The American Heart Association at 100: A Century of Scientific Progress and the Future of Cardiovascular Science: A Presidential Advisory From the American Heart Association

In 1924, the founders of the American Heart Association (AHA) envisioned an international society focused on the heart and aimed at facilitating research, disseminating information, increasing public awareness, and developing public health policy related to heart disease. This presidential advisory provides a comprehensive review of the past century of cardiovascular and stroke science, with a focus on the AHA's contributions, as well as informed speculation about the future of cardiovascular science into the next century of the organization's history. The AHA is a leader in fundamental, translational, clinical, and population science, and it promotes the concept of the "learning health system," in which a continuous cycle of evidence-based practice leads to practice-based evidence, permitting an iterative refinement in clinical evidence and care. This advisory presents the AHA's journey over the past century from instituting professional membership to establishing extraordinary research funding programs; translating evidence to practice through clinical practice guidelines; affecting systems of care through quality programs, certification, and implementation; leading important advocacy efforts at the federal, state and local levels; and building global coalitions around cardiovascular and stroke science and public health. Recognizing an exciting potential future for science and medicine, the advisory offers a vision for even greater impact for the AHA's second century in its continued mission to be a relentless force for longer, healthier lives.

Protein Kinase A Is a Master Regulator of Physiological and Pathological Cardiac Hypertrophy

BACKGROUND

The sympathoadrenergic system and its major effector PKA (protein kinase A) are activated to maintain cardiac output coping with physiological or pathological stressors. If and how PKA plays a role in physiological cardiac hypertrophy (PhCH) and pathological CH (PaCH) are not clear.

METHODS

Transgenic mouse models expressing the PKA inhibition domain (PKAi) of PKA inhibition peptide alpha (PKIalpha)-green fluorescence protein (GFP) fusion protein (PKAi-GFP) in a cardiac-specific and inducible manner (cPKAi) were used to determine the roles of PKA in physiological CH during postnatal growth or induced by swimming, and in PaCH induced by transaortic constriction (TAC) or augmented Ca2+ influx. Kinase profiling was used to determine cPKAi specificity. Echocardiography was used to determine cardiac morphology and function. Western blotting and immunostaining were used to measure protein abundance and phosphorylation. Protein synthesis was assessed by puromycin incorporation and protein degradation by measuring protein ubiquitination and proteasome activity. Neonatal rat cardiomyocytes (NRCMs) infected with AdGFP (GFP adenovirus) or AdPKAi-GFP (PKAi-GFP adenovirus) were used to determine the effects and mechanisms of cPKAi on myocyte hypertrophy. rAAV9.PKAi-GFP was used to treat TAC mice.

RESULTS

(1) cPKAi delayed postnatal cardiac growth and blunted exercise-induced PhCH; (2) PKA was activated in hearts after TAC due to activated sympathoadrenergic system, the loss of endogenous PKIα (PKA inhibition peptide α), and the stimulation by noncanonical PKA activators; (3) cPKAi ameliorated PaCH induced by TAC and increased Ca2+ influxes and blunted neonatal rat cardiomyocyte hypertrophy by isoproterenol and phenylephrine; (4) cPKAi prevented TAC-induced protein synthesis by inhibiting mTOR (mammalian target of rapamycin) signaling through reducing Akt (protein kinase B) activity, but enhancing inhibitory GSK-3α (glycogen synthase kinase-3α) and GSK-3β signals; (5) cPKAi reduced protein degradation by the ubiquitin-proteasome system via decreasing RPN6 phosphorylation; (6) cPKAi increased the expression of antihypertrophic atrial natriuretic peptide (ANP); (7) cPKAi ameliorated established PaCH and improved animal survival.

CONCLUSIONS

Cardiomyocyte PKA is a master regulator of PhCH and PaCH through regulating protein synthesis and degradation. cPKAi can be a novel approach to treat PaCH.

Thyroid Hormone Suppresses Medulloblastoma Progression Through Promoting Terminal Differentiation of Tumor Cells

Hypothyroidism is commonly detected in patients with medulloblastoma (MB). A possible link between thyroid hormone (TH) signaling and MB pathogenicity has not been reported. Here, we find that TH plays a critical role in promoting tumor cell differentiation. Reduction in TH levels frees the TH receptor, TRα1, to bind to EZH2 and repress expression of NeuroD1, a transcription factor that drives tumor cell differentiation. Increased TH reverses EZH2-mediated repression of NeuroD1 by abrogating the binding of EZH2 and TRα1, thereby stimulating tumor cell differentiation and reducing MB growth. Importantly, TH-induced differentiation of tumor cells is not restricted by the molecular subgroup of MB. These findings establish an unprecedented association between TH signaling and MB pathogenicity, providing solid evidence for TH as a promising modality for MB treatment.

miR-182/183-Rasa1 axis induced macrophage polarization and redox regulation promotes repair after ischemic cardiac injury

Few therapies have produced significant improvement in cardiac structure and function after ischemic cardiac injury (ICI). Our possible explanation is activation of local inflammatory responses negatively impact the cardiac repair process following ischemic injury. Factors that can alter immune response, including significantly altered cytokine levels in plasma and polarization of macrophages and T cells towards a pro-reparative phenotype in the myocardium post-MI is a valid strategy for reducing infarct size and damage after myocardial injury. Our previous studies showed that cortical bone stem cells (CBSCs) possess reparative effects after ICI. In our current study, we have identified that the beneficial effects of CBSCs appear to be mediated by miRNA in their extracellular vesicles (CBSC-EV). Our studies showed that CBSC-EV treated animals demonstrated reduced scar size, attenuated structural remodeling, and improved cardiac function versus saline treated animals. These effects were linked to the alteration of immune response, with significantly altered cytokine levels in plasma, and polarization of macrophages and T cells towards a pro-reparative phenotype in the myocardium post-MI. Our detailed in vitro studies demonstrated that CBSC-EV are enriched in miR-182/183 that mediates the pro-reparative polarization and metabolic reprogramming in macrophages, including enhanced OXPHOS rate and reduced ROS, via Ras p21 protein activator 1 (RASA1) axis under Lipopolysaccharides (LPS) stimulation. In summary, CBSC-EV deliver unique molecular cargoes, such as enriched miR-182/183, that modulate the immune response after ICI by regulating macrophage polarization and metabolic reprogramming to enhance repair.

Effects of maternal hypothyroidism on postnatal cardiomyocyte proliferation and cardiac disease responses of the progeny

Maternal hypothyroidism (MH) could adversely affect the cardiac disease responses of the progeny. This study tested the hypothesis that MH reduces early postnatal cardiomyocyte (CM) proliferation so that the adult heart of MH progeny has a smaller number of larger cardiac myocytes, which imparts adverse cardiac disease responses following injury. Thyroidectomy (TX) was used to establish MH. The progeny from mice that underwent sham or TX surgery were termed Ctrl (control) or MH (maternal hypothyroidism) progeny, respectively. MH progeny had similar heart weight (HW) to body weight (BW) ratios and larger CM size consistent with fewer CMs at postnatal day 60 (P60) compared with Ctrl (control) progeny. MH progeny had lower numbers of EdU+, Ki67+, and phosphorylated histone H3 (PH3)+ CMs, which suggests they had a decreased CM proliferation in the postnatal timeframe. RNA-seq data showed that genes related to DNA replication were downregulated in P5 MH hearts, including bone morphogenetic protein 10 (Bmp10). Both in vivo and in vitro studies showed Bmp10 treatment increased CM proliferation. After transverse aortic constriction (TAC), the MH progeny had more severe cardiac pathological remodeling compared with the Ctrl progeny. Thyroid hormone (T4) treatment for MH mothers preserved their progeny's postnatal CM proliferation capacity and prevented excessive pathological remodeling after TAC. Our results suggest that CM proliferation during early postnatal development was significantly reduced in MH progeny, resulting in fewer CMs with hypertrophy in adulthood. These changes were associated with more severe cardiac disease responses after pressure overload.NEW & NOTEWORTHY Our study shows that compared with Ctrl (control) progeny, the adult progeny of mothers who have MH (MH progeny) had fewer CMs. This reduction of CM numbers was associated with decreased postnatal CM proliferation. Gene expression studies showed a reduced expression of Bmp10 in MH progeny. Bmp10 has been linked to myocyte proliferation. In vivo and in vitro studies showed that Bmp10 treatment of MH progeny and their myocytes could increase CM proliferation. Differences in CM number and size in adult hearts of MH progeny were linked to more severe cardiac structural and functional remodeling after pressure overload. T4 (synthetic thyroxine) treatment of MH mothers during their pregnancy, prevented the reduction in CM number in their progeny and the adverse response to disease stress.

Functional LTCC-β2AR Complex Needs Caveolin-3 and Is Disrupted in Heart Failure

BACKGROUND

Beta-2 adrenergic receptors (β2ARs) but not beta-2 adrenergic receptors (β1ARs) form a functional complex with L-type Ca2+ channels (LTCCs) on the cardiomyocyte membrane. However, how microdomain localization in the plasma membrane affects the function of these complexes is unknown. We aim to study the coupling between LTCC and β adrenergic receptors in different cardiomyocyte microdomains, the distinct involvement of PKA and CAMKII (Ca2+/calmodulin-dependent protein kinase II) and explore how this functional complex is disrupted in heart failure.

METHODS

Global signaling between LTCCs and β adrenergic receptors was assessed with whole-cell current recordings and western blot analysis. Super-resolution scanning patch-clamp was used to explore the local coupling between single LTCCs and β1AR or β2AR in different membrane microdomains in control and failing cardiomyocytes.

RESULTS

LTCC open probability (Po) showed an increase from 0.054±0.003 to 0.092±0.008 when β2AR was locally stimulated in the proximity of the channel (<350 nm) in the transverse tubule microdomain. In failing cardiomyocytes, from both rodents and humans, this transverse tubule coupling between LTCC and β2AR was lost. Interestingly, local stimulation of β1AR did not elicit any change in the Po of LTCCs, indicating a lack of proximal functional interaction between the two, but we confirmed a general activation of LTCC via β1AR. By using blockers of PKA and CaMKII and a Caveolin-3-knockout mouse model, we conclude that the β2AR-LTCC regulation requires the presence of caveolin-3 and the activation of the CaMKII pathway. By contrast, at a cellular "global" level PKA plays a major role downstream β1AR and results in an increase in LTCC current.

CONCLUSIONS

Regulation of the LTCC activity by proximity coupling mechanisms occurs only via β2AR, but not β1AR. This may explain how β2ARs tune the response of LTCCs to adrenergic stimulation in healthy conditions. This coupling is lost in heart failure; restoring it could improve the adrenergic response of failing cardiomyocytes.

Combining three independent pathological stressors induces a heart failure with preserved ejection fraction phenotype

Heart failure (HF) with preserved ejection fraction (HFpEF) is defined as HF with an ejection fraction (EF) ≥ 50% and elevated cardiac diastolic filling pressures. The underlying causes of HFpEF are multifactorial and not well-defined. A transgenic mouse with low levels of cardiomyocyte (CM)-specific inducible Cavβ2a expression (β2a-Tg mice) showed increased cytosolic CM Ca2+, and modest levels of CM hypertrophy, and fibrosis. This study aimed to determine if β2a-Tg mice develop an HFpEF phenotype when challenged with two additional stressors, high-fat diet (HFD) and Nω-nitro-l-arginine methyl ester (l-NAME, LN). Four-month-old wild-type (WT) and β2a-Tg mice were given either normal chow (WT-N, β2a-N) or HFD and/or l-NAME (WT-HFD, WT-LN, WT-HFD-LN, β2a-HFD, β2a-LN, and β2a-HFD-LN). Some animals were treated with the histone deacetylase (HDAC) (hypertrophy regulators) inhibitor suberoylanilide hydroxamic acid (SAHA) (β2a-HFD-LN-SAHA). Echocardiography was performed monthly. After 4 mo of treatment, terminal studies were performed including invasive hemodynamics and organs weight measurements. Cardiac tissue was collected. Four months of HFD plus l-NAME treatment did not induce a profound HFpEF phenotype in FVB WT mice. β2a-HFD-LN (3-Hit) mice developed features of HFpEF, including increased atrial natriuretic peptide (ANP) levels, preserved EF, diastolic dysfunction, robust CM hypertrophy, increased M2-macrophage population, and myocardial fibrosis. SAHA reduced the HFpEF phenotype in the 3-Hit mouse model, by attenuating these effects. The 3-Hit mouse model induced a reliable HFpEF phenotype with CM hypertrophy, cardiac fibrosis, and increased M2-macrophage population. This model could be used for identifying and preclinical testing of novel therapeutic strategies.NEW & NOTEWORTHY Our study shows that three independent pathological stressors (increased Ca2+ influx, high-fat diet, and l-NAME) together produce a profound HFpEF phenotype. The primary mechanisms include HDAC-dependent-CM hypertrophy, necrosis, increased M2-macrophage population, fibroblast activation, and myocardial fibrosis. A role for HDAC activation in the HFpEF phenotype was shown in studies with SAHA treatment, which prevented the severe HFpEF phenotype. This "3-Hit" mouse model could be helpful in identifying novel therapeutic strategies to treat HFpEF.

Systemic Hypoxemia Induces Cardiomyocyte Hypertrophy and Right Ventricular Specific Induction of Proliferation

BACKGROUND

A recent study suggests that systemic hypoxemia in adult male mice can induce cardiac myocytes to proliferate. The goal of the present experiments was to confirm these results, provide new insights on the mechanisms that induce adult cardiomyocyte cell cycle reentry, and to determine if hypoxemia also induces cardiomyocyte proliferation in female mice.

METHODS

EdU-containing mini pumps were implanted in 3-month-old, male and female C57BL/6 mice. Mice were placed in a hypoxia chamber, and the oxygen was lowered by 1% every day for 14 days to reach 7% oxygen. The animals remained in 7% oxygen for 2 weeks before terminal studies. Myocyte proliferation was also studied with a mosaic analysis with double markers mouse model.

RESULTS

Hypoxia induced cardiac hypertrophy in both left ventricular (LV) and right ventricular (RV) myocytes, with LV myocytes lengthening and RV myocytes widening and lengthening. Hypoxia induced an increase (0.01±0.01% in normoxia to 0.11±0.09% in hypoxia) in the number of EdU+ RV cardiomyocytes, with no effect on LV myocytes in male C57BL/6 mice. Similar results were observed in female mice. Furthermore, in mosaic analysis with double markers mice, hypoxia induced a significant increase in RV myocyte proliferation (0.03±0.03% in normoxia to 0.32±0.15% in hypoxia of RFP+ myocytes), with no significant change in LV myocyte proliferation. RNA sequencing showed upregulation of mitotic cell cycle genes and a downregulation of Cullin genes, which promote the G1 to S phase transition in hypoxic mice. There was significant proliferation of nonmyocytes and mild cardiac fibrosis in hypoxic mice that did not disrupt cardiac function. Male and female mice exhibited similar gene expression following hypoxia.

CONCLUSIONS

Systemic hypoxia induces a global hypertrophic stress response that was associated with increased RV proliferation, and while LV myocytes did not show increased proliferation, our results minimally confirm previous reports that hypoxia can induce cardiomyocyte cell cycle activity in vivo.

RNA-Binding Protein LIN28a Regulates New Myocyte Formation in the Heart Through Long Noncoding RNA-H19

BACKGROUND

Developmental cardiac tissue holds remarkable capacity to regenerate after injury and consists of regenerative mononuclear diploid cardiomyocytes. On maturation, mononuclear diploid cardiomyocytes become binucleated or polyploid and exit the cell cycle. Cardiomyocyte metabolism undergoes a profound shift that coincides with cessation of regeneration in the postnatal heart. However, whether reprogramming metabolism promotes persistence of regenerative mononuclear diploid cardiomyocytes enhancing cardiac function and repair after injury is unknown. Here, we identify a novel role for RNA-binding protein LIN28a, a master regulator of cellular metabolism in cardiac repair after injury.

METHODS

LIN28a overexpression was tested using mouse transgenesis on postnatal cardiomyocyte numbers, cell cycle, and response to apical resection injury. With the use of neonatal and adult cell culture systems and adult and Mosaic Analysis with Double Markers myocardial injury models in mice, the effect of LIN28a overexpression on cardiomyocyte cell cycle and metabolism was tested. Last, isolated adult cardiomyocytes from LIN28a and wild-type mice 4 days after myocardial injury were used for RNA-immunoprecipitation sequencing.

RESULTS

LIN28a was found to be active primarily during cardiac development and rapidly decreases after birth. LIN28a reintroduction at postnatal day (P) 1, P3, P5, and P7 decreased maturation-associated polyploidization, nucleation, and cell size, enhancing cardiomyocyte cell cycle activity in LIN28a transgenic pups compared with wild-type littermates. Moreover, LIN28a overexpression extended cardiomyocyte cell cycle activity beyond P7 concurrent with increased cardiac function 30 days after apical resection. In the adult heart, LIN28a overexpression attenuated cardiomyocyte apoptosis, enhanced cell cycle activity, cardiac function, and survival in mice 12 weeks after myocardial infarction compared with wild-type littermate controls. Instead, LIN28a small molecule inhibitor attenuated the proreparative effects of LIN28a on the heart. Neonatal rat ventricular myocytes overexpressing LIN28a mechanistically showed increased glycolysis, ATP production, and levels of metabolic enzymes compared with control. LIN28a immunoprecipitation followed by RNA-immunoprecipitation sequencing in cardiomyocytes isolated from LIN28a-overexpressing hearts after injury identified long noncoding RNA-H19 as its most significantly altered target. Ablation of long noncoding RNA-H19 blunted LIN28a-induced enhancement on cardiomyocyte metabolism and cell cycle activity.

CONCLUSIONS

Collectively, LIN28a reprograms cardiomyocyte metabolism and promotes persistence of mononuclear diploid cardiomyocytes in the injured heart, enhancing proreparative processes, thereby linking cardiomyocyte metabolism to regulation of ploidy/nucleation and repair in the heart.

Assessing the Impact of the American Heart Association's Research Portfolio: A Scientific Statement From the American Heart Association

A task force composed of American Heart Association (AHA) Research Committee members established processes to measure the performance of the AHA's research portfolio and evaluated key outcomes that are fundamental to the overall success of the program. This report reviews progress that the AHA research program has had in achieving its goals relevant to the research programs in the AHA's research portfolio from 2008 to 2017. Comprehensive performance metrics were identified to assess the impact of AHA funding on researchers' career progress and research outcomes. Metrics included bibliometric analysis (ie, tracking of publications and their impact) and career development measures (ie, subsequent grant funding, intellectual property, faculty appointment/promotion, or industry position). Publication rates ranged from ≈0.5 to 4 publications per year, with a strong correlation between number of publications per year and later career stage. The Field-Weighted Citation Index, a metric of bibliometric impact, was between 1.5 and 3.0 for all programs, indicating that AHA awardee publications had a higher citation impact compared with similar publications. To gain insight into the career progression of AHA awardees, a 2-year postaward survey was distributed. Of the Postdoctoral Fellowship recipient respondents, 72% obtained academic research positions, with the remaining working in industry or government research settings; 72% of those in academic positions obtained additional funding. Among respondents who were Beginning Grant-in-Aid and Scientist Development Grant awardees, 45% received academic promotions and 83% obtained additional funding. Measuring performance of the AHA's research portfolio is critical to ensure that its strategic goals are met and to show the AHA's commitment to high-quality, impactful research.

Sex-specific responses to slow progressive pressure overload in a large animal model of HFpEF

Approximately 50% of all heart failure (HF) diagnoses can be classified as HF with preserved ejection fraction (HFpEF). HFpEF is more prevalent in females compared with males, but the underlying mechanisms are unknown. We previously showed that pressure overload (PO) in male felines induces a cardiopulmonary phenotype with essential features of human HFpEF. The goal of this study was to determine if slow progressive PO induces distinct cardiopulmonary phenotypes in females and males in the absence of other pathological stressors. Female and male felines underwent aortic constriction (banding) or sham surgery after baseline echocardiography, pulmonary function testing, and blood sampling. These assessments were repeated at 2 and 4 mo postsurgery to document the effects of slow progressive pressure overload. At 4 mo, invasive hemodynamic studies were also performed. Left ventricle (LV) tissue was collected for histology, myofibril mechanics, extracellular matrix (ECM) mass spectrometry, and single-nucleus RNA sequencing (snRNAseq). The induced pressure overload (PO) was not different between sexes. PO also induced comparable changes in LV wall thickness and myocyte cross-sectional area in both sexes. Both sexes had preserved ejection fraction, but males had a slightly more robust phenotype in hemodynamic and pulmonary parameters. There was no difference in LV fibrosis and ECM composition between banded male and female animals. LV snRNAseq revealed changes in gene programs of individual cell types unique to males and females after PO. Based on these results, both sexes develop cardiopulmonary dysfunction but the phenotype is somewhat less advanced in females.NEW & NOTEWORTHY We performed a comprehensive assessment to evaluate the effects of slow progressive pressure overload on cardiopulmonary function in a large animal model of heart failure with preserved ejection fraction (HFpEF) in males and females. Functional and structural assessments were performed at the organ, tissue, cellular, protein, and transcriptional levels. This is the first study to compare snRNAseq and ECM mass spectrometry of HFpEF myocardium from males and females. The results broaden our understanding of the pathophysiological response of both sexes to pressure overload. Both sexes developed a robust cardiopulmonary phenotype, but the phenotype was equal or a bit less robust in females.

Abstract P1030: LIN28a-induced Metabolic Reprogramming Regulates New Myocyte Formation In The Heart Via Lncrna-H19

Developmental cardiac tissue holds remarkable capacity to regenerate after injury and consists of regenerative mononuclear and diploid cardiomyocytes (MNDCMs). Upon maturation, MNDCMs become binucleated or polyploid and exit the cell cycle. Interestingly, CM metabolism undergoes a profound shift that coincides with cessation of regeneration in the postnatal heart. However, whether reprogramming metabolism promotes persistence of regenerative MNDCMs enhancing cardiac function and repair after injury is unknown. Here, we identify a novel role for RNA-binding protein LIN28a, a master regulator of cellular metabolism, in cardiac repair following injury. LIN28a was found as primarily active during cardiac development and rapidly decreases after birth. LIN28a reintroduction at P1, P3, P5, and P7 decreased maturation-associated polyploidization, nucleation, and cell size, enhancing CM cell cycle activity in LIN28a transgenic pups compared to WT littermates. Moreover, LIN28a overexpression extended CM cell cycle activity beyond P7 concurrent with increased cardiac function 30 days after apical resection. In the adult heart, LIN28a overexpression attenuated CM apoptosis, enhanced cell cycle activity, cardiac function, and survival in mice 12 weeks after myocardial infarction compared to WT littermate controls. Alternatively, LIN28a small molecule inhibitor attenuated pro-reparative effects of LIN28a on the heart. Mechanistically, Neonatal rat ventricular myocytes (NRVMs) overexpressing LIN28a showed increased glycolysis, ATP production and levels of metabolic enzymes compared to control. LIN28a immunoprecipitation followed by RNA sequencing (RIPseq) in CMs isolated from LIN28a injured hearts identified lncRNA-H19 as its most significantly altered target. Ablation of lncRNA-H19 blunted LIN28a-induced enhancement on CM metabolism and cell cycle activity. Collectively, LIN28a reprograms CM metabolism and promotes persistence of MNDCMs in the injured heart enhancing pro-reparative processes thereby linking CM metabolism to regulation of ploidy/nucleation and repair in the heart.

HDAC Inhibition Regulates Cardiac Function by Increasing Myofilament Calcium Sensitivity and Decreasing Diastolic Tension

We recently established a large animal model that recapitulates key clinical features of heart failure with preserved ejection fraction (HFpEF) and tested the effects of the pan-HDAC inhibitor suberoylanilide hydroxamic acid (SAHA). SAHA reversed and prevented the development of cardiopulmonary impairment. This study evaluated the effects of SAHA at the level of cardiomyocyte and contractile protein function to understand how it modulates cardiac function. Both isolated adult feline ventricular cardiomyocytes (AFVM) and left ventricle (LV) trabeculae isolated from non-failing donors were treated with SAHA or vehicle before recording functional data. Skinned myocytes were isolated from AFVM and human trabeculae to assess myofilament function. SAHA-treated AFVM had increased contractility and improved relaxation kinetics but no difference in peak calcium transients, with increased calcium sensitivity and decreased passive stiffness of myofilaments. Mass spectrometry analysis revealed increased acetylation of the myosin regulatory light chain with SAHA treatment. SAHA-treated human trabeculae had decreased diastolic tension and increased developed force. Myofilaments isolated from human trabeculae had increased calcium sensitivity and decreased passive stiffness. These findings suggest that SAHA has an important role in the direct control of cardiac function at the level of the cardiomyocyte and myofilament by increasing myofilament calcium sensitivity and reducing diastolic tension.

G protein-coupled receptor kinase 5 (GRK5) contributes to impaired cardiac function and immune cell recruitment in post-ischemic heart failure

AIMS

Myocardial infarction (MI) is the most common cause of heart failure (HF) worldwide. G protein-coupled receptor kinase 5 (GRK5) is upregulated in failing human myocardium and promotes maladaptive cardiac hypertrophy in animal models. However, the role of GRK5 in ischemic heart disease is still unknown. In this study, we evaluated whether myocardial GRK5 plays a critical role post-MI in mice and included the examination of specific cardiac immune and inflammatory responses.

METHODS AND RESULTS

Cardiomyocyte-specific GRK5 overexpressing transgenic mice (TgGRK5) and non-transgenic littermate control (NLC) mice as well as cardiomyocyte-specific GRK5 knockout mice (GRK5cKO) and wild type (WT) were subjected to MI and, functional as well as structural changes together with outcomes were studied. TgGRK5 post-MI mice showed decreased cardiac function, augmented left ventricular dimension and decreased survival rate compared to NLC post-MI mice. Cardiac hypertrophy and fibrosis as well as fetal gene expression were increased post-MI in TgGRK5 compared to NLC mice. In TgGRK5 mice, GRK5 elevation produced immuno-regulators that contributed to the elevated and long-lasting leukocyte recruitment into the injured heart and ultimately to chronic cardiac inflammation. We found an increased presence of pro-inflammatory neutrophils and macrophages as well as neutrophils, macrophages and T-lymphocytes at 4-days and 8-weeks respectively post-MI in TgGRK5 hearts. Conversely, GRK5cKO mice were protected from ischemic injury and showed reduced early immune cell recruitment (predominantly monocytes) to the heart, improved contractility and reduced mortality compared to WT post-MI mice. Interestingly, cardiomyocyte-specific GRK2 transgenic mice did not share the same phenotype of TgGRK5 mice and did not have increased cardiac leukocyte migration and cytokine or chemokine production post-MI.

CONCLUSIONS

Our study shows that myocyte GRK5 has a crucial and GRK-selective role on the regulation of leucocyte infiltration into the heart, cardiac function and survival in a murine model of post-ischemic HF, supporting GRK5 inhibition as a therapeutic target for HF.

Flow-induced endothelial mitochondrial remodeling mitigates mitochondrial reactive oxygen species production and promotes mitochondrial DNA integrity in a p53-dependent manner

Tumor suppressor p53 plays a pivotal role in orchestrating mitochondrial remodeling by regulating their content, fusion/fission processes, and intracellular signaling molecules that are associated with mitophagy and apoptosis pathways. In order to determine a molecular mechanism underlying flow-mediated mitochondrial remodeling in endothelial cells, we examined, herein, the role of p53 on mitochondrial adaptations to physiological flow and its relevance to vascular function using endothelial cell-specific p53 deficient mice. We observed no changes in aerobic capacity, basal blood pressure, or endothelial mitochondrial phenotypes in the endothelial p53 mull animals. However, after 7 weeks of voluntary wheel running exercise, blood pressure reduction and endothelial mitochondrial remodeling (biogenesis, elongation, and mtDNA replication) were substantially blunted in endothelial p53 null animals compared to the wild-type, subjected to angiotensin II-induced hypertension. In addition, endothelial mtDNA lesions were significantly reduced following voluntary running exercise in wild-type mice, but not in the endothelial p53 null mice. Moreover, in vitro studies demonstrated that unidirectional laminar flow exposure significantly increased key putative regulators for mitochondrial remodeling and reduced mitochondrial reactive oxygen species generation and mtDNA damage in a p53-dependent manner. Mechanistically, unidirectional laminar flow instigated translocalization of p53 into the mitochondrial matrix where it binds to mitochondrial transcription factor A, TFAM, resulting in improving mtDNA integrity. Taken together, our findings suggest that p53 plays an integral role in mitochondrial remodeling under physiological flow condition and the flow-induced p53-TFAM axis may be a novel molecular intersection for enhancing mitochondrial homeostasis in endothelial cells.

Cortical bone stem cell-derived exosomes' therapeutic effect on myocardial ischemia-reperfusion and cardiac remodeling

Heart failure is the one of the leading causes of death in the United States. Heart failure is a complex syndrome caused by numerous diseases, including severe myocardial infarction (MI). MI occurs after an occlusion of a cardiac artery causing downstream ischemia. MI is followed by cardiac remodeling involving extensive remodeling and fibrosis, which, if the original insult is severe or prolonged, can ultimately progress into heart failure. There is no "cure" for heart failure because therapies to regenerate dead tissue are not yet available. Previous studies have shown that in both post-MI and post-ischemia-reperfusion (I/R) models of heart failure, administration of cortical bone stem cell (CBSC) treatment leads to a reduction in scar size and improved cardiac function. Our first study investigated the ability of mouse CBSC-derived exosomes (mCBSC-dEXO) to recapitulate mouse CBSCs (mCBSC) therapeutic effects in a 24-h post-I/R model. This study showed that injection of mCBSCs and mCBSC-dEXOs into the ischemic region of an infarct had a protective effect against I/R injury. mCBSC-dEXOs recapitulated the effects of CBSC treatment post-I/R, indicating exosomes are partly responsible for CBSC's beneficial effects. To examine if exosomes decrease fibrotic activation, adult rat ventricular fibroblasts (ARVFs) and adult human cardiac fibroblasts (NHCFs) were treated with transforming growth factor β (TGFβ) to activate fibrotic signaling before treatment with mCBSC- and human CBSC (hCBSC)-dEXOs. hCBSC-dEXOs caused a 100-fold decrease in human fibroblast activation. To further understand the signaling mechanisms regulating the protective decrease in fibrosis, we performed RNA sequencing on the NHCFs after hCBSC-dEXO treatment. The group treated with both TGFβ and exosomes showed a decrease in small nucleolar RNA (snoRNA), known to be involved with ribosome stability.NEW & NOTEWORTHY Our work is noteworthy due to the identification of factors within stem cell-derived exosomes (dEXOs) that alter fibroblast activation through the hereto-unknown mechanism of decreasing small nucleolar RNA (snoRNA) signaling within cardiac fibroblasts. The study also shows that the injection of stem cells or a stem-cell-derived exosome therapy at the onset of reperfusion elicits cardioprotection, emphasizing the importance of early treatment in the post-ischemia-reperfusion (I/R) wounded heart.

Cortical bone stem cells modify cardiac inflammation after myocardial infarction by inducing a novel macrophage phenotype

Acute damage to the heart, as in the case of myocardial infarction (MI), triggers a robust inflammatory response to the sterile injury that is part of a complex and highly organized wound-healing process. Cortical bone stem cell (CBSC) therapy after MI has been shown to reduce adverse structural and functional remodeling of the heart after MI in both mouse and swine models. The basis for these CBSC treatment effects on wound healing are unknown. The present experiments show that CBSCs secrete paracrine factors known to have immunomodulatory properties, most notably macrophage colony-stimulating factor (M-CSF) and transforming growth factor-β, but not IL-4. CBSC therapy increased the number of galectin-3+ macrophages, CD4+ T cells, and fibroblasts in the heart while decreasing apoptosis in an in vivo swine model of MI. Macrophages treated with CBSC medium in vitro polarized to a proreparative phenotype are characterized by increased CD206 expression, increased efferocytic ability, increased IL-10, TGF-β, and IL-1RA secretion, and increased mitochondrial respiration. Next generation sequencing revealed a transcriptome significantly different from M2a or M2c macrophage phenotypes. Paracrine factors from CBSC-treated macrophages increased proliferation, decreased α-smooth muscle actin expression, and decreased contraction by fibroblasts in vitro. These data support the idea that CBSCs are modulating the immune response to MI to favor cardiac repair through a unique macrophage polarization that ultimately reduces cell death and alters fibroblast populations that may result in smaller scar size and preserved cardiac geometry and function.NEW & NOTEWORTHY Cortical bone stem cell (CBSC) therapy after myocardial infarction alters the inflammatory response to cardiac injury. We found that cortical bone stem cell therapy induces a unique macrophage phenotype in vitro and can modulate macrophage/fibroblast cross talk.

Abstract MP202: The Effects Of Maternal Hypothyroidism On Fetal And Adult Cardiac Function

Objectives: Maternal hypothyroidism (MH), a common clinical condition with a reported prevalence from 2.5% to 13%. MH could have an adverse effect on fetal cardiac development and adult heart function. However, there is a lack of systematic research for its effect on fetal and offspring’s development and cardiac function. This study aimed to determine the impact of MH on fetal and offspring’s organ structural and functional development at different gestation stages and during postnatal and puberty.

Methods: MH model had been built through thyroidectomy (TX) with total thyroxine (TT4) under 1ng/dl after surgery. Pups from mice that underwent TX and Sham surgery were named THD (Deficient) and THN (Normal). Times of parturition and miscarriage from TX and Sham groups were recorded. Ultrasound was performed for fetuses and/or offspring to check the gestation, miscarriage, embryo arrest, development, malformation, and cardiac function. At different postnatal days, mice were euthanized for organ development evaluation.

Result: TX mice had reduced parturition frequencies and smaller litter size but increased miscarriage frequency and malformed fetuses than the sham group. In addition, THD fetuses had smaller biparietal diameter (BPD) and abdominal circumference (AC) and significantly lower left ventricular ejection fraction (LVEF) on E14.5, but not at E18.5. Tei index, a parameter representing both systolic and diastolic cardiac function, was lower in THD fetuses than in THN fetuses at both E14.5 and E18.5. The cardiac systolic and diastolic function of female TX mice after a 9-month breeding period was also abnormal. The Postnatal T4 level was not significantly different between the two groups. On and after d21 after birth, THD mice had a higher heart weight/body weight ratio and lower LVEF still d21.

Conclusion: MH impaired the development and cardiac function of the fetus and young adult. In addition, MH impaired the mother's fertility and depressed cardiac function.

Abstract P411: Sex-based Differences In A Feline Model Of Hfpef

Rationale: Heart Failure with preserved Ejection Fraction (HFpEF) accounts for approximately 50% of all HF diagnoses with no FDA approved therapies. HFpEF is more prevalent in females versus males, but the mechanisms driving the development of HFpEF as a sex-based disorder are not well understood. We have recently shown that slow progressive pressure overload (PO) in male felines induces a HFpEF phenotype but have not investigated the differences in response to the same physiological stress in females.

Hypothesis: Females will develop a phenotype that is distinct from males in response to PO.

Methods and Results: Male (m) and female (f) domestic short felines (age 2mo) underwent either a sham procedure (m: n=7; f: n=7) or aortic constriction (m: n=11; f: n=10) using a customized pre-shaped band. At baseline (prior to surgery), there was no difference in body weight between groups and echocardiography revealed no significant difference in the ratio of left atrium to aortic root (LA/Ao), LA ejection fraction (LA EF), left ventricle (LV) ejection fraction, LV wall-thickness, and E/A ratio. At 4mo post-surgery, both males and females developed cardiac dysfunction. Females gained significantly less weight than males throughout the study. Despite the size difference, both sexes developed comparable LV wall thickness and changes in E/A ratio vs. sham groups. There was no change in LV EF. Furthermore, there was a decrease in LA EF and increased LA/Ao, indicating LA dysfunction and enlargement. Invasive hemodynamics at 4mo post-surgery showed no differences between sexes for the systolic pressure gradient generated by the aortic banding. Banded males had a significantly higher LV end-diastolic pressure vs. banded females, but there was a trend towards prolongation of tau and lower dp/dt min in banded females, reflective of worse active relaxation. Both sexes had comparable dP/dt max . There were no differences between banded males and females in heart weight to body weight or cardiomyocyte cross-sectional area.

Conclusion: Despite similar pressure gradients as a result of PO and the development of similar cardiac hypertrophy between sexes and a higher LVEDP in males, females had a trend towards worse relaxation. Other causes of HFpEF may have sex-based differences.

Molecular Signature of HFpEF: Systems Biology in a Cardiac-Centric Large Animal Model

In this study the authors used systems biology to define progressive changes in metabolism and transcription in a large animal model of heart failure with preserved ejection fraction (HFpEF). Transcriptomic analysis of cardiac tissue, 1-month post-banding, revealed loss of electron transport chain components, and this was supported by changes in metabolism and mitochondrial function, altogether signifying alterations in oxidative metabolism. Established HFpEF, 4 months post-banding, resulted in changes in intermediary metabolism with normalized mitochondrial function. Mitochondrial dysfunction and energetic deficiencies were noted in skeletal muscle at early and late phases of disease, suggesting cardiac-derived signaling contributes to peripheral tissue maladaptation in HFpEF. Collectively, these results provide insights into the cellular biology underlying HFpEF progression.

Cardiomyocyte Proliferation as a Source of New Myocyte Development in the Adult Heart

Cardiac diseases such as myocardial infarction (MI) can lead to adverse remodeling and impaired contractility of the heart due to widespread cardiomyocyte death in the damaged area. Current therapies focus on improving heart contractility and minimizing fibrosis with modest cardiac regeneration, but MI patients can still progress to heart failure (HF). There is a dire need for clinical therapies that can replace the lost myocardium, specifically by the induction of new myocyte formation from pre-existing cardiomyocytes. Many studies have shown terminally differentiated myocytes can re-enter the cell cycle and divide through manipulations of the cardiomyocyte cell cycle, signaling pathways, endogenous genes, and environmental factors. However, these approaches result in minimal myocyte renewal or cardiomegaly due to hyperactivation of cardiomyocyte proliferation. Finding the optimal treatment that will replenish cardiomyocyte numbers without causing tumorigenesis is a major challenge in the field. Another controversy is the inability to clearly define cardiomyocyte division versus myocyte DNA synthesis due to limited methods. In this review, we discuss several studies that induced cardiomyocyte cell cycle re-entry after cardiac injury, highlight whether cardiomyocytes completed cytokinesis, and address both limitations and methodological advances made to identify new myocyte formation.

HDAC Inhibition Reverses Preexisting Diastolic Dysfunction and Blocks Covert Extracellular Matrix Remodeling

BACKGROUND

Diastolic dysfunction (DD) is associated with the development of heart failure and contributes to the pathogenesis of other cardiac maladies, including atrial fibrillation. Inhibition of histone deacetylases (HDACs) has been shown to prevent DD by enhancing myofibril relaxation. We addressed the therapeutic potential of HDAC inhibition in a model of established DD with preserved ejection fraction.

METHODS

Four weeks after uninephrectomy and implantation with deoxycorticosterone acetate pellets, when DD was clearly evident, 1 cohort of mice was administered the clinical-stage HDAC inhibitor ITF2357/Givinostat. Echocardiography, blood pressure measurements, and end point invasive hemodynamic analyses were performed. Myofibril mechanics and intact cardiomyocyte relaxation were assessed ex vivo. Cardiac fibrosis was evaluated by picrosirius red staining and second harmonic generation microscopy of left ventricle (LV) sections, RNA sequencing of LV mRNA, mass spectrometry-based evaluation of decellularized LV biopsies, and atomic force microscopy determination of LV stiffness. Mechanistic studies were performed with primary rat and human cardiac fibroblasts.

RESULTS

HDAC inhibition normalized DD without lowering blood pressure in this model of systemic hypertension. In contrast to previous models, myofibril relaxation was unimpaired in uninephrectomy/deoxycorticosterone acetate mice. Furthermore, cardiac fibrosis was not evident in any mouse cohort on the basis of picrosirius red staining or second harmonic generation microscopy. However, mass spectrometry revealed induction in the expression of >100 extracellular matrix proteins in LVs of uninephrectomy/deoxycorticosterone acetate mice, which correlated with profound tissue stiffening based on atomic force microscopy. ITF2357/Givinostat treatment blocked extracellular matrix expansion and LV stiffening. The HDAC inhibitor was subsequently shown to suppress cardiac fibroblast activation, at least in part, by blunting recruitment of the profibrotic chromatin reader protein BRD4 (bromodomain-containing protein 4) to key gene regulatory elements.

CONCLUSIONS

These findings demonstrate the potential of HDAC inhibition as a therapeutic intervention to reverse existing DD and establish blockade of extracellular matrix remodeling as a second mechanism by which HDAC inhibitors improve ventricular filling. Our data reveal the existence of pathophysiologically relevant covert or hidden cardiac fibrosis that is below the limit of detection of histochemical stains such as picrosirius red, highlighting the need to evaluate fibrosis of the heart using diverse methodologies.

Cardiac Remodeling During Pregnancy With Metabolic Syndrome: Prologue of Pathological Remodeling

BACKGROUND

The heart undergoes physiological hypertrophy during pregnancy in healthy individuals. Metabolic syndrome (MetS) is now prevalent in women of child-bearing age and might add risks of adverse cardiovascular events during pregnancy. The present study asks if cardiac remodeling during pregnancy in obese individuals with MetS is abnormal and whether this predisposes them to a higher risk for cardiovascular disorders.

METHODS

The idea that MetS induces pathological cardiac remodeling during pregnancy was studied in a long-term (15 weeks) Western diet-feeding animal model that recapitulated features of human MetS. Pregnant female mice with Western diet (45% kcal fat)-induced MetS were compared with pregnant and nonpregnant females fed a control diet (10% kcal fat).

RESULTS

Pregnant mice fed a Western diet had increased heart mass and exhibited key features of pathological hypertrophy, including fibrosis and upregulation of fetal genes associated with pathological hypertrophy. Hearts from pregnant animals with WD-induced MetS had a distinct gene expression profile that could underlie their pathological remodeling. Concurrently, pregnant female mice with MetS showed more severe cardiac hypertrophy and exacerbated cardiac dysfunction when challenged with angiotensin II/phenylephrine infusion after delivery.

CONCLUSIONS

These results suggest that preexisting MetS could disrupt physiological hypertrophy during pregnancy to produce pathological cardiac remodeling that could predispose the heart to chronic disorders.

Postsurgery echocardiography can predict the amount of ischemia-reperfusion injury and the resultant scar size

Despite advances in the diagnosis and treatment of ischemic heart disease (IHD), it remains the leading cause of death globally. Thus, there is a need to investigate the underlying pathophysiology and develop new therapies for the prevention and treatment of IHD. Murine models are widely used in IHD research because they are readily available, relatively inexpensive, and can be genetically modified to explore mechanistic questions. Ischemia-reperfusion (I/R)-induced myocardial infarction in mice is produced by the blockage followed by reperfusion of the left anterior descending branch (LAD) to imitate human IHD disease and its treatment. This I/R model can be widely used to investigate the potential reparative effect of putative treatments in the setting of reperfusion. However, the surgical technique is demanding and can produce an inconsistent amount of damage, which can make identification of treatment effects challenging. Therefore, determining which hearts have been significantly damaged by I/R is an important consideration in studies designed to either explore the mechanisms of disrupted function or test possible therapies. Noninvasive echocardiography (ECHO) is often used to determine structural and functional changes in the mouse heart following injury. In the present study, we determined that ECHO performed 3 days post I/R surgery could predict the permanent injury produced by the ischemic insult.NEW & NOTEWORTHY We believe our work is noteworthy due to its creation of standards for early evaluation of the level of myocardial injury in mouse models of ischemia-reperfusion. This improvement to study design could reduce the sample sizes used in evaluating therapeutics and lead to increased confidence in conclusions drawn regarding the therapeutic efficacy of treatments tested in these translational mouse models.

Interaction of the Joining Region in Junctophilin-2 With the L-Type Ca2+ Channel Is Pivotal for Cardiac Dyad Assembly and Intracellular Ca2+ Dynamics

RATIONALE

Ca2+-induced Ca2+ release (CICR) in normal hearts requires close approximation of L-type calcium channels (LTCCs) within the transverse tubules (T-tubules) and RyR (ryanodine receptors) within the junctional sarcoplasmic reticulum. CICR is disrupted in cardiac hypertrophy and heart failure, which is associated with loss of T-tubules and disruption of cardiac dyads. In these conditions, LTCCs are redistributed from the T-tubules to disrupt CICR. The molecular mechanism responsible for LTCCs recruitment to and from the T-tubules is not well known. JPH (junctophilin) 2 enables close association between T-tubules and the junctional sarcoplasmic reticulum to ensure efficient CICR. JPH2 has a so-called joining region that is located near domains that interact with T-tubular plasma membrane, where LTCCs are housed. The idea that this joining region directly interacts with LTCCs and contributes to LTCC recruitment to T-tubules is unknown.

OBJECTIVE

To determine if the joining region in JPH2 recruits LTCCs to T-tubules through direct molecular interaction in cardiomyocytes to enable efficient CICR.

METHODS AND RESULTS

Modified abundance of JPH2 and redistribution of LTCC were studied in left ventricular hypertrophy in vivo and in cultured adult feline and rat ventricular myocytes. Protein-protein interaction studies showed that the joining region in JPH2 interacts with LTCC-α1C subunit and causes LTCCs distribution to the dyads, where they colocalize with RyRs. A JPH2 with induced mutations in the joining region (mutPG1JPH2) caused T-tubule remodeling and dyad loss, showing that an interaction between LTCC and JPH2 is crucial for T-tubule stabilization. mutPG1JPH2 caused asynchronous Ca2+-release with impaired excitation-contraction coupling after β-adrenergic stimulation. The disturbed Ca2+ regulation in mutPG1JPH2 overexpressing myocytes caused calcium/calmodulin-dependent kinase II activation and altered myocyte bioenergetics.

CONCLUSIONS

The interaction between LTCC and the joining region in JPH2 facilitates dyad assembly and maintains normal CICR in cardiomyocytes.

Identification and Comparison of Hyperglycemia-Induced Extracellular Vesicle Transcriptome in Different Mouse Stem Cells

Extracellular vesicles (EVs) derived from stem /progenitor cells harbor immense potential to promote cardiomyocyte survival and neovascularization, and to mitigate ischemic injury. However, EVs’ parental stem/progenitor cells showed modest benefits in clinical trials, suggesting autologous stem cell/EV quality might have been altered by stimuli associated with the co-morbidities such as hyperglycemia associated with diabetes. Hyperglycemia is a characteristic of diabetes and a major driving factor in cardiovascular disease. The functional role of stem/progenitor cell-derived EVs and the molecular signature of their secreted EV cargo under hyperglycemic conditions remain elusive. Therefore, we hypothesized that hyperglycemic stress causes transcriptome changes in stem/progenitor cell-derived EVs that may compromise their reparative function. In this study, we performed an unbiased analysis of EV transcriptome signatures from 3 different stem/progenitor cell types by RNA sequencing. The analysis revealed differential expression of a variety of RNA species in EVs. Specifically, we identified 241 common-dysregulated mRNAs, 21 ncRNAs, and 16 miRNAs in three stem cell-derived EVs. Gene Ontology revealed that potential function of common mRNAs mostly involved in metabolism and transcriptional regulation. This study provides potential candidates for preventing the adverse effects of hyperglycemia-induced stem/progenitor cell-derived EV dysfunction, and reference data for future biological studies and application of stem/progenitor cell-derived EVs.

Uncoupling protein 2-mediated metabolic adaptations define cardiac cell function in the heart during transition from young to old age

Cellular replacement in the heart is restricted to postnatal stages with the adult heart largely postmitotic. Studies show that loss of regenerative properties in cardiac cells seems to coincide with alterations in metabolism during postnatal development and maturation. Nevertheless, whether changes in cellular metabolism are linked to functional alternations in cardiac cells is not well studied. We report here a novel role for uncoupling protein 2 (UCP2) in regulation of functional properties in cardiac tissue derived stem‐like cells (CTSCs). CTSC were isolated from C57BL/6 mice aged 2 days (nCTSC), 2 month (CTSC), and 2 years old (aCTSC), subjected to bulk‐RNA sequencing that identifies unique transcriptome significantly different between CTSC populations from young and old heart. Moreover, results show that UCP2 is highly expressed in CTSCs from the neonatal heart and is linked to maintenance of glycolysis, proliferation, and survival. With age, UCP2 is reduced shifting energy metabolism to oxidative phosphorylation inversely affecting cellular proliferation and survival in aged CTSCs. Loss of UCP2 in neonatal CTSCs reduces extracellular acidification rate and glycolysis together with reduced cellular proliferation and survival. Mechanistically, UCP2 silencing is linked to significant alteration of mitochondrial genes together with cell cycle and survival signaling pathways as identified by RNA‐sequencing and STRING bioinformatic analysis. Hence, our study shows UCP2‐mediated metabolic profile regulates functional properties of cardiac cells during transition from neonatal to aging cardiac states.

Abstract 342: Cortical Bone Stem Cell Therapy Alters Macrophage Phenotype and Reduces Cardiac Cell Death After Myocardial Infarction

Acute injuries to the heart, like myocardial infarction (MI), contribute to the development and pathology of heart failure (HF). Reperfusion of the ischemic heart greatly increases survival but results in reperfusion injury that can account for up to 50% of the final infarct size. The inflammatory response to MI-induced myocardial injury is thought to be responsible for the propagation of reperfusion injury into the infarct border zone, expanding myocardial damage. We have previously shown in a swine model of MI that intramyocardial injections of cortical bone-derived stem cells (CBSCs) into the infarct border zone has no acute cardioprotective effect but reduces scar size by half and prevents the decline of ejection fraction and LV dilation 3 months after MI. Our new preliminary data show that CBSCs have potent immunoregulatory capabilities. Therefore, we hypothesize that CBSC treatment has an effect on the immune response to MI that improves the wound healing response to myocardial injury and mitigates LV remodeling and infarct size 3 months later. To test this hypothesis, we characterized the effects of CBSC paracrine factors on macrophages in vitro and found that CBSC-treated macrophages express higher levels of CD206, produce more IL-1RA and IL-10, and phagocytose apoptotic myocytes more efficiently. In addition, macrophages were increased in CBSC-treated swine hearts 7 days after MI compared to controls with a corresponding increase in IL-1RA and TIMP-2. Apoptosis was decreased overall and in macrophages specifically in CBSC-treated animals. From these data we conclude CBSCs may exert an acute pro-reparative effect on the immune response after MI, reducing reperfusion injury and adverse remodeling resulting in improved functional outcomes at later time points.

A low voltage activated Ca2+ current found in a subset of human ventricular myocytes

Low voltage activated (I_Ca-LVA) calcium currents including Cav1.3 and T-type calcium current (I_Ca-T) have not been reported in adult human left ventricular myocytes (HLVMs). We tried to examine their existence and possible correlation with etiology and patient characteristics in a big number of human LVMs isolated from explanted terminally failing (F) hearts, failing hearts with left ventricular assist device (F-LVAD) and nonfailing (NF) human hearts. LVA (I_Ca-LVA) was determined by subtracting L-type Ca²⁺ current (I_Ca-L) recorded with the holding potential of −50 mV from total Ca²⁺ current recorded with the holding potential of −90 mV or −70 mV. I_{Ca- LVA} was further tested with its sensitivity to 100 µM CdCl₂ and tetrodotoxin. Three HLVMs (3 of 137 FHLVMs) from 2 (N = 30 hearts) failing human hearts, of which one was idiopathic and the other was due to primary pulmonary hypertension, were found with I_Ca-LVA. I_Ca-LVA in one FHLVM was not sensitive to 100 µM CdCl₂ while I_Ca-LVA in another two FHLVMs was not sensitive to tetrodotoxin. It peaked at the voltage of −40~-20 mV and had a time-dependent decay faster than I_Ca-L but slower than sodium current (I_Na). I_Ca-LVA was not found in any HLVMs from NF (75 HLVMs from 17 hearts) or F-LVAD hearts (82 HLVMs from 18 hearts) but a statistically significant correlation could not be established. In conclusion, I_Ca-LVA was detected in some HLVMs of a small portion of human hearts that happened to be nonischemic failing hearts.

Loss of Protease-Activated Receptor 4 Prevents Inflammation Resolution and Predisposes the Heart to Cardiac Rupture After Myocardial Infarction

BACKGROUND

Cardiac rupture is a major lethal complication of acute myocardial infarction (MI). Despite significant advances in reperfusion strategies, mortality from cardiac rupture remains high. Studies suggest that cardiac rupture can be accelerated by thrombolytic therapy, but the relevance of this risk factor remains controversial.

METHODS

We analyzed protease-activated receptor 4 (Par4) expression in mouse hearts with MI and investigated the effects of Par4 deletion on cardiac remodeling and function after MI by echocardiography, quantitative immunohistochemistry, and flow cytometry.

RESULTS

Par4 mRNA and protein levels were increased in mouse hearts after MI and in isolated cardiomyocytes in response to hypertrophic and inflammatory stimuli. Par4-deficient mice showed less myocyte apoptosis, reduced infarct size, and improved functional recovery after acute MI relative to wild-type (WT). Conversely, Par4^-/- mice showed impaired cardiac function, greater rates of myocardial rupture, and increased mortality after chronic MI relative to WT. Pathological evaluation of hearts from Par4^-/- mice demonstrated a greater infarct expansion, increased cardiac hemorrhage, and delayed neutrophil accumulation, which resulted in impaired post-MI healing compared with WT. Par4 deficiency also attenuated neutrophil apoptosis in vitro and after MI in vivo and impaired inflammation resolution in infarcted myocardium. Transfer of Par4^-/- neutrophils, but not of Par4^-/- platelets, in WT recipient mice delayed inflammation resolution, increased cardiac hemorrhage, and enhanced cardiac dysfunction. In parallel, adoptive transfer of WT neutrophils into Par4^-/- mice restored inflammation resolution, reduced cardiac rupture incidence, and improved cardiac function after MI.

CONCLUSIONS

These findings reveal essential roles of Par4 in neutrophil apoptosis and inflammation resolution during myocardial healing and point to Par4 inhibition as a potential therapy that should be limited to the acute phases of ischemic insult and avoided for long-term treatment after MI.

Abcg2-expressing side population cells contribute to cardiomyocyte renewal through fusion

The adult mammalian heart has a limited regenerative capacity. Therefore, identification of endogenous cells and mechanisms that contribute to cardiac regeneration is essential for the development of targeted therapies. The side population (SP) phenotype has been used to enrich for stem cells throughout the body; however, SP cells isolated from the heart have been studied exclusively in cell culture or after transplantation, limiting our understanding of their function in vivo. We generated a new Abcg2-driven lineage-tracing mouse model with efficient labeling of SP cells. Labeled SP cells give rise to terminally differentiated cells in bone marrow and intestines. In the heart, labeled SP cells give rise to lineage-traced cardiomyocytes under homeostatic conditions with an increase in this contribution following cardiac injury. Instead of differentiating into cardiomyocytes like proposed cardiac progenitor cells, cardiac SP cells fuse with preexisting cardiomyocytes to stimulate cardiomyocyte cell cycle reentry. Our study is the first to show that fusion between cardiomyocytes and non-cardiomyocytes, identified by the SP phenotype, contribute to endogenous cardiac regeneration by triggering cardiomyocyte cell cycle reentry in the adult mammalian heart.

Cardiac Expression of Factor X Mediates Cardiac Hypertrophy and Fibrosis in Pressure Overload

•

Factor X expression was increased in the heart following pressure overload and in isolated cardiac myocytes and fibroblasts.

•

Rivaroxaban treatment at doses that do not affect thrombin generation, blood coagulation or cardiac hemostasis attenuated cardiac inflammation, hypertrophy, and fibrosis caused by pressure overload and improved cardiac diastolic function.

•

Activated coagulation factor X induced PAR-1/-2–mediated elongated cardiomyocyte hypertrophy and PAR1-mediated cardiac fibroblast proliferation, migration and differentiation.

•

Activated coagulation factor X derived from a cardiac source may represent an important physiologic and pathophysiologic activator of PAR-1/PAR-2.

•

Non-anticoagulation dosage of rivaroxaban could provide an effective therapy to attenuate early phases of heart failure development.

Activated factor X is a key component of the coagulation cascade, but whether it directly regulates pathological cardiac remodeling is unclear. In mice subjected to pressure overload stress, cardiac factor X mRNA expression and activity increased concurrently with cardiac hypertrophy, fibrosis, inflammation and diastolic dysfunction, and responses blocked with a low coagulation-independent dose of rivaroxaban. In vitro, neurohormone stressors increased activated factor X expression in both cardiac myocytes and fibroblasts, resulting in activated factor X-mediated activation of protease-activated receptors and pro-hypertrophic and -fibrotic responses, respectively. Thus, inhibition of cardiac-expressed activated factor X could provide an effective therapy for the prevention of adverse cardiac remodeling in hypertensive patients.

Differential microRNA-21 and microRNA-221 Upregulation in the Biventricular Failing Heart Reveals Distinct Stress Responses of Right Versus Left Ventricular Fibroblasts

BACKGROUND

The failing right ventricle (RV) does not respond like the left ventricle (LV) to guideline-directed medical therapy of heart failure, perhaps due to interventricular differences in their molecular pathophysiology.

METHODS

Using the canine tachypacing-induced biventricular heart failure (HF) model, we tested the hypothesis that interventricular differences in microRNAs (miRs) expression distinguish failing RV from failing LV.

RESULTS

Severe RV dysfunction was indicated by elevated end-diastolic pressure (11.3±2.5 versus 5.7±2.0 mm Hg; P<0.0001) and diminished fractional area change (24.9±7.1 versus 48.0±3.6%; P<0.0001) relative to prepacing baselines. Microarray analysis of ventricular tissue revealed that miR-21 and miR-221, 2 activators of profibrotic and proliferative processes, increased the most, at 4- and 2-fold, respectively, in RV-HF versus RV-Control. Neither miR-21 or miR-221 was statistically significantly different in LV-HF versus LV-Control. These changes were accompanied by more extensive fibrosis in RV-HF than LV-HF. To test whether miR-21 and miR-221 upregulation is specific to RV cellular response to mechanical and hormonal stimuli associated with HF, we subjected fibroblasts and cardiomyocytes isolated from normal canine RV and LV to cyclic overstretch and aldosterone. These 2 stressors markedly upregulated miR-21 and miR-221 in RV fibroblasts but not in LV fibroblasts nor cardiomyocytes of either ventricle. Furthermore, miR-21/221 knockdown significantly attenuated RV but not LV fibroblast proliferation.

CONCLUSIONS

We identified a novel, biological difference between RV and LV fibroblasts that might underlie distinctions in pathological remodeling of the RV in biventricular HF.

HDAC inhibition improves cardiopulmonary function in a feline model of diastolic dysfunction

Heart failure with preserved ejection fraction (HFpEF) is a major health problem without effective therapies. This study assessed the effects of histone deacetylase (HDAC) inhibition on cardiopulmonary structure, function, and metabolism in a large mammalian model of pressure overload recapitulating features of diastolic dysfunction common to human HFpEF. Male domestic short-hair felines (n = 31, aged 2 months) underwent a sham procedure (n = 10) or loose aortic banding (n = 21), resulting in slow-progressive pressure overload. Two months after banding, animals were treated daily with suberoylanilide hydroxamic acid (b + SAHA, 10 mg/kg, n = 8), a Food and Drug Administration-approved pan-HDAC inhibitor, or vehicle (b + veh, n = 8) for 2 months. Echocardiography at 4 months after banding revealed that b + SAHA animals had significantly reduced left ventricular hypertrophy (LVH) (P < 0.0001) and left atrium size (P < 0.0001) versus b + veh animals. Left ventricular (LV) end-diastolic pressure and mean pulmonary arterial pressure were significantly reduced in b + SAHA (P < 0.01) versus b + veh. SAHA increased myofibril relaxation ex vivo, which correlated with in vivo improvements of LV relaxation. Furthermore, SAHA treatment preserved lung structure, compliance, blood oxygenation, and reduced perivascular fluid cuffs around extra-alveolar vessels, suggesting attenuated alveolar capillary stress failure. Acetylation proteomics revealed that SAHA altered lysine acetylation of mitochondrial metabolic enzymes. These results suggest that acetylation defects in hypertrophic stress can be reversed by HDAC inhibitors, with implications for improving cardiac structure and function in patients.

Echocardiographic Strain Analysis for the Early Detection of Left Ventricular Systolic/Diastolic Dysfunction and Dyssynchrony in a Mouse Model of Physiological Aging

Heart disease is the leading cause of hospitalization and death worldwide, severely affecting health care costs. Aging is a significant risk factor for heart disease, and the senescent heart is characterized by structural and functional changes including diastolic and systolic dysfunction as well as left ventricular (LV) dyssynchrony. Speckle tracking-based strain echocardiography (STE) has been shown as a noninvasive, reproducible, and highly sensitive methodology to evaluate LV function in both animal models and humans. Herein, we describe the efficiency of this technique as a comprehensive and sensitive method for the detection of age-related cardiac dysfunction in mice. Compared with conventional echocardiographic measurements, radial and longitudinal strain, and reverse longitudinal strain were able to detect subtle changes in systolic and diastolic cardiac function in mice at an earlier time point during aging. Additionally, the data show a gradual and consistent decrease with age in regional contractility throughout the entire LV, in both radial and longitudinal axes. Furthermore, we observed that LV segmental dyssynchrony in longitudinal axis reliably differentiated between aged and young mice. Therefore, we propose the use of echocardiographic strain as a highly sensitive and accurate technology enabling and evaluating the effect of new treatments to fight age-induced cardiac disease.

Outcomes Associated With a Strategy of Adjuvant Metolazone or High-Dose Loop Diuretics in Acute Decompensated Heart Failure: A Propensity Analysis

Background

In acute decompensated heart failure, guidelines recommend increasing loop diuretic dose or adding a thiazide diuretic when diuresis is inadequate. We set out to determine the adverse events associated with a diuretic strategy relying on metolazone or high‐dose loop diuretics.

Methods and Results

Patients admitted to 3 hospitals using a common electronic medical record with a heart failure discharge diagnosis who received intravenous loop diuretics were studied in a propensity‐adjusted analysis of all‐cause mortality. Secondary outcomes included hyponatremia (sodium <135 mEq/L), hypokalemia (potassium <3.5 mEq/L) and worsening renal function (a ≥20% decrease in estimated glomerular filtration rate). Of 13 898 admissions, 1048 (7.5%) used adjuvant metolazone. Metolazone was strongly associated with hyponatremia, hypokalemia, and worsening renal function (P<0.0001 for all) with minimal effect attenuation following covariate and propensity adjustment. Metolazone remained associated with increased mortality after multivariate and propensity adjustment (hazard ratio=1.20, 95% confidence interval 1.04–1.39, P=0.01). High‐dose loop diuretics were associated with hypokalemia and hyponatremia (P<0.002) but only worsening renal function retained significance (P<0.001) after propensity adjustment. High‐dose loop diuretics were not associated with reduced survival after multivariate and propensity adjustment (hazard ratio=0.97 per 100 mg of IV furosemide, 95% confidence interval 0.90–1.06, P=0.52).

Conclusions

During acute decompensated heart failure, metolazone was independently associated with hypokalemia, hyponatremia, worsening renal function and increased mortality after controlling for the propensity to receive metolazone and baseline characteristics. However, under the same experimental conditions, high‐dose loop diuretics were not associated with hypokalemia, hyponatremia, or reduced survival. The current findings suggest that until randomized control trial data prove otherwise, uptitration of loop diuretics may be a preferred strategy over routine early addition of thiazide type diuretics when diuresis is inadequate.

GDF11 Decreases Pressure Overload-Induced Hypertrophy, but Can Cause Severe Cachexia and Premature Death

RATIONALE

Possible beneficial effects of GDF11 (growth differentiation factor 11) on the normal, diseased, and aging heart have been reported, including reversing aging-induced hypertrophy. These effects have not been well validated. High levels of GDF11 have also been shown to cause cardiac and skeletal muscle wasting. These controversies could be resolved if dose-dependent effects of GDF11 were defined in normal and aged animals as well as in pressure overload-induced pathological hypertrophy.

OBJECTIVE

To determine dose-dependent effects of GDF11 on normal hearts and those with pressure overload-induced cardiac hypertrophy.

METHODS AND RESULTS

Twelve- to 13-week-old C57BL/6 mice underwent transverse aortic constriction (TAC) surgery. One-week post-TAC, these mice received rGDF11 (recombinant GDF11) at 1 of 3 doses: 0.5, 1.0, or 5.0 mg/kg for up to 14 days. Treatment with GDF11 increased plasma concentrations of GDF11 and p-SMAD2 in the heart. There were no significant differences in the peak pressure gradients across the aortic constriction between treatment groups at 1 week post-TAC. Two weeks of GDF11 treatment caused dose-dependent decreases in cardiac hypertrophy as measured by heart weight/tibia length ratio, myocyte cross-sectional area, and left ventricular mass. GDF11 improved cardiac pump function while preventing TAC-induced ventricular dilation and caused a dose-dependent decrease in interstitial fibrosis (in vivo), despite increasing markers of fibroblast activation and myofibroblast transdifferentiation (in vitro). Treatment with the highest dose (5.0 mg/kg) of GDF11 caused severe body weight loss, with significant decreases in both muscle and organ weights and death in both sham and TAC mice.

CONCLUSIONS

Although GDF11 treatment can reduce pathological cardiac hypertrophy and associated fibrosis while improving cardiac pump function in pressure overload, high doses of GDF11 cause severe cachexia and death. Use of GDF11 as a therapy could have potentially devastating actions on the heart and other tissues.

Circular RNA CircFndc3b modulates cardiac repair after myocardial infarction via FUS/VEGF-A axis

Circular RNAs are generated from many protein-coding genes, but their role in cardiovascular health and disease states remains unknown. Here we report identification of circRNA transcripts that are differentially expressed in post myocardial infarction (MI) mouse hearts including circFndc3b which is significantly down-regulated in the post-MI hearts. Notably, the human circFndc3b ortholog is also significantly down-regulated in cardiac tissues of ischemic cardiomyopathy patients. Overexpression of circFndc3b in cardiac endothelial cells increases vascular endothelial growth factor-A expression and enhances their angiogenic activity and reduces cardiomyocytes and endothelial cell apoptosis. Adeno-associated virus 9 -mediated cardiac overexpression of circFndc3b in post-MI hearts reduces cardiomyocyte apoptosis, enhances neovascularization and improves left ventricular functions. Mechanistically, circFndc3b interacts with the RNA binding protein Fused in Sarcoma to regulate VEGF expression and signaling. These findings highlight a physiological role for circRNAs in cardiac repair and indicate that modulation of circFndc3b expression may represent a potential strategy to promote cardiac function and remodeling after MI.

Circular RNAs (circRNAs) are non-coding RNAs generated from pre-mRNAs of coding genes by the splicing machinery whose function in the heart is poorly understood. Here the authors show that AAV-mediated delivery of the circRNA circFndc3b prevents cardiomyocyte apoptosis, enhances angiogenesis, and attenuates LV dysfunction post-MI in mice by regulating FUS-VEGF-A signalling.

Cortical bone-derived stem cell therapy reduces apoptosis after myocardial infarction

Ischemic heart diseases such as myocardial infarction (MI) are the largest contributors to cardiovascular disease worldwide. The resulting cardiac cell death impairs function of the heart and can lead to heart failure and death. Reperfusion of the ischemic tissue is necessary but causes damage to the surrounding tissue by reperfusion injury. Cortical bone stem cells (CBSCs) have been shown to increase pump function and decrease scar size in a large animal swine model of MI. To investigate the potential mechanism for these changes, we hypothesized that CBSCs were altering cardiac cell death after reperfusion. To test this, we performed TUNEL staining for apoptosis and antibody-based immunohistochemistry on tissue from Göttingen miniswine that underwent 90 min of lateral anterior descending coronary artery ischemia followed by 3 or 7 days of reperfusion to assess changes in cardiomyocyte and noncardiomyocyte cell death. Our findings indicate that although myocyte apoptosis is present 3 days after ischemia and is lower in CBSC-treated animals, myocyte apoptosis accounts for <2% of all apoptosis in the reperfused heart. In addition, nonmyocyte apoptosis trends toward decreased in CBSC-treated hearts, and although CBSCs increase macrophage and T-cell populations in the infarct region, the occurrence of apoptosis in CD45⁺ cells in the myocardium is not different between groups. From these data, we conclude that CBSCs may be influencing cardiomyocyte and noncardiomyocyte cell death and immune cell recruitment dynamics in the heart after MI, and these changes may account for some of the beneficial effects conferred by CBSC treatment.NEW & NOTEWORTHY The following research explores aspects of cell death and inflammation that have not been previously studied in a large animal model. In addition, apoptosis and cell death have not been studied in the context of cell therapy and myocardial infarction. In this article, we describe interactions between cell therapy and inflammation and the potential implications for cardiac wound healing.

Abstract 360: PKA is Needed for Acute Adaptation for Cardiac Stress

In adult mammalian hearts, the ventricles are composed of mostly binucleated myocytes (BVMs) and some mononucleated myocytes (MVMs), which have different properties. However, if the gene expression profile and pathological responses of these two populations of myocytes are different have not reported. We found that these two populations of myocytes differentially expressed 250 genes. While many RNA synthesis and processing genes, and some antiapoptotic genes were highly expressed in MVMs, BVMs had genes related to self-destruction (autophagy and ubiquitination system genes) enriched. In general, expression of genes involved in carbonhydrate metabolism and cell proliferation was also more but the expression of genes involved in fatty acid metabolism was less in MVMs. The expression of some of these genes was confirmed in single-molecule pulldown (SiMPull) method in separated MVMs and BVMs. MVMs grew more in pressure overloaded hearts. MVMs were more resistant to apoptosis induced by β-adrenergic stimulation both in vitro and in vivo , which was due to cytosolic and mitochondrial Ca 2+ and ROS could be more easily increased in BVMs leading to more damage to mitochondria. Ca 2+ current, myocyte contraction and Ca 2+ transients in MVMs had less responses to β-adrenergic stimulation (isoproterenol, 1uM). Furthermore, MVMs gene expression upon β-adrenergic stimulation showed more adaptive responses while BVMs showed more proapoptotic gene (e.g., p53 and AIF), protein post-translational modification and muscle differentiation gene expression. This study suggests that MVMs and BVMs are distinct subpopulations of VMs with different gene expression profile and pathological responses. It underscores the importance of differential pathological responses of cells having different nuclear numbers .

Abstract 826: Histone Deacetylase Inhibition Improves Heart Failure With Preserved Ejection Fraction Cardiopulmonary Phenotype and Induces Metabolomic Switch

Rationale: Approximately 50% of heart failure patients are diagnosed with Heart Failure with preserved Ejection Fraction (HFpEF), but there are currently no effective treatments.

Hypothesis: Treatment of a feline HFpEF animal model with a pan HDAC inhibitor, SAHA, will improve the cardiopulmonary phenotype and mediate changes in the metabolome and skeletal muscle composition.

Methods and results: Male domestic short hair cats (n=21, age 2mo) underwent either a sham procedure (n=5) or aortic constriction (n=16) using a customized pre-shaped band causing slow progressive pressure overload during maturation. At 2-months post-banding, banded animals received either daily treatment with 10mg/kg SAHA (b+SAHA) (n=8) or vehicle (b+veh) (n=8) for 2 months. At 4 months post-banding, b+ SAHA animals had significantly reduced LV wall thickness, LA size (LA/Ao), and improved LA function (LA EF) vs. b+ veh animals (fig). Invasive hemodynamics and lung mechanics were performed after 2 months of treatment. Banded animals had significantly increased filling pressures (LVEDP), increased pulmonary arterial pressures (mPAP), decreased lung compliance and arterial oxygenation (A-aDO 2 ). SAHA significantly reduced LVEDP, mPAP, and A-aDO 2 and increased lung compliance (fig). b+SAHA animals had an increase in the percentage of type 1 muscle fibers (increased oxidative capacity) compared to type 2 (fig). Blood-based metabolomics revealed SAHA-induced a metabolic shift towards increased lipolysis and mitochondrial oxidation.

Conclusion: Treatment with SAHA improved cardiopulmonary structure and function in banded animals and caused changes in the metabolome and skeletal muscle.

Abstract 760: Metabolic Syndrome Impairs Cardiac Remodeling During Pregnancy in Mice

Rationale: Due to the change of life style in the past decades, the incidence of metabolic syndrome (MetS) and obesity in women of childbearing age has been increased. Evidences have shown that complications during pregnancy, such as obesity and gestational diabetes, strongly link to future heart diseases. During normal pregnancy, the heart undergoes a physiological remodeling with mild ventricular dilation and hypertrophy. However, the effects of MetS on cardiac phenotype during pregnancy are not well understood. Moreover, animal models for MetS so far are not well established, which are usually species limited, gender limited and lack of translational significance. Thus, it’s important to develop an animal model which resembles the etiology of MetS in human beings.

Objective: Establish a model of MetS in female C57BL/6J mice and determine the effects of MetS on cardiac remodeling during pregnancy.

Methods and Results: To establish a mouse model of MetS, high fat (49% kcal)/high carbohydrates (HF-HC) diet were given to C57BL/6J female mice at the age of 8-week. Mice fed with normal diet (10% kcal fat) served as control. After 14 weeks feeding, mice fed with HF-HC diet showed significantly higher body weight and gonadal fat weight compared with control mice. Moreover, mice fed with HF-HC diet showed impaired glucose tolerance and higher serum total cholesterol level. The symptoms of obesity, impaired glucose tolerance and dyslipidemia suggest the development of MetS. Female mice after 14-week special diet feeding were subjected to breeding. Cardiac function was evaluated by echocardiography during pregnancy and 1-day post-partum, then the mice were terminated 1-day post-partum. Female mice that developed MetS showed impaired cardiac function and pathological remodeling during pregnancy. Moreover, mice fed with HF-HC diet showed more myocardium interstitial fibrosis accompanied with upregulation of fibrosis related genes in the heart compared with Ctrl diet.

Conclusion: We’ve developed a mouse model of MetS in C57BL/6J mice strain with 14 weeks feeding of HF-HC diet, which resemble the western diet that affects human beings nowadays. Females that have MetS showed impaired cardiac function and pathological remodeling during pregnancy.

Long-Term Caloric Restriction Improves Cardiac Function, Remodeling, Adrenergic Responsiveness, and Sympathetic Innervation in a Model of Postischemic Heart Failure

BACKGROUND

Caloric restriction (CR) has been described to have cardioprotective effects and improve functional outcomes in animal models and humans. Chronic ischemic heart failure (HF) is associated with reduced cardiac sympathetic innervation, dysfunctional β-adrenergic receptor signaling, and decreased cardiac inotropic reserve. We tested the effects of a long-term CR diet, started late after myocardial infarction on cardiac function, sympathetic innervation, and β-adrenergic receptor responsiveness in a rat model of postischemic HF.

METHODS AND RESULTS

Adult male rats were randomly assigned to myocardial infarction or sham operation and 4 weeks later were further randomized to a 1-year CR or normal diet. One year of CR resulted in a significant reduction in body weight, heart weight, and heart weight/tibia length ratio when compared with normal diet in HF groups. At the end of the study period, echocardiography and histology revealed that HF animals under the CR diet had ameliorated left ventricular remodeling compared with HF rats fed with normal diet. Invasive hemodynamic showed a significant improvement of cardiac inotropic reserve in CR HF rats compared with HF-normal diet animals. Importantly, CR dietary regimen was associated with a significant increase of cardiac sympathetic innervation and with normalized cardiac β-adrenergic receptor levels in HF rats when compared with HF rats on the standard diet.

CONCLUSIONS

We demonstrate, for the first time, that chronic CR, when started after HF established, can ameliorate cardiac dysfunction and improve inotropic reserve. At the molecular level, we find that chronic CR diet significantly improves sympathetic cardiac innervation and β-adrenergic receptor levels in failing myocardium.

Transient Introduction of miR-294 in the Heart Promotes Cardiomyocyte Cell Cycle Reentry After Injury

RATIONALE

Embryonic heart is characterized of rapidly dividing cardiomyocytes required to build a working myocardium. Cardiomyocytes retain some proliferative capacity in the neonates but lose it in adulthood. Consequently, a number of signaling hubs including microRNAs are altered during cardiac development that adversely impacts regenerative potential of cardiac tissue. Embryonic stem cell cycle miRs are a class of microRNAs exclusively expressed during developmental stages; however, their effect on cardiomyocyte proliferation and heart function in adult myocardium has not been studied previously.

OBJECTIVE

To determine whether transient reintroduction of embryonic stem cell cycle miR-294 promotes cardiomyocyte cell cycle reentry enhancing cardiac repair after myocardial injury.

METHODS AND RESULTS

miR-294 is expressed in the heart during development, prenatal stages, lost in the neonate, and adult heart confirmed by qRT-PCR and in situ hybridization. Neonatal ventricular myocytes treated with miR-294 showed elevated expression of Ki67, p-histone H3, and Aurora B confirmed by immunocytochemistry compared with control cells. miR-294 enhanced oxidative phosphorylation and glycolysis in Neonatal ventricular myocytes measured by seahorse assay. Mechanistically, miR-294 represses Wee1 leading to increased activity of the cyclin B1/CDK1 complex confirmed by qRT-PCR and immunoblot analysis. Next, a doxycycline-inducible AAV9-miR-294 vector was delivered to mice for activating miR-294 in myocytes for 14 days continuously after myocardial infarction. miR-294-treated mice significantly improved left ventricular functions together with decreased infarct size and apoptosis 8 weeks after MI. Myocyte cell cycle reentry increased in miR-294 hearts analyzed by Ki67, pH3, and AurB (Aurora B kinase) expression parallel to increased small myocyte number in the heart. Isolated adult myocytes from miR-294 hearts showed increased 5-ethynyl-2'-deoxyuridine+ cells and upregulation of cell cycle markers and miR-294 targets 8 weeks after MI.

CONCLUSIONS

Ectopic transient expression of miR-294 recapitulates developmental signaling and phenotype in cardiomyocytes promoting cell cycle reentry that leads to augmented cardiac function in mice after myocardial infarction.