STRONG IMMUNOREACTIVITY OF CATHEPSIN L AT THE SITE OF RIMMED VACUOLES IN DISEASED MUSCLES

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Abstract
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.

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