αB-crystallin in oxidative muscle fibers and its accumulation in ragged-red fibers: a comparative immunohistochemical and histochemical study in human skeletal muscle

The αB-crystallin gene is abundantly experssed in the vertebrate lens and at lower levels in various non-lenticular tissues. Among the non-lenticular tissues, αB-crystallin is present at high levels in the heart and skeletal muscle. Using a specific antibody against αB-crystallin, the cellular localization of αB-crystallin was studied in biopsies of human skeletal muscles. Expression of αB-crystallin was observed in normal oxidative muscle fibers that show positive reactions for NADH-tetrazolium reductase and cytochrome c oxidase. In muscle diseases increased immunoreactivity for αB-crystallin was found in ragged-red fibers, which stained darkly with histochemistry for succinate dehydrogenase. Since αB-crystallin is related to small heat-shock proteins and can be induced by various stress conditions, the increased αB-crystallin immunoreactivity of ragged-red fibers could result from profound oxidative stress produced by the abnormal mitochondrial metabolism.