chondroitin-sulfates and Muscular-Dystrophies

Skeletal muscle formation and regeneration require myoblast fusion to form multinucleated myotubes or myofibers, yet their molecular regulation remains incompletely understood. We show here that the levels of extra- and/or pericellular chondroitin sulfate (CS) chains in differentiating C2C12 myoblast culture are dramatically diminished at the stage of extensive syncytial myotube formation. Forced down-regulation of CS, but not of hyaluronan, levels enhanced myogenic differentiation in vitro. This characteristic CS reduction seems to occur through a cell-autonomous mechanism that involves HYAL1, a known catabolic enzyme for hyaluronan and CS. In vivo injection of a bacterial CS-degrading enzyme boosted myofiber regeneration in a mouse cardiotoxin-induced injury model and ameliorated dystrophic pathology in mdx muscles. Our data suggest that the control of CS abundance is a promising new therapeutic approach for the treatment of skeletal muscle injury and progressive muscular dystrophies.

Topics: Animals; Cardiotoxins; Cell Differentiation; Cells, Cultured; Chondroitin Sulfates; Gene Expression Regulation; Glycosaminoglycans; Hyaluronic Acid; Hyaluronoglucosaminidase; Mice; Mice, Inbred C57BL; Mice, Inbred mdx; Muscle Development; Muscle, Skeletal; Muscular Dystrophies; Proteoglycans; Regeneration; Time Factors

The dystrophin-associated protein complex (DAPC) is necessary for maintaining the integrity of the muscle cell plasma membrane and may also play a role in coordinating signaling events at the cell surface. The alpha-/beta-dystroglycan subcomplex of the DAPC forms a critical link between the cytoskeleton and the extracellular matrix. A ligand blot overlay assay was used to search for novel dystroglycan binding partners in postsynaptic membranes from Torpedo electric organ. An approximately 125-kD dystroglycan-binding polypeptide was purified and shown by peptide microsequencing to be the Torpedo ortholog of the small leucine-rich repeat chondroitin sulfate proteoglycan biglycan. Biglycan binding to alpha-dystroglycan was confirmed by coimmunoprecipitation with both native and recombinant alpha-dystroglycan. The biglycan binding site was mapped to the COOH-terminal third of alpha-dystroglycan. Glycosylation of alpha-dystroglycan is not necessary for this interaction, but binding is dependent upon the chondroitin sulfate side chains of biglycan. In muscle, biglycan is detected at both synaptic and nonsynaptic regions. Finally, biglycan expression is elevated in muscle from the dystrophic mdx mouse. These findings reveal a novel binding partner for alpha-dystroglycan and demonstrate a novel avenue for interaction of the DAPC and the extracellular matrix. These results also raise the possibility of a role for biglycan in the pathogenesis, and perhaps the treatment, of muscular dystrophy.

Topics: Amino Acid Sequence; Animals; Biglycan; Binding Sites; Chondroitin Sulfates; Cytoskeletal Proteins; Dystroglycans; Dystrophin; Extracellular Matrix Proteins; Glycosylation; Humans; Leucine; Membrane Glycoproteins; Mice; Mice, Mutant Strains; Molecular Sequence Data; Molecular Weight; Muscles; Muscular Dystrophies; Neuromuscular Junction; Protein Binding; Proteoglycans; Repetitive Sequences, Amino Acid; Synapses; Torpedo; Up-Regulation

The immunohistological localization of chondroitin sulfate (CS) has been studied in normal and pathological human muscle. The bovine nasal cartilage proteoglycan digested with chondroitinase ABC (BNC-PG-Ch ABC) has been utilized for the production of a rabbit polyclonal antiserum. In vitro studies showed that the antiserum binds to the unsaturated disaccharide that remains attached to the core protein after digestion of the CS chains with chondroitinase ABC (Ch ABC). As the disaccharide is created specifically by Ch ABC digestion of the CS chains, the antiserum allows the immunolocalization of CS on tissue sections digested with Ch ABC. The immunohistochemical study on normal and pathological muscle demonstrated a localization of CS in all the extracellular structures: endomysium, perimysium, muscle spindle capsule and intrafusal space. In pathological conditions, the CS was raised in all the cases with increased connective tissue, showing a pattern comparable to that obtained with fibronectin and collagen III. None of the pathological conditions displayed any peculiar character of CS distribution. This finding does not support a primary role for CS in the pathogenesis of muscular dystrophy.

Topics: Antibody Specificity; Blood Vessels; Chondroitin; Chondroitin Sulfates; Humans; Muscles; Muscular Dystrophies; Neuromuscular Diseases; Syndrome