post-MI Mice Research Articles

QGC606: A Best-in-Class Orally Active Centrally Acting Aminopeptidase A Inhibitor Prodrug for Treating Heart Failure Following Myocardial Infarction.

Blockade of brain renin-angiotensin system (RAS) overactivity by firibastat, the first centrally acting aminopeptidase A (APA) inhibitor prodrug, has already demonstrated its effectiveness in improving cardiac function after myocardial infarction (MI). We developed QGC606, a more potent and more selective APA inhibitor prodrug and studied its effects after long-term oral administration in mice post-MI. Two days after MI induced by the left anterior descending artery ligation, adult male mice were randomized into 4 groups to receive oral treatment during 4 weeks with vehicle; QGC606; firibastat; or the angiotensin-I converting enzyme inhibitor ramipril, used as positive control. Four weeks post-MI, brain APA was overactivated in vehicle-treated MI mice. QGC606 treatment normalized brain APA hyperactivity to control values measured in sham-operated mice. Four weeks post-MI, QGC606-treated mice had higher left ventricular (LV) ejection fractions, significantly smaller LV end-systolic diameter and volume, significantly lower HF biomarkers mRNA expression (Myh7 and Anf) and plasma N-terminal pro B-type natriuretic peptide (NT-pro-BNP) and noradrenaline levels than saline-treated mice. QGC606 treatment significantly improved the dP/dt max and min, LV end-diastolic pressure without affecting blood pressure (BP), whereas we observed a decrease in BP in ramipril-treated mice. We observed also a reduction of cardiac fibrosis, highlighted by lower connective tissue growth factor mRNA levels and a reduction of both the fibrotic area and MI size in QGC606-treated mice. Chronic oral QGC606 administration in post-MI mice showed beneficial effects in improving cardiac function and reducing cardiac remodeling and fibrosis but, unlike ramipril, without lowering BP.

Novel Insights into the Cardioprotective Effects of Calcitriol in Myocardial Infarction.

Background: Increasing evidence indicates that vitamin D deficiency negatively affects the cardiovascular system. Here we studied the therapeutic effects of calcitriol in myocardial infarction (MI) and investigated its underlying mechanisms. Methods: A MI model of Kun-ming mice induced by left anterior descending coronary artery ligation was utilized to study the potential therapeutic effects of calcitriol on MI. AC16 human cardiomyocyte-like cells treated with TNF-α were used for exploring the mechanisms that underlie the cardioprotective effects of calcitriol. Results: We observed that calcitriol reversed adverse cardiovascular function and cardiac remodeling in post-MI mice. Mechanistically, calcitriol suppressed MI-induced cardiac inflammation, ameliorated cardiomyocyte death, and promoted cardiomyocyte proliferation. Specifically, calcitriol exerted these cellular effects by upregulating Vitamin D receptor (VDR). Increased VDR directly interacted with p65 and retained p65 in cytoplasm, thereby dampening NF-κB signaling and suppressing inflammation. Moreover, up-regulated VDR was translocated into nuclei where it directly bound to IL-10 gene promoters to activate IL-10 gene transcription, further inhibiting inflammation. Conclusion: We provide new insights into the cellular and molecular mechanisms underlying the cardioprotective effects of calcitriol, and we present comprehensive evidence to support the preventive and therapeutic effects of calcitriol on MI.

Osteoblast MR deficiency protects against adverse ventricular remodeling after myocardial infarction

RationaleMineralocorticoid receptor (MR) antagonists have been clinically used to treat heart failure. However, the underlying cellular and molecular mechanisms remain incompletely understood. Methods and resultsUsing osteoblast MR knockout (MRobko) mouse in combination with myocardial infarction (MI) model, we demonstrated that MR deficiency in osteoblasts significantly improved cardiac function, promoted myocardial healing, as well as attenuated cardiac hypertrophy, fibrosis and inflammatory response after MI. Gene expression profiling using RNA sequencing revealed suppressed expression of osteocalcin (OCN) in calvaria from MRobko mice compared to littermate control (MRfl/fl) mice with or without MI. Plasma levels of undercarboxylated OCN (ucOCN) were also markedly decreased in MRobko mice compared to MRfl/fl mice. Administration of ucOCN abolished the protective effects of osteoblast MR deficiency on infarcted hearts. Mechanistically, ucOCN treatment promoted proliferation and inflammatory cytokine secretion in macrophages. Spironolactone, an MR antagonist, significantly inhibited the expression and secretion of OCN in post-MI mice. More importantly, spironolactone decreased plasma levels of ucOCN and inflammatory cytokines in heart failure patients. ConclusionsMR deficiency in osteoblasts alleviates pathological ventricular remodeling after MI, likely through its regulation on OCN. Spironolactone may work through osteoblast MR/OCN axis to exert its therapeutic effects on pathological ventricular remodeling and heart failure in mice and human patients.

Abstract 14338: Mitochondria-Targeted ROS Scavenger JP4-039 Induces Coronary Angiogenesis in Ischemic Myocardium Resulting in the Improvement of Cardiac Function in Post-MI Animals

Introduction: A reduction of mitochondrial reactive oxygen species (mito-ROS) has been sought as a potential approach for recovering energy supply and improving cardiac function in cardiovascular disease. Here, we evaluated JP4-039, a mito-ROS scavenger, for post-myocardial infarction (MI) recovery. Hypothesis: We hypothesized that mitochondrial antioxidant JP4-039 will induce coronary angiogenesis and improve post-MI cardiac function in mice. Methods: FVB mice (n=8/group) underwent MI surgery and were assigned to either vehicle (sunflower seed oil) or JP4-039 group (1mg/kg, i.p., 3x/week for 4 weeks). A SHAM surgery group received vehicle only. Left ventricle (LV) ejection fraction (EF), fractional shortening (FS), and fractional area change (FAC) were assessed by echocardiography 28 days post-MI. Capillary (CD31 antibody) and arteriole density (α-SMA antibody) were quantified by immunofluorescence of ischemic heart sections 28 days post-MI. Western blot of myocardial homogenates was conducted to evaluate activation of Akt, ERK1/2, and AMPKα. Data were analyzed by One-way ANOVA and Tukey’s post-hoc, and a p value <0.05 was taken as significant. Results: Mice treated with JP4-039 presented with a 35% decrease in infarction size, and a 57% increase in EF compared to the vehicle group (43.6±5.1 vs. 27.8±5.3). FS and FAC of JP4-039-treated mice increased by 65% (21.9±2.9 vs. 13.3±2.6) and 90% (38.0±5.6 vs. 20.0±4.0), respectively. In ischemic myocardium, the JP4-039 group showed an increase in capillary density of 39% in comparison to vehicle (208.6±21.7 vs 149.9±18.0). Interestingly, arteriogenesis was decreased in ischemic myocardium by 31% in JP4-039-treated mice compared to vehicle group (9.0±1.1 vs. 13.1±1.5). Although activation of Akt or ERK1/2 signaling were unchanged, p-AMPKα was decreased by 67% in JP4-039 vs. vehicle (0.39±0.07 vs. 0.65±0.03) in myocardium. Conclusions: The findings suggest that mitochondrial antioxidant JP4-039 improves capillary angiogenesis in ischemic myocardium, resulting in improved cardiac function in post-MI mice. Mechanisms involved in differential levels of capillary and arteriole densities in ischemic myocardium are being examined in human coronary ECs and will be presented at the meeting.

Abstract 13056: The Novel Cardiokine GDF3 Predicts Fibrotic Remodeling Post-Myocardial Infarction

Introduction: Myocardial infarction (MI) induces a repair response that ultimately generates a stable fibrotic scar. Although the scar prevents cardiac rupture, an excessive profibrotic response impairs optimal recovery. Hypothesis: To explore the regulation of fibroblasts proliferation through a paracrine action of cardiac stromal cells post-MI Methods: We carried out a bioinformatic secretome analysis of cardiac stromal PW1 + cells isolated from normal and post-MI mouse hearts to identify novel secreted proteins. Functional assays were used to screen secreted proteins that promote fibroblast proliferation. The expressions of secreted proteins candidates were subsequently analyzed in mouse and human hearts and plasmas. The relation between levels of circulating protein candidates and adverse post-MI cardiac remodeling was examined in a cohort of 80 patients with a first ST-elevation MI and serial cardiac magnetic resonance imaging (MRI) evaluations. Results: Cardiac stromal PW1 + cells undergo a change in paracrine behavior post-MI and secrete factors that promote fibroblast proliferation. Among these factors, growth differentiation factor 3 (GDF3), a member of the transforming growth factor-β family, was markedly upregulated in the ischemic hearts and induced fibroblast proliferation at high level. In humans, GDF3 was detected in the plasma at day 4 post-MI and GDF3 circulating levels were significantly associated with an increased risk of adverse remodeling 6-month post-MI (adjusted Odds Ratio (OR) = 1.76 [1.03 - 3.00], p = 0.037). Conclusions: Our findings define a mechanism for the pro-fibrotic action of cardiac stromal cells through secreted cardiokines, such as GDF3, a candidate marker of adverse fibrotic remodeling following MI.

Abstract MP255: Intercellular Model Predicts Macrophage Signaling As A Driver Of Cardiac Fibroblast Response Post Myocardial Infarction

Introduction: Post-myocardial infarction (MI), cardiac fibroblasts and macrophages work together to regulate tissue homeostasis and infarct repair. Macrophage-fibroblast interactions in healthy tissue are stable and resistant to perturbations. However, this robustness post-MI has not been assessed. This study designs and implements an intercellular communication model of macrophage-fibroblast crosstalk to determine drivers of infarct repair. Methods: An ordinary differential equation model of post-MI cellular dynamics was developed ( Figure 1A ). Model inputs are time courses of cardiomyocytes, neutrophils, and monocytes. These cells, along with simulated macrophages and fibroblasts, secrete chemokines and cytokines which directed cell proliferation, removal, and chemical secretion. The outputs are macrophage and fibroblast densities, secreted factor dynamics, and produced collagen. Model validation was done using published data in post-MI mice. A sensitivity analysis was conducted by knocking down individual parameters to identify key drivers of fibroblast collagen production. Results: The simulated trends matched the validation time courses. Of the 28 validation relationships, 12 were input-output, 7 were knockouts, and 9 were inhibitor relationships. The validation passed at 78.5%; the 6 failed validations were due to the independent nature of the input curves. Sensitivity analysis ( Figure 1B ) identified macrophage differentiation rate, removal rate, and transforming growth factor-beta (TGFB) secretion rate as pro-fibrotic. Prolonged exposure to TGFB and granulocyte-macrophage colony stimulating factor was anti-fibrotic. Several clustered parameters differentially regulated macrophages and collagen production. Conclusions: The multicellular model identified macrophage density as a pro-fibrotic driver in the healing infarct. Differential regulation of macrophages and collagen production was predicted by the model.

Abstract P375: Gender-based Cardio-protective Functional Dimorphism Of Bone Marrow Endothelial Progenitor Cells And Their Exosomes: Estrogen-independent Epigenetic Mechanisms

Introduction: Estrogen or estrogen receptor-dependent mechanisms in enhancing the cardioprotective efficacy of bone marrow endothelial progenitor cells (BM-EPC) is well-established in preclinical studies. However, the efficacy of estrogen does not reflect in the data from randomized cardiovascular clinical trials, suggesting an estrogen-independent role of female BM-EPC in eliciting enhanced cardiac protection compared to males. Hypothesis: Epigenetic mechanisms may contribute to the sex-specific dimorphism of Sca-1 + /CD31 + BM-EPC in regulating cell-homing, pro-angiogenic and anti-inflammatory functions in the ischemic myocardium leading to enhanced reparative function of female progenitor cells. Methods & Results: Transplantation of GFP-BM-mononuclear cells from male and female GFP transgenic mice into the BM of lethally irradiated recipient male C57BL/6 mice resulted in the enhanced mobilization of female Sca-1 + CD31 + /GFP + BM-EPC into circulation post-MI. A higher number of female BM-EPC homed to the ischemic myocardium and significantly improved LV functions and capillary density post-MI compared to male BM-EPC. Female BM-EPC showed increased expression of bFGF, VEGFR2, SDF-1α, and IL-10 genes, thereby efficiently promoted endothelial tube formation in vitro compared to male BM-EPC. Transplantation of female BM-EPC and their exosomes into post-MI male mice improved LV cardiac function, reduced scar size, and improved capillary density compared to male BM-EPC and exosomes. Male BM-EPC showed an increased expression of G9a/Ehmt2, an H3K9me3 methyltransferase, and Dnmt3a DNA methyltransferase compared to female BM-EPC. In contrast, Kdm6b/JMJD3, H3K27me3 demethylase was highly expressed in female BM-EPC compared to males. Treatment of BM-EPC of both sexes with 17-β-estradiol did not alter the expression of Kdm6b/JMJD3. Male BM-EPC highly expressed repressive gene marks, H3K9me3, and H3K27me3 compared to females. Compared to the male, BM-EPC from female and ovariectomized (OXV) female mice showed equally high expression of angiogenic genes ANGPT-1, MDK, PLAU, Tie-2, and VEGFR2 and lower levels of inflammatory cytokines, TNFα, IFNγ, IL-1β, and CCL3. Conditioned medium from female and OVX BM-EPC equally promoted enhanced migration and tube formation of HUVEC in vitro, compared to male BM-EPC. Conclusions: An estrogen-independent epigenetic mechanism likely governs the enhanced cardiac reparative properties of female BM-EPC.

Gastrin exerts a protective effect against myocardial infarction via promoting angiogenesis

BackgroundIt is known that increased gastrin concentration is negatively correlated with cardiovascular mortality, and plasma gastrin levels are increased in patients after myocardial infarction (MI). However, whether gastrin can play a protective role in MI remains unknown.MethodsAdult C57BL/6 mice were subjected to ligation of the left anterior descending coronary artery (LAD) and subcutaneous infusion of gastrin (120 μg/Kg body weight/day, 100 μL in the pump) for 28 days after MI. Plasma gastrin concentrations were measured through an ELISA detection kit. Mice were analyzed by echocardiography after surgery. CD31 and VEGF expression were quantified using immunofluorescence staining or/and western blot to assess the angiogenesis in peri-infarct myocardium. Capillary-like tube formation and cell migration assays were performed to detect gastrin-induced angiogenesis.ResultsWe found that gastrin administration significantly ameliorated MI-induced cardiac dysfunction and reduced fibrosis at 28 days in post-MI hearts. Additionally, gastrin treatment significantly decreased cardiomyocyte apoptosis and increased angiogenesis in the infarct border zone without influencing cardiomyocyte proliferation. In vitro results revealed that gastrin up-regulated the PI3K/Akt/vascular endothelial growth factor (VEGF) signaling pathway and promoted migration and tube formation of human coronary artery endothelial cells (HCAECs). Cholecystokinin 2 receptor (CCK2R) mediated the protective effect of gastrin since the CCK2R blocker CI988 attenuated the gastrin-mediated angiogenesis and cardiac function protection.ConclusionOur data revealed that gastrin promoted angiogenesis and improved cardiac function in post-MI mice, highlighting its potential as a therapeutic target candidate.

Ischemic heart injury leads to HIF1-dependent differential splicing of CaMK2\u03b3

Ischemic heart disease is a leading cause of heart failure and hypoxia inducible factor 1 (HIF1) is a key transcription factor in the response to hypoxic injury. Our lab has developed a mouse model in which a mutated, oxygen-stable form of HIF1α (HIF-PPN) can be inducibly expressed in cardiomyocytes. We observed rapid cardiac dilation and loss of contractility in these mice due to lower expression of excitation–contraction coupling genes and reduced calcium flux. As alternative splicing plays an underappreciated role in transcriptional regulation, we used RNA sequencing to search for splicing changes in calcium-handling genes of HIF-PPN hearts and compared them to previous sequencing data from a model of myocardial infarction (MI) to select for transcripts that are modified in a pathological setting. We found overlap between genes differentially expressed in HIF-PPN and post-MI mice (54/131 genes upregulated in HIF-PPN hearts at 1 day and/or 3 days post-MI, and 45/78 downregulated), as well as changes in alternative splicing. Interestingly, calcium/calmodulin dependent protein kinase II, gamma (CAMK2G) was alternatively spliced in both settings, with variant 1 (v1) substantially decreased compared to variants 2 (v2) and 3 (v3). These findings were also replicated in vitro when cells were transfected with HIF-PPN or exposed to hypoxia. Further analysis of CAMK2γ protein abundance revealed only v1 was detectable and substantially decreased up to 7 days post-MI. Rbfox1, a splicing factor of CAMK2G, was also decreased in HIF-PPN and post-MI hearts. Subcellular fractionation showed CAMK2γ v1 was found in the nuclear and cytoplasmic fractions, and abundance decreased in both fractions post-MI. Chromatin immunoprecipitation analysis of HIF1 in post-MI hearts also demonstrated direct HIF1 binding to CAMK2G. CaMK2 is a key transducer of calcium signals in both physiological and pathological settings. The predominantly expressed isoform in the heart, CaMK2δ, has been extensively studied in cardiac injury, but the specific role of CaMK2γ is not well defined. Our data suggest that loss of CaMK2γ after MI is HIF1-dependent and may play an important role in the heart’s calcium signaling and transcriptional response to hypoxia.

Microenvironment stiffness requires extracellular matrix proteins to modulate heart regeneration

Introduction Injecting decellularized cardiac extracellular matrix (dECM) into the myocardium stimulates heart regeneration in rodent and porcine myocardial infarction (MI) models. Early-age cardiac dECM showed higher therapeutic efficacy than adult dECM for MI in animal models. In this study, we demonstrate that decreasing microenvironment stiffness further improves the therapeutic efficacy of fetal dECM on post-ischemia heart regeneration through YAP-regulated cardiomyocyte proliferation and CAPG-regulated fibroblast differentiation. Decreasing heart stiffness has been reported to preserve the heart regenerative capacity in newborn mice. However, how microenvironment stiffness affects cardiomyocyte proliferation and heart regeneration has not been fully understood. Using in vivo and in vitro cardiac injury models of various tissue stiffness, we investigated how tissue stiffness modulates heart post-injury response and exogenous fetal dECM induced heart recovery at different time points. We also examined the total mRNA expression and identified signaling pathways regulating the synergistic effect of tissue stiffness and dECM treatment on heart regeneration. Methods P5 neonatal mouse heart stiffness was lowered by injecting BAPN, and increased by genipin. Solubilized porcine fetal dECM was injected immediately after ligating coronary artery. Heart function and histology were conducted at week 3 post-MI. Cardiomyocyte cell cycle activity, fibrosis, fibroblast differentiation, and vascularization were examined. Post-MI mice at day3 and day21 were investigated for relevant signaling pathways. A mice ventricle explant model was used to investigate the role of mechanosensitive proteins and cytoskeleton organization in cardiomyocyte proliferation regulation. Results Tissue stiffness was measured by atomic force microscopy (AFM). Heart stiffness was lowered from 50kPa to 9kPa by BAPN and increased to 142kPa by genipin. We observed that fetal dECM treatment preserved cardiac output, reduced fibrosis, and promoted cardiomyocyte cell cycle activity on week 3 post-MI. Decreasing tissue stiffness further improved the therapeutic efficacy of fetal dECM on heart post-MI response (Fig.1). Decreasing tissue stiffness lowered the ratio of fibrotic area in no-dECM treated MI control hearts, but did not affect the other aspects. Using a ventricle explant model of various stiffness, molecular evidence demonstrated that agrin-YAP signaling pathway is involved in the mechano-regulation of fetal dECM-induced heart regeneration. Agrin expression was elevated and cardiomyocyte YAP activation was not affected by changing tissue stiffness in control (no-dECM) mechano-modulated explants. However, YAP activation in fetal-dECM treated explants was increased by softening tissue. Disrupting cytoskeleton organization reduced YAP activity and cardiomyocyte cell cycle activity induced by fetal dECM. We also demonstrated that dECM inhibits fibroblast to myofibroblast differentiation. RNA sequencing and western blot revealed that macrophage-capping protein (CAPG) expression was lowered by dECM treatments. Interfering CAPG expression in fibroblasts inhibits fibroblast differentiation.

Myocardial Infarction Induces B Lymphopenia via a Mechanism Involving Cell Redistribution Between Peripheral Lymphoid Tissues and Bone Marrow

Lymphopenia, a reduction in peripheral blood lymphocyte count, correlates with worse cardiac function and poor outcome in patients with myocardial infarction (MI) and is considered an independent prognostic biomarker. How it occurs after MI, however, is largely unknown. The objective of this study was to elucidate the underlying mechanisms by which MI drives B lymphopenia. Adult male C57BL/6J mice underwent permanent ligation of coronary artery to create MI and were sacrificed at days 1 and 3 post-MI. Quantitative flow cytometric measurement revealed that blood B cell count dramatically decreased at days 1 and 3 post-MI, compared to non-MI controls, consistent with B lymphopenia. This was also confirmed in a mouse myocardial ischemia/reperfusion (I/R) model. The observation that MI did not increase apoptosis in blood B cells argues against apoptosis as the major contributing factor for MI-induced B lymphopenia. We then investigated whether blood B cells migrate to and are retained in lymphoid organs. Similar to what was shown in the blood, the spleen and mesenteric lymph node in MI mice had lower mature B cell numbers and exhibited profound atrophy; in contrast, the bone marrow in post-MI mice had more mature B cells than non-MI controls, supporting that peripheral B cells travel to the bone marrow in response to MI. In conclusion, our study provides the first line of evidence suggesting that MI-associated B lymphopenia involves B cell redistribution from peripheral lymphoid tissues to the bone marrow.

Chromatin remodeling and mitochondrial biogenesis underlie the improved cardiac function in heart failure induced by ketogenic diet and beta‐hydroxibutiyrate supplementation

Background : Beta Hydroxybutyrate (BHB) is the main ketone body produced during fasting or carbohydrate deprivation as an alternative fuel. A key aspect of metabolic remodeling in heart failure (HF) is the down-regulation of fatty acid utilization. Moreover, the myocardial metabolic profile reveals that the failing heart shift towards oxidizing ketones bodies. Emerging evidence suggests that after myocardial infarction (MI) the metabolic failure coincides with increased levels and utilization of BHB; equally important, the key enzyme involved in BHB catabolism, BHB-dehydrogenase 1, is up-regulated in HF. However, whether such modifications are adaptive or maladaptive in the damaged myocardium has never been evaluated. On these grounds, our main aim is to explore the effects of BHB on cardiac function after ischemic injury in vivo, in vitro, and ex vivo. Methods and Results A layout of the experimental design is shown in Figure 1. Our in vitro experiments, performed in cultured H9C2 cardiac cells, demonstrated that the administration of BHB (3 mM) reduced the activation of caspase 3 in response to ischemia, as well as the number of TUNEL+ nuclei. Specifically, the mitochondrial apoptotic pathway was affected, as BHB reduced mitochondrial cytochrome-C release in the cytosol induced by ischemia. Mitochondrial structure and interconnections, markedly affected by ischemia, were significantly retained in presence of BHB, as well as mitochondrial membrane potential (assessed via TMRE). The preserved mitochondrial health was further supported by higher levels of PGC-1α detected in cells exposed to ischemia plus BHB compared to ischemia alone. Then, in order to investigate the in vivo effects of BHB on ischemia-damaged myocardium, we administrated carbohydrate-null diet (ketogenic diet, KD) or standard diet-supplemented with BHB, to post-MI mice. The MI was obtained by permanent ligation of the left anterior descending coronary artery. Both groups treated with KD and BHB-supplemented diet displayed a significantly preserved left ventricular ejection fraction compared to untreated infarcted mice. The protective effects of BHB on cardiac phenotype were mirrored by increased levels of PGC-1α in the myocardium of treated mice, both in terms of protein and transcription levels. Additionally, in the hearts of mice fed KD and BHB supplemented diet, we observed a distinct difference in chromatin remodeling and in the histone acetylation pattern. Strikingly, these results were confirmed both in our ex vivo and in vitro assays. Conclusions BHB protects cardiac cells from apoptotic and mitochondrial damage induced by ischemia. Through its ability to regulate fundamental epigenetic modifications, BHB activates a gene expression program that specifically supports mitochondrial biogenesis and function, thereby representing an unprecedented and powerful therapeutic strategy in heart failure.

Characterizing a long-term chronic heart failure model by transcriptomic alterations and monitoring of cardiac remodeling.

The long-term characteristics of transcriptomic alterations and cardiac remodeling in chronic heart failure (CHF) induced by myocardial infarction (MI) in mice are not well elucidated. This study aimed to reveal the dynamic changes in the transcriptome and cardiac remodeling in post-MI mice over a long time period. Monitoring C57BL/6 mice with MI for 8 months showed that approximately 44% of mice died of cardiac rupture in the first 2 weeks and others survived to 8 months with left ventricular (LV) aneurysm. The transcriptomic profiling analysis of cardiac tissues showed that the Integrin and WNT pathways were activated at 8 months after MI while the metabolism-related pathways were inversely inhibited. Subsequent differential analysis at 1 and 8 months post-MI revealed significant enrichments in biological processes, including consistent regulation of metabolism-related pathways. Moreover, echocardiographic monitoring showed a progressive increase in LV dimensions and a decrease in the LV fractional shortening during the first 4 weeks, and these parameters progressed at a lower rate till 8 months. A similar trend was found in the invasive LV hemodynamics, cardiac morphological and histological analyses. These results suggested that mouse MI model is ideal for long-term studies, and transcriptomic findings may provide new CHF therapeutic targets.

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.

Taohong siwu decoction attenuates myocardial fibrosis by inhibiting fibrosis proliferation and collagen deposition via TGFBR1 signaling pathway

Ethnopharmacological relevanceMyocardial fibrosis after myocardial infarction (MI) leads to cardiac remodeling and loss of function. Taohong siwu decoction (THSWD), a well-known traditional Chinese medicinal prescription, has been clinically used to treat various cardiovascular and cerebrovascular diseases, but its potential functions in myocardial fibrosis after MI remain uncharacterized. Aim of the studyThe purpose of current study was to explore the potential mechanism action and anti-myocardial fibrosis effects of treatment with THSWD in vivo and in vitro. Materials and methodsMouse underwent ligation of coronary artery to induce MI and divided equally into the sham group, model group and THSWD treatment groups. After 4 weeks, the effects of THSWD treatment on cardiac function were estimated by echocardiography. HE staining was used to detect the pathologic changes and Masson trichrome staining was used to estimate tissue fibrosis. To further explore the regulatory molecular mechanisms of THSWD, transcriptome analysis was performed. Furthermore, in vitro, we investigated the effect of THSWD on cell proliferation and collagen deposition in primary cardiac fibrosis cells and its possible mechanism of action. Overexpression of TGFBR1 was achieved by infection with an adenovirus vector encoding TGFBR1. ResultsTreatment with THSWD significantly decreased myocardial fibrosis and recovered cardiac function in the post-MI mouse. The transcriptomics data imply that the TGF-β pathway might be a target in the anti-fibrosis effect of THSWD. THSWD inhibits TGF-β1-induced proliferation of primary cardiac fibroblasts. THSWD decreased collagen expression and TGFBR1 and Smad2/3 phosphorylation. Moreover, the inhibitory effect of THSWD on CFs proliferation and collagen deposition, as well as TGFBR1 signaling pathway-associated proteins expression was partially abrogated by overexpression of TGFBR1. ConclusionCollectively, the results implicate that THSWD attenuates myocardial fibrosis by inhibiting fibrosis proliferation and collagen deposition via inhibiting TGFBR1, and might be a potential therapeutic agent for treatment of myocardial fibrosis post-MI.

MD1 Depletion Predisposes to Ventricular Arrhythmias in the Setting of Myocardial Infarction

Myeloid differentiation protein 1 (MD1) is expressed in the human heart and is a negative regulator of Toll-like receptor 4 (TLR4) signalling. MD1 exerts anti-arrhythmic effects. The aim of this study was to determine the role of MD1 in myocardial infarction (MI)-related ventricular arrhythmias (VAs). Myocardial infarction was induced by surgical ligation of the left anterior coronary artery in MD1 knockout (KO) mice and their wild-type littermates. Myocardial infarction-induced vulnerability to VAs and its underlying mechanisms were evaluated. Myeloid differentiation protein 1 was downregulated in the MI mice. Myeloid differentiation protein 1 deficiency decreased post-MI left ventricular (LV) function and increased the infarct size. The MI mice exhibited prolonged action potential duration (APD), enhanced APD alternans thresholds, and a higher incidence of VAs. Myocardial infarction-induced LV fibrosis and inflammation decreased the expression levels of Kv4.2, Kv4.3, Kv1.5, and Kv2.1, increased Cav1.2 expression, and disturbed Ca2+ handling protein expression. These MI-induced adverse effects were further exacerbated in KO mice. Mechanistically, MD1 deletion markedly enhanced the activation of the TLR4/calmodulin-dependent protein kinase II (CaMKII) signalling pathway in post-MI mice. Myeloid differentiation protein 1 deletion increases the vulnerability to VAs in post-MI mice. This is mainly caused by the aggravated maladaptive LV fibrosis and inflammation and interference with the expressions of ion channels and Ca2+ handling proteins, which is related to enhanced activation of the TLR4/CaMKII signalling pathway.

Abstract 209: Ketone Bodies Ameliorate Cardiac Function in Heart Failure

Background: Beta hydroxibutirrate (BHB) is the main ketone body produced during fasting or carbohydrate deprivation as an alternative fuel. Mounting evidence suggests that after myocardial infarction (MI), the mitochondrial impairment and metabolic failure coincide with increased levels and utilization of BHB. However, whether the BHB increase is adaptive or maladaptive in damaged myocardium, has never been evaluated. Aim: Our scope was to explore the effects of BHB on cardiac function after ischemia both in vivo and in vitro . Methods and Results: In cultured cardiomyoblasts, the administration of BHB (3 mMol) reduces the activation of caspase-3 in response to ischemia, as well as the number of tunnel positive nuclei. Specifically, the mitochondrial apoptotic pathway seems affected, as BHB reduces cytochrome-C release induced by ischemia. Mitochondrial structure and interconnections, soundly affected by ischemia, were significantly retained in presence of BHB, as well as mitochondrial membrane potential (assessed via TMRE). The preserved mitochondrial health was further supported by higher levels of PGC1-alpha detected in cells exposed to ischemia plus BHB compared to ischemia alone. To explore the in vivo effects of BHB on ischemia damaged- myocardium, we administrated carbohydrate-null diet ( ketogenic diet , KD) or standard diet-supplemented with BHB, to post-MI mice. Both groups treated with KD and BHB supplemented diet displayed preserved left ventricular ejection fraction respect to untreated infarcted mice. The protective effects of BHB on cardiac phenotype were mirrored by increased levels of PGC1-alpha in the myocardium of treated mice, in terms of protein and transcription levels. Interestingly, in the hearts of mice fed KD and BHB supplemented diet, we observed a marked difference in histone acetylation pattern. Conclusions: BHB protects cardiac cells from apoptotic and mitochondrial damage induced by ischemia. Through its ability to regulate epigenetic modifications, BHB could activate a gene expression program able to support mitochondrial function, thereby representing a powerful therapeutic strategy.

Comparative bulk and single-cell transcriptome analyses revealed distinct functional polarization of cardiac macrophages in regenerative and non-regenerative mouse hearts

Abstract Background Heart failure is a major cause of morbidity and mortality, in part owing to the inability of the human heart to replenish lost cardiomyocytes following cardiac injury. Recent studies have demonstrated that neonatal human and mouse heart can fully regenerate in response to injury. This regenerative capacity, however, is transient and age-dependent. The regenerative capacity of neonatal mouse heart, for example, declines sharply by 7 days of age. It has been demonstrated that tissue-resident macrophages in neonatal hearts are required for cardiac repair and recovery from injuries by promoting angiogenesis and cardiomyocyte proliferation. The cellular and molecular determinants underlying the reparative/pro-regenerative properties of neonatal cardiac macrophages, however, remain elusive. Purpose To reciprocally characterize macrophage heterogeneity and functionality that are critical for myocardial repair and regeneration following myocardial infarction (MI) injury in neonatal (regenerative) and adult (non-regenerative) mouse hearts. Methods and results Cardiac tissue-sorted macrophages (CD45+CD11b+CD64+) from neonatal (P1–3) and adult (8 weeks) mouse heart 10 days following MI (by permanent coronary artery ligation) were subjected to bulk and single-cell RNA sequencing (scRNA-Seq) analyses. In response to MI injury, CCR2+ monocyte-derived macrophages predominate in adult, whereas CCR2- resident macrophages expand markedly in neonatal mouse hearts. Comparing to sham-operated controls, bulk RNA-Seq revealed that the expression levels of a total of 482 and 614 mRNAs were significantly (absolute fold change >2, P<0.05) altered in adult and neonatal cardiac macrophages following MI, respectively. Pathway analyses showed that genes involved in olfactory function and Wnt-signaling were dysregulated in adult, whereas transcripts involved in oxidative phosphorylation and interferon-g (IFN-g) pathway were upregulated in neonatal cardiac macrophages after MI. scRNA-Seq analysis identified 11 distinct cardiac macrophage clusters in adult mouse heart following MI, several of which showed strong upregulation in inflammatory mediators (Ly6c2, Clec4b1, Cxcl3 and Lilra5) and extracellular matrix protein genes (Fn1, and Dcn), suggesting macrophage polarization towards a pro-inflammatory and fibrogenic phenotype in post-injury adult heart. Conclusion As distinct macrophage populations mentioned in current study, our results revealed divergent transcriptionl signatures of cardiac macrophages in post-MI neonatal and adult mouse hearts. While Wnt signaling, inflammation and fibrogenic activities are increased in adult cardiac macrophages, oxidative phosphorylation and IFN-g signaling are markedly activated in neonatal cardiac macrophages in response to injury. Phenotypic switching toward enhanced oxidative phosphorylation and IFN-g signaling in cardiac macrophages, therefore, could be the key to develop novel therapeutics to promote cardiac regeneration. Funding Acknowledgement Type of funding source: None

Impaired therapeutic efficacy of bone marrow cells from post-myocardial infarction patients in the TIME and LateTIME clinical trials.

Implantation of bone marrow-derived cells (BMCs) into mouse hearts post-myocardial infarction (MI) limits cardiac functional decline. However, clinical trials of post-MI BMC therapy have yielded conflicting results. While most laboratory experiments use healthy BMC donor mice, clinical trials use post-MI autologous BMCs. Post-MI mouse BMCs are therapeutically impaired, due to inflammatory changes in BMC composition. Thus, therapeutic efficacy of the BMCs progressively worsens after MI but recovers as donor inflammatory response resolves. The availability of post-MI patient BM mononuclear cells (MNCs) from the TIME and LateTIME clinical trials enabled us to test if human post-MI MNCs undergo a similar period of impaired efficacy. We hypothesized that MNCs from TIME trial patients would be less therapeutic than healthy human donor MNCs when implanted into post-MI mouse hearts, and that therapeutic properties would be restored in MNCs from LateTIME trial patients. Post-MI SCID mice received MNCs from healthy donors, TIME patients, or LateTIME patients. Cardiac function improved considerably in the healthy donor group, but neither the TIME nor LateTIME group showed therapeutic effect. Conclusion: post-MI human MNCs lack therapeutic benefits possessed by healthy MNCs, which may partially explain why BMC clinical trials have been less successful than mouse studies.

Abstract 277: MicroRNA-125a-5p Protects the Mouse Heart From Ischemic Injury by Repressing Pro-apoptotic Bak1 and Klf13 in Cardiomyocytes

Background: Cardiac injury is accompanied by dynamic changes in the expression of microRNAs (miRs), which are small noncoding RNAs to downregulate target genes. MiR-125a-5p (miR-125a) is downregulated in patients with myocardial infarction (MI). We reported that miR-125a is upregulated by the β-blocker carvedilol (Carv) acting through β-arrestin1-biased β1-adrenergic receptor (β1AR; receptor found mainly in cardiomyocytes [CMs]) cardioprotective signaling (Figure A). We also showed that pro-apoptotic genes bak1 and klf13 are downregulated by Carv and are upregulated after MI. Here, we hypothesize that miR-125a in CMs favorably regulates cardiac functional and structural remodeling after MI by repressing bak1 and klf13. Methods and Results: Fractionation of cardiac cell types from heart tissues reveals that the expression of miR-125a is higher in CMs than other myocardial cells. Using cultured CM and in vivo approaches, we show that miR-125a is an ischemic stress-responsive protector against CM apoptosis. CMs lacking miR-125a exhibit an increased sensitivity to apoptosis, while CMs overexpressing miR-125a have increased phospho-AKT pro-survival signaling. Moreover, we show that miR-125a is downregulated in post-MI mouse hearts and miR-125a overexpression protects mouse hearts against MI. We also show that global genetic deletion of miR-125a in mice worsens maladaptive post-MI remodeling. Mechanistically, the cardioprotective role of miR-125a during MI is in part attributed to direct repression of the pro-apoptotic genes bak1 and klf13 in CMs (Figure B). Conclusions: These findings reveal a pivotal role for miR-125a in regulating CM survival during MI.