Modulation of Oxytocin Receptors in Right Ventricular Hypertrophy

L’hypertension pulmonaire (HP) est une maladie dont l’étiologie est inconnue et qui entraîne ultimement une défaillance du ventricule droit (VD) et le décès. L’HP peut être induite chez le rat par la la monocrotaline (MCT), un alcaloïde pyrrolizidique extrait de la plante Crotalaria Spectabilis, causant des lésions à l’endothélium des artères pulmonaires, menant à un épaississement de ces dernières et à une augmentation de la résistance vasculaire. Ceci à pour conséquence de causer une hypertrophie du VD, de l’inflammation, une dysfonction endothéliale NO-dépendante des artères coronariennes et une augmentation des peptides natriurétiques circulants. Objectif: Nous avons testé l’hypothèse selon laquelle l’étiopathologie de l’HP impliquerait le récepteur à ocytocine (OTR) dû à son implication fonctionnelle avec les cytokines inflammatoires et la libération du peptide natriurétique atrial (ANP) et du NO. Méthodes: Des rats mâles Sprague-Dawley pesant 220-250g reçurent une seule injection sous-cutanée de MCT (60 mg/kg). 6 à 7 semaines (46±1 jours) suivant l’injection, les rats furent sacrifiés et l’expression génique et protéique fut déterminée par PCR en temps réel et par western blot, respectivement, dans le VD et le ventricule gauche (VG) Résultats: Les rats traités au MCT démontrèrent une augmentation significative du VD. Une hypertrophie du VD était évidente puisque le ratio du VD sur le VG ainsi que le poids du septum étaient près de 77% plus élevés chez les rats traités au MCT que chez les rats contrôles. Le traitement au MCT augmenta l’expression génique d’ANP (3.7-fois dans le VG et 8-fois dans le VD) ainisi que le NP du cerveau (2.7-fois dans le VG et 10-fois dans le VD). Les transcrits de trois récepteurs de NP augmentèrent significativement (0.3-2 fois) seulement dans le VD. L’expression protéique de la NO synthase (iNOS) fut également augmentée de façon sélective dans le VD. Par contre, les transcripts de NOS endothéliale et de NOS neuronale étaient plus élevés (0.5-2 fold) dans le VG. L’ARNm et l’expression protéique d’OTR furent diminués de 50% dans le VD, tandis qu’une augmentation de l’expression des cytokines IL-1β and IL-6 fut observée. L’ARNm de Nab1, un marqueur d’hypertrophie pathologique, fut augmentée de deux-fois dans le VD. Conclusion: L’augmentation d’expression génique de NP dans le VD des rats traités au MCT est associée à une augmentation des transcripts du récepteur NP, suggérant une action locale de NP dans le VD durant l’HP. L’expression d’OTR est atténuée dans le VD, possiblement par des cytokines inflammatoires puisque le promoteur du gène de l’OTR contient de multiples éléments de réponse aux interleukines. Diminuer l’expression d’OTR dans le VD durant l’hypertension pulmonaire pourrait influencer de manière positive la fonction cardiaque car l’OTR régule la contractilité et le rythme cardiaque. Mots clés: hypertension pulmonaire, hypertrophie du ventricule droit monocrotaline, récepteur à ocytocine, inflammation, peptides natriurétiques.

Pro-fibrotic role of ERK3-MK5 during pressure-overload induced cardiac hypertrophy

Il y a 4 isoforme de p38 : α, β, δ, and γ. MK5, à l'origine identifié comme étant un régulateur de PRAK (Regulated/Activated Protein Kinase), est maintenant connu pour être activée par la protéine kinase p38 (qui est un mitogène activé par la protéine kinase, MAPK). Cette dernière est impliquée dans les mécanismes de fibrose et d'apoptose pendant l'hypertrophie cardiaque. De plus, MK5 est également activée par les MAPKs atypiques; ERK3 et ERK4. Bien qu’elles soient fortement exprimées dans le coeur, le rôle physiologique de MK5 et ERK3 demeure inconnu. Par conséquent, nous avons étudié l'effet de la constriction aortique transversale (TAC) – induisant un surcharge chronique de pression chez les souris hétèrozygotes knockout pour MK5 (MK5+/-) ou ERK3 (ERK3+/-) et pour leurs types sauvages (MK5+/+ et ERK3+/+). Deux sem post-TAC; le ratio de poids du coeur/poids corporel a été augmenté chez les 2 souris MK5+/- et MK5+/+. L'échocardiographie de la trans-thoracique démontre que la surcharge de pression a altéré la fonction diastolique du ventricule gauche chez MK5+/+, mais pas chez la souris MK5+/-. De plus, nous avons observé moins de dépôt de collagène, évalué par une coloration au trichrome de Masson, 2 et 3 sem post-TAC chez les souris MK5+/-. Parallèlement, le niveau de l’ARNm de collagène type1 alpha-1 a été significativement diminué dans les coeurs des souris MK5+/-, 2 et 3 sem post-TAC. De même, ERK3, mais pas ERK5 ni p38α, co-IP avec MK5 dans les 2 modèles des coeurs TAC; aigus ou chroniques. En revanche, l’ajout exogénique de GST-MK5 a abaissé ERK4 et p38α, mais pas ERK3 dans les lysâtes de coeur de souris. Par contre, GST-ERK3 et GST-p38α ne démontrent aucune co-IP avec MK5. Ces données suggèrent que dans le coeur seul ERK3, et non ERK4 ou p38α, est capable d’interagir avec, et réguler MK5. A niveau physiologique MK5 interagit entièrement avec ERK3 et par conséquent MK5 n’est pas disponible pour lier les protéines exogéniques. Les souris hétérozygotes pour ERK3 (ERK3+/-) ont également démontré une réduction ou une absence de collagène et une faible expression d’ARNm du collagène type1 alpha1, 3 sem post-TAC. Ces résultats démontrent un important rôle pro-fibrotique de la signalisation MK5-ERK3 pendant une surcharge chronique de pression.Nous avons également démontré 5 variant d'épissage de (MK5.1-5), y compris la forme originale (MK5.1). MK5.2 et MK5.5 subissent une délétion de 6 paires de base dans l’exon 12 : MK5.3 manque l'exon 12 : MK5.4 et MK5.5 manquent les exons 2-6. L'expression des ARNm des différents variant d'épissage a été vérifiée par PCR en temps réel (qPCR). Bien que l’expression est ubiquitaire, l'abondance relative de chaque variant était tissu-spécifique (coeur, rein, pancréas, muscle squelettique, poumon, foie, et cerveau). En plus, l'abondance relative des variant d’épissage varie pendant la surcharge de pression et le développement postnatal du coeur. En outre, l'immunofluorescence a indiqué que MK5.1-5.3 se localise au noyau alors que MK5.4-5.5 est situé au niveau cytoplasmic dans les cellules HEK 293 non stimulées. Suite à une stimulation avec l'anisomycin, un activateur de p38 MAPK, MK5.1-5.3 se translocalise du noyau au cytoplasme alors qu’une petite fraction de MK5.4-5.5 translocalise vers le noyau. Ces variant d'épissage peuvent diversifier la signalisation de MK5-ERK3 dans coeur, mais leur rôle exact oblige des recherches supplémentaires. Excepté l’isoforme δ, toutes les isoformes de p38 sont exprimées dans le coeur et la forme α est considérée comme étant l'isoforme dominante. L’analyse par qPCR et immunobuvardage de type western ont démontré que p38α et p38γ sont les deux isoformes prédominantes alors que p38β et p38δ sont exprimées aux mêmes niveaux dans le coeur de rat adulte. L'immunofluorescence a démontré que p38α et p38γ se trouvent dans le cytoplasme et le noyau. Cependant, suite à la surcharge par TAC, p38γ s'est accumulé dans noyau tandis que la distribution de p38α est demeurée inchangée. Ainsi, l'abondance de p38γ et sa translocalisation nucléaire suite à la surcharge de pression indique un rôle potentiel dans l'expression génique pendant le remodelage cardiaque. En conclusion, nous avons mis en évidence pour la première fois un rôle pro-fibrotique pour la signalisation MK5-ERK3 pendant une surcharge chronique de pression. D'ailleurs, les niveaux comparables d'expression de p38γ avec p38α, et la localisation différentielle de p38γ pendant la surcharge aiguë ou chronique de pression suggèrent différents rôles possibles pour ces isoformes pendant le remodelage hypertrophique cardiaque.

Characterisation and regulation of E2F-6 and E2F-6b in the rat heart: a potential target for myocardial regeneration?

The E2F transcription factors are instrumental in regulating cell cycle progression and growth, including that in cardiomyocytes, which exit the cell cycle shortly after birth. E2F-6 has been demonstrated to act as a transcriptional repressor; however, its potential role in normal cardiomyocyte proliferation and hypertrophy has not previously been investigated. Here we report the isolation and characterisation of E2F-6 and E2F-6b in rat cardiomyocytes and consider its potential as a target for myocardial regeneration following injury. At the mRNA level, both rat E2F-6 and the alternatively spliced variant, E2F-6b, were expressed in E18 myocytes and levels were maintained throughout development into adulthood. Interestingly, E2F-6 protein expression was down-regulated during myocyte development suggesting that it is regulated post-transcriptionally in these cells. During myocyte hypertrophy, the mRNA expressions of E2F-6 and E2F-6b were not regulated whereas E2F-6 protein was up-regulated significantly. Indeed, E2F-6 protein expression levels closely parallel the developmental withdrawal of myocytes from the cell cycle and the subsequent reactivation of their cell cycle machinery during hypertrophic growth. Furthermore, depletion of E2F-6, using anti-sense technology, results in death of cultured neonatal myocytes. Taken together, abrogation of E2F-6 expression in neonatal cardiomyocytes leads to a significant decrease in their viability, consistent with the notion that E2F-6 might be required for maintaining normal myocyte growth.

Inhibition of E2F abrogates the development of cardiac myocyte hypertrophy

Growth of the post- natal mammalian heart occurs primarily by cardiac myocyte hypertrophy. Previously, we and others have shown that a partial re- activation of the cell cycle machinery occurs in myocytes undergoing hypertrophy such that cells progress through the G(1)/ S transition. In this study, we have examined the regulation of the E2F family of transcription factors that are crucial for the G(1)/ S phase transition during normal cardiac development and the development of myocyte hypertrophy in the rat. Thus, mRNA and protein levels of E2F- 1, 3, and 4 and DP- 1 and DP- 2 were down- regulated during development to undetectable levels in adult myocytes. Interestingly, E2F- 5 protein levels were substantially up- regulated during development. In contrast, an induction of E2F- 1, 3, and 4 and the DP- 1 protein was observed during the development of myocyte hypertrophy in neonatal myocytes treated with serum or phenylephrine, whereas the protein levels of E2F- 5 were decreased with serum stimulation. E2F activity, as measured by a cyclin E promoter luciferase assay and E2F- DNA binding activity, increased significantly during the development of hypertrophy with serum and phenylephrine compared with non- stimulated cells. Inhibiting E2F activity with a specific peptide that blocks E2F- DP heterodimerization prevented the induction of hypertrophic markers ( atrial natriuretic factor and brain natriuretic peptide) in response to serum and phenylephrine, reduced the increase in myocyte size, and inhibited protein synthesis in stimulated cells. Thus, we have shown that the inhibition of E2F function prevents the development of hypertrophy. Targeting E2F function might be a useful approach for treating diseases that cause pathophysiological hypertrophic growth.

Downregulation of cyclin-dependent kinase inhibitors p21 and p27 in pressure-overload hypertrophy

We postulated that the cyclin-dependent kinase inhibitors p21 and p27 could regulate the alterations in growth potential of cardiomyocytes during left ventricular hypertrophy (LVH). LVH was induced in adult rat hearts by aortic constriction (AC) and was monitored at days 0, 1, 3, 7, 14, 21, and 42 postoperation. Relative to sham-operated controls (SH), left ventricle (LV) weight-to-body weight ratio in AC increased progressively with time without significant differences in body weight or right ventricle weight-to-body weight ratio. Atrial natriuretic factor mRNA increased significantly in AC to 287% at day 42 compared with SH (P < 0.05), whereas p21 and p27 mRNA expression in AC rats decreased significantly by 58% (P < 0.03) and 40% (P < 0.05) at day 7, respectively. p21 and p27 protein expression decreased significantly from days 3 to 21 in AC versus SH, concomitant with LV adaptive growth. Immunocytochemistry showed p21 and p27 expression in cardiomyocyte nuclei. Thus downregulation of p21 and p27 may modulate the adaptive growth of cardiomyocytes during pressure overload-induced LVH.

Glycogen synthase kinase 3 (GSK3) in the heart: a point of integration in hypertrophic signalling and a therapeutic target? A critical analysis

Glycogen synthase kinase 3 (GSK3, of which there are two isoforms, GSK3alpha and GSK3beta) was originally characterized in the context of regulation of glycogen metabolism, though it is now known to regulate many other cellular processes. Phosphorylation of GSK3alpha(Ser21) and GSK3beta(Ser9) inhibits their activity. In the heart, emphasis has been placed particularly on GSK3beta, rather than GSK3alpha. Importantly, catalytically-active GSK3 generally restrains gene expression and, in the heart, catalytically-active GSK3 has been implicated in anti-hypertrophic signalling. Inhibition of GSK3 results in changes in the activities of transcription and translation factors in the heart and promotes hypertrophic responses, and it is generally assumed that signal transduction from hypertrophic stimuli to GSK3 passes primarily through protein kinase B/Akt (PKB/Akt). However, recent data suggest that the situation is far more complex. We review evidence pertaining to the role of GSK3 in the myocardium and discuss effects of genetic manipulation of GSK3 activity in vivo. We also discuss the signalling pathways potentially regulating GSK3 activity and propose that, depending on the stimulus, phosphorylation of GSK3 is independent of PKB/Akt. Potential GSK3 substrates studied in relation to myocardial hypertrophy include nuclear factors of activated T cells, beta-catenin, GATA4, myocardin, CREB, and eukaryotic initiation factor 2Bvarepsilon. These and other transcription factor substrates putatively important in the heart are considered. We discuss whether cardiac pathologies could be treated by therapeutic intervention at the GSK3 level but conclude that any intervention would be premature without greater understanding of the precise role of GSK3 in cardiac processes.

Are transgenic mice the 'alkahest' to understanding myocardial hypertrophy and failure?

Murine transgenesis using cardioselective promoters has become increasingly common in studies of cardiac hypertrophy and heart failure, with expression mediated by pronuclear microinjection being the commonest format. Without wishing to decry their usefulness, in our view, such studies are not necessarily as unambiguous as sometimes portrayed and clarity is not always their consequence. We describe broadly the types of approach undertaken in the heart and point out some of the drawbacks. We provide three arbitrarily-chosen examples where, in spite of a number of often-independent studies, no consensus has yet been achieved. These include glycogen synthase kinase 3, the extracellular signal-regulated kinase pathway and the ryanodine receptor 2. We believe that the transgenic approach should not be viewed in an empyreal light and, depending on the questions asked, we suggest that other experimental systems provide equal (or even more) valuable outcomes.

Conditional transgenic expression of fibroblast growth factor 9 in the adult mouse heart reduces heart failure mortality after myocardial infarction

BACKGROUND: Fibroblast growth factor 9 (FGF9) is secreted from bone marrow cells, which have been shown to improve systolic function after myocardial infarction (MI) in a clinical trial. FGF9 promotes cardiac vascularization during embryonic development but is only weakly expressed in the adult heart. METHODS AND RESULTS: We used a tetracycline-responsive binary transgene system based on the α-myosin heavy chain promoter to test whether conditional expression of FGF9 in the adult myocardium supports adaptation after MI. In sham-operated mice, transgenic FGF9 stimulated left ventricular hypertrophy with microvessel expansion and preserved systolic and diastolic function. After coronary artery ligation, transgenic FGF9 enhanced hypertrophy of the noninfarcted left ventricular myocardium with increased microvessel density, reduced interstitial fibrosis, attenuated fetal gene expression, and improved systolic function. Heart failure mortality after MI was markedly reduced by transgenic FGF9, whereas rupture rates were not affected. Adenoviral FGF9 gene transfer after MI similarly promoted left ventricular hypertrophy with improved systolic function and reduced heart failure mortality. Mechanistically, FGF9 stimulated proliferation and network formation of endothelial cells but induced no direct hypertrophic effects in neonatal or adult rat cardiomyocytes in vitro. FGF9-stimulated endothelial cell supernatants, however, induced cardiomyocyte hypertrophy via paracrine release of bone morphogenetic protein 6. In accord with this observation, expression of bone morphogenetic protein 6 and phosphorylation of its downstream targets SMAD1/5 were increased in the myocardium of FGF9 transgenic mice. CONCLUSIONS: Conditional expression of FGF9 promotes myocardial vascularization and hypertrophy with enhanced systolic function and reduced heart failure mortality after MI. These observations suggest a previously unrecognized therapeutic potential for FGF9 after MI.

Endothelin-1 and fibroblast growth factors stimulate the mitogen-activated protein kinase signaling cascade in cardiac myocytes. The potential role of the cascade in the integration of two signaling pathways leading to myocyte hypertrophy.

Maximally effective concentrations of endothelin-1 (ET-1), acidic FGF (aFGF), or 12-O-tetradecanoylphorbol-13-acetate (TPA) activated mitogen-activated protein kinase (MAPK) by 3-4-fold in crude extracts of myocytes cultured from neonatal rat heart ventricles. Maximal activation was achieved after 5 min. Thereafter, MAPK activity stimulated by ET-1 or aFGF declined to control values within 1-2 h, whereas activation by TPA was more sustained. Two peaks of MAPK activity (a 42- and a 44-kDa MAPK) were resolved in cells exposed to ET-1 or aFGF by fast protein liquid chromatography on a Mono Q column. One major and one minor peak of MAPK kinase (MAPKK) was stimulated by ET-1 or aFGF. Cardiac myocytes expressed protein kinase C (PKC)-alpha, -delta, -epsilon and -zeta as shown immunoblotting. Exposure to 1 microM TPA for 24 h down-regulated PKC-alpha, -delta, and -epsilon, but not PKC-zeta. This maneuver wholly abolished the activation of MAPK on re-exposure to TPA but did not affect the response to aFGF. The effect of ET-1 was partially down-regulated. ET-1 stimulated phospho[3H]inositide hydrolysis 18-fold, whereas aFGF stimulated by only 30%. Agonists which initially utilize dissimilar signaling pathways may therefore converge at the level of MAPKK/MAPK and this may be relevant to the hypertrophic response of the heart.

Adrenergic receptor stimulation of the mitogen-activated protein kinase cascade and cardiac hypertrophy.

Phenylephrine and noradrenaline (alpha-adrenergic agonism) or isoprenaline (beta-adrenergic agonism) stimulated protein synthesis rates, increased the activity of the atrial natriuretic factor gene promoter and activated mitogen-activated protein kinase (MAPK). The EC50 for MAPK activation by noradrenaline was 2-4 microM and that for isoprenaline was 0.2-0.3 microM. Maximal activation of MAPK by isoprenaline was inhibited by the beta-adrenergic antagonist, propranolol, whereas the activation by noradrenaline was inhibited by the alpha1-adrenergic antagonist, prazosin. FPLC on a Mono-Q column separated two peaks of MAPK (p42MAPK and p44MAPK) and two peaks of MAPK-activating activity (MEK) activated by isoprenaline or noradrenaline. Prolonged phorbol ester exposure partially down-regulated the activation of MAPK by noradrenaline but not by isoprenaline. This implies a role for protein kinase C in MAPK activation by noradrenaline but not isoprenaline. A role for cyclic AMP in activation of the MAPK pathway was eliminated when other agonists that elevate cyclic AMP in the cardiac myocyte did not activate MAPK. In contrast, MAPK was activated by exposure to ionomycin, Bay K8644 or thapsigargin that elevate intracellular Ca2+. Furthermore, depletion of extracellular Ca2+ concentrations with bis-(o-aminophenoxy)ethane-NNN'N'-tetra-acetic acid (BAPTA) or blocking of the L-type Ca2+ channel with nifepidine or verapamil inhibited the response to isoprenaline without inhibiting the responses to noradrenaline. We conclude that alpha- and beta-adrenergic agonists can activate the MEK/MAPK pathway in the heart by different signalling pathways. Elevation of intracellular Ca2+ rather than cyclic AMP appears important in the activation of MAPK by isoprenaline in the cardiac myocyte.

Cellular mechanisms of cardiac hypertrophy.

Hypertrophy of myocytes in the heart ventricles is an important adaptation that in vivo occurs in response to a requirement for increased contractile power. It involves changes at the level of gene transcription, stimulation of the rate of protein synthesis (translation), and increased assembly of myofibrils. There is mounting evidence of the involvement of reversible protein phosphorylation and dephosphorylation in most of these processes. Protein kinase C, mitogen-activated protein kinases, and transcription factors have been implicated in the modulation of the transcriptional changes. Activation of translation may also be mediated through protein phosphorylation/dephosphorylation, although this has not been clearly established in the heart. Here we provide a critical overview of the signalling pathways involved in the hypertrophic response and provide a scheme to account for many of its features.

Activation of protein kinase cascades in the heart by hypertrophic G protein-coupled receptor agonists.

Cardiac myocyte hypertrophy involves changes in cell structure and alterations in protein expression regulated at both the transcriptional and translational levels. Hypertrophic G protein-coupled receptor (GPCR) agonists such as endothelin-(ET-1) and phenylephrine stimulate a number of protein kinase cascades in the heart. Mitogen-activated protein kinase (MAPK) cascades stimulated include the extracellularly regulated kinase cascade, the stress-activated protein kinase/c-Jun N-terminal kinase cascade, and the p38 MAPK cascade. All 3 pathways have been implicated in hypertrophy, but recent ex vivo evidence also suggests that there may be additional effects on cell survival. ET-1 and phenylephrine also stimulate the protein kinase B pathway, and this may be involved in the regulation of protein synthesis by these agonists. Thus, protein kinase-mediated signaling may be important in the regulation of the development of myocyte hypertrophy.

Small guanine nucleotide-binding proteins and myocardial hypertrophy.

The small (21 kDa) guanine nucleotide-binding protein (small G protein) superfamily comprises 5 subfamilies (Ras, Rho, ADP ribosylation factors [ARFs], Rab, and Ran) that act as molecular switches to regulate numerous cellular responses. Cardiac myocyte hypertrophy is associated with cell growth and changes in the cytoskeleton and myofibrillar apparatus. In other cells, the Ras subfamily regulates cell growth whereas the Rho subfamily (RhoA, Rac1, and Cdc42) regulates cell morphology. Thus, the involvement of small G proteins in hypertrophy has become an area of significant interest. Hearts from transgenic mice expressing activated Ras develop features consistent with hypertrophy, whereas mice overexpressing RhoA develop lethal heart failure. In isolated neonatal rat cardiac myocytes, transfection or infection with activated Ras, RhoA, or Rac1 induces many of the features of hypertrophy. We discuss the mechanisms of activation of the small G proteins and the downstream signaling pathways involved. The latter may include protein kinases, particularly the mitogen-activated or Rho-activated protein kinases. We conclude that although there is significant evidence implicating Ras, RhoA, and Rac1 in hypertrophy, the mechanisms are not fully understood.

Regulation of gene and protein expression in cardiac myocyte hypertrophy and apoptosis

Considerable efforts have been expended in elucidating the inter-cellular and intra-cellular signaling pathways which elicit cardiac myocyte hypertrophy or apoptosis, and in identifying the changes which are associated with the end-stage of the response. The challenge now is to link the two. Although some of the signaling effects will be the acute modulation of existing protein function, long-term effects which bring about and maintain the hypertrophic state or which culminate in cell death are mediated at the level of gene and protein expression. With the advances in micro-array technology and genome sequencing, it is now possible to obtain a picture of the global gene expression profile in myocytes or in whole heart which dictates the proteins which could be made. This is not the final picture since additional regulation at the level of translation modulates the relative proportions of each protein that can be made from the transcriptome. Even here, further regulation of protein stability and turnover means that ultimately it is still necessary to examine the proteome to determine what may cause the functional changes in a cell. Thus, in order to gain a full picture of events which regulate the response and gain some insight into possible points of intervention for therapy, it is necessary to examine gene expression, mRNA translation and protein expression in concert.

Targeting myocardial remodelling to develop novel therapies for heart failure: a position paper from the Working Group on Myocardial Function of the European Society of Cardiology

The failing heart is characterized by complex tissue remodelling involving increased cardiomyocyte death, and impairment of sarcomere function, metabolic activity, endothelial and vascular function, together with increased inflammation and interstitial fibrosis. For years, therapeutic approaches for heart failure (HF) relied on vasodilators and diuretics which relieve cardiac workload and HF symptoms. The introduction in the clinic of drugs interfering with beta-adrenergic and angiotensin signalling have ameliorated survival by interfering with the intimate mechanism of cardiac compensation. Current therapy, though, still has a limited capacity to restore muscle function fully, and the development of novel therapeutic targets is still an important medical need. Recent progress in understanding the molecular basis of myocardial dysfunction in HF is paving the way for development of new treatments capable of restoring muscle function and targeting specific pathological subsets of LV dysfunction. These include potentiating cardiomyocyte contractility, increasing cardiomyocyte survival and adaptive hypertrophy, increasing oxygen and nutrition supply by sustaining vessel formation, and reducing ventricular stiffness by favourable extracellular matrix remodelling. Here, we consider drugs such as omecamtiv mecarbil, nitroxyl donors, cyclosporin A, SERCA2a (sarcoplasmic/endoplasmic Ca(2 +) ATPase 2a), neuregulin, and bromocriptine, all of which are currently in clinical trials as potential HF therapies, and discuss novel molecular targets with potential therapeutic impact that are in the pre-clinical phases of investigation. Finally, we consider conceptual changes in basic science approaches to improve their translation into successful clinical applications.