Regeneration in sarcoglycanopathies: expression studies of sarcoglycans and other muscle proteins

We have studied the immunohistochemical expression of 14 different muscle proteins of the basal lamina, sarcolemma and cytoskeleton in primary sarcoglycanopathies (13 cases) and compared it with Duchenne dystrophy (6 cases) and myositis (5 cases). Sarcolemmal proteins (i.e. 4 sarcoglycans, beta-dystroglycan, dystrophin, beta-spectrin) were reduced both in sarcoglycanopathies and Duchenne dystrophy, because of structural and functional impairment of the plasma membrane. Sarcolemmal proteins are poorly expressed in regenerating fibers of all muscle disorders, due to a developmental delay or to an abnormal assembly. Laminins (alpha2 and beta chains) were preserved in all cases while utrophin was expressed in Duchenne muscle but not in sarcoglycanopathies. Regenerating fibers were studied with different markers (i.e. fetal myosin, desmin, vimentin, laminin alpha1). Fetal myosin positive fibers (as well as desmin and laminin alpha1), were significantly higher in Duchenne dystrophy (25%) than in age-matched sarcoglycanopathies (7%). Vimentin, a marker of early regeneration, was expressed at higher level in sarcoglycanopathies than in Duchenne dystrophy, suggesting in the former a lower extent of regeneration or a shorter regeneration cycle.