Raf-1 Kinase Is Required for Cardiac Hypertrophy and Cardiomyocyte Survival in Response to Pressure Overload

Identifying plasma proteomic signatures from health to heart failure, across the ejection fraction spectrum

Circulating proteins may provide insights into the varying biological mechanisms involved in heart failure (HF) with preserved ejection fraction (HFpEF) and reduced ejection fraction (HFrEF). We aimed to identify specific proteomic patterns for HF, by comparing proteomic profiles across the ejection fraction spectrum. We investigated 4210 circulating proteins in 739 patients with normal (Stage A/Healthy) or elevated (Stage B) filling pressures, HFpEF, or ischemic HFrEF (iHFrEF). We found 2122 differentially expressed proteins between iHFrEF-Stage A/Healthy, 1462 between iHFrEF-HFpEF and 52 between HFpEF-Stage A/Healthy. Of these 52 proteins, 50 were also found in iHFrEF vs. Stage A/Healthy, leaving SLITRK6 and NELL2 expressed in lower levels only in HFpEF. Moreover, 108 proteins, linked to regulation of cell fate commitment, differed only between iHFrEF-HFpEF. Proteomics across the HF spectrum reveals overlap in differentially expressed proteins compared to stage A/Healthy. Multiple proteins are unique for distinguishing iHFrEF from HFpEF, supporting the capacity of proteomics to discern between these conditions.

RAF1 facilitates KIT signaling and serves as a potential treatment target for gastrointestinal stromal tumor

The aberrant activation of RAS/RAF/MEK/ERK signaling is important for KIT mutation-mediated tumorigenesis of gastrointestinal stromal tumor (GIST). In this study, we found that inhibition of RAF1 suppresses the activation of both wild-type KIT and primary KIT mutations in GIST, with primary KIT mutations showing greater sensitivity. This suggests a positive feedback loop between KIT and RAF1, wherein RAF1 facilitates KIT signaling. We further demonstrated that RAF1 associates with KIT and the kinase activity of RAF1 is necessary for its contribution to KIT activation. Accordingly, inhibition of RAF1 suppressed cell survival, proliferation, and cell cycle progression in vitro mediated by both wild-type KIT and primary KIT mutations. Inhibition of RAF1 in vivo suppressed GIST growth in a transgenic mouse model carrying germline KIT/V558A mutation, showing a similar treatment efficiency as imatinib, the first-line targeted therapeutic drug of GIST, while the combination use of imatinib and RAF1 inhibitor further suppressed tumor growth. Acquisition of drug-resistant secondary mutation of KIT is a major cause of treatment failure of GIST following targeted therapy. Like wild-type KIT and primary KIT mutations, inhibition of RAF1 suppressed the activation of secondary KIT mutation, and the cell survival, proliferation, cell cycle progression in vitro, and tumor growth in vivo mediated by secondary KIT mutation. However, the activation of secondary KIT mutation is less dependent on RAF1 compared with that of primary KIT mutations. Taken together, our results revealed that RAF1 facilitates KIT signaling and KIT mutation-mediated tumorigenesis of GIST, providing a rationale for further investigation into the use of RAF1 inhibitors alone or in combination with KIT inhibitor in the treatment of GIST, particularly in cases resistant to KIT inhibitors.

MEK Inhibition for RASopathy-Associated Hypertrophic Cardiomyopathy: Clinical Application of a Basic Concept

The term "RASopathies" designates a group of developmental syndromes that are caused by activating variants of the rat sarcoma virus protein (RAS)/mitogen-activated protein kinase (MAPK) cascade. The most prevalent clinical diagnosis is Noonan syndrome, and other, less prevalent conditions include Noonan syndrome with multiple lentigines, Costello syndrome, cardiofaciocutaneous syndrome, and others. Hypertrophic cardiomyopathy occurs in 10% of these patients and can be severe and life-threating. Recently, repurposing of medications inhibiting the RAS/MAPK on a compassionate use basis has emerged as a promising concept to improve the outcome of these patients. Herein, we specifically review the role of the RAS/MAPK pathway in RASopathy-associated cardiomyopathy, and discuss the role of small-molecule inhibition in the treatment of this condition. We describe how drug repurposing of trametinib (mitogen-activated protein/extracellular signal-regulated kinase inhibition) and sirolimus/everolimus (mammalian target of rapamycin inhibition) was performed, how genotype-specific therapies are chosen and followed, as well as initial outcomes from early case series. Finally, we lay out the challenges and opportunities for trials that aim to quantify the benefits of this approach.

Novel insights into cardiovascular toxicity of cancer targeted and immune therapies: Beyond ischemia with non-obstructive coronary arteries (INOCA)

Novel immune and targeted therapies approved over the past 2 decades have resulted in dramatic improvements in cancer-specific outcomes for many cancer patients. However, many of these agents can induce cardiovascular toxicity in a subset of patients. The field of cardio-oncology was established based on observations that anti-neoplastic chemotherapies and mantle radiation can lead to premature cardiomyopathy in cancer survivors. While conventional chemotherapy, targeted therapy, and immune therapies can all result in cardiovascular adverse events, the mechanisms, timing, and incidence of these events are inherently different. Many of these effects converge upon the coronary microvasculature to involve, through endocardial endothelial cells, a more direct effect through close proximity to cardiomyocyte with cellular communication and signaling pathways. In this review, we will provide an overview of emerging paradigms in the field of Cardio-Oncology, particularly the role of the coronary microvasculature in mediating cardiovascular toxicity of important cancer targeted and immune therapies. As the number of cancer patients treated with novel immune and targeted therapies grows exponentially and subsequently the number of long-term cancer survivors dramatically increases, it is critical that cardiologists and cardiology researchers recognize the unique potential cardiovascular toxicities of these agents.

Exploring TTN variants as genetic insights into cardiomyopathy pathogenesis and potential emerging clues to molecular mechanisms in cardiomyopathies

The giant protein titin (TTN) is a sarcomeric protein that forms the myofibrillar backbone for the components of the contractile machinery which plays a crucial role in muscle disorders and cardiomyopathies. Diagnosing TTN pathogenic variants has important implications for patient management and genetic counseling. Genetic testing for TTN variants can help identify individuals at risk for developing cardiomyopathies, allowing for early intervention and personalized treatment strategies. Furthermore, identifying TTN variants can inform prognosis and guide therapeutic decisions. Deciphering the intricate genotype-phenotype correlations between TTN variants and their pathologic traits in cardiomyopathies is imperative for gene-based diagnosis, risk assessment, and personalized clinical management. With the increasing use of next-generation sequencing (NGS), a high number of variants in the TTN gene have been detected in patients with cardiomyopathies. However, not all TTN variants detected in cardiomyopathy cohorts can be assumed to be disease-causing. The interpretation of TTN variants remains challenging due to high background population variation. This narrative review aimed to comprehensively summarize current evidence on TTN variants identified in published cardiomyopathy studies and determine which specific variants are likely pathogenic contributors to cardiomyopathy development.

FGF23 and klotho at the intersection of kidney and cardiovascular disease

Cardiovascular disease is the leading cause of death in patients with chronic kidney disease (CKD). As CKD progresses, CKD-specific risk factors, such as disordered mineral homeostasis, amplify traditional cardiovascular risk factors. Fibroblast growth factor 23 (FGF23) regulates mineral homeostasis by activating complexes of FGF receptors and transmembrane klotho co-receptors. A soluble form of klotho also acts as a 'portable' FGF23 co-receptor in tissues that do not express klotho. In progressive CKD, rising circulating FGF23 levels in combination with decreasing kidney expression of klotho results in klotho-independent effects of FGF23 on the heart that promote left ventricular hypertrophy, heart failure, atrial fibrillation and death. Emerging data suggest that soluble klotho might mitigate some of these effects via several candidate mechanisms. More research is needed to investigate FGF23 excess and klotho deficiency in specific cardiovascular complications of CKD, but the pathophysiological primacy of FGF23 excess versus klotho deficiency might never be precisely resolved, given the entangled feedback loops that they share. Therefore, randomized trials should prioritize clinical practicality over scientific certainty by targeting disordered mineral homeostasis holistically in an effort to improve cardiovascular outcomes in patients with CKD.

An Assessment of the Therapeutic Landscape for the Treatment of Heart Disease in the RASopathies

The RAS/mitogen-activated protein kinase (MAPK) pathway controls a plethora of developmental and post-developmental processes. It is now clear that mutations in the RAS-MAPK pathway cause developmental diseases collectively referred to as the RASopathies. The RASopathies include Noonan syndrome, Noonan syndrome with multiple lentigines, cardiofaciocutaneous syndrome, neurofibromatosis type 1, and Costello syndrome. RASopathy patients exhibit a wide spectrum of congenital heart defects (CHD), such as valvular abnormalities and hypertrophic cardiomyopathy (HCM). Since the cardiovascular defects are the most serious and recurrent cause of mortality in RASopathy patients, it is critical to understand the pathological signaling mechanisms that drive the disease. Therapies for the treatment of HCM and other RASopathy-associated comorbidities have yet to be fully realized. Recent developments have shown promise for the use of repurposed antineoplastic drugs that target the RAS-MAPK pathway for the treatment of RASopathy-associated HCM. However, given the impact of the RAS-MAPK pathway in post-developmental physiology, establishing safety and evaluating risk when treating children will be paramount. As such insight provided by preclinical and clinical information will be critical. This review will highlight the cardiovascular manifestations caused by the RASopathies and will discuss the emerging therapies for treatment.

Recent Perspectives on Cardiovascular Toxicity Associated with Colorectal Cancer Drug Therapy

Cardiotoxicity is a well-known adverse effect of cancer-related therapy that has a significant influence on patient outcomes and quality of life. The use of antineoplastic drugs to treat colorectal cancers (CRCs) is associated with a number of undesirable side effects including cardiac complications. For both sexes, CRC ranks second and accounts for four out of every ten cancer deaths. According to the reports, almost 39% of patients with colorectal cancer who underwent first-line chemotherapy suffered cardiovascular impairment. Although 5-fluorouracil is still the backbone of chemotherapy regimen for colorectal, gastric, and breast cancers, cardiotoxicity caused by 5-fluorouracil might affect anywhere from 1.5% to 18% of patients. The precise mechanisms underlying cardiotoxicity associated with CRC treatment are complex and may involve the modulation of various signaling pathways crucial for maintaining cardiac health including TKI ErbB2 or NRG-1, VEGF, PDGF, BRAF/Ras/Raf/MEK/ERK, and the PI3/ERK/AMPK/mTOR pathway, resulting in oxidative stress, mitochondrial dysfunction, inflammation, and apoptosis, ultimately damaging cardiac tissue. Thus, the identification and management of cardiotoxicity associated with CRC drug therapy while minimizing the negative impact have become increasingly important. The purpose of this review is to catalog the potential cardiotoxicities caused by anticancer drugs and targeted therapy used to treat colorectal cancer as well as strategies focused on early diagnosing, prevention, and treatment of cardiotoxicity associated with anticancer drugs used in CRC therapy.

Decoding of miR-7-5p in Colony Forming Unit-Hill Colonies as a Biomarker of Subclinical Cardiovascular Disease-A MERIT Study

Colony forming unit-Hill (CFU-Hill) colonies were established to serve as a sensitive biomarker for vascular health. In animals, the overexpression of miR-7-5p was shown to be pro-atherogenic and associated with increased cardiovascular disease (CVD) risk. In a MERIT study, we aimed to explore the role of miR-7-5p expression in CFU-Hill colonies in type 1 diabetes mellitus (T1DM) and the effect of metformin in subclinical CVD. The expression of miR-7-5p in CFU-Hill colonies in 29 T1DM subjects without CVD and 20 healthy controls (HC) was measured. Metformin was administered to T1DM subjects for eight weeks. MiR-7-5p was upregulated in T1DM whereas metformin reduced it to HC levels. MiR-7-5p was positively correlated with c-reactive protein, and C-X-C motif chemokine ligand 10. The receiver operating characteristic curve revealed miR-7-5p as a biomarker of CVD, and upregulated miR-7-5p, defining subclinical CVD at a HbA1c level of 44.3 mmol/mol. Ingenuity pathway analysis predicted miR-7-5p to inhibit the mRNA expression of Krüppel-like factor 4, epidermal growth factor receptor, insulin-like growth factor 1 receptor, v-raf-1 murine leukemia viral oncogene homolog 1 and insulin receptor substrate ½, and insulin receptor, while metformin activated these miRNAs via transforming growth factor-β1 and Smad2/3. We proved the pro-atherogenic effect of miR-7-5p that maybe used as a prognostic biomarker.

Inhibiting O-GlcNAcylation impacts p38 and Erk1/2 signaling and perturbs cardiomyocyte hypertrophy

The dynamic cycling of O-linked GlcNAc (O-GlcNAc) on and off Ser/Thr residues of intracellular proteins, termed O-GlcNAcylation, is mediated by the conserved enzymes O-GlcNAc transferase (OGT) and O-GlcNAcase. O-GlcNAc cycling is important in homeostatic and stress responses, and its perturbation sensitizes the heart to ischemic and other injuries. Despite considerable progress, many molecular pathways impacted by O-GlcNAcylation in the heart remain unclear. The mitogen-activated protein kinase (MAPK) pathway is a central signaling cascade that coordinates developmental, physiological, and pathological responses in the heart. The developmental or adaptive arm of MAPK signaling is primarily mediated by Erk kinases, while the pathophysiologic arm is mediated by p38 and Jnk kinases. Here, we examine whether O-GlcNAcylation affects MAPK signaling in cardiac myocytes, focusing on Erk1/2 and p38 in basal and hypertrophic conditions induced by phenylephrine. Using metabolic labeling of glycans coupled with alkyne-azide "click" chemistry, we found that Erk1/2 and p38 are O-GlcNAcylated. Supporting the regulation of p38 by O-GlcNAcylation, the OGT inhibitor, OSMI-1, triggers the phosphorylation of p38, an event that involves the NOX2-Ask1-MKK3/6 signaling axis and also the noncanonical activator Tab1. Additionally, OGT inhibition blocks the phenylephrine-induced phosphorylation of Erk1/2. Consistent with perturbed MAPK signaling, OSMI-1-treated cardiomyocytes have a blunted hypertrophic response to phenylephrine, decreased expression of cTnT (key component of the contractile apparatus), and increased expression of maladaptive natriuretic factors Anp and Bnp. Collectively, these studies highlight new roles for O-GlcNAcylation in maintaining a balanced activity of Erk1/2 and p38 MAPKs during hypertrophic growth responses in cardiomyocytes.

The Role of PKC-MAPK Signalling Pathways in the Development of Hyperglycemia-Induced Cardiovascular Complications

Cardiovascular disease is the most common cause of death among diabetic patients worldwide. Hence, cardiovascular wellbeing in diabetic patients requires utmost importance in disease management. Recent studies have demonstrated that protein kinase C activation plays a vital role in the development of cardiovascular complications via its activation of mitogen-activated protein kinase (MAPK) cascades, also known as PKC-MAPK pathways. In fact, persistent hyperglycaemia in diabetic conditions contribute to preserved PKC activation mediated by excessive production of diacylglycerol (DAG) and oxidative stress. PKC-MAPK pathways are involved in several cellular responses, including enhancing oxidative stress and activating signalling pathways that lead to uncontrolled cardiac and vascular remodelling and their subsequent dysfunction. In this review, we discuss the recent discovery on the role of PKC-MAPK pathways, the mechanisms involved in the development and progression of diabetic cardiovascular complications, and their potential as therapeutic targets for cardiovascular management in diabetic patients.

Mechanistic and Clinical Overview Cardiovascular Toxicity of BRAF and MEK Inhibitors: JACC: CardioOncology State-of-the-Art Review

Rapidly accelerated fibrosarcoma B-type (BRAF) and mitogen-activated extracellular signal-regulated kinase (MEK) inhibitors have revolutionized melanoma treatment. Approximately half of patients with melanoma harbor a BRAF gene mutation with subsequent dysregulation of the RAF-MEK-ERK signaling pathway. Targeting this pathway with BRAF and MEK blockade results in control of cell proliferation and, in most cases, disease control. These pathways also have cardioprotective effects and are necessary for normal vascular and cardiac physiology. BRAF and MEK inhibitors are associated with adverse cardiovascular effects including hypertension, left ventricular dysfunction, venous thromboembolism, atrial arrhythmia, and electrocardiographic QT interval prolongation. These effects may be underestimated in clinical trials. Baseline cardiovascular assessment and follow-up, including serial imaging and blood pressure assessment, are essential to balance optimal anti-cancer therapy while minimizing cardiovascular side effects. In this review, an overview of BRAF/MEK inhibitor-induced cardiovascular toxicity, the mechanisms underlying these, and strategies for surveillance, prevention, and treatment of these effects are provided.

The RAF Kinase Inhibitor Protein (RKIP): Good as Tumour Suppressor, Bad for the Heart

The RAF kinase inhibitor protein, RKIP, is a dual inhibitor of the RAF1 kinase and the G protein-coupled receptor kinase 2, GRK2. By inhibition of the RAF1-MAPK (mitogen-activated protein kinase) pathway, RKIP acts as a beneficial tumour suppressor. By inhibition of GRK2, RKIP counteracts GRK2-mediated desensitisation of G protein-coupled receptor (GPCR) signalling. GRK2 inhibition is considered to be cardioprotective under conditions of exaggerated GRK2 activity such as heart failure. However, cardioprotective GRK2 inhibition and pro-survival RAF1-MAPK pathway inhibition counteract each other, because inhibition of the pro-survival RAF1-MAPK cascade is detrimental for the heart. Therefore, the question arises, what is the net effect of these apparently divergent functions of RKIP in vivo? The available data show that, on one hand, GRK2 inhibition promotes cardioprotective signalling in isolated cardiomyocytes. On the other hand, inhibition of the pro-survival RAF1-MAPK pathway by RKIP deteriorates cardiomyocyte viability. In agreement with cardiotoxic effects, endogenous RKIP promotes cardiac fibrosis under conditions of cardiac stress, and transgenic RKIP induces heart dysfunction. Supported by next-generation sequencing (NGS) data of the RKIP-induced cardiac transcriptome, this review provides an overview of different RKIP functions and explains how beneficial GRK2 inhibition can go awry by RAF1-MAPK pathway inhibition. Based on RKIP studies, requirements for the development of a cardioprotective GRK2 inhibitor are deduced.

Cardiomyocyte BRAF and type 1 RAF inhibitors promote cardiomyocyte and cardiac hypertrophy in mice in vivo

The extracellular signal-regulated kinase 1/2 (ERK1/2) cascade promotes cardiomyocyte hypertrophy and is cardioprotective, with the three RAF kinases forming a node for signal integration. Our aims were to determine if BRAF is relevant for human heart failure, whether BRAF promotes cardiomyocyte hypertrophy, and if Type 1 RAF inhibitors developed for cancer (that paradoxically activate ERK1/2 at low concentrations: the 'RAF paradox') may have the same effect. BRAF was up-regulated in heart samples from patients with heart failure compared with normal controls. We assessed the effects of activated BRAF in the heart using mice with tamoxifen-activated Cre for cardiomyocyte-specific knock-in of the activating V600E mutation into the endogenous gene. We used echocardiography to measure cardiac dimensions/function. Cardiomyocyte BRAFV600E induced cardiac hypertrophy within 10 d, resulting in increased ejection fraction and fractional shortening over 6 weeks. This was associated with increased cardiomyocyte size without significant fibrosis, consistent with compensated hypertrophy. The experimental Type 1 RAF inhibitor, SB590885, and/or encorafenib (a RAF inhibitor used clinically) increased ERK1/2 phosphorylation in cardiomyocytes, and promoted hypertrophy, consistent with a 'RAF paradox' effect. Both promoted cardiac hypertrophy in mouse hearts in vivo, with increased cardiomyocyte size and no overt fibrosis. In conclusion, BRAF potentially plays an important role in human failing hearts, activation of BRAF is sufficient to induce hypertrophy, and Type 1 RAF inhibitors promote hypertrophy via the 'RAF paradox'. Cardiac hypertrophy resulting from these interventions was not associated with pathological features, suggesting that Type 1 RAF inhibitors may be useful to boost cardiomyocyte function.

Inside the Noonan "universe": Literature review on growth, GH/IGF axis and rhGH treatment: Facts and concerns

Noonan syndrome (NS) is a disorder characterized by a typical facial gestalt, congenital heart defects, variable cognitive deficits, skeletal defects, and short stature. NS is caused by germline pathogenic variants in genes coding proteins with a role in the RAS/mitogen-activated protein kinase signaling pathway, and it is typically associated with substantial genetic and clinical complexity and variability. Short stature is a cardinal feature in NS, with evidence indicating that growth hormone (GH) deficiency, partial GH insensitivity, and altered response to insulin-like growth factor I (IGF-1) are contributing events for growth failure in these patients. Decreased IGF-I, together with low/normal responses to GH pharmacological provocation tests, indicating a variable presence of GH deficiency/resistance, in particular in subjects with pathogenic PTPN11 variants, are frequently reported. Nonetheless, short- and long-term studies have demonstrated a consistent and significant increase in height velocity (HV) in NS children and adolescents treated with recombinant human GH (rhGH). While the overall experience with rhGH treatment in NS patients with short stature is reassuring, it is difficult to systematically compare published data due to heterogeneous protocols, potential enrolment bias, the small size of cohorts in many studies, different cohort selection criteria and varying durations of therapy. Furthermore, in most studies, the genetic information is lacking. NS is associated with a higher risk of benign and malignant proliferative disorders and hypertrophic cardiomyopathy, and rhGH treatment may further increase risk in these patients, especially as dosages vary widely. Herein we provide an updated review of aspects related to growth, altered function of the GH/IGF axis and cell response to GH/IGF stimulation, rhGH treatment and its possible adverse events. Given the clinical variability and genetic heterogeneity of NS, treatment with rhGH should be personalized and a conservative approach with judicious surveillance is recommended. Depending on the genotype, an individualized follow-up and close monitoring during rhGH treatments, also focusing on screening for neoplasms, should be considered.

Identification of Diarylurea Inhibitors of the Cardiac-Specific Kinase TNNI3K by Designing Selectivity Against VEGFR2, p38α, and B-Raf

A series of diarylurea inhibitors of the cardiac-specific kinase TNNI3K were developed to elucidate the biological function of TNNI3K and evaluate TNNI3K as a therapeutic target for the treatment of cardiovascular diseases. Utilizing a structure-based design, enhancements in kinase selectivity were engineered into the series, capitalizing on the established X-ray crystal structures of TNNI3K, VEGFR2, p38α, and B-Raf. Our efforts culminated in the discovery of an in vivo tool compound 47 (GSK329), which exhibited desirable TNNI3K potency and rat pharmacokinetic properties as well as promising kinase selectivity against VEGFR2 (40-fold), p38α (80-fold), and B-Raf (>200-fold). Compound 47 demonstrated positive cardioprotective outcomes in a mouse model of ischemia/reperfusion cardiac injury, indicating that optimized exemplars from this series, such as 47, are favorable leads for discovering novel medicines for cardiac diseases.

Molecules linked to Ras signaling as therapeutic targets in cardiac pathologies

Abstract

The Ras family of small Guanosine Triphosphate (GTP)-binding proteins (G proteins) represents one of the main components of intracellular signal transduction required for normal cardiac growth, but is also critically involved in the development of cardiac hypertrophy and heart failure. The present review provides an update on the role of the H-, K- and N-Ras genes and their related pathways in cardiac diseases. We focus on cardiac hypertrophy and heart failure, where Ras has been studied the most. We also review other cardiac diseases, like genetic disorders related to Ras. The scope of the review extends from fundamental concepts to therapeutic applications. Although the three Ras genes have a nearly identical primary structure, there are important functional differences between them: H-Ras mainly regulates cardiomyocyte size, whereas K-Ras regulates cardiomyocyte proliferation. N-Ras is the least studied in cardiac cells and is less associated to cardiac defects. Clinically, oncogenic H-Ras causes Costello syndrome and facio-cutaneous-skeletal syndromes with hypertrophic cardiomyopathy and arrhythmias. On the other hand, oncogenic K-Ras and alterations of other genes of the Ras-Mitogen-Activated Protein Kinase (MAPK) pathway, like Raf, cause Noonan syndrome and cardio-facio-cutaneous syndromes characterized by cardiac hypertrophy and septal defects. We further review the modulation by Ras of key signaling pathways in the cardiomyocyte, including: (i) the classical Ras-Raf-MAPK pathway, which leads to a more physiological form of cardiac hypertrophy; as well as other pathways associated with pathological cardiac hypertrophy, like (ii) The SAPK (stress activated protein kinase) pathways p38 and JNK; and (iii) The alternative pathway Raf-Calcineurin-Nuclear Factor of Activated T cells (NFAT). Genetic alterations of Ras isoforms or of genes in the Ras-MAPK pathway result in Ras-opathies, conditions frequently associated with cardiac hypertrophy or septal defects among other cardiac diseases. Several studies underline the potential role of H- and K-Ras as a hinge between physiological and pathological cardiac hypertrophy, and as potential therapeutic targets in cardiac hypertrophy and failure.

Graphic abstract

The Ras (Rat Sarcoma) gene family is a group of small G proteins

Ras is regulated by growth factors and neurohormones affecting cardiomyocyte growth and hypertrophy

Ras directly affects cardiomyocyte physiological and pathological hypertrophy

Genetic alterations of Ras and its pathways result in various cardiac phenotypes

Ras and its pathway are differentially regulated in acquired heart disease

Ras modulation is a promising therapeutic target in various cardiac conditions.

The anti-cancer drug dabrafenib is not cardiotoxic and inhibits cardiac remodelling and fibrosis in a murine model of hypertension

Raf kinases signal via extracellular signal-regulated kinases 1/2 (ERK1/2) to drive cell division. Since activating mutations in BRAF (B-Raf proto-oncogene, serine/threonine kinase) are highly oncogenic, BRAF inhibitors including dabrafenib have been developed for cancer. Inhibitors of ERK1/2 signalling used for cancer are cardiotoxic in some patients, raising the question of whether dabrafenib is cardiotoxic. In the heart, ERK1/2 signalling promotes not only cardiomyocyte hypertrophy and is cardioprotective but also promotes fibrosis. Our hypothesis is that ERK1/2 signalling is not required in a non-stressed heart but is required for cardiac remodelling. Thus, dabrafenib may affect the heart in the context of, for example, hypertension. In experiments with cardiomyocytes, cardiac fibroblasts and perfused rat hearts, dabrafenib inhibited ERK1/2 signalling. We assessed the effects of dabrafenib (3 mg/kg/d) on male C57BL/6J mouse hearts in vivo. Dabrafenib alone had no overt effects on cardiac function/dimensions (assessed by echocardiography) or cardiac architecture. In mice treated with 0.8 mg/kg/d angiotensin II (AngII) to induce hypertension, dabrafenib inhibited ERK1/2 signalling and suppressed cardiac hypertrophy in both acute (up to 7 d) and chronic (28 d) settings, preserving ejection fraction. At the cellular level, dabrafenib inhibited AngII-induced cardiomyocyte hypertrophy, reduced expression of hypertrophic gene markers and almost completely eliminated the increase in cardiac fibrosis both in interstitial and perivascular regions. Dabrafenib is not overtly cardiotoxic. Moreover, it inhibits maladaptive hypertrophy resulting from AngII-induced hypertension. Thus, Raf is a potential therapeutic target for hypertensive heart disease and drugs such as dabrafenib, developed for cancer, may be used for this purpose.

Schisandrin Protects against Norepinephrine-Induced Myocardial Hypertrophic Injury by Inhibiting the JAK2/STAT3 Signaling Pathway

Aims. Heart failure is closely associated with norepinephrine-(NE-) induced cardiomyocyte hypertrophy. Schisandrin is derived from the traditional Chinese medicine Schisandra; it has a variety of pharmacological activities, and the mechanism of schisandrin-mediated protection of the cardiovascular system is not clear. Main Methods. NE was used to establish a cardiomyocyte hypertrophy model to explore the mechanism of action of schisandrin. An MTT assay was used for cell viability; Hoechst fluorescence staining was used to observe the cell morphology and calculate the apoptosis rate. The cell surface area was measured and the protein to DNA ratio was calculated, changes in mitochondrial membrane potential were detected, and the degree of hypertrophic cell damage was evaluated. WB, QRT-PCR, and immunofluorescence were used to qualitatively, quantitatively, and quantitatively detect apoptotic proteins in the JAK2/STAT3 signaling pathway. Key Findings. In the NE-induced model, schisandrin treatment reduced the apoptosis rate of cardiomyocytes, increased the ratio of the cell surface area to cardiomyocyte protein/DNA, and also, increased the membrane potential of the mitochondria. The expression of both JAK2 and STAT3 was downregulated, and the BAX/Bcl-2 ratio was significantly reduced. In conclusion, schisandrin may protect against NE-induced cardiomyocyte hypertrophy by inhibiting the JAK2/STAT3 signaling pathway and reducing cardiomyocyte apoptosis.

ERK1/2: An Integrator of Signals That Alters Cardiac Homeostasis and Growth

Integration of cellular responses to extracellular cues is essential for cell survival and adaptation to stress. Extracellular signal-regulated kinase (ERK) 1 and 2 serve an evolutionarily conserved role for intracellular signal transduction that proved critical for cardiomyocyte homeostasis and cardiac stress responses. Considering the importance of ERK1/2 in the heart, understanding how these kinases operate in both normal and disease states is critical. Here, we review the complexity of upstream and downstream signals that govern ERK1/2-dependent regulation of cardiac structure and function. Particular emphasis is given to cardiomyocyte hypertrophy as an outcome of ERK1/2 activation regulation in the heart.

Mechanisms of the Cardiac Myocyte-Damaging Effects of Dasatinib

The anticancer drug dasatinib (Sprycel) is a BCR-ABL1-targeted tyrosine kinase inhibitor used in treating chronic myelogenous leukemia that has been shown in clinical trials to display cardiovascular toxicities. While dasatinib potently inhibits BCR-ABL1, it is not a highly selective kinase inhibitor and may have off-target effects. A neonatal rat cardiac myocyte model was used to investigate potential mechanisms by which dasatinib damaged myocytes. The anthracycline cardioprotective drug dexrazoxane was shown to be ineffective in preventing dasatinib-induced myocyte damage. Dasatinib treatment increased doxorubicin accumulation in myocytes and doxorubicin-induced myocyte damage, likely through its ability to bind to one or more ABC-type efflux transporters. Dasatinib induced myocyte damage either after a brief treatment that mimicked the clinical situation, or more potently after continuous treatment. Dasatinib slightly induced apoptosis in myocytes as evidenced by increases in caspase-3/7 activity. Dasatinib treatment reduced pERK levels in myocytes most likely through inhibition of RAF, which dasatinib strongly inhibits. Thus, inhibition of the RAF/MEK/ERK pro-survival pathway in the heart may be, in part, a mechanism by which dasatinib induces cardiovascular toxicity.

Cardiotoxic effects of angiogenesis inhibitors

The development of new therapies for cancer has led to dramatic improvements in survivorship. Angiogenesis inhibitors represent one such advancement, revolutionising treatment for a wide range of malignancies. However, these drugs are associated with cardiovascular toxicities which can impact optimal cancer treatment in the short-term and may lead to increased morbidity and mortality in the longer term. Vascular endothelial growth factor inhibitors (VEGFIs) are associated with hypertension, left ventricular systolic dysfunction (LVSD) and heart failure as well as arterial and venous thromboembolism, QTc interval prolongation and arrhythmia. The mechanisms behind the development of VEGFI-associated LVSD and heart failure likely involve the combination of a number of myocardial insults. These include direct myocardial effects, as well as secondary toxicity via coronary or peripheral vascular damage. Cardiac toxicity may result from the 'on-target' effects of VEGF inhibition or 'off-target' effects resulting from inhibition of other tyrosine kinases. Similar mechanisms may be involved in the development of VEGFI-associated right ventricular (RV) dysfunction. Some VEGFIs can be associated with QTc interval prolongation and an increased risk of ventricular and atrial arrhythmia. Further pre-clinical and clinical studies and trials are needed to better understand the impact of VEGFI on the cardiovascular system. Once mechanisms are elucidated, therapies can be investigated in clinical trials and surveillance strategies for identifying VEGFI-associated cardiovascular complications can be developed.

Role of extracellular signal-regulated kinase 1/2 signaling underlying cardiac hypertrophy

Cardiac hypertrophy is the result of increased myocardial cell size responding to an increased workload and developmental signals. These extrinsic and intrinsic stimuli as key drivers of cardiac hypertrophy have spurred efforts to target their associated signaling pathways. The extracellular signal-regulated kinases 1/2 (ERK1/2), as an essential member of mitogen-activated protein kinases (MAPKs), has been widely recognized for promoting cardiac growth. Several modified transgenic mouse models have been generated through either affecting the upstream kinase to change ERK1/2 activity, manipulating the direct role of ERK1/2 in the heart, or targeting phosphatases or MAPK scaffold proteins to alter total ERK1/2 activity in response to an increased workload. Using these models, both regulation of the upstream events and modulation of each isoform and indirect effector could provide important insights into how ERK1/2 modulates cardiomyocyte biology. Furthermore, a plethora of compounds, inhibitors, and regulators have emerged in consideration of ERK, or its MAPK kinases, are possible therapeutic targets against cardiac hypertrophic diseases. Herein, is a review of the available evidence regarding the exact role of ERK1/2 in regulating cardiac hypertrophy and a discussion of pharmacological strategy for treatment of cardiac hypertrophy.

[Mechanisms of cardiotoxicity of oncological therapies]

BACKGROUND

Oncological therapies show a number of undesired adverse effects on the cardiovascular system. In particular, the side effects of recently established oncological therapies are incompletely understood and clinical data are lacking in the interpretation of novel cardiac complications.

OBJECTIVE

This article provides a short overview of the mechanisms of cardiac side effects of certain oncological therapies.

MATERIAL AND METHODS

The review is mainly based on data from preclinical studies.

RESULTS

Numerous toxic side effects have already been described and investigated in preclinical models. For certain groups of drugs (e.g. anthracyclines, tyrosine kinase inhibitors and immune checkpoint inhibitors) the underlying molecular mechanisms are still not fully understood.

CONCLUSION

An improved understanding of the molecular mechanism involved in cardiotoxicity might help improve the quality of clinical decisions. Additionally, it will provide new insights into the pathophysiology of cardiac diseases. The aim is to use the results of translational research and to clinically implement them in suitable cardio-oncology units.

MEK1/2 Inhibition in Murine Heart and Aorta After Oral Administration of Refametinib Supplemented Drinking Water

Upregulation of the RAS-RAF-MEK-ERK-MAPK pathway is involved in the development of several human tumors, aortic aneurysms, atherosclerosis, and cardiomyopathy. Refametinib, a highly selective MEK-inhibitor, has already shown antineoplastic activity in phase II trials. Furthermore, it showed potency to attenuate aortic root growth in murine models. Current formulations of this drug however necessitate oral gavage as a delivery method for long-term studies, which is labor-intensive and induces stress and occasional injury, potentially confounding results. Therefore, we developed a novel oral administration method for refametinib. A 2-hydroxypropyl-beta-cyclodextrin (HPBCD) based drinking water preparation of refametinib was formulated, for which a selective, analytical UHPLC-UV method was developed to assess the in-use stability. Next, 16 week old male wild-type C57Bl/6J mice received either a daily dose of 50 or 75 mg/kg/day refametinib or were given regular drinking water during 7 days. In both dosage groups the refametinib plasma levels were measured (n = 10 or 7, respectively). Furthermore, pERK/total ERK protein levels were calculated in the myocardial and aortic tissue of mice receiving a daily dose of 50 mg/kg/day refametinib and untreated mice (n = 4/group). After 7 days no significant degradation of refametinib was observed when dissolved in drinking water provided that drinking bottles were protected from UV/visible light. Furthermore, a dose-dependent increase in refametinib plasma levels was found whereby active plasma levels (> 1.2 µg/mL) were obtained even in the lowest dose-group of 50 mg/kg/day. A significant reduction of pERK/total ERK protein levels compared to untreated mice was observed in aortic and myocardial tissue of mice receiving a daily dose of 50 mg/kg/day refametinib. Importantly, a relatively high mortality rate was noted in the highest dose group (n = 5). This approach provides a valid alternative oral administration method for refametinib with a reduced risk of complications due to animal manipulation and without loss of functionality, which can be implemented in future research regarding the malignant upregulation of the RAS-RAF-MEK-ERK-MAPK pathway. However, care must be taken not to exceed the toxic dose.

Inhibition of the NFATc4/ERK/AKT Pathway and Improvement of Thiol-Specific Oxidative Stress by Dronedarone Possibly Secondary to the Reduction of Blood Pressure in an Animal Model of Ventricular Hypertrophy

Untreated chronic hypertension causes left ventricular hypertrophy, which is related to the occurrence of atrial fibrillation. Dronedarone is an antiarrhythmic agent recently approved for atrial fibrillation. Our group previously demonstrated that dronedarone produced an early regression of left ventricular hypertrophy after 14 days of treatment in an experimental study. In this study, we analyze the possible mechanisms responsible for this effect. Ten-month-old male spontaneously hypertensive rats (SHRs, n = 16) were randomly divided into therapy groups: SHR-D, which received dronedarone, and hypertensive controls, SHR, which received saline. Ten-month-old male Wistar Kyoto rats (WKY, n = 8), which also received a saline solution, were selected as normotensive controls. After 14 days of treatment, echocardiographic measurements of the left ventricle were performed, blood samples were collected for thiol-specific oxidative stress analysis, and the left ventricles were processed for western blot analysis. Dronedarone significantly lowered the left ventricular mass index and relative wall thickness compared with the SHR control group, and no differences were observed between the SHR-D group and the WKY rats. Interestingly, the SHR-D group showed significantly decreased levels of nuclear factor of activated T cells 4 (p-NFATc4), extracellular-signal-regulated kinase 1/2 (p-ERK1/2), and protein kinase B (p-AKT) compared with the hypertensive controls without statistical differences when compared with the WKY rats. Moreover, the SHR control group showed elevated thiolated protein levels and protein thiolation index (PTI) compared with the WKY rats. After treatment with dronedarone, both parameters decreased with respect to the SHR control group until reaching similar levels to the WKY rats. Our study suggests that dronedarone produces inhibition of the NFATc4/ERK/AKT pathway and improvement of thiol-specific oxidative stress possibly secondary to the reduction of blood pressure in an animal model of ventricular hypertrophy.

Interference with ERK-dimerization at the nucleocytosolic interface targets pathological ERK1/2 signaling without cardiotoxic side-effects

Dysregulation of extracellular signal-regulated kinases (ERK1/2) is linked to several diseases including heart failure, genetic syndromes and cancer. Inhibition of ERK1/2, however, can cause severe cardiac side-effects, precluding its wide therapeutic application. ERK^T188-autophosphorylation was identified to cause pathological cardiac hypertrophy. Here we report that interference with ERK-dimerization, a prerequisite for ERK^T188-phosphorylation, minimizes cardiac hypertrophy without inducing cardiac adverse effects: an ERK-dimerization inhibitory peptide (EDI) prevents ERK^T188-phosphorylation, nuclear ERK1/2-signaling and cardiomyocyte hypertrophy, protecting from pressure-overload-induced heart failure in mice whilst preserving ERK1/2-activity and cytosolic survival signaling. We also examine this alternative ERK1/2-targeting strategy in cancer: indeed, ERK^T188-phosphorylation is strongly upregulated in cancer and EDI efficiently suppresses cancer cell proliferation without causing cardiotoxicity. This powerful cardio-safe strategy of interfering with ERK-dimerization thus combats pathological ERK1/2-signaling in heart and cancer, and may potentially expand therapeutic options for ERK1/2-related diseases, such as heart failure and genetic syndromes.

Drugs targeting dysregulated ERK1/2 signaling can cause severe cardiac side effects, precluding their wide therapeutic application. Here, a new and cardio-safe targeting strategy is presented that interferes with ERK dimerization to prevent pathological ERK1/2 signaling in the heart and cancer.

CD47 Deficiency Attenuates Isoproterenol-Induced Cardiac Remodeling in Mice

In this study, we investigated whether CD47 deficiency attenuates isoproterenol- (ISO-) induced cardiac remodeling in mice. Cardiac remodeling was induced by intraperitoneal (i.p.) injection of ISO (60 mg·kg⁻¹·d⁻¹ in 100 μl of sterile normal saline) daily for 14 days and was confirmed by increased levels of lactate dehydrogenase (LDH) and creatine kinase MB (CK-MB), increased heart weight to body weight (HW/BW) ratios, and visible cardiac fibrosis. Apoptosis was evaluated by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining. Levels of malondialdehyde (MDA) and reactive oxygen species (ROS) were found to be significantly higher in the ISO group than in the control group, while superoxide dismutase (SOD) levels were suppressed in the ISO group. However, CD47 knockout significantly limited ISO-induced increases in LDH, CK-MB, and HW/BW ratios, cardiac fibrosis, oxidative stress, and apoptosis in the heart. In addition, CD47 deficiency also increased p-AMPK and LAMP2 expression and decreased HDAC3, cleaved Caspase-3, cleaved Caspase-9, LC3II, and p62 expression in cardiac tissues. In conclusion, CD47 deficiency reduced i.p. ISO-induced cardiac remodeling probably by inhibiting the HDAC3 pathway, improving AMPK signaling and autophagy flux, and rescuing autophagic clearance.

Structural and Functional Changes in the Na+/H+ Exchanger Isoform 1, Induced by Erk1/2 Phosphorylation

The human Na⁺/H⁺ exchanger isoform 1 (NHE1) is a plasma membrane transport protein that plays an important role in pH regulation in mammalian cells. Because of the generation of protons by intermediary metabolism as well as the negative membrane potential, protons accumulate within the cytosol. Extracellular signal-regulated kinase (ERK)-mediated regulation of NHE1 is important in several human pathologies including in the myocardium in heart disease, as well as in breast cancer as a trigger for growth and metastasis. NHE1 has a N-terminal, a 500 amino acid membrane domain, and a C-terminal 315 amino acid cytosolic domain. The C-terminal domain regulates the membrane domain and its effects on transport are modified by protein binding and phosphorylation. Here, we discuss the physiological regulation of NHE1 by ERK, with an emphasis on the critical effects on structure and function. ERK binds directly to the cytosolic domain at specific binding domains. ERK also phosphorylates NHE1 directly at multiple sites, which enhance NHE1 activity with subsequent downstream physiological effects. The NHE1 cytosolic regulatory tail possesses both ordered and disordered regions, and the disordered regions are stabilized by ERK-mediated phosphorylation at a phosphorylation motif. Overall, ERK pathway mediated phosphorylation modulates the NHE1 tail, and affects the activity, structure, and function of this membrane protein.

ERK: A Key Player in the Pathophysiology of Cardiac Hypertrophy

Cardiac hypertrophy is an adaptive and compensatory mechanism preserving cardiac output during detrimental stimuli. Nevertheless, long-term stimuli incite chronic hypertrophy and may lead to heart failure. In this review, we analyze the recent literature regarding the role of ERK (extracellular signal-regulated kinase) activity in cardiac hypertrophy. ERK signaling produces beneficial effects during the early phase of chronic pressure overload in response to G protein-coupled receptors (GPCRs) and integrin stimulation. These functions comprise (i) adaptive concentric hypertrophy and (ii) cell death prevention. On the other hand, ERK participates in maladaptive hypertrophy during hypertension and chemotherapy-mediated cardiac side effects. Specific ERK-associated scaffold proteins are implicated in either cardioprotective or detrimental hypertrophic functions. Interestingly, ERK phosphorylated at threonine 188 and activated ERK5 (the big MAPK 1) are associated with pathological forms of hypertrophy. Finally, we examine the connection between ERK activation and hypertrophy in (i) transgenic mice overexpressing constitutively activated RTKs (receptor tyrosine kinases), (ii) animal models with mutated sarcomeric proteins characteristic of inherited hypertrophic cardiomyopathies (HCMs), and (iii) mice reproducing syndromic genetic RASopathies. Overall, the scientific literature suggests that during cardiac hypertrophy, ERK could be a “good” player to be stimulated or a “bad” actor to be mitigated, depending on the pathophysiological context.

Raf kinase inhibitor protein mediates myocardial fibrosis under conditions of enhanced myocardial oxidative stress

Fibrosis is a hallmark of maladaptive cardiac remodelling. Here we report that genome-wide quantitative trait locus (QTL) analyses in recombinant inbred mouse lines of C57BL/6 J and DBA2/J strains identified Raf Kinase Inhibitor Protein (RKIP) as genetic marker of fibrosis progression. C57BL/6 N-RKIP^−/− mice demonstrated diminished fibrosis induced by transverse aortic constriction (TAC) or CCl₄ (carbon tetrachloride) treatment compared with wild-type controls. TAC-induced expression of collagen Iα2 mRNA, Ki67⁺ fibroblasts and marker of oxidative stress 8-hydroxyguanosine (8-dOHG)⁺ fibroblasts as well as the number of fibrocytes in the peripheral blood and bone marrow were markedly reduced in C57BL/6 N-RKIP^−/− mice. RKIP-deficient cardiac fibroblasts demonstrated decreased migration and fibronectin production. This was accompanied by a two-fold increase of the nuclear accumulation of nuclear factor erythroid 2-related factor 2 (Nrf2), the main transcriptional activator of antioxidative proteins, and reduced expression of its inactivators. To test the importance of oxidative stress for this signaling, C57BL/6 J mice were studied. C57BL/6 J, but not the C57BL/6 N-strain, is protected from TAC-induced oxidative stress due to mutation of the nicotinamide nucleotide transhydrogenase gene (Nnt). After TAC surgery, the hearts of Nnt-deficient C57BL/6 J-RKIP^−/− mice revealed diminished oxidative stress, increased left ventricular (LV) fibrosis and collagen Iα2 as well as enhanced basal nuclear expression of Nrf2. In human LV myocardium from both non-failing and failing hearts, RKIP-protein correlated negatively with the nuclear accumulation of Nrf2. In summary, under conditions of Nnt-dependent enhanced myocardial oxidative stress induced by TAC, RKIP plays a maladaptive role for fibrotic myocardial remodeling by suppressing the Nrf2-related beneficial effects.

4,6-Diaminopyrimidines as Highly Preferred Troponin I-Interacting Kinase (TNNI3K) Inhibitors

Structure-guided progression of a purine-derived series of TNNI3K inhibitors directed design efforts that produced a novel series of 4,6-diaminopyrimidine inhibitors, an emerging kinase binding motif. Herein, we report a detailed understanding of the intrinsic conformational preferences of the scaffold, which impart high specificity for TNNI3K. Further manipulation of the template based on the conformational analysis and additional structure-activity relationship studies provided enhancements in kinase selectivity and pharmacokinetics that furnished an advanced series of potent inhibitors. The optimized compounds (e.g., GSK854) are suitable leads for identifying new cardiac medicines and have been employed as in vivo tools in investigational studies aimed at defining the role of TNNI3K within heart failure.

Cardio-Oncology: mechanisms of cardiovascular toxicity

The therapeutic options available to treat a wide range of malignancies are rapidly increasing. At the same time, the population being treated is aging with more cardiovascular risk factors, comorbid conditions, and associated poor cardiac reserve. Both traditional chemotherapeutic agents (for example, anthracyclines) and newer therapies (for example, targeted tyrosine kinase inhibitors and immune checkpoint inhibitors) have demonstrated profound cardiovascular toxicities. It is important to understand the mechanisms of these toxicities to establish strategies for the prevention and management of complications—arrhythmias, heart failure, and even death. In the first of this two-part review series, we focus on what is known and hypothesized about the mechanisms of cardiovascular toxicity from anthracyclines, HER2/ErbB2 inhibitors, immune checkpoint inhibitors, and vascular endothelial growth factor inhibitors.

Analyzing ERK 1/2 signalling and targets

The ERK cascade (e.g. Raf-1) protects the heart from cell death and ischemic injury but can also turn maladaptive. Furthermore, an additional autophosphorylation of ERK2 at Thr188 (Erk1 at Thr208) allows ERK to phosphorylate nuclear targets involved in hypertrophy, stressing this additional phosphorylation as a promising pharmacological target. An in silico model was assembled and setup to reproduce different phosphorylation states of ERK 1/2 and various types of stimuli (hypertrophic versus non-hypertrophic). Synergistic and antagonistic receptor stimuli can be predicted in a semi-quantitative model, simulated time courses were experimentally validated. Furthermore, we detected new targets of ERK 1/2, which possibly contribute to the development of pathological hypertrophy. In addition we modeled further interaction partners involved in the protective and maladaptive cascade. Experimental validation included different gene expression data sets supporting key components and novel interaction partners as well as time courses in chronic heart failure.

H-Ras Isoform Mediates Protection Against Pressure Overload-Induced Cardiac Dysfunction in Part Through Activation of AKT

BACKGROUND

In general, Ras proteins are thought to promote cardiac hypertrophy, an important risk factor for cardiovascular disease and heart failure. However, the contribution of different Ras isoforms has not been investigated. The objective of this study was to define the role of H- and K-Ras in modulating stress-induced myocardial hypertrophy and failure.

METHODS AND RESULTS

We used H- and K-Ras gene knockout mice and subjected them to pressure overload to induce cardiac hypertrophy and dysfunction. We observed a worsened cardiac phenotype in Hras^-/- mice, while outcomes were improved in Kras^+/- mice. We also used a neonatal rat cardiomyocyte culture system to elucidate the mechanisms underlying these observations. Our findings demonstrate that H-Ras, but not K-Ras, promotes cardiomyocyte hypertrophy both in vivo and in vitro. This response was mediated in part through the phosphoinositide 3-kinase-AKT signaling pathway. Adeno-associated virus-mediated increase in AKT activation improved the cardiac function in pressure overloaded Hras null hearts in vivo. These findings further support engagement of the phosphoinositide 3-kinase-AKT signaling axis by H-Ras.

CONCLUSIONS

Taken together, these findings indicate that H- and K-Ras have divergent effects on cardiac hypertrophy and heart failure in response to pressure overload stress.

Raf kinase inhibitor protein: lessons of a better way for β-adrenergic receptor activation in the heart

Stimulation of β-adrenergic receptors (βARs) provides the most efficient physiological mechanism to enhance contraction and relaxation of the heart. Activation of βARs allows rapid enhancement of myocardial function in order to fuel the muscles for running and fighting in a fight-or-flight response. Likewise, βARs become activated during cardiovascular disease in an attempt to counteract the restrictions of cardiac output. However, long-term stimulation of βARs increases the likelihood of cardiac arrhythmias, adverse ventricular remodelling, decline of cardiac performance and premature death, thereby limiting the use of βAR agonists in the treatment of heart failure. Recently the endogenous Raf kinase inhibitor protein (RKIP) was found to activate βAR signalling of the heart without adverse effects. This review will summarize the current knowledge on RKIP-driven compared to receptor-mediated signalling in cardiomyocytes. Emphasis is given to the differential effects of RKIP on β1 - and β2 -ARs and their downstream targets, the regulation of myocyte calcium cycling and myofilament activity.

Cellular interplay via cytokine hierarchy causes pathological cardiac hypertrophy in RAF1-mutant Noonan syndrome

Noonan syndrome (NS) is caused by mutations in RAS/ERK pathway genes, and is characterized by craniofacial, growth, cognitive and cardiac defects. NS patients with kinase-activating RAF1 alleles typically develop pathological left ventricular hypertrophy (LVH), which is reproduced in Raf1^L613V/+ knock-in mice. Here, using inducible Raf1^L613V expression, we show that LVH results from the interplay of cardiac cell types. Cardiomyocyte Raf1^L613V enhances Ca²⁺ sensitivity and cardiac contractility without causing hypertrophy. Raf1^L613V expression in cardiomyocytes or activated fibroblasts exacerbates pressure overload-evoked fibrosis. Endothelial/endocardial (EC) Raf1^L613V causes cardiac hypertrophy without affecting contractility. Co-culture and neutralizing antibody experiments reveal a cytokine (TNF/IL6) hierarchy in Raf1^L613V-expressing ECs that drives cardiomyocyte hypertrophy in vitro. Furthermore, postnatal TNF inhibition normalizes the increased wall thickness and cardiomyocyte hypertrophy in vivo. We conclude that NS-cardiomyopathy involves cardiomyocytes, ECs and fibroblasts, TNF/IL6 signalling components represent potential therapeutic targets, and abnormal EC signalling might contribute to other forms of LVH.

The human congenital disorder Noonan Syndrome (NS) is caused by germ-line mutations that hyperactivate the RAS/ERK signalling pathway, and can feature pathologic cardiac enlargement. Here, the authors find that a complex cellular and molecular interplay involving a cytokine hierarchy underlies cardiac hypertrophy caused by a NS-associated Raf allele.

Sorafenib-Associated Heart Failure Complicated by Cardiogenic Shock after Treatment of Advanced Stage Hepatocellular Carcinoma: A Clinical Case Discussion

Background. Sorafenib, an oral tyrosine kinase inhibitor (TKI), targets multiple tyrosine kinase receptors (TKRs) involved in angiogenesis and tumor growth. Studies suggest that inhibition of TKR impacts cardiomyocyte survival. Inhibition of VEGF signaling interrupts angiogenesis and is associated with the development of hypertension and compensatory hypertrophy. Compensated hypertrophy ultimately leads to heart failure. Case Description. A 76-year-old man with a past medical history of systolic heart failure due to ischemic cardiomyopathy and stage IIIC hepatocellular carcinoma (HCC) presented with symptoms of decompensated heart failure. Four months prior to admission, he was started on sorafenib. Results. Our patient was treated with intravenous furosemide and guideline directed therapy. Clinical status was complicated by the development of low cardiac output and shock requiring inotropic support. Careful titration of heart failure medication led to hemodynamic improvement and discontinuation of dobutamine. Conclusion. Greater awareness of sorafenib cardiotoxicity is essential. As TKI usage grows for treatment of cancers, heart failure-related complications will increase. In our patient, routine heart failure management and cessation of sorafenib led to clinical improvement. Future studies on the treatment of sorafenib cardiotoxicity should be explored further in this unique patient population.

Signaling Pathways in Cardiac Myocyte Apoptosis

Cardiovascular diseases, the number 1 cause of death worldwide, are frequently associated with apoptotic death of cardiac myocytes. Since cardiomyocyte apoptosis is a highly regulated process, pharmacological intervention of apoptosis pathways may represent a promising therapeutic strategy for a number of cardiovascular diseases and disorders including myocardial infarction, ischemia/reperfusion injury, chemotherapy cardiotoxicity, and end-stage heart failure. Despite rapid growth of our knowledge in apoptosis signaling pathways, a clinically applicable treatment targeting this cellular process is currently unavailable. To help identify potential innovative directions for future research, it is necessary to have a full understanding of the apoptotic pathways currently known to be functional in cardiac myocytes. Here, we summarize recent progress in the regulation of cardiomyocyte apoptosis by multiple signaling molecules and pathways, with a focus on the involvement of these pathways in the pathogenesis of heart disease. In addition, we provide an update regarding bench to bedside translation of this knowledge and discuss unanswered questions that need further investigation.

Regulation of cardiac hypertrophy and remodeling through the dual-specificity MAPK phosphatases (DUSPs)

Mitogen-activated protein kinases (MAPKs) play a critical role in regulating cardiac hypertrophy and remodeling in response to increased workload or pathological insults. The spatiotemporal activities and inactivation of MAPKs are tightly controlled by a family of dual-specificity MAPK phosphatases (DUSPs). Over the past 2 decades, we and others have determined the critical role for selected DUSP family members in controlling MAPK activity in the heart and the ensuing effects on ventricular growth and remodeling. More specifically, studies from mice deficient for individual Dusp genes as well as heart-specific inducible transgene-mediated overexpression have implicated select DUSPs as essential signaling effectors in the heart that function by dynamically regulating the level, subcellular and temporal activities of the extracellular signal-regulated kinases (ERKs), c-Jun N-terminal kinases (JNKs) and p38 MAPKs. This review summarizes recent literature on the physiological and pathological roles of MAPK-specific DUSPs in regulating MAPK signaling in the heart and the effect on cardiac growth and remodeling.

Phosphorylating Titin's Cardiac N2B Element by ERK2 or CaMKIIδ Lowers the Single Molecule and Cardiac Muscle Force

Titin is a large filamentous protein that is responsible for the passive force of the cardiac sarcomere. Titin's force is generated by its I-band region, which includes the cardiac-specific N2B element. The N2B element consists of three immunoglobulin domains, two small unique sequence insertions, and a large 575-residue unique sequence, the N2B-Us. Posttranslational modifications of the N2B element are thought to regulate passive force, but the underlying mechanisms are unknown. Increased passive-force levels characterize diastolic stiffening in heart-failure patients, and it is critical to understand the underlying molecular mechanisms and identify therapeutic targets. Here, we used single-molecule force spectroscopy to study the mechanical effects of the kinases calcium/calmodulin-dependent protein kinase II delta (CaMKIIδ) and extracellular signal-regulated kinase 2 (ERK2) on the single-molecule mechanics of the N2B element. Both CaMKIIδ and ERK2 were found to phosphorylate the N2B element, and single-molecule force spectroscopy revealed an increase in the persistence length (Lp) of the molecule, indicating that the bending rigidity of the molecule was increased. Experiments performed under oxidizing conditions and with a recombinant N2B element that had a simplified domain composition provided evidence that the Lp increase requires the N2B-Us of the N2B element. Mechanical experiments were also performed on skinned myocardium before and after phosphorylation. The results revealed a large (∼30%) passive force reduction caused by CaMKIIδ and a much smaller (∼6%) reduction caused by ERK2. These findings support the notion that the important kinases ERK2 and CaMKIIδ can alter the passive force of myocytes in the heart (although CaMKIIδ appears to be more potent) during physiological and pathophysiological states.

Autonomous and Non-autonomous Defects Underlie Hypertrophic Cardiomyopathy in BRAF-Mutant hiPSC-Derived Cardiomyocytes

Germline mutations in BRAF cause cardio-facio-cutaneous syndrome (CFCS), whereby 40% of patients develop hypertrophic cardiomyopathy (HCM). As the role of the RAS/MAPK pathway in HCM pathogenesis is unclear, we generated a human induced pluripotent stem cell (hiPSC) model for CFCS from three patients with activating BRAF mutations. By cell sorting for SIRPα and CD90, we generated a method to examine hiPSC-derived cell type-specific phenotypes and cellular interactions underpinning HCM. BRAF-mutant SIRPα⁺/CD90⁻ cardiomyocytes displayed cellular hypertrophy, pro-hypertrophic gene expression, and intrinsic calcium-handling defects. BRAF-mutant SIRPα⁻/CD90⁺ cells, which were fibroblast-like, exhibited a pro-fibrotic phenotype and partially modulated cardiomyocyte hypertrophy through transforming growth factor β (TGFβ) paracrine signaling. Inhibition of TGFβ or RAS/MAPK signaling rescued the hypertrophic phenotype. Thus, cell autonomous and non-autonomous defects underlie HCM due to BRAF mutations. TGFβ inhibition may be a useful therapeutic option for patients with HCM due to RASopathies or other etiologies.

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Cardiomyocytes and fibroblast-like cells can be purified separately from EBs

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BRAF-mutant cardiomyocytes display hypertrophy and intrinsic Ca²⁺-handling defects

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BRAF-mutant fibroblast-like cells influence cardiomyocyte hypertrophy through TGFβ

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The hypertrophic phenotype can be rescued by TGFβ or RAS/MAPK inhibition

Selumetinib, an Oral Anti-Neoplastic Drug, May Attenuate Cardiac Hypertrophy via Targeting the ERK Pathway

Aims

Although extracellular-regulated kinases (ERK) are a well-known central mediator in cardiac hypertrophy, no clinically available ERK antagonist has been tested for preventing cardiac hypertrophy. Selumetinib is a novel oral MEK inhibitor that is currently under Phase II and Phase III clinical investigation for advanced solid tumors. In this study, we investigated whether Selumetinib could inhibit the aberrant ERK activation of the heart in response to stress as well as prevent cardiac hypertrophy.

Methods and Results

In an in vitro model of PE-induced cardiac hypertrophy, Selumetinib significantly inhibited the ERK activation and prevented enlargement of cardiomyocytes or reactivation of certain fetal genes. In the pathologic cardiac hypertrophy model of ascending aortic constriction, Selumetinib provided significant ERK inhibition in the stressed heart but not in the other organs. This selective ERK inhibition prevented left ventricular (LV) wall thickening, LV mass increase, fetal gene reactivation and cardiac fibrosis. In another distinct physiologic cardiac hypertrophy model of a swimming rat, Selumetinib provided a similar anti-hypertrophy effect, except that no significant fetal gene reactivation or cardiac fibrosis was observed.

Conclusions

Selumetinib, a novel oral anti-cancer drug with good safety records in a number of Phase II clinical trials, can inhibit ERK activity in the heart and prevent cardiac hypertrophy. These promising results indicate that Selumetinib could potentially be used to treat cardiac hypertrophy. However, this hypothesis needs to be validated in human clinical trials.

Regulator of G protein signalling 14 attenuates cardiac remodelling through the MEK-ERK1/2 signalling pathway

In the past 10 years, several publications have highlighted the role of the regulator of G protein signalling (RGS) family in multiple diseases, including cardiovascular diseases. As one of the multifunctional family members, RGS14 is involved in various biological processes, such as synaptic plasticity, cell division, and phagocytosis. However, the role of RGS14 in cardiovascular diseases remains unclear. In the present study, we used a genetic approach to examine the role of RGS14 in pathological cardiac remodelling in vivo and in vitro. We observed that RGS14 was down-regulated in human failing hearts, murine hypertrophic hearts, and isolated hypertrophic cardiomyocytes. Moreover, the extent of aortic banding-induced cardiac hypertrophy and fibrosis was exacerbated in RGS14 knockout mice, whereas RGS14 transgenic mice exhibited a significantly alleviated response to pressure overload. Furthermore, research of the underlying mechanism revealed that the RGS14-dependent rescue of cardiac remodelling was attributed to the abrogation of mitogen-activated protein kinase (MEK)–extracellular signal-regulated protein kinase (ERK) 1/2 signalling. The results showed that constitutive activation of MEK1 nullified the cardiac protection in RGS14 transgenic mice, and inhibition of MEK–ERK1/2 by U0126 reversed RGS14 deletion-related hypertrophic aggravation. These results demonstrated that RGS14 attenuated the development of cardiac remodelling through MEK–ERK1/2 signalling. RGS14 exhibited great potential as a target for the treatment of pathological cardiac remodelling.

Ubiquitin-Specific Protease 4 Is an Endogenous Negative Regulator of Pathological Cardiac Hypertrophy

Dysregulation of the ubiquitin proteasome system components ubiquitin ligases and proteasome plays an important role in the pathogenesis of cardiac hypertrophy. However, little is known about the role of another ubiquitin proteasome system component, the deubiquitinating enzymes, in cardiac hypertrophy. Here, we revealed a crucial role of ubiquitin specific protease 4 (USP4), a deubiquitinating enzyme prominently expressed in the heart, in attenuating pathological cardiac hypertrophy and dysfunction. USP4 levels were consistently decreased in human failing hearts and in murine hypertrophied hearts. Adenovirus-mediated gain- and loss-of-function approaches indicated that deficiency of endogenous USP4 promoted myocyte hypertrophy induced by angiotensin II in vitro, whereas restoration of USP4 significantly attenuated the prohypertrophic effect of angiotensin II. To corroborate the role of USP4 in vivo, we generated USP4 global knockout mice and mice with cardiac-specific overexpression of USP4. Consistent with the in vitro study, USP4 depletion exacerbated the hypertrophic phenotype and cardiac dysfunction in mice subjected to pressure overload, whereas USP4 transgenic mice presented ameliorated pathological cardiac hypertrophy compared with their control littermates. Molecular analysis revealed that USP4 deficiency augmented the activation of the transforming growth factor β–activated kinase 1 (TAK1)-(JNK1/2)/P38 signaling in response to hypertrophic stress, and blockage of TAK1 activation abolished the pathological effects of USP4 deficiency in vivo. These findings provide the first evidence for the involvement of USP4 in cardiac hypertrophy, and shed light on the therapeutic potential of targeting USP4 in the treatment of cardiac hypertrophy.

GSK114: A selective inhibitor for elucidating the biological role of TNNI3K

A series of selective TNNI3K inhibitors were developed by modifying the hinge-binding heterocycle of a previously reported dual TNNI3K/B-Raf inhibitor. The resulting quinazoline-containing compounds exhibit a large preference (up to 250-fold) for binding to TNNI3K versus B-Raf, are useful probes for elucidating the biological pathways associated with TNNI3K, and are leads for discovering novel cardiac medicines. GSK114 emerged as a leading inhibitor, displaying significant bias (40-fold) for TNNI3K over B-Raf, exceptional broad spectrum kinase selectivity, and adequate oral exposure to enable its use in cellular and in vivo studies.

Pivotal Role of Regulator of G-protein Signaling 12 in Pathological Cardiac Hypertrophy

Cardiac hypertrophy is a major predictor of heart failure and is regulated by diverse signaling pathways. As a typical multi-domain member of the regulator of G-protein signaling (RGS) family, RGS12 plays a regulatory role in various signaling pathways. However, the precise effect of RGS12 on cardiac hypertrophy remains largely unknown. In this study, we observed increased expression of RGS12 in the development of pathological cardiac hypertrophy and heart failure. We then generated genetically engineered mice and neonatal rat cardiomyocytes to investigate the effects of RGS12 during this pathological process. Four weeks after aortic banding, RGS12-deficient hearts showed decreased cardiomyocyte cross area (374.7±43.2 μm(2) versus 487.1±47.9 μm(2) in controls; P<0.05) with preserved fractional shortening (43.0±3.4% versus 28.4±2.2% in controls; P<0.05), whereas RGS12-overexpressing hearts exhibited increased cardiomyocyte cross area (582.4±46.7 μm(2) versus 474.8±40.0 μm(2) in controls; P<0.05) and reduced fractional shortening (20.8±4.1% versus 28.6±3.2% in controls; P<0.05). RGS12 also contributed to angiotensin II-induced hypertrophy in isolated cardiomyocytes. Mechanistically, our data indicated that the activation of MEK1/2-ERK1/2 signaling may be responsible for the prohypertrophic action of RGS12. In addition, the requirement of the MEK1/2-ERK1/2 signaling for RGS12-mediated cardiac hypertrophy was confirmed in rescue experiments using the MEK1/2-specific inhibitor U0126. In conclusion, our findings provide a novel diagnostic and therapeutic target for pathological cardiac hypertrophy and heart failure.

The Effect of Sorafenib, Tadalafil and Macitentan Treatments on Thyroxin-Induced Hemodynamic Changes and Cardiac Abnormalities

Multikinase inhibitors (e.g. Sorafenib), phosphodiesterase-5 inhibitors (e.g. Tadalafil), and endothelin-1 receptor blockers (e.g. Macitentan) exert influential protection in a variety of animal models of cardiomyopathy; however, their effects on thyroxin-induced cardiomyopathy have never been investigated. The goal of the present study was to assess the functional impact of these drugs on thyroxin-induced hemodynamic changes, cardiac hypertrophy and associated altered responses of the contractile myocardium both in-vivo at the whole heart level and ex-vivo at the cardiac tissue level. Control and thyroxin (500 μg/kg/day)-treated mice with or without 2-week treatments of sorafenib (10 mg/kg/day; I.P), tadalafil (1 mg/kg/day; I.P or 4 mg/kg/day; oral), macitentan (30 and 100 mg/kg/day; oral), and their vehicles were studied. Blood pressure, echocardiography and electrocardiogram were non-invasively evaluated, followed by ex-vivo assessments of isolated multicellular cardiac preparations. Thyroxin increased blood pressure, resulted in cardiac hypertrophy and left ventricular dysfunction in-vivo. Also, it caused contractile abnormalities in right ventricular papillary muscles ex-vivo. None of the drug treatments were able to significantly attenuate theses hemodynamic changes or cardiac abnormalities in thyroxin-treated mice. We show here for the first time that multikinase (raf1/b, VEGFR, PDGFR), phosphodiesterase-5, and endothelin-1 pathways have no major role in thyroxin-induced hemodynamic changes and cardiac abnormalities. In particular, our data show that the involvement of endothelin-1 pathway in thyroxine-induced cardiac hypertrophy/dysfunction seems to be model-dependent and should be carefully interpreted.