Activation of the intramyofibral autophagic-lysosomal system in muscular dystrophy

Skeletal muscles obtained from myopathies with myofiber necrosis, including mdx dystrophic mice, plasmocid-induced myopathy in rats, and patients with Duchenne muscular dystrophy, were examined immunohistochemically with anticathepsin-peroxidase conjugates. Strong reactions for lysosomal cysteine proteinases, which can degrade myofibrillar proteins, were demonstrated in macrophages invading and surrounding the necrotic areas and some degenerative myofibers and also in intramyofibral portions of atrophic fibers of dystrophic mice and humans. Apparently normal and regenerating myofibers did not stain for lysosomal cathepsins. Abnormal increases of cathepsins L and B were seen even in the early stage of plasmocid myopathy and in a 20-day-old young mdx mouse before infiltration of macrophages, suggesting that autodigestion by intramyofibral lysosomal proteinases is an important event before digestion of the necrotic fibers by macrophage proteinases. Activation of the intramyofibral lysosomal system, as in muscular dystrophy, was also observed in distal myopathy with rimmed vacuoles without macrophageal infiltration (Am J Pathol 1986, 122:193-198). Thus, this activation seems to be an important, early response to myocellular damage.