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J Orthop Res. 2012 Sep;30(9):1440-6. doi: 10.1002/jor.22096. Epub 2012 Feb 29.

Evaluation of Akt/mTOR activity in muscle atrophy after rotator cuff tears in a rat model.

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1
Department of Veterans Affairs, San Francisco Veterans Affairs Medical Center, San Francisco, Califronia, USA.

Abstract

Atrophy of the rotator cuff muscles is a factor that complicates the treatment of a massive rotator cuff tear (RCT). However, the molecular mechanisms that govern the development of muscle atrophy after RCTs have not been well defined. The Akt/mammalian target of rapamycin (mTOR) signaling pathway plays a central role in maintaining muscle mass in response to mechanical loading. The role of this pathway in the development of muscle atrophy after a massive RCT remains unknown. The purpose of this study was to investigate the regulation of the Akt/mTOR pathway in the development of muscle atrophy after a RCT and suprascapular nerve (SSN) injury. We evaluated the activity of the Akt/mTOR signaling pathway and how this pathway interacts with two atrophy-related genes, MuRF-1 and MAFbx, in supraspinatus muscles of rats that underwent unilateral complete rotator cuff tendon transection or SSN transection. Akt/mTOR activity was significantly reduced after tendon rupture, but increased after nerve injury. MuRF-1 and MAFbx were only up-regulated following denervation. These results suggest that tendon transection leads to a decrease in protein synthesis with down-regulation of the Akt/mTOR signaling pathway, whereas denervation leads to an increase in protein degradation via up-regulation of expression of MuRF-1 and MAFbx.

PMID:
22378614
DOI:
10.1002/jor.22096
[Indexed for MEDLINE]
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