MicroRNAs in extracellular vesicles released from epicardial adipose tissue promote arrhythmogenic conduction slowing.

Background: Patients with excess epicardial adipose tissue (EAT) are at increased risk of developing cardiac arrhythmias. EAT promotes arrhythmias by depolarizing the resting membrane of cardiomyocytes, which slows down conduction and facilitates re-entrant arrhythmias. We hypothesized that EAT slows conduction by secreting extracellular vesicles (EVs) and their microRNA (miRNA) cargo.

MicroRNAs in atrial fibrillation target genes in structural remodelling.

We aim to elucidate how miRNAs regulate the mRNA signature of atrial fibrillation (AF), to gain mechanistic insight and identify candidate targets for future therapies. We present combined miRNA-mRNA sequencing using atrial tissues of patient without AF (n = 22), with paroxysmal AF (n = 22) and with persistent AF (n = 20). mRNA sequencing previously uncovered upregulated epithelial to mesenchymal transition, endothelial cell proliferation and extracellular matrix remodelling involving glycoproteins and proteoglycans in AF.

Quaking regulates circular RNA production in cardiomyocytes.

Circular RNAs (circRNAs) are a class of non-coding RNA molecules that are gaining increasing attention for their roles in various pathophysiological processes. The RNA-binding protein quaking (QKI) has been identified as a regulator of circRNA formation. In this study, we investigate the role of QKI in the formation of circRNAs in the heart by performing RNA-sequencing on Qki-knockout mice.

The RNA-binding protein QKI governs a muscle-specific alternative splicing program that shapes the contractile function of cardiomyocytes.

Aims: In the heart, splicing factors orchestrate the functional properties of cardiomyocytes by regulating the alternative splicing of multiple genes. Work in embryonic stem cells has shown that the splicing factor Quaking (QKI) regulates alternative splicing during cardiomyocyte differentiation. However, the relevance and function of QKI in adult cardiomyocytes remains unknown.

shRNAs Targeting a Common Variant Could Alleviate Long-QT1 Disease Severity by Inhibiting a Mutant Allele.

Long-QT syndrome type 1 (LQT1) is caused by mutations in . Patients heterozygous for such a mutation co-assemble both mutant and wild-type -encoded subunits into tetrameric Kv7.1 potassium channels.

Inhibition of minor intron splicing reduces Na+ and Ca2+ channel expression and function in cardiomyocytes.

Eukaryotic genomes contain a tiny subset of 'minor class' introns with unique sequence elements that require their own splicing machinery. These minor introns are present in certain gene families with specific functions, such as voltage-gated Na+ and voltage-gated Ca2+ channels. Removal of minor introns by the minor spliceosome has been proposed as a post-transcriptional regulatory layer, which remains unexplored in the heart.

Dietary restriction in the long-chain acyl-CoA dehydrogenase knockout mouse.

Patients with a disorder of mitochondrial long-chain fatty acid β-oxidation (FAO) have reduced fasting tolerance and may present with hypoketotic hypoglycemia, hepatomegaly, (cardio)myopathy and rhabdomyolysis. Patients should avoid a catabolic state because it increases reliance on FAO as energy source. It is currently unclear whether weight loss through a reduction of caloric intake is safe in patients with a FAO disorder.

Titin Circular RNAs Create a Back-Splice Motif Essential for SRSF10 Splicing.

Background: TTN (Titin), the largest protein in humans, forms the molecular spring that spans half of the sarcomere to provide passive elasticity to the cardiomyocyte. Mutations that disrupt the transcript are the most frequent cause of hereditary heart failure. We showed before that produces a class of circular RNAs (circRNAs) that depend on RBM20 to be formed.

Low miR-19b-1-5p Expression Is Related to Aspirin Resistance and Major Adverse Cardio- Cerebrovascular Events in Patients With Acute Coronary Syndrome.

Background Because of a nonresponse to aspirin (aspirin resistance), patients with acute coronary syndrome (ACS) are at increased risk of developing recurrent event. The in vitro platelet function tests have potential limitations, making them unsuitable for the detection of aspirin resistance. We investigated whether miR-19b-1-5p could be utilized as a biomarker for aspirin resistance and future major adverse cardio-cerebrovascular (MACCE) events in patients with ACS.

Functional modulation of atrio-ventricular conduction by enhanced late sodium current and calcium-dependent mechanisms in Scn5a1798insD/+ mice.

Aims: SCN5A mutations are associated with arrhythmia syndromes, including Brugada syndrome, long QT syndrome type 3 (LQT3), and cardiac conduction disease. Long QT syndrome type 3 patients display atrio-ventricular (AV) conduction slowing which may contribute to arrhythmogenesis. We here investigated the as yet unknown underlying mechanisms.

Loss-of-function variants in myocardin cause congenital megabladder in humans and mice.

Myocardin (MYOCD) is the founding member of a class of transcriptional coactivators that bind the serum-response factor to activate gene expression programs critical in smooth muscle (SM) and cardiac muscle development. Insights into the molecular functions of MYOCD have been obtained from cell culture studies, and to date, knowledge about in vivo roles of MYOCD comes exclusively from experimental animals. Here, we defined an often lethal congenital human disease associated with inheritance of pathogenic MYOCD variants.

Conserved NPPB+ Border Zone Switches From MEF2- to AP-1-Driven Gene Program.

Background: Surviving cells in the postinfarction border zone are subjected to intense fluctuations of their microenvironment. Recently, border zone cardiomyocytes have been specifically implicated in cardiac regeneration. Here, we defined their unique transcriptional and regulatory properties, and comprehensively validated new molecular markers, including Nppb, encoding B-type natriuretic peptide, after infarction.

Renal cystic disease in the Fbn1 Marfan mouse is associated with enhanced aortic aneurysm formation.

Marfan syndrome (MFS) is a connective tissue disorder caused by mutations in the fibrillin-1 gene (FBN1), resulting in aortic aneurysm formation and dissections. Interestingly, variable aortopathy is observed even within MFS families with the same mutation. Thus, additional risk factors determine disease severity.

AAV9-mediated Rbm24 overexpression induces fibrosis in the mouse heart.

The RNA-binding protein Rbm24 has recently been identified as a pivotal splicing factor in the developing heart. Loss of Rbm24 in mice disrupts cardiac development by governing a large number of muscle-specific splicing events. Since Rbm24 knockout mice are embryonically lethal, the role of Rbm24 in the adult heart remained unexplored.

A common co-morbidity modulates disease expression and treatment efficacy in inherited cardiac sodium channelopathy.

Aims: Management of patients with inherited cardiac ion channelopathy is hindered by variability in disease severity and sudden cardiac death (SCD) risk. Here, we investigated the modulatory role of hypertrophy on arrhythmia and SCD risk in sodium channelopathy.

Methods And Results: Follow-up data was collected from 164 individuals positive for the SCN5A-1795insD founder mutation and 247 mutation-negative relatives.

RBM20 Mutations Induce an Arrhythmogenic Dilated Cardiomyopathy Related to Disturbed Calcium Handling.

Background: Mutations in RBM20 (RNA-binding motif protein 20) cause a clinically aggressive form of dilated cardiomyopathy, with an increased risk of malignant ventricular arrhythmias. RBM20 is a splicing factor that targets multiple pivotal cardiac genes, such as Titin (TTN) and CAMK2D (calcium/calmodulin-dependent kinase II delta). Aberrant TTN splicing is thought to be the main determinant of RBM20-induced dilated cardiomyopathy, but is not likely to explain the increased risk of arrhythmias.

The MEF2 transcriptional target DMPK induces loss of sarcomere structure and cardiomyopathy.

Aims: The pathology of heart failure is characterized by poorly contracting and dilated ventricles. At the cellular level, this is associated with lengthening of individual cardiomyocytes and loss of sarcomeres. While it is known that the transcription factor myocyte enhancer factor-2 (MEF2) is involved in this cardiomyocyte remodelling, the underlying mechanism remains to be elucidated.

Cardiac circRNAs arise mainly from constitutive exons rather than alternatively spliced exons.

Circular RNAs (circRNAs) are a relatively new class of RNA molecules, and knowledge about their biogenesis and function is still in its infancy. It was recently shown that alternative splicing underlies the formation of circular RNAs (circRNA) arising from the Titin gene. Since the main mechanism by which circRNAs are formed is still unclear, we hypothesized that alternative splicing, and in particular exon skipping, is a major driver of circRNA production.

Z-disc protein CHAPb induces cardiomyopathy and contractile dysfunction in the postnatal heart.

Aims: The Z-disc is a crucial structure of the sarcomere and is implicated in mechanosensation/transduction. Dysregulation of Z-disc proteins often result in cardiomyopathy. We have previously shown that the Z-disc protein Cytoskeletal Heart-enriched Actin-associated Protein (CHAP) is essential for cardiac and skeletal muscle development.

The RNA-binding protein Rbm38 is dispensable during pressure overload-induced cardiac remodeling in mice.

The importance of tightly controlled alternative pre-mRNA splicing in the heart is emerging. The RNA binding protein Rbm24 has recently been identified as a pivotal cardiac splice factor, which governs sarcomerogenesis in the heart by controlling the expression of alternative protein isoforms. Rbm38, a homolog of Rbm24, has also been implicated in RNA processes such as RNA splicing, RNA stability and RNA translation, but its function in the heart is currently unknown.

Aortic microcalcification is associated with elastin fragmentation in Marfan syndrome.

Marfan syndrome (MFS) is a connective tissue disorder in which aortic rupture is the major cause of death. MFS patients with an aortic diameter below the advised limit for prophylactic surgery (<5 cm) may unexpectedly experience an aortic dissection or rupture, despite yearly monitoring. Hence, there is a clear need for improved prognostic markers to predict such aortic events.

High miR-124-3p expression identifies smoking individuals susceptible to atherosclerosis.

Background And Aims: The risk of developing cardiovascular disease (CVD) is twice as high among smoking individuals compared to non-smokers. Monocytes are involved in smoking-related atherosclerotic plaque formation. In this study, we investigated whether smokers with an increased risk of developing CVD can be identified on the basis of monocyte-derived miRNA expression levels.

RBM20 Regulates Circular RNA Production From the Titin Gene.

Rationale: RNA-binding motif protein 20 (RBM20) is essential for normal splicing of many cardiac genes, and loss of RBM20 causes dilated cardiomyopathy. Given its role in splicing, we hypothesized an important role for RBM20 in forming circular RNAs (circRNAs), a novel class of noncoding RNA molecules.

Objective: To establish the role of RBM20 in the formation of circRNAs in the heart.