Matrix metalloproteinases: regulation and dysregulation in the failing heart

Matrix metalloproteinases (MMPs) are a family of proteolytic enzymes responsible for myocardial extracellular protein degradation. Several MMP species identified within the human myocardium may be dysregulated in congestive heart failure (CHF). For example, MMPs that are expressed at very low levels in normal myocardium, such as collagenase-3 (MMP-13) and the membrane-type-1 MMPs, are substantially upregulated in CHF. However, MMP species are not uniformly increased in patients with end-stage CHF, suggesting that a specific portfolio of MMPs are expressed in the failing myocardium. With the use of animal models of CHF, a mechanistic relationship has been demonstrated with respect to myocardial MMP expression and the left ventricular (LV) remodeling process. The tissue inhibitors of the MMPs (TIMPs) are locally synthesized proteins that bind to active MMPs and thereby regulate net proteolytic activity. However, there does not appear to be a concomitant increase in myocardial TIMPs during the LV remodeling process and progression to CHF. This disparity between MMP and TIMP levels favors a persistent MMP activation state within the myocardium and likely contributes to the LV remodeling process in the setting of developing CHF. The elucidation of upstream signaling mechanisms that contribute to the selective induction of MMP species within the myocardium as well as strategies to normalize the balance between MMPs and TIMPs may yield some therapeutic strategies by which to control myocardial extracellular remodeling and thereby slow the progression of the CHF process.