Integration of calcium with the signaling network in cardiac myocytes

Integrated virtual screening and in vitro studies for exploring the mechanism of triterpenoids in Chebulae Fructus alleviating mesaconitine-induced cardiotoxicity via TRPV1 channel

Background: In traditional Mongolian or Tibetan medicine in China, Chebulae Fructus (CF) is widely used to process or combine with aconitums to decrease the severe toxicity of aconitums. Researches in this area have predominantly focused on tannins, with few research on other major CF components for cardiotoxicity mitigation. The present study aimed to clarify whether triterpenoids can attenuate the cardiotoxicity caused by mesaconitine (MA) and investigate the mechanism of cardiotoxicity attenuation. Methods: Firstly, the pharmacophore model, molecular docking, and 3D-QSAR model were used to explore the mechanism of CF components in reducing the toxicity of MA mediated by the TRPV1 channel. Then three triterpenoids were selected to verify whether the triterpenoids had the effect of lowering the cardiotoxicity of MA using H9c2 cells combined with MTT, Hoechst 33258, and JC-1. Finally, Western blot, Fluo-3AM, and MTT assays combined with capsazepine were used to verify whether the triterpenoids reduced H9c2 cardiomyocyte toxicity induced by MA was related to the TRPV1 channel. Results: Seven triterpenoids in CF have the potential to activate the TRPV1 channel. And they exhibited greater affinity for TRPV1 compared to other compounds and MA. However, their activity was relatively lower than that of MA. Cell experiments revealed that MA significantly reduced H9c2 cell viability, resulting in diminished mitochondrial membrane potential and nuclear pyknosis and damage. In contrast, the triterpenoids could improve the survival rate significantly and counteract the damage of MA to the cells. We found that MA, arjungenin (AR), and maslinic acid (MSA) except corosolic acid (CRA) upregulated the expression of TRPV1 protein. MA induced a significant influx of calcium, whereas all three triterpenoids alleviated this trend. Blocking the TRPV1 channel with capsazepine only increased the cell viability that had been simultaneously treated with MA, and AR, or MSA. However, there was no significant difference in the CRA groups treated with or without capsazepine. Conclusion: The triterpenoids in CF can reduce the cardiotoxicity caused by MA. The MSA and AR function as TRPV1 agonists with comparatively reduced activity but a greater capacity to bind to TRPV1 receptors, thus antagonizing the excessive activation of TRPV1 by MA.

Liver Transcriptome Response to Heat Stress in Beijing You Chickens and Guang Ming Broilers

Heat stress is one of the most prevalent issues in poultry production that reduces performance, robustness, and economic gains. Previous studies have demonstrated that native chickens are more tolerant of heat than commercial breeds. However, the underlying mechanisms of the heat tolerance observed in native chicken breeds remain unelucidated. Therefore, we performed a phenotypical, physiological, liver transcriptome comparative analysis and WGCNA in response to heat stress in one native (Beijing You, BY) and one commercial (Guang Ming, GM) chicken breed. The objective of this study was to evaluate the heat tolerance and identify the potential driver and hub genes related to heat stress in these two genetically distinct chicken breeds. In brief, 80 BY and 60 GM, 21 days old chickens were submitted to a heat stress experiment for 5 days (33 °C, 8 h/day). Each breed was divided into experimental groups of control (Ctl) and heat stress (HS). The results showed that BY chickens were less affected by heat stress and displayed reduced DEGs than GM chickens, 365 DEGs and 382 DEGs, respectively. The transcriptome analysis showed that BY chickens exhibited enriched pathways related to metabolism activity, meanwhile GM chickens’ pathways were related to inflammatory reactions. CPT1A and ANGPTL4 for BY chickens, and HSP90B1 and HSPA5 for GM chickens were identified as potential candidate genes associated with HS. The WGCNA revealed TLR7, AR, BAG3 genes as hub genes, which could play an important role in HS. The results generated in this study provide valuable resources for studying liver transcriptome in response to heat stress in native and commercial chicken lines.

Potential Mechanism of Dingji Fumai Decoction Against Atrial Fibrillation Based on Network Pharmacology, Molecular Docking, and Experimental Verification Integration Strategy

Background: Dingji Fumai Decoction (DFD), a traditional herbal mixture, has been widely used to treat arrhythmia in clinical practice in China. However, the exploration of the active components and underlying mechanism of DFD in treating atrial fibrillation (AF) is still scarce.

Methods: Compounds of DFD were collected from TCMSP, ETCM, and literature. The targets of active compounds were explored using SwissTargetPrediction. Meanwhile, targets of AF were collected from DrugBank, TTD, MalaCards, TCMSP, DisGeNET, and OMIM. Then, the H-C-T-D and PPI networks were constructed using STRING and analyzed using CytoNCA. Meanwhile, VarElect was utilized to detect the correlation between targets and diseases. Next, Metascape was employed for systematic analysis of the mechanism of potential targets and protein complexes in treating AF. AutoDock Vina, Pymol, and Discovery Studio were applied for molecular docking. Finally, the main findings were validated through molecular biology experiments.

Results: A total of 168 active compounds and 1,093 targets of DFD were collected, and there were 89 shared targets between DFD and AF. H-C-T-D network showed the relationships among DFD, active compounds, targets, and AF. Three functional protein complexes of DFD were extracted from the PPI network. Further systematic analysis revealed that the regulation of cardiac oxidative stress, cardiac inflammation, and cardiac ion channels were the potential mechanism of DFD in treating AF. Addtionally, molecular docking verified the interactions between active compounds and targets. Finally, we found that DFD significantly increased the level of SIRT1 and reduced the levels of ACE, VCAM-1, and IL-6.

Conclusions: DFD could be utilized in treating AF through a complicated mechanism, including interactions between related active compounds and targets, promoting the explanation and understanding of the molecular biological mechanism of DFD in the treatment of AF.

Genomic Analyses Reveal Genetic Adaptations to Tropical Climates in Chickens

The genetic footprints of adaptations to naturally occurring tropical stress along with domestication are poorly reported in chickens. Here, by conducting population genomic analyses of 67 chickens inhabiting distinct climates, we found signals of gene flow from Tibetan chickens to Sri Lankan and Saudi Arabian breeds and identified 12 positively selected genes that are likely involved in genetic adaptations to both tropical desert and tropical monsoon island climates. Notably, in tropical desert climate, advantageous alleles of TLR7 and ZC3HAV1, which could inhibit replication of viruses in cells, suggest immune adaptation to the defense against zoonotic diseases in chickens. Furthermore, comparative genomic analysis showed that four genes (OC90, PLA2G12B, GPR17 and TNFRSF11A) involved in arachidonic acid metabolism have undergone convergent adaptation to tropical desert climate between birds and mammals. Our study offers insights into the genetic mechanisms of adaptations to tropical climates in birds and other animals and provides practical value for breeding design and medical research on avian viruses.

Aconitine induces cardiotoxicity through regulation of calcium signaling pathway in zebrafish embryos and in H9c2 cells

Fuzi, the processed lateral roots of Aconitum carmichaelii Debx., is a traditional herbal medicine that is well known for its excellent pharmacological effects and acute toxicity. Aconitine is one of the diester-diterpene alkaloids and well-known for its arrhythmogenic effects. However, the effects of aconitine in zebrafish have rarely been studied. Therefore, we investigated the effects of aconitine on zebrafish embryos and H9c2 cells. Zebrafish embryos at 48 hours postfertilization were exposed to aconitine, and then, cardiac function and apoptosis were measured. Through transcriptomic analysis, the cardiotoxicity of aconitine in zebrafish embryos was involved in regulating Ca²⁺ signal pathways. A reverse transcription-polymerase chain reaction was performed to verify the expression of Ca²⁺ pathway-related genes after 12, 24, 36 and 48 hours of treatment. Meanwhile, intracellular Ca²⁺ concentrations and cell apoptosis were observed in H9c2 cells treated with half-maximal inhibitory concentration values of aconitine for 30 minutes. The protein levels of troponin T (TnT), caspase 3, Bcl-2 and Bax were detected by western blot analysis. In vivo, 2.0 and 8.0 μm aconitine decreased the heart rate and inhibited the contraction of ventricles and atria in a dose- and time-dependent manner. Furthermore, aconitine increased expression of cacna1c, RYR2, atp2a2b, Myh6, troponin C, p38, caspase 3, Bcl-2 and Bax for 12 hours. In vitro, 1.5 and 4.5 mm aconitine caused intracellular Ca²⁺ ion oscillation, increased rates of apoptosis, inhibited TnT and Bcl-2 protein expression, and promoted caspase 3 and Bax protein expression. These data confirmed that aconitine at various concentrations induced cardiac dysfunction and apoptosis were related to the Ca²⁺ signaling pathway.

Dexmedetomidine Postconditioning Reduces Brain Injury after Brain Hypoxia-Ischemia in Neonatal Rats

Perinatal asphyxia can lead to death and severe disability. Brain hypoxia-ischemia (HI) injury is the major pathophysiology contributing to death and severe disability after perinatal asphyxia. Here, seven-day old Sprague-Dawley rats were subjected to left brain HI. Dexmedetomidine was given intraperitoneally after the brain HI. Yohimbine or atipamezole, two α2 adrenergic receptor antagonists, were given 10 min before the dexmedetomidine injection. Neurological outcome was evaluated 7 or 28 days after the brain HI. Frontal cerebral cortex was harvested 6 h after the brain HI. Left brain HI reduced the left cerebral hemisphere weight assessed 7 days after the brain HI. This brain tissue loss was dose-dependently attenuated by dexmedetomidine. Dexmedetomidine applied within 1 h after the brain HI produced this effect. Dexmedetomidine attenuated the brain HI-induced brain tissue and cell loss as well as neurological and cognitive dysfunction assessed from 28 days after the brain HI. Dexmedetomidine postconditioning-induced neuroprotection was abolished by yohimbine or atipamezole. Brain HI increased tumor necrosis factor α and interleukin 1β in the brain tissues. This increase was attenuated by dexmedetomidine. Atipamezole inhibited this dexmedetomidine effect. Our results suggest that dexmedetomidine postconditioning reduces HI-induced brain injury in the neonatal rats. This effect may be mediated by α2 adrenergic receptor activation that inhibits inflammation in the ischemic brain tissues.

Arsenic trioxide triggered calcium homeostasis imbalance and induced endoplasmic reticulum stress-mediated apoptosis in adult rat ventricular myocytes

Arsenic trioxide (ATO) is a potent anticancer drug agent but its clinical use is often limited by severe cardiotoxicity. However, its exact mechanism remains poorly understood. In this study, we simultaneously explored the direct effect of ATO on cardiac contraction in adult rat ventricular myocytes and its effects on Ca²⁺ transient in real time by using an IonOptix MyoCam system. The results showed that ATO increased the amplitude of sarcomere shortening, the maximal velocity of relengthening and shortening (-dL/dt_max and +dL/dt_max), time-to-90% relengthening (TR90), and time-to-peak shortening (TPS), resulting in abnormal cardiomyocyte contraction. Meanwhile, ATO markedly increased the resting Ca²⁺ ratio, amplitude/resting calcium, the maximal velocity of Ca²⁺ shortening and relaxation (+d[Ca²⁺]/dt_max and -d[Ca²⁺]/dt_max), time-to-50% peak [Ca²⁺] _i and the decay rate of [Ca²⁺] _i transients, suggesting that ATO leads to intracellular imbalance of calcium homeostasis. ATO also inhibited sarcoplasmic reticulum Ca²⁺-ATPase 2a (SERCA2a) activity in a time-dependent manner and activated the endoplasmic reticulum (ER) stress reaction. These results revealed that ATO dramatically aggravates Ca²⁺ overload and promotes ER stress, eventually causing abnormal cardiomyocyte contraction in a dose-dependent and time-dependent manner.

H2O 2 induces myocardial hypertrophy in H9c2 cells: a potential role of Ube3a

Myocardial hypertrophy that often leads to eventual heart failure is a leading cause of mortality worldwide. While both apoptosis and cell proliferation have been reported to play an important part in heart failure, its exact triggering mechanism is still unclear. Reports have shown that low concentrations of H2O2 (10-30 µM) can induce myocardial hypertrophy without affecting survival. The ubiquitin ligase Ube3a has been reported to have a close affiliation with Angelman syndrome; but many ubiquitin ligases have been reported in a variety of cardiovascular conditions including myocardial hypertrophy. However, the relationship between Ube3a and myocardial hypertrophy has never been reported in literature. The rat cardiac myoblast cell line H9c2 and primary neonatal cardiomyocytes showed similar hypertrophic responses in vitro. In this report, we utilized H2O2 treatment on H9c2 cells to induce myocardial hypertrophy and determined the relationship between Ube3a and myocardial hypertrophy. Our results showed that 10-20 μM H2O2 can induce myocardial hypertrophy without affecting cell viability and inducing cell apoptosis, while the corresponding transcription and translation levels of Ube3a are significantly increased during the process. Therefore, these findings underline that Ube3a may play an important role in myocardial hypertrophy.

Emerging Novel Therapies for Heart Failure

Heart function fails when the organ is unable to pump blood at a rate proportional to the body’s need for oxygen or when this function leads to elevated cardiac chamber filling pressures (cardiogenic pulmonary edema). Despite our sophisticated knowledge of heart failure, even so-called ejection fraction-preserved heart failure has high rates of mortality and morbidity. So, novel therapies are sorely needed. This review discusses current standard therapies for heart failure and launches an exploration into emerging novel treatments on the heels of recently-approved sacubitril and ivbradine. For example, Vasoactive Intestinal Peptide (VIP) is protective of the heart, so in the absence of VIP, VIP knockout mice have dysregulation in key heart failure genes: 1) Force Generation and Propagation; 2) Energy Production and Regulation; 3) Ca⁺² Cycling; 4) Transcriptional Regulators. VIP administration leads to coronary dilation in human subjects. In heart failure patients, VIP levels are elevated as a plausible endogenous protective effect. With the development of elastin polymers to stabilize VIP and prevent its degradation, VIP may therefore have a chance to satisfy the unmet need as a potential treatment for acute heart failure.

Dysregulation of intracellular calcium transporters in animal models of sepsis-induced cardiomyopathy

Sepsis-induced cardiomyopathy (SIC) develops as the result of myocardial calcium (Ca) dysregulation. Here we reviewed all published studies that quantified the dysfunction of intracellular Ca transporters and the myofilaments in animal models of SIC. Cardiomyocytes isolated from septic animals showed, invariably, a decreased twitch amplitude, which is frequently caused by a decrease in the amplitude of cellular Ca transients (ΔCai) and sarcoplasmic reticulum (SR) Ca load (CaSR). Underlying these deficits, the L-type Ca channel is downregulated, through mechanisms that may involve adrenomedullin-mediated redox signaling. The SR Ca pump is also inhibited, through oxidative modifications (sulfonylation) of one reactive thiol group (on Cys) and/or modulation of phospholamban. Diastolic Ca leak of ryanodine receptors is frequently increased. In contrast, Na/Ca exchange inhibition may play a partially compensatory role by increasing CaSR and ΔCai. The action potential is usually shortened. Myofilaments show a bidirectional regulation, with decreased Ca sensitivity in milder forms of disease (due to troponin I hyperphosphorylation) and an increase (redox mediated) in more severe forms. Most deficits occurred similarly in two different disease models, induced by either intraperitoneal administration of bacterial lipopolysaccharide or cecal ligation and puncture. In conclusion, substantial cumulative evidence implicates various Ca transporters and the myofilaments in SIC pathology. What is less clear, however, are the identity and interplay of the signaling pathways that are responsible for Ca transporters dysfunction. With few exceptions, all studies we found used solely male animals. Identifying sex differences in Ca dysregulation in SIC becomes, therefore, another priority.

The importance of Ca(2+)-dependent mechanisms for the initiation of the heartbeat

Mechanisms underlying pacemaker activity in the sinus node remain controversial, with some ascribing a dominant role to timing events in the surface membrane (“membrane clock”) and others to uptake and release of calcium from the sarcoplasmic reticulum (SR) (“calcium clock”). Here we discuss recent evidence on mechanisms underlying pacemaker activity with a particular emphasis on the many roles of calcium. There are particular areas of controversy concerning the contribution of calcium spark-like events and the importance of I(f) to spontaneous diastolic depolarisation, though it will be suggested that neither of these is essential for pacemaking. Sodium-calcium exchange (NCX) is most often considered in the context of mediating membrane depolarisation after spark-like events. We present evidence for a broader role of this electrogenic exchanger which need not always depend upon these spark-like events. Short (milliseconds or seconds) and long (minutes) term influences of calcium are discussed including direct regulation of ion channels and NCX, and control of the activity of calcium-dependent enzymes (including CaMKII, AC1, and AC8). The balance between the many contributory factors to pacemaker activity may well alter with experimental and clinical conditions, and potentially redundant mechanisms are desirable to ensure the regular spontaneous heart rate that is essential for life. This review presents evidence that calcium is central to the normal control of pacemaking across a range of temporal scales and seeks to broaden the accepted description of the “calcium clock” to cover these important influences.

A compartmentalized mathematical model of the β1-adrenergic signaling system in mouse ventricular myocytes

The β₁-adrenergic signaling system plays an important role in the functioning of cardiac cells. Experimental data shows that the activation of this system produces inotropy, lusitropy, and chronotropy in the heart, such as increased magnitude and relaxation rates of [Ca²⁺]_i transients and contraction force, and increased heart rhythm. However, excessive stimulation of β₁-adrenergic receptors leads to heart dysfunction and heart failure. In this paper, a comprehensive, experimentally based mathematical model of the β₁-adrenergic signaling system for mouse ventricular myocytes is developed, which includes major subcellular functional compartments (caveolae, extracaveolae, and cytosol). The model describes biochemical reactions that occur during stimulation of β₁-adrenoceptors, changes in ionic currents, and modifications of Ca²⁺ handling system. Simulations describe the dynamics of major signaling molecules, such as cyclic AMP and protein kinase A, in different subcellular compartments; the effects of inhibition of phosphodiesterases on cAMP production; kinetics and magnitudes of phosphorylation of ion channels, transporters, and Ca²⁺ handling proteins; modifications of action potential shape and duration; magnitudes and relaxation rates of [Ca²⁺]_i transients; changes in intracellular and transmembrane Ca²⁺ fluxes; and [Na⁺]_i fluxes and dynamics. The model elucidates complex interactions of ionic currents upon activation of β₁-adrenoceptors at different stimulation frequencies, which ultimately lead to a relatively modest increase in action potential duration and significant increase in [Ca²⁺]_i transients. In particular, the model includes two subpopulations of the L-type Ca²⁺ channels, in caveolae and extracaveolae compartments, and their effects on the action potential and [Ca²⁺]_i transients are investigated. The presented model can be used by researchers for the interpretation of experimental data and for the developments of mathematical models for other species or for pathological conditions.

Generation and characterization of functional cardiomyocytes derived from human T cell-derived induced pluripotent stem cells

Induced pluripotent stem cells (iPSCs) have been proposed as novel cell sources for genetic disease models and revolutionary clinical therapies. Accordingly, human iPSC-derived cardiomyocytes are potential cell sources for cardiomyocyte transplantation therapy. We previously developed a novel generation method for human peripheral T cell-derived iPSCs (TiPSCs) that uses a minimally invasive approach to obtain patient cells. However, it remained unknown whether TiPSCs with genomic rearrangements in the T cell receptor (TCR) gene could differentiate into functional cardiomyocyte in vitro. To address this issue, we investigated the morphology, gene expression pattern, and electrophysiological properties of TiPSC-derived cardiomyocytes differentiated by floating culture. RT-PCR analysis and immunohistochemistry showed that the TiPSC-derived cardiomyocytes properly express cardiomyocyte markers and ion channels, and show the typical cardiomyocyte morphology. Multiple electrode arrays with application of ion channel inhibitors also revealed normal electrophysiological responses in the TiPSC-derived cardiomyocytes in terms of beating rate and the field potential waveform. In this report, we showed that TiPSCs successfully differentiated into cardiomyocytes with morphology, gene expression patterns, and electrophysiological features typical of native cardiomyocytes. TiPSCs-derived cardiomyocytes obtained from patients by a minimally invasive technique could therefore become disease models for understanding the mechanisms of cardiac disease and cell sources for revolutionary cardiomyocyte therapies.

Integration of microarray profiles associated with cardiomyopathy and the potential role of Ube3a in apoptosis

Cardiomyopathy is the one of the primary causes of mortality. High‑throughput genome datasets provide novel information that aids the understanding of the complex mechanisms involved in cardiomyopathy. However, the causative mechanisms underlying cardiomyopathy are yet to be elucidated. In order to improve the use of the high‑throughput genome datasets, the present study employed 9 microarray datasets to mine for differentially expressed cardiomyopathy‑associated genes using bioinformatic methods. Following validation using quantitative polymerase chain reaction, ubiquitin‑protein ligase E3a (Ube3a) was selected as a candidate gene for the disease. Substantial evidence suggests that apoptosis may be involved in the pathophysiology of cardiomyopathies. Therefore, in the present study, H2O2 was utilized to induce apoptosis in H9C2 cells in order to understand the interrelation between Ube3a and the apoptosis-related protein p53. Ube3a and p53 were observed to be significantly increased at the transcriptional and translational levels in response to H2O2 treatment. The results of this study indicate the efficiency of the data integration and the significant interrelation between Ube3a and p53 in myocardial cells during apoptosis.

Decoy peptides targeted to protein phosphatase 1 inhibit dephosphorylation of phospholamban in cardiomyocytes

Cardiac sarcoplasmic reticulum Ca(2+)-ATPase (SERCA2a) plays a crucial role in Ca(2+) handling in cardiomyocytes. Phospholamban (PLB) is an endogenous inhibitor of SERCA2a and its inhibitory activity is enhanced via dephosphorylation by protein phosphatase 1 (PP1). Therefore, the inhibition of PP1-mediated dephosphorylation of PLB might be an efficient strategy for the restoration of reduced SERCA2a activity in failing hearts. We sought to develop decoy peptides that would mimic phosphorylated PLB and thus competitively inhibit the PP1-mediated dephosphorylation of endogenous PLB. The phosphorylation sites Ser16 and Thr17 are located within the flexible loop region (amino acids 14-22) of PLB. We therefore synthesized a 9-mer peptide derived from this region (ΨPLB-wt) and two pseudo-phosphorylated peptides where Ser16 was replaced with Glu (ΨPLB-SE) or Thr17 was replaced with Glu (ΨPLB-TE). These peptides were coupled to the cell-permeable peptide TAT to facilitate cellular uptake. Treatment of adult rat cardiomyocytes with ΨPLB-SE or ΨPLB-TE, but not with ΨPLB-wt, significantly elevated the phosphorylation levels of PLB at Ser16 and Thr17. This increased phosphorylation of PLB correlated with an increase in contractile parameters in vitro. Furthermore, the perfusion of isolated rat hearts with ΨPLB-SE or ΨPLB-TE, but not with ΨPLB-wt, significantly improved left ventricular developed pressure that had been previously impaired by ischemia. These data indicate that ΨPLB-SE and ΨPLB-TE efficiently prevented dephosphorylation of PLB by serving as decoys for PP1. Therefore, these peptides may provide an effective modality to regulate SERCA2a activity in failing hearts.

hERG K+ Channels: Structure, Function, and Clinical Significance

The human ether-a-go-go related gene (hERG) encodes the pore-forming subunit of the rapid component of the delayed rectifier K+ channel, Kv11.1, which are expressed in the heart, various brain regions, smooth muscle cells, endocrine cells, and a wide range of tumor cell lines. However, it is the role that Kv11.1 channels play in the heart that has been best characterized, for two main reasons. First, it is the gene product involved in chromosome 7-associated long QT syndrome (LQTS), an inherited disorder associated with a markedly increased risk of ventricular arrhythmias and sudden cardiac death. Second, blockade of Kv11.1, by a wide range of prescription medications, causes drug-induced QT prolongation with an increase in risk of sudden cardiac arrest. In the first part of this review, the properties of Kv11.1 channels, including biogenesis, trafficking, gating, and pharmacology are discussed, while the second part focuses on the pathophysiology of Kv11.1 channels.

Analysis of p53 and NF-κB signaling in modulating the cardiomyocyte fate during hypertrophy

Cardiac hypertrophy leading to eventual heart failure is the most common cause of mortality throughout the world. The triggering mechanisms for cardiac hypertrophy are not clear but both apoptosis and cell proliferation have been reported in sections of failing hearts. In this study, we utilized both angiotensin II (AngII) treatment of cardiomyocytes and aortic ligation in rats (Rattus norvegicus, Wistar strain) for induction of hypertrophy to understand the cellular factors responsible for activation of apoptotic or anti-apoptotic pathway. Hypertrophy markers (ANF, β-MHC), apoptotic proteins (Bax, Bad, Fas, p53, caspase-3, PARP), and anti-apoptotic or cell proliferation marker proteins (Bcl2, NF-κB, Ki-67) were induced significantly during hypertrophy, both in vitro as well as in vivo. Co-localization of both active caspase-3 and Ki-67 was observed in hypertrophied myocytes. p53 and NF-κBp65 binding to co-activator p300 was also increased in AngII treated myocytes. Inhibition of p53 resulted in downregulation of apoptosis, NF-κB activation, and NF-κB-p300 binding; however, NF-κB inhibition did not inhibit apoptosis or p53-p300 binding. Blocking of either p53 or NF-κB by specific inhibitors resulted in decrease in cell proliferation and hypertrophy markers, suggesting that p53 initially binds to p300 and then this complex recruits NF-κB. Thus, these results indicate the crucial role of p53 in regulating both apoptotic and cell proliferation during hypertrophy.

S100A1 and calmodulin regulation of ryanodine receptor in striated muscle

The release of Ca2+ ions from the sarcoplasmic reticulum through ryanodine receptor calcium release channels represents the critical step linking electrical excitation to muscular contraction in the heart and skeletal muscle (excitation-contraction coupling). Two small Ca2+ binding proteins, S100A1 and calmodulin, have been demonstrated to bind and regulate ryanodine receptor in vitro. This review focuses on recent work that has revealed new information about the endogenous roles of S100A1 and calmodulin in regulating skeletal muscle excitation-contraction coupling. S100A1 and calmodulin bind to an overlapping domain on the ryanodine receptor type 1 to tune the Ca2+ release process, and thereby regulate skeletal muscle function. We also discuss past, current and future work surrounding the regulation of ryanodine receptors by calmodulin and S100A1 in both cardiac and skeletal muscle, and the implications for excitation-contraction coupling.

Molecular mechanisms in evolutionary cardiology failure

Integration of the relevant evolutionary paradigm in cardiology has not yet been fully achieved: In the past, heart failure (HF) was mainly ascribed to infections, and the origins of cardiac hypertrophy (CH) were regarded as mechanical. Recent changes in lifestyle have both reduced the incidence of infections and increased lifespan, and HF is now seen as a complex disease--one that is still caused by mechanical disorder, but also associated with ischemia and senescence. The long-held view that CH serves to restore myocardial economy back to normal is still valid. The adaptive process is characterized by a quantitative and a qualitative fetal gene reprogramming, which is now being confirmed by recent advances in microRNA research. It underscores the fact CH is the physiologic reaction of the heart to a pathologic stimulus. The goal for therapy is economic, not inotropic. Another major issue is myocardial fibrosis, a major determinant of diastolic function and arrhythmias. Recent changes in lifestyle have crucially modified the context in which HF occurs.

Targeting cancer with phosphodiesterase inhibitors

IMPORTANCE OF THE FIELD

For many cancers, there has been a shift from management with traditional, nonspecific cytotoxic chemotherapies to treatment with molecule-specific targeted therapies that are used either alone or in combination with traditional chemotherapy and radiation therapy. Accumulating data suggest that multi-targeted agents may produce greater benefits than those observed with single-targeted therapies, may have acceptable tolerability profiles, and may be active against a broader range of tumour types. Thus, regulation of cyclic nucleotide signalling is properly regarded as a composite of multiple component pathways involved in diverse aspects of tumour cell function. The impairment of cAMP and/or cGMP generation by overexpression of PDE isoforms that has been described in various cancer pathologies, and the effects of PDE inhibitors in tumour models in vitro and in vivo, may offer promising insight into future cancer treatments because of the numerous advantages of PDE inhibitors.

AREAS COVERED IN THIS REVIEW

In this review, we focus on the expression and regulation of cyclic nucleotide phosphodiesterases (PDEs) in tumour progression and provide evidence that PDE inhibitors may be effective agents for treating cancer; the review covers literature from the past several years.

WHAT THE READER WILL GAIN

PDEs have been studied in a variety of tumours; data have suggested that the levels of PDE activity are elevated and, therefore, the ratio of cGMP to cAMP is affected. In addition, PDE inhibitors may be potential targets for tumour cell growth inhibition and induction of apoptosis. This review explores the prospects of targeting PDEs with therapeutic agents for cancer, as well as the shortcomings of this approach such as dose-limiting side effects, toxicity/efficacy ratio and selectivity towards tumour tissue. In addition, it includes opinions and suggestion for developing PDE inhibition for cancer treatment from initial concept to potential therapeutic application and final relevance in clinical use.

TAKE HOME MESSAGE

Impaired cAMP and/or cGMP generation upon overexpression of PDE isoforms has been described in various cancer pathologies. Inhibition of selective PDE isoforms, which raises the levels of intracellular cAMP and/or cGMP, induces apoptosis and cell cycle arrest in a broad spectrum of tumour cells and regulates the tumour microenvironment. Therefore, the development and clinical application of inhibitors specific for individual PDE isoenzymes may selectively restore normal intracellular signalling, providing antitumour therapy with reduced adverse effects.

Functional characterization of the cAMP-binding proteins Epac in cardiac myocytes

The cyclic AMP (cAMP)-binding proteins, Epac, are guanine nucleotide exchange factors for the Ras-like small GTPases. Since their discovery in 1998 and with the development of specific Epac agonists, many data in the literature have illustrated their critical role in multiple cellular events mediated by the second messenger cAMP. Given the importance of cAMP in cardiovascular physiology and physiopathology, there is a growing interest to delineate the role of these multi-domain Epac in the cardiovascular system. This review will focus on recent pharmacological and biochemical studies aiming at understanding the role of Epac in cardiomyocyte signaling and hypertrophy.

Myocardial ischemic-reperfusion injury in a rat model of metabolic syndrome

Hearts of NaCl-induced hypertensive-glucose intolerant (HGI) rats develop reduced infarcts after ischemia-reperfusion injury (IRI) than their hypertensive (H) counterparts. Because high intake of saturated fat is a major risk factor for ischemic heart disease, we tested the hypothesis that chronic (18 weeks) consumption of a high saturated fat diet increases susceptibility to IRI, an effect more marked in the HGI rats than in the H rats. The fat-fed H (HFAT) rat displayed significantly higher body weight and plasma leptin content compared to the H, HGI, or fat-fed HGI (HGIFAT) rats which all showed similar values. In contrast, plasma triglyceride concentration was significantly higher in the HGIFAT rat than in the other three groups. Plasma insulin concentration was similar in the two H groups but higher than that of the two HGI groups. Compared to the H rat, the HGI rat was markedly glucose intolerant, with fat feeding causing comparable worsening of glucose intolerance in each group. The HGIFAT rats displayed a reduction in baseline myocardial contractility and relaxation and a higher end-diastolic pressure compared to the other three groups. Infarct size was significantly lower in the HGI rats than in the H rats. Although fat feeding did not affect infarct size of the H rat, it worsened that of the HGIFAT rat thereby abrogating the differential that existed between the H and HGI rats. In conclusion, excess fat feeding impairs myocardial function of HGI rats and increases their susceptibility to IRI. These findings are of relevance to the metabolic syndrome that manifests as a cluster of insulin resistance, dyslipidemia, and systemic hypertension.

Treatment with alpha-melanocyte stimulating hormone preserves calcium regulatory proteins in rat heart allografts

Prevention of graft dysfunction is a major objective in transplantation medicine. Previous research on experimental heart transplantation indicated that treatment with the immunomodulatory peptide alpha-melanocyte stimulating hormone (alpha-MSH) improves histopathology, prolongs allograft survival, and reduces expression of the main tissue injury mediators. Because calcium-handling is critical in heart graft function, we determined the effects of transplantation injury and influences of alpha-MSH treatment on representative calcium regulatory proteins in rat heart allografts. Hearts from Brown Norway rats were transplanted heterotopically into MHC incompatible Lewis rats. Ca(2+)/calmodulin-dependent protein kinase II (CaMKII), protein kinase C epsilon (PKC epsilon), sarcoplasmic/endoplasmic reticulum calcium-ATPase 2 (SERCA2a), arrestin-beta1 (Arrb1), cholinergic receptor M2 (Chrm2), and inositol 1,4,5-triphosphate receptor 1 (InsP(3)R1) were examined in: (1) non-transplanted donor hearts; (2) allografts from saline-treated rats; and (3) allografts from rats treated with the synthetic alpha-MSH analog Nle4-DPhe7-alpha-MSH (NDP-alpha-MSH) (100 microg i.p. every 12h). Transplantation injury was associated with severe reduction in calcium regulatory protein transcription and expression level. NDP-alpha-MSH administration partly reversed inhibition of protein transcription and almost completely prevented protein loss. Finally, because certain effects of cyclic 3'-5'-adenosine monophosphate (cAMP) signaling on calcium handling in cardiac myocytes depend on activation of exchange protein directly activated by cAMP 1 (Epac1), we determined Epac1 mRNA and protein expression in heart allografts. Transplantation injury markedly reduced Epac1. NDP-alpha-MSH treatment significantly preserved both Epac1 protein and mRNA in the allografts. Administration of alpha-MSH or related melanocortins could reduce transplantation-induced dysfunction through protection of heart calcium regulatory proteins.

The L-Type Ca+ and KATP channels may contribute to pacing-induced protection against anoxia-reoxygenation in the embryonic heart model

L-Type Ca(2+) and K(ATP) Channels in Pacing-Induced Cardioprotection.

AIMS

The L-type Ca(2+) channel, the sarcolemmal (sarcK(ATP)), and mitochondrial K(ATP) (mitoK(ATP)) channels are involved in myocardial preconditioning. We aimed at determining to what extent these channels can also participate in pacing-induced cardioprotection.

METHODS

Hearts of 4-day-old chick embryos were paced in ovo during 12 hour using asynchronous intermittent ventricular stimulation at 110% of the intrinsic rate. Sham operated and paced hearts were then submitted in vitro to anoxia (30 minutes) and reoxygenation (60 minutes). These hearts were exposed to L-type Ca(2+) channel agonist Bay-K-8644 (BAY-K) or blocker verapamil, nonselective K(ATP) channel antagonist glibenclamide (GLIB), mitoK(ATP) channel agonist diazoxide (DIAZO), or antagonist 5-hydroxydecanoate. Electrocardiogram, electromechanical delay (EMD) reflecting excitation-contraction (E-C) coupling, and contractility were determined.

RESULTS

Under normoxia, heart rate, QT duration, conduction, EMD, and ventricular shortening were similar in sham and paced hearts. During reoxygenation, arrhythmias ceased earlier and ventricular EMD recovered faster in paced hearts than in sham hearts. In sham hearts, BAY-K (but not verapamil), DIAZO (but not 5-hydroxydecanoate) or GLIB accelerated recovery of ventricular EMD, reproducing the pacing-induced protection. By contrast, none of these agents further ameliorated recovery of the paced hearts.

CONCLUSION

The protective effect of chronic asynchronous pacing at near physiological rate on ventricular E-C coupling appears to be associated with subtle activation of L-type Ca(2+) channel, inhibition of sarcK(ATP) channel, and/or opening of mitoK(ATP) channel.

Modulation of the c-Jun N-terminal kinase activity in the embryonic heart in response to anoxia-reoxygenation: involvement of the Ca2+ and mitoKATP channels

Whether the response of the fetal heart to ischemia-reperfusion is associated with activation of the c-Jun N-terminal kinase (JNK) pathway is not known. In contrast, involvement of the sarcolemmal L-type Ca2+ channel (LCC) and the mitochondrial KATP (mitoKATP) channel has been established. This work aimed at investigating the profile of JNK activity during anoxia-reoxygenation and its modulation by LCC and mitoK(ATP) channel. Hearts isolated from 4-day-old chick embryos were submitted to anoxia (30 min) and reoxygenation (60 min). Using the kinase assay method, the profile of JNK activity in the ventricle was determined every 10 min throughout anoxia-reoxygenation. Effects on JNK activity of the LCC blocker verapamil (10 nM), the mitoK(ATP) channel opener diazoxide (50 microM) and the blocker 5-hydroxydecanoate (5-HD, 500 microM), the mitochondrial Ca2+ uniporter (MCU) inhibitor Ru360 (10 microM), and the antioxidant N-(2-mercaptopropionyl) glycine (MPG, 1 mM) were determined. In untreated hearts, JNK activity was increased by 40% during anoxia and peaked fivefold relative to basal level after 30-40 min reoxygenation. This peak value was reduced by half by diazoxide and was tripled by 5-HD. Furthermore, the 5-HD-mediated stimulation of JNK activity during reoxygenation was abolished by diazoxide, verapamil or Ru360. MPG had no effect on JNK activity, whatever the conditions. None of the tested pharmacological agents altered JNK activity under basal normoxic conditions. Thus, in the embryonic heart, JNK activity exhibits a characteristic pattern during anoxia and reoxygenation and the respective open-state of LCC, MCU and mitoKATP channel can be a major determinant of JNK activity in a ROS-independent manner.

S100A1: a novel inotropic regulator of cardiac performance. Transition from molecular physiology to pathophysiological relevance

Here we review the considerable body of evidence that has accumulated to support the notion of S100A1, a cardiac-specific Ca2+-sensor protein of the EF-hand type, as a physiological regulator of excitation-contraction coupling and inotropic reserve mechanisms in the mammalian heart. In particular, molecular mechanisms will be discussed conveying the Ca2+-dependent inotropic actions of S100A1 protein in cardiomyocytes occurring independently of β-adrenergic signaling. Moreover, we will shed light on the molecular structure-function relationship of S100A1 with its cardiac target proteins at the sarcoplasmic reticulum, the sarcomere, and the mitochondria. Furthermore, pathophysiological consequences of disturbed S100A1 protein expression on altered Ca2+handling and intertwined systems in failing myocardium will be highlighted. Subsequently, therapeutic options by means of genetic manipulation of cardiac S100A1 expression will be discussed, aiming to complete our current understanding of the role of S100A1 in diseased myocardium.

Comprehensive identification and characterization of novel cardiac genes in mouse

Comprehensive understanding of the molecular and physiological events occurring in cardiac muscle requires identification of unknown genes expressed in this tissue. We analyzed the mouse cardiac muscle UniGene library containing 827 gene-oriented transcript clusters, predicting that 19% of these genes are unknown. We systematically identified 15 authentic novel genes abundantly expressed in cardiac muscle. Northern blot analysis revealed transcriptional characteristics of the genes, such as transcript size and presence of isoforms. Transfection assays performed using various cell lines including mouse cardiac muscle cells provided information on the cellular characteristics of the novel proteins. Using correlation analysis, we identified co-regulated genes from previously reported microarray data sets. Our in silico and in vitro data suggest that a number of the novel genes are implicated in calcium metabolism, mitochondrial functions and gene transcription. In particular, we obtained new and direct evidence that one of the novel proteins is a calcium-binding protein. Taken together, we identified and characterized a number of novel cardiac genes by integrative approach. Our inclusive data establish a firm basis for future investigation into the cardiac gene network and functions of these genes.

cAMP and cGMP signaling cross-talk: role of phosphodiesterases and implications for cardiac pathophysiology

Cyclic nucleotide phosphodiesterases regulate cAMP-mediated signaling by controlling intracellular cAMP content. The cAMP-hydrolyzing activity of several families of cyclic nucleotide phosphodiesterases found in human heart is regulated by cGMP. In the case of PDE2, this regulation primarily involves the allosteric stimulation of cAMP hydrolysis by cGMP. For PDE3, cGMP acts as a competitive inhibitor of cAMP hydrolysis. Several cGMP-mediated responses in cardiac cells, including a potentiation of Ca(2+) currents and a diminution of the responsiveness to beta-adrenergic receptor agonists, have been shown to result from the effects of cGMP on cAMP hydrolysis. These effects appear to be dependent on the specific spatial distribution of the cGMP-generating and cAMP-hydrolyzing proteins, as well as on the intracellular concentrations of the two cyclic nucleotides. Gaining a more precise understanding of how these cross-talk mechanisms are individually regulated and coordinated is an important direction for future research.

New perspectives on the role of SERCA2's Ca2+ affinity in cardiac function

Cardiomyocyte relaxation and contraction are tightly controlled by the activity of the cardiac sarco(endo)plasmic reticulum (SR) Ca2+ transport ATPase (SERCA2a). The SR Ca2+ -uptake activity not only determines the speed of Ca(2+) removal during relaxation, but also the SR Ca2+ content and therefore the amount of Ca2+ released for cardiomyocyte contraction. The Ca2+ affinity is the major determinant of the pump's activity in the physiological Ca2+ concentration range. In the heart, the affinity of the pump for Ca2+ needs to be controlled between narrow borders, since an imbalanced affinity may evoke hypertrophic cardiomyopathy. Several small proteins (phospholamban, sarcolipin) adjust the Ca2+ affinity of the pump to the physiological needs of the cardiomyocyte. It is generally accepted that a chronically reduced Ca2+ affinity of the pump contributes to depressed SR Ca2+ handling in heart failure. Moreover, a persistently lower Ca2+ affinity is sufficient to impair cardiomyocyte SR Ca2+ handling and contractility inducing dilated cardiomyopathy in mice and humans. Conversely, the expression of SERCA2a, a pump with a lower Ca2+ affinity than the housekeeping isoform SERCA2b, is crucial to maintain normal cardiac function and growth. Novel findings demonstrated that a chronically increased Ca2+ affinity also may trigger cardiac hypertrophy in mice and humans. In addition, recent studies suggest that some models of heart failure are marked by a higher affinity of the pump for Ca2+, and hence by improved cardiomyocyte relaxation and contraction. Depressed cardiomyocyte SR Ca2+ uptake activity may therefore not be a universal hallmark of heart failure.