201
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Rando TA. The dystrophin-glycoprotein complex, cellular signaling, and the regulation of cell survival in the muscular dystrophies. Muscle Nerve 2001; 24:1575-94. [PMID: 11745966 DOI: 10.1002/mus.1192] [Citation(s) in RCA: 281] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Mutations of different components of the dystrophin-glycoprotein complex (DGC) cause muscular dystrophies that vary in terms of severity, age of onset, and selective involvement of muscle groups. Although the primary pathogenetic processes in the muscular dystrophies have clearly been identified as apoptotic and necrotic muscle cell death, the pathogenetic mechanisms that lead to cell death remain to be determined. Studies of components of the DGC in muscle and in nonmuscle tissues have revealed that the DGC is undoubtedly a multifunctional complex and a highly dynamic structure, in contrast to the unidimensional concept of the DGC as a mechanical component in the cell. Analysis of the DGC reveals compelling analogies to two other membrane-associated protein complexes, namely integrins and caveolins. Each of these complexes mediates signal transduction cascades in the cell, and disruption of each complex causes muscular dystrophies. The signal transduction cascades associated with the DGC, like those associated with integrins and caveolins, play important roles in cell survival signaling, cellular defense mechanisms, and regulation of the balance between cell survival and cell death. This review focuses on the functional components of the DGC, highlighting the evidence of their participation in cellular signaling processes important for cell survival. Elucidating the link between these functional components and the pathogenetic processes leading to cell death is the foremost challenge to understanding the mechanisms of disease expression in the muscular dystrophies due to defects in the DGC.
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Affiliation(s)
- T A Rando
- Department of Neurology and Neurological Sciences, Stanford University Medical Center, Room A-343, Stanford, California 94305-5235, USA.
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202
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Hernández-González EO, Martínez-Rojas D, Mornet D, Rendon A, Mújica A. Comparative distribution of short dystrophin superfamily products in various guinea pig spermatozoa domains. Eur J Cell Biol 2001; 80:792-8. [PMID: 11831393 DOI: 10.1078/0171-9335-00202] [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: 11/18/2022] Open
Abstract
In this study, the presence and cellular distribution of dystrophin family products (i.e. Dp71d, Dp71f-like protein and dystrobrevin) was examined by indirect immunofluorescence and Western blotting in guinea pig spermatozoa. Two dystrophin-associated proteins, beta-dystroglycan and alpha-syntrophin, and nNOS a protein frequently associated with alpha-syntrophin, were determined. In spermatozoa lacking plasma membrane and acrosome, Dp71f-like protein was found in the postacrosomal perinuclear theca and also in the middle piece of the flagellum. In the flagellum, Dp71f-like protein is localized together with alpha-syntrophin and nNOS. Dp71d was present in the plasma membrane of the middle piece with beta-dystroglycan, alpha-syntrophin and nNOS. Dp71d was also present in plasma membrane of the post acrosomal region, but only with nNOS. Finally, dystrobrevin was located all along skeletal flagellum structures and in the subacrosomal hemisphere of the perinuclear theca. This distinct and complementary distribution in various domains of spermatozoa may reveal a specific function for each short dystrophin family product, in the stabilization of the domains where they are located.
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203
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Rando TA. Role of nitric oxide in the pathogenesis of muscular dystrophies: a "two hit" hypothesis of the cause of muscle necrosis. Microsc Res Tech 2001; 55:223-35. [PMID: 11748861 DOI: 10.1002/jemt.1172] [Citation(s) in RCA: 103] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Although the genetic and biochemical bases of many of the muscular dystrophies have been elucidated, the pathophysiological mechanisms leading to muscle cell death and degeneration remain elusive. Among the most well studied of the dystrophies are those due to defects in proteins that make up the dystrophin-glycoprotein complex (DGC). There has been much interest in the role of nitric oxide (NO(*)) in the pathogenesis of these diseases because the enzyme that synthesizes NO(*), nitric oxide synthase (NOS), is associated with the DGC. Recent studies of dystrophies related to DGC defects suggest that one mechanism of cellular injury is functional ischemia related to alterations in cellular NOS and disruption of a normal protective action of NO(*). This protective action is the prevention of local ischemia during contraction-induced increases in sympathetic vasoconstriction. However, the loss of this protection, alone, does not explain the subsequent muscle cell death and degeneration since mice lacking neuronal NOS (the predominant isoform expressed in muscle) do not develop a muscular dystrophy. Thus, there must be additional biochemical changes conferred upon the cells by these DGC defects, and these changes are discussed in terms of a proposed "two hit" hypothesis of the pathogenetic mechanisms that underlie the muscular dystrophies. According to this hypothesis, pathogenic defects in the DGC have at least two biochemical consequences: a reduction in NO(*)-mediated protection against ischemia, and an increase in cellular susceptibility to metabolic stress. Either one alone may be insufficient to lead to muscle cell death. However, in combination, the biochemical consequences are sufficient to cause muscle degeneration. The role of oxidative stress as a final common pathophysiologic pathway is discussed in terms of data showing that oxidative injury precedes pathologic changes and that muscle cells with defects in the DGC have an increased susceptibility to oxidant challenges. Accordingly, this "two hit" hypothesis may explain many of the complex spatial and temporal variations in disease expression that characterize the muscular dystrophies, such as grouped necrosis, a pre-necrotic phase of the disease, and selective muscle involvement.
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Affiliation(s)
- T A Rando
- GRECC, Palo Alto VA Medical Center, Palo Alto, California 94304, USA.
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204
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Loh NY, Nebenius-Oosthuizen D, Blake DJ, Smith AJ, Davies KE. Role of beta-dystrobrevin in nonmuscle dystrophin-associated protein complex-like complexes in kidney and liver. Mol Cell Biol 2001; 21:7442-8. [PMID: 11585924 PMCID: PMC99916 DOI: 10.1128/mcb.21.21.7442-7448.2001] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
beta-Dystrobrevin is a dystrophin-related and -associated protein that is highly expressed in brain, kidney, and liver. Recent studies with the kidneys of the mdx3Cv mouse, which lacks all dystrophin isoforms, suggest that beta-dystrobrevin, and not the dystrophin isoforms, may be the key component in the assembly of complexes similar to the muscle dystrophin-associated protein complexes (DPC) in nonmuscle tissues. To understand the role of beta-dystrobrevin in the function of nonmuscle tissues, we generated beta-dystrobrevin-deficient (dtnb(-/-)) mice by gene targeting. dtnb(-/-) mice are healthy, fertile, and normal in appearance. No beta-dystrobrevin was detected in these mice by Western blotting or immunocytochemistry. In addition, the levels of several beta-dystrobrevin-interacting proteins, namely Dp71 isoforms and the syntrophins, were greatly reduced from the basal membranes of kidney tubules and liver sinusoids and on Western blots of crude kidney and liver microsomes of beta-dystrobrevin-deficient mice. However, no abnormality was detected in the ultrastructure of membranes of kidney and liver cells or in the renal function of these mice. beta-Dystrobrevin may therefore be an anchor or scaffold for Dp71 and syntrophin isoforms, as well as other associating proteins at the basal membranes of kidney and liver, but is not necessary for the normal function of these mice.
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Affiliation(s)
- N Y Loh
- Department of Human Anatomy and Genetics, University of Oxford, Oxford OX1 3QX, United Kingdom
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205
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Blottner D, Lück G. Just in time and place: NOS/NO system assembly in neuromuscular junction formation. Microsc Res Tech 2001; 55:171-80. [PMID: 11747092 DOI: 10.1002/jemt.1168] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Recent advances in the molecular, biochemical, and anatomical aspects of postsynaptic membrane components at the neuromuscular junction (NMJ) are briefly reviewed focussing on assembly, architecture, and function of the multi-subunit dystrophin-protein complex (DPC) and its associated nitric oxide (NO)-signaling complex. Elucidation of unique structural binding motifs of NO-synthases (NOS), and microscopical codistribution of neuronal NOS (nNOS), the major isoform of NOS expressed at the NMJ, with known synaptic proteins, i.e., family members of the DPC, nicotinic acetylcholine receptor (AChR), NMDA-receptor, type-1 sodium and Shaker K(+)-channel proteins, and linker proteins (e.g., PSD-95, 43K-rapsyn), suggests targeting and assembly of the NO-signaling pathway at postsynaptic membrane components. NO mediates agrin-induced AChR-aggregation and downstream signal transduction in C2 skeletal myotubes while administration of L-arginine, the limiting substrate for NO-biosynthesis, enhances aggregation of synapse-specific components such as utrophin. At the NMJ, NO appears to be a mediator of (1) early synaptic protein clustering, (2) synaptic receptor activity and transmitter release, or (3) downstream signaling for transcriptional control. Multidisciplinary data obtained from cellular and molecular studies and from immunolocalization investigations have led us to propose a working model for step-by-step binding of nNOS, e.g., to subunit domains of targeted and/or preexisting membrane components. Formation of NOS-membrane complexes appears to be governed by agrin-signaling as well as by NO-signaling, supporting the idea that parallel signaling pathways may account for the spatiotemporally defined postsynaptic assembly thereby linking the NOS/NO-signaling cascade to early membrane aggregations and at the right places nearby preexisting targets (e.g., juxtaposition of NO source and target) in synapse formation.
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Affiliation(s)
- D Blottner
- Department of Anatomy 1, Neurobiology Group, Freie Universität Berlin, Königin-Luise-Strasse 15, D-14195 Berlin-Dahlem, Germany.
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206
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Connolly AM, Keeling RM, Mehta S, Pestronk A, Sanes JR. Three mouse models of muscular dystrophy: the natural history of strength and fatigue in dystrophin-, dystrophin/utrophin-, and laminin alpha2-deficient mice. Neuromuscul Disord 2001; 11:703-12. [PMID: 11595512 DOI: 10.1016/s0960-8966(01)00232-2] [Citation(s) in RCA: 107] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
To optimize and evaluate treatments for muscular dystrophy, it is important to know the natural history of the disease in the absence of therapeutic intervention. Here we characterized disease progression of three mutant mouse strains of muscular dystrophy: mdx mice, which lack dystrophin; mdx:utrn-/- mice, which also lack utrophin; and dy/dy mice, which are deficient in laminin alpha2. Normal mice show a marked increase in forelimb strength over the first 10 weeks of life and little fatigue (<5%) over five consecutive strength trials. Mdx and mdx:utrn-/- mice demonstrate less strength then normal mice and approximately 40% fatigue at each age. Mdx mice become obese but mdx:utrn-/- mice do not. Dy/dy mice remain small and are much weaker than mdx and mdx:utrn-/- mice at all ages even when normalized to weight; however, they show only minimal fatigue (10%). This work demonstrates a distinct pattern of disease progression in each model and provides a foundation for assessing strategies for improving strength in each model.
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Affiliation(s)
- A M Connolly
- Department of Neurology, Washington University School of Medicine, Box 8111 660 S. Euclid, Saint Louis, MO 63110, USA.
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207
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Miyagoe-Suzuki Y, Takeda SI. Association of neuronal nitric oxide synthase (nNOS) with alpha1-syntrophin at the sarcolemma. Microsc Res Tech 2001; 55:164-70. [PMID: 11747091 DOI: 10.1002/jemt.1167] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
alpha1-syntrophin is a PDZ-containing dystrophin-associated protein, expressed predominantly in striated muscle and brain. alpha1-syntrophin null mice generated by gene targeting technique showed no overt muscular dystrophic phenotype. Though other dystrophin-associated proteins were localized at the sarcolemma, neuronal nitric oxide synthase (nNOS) was selectively lost from the membrane fraction but remained in the cytoplasm. Thus, the alpha1-syntrophin null mice are useful in the elucidation of the functional importance of nNOS targeting at the sarcolemma. In addition, the mice would facilitate identification of other signaling molecules, which are targeted to dystrophin complex via interaction with alpha1-syntrophin.
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Affiliation(s)
- Y Miyagoe-Suzuki
- Department of Molecular Therapy, National Institute of Neuroscience, National Center of Neurology and Psychiatry, 4-1-1 Ogawa-higashi, Kodaira, Tokyo 187-8502, Japan
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208
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Patton BL, Cunningham JM, Thyboll J, Kortesmaa J, Westerblad H, Edström L, Tryggvason K, Sanes JR. Properly formed but improperly localized synaptic specializations in the absence of laminin alpha4. Nat Neurosci 2001; 4:597-604. [PMID: 11369940 DOI: 10.1038/88414] [Citation(s) in RCA: 162] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Precise apposition of pre- to postsynaptic specializations is required for optimal function of chemical synapses, but little is known about how it is achieved. At the skeletal neuromuscular junction, active zones (transmitter release sites) in the nerve terminal lie directly opposite junctional folds in the postsynaptic membrane. Few active zones or junctional folds form in mice lacking the laminin beta2 chain, which is normally concentrated in the synaptic cleft. beta2 and the broadly expressed gamma1 chain form heterotrimers with alpha chains, three of which, alpha2, alpha4 and alpha5, are present in the synaptic cleft. Thus, alpha2beta2gamma1, alpha4beta2gamma1 and alpha5beta2gamma1 heterotrimers are all lost in beta2 mutants. In mice lacking laminin alpha4, active zones and junctional folds form in normal numbers, but are not precisely apposed to each other. Thus, formation and localization of synaptic specializations are regulated separately, and alpha4beta2gamma1 (called laminin-9) is critical in the latter process.
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MESH Headings
- Animals
- Crosses, Genetic
- Exons
- Heterozygote
- Homozygote
- Laminin/analysis
- Lamins
- Macromolecular Substances
- Mice
- Mice, Inbred C57BL
- Mice, Knockout
- Muscle Contraction/physiology
- Muscle Fibers, Skeletal/pathology
- Muscle Fibers, Skeletal/physiology
- Muscle Fibers, Skeletal/ultrastructure
- Muscle, Skeletal/cytology
- Muscle, Skeletal/innervation
- Muscle, Skeletal/pathology
- Necrosis
- Nuclear Proteins/deficiency
- Nuclear Proteins/genetics
- Nuclear Proteins/physiology
- Protein Subunits
- Recombination, Genetic
- Stem Cells
- Synapses/pathology
- Synapses/physiology
- Synapses/ultrastructure
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Affiliation(s)
- B L Patton
- Department of Anatomy and Neurobiology, Washington University Medical Center, 660 South Euclid Avenue, St. Louis, Missouri 63110, USA.
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209
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Benson MA, Newey SE, Martin-Rendon E, Hawkes R, Blake DJ. Dysbindin, a novel coiled-coil-containing protein that interacts with the dystrobrevins in muscle and brain. J Biol Chem 2001; 276:24232-41. [PMID: 11316798 DOI: 10.1074/jbc.m010418200] [Citation(s) in RCA: 252] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The dystrophin-associated protein complex (DPC) is required for the maintenance of muscle integrity during the mechanical stresses of contraction and relaxation. In addition to providing a membrane scaffold, members of the DPC such as the alpha-dystrobrevin protein family are thought to play an important role in intracellular signal transduction. To gain additional insights into the function of the DPC, we performed a yeast two-hybrid screen for dystrobrevin-interacting proteins. Here we describe the identification of a dysbindin, a novel dystrobrevin-binding protein. Dysbindin is an evolutionary conserved 40-kDa coiled-coil-containing protein that binds to alpha- and beta-dystrobrevin in muscle and brain. Dystrophin and alpha-dystrobrevin are co-immunoprecipitated with dysbindin, indicating that dysbindin is DPC-associated in muscle. Dysbindin co-localizes with alpha-dystrobrevin at the sarcolemma and is up-regulated in dystrophin-deficient muscle. In the brain, dysbindin is found primarily in axon bundles and especially in certain axon terminals, notably mossy fiber synaptic terminals in the cerebellum and hippocampus. These findings have implications for the molecular pathology of Duchenne muscular dystrophy and may provide an alternative route for anchoring dystrobrevin and the DPC to the muscle membrane.
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Affiliation(s)
- M A Benson
- Department of Human Anatomy and Genetics, University of Oxford, South Parks Road, Oxford OX1 3QX, United Kingdom
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210
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Abstract
Arrhythmia and cardiomyopathy frequently accompany muscular dystrophy. In the last year, the cardiovascular consequences of muscular dystrophy gene mutations have been established through studies of murine models. These models have highlighted the potential role of primary defects in cardiac muscle as well as those secondary cardiovascular outcomes that arise from severe muscle disease. This review focuses on three areas. Recent studies using mouse models have shown that the dystrophin-associated proteins, the sarcoglycans and alpha-dystrobrevin, are critical for both cardiac and skeletal muscle membrane function, yet may exert their roles by different molecular mechanisms. New findings have shown that cytoskeletal proteins at the nuclear membrane, such as emerin and lamin AC, cause muscular dystrophy and cardiomyopathy with cardiac conduction system disease. Finally, the mechanism of cardiac and muscle degeneration in myotonic dystrophy has been re-evaluated through a series of studies using murine models. Implications for human therapy are considered in light of these new findings.
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Affiliation(s)
- A Heydemann
- Department of Medicine, Section of Cardiology, The University of Chicago, Chicago, Illinois, USA
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211
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Dalloz C, Claudepierre T, Rodius F, Mornet D, Sahel J, Rendon A. Differential Distribution of the Members of the Dystrophin Glycoprotein Complex in Mouse Retina: Effect of the mdx3Cv Mutation. Mol Cell Neurosci 2001; 17:908-20. [PMID: 11358487 DOI: 10.1006/mcne.2001.0978] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Dystrophin glycoprotein complex (DGC) assembly and function require mediation by dystrophin in skeletal muscle. The existence of such complexes and the correlation with DMD phenotypes are not yet established in the central nervous system. Here we have studied the expression of DMD gene mRNAs and proteins in retina from C57BL/6 and mdx(3Cv) mouse strains. Then we have comparatively investigated the localization of dystrophin and dystrophin-associated proteins (DAPs) in both strains to analyze the repercussion of the mdx(3Cv) mutation on the retinal distributions of alpha/beta-dystroglycan, alpha1-syntrophin, alpha-dystrobrevin, and delta/gamma-sarcoglycan. Results showed that DMD gene product deficiency affects the expression of dystroglycan assembly exclusively at the outer plexiform layer without an apparent effect on the other DAPs. We conclude that the localization of members of the DGC could be independent of the presence of the DMD gene products and/or utrophin.
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MESH Headings
- Animals
- Calcium-Binding Proteins
- Cytoskeletal Proteins/genetics
- Cytoskeletal Proteins/metabolism
- Dystroglycans
- Dystrophin/genetics
- Dystrophin/metabolism
- Dystrophin-Associated Proteins
- Gene Expression/physiology
- Membrane Glycoproteins/genetics
- Membrane Glycoproteins/metabolism
- Membrane Proteins/genetics
- Membrane Proteins/metabolism
- Mice
- Mice, Inbred C57BL/embryology
- Mice, Inbred C57BL/genetics
- Mice, Inbred C57BL/metabolism
- Mice, Inbred mdx/abnormalities
- Mice, Inbred mdx/genetics
- Mice, Inbred mdx/metabolism
- Muscle Proteins/genetics
- Muscle Proteins/metabolism
- Muscular Dystrophy, Duchenne/complications
- Muscular Dystrophy, Duchenne/genetics
- Muscular Dystrophy, Duchenne/metabolism
- Mutation/genetics
- RNA, Messenger/metabolism
- Retina/abnormalities
- Retina/metabolism
- Retina/physiopathology
- Retinal Diseases/genetics
- Retinal Diseases/metabolism
- Retinal Diseases/physiopathology
- Sarcoglycans
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Affiliation(s)
- C Dalloz
- Laboratoire de Physiopathologie Cellulaire et Moléculaire de la Rétine, Médicale A, INSERM EMI 99-18, CHRU, 1 Place de l'Hôpital, 67091 Strasbourg Cedex, France
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212
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Zhuang W, Eby JC, Cheong M, Mohapatra PK, Bredt DS, Disatnik MH, Rando TA. The susceptibility of muscle cells to oxidative stress is independent of nitric oxide synthase expression. Muscle Nerve 2001; 24:502-11. [PMID: 11268022 DOI: 10.1002/mus.1033] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
The free radical, nitric oxide (NO.), has been implicated in the pathogenesis of muscular dystrophies because the enzyme, nitric oxide synthase (NOS), which produces NO., binds to the dystrophin-glycoprotein complex (DGC). In various studies of tissue samples from human and animal muscular dystrophies due to DGC defects, correlations between reductions of NOS activity and disease severity have been reported. To test for any direct effect of NOS expression on muscle cell susceptibility, we examined muscle cells in vitro under conditions of experimentally altered NOS activity. There were no differences in susceptibility to oxidative stress between differentiated myotube cultures from wild-type and from neuronal NOS (nNOS)-deficient mice. Likewise, pharmacological inhibition of NOS did not alter cellular susceptibility to oxidative challenges. Overexpression of NOS neither enhanced nor diminished cellular susceptibility to oxidative stress. Finally, we assessed the effect of NOS overexpression on myotube cultures from dystrophin-deficient (mdx) mice. NOS protein was localized to both membrane and cytosolic compartments in the transduced cells. Still, no difference in susceptibility to oxidative stress was found between the NOS-overexpressing cells and control cells. These data suggest that muscle cell susceptibility to oxidative challenges is independent of the level of NOS expression. Therefore, any role NO. may play in the pathogenesis of muscular dystrophies is likely to be independent of its effect on the redox state of the cell.
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MESH Headings
- Animals
- Cell Differentiation
- Cells, Cultured
- Disease Models, Animal
- Dose-Response Relationship, Drug
- Enzyme Inhibitors/pharmacology
- Gene Expression/drug effects
- Mice
- Mice, Inbred C57BL
- Mice, Inbred mdx
- Mice, Knockout
- Muscle, Skeletal/cytology
- Muscle, Skeletal/drug effects
- Muscle, Skeletal/metabolism
- Muscular Dystrophy, Animal/genetics
- Muscular Dystrophy, Animal/metabolism
- Myofibrils/drug effects
- Myofibrils/metabolism
- Nitric Oxide Synthase/antagonists & inhibitors
- Nitric Oxide Synthase/biosynthesis
- Nitric Oxide Synthase/deficiency
- Nitric Oxide Synthase/genetics
- Nitric Oxide Synthase Type I
- Oxidants/pharmacology
- Oxidative Stress/physiology
- Reactive Oxygen Species/metabolism
- Transfection
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Affiliation(s)
- W Zhuang
- Department of Neurology and Neurological Sciences, Veterans Affairs Medical Center and Stanford University School of Medicine, Room A-343, Stanford, California 94305-5235, USA
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213
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Abstract
In this article, we review the molecular pathology of muscular dystrophies caused by defects of proteins located within or near cell membranes. These disorders include Bethlem myopathy, merosinopathy, dystrophinopathy, sarcoglycanopathies, integrinopathy, dysferlinopathy and caveolinopathy. We refer to these diseases collectively as sarcolemmopathy. Here, we describe the biological functions of these proteins in the context of muscular contractions and their roles in the infrastructure of muscle; defects of muscle infrastructures cause those diseases. As an example, in dystrophinopathy, cell membranes have mechanical defects due to the absence of dystrophin. Cracks of the cell membrane induced by muscle contraction may allow the influx and efflux of substances that trigger muscle cell degeneration. However, such cracks may be resealed on relaxation. In addition, dystrophinopathy causes secondary defects of various dystrophin-associated proteins suggesting that defects in cell signaling participate in the pathologic process. With regard to other sarcolemmopathies, we discuss pathological mechanisms based on available data.
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Affiliation(s)
- E Ozawa
- National Institute of Neuroscience, NCNP, Tokyo, Japan.
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214
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Burkin DJ, Wallace GQ, Nicol KJ, Kaufman DJ, Kaufman SJ. Enhanced expression of the alpha 7 beta 1 integrin reduces muscular dystrophy and restores viability in dystrophic mice. J Cell Biol 2001; 152:1207-18. [PMID: 11257121 PMCID: PMC2199213 DOI: 10.1083/jcb.152.6.1207] [Citation(s) in RCA: 220] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Muscle fibers attach to laminin in the basal lamina using two distinct mechanisms: the dystrophin glycoprotein complex and the alpha 7 beta 1 integrin. Defects in these linkage systems result in Duchenne muscular dystrophy (DMD), alpha 2 laminin congenital muscular dystrophy, sarcoglycan-related muscular dystrophy, and alpha 7 integrin congenital muscular dystrophy. Therefore, the molecular continuity between the extracellular matrix and cell cytoskeleton is essential for the structural and functional integrity of skeletal muscle. To test whether the alpha 7 beta 1 integrin can compensate for the absence of dystrophin, we expressed the rat alpha 7 chain in mdx/utr(-/-) mice that lack both dystrophin and utrophin. These mice develop a severe muscular dystrophy highly akin to that in DMD, and they also die prematurely. Using the muscle creatine kinase promoter, expression of the alpha 7BX2 integrin chain was increased 2.0-2.3-fold in mdx/utr(-/-) mice. Concomitant with the increase in the alpha 7 chain, its heterodimeric partner, beta 1D, was also increased in the transgenic animals. Transgenic expression of the alpha 7BX2 chain in the mdx/utr(-/-) mice extended their longevity by threefold, reduced kyphosis and the development of muscle disease, and maintained mobility and the structure of the neuromuscular junction. Thus, bolstering alpha 7 beta 1 integrin-mediated association of muscle cells with the extracellular matrix alleviates many of the symptoms of disease observed in mdx/utr(-/-) mice and compensates for the absence of the dystrophin- and utrophin-mediated linkage systems. This suggests that enhanced expression of the alpha 7 beta 1 integrin may provide a novel approach to treat DMD and other muscle diseases that arise due to defects in the dystrophin glycoprotein complex. A video that contrasts kyphosis, gait, joint contractures, and mobility in mdx/utr(-/-) and alpha 7BX2-mdx/utr(-/-) mice can be accessed at http://www.jcb.org/cgi/content/full/152/6/1207.
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MESH Headings
- Animals
- Blotting, Western
- Body Weight
- Contracture/physiopathology
- Creatine Kinase/genetics
- Creatine Kinase, MM Form
- Cytoskeletal Proteins/genetics
- Cytoskeletal Proteins/metabolism
- Dystrophin/genetics
- Dystrophin/metabolism
- Female
- Hindlimb
- Humans
- Integrins/genetics
- Integrins/metabolism
- Isoenzymes/genetics
- Joints
- Kyphosis
- Magnetic Resonance Imaging
- Male
- Membrane Proteins/genetics
- Membrane Proteins/metabolism
- Mice
- Mice, Inbred mdx
- Mice, Transgenic
- Microscopy, Fluorescence
- Muscle, Skeletal/pathology
- Muscle, Skeletal/physiopathology
- Muscular Dystrophy, Animal/genetics
- Muscular Dystrophy, Animal/pathology
- Muscular Dystrophy, Animal/physiopathology
- Muscular Dystrophy, Duchenne/genetics
- Muscular Dystrophy, Duchenne/pathology
- Muscular Dystrophy, Duchenne/physiopathology
- Neuromuscular Junction/ultrastructure
- Promoter Regions, Genetic
- Rats
- Receptors, Cholinergic/metabolism
- Receptors, Cholinergic/ultrastructure
- Survival Rate
- Transgenes
- Utrophin
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Affiliation(s)
- Dean J. Burkin
- Department of Cell and Structural Biology, University of Illinois, Urbana, Illinois 61801
| | - Gregory Q. Wallace
- Department of Cell and Structural Biology, University of Illinois, Urbana, Illinois 61801
| | - Kimberly J. Nicol
- Department of Cell and Structural Biology, University of Illinois, Urbana, Illinois 61801
| | | | - Stephen J. Kaufman
- Department of Cell and Structural Biology, University of Illinois, Urbana, Illinois 61801
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215
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Gieseler K, Mariol MC, Bessou C, Migaud M, Franks CJ, Holden-Dye L, Ségalat L. Molecular, genetic and physiological characterisation of dystrobrevin-like (dyb-1) mutants of Caenorhabditis elegans. J Mol Biol 2001; 307:107-17. [PMID: 11243807 DOI: 10.1006/jmbi.2000.4480] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Dystrobrevins are protein components of the dystrophin complex, whose disruption leads to Duchenne muscular dystrophy and related diseases. The Caenorhabditis elegans dystrobrevin gene (dyb-1) encodes a protein 38 % identical with its mammalian counterparts. The C. elegans dystrobrevin is expressed in muscles and neurons. We characterised C. elegans dyb-1 mutants and showed that: (1) their behavioural phenotype resembles that of dystrophin (dys-1) mutants; (2) the phenotype of dyb-1 dys-1 double mutants is not different from the single ones; (3) dyb-1 mutants are more sensitive than wild-type animals to reductions of acetylcholinesterase levels and have an increased response to acetylcholine; (4) dyb-1 mutations alone do not lead to muscle degeneration, but synergistically produce a progressive myopathy when combined with a mild MyoD/hlh-1 mutation. All together, these findings further substantiate the role of dystrobrevins in cholinergic transmission and as functional partners of dystrophin.
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Affiliation(s)
- K Gieseler
- CGMC, CNRS-UMR 5534, Université Lyon1, 43 bld du 11 Novembre, 69622 Villeurbanne cedex, France
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216
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Ichida F, Tsubata S, Bowles KR, Haneda N, Uese K, Miyawaki T, Dreyer WJ, Messina J, Li H, Bowles NE, Towbin JA. Novel gene mutations in patients with left ventricular noncompaction or Barth syndrome. Circulation 2001; 103:1256-63. [PMID: 11238270 DOI: 10.1161/01.cir.103.9.1256] [Citation(s) in RCA: 331] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND Mutations in the gene G4.5 result in a wide spectrum of severe infantile cardiomyopathic phenotypes, including isolated left ventricular noncompaction (LVNC), as well as Barth syndrome (BTHS) with dilated cardiomyopathy (DCM). The purpose of this study was to investigate patients with LVNC or BTHS for mutations in G4.5 or other novel genes. METHODS AND RESULTS DNA was isolated from 2 families and 3 individuals with isolated LVNC or LVNC with congenital heart disease (CHD), as well as 4 families with BTHS associated with LVNC or DCM, and screened for mutations by single-strand DNA conformation polymorphism analysis and DNA sequencing. In 1 family with LVNC and CHD, a C-->T mutation was identified at nucleotide 362 of alpha-dystrobrevin, changing a proline to leucine (P121L). Mutations in G4.5 were identified in 2 families with isolated LVNC: a missense mutation in exon 4 (C118R) in 1 and a splice donor mutation (IVS10+2T-->A) in intron 10 in the other. In a family with cardiomyopathies ranging from BTHS or fatal infantile cardiomyopathy to asymptomatic DCM, a splice acceptor mutation in exon 2 of G4.5 (398-2 A-->G) was identified, and a 1-bp deletion in exon 2 of G4.5, resulting in a stop codon after amino acid 41, was identified in a sporadic case of BTHS. CONCLUSIONS These data demonstrate genetic heterogeneity in LVNC, with mutation of a novel gene, alpha-dystrobrevin, identified in LVNC associated with CHD. In addition, these results confirm that mutations in G4.5 result in a wide phenotypic spectrum of cardiomyopathies.
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Affiliation(s)
- F Ichida
- Department of Pediatrics, Toyama Medical and Pharmaceutical University, Toyama, Japan
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217
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Newey SE, Howman EV, Ponting CP, Benson MA, Nawrotzki R, Loh NY, Davies KE, Blake DJ. Syncoilin, a novel member of the intermediate filament superfamily that interacts with alpha-dystrobrevin in skeletal muscle. J Biol Chem 2001; 276:6645-55. [PMID: 11053421 DOI: 10.1074/jbc.m008305200] [Citation(s) in RCA: 98] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Dystrophin coordinates the assembly of a complex of structural and signaling proteins that are required for normal muscle function. A key component of the dystrophin protein complex is alpha-dystrobrevin, a dystrophin-associated protein whose absence results in neuromuscular junction defects and muscular dystrophy. To gain further insights into the role of alpha-dystrobrevin in skeletal muscle, we used the yeast two-hybrid system to identify a novel alpha-dystrobrevin-binding partner called syncoilin. Syncoilin is a new member of the intermediate filament superfamily and is highly expressed in skeletal and cardiac muscle. In normal skeletal muscle, syncoilin is concentrated at the neuromuscular junction, where it colocalizes and coimmunoprecipitates with alpha-dystrobrevin-1. Expression studies in mammalian cells demonstrate that, while alpha-dystrobrevin and syncoilin associate directly, overexpression of syncoilin does not result in the self-assembly of intermediate filaments. Finally, unlike many components of the dystrophin protein complex, we show that syncoilin expression is up-regulated in dystrophin-deficient muscle. These data suggest that alpha-dystrobrevin provides a link between the dystrophin protein complex and the intermediate filament network at the neuromuscular junction, which may be important for the maintenance and maturation of the synapse.
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Affiliation(s)
- S E Newey
- Department of Human Anatomy and Genetics, University of Oxford, South Parks Road, Oxford OX1 3QX, United Kingdom
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218
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Porter JD, Merriam AP, Hack AA, Andrade FH, McNally EM. Extraocular muscle is spared despite the absence of an intact sarcoglycan complex in gamma- or delta-sarcoglycan-deficient mice. Neuromuscul Disord 2001; 11:197-207. [PMID: 11257478 DOI: 10.1016/s0960-8966(00)00171-1] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
Models of the dystrophin-glycoprotein complex do not reconcile the novel sparing of extraocular muscle in muscular dystrophy. Extraocular muscle sparing in Duchenne muscular dystrophy implies the existence of adaptive properties in these muscles that may extend protection to other neuromuscular diseases. We studied the extraocular muscle morphology and dystrophin-glycoprotein complex organization in murine targeted deletion of the gamma-sarcoglycan (gsg(-/-)) and delta-sarcoglycan (dsg(-/-)) genes, two models of autosomal recessive limb girdle muscular dystrophy. In contrast to limb and diaphragm, the principal extraocular muscles were intact in gsg(-/-) and dsg(-/-) mice. However, central nucleated, presumptive regenerative, fibers were seen in the accessory extraocular muscles (retractor bulbi, levator palpebrae superioris) of both strains. Skeletal muscles of gsg(-/-) mice exhibited in vivo Evans Blue dye permeability, while the principal extraocular muscles did not. Disruption of gamma-sarcoglycan produced secondary displacement of alpha- and beta-sarcoglycans in the extraocular muscles. The intensity of immunofluorescence for dystrophin and alpha- and beta-dystroglycan also appeared to be slightly reduced. Utrophin localization was unchanged. The finding that sarcoglycan disruption was insufficient to elicit alterations in extraocular muscle suggests that loss of mechanical stability and increased sarcolemmal permeability are not inevitable consequences of mutations that disrupt the dystrophin-glycoprotein complex organization and must be accounted for in models of muscular dystrophy.
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Affiliation(s)
- J D Porter
- Department of Ophthalmology, Case Western Reserve University and The Research Institute of University Hospitals of Cleveland, 11100 Euclid Avenue, Cleveland, OH 44106-5068, USA.
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219
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Newey SE, Gramolini AO, Wu J, Holzfeind P, Jasmin BJ, Davies KE, Blake DJ. A novel mechanism for modulating synaptic gene expression: differential localization of alpha-dystrobrevin transcripts in skeletal muscle. Mol Cell Neurosci 2001; 17:127-40. [PMID: 11161474 DOI: 10.1006/mcne.2000.0918] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Alpha-dystrobrevin is a dystrophin-related and -associated protein that is involved in synapse maturation and is required for normal muscle function. There are three protein isoforms in skeletal muscle, alpha-dystrobrevin-1, -2, and -3 that are encoded by the single alpha-dystrobrevin gene. To understand the role of these proteins in muscle we have investigated the localisation and transcript distribution of the different alpha-dystrobrevin isoforms. Alpha-dystrobrevin-1 and -2 are concentrated at the neuromuscular junction and are both recruited into agrin-induced acetylcholine receptor clusters in cultured myotubes. We also demonstrate that all alpha-dystrobrevin mRNAs are transcribed from a single promoter in skeletal muscle. However, only transcripts encoding alpha-dystrobrevin-1 are preferentially accumulated at postsynaptic sites. These data suggest that the synaptic accumulation of alpha-dystrobrevin-1 mRNA occurs posttranscriptionally, identifying a novel mechanism for synaptic gene expression. Taken together, these results indicate that different isoforms possess distinct roles in synapse formation and possibly in the pathogenesis of muscular dystrophy.
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Affiliation(s)
- S E Newey
- Department of Human Anatomy and Genetics, MRC Functional Genetics Unit, University of Oxford, South Parks Road, Oxford, OX1 3QX, United Kingdom
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220
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Abstract
SUMMARY A unique arrangement of domains makes up the common region of two otherwise very different proteins - long, elegant dystrophin, and its rather dumpy distant cousin, dystrobrevin. The two work in concert, forming the core of a large membrane-bound complex in all metazoa. Like many proteins, dystrophin and dystrobrevin have diversified in the vertebrate clade, as have their binding partners, yielding specialized complexes tailored to different cellular and subcellular locations. Disruption of several components of the complex is known to result in syndromes that include progressive myopathy, sometimes combined with cognitive defects; the best known of these is Duchenne muscular dystrophy. Despite a wealth of biochemical, cell biological and genetic information, the precise role of dystrophins, dystrobrevins and their collaborators remains unclear.
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Affiliation(s)
- R G Roberts
- Division of Medical and Molecular Genetics, Guy's, King's and St Thomas' Medical School, Guy's Hospital, London, SE1 9RT, UK.
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221
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Chamberlain JS. Muscular dystrophy meets the gene chip: new insights into disease pathogenesis. J Cell Biol 2000; 151:F43-5. [PMID: 11121429 PMCID: PMC2190594 DOI: 10.1083/jcb.151.6.f43] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Affiliation(s)
- J S Chamberlain
- Department of Neurology, University of Washington School of Medicine, Seattle, Washington 98195, USA
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222
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Barresi R, Moore SA, Stolle CA, Mendell JR, Campbell KP. Expression of gamma -sarcoglycan in smooth muscle and its interaction with the smooth muscle sarcoglycan-sarcospan complex. J Biol Chem 2000; 275:38554-60. [PMID: 10993904 DOI: 10.1074/jbc.m007799200] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The sarcoglycan complex in striated muscle is a heterotetrameric unit integrally associated with sarcospan in the dystrophin-glycoprotein complex. The sarcoglycans, alpha, beta, gamma, and delta, are mutually dependent with regard to their localization at the sarcolemma, and mutations in any of the sarcoglycan genes lead to limb-girdle muscular dystrophies type 2C-2F. In smooth muscle beta- and delta-sarcoglycans are associated with epsilon-sarcoglycan, a glycoprotein homologous to alpha-sarcoglycan. Here, we demonstrate that gamma-sarcoglycan is also a component of the sarcoglycan complex in the smooth muscle. First, we show the presence of gamma-sarcoglycan in a number of smooth muscle-containing organs, and we verify the existence of identical transcripts in skeletal and smooth muscle. The specificity of the expression of gamma-sarcoglycan in smooth muscle was confirmed by analysis of smooth muscle cells in culture. Next, we provide evidence for the association of gamma-sarcoglycan with the sarcoglycan-sarcospan complex by biochemical analysis and comparison among animal models for muscular dystrophy. Moreover, we find disruption of the sarcoglycan complex in the vascular smooth muscle of a patient with gamma-sarcoglycanopathy. Taken together, our results prove that the sarcoglycan complex in vascular and visceral smooth muscle consists of epsilon-, beta-, gamma-, and delta-sarcoglycans and is associated with sarcospan.
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Affiliation(s)
- R Barresi
- Howard Hughes Medical Institute, Department of Physiology and Biophysics and Department of Neurology, University of Iowa College of Medicine, Iowa City, Iowa 52242, USA
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223
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Sander M, Chavoshan B, Harris SA, Iannaccone ST, Stull JT, Thomas GD, Victor RG. Functional muscle ischemia in neuronal nitric oxide synthase-deficient skeletal muscle of children with Duchenne muscular dystrophy. Proc Natl Acad Sci U S A 2000; 97:13818-23. [PMID: 11087833 PMCID: PMC17659 DOI: 10.1073/pnas.250379497] [Citation(s) in RCA: 329] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Duchenne muscular dystrophy (DMD) is a fatal disease caused by mutation of the gene encoding the cytoskeletal protein dystrophin. Despite a wealth of recent information about the molecular basis of DMD, effective treatment for this disease does not exist because the mechanism by which dystrophin deficiency produces the clinical phenotype is unknown. In both mouse and human skeletal muscle, dystrophin deficiency results in loss of neuronal nitric oxide synthase, which normally is localized to the sarcolemma as part of the dystrophin-glycoprotein complex. Recent studies in mice suggest that skeletal muscle-derived nitric oxide may play a key role in the regulation of blood flow within exercising skeletal muscle by blunting the vasoconstrictor response to alpha-adrenergic receptor activation. Here we report that this protective mechanism is defective in children with DMD, because the vasoconstrictor response (measured as a decrease in muscle oxygenation) to reflex sympathetic activation was not blunted during exercise of the dystrophic muscles. In contrast, this protective mechanism is intact in healthy children and those with polymyositis or limb-girdle muscular dystrophy, muscle diseases that do not result in loss of neuronal nitric oxide synthase. This clinical investigation suggests that unopposed sympathetic vasoconstriction in exercising human skeletal muscle may constitute a heretofore unappreciated vascular mechanism contributing to the pathogenesis of DMD.
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Affiliation(s)
- M Sander
- Copenhagen Muscle Research Center, Rigshospitalet, DK-2200, Copenhagen N, Denmark
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224
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Abstract
A new animal model for studying muscular dystrophy, a mutant form of the nematode Caenorhabditis elegans, brings the power of worm genetics to bear on the search for a cure for this disease; work on this worm has already led to the identification of a novel component that can suppress the mutant phenotype.
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Affiliation(s)
- J S Chamberlain
- Department of Human Genetics, Center for Gene Therapy, University of Michigan Medical School, Ann Arbor, Michigan 48109, USA.
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225
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Newey SE, Benson MA, Ponting CP, Davies KE, Blake DJ. Alternative splicing of dystrobrevin regulates the stoichiometry of syntrophin binding to the dystrophin protein complex. Curr Biol 2000; 10:1295-8. [PMID: 11069112 DOI: 10.1016/s0960-9822(00)00760-0] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Dystrophin coordinates the assembly of a complex of structural and signalling proteins that is required for normal muscle function. A key component of the dystrophin-associated protein complex (DPC) is alpha-dystrobrevin, a dystrophin-related and -associated protein whose absence results in muscular dystrophy and neuromuscular junction defects [1,2]. The current model of the DPC predicts that dystrophin and dystrobrevin each bind a single syntrophin molecule [3]. The syntrophins are PDZ-domain-containing proteins that facilitate the recruitment of signalling proteins such as nNOS (neuronal nitric oxide synthase) to the DPC [4]. Here we show, using yeast two-hybrid analysis and biochemical binding studies, that alpha-dystrobrevin in fact contains two independent syntrophin-binding sites in tandem. The previously undescribed binding site is situated within an alternatively spliced exon of alpha-dystrobrevin, termed the variable region-3 (vr3) sequence, which is specifically expressed in skeletal and cardiac muscle [5,6]. Analysis of the syntrophin-binding region of dystrobrevin reveals a tandem pair of predicted alpha helices with significant sequence similarity. These alpha helices, each termed a syntrophin-binding motif, are also highly conserved in dystrophin and utrophin. Together these data show that there are four potential syntrophin-binding sites per dystrophin complex in skeletal muscle: two on dystrobrevin and two on dystrophin or utrophin. Furthermore, alternative splicing of dystrobrevin provides a mechanism for regulating the stoichiometry of syntrophin association with the DPC. This is likely to have important consequences for the recruitment of specific signalling molecules to the DPC and ultimately for its function.
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Affiliation(s)
- S E Newey
- Department of Human Anatomy and Genetics, University of Oxford, UK
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226
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Apel ED, Lewis RM, Grady RM, Sanes JR. Syne-1, a dystrophin- and Klarsicht-related protein associated with synaptic nuclei at the neuromuscular junction. J Biol Chem 2000; 275:31986-95. [PMID: 10878022 DOI: 10.1074/jbc.m004775200] [Citation(s) in RCA: 217] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We describe a novel protein, Syne-1, that is associated with nuclear envelopes in skeletal, cardiac, and smooth muscle cells. Syne-1 contains multiple spectrin repeats similar to those found in dystrophin and utrophin, as well as a domain homologous to the carboxyl-terminal of Klarsicht, a protein associated with nuclei and required for a subset of nuclear migrations in Drosophila. In adult skeletal muscle fibers, levels of Syne-1 are highest in the nuclei that lie beneath the postsynaptic membrane at the neuromuscular junction. These nuclei are transcriptionally specialized, expressing genes for synaptic components at higher levels than extrasynaptic nuclei in the same cytoplasm. Syne-1 is the first protein found to be selectively associated with synaptic nuclei. Syne-1 becomes concentrated in synaptic nuclei postnatally. It remains synaptically enriched following denervation or degeneration/regeneration, and is also present at high levels in the central nuclei of dystrophic myotubes. The location and structure of Syne-1 suggest that it may participate in the migration of myonuclei in myotubes and/or their anchoring at the postsynaptic apparatus. Finally, we identify a homologous gene, syne-2, that is expressed in an overlapping but distinct pattern.
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Affiliation(s)
- E D Apel
- Department of Anatomy and Neurobiology and Department of Pediatrics, Washington University Medical School, St. Louis, Missouri 63110, USA
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227
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Abstract
Muscular dystrophies represent a heterogeneous group of disorders, which have been largely classified by clinical phenotype. In the last 10 years, identification of novel skeletal muscle genes including extracellular matrix, sarcolemmal, cytoskeletal, cytosolic, and nuclear membrane proteins has changed the phenotype-based classification and shed new light on the molecular pathogenesis of these disorders. A large number of genes involved in muscular dystrophy encode components of the dystrophin-glycoprotein complex (DGC) which normally links the intracellular cytoskeleton to the extracellular matrix. Mutations in components of this complex are thought to lead to loss of sarcolemmal integrity and render muscle fibers more susceptible to damage. Recent evidence suggests the involvement of vascular smooth muscle DGC in skeletal and cardiac muscle pathology in some forms of sarcoglycan-deficient limb-girdle muscular dystrophy. Intriguingly, two other forms of limb-girdle muscular dystrophy are possibly caused by perturbation of sarcolemma repair mechanisms. The complete clarification of these various pathways will lead to further insights into the pathogenesis of this heterogeneous group of muscle disorders.
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Affiliation(s)
- R D Cohn
- Howard Hughes Medical Institute, Department of Physiology and Biophysics and of Neurology, University of Iowa College of Medicine, 400 EMRB, Iowa City, Iowa 52242, USA
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228
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Abstract
Defects in the dystrophin complex (DC) underlie several human genetic disorders, but our dissection of its function is complicated by potential redundancy of the multiple vertebrate isoforms of most DC components. We here complete our previous description of Drosophila dystrophin, and show that the fly retains all essential components of the DC, but with substantially less diversity. Seventeen known human components (three dystrophin-related proteins, two dystrobrevins, five sarcoglycans, five syntrophins, one dystroglycan and one sarcospan) appear to be reduced to eight in Drosophila (one, one, three, two, one and none, respectively). The simplicity of this system recommends it as a model for its human counterpart.
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Affiliation(s)
- M J Greener
- Division of Medical and Molecular Genetics, 8th Floor Guy's Tower, Guy's King's and St. Thomas' Medical School, London SE1 9RT, UK
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229
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Abdelmoity A, Padre RC, Burzynski KE, Stull JT, Lau KS. Neuronal nitric oxide synthase localizes through multiple structural motifs to the sarcolemma in mouse myotubes. FEBS Lett 2000; 482:65-70. [PMID: 11018524 DOI: 10.1016/s0014-5793(00)02038-x] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
In skeletal muscle, neuronal nitric oxide synthase is localized at the sarcolemma in association with the dystrophin glycoprotein complex (DGC). The nNOS N-terminal 231 amino acids comprise a PDZ domain (residues 1-100) and a beta-hairpin finger loop (residues 101-130) which binds alpha-syntrophin located in the DGC. Endogenous nNOS and GFP-tagged nNOS localize to the sarcolemma in mouse C2C12 myotubes. Expression of GFP-tagged nNOS domains in C2C12 myotubes reveals that the PDZ domain and the beta-hairpin finger loop of nNOS are independently capable of localizing to the sarcolemma of C2C12 myotubes. Binding studies indicate that alpha-syntrophin binds only to the beta-hairpin finger loop and not the PDZ domain of nNOS. nNOS may bind to proteins in addition to alpha-syntrophin at muscle sarcolemma.
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Affiliation(s)
- A Abdelmoity
- Department of Physiology, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390-9040, USA
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230
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Crawford GE, Faulkner JA, Crosbie RH, Campbell KP, Froehner SC, Chamberlain JS. Assembly of the dystrophin-associated protein complex does not require the dystrophin COOH-terminal domain. J Cell Biol 2000; 150:1399-410. [PMID: 10995444 PMCID: PMC2150715 DOI: 10.1083/jcb.150.6.1399] [Citation(s) in RCA: 158] [Impact Index Per Article: 6.6] [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
Dystrophin is a multidomain protein that links the actin cytoskeleton to laminin in the extracellular matrix through the dystrophin associated protein (DAP) complex. The COOH-terminal domain of dystrophin binds to two components of the DAP complex, syntrophin and dystrobrevin. To understand the role of syntrophin and dystrobrevin, we previously generated a series of transgenic mouse lines expressing dystrophins with deletions throughout the COOH-terminal domain. Each of these mice had normal muscle function and displayed normal localization of syntrophin and dystrobrevin. Since syntrophin and dystrobrevin bind to each other as well as to dystrophin, we have now generated a transgenic mouse deleted for the entire dystrophin COOH-terminal domain. Unexpectedly, this truncated dystrophin supported normal muscle function and assembly of the DAP complex. These results demonstrate that syntrophin and dystrobrevin functionally associate with the DAP complex in the absence of a direct link to dystrophin. We also observed that the DAP complexes in these different transgenic mouse strains were not identical. Instead, the DAP complexes contained varying ratios of syntrophin and dystrobrevin isoforms. These results suggest that alternative splicing of the dystrophin gene, which naturally generates COOH-terminal deletions in dystrophin, may function to regulate the isoform composition of the DAP complex.
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Affiliation(s)
- G E Crawford
- Program in Cellular and Molecular Biology, University of Michigan, Ann Arbor, Michigan 48109-0618, USA
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231
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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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232
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Abstract
Muscular dystrophy is a group of genetically determined muscular disorders marked by progressive wasting and weakness of the skeletal muscle, but which often affect cardiac and smooth muscles or other tissues. The patterns of inheritance are either dominant or recessive although the gene may be defective because of a new mutation. Growing evidence revealed the marked heterogeneity of the muscle disorders, and considerable numbers of Japanese scientists and physicians have contributed to the research progress in muscular dystrophy. Among these the discovery of an increased serum creatine kinase activity in muscular dystrophy opened the way for the most reliable laboratory test for muscular dystrophy in 1959, and subsequently accelerated progress in a broad range of research areas in medicine. Progress in modern genetics and molecular pathology provided another breakthrough in muscular dystrophy research and, in 1987, dystrophin was identified, a deficiency of which causes DMD. The present review article highlights contributions of Japanese scientists to muscular dystrophy research.
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Affiliation(s)
- K Arahata
- Department of Neuromuscular Research, National Institute of Neuroscience, National Center of Neurology and Psychiatry, Kodaira, Tokyo, Japan.
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233
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Sorokin LM, Maley MA, Moch H, von der Mark H, von der Mark K, Cadalbert L, Karosi S, Davies MJ, McGeachie JK, Grounds MD. Laminin alpha4 and integrin alpha6 are upregulated in regenerating dy/dy skeletal muscle: comparative expression of laminin and integrin isoforms in muscles regenerating after crush injury. Exp Cell Res 2000; 256:500-14. [PMID: 10772822 DOI: 10.1006/excr.2000.4842] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The expression of laminin isoforms and laminin-binding integrin receptors known to occur in muscle was investigated during myogenic regeneration after crush injury. Comparisons were made between dystrophic 129ReJ dy/dy mice, which have reduced laminin alpha2 expression, and their normal littermates. The overall histological pattern of regeneration after crush injury was similar in dy/dy and control muscle, but proceeded faster in dy/dy mice. In vitro studies revealed a greater yield of mononuclear cells extracted from dy/dy muscle and a reduced proportion of desmin-positive cells upon in vitro cultivation, reflecting the presence of inflammatory cells and "preactivated" myoblasts due to ongoing regenerative processes within the endogenous dystrophic lesions. Laminin alpha1 was not detectable in skeletal muscle. Laminin alpha2 was present in basement membranes of mature myofibers and newly formed myotubes in control and dy/dy muscles, albeit weaker in dy/dy. Laminin alpha2-negative myogenic cells were detected in dy/dy and control muscle, suggesting the involvement of other laminin alpha chains in early myogenic differentiation, such as laminin alpha4 and alpha5 which were both transiently expressed in basement membranes of newly formed myotubes of dy/dy and control mice. Integrin beta1 was expressed on endothelial cells, muscle fibers, and peripheral nerves in uninjured muscle and broadened after crush injury to the interstitium where it occurred on myogenic and nonmyogenic cells. Integrin alpha3 was not expressed in uninjured or regenerating muscle, while integrin alpha6 was expressed mainly on endothelial cells and peripheral nerves in uninjured muscle. Upon crush injury integrin alpha6 increased in the interstitium mainly on nonmyogenic cells, including infiltrating leukocytes, endothelial cells, and fibroblasts. In dy/dy muscle, integrin alpha6 occurred on some newly formed myotubes. Integrin alpha7 was expressed on muscle fibers at the myotendinous junction and showed weak and irregular expression on muscle fibers. After crush injury, integrin alpha7 expression extended to the newly formed myotubes and some myoblasts. However, many myoblasts and newly formed myotubes were integrin alpha7 negative. No marked difference was observed in integrin alpha7 expression between dy/dy and control muscle, either uninjured or after crush injury. Only laminin alpha4 and integrin alpha6 expression patterns were notably different between dy/dy and control muscle. Expression of both molecules was more extensive in dy/dy muscle, especially in the interstitium of regenerating areas and on newly formed myotubes. In view of the faster myogenic regeneration observed in dy/dy mice, the data suggest that laminin alpha4 and integrin alpha6 support myogenic regeneration. However, whether these accelerated myogenic effects are a direct consequence of the reduced laminin alpha2 expression in dy/dy mice, or an accentuation of the ongoing regenerative events in focal lesions in the muscle, requires further investigation.
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Affiliation(s)
- L M Sorokin
- Interdisciplinary Center for Clinical Research (IZKF), University of Erlangen-Nuremberg, Germany
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234
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Ueda H, Baba T, Terada N, Kato Y, Fujii Y, Takayama I, Mei X, Ohno S. Immunolocalization of dystrobrevin in the astrocytic endfeet and endothelial cells in the rat cerebellum. Neurosci Lett 2000; 283:121-4. [PMID: 10739890 DOI: 10.1016/s0304-3940(00)00925-3] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
Dystrobrevin is a newly discovered dystrophin-associated protein that is classified as alpha- and beta-dystrobrevin. Previous studies reported that dystrophin, utrophin, syntrophin and beta-dystroglycan were expressed in the cerebellum. In the present study, we examined cellular and subcellular localization of dystrobrevin in the adult rat cerebellum immunohistochemically. Confocal microscopy showed that dystrobrevin was expressed around blood vessels and under the pia mater as dystrophin, utrophin and beta-dystroglycan were. Immunoelectron microscopy demonstrated that dystrobrevin was localized not only in the astrocytic endfeet around blood vessels and under the pia mater, but also in endothelial cells. Considering the fact that dystrobrevin possesses multiple phosphotyrosine kinase residues, these data suggest that dystrobrevin plays a role in blood-brain barrier functions as a component of the dystrophin complex.
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Affiliation(s)
- H Ueda
- Department of Anatomy, Yamanashi Medical University, Yamanashi, Japan.
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235
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Lebakken CS, Venzke DP, Hrstka RF, Consolino CM, Faulkner JA, Williamson RA, Campbell KP. Sarcospan-deficient mice maintain normal muscle function. Mol Cell Biol 2000; 20:1669-77. [PMID: 10669744 PMCID: PMC85350 DOI: 10.1128/mcb.20.5.1669-1677.2000] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Sarcospan is an integral membrane component of the dystrophin-glycoprotein complex (DGC) found at the sarcolemma of striated and smooth muscle. The DGC plays important roles in muscle function and viability as evidenced by defects in components of the DGC, which cause muscular dystrophy. Sarcospan is unique among the components of the complex in that it contains four transmembrane domains with intracellular N- and C-terminal domains and is a member of the tetraspan superfamily of proteins. Sarcospan is tightly linked to the sarcoglycans, and together these proteins form a subcomplex within the DGC. Stable expression of sarcospan at the sarcolemma is dependent upon expression of the sarcoglycans. Here we describe the generation and analysis of mice carrying a null mutation in the Sspn gene. Surprisingly, the Sspn-deficient muscle maintains expression of other components of the DGC at the sarcolemma, and no gross histological abnormalities of muscle from the mice are observed. The Sspn-deficient muscle maintains sarcolemmal integrity as determined by serum creatine kinase and Evans blue uptake assays, and the Sspn-deficient muscle maintains normal force and power generation capabilities. These data suggest either that sarcospan is not required for normal DGC function or that the Sspn-deficient muscle is compensating for the absence of sarcospan, perhaps by utilizing another protein to carry out its function.
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Affiliation(s)
- C S Lebakken
- Departments of Physiology and Biophysics and Neurology, Howard Hughes Medical Institute, Iowa City, Iowa 52242, USA
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236
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Abstract
Several forms of inherited muscular dystrophy are associated with brain abnormalities and cognitive impairment. One of the most common and severe of these diseases is Duchenne muscular dystrophy (DMD). Dystrophin, the product of the DMD gene, is found in neurones, where it is associated with the postsynaptic membrane. Cognitive impairment in individuals with DMD is thought to be due to an abnormality in the neuronal membrane that is caused by lack of dystrophin. Recent experimental evidence has provided valuable clues in our understanding of the complex molecular neurobiology of muscular dystrophy.
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Affiliation(s)
- D J Blake
- Dept of Human Anatomy and Genetics, University of Oxford, UK OX1 3QX
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237
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Grady RM, Zhou H, Cunningham JM, Henry MD, Campbell KP, Sanes JR. Maturation and maintenance of the neuromuscular synapse: genetic evidence for roles of the dystrophin--glycoprotein complex. Neuron 2000; 25:279-93. [PMID: 10719885 DOI: 10.1016/s0896-6273(00)80894-6] [Citation(s) in RCA: 230] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The dystrophin-glycoprotein complex (DGC) links the cytoskeleton of muscle fibers to their extracellular matrix. Using knockout mice, we show that a cytoplasmic DGC component, alpha-dystrobrevin (alpha-DB), is dispensable for formation of the neuromuscular junction (NMJ) but required for maturation of its postsynaptic apparatus. We also analyzed double and triple mutants lacking other cytoskeletal DGC components (utrophin and dystrophin) and myotubes lacking a alpha-DB or a transmembrane DGC component (dystroglycan). Our results suggest that alpha-DB acts via its linkage to the DGC to enhance the stability of postsynaptic specializations following their DGC-independent formation; dystroglycan may play additional roles in assembling synaptic basal lamina. Together, these results demonstrate involvement of distinct protein complexes in the formation and maintenance of the synapse and implicate the DGC in the latter process.
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Affiliation(s)
- R M Grady
- Department of Pediatrics, Washington University Medical School, St. Louis, Missouri 63110, USA
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238
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Blake DJ, Hawkes R, Benson MA, Beesley PW. Different dystrophin-like complexes are expressed in neurons and glia. J Cell Biol 1999; 147:645-58. [PMID: 10545507 PMCID: PMC2151186 DOI: 10.1083/jcb.147.3.645] [Citation(s) in RCA: 187] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
Duchenne muscular dystrophy is a fatal muscle disease that is often associated with cognitive impairment. Accordingly, dystrophin is found at the muscle sarcolemma and at postsynaptic sites in neurons. In muscle, dystrophin forms part of a membrane-spanning complex, the dystrophin-associated protein complex (DPC). Whereas the composition of the DPC in muscle is well documented, the existence of a similar complex in brain remains largely unknown. To determine the composition of DPC-like complexes in brain, we have examined the molecular associations and distribution of the dystrobrevins, a widely expressed family of dystrophin-associated proteins, some of which are components of the muscle DPC. beta-Dystrobrevin is found in neurons and is highly enriched in postsynaptic densities (PSDs). Furthermore, beta-dystrobrevin forms a specific complex with dystrophin and syntrophin. By contrast, alpha-dystrobrevin-1 is found in perivascular astrocytes and Bergmann glia, and is not PSD-enriched. alpha-Dystrobrevin-1 is associated with Dp71, utrophin, and syntrophin. In the brains of mice that lack dystrophin and Dp71, the dystrobrevin-syntrophin complexes are still formed, whereas in dystrophin-deficient muscle, the assembly of the DPC is disrupted. Thus, despite the similarity in primary sequence, alpha- and beta-dystrobrevin are differentially distributed in the brain where they form separate DPC-like complexes.
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Affiliation(s)
- D J Blake
- Department of Human Anatomy and Genetics, University of Oxford, Oxford OX1 3QX, United Kingdom.
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