Stress protein and fiber type

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The sequence of alphaB-crystallin has striking similarity to the suquence of small heat shock proteins (HSPs#) and increasing evidence indicates that it has also functional similarities with the small HSPs. The expression of alphaB-crystallin is induced upon stress. Similarly, amorphous alphaB-acrystallin aggregates are formed after ischemia. alphaB-crystallin can function as a molecular chaperone, by suppressing heat induced aggregation of other proteins, and by assisting refolding of denatured protein. These observations from in vitro experiments suggest that alphaB-crystallin has to be considered a member of the small HSPs. It seems reasonable to assume that the constitutive expression is required in soleus muscle because this muscle is continuously subjected to a more stressful environment, such as high temperature, oxidant injury, and higher rate of protein turnover, than other muscles and requires stress related functions provided by alphaB-crystallin. This drives us to the question whether the expression of alphaB-crystallin in stressful muscle is directly regulated with its high rate recruitment, which causes stressful environment, or indirectly regulated in a manner of expression as a fiber type specific protein. The relationship between the expression of alphaB-crystallin as stress protein and fiber-type were examined in three experiments of 1) those distributions in control rats, 2) relative changes due to muscle atropphy by hindlimb suspension, and 3) relative changes due to the treatment of thiroid hormone and PTU.For this purpose we used immuno-histochemical method to investigate these relationship using mouse monoclonal anti-myosin antibodies and rabbit anti-alphaB-crystallin polyclonal antibodies. In soleus muscles, type I fibers reacted much stronger with anti-alphaB-crystallin Ig, than type IIA fibers. In EDL muscles, type I fibers showed strong reactivity for anti-alphaB-crystallin Ig than type II fibers. In addition to the differences between ty