Cdc42 is an antihypertrophic molecular switch in the mouse heart

Unveiling MiRNA-124 as a biomarker in hypertrophic cardiomyopathy: An innovative approach using machine learning and intelligent data analysis

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is a widespread hereditary cardiac pathology characterized by thickened heart walls and rearrangement of cardiomyocytes. Despite extensive research, the mechanisms underlying HCM development remain poorly understood, impeding the development of effective therapeutic and diagnostic strategies. Recent studies have suggested a polygenic nature of HCM development alongside monogenic forms. Transcriptomic profiling is a valuable tool for investigating such diseases. In this study, we propose a novel approach to study regulatory microRNAs (miRNAs) in the context of HCM, utilizing state-of-the-art data analysis tools.

METHODS AND RESULTS

Our method involves applying the Monte Carlo simulation and machine learning algorithm to transcriptomic data to generate high-capacity classifiers for HCM. From these classifiers, we extract key genes crucial for their performance, resulting in the identification of 16 key genes. Subsequently, we narrow down the pool of miRNAs by selecting those that may target the greatest number of key genes within the best models. We particularly focused on miR-124-3p, which we validated to have an association with HCM on an independent dataset. Subsequent investigation of its function revealed involvement of miR-124-3p in the RhoA signaling pathway.

CONCLUSIONS

In this study we propose a new approach to analyze transcriptomic data to search for microRNAs associated with a disease. Using this approach for transcriptomic profiling data of patients with HCM, we identified miR-124-3p as a potential regulator of the RhoA signaling pathway in the pathogenesis of HCM.

Systemic aging fuels heart failure: Molecular mechanisms and therapeutic avenues

Systemic aging influences various physiological processes and contributes to structural and functional decline in cardiac tissue. These alterations include an increased incidence of left ventricular hypertrophy, a decline in left ventricular diastolic function, left atrial dilation, atrial fibrillation, myocardial fibrosis and cardiac amyloidosis, elevating susceptibility to chronic heart failure (HF) in the elderly. Age-related cardiac dysfunction stems from prolonged exposure to genomic, epigenetic, oxidative, autophagic, inflammatory and regenerative stresses, along with the accumulation of senescent cells. Concurrently, age-related structural and functional changes in the vascular system, attributed to endothelial dysfunction, arterial stiffness, impaired angiogenesis, oxidative stress and inflammation, impose additional strain on the heart. Dysregulated mechanosignalling and impaired nitric oxide signalling play critical roles in the age-related vascular dysfunction associated with HF. Metabolic aging drives intricate shifts in glucose and lipid metabolism, leading to insulin resistance, mitochondrial dysfunction and lipid accumulation within cardiomyocytes. These alterations contribute to cardiac hypertrophy, fibrosis and impaired contractility, ultimately propelling HF. Systemic low-grade chronic inflammation, in conjunction with the senescence-associated secretory phenotype, aggravates cardiac dysfunction with age by promoting immune cell infiltration into the myocardium, fostering HF. This is further exacerbated by age-related comorbidities like coronary artery disease (CAD), atherosclerosis, hypertension, obesity, diabetes and chronic kidney disease (CKD). CAD and atherosclerosis induce myocardial ischaemia and adverse remodelling, while hypertension contributes to cardiac hypertrophy and fibrosis. Obesity-associated insulin resistance, inflammation and dyslipidaemia create a profibrotic cardiac environment, whereas diabetes-related metabolic disturbances further impair cardiac function. CKD-related fluid overload, electrolyte imbalances and uraemic toxins exacerbate HF through systemic inflammation and neurohormonal renin-angiotensin-aldosterone system (RAAS) activation. Recognizing aging as a modifiable process has opened avenues to target systemic aging in HF through both lifestyle interventions and therapeutics. Exercise, known for its antioxidant effects, can partly reverse pathological cardiac remodelling in the elderly by countering processes linked to age-related chronic HF, such as mitochondrial dysfunction, inflammation, senescence and declining cardiomyocyte regeneration. Dietary interventions such as plant-based and ketogenic diets, caloric restriction and macronutrient supplementation are instrumental in maintaining energy balance, reducing adiposity and addressing micronutrient and macronutrient imbalances associated with age-related HF. Therapeutic advancements targeting systemic aging in HF are underway. Key approaches include senomorphics and senolytics to limit senescence, antioxidants targeting mitochondrial stress, anti-inflammatory drugs like interleukin (IL)-1β inhibitors, metabolic rejuvenators such as nicotinamide riboside, resveratrol and sirtuin (SIRT) activators and autophagy enhancers like metformin and sodium-glucose cotransporter 2 (SGLT2) inhibitors, all of which offer potential for preserving cardiac function and alleviating the age-related HF burden.

Estrogen inhibits TGF‑β1‑stimulated cardiac fibroblast differentiation and collagen synthesis by promoting Cdc42

17β‑estradiol (E2) can inhibit cardiac fibrosis in female patients with heart failure (HF) and activate cell division cycle 42 (Cdc42), however it is unknown whether 17β‑estradiol (E2) can ameliorate differentiation and collagen synthesis in TGF‑β1‑stimulated mouse cardiac fibroblasts (MCFs) by regulating cell division cycle 42 (Cdc42). The present study aimed to investigate the roles of estrogen and Cdc42 in preventing myocardial fibrosis and the underlying molecular mechanisms. An ELISA was used to measure the levels of E2 and Cdc42 in the serum of patients with heart failure (HF), and western blotting was used to measure the expression levels of Cdc42 in TGF‑β1‑stimulated immortalized MCFs. MCFs were transfected with a Cdc42 overexpression (OE) lentivirus or small interfering RNA (siRNA), or treated with a Cdc42 inhibitor (MLS‑573151), and the function of Cdc42 was assessed by western blotting, immunofluorescence staining, reverse transcription‑quantitative PCR and dual‑luciferase reporter assays. Western blotting and immunofluorescence staining were performed to verify the protective effect of E2 on TGF‑β1‑stimulated MCFs, and the association between the protective effect and Cdc42. The results demonstrated that Cdc42 levels were increased in the serum of patients with HF and were positively correlated with the levels of E2; however, Cdc42 levels were decreased in TGF‑β1‑stimulated MCFs. Cdc42 inhibited MCF differentiation and collagen synthesis, as indicated by the protein expression of α‑smooth muscle actin, collagen I and collagen III. Mechanistically, Cdc42 inhibited the transcription of TGF‑β1 by promoting the expression of p21 (RAC1)‑activated kinase 1 (Pak1)/JNK/c‑Jun signaling pathway proteins and inhibiting the activity of the Tgfb1 gene promoter. In addition, E2 inhibited the differentiation and collagen synthesis of TGF‑β1‑stimulated MCFs, and promoted the protein expression of Pak1, JNK and c‑Jun, consistent with the effects of Cdc42, whereas the effects of E2 were abolished when Cdc42 was knocked down. The aforementioned findings suggested that E2 could inhibit differentiation and collagen synthesis in TGF‑β1‑stimulated MCFs by regulating Cdc42 and the downstream Pak1/JNK/c‑Jun signaling pathway.

Palmitoylation-dependent regulation of cardiomyocyte Rac1 signaling activity and minor effects on cardiac hypertrophy

S-palmitoylation is a reversible lipid modification catalyzed by 23 S-acyltransferases with a conserved zinc finger aspartate-histidine-histidine-cysteine (zDHHC) domain that facilitates targeting of proteins to specific intracellular membranes. Here we performed a gain-of-function screen in the mouse and identified the Golgi-localized enzymes zDHHC3 and zDHHC7 as regulators of cardiac hypertrophy. Cardiomyocyte-specific transgenic mice overexpressing zDHHC3 show cardiac disease, and S-acyl proteomics identified the small GTPase Rac1 as a novel substrate of zDHHC3. Notably, cardiomyopathy and congestive heart failure in zDHHC3 transgenic mice is preceded by enhanced Rac1 S-palmitoylation, membrane localization, activity, downstream hypertrophic signaling, and concomitant induction of all Rho family small GTPases whereas mice overexpressing an enzymatically dead zDHHC3 mutant show no discernible effect. However, loss of Rac1 or other identified zDHHC3 targets Gαq/11 or galectin-1 does not diminish zDHHC3-induced cardiomyopathy, suggesting multiple effectors and pathways promoting decompensation with sustained zDHHC3 activity. Genetic deletion of Zdhhc3 in combination with Zdhhc7 reduces cardiac hypertrophy during the early response to pressure overload stimulation but not over longer time periods. Indeed, cardiac hypertrophy in response to 2 weeks of angiotensin-II infusion is not diminished by Zdhhc3/7 deletion, again suggesting other S-acyltransferases or signaling mechanisms compensate to promote hypertrophic signaling. Taken together, these data indicate that the activity of zDHHC3 and zDHHC7 at the cardiomyocyte Golgi promote Rac1 signaling and maladaptive cardiac remodeling, but redundant signaling effectors compensate to maintain cardiac hypertrophy with sustained pathological stimulation in the absence of zDHHC3/7.

Mixed lineage kinase 3 requires a functional CRIB domain for regulation of blood pressure, cardiac hypertrophy, and left ventricular function

Mixed lineage kinase 3 (MLK3) modulates blood pressure and left ventricular function, but the mechanisms governing these effects remain unclear. In the current study, we therefore investigated the role of the MLK3 Cdc42/Rac interactive binding (CRIB) domain in cardiovascular physiology. We examined baseline and left ventricular pressure overload responses in a MLK3 CRIB mutant (MLK3C/C) mouse, which harbors point mutations in the CRIB domain to disrupt MLK3 activation by Cdc42. Male and female MLK3C/C mice displayed increased invasively measured blood pressure compared with wild-type (MLK3+/+) littermate controls. MLK3C/C mice of both sexes also developed left and right ventricular hypertrophy but normal baseline LV function by echocardiography and invasive hemodynamics. In LV tissue from MLK3C/C mice, map3k11 mRNA, which encodes MLK3, and MLK3 protein were reduced by 74 ± 6% and 73 ± 7%, respectively. After 1-wk LV pressure overload with 25-gauge transaortic constriction (TAC), male MLK3C/C mice developed no differences in LV hypertrophy but displayed reduction in the LV systolic indices ejection fraction and dP/dt normalized to instantaneous pressure. JNK activation was also reduced in LV tissue of MLK3C/C TAC mice. TAC induced MLK3 translocation from cytosolic fraction to membrane fraction in LV tissue from MLK3+/+ but not MLK3C/C mice. These findings identify a role of the MLK3 CRIB domain in MLK3 regulation of basal blood pressure and cardiac morphology, and in promoting the compensatory LV response to pressure overload.NEW & NOTEWORTHY Here, we identified that the presence of two discrete point mutations within the Cdc42/Rac interaction and binding domain of the protein MLK3 recapitulates the effects of whole body MLK3 deletion on blood pressure, cardiac hypertrophy, and left ventricular compensation after pressure overload. These findings implicate the CRIB domain, and thus MLK3 activation by this domain, as critical for maintenance of cardiovascular homeostasis.

Dock10 Regulates Cardiac Function under Neurohormonal Stress

Dedicator of cytokinesis 10 (Dock10) is a guanine nucleotide exchange factor for Cdc42 and Rac1 that regulates the JNK (c-Jun N-terminal kinase) and p38 MAPK (mitogen-activated protein kinase) signaling cascades. In this study, we characterized the roles of Dock10 in the myocardium. In vitro: we ablated Dock10 in neonatal mouse floxed Dock10 cardiomyocytes (NMCMs) and cardiofibroblasts (NMCFs) by transduction with an adenovirus expressing Cre-recombinase. In vivo, we studied mice in which the Dock10 gene was constitutively and globally deleted (Dock10 KO) and mice with cardiac myocyte-specific Dock10 KO (Dock10 CKO) at baseline and in response to two weeks of Angiotensin II (Ang II) infusion. In vitro, Dock10 ablation differentially inhibited the α-adrenergic stimulation of p38 and JNK in NMCM and NMCF, respectively. In vivo, the stimulation of both signaling pathways was markedly attenuated in the heart. The Dock10 KO mice had normal body weight and cardiac size. However, echocardiography revealed mildly reduced systolic function, and IonOptix recordings demonstrated reduced contractility and elevated diastolic calcium levels in isolated cardiomyocytes. Remarkably, Dock10 KO, but not Dock10 CKO, exaggerated the pathological response to Ang II infusion. These data suggest that Dock10 regulates cardiac stress-related signaling. Although Dock10 can regulate MAPK signaling in both cardiomyocytes and cardiofibroblasts, the inhibition of pathological cardiac remodeling is not apparently due to the Dock10 signaling in the cardiomyocyte.

Exercise-induced signaling pathways to counteracting cardiac apoptotic processes

Cardiovascular diseases are the most common cause of death in the world. One of the major causes of cardiac death is excessive apoptosis. However, multiple pathways through moderate exercise can reduce myocardial apoptosis. After moderate exercise, the expression of anti-apoptotic proteins such as IGF-1, IGF-1R, p-PI3K, p-Akt, ERK-1/2, SIRT3, PGC-1α, and Bcl-2 increases in the heart. While apoptotic proteins such as PTEN, PHLPP-1, GSK-3, JNK, P38MAPK, and FOXO are reduced in the heart. Exercise-induced mechanical stress activates the β and α5 integrins and subsequently, focal adhesion kinase phosphorylation activates the Akt/mTORC1 and ERK-1/2 pathways, leading to an anti-apoptotic response. One of the reasons for the decrease in exercise-induced apoptosis is the decrease in Fas-ligand protein, Fas-death receptor, TNF-α receptor, Fas-associated death domain (FADD), caspase-8, and caspase-3. In addition, after exercise mitochondrial-dependent apoptotic factors such as Bid, t-Bid, Bad, p-Bad, Bak, cytochrome c, and caspase-9 are reduced. These changes lead to a reduction in oxidative damage, a reduction in infarct size, a reduction in cardiac apoptosis, and an increase in myocardial function. After exercising in the heart, the levels of RhoA, ROCK1, Rac1, and ROCK2 decrease, while the levels of PKCε, PKCδ, and PKCɑ are activated to regulate calcium and prevent mPTP perforation. Exercise has an anti-apoptotic effect on heart failure by increasing the PKA-Akt-eNOS and FSTL1-USP10-Notch1 pathways, reducing the negative effects of CaMKIIδ, and increasing the calcineurin/NFAT pathway. Exercise plays a protective role in the heart by increasing HSP20, HSP27, HSP40, HSP70, HSP72, and HSP90 along with increasing JAK2 and STAT3 phosphorylation. However, research on exercise and factors such as Pim-1, Notch, and FAK in cardiac apoptosis is scarce, so further research is needed. Future research is recommended to discover more anti-apoptotic pathways. It is also recommended to study the synergistic effect of exercise with gene therapy, dietary supplements, and cell therapy for future research.

Proteomic and Metabolomic Analyses of Right Ventricular Failure due to Pulmonary Arterial Hypertension

Right ventricular failure (RVF) is the independent and strongest predictor of mortality in pulmonary arterial hypertension (PAH), but, at present, there are no preventive and therapeutic strategies directly targeting the failing right ventricle (RV). The underlying mechanism of RV hypertrophy (RVH) and dysfunction needs to be explored in depth. In this study, we used myocardial proteomics combined with metabolomics to elucidate potential pathophysiological changes of RV remodeling in a monocrotaline (MCT)-induced PAH rat model. The proteins and metabolites extracted from the RV myocardium were identified using label-free liquid chromatography–tandem mass spectrometry (LC-MS/MS). The bioinformatic analysis indicated that elevated intracellular Ca²⁺ concentrations and inflammation may contribute to myocardial proliferation and contraction, which may be beneficial for maintaining the compensated state of the RV. In the RVF stage, ferroptosis, mitochondrial metabolic shift, and insulin resistance are significantly involved. Dysregulated iron homeostasis, glutathione metabolism, and lipid peroxidation related to ferroptosis may contribute to RV decompensation. In conclusion, we depicted a proteomic and metabolomic profile of the RV myocardium during the progression of MCT-induced PAH, and also provided the insights for potential therapeutic targets facilitating the retardation or reversal of RV dysfunction in PAH.

Calcineurin in the heart: New horizons for an old friend

Calcineurin, also known as PP2B or PPP3, is a member of the PPP family of protein phosphatases that also includes PP1 and PP2A. Together these three phosphatases carryout the majority of dephosphorylation events in the heart. Calcineurin is distinct in that it is activated by the binding of calcium/calmodulin (Ca2+/CaM) and therefore acts as a node for integrating Ca2+ signals with changes in phosphorylation, two fundamental intracellular signaling cascades. In the heart, calcineurin is primarily thought of in the context of pathological cardiac remodeling, acting through the Nuclear Factor of Activated T-cell (NFAT) family of transcription factors. However, calcineurin activity is also essential for normal heart development and homeostasis in the adult heart. Furthermore, it is clear that NFAT-driven changes in transcription are not the only relevant processes initiated by calcineurin in the setting of pathological remodeling. There is a growing appreciation for the diversity of calcineurin substrates that can impact cardiac function as well as the diversity of mechanisms for targeting calcineurin to specific sub-cellular domains in cardiomyocytes and other cardiac cell types. Here, we will review the basics of calcineurin structure, regulation, and function in the context of cardiac biology. Particular attention will be given to: the development of improved tools to identify and validate new calcineurin substrates; recent studies identifying new calcineurin isoforms with unique properties and targeting mechanisms; and the role of calcineurin in cardiac development and regeneration.

CREG ameliorates the phenotypic switching of cardiac fibroblasts after myocardial infarction via modulation of CDC42

Phenotype switching of cardiac fibroblasts into myofibroblasts plays important role in cardiac fibrosis following myocardial infarction (MI). Cellular repressor of E1A-stimulated genes (CREG) protects against vascular and cardiac remodeling induced by angiotensin-II. However, the effects and mechanisms of CREG on phenotype switching of cardiac fibroblasts after MI are unknown. This study aimed to investigate the role of CREG on the phenotype switching of cardiac fibroblasts following MI and its mechanism. Our findings demonstrated that, compared with littermate control mice, cardiac function was deteriorated in CREG+/- mice on day 14 post-MI. Fibrosis size, αSMA, and collagen-1 expressions were increased in the border regions of CREG+/- mice on day 14 post-MI. Conversely, exogenous CREG protein significantly improved cardiac function, inhibited fibrosis, and reduced the expressions of αSMA and collagen-1 in the border regions of C57BL/6J mice on day 14. In vitro, CREG recombinant protein inhibited αSMA and collagen-1 expression and blocked the hypoxia-induced proliferation and migration of cardiac fibroblasts, which was mediated through the inhibition of cell division control protein 42 (CDC42) expression. Our findings could help in establishing new strategies based on the clarification of the role of the key molecule CREG in phenotype switching of cardiac fibroblasts following MI.

Deletion of P21-activated kinase-1 induces age-dependent increased visceral adiposity and cardiac dysfunction in female mice

It is known that there is an age-related progression in diastolic dysfunction, especially prevalent in postmenopausal women, who develop heart failure with preserved ejection fraction (HFpEF, EF > 50%). Mechanisms and therapies are poorly understood, but there are strong correlations between obesity and HFpEF. We have tested the hypothesis that P21-activated kinase-1 (PAK1) preserves cardiac function and adipose tissue homeostasis during aging in female mice. Previous demonstrations in male mice by our lab that PAK1 activity confers cardio-protection against different stresses formed the rationale for this hypothesis. Our studies compared young (3-6 months) and middle-aged (12-15 months) female and male PAK1 knock-out mice (PAK1-/-) and wild-type (WT) equivalent. Female WT mice exhibited increased cardiac PAK1 abundance during aging. By echocardiography, compared to young WT female mice, middle-aged WT female mice showed enlargement of the left atrium as well as thickening of posterior wall and increased left ventricular mass; however, all contraction and relaxation parameters were preserved during aging. Compared to WT controls, middle-aged PAK1-/- female mice demonstrated worsening of cardiac function involving a greater enlargement of the left atrium, ventricular hypertrophy, and diastolic dysfunction. Moreover, with aging PAK1-/- female mice, unlike male PAK1-/- mice, exhibited increased adiposity with increased accumulation of visceral adipose tissue. Our data provide evidence for the significance of PAK1 signaling as an element in the preservation of cardiac function and adipose tissue homeostasis in females during aging.

cGMP Signaling and Modulation in Heart Failure

Cyclic GMP (cGMP) represents a classic intracellular second messenger molecule. Over the past 2 decades, important discoveries have identified that cGMP signaling becomes deranged in heart failure (HF) and that cGMP and its main kinase effector, protein kinase G, generally oppose the biological abnormalities contributing to HF, in experimental studies. These findings have influenced the design of clinical trials of cGMP-augmenting drugs in HF patients. At present, the trial results of cGMP-augmenting therapies in HF remain mixed. As detailed in this review, strong evidence now exists that protein kinase G opposes pathologic cardiac remodeling through regulation of diverse biological processes and myocardial substrates. Potential reasons for the failures of cGMP-augmenting drugs in HF may be related to biological mechanisms opposing cGMP or because of certain features of clinical trials, all of which are discussed.

JNK and cardiometabolic dysfunction

Cardiometabolic syndrome (CMS) describes the cluster of metabolic and cardiovascular diseases that are generally characterized by impaired glucose tolerance, intra-abdominal adiposity, dyslipidemia, and hypertension. CMS currently affects more than 25% of the world’s population and the rates of diseases are rapidly rising. These CMS conditions represent critical risk factors for cardiovascular diseases including atherosclerosis, heart failure, myocardial infarction, and peripheral artery disease (PAD). Therefore, it is imperative to elucidate the underlying signaling involved in disease onset and progression. The c-Jun N-terminal Kinases (JNKs) are a family of stress signaling kinases that have been recently indicated in CMS. The purpose of this review is to examine the in vivo implications of JNK as a potential therapeutic target for CMS. As the constellation of diseases associated with CMS are complex and involve multiple tissues and environmental triggers, carefully examining what is known about the JNK pathway will be important for specificity in treatment strategies.

Mitoquinone ameliorates pressure overload-induced cardiac fibrosis and left ventricular dysfunction in mice

Increasing evidence indicates that mitochondrial-associated redox signaling contributes to the pathophysiology of heart failure (HF). The mitochondrial-targeted antioxidant, mitoquinone (MitoQ), is capable of modifying mitochondrial signaling and has shown beneficial effects on HF-dependent mitochondrial dysfunction. However, the potential therapeutic impact of MitoQ-based mitochondrial therapies for HF in response to pressure overload is reliant upon demonstration of improved cardiac contractile function and suppression of deleterious cardiac remodeling. Using a new (patho)physiologically relevant model of pressure overload-induced HF we tested the hypothesis that MitoQ is capable of ameliorating cardiac contractile dysfunction and suppressing fibrosis. To test this C57BL/6J mice were subjected to left ventricular (LV) pressure overload by ascending aortic constriction (AAC) followed by MitoQ treatment (2 µmol) for 7 consecutive days. Doppler echocardiography showed that AAC caused severe LV dysfunction and hypertrophic remodeling. MitoQ attenuated pressure overload-induced apoptosis, hypertrophic remodeling, fibrosis and LV dysfunction. Profibrogenic transforming growth factor-β1 (TGF-β1) and NADPH oxidase 4 (NOX4, a major modulator of fibrosis related redox signaling) expression increased markedly after AAC. MitoQ blunted TGF-β1 and NOX4 upregulation and the downstream ACC-dependent fibrotic gene expressions. In addition, MitoQ prevented Nrf2 downregulation and activation of TGF-β1-mediated profibrogenic signaling in cardiac fibroblasts (CF). Finally, MitoQ ameliorated the dysregulation of cardiac remodeling-associated long noncoding RNAs (lncRNAs) in AAC myocardium, phenylephrine-treated cardiomyocytes, and TGF-β1-treated CF. The present study demonstrates for the first time that MitoQ improves cardiac hypertrophic remodeling, fibrosis, LV dysfunction and dysregulation of lncRNAs in pressure overload hearts, by inhibiting the interplay between TGF-β1 and mitochondrial associated redox signaling.

Mixed lineage kinase-3 prevents cardiac dysfunction and structural remodeling with pressure overload

Myocardial hypertrophy is an independent risk factor for heart failure (HF), yet the mechanisms underlying pathological cardiomyocyte growth are incompletely understood. The c-Jun NH2-terminal kinase (JNK) signaling cascade modulates cardiac hypertrophic remodeling, but the upstream factors regulating myocardial JNK activity remain unclear. In this study, we sought to identify JNK-activating molecules as novel regulators of cardiac remodeling in HF. We investigated mixed lineage kinase-3 (MLK3), a master regulator of upstream JNK-activating kinases, whose role in the remodeling process had not previously been studied. We observed increased MLK3 protein expression in myocardium from patients with nonischemic and hypertrophic cardiomyopathy and in hearts of mice subjected to transverse aortic constriction (TAC). Mice with genetic deletion of MLK3 (MLK3-/-) exhibited baseline cardiac hypertrophy with preserved cardiac function. MLK3-/- mice subjected to chronic left ventricular (LV) pressure overload (TAC, 4 wk) developed worsened cardiac dysfunction and increased LV chamber size compared with MLK3+/+ littermates ( n = 8). LV mass, pathological markers of hypertrophy ( Nppa, Nppb), and cardiomyocyte size were elevated in MLK3-/- TAC hearts. Phosphorylation of JNK, but not other MAPK pathways, was selectively impaired in MLK3-/- TAC hearts. In adult rat cardiomyocytes, pharmacological MLK3 kinase inhibition using URMC-099 blocked JNK phosphorylation induced by neurohormonal agents and oxidants. Sustained URMC-099 exposure induced cardiomyocyte hypertrophy. These data demonstrate that MLK3 prevents adverse cardiac remodeling in the setting of pressure overload. Mechanistically, MLK3 activates JNK, which in turn opposes cardiomyocyte hypertrophy. These results support modulation of MLK3 as a potential therapeutic approach in HF. NEW & NOTEWORTHY Here, we identified a role for mixed lineage kinase-3 (MLK3) as a novel antihypertrophic and antiremodeling molecule in response to cardiac pressure overload. MLK3 regulates phosphorylation of the stress-responsive JNK kinase in response to pressure overload and in cultured cardiomyocytes stimulated with hypertrophic agonists and oxidants. This study reveals MLK3-JNK signaling as a novel cardioprotective signaling axis in the setting of pressure overload.

CDC42 is required for epicardial and pro-epicardial development by mediating FGF receptor trafficking to the plasma membrane

The epicardium contributes to multiple cardiac lineages and is essential for cardiac development and regeneration. However, the mechanism of epicardium formation is unclear. This study aimed to establish the cellular and molecular mechanisms underlying the dissociation of pro-epicardial cells (PECs) from the pro-epicardium (PE) and their subsequent translocation to the heart to form the epicardium. We used lineage tracing, conditional deletion, mosaic analysis and ligand stimulation in mice to determine that both villous protrusions and floating cysts contribute to PEC translocation to myocardium in a CDC42-dependent manner. We resolved a controversy by demonstrating that physical contact of the PE with the myocardium constitutes a third mechanism for PEC translocation to myocardium, and observed a fourth mechanism in which PECs migrate along the surface of the inflow tract to reach the ventricles. Epicardial-specific Cdc42 deletion disrupted epicardium formation, and Cdc42 null PECs proliferated less, lost polarity and failed to form villous protrusions and floating cysts. FGF signaling promotes epicardium formation in vivo, and biochemical studies demonstrated that CDC42 is involved in the trafficking of FGF receptors to the cell membrane to regulate epicardium formation.

Highlighted article: During epicardial formation in mice, four different mechanisms of pro-epicardial cell translocation to the myocardium can be identified, with CDC42 playing a key role.

Conserved signaling mechanisms in Drosophila heart development

Signal transduction through multiple distinct pathways regulates and orchestrates the numerous biological processes comprising heart development. This review outlines the roles of the FGFR, EGFR, Wnt, BMP, Notch, Hedgehog, Slit/Robo, and other signaling pathways during four sequential phases of Drosophila cardiogenesis-mesoderm migration, cardiac mesoderm establishment, differentiation of the cardiac mesoderm into distinct cardiac cell types, and morphogenesis of the heart and its lumen based on the proper positioning and cell shape changes of these differentiated cardiac cells-and illustrates how these same cardiogenic roles are conserved in vertebrates. Mechanisms bringing about the regulation and combinatorial integration of these diverse signaling pathways in Drosophila are also described. This synopsis of our present state of knowledge of conserved signaling pathways in Drosophila cardiogenesis and the means by which it was acquired should facilitate our understanding of and investigations into related processes in vertebrates. Developmental Dynamics 246:641-656, 2017. © 2017 Wiley Periodicals, Inc.

The p21-activated kinase 1 (Pak1) signalling pathway in cardiac disease: from mechanistic study to therapeutic exploration

p21-activated kinase 1 (Pak1) is a member of the highly conserved family of serine/threonine protein kinases regulated by Ras-related small G-proteins, Cdc42/Rac1. It has been previously demonstrated to be involved in cardiac protection. Based on recent studies, this review provides an overview of the role of Pak1 in cardiac diseases including disrupted Ca²⁺ homoeostasis-related cardiac arrhythmias, adrenergic stress- and pressure overload-induced hypertrophy, and ischaemia/reperfusion injury. These findings demonstrate the important role of Pak1 mediated through the phosphorylation and transcriptional modification of hypertrophy and/or arrhythmia-related genes. This review also discusses the anti-arrhythmic and anti-hypertrophic, protective function of Pak1 and the beneficial effects of fingolimod (an FDA-approved sphingolipid drug), a Pak1 activator, and its ability to prevent arrhythmias and cardiac hypertrophy. These findings also highlight the therapeutic potential of Pak1 signalling in the treatment and prevention of cardiac diseases.

LINKED ARTICLES

This article is part of a themed section on Spotlight on Small Molecules in Cardiovascular Diseases. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.8/issuetoc.

Cdc42 Promotes Schwann Cell Proliferation and Migration Through Wnt/β-Catenin and p38 MAPK Signaling Pathway After Sciatic Nerve Injury

Schwann cells (SCs) are unique glial cells in the peripheral nerve and may secrete multiple neurotrophic factors, adhesion molecules, extracellular matrix molecules to form the microenvironment of peripheral nerve regeneration, guiding and supporting nerve proliferation and migration. Cdc42 plays an important regulatory role in dynamic changes of the cytoskeleton. However, there is a little study referred to regulation and mechanism of Cdc42 on glial cells after peripheral nerve injury. The present study investigated the role of Cdc42 in the proliferation and migration of SCs after sciatic nerve injury. Cdc42 expression was tested, showing that the mRNA and protein expression levels of Cdc42 were significantly up-regulated after sciatic nerve injury. Then, we isolated and purified SCs from injuried sciatic nerve at day 7. The purified SCs were transfected with Cdc42 siRNA and pcDNA3.1-Cdc42, and the cell proliferation, cell cycle and migration were assessed. The results implied that Cdc42 siRNA remarkably inhibited Schwann cell proliferation and migration, and resulted in S phase arrest. While pcDNA3.1-Cdc42 showed a contrary effect. Besides, we also observed that Cdc42 siRNA down-regulated the protein expression of β-catenin, Cyclin D1, c-myc and p-p38, which were up-regulated by pcDNA3.1-Cdc42. Meanwhile, the inhibitor of Wnt/β-catenin and p38 MAPK signaling pathway IWP-2 and SB203580 significantly inhibited the effect of pcDNA3.1-Cdc42 on cell proliferation and migration. Overall, our data indicate that Cdc42 regulates Schwann cell proliferation and migration through Wnt/β-catenin and p38 MAPK signaling pathway after sciatic nerve injury, which provides further insights into the therapy of the sciatic nerve injury.

Signaling Pathways in Cardiac Myocyte Apoptosis

Cardiovascular diseases, the number 1 cause of death worldwide, are frequently associated with apoptotic death of cardiac myocytes. Since cardiomyocyte apoptosis is a highly regulated process, pharmacological intervention of apoptosis pathways may represent a promising therapeutic strategy for a number of cardiovascular diseases and disorders including myocardial infarction, ischemia/reperfusion injury, chemotherapy cardiotoxicity, and end-stage heart failure. Despite rapid growth of our knowledge in apoptosis signaling pathways, a clinically applicable treatment targeting this cellular process is currently unavailable. To help identify potential innovative directions for future research, it is necessary to have a full understanding of the apoptotic pathways currently known to be functional in cardiac myocytes. Here, we summarize recent progress in the regulation of cardiomyocyte apoptosis by multiple signaling molecules and pathways, with a focus on the involvement of these pathways in the pathogenesis of heart disease. In addition, we provide an update regarding bench to bedside translation of this knowledge and discuss unanswered questions that need further investigation.

Essential role of Cdc42 in cardiomyocyte proliferation and cell-cell adhesion during heart development

Cdc42 is a member of the Rho GTPase family and functions as a molecular switch in regulating cell migration, proliferation, differentiation and survival. However, the role of Cdc42 in heart development remains largely unknown. To determine the function of Cdc42 in heart formation, we have generated a Cdc42 cardiomyocyte knockout (CCKO) mouse line by crossing Cdc42 flox mice with myosin light chain (MLC) 2a-Cre mice. The inactivation of Cdc42 in embryonic cardiomyocytes induced lethality after embryonic day 12.5. Histological analysis of CCKO embryos showed cardiac developmental defects that included thin ventricular walls and ventricular septum defects. Microarray and real-time PCR data also revealed that the expression level of p21 was significantly increased and cyclin B1 was dramatically decreased, suggesting that Cdc42 is required for cardiomyocyte proliferation. Phosphorylated Histone H3 staining confirmed that the inactivation of Cdc42 inhibited cardiomyocytes proliferation. In addition, transmission electron microscope studies showed disorganized sarcomere structure and disruption of cell-cell contact among cardiomyocytes in CCKO hearts. Accordingly, we found that the distribution of N-cadherin/β-Catenin in CCKO cardiomyocytes was impaired. Taken together, our data indicate that Cdc42 is essential for cardiomyocyte proliferation, sarcomere organization and cell-cell adhesion during heart development.

Histone Deacetylase Inhibitor Phenylbutyrate Exaggerates Heart Failure in Pressure Overloaded Mice independently of HDAC inhibition

4-Sodium phenylbutyrate (PBA) has been reported to inhibit endoplasmic reticulum stress and histone deacetylation (HDAC), both of which are novel therapeutic targets for cardiac hypertrophy and heart failure. However, it is unclear whether PBA can improve heart function. Here, we tested the effects of PBA and some other HDAC inhibitors on cardiac dysfunction induced by pressure overload. Transverse aortic constriction (TAC) was performed on male C57BL/6 mice. PBA treatment (100 mg/kg, 6 weeks) unexpectedly led to a higher mortality, exacerbated cardiac remodelling and dysfunction. Similar results were noted in TAC mice treated with butyrate sodium (BS), a PBA analogue. In contrast, other HDAC inhibitors, valproic acid (VAL) and trichostatin A (TSA), improved the survival. All four HDAC inhibitors induced histone H3 acetylation and inhibited HDAC total activity. An individual HDAC activity assay showed that rather than class II_a members (HDAC4 and 7), PBA and BS predominantly inhibited class I members (HDAC2 and 8), whereas VAL and TSA inhibited all of them. These findings indicate that PBA and BS accelerate cardiac hypertrophy and dysfunction, whereas VAL and TSA have opposing effects.

Association of decreased serum vasostatin-2 level with ischemic chronic heart failure and with MACE in 3-year follow-up: Vasostatin-2 prevents heart failure in myocardial infarction rats

BACKGROUND

We investigated whether serum vasostatin-2 level is related to chronic heart failure (CHF) in patients with previous myocardial infarction (MI) and MACE in 3-year follow-up. The biological effect of vasostatin-2 on ischemic HF was evaluated in animal experiments.

METHODS

After exclusion of the subjects not eligible, this study included 450 patients with CHF and previous MI, and 149 healthy controls. Serum vasostatin-2 level was analyzed. CHF patients were followed up for three years and major adverse cardiac events (MACE) were recorded, defined as reinfarction, target-vessel revascularization, cardiovascular death and refractory HF requiring hospitalizations.

RESULTS

Notably, serum vasostatin-2 level was decreased in CHF patients than in controls, and significant difference was observed between CHF patients with MACE and those without (both P<0.05). Vasostatin-2 level was correlated with HF stages (Spearman's r=-0.288, P<0.05), LVEF (r=0.377, P<0.05) and pro-BNP level (r=-0.294, P<0.05). Multivariable logistic regression analysis suggested that vasostatin-2, conventional risk factors, severity of HF stages and LVEF were independently associated with MACE in CHF patients. Vasostatin-2 (100μg) or PBS was injected intraperitoneally every other day in MI rats, follow by echocardiography, hemodynamic analysis after 2months. Compared with PBS, vasostatin-2 treatment prevented ischemic HF in MI rats, accompanied with reduction of infarct size, remodeling, fibrosis and inflammation, mainly through inhibition of Rho, Wnt and TLR-4 pathways and modulation of renin-angiotensin system.

CONCLUSION

Decreased serum vasostatin-2 level is associated with ischemic CHF and with MACE in three-year follow-up. Intraperitoneal injection of vasostatin-2 protects against ischemic HF in MI rats.

Genome-Wide Polyadenylation Maps Reveal Dynamic mRNA 3′-End Formation in the Failing Human Heart

Rationale:

Alternative cleavage and polyadenylation (APA) of mRNA represents a layer of gene regulation that to date has remained unexplored in the heart. This phenomenon may be relevant, as the positioning of the poly(A) tail in mRNAs influences the length of the 3′-untranslated region (UTR), a critical determinant of gene expression.

Objective:

To investigate whether the 3′UTR length is regulated by APA in the human heart and whether this changes in the failing heart.

Methods and Results:

We used 3′end RNA sequencing (e3′-Seq) to directly measure global patterns of APA in healthy and failing human heart specimens. By monitoring polyadenylation profiles in these hearts, we identified disease-specific APA signatures in numerous genes. Interestingly, many of the genes with shortened 3′UTRs in heart failure were enriched for functional groups such as RNA binding, whereas genes with longer 3′UTRs were enriched for cytoskeletal organization and actin binding. RNA sequencing in a larger series of human hearts revealed that these APA candidates are often differentially expressed in failing hearts, with an inverse correlation between 3′UTR length and the level of gene expression. Protein levels of the APA regulator, poly(A)-binding protein nuclear-1 were substantially downregulated in failing hearts.

Conclusions:

We provide genome-wide, high-resolution polyadenylation maps of the human heart and show that the 3′end formation of mRNA is dynamic in heart failure, suggesting that APA-mediated 3′UTR length modulation represents an additional layer of gene regulation in failing hearts.

miR-30c Mediates Upregulation of Cdc42 and Pak1 in Diabetic Cardiomyopathy

AIM

Cardiac hypertrophy and myocardial fibrosis significantly contribute to the pathogenesis of diabetic cardiomyopathy (DCM). Altered expression of several genes and their regulation by microRNAs has been reported in hypertrophied failing hearts. This study aims to examine the role of Cdc42, Pak1, and miR-30c in the pathogenesis of cardiac hypertrophy in DCM.

METHODS

DCM was induced in Wistar rats by low-dose streptozotocin-high-fat diet for 12 weeks. Cardiac expression of Cdc42, Pak1 and miR-30c, and hypertrophy markers (ANP and β-MHC) was studied in DCM vs control rats and in high-glucose (HG)-treated H9c2 cardiomyocytes.

RESULTS

Diabetic rats showed cardiomyocyte hypertrophy, increased heart-to-body weight ratio, and an increased expression of ANP and β-MHC. Cardiac expression of Cdc42 and Pak1 genes was increased in diabetic hearts and in HG-treated cardiomyocytes. miR-30c was identified to target Cdc42 and Pak1 genes, and cardiac miR-30c expression was found to be decreased in DCM rats, patients with DCM, and in HG-treated cardiomyocytes. miR-30c overexpression decreased Cdc42 and Pak1 genes and attenuated HG-induced cardiomyocyte hypertrophy, whereas miR-30c inhibition increased Cdc42 and Pak1 gene expression and myocyte hypertrophy in HG-treated cardiomyocytes.

CONCLUSION

Downregulation of miR-30c mediates prohypertrophic effects of hyperglycemia in DCM by upregulation of Cdc42 and Pak1 genes.

MicroRNA-137 Negatively Regulates H₂O₂-Induced Cardiomyocyte Apoptosis Through CDC42

BACKGROUND

Oxidative stress, inducing cardiomyocyte apoptosis or myocardial ischemia, is the major denominator of many cardiac diseases. In this study, we intended to explore the regulatory function of microRNA-137 (miR-137) in oxidative stress-induced cardiomyocyte apoptosis.

MATERIAL AND METHODS

Cardiomyocytes were extracted from newborn C57BL/6 mice and cultured in vitro. Apoptosis was induced by H2O2, and evaluated by TUNEL assay. The effect of cardiomyocyte apoptosis on gene expression of miR-137 was evaluated by qRT-PCR. Lentivirus was used to stably down-regulate miR-137, and the subsequent effects of miR-137 down-regulation on cardiomyocyte apoptosis, its targeted gene CDC42, and caspase pathway were evaluated by TUNEL assay, dual-luciferase reporter assay, and Western blot assay, respectively. Finally, CDC42 was down-regulated by siRNA and its effect on miR-137-mediated cardiomyocyte apoptosis protection was examined.

RESULTS

H2O2 induced significant apoptosis and up-regulated miR-137 in cardiomyocytes, whereas lentivirus-mediated miR-137 down-regulation protected against apoptosis. CDC42 was the direct target gene of miR-137 and proteins of CDC42, caspase-3, and caspase-9 were all regulated by miR-137 down-regulation in cardiomyocyte apoptosis. SiRNA-mediated CDC42 down-regulation reversed the protection of miR-137 down-regulation against cardiomyocyte apoptosis.

CONCLUSIONS

Our work demonstrated miR-137 and CDC42 are critical regulators in cardiomyocyte apoptosis. It may help to identify the molecular targets to prevent myocardial injury in human patients.

Cellular Mechanisms of Drosophila Heart Morphogenesis

Many of the major discoveries in the fields of genetics and developmental biology have been made using the fruit fly, Drosophila melanogaster. With regard to heart development, the conserved network of core cardiac transcription factors that underlies cardiogenesis has been studied in great detail in the fly, and the importance of several signaling pathways that regulate heart morphogenesis, such as Slit/Robo, was first shown in the fly model. Recent technological advances have led to a large increase in the genomic data available from patients with congenital heart disease (CHD). This has highlighted a number of candidate genes and gene networks that are potentially involved in CHD. To validate genes and genetic interactions among candidate CHD-causing alleles and to better understand heart formation in general are major tasks. The specific limitations of the various cardiac model systems currently employed (mammalian and fish models) provide a niche for the fly model, despite its evolutionary distance to vertebrates and humans. Here, we review recent advances made using the Drosophila embryo that identify factors relevant for heart formation. These underline how this model organism still is invaluable for a better understanding of CHD.

Developmental and extracellular matrix-remodeling processes in rosiglitazone-exposed neonatal rat cardiomyocytes

OBJECTIVE

The objective of this study was to investigate the effects of rosiglitazone (Avandia(®)) on gene expression in neonatal rat ventricular myocytes.

MATERIALS & METHODS

Myocytes were exposed to rosiglitazone ex vivo. The two factors examined in the experiment were drug exposure (rosiglitazone and dimethyl sulfoxide vs dimethyl sulfoxide), and length of exposure to drug (½ h, 1 h, 2 h, 4 h, 6 h, 8 h, 12 h, 18 h, 24 h, 36 h and 48 h).

RESULTS

Transcripts that were consistently expressed in response to the drug were identified. Cardiovascular system development, extracellular matrix and immune response are represented prominently among the significantly modified gene ontology terms.

CONCLUSION

Hmgcs2, Angptl4, Cpt1a, Cyp1b1, Ech1 and Nqo1 mRNAs were strongly upregulated in cells exposed to rosiglitazone. Enrichment of transcripts involved in cardiac muscle cell differentiation and the extracellular matrix provides a panel of biomarkers for further analysis in the context of adverse cardiac outcomes in humans. Original submitted 15 November 2013; Revision submitted 14 February 2014.

Cdc42 and formin activity control non-muscle myosin dynamics during Drosophila heart morphogenesis

Cdc42 and the formins dDAAM and Diaphanous play pivotal roles in heart lumen formation through the spatiotemporal regulation of the actomyosin network.

During heart formation, a network of transcription factors and signaling pathways guide cardiac cell fate and differentiation, but the genetic mechanisms orchestrating heart assembly and lumen formation remain unclear. Here, we show that the small GTPase Cdc42 is essential for Drosophila melanogaster heart morphogenesis and lumen formation. Cdc42 genetically interacts with the cardiogenic transcription factor tinman; with dDAAM which belongs to the family of actin organizing formins; and with zipper, which encodes nonmuscle myosin II. Zipper is required for heart lumen formation, and its spatiotemporal activity at the prospective luminal surface is controlled by Cdc42. Heart-specific expression of activated Cdc42, or the regulatory formins dDAAM and Diaphanous caused mislocalization of Zipper and induced ectopic heart lumina, as characterized by luminal markers such as the extracellular matrix protein Slit. Placement of Slit at the lumen surface depends on Cdc42 and formin function. Thus, Cdc42 and formins play pivotal roles in heart lumen formation through the spatiotemporal regulation of the actomyosin network.

Carabin protects against cardiac hypertrophy by blocking calcineurin, Ras, and Ca2+/calmodulin-dependent protein kinase II signaling

BACKGROUND

Cardiac hypertrophy is an early hallmark during the clinical course of heart failure and is regulated by various signaling pathways. However, the molecular mechanisms that negatively regulate these signal transduction pathways remain poorly understood.

METHODS AND RESULTS

Here, we characterized Carabin, a protein expressed in cardiomyocytes that was downregulated in cardiac hypertrophy and human heart failure. Four weeks after transverse aortic constriction, Carabin-deficient (Carabin(-/-)) mice developed exaggerated cardiac hypertrophy and displayed a strong decrease in fractional shortening (14.6±1.6% versus 27.6±1.4% in wild type plus transverse aortic constriction mice; P<0.0001). Conversely, compensation of Carabin loss through a cardiotropic adeno-associated viral vector encoding Carabin prevented transverse aortic constriction-induced cardiac hypertrophy with preserved fractional shortening (39.9±1.2% versus 25.9±2.6% in control plus transverse aortic constriction mice; P<0.0001). Carabin also conferred protection against adrenergic receptor-induced hypertrophy in isolated cardiomyocytes. Mechanistically, Carabin carries out a tripartite suppressive function. Indeed, Carabin, through its calcineurin-interacting site and Ras/Rab GTPase-activating protein domain, functions as an endogenous inhibitor of calcineurin and Ras/extracellular signal-regulated kinase prohypertrophic signaling. Moreover, Carabin reduced Ca(2+)/calmodulin-dependent protein kinase II activation and prevented nuclear export of histone deacetylase 4 after adrenergic stimulation or myocardial pressure overload. Finally, we showed that Carabin Ras-GTPase-activating protein domain and calcineurin-interacting domain were both involved in the antihypertrophic action of Carabin.

CONCLUSIONS

Our study identifies Carabin as a negative regulator of key prohypertrophic signaling molecules, calcineurin, Ras, and Ca(2+)/calmodulin-dependent protein kinase II and implicates Carabin in the development of cardiac hypertrophy and failure.

Vitamin C and E supplementation hampers cellular adaptation to endurance training in humans: a double-blind, randomised, controlled trial

In this double-blind, randomised, controlled trial, we investigated the effects of vitamin C and E supplementation on endurance training adaptations in humans. Fifty-four young men and women were randomly allocated to receive either 1000 mg of vitamin C and 235 mg of vitamin E or a placebo daily for 11 weeks. During supplementation, the participants completed an endurance training programme consisting of three to four sessions per week (primarily of running), divided into high-intensity interval sessions [4-6 × 4-6 min; >90% of maximal heart rate (HRmax)] and steady state continuous sessions (30-60 min; 70-90% of HRmax). Maximal oxygen uptake (VO2 max ), submaximal running and a 20 m shuttle run test were assessed and blood samples and muscle biopsies were collected, before and after the intervention. Participants in the vitamin C and E group increased their VO2 max (mean ± s.d.: 8 ± 5%) and performance in the 20 m shuttle test (10 ± 11%) to the same degree as those in the placebo group (mean ± s.d.: 8 ± 5% and 14 ± 17%, respectively). However, the mitochondrial marker cytochrome c oxidase subunit IV (COX4) and cytosolic peroxisome proliferator-activated receptor-γ coactivator 1 α (PGC-1α) increased in the m. vastus lateralis in the placebo group by 59 ± 97% and 19 ± 51%, respectively, but not in the vitamin C and E group (COX4: -13 ± 54%; PGC-1α: -13 ± 29%; P ≤ 0.03, between groups). Furthermore, mRNA levels of CDC42 and mitogen-activated protein kinase 1 (MAPK1) in the trained muscle were lower in the vitamin C and E group than in the placebo group (P ≤ 0.05). Daily vitamin C and E supplementation attenuated increases in markers of mitochondrial biogenesis following endurance training. However, no clear interactions were detected for improvements in VO2 max and running performance. Consequently, vitamin C and E supplementation hampered cellular adaptations in the exercised muscles, and although this did not translate to the performance tests applied in this study, we advocate caution when considering antioxidant supplementation combined with endurance exercise.

Transcriptional networks regulating the costamere, sarcomere, and other cytoskeletal structures in striated muscle

Structural abnormalities in striated muscle have been observed in numerous transcription factor gain- and loss-of-function phenotypes in animal and cell culture model systems, indicating that transcription is important in regulating the cytoarchitecture. While most characterized cytoarchitectural defects are largely indistinguishable by histological and ultrastructural criteria, analysis of dysregulated gene expression in each mutant phenotype has yielded valuable information regarding specific structural gene programs that may be uniquely controlled by each of these transcription factors. Linking the formation and maintenance of each subcellular structure or subset of proteins within a cytoskeletal compartment to an overlapping but distinct transcription factor cohort may enable striated muscle to control cytoarchitectural function in an efficient and specific manner. Here we summarize the available evidence that connects transcription factors, those with established roles in striated muscle such as MEF2 and SRF, as well as other non-muscle transcription factors, to the regulation of a defined cytoskeletal structure. The notion that genes encoding proteins localized to the same subcellular compartment are coordinately transcriptionally regulated may prompt rationally designed approaches that target specific transcription factor pathways to correct structural defects in muscle disease.

NOD2 deletion promotes cardiac hypertrophy and fibrosis induced by pressure overload

Nucleotide-binding oligomerization domain-2 (NOD2, also designated CARD15), a member of the NOD-leucine-rich repeat (LRR) protein family (also called the CATERPILLAR family), is upregulated in atheroma lesions and has an important role in regulating the intracellular recognition of bacterial components by immune cells. However, the effect of NOD2 on cardiac hypertrophy induced by a pathological stimulus has not been determined. Here, we investigated the effects of NOD2 deficiency on cardiac hypertrophy induced by aortic banding (AB) in mice. Cardiac hypertrophy was evaluated by echocardiographic, hemodynamic, pathological, and molecular analyses. NOD2 expression was upregulated in cardiomyocytes after aortic banding surgery in wild-type (WT) mice. NOD2 deficiency promoted cardiac hypertrophy and fibrosis 4 weeks after AB. Further, the enhanced activation of TLR4 and the MAPKs, NF-κB and TGF-β/Smad pathways were found in NOD2-knockout (KO) mice compared with WT mice. Our results suggest that NOD2 attenuates cardiac hypertrophy and fibrosis via regulation of multiple pathways.

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.

Tbx20 promotes cardiomyocyte proliferation and persistence of fetal characteristics in adult mouse hearts

While differentiated cardiomyocytes proliferate prior to birth, adult cardiomyocytes in mammals exhibit relatively little proliferative activity. The T-box transcription factor Tbx20 is necessary and sufficient to promote prenatal cardiomyocyte proliferation, and Tbx20 also is required for adult cardiac homeostasis. The ability of Tbx20 to promote post-natal and adult cardiomyocyte proliferation was examined in mice with cardiomyocyte-specific Tbx20 gain-of-function beginning in the fetal period. In adult hearts, increased Tbx20 expression promotes cardiomyocyte proliferation and results in increased numbers of small, cycling, mononucleated cardiomyocytes, marked by persistent expression of fetal contractile protein genes. In adult cardiomyocytes in vivo and in neonatal rat cardiomyocytes in culture, Tbx20 promotes the activation of BMP2/pSmad1/5/8 and PI3K/AKT/GSK3β/β-catenin signaling pathways concomitant with increased cell proliferation. Inhibition of PI3K/AKT/GSK3β/β-catenin signaling reduces, but does not eliminate, Tbx20-mediated increases in cell proliferation, providing evidence for parallel regulatory pathways downstream of BMP/Smad1/5/8 signaling in promoting cardiomyocyte proliferation after birth. Thus, Tbx20 overexpression beginning in the fetal period activates multiple cardiac proliferative pathways after birth and maintains adult cardiomyocytes in an immature state in vivo.

Nebivolol induces distinct changes in profibrosis microRNA expression compared with atenolol, in salt-sensitive hypertensive rats

Nebivolol is a selective β1-blocker with nitric oxide-enhancing effects. MicroRNAs are small noncoding RNA molecules that downregulate gene expression. We compared the effects of nebivolol and atenolol, a first generation β1-selective blocker, on left ventricular hypertrophy, fibrosis, and function and microRNA expression in a rodent model of hypertension. Dahl salt-sensitive rats received either low-salt chow (control) or AIN-76A high-salt (8% NaCl) diet and randomized to vehicle (high-salt), nebivolol (20 mg/kg per day), or atenolol (50 mg/kg per day) for 8 weeks. High-salt induced left ventricular hypertrophy and fibrosis and decreased the expression of miR-27a, -29a, and -133a. Nebovolol attenuated deterioration of left ventricular systolic function, remodeling, and fibrosis more than atenolol, despite similar effects on heart rate and blood pressure. Nebivolol, but not atenolol, prevented the decrease in miR-27a and -29a induced by high-salt. Nebivolol and atenolol equally attenuated the decrease in miR-133a. In vitro overexpression of miR-27a,-29a, and -133a inhibited cardiomyocyte hypertrophy and reduced collagen expression. Both miR-27a and -29a target Sp1, and miR-133a targets Cdc42. Pharmacological inhibition of Sp1 and Cdc42 decreased myocardial fibrosis and hypertrophy. Our data support a differential microRNAs expression profile in salt-induced hypertension. Nebivolol substantially attenuated cardiac remodeling, hypertrophy, and fibrosis more than atenolol. These effects are related to attenuation of the hypertension-induced decrease in miR-27a and -29a (with a subsequent decrease in Sp1 expression) and miR-133a (with a subsequent decrease in Cdc42).

Role of Rac1-mineralocorticoid-receptor signalling in renal and cardiac disease

The Rho-family small GTPase, Ras-related C3 botulinum toxin substrate 1 (Rac1), has been implicated in renal and cardiac disease. Rac1 activation in podocytes has been shown in several models of proteinuric kidney disease and a concept involving motile podocytes has been proposed. Evidence also exists for a critical role of Rac1-mediated oxidative stress in cardiac hypertrophy, cardiomyopathy and arrhythmia, and of the aldosterone-mineralocorticoid-receptor system in proteinuria and cardiac disorders. However, plasma aldosterone concentrations are not always increased in these conditions and the mechanisms of mineralocorticoid-receptor overactivation are difficult to determine. Using knockout mice, we identified a novel mechanism of Rac1-mediated podocyte impairment; Rac1 potentiates the activity of the mineralocorticoid receptor, thereby accelerating podocyte injury. We subsequently demonstrated that the Rac1-mineralocorticoid-receptor pathway contributes to ligand-independent mineralocorticoid-receptor activation in several animal models of kidney and cardiac injury. Hyperkalaemia is a major concern associated with the use of mineralocorticoid-receptor antagonists; however, agents that modulate the activity of the Rac1-mineralocorticoid-receptor pathway in target cells, such as cell-type-specific Rac inhibitors and selective mineralocorticoid-receptor modulators, could potentially be novel therapeutic candidates with high efficacy and a low risk of adverse effects in patients with renal and cardiac diseases.

CMV promoter is repressed by p53 and activated by JNK pathway

Viral promoters are widely utilized in commercial and customized vectors to drive expression of genes of interest including reporter, effector and transfection control, because of their high transcription efficiency in a variety of primary and transformed cell lines. However, we observed altered rate of transcription for these promoters under conditions such as presence of an effector protein. These variations in viral promoter driven expressions can potentially lead to incorrect conclusion, especially in comparative and quantitative experiments. We found significantly reduced viral promoter activity in cells overexpressing tumor suppressor protein p53, whereas markedly induced transcription in cells overexpressing MAP/ERK kinase kinase 1 (Mekk 1). Using deletion constructs generated from the CMV promoter, we found the transcription reduction by p53 is possibly mediated through the TATA motif present in proximal CMV promoter. The activation of the CMV promoter by Mekk 1, on the other hand, is attributed to the proximal CRE binding site in the promoter. These findings may be of interest to investigators who use CMV (or other viral) promoter driven vectors for either comparative or quantitative gene expression, or effect on promoter activity.

CDC42 is required for structural patterning of the lung during development

The formation of highly branched epithelial structures is critical for the development of many essential organs, including lung, liver, pancreas, kidney and mammary glands. Elongation and branching of these structures require precise control of complex morphogenetic processes that are dependent upon coordinate regulation of cell shape, apical-basal polarity, proliferation, migration, and interactions among multiple cell types. Herein, we demonstrate that temporal-spatial regulation of epithelial cell polarity by the small GTPase, CDC42, is essential for branching morphogenesis of the developing lung. Epithelial cell-specific deletion of CDC42 in fetal mice disrupted epithelial cell polarity, the actin cytoskeleton, intercellular contacts, directional trafficking of proteins, proliferation and mitotic spindle orientation, impairing the organization and patterning of the developing respiratory epithelium and adjacent mesenchyme. Transition from a pseudostratified to a simple columnar epithelium was impaired, consistent with coordinate dysregulation of epithelial cell polarity, mitotic spindle orientation, and repositioning of mitotic cells within the epithelium during cell cycle progression. Expression of sonic hedgehog and its receptor, patched-1, was decreased, while fibroblast growth factor 10 expression in the mesenchyme was expanded, resulting in disruption of branching morphogenesis and bronchiolar smooth muscle formation in this model. CDC42 is required for spatial positioning of proliferating epithelial cells, as well as signaling interactions between the epithelium and mesenchyme and is, therefore, essential for formation and maintenance of the respiratory tract during morphogenesis of the fetal lung.

Protein kinase g iα inhibits pressure overload-induced cardiac remodeling and is required for the cardioprotective effect of sildenafil in vivo

BACKGROUND

Cyclic GMP (cGMP) signaling attenuates cardiac remodeling, but it is unclear which cGMP effectors mediate these effects and thus might serve as novel therapeutic targets. Therefore, we tested whether the cGMP downstream effector, cGMP-dependent protein kinase G Iα (PKGIα), attenuates pressure overload-induced remodeling in vivo.

METHODS AND RESULTS

The effect of transaortic constriction (TAC)-induced left ventricular (LV) pressure overload was examined in mice with selective mutations in the PKGIα leucine zipper interaction domain. Compared with wild-type littermate controls, in response to TAC, these Leucine Zipper Mutant (LZM) mice developed significant LV systolic and diastolic dysfunction by 48 hours (n=6 WT sham, 6 WT TAC, 5 LZM sham, 9 LZM TAC). In response to 7-day TAC, the LZM mice developed increased pathologic hypertrophy compared with controls (n=5 WT sham, 4 LZM sham, 8 WT TAC, 11 LZM TAC). In WT mice, but not in LZM mice, phosphodiesterase 5 (PDE5) inhibition with sildenafil (Sil) significantly inhibited TAC-induced cardiac hypertrophy and LV systolic dysfunction in WT mice, but this was abolished in the LZM mice (n=3 WT sham, 4 LZM sham, 3 WT TAC vehicle, 6 LZM TAC vehicle, 4 WT TAC Sil, 6 LZM TAC Sil). And in response to prolonged, 21-day TAC (n=8 WT sham, 7 LZM sham, 21 WT TAC, 15 LZM TAC), the LZM mice developed markedly accelerated mortality and congestive heart failure. TAC induced activation of JNK, which inhibits cardiac remodeling in vivo, in WT, but not in LZM, hearts, identifying a novel signaling pathway activated by PKGIα in the heart in response to LV pressure overload.

CONCLUSIONS

These findings reveal direct roles for PKGIα in attenuating pressure overload-induced remodeling in vivo and as a required effector for the cardioprotective effects of sildenafil.

Mechanisms of cardiogenesis in cardiovascular progenitor cells

Self-renewing cells of the vertebrate heart have become a major subject of interest in the past decade. However, many researchers had a hard time to argue against the orthodox textbook view that defines the heart as a postmitotic organ. Once the scientific community agreed on the existence of self-renewing cells in the vertebrate heart, their origin was again put on trial when transdifferentiation, dedifferentiation, and reprogramming could no longer be excluded as potential sources of self-renewal in the adult organ. Additionally, the presence of self-renewing pluripotent cells in the peripheral blood challenges the concept of tissue-specific stem and progenitor cells. Leaving these unsolved problems aside, it seems very desirable to learn about the basic biology of this unique cell type. Thus, we shall here paint a picture of cardiovascular progenitor cells including the current knowledge about their origin, basic nature, and the molecular mechanisms guiding proliferation and differentiation into somatic cells of the heart.

Pak1 as a novel therapeutic target for antihypertrophic treatment in the heart

BACKGROUND

Stress-induced hypertrophic remodeling is a critical pathogenetic process leading to heart failure. Although many signal transduction cascades are demonstrated as important regulators to facilitate the induction of cardiac hypertrophy, the signaling pathways for suppressing hypertrophic remodeling remain largely unexplored. In this study, we identified p21-activated kinase 1 (Pak1) as a novel signaling regulator that antagonizes cardiac hypertrophy.

METHODS AND RESULTS

Hypertrophic stress applied to primary neonatal rat cardiomyocytes (NRCMs) or murine hearts caused the activation of Pak1. Analysis of NRCMs expressing constitutively active Pak1 or in which Pak1 was silenced disclosed that Pak1 played an antihypertrophic role. To investigate the in vivo role of Pak1 in the heart, we generated mice with a cardiomyocyte-specific deletion of Pak1 (Pak1(cko)). When subjected to 2 weeks of pressure overload, Pak1(cko) mice developed greater cardiac hypertrophy with attendant blunting of JNK activation compared with controls, and these knockout mice underwent the transition into heart failure when prolonged stress was applied. Chronic angiotensin II infusion also caused increased cardiac hypertrophy in Pak1(cko) mice. Moreover, we discovered that the Pak1 activator FTY720, a sphingosine-like analog, was able to prevent pressure overload-induced hypertrophy in wild-type mice without compromising their cardiac functions. Meanwhile, FTY720 failed to exert such an effect on Pak1(cko) mice, suggesting that the antihypertrophic effect of FTY720 likely acts through Pak1 activation.

CONCLUSIONS

These results, for the first time, establish Pak1 as a novel antihypertrophic regulator and suggest that it may be a potential therapeutic target for the treatment of cardiac hypertrophy and heart failure.

Ablation of p21-activated kinase-1 in mice promotes isoproterenol-induced cardiac hypertrophy in association with activation of Erk1/2 and inhibition of protein phosphatase 2A

Earlier investigations in our lab indicated an anti-adrenergic effect induced by activation of p21-activated kinase (Pak-1) and protein phosphatase 2A (PP2A). Our objective was to test the hypothesis that Pak-1/PP2A is a signaling cascade controlling stress-induced cardiac growth. We determined the effects of ablation of the Pak-1 gene on the response of the myocardium to chronic stress of isoproterenol (ISO) administration. Wild-type (WT) and Pak-1-knockout (Pak-1-KO) mice were randomized into six groups to receive either ISO, saline (CTRL), or ISO and FR180204, a selective inhibitor of Erk1/2. Echocardiography revealed that hearts of the Pak-1-KO/ISO group had increased LV fractional shortening, reduced LV chamber volume in diastole and systole, increased cardiac hypertrophy, and enhanced transmitral early filling deceleration time, compared to all other groups. The changes were associated with an increase in relative Erk1/2 activation in Pak-1-KO/ISO mice versus all other groups. ISO-induced cardiac hypertrophy and Erk1/2 activation in Pak-1-KO/ISO were attenuated when the selective Erk1/2 inhibitor FR180204 was administered. Immunoprecipitation showed an association between Pak-1, PP2A, and Erk1/2. Cardiac myocytes infected with an adenoviral vector expressing constitutively active Pak-1 showed a repression of Erk1/2 activation. p38 MAPK phosphorylation was decreased in Pak-1-KO/ISO and Pak-1-KO/CTRL mice compared to WT. Levels of phosphorylated PP2A were increased in ISO-treated Pak-1-KO mice, indicating reduced phosphatase activity. Maximum Ca(2+)-activated tension in detergent-extracted bundles of papillary fibers from ISO-treated Pak-1-KO mice was higher than in all other groups. Analysis of cTnI phosphorylation indicated that compared to WT, ISO-induced phosphorylation of cTnI was blunted in Pak-1-KO mice. Active Pak-1 is a natural inhibitor of Erk1/2 and a novel anti-hypertrophic signaling molecule upstream of PP2A.

Cdc42 and Tinman march to the same beat

Study describes a conserved genetic network that regulates heart function in flies and mammals.

Tinman/Nkx2-5 acts via miR-1 and upstream of Cdc42 to regulate heart function across species

Cdc42 regulates cardiac function in mice and flies downstream of a conserved Tinman/Nkx2-5–miR-1 signaling network.

Unraveling the gene regulatory networks that govern development and function of the mammalian heart is critical for the rational design of therapeutic interventions in human heart disease. Using the Drosophila heart as a platform for identifying novel gene interactions leading to heart disease, we found that the Rho-GTPase Cdc42 cooperates with the cardiac transcription factor Tinman/Nkx2-5. Compound Cdc42, tinman heterozygous mutant flies exhibited impaired cardiac output and altered myofibrillar architecture, and adult heart–specific interference with Cdc42 function is sufficient to cause these same defects. We also identified K⁺ channels, encoded by dSUR and slowpoke, as potential effectors of the Cdc42–Tinman interaction. To determine whether a Cdc42–Nkx2-5 interaction is conserved in the mammalian heart, we examined compound heterozygous mutant mice and found conduction system and cardiac output defects. In exploring the mechanism of Nkx2-5 interaction with Cdc42, we demonstrated that mouse Cdc42 was a target of, and negatively regulated by miR-1, which itself was negatively regulated by Nkx2-5 in the mouse heart and by Tinman in the fly heart. We conclude that Cdc42 plays a conserved role in regulating heart function and is an indirect target of Tinman/Nkx2-5 via miR-1.