title: Compensatory hypertrophy of the teres minor muscle after large rotator cuff tear model in adult male rat.
abstract: BACKGROUND
  Rotator cuff tear (RCT) is a common musculoskeletal disorder in the elderly. The large RCT is often irreparable due to the retraction and degeneration of the rotator cuff muscle. The integrity of the teres minor (TM) muscle is thought to affect postoperative functional recovery in some surgical treatments. Hypertrophy of the TM is found in some patients with large RCTs; however, the process underlying this hypertrophy is still unclear. The objective of this study was to determine if compensatory hypertrophy of the TM muscle occurs in a large RCT rat model.
  
  
  METHODS
  Twelve Wistar rats underwent transection of the suprascapular nerve and the supraspinatus and infraspinatus tendons in the left shoulder. The rats were euthanized 4 weeks after the surgery, and the cuff muscles were collected and weighed. The cross-sectional area and the involvement of Akt/mammalian target of rapamycin (mTOR) signaling were examined in the remaining TM muscle.
  
  
  RESULTS
  The weight and cross-sectional area of the TM muscle was higher in the operated-on side than in the control side. The phosphorylated Akt/Akt protein ratio was not significantly different between these sides. The phosphorylated-mTOR/mTOR protein ratio was significantly higher on the operated-on side.
  
  
  CONCLUSIONS
  Transection of the suprascapular nerve and the supraspinatus and infraspinatus tendons activates mTOR signaling in the TM muscle, which results in muscle hypertrophy. The Akt-signaling pathway may not be involved in this process. Nevertheless, activation of mTOR signaling in the TM muscle after RCT may be an effective therapeutic target of a large RCT.
authors.affiliation: Department of Orthopaedic Surgery, Gunma University Graduate School of Medicine, Maebashi, Gunma, Japan. Electronic address: t-ichinose@gunma-u.ac.jp.
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Ichinose
authors.affiliation: Department of Orthopaedic Surgery, Gunma University Graduate School of Medicine, Maebashi, Gunma, Japan.
authors.forename: Atsushi
authors.initials: A
authors.lastname: Yamamoto
authors.affiliation: Department of Physical Therapy, Takasaki University of Health and Welfare, Takasaki, Gunma, Japan.
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Kobayashi
authors.affiliation: Department of Orthopaedic Surgery, Gunma University Graduate School of Medicine, Maebashi, Gunma, Japan.
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Shitara
authors.affiliation: Department of Orthopaedic Surgery, Gunma University Graduate School of Medicine, Maebashi, Gunma, Japan.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Shimoyama
authors.affiliation: Department of Orthopaedic Surgery, Gunma University Graduate School of Medicine, Maebashi, Gunma, Japan.
authors.forename: Haku
authors.initials: H
authors.lastname: Iizuka
authors.affiliation: Department of Integrative Physiology, Gunma University Graduate School of Medicine, Maebashi, Gunma, Japan.
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Koibuchi
authors.affiliation: Department of Orthopaedic Surgery, Gunma University Graduate School of Medicine, Maebashi, Gunma, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Takagishi
mesh_terms: D000818:Animals; D004195:Disease Models, Animal; D006984:Hypertrophy / Q000378:metabolism / Q000473:pathology; D008297:Male; D059348:Peripheral Nerve Injuries / Q000378:metabolism; D010766:Phosphorylation; D051381:Rats; D017208:Rats, Wistar; D017006:Rotator Cuff / Q000378:metabolism / Q000473:pathology*; D000070636:Rotator Cuff Injuries; D012421:Rupture / Q000378:metabolism / Q000473:pathology; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism*
chemical_list: C546845:mTOR protein, rat; D058570:TOR Serine-Threonine Kinases
keywords: Shoulder joint; animal study; functional compensation; muscle hypertrophy; rotator cuff tear