cAMP-mediated beta-adrenergic signaling negatively regulates Gq-coupled receptor-mediated fetal gene response in cardiomyocytes

The treatment with β-blockers causes an enhancement of the norepinephrine-induced fetal gene response in cultured cardiomyocytes. Here, we tested whether the activation of cAMP-mediated β-adrenergic signaling antagonizes α₁-adrenergic receptor (AR)-mediated fetal gene response. To address this question, the fetal gene program, of which atrial natriuretic peptide (ANP) and the β-isoform of myosin heavy chain are classical members, was induced by phenylephrine (PE), an α₁-AR agonist. In cultured neonatal rat cardiomyocytes, we found that stimulation of β-ARs with isoproterenol, a β-AR agonist, inhibited the fetal gene expression induced by PE. Similar results were also observed when cardiomyocytes were treated with forskolin (FSK), a direct activator of adenylyl cyclase, or 8-CPT-6-Phe-cAMP, a selective activator of protein kinase A (PKA). Conversely, the PE-induced fetal gene expression was further upregulated by H89, a selective PKA inhibitor. To evaluate whether these results could be generalized to Gq-mediated signaling and not specifically to α₁-ARs, cardiomyocytes were treated with prostaglandin F₂α, another Gq-coupled receptor agonist, which is able to promote fetal gene expression. This treatment caused an increase of both ANP mRNA and protein levels, which was almost completely abolished by FSK treatment. The capability of β-adrenergic signaling to regulate the fetal gene expression was also evaluated in vivo conditions by using β1- and β2-AR double knockout mice, in which the predominant cardiac β-AR subtypes are lacking, or by administering isoproterenol (ISO), a β-AR agonist, at a subpressor dose. A significant increase of the fetal gene expression was found in β₁- and β₂-AR gene deficient mice. Conversely, we found that ANP, β-MHC and skACT mRNA levels were significantly decreased in ISO-treated hearts. Collectively, these data indicate that cAMP-mediated β-adrenergic signaling negatively regulates Gq cascade activation-induced fetal gene expression in cultured cardiomyocytes and that this inhibitory regulation is already operative in the mouse heart under physiological conditions.     

Mycophenolate mofetil prevents the development of experimental autoimmune myocarditis

Experimental autoimmune myocarditis (EAM) is characterized by the appearance of multinucleated giant cells. EAM leads to severe myocardial damage and is a useful model of human giant cell myocarditis. We investigated whether mycophenolate mofetil (MMF), which is a potent immunosuppressant, prevents the development of myocarditis in a rat EAM model, and focused on the role of osteopontin (OPN) in the pathogenesis of this disorder. Adult Lewis rats were immunized with porcine cardiac myosin to establish EAM. The early MMF treatment completely prevented the development of EAM, and the late MMF treatment was also effective even against established EAM. Echocardiogram demonstrated that left ventricular function was also improved by the treatment with MMF. Real-time RT-PCR analysis showed that both early and late MMF treatments significantly inhibited myocarditis-induced OPN mRNA expression in the heart. Immunohistochemistry revealed that OPN expression was prominent in the myocardium on day 14, whereas expression was observed in the infiltrated macrophages on day 21. Mycophenolic acid (MPA) did inhibit agonist-induced OPN expression in cultured cardiomyocytes. These results show the therapeutic potential of MMF for autoimmune myocarditis and provide new insights into the pathogenesis of this disease.     

一氧化氮在乳鼠心肌细胞缺氧—复氧预处理延迟保护效应中的作用

探讨缺氧—复氧损伤对乳鼠心肌细胞一氧化氮释放和一氧化氮合酶活性的影响以及一氧化氮在心肌细胞延迟缺氧预处理中的作用。在培养乳鼠心肌细胞缺氧预处理的模型上，测定缺氧—复氧损伤对乳鼠心肌细胞一氧化氮释放和一氧化氮合酶活性，观察延迟缺氧预处理以及N-硝基-L-精氨酸、L广精氨酸、硝普钠对心肌细胞延迟缺氧预处理的影响。结果发现，缺氧—复氧后乳鼠心肌细胞一氧化氮释放增加，一氧化氮合酶活性升高。延迟缺氧预处理可以减少缺氧一复氧对心肌细胞的损伤。非选择性一氧化氮合酶抑制剂N-硝基-L-广精氨酸可以阻断延迟缺氧预处理的心肌保护作用，L广精氨酸不能模拟延迟缺氧预处理，硝普钠可以模拟延迟缺氧预处理。结果提示，一氧化氮可以诱导心肌细胞的延迟缺氧预处理。     

Glutamate loading protects freshly isolated and perfused adult cardiomyocytes against intracellular ROS generation

Glutamate loading has been shown to protect single isolated perfused cardiomyocytes against metabolic inhibition and wash-off. The mechanism underpinning this protection is unknown. This study aimed to investigate whether reactive oxygen species (ROS) are generated by single isolated perfused cardiomyocytes and whether the protective effect of glutamate loading on cell metabolism is linked to ROS. Single rat cardiomyocytes were isolated with or without glutamate to stimulate glutamate loading. ROS production was measured using 5-(and-6)-chloromethyl-2', 7'-dichlorodihydrofluorescein diacetate in various stressful conditions including metabolic inhibition and wash-off with/without antimycin A or myxothiazol; simulated ischaemia (without cyanide) and glucose reintroduction; and H(2)O(2) perfusion. Reduced glutathione (GSH) levels were measured in control and glutamate-loaded cells with/without exposure to H(2)O(2). Finally, the effect of glutamate on glutathione reductase and glutathione peroxidase activity was measured. In every stressful condition studied, ROS production was significantly lower in glutamate-loaded cells compared to controls. This occurred regardless of whether ROS were produced intracellularly (e.g. from the respiratory chain inhibited with antimycin A) or via the extracellular precursor H(2)O(2). Glutamate-loaded cells also maintained their morphological integrity at higher H(2)O(2) concentrations than control cells. Furthermore, during H(2)O(2) exposure GSH levels decreased in glutamate-loaded cells but stayed constant in control cells. Glutamate stimulated the activity of glutathione peroxidase in a concentration-dependent fashion. These results provide new evidence to show that the cardioprotective effect of glutamate loading may be mediated through an enhanced ability to destroy ROS in the cell.     

诱导人脐带间充质干细胞向心肌细胞分化及对小鼠心肌梗死的治疗作用

目的研究脐带间充质干细胞(UC-MSC)体外分化为心肌细胞的可行性以及观察UC- MSC体内移植对心肌梗死模型小鼠的治疗效果。方法10 μmol/L 5-氮胞苷(5-aza)体外诱导UC-MSC 14 d,通过RT-PCR、免疫荧光染色鉴定其分化效果；采用腹腔注射盐酸异丙肾上腺素(ISO)每只3.0 mg/(kg/d),制作心肌梗死模型鼠；在注射ISO 48 h后,实验组将DAPI标记的UC-MSC经两次尾静脉移植给心肌梗死模型鼠,移植后第4周和第8周,分别采集实验小鼠的心脏、脾脏,以未移植细胞组的小鼠心肌损伤模型作为对照, 通过心脏指数和脾脏指数测量,免疫荧光和碱性复红-苦味酸(HBFP)染色鉴定其体内分化和修复作用。结果RT-PCR分析表明诱导的UC-MSC表达心肌特异性基因:心肌α-actin、TBX5、GATA4 和NKx2.5,免疫荧光染色显示诱导细胞呈心肌α-actin和NKx2.5阳性,且呈双核现象。尾静脉移植后第4周和第8周,模型受体鼠心脏均发现有DAPI阳性细胞迁移至心肌组织且呈现心肌α-actin阳性,HBFP染色及心脏和脾脏指数结果显示移植UC-MSC对心肌损伤的模型鼠有明显的修复和治疗效果。结论UC- MSC在体外经5-aza诱导可定向分化为心肌细胞,尾静脉体内移植UC- MSC对心肌损伤小鼠有明显的治疗效果。     

PTC124不影响豚鼠心室肌细胞的电生理特性

目的无义突变产生提早出现的终止密码子（Premature termination codon,PTC）,其主要致病机制是突变基因单倍体表达不足,见于心脏钠通道SCN5A基因。SCN5A无义突变导致心脏传导功能障碍、扩张性心肌病和Brugada综合征（BrS）等疾病,目前尚无有效方法根治这类疾病,但药物将是治疗这类突变相关性疾病的最佳选择。近年来开发的口服药物PTC124,能够选择地抑制过早出现的终止密码子,诱导核糖体通读,不影响正常的终止密码子。为了评价该药物的安全性,本研究检测了PTC124对豚鼠心室肌细胞动作电位特性的急性效应。方法应用膜片钳方法研究PTC124对豚鼠心肌细胞动作电位的影响。采用酶法分离豚鼠心肌细胞,测定PTC124对心肌细胞的急性毒性作用。结果 PTC124对豚鼠心肌细胞静息膜电位、最大上升速率、动作电位幅度和动作电位持续时间在50和90%的复极期均没有受到影响。结论 PTC124不影响豚鼠心室肌细胞动作电位。该研究为今后评估这种疗法的使用价值,治疗具有潜在的致命性心律失常的BrS和/或传导障碍性疾病患者的安全性提供依据。     

Cardiomyocyte apoptosis in the failing heart — A critical review from definition and classification of cell death

It has been suggested that apoptosis may be responsible for a significant amount of the cardiomyocyte death that contributes to the development and progression of heart failure. However, studies of actual heart disease and in vivo experimental models have provided little or no direct morphological evidence that cardiomyocyte apoptosis occurs at any stage of heart failure, despite the availability of much indirect evidence that includes detection of DNA fragmentation and apoptosis-related factors. The Nomenclature Committee on Cell Death (NCCD), an international organization consulting on cell death, proposed an international standard for the definition and classification of cell death, in which cell death was defined based purely on morphological criteria. This is because there is no clear-cut equivalence between ultrastructural alterations and biochemical cell death characteristics. This review will first introduce the NCCD definition and classification of cell death and, based on this classification, survey the available data from both animals and humans to critically assess the impact of cardiomyocyte apoptosis during the progression of heart failure of various etiologies. Particularly noteworthy is the wide variation in the reported rates of apoptosis – e.g., the difference was > 1000-fold in one heart failure model – but even more importantly, no morphological (ultrastructural) data has ever been shown definitively demonstrating apoptosis of a cardiomyocyte. We conclude from our survey that even the existence of cardiomyocyte apoptosis in heart failure remains controversial.