Pressure-overload Hypertrophy Research Articles

Metabolic adaptations in pressure overload hypertrophic heart.

This review article offers a detailed examination of metabolic adaptations in pressure overload hypertrophic hearts, a condition that plays a pivotal role in the progression of heart failure with preserved ejection fraction (HFpEF) to heart failure with reduced ejection fraction (HFrEF). The paper delves into the complex interplay between various metabolic pathways, including glucose metabolism, fatty acid metabolism, branched-chain amino acid metabolism, and ketone body metabolism. In-depth insights into the shifts in substrate utilization, the role of different transporter proteins, and the potential impact of hypoxia-induced injuries are discussed. Furthermore, potential therapeutic targets and strategies that could minimize myocardial injury and promote cardiac recovery in the context of pressure overload hypertrophy (POH) are examined. This work aims to contribute to a better understanding of metabolic adaptations in POH, highlighting the need for further research on potential therapeutic applications.

Abstract P2042: Linking Extracellular Matrix Stiffness With Cardiomyocyte Structure And Function

The composition and organization of the extracellular matrix (ECM) provides cues to myocardial cells that direct normal function and responses to stress. However, little is known about how exactly a change in environmental tension leads to alterations in cardiomyocyte cell size and contractile force. Collagen I comprises the majority of cardiac ECM where it is crosslinked and matured by the lysyl oxidase (LOX) family of enzymes that includes LOX and LOX-like (LOXL) proteins. LOX and LOXLs are frequently upregulated in the heart after injury, and their inhibition has been shown to alleviate increases in tissue stiffness. Cardiac injury models result in activation and recruitment of many cells that secrete growth factors and modify the ECM, which makes it difficult to address specifically how cardiomyocytes are responding to changes in matrix tension alone. Therefore, we utilized LOX or LOXL overexpression as a tool to stiffen the ECM in the absence of pathophysiologic injury and paracrine factors. Transgenic overexpression of LOX increases myocardial stiffness and results in mild cardiac dysfunction by 9 months of age. While younger adult mice do not display a phenotype at baseline, they have an exaggerated response to pressure overload hypertrophy. In a different set of experiments, adeno-associated viruses (AAV9) for LOXL1, -2, or -3 were administered to mouse pups via cardiac injection at perinatal day 7. By 12 weeks of age, LOXL1 overexpression leads to cardiac hypertrophy with preserved ejection fraction, while increased LOXL2 or LOXL3 results in decreased cardiac function (each with differential patterns of myocardial fibrosis). Ongoing studies are assessing how these functional changes are associated with alterations in tissue stiffness and cardiomyocyte behavior. Determining how cardiomyocytes respond to alterations in the physical properties of the ECM will improve our understanding of the etiology of progressive cardiomyopathies and fibrosis.

Regulatory T Cells in Pathological Cardiac Hypertrophy: Mechanisms and Therapeutic Potential.

Pathological cardiac hypertrophy is linked to immune-inflammatory injury, and regulatory T cells (Tregs) play a crucial role in suppressing immune-inflammatory responses. However, the precise role of Tregs in pathological cardiac hypertrophy remains unclear. To summarize the current knowledge on the role and mechanisms of Tregs in pathological cardiac hypertrophy and explore their perspectives and challenges as a new therapeutic approach. Treg cells may play an important protective role in pressure overload (hypertension, aortic stenosis), myocardial infarction, metabolic disorders (diabetes, obesity), acute myocarditis, cardiomyopathy (hypertrophic cardiomyopathy, storage diseases), and chronic obstructive pulmonary disease-related pathological cardiac hypertrophy. Although some challenges remain, the safety and efficacy of Treg-based therapies have been confirmed in some clinical trials, and engineered antigen-specific Treg cells may have better clinical application prospects due to stronger immunosuppressive function and stability. Targeting the immune-inflammatory response via Treg-based therapies might provide a promising and novel future approach to the prevention and treatment of pathological cardiac hypertrophy.

The role of androgens in pressure overload myocardial hypertrophy.

Pressure overload hypertrophy of the left ventricle is a common result of many cardiovascular diseases. Androgens show anabolic effects in skeletal muscles, but also in myocardial hypertrophy. We carefully reviewed literature regarding possible effects of androgens on specific left ventricular hypertrophy in pressure overload conditions excluding volume overload conditions or generel sex differences.

Rpl3l gene deletion in mice reduces heart weight over time.

Introduction: The ribosomal protein L3-like (RPL3L) is a heart and skeletal muscle-specific ribosomal protein and paralogue of the more ubiquitously expressed RPL3 protein. Mutations in the human RPL3L gene are linked to childhood cardiomyopathy and age-related atrial fibrillation, yet the function of RPL3L in the mammalian heart remains unknown. Methods and Results: Here, we observed that mouse cardiac ventricles express RPL3 at birth, where it is gradually replaced by RPL3L in adulthood but re-expressed with induction of hypertrophy in adults. Rpl3l gene-deleted mice were generated to examine the role of this gene in the heart, although Rpl3l -/- mice showed no overt changes in cardiac structure or function at baseline or after pressure overload hypertrophy, likely because RPL3 expression was upregulated and maintained in adulthood. mRNA expression analysis and ribosome profiling failed to show differences between the hearts of Rpl3l null and wild type mice in adulthood. Moreover, ribosomes lacking RPL3L showed no differences in localization within cardiomyocytes compared to wild type controls, nor was there an alteration in cardiac tissue ultrastructure or mitochondrial function in adult Rpl3l -/- mice. Similarly, overexpression of either RPL3 or RPL3L with adeno-associated virus -9 in the hearts of mice did not cause discernable pathology. However, by 18months of age Rpl3l -/- null mice had significantly smaller hearts compared to wild type littermates. Conclusion: Thus, deletion of Rpl3l forces maintenance of RPL3 expression within the heart that appears to fully compensate for the loss of RPL3L, although older Rpl3l -/- mice showed a mild but significant reduction in heart weight.

Stabilizing cardiac ryanodine receptor with dantrolene treatment prevents left ventricular remodeling in pressure-overloaded heart failure mice

Dantrolene (DAN) directly binds to cardiac ryanodine receptor 2 (RyR2) through Leu601–Cys620 in the N-terminal domain and subsequently inhibits diastolic Ca2+ leakage through RyR2. We previously reported that therapy using RyR2 V3599K mutation, which inhibits diastolic Ca2+ leakage by enhancing calmodulin (CaM) binding ability to RyR2, prevents left ventricular (LV) remodeling in transverse aortic constriction (TAC) heart failure. Here, we examined whether chronic administration of DAN prevents LV remodeling in TAC heart failure via the same mechanism as genetic therapy. A pressure-overloaded hypertrophy mouse model was developed using TAC. Wild-type (WT) mice were divided into three groups: sham-operated mice (Sham group), TAC mice (TAC group), and TAC mice treated with DAN (TAC-DAN group, 20 mg/kg/day, i.p.). They were then followed up for 8 weeks. The survival rate was higher in the TAC-DAN group (83%) than in the TAC group (49%), and serial echocardiography studies and pathological tissue analysis showed that LV remodeling was significantly prevented in the TAC-DAN group compared to the TAC group. An increase in the diastolic Ca2+ spark frequency and a decrease in the binding affinity of CaM to RyR2 were observed at 8 weeks in the TAC group but not in the TAC-DAN group. Stabilization of RyR2 with DAN prevented LV remodeling and improved survival after TAC by enhancing CaM binding to RyR2 and inhibiting RyR2-mediated diastolic Ca2+ leakage.

A brief morning rest period benefits cardiac repair in pressure overload hypertrophy and postmyocardial infarction.

Rest has long been considered beneficial to patient healing; however, remarkably, there are no evidence-based experimental models determining how it benefits disease outcomes. Here, we created an experimental rest model in mice that briefly extends the morning rest period. We found in 2 major cardiovascular disease conditions (cardiac hypertrophy, myocardial infarction) that imposing a short, extended period of morning rest each day limited cardiac remodeling compared with controls. Mechanistically, rest mitigates autonomic-mediated hemodynamic stress on the cardiovascular system, relaxes myofilament contractility, and attenuates cardiac remodeling genes, consistent with the benefits on cardiac structure and function. These same rest-responsive gene pathways underlie the pathophysiology of many major human cardiovascular conditions, as demonstrated by interrogating open-source transcriptomic data; thus, patients with other conditions may also benefit from a morning rest period in a similar manner. Our findings implicate rest as a key driver of physiology, creating a potentially new field - as broad and important as diet, sleep, or exercise - and provide a strong rationale for investigation of rest-based therapy for major clinical diseases.

First comprehensive identification of cardiac proteins with putative increased O-GlcNAc levels during pressure overload hypertrophy.

Protein posttranslational modifications (PTMs) by O-GlcNAc globally rise during pressure-overload hypertrophy (POH). However, a major knowledge gap exists on the specific proteins undergoing changes in O-GlcNAc levels during POH primarily because this PTM is low abundance and easily lost during standard mass spectrometry (MS) conditions used for protein identification. Methodologies have emerged to enrich samples for O-GlcNAcylated proteins prior to MS analysis. Accordingly, our goal was to identify the specific proteins undergoing changes in O-GlcNAc levels during POH. We used C57/Bl6 mice subjected to Sham or transverse aortic constriction (TAC) to create POH. From the hearts, we labelled the O-GlcNAc moiety with tetramethylrhodamine azide (TAMRA) before sample enrichment by TAMRA immunoprecipitation (IP). We used LC-MS/MS to identify and quantify the captured putative O-GlcNAcylated proteins. We identified a total of 700 putative O-GlcNAcylated proteins in Sham and POH. Two hundred thirty-three of these proteins had significantly increased enrichment in POH over Sham suggesting higher O-GlcNAc levels whereas no proteins were significantly decreased by POH. We examined two MS identified metabolic enzymes, CPT1B and the PDH complex, to validate by immunoprecipitation. We corroborated increased O-GlcNAc levels during POH for CPT1B and the PDH complex. Enzyme activity assays suggests higher O-GlcNAcylation increases CPT1 activity and decreases PDH activity during POH. In summary, we generated the first comprehensive list of proteins with putative changes in O-GlcNAc levels during POH. Our results demonstrate the large number of potential proteins and cellular processes affected by O-GlcNAc and serve as a guide for testing specific O-GlcNAc-regulated mechanisms during POH.

Modification of cardiac disease by transgenically altered histone deacetylase 6

Histone deacetylase 6 (HDAC6) is known to deacetylate amino acid lysine in alpha-tubulin. However, the functional role of HDAC6 in the progression of cardiac disease remains uncertain. The functional role of HDAC6 in the hearts was examined using transgenic (TG) mice expressing either human wild-type HDAC6, deacetylase inactive HDAC6 (HDAC6H216A, H611A), and human HDAC6 replaced all serine or threonine residues with aspartic acid at N-terminal 1- 43 amino acids (HDAC6NT-allD) specifically in the hearts. Overexpression of wild-type HDAC6 significantly reduced acetylated tubulin levels, and overexpression of HDAC6H216A, H611A significantly increased it in the mouse hearts. Detectable acetylated tubulin disappeared in HDAC6NT-allD TG mouse hearts. Neither histological alteration nor alteration of cardiac function was observed in the HDAC6 TG mouse hearts. To analyze the role of HDAC6 and acetylated tubulin in disease conditions, we examined HDAC6 in isoprenaline-induced hypertrophy or pressure-overload hypertrophy (TAC). No obvious alteration in the heart weight/body weight ratio or gene expressions of hypertrophic markers between NTG and HDAC6NT-allD mice was observed following treatment with isoprenaline. In contrast, a marked reduction in the shortening fraction and dilated chamber dilatation was detected in the HDAC6NT-allD TG mouse hearts 2 weeks after TAC. A sustained low level of acetylated tubulin and acetylated cortactin was observed in the TAC HDAC6NT-allD TG mouse hearts. Cardiac HDAC6 activity that can regulate acetylated levels of tubulin and cortactin may be critical factors involved in cardiac disease such as pressure-overload hypertrophy.

A pacing-controlled protocol for frequency-diastolic relations distinguishes diastolic dysfunction specific to a mouse HFpEF model.

Heart failure with preserved ejection fraction (HFpEF), characterized by diastolic dysfunction and insufficient exercise capacity, is a growing health problem worldwide. One major difficulty with experimental research on HFpEF is the lack of methods to consistently detect diastolic dysfunction in mouse models. We developed a pacing-controlled pressure-volume (PV) loop protocol for the assessment of diastolic function at different heart rates in mice and tested if the protocol could detect diastolic dysfunction specific to a HFpEF model. A HFpEF model was generated by high-fat diet (HFD) feeding with concomitant NG-nitro-l-arginine methyl ester administration, and a pressure-overload hypertrophy (PO) model was produced by surgical constriction of the transverse aorta (TAC). Heart rate (HR) was slowed below 400 beats/min by intraperitoneal injection of ivabradine. PV loop data were acquired and analyzed at HR incrementing from 400 to 700 beats/min via atrial pacing using a miniature pacing catheter inserted into the esophagus, and comparisons were made among control, HFpEF, and PO mice. At baseline without pacing, no diastolic abnormalities were detected in either PO or HFpEF models. Frequency-diastolic relations, however, revealed the significant diastolic impairment specific to the HFpEF model; both relaxation time constant (Tau) and end-diastolic pressure-volume relationship (EDPVR) were worsened as heart rate increased. Peak positive first derivative of left ventricular pressure (dP/dtmax) was significantly lower in HFpEF versus controls only at a high HR of 700 beats/min. A pacing-controlled protocol would be a feasible and potent method to detect diastolic dysfunction specific to a mouse HFpEF model.NEW & NOTEWORTHY We developed a pacing-controlled PV loop protocol for the assessment of diastolic function at different heart rates in mice, which is a feasible and potent method for the characterization of diastolic dysfunction in a murine HFpEF model whose diastolic dysfunction might be difficult to be detected under resting conditions without pacing.

Lack of food intake during shift work alters the heart transcriptome and leads to cardiac tissue fibrosis and inflammation in rats

BackgroundMany epidemiological studies revealed that shift work is associated with an increased risk of a number of pathologies, including cardiovascular diseases. An experimental model of shift work in rats has additionally been shown to recapitulate aspects of metabolic disorders observed in human shift workers, including increased fat content and impaired glucose tolerance, and used to demonstrate that restricting food consumption outside working hours prevents shift work-associated obesity and metabolic disturbance. However, the way distinct shift work parameters, such as type of work, quantity, and duration, affect cardiovascular function and the underlying mechanisms, remains poorly understood. Here, we used the rat as a model to characterize the effects of shift work in the heart and determine whether they can be modulated by restricting food intake during the normal active phase.ResultsWe show that experimental shift work reprograms the heart cycling transcriptome independently of food consumption. While phases of rhythmic gene expression are distributed across the 24-h day in control rats, they are clustered towards discrete times in shift workers. Additionally, preventing food intake during shift work affects the expression level of hundreds of genes in the heart, including genes encoding components of the extracellular matrix and inflammatory markers found in transcriptional signatures associated with pressure overload and cardiac hypertrophy. Consistent with this, the heart of shift worker rats not eating during work hours, but having access to food outside of shift work, exhibits increased collagen 1 deposition and displays increased infiltration by immune cells. While maintaining food access during shift work has less effects on gene expression, genes found in transcriptional signatures of cardiac hypertrophy remain affected, and the heart of shift worker rats exhibits fibrosis without inflammation.ConclusionsTogether, our findings unraveled differential effects of food consumption on remodeled transcriptional profiles of the heart in shift worker rats. They also provide insights into how shift work affects cardiac function and suggest that some interventions aiming at mitigating metabolic disorders in shift workers may have adverse effects on cardiovascular diseases.

Abnormalities in lysine degradation are involved in early cardiomyocyte hypertrophy development in pressure-overloaded rats

BackgroundCardiomyocyte metabolism changes before cardiac remodeling, but its role in early cardiac hypertrophy detection remains unclear. This study investigated early changes in plasma metabolomics in a pressure-overload cardiac hypertrophy model induced by transverse aortic constriction (TAC).MethodsThe TAC model was constructed by partly ligating the aortic arch. Twelve Sprague–Dawley rats were randomly divided into the TAC group (n = 6) and sham group (n = 6). Three weeks after surgery, cardiac echocardiography was performed to assess cardiac remodeling and function. Hematoxylin/eosin (HE), Masson, and wheat germ agglutinin (WGA) stains were used to observe pathological changes. Plasma metabolites were detected by UPLC-QTOFMS and Q-TOFMS. Specific metabolites were screened by orthogonal partial least squares discriminant analysis (OPLS-DA). Metabolic pathways were characterized by Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis, and the predictive value of the screened metabolites was analyzed by receiver operating characteristic (ROC) curve analysis.ResultsThree weeks after surgery, the TAC and sham groups had similar left heart function and interventricular septum and diastolic left ventricular posterior wall thicknesses. However, on pathological examination, the cross-sectional area of cardiomyocytes and myocardial fibrosis severity were significantly elevated in TAC rats. OPLS-DA showed different metabolic patterns between the TAC and sham groups. Based on the criteria VIP > 1 and P < 0.05, 13 metabolites were screened out. KEGG analysis identified disrupted lysine degradation through the related metabolites 5-aminopentanoic acid, N6-acetyl-l-lysine, and l-lysine, with areas under the ROC curve (AUCs) of 0.917, 0.889, and 0.806, respectively, for predicting compensated cardiomyocyte hypertrophy.ConclusionDisruption of lysine degradation might be involved in early cardiac hypertrophy development, and related metabolites might be potential predictive and interventional targets for subclinical cardiomyocyte hypertrophy.

Temporal regulation of protein O-GlcNAc levels during pressure-overload cardiac hypertrophy.

Protein posttranslational modifications (PTMs) by O‐linked β‐N‐acetylglucosamine (O‐GlcNAc) rise during pressure‐overload hypertrophy (POH) to affect hypertrophic growth. The hexosamine biosynthesis pathway (HBP) branches from glycolysis to make the moiety for O‐GlcNAcylation. It is speculated that greater glucose utilization during POH augments HBP flux to increase O‐GlcNAc levels; however, recent results suggest glucose availability does not primarily regulate cardiac O‐GlcNAc levels. We hypothesize that induction of key enzymes augment protein O‐GlcNAc levels primarily during active myocardial hypertrophic growth and remodeling with early pressure overload. We further speculate that downregulation of protein O‐GlcNAcylation inhibits ongoing hypertrophic growth during prolonged pressure overload with established hypertrophy. We used transverse aortic constriction (TAC) to create POH in C57/Bl6 mice. Experimental groups were sham, 1‐week TAC (1wTAC) for early hypertrophy, or 6‐week TAC (6wTAC) for established hypertrophy. We used western blots to determine O‐GlcNAc regulation. To assess the effect of increased protein O‐GlcNAcylation with established hypertrophy, mice received thiamet‐g (TG) starting 4 weeks after TAC. Protein O‐GlcNAc levels were significantly elevated in 1wTAC versus Sham with a fall in 6wTAC. OGA, which removes O‐GlcNAc from proteins, fell in 1wTAC versus sham. GFAT is the rate‐limiting HBP enzyme and the isoform GFAT1 substantially rose in 1wTAC. With established hypertrophy, TG increased protein O‐GlcNAc levels but did not affect cardiac mass. In summary, protein O‐GlcNAc levels vary during POH with elevations occurring during active hypertrophic growth early after TAC. O‐GlcNAc levels appear to be regulated by changes in key enzyme levels. Increasing O‐GlcNAc levels during established hypertrophy did not restart hypertrophic growth.

The GABAA Receptor Influences Pressure Overload-Induced Heart Failure by Modulating Macrophages in Mice.

BackgroundMyocardial macrophages have key roles in cardiac remodeling and dysfunction. The gamma-aminobutyric acid subtype A (GABAA) receptor was recently found to be distributed in macrophages, allowing regulation of inflammatory responses to various diseases. This study aimed to clarify the role of GABAA receptor-mediated macrophage responses in pressure overload-induced heart failure.Methods and ResultsC57BL/6J mice underwent transverse aortic constriction for pressure-overload hypertrophy (POH) and were intraperitoneally treated with a specific GABAA receptor agonist (topiramate) or antagonist (bicuculline). Echocardiography, histology, and flow cytometry were performed to evaluate the causes and effects of myocardial hypertrophy and fibrosis. Activation of the GABAA receptor by topiramate reduced ejection fraction and fractional shortening, enlarged the end-diastolic and end-systolic left ventricular internal diameter, aggravated myocardial hypertrophy and fibrosis, and accelerated heart failure in response to pressure overload. Mechanistically, topiramate increased the number of Ly6Clow macrophages in the heart during POH and circulating Ly6Chigh classic monocyte infiltration in late-phase POH. Further, topiramate drove Ly6Clow macrophages toward MHCIIhigh macrophage polarization. As a result, Ly6Clow macrophages activated the amphiregulin-induced AKT/mTOR signaling pathway, and Ly6ClowMHCIIhigh macrophage polarization increased expression levels of osteopontin and TGF-β, which led to myocardial hypertrophy and fibrosis. Conversely, GABAA receptor blockage with bicuculline reversed these effects.ConclusionsControl of the GABAA receptor activity in monocytes/macrophages plays an important role in myocardial hypertrophy and fibrosis after POH. Blockade of the GABAA receptor has the potential to improve pressure overload-induced heart failure.

A peptide of the N terminus of GRK5 attenuates pressure-overload hypertrophy and heart failure.

Aberrant changes in gene expression underlie the pathogenesis and progression of pressure-overload heart failure, leading to maladaptive cardiac hypertrophy, ventricular remodeling, and contractile dysfunction. Signaling through the G protein Gq triggers maladaptation and heart failure, in part through the activation of G protein-coupled receptor kinase 5 (GRK5). Hypertrophic stimuli induce the accumulation of GRK5 in the nuclei of cardiomyocytes, where it regulates pathological gene expression through multiple transcription factors including NFAT. The nuclear targeting of GRK5 is mediated by an amino-terminal (NT) domain that binds to calmodulin (CaM). Here, we sought to prevent GRK5-mediated pathology in pressure-overload maladaptation and heart failure by expressing in cardiomyocytes a peptide encoding the GRK5 NT (GRK5nt) that encompasses the CaM binding domain. In cultured cardiomyocytes, GRK5nt expression abrogated Gq-coupled receptor-mediated hypertrophy, including attenuation of pathological gene expression and the transcriptional activity of NFAT and NF-κB. We confirmed that GRK5nt bound to and blocked Ca2+-CaM from associating with endogenous GRK5, thereby preventing GRK5 nuclear accumulation after pressure overload. We generated mice that expressed GRKnt in a cardiac-specific fashion (TgGRK5nt mice), which exhibited reduced cardiac hypertrophy, ventricular dysfunction, pulmonary congestion, and cardiac fibrosis after chronic transverse aortic constriction. Together, our data support a role for GRK5nt as an inhibitor of pathological GRK5 signaling that prevents heart failure.

Mapping drug-target interactions and synergy in multi-molecular therapeutics for pressure-overload cardiac hypertrophy

Advancements in systems biology have resulted in the development of network pharmacology, leading to a paradigm shift from “one-target, one-drug” to “target-network, multi-component therapeutics”. We employ a chimeric approach involving in-vivo assays, gene expression analysis, cheminformatics, and network biology to deduce the regulatory actions of a multi-constituent Ayurvedic concoction, Amalaki Rasayana (AR) in animal models for its effect in pressure-overload cardiac hypertrophy. The proteomics analysis of in-vivo assays for Aorta Constricted and Biologically Aged rat models identify proteins expressed under each condition. Network analysis mapping protein–protein interactions and synergistic actions of AR using multi-component networks reveal drug targets such as ACADM, COX4I1, COX6B1, HBB, MYH14, and SLC25A4, as potential pharmacological co-targets for cardiac hypertrophy. Further, five out of eighteen AR constituents potentially target these proteins. We propose a distinct prospective strategy for the discovery of network pharmacological therapies and repositioning of existing drug molecules for treating pressure-overload cardiac hypertrophy.

Abstract 15945: Temporal Analyses of Chromatin Accessibility, Dna Methylation and Epigenomic Structure Identify Mechanisms of Locus-specific Regulation in the Heart

Heart failure can be induced or ameliorated in animal models by regulation of chromatin modifying enzymes, yet the chromatin level actions of these enzymes during pathogenesis is unknown. Because many histone modifiers and transcription factors regulate gene expression, we sought to directly measure chromatin accessibility through an unbiased method (ATAC-seq) that reports the status of a given locus at any time—the sum total of all epigenetic modifiers—in a mouse model of pressure overload hypertrophy. Early compensation of pressure overload at 3 days was associated with widespread changes in chromatin accessibility and DNA methylation, primarily in noncoding regions. The majority of changes that persisted to the decompensated phase (3weeks) were already established at the earlier time point, revealing a temporal nature of epigenomic compensation to pathologic stimuli. A cardiac-specific CTCF depletion model was used to examine basal cardiac chromatin function and revealed that disruption of this structure by loss of CTCF causes widespread changes in accessibility and methylation distinct from those in pressure overload. Less than half of the gene expression changes occurring at either time point after pressure overload were explained by DNA methylation alone and accessibility was likewise an imperfect predictor of transcription. Distal enhancers were paired with genes based on chromatin structural data and the regulatory actions of these elements examined in the context of DNA methylation and accessibility: enhancer actions require specific combinations of transcription factors and histone modifications at different stages of disease and to execute aspecific transcriptional event (methylation or accessibility alone was insufficient to predict the behavior). For example, the subset of differentially accessible enhancers in both 3 weeks TACand CTCF depletion significantly overlaps with cardiac transcription factors Gata4 (p=4.13x10 -6 ),Nkx2-5 (p=2.49x10 -5 ) and P300 (p=8.38x10 -7 ). In summary, these studies characterize the logic employed at coding, regulatory, and noncoding regions to regulate chromatin accessibility and transcription, providing a resource of epigenomic data at distinct temporal stages of heart failure.

Targeting MEF2 acetylation improves myocardial recovery and overall survival in mice

Abstract Background Post-myocardial infarct remodeling is a complex process that is strongly associated with the eventual development of heart failure, and involves myocyte hypertrophy, specific alterations in gene expression and mitochondrial metabolism, myocyte death, fibrosis, and incursion of inflammatory mediators. Many of these alterations involve dynamic changes in lysine acetylation (KAc), a key regulatory post-transcriptional modification in the nucleus and cytosol, and can be blocked by small molecules with broad activity against histone deacetylases (HDACi). The downstream targets of HDACi and other KAc modulators remain to be established, and the safety of this class of agent for long-term administration in heart failure is similarly unknown. We recently reported that a small molecule probe (8MI) selectively blocking acetylation of transcription factor MEF2 is effective in preventing and reversing pressure overload hypertrophy in vivo, without altering overall histone acetylation. Hypothesis Treatment with a MEF2-selective KAc modulator will accelerate cardiac functional recovery after myocardial infarction. Methods The left coronary artery was permanently ligated (PCO) in 8–10 week C57BL/6J mice; controls underwent thoracotomy only (Sham). Within each group, half received 8MI (20–100mg/kg) by gavage daily, beginning at 30 min, and half received diluent only (DMSO). Treatment was continued for 31 days with weekly echocardiography. Mice from each group (n=3–6) were euthanized weekly for gross and histological analysis. Separately, mice were subjected to transverse aortic banding (TAC) +/− 8MI. Comparative LV RNASeq data were analysed using Gene Set Enrichment Analysis at 4 weeks, and median survival was determined. Results At 24 hours all PCO vs. Sham mice had reduced ejection fraction (62.1±1.08% vs. 80.9±1.08%), increased LV diastolic dimensions, and decreased systolic wall thickening (n =min. 8 per group, p &amp;lt; E-001). Over 4 weeks, heart weights progressively increased in PCO mice together with lung and liver congestion. 8MI dose-dependently improvedeach of these parameters, with near-normal function and organ weights at 4 weeks in higher-dose groups. 8MI also reduced infarct size, compensatory hypertrophy, and fibrosis at 4 weeks. In parallel, 8MI extended median survival by 1.67-fold after TAC (127.5 vs 76 days, p&amp;lt;0.0001, 8MI vs DMSO). RNASeq +GSEA analysis revealed that 8MI treatment blocked MEF2 target gene induction, while enriching for gene sets Oxidative Phosphorylation and Myc Targets (FDR q values 0.000 and 0.041) compared with DMSO. Conclusion An inhibitor of MEF2 acetylation promoted significant functional and pathological recovery in a mouse model of myocardial infarction, associated with suppression of MEF2-dependent transcription. These findings point to a novel approach to preventing myocardial functional decline, and improving survival, after myocardial injury. Funding Acknowledgement Type of funding source: Public grant(s) – National budget only. Main funding source(s): National Institutes of Health; Miami Heart Research Institute

Bone marrow mesenchymal stem cell-derived exosomes attenuate cardiac hypertrophy and fibrosis in pressure overload induced remodeling.

The multiple therapeutic effects of bone marrow mesenchymal stem cells (BM-MSCs) have been verified in ischemic and reperfusion diseases. Exosomes are thought to play vital roles in MSCs-related cardioprotective effects. Recently, more and more evidences indicated that apoptosis and fibrosis were crucial pathological mechanisms in cardiac remodeling. Whether MSCs-derived exosomes could regulate cardiac hypertrophy and remodeling need to be explored. Murine BM-MSCs-derived exosomes were isolated by differential gradient centrifugation method. The transverse aortic constriction (TAC) mice model was established to promote cardiac remodeling. Cardiac function and remodeling were assessed via echocardiography and histology analysis. Myocytes apoptosis was determined by TUNEL fluorescence staining. Meanwhile, premature senescence was detected by β-galactosidase (SA-β-gal) staining. Related proteins and mRNA alternation were assessed via western blotting and quantitative reverse transcription polymerase chain reaction, respectively. MSCs-derived exosomes significantly protected myocardium against cardiac hypertrophy, attenuated myocardial apoptosis, and fibrosis and preserved heart function when pressure overload. In cultured myocytes, MSCs-derived exosomes also prevented cell hypertrophy stimulated with angiotensin II. One the other hand, exosomes promoted premature senescence of myofibroblasts vitro, indicating its anti-fibrosis effect in cardiac remodeling. Exosomes protected cardiomyocytes against pathological hypertrophy. It may provide a promising future treatment for heart failure.

Abstract 381: Mcur1 is a Potential Target to Modulate Cardiac Contractility and Alleviate Cardiac Function During Heart Failure

Cardiac contractility is regulated by the intracellular Ca 2+ concentration fluxes which are actively regulated by multiple channels and transporters. Ca 2+ uptake into the mitochondrial matrix is precisely controlled by the highly Ca 2+ selective channel, Mitochondrial Calcium Uniporter (MCU). Earlier studies on the cardiac-specific acute MCU knockout and a transgenic dominant-negative MCU mice have demonstrated that mitochondrial Ca 2+ ( m Ca 2+ ) signaling is necessary for cardiac ‘‘fight-or-flight’’ contractile response, however, the role of m Ca 2+ buffering to shape global cytosolic Ca 2+ levels and affect E-C coupling, particularly the Ca 2+ transient, on a beat-to-beat basis still remains to be solved. Our earlier studies have demonstrated that loss of MCU Regulator 1 (MCUR1) in cardiomyocytes results in the impaired m Ca 2+ uptake. We have now employed the cardiac-specific MCUR1 knockout mouse to dissect the precise role of MCU in regulating cytosolic Ca 2+ transients associated with excitation-contraction (E-C) coupling and cardiac function. Results from our studies including the in vivo analyses of cardiac physiology during normal and pressure-overloaded mouse models and in vitro experiments including single-cell cardiac contractility, calcium transients, and electrophysiology measurements demonstrate that MCUR1/MCU regulated m Ca 2+ buffering in cardiomyocytes, although insignificant under basal condition, becomes critical in stress induced conditions and actively participates in regulating the c Ca 2+ transients. Also, the ablation of MCUR1 in cardiomyocytes during stress conditions prevents m Ca 2+ overload and subsequent mROS overproduction. Our data indicate that MCUR1 ablation offers protection against pressure-overload cardiac hypertrophy. In summary, our results provide critical insights into the mechanisms by which the MCU channel contributes in regulating the contractile function of the cardiomyocytes and the role of m Ca 2+ in the development and progression of heart failure.