Changes in αB-crystallin, tubulin, and MHC isoforms by hindlimb unloading show different expression patterns in various hindlimb muscles = Changes in αB-crystallin, tubulin, and MHC isoforms by hindlimb unloading show different expression patterns in various hindlimb muscles

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Hyun Seok Jee, Takashi Sakurai, Jae-Young Lim and Hideo Hatta. Changes in αB-crystallin, tubulin, and MHC isoforms by hindlimbunloading show different expression patterns in various hindlimb muscles. JENB., Vol. 18, No. 2, pp.161-168, 2014 [Purpose]αB-crystallin is a small heat shock protein that acts as a molecular chaperone under various stress conditions. Microtubules, whichconsist of tubulin, are related to maintain the intracellular organelles and cellular morphology. These two proteins have been shownto be related to the properties of different types of myofibers based on their contractile properties. The response of these proteinsduring muscular atrophy, which induces a myofibril component change, is not clearly understood. [Methods] We performed 15days of hindlimb unloading on rats to investigate the transitions of these proteins by analyzing their absolute quantities. Proteincontents were analyzed in the soleus, plantaris, and gastrocnemius muscles of the unloading and control groups (N = 6). [Results]All three muscles were significantly atrophied by hindlimb unloading (P < 0.01): soleus (47.5%), plantaris (16.3%), and gastrocnemius(21.3%) compared to each control group. αB-crystallin was significantly reduced in all three examined unloaded hindlimb musclescompared to controls (P < 0.01) during the transition of the myosin heavy chain to fast twitch muscles. α-Tubulin responded onlyin the unloaded soleus muscle. Muscle atrophy induced the reduction of αB-crystallin and α-tubulin expressions in plantar flexormuscles with a shift to the fast muscle fiber compared to the control. [Conclusion] The novel finding of this study is that bothproteins, αB-crystallin and α-tubulin, were downregulated in slow muscles (P < 0.01); However, α-tubulin was not significantly reduced compared to the control in fast muscles (P < 0.01). [Keyword] Microtubule, αB-crystallin, tubulin, myosin heavy chainisoform, skeletal muscle