Angiotensin II type1a receptor gene expression in the heart: AP-1 and GATA-4 participate in the response to pressure overload

Maintenance of Cardiac Microenvironmental Homeostasis: A Joint Battle of Multiple Cells

Various cells such as cardiomyocytes, fibroblasts and endothelial cells constitute integral components of cardiac tissue. The health and stability of cardiac ecosystem are ensured by the action of a certain type of cell and the intricate interactions between multiple cell types. The dysfunctional cells exert a profound impact on the development of cardiovascular diseases by involving in the pathological process. In this paper, we introduce the dynamic activity, cell surface markers as well as biological function of the various cells in the heart. Besides, we discuss the multiple signaling pathways involved in the cardiac injury including Hippo/YAP, TGF-β/Smads, PI3K/Akt, and MAPK signaling. The complexity of different cell types poses a great challenge to the disease treatment. By characterizing the roles of various cell types in cardiovascular diseases, we sought to discuss the potential strategies for preventing and treating cardiovascular diseases.

Intrinsic GATA4 expression sensitizes the aortic root to dilation in a Loeys-Dietz syndrome mouse model

Loeys-Dietz syndrome (LDS) is a connective tissue disorder caused by mutations that decrease transforming growth factor-β signaling. LDS-causing mutations increase the risk of aneurysm throughout the arterial tree, yet the aortic root is a site of heightened susceptibility. Here we investigate the heterogeneity of vascular smooth muscle cells (VSMCs) in the aorta of Tgfbr1M318R/+ LDS mice by single-cell transcriptomics to identify molecular determinants of this vulnerability. Reduced expression of components of the extracellular matrix-receptor apparatus and upregulation of stress and inflammatory pathways were observed in all LDS VSMCs. However, regardless of genotype, a subset of Gata4-expressing VSMCs predominantly located in the aortic root intrinsically displayed a less differentiated, proinflammatory profile. A similar population was also identified among aortic VSMCs in a human single-cell RNA sequencing dataset. Postnatal VSMC-specific Gata4 deletion reduced aortic root dilation in LDS mice, suggesting that this factor sensitizes the aortic root to the effects of impaired transforming growth factor-β signaling.

Fibrosis and Hepatocarcinogenesis: Role of Gene-Environment Interactions in Liver Disease Progression

The liver is a complex organ that performs vital functions in the body. Despite its extraordinary regenerative capacity compared to other organs, exposure to chemical, infectious, metabolic and immunologic insults and toxins renders the liver vulnerable to inflammation, degeneration and fibrosis. Abnormal wound healing response mediated by aberrant signaling pathways causes chronic activation of hepatic stellate cells (HSCs) and excessive accumulation of extracellular matrix (ECM), leading to hepatic fibrosis and cirrhosis. Fibrosis plays a key role in liver carcinogenesis. Once thought to be irreversible, recent clinical studies show that hepatic fibrosis can be reversed, even in the advanced stage. Experimental evidence shows that removal of the insult or injury can inactivate HSCs and reduce the inflammatory response, eventually leading to activation of fibrolysis and degradation of ECM. Thus, it is critical to understand the role of gene-environment interactions in the context of liver fibrosis progression and regression in order to identify specific therapeutic targets for optimized treatment to induce fibrosis regression, prevent HCC development and, ultimately, improve the clinical outcome.

Intrinsic Gata4 expression sensitizes the aortic root to dilation in a Loeys-Dietz syndrome mouse model

Loeys-Dietz syndrome (LDS) is an aneurysm disorder caused by mutations that decrease transforming growth factor-β (TGF-β) signaling. Although aneurysms develop throughout the arterial tree, the aortic root is a site of heightened risk. To identify molecular determinants of this vulnerability, we investigated the heterogeneity of vascular smooth muscle cells (VSMCs) in the aorta of Tgfbr1 M318R/+ LDS mice by single cell and spatial transcriptomics. Reduced expression of components of the extracellular matrix-receptor apparatus and upregulation of stress and inflammatory pathways were observed in all LDS VSMCs. However, regardless of genotype, a subset of Gata4-expressing VSMCs predominantly located in the aortic root intrinsically displayed a less differentiated, proinflammatory profile. A similar population was also identified among aortic VSMCs in a human scRNAseq dataset. Postnatal VSMC-specific Gata4 deletion reduced aortic root dilation in LDS mice, suggesting that this factor sensitizes the aortic root to the effects of impaired TGF-β signaling.

Cardiac-specific BACH1 ablation attenuates pathological cardiac hypertrophy by inhibiting the Ang II type 1 receptor expression and the Ca2+/CaMKII pathway

AIMS

BACH1 is up-regulated in hypertrophic hearts, but its function in cardiac hypertrophy remains largely unknown. This research investigates the function and mechanisms of BACH1 in the regulation of cardiac hypertrophy.

METHODS AND RESULTS

Male cardiac-specific BACH1 knockout mice or cardiac-specific BACH1 transgenic (BACH1-Tg) mice and their respective wild-type littermates developed cardiac hypertrophy induced by angiotensin II (Ang II) or transverse aortic constriction (TAC). Cardiac-specific BACH1 knockout in mice protected the hearts against Ang II- and TAC-induced cardiac hypertrophy and fibrosis, and preserved cardiac function. Conversely, cardiac-specific BACH1 overexpression markedly exaggerated cardiac hypertrophy and fibrosis and reduced cardiac function in mice with Ang II- and TAC-induced hypertrophy. Mechanistically, BACH1 silencing attenuated Ang II- and norepinephrine-stimulated calcium/calmodulin-dependent protein kinase II (CaMKII) signalling, the expression of hypertrophic genes, and hypertrophic growth of cardiomyocytes. Ang II stimulation promoted the nuclear localization of BACH1, facilitated the recruitment of BACH1 to the Ang II type 1 receptor (AT1R) gene promoter, and then increased the expression of AT1R. Inhibition of BACH1 attenuated Ang II-stimulated AT1R expression, cytosolic Ca2+ levels, and CaMKII activation in cardiomyocytes, whereas overexpression of BACH1 led to the opposite effects. The increased expression of hypertrophic genes induced by BACH1 overexpression upon Ang II stimulation was suppressed by CaMKII inhibitor KN93. The AT1R antagonist, losartan, significantly attenuated BACH1-mediated CaMKII activation and cardiomyocyte hypertrophy under Ang II stimulation in vitro. Similarly, Ang II-induced myocardial pathological hypertrophy, cardiac fibrosis, and dysfunction in BACH1-Tg mice were blunted by treatment with losartan.

CONCLUSION

This study elucidates a novel important role of BACH1 in pathological cardiac hypertrophy by regulating the AT1R expression and the Ca2+/CaMKII pathway, and highlights potential therapeutic target in pathological cardiac hypertrophy.

Heart Failure Pathogenesis Elucidation and New Treatment Method Development

Heart failure (HF) is a leading cause of death worldwide. In Japan, the number of HF patients has increased with its aging population, resulting in "HF pandemic." HF is the final stage of various cardiovascular diseases, including valvular heart disease, ischemic heart disease, atrial fibrillation, and hypertension. Cardiac hypertrophy is a compensatory response to increased workload and maintains cardiac function. Pressure overload due to mechanical stress causes cardiac hypertrophy, whereas continuous cardiac stress reduces wall thickness and consequently causes HF. Understanding the molecular mechanisms underlying this process is crucial to elucidate HF pathophysiology. We demonstrated that ischemia and DNA damage are important in the progression of hypertrophy to HF. Genetic mutations associated with cardiomyopathy and prognosis has been identified. To realize precision medicines for HF, the underlying molecular mechanisms need to be elucidated. In this review, we introduce new paradigms for understanding HF pathophysiology discovered through basic research.

B-Type Natriuretic Peptide (BNP) Revisited—Is BNP Still a Biomarker for Heart Failure in the Angiotensin Receptor/Neprilysin Inhibitor Era?

Simple Summary

Active BNP-32, less active proBNP-108, and inactive N-terminal proBNP-76 all circulate in the blood. The circulating protease neprilysin has lower substrate specificity for BNP than ANP, while proBNP and N-terminal proBNP are not degraded by neprilysin. Currently available BNP immunoassays react with both mature BNP and proBNP; therefore, measured plasma BNP is mature BNP + proBNP. Because ARNI administration increases mature BNP, measured plasma BNP initially increases with ARNI administration by the amount of the increase in mature BNP. Later, ARNI administration reduces myocardial wall stress, and the resultant reduction in BNP production more than offsets the increase of mature BNP due to inhibition of degradation by neprilysin, resulting in lower plasma BNP levels. In the ARNI era, BNP remains a useful biomarker for heart failure, though mild increases early during ARNI administration should be taken into consideration.

Abstract

Myocardial wall stress, cytokines, hormones, and ischemia all stimulate B-type (or brain) natriuretic peptide (BNP) gene expression. Within the myocardium, ProBNP-108, a BNP precursor, undergoes glycosylation, after which a portion is cleaved by furin into mature BNP-32 and N-terminal proBNP-76, depending on the glycosylation status. As a result, active BNP, less active proBNP, and inactive N-terminal proBNP all circulate in the blood. There are three major pathways for BNP clearance: (1) cellular internalization via natriuretic peptide receptor (NPR)-A and NPR-C; (2) degradation by proteases in the blood, including neprilysin, dipeptidyl-peptidase-IV, insulin degrading enzyme, etc.; and (3) excretion in the urine. Because neprilysin has lower substrate specificity for BNP than atrial natriuretic peptide (ANP), the increase in plasma BNP after angiotensin receptor neprilysin inhibitor (ARNI) administration is much smaller than the increase in plasma ANP. Currently available BNP immunoassays react with both mature BNP and proBNP. Therefore, BNP measured with an immunoassay is mature BNP + proBNP. ARNI administration increases mature BNP but not proBNP, as the latter is not degraded by neprilysin. Consequently, measured plasma BNP initially increases with ARNI administration by the amount of the increase in mature BNP. Later, ARNI reduces myocardial wall stress, and the resultant reduction in BNP production more than offsets the increase in mature BNP mediated by inhibiting degradation by neprilysin, which lowers plasma BNP levels. These results suggest that even in the ARNI era, BNP can be used for diagnosis and assessment of the pathophysiology and prognosis of heart failure, though the mild increases early during ARNI administration should be taken into consideration.

Angiotensin II Mediates Cardiomyocyte Hypertrophy in Atrial Cardiomyopathy via Epigenetic Transcriptional Regulation

Aims

European Heart Rhythm Association established an expert consensus to define, characterize, and classify atrial cardiomyopathy into four subgroups based on their histopathological features. The predominant pathological feature of classes I and III is the hypertrophy of atrial cardiomyocytes. Here, we aim to investigate the mechanism of epigenetic transcriptional regulation of cardiomyocyte hypertrophy in atrial cardiomyopathy.

Methods and Results

Compared with that of sinus rhythm control individuals, the myocardium of patients with atrial fibrillation exhibited increased levels of angiotensin II (AngII), chromatin-bound myocyte enhancer factor 2 (MEF2), acetylated histone H4 (H4ac), and H3K27ac; upregulation of hypertrophy-related genes; and decreased levels of histone deacetylase (HDAC) 4 and HDAC5 bound to the promoters of hypertrophy-related genes. Furthermore, incubation of atrial cardiomyocytes with AngII increased their cross-sectional area and improved the expression of hypertrophy-related genes. AngII also promoted the phosphorylation of HDAC4 and HDAC5 and induced their nuclear export. RNA sequencing analyses revealed that AngII significantly upregulated genes associated with cardiac hypertrophy. Chromatin immunoprecipitation showed that this correlated with increased levels of chromatin-bound MEF2, H4ac, and H3K27ac and decreased HDAC4 and HDAC5 enrichment in the promoters of hypertrophy-related genes. Moreover, these AngII-induced prohypertrophic effects could be partially reverted by treatment with the AngII receptor blocker losartan.

Conclusions

AngII had a prohypertrophic effect on atrial cardiomyopathy which was epigenetic-dependent. Patients with atrial fibrillation manifest an increased susceptibility to hypertrophy and exhibit epigenetic characteristics that are permissive for the transcription of hypertrophy-related genes. AngII induces histone acetylation via the cytoplasmic-nuclear shuttling of HDACs, which constitutes a novel mechanism of atrial hypertrophy regulation and might provide a promising therapeutic strategy for atrial cardiomyopathy.

Neuraminidase 1 is a driver of experimental cardiac hypertrophy

AIMS 

Despite considerable therapeutic advances, there is still a dearth of evidence on the molecular determinants of cardiac hypertrophy that culminate in heart failure. Neuraminidases are a family of enzymes that catalyze the cleavage of terminal sialic acids from glycoproteins or glycolipids. This study sought to characterize the role of neuraminidases in pathological cardiac hypertrophy and identify pharmacological inhibitors targeting mammalian neuraminidases.

METHODS AND RESULTS 

Neuraminidase 1 (NEU1) was highly expressed in hypertrophic hearts of mice and rats, and this elevation was confirmed in patients with hypertrophic cardiomyopathy (n = 7) compared with healthy controls (n = 7). The increased NEU1 was mainly localized in cardiomyocytes by co-localization with cardiac troponin T. Cardiomyocyte-specific NEU1 deficiency alleviated hypertrophic phenotypes in response to transverse aortic constriction or isoproterenol hydrochloride infusion, while NEU1 overexpression exacerbated the development of cardiac hypertrophy. Mechanistically, co-immunoprecipitation coupled with mass spectrometry, chromatin immunoprecipitation, and luciferase assays demonstrated that NEU1 translocated into the nucleus and interacted with GATA4, leading to Foetal gene (Nppa and Nppb) expression. Virtual screening and experimental validation identified a novel compound C-09 from millions of compounds that showed favourable binding affinity to human NEU1 (KD = 0.38 μM) and effectively prevented the development of cardiac remodelling in cellular and animal models. Interestingly, anti-influenza drugs zanamivir and oseltamivir effectively inhibited mammalian NEU1 and showed new indications of cardio-protection.

CONCLUSIONS 

This work identifies NEU1 as a critical driver of cardiac hypertrophy and inhibition of NEU1 opens up an entirely new field of treatment for cardiovascular diseases.

Vascular smooth muscle remodeling in health and disease

In blood vessels, vascular smooth muscle cells (VSMCs) generally exist in two major phenotypes: contractile and non-contractile (synthetic). The contractile phenotype is predominant and includes quiescent or differentiated VSMCs, which function as the regulators of blood vessel diameter and blood flow. According to some literature in the field, contractile VSMCs do not switch to the non-contractile phenotype due to the activation of specific transcription factors that are considered as guardians of the contractile phenotype. However, a vast amount of the literature uses the terms remodeling and phenotype switching of contractile VSMCs interchangeably based mainly on studies dealing with atherosclerosis. The use of the terms remodeling and switching to describe changes in phenotype based on morphological criteria can be confusing. The term remodeling was first used to describe morphological changes in the heart and was soon used to describe phenotype changes of contractile VSMCs based on morphological criteria. The latter were introduced in early studies, and new molecular criteria were later added, including changes in gene expression, which could be irreversible. In this review, we will discuss the different views concerning remodeling and possible switching of contractile VSMCs to a non-contractile phenotype. We conclude that only remodeling of contractile VSMCs may take place upon vascular injury and disease.

Phosphorylation of GATA4 at serine 105 is required for left ventricular remodelling process in angiotensin II-induced hypertension in rats

In this study, we investigated whether local intramyocardial GATA4 overexpression affects the left ventricular (LV) remodelling process and the importance of phosphorylation at serine 105 (S105) for the actions of GATA4 in an angiotensin II (AngII)‐induced hypertension rat model. Adenoviral constructs overexpressing wild‐type GATA4 or GATA4 mutated at S105 were delivered into the anterior LV free wall. AngII (33.3 µg/kg/h) was administered via subcutaneously implanted minipumps. Cardiac function and structure were examined by echocardiography, followed by histological immunostainings of LV sections and gene expression measurements by RT‐qPCR. The effects of GATA4 on cultured neonatal rat ventricular fibroblasts were evaluated. In AngII‐induced hypertension, GATA4 overexpression repressed fibrotic gene expression, reversed the hypertrophic adult‐to‐foetal isoform switch of myofibrillar genes and prevented apoptosis, whereas histological fibrosis was not affected. Overexpression of GATA4 mutated at S105 resulted in LV chamber dilatation, cardiac dysfunction and had minor effects on expression of myocardial remodelling genes. Fibrotic gene expression in cardiac fibroblasts was differently affected by overexpression of wild‐type or mutated GATA4. Our results indicate that GATA4 reduces AngII‐induced responses by interfering with pro‐fibrotic and hypertrophic gene expressions. GATA4 actions on LV remodelling and fibroblasts are dependent on phosphorylation site S105.

MiR-21, MiR-29a, GATA4, and MEF2c Expression Changes in Endothelin-1 and Angiotensin II Cardiac Hypertrophy Stimulated Isl-1+Sca-1+c-kit+ Porcine Cardiac Progenitor Cells In Vitro

Cost- and time-intensive porcine translational disease models offer great opportunities to test drugs and therapies for pathological cardiac hypertrophy and can be supported by porcine cell culture models that provide further insights into basic disease mechanisms. Cardiac progenitor cells (CPCs) residing in the adult heart have been shown to differentiate in vitro into cardiomyocytes and could contribute to cardiac regeneration. Therefore, it is important to evaluate their changes on the cellular level caused by disease. We successfully isolated Isl1⁺Sca1⁺cKit⁺ porcine CPCs (pCPCs) from pig hearts and stimulated them with endothelin-1 (ET-1) and angiotensin II (Ang II) in vitro. We also performed a cardiac reprogramming transfection and tested the same conditions. Our results show that undifferentiated Isl1⁺Sca1⁺cKit⁺ pCPCs were significantly upregulated in GATA4, MEF2c, and miR-29a gene expressions and in BNP and MCP-1 protein expressions with Ang II stimulation, but they showed no significant changes in miR-29a and MCP-1 when stimulated with ET-1. Differentiated Isl1⁺Sca1⁺cKit⁺ pCPCs exhibited significantly higher levels of MEF2c, GATA4, miR-29a, and miR-21 as well as Cx43 and BNP with Ang II stimulation. pMx-MGT-transfected Isl1⁺Sca1⁺cKit⁺ pCPCs showed significant elevations in MEF2c, GATA4, and BNP expressions when stimulated with ET-1. Our model demonstrates that in vitro stimulation leads to successful Isl1⁺Sca1⁺cKit⁺ pCPC hypertrophy with upregulation of cardiac remodeling associated genes and profibrotic miRNAs and offers great possibilities for further investigations of disease mechanisms and treatment.

Curcumin in heart failure: A choice for complementary therapy?

Heart failure is a major public health concern and one of the most common reasons for a cardiac hospital admission. Heart failure may be classified as having a reduced or preserved ejection fraction and its severity is based on the symptom score. Given the aging population, it is predicted that admissions with heart failure will increase. Whilst pharmacological therapy has improved the associated morbidity and mortality, there is a need for additional therapies to improve the clinical outcome as the death rate remains high. Curcumin is a natural product derived from turmeric that appears to have cardiovascular benefit through a number of mechanisms. In this review, we have assessed the mechanisms by which curcumin may exert its effects in different models of heart failure and show that it has promise as a complementary treatment in heart failure.

Zinc-finger protein 418 overexpression protects against cardiac hypertrophy and fibrosis

Background

This study aimed to investigated the effect and mechanism of zinc-finger protein 418 (ZNF418) on cardiac hypertrophy caused by aortic banding (AB), phenylephrine (PE) or angiotensin II (Ang II) in vivo and in vitro.

Methods

The expression of ZNF418 in hearts of patients with dilated cardiomyopathy (DCM) or hypertrophic cardiomyopathy (HCM) and AB-induced cardiac hypertrophy mice, as well as in Ang II- or PE-induced hypertrophic primary cardiomyocytes was detected by western blotting. Then, the expression of ZNF418 was up-regulated or down-regulated in AB-induced cardiac hypertrophy mice and Ang II -induced hypertrophic primary cardiomyocytes. The hypertrophic responses and fibrosis were evaluated by echocardiography and histological analysis. The mRNA levels of hypertrophy markers and fibrotic markers were detected by RT-qPCR. Furthermore, the phosphorylation and total levels of c-Jun were measured by western blotting.

Results

ZNF418 was markedly down-regulated in hearts of cardiac hypertrophy and hypertrophic primary cardiomyocytes. Down-regulated ZNF418 exacerbated the myocyte size and fibrosis, moreover increased the mRNA levels of ANP, BNP, β-MHC, MCIP1.4, collagen 1a, collagen III, MMP-2 and fibronection in hearts of AB-treated ZNF418 knockout mice or Ang II-treated cardiomyocytes with AdshZNF418. Conversely, these hypertrophic responses were reduced in the ZNF418 transgenic (TG) mice treated by AB and the AdZNF418-transfected primary cardiomyocytes treated by Ang II. Additionally, the deficiency of ZNF418 enhanced the phosphorylation level of c-jun, and overexpression of ZNF418 suppressed the phosphorylation level of c-jun in vivo and in vitro.

Conclusion

ZNF418 maybe attenuate hypertrophic responses by inhibiting the activity of c-jun/AP-1.

Regulation of Cardiac Transcription Factor GATA4 by Post-Translational Modification in Cardiomyocyte Hypertrophy and Heart Failure

Heart failure is a leading cause of cardiovascular mortality in industrialized countries. During development and deterioration of heart failure, cardiomyocytes undergo maladaptive hypertrophy, and changes in the cellular phenotype are accompanied by reinduction of the fetal gene program. Gene expression in cardiomyocytes is regulated by various nuclear transcription factors, co-activators, and co-repressors. The zinc finger protein GATA4 is one such transcription factor involved in the regulation of cardiomyocyte hypertrophy. In response to hypertrophic stimuli such as those involving the sympathetic nervous and renin-angiotensin systems, changes in protein interaction and/or post-translational modifications of GATA4 cause hypertrophic gene transcription in cardiomyocytes. In this article, we focus on cardiac nuclear signaling molecules, especially GATA4, that are promising as potential targets for heart failure therapy.

Calcineurin/NFAT Activation-Dependence of Leptin Synthesis and Vascular Growth in Response to Mechanical Stretch

Background and Aims: Hypertension and obesity are important risk factors of cardiovascular disease. They are both associated with high leptin levels and have been shown to promote vascular hypertrophy, through the RhoA/ROCK and ERK1/2 phosphorylation. Calcineurin/NFAT activation also induces vascular hypertrophy by upregulating various genes. This study aimed to decipher whether a crosstalk exists between the RhoA/ROCK pathway, Ca²⁺/calcineurin/NFAT pathway, and ERK1/2 phosphorylation in the process of mechanical stretch-induced vascular smooth muscle cell (VSMC) hypertrophy and leptin synthesis.

Methods and Results: Rat portal vein (RPV) organ culture was used to investigate the effect of mechanical stretch and exogenous leptin (3.1 nM) on VSMC hypertrophy and leptin synthesis. Results showed that stretching the RPV significantly upregulated leptin secretion, mRNA, and protein expression, which were inhibited by the calcium channel blocker nifedipine (10 μM), the selective calcineurin inhibitor FK506 (1 nM), and the ERK1/2 inhibitor PD98059 (1 μM). The transcription inhibitor actinomycin D (0.1 μM) and the translation inhibitor cycloheximide (1 mM) significantly decreased stretch-induced leptin protein expression. Mechanical stretch or leptin caused an increase in wet weight changes and protein synthesis, considered as hypertrophic markers, while they were inhibited by FK506 (0.1 nM; 1 nM). In addition, stretch or exogenous leptin significantly increased calcineurin activity and MCIP1 expression whereas leptin induced NFAT nuclear translocation in VSMCs. Moreover, in response to stretch or exogenous leptin, the Rho inhibitor C3 exoenzyme (30 ng/mL), the ROCK inhibitor Y-27632 (10 μM), and the actin depolymerization agents Latrunculin B (50 nM) and cytochalasin D (1 μM) reduced calcineurin activation and NFAT nuclear translocation. ERK1/2 phosphorylation was inhibited by FK506 and C3.

Conclusions: Mechanical stretch-induced VSMC hypertrophy and leptin synthesis and secretion are mediated by Ca²⁺/calcineurin/NFAT activation. RhoA/ROCK and ERK1/2 activation are critical for mechanical stretch-induced calcineurin activation.

Myocardial plasticity: cardiac development, regeneration and disease

The adult mammalian heart is unable to recover from myocardial cell loss due to cardiac ischemia and infarction because terminally differentiated cardiomyocytes proliferate at a low rate. However, cardiomyocytes in other vertebrate animal models such as zebrafish, axolotls, newts and mammalian mouse neonates are capable of de-differentiating in order to promote cardiomyocyte proliferation and subsequent cardiac regeneration after injury. Although de-differentiation may occur in adult mammalian cardiomyocytes, it is typically associated with diseased hearts and pathologic remodeling rather than repair and regeneration. Here, we review recent studies of cardiac development, regeneration and disease that highlight how changes in myocardial identity (plasticity) is regulated and impacts adaptive and maladaptive cardiac responses.

TRAF3IP2 mediates aldosterone/salt-induced cardiac hypertrophy and fibrosis

Aberrant activation of the renin-angiotensin-aldosterone system (RAAS) contributes to adverse cardiac remodeling and eventual failure. Here we investigated whether TRAF3 Interacting Protein 2 (TRAF3IP2), a redox-sensitive cytoplasmic adaptor molecule and an upstream regulator of nuclear factor-κB (NF-κB) and activator protein-1 (AP-1), mediates aldosterone-induced cardiac hypertrophy and fibrosis. Wild type (WT) and TRAF3IP2-null mice were infused with aldosterone (0.2 mg/kg/day) for 4 weeks along with 1%NaCl in drinking water. Aldosterone/salt, but not salt alone, upregulated TRAF3IP2 expression in WT mouse hearts. Further, aldosterone elevated blood pressure to a similar extent in both WT and TRAF3IP2-null groups. However, TRAF3IP2 gene deletion attenuated aldosterone/salt-induced (i) p65 and c-Jun activation, (ii) extracellular matrix (collagen Iα1 and collagen IIIα1), matrix metalloproteinase (MMP2), lysyl oxidase (LOX), inflammatory cytokine (IL-6 and IL-18), chemokine (CXCL1 and CXCL2), and adhesion molecule (ICAM1) mRNA expression in hearts, (iii) IL-6, IL-18, and MMP2 protein levels, (iv) systemic IL-6 and IL-18 levels, and (iv) cardiac hypertrophy and fibrosis. These results indicate that TRAF3IP2 is a critical signaling intermediate in aldosterone/salt-induced myocardial hypertrophy and fibrosis, and thus a potential therapeutic target in hypertensive heart disease.

Molecular mechanisms in H2O2-induced increase in AT1 receptor gene expression in cardiac fibroblasts: A role for endogenously generated Angiotensin II

The AT1 receptor (AT1R) mediates the manifold actions of angiotensin II in the cardiovascular system. This study probed the molecular mechanisms that link altered redox status to AT1R expression in cardiac fibroblasts. Real-time PCR and western blot analysis showed that H2O2 enhances AT1R mRNA and protein expression via NADPH oxidase-dependent reactive oxygen species induction. Activation of NF-κB and AP-1, demonstrated by electrophoretic mobility shift assay, abolition of AT1R expression by their inhibitors, Bay-11-7085 and SR11302, respectively, and luciferase and chromatin immunoprecipitation assays confirmed transcriptional control of AT1R by NF-κB and AP-1 in H2O2-treated cells. Further, inhibition of ERK1/2, p38 MAPK and c-Jun N-terminal kinase (JNK) using chemical inhibitors or by RNA interference attenuated AT1R expression. Inhibition of the MAPKs showed that while ERK1/2 and p38 MAPK suffice for NF-κB activation, all three kinases are required for AP-1 activation. H2O2 also increased collagen type I mRNA and protein expression. Interestingly, the AT1R antagonist, candesartan, attenuated H2O2-stimulated AT1R and collagen mRNA and protein expression, suggesting that H2O2 up-regulates AT1R and collagen expression via local Angiotensin II generation, which was confirmed by real-time PCR and ELISA. To conclude, oxidative stress enhances AT1R gene expression in cardiac fibroblasts by a complex mechanism involving the redox-sensitive transcription factors NF-κB and AP-1 that are activated by the co-ordinated action of ERK1/2, p38 MAPK and JNK. Importantly, by causally linking oxidative stress to Angiotensin II and AT1R up-regulation in cardiac fibroblasts, this study offers a novel perspective on the pathogenesis of cardiovascular diseases associated with oxidative stress.

Computational Detection of Stage-Specific Transcription Factor Clusters during Heart Development

Transcription factors (TFs) regulate gene expression in living organisms. In higher organisms, TFs often interact in non-random combinations with each other to control gene transcription. Understanding the interactions is key to decipher mechanisms underlying tissue development. The aim of this study was to analyze co-occurring transcription factor binding sites (TFBSs) in a time series dataset from a new cell-culture model of human heart muscle development in order to identify common as well as specific co-occurring TFBS pairs in the promoter regions of regulated genes which can be essential to enhance cardiac tissue developmental processes. To this end, we separated available RNAseq dataset into five temporally defined groups: (i) mesoderm induction stage; (ii) early cardiac specification stage; (iii) late cardiac specification stage; (iv) early cardiac maturation stage; (v) late cardiac maturation stage, where each of these stages is characterized by unique differentially expressed genes (DEGs). To identify TFBS pairs for each stage, we applied the MatrixCatch algorithm, which is a successful method to deduce experimentally described TFBS pairs in the promoters of the DEGs. Although DEGs in each stage are distinct, our results show that the TFBS pair networks predicted by MatrixCatch for all stages are quite similar. Thus, we extend the results of MatrixCatch utilizing a Markov clustering algorithm (MCL) to perform network analysis. Using our extended approach, we are able to separate the TFBS pair networks in several clusters to highlight stage-specific co-occurences between TFBSs. Our approach has revealed clusters that are either common (NFAT or HMGIY clusters) or specific (SMAD or AP-1 clusters) for the individual stages. Several of these clusters are likely to play an important role during the cardiomyogenesis. Further, we have shown that the related TFs of TFBSs in the clusters indicate potential synergistic or antagonistic interactions to switch between different stages. Additionally, our results suggest that cardiomyogenesis follows the hourglass model which was already proven for Arabidopsis and some vertebrates. This investigation helps us to get a better understanding of how each stage of cardiomyogenesis is affected by different combination of TFs. Such knowledge may help to understand basic principles of stem cell differentiation into cardiomyocytes.

Mechanical stretch-induced vascular hypertrophy occurs through modulation of leptin synthesis-mediated ROS formation and GATA-4 nuclear translocation

Background: Obesity and hypertension are associated with increased leptin production contributing to cardiovascular remodeling. Mechanisms involving mechanical stretch-induced leptin production and the cross talk between signaling pathways leading to vascular remodeling have not been fully elucidated.

Methods and Results: Rat portal vein (RPV) organ culture was used to investigate the effect of mechanical stretch on leptin protein expression in vascular smooth muscle cells (VSMCs). Moreover, the involvement of reactive oxygen species (ROS), the RhoA/ROCK pathway, actin cytoskeleton dynamics and the transcriptional factor GATA-4 activation in mechanical stretch-induced vascular remodeling were investigated. Stretching the RPV for 1 or 24 h significantly increased leptin protein level and ROS formation in VSMCs, which was prevented by 1 h pretreatment with the ROCK inhibitor Y-27632 and the actin cytoskeleton depolymerization agent cytochalasin D. Moreover, Western blotting and immunohistochemistry revealed that mechanical stretch or treatment with 3.1 nmol/L leptin for 24 h significantly increased actin polymerization, as reflected by an increase in the F-actin to G-actin ratio. Increases in blood vessels’ wet weight and [³H]-leucine incorporation following a 24 h treatment with conditioned media from cultured stretched RPVs indicated RPV hypertrophy. This effect was prevented by 1 h pretreatment with anti-leptin antibody, indicating leptin’s crucial role in promoting VSMC hypertrophy. As an index of GATA-4 activation, GATA-4 nuclear translocation was assessed by immunohistochemistry method. Pretreating VSMC with leptin for 1 h significantly activated GATA-4 nuclear translocation, which was potently attenuated by the NADPH oxidase inhibitor apocynin, Y-27632, and cytochalasin D.

Conclusion: Our results demonstrate that ROS formation, RhoA/ROCK pathway, and GATA-4 activation play a pivotal role in mechanical stretch-induced leptin synthesis leading to VSMC remodeling.

Contractile Function During Angiotensin-II Activation: Increased Nox2 Activity Modulates Cardiac Calcium Handling via Phospholamban Phosphorylation

BACKGROUND

Renin-angiotensin system activation is a feature of many cardiovascular conditions. Activity of myocardial reduced nicotinamide adenine dinucleotide phosphate oxidase 2 (NADPH oxidase 2 or Nox2) is enhanced by angiotensin II (Ang II) and contributes to increased hypertrophy, fibrosis, and adverse remodeling. Recent studies found that Nox2-mediated reactive oxygen species production modulates physiological cardiomyocyte function.

OBJECTIVES

This study sought to investigate the effects of cardiomyocyte Nox2 on contractile function during increased Ang II activation.

METHODS

We generated a cardiomyocyte-targeted Nox2-transgenic mouse model and studied the effects of in vivo and ex vivo Ang II stimulation, as well as chronic aortic banding.

RESULTS

Chronic subpressor Ang II infusion induced greater cardiac hypertrophy in transgenic than wild-type mice but unexpectedly enhanced contractile function. Acute Ang II treatment also enhanced contractile function in transgenic hearts in vivo and transgenic cardiomyocytes ex vivo. Ang II-stimulated Nox2 activity increased sarcoplasmic reticulum (SR) Ca(2+) uptake in transgenic mice, increased the Ca(2+) transient and contractile amplitude, and accelerated cardiomyocyte contraction and relaxation. Elevated Nox2 activity increased phospholamban phosphorylation in both hearts and cardiomyocytes, related to inhibition of protein phosphatase 1 activity. In a model of aortic banding-induced chronic pressure overload, heart function was similarly depressed in transgenic and wild-type mice.

CONCLUSIONS

We identified a novel mechanism in which Nox2 modulates cardiomyocyte SR Ca(2+) uptake and contractile function through redox-regulated changes in phospholamban phosphorylation. This mechanism can drive increased contractility in the short term in disease states characterized by enhanced renin-angiotensin system activation.

Chronic high fat diet induces cardiac hypertrophy and fibrosis in mice

BACKGROUND

Obesity can cause pathological changes in organs. We determined the effects of chronic high fat diet (HFD) and intermittent fasting, a paradigm providing organ protection, on mouse heart.

METHODS

Seven-week old CD1 male mice were randomly assigned to control, HFD and intermittent fasting groups. Control mice had free access to regular diet (RD). RD was provided every other day to mice in the intermittent fasting group. Mice in HFD group had free access to HFD. Their left ventricles were harvested 11 months after they had been on these diet regimens.

RESULTS

HFD increased cardiomyocyte cross-section area and fibrosis. HFD decreased active caspase 3, an apoptosis marker, and the ratio of microtubule-associated protein 1A/1B-light chain 3 (LC3) II/LC3I, an autophagy marker. HFD increased the phospho-glycogen synthase kinase-3β (GSK-3β) at Ser9, a sign of GSK-3β inhibition. Nuclear GATA binding protein 4 and yes-associated protein, two GSK-3β targeting transcription factors that can induce hypertrophy-related gene expression, were increased in HFD-fed mice. Mice on intermittent fasting did not have these changes except for the increased active caspase 3 and decreased ratio of LC3II/LC3I.

CONCLUSIONS

These results suggest that chronic HFD induces myocardial hypertrophy and fibrosis, which may be mediated by GSK-3β inhibition.

Modulation of angiotensin II signaling following exercise training in heart failure

Sympathetic activation is a consistent finding in the chronic heart failure (CHF) state. Current therapy for CHF targets the renin-angiotensin II (ANG II) and adrenergic systems. Angiotensin converting enzyme (ACE) inhibitors and ANG II receptor blockers are standard treatments along with β-adrenergic blockade. However, the mortality and morbidity of this disease is still extremely high, even with good medical management. Exercise training (ExT) is currently being used in many centers as an adjunctive therapy for CHF. Clinical studies have shown that ExT is a safe, effective, and inexpensive way to improve quality of life, work capacity, and longevity in patients with CHF. This review discusses the potential neural interactions between ANG II and sympatho-excitation in CHF and the modulation of this interaction by ExT. We briefly review the current understanding of the modulation of the angiotensin type 1 receptor in sympatho-excitatory areas of the brain and in the periphery (i.e., in the carotid body and skeletal muscle). We discuss possible cellular mechanisms by which ExT may impact the sympatho-excitatory process by reducing oxidative stress, increasing nitric oxide. and reducing ANG II. We also discuss the potential role of ACE2 and Ang 1-7 in the sympathetic response to ExT. Fruitful areas of further investigation are the role and mechanisms by which pre-sympathetic neuronal metabolic activity in response to individual bouts of exercise regulate redox mechanisms and discharge at rest in CHF and other sympatho-excitatory states.

Characterization of the regulatory mechanisms of activating transcription factor 3 by hypertrophic stimuli in rat cardiomyocytes

Aims

Activating transcription factor 3 (ATF3) is a stress-activated immediate early gene suggested to have both detrimental and cardioprotective role in the heart. Here we studied the mechanisms of ATF3 activation by hypertrophic stimuli and ATF3 downstream targets in rat cardiomyocytes.

Methods and Results

When neonatal rat cardiomyocytes were exposed to endothelin-1 (ET-1, 100 nM) and mechanical stretching in vitro, maximal increase in ATF3 expression occurred at 1 hour. Inhibition of extracellular signal-regulated kinase (ERK) by PD98059 decreased ET-1– and stretch–induced increase of ATF3 protein but not ATF3 mRNA levels, whereas protein kinase A (PKA) inhibitor H89 attenuated both ATF3 mRNA transcription and protein expression in response to ET-1 and stretch. To characterize further the regulatory mechanisms upstream of ATF3, p38 mitogen-activated protein kinase (MAPK) signaling was investigated using a gain-of-function approach. Adenoviral overexpression of p38α, but not p38β, increased ATF3 mRNA and protein levels as well as DNA binding activity. To investigate the role of ATF3 in hypertrophic process, we overexpressed ATF3 by adenovirus-mediated gene transfer. In vitro, ATF3 gene delivery attenuated the mRNA transcription of interleukin-6 (IL-6) and plasminogen activator inhibitor-1 (PAI-1), and enhanced nuclear factor-κB (NF-κB) and Nkx-2.5 DNA binding activities. Reduced PAI-1 expression was also detected in vivo in adult rat heart by direct intramyocardial adenovirus-mediated ATF3 gene delivery.

Conclusions

These data demonstrate that ATF3 activation by ET-1 and mechanical stretch is partly mediated through ERK and cAMP-PKA pathways, whereas p38 MAPK pathway is involved in ATF3 activation exclusively through p38α isoform. ATF3 activation caused induction of modulators of the inflammatory response NF-κB and Nkx-2.5, as well as attenuation of pro-fibrotic and pro-inflammatory proteins IL-6 and PAI-1, suggesting cardioprotective role for ATF3 in the heart.

COUGER--co-factors associated with uniquely-bound genomic regions

Most transcription factors (TFs) belong to protein families that share a common DNA binding domain and have very similar DNA binding preferences. However, many paralogous TFs (i.e. members of the same TF family) perform different regulatory functions and interact with different genomic regions in the cell. A potential mechanism for achieving this differential in vivo specificity is through interactions with protein co-factors. Computational tools for studying the genomic binding profiles of paralogous TFs and identifying their putative co-factors are currently lacking. Here, we present an interactive web implementation of COUGER, a classification-based framework for identifying protein co-factors that might provide specificity to paralogous TFs. COUGER takes as input two sets of genomic regions bound by paralogous TFs, and it identifies a small set of putative co-factors that best distinguish the two sets of sequences. To achieve this task, COUGER uses a classification approach, with features that reflect the DNA-binding specificities of the putative co-factors. The identified co-factors are presented in a user-friendly output page, together with information that allows the user to understand and to explore the contributions of individual co-factor features. COUGER can be run as a stand-alone tool or through a web interface: http://couger.oit.duke.edu.

Promyelocytic leukemia zinc finger protein activates GATA4 transcription and mediates cardiac hypertrophic signaling from angiotensin II receptor 2

BACKGROUND

Pressure overload and prolonged angiotensin II (Ang II) infusion elicit cardiac hypertrophy in Ang II receptor 1 (AT(1)) null mouse, whereas Ang II receptor 2 (AT(2)) gene deletion abolishes the hypertrophic response. The roles and signals of the cardiac AT(2) receptor still remain unsettled. Promyelocytic leukemia zinc finger protein (PLZF) was shown to bind to the AT(2) receptor and transmit the hypertrophic signal. Using PLZF knockout mice we directed our studies on the function of PLZF concerning the cardiac specific transcription factor GATA4, and GATA4 targets.

METHODOLOGY AND PRINCIPAL FINDINGS

PLZF knockout and age-matched wild-type (WT) mice were treated with Ang II, infused at a rate of 4.2 ng·kg(-1)·min(-1) for 3 weeks. Ang II elevated systolic blood pressure to comparable levels in PLZF knockout and WT mice (140 mmHg). WT mice developed prominent cardiac hypertrophy and fibrosis after Ang II infusion. In contrast, there was no obvious cardiac hypertrophy or fibrosis in PLZF knockout mice. An AT(2) receptor blocker given to Ang II-infused wild type mice prevented hypertrophy, verifying the role of AT(2) receptor for cardiac hypertrophy. Chromatin immunoprecipitation and electrophoretic mobility shift assay showed that PLZF bound to the GATA4 gene regulatory region. A Luciferase assay verified that PLZF up-regulated GATA4 gene expression and the absence of PLZF expression in vivo produced a corresponding repression of GATA4 protein.

CONCLUSIONS

PLZF is an important AT(2) receptor binding protein in mediating Ang II induced cardiac hypertrophy through an AT(2) receptor-dependent signal pathway. The angiotensin II-AT(2)-PLZF-GATA4 signal may further augment Ang II induced pathological effects on cardiomyocytes.

Cell signaling pathways for the regulation of GATA4 transcription factor: Implications for cell growth and apoptosis

GATA4 is a member of the GATA family of zinc finger transcription factor, which regulates gene transcription by binding to GATA elements. GATA4 was originally discovered as a regulator of cardiac development and subsequently identified as a major regulator of adult cardiac hypertrophy. GATA4 regulates gene expression of various genes, which are involved in cardiac development and cardiac hypertrophy and heart failure. In addition to the heart, GATA4 plays important roles in the reproductive system, gastrointestinal system, respiratory system and cancer. Positive and negative regulations of GATA4 therefore are important components of biologic functions. The activation of GATA4 occurs via various cell signaling events. Earlier studies have identified protein-protein interactions of GATA4 with other factors. The discovery of interactions of GATA4 with nuclear factor for activated T cells (NFAT) revealed the importance of calcium signaling in the activation of GATA4. GATA4 can also be phosphorylated by mitogen activated protein kinases and protein kinase A. Lysine modifications also occur on the GATA4 molecule including acetylation and sumoylation. Both reactive oxygen-dependent and -independent antioxidant-sensitive pathways for GATA4 activation have also been demonstrated. The GATA4 activity is also regulated by modulating the level of GATA4 expression via transcriptional as well as translational mechanisms. This work summarizes the current understanding of regulatory mechanisms for modulating GATA4 activity.

Distinct regulation of B-type natriuretic peptide transcription by p38 MAPK isoforms

Persistent controversy underlies the functional roles of specific p38 MAPK isoforms in cardiac biology and regulation of hypertrophy-associated genes. Here we show that adenoviral gene transfer of p38β but not p38α increased B-type natriuretic peptide (BNP) mRNA levels in vitro as well as atrial natriuretic peptide mRNA levels both in vitro and in vivo. Overexpression of p38α, in turn, augmented the expression fibrosis-related genes connective tissue growth factor, basic fibroblast growth factor and matrix metalloproteinase-9 both in vitro and in vivo. p38β-induced BNP transcription was diminished by mutation of GATA-4 binding site, whereas overexpression of MKK6b, an upstream regulator of p38α and p38β, activated BNP transcription through both GATA-4 and AP-1. Overexpression of MKK3, upstream regulator of p38α, induced BNP transcription independently from AP-1 and GATA-4. These data provide new evidence for diversity in downstream targets and functional roles of p38 pathway kinases in regulation of hypertrophy-associated cardiac genes.

Gene expression for the renin system in the myocardium of hypertensive ISIAH rats

The concentration of mRNA for angiotensin-converting enzyme (ACE) and angiotensin type 1A receptor (AT1A) in the myocardium of hypertensive ISIAH rats and normotensive WAG rats was measured by real-time PCR. Gene expression of the angiotensin type 1A receptor in the myocardium of 4-month-old ISIAH rats was lower than in WAG rats. The content of mRNA for angiotensin-converting enzyme in the myocardium of adult ISIAH rats was elevated by 80%. Therefore, the development of myocardial hypertrophy anticipates the increase in enzyme expression in the myocardium. Water deprivation (17 h) was accompanied by a decrease in the concentration of mRNA for angiotensin-converting enzyme in the myocardium of ISIAH rats, which did not differ from that in normotensive animals. Our results suggest that the decrease in cardiac preload and increase in plasma renin activity during dehydration reduce requirements for hyperactivity of the local cardiac renin-angiotensin system.

Interaction between renin-angiotensin and sympathetic nervous systems in a rat model of pressure overload cardiac hypertrophy

1 A raised cardiac workload activates neurohormones which will increase muscle mass and shift contractility to the right along the Frank-Starling curve. 2 This study examined the interaction between the SNS and RAS in contributing to vascular responsiveness following the development of cardiac hypertrophy due to aortic banding. 3 Sprague Dawley rats (180-200 g) were assigned to one of six groups; Normal, Sham-operated, Aortic Banded (AB), Aortic Banded treated with losartan (ABLOS), Aortic Banded treated with 6-hydroxydopamine (ABSYMP) and Aortic banded treated with both losartan and 6-hydroxydopamine (ABSYMPLOS). A constricting band was placed around the supra renal aorta on day zero with drug treatment from day 37 to day 44. Vasopressor responses to noradrenaline, phenylephrine, methoxamine and angiotensin II were measured on day 45. 4 The magnitudes of the MAP responses to all vasoactive agents, expressed as percentage changes, were similar in Normal and Sham groups, but reduced in the AB group. ABLOS group showed attenuated response to ANGII whereas all responses were enhanced in the ABSYM group. 5 A positive interaction between the two systems was observed with alpha(1A)-adrenoceptors identified as a major component of SNS and AT(1) receptors of RAS to induce vasopressor effects.

The protective role of curcumin in cardiovascular diseases

Curcumin (diferuloylmethane) is a polyphenol responsible for the yellow color of the curry spice turmeric. It has been used in a variety of diseases in traditional medicine. Modern scientific research has demonstrated its anti-inflammatory, anti-oxidant, anti-carcinogenic, anti-thrombotic, and cardiovascular protective effects. In this review, we focused mainly on the effects of curcumin on the cardiovascular system. The antioxidant effects of curcumin have been shown to attenuate adriamycin-induced cardiotoxicity and may prevent diabetic cardiovascular complications. The anti-thrombotic, anti-proliferative, and anti-inflammatory effects of curcumin and the effect of curcumin in decreasing the serum cholesterol level may protect against the pathological changes occurring with atherosclerosis. The p300-HAT inhibitory effects of curcumin have been demonstrated to ameliorate the development of cardiac hypertrophy and heart failure in animal models. The inflammatory effects of curcumin may have the possibility of preventing atrial arrhythmias and the possible effect of curcumin for correcting the Ca(2+) homeostasis may play a role in the prevention of some ventricular arrhythmias. The preclinical studies from animal to clinical data in human are discussed.

Chapter 2. Calcineurin signaling and the slow oxidative skeletal muscle fiber type

Calcineurin, also known as protein phosphatase 2B (PP2B), is a calcium-calmodulin-dependent phosphatase. It couples intracellular calcium to dephosphorylate selected substrates resulting in diverse biological consequences depending on cell type. In mammals, calcineurin's functions include neuronal growth, development of cardiac valves and hypertrophy, activation of lymphocytes, and the regulation of ion channels and enzymes. This chapter focuses on the key roles of calcineurin in skeletal muscle differentiation, regeneration, and fiber type conversion to an oxidative state, all of which are crucial to muscle development, metabolism, and functional adaptations. It seeks to integrate the current knowledge of calcineurin signaling in skeletal muscle and its interactions with other prominent regulatory pathways and their signaling intermediates to form a molecular overview that could provide directions for possible future exploitations in human metabolic health.

The dietary compound curcumin inhibits p300 histone acetyltransferase activity and prevents heart failure in rats

Hemodynamic overload in the heart can trigger maladaptive hypertrophy of cardiomyocytes. A key signaling event in this process is nuclear acetylation by histone deacetylases and p300, an intrinsic histone acetyltransferase (HAT). It has been previously shown that curcumin, a polyphenol responsible for the yellow color of the spice turmeric, possesses HAT inhibitory activity with specificity for the p300/CREB-binding protein. We found that curcumin inhibited the hypertrophy-induced acetylation and DNA-binding abilities of GATA4, a hypertrophy-responsive transcription factor, in rat cardiomyocytes. Curcumin also disrupted the p300/GATA4 complex and repressed agonist- and p300-induced hypertrophic responses in these cells. Both the acetylated form of GATA4 and the relative levels of the p300/GATA4 complex markedly increased in rat hypertensive hearts in vivo. The effects of curcumin were examined in vivo in 2 different heart failure models: hypertensive heart disease in salt-sensitive Dahl rats and surgically induced myocardial infarction in rats. In both models, curcumin prevented deterioration of systolic function and heart failure-induced increases in both myocardial wall thickness and diameter. From these results, we conclude that inhibition of p300 HAT activity by the nontoxic dietary compound curcumin may provide a novel therapeutic strategy for heart failure in humans.

Activation of the calcineurin/NFAT signalling cascade starts early in human hypertrophic myocardium

Cardiac hypertrophy is an independent risk factor for heart failure. Recent studies on gene regulation of proteins have involved intracellular Ca2+ homeostasis. The Ca2+-sensitive phosphatase, calcineurin, is one potential regulator of the hypertrophic response, so we aimed to investigate the calcineurin-dependent signal pathway at different stages of hypertrophy in human myocardium. We found the calcineurin pathway to be significantly activated in hypertrophic compared with non-hypertrophic myocardium as demonstrated by increased calcineurin activity and expression of calcineurin A-beta and B, and GATA-4, and a shift of phosphorylated cytoplasmic NFAT-3 into the nucleus as dephosphorylated nuclear NFAT-3. There was a tendency for these changes to be more pronounced in the decompensated compared with the compensated hypertrophic myocardium. The present study provides evidence for significant activation of the Ca2+-triggered calcineurin pathway in hypertrophic humans. Already present in compensated hypertrophy it showed a tendency to a further increase following transition to decompensated hypertrophy.

Upregulation of AT1 receptor gene on activation of protein kinase Cbeta/nicotinamide adenine dinucleotide diphosphate oxidase/ERK1/2/c-fos signaling cascade mediates long-term pressor effect of angiotensin II in rostral ventrolateral medulla

OBJECTIVE

Angiotensin II induces the phosphorylation of p38 mitogen-activated protein kinase (MAPK) and extracellular signal-regulated kinase (ERK) 1/2 via the activation of nicotinamide adenine dinucleotide diphosphate (NADPH) oxidase on stimulation of the angiotensin subtype 1 receptor (AT1R) in the rostral ventrolateral medulla (RVLM), where sympathetic premotor neurons for the maintenance of vasomotor tone and blood pressure are located. Angiotensin II-activated p38 MAPK in RVLM promotes a short-term pressor effect via augmented glutamatergic neurotransmission. We tested the hypothesis that the NADPH oxidase-dependent phosphorylation of ERK1/2 after the activation of conventional protein kinase C (PKC) mediates the AT1R-dependent long-term pressor effects of angiotensin II via transcriptional induction of the proto-oncogene c-fos gene in RVLM.

METHODS AND RESULTS

In Sprague-Dawley rats, a microinjection of angiotensin II bilaterally into the RVLM induced membrane-bound translocation of the conventional PKCalpha, PKCbeta or PKCgamma isoform, phosphorylation of the p47 subunit of NADPH oxidase and ERK1/2, followed by phosphorylation of the transcription factor cyclic adenosine monophosphate response element binding protein (CREB), and c-fos induction. The PKC inhibitor antagonized angiotensin II-induced p47 phosphorylation, and an antisense oligonucleotide (ASON) complementary to PKCbeta messenger RNA suppressed angiotensin II-induced ERK1/2 activation, phosphorylation or DNA binding activity of CREB, and upregulation of c-fos mRNA expression in the ventrolateral medulla. Furthermore, a microinjection of ERK1/2, CREB or c-fos ASON into the RVLM significantly reduced the long-term pressor effect and augmented AT1R expression in the ventrolateral medulla induced by intracerebroventricular infusion of angiotensin II.

CONCLUSION

We concluded that the PKCbeta/NADPH oxidase/ERK1/2/CREB/c-fos cascade represents a novel signaling cascade that mediates the long-term pressor effect induced by angiotensin II in the RVLM.

Identification of a chromosome 8p locus for early-onset coronary heart disease in a French Canadian population

Susceptibility to coronary heart disease (CHD) has long been known to exhibit familial aggregation, with heritability estimated to be greater than 50%. The French Canadian population of the Saguenay-Lac Saint-Jean region of Quebec, Canada is descended from a founder population that settled this region 300-400 years ago and this may provide increased power to detect genes contributing to complex traits such as CHD. Probands with early-onset CHD, defined by angiographically determined coronary stenosis, and their relatives were recruited from this population (average sibship size of 6.4). Linkage analysis was performed following a genome-wide microsatellite marker scan on 42 families with 284 individuals. Nonparametric linkage (NPL) analysis provided suggestive evidence for a CHD susceptibility locus on chromosome 8 with an NPL score of 3.14 (P=0.001) at D8S1106. Linkage to this locus was verified by fine mapping in an enlarged sample of 50 families with 320 individuals. This analysis provided evidence of linkage at D8S552 (NPL score=3.53, P=0.0003), a marker that maps to the same location as D8S1106. Candidate genes in this region, including macrophage scavenger receptor 1, farnesyl-diphosphate farnesyltransferase 1, fibrinogen-like 1, and GATA-binding protein 4, were resequenced in all coding exons in both affected and unaffected individuals. Association studies with variants in these and five other genes did not identify a disease-associated mutation. In conclusion, a genome-wide scan and additional fine mapping provide evidence for a locus on chromosome 8 that contributes to CHD in a French Canadian population.

Overt expression of AP-1 reduces alpha myosin heavy chain expression and contributes to heart failure from chronic volume overload

Reduced expression of alpha-MHC plays a significant role in cardiac contractile dysfunction from hemodynamic overload. Previously, Pur proteins and YY1 have been shown to play a role in alpha-MHC repression during heart failure induced by pressure overload and by spontaneous hypertension, respectively. This was not observed in volume-overload-induced heart failure, suggesting additional regulatory mechanisms for alpha-MHC repression. The present study was performed to identify volume overload responsive transcription factors involved in alpha-MHC gene regulation. DNA binding activity of several transcription factors was evaluated in a functionally characterized rat model of heart failure induced by aorto-caval shunt. After 10 weeks of shunt, severe LV dilatation and reduced LV function were accompanied by increased expression of ANF and beta-MHC, and decreased expression of alpha-MHC. This was associated with dramatic (10-fold) activation of AP-1 together with increased expression of c-fos and c-jun. AP-1 activation was not observed following 4 weeks of shunt when cardiac function was preserved. In cultured cardiomyocytes, induction of AP-1 by PMA attenuated alpha-MHC mRNA by 60%. Transient transfection assays mapped PMA responsive sequence to -582 to -588 bp of alpha-MHC promoter. Deletion or mutation of these nucleotides had minimal effect on basal promoter activity but played a dominant role in PMA-mediated repression of alpha-MHC promoter activity. Over-expression of c-fos and c-jun in cardiomyocytes inhibited alpha-MHC promoter activity in a concentration dependent manner. Data suggest a repressive role of AP-1 in alpha-MHC expression and its possible involvement in the transition from compensatory hypertrophy to heart failure in chronic volume overload.

Cardiac BNP gene activation by angiotensin II in vivo

The transcription factors involved in the activation of cardiac gene expression by angiotensin II (Ang II) in vivo are not well understood. Here we studied the contribution of transcriptional elements to the activation of the cardiac B-type natriuretic peptide (BNP) gene promoter by Ang II in conscious rats and in angiotensin II type 1 receptor (AT1R) transgenic mice. Rat BNP luciferase reporter gene constructs were injected into the left ventricular wall. The mean luciferase activity was 1.8-fold higher (P<0.05) in the ventricles of animals subjected to 2-week Ang II infusion as compared with vehicle infusion. Our results indicate that GATA binding sites at -90 and -81 in the rat BNP promoter are essential for the in vivo response to Ang II. The GATA factor binding to these sites is GATA-4. BNP mRNA levels and GATA-4 binding activity are also increased in the hypertrophied hearts of aged AT1R transgenic mice.

Regulation of the rat CYP4A2 gene promoter by c-Jun and octamer binding protein-1

The physiologically important cytochrome P450 (CYP) 4A2 arachidonic acid omega-hydroxylase gene is widely expressed in rat tissues. Although the induction of CYPs 4A by peroxisome proliferators and dietary lipids is established there is minimal information on the factors that control constitutive expression. To address this issue we cloned 1.4 kb of the CYP4A2 5'-upstream region and identified several DNA elements that resembled the activator protein-1 (AP-1) consensus sequence. Using a series of 5'-truncated reporter constructs a 42 bp region was detected that was responsive to the AP-1 factor c-Jun, which is important in basal gene regulation. The roles of two putative AP-1 elements at -47/-41 and -31/-25 were tested, with the former emerging from studies with mutagenised constructs as the functionally important site. These findings were supported by electromobility shift assay (EMSA) studies that indicated the interaction of the -47/-41 element with c-Jun. The -31/-25 element mediated the suppression of CYP4A2 transactivation by octamer binding protein-1 (oct-1). Thus, mutagenesis of this element relieved the modulatory effect of oct-1 on c-Jun-mediated transactivation. In EMSAs, the binding of nuclear proteins to the -31/-25 element was competed by an oct-1 consensus sequence and supershifted by an anti-oct-1 antibody. Overexpression of c-Jun in rat liver-derived H4IIE cells increased CYP4A2 mRNA to approximately 2-fold of control, but oct-1 overexpression was without significant effect. From chromatin immunoprecipitation assays both c-Jun and oct-1 bound to the CYP4A2 5'-upstream sequence in H4IIE cells. These findings implicate c-Jun and oct-1 as potentially important constitutive factors that modulate the transactivation of the CYP4A2 gene promoter.

Protein kinase C regulates internal initiation of translation of the GATA-4 mRNA following vasopressin-induced hypertrophy of cardiac myocytes

GATA-4 is a key member of the GATA family of transcription factors involved in cardiac development and growth as well as in cardiac hypertrophy and heart failure. Our previous studies suggest that GATA-4 protein synthesis may be translationally regulated. We report here that the 518-nt long 5'-untranslated region (5'-UTR) of the GATA-4 mRNA, which is predicted to form stable secondary structures (-65 kcal/mol) such as to be inhibitory to cap-dependent initiation, confers efficient translation to monocistronic reporter mRNAs in cell-free extracts. Moreover, uncapped GATA-4 5'-UTR containing monocistronic reporter mRNAs continue to be well translated while capped reporters are insensitive to the inhibition of initiation by cap-analog, suggesting a cap-independent mechanism of initiation. Utilizing a dicistronic luciferase mRNA reporter containing the GATA-4 5'-UTR within the intercistronic region, we demonstrate that this leader sequence confers functional internal ribosome entry site (IRES) activity. The activity of the GATA-4 IRES is unaffected in trans-differentiating P19CL6 cells, however, is strongly stimulated immediately following arginine-vasopressin exposure of H9c2 ventricular myocytes. IRES activity is then maintained at submaximal levels during hypertrophic growth of these cells. Supraphysiological Ca(2+) levels diminished stimulation of IRES activity immediately following exposure to vasopressin and inhibition of protein kinase C activity utilizing a pseudosubstrate peptide sequence blocked IRES activity during hypertrophy. Thus, our data suggest a mechanism for GATA-4 protein synthesis under conditions of reduced global cap-dependent translation, which is maintained at a submaximal level during hypertrophic growth and point to the regulation of GATA-4 IRES activity by sarco(ER)-reticular Ca(2+) stores and PKC.

Re-employment of developmental transcription factors in adult heart disease

A finite number of transcription factors constitute a combinatorial code that orchestrates cardiac development and the specification and differentiation of myocytes. Many, if not all of these same transcription factors are re-employed in the adult heart in response to disease stimuli that promote hypertrophic enlargement and/or dilated cardiomyopathy, as part of the so-called "fetal gene program". This review will discuss the transcription factors that regulate the hypertrophic growth response of the adult heart, with a special emphasis on those regulators that participate in cardiac development.

Regulation of Ncx1 expression. Identification of regulatory elements mediating cardiac-specific expression and up-regulation

The Na+-Ca2+ exchanger (NCX1) is up-regulated in hypertrophy and is often found up-regulated in end-stage heart failure. Studies have shown that the change in its expression contributes to contractile dysfunction. We have previously shown that the 1831-bp Ncx1 H1 (1831Ncx1) promoter directs cardiac-specific expression of the exchanger in both development and in the adult, and is sufficient for the up-regulation of Ncx1 in response to pressure overload. Here, we utilized adenoviral mediated gene transfer and transgenics to identify minimal regions and response elements that mediate Ncx1 expression in the heart. We demonstrate that the proximal 184 bp of the Ncx1 H1 (184Ncx1) promoter is sufficient for expression of reporter genes in adult cardiomyocytes and for the correct spatiotemporal pattern of Ncx1 expression in development but not for up-regulation in response to pressure overload. Mutational analysis revealed that both the -80 CArG and the -50 GATA elements were required for expression in isolated adult cardiomyocytes. Chromatin immunoprecipitation assays in adult cardiocytes demonstrate that SRF and GATA4 are associated with the proximal region of the endogenous Ncx1 promoter. Transgenic lines were established for the 1831Ncx1 promoter-luciferase containing mutations in the -80 CArG or -50 GATA element. No luciferase activity was detected during development, in the adult, or after pressure overload in any of the -80 CArG transgenic lines. The Ncx1 -50 GATA mutant promoter was sufficient for driving the normal spatiotemporal pattern of Ncx1 expression in development and for up-regulation in response to pressure overload but importantly, expression was no longer cardiac restricted. This work is the first in vivo study that demonstrates which cis elements are important for Ncx1 regulation.