Myocardin mRNA is augmented in the failing myocardium: expression profiling in the porcine model and human dilated cardiomyopathy

Actin-related protein 5 suppresses the cooperative activation of cardiac gene transcription by myocardin and MEF2

MYOCD is a transcription factor important for cardiac and smooth muscle development. We previously identified that actin-related protein 5 (ARP5) binds to the N-terminus of MYOCD. Here, we demonstrate that ARP5 inhibits the cooperative action of the cardiac-specific isoform of MYOCD with MEF2. ARP5 overexpression in murine hearts induced cardiac hypertrophy and fibrosis, whereas ARP5 knockdown in P19CL6 cells significantly increased cardiac gene expression. ARP5 was found to bind to a MEF2-binding motif of cardiac MYOCD and inhibit MEF2-mediated transactivation by MYOCD. RNA-seq analysis revealed 849 genes that are upregulated by MYOCD-MEF2 and 650 genes that are repressed by ARP5. ARP5 expression increased with cardiomyopathy and was negatively correlated with the expression of Tnnt2 and Ttn, which were regulated by cardiac MYOCD-MEF2. Overall, our data suggest that ARP5 is a potential suppressor of cardiac MYOCD during physiological and pathological processes.

Dilated cardiomyopathy: a new insight into the rare but common cause of heart failure

Heart failure is a global health burden responsible for high morbidity and mortality with a prevalence of greater than 60 million individuals worldwide. One of the major causes of heart failure is dilated cardiomyopathy (DCM), characterized by associated systolic dysfunction. During the last few decades, there have been remarkable advances in our understanding about the genetics of dilated cardiomyopathy. The genetic causes were initially thought to be associated with mutations in genes encoding proteins that are localized to cytoskeleton and sarcomere only; however, with the advancement in mechanistic understanding, the roles of ion channels, Z-disc, mitochondria, nuclear proteins, cardiac transcription factors (e.g., NKX-2.5, TBX20, GATA4), and the factors involved in calcium homeostasis have also been identified and found to be implicated in both familial and sporadic DCM cases. During past few years, next-generation sequencing (NGS) has been established as a diagnostic tool for genetic analysis and it has added significantly to the existing candidate gene list for DCM. The animal models have also provided novel insights to develop a better treatment strategy based on phenotype-genotype correlation, epigenetic and phenomic profiling. Most of the DCM biomarkers that are used in routine genetic and clinical testing are structural proteins, but during the last few years, the role of mi-RNA has also emerged as a biomarker due to their accessibility through noninvasive methods. Our increasing genetic knowledge can improve the clinical management of DCM by bringing clinicians and geneticists on one platform, thereby influencing the individualized clinical decision making and leading to precision medicine.

Long-term prognostic value of myocardin expression levels in non-ischemic dilated cardiomyopathy

The mortality of patients with non-ischemic dilated cardiomyopathy (NIDCM) remains substantial. We evaluated gene expression levels of myocardin, an early cardiac gene, in the peripheral blood cells of NIDCM patients as a prognostic biomarker in their long-term outcome and mortality from congestive HF (CHF). We retrospectively analyzed 101 consecutives optimally treated NIDCM patients of Cretan origin who were enrolled from the HF clinic of our hospital from November 2005 to December 2008. Our patient data were either taken from their medical files or recorded during visits to the HF unit or hospitalizations. Follow-up was carried out by telephone interview and by accessing information from general practitioners and cardiologists in private practice. The median follow-up period was 8 years (mean follow-up 7 ± 3.4 years). The overall mortality during follow-up was 61.4%, while mortality due to congestive heart failure (CHF) was 49.5%. Higher CHF and all-cause mortality were observed in patients with myocardin levels < 14.26 (p < 0.001 for both CHF and all-cause mortality). A multivariate Cox regression analysis showed that myocardin level of expression had independent significant prognostic value for the risk of death from CHF (HR 14.5, 95% confidence interval (CI) 5.3-39) in those patients. Peripheral blood cells gene expression of myocardin, an early myocardial marker, may serve as prognostic biomarkers of the long-term outcome of patients with NIDCM. Our findings open new prospects in the risk stratification of these patients.

Wound Healing-related Functions of the p160 Steroid Receptor Coactivator Family

Multicellular organisms have evolved sophisticated mechanisms to recover and maintain original tissue functions following injury. Injury responses require a robust transcriptomic response associated with cellular reprogramming involving complex gene expression programs critical for effective tissue repair following injury. Steroid receptor coactivators (SRCs) are master transcriptional regulators of cell-cell signaling that is integral for embryogenesis, reproduction, normal physiological function, and tissue repair following injury. Effective therapeutic approaches for facilitating improved tissue regeneration and repair will likely involve temporal and combinatorial manipulation of cell-intrinsic and cell-extrinsic factors. Pleiotropic actions of SRCs that are critical for wound healing range from immune regulation and angiogenesis to maintenance of metabolic regulation in diverse organ systems. Recent evidence derived from studies of model organisms during different developmental stages indicates the importance of the interplay of immune cells and stromal cells to wound healing. With SRCs being the master regulators of cell-cell signaling integral to physiologic changes necessary for wound repair, it is becoming clear that therapeutic targeting of SRCs provides a unique opportunity for drug development in wound healing. This review will provide an overview of wound healing-related functions of SRCs with a special focus on cellular and molecular interactions important for limiting tissue damage after injury. Finally, we review recent findings showing stimulation of SRCs following cardiac injury with the SRC small molecule stimulator MCB-613 can promote cardiac protection and inhibit pathologic remodeling after myocardial infarction.

CRISPR-Cas9-Mediated Epitope Tagging Provides Accurate and Versatile Assessment of Myocardin-Brief Report

Objective- Unreliable antibodies often hinder the accurate detection of an endogenous protein, and this is particularly true for the cardiac and smooth muscle cofactor, MYOCD (myocardin). Accordingly, the mouse Myocd locus was targeted with 2 independent epitope tags for the unambiguous expression, localization, and activity of MYOCD protein. Approach and Results- 3cCRISPR (3-component clustered regularly interspaced short palindromic repeat) was used to engineer a carboxyl-terminal 3×FLAG or 3×HA epitope tag in mouse embryos. Western blotting with antibodies to each tag revealed a MYOCD protein product of ≈150 kDa, a size considerably larger than that reported in virtually all publications. MYOCD protein was most abundant in some adult smooth muscle-containing tissues with surprisingly low-level expression in the heart. Both alleles of Myocd are active in aorta because a 2-fold increase in protein was seen in mice homozygous versus heterozygous for FLAG-tagged Myocd. ChIP (chromatin immunoprecipitation)-quantitative polymerase chain reaction studies provide proof-of-principle data demonstrating the utility of this mouse line in conducting genome-wide ChIP-seq studies to ascertain the full complement of MYOCD-dependent target genes in vivo. Although FLAG-tagged MYOCD protein was undetectable in sections of adult mouse tissues, low-passaged vascular smooth muscle cells exhibited expected nuclear localization. Conclusions- This report validates new mouse models for analyzing MYOCD protein expression, localization, and binding activity in vivo and highlights the need for rigorous authentication of antibodies in biomedical research.

Myocardin ablation in a cardiac-renal rat model

Cardiorenal syndrome is defined by primary heart failure conditions influencing or leading to renal injury or dysfunction. Dilated cardiomyopathy (DCM) is a major co-existing form of heart failure (HF) with renal diseases. Myocardin (MYOCD), a cardiac-specific co-activator of serum response factor (SRF), is increased in DCM porcine and patient cardiac tissues and plays a crucial role in the pathophysiology of DCM. Inhibiting the increased MYOCD has shown to be partially rescuing the DCM phenotype in porcine model. However, expression levels of MYOCD in the cardiac tissues of the cardiorenal syndromic patients and the effect of inhibiting MYOCD in a cardiorenal syndrome model remains to be explored. Here, we analyzed the expression levels of MYOCD in the DCM patients with and without renal diseases. We also explored, whether cardiac specific silencing of MYOCD expression could ameliorate the cardiac remodeling and improve cardiac function in a renal artery ligated rat model (RAL). We observed an increase in MYOCD levels in the endomyocardial biopsies of DCM patients associated with renal failure compared to DCM alone. Silencing of MYOCD in RAL rats by a cardiac homing peptide conjugated MYOCD siRNA resulted in attenuation of cardiac hypertrophy, fibrosis and restoration of the left ventricular functions. Our data suggest hyper-activation of MYOCD in the pathogenesis of the cardiorenal failure cases. Also, MYOCD silencing showed beneficial effects by rescuing cardiac hypertrophy, fibrosis, size and function in a cardiorenal rat model.

Myocardial transcription factors in diastolic dysfunction: clues for model systems and disease

There are multiple intrinsic mechanisms for diastolic dysfunction ranging from molecular to structural derangements in ventricular myocardium. The molecular mechanisms regulating the progression from normal diastolic function to severe dysfunction still remain poorly understood. Recent studies suggest a potentially important role of core cardio-enriched transcription factors (TFs) in the control of cardiac diastolic function in health and disease through their ability to regulate the expression of target genes involved in the process of adaptive and maladaptive cardiac remodeling. The current relevant findings on the role of a variety of such TFs (TBX5, GATA-4/6, SRF, MYOCD, NRF2, and PITX2) in cardiac diastolic dysfunction and failure are updated, emphasizing their potential as promising targets for novel treatment strategies. In turn, the new animal models described here will be key tools in determining the underlying molecular mechanisms of disease. Since diastolic dysfunction is regulated by various TFs, which are also involved in cross talk with each other, there is a need for more in-depth research from a biomedical perspective in order to establish efficient therapeutic strategies.

The mechanism of myocardial hypertrophy regulated by the interaction between mhrt and myocardin

As a strong transactivator of promoters containing CarG boxes, myocardin was critical for the cardiac muscle program and necessary for normal cardiogenesis. So it probably represents a viable therapeutic biomarker in the setting of cardiac hypertrophy and failure. In recent years, the studies of regulation of cardiac hypertrophy via myocardin are so common, and the molecular mechanism is becoming more and more clear. Here, we have revealed a kind of interaction between mhrt and myocardin shown as a feedback regulatory mechanism in the regulation of cardiac hypertrophy. That is, the lncRNA mhrt can affect the acetylation of myocardin by HDAC5 to inhibit cardiac hypertrophy induced by myocardin. Moreover, myocardin also can directly activate the mhrt transcription through binding to the CarG box. Thus, mhrt and myocardin form a regulation loop in the process of cardiac hypertrophy. This finding may play a positive role in revealing the complete mechanisms of cardiac hypertrophy.

Role of cardiac TBX20 in dilated cardiomyopathy

Dilated cardiomyopathy (DCM) is an important cause of heart failure and sudden cardiac death worldwide. Transcription factor TBX20 has been shown to play a crucial role in cardiac development and maintenance of adult mouse heart. Recent studies suggest that TBX20 may have a role in pathophysiology of DCM. In the present study, we examined TBX20 expression in idiopathic DCM patients and in an animal model of cardiomyopathy, and studied its correlation with echocardiographic indices of LV function. Endomyocardial biopsies (EMBs) from intraventricular septal from the right ventricle region were obtained from idiopathic DCM patients (IDCM, n = 30) and from patients with ventricular septal defect (VSD, n = 14) with normal LVEF who served as controls. An animal model of DCM was developed by right renal artery ligation in Wistar rats. Cardiac TBX20 mRNA levels were measured by real-time PCR in IDCM, controls, and in rats. The role of DNA promoter methylation and copy number variation (CNVs) in regulating TBX20 gene expression was also investigated. Cardiac TBX20 mRNA levels were significantly increased (8.9 fold, p < 0.001) in IDCM patients and in RAL rats as compared to the control group. Cardiac TBX20 expression showed a negative correlation with LVEF (r = -0.71, p < 0.001) and a positive correlation with left ventricular end-systolic volume (r = 0.39, p = 0.038). No significant difference in TBX20 CNVs and promoter methylation was observed between IDCM patients and control group. Our results suggest a potential role of TBX20 in pathophysiology of DCM.

Myocardin in biology and disease

Myocardin (MYOCD) is a potent transcriptional coactivator that functions primarily in cardiac muscle and smooth muscle through direct contacts with serum response factor (SRF) over cis elements known as CArG boxes found near a number of genes encoding for contractile, ion channel, cytoskeletal, and calcium handling proteins. Since its discovery more than 10 years ago, new insights have been obtained regarding the diverse isoforms of MYOCD expressed in cells as well as the regulation of MYOCD expression and activity through transcriptional, post-transcriptional, and post-translational processes. Curiously, there are a number of functions associated with MYOCD that appear to be independent of contractile gene expression and the CArG-SRF nucleoprotein complex. Further, perturbations in MYOCD gene expression are associated with an increasing number of diseases including heart failure, cancer, acute vessel disease, and diabetes. This review summarizes the various biological and pathological processes associated with MYOCD and offers perspectives to several challenges and future directions for further study of this formidable transcriptional coactivator.

Kruppel-like factor 4 protein regulates isoproterenol-induced cardiac hypertrophy by modulating myocardin expression and activity

Kruppel-like factor 4 (KLF4) plays an important role in vascular diseases, including atherosclerosis and vascular injury. Although KLF4 is expressed in the heart in addition to vascular cells, the role of KLF4 in cardiac disease has not been fully determined. The goals of this study were to investigate the role of KLF4 in cardiac hypertrophy and to determine the underlying mechanisms. Cardiomyocyte-specific Klf4 knockout (CM Klf4 KO) mice were generated by the Cre/LoxP technique. Cardiac hypertrophy was induced by chronic infusion of the β-adrenoreceptor agonist isoproterenol (ISO). Results showed that ISO-induced cardiac hypertrophy was enhanced in CM Klf4 KO mice compared with control mice. Accelerated cardiac hypertrophy in CM Klf4 KO mice was accompanied by the augmented cellular enlargement of cardiomyocytes as well as the exaggerated expression of fetal cardiac genes, including atrial natriuretic factor (Nppa). Additionally, induction of myocardin, a transcriptional cofactor regulating fetal cardiac genes, was enhanced in CM Klf4 KO mice. Interestingly, KLF4 regulated Nppa expression by modulating the expression and activity of myocardin, providing a mechanical basis for accelerated cardiac hypertrophy in CM Klf4 KO mice. Moreover, we showed that KLF4 mediated the antihypertrophic effect of trichostatin A, a histone deacetylase inhibitor, because ISO-induced cardiac hypertrophy in CM Klf4 KO mice was attenuated by olmesartan, an angiotensin II type 1 antagonist, but not by trichostatin A. These results provide novel evidence that KLF4 is a regulator of cardiac hypertrophy by modulating the expression and the activity of myocardin.

Pitx2c is reactivated in the failing myocardium and stimulates myf5 expression in cultured cardiomyocytes

BACKGROUND

Pitx2 (paired-like homeodomain 2 transcription factor) is crucial for heart development, but its role in heart failure (HF) remains uncertain. The present study lays the groundwork implicating Pitx2 signalling in different modalities of HF.

METHODOLOGY/PRINCIPAL FINDINGS

A variety of molecular, cell-based, biochemical, and immunochemical assays were used to evaluate: (1) Pitx2c expression in the porcine model of diastolic HF (DHF) and in patients with systolic HF (SHF) due to dilated and ischemic cardiomyopathy, and (2) molecular consequences of Pitx2c expression manipulation in cardiomyocytes in vitro. In pigs, the expression of Pitx2c, physiologically downregulated in the postnatal heart, is significantly re-activated in left ventricular (LV) failing myocardium which, in turn, is associated with increased expression of a restrictive set of Pitx2 target genes. Among these, Myf5 was identified as the top upregulated gene. In vitro, forced expression of Pitx2c in cardiomyocytes, but not in skeletal myoblasts, activates Myf5 in dose-dependent manner. In addition, we demonstrate that the level of Pitx2c is upregulated in the LV-myocardium of SHF patients.

CONCLUSIONS/SIGNIFICANCE

The results provide previously unrecognized evidence that Pitx2c is similarly reactivated in postnatal/adult heart at distinct HF phenotypes and suggest that Pitx2c is involved, directly or indirectly, in the regulation of Myf5 expression in cardiomyocytes.

Overexpression of myocardin induces partial transdifferentiation of human-induced pluripotent stem cell-derived mesenchymal stem cells into cardiomyocytes

Mesenchymal stem cells (MSCs) derived from human‐induced pluripotent stem cells (iPSCs) show superior proliferative capacity and therapeutic potential than those derived from bone marrow (BM). Ectopic expression of myocardin further improved the therapeutic potential of BM‐MSCs in a mouse model of myocardial infarction. The aim was of this study was to assess whether forced myocardin expression in iPSC‐MSCs could further enhance their transdifferentiation to cardiomyocytes and improve their electrophysiological properties for cardiac regeneration. Myocardin was overexpressed in iPSC‐MSCs using viral vectors (adenovirus or lentivirus). The expression of smooth muscle cell and cardiomyocyte markers, and ion channel genes was examined by reverse transcription‐polymerase chain reaction (RT‐PCR), immunofluorescence staining and patch clamp. The conduction velocity of the neonatal rat ventricular cardiomyocytes cocultured with iPSC‐MSC monolayer was measured by multielectrode arrays recording plate. Myocardin induced the expression of α‐MHC, GATA4, α‐actinin, cardiac MHC, MYH11, calponin, and SM α‐actin, but not cTnT, β‐MHC, and MLC2v in iPSC‐MSCs. Overexpression of myocardin in iPSC‐MSC enhanced the expression of SCN9A and CACNA1C, but reduced that of KCa3.1 and Kir2.2 in iPSC‐MSCs. Moreover, BK_Ca, I_Kir, I_Cl, I_to and I_Na.TTX were detected in iPSC‐MSC with myocardin overexpression; while only BK_Ca, I_Kir, I_Cl, IK_DR, and IK_Ca were noted in iPSC‐MSC transfected with green florescence protein. Furthermore, the conduction velocity of iPSC‐MSC was significantly increased after myocardin overexpression. Overexpression of myocardin in iPSC‐MSCs resulted in partial transdifferentiation into cardiomyocytes phenotype and improved the electrical conduction during integration with mature cardiomyocytes.

Forced myocardin expression in human‐induced pluripotent stem cell (hiPSC)‐derived mesenchymal stem cells lead to partial transdifferentiation into cardiomyocytes and smooth muscle cells phenotypes through modification in ion channel expression profile and electrical conduction velocity.

miR-1/133a clusters cooperatively specify the cardiomyogenic lineage by adjustment of myocardin levels during embryonic heart development

miRNAs are small RNAs directing many developmental processes by posttranscriptional regulation of protein-coding genes. We uncovered a new role for miR-1-1/133a-2 and miR-1-2/133a-1 clusters in the specification of embryonic cardiomyocytes allowing transition from an immature state characterized by expression of smooth muscle (SM) genes to a more mature fetal phenotype. Concomitant knockout of miR-1-1/133a-2 and miR-1-2/133a-1 released suppression of the transcriptional co-activator myocardin, a major regulator of SM gene expression, but not of its binding partner SRF. Overexpression of myocardin in the embryonic heart essentially recapitulated the miR-1/133a mutant phenotype at the molecular level, arresting embryonic cardiomyocytes in an immature state. Interestingly, the majority of postulated miR-1/133a targets was not altered in double mutant mice, indicating that the ability of miR-1/133a to suppress target molecules strongly depends on the cellular context. Finally, we show that myocardin positively regulates expression of miR-1/133a, thus constituting a negative feedback loop that is essential for early cardiac development.

Regulation of fetal gene expression in heart failure

During the processes leading to adverse cardiac remodeling and heart failure, cardiomyocytes react to neurohumoral stimuli and biomechanical stress by activating pathways that induce pathological hypertrophy. The gene expression patterns and molecular changes observed during cardiac hypertrophic remodeling bare resemblance to those observed during fetal cardiac development. The re-activation of fetal genes in the adult failing heart is a complex biological process that involves transcriptional, posttranscriptional and epigenetic regulation of the cardiac genome. In this review, the mechanistic actions of transcription factors, microRNAs and chromatin remodeling processes in regulating fetal gene expression in heart failure are discussed.

Effects of cyclic stretch on the molecular regulation of myocardin in rat aortic vascular smooth muscle cells

BACKGROUND

The expression of myocardin, a cardiac-restricted gene, increases during environmental stress. How mechanical stretch affects the regulation of myocardin in vascular smooth muscle cells (VSMCs) is not fully understood. We identify the mechanisms and pathways through which mechanical stretch induces myocardin expression in VSMCs.

RESULTS

Rat VSMCs grown on a flexible membrane base were stretched to 20% of maximum elongation, at 60 cycles per min. An in vivo model of aorta-caval shunt in adult rats was also used to investigate myocardin expression. Cyclic stretch significantly increased myocardin and angiotensin II (AngII) expression after 18 and 6 h of stretch. Addition of extracellular signal-regulated kinases (ERK) pathway inhibitor (PD98059), ERK small interfering RNA (siRNA), and AngII receptor blocker (ARB; losartan) before stretch inhibited the expression of myocardin protein. Gel shift assay showed that myocardin-DNA binding activity increased after stretch. PD98059, ERK siRNA and ARB abolished the binding activity induced by stretch. Stretch increased while myocardin-mutant plasmid, PD98059, and ARB abolished the promoter activity. Protein synthesis by measuring [3H]proline incorporation into the cells increased after cyclic stretch, which represented hypertrophic change of VSMCs. An in vivo model of aorta-caval shunt also demonstrated increased myocardin protein expression in the aorta. Confocal microscopy showed increased VSMC size 24 h after cyclic stretch and VSMC hypertrophy after creation of aorta-caval shunt for 3 days.

CONCLUSIONS

Cyclic stretch enhanced myocardin expression mediated by AngII through the ERK pathway in cultured rat VSMCs. These findings suggest that myocardin plays a role in stretch-induced VSMC hypertrophy.

Recapitulating maladaptive, multiscale remodeling of failing myocardium on a chip

The lack of a robust pipeline of medical therapeutic agents for the treatment of heart disease may be partially attributed to the lack of in vitro models that recapitulate the essential structure-function relationships of healthy and diseased myocardium. We designed and built a system to mimic mechanical overload in vitro by applying cyclic stretch to engineered laminar ventricular tissue on a stretchable chip. To test our model, we quantified changes in gene expression, myocyte architecture, calcium handling, and contractile function and compared our results vs. several decades of animal studies and clinical observations. Cyclic stretch activated gene expression profiles characteristic of pathological remodeling, including decreased α- to β-myosin heavy chain ratios, and induced maladaptive changes to myocyte shape and sarcomere alignment. In stretched tissues, calcium transients resembled those reported in failing myocytes and peak systolic stress was significantly reduced. Our results suggest that failing myocardium, as defined genetically, structurally, and functionally, can be replicated in an in vitro microsystem by faithfully recapitulating the structural and mechanical microenvironment of the diseased heart.

In search of novel targets for heart disease: myocardin and myocardin-related transcriptional cofactors

Growing evidence suggests that gene-regulatory networks, which are responsible for directing cardiovascular development, are altered under stress conditions in the adult heart. The cardiac gene regulatory network is controlled by cardioenriched transcription factors and multiple-cell-signaling inputs. Transcriptional coactivators also participate in gene-regulatory circuits as the primary targets of both physiological and pathological signals. Here, we focus on the recently discovered myocardin-(MYOCD) related family of transcriptional cofactors (MRTF-A and MRTF-B) which associate with the serum response transcription factor and activate the expression of a variety of target genes involved in cardiac growth and adaptation to stress via overlapping but distinct mechanisms. We discuss the involvement of MYOCD, MRTF-A, and MRTF-B in the development of cardiac dysfunction and to what extent modulation of the expression of these factors in vivo can correlate with cardiac disease outcomes. A close examination of the findings identifies the MYOCD-related transcriptional cofactors as putative therapeutic targets to improve cardiac function in heart failure conditions through distinct context-dependent mechanisms. Nevertheless, we are in support of further research to better understand the precise role of individual MYOCD-related factors in cardiac function and disease, before any therapeutic intervention is to be entertained in preclinical trials.

Use of atorvastatin to inhibit hypoxia-induced myocardin expression

BACKGROUND

Hypoxia induces the formation of reactive oxygen species (ROS), myocardin expression and cardiomyocyte hypertrophy. The 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) have been demonstrated to have both antioxidant and antihypertrophic effects. We evaluated the pathways of atorvastatin in repressing ROS and myocardin after hypoxia to prevent cardiomyocyte hypertrophy.

MATERIALS AND METHODS

Cultured rat neonatal cardiomyocytes were subjected to hypoxia, and the expression of myocardin and ROS were evaluated. Different signal transduction inhibitors, atorvastatin and N-acetylcysteine (NAC) were used to identify the pathways that inhibited myocardin expression and ROS. Electrophoretic motility shift assay (EMSA) and luciferase assay were used to identify the binding of myocardin/serum response factor (SRF) and transcription to cardiomyocytes. Cardiomyocyte hypertrophy was assessed by (3)H-proline incorporation assay.

RESULTS

Myocardin expression after hypoxia was inhibited by atorvastatin, RhoA/Rho kinase inhibitor (Y27632), extracellular signal-regulated kinase (ERK) small interfering RNA (siRNA)/ERK pathway inhibitor (PD98059), myocardin siRNA and NAC. Bindings of myocardin/SRF, transcription of myocardin/SRF to cardiomyocytes, presence of myocardin in the nuclei of cardiomyocytes and protein synthesis after hypoxia were identified by EMSA, luciferase assay, confocal microscopy and (3)H-proline assay and were suppressed by atorvastatin, Y27632, PD98059 and NAC.

CONCLUSIONS

Hypoxia in neonatal cardiomyocytes increases myocardin expression and ROS to cause cardiomyocyte hypertrophy, which can be prevented by atorvastatin by suppressing ROS and myocardin expression.

Targeted gene-silencing reveals the functional significance of myocardin signaling in the failing heart

Background

Myocardin (MYOCD), a potent transcriptional coactivator of smooth muscle (SM) and cardiac genes, is upregulated in failing myocardium in animal models and human end-stage heart failure (HF). However, the molecular and functional consequences of myocd upregulation in HF are still unclear.

Methodology/Principal Findings

The goal of the present study was to investigate if targeted inhibition of upregulated expression of myocd could influence failing heart gene expression and function. To this end, we used the doxorubicin (Dox)-induced diastolic HF (DHF) model in neonatal piglets, in which, as we show, not only myocd but also myocd-dependent SM-marker genes are highly activated in failing left ventricular (LV) myocardium. In this model, intra-myocardial delivery of short-hairpin RNAs, designed to target myocd variants expressed in porcine heart, leads on day 2 post-delivery to: (1) a decrease in the activated expression of myocd and myocd-dependent SM-marker genes in failing myocardium to levels seen in healthy control animals, (2) amelioration of impaired diastolic dysfunction, and (3) higher survival rates of DHF piglets. The posterior restoration of elevated myocd expression (on day 7 post-delivery) led to overexpression of myocd-dependent SM-marker genes in failing LV-myocardium that was associated with a return to altered diastolic function.

Conclusions/Significance

These data provide the first evidence that a moderate inhibition (e.g., normalization) of the activated MYOCD signaling in the diseased heart may be promising from a therapeutic point of view.

Ovine models for chronic heart failure

PURPOSE

Testing and optimizing of surgical therapies for chronic heart failure (CHF) requires large animal models. CHF has been induced in several large animal species. Sheep have modest body mass increase and demonstrate docile behavior and are therefore a preferred species in research on surgical therapies for CHF METHODS: A literature search for existing ovine CHF models was performed, using search terms "sheep" and "heart failure". Relevant secondary references were traced.

RESULTS

Rapid ventricular pacing produces rapid-onset CHFE Its severity ranges from moderate left ventricular failure to severe biventricular failure, depending on length and frequency of pacing. Its counterpart in human CHF is tachycardia-induced HF since it is reversible upon cessation of pacing. Myocardial damage models include CHF induced by cardiototoxic drugs and ischemia. Ischemia-based models include coronary microembolization, occlusion and ischemia/reperfusion models. The microembolization model is relevant to diabetic cardiomyopathy. Coronary occlusion models exhibit variable functional impairment, some with aneurysm formation, and some with mitral valve regurgitation, depending on occlusion localization. They are relevant to CHF following non-reperfused myocardial infarction. Coronary occlusion/reperfusion models are relevant to the occurrence of human ãã despite coronary artery recanalization. Pressure overload of left and right ventricle is induced by aortic and pulmonary artery banding, respectively. Hypertrophy precedes CHF as in patients with valve stenosis and hypertension. Volume overload is induced by valve damage or shunt creation. Atrioventricular valve regurgitation is the most important clinical counterpart.

CONCLUSION

Several ovine CHF models exist. Since they exhibit important cardiac pathology differences, the choice of model should be based on the specific experimental question.

Homeodomain only protein x is down-regulated in human heart failure

Homeodomain only protein x (Hopx) is an unusual homeodomain protein that has diverse effects on cardiac growth. Manipulation of Hopx function in murine models is associated with cardiac hypertrophy, dilation and fibrosis. In the present study, we examined the expression profile of Hopx in various models of pathologic cardiac hypertrophy and failure. Hopx expression is significantly reduced in neonatal rat cardiac myocytes after α/β adrenergic receptor agonist treatment. Cardiac hypertrophy and failure induced by transaortic constriction in mice causes marked down-regulation of Hopx expression. Interestingly, HOPX expression was significantly reduced in hearts of humans with end-stage heart failure when compared to non-failing control hearts, and HOPX levels remain low after LVAD support. Our findings suggest that HOPX/Hopx expression is reduced in multiple examples of human and murine cardiac hypertrophy and failure.

Transient expression of OCT4 is sufficient to allow human keratinocytes to change their differentiation pathway

In this study, we describe a simple system in which human keratinocytes can be redirected to an alternative differentiation pathway. We transiently transfected freshly isolated human skin keratinocytes with the single transcription factor OCT4. Within 2 days these cells displayed expression of endogenous embryonic genes and showed reduced genomic methylation. More importantly, these cells could be specifically converted into neuronal and contractile mesenchymal cell types. Redirected differentiation was confirmed by expression of neuronal and mesenchymal cell mRNA and protein, and through a functional assay in which the newly differentiated mesenchymal cells contracted collagen gels as efficiently as authentic myofibroblasts. Thus, to generate patient-specific cells for therapeutic purposes, it may not be necessary to completely reprogram somatic cells into induced pluripotent stem cells before altering their differentiation and grafting them into new tissues.

Exon-skipping brain natriuretic peptide variant is overexpressed in failing myocardium and attenuates brain natriuretic peptide production in vitro

Brain natriuretic peptide/natriuretic peptide precursor B (NPPB) is one of the most studied genes in relation to heart failure (HF) conditions. However, it is still unclear as to whether alternative splicing could create NPPB mRNA variants, which may be expressed in normal and diseased myocardium. We aimed to identify and characterize a novel alternatively spliced variant of porcine and human NPPB resulting from exon 2 skipping (designated as ΔE2-NPPB). A variety of conventional molecular, biochemical and immunochemical methods were used to examine the expression and functional consequences of ΔE2-NPPB in vitro and in vivo. The pig ΔE2-NPPB mRNA is effectively translated into stable protein in cell-based assays but, in contrast to normally spliced NPPB, the ΔE2-NPPB protein is not secreted into the media. Co-transfection assays demonstrate that ΔE2-NPPB attenuates production and secretion of normally spliced NPPB, suggesting a negative feedback loop of NPPB signaling through generation of ΔE2-NPPB. The inhibitory effects of ΔE2-NPPB on the expression of NPPB are associated with sequence elements residing in exon 3 of ΔE2-NPPB. In piglets, ΔE2-NPPB gene expression is downregulated in both ventricles after birth, but it is markedly re-activated in the postnatal myocardium in experimental diastolic heart failure. In addition, we demonstrate that the exon-skipped NPPB variants are expressed in the postnatal and adult human myocardium and upregulated at end-stage HF due to dilated cardiomyopathy. Our work uncovers an important role of alternative exon skipping in the regulation of NPPB gene expression, thereby pinpointing a putative new mechanism for post-transcriptional regulation of NPPB production and secretion.

Angiotensin II and the ERK pathway mediate the induction of myocardin by hypoxia in cultured rat neonatal cardiomyocytes

Hypoxic injury to cardiomyocytes is a stress that causes cardiac pathology through cardiac-restricted gene expression. SRF (serum-response factor) and myocardin are important for cardiomyocyte growth and differentiation in response to myocardial injuries. Previous studies have indicated that AngII (angiotensin II) stimulates both myocardin expression and cardiomyocyte hypertrophy. In the present study, we evaluated the expression of myocardin and AngII after hypoxia in regulating gene transcription in neonatal cardiomyocytes. Cultured rat neonatal cardiomyocytes were subjected to hypoxia, and the expression of myocardin and AngII were evaluated. Different signal transduction pathway inhibitors were used to identify the pathway(s) responsible for myocardin expression. An EMSA (electrophoretic mobility-shift assay) was used to identify myocardin/SRF binding, and a luciferase assay was used to identify transcriptional activity of myocardin/SRF in neonatal cardiomyocytes. Both myocardin and AngII expression increased after hypoxia, with AngII appearing at an earlier time point than myocardin. Myocardin expression was stimulated by AngII and ERK (extracellular-signal-regulated kinase) phosphorylation, but was suppressed by an ARB (AngII type 1 receptor blocker), an ERK pathway inhibitor and myocardin siRNA (small interfering RNA). AngII increased both myocardin expression and transcription in neonatal cardiomyocytes. Binding of myocardin/SRF was identified using an EMSA, and a luciferase assay indicated the transcription of myocardin/SRF in neonatal cardiomyocytes. Increased BNP (B-type natriuretic peptide), MHC (myosin heavy chain) and [³H]proline incorporation into cardiomyocytes was identified after hypoxia with the presence of myocardin in hypertrophic cardiomyocytes. In conclusion, hypoxia in cardiomyocytes increased myocardin expression, which is mediated by the induction of AngII and the ERK pathway, to cause cardiomyocyte hypertrophy. Myocardial hypertrophy was identified as an increase in transcriptional activities, elevated hypertrophic and cardiomyocyte phenotype markers, and morphological hypertrophic changes in cardiomyocytes.

Linking actin dynamics and gene transcription to drive cellular motile functions

Numerous physiological and pathological stimuli promote the rearrangement of the actin cytoskeleton, thereby modulating cellular motile functions. Although it seems intuitively obvious that cell motility requires coordinated protein biosynthesis, until recently the linkage between cytoskeletal actin dynamics and correlated gene activities remained unknown. This knowledge gap was filled in part by the discovery that globular actin polymerization liberates myocardin-related transcription factor (MRTF) cofactors, thereby inducing the nuclear transcription factor serum response factor (SRF) to modulate the expression of genes encoding structural and regulatory effectors of actin dynamics. This insight stimulated research to better understand the actin-MRTF-SRF circuit and to identify alternative mechanisms that link cytoskeletal dynamics and genome activity.

Myocardial gene expression alterations in peripheral blood mononuclear cells of patients with idiopathic dilated cardiomyopathy

AIMS

To assess cardiac gene expression in peripheral blood cells of patients with idiopathic dilated cardiomyopathy (IDCM) and its relationship to echocardiographic left ventricular (LV) function.

METHODS AND RESULTS

A complete echocardiographic study and blood sampling were performed in 65 consecutive stable IDCM patients with LV ejection fraction (LVEF) 31.76 +/- 10.07% and chronic mild to moderate heart failure (NYHA functional class II to III) for > or =9 months. Blood samples from 19 healthy individuals were included for comparison. Transcript levels of myocardin, GATA4, alpha- and beta-myosin heavy chain (MHC), sarcoplasmic reticulum calcium ATPase 2 (SERCA2), and phospholamban were determined by quantitative real-time reverse transcription-polymerase chain reaction. Myocardin (24.88 +/- 4.93 vs. 3.98 +/- 1.12, P = 0.0048) and GATA4 (17.85 +/- 4.85 vs. 0.45 +/- 0.15, P = 0.0069 x 10(-5)) were upregulated in IDCM patients compared with controls, whereas SERCA2 (5.11 +/- 0.42 vs. 8.93 +/- 1.07, P = 0.001) was downregulated. In IDCM patients, myocardin (r = 0.279, P = 0.025), GATA4 (r = 0.314, P = 0.011), beta-MHC (r = 0.444, P=0.0002), and alpha-MHC (r = 0.272, P = 0.034) showed positive correlations, whereas SERCA2 (r = -0.264, P = 0.034) exhibited a negative correlation with LVEF. Patients with elevated LV filling pressures had lower myocardin (15.06 +/- 3.10 vs. 43.12 +/- 12.03, P = 0.048), GATA4 (8.96 +/- 2.17 vs. 34.38 +/- 12.60, P = 0.026), beta-MHC (10.59 +/- 4.05 vs. 16.43 +/- 4.91, P = 0.013), and alpha-MHC (0.27 +/- 0.08 vs. 0.79 +/- 0.20, P = 0.033) and higher SERCA2 (5.65 +/- 0.54 vs. 3.90 +/- 0.61, P = 0.037) levels. Patients with atrial fibrillation (AF) had higher SERCA2 levels compared with sinus rhythm patients (6.75 +/- 0.84 vs. 4.54 +/- 0.45, P = 0.017).

CONCLUSION

Our data indicate that cardiac gene expression alterations in peripheral blood cells of IDCM patients may reflect alterations in LV function, whereas the presence of AF may be associated with increased SERCA2 levels in these patients.

Identification of candidate genes potentially relevant to chamber-specific remodeling in postnatal ventricular myocardium

Molecular predisposition of postnatal ventricular myocardium to chamber-dependent (concentric or eccentric) remodeling remains largely elusive. To this end, we compared gene expression in the left (LV) versus right ventricle (RV) in newborn piglets, using a differential display reverse transcription-PCR (DDRT-PCR) technique. Out of more than 5600 DDRT-PCR bands, a total of 153 bands were identified as being differentially displayed. Of these, 96 bands were enriched in the LV, whereas the remaining 57 bands were predominant in the RV. The transcripts, displaying over twofold LV-RV expression differences, were sequenced and identified by BLAST comparison to known mRNA sequences. Among the genes, whose expression was not previously recognized as being chamber-dependent, we identified a small cohort of key regulators of muscle cell growth/proliferation (MAP3K7IP2, MSTN, PHB2, APOBEC3F) and gene expression (PTPLAD1, JMJD1C, CEP290), which may be relevant to the chamber-dependent predisposition of ventricular myocardium to respond differentially to pressure (LV) and volume (RV) overloads after birth. In addition, our data demonstrate chamber-dependent alterations in expression of as yet uncharacterized novel genes, which may also be suitable candidates for association studies in animal models of LV/RV hypertrophy.

Intron retention generates ANKRD1 splice variants that are co-regulated with the main transcript in normal and failing myocardium

The cardiac ankyrin repeat domain 1 protein (ANKRD1, also known as CARP) has been extensively characterized with regard to its proposed functions as a cardio-enriched transcriptional co-factor and stress-inducible myofibrillar protein. The present results show the occurrence of alternative splicing by intron retention events in the pig and human ankrd1 gene. In pig heart, ankrd1 is expressed as four alternatively spliced transcripts, three of which have non-excised introns: ankrd1-contained introns 6, 7 and 8 (i.e., ankrd1-i6,7,8), ankrd1-contained introns 7 and 8 (i.e., ankrd1-i7,8), and ankrd1 retained only intron 8 (i.e., ankrd1-i8). In the human heart, two orthologues of porcine intron-retaining ankrd1 variants (i.e., ankrd1-i8 and ankrd1-i7,8) are detected. We demonstrate that these newly-identified intron-retaining ankrd1 transcripts are functionally intact, efficiently translated into protein in vitro and exported to the cytoplasm in cardiomyocytes in vivo. In the piglet heart, both the intronless and intron-retaining ankrd1 mRNAs are co-expressed in a chamber-dependent manner being more abundant in the left as compared to the right myocardium. Our data further indicate co-upregulation of the ankrd1 spliced variants in myocardium in the porcine model of diastolic heart failure. Most significantly, we demonstrate that in vivo forced expression of recombinant intronless ankrd1 markedly increases the levels of intron-retaining ankrd1 variants (but not of the endogenous main transcript) in piglet myocardium, suggesting that ANKRD1 may positively regulate the expression of its own intron-containing RNAs in response to cardiac stress. Overall, our findings demonstrate that in cardiomyocytes ANKRD1 can exist in multiple isoforms which may contribute to the functional diversity of this factor in heart development and disease.

RhoA-ROCK signaling is involved in contraction-mediated inhibition of SERCA2a expression in cardiomyocytes

In neonatal ventricular cardiomyocytes (NVCM), decreased contractile activity stimulates sarco-endoplasmic reticulum Ca(2+)-ATPase2a (SERCA2a), analogous to reduced myocardial load in vivo. This study investigated in contracting NVCM the role of load-dependent RhoA-ROCK signaling in SERCA2a regulation. Contractile arrest of NVCM resulted in low peri-nuclear localized RhoA levels relative to contracting NVCM. In arrested NVCM, ROCK activity was decreased (59%) and paralleled a loss in F-actin levels. Y-27632-induced ROCK inhibition in contracting NVCM increased SERCA2a messenger RNA expression by 150%. This stimulation was transcriptional, as evident from transfections with the SERCA2a promoter. A reciprocal effect of Y-27632 treatment on the promoter activity of atrial natriuretic factor was observed. SERCA2a transcription was not altered by co-transfection of the RhoA-ROCK-dependent serum response factor (SRF) alone or in combination with myocardin. Furthermore, GATA4, another ROCK-dependent transcription factor, induced rather than repressed SERCA2a transcription. This study shows that contractile activity suppresses SERCA2a gene expression via RhoA-ROCK-dependent transcription modulation. This modulation is likely to be accomplished by a transcription factor other than SRF, myocardin, or GATA4.

Induction of microRNA-221 by platelet-derived growth factor signaling is critical for modulation of vascular smooth muscle phenotype

The platelet-derived growth factor (PDGF) signaling pathway is a critical regulator of animal development and homeostasis. Activation of the PDGF pathway leads to neointimal proliferative responses to artery injury; it promotes a switch of vascular smooth muscle cells (vSMC) to a less contractile phenotype by inhibiting the SMC-specific gene expression and increasing the rate of proliferation and migration. The molecular mechanism for these pleiotropic effects of PDGFs has not been fully described. Here, we identify the microRNA-221 (miR-221), a small noncoding RNA, as a modulator of the phenotypic change of vSMCs in response to PDGF signaling. We demonstrate that miR-221 is transcriptionally induced upon PDGF treatment in primary vSMCs, leading to down-regulation of the targets c-Kit and p27Kip1. Down-regulation of p27Kip1 by miR-221 is critical for PDGF-mediated induction of cell proliferation. Additionally, decreased c-Kit causes inhibition of SMC-specific contractile gene transcription by reducing the expression of Myocardin (Myocd), a potent SMC-specific nuclear coactivator. Our study demonstrates that PDGF signaling, by modulating the expression of miR-221, regulates two critical determinants of the vSMC phenotype; they are SMC gene expression and cell proliferation.

Induction of microRNA-221 by platelet-derived growth factor signaling is critical for modulation of vascular smooth muscle phenotype

The platelet-derived growth factor (PDGF) signaling pathway is a critical regulator of animal development and homeostasis. Activation of the PDGF pathway leads to neointimal proliferative responses to artery injury; it promotes a switch of vascular smooth muscle cells (vSMC) to a less contractile phenotype by inhibiting the SMC-specific gene expression and increasing the rate of proliferation and migration. The molecular mechanism for these pleiotropic effects of PDGFs has not been fully described. Here, we identify the microRNA-221 (miR-221), a small noncoding RNA, as a modulator of the phenotypic change of vSMCs in response to PDGF signaling. We demonstrate that miR-221 is transcriptionally induced upon PDGF treatment in primary vSMCs, leading to down-regulation of the targets c-Kit and p27Kip1. Down-regulation of p27Kip1 by miR-221 is critical for PDGF-mediated induction of cell proliferation. Additionally, decreased c-Kit causes inhibition of SMC-specific contractile gene transcription by reducing the expression of Myocardin (Myocd), a potent SMC-specific nuclear coactivator. Our study demonstrates that PDGF signaling, by modulating the expression of miR-221, regulates two critical determinants of the vSMC phenotype; they are SMC gene expression and cell proliferation.

Myocardin is sufficient for a smooth muscle-like contractile phenotype

BACKGROUND

Myocardin (Myocd) is a strong coactivator that binds the serum response factor (SRF) transcription factor over CArG elements embedded within smooth muscle cell (SMC) and cardiac muscle cyto-contractile genes. Here, we sought to ascertain whether Myocd-mediated gene expression confers a structural and physiological cardiac or SMC phenotype.

METHODS AND RESULTS

Adenoviral-mediated expression of Myocd in the BC(3)H1 cell line induces cardiac and SMC genes while suppressing both skeletal muscle markers and cell growth. Immunofluorescence microscopy shows that SRF and a SMC-like cyto-contractile apparatus are elevated with Myocd overexpression. A short hairpin RNA to Srf impairs BC(3)H1 cyto-architecture; however, cotransduction with Myocd results in complete restoration of the cyto-architecture. Electron microscopic studies demonstrate a SMC ultrastructural phenotype with no evidence for cardiac sarcomerogenesis. Biochemical and time-lapsed videomicroscopy assays reveal clear evidence for Myocd-induced SMC-like contraction.

CONCLUSIONS

Myocd is sufficient for the establishment of a SMC-like contractile phenotype.

Altered expression of early cardiac marker genes in circulating cells of patients with hypertrophic cardiomyopathy

BACKGROUND

Early cardiac marker genes, such as cardiac-specific homeobox (Csx/Nkx2.5), myocardin, homeodomain only protein, GATA4, and myocyte enhancer factor 2C, are thought to participate in cardiomyocyte differentiation and to contribute to heart hypertrophy in animal models. In this study, we investigated whether the expression of early cardiac genes is altered in the peripheral blood of patients with hypertrophic cardiomyopathy.

METHODS

Peripheral blood mononuclear cells were isolated from 30 consecutive hypertrophic cardiomyopathy patients and 20 healthy controls, and gene expression was determined by quantitative real-time reverse transcription-polymerase chain reaction.

RESULTS

Csx/Nkx2.5, myocardin, and GATA4 expressions were significantly higher in hypertrophic cardiomyopathy patients by 5.14+/-0.89 (P<.001), 1.65+/-0.21 (P<.05), and 2.04+/-0.41 (P<.04) times, respectively, while homeodomain only protein showed a fourfold decrease in expression (P<.02) compared to controls. In addition, expression of the differentiation-specific marker genes beta-myosin heavy chain and smooth muscle myosin heavy chain was significantly higher in hypertrophic cardiomyopathy patients by 3.72+/-0.82 (P<.02) and 2.57+/-0.72 (P<.05) times, respectively, compared to controls. Myocyte enhancer factor 2C expression was not different between patients and controls. Furthermore, increased expression of GATA4, myocardin, and beta-myosin heavy chain positively correlated with increased left ventricular mass.

CONCLUSIONS

In conclusion, we found altered expressions of early cardiac marker genes and differentiation-specific marker genes in peripheral blood mononuclear cells of hypertrophic cardiomyopathy patients compared to control individuals, possibly reflecting changes in response to disease.

Myocardin-related transcription factors: critical coactivators regulating cardiovascular development and adaptation

The association of transcriptional coactivators with DNA-binding proteins provides an efficient mechanism to expand and modulate genetic information encoded within the genome. Myocardin-related transcription factors (MRTFs), including myocardin, MRTF-A/MKL1/MAL, and MRTF-B/MKL2, comprise a family of related transcriptional coactivators that physically associate with the MADS box transcription factor, serum response factor, and synergistically activate transcription. MRTFs transduce cytoskeletal signals to the nucleus, activating a subset of serum response factor-dependent genes promoting myogenic differentiation and cytoskeletal organization. MRTFs are multifunctional proteins that share evolutionarily conserved domains required for actin-binding, homo- and heterodimerization, high-order chromatin organization, and transcriptional activation. Mice harboring loss-of-function mutations in myocardin, MRTF-A, and MRTF-B, respectively, display distinct phenotypes, including cell autonomous defects in vascular smooth muscle cell and myoepithelial cell differentiation and function. This article reviews the molecular basis of MRTF function with particular focus on the role MRTFs play in regulating cardiovascular patterning, vascular smooth muscle cell and cardiomyocyte differentiation and in the pathogenesis of congenital heart disease and vascular proliferative syndromes.

Transdifferentiation of pulmonary arteriolar endothelial cells into smooth muscle-like cells regulated by myocardin involved in hypoxia-induced pulmonary vascular remodelling

Myocardin gene has been identified as a master regulator of smooth muscle cell differentiation. Smooth muscle cells play a critical role in the pathogenesis of hypoxia-induced pulmonary hypertension (PH) and pulmonary vascular remodelling (PVR). The purpose of this study was to investigate the change of myocardin gene expression in the pulmonary vessels of hypoxia-induced PH affected by Sildenafil treatment and the involvement of endothelial cells transdifferentiation into smooth muscle cells in the process of hypoxia-induced PH and PVR. Myocardin and relative markers were investigated in animal models and cultured endothelial cells. Mean pulmonary artery pressure (mPAP) was measured. Immunohistochemistry and immunofluorescence were used to show the expression of smooth muscle alpha-actin (SMA), in situ hybridization (ISH) and reverse transcription polymerase chain reaction (RT-PCR) were performed respectively to detect the myocardin and SMA expression at mRNA levels. Small interfering RNA (siRNA) induced suppression of myocardin in cultured cells. We confirmed that hypoxia induced the PH and PVR in rats. Sildenafil could attenuate the hypoxia-induced PH. We found that myocardin mRNA expression is upregulated significantly in the hypoxic pulmonary vessels and cultured cells but downregulated in PH with Sildenafil treatment. The porcine pulmonary artery endothelial cells (PAECs) transdifferentiate into smooth muscle-like cells in hypoxic culture while the transdifferentiation did not occur when SiRNA of myocardin was applied. Our results suggest that myocardin gene, as a marker of smooth muscle cell differentiation, was expressed in the pulmonary vessels in hypoxia-induced PH rats, which could be downregulated by Sildenafil treatment, as well as in hypoxic cultured endothelial cells. Hypoxia induced the transdifferentiation of endothelial cells of vessels into smooth muscle-like cells which was regulated by myocardin.

Myocardin is a direct transcriptional target of Mef2, Tead and Foxo proteins during cardiovascular development

Myocardin is a transcriptional co-activator of serum response factor (Srf), which is a key regulator of the expression of smooth and cardiac muscle genes. Consistent with its role in regulating cardiovascular development, myocardin is the earliest known marker specific to both the cardiac and smooth muscle lineages during embryogenesis. To understand how the expression of this early transcriptional regulator is initiated and maintained, we scanned 90 kb of genomic DNA encompassing the myocardin gene for cis-regulatory elements capable of directing myocardin transcription in cardiac and smooth muscle lineages in vivo. Here, we describe an enhancer that controls cardiovascular expression of the mouse myocardin gene during mouse embryogenesis and adulthood. Activity of this enhancer in the heart and vascular system requires the combined actions of the Mef2 and Foxo transcription factors. In addition, the Tead transcription factor is required specifically for enhancer activation in neural-crest-derived smooth muscle cells and dorsal aorta. Notably, myocardin also regulates its own enhancer, but in contrast to the majority of myocardin target genes, which are dependent on Srf, myocardin acts through Mef2 to control its enhancer. These findings reveal an Srf-independent mechanism for smooth and cardiac muscle-restricted transcription and provide insight into the regulatory mechanisms responsible for establishing the smooth and cardiac muscle phenotypes during development.

The myocardin family of transcriptional coactivators: versatile regulators of cell growth, migration, and myogenesis

The association of transcriptional coactivators with sequence-specific DNA-binding proteins provides versatility and specificity to gene regulation and expands the regulatory potential of individual cis-regulatory DNA sequences. Members of the myocardin family of coactivators activate genes involved in cell proliferation, migration, and myogenesis by associating with serum response factor (SRF). The partnership of myocardin family members and SRF also controls genes encoding components of the actin cytoskeleton and confers responsiveness to extracellular growth signals and intracellular changes in the cytoskeleton, thereby creating a transcriptional-cytoskeletal regulatory circuit. These functions are reflected in defects in smooth muscle differentiation and function in mice with mutations in myocardin family members. This article reviews the functions and mechanisms of action of the myocardin family of coactivators and the physiological significance of transcriptional coactivation in the context of signal-dependent and cell-type-specific gene regulation.

Differential atrial versus ventricular ANKRD1 gene expression is oppositely regulated at diastolic heart failure

Diastolic heart failure (DHF) was produced in 6-day-old piglets by intravenous administration of Doxorubicin, and ANKRD1 protein and mRNA levels were determined in atrial (A) and ventricular (V) chambers of failing vs control hearts. In controls, ANKRD1 showed a left-right (L-R) asymmetric distribution with protein levels 2-fold higher in the LA as compared to the RA, and 8-fold higher in the LV than the RV. In failing hearts, ANKRD1 levels were augmented about 2-fold in each ventricle but equally reduced in both atria as compared to controls. ANKRD1 downregulation in atria is discussed as a process associated with advanced DHF.

Myocardin induces cardiomyocyte hypertrophy

In response to stress signals, postnatal cardiomyocytes undergo hypertrophic growth accompanied by activation of a fetal gene program, assembly of sarcomeres, and cellular enlargement. We show that hypertrophic signals stimulate the expression and transcriptional activity of myocardin, a cardiac and smooth muscle-specific coactivator of serum response factor (SRF). Consistent with a role for myocardin as a transducer of hypertrophic signals, forced expression of myocardin in cardiomyocytes is sufficient to substitute for hypertrophic signals and induce cardiomyocyte hypertrophy and the fetal cardiac gene program. Conversely, a dominant-negative mutant form of myocardin, which retains the ability to associate with SRF but is defective in transcriptional activation, blocks cardiomyocyte hypertrophy induced by hypertrophic agonists such as phenylephrine and leukemia inhibitory factor. Myocardin-dependent hypertrophy can also be partially repressed by histone deacetylase 5, a transcriptional repressor of myocardin. These findings identify myocardin as a nuclear effector of hypertrophic signaling pathways that couples stress signals to a transcriptional program for postnatal cardiac growth and remodeling.

Control of cardiac growth by histone acetylation/deacetylation

Histones control gene expression by modulating the structure of chromatin and the accessibility of regulatory DNA sequences to transcriptional activators and repressors. Posttranslational modifications of histones have been proposed to establish a "code" that determines patterns of cellular gene expression. Acetylation of histones by histone acetyltransferases stimulates gene expression by relaxing chromatin structure, allowing access of transcription factors to DNA, whereas deacetylation of histones by histone deacetylases promotes chromatin condensation and transcriptional repression. Recent studies demonstrate histone acetylation/deacetylation to be a nodal point for the control of cardiac growth and gene expression in response to acute and chronic stress stimuli. These findings suggest novel strategies for "transcriptional therapies" to control cardiac gene expression and function. Manipulation of histone modifying enzymes and the signaling pathways that impinge on them in the settings of pathological cardiac growth, remodeling, and heart failure represents an auspicious therapeutic approach.

Control of smooth muscle development by the myocardin family of transcriptional coactivators

Differentiation of smooth muscle cells (SMCs) is accompanied by the transcriptional activation of an array of muscle-specific genes that confer the unique contractile and physiologic properties of this muscle cell type. The majority of smooth muscle genes are controlled by serum response factor (SRF), a widely expressed transcription factor that also regulates genes involved in cell proliferation. Myocardin and myocardin-related transcription factors (MRTFs) interact with SRF and potently stimulate SRF-dependent transcription. Gain- and loss-of-function experiments have shown myocardin to be sufficient and necessary for SMC differentiation. SMCs are highly plastic and can switch between differentiated and proliferative states in response to extracellular cues. Suppression of SMC differentiation by growth factor signaling is mediated, at least in part, by the displacement of myocardin from SRF by growth factor-dependent ternary complex factors. The association of SRF with myocardin and MRTFs provides a molecular basis for the activation of SMC genes by SRF and the responsiveness of the smooth muscle differentiation program to growth factor signaling.