Targeted deletion of ERK2 in cardiomyocytes attenuates hypertrophic response but provokes pathological stress induced cardiac dysfunction

Tanshinol alleviates ischemia-induced myocardial fibrosis via targeting ERK2 and disturbing the intermolecular autophosphorylation of ERK2Thr188

Myocardial fibrosis is the fundamental remodeling process in myocardial ischemia (MI) and also the major contributor of heart failure and death. Tanshinol (Danshensu in Chinese, DSS), a major ingredient of salvia mitiorrhiza Bunge (Lamiaceae) root, exerted significant cardio protection effects. In this study, we aimed to identify the action target and then uncover the mechanism of DSS alleviating myocardial fibrosis. The pharmacological activities of DSS protecting ischemic cardiac was assessed and the myocardial proteomics was carried out. To identify the target of DSS, a cellular thermal shift assay combined with LC-MS identification was conducted. Surface plasmon resonance assay, molecular dynamics simulation and pharmacological and molecular biology approaches were adopted to explore the action mechanisms of DSS. Our results revealed that DSS effectively alleviated MI-induced left ventricle dysfunctions and the increasements of circulating myocardial markers. Besides, DSS significantly reversed the proteomic profile related to myocardial fibrotic processes and the ERK2 was identified as a crucial cellular target of DSS. DSS abated the temperature-dependent denaturation of ERK2 in a dose-dependent manner and the KD value of DSS and ERK2 was 60.19 μM. After Ang II stimulation, DSS suppressed the phosphorylation of Thr188 rather than the classic residues in TEY motif. DSS interfered the ERK2 homo-dimerization and then blocked the intermolecular autophosphorylation at Thr188 site. Thereout, DSS inhibited the nuclear translocation of ERK2 and the expression of downstream fibrotic biomolecules. Collectively, our results demonstrated that DSS targeted ERK2 and suppressed the intermolecular autophosphorylation at Thr188 residue, thus protecting ischemic myocardia from fibrosis remodeling.

MSK-Mediated Phosphorylation of Histone H3 Ser28 Couples MAPK Signalling with Early Gene Induction and Cardiac Hypertrophy

Heart failure is a leading cause of death that develops subsequent to deleterious hypertrophic cardiac remodelling. MAPK pathways play a key role in coordinating the induction of gene expression during hypertrophy. Induction of the immediate early gene (IEG) response including activator protein 1 (AP-1) complex factors is a necessary and early event in this process. How MAPK and IEG expression are coupled during cardiac hypertrophy is not resolved. Here, in vitro, in rodent models and in human samples, we demonstrate that MAPK-stimulated IEG induction depends on the mitogen and stress-activated protein kinase (MSK) and its phosphorylation of histone H3 at serine 28 (pH3S28). pH3S28 in IEG promoters in turn recruits Brg1, a BAF60 ATP-dependent chromatin remodelling complex component, initiating gene expression. Without MSK activity and IEG induction, the hypertrophic response is suppressed. These studies provide new mechanistic insights into the role of MAPK pathways in signalling to the epigenome and regulation of gene expression during cardiac hypertrophy.

Inhibition of mTOR or MAPK ameliorates vmhcl/myh7 cardiomyopathy in zebrafish

Myosin heavy chain 7 (MYH7) is a major causative gene for hypertrophic cardiomyopathy, but the affected signaling pathways and therapeutics remain elusive. In this research, we identified ventricle myosin heavy chain like (vmhcl) as a zebrafish homolog of human MYH7, and we generated vmhcl frameshift mutants. We noted vmhcl-based embryonic cardiac dysfunction (VEC) in the vmhcl homozygous mutants and vmhcl-based adult cardiomyopathy (VAC) phenotypes in the vmhcl heterozygous mutants. Using the VEC model, we assessed 7 known cardiomyopathy signaling pathways pharmacologically and 11 candidate genes genetically via CRISPR/Cas9 genome editing technology based on microhomology-mediated end joining (MMEJ). Both studies converged on therapeutic benefits of mTOR or mitogen-activated protein kinase (MAPK) inhibition of VEC. While mTOR inhibition rescued the enlarged nuclear size of cardiomyocytes, MAPK inhibition restored the prolonged cell shape in the VEC model. The therapeutic effects of mTOR and MAPK inhibition were later validated in the VAC model. Together, vmhcl/myh7 loss of function is sufficient to induce cardiomyopathy in zebrafish. The VEC and VAC models in zebrafish are amenable to both efficient genetic and chemical genetic tools, offering a rapid in vivo platform for discovering candidate signaling pathways of MYH7 cardiomyopathy.

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.

PIM1 Promotes Survival of Cardiomyocytes by Upregulating c-Kit Protein Expression

Enhancing cardiomyocyte survival is crucial to blunt deterioration of myocardial structure and function following pathological damage. PIM1 (Proviral Insertion site in Murine leukemia virus (PIM) kinase 1) is a cardioprotective serine threonine kinase that promotes cardiomyocyte survival and antagonizes senescence through multiple concurrent molecular signaling cascades. In hematopoietic stem cells, PIM1 interacts with the receptor tyrosine kinase c-Kit upstream of the ERK (Extracellular signal-Regulated Kinase) and Akt signaling pathways involved in cell proliferation and survival. The relationship between PIM1 and c-Kit activity has not been explored in the myocardial context. This study delineates the interaction between PIM1 and c-Kit leading to enhanced protection of cardiomyocytes from stress. Elevated c-Kit expression is induced in isolated cardiomyocytes from mice with cardiac-specific overexpression of PIM1. Co-immunoprecipitation and proximity ligation assay reveal protein–protein interaction between PIM1 and c-Kit. Following treatment with Stem Cell Factor, PIM1-overexpressing cardiomyocytes display elevated ERK activity consistent with c-Kit receptor activation. Functionally, elevated c-Kit expression confers enhanced protection against oxidative stress in vitro. This study identifies the mechanistic relationship between PIM1 and c-Kit in cardiomyocytes, demonstrating another facet of cardioprotection regulated by PIM1 kinase.

Inhibition of the ROS-EGFR Pathway Mediates the Protective Action of Nox1/4 Inhibitor GKT137831 against Hypertensive Cardiac Hypertrophy via Suppressing Cardiac Inflammation and Activation of Akt and ERK1/2

Oxidative stress, inflammation, and hypertension constitute a self-perpetuating vicious circle to exacerbate hypertension and subsequent hypertensive cardiac hypertrophy. NADPH oxidase (Nox) 1/4 inhibitor GKT137831 alleviates hypertensive cardiac hypertrophy in models of secondary hypertension; however, it remains unclear about its effect on hypertensive cardiac hypertrophy in models of essential hypertension. This study is aimed at determining the beneficial role of GKT137831 in hypertensive cardiac hypertrophy in spontaneously hypertensive rats (SHRs) and its mechanisms of action. Treating with GKT137831 prevented cardiac hypertrophy in SHRs. Likewise, decreasing production of reactive oxygen species (ROS) with GKT137831 reduced epidermal growth factor receptor (EGFR) activity in the left ventricle of SHRs. Additionally, EGFR inhibition also reduced ROS production in the left ventricle and blunted hypertensive cardiac hypertrophy in SHRs. Moreover, inhibition of the ROS-EGFR pathway with Nox1/4 inhibitor GKT137831 or selective EGFR inhibitor AG1478 reduced protein and mRNA levels of proinflammatory cytokines tumor necrosis factor α (TNF-α), interleukin 6 (IL-6), and interleukin 1β (IL-1β), as well as the activities of Akt and extracellular signal-regulated kinase (ERK) 1/2 in the left ventricle of SHRs. In summary, GKT137831 prevents hypertensive cardiac hypertrophy in SHRs, Nox-deprived ROS regulated EGFR activation through positive feedback in the hypertrophic myocardium, and inhibition of the ROS-EGFR pathway mediates the protective role of GKT137831 in hypertensive cardiac hypertrophy via repressing cardiac inflammation and activation of Akt and ERK1/2. This research will provide additional details for GKT137831 to prevent hypertensive cardiac hypertrophy.

Left ventricular phosphorylation patterns of Akt and ERK1/2 after triiodothyronine intracoronary perfusion in isolated hearts and short-term in vivo treatment in Wistar rats

OBJECTIVES

To determine the effects of triiodothyronine (T3) intracoronary perfusion in isolated hearts and short-term administration in rats on the left ventricular (LV) phosphorylation patterns of Akt and ERK1/2.

MATERIALS AND METHODS

Cardiodynamic and hemodynamic parameters were evaluated in Langendorff-perfused hearts. Left ventricles were used for histomorphometric and Western blot analyses. Short-term hyperthyroidism was established by T3 (500 μg.kg^-1.d^-1; subcutaneous injection) for 1 (T3_1d), 3 (T3_3d), and 10 (T3_10d) days.

RESULTS

Isolated hearts receiving T3 perfusion did not modify LV developed pressure, +dP/dt_max, -dP/dt_min, heart rate, and coronary perfusion pressure compared with vehicle-perfused hearts. P-ERK1/2 and p-Akt levels in LV tissues after 5, 15, or 60 min of T3 or vehicle perfusion were similar. Compared with their time-matched controls, isolated hearts of T3_3d and T3_10d rats exhibited LV hypertrophy and increased absolute values of +dP/dt_max and -dP/dt_min (i.e., positive inotropic and lusitropic effects). P-ERK1/2 decreased in LV tissues of T3_1d and T3_10d but not in those of T3_3d rats, and p-Akt levels augmented in left ventricles of T3_3d and stayed unaltered in those of T3_1d and T3_10d rats.

CONCLUSION

T3 intracoronary perfusion did not alter cardiodynamics and hemodynamics nor influence the activation of Akt and ERK of normal hearts. Accordingly, the rapid non-genomic effects of T3 were not evident. Short-term T3 treatment provoked cardiac hypertrophy coincidental with increased LV function and associated with transient Akt activation and cyclic ERK1/2 inhibition; which implies activation of physiological hypertrophy signaling and deactivation of pathological hypertrophy signaling, respectively.

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.

Long-term diabetes causes molecular alterations related to fibrosis and apoptosis in rat urinary bladder

Diabetes induces time-dependent alterations in urinary bladders. Long-term diabetes causes an underactive bladder. However, the fundamental mechanisms are still elusive. This study aimed to examine the histological changes and the potential molecular pathways affected by long-term diabetes in the rat bladder. Diabetes was induced in 8-week-old male Lewis rats by streptozotocin, while age-matched control rats received citrate buffer only. Forty-four weeks after diabetes induction, bladders were harvested for histological and molecular analyses. The expressions of proteins related to fibrosis, apoptosis and oxidative stress as well as the cellular signaling pathway in the bladder were examined by immunoblotting. Histological examinations illustrated diabetes caused detrusor hypertrophy and fibrotic changes in the bladder. Immunoblotting analysis demonstrated higher collagen I but lower elastin expression in the bladder in diabetic rats. These were accompanied by an increase in the expression of transforming growth factor-beta1, along with the downregulation of matrix metalloptoteinase-1, and upregulation of tissue inhibitor of metalloproteinase-1. Diabetic rats showed an increase in nitrotyrosine, but decrease in nuclear factor erythroid-related factor 2 (Nrf2) levels in the bladder. Enhanced apoptotic signaling was observed, characterized by increased expression of Bcl-2-associated X protein (Bax), decreased expression of Bcl-2, in the diabetic bladder. The nerve growth factor level was decreased in the diabetic bladder. A significant suppression in the protein expressions of phosphorylated extracellular signal-regulated kinases 1/2 was found in diabetic bladders. This study demonstrated that long-term diabetes caused molecular changes that could promote fibrosis and apoptosis in the bladder. Oxidative stress may be involved in this context.

Assessing the role of extracellular signal-regulated kinases 1 and 2 in volume overload-induced cardiac remodelling

AIMS

Volume overload (VO) and pressure overload (PO) induce differential cardiac remodelling responses including distinct signalling pathways. Extracellular signal-regulated kinases 1 and 2 (ERK1/2), key signalling components in the mitogen-activated protein kinase (MAPK) pathways, modulate cardiac remodelling during pressure overload (PO). This study aimed to assess their role in VO-induced cardiac remodelling as this was unknown.

METHODS AND RESULTS

Aortocaval fistula (Shunt) surgery was performed in mice to induce cardiac VO. Two weeks of Shunt caused a significant reduction of cardiac ERK1/2 activation in wild type (WT) mice as indicated by decreased phosphorylation of the TEY (Thr-Glu-Tyr) motif (-28% as compared with Sham controls, P < 0.05). Phosphorylation of other MAPKs was unaffected. For further assessment, transgenic mice with cardiomyocyte-specific ERK2 overexpression (ERK2tg) were studied. At baseline, cardiac ERK1/2 phosphorylation in ERK2tg mice remained unchanged compared with WT littermates, and no overt cardiac phenotype was observed; however, cardiac expression of the atrial natriuretic peptide was increased on messenger RNA (3.6-fold, P < 0.05) and protein level (3.1-fold, P < 0.05). Following Shunt, left ventricular dilation and hypertrophy were similar in ERK2tg mice and WT littermates. Left ventricular function was maintained, and changes in gene expression indicated reactivation of the foetal gene program in both genotypes. No differences in cardiac fibrosis and kinase activation was found amongst all experimental groups, whereas apoptosis was similarly increased through Shunt in ERK2tg and WT mice.

CONCLUSIONS

VO-induced eccentric hypertrophy is associated with reduced cardiac ERK1/2 activation in vivo. Cardiomyocyte-specific overexpression of ERK2, however, does not alter cardiac remodelling during VO. Future studies need to define the pathophysiological relevance of decreased ERK1/2 signalling during VO.

Smooth muscle-specific TMEM16A expression protects against angiotensin II-induced cerebrovascular remodeling via suppressing extracellular matrix deposition

Cerebrovascular remodeling is the leading factor for stroke and characterized by increased extracellular matrix deposition, migration and proliferation of vascular smooth muscle cells, and inhibition of their apoptosis. TMEM16A is an important component of Ca²⁺-activated Cl^- channels. Previously, we showed that downregulation of TMEM16A in the basilar artery was negatively correlated with cerebrovascular remodeling during hypertension. However, it is unclear whether TMEM16A participates in angiotensin II (Ang II)-induced vascular remodeling in mice that have TMEM16A gene modification. In this study, we generated a transgenic mouse that overexpresses TMEM16A specifically in vascular smooth muscle cells. We observed that vascular remodeling in the basilar artery during Ang II-induced hypertension was significantly suppressed upon vascular smooth muscle-specific overexpression of TMEM16A relative to control mice. Specifically, we observed a large reduction in the deposition of fibronectin and collagen I. The expression of matrix metalloproteinases (MMP-2, MMP-9, and MMP-14), and tissue inhibitors of metalloproteinases (TIMP-1 and TIMP-2) were upregulated in the basilar artery during Ang II-induced hypertension, but this was suppressed upon overexpression of TMEM16A in blood vessels. Furthermore, TMEM16A overexpression alleviated the overactivity of the canonical TGF-β1/Smad3, and non-canonical TGF-β1/ERK and JNK pathways in the basilar artery during Ang II-induced hypertension. These in vivo results were similar to the results derived in vitro with basilar artery smooth muscle cells stimulated by Ang II. Moreover, we observed that the inhibitory effect of TMEM16A on MMPs was mediated by decreasing the activation of WNK1, which is a Cl^--sensitive serine/threonine kinase. In conclusion, this study demonstrates that TMEM16A protects against cerebrovascular remodeling during hypertension by suppressing extracellular matrix deposition. We also showed that TMEM16A exerts this effect by reducing the expression of MMPs via inhibiting WNK1, and decreasing the subsequent activities of TGF-β1/Smad3, ERK, and JNK. Accordingly, our results suggest that TMEM16A may serve as a novel therapeutic target for vascular remodeling.

Maduramicin induces cardiac muscle cell death by the ROS-dependent PTEN/Akt-Erk1/2 signaling pathway

Maduramicin (Mad), a polyether ionophore antibiotic, has been reported to be toxic to animals and humans because of being used at high doses or for long time, resulting in heart failure. However, the toxic mechanism of Mad in cardiac muscle cells is not well understood. Here, we show that Mad induced cell viability reduction and apoptosis in cardiac-derived H9c2, HL-1 cells, primary cardiomyocytes, and murine cardiac muscles, which was because of the inhibition of extracellular-signal-regulated kinase 1/2 (Erk1/2). Expression of constitutively active mitogen-activated protein kinase kinase 1 (MKK1) attenuated Mad-induced cell death in H9c2 cells, whereas silencing Erk1/2 or ectopic expression of dominant negative MKK1 strengthened Mad-induced cell death. Moreover, we found that both phosphatase and tensin homolog on chromosome 10 (PTEN) and protein kinase B (Akt) were implicated in the regulation of Erk1/2 inactivation and apoptosis in the cells and tissues exposed to Mad. Overexpression of dominant negative PTEN and/or constitutively active Akt, or constitutively active Akt and/or constitutively active MKK1 rescued the cells from Mad-induced dephosphorylated-Erk1/2 and cell death. Furthermore, Mad-induced reactive oxygen species (ROS) activated PTEN and inactivated Akt-Erk1/2 contributing to cell death, as N-acetyl- L-cysteine ameliorated the event. Taken together, the results disclose that Mad inhibits Erk1/2 via ROS-dependent activation of PTEN and inactivation of Akt, leading to cell death in cardiac muscle cells. Our findings suggest that manipulation of the ROS-PTEN-Akt-Erk1/2 pathway may be a potential approach to prevent Mad-induced cardiotoxicity.

Soluble adenylyl cyclase: A novel player in cardiac hypertrophy induced by isoprenaline or pressure overload

Aims

In contrast to the membrane bound adenylyl cyclases, the soluble adenylyl cyclase (sAC) is activated by bicarbonate and divalent ions including calcium. sAC is located in the cytosol, nuclei and mitochondria of several tissues including cardiac muscle. However, its role in cardiac pathology is poorly understood. Here we investigate whether sAC is involved in hypertrophic growth using two different model systems.

Methods and results

In isolated adult rat cardiomyocytes hypertrophy was induced by 24 h β₁-adrenoceptor stimulation using isoprenaline (ISO) and a β₂-adrenoceptor antagonist (ICI118,551). To monitor hypertrophy cell size along with RNA/DNA- and protein/DNA ratios as well as the expression level of α-skeletal actin were analyzed. sAC activity was suppressed either by treatment with its specific inhibitor KH7 or by knockdown. Both pharmacological inhibition and knockdown blunted hypertrophic growth and reduced expression levels of α-skeletal actin in ISO/ICI treated rat cardiomyocytes. To analyze the underlying cellular mechanism expression levels of phosphorylated CREB, B-Raf and Erk1/2 were examined by western blot. The results suggest the involvement of B-Raf, but not of Erk or CREB in the pro-hypertrophic action of sAC. In wild type and sAC knockout mice pressure overload was induced by transverse aortic constriction. Hemodynamics, heart weight and the expression level of the atrial natriuretic peptide were analyzed. In accordance, transverse aortic constriction failed to induce hypertrophy in sAC knockout mice. Mechanistic analysis revealed a potential role of Erk1/2 in TAC-induced hypertrophy.

Conclusion

Soluble adenylyl cyclase might be a new pivotal player in the cardiac hypertrophic response either to long-term β₁-adrenoceptor stimulation or to pressure overload.

Endothelin-1 promotes hypertrophic remodelling of cardiac myocytes by activating sustained signalling and transcription downstream of endothelin type A receptors

G-protein coupled receptor (GPCR) mediated activation of the MAPK signalling cascade is a key pathway in the induction of hypertrophic remodelling of the heart – a response to pathological cues including hypertension and myocardial infarction. While levels of pro-hypertrophic hormone agonists of GPCRs increase during periods of greater workload to enhance cardiac output, hypertrophy does not necessarily result. Here we investigated the relationship between the duration of exposure to the pro-hypertrophic GPCR agonist endothelin-1 (ET-1) and the induction of hypertrophic remodelling in neonatal rat ventricular myocytes (NRVM) and in the adult rat heart in vivo. Notably, a 15 min pulse of ET-1 was sufficient to induce markers of hypertrophy that were present when measured at 24 h in vivo and 48 h in vitro. The persistence of ET-1 action was insensitive to ET type A receptor (ET_A receptor) antagonism with BQ123. The extended effects of ET-1 were dependent upon sustained MAPK signalling and involved persistent transcription. Inhibitors of endocytosis however conferred sensitivity upon the hypertrophic response to BQ123, suggesting that endocytosis of ET_A receptors following ligand binding preserves their active state by protection against antagonist. Contrastingly, α₁ adrenergic-induced hypertrophic responses required the continued presence of agonist and were sensitive to antagonist. These studies shed new light on strategies to pharmacologically intervene in the action of different pro-hypertrophic mediators.

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Acute ET-1 exposure elicits a long-lasting cardiac myocyte hypertrophic response.

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ET-1 effects depend on persistent MAPK signalling and active transcription.

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ET-1 elicited hypertrophy is insensitive to subsequent ET_A receptor antagonism.

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Endocytosis inhibition potentiates ET-1-induction of hypertrophy markers.

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Endocytosis inhibition sensitises effects of ET-1 to ET_A receptor antagonist.

Mechanisms of Chinese Medicine Xinmailong's protection against heart failure in pressure-overloaded mice and cultured cardiomyocytes

Patients with heart failure (HF) have high mortality and mobility. Xinmailong (XML) injection, a Chinese Medicine, is clinically effective in treating HF. However, the mechanism of XML's effectiveness on HF was unclear, and thus, was the target of the present study. We created a mouse model of pressure-overload-induced HF with transverse aortic constriction (TAC) surgery and compared among 4 study groups: SHAM (n = 10), TAC (n = 12), MET (metoprolol, positive drug treatment, n = 7) and XML (XML treatment, n = 14). Dynamic changes in cardiac structure and function were evaluated with echocardiography in vivo. In addition, H9C2 rat cardiomyocytes were cultured in vitro and the phosphorylation of ERK1/2, AKT, GSK3β and protein expression of GATA4 in nucleus were detected with Western blot experiment. The results showed that XML reduced diastolic thickness of left ventricular posterior wall, increased ejection fraction and fraction shortening, so as to inhibit HF at 2 weeks after TAC. Moreover, XML inhibited the phosphorylation of ERK1/2, AKT and GSK3β, subsequently inhibiting protein expression of GATA4 in nucleus (P < 0.001). Together, our data demonstrated that XML inhibited the TAC-induced HF via inactivating the ERK1/2, AKT/GSK3β, and GATA4 signaling pathway.

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.

The Role of ERK1/2 in the Development of Diabetic Cardiomyopathy

Diabetes mellitus is a chronic metabolic condition that affects carbohydrate, lipid and protein metabolism and may impair numerous organs and functions of the organism. Cardiac dysfunction afflicts many patients who experience the oxidative stress of the heart. Diabetic cardiomyopathy (DCM) is one of the major complications that accounts for more than half of diabetes-related morbidity and mortality cases. Chronic hyperglycemia and hyperlipidemia from diabetes mellitus cause cardiac oxidative stress, endothelial dysfunction, impaired cellular calcium handling, mitochondrial dysfunction, metabolic disturbances, and remodeling of the extracellular matrix, which ultimately lead to DCM. Although many studies have explored the mechanisms leading to DCM, the pathophysiology of DCM has not yet been fully clarified. In fact, as a potential mechanism, the associations between DCM development and mitogen-activated protein kinase (MAPK) activation have been the subjects of tremendous interest. Nonetheless, much remains to be investigated, such as tissue- and cell-specific processes of selection of MAPK activation between pro-apoptotic vs. pro-survival fate, as well as their relation with the pathogenesis of diabetes and associated complications. In general, it turns out that MAPK signaling pathways, such as extracellular signal-regulated kinase 1/2 (ERK1/2), c-Jun N-terminal protein kinase (JNK) and p38 MAP kinase, are demonstrated to be actively involved in myocardial dysfunction, hypertrophy, fibrosis and heart failure. As one of MAPK family members, the activation of ERK1/2 has also been known to be involved in cardiac hypertrophy and dysfunction. However, many recent studies have demonstrated that ERK1/2 signaling activation also plays a crucial role in FGF21 signaling and exerts a protective environment of glucose and lipid metabolism, therefore preventing abnormal healing and cardiac dysfunction. The duration, extent, and subcellular compartment of ERK1/2 activation are vital to differential biological effects of ERK1/2. Moreover, many intracellular events, including mitochondrial signaling and protein kinases, manipulate signaling upstream and downstream of MAPK, to influence myocardial survival or death. In this review, we will summarize the roles of ERK1/2 pathways in DCM development by the evidence from current studies and will present novel opinions on "differential influence of ERK1/2 action in cardiac dysfunction, and protection against myocardial ischemia-reperfusion injury".

Salvianolic Acid B Alleviates Heart Failure by Inactivating ERK1/2/GATA4 Signaling Pathway after Pressure Overload in Mice

BACKGROUND

Heart failure(HF) is a dangerous disease that affects millions of patients. Radix Salvia is widely used in Chinese clinics to treat heart diseases. Salvianolic acid B(SalB) is the major active component of Radix Salvia. This study investigated the mechanisms of action and effects of SalB on HF in an experimental mouse model of HF.

METHODS

We created a mouse model of HF by inducing pressure overload with transverse aortic constriction(TAC) surgery for 2 weeks and compared among 4 study groups: SHAM group (n = 10), TAC group (n = 9), TAC+MET group (metprolol, positive drug treatment, n = 9) and TAC+SalB group (SalB, 240 mg•kg-1•day-1, n = 9). Echocardiography was used to evaluate the dynamic changes in cardiac structure and function in vivo. Plasma brain natriuretic peptide (BNP) concentration was detected by Elisa method. In addition, H9C2 rat cardiomyocytes were cultured and Western blot were implemented to evaluate the phosphorylation of ERK1/2, AKT, and protein expression of GATA4.

RESULTS

SalB significantly inhibited the phosphorylation of Thr202/Tyr204 sites of ERK1/2, but not Ser473 site of AKT, subsequently inhibited protein expression of GATA4 and plasma BNP(P < 0.001), and then inhibited HF at 2 weeks after TAC surgery.

CONCLUSIONS

Our data provide a mechanism of inactivating the ERK1/2/GATA4 signaling pathway for SalB inhibition of the TAC-induced HF.

Identification of the Mtus1 Splice Variant as a Novel Inhibitory Factor Against Cardiac Hypertrophy

Background

In cardiac hypertrophy and failure, there is a widespread alteration in mRNA splicing, but the role of splice variants in cardiac hypertrophy has not yet been fully elucidated. In this study, we used an exon array to identify novel splice variants associated with cardiac hypertrophy.

Methods and Results

We performed genome‐wide exon array analysis and developed a splicing profile in murine hearts with hypertrophy induced by transverse aortic constriction for 8 weeks. Following global analysis of splice variants using the Mouse Exon 1.0 ST Array, we identified 46 spliced genes and narrowed our focus to 1 gene, mitochondrial tumor suppressor 1 (Mtus1), whose splice variants were registered in the NCBI RefSeq database. Notably, one of the splice variants Mtus1A was specifically upregulated, although the total expression of the Mtus1 gene remained unchanged. We showed that Mtus1A was localized in the mitochondria, and its expression level increased with the degree of cardiac hypertrophy. In cultured cardiomyocytes, Mtus1A overexpression reduced phenylephrine‐induced reactive oxygen species production and consequent ERK phosphorylation, resulting in a decrease in both cell size and protein synthesis. In vivo, cardiac‐specific Mtus1A transgenic mice showed left ventricle wall thinning and a reduced hypertrophic response to pressure overload and phenylephrine treatment.

Conclusions

We found that Mtus1 is specifically spliced in hypertrophic hearts and that the Mtus1A variant has an inhibitory effect on cardiac hypertrophy. Mtus1A is, therefore, a possible diagnostic and therapeutic target for cardiac hypertrophy and failure.

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.

ERK1 and ERK2 Map Kinases: Specific Roles or Functional Redundancy?

The MAP kinase signaling cascade Ras/Raf/MEK/ERK has been involved in a large variety of cellular and physiological processes that are crucial for life. Many pathological situations have been associated to this pathway. More than one isoform has been described at each level of the cascade. In this review we devoted our attention to ERK1 and ERK2, which are the effector kinases of the pathway. Whether ERK1 and ERK2 specify functional differences or are in contrast functionally redundant, constitutes an ongoing debate despite the huge amount of studies performed to date. In this review we compiled data on ERK1 vs. ERK2 gene structures, protein sequences, expression levels, structural and molecular mechanisms of activation and substrate recognition. We have also attempted to perform a rigorous analysis of studies regarding the individual roles of ERK1 and ERK2 by the means of morpholinos, siRNA, and shRNA silencing as well as gene disruption or gene replacement in mice. Finally, we comment on a recent study of gene and protein evolution of ERK isoforms as a distinct approach to address the same question. Our review permits the evaluation of the relevance of published studies in the field especially when measurements of global ERK activation are taken into account. Our analysis favors the hypothesis of ERK1 and ERK2 exhibiting functional redundancy and points to the concept of the global ERK quantity, and not isoform specificity, as being the essential determinant to achieve ERK function.

RSK3 is required for concentric myocyte hypertrophy in an activated Raf1 model for Noonan syndrome

Noonan syndrome (NS) is a congenital disorder resulting from mutations of the Ras-Raf signaling pathway. Hypertrophic cardiomyopathy associated with RAF1 "RASopathy" mutations is a major risk factor for heart failure and death in NS and has been attributed to activation of MEK1/2-ERK1/2 mitogen-activated protein kinases. We recently discovered that type 3 p90 ribosomal S6 kinase (RSK3) is an ERK effector that is required, like ERK1/2, for concentric myocyte hypertrophy in response to pathological stress such as pressure overload. In order to test whether RSK3 also contributes to NS-associated hypertrophic cardiomyopathy, RSK3 knock-out mice were crossed with mice bearing the Raf1(L613V) human NS mutation. We confirmed that Raf1(L613V) knock-in confers a NS-like phenotype, including cardiac hypertrophy. Active RSK3 was increased in Raf1(L613V) mice. Constitutive RSK3 gene deletion prevented the Raf1(L613V)-dependent concentric growth in width of the cardiac myocyte and attenuated cardiac hypertrophy in female mice. These results are consistent with RSK3 being an important mediator of ERK1/2-dependent growth in RASopathy. In conjunction with previously published data showing that RSK3 is important for pathological remodeling of the heart, these data suggest that targeting of this downstream MAP-kinase pathway effector should be considered in the treatment of RASopathy-associated hypertrophic cardiomyopathy.

Cardiac concentric hypertrophy promoted by activated Met receptor is mitigated in vivo by inhibition of Erk1,2 signalling with Pimasertib

Cardiac hypertrophy is a major risk factor for heart failure. Hence, its attenuation represents an important clinical goal. Erk1,2 signalling is pivotal in the cardiac response to stress, suggesting that its inhibition may be a good strategy to revert heart hypertrophy. In this work, we unveiled the events associated with cardiac hypertrophy by means of a transgenic model expressing activated Met receptor. c-Met proto-oncogene encodes for the tyrosine kinase receptor of Hepatocyte growth factor and is a strong inducer of Ras-Raf-Mek-Erk1,2 pathway. We showed that three weeks after the induction of activated Met, the heart presents a remarkable concentric hypertrophy, with no signs of congestive failure and preserved contractility. Cardiac enlargement is accompanied by upregulation of growth-regulating transcription factors, natriuretic peptides, cytoskeletal proteins, and Extracellular Matrix remodelling factors (Timp1 and Pai1). At a later stage, cardiac hypertrophic remodelling results into heart failure with preserved systolic function. Prevention trial by suppressing activated Met showed that cardiac hypertrophy is reversible, and progression to heart failure is prevented. Notably, treatment with Pimasertib, Mek1 inhibitor, attenuates cardiac hypertrophy and remodelling. Our results suggest that modulation of Erk1.2 signalling may constitute a new therapeutic approach for treating cardiac hypertrophies.

Regulator of G-Protein Signaling 10 Negatively Regulates Cardiac Remodeling by Blocking Mitogen-Activated Protein Kinase–Extracellular Signal-Regulated Protein Kinase 1/2 Signaling

Regulator of G-protein signaling 10 (RGS10) is an important member of the RGS family and produces biological effects in multiple organs. We used a genetic approach to study the role of RGS10 in the regulation of pathological cardiac hypertrophy and found that RGS10 can negatively influence pressure overload–induced cardiac remodeling. RGS10 expression was markedly decreased in failing human hearts and hypertrophic murine hearts. The extent of aortic banding–induced cardiac hypertrophy, dysfunction, and fibrosis in RGS10-knockout mice was exacerbated, whereas the heart of transgenic mice with cardiac-specific RGS10 overexpression exhibited an alleviated response to pressure overload. Consistently, RGS10 also inhibited an angiotensin II–induced hypertrophic response in isolated cardiomyocytes. Mechanistically, cardiac remodeling improvement elicited by RGS10 was associated with the abrogation of mitogen-activated protein kinase kinase 1/2–extracellular signal-regulated protein kinase 1/2 signaling. Furthermore, the inhibition of mitogen-activated protein kinase kinase–extracellular signal-regulated protein kinase 1/2 transduction abolished RGS10 deletion-induced hypertrophic aggravation. These findings place RGS10 and its downstream signaling mitogen-activated protein kinase kinase–extracellular signal-regulated protein kinase 1/2 as crucial regulators of pathological cardiac hypertrophy after pressure overload and identify this pathway as a potential therapeutic target to attenuate the pressure overload–driven cardiac remodeling.

RSK3: A regulator of pathological cardiac remodeling

The family of p90 ribosomal S6 kinases (RSKs) are pleiotropic effectors for extracellular signal-regulated kinase signaling pathways. Recently, RSK3 was shown to be important for pathological remodeling of the heart. Although cardiac myocyte hypertrophy can be compensatory for increased wall stress, in chronic heart diseases, this nonmitotic cell growth is usually associated with interstitial fibrosis, increased cell death, and decreased cardiac function. Although RSK3 is less abundant in the cardiac myocyte than other RSK family members, RSK3 appears to serve a unique role in cardiac myocyte stress responses. A potential mechanism conferring the unique function of RSK3 in the heart is anchoring by the scaffold protein muscle A-kinase anchoring protein β (mAKAPβ). Recent findings suggest that RSK3 should be considered as a therapeutic target for the prevention of heart failure, a clinical syndrome of major public health significance.

Direct activation of the proposed anti-diabetic receptor, GPR119 in cardiomyoblasts decreases markers of muscle metabolic activity

GPR119 agonists are emerging rapidly as a pharmaceutical treatment of diabetes. Diabetes is a known risk factor for cardiovascular disease yet the cardiac-specific consequences of GPR119 activation are unknown. This study demonstrated that GPR119 agonism in cardiac myoblasts reduces metabolic activity in high and low concentrations of fatty acids, with high concentrations of palmitate largely attenuating the effects of the GPR119 agonist, PSN632408. The effects of GPR119 activation on gene and protein markers of metabolism were dependent on fatty acid exposure. Activating GPR119 did not affect cell hypertrophy of lipid accumulation regardless of lipid exposure. These results suggest that the pathways activated in response to GPR119 modulation in cardiac muscle cells differ between healthy and metabolically dysregulated states. However regardless of the pathway activated by GPR119, these effects may cause detrimental reductions to oxidative/metabolic capacity under both conditions. Thus further development of GPR119 agonists for treating metabolic diseases is warranted.

DNA methylation in cardiac fibrosis: new advances and perspectives

Cardiac fibrosis is characterized by net accumulation of extracellular matrix (ECM) proteins in the cardiac interstitium, and contributes to both systolic and diastolic dysfunction in many cardiac pathophysiologic conditions. More specifically, cardiac fibroblasts are activated by a variety of pathological stimuli, thereby undergoing proliferation, differentiation to myofibroblasts, and production of various cytokines and ECM proteins. Thus, understanding the biological processes of cardiac fibroblasts will provide novel insights into the underlying mechanisms of cardiac fibrosis. DNA methylation is an important epigenetic mechanism, which often occurs in response to environmental stimuli and is crucial in regulating gene expression. The aberrant methylation of CpG island promoters of selected genes is the prominent epigenetic mechanism by which gene transcription can be effectively silenced. Aberrant hypermethylation of a few selected genes such as RASSF1A plays an important role in facilitating fibrotic fibroblast activation and in driving fibrosis. In this review we will discuss the mechanisms of DNA methylation and their implications for cardiac fibroblasts activation and fibrosis. Control of DNA methylation may serve as a new strategy for anti-fibrotic therapy.

Apocynum Tablet Protects against Cardiac Hypertrophy via Inhibiting AKT and ERK1/2 Phosphorylation after Pressure Overload

Background. Cardiac hypertrophy occurs in many cardiovascular diseases. Apocynum tablet (AT), a traditional Chinese medicine, has been widely used in China to treat patients with hypertension. However, the underlying molecular mechanisms of AT on the hypertension-induced cardiac hypertrophy remain elusive. The current study evaluated the effect and mechanisms of AT on cardiac hypertrophy. Methods. We created a mouse model of cardiac hypertrophy by inducing pressure overload with surgery of transverse aortic constriction (TAC) and then explored the effect of AT on the development of cardiac hypertrophy using 46 mice in 4 study groups (combinations of AT and TAC). In addition, we evaluated the signaling pathway of phosphorylation of ERK1/2, AKT, and protein expression of GATA4 in the cardioprotective effects of AT using Western blot. Results. AT inhibited the phosphorylation of Thr202/Tyr204 sites of ERK1/2, Ser473 site of AKT, and protein expression of GATA4 and significantly inhibited cardiac hypertrophy and cardiac fibrosis at 2 weeks after TAC surgery (P < 0.05). Conclusions. We experimentally demonstrated that AT inhibits cardiac hypertrophy via suppressing phosphorylation of ERK1/2 and AKT.