This study, for the first time, identified specific differences in cellular and extracellular processes that likely contribute to age-dependent ECM remodeling.

Alterations in matrix metalloproteinases (MMPs) and tissue inhibitors of MMPs (TIMPs) have been implicated in adverse left ventricular (LV) remodeling after myocardial infarction (MI). However, the direct mechanistic role of TIMPs in the post-MI remodeling process has not been completely established. The goal of this project was to define the effects of altering endogenous MMP inhibitory control through combined genetic and pharmacological approaches on post-MI remodeling in mice. This study examined the effects of MMP inhibition (MMPi) with PD-166793 (30 mg.kg(-1).day(-1)) on LV geometry and function (conductance volumetry) after MI in wild-type (WT) mice and mice deficient in the TIMP-1 gene [TIMP-1 knockout (TIMP1-KO)]. At 3 days after MI (coronary ligation), mice were randomized into four groups: WT-MI/MMPi (n = 10), TIMP1-KO-MI/MMPi (n = 10), WT-MI (n = 22), and TIMP1-KO-MI (n = 23). LV end-diastolic volume (EDV) and ejection fraction were determined 14 days after MI. Age-matched WT (n = 20) and TIMP1-KO (n = 28) mice served as reference controls. LVEDV was similar under control conditions in WT and TIMP1-KO mice (36 +/- 2 and 40 +/- 2 microl, respectively) but was greater in TIMP1-KO-MI than in WT-MI mice (48 +/- 2 vs. 61 +/- 5 microl, P < 0.05). LVEDV was reduced from MI-only values in WT-MI/MMPi and TIMP1-KO-MI/MMPi mice (42 +/- 2 and 36 +/- 2 microl, respectively, P < 0.05) but was reduced to the greatest degree in TIMP1-KO mice (P < 0.05). LV ejection fraction was reduced in both groups after MI and increased in TIMP1-KO-MI/MMPi, but not in WT-MI/MMPi, mice. These unique results demonstrated that myocardial TIMP-1 plays a regulatory role in post-MI remodeling and that the accelerated myocardial remodeling induced by TIMP-1 gene deletion can be pharmacologically "rescued" by MMP inhibition. These results define the importance of local endogenous control of MMP activity with respect to regulating LV structure and function after MI.

Background-A cause-and-effect relationship exists between matrix metalloproteinase (MMP) induction and left ventricular (LV) remodeling after myocardial infarction (MI). Whether broad-spectrum MMP inhibition is necessary and the timing at which MMP inhibition should be instituted after MI remain unclear. This study examined the effects of MMP-1 and MMP-7-sparing inhibition (sMMPi) on regional and global LV remodeling when instituted before or after MI. Methods and Results-Pigs instrumented with coronary snares and radiopaque markers within the area at risk were randomized to MI only (nϭ11) or sMMPi (PGE-530742, 10 mg/kg PO TID) begun 3 days before MI (nϭ11) or 3 days after MI (nϭ10). Eleven weight-matched noninstrumented pigs served as reference controls. At 10 days after MI, infarct size was similar between groups (47Ϯ3% of the area at risk

The left ventricular (LV) myocardial collagen matrix has been proposed to participate in the maintenance of LV geometry. Thus alterations in the composition of the LV myocardial collagen matrix may influence LV function. The matrix metalloproteinases (MMPs) are a family of enzymes that contribute to extracellular remodeling in several disease states. However, the types of MMPs expressed in the normal and congestive heart failure (CHF) state and the relation to MMP activity remained unclear. Accordingly, after 3 wk of pacing (240 beats/min), changes in LV function, substrate-specific MMP activity, and MMP subclass abundance were measured in comparison with control pigs ( n = 6). Changes in LV function and geometry were measured by echocardiography; LV end-diastolic dimension increased (3.6 ± 0.1 vs. 6.0 ± 0.1 cm, P < 0.05) and LV fractional shortening decreased (47 ± 1 vs. 15 ± 1%, P < 0.05) compared with controls. Degradation of fibrillar collagen is achieved through the combined action of interstitial collagenase (MMP-1), gelatinase A (MMP-2), and stromelysin (MMP-3) (He, C., S. Wilheilm, A. Pentland, B. Marmer, G. Grant, A. Eisen, and G. Goldberg. Proc. Natl. Acad. Sci. USA 86: 2632–2636, 1989; Woessner, J. FASEB J. 5: 2145–2154, 1991). Accordingly, the relative abundance of specific MMPs (MMP-1, MMP-2, and MMP-3) was examined by immunoblotting. With pacing CHF, the relative abundance for MMP-1 increased to 319 ± 94%, MMP-2 increased to 194 ± 31%, and MMP-3 increased to 493 ± 159% (all P < 0.05). With pacing CHF, LV myocardial zymographic activity for the substrate gelatin increased by 119% ( P < 0.05) and for the substrate collagen III by 153% ( P < 0.05) over controls. Caseinolytic activity also increased with pacing CHF by 139% ( P < 0.05) over controls. In conclusion, LV myocardial MMP activity and abundance increased with pacing-induced CHF. These findings demonstrate that pacing-induced CHF leads to changes in myocardial MMP activity and expression that may be responsible for LV remodeling in CHF.

Background-Whether

Increased plasma levels of endothelin-1 (ET-1) have been identified in congestive heart failure (CHF), but local myocardial interstitial ET-1 levels and the relation to determinants of ET-1 synthesis remain to be defined. Accordingly, myocardial interstitial ET-1 levels and myocyte endothelin-converting enzyme (ECE)-1 activity and expression with the development of CHF were examined. Pigs were instrumented with a microdialysis system to measure myocardial interstitial ET-1 levels with pacing CHF (240 beats/min, 3 wk; n = 9) and in controls (n = 14). Plasma ET-1 was increased with CHF (15 +/- 1 vs. 9 +/- 1 fmol/ml, P < 0.05) as was total myocardial ET-1 content (90 +/- 15 vs. 35 +/- 5 fmol/g, P < 0.05). Paradoxically, myocardial interstitial ET-1 was decreased in CHF (32 +/- 4 vs. 21 +/- 2 fmol/ml, P < 0.05), which indicated increased ET-1 uptake by the left ventricular (LV) myocardium with CHF. In isolated LV myocyte preparations, ECE-1 activity was increased by twofold with CHF (P < 0.05). In LV myocytes, both ECE-1a and ECE-1c mRNAs were detected, and ECE-1a expression was upregulated fivefold in CHF myocytes (P < 0.05). In conclusion, this study demonstrated compartmentalization of ET-1 in the myocardial interstitium and enhanced ET-1 uptake with CHF. Thus a local ET-1 system exists at the level of the myocyte, and determinants of ET-1 biosynthesis are selectively regulated within this myocardial compartment in CHF.

Left ventricular (LV) remodeling occurs after myocardial infarction (MI), and the matrix metalloproteinases (MMPs) contribute to adverse LV remodeling after MI. Short-term pharmacological MMP inhibition (MMPi; days to weeks) in animal models of MI have demonstrated a reduction in adverse LV remodeling. However, the long-term effects (months) of MMPi on survival and LV remodeling after MI have not been examined. MI was induced in adult mice (n ϭ 131) and, at 3 days post-MI, assigned to MMPi [MI-MMPi: (s)-2-(4-bromo-biphenyl-4-sulfonylamino)-3-methyl-butyric acid (PD200126), 7.5 mg/day/p.o., n ϭ 64] or untreated (MI-only, n ϭ 67). Unoperated mice (n ϭ 16) served as controls. The median survival in the MI-only group was 5 days, whereas median survival was significantly greater in the MI-MMPi group at 38 days (p Ͻ 0.05). However, with prolonged MMPi (Ͼ120 days), a significant divergence in the survival curves occurred in which significantly greater mortality was observed with prolonged MMPi (p Ͻ 0.05). LV echocardiography at 6 months revealed LV dilation in the MI-only and MI-MMPi groups (154 Ϯ 14 and 219 Ϯ 24 l) compared with control (67 Ϯ 4 l, p Ͻ 0.05), with a greater degree of dilation in the MI-MMPi group (p Ͻ 0.05). MMPi conferred a beneficial effect on survival early post-MI, but prolonged MMPi (Ͼ3 months) was associated with higher mortality and adverse LV remodeling. These unique results suggest that an optimal temporal window exists with respect to pharmacological interruption of MMP activity in the post-MI period.Myocardial infarction (MI) evokes changes within the architecture of the left ventricular (LV) wall leading to chamber dilation. This process, which is termed post-MI remodeling, has been shown to be an independent predictor of morbidity and mortality in several large clinical trials. Thus, identifying and interrupting cellular and molecular pathways that contribute to LV structural remodeling post-MI hold significant clinical and scientific interest. Whereas the LV remodeling process evokes changes within both the cellular and extracellular compartment, recent studies have demonstrated that changes in extracellular structure and composition occur within the MI region as well as surviving myocardium (Frangogiannis et al

Left ventricular hypertrophy (LVH) is a leading cause of congestive heart failure. The exact mechanisms that control cardiac growth and regulate the transition to failure are not fully understood, in part due to the lack of a complete inventory of proteins associated with LVH. We investigated the proteomic basis of LVH using the transverse aortic constriction model of pressure overload in mice coupled with a multidimensional approach to identify known and novel proteins that may be relevant to the development and maintenance of LVH. We identified 123 proteins that were differentially expressed during LVH, including LIM proteins, thioredoxin, myoglobin, fatty acid binding protein 3, the abnormal spindle-like microcephaly protein (ASPM), and cytoskeletal proteins such as actin and myosin. In addition, proteins with unknown functions were identified, providing new directions for future research in this area. We also discuss common pitfalls and strategies to overcome the limitations of current proteomic technologies. Together, the multidimensional approach provides insight into the proteomic changes that occur in the LV during hypertrophy.