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Molecular bases of muscle atrophy in mammals: comparative studies on bats and rats     Kisoo Lee¹, Taesik Gwag¹, Woojae Yoo¹, Ju Woon Lee², Myungwoo Byun² and Inho Choi^{1        1}Dept. of Life Science, Yonsei Univ., Wonju, Gangwon-Do and ²Radiation Application Research Institute, Korea Atomic Energy Research Institute, Jeongeup, Jeonbuk, Republic of Korea

   Mammalian hibernators and nonhibernators display different degrees of muscle loss after a prolonged period of unloading. To comprehend molecular bases of this difference, we investigated expression levels of sarcomeric and stress proteins using 2-dimenstional electrophoresis and immunoblotting analysis on the soleus muscle of Sprague-Dawley rats and the pectoral muscle of bat Murina leucogaster. The rats were divided into a vivarium control and a 3-wk hindlimb suspension group (HS). Bats were collected as a summer-active group and winter hibernation group (HB, spending about 3 months of dormancy). Muscle mass to body mass, tension production capacity, and actin to myosin filaments (based on electron micrograms) were determined as well. We found the rat soleus muscle showed 31% - 50% reduction in the relative muscle mass, maximum tetanic tension, the myofilament ratio for the 3-wk unloading, whereas the bat pectoral muscle did not show any sign of atrophy or functional depression for 3-mo dormancy. In parallel with these differences, expressions of sarcomeric proteins (alpha-actin, tropomyosin, myosin light chain, troponin T1 and T2) and heat shock proteins (HSP90, p27, alpha crystalline B-chain) of HS decreased 0.3- to 0.7-fold those of the control, while expressions of most of those proteins were maintained or even elevated 1.7- to 1.9-fold for HSP70 and HSP27 in HB. Because HSPs are known to play a role of molecular chaperones as well as maintenance of myofibrillar organization and integrity against mechanical and heat stresses, the expression level of stress proteins may be an important factor limiting the extent of muscle atrophy and contractile depression against a prolonged disuse.

(This work was supported by Korea Atomic Energy Research Institute in 2007.)