小鼠急性心肌梗死后心脏破裂的性别差异及机制探讨

目的:探讨小鼠急性心肌梗死(AMI)后心脏破裂的性别差异及其机制。方法:不同性别C57BL小鼠,随机分入假手术组、心肌梗死组。建立AMI模型后,观察不同性别组心脏破裂发生率,并于AMI后第7天行超声和血流动力学检查;应用酶谱法、病理染色及免疫组化方法,分别于AMI后第3天、第7天检测基质金属蛋白酶(MMP-2,MMP-9)活性表达,心肌间质胶原含量(CVF)和类型的变化,检测AMI后第3天炎性细胞浸润程度。结果:1.AMI后雄性组心脏破裂率显著高于雌性组(42.2%与18.4%,P<0.05)。2.与雌性组比较,雄性心肌梗死(MI)组AMI后第3天炎性细胞浸润程度明显增加(P<0.05),第3天、第7天MMP-9表达增加,心肌间质胶原含量较低。3.雄性假手术组平均动脉压(MAP)、左心室收缩压(LVSP)均高于雌性假手术组(P均<0.05),术后第7天时,雄性MI组较雌性MI组表现出显著的左心室扩张、梗死区变薄、心功能障碍以及血流动力学恶化。结论:小鼠AMI后心脏破裂率存在性别差异,雄性明显高于雌性。炎性细胞浸润程度增加、MMP-9活性增高、原有间质胶原过度降解和左心室早期重塑恶化可能是雄性小鼠心脏破裂率增加的重要原因。     

不同月龄鼠急性心肌梗死后心室重构和心脏破裂的观察

目的 探讨老龄对小鼠急性心肌梗死(AMI)后心室重构心脏破裂的影响. 方法 老龄和低龄C57BL/6小鼠,随机分为假手术组、心肌梗死组.建立AMI模型后,观察心脏破裂发生率,并于AMI后第7天行超声和血流动力学检查;应用酶谱法、病理染色及免疫组化方法 ,分别于AMI后第3、7天检测基质金属蛋白酶-2、-9(MMP-2、MMP-9)活性表达,炎性细胞浸润程度,心肌间质胶原含量(CVF)和类型的变化. 结果 AMI后老龄组心脏破裂率高于低龄组(38.0%与16.0%,X2=6.139,P＜0.05);第7天时,较低龄组出现明显的梗死区扩张、左心室重构、心功能障碍及血流动力学变化(t=5.754,P＜0.05).与低龄组比较,老龄AMI组AMI后第3天炎性细胞浸润程度、MMP-9表达明显增加(P＜0.05).与低龄组比较,老龄组心肌间质胶原含量、Ⅲ型胶原表达增加(P＜0.05). 结论 老龄是小鼠AMI后心脏破裂的高危因素,其原因可能与AMI早期炎性细胞浸润程度增加、MMP-9、Ⅲ型胶原过度表达和早期左心室重构恶化有关.     

Regional cardiac dysfunction is associated with specific alterations in inflammatory cytokines and matrix metalloproteinases after acute myocardial infarction in sheep

Cardiac remodeling following myocardial infarction (MI) is a maladaptive process, fundamental to the progression of ischemic heart failure. The extent of remodeling is influenced by mechanical stress, inflammatory response and activation of matrix metalloproteinases (MMPs). This study examined regional association between these parameters in response to acute MI. Coronary ligation was performed in ten sheep. Sonomicrometer transducers measured segmental length in the infarcted, border and non-infarcted region. Regional tissue samples obtained 3 h post MI from six sheep were analysed using RT-PCR, gelatin zymography and Western blot. Six sham-operated sheep served as controls. Region-specific dilation and reduced contraction was associated with corresponding alterations in matrix molecules.IL-6 and MMP-9 mRNA were increased in the infarcted and border regions compared to controls.MMP-2 and TIMP-1 mRNA increased in non–infarcted myocardium and both correlated positively with segmental shortening. IL-6 mRNA levels, in contrast, were negatively associated with segmental shortening. In summary, inflammatory cytokines and MMPs are altered early after MI in a region-specific manner, and these changes correspond to acute regional myocardial dysfunction. Therapies for LV remodeling from the time of reperfusion may benefit from further understanding this portfolio of acute alterations.     

Effect of Matrix Metalloproteinase Inhibition by Doxycycline on Myocardial Healing and Remodeling after Myocardial Infarction

Summary The aim of conducting this study was to assess the clinical relevance of matrix metalloproteinase (MMP) inhibition by doxycycline, an effective MMP inhibitor, in a rat model of extensive myocardial infarction (MI) and left ventricular (LV) dysfunction. Rats (n = 22) were subjected to extensive anterior MI. Doxycycline (25 mg SC, daily) or saline (control) injections were started for nine days thereafter. The effect of doxycycline on MMP activity in the infarcted and remote myocardium was measured by zymography, in another subgroup (n = 8), nine days after MI. Echocardiography and magnetic resonance imaging (MRI) studies were performed at one and thirty days after MI to assess LV remodeling and function. After 4 weeks, hearts were fixed, and subjected to morphometric and histological analysis. Compared with control, doxycycline treatment attenuated MMP-9 and -2 activity in both infarcted and remote myocardium. Serial echocardiography studies showed that doxycycline failed to attenuate scar thinning, LV dilatation and dysfunction. MRI study showed that doxycycline impaired LV compensatory hypertrophy. Furthermore, compared with control, doxycycline reduced vessel density (/mm² ± SEM) in the infarcted myocardium (84 ± 16 vs. 46 ± 9/mm², respectively; p < 0.05). Our work suggest that effective MMPs’ inhibition in the infarcted and remote myocardium by doxycycline does not prevent LV remodeling and dysfunction but impairs angiogenesis and compensatory LV hypertrophy. Our findings caution against aggressive, non-selective inhibition of MMPs in the early healing phase after MI.     

Collagen accumulation after myocardial infarction: effects of ETA receptor blockade and implications for early remodeling

OBJECTIVES: Endothelin A (ETA) receptor blockade started early after myocardial infarction (MI) promotes adverse left ventricular (LV) dilatation. We tested the hypothesis that inhibition of ETA receptors during the early phase of healing affects collagen synthesis and accumulation, and induces expansion of infarcted myocardium. METHODS: Starting 3 h after coronary ligation, female Wistar rats were treated with the selective ETA receptor antagonist LU 135252 (30 mg/kg body wt/day) or placebo. A period of 7 days after MI, hemodynamic, morphometric and biochemical studies were performed. RESULTS: ET(A) receptor blockade enhanced infarct expansion index and decreased LV systolic function. Infarct scar of LU 135252-treated rats displayed decreased gene expression of fibrillar type I/III collagens and of transforming growth factor-beta(1) (TGF-beta(1)). Collagen content in the infarct scar and border regions was lower after ETA inhibition. In addition, Western blot analysis revealed, after ETA receptor blockade, enhanced matrix metalloproteinases MMP-13, and MMP-2 expression in the infarcted LV myocardium. CONCLUSIONS: These data demonstrate that endothelin stimulates collagen accumulation at the site of infarction. Decreased collagen and TGF-beta(1) gene expression, associated with enhanced infarct expansion and MMP up-regulation likely contributes to ETA receptor blockade-mediated deleterious effects on ventricular remodeling after infarction.     

Role of osteopontin in heart failure associated with aging

Cardiovascular disease is one of the leading causes of death in the elderly. Much of the morbidity and mortality in the elderly is attributable to acute ischemic events leading to myocardial infarction (MI) and death of cardiac myocytes. Evidence has been provided that aging associated with adverse remodeling post MI as demonstrated by less effective myocardial repair, greater infarct expansion, and septal hypertrophy. Expression of osteopontin (OPN) increases in the heart post MI. Transgenic mice studies suggest that increased expression of OPN plays a protective role in post-MI LV remodeling by modulating collagen deposition and fibrosis. OPN, a multifunctional protein, has the potential to influence the molecular and cellular changes associated with infarct healing. The post-MI infarct healing process involves temporarily overlapping phases that include the following—(1) inflammation with migration and adhesion of neutrophils and macrophages, phagocytosis and inflammatory gene expression; (2) tissue repair with fibroblast adhesion and proliferation, myofibroblast differentiation, extracellular matrix deposition and scar formation; and (3) structural and functional remodeling of infarcted and non-infarcted myocardium through cardiac myocyte apoptosis, hypertrophy and myocardial angiogenesis. This review is focused on the expression of OPN in the heart post MI and its role in various phases of infarct healing.     

P. gingivalis lipopolysaccharide intensifies inflammation post-myocardial infarction through matrix metalloproteinase-9

Periodontal disease (PD) strongly correlates with increased mortality post-myocardial infarction (MI); however, the underlying mechanisms are unknown. Matrix metalloproteinase (MMP)-9 levels directly correlate with dysfunction and remodeling of the left ventricle (LV) post-MI. Post-MI, MMP-9 is produced by leukocytes and modulates inflammation. We have shown that exposure to Porphyromonas gingivalis lipopolysaccharide (PgLPS), an immunomodulatory molecule identified in PD patients, increases LV MMP-9 levels in mice and leads to cardiac inflammation and dysfunction. The aim of the study was to determine if circulating PgLPS exacerbates the LV inflammatory response post-MI through MMP-9 dependent mechanisms. We exposed wild type C57BL/6J and MMP-9^−/− mice to PgLPS (ATCC 33277) for a period of 28 days before performing MI, and continued to deliver PgLPS for up to 7 days post-MI. We found systemic levels of PgLPS 1) increased MMP-9 levels in both plasma and infarcted LV resulting in reduced wall thickness and increased incidence of LV rupture post-MI and 2) increased systemic and local macrophage chemotaxis leading to accelerated M1 macrophage infiltration post-MI and decreased LV function. MMP-9 deletion played a protective role by attenuating the inflammation induced by systemic delivery of PgLPS. In conclusion, MMP-9 deletion has a cardioprotective role against PgLPS exposure, by attenuating macrophage mediated inflammation.     

Age-dependent changes in myocardial matrix metalloproteinase/tissue inhibitor of metalloproteinase profiles and fibroblast function

OBJECTIVE: To evaluate the effects of aging on left ventricular (LV) geometry, collagen levels, matrix metalloproteinase (MMP) and tissue inhibitor of metalloproteinase (TIMP) abundance, and myocardial fibroblast function. METHODS: Young (3-month-old; n=28), middle-aged (MA; 15-month-old; n=17), and old (23-month-old; n=16) CB6F1 mice of both sexes were used in this study. Echocardiographic parameters were measured; collagen, MMP, and TIMP levels were determined for both the soluble and insoluble protein fractions; and fibroblast function was evaluated. RESULTS: LV end-diastolic dimensions and wall thickness increased in both MA and old mice, accompanied by increased soluble protein and decreased insoluble collagen. Immunoblotting revealed differential MMP/TIMP profiles. Compared to MA levels, MMP-3, MMP-8, MMP-9, MMP-12, and MMP-14 increased, and TIMP-3 and TIMP-4 decreased in the insoluble fraction of old mice, suggesting increased extracellular matrix (ECM) degradative capacity. Fibroblast proliferation was blunted with age. CONCLUSION: This study, for the first time, identified specific differences in cellular and extracellular processes that likely contribute to age-dependent ECM remodeling.     

白细胞介素-10对急性心肌梗死后细胞外基质重构影响的实验研究

目的 观察白细胞介素-10(IL-10)对大鼠急性心肌梗死后心肌基质金属蛋白酶(MMP)-2、9,金属蛋白酶组织抑制因子(TIMP)-1表达及胶原代谢的作用,探讨其对急性心肌梗死后心肌基质重构的影响.方法 18只大鼠随机分为假手术组、MI/AAV2转染组作为对照和MI/AAV2-IL-10转染组,每组6只.结扎大鼠左冠状动脉前降支建立急性心肌梗死动物模型,同时应用基因重组2型腺相关病毒(AAV-2)携带IL-10基因转染心肌组织.RT-PCR和ELISA观察心肌IL-10 mRNA和蛋白的表达.逆转录聚合酶链反应、免疫印迹法、明胶酶谱、免疫组化检测转染后心肌组织表达MMP-2、9,TIMP-1,Ⅰ、Ⅲ型胶原水平的变化.结果 心肌梗死5 d后,MI/AAV2-IL-10组检测到IL-10 mRNA和蛋白的表达;MI/AAV2组较假手术组心肌MMP-2、9,Ⅰ、Ⅲ型胶原表达明显升高;而MI/AAV2-IL-10组较MI/AAV2组梗死心肌各部位MMP-2、9表达减少,TIMP-1表达升高,其中,梗死边缘区的MMP-2表达降低14.6%(P＜0.01),MMP-9降低24.7%(P＜0.01),TIMP-1升高73.1%(P＜0.01),Ⅰ、Ⅲ型胶原表达分别下降了47.6%(P＜0.01)、23.6%(P＜0.05),Ⅰ/Ⅲ型胶原比值下降.结论 IL-10通过对MMP/TIMP的作用,改善大鼠急性心肌梗死后心肌胶原沉积和组织重构.     

Exaggerated left ventricular dilation and reduced collagen deposition after myocardial infarction in mice lacking osteopontin

Osteopontin (OPN), an extracellular matrix protein, is expressed in the myocardium with hypertrophy and failure. We tested the hypothesis that OPN plays a role in left ventricular (LV) remodeling after myocardial infarction (MI). Accordingly, OPN expression and LV structural and functional remodeling were determined in wild-type (WT) and OPN knockout (KO) mice 4 weeks after MI. Northern analysis showed increased OPN expression in the infarcted region, peaking 3 days after MI and gradually decreasing over the next 28 days. In the remote LV, OPN expression was biphasic, with peaks at 3 and 28 days. In situ hybridization and immunohistochemical analyses showed increased OPN mRNA and protein primarily in the interstitium. Infarct size, heart weight, and survival were similar in KO and WT mice after MI (P=NS), whereas the lung wet weight/dry weight ratio was increased in the KO mice (P<0.005 versus sham-operated mice). Peak LV developed pressure was reduced to a similar degree after MI in the KO and WT mice. The number of terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL)-positive myocytes was similar in KO and WT mice after MI. In contrast, post-MI LV chamber dilation was approximately twice as great in KO versus WT mice (P<0.001). Myocyte length increased after MI in WT mice (P<0.001) but not in KO mice. Electron microscopy showed increased collagen content in WT mice after MI but not in KO mice after MI. Type I collagen content was increased approximately 3-fold and approximately 7-fold in remote and infarcted regions, respectively, of WT hearts after MI but not in KO hearts (P<0.01 versus WT hearts). Likewise, Northern analyses showed increased collagen I(alpha(1)) mRNA after MI in remote regions of WT hearts but not in KO hearts. Thus, increased OPN expression plays an important role in regulating post-MI LV remodeling, at least in part, by promoting collagen synthesis and accumulation.     

MMP Induction and Inhibition in Myocardial Infarction

Short-term survival following a myocardial infarction (MI) has greatly improved, due in part to therapeutic interventions that restore blood flow and limit infarct size. The increased incidence of infarct-stimulated left ventricular (LV) remodeling that advances to congestive heart failure (CHF), however, is a significant long-term complication and a leading cause of mortality. Changes to ECM structure and function are primary components of LV remodeling and are precipitated by the early increase in infarct area collagen levels that replace necrotic myocytes and form a scar. ECM turnover is coordinated through the synthesis and degradation of ECM and non-ECM components, particularly the matrix metalloproteinases (MMP), a family of proteolytic enzymes that cleave ECM. MMPs have multiple roles in remodeling events that lead to LV dilation. The inhibition or targeted deletion of specific MMPs attenuates LV remodeling events post-MI. MMP inhibitors have been used in animal models to delineate LV remodeling mechanisms and to evaluate the pharmacologic potential of targeting the ECM to modify LV remodeling post-MI. This review summarizes the current knowledge and limitations of MMP inhibition in the post-MI myocardium.     

Protection from adverse myocardial remodeling secondary to chronic volume overload in mast cell deficient rats

Mast cells have diverse roles throughout the body as evidenced by their heterogeneous nature. In the heart, cardiac mast cells have been implicated in left ventricular (LV) remodeling in response to elevated myocardial stress. Accordingly, the purpose of this study was to use mast cell deficient rats (Ws/Ws) to delineate the interaction between cardiac mast cell activation and LV remodeling. LV matrix metalloproteinase (MMP) activity, fibrillar collagen, TNF-α levels, and LV diameter were compared in Ws/Ws and wild type (WT) rats subjected to 5 d (n = 3/group) and 8 weeks (n = 4/group) of aortocaval fistula-induced volume overload. In contrast to attenuation of myocardial remodeling in the Ws/Ws group: 1) MMP-2 activity was significantly increased in the WT group at 5 days; 2) there was marked degradation of the extracellular collagen matrix in WT at 5 days and 8 weeks; 3) the percent increase in LV diameter from baseline was significantly greater in WT at 2, 4, 6, and 8 weeks post-fistula; and 4) myocardial TNF-α levels were markedly elevated in the WT group at 5 days post-fistula. These results underscore the importance of cardiac mast cells in mediating MMP activation, collagen degradation and LV dilatation and suggest that mast cell-derived TNF-α plays a role in early myocardial remodeling.     

The plasminogen-MMP system is more activated in the scar than in viable myocardium 3 months post-MI in the rat

Left ventricular (LV) remodeling following myocardial infarction (MI) is a complex process involving extracellular matrix degradation and fibrosis. While early remodeling is beneficial, chronic remodeling leads to decompensated heart failure (HF). We assessed the hypothesis that activation of the plasminogen-MMP system is involved in the remodeling of the infarct scar and compared it to the remaining viable myocardium. MI was induced by coronary artery ligature in 42 male Wistar rats. Three months following surgery, animals were divided into compensated (n=26) or decompensated (n=16) groups and compared to sham-operated rats (n=17). Scar and remaining viable LV myocardium (LVM) were separately analyzed for MMP-2, -7, -9, urokinase type and tissue type plasminogen activator (uPA and tPA) mRNA levels by RT-PCR. Their protein or activity levels, plus those of plasminogen/plasmin, tissue inhibitor of metalloproteinase-1, -2, -4 (TIMP-1, -2, -4) and plasminogen activator inhibitor-1 (PAI-1) were analyzed in tissue conditioned media by Western blot, ELISA and/or zymography. MMP and plasmin proteolytic activities were increased in the scar as compared to paired LVM thus indicating that activation of plasminogen and pro-MMPs is a key event in scar tissue remodeling. MMP and plasminogen activators (uPA, tPA) mRNAs were increased accordingly. Furthermore, inhibitors of the proteolytic enzymes, TIMP-1 and PAI-1 were increased in the scars from failing hearts and LVM thus suggesting a dynamic interplay between proteolysis and its inhibitors. This study shows a high degree of activation of the MMP-plasminogen system and the balance with their inhibitors in the infarcted myocardium, and suggests that this activation participates more to the remodeling of the scar tissue than to the remaining myocardium.     

Myocardial matrix degradation and metalloproteinase activation in the failing heart: a potential therapeutic target

A fundamental structural event in the progression of heart failure due to dilated cardiomyopathy is left ventricular (LV) myocardial remodeling. The matrix metalloproteinases (MMPs) are an endogenous family of enzymes which contribute to matrix remodeling in several disease states. The goal of this report is to summarize recent findings regarding the myocardial MMP system and the relation to matrix remodeling in the failing heart. In both experimental and clinical forms of dilated cardiomyopathy (DCM), increased expression of certain species of myocardial MMPs have been demonstrated. Specifically, increased myocardial levels of the gelatinase, MMP-9 has been identified in both ischemic and non-ischemic forms of human DCM. In addition, stromelysin or MMP-3 increased by over four-fold in DCM. The increased levels of MMP-3 in DCM may have particular importance since this MMP degrades a wide range of extracellular proteins and can activate other MMPs. In normal human LV myocardium, the membrane type 1 MMP (MT1-MMP) was detected. These MT-MMPs may provide important sites for local MMP activation within the myocardium. In a pacing model of LV failure, MMP expression and activity increased early and were temporally associated with LV myocardial matrix remodeling. Using a broad-spectrum pharmacological MMP inhibitor in this pacing model, the degree of LV dilation was attenuated and associated with an improvement in LV pump function. Thus, increased LV myocardial MMP expression and activity are contributory factors in the LV remodeling process in cardiomyopathic disease states. Regulation of myocardial MMP expression and activity may be an important therapeutic target for controlling myocardial matrix remodeling in the setting of developing heart failure.     

Phosphatase PTEN is critically involved in post-myocardial infarction remodeling through the Akt/interleukin-10 signaling pathway

The inflammatory cytokines interleukin (IL)-10 and tumor necrosis factor (TNF)-α play an important role in left ventricular (LV) remodeling after myocardial infarction (MI). Phosphatase and tensin homolog deleted on chromosome ten (PTEN) inactivates protein kinase Akt and promotes cell death in the heart. However, it is not known whether PTEN promotes post-MI remodeling by regulating IL-10 and TNF-α. MI was induced in wild-type (WT) mice and Pten heterozygous mutant (HET) mice. Pten adenoviruses (adPten) or empty vectors (adNull) were injected into the peri-infarct area of WT mice. LV dilation was attenuated and fractional shortening was increased in HET mice compared to WT mice. Survival rate and fractional shortening were decreased in adPten mice compared to adNull mice. Leukocyte infiltration into the peri-infarct area was attenuated in HET mice and worsened in adPten mice. PTEN expression was upregulated in the infarcted heart of WT mice. Partial inactivation of PTEN increased the production of IL-10 and decreased the expression of TNF-α and matrix metalloproteinase (MMP)-2 and -9 after MI in HET mice. PTEN overexpression caused opposite effects in the infarcted heart. Moreover in the infarcted heart of HET mice, Akt inhibition decreased Stat3 phosphorylation and IL-10 expression, and blockade of the IL-10 receptor increased TNF-α and MMP-2 expression. Both Akt inhibition and IL-10 receptor blockade abolished the attenuation of post-MI remodeling in HET mice. In conclusion, PTEN is critically involved in post-MI remodeling through the Akt/IL-10 signaling pathway. Therefore, targeting PTEN may be an effective approach to post-MI remodeling.     

Effect of ramipril and furosemide treatment on interstitial remodeling in post-infarction heart failure rat hearts

Extracellular matrix (ECM) remodeling and increased matrix metalloproteinase (MMP) expression and activity have been observed to be relevant in the development of heart failure (HF). We examined the effects of ramipril alone or with furosemide on ECM in a heart failure model. HF was induced by occlusion of the left coronary artery in spontaneously hypertensive rats (SHR). Rats were assigned to placebo (n=9), ramipril 1 mg/kg/day (n=11), furosemide 2 x 2 mg/kg/day (n=7) or both (1 mg/kg/day + 2 x 2 mg/kg/day n=8). LV-function, collagen content, MMP/TIMP (tissue inhibitor of matrix metalloproteinases) protein- and mRNA-expression were examined in non-infarcted LV tissue. MMP-2/TIMP-4 ratio was increased in HF. Ramipril reduced MMP-2 expression (active form), collagen type I mRNA expression and content and increased TIMP-4 levels associated with decreased left ventricular end diastolic pressure (LVEDP), mortality rate and increased LV pressure (LVP). Combination therapy with furosemide is less efficient with regard to collagen content and MMP-2 (active form) reduction but did not worsen beneficial effects of ramipril on LV function and mortality rate. Furosemide alone had no effect on MMP-2 (active form) expression, collagen content, LV function and mortality rate. Prevention of LV dilatation by ramipril was associated with decreased gelatinolytic activity and increased MMP-inhibition in heart failure SHR. Furthermore, ramipril reduced fibrosis by enhanced interstitial collagenase expression. Furosemide did not show the beneficial effects of ramipril on ECM remodeling but did not worsen LV function. Positive effects of furosemide treatment alone on LV remodeling and function were not observed.     

Cardiac fibrogenesis following infarction in mice with deletion of inducible nitric oxide synthase

BACKGROUND: Studies have shown that the absence of inducible nitric oxide synthase (iNOS) improves cardiac function and survival after myocardial infarction (MI). The responsible mechanisms, however, remain uncertain. Cardiac iNOS is significantly increased after MI, which is colocalized with fibrous tissue formation. Herein, we tested our hypothesis that iNOS is involved in the development of cardiac fibrosis. METHODS: Wild-type and iNOS-knockout mice were subjected to MI by left coronary artery ligation. At week 1, 2, 3, and 4 post-MI, we addressed cardiac expression of profibrogenic mediator, growth of collagen-producing cells, collagen synthesis, and degradation. RESULTS: In the infarcted myocardium of wild-type and iNOS-knockout mice, transforming growth factor (TGF)-beta1 expression was significantly increased, particularly in the early stage; myofibroblasts appeared and became abundant for over 4 weeks; matrix metalloproteinase-1 expression was low, whereas tissue inhibitor of matrix metalloproteinase-1 was significantly elevated; type-I collagen mRNA was significantly increased and collagen was continuously accumulated. In the noninfarcted myocardium, TGF-beta1 and type-I collagen mRNA levels as well as collagen volume were also elevated, but less evident than infarcted myocardium. However, there was no significant difference in cardiac TGF-beta1 expression, myofibroblast population, collagen synthesis/degradation, and collagen volume between wild-type and iNOS-knockout mice with MI. CONCLUSION: The current study suggests that iNOS-induced nitric oxide production may not mediate cardiac fibrosis after MI. Thus, other mechanisms are involved in nitrosative stress-induced cardiac dysfunction after MI.     

Cardiac mast cell- and chymase-mediated matrix metalloproteinase activity and left ventricular remodeling in mitral regurgitation in the dog

The present study tested the hypothesis that cardiac mast cells and chymase are associated with matrix metalloproteinase (MMP) activation and extracellular matrix (ECM) degradation in the evolution of left ventricular (LV) chamber remodeling secondary to experimental mitral regurgitation (MR) in dogs. LV mast cell density, chymase activity, and angiotensin II (ANG II) levels were significantly increased 2 and 4 weeks post-MR, while an increase in angiotensin-converting enzyme (ACE) activity was not seen prior to the chronic 24 week stage. As early as 2 and 4 weeks, there was a significant decrease in interstitial myocardial collagen content that was associated with an increase in LV end-diastolic diameter (LVEDD) but a normal LVEDD/wall thickness ratio. While mast cell density decreased to normal at 24 weeks, both chymase and MMP-2 activity remained increased throughout the entire 24-week period post-MR. By 24 weeks a transition to an adverse pattern of LV remodeling characterized by a 2-fold increase in the LVEDD/wall thickness ratio had occurred. Thus, this study supports the hypothesis that mast cells and chymase are important modulators of MMP activity and ECM degradation, contributing to adverse LV remodeling in chronic volume overload secondary to MR.     

Cardiomyocyte-specific overexpression of nitric oxide synthase 3 improves left ventricular performance and reduces compensatory hypertrophy after myocardial infarction

Nitric oxide (NO) is an important modulator of cardiac performance and left ventricular (LV) remodeling after myocardial infarction (MI). We tested the effect of cardiomyocyte-restricted overexpression of one NO synthase isoform, NOS3, on LV remodeling after MI in mice. LV structure and function before and after permanent LAD coronary artery ligation were compared in transgenic mice with cardiomyocyte-restricted NOS3 overexpression (NOS3-TG) and their wild-type littermates (WT). Before MI, systemic hemodynamic measurements, echocardiographic assessment of LV fractional shortening (FS), heart weight, and myocyte width (as assessed histologically) did not differ in NOS3-TG and WT mice. The inotropic response to graded doses of isoproterenol was significantly reduced in NOS3-TG mice. One week after LAD ligation, the infarcted fraction of the LV did not differ in WT and NOS3-TG mice (34+/-4% versus 36+/-12%, respectively). Four weeks after MI, however, end-systolic LVID was greater, and fractional shortening and maximum and minimum rates of LV pressure development were less in WT than in NOS3-TG mice. LV weight/body weight ratio was greater in WT than in NOS3-TG mice (5.3+/-0.2 versus 4.6+/-0.5 mg/g; P<0.01). Myocyte width in noninfarcted myocardium was greater in WT than in NOS3-TG mice (18.8+/-2.0 versus 16.6+/-1.6 microm; P<0.05), whereas fibrosis in noninfarcted myocardium was similar in both genotypes. Cardiomyocyte-restricted overexpression of NOS3 limits LV dysfunction and remodeling after MI, in part by decreasing myocyte hypertrophy in noninfarcted myocardium.