Ventricular Tissue Research Articles

Male and female atria exhibit distinct acute electrophysiological responses to sex steroids

The electrophysiological properties of the hearts of women and men are different. These differences are at least partly mediated by the actions of circulating estrogens and androgens on the cardiomyocytes. Experimentally, much of our understanding in this field is based on studies focusing on ventricular tissue, with considerably less known in the context of atrial electrophysiology. The aim of this investigation was to compare the electrophysiological properties of male and female atria and assess responses to acute sex steroid exposure. Age-matched adult male and female C57BL/6 mice were anesthetized (4 % isoflurane) and left atria isolated. Atria were loaded with Di-4-ANEPPS voltage sensitive dye and optical mapping performed to assess action potential duration (APD; at 10 %, 20 %, 30 %, 50 %, and 70 % repolarization) and conduction velocity in the presence of 1 nM and 100 nM 17β-estradiol or testosterone. Male and female left atria demonstrated similar baseline action potential duration and conduction velocity, with significantly greater APD70 spatial heterogeneity evident in females. 17β-estradiol prolonged action potential duration in both sexes – an effect that was augmented in females. Atrial conduction was slowed in the presence of 100 nM 17β-estradiol in both males and females. Testosterone prolonged action potential duration in males only and did not modulate conduction velocity in either sex. This study provides novel insights into male and female atrial electrophysiology and its regulation by sex steroids. As systemic sex steroid levels change and intra-cardiac estrogen synthesis capacity increases with aging, these actions may have an increasingly important role in determining atrial arrhythmia vulnerability.

The ric-8b protein (resistance to inhibitors of cholinesterase 8b) is key to preserving contractile function in the adult heart

Resistance to inhibitors of cholinesterases (ric-8 proteins) are involved in modulating G-protein function, but little is known of their potential physiological importance in the heart. In the present study, we assessed the role of resistance to inhibitors of cholinesterase 8b (Ric-8b) in determining cardiac contractile function. We developed a murine model in which it was possible to conditionally delete ric-8b in cardiac tissue in the adult animal after the addition of tamoxifen. Deletion of ric-8b led to severely reduced contractility as measured using echocardiography days after administration of tamoxifen. Histological analysis of the ventricular tissue showed highly variable myocyte size, prominent fibrosis, and an increase in cellular apoptosis. RNA sequencing revealed transcriptional remodeling in response to cardiac ric-8b deletion involving the extracellular matrix and inflammation. Phosphoproteomic analysis revealed substantial downregulation of phosphopeptides related to myosin light chain 2. At the cellular level, the deletion of ric-8b led to loss of activation of the L-type calcium channel through the β-adrenergic pathways. Using fluorescence resonance energy transfer-based assays, we showed ric-8b protein selectively interacts with the stimulatory G-protein, Gαs. We explored if deletion of Gnas (the gene encoding Gαs) in cardiac tissue using a similar approach in the mouse led to an equivalent phenotype. The conditional deletion of the Gαs gene in the ventricle led to comparable effects on contractile function and cardiac histology. We conclude that ric-8b is essential to preserve cardiac contractile function likely through an interaction with the stimulatory G-protein and downstream phosphorylation of myosin light chain2.

Endothelial-mesenchymal transition, ventricular remodeling after myocardial infarction, and research progress of Chinese medicine intervention

Ventricular remodeling after myocardial infarction(VRAMI) is a pathological phenomenon triggered by the abrupt occlusion of coronary arteries, leading to myocardial ischemia and hypoxia. This intricate process encompasses alterations in the dimensions, composition, and elasticity of the ventricular tissue and reflects pathophysiological reactions and self-repair after cardiomyocytes are damaged. The characteristic pathological manifestation of VRAMI is the presence of myocardial fibrosis(MF), wherein fibrotic cardiac tissue undergoes a loss of contractile and relaxation capacity, ultimately culminating in heart failure(HF) and significantly impacting the patient's prognosis. Endothelial-mesenchymal transition(EndMT) is a biological process in which endothelial cells, in response to diverse pathological stimuli such as ischemia and hypoxia in the embryonic development period, undergo morphological alterations and functional impairment, progressively acquiring mesenchymal cell properties and ultimately differentiating into mesenchymal cells. The ongoing advancement of the EndMT process will result in an excessive buildup of collagen, thereby inducing structural harm to the myocardium and exacerbating the processes of VRAMI and MF. Recent investigations have demonstrated the pivotal involvement of EndMT in the pathological advancement of VRAMI. Consequently, a targeted intervention aimed at effectively impeding VRAMI, safeguarding cardiac function, and potentially serving as a novel therapeutic target for the prevention and treatment of VRAMI. This article provides a comprehensive review of recent Chinese and international literature, focusing on the role and pathophysiological mechanisms of EndMT in VRAMI. Additionally, it discusses the research progress of innovative targeted interventions using both traditional Chinese and Western medicine, so as to offer new insights and a theoretical foundation for the clinical treatment of the disease.

Sex-specific ventricular morphology, function, and tissue characteristics in arterial hypertension: a magnetic resonance study of the Hamburg city health cohort

ObjectiveTo determine the influence of arterial hypertension (AHT), sex, and the interaction between both left- and right ventricular (LV, RV) morphology, function, and tissue characteristics.MethodsThe Hamburg City Health Study (HCHS) is a population-based, prospective, monocentric study. 1972 individuals without a history of cardiac diseases/ interventions underwent 3 T cardiac MR imaging (CMR). Generalized linear models were conducted, including AHT, sex (and the interaction if significant), age, body mass index, place of birth, diabetes mellitus, smoking, hyperlipoproteinemia, atrial fibrillation, and medication.ResultsOf 1972 subjects, 68% suffered from AHT. 42% with AHT and 49% controls were female. Females overall showed a higher ejection fraction (EF) (LV: regression coefficient +2.4% [95% confidence interval: 1.7; 3.1]), lower volumes and LV mass (−19.8% [−21.3; −18.5]), and prolonged native septal T1 (+22.1 ms [18.3; 25.9])/T2 relaxation times (+1.1 ms [0.9; 1.3]) (all p < 0.001) compared to males. Subjects with AHT showed a higher EF (LV: +1.2% [0.3; 2.0], p = 0.009) and LV mass (+6.6% [4.3; 9.0], p < 0.001) than controls. The interaction between sex and AHT influenced mapping. After excluding segments with LGE, males (−0.7 ms [−1.0; −0.3 | ) and females with AHT (−1.1 ms [−1.6; −0.6]) showed shorter T2 relaxation times than the sex-respective controls (p < 0.001), but the effect was stronger in females.ConclusionIn the HCHS, female and male subjects with AHT likewise showed a higher EF and LV mass than controls, independent of sex. However, differences in tissue characteristics between subjects with AHT and controls appeared to be sex-specific.Clinical relevance statementThe interaction between sex and cardiac risk factors is an underestimated factor that should be considered when comparing tissue characteristics between hypertensive subjects and controls, and when establishing cut-off values for normal and pathological relaxation times.Key PointsThere are sex-dependent differences in arterial hypertension, but it is unclear if cardiac MR parameters are sex-specific.Differences in cardiac MR parameters between hypertensive subjects and healthy controls appeared to be sex-specific for tissue characteristics.Sex needs to be considered when comparing tissue characteristics in patients with arterial hypertension to healthy controls.Graphical

Asprosin as a potential new paracrine regulator in the heart

Abstract Funding Acknowledgements None. Background Asprosin was recently described as a novel hormone that is released by white adipose tissue upon fasting. However, a functional role of asprosin in human cardiovascular tissues has not been yet investigated at the tissue level. Asprosin is the C-terminal propeptide of the extracellular matrix (ECM) glycoprotein fibrillin-1 and is cleaved off from the pro-fibrillin-1 precursor by the endopeptidase furin. Fibrillin-1 is expressed in the heart and aorta, and FBN1 mutations are causative for aortic aneurysm formation and cardiomyopathy. Whether asprosin is also present in cardiac tissues and utilized by cardiac resident cells remains unknown. Purpose In the present study, we investigated the localization and distribution of asprosin protein in human atrial and ventricular heart tissue. Methods Human heart tissue was obtained from patients undergoing aortic valve replacement. In addition, we used ventricular tissue from mice. Cryosections from human (n=8) and mouse (n=8) heart samples were analysed by immunohistochemistry. The anti-asprosin antibodies were raised against human or mouse asprosin respectively and applied in combination with anti-CD31/PECAM, an endothelial cell marker, or anti-sarcomeric alpha-actinin, a Z-line marker. The immunofluorescence of incubated specimens was examined by confocal microscopy. Results Our data suggest that asprosin is localized in myocardium in different cell types: cardiomyocytes (Figure 1 a-d), arterial smooth muscle cells (Figure 1 a), micro- and vascular endothelial cells (Figure 1 d), and with the lowest intensity, in periarterial located epicardial adipocytes (Figure 1 e). In cardiomyocytes, incubation with anti-asprosin resulted in a high signal intensity. Asprosin immunoreactivity was observed: in intercalary discs (Figure 1 b-d), as striated pattern in the sarcoplasm, and as weak signal in the perinuclear area (Figure 1 b, c). In human tissue, the anti-asprosin signal was about four times higher in intercalated discs than in the sarcoplasm. The distribution pattern in ventricular cardiomyocytes of mice were similar. Conclusion Our results show that in human myocardium, asprosin localises mainly intracellular. Asprosin accumulations were found in intercalary discs. In short, asprosin was found at locations that are known to be crucial for regulation of cardiac function. Intracellular presence of asprosin may indicate cellular utilization by uptake from extracellular asprosin pools. Whether these pools are replenished exclusively by resident cells or by other tissues such as WAT is currently unknown. However, further research is needed to prove this hypothesis. Figure. 1. Confocal microscopy of asprosin localization in human myocardium. Cryosections incubated with anti-asprosin (red) or combined with anti-alpha actinin (sarcomeric) or anti-CD31/PECAM (green) antibodies and DAPI (blue, nuclei). SM: vascular smooth muscle cells, BV: blood vessels, Arrowheads: Intercalated disks.

2-Aminoethoxydiphenyl borate prolongs atrial and shortens ventricular action potential duration through modulation of ion channels in the sarcolemma

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): PPP allowance, Health holland ZonmW Background 2-Aminoethoxydiphenyl Borate (2-APB) has been shown to prevent atrial fibrillation in animal models, supposedly through its inhibitory action on the intracellular IP3 receptor and subsequent calcium regulation. However, 2-APB may modulate other ion channels or transporters and the cellular mechanisms associated with the prevention of atrial fibrillation are not well established. We aimed at unravelling the cellular effects of 2-APB on atrial and ventricular action potential and currents. Methods Rabbit (New Zealand White) left atrial and ventricular cardiomyocytes were isolated from Langendorff-perfused hearts by enzymatic dissociation. Adult human atrial cardiomyocytes were obtained by enzymatic dissociation from left atrial appendages (LAA) routinely removed from AF patients undergoing minimally invasive surgical pulmonary vein isolation. Action potentials (APs) and K+ currents were recorded at 36.5 °C with the amphotericin-B-perforated or whole cell patch clamp technique. RNA was isolated from left atrial and ventricular tissue and sequenced on an Illumina HiSeq4000 platform. Results In rabbit atrial cardiomyocytes, extracellular application of 5 uM 2-APB had no effect on action potential duration (APD), but extracellular application of 50 uM 2-APB prolonged the APD by 40% and inhibited an outward K+-current. Inversely, extracellular application of 5 uM 2-APB shortened the APD of rabbit left ventricular cardiomyocytes by 20% while extracellular application 50 uM 2-APB did not prolong the APD. Additionally, 2-APB did not modulate K+ currents in ventricular rabbit cardiomyocytes. Intracellular application (in the patch pipet) of 50 uM 2-APB did not have any effects on atrial APD, suggesting that IP3 receptor inhibition is not involved. However, subsequent application of 50 uM 2-APB in the bath prolonged the APD by 40% indicating that 2-APB prolongs atrial APD by inhibiting one or more K+ channel types in the sarcolemmal membrane from the extracellular site. RNA sequencing analysis revealed potential targets channel including TRP and Kv channels differentially expressed in atria versus ventricle. In human atrial cardiomyocytes from AF patients, application of 50 uM 2-APB prolonged APD by 25%. Conclusions 2-APB prolongs rabbit and human atrial APD and shortens rabbit ventricular APD in a concentration dependent manner, most likely due to modulation of sarcolemmal K+ channels, differentially expressed in the two cell types. Pharmacological studies with 2-APB may reveal novel cellular mechanisms identifying potential new targets for the treatment of atrial fibrillation.

High-throughput proteomic analysis unveils metabolic and mitochondrial signaling rewiring by chronic ivabradine treatment in duchenne muscular dystrophy

Abstract Funding Acknowledgements Type of funding sources: Public Institution(s). Main funding source(s): Austrian Science Fund (FWF) Objective Ivabradine (IVA) is indicated in symptomatic treatment of chronic stable angina, heart failure, and also in those who are unable to tolerate or have contraindications to the use of beta-blockers. It has been showed IVA may have cardiovascular benefits in Duchenne muscular dystrophy (DMD) patients. This study was aimed to investigate the sustained impact of chronic ivabradine (IVA) administration on cardiac function and potential underlying mechanism using high throutput proteomic analysis. Methods DMDmdx male and Sprague–Dawley wt (Sprague–Dawley) male rats were randomly allocated to vehicle (n = 6) or IVA (n=6; 10 mg/kg/day via drinking water for four months). Transthoracic echocardiography and unbiased proteomic analysis were performed to assess cardiac function and left ventricular (LV) tissue, respectively. Protein-protein interactions were graphically represented, and cluster analysis with subsequent enrichment analyses was conducted. Results Chronic IVA treatment significantly enhanced the LV ejection fraction (p&amp;lt;0.05 compared to vehicle-treated DMDmdx rats). Proteomic data identified possible transcription factors (SPI1, IRF1, PPARA), consistent with previous studies. The reduction in copper metabolic changes associated with DMD can be attributed to the upregulation of Atox1 following IVA treatment. Mitochondrial dysfunction was effectively mitigated by IVA, as indicated by the different abundance of mitochondrial proteins. In addition, intercellular adhesion molecule 1 showed a reduction in the number of animals treated with ivabradine, indicating a further positive effect of the treatment. Conclusion In summary, this study demonstrated the beneficial effects of IVA in DMDmdx rat hearts. Cluster analysis of proteomic data revealed notable changes in cardiac metabolism, inflammation, and mitochondrial function. Ivabradine has emerged as a potential therapeutic approach to address these shifts, while proteomic pathway analysis may uncover new drugable targets to alleviate cardiomyopathy progression in DMD.Interaction of IvabradinProtein-protein interaction network

Beyond the matrix: exploring tenascin-c (TNC) as a crucial player in diabetic cardiovascular dysfunction

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Burgermeister Found Wien-Project number : 21001 Introduction Diabetic cardiomyopathy (CMP) is a complex manifestation of diabetes-linked cardiac and vascular dysfunction, but the molecular pathogenesis is still largely unknown. Notably the expression of Tenascin-C (TNC), an extracellular matrix glycoprotein, contributes to the development of cardiovascular diseases and diabetic patients have elevated serum TNC levels. However, the role and mechanism of TNC to diabetic CMP progression remains elusive. Purpose Here, we longitudinally evaluated functional and molecular role of TNC in CMP-induced cardiovascular dysfunction in a murine model. In addition, we used RNA sequencing with cardiac tissues from non-diabetic and diabetic wild type (wt) and TNC KO mice for further investigation. Methods Diabetes was induced in adult male mice, wt (AJ) and TNC-KO strains, by repeated Streptozotocin (STZ) injections (50 mg/kg). Echocardiography, myography, hemodynamics, histology, molecular and cellular analyses were performed to assess the role of TNC in diabetes-associated CV complications. Additionally, RNA-sequencing was analyzed in left ventricular (LV) tissue samples from diabetic and non-diabetic wt and TNC-KO mice providing further molecular insights. Results TNC KO mice showed preserved LV ejection fraction, and endothelium-dependent relaxation (p&amp;lt;0.05 and p&amp;lt;0.001, respectively), reduced cardiac fibrosis and distinctive coronary vessel characteristics, implying enhanced LV perfusion. In addition, the plasma levels of oxidative stress marker malondialdehyde was significantly alleviated in TNC KO diabetic mice in comparison to diabetic wt mice. Cardiomyocytes from diabetic wt mice exhibited stiffness (Fpassive and Factive), which was corrected to control level in cardiomyocytes from TNC KO diabetic hearts. Further, ex vivo isolated heart experiments demonstrated that the administration of recombinant human TNC (80 ng/ml) resulted in a significant reduction in LV hemodynamics (p&amp;lt;0.01) and myocardial energetics (ATP levels, p&amp;lt;0.01). Analysis of RNA sequencing data demonstrated that decreased expression of matrix remodeling genes Serpin1 and Ccn1 links to alleviation of fibrosis in TNC KO diabetic heart. Furthermore, Gene Ontology (GO) enrichment analysis shed light on mitochondrial changes in diabetic hearts. Our pathway analysis also identified that Hsp90aa1 as a crucial gene associated with preprotein import into the mitochondrial membrane, may suggest potential mitochondrial dysfunction in diabetic hearts. Conclusion In conclusion, lack of TNC improved long-term cardiac function in diabetes by reducing cardiac fibrosis, vascular dysfunction, oxidative stress and cardiac energetics. Thus, inhibition of TNC may prevent the diabetic heart from extensive fibrosis and energetics dysfunction that accelerates the development of HF, providing a potential targeted therapy.

Soluble guanylate cyclase stimulator as an emerging therapeutic option in the management of arrhythmias in heart failure rat model

Abstract Funding Acknowledgements Type of funding sources: Foundation. Main funding source(s): This research was supported by VEGA grant no. 2/0002/20 and 2/0006/23, the Slovak Research and Development Agency under contract no. 21-0410, European Regional Development Fund: ITMS2014+: 313011AVG3. This research was also partially supported by the Ministry of Health of the Czech Republic within the project for the development of the research organization [grant number 00023001 (IKEM)—institutional support] and also supported by the project National Institute for Research of Metabolic and Cardiovascular Diseases (Program EXCELES, Project No. LX22NPO5104)—Funded by the European Union—Next Generation EU Heart failure (HF) is a complex clinical syndrome characterized by a decrease in the efficiency of the heart pump, leading to a decline in hemodynamic status and cardiac remodelling, that can contribute to the formation of a substrate for arrhythmias. Antiarrhythmic drug therapy is still suboptimal and current therapies are not efficacious enough. The purpose of the current study was therefore to examine the efficiency of nitric oxide (NO)/soluble guanylyl cyclase (sGC)/cyclic guanosine monophosphate (cGMP) stimulator. We used as an experimental model male hypertensive Ren-2 transgenic rats (TGR, n = 16), normotensive Hannover Sprague–Dawley rats (HSD, n = 17), and a rat model of HF surgically induced by aortocaval fistula (ACF) in rats of both strains (n = 27). After ACF induction were rats treated by sGC stimulator BAY41-8543 (3 mg/kg/day for 30 weeks) alone or combined with angiotensin-converting enzyme inhibitor (ACEi) Trandolapril (0.25 mg/kg/day for 30 weeks). Age of the animals at the end of the experiment was 40 weeks. Left ventricle tissue and plasma samples were used for further analyses. Treatment by sGC stimulator significantly decreased rats' mortality, and systolic blood pressure, and significantly increased levels of antioxidant enzyme superoxide dismutase 1, matrix metalloproteinase 2, total and phosphorylated connexin 43 as well as protein kinase C epsilon, implicated in remodelling of extracellular matrix and intercellular communication, in the left ventricle of TGR rats. Application of sGC stimulator slightly normalized elevated collagen deposition and hydroxyproline content in the left ventricular tissue of TGR rats. Unfortunately, we did not observe any effect of the sGC stimulator in the TGR ACF group. These results support the hypothesis that sGC stimulators might represent a class of drugs suitable for combating heart failure with partially anti-arrhythmic potential, but further studies are needed.

Increased perivascular fibrosis and pro-fibrotic cellular transition in intramyocardial blood vessels in patients with myocardial infarction

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): China Scholarship Council Background Myocardial infarction (MI) is pathologically characterized by irreversible myocardial necrosis caused by ischemia. Intramyocardial vascular dysfunction is believed to increase the risk of MI. In this study, we investigated intramyocardial blood vessels in deceased patients during the early and chronic phases of MI to explore the involvement of perivascular fibrosis and pro-fibrotic cellular transitions in the pathological process of MI. Methods Left ventricular tissue (LV) was obtained from the infarction area of autopsied patients with early-phase MI (3-6 hours old; n=23), chronic-phase MI (5-14 days old; n=12), and from non-infarcted controls (n=14). We quantified perivascular fibrosis using EVG staining and fibroblast activation protein (FAP) expression using immunohistochemistry. Co-localization of smooth muscle actin (SMA) or CD31 with fibroblast marker S100A4 indicative of transition of smooth muscle cells (SMC) and endothelial cells (EC) toward fibroblast-like cells in intramyocardial vessels was quantified using immunofluorescent microscopy. Results Compared to controls (61.03%), perivascular fibrosis was significantly elevated in MI patients (early-phase 77.20%; chronic-phase 82.58%)(p&amp;lt;0.0001), with the highest level observed in the infarct cores of chronic-phase patients (95.18%). Compared to controls, FAP expression was 3.5-fold higher in early-phase- and 15.3-fold higher in chronic-phase MI patients (p&amp;lt;0.05), wherein FAP expression again was highest in the infarct cores. Furthermore, in both early- and chronic-phase MI, SMC- and EC fibroblast-like cellular transition was increased. The fraction of SMA+S100A4+ vessels was significantly higher in early-phase MI (31.96%) and chronic-phase MI (21.9%: border zone; 37.25%: infarct core) compared to controls (8.95%)(p&amp;lt;0.05). Similarly, the fraction of CD31+S100A4+ area was significantly increased in early-phase MI (10.14%) and chronic-phase MI (8.31%: border zone 10.15%: infarct core) compared to controls (2.67%)(p&amp;lt;0.05). Conclusion We observed increased perivascular fibrosis, fibroblast activation and fibroblast-like cellular transition toward a pro-fibrotic phenotype of vascular cells in intramyocardial blood vessels in MI patients, that may contribute to the development of MI. The further increase of FAP expression and perivascular fibrosis, particularly in the infarct core, in the chronic-phase suggest that MI itself can exacerbate fibroblast activation and perivascular fibrosis, theoretically increasing the risk of reinfarction.FAP expression and perivascular fibrosispro-fibrotic vascular cellular transitio

Ventricular hyperinnervation in a mouse model of catecholaminergic polymorphic ventricular tachycardia

Abstract Funding Acknowledgements Type of funding sources: Foundation. Main funding source(s): European Society of Cardiology Basic Research Fellowship. Dutch Heart Foundation Dekker Grant Background Inherited arrhythmia syndromes are a leading cause of sudden cardiac death in young and otherwise healthy patients. They are often caused by mutations in genes that encode ion channels or transporters, leading to conditions such as Catecholaminergic Polymorphic Ventricular Tachycardia (CPVT). CPVT is caused by mutations in RYR2 (encoding ryanodine receptor 2, RyR2). In arrhythmia research, investigation into the effects of these mutations have exclusively been performed in cardiac cells. However, RyR2 is also present in neuronal tissue, including intracardiac neurons [1] (which modulate cardiac function). Moreover, patients often present with clinical signs of autonomic nervous system (ANS) dysfunction, and treatment strategies frequently target the ANS. Aim Our novel research line aims to investigate the neuronal phenotype induced by RyR2 mutations, using a CPVT mouse model to assess functional alterations as well as broader autonomic remodelling. Results Using immunocytochemistry, we reveal for the first time that RyR2 is also expressed in mouse stellate ganglia (crucial autonomic modulators of cardiac function). Through analysis of published RNA sequencing datasets, we find that RYR2 is more abundantly expressed in both stellate ganglion and intracardiac neurons than characteristic neuronal markers such as CHAT, SYN1 and SCN8A [2,3]. Functional patch clamp investigation of isolated stellate ganglion neurons have revealed two distinct populations based on their patterns of action potential (AP) firing, identifying both phasic-firing and tonic-firing type neurons. Investigation of an established CPVT mouse model (RyR2-R2474S) has thus far not revealed any differences in the AP firing frequency of isolated stellate ganglion neurons during sustained depolarising stimuli of various amplitudes. Assessment of calcium homeostasis and neurotransmitter release is currently ongoing. We have furthermore investigated broader autonomic remodelling using immunohistochemistry in mouse heart cryosections. Neuronal innervation density was assessed by staining 10 µm sections of mid-ventricular myocardium for the sympathetic neuron marker tyrosine hydroxylase (TH). Quantification of the TH-positive area revealed a significant increase in the percentage of sympathetic neuronal innervation in ventricular tissue of CPVT mice (5.7% wild-type vs 7.2% RyR2-R2474S, p=0.0253, N=6). Conclusions The neurons that modulate heart function (stellate ganglion and intracardiac neurons) abundantly express RyR2. The RyR2-R2474S mutation leads to significant sympathetic hyper-innervation of ventricular myocardium, which may have important consequences for neurotransmitter release and hence cardiac (electrical) function and arrhythmogenesis.

Leaky RyR2 channels as pro-arrhythmic trigger in the PKP2-deficient atrial myocardium

Abstract Funding Acknowledgements Type of funding sources: Public Institution(s). Main funding source(s): American Heart Association National Institutes of Health Introduction Atrial arrhythmias, like atrial fibrillation, occur in 20–40% of patients with Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC). Atrial fibrillation in ARVC patients is often associated with an increased risk of sustained ventricular arrhythmias and inappropriate ICD shocks. However, the pathophysiology behind the development of atrial arrhythmias in ARVC is far from clear. A genome-wide association study, based on UK-biobank data, revealed a link between atrial fibrillation and variants in the desmosomal gene plakophilin-2 (PKP2). Previous studies show that PKP2 is necessary to maintain the transcription of genes that control intracellular calcium (Ca2+) cycling and that loss of PKP2 expression in adult mouse ventricular tissue leads to disruption of intracellular Ca2+ homeostasis. In this study, we test the hypothesis that loss of PKP2 expression leads to pro-arrhythmic changes in atrial myocytes. Methods Experiments were carried out using a cardiac-specific, tamoxifen (TAM)-activated PKP2 knockout murine model (PKP2-cKO). Cre-negative, flox-positive, TAM-injected littermates were used as controls. We used RNA sequencing, quantitative imaging modalities, as well as biochemical and electrophysiological methods to study the functional and structural properties of atrial PKP2cKO tissue. Studies were carried out 21 days post-tamoxifen injection, a time point at which an arrhythmogenic cardiomyopathy of right ventricular predominance is manifest. Results In contrast to the previously-reported observations in PKP2cKO ventricular myocytes, atrial PKP2cKO myocytes presented no significant differences in Ca2+ transient dynamics, SR load and action potential duration. However, PKP2cKO atrial myocytes showed an increased frequency and amplitude of Ca2+ sparks, in combination with increased diastolic Ca2+ levels as well as an increase in cellular ROS levels. RNAseq data showed an under-representation of mRNA for Integrinα7, a stabilizer of Ryr2 that reduces its phosphorylation. Separate studies showed that PKP2cKO atrial myocytes present impaired relaxation and enhanced sarcomere shortening, a finding consistent with a downregulation in the expression of Myosin Binding Protein C. Isoproterenol (ISO) exposure further increased the frequency of Ca2+ sparks and the levels of diastolic Ca2+, and these effects were reversed by acute (30 minute) in vivo treatment with Ryanodex (medical grade Dantrolene), a known RyR blocker. Conclusion Loss of PKP2 expression affects cellular Ca2+ handling and electrophysiology differently in the atrial versus ventricular myocardium. We speculate that an increased probability of opening of Ryr2 channels, caused by ROS-induced RyR2 oxidation and/or Integrinα7-induced RyR2 phosphorylation, serve as pro-arrhythmic trigger in the PKP2-deficient atrial myocardium, that these effects can be amplified by a catecholaminergic input and that RyR blockers can dampen these pro-arrhythmic effects.

Cryopreservation of human adult ventricular tissue for the preparation of viable myocardial slices

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – EU funding. Main funding source(s): REGeRNA Myocardial slices are ultra-thin slices of living adult myocardium which can be cultured. As a multicellular 3-D culture model, myocardial slices offer a novel opportunity to investigate how adult cardiomyocytes (CMs) interact with other cardiac cell types and the extracellular matrix, while providing long-term preservation of CMs cytoarchitecture and electrical phenotype. Additionally, myocardial slices are a new tool in drug discovery by allowing to test chronic treatments, as opposed to isolated CMs which are limited to acute timepoints. Despite their benefits over other cardiac preparations, myocardial slices also have several limitations, of which one is the quality of the slices. The main determinant of myocardial slice quality is the procedure by which the cardiac tissue block is handled. Current methods depend on the preparation of slices directly after tissue excision, therefore limiting the moment when the experiment is performed. We developed a protocol for the cryopreservation of human adult ventricular tissue allowing preparation of viable myocardial slices afterwards. Fresh and cryopreserved cardiac tissue from donor hearts was processed and evaluated for viability, tissue integrity, and inflammatory markers using molecular biology and histological assays. The tissue samples retained viability, biomass, and tissue and vascular integrity following cryopreservation compared to fresh tissue. Additionally, we compared myocardial slices obtained from fresh or cryopreserved tissue and cultured for 24 hours. Histologically, normal cytomorphological features and gap junctions between CMs were preserved in all slices. Comparable retention of tissue viability and structural integrity post cryopreservation (4-6 weeks) and culture (up to 7 days) was observed in cardiac samples from 3 additional donors. In summary, cold storage extends the time-interval between sample collection and slice preparation, allowing for more long-term, complex endpoints. Moreover, efficient banking of cryopreserved cardiac samples from various donors and disease states is critical for regular use of myocardial tissue slices in drug discovery and development. Additional research on the effects of cryopreservation on different cardiac cell types will allow to improve donor organ management to extend the donor pool and increase utilization rate.

Hypertension-induced cardiac pro-arrhythmic disorders of connexin-43 and extracellular matrix are attenuated in hairless versus wild-type of spontaneously hypertensive rats

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Development Agency under the contract no. 21-0410 VEGA grants no. 2/0002/20, 2/0006/23 Background Mechanical dysfunction and occurrence of malignant ventricular fibrillation (VF) are hallmarks of hypertensive heart disease and major health issue. Spontaneously hypertensive rats (SHR) that imitates human primary hypertension are prone to develop VF, mainly due to myocardial remodelling associated with disorders of electrical coupling protein connexin-43 (Cx43) and extracellular matrix (ECM) resulting in electrical instability. However, it is not known whether postnatal acclimation of hairless strain of SHR to surrounding temperature may induce cardio-protection. Therefore, we aimed to explore Cx43 and ECM alterations as well as susceptibility to inducible VF in hairless versus wild type SHR. Design and Methods Six-month-old wild type SHR males and females and hairless SHR housed at standard 22°C were examined. Biometric parameters, including electro- and echocardiography were registered. Left ventricular tissue was used for immunolabeling of Cx43 to reveal its topology and for western blotting to determine protein levels of Cx43 and its function modulating protein kinases, PKCε, PKCδ and PKCα as well as for ECM markers, TGF-β, SMAD2/3, MMP-2, collagen-1 and its histological deposition. Susceptibility of the heart to electrically-inducible VF was tested using isolated perfused heart technique. Key results Comparing to wild type males, hairless SHR exhibited less pronounced prolongation of QT and QRS interval as well as an increase of ejection fraction. Myocardial Cx43 and its variant phosphorylated at serine-368, which preserve electrical coupling, were increased and pro-arrhythmic cardiomyocyte Cx43 topology was attenuated in males and females hairless vs wild type SHR. Moreover, the level of β-catenin, which ensures mechano-electrical coupling, was also increased in hairless SHR. On the other hand, collagen-1 and hydroxyproline were lower and the TGF-β1 and SMAD2/3 proteins were suppressed in males hairless vs wild type SHR. Myocardial ECM remodelling was less pronounced in females regardless rat strain. Hairless SHR males were less susceptible to inducible VF compared to wild type SHR, while females were less prone to develop VF regardless the strain. In conclusion, our findings imply that postnatal acclimation of hairless SHR is accompanied by attenuation of hypertension-induced adverse down-regulation of Cx43 and up-regulation of extracellular matrix proteins. It may contribute, at least in part, to the protection from malignant cardiac arrhythmias and mechanical dysfunction.

FgF23 and soluble klotho effects on the myocardium: an ex vivo study

Abstract Funding Acknowledgements Type of funding sources: Foundation. Main funding source(s): German Center for Cardiovascular research Background Fibroblast Growth Factor 23 (FGF23) and soluble Klotho (sKL) play a critical role in mineral homeostasis in the body by acting on the kidney to regulate phosphate levels. Circulating FGF23 levels rise in patients with kidney disease and dysregulation of the FGF23 –sKL- axis is a common phenomenon in uremic cardiomyopathy. Studies have shown that elevated FGF23 levels induce cardiac hypertrophy by targeting cardiac myocytes via FGF receptor isoform 4 (FGFR4), while sKL mitigates these effects and may also exert an independent protective effect on the heart(1,2). Purpose We aimed to study the effects of FGF23 and sKL on myocardial contractility, calcium handling and molecular signaling pathways in the human heart using an ex vivo model of cultured contracting myocardial slices. Methods We obtained human heart slices from explanted hearts from patients undergoing cardiac transplantation at the LMU Klinikum Munich, Germany. The 300 µm thick slices were cultured under continuous stimulation (1 Hz, 3 ms pulse width) with 1 mN preload, and contractile function were recorded continuously. Slices with vehicle, recombinant FGF23 protein (100ug/ml), recombinant sKL protein (200ug/ml) and both FGF23((100ug/ml)+sKL (200ug/ml) were continuously monitored over 10 days. We checked for mRNA expression using RT PCR. Results Treatment of human left ventricular tissue with recombinant FGF23 protein resulted in enhanced mRNA expression of the FGFR4. sKL treatment alone induced downregulation of the FGFR4 gene and mitigated upregulation of FGFR4 in FGF23+ sKL treated slices. Post pause potentiation (PPP), assessed by pausing the stimulation of the slices for 120s and then measuring the relative height of the first beat after resumption of pacing, is an indirect measure of sarcoplasmic reticulum Ca2+ handling capacity. PPP was reduced in FGF23 treated slices and heightened in the slices with sKL compared to vehicle treated ones, indicating that FGF23 and sKL play a role in intracellular Ca2+ handling. Conclusions sKL and FGF23 have opposite effects on human cardiac muscle with sKL mitigating FGF23-induced upregulation of FGFR4. Furthermore, sKL improves, while FGF23 impairs myocardial calcium handling . As altered calcium handling may also be involved in hypertrophic signaling altered calcium handling may provide a means by which FGF23 promotes and sKL inhibits myocardial hypertrophy. sKL is advocated as a promising candidate in exploring it therapeutic role in FGF23 mediated cardiomyopathy. We intend to advance our understanding of sKL-FGF23signaling mechanisms by combining transcriptomic analysis with functional data in this model of myocardial slice culture.

Vasodilator reactive oxygen species ameliorate perturbed myocardial oxygen delivery in exercising swine with multiple comorbidities.

Multiple common cardiovascular comorbidities produce coronary microvascular dysfunction. We previously observed in swine that a combination of diabetes mellitus (DM), high fat diet (HFD) and chronic kidney disease (CKD) induced systemic inflammation, increased oxidative stress and produced coronary endothelial dysfunction, altering control of coronary microvascular tone via loss of NO bioavailability, which was associated with an increase in circulating endothelin (ET). In the present study, we tested the hypotheses that (1) ROS scavenging and (2) ETA+B-receptor blockade improve myocardial oxygen delivery in the same female swine model. Healthy female swine on normal pig chow served as controls (Normal). Five months after induction of DM (streptozotocin, 3 × 50mgkg-1 i.v.), hypercholesterolemia (HFD) and CKD (renal embolization), swine were chronically instrumented and studied at rest and during exercise. Sustained hyperglycemia, hypercholesterolemia and renal dysfunction were accompanied by systemic inflammation and oxidative stress. In vivo ROS scavenging (TEMPOL + MPG) reduced myocardial oxygen delivery in DM + HFD + CKD swine, suggestive of a vasodilator influence of endogenous ROS, while it had no effect in Normal swine. In vitro wire myography revealed a vasodilator role for hydrogen peroxide (H2O2) in isolated small coronary artery segments from DM + HFD + CKD, but not Normal swine. Increased catalase activity and ceramide production in left ventricular myocardial tissue of DM + HFD + CKD swine further suggest that increased H2O2 acts as vasodilator ROS in the coronary microvasculature. Despite elevated ET-1 plasma levels in DM + HFD + CKD swine, ETA+B blockade did not affect myocardial oxygen delivery in Normal or DM + HFD + CKD swine. In conclusion, loss of NO bioavailability due to 5 months exposure to multiple comorbidities is partially compensated by increased H2O2-mediated coronary vasodilation.

Correlation between ventricular local impedance and tissue composition by MRI in chronic infarction

Abstract Background Local impedance (LI) mapping is feasible and provides additional tissue characterization of the ventricular tachycardia substrate. Data on tissue composition underlying different LI values are lacking. Purpose To correlate LI with tissue composition evaluated by magnetic resonance imaging (MRI) in a chronic myocardial infarction (MI) swine model. Methods One-month after a non-reperfused anterior MI, eighteen Landrace X Large White pigs underwent delayed-enhancement MRI (deMRI) and endocardial LI mapping. deMRI images were post-processed off-line with commercially available dedicated software; scar subtypes (with thresholds set at 40-60% of maximal pixel signal intensity [PSI]), border-zone corridors and left ventricular wall thickness were measured. LI thresholds were set using the blood-pool LI value to define low, intermediate, and high tissue resistance subtypes. LI maps were co-registered with deMRI for analyses. Results Low LI zones correlated with deMRI dense and transmural scar (exhibiting endo and epicardial PSI &amp;gt;60% in 91% and 80% of the cases, respectively). Intermediate LI tissue exhibited predominantly subendocardial scar with more heterogeneous composition (8%, 47% and 45% of the points had &amp;lt;40%, 40-60% and &amp;gt;60% endocardial PSI, respectively), and with less epicardial involvement (50% of points had epicardial PSI &amp;lt;40%). Border-zone corridors co-localized with intermediate LI tissue in most of the cases (77%). Low LI zones exhibited more pronounced wall thinning compared to intermediate LI tissue (p&amp;lt;0.001) (Figure 1). Conclusions LI correlated with scar density and transmurality on deMRI. Areas of low LI had higher proportion of dense, transmural scar and wall thinning compared to intermediate LI areas. MRI-detected border-zone corridors colocalized with intermediate LI in most cases.LI and deMRI data (endo and epi scar)LI and deMRI data (tissue thickness)

Linking ablation curves with transmural lesions using a thoracoscopic bipolar biparietal irrigated radiofrequent clamp

Abstract Background The cornerstone of atrial fibrillation (AF) ablation is the achievement of long-lasting transmural lesions. However, it is currently unknown when transmurality is reached during ablation using the thoracoscopic bipolar biparietal irrigated radiofrequent (RF) clamp. Purpose To study the relation between transmural lesions and their corresponding ablation curves using a thoracoscopic bipolar biparietal irrigated RF clamp in pigs. Methods In 4 ventilated pigs, endo-epicardial beating-heart ablation was conducted via sternotomy. In the first 3 pigs, 1 up to 4 ablations were performed at multiple sites on right and left ventricular tissue. Objective indicators of transmurality in the ablation curves were retrospectively identified by visual inspection. After the ablation procedure, the pigs were sacrificed and subsequent macroscopic evaluation was performed. The ablated tissue was excised and immersed in 2,3,5-triphenyltetrazolium chloride-staining at 36 °C. After 90 minutes the lesions were sectioned longitudinally and photographed. The ablated nonviable muscle appears white, and the viable muscle appears red (see Figure 1). In the 4th pig, ablations (up to 5) were applied to the ventricles at multiple sites until one or more of the potential identified indicators were observed in the ablation curve. Subsequent histology was performed as described in the first three pigs. Results Three indicators of transmurality were identified in the ablation curves: type I, a sharp impedance rise (blue peak); type II, three power drops with more than one energy level decline in one curve and type III, a first power drop before 11 seconds with subsequent hovering of power levels between 15 and 25 Wattage (Figure 1). In the first 3 pigs, a total of 20 ablations were performed, with 50% (n = 10) of the ablations considered transmural. In 80% of the transmural lesions one of the three types was observed. Among the transmural lesions, 50%, 10%, and 20% corresponds to type I, II, and III indicators of transmurality, respectively, with 20% remaining inconclusive. In the lesions classified not transmural (n = 10, 50%), no type I, II, or III indicators of transmurality was observed. In the fourth pig, all lesions (n=7) were considered transmural based on macroscopic evaluation, comprising 86% of type I and 14% of type III indicators of transmurality. Conclusion Three promising ablation curve types of transmurality have been identified that are associated with transmural lesions using the bipolar biparietal irrigated RF clamp. Transmurality of the lesion was confirmed by macroscopic histological evaluation. In the next step, these ablation curve types will be tested and validated in the clinical setting.Figure 1

Optimizing Resuscitation of the Donation after Circulatory Death Heart by Mitochondrial Protection in a Female Porcine Model.

Due to the shortage of donor organs, an increasing number of transplant organs are harvested after circulatory arrest (donation after circulatory death [DCD]). Using a translational porcine model of DCD, this study developed and evaluated a protocol based on cardioprotection by multidrug postconditioning to optimize resuscitation of DCD hearts during ex situ heart perfusion (ESHP). Hearts of female pigs (45.0 ± 4.5 kg) were procured following a clinically identical DCD protocol, consisting of the termination of ventilator support and confirmation of circulatory arrest, followed by a 15-min standoff period. DCD hearts were randomly allocated to ESHP (38.4°C) in the absence (untreated, N = 5) or presence (treated, N = 5) of a postconditioning treatment added to the perfusate, consisting of Intralipid (1%), sevoflurane (2% v/v), and remifentanil (3 nM). All hearts were perfused with blood and Krebs-Henseleit solution (1:1) for 60 min in Langendorff mode and for an additional 300 min in working mode for a total perfusion time of 6 h. Oxidative capacity and detailed left ventricular mechanical function under an increasing workload (left atrial pressure, 6 to 12 mmHg) were assessed hourly. Left ventricular tissue was snap-frozen at the end of ESHP and used for molecular analyses. Left ventricular inotropy (LVdP/dtmax) did not decline over time in treated DCD hearts and was significantly higher at the end of the protocol as compared with untreated DCD hearts (ΔLVdP/dtmax = 440 mmHg/s; P = 0.009). Treated DCD hearts exhibited persistently higher left ventricular stroke work index during the 6-h period of ESHP, whereas untreated DCD hearts displayed a significant decline (change in left ventricular stroke work index = -3.10 ml · mmHg/g; P(time within untreated group) < 0.001). Treated DCD hearts displayed higher metabolic activity as measured by oxygen consumption (ΔO2 = 3.11 ml O2 · min-1 · 100 g-1; P = 0.004) and released lower amounts of cell-free mitochondrial DNA into the perfusate, a marker of potential graft dysfunction. Treated hearts also used fatty acids from Intralipid as an energy source, whereas untreated DCD hearts showed glyceroneogenesis with triglyceride accumulation and depletion of tricarboxylic acid cycle intermediates; reduced mitochondrial complex I, II, and III activities with accumulation of mitochondrial NADH, and signs of ultrastructural damage. A translationally relevant protective ESHP protocol consisting of treatment with Intralipid, sevoflurane, and remifentanil markedly accelerated functional recovery and improved viability of DCD hearts.

Preclinical Study of Pulsed Field Ablation of Difficult Ventricular Targets: Intracavitary Mobile Structures, Interventricular Septum, and Left Ventricular Free Wall.

Endocardial catheter-based pulsed field ablation (PFA) of the ventricular myocardium is promising. However, little is known about PFA's ability to target intracavitary structures, epicardium, and ways to achieve transmural lesions across thick ventricular tissue. A lattice-tip catheter was used to deliver biphasic monopolar PFA to swine ventricles under general anesthesia, with electroanatomical mapping, fluoroscopy and intracardiac echocardiography guidance. We conducted experiments to assess the feasibility and safety of repetitive monopolar PFA applications to ablate (1) intracavitary papillary muscles and moderator bands, (2) epicardial targets, and (3) bipolar PFA for midmyocardial targets in the interventricular septum and left ventricular free wall. (1) Papillary muscles (n=13) were successfully ablated and then evaluated at 2, 7, and 21 days. Nine lesions with stable contact measured 18.3±2.4 mm long, 15.3±1.5 mm wide, and 5.8±1.0 mm deep at 2 days. Chronic lesions demonstrated preserved chordae without mitral regurgitation. Two targeted moderator bands were transmurally ablated without structural disruption. (2) Transatrial saline/carbon dioxide assisted epicardial access was obtained successfully and epicardial monopolar lesions had a mean length, width, and depth of 30.4±4.2, 23.5±4.1, and 9.1±1.9 mm, respectively. (3) Bipolar PFA lesions were delivered across the septum (n=11) and the left ventricular free wall (n=7). Twelve completed bipolar lesions had a mean length, width, and depth of 29.6±5.5, 21.0±7.3, and 14.3±4.7 mm, respectively. Chronically, these lesions demonstrated uniform fibrotic changes without tissue disruption. Bipolar lesions were significantly deeper than the monopolar epicardial lesions. This in vivo evaluation demonstrates that PFA can successfully ablate intracavitary structures and create deep epicardial lesions and transmural left ventricular lesions.