Cardiology
Abstract
Background: Loss-of-function variants in SCN1B, encoding voltage-gated sodium channel β1 subunits, are linked to human diseases with high risk of sudden death, including epileptic encephalopathy and cardiac arrhythmia. β1 subunits modulate the cell-surface localization, gating, and kinetics of sodium channel pore-forming a subunits. They also participate in cell-cell and cell-matrix adhesion, resulting in intracellular signal transduction, promotion of cell migration, calcium handling, and regulation of cell morphology. Methods: We investigated regulated intramembrane proteolysis (RIP) of β1 by BACE1 and γ-secretase.Results: We show that β1 subunits are substrates for sequential RIP by BACE1 and γ-secretase, resulting in the generation of a soluble intracellular domain (ICD) that is translocated to the nucleus. Using RNA-seq, we identified a subset of genes that are downregulated by β1-ICD overexpression in heterologous cells but upregulated in Scn1b null cardiac tissue which, by definition, lacks β1-ICD signaling, suggesting that the β1-ICD may normally function as a molecular brake on gene transcription in vivo. Conclusion: We propose that human disease variants resulting in SCN1B loss-of-function cause transcriptional dysregulation that contributes to altered excitability. These results provide important new insights into the mechanism of SCN1B-linked channelopathies, adding RIP-excitation coupling to the multi-functionality of sodium channel β1 subunits.
Authors
Alexandra A. Bouza, Nnamdi Edokobi, Samantha L. Hodges, Alexa M. Pinsky, James Offord, Lin Piao, Yan-Ting Zhao, Anatoli N. Lopatin, Luis F. Lopez-Santiago, Lori L. Isom
Abstract
The pathogenesis of preeclampsia and other hypertensive disorders of pregnancy remains poorly-defined despite the substantial burden of maternal and neonatal morbidity associated with these conditions. In particular, the role of genetic variants as determinants of disease susceptibility remains unknown. Storkhead-box protein 1 (STOX1) was first identified as a preeclampsia risk gene through family-based genetic linkage studies in which loss-of-function variants were proposed to underlie increased preeclampsia susceptibility. We generated a genetic Stox1 loss-of-function mouse model (Stox1 KO), to evaluate whether STOX1 regulates blood pressure in pregnancy. Pregnant Stox1 KO mice developed gestational hypertension evidenced by a significant increase in blood pressure compared with wild type by E17.5. While severe renal, placental, or fetal growth abnormalities were not observed, the Stox1 KO phenotype was associated with placental vascular and extracellular matrix abnormalities. Mechanistically, we found that gestational hypertension in Stox1 KO mice resulted from activation of the uteroplacental renin-angiotensin system. We confirmed this mechanism by showing that treatment of pregnant Stox1 KO mice with an angiotensin II receptor blocker rescued the phenotype. Our study demonstrates the utility of genetic mouse models for uncovering links between genetic variants and effector pathways implicated in the pathogenesis of hypertensive disorders of pregnancy.
Authors
Jacqueline G. Parchem, Keizo Kanasaki, Soo Bong Lee, Megumi Kanasaki, Joyce L. Yang, Yong Xu, Kadeshia M. Earl, Rachel A. Keuls, Vincent H. Gattone, Raghu Kalluri
Abstract
Cardiopulmonary bypass (CPB) is required during most cardiac surgeries. CBP drives systemic inflammation and multi-organ dysfunction that is more severe in neonatal patients. Limited understanding of molecular mechanisms underlying CPB-associated inflammation presents a significant barrier to improving clinical outcomes. To better understand these clinical issues, we performed the first mRNA-sequencing on total circulating leukocytes from neonatal patients undergoing CPB. These data identified myeloid cells, particularly monocytes, as the major cell type driving transcriptional responses to CPB. Furthermore, Interleukin-8 (IL8) and Tumor Necrosis Factor-α (TNFα) were inflammatory cytokines robustly upregulated in leukocytes from both patients and piglets exposed to CPB. To delineate a molecular mechanism, we exposed THP-1 human monocytic cells to CPB-like conditions including artificial surfaces, high shear stress, and cooling/rewarming. Here, shear stress was found to drive cytokine upregulation via calcium-dependent signaling pathways. We also observed a subpopulation of THP-1 cells died via TNFα-mediated necroptosis in our model, which we hypothesize contributes to post-CPB inflammation. Together, our study identifies a shear-stress modulated molecular mechanism that drives systemic inflammation in pediatric CPB patients. These are also the first data to demonstrate that shear-stress causes necroptosis. Finally, we observe that calcium and TNFα signaling are novel targets to ameliorate post-CPB inflammation.
Authors
Lan N. Tu, Lance Hsieh, Masaki Kajimoto, Kevin Charette, Nataliya Kibiryeva, Adriana Forero, Sarah E. Hampson, Jennifer Marshall, James O’Brien, Marta Scatena, Michael A. Portman, Ram Savan, Christopher Benner, Alberto Aliseda, Muhammad Nuri, Douglas Bittel, Peter Pastuszko, Vishal Nigam
Abstract
Cardiac fibrosis is a pathophysiologic hallmark of the aging heart. In the uninjured heart, cardiac fibroblasts exist in the quiescent state, but little is known about how proliferation rates and fibroblast transcriptional programs change throughout the lifespan of the organism from the immediate postnatal period to adult life and old age. Using EdU pulse labeling, we demonstrate that more than 50% of cardiac fibroblasts are actively proliferating in the first day of post-natal life. However, within 4 weeks of birth in the juvenile animal, only 10% of cardiac fibroblasts are proliferating. By early adulthood, the fraction of proliferating cardiac fibroblasts further decreases to approximately 2%, where it so remains throughout the rest of the organism’s life span. Examination of absolute cardiac fibroblast numbers demonstrated concordance with age related changes in fibroblast proliferation with no significant differences in absolute cardiac fibroblast numbers between animals 14 weeks and 1.5 years of age. We demonstrate that the maximal changes in cardiac fibroblast transcriptional programs and in particular collagen expression occur within the first weeks of life from the immediate postnatal to the juvenile period. We show that even though the aging heart exhibits an increase in the total amount of accumulated collagen, transcription of various collagens and ECM genes both in the heart and cardiac fibroblast is maximal in the newly born and juvenile animal and decreases with organismal aging. Examination of DNA methylation changes both in the heart and in cardiac fibroblasts did not demonstrate significant changes in differentially methylated regions between young and old mice. Our observations demonstrate that cardiac fibroblasts attain a stable proliferation rate and transcriptional program early in the life span of the organism and suggest a model of cardiac aging where phenotypic changes in the aging heart are not directly attributable to changes in proliferation rate or altered collagen expression in cardiac fibroblasts.
Authors
Rimao Wu, Feiyang Ma, Anela Tosevska, Colin Farrell, Matteo Pellegrini, Arjun Deb
Abstract
Atrial fibrillation (AF) commonly occurs after surgery and is associated with atrial remodeling. TRPV4 is functionally expressed in the heart, and its activation affects cardiac structure and functions. We hypothesized that TRPV4 blockade alleviates atrial remodeling and reduces AF induction in sterile pericarditis (SP) rats. TRPV4 antagonist GSK2193874 or vehicle was orally administered 1 d before pericardiotomy. AF susceptibility and atrial function were assessed using in vivo electrophysiology, ex vivo optical mapping, patch-clamp, and molecular biology on day 3 after surgery. TRPV4 expression increased in the atria of SP rats and patients with AF. GSK2193874 significantly reduced AF vulnerability in vivo and the frequency of atrial ectopy and AF with a reentrant pattern ex vivo. Mechanistically, GSK2193874 reversed the abnormal action potential duration (APD) prolongation in atrial myocytes through the regulation of voltage-gated K+ currents (IK), reduced the activation of atrial fibroblasts by inhibiting P38, AKT, and STAT3 pathways, and alleviated the infiltration of immune cells. Our results reveal that TRPV4 blockade prevents abnormal changes in atrial myocyte electrophysiology and ameliorated atrial fibrosis and inflammation in SP rats, and, therefore, might be a promising strategy to treat AF, particularly post-operative AF.
Authors
Jie Liao, Qiongfeng Wu, Cheng Qian, Ning Zhao, Zhaoyang Zhao, Kai Lu, Shaoshao Zhang, Qian Dong, Lei Chen, Qince Li, Yimei Du
Abstract
Cardiac ischemia is associated with arrhythmias, but effective therapies are limited. The cardiac voltage gated sodium channel α-subunit (SCN5A), encoding the Nav1.5 current, plays a key role in the cardiac electrical conduction and arrhythmic risk. Here, we show that hypoxia reduces Nav1.5 through effects on a microRNA (miR), miR-448. The expression of miR-448 is increased in ischemic cardiomyopathy. miR-448 has a conserved binding site in 3’-UTR of SCN5A. miR-448 binding to this site suppressed SCN5A expression and sodium currents. Hypoxia-induced HIF1α and NF-κB were major transcriptional regulators for MIR448. Hypoxia also relieved MIR448 transcriptional suppression by RE1 silencing transcription factor (REST). Inhibition of miR-448 reduced arrhythmic risk after myocardial infarction. These results indicated that ischemia drove miR-448 expression, reduced Nav1.5 current and increased arrhythmic risk. Arrhythmic risk was improved by preventing Nav1.5 downregulation, suggesting a new approach to antiarrhythmic therapy.
Authors
Gyeoung-Jin Kang, An Xie, Hong Liu, Samuel C. Dudley, Jr.
Abstract
Background: Psoriasis is a chronic inflammatory skin disease with increased obesity, non-calcified coronary artery burden (NCB), and incident myocardial infarction. We sought to assess the relationship between inflammation, visceral adipose tissue (VAT), and NCB. Furthermore, we evaluated whether improvement in VAT would be associated with reduction in NCB over time in psoriasis. Methods: Consecutive psoriasis patients (PSO) underwent coronary computed-tomography angiography to quantify NCB and abdominal computed tomography to calculate VAT, at baseline (n=237), one year (n=176), and four-years (n=50). Results: Patients with high hs-CRP had significantly greater visceral adiposity (17952.9±849.2 vs 13370.7±806.8 cc3, p<0.001) and non-calcified coronary burden (1.26±0.03 vs 1.07±0.02 mm2) than those with low hs-CRP. Those with higher VAT had more systemic inflammation [hs-CRP: 2.5 (1.0-5.3) vs 1.2 (0.6-2.9) mg/L] with ~50% higher NCB (1.42±0.6 vs 0.91±0.2 mm2 , p<0.001). VAT associated with NCB in fully adjusted models (β=0.47, p<0.001). At one-year follow up, patients who had worsening hs-CRP had an increase in VAT (14748.7±878.1 to 15158.7±881.5 cc3; p=0.03), whereas those who improved hs-CRP improved their VAT (16876.1±915.2 to 16310.4±889.6 cc3; p=0.04). At one-year, in those who decreased VAT, there was 10.3% reduction in NCB (β=0.26, p<0.0001), which persisted in a subset at four-years (β=0.39, p=0.003). Conclusions: Inflammation drives development of VAT, increased cardiometabolic risk, and NCB in psoriasis. Reduction of inflammation associated with reduction in VAT, and associated with longitudinal improvement in NCB. These findings demonstrate the important role of inflammation in the development of VAT in humans and its impact on early atherogenesis.
Authors
Aparna Sajja, Khaled M. Abdelrahman, Aarthi S. Reddy, Amit K. Dey, Domingo E. Uceda, Sundus S. Lateef, Alexander V. Sorokin, Heather L. Teague, Jonathan H. Chung, Joshua P. Rivers, Aditya A. Joshi, Youssef A. Elnabawi, Aditya Goyal, Justin Rodante, Andrew Keel, Julie A. Erb-Alvarez, Benjamin Lockshin, Ronald Prussick, Evan L. Siegel, Martin P. Playford, Marcus Y. Chen, David A. Bluemke, Joel M. Gelfand, Nehal N. Mehta
Abstract
Heart failure is often accompanied by titin-dependent myocardial stiffness. Phosphorylation of titin by cGMP-dependent protein kinase (PKG)I increases cardiomyocyte distensibility. The upstream pathways stimulating PKGI-mediated titin phosphorylation are unclear. We studied whether C-type natriuretic peptide (CNP), via its guanylyl cyclase-B (GC-B) receptor and cGMP/PKGI signalling, modulates titin-based ventricular compliance. To dissect GC-B-mediated effects of endogenous CNP in cardiomyocytes, we generated mice with cardiomyocyte (CM)-restricted GC-B deletion. The impact on heart morphology and function, myocyte passive tension and titin isoform expression and phosphorylation was studied at baseline and after increased afterload induced by transverse aortic constriction (TAC).Pressure-overload increased left ventricular, especially endothelial CNP expression, with an early peak after 3 days. Concomitantly, titin phosphorylation at Ser4080, the site phosphorylated by PKGI, was augmented. Notably, in CM GC-B KO mice this titin response was abolished. TAC-induced hypertrophy and fibrosis were not different between genotypes. However, the KO mice presented mild systolic and diastolic dysfunction together with myocyte stiffness, which were not observed in control littermates. In vitro, recombinant PKGI rescued reduced Titin-Ser4080 phosphorylation and reverted passive stiffness of GC-B-deficient cardiomyocytes. CNP-induced activation of GC-B/cGMP/PKGI signalling in cardiomyocytes provides a protecting regulatory circuit preventing titin-based myocyte stiffening during early phases of pressure-overload.
Authors
Konstanze Michel, Melissa Herwig, Franziska Werner, Katarina Špiranec Spes, Marco Abeßer, Kai Schuh, Swati Dabral, Andreas Mügge, Hideo A. Baba, Boris V. Skryabin, Nazha Hamdani, Michaela Kuhn
Abstract
The spontaneously hypertensive rat (SHR) is a genetic model of primary hypertension with an etiology that includes sympathetic overdrive. To elucidate the neurogenic mechanisms underlying the pathophysiology of this model, we analyzed the dynamic baroreflex response to spontaneous fluctuations in arterial pressure in conscious SHRs, as well as in the Wistar-Kyoto (WKY), the Dahl salt-sensitive, the Dahl salt-resistant, and the Sprague-Dawley rat. Observations revealed the existence of long intermittent periods (lasting up to several minutes) of engagement and disengagement of baroreflex control of heart rate. Analysis of these intermittent periods revealed a predictive relationship between increased mean arterial pressure and progressive baroreflex disengagement that was present in the SHR and WKY strains but absent in others. This relationship yielded the hypothesis that a lower proportion of engagement versus disengagement of the baroreflex in SHR compared with WKY contributes to the hypertension (or increased blood pressure) in SHR compared with WKY. Results of experiments using sinoaortic baroreceptor denervation were consistent with the hypothesis that dysfunction of the baroreflex contributes to the etiology of hypertension in the SHR. Thus, this study provides experimental evidence for the roles of the baroreflex in long-term arterial pressure regulation and in the etiology of primary hypertension in this animal model.
Authors
Feng Gu, E. Benjamin Randall, Steven Whitesall, Kimber Converso-Baran, Brian E. Carlson, Gregory D. Fink, Daniel E. Michele, Daniel A. Beard
Abstract
Dilated cardiomyopathy (DCM) is often associated with sarcomere protein mutations that confer reduced myofilament tension-generating capacity. We demonstrate that cardiac twitch tension-time integrals can be targeted and tuned to prevent DCM remodeling in hearts with contractile dysfunction. We employ a transgenic murine model of DCM caused by the D230N tropomyosin (Tm) mutation and design a sarcomere-based intervention specifically targeting the twitch tension-time integral of D230N-Tm hearts using multiscale computational models of intra- and inter-molecular interactions in the thin filament and cell-level contractile simulations. Our models predict that increasing the calcium-sensitivity of thin filament activation using the cardiac troponin C (cTnC) variant L48Q can sufficiently augment twitch tension-time integrals of D230N-Tm hearts. Indeed, cardiac muscle isolated from double-transgenic (DTG) hearts expressing D230N Tm and L48Q cTnC have increased calcium-sensitivity of tension development and increased twitch tension-time integrals compared to preparations from hearts with D230N Tm alone. Longitudinal echocardiographic measurements revealed that DTG hearts retain normal cardiac morphology and function, while D230N-Tm hearts develop progressive DCM. We present a computational and experimental framework for targeting molecular mechanisms governing the twitch tension of cardiomyopathic hearts to counteract putative mechanical drivers of adverse remodeling, and open new possibilities for tension-based treatments of genetic cardiomyopathies.
Authors
Joseph D. Powers, Kristina B. Kooiker, Allison B. Mason, Abigail E. Teitgen, Galina V. Flint, Jil C. Tardiff, Steven D. Schwartz, Andrew D. McCulloch, Michael Regnier, Jennifer Davis, Farid Moussavi-Harami
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