PKA, Rap1, ERK1/2, and p90RSK mediate PGE2 and EP4 signaling in neonatal ventricular myocytes

Critical Appraisal of Pharmaceutical Therapy in Diabetic Cardiomyopathy-Challenges and Prospectives

Diabetes mellitus (DM) is a multifaceted disorder with a pandemic spread and a remarkable burden of cardiovascular mortality and morbidity. Diabetic cardiomyopathy (DBCM) has been increasingly recognized as the development of cardiac dysfunction, which is accompanied by heart failure (HF) symptoms in the absence of obvious reasons like ischemic heart disease, hypertension, or valvulopathies. Several pathophysiological mechanisms have been proposed, including metabolic disorders (e.g., glycation products), oxidative stress, low-grade inflammation, mitochondrial dysfunction, etc., which should guide the development of new therapeutic strategies. Up to now, HF treatment has not differed between patients with and without diabetes, which limits the expected benefits despite the high cardiovascular risk in the former group. However, DBCM patients may require different management, which prioritize anti-diabetic medications or testing other novel therapies. This review aims to appraise the challenges and prospectives of the individualized pharmaceutical therapy for DBCM.

Pharmacological activation of mesenchymal stem cells increases gene expression pattern of cell adhesion molecules and fusion with neonatal cardiomyocytes

Cellular therapy is considered a better option for the treatment of degenerative disorders. Different cell types are being used for tissue regeneration. Despite extensive research in this field, several issues remain to be addressed concerning cell transplantation. One of these issues is the survival and homing of administered cells in the injured tissue, which depends on the ability of these cells to adhere. To enhance cell adherence and survival, Rap1 GTPase was activated in mesenchymal stem cells (MSCs) as well as in cardiomyocytes (CMs) by using 8-pCPT-2'-O-Me-cAMP, and the effect on gene expression dynamics was determined through quantitative reverse transcriptase-polymerase chain reaction analysis. Pharmacological activation of MSCs and CMs resulted in the upregulation of connexin-43 and cell adhesion genes, which increased the cell adhesion ability of MSCs and CMs, and increased the fusion of MSCs with neonatal CMs. Treating stem cells with a pharmacological agent that activates Rap1a before transplantation can enhance their fusion with CMs and increase cellular regeneration.

The Role of p90 Ribosomal S6 Kinase (RSK) in Tyrosine Kinase Inhibitor (TKI)-Induced Cardiotoxicity

Targeted therapy, such as tyrosine kinase inhibitors (TKIs), has been approved to manage various cancer types. However, TKI-induced cardiotoxicity is a limiting factor for their use. This issue has raised the need for investigating potential cardioprotective techniques to be combined with TKIs. Ribosomal S6-kinases (RSKs) are a downstream effector of the mitogen-activated-protein-kinase (MAPK) pathway; specific RSK isoforms, such as RSK1 and RSK2, have been expressed in cancer cells, in which they increase tumour proliferation. Selective targeting of those isoforms would result in tumour suppression. Moreover, activation of RSKs expressed in the heart has resulted in cardiac hypertrophy and arrhythmia; thus, inhibiting RSKs would result in cardio-protection. This review article presents an overview of the usefulness of RSK inhibitors that can be novel agents to be assessed in future research for their effect in reducing cancer proliferation, as well as protecting the heart from cardiotoxicity induced by TKIs.

MicroRNA-186-5p inhibits H9c2 cells apoptosis induced by oxygen-glucose deprivation by targeting ERK1/2

Background

Serum miR-186-5p levels are increased in acute myocardial infarction (AMI) patients and might contribute to assessing the prognosis of AMI patients. In this study, we further investigated the underlying molecular mechanism of miR-186-5p that participated in the pathological processes of myocardial ischemia.

Methods

The AMI models of rats and oxygen-glucose deprivation (OGD) models of H9c2 cells were established. Bioinformatics databases, luciferase reporting, and western blotting assays were performed to identify the regulatory target of miR-186-5p. Transfection and functional experiments were conducted to further define the possible molecular mechanism of miR-186-5p during the process of glucose deficiency and hypoxia.

Results

The level of miR-186-5p was found to significantly decrease in H9c2 cells after OGD treatment, while it increased in the culture medium from OGD-treated H9c2 cells. Using bioinformatics databases, luciferase reporting, and western blotting assays, we identified that ERK1/2 might serve as the negative regulatory target of miR-186-5p. Combined with further transfection experiments, we indicated that miR-186-5p might inhibit the expression and activation of ERK1/2. This finding was also reflected in the reduction of their downstream cleaved caspase-3. Through functional experiments, we revealed that miR-186-5p might inhibit apoptosis and promote proliferation in OGD-treated H9c2 cells.

Conclusions

We demonstrated that miR-186-5p might suppress OGD-induced apoptosis in H9c2 cells by targeting the ERK1/2 pathway.

Inhibitory effects of 6'-sialyllactose on angiotensin II-induced proliferation, migration, and osteogenic switching in vascular smooth muscle cells

Excessive production and migration of vascular smooth muscle cells (VSMCs) are associated with vascular remodeling that causes vascular diseases, such as restenosis and hypertension. Angiotensin II (Ang II) stimulation is a key factor in inducing abnormal VSMC function. This study aimed to investigate the effects of 6'-sialyllactose (6'SL), a human milk oligosaccharide, on Ang II-stimulated cell proliferation, migration and osteogenic switching in rat aortic smooth muscle cells (RASMCs) and human aortic smooth muscle cells (HASMCs). Compared with the control group, Ang II increased cell proliferation by activating MAPKs, including ERK1/2/p90RSK/Akt/mTOR and JNK pathways. However, 6'SL reversed Ang II-stimulated cell proliferation and the ERK1/2/p90RSK/Akt/mTOR pathways in RASMCs and HASMCs. Moreover, 6'SL suppressed Ang II-stimulated cell cycle progression from G0/G1 to S and G2/M phases in RASMCs. Furthermore, 6'SL effectively inhibited cell migration by downregulating NF-κB-mediated MMP2/9 and VCAM-1 expression levels. Interestingly, in RASMCs, 6'SL attenuated Ang II-induced osteogenic switching by reducing the production of p90RSK-mediated c-fos and JNK-mediated c-jun, leading to the downregulation of AP-1-mediated osteopontin production. Taken together, our data suggest that 6'SL inhibits Ang II-induced VSMC proliferation and migration by abolishing the ERK1/2/p90RSK-mediated Akt and NF-κB signaling pathways, respectively, and osteogenic switching by suppressing p90RSK- and JNK-mediated AP-1 activity.

Cardioprotection of Immature Heart by Simultaneous Activation of PKA and Epac: A Role for the Mitochondrial Permeability Transition Pore

Metabolic and ionic changes during ischaemia predispose the heart to the damaging effects of reperfusion. Such changes and the resulting injury differ between immature and adult hearts. Therefore, cardioprotective strategies for adults must be tested in immature hearts. We have recently shown that the simultaneous activation of protein kinase A (PKA) and exchange protein activated by cAMP (Epac) confers marked cardioprotection in adult hearts. The aim of this study is to investigate the efficacy of this intervention in immature hearts and determine whether the mitochondrial permeability transition pore (MPTP) is involved. Isolated perfused Langendorff hearts from both adult and immature rats were exposed to global ischaemia and reperfusion injury (I/R) following control perfusion or perfusion after an equilibration period with activators of PKA and/or Epac. Functional outcome and reperfusion injury were measured and in parallel, mitochondria were isolated following 5 min of reperfusion to determine whether cardioprotective interventions involved changes in MPTP opening behaviour. Perfusion for 5 min preceding ischaemia of injury-matched adult and immature hearts with 5 µM 8-Br (8-Br-cAMP-AM), an activator of both PKA and Epac, led to significant reduction in post-reperfusion CK release and infarct size. Perfusion with this agent also led to a reduction in MPTP opening propensity in both adult and immature hearts. These data show that immature hearts are innately more resistant to I/R injury than adults, and that this is due to a reduced tendency of MPTP opening following reperfusion. Furthermore, simultaneous stimulation of PKA and Epac causes cardioprotection, which is additive to the innate resistance.

Crosstalk between Sodium-Glucose Cotransporter Inhibitors and Sodium-Hydrogen Exchanger 1 and 3 in Cardiometabolic Diseases

Abnormality in glucose homeostasis due to hyperglycemia or insulin resistance is the hallmark of type 2 diabetes mellitus (T2DM). These metabolic abnormalities in T2DM lead to cellular dysfunction and the development of diabetic cardiomyopathy leading to heart failure. New antihyperglycemic agents including glucagon-like peptide-1 receptor agonists and the sodium-glucose cotransporter-2 inhibitors (SGLT2i) have been shown to attenuate endothelial dysfunction at the cellular level. In addition, they improved cardiovascular safety by exhibiting cardioprotective effects. The mechanism by which these drugs exert their cardioprotective effects is unknown, although recent studies have shown that cardiovascular homeostasis occurs through the interplay of the sodium-hydrogen exchangers (NHE), specifically NHE1 and NHE3, with SGLT2i. Another theoretical explanation for the cardioprotective effects of SGLT2i is through natriuresis by the kidney. This theory highlights the possible involvement of renal NHE transporters in the management of heart failure. This review outlines the possible mechanisms responsible for causing diabetic cardiomyopathy and discusses the interaction between NHE and SGLT2i in cardiovascular diseases.

Prostaglandin-E2 receptor-4 stimulant rescues cardiac malfunction during myocarditis and protects the heart from adverse ventricular remodeling after myocarditis

Cardioprotective effect of prostaglandin-E2 receptor-4 (EP4) stimulation on the ischemic heart has been demonstrated. Its effect on the heart affected by myocarditis, however, remains uncertain. In this study, we investigated therapeutic effect of EP4 stimulant using a mouse model of autoimmune myocarditis (EAM) that progresses to dilated cardiomyopathy (DCM). EP4 was present in the hearts of EAM mice. Treatment with EP4 agonist (ONO-0260164: 20 mg/kg/day) improved an impaired left ventricular (LV) contractility and reduction of blood pressure on day 21, a peak myocardial inflammation. Alternatively, DCM phenotype, characterized by LV dilation, LV systolic dysfunction, and collagen deposition, was observed on day 56, along with activation of matrix metalloproteinase (MMP)-2 critical for myocardial extracellular matrix disruption, indicating an important molecular mechanism underlying adverse ventricular remodeling after myocarditis. Continued treatment with ONO-0260164 alleviated the DCM phenotype, but this effect was counteracted by its combination with a EP4 antagonist. Moreover, ONO-0260164 inhibited in vivo proteolytic activity of MMP-2 in association with up-regulation of tissue inhibitor of metalloproteinase (TIMP)-3. EP4 stimulant may be a promising and novel therapeutic agent that rescues cardiac malfunction during myocarditis and prevents adverse ventricular remodeling after myocarditis by promoting the TIMP-3/MMP-2 axis.

Investigation of Omega-3 Polyunsaturated Fatty Acid Biological Activity in a Tissue-Engineered Skin Model Involving Psoriatic Cells

Clinical studies have shown that diets enriched with omega-3 (also know as n-3) polyunsaturated fatty acids could relieve the symptoms of patients with psoriasis. However, the mechanisms involved remain poorly understood. The aim of this study was to investigate the effects of α-linolenic acid (ALA) on the proliferation and differentiation of psoriatic keratinocytes in a three-dimensional skin model. Skin models featuring healthy (healthy substitute) or psoriatic (psoriatic substitute) cells were engineered by the self-assembly method of tissue engineering using a culture medium supplemented with 10 μM ALA in comparison with the regular unsupplemented medium. ALA decreased keratinocyte proliferation and improved psoriatic substitute epidermal differentiation, as measured by decreased Ki67 staining and increased protein expression of FLG and loricrin. The added ALA was notably incorporated into the epidermal phospholipids and metabolized into long-chain n-3 polyunsaturated fatty acids, mainly eicosapentaenoic acid and n-3 docosapentaenoic acid. ALA supplementation led to increased levels of eicosapentaenoic acid derivatives (15-hydroxyeicosapentaenoic acid and 18-hydroxyeicosapentaenoic acid) as well as a decrease in levels of omega-6 (also know as n-6) polyunsaturated fatty acid lipid mediators (9-hydroxyoctadecadienoic acid, 12-hydroxyeicosatetraenoic acid, and leukotriene B₄). Furthermore, the signal transduction mediators extracellular signal‒regulated kinases 1 and 2 were the kinases most activated after ALA supplementation. Taken together, these results show that ALA decreases the pathologic phenotype of psoriatic substitutes by normalizing keratinocyte proliferation and differentiation in vitro.

A new trick for an old dog? Myocardial-specific roles for prostaglandins as mediators of ischemic injury and repair

The small lipid-derived paracrine signaling molecules known as prostaglandins have been recognized for their ability to modulate many facets of cardiovascular physiology since their initial discovery more than 85 years ago. Although the role of prostaglandins in the vasculature has gained significant attention across time, a handful of historical studies have also directly implicated the cardiomyocyte in both prostaglandin synthesis and release. Recently, our understanding of how prostaglandin receptor modulation impacts and contributes to myocardial structure and function has gained attention while leaving most other components of myocardial prostaglandin metabolism and signaling unexplored. This mini-review highlights both the key historical studies that underpin modern prostaglandin research in the heart, while concurrently presenting the latest findings related to how prostaglandin metabolism and signaling impact myocardial injury and repair.

Rap1a Overlaps the AGE/RAGE Signaling Cascade to Alter Expression of α-SMA, p-NF-κB, and p-PKC-ζ in Cardiac Fibroblasts Isolated from Type 2 Diabetic Mice

Cardiovascular disease, specifically heart failure, is a common complication for individuals with type 2 diabetes mellitus. Heart failure can arise with stiffening of the left ventricle, which can be caused by “active” cardiac fibroblasts (i.e., myofibroblasts) remodeling the extracellular matrix (ECM). Differentiation of fibroblasts to myofibroblasts has been demonstrated to be an outcome of AGE/RAGE signaling. Hyperglycemia causes advanced glycated end products (AGEs) to accumulate within the body, and this process is greatly accelerated under chronic diabetic conditions. AGEs can bind and activate their receptor (RAGE) to trigger multiple downstream outcomes, such as altering ECM remodeling, inflammation, and oxidative stress. Previously, our lab has identified a small GTPase, Rap1a, that possibly overlaps the AGE/RAGE signaling cascade to affect the downstream outcomes. Rap1a acts as a molecular switch connecting extracellular signals to intracellular responses. Therefore, we hypothesized that Rap1a crosses the AGE/RAGE cascade to alter the expression of AGE/RAGE associated signaling proteins in cardiac fibroblasts in type 2 diabetic mice. To delineate this cascade, we used genetically different cardiac fibroblasts from non-diabetic, diabetic, non-diabetic RAGE knockout, diabetic RAGE knockout, and Rap1a knockout mice and treated them with pharmacological modifiers (exogenous AGEs, EPAC, Rap1a siRNA, and pseudosubstrate PKC-ζ). We examined changes in expression of proteins implicated as markers for myofibroblasts (α-SMA) and inflammation/oxidative stress (NF-κB and SOD-1). In addition, oxidative stress was also assessed by measuring hydrogen peroxide concentration. Our results indicated that Rap1a connects to the AGE/RAGE cascade to promote and maintain α-SMA expression in cardiac fibroblasts. Moreover, Rap1a, in conjunction with activation of the AGE/RAGE cascade, increased NF-κB expression as well as hydrogen peroxide concentration, indicating a possible oxidative stress response. Additionally, knocking down Rap1a expression resulted in an increase in SOD-1 expression suggesting that Rap1a can affect oxidative stress markers independently of the AGE/RAGE signaling cascade. These results demonstrated that Rap1a contributes to the myofibroblast population within the heart via AGE/RAGE signaling as well as promotes possible oxidative stress. This study offers a new potential therapeutic target that could possibly reduce the risk for developing diabetic cardiovascular complications attributed to AGE/RAGE signaling.

R. Tafazzin Mutation Affecting Cardiolipin Leads to Increased Mitochondrial Superoxide Anions and Mitophagy Inhibition in Barth Syndrome

Tafazzin is a phospholipid transacylase that catalyzes the remodeling of cardiolipin, a mitochondrial phospholipid required for oxidative phosphorylation. Mutations of the tafazzin gene cause Barth syndrome, which is characterized by mitochondrial dysfunction and dilated cardiomyopathy, leading to premature death. However, the molecular mechanisms underlying the cause of mitochondrial dysfunction in Barth syndrome remain poorly understood. We again highlight the fact that the tafazzin deficiency is also linked to defective oxidative phosphorylation associated with oxidative stress. All the mitochondrial events are positioned in a context where mitophagy is a key element in mitochondrial quality control. Here, we investigated the role of tafazzin in mitochondrial homeostasis dysregulation and mitophagy alteration. Using a HeLa cell model of tafazzin deficiency, we show that dysregulation of tafazzin in HeLa cells induces alteration of mitophagy. Our findings provide some additional insights into mitochondrial dysfunction associated with Barth syndrome, but also show that mitophagy inhibition is concomitant with apoptosis dysfunction through the inability of abnormal mitochondrial cardiolipin to assume its role in cytoplasmic signal transduction. Our work raises hope that pharmacological manipulation of the mitophagic pathway together with mitochondrially targeted antioxidants may provide new insights leading to promising treatment for these highly lethal conditions.

Inflammation leads through PGE/EP3 signaling to HDAC5/MEF2-dependent transcription in cardiac myocytes

The myocyte enhancer factor 2 (MEF2) regulates transcription in cardiac myocytes and adverse remodeling of adult hearts. Activators of G protein-coupled receptors (GPCRs) have been reported to activate MEF2, but a comprehensive analysis of GPCR activators that regulate MEF2 has to our knowledge not been performed. Here, we tested several GPCR agonists regarding their ability to activate a MEF2 reporter in neonatal rat ventricular myocytes. The inflammatory mediator prostaglandin E₂ (PGE₂) strongly activated MEF2. Using pharmacological and protein-based inhibitors, we demonstrated that PGE₂ regulates MEF2 via the EP₃ receptor, the βγ subunit of G_i/o protein and two concomitantly activated downstream pathways. The first consists of Tiam1, Rac1, and its effector p21-activated kinase 2, the second of protein kinase D. Both pathways converge on and inactivate histone deacetylase 5 (HDAC5) and thereby de-repress MEF2. In vivo, endotoxemia in MEF2-reporter mice induced upregulation of PGE₂ and MEF2 activation. Our findings provide an unexpected new link between inflammation and cardiac remodeling by de-repression of MEF2 through HDAC5 inactivation, which has potential implications for new strategies to treat inflammatory cardiomyopathies.

Role of p90RSK in Kidney and Other Diseases

The 90 kDa ribosomal s6 kinases (RSKs) are a group of serine/threonine kinases consisting of 4 RSK isoforms (RSK1-4), of which RSK1 is also designated as p90RSK. p90RSK plays an important role in the Ras-mitogen-activated protein kinase (MAPK) signalling cascade and is the direct downstream effector of Ras-extracellular signal-regulated kinase (ERK1/2) signalling. ERK1/2 activation directly phosphorylates and activates p90RSK, which, in turn, activates various signalling events through selection of different phosphorylation substrates. Upregulation of p90RSK has been reported in numerous human diseases. p90RSK plays an important role in the regulation of diverse cellular processes. Thus, aberrant activation of p90RSK plays a critical role in the pathogenesis of organ dysfunction and damage. In this review, we focus on the current understanding of p90RSK functions and roles in the development and progression of kidney diseases. Roles of p90RSK, as well as other RSKs, in cardiovascular disorders and cancers are also discussed.

Assessing the toxicity of triphenyltin to different life stages of the marine medaka Oryzias melastigma through a series of life-cycle based experiments

Toxic effects of triphenyltin (TPT) to different life stages of the marine medaka Oryzias melastigma were investigated through a series of life-cycle based exposure experiments. In embryo stage, TPT exposure could elevate the heartbeat rate at Day 6-8 post-fertilization and increase the expression levels of five heart development related genes (i.e., ATPase, COX2, BMP4, GATA4 and NKX2.5). In larval stage, TPT shortened the body length at ≥10μg/L and suppressed the swimming activity of the fish larvae at Day 1 post-hatching at 50μg/L. In reproductive stage, TPT exposure resulted in a male-biased sex ratio (2μg/L) and reduced the gonadosomatic index (GSI) in females (≥ 0.1μg/L), which might in turn lead to a decline in their population fitness. The reproductive stage of O. melastigma was more sensitive to TPT than other stages, while the GSI of female medaka was the most sensitive endpoint.

Epac-Rap1-activated mesenchymal stem cells improve cardiac function in rat model of myocardial infarction

INTRODUCTION

Rap1, a member of Ras superfamily of small GTP-binding proteins, is involved in cardiovascular biology in numerous ways. It is an evolutionary conserved regulator of adhesion, polarity, differentiation and growth.

AIMS

Our aim was to analyze Rap1-activated rat bone marrow mesenchymal stem cells (MSCs) for their potential role in adhesion and cardiac differentiation.

METHODS

Myocardial infarction (MI) was produced in Sprague Dawley (SD) rats through occlusion of the left anterior descending coronary artery. MSCs were treated with 8-pCPT-2'-O-Me-cAMP (CPT) to activate Rap1. Normal (untreated) and CPT-treated MSCs were transplanted through intramyocardial injection in respective groups. Cardiac function was assessed by echocardiography at 2 and 4 weeks after cell transplantation. Histological analysis was performed to observe changes at tissue level.

RESULTS

Homing of CPT-treated MSCs was significantly (***P<.001) higher as compared to normal MSCs in the infarcted hearts. This may be due to increase in the gene expression of some of the cell adhesion molecules as evident by qRT-PCR analysis. Significant (***P<.001) improvement in the restoration of heart function in terms of left ventricular diastolic and systolic internal diameters (LVIDd, LVIDs), % ejection fraction, % fraction shortening and end-systolic and end-diastolic volumes were observed in CPT-treated MSCs as compared to the MI model. Histological analyses showed significant (***P<.001) reduction in scar formation in the CPT-treated group. Differentiation of treated MSCs into functional cardiomyocytes was evident through immunohistochemical staining. LV wall thickness was also preserved significantly (***P<.001). Blood vessel formation was more pronounced in CPT-treated group although both cell therapy groups showed significant increase as compared to MI model.

CONCLUSION

Our findings showed that pharmacological activation of Epac-Rap1 improves cardiac function through better survival, adhesion and differentiation of transplanted cells. Transplantation of these MSCs in the infarct area restored functional myocardium.

An EP4 Receptor Agonist Inhibits Cardiac Fibrosis Through Activation of PKA Signaling in Hypertrophied Heart

Cardiac fibrosis is a pathological feature of myocardium of failing heart and plays causative roles in arrhythmia and cardiac dysfunction, but its regulatory mechanisms remain largely elusive. In this study, we investigated the effects of the novel EP4 receptor agonist ONO-0260164 on cardiac fibrosis in hypertrophied heart and explored the regulatory mechanisms in cardiac fibroblasts.In a mouse model of cardiac hypertrophy generated by transverse aortic constriction (TAC), ONO-0260164 treatment significantly prevented systolic dysfunction and progression of myocardial fibrosis at 5 weeks after TAC. In cultured neonatal rat cardiac fibroblasts, transforming growth factor-β1 (TGF-β1) induced upregulation of collagen type 1, alpha 1 (Col1a1) and type 3, alpha 1 (Col3a1), which was inhibited by ONO-0260164 treatment. ONO-0260164 activated protein kinase A (PKA) in the presence of TGF-β1 in the cardiac fibroblasts. PKA activation suppressed an increase in collagen expression induced by TGF-β1, indicating the important inhibitory roles of PKA activation in TGF-β1mediated collagen induction.We have demonstrated for the first time the antifibrotic effects of the novel EP4 agonist ONO-0260164 in vivo and in vitro, and the important role of PKA activation in the effects.

Stimulating TRPV1 externalization and synthesis in dorsal root ganglion neurons contributes to PGE2 potentiation of TRPV1 activity and nociceptor sensitization

BACKGROUND

Persistent peripheral sensitization contributes to chronic pain. Plasticity of nociceptive dorsal root ganglion (DRG) neurons (nociceptors) induced by pro-inflammatory mediators contributes to sensitization. Prostaglandin E2 (PGE2) enriched in injured tissues is known not only directly to sensitize DRG neurons, but also to potentiate sensitizing effects of other pain mediators such as capsaicin and its receptor transient receptor potential vanilloid-1 (TRPV1). It remains unknown whether PGE2 potentiates TRPV1 activity by stimulating its synthesis, cell surface and axonal trafficking in DRG neurons.

METHODS

Combined biochemical, morphological, pharmacological and behavioral approaches have been used to address this issue in both in vitro and in vivo models.

RESULTS

PGE2 increased TRPV1 externalization in cultured rat DRG neurons in a time- and concentration-dependent manner, an event blocked by an inhibitor of protein synthesis or anterograde export. EP1 and EP4, but not EP2 and EP3, mediated this event. EP1 agonist-induced TRPV1 externalization was suppressed by inhibitors of CaMKII, PLC, PKC and PKCε, while EP4 agonist-induced TRPV1 externalization by inhibitors of cAMP/PKA and ERK/MAPK. Pre-exposure to PGE2 potentiated release of calcitonin gene-related peptide from cultured DRG neurons evoked by subsequent capsaicin stimulation. This event was blocked by an inhibitor of protein synthesis or export, suggesting that PGE2-induced TRPV1 synthesis and externalization is coupled to enhanced TRPV1 activity. Pre-exposure to PGE2 not only prolonged tactile allodynia evoked by subsequent capsaicin challenge, but also increased TRPV1 levels in L4-6 DRG, sciatic nerves and plantar skin.

CONCLUSIONS

Our data indicate that facilitating TRPV1 synthesis, cell surface and axonal trafficking is a novel mechanism underlying PGE2 potentiation of TRPV1 activity.

Polymorphisms in MIR137HG and microRNA-137-regulated genes influence gray matter structure in schizophrenia

Evidence suggests that microRNA-137 (miR-137) is involved in the genetic basis of schizophrenia. Risk variants within the miR-137 host gene (MIR137HG) influence structural and functional brain-imaging measures, and miR-137 itself is predicted to regulate hundreds of genes. We evaluated the influence of a MIR137HG risk variant (rs1625579) in combination with variants in miR-137-regulated genes TCF4, PTGS2, MAPK1 and MAPK3 on gray matter concentration (GMC). These genes were selected based on our previous work assessing schizophrenia risk within possible miR-137-regulated gene sets using the same cohort of subjects. A genetic risk score (GRS) was determined based on genotypes of these four schizophrenia risk-associated genes in 221 Caucasian subjects (89 schizophrenia patients and 132 controls). The effects of the rs1625579 genotype with the GRS of miR-137-regulated genes in a three-way interaction with diagnosis on GMC patterns were assessed using a multivariate analysis. We found that schizophrenia subjects homozygous for the MIR137HG risk allele show significant decreases in occipital, parietal and temporal lobe GMC with increasing miR-137-regulated GRS, whereas those carrying the protective minor allele show significant increases in GMC with GRS. No correlations of GMC and GRS were found in control subjects. Variants within or upstream of genes regulated by miR-137 in combination with the MIR137HG risk variant may influence GMC in schizophrenia-related regions in patients. Given that the genes evaluated here are involved in protein kinase A signaling, dysregulation of this pathway through alterations in miR-137 biogenesis may underlie the gray matter loss seen in the disease.

Prostaglandin E Receptor Subtype 4 Signaling in the Heart: Role in Ischemia/Reperfusion Injury and Cardiac Hypertrophy

Prostaglandin E2 (PGE2) is an endogenous lipid mediator, produced from the metabolism of arachidonic acids, upon the sequential actions of phospholipase A2, cyclooxygenases, and prostaglandin E synthases. The various biological functions governed by PGE2 are mediated through its four distinct prostaglandin E receptors (EPs), designated as EP1, EP2, EP3, and EP4, among which the EP4 receptor is the one most widely distributed in the heart. The availability of global or cardiac-specific EP4 knockout mice and the development of selective EP4 agonists/antagonists have provided substantial evidence to support the role of EP4 receptor in the heart. However, like any good drama, activation of PGE2-EP4 signaling exerts both protective and detrimental effects in the ischemic heart disease. Thus, the primary object of this review is to provide a comprehensive overview of the current progress of the PGE2-EP4 signaling in ischemic heart diseases, including cardiac hypertrophy and myocardial ischemia/reperfusion injury. A better understanding of PGE2-EP4 signaling should promote the development of more effective therapeutic approaches to treat the ischemic heart diseases without triggering unwanted side effects.

Interactions between the regulatory subunit of type I protein kinase A and p90 ribosomal S6 kinase1 regulate cardiomyocyte apoptosis

Cardiomyocyte apoptosis contributes toward the loss of muscle mass in myocardial pathologies. Previous reports have implicated type I cAMP-dependent protein kinase (PKA) and p90 ribosomal S6 kinase (RSK) in cardiomyocyte apoptosis. However, the precise mechanisms and the isoform of RSK involved in this process remain undefined. Using adult rat ventricular myocytes and mouse-derived cardiac HL-1 cardiomyocytes, we demonstrate that hypoxia/reoxygenation (H/R)-induced apoptosis is accompanied by a decrease in the type I PKA regulatory subunit (PKARIα) and activation of RSK1. As previously described by us for other cell types, in cardiomyocytes, inactive RSK1 also interacts with PKARIα, whereas the active RSK1 interacts with the catalytic subunit of PKA. Additionally, small interfering (siRNA)-mediated silencing of PKARIα or disrupting the RSK1/PKARIα interactions with a small, cell-permeable peptide activates RSK1 and recapitulates the H/R-induced apoptosis. Inhibition of RSK1 or siRNA-mediated silencing of RSK1 attenuates H/R-induced apoptosis, demonstrating the role of RSK1 in cardiomyocyte apoptosis. Furthermore, silencing of RSK1 decreases the H/R-induced phosphorylation of sodium-hydrogen exchanger 1 (NHE1), and inhibition of NHE1 with 5'-N-ethyl-N-isopropyl-amiloride blocks H/R induced apoptosis, indicating the involvement of NHE1 in apoptosis. Overall, our findings demonstrate that H/R-mediated decrease in PKARIα protein levels leads to activation of RSK1, which via phosphorylation of NHE1 induces cardiomyocyte apoptosis.

The induction of cardiac ornithine decarboxylase by β2 -adrenergic agents is associated with calcium channels and phosphorylation of ERK1/2

The role that the induction of cardiac ornithine decarboxylase (ODC), a key enzyme in polyamine biosynthesis, by beta-adrenergic agents may have in heart hypertrophy is a controversial issue. Besides, the signaling pathways related to cardiac ODC regulation have not been fully elucidated. Here we show that in Balb C mice the stimulation of cardiac ODC activity by adrenergic agents was mainly mediated by β2 -adrenergic receptors, and that this induction was lower in the hypertrophic heart. Interestingly, this stimulation was abolished by the L-calcium channel antagonists verapamil and nifedipine. In addition, whereas the treatment with β2 -adrenergic agents was associated to both the increases in ODC, ODC-antizyme inhibitor 1 (AZIN1), c-fos and c-myc mRNA levels and the phosphorylation of CREB and MAP kinases ERK1 and ERK2 (ERK1/2), the co-treatment with L-calcium channel blockers differentially prevented most of these changes. These results suggest that the stimulation of cardiac ODC by β2 -adrenergic agents is associated with the activation of MAP kinases through the participation of L-calcium channels, and that by itself p-CREB does not appear to be sufficient for the transcriptional activation of ODC. In addition, post-translational mechanisms related with the induction of AZIN1 appear to be related to the increase of cardiac ODC activity.

Small G Proteins in the Cardiovascular System: Physiological and Pathological Aspects

Small G proteins exist in eukaryotes from yeast to human and constitute the Ras superfamily comprising more than 100 members. This superfamily is structurally classified into five families: the Ras, Rho, Rab, Arf, and Ran families that control a wide variety of cell and biological functions through highly coordinated regulation processes. Increasing evidence has accumulated to identify small G proteins and their regulators as key players of the cardiovascular physiology that control a large panel of cardiac (heart rhythm, contraction, hypertrophy) and vascular functions (angiogenesis, vascular permeability, vasoconstriction). Indeed, basal Ras protein activity is required for homeostatic functions in physiological conditions, but sustained overactivation of Ras proteins or spatiotemporal dysregulation of Ras signaling pathways has pathological consequences in the cardiovascular system. The primary object of this review is to provide a comprehensive overview of the current progress in our understanding of the role of small G proteins and their regulators in cardiovascular physiology and pathologies.

The prostanoid EP4 receptor and its signaling pathway

The EP4 prostanoid receptor is one of four receptor subtypes for prostaglandin E2. It belongs to the family of G protein-coupled receptors. It was originally identified, similar to the EP2 receptor as a G(s)α-coupled, adenylyl cyclase-stimulating receptor. EP4 signaling plays a variety of roles through cAMP effectors, i.e., protein kinase A and exchange protein activated by cAMP. However, emerging evidence from studies using pharmacological approaches and genetically modified mice suggests that EP4, unlike EP2, can also be coupled to G(i)α, phosphatidylinositol 3-kinase, β-arrestin, or β-catenin. These signaling pathways constitute unique roles for the EP4 receptor. EP4 is widely distributed in the body and thus plays various physiologic and pathophysiologic roles. In particular, EP4 signaling is closely related to carcinogenesis, cardiac hypertrophy, vasodilation, vascular remodeling, bone remodeling, gastrointestinal homeostasis, renal function, and female reproductive function. In addition to the classic anti-inflammatory action of EP4 on mononuclear cells and T cells, recent evidence has shown that EP4 signaling contributes to proinflammatory action as well. The aim of this review is to present current findings on the biologic functions of the EP4 receptor. In particular, we will discuss its diversity from the standpoint of EP4-mediated signaling.

Serpinins: role in granule biogenesis, inhibition of cell death and cardiac function

Serpinins are a family of peptides derived from proteolytic cleavage of the penultimate and the last pair of basic residues at the C-terminus of Chromogranin A. Three forms of naturally occurring serpinin have been found in AtT-20 pituitary cells and rat heart. They are serpinin, pyrogutaminated (pGlu) -serpinin and a C-terminally extended form, serpinin-RRG. In addition pGlu-serpinin has been found in brain, primarily in neurites and nerve terminals and shown to have protective effects against oxidative stress on neurons and pituitary cells. Serpinin has also been demonstrated to regulate granule biogenesis in endocrine cells by up-regulating the protease inhibitor, protease nexin-1 transcription via a cAMP-PKA-sp1 pathway. This leads to inhibition of granule protein degradation in the Golgi complex which in turn promotes granule formation. More recently, pGlu-serpinin has been demonstrated to enhance both myocardial contractility (inotropy) and relaxation (lusitropy). In the Langendorff perfused rat heart, pGlu-serpinin showed a concentration-dependent positive inotropic effect exerted through a cAMP-PKA dependent pathway. In conclusion, the serpinin peptides have profound effects at many levels that affect the endocrine and nervous systems and cardiac function.

Tungstate reduces the expression of gluconeogenic enzymes in STZ rats

Aims

Oral administration of sodium tungstate has shown hyperglycemia-reducing activity in several animal models of diabetes. We present new insights into the mechanism of action of tungstate.

Methods

We studied protein expression and phosphorylation in the liver of STZ rats, a type I diabetes model, treated with sodium tungstate in the drinking water (2 mg/ml) and in primary cultured-hepatocytes, through Western blot and Real Time PCR analysis.

Results

Tungstate treatment reduces the expression of gluconeogenic enzymes (PEPCK, G6Pase, and FBPase) and also regulates transcription factors accountable for the control of hepatic metabolism (c-jun, c-fos and PGC1α). Moreover, ERK, p90rsk and GSK3, upstream kinases regulating the expression of c-jun and c-fos, are phosphorylated in response to tungstate. Interestingly, PKB/Akt phosphorylation is not altered by the treatment. Several of these observations were reproduced in isolated rat hepatocytes cultured in the absence of insulin, thereby indicating that those effects of tungstate are insulin-independent.

Conclusions

Here we show that treatment with tungstate restores the phosphorylation state of various signaling proteins and changes the expression pattern of metabolic enzymes.

Lack of Microsomal Prostaglandin E 2 Synthase-1 in Bone Marrow–Derived Myeloid Cells Impairs Left Ventricular Function and Increases Mortality After Acute Myocardial Infarction

Background—

Microsomal prostaglandin E 2 synthase-1 (mPGES-1), encoded by the Ptges gene, catalyzes prostaglandin E 2 biosynthesis and is expressed by leukocytes, cardiac myocytes, and cardiac fibroblasts. Ptges −/− mice develop more left ventricle (LV) dilation, worse LV contractile function, and higher LV end-diastolic pressure than Ptges +/+ mice after myocardial infarction. In this study, we define the role of mPGES-1 in bone marrow–derived leukocytes in the recovery of LV function after coronary ligation.

Methods and Results—

Cardiac structure and function in Ptges +/+ mice with Ptges +/+ bone marrow ( BM +/+ ) and Ptges +/+ mice with Ptges −/− BM ( BM −/− ) were assessed by morphometric analysis, echocardiography, and invasive hemodynamics before and 7 and 28 days after myocardial infarction. Prostaglandin levels and prostaglandin biosynthetic enzyme gene expression were measured by liquid chromatography–tandem mass spectrometry and real-time polymerase chain reaction, immunoblotting, immunohistochemistry, and immunofluorescence microscopy, respectively. After myocardial infarction, BM −/− mice had more LV dilation, worse LV systolic and diastolic function, higher LV end-diastolic pressure, more cardiomyocyte hypertrophy, and higher mortality but similar infarct size and pulmonary edema compared with BM +/+ mice. BM −/− mice also had higher levels of COX-1 protein and more leukocytes in the infarct, but not the viable LV, than BM +/+ mice. Levels of prostaglandin E 2 were higher in the infarct and viable myocardium of BM −/− mice than in BM +/+ mice.

Conclusions—

Lack of mPGES-1 in bone marrow–derived leukocytes negatively regulates COX-1 expression, prostaglandin E 2 biosynthesis, and inflammation in the infarct and leads to impaired LV function, adverse LV remodeling, and decreased survival after acute myocardial infarction.

The novel chromogranin A-derived serpinin and pyroglutaminated serpinin peptides are positive cardiac β-adrenergic-like inotropes

Three forms of serpinin peptides, serpinin (Ala26Leu), pyroglutaminated (pGlu)-serpinin (pGlu23Leu), and serpinin-Arg-Arg-Gly (Ala29Gly), are derived from cleavage at pairs of basic residues in the highly conserved C terminus of chromogranin A (CgA). Serpinin induces PN-1 expression in neuroendocrine cells to up-regulate granule biogenesis via a cAMP-protein kinase A-Sp1 pathway, while pGlu-serpinin inhibits cell death. The aim of this study was to test the hypothesis that serpinin peptides are produced in the heart and act as novel β-adrenergic-like cardiac modulators. We detected serpinin peptides in the rat heart by HPLC and ELISA methods. The peptides included predominantly Ala29Gly and pGlu-serpinin and a small amount of serpinin. Using the Langendorff perfused rat heart to evaluate the hemodynamic changes, we found that serpinin and pGlu-serpinin exert dose-dependent positive inotropic and lusitropic effects at 11-165 nM, within the first 5 min after administration. The pGlu-serpinin-induced contractility is more potent than that of serpinin, starting from 1 nM. Using the isolated rat papillary muscle preparation to measure contractility in terms of tension development and muscle length, we further corroborated the pGlu-serpinin-induced positive inotropism. Ala29Gly was unable to affect myocardial performance. Both pGlu-serpinin and serpinin act through a β1-adrenergic receptor/adenylate cyclase/cAMP/PKA pathway, indicating that, contrary to the β-blocking profile of the other CgA-derived cardiosuppressive peptides, vasostatin-1 and catestatin, these two C-terminal peptides act as β-adrenergic-like agonists. In cardiac tissue extracts, pGlu-serpinin increased intracellular cAMP levels and phosphorylation of phospholamban (PLN)Ser16, ERK1/2, and GSK-3β. Serpinin and pGlu-serpinin peptides emerge as novel β-adrenergic inotropic and lusitropic modulators, suggesting that CgA and the other derived cardioactive peptides can play a key role in how the myocardium orchestrates its complex response to sympathochromaffin stimulation.

Interleukin-6 synthesis in human chondrocytes is regulated via the antagonistic actions of prostaglandin (PG)E2 and 15-deoxy-Δ(12,14)-PGJ2

BACKGROUND

Elevated levels of interleukin-6 (IL-6), prostaglandin (PG)E(2), PGD(2) and its dehydration end product 15-deoxy-Δ(12,14)-PGJ(2) (15d-PGJ(2)) have been detected in joint synovial fluids from patients with rheumatoid arthritis (RA). PGE(2) directly stimulates IL-6 production in human articular chondrocytes. However, the effects of PGD(2) and 15d-PGJ(2) in the absence or presence of PGE(2) on IL-6 synthesis in human chondrocytes have yet to be determined. It is believed that dysregulated overproduction of IL-6 is responsible for the systemic inflammatory manifestations and abnormal laboratory findings in RA patients.

METHODOLOGY/PRINCIPAL FINDINGS

Using the T/C-28a2 chondrocyte cell line as a model system, we report that exogenous PGE(2) and PGD(2)/15d-PGJ(2) exert antagonistic effects on IL-6 synthesis in human T/C-28a2 chondrocytes. Using a synthesis of sophisticated molecular biology techniques, we determined that PGE(2) stimulates Toll-like receptor 4 (TLR4) synthesis, which is in turn responsible for the activation of the ERK1/2, PI3K/Akt and PKA/CREB pathways that phosphorylate the NF-κB p65 subunit leading to NF-κB activation. Binding of the activated NF-κB p65 subunit to IL-6 promoter induces IL-6 synthesis in human T/C28a2 chondrocytes. PGD(2) or 15d-PGJ(2) concurrently downregulates TLR4 and upregulates caveolin-1, which in turn inhibit the PGE(2)-dependent ERK1/2, PI3-K and PKA activation, and ultimately with NF-κB-dependent IL-6 synthesis in chondrocytes.

CONCLUSIONS/SIGNIFICANCE

We have delineated the signaling cascade by which PGE(2) and PGD(2)/15d-PGJ(2) exert opposing effects on IL-6 synthesis in human chondrocytes. Elucidation of the molecular pathway of IL-6 synthesis and secretion by chondrocytes will provide insights for developing strategies to reduce inflammation and pain in RA patients.

International Union of Basic and Clinical Pharmacology. LXXXIII: classification of prostanoid receptors, updating 15 years of progress

It is now more than 15 years since the molecular structures of the major prostanoid receptors were elucidated. Since then, substantial progress has been achieved with respect to distribution and function, signal transduction mechanisms, and the design of agonists and antagonists (http://www.iuphar-db.org/DATABASE/FamilyIntroductionForward?familyId=58). This review systematically details these advances. More recent developments in prostanoid receptor research are included. The DP(2) receptor, also termed CRTH2, has little structural resemblance to DP(1) and other receptors described in the original prostanoid receptor classification. DP(2) receptors are more closely related to chemoattractant receptors. Prostanoid receptors have also been found to heterodimerize with other prostanoid receptor subtypes and nonprostanoids. This may extend signal transduction pathways and create new ligand recognition sites: prostacyclin/thromboxane A(2) heterodimeric receptors for 8-epi-prostaglandin E(2), wild-type/alternative (alt4) heterodimers for the prostaglandin FP receptor for bimatoprost and the prostamides. It is anticipated that the 15 years of research progress described herein will lead to novel therapeutic entities.

Response of chondrocytes to shear stress: antagonistic effects of the binding partners Toll-like receptor 4 and caveolin-1

Osteoarthritis (OA) is often a consequence of excessive mechanical loading of cartilage, which produces hydrostatic stress, tensile strain, and fluid flow. Application of high fluid shear to chondrocytes recapitulates the earmarks of OA, as evidenced by the induction of cyclooxygenase-2, prostaglandins (PGs), and interleukin-6 (IL-6). Here, we delineated the signaling pathway by which high fluid shear mediates the temporal regulation of IL-6 synthesis in human chondrocytes. We determined that Toll-like receptor 4 (TLR4) and caveolin-1 are binding partners in chondrocytes. Their expression is temporally regulated by fluid shear via the sequential up-regulation of microsomal PGE synthase-1 (mPGES-1) and L-PGDS. High shear stress rapidly induces an 8-fold up-regulation of TLR4 expression via an mPGES-1-dependent pathway, whereas prolonged shear exposure concurrently down-regulates TLR4 by >4-fold and up-regulates caveolin-1 expression by > 2.5-fold in an L-PGDS-dependent manner. TLR4 and caveolin-1 exert opposing effects on the activation of ERK1/2, PI3-K and PKA signaling pathways, which, in turn, regulate the NF-κB-dependent IL-6 synthesis in a time-dependent fashion. Reconstructing the signaling network regulating shear-induced IL-6 expression in chondrocytes may provide insights for developing therapeutic strategies to combat osteoarthritis.

Methods in cardiomyocyte isolation, culture, and gene transfer

Since techniques for cardiomyocyte isolation were first developed 35 years ago, experiments on single myocytes have yielded great insight into their cellular and sub-cellular physiology. These studies have employed a broad range of techniques including electrophysiology, calcium imaging, cell mechanics, immunohistochemistry and protein biochemistry. More recently, techniques for cardiomyocyte culture have gained additional importance with the advent of gene transfer technology. While such studies require a high quality cardiomyocyte population, successful cell isolation and maintenance during culture remain challenging. In this review, we describe methods for the isolation of adult and neonatal ventricular myocytes from rat and mouse heart. This discussion outlines general principles for the beginner, but also provides detailed specific protocols and advice for common caveats. We additionally review methods for short-term myocyte culture, with particular attention given to the importance of substrate and media selection, and describe time-dependent alterations in myocyte physiology that should be anticipated. Gene transfer techniques for neonatal and adult cardiomyocytes are also reviewed, including methods for transfection (liposome, electroporation) and viral-based gene delivery.

Rap1 GTPases: an emerging role in the cardiovasculature

The Ras related GTPase Rap has been implicated in multiple cellular functions. A vital role for Rap GTPase in the cardiovasculature is emerging from recent studies. These small monomeric G proteins act as molecular switches, coupling extracellular stimulation to intracellular signaling through second messengers. This member of the Ras superfamily was once described as the transformation suppressor with the ability to ameliorate the Ras transformed phenotype; however, further studies uncovered a unique set of guanine nucleotide exchange factors (GEFs), GTPase activating proteins (GAPs) and effector proteins for Rap suggesting a more sophisticated role for this small GTPase. At least three different second messengers can activate Rap, namely cyclic AMP (cAMP), calcium and diacylglycerol. More recently, an investigation of Rap in the cardiovasculature has revealed multiple pathways of regulation involving Rap in this system. Two closely related isoforms of Rap1 exist, 1a and 1b. Murine genetic models exist for both and have been described. Although thought at first to be functionally redundant, these isoforms have differing roles in the cardiovasculature. The activation of Rap1a and 1b in various cell types of the cardiovasculature leads to alterations in cell attachment, migration and cell junction formation. This review will focus on the role of these Rap1 GTPases in hematopoietic, endothelial, smooth muscle, and cardiac myocyte function, and conclude with their potential role in human disease.

Lack of microsomal prostaglandin E synthase-1 reduces cardiac function following angiotensin II infusion

Our laboratory previously reported that inducible PGE(2) synthase, mPGES-1, contributes to micromolar production of PGE(2) in neonatal ventricular myocytes in vitro, which stimulates their growth. We therefore hypothesized that mPGES-1 contributes to cardiac hypertrophy following angiotensin II (ANG II) infusion. To test this hypothesis, we used 10- to 12-wk-old mPGES-1 knockout mice (mPGES-1 KO) and C57Bl/6 control mice infused for 8 wk with either 1.4 mg · kg(-1) · day(-1) ANG II or vehicle subcutaneously. Blood pressure [systolic blood pressure (SBP)] was measured throughout the study, and cardiac function was assessed by M-mode echocardiography at baseline and at 8 wk of infusion. At the conclusion of the study, immunohistochemistry was used to evaluate collagen fraction, myocyte cross-sectional area (MCSA), and apoptosis. At baseline, there was no difference in SBP between mPGES-1 KO mice and C57BL/6 controls. ANG II infusion increased SBP to similar levels in both strains. In control mice, infusion of ANG II increased MCSA and posterior wall thickness at diastole (PWTd) but had little effect on cardiac function, consistent with compensatory hypertrophy. In contrast, cardiac function was worse in mPGES-1 KO mice after ANG II treatment. Ejection fraction declined from 76.2 ± 2.7 to 63.3 ± 3.4% after ANG II, and left ventricular dimension at systole and diastole increased from 1.29 ± 0.02 to 1.78 ± 0.15 mm and from 2.57 ± 0.03 to 2.90 ± 0.13 mm, respectively. Infusion of ANG II increased both the LV-to-body weight and the mass-to-body weight ratios to a similar extent in both strains. However, PWTd increased by a lesser extent in KO mice, suggesting an impaired hypertrophic response. ANG II infusion increased collagen staining similarly in both strains, but TdT-dUTP nick end labeling staining was greater in mPGES-1 KO mice. Overall, these results are consistent with a beneficial effect for mPGES-1 in the maintenance of cardiac function in ANG II-dependent hypertension.

Extracellular signal-regulated kinases 1 and 2 regulate the balance between eccentric and concentric cardiac growth

RATIONALE

An increase in cardiac afterload typically produces concentric hypertrophy characterized by an increase in cardiomyocyte width, whereas volume overload or exercise results in eccentric growth characterized by cellular elongation and addition of sarcomeres in series. The signaling pathways that control eccentric versus concentric heart growth are not well understood.

OBJECTIVE

To determine the role of extracellular signal-regulated kinase 1 and 2 (ERK1/2) in regulating the cardiac hypertrophic response.

METHODS AND RESULTS

Here, we used mice lacking all ERK1/2 protein in the heart (Erk1(-/-) Erk2(fl/fl-Cre)) and mice expressing activated mitogen-activated protein kinase kinase (Mek)1 in the heart to induce ERK1/2 signaling, as well as mechanistic experiments in cultured myocytes to assess cellular growth characteristics associated with this signaling pathway. Although genetic deletion of all ERK1/2 from the mouse heart did not block the cardiac hypertrophic response per se, meaning that the heart still increased in weight with both aging and pathological stress stimulation, it did dramatically alter how the heart grew. For example, adult myocytes from hearts of Erk1(-/-) Erk2(fl/fl-Cre) mice showed preferential eccentric growth (lengthening), whereas myocytes from Mek1 transgenic hearts showed concentric growth (width increase). Isolated adult myocytes acutely inhibited for ERK1/2 signaling by adenoviral gene transfer showed spontaneous lengthening, whereas infection with an activated Mek1 adenovirus promoted constitutive ERK1/2 signaling and increased myocyte thickness. A similar effect was observed in engineered heart tissue under cyclic stretching, where ERK1/2 inhibition led to preferential lengthening.

CONCLUSIONS

Taken together, these data demonstrate that the ERK1/2 signaling pathway uniquely regulates the balance between eccentric and concentric growth of the heart.

TCDD induced pericardial edema and relative COX-2 expression in medaka (Oryzias Latipes) embryos

Exposure to dioxin and other aryl hydrocarbon receptor (AhR) ligands results in multiple, specific developmental cardiovascular phenotypes including pericardial edema and circulatory failure in small aquarium fish models. Although phenotypes are well described, mechanistic underpinnings for such toxicities remain elusive. Here we suggest that AhR activation results in stimulation of inflammation and "eicosanoid" pathways, which contribute to the observed developmental, cardiovascular phenotypes. We demonstrate that medaka embryos exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) (0.05-1 ppb) during early development result in a dose-related increase in the prevalence of pericardial edema and that this phenotype correlates with an increase in cyclooxygenase-2 (COX-2) gene expression. Those individuals exhibiting the edema phenotype had significantly greater COX-2 mRNA than their nonedematous cohort. Selective pharmacological inhibition of COX-2, with NS-398, and genetic knock down of COX-2 with a translation initiation morpholino significantly attenuated prevalence and severity of edema phenotype. Subsequently, exposures of medaka embryos to arachidonic acid (AA) resulted in recapitulation of the pericardial edema phenotype and significantly increased COX-2 expression only in those individuals exhibiting the edema phenotype compared with their nonedematous cohort. AA exposure does not result in significant induction of cytochrome P450 1A expression, suggesting that pericardial edema can be induced independent of AhR/aryl hydrocarbon receptor nuclear translocator/dioxin response element interactions. Results from this study demonstrate that developmental exposure to TCDD results in an induction of inflammatory mediators including COX-2, which contribute to the onset, and progression of heart dysmorphogenesis in the medaka model.

Tafazzin knockdown causes hypertrophy of neonatal ventricular myocytes

Mutation of the mitochondrial protein tafazzin causes dilated cardiomyopathy in Barth syndrome. We employed an adenovirus as a vector to transfer tafazzin small hairpin RNA (shRNA) into neonatal ventricular myocytes (NVMs) to investigate the effects of tafazzin knockdown. The tafazzin shRNA adenovirus consistently knocked down tafazzin mRNA and lowered cardiolipin while significantly decreasing the production of ATP by the mitochondria. The phosphorylation of AMP-activated protein kinase and mitochondrial density were both increased in tafazzin knockdown NVMs compared with scrambled shRNA controls. When we tested whether tafazzin knockdown causes hypertrophy in vitro, we found that the surface area of NVMs infected with tafazzin shRNA adenovirus was significantly increased, as were the protein synthesis and expression of the hypertrophic marker gene, brain natriuretic peptide. Taken together, our data support the concept that a decreased tafazzin expression causes cardiomyocyte hypertrophy in vitro.