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.     

Extracellular superoxide dismutase protects the heart against oxidative stress and hypertrophy after myocardial infarction

Extracellular superoxide dismutase (EC-SOD) contributes only a small fraction to total SOD activity in the heart but is strategically located to scavenge free radicals in the extracellular compartment. EC-SOD expression is decreased in myocardial-infarction (MI)-induced heart failure, but whether EC-SOD can abrogate oxidative stress or modify MI-induced ventricular remodeling has not been previously studied. Consequently, the effects of EC-SOD gene deficiency (EC-SOD KO) on left ventricular (LV) oxidative stress, hypertrophy, and fibrosis were studied in EC-SOD KO and wild-type mice under control conditions, and at 4 and 8 weeks after permanent coronary artery ligation. EC-SOD KO had no detectable effect on LV function in normal hearts but caused small but significant increases of LV fibrosis. At 8 weeks after MI, EC-SOD KO mice developed significantly more LV hypertrophy (LV mass increased 1.64-fold in KO mice compared to 1.35-fold in wild-type mice; p<0.01) and more fibrosis and myocyte hypertrophy which was more prominent in the peri-infarct region than in the remote myocardium. EC-SOD KO mice had greater increases of nitrotyrosine in the peri-infarct myocardium, and this was associated with a greater reduction of LV ejection fraction, a greater decrease of sarcoplasmic or endoplasmic reticulum calcium2+ ATPase, and a greater increase of atrial natriuretic peptide in the peri-infarct zone compared to wild-type mice. EC-SOD KO was associated with more increases of phosphorylated p38 (p-p38(Thr180/Tyr182)), p42/44 extracellular signal-regulated kinase (p-Erk(Thr202/Tyr204)), and c-Jun N-terminal kinase (p-JNK(Thr183/Tyr185)) both under control conditions and after MI, indicating that EC-SOD KO increases activation of mitogen-activated protein kinase signaling pathways. These findings demonstrate that EC-SOD plays an important role in protecting the heart against oxidative stress and infarction-induced ventricular hypertrophy.     

Toll-like receptor-4 modulates survival by induction of left ventricular remodeling after myocardial infarction in mice

Left ventricular (LV) remodeling is known to contribute to morbidity and mortality after myocardial infarction (MI). Because LV remodeling is strongly associated with an inflammatory response, we investigated whether or not TLR-4 influences LV remodeling and survival in a mice model of MI. Six days after MI induction, TLR4 knockout (KO)-MI mice showed improved LV function 32 and reduced LV remodeling as indexed by reduced levels of atrial natriuretic factor and total collagen as well as by a reduced heart weight to body weight ratio when compared with WT-MI mice. This was associated with a reduction of protein levels of the intracellular TLR4 adapter protein MyD88 and enhanced protein expression of the anti-hypertrophic JNK in KO-MI mice when compared with wild-type (WT)-MI mice. In contrast, protein activation of the pro-hypertrophic kinases protein kinase Cdelta and p42/44 were not regulated in KO-MI mice when compared with WT-MI mice. Improved LV function, reduced cardiac remodeling, and suppressed intracellular TLR4 signaling in KO-MI mice were associated with significantly improved survival compared with WT-MI mice (62 vs 23%; p < 0.0001). TLR4 deficiency led to improved survival after MI mediated by attenuated left ventricular remodeling.     

Breeding Strategy Determines Rupture Incidence in Post-Infarct Healing WARPing Cardiovascular Research

Background

Von Willebrand A domain Related Protein (WARP), is a recently identified extracellular matrix protein. Based upon its involvement in matrix biology and its expression in the heart, we hypothesized that WARP regulates cardiac remodeling processes in the post-infarct healing process.

Methods and results

In the mouse model of myocardial infarction (MI), WARP expression increased in the infarcted area 3-days post-MI. In the healthy myocardium WARP localized with perlecan in the basement membrane, which was disrupted upon injury. In vitro studies showed high expression of WARP by cardiac fibroblasts, which further increases upon TGFβ stimulation. Furthermore, WARP expression correlated with aSMA and COL1 expression, markers of fibroblast to myofibroblast transition, in vivo and in vitro. Finally, WARP knockdown in vitro affected extra- and intracellular basic fibroblast growth factor production in myofibroblasts. To investigate the function for WARP in infarction healing, we performed an MI study in WARP knockout (KO) mice backcrossed more than 10 times on an Australian C57Bl/6-J background and bred in-house, and compared to wild type (WT) mice of the same C57Bl/6-J strain but of commercial European origin. WARP KO mice showed no mortality after MI, whereas 40% of the WT mice died due to cardiac rupture. However, when WARP KO mice were backcrossed on the European C57Bl/6-J background and bred heterozygous in-house, the previously seen protective effect in the WARP KO mice after MI was lost. Importantly, comparison of the cardiac response post-MI in WT mice bred heterozygous in-house versus commercially purchased WT mice revealed differences in cardiac rupture.

Conclusion

These data demonstrate a redundant role for WARP in the wound healing process after MI but demonstrate that the continental/breeding/housing origin of mice of the same C57Bl6-J strain is critical in determining the susceptibility to cardiac rupture and stress the importance of using the correct littermate controls.     

Testosterone enhances early cardiac remodeling after myocardial infarction, causing rupture and degrading cardiac function

Cardiac rupture can be fatal after myocardial infarction (MI). Experiments in animals revealed gender differences in rupture rate; however, patient data are controversial. We found a significantly higher rupture rate in testosterone-treated female mice within 1 wk after MI, whereas castration in males significantly reduced rupture. We hypothesized that testosterone may adversely affect remodeling after MI, exaggerating the inflammatory response and increasing cardiac rupture, whereas estrogen may be cardioprotective, attenuating early remodeling and reducing rupture rate. We studied the effect of gender and hormone manipulation on morphological and histological changes during early remodeling after MI in 4-wk-old male and female C57BL/6J mice and how these events could affect cardiac function. Females were randomly divided into 1) sham ovariectomy + placebo (s-ovx + P), 2) s-ovx + testosterone (T), 3) ovx + P, and 4) ovx + T; males were divided into 1) sham castration + P (s-cas + P), 2) s-cas + 17beta-estradiol (E), 3) cas + P, and 4) cas + E. At 6 wk after gonadectomy and hormone manipulation, MI was induced. Mice were randomly killed 1, 2, 4, 7, and 14 days after MI. The left ventricle was weighed and sectioned for evaluation of MI size, infarct expansion index (IEI), and neutrophil infiltration. Transthoracic echocardiography was performed in conscious mice in the 14-day group before organ harvest. Cardiac rupture rate and IEI were significantly higher in testosterone-treated females and noncastrated males than in controls; these effects were accompanied by enhanced neutrophil infiltration and pronounced deterioration of cardiac function and left ventricular dilatation. Ovariectomy in females and estrogen supplementation in males did not confer significant protection from cardiac rupture, IEI, or neutrophil infiltration. We concluded that, in mice, high testosterone levels enhance acute myocardial inflammation, adversely affecting myocardial healing and early remodeling, as indicated by increased cardiac rupture, and possibly causing deterioration of cardiac function after MI, and, conversely, estrogen seems to have no significant protective effect in the acute phase after MI.     

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.     

Cardiac-specific overexpression of diacylglycerol kinase zeta attenuates left ventricular remodeling and improves survival after myocardial infarction

Left ventricular (LV) remodeling, including cardiomyocyte necrosis, scar formation, LV geometric changes, and cardiomyocyte hypertrophy, contributes to cardiac dysfunction and mortality after myocardial infarction (MI). Although precise cellular signaling mechanisms for LV remodeling are not fully elucidated, G(q) protein-coupled receptor signaling pathway, including diacylglycerol (DAG) and PKC, are involved in this process. DAG kinase (DGK) phosphorylates DAG and controls cellular DAG levels, thus acting as a negative regulator of PKC and subsequent cellular signaling. We previously reported that DGK inhibited angiotensin II and phenylephrine-induced activation of the DAG-PKC signaling and subsequent cardiac hypertrophy. The purpose of this study was to examine whether DGK modifies LV remodeling after MI. Left anterior descending coronary artery was ligated in transgenic mice with cardiac-specific overexpression of DGKzeta (DGKzeta-TG) and wild-type (WT) mice. LV chamber dilatation (4.12 +/- 0.10 vs. 4.53 +/- 0.32 mm, P < 0.01), reduction of LV systolic function (34.8 +/- 8.3% vs. 28.3 +/- 4.8%, P < 0.01), and increases in LV weight (95 +/- 3.6 vs. 111 +/- 4.1 mg, P < 0.05) and lung weight (160 +/- 15 vs. 221 +/- 25 mg, P < 0.05) at 4 wk after MI were attenuated in DGKzeta-TG mice compared with WT mice. In the noninfarct area, fibrosis fraction (0.51 +/- 0.04, P < 0.01) and upregulation of profibrotic genes, such as transforming growth factor-beta1 (P < 0.01), collagen type I (P < 0.05), and collagen type III (P < 0.01), were blocked in DGKzeta-TG mice. The survival rate at 4 wk after MI was higher in DGKzeta-TG mice than in WT mice (61% vs. 37%, P < 0.01). In conclusion, these results demonstrate the first evidence that DGKzeta suppresses LV structural remodeling and fibrosis and improves survival after MI. DGKzeta may be a potential novel therapeutic target to prevent LV remodeling after MI.     

ANG II type 1A receptor signaling causes unfavorable scar dynamics in the postinfarct heart

Blockade of ANG II type 1A receptor (AT(1A)) is known to attenuate postinfarction [postmyocardial infarction (post-MI)] heart failure, accompanying reduction in fibrosis of the noninfarcted area. In the present study, we investigated the influence of AT(1A) blockade on the infarcted tissue itself. Consistent with earlier reports, AT(1A) knockout (AT(1A)KO) mice showed significantly attenuated left ventricular (LV) remodeling (dilatation) and dysfunction compared with wild-type (WT) mice. Morphometry revealed that the infarcted wall was thicker and had a smaller circumferential length in AT(1A)KO than WT hearts. In addition, significantly greater numbers of cells were present within infarcts in AT(1A)KO hearts 4 wk post-MI; most notably, there was an abundance of vessels and myofibroblasts. One week post-MI, the incidence of apoptosis among granulation tissue cells was fewer (3.3 +/- 0.4 vs. 4.4 +/- 0.5% in WT, P < 0.05), whereas vessel proliferation was higher in AT(1A)KO hearts, which likely explains the later abundance of cells within the scar tissue. Insulin-like growth factor receptor-I was upregulated and its downstream signal protein kinase B (Akt) was significantly activated in infarcted AT(1A)KO hearts compared with WT hearts. Inactivation of Akt with wortmannin partially but significantly prevented the benefits observed in AT(1A)KO. Collectively, in AT(1A)KO hearts, Akt-mediated granulation tissue cell proliferation and preservation resulting from antiapoptosis likely contributed to an abundant cell population that altered the infarct scar structure, thereby reducing wall stress and attenuating LV dilatation and dysfunction at the chronic stage. In conclusion, altered structural dynamics of infarct scar and increasing myocardial fibrosis may be responsible for the deleterious effects of AT(1A) signaling following MI.     

Depression Increases Sympathetic Activity and Exacerbates Myocardial Remodeling after Myocardial Infarction: Evidence from an Animal Experiment

Depression is an independent risk factor for cardiovascular events and mortality in patients with myocardial infarction (MI). Excessive sympathetic activation and serious myocardial remodeling may contribute to this association. The aim of this study was to discuss the effect of depression on sympathetic activity and myocardial remodeling after MI. Wild-type (WT) rats were divided into a sham group (Sham), a myocardial infarction group (MI), a depression group (D), and a myocardial infarction plus depression group (MI+D). Compared with controls, the MI+D animals displayed depression-like behaviors and attenuated body weight gain. The evaluation of sympathetic activity showed an increased level in plasma concentrations of epinephrine and norepinephrine and higher expression of myocardial tyrosine hydroxylase in the MI+D group than the control groups (p<0.05 for all). Cardiac function and morphologic analyses revealed a decreased fractional shortening accompanied by increased left ventricular dimensions, thinning myocardium wall, and reduced collagen repair in the MI+D group compared with the MI group (p<0.05 for all). Frequent premature ventricular contractions, prolonged QT duration and ventricular repolarization duration, shorted effective refractory period, and increased susceptibility to ventricular arrhythmia were displayed in MI+D rats. These results indicate that sympathetic hyperactivation and exacerbated myocardial remodeling may be a plausible mechanism linking depression to an adverse prognosis after MI.     

Deficiency of TIMP-1 exacerbates LV remodeling after myocardial infarction in mice

Recent studies have been directed at modulating the heart failure process through inhibition of activated matrix metalloproteinases (MMPs). We hypothesized that a loss of MMP inhibitory control by tissue inhibitor of MMP (TIMP)-1 deficiency alters the course of postinfarction chamber remodeling and induced chronic myocardial infarction (MI) in wild-type (WT) and TIMP-1(-/-) mice. Left ventricular (LV) pressure-volume loops obtained from WT and TIMP-1(-/-) mice demonstrated that LV end-diastolic volume [52 +/- 4 (WT) vs. 71 +/- 6 (TIMP-1(-/-)) microl] and LV end-diastolic pressure [9.0 +/- 1.2 (WT) vs. 12.7 +/- 1.4 (TIMP-1(-/-)) mmHg] were significantly increased in the TIMP-1(-/-) mice 2 wk after MI. LV contractility was reduced to a similar degree in the WT and TIMP-1(-/-) groups after MI, as indicated by a significant fall in the LV end-systolic pressure-volume relationship. Ventricular weight and cross-sectional areas of LV myocytes were significantly increased in TIMP-1(-/-) mice, indicating that the hypertrophic response was more pronounced. The observed significant loss of fibrillar collagen in the TIMP-1(-/-) controls may have been an important contributory factor for the observed LV alterations in the TIMP-1(-/-) mice after MI. These findings demonstrate that TIMP-1 deficiency amplifies adverse LV remodeling after MI in mice and emphasizes the importance of local endogenous control of cardiac MMP activity by TIMP-1.     

Interaction between bradykinin subtype 2 and angiotensin II type 2 receptors during post-MI left ventricular remodeling

Angiotensin II type 2 receptor (AT(2)R) overexpression (AT(2)TG) attenuates left ventricular remodeling in a mouse model of anterior myocardial infarction (MI). We hypothesized that the beneficial effects of cardiac AT(2)TG are mediated via the bradykinin subtype 2 receptor (B(2)R). Fourteen transgenic mice overexpressing the AT(2)R (AT(2)TG mice), 10 mice with a B(2)R deletion (B(2)KO mice), 13 AT(2)TG mice with B(2)R deletion (AT(2)TG/B(2)KO mice), and 11 wild-type (WT) mice were studied. All mice were on a C57BL/6 background. Mice were studied by cardiac magnetic resonance imaging at baseline and days 1, 7, and 28 after MI induced by 1 h of occlusion of the left anterior descending artery followed by reperfusion. Short-axis images from apex to base were used to compare ventricular volumes and ejection fraction (EF). At baseline, end-diastolic volume index (EDVI) and end-systolic volume index (ESVI) were lower and EF higher in AT(2)TG mice compared with the other three strains. Infarct size was similar between groups. No differences were observed in global remodeling parameters at day 28 between AT(2)TG and AT(2)TG/B(2)KO mice; however, EDVI and ESVI were lower and EF higher in both transgenic groups than in WT or B(2)KO mice. Both strains lacking B(2)R demonstrated increased collagen content and less hypertrophy in adjacent noninfarcted regions at day 28. Attenuation of postinfarct remodeling by overexpression of AT(2)R is not directly mediated via a B(2)R pathway. However, B(2)R does appear to have a role in the smaller cavity size and hyperdynamic function observed at baseline in AT(2)TG mice and in limiting collagen deposition during postinfarct remodeling.     

Heart extracellular matrix gene expression profile in the vitamin D receptor knockout mice

1,25-Dihydroxyvitamin D₃ [1,25D] deficiency and vitamin D receptor [VDR] genotypes are risk factors for several diseases and disorders including heart diseases. Extracellular matrix (ECM) remodeling mediated by matrix metalloproteinases [MMPs] contributes to progressive left ventricular remodeling, dilation, and heart failure. In the present study, we used high-density oligonucleotide microarray to examine gene expression profile in wild type [WT] and vitamin D receptor knockout mice (VDR KO) which was further validated by RT-PCR. Microarray analysis revealed tissue inhibitors of metalloproteinases [TIMP-1 and TIMP-3] were significantly under expressed in VDR KO mice as compared to WT mice which was further validated by RT-PCR. Zymography and RT-PCR showed that MMP-2 and MMP-9 were up regulated in VDR KO mice. In addition, cross-sectional diameter and longitudinal width of the VDR KO heart myofibrils showed highly significant cellular hypertrophy. Trichrome staining showed marked increase in fibrotic lesions in the VDR KO mice. Heart weight to body weight ratio showed 41% increase in VDR KO mice when compared to WT mice. This data supports a role for 1,25D in heart ECM metabolism and suggests that MMPs and TIMPs expression may be modulated by vitamin D.     

p53 Gene deficiency promotes hypoxia-induced pulmonary hypertension and vascular remodeling in mice

Chronic hypoxia induces pulmonary arterial remodeling, resulting in pulmonary hypertension and right ventricular hypertrophy. Hypoxia has been implicated as a physiological stimulus for p53 induction and hypoxia-inducible factor-1α (HIF-1α). However, the subcellular interactions between hypoxic exposure and expression of p53 and HIF-1α remain unclear. To examine the role of p53 and HIF-1α expression on hypoxia-induced pulmonary arterial remodeling, wild-type (WT) and p53 knockout (p53KO) mice were exposed to either normoxia or hypoxia for 8 wk. Following chronic hypoxia, both genotypes demonstrated elevated right ventricular pressures, right ventricular hypertrophy as measured by the ratio of the right ventricle to the left ventricle plus septum weights, and vascular remodeling. However, the right ventricular systolic pressures, the ratio of the right ventricle to the left ventricle plus septum weights, and the medial wall thickness of small vessels were significantly greater in the p53KO mice than in the WT mice. The p53KO mice had lower levels of p21 and miR34a expression, and higher levels of HIF-1α, VEGF, and PDGF expression than WT mice following chronic hypoxic exposure. This was associated with a higher proliferating cell nuclear antigen expression of pulmonary artery in p53KO mice. We conclude that p53 plays a critical role in the mitigation of hypoxia-induced small pulmonary arterial remodeling. By interacting with p21 and HIF-1α, p53 may suppress hypoxic pulmonary arterial remodeling and pulmonary arterial smooth muscle cell proliferation under hypoxia.     

培养于生物降解支架膜内的胚胎干细胞可修复小鼠的梗塞心肌

我们以往的研究表明,直接在心肌梗塞（myocardial infarction,MI）动物的心脏缺血区注射胚胎干细胞（embryonic stemceils,ESCs）可以提高其心肌功能,干细胞组织工程学可以使组织再生、修复。本研究旨在观察将ESCs接种到生物降解膜内并移植到梗塞部位的效果。通过结扎小鼠左冠状动脉制作MI模型,将培养3d的带有小鼠ESCs的聚羟基乙酸膜（polyglycolicacid,PGA）移植到心肌缺血及边缘区表面。实验小鼠分成4组：假手术组、MI组、MI＋PGA组、MI＋ESC组,移植操作8周后检测血流动力学和心肌功能。MI组的血压和左心室功能显著降低。与MI组和MI＋PGA组相比,MI＋ESC组的血压和心室功能显著改善,存活率也显著增高,在梗塞区检测到GFP阳性组织,表明ESCs存活,并可能有心肌再生。以上结果表明,移植生物降解膜内的ESCs可修复小鼠梗塞区心肌细胞并提高心脏功能。将ESCs和生物降解材料联合运用可能为修复受损心脏提供一个新的治疗方法。     

Caveolin-1 deficiency exacerbates cardiac dysfunction and reduces survival in mice with myocardial infarction

Caveolin (Cav)-1 has been involved in the pathogenesis of ischemic injuries. For instance, modulations of Cav-1 expression have been reported in animal models of myocardial infarction and cerebral ischemia-reperfusion. Furthermore, ablation of the Cav-1 gene in mice has been shown to increase the extent of ischemic injury in models of cerebral and hindlimb ischemia. Cav-1 has also been suggested to play a role in myocardial ischemic preconditioning. However, the role of Cav-1 in myocardial ischemia (MI)-induced cardiac dysfunction still remains to be determined. We determined the outcome of a permanent left anterior descending coronary artery (LAD) ligation in Cav-1 knockout (KO) mice. Wild-type (WT) and Cav-1 KO mice were subjected to permanent LAD ligation for 24 h. The progression of ischemic injury was monitored by echocardiography, hemodynamic measurements, 2,3,5-triphenyltetrazolium chloride staining, β-binding analysis, cAMP level measurements, and Western blot analyses. Cav-1 KO mice subjected to LAD ligation display reduced survival compared with WT mice. Despite similar infarct sizes, Cav-1 KO mice subjected to MI showed reduced left ventricular (LV) ejection fraction and fractional shortening as well as increased LV end-diastolic pressures compared with their WT counterparts. Mechanistically, Cav-1 KO mice subjected to MI exhibit reduced β-adrenergic receptor density at the plasma membrane as well as decreased cAMP levels and PKA phosphorylation. In conclusion, ablation of the Cav-1 gene exacerbates cardiac dysfunction and reduces survival in mice subjected to MI. Mechanistically, Cav-1 KO mice subjected to LAD ligation display abnormalities in β-adrenergic signaling.     

Role of inducible nitric oxide synthase in cardiac function and remodeling in mice with heart failure due to myocardial infarction

Using inducible nitric oxide (NO) synthase (iNOS) knockout mice (iNOS-/-), we tested the hypotheses that 1) lack of iNOS attenuates cardiac remodeling and dysfunction and improves cardiac reserve postmyocardial infarction (MI), an effect that is partially mediated by reduction of oxidative stress due to reduced interaction between NO and reactive oxygen species (ROS); and 2) the cardioprotection afforded by iNOS deletion is eliminated by Nomega-nitro-L-arginine methyl ester (L-NAME) due to inhibition of endothelial NOS (eNOS) and neuronal NOS (nNOS). MI was induced by ligating the left anterior descending coronary artery. Male iNOS-/- mice and wild-type controls (WT, C57BL/6J) were divided into sham MI, MI+vehicle, and MI+l-NAME (100 mg.kg(-1).day(-1) in drinking water for 8 wk). Cardiac function was evaluated by echocardiography. Left ventricular (LV) maximum rate of rise of ventricular pressure divided by pressure at the moment such maximum occurs (dP/dt/instant pressure) in response to isoproterenol (100 ng.kg(-1).min(-1) iv) was measured with a Millar catheter. Collagen deposition, myocyte cross-sectional area, and expression of nitrotyrosine and 4-hydroxy-2-nonenal (4-HNE), markers for ROS, were determined by histopathological and immunohistochemical staining. We found that the MI-induced increase in LV chamber dimension and the decrease in ejection fraction, an index of systolic function, were less severe in iNOS-/- compared with WT mice. L-NAME worsened LV remodeling and dysfunction further, and these detrimental effects were also attenuated in iNOS-/- mice, associated with better preservation of cardiac function. Lack of iNOS also reduced nitrotyrosine and 4-HNE expression after MI, indicating reduced oxidative stress. We conclude that iNOS does not seem to be a pathological mediator of heart failure; however, the lack of iNOS improves cardiac reserve post-MI, particularly when constitutive NOS isoforms are blocked. Decreased oxidative stress and other adaptive mechanisms independent of NOS may be partially responsible for such an effect, which needs to be studied further.     

Senescence Marker Protein 30 Has a Cardio-Protective Role in Doxorubicin-Induced Cardiac Dysfunction

Background

Senescence marker protein 30 (SMP30), which was originally identified as an aging marker protein, is assumed to act as a novel anti-aging factor in the liver, lungs and brain. We hypothesized that SMP30 has cardio-protective function due to its anti-aging and anti-oxidant effects on doxorubicin (DOX)-induced cardiac dysfunction.

Methods and Results

SMP30 knockout (SMP30 KO) mice, SMP30 transgenic (SMP30 TG) mice with cardiac-specific overexpression of SMP30 gene and wild-type (WT) littermate mice at 12–14 weeks of age were given intra-peritoneal injection of DOX (20 mg/kg) or saline. Five days after DOX injection, echocardiography revealed that left ventricular ejection fraction was more severely reduced in the DOX-treated SMP30 KO mice than in the DOX-treated WT mice, but was preserved in the DOX-treated SMP30 TG mice. Generation of reactive oxygen species and oxidative DNA damage in the myocardium were greater in the DOX-treated SMP30 KO mice than in the DOX-treated WT mice, but much less in the SMP30 TG mice. The numbers of deoxynucleotidyltransferase-mediated dUTP nick end-labeling positive nuclei in the myocardium, apoptotic signaling pathways such as caspase-3 activity, Bax/Bcl-2 ratio and phosphorylation activity of c-Jun N-terminal kinase were increased in SMP30 KO mice and decreased in SMP30 TG mice compared with WT mice after DOX injection.

Conclusions

SMP30 has a cardio-protective role by anti-oxidative and anti-apoptotic effects in DOX-induced cardiotoxicity, and can be a new therapeutic target to prevent DOX-induced heart failure.     

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.