Extracellular signal-regulated kinase (ERK) activation preserves cardiac function in pressure overload induced hypertrophy

Time-dependent effects of BRAF-V600E on cell cycling, metabolism, and function in engineered myocardium

Candidate cardiomyocyte (CM) mitogens such as those affecting the extracellular signal-regulated kinase (ERK) signaling pathway represent potential targets for functional heart regeneration. We explored whether activating ERK via a constitutively active mutant of B-raf proto-oncogene (BRAF), BRAF-V600E (caBRAF), can induce proproliferative effects in neonatal rat engineered cardiac tissues (ECTs). Sustained CM-specific caBRAF expression induced chronic ERK activation, substantial tissue growth, deficit in sarcomeres and contractile function, and tissue stiffening, all of which persisted for at least 4 weeks of culture. caBRAF-expressing CMs in ECTs exhibited broad transcriptomic changes, shift to glycolytic metabolism, loss of connexin-43, and a promigratory phenotype. Transient, doxycycline-controlled caBRAF expression revealed that the induction of CM cycling is rapid and precedes functional decline, and the effects are reversible only with short-lived ERK activation. Together, direct activation of the BRAF kinase is sufficient to modulate CM cycling and functional phenotype, offering mechanistic insights into roles of ERK signaling in the context of cardiac development and regeneration.

RNA binding protein IGF2BP2 expression is induced by stress in the heart and mediates dilated cardiomyopathy

The IGF2BP family of RNA binding proteins consists of three paralogs that regulate intracellular RNA localization, RNA stability, and translational control. Although IGF2BP1 and 3 are oncofetal proteins, IGF2BP2 expression is maintained in many tissues, including the heart, into adulthood. IGF2BP2 is upregulated in cardiomyocytes during cardiac stress and remodeling and returns to normal levels in recovering hearts. We wondered whether IGF2BP2 might play an adaptive role during cardiac stress and recovery. Enhanced expression of an IGF2BP2 transgene in a conditional, inducible mouse line leads to dilated cardiomyopathy (DCM) and death within 3-4 weeks in newborn or adult hearts. Downregulation of the transgene after 2 weeks, however, rescues these mice, with complete recovery by 12 weeks. Hearts overexpressing IGF2BP2 downregulate sarcomeric and mitochondrial proteins and have fragmented mitochondria and elongated, thinner sarcomeres. IGF2BP2 is also upregulated in DCM or myocardial infarction patients. These results suggest that IGF2BP2 may be an attractive target for therapeutic intervention in cardiomyopathies.

A conserved arginine within the αC-helix of Erk1/2 is a latch of autoactivation and of oncogenic capabilities

Eukaryotic protein kinases (EPKs) adopt an active conformation following phosphorylation of a particular activation loop residue. Most EPKs spontaneously autophosphorylate this residue. While structure-function relationships of the active conformation are essentially understood, those of the "prone-to-autophosphorylate" conformation are unclear. Here, we propose that a site within the αC-helix of EPKs, occupied by Arg in the mitogen-activated protein kinase (MAPK) Erk1/2 (Arg84/65), impacts spontaneous autophosphorylation. MAPKs lack spontaneous autoactivation, but we found that converting Arg84/65 of Erk1/2 to various residues enables spontaneous autophosphorylation. Furthermore, Erk1 molecules mutated in Arg84 are oncogenic. Arg84/65 thus obstructs the adoption of the "prone-to-autophosphorylate" conformation. All MAPKs harbor an Arg that is equivalent to Arg84/65 of Erks, whereas Arg is rarely found at the equivalent position in other EPKs. We observed that Arg84/65 of Erk1/2 interacts with the DFG motif, suggesting that autophosphorylation may be inhibited by the Arg84/65-DFG interactions. Erk1/2s mutated in Arg84/65 autophosphorylate not only the TEY motif, known as critical for catalysis, but also on Thr207/188. Our MS/MS analysis revealed that a large proportion of the Erk2R65H population is phosphorylated on Thr188 or on Tyr185 + Thr188, and a small fraction is phosphorylated on the TEY motif. No molecules phosphorylated on Thr183 + Thr188 were detected. Thus, phosphorylation of Thr183 and Thr188 is mutually exclusive suggesting that not only TEY-phosphorylated molecules are active but perhaps also those phosphorylated on Tyr185 + Thr188. The effect of mutating Arg84/65 may mimic a physiological scenario in which allosteric effectors cause Erk1/2 activation by autophosphorylation.

The Role of Extracellular Signal-Regulated Kinase Pathways in Different Models of Cardiac Hypertrophy in Rats

Cardiac hypertrophy develops following different triggers of pressure or volume overload. In several previous studies, different hypertrophy types were demonstrated following alterations in extracellular signal-regulated kinase (ERK) pathway activation. In the current study, we studied two types of cardiac hypertrophy models in rats: eccentric and concentric hypertrophy. For the eccentric hypertrophy model, iron deficiency anemia caused by a low-iron diet was implemented, while surgical aortic constriction was used to induce aortic stenosis (AS) and concentric cardiac hypertrophy. The hearts were evaluated using echocardiography, histological sections, and scanning electron microscopy. The expression of ERK1/2 was analyzed using Western blot. During the study period, anemic rats developed eccentric hypertrophy characterized by an enlarged left ventricle (LV) cavity cross-sectional area (CSA) (59.9 ± 5.1 mm2 vs. 47 ± 8.1 mm2, p = 0.002), thinner septum (2.1 ± 0.3 mm vs. 2.5 ± 0.2 mm, p < 0.05), and reduced left ventricular ejection fraction (LVEF) (52.6% + 4.7 vs. 60.3% + 2.8, p < 0.05). Rats with AS developed concentric hypertrophy with a thicker septum (2.8 ± 0.6 vs. 2.4 ± 0.1 p < 0.05), increased LV muscle cross-sectional area (79.5 ± 9.33 mm2 vs. 57.9 ± 5.0 mm2, p < 0.001), and increased LVEF (70.3% + 2.8 vs. 60.0% + 2.1, p < 0.05). ERK1/2 expression decreased in the anemic rats and increased in the rats with AS. Nevertheless, the p-ERK and the p-MEK did not change significantly in all the examined models. We concluded that ERK1/2 expression was altered by the type of hypertrophy and the change in LVEF.

Internalized β2-Adrenergic Receptors Inhibit Subcellular Phospholipase C-Dependent Cardiac Hypertrophic Signaling

Chronically elevated neurohumoral drive, and particularly elevated adrenergic tone leading to β-adrenergic receptor (β-AR) overstimulation in cardiac myocytes, is a key mechanism involved in the progression of heart failure. β1-AR and β2-ARs are the two major subtypes of β-ARs present in the human heart, however, they elicit different or even opposite effects on cardiac function and hypertrophy. For example, chronic activation of β1ARs drives detrimental cardiac remodeling while β2AR signaling is protective. The underlying molecular mechanisms for cardiac protection through β2ARs remain unclear. Here we show that β2-AR protects against hypertrophy through inhibition of PLCε signaling at the Golgi apparatus. The mechanism for β2AR-mediated PLC inhibition requires internalization of β2AR, activation of Gi and Gβγ subunit signaling at endosomes and ERK activation. This pathway inhibits both angiotensin II and Golgi-β1-AR-mediated stimulation of phosphoinositide hydrolysis at the Golgi apparatus ultimately resulting in decreased PKD and HDAC5 phosphorylation and protection against cardiac hypertrophy. This reveals a mechanism for β2-AR antagonism of the PLCε pathway that may contribute to the known protective effects of β2-AR signaling on the development of heart failure.

Inhibition of Eicosanoid Degradation Mitigates Fibrosis of the Heart

BACKGROUND

Organ fibrosis due to excessive production of extracellular matrix by resident fibroblasts is estimated to contribute to >45% of deaths in the Western world, including those due to cardiovascular diseases such as heart failure. Here, we screened for small molecule inhibitors with a common ability to suppress activation of fibroblasts across organ systems.

METHODS

High-content imaging of cultured cardiac, pulmonary, and renal fibroblasts was used to identify nontoxic compounds that blocked induction of markers of activation in response to the profibrotic stimulus, transforming growth factor-β1. SW033291, which inhibits the eicosanoid-degrading enzyme, 15-hydroxyprostaglandin dehydrogenase, was chosen for follow-up studies with cultured adult rat ventricular fibroblasts and human cardiac fibroblasts (CF), and for evaluation in mouse models of cardiac fibrosis and diastolic dysfunction. Additional mechanistic studies were performed with CFs treated with exogenous eicosanoids.

RESULTS

Nine compounds, including SW033291, shared a common ability to suppress transforming growth factor-β1-mediated activation of cardiac, pulmonary, and renal fibroblasts. SW033291 dose-dependently inhibited transforming growth factor-β1-induced expression of activation markers (eg, α-smooth muscle actin and periostin) in adult rat ventricular fibroblasts and normal human CFs, and reduced contractile capacity of the cells. Remarkably, the 15-hydroxyprostaglandin dehydrogenase inhibitor also reversed constitutive activation of fibroblasts obtained from explanted hearts from patients with heart failure. SW033291 blocked cardiac fibrosis induced by angiotensin II infusion and ameliorated diastolic dysfunction in an alternative model of systemic hypertension driven by combined uninephrectomy and deoxycorticosterone acetate administration. Mechanistically, SW033291-mediated stimulation of extracellular signal-regulated kinase 1/2 mitogen-activated protein kinase signaling was required for the compound to block CF activation. Of the 12 exogenous eicosanoids that were tested, only 12(S)-hydroxyeicosatetraenoic acid, which signals through the G protein-coupled receptor, GPR31, recapitulated the suppressive effects of SW033291 on CF activation.

CONCLUSIONS

Inhibition of degradation of eicosanoids, arachidonic acid-derived fatty acids that signal through G protein-coupled receptors, is a potential therapeutic strategy for suppression of pathological organ fibrosis. In the heart, we propose that 15-hydroxyprostaglandin dehydrogenase inhibition triggers CF-derived autocrine/paracrine signaling by eicosanoids, including 12(S)-hydroxyeicosatetraenoic acid, to stimulate extracellular signal-regulated kinase 1/2 and block conversion of fibroblasts into activated cells that secrete excessive amounts of extracellular matrix and contribute to heart failure pathogenesis.

Pentraxin 3 regulates tyrosine kinase inhibitor-associated cardiomyocyte contraction and mitochondrial dysfunction via ERK/JNK signalling pathways

BACKGROUND

Hepatocellular carcinoma (HCC) patients suffer varying degrees of heart dysfunction after tyrosine kinase inhibitor (TKI) treatment. Interestingly, HCC patients often have higher levels of pentraxin 3 (PTX3), and PTX3 inhibition was found to improve left ventricular dysfunction in animal models.

OBJECTIVES

We sought to assess the therapeutic potential of PTX3 inhibition on TKI-associated cardiotoxicity.

METHODS

We used a human embryonic stem cell line, RUES2, to generate cardiomyocyte cultures (RUES2-CM) for functional testing. We also assessed heart function and PTX3 expression levels in 16 HCC patients who received TKI treatment, 3 HCC patients who did not receive TKIs, and 7 healthy volunteers.

RESULTS

Significantly higher PTX3 expression was noted in HCC patients with TKI treatment versus those without, and 38% of male and 33% of female patients had QTc prolongation after TKI treatment. Treatment of cardiomyocyte cultures with sorafenib also increased PTX3 expression and induced cytoskeletal remodelling, contraction reduction, sodium current inhibition, and mitochondrial respiratory dysfunction. PTX3 colocalised with CD44 in cardiomyocytes, and cardiomyocyte contraction, mitochondrial respiratory function, and regular cytoskeletal and apoptotic protein expression were restored with PTX3 inhibition. CD44 knockdown confirmed PTX3/CD44 signalling. These results suggest a possible mechanism in which sorafenib treatment increases PTX3 expression, thereby resulting in reduced extracellular signal-regulated kinase (ERK) 1/2 expression that affects cardiomyocyte contraction, while also activating c-Jun N-terminal kinase (JNK) downstream pathways to disrupt mitochondrial respiration and trigger apoptosis.

CONCLUSIONS

TKI-induced cardiotoxicity may be partly mediated by the upregulation of PTX3, and thus PTX3 inhibition has potential as a therapeutic strategy.

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.

In-Silico and In-Vitro Analysis of Human SOS1 Protein Causing Noonan Syndrome - A Novel Approach to Explore the Molecular Pathways

Aims

Perform in-silico analysis of human SOS1 mutations to elucidate their pathogenic role in Noonan syndrome (NS).

Background

NS is an autosomal dominant genetic disorder caused by single nucleotide mutation in PTPN11, SOS1, RAF1, and KRAS genes. NS is thought to affect approximately 1 in 1000. NS patients suffer different pathogenic effects depending on the mutations they carry. Analysis of the mutations would be a promising predictor in identifying the pathogenic effect of NS.

Methods

We performed computational analysis of the SOS1 gene to identify the pathogenic nonsynonymous single nucleotide polymorphisms (nsSNPs) th a t cause NS. SOS1 variants were retrieved from the SNP database (dbSNP) and analyzed by in-silico tools I-Mutant, iPTREESTAB, and MutPred to elucidate their structural and functional characteristics.

Results

We found that 11 nsSNPs of SOS1 that were linked to NS. 3D modeling of the wild-type and the 11 nsSNPs of SOS1 showed that SOS1 interacts with cardiac proteins GATA4, TNNT2, and ACTN2. We also found that GRB2 and HRAS act as intermediate molecules between SOS1 and cardiac proteins. Our in-silico analysis findings were further validated using induced cardiomyocytes (iCMCs) derived from NS patients carrying SOS1 gene variant c.1654A>G (NSiCMCs) and compared to control human skin fibroblast-derived iCMCs (C-iCMCs). Our in vitro data confirmed that the SOS1, GRB2 and HRAS gene expressions as well as the activated ERK protein, were significantly decreased in NS-iCMCs when compared to C-iCMCs.

Conclusion

This is the first in-silico and in vitro study demonstrating that 11 nsSNPs of SOS1 play deleterious pathogenic roles in causing NS.

Dual specific phosphatases (DUSPs) in cardiac hypertrophy and failure

Pressure overload and other stress stimuli elicit a host of adaptive and maladaptive signaling cascades that eventually lead to cardiac hypertrophy and heart failure. Among those, the mitogen-activated protein kinase (MAPK) signaling pathway has been shown to play a prominent role. The dual specificity phosphatases (DUSPs), also known as MAPK specific phosphatases (MKPs), that can dephosphorylate the MAPKs and inactivate them are gaining increasing attention as potential drug targets. Here we try to review recent advancements in understanding the roles of the different DUSPs, and the pathways that they regulate in cardiac remodeling. We focus on the regulation of three main MAPK branches - the p38 kinases, the c-Jun-N-terminal kinases (JNKs) and the extracellular signal-regulated kinases (ERK) by various DUSPs and try to examine their roles.

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.

Inorganic arsenic induces sex-dependent pathological hypertrophy in the heart

Arsenic exposure though drinking water is widespread and well associated with adverse cardiovascular outcomes, yet the pathophysiological mechanisms by which iAS induces these effects are largely unknown. Recently, an epidemiological study in an American population with a low burden of cardiovascular risk factors found that iAS exposure was associated with altered left ventricular geometry. Considering the possibility that iAS directly induces cardiac remodeling independently of hypertension, we investigated the impact of an environmentally relevant iAS exposure on the structure and function of male and female hearts. Adult male and female C56BL/6J mice were exposed to 615 μg/L iAS for 8 wk. Males exhibited increased systolic blood pressure via tail cuff photoplethysmography, left ventricular wall thickening via transthoracic echocardiography, and increased plasma atrial natriuretic peptide via enzyme immunoassay. RT-qPCR revealed increased myocardial RNA transcripts of Acta1, Myh7, and Nppa and decreased Myh6, providing evidence of pathological hypertrophy in the male heart. Similar changes were not detected in females, and nitric oxide-dependent mechanisms of cardioprotection in the heart appeared to remain intact. Further investigation found that Rcan1 was upregulated in male hearts and that iAS activated NFAT in HEK-293 cells via luciferase assay. Interestingly, iAS induced similar hypertrophic gene expression changes in neonatal rat ventricular myocytes, which were blocked by calcineurin inhibition, suggesting that iAS may induce pathological cardiac hypertrophy in part by targeting the calcineurin-NFAT pathway. As such, these results highlight iAS exposure as an independent cardiovascular risk factor and provide biological impetus for its removal from human consumption.NEW & NOTEWORTHY This investigation provides the first mechanistic link between an environmentally relevant dose of inorganic arsenic (iAS) and pathological hypertrophy in the heart. By demonstrating that iAS exposure may cause pathological cardiac hypertrophy not only by increasing systolic blood pressure but also by potentially activating calcineurin-nuclear factor of activated T cells and inducing fetal gene expression, these results provide novel mechanistic insight into the theat of iAS exposure to the heart, which is necessary to identify targets for medical and public health intervention.

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.

Cardiac Effects of Treadmill Running at Different Intensities in a Rat Model

Purpose: In this study, we investigated the effect of treadmill exercise training on cardiac hypertrophy, collagen deposition, echo parameters and serum levels of cardiac troponin I (cTnI) in rats, and how they differ with various exercise intensities, hence exploring potential signal transduction. Methods: Male Sprague-Dawley rats were randomly divided into sedentary (SED), low-intensity running (LIR), medium-intensity running (MIR), and high-intensity running (HIR) groups. Each exercise group had 3 subgroups that were sacrificed for cardiac tissue analyses at 1, 4, and 8 weeks, respectively, and all rats participated in a daily 1 h treadmill routine 5 days per week. Echocardiographic measurements were performed 24 h after the last exercise session. Additionally, myocardium samples and blood were collected for histological and biochemical examinations. Changes in the extracellular signal-regulated kinases 1/2 (ERK1/2) signal pathway were detected by Western blotting. Results: After a week of running, ventricular myocyte size and the phosphorylation of ERK1/2 increased in the HIR group, while left ventricular (LV) diastolic diameter values and LV relative wall thickness increased in the LIR and MIR groups. In addition, we observed heart enlargement, cTnI decrease, and ERK1/2 signal activation in each of the exercise groups after 4 weeks of running. However, the HIR group displayed substantial rupture and increased fibrosis in myocardial tissue. In addition, compared with the LIR and MIR groups, 8 weeks of HIR resulted in structural damage, fiber deposition, and increased cTnI. However, there was no difference in the activation of ERK1/2 signaling between the exercise and SED groups. Conclusion: The effect of running on cardiac hypertrophy was intensity dependent. In contrast to LIR and MIR, the cardiac hypertrophy induced by 8 weeks of HIR was characterized by potential cardiomyocyte injury, which increased the risk of pathological development. Furthermore, the ERK signaling pathway was mainly involved in the compensatory hypertrophy process of the myocardium in the early stage of exercise and was positively correlated with exercise load. However, long-term exercise may attenuate ERK signaling activation.

C-C chemokine receptor 5 signaling contributes to cardiac remodeling and dysfunction under pressure overload

Aortic stenosis (AS) leads to chronic pressure overload, cardiac remodeling and eventually heart failure. Chemokines and their receptors have been implicated in pressure overload‑induced cardiac remodeling and dysfunction. In the present study, the role of C‑C chemokine receptor 5 (CCR5) in pressure overload‑induced cardiac remodeling and dysfunction was investigated in mice subjected to transverse aortic constriction (TAC). Cardiac levels of CCR5 and C‑C motif chemokine ligands (CCLs)3, 4 and 5 were determined by western blotting and reverse transcription‑quantitative PCR, respectively. Cardiac functional parameters were evaluated by echocardiographic and hemodynamic measurements. Myocardial fibrosis was assessed by Masson's trichrome staining and α‑smooth muscle actin immunostaining. Myocardial hypertrophy and inflammatory cell infiltration were evaluated by hematoxylin and eosin staining. Angiotensin II (Ang II)‑induced hypertrophy of H9c2 cardiomyocytes was assessed by F‑actin immunostaining. ERK1/2 and P38 phosphorylation was examined by western blotting. TAC mice exhibited higher myocardial CCL3, CCL4, CCL5 and CCR5 levels compared with sham mice. Compared with sham mice, TAC mice also exhibited impaired cardiac function along with myocardial hypertrophy, fibrosis and inflammatory cell infiltration. TAC‑induced cardiac remodeling and dysfunction were effectively ameliorated by administration of anti‑CCR5 but not by IgG control antibody. Mechanistically, increased ERK1/2 and P38 phosphorylation was detected in TAC hearts and Ang II‑stimulated H9c2 cardiomyocytes. Treatment with anti‑CCR5 antibody decreased ERK1/2 and P38 phosphorylation and attenuated Ang II‑induced H9c2 cell hypertrophy. CCR5 inhibition protected against pressure overload‑induced cardiac abnormality. The findings of the present study indicate that ERK1/2 and P38 signaling pathways may be involved in the cardioprotective effects of CCR5 inhibition.

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.

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.

Exploratory Analysis of Circulating miRNA Signatures in Atrial Fibrillation Patients Determining Potential Biomarkers to Support Decision-Making in Anticoagulation and Catheter Ablation

Novel biomarkers are desired to improve risk management for patients with atrial fibrillation (AF). We measured 179 plasma miRNAs in 83 AF patients using multiplex qRT-PCR. Plasma levels of eight (i.e., hsa-miR-22-3p, hsa-miR-128-3p, hsa-miR-130a-3p, hsa-miR-140-5p, hsa-miR-143-3p, hsa-miR-148b-3p, hsa-miR-497-5p, hsa-miR-652-3p) and three (i.e., hsa-miR-144-5p, hsa-miR-192-5p, hsa-miR-194-5p) miRNAs showed positive and negative correlations with CHA₂DS₂-VASc scores, respectively, which also showed negative and positive correlations with catheter ablation (CA) procedure, respectively, within the follow-up observation period up to 6-month after enrollment. These 11 miRNAs were functionally associated with TGF-β signaling and androgen signaling based on pathway enrichment analysis. Seven of possible target genes of these miRNAs, namely TGFBR1, PDGFRA, ZEB1, IGFR1, BCL2, MAPK1 and DICER1 were found to be modulated by more than four miRNAs of the eleven. Of them, TGFBR1, PDGFRA, ZEB1 and BCL2 are reported to exert pro-fibrotic functions, suggesting that dysregulations of these eleven miRNAs may reflect pro-fibrotic condition in the high-risk patients. Although highly speculative, these miRNAs may potentially serve as potential biomarkers, providing mechanistic and quantitative information for pathophysiology in daily clinical practice with AF such as possible pro-fibrotic state in left atrium, which would enhance the risk of stroke and reduce the preference for performing CA.

YQWY decoction reverses cardiac hypertrophy induced by TAC through inhibiting GATA4 phosphorylation and MAPKs

To investigate the effect of Yiqi Wenyang (YQWY) decoction on reversing cardiac hypertrophy induced by the transverse aortic constriction (TAC). Wistar rats aged 7-8 weeks were subjected to TAC surgery and then randomly divided into 4 groups (n = 5/group): Sham group, TAC group, low-dose group and high dose group. After 16-week intragastric administration of YQWY decoction, the effect of YQWY decoction on alleviating cardiomyocyte hypertrophy was examined by transthoracic echocardiography (TTE), hematoxylin/eosin (HE), wheat germ agglutinin (WGA) staining, enzyme linked immunosorbent assay (ELISA), Western blot (WB), immunohistochemistry (IHC) and immunofluorescence (IF), respectively. The results showed significant differences in left ventricle volume-diastole/systole (LV Vol d/s), N-terminal pro-B-type brain natriuretic peptide (NT-proBNP) (P < 0.01), Ejection Fraction (EF), LV mass and fractional shortening (FS) (P < 0.05) between YQWY-treated group and TAC group. HE and WGA staining showed that treatment with YQWY decoction dramatically prevented TAC-induced cardiomycyte hypertrophy. Moreover, the results of WB, IHC and IF indicated that administration of YQWY could suppress the expressions of cardiac hypertrophic markers, which included the atrial natriuretic peptide (ANP), BNP and myosin heavy chain 7 (MYH7) (P < 0.05) and inhibit phosphorylation of GATA binding protein 4 (P-GATA4) (P < 0.05), phosphorylation of extracellular signal-regulated kinase (P-ERK) (P < 0.05), phosphorylation of P38 mitogen activated protein kinase (P-P38) (P < 0.05) and phosphorylation of c-Jun N-terminal kinase (P-JNK) (P < 0.05). Thus, we concluded that YQWY decoction suppressed cardiomyocyte hypertrophy and reversed the impaired heart function, and the curative effects of YQWY decoction were associated with the decreased phosphorylation of GATA4 and mitogen activated protein kinases (MAPKs), as well as the reduced expression of the downstream targets of GATA4, including ANP, BNP, and MYH7.

Mutations That Confer Drug-Resistance, Oncogenicity and Intrinsic Activity on the ERK MAP Kinases-Current State of the Art

Unique characteristics distinguish extracellular signal-regulated kinases (Erks) from other eukaryotic protein kinases (ePKs). Unlike most ePKs, Erks do not autoactivate and they manifest no basal activity; they become catalysts only when dually phosphorylated on neighboring Thr and Tyr residues and they possess unique structural motifs. Erks function as the sole targets of the receptor tyrosine kinases (RTKs)-Ras-Raf-MEK signaling cascade, which controls numerous physiological processes and is mutated in most cancers. Erks are therefore the executers of the pathway’s biology and pathology. As oncogenic mutations have not been identified in Erks themselves, combined with the tight regulation of their activity, Erks have been considered immune against mutations that would render them intrinsically active. Nevertheless, several such mutations have been generated on the basis of structure-function analysis, understanding of ePK evolution and, mostly, via genetic screens in lower eukaryotes. One of the mutations conferred oncogenic properties on Erk1. The number of interesting mutations in Erks has dramatically increased following the development of Erk-specific pharmacological inhibitors and identification of mutations that cause resistance to these compounds. Several mutations have been recently identified in cancer patients. Here we summarize the mutations identified in Erks so far, describe their properties and discuss their possible mechanism of action.

An Activating Mutation in ERK Causes Hyperplastic Tumors in a scribble Mutant Tissue in Drosophila

Receptor tyrosine kinase signaling plays prominent roles in tumorigenesis, and activating oncogenic point mutations in the core pathway components Ras, Raf, or MEK are prevalent in many types of cancer. Intriguingly, however, analogous oncogenic mutations in the downstream effector kinase ERK have not been described or validated in vivo To determine if a point mutation could render ERK intrinsically active and oncogenic, we have assayed in Drosophila the effects of a mutation that confers constitutive activity upon a yeast ERK ortholog and has also been identified in a few human tumors. Our analyses indicate that a fly ERK ortholog harboring this mutation alone (RolledR80S), and more so in conjunction with the known sevenmaker mutation (RolledR80S+D334N), suppresses multiple phenotypes caused by loss of Ras-Raf-MEK pathway activity, consistent with an intrinsic activity that is independent of upstream signaling. Moreover, expression of RolledR80S and RolledR80S+D334N induces tissue overgrowth in an established Drosophila cancer model. Our findings thus demonstrate that activating mutations can bestow ERK with pro-proliferative, tumorigenic capabilities and suggest that Drosophila represents an effective experimental system for determining the oncogenicity of ERK mutants and their response to therapy.

Isorhynchophylline enhances Nrf2 and inhibits MAPK pathway in cardiac hypertrophy

Isorhynchophylline (IRN) is one of the major tetracyclic oxindole alkaloids found in Uncaria rhynchophylla. Studies have found that IRN has diverse biological activities including antioxidant, anti-apoptosis, and neuroprotection. However, little is known about the effect of IRN on the development of cardiac hypertrophy. In this study, we investigated the change of the cell surface area and nascent protein synthesis of cultured H9c2 cardiomyocytes on exposure to phenylephrine (PE) plus IRN, and thus confirmed that IRN ameliorated cardiomyocyte hypertrophy induced by PE in vitro. Meanwhile, it turns out that IRN is also effective in neonatal rat ventricular myocytes (NRVMs) stimulated with angiotensin II (AngII). We also showed that IRN prevented cardiac dysfunction in mice with pressure overload due to transverse aortic constriction (TAC) and attenuated cardiac hypertrophy and fibrosis. IRN treatment improved the cardiac function assessed by echocardiographic parameters fractional shortening (FS) as well as suppressed the cardiac hypertrophy phenotypes, such as the increasing of ventricular mass/body weight and myocyte cross-sectional area. RT-PCR analysis showed that IRN treatment also alleviated the expression of fetal genes of ANP, BNP, Myh7, and the correlated fibrosis genes including TGF-β1, collagen I, collagen III, and CTGF in vivo. Meanwhile, IRN had anti-oxidative effects on cardiac remodeling with suppressed 4-HNE and MDA. Western blot analysis showed that the Nrf2 nuclear translocation and MAPK pathway were involved in the potential mechanisms of IRN on cardiac hypertrophy inhibition. The results of our study provide further evidence that IRN is a promising drug for the treatment of cardiac hypertrophy.

How to Steer and Control ERK and the ERK Signaling Cascade Exemplified by Looking at Cardiac Insufficiency

Mathematical optimization framework allows the identification of certain nodes within a signaling network. In this work, we analyzed the complex extracellular-signal-regulated kinase 1 and 2 (ERK1/2) cascade in cardiomyocytes using the framework to find efficient adjustment screws for this cascade that is important for cardiomyocyte survival and maladaptive heart muscle growth. We modeled optimal pharmacological intervention points that are beneficial for the heart, but avoid the occurrence of a maladaptive ERK1/2 modification, the autophosphorylation of ERK at threonine 188 (ERK Thr 188 phosphorylation), which causes cardiac hypertrophy. For this purpose, a network of a cardiomyocyte that was fitted to experimental data was equipped with external stimuli that model the pharmacological intervention points. Specifically, two situations were considered. In the first one, the cardiomyocyte was driven to a desired expression level with different treatment strategies. These strategies were quantified with respect to beneficial effects and maleficent side effects and then which one is the best treatment strategy was evaluated. In the second situation, it was shown how to model constitutively activated pathways and how to identify drug targets to obtain a desired activity level that is associated with a healthy state and in contrast to the maleficent expression pattern caused by the constitutively activated pathway. An implementation of the algorithms used for the calculations is also presented in this paper, which simplifies the application of the presented framework for drug targeting, optimal drug combinations and the systematic and automatic search for pharmacological intervention points. The codes were designed such that they can be combined with any mathematical model given by ordinary differential equations.

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.

Dapagliflozin Attenuates Cardiac Remodeling in Mice Model of Cardiac Pressure Overload

BACKGROUND

Dapagliflozin (DAPA) is an inhibitor of sodium-glucose cotransporter 2 prescribed for type 2 diabetes mellitus. DAPA plays a protective role against cardiovascular diseases. Nevertheless, the effect and mechanism of DAPA on pressure-overload-induced cardiac remodeling has not been determined.

METHODS

We used a transverse aortic constriction (TAC) induced cardiac remodeling model to evaluate the effect of DAPA. Twenty-four C57BL/6J mice were divided into 3 groups: Sham, TAC, and TAC + DAPA groups (n = 8, each). DAPA was administered by gavage (1.0 mg/kg/day) for 4 weeks in the TAC + DAPA group, and then the myocardial hypertrophy, cardiac systolic function, myocardial fibrosis, and cardiomyocyte apoptosis were evaluated.

RESULTS

Mice in TAC group showed increased heart weight/body weight, left ventricular (LV) diameter, LV posterior wall thickness, and decreased LV ejection fraction and LV fractional shortening. The collagen volume fraction and perivascular collagen area/luminal area ratio were significantly greater in the TAC group; the TUNEL-positive cell number and PARP level were also increased. We found that DAPA treatment reduced myocardial hypertrophy, myocardial interstitial and perivascular fibrosis, and cardiomyocyte apoptosis. Furthermore, DAPA administration inhibited phosphorylation of P38 and JNK in TAC group. In addition, the inhibited phosphorylation of FoxO1 in the TAC mice was upregulated by DAPA administration.

CONCLUSION

DAPA administration had a cardioprotective effect by improving cardiac systolic function, inhibiting myocardial fibrosis and cardiomyocyte apoptosis in a TAC mouse model, indicating that it could serve as a new therapy to prevent pathological cardiac remodeling in nondiabetics.