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RATIONALE: Myocardial infarction (MI) results in remodeling of the myocardium and the extracellular matrix (ECM). Tissue inhibitors of metalloproteinases (TIMPs) are critical regulators of ECM integrity via inhibiting matrix metalloproteinases (MMPs). TIMP2 is highly expressed in the heart and is the only TIMP that, in addition to inhibiting MMPs, is required for cell surface activation of pro-MMP2. Hence, it is difficult to predict the function of TIMP2 as protective (MMP-inhibiting) or harmful (MMP-activating) in heart disease. OBJECTIVE: We examined the role of TIMP2 in the cardiac response to MI. METHODS AND RESULTS: MI was induced in 11- to 12-week-old male TIMP2(-/-) and age-matched wild-type mice. Cardiac function was monitored by echocardiography at 1 and 4 weeks post-MI. ECM fibrillar structure was visualized using second harmonic generation and multiphoton imaging of unfixed/unstained hearts. Molecular analyses were performed at 3 days and 1 week post-MI on flash-frozen infarct, periinfarct, and noninfarct tissue. Membrane type 1 (MT1)-MMP levels and activity were measured in membrane protein fractions. TIMP2(-/-)-MI mice exhibited a 25% greater infarct expansion, markedly exacerbated left ventricular dilation (by 12%) and dysfunction (by 30%), and more severe inflammation compared to wild-type MI mice. Adverse ECM remodeling was detected by reduced density and enhanced disarray of fibrillar collagen in TIMP2(-/-)-MI compared to wild-type MI hearts. TIMP2 deficiency completely abrogated MMP2 activation but markedly increased collagenase activity, particularly MT1-MMP activity post-MI. CONCLUSIONS: The MMP-inhibitory function of TIMP2 is a key determinant of post-MI myocardial remodeling primarily because of its inhibitory action on MT1-MMP. TIMP2 replenishment in diseased myocardium could provide a potential therapy in reducing or preventing disease progression.
Kandalam et al. (Thu,) studied this question.