Changes in gene expression of individual matrix metalloproteinases differ in response to mechanical unloading of tendon fascicles in explant culture

Immobilization of the tendon and ligament has been shown to result in a rapid and significant decrease in material properties. It has been proposed that tissue degradation leading to tendon rupture or pain in humans may also be linked to mechanical unloading following focal tendon injury. Hence, understanding the remodeling mechanism associated with mechanical unloading has relevance for the human conditions of immobilization (e.g., casting), delayed repair of tendon ruptures, and potentially overuse injuries as well. This is the first study to investigate the time course of gene expression changes associated with tissue harvest and mechanical unloading culture in an explant model. Rat tail tendon fascicles were harvested and placed in culture unloaded for up to 48 h and then evaluated using qRT‐PCR for changes in two anabolic and four catabolic genes at 12 time points. Our data demonstrates that Type I Collagen, Decorin, Cathepsin K, and MMP2 gene expression are relatively insensitive to unloaded culture conditions. However, changes in both MMP3 and MMP13 gene expression are rapid, dramatic, sustained, and changing during at least the first 48 h of unloaded culture. This data will help to further elucidate the mechanism for the loss of mechanical properties associated with mechanical unloading in tendon. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 26:1306–1312, 2008