Myocardial Protection and Matrix Proteases

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DESCRIPTION (provided by applicant): Coronary artery disease can cause a prolonged period of reduced myocardial blood flow (ischemia) resulting in myocardial infarction (MI). However, paradoxically, re-establishing blood flow following a prolonged period of ischemia; termed ischemia-reperfusion (I/R), can in and of itself evoke a pathological process leading to LV dysfunction. Furthermore, patients with a pre-existing MI, which undergo a second I/R event are at much greater risk for LV dysfunction, morbidity and mortality. Increased release of the extracellular proteolytic enzymes, the matrix metalloproteinases (MMPs) occur with I/R and MI. Recently, we have demonstrated that a unique membrane specific MMP, the membrane type-1 MMP (MT1-MMP), is robustly expressed in cardiac fibroblasts and myocytes from patients, and is increased following I/R. Furthermore, our initial results have established that over- expression of MT1-MMP can exacerbate I/R injury. The central hypothesis of this project is that with I/R, increased interstitial MT1-MMP activity occurs which is dependent upon specific isoforms of the protein kinase (PKC) signaling pathway. Moreover, in the context of an existing MI, enhanced MT1- MMP induction occurs in the residual, viable myocardium causing a priming effect on overall MMP activity following a second episode of I/R, and directly contributes to LV dysfunction. We have developed a clinically relevant porcine model of I/R and will utilize this system to achieve the following aims. (1) Demonstrate a relationship between increased interstitial MT1-MMP activation and regional LV dysfunction which is PKC isoform dependent. (2) Demonstrate that enhanced MT1-MMP induction and activation occurs within the remote, viable myocardium following a defined MI- which will exacerbate regional LV contractility with a second period of I/R. (3) Demonstrate that regional modification of MT1-MMP expression will directly affect regional contractility following I/R. The outcome from these integrated studies will be to identify a unique extracellular mechanism contributing to LV dysfunction in the context of I/R with a particular focus on the clinically relevant condition of a previous MI and identify specific and novel therapeutic targets which will interrupt this process.