Adipogenic and myogenic gene expression in rotator cuff muscle of the sheep after tendon tear.

Chronic rotator cuff tendon tears lead to fatty infiltration and muscle atrophy with impaired physiological functions of the affected muscles. However, the cellular and molecular mechanisms of corresponding pathophysiological processes remain unknown. The purpose of this study was to characterize the expression pattern of adipogenic (PPAR gamma, C/EBP beta) and myogenic (myostatin, myogenin, Myf-5) transcription factors in infraspinatus muscle of sheep after tenotomy, implantation of a tension device, refixation of the tendon, and rehabilitation, reflecting a model of chronic rotator cuff tears. In contrast to human patients, the presented sheep model allows a temporal evaluation of the expression of a given marker in the same individual over time. Semiquantitative RT/PCR analysis of PPAR,15, myostatin, myogenin,Myf-5, and C/EBP beta transcript levels was carried out with sheep muscle biopsy-derived total RNA. We found a significantly increased expression of Myf-5 and PPAR, after tenotomy and a significant change for Myf-5 and C/EBP beta after continuous traction and refixation. This experimental sheep model allows the molecular analysis of pathomechanisms of muscular changes after rotator cuff tear. The results point to a crucial role of the transcription factors PPAR-gamma, C/EBP beta, and Myf-5 in impairment and regeneration of rotator cuff muscles after tendon tears in sheep. (C) 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 27:504-509, 2009