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Responses of protein expression to cardiotoxin-induced muscle injury.  F. Kawano¹, M. Terada², N. Nakai¹, T. Ohira², Y. Higo², N. Nishimoto² and Y. Ohira^{1, 2}.  Grad. Sch. of ¹ Med. and ² Frontier Biosci., Osaka Univ., Osaka, Japan.

   It is well-known that the severe muscle atrophy is induced during spaceflight and hindlimb suspension in slow antigravity muscle.  Although the muscle mass is gradually recovered following the reloading, the muscle damage is generally noted during the acute phase of reloading or exposure to hyper G.  The responses of the proteome in rat soleus muscle to acute muscle injury were investigated in the present study.  Twelve weeks old male Wistar Hannover rats were anesthetized and 0.1mL of cardiotoxin (CTX, 0.03% in phosphate-buffered saline) was intramuscularly injected in the left soleus muscle using a 30-gauge hypodermic needle.  The right soleus muscle was kept intact as the control.  Muscle sampling was performed 24 hours after the injection of CTX.  The muscle sampled was frozen at an optimal length in isopentane cooled with liquid nitrogen and was cut cross-sectionally into two portions.  Half of the muscle segment was used for histochemical analyses, and the remaining half was homogenized.  And soluble fraction was sampled and two-dimensional electrophoresis was performed.  Subsequently, the spots with different expression from the control were picked up and the protein was identified using a peptide mass fingerprinting method.  As the results, a loss of muscle fibers was noted in the cross-section of CTX-injected muscle.  Further, CTX-injection-related increase was observed in the expression of 26 proteins, including myosin heavy chain and light chain-associated fragment, serum-derived albumin, apolipoprotein A-I, haptoglobin, and vitamin D binding protein.  The results indicated that the fragmentation of myofibrillar protein was induced during the acute phase of muscle degeneration.  It was suggested that the infiltration of blood plasma proteins to the injured muscle may play a role in the regulation of the subsequent inflammation and muscle regeneration, since it was reported that apolipoprotein and haptoglobin have anti-inflammatory function, whereas vitamin D binding protein, which is the precursor of macrophage-activating factor, could be a pro-inflammatory regulator. 

(Supported by the Grant-in-Aid for Scientific Research (S, 19100009) from Japan Society for the Promotion of Science)