Arrhythmogenic cardiomyopathy (AC) is a heart disease often caused by mutations in genes coding for desmosomal proteins including desmoglein-2 (DSG2), plakoglobin (PG), and desmoplakin (DP). Therapy is symptomatic to limit arrhythmia since the mechanisms by which desmosomal components control cardiomyocyte function are largely unknown. A new paradigm would be to stabilize desmosomal cardiomyocyte adhesion and hyper-adhesion, which renders desmosomal adhesion independent from Ca2+. Here, we further characterized the mechanisms behind enhanced cardiomyocyte adhesion and hyper-adhesion. Dissociation assays performed in HL-1 cells and murine ventricular cardiac slice cultures allowed us to define a set of signaling pathways regulating cardiomyocyte adhesion under basal and hyper-adhesive conditions. Adrenergic signaling, activation of PKC and inhibition of p38MAPK enhanced cardiomyocyte adhesion, referred to as positive adhesiotropy, and induced hyper-adhesion. Activation of ERK1/2 paralleled positive adhesiotropy, whereas adrenergic signaling induced Pg phosphorylation at S665 under both basal and hyper-adhesive conditions. Adrenergic signaling and p38MAPK inhibition recruited DSG2 to cell junctions. In PG-deficient mice with an AC phenotype, only PKC activation and p38MAPK inhibition enhanced cardiomyocyte adhesion. Our results demonstrate that cardiomyocyte adhesion can be stabilized by different signaling mechanisms, which are in part off-set in PG-deficient AC.
Maria Shoykhet, Sebastian Trenz, Ellen Kempf, Tatjana Williams, Brenda Gerull, Camilla Schinner, Sunil Yeruva, Jens Waschke
Atrial fibrillation (AF) is the most common cardiac arrhythmia, yet the molecular signature of the vulnerable atrial substrate is not well understood. Here, we delineated a distinct transcriptional signature in right versus left atrial cardiomyocytes (CMs) at baseline, and identified chamber-specific gene expression changes in patients with history of AF in the setting of end-stage heart failure (AF+HF) that are not present in heart failure alone (HF). We observed that human left atrial (LA) CMs exhibit Notch pathway activation and increased ploidy in AF+HF, but not in HF alone. Transient activation of Notch signaling within adult CMs in a murine genetic model is sufficient to increase ploidy in both atrial chambers. Notch activation within LA CMs generated a transcriptomic fingerprint resembling AF, with dysregulation of transcription factor and ion channel genes including Pitx2, Tbx5, Kcnh2, Kcnq1, and Kcnip2. Notch activation also produced distinct cellular electrophysiologic responses in LA versus RA CMs, prolonging the action potential duration (APD) without altering the upstroke velocity in the LA, and reducing the maximal upstroke velocity without altering the APD in the RA. Our results support a shared human/murine model of increased Notch pathway activity predisposing to AF.
Catherine E. Lipovsky, Jesus Jimenez, Qiusha Guo, Gang Li, Tiankai Yin, Stephanie Hicks, Somya Bhatnagar, Kentaro Takahashi, David M. Zhang, Brittany D. Brumback, Uri Goldsztejn, Rangarajan D. Nadadur, Carlos Perez-Cervantes, Ivan P. Moskowitz, Shaopeng Liu, Bo Zhang, Stacey L. Rentschler
Nexilin (NEXN) was recently identified as a component of the junctional membrane complex required for development and maintenance of cardiac T-tubules. Loss of Nexn in mice leads to a rapidly progressive dilated cardiomyopathy (DCM) and premature death. A 3 bp deletion (1948–1950del) leading to loss of the glycine in position 650 (G650del) is classified as a variant of uncertain significance in humans and may function as an intermediate risk allele. To determine the effect of the G650del variant on cardiac structure and function, we generated a G645del-knockin (G645del is equivalent to human G650del) mouse model. Homozygous G645del mice express about 30% of the Nexn expressed by WT controls and exhibited a progressive DCM characterized by reduced T-tubule formation, with disorganization of the transverse-axial tubular system. On the other hand, heterozygous Nexn global KO mice and genetically engineered mice encoding a truncated Nexn missing the first N-terminal actin-binding domain exhibited normal cardiac function, despite expressing only 50% and 20% of the Nexn, respectively, expressed by WT controls, suggesting that not only quantity but also quality of Nexn is necessary for a proper function. These findings demonstrated that Nexn G645 is crucial for Nexn’s function in tubular system organization and normal cardiac function.
Canzhao Liu, Simone Spinozzi, Wei Feng, Ze’e Chen, Lunfeng Zhang, Siting Zhu, Tongbin Wu, Xi Fang, Kunfu Ouyang, Sylvia M. Evans, Ju Chen
BACKGROUND Genomic and experimental studies suggest a role for PITX2 in atrial fibrillation (AF). To assess if this association is relevant for recurrent AF in patients, we tested whether left atrial PITX2 affects recurrent AF after AF ablation.METHODS mRNA concentrations of PITX2 and its cardiac isoform, PITX2c, were quantified in left atrial appendages (LAAs) from patients undergoing thoracoscopic AF ablation, either in whole LAA tissue (n = 83) or in LAA cardiomyocytes (n = 52), and combined with clinical parameters to predict AF recurrence. Literature suggests that BMP10 is a PITX2-repressed, atrial-specific, secreted protein. BMP10 plasma concentrations were combined with 11 cardiovascular biomarkers and clinical parameters to predict recurrent AF after catheter ablation in 359 patients.RESULTS Reduced concentrations of cardiomyocyte PITX2, but not whole LAA tissue PITX2, were associated with AF recurrence after thoracoscopic AF ablation (16% decreased recurrence per 2–(ΔΔCt) increase in PITX2). RNA sequencing, quantitative PCR, and Western blotting confirmed that BMP10 is one of the most PITX2-repressed atrial genes. Left atrial size (HR per mm increase [95% CI], 1.055 [1.028, 1.082]); nonparoxysmal AF (HR 1.672 [1.206, 2.318]), and elevated BMP10 (HR 1.339 [CI 1.159, 1.546] per quartile increase) were predictive of recurrent AF. BMP10 outperformed 11 other cardiovascular biomarkers in predicting recurrent AF.CONCLUSIONS Reduced left atrial cardiomyocyte PITX2 and elevated plasma concentrations of the PITX2-repressed, secreted atrial protein BMP10 identify patients at risk of recurrent AF after ablation.TRIAL REGISTRATION ClinicalTrials.gov NCT01091389, NL50069.018.14, Dutch National Registry of Clinical Research Projects EK494-16.FUNDING British Heart Foundation, European Union (H2020), Leducq Foundation.
Jasmeet S. Reyat, Winnie Chua, Victor R. Cardoso, Anika Witten, Peter M. Kastner, S. Nashitha Kabir, Moritz F. Sinner, Robin Wesselink, Andrew P. Holmes, Davor Pavlovic, Monika Stoll, Stefan Kääb, Georgios V. Gkoutos, Joris R. de Groot, Paulus Kirchhof, Larissa Fabritz
Decreased cardiac myosin-binding protein C (cMyBPC) expression due to inheritable mutations is thought to contribute to the hypertrophic cardiomyopathy (HCM) phenotype, suggesting increasing cMyBPC content is of therapeutic benefit. In vitro assays show cMyBPC N-terminal domains (NTDs) contain structural elements necessary and sufficient to modulate acto-myosin interactions, but it is unknown if they can regulate in vivo myocardial function. To test if NTDs can recapitulate the effects of full-length (FL) cMyBPC in rescuing cardiac function in a cMyBPC-null mouse model of HCM, we assessed the efficacy of AAV9 gene transfer of a cMyBPC NTD containing domains C0C2 and compared its therapeutic potential with AAV9-FL gene replacement. AAV9 vectors were administered systemically at neonatal day 1, when early-onset disease phenotypes begin to manifest. A comprehensive analysis of in vivo and in vitro function was performed following cMyBPC gene transfer. Our results show that a systemic injection of AAV9-C0C2 gene transfer significantly improved cardiac function (e.g. 52.24±1.69 ejection fraction in C0C2 treated group compared to 40.07±1.97 in control cMyBPC-/- group, p<0.05) and reduced the histopathologic signs of cardiomyopathy. Furthermore, C0C2 significantly slowed and normalized the accelerated cross-bridge kinetics (32.41% decrease of krel) found in cMyBPC-/- control myocardium. Results indicate that C0C2 can rescue biomechanical defects of cMyBPC deficiency and the NTD may be a target region for therapeutic myofilament kinetic manipulation.
Jiayang Li, Ranganath Mamidi, Chang Yoon Doh, Joshua B. Holmes, Nikhil Bharambe, Rajesh Ramachandran, Julian E. Stelzer
We identified a novel homozygous duplication involving the promoter region and exons 1-4 of RYR2 that is responsible for highly penetrant, exertion-related sudden deaths/cardiac arrests in the Amish community without an overt phenotype to suggest RYR2-mediated catecholaminergic polymorphic ventricular tachycardia (CPVT). Homozygous RYR2-duplication (RYR2-DUP) induced pluripotent stem cell-cardiomyocytes (iPSC-CMs) were generated from two unrelated patients. There was no difference in baseline Ca2+ handling measurements between WT- and the RYR2-DUP-iPSC-CMs lines. However, compared to WT-iPSC-CMs, both patient lines demonstrated a dramatic reduction in caffeine and isoproterenol (ISO) stimulated Ca2+ transient amplitude, suggesting RyR2 loss-of-function. There was a >50% reduction in RYR2 transcript/RyR2 protein expression in both patient iPSC-CMs compared to WT. Delayed afterdepolarization was observed in the RYR2-DUP-iPSC-CMs but not in the WT-iPSC-CMs. Compared to WT-iPSC-CMs, there was a significantly elevated arrhythmic activity in the RYR2-DUP-iPSC-CMs in response to ISO. Nadolol, propranolol, and flecainide reduced erratic activity by 8.5 fold, 6.8 fold, and 2.4 fold, respectively from ISO challenge. Unlike the gain-of-function mechanism observed in RYR2-mediated CPVT, the homozygous multi-exon duplication precipitates a dramatic reduction in RYR2 transcription and RyR2 protein translation, a loss-of-function in calcium handling, and a calcium-induced calcium release apparatus that is insensitive to catecholamines and caffeine.
David J. Tester, CS John Kim, Samantha K. Hamrick, Dan Ye, Bailey J. O'Hare, Hannah M. Bombei, Kristi K. Fitzgerald, Carla M. Haglund-Turnquist, Dianne L. Atkins, Luis A. Ochoa Nunez, Ian H. Law, Joel D. Temple, Michael J. Ackerman
Recent evidence shows that the naïve heart harbors a population of intravascular recirculating B cells that make close contact with the microvascular endothelium of the heart and arrest their transit as they pass through the heart. However, the timing of their appearance and their organ specificity remain unknown. To address this knowledge gap, we performed a systematic analysis of B cells isolated from the myocardium and other organs, from embryonic life to early adulthood. We found that B cells are present in the developing heart by day E13.5. The phenotype of myocardial B cells changed dynamically during development. While neonatal heart B cells were mostly CD11b+ and CD11b-CD21-CD23-, adult B cells were predominantly CD11b-CD21+CD23+. Histological analysis and intravital microscopy of lung and liver showed that organ-associated B cells in contact with the microvascular endothelium were not specific to the heart. Flow cytometric analysis of perfused hearts, livers, lungs and spleen at different developmental stages showed that the dynamic changes in B cell subpopulations observed in the heart during development mirrored changes observed in the spleen, peripheral blood and other organs. Single cell RNAseq analysis of B cells showed that myocardial-associated B cells were part of a larger population of organ-associated B cells that had a distinct gene expression profile. These findings broaden our understanding of the biology of myocardial-associated B cells and suggest that current models of the dynamics of naïve B cell during development are incomplete.
Cibele Rocha-Resende, Wei Yang, Wenjun Li, Daniel Kreisel, Luigi Adamo, Douglas Mann
The bromodomain and extraterminal (BET) family of epigenetic reader proteins are key regulators of inflammatory and hypertrophic gene expression in the heart. We previously identified the activation of pro-inflammatory gene networks as a key early driver of dilated cardiomyopathy (DCM) in transgenic mice expressing a mutant form of phospholamban (PLNR9C) – a genetic cause of DCM in humans. We hypothesized that BETs coactivate this inflammatory process, representing a critical node in the progression of DCM. To test this hypothesis, PLNR9C or age-matched wild type mice were treated longitudinally with the small molecule BET bromodomain inhibitor JQ1 or vehicle. BET inhibition abrogated adverse cardiac remodeling, reduced cardiac fibrosis, and prolonged survival in PLNR9C mice by inhibiting expression of pro-inflammatory gene networks at all stages of disease. Specifically, JQ1 had profound effects on pro-inflammatory gene network expression in cardiac fibroblasts, while having little effect on gene expression in cardiomyocytes. Cardiac fibroblast proliferation was also substantially reduced by JQ1. Mechanistically, we demonstrated that BRD4 serves as a direct and essential regulator of NFkB-mediated pro-inflammatory gene expression in cardiac fibroblasts. Interdicting pro-inflammatory gene expression via BET bromodomain inhibition could be a novel therapeutic strategy for chronic DCM in humans.
Andrew Antolic, Hiroko Wakimoto, Zhe Jiao, Joshua M. Gorham, Steven R. DePalma, Madeleine E. Lemieux, David A. Conner, Da Young Lee, Jun Qi, Jonathan G. Seidman, James E. Bradner, Jonathan D. Brown, Saptarsi M. Haldar, Christine E. Seidman, Michael A. Burke
Noonan syndrome with multiple lentigines (NSML) is a rare autosomal dominant disorder that presents with cardio-cutaneous-craniofacial defects. Hypertrophic cardiomyopathy (HCM) represents the major life-threatening presentation in NSML. Mutations in the PTPN11 gene that encodes for the protein tyrosine phosphatase (PTP), SHP2, represents the predominant cause of HCM in NSML. NSML-associated PTPN11 mutations renders SHP2 catalytically inactive with an “open” conformation. NSML-associated PTPN11 mutations cause hypertyrosyl phosphorylation of the transmembrane glycoprotein, protein zero-related (PZR) resulting in increased SHP2 binding. Here we show that NSML mice harboring a tyrosyl phosphorylation-defective mutant of PZR (NSML/PZRY242F) that is defective for SHP2 binding fail to develop HCM. Enhanced AKT/S6K signaling in heart lysates of NSML mice was reversed in NSML/PZRY242F mice demonstrating that PZR/SHP2 interactions promote aberrant AKT/S6K activity in NSML. Enhanced PZR tyrosyl phosphorylation in the hearts of NSML mice was found to drive myocardial fibrosis by engaging a Src/NFkB pathway resulting in increased activation of interleukin-6 (IL6). Increased expression of IL6 in the hearts of NSML mice was reversed in NSML/PZRY242F mice and PZRY242F mutant fibroblasts were defective for IL6 secretion and STAT3-mediated fibrogenesis. These results demonstrate that NSML-associated PTPN11 mutations that induce PZR hypertyrosyl phosphorylation trigger pathophysiological signaling that promotes HCM and cardiac fibrosis.
Jae-Sung Yi, Sravan K. Perla, Liz E. Enyenihi, Anton M. Bennett
Infective endocarditis is a life-threatening infection of heart valves and adjacent structures characterized by vegetations on valves and other endocardial surfaces, with tissue destruction and risk of embolization. We used high-resolution mass spectrometry to define the proteome of staphylococcal and non-staphylococcal vegetations and Terminal Amine Isotopic Labeling of Substrates (TAILS) to define their proteolytic landscapes. These approaches identified over 2000 human proteins in staphylococcal and non-staphylococcal vegetations. Individual vegetation proteomes demonstrated comparable profiles of quantitatively major constituents that overlapped with serum, platelet and neutrophil proteomes. Staphylococcal vegetation proteomes resembled each other more than the proteomes of non-staphylococcal vegetations. TAILS demonstrated extensive proteolysis within vegetations, with numerous previously undescribed cleavages. Several proteases and pathogen-specific proteins, including virulence factors were identified in most vegetations. Proteolytic peptides in fibronectin and complement C3 were identified as potential infective endocarditis biomarkers. Overlap of staphylococcal and non-staphylococcal vegetation proteomes suggests a convergent thrombotic and immune response to endocardial infection by diverse pathogens. However, the differences between staphylococcal and non-staphylococcal vegetations and internal variance within the non-staphylococcal group indicates that additional pathogen- or patient-specific effects exist. Pervasive proteolysis of vegetation components may arise from vegetation-intrinsic proteases and destabilize vegetations, contributing to embolism.
Daniel R. Martin, James C. Witten, Carmela D. Tan, E. Rene Rodriguez, Eugene H. Blackstone, Gosta Pettersson, Deborah E. Seifert, Belinda Willard, Suneel Apte
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