Regulation of costamere turnover is associated with the loss of contractile tissue and seems to be impacted by nandrolone treatment. The early decrease of muscle volume is associated with reduction of fat while, the second stage is characterized by substantial loss of contractile tissue accompanied by massive fat accumulation. Taken together, these findings imply that muscle remodeling after tendon release occurs in two stages. Nandrolone administration mitigated the loss of contractile tissue by 26% and prevented fat accumulation, alterations in FAK activity, and talin cleavage. After 16 weeks, the muscle volume decreased by 36 cm(3), contractile tissue was quantitatively lost, and the fat content increased by 184%.
At 2 weeks after tendon release, muscle volume decreased by 17 cm from an initial 185 cm(3), the fatty tissue volume was halved, and the contractile tissue volume remained unchanged.
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This was accompanied by cleavage of the costamere protein talin into a 190 kDa fragment while full length talin remained unchanged. We found the activity of focal adhesion kinase (FAK), a main regulator of costamere turnover, was unchanged at 2 weeks but decreased by 27% 16 weeks after surgical release of the infraspinatus tendon. This study examined if costamere turnover is affected by a rotator cuff tear in a previously established ovine model. Previous studies suggested that degradation of contractile tissue requires cleavage of the costamere, a structural protein complex that holds sarcomeres in place. Journal of Orthopaedic Research, 36(1):272-281. Costamere protein expression and tissue composition of rotator cuff muscle after tendon release in sheep. Ruoss, Severin Möhl, Christoph B Benn, Mario C von Rechenberg, Brigitte Wieser, Karl Meyer, Dominik C Gerber, Christian Flück, Martin (2018).
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