Trafficking of the membrane type-1 matrix metalloproteinase in ischemia and reperfusion - Relation to interstitial membrane type-1 matrix metalloproteinase activity

Background - The matrix metalloproteinases ( MMPs) contribute to regional remodeling after prolonged periods of ischemia and reperfusion (I/ R), but specific MMP types activated during this process remain poorly understood. A novel class, the membrane-type MMPs (MT- MMPs), has been identified in the myocardium, but activity of these MMP types has not been assessed in vivo, particularly during I/R. Methods and Results - Pigs ( 30 kg, n = 8) were instrumented with microdialysis catheters to measure MT1-MMP activity in both ischemic and nonischemic (remote) myocardium. A validated MT1-MMP fluorogenic substrate was infused through the microdialysis system, and changes in fluorescence were reflective of MT1-MMP activity at steady state, during ischemia (90 minutes), and during reperfusion (120 minutes). At peak ischemia, MT1-MMP activity was increased by > 40 % in the ischemic region, with no change in the remote region, which persisted with reperfusion (P < 0.05). After I/R, MT1-MMP abundance was increased by > 50 % (P < 0.05). Differential centrifugation revealed that the endosomal fraction (which contains subcellular organelles) within the ischemic myocardium was associated with a > 135 % increase in MT1-MMP (P < 0.05). Furthermore, in an isolated left ventricular myocyte model of I/ R, hypoxia ( simulated ischemia) induced a > 70 % increase in MT1-MMP abundance in myocytes, and confocal microscopy revealed MT1-MMP internalization during this time period and reemergence to the membrane with reperfusion. Conclusions - These unique results demonstrate that a specific MMP type, MT1-MMP, is increased in abundance and activity with I/R and is likely attributed, at least in part, to changes in intracellular trafficking.