The sarcoplasmic reticulum Ca2+-ATPase (SERCA2) gene promoter activity is decreased in response to severe left ventricular pressure-overload hypertrophy in rat hearts

miR-731 modulates the zebrafish heart morphogenesis via targeting Calcineurin/Nfatc3a pathway

BACKGROUND

Zebrafish miR-731 is orthologous of human miR-425, which has been demonstrated to have cardio-protective roles by a variety of mechanisms. The miR-731 morphants show pericardium enlargement, and many DEGs (differentially expressed genes) are enriched in 'Cardiac muscle contraction' and 'Calcium signaling pathway', implying that miR-731 plays a potential role in heart function and development. However，the in vivo physiological role of miR-731 in the heart needs to be fully defined.

METHODS

Zebrafish miR-731 morphants were generated by morpholino knockdown, and miR-731 knockout zebrafish was generated by CRISRP/Cas9. We observed cardiac morphogenesis based on whole-mount in situ hybridization. Furthermore, RNA-seq and qRT-PCR were used to elucidate the molecular mechanism and analyze the gene expression. Double luciferase verification and Western blot were used to verify the target gene.

RESULTS

The depletion of miR-731 in zebrafish embryos caused the deficiency of cardiac development and function, which was associated with reduced heart rate, ventricular enlargement and heart looping disorder. In addition, mechanistic study demonstrated that Calcineurin/Nfatc3a signaling involved in miR-731 depletion induced abnormal cardiac function and developmental defects.

CONCLUSION

MiR-731 regulates cardiac function and morphogenesis through Calcineurin/Nfatc3a signaling.

GENERAL SIGNIFICANCE

Our studies highlight the potential importance of miR-731 in cardiac development.

Mitochondrial Ca2+ in heart failure: Not enough or too much?

Ca²⁺ serves as a ubiquitous second messenger mediating a variety of cellular processes including electrical excitation, contraction, gene expression, secretion, cell death and others. The identification of the molecular components of the mitochondrial Ca²⁺ influx and efflux pathways has created a resurgent interest in the regulation of mitochondrial Ca²⁺ balance and its physiological and pathophysiological roles. While the pace of discovery has quickened with the availability of new cellular and animal models, many fundamental questions remain to be answered regarding the regulation and functional impact of mitochondrial Ca²⁺ in health and disease. This review highlights several experimental observations pertaining to key aspects of mitochondrial Ca²⁺ homeostasis that remain enigmatic, particularly whether mitochondrial Ca²⁺ signaling is depressed or excessive in heart failure, which will determine the optimal approach to therapeutic intervention.

Metoprolol alleviates arginine vasopressin-induced cardiomyocyte hypertrophy by upregulating the AKT1-SERCA2 cascade in H9C2 cells

Background

Arginine vasopressin (AVP) is elevated in patients with heart failure, and the increase in the AVP concentration in plasma is positively correlated with disease severity and mortality. Metoprolol (Met) is a beta blocker that is widely used in the clinic to treat pathological cardiac hypertrophy and to improve heart function. However, the specific mechanism by which Met alleviates AVP-induced pathological cardiac hypertrophy is still unknown. Our current study aimed to evaluate the inhibitory effects of Met on AVP-induced cardiomyocyte hypertrophy and the underlying mechanisms.

Methods

AVP alone or AVP plus Met was added to the wild type or AKT1-overexpressing rat cardiac H9C2 cell line. The cell surface areas and ANP/BNP/β-MHC expressions were used to evaluate the levels of hypertrophy. Western bolting was used to analyze AKT1/P-AKT1, AKT2/P-AKT2, total AKT, SERCA2, and Phospholamban (PLN) expression. Fluo3-AM was used to measure the intracellular Ca²⁺ stores.

Results

In the current study, we found that AKT1 but not AKT2 mediated the pathogenesis of AVP-induced cardiomyocyte hypertrophy. Sustained stimulation (48 h) with AVP led to hypertrophy in the H9C2 rat cardiomyocytes, resulting in the downregulation of AKT1 (0.48 fold compared to control) and SERCA2 (0.62 fold), the upregulation of PLN (1.32 fold), and the increase in the cytoplasmic calcium concentration (1.52 fold). In addition, AKT1 overexpression increased the expression of SERCA2 (1.34 fold) and decreased the expression of PLN (0.48 fold) in the H9C2 cells. Moreover, we found that Met could attenuate the AVP-induced changes in AKT1, SERCA2 and PLN expression and decreased the cytoplasmic calcium concentration in the H9C2 cells.

Conclusions

Our results demonstrated that the AKT1-SERCA2 cascade served as an important regulatory pathway in AVP-induced pathological cardiac hypertrophy.

Sarcoplasmic reticulum and calcium signaling in muscle cells: Homeostasis and disease

The sarco/endoplasmic reticulum is an extensive, dynamic and heterogeneous membranous network that fulfills multiple homeostatic functions. Among them, it compartmentalizes, stores and releases calcium within the intracellular space. In the case of muscle cells, calcium released from the sarco/endoplasmic reticulum in the vicinity of the contractile machinery induces cell contraction. Furthermore, sarco/endoplasmic reticulum-derived calcium also regulates gene transcription in the nucleus, energy metabolism in mitochondria and cytosolic signaling pathways. These diverse and overlapping processes require a highly complex fine-tuning that the sarco/endoplasmic reticulum provides by means of its numerous tubules and cisternae, specialized domains and contacts with other organelles. The sarco/endoplasmic reticulum also possesses a rich calcium-handling machinery, functionally coupled to both contraction-inducing stimuli and the contractile apparatus. Such is the importance of the sarco/endoplasmic reticulum for muscle cell physiology, that alterations in its structure, function or its calcium-handling machinery are intimately associated with the development of cardiometabolic diseases. Cardiac hypertrophy, insulin resistance and arterial hypertension are age-related pathologies with a common mechanism at the muscle cell level: the accumulation of damaged proteins at the sarco/endoplasmic reticulum induces a stress response condition termed endoplasmic reticulum stress, which impairs proper organelle function, ultimately leading to pathogenesis.

Resveratrol and polydatin as modulators of Ca2+ mobilization in the cardiovascular system

In the cardiovascular system, Ca²⁺ controls cardiac excitation-contraction coupling and vascular contraction and dilation. Disturbances in intracellular Ca²⁺ homeostasis induce malfunctions of the cardiovascular system, including cardiac pump dysfunction, arrhythmia, remodeling, and apoptosis, as well as hypertension and impairment of vascular reactivity. Therefore, developing drugs and strategies manipulating Ca²⁺ handling are highly valued in the treatment of cardiovascular disease. Resveratrol (Res) and polydatin (PD), a Res glucoside, have been well established to have beneficial effects on improving cardiovascular function. Studies from our laboratory and others have demonstrated that they exhibit inotropic effects on normal heart and therapeutic effects on hypertension, cardiac ischemia/reperfusion injury, hypertrophy, and heart failure by manipulating Ca²⁺ mobilization. The actions of Res and PD on Ca²⁺ signals delicately manipulated by multiple Ca²⁺ -handling proteins are pleiotropic and somewhat controversial, depending on cellular species and intracellular oxidative status. Here, we focus on the effects of Res and PD on controlling Ca²⁺ homeostasis in the heart and vasculature under normal and diseased conditions and highlight the key direct and indirect molecules mediating these effects.

Short-term effects of β2-AR blocker ICI 118,551 on sarcoplasmic reticulum SERCA2a and cardiac function of rats with heart failure

The study was conducted to examine the effects of ICI 118,551 on the systolic function of cardiac muscle cells of rats in heart failure and determine the molecular mechanism of selective β2-adrenergic receptor (β2-AR) antagonist on these cells. The chronic heart failure model for rats was prepared through abdominal aortic constriction and separate cardiac muscle cells using the collagenase digestion method. The rats were then divided into Sham, HF and HF+ICI 50 nM goups and cultivated for 48 h. β2-AR, Gi/Gs and sarcoplasmic reticulum Ca²⁺-ATPase (SERCA2a) protein expression levels in the cardiac muscle cells were evaluated by western blotting and changes in the systolic function of cardiac muscle cells based on the boundary detection system of contraction dynamics for individual cells was measured. The results showed that compared with the Sham group, the survival rate, percentage of basic contraction and maximum contraction amplitude percentage of cardiac muscle cells with heart failure decreased, Gi protein expression increased while Gs and SERCA2a protein expression decreased. Compared with the HF group, the maximum contraction amplitude percentage of cardiac muscle cells in group HF+ICI 50 nM decreased, the Gi protein expression level increased while the SERCA2a protein expression level decreased. Following the stimulation of Ca²⁺ and ISO, the maximum contraction amplitude percentage of cardiac muscle cells in the HF+ICI 50 nM group was lower than that in group HF. This indicated that ICI 118,551 has negative inotropic effects on cardiac muscle cells with heart failure, which may be related to Gi protein. Systolic function of cardiac muscle cells with heart failure can therefore be reduced by increasing Gi protein expression and lowering SERCA2a protein expression.

Cardiac-protective effects and the possible mechanisms of alatamine during acute myocardial ischemia

Alatamine is a constituent in the extract of a traditional herbal medicine Ramulus euonymi widely used for cardiac protection. However, its precise effects remain unclear. In the present study, we found that alatamine was able to reduce acute myocardial ischemia (AMI)-induced cardiac dysfunction in a rat model, as reflected by significantly restored electrocardiograms, M-mode echocardiograms, and left ventricular hemodynamics. Also, Nagar Olsen staining revealed that alatamine markedly reduced AMI-induced cardiac injury and cardiac myocyte apoptosis. TUNEL and caspase-3 activity assay showed that cardiac myocytes underwent significant apoptosis during AMI, and levels of LDH and CK-MB increased in the serum. However, such changes were significantly inhibited by pre-administration of alatamine. Furthermore, such anti-apoptotic effects of alatamine was also confirmed in a cardiac myocyte model of isoproterenol (ISO)-induced damage. Mechanistically, it was also found that alatamine improved the expression and activity of sarcoplasmic/endoplasmic reticulum Ca2+ ATPase (SERCA), which were inhibited during AMI, promoting contractility and relaxation. Meanwhile, alatamine decreased Bax and increased Bcl-2 expressions both in vivo and in vitro, therefore inhibiting cardiac myocyte apoptosis and preventing cardiac dysfunction caused by AMI at the cellular level. The present study revealed the beneficial role of alatamine in cardiac protection and highlighted it as a potential therapeutic reagent for reduction of AMI-induced cardiac injury.

Silencing calcineurin A subunit reduces SERCA2 expression in cardiac myocytes

Resting intracellular Ca(2+) can be raised, in neonatal rat cardiac myocytes, by exposure to very low concentration of thapsigargin (TG). Such a Ca(2+) rise yields calcineurin (CN) activation demonstrated by increased expression of transfected luciferase cDNA under control of nuclear factor of activated T-cells (NFAT) promoter and increased translocation of NFAT to nuclei. We found that exposure of cardiac myocytes to TG is followed by increase of sarcroplasmic reticulum Ca(2+) transport ATPase (SERCA2) expression, which is further increased when CN inactivation by CAMKII (calmodulin-dependent kinase) is prevented with KN93 (CAMKII inhibitor). On the other hand, SERCA2 expression is reduced by CN inhibition with cyclosporine. We have now induced calcineurin A (CNA) α- or β-subunit gene silencing with small interfering RNA (siRNA) and observed strong interference with expression of SERCA2, both in control myocytes and following exposure to TG. Such interference is also obtained following NFAT displacement from CN with 9,10-dihydro-9,10[1',2']-benzenoanthracene-1,4-dione (INCA-6). We have also observed analogous effects on expression of phospholamban (PLB) and Na(+)/Ca(2+) exchanger (NCX). Pertinent to these findings, we have identified, by in-silico analysis, NFAT binding sites in SERCA2, PLB, and NCX1 promoters. Our experiments indicate that activation of the calcineurin-NFAT pathway by rise of resting cytosolic Ca(2+) elevates transcription/expression of SERCA2, PLB, and NCX1, providing a homeostatic mechanism for long-term control of cytosolic Ca(2+).

Increased FOG-2 in failing myocardium disrupts thyroid hormone-dependent SERCA2 gene transcription

Reduced expression of sarcoplasmic reticulum calcium ATPase (SERCA)2 and other genes in the adult cardiac gene program has raised consideration of an impaired responsiveness to thyroid hormone (T3) that develops in the advanced failing heart. Here, we show that human and murine cardiomyopathy hearts have increased expression of friend of GATA (FOG)-2, a cardiac nuclear hormone receptor corepressor protein. Cardiac-specific overexpression of FOG-2 in transgenic mice led to depressed cardiac function, activation of the fetal gene program, congestive heart failure, and early death. SERCA2 transcript and protein levels were reduced in FOG-2 transgenic hearts, and FOG-2 overexpression impaired T3-mediated SERCA2 expression in cultured cardiomyocytes. FOG-2 physically interacts with thyroid hormone receptor-alpha1 and abrogated even high levels of T3-mediated SERCA2 promoter activity. These results demonstrate that SERCA2 is an important target of FOG-2 and that increased FOG-2 expression may contribute to a decline in cardiac function in end-stage heart failure by impaired T3 signaling.

Regulation of phospholamban and sarcoplasmic reticulum Ca2+-ATPase by atorvastatin: implication for cardiac hypertrophy

Abnormal intracellular Ca2+ homeostasis in the myocardium has been suggested as the cause of cardiac hypertrophy, and this process can be prevented by the HMG-CoA reductase inhibitors, statins. In the present study, the effect of atorvastatin on left ventricular hypertrophy was investigated, and then whether the underlying mechanism was related to a defect in intracellular Ca2+ homeostasis explored. Twelve spontaneously hypertensive rats (SHR), at 8 weeks old, were used in this study, and received either distilled water or atorvastatin for ten weeks, with age-matched normotensive Wistar-Kyoto rats (WKY) used as controls. RT-PCR and western blotting were used to detect the mRNA and protein expressions of phospholamban (PLB) and sarcoplasmic reticulum Ca2+-ATPase (SERCA2a), respectively, and a colorimetric method used to examine the SERCA2a activity. Additionally, cardiac hypertrophic indices, such as the cardiosomatic ratio, left ventricular weight to body weight (LVW/BW) ratio and cardiomyocytes transverse diameter (TDM), together with the systolic blood pressure (SBP) and serum lipids levels were also examined. After ten weeks, significant decreases were observed in both the mRNA and protein expression levels of SERCA2a, as well as its activity, in the hypertrophied hearts of the SHR. The administration of atorvastatin to the same strains of rats effectively inhibited these decreases, and the above cardiac hypertrophic indices, as well as the SBP and serum lipids levels were significantly decreased. However, no significant changes in the expressions of PLB were observed in WKY, SHR and atorvastatin-treated SHR. These findings demonstrated that through regulation of the PLB and SERCA2a levels in the hearts of SHR, atorvastatin can prevent the cardiac hypertrophy caused due to pressure overload, which provides a relatively new insight into the mechanism of atorvastatin in the prevention of cardiac hypertrophy.

Ouabain decreases sarco(endo)plasmic reticulum calcium ATPase activity in rat hearts by a process involving protein oxidation

The effect of cardiac glycosides to increase cardiac inotropy by altering Ca(2+) cycling is well known but still poorly understood. The studies described in this report focus on defining the effects of ouabain signaling on sarcoplasmic reticulum Ca(2+)-ATPase function. Rat cardiac myocytes treated with 50 microM ouabain demonstrated substantial increases in systolic and diastolic Ca(2+) concentrations. The recovery time constant for the Ca(2+) transient, tau(Ca(2+)), was significantly prolonged by ouabain. Exposure to 10 microM H(2)O(2), which causes an increase in intracellular reactive oxygen species similar to that of 50 microM ouabain, caused a similar increase in tau(Ca(2+)). Concurrent exposure to 10 mM N-acetylcysteine or an aqueous extract from green tea (50 mg/ml) both prevented the increases in tau(Ca(2+)) as well as the changes in systolic or diastolic Ca(2+) concentrations. We also observed that 50 microM ouabain induced increases in developed pressure in addition to diastolic dysfunction in the isolated perfused rat heart. Coadministration of ouabain with N-acetylcysteine prevented these increases. Analysis of sarcoplasmic reticulum Ca(2+)-ATPase protein revealed increases in both the oxidation and nitrotyrosine content in the ouabain-treated hearts. Liquid chromatography-mass spectrometric analysis confirmed that the sarcoplasmic reticulum Ca(2+)-ATPase protein from ouabain-treated hearts had modifications consistent with oxidative and nitrosative stress. These data suggest that ouabain induces oxidative changes of the sarcoplasmic reticulum Ca(2+)-ATPase structure and function that may, in turn, produce some of the associated changes in Ca(2+) cycling and physiological function.

Regulation of the sarcoplasmic reticulum Ca2+-ATPase expression in the hypertrophic and failing heartThis paper is part of a series in the Journal's “Made in Canada” section. The paper has undergone peer review

The sarcoplasmic reticulum (SR) plays a central role in the contraction and relaxation coupling in the myocardium. The SR Ca2+-ATPase (SERCA2) transports Ca2+ inside the SR lumen during relaxation of the cardiac myocyte. It is well known that diminished contractility of the hypertrophic cardiac myocyte is the main factor of ventricular dysfunction in the failing heart. A key feature of the failing heart is a decreased content and activity of SERCA2, which is the cause of some of the physiological defects observed in the hypertrophic cardiomyocyte performance that are important during transition of compensated hypertrophy to heart failure. In this review different possible mechanisms responsible for decreased transcriptional regulation of the SERCA2 gene are examined, which appear to be the primary cause for decreased SERCA2 expression in heart failure. The experimental evidence suggests that several signalling pathways are involved in the downregulation of SERCA2 expression in the hypertrophic and failing cardiomyocyte. Therapeutic upregulation of SERCA2 expression using replication deficient adenoviral expression vectors, pharmacological interventions using thyroid hormone analogues, β-adrenergic receptor antagonists, and novel metabolically active compounds are currently under investigation for the treatment of uncompensated cardiac hypertrophy and heart failure.

Effect of β-Blockers on Cardiac Function and Calcium Handling Protein in Postinfarction Heart Failure Rats

OBJECTIVES

The normal expression of Ca2+-handling protein is critical for efficient myocardial function. The present study was designed to test the hypothesis that beta-blocker treatment may attenuate left ventricular (LV) remodeling and cardiac contractile dysfunction in the failing heart, which may be associated with alterations of Ca2+-handling protein

METHODS

We investigated the change of LV remodeling and function in a rat model of heart failure due to myocardial infarction (MI) with or without carvedilol (30 mg/kg/d) or metoprolol (60 mg/kg/d) treatment for 6 weeks (n = 9 in the MI plus carvedilol group, and n = 8 in every other group). The expression of messenger RNA and proteins of sarcoplasmic reticulum Ca2+-adenosine triphosphatase (SERCA) and phospholamban in cardiomyocytes of all rats were also measured

RESULTS

There was significant LV remodeling and cardiac contractile dysfunction in MI rats. The messenger RNA and protein expression of SERCA were down-regulated (p < 0.01), but the expression of phospholamban messenger RNA and protein were up-regulated (p < 0.01) in MI rats compared to sham-operated rats. After the treatment with beta-blockers, LV remodeling and function were clearly improved. Carvedilol was better in attenuating the weight of the LV and the relative weight of the right ventricle than metoprolol (p < 0.05). beta-Blockers restored the low expression of SERCA (p < 0.05) but showed no effect on phospholamban expression (p > 0.05). Moreover, carvedilol induced a more significant improvement of SERCA expression than metoprolol (p < 0.05)

CONCLUSIONS

Beta-blockers are effective in preventing LV remodeling and cardiac contractile dysfunction in the failing heart. The molecular mechanism may be related to normalization of SERCA expression.

Phosphorylation and binding of AUF1 to the 3'-untranslated region of cardiomyocyte SERCA2a mRNA

Experimental animals and patients with cardiac hypertrophy and heart failure display abnormally slowed myocardial relaxation, which is associated with downregulation of sarco(endo)plasmic reticulum calcium ATPase 2a (SERCA2a), the cardiomyocyte sarcoplasmic reticulum Ca2+ pump. We previously showed that SERCA2a downregulation can be simulated in cultured neonatal rat ventricular myocytes (NRVM) by treatment with the hypertrophic agonist phorbol myristate acetate (PMA) or by overexpression of the novel protein kinase C (PKC) isoenzymes PKCdelta and PKCepsilon. PKC activation, in turn, decreased SERCA2a promoter activity and destabilized the SERCA2a mRNA. Here we demonstrate by using an RSV beta-galactosidase reporter system that a 609-nt fragment of the SERCA2a mRNA 3'-untranslated region (UTR), containing five adenylate-uridylate (AU)-rich regions, may be responsible for destabilizing the message following PMA treatment. UV cross-linking analysis demonstrated that several proteins found in the NRVM cell extracts bind to the 609-nt fragment. In addition, protein binding was transiently increased in response to PMA stimulation. 3'-UTR mRNA pull-down assays and Western blot analysis indicated that the AU binding protein AUF1 interacted with the SERCA2a 3'-UTR. AUF1 binding activity was predominantly found in the nuclear fraction, and PMA-induced AUF1 binding was associated with increased threonine phosphorylation of AUF1. These data suggest that the phosphorylation, binding, and location of AUF1 affect the posttranscriptional regulation of the SERCA2a message in NRVM.

Left ventricular SERCA2a gene down-regulation does not parallel ANP gene up-regulation during post-MI remodelling in rats

BACKGROUND

In most animal models of chronic hemodynamic overload of the left ventricle (LV) as well as in human end stage heart failure, the sarcoplasmic reticulum (SR) Ca2+-ATPase (SERCA2a) mRNA levels are decreased in parallel with increased atrial natriuretic peptide (ANP) mRNA levels. The situation in the remote myocardium following myocardial infarction (MI) is unclear.

AIMS

(1) To examine SERCA2a mRNA levels in the non-infarcted LV myocardium of rats at the chronic stage of experimental MI and (2) To examine whether a negative linear correlation exists between SERCA2a and ANP mRNA levels in this model.

METHODS

Anesthetized adult male Wistar rats underwent left coronary artery ligation or sham operation. Three months later, the rats were divided into three groups: sham-operated rats (sham, n=21), HF-free rats with MI (non-failing (NF)-MI, n=29) and rats with both MI and HF (congestive heart failure (CHF)-MI, n=14). LV remodelling and function were assessed by echocardiography and hemodynamic measurements. SERCA2a and ANP mRNA levels were determined by Northern and dot blot analysis with specific cDNA probes.

RESULTS

LV SERCA2a mRNA levels varied markedly in sham-operated rats (0.9-1.8). Mean ANP mRNA level increased markedly and mean SERCA2a mRNA level decreased moderately in the remote myocardium. In some NF-MI rats, SERCA2a mRNA levels were higher than those in some sham controls. Whereas ANP mRNA levels correlated well with MI severity (r2=0.79, p<0.001), this was not the case for SERCA2a mRNA levels (r2=0.42, p<0.01). We found no negative correlation between ANP and SERCA2a mRNA levels.

CONCLUSION

SERCA2a gene down-regulation in the non-infarcted myocardium of rats with MI does not correlate with ANP gene up-regulation, suggesting that the two genes are not antithetically regulated.

PYK2 regulates SERCA2 gene expression in neonatal rat ventricular myocytes

The nonreceptor protein tyrosine kinase (PTK) proline-rich tyrosine kinase 2 (PYK2) has been implicated in cell signaling pathways involved in left ventricular hypertrophy and heart failure, but its exact role has not been elucidated. In this study, replication-defective adenoviruses (Adv) encoding green fluorescent protein (GFP)-tagged, wild-type (WT), and mutant forms of PYK2 were used to determine whether PYK2 overexpression activates MAPKs, and downregulates SERCA2 mRNA levels in neonatal rat ventricular myocytes (NRVM). PYK2 overexpression significantly decreased SERCA2 mRNA (as determined by Northern blot analysis and real-time RT-PCR) to 54 ± 4% of Adv-GFP-infected cells 48 h after Adv infection. Adv-encoding kinase-deficient (KD) and Y402F phosphorylation-deficient mutants of PYK2 also significantly reduced SERCA2 mRNA (WT>KD>Y402F). Conversely, the PTK inhibitor PP2 (which blocks PYK2 phosphorylation by Src-family PTKs) significantly increased SERCA2 mRNA levels. PYK2 overexpression had no effect on ERK1/2, but increased JNK1/2 and p38MAPKphosphorylation from fourfold to eightfold compared with GFP overexpression. Activation of both “stress-activated” protein kinase cascades appeared necessary to reduce SERCA2 mRNA levels. Adv-mediated overexpression of constitutively active (ca)MKK6 or caMKK7, which activated only p38MAPKor JNKs, respectively, was not sufficient, whereas combined infection with both Adv reduced SERCA2 mRNA levels to 45 ± 12% of control. WTPYK2 overexpression also significantly reduced SERCA2 promoter activity, as determined by transient transfection of a 3.8-kb SERCA2 promoter-luciferase construct. Thus a PYK2-dependent signaling cascade may have a role in abnormal cardiac Ca2+handling in left ventricular hypertrophy and heart failure via downregulation of SERCA2 gene transcription.

COMPARISON OF LOW and HIGH DOSES OF CARVEDILOL ON RESTORATION OF CARDIAC FUNCTION and CALCIUM-HANDLING PROTEINS IN RAT FAILING HEART

1. The beta-adrenoceptor antagonist carvedilol reverses cardiac dysfunction in the failing heart. A recent study showed that beta-adrenoceptor antagonists indirectly normalize Ca(2+)-regulatory proteins. The relationship between these two phenomena and the suitable dosage of carvedilol remains unclear. 2. We investigated the change in left ventricular (LV) remodelling and function in a rat model of heart failure due to myocardial infarction (MI) with or without carvedilol (30 or 2 mg/kg per day) treatment for 6 weeks. The expression of mRNA and proteins of sarcoplasmic reticulum Ca(2+)-ATPase (SERCA) and phospholamban (PLB) in cardiomyocytes was also measured. 3. There was significant LV remodelling and cardiac contractile dysfunction in MI rats. The expression of SERCA mRNA and protein were downregulated (P < 0.01), but the expression of PLB mRNA and protein were upregulated (P < 0.01) in MI rats compared with sham-operated rats. After treatment with carvedilol, LV remodelling and cardiac contractile dysfunction were clearly improved. Low-dose carvedilol was better at improving some parameters of LV remodelling and function than the high dose. Carvedilol partially restored the low expression of SERCA (P < 0.05), but had no effect on PLB expression (P > 0.05). Moreover, low-dose carvedilol induced a more significant improvement in SERCA expression than did the high dose (P < 0.05). 4. The results of the present study suggest that carvedilol is effective in improving LV remodelling and cardiac contractile dysfunction after MI. This may be related to the normalization of SERCA expression.

Phenotypes of SERCA and PMCA knockout mice

P-type Ca2+-ATPases of the sarco(endo)plasmic reticulum (SERCAs) and plasma membrane (PMCAs) are responsible for maintaining the Ca2+ gradients across cellular membranes that are required for regulation of Ca2+-mediated signaling and other biological processes. Gene-targeting studies of SERCA isoforms 1, 2, and 3 and PMCA isoforms 1, 2, and 4 have confirmed some of the general functions proposed for these pumps, such as a major role in excitation-contraction coupling for SERCA1 and SERCA2 and housekeeping functions for PMCA1 and SERCA2, but have also revealed some unexpected phenotypes. These include squamous cell cancer and plasticity in the regulation of Ca2+-mediated exocytosis in SERCA2 heterozygous mutant mice, modulation of Ca2+ signaling in SERCA3-deficient mice, deafness and balance disorders in PMCA2 null mice, and male infertility in PMCA4 null mice. These unique phenotypes provide new information about the cellular functions of these pumps, the requirement of their activities for higher order physiological processes, and the pathophysiological consequences of pump dysfunction.

Isoenzyme-selective regulation of SERCA2 gene expression by protein kinase C in neonatal rat ventricular myocytes

Patients with cardiac hypertrophy and heart failure display abnormally slowed myocardial relaxation, which is associated with downregulation of sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA2) gene expression. We previously showed that SERCA2 downregulation can be simulated in cultured neonatal rat ventricular myocytes (NRVM) by treatment with the protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (PMA). However, NRVM express three different PMA-sensitive PKC isoenzymes (PKCalpha, PKCepsilon, and PKCdelta), which may be differentially regulated and have specific functions in the cardiomyocyte. Therefore, in this study we used adenoviral vectors encoding wild-type (wt) and kinase-defective, dominant negative (dn) mutant forms of PKCalpha, PKCepsilon, and PKCdelta to analyze their individual effects in regulating SERCA2 gene expression in NRVM. Overexpression of wtPKCepsilon and wtPKCdelta, but not wtPKCalpha, was sufficient to downregulate SERCA2 mRNA levels, as assessed by Northern blotting and quantitative, real-time RT-PCR (69 +/- 7 and 61 +/- 9% of control levels for wtPKCepsilon and wtPKCdelta, respectively; P < 0.05 for each adenovirus; n = 8 experiments). Conversely, overexpression of all three dnPKCs appeared to significantly increase SERCA2 mRNA levels (dnPKCdelta > dnPKCepsilon > dnPKCalpha). dnPKCdelta overexpression produced the largest increase (2.8 +/- 1.0-fold; n = 11 experiments). However, PMA treatment was still sufficient to downregulate SERCA2 mRNA levels despite overexpression of each dominant negative mutant. These data indicate that the novel PKC isoenzymes PKCepsilon and PKCdelta selectively regulate SERCA2 gene expression in cardiomyocytes but that neither PKC alone is necessary for this effect if the other novel PKC can be activated.

Calcium dynamics in the failing heart: restoration by beta-adrenergic receptor blockade

Changes in calcium (Ca2+) regulation contribute to loss of contractile function in dilated cardiomyopathy. Clinical treatment using beta-adrenergic receptor antagonists (beta-blockers) slows deterioration of cardiac function in end-stage heart failure patients; however, the effects of beta-blocker treatment on Ca2+ dynamics in the failing heart are unknown. To address this issue, tropomodulin-overexpressing transgenic (TOT) mice, which suffer from dilated cardiomyopathy, were treated with a nonselective beta-receptor blocker (5 mg. kg-1. day-1 propranolol) for 2 wk. Ca2+ dynamics in isolated cardiomyocytes of TOT mice significantly improved after treatment compared with untreated TOT mice. Frequency-dependent diastolic and Ca2+ transient amplitudes were returned to normal in propranolol-treated TOT mice and but not in untreated TOT mice. Ca2+ kinetic measurements of time to peak and time decay of the caffeine-induced Ca2+ transient to 50% relaxation were also normalized. Immunoblot analysis of untreated TOT heart samples showed a 3.6-fold reduction of sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA), whereas Na+/Ca2+ exchanger (NCX) concentrations were increased 2.6-fold relative to nontransgenic samples. Propranolol treatment of TOT mice reversed the alterations in SERCA and NCX protein levels but not potassium channels. Although restoration of Ca2+ dynamics occurred within 2 wk of beta-blockade treatment, evidence of functional improvement in cardiac contractility assessed by echocardiography took 10 wk to materialize. These results demonstrate that beta-adrenergic blockade restores Ca2+ dynamics and normalizes expression of Ca2+-handling proteins, eventually leading to improved hemodynamic function in cardiomyopathic hearts.

Gene expression profiling of the aging mouse cardiac myocytes

Heart disease remains the most frequent cause of death in the general population with increasing incidence in the elderly population. The pathologic failure of the aging heart may be related to structural and functional alterations in cardiac muscle cells. However, the molecular mechanisms underlying the aging-related decline in cardiac muscle function are largely unknown. To provide the first analysis of cardiac aging at the level of gene expression, we established and compared cDNA libraries from apparently healthy young and aged mouse ventricular cardiac muscle cells. We report the identification of genes that exhibit aging-related changes of mRNA levels. Aging expression profiles in aged hearts indicate decreased cellular adaptation and protection against stress-induced injury together with the development of contractile dysfunction. The data suggest reduced activity of the mitochondrial electron transport system and reduced levels of cardiac-specific transcription regulators. The cardiomyocyte aging profile of gene expression displays similarities with known heart disorders. Genes whose mRNA levels change with aging in cardiomyocytes might profoundly affect pathological changes in the heart.

Therapeutic potential of CPT I inhibitors: cardiac gene transcription as a target

Inhibitors of carnitine palmitoyl-transferase I (CPT I), the key enzyme for the transport of long-chain acyl-coenzyme A (acyl-CoA) compounds into mitochondria, have been developed as agents for treating diabetes mellitus Type 2. Findings that the CPT I inhibitor, etomoxir, has effects on overloaded heart muscle, which are associated with an improved function, were unexpected and can be attributed to selective changes in the dysregulated gene expression of hypertrophied cardiomyocytes. Also, the first clinical trial with etomoxir in patients with heart failure showed that etomoxir improved the clinical status and several parameters of heart function. In view of the action of etomoxir on gene expression, putative molecular mechanisms involved in an increased expression of SERCA2, the Ca(2+) pump of sarcoplasmic reticulum (SR) and alpha-myosin heavy chain (MHC) of failing overloaded heart muscle are described. The first 225 bp of human, rabbit, rat and mouse SERCA2 promoter sequence have high identity. Various cis-regularory elements are also given for the promoter of the rat cardiac alpha-MHC gene. It is hypothesised that etomoxir increases glucose-phosphate intermediates resulting in activation of signalling pathway(s) mediated by phosphatases. Regarding the possible direct action of etomoxir on peroxisome proliferator activated receptor alpha (PPAR-alpha) activation, it could upregulate the expression of various enzymes that participate in beta-oxidation, thereby modulating some effects of CPT 1 inhibition. Any development of alternative drugs requires a better understanding of the signal pathways involved in the altered gene expression. In particular, signals need to be identified which are altered in overloaded hearts and can selectively be re-activated by etomoxir.

Alpha-adrenergic responsiveness in rat isolated perfused heart after abdominal aortic coarctation

Chronic isoproterenol pre-treatment, a well-known model of compensatory hypertrophy associated with cardiac beta-adrenoceptor desensitization, enhances the inotropic response to phenylephrine in rat isolated perfused hearts, supporting the hypothesis that myocardial alpha-adrenoceptor stimulation contributes to the maintenance of myocardial performance in situations in which cardiac beta-adrenoceptor function is compromised. To further corroborate this hypothesis, the effects of abdominal aortic coarctation on cardiac alpha-adrenergic responsiveness were investigated in Langendorff heart preparations. Abdominal aortic coarctation causes cardiac hypertrophy (21%) as shown by a significant increase in the ratio of ventricular dry weight to bodyweight. In preparations from hypertrophied rats, both maximum increases in left ventricular systolic pressure and heart rate elicited by isoproterenol (10(-12) to 10(-4) M) were significantly reduced (the isoproterenol concentration producing 50% of the maximum positive inotropic and chronotropic responses was enhanced almost 21- and 2-fold, respectively). However, the positive inotropic response to phenylephrine (10(-12) to 10(-4) M) remained unaffected following abdominal aortic coarctation, when compared with sham-operated rats. In preparations from both groups, phenylephrine infusion did not induce significant changes in heart rate. These results show that although abdominal aortic stenosis induced desensitization of cardiac beta-adrenoceptors, it did not enhance cardiac alpha-adrenoceptor responsiveness. This suggests that such an enhancement depends on the experimental model used to induce cardiac hypertrophy associated with desensitization of cardiac beta-adrenoceptors.

Transgenic mice with cardiac-specific expression of activating transcription factor 3, a stress-inducible gene, have conduction abnormalities and contractile dysfunction

Activating transcription factor 3 (ATF3) is a member of the CREB/ATF family of transcription factors. Previously, we demonstrated that the expression of the ATF3 gene is induced by many stress signals. In this report, we demonstrate that expression of ATF3 is induced by cardiac ischemia coupled with reperfusion (ischemia-reperfusion) in both cultured cells and an animal model. Transgenic mice expressing ATF3 under the control of the alpha-myosin heavy chain promoter have atrial enlargement, and atrial and ventricular hypertrophy. Microscopic examination showed myocyte degeneration and fibrosis. Functionally, the transgenic heart has reduced contractility and aberrant conduction. Interestingly, expression of sorcin, a gene whose product inhibits the release of calcium from sarcoplasmic reticulum, is increased in these transgenic hearts. Taken together, our results indicate that expression of ATF3, a stress-inducible gene, in the heart leads to altered gene expression and impaired cardiac function.

SERCA pump level is a critical determinant of Ca(2+)homeostasis and cardiac contractility

The control of intracellular calcium is central to regulation of cardiac contractility. A defect in SR Ca(2+)transport and SR Ca(2+)ATPase pump activity and expression level has been implicated as a major player in cardiac dysfunction. However, a precise cause-effect relationship between alterations in SERCA pump level and cardiac contractility could not be established from these studies. Progress in transgenic mouse technology and adenoviral gene transfer has provided new tools to investigate the role of SERCA pump level in the heart. This review focuses on how alterations in SERCA level affect Ca(2+)homeostasis and cardiac contractility. It discusses the consequences of altered SERCA pump levels for the expression and activity of other Ca(2+)handling proteins. Furthermore, the use of SERCA pump as a therapeutic target for gene therapy of heart failure is evaluated.

Recent developments in gene therapy for cardiac disease

Cardiovascular[TRACE;del] disease is the leading cause of death in the US and world-wide. Advances in molecular biology and the human genome project have revealed opportunities for novel strategies for cardiac gene therapy. This review discusses general and specific aspects of gene transfer strategies in cardiac tissues. These include 1) the selection and/or optimization of the vector for gene transfer; 2) the identification of the target gene(s); 3) the use of cardiac-specific promoters; and 4) the use of an appropriate delivery system for administration. Currently, several vectors (e.g., viral and nonviral vectors) have been developed and many target genes have been identified (e.g., VEGF, FGF, beta-AR, etc.). Many investigations have provided experimental models for gene delivery systems but the most efficient cardiac gene transfer was obtained from intramyocardial injection or perfusion of explanted myocardium. The data available thus far have suggested favorable immediate effects following gene transfer, but long-term value of cardiac gene therapy has not been proven. Further refinements in appropriate vectors that provide cell or tissue selectivity and long-lasting effects are necessary as well as the development of minimally invasive procedures for gene transfer.

Gene knockout studies of Ca2+-transporting ATPases

The biochemical functions of intracellular and plasma membrane Ca2+-transporting ATPases in the control of cytosolic and organellar Ca2+ levels are well established, but the physiological roles of specific isoforms are less well understood. There appear to be three different types of Ca2+ pumps in mammalian tissues: the sarco(endo)plasmic reticulum Ca2+-ATPases (SERCAs), which sequester Ca2+ within the endoplasmic or sarcoplasmic reticulum, the plasma membrane Ca2+-ATPases (PMCAs), which extrude Ca2+ from the cell, and the putative secretory pathway Ca2+-ATPase (SPCA), the function of which is poorly understood. This review describes the results of recent analyses of mouse models with null mutations in the genes encoding SERCA and PMCA isoforms and genetic studies of SERCA and SPCA dysfunction in both humans and model organisms. These studies are yielding important insights regarding the physiological functions of individual Ca2+-transporting ATPases in vivo.

Calcineurin is activated in rat hearts with physiological left ventricular hypertrophy induced by voluntary exercise training

BACKGROUND

Calcineurin may play a pivotal role in the signaling of cardiac hypertrophy; since this hypothesis was first put forward, controversial reports have been published using various experimental models. This study was designed to compare the physiological left ventricular hypertrophy (LVH) induced by voluntary exercise with LVH induced by aortic constriction and to determine whether calcineurin participates in the signaling of exercise-induced LVH.

METHODS AND RESULTS

Wistar rats were assigned to 1 of the following 5 groups: 10 weeks of voluntary exercise (EX), a sedentary regimen, a 1-week (AC1) or 4-week (AC4) ascending aortic constriction period, or a sham operation. EX rats ran 2.4+/-0.7 km/day voluntarily in specially manufactured cages; this was associated with an increase of LV diastolic dimension and stroke volume. Myocardial calcineurin activity markedly increased in EX rats (46.4+/-8.3 versus 18.4+/-0.5 pmol. min(-1). mg(-1) in sedentary rats; P<0.001) and in AC1 rats (44.9+/-6.7 versus 22.1+/-3.7 pmol. min(-1). mg(-1) in sham-operated rats; P<0.001), but not in AC4 rats (29.0+/-3.4 pmol. min(-1). mg(-1)). Treatment with cyclosporin A completely inhibited the development of LVH in EX rats, but it only partially attenuated the development of LVH in AC4 rats.

CONCLUSIONS

Calcineurin was activated in exercise-induced physiological LVH and in the developing phase of LVH (AC1), but not in decompensated pressure-overload hypertrophy (AC4). Cyclosporin therapy for the prevention of LVH may be harmful because it does not block the development of pathological hypertrophy but rather that of favorable adaptive hypertrophy.

Function and regulation of sarcoplasmic reticulum Ca2+-ATPase: advances during the past decade and prospects for the coming decade

In cardiac muscle, the contraction-relaxation cycle is tightly controlled by the regulated release and uptake of intracellular Ca2+ between sarcoplasmic reticulum and cytoplasm. A major protein controlling Ca2+ cycling is Ca2+-ATPase (SERCA2a) located in the sarcoplasmic reticulum membrane. The function of SERCA2a protein is regulated by the phosphorylatable protein, phospholamban. Phosphorylation of phospholamban releases its inhibitory effect on SERCA2a through direct molecular interaction. Recently, mice whose SERCA2a function is increased (overexpression of the gene) or lost (knock out) were developed. These mice demonstrated that SERCA2a pump levels are a major determinant of cardiac muscle contractility and relaxation. These studies open the prospect that the overexpression of SERCA2a can correct cardiac dysfunction seen in heart failure. Advances in knowledge concerning the function and gene regulation of SERCA2a are discussed in this review.