Yanyan Liang

Ryanodine Receptor Type 2 Is Required for the Development of Pressure Overload-Induced Cardiac Hypertrophy

Ryanodine receptor type 2 (RyR-2) mediates Ca2+ release from sarcoplasmic reticulum and contributes to myocardial contractile function. However, the role of RyR-2 in the development of cardiac hypertrophy is not completely understood. Here, mice with or without reduction of RyR-2 gene (RyR-2 +/− and wild-type, respectively) were analyzed. At baseline, there was no difference in morphology of cardiomyocyte and heart and cardiac contractility between RyR-2 +/− and wild-type mice, although Ca2+ release from sarcoplasmic reticulum was impaired in isolated RyR-2 +/− cardiomyocytes. During a 3-week period of pressure overload, which was induced by constriction of transverse aorta, isolated RyR-2 +/− cardiomyocytes displayed more reduction of Ca2+ transient amplitude, rate of an increase in intracellular Ca2+ concentration during systole, and percentile of fractional shortening, and hearts of RyR-2 +/− mice displayed less compensated hypertrophy, fibrosis, and contractility; more apoptosis with less autophagy of cardiomyocytes; and similar decrease of angiogenesis as compared with wild-type ones. Moreover, constriction of transverse aorta-induced increases in the activation of calcineurin, extracellular signal-regulated protein kinases, and protein kinase B/Akt but not that of Ca2+/calmodulin-dependent protein kinase II, and its downstream targets in the heart of wild-type mice were abolished in the RyR-2 +/− one, suggesting that RyR-2 is a regulator of calcineurin, extracellular signal-regulated protein kinases, and Akt but not of calmodulin-dependent protein kinase II activation during pressure overload. Taken together, our data indicate that RyR-2 contributes to the development of cardiac hypertrophy and adaptation of cardiac function during pressure overload through regulation of the sarcoplasmic reticulum Ca2+ release; activation of calcineurin, extracellular signal-regulated protein kinases, and Akt; and cardiomyocyte survival.

Association of Stat3 with HSF1 plays a critical role in G-CSF-induced cardio-protection against ischemia/reperfusion injury.

Granulocyte colony-stimulating factor (G-CSF) has been shown to be cardio-protective against ischemia through activating Jak2/Stat3 pathway, however, the mechanism is unclear. Heat shock transcription factor 1 (HSF1), a definite endogenous protective protein in cardiomyocytes, may interact with Stat family under stress conditions. We hypothesized that G-CSF could induce cardio-protection against ischemia/reperfusion (I/R) through association of HSF1 with Stat3. To test the hypothesis, we built cardiac I/R injury model with HSF1 knockout (KO) mice and wild type (WT) mice by occlusion of the left anterior descending (LAD) coronary artery for 30min and subsequent release of the occlusion for 24h. These mice were administered with G-CSF (100μg/kg/day) or vehicle subcutaneously for 3days before surgery. As expected, G-CSF induced significant cardio-protections against I/R injury, characterized by higher ejection fraction (EF%), lower left ventricular end diastolic pressure (LVEDP), increased dp/dt value and decreased infarct area as compared with the vehicle treatment in WT mice. In HSF1-KO mice, however, these cardio-protections induced by G-CSF were greatly attenuated. Inhibition of oxidative stress-induced cardiomyocyte apoptosis by G-CSF also disappeared due to the deficiency of HSF1 in vitro and in vivo. Furthermore, G-CSF increased the phosphorylation and the association of Stat3 with HSF1, which enhanced transcriptional activity of HSF1. Inhibition of either Stat3 or HSF1 by pharmacological agents suppressed G-CSF-induced association of the two proteins and anti-apoptotic effect on cardiomyocytes. Our data suggest that G-CSF stimulates phosphorylation and association of Stat3 with HSF1 and therefore enhances transcriptional activity of HSF1, leading to the cardio-protection against I/R injury.

Qiliqiangxin inhibits the development of cardiac hypertrophy, remodeling, and dysfunction during 4 weeks of pressure overload in mice.

Abstract Qiliqiangxin (QL), a traditional Chinese medicine, has been used in the treatment of chronic heart failure. However, whether QL can benefit cardiac remodeling in the hypertensive state is unknown. We here examined the effects of QL on the development of cardiac hypertrophy through comparing those of losartan in C57BL/6 mice underlying transverse aorta constriction for 4 weeks. QL and losartan were administrated at 0.6 mg and 13.4 mg·kg−1·d−1, respectively. Cardiac hypertrophy, function, and remodeling were evaluated by echocardiography, catheterization, histology, and examination of specific gene expression and ERK phosphorylation. Cardiac apoptosis, autophagy, tumor necrosis factor &agr;/insulin-like growth factor-1, and angiotensin II type 1 receptor expression and especially the proliferation of cardiomyocytes and phosphorylation of ErbB receptors were examined in vivo to elucidate the mechanisms. Transverse aorta constriction for 2 weeks resulted in a significant cardiac hypertrophy, which was significantly suppressed by either QL or losartan treatment. At 4 weeks after transverse aorta constriction, although the development of cardiac dysfunction and remodeling and the increases in apoptosis, autophagy, tumor necrosis factor &agr;/insulin-like growth factor-1, and angiotensin II type 1 receptor expression were abrogated comparably between QL and losartan treatments, QL, but not losartan, enhanced proliferation of cardiomyocytes, which was paralleled with dowregulation of CCAAT/enhancer-binding protein &bgr;, upregulation of CBP/p300-interacting transactivator with ED-rich carboxy-terminal domain 4, and increases in ErbB2 and ErbB4 phosphorylation. Furthermore, inhibition of either ErbB2 or CBP/p300-interacting transactivator with ED-rich carboxy-terminal domain 4 abolished the cardiac protective effects of QL. Thus, QL inhibits myocardial inflammation and cardiomyocyte death and promotes cardiomyocyte proliferation, leading to an ameliorated cardiac remodeling and function in a mouse model of pressure overload. The possible mechanisms may involve inhibition of angiotensin II type 1 receptor and activation of ErbB receptors.

Heat shock transcription factor 1 protects heart after pressure overload through promoting myocardial angiogenesis in male mice

Heat shock transcription factor 1 (HSF1) plays an important role not only in excise-induced cardiac hypertrophy but also in protection against pressure overload-induced cardiac dysfunction. However, the mechanism is not completely understood. We here elucidate the potential mechanisms by which HSF1 protects against pressure overload-induced cardiac remodeling and dysfunction. A sustained constriction of transverse aorta (TAC) was imposed to HSF1 transgenic (TG), knockout (KO) and their littermate wild type (WT) male mice. Four weeks later, adaptive responses to TAC, such as cardiac hypertrophy, contractility and angiogenesis evaluated by echocardiography, catheterization, coronary perfusion pressure and immunohistochemistry were well preserved in TG but not in KO compared with WT mice. An angiogenesis inhibitor TNP-470 abrogated all these adaptive responses in TG mice, while cardiac transfection of VEGF with angiopoietin-1 rescued the broken heart in KO mice. In response to TAC, p53 was downregulated and hypoxia-inducing transcription factor-1 (HIF-1) was upregulated not only in the heart but also in the cultured cardiac endothelial cells (EC) of TG mice as compared to WT mice whereas these changes became opposite in KO mice. A small interfering RNA (siRNA) of HIF-1 but not a p53 gene impaired the adaptive responses of the heart and EC in TG mice, and a siRNA of p53 but not a HIF-1 gene significantly reversed the heart and EC disorders in KO mice after TAC. We conclude that HSF1 promotes cardiac angiogenesis through suppression of p53 and subsequent upregulation of HIF-1 in endothelial cells during chronic pressure overload, leading to the maintenance of cardiac adaptation.

A role of myocardial stiffness in cell-based cardiac repair: a hypothesis

Determining which time point is optimal for bone marrow‐derived cell (BMC) transplantation for acute myocardial infarction (AMI) has attracted a great deal of attention. Studies have verified the interaction between cell treatment effect and transfer timing and have suggested that the optimal time frame for BMC therapy is day 4 to day 7 after AMI. However, the potential mechanism underlying the time‐dependent therapeutic response remains unclear. Recently, a growing body of in vitro evidence has suggested that stem cells are able to feel and respond to the stiffness of their microenvironment to commit to a relevant lineage, indicating that soft matrices that mimic brain are neurogenic, stiffer matrices that mimic muscle are myogenic and comparatively rigid matrices that mimic collagenous bone prove osteogenic. Simultaneously, considering the fact that the myocardium post‐infarction experiences a time‐dependent stiffness change from flexible to rigid as a result of myocardial remodelling following tissue necrosis and massive extracellular matrix deposition, we presume that the myocardial stiffness within a certain time frame (possibly day 4–7) post‐AMI might provide a more favourable physical microenvironment for the phenotypic plasticity and functional specification of engrafted BMCs committed to some cell lineages, such as endothelial cells, vascular smooth muscle cells or cardiomyocytes. The beneficial effect facilitates angiogenesis and myocardiogenesis in the infarcted heart, and subsequently leads to more amelioration of cardiac functions. If the present hypothesis were true, it would be of great help to understand the mechanism underlying the optimal timing for BMC transplantation and to establish a direction for the time selection of cell therapy.

COUP-TFII switches responses of venous endothelium to atherosclerotic factors through controlling the profile of various inherent genes expression†

Endothelial cells of arteries (AEC) have a strikingly greater responsiveness to atherosclerosis factors than venous endothelial cells (VEC). However, the reasons for this phenomenon remain unclear. Chicken ovalbumin upstream promoter‐transcription factor II (COUP‐TFII) plays an important role in regulating embryonic arterial‐venous differentiation. We therefore investigate whether COUP‐TFII is related to this different susceptibility between AEC and VEC. It is first confirmed that COUP‐TFII is expressed in VEC but not in AEC in the adult. Using a siRNA strategy, we identified the expression of Jagged1 and Notch1 in cultured human VEC, which usually exist only in AEC, after knocking down of COUP‐TFII. To further elucidate the role of COUP‐TFII, we performed DNA microarrays in VEC transfected with the siRNA of COUP‐TFII and subsequently stimulated with angiotensin II (AngII) and compared the expression profiles of 112 genes involved in various atherosclerosis‐related pathways. The results indicated that expression of atherogenic genes was significantly upregulated after AngII stimulation in VEC transfected with COUP‐TFII siRNA. Moreover, in vitro cell functional assay showed that knockdown of COUP‐TFII in VEC increased not only basal but also AngII‐induced cell adhesions. These results demonstrate that COUP‐TFII suppresses the susceptibility of VEC to atherosclerosis through controlling the expression of various atherosclerosis‐related molecules. J. Cell. Biochem. 112: 256–264, 2011.

Ryanodine Receptor Type 2 Plays a Role in the Development of Cardiac Fibrosis under Mechanical Stretch Through TGFβ-1

Ryanodine receptor type 2 (RyR-2), the main Ca2+ release channel from sarcoplasmic reticulum in cardiomyocytes, plays a vital role in the regulation ofmyocardial contractile function and cardiac hypertrophy. However, the role of RyR-2 in cardiac fibrosis during the development of cardiac hypertrophy remains unclear.In this study, we examined whether RyR-2 regulates TGFβ1, which is secreted from cardiomyocytes and exerts on cardiac fibrosis using cultured cardiomyocytes and cardiac fibroblasts of neonatal rats. The expression of RyR-2 was found only in cardiomyocytesbut not in cardiac fibroblasts. Mechanical stretch induced upregulation of TGFβ1 in cardiomyocytes and RyR-2 knockdown significantly suppressed the upregulation of TGFβ1 expression. The transcript levels of collagen genes were also decreased in fibroblasts compare with wild type, although the expression of both two kinds was higher than those in stationary cardiomyocytes (non-stretch). With the inhibition of the TGFβ1-neutralizing antibody, the expression of collagen genes has no significant difference between the mechanically stretched cardiomyocytes and non-stretchedones. These results indicate that RyR-2 regulated TGFβ1 expression in mechanically stretched cardiomyocytes and TGFβ1 promoted collagen formation of cardiac fibroblasts by a paracrine mechanism.RyR-2 in mechanical stretch could promote the development of cardiac fibrosis involving TGFβ1-dependent paracrine mechanism. Our findings provided more insight into comprehensively understanding the molecular role of RyR-2 in regulating cardiac fibrosis.

QILIQIANGXIN INHIBITS THE DEVELOPMENT OF CARDIAC HYPERTROPHY, REMODELLING, AND DYSFUNCTION DURING 4 WEEKS OF PRESSURE OVERLOAD IN MICE

Objectives Qiliqiangxin (QL), a traditional Chinese medicine, has been used in the treatment of chronic heart failure. However, whether QL can benefit cardiac remodelling in the hypertensive state is unknown. We here examined the effects of QL on the development of cardiac hypertrophy through comparing those of losartan in C57BL/6 mice underlying transverse aorta constriction for 4 weeks. Methods QL and losartan were administrated at 0.6 mg and 13.4 mg kg· , respectively. Cardiac hypertrophy, function, and remodelling were evaluated by echocardiography, catheterisation, histology, and examination of specific gene expression and ERK phosphorylation. Cardiac apoptosis, autophagy, tumour necrosis factor α/insulin-like growth factor-1, and angiotensin II type 1 receptor expression and especially the proliferation of cardiomyocytes and phosphorylation of ErbB receptors were examined in vivo to elucidate the mechanisms. Results Transverse aorta constriction for 2 weeks resulted in a significant cardiac hypertrophy, which was significantly suppressed by either QL or losartan treatment. At 4 weeks after transverse aorta constriction, although the development of cardiac dysfunction and remodelling and the increases in apoptosis, autophagy, tumour necrosis factor α/insulin-like growth factor-1, and angiotensin II type 1 receptor expression were abrogated comparably between QL and losartan treatments, QL, but not losartan, enhanced proliferation of cardiomyocytes, which was paralleled with dowregulation of CCAAT/enhancer-binding protein β, upregulation of CBP/p300-interacting transactivator with ED-rich carboxy-terminal domain 4, and increases in ErbB2 and ErbB4 phosphorylation. Furthermore, inhibition of either ErbB2 or CBP/p300-interacting transactivator with ED-rich carboxy-terminal domain 4 abolished the cardiac protective effects of QL. Conclusions QL inhibits myocardial inflammation and cardiomyocyte death and promotes cardiomyocyte proliferation, leading to an ameliorated cardiac remodelling and function in a mouse model of pressure overload. The possible mechanisms may involve inhibition of angiotensin II type 1 receptor and activation of ErbB receptors.

Evolution of Vertebrate Ryanodine Receptors Family in Relation to Functional Divergence and Conservation

Ryanodine receptors (RyRs), the large homotetrameric protein complexes, regulate the release of calcium from intracellular stores into the cytosol and play vital roles in the excitation-contraction coupling of cells. However, the evolutionary relationship of RyRs in vertebrates has yet to be elucidated. We identified 22 RyRs from Homo sapiens, Mus musculus, Rattus norvegicus, Gallus gallus, Anolis carolinensis, Rana catesbeiana, and Danio rerio. The phylogenetic relationship, motifs analysis and reconstruction of ancestral RyRs showed that the members of RyR family in vertebrates were grouped into three clades: the RyR1 clade, the RyR2 clade, and the RyR3 clade. Positive selection existed in RyR gene evolution, which is consistent in three site models, and gene ontology (GO) analysis showed that the evolution of RyR family in vertebrates promotes RyRs function differentiation. At last, we predicted 140 mutation sites which may be involved in diseases and 57 phosphorylation sites among RyR1 sequence in human, as well as 61 mutation sites and 70 phosphorylation sites in human RyR2 sequences. Most of these potential sites are arranged in clusters. Our work provides insight into the origin and evolutionary process of RyRs in vertebrates, facilitating their functional investigations in the future.

ASSOCIATION OF STAT3 WITH HSF1 PLAYS A CRITICAL ROLE IN G-CSF-INDUCED CARDIO-PROTECTION AGAINST ISCHAEMIA/REPERFUSION INJURY

Objectives Granulocyte Colony-stimulating Factor (G-CSF) has been shown to be cardio-protective against ischaemia through activating Jak2/Stat3 pathway, however, the mechanism is unclear. Heat shock transcription factor 1 (HSF1), a definite endogenous protective protein in cardiomyocytes, may interact with Stat family under stress conditions. We hypothesised that G-CSF could induce cardio-protection against ischaemia/reperfusion (I/R) through association of HSF1 with Stat3. Methods To test the hypothesis, we built cardiac I/R injury model with HSF1 knockout (KO) mice and wild type (WT) mice by occlusion of the left anterior descending (LAD) coronary artery for 30 min and subsequent release of the occlusion for 24 h. These mice were administered with G-CSF (100 µg/kg/day) or vehicle subcutaneously for three days before surgery. Results As expected, G-CSF induced significant cardio-protections against I/R injury, characterised by higher ejection fraction (EF%), lower left ventricular end diastolic pressure (LVEDP), increased dP/dt value and decreased infarct area as compared with the vehicle treatment in WT mice. In HSF1-KO mice, however, these cardio-protections induced by G-CSF were greatly attenuated. Inhibition of oxidative stress-induced cardiomyocyte apoptosis by G-CSF also disappeared due to the deficiency of HSF1 in vitro and in vivo. Furthermore, G-CSF increased the phosphorylation and the association of Stat3 with HSF1, which enhanced transcriptional activity of HSF1. Inhibition of either Stat3 or HSF1 by pharmacological agents suppressed G-CSF-induced association of the two proteins and anti-apoptotic effect on cardiomyocytes. Conclusions Our data suggest that G-CSF stimulates phosphorylation and association of Stat3 with HSF1 and therefore enhances transcriptional activity of HSF1, leading to the cardio-protection against I/R injury.