DH. Cardiac matrix metalloproteinase-2 expression independently induces marked ventricular remodeling and systolic dysfunction. Am J Physiol Heart Circ Physiol 292: H1847-H1860, 2007. First published December 8, 2006; doi:10.1152/ajpheart.00434.2006.-Although enhanced cardiac matrix metalloproteinase (MMP)-2 synthesis has been associated with ventricular remodeling and failure, whether MMP-2 expression is a direct mediator of this process is unknown. We generated transgenic mice expressing active MMP-2 driven by the ␣-myosin heavy chain promoter. At 4 mo MMP-2 transgenic hearts demonstrated expression of the MMP-2 transgene, myocyte hypertrophy, breakdown of Z-band registration, lysis of myofilaments, disruption of sarcomere and mitochondrial architecture, and cardiac fibroblast proliferation. Hearts from 8-mo-old transgenic mice displayed extensive myocyte disorganization and dropout with replacement fibrosis and perivascular fibrosis. Older transgenic mice also exhibited a massive increase in cardiac MMP-2 expression, representing recruitment of endogenous MMP-2 synthesis, with associated expression of MMP-9 and membrane type 1 MMP. Increases in diastolic [control (C) 33 Ϯ 3 vs. MMP 51 Ϯ 12 l; P ϭ 0.003] and systolic (C 7 Ϯ 2 vs. MMP 28 Ϯ 14 l; P ϭ 0.003) left ventricular (LV) volumes and relatively preserved stroke volume (C 26 Ϯ 4 vs. MMP 23 Ϯ 3 l; P ϭ 0.16) resulted in markedly decreased LV ejection fraction (C 78 Ϯ 7% vs. MMP 48 Ϯ 16%; P ϭ 0.0006). Markedly impaired systolic function in the MMP transgenic mice was demonstrated in the reduced preload-adjusted maximal power (C 240 Ϯ 84 vs. MMP 78 Ϯ 49 mW/l 2 ; P ϭ 0.0003) and decreased end-systolic pressure-volume relation (C 7.5 Ϯ 1.5 vs. MMP 4.7 Ϯ 2.0; P ϭ 0.016). Expression of active MMP-2 is sufficient to induce severe ventricular remodeling and systolic dysfunction in the absence of superimposed injury. heart failure; fibrosis; mitochondria; sarcomere THE PAST DECADE HAS WITNESSED an increasing interest in the interactions of cardiomyocytes with the extracellular matrix, particularly with regard to the development of cardiac failure and fibrosis. Modulation of the cardiac extracellular matrix by various members of the large matrix metalloproteinase (MMP) gene family has provided important mechanistic insights into the evolution of left ventricular failure in the setting of both ischemic and nonischemic disease (10,11,20,29,49,51). The MMP gene family includes Ͼ20 discrete members, including the interstitial collagenases (e.g., MMP-1 and -13), the gelatinases (MMP-2, -9), and membrane-associated enzymes, including membrane type 1(MT1)-MMP (60). MMP-2 has the been the focus of considerable interest, as previous studies in animal models of heart failure, including the salt-sensitive hypertensive rat (19, 43), mitral regurgitation in the dog (52), and experimental myocardial infarction in the rat (41), have all shown excessive activation of MMP-2 as heart failure progressed. Inhibition of MMP-2 activation with nonselective agents, including an angiotensin-...

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Matrix metalloproteinase-2 (MMP-2) is increasingly recognized as a major contributor to progressive cardiac injury within the setting of ischemia-reperfusion injury and ischemic ventricular remodeling. A common feature of these conditions is an increase in oxidative stress, a process that engages multiple pro-inflammatory and innate immunity cascades. We recently reported on the identification and characterization of an intracellular isoform of MMP-2 generated by oxidative stress-mediated activation of an alternative promoter located within the first intron of the MMP-2 gene. Transcription from this site generates an N-terminal truncated 65 kDa isoform of MMP-2 (NTT-MMP-2) that lacks the secretory sequence and the inhibitory prodomain region. The NTT-MMP-2 isoform is intracellular, enzymatically active and localizes in part to mitochondria. Expression of the NTT-MMP-2 isoform triggers Nuclear Factor of Activated T-cell (NFAT) and NF-κB signaling with the expression of a highly defined innate immunity transcriptome, including Interleukin-6, MCP-1, IRF-7 and pro-apoptotic transcripts. To determine the functional significance of the NTT-MMP-2 isoform in vivo we generated cardiac-specific NTT-MMP-2 transgenic mice. These mice developed progressive cardiomyocyte and ventricular hypertrophy associated with systolic heart failure. Further, there was evidence for cardiomyocyte apoptosis and myocardial infiltration with mononuclear cells. The NTT-MMP-2 transgenic hearts also demonstrated more severe injury following ex vivo ischemia-reperfusion injury. We conclude that a novel intracellular MMP-2 isoform induced by oxidant stress directly contributes, in the absence of superimposed injury, to cardiomyocyte hypertrophy. inflammation, systolic heart failure and enhanced susceptibility to ischemia-reperfusion injury.

Exposure to passive smoking increases myocardial infarct size in a rat model of ischemia and reperfusion. This increase of infarct size exhibited a dose-response relation. These results are consistent with epidemiological studies demonstrating that ETS increases the risk of heart death.