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

Generation of MicroRNA-34 Sponges and Tough Decoys for the Heart: Developments and Challenges

Heart failure (HF) is a debilitating and deadly chronic disease, with almost 50% of patients with HF dying within 5 years of diagnosis. With limited effective therapies to treat or cure HF, new therapies are greatly needed. microRNAs (miRNAs) are small non-coding RNA molecules that are powerful regulators of gene expression and play a key role in almost every biological process. Disruptions in miRNA gene expression has been functionally linked to numerous diseases, including cardiovascular disease. Molecular tools for manipulating miRNA activity have been developed, and there is evidence from preclinical studies demonstrating the potential of miRNAs to be therapeutic targets for cardiovascular disease. For clinical application, miRNA sponges and tough decoys have been developed for more stable suppression and targeted delivery of the miRNA of choice. The aim of this study was to generate miRNA sponges and tough decoys to target miR-34 in the mouse heart. We present data to show that using both approaches we were unable to get significant knockdown of miR-34 or regulate miR-34 target genes in the heart in vivo. We also review recent applications of this method in the heart and discuss further considerations for optimisation in construct design and testing, and the obstacles to be overcome before they enter the clinic.

Significance of non-coding circular RNAs and micro RNAs in the pathogenesis of cardiovascular diseases

Heart failure, coronary artery disease and myocardial infarction are the most prominent cardiovascular diseases contributing significantly to death worldwide. In the majority of situations, except for surgical interventions and transplantation, there are no reliable therapeutic approaches available to address these health problem. Despite several advances that led to the development of biomarkers and therapies based on the renin–angiotensin system, adrenergic pathways, etc, more definitive and consistent biomarkers and specific target based molecular therapies are still being sought. Recent advances in the field of genomic research has helped in identifying non-coding RNAs, including circular RNAs, piRNAs, micro RNAs, and long non-coding RNAs, that play a significant role in the regulation of gene expression and function and have direct impact on pathophysiological mechanisms. This new knowledge is currently being explored with much hope for the development of novel treatments and biomarkers. Circular RNAs and micro RNAs have been described in myocardium and aortic valves and were shown to be involved in the regulation of pathophysiological processes that potentially contribute to cardiovascular diseases. Approximately 32 000 human exonic circular RNAs have been catalogued and their functions are still being ascertained. In the heart, circular RNAs were shown to bind micro RNAs in a specific manner and regulate the expression of transcription factors and stress response genes, and expression of these non-coding RNAs were found to change in conditions such as cardiac hypertrophy, heart failure and cardiac remodelling, reflecting their significance as diagnostic and prognostic biomarkers. In this review, we address the present state of understanding on the biogenesis, regulation and pathophysiological roles of micro and circular RNAs in cardiovascular diseases, and on the potential future perspectives on their use as biomarkers and therapeutic agents.

Cardiac remodeling and pre-eclampsia: an overview of microRNA expression patterns

Pre-eclampsia (PE) is strongly associated with heart failure (HF) later in life. During PE pregnancy, the left ventricle undergoes concentric remodeling which often persists after delivery. This aberrant remodeling can induce a molecular signature that can be evaluated in terms of microRNAs (miRNAs) and which may help to explain the associated increased risk of HF. For this review, we performed a literature search of PubMed (National Center for Biotechnology Information), identifying studies on miRNA expression in concentric remodeling and on miRNA expression in PE. The miRNA data were stratified based on origin (isolated from humans or animals and from tissue or the circulation) and both datasets compared in order to generate a list of miRNA expression patterns in concentric remodeling and in PE. The nine miRNAs identified in both concentric remodeling and PE-complicated pregnancy were: miR-1, miR-18, miR-21, miR-29b, miR-30, miR-125b, miR-181b, miR-195 and miR-499-5p. We found five of these miRNAs (miR-18, miR-21, miR-125b, miR-195 and miR-499-5p) to be upregulated in both PE pregnancy and cardiac remodeling and two (miR-1 and miR-30) to be downregulated in both; the remaining two miRNAs (miR-29b and miR-181b) showed upregulation during PE but downregulation in cardiac remodeling. This innovative approach may be a step towards finding relevant biomarkers for complicated pregnancy and elucidating their relationship with remote cardiovascular disease. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd.

Noncoding RNAs in Cardiac Hypertrophy

Cardiac hypertrophy is classified as pathological and physiological hypertrophy. Pathological hypertrophy typically precedes the onset of heart failure, one of the largest contributors to disease burden and deaths worldwide. In contrast, physiological hypertrophy is an adaptive response and protects against adverse cardiac remodeling. Noncoding RNAs (ncRNAs) have drawn significant attention over the last couple of decades, and their dysregulation is increasingly being linked to cardiac hypertrophy and cardiovascular diseases. In this review, we will summarize the profiling, function, and molecular mechanism of microRNAs, long noncoding RNAs, and circular RNAs in pathological cardiac hypertrophy. Additionally, we also review microRNAs responsible for physiological hypertrophy. With better understanding of ncRNAs in cardiac hypertrophy, manipulation of the important ncRNAs will offer exciting avenues for the prevention and therapy of heart failure.

Marked disparity of microRNA modulation by cGMP-selective PDE5 versus PDE9 inhibitors in heart disease

MicroRNAs (miRs) posttranscriptionally regulate mRNA and its translation into protein, and are considered master controllers of genes modulating normal physiology and disease. There is growing interest in how miRs change with drug treatment, and leveraging this for precision guided therapy. Here we contrast 2 closely related therapies, inhibitors of phosphodiesterase type 5 or type 9 (PDE5-I, PDE9-I), given to mice subjected to sustained cardiac pressure overload (PO). Both inhibitors augment cyclic guanosine monophosphate (cGMP) to activate protein kinase G, with PDE5-I regulating nitric oxide (NO) and PDE9-I natriuretic peptide-dependent signaling. While both produced strong phenotypic improvement of PO pathobiology, they surprisingly showed binary differences in miR profiles; PDE5-I broadly reduces more than 120 miRs, including nearly half those increased by PO, whereas PDE9-I has minimal impact on any miR (P < 0.0001). The disparity evolves after pre-miR processing and is organ specific. Lastly, even enhancing NO-coupled cGMP by different methods leads to altered miR regulation. Thus, seemingly similar therapeutic interventions can be barcoded by profound differences in miR signatures, and reversing disease-associated miR changes is not required for therapy success.

Exploring miRNA-mRNA regulatory network in cardiac pathology in Na+/H+ exchanger isoform 1 transgenic mice

Numerous studies have demonstrated that Na⁺/H⁺ exchanger isoform 1 (NHE1) is elevated in myocardial diseases and its effect is detrimental. To better understand the involvement of NHE1, we have previously studied cardiac-specific NHE1 transgenic mice and shown that these mice develop cardiac hypertrophy, interstitial fibrosis, and cardiac dysfunction. The purpose of current study was to identify microRNAs and their mRNA targets involved in NHE1-mediated cardiac injury. An unbiased high-throughput sequencing study was performed on both microRNAs and mRNAs. RNA sequencing showed that differentially expressed genes were enriched in hypertrophic cardiomyopathy pathway by Kyoto Encyclopedia of Genes and Genomes annotation in NHE1 transgenic hearts. These genes were classified as contraction defects (e.g., Myl2, Myh6, Mybpc3, and Actb), impaired intracellular Ca²⁺ homeostasis (e.g., SERCA2a, Ryr2, Rcan1, and CaMKII delta), and signaling molecules for hypertrophic cardiomyopathy (e.g., Itga/b, IGF-1, Tgfb2/3, and Prkaa1/2). microRNA sequencing revealed that 15 microRNAs were differentially expressed (2-fold, P < 0.05). Six of them (miR-1, miR-208a-3p, miR-199a-5p, miR-21-5p, miR-146a-5p, and miR-30c-5p) were reported to be related to cardiac pathological functions. The integrative analysis of microRNA and RNA sequencing data identified several crucial microRNAs including miR-30c-5p, miR-199a-5p, miR-21-5p, and miR-34a-5p as well as 10 of their mRNA targets that may affect the heart via NFAT hypertrophy and cardiac hypertrophy signaling. Furthermore, important microRNAs and mRNA targets were validated by quantitative PCR. Our study comprehensively characterizes the expression patterns of microRNAs and mRNAs, establishes functional microRNA-mRNA pairs, elucidates the potential signaling pathways, and provides novel insights on the mechanisms underlying NHE1-medicated cardiac injury.

Noncoding RNAs in disease

Noncoding RNAs are emerging as potent and multifunctional regulators in all biological processes. In parallel, a rapidly growing number of studies has unravelled associations between aberrant noncoding RNA expression and human diseases. These associations have been extensively reviewed, often with the focus on a particular microRNA (miRNA) (family) or a selected disease/pathology. In this Mini‐Review, we highlight a selection of studies in order to demonstrate the wide‐scale involvement of miRNAs and long noncoding RNAs in the pathophysiology of three types of diseases: cancer, cardiovascular and neurological disorders. This research is opening new avenues to novel therapeutic approaches.

A MicroRNA Perspective on Cardiovascular Development and Diseases: An Update

In this review, we summarize the latest research pertaining to MicroRNAs (miRs) related to cardiovascular diseases. In today's molecular age, the key clinical aspects of diagnosing and treating these type of diseases are crucial, and miRs play an important role. Therefore, we have made a thorough analysis discussing the most important candidate protagonists of many pathways relating to such conditions as atherosclerosis, heart failure, myocardial infarction, and congenital heart disorders. We approach miRs initially from the fundamental molecular aspects and look at their role in developmental pathways, as well as regulatory mechanisms dysregulated under specific cardiovascular conditions. By doing so, we can better understand their functional roles. Next, we look at therapeutic aspects, including delivery and inhibition techniques. We conclude that a personal approach for treatment is paramount, and so understanding miRs is strategic for cardiovascular health.

MicroRNAs in Atrial Fibrillation: from Expression Signatures to Functional Implications

Atrial fibrillation (AF) is the most common sustained arrhythmia and is associated with pronounced morbidity and mortality. Its prevalence, expected to further increase for the forthcoming years, and associated frequent hospitalizations turn AF into a major health problem. Structural and electrical atrial remodelling underlie the substrate for AF, but the exact mechanisms driving this remodelling remain incompletely understood. Recent studies have shown that microRNAs (miRNA), short non-coding RNAs that regulate gene expression, may be involved in the pathophysiology of AF. MiRNAs have been implicated in AF-induced ion channel remodelling and fibrosis. MiRNAs could therefore provide insight into AF pathophysiology or become novel targets for therapy with miRNA mimics or anti-miRNAs. Moreover, circulating miRNAs have been suggested as a new class of diagnostic and prognostic biomarkers of AF. However, the origin and function of miRNAs in tissue and plasma frequently remain unknown and studies investigating the role of miRNAs in AF vary in design and focus and even present contradicting results. Here, we provide a systematic review of the available clinical and functional studies investigating the tissue and plasma miRNAs in AF and will thereafter discuss the potential of miRNAs as biomarkers or novel therapeutic targets in AF.

Non-coding RNAs as biomarkers for acute myocardial infarction

Acute myocardial infarction (AMI) is a main threat to human lives worldwide. Early and accurate diagnoses warrant immediate medical care, which would reduce mortality and improve prognoses. Circulating non-coding RNAs have been demonstrated to serve as competent biomarkers for various diseases. Following the identification of cardiac-specific microRNA miR-208a in circulation, more non-coding RNAs (miR-1, miR-499 and miR-133) have been identified as biomarkers not only for the diagnosis of AMI but also for prognosis post infarction. Here, we summarized recent findings on non-coding RNAs as biomarkers for early diagnosis of ST-segment elevation myocardial infarction and for disease monitoring of myocardial infarction. In addition, the prognostic potential of non-coding RNAs in patients treated with percutaneous coronary intervention was also described. We also include studies based on biobanks, and build a miRNA release spectrum after AMI, which provides quantitative and time-lapse monitoring of AMI progress. With this spectrum, we are able to customize personal medical care, which prevents further damage. By constructing a network of circulating non-coding RNAs with high specificity and sensitivity, detailed diagnostic information was provided for personalized medicine. Unveiling the roles and kinetics of circulating non-coding RNAs may lead to a revolution in clinical diagnosis.

The circulating non-coding RNA landscape for biomarker research: lessons and prospects from cardiovascular diseases

Pervasive transcription of the human genome is responsible for the production of a myriad of non-coding RNA molecules (ncRNAs) some of them with regulatory functions. The pivotal role of ncRNAs in cardiovascular biology has been unveiled in the last decade, starting from the characterization of the involvement of micro-RNAs in cardiovascular development and function, and followed by the use of circulating ncRNAs as biomarkers of cardiovascular diseases. The human non-coding secretome is composed by several RNA species that circulate in body fluids and could be used as biomarkers for diagnosis and outcome prediction. In cardiovascular diseases, secreted ncRNAs have been described as biomarkers of several conditions including myocardial infarction, cardiac failure, and atrial fibrillation. Among circulating ncRNAs, micro-RNAs (miRNAs), long noncoding RNAs (lncRNAs) and circular RNAs (circRNAs) have been proposed as biomarkers in different cardiovascular diseases. In comparison with standard biomarkers, the biochemical nature of ncRNAs offers better stability and flexible storage conditions of the samples, and increased sensitivity and specificity. In this review we describe the current trends and future prospects of the use of the ncRNA secretome components as biomarkers of cardiovascular diseases, including the opening questions related with their secretion mechanisms and regulatory actions.

Role of non-coding RNAs in cardiotoxicity of chemotherapy

The long-time paradoxical situation of non-coding RNAs (ncRNAs) has been terminated for they emerge as executive at full spectrum of gene expression and translation. More recently, it has been demonstrated that some ncRNAs apparently are associated with chemotherapy, causing cardiotoxicity, which taint long-term recovery of patients in growing body of evidence. The current review focused on up-to-date knowledge on regulation change and molecular signaling of ncRNAs, at mean time evaluate their potentials as diagnostic biomarkers or therapeutic targets to monitor and protect cardio function.

Circulating MicroRNAs: a Potential Biomarker for Cardiac Damage, Inflammatory Response, and Left Ventricular Function Recovery in Pediatric Viral Myocarditis

Viral myocarditis (VM) can be a life-threatening event resulting in cardiac failure, chronic cardiomyopathy, and death. VM typically includes three phases, i.e., acute, subacute, and resolution/chronic. We prospectively investigated cardiac- and inflammatory-associated plasma-circulating miRNA levels in eight pediatric patients with VM during the three stages of the disease. The level of cardiac-associated miR-208a was significantly elevated during the acute phase compared with the subacute and resolution/chronic phases. The level of cardiac- and inflammatory-associated miR-21 was significantly elevated during the acute phase compared to the resolution/chronic phase. Moreover, cardiac-associated miR-208b levels during the subacute phase correlated with systolic left ventricular function recovery as measured during the resolution/chronic phase. The findings of our study demonstrate an association between cardiac damage and the inflammatory response and the expression of miR-208a and miR-21 during the pathological progression of myocarditis. We also found that miR-208b levels exhibit a prognostic significance for left ventricular functional recovery.

At the heart of programming: the role of micro-RNAs

Epidemiological and experimental observations tend to prove that environment, lifestyle or nutritional challenges influence heart functions together with genetic factors. Furthermore, when occurring during sensitive windows of heart development, these environmental challenges can induce an 'altered programming' of heart development and shape the future heart disease risk. In the etiology of heart diseases driven by environmental challenges, epigenetics has been highlighted as an underlying mechanism, constituting a bridge between environment and heart health. In particular, micro-RNAs which are involved in each step of heart development and functions seem to play a crucial role in the unfavorable programming of heart diseases. This review describes the latest advances in micro-RNA research in heart diseases driven by early exposure to challenges and discusses the use of micro-RNAs as potential targets in the reversal of the pathophysiology.

miR-217 Promotes Cardiac Hypertrophy and Dysfunction by Targeting PTEN

Previously, we found that the miR-217 expression level was increased in hearts from chronic heart failure (CHF) patients by using miRNA profile analysis. This study aimed to explore the role of miR-217 in cardiac dysfunction. Heart tissue samples from CHF patients were used to detect miR-217 expression levels. A type 9 recombinant adeno-associated virus (rAAV9) was employed to manipulate miR-217 expression in mice with thoracic aortic constriction (TAC)-induced cardiac dysfunction. Cardiac structure and function were measured by echocardiography and invasive pressure-volume analysis. The expression levels of miR-217 were increased in hearts from both CHF patients and TAC mice. Overexpression of miR-217 in vivo aggravated pressure overload-induced cardiac hypertrophy, fibrosis, and cardiac dysfunction, whereas miR-217-TUD-mediated downregulation of miR-217 reversed these effects. PTEN was predicted and validated as a direct target of miR-217, and re-expression of PTEN attenuated miR-217-mediated cardiac hypertrophy and cardiac dysfunction. Importantly, cardiomyocyte-derived miR-217-containing exosomes enhanced proliferation of fibroblasts in vitro. All of these findings show that miR-217 participates in cardiac hypertrophy and cardiac fibrosis processes through regulating PTEN, which suggests a promising therapeutic target for CHF.

Non-coding RNAs and exercise: pathophysiological role and clinical application in the cardiovascular system

There is overwhelming evidence that regular exercise training is protective against cardiovascular disease (CVD), the main cause of death worldwide. Despite the benefits of exercise, the intricacies of their underlying molecular mechanisms remain largely unknown. Non-coding RNAs (ncRNAs) have been recognized as a major regulatory network governing gene expression in several physiological processes and appeared as pivotal modulators in a myriad of cardiovascular processes under physiological and pathological conditions. However, little is known about ncRNA expression and role in response to exercise. Revealing the molecular components and mechanisms of the link between exercise and health outcomes will catalyse discoveries of new biomarkers and therapeutic targets. Here we review the current understanding of the ncRNA role in exercise-induced adaptations focused on the cardiovascular system and address their potential role in clinical applications for CVD. Finally, considerations and perspectives for future studies will be proposed.

Pregnancy late in rodent life has detrimental effects on the heart

During pregnancy, the heart undergoes significant and numerous changes, including hypertrophy, that are usually described as physiological and reversible. Two aspects of the cardiac response to pregnancy are relatively understudied: advanced maternal age and multiple pregnancies (multiparity). Repeated breeder (RB) mice that have undergone five to seven consecutive pregnancies were euthanized 21 days after the weaning of their last pups and compared with age-matched primiparous, one-time pregnant (O1P) mice. The ages of the older mouse groups were similar (12 ± 1 mo). Pregnancy at a later age resulted in reduced fertility (40%); resorption was 29%, maternal mortality was 10%, and mortality of the pups was 17%. Contractile function as indicated by percent fractional shortening was significantly decreased in O1P and RB groups compared with the old nonpregnant control (ONP) group. There was no pathological induction of the fetal program of gene expression, with the exception of β-myosin heavy chain mRNA, which was induced in O1P compared with ONP mice ( P < 0.05) but not in RB mice. MicroRNA-208a was significantly increased in O1P compared with ONP mice ( P < 0.05) but significantly decreased in RB compared with ONP mice ( P < 0.05). mRNA of genes regulating angiogenesis (i.e., vascular endothelial growth factor-A) were significantly downregulated, whereas proinflammatory genes [i.e., interleukin-6, chemokine (C-C motif) ligand 2, and Cd36] were significantly upregulated in O1P ( P < 0.05) but not in RB mice. Overall, our results suggest that rather than multiparity, pregnancy in advanced age is a much more stressful event in both pregnant dams and fetuses, as evidenced by increased mortality, lower fertility, downregulation of angiogenesis, upregulation of inflammation, and cardiac dysfunction. NEW & NOTEWORTHY Pregnancy in older mice significantly decreases cardiac function, although repeated breeder mice demonstrated increased wall hypertrophy and dilated chamber size compared with one-time pregnant mice. Interestingly, many of the molecular changes were altered in one-time pregnant mice but not in repeated breeder mice, which may contribute to adverse pregnancy outcomes in a first pregnancy at a later age.

Analysis of the microRNA signature in left atrium from patients with valvular heart disease reveals their implications in atrial fibrillation

BACKGROUND

Among the potential factors which may contribute to the development and perpetuation of atrial fibrillation, dysregulation of miRNAs has been suggested. Thus in this study, we have quantified the basal expressions of 662 mature human miRNAs in left atrium (LA) from patients undergoing cardiac surgery for valve repair, suffering or not from atrial fibrillation (AF) by using TaqMan® Low Density arrays (v2.0).

RESULTS

Among the 299 miRNAs expressed in all patients, 42 miRNAs had altered basal expressions in patients with AF. Binding-site predictions with Targetscan (conserved sites among species) indicated that the up- and down-regulated miRNAs controlled respectively 3,310 and 5,868 genes. To identify the most relevant cellular functions under the control of the altered miRNAs, we focused on the 100 most targeted genes of each list and identified 5 functional protein-protein networks among these genes. Up-regulated networks were involved in synchronisation of circadian rythmicity and in the control of the AKT/PKC signaling pathway (i.e., proliferation/adhesion). Down-regulated networks were the IGF-1 pathway and TGF-beta signaling pathway and a network involved in RNA-mediated gene silencing, suggesting for the first time that alteration of miRNAs in AF would also perturbate the whole miRNA machinery. Then we crossed the list of miRNA predicted genes, and the list of mRNAs altered in similar patients suffering from AF and we found that respectively 44.5% and 55% of the up- and down-regulated mRNA are predicted to be conserved targets of the altered miRNAs (at least one binding site in 3'-UTR). As they were involved in the same biological processes mentioned above, these data demonstrated that a great part of the transcriptional defects previously published in LA from AF patients are likely due to defects at the post-transcriptional level and involved the miRNAs.

CONCLUSIONS

Our stringent analysis permitted us to identify highly targeted protein-protein networks under the control of miRNAs in LA and, among them, to highlight those specifically affected in AF patients with altered miRNA signature. Further studies are now required to determine whether alterations of miRNA levels in AF pathology are causal or represent an adaptation to prevent cardiac electrical and structural remodeling.

Diabetic Cardiomyopathy: Impact of Biological Sex on Disease Development and Molecular Signatures

Diabetic cardiomyopathy refers to a unique set of heart-specific pathological variables induced by hyperglycemia and insulin resistance. Given that cardiovascular disease (CVD) is the leading cause of death in the world, and type 2 diabetes incidence continues to rise, understanding the complex interplay between these two morbidities and developing novel therapeutic strategies is vital. Two hallmark characteristics specific to diabetic cardiomyopathy are diastolic dysfunction and cardiac structural mal-adaptations, arising from cardiac cellular responses to the complex toxicity induced by hyperglycemia with or without hyperinsulinemia. While type 2 diabetes is more prevalent in men compared to women, cardiovascular risk is higher in diabetic women than in diabetic men, suggesting that diabetic women take a steeper path to cardiomyopathy and heart failure. Accumulating evidence from randomized clinical trials indicate that although pre-menopausal women have lower risk of CVDs, compared to age-matched men, this advantage is lost in diabetic pre-menopausal women, which suggests estrogen availability does not protect from increased cardiovascular risk. Notably, few human studies have assessed molecular and cellular mechanisms regarding similarities and differences in the progression of diabetic cardiomyopathy in men versus women. Additionally, most pre-clinical rodent studies fail to include female animals, leaving a void in available data to truly understand the impact of biological sex differences in diabetes-induced dysfunction of cardiovascular cells. Elegant reviews in the past have discussed in detail the roles of estrogen-mediated signaling in cardiovascular protection, sex differences associated with telomerase activity in the heart, and cardiac responses to exercise. In this review, we focus on the emerging cellular and molecular markers that define sex differences in diabetic cardiomyopathy based on the recent clinical and pre-clinical evidence. We also discuss miR-208a, MED13, and AT2R, which may provide new therapeutic targets with hopes to develop novel treatment paradigms to treat diabetic cardiomyopathy uniquely between men and women.

Characterizing the role of atrial natriuretic peptide signaling in the development of embryonic ventricular conduction system

Patients born with congenital heart defects frequently encounter arrhythmias due to defects in the ventricular conduction system (VCS) development. Although recent studies identified transcriptional networks essential for the heart development, there is scant information on the mechanisms regulating VCS development. Based on the association of atrial natriuretic peptide (ANP) expression with VCS forming regions, it was reasoned that ANP could play a critical role in differentiation of cardiac progenitor cells (CPCs) and cardiomyocytes (CMs) toward a VCS cell lineage. The present study showed that treatment of embryonic ventricular cells with ANP or cell permeable 8-Br-cGMP can induce gene expression of important VCS markers such as hyperpolarization-activated cyclic nucleotide-gated channel-4 (HCN4) and connexin 40 (Cx40). Inhibition of protein kinase G (PKG) via Rp-8-pCPT-cGMPS further confirmed the role of ANP/NPRA/cGMP/PKG pathway in the regulation of HCN4 and Cx40 gene expression. Additional experiments indicated that ANP may regulate VCS marker gene expression by modulating levels of miRNAs that are known to control the stability of transcripts encoding HCN4 and Cx40. Genetic ablation of NPRA revealed significant decreases in VCS marker gene expression and defects in Purkinje fiber arborisation. These results provide mechanistic insights into the role of ANP/NPRA signaling in VCS formation.

A group of tissue-specific microRNAs contribute to the silencing of CUX1 in different cell lineages during development

Cut-like homeobox 1 (CUX1) is a highly conserved homeoprotein that functions as a transcriptional repressor of genes specifying terminal differentiation. We previously showed that liver-specific microRNA-122 (miR-122) regulates the timing of liver development by silencing CUX1 post-transcriptionally. Since the CUX1 protein is expressed in a subset of embryonic tissues, we hypothesized that it is regulated by specific microRNAs (miRNAs) in each cell type during development. Using a large-scale screening method, we identified ten tissue-specific miRNAs from different cell lineages that directly targeted CUX1. An analysis of the interaction between heart-specific microRNA-208a (miR-208a) and CUX1 in the hearts of developing mouse embryos and in P19CL6 cells undergoing cardiac differentiation indicated that CUX1 is regulated by miR-208a during heart development and cardiomyocyte differentiation. Functional analysis of miR-208a in P19CL6 cells using lentiviral-mediated over-expression showed that it regulates the transition between cellular proliferation and differentiation. These results suggest that these tissue-specific miRNAs might play a common role in timing the progression of terminal differentiation of different cell lineages, possibly by silencing the differentiation repressor CUX1.

Molecular mechanism of diabetic cardiomyopathy and modulation of microRNA function by synthetic oligonucleotides

Diabetic cardiomyopathy (DCM) is a chronic complication in individuals with diabetes and is characterized by ventricular dilation and hypertrophy, diastolic dysfunction, decreased or preserved systolic function and reduced ejection fraction eventually resulting in heart failure. Despite being well characterized, the fundamental mechanisms leading to DCM are still elusive. Recent studies identified the involvement of small non-coding small RNA molecules such as microRNAs (miRs) playing a key role in the etiology of DCM. Therefore, miRs associated with DCM represents a new class of targets for the development of mechanistic therapeutics, which may yield marked benefits compared to other therapeutic approaches. Indeed, few miRs currently under active clinical investigation, with many expressing cautious optimism that miRs based therapies will succeed in the coming years. The major caution in using miRs based therapy is the need to improve the stability and specificity following systemic injection, which can be achieved through chemical and structural modification. In this review, we first discuss the established role of miRs in DCM and the advances in miRs based therapeutic strategies for the prevention/treatment of DCM. We next discuss the currently employed chemical modification of miR oligonucleotides and their utility in therapies specifically focusing on the DCM. Finally, we summarize the commonly used delivery system and approaches for assessment of miRNA modulation and potential off-target effects.

Metazoan MicroRNAs

MicroRNAs (miRNAs) are ∼22 nt RNAs that direct posttranscriptional repression of mRNA targets in diverse eukaryotic lineages. In humans and other mammals, these small RNAs help sculpt the expression of most mRNAs. This article reviews advances in our understanding of the defining features of metazoan miRNAs and their biogenesis, genomics, and evolution. It then reviews how metazoan miRNAs are regulated, how they recognize and cause repression of their targets, and the biological functions of this repression, with a compilation of knockout phenotypes that shows that important biological functions have been identified for most of the broadly conserved miRNAs of mammals.

Shenfu Injection attenuates rat myocardial hypertrophy by up-regulating miR-19a-3p expression

Shenfu Injection (SFI) is a classical Chinese medicine used to treat heart failure. Our previous study demonstrated that miRNAs underwent changes in rats with myocardial hypertrophy induced by abdominal aortic constriction. Interestingly, there was a significant change in miR-19a-3p, whose target gene is known to be associated with MEF2 signaling. However, whether and how SFI regulates miR-19a-3p in the treatment of myocardial hypertrophy has not been investigated. The purpose of the present study was to investigate the regulatory effect of SFI on miR-19a-3p in MEF2 signaling in the rat hypertrophic myocardium. We found that the miR-19a-3p expression level was significantly decreased in the hypertrophic myocardium, and MEF2A was the target gene of miR-19a-3p. The protein expressions of MEF2A, β-MHC, BNP and TRPC1 were significantly increased in hypertrophic cardiomyocytes. MiR-19a-3p was up-regulated after SFI treatment, and the protein expressions of these genes were significantly decreased. In addition, miR-19a-3p over-expression in hypertrophic cardiomyocytes could decrease MEF2A mRNA and protein expressions, and anti-miR-19a-3p showed the opposite result. Our study provided substantial evidence that miR-19a-3p played a functional role in MEF2 signaling in myocardial hypertrophy. SFI attenuated cardiomyocyte hypertrophy probably through up-regulating or maintaining the miR-19a-3p levels and regulating the MEF2 signaling pathway.

Circulating Plasma MicroRNA-208a as Potential Biomarker of Chronic Indeterminate Phase of Chagas Disease

Chagas cardiomyopathy is the most severe clinical manifestation of chronic Chagas disease. The disease affects most of the Latin American countries, being considered one of the leading causes of morbidity and death in the continent. The pathogenesis of Chagas cardiomyopathy is very complex, with mechanisms involving parasite-dependent cytopathy, immune-mediated myocardial damage and neurogenic disturbances. These pathological changes eventually result in cardiac myocyte hypertrophy, arrhythmias, congestive heart failure and stroke during chronic infection phase. Herein, we show that miR-208a, a microRNA that is a key factor in promoting cardiovascular dysfunction during cardiac hypertrophy processes of heart failure, has its circulating levels increased during chronic indeterminate phase when compared to cardiac (CARD) clinical forms in patients with Chagas disease. In contrast, we have not found altered serum levels of miR-34a, a microRNA known to promote pro-apoptotic role in myocardial infarction during degenerative process of cardiac injuries thus indicating intrinsic differences in the nature of the mechanisms underlying the heart failure triggered by Trypanosoma cruzi infection. Our findings support that the chronic indeterminate phase is a progressive phase involved in the genesis of chagasic cardiopathy and point out the use of plasma levels of miR-208a as candidate biomarker in risk-prediction score for the clinical prognosis of Chagas disease.

Perinatal inflammation induces sex-related differences in cardiovascular morbidities in mice

Sex-related differences in cardiovascular health and disease have been identified, with males having a higher incidence of cardiovascular events but females more likely to develop arrhythmias. Adverse fetal environments are now accepted as a cause for the development of cardiovascular diseases in adulthood, but sex-related differences in response to adverse fetal environments have not been extensively explored. The combination of both in utero and postnatal exposure to inflammation is highly relevant for the infant that is born preterm or has clinical complications at birth or in early postnatal life. We have previously observed cardiac contractile deficiencies and dysregulation of Ca2+-handling proteins in our model of maternal lipopolysaccharide (LPS) and neonatal hyperoxia exposures (LPS/O2). This investigation tested the hypothesis that there are sex-related differences in the adult pathologies after exposure to perinatal inflammation. Using pressure-volume assessments, males exposed to LPS/O2 had more pronounced contractile deficiencies than similarly exposed females, but females tended to have long PR intervals. While both sexes demonstrated decreases in α-myosin heavy chain and connexin 43 after LPS/O2 exposure compared with saline/room air controls, females indicated aberrant increases in microRNA 208a, microRNA 208b, and desmin expression. Our study supports our hypothesis that early life exposure to inflammation results in sex-dependent deficits in cardiovascular function. NEW & NOTEWORTHY Sex-specific differences in cardiovascular disease are recognized, but the mechanisms and origins are not well understood. Adverse maternal environments can influence cardiac development and later cardiovascular disease. This study identifies sex-dependent differences in cardiac disease associated with perinatal inflammation.

Next generation sequencing applications for cardiovascular disease

The Human Genome Project (HGP), as the primary sequencing of the human genome, lasted more than one decade to be completed using the traditional Sanger's method. At present, next-generation sequencing (NGS) technology could provide the genome sequence data in hours. NGS has also decreased the expense of sequencing; therefore, nowadays it is possible to carry out both whole-genome (WGS) and whole-exome sequencing (WES) for the variations detection in patients with rare genetic diseases as well as complex disorders such as common cardiovascular diseases (CVDs). Finding new variants may contribute to establishing a risk profile for the pathology process of diseases. Here, recent applications of NGS in cardiovascular medicine are discussed; both Mendelian disorders of the cardiovascular system and complex genetic CVDs including inherited cardiomyopathy, channelopathies, stroke, coronary artery disease (CAD) and are considered. We also state some future use of NGS in clinical practice for increasing our information about the CVDs genetics and the limitations of this new technology. Key messages Traditional Sanger's method was the mainstay for Human Genome Project (HGP); Sanger sequencing has high fidelity but is slow and costly as compared to next generation methods. Within cardiovascular medicine, NGS has been shown to be successful in identifying novel causative mutations and in the diagnosis of Mendelian diseases which are caused by a single variant in a single gene. NGS has provided the opportunity to perform parallel analysis of a great number of genes in an unbiased approach (i.e. without knowing the underlying biological mechanism) which probably contribute to advance our knowledge regarding the pathology of complex diseases such as CVD.

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.

Cardioprotection and thyroid hormones

The evolution of cardiac disease after an acute ischemic event depends on a complex and dynamic network of mechanisms alternating from ischemic damage due to acute coronary occlusion to reperfusion injury due to the adverse effects of coronary revascularization till post-ischemic remodeling. Cardioprotection is a new purpose of the therapeutic interventions in cardiology with the goal to reduce infarct size and thus prevent the progression toward heart failure after an acute ischemic event. In a complex biological system such as the human one, an effective cardioprotective strategy should diachronically target the network of cross-talking pathways underlying the disease progression. Thyroid system is strictly interconnected with heart homeostasis, and recent studies highlighted its role in cardioprotection, in particular through the preservation of mitochondrial function and morphology, the antifibrotic and proangiogenetic effect and also to the potential induction of cell regeneration and growth. The objective of this review was to highlight the cardioprotective role of triiodothyronine in the complexity of post-ischemic disease evolution.

A Pilot Study of Tranilast for Cardiomyopathy of Muscular Dystrophy

Objective Heart failure is currently the most serious complication of muscular dystrophy. The transient receptor potential cation channel, subfamily V, member 2 (TRPV2) is a stretch-sensitive Ca channel. In damaged myocytes or cardiomyocytes, TRPV2 translocates to the cytoplasmic membrane and enhances Ca influx, triggering cell damage. Evidence suggests that the inhibition of TRPV2 may be a new therapeutic target in heart failure. We found that tranilast, which is widely used as an anti-allergic drug, inhibits TRPV2. A pilot study was conducted to assess the safety and efficacy of tranilast in muscular dystrophy patients with cardiomyopathy. Methods After obtaining informed consent, two muscular dystrophy patients with advanced heart failure took tranilast (300 mg/day) for three months. Blood tests, echocardiography, electrocardiography (ECG), Holter ECG, analyses of the TRPV2 expression in peripheral mononuclear cells, and circulating micro ribonucleic acid profiling were performed to assess the safety and efficacy of tranilast. Results The brain natriuretic peptide levels decreased after treatment. The expression of TRPV2 on the cytoplasmic membrane of peripheral mononuclear cells was enhanced before treatment and was decreased after treatment. Some heart-related micro ribonucleic acids (miR-208a-5p, miR-223-3p) were elevated and then decreased after treatment. Some adverse events, including the potentiation of warfarin, the worsening of renal dysfunction, an increased heart rate and premature ventricular contractions, were observed. Conclusion Tranilast can inhibit TRPV2 and can be effective for treating heart failure, even in patients with muscular dystrophy. Although careful attention is needed, the inhibition of TRPV2 can be a new treatment target for cardiomyopathy. A multi-center trial is planned.

A new miRNA regulator, miR-672, reduces cardiac hypertrophy by inhibiting JUN expression

Cardiac hypertrophy is one of the initial symptoms of many heart diseases. We found that miR-672-5p may participate in the regulation of heart disease development in mouse, but the association between miR-672-5p and cardiac hypertrophy remains unclear. In the present study, we found that the abundance of miR-672-5p decreased in hypertrophic cardiomyocytes induced by phenylephrine, angiotensin II (Ang II) and insulin-like growth factor 1. Putative target genes of miR-672-5p were identified using four pipelines, miRWalk, miRanda, RNA22 and Targetscan, and a total of 834 genes were predicted by all four pipelines. Among these target genes, 98 were associated with the development of heart disease. PPI networks showed that the Jun proto-oncogene product (JUN), a subunit of the AP-1 transcription factor, had the highest node degree, and it was defined as the hub gene of the PPI networks. Luciferase assays showed that miR-672-5p bound to the 3' UTR of the JUN gene and decreased luciferase activity, indicating that JUN is a target of miR-672-5p. Finally, we found that increasing the abundance of miR-672-5p in cardiomyocytes controlled the relative cell area in Ang II-stimulated hypertrophic cardiomyocytes. Correspondingly, the abundance of JUN, a target of miR-672-5p, was decreased in hypertrophic cardiomyocytes on both mRNA and protein levels, implying that miR-672-5p had suppressive effects on cardiac hypertrophy through regulating the expression of Jun in cardiomyocytes.

Down-regulation of miR-133a/b in patients with myocardial infarction correlates with the presence of ventricular fibrillation

MicroRNAs (miRNAs) are important regulators of physiologic and pathologic conditions of the heart. Animal models of heart diseases have shown that miRNAs may contribute to the development of arrhythmias. However, little is known about the expression of muscle- and cardiac-specific miRNAs in patients with myocardial infarction (MI) who have developed ventricular fibrillation (VF). Our study included 47 patients who had died from myocardial infarction (MI), 23 with clinically proven VF and 24 without VF. Autopsy samples of infarcted tissue and remote myocardium were available (n = 94). Heart tissue from 8 healthy trauma victims was included as control. Expression of miR-1, miR-133a/b and miR-208 was analyzed using real-time PCR (qPCR). In patients with MI with VF, we observed down-regulation of miR-133a/b, and this down-regulation was even stronger 2-7 days after MI. miR-208 was up-regulated in remote myocardium irrespective of the presence of VF. Deregulation of miR-1 and miR-208 was not related to the presence of VF. Our results suggest that down-regulation of miR-133a/b might contribute to the development of VF in patients with MI. However, up-regulation of miR-1 and miR-208 in remote myocardium might play a role in cardiac remodeling after MI, at least to certain degree.

Epigenetic mechanisms in coronary artery disease: The current state and prospects

Coronary artery disease (CAD) is the leading cause of morbidity and mortality. CAD has both genetic and environmental causes. In the past two decades, the understanding of epigenetics has advanced swiftly and vigorously. It has been demonstrated that epigenetic modifications are associated with the onset and progression of CAD. This review aims to improve the understanding of the epigenetic mechanisms closely related to CAD and to provide a novel perspective on the onset and development of CAD. Epigenetic changes include DNA methylation, histone modification, microRNA and lncRNA, which are interrelated with critical genes and influence the expression of those genes. In addition, miRNA plays a diverse role in the pathological process of CAD. Numerous studies have found that some cardiac-specific miRNAs have potential as certain diagnostic biomarkers and treatment targets for CAD. In this review, the aberrant epigenetic mechanisms that contribute to CAD will be discussed. We will also provide novel insight into the epigenetic mechanisms that target CAD.

Cardiovascular disease progression in female Zucker Diabetic Fatty rats occurs via unique mechanisms compared to males

Population studies have shown that compared to diabetic men, diabetic women are at a higher risk of cardiovascular disease. However, the mechanisms underlying this gender disparity are unclear. Our studies in young murine models of type 2 diabetes mellitus (T2DM) and cardiovascular disease show that diabetic male rats develop increased cardiac fibrosis and suppression of intracardiac anti-fibrotic cytokines, while premenopausal diabetic female rats do not. This protection from cardiac fibrosis in female rats can be an estrogen-related effect. However, diabetic female rats develop early subclinical myocardial deformation, cardiac hypertrophy via elevated expression of pro-hypertrophic miR-208a, myocardial damage, and suppression of cardio-reparative Angiotensin II receptor 2 (Agtr2). Diabetic rats of both sexes exhibit a reduction in cardiac capillary density. However, diabetic female rats have reduced expression of neuropilin 1 that attenuates cardiomyopathy compared to diabetic male rats. A combination of cardiac hypertrophy and reduced capillary density likely contributed to increased myocardial structural damage in diabetic female rats. We propose expansion of existing cardiac assessments in diabetic female patients to detect myocardial deformation, cardiac hypertrophy and capillary density via non-invasive imaging, as well as suggest miR-208a, AT2R and neuropilin 1 as potential therapeutic targets and mechanistic biomarkers for cardiac disease in females.

Loss of microRNA-22 prevents high-fat diet induced dyslipidemia and increases energy expenditure without affecting cardiac hypertrophy

Obesity is associated with development of diverse diseases, including cardiovascular diseases and dyslipidemia. MiRNA-22 (miR-22) is a critical regulator of cardiac function and targets genes involved in metabolic processes. Previously, we generated miR-22 null mice and we showed that loss of miR-22 blunted cardiac hypertrophy induced by mechanohormornal stress. In the present study, we examined the role of miR-22 in the cardiac and metabolic alterations promoted by high-fat (HF) diet. We found that loss of miR-22 attenuated the gain of fat mass and prevented dyslipidemia induced by HF diet, although the body weight gain, or glucose intolerance and insulin resistance did not seem to be affected. Mechanistically, loss of miR-22 attenuated the increased expression of genes involved in lipogenesis and inflammation mediated by HF diet. Similarly, we found that miR-22 mediates metabolic alterations and inflammation induced by obesity in the liver. However, loss of miR-22 did not appear to alter HF diet induced cardiac hypertrophy or fibrosis in the heart. Our study therefore establishes miR-22 as an important regulator of dyslipidemia and suggests it may serve as a potential candidate in the treatment of dyslipidemia associated with obesity.

Anthracycline induced cardiotoxicity: biomarkers and "Omics" technology in the era of patient specific care

Anthracyclines are highly effective against a variety of malignancies. However, their dose-dependent cardiotoxic effects can potentially limit their use. In the past decade, serum biomarkers have been used to diagnose, monitor, predict, and prognosticate disease. Biomarkers such as cardiac troponin and natriuretic peptides have some predictive value, but still lack reliability in this patient population. Novel biomarkers such as galectin-3, soluble ST-2 proteins, myeloperoxidase, and fibrocytes are being explored as potential biomarkers to reliably predict the onset of cardiotoxicity. Leveraging multiomics technology to map highly sensitive biomarkers in an integrated approach through pattern deconvolution may better define those at highest risk of developing cardiotoxicity and further the goal of precision medicine. In this work, we aim to provide a brief overview of traditional serum biomarkers, summarize current investigations on novel circulating biomarkers, and discuss a systems-based approach to anthracycline-induced cardiotoxicity through "omics" technology.

Noncoding RNAs in Heart Failure

Heart failure is a major contributor to the healthcare burden and mortality worldwide. Current treatment strategies are able to slow down the transition of healthy heart into the failing one; nevertheless better understanding of the complex genetic regulation of maladaptive remodeling in the failing heart is essential for new drug discovery. Noncoding RNAs are key epigenetic regulators of cardiac gene expression and thus significantly influence cardiac homeostasis and functions.In this chapter we will discuss characteristics of noncoding RNAs, especially miRNAs, long noncoding RNAs, and circular RNAs, and review recent evidences proving their profound involvement during different stages of heart failure progression. Several open questions still prevent the extensive use of noncoding RNA-modulating therapies in clinics; yet they are becoming an attractive target to define novel regulatory mechanisms in the heart. In-depth study of their interaction with gene networks will refine our current view of heart failure and revolutionize the drug development in coming years.

Carbon monoxide releasing molecule improves structural and functional cardiac recovery after myocardial injury

Carbon monoxide (CO), produced by heme oxygenase-1 (HO-1), is an endogenous paracrine factor involved in the regulation of cardiovascular structure and function. We studied the effects of a synthetic CO releasing molecule (CORM-3) on cardiac recovery and myocardial microRNA expression after myocardial infarction (MI). Male Wistar rats with MI (n = 75) or sham-operated controls (n = 75) were treated from day 4 to day 14 after MI either with synthetic CORM-3 or with inactive iCORM and killed 2, 4 or 8 weeks post-MI. Infarct size, vascular and capillary densities, the amount of cardiomyocytes in the infarct area, and cardiomyocyte proliferation and apoptosis were determined. PCR was used for microRNA and mRNA quantification, western blotting to evaluate protein expression and echocardiography to assess cardiac structure and function. CORM-3 treatment increased vascular density (P< 0.05 vs. iCORM) and the proportion of cardiomyocytes (P< 0.05 vs. iCORM) in the infarct area. Ejection fraction improved (P< 0.05) and left ventricular volumes decreased (P< 0.05) in CORM-3 treated MI groups compared to iCORM treatment. CORM-3 treatment decreased the amount of proliferating Ki67 positive cardiomyocytes in the infarct/border area at week 2 after MI compared to iCORM treatment, whereas the amount of apoptotic cardiomyocytes did not differ between CORM-3 and iCORM groups. Compared to iCORM treatment, CORM-3 decreased expression on miR-206 in the remote area at week 2 after MI. The CO releasing molecule CORM-3 improved structural and functional cardiac recovery after MI. Modulation of HO-1-CO axis may prove novel drug targets to facilitate cardiac recovery after myocardial injury.

Content of mitochondrial calcium uniporter (MCU) in cardiomyocytes is regulated by microRNA-1 in physiologic and pathologic hypertrophy

The mitochondrial Ca²⁺ uniporter complex (MCUC) is a multimeric ion channel which, by tuning Ca²⁺ influx into the mitochondrial matrix, finely regulates metabolic energy production. In the heart, this dynamic control of mitochondrial Ca²⁺ uptake is fundamental for cardiomyocytes to adapt to either physiologic or pathologic stresses. Mitochondrial calcium uniporter (MCU), which is the core channel subunit of MCUC, has been shown to play a critical role in the response to β-adrenoreceptor stimulation occurring during acute exercise. The molecular mechanisms underlying the regulation of MCU, in conditions requiring chronic increase in energy production, such as physiologic or pathologic cardiac growth, remain elusive. Here, we show that microRNA-1 (miR-1), a member of the muscle-specific microRNA (myomiR) family, is responsible for direct and selective targeting of MCU and inhibition of its translation, thereby affecting the capacity of the mitochondrial Ca²⁺ uptake machinery. Consistent with the role of miR-1 in heart development and cardiomyocyte hypertrophic remodeling, we additionally found that MCU levels are inversely related with the myomiR content, in murine and, remarkably, human hearts from both physiologic (i.e., postnatal development and exercise) and pathologic (i.e., pressure overload) myocardial hypertrophy. Interestingly, the persistent activation of β-adrenoreceptors is likely one of the upstream repressors of miR-1 as treatment with β-blockers in pressure-overloaded mouse hearts prevented its down-regulation and the consequent increase in MCU content. Altogether, these findings identify the miR-1/MCU axis as a factor in the dynamic adaptation of cardiac cells to hypertrophy.

Connexins in Cardiovascular and Neurovascular Health and Disease: Pharmacological Implications

Connexins are ubiquitous channel forming proteins that assemble as plasma membrane hemichannels and as intercellular gap junction channels that directly connect cells. In the heart, gap junction channels electrically connect myocytes and specialized conductive tissues to coordinate the atrial and ventricular contraction/relaxation cycles and pump function. In blood vessels, these channels facilitate long-distance endothelial cell communication, synchronize smooth muscle cell contraction, and support endothelial-smooth muscle cell communication. In the central nervous system they form cellular syncytia and coordinate neural function. Gap junction channels are normally open and hemichannels are normally closed, but pathologic conditions may restrict gap junction communication and promote hemichannel opening, thereby disturbing a delicate cellular communication balance. Until recently, most connexin-targeting agents exhibited little specificity and several off-target effects. Recent work with peptide-based approaches has demonstrated improved specificity and opened avenues for a more rational approach toward independently modulating the function of gap junctions and hemichannels. We here review the role of connexins and their channels in cardiovascular and neurovascular health and disease, focusing on crucial regulatory aspects and identification of potential targets to modify their function. We conclude that peptide-based investigations have raised several new opportunities for interfering with connexins and their channels that may soon allow preservation of gap junction communication, inhibition of hemichannel opening, and mitigation of inflammatory signaling.

MicroRNA-208a-3p contributes to connexin40 remolding in human chronic atrial fibrillation

Previous studies have demonstrated that connexin40 (Cx40) remolding is involved in atrial fibrillation (AF). GJA5 encoding Cx40 is a potential target mRNA of microRNA-208a-3p (miR-208a-3p), as indicated by preliminary bioinformatics analyses. However, the exact effect of miR-208a-3p on Cx40 in human chronic AF has remained elusive. The present study demonstrated the role of miR-208a-3p in human chronic AF and further investigated the effect of miR-208a-3p on Cx40 expression. A total of 19 patients with AF and 18 patients with sinus rhythm (SR) were enrolled. The AC16 cell line was treated with miR-208a-3p inhibitor or mimics. The miR-208a-3p in right atrial appendage (RAA) tissues of patients was measured by in situ hybridization and reverse-transcription quantitative polymerase chain reaction (RT-qPCR). Furthermore, the expression of Cx40 in the RAA of patients and in AC16 cells treated with miR-208a-3p inhibitor or mimics were detected by RT-qPCR and western blot analysis. A luciferase assay was performed to confirm whether Cx40 was directly targeted by miR-208a-3p. The miR-208a-3p levels in patients with AF were significantly increased compared with those in patients with SR. Conversely, the Cx40 protein levels were significantly decreased and lateralization of Cx40 was observed in patients with AF. miR-208a-3p inhibitor led to a significant upregulation of the protein expression of Cx40 in AC16 cells, while miR-208a-3p mimics led to a significant downregulation. However, the luciferase assay demonstrated that GJA5 was not a direct target gene of miR-208a-3p. The findings still suggested that miR-208a-3p may be involved in human chronic AF by mediating atrial Cx40 remolding, and may represent a potential therapeutic target for AF.

Targeting myocyte-specific enhancer factor 2D contributes to the suppression of cardiac hypertrophic growth by miR-92b-3p in mice

The role of microRNA-92b-3p (miR-92b-3p) in cardiac hypertrophy was not well illustrated. The present study aimed to investigate the expression and potential target of miR-92b-3p in angiotensin II (Ang-II)-induced mouse cardiac hypertrophy. MiR-92b-3p was markedly decreased in the myocardium of Ang-II-infused mice and of patients with cardiac hypertrophy. However, miR-92b-3p expression was revealed increased in Ang-II-induced neonatal mouse cardiomyocytes. Cardiac hypertrophy was shown attenuated in Ang-II-infused mice received tail vein injection of miR-92b-3p mimic. Moreover, miR-92b-3p inhibited the expression of atrial natriuretic peptide (ANP), skeletal muscle α-actin (ACTA1) and β-myosin heavy chain (MHC) in Ang-II-induced mouse cardiomyocytes in vitro. Myocyte-specific enhancer factor 2D (MEF2D), which was increased in Ang-II-induced mouse hypertrophic myocardium and cardiomyocytes, was identified as a target gene of miR-92b-3p. Functionally, miR-92b-3p mimic, consistent with MEF2D siRNA, inhibited cell size increase and protein expression of ANP, ACTA1 and β-MHC in Ang-II-treated mouse cardiomyocytes. Taken together, we demonstrated that MEF2D is a novel target of miR-92b-3p, and attenuation of miR-92b-3p expression may contribute to the increase of MEF2D in cardiac hypertrophy.

Connexins and microRNAs: Interlinked players in regulating islet function?

Pancreatic β-cells are connected to neighboring endocrine cells through the adherin proteins and gap junctions. Connexin 36 (Cx36) is one of the most well-studied and abundantly expressed gap-junction proteins within rodent islets, which is important in coordinated insulin secretion. The expression of connexins is regulated at various levels and by several mechanisms; one of which is via microRNAs. In past 2 decades, microRNAs (miRNAs) have emerged as key molecules in developmental, physiologic and pathological processes. However, very few studies have demonstrated miRNA-mediated regulation of connexins. Even though there are no reports yet on miRNAs and Cx36; we envisage that considering the important role of connexins and microRNAs in insulin secretion, there would be common pathways interlinking these biomolecules. Here, we discuss the current literature on connexins and miRNAs specifically with reference to islet function.

MicroRNAs in injury and repair

Organ damage and resulting pathologies often involve multiple deregulated pathways. MicroRNAs (miRNAs) are short, non-coding RNAs that regulate a multitude of genes at the post-transcriptional level. Since their discovery over two decades ago, miRNAs have been established as key players in the molecular mechanisms of mammalian biology including the maintenance of normal homeostasis and the regulation of disease pathogenesis. In recent years, there has been substantial progress in innovative techniques to measure miRNAs along with advances in targeted delivery of agents modulating their expression. This has expanded the scope of miRNAs from being important mediators of cell signaling to becoming viable quantitative biomarkers and therapeutic targets. Currently, miRNA therapeutics are in clinical trials for multiple disease areas and vast numbers of patents have been filed for miRNAs involved in various pathological states. In this review, we summarize miRNAs involved in organ injury and repair, specifically with regard to organs that are the most susceptible to injury: the liver, heart and kidney. In addition, we review the current state of knowledge on miRNA biology, miRNA biomarkers and nucleotide-based therapeutics designed to target miRNAs to prevent organ injury and promote repair.