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Heart failure with reduced ejection fraction (HFrEF) is associated with high mortality, highlighting an urgent need for new therapeutic strategies. As stress-activated cardiac signaling cascades converge on the nucleus to drive maladaptive gene programs, interdicting pathological transcription is a conceptually attractive approach for HFrEF therapy. Here, we demonstrate that CDK7/12/13 are critical regulators of transcription activation in the heart that can be pharmacologically inhibited to improve HFrEF. CDK7/12/13 inhibition using the first-in-class inhibitor THZ1 or RNAi blocks stress-induced transcription and pathologic hypertrophy in cultured rodent cardiomyocytes. THZ1 potently attenuates adverse cardiac remodeling and HFrEF pathogenesis in mice and blocks cardinal features of disease in human iPSC-derived cardiomyocytes. THZ1 suppresses Pol II enrichment at stress-transactivated cardiac genes and inhibits a specific pathologic gene program in the failing mouse heart. These data identify CDK7/12/13 as druggable regulators of cardiac gene transactivation during disease-related stress, suggesting that HFrEF features a critical dependency on transcription that can be therapeutically exploited.

Developing new and effective medicines is perhaps one of the most important, yet difficult endeavors that we pursue as a society. As a drug developer, I am part of a [...]

In diseased organs, stress-activated signalling cascades alter chromatin, thereby triggering maladaptive cell state transitions. Fibroblast activation is a common stress response in tissues that worsens lung, liver, kidney and heart disease, yet its mechanistic basis remains unclear1,2. Pharmacological inhibition of bromodomain and extra-terminal domain (BET) proteins alleviates cardiac dysfunction3-7, providing a tool to interrogate and modulate cardiac cell states as a potential therapeutic approach. Here we use single-cell epigenomic analyses of hearts dynamically exposed to BET inhibitors to reveal a reversible transcriptional switch that underlies the activation of fibroblasts. Resident cardiac fibroblasts demonstrated robust toggling between the quiescent and activated state in a manner directly correlating with BET inhibitor exposure and cardiac function. Single-cell chromatin accessibility revealed previously undescribed DNA elements, the accessibility of which dynamically correlated with cardiac performance. Among the most dynamic elements was an enhancer that regulated the transcription factor MEOX1, which was specifically expressed in activated fibroblasts, occupied putative regulatory elements of a broad fibrotic gene program and was required for TGFβ-induced fibroblast activation. Selective CRISPR inhibition of the single most dynamic cis-element within the enhancer blocked TGFβ-induced Meox1 activation. We identify MEOX1 as a central regulator of fibroblast activation associated with cardiac dysfunction and demonstrate its upregulation after activation of human lung, liver and kidney fibroblasts. The plasticity and specificity of BET-dependent regulation of MEOX1 in tissue fibroblasts provide previously unknown trans- and cis-targets for treating fibrotic disease.

BackgroundGene regulatory networks control tissue homeostasis and disease progression in a cell type-specific manner. Ubiquitously expressed chromatin regulators modulate these networks, yet the mechanisms governing how tissue specificity of their function is achieved are poorly understood. BRD4 (bromodomain-containing protein 4), a member of the BET (bromo- and extraterminal domain) family of ubiquitously expressed acetyl-lysine reader proteins, plays a pivotal role as a coactivator of enhancer signaling across diverse tissue types in both health and disease and has been implicated as a pharmacological target in heart failure. However, the cell-specific role of BRD4 in adult cardiomyocytes remains unknown.MethodsWe combined conditional mouse genetics, unbiased transcriptomic and epigenomic analyses, and classic molecular biology and biochemical approaches to understand the mechanism by which BRD4 in adult cardiomyocyte homeostasis.ResultsHere, we show that cardiomyocyte-specific deletion of Brd4 in adult mice leads to acute deterioration of cardiac contractile function with mutant animals demonstrating a transcriptomic signature characterized by decreased expression of genes critical for mitochondrial energy production. Genome-wide occupancy data show that BRD4 enriches at many downregulated genes (including the master coactivators Ppargc1a, Ppargc1b, and their downstream targets) and preferentially colocalizes with GATA4 (GATA binding protein 4), a lineage-determining cardiac transcription factor not previously implicated in regulation of adult cardiac metabolism. BRD4 and GATA4 form an endogenous complex in cardiomyocytes and interact in a bromodomain-independent manner, revealing a new functional interaction partner for BRD4 that can direct its locus and tissue specificity.ConclusionsThese results highlight a novel role for a BRD4-GATA4 module in cooperative regulation of a cardiomyocyte-specific gene program governing bioenergetic homeostasis in the adult heart.

Salt-inducible kinases (SIKs) are key regulators of cellular metabolism and growth, but their role in cardiomyocyte plasticity and heart failure pathogenesis remains unknown. Here, we showed that loss of SIK1 kinase activity protected against adverse cardiac remodeling and heart failure pathogenesis in rodent models and cardiomyocytes derived from human induced pluripotent stem cells. We found that SIK1 phosphorylated and stabilized histone deacetylase 7 (HDAC7) protein during cardiac stress, an event that is required for pathologic cardiomyocyte remodeling. Gain- and loss-of-function studies of HDAC7 in cultured cardiomyocytes implicated HDAC7 as a prohypertrophic signaling effector that can induce c-Myc expression, indicating a functional departure from the canonical MEF2 corepressor function of class IIa HDACs. Taken together, our findings reveal what we believe to be a previously unrecognized role for a SIK1/HDAC7 axis in regulating cardiac stress responses and implicate this pathway as a potential target in human heart failure.

RationaleSmall molecule inhibitors of the acetyl-histone binding protein BRD4 have been shown to block cardiac fibrosis in preclinical models of heart failure (HF). However, since the inhibitors target BRD4 ubiquitously, it is unclear whether this chromatin reader protein functions in cell type-specific manner to control pathological myocardial fibrosis. Furthermore, the molecular mechanisms by which BRD4 stimulates the transcriptional program for cardiac fibrosis remain unknown.ObjectiveWe sought to test the hypothesis that BRD4 functions in a cell-autonomous and signal-responsive manner to control activation of cardiac fibroblasts, which are the major extracellular matrix-producing cells of the heart.Methods and resultsRNA-sequencing, mass spectrometry, and cell-based assays employing primary adult rat ventricular fibroblasts demonstrated that BRD4 functions as an effector of TGF-β (transforming growth factor-β) signaling to stimulate conversion of quiescent cardiac fibroblasts into Periostin (Postn)-positive cells that express high levels of extracellular matrix. These findings were confirmed in vivo through whole-transcriptome analysis of cardiac fibroblasts from mice subjected to transverse aortic constriction and treated with the small molecule BRD4 inhibitor, JQ1. Chromatin immunoprecipitation-sequencing revealed that BRD4 undergoes stimulus-dependent, genome-wide redistribution in cardiac fibroblasts, becoming enriched on a subset of enhancers and super-enhancers, and leading to RNA polymerase II activation and expression of downstream target genes. Employing the Sertad4 (SERTA domain-containing protein 4) locus as a prototype, we demonstrate that dynamic chromatin targeting of BRD4 is controlled, in part, by p38 MAPK (mitogen-activated protein kinase) and provide evidence of a critical function for Sertad4 in TGF-β-mediated cardiac fibroblast activation.ConclusionsThese findings define BRD4 as a central regulator of the pro-fibrotic cardiac fibroblast phenotype, establish a p38-dependent signaling circuit for epigenetic reprogramming in heart failure, and uncover a novel role for Sertad4. The work provides a mechanistic foundation for the development of BRD4 inhibitors as targeted anti-fibrotic therapies for the heart.

Heart failure (HF) is a dominant cause of morbidity and mortality in the developed world, with available pharmacotherapies limited by high rates of residual mortality and a failure to directly target the changes in cell state that drive adverse cardiac remodeling. Pathologic cardiac remodeling is driven by stress-activated cardiac signaling cascades that converge on defined components of the chromatin regulatory apparatus in the nucleus, triggering broad shifts in transcription and cell state. Thus, studies focusing on how cytosolic signaling pathways couple to the nuclear gene control machinery has been an area of therapeutic interest in HF. In this review, we discuss current concepts pertaining to the role of chromatin regulators in HF pathogenesis, with a focus on specific proteins and RNA-containing macromolecular complexes that have shown promise as druggable targets in the experimental setting.

Advances in our understanding of the basic biology and biochemistry of chromatin structure and function at genome scales has led to tremendous growth in the fields of epigenomics and transcriptional biology. While it has long been appreciated that transcriptional pathways are dysregulated in failing hearts, only recently has the idea of disrupting altered transcription by targeting chromatin-associated proteins been explored. Here, we provide a brief overview of efforts to drug transcription in the context of heart failure, focusing on the bromo- and extra-terminal domain (BET) family of chromatin co-activator proteins.

Despite current standard of care, the average 5-year mortality after an initial diagnosis of heart failure (HF) is about 40%, reflecting an urgent need for new therapeutic approaches. Previous studies demonstrated that the epigenetic reader protein bromodomain-containing protein 4 (BRD4), an emerging therapeutic target in cancer, functions as a critical coactivator of pathologic gene transactivation during cardiomyocyte hypertrophy. However, the therapeutic relevance of these findings to human disease remained unknown. We demonstrate that treatment with the BET bromodomain inhibitor JQ1 has therapeutic effects during severe, preestablished HF from prolonged pressure overload, as well as after a massive anterior myocardial infarction in mice. Furthermore, JQ1 potently blocks agonist-induced hypertrophy in human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs). Integrated transcriptomic analyses across animal models and human iPSC-CMs reveal that BET inhibition preferentially blocks transactivation of a common pathologic gene regulatory program that is robustly enriched for NFκB and TGF-β signaling networks, typified by innate inflammatory and profibrotic myocardial genes. As predicted by these specific transcriptional mechanisms, we found that JQ1 does not suppress physiological cardiac hypertrophy in a mouse swimming model. These findings establish that pharmacologically targeting innate inflammatory and profibrotic myocardial signaling networks at the level of chromatin is effective in animal models and human cardiomyocytes, providing the critical rationale for further development of BET inhibitors and other epigenomic medicines for HF.

Classic physiology studies dating to the 1930s demonstrate that moderate or transient glucocorticoid (GC) exposure improves muscle performance. The ergogenic properties of GCs are further evidenced by their surreptitious use as doping agents by endurance athletes and poorly understood efficacy in Duchenne muscular dystrophy (DMD), a genetic muscle-wasting disease. A defined molecular basis underlying these performance-enhancing properties of GCs in skeletal muscle remains obscure. Here, we demonstrate that ergogenic effects of GCs are mediated by direct induction of the metabolic transcription factor KLF15, defining a downstream pathway distinct from that resulting in GC-related muscle atrophy. Furthermore, we establish that KLF15 deficiency exacerbates dystrophic severity and muscle GC-KLF15 signaling mediates salutary therapeutic effects in the mdx mouse model of DMD. Thus, although glucocorticoid receptor (GR)-mediated transactivation is often associated with muscle atrophy and other adverse effects of pharmacologic GC administration, our data define a distinct GR-induced gene regulatory pathway that contributes to therapeutic effects of GCs in DMD through proergogenic metabolic programming.

Heart failure (HF) with reduced contractile function is a common and lethal syndrome in which the heart cannot pump blood to adequately meet bodily demands, resulting in high mortality despite the current standard of care. In modern societies, the most common drivers of HF are ischemic heart disease and hypertension. However, in a substantial subset of cases, patients present with dilated and poorly contracting hearts without evidence of common inciting stressors, a syndrome called dilated cardiomyopathy (DCM). Genome sequencing has identified a host of deleterious germline variants in key cardiomyocyte genes as causes of heritable DCM, including mutations in LMNA, which encodes the nuclear lamina-associated protein lamin A/C. In this issue of the JCI, Auguste et al. generate a mouse model of DCM in which they delete Lmna in cardiomyocytes and discover that bromodomain and extraterminal (BET) protein activation is a druggable epigenetic mechanism of disease pathogenesis in this heritable HF syndrome., Laminopathies LMNA encodes an intermediate filament protein with several complex functions, including maintenance of nuclear ultrastructure, mechanotransduction, and regulation of gene expression (1). Autosomal dominant germline mutations in LMNA cause [...]

Delivery of oxygen to tissues is the primary function of the cardiovascular system. NO, a gasotransmitter that signals predominantly through protein S-nitrosylation to form S-nitrosothiols (SNOs) in target proteins, operates [...]

Sudden cardiac death exhibits diurnal variation in both acquired and hereditary forms of heart disease (1,2), but the molecular basis of this variation is unknown. A common mechanism that underlies susceptibility to ventricular arrhythmias is abnormalities in the duration (for example, short or long QT syndromes and heart failure) (3-5) or pattern (for example, Brugada's syndrome) (6) of myocardial repolarization. Here we provide molecular evidence that links circadian rhythms to vulnerability in ventricular arrhythmias in mice. Specifically, we show that cardiac ion-channel expression and QT-interval duration (an index of myocardial repolarization) exhibit endogenous circadian rhythmicity under the control of a clock-dependent oscillator, kruppel-like factor 15 (Klf15). Klf15 transcriptionally controls rhythmic expression of Kv channel-interacting protein 2 (KChIP2), a critical subunit required for generating the transient outward potassium current (7). Deficiency or excess of Klf15 causes loss of rhythmic QT variation, abnormal repolarization and enhanced susceptibility to ventricular arrhythmias. These findings identify circadian transcription of ion channels as a mechanism for cardiac arrhythmogenesis., Sudden cardiac death from ventricular arrhythmias is the principal cause of mortality from heart disease worldwide and remains a major unresolved public health problem. The incidence of sudden cardiac death [...]

Cardiac hypertrophy is a common response to injury and hemodynamic stress and an important harbinger of heart failure and death. Herein, we identify the Kruppel-like factor 15 (KLF15) as an inhibitor of cardiac hypertrophy. Myocardial expression of KLF15 is reduced in rodent models of hypertrophy and in biopsy samples from patients with pressure-overload induced by chronic valvular aortic stenosis. Overexpression of KLF15 in neonatal rat ventricular cardiomyocytes inhibits cell size, protein synthesis and hypertrophic gene expression. KLF15-null mice are viable but, in response to pressure overload, develop an eccentric form of cardiac hypertrophy characterized by increased heart weight, exaggerated expression of hypertrophic genes, left ventricular cavity dilatation with increased myocyte size, and reduced left ventricular systolic function. Mechanistically, a combination of promoter analyses and gel-shift studies suggest that KLF15 can inhibit GATA4 and myocyte enhancer factor 2 function. These studies identify KLF15 as part of a heretofore unrecognized pathway regulating the cardiac response to hemodynamic stress. heart | transcription