Sarcoplasmic reticulum Ca(2+)/Calmodulin-dependent protein kinase is altered in heart failure

Heart Failure with Preserved Ejection Fraction: a Pharmacotherapeutic Update

While guidelines for management of heart failure with reduced ejection fraction (HFrEF) are consensual and have led to improved survival, treatment options for heart failure with preserved ejection fraction (HFpEF) remain limited and aim primarily for symptom relief and improvement of quality of life. Due to the shortage of therapeutic options, several drugs have been investigated in multiple clinical trials. The majority of these trials have reported disappointing results and have suggested that HFpEF might not be as simply described by ejection fraction as previously though. In fact, HFpEF is a complex clinical syndrome with various comorbidities and overlapping distinct phenotypes that could benefit from personalized therapeutic approaches. This review summarizes the results from the most recent phase III clinical trials for HFpEF and the most promising drugs arising from phase II trials as well as the various challenges that are currently holding back the development of new pharmacotherapeutic options for these patients.

Ca2+ mishandling in heart failure: Potential targets

Ca²⁺ mishandling is a common feature in several cardiovascular diseases such as heart failure (HF). In many cases, impairment of key players in intracellular Ca²⁺ homeostasis has been identified as the underlying mechanism of cardiac dysfunction and cardiac arrhythmias associated with HF. In this review, we summarize primary novel findings related to Ca²⁺ mishandling in HF progression. HF research has increasingly focused on the identification of new targets and the contribution of their role in Ca²⁺ handling to the progression of the disease. Recent research studies have identified potential targets in three major emerging areas implicated in regulation of Ca²⁺ handling: the innate immune system, bone metabolism factors and post-translational modification of key proteins involved in regulation of Ca²⁺ handling. Here, we describe their possible contributions to the progression of HF.

CaMKII in Regulation of Cell Death During Myocardial Reperfusion Injury

Cardiovascular disease is the leading cause of death worldwide. In spite of the mature managements of myocardial infarction (MI), post-MI reperfusion (I/R) injury results in high morbidity and mortality. Cardiomyocyte Ca²⁺ overload is a major factor of I/R injury, initiating a cascade of events contributing to cardiomyocyte death and myocardial dysfunction. Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) plays a critical role in cardiomyocyte death response to I/R injury, whose activation is a key feature of myocardial I/R in causing intracellular mitochondrial swelling, endoplasmic reticulum (ER) Ca²⁺ leakage, abnormal myofilament contraction, and other adverse reactions. CaMKII is a multifunctional serine/threonine protein kinase, and CaMKIIδ, the dominant subtype in heart, has been widely studied in the activation, location, and related pathways of cardiomyocytes death, which has been considered as a potential targets for pharmacological inhibition. In this review, we summarize a brief overview of CaMKII with various posttranslational modifications and its properties in myocardial I/R injury. We focus on the molecular mechanism of CaMKII involved in regulation of cell death induced by myocardial I/R including necroptosis and pyroptosis of cardiomyocyte. Finally, we highlight that targeting CaMKII modifications and cell death involved pathways may provide new insights to understand the conversion of cardiomyocyte fate in the setting of myocardial I/R injury.

Complex functionality of protein phosphatase 1 isoforms in the heart

Protein phosphatase 1(PP1) is a key regulator of cardiac function through dephosphorylating serine/threonine residues within target proteins to oppose the function of protein kinases. Studies from failing hearts of animal models and human patients have demonstrated significant increase of PP1 activity in myocardium, while elevated PP1 activity in transgenic mice leads to cardiac dysfunction, suggesting that PP1 might be a therapeutic target to ameliorate cardiac dysfunction in failing hearts. In fact, cardiac overexpression of inhibitor 1, the endogenous inhibitor of PP1, increases cardiac contractility and suppresses heart failure progression. However, this notion of PP1 inhibition for heart failure treatment has been challenged by recent studies on the isoform-specific roles of PP1 in the heart. PP1 is a holoenzyme composed of catalytic subunits (PP1α, PP1β, or PP1γ) and regulatory proteins that target them to distinct subcellular locations for functional specificity. This review will summarize how PP1 regulates phosphorylation of some of the key cardiac proteins involved in Ca²⁺ handling and cardiac contraction, and the potential role of PP1 isoforms in controlling cardiac physiology and pathophysiology.

The role of PP5 and PP2C in cardiac health and disease

Protein phosphatases are important, for example, as functional antagonists of β-adrenergic stimulation of the mammalian heart. While β-adrenergic stimulations increase the phosphorylation state of regulatory proteins and therefore force of contraction in the heart, these phosphorylations are reversed and thus force is reduced by the activity of protein phosphatases. In this context the role of PP5 and PP2C is starting to unravel. They do not belong to the same family of phosphatases with regard to sequence homology, many similarities with regard to location, activation by lipids and putative substrates have been worked out over the years. We also suggest which pathways for regulation of PP5 and/or PP2C described in other tissues and not yet in the heart might be useful to look for in cardiac tissue. Both phosphatases might play a role in signal transduction of sarcolemmal receptors in the heart. Expression of PP5 and PP2C can be increased by extracellular stimuli in the heart. Because PP5 is overexpressed in failing animal and human hearts, and because overexpression of PP5 or PP2C leads to cardiac hypertrophy and KO of PP5 leads to cardiac hypotrophy, one might argue for a role of PP5 and PP2C in heart failure. Because PP5 and PP2C can reduce, at least in vitro, the phosphorylation state of proteins thought to be relevant for cardiac arrhythmias, a role of these phosphatases for cardiac arrhythmias is also probable. Thus, PP5 and PP2C might be druggable targets to treat important cardiac diseases like heart failure, cardiac hypertrophy and cardiac arrhythmias.

Comprehensive bioinformatics analysis reveals kinase activity profiling associated with heart failure

Heart failure is a complex clinical syndrome originating from cardiac injury, which leads to considerable morbidity and mortality. Among the dynamic molecular adaptations occurring in heart failure development, aggravation of the disease is often attributed to global or local abnormality of the kinase. Therefore, the overall monitoring of kinase activity is indispensable. In this study, a bioinformatics analysis method was developed to conduct deep mining of transcriptome and phosphoproteome in failing heart tissue. A total of 982 differentially expressed genes and 9781 phosphorylation sites on 3252 proteins were identified. Via upstream regulator relations and kinase-substrate relations, a dendrogram of kinases can be constructed to monitor its abnormality. The results show that, on the dendrogram, the distribution of kinases demonstrated complex kinase activity changes and certain rules that occur during heart failure. Finally, we also identified the hub kinases in heart failure and verified the expression of these kinases by reverse-transcription polymerase chain reaction and Western blot analysis. In conclusion, for the first time, we have systematically analyzed the differences in kinases during heart failure and provided an unprecedented breadth of multi-omics data. These results can bring about a sufficient data foundation and novel research perspectives.

Deletion of obscurin immunoglobulin domains Ig58/59 leads to age-dependent cardiac remodeling and arrhythmia

Obscurin comprises a family of giant modular proteins that play key structural and regulatory roles in striated muscles. Immunoglobulin domains 58/59 (Ig58/59) of obscurin mediate binding to essential modulators of muscle structure and function, including canonical titin, a smaller splice variant of titin, termed novex-3, and phospholamban (PLN). Importantly, missense mutations localized within the obscurin-Ig58/59 region that affect binding to titins and/or PLN have been linked to the development of myopathy in humans. To elucidate the pathophysiological role of this region, we generated a constitutive deletion mouse model, Obscn-ΔIg58/59, that expresses obscurin lacking Ig58/59, and determined the consequences of this manipulation on cardiac morphology and function under conditions of acute stress and through the physiological process of aging. Our studies show that young Obscn-ΔIg58/59 mice are susceptible to acute β-adrenergic stress. Moreover, sedentary Obscn-ΔIg58/59 mice develop left ventricular hypertrophy that progresses to dilation, contractile impairment, atrial enlargement, and arrhythmia as a function of aging with males being more affected than females. Experiments in ventricular cardiomyocytes revealed altered Ca2+ cycling associated with changes in the expression and/or phosphorylation levels of major Ca2+ cycling proteins, including PLN, SERCA2, and RyR2. Taken together, our work demonstrates that obscurin-Ig58/59 is an essential regulatory module in the heart and its deletion leads to age- and sex-dependent cardiac remodeling, ventricular dilation, and arrhythmia due to deregulated Ca2+ cycling.

NCX and EAAT transporters in ischemia: At the crossroad between glutamate metabolism and cell survival

Energy metabolism impairment is a central event in the pathophysiology of ischemia. The limited availability of glucose and oxygen strongly affects mitochondrial activity, thus leading to ATP depletion. In this setting, the switch to alternative energy sources could ameliorate cells survival by enhancing ATP production, thus representing an attractive strategy for ischemic treatment. In this regard, some studies have recently re-evaluated the metabolic role of glutamate and its potential to promote cell survival under pathological conditions. In the present review, we discuss the ability of glutamate to exert an "energizing role" in cardiac and neuronal models of hypoxia/reoxygenation (H/R) injury, focusing on the Na⁺/Ca²⁺ exchanger (NCX) and the Na⁺-dependent excitatory amino acid transporters (EAATs) as key players in this metabolic pathway.

Cardiac specific PRMT1 ablation causes heart failure through CaMKII dysregulation

Dysregulation of Ca²⁺/calmodulin-dependent protein kinase (CaMK)II is closely linked with myocardial hypertrophy and heart failure. However, the mechanisms that regulate CaMKII activity are incompletely understood. Here we show that protein arginine methyltransferase 1 (PRMT1) is essential for preventing cardiac CaMKII hyperactivation. Mice null for cardiac PRMT1 exhibit a rapid progression to dilated cardiomyopathy and heart failure within 2 months, accompanied by cardiomyocyte hypertrophy and fibrosis. Consistently, PRMT1 is downregulated in heart failure patients. PRMT1 depletion in isolated cardiomyocytes evokes hypertrophic responses with elevated remodeling gene expression, while PRMT1 overexpression protects against pathological responses to neurohormones. The level of active CaMKII is significantly elevated in PRMT1-deficient hearts or cardiomyocytes. PRMT1 interacts with and methylates CaMKII at arginine residues 9 and 275, leading to its inhibition. Accordingly, pharmacological inhibition of CaMKII restores contractile function in PRMT1-deficient mice. Thus, our data suggest that PRMT1 is a critical regulator of CaMKII to maintain cardiac function.

The mechanisms that regulate the activity of Ca^2 +/calmodulin-dependent protein kinase II (CaMKII) in the context of heart failure are incompletely understood. Here the authors show that protein arginine methyltransferase 1 (PRMT1) prevents cardiac hyperactivation of CaMKII and heart failure development by methylating CaMKII at arginine residues 9 and 275.

Effects of exercise training and TrkB blockade on cardiac function and BDNF-TrkB signaling postmyocardial infarction in rats

Exercise training is beneficial for preserving cardiac function postmyocardial infarction (post-MI), but the underlying mechanisms are not well understood. We investigated one possible mechanism, brain-derived neurotrophic factor (BDNF)-tropomyosin-related kinase B (TrkB) signaling, with the TrkB blocker ANA-12 (0.5 mg·kg^-1·day^-1). Male Wistar rats underwent sham surgery or ligation of the left descending coronary artery. The surviving MI rats were allocated as follows: sedentary MI rats treated with vehicle, exercise-trained MI rats treated with vehicle, and exercise-trained MI rats treated with ANA-12. Exercise training was done 5 days/wk for 4 wk on a motor-driven treadmill. At the end, left ventricular (LV) function was evaluated by echocardiography and a Millar catheter. Mature BDNF and downstream effectors of BDNF-TrkB signaling, Ca²⁺/calmodulin-dependent protein kinase II (CaMKII), Akt, and AMP-activated protein kinase (AMPK), were assessed in the noninfarct area of the LV by Western blot analysis. Exercise training increased stroke volume and cardiac index and attenuated the decrease in ejection fraction (EF) and increase in LV end-diastolic pressure post-MI. ANA-12 blocked the improvement of EF and attenuated the increases in stroke volume and cardiac index but did not affect LV end-diastolic pressure. Exercise training post-MI prevented decreases in mature BDNF, phosphorylated (p-)CaMKII, p-Akt, and p-AMPKα expression. These effects were all blocked by ANA-12 except for p-AMPKα. In conclusion, the exercise-induced improvement of EF is mediated by the BDNF-TrkB axis and the downstream effectors CaMKII and Akt. BDNF-TrkB signaling appears to contribute to the improvement in systolic function by exercise training. NEW & NOTEWORTHY Exercise training improves ejection fraction and left ventricular end-diastolic pressure (LVEDP) and increases stroke volume and cardiac index in rats postmyocardial infarction (post-MI). The improvement of EF but not LVEDP is mediated by activation of the brain-derived neurotrophic factor (BDNF)-tropomyosin-related kinase B (TrkB) axis and downstream effectors Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) and Akt. This suggests that activation of BDNF-TrkB signaling and CaMKII and Akt is a promising target to attenuate progressive cardiac dysfunction post-MI.

Activation of CaMKIIδA promotes Ca2+ leak from the sarcoplasmic reticulum in cardiomyocytes of chronic heart failure rats

Activation of the Ca²⁺/calmodulin-dependent protein kinase II isoform δA (CaMKIIδA) disturbs intracellular Ca²⁺ homeostasis in cardiomyocytes during chronic heart failure (CHF). We hypothesized that upregulation of CaMKIIδA in cardiomyocytes might enhance Ca²⁺ leak from the sarcoplasmic reticulum (SR) via activation of phosphorylated ryanodine receptor type 2 (P-RyR2) and decrease Ca²⁺ uptake by inhibition of SR calcium ATPase 2a (SERCA2a). In this study, CHF was induced in rats by ligation of the left anterior descending coronary artery. We found that CHF caused an increase in the expression of CaMKIIδA and P-RyR2 in the left ventricle (LV). The role of CaMKIIδA in regulation of P-RyR2 was elucidated in cardiomyocytes isolated from neonatal rats in vitro. Hypoxia induced upregulation of CaMKIIδA and activation of P-RyR2 in the cardiomyocytes, which both were attenuated by knockdown of CaMKIIδA. Furthermore, we showed that knockdown of CaMKIIδA significantly decreased the Ca²⁺ leak from the SR elicited by hypoxia in the cardiomyocytes. In addition, CHF also induced a downregulation of SERCA2a in the LV of CHF rats. Knockdown of CaMKIIδA normalized hypoxia-induced downregulation of SERCA2a in cardiomyocytes in vitro. The results demonstrate that the inhibition of CaMKIIδA may improve cardiac function by preventing SR Ca²⁺ leak through downregulation of P-RyR2 and upregulation of SERCA2a expression in cardiomyocytes in CHF.

HIF1 mediates a switch in pyruvate kinase isoforms after myocardial infarction

Alternative splicing of RNA is an underexplored area of transcriptional response. We expect that early changes in alternatively spliced genes may be important for responses to cardiac injury. Hypoxia inducible factor 1 (HIF1) is a key transcription factor that rapidly responds to loss of oxygen through alteration of metabolism and angiogenesis. The goal of this study was to investigate the transcriptional response after myocardial infarction (MI) and to identify novel, hypoxia-driven changes, including alternative splicing. After ligation of the left anterior descending artery in mice, we observed an abrupt loss of cardiac contractility and upregulation of hypoxic signaling. We then performed RNA sequencing on ischemic heart tissue 1 and 3 days after infarct to assess early transcriptional changes and identified 89 transcripts with altered splicing. Of particular interest was the switch in Pkm isoform expression (pyruvate kinase, muscle). The usually predominant Pkm1 isoform was less abundant in ischemic hearts, while Pkm2 and associated splicing factors (hnRNPA1, hnRNPA2B1, Ptbp1) rapidly increased. Despite increased Pkm2 expression, total pyruvate kinase activity remained reduced in ischemic myocardial tissue. We also demonstrated HIF1 binding to PKM by chromatin immunoprecipitation, indicating a direct role for HIF1 in mediating this isoform switch. Our study provides a new, detailed characterization of the early transcriptome after MI. From this analysis, we identified an HIF1-mediated alternative splicing event in the PKM gene. Pkm1 and Pkm2 play distinct roles in glycolytic metabolism and the upregulation of Pkm2 is likely to have important consequences for ATP synthesis in infarcted cardiac muscle.

Testosterone deficiency prevents left ventricular contractility dysfunction after myocardial infarction

Testosterone may affect myocardial contractility since its deficiency decreases the contraction and relaxation of the heart. Meanwhile, testosterone replacement therapy has raised concerns because it may worsen cardiac dysfunction and remodeling after myocardial infarction (MI). In this study, we evaluate cardiac contractility 60 days after MI in rats with suppressed testosterone. Male Wistar rats underwent bilateral orchidectomy one week before the ligation of the anterior descending left coronary artery. The animals were divided into orchidectomized (OCT); MI; orchidectomized + MI (OCT + MI); orchidectomized + MI + testosterone (OCT + MI + T) and control (Sham) groups. Eight weeks after MI, papillary muscle contractility was analyzed under increasing calcium (0.62, 1.25, 2.5 and 3.75 mM) and isoproterenol (10^-8 to 10^-2 M) concentrations. Ventricular myocytes were isolated for intracellular calcium measurements and assessment of Ca²⁺ handling proteins. Contractility was preserved in the orchidectomized animals after myocardial infarction and was reduced when testosterone was replaced (Ca²⁺ 3.75 mM: Sham: 608 ± 70 (n = 11); OCT: 590 ± 37 (n = 16); MI: 311 ± 33* (n = 9); OCT + MI: 594 ± 76 (n = 7); OCT + MI + T: 433 ± 38* (n=4), g/g *p < 0.05 vs Sham). Orchidectomy also increased the Ca²⁺ transient amplitude of the ventricular myocytes and SERCA-2a protein expression levels. PLB phosphorylation levels at Thr¹⁷ were not different in the orchidectomized animals compared to the Sham animals but were reduced after testosterone replacement. CAMKII phosphorylation and protein nitrosylation increased in the orchidectomized animals. Our results support the view that testosterone deficiency prevents MI contractility dysfunction by altering the key proteins involved in Ca²⁺ handling.

Deletion of Interleukin-6 Attenuates Pressure Overload-Induced Left Ventricular Hypertrophy and Dysfunction

RATIONALE

The role of interleukin (IL)-6 in the pathogenesis of cardiac myocyte hypertrophy remains controversial.

OBJECTIVE

To conclusively determine whether IL-6 signaling is essential for the development of pressure overload-induced left ventricular (LV) hypertrophy and to elucidate the underlying molecular pathways.

METHODS AND RESULTS

Wild-type and IL-6 knockout (IL-6(-/-)) mice underwent sham surgery or transverse aortic constriction (TAC) to induce pressure overload. Serial echocardiograms and terminal hemodynamic studies revealed attenuated LV hypertrophy and superior preservation of LV function in IL-6(-/-) mice after TAC. The extents of LV remodeling, fibrosis, and apoptosis were reduced in IL-6(-/-) hearts after TAC. Transcriptional and protein assays of myocardial tissue identified Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) and signal transducer and activator of transcription 3 (STAT3) activation as important underlying mechanisms during cardiac hypertrophy induced by TAC. The involvement of these pathways in myocyte hypertrophy was verified in isolated cardiac myocytes from wild-type and IL-6(-/-) mice exposed to prohypertrophy agents. Furthermore, overexpression of CaMKII in H9c2 cells increased STAT3 phosphorylation, and exposure of H9c2 cells to IL-6 resulted in STAT3 activation that was attenuated by CaMKII inhibition. Together, these results identify the importance of CaMKII-dependent activation of STAT3 during cardiac myocyte hypertrophy via IL-6 signaling.

CONCLUSIONS

Genetic deletion of IL-6 attenuates TAC-induced LV hypertrophy and dysfunction, indicating a critical role played by IL-6 in the pathogenesis of LV hypertrophy in response to pressure overload. CaMKII plays an important role in IL-6-induced STAT3 activation and consequent cardiac myocyte hypertrophy. These findings may have significant therapeutic implications for LV hypertrophy and failure in patients with hypertension.

Involvement of the dual-specificity tyrosine phosphorylation-regulated kinase 1A-alternative splicing factor-calcium/calmodulin-dependent protein kinase IIδ signaling pathway in myocardial infarction-induced heart failure of rats

BACKGROUND

Alternative splicing factor (ASF)-regulated alternative splicing of calcium/calmodulin-dependent protein kinase IIδ (CaMKIIδ) plays an important role in pathologic cardiac remodeling. ASF can be phosphorylated by dual-specificity tyrosine phosphorylation-regulated kinase 1A (Dyrk1A). This study aimed to investigate the possible involvement of the Dyrk1A-ASF-CaMKIIδ signaling pathway in the progression of myocardial infarction (MI)-induced heart failure (HF).

METHODS AND RESULTS

MI in rats was induced by means of left anterior descending coronary artery ligation. Seven weeks after MI, the increase in left ventricular internal diameter at end-diastole (LVIDd), and the decrease in both ejection fraction (EF) and fractional shortening (FS) indicated that MI rats had developed HF. Quantitative real time reverse-transcription polymerase chain reaction indicated the dysregulation of CaMKIIδ alternative splicing, ie, up-regulation of CaMKIIδA and CaMKIIδC and down-regulation of CaMKIIδB in the hearts of HF rats. Electrophoresis and immunostaining revealed that HF activated the phosphorylation of ASF and affected its subcellular localization. Western blot analysis demonstrated a significant elevation in the activity and expression of Dyrk1A in HF rats. Inversely, treatment of MI-induced HF rats with Dyrk1A inhibitor, either harmine or EGCG, improved the symptoms of HF, reversed the molecular changes of Dyrk1A and ASF, and regulated alternative splicing of CaMKIIδ in HF rats.

CONCLUSIONS

Enhanced activation of Dyrk1A-ASF-CaMKIIδ signaling pathway may underlie the mechanisms of HF after MI, and Dyrk1A inhibition may contribute to inactivation of this pathway and thereby retard the progression of MI-induced HF.

Role of protein phosphorylation in excitation-contraction coupling in taurine deficient hearts

Taurine is a beta-amino acid found in very high concentration in the heart. Depletion of these intracellular stores results in the development of cardiomyopathy, thought to be mediated by abnormal sarcoplasmic reticular (SR) Ca(2+) transport. There is also evidence that taurine directly alters the Ca(2+) sensitivity of myofibrillar proteins. Major regulators of SR Ca(2+) ATPase (SERCA2a) are the phosphorylation status of a regulatory protein, phospholamban, and SERCA2a expression, which are diminished in the failing heart. The failing heart also exhibits reductions in myofibrillar Ca(2+) sensitivity, a property regulated by the phosphorylation of the muscle protein, troponin I. Therefore, we tested the hypothesis that taurine deficiency leads to alterations in SR Ca(2+) ATPase activity related to reduced phospholamban phosphorylation and expression of SERCA2a. We found that a sequence of events, which included elevated protein phosphatase 1 activity, reduced autophosphorylation of CaMKII, and reduced phospholamban phosphorylation, supports the reduction in SR Ca(2+) ATPase activity. However, the reduction in SR Ca(2+) ATPase activity was not caused by reduced SERCA2a expression. Taurine transporter knockout (TauTKO) hearts also exhibited a rightward shift in the Ca(2+) dependence of the myofibrillar Ca(2+) ATPase, a property that is associated with an elevation in phosphorylated troponin I. The findings support the observation that taurine deficient hearts develop systolic and diastolic defects related to reduced SR Ca(2+) ATPase activity, a change mediated in part by reduced phospholamban phosphorylation.

Synthetic phosphopeptides enable quantitation of the content and function of the four phosphorylation states of phospholamban in cardiac muscle

We have studied the differential effects of phospholamban (PLB) phosphorylation states on the activity of the sarcoplasmic reticulum Ca-ATPase (SERCA). It has been shown that unphosphorylated PLB (U-PLB) inhibits SERCA and that phosphorylation of PLB at Ser-16 or Thr-17 relieves this inhibition in cardiac sarcoplasmic reticulum. However, the levels of the four phosphorylation states of PLB (U-PLB, P16-PLB, P17-PLB, and doubly phosphorylated 2P-PLB) have not been measured quantitatively in cardiac tissue, and their functional effects on SERCA have not been determined directly. We have solved both problems through the chemical synthesis of all four PLB species. We first used the synthetic PLB as standards for a quantitative immunoblot assay, to determine the concentrations of all four PLB phosphorylation states in pig cardiac tissue, with and without left ventricular hypertrophy (LVH) induced by aortic banding. In both LVH and sham hearts, all phosphorylation states were significantly populated, but LVH hearts showed a significant decrease in U-PLB, with a corresponding increase in the ratio of total phosphorylated PLB to U-PLB. To determine directly the functional effects of each PLB species, we co-reconstituted each of the synthetic peptides in phospholipid membranes with SERCA and measured calcium-dependent ATPase activity. SERCA inhibition was maximally relieved by P16-PLB (the most highly populated PLB state in cardiac tissue homogenates), followed by 2P-PLB, then P17-PLB. These results show that each PLB phosphorylation state uniquely alters Ca(2+) homeostasis, with important implications for cardiac health, disease, and therapy.

SERCA2a gene therapy can improve symptomatic heart failure in δ-sarcoglycan-deficient animals

The loss of dystrophin or its associated proteins results in the development of muscle wasting frequently associated with cardiomyopathy. Contractile cardiac tissue is injured and replaced by fibrous tissue or fatty infiltrates, leading to a progressive decrease of the contractile force and finally to end-stage heart failure. At the time symptoms appear, restoration of a functional allele of the causative gene might not be sufficient to prevent disease progression. Alterations in Ca(2+) transport and intracellular calcium levels have been implicated in many types of pathological processes, especially in heart disease. On the basis of a gene transfer strategy, we analyzed the therapeutic efficacy of primary gene correction in a δ-sarcoglycan (δ-SG)-deficient animal model versus gene transfer of the Ca(2+) pump hSERCA2a (human sarco-endoplasmic reticulum calcium ATPase 2a), at a symptomatic stage of heart disease. Our results strongly suggest that restoration of δ-SG at this stage of disease will not lead to improved clinical outcome. However, restoration of proper Ca(2+) handling by means of amplifying SERCA2a expression in the myocardium can lead to functional improvement. Abnormalities in Ca(2+) handling play an important role in disease progression toward heart failure, and increased SERCA2a levels appear to significantly improve cardiac contraction and relaxation. Beneficial effects persist at least over a period of 6 months, and the evolution of cardiac functional parameters paralleled those of normal controls. Furthermore, we demonstrate that a plasmid formulation based on amphiphilic block copolymers can provide a safe and efficient platform for myocardial gene therapies. The use of synthetic formulations for myocardial gene transfer might thus overcome one of the major hurdles linked to viral vectors, that is, repeat administrations.

The role of CaMKII regulation of phospholamban activity in heart disease

Phospholamban (PLN) is a phosphoprotein in cardiac sarcoplasmic reticulum (SR) that is a reversible regulator of the Ca²⁺-ATPase (SERCA2a) activity and cardiac contractility. Dephosphorylated PLN inhibits SERCA2a and PLN phosphorylation, at either Ser¹⁶ by PKA or Thr¹⁷ by Ca²⁺-calmodulin-dependent protein kinase (CaMKII), reverses this inhibition. Through this mechanism, PLN is a key modulator of SR Ca²⁺ uptake, Ca²⁺ load, contractility, and relaxation. PLN phosphorylation is also the main determinant of β1-adrenergic responses in the heart. Although phosphorylation of Thr¹⁷ by CaMKII contributes to this effect, its role is subordinate to the PKA-dependent increase in cytosolic Ca²⁺, necessary to activate CaMKII. Furthermore, the effects of PLN and its phosphorylation on cardiac function are subject to additional regulation by its interacting partners, the anti-apoptotic HAX-1 protein and Gm or the anchoring unit of protein phosphatase 1. Regulation of PLN activity by this multimeric complex becomes even more important in pathological conditions, characterized by aberrant Ca²⁺-cycling. In this scenario, CaMKII-dependent PLN phosphorylation has been associated with protective effects in both acidosis and ischemia/reperfusion. However, the beneficial effects of increasing SR Ca²⁺ uptake through PLN phosphorylation may be lost or even become deleterious, when these occur in association with alterations in SR Ca²⁺ leak. Moreover, a major characteristic in human and experimental heart failure (HF) is depressed SR Ca²⁺ uptake, associated with decreased SERCA2a levels and dephosphorylation of PLN, leading to decreased SR Ca²⁺ load and impaired contractility. Thus, the strategy of altering SERCA2a and/or PLN levels or activity to restore perturbed SR Ca²⁺ uptake is a potential therapeutic tool for HF treatment. We will review here the role of CaMKII-dependent phosphorylation of PLN at Thr¹⁷ on cardiac function under physiological and pathological conditions.

Novel aspects of excitation-contraction coupling in heart failure

Excitation-contraction coupling is the process by which electrical activation is translated into contraction of a cardiac myocyte and thus the heart. In heart failure, expression, phosphorylation, and function of several intracellular proteins that are involved in excitation-contraction coupling are altered. The present review article summarizes central principles and highlights novel aspects of alterations in heart failure, focusing especially on recent findings regarding altered sarcoplasmic reticulum Ca2+ -leak and late Na+ -current without being able to cover all changes in full detail. These two pathomechanisms seem to play interesting roles with respect to systolic and diastolic dysfunction and may also be important for cardiac arrhythmias. Furthermore, the article outlines the translation of these novel findings into potential therapeutic approaches.

The 140-kD isoform of CD56 (NCAM1) directs the molecular pathogenesis of ischemic cardiomyopathy

Despite recent advances in understanding the relevance of cell adhesion-related signaling in the pathogenesis of ischemic cardiomyopathy (ICM) in animal models, substantial questions remain unanswered in the human setting. We have previously shown that the neural cell adhesion molecule CD56 [neural cell adhesion molecule (NCAM1)] is specifically overexpressed in ICM; it was the aim of the current study to further elucidate the role of CD56 in the pathogenesis of human ICM. We used quantitative real-time PCR and IHC in human ICM and a rat model of coronary obstruction to demonstrate that CD56(140kD), the only extraneuronally expressed NCAM1 isoform with a cytoplasmic protein domain capable of inducing intracellular signaling, is the only up-regulated CD56 isoform in failing cardiomyocytes in human ICM in vivo. In subsequent analyses of the cellular effects of CD56(140kD) overexpression in the development of ICM using differential whole transcriptome expression analyses and functional in vitro cardiomyocyte cell culture assays, we further show that the up-regulation of CD56(140kD) is associated with profound gene expression changes, increased apoptosis, and reduced Ca(2+) signaling in failing human cardiomyocytes. Because apoptosis and Ca(2+)-related sarcomeric dysfunction are molecular hallmarks of ICM in humans, our results provide strong evidence that CD56(140kD) up-regulation plays a pivotal role in the pathogenesis of ICM and may be a target for future immunotherapeutic strategies in the treatment of this common and often fatal disease.

Altered sarcoplasmic reticulum calcium cycling--targets for heart failure therapy

Cardiac myocyte function is dependent on the synchronized movements of Ca(2+) into and out of the cell, as well as between the cytosol and sarcoplasmic reticulum. These movements determine cardiac rhythm and regulate excitation-contraction coupling. Ca(2+) cycling is mediated by a number of critical Ca(2+)-handling proteins and transporters, such as L-type Ca(2+) channels (LTCCs) and sodium/calcium exchangers in the sarcolemma, and sarcoplasmic/endoplasmic reticulum calcium ATPase 2a (SERCA2a), ryanodine receptors, and cardiac phospholamban in the sarcoplasmic reticulum. The entry of Ca(2+) into the cytosol through LTCCs activates the release of Ca(2+) from the sarcoplasmic reticulum through ryanodine receptor channels and initiates myocyte contraction, whereas SERCA2a and cardiac phospholamban have a key role in sarcoplasmic reticulum Ca(2+) sequesteration and myocyte relaxation. Excitation-contraction coupling is regulated by phosphorylation of Ca(2+)-handling proteins. Abnormalities in sarcoplasmic reticulum Ca(2+) cycling are hallmarks of heart failure and contribute to the pathophysiology and progression of this disease. Correcting impaired intracellular Ca(2+) cycling is a promising new approach for the treatment of heart failure. Novel therapeutic strategies that enhance myocyte Ca(2+) homeostasis could prevent and reverse adverse cardiac remodeling and improve clinical outcomes in patients with heart failure.

Ryanodine receptor phosphorylation, calcium/calmodulin-dependent protein kinase II, and life-threatening ventricular arrhythmias

Ryanodine receptor (RyR2) dysfunction, which may result from a variety of mechanisms, has been implicated in the pathogenesis of cardiac arrhythmias and heart failure. In this review, we discuss the important role of Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) in the regulation of RyR2-mediated Ca(2+) release. In particular, we examine how pathological activation of CaMKII can lead to an increased risk of sudden arrhythmic death. Finally, we discuss how reduction of CaMKII-mediated RyR2 hyperactivity might reduce the risk of arrhythmias and may serve as a rationale for future pharmacotherapeutic approaches.

What causes a broken heart--molecular insights into heart failure

Our understanding of the molecular processes which regulate cardiac function has grown immeasurably in recent years. Even with the advent of β-blockers, angiotensin inhibitors and calcium modulating agents, heart failure (HF) still remains a seriously debilitating and life-threatening condition. Here, we review the molecular changes which occur in the heart in response to increased load and the pathways which control cardiac hypertrophy, calcium homeostasis, and immune activation during HF. These can occur as a result of genetic mutation in the case of hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM) or as a result of ischemic or hypertensive heart disease. In the majority of cases, calcineurin and CaMK respond to dysregulated calcium signaling and adrenergic drive is increased, each of which has a role to play in controlling blood pressure, heart rate, and left ventricular function. Many major pathways for pathological remodeling converge on a set of transcriptional regulators such as myocyte enhancer factor 2 (MEF2), nuclear factors of activated T cells (NFAT), and GATA4 and these are opposed by the action of the natriuretic peptides ANP and BNP. Epigenetic modification has emerged in recent years as a major influence cardiac physiology and histone acetyl transferases (HATs) and histone deacetylases (HDACs) are now known to both induce and antagonize hypertrophic growth. The newly emerging roles of microRNAs in regulating left ventricular dysfunction and fibrosis also has great potential for novel therapeutic intervention. Finally, we discuss the role of the immune system in mediating left ventricular dysfunction and fibrosis and ways this can be targeted in the setting of viral myocarditis.

Involvement of sarcoplasmic reticulum in changing intracellular calcium due to Na+/K+-ATPase inhibition in cardiomyocytes

Earlier studies have demonstrated that ouabain-induced increase in [Ca2+]i, as a consequence of sarcolemma (SL) Na+/K+-ATPase inhibition, is associated with activation of both the SL Na+/Ca2+ exchanger and SL Ca2+ channels. In view of the importance of sarcoplasmic reticulum (SR) in the regulation of [Ca2+]i, this study examined the role of SR in ouabain-induced increase in [Ca2+]i in both quiescent and KCl-depolarized cardiomyocytes. For this purpose, adult rat cardiomyocytes were loaded with fura-2 and ouabain-induced changes in [Ca2+]i were monitored upon treatment with or without different agents that are known to influence Ca2+ handling by the intracellular organelles. Ouabain not only increased the basal [Ca2+]i and augmented KCl-induced increase in [Ca2+]i but also produced similar effects on the ATP-induced increase in [Ca2+]i. Treatments of cardiomyocytes with caffeine, ryanodine, or cyclopiazonic acid, which affect SR Ca2+ stores, attenuated the ouabain-induced increase in basal Ca2+ as well as augmentation of the KCl response. Both ryanodine and cyclopiazonic acid produced additional effects, when used in combination with a SL Ca2+ channel inhibitor (verapamil), but not with a Na+/Ca2+ exchange inhibitor (KB-R7943). Inhibitors of Ca2+/calmodulin kinase, protein kinase A, and inositol-3-phosphate receptors were also observed to depress the ouabain-induced increase in [Ca2+]i in cardiomyocytes. On the other hand, mitochondrial Ca2+ transport inhibitors did not exert any effect on the ouabain-induced alterations in [Ca2+]i in cardiomyocytes. Furthermore, ouabain did not show any direct effect on the Ca2+ uptake and Ca2+ release activities of SR or mitochondria. These results suggest an indirect involvement of SR Ca2+ stores in the ouabain-induced increase in [Ca2+]i in cardiomyocytes and indicate the participation of both Ca2+-induced Ca2+ release and regulatory mechanisms in this action.

A β(IV)-spectrin/CaMKII signaling complex is essential for membrane excitability in mice

Ion channel function is fundamental to the existence of life. In metazoans, the coordinate activities of voltage-gated Na(+) channels underlie cellular excitability and control neuronal communication, cardiac excitation-contraction coupling, and skeletal muscle function. However, despite decades of research and linkage of Na(+) channel dysfunction with arrhythmia, epilepsy, and myotonia, little progress has been made toward understanding the fundamental processes that regulate this family of proteins. Here, we have identified β(IV)-spectrin as a multifunctional regulatory platform for Na(+) channels in mice. We found that β(IV)-spectrin targeted critical structural and regulatory proteins to excitable membranes in the heart and brain. Animal models harboring mutant β(IV)-spectrin alleles displayed aberrant cellular excitability and whole animal physiology. Moreover, we identified a regulatory mechanism for Na(+) channels, via direct phosphorylation by β(IV)-spectrin-targeted calcium/calmodulin-dependent kinase II (CaMKII). Collectively, our data define an unexpected but indispensable molecular platform that determines membrane excitability in the mouse heart and brain.

Protein Kinases as Drug Development Targets for Heart Disease Therapy

Protein kinases are intimately integrated in different signal transduction pathways for the regulation of cardiac function in both health and disease. Protein kinase A (PKA), Ca²⁺-calmodulin-dependent protein kinase (CaMK), protein kinase C (PKC), phosphoinositide 3-kinase (PI3K) and mitogen-activated protein kinase (MAPK) are not only involved in the control of subcellular activities for maintaining cardiac function, but also participate in the development of cardiac dysfunction in cardiac hypertrophy, diabetic cardiomyopathy, myocardial infarction, and heart failure. Although all these kinases serve as signal transducing proteins by phosphorylating different sites in cardiomyocytes, some of their effects are cardioprotective whereas others are detrimental. Such opposing effects of each signal transduction pathway seem to depend upon the duration and intensity of stimulus as well as the type of kinase isoform for each kinase. In view of the fact that most of these kinases are activated in heart disease and their inhibition has been shown to improve cardiac function, it is suggested that these kinases form excellent targets for drug development for therapy of heart disease.

Proteome changes in CaMKIIδC-overexpressing cardiac myocytes

Recent studies have demonstrated that the expression as well as the activity of Ca/calmodulin-dependent protein kinase IIδ(C) (CaMKIIδ(C)) is increased in heart failure. Transgenic overexpression of CaMKIIδ(C) in mouse hearts results in severe dilated cardiomyopathy. So far, little is known about CaMKIIδ(C)-induced changes in gene expression and proteome alteration. We hypothesize that proteome changes similar to those found in advanced heart failure can be assessed even after short term overexpression of CaMKIIδ(C) in an in vitro culture model. Thus, we designed a study using a proteomic approach combined with adenovirus-mediated gene transfer of CaMKIIδ(C) to identify early CaMKIIδ(C)-induced changes in cardiac myocyte phenotype on proteome level. CaMKIIδ(C) was overexpressed by adenovirus-mediated gene transfer in isolated cardiac myocytes of adult rabbits for 48 h. Proteome changes were analyzed by two-dimensional gel electrophoresis and mass spectrometry (MS). Overexpression of CaMKIIδ(C) resulted in a decreased expression of 21 proteins (at least twofold change of expression, P<.05, n=10). Using in-gel digest and MS, we identified 13 out of these 21 proteins. CaMKIIδ(C) overexpression leads to a reduced abundance of NADH dehydrogenase, lactate dehydrogenase, pyruvate kinase, dihydrolipoamide succinyltransferase, creatine kinase M, heat shock protein 70, elongation factor Tu, and superoxide dismutase. The profile of the proteome changes induced by CaMKIIδ(C) overexpression after 48 h displayed striking alterations of metabolic proteins, cell-protecting proteins including antioxidants, and proteins involved in protein synthesis. Interestingly, the observed proteome changes are in common with the phenotype of failing cardiac myocytes on the protein level. These altered proteins may act individually as contributors to heart failure, which is observed after overexpression of CaMKIIδ(C) in genetically altered mice.

Critical role of nuclear calcium/calmodulin-dependent protein kinase IIdeltaB in cardiomyocyte survival in cardiomyopathy

Calcium/calmodulin-dependent protein kinase II (CaMKII) plays a central role in cardiac contractility and heart disease. However, the specific role of alternatively spliced variants of CaMKII in cardiac disease and apoptosis remains poorly explored. Here we report that the deltaB subunit of CaMKII (CaMKIIdeltaB), which is the predominant nuclear isoform of calcium/calmodulin-dependent protein kinases in heart muscle, acts as an anti-apoptotic factor and is a novel target of the antineoplastic and cardiomyopathic drug doxorubicin (Dox (adriamycin)). Hearts of rats that develop cardiomyopathy following chronic treatment with Dox also show down-regulation of CaMKIIdeltaB mRNA, which correlates with decreased cardiac function in vivo, reduced expression of sarcomeric proteins, and increased tissue damage associated with Dox cardiotoxicity. Overexpression of CaMKIIdeltaB in primary cardiac cells inhibits Dox-mediated apoptosis and prevents the loss of the anti-apoptotic protein Bcl-2. Specific silencing of CaMKIIdeltaB by small interfering RNA prevents the formation of organized sarcomeres and decreases the expression of Bcl-2, which all mimic the effect of Dox. CaMKIIdeltaB is required for GATA-4-mediated co-activation and binding to the Bcl-2 promoter. These results reveal that CaMKIIdeltaB plays an essential role in cardiomyocyte survival and provide a mechanism for the protective role of CaMKIIdeltaB. These results suggest that selective targeting of CaMKII in the nuclear compartment might represent a strategy to regulate cardiac apoptosis and to reduce Dox-mediated cardiotoxicity.

Calcium/calmodulin-dependent protein kinase II mediates cardioprotection of intermittent hypoxia against ischemic-reperfusion-induced cardiac dysfunction

Intermittent high-altitude (IHA) hypoxia-induced cardioprotection against ischemia-reperfusion (I/R) injury is associated with the preservation of sarcoplasmic reticulum (SR) function. Although Ca(2+)/calmodulin (CaM)-dependent protein kinase II (CaMKII) and phosphatase are known to modulate the function of cardiac SR under physiological conditions, the status of SR CaMKII and phosphatase during I/R in the hearts from IHA hypoxic rats is unknown. In the present study, we determined SR and cytosolic CaMKII activity during preischemia and I/R (30 min/30 min) in perfused hearts from normoxic and IHA hypoxic rats. The left ventricular contractile recovery, SR CaMKII activity as well as phosphorylation of phospholamban at Thr(17), and Ca(2+)/CaM-dependent SR Ca(2+)-uptake activity were depressed in the I/R hearts from normoxic rats, whereas these changes were prevented in the hearts from IHA hypoxic rats. Such beneficial effects of IHA hypoxia were lost by treating the hearts with a specific CaMKII inhibitor, KN-93. I/R also depressed cytosolic CaMKII and SR phosphatase activity, but these alterations remained unchanged in IHA hypoxic group. Furthermore, we found that the autophosphorylation at Thr(287), which confers Ca(2+)/CaM-independent activity, was not altered by I/R in both groups. These findings indicate that preservation of SR CaMKII activity plays an important role in the IHA hypoxia-induced cardioprotection against I/R injury via maintaining SR Ca(2+)-uptake activity.

Antinociceptive effects of 14-membered cyclopeptide alkaloids

The analgesic potential of six 14-membered-ring cyclopeptide alkaloids, namely, franganine (1), discarine B (2), scutianines B (3), C (4), and D (5), and adouetine X (6), have been investigated. Among the compounds tested, only franganine (1) and adouetine X (6) produced antinociceptive effects in a mouse model of acute pain, without inducing undesirable side effects. Furthermore, compound 6 also exhibited a pronounced analgesic effect in a chronic neuropathic pain model in mice. It has been found that adouetine X (6) can decrease the activities of Ca(2+)-ATPase and Na(+)/K(+)-ATPase in vitro. Thus, the present findings have demonstrated that adouetine X (6) is a promising analgesic agent.

Defective Ca2+ cycling as a key pathogenic mechanism of heart failure

Structural and functional alterations in the Ca(2+) regulatory proteins present in the sarcoplasmic reticulum (SR) have recently been shown to play a crucial role in the pathogenesis of heart failure (HF), and lethal arrhythmia as well. Chronic activation of the sympathetic nervous system induces abnormalities in both the function and structure of these proteins. For instance, the diastolic Ca(2+) leak through the SR Ca(2+) release channel (ryanodine receptor) reduces the SR Ca(2+) content, inducing contractile dysfunction. Moreover, the Ca(2+) leak provides a substrate for delayed after depolarization that leads to lethal arrhythmia. There is a considerable body of evidence regarding the role of Ca(2+) cycling abnormality in HF.

Role of activated CaMKII in abnormal calcium homeostasis and I(Na) remodeling after myocardial infarction: insights from mathematical modeling

Ca(2+)/calmodulin-dependent protein kinase II is a multifunctional serine/threonine kinase with diverse cardiac roles including regulation of excitation contraction, transcription, and apoptosis. Dynamic regulation of CaMKII activity occurs in cardiac disease and is linked to specific disease phenotypes through its effects on ion channels, transporters, transcription and cell death pathways. Recent mathematical models of the cardiomyocyte have incorporated limited elements of CaMKII signaling to advance our understanding of how CaMKII regulates cardiac contractility and excitability. Given the importance of CaMKII in cardiac disease, it is imperative that computer models evolve to capture the dynamic range of CaMKII activity. In this study, using mathematical modeling combined with biochemical and imaging techniques, we test the hypothesis that CaMKII signaling in the canine infarct border zone (BZ) contributes to impaired calcium homeostasis and electrical remodeling. We report that the level of CaMKII autophosphorylation is significantly increased in the BZ region. Computer simulations using an updated mathematical model of CaMKII signaling reproduce abnormal Ca(2+) transients and action potentials characteristic of the BZ. Our simulations show that CaMKII hyperactivity contributes to abnormal Ca(2+) homeostasis and reduced action potential upstroke velocity due to effects on I(Na) gating kinetics. In conclusion, we present a new mathematical tool for studying effects of CaMKII signaling on cardiac excitability and contractility over a dynamic range of kinase activities. Our experimental and theoretical findings establish abnormal CaMKII signaling as an important component of remodeling in the canine BZ.

Long-term postinfarction melatonin administration alters the expression of DHPR, RyR2, SERCA2, and MT2 and elevates the ANP level in the rat left ventricle

We investigated the effect of 2 wk continuous postinfarction subcutaneous melatonin supply on the expression of the rat left ventricular (LV) dihydropyridine receptor (DHPR), ryanodine receptor (RyR(2)), and sarco-endoplasmic reticulum Ca(2+)-ATPase2 (SERCA2), as they are fundamental proteins in cardiac contractility. The levels of plasma and LV atrial (ANP) and brain natriuretic peptide and melatonin were also measured, as was the expression of LV MT(1) and MT(2) receptors and pineal arylalkylamine N-acetyltransferase. Myocardial infarction (MI) was induced by ligation of the left anterior descending coronary artery and vehicle or melatonin (4.5 mg/kg per day) was administered by subcutaneous osmotic pumps. Echocardiography, real-time quantitative reverse transcription-polymerase chain reaction, and western blotting were used to analyze the samples. Echocardiography revealed that MI induced serious systolic LV dysfunction. The expression of DHPR, RyR(2), and SERCA2 mRNAs was significantly lower in the LVs of melatonin-treated MI rats compared with vehicle-treated rats (P < 0.01 for DHPR and P < 0.05 for RyR(2) and SERCA2). Melatonin also elevated the amount of LV MT(2) receptors to 1.9-fold (P < 0.05) and the concentration of LV ANP to over fivefold (P < 0.05) compared with vehicle rats after MI. Therefore, the results suggest that melatonin may influence the cardiac contractility after MI by regulating the expression of DHPR, RyR(2), and SERCA2, and melatonin receptors, particularly MT(2)s, might contribute to the postinfarction cardioprotective actions of melatonin. Furthermore, the finding of the relationship between melatonin and ANP suggests a novel mechanism for melatonin in protecting the heart after MI.

Toward biologically targeted therapy of calcium cycling defects in heart failure

A growing body of evidence indicates that heart failure progression is tightly associated with dysregulation of phosphorylation of Ca2+ regulators localized in the sub-cellular microdomain of the sarcoplasmic reticulum. Chemical or genetic correction of abnormalities in cardiac phosphorylation cascades is emerging as a potential target in the treatment of heart failure. Here, we review how specific kinases and phosphatases finely tune Ca2+ cycling and regulate excitation-contraction (E-C) coupling in cardiomyocytes.

Remodeling of excitation-contraction coupling in the heart: Inhibition of sarcoplasmic reticulum Ca2+ leak as a novel therapeutic approach

In the heart, excitation-contraction coupling is the central mechanism by which electrical activation is translated into cardiac contraction. In heart failure, several proteins involved in this finely concerted regulation are changed with respect to expression, phosphorylation status, and function leading to remodeling of excitation-contraction coupling. The present review article summarizes well known alterations in heart failure and focuses on recent findings especially regarding altered sarcoplasmic reticulum Ca(2+) release process due to two distinct kinases, namely protein kinase A and Ca(2+)/calmodulin-dependent kinase II. Furthermore, it highlights the translation of those findings into possible novel therapeutic approaches.

Antiplatelet therapy attenuates subcellular remodelling in congestive heart failure

Antiplatelet agents, sarpogrelate (SAR), a 5-HT(2A) receptor antagonist, and cilostazol (CIL), a phosphodiesterase III (PDE-III) inhibitor, are used for the treatment of peripheral vascular disease. We tested whether these agents affect cardiac function and subcellular remodelling in congestive heart failure (CHF) induced by myocardial infarction (MI). Three weeks after MI, rats were treated daily with 5 mg/kg SAR or CIL as well as vehicle for 5 weeks. Sham-operated animals served as controls. At end of the treatment period, haemodynamic measurements were performed and the left ventricle was processed for the determination of sarcoplasmic reticulum (SR) Ca(2+)-uptake and -release activities, and expression of SR Ca(2+)-pump, phospholamban and ryanodine receptors, as well as myofibrillar ATPase activities, expression of alpha- and beta-myosin heavy chain (MHC) isoforms, and phosphorylation of phospholamban and cardiac troponin-I (c Tn-I). Marked haemodynamic changes in the MI-induced CHF were associated with depressions in SR Ca (+)-uptake and -release activities as well as in protein content and gene expression for SR proteins. Furthermore, myofibrillar Ca(2+)-stimulated ATPase activity, as well as protein content and gene expression for alpha-MHC were decreased whereas those for beta-MHC were increased in the failing heart. Also, phosphorylation levels of phospholamban and cTn-I were reduced in failing hearts. The MI-associated changes in cardiac function, SR and myofibillar activities, as well as SR and myofibrillar protein and gene expression were attenuated by treatment with SAR or CIL. The results suggest that SAR and CIL improve cardiac function by ameliorating subcellular remodelling in the failing heart and indicate the potential therapy of CHF with antiplatelet agents.

Imbalance between CaM kinase II and calcineurin activities impairs caffeine-induced calcium release in hypertrophic cardiomyocytes

Cardiac hypertrophy impairs Ca(2+) handling in the sarcoplasmic reticulum, thereby impairing cardiac contraction. To identify the mechanisms underlying impaired Ca(2+) release from the sarcoplasmic reticulum in hypertrophic cardiomyocytes, we assessed Ca(2+)-dependent signaling and the phosphorylation of phospholamban, which regulates Ca(2+) uptake during myocardial relaxation and is in turn regulated by Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) and calcineurin. In cultured rat cardiomyocytes, treatment with endothelin-1, angiotensin II, and phenylephrine-induced hypertrophy and increased CaMKII autophosphorylation and calcineurin expression. The calcineurin level reached its maximum at 72h and remained elevated for at least 96h after endothelin-1 or angiotensin II treatment. By contrast, CaMKII autophosphorylation, phospholamban phosphorylation, and caffeine-induced Ca(2+) mobilization all peaked 48h after these treatments. By 96h after treatment, CaMKII autophosphorylation and phospholamban phosphorylation had returned to baseline, and caffeine-induced Ca(2+) mobilization was impaired relative to baseline. A similar biphasic change was observed in dystrophin levels in endothelin-1-induced hypertrophic cardiomyocytes, and treatment with the novel CaM antagonists DY-9760e and DY-9836 significantly inhibited the hypertrophy-induced dystrophin breakdown. Taken together, the abnormal Ca(2+) regulation in cardiomyocytes following hypertrophy is in part mediated by an imbalance in calcineurin and CaMKII activities, which leads to abnormal phospholamban activity.

Time course of changes in the expression of DHPR, RyR(2), and SERCA2 after myocardial infarction in the rat left ventricle

Postinfarction left ventricular remodeling leads to the functional decline of the left ventricle (LV). Since dihydropyridine receptor (DHPR), ryanodine receptor (RyR(2)), and sarco-endoplasmic reticulum (SR) Ca(2+)-ATPase2 (SERCA2a) play a major role in the contractility of the heart, the aim of our study was to evaluate the time course of changes in the expression of these proteins 1 day, 2 weeks and 4 weeks after myocardial infarction (MI). Myocardial infarction was produced by ligation of left anterior descending coronary artery of the rat. Transthoracic echocardiography was performed to characterize structural and functional changes after MI. To evaluate protein mRNA levels and the relative amount of proteins, real-time quantitative RT-PCR and Western blotting were used. LV ejection fraction and fractional shortening decreased significantly during the 4-week follow-up period (P < 0.001). Typical features of LV remodeling after MI were seen, with a decrease in anterior wall thickness (P < 0.001) and dilatation of the LV (P < 0.001). Expression of DHPR and RyR(2) mRNAs decreased and Serca2a mRNA tended to decrease 1 day after MI (P < 0.001, P < 0.01 and P = 0.06, respectively), followed by recovery of the expression during the next 4 weeks. In the infarcted hearts the quantities of SERCA2 proteins in the LV were significantly decreased at the time of 4 weeks. In conclusion, MI was associated with transient decrease in the expression of the DHPR and RyR(2) mRNAs and a reduced quantity of SERCA2 proteins in the LV. Since they have a key role in the contraction of the heart, changes in the expression of these proteins may be important regulators of LV systolic function after MI.

Arrhythmogenic Ion-Channel Remodeling in the Heart: Heart Failure, Myocardial Infarction, and Atrial Fibrillation

Rhythmic and effective cardiac contraction depends on appropriately timed generation and spread of cardiac electrical activity. The basic cellular unit of such activity is the action potential, which is shaped by specialized proteins (channels and transporters) that control the movement of ions across cardiac cell membranes in a highly regulated fashion. Cardiac disease modifies the operation of ion channels and transporters in a way that promotes the occurrence of cardiac rhythm disturbances, a process called “arrhythmogenic remodeling.” Arrhythmogenic remodeling involves alterations in ion channel and transporter expression, regulation and association with important protein partners, and has important pathophysiological implications that contribute in major ways to cardiac morbidity and mortality. We review the changes in ion channel and transporter properties associated with three important clinical and experimental paradigms: congestive heart failure, myocardial infarction, and atrial fibrillation. We pay particular attention to K+, Na+, and Ca2+channels; Ca2+transporters; connexins; and hyperpolarization-activated nonselective cation channels and discuss the mechanisms through which changes in ion handling processes lead to cardiac arrhythmias. We highlight areas of future investigation, as well as important opportunities for improved therapeutic approaches that are being opened by an improved understanding of the mechanisms of arrhythmogenic remodeling.

Chronic intermittent hypoxia alters Ca2+ handling in rat cardiomyocytes by augmented Na+/Ca2+ exchange and ryanodine receptor activities in ischemia-reperfusion

This study examined Ca(2+) handling mechanisms involved in cardioprotection induced by chronic intermittent hypoxia (CIH) against ischemia-reperfusion (I/R) injury. Adult male Sprague-Dawley rats were exposed to 10% inspired O(2) continuously for 6 h daily from 3, 7, and 14 days. In isolated perfused hearts subjected to I/R, CIH-induced cardioprotection was most significant in the 7-day group with less infarct size and lactate dehydrogenase release, compared with the normoxic group. The I/R-induced alterations in diastolic Ca(2+) level, amplitude, time-to-peak, and the decay time of both electrically and caffeine-induced Ca(2+) transients measured by spectrofluorometry in isolated ventricular myocytes of the 7-day CIH group were less than that of the normoxic group, suggesting an involvement of altered Ca(2+) handling of the sarcoplasmic reticulum (SR) and sarcolemma. We further determined the protein expression and activity of (45)Ca(2+) flux of SR-Ca(2+)-ATPase, ryanodine receptor (RyR) and sarcolemmal Na(+)/Ca(2+) exchange (NCX) in ventricular myocytes from the CIH and normoxic groups before and during I/R. There were no changes in expression levels of the Ca(2+)-handling proteins but significant increases in the RyR and NCX activities were remarkable during I/R in the CIH but not the normoxic group. The augmented RyR and NCX activities were abolished, respectively, by PKA inhibitor (0.5 microM KT5720 or 0.5 microM PKI(14-22)) and PKC inhibitor (5 microM chelerythrine chloride or 0.2 microM calphostin C) but not by Ca(2+)/calmodulin-dependent protein kinase II inhibitor KN-93 (1 microM). Thus, CIH confers cardioprotection against I/R injury in rat cardiomyocytes by altered Ca(2+) handling with augmented RyR and NCX activities via protein kinase activation.

Calcium signaling phenomena in heart diseases: a perspective

Ca(2+) is a major intracellular messenger and nature has evolved multiple mechanisms to regulate free intracellular (Ca(2+))(i) level in situ. The Ca(2+) signal inducing contraction in cardiac muscle originates from two sources. Ca(2+) enters the cell through voltage dependent Ca(2+) channels. This Ca(2+) binds to and activates Ca(2+) release channels (ryanodine receptors) of the sarcoplasmic reticulum (SR) through a Ca(2+) induced Ca(2+) release (CICR) process. Entry of Ca(2+) with each contraction requires an equal amount of Ca(2+) extrusion within a single heartbeat to maintain Ca(2+) homeostasis and to ensure relaxation. Cardiac Ca(2+) extrusion mechanisms are mainly contributed by Na(+)/Ca(2+) exchanger and ATP dependent Ca(2+) pump (Ca(2+)-ATPase). These transport systems are important determinants of (Ca(2+))(i) level and cardiac contractility. Altered intracellular Ca(2+) handling importantly contributes to impaired contractility in heart failure. Chronic hyperactivity of the beta-adrenergic signaling pathway results in PKA-hyperphosphorylation of the cardiac RyR/intracellular Ca(2+) release channels. Numerous signaling molecules have been implicated in the development of hypertrophy and failure, including the beta-adrenergic receptor, protein kinase C, Gq, and the down stream effectors such as mitogen activated protein kinases pathways, and the Ca(2+) regulated phosphatase calcineurin. A number of signaling pathways have now been identified that may be key regulators of changes in myocardial structure and function in response to mutations in structural components of the cardiomyocytes. Myocardial structure and signal transduction are now merging into a common field of research that will lead to a more complete understanding of the molecular mechanisms that underlie heart diseases. Recent progress in molecular cardiology makes it possible to envision a new therapeutic approach to heart failure (HF), targeting key molecules involved in intracellular Ca(2+) handling such as RyR, SERCA2a, and PLN. Controlling these molecular functions by different agents have been found to be beneficial in some experimental conditions.

Mechanisms of Diastolic Dysfunction in Heart Failure

Abnormalities of diastole are common to most forms of congestive heart failure (HF). Diastolic function is broadly defined as the ability of the heart to fill adequately and at normal pressure to charge the ventricular pump for each subsequent contraction. It is determined by both active and passive processes occurring at the level of the myocyte, extracellular matrix, and left ventricular chamber. Forces extrinsic to the myocardium-such as the influence of right heart filling, pericardial and extracardiac constraints, and cardiac preload and afterload also contribute. Nearly half of patients with HF have apparently preserved systolic function, and this has focused attention on diastolic dysfunction as a dominant contributor to symptoms, sparking interest for understanding and treating diastolic abnormalities. This review focuses on the mechanisms determining normal and pathologic cardiac relaxation and distensibility and highlights how these abnormalities may be therapeutically targeted to improve diastolic function in human HF.

Alterations in cardiac contractile performance and sarcoplasmic reticulum function in sucrose-fed rats is associated with insulin resistance

Diabetes mellitus (DM) causes the development of a specific cardiomyopathy that results from the metabolic derangements present in DM and manifests as cardiac contractile dysfunction. Although myocardial dysfunction in Type 1 DM has been associated with defects in the function and regulation of the sarcoplasmic reticulum (SR), very little is known about SR function in Type 2 DM. Accordingly, this study examined whether abnormalities in cardiac contractile performance and SR function occur in the prestage of Type 2 DM (i.e., during insulin resistance). Sucrose feeding was used to induce whole body insulin resistance, whereas cardiac contractile performance was assessed by echocardiography and SR function was measured by SR calcium (Ca2+) uptake. Sucrose-fed rats exhibited hyperinsulinemia, hyperglycemia, and hyperlipidemia relative to control rats. Serial echocardiographic assessments in the sucrose-fed rats revealed early abnormalities in diastolic function followed by late systolic dysfunction and concurrent alterations in myocardial structure. The hearts of the 10-wk sucrose-fed rats showed depressed SR function demonstrated by a significant reduction in SR Ca2+uptake. The decline in SR Ca2+uptake was associated with a significant decrease in the cAMP-dependent protein kinase and Ca2+/calmodulin-dependent protein kinase II-mediated phosphorylation of phospholamban. The results show that abnormalities in cardiac contractile performance and SR function occur at an insulin-resistant stage before the manifestation of overt Type 2 DM.

Subcellular remodeling as a viable target for the treatment of congestive heart failure

It is now well known that congestive heart failure (CHF) is invariably associated with cardiac hypertrophy, and changes in the shape and size of cardiomyocytes (cardiac remodeling) are considered to explain cardiac dysfunction in CHF. However, the mechanisms responsible for the transition of cardiac hypertrophy to heart failure are poorly understood. Several lines of evidence both from various experimental models of CHF and from patients with different types of CHF have indicated that the functions of different subcellular organelles such as extracellular matrix, sarcolemma, sarcoplasmic reticulum, myofibrils, mitochondria, and nucleus are defective. Subcellular abnormalities for protein contents, gene expression, and enzyme activities in the failing heart become evident as a consequence of prolonged hormonal imbalance, metabolic derangements, and cation maldistribution. In particular, the occurrence of oxidative stress, development of intracellular Ca2+ overload, activation of proteases and phospholipases, and alterations in cardiac gene expression result in changes in the biochemical composition, molecular structure, and function of different subcellular organelles (subcellular remodeling). Not only does subcellular remodeling appear to be intimately involved in the transition of cardiac hypertrophy to heart failure, the mismatching of the function of different subcellular organelles leads to the development of cardiac dysfunction. Although blockade of the renin-angiotensin system, sympathetic nervous system, and various other hormonal actions have been reported to produce beneficial effects on cardiac remodeling and heart dysfunction in CHF, the actions of various cardiac drugs on subcellular remodeling have not been examined extensively. Some recent studies have indicated that both the angiotensin-converting enzyme inhibitors and angiotensin receptor antagonists attenuate changes in sarcolemma, sarcoplasmic reticulum, and myofibril enzyme activities, protein contents, and gene expression, and partly improve cardiac function in the failing hearts. It is suggested that subcellular remodeling is an excellent target for the development of improved drug therapy for CHF. Furthermore, extensive studies should investigate the effects of different agents individually or in combination on reverse subcellular remodeling, cardiac remodeling, and cardiac dysfunction in various experimental models of CHF.

Mechanistic basis of differences in Ca2+ -handling properties of sarcoplasmic reticulum in right and left ventricles of normal rat myocardium

This study investigated Ca2+ -cycling properties of sarcoplasmic reticulum (SR) in right ventricle (RV) and left ventricle (LV) of normal rat myocardium. Intracellular Ca2+ transients and contractile function were monitored in freshly isolated myocytes from RV and LV. SR in RV displayed nearly fourfold lower rates of ATP-energized Ca2+ uptake in vitro than SR of LV. The Ca2+ concentration required for half-maximal activation of Ca2+ transport was nearly twofold higher in SR of RV. The lower Ca2+ -sequestering activity of SR in RV was accompanied by a matching decrement in Ca2+ -induced phosphoenzyme formation during the catalytic cycle of the Ca2+ -pumping ATPase (SERCA2). Western immunoblot analysis showed that protein levels of Ca2+ -ATPase and its inhibitor phospholamban (PLN) were only approximately 15% lower in SR of RV than in SR of LV. Coimmunoprecipitation experiments revealed that PLN-bound, functionally inert Ca2+ -ATPase molecules in SR of RV greatly exceed (> 50%) that in SR of LV. Endogenous Ca2+/calmodulin-dependent protein kinase-mediated phosphorylation of SR substrates did not abolish the huge disparity in SR Ca2+ pump function between RV and LV. Intracellular Ca2+ transients, evoked by electrical field stimulation, were significantly prolonged in RV myocytes compared with LV myocytes, mainly because of slow decay of intracellular Ca2+ concentration. The slow decay of intracellular Ca2+ concentration in RV and consequent decrease in the speed of RV relaxation may promote temporal synchrony of the end of diastole in RV and LV. The preponderance of functionally silent SR Ca2+ pumps in RV reflects a higher diastolic reserve required to protect and maintain RV function in the face of a sudden rise in afterload or resistance in the pulmonary circulation.

A role for calcium/calmodulin-dependent protein kinase II in cardiac disease and arrhythmia

More than 20 years have passed since the discovery that a collection of specific calcium/calmodulin-dependent phosphorylation events is the result of a single multifunctional kinase. Since that time, we have learned a great deal about this multifunctional and ubiquitous kinase, known today as calcium/calmodulin-dependent protein kinase II (CaMKII). CaMKII is interesting not only for its widespread distribution and broad specificity but also for its biophysical properties, most notably its activation by the critical second messenger complex calcium/calmodulin and its autophosphorylating capability. A central role for CaMKII has been identified in regulating a diverse array of fundamental cellular activities. Furthermore, altered CaMKII activity profoundly impacts function in the brain and heart. Recent findings that CaMKII expression in the heart changes during hypertrophy, heart failure, myocardial ischemia, and infarction suggest that CaMKII may be a viable therapeutic target for patients suffering from common forms of heart disease.

Reassessment of dobutamine, dopamine, and milrinone in the management of acute heart failure syndromes

The appropriate role of intravenous inodilator therapy (inotropic agents with vasodilator properties) in the management of acute heart failure syndromes (AHFS) has long been a subject of controversy, mainly because of the lack of prospective, placebo-controlled trials and a lack of alternative therapies. The use of intravenous inodilator infusions, however, remains common, but highly variable. As new options emerge for the treatment of AHFS, the available information should be reviewed to determine which approaches are supported by evidence, which are used empirically without evidence, and which should be considered inappropriate. For these purposes, we reviewed data available from randomized controlled trials on short-term, intermittent, and long-term use of intravenous inodilator agents (dobutamine, dopamine, and milrinone) in AHFS. Randomized controlled trials failed to show benefits with current medications and suggested that acute, intermittent, or continuous use of inodilator infusions may increase morbidity and mortality in patients with AHFS. Their use should be restricted to patients who are hypotensive as a result of low cardiac output despite a high left ventricular filling pressure.