Age-Related Changes in Collagen Degeneration of the Rotator Cuff in an Animal Model

Abstract

Rotator cuff tears are a common injury in the elderly and often impose limitations on the range of motion and cause pain. The cause of rotator cuff tearing is unknown, and degeneration of the supraspinatus tendon with age is poorly understood.In the present study, we examined collagen degeneration of the supraspinatus tendon in the rat shoulder joint. Using rats of different age (10 weeks: young, 6 months: adult, and 2 years: old), we examined the supraspinatus tendon by immunofluorescence staining (collagen types I and III), assessed the amount of collagen and mRNA expression for collagen type 1A1, 3A1 (COL1A1, COL3A1), matrix metalloproteinase 2,9 (MMP-2, -9).After immunofluorescence staining, the layer structure of tendon to bone attachment was apparent in the young. The amount of collagen decreased in the old group. In addition the mRNA expression of Col1a1 and Col3a1 was significantly reduced in the old group.On the one hand, the old groups showed higher mRNA levels of MMP-2 and MMP-9 than the young group. The ability to synthesize collagen decreases during aging and the amount of total collagen that is present in the supraspinatus tendon is decreased. These changes may contribute to tearing/breakage of the supraspinatus tendon.