RESUMO
The BIO14.6 hamster is an extensively used animal model of autosomal recessive cardiomyopathy and muscular dystrophy. Recently, a large deletion in the 5' end of the delta-sarcoglycan gene was found to be the primary genetic defect in the hamster. In the present investigation, we studied the effects of the delta-sarcoglycan deletion on transcription, expression, and function of the dystrophin-glycoprotein complex in skeletal and cardiac muscle. We demonstrated that in striated muscle the genetic defect leads to the complete deficiency of delta-sarcoglycan and a concomitant loss of alpha-, beta-, and gamma-sarcoglycan. In addition, absence of the sarcoglycan complex reduced the expression of alpha-dystroglycan in striated muscle fibers. These findings indicated that the primary defect in the BIO14.6 hamster leads to the dissociation of the dystroglycan complex from the sarcoglycan complex and disrupted anchorage of alpha-dystroglycan to the cell surface. Using intravenous injection of Evans blue dye as an in vivo tracer assay, we demonstrated that perturbation of the dystrophin-glycoprotein complex caused extensive fiber damage in skeletal and cardiac muscle of the BIO14.6 hamster. Based on our results, we propose that loss of delta-sarcoglycan results in the impairment of sarcolemmal integrity, finally leading to muscular dystrophy and cardiomyopathy.
Assuntos
Cardiomiopatias/genética , Cardiomiopatias/patologia , Proteínas do Citoesqueleto/genética , Glicoproteínas de Membrana/genética , Músculo Esquelético/patologia , Mutação , Miocárdio/patologia , Animais , Cricetinae , Proteínas do Citoesqueleto/deficiência , Proteínas do Citoesqueleto/metabolismo , Modelos Animais de Doenças , Distroglicanas , Distrofina/metabolismo , Feminino , Imuno-Histoquímica , Substâncias Macromoleculares , Masculino , Glicoproteínas de Membrana/deficiência , Glicoproteínas de Membrana/metabolismo , Mesocricetus , Fibras Musculares Esqueléticas/patologia , Sarcoglicanas , Sarcolema/metabolismo , Sarcolema/patologia , Transcrição GênicaRESUMO
The sarcoglycan complex is known to be involved in limb-girdle muscular dystrophy (LGMD) and is composed of at least three proteins: alpha-, beta-, and gamma-sarcoglycan. delta-Sarcoglycan has now been identified as a second 35-kDa sarcolemmal transmembrane glycoprotein that shares high homology with gamma-sarcoglycan and is expressed mainly in skeletal and cardiac muscle. Biochemical analysis has demonstrated that gamma- and delta-sarcoglycan are separate entities within the sarcoglycan complex and that all four sarcoglycans exist in the complex on a stoichiometrically equal basis. Immunohistochemical analysis of skeletal muscle biopsies from patients with LGMD2C, LGMD2D, and LGMD2E demonstrated a reduction of the entire sarcoglycan complex in these muscular dystrophies. Furthermore, we have mapped the human delta-sarcoglycan gene to chromosome 5q33-q34 in a region overlapping the recently linked autosomal recessive LGMD2F locus.
Assuntos
Proteínas do Citoesqueleto/química , Glicoproteínas de Membrana/química , Distrofias Musculares/metabolismo , Sequência de Aminoácidos , Sequência de Bases , Mapeamento Cromossômico , Proteínas do Citoesqueleto/genética , DNA Complementar/química , Humanos , Glicoproteínas de Membrana/genética , Modelos Moleculares , Dados de Sequência Molecular , Distrofias Musculares/genética , RNA Mensageiro/metabolismo , Sarcoglicanas , Distribuição TecidualRESUMO
The primary sequence of two components of the dystrophin-glycoprotein complex has been established by complementary, DNA cloning. The transmembrane 43K and extracellular 156K dystrophin-associated glycoproteins (DAGs) are encoded by a single messenger RNA and the extracellular 156K DAG binds laminin. Thus, the 156K DAG is a new laminin-binding glycoprotein which may provide a linkage between the sarcolemma and extracellular matrix. These results support the hypothesis that the dramatic reduction in the 156K DAG in Duchenne muscular dystrophy leads to a loss of a linkage between the sarcolemma and extracellular matrix and that this may render muscle fibres more susceptible to necrosis.
Assuntos
Proteínas do Citoesqueleto/química , Distrofina/metabolismo , Matriz Extracelular/metabolismo , Glicoproteínas de Membrana , Distrofias Musculares/metabolismo , Sarcolema/metabolismo , Sequência de Aminoácidos , Animais , Sequência de Bases , Clonagem Molecular , Proteínas do Citoesqueleto/genética , Proteínas do Citoesqueleto/metabolismo , Distroglicanas , Expressão Gênica , Humanos , Immunoblotting , Laminina/metabolismo , Dados de Sequência Molecular , Peso Molecular , Músculos/química , Músculos/metabolismo , Distrofias Musculares/genética , RNA Mensageiro/análise , Proteínas Recombinantes de Fusão , Mapeamento por Restrição , Distribuição TecidualRESUMO
Dystrophin-related protein (DRP) is an autosomal gene product with high homology to dystrophin. We have used highly specific antibodies to the unique C-terminal peptide sequences of DRP and dystrophin to examine the subcellular localization and biochemical properties of DRP in adult skeletal muscle. DRP is enriched in isolated sarcolemma from control and mdx mouse muscle, but is much less abundant than dystrophin. Immunofluorescence microscopy localized DRP almost exclusively to the neuromuscular junction region in rabbit and mouse skeletal muscle, as well as mdx mouse muscle and denervated mouse muscle. DRP is also present in normal size and abundance and localizes to the neuromuscular junction region in muscle from the dystrophic mouse model dy/dy. Thus, DRP is a junction-specific membrane cytoskeletal protein that may play an important role in the organization of the postsynaptic membrane of the neuromuscular junction.
