Mitogen-activated Protein Kinases p38 and ERK 1/2 Mediate the Wall Stress-induced Activation of GATA-4 Binding in Adult Heart

Cardiomyocyte SORBS2 expression increases in heart failure and regulates integrin interactions and extracellular matrix composition

AIMS

In this study, we aimed to uncover genes associated with stressed cardiomyocytes by combining single-cell transcriptomic data sets from failing cardiac tissue from both humans and mice.

METHODS AND RESULTS

Our bioinformatic analysis identified SORBS2 as conserved NPPA-correlated gene. Using mouse models and cardiac tissue from human heart failure patients, we demonstrated that SORBS2 expression is consistently increased during pathological remodelling, correlates to disease severity, and is regulated by GATA4. By affinity purification mass spectrometry, we showed SORBS2 to interact with the integrin-cytoskeleton connections. Cardiomyocyte-specific genetic loss of Sorbs2 in adult mice changed integrin interactions, indicated by the increased expression of several integrins and altered extracellular matrix components connecting to these integrins, leading to an exacerbated fibrotic response during pathological remodelling.

CONCLUSION

Sorbs2 is a cardiomyocyte-enriched gene that is increased during progression to heart failure in a GATA4-dependent manner and correlates to phenotypical hallmarks of cardiac failure. Our data indicate SORBS2 to function as a crucial regulator of integrin interactions and cardiac fibrosis.

Detection and identification of factors in the atrium responsible for blood pressure regulation in patients with hypertension

Resection of the left atrial appendage reportedly improves blood pressure in patients with hypertension. This study aimed to validate the transcriptional profiles of atrial genes responsible for blood pressure regulation in patients with hypertension as well as to identify the molecular mechanisms in rat biological systems. RNA sequencing data of left atrial appendages from patients with (n = 6) and without (n = 6) hypertension were subjected to unsupervised principal component analysis (PCA). Reduction of blood pressure was reflected by third and ninth principal components PC3 and PC9, and that eighteen transcripts, including endothelin-1, were revealed by PCA-based pathway analysis. Resection of the left atrial appendage in hypertensive rats improved their blood pressure accompanied by a decrease in serum endothelin-1 concentration. Expression of the endothelin-1 gene in the atrium and atrial appendectomy could play roles in blood pressure regulation in humans and rats.

Cardiomyocyte and endothelial cells play distinct roles in the tumour necrosis factor (TNF)-dependent atrial responses and increased atrial fibrillation vulnerability induced by endurance exercise training in mice

AIMS

Endurance exercise is associated with an increased risk of atrial fibrillation (AF). We previously established that adverse atrial remodelling and AF susceptibility induced by intense exercise in mice require the mechanosensitive and pro-inflammatory cytokine tumour necrosis factor (TNF). The cellular and mechanistic basis for these TNF-mediated effects is unknown.

METHODS AND RESULTS

We studied the impact of Tnf excision, in either atrial cardiomyocytes or endothelial cells (using Cre-recombinase expression controlled by Nppa or Tie2 promoters, respectively), on the cardiac responses to six weeks of intense swim exercise training. TNF ablation, in either cell type, had no impact on the changes in heart rate, autonomic tone, or left ventricular structure and function induced by exercise training. Tnf excision in atrial cardiomyocytes did, however, prevent atrial hypertrophy, fibrosis, and macrophage infiltration as well as conduction slowing and increased AF susceptibility arising from exercise training. In contrast, endothelial-specific excision only reduced the training-induced atrial hypertrophy. Consistent with these cell-specific effects of Tnf excision, inducing TNF loss from atrial cardiomyocytes prevented activation of p38MAPKinase, a strain-dependent downstream mediator of TNF signalling, without affecting the atrial stretch as assessed by atrial pressures induced by exercise. Despite TNF's established role in innate immune responses and inflammation, neither acute nor chronic exercise training caused measurable NLRP3 inflammasome activation.

CONCLUSIONS

Our findings demonstrate that adverse atrial remodelling and AF vulnerability induced by intense exercise require TNF in atrial cardiomyocytes whereas the impact of endothelial-derived TNF is limited to hypertrophy modulation. The implications of the cell autonomous effects of TNF and crosstalk between cells in the atria are discussed.

Sibjotang Protects against Cardiac Hypertrophy In Vitro and In Vivo

Cardiac hypertrophy is developed by various diseases such as myocardial infarction, valve diseases, hypertension, and aortic stenosis. Sibjotang (, Shizaotang, SJT), a classic formula in Korean traditional medicine, has been shown to modulate the equilibrium of body fluids and blood pressure. This research study sought to explore the impact and underlying process of Sibjotang on cardiotoxicity induced by DOX in H9c2 cells. In vitro, H9c2 cells were induced by DOX (1 μM) in the presence or absence of SJT (1-5 μg/mL) and incubated for 24 h. In vivo, SJT was administrated to isoproterenol (ISO)-induced cardiac hypertrophy mice (n = 8) at 100 mg/kg/day concentrations. Immunofluorescence staining revealed that SJT mitigated the enlargement of H9c2 cells caused by DOX in a dose-dependent way. Using SJT as a pretreatment notably suppressed the rise in cardiac hypertrophic marker levels induced by DOX. SJT inhibited the DOX-induced ERK1/2 and p38 MAPK signaling pathways. In addition, SJT significantly decreased the expression of the hypertrophy-associated transcription factor GATA binding factor 4 (GATA 4) induced by DOX. SJT also decreased hypertrophy-associated calcineurin and NFAT protein levels. Pretreatment with SJT significantly attenuated DOX-induced apoptosis-associated proteins such as Bax, caspase-3, and caspase-9 without affecting cell viability. In addition, the results of the in vivo study indicated that SJT significantly reduced the left ventricle/body weight ratio level. Administration of SJT reduced the expression of hypertrophy markers, such as ANP and BNP. These results suggest that SJT attenuates cardiac hypertrophy and heart failure induced by DOX or ISO through the inhibition of the calcineurin/NFAT/GATA4 pathway. Therefore, SJT may be a potential treatment for the prevention and treatment of cardiac hypertrophy that leads to heart failure.

DNA damage response and GATA4 signaling in cellular senescence and aging-related pathology

Aging is the continuous degradation of biological function and structure with time, and cellular senescence lies at its core. DNA damage response (DDR) can activate Ataxia telangiectasia-mutated serine/threonine kinase (ATM) and Rad3-related serine/threonine kinase (ATR), after which p53 activates p21, stopping the cell cycle and inducing cell senescence. GATA4 is a transcription factor that plays an important role in the development of many organs, such as the heart, testis, ovary, foregut, liver, and ventral pancreas. Studies have shown that GATA4 can also contribute to the DDR, leading to aging. Consistently, there is also evidence that the GATA4 signaling pathway is associated with aging-related diseases, including atherosclerosis and heart failure. This paper reviews the relationship between GATA4, DDR, and cellular senescence, as well as its effect on aging-related diseases.

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.

Edible folic acid and medicinal folinic acid produce cardioprotective effects in late-stage triple-transgenic Alzheimer's disease model mice by suppressing cardiac hypertrophy and fibrosis

Some clinical studies have indicated the patients with Alzheimer's disease (AD) display an increased risk of cardiovascular disease (CVD). Here, to examine the relationship between AD and CVDs, we investigated the changes in heart function in triple-transgenic late-stage AD model mice (3× Tg-AD; APPSwe, PS1M146V, and tauP301L). We fed the AD mice folic acid (FA) or folinic acid (FN) and analyzed the protective effects of the compounds on the heart; specifically, 20-month-old triple-transgenic AD mice, weighing 34-55 g, were randomly allocated into three groups-the AD, AD + FA, and AD + FN groups-and subject to gastric feeding with FA or FN once daily at 12 mg/kg body weight (BW) for 3 months. Mouse BWs were assessed throughout the trial, at the end of which the animals were sacrificed using carbon dioxide suffocation. We found that BW, whole-heart weight, and left-ventricle weight were reduced in the AD + FA and AD + FN groups as compared with the measurements in the AD group. Furthermore, western blotting of excised heart tissue revealed that the levels of the hypertrophy-related protein markers phospho(p)-p38 and p-c-Jun were markedly decreased in the AD + FA group, whereas p-GATA4, and ANP were strongly reduced in the AD + FN group. Moreover, the fibrosis-related proteins uPA, MMP-2, MEK1/2 and SP-1 were decreased in the heart in both AD + FN group. In summary, our results indicate that FA and FN can exert anti-cardiac hypertrophy and fibrosis effects to protect the heart in aged triple-transgenic AD model mice, particular in FN.

Insights Into the Roles of GATA Factors in Mammalian Testis Development and the Control of Fetal Testis Gene Expression

Defining how genes get turned on and off in a correct spatiotemporal manner is integral to our understanding of the development, differentiation, and function of different cell types in both health and disease. Testis development and subsequent male sex differentiation of the XY fetus are well-orchestrated processes that require an intricate network of cell-cell communication and hormonal signals that must be properly interpreted at the genomic level. Transcription factors are at the forefront for translating these signals into a coordinated genomic response. The GATA family of transcriptional regulators were first described as essential regulators of hematopoietic cell differentiation and heart morphogenesis but are now known to impact the development and function of a multitude of tissues and cell types. The mammalian testis is no exception where GATA factors play essential roles in directing the expression of genes crucial not only for testis differentiation but also testis function in the developing male fetus and later in adulthood. This minireview provides an overview of the current state of knowledge of GATA factors in the male gonad with a particular emphasis on their mechanisms of action in the control of testis development, gene expression in the fetal testis, testicular disease, and XY sex differentiation in humans.

Different activation of MAPKs and Akt/GSK3β after preload vs. afterload elevation

Aims

Pressure overload (PO) and volume overload (VO) lead to concentric or eccentric hypertrophy. Previously, we could show that activation of signalling cascades differ in in vivo mouse models. Activation of these signal cascades could either be induced by intrinsic load sensing or neuro‐endocrine substances like catecholamines or the renin‐angiotensin‐aldosterone system.

Methods and results

We therefore analysed the activation of classical cardiac signal pathways [mitogen‐activated protein kinases (MAPKs) (ERK, p38, and JNK) and Akt‐GSK3β] in in vitro of mechanical overload (ejecting heart model, rabbit and human isolated muscle strips). Selective elevation of preload in vitro increased AKT and GSK3β phosphorylation after 15 min in isolated rabbit muscles strips (AKT 49%, GSK3β 26%, P < 0.05) and in mouse ejecting hearts (AKT 51%, GSK49%, P < 0.05), whereas phosphorylation of MAPKs was not influenced by increased preload. Selective elevation of afterload revealed an increase in ERK phosphorylation in the ejecting heart (43%, P < 0.05), but not in AKT, GSK3β, and the other MAPKs. Elevation of preload and afterload in the ejecting heart induced a significant phosphorylation of ERK (95%, P < 0.001) and showed a moderate increased AKT (P = 0.14) and GSK3β (P = 0.21) phosphorylation, which did not reach significance. Preload and afterload elevation in muscles strips from human failing hearts showed neither AKT nor ERK phosphorylation changes.

Conclusions

Our data show that preload activates the AKT–GSK3β and afterload the ERK pathway in vitro, indicating an intrinsic mechanism independent of endocrine signalling.

Cardiomyocyte p38 MAPKα suppresses a heart-adipose tissue-neutrophil crosstalk in heart failure development

Although p38 MAP Kinase α (p38 MAPKα) is generally accepted to play a central role in the cardiac stress response, to date its function in maladaptive cardiac hypertrophy is still not unambiguously defined. To induce a pathological type of cardiac hypertrophy we infused angiotensin II (AngII) for 2 days via osmotic mini pumps in control and tamoxifen-inducible, cardiomyocyte (CM)-specific p38 MAPKα KO mice (iCMp38αKO) and assessed cardiac function by echocardiography, complemented by transcriptomic, histological, and immune cell analysis. AngII treatment after inactivation of p38 MAPKα in CM results in left ventricular (LV) dilatation within 48 h (EDV: BL: 83.8 ± 22.5 µl, 48 h AngII: 109.7 ± 14.6 µl) and an ectopic lipid deposition in cardiomyocytes, reflecting a metabolic dysfunction in pressure overload (PO). This was accompanied by a concerted downregulation of transcripts for oxidative phosphorylation, TCA cycle, and fatty acid metabolism. Cardiac inflammation involving neutrophils, macrophages, B- and T-cells was significantly enhanced. Inhibition of adipose tissue lipolysis by the small molecule inhibitor of adipocytetriglyceride lipase (ATGL) Atglistatin reduced cardiac lipid accumulation by 70% and neutrophil infiltration by 30% and went along with an improved cardiac function. Direct targeting of neutrophils by means of anti Ly6G-antibody administration in vivo led to a reduced LV dilation in iCMp38αKO mice and an improved systolic function (EF: 39.27 ± 14%). Thus, adipose tissue lipolysis and CM lipid accumulation augmented cardiac inflammation in iCMp38αKO mice. Neutrophils, in particular, triggered the rapid left ventricular dilatation. We provide the first evidence that p38 MAPKα acts as an essential switch in cardiac adaptation to PO by mitigating metabolic dysfunction and inflammation. Moreover, we identified a heart-adipose tissue-immune cell crosstalk, which might serve as new therapeutic target in cardiac pathologies.

Toward a New Paradigm for Targeted Natriuretic Peptide Enhancement in Heart Failure

The natriuretic peptide system (NPS) plays a fundamental role in maintaining cardiorenal homeostasis, and its potent filling pressure-regulated diuretic and vasodilatory effects constitute a beneficial compensatory mechanism in heart failure (HF). Leveraging the NPS for therapeutic benefit in HF has been the subject of intense investigation during the last three decades and has ultimately reached widespread clinical use in the form of angiotensin receptor-neprilysin inhibition (ARNi). NPS enhancement via ARNi confers beneficial effects on mortality and hospitalization in HF, but inhibition of neprilysin leads to the accumulation of a number of other vasoactive peptides in the circulation, often resulting in hypotension and raising potential concerns over long-term adverse effects. Moreover, ARNi is less effective in the large group of HF patients with preserved ejection fraction. Alternative approaches for therapeutic augmentation of the NPS with increased specificity and efficacy are therefore warranted, and are now becoming feasible particularly with recent development of RNA therapeutics. In this review, the current state-of-the-art in terms of experimental and clinical strategies for NPS augmentation and their implementation will be reviewed and discussed.

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.

GATA4-Twist1 Signalling in Disturbed Flow-Induced Atherosclerosis

BACKGROUND

Endothelial cell (EC) dysfunction (enhanced inflammation, proliferation and permeability) is the initial trigger for atherosclerosis. Atherosclerosis shows preferential development near branches and bends exposed to disturbed blood flow. By contrast, sites that are exposed to non-disturbed blood flow are atheroprotected. Disturbed flow promotes atherosclerosis by promoting EC dysfunction. Blood flow controls EC function through transcriptional and post-transcriptional mechanisms that are incompletely understood.

METHODS AND RESULTS

We identified the developmental transcription factors Twist1 and GATA4 as being enriched in EC at disturbed flow, atheroprone regions of the porcine aorta in a microarray study. Further work using the porcine and murine aortae demonstrated that Twist1 and GATA4 expression was enhanced at the atheroprone, disturbed flow sites in vivo. Using controlled in vitro flow systems, the expression of Twist1 and GATA4 was enhanced under disturbed compared to non-disturbed flow in cultured cells. Disturbed flow promoted Twist1 expression through a GATA4-mediated transcriptional mechanism as revealed by a series of in vivo and in vitro studies. GATA4-Twist1 signalling promoted EC proliferation, inflammation, permeability and endothelial-to-mesenchymal transition (EndoMT) under disturbed flow, leading to atherosclerosis development, as shown in a combination of in vitro and in vivo studies using GATA4 and Twist1-specific siRNA and EC-specific GATA4 and Twist1 Knock out (KO) mice.

CONCLUSIONS

We revealed that GATA4-Twist1-Snail signalling triggers EC dysfunction and atherosclerosis; this work could lead to the development of novel anti-atherosclerosis therapeutics.

Targeting GATA4 for cardiac repair

Various strategies have been applied to replace the loss of cardiomyocytes in order to restore reduced cardiac function and prevent the progression of heart disease. Intensive research efforts in the field of cellular reprogramming and cell transplantation may eventually lead to efficient in vivo applications for the treatment of cardiac injuries, representing a novel treatment strategy for regenerative medicine. Modulation of cardiac transcription factor (TF) networks by chemical entities represents another viable option for therapeutic interventions. Comprehensive screening projects have revealed a number of molecular entities acting on molecular pathways highly critical for cellular lineage commitment and differentiation, including compounds targeting Wnt- and transforming growth factor beta (TGFβ)-signaling. Furthermore, previous studies have demonstrated that GATA4 and NKX2-5 are essential TFs in gene regulation of cardiac development and hypertrophy. For example, both of these TFs are required to fully activate mechanical stretch-responsive genes such as atrial natriuretic peptide and brain natriuretic peptide (BNP). We have previously reported that the compound 3i-1000 efficiently inhibited the synergy of the GATA4-NKX2-5 interaction. Cellular effects of 3i-1000 have been further characterized in a number of confirmatory in vitro bioassays, including rat cardiac myocytes and animal models of ischemic injury and angiotensin II-induced pressure overload, suggesting the potential for small molecule-induced cardioprotection.

Phosphorylation of GATA4 serine 105 but not serine 261 is required for testosterone production in the male mouse

BACKGROUND

GATA4 is a transcription factor essential for male sex determination, testicular differentiation during fetal development, and male fertility in the adult. GATA4 exerts part of its function by regulating multiple genes in the steroidogenic enzyme pathway. In spite of these crucial roles, how the activity of this factor is regulated remains unclear.

OBJECTIVES

Studies in gonadal cell lines have shown that GATA4 is phosphorylated on at least two serine residues-serine 105 (S105) and serine 261 (S261)-and that this phosphorylation is important for GATA4 activity. The objective of the present study is to characterize the endogenous role of GATA4 S105 and S261 phosphorylation in the mouse testis.

MATERIALS AND METHODS

We examined both previously described GATA4 S105A mice and a novel GATA4 S261A knock-in mouse that we generated by CRISPR/Cas9 gene editing. The male phenotype of the mutants was characterized by assessing androgen-dependent organ weights, hormonal profiles, and expression of multiple testicular target genes using standard biochemical and molecular biology techniques.

RESULTS

The fecundity of crosses between GATA4 S105A mice was reduced but without a change in sex ratio. The weight of androgen-dependent organs was smaller when compared to wild-type controls. Plasma testosterone levels showed a 70% decrease in adult GATA4 S105A males. This decrease was associated with a reduction in Cyp11a1, Cyp17a1, and Hsd17b3 expression. GATA4 S261A mice were viable and testis morphology appeared normal. Testosterone production and steroidogenic enzyme expression were not altered in GATA4 S261A males.

DISCUSSION AND CONCLUSION

Our analysis showed that blocking GATA4 S105 phosphorylation is associated with decreased androgen production in males. In contrast, S261 phosphorylation by itself is dispensable for GATA4 function. These results confirm that endogenous GATA4 action is essential for normal steroid production in males and that this activity requires phosphorylation on at least one serine residue.

The status of MAPK cascades contributes to the induction and activation of Gata4 and Nkx2.5 during the stepwise process of cardiac differentiation

Cardiac differentiation in vitro is a complex, stepwise process that is rigidly governed by a subset of transcription factors and signaling cascades. In this study, we investigated the cooperation of cardiac-specific transcription factors Gata4 and Nkx2.5, as well as mitogen-activated protein kinase (MAPK) cascades. P19 embryonic carcinoma cells were induced into spontaneously beating cardiomyocytes utilizing a two-step protocol that comprised an early stage and a late stage of differentiation. During early-stage differentiation in suspension culture, P19 cells aggregated to form embryoid bodies (EBs), and the Gata4 and Nkx2.5 genes were induced. However, Gata4 expressed at the early stage of differentiation was incapable of activating downstream gene expression, as it was localized in the cytoplasm and prone to degradation. After EBs were plated for late-stage differentiation in adherent culture, the MAPK cascades were highly activated and contributed to the activation of Gata4 and Nkx2.5. Specifically, we revealed that p38 signaling participated in regulating the localization and stabilization of Gata4 and Nkx2.5. Additionally, the JNK cascade regulated late-stage cardiac differentiation; JNK kinase reduced Gata4 stabilization and conversely alleviated Nkx2.5 degradation by direct interaction and phosphorylation of Nkx2.5. Finally, we found that the C-terminal domain of Nkx2.5 was required for its stabilization under conditions of oxidative stress and JNK activation. Overall, our results indicated that the induction and activation of Gata4 and Nkx2.5 during early- and late-stage cardiac differentiation was closely associated with the function of the MAPK signaling cascades.

ADAP1 limits neonatal cardiomyocyte hypertrophy by reducing integrin cell surface expression

The ArfGAP with dual PH domains 1 (ADAP1) regulates the activation of the hypertrophic mitogen-activated protein kinase ERK1/2 pathway in non-cardiomyocytes. However, its role in cardiomyocytes is unknown. Our aim was to characterize the role of ADAP1 in the hypertrophic process of cardiomyocytes. We assessed the expression of ADAP1 in the hearts of adult and neonatal rats by RT-qPCR and Western blotting and showed that it is preferentially expressed in cardiomyocytes. Adenoviral-mediated ADAP1 overexpression in cultured rat neonatal ventricular cardiomyocytes limited their serum-induced hypertrophic response as measured by immunofluorescence microscopy. Furthermore, ADAP1 overexpression completely blocked phenylephrine- and Mek1 constitutively active (Mek1ca) mutant-induced hypertrophy in these cells. The anti-hypertrophic effect of ADAP1 was not caused by a reduction in protein synthesis, interference with the Erk1/2 pathway, or disruption of the fetal gene program activation, as assessed by nascent protein labeling, Western blotting, and RT-qPCR, respectively. An analysis of cultured cardiomyocytes by confocal microscopy revealed that ADAP1 partially re-organizes α-actinin into dense puncta, a phenomenon that is synergized by Mek1ca overexpression. Biotin labeling of cell surface proteins from cardiomyocytes overexpressing ADAP1 revealed that it reduces the surface expression of β1-integrin, an effect that is strongly potentiated by Mek1ca overexpression. Our findings provide insights into the anti-hypertrophic function of ADAP1 in cardiomyocytes.

Cardiac Actions of a Small Molecule Inhibitor Targeting GATA4-NKX2-5 Interaction

Transcription factors are fundamental regulators of gene transcription, and many diseases, such as heart diseases, are associated with deregulation of transcriptional networks. In the adult heart, zinc-finger transcription factor GATA4 is a critical regulator of cardiac repair and remodelling. Previous studies also suggest that NKX2-5 plays function role as a cofactor of GATA4. We have recently reported the identification of small molecules that either inhibit or enhance the GATA4–NKX2-5 transcriptional synergy. Here, we examined the cardiac actions of a potent inhibitor (3i-1000) of GATA4–NKX2-5 interaction in experimental models of myocardial ischemic injury and pressure overload. In mice after myocardial infarction, 3i-1000 significantly improved left ventricular ejection fraction and fractional shortening, and attenuated myocardial structural changes. The compound also improved cardiac function in an experimental model of angiotensin II -mediated hypertension in rats. Furthermore, the up-regulation of cardiac gene expression induced by myocardial infarction and ischemia reduced with treatment of 3i-1000 or when micro- and nanoparticles loaded with 3i-1000 were injected intramyocardially or intravenously, respectively. The compound inhibited stretch- and phenylephrine-induced hypertrophic response in neonatal rat cardiomyocytes. These results indicate significant potential for small molecules targeting GATA4–NKX2-5 interaction to promote myocardial repair after myocardial infarction and other cardiac injuries.

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.

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.

Nuclear Receptor-Like Structure and Interaction of Congenital Heart Disease-Associated Factors GATA4 and NKX2-5

AIMS

Transcription factor GATA4 is a dosage sensitive regulator of heart development and alterations in its level or activity lead to congenital heart disease (CHD). GATA4 has also been implicated in cardiac regeneration and repair. GATA4 action involves combinatorial interaction with other cofactors such as NKX2-5, another critical cardiac regulator whose mutations also cause CHD. Despite its critical importance to the heart and its evolutionary conservation across species, the structural basis of the GATA4-NKX2-5 interaction remains incompletely understood.

METHODS AND RESULTS

A homology model was constructed and used to identify surface amino acids important for the interaction of GATA4 and NKX2-5. These residues were subjected to site-directed mutagenesis, and the mutant proteins were characterized for their ability to bind DNA and to physically and functionally interact with NKX2-5. The studies identify 5 highly conserved amino acids in the second zinc finger (N272, R283, Q274, K299) and its C-terminal extension (R319) that are critical for physical and functional interaction with the third alpha helix of NKX2-5 homeodomain. Integration of the experimental data with computational modeling suggests that the structural arrangement of the zinc finger-homeodomain resembles the architecture of the conserved DNA binding domain of nuclear receptors.

CONCLUSIONS

The results provide novel insight into the structural basis for protein-protein interactions between two important classes of transcription factors. The model proposed will help to elucidate the molecular basis for disease causing mutations in GATA4 and NKX2-5 and may be relevant to other members of the GATA and NK classes of transcription factors.

GATA transcription factors as tissue-specific master regulators for induced responses

GATA transcription factors play important roles in directing developmental genetic programs and cell differentiation, and are conserved in animals, plants and fungi. C. elegans has 11 GATA-type transcription factors that orchestrate development of the gut, epidermis and vulva. However, the expression of certain GATA proteins persists into adulthood, where their function is less understood. Accumulating evidence demonstrates contributions of 2 terminal differentiation GATA transcription factors, ELT-2 and ELT-3, to epithelial immune responses in the adult intestine and epidermis (hypodermis), respectively. Involvement in other stress responses has also been documented. We recently showed that ELT-2 acted as a tissue-specific master regulator, cooperating with 2 transcription factors activated by the p38 pathway, ATF-7 and SKN-1, to control immune responses in the adult C. elegans intestine. Here, we discuss the broader implications of these findings for understanding the involvement of GATA transcription factors in adult stress responses, and draw parallels between ELT-2 and ELT-3 to speculate that the latter may fulfill similar tissue-specific functions in the epidermis.

Low-dose radiation affects cardiac physiology: gene networks and molecular signaling in cardiomyocytes

There are 160,000 cancer patients worldwide treated with particle radiotherapy (RT). With the advent of proton, and high (H) charge (Z) and energy (E) HZE ionizing particle RT, the cardiovascular diseases risk estimates are uncertain. In addition, future deep space exploratory-type missions will expose humans to unknown but low doses of particle irradiation (IR). We examined molecular responses using transcriptome profiling in left ventricular murine cardiomyocytes isolated from mice that were exposed to 90 cGy, 1 GeV proton ((1)H) and 15 cGy, 1 GeV/nucleon iron ((56)Fe) over 28 days after exposure. Unsupervised clustering analysis of gene expression segregated samples according to the IR response and time after exposure, with (56)Fe-IR showing the greatest level of gene modulation. (1)H-IR showed little differential transcript modulation. Network analysis categorized the major differentially expressed genes into cell cycle, oxidative responses, and transcriptional regulation functional groups. Transcriptional networks identified key nodes regulating expression. Validation of the signal transduction network by protein analysis and gel shift assay showed that particle IR clearly regulates a long-lived signaling mechanism for ERK1/2, p38 MAPK signaling and identified NFATc4, GATA4, STAT3, and NF-κB as regulators of the response at specific time points. These data suggest that the molecular responses and gene expression to (56)Fe-IR in cardiomyocytes are unique and long-lasting. Our study may have significant implications for the efforts of National Aeronautics and Space Administration to develop heart disease risk estimates for astronauts and for patients receiving conventional and particle RT via identification of specific HZE-IR molecular markers.

Extracellular signal-regulated kinases 1/2 as regulators of cardiac hypertrophy

Cardiac hypertrophy results from increased mechanical load on the heart and through the actions of local and systemic neuro-humoral factors, cytokines and growth factors. These mechanical and neuroendocrine effectors act through stretch, G protein–coupled receptors and tyrosine kinases to induce the activation of a myriad of intracellular signaling pathways including the extracellular signal-regulated kinases 1/2 (ERK1/2). Since most stimuli that provoke myocardial hypertrophy also elicit an acute phosphorylation of the threonine-glutamate-tyrosine (TEY) motif within the activation loops of ERK1 and ERK2 kinases, resulting in their activation, ERKs have long been considered promotors of cardiac hypertrophy. Several mouse models were generated in order to directly understand the causal role of ERK1/2 activation in the heart. These models include direct manipulation of ERK1/2 such as overexpression, mutagenesis or knockout models, manipulations of upstream kinases such as MEK1 and manipulations of the phosphatases that dephosphorylate ERK1/2 such as DUSP6. The emerging understanding from these studies, as will be discussed here, is more complex than originally considered. While there is little doubt that ERK1/2 activation or the lack of it modulates the hypertrophic process or the type of hypertrophy that develops, it appears that not all ERK1/2 activation events are the same. While much has been learned, some questions remain regarding the exact role of ERK1/2 in the heart, the upstream events that result in ERK1/2 activation and the downstream effector in hypertrophy.

The Early-Onset Myocardial Infarction Associated PHACTR1 Gene Regulates Skeletal and Cardiac Alpha-Actin Gene Expression

The phosphatase and actin regulator 1 (PHACTR1) locus is a very commonly identified hit in genome-wide association studies investigating coronary artery disease and myocardial infarction (MI). However, the function of PHACTR1 in the heart is still unknown. We characterized the mechanisms regulating Phactr1 expression in the heart, used adenoviral gene delivery to investigate the effects of Phactr1 on cardiac function, and analyzed the relationship between MI associated PHACTR1 allele and cardiac function in human subjects. Phactr1 mRNA and protein levels were markedly reduced (60%, P<0.01 and 90%, P<0.001, respectively) at 1 day after MI in rats. When the direct myocardial effects of Phactr1 were studied, the skeletal α-actin to cardiac α-actin isoform ratio was significantly higher (1.5-fold, P<0.05) at 3 days but 40% lower (P<0.05) at 2 weeks after adenovirus-mediated Phactr1 gene delivery into the anterior wall of the left ventricle. Similarly, the skeletal α-actin to cardiac α-actin ratio was lower at 2 weeks in infarcted hearts overexpressing Phactr1. In cultured neonatal cardiac myocytes, adenovirus-mediated Phactr1 overexpression for 48 hours markedly increased the skeletal α-actin to cardiac α-actin ratio, this being associated with an enhanced DNA binding activity of serum response factor. Phactr1 overexpression exerted no major effects on the expression of other cardiac genes or LV structure and function in normal and infarcted hearts during 2 weeks’ follow-up period. In human subjects, MI associated PHACTR1 allele was not associated significantly with cardiac function (n = 1550). Phactr1 seems to regulate the skeletal to cardiac α-actin isoform ratio.

The Developmental Intestinal Regulator ELT-2 Controls p38-Dependent Immune Responses in Adult C. elegans

GATA transcription factors play critical roles in cellular differentiation and development. However, their roles in mature tissues are less understood. In C. elegans larvae, the transcription factor ELT-2 regulates terminal differentiation of the intestine. It is also expressed in the adult intestine, where it was suggested to maintain intestinal structure and function, and where it was additionally shown to contribute to infection resistance. To study the function of elt-2 in adults we characterized elt-2-dependent gene expression following its knock-down specifically in adults. Microarray analysis identified two ELT-2-regulated gene subsets: one, enriched for hydrolytic enzymes, pointed at regulation of constitutive digestive functions as a dominant role of adult elt-2; the second was enriched for immune genes that are induced in response to Pseudomonas aeruginosa infection. Focusing on the latter, we used genetic analyses coupled to survival assays and quantitative RT-PCR to interrogate the mechanism(s) through which elt-2 contributes to immunity. We show that elt-2 controls p38-dependent gene induction, cooperating with two p38-activated transcription factors, ATF-7 and SKN-1. This demonstrates a mechanism through which the constitutively nuclear elt-2 can impact induced responses, and play a dominant role in C. elegans immunity.

WDR12, a Member of Nucleolar PeBoW-Complex, Is Up-Regulated in Failing Hearts and Causes Deterioration of Cardiac Function

Aims

In a recent genome-wide association study, WD-repeat domain 12 (WDR12) was associated with early-onset myocardial infarction (MI). However, the function of WDR12 in the heart is unknown.

Methods and Results

We characterized cardiac expression of WDR12, used adenovirus-mediated WDR12 gene delivery to examine effects of WDR12 on left ventricular (LV) remodeling, and analyzed relationship between MI associated WDR12 allele and cardiac function in human subjects. LV WDR12 protein levels were increased in patients with dilated cardiomyopathy and rats post-infarction. In normal adult rat hearts, WDR12 gene delivery into the anterior wall of the LV decreased interventricular septum diastolic and systolic thickness and increased the diastolic and systolic diameters of the LV. Moreover, LV ejection fraction (9.1%, P<0.05) and fractional shortening (12.2%, P<0.05) were declined. The adverse effects of WDR12 gene delivery on cardiac function were associated with decreased cellular proliferation, activation of p38 mitogen–activated protein kinase (MAPK)/heat shock protein (HSP) 27 pathway, and increased protein levels of Block of proliferation 1 (BOP1), essential for ribosome biogenesis. Post-infarction WDR12 gene delivery decreased E/A ratio (32%, P<0.05) suggesting worsening of diastolic function. In human subjects, MI associated WDR12 allele was associated significantly with diastolic dysfunction and left atrial size.

Conclusions

WDR12 triggers distinct deterioration of cardiac function in adult rat heart and the MI associated WDR12 variant is associated with diastolic dysfunction in human subjects.

ZAK induces cardiomyocyte hypertrophy and brain natriuretic peptide expression via p38/JNK signaling and GATA4/c-Jun transcriptional factor activation

Cardiomyocyte hypertrophy is an adaptive response of heart to various stress conditions. During the period of stress accumulation, transition from physiological hypertrophy to pathological hypertrophy results in the promotion of heart failure. Our previous studies found that ZAK, a sterile alpha motif and leucine zipper containing kinase, was highly expressed in infarcted human hearts and demonstrated that overexpression of ZAK induced cardiac hypertrophy. This study evaluates, cellular events associated with the expression of two doxycycline (Dox) inducible Tet-on ZAK expression systems, a Tet-on ZAK WT (wild-type), and a Tet-on ZAK DN (mutant, Dominant-negative form) in H9c2 myoblast cells; Tet-on ZAK WT was found to increase cell size and hypertrophic marker BNP in a dose-dependent manner. To ascertain the mechanism of ZAK-mediated hypertrophy, expression analysis with various inhibitors of the related upstream and downstream proteins was performed. Tet-on ZAK WT expression triggered the p38 and JNK pathway and also activated the expression and nuclear translocation of p-GATA4 and p-c-Jun transcription factors, without the involvement of p-ERK or NFATc3. However, Tet-on ZAK DN showed no effect on the p38 and JNK signaling cascade. The results showed that the inhibitors of JNK1/2 and p38 significantly suppressed ZAK-induced BNP expression. The results show the role of ZAK and/or the ZAK downstream events such as JNK and p38 phosphorylation, c-Jun, and GATA-4 nuclear translocation in cardiac hypertrophy. ZAK and/or the ZAK downstream p38, and JNK pathway could therefore be potential targets to ameliorate cardiac hypertrophy symptoms in ZAK-overexpressed patients.

Na+/H+ exchanger isoform 1 induced cardiomyocyte hypertrophy involves activation of p90 ribosomal s6 kinase

Studies using pharmacological and genetic approaches have shown that increased activity/expression of the Na⁺/H⁺ exchanger isoform 1 (NHE1) play a critical role in the pathogenesis of cardiac hypertrophy. Despite the importance of NHE1 in cardiac hypertrophy, severe cerebrovascular side effects were associated with the use of NHE1 inhibitors when administered to patients with myocardial infarctions. p90 ribosomal S6 Kinase (RSK), a downstream regulator of the mitogen-activated protein kinase pathway, has also been implicated in cardiac hypertrophy. We hypothesized that RSK plays a role in the NHE1 induced cardiomyocyte hypertrophic response. Infection of H9c2 cardiomyoblasts with the active form of the NHE1 adenovirus induced hypertrophy and was associated with an increase in the phosphorylation of RSK (P<0.05). Parameters of hypertrophy such as cell area, protein content and atrial natriuretic mRNA expression were significantly reduced in H9c2 cardiomyoblasts infected with active NHE1 in the presence of dominant negative RSK (DN-RSK) (P<0.05). These results confirm that NHE1 lies upstream of RSK. Increased phosphorylation and activation of GATA4 at Ser²⁶¹ was correlated with increased RSK phosphorylation. This increase was reversed upon inhibition of RSK or NHE1. These findings demonstrate for the first time that the NHE1 mediated hypertrophy is accounted for by increased activation and phosphorylation of RSK, which subsequently increased the phosphorylation of GATA4; eventually activating fetal gene transcriptional machinery.

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.

Gelsolin (GSN) induces cardiomyocyte hypertrophy and BNP expression via p38 signaling and GATA-4 transcriptional factor activation

Cardiomyocyte hypertrophy is an adaptive response of the heart to various types of stress. During the period of stress accumulation, the transition from physiological hypertrophy to pathological hypertrophy results in the promotion of heart failure. Gelsolin (GSN) is a member of the actin-binding proteins, which regulate dynamic actin filament organization by severing and capping. Moreover, GSN also regulates cell morphology, differentiation, movement, and apoptosis. In this study, we used H9c2 and H9c2-GSN stable clones in an attempt to understand the mechanisms of GSN overexpression in cardiomyocytes. These data showed that the overexpression of GSN in H9c2-induced cardiac hypertrophy and increased the pathological hypertrophy markers atrial natriuretic peptide brain natriuretic peptide. Furthermore, we found that E-cadherin expression decreased with the overexpression of GSN in H9c2, but β-catenin expression increased. These data presume that the cytoskeleton is loose. Further, previous studies show that the mitogen-activated protein kinase pathway can induce cardiac hypertrophy. Our data showed that p-p38 expression increased with the overexpression of GSN in H9c2, and the transcription factor p-GATA4 expression also increased, suggesting that the overexpression of GSN in H9c2-induced cardiac hypertrophy seemed to be regulated by the p38/GATA4 pathway. Moreover, we used both the p38 inhibitor (SB203580) and GSN siRNA to confirm our conjecture. We found that both of these factors significantly suppressed gelsolin-induced cardiac hypertrophy through p38/GATA4 signaling pathway. Therefore, we predict that the gene silencing of GSN and/or the downstream blocking of GSN along the p38 pathway could be applied to ameliorate pathological cardiac hypertrophy in the future.

Gene expression profiles in engineered cardiac tissues respond to mechanical loading and inhibition of tyrosine kinases

Engineered cardiac tissues (ECTs) are platforms to investigate cardiomyocyte maturation and functional integration, the feasibility of generating tissues for cardiac repair, and as models for pharmacology and toxicology bioassays. ECTs rapidly mature in vitro to acquire the features of functional cardiac muscle and respond to mechanical load with increased proliferation and maturation. ECTs are now being investigated as platforms for in vitro models for human diseases and for pharmacologic screening for drug toxicities. We tested the hypothesis that global ECT gene expression patterns are complex and sensitive to mechanical loading and tyrosine kinase inhibitors similar to the maturing myocardium. We generated ECTs from day 14.5 rat embryo ventricular cells, as previously published, and then conditioned constructs after 5 days in culture for 48 h with mechanical stretch (5%, 0.5 Hz) and/or the p38 MAPK (p38 mitogen-activated protein kinase) inhibitor BIRB796. RNA was isolated from individual ECTs and assayed using a standard Agilent rat 4 × 44k V3 microarray and Pathway Analysis software for transcript expression fold changes and changes in regulatory molecules and networks. Changes in expression were confirmed by quantitative-polymerase chain reaction (q-PCR) for selected regulatory molecules. At the threshold of a 1.5-fold change in expression, stretch altered 1559 transcripts, versus 1411 for BIRB796, and 1846 for stretch plus BIRB796. As anticipated, top pathways altered in response to these stimuli include cellular development, cellular growth and proliferation; tissue development; cell death, cell signaling, and small molecule biochemistry as well as numerous other pathways. Thus, ECTs display a broad spectrum of altered gene expression in response to mechanical load and/or tyrosine kinase inhibition, reflecting a complex regulation of proliferation, differentiation, and architectural alignment of cardiomyocytes and noncardiomyocytes within ECT.

Pivotal role of microRNAs in cardiac physiology and heart failure

Cardiac hypertrophy is a hallmark of heart failure (HF), a highly prevalent, debilitating and deadly condition in Western countries. Pronounced changes in molecular pathways governing cardiac physiology underlie hypertrophy and progression to HF. MicroRNAs, small nucleotide sequences that coordinate gene expression, may have a central role in orchestrating these changes since the hypertrophic and HF myocardium clearly shows disturbed microRNA profiles. Experimental interventions targeting miR disturbances have been shown beneficial in animal models of cardiac hypertrophy and HF. This short review discusses exciting potential diagnostic and therapeutic applications of microRNAs to cardiac hypertrophy and HF, highlighting the underlying molecular pathways.

Interferon regulatory factor 3 is a negative regulator of pathological cardiac hypertrophy

Interferon regulatory factor (IRF) 3, a member of the highly conserved IRF family transcription factors, plays a pivotal role in innate immune response, apoptosis, and oncogenesis. Recent studies have implicated IRF3 in a wide range of host defense. However, whether IRF3 induces defensive responses to hypertrophic stresses such as biomechanical stress and neurohumoral factors remains unclear. Herein, we employed an IRF3-deficient mouse model, cardiac-specific IRF3-overexpression mouse model and isolated cardiomyocytes to investigate the role of IRF3 in cardiac hypertrophy induced by aortic banding (AB) or isoproterenol (ISO). The extent of cardiac hypertrophy was quantitated by echocardiography as well as by pathological and molecular analysis. Our results demonstrate that IRF3 deficiency profoundly exacerbated cardiac hypertrophy, whereas overexpression of IRF3 in the heart significantly blunted pathological cardiac remodeling induced by pressure overload. Similar results were also observed in cultured cardiomyocytes upon the treatment with ISO. Mechanistically, we discovered that IRF3 interacted with ERK2 and thereby inhibited the ERK1/2 signaling. Furthermore, inactivation of ERK1/2 by U0126 offset the IRF3-deficient-mediated hypertrophic response induced by aortic banding. Altogether, these data demonstrate that IRF3 plays a protective role in AB-induced hypertrophic response by inactivating ERK1/2 in the heart. Therefore, IRF3 could be a new target for the prevention and therapy of cardiac hypertrophy and failure.

Regulation of cardiac melusin gene expression by hypertrophic stimuli in the rat

AIM

Melusin is an integrin β1-interacting protein proposed to act as a biomechanical sensor in the heart. We characterized mechanisms and signalling pathways regulating cardiac melusin expression.

METHODS

Infusion of arginine(8) -vasopressin (AVP) in Sprague-Dawley (SD) rats, spontaneously hypertensive rats (SHR) and double transgenic rats (dTGR) harbouring both human angiotensinogen and renin genes as well as infusion of angiotensin II (Ang II) in SD rats were used. The effect of direct left ventricular (LV) wall stretch was analysed by using isolated perfused rat heart preparation. For the cell culture studies, mouse atrial HL-1 cell line and neonatal rat ventricular myocytes (NRVMs) were used.

RESULTS

Left atrial melusin mRNA levels increased already after 30 min of AVP infusion. Ang II caused significant upregulation of left atrial melusin mRNA (2.1-fold at 6 h, P < 0.05) and protein (1.9-fold at 72 h, P < 0.05) levels. In contrast, LV melusin mRNA levels remained unchanged in response to both infusions, as well as to aortic banding-induced pressure overload. Direct LV wall stress or late-stage hypertensive heart disease did not modify LV melusin gene expression either. Interestingly, in atrial HL-1 cells, cyclic stretching increased melusin mRNA levels. Stretching and treatments with hypertrophic agonists increased melusin mRNA and protein levels in NRVMs, endothelin-1 being the most potent. PD98059, an extracellular signal-regulated protein kinase 1/2 inhibitor, markedly attenuated the endothelin-1-induced upregulation of melusin gene expression in NRVMs.

CONCLUSION

Multiple hypertrophic stimuli regulate melusin expression predominately in the atria, which may represent a necessary initial step in early adaptive remodelling processes.

Gadd45γ and Map3k4 interactions regulate mouse testis determination via p38 MAPK-mediated control of Sry expression

Loss of the kinase MAP3K4 causes mouse embryonic gonadal sex reversal due to reduced expression of the testis-determining gene, Sry. However, because of widespread expression of MAP3K4, the cellular basis of this misregulation was unclear. Here, we show that mice lacking Gadd45γ also exhibit XY gonadal sex reversal caused by disruption to Sry expression. Gadd45γ is expressed in a dynamic fashion in somatic cells of the developing gonads from 10.5 days postcoitum (dpc) to 12.5 dpc. Gadd45γ and Map3k4 genetically interact during sex determination, and transgenic overexpression of Map3k4 rescues gonadal defects in Gadd45γ-deficient embryos. Sex reversal in both mutants is associated with reduced phosphorylation of p38 MAPK and GATA4. In addition, embryos lacking both p38α and p38β also exhibit XY gonadal sex reversal. Taken together, our data suggest a requirement for GADD45γ in promoting MAP3K4-mediated activation of p38 MAPK signaling in embryonic gonadal somatic cells for testis determination in the mouse.

Inhibition of p38-MAPK alters SRC coactivation and estrogen receptor phosphorylation

The p38 mitogen activated protein kinase pathway (MAPK) is known to promote cell survival, endocrine therapy resistance and hormone independent breast cancer cell proliferation. Therefore, we utilized the novel p38 inhibitor RWJ67657 to investigate the relevance of targeting this pathway in the ER (+) breast cancer cell line MCF-7. Our results show that RWJ67657 inhibits both basal and estrogen stimulated phosphorylation of p38α, resulting in decreased activation of the downstream p38α targets hsp27 and MAPAPK. Furthermore, inhibition of p38α by RWJ67657 blocks clonogenic survival of MCF-7 cells with little effect on non-cancerous breast epithelial cells. Even though p38α is known to phosphorylate ERα at residue within ER's hinge region at Thr311, resulting in increased ERα transcriptional activation, our results suggest RWJ67657 inhibits the p38α-induced activation of ER by targeting both the AF-1 and AF-2 activation domains within ERα. We further show that RWJ67657 decreases the transcriptional activity of the ER coactivators SRC-1, SRC-2 and SRC-3. Taken together, our results strongly suggest that in addition to phosphorylating Thr311 within ERα, p38α indirectly activates the ER by phosphorylation and stimulation of the known ERα coactivators, SRC-1, -2 and-3. Overall, our data underscore the therapeutic potential of targeting the p38 MAPK pathway in the treatment of ER (+) breast cancer.

(Pro)renin receptor triggers distinct angiotensin II-independent extracellular matrix remodeling and deterioration of cardiac function

Background

Activation of the renin-angiotensin-system (RAS) plays a key pathophysiological role in heart failure in patients with hypertension and myocardial infarction. However, the function of (pro)renin receptor ((P)RR) is not yet solved. We determined here the direct functional and structural effects of (P)RR in the heart.

Methodology/Principal Findings

(P)RR was overexpressed by using adenovirus-mediated gene delivery in normal adult rat hearts up to 2 weeks. (P)RR gene delivery into the anterior wall of the left ventricle decreased ejection fraction (P<0.01), fractional shortening (P<0.01), and intraventricular septum diastolic and systolic thickness, associated with approximately 2–fold increase in left ventricular (P)RR protein levels at 2 weeks. To test whether the worsening of cardiac function and structure by (P)RR gene overexpression was mediated by angiotensin II (Ang II), we infused an AT₁ receptor blocker losartan via osmotic minipumps. Remarkably, cardiac function deteriorated in losartan-treated (P)RR overexpressing animals as well. Intramyocardial (P)RR gene delivery also resulted in Ang II-independent activation of extracellular-signal-regulated kinase1/2 phosphorylation and myocardial fibrosis, and the expression of transforming growth factor-β1 and connective tissue growth factor genes. In contrast, activation of heat shock protein 27 phosphorylation and apoptotic cell death by (P)RR gene delivery was Ang II-dependent. Finally, (P)RR overexpression significantly increased direct protein–protein interaction between (P)RR and promyelocytic zinc-finger protein.

Conclusions/Significance

These results indicate for the first time that (P)RR triggers distinct Ang II-independent myocardial fibrosis and deterioration of cardiac function in normal adult heart and identify (P)RR as a novel therapeutic target to optimize RAS blockade in failing hearts.

The many faces of p38 mitogen-activated protein kinase in progenitor/stem cell differentiation

Regulation of stem cells is essential for development and adult tissue homoeostasis. The proper control of stem cell self-renewal and differentiation maintains organ physiology, and disruption of such a balance results in disease. There are many mechanisms that have been established as stem cell regulators, such as Wnt or Notch signals. However, the intracellular mechanisms that mediate and integrate these signals are not well understood. A new intracellular pathway that has been reported to be involved in the regulation of many stem cell types is that of p38 MAPK (mitogen-activated protein kinase). In particular, p38α is essential for the proper differentiation of many haematopoietic, mesenchymal and epithelial stem/progenitor cells. Many reports have shown that disruption of this kinase pathway has pathological consequences in many organs. Understanding the extracellular cues and downstream targets of p38α in stem cell regulation may help to tackle some of the pathologies associated with improper differentiation and regulation of stem cell function. In the present review we present a vision of the current knowledge on the roles of the p38α signal as a regulator of stem/progenitor cells in different tissues in physiology and disease.

Asialoerythropoietin, a nonerythropoietic derivative of erythropoietin, displays broad anti-heart failure activity

BACKGROUND

We investigated the effects of asialoerythropoietin (asialoEPO), a nonerythrogenic erythropoietin derivative, on 3 murine models of heart failure with different etiologies.

METHODS AND RESULTS

Doxorubicin (15 mg/kg) induced heart failure within 2 weeks (toxic cardiomyopathy). Treatment with asialoEPO (6.9 μg/kg) for 2 weeks thereafter attenuated the associated left ventricular dysfunction and dilatation. In addition, the asialoEPO-treated heart showed less myocardial fibrosis, inflammation, and oxidative damage, and diminished atrophic cardiomyocyte degeneration, which was accompanied by restored expression of GATA-4 and sarcomeric proteins. Mice with large 6-week-old myocardial infarctions exhibited marked left ventricular dysfunction with adverse remodeling (ischemic cardiomyopathy). AsialoEPO treatment for 4 weeks significantly mitigated progression of the dysfunction and remodeling and reduced myocardial fibrosis, inflammation, and oxidative damage. Finally, 25-week-old δ-sarcoglycan-deficient mice (genetic cardiomyopathy) were treated with asialoEPO for 5 weeks. AsialoEPO mitigated the progressive cardiac remodeling and dysfunction through cardiomyocyte hypertrophy, and upregulated expression of GATA-4 and sarcomeric proteins. AsialoEPO appears to act by altering the activity of the downstream erythropoietin receptor signals extracellular signal-regulated protein kinase, Akt, signal transducer, and activator of transcription 3 and 5 in a model-specific manner.

CONCLUSIONS

The findings suggest that asialoEPO exerts broad cardioprotective effects through distinct mechanisms depending on the model, which are independent of the erythrogenic action. This compound may be promising for the treatment of heart failure of various etiologies.

Activation of vascular p38MAPK by mechanical stretch is independent of c-Src and NADPH oxidase: influence of hypertension and angiotensin II

Little is known about vascular MAPK regulation in response to mechanical strain. Whether mechanically-sensitive pathways are altered in hypertension is unclear. We examined effects of stretch and Ang II on activation of p38MAPK in vascular smooth muscle cells (VSMC) from WKY and SHR. The role of c-Src and redox-sensitive pathways in stretch-induced effects were examined. VSMC from mesenteric arteries were plated onto flexible silastic plates and exposed to acute or chronic cyclic stretch (10%, 1 Hz) with or without Ang II (0.1 uM). Acute stretch stimulated p38MAPK activation in WKY and SHR, independently of c-Src and reactive oxygen species (ROS), since PP2 (c-Src inhibitor) and apocynin (NADPH oxidase inhibitor), failed to alter stretch-mediated p38MAPK. Chronic stretch blunted p38MAPK phosphorylation in WKY and increased phosphorylation in SHR. Stretch, in the presence of Ang II, induced an increase in procollagen-1 expression. This was blocked by SB203580 (p38MAPK inhibitor). Accordingly, vascular p38MAPK is a mechano-sensitive MAPK, differentially regulated by acute and chronic stretch in WKY and SHR. Functionally, stretch and Ang II, amplify profibrotic responses in a p38MAPK-dependent manner, responses that are perturbed in SHR. Such molecular process may influence vascular fibrosis in hypertension and appear to be independent of c-Src and ROS.

GATA4 regulates ANF expression synergistically with Sp1 in a cardiac hypertrophy model

Cardiac hypertrophy in response to multiple stimuli has important physiological and pathological significances. GATA4 serves as a nuclear integrator of several signalling pathways during cardiac hypertrophy. Sp1 and Sp3 are also reported to be involved in this process. However, the mechanism by which GATA4 acts as a mediator, integrating these ubiquitously expressed transcriptional factors, is poorly understood. We found that the expression of GATA4 and Sp1 was up-regulated in the myocardium of a pressure overload hypertrophy rat model, as well in phenylephrine-induced (PE-induced) hypertrophic growth of neonatal cardiomyocytes. GST pull-down assays demonstrated that GATA4 could interact with Sp1 in vitro. Therefore, we proposed that GATA4 cooperates with Sp1 in regulating ANF expression, as its reactivation is closely linked with hypertrophy. Further studies demonstrated that GATA4 could activate the ANF promoter synergistically with Sp1 through direct interaction. In contrast, Sp3 exhibited antagonistic function, and overexpression of Sp3 repressed the transcriptional synergy between Sp1 and GATA4. We also found that Sp1 alone could activate the ANF promoter in cardiomyocytes, whereas Sp3 exerted negative effects on ANF expression. Bioinformatics analysis revealed novel Sp-binding sites on the ANF promoter. The recruitment of GATA4 and Sp1 on the ANF promoter was enhanced during phenylephrine-mediated hypertrophy, whereas the recruitment of Sp3 was reduced. The phosphorylation of GATA4 by ERK1/2 kinase could enhance the affinity between GATA4 and Sp1. Thus, our findings revealed the critical interaction of GATA4 and Sp1 in modulating ANF expression, indicating their involvement in cardiac hypertrophy.

Neuronostatin, a novel peptide encoded by somatostatin gene, regulates cardiac contractile function and cardiomyocyte survival

Neuronostatin, a recently discovered peptide encoded by somatostatin gene, is involved in regulation of neuronal function, blood pressure, food intake, and drinking behavior. However, the biological effects of neuronostatin on cardiac myocytes are not known, and the intracellular signaling mechanisms induced by neuronostatin remain unidentified. We analyzed the effect of neuronostatin in isolated perfused rat hearts and in cultured primary cardiomyocytes. Neuronostatin infusion alone had no effect on left ventricular (LV) contractile function or on isoprenaline- or preload-induced increase in cardiac contractility. However, infusion of neuronostatin significantly decreased the positive inotropic response to endothelin-1 (ET-1). This was associated with an increase in phosphorylation of p38 mitogen-activated protein kinase and c-Jun N-terminal kinase (JNK). Treatment of both neonatal and adult cardiomyocytes with neuronostatin resulted in reduced cardiomyocyte viability. Inhibition of JNK further increased the neuronostatin-induced cell death. We conclude that neuronostatin regulates cardiac contractile function and cardiomyocyte survival. Receptors for neuronostatin need to be identified to further characterize the biological functions of the peptide.

M-CAT element mediates mechanical stretch-activated transcription of B-type natriuretic peptide via ERK activation

The muscle-CAT (M-CAT) promoter element is found on promoters of most muscle-specific cardiac genes, but its role in cardiac pathology is poorly understood. Here we studied whether the M-CAT element is involved in hypertrophic process activated by mechanical stretch, and identified the intracellular pathways mediating the response. When an in vitro stretch model of cultured neonatal rat cardiomyocytes and luciferase reporter construct driven by rat B-type natriuretic peptide (BNP) promoter were used, mutation of M-CAT element inhibited not only the basal reporter activity (88%), but also the stretch-activated BNP transcription (58%, p < 0.001). Stretch-induced BNP promoter activation was associated with an increase in transcriptional enhancer factor-1 (TEF-1) binding activity after 24 h mechanical stretch (p < 0.05). Inhibition of mitogen-activated protein kinases ERK, JNK, or p38 attenuated stretch-induced BNP activation. Interestingly, as opposed to p38 and JNK, inhibition of ERK had no additional effect on transcriptional activity of BNP promoter harboring the M-CAT mutation, suggesting a pivotal role for ERK in regulating stretch-induced BNP transcription via M-CAT binding site. Finally, immunoprecipitation studies showed that mechanical stretch induced myocyte enhancer factor-2 (MEF-2) binding to TEF-1. These data suggest a central role for M-CAT element in regulation of mechanical stretch-induced hypertrophic response via ERK activation.