Strong immunoreactivity of cathepsin L at the site of rimmed vacuoles in diseased muscles.

Skeletal muscle samples from four patients with myopathies showing autophagic vacuole formation were examined by immunohistochemical, biochemical and immunoblot analyses. Immunochemical studies demonstrated strongly positive reactions of cathepsins B and L in and around the rimmed vacuoles and weak reactions in intramyofibral portions of degenerating muscle fibres. Faint staining of cathepsin H was also seen at the sites of rimmed vacuoles. Biochemical analyses showed increased activity of cathepsin B and L in muscle specimens from the patients with rimmed vacuole formation. However, there was no remarkable cathepsin H activity in the muscle specimens from these patients. Cathepsin L immunoblot analysis of muscle extracts showed three bands with molecular masses of 30 kDa, 36 kDa and 39 kDa. The immunostaining of cathepsin L from patients with rimmed vacuole formation was stronger than that of normal controls. Cathepsin B immunoblot analysis showed only faint bands in samples from patients with rimmed vacuole formation and normal controls. This study demonstrated, for the first time, strong immunoreactivity of cathepsin L at the sites of rimmed vacuoles. Possible mechanisms of rimmed vacuole formation are discussed.