HSP75 protects against cardiac hypertrophy and fibrosis

Cardiac hypertrophy, a major determinant of heart failure, is associated with heat shock proteins (HSPs). HSP75 has been reported to protect against environmental stresses; however, its roles in cardiac hypertrophy remain unclear. Here, we generated cardiac-specific inducible HSP75 transgenic mice (TG) and cardiac hypertrophy was developed at 4 weeks after aortic banding in TG mice and wild-type littermates. The results revealed that overexpression of HSP75 prevented cardiac hypertrophy and fibrosis as assessed by heart weight/body weight ratio, heart weight/tibia length ratio, echocardiographic and hemodynamic parameters, cardiomyocyte width, left ventricular collagen volume, and gene expression of hypertrophic markers. Further studies showed that overexpression of HSP75 inhibited the activation of TAK/P38, JNK, and AKT signaling pathways. Thus, HSP75 likely reduces the hypertrophy and fibrosis induced by pressure overload through blocking TAK/P38, JNK, and AKT signaling pathways.     

动脉压力感受性反射受损后血浆和心脏、肾脏组织AngⅡ含量的变化

既往的研究表明,动脉压力感受性反射（ABR）功能下降在高血压靶器官损伤中起独立作用。为进一步研究ABR功能下降致器官损伤的可能机制,实验采用去窦弓神经（SAD）大鼠作为ABR受损的动物模型,分别测定清醒、自由活动状态下SAD及对照的假手术组大鼠24h动脉血压、心率、血压波动性（BPV）及心率波动性（HRV）。并采用放免法测定血浆、心脏和肾脏组织的血管紧张素Ⅱ（AngⅡ）含量。结果发现,SAD术后1周大鼠的24h平均收缩压（SBP）、舒张压（DBP）均显著高于对照组及术后18周的慢性期SAD大鼠。SAD术后18周,24h平均SBP、DBP及HR与假手术对照组均无显著差异;24h收缩压波动性（SBPV）和舒张压波动性（DBPV）均显著高于对照组大鼠。SAD大鼠术后1周的血浆、心脏和肾脏组织的AngⅡ含量及术后18周的血浆AngⅡ水平与对照组之间相比无显著差异。而在术后慢性期（18周）,SAD大鼠的心肌及肾组织AngⅡ含量显著高于假手术对照组大鼠。在术后18周时,接受慢性应激刺激的SAD大鼠,其血浆、心肌及肾组织中AngⅡ水平显著高于同处应激状态下的假手术对照组大鼠及未接受应激刺激的SAD大鼠。这些结果表明,SAD术后急性期血压增高,但在慢性期平均血压并无增高,仅BPV增高;慢性期心、肾组织内AngⅡ的分泌增加。在慢性期接受应激可致AngⅡ过度分泌,上述结果提示,BPV增高和心、肾组织AngⅡ含量升高与SAD大鼠发生心脏、肾脏等器官损害有关。     

Cardiac Impairment Evaluated by Transesophageal Echocardiography and Invasive Measurements in Rats Undergoing Sinoaortic Denervation

Background

Sympathetic hyperactivity may be related to left ventricular (LV) dysfunction and baro- and chemoreflex impairment in hypertension. However, cardiac function, regarding the association of hypertension and baroreflex dysfunction, has not been previously evaluated by transesophageal echocardiography (TEE) using intracardiac echocardiographic catheter.

Methods and Results

We evaluated exercise tests, baroreflex sensitivity and cardiovascular autonomic control, cardiac function, and biventricular invasive pressures in rats 10 weeks after sinoaortic denervation (SAD). The rats (n = 32) were divided into 4 groups: 16 Wistar (W) with (n = 8) or without SAD (n = 8) and 16 spontaneously hypertensive rats (SHR) with (n = 8) or without SAD (SHRSAD) (n = 8). Blood pressure (BP) and heart rate (HR) did not change between the groups with or without SAD; however, compared to W, SHR groups had higher BP levels and BP variability was increased. Exercise testing showed that SHR had better functional capacity compared to SAD and SHRSAD. Echocardiography showed left ventricular (LV) concentric hypertrophy; segmental systolic and diastolic biventricular dysfunction; indirect signals of pulmonary arterial hypertension, mostly evident in SHRSAD. The end-diastolic right ventricular (RV) pressure increased in all groups compared to W, and the end-diastolic LV pressure increased in SHR and SHRSAD groups compared to W, and in SHRSAD compared to SAD.

Conclusions

Our results suggest that baroreflex dysfunction impairs cardiac function, and increases pulmonary artery pressure, supporting a role for baroreflex dysfunction in the pathogenesis of hypertensive cardiac disease. Moreover, TEE is a useful and feasible noninvasive technique that allows the assessment of cardiac function, particularly RV indices in this model of cardiac disease.     

Cardiac-specific attenuation of natriuretic peptide A receptor activity accentuates adverse cardiac remodeling and mortality in response to pressure overload

Atrial (ANP) and brain (BNP) natriuretic peptides are hormones of myocardial cell origin. These hormones bind to the natriuretic peptide A receptor (NPRA) throughout the body, stimulating cGMP production and playing a key role in blood pressure control. Because NPRA receptors are present on cardiomyocytes, we hypothesized that natriuretic peptides may have direct autocrine or paracrine effects on cardiomyocytes or adjacent cardiac cells. Because both natriuretic peptides and NPRA gene expression are upregulated in states of pressure overload, we speculated that the effects of the natriuretic peptides on cardiac structure and function would be most apparent after pressure overload. To attenuate cardiomyocyte NPRA activity, transgenic mice with cardiac specific expression of a dominant-negative (DN-NPRA) mutation (HCAT D 893A) in the NPRA receptor were created. Cardiac structure and function were assessed (avertin anesthesia) in the absence and presence of pressure overload produced by suprarenal aortic banding. In the absence of pressure overload, basal and BNP-stimulated guanylyl cyclase activity assessed in cardiac membrane fractions was reduced. However, systolic blood pressure, myocardial cGMP, log plasma ANP levels, and ventricular structure and function were similar in wild-type (WT-NPRA) and DN-NPRA mice. In the presence of pressure overload, myocardial cGMP levels were reduced, and ventricular hypertrophy, fibrosis, filling pressures, and mortality were increased in DN-NPRA compared with WT-NPRA mice. In addition to their hormonal effects, endogenous natriuretic peptides exert physiologically relevant autocrine and paracrine effects via cardiomyocyte NPRA receptors to modulate cardiac hypertrophy and fibrosis in response to pressure overload.     

Inhibition of Angiotensin II-Induced Cardiac Hypertrophy and Associated Ventricular Arrhythmias by a p21 Activated Kinase 1 Bioactive Peptide

Cardiac hypertrophy increases the risk of morbidity and mortality of cardiovascular disease and thus inhibiting such hypertrophy is beneficial. In the present study, we explored the effect of a bioactive peptide (PAP) on angiotensin II (Ang II)-induced hypertrophy and associated ventricular arrhythmias in in vitro and in vivo models. PAP enhances p21 activated kinase 1 (Pak1) activity by increasing the level of phosphorylated Pak1 in cultured neonatal rat ventricular myocytes (NRVMs). Such PAP-induced Pak1 activation is associated with a significant reduction of Ang II-induced hypertrophy in NRVMs and C57BL/6 mice, in vitro and in vivo, respectively. Furthermore, PAP antagonizes ventricular arrhythmias associated with Ang II-induced hypertrophy in mice. Its antiarrhythmic effect is likely to be involved in multiple mechanisms to affect both substrate and trigger of ventricular arrhythmogenesis. Thus our results suggest that Pak1 activation achieved by specific bioactive peptide represents a potential novel therapeutic strategy for cardiac hypertrophy and associated ventricular arrhythmias.     

Long‐term administration of pyridostigmine attenuates pressure overload‐induced cardiac hypertrophy by inhibiting calcineurin signalling

Cardiac hypertrophy is associated with autonomic imbalance, characterized by enhanced sympathetic activity and withdrawal of parasympathetic control. Increased parasympathetic function improves ventricular performance. However, whether pyridostigmine, a reversible acetylcholinesterase inhibitor, can offset cardiac hypertrophy induced by pressure overload remains unclear. Hence, this study aimed to determine whether pyridostigmine can ameliorate pressure overload‐induced cardiac hypertrophy and identify the underlying mechanisms. Rats were subjected to either sham or constriction of abdominal aorta surgery and treated with or without pyridostigmine for 8 weeks. Vagal activity and cardiac function were determined using PowerLab. Cardiac hypertrophy was evaluated using various histological stains. Protein markers for cardiac hypertrophy were quantitated by Western blot and immunoprecipitation. Pressure overload resulted in a marked reduction in vagal discharge and a profound increase in cardiac hypertrophy index and cardiac dysfunction. Pyridostigmine increased the acetylcholine levels by inhibiting acetylcholinesterase in rats with pressure overload. Pyridostigmine significantly attenuated cardiac hypertrophy based on reduction in left ventricular weight/body weight, suppression of the levels of atrial natriuretic peptide, brain natriuretic peptide and β‐myosin heavy chain, and a reduction in cardiac fibrosis. These effects were accompanied by marked improvement of cardiac function. Additionally, pyridostigmine inhibited the CaN/NFAT3/GATA4 pathway and suppressed Orai1/STIM1 complex formation. In conclusion, pressure overload resulted in cardiac hypertrophy, cardiac dysfunction and a significant reduction in vagal discharge. Pyridostigmine attenuated cardiac hypertrophy and improved cardiac function, which was related to improved cholinergic transmission efficiency (decreased acetylcholinesterase and increased acetylcholine), inhibition of the CaN/NFAT3/GATA4 pathway and suppression of the interaction of Orai1/STIM1.     

Cardiac remodeling caused by transgenic overexpression of a corn Rac gene

Rac1-GTPase activation plays a key role in the development and progression of cardiac remodeling. Therefore, we engineered a transgenic mouse model by overexpressing cDNA of a constitutively active form of Zea maize Rac gene (ZmRacD) specifically in the hearts of FVB/N mice. Echocardiography and MRI analyses showed cardiac hypertrophy in old transgenic mice, as evidenced by increased left ventricular (LV) mass and LV mass-to-body weight ratio, which are associated with relative ventricular chamber dilation and systolic dysfunction. LV hypertrophy in the hearts of old transgenic mice was further confirmed by an increased heart weight-to-body weight ratio and histopathology analysis. The cardiac remodeling in old transgenic mice was coupled with increased myocardial Rac-GTPase activity (372%) and ROS production (462%). There were also increases in α(1)-integrin (224%) and β(1)-integrin (240%) expression. This led to the activation of hypertrophic signaling pathways, e.g., ERK1/2 (295%) and JNK (223%). Pravastatin treatment led to inhibition of Rac-GTPase activity and integrin signaling. Interestingly, activation of ZmRacD expression with thyroxin led to cardiac dilation and systolic dysfunction in adult transgenic mice within 2 wk. In conclusion, this is the first study to show the conservation of Rho/Rac proteins between plant and animal kingdoms in vivo. Additionally, ZmRacD is a novel transgenic model that gradually develops a cardiac phenotype with aging. Furthermore, the shift from cardiac hypertrophy to dilated hearts via thyroxin treatment will provide us with an excellent system to study the temporal changes in cardiac signaling from adaptive to maladaptive hypertrophy and heart failure.     

Effect of pravastatin on left ventricular mass in the two-kidney, one-clip hypertensive rats

We have demonstrated that myocardial ATP-sensitive potassium (K(ATP)) channels are implicated in the development of cardiac hypertrophy in hyperlipidemic rabbits. We investigated the effect of pravastatin on development of ventricular hypertrophy in male normolipidemic Wistar rats with two-kidney, one-clip (2K1C) hypertension and whether the attenuated hypertrophic effect was via activation of K(ATP) channels. Twenty-four hours after the left renal artery was clipped, rats were treated with one of the following therapies for 8 wk: vehicle, nicorandil (an agonist of K(ATP) channels), pravastatin, glibenclamide (an antagonist of K(ATP) channels), hydralazine, nicorandil plus glibenclamide, or pravastatin plus glibenclamide. Systolic blood pressure, relative left ventricular (LV) weight, and cardiomyocyte sizes significantly increased in vehicle-treated 2K1C rats compared with those in sham-operated rats. Treatment with either nicorandil or pravastatin significantly attenuated LV hypertrophy/body weight compared with the vehicle, which was further confirmed by downregulation of LV atrial natriuretic peptide mRNA. Nicorandil-induced effects were abolished by administering glibenclamide. Similarly, pravastatin-induced beneficial effects were reversed by the addition of glibenclamide, implicating K(ATP) channels as the relevant target. A dissociation between the effects of blood pressure and cardiac structure was noted because pravastatin and hydralazine reduced arterial pressure similarly. These results suggest a crucial role of cardiac K(ATP) channel system in the development of ventricular hypertrophy in the 2K1C hypertensive rats. Pravastatin is endowed with cardiac antihypertrophic properties probably through activation of K(ATP) channels, independent of lipid and hemodynamic changes.     

Local atrial natriuretic peptide signaling prevents hypertensive cardiac hypertrophy in endothelial nitric-oxide synthase-deficient mice

The crucial functions of atrial natriuretic peptide (ANP) and endothelial nitric oxide/NO in the regulation of arterial blood pressure have been emphasized by the hypertensive phenotype of mice with systemic inactivation of either the guanylyl cyclase-A receptor for ANP (GC-A-/-) or endothelial nitric-oxide synthase (eNOS-/-). Intriguingly, similar levels of arterial hypertension are accompanied by marked cardiac hypertrophy in GC-A-/-, but not in eNOS-/-, mice, suggesting that changes in local pathways regulating cardiac growth accelerate cardiac hypertrophy in the former and protect the heart of the latter. Our recent observations in mice with conditional, cardiomyocyte-restricted GC-A deletion demonstrated that ANP locally inhibits cardiomyocyte growth. Abolition of these local, protective effects may enhance the cardiac hypertrophic response of GC-A-/- mice to persistent increases in hemodynamic load. Notably, eNOS-/- mice exhibit markedly increased cardiac ANP levels, suggesting that increased activation of cardiac GC-A can prevent hypertensive heart disease. To test this hypothesis, we generated mice with systemic inactivation of eNOS and cardiomyocyte-restricted deletion of GC-A by crossing eNOS-/- and cardiomyocyte-restricted GC-A-deficient mice. Cardiac deletion of GC-A did not affect arterial hypertension but significantly exacerbated cardiac hypertrophy and fibrosis in eNOS-/- mice. This was accompanied by marked cardiac activation of both the mitogen-activated protein kinase (MAPK) ERK 1/2 and the phosphatase calcineurin. Our observations suggest that local ANP/GC-A/cyclic GMP signaling counter-regulates MAPK/ERK- and calcineurin/nuclear factor of activated T cells-dependent pathways of cardiac myocyte growth in hypertensive eNOS-/- mice.     

A-Kinase Anchoring Protein Lbc Coordinates a p38 Activating Signaling Complex Controlling Compensatory Cardiac Hypertrophy

In response to stress, the heart undergoes a remodeling process associated with cardiac hypertrophy that eventually leads to heart failure. A-kinase anchoring proteins (AKAPs) have been shown to coordinate numerous prohypertrophic signaling pathways in cultured cardiomyocytes. However, it remains to be established whether AKAP-based signaling complexes control cardiac hypertrophy and remodeling in vivo. In the current study, we show that AKAP-Lbc assembles a signaling complex composed of the kinases PKN, MLTK, MKK3, and p38α that mediates the activation of p38 in cardiomyocytes in response to stress signals. To address the role of this complex in cardiac remodeling, we generated transgenic mice displaying cardiomyocyte-specific overexpression of a molecular inhibitor of the interaction between AKAP-Lbc and the p38-activating module. Our results indicate that disruption of the AKAP-Lbc/p38 signaling complex inhibits compensatory cardiomyocyte hypertrophy in response to aortic banding-induced pressure overload and promotes early cardiac dysfunction associated with increased myocardial apoptosis, stress gene activation, and ventricular dilation. Attenuation of hypertrophy results from a reduced protein synthesis capacity, as indicated by decreased phosphorylation of 4E-binding protein 1 and ribosomal protein S6. These results indicate that AKAP-Lbc enhances p38-mediated hypertrophic signaling in the heart in response to abrupt increases in the afterload.     

Altered myocardial gene expression reveals possible maladaptive processes in heterozygous and homozygous cardiac myosin-binding protein C knockout mice

Familial hypertrophic cardiomyopathy (FHC) is an autosomal dominant disease characterized by left ventricular hypertrophy (LVH) predominantly affecting the interventricular septum. Cardiac myosin-binding protein C (cMyBP-C) mutations are common causes of FHC. Gene expression profiling was performed in left ventricles of 9-week-old wild-type mice, heterozygous cMyBP-C KO mice displaying asymmetric septal hypertrophy, and homozygous mice developing eccentric LVH. Knocking out one or two cMyBP-C genes leads primarily to gene expression changes indicating an increased energy demand, activation of the JNK and p38 parts of the MAPK pathway and deactivation of the ERK part, and induction of apoptosis. Altered gene expression for processes related to cardiac structure, contractile proteins, and protein turnover was also identified. Many of the changes were more pronounced in the homozygous KO mice. These alterations point to physiological and pathological adaptations in the prehypertrophic heterozygous KO mice and the hypertrophic homozygous mice.     

Zerumbone prevents pressure overload-induced left ventricular systolic dysfunction by inhibiting cardiac hypertrophy and fibrosis

BackgroundCardiac hypertrophy and fibrosis are hallmarks of cardiac remodeling and are involved functionally in the development of heart failure (HF). However, it is unknown whether Zerumbone (Zer) prevents left ventricular (LV) systolic dysfunction by inhibiting cardiac hypertrophy and fibrosis.PurposeThis study investigated the effect of Zer on cardiac hypertrophy and fibrosis in vitro and in vivo.Study Design/methodsIn primary cultured cardiac cells from neonatal rats, the effect of Zer on phenylephrine (PE)-induced hypertrophic responses and transforming growth factor beta (TGF-β)-induced fibrotic responses was observed. To determine whether Zer prevents the development of pressure overload-induced HF in vivo, a transverse aortic constriction (TAC) mouse model was utilized. Cardiac function was evaluated by echocardiography. The changes of cardiomyocyte surface area were observed using immunofluorescence staining and histological analysis (HE and WGA staining). Collagen synthesis and fibrosis formation were measured by scintillation counter and picrosirius staining, respectively. The total mRNA levels of genes associated with hypertrophy (ANF and BNP) and fibrosis (Postn and α-SMA) were measured by qRT-PCR. The protein expressions (Akt and α-SMA) were assessed by western blotting.ResultsZer significantly suppressed PE-induced increase in cell size, mRNA levels of ANF and BNP, and Akt phosphorylation in cardiomyocytes. The TGF-β-induced increase in proline incorporation, mRNA levels of Postn and α-SMA, and protein expression of α-SMA were decreased by Zer in cultured cardiac fibroblasts. In the TAC male C57BL/6 mice, echocardiography results demonstrated that Zer improved cardiac function by increasing LV fractional shortening and reducing LV wall thickness compared with the vehicle group. ZER significantly reduced the level of phosphorylated Akt both in cultured cardiomyocytes treated with PE and in the hearts of TAC. Finally, Zer inhibited the pressure overload-induced cardiac hypertrophy and cardiac fibrosis.ConclusionZer ameliorates pressure overload-induced LV dysfunction, at least in part by suppressing both cardiac hypertrophy and fibrosis.     

A neutralizing leptin receptor antibody mitigates hypertrophy and hemodynamic dysfunction in the postinfarcted rat heart

The 16 kDa adipokine leptin has been shown to exert direct hypertrophic effects on cultured cardiomyocytes although its role as an endogenous contributor to postinfarction remodeling and heart failure has not been determined. We therefore investigated the effect of leptin receptor blockade in vivo on hemodynamic function and cardiac hypertrophy following coronary artery ligation (CAL). Cardiac function and biochemical parameters were measured in rats subjected to 7 or 28 days of left main CAL in the presence and absence of a leptin receptor antibody. Animals subjected to an identical treatment in which the artery was not tied served as sham-operated controls. CAL produced myocardial hypertrophy, which was most pronounced 28 days postinfarction as demonstrated by increases in both left ventricular weight-to-body weight ratio and atrial natriuretic peptide gene expression, both of which were abrogated by leptin receptor antagonism. Leptin receptor blockade also significantly improved left ventricular systolic function, attenuated the increased left ventricular end-diastolic pressure, and reduced the expression of genes associated with extracellular matrix remodeling 28 days following CAL. In conclusion, the ability of a leptin receptor-neutralizing antibody to improve cardiac function offers evidence that endogenous leptin contributes to cardiac hypertrophy following CAL. The possibility exists that targeting the myocardial leptin receptor represents a viable and novel approach toward attenuating postinfarction remodeling.     

Paeoniflorin attenuates pressure overload-induced cardiac remodeling via inhibition of TGFβ/Smads and NF-κB pathways

Cardiac remodeling is a key determinant in the clinical course and outcome of heart failure and characterized by cardiac hypertrophy, fibrosis, cardiomyocyte apoptosis and inflammation. The anti-inflammatory, anti-apoptotic and anti-fibrotic effects of paeoniflorin have been identified in various types of tissue and cells. However, the role of paeoniflorin in cardiac remodeling remains unclear. We performed aortic banding (AB) in mice to induce a cardiac remodeling model in response to pressure overload. Paeoniflorin (20 mg/kg) was administered by daily intraperitoneal (i.p.) injection. Paeoniflorin treatment promoted the survival rate and improved cardiac function of mice at 8 weeks post surgery. AB-induced cardiac hypertrophy, as assessed by heart weight, gross heart, HE and WGA staining, cross-sectional area of cardiomyocyte and mRNA expresssion of hypertrophic makers, was attenuated by paeoniflorin. Paeoniflorin also inhibited collagen deposition, expression of TGFβ, CTGF, collagen Iα and collagen IIIα, and phosphorylation of Smad2 and Smad3 in the heart exposed to pressure overload. Cardiomyocyte apoptosis and induction of Bax and cleaved caspase3 in response to AB were suppressed by paeoniflorin. Furthermore, paeoniflorin decreased the quantity of CD68+ cells, protein levels of TNF-α and IL-1β, and phosphorylation of IκBα and NFκB-p65 in the heart after AB. In conclusion, paeoniflorin attenuated cardiac hypertrophy, fibrosis, apoptosis and inflammation, and improved left ventricular function in pressure overloaded mice. The cardioprotective effect of paeoniflorin is associated with the inhibition of TGFβ/Smads and NF-κB pathways.     

Senescence marker protein 30 inhibits angiotensin II-induced cardiac hypertrophy and diastolic dysfunction

Background and objective

Senescence marker protein 30 (SMP30) is assumed to behave as an anti-aging factor. Recently, we have demonstrated that deficiency of SMP30 exacerbates angiotensin II-induced cardiac hypertrophy, dysfunction and remodeling, suggesting that SMP30 may have a protective role in the heart. Thus, this study aimed to test the hypothesis that up-regulation of SMP30 inhibits cardiac adverse remodeling in response to angiotensin II.

Methods

We generated transgenic mice with cardiac-specific overexpression of SMP30 gene using α-myosin heavy chain promoter. Transgenic mice and wild-type littermate mice were subjected to continuous angiotensin II infusion (800 ng/kg/min).

Results

After 14 days, heart weight and left ventricular weight were lower in transgenic mice than in wild-type mice, although blood pressure was similarly elevated during angiotensin II infusion. Cardiac hypertrophy and diastolic dysfunction in response to angiotensin II were prevented in transgenic mice compared with wild-type mice. The degree of cardiac fibrosis by angiotensin II was lower in transgenic mice than in wild-type mice. Angiotensin II-induced generation of superoxide and subsequent cellular senescence were attenuated in transgenic mouse hearts compared with wild-type mice.

Conclusions

Cardiac-specific overexpression of SMP30 inhibited angiotensin II-induced cardiac adverse remodeling. SMP30 has a cardio-protective role with anti-oxidative and anti-aging effects and could be a novel therapeutic target to prevent cardiac hypertrophy and remodeling due to hypertension.     

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.     

p38alpha mitogen-activated protein kinase plays a critical role in cardiomyocyte survival but not in cardiac hypertrophic growth in response to pressure overload

The molecular mechanism for the transition from cardiac hypertrophy, an adaptive response to biomechanical stress, to heart failure is poorly understood. The mitogen-activated protein kinase p38alpha is a key component of stress response pathways in various types of cells. In this study, we attempted to explore the in vivo physiological functions of p38alpha in hearts. First, we generated mice with floxed p38alpha alleles and crossbred them with mice expressing the Cre recombinase under the control of the alpha-myosin heavy-chain promoter to obtain cardiac-specific p38alpha knockout mice. These cardiac-specific p38alpha knockout mice were born normally, developed to adulthood, were fertile, exhibited a normal life span, and displayed normal global cardiac structure and function. In response to pressure overload to the left ventricle, they developed significant levels of cardiac hypertrophy, as seen in controls, but also developed cardiac dysfunction and heart dilatation. This abnormal response to pressure overload was accompanied by massive cardiac fibrosis and the appearance of apoptotic cardiomyocytes. These results demonstrate that p38alpha plays a critical role in the cardiomyocyte survival pathway in response to pressure overload, while cardiac hypertrophic growth is unaffected despite its dramatic down-regulation.     

Cardiac myocyte-specific ablation of follistatin-like 3 attenuates stress-induced myocardial hypertrophy

Transforming growth factor-β family cytokines have diverse actions in the maintenance of cardiac homeostasis. Follistatin-like 3 (Fstl3) is an extracellular regulator of certain TGF-β family members, including activin A. The aim of this study was to examine the role of Fstl3 in cardiac hypertrophy. Cardiac myocyte-specific Fstl3 knock-out (KO) mice and control mice were subjected to pressure overload induced by transverse aortic constriction (TAC). Cardiac hypertrophy was assessed by echocardiography and histological and biochemical methods. KO mice showed reduced cardiac hypertrophy, pulmonary congestion, concentric LV wall thickness, LV dilatation, and LV systolic dysfunction after TAC compared with control mice. KO mice displayed attenuated increases in cardiomyocyte cell surface area and interstitial fibrosis following pressure overload. Although activin A was similarly up-regulated in KO and control mice after TAC, a significant increase in Smad2 phosphorylation only occurred in KO mice. Knockdown of Fstl3 in cultured cardiomyocytes inhibited PE-induced cardiac hypertrophy. Conversely, adenovirus-mediated Fstl3 overexpression blocked the inhibitory action of activin A on hypertrophy and Smad2 activation. Transduction with Smad7, a negative regulator of Smad2 signaling, blocked the antihypertrophic actions of activin A stimulation or Fstl3 ablation. These findings identify Fstl3 as a stress-induced regulator of hypertrophy that controls myocyte size via regulation of Smad signaling.     

Cardiopulmonary resuscitation in a rat model of chronic myocardial ischemia.

Our group has developed a rat model of cardiac arrest and cardiopulmonary resuscitation (CPR). However, the current rat model uses healthy adult animals. In an effort to more closely reproduce the event of cardiac arrest and CPR in humans with chronic coronary disease, a rat model of coronary artery constriction was investigated during cardiac arrest and CPR. Left coronary artery constriction was induced surgically in anesthetized, mechanically ventilated Sprague-Dawley rats. Echocardiography was used to measure global cardiac performance before surgery and 4 wk postsurgery. Coronary constriction provoked significant decreases in ejection fraction, increases in left ventricular end-diastolic volume, and increases left ventricular end-systolic volume at 4 wk postintervention, just before induction of ventricular fibrillation (VF). After 6 min of untreated VF, CPR was initiated on three groups: 1) coronary artery constriction group, 2) sham-operated group, and 3) control group (without preceding surgery). Defibrillation was attempted after 6 min of CPR. All the animals were resuscitated. Postresuscitation myocardial function as measured by rate of left ventricular pressure increase at 40 mmHg and the rate of left ventricular pressure decline was more significantly impaired and left ventricular end-diastolic pressure was greater in the coronary artery constriction group compared with the sham-operated group and the control group. There were no differences in the total shock energy required for successful resuscitation and duration of survival among the groups. In summary, this rat model of chronic myocardial ischemia was associated with ventricular remodeling and left ventricular myocardial dysfunction 4 wk postintervention and subsequently with severe postresuscitation myocardial dysfunction. This model would suggest further clinically relevant investigation on cardiac arrest and CPR.