Enhanced synthesis of a specific matrix metalloproteinase, MMP-2, has been demonstrated in experimental models of ventricular failure and in cardiac extracts from patients with ischaemic cardiomyopathy. Cultured neonatal rat cardiac fibroblasts and myocytes were used to analyse the determinants of MMP-2 synthesis, including the effects of hypoxia. Culture of rat cardiac fibroblasts for 24 h in 1 % oxygen enhanced MMP-2 synthesis by more than 5-fold and augmented the MMP-2 synthetic responses of these cells to endothelin-1, angiotensin II and interleukin 1β. A series of MMP-2 promoter-luciferase constructs were used to map the specific enhancer element(s) that drive MMP-2 transcription in cardiac cells. Deletion studies mapped a region of potent transactivating function within the 91 bp region from k1433 to k1342 bp, the activity of which was increased by hypoxia. Oligonucleotides from this region were cloned in front of a heterologous simian-virus-40 (SV40) promoter and mapped the enhancer activity to a region between k1410 and k1362 bp that included a potential activating protein 1 (AP-1)-binding sequence, C −"$*% CTGACCTCC. Site-specific mutagenesis of the core TGAC sequence (indicated in bold) eliminated the transactivating activity within the k1410 to k1362 bp sequence. Electrophoretic mobility shift assays (EMSAs) using the k1410

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-...

Cardiac-specific, constitutively active MMP-2 expression leads to impaired contraction and diminished responses to inotropic stimulation. These findings indicate that MMP-2 can directly impair ventricular function in the absence of superimposed injury.

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