Cardiomyocyte Cross-sectional Area Research Articles

Long-term exposure to copper induces mitochondria-mediated apoptosis in mouse hearts

Copper is a trace element necessary for the normal functioning of organisms, but excessive copper contents may be toxic to the heart. The goal of this study was to investigate the role of excessive copper accumulation in mitochondrial damage and cell apoptosis inhibition. In vivo, the heart copper concentration and cardiac troponin I (c-TnI) and N-terminal forebrain natriuretic peptide (NT-pro-BNP) levels increased in the copper-laden model group compared to those of the control group. Histopathological and ultrastructural observations revealed that the myocardial collagen volume fraction (CVF), perivascular collagen area (PVCA) and cardiomyocyte cross-sectional area (CSA) were markedly elevated in the copper-laden model group compared with the control group. Furthermore, transmission electron microscopy (TEM) showed that the mitochondrial double-layer membrane was incomplete in the copper-laden model groups. Furthermore, cytochrome C (Cyt-C) expression was downregulated in mitochondria but upregulated in the cytoplasm in response to copper accumulation. In addition, Bcl-2 expression decreased, while Bax and cleaved caspase-3 levels increased. These results indicate that copper accumulation in cardiomyocyte mitochondria induces mitochondrial injury, and Cyt-C exposure and induces apoptosis, further resulting in heart damage.

Perinatal Combinational Exposure to Bisphenol A and a High-Fat Diet Contributes to Transgenerational Dysregulation of Cardiovascular and Metabolic Systems in Mice

Both bisphenol A (BPA) and high-fat diet (HFD) exert unfavorable effects on animals and humans; moreover, they could affect the health of their offspring. BPA and HFD often coexist in modern lifestyles; however, the long-term effects of simultaneous exposure of mothers to BPA and HFD during the perinatal period on the cardiovascular and metabolic systems of the offspring remain unclear. This study aimed to examine the effect of simultaneous exposure of mothers to BPA and HFD on the risk of metabolic and cardiovascular abnormalities in offspring. Institute of Cancer Research female mice (F0) were exposed to BPA and fed with HFD before and during gestation until the end of lactation. F0 mice were mated with untreated males to produce the first generation (F1); subsequently, adult F1 males/females were mated with normal females/males to produce the second generation (F2). Combined maternal exposure to BPA and HFD caused myocardial hypertrophy and aortic tunica media thickening as well as increased the cross-sectional area of cardiomyocytes and blood pressure in the matrilineal F2 generation. These cardiovascular changes might be associated with reduced endothelial nitric oxide synthase (eNOS) levels. The patrilineal female F2 was more likely to be obese than the patrilineal male F2. Re-feeding with a HFD showed a more significant weight gain and reduced energy expenditure. However, the aforementioned effects were not observed with exposure to HFD or BPA alone during the perinatal period. Our findings suggest that perinatal combinational exposure to BPA and HFD could cause metabolic and cardiovascular disorders in the offspring, Further, our findings demonstrate that the synergistic effects of HFD and BPA could be transmitted to future generations in a sex-dependent manner.

Macitentan attenuates cardiovascular remodelling in infant rats with chronic lung disease

BackgroundCardiovascular impairment contributes to increased mortality in preterm infants with chronic lung disease. Macitentan, an endothelin-1 receptor antagonist, has the potential to attenuate pulmonary and cardiovascular remodelling.MethodsIn a prospective randomized placebo-controlled intervention trial, Sprague–Dawley rats were exposed to 0.21 or 1.0 fraction of inspired oxygen (FiO2) for 19 postnatal days. Rats were treated via gavage with placebo or macitentan from days of life 5 to 19. Alveoli, pulmonary vessels, α-smooth muscle actin content in pulmonary arterioles, size of cardiomyocytes, right to left ventricular wall diameter ratio, and endothelin-1 plasma concentrations were assessed.ResultsFiO2 1.0 induced typical features of chronic lung disease with significant alveolar enlargement (p = 0.012), alveolar (p = 0.048) and pulmonary vessel rarefaction (p = 0.024), higher α-smooth muscle actin content in pulmonary arterioles (p = 0.009), higher right to left ventricular wall diameter ratio (p = 0.02), and larger cardiomyocyte cross-sectional area (p < 0.001). Macitentan treatment significantly increased pulmonary vessel count (p = 0.004) and decreased right to left ventricular wall diameter ratios (p = 0.002). Endothelin-1 plasma concentrations were higher compared to placebo (p = 0.015). Alveolar number and size, α-smooth muscle actin, and the cardiomyocyte cross-sectional area remained unchanged (all p > 0.05).ConclusionThe endothelin-1 receptor antagonist macitentan attenuated cardiovascular remodelling in an infant rat model for preterm chronic lung disease. This study underscores the potential of macitentan to reduce cardiovascular morbidity in preterm infants with chronic lung disease.

Hdac8 Inhibitor Alleviates Transverse Aortic Constriction-Induced Heart Failure in Mice by Downregulating Ace1.

Background Heart failure is characterized by activation of the renin-angiotensin-aldosterone system, which is involved in the regulation of cardiac hypertrophy and hypertension. Recently, we reported that Hdac8 inhibition alleviates isoproterenol-induced and angiotensin II-induced cardiac hypertrophy or hypertension in mice. Here, the effect and regulatory mechanisms of the Hdac8 selective inhibitor PCI34051 on pressure overload-induced heart failure were examined. Methods and Results At week 6 posttransverse aortic constriction (TAC), mice were administered with PCI34051 (3, 10, or 30 mg/kg bodyweight/day) for 2 weeks. The therapeutic effects of PCI34051 on TAC-induced cardiac and lung hypertrophy were determined by examining the heart weight-to-bodyweight and lung weight-to-bodyweight ratios and the cross-sectional cardiomyocyte area. Echocardiography analysis revealed that PCI34051 mitigated TAC-induced decreased ejection fraction and fractional shortening. Additionally, the expression of Hdac8 was upregulated in the cardiac and pulmonary tissues of TAC mice. The expression levels of Ace1 and Agtr1 were upregulated, whereas those of Ace2 and Agtr2 were downregulated in TAC mice. PCI34051 treatment or Hdac8 knockdown alleviated inflammation as evidenced by Rela downregulation and Nfkbia upregulation in mice, as well as in cardiomyocytes, but not in cardiac fibroblasts. Hdac8 overexpression-induced Rela pathway activation was downregulated in Ace1 knockdown cells. Picrosirius red staining, real-time polymerase chain reaction, and western blotting analyses revealed that PCI34051 alleviated fibrosis and downregulated fibrosis-related genes. Moreover, PCI34051 or Hdac8 knockdown in rat cardiac fibroblasts alleviated cardiac fibrosis through the Tgfb1-Smad2/3 pathway. The results of overexpression and knockdown experiments revealed that Hdac8 and Ace1 promote inflammation and fibrosis. Conclusions Treatment with PCI34051 enhanced cardiac and lung functions in the TAC-induced heart failure mouse model. These data suggest that HDAC8 is a potential novel therapeutic target for heart failure accompanied by pathological lung diseases.

Effects of Salvianolic Acid B/ginsenoside Rg1 Combination Against Chronic Pulmonary Embolism Induced by Polystyrene Microspheres

Pulmonary embolism (PE) is the most life-threatening complication of venous thromboembolism, but few effective treatments have been discovered to attenuate chronic PE currently. In this study, we investigated the protective effects of salvianolic acid B (SalB) and ginsenoside Rg1 (Rg1) combination (SalB/Rg1) on chronic PE and explored the potential mechanisms. The PE model was induced by 45 μm polystyrene microspheres and 20 mg/kg of SalB/Rg1 was administered to PE rats intraperitoneally. A histopathological analysis of the lungs and heart was performed through hematoxylin and eosin staining and immunohistochemical analysis. The pulmonary index and right ventricular cardiomyocyte cross-sectional area were evaluated. SalB/Rg1 markedly downregulated pulmonary index, attenuated pulmonary interstitial changes, suppressed neutrophil infiltration, prevented collagen deposition, and inhibited MMP-9 activities in the lung. We also found that SalB/Rg1 improved right ventricular hypertrophy accompanied by reducing the cardiomyocyte cross-sectional area. These data suggest that SalB/Rg1 played a protective role against microsphere-induced PE and holds a high potential for the treatment of PE in the future.

Guanylyl cyclase-A phosphorylation decreases cardiac hypertrophy and improves systolic function in male, but not female, mice.

Atrial natriuretic peptide (NP) and BNP increase cGMP, which reduces blood pressure and cardiac hypertrophy by activating guanylyl cyclase (GC)-A, also known as NPR-A or Npr1. Although GC-A is highly phosphorylated, and dephosphorylation inactivates the enzyme, the significance of GC-A phosphorylation to heart structure and function remains unknown. To identify in vivo processes that are regulated by GC-A phosphorylation, we substituted glutamates for known phosphorylation sites to make GC-A8E/8E mice that express an enzyme that cannot be inactivated by dephosphorylation. GC-A activity, but not protein, was increased in heart and kidney membranes from GC-A8E/8E mice. Activities were threefold higher in female compared to male cardiac ventricles. Plasma cGMP and testosterone were elevated in male and female GC-A8E/8E mice, but aldosterone was only increased in mutant male mice. Plasma and urinary creatinine concentrations were decreased and increased, respectively, but blood pressure and heart rate were unchanged in male GC-A8E/8E mice. Heart weight to body weight ratios for GC-A8E/8E male, but not female, mice were 12% lower with a 14% reduction in cardiomyocyte cross-sectional area. Subcutaneous injection of fsANP, a long-lived ANP analog, increased plasma cGMP and decreased aldosterone in male GC-AWT/WT and GC-A8E/8E mice at 15min, but only GC-A8E/8E mice had elevated levels of plasma cGMP and aldosterone at 60min. fsANP reduced ventricular ERK1/2 phosphorylation to a greater extent and for a longer time in the male mutant compared to WT mice. Finally, ejection fractions were increased in male but not female hearts from GC-A8E/8E mice. We conclude that increased phosphorylation-dependent GC-A activity decreases cardiac ERK activity, which results in smaller male hearts with improved systolic function.

Efficacy of Renshen (Radix Ginseng) plus Fuzi (Radix Aconiti Lateralis Preparata) on myocardial infarction by enhancing autophagy in rat.

To elucidate the protective effects of Renshen (Radix Ginseng) and Fuzi (Radix Aconiti Lateralis Preparata) on myocardial infarction (MI) through regulating myocardial autophagy. Thirty-one male Sprague-Dawley rats were randomized into five groups (n = 6 or 7 for each). After treatment for 3 weeks, electrocardiogram ( ECG ) and cardiac function were recorded. Hematoxylin and eosin (HE) staining was used to detect pathological changes in the heart. Enzyme-linked immunosorbent assay (ELISA) was used to detect serum B-type brain natriuretic peptide (BNP), cardiac troponin T (cTnT), tumor necrosis factor-α (TNF-α), and serum inflammatory cytokines. Metabolomic analysis was used to identify differential biomarkers of MI in rats. Immunohistochemistry and western blotting were used to detect BNP, cTnT, TNF-α, LC3B, Beclin-1, p62, and adenosine monophosphate activated protein kinase (AMPK) expression in cardiac tissue. Fuzi (Radix Aconiti Lateralis Preparata) alone or Renshen (Radix Ginseng) plus Fuzi (Radix Aconiti Lateralis Preparata) markedly ameliorated cardiac dysfunction and abnormal ECGs, demonstrated by decreases in the heart weight/body weight ratio, BNP, and cTnT. Pro-inflammation cytokine interleukin (IL)-1α significantly decreased and anti-inflammatory cytokine IL-10 significantly increased in Renshen (Radix Ginseng) single or Renshen (Radix Ginseng) plus Fuzi (Radix Aconiti Lateralis Preparata) groups compared with the control group. HE results suggested that co-treatment produced a greater reduction in cardiomyocyte cross-sectional area than Renshen (Radix Ginseng) or Fuzi (Radix Aconiti Lateralis Preparata) alone. Renshen (Radix Ginseng) plus Fuzi (Radix Aconiti Lateralis Preparata) reversed these changes to different degrees in MI rats. Furthermore, Renshen (Radix Ginseng) plus Fuzi (Radix Aconiti Lateralis Preparata) down-regulated LC3B, Beclin-1, and AMPK expression in cardiac tissue and upregulated p62 expression. Renshen (Radix Ginseng) plus Fuzi (Radix Aconiti Lateralis Preparata) may have a greater effect on heart injury induced by MI in rats than Fuzi (Radix Aconiti Lateralis Preparata) treatment alone, and the underlying mechanism may be associated with the regulation of myocardial autophagy and anti-inflammation effects. These results provide fresh insight into the mechanism of co-treatment with Renshen (Radix Ginseng) and Fuzi (Radix Aconiti Lateralis Preparata) for MI.

Efficacy of shear wave elasticity for evaluating myocardial hypertrophy in hypertensive rats

Shear wave (SW) imaging is a novel ultrasound-based technique for assessing tissue characteristics. SW elasticity may be useful to assess the severity of hypertensive left ventricular (LV) hypertrophy. This study aimed to evaluate the efficacy of SW elasticity for assessing the degree of myocardial hypertrophy using hypertensive rats. Rats were divided into hypertension group and control group. SW elasticity was measured on the excised heart. Myocardial hypertrophy was assessed histologically. LV weight was greater in hypertension group. An increase in interventricular septum and LV free wall thicknesses was observed in hypertension group. SW elasticity was significantly higher in hypertension group than in control group (14.6 ± 4.3 kPa vs. 6.5 ± 1.1 kPa, P < 0.01). The cross-sectional area of cardiomyocytes was larger in hypertension group than in control group (397 ± 50 μm2 vs. 243 ± 14 μm2, P < 0.01), and SW elasticity was positively correlated with the cross-sectional area of cardiomyocytes (R = 0.96, P < 0.01). This study showed that SW elasticity was higher in hypertensive rats and was closely correlated with the degree of myocardial hypertrophy, suggesting the efficacy of SW elasticity for estimating the severity of hypertensive LV hypertrophy.

Abstract 10935: Identification of Small-Molecule ERBB4 Agonists to Treat Heart Failure

Introduction: Heart failure is a complex syndrome with a poor prognosis. The neuregulin-1 (NRG1)/ERBB4 axis has been shown to be cardioprotective and is a possible target for heart failure therapy. Clinical trials with NRG1 are ongoing, but require intravenous administration. Our aim is to develop a small-molecule ERBB4 agonist with cardioprotective properties. Methods: A high-throughput diversity screening (HTS) of 10,240 compounds was performed on a cellular ERBB4/ERBB4 dimerization assay. Ligand binding of hit compounds was tested in co-administration studies with NRG1 (0.1 μM) and competition binding assays with fluorescently labeled NRG1 (0.03 μM). Selectivity, post-receptor phosphorylation, and cell toxicity of hit compounds were determined using Luminex® RTK phosphoprotein, U2OS ERBB2/ERBB3 dimerization and adenylate kinase assays. Biological effects were studied in vitro in different doses (4-32 μM) on TGF-β-induced collagen synthesis by human dermal and atrial fibroblasts, and on angiotensin II (AngII, 1000 ng/kg/min)-induced left ventricular (LV) remodeling in mice with 2 selected hit compounds (83 μg/kg/h), administrated through osmotic pumps (N=4-5/group). After 28 days, left ventricular myocardial fibrosis and cardiomyocyte cross sectional area (CSA) were analyzed. Results: The HTS resulted in 8 similar pyrimidine derivatives inducing ERBB4/ERBB4 but not ERBB2/ERBB3 dimerization (Emax 9 to 33% relative to NRG1, and EC50 6x10 -6 M to 2x10 -7 M). Two compounds were excluded due to in vitro toxicity. The other 6 compounds were non-toxic and induced ERBB4, but not ERBB1, ERBB2 or ERBB3 phosphorylation in EFO-21 cells. Competition assays showed allosteric binding, and co-administration studies with NRG1 revealed that compounds potentiated NRG1-induced ERBB4 receptor dimerization up to 2.5 fold. Selected compounds showed significant dose-dependent antifibrotic effects in cultured human atrial and dermal fibroblasts and significantly attenuated AngII-induced LV myocardial fibrosis by 76%±26%, whereas cardiomyocyte CSA was not affected. Conclusions: We identified novel pyrimidine derivative small-molecule ERBB4 agonists with antifibrotic properties, both in vitro and in a mouse model of AngII-induced LV fibrosis.

Abstract 8914: Selective Phosphodiesterase-9 Inhibition With IMR-687 Mitigates Cardiac Hypertrophy and Renal Injury in Preclinical Mouse Models of Heart Failure With Preserved Ejection Fraction

Introduction: Through degradation of the cardio- and renal-protective second messenger cyclic GMP, phosphodiesterase-9 (PDE9) excess may contribute to cardiomyocyte hypertrophy, fibrosis, and renal dysfunction, common features in heart failure with preserved ejection fraction (HFpEF) development and progression. Hypothesis: Selective PDE9 inhibition with IMR-687 mitigates an adverse cardiac and renal phenotype in mouse models of HFpEF. Methods: Cardiac and renal responses to IMR-687 (60 mg/kg, 100 mg/kg) compared with vehicle were examined over 6-8 weeks in 3 adult male mouse models of HFpEF (1.5 mg/kg/d angiotensin-II infusion [ang-II]; uninephrectomy + 0.30 ug/h d-aldosterone infusion + 1% NaCl drinking water [neph-aldo]; and db/db [db]). Phenotyping included wheat germ agglutinin staining for cardiomyocyte cross-sectional area (CSA); RT-PCR for myocardial PDE9, natriuretic peptide, inflammatory and fibrosis marker transcript abundances; ELISA for plasma natriuretic peptides; and urinary albumin to creatinine ratio (UACR). Results: IMR-687 reduced median cardiomyocyte size (CSA) by 54, 58, and 35% compared with vehicle in the ang-II, neph-aldo, and db models, respectively; p &lt; 0.003 for all. Myocardial PDE9, NPPA, NPPB, COL3A1, and IL-1β expression were decreased by IMR-687 in all models (Table). Median plasma BNP levels (pg/mL) were lower in IMR-687 vs. vehicle treated mice in all models (ang-II: 2376 vs. 5757; neph-aldo: 1216 vs. 1860; db: 830 vs. 1216); p &lt; 0.007 for all, with similar findings for ANP (Table). UACR was lower in IMR-687 compared with vehicle treated mice in all models (Table). Heart rate and blood pressure did not differ between IMR-687 and vehicle treated mice. Conclusion: Selective PDE9 inhibition with IMR-687 was effective for prevention and treatment of cardiac hypertrophy and renal dysfunction in 3 different preclinical models of HFpEF. IMR-687 may be a promising candidate therapy for testing in clinical trials of human HFpEF.

Abstract 8955: Cardiopulmonary Phenotyping of Sex-Based Differences in a Feline Model of HFpEF

Introduction: Approximately 50% of all heart failure (HF) diagnoses can be classified as HF with preserved ejection fraction (HFpEF), which has no FDA approved therapies. HFpEF is more prevalent in females compared to males, but the underlying mechanisms for the development as a sex-based disorder are unknown. We previously described how slow progressive pressure overload (PO) in male felines recapitulates the HFpEF phenotype but have not investigated the female phenotype. Hypothesis: Females will develop a less severe HFpEF phenotype compared to males under the same pathological stress. Methods &amp; Results: Male (m) and female (f) domestic short felines (age 2mo) underwent aortic constriction (m: n=11; f: n=10) using a customized pre-shaped band or a sham procedure (m: n=7; f: n=7). Before surgery (baseline), there was no difference in body weight (BW) between groups and lung compliance was not different. 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. By 4mo post-surgery, both males and females had developed cardiac dysfunction and decreased lung compliance. At this time, females had significantly smaller BWs than males. Despite the difference in BW, LV wall thickness and changes in E/A ratio were similar in both sexes in banded vs. shams. Importantly, LV EF did not change in any group. There was a decrease in LA EF and increased LA/Ao in all banded animals. Invasive hemodynamics at 4mo post-surgery showed no differences between sexes for the systolic pressure gradient generated by aortic banding. Banded males had higher LV end-diastolic pressure vs. banded females (m: 15.0±2.7mmHg; f: 8.1±1.9mmHg). However, there was a trend towards prolongation of tau and lower dp/dt min in banded females, suggestive of abnormal relaxation. There were no differences between banded males and females in heart weight/BW or cardiomyocyte cross-sectional area and both developed fibrosis. Conclusions: Exposure of male and female felines to PO resulted in similar cardiac hypertrophy, fibrosis, and decreased lung compliance. Females had lower LVEDP than males suggesting they may be protected from diastolic dysfunction.

Abstract 9815: Role for Btg1 and Btg2 in Postnatal Cardiomyocyte Cell Cycle Arrest and Maturation

Background: Adult mammalian cardiomyocytes (CM) are predominantly post-mitotic and cannot proliferatively repair the heart following myocardial infarction (MI). Overexpression of the transcription factor Tbx20 in adult mouse CMs promotes proliferative cardiac repair post-MI, via mechanisms including direct repression of anti-proliferative genes p21 , Meis1 , and Btg2 . Btg2 (B-cell translocation gene 2), a tumor suppressor and transcriptional co-regulator, exhibits high structural and functional similarity with Btg1. However, both Btg1 and Btg2 (Btg1/2) are virtually uncharacterized in the heart. Here, we investigate the role of Btg1/2 in postnatal cardiac maturation. Methods and Results: By immunostaining in embryonic, neonatal, and adult C57BL/6 mouse hearts, the highest expression of Btg1/2 was observed in late fetal and early neonatal ventricles, concurrent with upregulation of other CM cell cycle inhibitors. In neonatal mouse CMs in vitro, siRNA-mediated loss of Btg2 leads to increased CM proliferation. In vivo , Btg1/2 constitutive single- and double- knockout (SKO and DKO respectively) mice exhibit normal heart weight-to-body weight ratios compared to age-matched wildtype (WT) controls, at postnatal day (P)7, P30, and 1 year after birth. Interestingly, at P7, DKO mice have significantly higher CM mitotic activity, as indicated by pHH3 staining, compared to WT. In addition, DKO mice also exhibit significantly smaller CM cross-sectional area at P7 compared to WT. However, by P15, CM mitotic activity and cell size are comparable between WT and Btg1/2 KO mice. Currently, siRNA-mediated knockdown of Btg1/2 in neonatal rat ventricular cardiomyocyte cultures and RNAseq studies are being performed, to assess the transcriptional regulatory roles of Btg1/2 in rodent CMs. Conclusions: Here, we highlight two novel regulators of postnatal CM maturation, Btg1 and Btg2, which are upregulated coincident with CM mitotic arrest in mice. Similar to p21 and Meis1, Btg1/2 depletion in mice induces a brief period of increased CM proliferative activity before onset of CM cell cycle arrest. Our results provide evidence for Btg1/2 working in tandem with other cardiac transcription factors and cell cycle regulators, to control CM mitotic arrest after birth.

STING protects against cardiac dysfunction and remodelling by blocking autophagy

BackgroundHeart failure, which is characterized by cardiac remodelling, is one of the most common chronic diseases in the aged. Stimulator of interferon genes (STING) acts as an indispensable molecule modulating immune response and inflammation in many diseases. However, the effects of STING on cardiomyopathy, especially cardiac remodelling are still largely unknown. This study was designed to investigate whether STING could affect cardiac remodelling and to explore the potential mechanisms.MethodsIn vivo, aortic binding (AB) surgery was performed to construct the mice model of cardiac remodelling. A DNA microinjection system was used to trigger STING overexpression in mice. The STING mRNA and protein expression levels in mice heart were measured, and the cardiac hypertrophy, fibrosis, inflammation and cardiac function were also evaluated. In vitro, cardiomyocytes stimulated by Ang II and cardiac fibroblasts stimulated by TGF-β to performed to further study effects of STING on cardiac hypertrophy and fibroblast. In terms of mechanisms, the level of autophagy was detected in mice challenged with AB. Rapamycin, a canonical autophagy inducer, intraperitoneal injected into mice to study possible potential pathway.ResultsIn vivo, the STING mRNA and protein expression levels in mice heart challenged with AB for 6 weeks were significantly increased. STING overexpression significantly mitigated cardiac hypertrophy, fibrosis and inflammation, apart from improving cardiac function. In vitro, experiments further disclosed that STING overexpression in cardiomyocytes induced by Ang II significantly inhibited the level of cardiomyocyte cross-section area and the ANP mRNA. Meanwhile, TGF-β-induced the increase of α-SMA content and collagen synthesis in cardiac fibroblasts could be also blocked by STING overexpression. In terms of mechanisms, mice challenged with AB showed higher level of autophagy compared with the normal mice. However, STING overexpression could reverse the activation of autophagy triggered by AB. Rapamycin, a canonical autophagy inducer, offset the cardioprotective effects of STING in mice challenged with AB. Finally, further experiments unveiled that STING may inhibit autophagy by phosphorylating ULK1 on serine757.ConclusionsSTING may prevent cardiac remodelling induced by pressure overload by inhibiting autophagy, which could be a promising therapeutic target in heart failure.7L95hvXtvL9B9C8hEcizcQVideo

Ventricular TLR4 Levels Abrogate TLR2-Mediated Adverse Cardiac Remodeling upon Pressure Overload in Mice

Involvement of the Toll-like receptor 4 (TLR4) in maladaptive cardiac remodeling and heart failure (HF) upon pressure overload has been studied extensively, but less is known about the role of TLR2. Interplay and redundancy of TLR4 with TLR2 have been reported in other organs but were not investigated during cardiac dysfunction. We explored whether TLR2 deficiency leads to less adverse cardiac remodeling upon chronic pressure overload and whether TLR2 and TLR4 additively contribute to this. We subjected 35 male C57BL/6J mice (wildtype (WT) or TLR2 knockout (KO)) to sham or transverse aortic constriction (TAC) surgery. After 12 weeks, echocardiography and electrocardiography were performed, and hearts were extracted for molecular and histological analysis. TLR2 deficiency (n = 14) was confirmed in all KO mice by PCR and resulted in less hypertrophy (heart weight to tibia length ratio (HW/TL), smaller cross-sectional cardiomyocyte area and decreased brain natriuretic peptide (BNP) mRNA expression, p < 0.05), increased contractility (QRS and QTc, p < 0.05), and less inflammation (e.g., interleukins 6 and 1β, p < 0.05) after TAC compared to WT animals (n = 11). Even though TLR2 KO TAC animals presented with lower levels of ventricular TLR4 mRNA than WT TAC animals (13.2 ± 0.8 vs. 16.6 ± 0.7 mg/mm, p < 0.01), TLR4 mRNA expression was increased in animals with the largest ventricular mass, highest hypertrophy, and lowest ejection fraction, leading to two distinct groups of TLR2 KO TAC animals with variations in cardiac remodeling. This variation, however, was not seen in WT TAC animals even though heart weight/tibia length correlated with expression of TLR4 in these animals (r = 0.078, p = 0.005). Our data suggest that TLR2 deficiency ameliorates adverse cardiac remodeling and that ventricular TLR2 and TLR4 additively contribute to adverse cardiac remodeling during chronic pressure overload. Therefore, both TLRs may be therapeutic targets to prevent or interfere in the underlying molecular processes.

Activated myofibroblasts promote cardiac hypertrophy and systolic dysfunction independently of cardiac fibrosis in experimental autoimmune myocarditis

Abstract Background/Introduction Heart-specific inflammation – myocarditis is a common cause dilated cardiomyopathy which is characterized by pathological tissue remodeling, ventricular stiffening, cardiomyopathy and heart failure. In experimental autoimmune myocarditis (EAM) susceptible mice immunized with alpha myosin heavy chain (αMyHC) and complete Freund's adjuvant (CFA) develop acute myocarditis driven by autoreactive CD4+ T cells that is followed by progressive fibrosis, cardiomyopathy and systolic dysfunction. Purpose The aim of the study was to investigate the role of cardiac fibroblasts and myofibroblasts in myocarditis and post-inflammatory dilated cardiomyopathy in mouse model of EAM. Methods EAM was induced in BALB/c mice by immunization with αMyHC/CFA. We used reporter mice expressing EGFP under collagen type I promoter (Coll-EGFP) and RFP under a control of α-smooth muscle actin (αSMA) promoter (αSMA-RFP) and transgenic αSMA-TK mice with ganciclovir-inducible ablation of proliferating myofibroblasts. Cardiac cells were quantified using flow cytometry. Cardiac fibroblasts (CD45-CD31-EGFP+) were sorted from healthy and myocarditis-positive (day 21) mice using BD FACSAria™ II Cell Sorter and analyzed for the whole genome transcriptomics by RNA sequencing. Echocardiography was performed on Vevo 2100 Imaging System. Cardiac fibrosis was assessed by Trichrome Massons's staining and hydroxyproline assay, whereas cardiac hypertrophy by analysing cross-sectional cardiomyocyte area. Profibrotic gene expression was assessed by qRT-PCR. Results The total number of cardiac fibroblasts (CD45-CD31-EGFP+) and the subset of myofibroblasts (CD45-CD31-EGFP+RFP+) remained unchanged at inflammatory (d21) and fibrotic stages (d40). Analysis of differentially expressed genes (min. 2x fold change, p value &amp;lt;0.05) pointed out activation of immune processes (mainly chemokine production), response to stress, cytoskeletal and extracellular matrix re-organization in cardiac fibroblasts in response to myocarditis. αSMA-TK mice treated with ganciclovir (from day 21) showed comparable percent of fibrotic area, but significantly reduced heart weight, decreased cardiomyocyte hypertrophy and improved ejection fraction and cardiac output at day 40 comparing to PBS-treated mice. Ganciclovir-treated mice showed also attenuated cardiac Acta2 and Srf but markedly enhanced Mmp2 expression. Conclusions In EAM model cardiac fibroblasts actively participate in proinflammatory and profibrotic responses, while activated myofibroblasts contribute to dilated cardiomyopathy development independently of cardiac fibrosis. Funding Acknowledgement Type of funding sources: Public grant(s) – National budget only. Main funding source(s): National Science Centre (Poland)

Adaptation of the heart to Frataxin depletion: Evidence that integrated stress response can predominate over mTORC1 activation.

Friedreich's ataxia (FRDA) is an inherited disorder caused by depletion of frataxin (FXN), a mitochondrial protein required for iron-sulfur cluster (ISC) biogenesis. Cardiac dysfunction is the main cause of death. Yet pathogenesis, and, more generally, how the heart adapts to FXN loss, remain poorly understood, though are expected to be linked to an energy deficit. We modified a transgenic (TG) mouse model of inducible FXN depletion that permits phenotypic evaluation of the heart at different FXN levels, and focused on substrate-specific bioenergetics and stress signaling. When FXN protein in the TG heart was 17% of normal, bioenergetics and signaling were not different from control. When, 8weeks later, FXN was ~ 97% depleted in the heart, TG heart mass and cardiomyocyte cross-sectional area were less, without evidence of fibrosis or apoptosis. mTORC1 signaling was activated, as was the integrated stress response, evidenced by greater phosphorylation of eIF2α relative to total eIF2α, and decreased protein translation. We interpret these results to suggest that, in TG hearts, an anabolic stimulus was constrained by eIF2α phosphorylation. Cardiac contractility was maintained in the 97%-FXN-depleted hearts, possibly contributed by an unexpected preservation of β-oxidation, though pyruvate oxidation was lower. Bioenergetics alterations were matched by changes in the mitochondrial proteome, including a non-uniform decrease in abundance of ISC-containing proteins. Altogether, these findings suggest that the FXN depleted heart can suppress a major ATP demanding process such as protein translation, which, together with some preservation of β-oxidation, could be adaptive, at least in the short term.

Structural and functional alterations in heart and skeletal muscle following severe TAC in mice: impact of moderate exercise training

BackgroundHeart failure (HF) is the leading cause of death in western countries. Cardiac dysfunction is accompanied by skeletal alterations resulting in muscle weakness and fatigue. Exercise is an accepted interventional approach correcting cardiac and skeletal dysfunction, thereby improving mortality, re-hospitalization and quality of life. Animal models are used to characterize underpinning mechanisms. Transverse aortic constriction (TAC) results in cardiac pressure overload and finally HF. Whether exercise training improves cardiac remodeling and peripheral cachexia in the TAC mouse model was not analyzed yet. In this study, 2 weeks post TAC animals were randomized into two groups either performing a moderate exercise program (five times per week at 60% VO2 max for 40 min for a total of 8 weeks) or staying sedentary.ResultsIn both TAC groups HF characteristics reduced ejection fraction (− 15% compared to sham, p < 0.001), cardiac remodeling (+ 22.5% cardiomyocyte cross sectional area compared to sham; p < 0.001) and coronary artery congestion (+ 34% diameter compared to sham; p = 0.008) were observed. Unexpectedly, peripheral cachexia was not detected. Furthermore, compared to sedentary group animals from the exercise group showed aggravated HF symptoms [heart area + 9% (p = 0.026), heart circumference + 7% (p = 0.002), right ventricular wall thickness − 30% (p = 0.003)] while muscle parameters were unchanged [Musculus soleus fiber diameter (p = 0.55), Musculus extensor digitorum longus contraction force (p = 0.90)].ConclusionThe severe TAC model is inappropriate to study moderate exercise effects in HF with respect to cardiac and skeletal muscle improvements. Further, the phenotype induced by different TAC procedures should be well documented and taken into account when planning experiments.

Ischemic stroke induces cardiac dysfunction and alters transcriptome profile in mice

BackgroundStroke can induce cardiac dysfunction in the absence of primary cardiac disease; however, the mechanisms underlying the interaction between the neurological deficits and the heart are poorly understood. The objective of this study was to investigate the effects of stroke on cardiac function and to identify the transcriptome characteristics of the heart.ResultsStroke significantly decreased heart weight/tibia length ratio and cardiomyocyte cross-sectional areas and increased atrogin-1 and the E3 ubiquitin ligase MuRF-1, indicating myocardial atrophy in MCAO-induced mouse hearts. RNA sequencing of mRNA revealed 383 differentially expressed genes (DEGs) in MCAO myocardium, of which 221 were downregulated and 162 upregulated. Grouping of DEGs based on biological function and quantitative PCR validation indicated that suppressed immune response and collagen synthesis and altered activity of oxidoreductase, peptidase, and endopeptidase may be involved in MCAO-induced cardiomyopathy. The DEGs were mainly distributed in the membrane or extracellular region of cardiomyocytes and acted as potential mediators of stroke-induced cardiac dysregulation involved in cardiac atrophy.ConclusionStroke induced a unique transcriptome response in the myocardium and resulted in immediate cardiac atrophy and dysfunction.

Abstract P471: Mechanisms Controlling Regression Of Cardiac Fibrosis By Removal Of Pressure Overload

Background: Antecedent conditions, like aortic stenosis, can induce left ventricular pressure overload (LVPO), that can lead to Heart Failure with Preserved Ejection Fraction (HFpEF). Myocardial fibrosis and stiffness are key characteristics of HFpEF. Cardiac fibroblasts are the primary cell type regulating ECM production and deposition. In previous studies, biopsies isolated at the time of SAVR surgery, to correct stenosis, and then at 1-year and 5-years post-SAVR showed reductions in hypertrophy and fibrosis demonstrating these processes can regress. However, cellular mechanisms, including fibroblast activity, are poorly defined. Objective: Define mechanisms that contribute to remodeling of ECM before and after LVPO. Methods: LVPO was induced using transverse aortic constriction (TAC). LVPO was relieved by removal of the band (unTAC) at 4 wks. Cardiomyocyte cross-sectional area (CSA), collagen volume fraction (CVF), and protein production was measured by histology and immunoblot for five time points: nonTAC, 2wk TAC, 4wk TAC, 4wk TAC+2wk unTAC, and 4wk TAC+4wk unTAC. Results: In response to LVPO, myocyte CSA increased by 23% at 2wk TAC and by 47% at 4wk. CVF increased by 64% and 204% at 2wk and 4wk TAC, respectively, versus nonTAC. In 2wk TAC hearts, SMA, a marker of fibroblast activation was increased as was production of two collagen cross-linking enzymes, lysyl oxidase (LOX) and LOXL2, in the absence of significant increases in markers of ECM degradation. After unloading, myocyte CSA decreased by 20% in 2wk unTAC versus 4wk TAC and CVF decreased by 38% in 4wk unTAC versus 4wk TAC. Coincident with decreases in CVF, levels of pro-MMP2 increased at 2wk unTAC as did levels of degraded collagen measured by collagen hybridizing peptide reactivity. Whereas markers of ECM deposition, LOX and LOXL2, were not increased in unTAC myocardium, a resurgence of SMA production occurred in 2wk unTAC. Conclusions: In LVPO hearts, hypertrophy was characterized by increases in myocyte CSA, greater CVF, and fibroblast activation with increased production of pro-fibrotic ECM. After unloading, hypertrophy and fibrosis significantly decreased accompanied by increases in ECM degrading activity and reductions in proteins that contribute to collagen assembly.

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.