The nuclear deltaB isoform of Ca2+/calmodulin-dependent protein kinase II regulates atrial natriuretic factor gene expression in ventricular myocytes

IFDlong: an isoform and fusion detector for accurate annotation and quantification of long-read RNA-seq data

Advancements in long-read transcriptome sequencing (long-RNA-seq) technology have revolutionized the study of isoform diversity. These full-length transcripts enhance the detection of various transcriptome structural variations, including novel isoforms, alternative splicing events, and fusion transcripts. By shifting the open reading frame or altering gene expressions, studies have proved that these transcript alterations can serve as crucial biomarkers for disease diagnosis and therapeutic targets. In this project, we proposed IFDlong, a bioinformatics and biostatistics tool to detect isoform and fusion transcripts using bulk or single-cell long-RNA-seq data. Specifically, the software performed gene and isoform annotation for each long-read, defined novel isoforms, quantified isoform expression by a novel expectation-maximization algorithm, and profiled the fusion transcripts. For evaluation, IFDlong pipeline achieved overall the best performance when compared with several existing tools in large-scale simulation studies. In both isoform and fusion transcript quantification, IFDlong is able to reach more than 0.8 Spearman's correlation with the truth, and more than 0.9 cosine similarity when distinguishing multiple alternative splicing events. In novel isoform simulation, IFDlong can successfully balance the sensitivity (higher than 90%) and specificity (higher than 90%). Furthermore, IFDlong has proved its accuracy and robustness in diverse in-house and public datasets on healthy tissues, cell lines and multiple types of diseases. Besides bulk long-RNA-seq, IFDlong pipeline has proved its compatibility to single-cell long-RNA-seq data. This new software may hold promise for significant impact on long-read transcriptome analysis. The IFDlong software is available at https://github.com/wenjiaking/IFDlong.

Role of CAMK2D in neurodevelopment and associated conditions

The calcium/calmodulin-dependent protein kinase type 2 (CAMK2) family consists of four different isozymes, encoded by four different genes-CAMK2A, CAMK2B, CAMK2G, and CAMK2D-of which the first three have been associated recently with neurodevelopmental disorders. CAMK2D is one of the major CAMK2 proteins expressed in the heart and has been associated with cardiac anomalies. Although this CAMK2 isoform is also known to be one of the major CAMK2 subtypes expressed during early brain development, it has never been linked with neurodevelopmental disorders until now. Here we show that CAMK2D plays an important role in neurodevelopment not only in mice but also in humans. We identified eight individuals harboring heterozygous variants in CAMK2D who display symptoms of intellectual disability, delayed speech, behavioral problems, and dilated cardiomyopathy. The majority of the variants tested lead to a gain of function (GoF), which appears to cause both neurological problems and dilated cardiomyopathy. In contrast, loss-of-function (LoF) variants appear to induce only neurological symptoms. Together, we describe a cohort of individuals with neurodevelopmental disorders and cardiac anomalies, harboring pathogenic variants in CAMK2D, confirming an important role for the CAMK2D isozyme in both heart and brain function.

Palmitic acid methyl ester induces cardiac hypertrophy through activating the GPR receptor-mediated changes of intracellular calcium concentrations and mitochondrial functions

Myocardial hypertrophy is associated with a significant increase in intracellular Ca²⁺ , which can be induced by long-chain fatty acid. Palmitic acid methyl ester (PAME), a fatty acid ester released from adipose tissue, superior cervical ganglion, and retina, has been found to have anti-inflammation, antifibrosis, and peripheral vasodilation effects. However, the effects of PAME on cardiomyocytes are still unclear. The aim of this study was to determine whether PAME could disrupt the intracellular Ca²⁺ balance, leading to cardiomyocyte hypertrophy. Neonatal rat cardiomyocytes were treated with various concentrations (10-100 μM) of PAME for 1-4 days. Cytosolic Ca²⁺ and mitochondrial Ca²⁺ concentrations were examined using Fura-2 AM and Rhod-2, respectively. After treatment with PAME for 4 days, mitochondrial Ca²⁺ , an indicator of the state of mitochondrial permeability transition pore (MPTP), and cell death were monitored by flow cytometric analysis. ATP levels were detected using the ATP assay kit. Cardiomyocyte hypertrophy was analyzed by measuring the cardiac hypertrophy biomarker and cell area using quantitative real time-polymerase chain reaction, Western Blot analysis and immunofluorescence analysis. Our results show that PAME concentration- and time-dependently increased cytosolic and mitochondria Ca²⁺ through the mitochondrial calcium uniporter. Moreover, treatment with PAME for 4 days caused MPTP opening, thereby reducing ATP production and enhancing reactive oxygen species (ROS) generation, and finally led to cardiomyocyte hypertrophy. These effects caused by PAME treatment were attenuated by the G-protein coupled receptor 40 (GPR40) inhibitor. In conclusion, PAME impaired mitochondrial function, which in turn led to cardiomyocyte hypertrophy through increasing the mitochondrial Ca²⁺ levels mediated by activating the GPR40 signaling pathway.

CaMKII Splice Variants in Vascular Smooth Muscle Cells: The Next Step or Redundancy?

Vascular smooth muscle cells (VSMCs) help to maintain the normal physiological contractility of arterial vessels to control blood pressure; they can also contribute to vascular disease such as atherosclerosis. Ca²⁺/calmodulin-dependent kinase II (CaMKII), a multifunctional enzyme with four isoforms and multiple alternative splice variants, contributes to numerous functions within VSMCs. The role of these isoforms has been widely studied across numerous tissue types; however, their functions are still largely unknown within the vasculature. Even more understudied is the role of the different splice variants of each isoform in such signaling pathways. This review evaluates the role of the different CaMKII splice variants in vascular pathological and physiological mechanisms, aiming to show the need for more research to highlight both the deleterious and protective functions of the various splice variants.

Calcium/Calmodulin-Dependent Protein Kinase II in Cerebrovascular Diseases

Cerebrovascular disease is the most common life-threatening and debilitating condition that often leads to stroke. The multifunctional calcium/calmodulin-dependent protein kinase II (CaMKII) is a key Ca2+ sensor and an important signaling protein in a variety of biological systems within the brain, heart, and vasculature. In the brain, past stroke-related studies have been mainly focused on the role of CaMKII in ischemic stroke in neurons and established CaMKII as a major mediator of neuronal cell death induced by glutamate excitotoxicity and oxidative stress following ischemic stroke. However, with growing understanding of the importance of neurovascular interactions in cerebrovascular diseases, there are clearly gaps in our understanding of how CaMKII functions in the complex neurovascular biological processes and its contributions to cerebrovascular diseases. Additionally, emerging evidence demonstrates novel regulatory mechanisms of CaMKII and potential roles of the less-studied CaMKII isoforms in the ischemic brain, which has sparked renewed interests in this dynamic kinase family. This review discusses past findings and emerging evidence on CaMKII in several major cerebrovascular dysfunctions including ischemic stroke, hemorrhagic stroke, and vascular dementia, focusing on the unique roles played by CaMKII in the underlying biological processes of neuronal cell death, neuroinflammation, and endothelial barrier dysfunction triggered by stroke. We also highlight exciting new findings, promising therapeutic agents, and future perspectives for CaMKII in cerebrovascular systems.

CaMKIIδ Splice Variants in the Healthy and Diseased Heart

RNA splicing has been recognized in recent years as a pivotal player in heart development and disease. The Ca²⁺/calmodulin dependent protein kinase II delta (CaMKIIδ) is a multifunctional Ser/Thr kinase family and generates at least 11 different splice variants through alternative splicing. This enzyme, which belongs to the CaMKII family, is the predominant family member in the heart and functions as a messenger toward adaptive or detrimental signaling in cardiomyocytes. Classically, the nuclear CaMKIIδB and cytoplasmic CaMKIIδC splice variants are described as mediators of arrhythmias, contractile function, Ca²⁺ handling, and gene transcription. Recent findings also put CaMKIIδA and CaMKIIδ9 as cardinal players in the global CaMKII response in the heart. In this review, we discuss and summarize the new insights into CaMKIIδ splice variants and their (proposed) functions, as well as CaMKII-engineered mouse phenotypes and cardiac dysfunction related to CaMKIIδ missplicing. We also discuss RNA splicing factors affecting CaMKII splicing. Finally, we discuss the translational perspective derived from these insights and future directions on CaMKIIδ splicing research in the healthy and diseased heart.

Challenges and Opportunities for Therapeutic Targeting of Calmodulin Kinase II in Heart

Heart failure remains a major health burden around the world. Despite great progress in delineation of molecular mechanisms underlying development of disease, standard therapy has not advanced at the same pace. The multifunctional signaling molecule Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) has received considerable attention over recent years for its central role in maladaptive remodeling and arrhythmias in the setting of chronic disease. However, these basic science discoveries have yet to translate into new therapies for human patients. This review addresses both the promise and barriers to developing translational therapies that target CaMKII signaling to abrogate pathologic remodeling in the setting of chronic disease. Efforts in small molecule design are discussed, as well as alternative targeting approaches that exploit novel avenues for compound delivery and/or genetic approaches to affect cardiac CaMKII signaling. These alternative strategies provide hope for overcoming some of the challenges that have limited the development of new therapies.

The role of end-diastolic myocardial fibre stretch on infarct extension

Myocardial infarct extension, a process involving the enlargement of infarct and border zone, leads to progressive degeneration of left ventricular (LV) function and eventually gives rise to heart failure. Despite carrying a high risk, the causation of infarct extension is still a subject of much speculation. In this study, patient-specific LV models were developed to investigate the correlation between infarct extension and impaired regional mechanics. Subsequently, sensitivity analysis was performed to examine the causal factors responsible for the impaired regional mechanics observed in regions surrounding the infarct and border zone. From our simulations, fibre strain, fibre stress and fibre stress-strain loop (FSSL) were the key biomechanical variables affected in these regions. Among these variables, only FSSL was correlated with infarct extension, as reflected in its work density dissipation (WDD) index value, with high WDD indices recorded at regions with infarct extension. Impaired FSSL is caused by inadequate contraction force generation during the isovolumic contraction and ejection phases. Our further analysis revealed that the inadequacy in contraction force generation is not necessarily due to impaired myocardial intrinsic contractility, but at least in part, due to inadequate muscle fibre stretch at end-diastole, which depresses the ability of myocardium to generate adequate contraction force in the subsequent systole (according to the Frank-Starling law). Moreover, an excessively stiff infarct may cause its neighbouring myocardium to be understretched at end-diastole, subsequently depressing the systolic contractile force of the neighbouring myocardium, which was found to be correlated with infarct extension.

Preventive effect of Agnucastoside C against Isoproterenol-induced myocardial injury

An iridoid glycoside, agnucastoside C (ACC) was isolated from the leaves of Moringa oliefera and its cardio protective potential was investigated in adult rats by examining the effects of this test compound, ACC at 30 mg/kg for 14 days in isoproterenol (100 mg/kg)-induced myocardial injury. Isoproterenol (ISO) administration induced the myocardial injury as evidenced by the altered ECG pattern with ST-segment elevation and an increase in the levels of cardiac injury markers including troponin-I, creatine kinase-MB, alanine transaminase, aspartate transaminase, lactate dehydrogenase; inflammatory markers, interleukine-6 and tumor necrosis factor. In this group, there was also an increase in cardiac lipid peroxidation and a decrease in cellular antioxidants. However, pretreatment with ACC maintained the normal ECG pattern and nearly normal levels of all the cardiac markers in ISO-induced animals. Electron microscopic and histological studies also showed marked reduction in ISO-induced cardiac damages including infarct size by ACC. Analysis by 2-DE revealed the involvement of 19 different cardiac proteins, associated with energy metabolism, oxidative stress and maintenance of cytoskeleton. The expression of those proteins were altered by ISO, but maintained in ACC pretreated rats. Our findings reveal the potential of isolated ACC in the prevention of myocardial damage.

Calcium Signaling and Transcriptional Regulation in Cardiomyocytes

Calcium (Ca 2+ ) is a universal regulator of various cellular functions. In cardiomyocytes, Ca 2+ is the central element of excitation–contraction coupling, but also impacts diverse signaling cascades and influences the regulation of gene expression, referred to as excitation–transcription coupling. Disturbances in cellular Ca 2+ -handling and alterations in Ca 2+ -dependent gene expression patterns are pivotal characteristics of failing cardiomyocytes, with several excitation–transcription coupling pathways shown to be critically involved in structural and functional remodeling processes. Thus, targeting Ca 2+ -dependent transcriptional pathways might offer broad therapeutic potential. In this article, we (1) review cytosolic and nuclear Ca 2+ dynamics in cardiomyocytes with respect to their impact on Ca 2+ -dependent signaling, (2) give an overview on Ca 2+ -dependent transcriptional pathways in cardiomyocytes, and (3) discuss implications of excitation–transcription coupling in the diseased heart.

Ca2+/Calmodulin-Dependent Protein Kinase II and Androgen Signaling Pathways Modulate MEF2 Activity in Testosterone-Induced Cardiac Myocyte Hypertrophy

Testosterone is known to induce cardiac hypertrophy through androgen receptor (AR)-dependent and -independent pathways, but the molecular underpinnings of the androgen action remain poorly understood. Previous work has shown that Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) and myocyte-enhancer factor 2 (MEF2) play key roles in promoting cardiac myocyte growth. In order to gain mechanistic insights into the action of androgens on the heart, we investigated how testosterone affects CaMKII and MEF2 in cardiac myocyte hypertrophy by performing studies on cultured rat cardiac myocytes and hearts obtained from adult male orchiectomized (ORX) rats. In cardiac myocytes, MEF2 activity was monitored using a luciferase reporter plasmid, and the effects of CaMKII and AR signaling pathways on MEF2C were examined by using siRNAs and pharmacological inhibitors targeting these two pathways. In the in vivo studies, ORX rats were randomly assigned to groups that were administered vehicle or testosterone (125 mg⋅kg^-1⋅week^-1) for 5 weeks, and plasma testosterone concentrations were determined using ELISA. Cardiac hypertrophy was evaluated by measuring well-characterized hypertrophy markers. Moreover, western blotting was used to assess CaMKII and phospholamban (PLN) phosphorylation, and MEF2C and AR protein levels in extracts of left-ventricle tissue from control and testosterone-treated ORX rats. Whereas testosterone treatment increased the phosphorylation levels of CaMKII (Thr286) and phospholambam (PLN) (Thr17) in cardiac myocytes in a time- and concentration-dependent manner, testosterone-induced MEF2 activity and cardiac myocyte hypertrophy were prevented upon inhibition of CaMKII, MEF2C, and AR signaling pathways. Notably, in the hypertrophied hearts obtained from testosterone-administered ORX rats, both CaMKII and PLN phosphorylation levels and AR and MEF2 protein levels were increased. Thus, this study presents the first evidence indicating that testosterone activates MEF2 through CaMKII and AR signaling. Our findings suggest that an orchestrated mechanism of action involving signal transduction and transcription pathways underlies testosterone-induced cardiac myocyte hypertrophy.

MicroRNA-200c modulates DUSP-1 expression in diabetes-induced cardiac hypertrophy

Mitogen-activated protein kinases (MAPKs) (ERK1/2, JNK, and p38) are upregulated in diabetic cardiomyopathy (DCM). Dual-specific phosphatase-1 (DUSP-1) has been reported to regulate the activity of MAPKs in cardiac hypertrophy; however, the role of DUSP-1 in regulating MAPKs activity in DCM is not known. MicroRNAs have been reported to regulate the expression of several genes in hypertrophied failing hearts. However, little is known about the microRNAs regulating DUSP-1 expression in diabetes-related cardiac hypertrophy. In the present study, we investigated the role of DUSP-1 and miR-200c in diabetes-induced cardiac hypertrophy. DCM was induced in Wistar rats by low-dose Streptozotocin high-fat diet for 12 weeks. Cardiac expression of ERK, p-38, JNK, DUSP-1, miR-200c, and hypertrophy markers (ANP and β-MHC) was studied in DCM in control rats and in high-glucose (HG)-treated rat neonatal cardiomyocytes. miR-200c inhibition was performed to validate DUSP-1 as target. A significant increase in phosphorylated ERK, p38, and JNK was observed in DCM model and in HG-treated cardiomyocytes (p < 0.05). Expression of DUSP-1 was significantly decreased in diabetes group and in HG-treated cardiomyocytes (p < 0.05). Increased expression of miR-200c was observed in DCM model and in HG-treated cardiomyocytes (p < 0.05). Inhibition of miR-200c induces the expression of the DUSP-1 causing decreased expression of phosphorylated ERK, p38, and JNK and attenuated cardiomyocyte hypertrophy in HG-treated cardiomyocytes. miR-200c plays a role in diabetes-associated cardiac hypertrophy by modulating expression of DUSP-1.

Physiological and pathological cardiac hypertrophy

The heart must continuously pump blood to supply the body with oxygen and nutrients. To maintain the high energy consumption required by this role, the heart is equipped with multiple complex biological systems that allow adaptation to changes of systemic demand. The processes of growth (hypertrophy), angiogenesis, and metabolic plasticity are critically involved in maintenance of cardiac homeostasis. Cardiac hypertrophy is classified as physiological when it is associated with normal cardiac function or as pathological when associated with cardiac dysfunction. Physiological hypertrophy of the heart occurs in response to normal growth of children or during pregnancy, as well as in athletes. In contrast, pathological hypertrophy is induced by factors such as prolonged and abnormal hemodynamic stress, due to hypertension, myocardial infarction etc. Pathological hypertrophy is associated with fibrosis, capillary rarefaction, increased production of pro-inflammatory cytokines, and cellular dysfunction (impairment of signaling, suppression of autophagy, and abnormal cardiomyocyte/non-cardiomyocyte interactions), as well as undesirable epigenetic changes, with these complex responses leading to maladaptive cardiac remodeling and heart failure. This review describes the key molecules and cellular responses involved in physiological/pathological cardiac hypertrophy.

ROS-Induced Nuclear Translocation of Calpain-2 Facilitates Cardiomyocyte Apoptosis in Tail-Suspended Rats

Isoproterenol (ISO) induced nuclear translocation of calpain-2 which further increased susceptibility of cardiomyocyte apoptosis in tail-suspended rats. The underlying mechanisms remain elusive. In the present study, the results showed that ISO (10 nM) significantly elevated NADPH oxidases (NOXs) activity and NOXs-derived ROS productions which induced nuclear translocation of calpain-2 in cardiomyocytes of tail-suspended rats. In contrast, the inhibition of NADPH oxidase or cleavage of ROS not only reduced ROS productions, but also resisted nuclear translocation of calpain-2 and decreased ISO-induced apoptosis of cardiomyocyte in tail-suspended rats. ISO also increased the constitutive binding between calpain-2 and Ca(2+)/calmodulin-dependent protein kinase II δB (CaMK II δB) in nuclei, concomitant with the promotion of CaMK II δB degradation and subsequent down-regulation of Bcl-2 mRNA expression and the ratio of Bcl-2 to Bax protein in tail-suspended rat cardiomyocytes. These effects of ISO on cardiomyocytes were abolished by a calpain inhibitor PD150606. Inhibition of calpain significantly reduced ISO-induced loss of the mitochondrial membrane potential, cytochrome c release into the cytoplasm, as well as the activation of caspase-3 and caspase-9 in mitochondrial apoptotic pathway. In summary, the above results suggest that ISO increased NOXs-derived ROS which activated nuclear translocation of calpain-2, subsequently nuclear calpain-2 degraded CaMK II δB which reduced the ratio of Bcl-2 to Bax, and finally the mitochondria apoptosis pathway was triggered in tail-suspended rat cardiomyocytes. Therefore, calpain-2 may represent a potentially therapeutic target for prevention of oxidative stress-associated cardiomyocyte apoptosis.

Isoform-specific dynamic translocation of PKC by α1-adrenoceptor stimulation in live cells

Protein kinase C (PKC) plays key roles in the regulation of signal transduction and cellular function in various cell types. At least ten PKC isoforms have been identified and intracellular localization and trafficking of these individual isoforms are important for regulation of enzyme activity and substrate specificity. PKC can be activated downstream of Gq-protein coupled receptor (GqPCR) signaling and translocate to various cellular compartments including plasma membrane (PM). Recent reports suggested that different types of GqPCRs would activate different PKC isoforms (classic, novel and atypical PKCs) with different trafficking patterns. However, the knowledge of isoform-specific activation of PKC by each GqPCR is limited. α1-Adrenoceptor (α1-AR) is one of the GqPCRs highly expressed in the cardiovascular system. In this study, we examined the isoform-specific dynamic translocation of PKC in living HEK293T cells by α1-AR stimulation (α1-ARS). Rat PKCα, βI, βII, δ, ε and ζ fused with GFP at C-term were co-transfected with human α1A-AR into HEK293T cells. The isoform-specific dynamic translocation of PKC in living HEK293T cells by α1-ARS using phenylephrine was measured by confocal microscopy. Before stimulation, GFP-PKCs were localized at cytosolic region. α1-ARS strongly and rapidly translocated a classical PKC (cPKC), PKCα, (<30 s) to PM, with PKCα returning diffusively into the cytosol within 5 min. α1-ARS rapidly translocated other cPKCs, PKCβI and PKCβII, to the PM (<30 s), with sustained membrane localization. One novel PKC (nPKC), PKCε, but not another nPKC, PKCδ, was translocated by α1-AR stimulation to the PM (<30 s) and its membrane localization was also sustained. Finally, α1-AR stimulation did not cause a diacylglycerol-insensitive atypical PKC, PKCζ translocation. Our data suggest that PKCα, β and ε activation may underlie physiological and pathophysiological responses of α1-AR signaling for the phosphorylation of membrane-associated substrates including ion-channel and transporter proteins in the cardiovascular system.

Chasing cardiac physiology and pathology down the CaMKII cascade

Calcium dynamics is central in cardiac physiology, as the key event leading to the excitation-contraction coupling (ECC) and relaxation processes. The primary function of Ca(2+) in the heart is the control of mechanical activity developed by the myofibril contractile apparatus. This key role of Ca(2+) signaling explains the subtle and critical control of important events of ECC and relaxation, such as Ca(2+) influx and SR Ca(2+) release and uptake. The multifunctional Ca(2+)-calmodulin-dependent protein kinase II (CaMKII) is a signaling molecule that regulates a diverse array of proteins involved not only in ECC and relaxation but also in cell death, transcriptional activation of hypertrophy, inflammation, and arrhythmias. CaMKII activity is triggered by an increase in intracellular Ca(2+) levels. This activity can be sustained, creating molecular memory after the decline in Ca(2+) concentration, by autophosphorylation of the enzyme, as well as by oxidation, glycosylation, and nitrosylation at different sites of the regulatory domain of the kinase. CaMKII activity is enhanced in several cardiac diseases, altering the signaling pathways by which CaMKII regulates the different fundamental proteins involved in functional and transcriptional cardiac processes. Dysregulation of these pathways constitutes a central mechanism of various cardiac disease phenomena, like apoptosis and necrosis during ischemia/reperfusion injury, digitalis exposure, post-acidosis and heart failure arrhythmias, or cardiac hypertrophy. Here we summarize significant aspects of the molecular physiology of CaMKII and provide a conceptual framework for understanding the role of the CaMKII cascade on Ca(2+) regulation and dysregulation in cardiac health and disease.

CaMKII content affects contractile, but not mitochondrial, characteristics in regenerating skeletal muscle

Background

The multi-meric calcium/calmodulin-dependent protein kinase II (CaMKII) is the main CaMK in skeletal muscle and its expression increases with endurance training. CaMK family members are implicated in contraction-induced regulation of calcium handling, fast myosin type IIA expression and mitochondrial biogenesis. The objective of this study was to investigate the role of an increased CaMKII content for the expression of the contractile and mitochondrial phenotype in vivo. Towards this end we attempted to co-express alpha- and beta-CaMKII isoforms in skeletal muscle and characterised the effect on the contractile and mitochondrial phenotype.

Results

Fast-twitch muscle m. gastrocnemius (GM) and slow-twitch muscle m. soleus (SOL) of the right leg of 3-month old rats were transfected via electro-transfer of injected expression plasmids for native α/β CaMKII. Effects were identified from the comparison to control-transfected muscles of the contralateral leg and non-transfected muscles. α/β CaMKII content in muscle fibres was 4-5-fold increased 7 days after transfection. The transfection rate was more pronounced in SOL than GM muscle (i.e. 12.6 vs. 3.5%). The overexpressed α/β CaMKII was functional as shown through increased threonine 287 phosphorylation of β-CaMKII after isometric exercise and down-regulated transcripts COXI, COXIV, SDHB after high-intensity exercise in situ. α/β CaMKII overexpression under normal cage activity accelerated excitation-contraction coupling and relaxation in SOL muscle in association with increased SERCA2, ANXV and fast myosin type IIA/X content but did not affect mitochondrial protein content. These effects were observed on a background of regenerating muscle fibres.

Conclusion

Elevated CaMKII content promotes a slow-to-fast type fibre shift in regenerating muscle but is not sufficient to stimulate mitochondrial biogenesis in the absence of an endurance stimulus.

Integrated mechanisms of CaMKII-dependent ventricular remodeling

CaMKII has been shown to be activated during different cardiac pathological processes, and CaMKII-dependent mechanisms contribute to pathological cardiac remodeling, cardiac arrhythmias, and contractile dysfunction during heart failure. Activation of CaMKII during cardiac stress results in a broad number of biological effects such as, on the one hand, acute effects due to phosphorylation of distinct cellular proteins as ion channels and calcium handling proteins and, on the other hand, integrative mechanisms by changing gene expression. This review focuses on transcriptional and epigenetic effects of CaMKII activation during chronic cardiac remodeling. Multiple mechanisms have been described how CaMKII mediates changes in cardiac gene expression. CaMKII has been shown to directly phosphorylate components of the cardiac gene regulation machinery. CaMKII phosphorylates several transcription factors such as CREB that induces the activation of specific gene programs. CaMKII activates transcriptional regulators also indirectly by phosphorylating histone deacetylases, especially HDAC4, which in turn inhibits transcription factors that drive cardiac hypertrophy, fibrosis, and dysfunction. Recent studies demonstrate that CaMKII also phosphorylate directly histones, which may contribute to changes in gene expression. These findings of CaMKII-dependent gene regulation during cardiac remodeling processes suggest novel strategies for CaMKII-dependent “transcriptional or epigenetic therapies” to control cardiac gene expression and function. Manipulation of CaMKII-dependent signaling pathways in the settings of pathological cardiac growth, remodeling, and heart failure represents an auspicious therapeutic approach.

CaMKIIdelta subtypes: localization and function

In this review we discuss the localization and function of the known subtypes of calcium/calmodulin dependent protein kinase IIδ (CaMKIIδ) and their role in cardiac physiology and pathophysiology. The CaMKII holoenzyme is comprised of multiple subunits that are encoded by four different genes called CaMKIIα, β, γ, and δ. While these four genes have a high degree of sequence homology, they are expressed in different tissues. CaMKIIα and β are expressed in neuronal tissue while γ and δ are present throughout the body, including in the heart. Both CaMKIIγ and δ are alternatively spliced in the heart to generate multiple subtypes. CaMKIIδ is the predominant cardiac isoform and is alternatively spliced in the heart to generate the CaMKIIδ_B subtype or the slightly less abundant δ_C subtype. The CaMKIIδ_B mRNA sequence contains a 33bp insert not present in δ_C that codes for an 11-amino acid nuclear localization sequence. This review focuses on the localization and function of the CaMKIIδ subtypes δ_B and δ_C and the role of these subtypes in arrhythmias, contractile dysfunction, gene transcription, and the regulation of Ca²⁺ handling.

β-adrenergic receptor responsiveness in aging heart and clinical implications

Elderly healthy individuals have a reduced exercise tolerance and a decreased left ventricle inotropic reserve related to increased vascular afterload, arterial-ventricular load mismatching, physical deconditioning and impaired autonomic regulation (the so called "β-adrenergic desensitization"). Adrenergic responsiveness is altered with aging and the age-related changes are limited to the β-adrenergic receptor density reduction and to the β-adrenoceptor-G-protein(s)-adenylyl cyclase system abnormalities, while the type and level of abnormalities change with species and tissues. Epidemiological studies have shown an high incidence and prevalence of heart failure in the elderly and a great body of evidence correlate the changes of β-adrenergic system with heart failure pathogenesis. In particular it is well known that: (a) levels of cathecolamines are directly correlated with mortality and functional status in heart failure, (b) β1-adrenergic receptor subtype is down-regulated in heart failure, (c) heart failure-dependent cardiac adrenergic responsiveness reduction is related to changes in G proteins activity. In this review we focus on the cardiovascular β-adrenergic changes involvement in the aging process and on similarities and differences between aging heart and heart failure.

The promise of CaMKII inhibition for heart disease: preventing heart failure and arrhythmias

INTRODUCTION

Calcium-calmodulin-dependent protein kinase II (CaMKII) has emerged as a central mediator of cardiac stress responses which may serve several critical roles in the regulation of cardiac rhythm, cardiac contractility and growth. Sustained and excessive activation of CaMKII during cardiac disease has, however, been linked to arrhythmias, and maladaptive cardiac remodeling, eventually leading to heart failure (HF) and sudden cardiac death.

AREAS COVERED

In the current review, the authors describe the unique structural and biochemical properties of CaMKII and focus on its physiological effects in cardiomyocytes. Furthermore, they provide evidence for a role of CaMKII in cardiac pathologies, including arrhythmogenesis, myocardial ischemia and HF development. The authors conclude by discussing the potential for CaMKII as a target for inhibition in heart disease.

EXPERT OPINION

CaMKII provides a promising nodal point for intervention that may allow simultaneous prevention of HF progression and development of arrhythmias. For future studies and drug development there is a strong rationale for the development of more specific CaMKII inhibitors. In addition, an improved understanding of the differential roles of CaMKII subtypes is required.

Visualizing CaMKII and CaM activity: a paradigm of compartmentalized signaling

Calcium (Ca(2+)) has long been recognized as a crucial intracellular messenger attaining stimuli-specific cellular outcomes via localized signaling. Ca(2+)-binding proteins, such as calmodulin (CaM), and its target proteins are key to the segregation and refinement of these Ca(2+)-dependent signaling events. This review not only summarizes the recent technological advances enabling the study of subcellular Ca(2+)-CaM and Ca(2+)-CaM-dependent protein kinase (CaMKII) signaling events but also highlights the outstanding challenges in the field.

Oxidative stress-mediated effects of angiotensin II in the cardiovascular system

Angiotensin II (Ang II), an endogenous peptide hormone, plays critical roles in the pathophysiological modulation of cardiovascular functions. Ang II is the principle effector of the renin-angiotensin system for maintaining homeostasis in the cardiovascular system, as well as a potent stimulator of NAD(P)H oxidase, which is the major source and primary trigger for reactive oxygen species (ROS) generation in various tissues. Recent accumulating evidence has demonstrated the importance of oxidative stress in Ang II-induced heart diseases. Here, we review the recent progress in the study on oxidative stress-mediated effects of Ang II in the cardiovascular system. In particular, the involvement of Ang II-induced ROS generation in arrhythmias, cell death/heart failure, ischemia/reperfusion injury, cardiac hypertrophy and hypertension are discussed. Ca²⁺/calmodulin-dependent protein kinase II is an important molecule linking Ang II, ROS and cardiovascular pathological conditions.

Cell excitability necessary for male mating behavior in Caenorhabditis elegans is coordinated by interactions between big current and ether-a-go-go family K(+) channels

Variations in K(+) channel composition allow for differences in cell excitability and, at an organismal level, provide flexibility to behavioral regulation. When the function of a K(+) channel is disrupted, the remaining K(+) channels might incompletely compensate, manifesting as abnormal organismal behavior. In this study, we explored how different K(+) channels interact to regulate the neuromuscular circuitry used by Caenorhabditis elegans males to protract their copulatory spicules from their tail and insert them into the hermaphrodite's vulva during mating. We determined that the big current K(+) channel (BK)/SLO-1 genetically interacts with ether-a-go-go (EAG)/EGL-2 and EAG-related gene/UNC-103 K(+) channels to control spicule protraction. Through rescue experiments, we show that specific slo-1 isoforms affect spicule protraction. Gene expression studies show that slo-1 and egl-2 expression can be upregulated in a calcium/calmodulin-dependent protein kinase II-dependent manner to compensate for the loss of unc-103 and conversely, unc-103 can partially compensate for the loss of SLO-1 function. In conclusion, an interaction between BK and EAG family K(+) channels produces the muscle excitability levels that regulate the timing of spicule protraction and the success of male mating behavior.

Location matters: clarifying the concept of nuclear and cytosolic CaMKII subtypes

RATIONALE

Differential effects of δ(B) and δ(C) subtypes of Ca²⁺/calmodulin-dependent protein kinase (CaMKII) on cardiomyocyte Ca²⁺ handling and survival have been suggested to result from their respective nuclear versus cytosolic localizations. CaMKIIδ subtype localization and its relationship to enzyme activation and target phosphorylation have not, however, been systematically evaluated.

OBJECTIVE

To determine whether CaMKIIδ subtypes are restricted to a particular subcellular location and assess the relationship of localization to enzyme activation and function.

METHODS AND RESULTS

CaMKIIδ is highly expressed in mouse heart and cardiomyocytes and concentrated in sarcoplasmic reticulum (SR)/membrane and nuclear fractions. CaMKIIδ(B) and δ(C) subtypes differ by a nuclear localization sequence, but both are present in nuclear and SR/membrane fractions. Nonselective subtype distribution is also seen in mice overexpressing CaMKIIδ(B) or δ(C), even in a CaMKIIδ null background. Fluorescently tagged CaMKIIδ(B) expressed in cardiomyocytes concentrates in nuclei whereas δ(C) concentrates in cytosol, but neither localization is exclusive. Mouse hearts exposed to phenylephrine show selective CaMKIIδ activation in the nuclear (versus SR) compartment, whereas caffeine selectively activates CaMKIIδ in SR (versus nuclei), independent of subtype. Compartmentalized activation extends to functional differences in target phosphorylation at CaMKII sites: phenylephrine increases histone deacetylase 5 phosphorylation (Ser498) but not phospholamban (Thr17), whereas the converse holds for caffeine.

CONCLUSIONS

These studies demonstrate that CaMKIIδ(B) and δ(C) are not exclusively restricted to the nucleus and cytosol and that spatial and functional specificity in CaMKIIδ activation is elicited by mobilization of different Ca²⁺ stores rather than by compartmentalized subtype localization.

CaMKIIδB mediates aberrant NCX1 expression and the imbalance of NCX1/SERCA in transverse aortic constriction-induced failing heart

Ca²⁺/calmodulin-dependent protein kinase II δB (CaMKIIδB) is one of the predominant isoforms of CaMKII in the heart. The precise role of CaMKIIδB in the transcriptional cross-talk of Ca²⁺-handling proteins during heart failure remains unclear. In this work, we aim to determine the mechanism of CaMKIIδB in modulating the expression of sarcolemmal Na⁺–Ca²⁺ exchange (NCX1). We also aim to address the potential effects of calmodulin antagonism on the imbalance of NCX1 and sarcoendoplasmic reticulum Ca²⁺ ATPase (SERCA) during heart failure. Eight weeks after transverse aortic constriction (TAC)-induced heart failure in mice, we found that the heart weight/tibia length (HW/TL) ratio and the lung weight/body weight (LW/BW) ratio increased by 59% and 133%, respectively. We further found that the left ventricle-shortening fraction decreased by 40% compared with the sham-operated controls. Immunoblotting revealed that the phosphorylation of CaMKIIδB significantly increased 8 weeks after TAC-induced heart failure. NCX1 protein levels were also elevated, whereas SERCA2 protein levels decreased in the same animal model. Moreover, transfection of active CaMKIIδB significantly increased NCX1 protein levels in adult mouse cardiomyocytes via class IIa histone deacetylase (HDAC)/myocyte enhancer factor-2 (MEF2)-dependent signaling. In addition, pharmacological inhibition of calmodulin/CaMKIIδB activity improved cardiac function in TAC mice, which partially normalized the imbalance between NCX1 and SERCA2. These data identify NCX1 as a cellular target for CaMKIIδB. We also suggest that the CaMKIIδB-induced imbalance between NCX1 and SERCA2 is partially responsible for the disturbance of intracellular Ca²⁺ homeostasis and the pathological process of heart failure.

CaMKII in the cardiovascular system: sensing redox states

The multifunctional Ca(2+)- and calmodulin-dependent protein kinase II (CaMKII) is now recognized to play a central role in pathological events in the cardiovascular system. CaMKII has diverse downstream targets that promote vascular disease, heart failure, and arrhythmias, so improved understanding of CaMKII signaling has the potential to lead to new therapies for cardiovascular disease. CaMKII is a multimeric serine-threonine kinase that is initially activated by binding calcified calmodulin (Ca(2+)/CaM). Under conditions of sustained exposure to elevated Ca(2+)/CaM, CaMKII transitions into a Ca(2+)/CaM-autonomous enzyme by two distinct but parallel processes. Autophosphorylation of threonine-287 in the CaMKII regulatory domain "traps" CaMKII into an open configuration even after Ca(2+)/CaM unbinding. More recently, our group identified a pair of methionines (281/282) in the CaMKII regulatory domain that undergo a partially reversible oxidation which, like autophosphorylation, prevents CaMKII from inactivating after Ca(2+)/CaM unbinding. Here we review roles of CaMKII in cardiovascular disease with an eye to understanding how CaMKII may act as a transduction signal to connect pro-oxidant conditions into specific downstream pathological effects that are relevant to rare and common forms of cardiovascular disease.

Different subcellular populations of L-type Ca2+ channels exhibit unique regulation and functional roles in cardiomyocytes

Influx of Ca(2+) through L-type Ca(2+) channels (LTCCs) contributes to numerous cellular processes in cardiomyocytes including excitation-contraction (EC) coupling, membrane excitability, and transcriptional regulation. Distinct subpopulations of LTCCs have been identified in cardiac myocytes, including those at dyadic junctions and within different plasma membrane microdomains such as lipid rafts and caveolae. These subpopulations of LTCCs exhibit regionally distinct functional properties and regulation, affording precise spatiotemporal modulation of L-type Ca(2+) current (I(Ca,L)). Different subcellular LTCC populations demonstrate variable rates of Ca(2+)-dependent inactivation and sometimes coupled gating of neighboring channels, which can lead to focal, persistent I(Ca,L). In addition, the assembly of spatially defined macromolecular signaling complexes permits compartmentalized regulation of I(Ca,L) by a variety of neurohormonal pathways. For example, β-adrenergic receptor subtypes signal to different LTCC subpopulations, with β(2)-adrenergic activation leading to enhanced I(Ca,L) through caveolar LTCCs and β(1)-adrenergic stimulation modulating LTCCs outside of caveolae. Disruptions in the normal subcellular targeting of LTCCs and associated signaling proteins may contribute to the pathophysiology of a variety of cardiac diseases including heart failure and certain arrhythmias. Further identifying the characteristic functional properties and array of regulatory molecules associated with specific LTCC subpopulations will provide a mechanistic framework to understand how LTCCs contribute to diverse cellular processes in normal and diseased myocardium. This article is part of a Special Issue entitled "Local Signaling in Myocytes".

Chronic CaMKII inhibition blunts the cardiac contractile response to exercise training

Activation of the multifunctional Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) plays a critical role modulating cardiac function in both health and disease. Here, we determined the effect of chronic CaMKII inhibition during an exercise training program in healthy mice. CaMKII was inhibited by KN-93 injections. Mice were randomized to the following groups: sham sedentary, sham exercise, KN-93 sedentary, and KN-93 exercise. Cardiorespiratory function was evaluated by ergospirometry during treadmill running, echocardiography, and cardiomyocyte fractional shortening and calcium handling. The results revealed that KN-93 alone had no effect on exercise capacity or fractional shortening. In sham animals, exercise training increased maximal oxygen uptake by 8% (p < 0.05) compared to a 22% (p < 0.05) increase after exercise in KN-93 treated mice (group difference p < 0.01). In contrast, in vivo fractional shortening evaluated by echocardiography improved after exercise in sham animals only: from 25 to 32% (p < 0.02). In inactive mice, KN-93 reduced rates of diastolic cardiomyocyte re-lengthening (by 25%, p < 0.05) as well as Ca(2+) transient decay (by 16%, p < 0.05), whereas no such effect was observed after exercise training. KN-93 blunted exercise training response on cardiomyocyte fractional shortening (63% sham vs. 18% KN-93; p < 0.01 and p < 0.05, respectively). These effects could not be solely explained by the Ca(2+) transient amplitude, as KN-93 reduced it by 20% (p < 0.05) and response to exercise training was equal (64% sham and 47% KN-93; both p < 0.01). We concluded that chronic CaMKII inhibition increased time to 50% re-lengthening which were recovered by exercise training, but paradoxically led to a greater increase in maximal oxygen uptake compared to sham mice. Thus, the effect of chronic CaMKII inhibition is multifaceted and of a complex nature.

Ca2+-calmodulin-dependent protein kinase II represses cardiac transcription of the L-type calcium channel alpha(1C)-subunit gene (Cacna1c) by DREAM translocation

Recent studies have demonstrated that changes in the activity of calcium-calmodulin-dependent protein kinase II (CaMKII) induce a unique cardiomyocyte phenotype through the regulation of specific genes involved in excitation-contraction (E-C)-coupling. To explain the transcriptional effects of CaMKII we identified a novel CaMKII-dependent pathway for controlling the expression of the pore-forming α-subunit (Cav1.2) of the L-type calcium channel (LTCC) in cardiac myocytes. We show that overexpression of either cytosolic (δC) or nuclear (δB) CaMKII isoforms selectively downregulate the expression of the Cav1.2. Pharmacological inhibition of CaMKII activity induced measurable changes in LTCC current density and subsequent changes in cardiomyocyte calcium signalling in less than 24 h. The effect of CaMKII on the α1C-subunit gene (Cacna1c) promoter was abolished by deletion of the downstream regulatory element (DRE), which binds transcriptional repressor DREAM/calsenilin/KChIP3. Imaging DREAM-GFP (green fluorescent protein)-expressing cardiomyocytes showed that CaMKII potentiates the calcium-induced nuclear translocation of DREAM. Thereby CaMKII increases DREAM binding to the DRE consensus sequence of the endogenous Cacna1c gene. By mathematical modelling we demonstrate that the LTCC downregulation through the Ca2+-CaMKII-DREAM cascade constitutes a physiological feedback mechanism enabling cardiomyocytes to adjust the calcium intrusion through LTCCs to the amount of intracellular calcium detected by CaMKII.

CaMKII in myocardial hypertrophy and heart failure

Many signals have risen and fallen in the tide of investigation into mechanisms of myocardial hypertrophy and heart failure (HF). In our opinion, the multifunctional Ca and calmodulin-dependent protein kinase II (CaMKII) has emerged as a molecule to watch, in part because a solid body of accumulated data essentially satisfy Koch's postulates, showing that the CaMKII pathway is a core mechanism for promoting myocardial hypertrophy and heart failure. Multiple groups have now confirmed the following: (1) that CaMKII activity is increased in hypertrophied and failing myocardium from animal models and patients; (2) CaMKII overexpression causes myocardial hypertrophy and HF and (3) CaMKII inhibition (by drugs, inhibitory peptides and gene deletion) improves myocardial hypertrophy and HF. Patients with myocardial disease die in equal proportion from HF and arrhythmias, and a major therapeutic obstacle is that drugs designed to enhance myocardial contraction promote arrhythmias. In contrast, inhibiting the CaMKII pathway appears to reduce arrhythmias and improve myocardial responses to pathological stimuli. This brief paper will introduce the molecular physiology of CaMKII and discuss the impact of CaMKII on ion channels, Ca handling proteins and transcription in myocardium. This article is part of a special issue entitled "Key Signaling Molecules in Hypertrophy and Heart Failure".

Cardiac hypertrophy and heart failure development through Gq and CaM kinase II signaling

The molecular events associated with the development of pathological hypertrophy have been shown to be stimulated through G-protein–coupled receptors that activate Gq signaling pathways in neonatal cardiomyocytes and in transgenic (TG) and knockout mice. We demonstrated that CaMKII, a multifunctional Ca(2+)-regulated protein kinase, was activated through G-protein–coupled receptor and inositol trisphosphate–mediated Ca(2+) release and suggested that CaMKII was a downstream mediator of Gq-coupled hypertrophic signaling. This was supported by the demonstration of CaMKII activation by pressure overload [(transverse aortic constriction (TAC)] and induction of hypertrophy by TG CaMKII expression. CaMKII also phosphorylates Ca(2+) handling proteins including the ryanodine receptor (RyR2), phosphorylation of which markedly increases sarcoplasmic reticulum Ca(2+) leak. Increased RyR2 phosphorylation is associated with heart failure development in CaMKII TG mice, and mice genetically deleted for CaMKII (KO) have attenuated RyR2 phosphorylation, sarcoplasmic reticulum Ca(2+) leak, and heart failure development after long-term TAC. Genetic ablation of CaMKII also decreases development of heart failure in Gq TG mice and decreases infarct size, while improving functional recovery in mice subject to ischemia/reperfusion and preventing adverse remodeling after coronary artery occlusion. The underlying mechanisms are currently under study.

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.

Garlic Oil Alleviates MAPKs- and IL-6-mediated Diabetes-related Cardiac Hypertrophy in STZ-induced DM Rats

Garlic oil has been reported to protect the cardiovascular system; however, the effects and mechanisms behind the cardioprotection of garlic oil on diabetes-induced cardiaomyopathy are unclear. In this study, we used streptozotocin (STZ)-induced diabetic rats to investigate whether garlic oil could protect the heart from diabetes-induced cardiomyopathy. Wistar STZ-induced diabetic rats received garlic oil (0, 10, 50 or 100 mg kg^_1 body weight) by gastric gavage every 2 days for 16 days. Normal rats without diabetes were used as control. Cardiac contractile dysfunction and cardiac pathologic hypertrophy responses were observed in diabetic rat hearts. Cardiac function was examined using echocardiography. In addition to cardiac hypertrophy-related mitogen-activated protein kinases (MAPK) pathways (e.g., p38, c-Jun N-terminal kinases (JNK) and extracellularly responsive kinase (ERK1/2)), the IL-6/MEK5/ERK5 signaling pathway was greatly activated in the diabetic rat hearts, which contributes to the up-regulation of cardiac pathologic hypertrophy markers including atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP), and leads to cardiac contractile dysfunction. Garlic oil treatment significantly inhibited the up-regulation in MAPK (e.g., p38, JNK and ERK1/2) and IL-6/MEK5/ERK5 signaling pathways in the diabetic rat hearts, reducing the levels of cardiac pathologic hypertrophy markers such as ANP and BNP, and improving the cardiac contractile function. Collectively, data from these studies demonstrate that garlic oil shows the potential cardioprotective effects for protecting heart from diabetic cardiomyopathy.

Molecular distinction between physiological and pathological cardiac hypertrophy: experimental findings and therapeutic strategies

Cardiac hypertrophy can be defined as an increase in heart mass. Pathological cardiac hypertrophy (heart growth that occurs in settings of disease, e.g. hypertension) is a key risk factor for heart failure. Pathological hypertrophy is associated with increased interstitial fibrosis, cell death and cardiac dysfunction. In contrast, physiological cardiac hypertrophy (heart growth that occurs in response to chronic exercise training, i.e. the 'athlete's heart') is reversible and is characterized by normal cardiac morphology (i.e. no fibrosis or apoptosis) and normal or enhanced cardiac function. Given that there are clear functional, structural, metabolic and molecular differences between pathological and physiological hypertrophy, a key question in cardiovascular medicine is whether mechanisms responsible for enhancing function of the athlete's heart can be exploited to benefit patients with pathological hypertrophy and heart failure. This review summarizes key experimental findings that have contributed to our understanding of pathological and physiological heart growth. In particular, we focus on signaling pathways that play a causal role in the development of pathological and physiological hypertrophy. We discuss molecular mechanisms associated with features of cardiac hypertrophy, including protein synthesis, sarcomeric organization, fibrosis, cell death and energy metabolism and provide a summary of profiling studies that have examined genes, microRNAs and proteins that are differentially expressed in models of pathological and physiological hypertrophy. How gender and sex hormones affect cardiac hypertrophy is also discussed. Finally, we explore how knowledge of molecular mechanisms underlying pathological and physiological hypertrophy may influence therapeutic strategies for the treatment of cardiovascular disease and heart failure.

Transcriptional upregulation of calcineurin Abeta by endothelin-1 is partially mediated by calcium/calmodulin-dependent protein kinase IIdelta3 in rat cardiomyocytes

Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) and calcineurin (CaN) are positive regulators of cardiac hypertrophy, but the nature of cross-talk between CaMKII and CaN signaling pathways in hypertrophic cardiomyocytes remains unclear. Here we documented that CaMKIIdelta3 activation enhances transcription of the CaN gene through activation of the CaN-Abeta subunit (CnAbeta) promoter in rat cultured cardiomyocytes. Co-immunoprecipitation assays showed that MEF2 forms a complex with GATA4 following transfection of an active CaMKIIdelta3 (T278D) mutant in neonatal cardiomyocytes. Inversely, transfection of a dominant negative CaMKIIdelta3 mutant failed to promote a MEF2-GATA4 complex. Consistent with these observations, immunocytochemistry indicated nuclear co-localization of MEF2 with GATA4 after hypertrophic agonist stimulation or CaMKIIdelta3 (T278D) transfection. These data demonstrate that CaMKII can enhance CnAbeta promoter activity by enhancing MEF2-GATA4 synergy, suggesting a novel mechanism for CaMKII-mediated hypertrophic signaling, which contributes to induction and development of the hypertrophic response through CaN activation.

Phosphorylation of TRPC6 channels at Thr69 is required for anti-hypertrophic effects of phosphodiesterase 5 inhibition

Activation of Ca(2+) signaling induced by receptor stimulation and mechanical stress plays a critical role in the development of cardiac hypertrophy. A canonical transient receptor potential protein subfamily member, TRPC6, which is activated by diacylglycerol and mechanical stretch, works as an upstream regulator of the Ca(2+) signaling pathway. Although activation of protein kinase G (PKG) inhibits TRPC6 channel activity and cardiac hypertrophy, respectively, it is unclear whether PKG suppresses cardiac hypertrophy through inhibition of TRPC6. Here, we show that inhibition of cGMP-selective PDE5 (phosphodiesterase 5) suppresses endothelin-1-, diacylglycerol analog-, and mechanical stretch-induced hypertrophy through inhibition of Ca(2+) influx in rat neonatal cardiomyocytes. Inhibition of PDE5 suppressed the increase in frequency of Ca(2+) spikes induced by agonists or mechanical stretch. However, PDE5 inhibition did not suppress the hypertrophic responses induced by high KCl or the activation of protein kinase C, suggesting that PDE5 inhibition suppresses Ca(2+) influx itself or molecule(s) upstream of Ca(2+) influx. PKG activated by PDE5 inhibition phosphorylated TRPC6 proteins at Thr(69) and prevented TRPC6-mediated Ca(2+) influx. Substitution of Ala for Thr(69) in TRPC6 abolished the anti-hypertrophic effects of PDE5 inhibition. In addition, chronic PDE5 inhibition by oral sildenafil treatment actually induced TRPC6 phosphorylation in mouse hearts. Knockdown of RGS2 (regulator of G protein signaling 2) and RGS4, both of which are activated by PKG to reduce G alpha(q)-mediated signaling, did not affect the suppression of receptor-activated Ca(2+) influx by PDE5 inhibition. These results suggest that phosphorylation and functional suppression of TRPC6 underlie prevention of pathological hypertrophy by PDE5 inhibition.

Regulation and significance of atrial and brain natriuretic peptides as cardiac hormones

Atrial and brain natriuretic peptides (ANP and BNP, respectively) are cardiac hormones. During cardiac development, their expression is a maker of cardiomyocyte differentiation and is under tight spatiotemporal regulation. After birth, however, their ventricular expression is only up-regulated in response to various cardiovascular diseases. As a result, analysis of ANP and BNP gene expression has led to discoveries of transcriptional regulators and signaling pathways involved in both cardiac differentiation and cardiac disease. Studies using genetically engineered mice have shed light on the molecular mechanisms regulating ANP and BNP gene expression, as well as the physiological and pathophysiological relevance of the cardiac natriuretic peptide system. In this review we will summarize what is currently known about their regulation and the significance of ANP and BNP as hormones derived from the heart.

Cardioprotection by CaMKII-deltaB is mediated by phosphorylation of heat shock factor 1 and subsequent expression of inducible heat shock protein 70

RATIONALE

Ca2+/calmodulin-dependent protein kinase (CaMK)II is a multifunctional kinase involved in vital cellular processes such as Ca(2+) handling and cell fate regulation. In mammalian heart, 2 primary CaMKII isoforms, deltaB and deltaC, localize in nuclear and cytosolic compartments, respectively. Although previous studies have established an essential role of CaMKII-deltaC in cardiomyocyte apoptosis, the functional role of the more abundant isoform, CaMKII-deltaB, remains elusive.

OBJECTIVE

Here, we determined the potential role of CaMKII-deltaB in regulating cardiomyocyte viability and explored the underlying mechanism.

METHODS AND RESULTS

In cultured neonatal rat cardiomyocytes, the expression of CaMKII-deltaB and CaMKII-deltaC was inversely regulated in response to H2O2-induced oxidative stress with a profound reduction of the former and an increase of the later. Similarly, in vivo ischemia/reperfusion (IR) led to an opposite regulation of these CaMKII isoforms in a rat myocardial IR model. Notably, overexpression of CaMKII-deltaB protected cardiomyocytes against oxidative stress-, hypoxia-, and angiotensin II-induced apoptosis, whereas overexpression of its cytosolic counterpart promoted apoptosis. Using cDNA microarray, real-time PCR and Western blotting, we demonstrated that overexpression of CaMKII-deltaB but not CaMKII-deltaC elevated expression of heat shock protein (HSP)70 family members, including inducible (i)HSP70 and its homolog (Hst70). Moreover, overexpression of CaMKII-deltaB led to phosphorylation and activation of heat shock factor (HSF)1, the primary transcription factor responsible for HSP70 gene regulation. Importantly, gene silencing of iHSP70, but not Hst70, abolished CaMKII-deltaB-mediated protective effect, indicating that only iHSP70 was required for CaMKII-deltaB elicited antiapoptotic signaling.

CONCLUSIONS

We conclude that cardiac CaMKII-deltaB and CaMKII-deltaC were inversely regulated in response to oxidative stress and IR injury, and that in contrast to CaMKII-deltaC, CaMKII-deltaB serves as a potent suppressor of cardiomyocyte apoptosis triggered by multiple death-inducing stimuli via phosphorylation of HSF1 and subsequent induction of iHSP70, marking both CaMKII-delta isoforms as promising therapeutic targets for the treatment of ischemic heart disease.

CaMKII negatively regulates calcineurin-NFAT signaling in cardiac myocytes

RATIONALE

Pathological cardiac myocyte hypertrophy is thought to be induced by the persistent increases in intracellular Ca(2+) needed to maintain cardiac function when systolic wall stress is increased. Hypertrophic Ca(2+) binds to calmodulin (CaM) and activates the phosphatase calcineurin (Cn) and CaM kinase (CaMK)II. Cn dephosphorylates cytoplasmic NFAT (nuclear factor of activated T cells), inducing its translocation to the nucleus where it activates antiapoptotic and hypertrophic target genes. Cytoplasmic CaMKII regulates Ca(2+) handling proteins but whether or not it is directly involved in hypertrophic and survival signaling is not known.

OBJECTIVE

This study explored the hypothesis that cytoplasmic CaMKII reduces NFAT nuclear translocation by inhibiting the phosphatase activity of Cn.

METHODS AND RESULTS

Green fluorescent protein-tagged NFATc3 was used to determine the cellular location of NFAT in cultured neonatal rat ventricular myocytes (NRVMs) and adult feline ventricular myocytes. Constitutively active (CaMKII-CA) or dominant negative (CaMKII-DN) mutants of cytoplasmic targeted CaMKII(deltac) were used to activate and inhibit cytoplasmic CaMKII activity. In NRVM CaMKII-DN (48.5+/-3%, P<0.01 versus control) increased, whereas CaMKII-CA decreased (5.9+/-1%, P<0.01 versus control) NFAT nuclear translocation (Control: 12.3+/-1%). Cn inhibitors were used to show that these effects were caused by modulation of Cn activity. Increasing Ca(2+) increased Cn-dependent NFAT translocation (to 71.7+/-7%, P<0.01) and CaMKII-CA reduced this effect (to 17.6+/-4%). CaMKII-CA increased TUNEL and caspase-3 activity (P<0.05). CaMKII directly phosphorylated Cn at Ser197 in CaMKII-CA infected NRVMs and in hypertrophied feline hearts.

CONCLUSION

These data show that activation of cytoplasmic CaMKII inhibits NFAT nuclear translocation by phosphorylation and subsequent inhibition of Cn.

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.

Oestrogen confers cardioprotection by suppressing Ca2+/calmodulin-dependent protein kinase II

BACKGROUND AND PURPOSE

Oestrogen confers cardioprotection by down-regulating the beta(1)-adrenoceptor and suppressing the expression and activity of protein kinase A. We hypothesized that oestrogen may also protect the heart by suppressing Ca(2+)/calmodulin-dependent protein kinase II (CaMKII), another signalling messenger activated by the beta(1)-adrenoceptor, that enhances apoptosis.

EXPERIMENTAL APPROACH

We first determined the expression of CaMKII in the heart from sham and ovariectomized rats with and without oestrogen replacement. We then determined the effects of CaMKII inhibition (KN93, 2.5 micromolxL(-1)) in the presence or absence of 10(-7) molxL(-1) isoprenaline, a non-selective beta-adrenoceptor agonist. We also determined the percentage apoptosis in myocytes from rats in each group with or without beta-adrenoceptor stimulation.

KEY RESULTS

Both CaMKIIdelta and phosphorylated CaMKII were up-regulated in the hearts from ovariectomized rats, and they were restored to normal by oestrogen replacement. The infarct size and lactate dehydrogenase release were significantly greater after ovariectomy. Similarly, cardiac contractility, the amplitude of the electrically induced intracellular Ca(2+) transient and the number of apoptotic cells were also greater in ovariectomized rats upon ischaemia/reperfusion in the presence or absence of isoprenaline. Most importantly, the responses to ischaemic insult in ovariectomized rats were reversed not only by oestrogen replacement, but by blockade of CaMKII with KN93.

CONCLUSIONS AND IMPLICATIONS

Oestrogen confers cardioprotection at least partly by suppressing CaMKIIdelta. This effect of oestrogen on CaMKII is independent of the beta-adrenoceptor and occurs in addition to down-regulation of the receptor.

Requirement for Ca2+/calmodulin-dependent kinase II in the transition from pressure overload-induced cardiac hypertrophy to heart failure in mice

Ca2+/calmodulin-dependent kinase II (CaMKII) has been implicated in cardiac hypertrophy and heart failure. We generated mice in which the predominant cardiac isoform, CaMKIIdelta, was genetically deleted (KO mice), and found that these mice showed no gross baseline changes in ventricular structure or function. In WT and KO mice, transverse aortic constriction (TAC) induced comparable increases in relative heart weight, cell size, HDAC5 phosphorylation, and hypertrophic gene expression. Strikingly, while KO mice showed preserved hypertrophy after 6-week TAC, CaMKIIdelta deficiency significantly ameliorated phenotypic changes associated with the transition to heart failure, such as chamber dilation, ventricular dysfunction, lung edema, cardiac fibrosis, and apoptosis. The ratio of IP3R2 to ryanodine receptor 2 (RyR2) and the fraction of RyR2 phosphorylated at the CaMKII site increased significantly during development of heart failure in WT mice, but not KO mice, and this was associated with enhanced Ca2+ spark frequency only in WT mice. We suggest that CaMKIIdelta contributes to cardiac decompensation by enhancing RyR2-mediated sarcoplasmic reticulum Ca2+ leak and that attenuating CaMKIIdelta activation can limit the progression to heart failure.

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.

Lipopolysaccharide induces cellular hypertrophy through calcineurin/NFAT-3 signaling pathway in H9c2 myocardiac cells

Evidences suggest that lipopolysaccharide (LPS) participates in the inflammatory response in the cardiovascular system; however, it is unknown if LPS is sufficient to cause the cardiac hypertrophy. In the present study, we treated H9c2 myocardiac cells with LPS to explore whether LPS causes cardiac hypertrophy, and to identify the precise molecular and cellular mechanisms behind hypertrophic responses. Here we show that LPS challenge induces pathological hypertrophic responses such as the increase in cell size, the reorganization of actin filaments, and the upregulation of hypertrophy markers including atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP) in H9c2 cells. LPS treatment significantly promotes the activation of GATA-4 and the nuclear translocation of NFAT-3, which act as transcription factors mediating the development of cardiac hypertrophy. After administration of inhibitors including U0126 (ERK1/2 inhibitor), SB203580 (p38 MAPK inhibitor), SP600125 (JNK1/2 inhibitor), CsA (calcineurin inhibitor), FK506 (calcineurin inhibitor), and QNZ (NFkappaB inhibitor), LPS-induced hypertrophic characteristic features, such as increases in cell size, actin fibers, and levels of ANP and BNP, and the nuclear localization of NFAT-3 are markedly inhibited only by calcineurin inhibitors, CsA and FK506. Collectively, these results suggest that LPS leads to myocardiac hypertrophy through calcineurin/NFAT-3 signaling pathway in H9c2 cells. Our findings further provide a link between the LPS-induced inflammatory response and the calcineurin/NFAT-3 signaling pathway that mediates the development of cardiac hypertrophy.