Background-Tumor necrosis factor-␣ (TNF-␣) and angiotensin II (Ang II) are implicated in the development and further progression of heart failure, which might be, at least in part, mediated by the production of reactive oxygen species (ROS). However, the cause and consequences of this agonist-mediated ROS production in cardiac myocytes have not been well defined. Recently, we demonstrated that increased ROS production was associated with mitochondrial DNA (mtDNA) damage and dysfunction in failing hearts. We thus investigated whether the direct exposure of cardiac myocytes to TNF-␣ and Ang II in vitro could induce mtDNA damage via production of ROS. Methods and Results-TNF-␣ increased ROS production within cultured neonatal rat ventricular myocytes after 1 hour, as assessed by 2Ј,7Ј-dichlorofluorescin diacetate fluorescence microscopy. TNF-␣ also decreased mtDNA copy number by Southern blot analysis in association with complex III activity, which was prevented in the presence of the antioxidant ␣-tocopherol. A direct exposure of myocytes to H 2 O 2 caused a similar decrease in mtDNA copy number. In contrast, Ang II did not affect mtDNA copy number, despite the similar increase in ROS production. TNF-␣-mediated ROS production and a decrease in mtDNA copy number were inhibited by the sphingomyelinase inhibitor D609. Furthermore, N-acetylsphingosine (C2-ceramide), a synthetic cell-permeable ceramide analogue, increased myocyte ROS production, suggesting that TNF-␣-mediated ROS production and subsequent mtDNA damage were mediated by the sphingomyelin-ceramide signaling pathway. Conclusions-The intimate link between TNF-␣, ROS, and mtDNA damage might play an important role in myocardial remodeling and failure.

. Targeted deletion of MMP-2 attenuates early LV rupture and late remodeling after experimental myocardial infarction. Am J Physiol Heart Circ Physiol 285: H1229-H1235, 2003. First published May 29, 2003 10.1152/ ajpheart.00207.2003.-Matrix metalloproteinase-2 (MMP-2) is prominently overexpressed both after myocardial infarction (MI) and in heart failure. However, its pathophysiological significance in these conditions is still unclear. We thus examined the effects of targeted deletion of MMP-2 on post-MI left ventricular (LV) remodeling and failure. Anterior MI was produced in 10-to 12-wk-old male MMP-2 knockout (KO) and sibling wild-type (WT) mice by ligating the left coronary artery. By day 28, MI resulted in a significant increase in mortality in association with LV cavity dilatation and dysfunction. The MMP-2 KO mice had a significantly better survival rate than WT mice (56% vs. 85%, P Ͻ 0.05), despite a comparable infarct size (50 Ϯ 3% vs. 51 Ϯ 3%, P ϭ not significant), heart rate, and arterial blood pressure. The KO mice had a significantly lower incidence of LV rupture (10% vs. 39%, P Ͻ 0.05), which occurred within 7 days of MI. The KO mice exerted less LV cavity dilatation and improved fractional shortening after MI by echocardiography. The LV zymographic MMP-2 level significantly increased in WT mice after coronary artery ligation; however, this was completely prevented in KO mice. In contrast, the increase in the LV zymographic MMP-9 level after MI was similar between KO and WT mice. MMP-2 activation is therefore considered to contribute to an early cardiac rupture as well as late LV remodeling after MI. The inhibition of MMP-2 activation may therefore be a potentially useful therapeutic strategy to manage post-MI hearts. matrix metalloproteinase; cardiac rupture; heart failure; myocyte; extracellular matrix; mouse MYOCARDIAL INFARCTION (MI) leads to complex structural alterations (remodeling) involving both the infarcted and noninfarcted left ventricular (LV) myocardium (21). Early remodeling as LV cavity dilatation occurs during the early phase of MI, which is likely due to wall thinning in the infarct region. This might lead to a cardiac rupture, thereby accounting for the 5-30% of in-hospital mortality after acute MI (1). During the first several days, LV enlargement follows, and, thereafter, a progressive dilatation of the noninfarcted LV occurs over weeks (21). These progressive changes in LV geometry contribute to the development of depressed cardiac function, clinical heart failure, and increased mortality. Accordingly, it is of critical importance to explore the mechanisms of LV remodeling and develop therapeutic strategies that will effectively inhibit this deleterious process.The dynamic synthesis and breakdown of extracellular matrix (ECM) proteins play an important role in post-MI LV remodeling. In particular, the increased expression and activation of matrix metalloproteinases (MMPs) have been implicated in this process (4,5). Several studies have demonstrated that MMPs are involved not...

Background-Mitochondrial DNA (mtDNA) copy number is decreased not only in mtDNA-mutation diseases but also in a wide variety of acquired degenerative and ischemic diseases. Mitochondrial transcription factor A (TFAM) is essential for mtDNA transcription and replication. Myocardial mtDNA copy number and TFAM expression both decreased in cardiac failure. However, the functional significance of TFAM has not been established in this disease state. Methods and Results-We have now addressed this question by creating transgenic (Tg) mice that overexpress human TFAM gene and examined whether TFAM could protect the heart from mtDNA deficiencies and attenuate left ventricular (LV) remodeling and failure after myocardial infarction (MI) created by ligating the left coronary artery. TFAM overexpression could ameliorate the decrease in mtDNA copy number and mitochondrial complex enzyme activities in post-MI hearts. Survival rate during 4 weeks of MI was significantly higher in Tg-MI than in wild-type (WT) littermates (WT-MI), although infarct size was comparable. LV cavity dilatation and dysfunction were significantly attenuated in Tg-MI. LV end-diastolic pressure was increased in WT-MI, and it was also reduced in Tg-MI. Improvement of LV function in Tg-MI was accompanied by a decrease in myocyte hypertrophy, apoptosis, and interstitial fibrosis as well as oxidative stress in the noninfarcted LV. Conclusions-Overexpression