Autophagy maintains cardiac function in the starved adult

To examine the functional significance and detailed morphological characteristics of starvation-induced autophagy in the adult heart, we starved green fluorescent protein (GFP)-microtubule-associated protein 1 light chain 3 (LC3) transgenic mice for up to 3 days. Electron microscopy revealed that, after as little as 12 hours of starvation, round and homogenously electron-dense lipid droplet-like vacuoles appeared in cardiomyocytes. These were determined to be lysosomes based on cathepsin D immunopositivity and acid phosphatase activity. The numbers of these lysosomes increased with starvation time, and typical autolysosomes with intracellular organelles destined for degradation appeared and increased in number at later times during the starvation period. Myocardial expression of the autophagy-related proteins LC3-II, cathepsin D, and ubiquitin increased, while myocardial ATP content decreased, as the starvation interval proceeded. Treatment with bafilomycin A1, an autophagy inhibitor, did not affect cardiac function in normally fed mice, but it significantly depressed cardiac function and caused significant left ventricular dilatation in the mice starved for 3 days. Cardiomyocytes from starved mice treated with bafilomycin A1 showed marked accumulation of lysosomes, and the myocardial amino acid content, which increased during starvation in normally fed mice, as well as the myocardial ATP content, were severely reduced, which likely contributed to the cardiac dysfunction. The present findings suggest autophagy plays a critical role in the maintenance of cardiac function during starvation in the adult.     

Mesenchymal stem cell injection after myocardial infarction improves myocardial compliance

Cellular therapy for myocardial injury has improved ventricular function in both animal and clinical studies, though the mechanism of benefit is unclear. This study was undertaken to examine the effects of cellular injection after infarction on myocardial elasticity. Coronary artery ligation of Lewis rats was followed by direct injection of human mesenchymal stem cells (MSCs) into the acutely ischemic myocardium. Two weeks postinfarct, myocardial elasticity was mapped by atomic force microscopy. MSC-injected hearts near the infarct region were twofold stiffer than myocardium from noninfarcted animals but softer than myocardium from vehicle-treated infarcted animals. After 8 wk, the following variables were evaluated: MSC engraftment and left ventricular geometry by histological methods, cardiac function with a pressure-volume conductance catheter, myocardial fibrosis by Masson Trichrome staining, vascularity by immunohistochemistry, and apoptosis by TdT-mediated dUTP nick-end labeling assay. The human cells engrafted and expressed a cardiomyocyte protein but stopped short of full differentiation and did not stimulate significant angiogenesis. MSC-injected hearts showed significantly less fibrosis than controls, as well as less left ventricular dilation, reduced apoptosis, increased myocardial thickness, and preservation of systolic and diastolic cardiac function. In summary, MSC injection after myocardial infarction did not regenerate contracting cardiomyocytes but reduced the stiffness of the subsequent scar and attenuated postinfarction remodeling, preserving some cardiac function. Improving scarred heart muscle compliance could be a functional benefit of cellular cardiomyoplasty.     

Acute induction of autophagy as a novel strategy for cardioprotection

There is no question that necrosis and apoptosis contribute to cardiomyocyte death in the setting of myocardial ischemia-reperfusion. Indeed, considerable effort and resources have been invested in the development of novel therapies aimed at attenuating necrotic and apoptotic cell death, with the ultimate goal of applying these strategies to reduce infarct size and improve outcome in patients suffering acute myocardial infarction (MI) or ‘heart attack’. However, an issue that remains controversial is the role of autophagy in determining the fate of ischemic-reperfused cardiomyocytes: i.e., is induction of autophagy detrimental or protective? Recent data from our group obtained in the clinically relevant, in vivo swine model of acute MI provide novel evidence of a positive association between pharmacological upregulation of autophagy (achieved by administration of chloramphenicol succinate (CAPS)) and increased resistance to myocardial ischemia-reperfusion injury.     

p27 Protein Protects Metabolically Stressed Cardiomyocytes from Apoptosis by Promoting Autophagy

p27^Kip1 (p27), a key regulator of cell division, has been implicated in autophagy of cancer cells. However, its role in autophagy, the evolutionarily conserved catabolic process that enables cells to remove unwanted proteins and damaged organelles, had not been examined in the heart. Here we report that ectopic delivery of a p27 fusion protein (TAT-p27) was sufficient to induce autophagy in neonatal rat ventricular cardiomyocytes in vitro, under basal conditions and after glucose deprivation. Conversely, lentivirus-delivered shRNA against p27 successfully reduced p27 levels and suppressed basal and glucose-deprived levels of autophagy in cardiomyocytes in vitro. Glucose deprivation mimics myocardial ischemia and induces apoptosis in cardiomyocytes. During glucose deprivation, TAT-p27 inhibited apoptosis, whereas down-regulation of p27 decreased survival of cardiomyocytes. However, inhibition of autophagy by pharmacological (3-methyladenine, chloroquine, or bafilomycin A1) or genetic approaches (siRNA-mediated knockdown of Atg5) sensitized cardiomyocytes to glucose deprivation-induced apoptosis, even in the presence of TAT-p27. TAT-p27 was also able to provoke greater levels of autophagy in resting and fasting cardiomyocytes in vivo. Further, TAT-p27 enhanced autophagy and repressed cardiomyocytes apoptosis, improved cardiac function, and reduced infarct size following myocardial infarction. Again, these effects were lost when cardiac autophagy in vivo was blocked by chloroquine. Taken together, these data show that p27 positively regulates cardiac autophagy in vitro and in vivo, at rest and after metabolic stress, and that TAT-p27 inhibits apoptosis by promoting autophagy in glucose-deprived cardiomyocytes in vitro and in post-myocardial infarction hearts in vivo.     

Periostin induces proliferation of differentiated cardiomyocytes and promotes cardiac repair

Adult mammalian hearts respond to injury with scar formation and not with cardiomyocyte proliferation, the cellular basis of regeneration. Although cardiogenic progenitor cells may maintain myocardial turnover, they do not give rise to a robust regenerative response. Here we show that extracellular periostin induced reentry of differentiated mammalian cardiomyocytes into the cell cycle. Periostin stimulated mononucleated cardiomyocytes to go through the full mitotic cell cycle. Periostin activated alphaV, beta1, beta3 and beta5 integrins located in the cardiomyocyte cell membrane. Activation of phosphatidylinositol-3-OH kinase was required for periostin-induced reentry of cardiomyocytes into the cell cycle and was sufficient for cell-cycle reentry in the absence of periostin. After myocardial infarction, periostin-induced cardiomyocyte cell-cycle reentry and mitosis were associated with improved ventricular remodeling and myocardial function, reduced fibrosis and infarct size, and increased angiogenesis. Thus, periostin and the pathway that it regulates may provide a target for innovative strategies to treat heart failure.     

Autophagy in myocardium of murine hearts subjected to ischemia followed by reperfusion

Autophagy in myocardium has been thought to be cardioprotective, but its extent after transient or prolonged myocardial ischemia remains unclear. Accordingly, we characterized its magnitude in myocardium of murine hearts subjected to ischemia with or without reperfusion. Ten-week-old transgenic GFP-LC3 mice and C57Bl6 mice were subjected to coronary ligation for 1 or 4 h followed by 24 h of reperfusion (1HTL, 4HTL) or to 24 h of persistent ligation (24HPL). Their hearts were analyzed by fluorescence microscopy, electron microscopy, and by Western blotting. Fluorescent GFP-LC3 dots indicative of autophagy were absent in infarct zones and reduced markedly in the peri-infarct zones compared with dots in sham controls (p ≤ 0.05). The LC3-II/LC3-I ratio indicative of autophagy did not increase in LV homogenates from hearts following ischemia. Phosphorylation of ribosomal protein S6 increased in LV homogenates in hearts from mice subjected to 4HTL and 24HPL (p ≤ 0.05). Virtually no autophagic cells recognizable by electron microscopy were evident in infarct or peri-infarct zones. Autophagy is virtually absent within 24 h in the center of zones of infarction and is decreased significantly in the peri-infarct zones compared with that in normal hearts.     

The cardiac Na-H exchanger: a key downstream mediator for the cellular hypertrophic effects of paracrine, autocrine and hormonal factors.

The major mechanism by which the heart cell regulates intracellular pH is the Na(+)-H(+) exchanger (NHE) with the NHE-1 isoform as the primary cardiac subtype. Although NHE-1 has been implicated in mediating ischemic injury, more recent evidence implicates the antiporter as a key mediator of hypertrophy, which is produced by various autocrine, paracrine and hormonal factors such as endothelin-1, angiotensin II, and alpha(1) adrenoceptor agonists. These agonists activate the antiporter via phosphorylation-dependent processes. NHE-1 inhibition is likely conducive to attenuating the remodelling process after myocardial infarction. These effects probably occur independently of infarct size reduction and involve attenuation of subsequent postinfarction heart failure. As such, inhibitors of NHE offer substantial promise for clinical development that will attenuate acute responses to myocardial postinfarction and chronic pos t infarction, which evolve toward heart failure. The regulation of NHE-1 is discussed as is its potential role in mediating cardiomyocyte hypertrophy.     

Acute induction of autophagy as a novel strategy for cardioprotection: getting to the heart of the matter

There is no question that necrosis and apoptosis contribute to cardiomyocyte death in the setting of myocardial ischemia-reperfusion. Indeed, considerable effort and resources have been invested in the development of novel therapies aimed at attenuating necrotic and apoptotic cell death, with the ultimate goal of applying these strategies to reduce infarct size and improve outcome in patients suffering acute myocardial infarction (MI) or ‘heart attack’. However, an issue that remains controversial is the role of autophagy in determining the fate of ischemic-reperfused cardiomyocytes: i.e., is induction of autophagy detrimental or protective? Recent data from our group obtained in the clinically relevant, in vivo swine model of acute MI provide novel evidence of a positive association between pharmacological upregulation of autophagy (achieved by administration of chloramphenicol succinate (CAPS)) and increased resistance to myocardial ischemia-reperfusion injury.Key words: myocardial ischemia, myocardial infarction, ischemia-reperfusion injury, autophagy, chloramphenicolOngoing controversy concerning the role of autophagy in myocardial ischemia-reperfusion injury (pro-survival versus pro-death) may be an example of the ‘Goldilocks Principle’: uncontrolled ‘pathophysiological’ induction of autophagy in response to an extreme or prolonged stress reportedly contributes to cardiac cell death, whereas a modest ‘physiological’ upregulation of autophagy may be beneficial. Indeed, in support of this latter concept, a growing body of evidence obtained in isolated cardiomyocytes and rodent models has revealed that acute, pre-ischemic induction of autophagy can confer a cardioprotective phenotype. The objective of our recent publication was to extend this paradigm to a clinically relevant, large animal (swine) model and establish whether pharmacological upregulation of autophagy would render the heart resistant to lethal ischemia-reperfusion injury and thus limit myocardial infarct size.To test this concept, anesthetized pigs were assigned to receive our candidate drug, chloramphenicol succinate (CAPS) or placebo and, at 10 min after treatment, underwent 45 min of coronary artery occlusion followed by 3 h of reperfusion. Administration of CAPS results in a rapid and robust upregulation in molecular markers of autophagy: at 10 min post-treatment (the time corresponding to the onset of the sustained ischemic insult), we observed a 2.4- and 6.2-fold increase in expression of Beclin 1 and LC3-II, respectively, versus baseline. However, most notably, CAPS-treated pigs displayed a profound, ~50% reduction in infarct size when compared with placebo-controls. To investigate whether the favorable effect of CAPS was retained when administered in a more clinically relevant manner, an additional cohort of pigs received CAPS at 15 min before the onset of reperfusion. Efficacy was maintained (albeit attenuated) with delayed treatment, with mean infarct size reduced by ~27% versus controls.The novel aspect of our study is the unequivocal documentation of a significant infarct-sparing effect of CAPS in a well-established pre-clinical model of ischemia-reperfusion injury, thereby bringing the concept of cardioprotection via pharmacological upregulation of autophagy one step closer to future clinical evaluation. Nonetheless, our use of the swine model has an inherent weakness: although we have shown compelling evidence of an association between induction of autophagy and reduction of infarct size, the pig is not amenable to the application of genetic and molecular tools that would yield definitive documentation of cause-and-effect.As acknowledged in our recent publication, an issue of particular relevance in establishing the mechanism by which CAPS confers cardioprotection is the tight and complex interaction between autophagy and the PtdIns3K-Akt-mTOR signaling pathway. Specifically, class III PtdIns3K is an activator of autophagy and, via its interaction with Beclin 1, plays a pivotal role in initiating autophagosome formation, whereas class I PtdIns3K purportedly suppresses autophagy. Interaction at the level of mTOR is multifaceted, bi-directional and has been reported to exert both positive and negative feedback; i.e., while activation of mTOR is associated with inhibition of autophagy, there is evidence of self-regulation of autophagy by autophagy-induced inhibition of mTOR and, in at least one model, co-activation of autophagy and mTOR. PtdIns3K-Akt-mTOR are also components of the ‘Reperfusion Injury Salvage Kinase’ or RISK pathway, a canonical cardioprotective signal transduction pathway that, when activated, has been shown in multiple models to attenuate lethal ischemia-reperfusion injury. Akt signaling is upregulated by a host of protective strategies including ischemic preconditioning (considered the ‘gold standard’ of cardioprotection) and pharmacological preconditioning-mimetic agents. It is therefore perhaps not surprising that administration of CAPS is accompanied by an increase in expression of phospho-Akt.If CAPS treatment is associated with both an induction of autophagy (as documented in our study) and, as with many cardioprotective strategies, upregulation of Akt signaling, this raises two intriguing and interrelated possibilities. First, autophagy and PtdIns3K-Akt-mTOR signaling may yield additive benefit. Second, we speculate that co-activation of the Akt signaling pathway may, by these complex bi-directional interactions, assist in establishing an appropriate balance and maintaining autophagy in a favorable, pro-survival ‘Goldilocks’ state. Our data clearly demonstrate that CAPS is cardioprotective, and may, via induction of autophagy, provide a novel and clinically relevant therapy to attenuate myocardial ischemia-reperfusion injury. However, detailed molecular investigation will be required to ‘get to the heart’ of the mechanisms underlying the reduction of infarct size seen with CAPS treatment.     

瞬时受体电位香草酸亚型1激活通过抑制线粒体通透性转换孔开放保护急性心肌梗死小鼠的心肌细胞抗凋亡

瞬时受体电位香草酸亚型1（TRPV1）在心肌缺血激活后可传导心绞痛信号,释放神经肽,减轻心肌梗死后的心肌细胞凋亡。目前,TRPV1激活抑制心肌梗死后细胞凋亡的具体机制尚不清楚。线粒体通透性转换孔（MPTP）的开放与心肌细胞缺血再灌注损伤密切相关,抑制其开放可保护心肌缺血后的心肌细胞抗凋亡。本研究证明,TRPV1激活通过抑制MPTP开放而减少心肌细胞凋亡。首先,本研究利用左冠状动脉前降支结扎术建立了TRPV1基因敲除（TRPV1-/-）和野生型（WT）小鼠心肌梗死模型,辅以环孢素A（CSA）预处理抑制 MPTP开放,比较观察TRPV1、MPTP在心肌梗死中的作用。心肌组织切片氯化三苯基四氮唑（TTC）染色显示,心肌缺血24 h,TRPV1-/-小鼠的心肌梗死面积明显大于WT型小鼠。而经CSA预处理的TRPV1-/-小鼠比TRPV1-/-小鼠梗死面积明显减小。TUNEL检测心肌细胞凋亡指数（AI）揭示,WT型心肌梗死小鼠的AI明显低于TRPV1-/- 心肌梗死小鼠,而CSA预处理明显降低TRPV1-/-小鼠心肌细胞的AI。Western印迹检测胱天蛋白酶3、胱天蛋白酶9、Bcl-2、Bax、p53和细胞色素C（Cyt-C）水平。结果证明,TRPV1的激活可抑制MPTP的开放,减少线粒体Cyt-C的外溢,降低胱天蛋白酶9和胱天蛋白酶3的表达。GENMEN光度法检测MPTP开放实验显示,激活的TRPV1明显抑制了MPTP的开放。本研究证实,急性心肌梗死后的TRPV1激活可能通过抑制MPTP开放而抵抗心肌细胞凋亡,对心肌起保护作用。     

Suppression of autophagy is protective in high glucose-induced cardiomyocyte injury

Hyperglycemia is linked to increased heart failure among diabetic patients. However, the mechanisms that mediate hyperglycemia-induced cardiac damage remain poorly understood. Autophagy is a cellular degradation pathway that plays important roles in cellular homeostasis. Autophagic activity is altered in the diabetic heart, but its functional role has been unclear. In this study, we determined if mimicking hyperglycemia in cultured cardiomyocytes from neonatal rats and adult mice could affect autophagic activity and myocyte viability. High glucose (17 or 30 mM) reduced autophagic flux compared with normal glucose (5.5 mM) as indicated by the difference in protein levels of LC3-II (microtubule-associated protein 1 light chain 3 form II) or the changes of punctate fluorescence patterns of GFP-LC3 and mRFP-LC3 in the absence and presence of the lysosomal inhibitor bafilomycin A(1). Unexpectedly, the inhibited autophagy turned out to be an adaptive response that functioned to limit high glucose cardiotoxicity. Indeed, suppression of autophagy by 3-methyladenine or short hairpin RNA-mediated silencing of the Becn1 or Atg7 gene attenuated high glucose-induced cardiomyocyte death. Conversely, upregulation of autophagy with rapamycin or overexpression of Becn1 or Atg7 predisposed cardiomyocytes to high glucose toxicity. Mechanistically, the high glucose-induced inhibition of autophagy was mediated at least partly by increased mTOR signaling that likely inactivated ULK1 through phosphorylation at serine 467. Together, these findings demonstrate that high glucose inhibits autophagy, which is a beneficial adaptive response that protects cardiomyocytes against high glucose toxicity. Future studies are warranted to determine if autophagy plays a similar role in diabetic heart in vivo.     

Emodin-mediated protection from acute myocardial infarction via inhibition of inflammation and apoptosis in local ischemic myocardium

Acute myocardial infarction (AMI) is associated with inflammation and apoptosis. Emodin plays an anti-inflammatory role in several inflammatory diseases. Recent studies have demonstrated that emodin protects against myocardial ischemia/reperfusion injury. However, its mechanism underlying its effects remains unknown. In a murine model of AMI, based on ligation of the left coronary artery, administration of emodin reduced myocardial infarct size (MIS) in a dose-dependent manner. Emodin significantly suppressed TNF-alpha expression and NF-kappaB activation in the local myocardial infarction area. Treatment with emodin inhibited myocardial cell apoptosis by inhibiting caspase-3 activation. Therefore, these studies demonstrate that emodin protects against myocardial cell injury via suppression of local inflammation and apoptosis.     

Local delivery of soluble TNF-alpha receptor 1 gene reduces infarct size following ischemia/reperfusion injury in rats

Apoptosis in the myocardium is linked to ischemia/reperfusion injury, and TNF-alpha induces apoptosis in cardiomyocytes. A significant amount of TNF-alpha is detected after ischemia and reperfusion. Soluble TNF-alpha receptor 1 (sTNFR1) is an extracellular domain of TNF-alpha receptor 1 and is an antagonist to TNF-alpha. In the present study, we examined the effects of sTNFR1 on infarct size in acute myocardial infarction (AMI) following ischemia/reperfusion. Male Wistar rats were subjected to left coronary artery (LCA) ligation. After 30 min of LCA occlusion, the temporary ligature on the LCA was released and blood flow was restored. Immediately after reperfusion, a total of 200 microg of sTNFR1 or LacZ plasmid was injected into three different sites of the left ventricular wall. At 6 h, 1 and 2 days after reperfusion, the TNF-alpha bioactivity in the myocardium was significantly higher in rats receiving LacZ plasmid than in sham-operated rats, whereas sTNFR1 plasmid significantly suppressed the increase in the TNF-alpha bioactivity. The sTNFR1 plasmid significantly reduced DNA fragmentation and caspase activity compared to the LacZ plasmid. Finally, the sTNFR1 expression-plasmid treatment significantly reduced the area of myocardial infarction at 2 days after ischemia/reperfusion compared to LacZ plasmid. In conclusion, the TNF-alpha bioactivity in the heart increased from the early stage of ischemia/reperfusion, and this increase was thought to contribute in part to the increased area of myocardial infarction. Suppression of TNF-alpha bioactivity with the sTNFR1 plasmid reduced the infarct size in AMI following ischemia and reperfusion.     

Adenoviral short hairpin RNA therapy targeting phosphodiesterase 5a relieves cardiac remodeling and dysfunction following myocardial infarction

We previously showed that treatment with tadalafil, a long-acting phosphodiesterase-5a (PDE5a) inhibitor, effectively prevented adverse left ventricular (LV) remodeling of the infarcted heart. We hypothesized that short-hairpin RNA (shRNA) therapy targeting PDE5a would simulate the effects of pharmacological intervention for treatment of postinfarction LV remodeling and dysfunction. Experimental model of myocardial infarction was developed in female mice by permanent ligation of left coronary artery. Immediately after that, an adenoviral vector encoding for shRNA sequence targeting PDE5a (Ad-shPDE5a) was injected intramyocardially, which specifically inhibited PDE5a in the heart. Four weeks later, Ad-shPDE5a treated mice showed significant mitigation of the left ventricle (LV) dilatation and dysfunction as indicated by smaller LV cavity and more preserved ejection fraction and fractional shortening. Infarction size and fibrosis were significantly reduced in Ad-shPDE5a-treated mice. Additionally, more salvaged cardiomyocytes, significantly reduced collagen contents, and higher blood vessel density were observed in Ad-shPDE5a-treated mice. The cytoprotective effects of Ad-shPDE5a were demonstrated in vitro in Ad-shPDE5a transfected cardiomyocytes cultured under oxygen glucose deprivation. Among downstream mediators of PDE5a signaling, cyclic GMP (cGMP) and cGMP-dependent protein kinase G (PKG) were activated with concomitant reduction in caspase-3 activity. However, no significant change in PKA and cAMP activities were observed in Ad-shPDE5a-treated hearts. Inhibition with shRNA improved cardiac remodeling and dysfunction by reducing infarction size and cardiac fibrosis and increased cGMP and PKG activity. These findings suggest that PDE5 inhibition with Ad-shPDE5a is a novel approach for treatment of myocardial infarction.     

Granulocyte colony-stimulating factor treatment enhances the efficacy of cellular cardiomyoplasty with transplantation of embryonic stem cell-derived cardiomyocytes in infarcted myocardium

We tested the hypothesis that granulocyte colony-stimulating factor (G-CSF) administration would enhance the efficacy of cellular cardiomyoplasty with embryonic stem (ES) cell-derived cardiomyocytes in infarcted myocardium. Three weeks after myocardial infarction by cryoinjury, Sprague-Dawley rats were randomized to receive either an injection of medium, ES cell-derived cardiomyocyte transplantation, G-CSF administration, or a combination of G-CSF administration and ES cell-derived cardiomyocyte transplantation. Eight weeks after treatment, the cardiac tissue formation, neovascularization, and apoptotic activity in the infarct regions were evaluated by histology and immunohistochemistry. The left ventricular (LV) dimensions and function of the treated heart were evaluated by echocardiography. Transplanted ES cell-derived cardiomyocytes survived and participated in the myocardial regeneration in the infarcted heart. A combination of G-CSF treatment and ES cell-derived cardiomyocyte transplantation significantly promoted angiogenesis and reduced the infarct area and cell apoptosis in the infarcted myocardium compared with ES cell-derived cardiomyocyte transplantation alone. The combination therapy also attenuated LV dilation, as compared with ES cell-derived cardiomyocyte transplantation alone. G-CSF treatment can enhance the efficacy of cellular cardiomyoplasty by ES cell-derived cardiomyocyte transplantation to treat myocardial infarction.     

G-CSF prevents cardiac remodeling after myocardial infarction by activating the Jak-Stat pathway in cardiomyocytes

Granulocyte colony-stimulating factor (G-CSF) was reported to induce myocardial regeneration by promoting mobilization of bone marrow stem cells to the injured heart after myocardial infarction, but the precise mechanisms of the beneficial effects of G-CSF are not fully understood. Here we show that G-CSF acts directly on cardiomyocytes and promotes their survival after myocardial infarction. G-CSF receptor was expressed on cardiomyocytes and G-CSF activated the Jak/Stat pathway in cardiomyocytes. The G-CSF treatment did not affect initial infarct size at 3 d but improved cardiac function as early as 1 week after myocardial infarction. Moreover, the beneficial effects of G-CSF on cardiac function were reduced by delayed start of the treatment. G-CSF induced antiapoptotic proteins and inhibited apoptotic death of cardiomyocytes in the infarcted hearts. G-CSF also reduced apoptosis of endothelial cells and increased vascularization in the infarcted hearts, further protecting against ischemic injury. All these effects of G-CSF on infarcted hearts were abolished by overexpression of a dominant-negative mutant Stat3 protein in cardiomyocytes. These results suggest that G-CSF promotes survival of cardiac myocytes and prevents left ventricular remodeling after myocardial infarction through the functional communication between cardiomyocytes and noncardiomyocytes.     

Mesenchymal stem cell transplantation for myocardial reparation of rat experimental heart failure

Mesenchymal stem cells (MSC) are resident pluripotent cells of bone marrow stroma. MSC have the ability to differentiate into osteoblasts, chondroblasts and adipocytes, neurons, glia and also into cardiomyocytes. The problem of MSC use in cell therapy of various diseases and in myocardial infarction therapy is widely discussed at present. The experiments were carried out on the inbred line Wistar--Kyoto rats. Myocardial experimental infarction (EI) was induced by left descending coronary artery ligation. MSC were isolated from bone marrow, cultivated in vitro and injected into the tail vein on the day of experimental infarction operation. It was shown that the structure of injured myocardium in experimental group significantly differed from that in control group. MSC transplantation led to inflammatory process acceleration and to increased angiogenesis in the damaged myocardium; also, live cardiomyocyte layers were detected in the scar. As a result, ventricular dilatation and overload of the border zone of infarct region decreased, no features of infarction relapse were shown in the border zone.     

Additive beneficial effects of two inhibitors of vasoconstrictor mediators in acute myocardial ischemia

A specific inhibitor of thromboxane A2 (TxA2) synthesis, CGS-12970, a new angiotensin-converting enzyme (ACE) inhibitor, CGS-16617, and a combination of both agents were evaluated for their ability to reduce the extension of myocardial infarct size in rats. Myocardial creatine kinase (CK) loss from the left ventricular free wall (LVFW) 48 hr after left coronary artery ligation was used as an index of ischemic damage. Treatment with either CGS-12970 (4 mg/kg) or CGS-16617 (1 microgram/kg) alone did not attenuate the loss of CK from LVFW significantly, compared with animals receiving only the vehicles for these drugs. However, the combined use of both agents significantly reduced CK depletion from LFVW (P less than 0.01). These findings support the interrelated role of TxA2 and angiotensin II as mediators of myocardial ischemia and suggest that combined inhibition of their formation may be useful in the treatment of acute myocardial infarction.     

The Effect of c-fos on Acute Myocardial Infarction and the Significance of Metoprolol Intervention in a Rat Model

Over-expression of c-fos may play a role in some diseases. Research pertaining to the expression of c-fos in acute myocardial ?nfarction (AMI) is rare, and the detailed role of c-fos in AMI has not been reported. Therefore, the purpose of this project was to elucidate the detailed effect of c-fos on AMI rats and evaluate the effect of a metoprolol intervention. An AMI rat model was established for the purposes of this study. The expression of c-fos in AMI was evaluated via immunohistochemical analysis and in situ hybridization. Simultaneously, we investigated the effect of c-fos on AMI rats via medicinal treatment with c-fos monoclonal antibody, isoproterenol, and metoprolol. Positive c-Fos protein expression and c-fos mRNA expression in cardiomyocytes were increased at 1, 3, 7, and 10 days after ligation in AMI rats compared with a sham-operated group. Peak expression occurred at 3 days after ligation. The weight percentage fraction of infarct size was decreased in rats treated with c-fos monoclonal antibody compared with the control normal saline treatment group. The weight percentage fraction of infarction size was increased after c-fos was increased via the administration of isoproterenol. c-Fos protein expression and the infarct size in rats treated with metoprolol were also decreased compared with the control normal saline treatment group. The results showed that c-fos expression rapidly increased after coronary ligation; c-fos plays an important role in myocardial lesions and is likely to be involved in the pathogenesis of AMI as well. Metoprolol can inhibit the expression of c-fos and has a positive therapeutic effect on rats after AMI; the involvement effect of metoprolol on myocardial infarction might be correlated with its effect on the inhibition of c-fos.     

Suppression of autophagy is protective in high glucose-induced cardiomyocyte injury

Hyperglycemia is linked to increased heart failure among diabetic patients. However, the mechanisms that mediate hyperglycemia-induced cardiac damage remain poorly understood. Autophagy is a cellular degradation pathway that plays important roles in cellular homeostasis. Autophagic activity is altered in the diabetic heart, but its functional role has been unclear. In this study, we determined if mimicking hyperglycemia in cultured cardiomyocytes from neonatal rats and adult mice could affect autophagic activity and myocyte viability. High glucose (17 or 30 mM) reduced autophagic flux compared with normal glucose (5.5 mM) as indicated by the difference in protein levels of LC3-II (microtubule-associated protein 1 light chain 3 form II) or the changes of punctate fluorescence patterns of GFP-LC3 and mRFP-LC3 in the absence and presence of the lysosomal inhibitor bafilomycin A₁. Unexpectedly, the inhibited autophagy turned out to be an adaptive response that functioned to limit high glucose cardiotoxicity. Indeed, suppression of autophagy by 3-methyladenine or short hairpin RNA-mediated silencing of the Becn1 or Atg7 gene attenuated high glucose-induced cardiomyocyte death. Conversely, upregulation of autophagy with rapamycin or overexpression of Becn1 or Atg7 predisposed cardiomyocytes to high glucose toxicity. Mechanistically, the high glucose-induced inhibition of autophagy was mediated at least partly by increased mTOR signaling that likely inactivated ULK1 through phosphorylation at serine 467. Together, these findings demonstrate that high glucose inhibits autophagy, which is a beneficial adaptive response that protects cardiomyocytes against high glucose toxicity. Future studies are warranted to determine if autophagy plays a similar role in diabetic heart in vivo.