ABSTRACT
Sodium-glucose co-transporter 2 inhibitors (SGLT2i) are novel, potent heart failure medications with an unknown mechanism of action. We sought to determine if the beneficial actions of SGLT2i in heart failure were on- or off-target, and related to metabolic reprogramming, including increased lipolysis and ketogenesis. The phenotype of mice treated with empagliflozin and genetically engineered mice constitutively lacking SGLT2 mirrored metabolic changes seen in human clinical trials (including reduced blood glucose, increased ketogenesis, and profound glucosuria). In a mouse heart failure model, SGLT2i treatment, but not generalized SGLT2 knockout, resulted in improved systolic function and reduced pathologic cardiac remodeling. SGLT2i treatment of the SGLT2 knockout mice sustained the cardiac benefits, demonstrating an off-target role for these drugs. This benefit is independent of metabolic changes, including ketosis. The mechanism of action and target of SGLT2i in HF remain elusive.
ABSTRACT
Chronic inflammation and tissue fibrosis are common stress responses that worsen organ function, yet the molecular mechanisms governing their crosstalk are poorly understood. In diseased organs, stress-induced changes in gene expression fuel maladaptive cell state transitions and pathological interaction between diverse cellular compartments. Although chronic fibroblast activation worsens dysfunction of lung, liver, kidney, and heart, and exacerbates many cancers, the stress-sensing mechanisms initiating the transcriptional activation of fibroblasts are not well understood. Here, we show that conditional deletion of the transcription co-activator Brd4 in Cx3cr1-positive myeloid cells ameliorates heart failure and is associated with a dramatic reduction in fibroblast activation. Analysis of single-cell chromatin accessibility and BRD4 occupancy in vivo in Cx3cr1-positive cells identified a large enhancer proximal to Interleukin-1 beta (Il1b), and a series of CRISPR deletions revealed the precise stress-dependent regulatory element that controlled expression of Il1b in disease. Secreted IL1B functioned non-cell autonomously to activate a p65/RELA-dependent enhancer near the transcription factor MEOX1, resulting in a profibrotic response in human cardiac fibroblasts. In vivo, antibody-mediated IL1B neutralization prevented stress-induced expression of MEOX1, inhibited fibroblast activation, and improved cardiac function in heart failure. The elucidation of BRD4-dependent crosstalk between a specific immune cell subset and fibroblasts through IL1B provides new therapeutic strategies for heart disease and other disorders of chronic inflammation and maladaptive tissue remodeling.
ABSTRACT
Circadian time of intake determines the cardioprotective outcome of glucocorticoids in normal and infarcted hearts. The cardiomyocyte-specific glucocorticoid receptor (GR) is genetically required to preserve normal heart function in the long-term. The GR co-factor KLF15 is a pleiotropic regulator of cardiac metabolism. However, the cardiomyocyte-autonomous metabolic targets of the GR-KLF15 concerted epigenetic action remain undefined. Here we report that circadian time of intake determines the activation of a transcriptional and functional glucose oxidation program in heart by the glucocorticoid prednisone with comparable magnitude between sexes. We overlayed transcriptomics, epigenomics and cardiomyocyte-specific inducible ablation of either GR or KLF15. Downstream of a light-phase prednisone stimulation in mice, we found that both factors are non-redundantly required in heart to transactivate the adiponectin receptor expression (Adipor1) and promote insulin-stimulated glucose uptake, as well as transactivate the mitochondrial pyruvate complex expression (Mpc1/2) and promote pyruvate oxidation. We then challenged this time-specific drug effect in obese diabetic db/db mice, where the heart shows insulin resistance and defective glucose oxidation. Opposite to dark-phase dosing, light-phase prednisone rescued glucose oxidation in db/db cardiomyocytes and diastolic function in db/db hearts towards control-like levels with sex-independent magnitude of effect. In summary, our study identifies novel cardiomyocyte-autonomous metabolic targets of the GR-KLF15 concerted program mediating the time-specific cardioprotective effects of glucocorticoids on cardiomyocyte glucose utilization.
ABSTRACT
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.
Subject(s)
Cyclin-Dependent Kinases , Heart Failure , Animals , Cell Line, Tumor , Cyclin-Dependent Kinases/genetics , Heart Failure/drug therapy , Heart Failure/genetics , Humans , Mice , RNA Polymerase II , Stroke VolumeABSTRACT
Skeletal muscle dynamically regulates systemic nutrient homeostasis through transcriptional adaptations to physiological cues. In response to changes in the metabolic environment (e.g., alterations in circulating glucose or lipid levels), networks of transcription factors and coregulators are recruited to specific genomic loci to fine-tune homeostatic gene regulation. Elucidating these mechanisms is of particular interest as these gene regulatory pathways can serve as potential targets to treat metabolic disease. The zinc-finger transcription factor Krüppel-like factor 15 (KLF15) is a critical regulator of metabolic homeostasis; however, its genome-wide distribution in skeletal muscle has not been previously identified. Here, we characterize the KLF15 cistrome in vivo in skeletal muscle and find that the majority of KLF15 binding is localized to distal intergenic regions and associated with genes related to circadian rhythmicity and lipid metabolism. We also identify critical interdependence between KLF15 and the nuclear receptor PPARδ in the regulation of lipid metabolic gene programs. We further demonstrate that KLF15 and PPARδ colocalize genome-wide, physically interact, and are dependent on one another to exert their transcriptional effects on target genes. These findings reveal that skeletal muscle KLF15 plays a critical role in metabolic adaptation through its direct actions on target genes and interactions with other nodal transcription factors such as PPARδ.
Subject(s)
Kruppel-Like Transcription Factors , Lipid Metabolism , Muscle, Skeletal , PPAR delta , Animals , Kruppel-Like Transcription Factors/genetics , Kruppel-Like Transcription Factors/metabolism , Lipid Metabolism/genetics , Mice , Muscle, Skeletal/metabolism , PPAR delta/genetics , PPAR delta/metabolismABSTRACT
Circulating corticosteroids orchestrate stress adaptation, including inhibition of inflammation. While pathways governing corticosteroid biosynthesis and intracellular signaling are well understood, less is known about mechanisms controlling plasma corticosteroid transport. Here, we show that hepatocyte KLF15 (Kruppel-like factor 15) controls plasma corticosteroid transport and inflammatory responses through direct transcriptional activation of Serpina6, which encodes corticosteroid-binding globulin (CBG). Klf15-deficient mice have profoundly low CBG, reduced plasma corticosteroid binding capacity, and heightened mortality during inflammatory stress. These defects are completely rescued by reconstituting CBG, supporting that KLF15 works primarily through CBG to control plasma corticosterone homeostasis. To understand transcriptional mechanisms, we generated the first KLF15 cistromes using newly engineered Klf153xFLAG mice. Unexpectedly, liver KLF15 is predominantly promoter enriched, including Serpina6, where it binds a palindromic GC-rich motif, opens chromatin, and transactivates genes with minimal associated direct gene repression. Overall, we provide critical mechanistic insight into KLF15 function and identify a hepatocyte-intrinsic transcriptional module that potently regulates systemic corticosteroid transport and inflammation.
ABSTRACT
Compelling evidence supports a causal role for lipoprotein(a) (Lp(a)) in cardiovascular disease. No pharmacotherapies directly targeting Lp(a) are currently available for clinical use. Here we report the discovery and development of olpasiran, a first-in-class, synthetic, double-stranded, N-acetylgalactosamine-conjugated small interfering RNA (siRNA) designed to directly inhibit LPA messenger RNA translation in hepatocytes and potently reduce plasma Lp(a) concentration. Olpasiran reduced Lp(a) concentrations in transgenic mice and cynomolgus monkeys in a dose-responsive manner, achieving up to over 80% reduction from baseline for 5-8 weeks after administration of a single dose. In a phase 1 dose-escalation trial of olpasiran (ClinicalTrials.gov: NCT03626662 ), the primary outcome was safety and tolerability, and the secondary outcomes were the change in Lp(a) concentrations and olpasiran pharmacokinetic parameters. Participants tolerated single doses of olpasiran well and experienced a 71-97% reduction in Lp(a) concentration with effects persisting for several months after administration of doses of 9 mg or higher. Serum concentrations of olpasiran increased approximately dose proportionally. Collectively, these results validate the approach of using hepatocyte-targeted siRNA to potently lower Lp(a) in individuals with elevated plasma Lp(a) concentration.
Subject(s)
Lipoprotein(a) , RNA, Small Interfering , Adult , Animals , Female , Humans , Male , Mice , Middle Aged , Hyperlipidemias/drug therapy , Lipoprotein(a)/blood , Lipoprotein(a)/genetics , Macaca fascicularis , Mice, Transgenic , RNA, Small Interfering/geneticsABSTRACT
Amyotrophic Lateral Sclerosis (ALS) is a currently incurable disease that causes progressive motor neuron loss, paralysis and death. Skeletal muscle pathology occurs early during the course of ALS. It is characterized by impaired mitochondrial biogenesis, metabolic dysfunction and deterioration of the neuromuscular junction (NMJ), the synapse through which motor neurons communicate with muscles. Therefore, a better understanding of the molecules that underlie this pathology may lead to therapies that slow motor neuron loss and delay ALS progression. Kruppel Like Factor 15 (KLF15) has been identified as a transcription factor that activates alternative metabolic pathways and NMJ maintenance factors, including Fibroblast Growth Factor Binding Protein 1 (FGFBP1), in skeletal myocytes. In this capacity, KLF15 has been shown to play a protective role in Duchenne muscular dystrophy (DMD) and spinal muscular atrophy (SMA), however its role in ALS has not been evaluated. Here, we examined whether muscle-specific KLF15 overexpression promotes the health of skeletal muscles and NMJs in the SOD1G93A ALS mouse model. We show that muscle-specific KLF15 overexpression did not elicit a significant beneficial effect on skeletal muscle atrophy, NMJ health, motor function, or survival in SOD1G93A ALS mice. Our findings suggest that, unlike in mouse models of DMD and SMA, KLF15 overexpression has a minimal impact on ALS disease progression in SOD1G93A mice.
Subject(s)
Amyotrophic Lateral Sclerosis , Kruppel-Like Transcription Factors , Amyotrophic Lateral Sclerosis/genetics , Amyotrophic Lateral Sclerosis/metabolism , Animals , Disease Models, Animal , Intercellular Signaling Peptides and Proteins/metabolism , Kruppel-Like Transcription Factors/genetics , Kruppel-Like Transcription Factors/metabolism , Longevity , Mice , Mice, Transgenic , Motor Neurons/pathology , Muscle Cells/metabolism , Muscle Cells/pathology , Muscle, Skeletal/pathology , Neuromuscular Junction/metabolism , Superoxide Dismutase-1/genetics , Superoxide Dismutase-1/metabolismABSTRACT
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 TGFß-induced fibroblast activation. Selective CRISPR inhibition of the single most dynamic cis-element within the enhancer blocked TGFß-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.
Subject(s)
Enhancer Elements, Genetic , Fibroblasts/cytology , Heart Diseases/genetics , Homeodomain Proteins/metabolism , Transcription Factors/metabolism , Animals , Chromatin/metabolism , Epigenomics , Gene Expression Regulation , Humans , Mice , Proteins/antagonists & inhibitors , Single-Cell Analysis , Transcriptome , Transforming Growth Factor beta/metabolismABSTRACT
BACKGROUND: Heart failure (HF) with preserved ejection fraction (HFpEF) constitutes half of all HF but lacks effective therapy. Understanding of its myocardial biology remains limited because of a paucity of heart tissue molecular analysis. METHODS: We performed RNA sequencing on right ventricular septal endomyocardial biopsies prospectively obtained from patients meeting consensus criteria for HFpEF (n=41) contrasted with right ventricular septal tissue from patients with HF with reduced ejection fraction (HFrEF, n=30) and donor controls (n=24). Principal component analysis and hierarchical clustering tested for transcriptomic distinctiveness between groups, effect of comorbidities, and differential gene expression with pathway enrichment contrasted HF groups and donor controls. Within HFpEF, non-negative matrix factorization and weighted gene coexpression analysis identified molecular subgroups, and the resulting clusters were correlated with hemodynamic and clinical data. RESULTS: Patients with HFpEF were more often women (59%), African American (68%), obese (median body mass index 41), and hypertensive (98%), with clinical HF characterized by 65% New York Heart Association Class III or IV, nearly all on a loop diuretic, and 70% with a HF hospitalization in the previous year. Principal component analysis separated HFpEF from HFrEF and donor controls with minimal overlap, and this persisted after adjusting for primary comorbidities: body mass index, sex, age, diabetes, and renal function. Hierarchical clustering confirmed group separation. Nearly half the significantly altered genes in HFpEF versus donor controls (1882 up, 2593 down) changed in the same direction in HFrEF; however, 5745 genes were uniquely altered between HF groups. Compared with controls, uniquely upregulated genes in HFpEF were enriched in mitochondrial adenosine triphosphate synthesis/electron transport, pathways downregulated in HFrEF. HFpEF-specific downregulated genes engaged endoplasmic reticulum stress, autophagy, and angiogenesis. Body mass index differences largely accounted for HFpEF upregulated genes, whereas neither this nor broader comorbidity adjustment altered pathways enriched in downregulated genes. Non-negative matrix factorization identified 3 HFpEF transcriptomic subgroups with distinctive pathways and clinical correlates, including a group closest to HFrEF with higher mortality, and a mostly female group with smaller hearts and proinflammatory signaling. These groupings remained after sex adjustment. Weighted gene coexpression analysis yielded analogous gene clusters and clinical groupings. CONCLUSIONS: HFpEF exhibits distinctive broad transcriptomic signatures and molecular subgroupings with particular clinical features and outcomes. The data reveal new signaling targets to consider for precision therapeutics.
Subject(s)
Heart Failure/genetics , Heart Failure/metabolism , Myocardium/metabolism , Stroke Volume/physiology , Transcriptome/physiology , Aged , Cardiac Catheterization/methods , Female , Heart Failure/pathology , Humans , Male , Middle Aged , Myocardium/pathology , Prospective StudiesABSTRACT
BACKGROUND: Gene 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. METHODS: We 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. RESULTS: Here, 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. CONCLUSIONS: These 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.
Subject(s)
Energy Metabolism , GATA4 Transcription Factor/metabolism , Mitochondria, Heart/metabolism , Myocytes, Cardiac/metabolism , Nuclear Proteins/metabolism , Transcription Factors/metabolism , Ventricular Dysfunction, Left/metabolism , Animals , Energy Metabolism/genetics , GATA4 Transcription Factor/genetics , Gene Expression Profiling , Gene Expression Regulation , Genotype , HEK293 Cells , Homeostasis , Humans , Mice, Inbred C57BL , Mice, Knockout , Mitochondria, Heart/genetics , Mitochondria, Heart/ultrastructure , Myocytes, Cardiac/ultrastructure , Nuclear Proteins/genetics , Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha/genetics , Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha/metabolism , Phenotype , Protein Binding , Rats, Sprague-Dawley , Transcription Factors/genetics , Transcriptome , Ventricular Dysfunction, Left/genetics , Ventricular Dysfunction, Left/pathology , Ventricular Dysfunction, Left/physiopathology , Ventricular Function, LeftABSTRACT
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.
Subject(s)
Heart Failure , Lamin Type A , Animals , Heart Failure/genetics , Humans , Lamin Type A/genetics , Mice , Mutation , Nuclear Proteins , Phenotype , Transcription FactorsABSTRACT
The bromodomain and extraterminal (BET) family comprises epigenetic reader proteins that are important regulators of inflammatory and hypertrophic gene expression in the heart. We previously identified the activation of proinflammatory gene networks as a key early driver of dilated cardiomyopathy (DCM) in transgenic mice expressing a mutant form of phospholamban (PLNR9C) - a genetic cause of DCM in humans. We hypothesized that BETs coactivate this inflammatory process, representing a critical node in the progression of DCM. To test this hypothesis, we treated PLNR9C or age-matched WT mice longitudinally with the small molecule BET bromodomain inhibitor JQ1 or vehicle. BET inhibition abrogated adverse cardiac remodeling, reduced cardiac fibrosis, and prolonged survival in PLNR9C mice by inhibiting expression of proinflammatory gene networks at all stages of disease. Specifically, JQ1 had profound effects on proinflammatory gene network expression in cardiac fibroblasts, while having little effect on gene expression in cardiomyocytes. Cardiac fibroblast proliferation was also substantially reduced by JQ1. Mechanistically, we demonstrated that BRD4 serves as a direct and essential regulator of NF-κB-mediated proinflammatory gene expression in cardiac fibroblasts. Suppressing proinflammatory gene expression via BET bromodomain inhibition could be a novel therapeutic strategy for chronic DCM in humans.
Subject(s)
Azepines/pharmacology , Calcium-Binding Proteins/physiology , Cardiomyopathy, Dilated/prevention & control , Fibrosis/prevention & control , Gene Expression Regulation/drug effects , Gene Regulatory Networks/drug effects , Nuclear Proteins/antagonists & inhibitors , Transcription Factors/antagonists & inhibitors , Triazoles/pharmacology , Animals , Cardiomyopathy, Dilated/etiology , Cardiomyopathy, Dilated/metabolism , Cardiomyopathy, Dilated/pathology , Fibrosis/etiology , Fibrosis/metabolism , Fibrosis/pathology , Gene Expression Profiling , Male , Mice , Mice, Inbred C57BL , Mice, KnockoutABSTRACT
Atrial fibrillation (AF) is a highly prevalent cardiac arrhythmia and cause of significant morbidity and mortality. Its increasing prevalence in aging societies constitutes a growing challenge to global healthcare systems. Despite substantial unmet needs in AF prevention and treatment, drug developments hitherto have been challenging, and the current pharmaceutical pipeline is nearly empty. In this review, we argue that current drugs for AF are inadequate because of an oversimplified system for patient classification and the development of drugs that do not interdict underlying disease mechanisms. We posit that an improved understanding of AF molecular pathophysiology related to the continuous identification of novel disease-modifying drug targets and an increased appreciation of patient heterogeneity provide a new framework to personalize AF drug development. Together with recent innovations in diagnostics, remote rhythm monitoring, and big data capabilities, we anticipate that adoption of a new framework for patient subsegmentation based on pathophysiological, genetic, and molecular subsets will improve success rates of clinical trials and advance drugs that reduce the individual patient and public health burden of AF.
Subject(s)
Anti-Arrhythmia Agents/therapeutic use , Atrial Fibrillation/drug therapy , Drug Development/methods , Animals , Atrial Fibrillation/genetics , Atrial Fibrillation/metabolism , Humans , Molecular Targeted Therapy/methodsABSTRACT
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.
Subject(s)
Histone Deacetylases/metabolism , Myocytes, Cardiac/metabolism , Protein Serine-Threonine Kinases/metabolism , Ventricular Remodeling , Animals , Humans , Mice , Myocytes, Cardiac/pathology , Phosphorylation , Rats , Rats, Sprague-DawleyABSTRACT
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.
Subject(s)
Chromatin , Heart Failure , Heart , Heart Failure/genetics , HumansABSTRACT
In humans, chronic glucocorticoid use is associated with side effects like muscle wasting, obesity, and metabolic syndrome. Intermittent steroid dosing has been proposed in Duchenne Muscular Dystrophy patients to mitigate the side effects seen with daily steroid intake. We evaluated biomarkers from Duchenne Muscular Dystrophy patients, finding that, compared with chronic daily steroid use, weekend steroid use was associated with reduced serum insulin, free fatty acids, and branched chain amino acids, as well as reduction in fat mass despite having similar BMIs. We reasoned that intermittent prednisone administration in dystrophic mice would alter muscle epigenomic signatures, and we identified the coordinated action of the glucocorticoid receptor, KLF15 and MEF2C as mediators of a gene expression program driving metabolic reprogramming and enhanced nutrient utilization. Muscle lacking Klf15 failed to respond to intermittent steroids. Furthermore, coadministration of the histone acetyltransferase inhibitor anacardic acid with steroids in mdx mice eliminated steroid-specific epigenetic marks and abrogated the steroid response. Together, these findings indicate that intermittent, repeated exposure to glucocorticoids promotes performance in dystrophic muscle through an epigenetic program that enhances nutrient utilization.
Subject(s)
Glucocorticoids/administration & dosage , Muscle, Skeletal/drug effects , Muscular Dystrophy, Duchenne/drug therapy , Prednisone/administration & dosage , Anacardic Acids/administration & dosage , Animals , Biomarkers/blood , Biomarkers/metabolism , Child , Cross-Sectional Studies , Disease Models, Animal , Drug Therapy, Combination , Epigenesis, Genetic/drug effects , Epigenomics , Gene Expression Regulation/drug effects , Histone Acetyltransferases/antagonists & inhibitors , Histone Acetyltransferases/metabolism , Humans , Kruppel-Like Transcription Factors/genetics , Kruppel-Like Transcription Factors/metabolism , MEF2 Transcription Factors/metabolism , Male , Metabolomics , Mice , Mice, Inbred mdx , Muscle, Skeletal/metabolism , Muscle, Skeletal/pathology , Muscular Dystrophy, Duchenne/blood , Muscular Dystrophy, Duchenne/diagnosis , Muscular Dystrophy, Duchenne/genetics , Nutrients/blood , Nutrients/metabolism , Pulse Therapy, DrugABSTRACT
Long intergenic non-coding RNAs (lincRNAs) have been implicated in gene regulation, but their requirement for development needs empirical interrogation. We computationally identified nine murine lincRNAs that have developmentally regulated transcriptional and epigenomic profiles specific to early heart differentiation. Six of the nine lincRNAs had in vivo expression patterns supporting a potential function in heart development, including a transcript downstream of the cardiac transcription factor Hand2, which we named Handlr (Hand2-associated lincRNA), Rubie and Atcayos We genetically ablated these six lincRNAs in mouse, which suggested genomic regulatory roles for four of the cohort. However, none of the lincRNA deletions led to severe cardiac phenotypes. Thus, we stressed the hearts of adult Handlr and Atcayos mutant mice by transverse aortic banding and found that absence of these lincRNAs did not affect cardiac hypertrophy or left ventricular function post-stress. Our results support roles for lincRNA transcripts and/or transcription in the regulation of topologically associated genes. However, the individual importance of developmentally specific lincRNAs is yet to be established. Their status as either gene-like entities or epigenetic components of the nucleus should be further considered.