Increased MMP-2 activity during intervertebral disc degeneration is correlated to MMP-14 levels

Intervertebral disc (IVD) degeneration is associated with the increased expression of several matrix metalloproteinases (MMPs), in particular MMP-2. However, little is known about the actual activity of MMP-2 in healthy and degenerated discs, or what mechanisms are involved in its activation. A major activation pathway involves complex formation with MMP-14 and a tissue inhibitor of metalloproteinases-2 (TIMP-2). In a series of 56 human IVDs, obtained at autopsy and graded according to the Thompson score (I-V), we analysed whether MMP-2 activity was increased in different stages of IVD degeneration and to what extent activation was related to the production of MMP-14 and TIMP-2. MMP-2 activation and production were quantified by gelatin zymography. Immunohistochemical staining of MMP-14 and TIMP-2 was quantified with a video overlay-based system. A positive correlation was observed between the amount of active MMP-2 and pro-MMP-2 and degeneration grade (p < 0.001, correlation coefficient (CC) 0.557; and p < 0.001, CC 0.556, respectively). MMP-2 activity correlated positively with MMP-14 and less strongly with TIMP-2 (p = 0.001, CC 0.436; and p = 0.03, CC 0.288, respectively). Moreover, immunopositivity for MMP-14 correlated to degeneration grade (p = 0.002, CC 0.398). IVD degeneration was associated with the activity of MMP-2 and the correlation of its activation with MMP-14 production suggests MMP-14 activates MMP-2 during degeneration. As MMP-14 is capable of activating several other enzymes that are also thought to be involved in IVD degeneration, it may be a key mediator of the degenerative process.