Correlates of Plasma NT-proBNP/Cyclic GMP Ratio in Heart Failure With Preserved Ejection Fraction: An Analysis of the RELAX Trial

BACKGROUND

Phosphodiesterases degrade cyclic GMP (cGMP), the second messenger that mediates the cardioprotective effects of natriuretic peptides. High natriuretic peptide/cGMP ratio may reflect, in part, phosphodiesterase activity. Correlates of natriuretic peptide/cGMP in patients with heart failure with preserved ejection fraction are not well understood. Among patients with heart failure with preserved ejection fraction in the RELAX (Phosphodiesterase-5 Inhibition to Improve Clinical Status and Exercise Capacity in Heart Failure With Preserved Ejection Fraction) trial, we examined (1) cross-sectional correlates of circulating NT-proBNP (N-terminal pro-B-type natriuretic peptide)/cGMP ratio, (2) whether selective phosphodiesterase-5 inhibition by sildenafil changed the ratio, and (3) whether the effect of sildenafil on 24-week outcomes varied by baseline ratio.

METHODS AND RESULTS

In 212 subjects, NT-proBNP/cGMP ratio was calculated at randomization and 24 weeks. Correlates of the ratio and its change were examined in multivariable proportional odds models. Whether baseline ratio modified the sildenafil effect on outcomes was examined by interaction terms. Higher NT-proBNP/cGMP ratio was associated with greater left ventricular mass and troponin, the presence of atrial fibrillation, and lower estimated glomerular filtration rate and peak oxygen consumption. Compared with placebo, sildenafil did not alter the ratio from baseline to 24 weeks (P=0.17). The effect of sildenafil on 24-week change in peak oxygen consumption, left ventricular mass, or clinical composite outcome was not modified by baseline NT-proBNP/cGMP ratio (P-interaction >0.30 for all).

CONCLUSIONS

Among patients with heart failure with preserved ejection fraction, higher NT-proBNP/cGMP ratio associated with an adverse cardiorenal phenotype, which was not improved by selective phosphodiesterase-5 inhibition. Other phosphodiesterases may be greater contributors than phosphodiesterase-5 to the adverse phenotype associated with a high natriuretic peptide/cGMP ratio in HFpEF.

REGISTRATION INFORMATION

clinicaltrials.gov. Identifier: NCT00763867.

Clinical outcomes associated with anti-Xa-monitored enoxaparin for venous thromboembolism prophylaxis

STUDY OBJECTIVE

The objective of the study was to assess clinical outcomes (composite of any venous thromboembolism [VTE], any bleeding, and mortality) associated with anti-Xa monitoring in the 30 days following enoxaparin initiation for VTE prophylaxis.

DESIGN

Retrospective cohort study.

SETTING

Hospital within an academic healthcare system.

PATIENTS

Propensity score-matched hospitalized adults receiving enoxaparin for VTE prophylaxis.

INTERVENTION

Low-molecular-weight heparin anti-Xa monitoring.

MEASUREMENTS AND MAIN RESULTS

During the 13-month study period, a total of 6611 patients received enoxaparin for VTE prophylaxis, 301 in the anti-Xa monitored group and 6310 in the unmonitored group (4.6% received monitoring). The mean age was 52.9 years and 52% of patients were male. The mean body mass index was 31 kg/m2 and the mean creatinine clearance was 109 mL/min. Twenty percent of patients had active cancer. The most common indication for enoxaparin prophylaxis was hospitalization for medical illness (52%) followed by nonorthopedic surgery (37%). The adjusted odds ratio for the primary outcome comparing monitored to unmonitored patients was 1.26 (95% confidence interval, 0.75-2.11). None of the between-group differences in the individual components of the composite outcome were statistically significant.

CONCLUSIONS

Thirty-day clinical outcomes in patients receiving enoxaparin for VTE prophylaxis were not improved by anti-Xa monitoring. Our results support current evidence-based guideline recommendations against anti-Xa monitoring for patients receiving enoxaparin for VTE prophylaxis.

The MYPT2-regulated striated muscle-specific myosin light chain phosphatase limits cardiac myosin phosphorylation in vivo

The physiological importance of cardiac myosin regulatory light chain (RLC) phosphorylation by its dedicated cardiac myosin light chain kinase has been established in both humans and mice. Constitutive RLC-phosphorylation, regulated by the balanced activities of cardiac myosin light chain kinase and myosin light chain phosphatase (MLCP), is fundamental to the biochemical and physiological properties of myofilaments. However, limited information is available on cardiac MLCP. In this study, we hypothesized that the striated muscle-specific MLCP regulatory subunit, MYPT2, targets the phosphatase catalytic subunit to cardiac myosin, contributing to the maintenance of cardiac function in vivo through the regulation of RLC-phosphorylation. To test this hypothesis, we generated a floxed-PPP1R12B mouse model crossed with a cardiac-specific Mer-Cre-Mer to conditionally ablate MYPT2 in adult cardiomyocytes. Immunofluorescence microscopy using the gene-ablated tissue as a control confirmed the localization of MYPT2 to regions where it overlaps with a subset of RLC. Biochemical analysis revealed an increase in RLC-phosphorylation in vivo. The loss of MYPT2 demonstrated significant protection against pressure overload-induced hypertrophy, as evidenced by heart weight, qPCR of hypertrophy-associated genes, measurements of myocyte diameters, and expression of β-MHC protein. Furthermore, mantATP chase assays revealed an increased ratio of myosin heads distributed to the interfilament space in MYPT2-ablated heart muscle fibers, confirming that RLC-phosphorylation regulated by MLCP, enhances cardiac performance in vivo. Our findings establish MYPT2 as the regulatory subunit of cardiac MLCP, distinct from the ubiquitously expressed canonical smooth muscle MLCP. Targeting MYPT2 to increase cardiac RLC-phosphorylation in vivo may improve baseline cardiac performance, thereby attenuating pathological hypertrophy.

Single-cell transcriptional landscape of long non-coding RNAs orchestrating mouse heart development

Long non-coding RNAs (lncRNAs) comprise the most representative transcriptional units of the mammalian genome. They are associated with organ development linked with the emergence of cardiovascular diseases. We used bioinformatic approaches, machine learning algorithms, systems biology analyses, and statistical techniques to define co-expression modules linked to heart development and cardiovascular diseases. We also uncovered differentially expressed transcripts in subpopulations of cardiomyocytes. Finally, from this work, we were able to identify eight cardiac cell-types; several new coding, lncRNA, and pcRNA markers; two cardiomyocyte subpopulations at four different time points (ventricle E9.5, left ventricle E11.5, right ventricle E14.5 and left atrium P0) that harbored co-expressed gene modules enriched in mitochondrial, heart development and cardiovascular diseases. Our results evidence the role of particular lncRNAs in heart development and highlight the usage of co-expression modular approaches in the cell-type functional definition.

Impaired T cell IRE1α/XBP1 signaling directs inflammation in experimental heart failure with preserved ejection fraction

Heart failure with preserved ejection fraction (HFpEF) is a widespread syndrome with limited therapeutic options and poorly understood immune pathophysiology. Using a 2-hit preclinical model of cardiometabolic HFpEF that induces obesity and hypertension, we found that cardiac T cell infiltration and lymphoid expansion occurred concomitantly with cardiac pathology and that diastolic dysfunction, cardiomyocyte hypertrophy, and cardiac phospholamban phosphorylation were T cell dependent. Heart-infiltrating T cells were not restricted to cardiac antigens and were uniquely characterized by impaired activation of the inositol-requiring enzyme 1α/X-box-binding protein 1 (IRE1α/XBP1) arm of the unfolded protein response. Notably, selective ablation of XBP1 in T cells enhanced their persistence in the heart and lymphoid organs of mice with preclinical HFpEF. Furthermore, T cell IRE1α/XBP1 activation was restored after withdrawal of the 2 comorbidities inducing HFpEF, resulting in partial improvement of cardiac pathology. Our results demonstrated that diastolic dysfunction and cardiomyocyte hypertrophy in preclinical HFpEF were T cell dependent and that reversible dysregulation of the T cell IRE1α/XBP1 axis was a T cell signature of HFpEF.

Rapid, accurate publication and dissemination of clinical trial results: benefits and challenges

Large-scale clinical trials are essential in cardiology and require rapid, accurate publication, and dissemination. Whereas conference presentations, press releases, and social media disseminate information quickly and often receive considerable coverage by mainstream and healthcare media, they lack detail, may emphasize selected data, and can be open to misinterpretation. Preprint servers speed access to research manuscripts while awaiting acceptance for publication by a journal, but these articles are not formally peer-reviewed and sometimes overstate the findings. Publication of trial results in a major journal is very demanding but the use of existing checklists can help accelerate the process. In case of rejection, procedures such as easing formatting requirements and possibly carrying over peer-review to other journals could speed resubmission. Secondary publications can help maximize benefits from clinical trials; publications of secondary endpoints and subgroup analyses further define treatment effects and the patient populations most likely to benefit. These rely on data access, and although data sharing is becoming more common, many challenges remain. Beyond publication in medical journals, there is a need for wider knowledge dissemination to maximize impact on clinical practice. This might be facilitated through plain language summary publications. Social media, websites, mainstream news outlets, and other publications, although not peer-reviewed, are important sources of medical information for both the public and for clinicians. This underscores the importance of ensuring that the information is understandable, accessible, balanced, and trustworthy. This report is based on discussions held on December 2021, at the 18th Global Cardiovascular Clinical Trialists meeting, involving a panel of editors of some of the top medical journals, as well as members of the lay press, industry, and clinical trialists.

Impact of Short-Term (+)-JQ1 Exposure on Mouse Aorta: Unanticipated Inhibition of Smooth Muscle Contractility

(+)-JQ1, a specific chemical inhibitor of bromodomain and extraterminal (BET) family protein 4 (BRD4), has been reported to inhibit smooth muscle cell (SMC) proliferation and mouse neointima formation via BRD4 regulation and modulate endothelial nitric oxide synthase (eNOS) activity. This study aimed to investigate the effects of (+)-JQ1 on smooth muscle contractility and the underlying mechanisms. Using wire myography, we discovered that (+)-JQ1 inhibited contractile responses in mouse aortas with or without functional endothelium, reducing myosin light chain 20 (LC20) phosphorylation and relying on extracellular Ca2+. In mouse aortas lacking functional endothelium, BRD4 knockout did not alter the inhibition of contractile responses by (+)-JQ1. In primary cultured SMCs, (+)-JQ1 inhibited Ca2+ influx. In aortas with intact endothelium, (+)-JQ1 inhibition of contractile responses was reversed by NOS inhibition (L-NAME) or guanylyl cyclase inhibition (ODQ) and by blocking the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT) pathway. In cultured human umbilical vein endothelial cells (HUVECs), (+)-JQ1 rapidly activated AKT and eNOS, which was reversed by PI3K or ATK inhibition. Intraperitoneal injection of (+)-JQ1 reduced mouse systolic blood pressure, an effect blocked by co-treatment with L-NAME. Interestingly, (+)-JQ1 inhibition of aortic contractility and its activation of eNOS and AKT were mimicked by the (-)-JQ1 enantiomer, which is structurally incapable of inhibiting BET bromodomains. In summary, our data suggest that (+)-JQ1 directly inhibits smooth muscle contractility and indirectly activates the PI3K/AKT/eNOS cascade in endothelial cells; however, these effects appear unrelated to BET inhibition. We conclude that (+)-JQ1 exhibits an off-target effect on vascular contractility.

Inflammatory Mechanisms in Heart Failure with Preserved Ejection Fraction

HFpEF (heart failure with preserved ejection fraction) is now the most common form of heart failure and a significant public health concern for which limited effective therapies exist. Inflammation triggered by comorbidity burden is a critical element of HFpEF pathophysiology. Here, we discuss evidence for comorbidity-driven systemic and myocardial inflammation and the mechanistic role of inflammation in pathological myocardial remodeling in HFpEF.

Methods for studying primary cilia in heart tissue after ischemia-reperfusion injury

Cardiovascular diseases are the leading cause of death and disability worldwide. After heart injury triggered by myocardial ischemia or myocardial infarction, extensive zones of tissue are damaged and some of the tissue dies by necrosis and/or apoptosis. The loss of contractile mass activates a series of biochemical mechanisms that allow, through cardiac remodeling, the replacement of the dysfunctional heart tissue by fibrotic material. Our previous studies have shown that primary cilia, non-motile antenna-like structures at the cell surface required for the activation of specific signaling pathways, are present in cardiac fibroblasts and required for cardiac fibrosis induced by ischemia/reperfusion (I/R) in mice. I/R-induced myocardial fibrosis promotes the enrichment of ciliated cardiac fibroblasts where the myocardial injury occurs. Given discussions about the existence of cilia in specific cardiac cell types, as well as the functional relevance of studying cilia-dependent signaling in cardiac fibrosis after I/R, here we describe our methods to evaluate the presence and roles of primary cilia in cardiac fibrosis after I/R in mice.

A coagulation factor moonlights in the heart

Liver-derived coagulation factor XI protects the heart from failure.

Abstract P3016: Role Of AMPK/Sirtuin3 Signaling In HFpEF-associated Atrial Myopathy

Background: Patients with heart failure with preserved ejection fraction (HFpEF) are uniquely predisposed to atrial fibrillation (AF), which significantly worsens clinical outcomes. Pathological atrial remodeling, i.e. atrial myopathy, usually precedes clinical AF and is deemed to be an underlying cause of AF. However, little is known about its molecular features, and no effective treatments have been identified.

Method: Wild type C57Bl6 mice were fed a high fat diet (HFD) and received L-NAME via drinking water (5-8 weeks). Atrial morphology and function were assessed by echocardiography. AF was induced by transesophageal pacing.

Results: We discovered that HFpEF mice manifest prominent sinoatrial node (SAN) dysfunction and are highly susceptible to pacing-induced AF, suggesting that this is an ideal model for studying HFpEF-associated atrial changes. Our findings revealed that atrial hypertrophy, contractile dysfunction, and conduction abnormalities are key features of HFpEF-associated atrial myopathy. Interestingly, we did not observe significant atrial fibrosis in this model, a prominent feature of other AF models. Importantly, we discovered impaired AMPK/Sirt3 signaling in the atria of HFpEF mice, and similar atrial defects were observed in mice with cardiomyocyte-specific loss of sirtuin3 (Sirt3) or AMPK, indicating a critical role of AMPK/Sirt3 signaling in HFpEF-associated atrial myopathy. Lastly, we found that metformin, a widely used clinical AMPK agonist, significantly attenuated AF inducibility and SAN dysfunction in HFpEF mice.

Conclusion: Our “two-hit” HFpEF model successfully recapitulates HFpEF-associated atrial phenotypes. Using this model, we unveiled molecular features of a distinct atrial myopathy. We identified a critical role of AMPK/Sirt3 signaling in HFpEF-associated atrial remodeling and demonstrated the therapeutic effect of metformin. As next steps, confirming this benefit in a clinical trial is warranted.

ATF4 Protects the Heart From Failure by Antagonizing Oxidative Stress

BACKGROUND

Cellular redox control is maintained by generation of reactive oxygen/nitrogen species balanced by activation of antioxidative pathways. Disruption of redox balance leads to oxidative stress, a central causative event in numerous diseases including heart failure. Redox control in the heart exposed to hemodynamic stress, however, remains to be fully elucidated.

METHODS

Pressure overload was triggered by transverse aortic constriction in mice. Transcriptomic and metabolomic regulations were evaluated by RNA-sequencing and metabolomics, respectively. Stable isotope tracer labeling experiments were conducted to determine metabolic flux in vitro. Neonatal rat ventricular myocytes and H9c2 cells were used to examine molecular mechanisms.

RESULTS

We show that production of cardiomyocyte NADPH, a key factor in redox regulation, is decreased in pressure overload-induced heart failure. As a consequence, the level of reduced glutathione is downregulated, a change associated with fibrosis and cardiomyopathy. We report that the pentose phosphate pathway and mitochondrial serine/glycine/folate metabolic signaling, 2 NADPH-generating pathways in the cytosol and mitochondria, respectively, are induced by transverse aortic constriction. We identify ATF4 (activating transcription factor 4) as an upstream transcription factor controlling the expression of multiple enzymes in these 2 pathways. Consistently, joint pathway analysis of transcriptomic and metabolomic data reveal that ATF4 preferably controls oxidative stress and redox-related pathways. Overexpression of ATF4 in neonatal rat ventricular myocytes increases NADPH-producing enzymes' whereas silencing of ATF4 decreases their expression. Further, stable isotope tracer experiments reveal that ATF4 overexpression augments metabolic flux within these 2 pathways. In vivo, cardiomyocyte-specific deletion of ATF4 exacerbates cardiomyopathy in the setting of transverse aortic constriction and accelerates heart failure development, attributable, at least in part, to an inability to increase the expression of NADPH-generating enzymes.

CONCLUSIONS

Our findings reveal that ATF4 plays a critical role in the heart under conditions of hemodynamic stress by governing both cytosolic and mitochondrial production of NADPH.

Heart Failure With Preserved Ejection Fraction: Heterogeneous Syndrome, Diverse Preclinical Models

Heart failure with preserved ejection fraction (HFpEF) represents one of the greatest challenges facing cardiovascular medicine today. Despite being the most common form of heart failure worldwide, there has been limited success in developing therapeutics for this syndrome. This is largely due to our incomplete understanding of the biology driving its systemic pathophysiology and the heterogeneity of clinical phenotypes, which are increasingly being recognized as distinct HFpEF phenogroups. Development of efficacious therapeutics fundamentally relies on robust preclinical models that not only faithfully recapitulate key features of the clinical syndrome but also enable rigorous investigation of putative mechanisms of disease in the context of clinically relevant phenotypes. In this review, we propose a preclinical research strategy that is conceptually grounded in model diversification and aims to better align with our evolving understanding of the heterogeneity of clinical HFpEF. Although heterogeneity is often viewed as a major obstacle in preclinical HFpEF research, we challenge this notion and argue that embracing it may be the key to demystifying its pathobiology. Here, we first provide an overarching guideline for developing HFpEF models through a stepwise approach of comprehensive cardiac and extra-cardiac phenotyping. We then present an overview of currently available models, focused on the 3 leading phenogroups, which are primarily based on aging, cardiometabolic stress, and chronic hypertension. We discuss how well these models reflect their clinically relevant phenogroup and highlight some of the more recent mechanistic insights they are providing into the complex pathophysiology underlying HFpEF.

Immunometabolic Mechanisms of Heart Failure with Preserved Ejection Fraction

Heart failure with preserved ejection fraction (HFpEF) is increasing in prevalence worldwide, already accounting for at least half of all heart failure (HF). As most patients with HFpEF are obese with metabolic syndrome, metabolic stress has been implicated in syndrome pathogenesis. Recently, compelling evidence for bidirectional crosstalk between metabolic stress and chronic inflammation has emerged, and alterations in systemic and cardiac immune responses are held to participate in HFpEF pathophysiology. Indeed, based on both preclinical and clinical evidence, comorbidity-driven systemic inflammation, coupled with metabolic stress, have been implicated together in HFpEF pathogenesis. As metabolic alterations impact immune function(s) in HFpEF, major changes in immune cell metabolism are also recognized in HFpEF and in HFpEF-predisposing conditions. Both arms of immunity - innate and adaptive - are implicated in the cardiomyocyte response in HFpEF. Indeed, we submit that crosstalk among adipose tissue, the immune system, and the heart represents a critical component of HFpEF pathobiology. Here, we review recent evidence in support of immunometabolic mechanisms as drivers of HFpEF pathogenesis, discuss pivotal biological mechanisms underlying the syndrome, and highlight questions requiring additional inquiry.

Matricellular Protein Cilp1 Promotes Myocardial Fibrosis in Response to Myocardial Infarction

[Figure: see text].

Fli1 Promotes Vascular Morphogenesis by Regulating Endothelial Potential of Multipotent Myogenic Progenitors

[Figure: see text].

Abstract P464: Cardiac Dysfunction In A Mouse Model For Autosomal Dominant Polycystic Kidney Disease

Mutations in polycystin-1 (PC1) cause autosomal dominant polycystic kidney disease (ADPKD), a disorder that manifests with cardiac hypertrophy and dysfunction. We recently showed that cardiomyocyte-specific PC1 KO mice exhibit both systolic and diastolic dysfunction without signs of cardiac hypertrophy. The purpose of this study was to determine the effects of ADPKD-causing PC1 mutations on cardiac function using a mouse model for ADPKD harboring a mutation in PC1 R3277C (RC/RC). We used echocardiography to determine cardiac function and Western blot analysis to explore signaling pathways in WT and RC/RC mice (2-4 months of age).We observed a slight but significant decrease in ejection fraction (77.2±0.7 vs 86.2±2.4 %, N=5, 4, P=0.015) without signs of left ventricular hypertrophy (LV mass 78.4±5.5 vs 93.5±4.2 mg, N=5, 4, P>0.05) in RC/RC compared to WT mice. Western blot analysis from total heart lysates (WT and RC/RC; N=5) revealed no changes in protein levels of hypertrophic markers: beta myosin heavy chain (β-MHC) and regulator of calcineurin 1 (RCAN1). In addition, we studied multiple signaling pathways involved in cardiac hypertrophy by analyzing their phosphorylation status by Western blot (phosphorylated/total protein). We observed no changes in mTOR, S6K1 and S6 phosphorylation. However, a decrease in p-4EBP1 and p-eIF4B was observed in RC/RC compared to WT. Moreover, we observed a significant increase in p-ERK and p-CaMKII. Our data suggest that alterations in PC1 signaling promote cardiac dysfunction but do not promote hypertrophy in young mice (2-4 months of age). Published evidence (PMID: 32730856) suggest that RC/RC hearts become hypertrophic at 6 months of age. However, our data suggest there may be dysfunction prior to cardiac hypertrophy. This warrants further investigation into the more primary role of ADPKD-associated co-morbidities. More studies, with a larger animal cohort, are necessary to unveil the effects of mutant PC1 on cardiac function.

A Call to Action for New Global Approaches to Cardiovascular Disease Drug Solutions

While we continue to wrestle with the immense challenge of implementing equitable access to established evidence-based treatments, substantial gaps remain in our pharmacotherapy armament for common forms of cardiovascular disease including coronary and peripheral arterial disease, heart failure, hypertension, and arrhythmia. We need to continue to invest in the development of new approaches for the discovery, rigorous assessment, and implementation of new therapies. Currently, the time and cost to progress from lead compound/product identification to the clinic, and the success rate in getting there reduces the incentive for industry to invest, despite the enormous burden of disease and potential size of market. There are tremendous opportunities with improved phenotyping of patients currently batched together in syndromic "buckets." Use of advanced imaging and molecular markers may allow stratification of patients in a manner more aligned to biological mechanisms that can, in turn, be targeted by specific approaches developed using high-throughput molecular technologies. Unbiased "omic" approaches enhance the possibility of discovering completely new mechanisms in such groups. Furthermore, advances in drug discovery platforms, and models to study efficacy and toxicity more relevant to the human disease, are valuable. Re-imagining the relationships among discovery, translation, evaluation, and implementation will help reverse the trend away from investment in the cardiovascular space, establishing innovative platforms and approaches across the full spectrum of therapeutic development.

Activation of Autophagic Flux Blunts Cardiac Ischemia/Reperfusion Injury

[Figure: see text].

High-sugar feeding and increasing cholesterol levels in infants

Hypercholesterolaemia is an important risk factor for cardiovascular disease. Both total and LDL cholesterol levels are three-fold higher at the end of the first year of life and about four-fold higher in adulthood compared with the neonatal period. In the USA, only 25% of infants are exclusively breastfed and simple carbohydrate-rich formulas are preferentially consumed. Spikes in fasting glucose and insulin have been reported in formula-fed infants and are associated with higher levels of proprotein convertase subtilisin/kexin type 9, suggesting a potential link between high simple sugar intake and consequent increase in LDL cholesterol in early childhood.

NAD+ Repletion Reverses Heart Failure With Preserved Ejection Fraction

[Figure: see text].

A call to action for new global approaches to cardiovascular disease drug solutions

Whilst we continue to wrestle with the immense challenge of implementing equitable access to established evidence-based treatments, substantial gaps remain in our pharmacotherapy armament for common forms of cardiovascular disease including coronary and peripheral arterial disease, heart failure, hypertension, and arrhythmia. We need to continue to invest in the development of new approaches for the discovery, rigorous assessment, and implementation of new therapies. Currently, the time and cost to progress from lead compound/product identification to the clinic, and the success rate in getting there reduces the incentive for industry to invest, despite the enormous burden of disease and potential size of market. There are tremendous opportunities with improved phenotyping of patients currently batched together in syndromic 'buckets'. Use of advanced imaging and molecular markers may allow stratification of patients in a manner more aligned to biological mechanisms that can, in turn, be targeted by specific approaches developed using high-throughput molecular technologies. Unbiased 'omic' approaches enhance the possibility of discovering completely new mechanisms in such groups. Furthermore, advances in drug discovery platforms, and models to study efficacy and toxicity more relevant to the human disease, are valuable. Re-imagining the relationships among discovery, translation, evaluation, and implementation will help reverse the trend away from investment in the cardiovascular space, establishing innovative platforms and approaches across the full spectrum of therapeutic development.

Cooperative Binding of ETS2 and NFAT Links Erk1/2 and Calcineurin Signaling in the Pathogenesis of Cardiac Hypertrophy

Supplemental Digital Content is available in the text.

Cardiac hypertrophy is an independent risk factor for heart failure, a leading cause of morbidity and mortality globally. The calcineurin/NFAT (nuclear factor of activated T cells) pathway and the MAPK (mitogen-activated protein kinase)/Erk (extracellular signal-regulated kinase) pathway contribute to the pathogenesis of cardiac hypertrophy as an interdependent network of signaling cascades. How these pathways interact remains unclear and few direct targets responsible for the prohypertrophic role of NFAT have been described.

Xbp1s-FoxO1 axis governs lipid accumulation and contractile performance in heart failure with preserved ejection fraction

Heart failure with preserved ejection fraction (HFpEF) is now the dominant form of heart failure and one for which no efficacious therapies exist. Obesity and lipid mishandling greatly contribute to HFpEF. However, molecular mechanism(s) governing metabolic alterations and perturbations in lipid homeostasis in HFpEF are largely unknown. Here, we report that cardiomyocyte steatosis in HFpEF is coupled with increases in the activity of the transcription factor FoxO1 (Forkhead box protein O1). FoxO1 depletion, as well as over-expression of the Xbp1s (spliced form of the X-box-binding protein 1) arm of the UPR (unfolded protein response) in cardiomyocytes each ameliorates the HFpEF phenotype in mice and reduces myocardial lipid accumulation. Mechanistically, forced expression of Xbp1s in cardiomyocytes triggers ubiquitination and proteasomal degradation of FoxO1 which occurs, in large part, through activation of the E3 ubiquitin ligase STUB1 (STIP1 homology and U-box-containing protein 1) a novel and direct transcriptional target of Xbp1s. Our findings uncover the Xbp1s-FoxO1 axis as a pivotal mechanism in the pathogenesis of cardiometabolic HFpEF and unveil previously unrecognized mechanisms whereby the UPR governs metabolic alterations in cardiomyocytes.

Epigenetic Reader BRD4 (Bromodomain-Containing Protein 4) Governs Nucleus-Encoded Mitochondrial Transcriptome to Regulate Cardiac Function

BACKGROUND

BET (bromodomain and extraterminal) epigenetic reader proteins, in particular BRD4 (bromodomain-containing protein 4), have emerged as potential therapeutic targets in a number of pathological conditions, including cancer and cardiovascular disease. Small-molecule BET protein inhibitors such as JQ1 have demonstrated efficacy in reversing cardiac hypertrophy and heart failure in preclinical models. Yet, genetic studies elucidating the biology of BET proteins in the heart have not been conducted to validate pharmacological findings and to unveil potential pharmacological side effects.

METHODS

By engineering a cardiomyocyte-specific BRD4 knockout mouse, we investigated the role of BRD4 in cardiac pathophysiology. We performed functional, transcriptomic, and mitochondrial analyses to evaluate BRD4 function in developing and mature hearts.

RESULTS

Unlike pharmacological inhibition, loss of BRD4 protein triggered progressive declines in myocardial function, culminating in dilated cardiomyopathy. Transcriptome analysis of BRD4 knockout mouse heart tissue identified early and specific disruption of genes essential to mitochondrial energy production and homeostasis. Functional analysis of isolated mitochondria from these hearts confirmed that BRD4 ablation triggered significant changes in mitochondrial electron transport chain protein expression and activity. Computational analysis identified candidate transcription factors participating in the BRD4-regulated transcriptome. In particular, estrogen-related receptor α, a key nuclear receptor in metabolic gene regulation, was enriched in promoters of BRD4-regulated mitochondrial genes.

CONCLUSIONS

In aggregate, we describe a previously unrecognized role for BRD4 in regulating cardiomyocyte mitochondrial homeostasis, observing that its function is indispensable to the maintenance of normal cardiac function.

Cardiomyocyte-derived small extracellular vesicles can signal eNOS activation in cardiac microvascular endothelial cells to protect against Ischemia/Reperfusion injury

Rationale: The crosstalk between cardiac microvascular endothelial cells (CMECs) and cardiomyocytes (CMs) has emerged as a key component in the development of, and protection against, cardiac diseases. For example, activation of endothelial nitric oxide synthase (eNOS) in CMECs, by therapeutic strategies such as ischemic preconditioning, plays a critical role in the protection against myocardial ischemia/reperfusion (I/R) injury. However, much less is known about the signals produced by CMs that are able to regulate CMEC biology. Here we uncovered one such mechanism using Tongxinluo (TXL), a traditional Chinese medicine, that alleviates myocardial ischemia/reperfusion (I/R) injury by activating CMEC eNOS. The aim of our study is to identify the signals produced by CMs that can regulate CMEC biology during I/R. Methods: Ex vivo, in vivo, and in vitro settings of ischemia-reperfusion were used in our study, with the protective signaling pathways activated in CMECs identified using genetic inhibition (p70s6k1 siRNA, miR-145-5p mimics, etc.), chemical inhibitors (the eNOS inhibitor, L-NNA, and the small extracellular vesicles (sEVs) inhibitor, GW4869) and Western blot analyses. TritonX-100 at a dose of 0.125% was utilized to inactivate the eNOS activity in endothelium to investigate the role of CMEC-derived eNOS in TXL-induced cardioprotection. Results: We found that while CMEC-derived eNOS activity was required for the cardioprotection of TXL, activation of eNOS in CMECs by TXL did not occur directly. Instead, eNOS activation in CMECs required a crosstalk between CMs and CMECs through the uptake of CM-derived sEVs. We further demonstrate that TXL induced CM-sEVs contain increased levels of Long Intergenic Non-Protein Coding RNA, Regulator Of Reprogramming (Linc-ROR). Upon uptake into CMECs, linc-ROR downregulates its target miR-145-5p leading to activation of the eNOS pathway by facilitating the expression of p70s6k1 in these cells. The activation of CMEC-derived eNOS works to increase survival in both the CMECs and the CMs themselves. Conclusions: These data uncover a mechanism by which the crosstalk between CMs and CMECs leads to the increased survival of the heart after I/R injury and point to a new therapeutic target for the blunting of myocardial I/R injury.

Abstract MP161: A Calcineurin-hoxb13 Axis Regulates Growth Mode of Mammalian Cardiomyocytes

A major factor in the progression to heart failure in humans is the inability of the adult heart to repair itself after injury. Our group recently demonstrated that the early postnatal mammalian heart is capable of regeneration following injury through proliferation of preexisting cardiomyocytes1,2. We recently also showed that Meis1, a TALE family homeodomain transcription factor, translocates to cardiomyocyte nuclei shortly after birth and mediates postnatal cell cycle arrest3. Here we report that Hoxb13 acts as a Meis1 cofactor in postnatal cardiomyocytes. Cardiomyocyte-specific deletion of Hoxb13 can both extend the postnatal window of cardiomyocyte proliferation and reactivate cardiomyocyte cell cycle in the adult heart. Moreover, adult Meis1/Hoxb13 double knockout hearts display widespread cardiomyocyte mitosis, sarcomere disassembly and an improvement in left ventricular systolic function following myocardial infarction both by echocardiography and MRI. ChIP-seq analysis demonstrates that Meis1 and Hoxb13 act cooperatively to regulate cardiomyocyte maturation and cell cycle. Finally, we show that the calcium-activated protein phosphatase calcineurin dephosphorylates Hoxb13 at serine-204 (S204), resulting in its nuclear localization and cell cycle arrest. Collectively, these results demonstrate that Meis1 and Hoxb13 act cooperatively to regulate cardiomyocyte maturation and proliferation and provide mechanistic insights into the link between hyperplastic and hypertrophic growth of cardiomyocytes.

Metabolic inflammation in heart failure with preserved ejection fraction

One in 10 persons in the world aged 40 years and older will develop the syndrome of HFpEF (heart failure with preserved ejection fraction), the most common form of chronic cardiovascular disease for which no effective therapies are currently available. Metabolic disturbance and inflammatory burden contribute importantly to HFpEF pathogenesis. The interplay within these two biological processes is complex; indeed, it is now becoming clear that the notion of metabolic inflammation-metainflammation-must be considered central to HFpEF pathophysiology. Inflammation and metabolism interact over the course of syndrome progression, and likely impact HFpEF treatment and prevention. Here, we discuss evidence in support of a causal, mechanistic role of metainflammation in shaping HFpEF, proposing a framework in which metabolic comorbidities profoundly impact cardiac metabolism and inflammatory pathways in the syndrome.

PKD2/polycystin-2 induces autophagy by forming a complex with BECN1

Macroautophagy/autophagy is an intracellular process involved in the breakdown of macromolecules and organelles. Recent studies have shown that PKD2/PC2/TRPP2 (polycystin 2, transient receptor potential cation channel), a nonselective cation channel permeable to Ca²⁺ that belongs to the family of transient receptor potential channels, is required for autophagy in multiple cell types by a mechanism that remains unclear. Here, we report that PKD2 forms a protein complex with BECN1 (beclin 1), a key protein required for the formation of autophagic vacuoles, by acting as a scaffold that interacts with several co-modulators via its coiled-coil domain (CCD). Our data identified a physical and functional interaction between PKD2 and BECN1, which depends on one out of two CCD domains (CC1), located in the carboxy-terminal tail of PKD2. In addition, depletion of intracellular Ca²⁺ with BAPTA-AM not only blunted starvation-induced autophagy but also disrupted the PKD2-BECN1 complex. Consistently, PKD2 overexpression triggered autophagy by increasing its interaction with BECN1, while overexpression of PKD2^D509V, a Ca²⁺ channel activity-deficient mutant, did not induce autophagy and manifested diminished interaction with BECN1. Our findings show that the PKD2-BECN1 complex is required for the induction of autophagy, and its formation depends on the presence of the CC1 domain of PKD2 and on intracellular Ca²⁺ mobilization by PKD2. These results provide new insights regarding the molecular mechanisms by which PKD2 controls autophagy.Abbreviations: ADPKD: autosomal dominant polycystic kidney disease; ATG: autophagy-related; ATG14/ATG14L: autophagy related 14; Baf A1: bafilomycin A₁; BCL2/Bcl-2: BCL2 apoptosis regulator; BCL2L1/BCL-XL: BCL2 like 1; BECN1: beclin 1; CCD: coiled-coil domain; EBSS: Earle's balanced salt solution; ER: endoplasmic reticulum; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GFP: green fluorescent protein; GOLGA2/GM130: golgin A2; GST: glutathione s-transferase; LAMP1: lysosomal associated membrane protein 1; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MTORC1: mechanistic target of rapamycin kinase complex 1; NBR1: NBR1 autophagy cargo receptor; PIK3C3/VPS34: phosphatidylinositol 3-kinase catalytic subunit type 3; PKD2/PC2: polycystin 2, transient receptor potential cation channel; RTN4/NOGO: reticulon 4; RUBCN/RUBICON: rubicon autophagy regulator; SQSTM1/p62: sequestosome 1; UVRAG: UV radiation resistance associated; WIPI2: WD repeat domain, phosphoinositide interacting 2.

A calcineurin-Hoxb13 axis regulates growth mode of mammalian cardiomyocytes

A major factor in the progression to heart failure in humans is the inability of the adult heart to repair itself after injury. We recently demonstrated that the early postnatal mammalian heart is capable of regeneration following injury through proliferation of preexisting cardiomyocytes1,2 and that Meis1, a three amino acid loop extension (TALE) family homeodomain transcription factor, translocates to cardiomyocyte nuclei shortly after birth and mediates postnatal cell cycle arrest3. Here we report that Hoxb13 acts as a cofactor of Meis1 in postnatal cardiomyocytes. Cardiomyocyte-specific deletion of Hoxb13 can extend the postnatal window of cardiomyocyte proliferation and reactivate the cardiomyocyte cell cycle in the adult heart. Moreover, adult Meis1-Hoxb13 double-knockout hearts display widespread cardiomyocyte mitosis, sarcomere disassembly and improved left ventricular systolic function following myocardial infarction, as demonstrated by echocardiography and magnetic resonance imaging. Chromatin immunoprecipitation with sequencing demonstrates that Meis1 and Hoxb13 act cooperatively to regulate cardiomyocyte maturation and cell cycle. Finally, we show that the calcium-activated protein phosphatase calcineurin dephosphorylates Hoxb13 at serine-204, resulting in its nuclear localization and cell cycle arrest. These results demonstrate that Meis1 and Hoxb13 act cooperatively to regulate cardiomyocyte maturation and proliferation and provide mechanistic insights into the link between hyperplastic and hypertrophic growth of cardiomyocytes.

FoxO1-Dio2 signaling axis governs cardiomyocyte thyroid hormone metabolism and hypertrophic growth

Forkhead box O (FoxO) proteins and thyroid hormone (TH) have well established roles in cardiovascular morphogenesis and remodeling. However, specific role(s) of individual FoxO family members in stress-induced growth and remodeling of cardiomyocytes remains unknown. Here, we report that FoxO1, but not FoxO3, activity is essential for reciprocal regulation of types II and III iodothyronine deiodinases (Dio2 and Dio3, respectively), key enzymes involved in intracellular TH metabolism. We further show that Dio2 is a direct transcriptional target of FoxO1, and the FoxO1-Dio2 axis governs TH-induced hypertrophic growth of neonatal cardiomyocytes in vitro and in vivo. Utilizing transverse aortic constriction as a model of hemodynamic stress in wild-type and cardiomyocyte-restricted FoxO1 knockout mice, we unveil an essential role for the FoxO1-Dio2 axis in afterload-induced pathological cardiac remodeling and activation of TRα1. These findings demonstrate a previously unrecognized FoxO1-Dio2 signaling axis in stress-induced cardiomyocyte growth and remodeling and intracellular TH homeostasis.