Rotator cuff tear reduces muscle fiber specific force production and induces macrophage accumulation and autophagy.
Full-thickness tears to the rotator cuff can cause severe pain and disability. Untreated tears progress in size and are associated with muscle atrophy and an infiltration of fat to the area, a condition known as "fatty degeneration." To improve the treatment of rotator cuff tears, a greater understanding of the changes in the contractile properties of muscle fibers and the molecular regulation of fatty degeneration is essential. Using a rat model of rotator cuff injury, we measured the force generating capacity of individual muscle fibers and determined changes in muscle fiber type distribution that develop after a full thickness rotator cuff tear. We also measured the expression of mRNA and miRNA transcripts involved in muscle atrophy, lipid accumulation, and matrix synthesis. We hypothesized that a decrease in specific force of rotator cuff muscle fibers, an accumulation of type IIb fibers, and an upregulation in fibrogenic, adipogenic, and inflammatory gene expression occur in torn rotator cuff muscles. Thirty days following rotator cuff tear, we observed a reduction in muscle fiber force production, an induction of fibrogenic, adipogenic, and autophagocytic mRNA and miRNA molecules, and a dramatic accumulation of macrophages in areas of fat accumulation.
Department of Orthopaedic Surgery, University of Michigan Medical School, 109 Zina Pitcher Place, BSRB 2017, Ann Arbor, Michigan 48109-2200, USA.
Jonathan P
JP
Gumucio
Max E
ME
Davis
Joshua R
JR
Bradley
Patrick L
PL
Stafford
Corey J
CJ
Schiffman
Evan B
EB
Lynch
Dennis R
DR
Claflin
Asheesh
A
Bedi
Christopher L
CL
Mendias
D017667:Adipocytes / Q000166:cytology; D000273:Adipose Tissue / Q000473:pathology; D000818:Animals; D001343:Autophagy; D007150:Immunohistochemistry / Q000379:methods; D008264:Macrophages / Q000378:metabolism*; D008297:Male; D035683:MicroRNAs / Q000378:metabolism; D018485:Muscle Fibers, Skeletal / Q000473:pathology*; D009132:Muscles / Q000473:pathology*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D017006:Rotator Cuff / Q000473:pathology*; D000070636:Rotator Cuff Injuries; D013314:Stress, Mechanical; D013708:Tendon Injuries / Q000473:pathology*
D035683:MicroRNAs; D012333:RNA, Messenger