Inhibition of matrix metalloproteinases improves left ventricular function in mice lacking osteopontin after myocardial infarction

Osteopontin (OPN) plays an important role in left ventricular (LV) remodeling after myocardial infarction (MI) by promoting collagen synthesis and accumulation. This study tested the hypothesis that MMP inhibition modulates post-MI LV remodeling in mice lacking OPN. Wild-type (WT) and OPN knockout (KO) mice were treated daily with MMP inhibitor (PD166793, 30 mg/kg/day) starting 3 days post-MI. LV functional and structural remodeling was measured 14 days post-MI. Infarct size was similar in WT and KO groups with or without MMP inhibition. M-mode echocardiography showed greater increase in LV end-diastolic (LVEDD) and end-systolic diameters (LVESD) and decrease in percent fractional shortening (%FS) and ejection fraction in KO-MI versus WT-MI. MMP inhibition decreased LVEDD and LVESD, and increased %FS in both groups. Interestingly, the effect was more pronounced in KO-MI group versus WT-MI (P < 0.01). MMP inhibition significantly decreased post-MI LV dilation in KO-MI group as measured by Langendorff-perfusion analysis. MMP inhibition improved LV developed pressures in both MI groups. However, the improvement was significantly higher in KO-MI group versus WT-MI (P < 0.05). MMP inhibition increased heart weight-to-body weight ratio, myocyte cross-sectional area, fibrosis and septal wall thickness only in KO-MI. Percent apoptotic myocytes in the non-infarct area was not different between the treatment groups. Expression and activity of MMP-2 and MMP-9 in the non-infarct area was higher in KO-MI group 3 days post-MI. MMP inhibition reduced MMP-2 activity in KO-MI with no effect on the expression of TIMP-2 and TIMP-4 14 days post-MI. Thus, activation of MMPs contributes to reduced fibrosis and LV dysfunction in mice lacking OPN.     

Myocardial and interstitial matrix metalloproteinase activity after acute myocardial infarction in pigs

A structural event during the evolution of a myocardial infarction (MI) is left ventricular (LV) remodeling. The mechanisms that contribute to early changes in LV myocardial remodeling in the post-MI period remain poorly understood. Matrix metalloproteinases (MMPs) contribute to tissue remodeling in several disease states. Whether and to what degree MMP activation occurs within the myocardial interstitium after acute MI remains to be determined. Adult pigs (n = 15) were instrumented to measure regional myocardial function and interstitial MMP levels within regions served by the circumflex and left anterior descending arteries. Regional function was measured by sonomicrometry, and interstitial MMP levels were determined by selective microdialysis and zymography as well as by MMP interstitial fluorogenic activity. Measurements were performed at baseline and sequentially for up to 3 h after ligation of the obtuse marginals of the circumflex artery. Regional fractional shortening fell by over 50% in the MI region but remained unchanged in the remote region after coronary occlusion. Release of soluble MMPs, as revealed by zymographic activity of myocardial interstitial samples, increased by 2 h post-MI. The increased zymographic activity after MI was consistent with MMP-9. Myocardial interstitial MMP fluorogenic activity became detectable within the ischemic region as early as 10 min after coronary occlusion and significantly increased after 1 h post-MI. MMP fluorogenic activity remained unchanged from baseline values in the remote region. The present study demonstrated that myocardial MMP activation can occur within the MI region in the absence of reperfusion. These unique results suggest that MMP release and activation occurs within the ischemic myocardial interstitium in the early post-MI period.     

Progressive left ventricular remodeling and apoptosis late after myocardial infarction in mouse heart

We tested the hypothesis that left ventricular (LV) remodeling late after myocardial infarction (MI) is associated with myocyte apoptosis in myocardium remote from the infarcted area and is related temporally to LV dilation and contractile dysfunction. One, four, and six months after MI caused by coronary artery ligation, LV volume and contractile function were determined using an isovolumic balloon-in-LV Langendorff technique. Apoptosis and nuclear morphology were determined by terminal deoxynucleotidyl transferase-mediated nick end-labeling (TUNEL) and Hoechst 33258 staining. Progressive LV dilation 1-6 mo post-MI was associated with reduced peak LV developed pressure (LVDP). In myocardium remote from the infarct, there was increased wall thickness and expression of atrial natriuretic peptide mRNA consistent with reactive hypertrophy. There was a progressive increase in the number of TUNEL-positive myocytes from 1 to 6 mo post-MI (2.9-fold increase at 6 mo; P < 0. 001 vs. sham). Thus LV remodeling late post-MI is associated with increased apoptosis in myocardium remote from the area of ischemic injury. The frequency of apoptosis is related to the severity of LV dysfunction.     

Selective spatiotemporal induction of matrix metalloproteinase-2 and matrix metalloproteinase-9 transcription after myocardial infarction

Myocardial remodeling after myocardial infarction (MI) is associated with increased levels of the matrix metalloproteinases (MMPs). Levels of two MMP species, MMP-2 and MMP-9, are increased after MI, and transgenic deletion of these MMPs attenuates post-MI left ventricular (LV) remodeling. This study characterized the spatiotemporal patterns of gene promoter induction for MMP-2 and MMP-9 after MI. MI was induced in transgenic mice in which the MMP-2 or MMP-9 promoter sequence was fused to the beta-galactosidase reporter, and reporter level was assayed up to 28 days after MI. Myocardial localization with respect to cellular sources of MMP-2 and MMP-9 promoter induction was examined. After MI, LV diameter increased by 70% (P < 0.05), consistent with LV remodeling. beta-Galactosidase staining in MMP-2 reporter mice was increased by 1 day after MI and increased further to 64 +/- 6% of LV epicardial area by 7 days after MI (P < 0.05). MMP-2 promoter activation occurred in fibroblasts and myofibroblasts in the MI region. In MMP-9 reporter mice, promoter induction was detected after 3 days and peaked at 7 days after MI (53 +/- 6%, P < 0.05) and was colocalized with inflammatory cells at the peri-infarct region. Although MMP-2 promoter activation was similarly distributed in the MI and border regions, activation of the MMP-9 promoter was highest at the border between the MI and remote regions. These unique findings visually demonstrated that activation of the MMP-2 and MMP-9 gene promoters occurs in a distinct spatial relation with reference to the MI region and changes in a characteristic time-dependent manner after MI.     

Matrix metalloproteinase-9 gene deletion facilitates angiogenesis after myocardial infarction

Matrix metalloproteinases (MMPs) are postulated to be necessary for neovascularization during wound healing. MMP-9 deletion alters remodeling postmyocardial infarction (post-MI), but whether and to what degree MMP-9 affects neovascularization post-MI is unknown. Neovascularization was evaluated in wild-type (WT; n = 63) and MMP-9 null (n = 55) mice at 7-days post-MI. Despite similar infarct sizes, MMP-9 deletion improved left ventricular function as evaluated by hemodynamic analysis. Blood vessel quantity and quality were evaluated by three independent studies. First, vessel density was increased in the infarct of MMP-9 null mice compared with WT, as quantified by Griffonia (Bandeiraea) simplicifolia lectin I (GSL-I) immunohistochemistry. Second, preexisting vessels, stained in vivo with FITC-labeled GSL-I pre-MI, were present in the viable but not MI region. Third, a technetium-99m-labeled peptide (NC100692), which selectively binds to activated alpha(v)beta3-integrin in angiogenic vessels, was injected into post-MI mice. Relative NC100692 activity in myocardial segments with diminished perfusion (0-40% nonischemic) was higher in MMP-9 null than in WT mice (383 +/- 162% vs. 250 +/- 118%, respectively; P = 0.002). The unique finding of this study was that MMP-9 deletion stimulated, rather than impaired, neovascularization in remodeling myocardium. Thus targeted strategies to inhibit MMP-9 early post-MI will likely not impair the angiogenic response.     

Ghrelin对心肌梗死后心肌重塑及心脏功能的影响及其机制研究

目的:观察ghrelin对心肌梗死(MI)大鼠心肌重塑和心脏功能的影响,并探讨其可能的机制。方法:应用冠状动脉结扎术创建大鼠MI模型,并设立假手术组作为对照;造模成功后每天2次注射ghrelin(100μg/kg),持续4周,以此作为MI-ghrelin组,并以每天注射生理盐水的MI大鼠作为MI-生理盐水组。检测和比较各组大鼠左心室重塑和血流动力学的改变情况;非梗死心肌中白介素(IL)-1β、肿瘤坏死因子-α(TNF-α)、基质金属蛋白酶(MMP)-2、MMP-9 mRNA和蛋白的表达;梗死边界心肌细胞的凋亡情况。结果:Ghrelin可使心肌梗死后的MI大鼠降低的缩短分数(FS)、左室内压最大变化率均显著下降(dP/dtmax)、疤痕厚度明显升高,增加左室舒张末压(LVEDP)、左室收缩末内径(LVESD)、左室舒张末期内径(LVEDD)、梗死边界心肌细胞的凋亡指数显著降低。此外,ghrelin可抑制心肌梗死后的MI大鼠非梗死心肌中白介素(IL)-1β、肿瘤坏死因子-α(TNF-α)、质金属蛋白酶(MMP)-2和MMP-9的mRNA和蛋白的表达。结论:Ghrelin可缓解MI后大鼠LV功能紊乱及心室重塑,这可能与其抑制炎症反应及基质金属蛋白酶的表达有关。     

Abnormal cardiac wall motion and early matrix metalloproteinase activity

Activation of matrix metalloproteinases (MMPs) in the heart is known to facilitate cardiac remodeling and progression to failure. We hypothesized that regional dyskinetic wall motion of the left ventricle would stimulate activation of MMPs. Abnormal wall motion at a target site on the anterior lateral wall of the left ventricle was induced by pacing atrial and ventricular sites of five open-chest anesthetized dogs. Changes in shortening at the left ventricular (LV) pacing site and at a remote site at the anterior base of the left ventricle were monitored with piezoelectric crystals. Simultaneous atrial and ventricular pacing resulted in abnormal motion at the LV pacing site, yielding early shortening and late systolic lengthening, whereas the shortening pattern at the remote site remained unaffected. Assessment of global myocardial MMP activity showed a sevenfold increase in substrate cleavage (P < 0.02) at the LV pacing site relative to the remote site. Gelatin zymography revealed increases in 92-kDa MMP-9 activity and 86-kDa MMP-9 activity at the LV pacing site relative to the remote site, whereas MMP-2 activity was unaffected. Abnormal wall motion was associated with increases in collagen degradation (approximately 2-fold; P < 0.03), plasmin activity (approximately 1.5-fold; P < 0.05), nitrotyrosine levels (approximately 20-fold; P = 0.05), and inflammatory infiltrate (approximately 2-fold; P < 0.02) relative to the remote site. Results indicate that regional dyskinesis induced by epicardial activation is sufficient to stimulate significant MMP activity in the heart, suggesting that abnormal wall motion is a stimulus for MMP activation.     

Serum MMP-8: A Novel Indicator of Left Ventricular Remodeling and Cardiac Outcome in Patients after Acute Myocardial Infarction

Objective

Left ventricular (LV) remodeling following myocardial infarction (MI) is characterized by progressive alterations of structure and function, named LV remodeling. Although several risk factors such as infarct size have been identified, LV remodeling remains difficult to predict in clinical practice. Changes within the extracellular matrix, involving matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs), are an integral part of left ventricular (LV) remodeling after myocardial infarction (MI). We investigated the temporal profile of circulating MMPs and TIMPs and their relations with LV remodeling at 1 year and clinical outcome at 3 years in post-MI patients.

Methods

This prospective multicentre study included 246 patients with a first anterior MI. Serial echocardiographic studies were performed at hospital discharge, 3 months, and 1 year after MI, and analysed at a core laboratory. LV remodeling was defined as the percent change in LV end-diastolic volume (EDV) from baseline to 1 year. Serum samples were obtained at hospital discharge, 1, 3, and 12 months. Multiplex technology was used for analysis of MMP-1, -2, -3, -8, -9, -13, and TIMP-1, -2, -3, -4 serum levels.

Results

Baseline levels of MMP-8 and MMP-9 were positively associated with changes in LVEDV (P = 0.01 and 0.02, respectively). When adjusted for major baseline characteristics, MMP-8 levels remained an independent predictor LV remodeling (P = 0.025). By univariate analysis, there were positive relations between cardiovascular death or hospitalization for heart failure during the 3-year follow-up and the baseline levels of MMP-2 (P = 0.03), MMP-8 (P = 0.002), and MMP-9 (P = 0.03). By multivariate analysis, MMP-8 was the only MMP remaining significantly associated with clinical outcome (P = 0.02).

Conclusion

Baseline serum MMP-8 is a significant predictor of LV remodeling and cardiovascular outcome after MI and may help to improve risk stratification.     

Targeted deletion of MMP-2 attenuates early LV rupture and late remodeling after experimental myocardial infarction

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 < 0.05), despite a comparable infarct size (50 +/- 3% vs. 51 +/- 3%, P = not significant), heart rate, and arterial blood pressure. The KO mice had a significantly lower incidence of LV rupture (10% vs. 39%, P < 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.     

Endothelin antagonism prevents early EGFR transactivation but not increased matrix metalloproteinase activity in diabetes

Although past studies have demonstrated decreased renal matrix metalloproteinase (MMP) activity in type 1 diabetes and in mesangial cells grown under high glucose conditions, renal MMP expression and activity in type 2 diabetes and the regulation of MMPs by profibrotic factors involved in diabetic renal complications such as endothelin-1 (ET-1) remained unknown. The renal expression and activity of MMPs in type 2 diabetic Goto-Kakizaki (GK) rats treated with vehicle or ET(A) receptor selective antagonist ABT-627 for 4 wk were assessed by gelatin zymography, fluorogenic gelatinase assay, and immunoblotting. In addition, expression and phosphorylation of epidermal growth factor receptor (EGFR) and connective tissue growth factor were evaluated by immunoblotting. Renal sections stained with Masson trichrome were used to investigate kidney structure. MMP-2 activity and protein levels were significantly increased in both cortical and medullary regions in the GK rats. Membrane-bound MMP (MT1-MMP), MMP-9, and fibronectin levels were also increased, and ABT-627 treatment did not have an effect on MMP activity and expression. Histological analysis of kidneys did not reveal any structural changes. Phosphorylation of EGFR was significantly increased in the diabetic animals, and ABT-627 treatment prevented this increase, suggesting ET-1-mediated transactivation of EGFR. These results suggest that there is early upregulation of renal MMPs in the absence of any kidney damage. Although the ET(A) receptor subtype is not involved in the early activation of MMPs in type 2 diabetes, ET-1 contributes to transactivation of growth-promoting and profibrotic EGFR.     

Age-related differences in postinfarct left ventricular rupture and remodeling

Cardiac rupture is more prevalent in elderly patients with first onset of acute myocardial infarct (MI), but the mechanism remains unexplored. We investigated the differences in the incidence of cardiac rupture and early left ventricular (LV) remodeling following coronary artery ligation between old (12-mo) and young (3-mo) C57Bl/6 male mice and explored responsible mechanisms. The incidence of rupture within 1 wk after MI was significantly higher in old than in young mice (40.7 vs. 18.3%, P = 0.013) despite a similar infarct size in both age groups. Old mice dying of rupture had more severe infarct expansion than young counterparts. Echocardiography and catheterization at day 7 revealed more profound LV chamber dilatation and dysfunction as well as higher blood pressures in aged mice. At day 3 after MI immediately before the peak of rupture occurrence, we observed significantly higher content of type I and III collagen, a greater density of macrophage and neutrophil, and markedly enhanced mRNA expression of inflammatory cytokines in the infarcted myocardium in old than in young mice. Furthermore, a more dramatic increment of matrix metalloproteinase (MMP)-9 activity was found in old than in young infarcted hearts, in keeping with enhanced inflammatory response. Collectively, these results revealed that old mice had a higher risk of post-MI cardiac rupture despite a higher level of collagen content and cross-linking. Enhanced inflammatory response and subsequent increase in MMP-9 activity together with higher blood pressure are important factors responsible for the higher risk of cardiac rupture and more severe LV remodeling in the aged heart following acute MI.     

Temporal changes in matrix metalloproteinase expression and inflammatory response associated with cardiac rupture after myocardial infarction in mice

We previously found that male mice with myocardial infarction (MI) had a high rate of cardiac rupture, which generally occurred at 3 to 5 days after MI. Since matrix metalloproteinases (MMPs) play an important role in infarct healing, tissue repair and extracellular matrix (ECM) remodeling post-MI, we studied the temporal relationship of MMP expression and inflammatory response to cardiac rupture after acute MI. Male C57BL/6J mice were subjected to MI (induced by ligating the left anterior descending coronary artery) and killed 1, 2, 4, 7 or 14 days after MI. MMP-2 and MMP-9 activity in the heart were measured by zymography. Collagen content was measured by hydroxyproline assay. We found that after MI, MMP-9 activity increased as early as 1 day and reached a maximum by 2-4 days, associated with a similar increase in neutrophil and macrophage infiltration in the infarct area. MMP-2 started to increase rapidly within 4 days, reaching a maximum by 7 days and remaining high even at 14 days. Intense macrophage infiltration appeared by 4 days after MI and then gradually decreased within 7 to 14 days. Collagen content was unchanged until 4 days after MI, at which point it increased and remained high thereafter. Our data suggest that in mice, overexpression of MMP-2 and MMP-9 (possibly expressed mainly by neutrophils and macrophages) may lead to excessive ECM degradation in the early phase of MI, impairing infarct healing and aggravating early remodeling which in turn causes cardiac rupture.     

Accelerated LV remodeling after myocardial infarction in TIMP-1-deficient mice: effects of exogenous MMP inhibition

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.     

Differential effects of pressure or volume overload on myocardial MMP levels and inhibitory control

Left ventricular (LV) pressure (PO) or volume (VO) overload is accompanied by myocardial remodeling, but mechanisms that contribute to this progressive remodeling process remain unclear. The matrix metalloproteinases (MMPs) contribute to tissue remodeling in a number of disease states. This study tested the hypothesis that increased MMP expression and activity occur after the induction of an LV overload, which is accompanied by a loss of endogenous MMP inhibitory control. LV MMP zymographic activity and species abundance were measured in dogs under the following conditions: acute PO induced by ascending aortic balloon inflation (6 h, n = 9), prolonged PO by aortic banding (10 days, n = 5), acute VO through mitral regurgitation secondary to chordal rupture (6 h, n = 6), prolonged VO due to mitral regurgitation (14 days, n = 7), and sham controls (n = 11). MMP zymographic activity in the 92-kDa region, indicative of MMP-9 activity, increased over threefold in acute PO and VO and fell to control levels in prolonged PO and VO. The MMP-9 activity-to-abundance ratio increased by over fourfold with acute VO and twofold in acute PO, suggesting a loss of inhibitory control. Endogenous MMP inhibitor content was unchanged with either PO or VO. Interstitial collagenase (MMP-1) content decreased by 50% with acute VO but not with acute PO. Stromelysin (MMP-3) levels increased by 40% with acute VO and increased by 80% with prolonged PO. Although changes in LV myocardial MMP activity and inhibitory control occurred in both acute and prolonged PO and VO states, these changes were not identical. These results suggest that the type of overload stimulus may selectively influence myocardial MMP activity and expression, which in turn would affect the overall LV myocardial remodeling process in LV overload.     

Electrotonic remodeling following myocardial infarction in dogs susceptible and resistant to sudden cardiac death.

Passive electrical remodeling following myocardial infarction (MI) is well established. These changes can alter electrotonic loading and trigger the remodeling of repolarization currents, a potential mechanism for ventricular fibrillation (VF). However, little is known about the role of passive electrical markers as tools to identify VF susceptibility post-MI. This study investigated electrotonic remodeling in the post-MI ventricle, as measured by myocardial electrical impedance (MEI), in animals prone to and resistant to VF. MI was induced in dogs by a two-stage left anterior descending (LAD) coronary artery ligation. Before infarction, MEI electrodes were placed in remote (left circumflex, LCX) and infarcted (LAD) myocardium. MEI was measured in awake animals 1, 2, 7, and 21 days post-MI. Subsequently, VF susceptibility was tested by a 2-min LCX occlusion during exercise; 12 animals developed VF (susceptible, S) and 12 did not (resistant, R). The healing infarct had lower MEI than the normal myocardium. This difference was stable by day 2 post-MI (287 +/- 32 Omega vs. 425 +/- 62 Omega, P < 0.05). Significant differences were observed between resistant and susceptible animals 7 days post-MI; susceptible dogs had a wider electrotonic gradient between remote and infarcted myocardium (R: 89 +/- 60 Omega vs. S: 180 +/- 37 Omega). This difference increased over time in susceptible animals (252 +/- 53 Omega at 21 days) due to post-MI impedance changes on the remote myocardium. These data suggest that early electrotonic changes post-MI could be used to assess later arrhythmia susceptibility. In addition, passive-electrical changes could be a mechanism driving active-electrical remodeling post-MI, thereby facilitating the induction of arrhythmias.     

Effects of hydrogel injection on borderzone contractility post-myocardial infarction

Injectable hydrogels are a potential therapy for mitigating adverse left ventricular (LV) remodeling after myocardial infarction (MI). Previous studies using magnetic resonance imaging (MRI) have shown that hydrogel treatment improves systolic strain in the borderzone (BZ) region surrounding the infarct. However, the corresponding contractile properties of the BZ myocardium are still unknown. The goal of the current study was to quantify the in vivo contractile properties of the BZ myocardium post-MI in an ovine model treated with an injectable hydrogel. Contractile properties were determined 8 weeks following posterolateral MI by minimizing the difference between in vivo strains and volume calculated from MRI and finite element model predicted strains and volume. This was accomplished by using a combination of MRI, catheterization, finite element modeling, and numerical optimization. Results show contractility in the BZ of animals treated with hydrogel injection was significantly higher than untreated controls. End-systolic (ES) fiber stress was also greatly reduced in the BZ of treated animals. The passive stiffness of the treated infarct region was found to be greater than the untreated control. Additionally, the wall thickness in the infarct and BZ regions was found to be significantly higher in the treated animals. Treatment with hydrogel injection significantly improved BZ function and reduced LV remodeling, via altered MI properties. These changes are linked to a reduction in the ES fiber stress in the BZ myocardium surrounding the infarct. The current results imply that injectable hydrogels could be a viable therapy for maintaining LV function post-MI.     

Influence of gender on the response to hemodynamic overload after myocardial infarction

After myocardial infarction (MI), the left ventricle (LV) undergoes ventricular remodeling characterized by progressive global dilation, infarct expansion, and compensatory hypertrophy of the noninfarcted myocardium. Little attention has been given to the response of remodeling myocardium to additional hemodynamic overload. Studies have indicated that gender may influence remodeling and the response to both MI and hemodynamic overload. We therefore determined 1) structural and function consequences of superimposing hemodynamic overload (systemic hypertension) on remodeling myocardium after a MI and 2) the potential influence of gender on this remodeling response. Male and female Dahl salt-sensitive and salt-resistant rats underwent coronary ligation, resulting in similar degrees of MI. One week post-MI, all rats were placed on a high-salt diet. Four groups were then studied 4 wk after initiation of high-salt feeding: MI female, MI female + hypertension, MI male, and MI male + hypertension. Hypertension-induced pressure overload resulted in additional comparable degrees of myocardial hypertrophy in both females and males. In females, hypertension post-MI resulted in concentric hypertrophy with no additional cavity dilation and no measurable scar thinning. In contrast, in males, hypertension post-MI resulted in eccentric hypertrophy, further LV cavity dilation, and scar thinning. Physiologically, concentric hypertrophy in post-MI hypertensive females resulted in elevated contractile function, whereas eccentrically hypertrophied males had no such increase. Female gender influences favorably the remodeling and physiological response to hemodynamic overload after large MI.     

Effects of timed administration of doxycycline or methylprednisolone on post-myocardial infarction inflammation and left ventricular remodeling in the rat heart

The development of strategies to ameliorate post-myocardial infarction (MI) remodeling and improve function continues to be an area of clinical importance. Use of steroids for this purpose is controversial since the effects of timed treatment on relevant inflammatory, biochemical and structure/function endpoints are unclear. In a previous report, we demonstrated that use of doxycycline pre-treatment improves post-MI remodeling and passive left ventricular (LV) function. However, the effects of timed doxycyline post-MI treatment are unknown. To examine these issues, we performed a study using a rat MI model. Animals were administered one of the following: doxycycline (DOX), the corticosteroid methylprednisolone (MP), or aqueous vehicle. Treatment was given early, short-term (at time of MI to 24 h post-MI) or late, long term (2–7 days post-MI). Animals were sacrificed at 3, 7 or 42 days post-surgery. We assessed LV hemodynamics, pressure–volume, and pressure–scar strains, histomorphometry, inflammation via measurements of myeloperoxidase activity, and matrix metalloproteinase (MMP) activity. Late MP treatment yielded a robust right-shifted pressure–volume curve, which was accompanied by increased scar strains. Late DOX treatment yielded reduced average heart weight and size and preserved scar thickness. DOX treatment did not suppress inflammation, which contrasts with the suppressive effects of MP. Use of early or late MP yielded increased MMP activity in infarcted and non-infarcted regions. Early and late treatment with DOX yielded infarct–associated MMP activity levels comparable to those of vehicle–treated animals. In conclusion, results indicate that late use of MP yields adverse post-MI structure/function outcomes that correlate with suppression of inflammation and increased MMP activity. These observations contrast with those of DOX, in particular, late treatment where improved outcomes were observed in LV structure and were accompanied by the lack of suppression of inflammation.     

Toll-like Receptor 4 Mediates the Inflammatory Responses and Matrix Protein Remodeling in Remote Non-Ischemic Myocardium in a Mouse Model of Myocardial Ischemia and Reperfusion

The signaling mechanism that mediates inflammatory responses in remote non-ischemic myocardium following regional ischemia/reperfusion (I/R) remains incompletely understood. Myocardial Toll-like receptor 4 (TLR4) can be activated by multiple proteins released from injured cells and plays a role in myocardial inflammation and injury expansion. We tested the hypothesis that TLR4 occupies an important role in mediating the inflammatory responses and matrix protein remodeling in the remote non-ischemic myocardium following regional I/R injury. Methods and results: TLR4-defective (C3H/HeJ) and TLR4-competent (C3H/HeN) mice were subjected to coronary artery ligation (30 min) and reperfusion for 1, 3, 7 or 14 days. In TLR4-competent mice, levels of monocyte chemoattractant protein -1 (MCP-1), keratinocyte chemoattractant (KC), intercellular adhesion molecule 1 (ICAM-1) and vascular cell adhesion molecule 1 (VCAM-1) were elevated in the remote non-ischemic myocardium at day 1, 3, and 7 of reperfusion. Levels of collagen I, collagen IV, matrix metalloproteinase (MMP) 2 and MMP 9 were increased in the remote non-ischemic myocardium at day 7 and 14 of reperfusion. MMP 2 and MMP 9 activities were also increased. TLR4 deficiency resulted in a moderate reduction in myocardial infarct size. However, it markedly downgraded the changes in the levels of chemokines, adhesion molecules and matrix proteins in the remote non-ischemic myocardium. Further, left ventricular function at day 14 was significantly improved in TLR4-defective mice. In conclusion, TLR4 mediates the inflammatory responses and matrix protein remodeling in the remote non-ischemic myocardium following regional myocardial I/R injury and contributes to the mechanism of adverse cardiac remodeling.     

Cardiac Restricted Overexpression of Membrane Type-1 Matrix Metalloproteinase Causes Adverse Myocardial Remodeling following Myocardial Infarction

The membrane type-1 matrix metalloproteinase (MT1-MMP) is a unique member of the MMP family, but induction patterns and consequences of MT1-MMP overexpression (MT1-MMPexp), in a left ventricular (LV) remodeling process such as myocardial infarction (MI), have not been explored. MT1-MMP promoter activity (murine luciferase reporter) increased 20-fold at 3 days and 50-fold at 14 days post-MI. MI was then induced in mice with cardiac restricted MT1-MMPexp (n = 58) and wild type (WT, n = 60). Post-MI survival was reduced (67% versus 46%, p < 0.05), and LV ejection fraction was lower in the post-MI MT1-MMPexp mice compared with WT (41 ± 2 versus 32 ± 2%,p < 0.05). In the post-MI MT1-MMPexp mice, LV myocardial MMP activity, as assessed by radiotracer uptake, and MT1-MMP-specific proteolytic activity using a specific fluorogenic assay were both increased by 2-fold. LV collagen content was increased by nearly 2-fold in the post-MI MT1-MMPexp compared with WT. Using a validated fluorogenic construct, it was discovered that MT1-MMP proteolytically processed the pro-fibrotic molecule, latency-associated transforming growth factor-1 binding protein (LTBP-1), and MT1-MMP-specific LTBP-1 proteolytic activity was increased by 4-fold in the post-MI MT1-MMPexp group. Early and persistent MT1-MMP promoter activity occurred post-MI, and increased myocardial MT1-MMP levels resulted in poor survival, worsening of LV function, and significant fibrosis. A molecular mechanism for the adverse LV matrix remodeling with MT1-MMP induction is increased processing of pro-fibrotic signaling molecules. Thus, a proteolytically diverse portfolio exists for MT1-MMP within the myocardium and likely plays a mechanistic role in adverse LV remodeling.