New molecular mechanisms for cardiovascular disease:transcriptional pathways and novel therapeutic targets in heart failure

Meta-Analysis of Mechano-Sensitive Ion Channels in Human Hearts: Chamber- and Disease-Preferential mRNA Expression

The cardiac cell mechanical environment changes on a beat-by-beat basis as well as in the course of various cardiac diseases. Cells sense and respond to mechanical cues via specialized mechano-sensors initiating adaptive signaling cascades. With the aim of revealing new candidates underlying mechano-transduction relevant to cardiac diseases, we investigated mechano-sensitive ion channels (MSC) in human hearts for their chamber- and disease-preferential mRNA expression. Based on a meta-analysis of RNA sequencing studies, we compared the mRNA expression levels of MSC in human atrial and ventricular tissue samples from transplant donor hearts (no cardiac disease), and from patients in sinus rhythm (underlying diseases: heart failure, coronary artery disease, heart valve disease) or with atrial fibrillation. Our results suggest that a number of MSC genes are expressed chamber preferentially, e.g., CHRNE in the atria (compared to the ventricles), TRPV4 in the right atrium (compared to the left atrium), CACNA1B and KCNMB1 in the left atrium (compared to the right atrium), as well as KCNK2 and KCNJ2 in ventricles (compared to the atria). Furthermore, 15 MSC genes are differentially expressed in cardiac disease, out of which SCN9A (lower expressed in heart failure compared to donor tissue) and KCNQ5 (lower expressed in atrial fibrillation compared to sinus rhythm) show a more than twofold difference, indicative of possible functional relevance. Thus, we provide an overview of cardiac MSC mRNA expression in the four cardiac chambers from patients with different cardiac diseases. We suggest that the observed differences in MSC mRNA expression may identify candidates involved in altered mechano-transduction in the respective diseases.

Detrimental Role of PDZ-RhoGEF in Pathological Cardiac Hypertrophy

BACKGROUND

Postsynaptic density 95/disk-large/ZO-1 Rho guanine nucleotide exchange factor (PDZ-RhoGEF, PRG) functions as a RhoGEF for activated Gα13 and transmits activation signals to downstream signaling pathways in various pathological processes. Although the prohypertrophic effect of activated Gα13 (guanine nucleotide binding protein alpha 13; a heterotrimeric G protein) is well-established, the role of PDZ-RhoGEF in pathological cardiac hypertrophy is still obscure.

METHODS

Genetically engineered mice and neonatal rat ventricular myocytes were generated to investigate the function of PRG in pathological myocardial hypertrophy. The prohypertrophic stimuli-induced alternations in the morphology and intracellular signaling were measured in myocardium and neonatal rat ventricular myocytes. Furthermore, multiple molecular methodologies were used to identify the precise molecular mechanisms underlying PDZ-RhoGEF function.

RESULTS

Increased PDZ-RhoGEF expression was documented in both hypertrophied hearts and neonatal rat ventricular myocytes. Upon prohypertrophic stimuli, the PDZ-RhoGEF-deficient hearts displayed alleviated cardiomyocyte enlargement and attenuated collagen deposition with improved cardiac function, whereas the adverse hypertrophic responses in hearts and neonatal rat ventricular myocytes were markedly exaggerated by PDZ-RhoGEF overexpression. Mechanistically, RhoA (ras homolog family member A)-dependent signaling pathways may function as the downstream effectors of PDZ-RhoGEF in hypertrophic remodeling, as confirmed by rescue experiments using a RhoA inhibitor and dominant-negative RhoA. Furthermore, PDZ-RhoGEF is associated with activated Gα13 and contributes to Gα13-mediated activation of RhoA-dependent signaling.

CONCLUSIONS

Our data provide the first evidence that PDZ-RhoGEF promotes pathological cardiac hypertrophy by linking activated Gα13 to RhoA-dependent signaling pathways. Therefore, PDZ-RhoGEF has the potential to be a diagnostic marker or therapeutic target for pathological cardiac hypertrophy.

Single-cell transcriptomics reveal extracellular vesicles secretion with a cardiomyocyte proteostasis signature during pathological remodeling

Aberrant Wnt activation has been reported in failing cardiomyocytes. Here we present single cell transcriptome profiling of hearts with inducible cardiomyocyte-specific Wnt activation (β-catΔex3) as well as with compensatory and failing hypertrophic remodeling. We show that functional enrichment analysis points to an involvement of extracellular vesicles (EVs) related processes in hearts of β-catΔex3 mice. A proteomic analysis of in vivo cardiac derived EVs from β-catΔex3 hearts has identified differentially enriched proteins involving 20 S proteasome constitutes, protein quality control (PQC), chaperones and associated cardiac proteins including α-Crystallin B (CRYAB) and sarcomeric components. The hypertrophic model confirms that cardiomyocytes reacted with an acute early transcriptional upregulation of exosome biogenesis processes and chaperones transcripts including CRYAB, which is ameliorated in advanced remodeling. Finally, human induced pluripotent stem cells (iPSC)-derived cardiomyocytes subjected to pharmacological Wnt activation recapitulated the increased expression of exosomal markers, CRYAB accumulation and increased PQC signaling. These findings reveal that secretion of EVs with a proteostasis signature contributes to early patho-physiological adaptation of cardiomyocytes, which may serve as a read-out of disease progression and can be used for monitoring cellular remodeling in vivo with a possible diagnostic and prognostic role in the future.

DDX3X alleviates doxorubicin-induced cardiotoxicity by regulating Wnt/β-catenin signaling pathway in an in vitro model

The life-threatening adverse effects of doxorubicin (Dox) caused by its cardiotoxic properties limit its clinical application. DDX3X has been shown to participate in a variety of physiological processes, and it acts as a regulator of Wnt/β-catenin signaling. However, the role of DDX3X in Dox-induced cardiotoxicity (DIC) remains unclear. In this study, we found that DDX3X expression was significantly decreased in H9c2 cardiomyocytes treated with Dox. Ddx3x knockdown and RK-33 (DDX3X ATPase activity inhibitor) pretreatment exacerbated cardiomyocyte apoptosis and mitochondrial dysfunction induced by Dox treatment. In contrast, Ddx3x overexpression ameliorated the DIC response. Moreover, Wnt/β-catenin signaling in cardiomyocytes treated with Dox was suppressed, but this suppression was reversed by Ddx3x overexpression. Overall, this study demonstrated that DDX3X plays a protective role in DIC by activating Wnt/β-catenin signaling.

MRTF: Basic Biology and Role in Kidney Disease

A lesser known but crucially important downstream effect of Rho family GTPases is the regulation of gene expression. This major role is mediated via the cytoskeleton, the organization of which dictates the nucleocytoplasmic shuttling of a set of transcription factors. Central among these is myocardin-related transcription factor (MRTF), which upon actin polymerization translocates to the nucleus and binds to its cognate partner, serum response factor (SRF). The MRTF/SRF complex then drives a large cohort of genes involved in cytoskeleton remodeling, contractility, extracellular matrix organization and many other processes. Accordingly, MRTF, activated by a variety of mechanical and chemical stimuli, affects a plethora of functions with physiological and pathological relevance. These include cell motility, development, metabolism and thus metastasis formation, inflammatory responses and—predominantly-organ fibrosis. The aim of this review is twofold: to provide an up-to-date summary about the basic biology and regulation of this versatile transcriptional coactivator; and to highlight its principal involvement in the pathobiology of kidney disease. Acting through both direct transcriptional and epigenetic mechanisms, MRTF plays a key (yet not fully appreciated) role in the induction of a profibrotic epithelial phenotype (PEP) as well as in fibroblast-myofibroblast transition, prime pathomechanisms in chronic kidney disease and renal fibrosis.

Wnt Signaling Plays a Key Role in the Regulation of the Immune Response and Cardiac Damage during Trypanosoma cruzi Infection

Chagas cardiomyopathy is the consequence of a compromised electrical and mechanical cardiac function, with parasite persistence, unbalanced inflammation, and pathological tissue remodelling, being intricately related to myocardial aggression and impaired function. Recent studies have shown that Wnt signaling pathways play a critical role in the pathogenesis of cardiac and vascular diseases. In addition, we have reported that Trypanosoma cruzi infection activates Wnt signaling to promote intracellular replication of the parasites in macrophages, with the treatment of mice with IWP-L6 (an inhibitor of the O-acyl-transferase, PORCN, responsible for the post-translational modifications necessary for Wnt protein secretion) being able to diminish parasitemia and tissue parasitism. Here, we show that inhibition of Wnt signaling during the acute phase of T. cruzi infection controls the parasite replication, inhibits the development of parasite-prone and fibrosis-prone Th2-type immune response, and prevents the development of cardiac abnormalities characteristics of chronic Chagas disease. Our results suggest that the Wnt signaling pathway might be a potential target to prevent the development of T. cruzi-induced cardiomyopathy.

WNT Signaling in Disease

Developmental signaling pathways control a vast array of biological processes during embryogenesis and in adult life. The WNT pathway was discovered simultaneously in cancer and development. Recent advances have expanded the role of WNT to a wide range of pathologies in humans. Here, we discuss the WNT pathway and its role in human disease and some of the advances in WNT-related treatments.

Review of Transient Receptor Potential Canonical (TRPC5) Channel Modulators and Diseases

Transient receptor potential canonical (TRPC) channels are highly homologous, nonselective cation channels that form many homo- and heterotetrameric channels. These channels are highly abundant in the brain and kidney and have been implicated in numerous diseases, such as depression, addiction, and chronic kidney disease, among others. Historically, there have been very few selective modulators of the TRPC family in order to fully understand their role in disease despite their physiological significance. However, that has changed recently and there has been a significant increase in interest in this family of channels which has led to the emergence of selective tool compounds, and even preclinical drug candidates, over the past few years. This review will cover these new advancements in the discovery of TRPC modulators and the emergence of newly reported structural information which will undoubtedly lead to even greater advancements.

TRP channels in cardiac and intestinal fibrosis

It is now widely accepted that advanced fibrosis underlies many chronic inflammatory disorders and is the main cause of morbidity and mortality of the modern world. The pathogenic mechanism of advanced fibrosis involves diverse and intricate interplays between numerous extracellular and intracellular signaling molecules, among which the non-trivial roles of a stress-responsive Ca²⁺/Na⁺-permeable cation channel superfamily, the transient receptor potential (TRP) protein, are receiving growing attention. Available evidence suggests that several TRP channels such as TRPC3, TRPC6, TRPV1, TRPV3, TRPV4, TRPA1, TRPM6 and TRPM7 may play central roles in the progression and/or prevention of fibroproliferative disorders in vital visceral organs such as lung, heart, liver, kidney, and bowel as well as brain, blood vessels and skin, and may contribute to both acute and chronic inflammatory processes involved therein. This short paper overviews the current knowledge accumulated in this rapidly growing field, with particular focus on cardiac and intestinal fibrosis, which are tightly associated with the pathogenesis of atrial fibrillation and inflammatory bowel diseases such as Crohn's disease.

HCN4 pacemaker channels attenuate the parasympathetic response and stabilize the spontaneous firing of the sinoatrial node

Key points

The contribution of HCN4 pacemaker channels in the autonomic regulation of the sino‐atrial node (SAN) has been a matter of debate.

The transgenic overexpression of HCN4 did not induce tachycardia, but reduced heart rate variability, while the conditional knockdown of HCN4 gave rise to sinus arrhythmia.

The response of the SAN to β‐adrenergic stimulation was not affected by overexpression or knockdown of HCN4 channels.

When HCN4 channels were knocked down, the parasympathetic response examined by cervical vagus nerve stimulation (CVNS) was enhanced; the CVNS induced complete sinus pause. The overexpression of HCN4 attenuated bradycardia induced by CVNS only during β‐adrenergic stimulation.

We concluded that HCN4 pacemaker channels stabilize the spontaneous firing by attenuating the parasympathetic response of the SAN.

Abstract

The heart rate is dynamically controlled by the sympathetic and parasympathetic nervous systems that regulate the sinoatrial node (SAN). HCN4 pacemaker channels are the well‐known causative molecule of congenital sick sinus syndrome. Although HCN4 channels are activated by cAMP, the sympathetic response of the SAN was preserved in patients carrying loss‐of‐function mutations of the HCN4 gene. In order to clarify the contribution of HCN4 channels in the autonomic regulation of the SAN, we developed novel gain‐of‐function mutant mice in which the expression level of HCN4 channels could be reversibly changed from zero to ∼3 times that in wild‐type mice, using tetracycline transactivator and the tetracycline responsive element. We recorded telemetric ECGs in freely moving conscious mice and analysed the heart rate variability. We also evaluated the response of the SAN to cervical vagus nerve stimulation (CVNS). The conditional overexpression of HCN4 did not induce tachycardia, but reduced heart rate variability. The HCN4 overexpression also attenuated bradycardia induced by the CVNS only during the β‐adrenergic stimulation. In contrast, the knockdown of HCN4 gave rise to sinus arrhythmia, and enhanced the parasympathetic response; complete sinus pause was induced by the CVNS. In vitro, we compared the effects of acetylcholine on the spontaneous action potentials of single pacemaker cells, and found that similar phenotypic changes were induced by genetic manipulation of HCN4 expression both in the presence and absence of β‐adrenergic stimulation. Our study suggests that HCN4 channels attenuate the vagal response of the SAN, and thereby stabilize the spontaneous firing of the SAN.

The contribution of HCN4 pacemaker channels in the autonomic regulation of the sino‐atrial node (SAN) has been a matter of debate.

The transgenic overexpression of HCN4 did not induce tachycardia, but reduced heart rate variability, while the conditional knockdown of HCN4 gave rise to sinus arrhythmia.

The response of the SAN to β‐adrenergic stimulation was not affected by overexpression or knockdown of HCN4 channels.

When HCN4 channels were knocked down, the parasympathetic response examined by cervical vagus nerve stimulation (CVNS) was enhanced; the CVNS induced complete sinus pause. The overexpression of HCN4 attenuated bradycardia induced by CVNS only during β‐adrenergic stimulation.

We concluded that HCN4 pacemaker channels stabilize the spontaneous firing by attenuating the parasympathetic response of the SAN.

WNT Signaling in Cardiac and Vascular Disease

WNT signaling is an elaborate and complex collection of signal transduction pathways mediated by multiple signaling molecules. WNT signaling is critically important for developmental processes, including cell proliferation, differentiation and tissue patterning. Little WNT signaling activity is present in the cardiovascular system of healthy adults, but reactivation of the pathway is observed in many pathologies of heart and blood vessels. The high prevalence of these pathologies and their significant contribution to human disease burden has raised interest in WNT signaling as a potential target for therapeutic intervention. In this review, we first will focus on the constituents of the pathway and their regulation and the different signaling routes. Subsequently, the role of WNT signaling in cardiovascular development is addressed, followed by a detailed discussion of its involvement in vascular and cardiac disease. After highlighting the crosstalk between WNT, transforming growth factor-β and angiotensin II signaling, and the emerging role of WNT signaling in the regulation of stem cells, we provide an overview of drugs targeting the pathway at different levels. From the combined studies we conclude that, despite the sometimes conflicting experimental data, a general picture is emerging that excessive stimulation of WNT signaling adversely affects cardiovascular pathology. The rapidly increasing collection of drugs interfering at different levels of WNT signaling will allow the evaluation of therapeutic interventions in the pathway in relevant animal models of cardiovascular diseases and eventually in patients in the near future, translating the outcomes of the many preclinical studies into a clinically relevant context.

Altered Mitochondrial Metabolism and Mechanosensation in the Failing Heart: Focus on Intracellular Calcium Signaling

The heart consists of millions of cells, namely cardiomyocytes, which are highly organized in terms of structure and function, at both macroscale and microscale levels. Such meticulous organization is imperative for assuring the physiological pump-function of the heart. One of the key players for the electrical and mechanical synchronization and contraction is the calcium ion via the well-known calcium-induced calcium release process. In cardiovascular diseases, the structural organization is lost, resulting in morphological, electrical, and metabolic remodeling owing the imbalance of the calcium handling and promoting heart failure and arrhythmias. Recently, attention has been focused on the role of mitochondria, which seem to jeopardize these events by misbalancing the calcium processes. In this review, we highlight our recent findings, especially the role of mitochondria (dys)function in failing cardiomyocytes with respect to the calcium machinery.

Mitochondrial Mechanosensor Microdomains in Cardiovascular Disorders

The cardiomyocytes populating the 'working myocardium' are highly organized and such organization ranges from macroscale (e.g. the geometrical rod shape) to microscale (dyad/t-tubules) domains. This meticulous level of organization is imperative for assuring the normal and physiological pump-function of the heart. In the pathological cardiac tissue, the domains-related architecture is partially lost, resulting in morphological, electrical and metabolic remodeling and promoting cardiovascular diseases including heart failure and arrhythmias. Indeed, arrhythmogenesis during heart failure is a major clinical problem. Arrhythmias have been extensively studied from an electrical etiology, but only recently, physiologists and scientists have focused their attention on cellular and subcellular mechanosensors. We and others have investigated whether the nanoscale mechanosensitive properties of cardiomyocytes from failing hearts have a bearing upon the initiation of abnormal electrical activity. This chapter highlights the recent findings in the field, especially the role of mitochondria function and alignment in failing cardiomyocytes interrogated via nanomechanical stimuli.

MicroRNA-101b attenuates cardiomyocyte hypertrophy by inhibiting protein kinase C epsilon signaling

Previously, a surgical regression model identified microRNA-101b (miR-101b) as a potential inhibitor of cardiac hypertrophy. Here, we investigated the antihypertrophic mechanism of miR-101b using neonatal rat ventricular myocytes. miR-101b markedly suppressed agonist-induced cardiac hypertrophy as shown by cell size and fetal gene expression. By systems biology approaches, we identified protein kinase C epsilon (PKCε) as the major target of miR-101b. Our results from qRT-PCR, western blot, and luciferase reporter assays confirm that PKCε is a direct target of miR-101b. In addition, we found that effectors downstream of PKCε (p-AKT, p-ERK1/2, p-NFAT, and p-GSK3β) are also affected by miR-101b. Our study reveals a novel inhibitory mechanism for miR-101b as a negative regulator of cardiac hypertrophy.

ZIP4 silencing improves bone loss in pancreatic cancer

Metabolic bone disorders are associated with several types of human cancers. Pancreatic cancer patients usually suffer from severe nutrition deficiency, muscle wasting, and loss of bone mass. We have previously found that silencing of a zinc transporter ZIP4 prolongs the survival and reduces the severity of the cachexia in vivo. However, the role of ZIP4 in the pancreatic cancer related bone loss remains unknown. In this study we investigated the effect of ZIP4 knockdown on the bone structure, composition and mechanical properties of femurs in an orthotopic xenograft mouse model. Our data showed that silencing of ZIP4 resulted in increased bone tissue mineral density, decreased bone crystallinity and restoration of bone strength through the RANK/RANKL pathway. The results further support the impact of ZIP4 on the progression of pancreatic cancer, and suggest its potential significance as a therapeutic target for treating patients with such devastating disease and cancer related disorders.

Fractal Dimension in Quantifying Experimental-Pulmonary-Hypertension-Induced Cardiac Dysfunction in Rats

BACKGROUND

Right-sided heart failure has high morbidity and mortality, and may be caused by pulmonary arterial hypertension. Fractal dimension is a differentiated and innovative method used in histological evaluations that allows the characterization of irregular and complex structures and the quantification of structural tissue changes.

OBJECTIVE

To assess the use of fractal dimension in cardiomyocytes of rats with monocrotaline-induced pulmonary arterial hypertension, in addition to providing histological and functional analysis.

METHODS

Male Wistar rats were divided into 2 groups: control (C; n = 8) and monocrotaline-induced pulmonary arterial hypertension (M; n = 8). Five weeks after pulmonary arterial hypertension induction with monocrotaline, echocardiography was performed and the animals were euthanized. The heart was dissected, the ventricles weighed to assess anatomical parameters, and histological slides were prepared and stained with hematoxylin/eosin for fractal dimension analysis, performed using box-counting method. Data normality was tested (Shapiro-Wilk test), and the groups were compared with non-paired Student t test or Mann Whitney test (p < 0.05).

RESULTS

Higher fractal dimension values were observed in group M as compared to group C (1.39 ± 0.05 vs. 1.37 ± 0.04; p < 0.05). Echocardiography showed lower pulmonary artery flow velocity, pulmonary acceleration time and ejection time values in group M, suggesting function worsening in those animals.

CONCLUSION

The changes observed confirm pulmonary-arterial-hypertension-induced cardiac dysfunction, and point to fractal dimension as an effective method to evaluate cardiac morphological changes induced by ventricular dysfunction.

Wnt Signaling in Cardiac Disease

Wnt signaling encompasses multiple and complex signaling cascades and is involved in many developmental processes such as tissue patterning, cell fate specification, and control of cell division. Consequently, accurate regulation of signaling activities is essential for proper embryonic development. Wnt signaling is mostly silent in the healthy adult organs but a reactivation of Wnt signaling is generally observed under pathological conditions. This has generated increasing interest in this pathway from a therapeutic point of view. In this review article, the involvement of Wnt signaling in cardiovascular development will be outlined, followed by its implication in myocardial infarct healing, cardiac hypertrophy, heart failure, arrhythmias, and atherosclerosis. The initial experiments not always offer consensus on the effects of activation or inactivation of the pathway, which may be attributed to (i) the type of cardiac disease, (ii) timing of the intervention, and (iii) type of cells that are targeted. Therefore, more research is needed to determine the exact implication of Wnt signaling in the conditions mentioned above to exploit it as a powerful therapeutic target.

Hypoxic induction of T-type Ca(2+) channels in rat cardiac myocytes: role of HIF-1α and RhoA/ROCK signalling

T-type Ca(2+) channels are expressed in the ventricular myocytes of the fetal and perinatal heart, but are normally downregulated as development progresses. Interestingly, however, these channels are re-expressed in adult cardiomyocytes under pathological conditions. We investigated low voltage-activated T-type Ca(2+) channel regulation in hypoxia in rat cardiomyocytes. Molecular studies revealed that hypoxia induces the upregulation of Cav 3.2 mRNA, whereas Cav 3.1 mRNA is not significantly altered. The effect of hypoxia on Cav 3.2 mRNA was time- and dose-dependent, and required hypoxia inducible factor-1α (HIF-1α) stabilization. Patch-clamp recordings confirmed that T-type Ca(2+) channel currents were upregulated in hypoxic conditions, and the addition of 50 μm NiCl2 (a T-type channel blocker) demonstrated that the Cav 3.2 channel is responsible for this upregulation. This increase in current density was not accompanied by significant changes in the Cav 3.2 channel electrophysiological properties. The small monomeric G-protein RhoA and its effector Rho-associated kinase I (ROCKI), which are known to play important roles in cardiovascular physiology, were also upregulated in neonatal rat ventricular myocytes subjected to hypoxia. Pharmacological experiments indicated that both proteins were involved in the observed upregulation of the Cav 3.2 channel and the stabilization of HIF-1α that occurred in response to hypoxia. These results suggest a possible role for Cav 3.2 channels in the increased probability of developing arrhythmias observed in ischaemic situations, and in the pathogenesis of diseases associated with hypoxic Ca(2+) overload.

Resveratrol and derivatives for the treatment of atrial fibrillation

Resveratrol is a bioactive polyphenol, found in grapes, red wine, and peanuts, and has recently garnered much media and scientific attention for its diverse beneficial health effects as a nutritional supplement or nutraceutical. Of particular interest are the well-documented cardioprotective effects of resveratrol that are mediated by diverse mechanisms, including its antioxidant and vascular effects. However, it is now becoming clear that resveratrol may also exhibit direct effects on cardiac function and rhythm through modulation of signaling pathways that regulate cardiac remodeling and ion channel activity that controls cardiac excitability. Resveratrol may therefore possess antiarrhythmic properties that contribute to the cardiovascular benefits of resveratrol. Atrial fibrillation (AF) is the most common cardiac arrhythmia, although current therapies are suboptimal. Our laboratory has been studying resveratrol's effects on cardiac ion channels and remodeling pathways, and we initiated a drug development program aimed at generating novel resveratrol derivatives with improved efficacy against AF when compared to currently available therapeutics. This review therefore focuses on the effects of resveratrol and new derivatives on a variety of cardiac ion channels and molecular pathways that contribute to the development and maintenance of atrial fibrillation.

Cardiac CaM Kinase II genes δ and γ contribute to adverse remodeling but redundantly inhibit calcineurin-induced myocardial hypertrophy

BACKGROUND

Ca(2+)-dependent signaling through CaM Kinase II (CaMKII) and calcineurin was suggested to contribute to adverse cardiac remodeling. However, the relative importance of CaMKII versus calcineurin for adverse cardiac remodeling remained unclear.

METHODS AND RESULTS

We generated double-knockout mice (DKO) lacking the 2 cardiac CaMKII genes δ and γ specifically in cardiomyocytes. We show that both CaMKII isoforms contribute redundantly to phosphorylation not only of phospholamban, ryanodine receptor 2, and histone deacetylase 4, but also calcineurin. Under baseline conditions, DKO mice are viable and display neither abnormal Ca(2+) handling nor functional and structural changes. On pathological pressure overload and β-adrenergic stimulation, DKO mice are protected against cardiac dysfunction and interstitial fibrosis. But surprisingly and paradoxically, DKO mice develop cardiac hypertrophy driven by excessive activation of endogenous calcineurin, which is associated with a lack of phosphorylation at the auto-inhibitory calcineurin A site Ser411. Likewise, calcineurin inhibition prevents cardiac hypertrophy in DKO. On exercise performance, DKO mice show an exaggeration of cardiac hypertrophy with increased expression of the calcineurin target gene RCAN1-4 but no signs of adverse cardiac remodeling.

CONCLUSIONS

We established a mouse model in which CaMKII's activity is specifically and completely abolished. By the use of this model we show that CaMKII induces maladaptive cardiac remodeling while it inhibits calcineurin-dependent hypertrophy. These data suggest inhibition of CaMKII but not calcineurin as a promising approach to attenuate the progression of heart failure.

Matrix as an interstitial transport system

The extracellular matrix (ECM) is best known for its function as a structural scaffold for the tissue and more recently as a microenvironment to sequester growth factors and cytokines allowing for rapid and localized changes in their activity in the absence of new protein synthesis. In this review, we explore this and additional new aspects of ECM function in mediating cell-to-cell communications. Fibrillar and nonfibrillar components of ECM can limit and facilitate the transport of molecules through the extracellular space while also regulating interstitial hydrostatic pressure. In turn, transmembrane communications via molecules, such as ECM metalloproteinase inducer, thrombospondins, and integrins, can further mediate cell response to extracellular cues and affect ECM composition and tissue remodeling. Other means of cell-to-cell communication include extracellular microRNA transport and its contribution to gene expression in target cells and the nanotube formation between distant cells, which has recently emerged as a novel conduit for intercellular organelle sharing thereby influencing cell survival and function. The information summarized and discussed here are not limited to the cardiovascular ECM but encompass ECM in general with specific references to the cardiovascular system.

Mice with cardiac-restricted overexpression of Myozap are sensitized to biomechanical stress and develop a protein-aggregate-associated cardiomyopathy

The intercalated disc (ID) is a major component of the cell-cell contact structures of cardiomyocytes and has been recognized as a hot spot for cardiomyopathy. We have previously identified Myozap as a novel cardiac-enriched ID protein, which interacts with several other ID proteins and is involved in RhoA/SRF signaling in vitro. To now study its potential role in vivo we generated a mouse model with cardiac overexpression of Myozap. Transgenic (Tg) mice developed cardiomyopathy with hypertrophy and LV dilation. Consistently, these mice displayed upregulation of the hypertrophy-associated and SRF-dependent gene expression. Pressure overload (transverse aortic constriction, TAC) caused exaggerated cardiac hypertrophy, further loss of contractility and LV dilation. Similarly, a physiological stimulus (voluntary running) also led to significant LV dysfunction. On the ultrastructural level, Myozap-Tg mouse hearts exhibited massive protein aggregates composed of Myozap, desmoplakin and other ID proteins. This aggregate-associated pathology closely resembled the alterations observed in desmin-related cardiomyopathy. Interestingly, desmin was not detectable in the aggregates, yet was largely displaced from the ID. Molecular analyses revealed induction of autophagy and dysregulation of the unfolded protein response (UPR), associated with apoptosis. Taken together, cardiac overexpression of Myozap leads to cardiomyopathy, mediated, at least in part by induction of Rho-dependent SRF signaling in vivo. Surprisingly, this phenotype was also accompanied by protein aggregates in cardiomyocytes, UPR alteration, accelerated autophagy and apoptosis. Thus, this mouse model may also offer additional insight into the pathogenesis of protein-aggregate-associated cardiomyopathies and represents a new candidate gene itself.

Dysbindin is a potent inducer of RhoA-SRF-mediated cardiomyocyte hypertrophy

Dysbindin activates RhoA–SRF and MEK1–ERK1 signaling pathways in cardiomyocytes to promote cardiac hypertrophy.

Dysbindin is an established schizophrenia susceptibility gene thoroughly studied in the context of the brain. We have previously shown through a yeast two-hybrid screen that it is also a cardiac binding partner of the intercalated disc protein Myozap. Because Dysbindin is highly expressed in the heart, we aimed here at deciphering its cardiac function. Using a serum response factor (SRF) response element reporter-driven luciferase assay, we identified a robust activation of SRF signaling by Dysbindin overexpression that was associated with significant up-regulation of SRF gene targets, such as Acta1 and Actc1. Concurrently, we identified RhoA as a novel binding partner of Dysbindin. Further phenotypic and mechanistic characterization revealed that Dysbindin induced cardiac hypertrophy via RhoA–SRF and MEK1–ERK1 signaling pathways. In conclusion, we show a novel cardiac role of Dysbindin in the activation of RhoA–SRF and MEK1–ERK1 signaling pathways and in the induction of cardiac hypertrophy. Future in vivo studies should examine the significance of Dysbindin in cardiomyopathy.

Regulation of the cell fate by DNA damage and hypoxia

In order to provide the means for the design of novel rational anti-cancer drug therapies research efforts are concentrated on unravelling the molecular circuits which induce programmed cell death and block proliferation of cancer cells. Modern therapeutic strategies are based on the understanding of the complexity of physiological functions such as differentiation, development, immune responses, cell-cycle arrest, DNA damage repair, apoptosis, autophagy, energy metabolism, and senescence. It has become evident that this knowledge will provide the means to target the components of the pathways involved in these processes in a specific and selective manner thus paving the way for the development of effective and personalised anti-cancer therapies. Transcription is a crucial cellular process that regulates a multitude of physiological functions, which are essential in disease progression and cellular response to therapy. Transcription factors such as the p53 tumor suppressor and the hypoxia-inducible factor-α (HIF-α) are key players in carcinogenesis and cellular response to cancer therapies. Both of these transcription factors regulate gene expression of genes involved in cell death and proliferation, in some cases cooperating towards producing the same outcome and in some others mediating opposing effects. It is thus apparent that fine tuning of the activity of these transcription factors is essential to determine the cellular response to therapeutic regimens, in other words whether tumor cells will commit to apoptosis or evade engagement with the anti-proliferative effects of drugs leading to drug resistance. Our observations support the notion that the functional crosstalk between HIF-1α and p53 pathways and thus the fine tuning of their transcriptional activity is mediated by cofactors shared between the two transcription factors such as components of the p300 co-activator multiprotein complex. In particular, there is evidence to suggest that differential composition of the co-modulatory protein complexes associated with p53 and HIF-1α under diverse types of stress conditions differentially regulate the expression of distinct subsets of p53 and HIF-1α target genes involved in processes such as cell cycle arrest, apoptosis, chronic inflammation, and cellular energy metabolism thereby determining the cellular fate under particular types of micro-environmental stress.

Mechanobiology in cardiac physiology and diseases

Mechanosensitivity is essential for heart function just as for all other cells and organs in the body, and it is involved in both normal physiology and diseases processes of the cardiovascular system. In this review, we have outlined the relationship between mechanosensitivity and heart physiology, including the Frank-Starling law of the heart and mechanoelectric feedback. We then focused on molecules involved in mechanotransduction, particularly mechanosensitive ion channels. We have also discussed the involvement of mechanosensitivity in heart diseases, such as arrhythmias, hypertrophy and ischaemic heart disease. Finally, mechanobiology in cardiogenesis is described with regard to regenerative medicine.

Effects of exercise on monocrotaline-induced changes in right heart function and pulmonary artery remodeling in rats

Pulmonary arterial hypertension (PAH) induced by monocrotaline (MCT) is an experimental protocol of right heart failure. We analyzed the role of exercise training on the right ventricle structure and function, pulmonary artery remodeling, and GSK-3β expression. Rats were divided among the following groups: sedentary control (SC), sedentary monocrotaline (SM), trained control (TC), and trained monocrotaline (TM). Rats underwent exercise training for a period of 5 weeks, with 3 weeks post-MCT injection. Rats in the SM and TM groups presented with an increase in right ventricle hypertrophy indexes and lung congestion. The right ventricular end diastolic pressure (RVEDP), right ventricular systolic pressure (RVSP), and its minimum and maximal pressure derivates were increased in the SM and TM groups. The right ventricle interstitial volume pulmonary artery thickness and p-GSK-3β/GSK-3β were increased in the MCT groups as compared with the control groups. The TM group had a reduction in interstitial volume, p-GSK-3β/GSK-3β ratio, pulmonary artery thickness, RVEDP, and an increase in intramyocardial vessels volume as compared with the SM group. The overall results have shown that the exercise protocol used promoted positive changes in right ventricle and pulmonary artery remodeling. These observations also suggest that structural remodeling may be influenced by signaling proteins, such as GSK-3β.

Targeting the Wnt/frizzled signaling pathway after myocardial infarction: a new tool in the therapeutic toolbox?

Wnt/frizzled signaling in the adult heart is quiescent under normal conditions; however it is reactivated after myocardial infarction (MI). Any intervention at the various levels of this pathway can modulate its signaling. Several studies have targeted Wnt/frizzled signaling after MI with the majority of them indicating that the inhibition of the pathway is beneficial since it improves infarct healing and prevents heart failure. This suggests that blocking the Wnt/frizzled signaling pathway could be a potential novel therapeutic target to prevent the adverse cardiac remodeling after MI.

Molecular pathogenesis of myocardial remodeling and new potential therapeutic targets in chronic heart failure

It is well known that the natural history of chronic heart failure (CHF),regardless of age and aetiology,is characterized by progressive cardiac dysfunction refractory to conventional cardiokinetic, diuretic and peripheral vasodilator therapy. Several previous studies, both in animals and humans, showed that the key pathogenetic element of CHF negative clinical evolution is constituted by myocardial remodeling. This is a complex pathologic process of ultrastructural rearrangement of the heart induced by various neuro-humoral factors released by cardiac fibrocells in response to biomechanical stress connected to chronic haemodynamic overload. Typical features of myocardial remodeling are represented by cardiomyocytes hypertrophy and apoptosis, extracellular matrix alterations, mesenchymal fibrotic and phlogistic processes and by cardiac gene expression modifications with fetal genetic program reactivation. In the last years, increasing knowledge of subtle molecular and cellular mechanisms involved in myocardial remodeling has led to the discovery of some new potential therapeutic targets capable of inducing its regression. In this paper our attention is focused on the possible use of antiapoptotic and antifibrotic agents, and on the fascinating perspectives offered by the development of myocardial gene therapy and, in particular, by myocardial regenerative therapy.

Interventions in Wnt signaling as a novel therapeutic approach to improve myocardial infarct healing

Following myocardial infarction, wound healing takes place in the infarct area where the non-viable cardiac tissue is replaced by a scar. Inadequate wound healing or insufficient maintenance of the extracellular matrix in the scar can lead to excessive dilatation of the ventricles, one of the hallmarks of congestive heart failure. Therefore, it is important to better understand the wound-healing process in the heart and to develop new therapeutic agents that target the infarct area in order to maintain an adequate cardiac function. One of these potential novel therapeutic targets is Wnt signaling. Wnt signaling plays an important role in embryonic myocardial development but in the adult heart the pathway is thought to be silent. However, there is increasing evidence that components of the Wnt pathway are re-expressed during cardiac repair, implying a regulatory role. Recently, several studies have been published where the effect of interventions in Wnt signaling on infarct healing has been studied. In this review, we will summarize the results of these studies and discuss the effects of these interventions on the different cell types that are involved in the wound healing process.

In search of novel targets for heart disease: myocardin and myocardin-related transcriptional cofactors

Growing evidence suggests that gene-regulatory networks, which are responsible for directing cardiovascular development, are altered under stress conditions in the adult heart. The cardiac gene regulatory network is controlled by cardioenriched transcription factors and multiple-cell-signaling inputs. Transcriptional coactivators also participate in gene-regulatory circuits as the primary targets of both physiological and pathological signals. Here, we focus on the recently discovered myocardin-(MYOCD) related family of transcriptional cofactors (MRTF-A and MRTF-B) which associate with the serum response transcription factor and activate the expression of a variety of target genes involved in cardiac growth and adaptation to stress via overlapping but distinct mechanisms. We discuss the involvement of MYOCD, MRTF-A, and MRTF-B in the development of cardiac dysfunction and to what extent modulation of the expression of these factors in vivo can correlate with cardiac disease outcomes. A close examination of the findings identifies the MYOCD-related transcriptional cofactors as putative therapeutic targets to improve cardiac function in heart failure conditions through distinct context-dependent mechanisms. Nevertheless, we are in support of further research to better understand the precise role of individual MYOCD-related factors in cardiac function and disease, before any therapeutic intervention is to be entertained in preclinical trials.

Angiotensin II signalling and calcineurin in cardiac fibroblasts: differential effects of calcineurin inhibitors FK506 and cyclosporine A

INTRODUCTION

Cardiac remodelling is controlled by complex systems, including activation of the renin-angiotensin system (RAS) and signalling through MAP kinases and Ca2+-activated calcineurin. Whether Ang II, which increases [Ca2+]i and stimulates MAP kinases, mediates myocardial effects through calcineurin-dependent pathways remain unclear. We investigated effects of two calcineurin inhibitors, cyclosporine A (CsA) and tacrolimus (FK506) (10-10-10-6 mol/L, 20 mins) on activation of MAP kinases and on growth, pro-fibrotic and pro-inflammatory responses in Ang II-stimulated rat cardiac fibroblasts.

METHODS AND RESULTS

Ang II increased phosphorylation of ERK1/2 and p38MAPK (1.5-1.8-fold, p<0.05) without effect on JNK. FK506, but not CsA, attenuated Ang II-stimulated MAP kinase activation. Molecular indices of cell growth (proliferating cell nuclear antigen (PCNA)), fibrosis (fibronectin, pro-collagen) and inflammation (iNOS), were upregulated by Ang II (12 hrs). FK506 and CsA inhibited PCNA effects. Ang II-induced pro-fibrotic and pro-inflammatory responses were inhibited by CsA. Ang II receptors, AT1R and AT2R, were not influenced by calcineurin inhibitors. Our data indicate differential calcineurin inhibitor sensitivity of MAP kinases and cellular responses in Ang II-stimulated fibroblasts. p38MAP kinase and ERK1/2 are regulated in a FK506-sensitive manner, whereas fibrosis and inflammation are CsA-sensitive. Cell proliferation is inhibited by both FKC506 and CsA. These are post-receptor phenomena, since AT1R and AT2R status was unaltered by treatment.

CONCLUSIONS

Our findings identify an important role for calcineurin in MAP kinase/growth/pro-fibrotic/pro-inflammatory signalling by Ang II in cardiac fibroblasts. Although both FK506 and CsA inhibit calcineurin, they exert differential effects on molecular and cellular responses. Such differences may contribute to variable clinical responses of these agents.

Function and regulation of endothelin type A receptor-operated transient receptor potential canonical channels

The purpose of this study is to identify transient receptor potential canonical (TRPC) channels responsible for receptor-operated Ca(2+) entry (ROCE) triggered by activation of endothelin type A receptor (ET(A)R) and to clarify the importance of calmodulin (CaM) / inositol 1,4,5-trisphosphate (IP(3)) receptor binding (CIRB) domain at the C terminus of TRPC channels in ET(A)R-activated channel regulation. In HEK293 cells coexpressing ET(A)R and one of seven TRPC isoforms, ET(A)R stimulation induced ROCE through TRPC3, TRPC5, TRPC6, and TRPC7. The TRPC3- and TRPC6-mediated ROCE was inhibited by selective inhibitors of G(q) protein, phospholipase C (PLC), and CaM. The CIRB domain deletion mutants of TRPC3 and TRPC6 failed to induce ET(A)R-mediated ROCE. Either deletion of the CIRB domain or pharmacological inhibition of CaM did not inhibit the targeting of these channels to the plasma membrane. These results suggest that 1) TRPC3, TRPC5, TRPC6, and TRPC7 can function as ET(A)R-operated Ca(2+) channels; 2) G(q) protein, PLC, and CaM are involved in TRPC3- and TRPC6-mediated ROCE; 3) ET(A)R-mediated activation of TRPC3 and TRPC6 requires the CIRB domain; and 4) abolition of ET(A)R-induced ROCE by CIRB domain deletion and CaM inhibition is due to loss of CaM binding to the channels but not loss of cell surface TRPC3 and TRPC6.