Human Myocardium Research Articles

Modulation of STIM1 by a risk insertion/deletion polymorphism underlying genetics susceptibility to sudden cardiac death originated from coronary artery disease

Stromal interaction molecule 1 (STIM1), as a dynamic calcium signal transducer and key regulator of cardiomyocyte Ca2+ homeostasis, has been implicated in various pathological processes related to sudden cardiac death originated from coronary artery disease (SCD-CAD). In this study, we performed a systematic variant screening on promoter region of STIM1 to filter potential functional genetic variations. Based on the screening results, a 5-bp insertion/deletion (indel) polymorphism (rs3061890) in promoter region of STIM1 was selected as the candidate variant. We investigated the association of rs3061890 with SCD-CAD susceptibility in Chinese Han populations. The homozygote del/del genotype significantly increased risk for SCD-CAD as compared with the ins/ins genotype (odds ratio, 2.86 [95% confidence interval, 1.69–4.29]; P = 2.3 × 10–5). Compared with the common allele, the 5-bp deletion risk allele exhibited lower transcriptional capacity in luciferase assays. Intriguingly, genotype-phenotype correlation studies using human myocardium tissue samples revealed that the expression of STIM1 was associated with the genotype of rs3061890. Computational prediction combined with electrophoretic mobility shift (EMSA) and chromatin immunoprecipitation (ChIP) assays provided convincing evidence for stronger binding affinity of ELF1 (E74 like ETS transcription factor 1) with the deletion allele promoter. Taken together, our findings implied an allele-specific mechanism of regulating the transcription of STIM1 via ELF1, which contribute to SCD-CAD susceptibility. rs3061890 may thus considered as a candidate genetic marker for SCD-CAD prediction and prevention.

A viscoelastic model for human myocardium

Understanding the biomechanics of the heart in health and disease plays an important role in the diagnosis and treatment of heart failure. The use of computational biomechanical models for therapy assessment is paving the way for personalized treatment, and relies on accurate constitutive equations mapping strain to stress. Current state-of-the art constitutive equations account for the nonlinear anisotropic stress-strain response of cardiac muscle using hyperelasticity theory. While providing a solid foundation for understanding the biomechanics of heart tissue, most current laws neglect viscoelastic phenomena observed experimentally. Utilizing experimental data from human myocardium and knowledge of the hierarchical structure of heart muscle, we present a fractional nonlinear anisotropic viscoelastic constitutive model. The model is shown to replicate biaxial stretch, triaxial cyclic shear and triaxial stress relaxation experiments (mean error ∼7.68%), showing improvements compared to its hyperelastic (mean error ∼24%) counterparts. Model sensitivity, fidelity and parameter uniqueness are demonstrated. The model is also compared to rate-dependent biaxial stretch as well as different modes of biaxial stretch, illustrating extensibility of the model to a range of loading phenomena. Statement of SignificanceThe viscoelastic response of human heart tissues has yet to be integrated into common constitutive models describing cardiac mechanics. In this work, a fractional viscoelastic modeling approach is introduced based on the hierarchical structure of heart tissue. From these foundations, the current state-of-the-art biomechanical models of the heart muscle are transformed using fractional viscoelasticity, replicating passive muscle function across multiple experimental tests. Comparisons are drawn with current models to highlight the improvements of this approach and predictive responses show strong qualitative agreement with experimental data. The proposed model presents the first constitutive model aimed at capturing viscoelastic nonlinear response across multiple testing regimes, providing a platform for better understanding the biomechanics of myocardial tissue in health and disease.

Abstract P494: Truncated Titin Protein In Dilated Cardiomyopathy

Truncating variations in the gene coding for titin (TTNtv) have been known to cause dilated cardiomyopathy for nearly 20 years. Efforts to detect direct evidence of either haploinsufficiency or dominant negative mechanisms have thus far failed, leaving the mechanism open to controversy. By analyzing a collection of 184 post-transplant human hearts, 22 of which bear TTNtv’s, we show evidence supporting both haploinsufficient (lack of sufficient full length titin to maintain normal cardiomyocyte contractility) and dominant-negative (toxic gain of function due to truncated titin) mechanisms. Using allele specific proteomics as well as epitope specific agarose gel immunoblotting we show that TTNtv are present in human myocardium at the expected molecular weight and bear only the epitopes expected to be present in TTNtv protein. TTNtv associate with the sarcomere bearing insoluble fraction of human myocardium but are more weakly attached to the sarcomere than full length titin, consistent with their lack of thick filament and M-line attachment sites. We further show that DCM hearts bearing TTNtv have less full length titin than non-TTNtv bearing DCM hearts, by both total protein and in ratio to sarcomeric proteins, indicating TTN haploinsufficiency is also present in TTNtv hearts. This unambiguous detection of TTNtv protein in the myocardium of DCM combined with a reduction in full length titin supports a combined dominant negative and haploinsufficient mechanism of pathogenesis of TTNtv induced DCM.

Abstract P350: Myofibril Orientation In Cardiac Muscle And Its Implication For Heart Disease

Rationale: Myocyte disarray is a hallmark of cardiomyopathy. However, the orientation of individual myofibrils and myofilaments and how their alignment may be altered in disease progression have been largely underexplored. This oversight has been predominantly due to a paucity of methods for objective and quantitative analysis. Objective: To introduce a novel, less-biased approach to quantify myofibrillar and myofilament orientation in cardiac muscle under near physiological conditions and demonstrate its superiority versus traditional histological assessments. Methods and Results: Using small-angle X-ray diffraction, we first investigated changes in myofibrillar orientation at increasing sarcomere lengths in skinned, relaxed, wildtype mouse myocardium by assessing the angular spread of the 1,0 equatorial reflection (angle σ). At a sarcomere length (SL) of 1.9 μm, the angle σ was 0.23±0.01 rad, decreased to 0.19±0.01 rad at a SL of 2.1 μm, and further decreased to 0.15±0.01 rad at a SL of 2.3 μm (p<0.0001). Angle σ was significantly larger in R403Q (a MYH7 HCM model) porcine myocardium (0.24±0.01 rad) compared to WT myocardium (0.14±0.005 rad, p<0.0001) as well as in biopsied human heart failure tissue (0.19±0.006 rad) when compared to non-failing samples (0.17±0.007 rad, p=0.01). These data indicate that diseased myocardium suffers from myofibrillar disorientation compared to healthy controls. Finally, using control samples, we showed that traditional, histological-based analysis of disarray can be subject to user bias and/or sampling error and lead to false positives. Conclusions: Our method for assessing myofibrillar orientation limits the artifacts introduced by traditional histological processing and provides a precise and objective metric for phenotypically characterizing myocardium. The ability to obtain excellent X-ray diffraction patterns from frozen, biopsied human myocardium opens up new avenues of inquiry regarding the relation of myofibrillar structure to function in health and disease.

Abstract P506: Sirt6 Overexpression Inhibits Senescence And Inflammation In Human Mesenchymal Stem Cells

Background: Mesenchymal Stem Cells (MSCs) offer regenerative and therapeutic potential in an injured tissue in diabetic conditions. But the functional efficiency of MSCs has been shown to decrease with diabetes and aging. This reduces the potential of cell-based therapy in diabetic patients. Recent studies have established the role of sirtuin family proteins in metabolic disease, inflammation, longevity, and DNA repair. However, their potential to be used as a therapeutic target in cardiomyopathy and heart failure remain unexplored. Objective: To investigate the role of Sirtuin 6 (SIRT6) in mesenchymal stem cells senescence and cardiac regeneration. Methods and Results: We performed genomics and proteomics in the human control and diabetic heart tissues collected from the heart transplant. Human MSCs were treated with high glucose and mouse MSCs were derived from the bone marrow of diabetic db/db mice for this study. We found that SIRT6 expression is reduced in the myocardium of diabetic patients compared to non-diabetic controls. The SIRT6 expression decreased in high glucose-treated human MSCs compared to mannitol-treated control MSCs as well as in db/db mice MSCs compared to control mice MSCs. These high glucose-treated human MSCs and db/db mice MSCs showed increased expression of senescence and inflammation-related markers like that in diabetic human myocardium. Furthermore, we used small interfering RNA (SIRT6-siRNA) in human MSCs to knock down the SIRT6 gene and validated our findings. Indeed, the knockdown of SIRT6 promoted senescence and inflammation in those MSCs. Finally, we used adeno-associated viruses (AAV-SIRT6) to overexpress SIRT6 in MSCs treated with high glucose and performed proteomic analysis. SIRT6 overexpression in high glucose-treated MSCs reduced the expression of senescence and inflammation related genes and proteins. Conclusion: Our results highlight the importance of SIRT6 in diabetic myocardium and its role in balancing senescence and inflammation in MSCs. The validation of such in vitro studies in a diabetic mouse model ( db/db ) along with transplantation of SIRT6 overexpressed db/db MSCs into the myocardium of diabetic mice could open doors to successfully use MSC therapy in diabetic patients in the future.

Cardiac Na/Ca Exchange Suppression: A Late‐Breaking Knockout Story Showing That There Is No Free Lunch

Cardiac Na/Ca Exchange Suppression: A Late‐Breaking Knockout Story Showing That There Is No Free Lunch

Chalcone-Supported Cardiac Mesoderm Induction in Human Pluripotent Stem Cells for Heart Muscle Engineering.

Human pluripotent stem cells (hPSCs) hold great promise for applications in cell therapy and drug screening in the cardiovascular field. Bone morphogenetic protein 4 (BMP4) is key for early cardiac mesoderm induction in hPSC and subsequent cardiomyocyte derivation. Small‐molecular BMP4 mimetics may help to standardize cardiomyocyte derivation from hPSCs. Based on observations that chalcones can stimulate BMP4 signaling pathways, we hypothesized their utility in cardiac mesoderm induction. To test this, we set up a two‐tiered screening strategy, (1) for directed differentiation of hPSCs with commercially available chalcones (4’‐hydroxychalcone [4’HC] and Isoliquiritigen) and 24 newly synthesized chalcone derivatives, and (2) a functional screen to assess the propensity of the obtained cardiomyocytes to self‐organize into contractile engineered human myocardium (EHM). We identified 4’HC, 4‐fluoro‐4’‐methoxychalcone, and 4‐fluoro‐4’‐hydroxychalcone as similarly effective in cardiac mesoderm induction, but only 4’HC as an effective replacement for BMP4 in the derivation of contractile EHM‐forming cardiomyocytes.

Resident Macrophages and Their Potential in Cardiac Tissue Engineering.

Many facets of tissue engineered models aim at understanding cellular mechanisms to recapitulate in vivo behavior, to study and mimic diseases for drug interventions, and to provide a better understanding toward improving regenerative medicine. Recent and rapid advances in stem cell biology, material science and engineering, have made the generation of complex engineered tissues much more attainable. One such tissue, human myocardium, is extremely intricate, with a number of different cell types. Recent studies have unraveled cardiac resident macrophages as a critical mediator for normal cardiac function. Macrophages within the heart exert phagocytosis and efferocytosis, facilitate electrical conduction, promote regeneration, and remove cardiac exophers to maintain homeostasis. These findings underpin the rationale of introducing macrophages to engineered heart tissue (EHT), to more aptly capitulate in vivo physiology. Despite the lack of studies using cardiac macrophages in vitro, there is enough evidence to accept that they will be key to making EHTs more physiologically relevant. In this review, we explore the rationale and feasibility of using macrophages as an additional cell source in engineered cardiac tissues. Impact statement Macrophages play a critical role in cardiac homeostasis and in disease. Over the past decade, we have come to understand the many vital roles played by cardiac resident macrophages in the heart, including immunosurveillance, regeneration, electrical conduction, and elimination of exophers. There is a need to improve our understanding of the resident macrophage population in the heart in vitro, to better recapitulate the myocardium through tissue engineered models. However, obtaining them in vitro remains a challenge. Here, we discuss the importance of cardiac resident macrophages and potential ways to obtain cardiac resident macrophages in vitro. Finally, we critically discuss their potential in realizing impactful in vitro models of cardiac tissue and their impact in the field.

Multicellular Human Cardiac Organoids Transcriptomically Model Distinct Tissue-Level Features of Adult Myocardium.

Human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) have been widely used for disease modeling and drug cardiotoxicity screening. To this end, we recently developed human cardiac organoids (hCOs) for modeling human myocardium. Here, we perform a transcriptomic analysis of various in vitro hiPSC-CM platforms (2D iPSC-CM, 3D iPSC-CM and hCOs) to deduce the strengths and limitations of these in vitro models. We further compared iPSC-CM models to human myocardium samples. Our data show that the 3D in vitro environment of 3D hiPSC-CMs and hCOs stimulates the expression of genes associated with tissue formation. The hCOs demonstrated diverse physiologically relevant cellular functions compared to the hiPSC-CM only models. Including other cardiac cell types within hCOs led to more transcriptomic similarities to adult myocardium. hCOs lack matured cardiomyocytes and immune cells, which limits a complete replication of human adult myocardium. In conclusion, 3D hCOs are transcriptomically similar to myocardium, and future developments of engineered 3D cardiac models would benefit from diversifying cell populations, especially immune cells.

Human left ventricle transcriptome signatures and signalling pathways in patients with high and low intramyocardial lipid

Background and Aims: The aim of this study was to determine transcriptomic signatures and signalling pathways in human left ventricular myocardium (LV) with low or high intramyocellular (IMCL) lipid content.

Effects of canagliflozin on human myocardial redox signalling: clinical implications.

AimsRecent clinical trials indicate that sodium-glucose cotransporter 2 (SGLT2) inhibitors improve cardiovascular outcomes in heart failure patients, but the underlying mechanisms remain unknown. We explored the direct effects of canagliflozin, an SGLT2 inhibitor with mild SGLT1 inhibitory effects, on myocardial redox signalling in humans.Methods and resultsStudy 1 included 364 patients undergoing cardiac surgery. Right atrial appendage biopsies were harvested to quantify superoxide () sources and the expression of inflammation, fibrosis, and myocardial stretch genes. In Study 2, atrial tissue from 51 patients was used ex vivo to study the direct effects of canagliflozin on NADPH oxidase activity and nitric oxide synthase (NOS) uncoupling. Differentiated H9C2 and primary human cardiomyocytes (hCM) were used to further characterize the underlying mechanisms (Study 3). SGLT1 was abundantly expressed in human atrial tissue and hCM, contrary to SGLT2. Myocardial SGLT1 expression was positively associated with production and pro-fibrotic, pro-inflammatory, and wall stretch gene expression. Canagliflozin reduced NADPH oxidase activity via AMP kinase (AMPK)/Rac1signalling and improved NOS coupling via increased tetrahydrobiopterin bioavailability ex vivo and in vitro. These were attenuated by knocking down SGLT1 in hCM. Canagliflozin had striking ex vivo transcriptomic effects on myocardial redox signalling, suppressing apoptotic and inflammatory pathways in hCM.ConclusionsWe demonstrate for the first time that canagliflozin suppresses myocardial NADPH oxidase activity and improves NOS coupling via SGLT1/AMPK/Rac1 signalling, leading to global anti-inflammatory and anti-apoptotic effects in the human myocardium. These findings reveal a novel mechanism contributing to the beneficial cardiac effects of canagliflozin.

Myocardial T2 values by a segmental approach with healthy ageing and gender

Abstract Funding Acknowledgements Type of funding sources: None. Introduction. No data are available in literature about normal ranges for T2 in human myocardium using GE scanners. Aims. Our aims were to obtain myocardial regional and global T2 values as a reference for normality for the first time using a GE scanner and to assess their association with physiological variables. Methods. A stratified approach was adopted for healthy volunteers recruitment, ensuring the presence of 10 participants for both genders in each age decile: 20–30, 30–40, 40-50, 50-60, 60-70 years. Basal, medium, and apical short-axis slices of the left ventricle were acquired by a multi-echo fast-spin-echo (MEFSE) sequence. Image analysis was performed with a commercially available software package. T2 value was assessed in all 16 myocardial segments and global value was the mean. Results. The global T2 value averaged across all subjects was 52.2 ± 2.5 ms (range: 47.0-59.9 ms). Inter-study, intra-observer, and inter-observer reproducibility was good (coefficient of variation < 5%). The 3.6% of segments was excluded because of artifacts and/or partial-volume effects. Segmental T2 values differed significantly (P < 0.0001), with the lowest value in the basal anterolateral segment (50.0 ± 3.5 ms) and the highest in the apical lateral segment (54.9 ± 5.1 ms). Mean T2 was significantly lower in the basal slice compared to both medium (51.0 ± 2.4 vs 51.8 ± 2.6 ms; P < 0.0001) and apical slices (51.0 ± 2.4 vs 54.2 ± 3.7 ms; P < 0.0001), and in the medium slice than in the apical slice (51.8 ± 2.6 vs 54.2 ± 3.7 ms; P < 0.0001). Aging was associated with increased segmental and global T2 values. Females showed higher T2 values than males. T2 values were not correlated to heart rate. Mean T2 values, standard deviation, and lower and upper limits of normal for all 16 myocardial segments are shown in Figure 1 for males and in Figure 2 for females, considering separately each age group. Conclusion. The optimized MEFSE sequence allows for robust, reliable, and reproducible quantification of segmental T2 values. T2 values differ among myocardial slices and are influenced by age and gender, making mandatory to define gender- and age-specific segmental reference values for distinguishing between healthy and diseased myocardium. The normal ranges defined in this study on a large cohort of healthy subjects could be used as reference by other sites using the same sequence, allowing them to recruit a smaller population and accelerating the spread of myocardial T2 mapping in the clinical arena.

A computational model of pig ventricular cardiomyocyte electrophysiology and calcium handling: Translation from pig to human electrophysiology.

The pig is commonly used as an experimental model of human heart disease, including for the study of mechanisms of arrhythmia. However, there exist differences between human and porcine cellular electrophysiology: The pig action potential (AP) has a deeper phase-1 notch, a longer duration at 50% repolarization, and higher plateau potentials than human. Ionic differences underlying the AP include larger rapid delayed-rectifier and smaller inward-rectifier K+-currents (IKr and IK1 respectively) in humans. AP steady-state rate-dependence and restitution is steeper in pigs. Porcine Ca2+ transients can have two components, unlike human. Although a reliable computational model for human ventricular myocytes exists, one for pigs is lacking. This hampers translation from results obtained in pigs to human myocardium. Here, we developed a computational model of the pig ventricular cardiomyocyte AP using experimental datasets of the relevant ionic currents, Ca2+-handling, AP shape, AP duration restitution, and inducibility of triggered activity and alternans. To properly capture porcine Ca2+ transients, we introduced a two-step process with a faster release in the t-tubular region, followed by a slower diffusion-induced release from a non t-tubular subcellular region. The pig model behavior was compared with that of a human ventricular cardiomyocyte (O'Hara-Rudy) model. The pig, but not the human model, developed early afterdepolarizations (EADs) under block of IK1, while IKr block led to EADs in the human but not in the pig model. At fast rates (pacing cycle length = 400 ms), the human cell model was more susceptible to spontaneous Ca2+ release-mediated delayed afterdepolarizations (DADs) and triggered activity than pig. Fast pacing led to alternans in human but not pig. Developing species-specific models incorporating electrophysiology and Ca2+-handling provides a tool to aid translating antiarrhythmic and arrhythmogenic assessment from the bench to the clinic.

Functional Calsequestrin-1 Is Expressed in the Heart and Its Deficiency Is Causally Related to Malignant Hyperthermia-Like Arrhythmia.

Calsequestrins (Casqs), comprising the Casq1 and Casq2 isoforms, buffer Ca2+ and regulate its release in the sarcoplasmic reticulum of skeletal and cardiac muscle, respectively. Human inherited diseases associated with mutations in CASQ1 or CASQ2 include malignant hyperthermia/environmental heat stroke (MH/EHS) and catecholaminergic polymorphic ventricular tachycardia. However, patients with an MH/EHS event often experience arrhythmia for which the underlying mechanism remains unknown. Working hearts from conventional (Casq1-KO) and cardiac-specific (Casq1-CKO) Casq1 knockout mice were monitored in vivo and ex vivo by ECG and electric mapping, respectively. MH was induced by 2% isoflurane and treated intraperitoneally with dantrolene. Time-lapse imaging was used to monitor intracellular Ca2+ activity in isolated mouse cardiomyocytes or neonatal rat ventricular myocytes with knockdown, overexpression, or truncation of the Casq1 gene. Conformational change in both Casqs was determined by cross-linking Western blot analysis. Like patients with MH/EHS, Casq1-KO and Casq1-CKO mice had faster basal heart rate and ventricular tachycardia on exposure to 2% isoflurane, which could be relieved by dantrolene. Basal sinus tachycardia and ventricular ectopic electric triggering also occurred in Casq1-KO hearts ex vivo. Accordingly, the ventricular cardiomyocytes from Casq1-CKO mice displayed dantrolene-sensitive increased Ca2+ waves and diastole premature Ca2+ transients/oscillations on isoflurane. Neonatal rat ventricular myocytes with Casq1-knockdown had enhanced spontaneous Ca2+ sparks/transients on isoflurane, whereas cells overexpressing Casq1 exhibited decreased Ca2+ sparks/transients that were absent in cells with truncation of 9 amino acids at the C terminus of Casq1. Structural evaluation showed that most of the Casq1 protein was present as a polymer and physically interacted with ryanodine receptor-2 in the ventricular sarcoplasmic reticulum. The Casq1 isoform was also expressed in human myocardium. Mechanistically, exposure to 2% isoflurane or heating at 41 °C induced Casq1 oligomerization in mouse ventricular and skeletal muscle tissues, leading to a reduced Casq1/ryanodine receptor-2 interaction and increased ryanodine receptor-2 activity in the ventricle. Casq1 is expressed in the heart, where it regulates sarcoplasmic reticulum Ca2+ release and heart rate. Casq1 deficiency independently causes MH/EHS-like ventricular arrhythmia by trigger-induced Casq1 oligomerization and a relief of its inhibitory effect on ryanodine receptor-2-mediated Ca2+ release, thus revealing a new inherited arrhythmia and a novel mechanism for MH/EHS arrhythmogenesis.

Tunable Human Myocardium Derived Decellularized Extracellular Matrix for 3D Bioprinting and Cardiac Tissue Engineering.

The generation of 3D tissue constructs with multiple cell types and matching mechanical properties remains a challenge in cardiac tissue engineering. Recently, 3D bioprinting has become a powerful tool to achieve these goals. Decellularized extracellular matrix (dECM) is a common scaffold material due to providing a native biochemical environment. Unfortunately, dECM’s low mechanical stability prevents usage for bioprinting applications alone. In this study, we developed bioinks composed of decellularized human heart ECM (dhECM) with either gelatin methacryloyl (GelMA) or GelMA-methacrylated hyaluronic acid (MeHA) hydrogels dual crosslinked with UV light and microbial transglutaminase (mTGase). We characterized the bioinks’ mechanical, rheological, swelling, printability, and biocompatibility properties. Composite GelMA–MeHA–dhECM (GME) hydrogels demonstrated improved mechanical properties by an order of magnitude compared to the GelMA–dhECM (GE) hydrogels. All hydrogels were extrudable and compatible with human induced pluripotent stem cell derived cardiomyocytes (iCMs) and human cardiac fibroblasts (hCFs). Tissue-like beating of the printed constructs with striated sarcomeric alpha-actinin and connexin 43 expression was observed. The order of magnitude difference between the elastic modulus of these hydrogel composites offers applications in in vitro modeling of the myocardial infarct boundary. Here, as a proof of concept, we created an infarct boundary region with control over the mechanical properties along with the cellular and macromolecular content through printing iCMs with GE bioink and hCFs with GME bioink.

Chronological and biological aging of the human left ventricular myocardium: Analysis of microRNAs contribution.

Aging is the main risk factor for cardiovascular diseases. In humans, cardiac aging remains poorly characterized. Most studies are based on chronological age (CA) and disregard biological age (BA), the actual physiological age (result of the aging rate on the organ structure and function), thus yielding potentially imperfect outcomes. Deciphering the molecular basis of ventricular aging, especially by BA, could lead to major progresses in cardiac research. We aim to describe the transcriptome dynamics of the aging left ventricle (LV) in humans according to both CA and BA and characterize the contribution of microRNAs, key transcriptional regulators. BA is measured using two CA‐associated transcriptional markers: CDKN2A expression, a cell senescence marker, and apparent age (AppAge), a highly complex transcriptional index. Bioinformatics analysis of 132 LV samples shows that CDKN2A expression and AppAge represent transcriptomic changes better than CA. Both BA markers are biologically validated in relation to an aging phenotype associated with heart dysfunction, the amount of cardiac fibrosis. BA‐based analyses uncover depleted cardiac‐specific processes, among other relevant functions, that are undetected by CA. Twenty BA‐related microRNAs are identified, and two of them highly heart‐enriched that are present in plasma. We describe a microRNA‐gene regulatory network related to cardiac processes that are partially validated in vitro and in LV samples from living donors. We prove the higher sensitivity of BA over CA to explain transcriptomic changes in the aging myocardium and report novel molecular insights into human LV biological aging. Our results can find application in future therapeutic and biomarker research.

Long-chain acylcarnitine 18:1 acutely increases human atrial myocardial contractility and arrhythmia susceptibility.

Long-chain acylcarnitines (LCACs) are known to directly alter cardiac contractility and electrophysiology. However, the acute effect of LCACs on human cardiac function is unknown. We aimed to determine the effect of LCAC 18:1, which has been associated with cardiovascular disease, on the contractility and arrhythmia susceptibility of human atrial myocardium. Additionally, we aimed to assess how LCAC 18:1 alters Ca2+ influx and spontaneous Ca2+ release in vitro. Human right atrial trabeculae (n = 32) stimulated at 1 Hz were treated with LCAC 18:1 at a range of concentrations (1-25 µM) for a 45-min period. Exposure to the LCAC induced a dose-dependent positive inotropic effect on myocardial contractility (maximal 1.5-fold increase vs. control). At the 25 µM dose (n = 8), this was paralleled by an enhanced propensity for spontaneous contractions (50% increase). Furthermore, all LCAC 18:1 effects on myocardial function were reversed following LCAC 18:1 washout. In fluo-4-AM-loaded HEK293 cells, LCAC 18:1 dose dependently increased cytosolic Ca2+ influx relative to vehicle controls and the short-chain acylcarnitine C3. In HEK293 cells expressing ryanodine receptor (RyR2), this increased Ca2+ influx was linked to an increased propensity for RyR2-mediated spontaneous Ca2+ release events. Our study is the first to show that LCAC 18:1 directly and acutely alters human myocardial function and in vitro Ca2+ handling. The metabolite promotes proarrhythmic muscle contractions and increases contractility. The exploratory findings in vitro suggest that LCAC 18:1 increases proarrhythmic RyR2-mediated spontaneous Ca2+ release propensity. The direct effects of metabolites on human myocardial function are essential to understand cardiometabolic dysfunction.NEW & NOTEWORTHY For the first time, the fatty acid metabolite, long-chain acylcarnitine 18:1, is shown to acutely increase the arrhythmia susceptibility and contractility of human atrial myocardium. In vitro, this was linked to an influx of Ca2+ and an enhanced propensity for spontaneous RyR2-mediated Ca2+ release.

An under-recognized phenomenon: Myocardial volume change during the cardiac cycle.

Myocardial volume is assumed to be constant over the cardiac cycle in the echocardiographic models used by professional guidelines, despite evidence that suggests otherwise. The aim of this paper is to use literature-derived myocardial strain values from healthy patients to determine if myocardial volume changes during the cardiac cycle. A systematic review for studies with longitudinal, radial, and circumferential strain from echocardiography in healthy volunteers ultimately yielded 16 studies, corresponding to 2917 patients. Myocardial volume in systole (MVs) and diastole (MVd) was used to calculate MVs/MVd for each study by applying this published strain data to three models: the standard ellipsoid geometric model, a thin-apex geometric model, and a strain-volume ratio. MVs/MVd<1 in 14 of the 16 studies, when computed using these three models. A sensitivity analysis of the two geometric models was performed by varying the dimensions of the ellipsoid and calculating MVs/MVd. This demonstrated little variability in MVs/MVd, suggesting that strain values were the primary determinant of MVs/MVd rather than the geometric model used. Another sensitivity analysis using the 97.5th percentile of each orthogonal strain demonstrated that even with extreme values, in the largest two studies of healthy populations, the calculated MVs/MVd was <1. Healthy human myocardium appears to decrease in volume during systole. This is seen in MRI studies and is clinically relevant, but this study demonstrates that this characteristic was also present but unrecognized in the existing echocardiography literature.

Serum Anti-Heart and Anti-Intercalated Disk Autoantibodies: Novel Autoimmune Markers in Cardiac Sarcoidosis.

Background: Sarcoidosis is an immune-mediated disease. Cardiac involvement, a granulomatous form of myocarditis, is under-recognized and prognostically relevant. Anti-heart autoantibodies (AHAs) and anti-intercalated disk autoantibodies (AIDAs) are autoimmune markers in nonsarcoidosis myocarditis forms. Objective: The aim was to assess serum AHAs and AIDAs as autoimmune markers in cardiac sarcoidosis. Methods: This is a cross-sectional study on AHA and AIDA frequency in: 29 patients (aged 46 ± 12, 20 male) with biopsy-proven extracardiac sarcoidosis and biopsy-proven or clinically suspected and confirmed by 18-fluorodeoxyglucose positron emission tomography and/or cardiovascular magnetic resonance (CMR) cardiac involvement; 30 patients (aged 44 ± 11, 12 male) with biopsy-proven extracardiac sarcoidosis without cardiac involvement (no cardiac symptoms, normal 12-lead electrocardiogram, echocardiography and CMR), and control patients with noninflammatory cardiac disease (NICD) (n = 160), ischemic heart failure (IHF) (n = 141) and normal blood donors (NBDs) (n = 270). Sarcoidosis patients were recruited in two recruiting tertiary centers in the USA and Italy. AHAs and AIDAs were detected by indirect immunofluorescence on the human myocardium and skeletal muscle. Results: AHA and AIDA frequencies were higher in sarcoidosis with cardiac involvement (86%; 62%) than in sarcoidosis without cardiac involvement (0%; 0%), NICD (8%; 4%), IHF (7%; 2%) and NBD (9%; 0%) (p = 0.0001; p = 0.0001, respectively). Sensitivity and specificity for cardiac sarcoidosis were 86% and 92% for positive AHAs and 62% and 98% for positive AIDAs, respectively. AIDAs in cardiac sarcoidosis were associated with a higher number of involved organs (p = 0.04). Conclusions: Serum AHAs and AIDAs provide novel noninvasive diagnostic autoimmune markers for cardiac sarcoidosis.

A Functional Indel Polymorphism Within MIR155HG Is Associated With Sudden Cardiac Death Risk in a Chinese Population.

Sudden cardiac death (SCD) is a devastating complication of multiple disease processes and has gradually became a major public health issue. miR-155 is one of the best characterized miRNAs and plays a critical role in several physiological and pathological process, including cardiovascular diseases. In this study, we systematically screened the whole region of miR-155 host gene (MIR155HG) and identified a 4-bp insertion/deletion variant (rs72014506) residing in the intron region of MIR155HG as the candidate polymorphism. The association of rs72014506 with SCD susceptibility was evaluated using 166 SCD cases and 830 healthy controls in a Chinese population. Logistic regression analysis suggested that the homozygote del/del genotype significantly decreased the risk of SCD [odds ratio (OR) = 0.29; 95% confidence interval (CI) = 0.12–0.74; Ptrend = 0.0004]. Further genotype–expression association study using human myocardium tissue samples suggested that the deletion allele was intimately linked to lower the expression of both MIR155HG and mature miR155. Luciferase activity assay also revealed that the deletion allele of rs72014506 inhibited gene transcriptional activity. Finally, we performed electrophoretic mobility shift assay and verified the preferential binding affinity of the deletion allele with POU2F1 (POU domain class 2 transcription factor 1). Collectively, we have successfully identified a SCD risk conferring polymorphism in the MIR155HG gene and a likely biological mechanism for the decreased risk of SCD associated with the deletion allele. This novel variant may thus serve as a potential genetic marker for SCD diagnosis and prevention in natural populations, if validated by further studies with a larger sample size.