"iDoctor – Medical Blog"

Publication year: 2011
Source: Journal of Molecular and Cellular Cardiology, Available online 29 December 2011

Xu Wang, Lei Cui, Jacob Joseph, Bingbing Jiang, David Pimentel, …

Elevated plasma homocysteine (Hcy) is a risk factor for cardiovascular disease. While Hcy has been shown to promote endothelial dysfunction by decreasing the bioavailability of nitric oxide and increasing oxidative stress in the vasculature, the effects of Hcy on cardiomyocytes remain less understood. In this study we explored the effects of hyperhomocysteinemia (HHcy) on myocardial functionex vivoand examined the direct effects of Hcy on cardiomyocyte function and survivalin vitro. Studies with isolated hearts from wild type and HHcy mice (heterozygous cystathionine-beta synthase deficient mice) demonstrated that HHcy mouse hearts had more severely impaired cardiac relaxation and contractile function and increased cell death following ischemia reperfusion (I/R). In isolated cultured adult rat ventricular myocytes, exposure to Hcy for 24 hours impaired cardiomyocyte contractility in a concentration-dependent manner, and promoted apoptosis as revealed by terminal dUTP nick-end labeling and cleaved caspase-3 immunoblotting. These effects were associated with activation of p38 MAPK, decreased expression of thioredoxin (TRX) protein, and increased production of reactive oxygen species (ROS). Inhibition of p38 MAPK by the selective inhibitor SB203580 (5 μM) prevented all of these Hcy-induced changes. Furthermore, adenovirus-mediated overexpression of TRX in cardiomyocytes significantly attenuated Hcy-induced ROS generation, apoptosis, and impairment of myocyte contractility. Thus, Hcy may increase the risk for CVD not only by causing endothelial dysfunction, but also by directly exerting detrimental effects on cardiomyocytes.

Highlights

► Effects of hyperhomocysteinemia on myocardium are not well understood. ► Ischemia-reperfusion caused worse injury in hyperhomocysteinemic mice. ► Homocysteine impaired contractility and promoted apoptosis in cardiomyocytes. ► Mechanism is via activation of p38MAPK and increase in oxidant stress. ► Overexpression of thioredoxin decreased oxidant stress and rescued cardiomyocytes.

Publication year: 2011
Source: Journal of Molecular and Cellular Cardiology, Available online 22 December 2011

Vedat Tiyerili, Cornelius F.H. Mueller, Ulrich M. Becher, Thomas Czech, Martin van Eickels, …

AT1 receptor blockers (ARB) and in part ACE inhibitors (ACI) potentially exert beneficial effects on atherogenesis independent of AT1 receptor inhibition. These pleiotropic effects might be related to angiotensin II mediated activation of the AT2 receptor. To analyze this hypothesis we investigated the development of atherosclerosis and the role of ACIs and ARBs in Apolipoprotein E-deficient (ApoE) mice and in ApoE/AT1A receptor double knockout mice (ApoE/AT1A). ApoEmice and ApoE/AT1Amice were fed cholesterol-rich diet for 7 weeks. Vascular oxidative stress, endothelial dysfunction, and atherosclerotic lesion formation were evident in ApoEmice, but were markedly reduced in ApoE/AT1Amice. Concomitant treatment of ApoE/AT1Amice with either telmisartan or ramipril had no additional effect on blood pressure, vascular oxidative stress, AT2 receptor expression, and endothelial function. Remarkably, atherosclerotic lesion formation was increased in ramipril treated ApoE/AT1Amice compared to untreated ApoE/AT1Amice whereas pharmacological AT1 receptor inhibition with Telmisartan had no additional effect on atherogenesis. Moreover, chronic AT2 receptor inhibition with PD123,319 significantly increased plaque development in ApoE/AT1Amice. In additional experiments, direct AT2 receptor stimulation reduced atherogenesis in ApoE/AT1Amice. Taken together, our data demonstrate a relevant antiatherosclerotic role of the AT2 receptor in atherosclerotic mice and provide novel insight in RAS-physiology.

Highlights

► Atherogenesis was increased in ramipril treated ApoE−/−/AT1A−/− mice. ► PD123,319 increased plaque development in ApoE−/−/AT1A−/− mice. ► AT2 receptor confers atheroprotective effects when AT1 receptor action is inhibited. ► Relevant antiatherosclerotic role of the AT2 receptor in atherosclerotic mice.

Publication year: 2011
Source: Journal of Molecular and Cellular Cardiology, Available online 22 December 2011

Lorena A. Vargas, Bernardo V. Alvarez

Two AE3 transcripts, full-length (AE3fl) and cardiac (AE3c) are expressed in the heart. AE3 catalyzes electroneutral Cl/HCO3exchange across cardiomyocyte sarcolemma. AE proteins associate with carbonic anhydrases (CA), including CAII and CAIV, forming a HCO3transport metabolon (BTM),increasingHCO3fluxes and regulating cardiomyocytes pH. CAXIV, which is also expressed in the heart’s sarcolemma, is a transmembrane enzyme with an extracellular catalytic domain. Herein, AE3/CAXIV physical association was examined by coimmunoprecipitation using rodent heart lysates. CAXIV immunoprecipitated with anti-AE3 antibody and both AE3fl and AE3c were reciprocally immunoprecipitated using anti-CAXIV antibody, indicating AE3fl-AE3c/CAXIV interaction in the myocardium. Coimmunoprecipitation experiments on heart lysates from a mouse with targeted disruption of theae3gene, failed to pull down AE3 with the CAXIV antibody. Confocal images demonstrated colocalization of CAXIV and AE3 in mouse ventricularmyocytes. Functional association of AE3fl and CAXIV was examined in isolated hypertrophic rat cardiomyocytes, using fluorescence measurements of BCECF to monitor cytosolic pH. Hypertrophic cardiomyocytes of spontaneously hypertensive rats (SHR) presented elevated myocardial AE-mediated Cl/HCO3exchange activity (JHCO3-mM.min) compared to normal (Wistar) rats (7.5 ± 1.3, n = 4versus2.9 ± 0.1, n = 6, respectively).AE3fl, AE3c,CAII, CAIV, and CAIX protein expression were similar in SHR and Wistar rat heart. However, immunoblots revealed a twofold increase of CAXIV protein expression in the SHR myocardium compared to normal hearts (n = 11). Furthermore, the CA-inhibitor, benzolamide, neutralized the stimulatory effect of extracellular CA on AE3 transport activity (3.7 ± 1.5, n = 3), normalizing AE3-dependent HCO3fluxes in SHR. CAXIV/AE3 interaction constitutes an extracellular component of a BTM which potentiates AE3-mediated HCO3transport in the heart. Increased CAXIV expression and consequent AE3/CAXIV complex formation would render AE3 hyperactive in the SHR heart.

Highlights

► AE3 Cl/HCO3exchanger interacts with the CAXIV enzyme in the heart. ► CAXIV bound to and enhanced AE3 transport, establishing a physical/functional coupling. ► Hypertrophic rat hearts showed elevated CAXIV protein expression. ► AE-mediated HCO3fluxes increased in the hypertrophic myocardium compared to normal. ► AE3/CAXIV complex formation would render AE3 hyperactive in the hypertrophic heart.

Publication year: 2012
Source: Journal of Molecular and Cellular Cardiology, Volume 52, Issue 1, January 2012, Pages i

[No author name available]

Publication year: 2011
Source: Journal of Molecular and Cellular Cardiology, Available online 20 December 2011

Ku-Chung Chen, Yi-Chu Liao, I-Chung Hsieh, Yung-Song Wang, Ching-Yu Hu, …

MicroRNA-29b has been reported to epigenetically regulate proatherogenic genes in response to oxLDL. Since transcription factors and epigenetic regulations are important mechanisms to regulate gene expression, we investigated whether these mechanisms are involved in oxLDL-induced microRNA-29b upregulation. First, we confirmed microRNA-29b expression was increased in the aorta of mice fed with a high-fat diet, which was consistent with our previous in vitro findings. Next, we found that oxLDL only activated the microRNA-29b-1/microRNA-29a cluster gene on chromosome 7 but not the other distinct microRNA-29b gene located on chromosome 1. Using the promoter reporter assay and chromatin immunoprecipitation, activator protein-1 (AP-1) was shown to bind to the microRNA-29b-1 promoter. We further identified the signaling pathway of LOX-1/Ca/ROS/ERK/c-Fos was involved in oxLDL-mediated microRNA-29b overexpression after treating with the MAPTAM (Cachelator), NAC (ROS scavenger), U0126 (ERK inhibitor) and c-Fos (one of the AP-1 proteins) shRNA, respectively. To investigate epigenetic regulations, we found microRNA-29b promoter contained no CpG islands for DNA methylation. Therefore we investigated whether histone modifications influence microRNA-29b promoter activity. We showed that down-regulation of HDAC1 and the modifications on histone 3 lysine 4 (H3K4) and H3K9 significantly affected microRNA-29b expression. Furthermore, knockdown of c-Fos expression attenuated the effect of oxLDL-induced histone modifications on the microRNA-29b gene expression. Taken together, our data suggest that both transcription factor activation and histone modifications are important regulatory mechanisms of oxLDL-induced atherogenic process. This article is part of a Special Issue entitled OxLDL causes both epigenetic modification and signaling regulation on the microRNA-29b gene: Novel mechanisms for cardiovascular diseases.

Highlights

► In this study we studied mechanisms of oxLDL-upregulated miR-29b. ► OxLDL activated miR-29b from microRNA-29b-1/microRNA-29a cluster gene. ► The LOX-1/Ca/ROS/ERK/c-Fos involved in oxLDL-mediated miR-29b overexpression. ► OxLDL-downregulated HDAC1 affected miR-29b expression. ► OxLDL-mediated histone 3 lysine 4 (H3K4) and H3K9 regulated miR-29b expression.

Publication year: 2011
Source: Journal of Molecular and Cellular Cardiology, Available online 19 December 2011

Guangdong Yang, Hongzhu Li, Guanghua Tang, Lingyun Wu, Kexin Zhao, …

The physiological and pathological roles of hydrogen sulfide (H2S) in the regulation of cardiovacular functions have been recogenized. Vascular smooth muscle cells (SMCs) express cystathionine gamma-lyase (CSE) and produce significant amount of H2S. Although growing evidence demonstated the anti-atherosclerotic effect of H2S, less is known about the contribution of the endogenous CSE/H2S pathway to the development of vascular remodeling. This study investigated the roles of the CSE/H2S pathway on SMC migration and neoimtimal formation by using CSE knockout (KO) mice. SMCs and aortic explants isolated from CSE KO mice exhibited more migration and outgrowth compared with that from wild-type (WT) mice, and exogenously applied NaHS (a H2S donor) at 100 μM significantly inhibited SMC migration and outgrowth. SMCs became more elongated and spread in the absence of CSE, and fibronectin significantly stimulated adhesion and migration of SMCs from CSE KO mice (KO-SMCs) in comparison with SMCs from WT mice (WT-SMCs). The expressions of α5- and β1-integrins were significantly higher in KO-SMCs, and functional blocking of α5β1-integrin effectively abrogated KO-SMC migration. CSE deficiency also enhanced matrix metalloproteinase-2 (MMP-2) expression, and the selective blocking of MMP-2 decreased KO-SMC migration. NaHS treatment decreased both the expressions of α5- and β1-integrins and MMP-2. We further found that the expressions of α5- and β1-integrins as well as MMP-2, were stimulated by fibronectin, and that the blockage of α5β1-integrin reduced but overexpression of α5β1-integrin induced MMP-2 expression in both WT-SMCs and KO-SMCs. We also noticed that CSE deficiency in mice led to increased neointima formation in carotid arteries 4 weeks after ligation, which were attenuated by NaHS administration. In conclusion, inhibition of SMC migration by H2S may be a novel target for the treatment of vascular occlusive disorder.

Highlights

► Cystathionine gamma-lyase deficiency induces smooth muscle cell migration. ► H2S inhibits the expressions of α5β1-integrin and MMP-2. ► Cystathionine gamma-lyase induces neointima formation in mice. ► H2S attenuates neointima formation in mice.

Publication year: 2011
Source: Journal of Molecular and Cellular Cardiology, Available online 19 December 2011

William M. Chilian, Marc S. Penn, Yuh Fen Pung, Feng Dong, Maritza Mayorga, …

The coronary collateral circulation is critically important as an adaptation of the heart to prevent the damage from ischemic insults. In their native state, collaterals in the heart would be classified as part of the microcirculation, existing as arterial-arterial anastomotic connections in the range of 30 to 100 μM in diameter. However, these vessels also show a propensity to remodel into components of the macrocirculation and can become arteries larger than a 1000 μM in diameter. This process of outward remodelling is critically important in the adaptation of the heart to ischemia because the resistance to blood flow is inversely related to the fourth power of the diameter of the vessel. Thus, an expansion of a vessel from 100 to 1000 μM would reduce resistance (in this part of the circuit) to a negligible amount and enable delivery of flow to the region at risk. Our goal in this review is to highlight the voids in understanding this adaptation to ischemia—the growth of the coronary collateral circulation. In doing so we discuss the controversies and unknown aspects of the causal factors that stimulate growth of the collateral circulation, the role of genetics, and the role of endogenous stem and progenitor cells in the context of the normal, physiological situation and under more pathological conditions of ischemic heart disease or with some of the underlying risk factors, e.g., diabetes. The major conclusion of this review is that there are many gaps in our knowledge of coronary collateral growth and this knowledge is critical before the potential of stimulating collateralization in the hearts of patients can be realized. This article is part of a Special Issue entitled Coronary Blood Flow SI Review Article.

Highlights

► This review focuses on what is not known about coronary collateral growth. ► This review raises fundamental questions about the regulation of coronary collateral growth. ► We present a schematic that we hope will facilitate the goal of therapeutic collateral growth.

Publication year: 2011
Source: Journal of Molecular and Cellular Cardiology, Available online 16 December 2011

Jonathan D. Moreno, Colleen E. Clancy

A pathological increase in the late component of the cardiac Nacurrent, INaL, has been linked to disease manifestation in inherited and acquired cardiac diseases including the long QT variant 3 (LQT3) syndrome and heart failure. Disruption in INaLleads to action potential prolongation, disruption of normal cellular repolarization, development of arrhythmia triggers, and propensity to ventricular arrhythmia. Attempts to treat arrhythmogenic sequelae from inherited and acquired syndromes pharmacologically with common Nachannel blockers (e.g. flecainide, lidocaine, and amiodarone) have been largely unsuccessful. This is due to drug toxicity and the failure of most current drugs to discriminate between the peak current component, chiefly responsible for single cell excitability and propagation in coupled tissue, and the late component (INaL) of the Nacurrent. Although small in magnitude as compared to the peak Nacurrent (~ 1 – 3%), INaLalters action potential properties and increases Naloading in cardiac cells. With the increasing recognition that multiple cardiac pathological conditions share phenotypic manifestations of INaLupregulation, there has been renewed interest in specific pharmacological inhibition of INa.The novel antianginal agent ranolazine, which shows a marked selectivity for late versus peak Nacurrent, may represent a novel drug archetype for targeted reduction of INaL. This article aims to review common pathophysiological mechanisms leading to enhanced INaLin LQT3 and heart failure as prototypical disease conditions. Also reviewed are promising therapeutic strategies tailored to alter the molecular mechanisms underlying INamediated arrhythmia triggers.

Highlights

► INaLcan disrupt cellular repolarization and increase propensity to ventricular arrhythmia. ► Although small compared to peak Nacurrent, INaLincreases Naloading in cardiac cells. ► Multiple cardiac pathological conditions share phenotypic manifestations of INaLupregulation. ► Specific pharmacological inhibition of INais desired

Publication year: 2011
Source: Journal of Molecular and Cellular Cardiology, Available online 14 December 2011

Seung Hee Lee, Jooyeon Kim, Joo Young Ryu, Suho Lee, Dong Kwon Yang, …

Despite its significant clinical implications, physiological hypertrophy remains poorly understood. In this study, the transcription coactivator Eya2 was shown to be up-regulated during physiological hypertrophy. Transgene- or adenovirus-mediated overexpression of Eya2 led to up-regulation of mTOR, a critical mediator of physiological hypertrophy. Luciferase reporter and chromatin immunoprecipitation assays revealed that Eya2 directly binds to and activates mTOR expression. The phosphorylation of mTOR downstream molecules was significantly enhanced in Eya2 transgenic (TG) hearts, implying that the Eya2-mediated induction of mTOR expression leads to an elevated mTOR activity. The transcription factor Six1 was also up-regulated during physiological hypertrophy and formed a complex with Eya2. Luciferase reporter and electrophoretic mobility shift assays revealed that the Eya2-Six1 complex binds to and enhances the expression of mTOR in a synergistic manner. Under pressure overload, Eya2 transgenic hearts developed hypertrophy which exhibited important molecular signatures of physiological hypertrophy, as assessed by gene expression profiling and measurements of expression levels of physiological hypertrophy-related genes by quantitative (q) RT-PCR. Examination of heart sections under electron microscopy revealed that the mitochondrial integrity remained largely intact in Eya2 transgenic mice, but not in wild-type littermates, under pressure overload. This finding was confirmed by measurements of mitochondrial DNA contents and the expression levels of mitochondrial function-related genes by qRT-PCR. These data suggest that Eya2 in a physical complex with Six1 plays a critical role in physiological hypertrophy. The cardioprotective effect of Eya2 appears to be due, at least in part, to its preservation of mitochondrial integrity upon pressure overload.

Highlights

► Eya2 directly regulates the expression of mTOR during physiological hypertrophy. ► Eya2 and Six1 synergistically up-regulate mTOR expression. ► Eya2 TG exhibits characteristics of physiological cardiac hypertrophy. ► Mitochondrial integrity is preserved in Eya2 TG hearts under pressure overload. ► Activation of Eya2 and Six1 transcriptional complex is cardioprotective.

Publication year: 2011
Source: Journal of Molecular and Cellular Cardiology, Available online 11 December 2011

Derk Frank, Johanne Gantenberg, Inka Boomgaarden, Christian Kuhn, Rainer Will, …

Excessive stress, e.g. due to biomechanical overload or ischemia/reperfusion is a potent inductor of cardiomyocyte apoptosis, which contributes to maladaptive remodeling. Despite substantial progress in the understanding of the molecular pathophysiology, many components of the signaling pathways underlying remodeling in general and apoptosis in particular still remain unknown. Recent evidence suggests that microRNAs (miRs) play an important role in the heart´s response to increased cardiac stress.To identify novel modulators of stress-dependent remodeling, we conducted a genome-wide miR-screen of mechanically stretched neonatal rat cardiomyocytes (NRCM). Out of 351 miRs, eight were significantly regulated by biomechanical stress, including microRNA-20a, which is part of the miR17 ~ 92 cluster. Interestingly, further expression analyses also revealed upregulation of microRNA-20a in anin vitrohypoxia/”reperfusion” model. Given the potential apoptosis-modulating properties of the miR17 ~ 92 cluster, we subjected NRCM to hypoxia and subsequent reoxygenation. AdmiR-20a significantly inhibited hypoxia-mediated apoptosis in a dose-dependent fashion, while targeted knockdown of miR-20a in NRCM induced cardiomyocyte apoptosis. Mechanistically, the antiapoptotic effect of miR-20a appears to be mediated through direct targeting and subsequent downregulation of the proapoptotic factor Egln3.Thus, miR-20a is upregulated in acute biomechanical stress as well as hypoxia and inhibits apoptosis in cardiomyocytes. These properties reveal miR-20a as a cardioprotective micro-RNA and a potential target for novel therapeutic strategies to prevent cardiac remodeling.

Highlights

► Excessive stress, such as ischemia, is a potent inductor of cardiomyocyte apoptosis. ► In a genome-wide screen for differentially regulated microRNAs in stressed cardiomyocytes we identified miR-20a ► MiR-20a inhibited hypoxia-mediated apoptosis, while knockdown of miR-20a induced cardiomyocyte apoptosis. ► The antiapoptotic effect of miR-20a appears to be mediated through direct targeting of the proapoptotic factor Egln3.