Pathogenic variants damage cell composition and single cell transcription in cardiomyopathies.

Pathogenic variants in genes that cause dilated cardiomyopathy (DCM) and arrhythmogenic cardiomyopathy (ACM) convey high risks for the development of heart failure through unknown mechanisms. Using single-nucleus RNA sequencing, we characterized the transcriptome of 880,000 nuclei from 18 control and 61 failing, nonischemic human hearts with pathogenic variants in DCM and ACM genes or idiopathic disease. We performed genotype-stratified analyses of the ventricular cell lineages and transcriptional states.

Cardiomyocyte BRAF and type 1 RAF inhibitors promote cardiomyocyte and cardiac hypertrophy in mice in vivo.

The extracellular signal-regulated kinase 1/2 (ERK1/2) cascade promotes cardiomyocyte hypertrophy and is cardioprotective, with the three RAF kinases forming a node for signal integration. Our aims were to determine if BRAF is relevant for human heart failure, whether BRAF promotes cardiomyocyte hypertrophy, and if Type 1 RAF inhibitors developed for cancer (that paradoxically activate ERK1/2 at low concentrations: the 'RAF paradox') may have the same effect. BRAF was up-regulated in heart samples from patients with heart failure compared with normal controls.

Redefining IL11 as a regeneration-limiting hepatotoxin and therapeutic target in acetaminophen-induced liver injury.

Acetaminophen (-acetyl--aminophenol; APAP) toxicity is a common cause of liver damage. In the mouse model of APAP-induced liver injury (AILI), interleukin 11 (IL11) is highly up-regulated and administration of recombinant human IL11 (rhIL11) has been shown to be protective. Here, we demonstrate that the beneficial effect of rhIL11 in the mouse model of AILI is due to its inhibition of endogenous mouse IL11 activity.

Reevaluating the Genetic Contribution of Monogenic Dilated Cardiomyopathy.

Background: Dilated cardiomyopathy (DCM) is genetically heterogeneous, with >100 purported disease genes tested in clinical laboratories. However, many genes were originally identified based on candidate-gene studies that did not adequately account for background population variation. Here we define the frequency of rare variation in 2538 patients with DCM across protein-coding regions of 56 commonly tested genes and compare this to both 912 confirmed healthy controls and a reference population of 60 706 individuals to identify clinically interpretable genes robustly associated with dominant monogenic DCM.

Author Correction: WWP2 regulates pathological cardiac fibrosis by modulating SMAD2 signaling.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

WWP2 regulates pathological cardiac fibrosis by modulating SMAD2 signaling.

Cardiac fibrosis is a final common pathology in inherited and acquired heart diseases that causes cardiac electrical and pump failure. Here, we use systems genetics to identify a pro-fibrotic gene network in the diseased heart and show that this network is regulated by the E3 ubiquitin ligase WWP2, specifically by the WWP2-N terminal isoform. Importantly, the WWP2-regulated pro-fibrotic gene network is conserved across different cardiac diseases characterized by fibrosis: human and murine dilated cardiomyopathy and repaired tetralogy of Fallot.

Widespread Translational Control of Fibrosis in the Human Heart by RNA-Binding Proteins.

Background: Fibrosis is a common pathology in many cardiac disorders and is driven by the activation of resident fibroblasts. The global posttranscriptional mechanisms underlying fibroblast-to-myofibroblast conversion in the heart have not been explored.

Methods: Genome-wide changes of RNA transcription and translation during human cardiac fibroblast activation were monitored with RNA sequencing and ribosome profiling.

The Translational Landscape of the Human Heart.

Gene expression in human tissue has primarily been studied on the transcriptional level, largely neglecting translational regulation. Here, we analyze the translatomes of 80 human hearts to identify new translation events and quantify the effect of translational regulation. We show extensive translational control of cardiac gene expression, which is orchestrated in a process-specific manner.

A gene-centric strategy for identifying disease-causing rare variants in dilated cardiomyopathy.

Purpose: We evaluated strategies for identifying disease-causing variants in genetic testing for dilated cardiomyopathy (DCM).

Methods: Cardiomyopathy gene panel testing was performed in 532 DCM patients and 527 healthy control subjects. Rare variants in 41 genes were stratified using variant-level and gene-level characteristics.

Natural genetic variation of the cardiac transcriptome in non-diseased donors and patients with dilated cardiomyopathy.

Background: Genetic variation is an important determinant of RNA transcription and splicing, which in turn contributes to variation in human traits, including cardiovascular diseases.

Results: Here we report the first in-depth survey of heart transcriptome variation using RNA-sequencing in 97 patients with dilated cardiomyopathy and 108 non-diseased controls. We reveal extensive differences of gene expression and splicing between dilated cardiomyopathy patients and controls, affecting known as well as novel dilated cardiomyopathy genes.

Defining the genetic architecture of hypertrophic cardiomyopathy: re-evaluating the role of non-sarcomeric genes.

Aim: Hypertrophic cardiomyopathy (HCM) exhibits genetic heterogeneity that is dominated by variation in eight sarcomeric genes. Genetic variation in a large number of non-sarcomeric genes has also been implicated in HCM but not formally assessed. Here we used very large case and control cohorts to determine the extent to which variation in non-sarcomeric genes contributes to HCM.

The Calcineurin Variant CnAβ1 Controls Mouse Embryonic Stem Cell Differentiation by Directing mTORC2 Membrane Localization and Activation.

Embryonic stem cells (ESC) have the potential to generate all the cell lineages that form the body. However, the molecular mechanisms underlying ESC differentiation and especially the role of alternative splicing in this process remain poorly understood. Here, we show that the alternative splicing regulator MBNL1 promotes generation of the atypical calcineurin Aβ variant CnAβ1 in mouse ESCs (mESC).

ZBTB17 (MIZ1) Is Important for the Cardiac Stress Response and a Novel Candidate Gene for Cardiomyopathy and Heart Failure.

Background: Mutations in sarcomeric and cytoskeletal proteins are a major cause of hereditary cardiomyopathies, but our knowledge remains incomplete as to how the genetic defects execute their effects.

Methods And Results: We used cysteine and glycine-rich protein 3, a known cardiomyopathy gene, in a yeast 2-hybrid screen and identified zinc-finger and BTB domain-containing protein 17 (ZBTB17) as a novel interacting partner. ZBTB17 is a transcription factor that contains the peak association signal (rs10927875) at the replicated 1p36 cardiomyopathy locus.

Integrated allelic, transcriptional, and phenomic dissection of the cardiac effects of titin truncations in health and disease.

The recent discovery of heterozygous human mutations that truncate full-length titin (TTN, an abundant structural, sensory, and signaling filament in muscle) as a common cause of end-stage dilated cardiomyopathy (DCM) promises new prospects for improving heart failure management. However, realization of this opportunity has been hindered by the burden of TTN-truncating variants (TTNtv) in the general population and uncertainty about their consequences in health or disease. To elucidate the effects of TTNtv, we coupled TTN gene sequencing with cardiac phenotyping in 5267 individuals across the spectrum of cardiac physiology and integrated these data with RNA and protein analyses of human heart tissues.

Regulated inositol-requiring protein 1-dependent decay as a mechanism of corin RNA and protein deficiency in advanced human systolic heart failure.

Background: The compensatory actions of the endogenous natriuretic peptide system require adequate processing of natriuretic peptide pro‐hormones into biologically active, carboxyl‐terminal fragments. Natriuretic peptide pro‐peptide processing is accomplished by corin, a transmembrane serine protease expressed by cardiomyocytes. Brain natriuretic peptide (BNP) processing is inadequate in advanced heart failure and is independently associated with adverse outcomes; however, the molecular mechanisms causing impaired BNP processing are not understood.

Heat shock protein-27 delays acute rejection after cardiac transplantation: an experimental model.

Background: Rejection is the major obstacle to survival after cardiac transplantation. We investigated whether overexpression of heat shock protein (Hsp)-27 in mouse hearts protects against acute rejection and the mechanisms of such protection.

Methods: Hearts from B10.

Follistatin-like 3 mediates paracrine fibroblast activation by cardiomyocytes.

Follistatins are extracellular inhibitors of the TGF-β family ligands including activin A, myostatin and bone morphogenetic proteins. Follistatin-like 3 (FSTL3) is a potent inhibitor of activin signalling and antagonises the cardioprotective role of activin A in the heart. FSTL3 expression is elevated in patients with heart failure and is upregulated in cardiomyocytes by hypertrophic stimuli, but its role in cardiac remodelling is largely unknown.

Endonuclease G is a novel determinant of cardiac hypertrophy and mitochondrial function.

Left ventricular mass (LVM) is a highly heritable trait and an independent risk factor for all-cause mortality. So far, genome-wide association studies have not identified the genetic factors that underlie LVM variation, and the regulatory mechanisms for blood-pressure-independent cardiac hypertrophy remain poorly understood. Unbiased systems genetics approaches in the rat now provide a powerful complementary tool to genome-wide association studies, and we applied integrative genomics to dissect a highly replicated, blood-pressure-independent LVM locus on rat chromosome 3p.

Telethonin deficiency is associated with maladaptation to biomechanical stress in the mammalian heart.

Rationale: Telethonin (also known as titin-cap or t-cap) is a 19-kDa Z-disk protein with a unique β-sheet structure, hypothesized to assemble in a palindromic way with the N-terminal portion of titin and to constitute a signalosome participating in the process of cardiomechanosensing. In addition, a variety of telethonin mutations are associated with the development of several different diseases; however, little is known about the underlying molecular mechanisms and telethonin's in vivo function.

Objective: Here we aim to investigate the role of telethonin in vivo and to identify molecular mechanisms underlying disease as a result of its mutation.

Calcineurin splicing variant calcineurin Aβ1 improves cardiac function after myocardial infarction without inducing hypertrophy.

Background: Calcineurin is a calcium-regulated phosphatase that plays a major role in cardiac hypertrophy. We previously described that alternative splicing of the calcineurin Aβ (CnAβ) gene generates the CnAβ1 isoform, with a unique C-terminal region that is different from the autoinhibitory domain present in all other CnA isoforms. In skeletal muscle, CnAβ1 is necessary for myoblast proliferation and stimulates regeneration, reducing fibrosis and accelerating the resolution of inflammation.

Reverse remodelling and recovery from heart failure are associated with complex patterns of gene expression.

Combined left ventricular assist device (LVAD) support and pharmacological management of the failing heart can induce reversal of maladaptive cardiac remodelling leading to normalisation of cardiac structure and recovery of cardiac function. The purpose of this study was to compare the gene expression profiles of recovered and non-recovered LVAD patients in order to identify mechanisms underlying the recovery process and differences which may determine outcome. Myocardial expression of 54 genes chosen for their potential role in heart failure and tissue repair was measured using quantitative PCR at the time of LVAD implantation and again at explantation (recovery, n = 13) or transplantation (non-recovery, n = 5).

Clenbuterol induces cardiac myocyte hypertrophy via paracrine signalling and fibroblast-derived IGF-1.

The β(2)-selective adrenoreceptor agonist clenbuterol promotes both skeletal and cardiac muscle hypertrophy and is undergoing clinical trials in the treatment of muscle wasting and heart failure. We have previously demonstrated that clenbuterol induces a mild physiological ventricular hypertrophy in vivo with normal contractile function and without induction of α-skeletal muscle actin (αSkA), a marker of pathological hypertrophy. The mechanisms of this response remain poorly defined.

A gene expression profile of the myocardial response to clenbuterol.

Clenbuterol is currently being used as part of a clinical trial into a novel therapeutic approach for the treatment of end-stage heart failure. The purpose of this study was to determine the global pattern of myocardial gene expression in response to clenbuterol and to identify novel targets and pathways involved. Rats were treated with clenbuterol (n = 6) or saline (n = 6) for periods of 1, 3, 9, or 28 days.

Overexpression of the transcription factor Hand1 causes predisposition towards arrhythmia in mice.

Elevated levels of the cardiac transcription factor Hand1 have been reported in several adult cardiac diseases but it is unclear whether this change is itself maladaptive with respect to heart function. To test this possibility, we have developed a novel, inducible transgenic system, and used it to overexpress Hand1 in adult mouse hearts. Overexpression of Hand1 in the adult mouse heart leads to mild cardiac hypertrophy and a reduction in life expectancy.