Molecular events in tendinopathy: a role for metalloproteases.

Disorganized, haphazard ineffective healing is a constant feature of chronic tendinopathy. Normal tendon is composed mostly of type I collagen. Tendinopathic tendons, conversely, have a greater proportion of type III collagen, which is associated with tendon rupture. Matrix metalloproteinases (MMPs) are involved in remodelling of the extracellular matrix (ECM) of tendons, because they are either up- or down-regulated in tendinopathy. A balance between MMPs and tissue inhibitors of metalloproteinases is required to maintain tendon homeostasis. The mechanism of activation of MMPs is poorly understood, and their precise role in tendinopathy is unclear.