channels/analysis
- Calcium Channels/metabolism
- Cell Fractionation
- Cell Line
- Dystrophin/deficiency
- Dystrophin/genetics
- Electrophysiology
- Humans
- Inositol 1,4,5-Trisphosphate/analysis
- Inositol 1,4,5-Trisphosphate/metabolism
- Inositol 1,4,5-Trisphosphate/pharmacology
- Inositol 1,4,5-Trisphosphate Receptors
- Membrane Potentials/drug effects
- Membrane Potentials/physiology
- Mice
- Mice, Inbred C57BL
- Mice, Inbred mdx
- Muscle, Skeletal/chemistry
- Muscle, Skeletal/cytology
- Muscle, Skeletal/metabolism
- Muscular Dystrophy, Animal/metabolism
- Potassium Chloride/pharmacology
- Radioligand Assay
- Receptors, Cytoplasmic and Nuclear/agonists
- Receptors, Cytoplasmic and Nuclear/analysis
- Receptors, Cytoplasmic and Nuclear/metabolism
- Ryanodine/pharmacology
- Tritium
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Affiliation(s)
- J L Liberona
- Department of Physiology and Biophysics, Faculty of Medicine, University of Chile, Santiago, Chile
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46
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Wood SJ, Slater CR. beta-Spectrin is colocalized with both voltage-gated sodium channels and ankyrinG at the adult rat neuromuscular junction. J Cell Biol 1998; 140:675-84. [PMID: 9456326 PMCID: PMC2140176 DOI: 10.1083/jcb.140.3.675] [Citation(s) in RCA: 90] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/1997] [Revised: 12/05/1997] [Indexed: 02/06/2023] Open
Abstract
Voltage-gated sodium channels (VGSCs) are concentrated in the depths of the postsynaptic folds at mammalian neuromuscular junctions (NMJs) where they facilitate action potential generation during neuromuscular transmission. At the nodes of Ranvier and the axon hillocks of central neurons, VGSCs are associated with the cytoskeletal proteins, beta-spectrin and ankyrin, which may help to maintain the high local density of VGSCs. Here we show in skeletal muscle, using immunofluorescence, that beta-spectrin is precisely colocalized with both VGSCs and ankyrinG, the nodal isoform of ankyrin. In en face views of rat NMJs, acetylcholine receptors (AChRs), and utrophin immunolabeling are organized in distinctive linear arrays corresponding to the crests of the postsynaptic folds. In contrast, beta-spectrin, VGSCs, and ankyrinG have a punctate distribution that extends laterally beyond the AChRs, consistent with a localization in the depths of the folds. Double antibody labeling shows that beta-spectrin is precisely colocalized with both VGSCs and ankyrinG at the NMJ. Furthermore, quantification of immunofluorescence in labeled transverse sections reveals that beta-spectrin is also concentrated in perijunctional regions, in parallel with an increase in labeling of VGSCs and ankyrinG, but not of dystrophin. These observations suggest that interactions with beta-spectrin and ankyrinG help to maintain the concentration of VGSCs at the NMJ and that a common mechanism exists throughout the nervous system for clustering VGSCs at a high density.
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Affiliation(s)
- S J Wood
- School of Neurosciences, The Medical School, University of Newcastle upon Tyne NE2 4HH, United Kingdom.
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Interaction of muscle and brain sodium channels with multiple members of the syntrophin family of dystrophin-associated proteins. J Neurosci 1998. [PMID: 9412493 DOI: 10.1523/jneurosci.18-01-00128.1998] [Citation(s) in RCA: 252] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Syntrophins are cytoplasmic peripheral membrane proteins of the dystrophin-associated protein complex (DAPC). Three syntrophin isoforms, alpha1, beta1, and beta2, are encoded by distinct genes. Each contains two pleckstrin homology (PH) domains, a syntrophin-unique (SU) domain, and a PDZ domain. The name PDZ comes from the first three proteins found to contain repeats of this domain (PSD-95, Drosophila discs large protein, and the zona occludens protein 1). PDZ domains in other proteins bind to the C termini of ion channels and neurotransmitter receptors containing the consensus sequence (S/T)XV-COOH and mediate the clustering or synaptic localization of these proteins. Two voltage-gated sodium channels (NaChs), SkM1 and SkM2, of skeletal and cardiac muscle, respectively, have this consensus sequence. Because NaChs are sarcolemmal components like syntrophins, we have investigated possible interactions between these proteins. NaChs copurify with syntrophin and dystrophin from extracts of skeletal and cardiac muscle. Peptides corresponding to the C-terminal 10 amino acids of SkM1 and SkM2 are sufficient to bind detergent-solubilized muscle syntrophins, to inhibit the binding of native NaChs to syntrophin PDZ domain fusion proteins, and to bind specifically to PDZ domains from alpha1-, beta1-, and beta2-syntrophin. These peptides also inhibit binding of the syntrophin PDZ domain to the PDZ domain of neuronal nitric oxide synthase, an interaction that is not mediated by C-terminal sequences. Brain NaChs, which lack the (S/T)XV consensus sequence, also copurify with syntrophin and dystrophin, an interaction that does not appear to be mediated by the PDZ domain of syntrophin. Collectively, our data suggest that syntrophins link NaChs to the actin cytoskeleton and the extracellular matrix via dystrophin and the DAPC.
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Gee SH, Madhavan R, Levinson SR, Caldwell JH, Sealock R, Froehner SC. Interaction of muscle and brain sodium channels with multiple members of the syntrophin family of dystrophin-associated proteins. J Neurosci 1998; 18:128-37. [PMID: 9412493 PMCID: PMC6793384] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Syntrophins are cytoplasmic peripheral membrane proteins of the dystrophin-associated protein complex (DAPC). Three syntrophin isoforms, alpha1, beta1, and beta2, are encoded by distinct genes. Each contains two pleckstrin homology (PH) domains, a syntrophin-unique (SU) domain, and a PDZ domain. The name PDZ comes from the first three proteins found to contain repeats of this domain (PSD-95, Drosophila discs large protein, and the zona occludens protein 1). PDZ domains in other proteins bind to the C termini of ion channels and neurotransmitter receptors containing the consensus sequence (S/T)XV-COOH and mediate the clustering or synaptic localization of these proteins. Two voltage-gated sodium channels (NaChs), SkM1 and SkM2, of skeletal and cardiac muscle, respectively, have this consensus sequence. Because NaChs are sarcolemmal components like syntrophins, we have investigated possible interactions between these proteins. NaChs copurify with syntrophin and dystrophin from extracts of skeletal and cardiac muscle. Peptides corresponding to the C-terminal 10 amino acids of SkM1 and SkM2 are sufficient to bind detergent-solubilized muscle syntrophins, to inhibit the binding of native NaChs to syntrophin PDZ domain fusion proteins, and to bind specifically to PDZ domains from alpha1-, beta1-, and beta2-syntrophin. These peptides also inhibit binding of the syntrophin PDZ domain to the PDZ domain of neuronal nitric oxide synthase, an interaction that is not mediated by C-terminal sequences. Brain NaChs, which lack the (S/T)XV consensus sequence, also copurify with syntrophin and dystrophin, an interaction that does not appear to be mediated by the PDZ domain of syntrophin. Collectively, our data suggest that syntrophins link NaChs to the actin cytoskeleton and the extracellular matrix via dystrophin and the DAPC.
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Affiliation(s)
- S H Gee
- Department of Physiology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7545, USA
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Peters MF, O'Brien KF, Sadoulet-Puccio HM, Kunkel LM, Adams ME, Froehner SC. beta-dystrobrevin, a new member of the dystrophin family. Identification, cloning, and protein associations. J Biol Chem 1997; 272:31561-9. [PMID: 9395493 DOI: 10.1074/jbc.272.50.31561] [Citation(s) in RCA: 88] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Dystrophin, the protein disrupted in Duchenne muscular dystrophy, is one of several related proteins that are key components of the submembrane cytoskeleton. Three dystrophin-related proteins (utrophin, dystrophin-related protein-2 (DRP2), and dystrobrevin) have been described. Here, we identify a human gene on chromosome 2p22-23 that encodes a novel protein, beta-dystrobrevin, with significant homology to the other known dystrobrevin (now termed alpha-dystrobrevin). Sequence alignments including this second dystrobrevin strongly support the concept that two distinct subfamilies exist within the dystrophin family, one composed of dystrophin, utrophin, and DRP2 and the other composed of alpha- and beta-dystrobrevin. The possibility that members of each subfamily form distinct protein complexes was examined by immunopurifying dystrobrevins and dystrophin. A beta-dystrobrevin antibody recognized a protein of the predicted size (71 kDa) that copurified with the dystrophin short form, Dp71. Thus, like alpha-dystrobrevin, beta-dystrobrevin is likely to associate directly with dystrophin. alpha- and beta-dystrobrevins failed to copurify with each other, however. These results suggest that members of the dystrobrevin subfamily form heterotypic associations with dystrophin and raise the possibility that pairing of a particular dystrobrevin with dystrophin may be regulated, thereby providing a mechanism for assembly of distinct submembrane protein complexes.
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Affiliation(s)
- M F Peters
- Department of Physiology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7545, USA
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Abstract
Acetylcholine receptors (AChRs) are present at the top of the postsynaptic membrane of the neuromuscular junction (NMJ) at very high density, possibly anchored to cytoskeletal elements. The present study investigated whether AChR degradation is affected in animals lacking dystrophin, a protein that is an integral part of the cytoskeletal complex and is missing in Duchenne muscular dystrophy. The animal model for Duchenne muscular dystrophy, the mutant mdx mouse, was used to determine whether disruption of the cytoskeleton, caused by the absence of dystrophin, affects AChR degradation. Of the two populations of junctional AChRs, Rs (expressed in innervated adult muscles) and Rr (expressed in embryonic or denervated muscles), only Rs are affected in mdx animals. In innervated mdx soleus, diaphragm, and sternomastoid muscles, the AChRs have an accelerated degradation rate (t1/2 of approximately 3-5 d), similar to that acquired by Rs in control muscles after denervation. The Rs in mdx NMJs do not accelerate further when the muscles are denervated. The absence of dystrophin does not affect the degradation rate of the Rr AChRs (t1/2 of 1 d), which are expressed after denervation in mdx as in control muscles. These results suggest that dystrophin or an intact cytoskeletal complex may be required for neuronal stabilization of Rs receptors at the adult neuromuscular junctions.
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