Achilles Tendon Repair Response to Injury is Enhanced by the Absence of Decorin

Introduction Achilles tendon ruptures are a common problem preventing athletic participation and daily life activities, often requiring surgical repair and extensive rehabilitation. In rabbit Achilles tenocytes in vitro, down-regulation of the proteoglycan decorin suppressed the expression of TGF-b1, a growth factor associated with fibrotic scar. Similarly, in the medial collateral ligament in vivo, down-regulation of decorin improved healing. Conversely, in mouse patellar tendon, the absence of decorin reduced uninjured tendon mechanical properties and had no effect on healing tendons 6 weeks after injury. The effects of reduced decorin appear dependent on the site investigated and its effect on Achilles tendon in particular is unknown. Since decorin plays a key role in collagen fibrillogenesis, inhibition of decorin would be expected to alter Achilles tendon properties. Therefore, the objective of this study was to investigate the effect of the absence of decorin in vivo on native and healing mouse Achilles tendons. We hypothesized that the absence of decorin would 1) impair the native mechanical properties of the Achilles tendon and 2) improve the healing mechanical properties of the Achilles tendon.