title: Changes in αB-crystallin, tubulin, and MHC isoforms by hindlimb unloading show different expression patterns in various hindlimb muscles.
abstract: OBJECTIVE
  αB-crystallin is a small heat shock protein that acts as a molecular chaperone under various stress conditions. Microtubules, which consist of tubulin, are related to maintain the intracellular organelles and cellular morphology. These two proteins have been shown to be related to the properties of different types of myofibers based on their contractile properties. The response of these proteins during muscular atrophy, which induces a myofibril component change, is not clearly understood.
  
  
  METHODS
  We performed 15 days of hindlimb unloading on rats to investigate the transitions of these proteins by analyzing their absolute quantities. Protein contents 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 muscles compared to controls (P < 0.01) during the transition of the myosin heavy chain to fast twitch muscles. α-Tubulin responded only in the unloaded soleus muscle. Muscle atrophy induced the reduction of αB-crystallin and α-tubulin expressions in plantar flexor muscles with a shift to the fast muscle fiber compared to the control.
  
  
  CONCLUSIONS
  The novel finding of this study is that both proteins, 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).
authors.affiliation: Seoul National University Bundang Hospital, Gyeonggi-do, Korea ; The University of Tokyo, Tokyo, Japan.
authors.forename: Hyunseok
authors.initials: H
authors.lastname: Jee
authors.affiliation: The University of Tokyo, Tokyo, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Sakurai
authors.affiliation: Seoul National University Bundang Hospital, Gyeonggi-do, Korea.
authors.forename: Jae-Young
authors.initials: JY
authors.lastname: Lim
authors.affiliation: The University of Tokyo, Tokyo, Japan.
authors.forename: Hideo
authors.initials: H
authors.lastname: Hatta
keywords: Microtubule; myosin heavy chain isoform; skeletal muscle; tubulin; αB-crystallin