Mechanism of Antigravity Muscle Atrophy

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Abstract Atrophy of rat soleus muscles is characterized by an early dramatic decrease in a 22-kDa protein. This protein is found in the soluble compartment of muscle and in the myofibrillar Z-band. The 22-kDa protein shows a 95% sequence homology with the B chain of bovine lens alpha-crystallin (alphaB-crystallin). alphaB-Crystallin cDNA was cloned from rat heart cDNA library and the DNA sequence for the complete coding region and for partial non-coding regions were determined. A polyclonal antibody was also produced to rat muscle alphaB-crystallin. Northern analysis and immunoblotting revealed alphaB-crystallin gene and protein expression in slow skeletal and cardiac muscle, and low levels of expression in fast skeletal muscle. Immunocytochemistry at the light and electron microscope levels revealed localization of muscle alphaB-crystallin in Z-bands of isolated myofibrils of skeletal muscles. Northern analysis revealed that alphaB-crystallin gene expression inhibition is one of the early events of induced acute muscular atrophy. Based upon sequence homology with lens alphaB-crystallin, a functional role is tentatively assigned suggesting that muscle alphaB-crystallin is a myofibril-stabilizing protein that is transcriptionally regulated during early changes in muscle atrophy.