title: Muscle degeneration without mechanical injury in sarcoglycan deficiency.
abstract: In humans, mutations in the genes encoding components of the dystrophin-glycoprotein complex cause muscular dystrophy. Specifically, primary mutations in the genes encoding alpha-, beta-, gamma-, and delta-sarcoglycan have been identified in humans with limb-girdle muscular dystrophy. Mice lacking gamma-sarcoglycan develop progressive muscular dystrophy similar to human muscular dystrophy. Without gamma-sarcoglycan, beta- and delta-sarcoglycan are unstable at the muscle membrane and alpha-sarcoglycan is severely reduced. The expression and localization of dystrophin, dystroglycan, and laminin-alpha2, a mechanical link between the actin cytoskeleton and the extracellular matrix, appears unaffected by the loss of sarcoglycan. We assessed the functional integrity of this mechanical link and found that isolated muscles lacking gamma-sarcoglycan showed normal resistance to mechanical strain induced by eccentric muscle contraction. Sarcoglycan-deficient muscles also showed normal peak isometric and tetanic force generation. Furthermore, there was no evidence for contraction-induced injury in mice lacking gamma-sarcoglycan that were subjected to an extended, rigorous exercise regimen. These data demonstrate that mechanical weakness and contraction-induced muscle injury are not required for muscle degeneration and the dystrophic process. Thus, a nonmechanical mechanism, perhaps involving some unknown signaling function, likely is responsible for muscular dystrophy where sarcoglycan is deficient.
authors.affiliation: Department of Molecular Genetics and Cell Biology, Section of Cardiology, University of Chicago, 5841 South Maryland Avenue, Chicago, IL 60637, USA.
authors.forename: A A
authors.initials: AA
authors.lastname: Hack
authors.forename: L
authors.initials: L
authors.lastname: Cordier
authors.forename: D I
authors.initials: DI
authors.lastname: Shoturma
authors.forename: M Y
authors.initials: MY
authors.lastname: Lam
authors.forename: H L
authors.initials: HL
authors.lastname: Sweeney
authors.forename: E M
authors.initials: EM
authors.lastname: McNally
mesh_terms: D000367:Age Factors; D000818:Animals; D001835:Body Weight; D003402:Creatine Kinase / Q000097:blood; D003598:Cytoskeletal Proteins / Q000172:deficiency* / Q000235:genetics / Q000502:physiology*; D008562:Membrane Glycoproteins / Q000172:deficiency* / Q000235:genetics / Q000502:physiology*; D051379:Mice; D018482:Muscle, Skeletal / Q000033:anatomy & histology / Q000293:injuries / Q000502:physiology; D009137:Muscular Dystrophy, Animal / Q000201:enzymology*; D016296:Mutagenesis; D010805:Physical Conditioning, Animal / Q000502:physiology; D049031:Sarcoglycans; D013314:Stress, Mechanical; D013997:Time Factors
chemical_list: D003598:Cytoskeletal Proteins; D008562:Membrane Glycoproteins; D049031:Sarcoglycans; D003402:Creatine Kinase