MicroRNA-208a is a regulator of cardiac hypertrophy and conduction in mice

Emerging Roles for MicroRNAs in Perioperative Medicine

MicroRNAs (miRNAs) are small, non-protein-coding, single-stranded RNAs. They function as posttranscriptional regulators of gene expression by interacting with target mRNAs. This process prevents translation of target mRNAs into a functional protein. miRNAs are considered to be functionally involved in virtually all physiologic processes, including differentiation and proliferation, metabolism, hemostasis, apoptosis, and inflammation. Many of these functions have important implications for anesthesiology and critical care medicine. Studies indicate that miRNA expression levels can be used to predict the risk for eminent organ injury or sepsis. Pharmacologic approaches targeting miRNAs for the treatment of human diseases are currently being tested in clinical trials. The present review highlights the important biological functions of miRNAs and their usefulness as perioperative biomarkers and discusses the pharmacologic approaches that modulate miRNA functions for disease treatment. In addition, the authors discuss the pharmacologic interactions of miRNAs with currently used anesthetics and their potential to impact anesthetic toxicity and side effects.

Nutrition has a pervasive impact on cardiac microRNA expression in isogenic mice

The complex interaction between obesity, Western-style diets, and cardiovascular disease is of increasing interest, with a growing number of children being born to obese parents with poor lifestyle choices. These offspring have themselves an increased susceptibility to obesity and subsequent cardiovascular disease in adult life, which may be 'programmed' by their intrauterine environment. Cardiac microRNAs (miRNAs) are affected by multiple disease states, and have also been shown to be capable of exerting a hormone-like control on whole body metabolism. Here we sought to determine the effect of prenatal exposure to maternal obesity and/or postnatal exposure to a Western diet on miRNA expression in the heart. Unbiased small RNA sequencing was carried out on cardiac tissue from young adult mice born to lean or obese mothers; offspring were weaned onto either a low-fat control diet or a high-fat Western-style diet. We found 8 cardiac miRNAs that were significantly altered in response to maternal obesity, but only when the offspring were challenged postnatally with the Western diet. In contrast, postnatal exposure to the diet alone induced significant changes to the expression of a much larger number of miRNAs (33 in offspring of lean and 46 in offspring of obese). Many of the affected miRNAs have previously been implicated in various cardiac pathologies. The pervasive cardiac miRNA changes induced by a Western diet suggest that an individual's lifestyle choices outweigh the impact of any programming effects by maternal obesity on miRNA-related cardiac health.

Functions of miRNAs during Mammalian Heart Development

MicroRNAs (miRNAs) play essential roles during mammalian heart development and have emerged as attractive therapeutic targets for cardiovascular diseases. The mammalian embryonic heart is mainly derived from four major cell types during development. These include cardiomyocytes, endocardial cells, epicardial cells, and neural crest cells. Recent data have identified various miRNAs as critical regulators of the proper differentiation, proliferation, and survival of these cell types. In this review, we briefly introduce the contemporary understanding of mammalian cardiac development. We also focus on recent developments in the field of cardiac miRNAs and their functions during the development of different cell types.

Common miR-590 Variant rs6971711 Present Only in African Americans Reduces miR-590 Biogenesis

MicroRNAs (miRNAs) are recognized as important regulators of cardiac development, hypertrophy and fibrosis. Recent studies have demonstrated that genetic variations which cause alterations in miRNA:target interactions can lead to disease. We hypothesized that genetic variations in miRNAs that regulate cardiac hypertrophy/fibrosis might be involved in generation of the cardiac phenotype in patients diagnosed with hypertrophic cardiomyopathy (HCM). To investigate this question, we Sanger sequenced 18 miRNA genes previously implicated in myocyte hypertrophy/fibrosis and apoptosis, using genomic DNA isolated from the leukocytes of 199 HCM patients. We identified a single nucleotide polymorphism (rs6971711, C57T SNP) at the 17th position of mature miR-590-3p (= 57th position of pre-miR-590) that is common in individuals of African ancestry. SNP frequency was higher in African American HCM patients (n = 55) than ethnically-matched controls (n = 100), but the difference was not statistically significant (8.2% vs. 6.5%; p = 0.5). Using a cell culture system, we discovered that presence of this SNP resulted in markedly lower levels of mature miR-590-5p (39 ± 16%, p<0.003) and miR-590-3p (20 ± 2%, p<0.003), when compared with wild-type (WT) miR-590, without affecting levels of pri-miR-590 and pre-miR-590. Consistent with this finding, the SNP resulted in reduced target suppression when compared to WT miR-590 (71% suppression by WT vs 60% suppression by SNP, p<0.03). Since miR-590 can regulate TGF-β, Activin A and Akt signaling, SNP-induced reduction in miR-590 biogenesis could influence cardiac phenotype by de-repression of these signaling pathways. Since the SNP is only present in African Americans, population studies in this patient population would be valuable to investigate effects of this SNP on myocyte function and cardiac physiology.

Overview of MicroRNAs in Cardiac Hypertrophy, Fibrosis, and Apoptosis

MicroRNAs (miRNAs) are non-coding RNAs that play essential roles in modulating the gene expression in almost all biological events. In the past decade, the involvement of miRNAs in various cardiovascular disorders has been explored in numerous in vitro and in vivo studies. In this paper, studies focused upon the discovery of miRNAs, their target genes, and functionality are reviewed. The selected miRNAs discussed herein have regulatory effects on target gene expression as demonstrated by miRNA/3′ end untranslated region (3′UTR) interaction assay and/or gain/loss-of-function approaches. The listed miRNA entities are categorized according to the biological relevance of their target genes in relation to three cardiovascular pathologies, namely cardiac hypertrophy, fibrosis, and apoptosis. Furthermore, comparison across 86 studies identified several candidate miRNAs that might be of particular importance in the ontogenesis of cardiovascular diseases as they modulate the expression of clusters of target genes involved in the progression of multiple adverse cardiovascular events. This review illustrates the involvement of miRNAs in diverse biological signaling pathways and provides an overview of current understanding of, and progress of research into, of the roles of miRNAs in cardiovascular health and disease.

Autophagy inhibition of hsa-miR-19a-3p/19b-3p by targeting TGF-β R II during TGF-β1-induced fibrogenesis in human cardiac fibroblasts

Transforming growth factor-β1 (TGF-β1) plays an important role on fibrogenesis in heart disease. MicroRNAs have exhibited as crucial regulators of cardiac homeostasis and remodeling in various heart diseases. MiR-19a-3p/19b-3p expresses with low levels in the plasma of heart failure patients. The purpose of our study is to determine the role of MiR-19a-3p/19b-3p in regulating autophagy-mediated fibrosis of human cardiac fibroblasts. We elucidate our hypothesis in clinical samples and human cardiac fibroblasts (HCF) to provide valuable basic information. TGF-β1 promotes collagen I α2 and fibronectin synthesis in HCF and that is paralleled by autophagic activation in these cells. Pharmacological inhibition of autophagy by 3-methyladenine decreases the fibrotic response, while autophagy induction of rapamycin increases the response. BECN1 knockdown and Atg5 over-expression either inhibits or enhances the fibrotic effect of TGF-β1 in experimental HCF. Furthermore, miR-19a-3p/19b-3p mimics inhibit epithelial mesenchymal transition (EMT) and extracellular matrix (ECM) prodution and invasion of HCF. Functional studies suggest that miR-19a-3p/19b-3p inhibits autophagy of HCF through targeting TGF-β R II mRNA. Moreover, enhancement of autophagy rescues inhibition effect of miR-19a-3p/19b-3p on Smad 2 and Akt phosphorylation through TGF-β R II signaling. Our study uncovers a novel mechanism that miR-19a-3p/19b-3p inhibits autophagy-mediated fibrogenesis by targeting TGF-β R II.

Analysis of microRNA expression during the torpor-arousal cycle of a mammalian hibernator, the 13-lined ground squirrel

Hibernation is a highly regulated stress response that is utilized by some mammals to survive harsh winter conditions and involves a complex metabolic reprogramming at the cellular level to maintain tissue protections at low temperature. In this study, we profiled the expression of 117 conserved microRNAs in the heart, muscle, and liver of the 13-lined ground squirrel (Ictidomys tridecemlineatus) across four stages of the torpor-arousal cycle (euthermia, early torpor, late torpor, and interbout arousal) by real-time PCR. We found significant differential regulation of numerous microRNAs that were both tissue specific and torpor stage specific. Among the most significant regulated microRNAs was miR-208b, a positive regulator of muscle development that was found to be upregulated by fivefold in the heart during late torpor (13-fold during arousal), while decreased by 3.7-fold in the skeletal muscle, implicating a potential regulatory role in the development of cardiac hypertrophy and skeletal muscle atrophy in the ground squirrels during torpor. In addition, the insulin resistance marker miR-181a was upregulated by 5.7-fold in the liver during early torpor, which supports previous suggestions of hyperinsulinemia in hibernators during the early stages of the hibernation cycle. Although microRNA expression profiles were largely unique between the three tissues, GO annotation analysis revealed that the putative targets of upregulated microRNAs tend to enrich toward suppression of progrowth-related processes in all three tissues. These findings implicate microRNAs in the regulation of both tissue-specific processes and general suppression of cell growth during hibernation.

MicroRNA and Heart Failure

Heart failure (HF) imposes significant economic and public health burdens upon modern society. It is known that disturbances in neurohormonal status play an important role in the pathogenesis of HF. Therapeutics that antagonize selected neurohormonal pathways, specifically the renin-angiotensin-aldosterone and sympathetic nervous systems, have significantly improved patient outcomes in HF. Nevertheless, mortality remains high with about 50% of HF patients dying within five years of diagnosis thus mandating ongoing efforts to improve HF management. The discovery of short noncoding microRNAs (miRNAs) and our increasing understanding of their functions, has presented potential therapeutic applications in complex diseases, including HF. Results from several genome-wide miRNA studies have identified miRNAs differentially expressed in HF cohorts suggesting their possible involvement in the pathogenesis of HF and their potential as both biomarkers and as therapeutic targets. Unravelling the functional relevance of miRNAs within pathogenic pathways is a major challenge in cardiovascular research. In this article, we provide an overview of the role of miRNAs in the cardiovascular system. We highlight several HF-related miRNAs reported from selected cohorts and review their putative roles in neurohormonal signaling.

Cardiac-specific miRNA in cardiogenesis, heart function, and cardiac pathology (with focus on myocardial infarction)

Cardiac miRNAs (miR-1, miR133a, miR-208a/b, and miR-499) are abundantly expressed in the myocardium. They play a central role in cardiogenesis, heart function and pathology. While miR-1 and miR-133a predominantly control early stages of cardiogenesis supporting commitment of cardiac-specific muscle lineage from embryonic stem cells and mesodermal precursors, miR-208 and miR-499 are involved in the late cardiogenic stages mediating differentiation of cardioblasts to cardiomyocytes and fast/slow muscle fiber specification. In the heart, miR-1/133a control cardiac conductance and automaticity by regulating all phases of the cardiac action potential. miR-208/499 located in introns of the heavy chain myosin genes regulate expression of sarcomeric contractile proteins. In cardiac pathology including myocardial infarction (MI), expression of cardiac miRNAs is markedly altered that leads to deleterious effects associated with heart wounding, arrhythmia, increased apoptosis, fibrosis, hypertrophy, and tissue remodeling. In acute MI, circulating levels of cardiac miRNAs are significantly elevated making them to be a promising diagnostic marker for early diagnosis of acute MI. Great cardiospecific capacity of these miRNAs is very helpful for enhancing regenerative properties and survival of stem cell and cardiac progenitor transplants and for reprogramming of mature non-cardiac cells to cardiomyocytes.

Integrative Tissue-Specific Functional Annotations in the Human Genome Provide Novel Insights on Many Complex Traits and Improve Signal Prioritization in Genome Wide Association Studies

Extensive efforts have been made to understand genomic function through both experimental and computational approaches, yet proper annotation still remains challenging, especially in non-coding regions. In this manuscript, we introduce GenoSkyline, an unsupervised learning framework to predict tissue-specific functional regions through integrating high-throughput epigenetic annotations. GenoSkyline successfully identified a variety of non-coding regulatory machinery including enhancers, regulatory miRNA, and hypomethylated transposable elements in extensive case studies. Integrative analysis of GenoSkyline annotations and results from genome-wide association studies (GWAS) led to novel biological insights on the etiologies of a number of human complex traits. We also explored using tissue-specific functional annotations to prioritize GWAS signals and predict relevant tissue types for each risk locus. Brain and blood-specific annotations led to better prioritization performance for schizophrenia than standard GWAS p-values and non-tissue-specific annotations. As for coronary artery disease, heart-specific functional regions was highly enriched of GWAS signals, but previously identified risk loci were found to be most functional in other tissues, suggesting a substantial proportion of still undetected heart-related loci. In summary, GenoSkyline annotations can guide genetic studies at multiple resolutions and provide valuable insights in understanding complex diseases. GenoSkyline is available at http://genocanyon.med.yale.edu/GenoSkyline.

MicroRNA-Detargeted Mengovirus for Oncolytic Virotherapy

Mengovirus, a member of the Picornaviridae family, has a broad cell tropism and can cause encephalitis and myocarditis in multiple mammalian species. Attenuation has been achieved by shortening the polycytidine tract in the 5′ noncoding region (NCR). A poly(C)-truncated strain of mengovirus, vMC₂₄, resulted in significant tumor regression in immunocompetent BALB/c mice bearing syngeneic MPC-11 plasmacytomas, but the associated toxicities were unacceptable. To enhance its safety profile, microRNA target sequences complementary to miR-124 or miR-125 (enriched in nervous tissue), miR-133 and miR-208 (enriched in cardiac tissue), or miR-142 (control; enriched in hematopoietic tissues) were inserted into the vMC₂₄ NCRs. The microRNA-detargeted viruses showed reduced replication and cell killing specifically in cells expressing the cognate microRNAs, but certain insertions additionally were associated with nonspecific suppression of viral fitness in vivo. In vivo toxicity testing confirmed that miR-124 targets within the 5′ NCR suppressed virus replication in the central nervous system while miR-133 and miR-208 targets in the 3′ NCR suppressed viral replication in cardiac tissue. A dual-detargeted virus named vMC₂₄-NC, with miR-124 targets in the 5′ NCR and miR-133 plus miR-208 targets in the 3′ NCR, showed the suppression of replication in both nervous and cardiac tissues but retained full oncolytic potency when administered by intratumoral (10⁶ 50% tissue culture infectious doses [TCID₅₀]) or intravenous (10⁷ to 10⁸ TCID₅₀) injection into BALB/c mice bearing MPC-11 plasmacytomas. Overall survival of vMC₂₄-NC-treated tumor-bearing mice was significantly improved compared to that of nontreated mice. MicroRNA-detargeted mengoviruses offer a promising oncolytic virotherapy platform that merits further development for clinical translation.

IMPORTANCE The clinical potential of oncolytic virotherapy for cancer treatment has been well demonstrated, justifying the continued development of novel oncolytic viruses with enhanced potency. Here, we introduce mengovirus as a novel oncolytic agent. Mengovirus is appealing as an oncolytic virotherapy platform because of its small size, simple genome structure, rapid replication cycle, and broad cell/species tropism. However, mengovirus can cause encephalomyelitis and myocarditis. It can be partially attenuated by shortening the poly(C) tract in the 5′ NCR but remains capable of damaging cardiac and nervous tissue. Here, we further enhanced the safety profile of a poly(C)-truncated mengovirus by incorporating muscle- and neuron-specific microRNA target sequences into the viral genome. This dual-detargeted virus has reduced pathogenesis but retained potent oncolytic activity. Our data show that microRNA targeting can be used to further increase the safety of an attenuated mengovirus, providing a basis for its development as an oncolytic platform.

MicroRNA-34a and Impaired FGF19/21 Signaling in Obesity

The obesity epidemic and the urgent need for effective and safe drugs to treat obesity-related diseases have greatly increased research interest in the metabolic hormones, fibroblast growth factor-19 (FGF19, FGF15 in mice), and FGF21. FGF19 and FGF21 function as endocrine hormones that play key roles in energy metabolism and counteract obesity. Importantly, in obese humans and lab animals, circulating FGF19 and FGF21 levels are elevated, and metabolic actions of these hormones are impaired but the underlying mechanisms remained unknown. Recent microRNA (miR) studies have revealed that aberrantly elevated miR-34a in obesity directly targets β-Klotho, the obligate coreceptor for both FGF19 and FGF21, and attenuates metabolic signaling of these hormones. In this review, we will discuss recent findings in the miR and FGF19/21 fields, emphasizing the novel function of obesity-associated miR-34a in attenuation of FGF19/21 metabolic actions, and further discuss miRs, including miR-34a, as potential drug targets for obesity-related diseases.

Epigenetic and lncRNA regulation of cardiac pathophysiology

Our developmental studies provide an insight into the pathogenesis of heart failure in adults. These studies reveal a mechanistic link between fetal cardiomyocytes and pathologically stressed adult cardiomyocytes at the level of chromatin regulation. In embryos, chromatin-regulating factors within the cardiomyocytes respond to developmental signals to program cardiac gene expression to promote cell proliferation and inhibit premature cell differentiation. In the neonatal period, the activity of these developmental chromatin regulators is quickly turned off in cardiomyocytes, coinciding with the cessation of cell proliferation and advance in cell differentiation toward adult maturity. When the mature hearts are pathologically stressed, those chromatin regulators essential for cardiomyocyte development in embryos are reactivated, triggering gene reprogramming to a fetal-like state and pathological cardiac hypertrophy. Furthermore, in the study of chromatin regulation and cardiac gene expression, we identified a long noncoding RNA that interacts with chromatin remodeling factor to regulate the cardiac response to environmental changes. This article is part of a Special Issue entitled: Cardiomyocyte Biology: Integration of Developmental and Environmental Cues in the Heart edited by Marcus Schaub and Hughes Abriel.

MicroRNA deep sequencing reveals chamber-specific miR-208 family expression patterns in the human heart

BACKGROUND

Heart chamber-specific mRNA expression patterns have been extensively studied, and dynamic changes have been reported in many cardiovascular diseases. MicroRNAs (miRNAs) are also important regulators of normal cardiac development and functions that generally suppress gene expression at the posttranscriptional level. Recent focus has been placed on circulating miRNAs as potential biomarkers for cardiac disorders. However, miRNA expression levels in human normal hearts have not been thoroughly studied, and chamber-specific miRNA expression signatures in particular remain unclear.

METHODS AND RESULTS

We performed miRNA deep sequencing on human paired left atria (LA) and ventricles (LV) under normal physiologic conditions. Among 438 miRNAs, miR-1 was the most abundant in both chambers, representing 21% of the miRNAs in LA and 26% in LV. A total of 25 miRNAs were differentially expressed between LA and LV; 14 were upregulated in LA, and 11 were highly expressed in LV. Notably, the miR-208 family in particular showed prominent chamber specificity; miR-208a-3p and miR-208a-5p were abundant in LA, whereas miR-208b-3p and miR-208b-5p were preferentially expressed in LV. Subsequent real-time polymerase chain reaction analysis validated the predominant expression of miR-208a in LA and miR-208b in LV.

CONCLUSIONS

Human atrial and ventricular tissues display characteristic miRNA expression signatures under physiological conditions. Notably, miR-208a and miR-208b show significant chamber-specificity as do their host genes, α-MHC and β-MHC, which are mainly expressed in the atria and ventricles, respectively. These findings might also serve to enhance our understanding of cardiac miRNAs and various heart diseases.

Micromanaging cardiac regeneration: Targeted delivery of microRNAs for cardiac repair and regeneration

The loss of cardiomyocytes during injury and disease can result in heart failure and sudden death, while the adult heart has a limited capacity for endogenous regeneration and repair. Current stem cell-based regenerative medicine approaches modestly improve cardiomyocyte survival, but offer neglectable cardiomyogenesis. This has prompted the need for methodological developments that crease de novo cardiomyocytes. Current insights in cardiac development on the processes and regulatory mechanisms in embryonic cardiomyocyte differentiation provide a basis to therapeutically induce these pathways to generate new cardiomyocytes. Here, we discuss the current knowledge on embryonic cardiomyocyte differentiation and the implementation of this knowledge in state-of-the-art protocols to the direct reprogramming of cardiac fibroblasts into de novo cardiomyocytes in vitro and in vivo with an emphasis on microRNA-mediated reprogramming. Additionally, we discuss current advances on state-of-the-art targeted drug delivery systems that can be employed to deliver these microRNAs to the damaged cardiac tissue. Together, the advances in our understanding of cardiac development, recent advances in microRNA-based therapeutics, and innovative drug delivery systems, highlight exciting opportunities for effective therapies for myocardial infarction and heart failure.

MicroRNA Signature and Cardiovascular Dysfunction

The worldwide increase in the prevalence of obesity and type 2 diabetes and the associated elevated risk of cardiovascular disease (CVD) has emphasized the need to seek new therapeutic targets to offset the negative impact on human health outcomes. In this regards, microRNAs (miRNAs), a class of small noncoding RNAs that mediate posttranscriptional gene silencing, have received considerable interest. miRNAs repress gene expression by their ability to pair with target sequences in the 3' untranslated region of the messenger RNA. miRNAs play a crucial role in the biogenesis and function of the cardiovascular system and are implicated as dynamic regulators of cardiac and vascular signaling and pathophysiology. Numerous miRNAs have been identified as novel biomarkers and potential therapeutic targets for CVD. In this review, we discuss the contribution of miRNAs to the regulation of CVD, their role in macrovascular/microvascular (dys)function, their potential as important biomarkers for the early detection of CVD, and, finally, as therapeutic targets.

Exploiting the hypoxia sensitive non-coding genome for organ-specific physiologic reprogramming

In this review we highlight the role of non-coding RNAs in the development and progression of cardiac pathology and explore the possibility of disease-associated RNAs serving as targets for cardiac-directed therapeutics. Contextually, we focus on the role of stress-induced hypoxia as a driver of disease development and progression through activation of hypoxia inducible factor 1α (HIF1α) and explore mechanisms underlying HIFα function as an enforcer of cardiac pathology through direct transcriptional coupling with the non-coding transcriptome. In the interest of clarity, we will confine our analysis to cardiac pathology and focus on three defining features of the diseased state, namely metabolic, growth and functional reprogramming. It is the aim of this review to explore possible mechanisms through which HIF1α regulation of the non-coding transcriptome connects to spatiotemporal control of gene expression to drive establishment of the diseased state, and to propose strategies for the exploitation of these unique RNAs as targets for clinical therapy. This article is part of a Special Issue entitled: Cardiomyocyte Biology: Integration of Developmental and Environmental Cues in the Heart edited by Marcus Schaub and Hughes Abriel.

Role of the Thyroid System in the Dynamic Complex Network of Cardioprotection

Cardioprotection is a common goal of new therapeutic strategies in patients with coronary artery disease and/or left ventricular dysfunction. Myocardial damage following ischaemia/reperfusion injury lead to left ventricular adverse remodelling through many mechanisms arising from different cell types in different myocardial districts, namely the border and remote zone. Cardioprotection must face this complex, dynamic network of cooperating units. In this scenario, thyroid hormones can represent an effective therapeutic strategy due to the numerous actions and regulating mechanisms carried out at the level of the myocytes, interstitium and the vasculature, as well as to the activation of different pro-survival intracellular pathways involved in cardioprotection.

MicroRNA 214 Is a Potential Regulator of Thyroid Hormone Levels in the Mouse Heart Following Myocardial Infarction, by Targeting the Thyroid-Hormone-Inactivating Enzyme Deiodinase Type III

Cardiac thyroid-hormone signaling is a critical determinant of cellular metabolism and function in health and disease. A local hypothyroid condition within the failing heart in rodents has been associated with the re-expression of the fetally expressed thyroid-hormone-inactivating enzyme deiodinase type III (Dio3). While this enzyme emerges as a common denominator in the development of heart failure, the mechanism underlying its regulation remains largely unclear. In the present study, we investigated the involvement of microRNAs (miRNAs) in the regulation of Dio3 mRNA expression in the remodeling left ventricle (LV) of the mouse heart following myocardial infarction (MI). In silico analysis indicated that of the miRNAs that are differentially expressed in the post-MI heart, miR-214 has the highest potential to target Dio3 mRNA. In accordance, a luciferase reporter assay, including the full-length 3'UTR of mouse Dio3 mRNA, showed a 30% suppression of luciferase activity by miR-214. In the post-MI mouse heart, miR-214 and Dio3 protein were shown to be co-expressed in cardiomyocytes, while time-course analysis revealed that Dio3 mRNA expression precedes miR-214 expression in the post-MI LV. This suggests that a Dio3-induced decrease of T3 levels is involved in the induction of miR-214, which was supported by the finding that cardiac miR-214 expression is down regulated by T3 in mice. In vitro analysis of human DIO3 mRNA furthermore showed that miR-214 is able to suppress both mRNA and protein expression. Dio3 mRNA is a target of miR-214 and the Dio3-dependent stimulation of miR-214 expression in post-MI cardiomyocytes supports the involvement of a negative feedback mechanism regulating Dio3 expression.

MicroRNA Expression Signature Is Altered in the Cardiac Remodeling Induced by High Fat Diets

Recent studies have revealed the involvement of microRNAs (miRNAs) in the control of cardiac hypertrophy and myocardial function. In addition, several reports have demonstrated that high fat (HF) diet induces cardiac hypertrophy and remodeling. In the current study, we investigated the effect of diets containing different percentages of fat on the cardiac miRNA expression signature. To address this question, male C57Bl/6 mice were fed with a low fat (LF) diet or two HF diets, containing 45 kcal% fat (HF45%) and 60 kcal% fat (HF60%) for 10 and 20 weeks. HF60% diet promoted an increase on body weight, fasting glycemia, insulin, leptin, total cholesterol, triglycerides, and induced glucose intolerance. HF feeding promoted cardiac remodeling, as evidenced by increased cardiomyocyte transverse diameter and interstitial fibrosis. RNA sequencing analysis demonstrated that HF feeding induced distinct miRNA expression patterns in the heart. HF45% diet for 10 and 20 weeks changed the abundance of 64 and 26 miRNAs in the heart, respectively. On the other hand, HF60% diet for 10 and 20 weeks altered the abundance of 27 and 88 miRNAs in the heart, respectively. Bioinformatics analysis indicated that insulin signaling pathway was overrepresented in response to HF diet. An inverse correlation was observed between cardiac levels of GLUT4 and miRNA-29c. Similarly, we found an inverse correlation between expression of GSK3β and the expression of miRNA-21a-3p, miRNA-29c-3p, miRNA-144-3p, and miRNA-195a-3p. In addition, miRNA-1 overexpression prevented cardiomyocyte hypertrophy. Taken together, our results revealed differentially expressed miRNA signatures in the heart in response to different HF diets. J. Cell. Physiol. 231: 1771-1783, 2016. © 2015 Wiley Periodicals, Inc.

Diagnostic and prognostic value of circulating microRNAs in heart failure with preserved and reduced ejection fraction

microRNAs (miRNAs) are powerful regulators of posttranscriptional gene expression and play an important role in pathophysiological processes. Circulating miRNAs can be quantified in body liquids and are promising biomarkers in numerous diseases. In cardiovascular disease miRNAs have been proven to be reliable diagnostic biomarkers for different disease entities. In cardiac fibrosis (CF) and heart failure (HF) dysregulated circulating miRNAs have been identified, indicating their promising applicability as diagnostic biomarkers. Some miRNAs were successfully tested in risk stratification of HF implementing their potential use as prognostic biomarkers. In this respect miRNAs might soon be implemented in diagnostic clinical routine. In the young field of miRNA based research advances have been made in identifying miRNAs as potential targets for the treatment of experimental CF and HF. Promising study results suggest their potential future application as therapeutic agents in treatment of cardiovascular disease. This article summarizes the current state of the various aspects of miRNA research in the field of CF and HF with reduced ejection fraction as well as preserved ejection fraction. The review provides an overview of the application of circulating miRNAs as biomarkers in CF and HF and current approaches to therapeutically utilize miRNAs in this field of cardiovascular disease.

CDK6 mediates the effect of attenuation of miR-1 on provoking cardiomyocyte hypertrophy

MicroRNA-1 (miR-1) is approved involved in cardiac hypertrophy, but the underlying molecular mechanisms of miR-1 in cardiac hypertrophy are not well elucidated. The present study aimed to investigate the potential role of miR-1 in modulating CDKs-Rb pathway during cardiomyocyte hypertrophy. A rat model of hypertrophy was established with abdominal aortic constriction, and a cell model of hypertrophy was also achieved based on PE-promoted neonatal rat ventricular cardiomyocytes (NRVCs). We demonstrated that miR-1 expression was markedly decreased in hypertrophic myocardium and hypertrophic cardiomyocytes. Dual luciferase reporter assays revealed that miR-1 interacted with the 3'UTR of CDK6, and miR-1 was verified to inhibit CDK6 expression at the posttranscriptional level. CDK6 protein expression was observed increased in hypertrophic myocardium and hypertrophic cardiomyocytes. Morover, miR-1 mimic, in parallel to CDK6 siRNA, could inhibit PE-induced hypertrophy of NRVCs, with decreases in cell size, newly transcribed RNA, expressions of ANF and β-MHC, and the phosphorylated pRb. Taken together, our results reveal that derepression of CDK6 and activation of Rb pathway contributes to the effect of attenuation of miR-1 on provoking cardiomyocyte hypertrophy.

The role of microRNAs in cardiac development and regenerative capacity

The mammalian heart has long been considered to be a postmitotic organ. It was thought that, in the postnatal period, the heart underwent a transition from hyperplasic growth (more cells) to hypertrophic growth (larger cells) due to the conversion of cardiomyocytes from a proliferative state to one of terminal differentiation. This hypothesis was gradually disproven, as data were published showing that the myocardium is a more dynamic tissue in which cardiomyocyte karyokinesis and cytokinesis produce new cells, leading to the hyperplasic regeneration of some of the muscle mass lost in various pathological processes. microRNAs have been shown to be critical regulators of cardiomyocyte differentiation and proliferation and may offer the novel opportunity of regenerative hyperplasic therapy. Here we summarize the relevant processes and recent progress regarding the functions of specific microRNAs in cardiac development and regeneration.

Luteolin Inhibits Ischemia/Reperfusion-Induced Myocardial Injury in Rats via Downregulation of microRNA-208b-3p

BACKGROUND

Luteolin (LUT), a kind of flavonoid which is extracted from a variety of diets, has been reported to convey protective effects of various diseases. Recent researches have suggested that LUT can carry out cardioprotective effects during ischemia/reperfusion (I/R). However, there have no reports on whether LUT can exert protective effects against myocardial I/R injury through the actions of specific microRNAs (miRs). The purpose of this study was to determine which miRs and target genes LUT exerted such function through.

METHODS

Expression of various miRs in perfused rat hearts was detected using a gene chip. Target genes were predicted with TargetScan, MiRDB and MiRanda. Anoxia/reoxygenation was used to simulate I/R. Cells were transfected by miR-208b-3p mimic, inhibitor and small interfering RNA of Ets1 (avian erythroblastosis virus E26 (v ets) oncogene homolog 1). MiR-208b-3p and Ets1 mRNA were quantified by real-time quantitative polymerase chain reaction. The percentage of apoptotic cells was detected by annexin V-fluorescein isothiocyanate/propidium iodide dyeing and flow cytometry. The protein expression levels of cleaved caspase-3, Bcl-2, Bax, and Ets1 were examined by western blot analysis. A luciferase reporter assay was used to verify the combination between miR-208b-3p and the 3'-untranslated region of Ets1.

RESULTS

LUT pretreatment reduced miR-208b-3p expression in myocardial tissue, as compared to the I/R group. And LUT decreased miR-208b-3p expression and apoptosis caused by I/R. However, overexpression of miR-208b-3p further aggravated the changes caused by I/R and blocked all the effects of LUT. Knockdown of miR-208b-3p expression also attenuated apoptosis, while knockdown of Ets1 promoted apoptosis. Further, the luciferase reporter assay showed that miR-208b-3p could inhibit Ets1 expression.

CONCLUSION

LUT pretreatment conveys anti-apoptotic effects after myocardial I/R injury by decreasing miR-208b-3p and increasing Ets1 expression levels.

Transfection of microRNA Mimics Should Be Used with Caution

Transient transfection of chemically synthesized microRNA (miRNA) mimics is being used extensively to study the functions and mechanisms of endogenous miRNAs. However, it remains unclear whether transfected miRNAs behave similarly to endogenous miRNAs. Here we show that transient transfection of miRNA mimics into HeLa cells by a commonly used method led to the accumulation of high molecular weight RNA species and a few hundred fold increase in mature miRNA levels. In contrast, expression of the same miRNAs through lentiviral infection or plasmid transfection of HeLa cells, transgenic expression in primary lymphocytes, and endogenous overexpression in lymphoma and leukemia cell lines did not lead to the appearance of high molecular weight RNA species. The increase of mature miRNA levels in these cells was below 10-fold, which was sufficient to suppress target gene expression and to drive lymphoma development in mice. Moreover, transient transfection of miRNA mimics at high concentrations caused non-specific alterations in gene expression, while at low concentrations achieved expression levels comparable to other methods but failed to efficiently suppress target gene expression. Small RNA deep sequencing analysis revealed that the guide strands of miRNA mimics were frequently mutated, while unnatural passenger strands of some miRNA mimics accumulated to high levels. The high molecular weight RNA species were a heterogeneous mixture of several classes of RNA species generated by concatemerization, 5'- and 3'-end tailing of miRNA mimics. We speculate that the supraphysiological levels of mature miRNAs and these artifactual RNA species led to non-specific changes in gene expression. Our results have important implications for the design and interpretation of experiments primarily employing transient transfection of miRNA mimics.

The Role of MicroRNAs in Antiarrhythmic Therapy for Atrial Fibrillation

Atrial fibrillation (AF) is the most common arrhythmia worldwide and has an enormous impact on our healthcare system as it is a major contributor of morbidity and mortality. Although there are several therapeutic options available, treatment of AF still remains challenging. AF pathophysiology is complex and still incompletely understood. In general, our understanding of AF is based on two mechanistic paradigms as functional hallmarks of AF: ectopic activity and reentry. Both ectopic activity and reentry are the result of remodelling processes. Functional and/or expressional changes in ion channels, connexins or calcium-handling proteins are important factors in electrical remodelling, whereas signalling processes leading to atrial dilatation and atrial fibrosis are key factors of structural remodelling. In recent years, new intriguing key players in AF pathophysiology have been identified: microRNAs (miRNAs). MiRNAs are short, non-coding RNA fragments that can regulate gene expression and have been demonstrated as important modifiers in signalling cascades leading to electrical and structural remodelling. In this article we review the miRNA-mediated molecular mechanisms underlying AF with special emphasis on the perspective of miRNAs as potential therapeutic targets for AF treatment.

MicroRNA-208a Dysregulates Apoptosis Genes Expression and Promotes Cardiomyocyte Apoptosis during Ischemia and Its Silencing Improves Cardiac Function after Myocardial Infarction

Aims. miR-208a is associated with adverse outcomes in several cardiac pathologies known to have increased apoptosis, including myocardial infarction (MI). We investigated if miR-208a has proapoptotic effects on ischemic cardiomyocytes and if its silencing has therapeutic benefits in MI. Methods and Results. The effect of miR-208a on apoptosis during ischemia was studied in cultured neonatal mice myocytes transfected with agomir or antagomir. Differential gene expression was assessed using microarrays. MI was induced in male C57BL/6 mice randomly assigned to antagomir (n = 6) or control group (n = 7), while sham group (n = 7) had sham operation done. Antagomir group received miR208a antagomir, while control and sham group mice received vehicle only. At 7 and 28 days, echocardiography was done and thereafter hearts were harvested for analysis of apoptosis by TUNEL method, fibrosis using Masson's trichrome, and hypertrophy using hematoxylin and eosin. miR-208a altered apoptosis genes expression and increased apoptosis in ischemic cardiomyocytes. Therapeutic inhibition of miR-208a decreased cardiac fibrosis, hypertrophy, and apoptosis and significantly improved cardiac function 28 days after MI. Conclusion. miR-208a alters apoptosis genes expression and promotes apoptosis in ischemic cardiomyocytes, and its silencing attenuates apoptosis, fibrosis, and hypertrophy after MI, with significant improvement in cardiac function.

MicroRNA-208b progressively declines after spinal cord injury in humans and is inversely related to myostatin expression

The effects of long-term physical inactivity on the expression of microRNAs involved in the regulation of skeletal muscle mass in humans are largely unknown. MicroRNAs are short, noncoding RNAs that fine-tune target expression through mRNA degradation or by inhibiting protein translation. Intronic to the slow, type I, muscle fiber type genes MYH7 and MYH7b, microRNA-208b and microRNA-499-5p are thought to fine-tune the expression of genes important for muscle growth, such as myostatin. Spinal cord injured humans are characterized by both skeletal muscle atrophy and transformation toward fast-twitch, type II fibers. We determined the expression of microRNA-208b, microRNA-499-5p, and myostatin in human skeletal muscle after complete cervical spinal cord injury. We also determined whether these microRNAs altered myostatin expression in rodent skeletal muscle. A progressive decline in skeletal muscle microRNA-208b and microRNA-499-5p expression occurred in humans during the first year after spinal cord injury and with long-standing spinal cord injury. Expression of myostatin was inversely correlated with microRNA-208b and microRNA-499-5p in human skeletal muscle after spinal cord injury. Overexpression of microRNA-208b in intact mouse skeletal muscle decreased myostatin expression, whereas microRNA-499-5p was without effect. In conclusion, we provide evidence for an inverse relationship between expression of microRNA-208b and its previously validated target myostatin in humans with severe skeletal muscle atrophy. Moreover, we provide direct evidence that microRNA-208b overexpression decreases myostatin gene expression in intact rodent muscle. Our results implicate that microRNA-208b modulates myostatin expression and this may play a role in the regulation of skeletal muscle mass following spinal cord injury.

Regulation of connexin signaling by the epigenetic machinery

Connexins and their channels are involved in the control of all aspects of the cellular life cycle, ranging from cell growth to cell death, by mediating extracellular, intercellular and intracellular communication. These multifaceted aspects of connexin-related cellular signaling obviously require strict regulation. While connexin channel activity is mainly directed by posttranslational modifications, connexin expression as such is managed by classical cis/trans mechanisms. Over the past few years, it has become clear that connexin production is equally dictated by epigenetic actions. This paper provides an overview of the role of major determinants of the epigenome, including DNA methylation, histone acetylation and microRNA species, in connexin expression.

Regulation of cardiac miR-208a, an inducer of obesity, by rapamycin and nebivolol

OBJECTIVE

Resistance to obesity is observed in rodents and humans treated with rapamycin (Rap) or nebivolol (Neb). Because cardiac miR-208a promotes obesity, this study tested whether the modes of actions of Rap and Neb involve inhibition of miR-208a.

METHODS

Mouse cardiomyocyte HL-1 cells and Zucker obese (ZO) rats were used to investigate regulation of cardiac miR-208a.

RESULTS

Angiotensin II (Ang II) increased miR-208a expression in HL-1 cells. Pretreatment with an AT1 receptor (AT1R) antagonist, losartan (1 μM), antagonized this effect, whereas a phospholipase C inhibitor, U73122 (10 μM), and an NADPH oxidase inhibitor, apocynin (0.5 mM), did not. Ang II-induced increase in miR-208a was suppressed by Rap (10 nM), an inhibitor of nutrient sensor kinase mTORC1, and Neb (1 μM), a 3rd generation β-blocker that suppressed bioavailable AT1R binding of (125) I-Ang II. Thus, suppression of AT1R expression by Neb, inhibition of AT1R activation by losartan, and inhibition of AT1R-induced activation of mTORC1 by Rap attenuated the Ang II-induced increase in miR-208a. In ZO rats, Rap treatment (750 μg kg(-1)  day(-1) ; 12 weeks) reduced obesity despite similar food intake, suppressed cardiac miR-208a, and increased cardiac MED13, a suppresser of obesity.

CONCLUSIONS

Rap and Neb suppressed cardiac miR-208a. Suppression of miR-208a and increase in MED13 correlated with attenuated weight gain despite leptin resistance.

Transdifferentiation via transcription factors or microRNAs: Current status and perspective

Transdifferentiation as a new approach for obtaining the ideal cells for transplantation has gradually become a hot research topic. Compared with the induced pluripotent stem cells technique, transdifferentiation may have better efficiency and safety. Although the mechanism of transdifferentiation is still unknown, many studies have achieved transformation of one cell type to another through transcription factors or microRNA. The current major strategy for transdifferentiation is via transcription factors; however, there are some safety issues with the use of transcription factors. In contrast, microRNA as a novel tool for inducing transdifferentiation through post-transcriptional regulation may be more safe and efficient. In addition, the present transdifferentiation strategies involve obtaining the terminal cell directly, so the amount of cells produced may not be sufficient and they may have low capacity for cell immigration and integration. Therefore, an indirect transdifferentiation strategy for producing unipotent cells is ideal as it can preserve the proliferation capacity and differentiation pathway.

Developmental regulation and evolution of muscle-specific microRNAs

MicroRNAs (miRs) are a group of small RNAs that play a major role in post-transcriptional regulation of gene expression. In animals, many of the miRs are expressed in a conserved spatiotemporal manner. Muscle tissues, the major cellular systems involved in the locomotion and physiological functions of animals, have been one of the main sites for verification of miR targets and analysis of their developmental functions. During the determination and differentiation of muscle cells, numerous miRs bind to and repress target mRNAs in a highly specific but redundant manner. Interspecific comparisons of the sequences and expression of miRs have suggested that miR regulation became increasingly important during the course of vertebrate evolution. However, the detailed molecular interactions that have led to the highly complex morphological structures still await investigation. In this review, we will summarize the recent findings on the functional and developmental characteristics of miRs that have played major roles in vertebrate myogenesis, and discuss how the evolution of miRs is related to the morphological complexity of the vertebrates.

Involvement of AMPK in regulating slow-twitch muscle atrophy during hindlimb unloading in mice

AMPK is considered to have a role in regulating skeletal muscle mass. However, there are no studies investigating the function of AMPK in modulating skeletal muscle mass during atrophic conditions. In the present study, we investigated the difference in unloading-associated muscle atrophy and molecular functions in response to 2-wk hindlimb suspension between transgenic mice overexpressing the dominant-negative mutant of AMPK (AMPK-DN) and their wild-type (WT) littermates. Male WT (n = 24) and AMPK-DN (n = 24) mice were randomly divided into two groups: an untreated preexperimental control group (n = 12 in each group) and an unloading (n = 12 in each group) group. The relative soleus muscle weight and fiber cross-sectional area to body weight were decreased by ∼30% in WT mice by hindlimb unloading and by ∼20% in AMPK-DN mice. There were no changes in puromycin-labeled protein or Akt/70-kDa ribosomal S6 kinase signaling, the indicators of protein synthesis. The expressions of ubiquitinated proteins and muscle RING finger 1 mRNA and protein, markers of the ubiquitin-proteasome system, were increased by hindlimb unloading in WT mice but not in AMPK-DN mice. The expressions of molecules related to the protein degradation system, phosphorylated forkhead box class O3a, inhibitor of κBα, microRNA (miR)-1, and miR-23a, were decreased only in WT mice in response to hindlimb unloading, and 72-kDa heat shock protein expression was higher in AMPK-DN mice than in WT mice. These results imply that AMPK partially regulates unloading-induced atrophy of slow-twitch muscle possibly through modulation of the protein degradation system, especially the ubiquitin-proteasome system.

miRNA therapeutics: a new class of drugs with potential therapeutic applications in the heart

miRNAs are small non-coding RNAs (ncRNAs), which regulate gene expression. Here, the authors describe the contribution of miRNAs to cardiac biology and disease. They discuss various strategies for manipulating miRNA activity including antisense oligonucleotides (antimiRs, blockmiRs), mimics, miRNA sponges, Tough Decoys and miRNA mowers. They review developments in chemistries (e.g., locked nucleic acid) and modifications (sugar, 'ZEN', peptide nucleic acids) and miRNA delivery tools (viral vectors, liposomes, nanoparticles, pHLIP). They summarize potential miRNA therapeutic targets for heart disease based on preclinical studies. Finally, the authors review current progress of miRNA therapeutics in clinical development for HCV and cancer, and discuss challenges that will need to be overcome for similar therapies to enter the clinic for patients with cardiac disease.

Cardiovascular and Cerebrovascular Disease Associated microRNAs Are Dysregulated in Placental Tissues Affected with Gestational Hypertension, Preeclampsia and Intrauterine Growth Restriction

Aims

To demonstrate that pregnancy-related complications are associated with alterations in cardiovascular and cerebrovascular microRNA expression. Gene expression of 32 microRNAs (miR-1-3p, miR-16-5p, miR-17-5p, miR-20a-5p, miR-20b-5p, miR-21-5p, miR-23a-3p, miR-24-3p, miR-26a-5p, miR-29a-3p, miR-33a-5p, miR-92a-3p, miR-100-5p, miR-103a-3p, miR-122-5p, miR-125b-5p, miR-126-3p, miR-130b-3p, miR-133a-3p, miR-143-3p, miR-145-5p, miR-146a-5p, miR-155-5p, miR-181a-5p, miR-195-5p, miR-199a-5p, miR-208a-3p, miR-210-3p, miR-221-3p, miR-342-3p, miR-499a-5p, and miR-574-3p) was assessed in placental tissues, compared between groups (35 gestational hypertension, 80 preeclampsia, 35 intrauterine growth restriction and 20 normal pregnancies) and correlated with the severity of the disease with respect to clinical signs, delivery date, and Doppler ultrasound parameters. Initially, selection and validation of endogenous controls for microRNA expression studies in placental tissues affected by pregnancy-related complications have been carried out.

Results

The expression profile of microRNAs was different between pregnancy-related complications and controls. The up-regulation of miR-499a-5p was a common phenomenon shared between gestational hypertension, preeclampsia, and intrauterine growth restriction. Preeclamptic pregnancies delivering after 34 weeks of gestation and IUGR with abnormal values of flow rate in the umbilical artery demonstrated up-regulation of miR-1-3b. Preeclampsia and IUGR requiring termination of gestation before 34 weeks of gestation were associated with down-regulation of miR-26a-5p, miR-103a-3p and miR-145-5p. On the other hand, some of microRNAs (miR-16-5p, miR-100-5p, miR-122-5p, miR-125b-5p, miR-126-3p, miR-143-3p, miR-195-5p, miR-199a-5p, miR-221-3p, miR-342-3p, and miR-574-3p) were only down-regulated or showed a trend to down-regulation just in intrauterine growth restriction pregnancies requiring the delivery before 34 weeks of gestation.

Conclusion

Epigenetic changes induced by pregnancy-related complications in placental tissue may cause later onset of cardiovascular and cerebrovascular diseases in offspring.

Small indels induced by CRISPR/Cas9 in the 5' region of microRNA lead to its depletion and Drosha processing retardance

MicroRNA knockout by genome editing technologies is promising. In order to extend the application of the technology and to investigate the function of a specific miRNA, we used CRISPR/Cas9 to deplete human miR-93 from a cluster by targeting its 5’ region in HeLa cells. Various small indels were induced in the targeted region containing the Drosha processing site and seed sequences. Interestingly, we found that even a single nucleotide deletion led to complete knockout of the target miRNA with high specificity. Functional knockout was confirmed by phenotype analysis. Furthermore, de novo microRNAs were not found by RNA-seq. Nevertheless, expression of the pri-microRNAs was increased. When combined with structural analysis, the data indicated that biogenesis was impaired. Altogether, we showed that small indels in the 5’ region of a microRNA result in sequence depletion as well as Drosha processing retard.

Activation of common signaling pathways during remodeling of the heart and the bladder

The heart and the urinary bladder are hollow muscular organs, which can be afflicted by pressure overload injury due to pathological conditions such as hypertension and bladder outlet obstruction. This increased outflow resistance induces hypertrophy, marked by dramatic changes in the organs' phenotype and function. The end result in both the heart and the bladder can be acute organ failure due to advanced fibrosis and the subsequent loss of contractility. There is emerging evidence that microRNAs (miRNAs) play an important role in the pathogenesis of heart failure and bladder dysfunction. MiRNAs are endogenous non-coding single-stranded RNAs, which regulate gene expression and control adaptive and maladaptive organ remodeling processes. This Review summarizes the current knowledge of molecular alterations in the heart and the bladder and highlights common signaling pathways and regulatory events. The miRNA expression analysis and experimental target validation done in the heart provide a valuable source of information for investigators working on the bladder and other organs undergoing the process of fibrotic remodeling. Aberrantly expressed miRNA are amendable to pharmacological manipulation, offering an opportunity for development of new therapies for cardiac and bladder hypertrophy and failure.

MiRNAs as potential molecular targets in heart failure

Pathogenesis of heart diseases is associated with an altered expression profile of hundreds of genes. miRNAs are a newly identified layer of gene regulation operating at the post-transcriptional level by pairing to complementary base sequences in target mRNAs. Genetic data have identified the roles of miRNAs in basic pathological processes associated with heart failure: apoptosis, fibrosis, myocardial hypertrophy and cardiac remodeling. Many reports demonstrated that aberrantly expressed miRNAs and their modulation have effects on cardiac insufficiency. Here, we overview the advances in miRNAs as potential targets in the modulation of the heart failure phenotype. miRNA-based therapy holds great promise as a future strategy for treating heart diseases and identifying emerging signaling pathways responsible for the progression of heart failure.

Protein kinase Cα inhibits myocardin-induced cardiomyocyte hypertrophy through the promotion of myocardin phosphorylation

Myocardin plays a key role in the development of cardiac hypertrophy. However, the upstream signals that control the stability and transactivity of myocardin remain to be fully understood. The expression of protein kinase Cα (PKCα) also induces cardiac hypertrophy. An essential downstream molecule of PKCα, extracellular signal-regulated kinase 1/2, was reported to negatively regulate the activities of myocardin. But, the effect of cooperation between PKCα and myocardin and the potential molecular mechanism by which PKCα regulates myocardin-mediated cardiac hypertrophy are unclear. In this study, a luciferase assay was performed using H9C2 cells transfected with expression plasmids for PKCα and myocardin. Surprisingly, the results showed that PKCα inhibited the transcriptional activity of myocardin. PKCα inhibited myocardin-induced cardiomyocyte hypertrophy, demonstrated by the decrease in cell surface area and fetal gene expression, in cardiomyocyte cells overexpressing PKCα and myocardin. The potential mechanism underlying the inhibition effect of PKCα on the function of myocardin is further explored. PKCα directly promoted the basal phosphorylation of endogenous myocardin at serine and threonine residues. In myocardin-overexpressing cardiomyocyte cells, PKCα induced the excessive phosphorylation of myocardin, resulting in the degradation of myocardin and a transcriptional suppression of hypertrophic genes. These results demonstrated that PKCα inhibits myocardin-induced cardiomyocyte hypertrophy through the promotion of myocardin phosphorylation.

Elevated hsa-miR-99a levels in maternal plasma may indicate congenital heart defects

The current standard for prenatal screening is mostly based on biochemical marker tests and the use of ultrasonography. There is no secure stand-alone screening marker for congenital heart defects (CHDs). MicroRNAs (miRNAs) that are associated with cardiogenesis enter the maternal peripheral bloodstream during pregnancy and allow non-invasive prenatal testing (NIPT). The present study investigated the plasma expression profile of fetal hsa-miR-99a in maternal blood. Peripheral blood samples were collected from 39 pregnant patients, comprising 22 with CHD-positive fetuses and 17 with CHD-free controls. miRNAs were isolated from the maternal serum and reverse transcription-quantitative polymerase chain reaction was carried out to determine the expression of hsa-miR-99a. While the miRNA concentrations were almost identical among the affected and control groups (5.54 vs. 6.40 ng/µl), significantly upregulated hsa-miR-99a levels were identified in the affected group (1.78×10^-2±3.53×10^-2 vs. 1.09×10^-3±3.55×10^-3 ng/µl, P=0.038). In conclusion, according to the present study, hsa-miR-99a is involved in cardiac malformation and may serve as a biomarker during fetal development, and therefore presents as a candidate for monitoring cardiomyogenesis and potential use as a NIPT-biomarker for fetal CHD.

Myostatin: expanding horizons

Myostatin is a secreted growth and differentiation factor that belongs to the TGF-β superfamily. Myostatin is predominantly synthesized and expressed in skeletal muscle and thus exerts a huge impact on muscle growth and function. In keeping with its negative role in myogenesis, myostatin expression is tightly regulated at several levels including epigenetic, transcriptional, post-transcriptional, and post-translational. New revelations regarding myostatin regulation also offer mechanisms that could be exploited for developing myostatin antagonists. Increasingly, it is becoming clearer that besides its conventional role in muscle, myostatin plays a critical role in metabolism. Hence, molecular mechanisms by which myostatin regulates several key metabolic processes need to be further explored.

Exome analysis of a family with Wolff-Parkinson-White syndrome identifies a novel disease locus

Wolff-Parkinson-White (WPW) syndrome is a common cause of supraventricular tachycardia that carries a risk of sudden cardiac death. To date, mutations in only one gene, PRKAG2, which encodes the 5'-AMP-activated protein kinase subunit γ-2, have been identified as causative for WPW. DNA samples from five members of a family with WPW were analyzed by exome sequencing. We applied recently designed prioritization strategies (VAAST/pedigree VAAST) coupled with an ontology-based algorithm (Phevor) that reduced the number of potentially damaging variants to 10: a variant in KCNE2 previously associated with Long QT syndrome was also identified. Of these 11 variants, only MYH6 p.E1885K segregated with the WPW phenotype in all affected individuals and was absent in 10 unaffected family members. This variant was predicted to be damaging by in silico methods and is not present in the 1,000 genome and NHLBI exome sequencing project databases. Screening of a replication cohort of 47 unrelated WPW patients did not identify other likely causative variants in PRKAG2 or MYH6. MYH6 variants have been identified in patients with atrial septal defects, cardiomyopathies, and sick sinus syndrome. Our data highlight the pleiotropic nature of phenotypes associated with defects in this gene.

Heart over mind: metabolic control of white adipose tissue and liver

Increasing evidence suggests that the heart controls the metabolism of peripheral organs. Olson and colleagues previously demonstrated that miR-208a controls systemic energy homeostasis through the regulation of MED13 in cardiomyocytes (Grueter et al, 2012). In their follow-up study in this issue of EMBO Molecular Medicine, white adipose tissue (WAT) and liver are identified as the physiological targets of cardiac MED13 signaling, most likely through cardiac-derived circulating factors, which boost energy consumption by upregulating metabolic gene expression and increasing mitochondrial numbers (Baskin et al, 2014). In turn, increased energy expenditure in WAT and the liver confers leanness. These findings strengthen the evidence of metabolic crosstalk between the heart and peripheral tissues through cardiokines and also set the stage for the development of novel treatments for metabolic syndrome.

MicroRNAs and Cardiac Regeneration

The human heart has a limited capacity to regenerate lost or damaged cardiomyocytes after cardiac insult. Instead, myocardial injury is characterized by extensive cardiac remodeling by fibroblasts, resulting in the eventual deterioration of cardiac structure and function. Cardiac function would be improved if these fibroblasts could be converted into cardiomyocytes. MicroRNAs (miRNAs), small noncoding RNAs that promote mRNA degradation and inhibit mRNA translation, have been shown to be important in cardiac development. Using this information, various researchers have used miRNAs to promote the formation of cardiomyocytes through several approaches. Several miRNAs acting in combination promote the direct conversion of cardiac fibroblasts into cardiomyocytes. Moreover, several miRNAs have been identified that aid the formation of inducible pluripotent stem cells and miRNAs also induce these cells to adopt a cardiac fate. MiRNAs have also been implicated in resident cardiac progenitor cell differentiation. In this review, we discuss the current literature as it pertains to these processes, as well as discussing the therapeutic implications of these findings.