Myocardial recovery from ischemia-reperfusion is compromised in the absence of tissue inhibitor of metalloproteinase 4.

BACKGROUND: Myocardial reperfusion after ischemia (I/R), although an effective approach in rescuing the ischemic myocardium, can itself trigger several adverse effects including aberrant remodeling of the myocardium and its extracellular matrix. Tissue inhibitor of metalloproteinases (TIMPs) protect the extracellular matrix against excess degradation by matrix metalloproteinases (MMPs). TIMP4 levels are reduced in myocardial infarction; however, its causal role in progression of post-I/R injury has not been explored. METHODS AND
RESULTS: In vivo I/R (20-minute ischemia, 1-week reperfusion) resulted in more severe systolic and diastolic dysfunction in TIMP4(-/-) mice with enhanced inflammation, oxidative stress (1 day post-I/R), hypertrophy, and interstitial fibrosis (1 week). After an initial increase in TIMP4 (1 day post-I/R), TIMP4 mRNA and protein decreased in the ischemic myocardium from wild-type mice by 1 week post-I/R and in tissue samples from patients with myocardial infarction, which correlated with enhanced activity of membrane-bound MMP, membrane-type 1 MMP. By 4 weeks post-I/R, wild-type mice showed no cardiac dysfunction, elevated TIMP4 levels (to baseline), and normalized membrane-type 1 MMP activity. TIMP4-deficient mice, however, showed exacerbated diastolic dysfunction, sustained elevation of membrane-type 1 MMP activity, and worsened myocardial hypertrophy and fibrosis. Ex vivo I/R (20- or 30-minute ischemia, 45-minute reperfusion) resulted in comparable cardiac dysfunction in wild-type and TIMP4(-/-) mice.
CONCLUSIONS: TIMP4 is essential for recovery from myocardial I/R in vivo, primarily because of its membrane-type 1 MMP inhibitory function. TIMP4 deficiency does not increase susceptibility to ex vivo I/R injury. Replenishment of myocardial TIMP4 could serve as an effective therapy in post-I/R recovery for patients with reduced TIMP4.