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Electrophysiological effects of natriuretic peptides in the heart are mediated by multiple receptor subtypes. - Progress in biophysics and molecular biology
Natriuretic peptides (NPs) are a family of cardioprotective hormones with numerous beneficial effects in cardiovascular system. The NP family includes several peptides including atrial NP (ANP), B-type NP (BNP), C-type NP (CNP) and Dendroaspis NP (DNP). These peptides elicit their effects by binding to three distinct cell surface receptors called natriuretic peptide receptors A, B and C (NPR-A, NPR-B and NPR-C). NPR-A (which binds ANP, BNP and DNP) and NPR-B (which is selective for CNP) are particulate guanylyl cyclase (GC)-linked receptors that mediate increases in cGMP upon activation. cGMP can then target several downstream signaling molecules including protein kinase G (PKG), phosphodiesterase 2 (PDE2) and phosphodiesterase 3 (PDE3). NPR-C, which is able to bind all NPs with comparable affinity, is coupled to the activation of inhibitory G-proteins (Gi) that inhibit adenylyl cyclase (AC) activity and reduce cAMP levels. NPs are best known for their ability to regulate blood volume and fluid homeostasis. More recently, however, it has become apparent that NPs are essential regulators of cardiac electrophysiology and arrhythmogenesis. Evidence for this comes from numerous studies of the effects of NPs on cardiac electrophysiology and ion channel function in different regions and cell types within the heart, as well as the identification of mutations in the NP system that cause atrial fibrillation in humans. Despite the strong evidence that NPs regulate cardiac electrophysiology different studies have reported varying effects of NPs. The reasons for disparate observations are not fully understood, but likely occur as a result of several factors, including the fact that NP signaling can be highly complex and involve multiple receptors and/or downstream signaling molecules which may be differentially activated in different conditions. The goal of this review is to provide a comprehensive summary of the different effects of NPs on cardiac electrophysiology that have been described and to provide rationale and explanation for why different results may be obtained in different studies.Copyright Â© 2015 Elsevier Ltd. All rights reserved.
Effects of Wild-Type and Mutant Forms of Atrial Natriuretic Peptide on Atrial Electrophysiology and Arrhythmogenesis. - Circulation. Arrhythmia and electrophysiology
Atrial natriuretic peptide (ANP) is a hormone with numerous beneficial cardiovascular effects. Recently, a mutation in the ANP gene, which results in the generation of a mutant form of ANP (mANP), was identified and shown to cause atrial fibrillation in people. The mechanism(s) through which mANP causes atrial fibrillation is unknown. Our objective was to compare the effects of wild-type ANP and mANP on atrial electrophysiology in mice and humans.Action potentials (APs), L-type Ca(2+) currents (ICa,L), and Na(+) current were recorded in atrial myocytes from wild-type or natriuretic peptide receptor C knockout (NPR-C(-/-)) mice. In mice, ANP and mANP (10-100 nmol/L) had opposing effects on atrial myocyte AP morphology and ICa,L. ANP increased AP upstroke velocity (Vmax), AP duration, and ICa,L similarly in wild-type and NPR-C(-/-) myocytes. In contrast, mANP decreased Vmax, AP duration, and ICa,L, and these effects were completely absent in NPR-C(-/-) myocytes. ANP and mANP also had opposing effects on ICa,L in human atrial myocytes. In contrast, neither ANP nor mANP had any effect on Na(+) current in mouse atrial myocytes. Optical mapping studies in mice demonstrate that ANP sped electric conduction in the atria, whereas mANP did the opposite and slowed atrial conduction. Atrial pacing in the presence of mANP induced arrhythmias in 62.5% of hearts, whereas treatment with ANP completely prevented the occurrence of arrhythmias.These findings provide mechanistic insight into how mANP causes atrial fibrillation and demonstrate that wild-type ANP is antiarrhythmic.Â© 2015 American Heart Association, Inc.
Protein phosphatase 2A regulatory subunit B56Î± limits phosphatase activity in the heart. - Science signaling
Protein phosphatase 2A (PP2A) is a serine/threonine-selective holoenzyme composed of a catalytic, scaffolding, and regulatory subunit. In the heart, PP2A activity is requisite for cardiac excitation-contraction coupling and central in adrenergic signaling. We found that mice deficient in the PP2A regulatory subunit B56Î± (1 of 13 regulatory subunits) had altered PP2A signaling in the heart that was associated with changes in cardiac physiology, suggesting that the B56Î± regulatory subunit had an autoinhibitory role that suppressed excess PP2A activity. The increase in PP2A activity in the mice with reduced B56Î± expression resulted in slower heart rates and increased heart rate variability, conduction defects, and increased sensitivity of heart rate to parasympathetic agonists. Increased PP2A activity in B56Î±(+/-) myocytes resulted in reduced Ca(2+) waves and sparks, which was associated with decreased phosphorylation (and thus decreased activation) of the ryanodine receptor RyR2, an ion channel on intracellular membranes that is involved in Ca(2+) regulation in cardiomyocytes. In line with an autoinhibitory role for B56Î±, in vivo expression of B56Î± in the absence of altered abundance of other PP2A subunits decreased basal phosphatase activity. Consequently, in vivo expression of B56Î± suppressed parasympathetic regulation of heart rate and increased RyR2 phosphorylation in cardiomyocytes. These data show that an integral component of the PP2A holoenzyme has an important inhibitory role in controlling PP2A enzyme activity in the heart.Copyright Â© 2015, American Association for the Advancement of Science.
Cadherin-13 gene is associated with hyperactive/impulsive symptoms in attention/deficit hyperactivity disorder. - American journal of medical genetics. Part B, Neuropsychiatric genetics : the official publication of the International Society of Psychiatric Genetics
Several efforts have been made to find new genetic risk variants which explain the high heritability of ADHD. At the genome level, genes involved in neurodevelopmental pathways were pointed as candidates. CDH13 and CTNNA2 genes are within GWAS top hits in ADHD and there are emerging notions about their contribution to ADHD pathophysiology. The main goal of this study is to test the association between SNPs in CDH13 and CTNNA2 genes and ADHD across the life cycle in subjects with ADHD. This study included 1,136 unrelated ADHD cases and 946 individuals without ADHD. No significant association between CDH13 and CTNNA2 was observed between cases and controls across different samples (Pâ€‰â‰¥â€‰0.096 for all comparisons). No allele was significantly more transmitted than expected from parents to ADHD probands. The CDH13 rs11150556 CC genotype was associated with more hyperactive/impulsive symptoms in youths with ADHD (children/adolescents clinical sample: Fâ€‰=â€‰7.666, Pâ€‰=â€‰0.006, FDR P-valueâ€‰=â€‰0.032; Pelotas Birth Cohort sample: Fâ€‰=â€‰6.711, Pâ€‰=â€‰0.011, FDR P-valueâ€‰=â€‰0.032). Although there are many open questions regarding the role of neurodevelopmental genes in ADHD symptoms, the present study suggests that CDH13 is associated with hyperactive/impulsive symptoms in youths with ADHD.Â© 2015 Wiley Periodicals, Inc.
Impaired sinoatrial node function and increased susceptibility to atrial fibrillation in mice lacking natriuretic peptide receptor C. - The Journal of physiology
Natriuretic peptides (NPs) are critical regulators of the cardiovascular system that are currently viewed as possible therapeutic targets for the treatment of heart disease. Recent work demonstrates potent NP effects on cardiac electrophysiology, including in the sinoatrial node (SAN) and atria. NPs elicit their effects via three NP receptors (NPR-A, NPR-B and NPR-C). Among these receptors, NPR-C is poorly understood. Accordingly, the goal of this study was to determine the effects of NPR-C ablation on cardiac structure and arrhythmogenesis. Cardiac structure and function were assessed in wild-type (NPR-C(+/+)) and NPR-C knockout (NPR-C(-/-)) mice using echocardiography, intracardiac programmed stimulation, patch clamping, high-resolution optical mapping, quantitative polymerase chain reaction and histology. These studies demonstrate that NPR-C(-/-) mice display SAN dysfunction, as indicated by a prolongation (30%) of corrected SAN recovery time, as well as an increased susceptibility to atrial fibrillation (6% in NPR-C(+/+) vs. 47% in NPR-C(-/-)). There were no differences in SAN or atrial action potential morphology in NPR-C(-/-) mice; however, increased atrial arrhythmogenesis in NPR-C(-/-) mice was associated with reductions in SAN (20%) and atrial (15%) conduction velocity, as well as increases in expression and deposition of collagen in the atrial myocardium. No differences were seen in ventricular arrhythmogenesis or fibrosis in NPR-C(-/-) mice. This study demonstrates that loss of NPR-C results in SAN dysfunction and increased susceptibility to atrial arrhythmias in association with structural remodelling and fibrosis in the atrial myocardium. These findings indicate a critical protective role for NPR-C in the heart.Â© 2014 The Authors. The Journal of Physiology Â© 2014 The Physiological Society.
The -308G>a polymorphism of the TNF gene is associated with proliferative diabetic retinopathy in Caucasian Brazilians with type 2 diabetes. - Investigative ophthalmology & visual science
We tested the hypothesis that tumor necrosis factor (TNF) gene polymorphisms are associated with diabetic retinopathy (DR) in Caucasians with type 2 diabetes mellitus.In a case-control study, the -238G>A (rs361525), -308G>A (rs1800629), and -857C>T (rs1799724) polymorphisms of the TNF gene were genotyped in 745 outpatients with type 2 diabetes, including 331 subjects without DR, 246 with nonproliferative DR (NPDR), and 168 with proliferative DR (PDR).Genotype and allele frequencies of the -238G>A, -308G>A, and -857C>T polymorphisms in subjects with NPDR were not significantly different from those of subjects without DR (P > 0.05 for all comparisons). However, the A allele of the -308G>A polymorphism was more frequent in subjects with PDR than in those with no DR (18.1% vs. 11.5%, corrected P = 0.035). Multivariate logistic regression analysis showed that the -308A allele was independently associated with an increased risk of PDR, under a dominant model (adjusted odds ratio [aOR], 1.82; 95% confidence interval [CI], 1.11-2.98). The combined analysis of the three polymorphisms also showed that haplotypes containing the -308A allele were associated with an increased risk of PDR (aOR, 2.36; 95% CI, 1.29-4.32).This study detected, for the first time to our knowledge, an independent association of the -308G>A polymorphism in the TNF gene with PDR in Caucasian Brazilians with type 2 diabetes. This finding suggests that TNF is a potential susceptibility gene for PDR.Copyright 2015 The Association for Research in Vision and Ophthalmology, Inc.
Dysfunction in the Î²II spectrin-dependent cytoskeleton underlies human arrhythmia. - Circulation
The cardiac cytoskeleton plays key roles in maintaining myocyte structural integrity in health and disease. In fact, human mutations in cardiac cytoskeletal elements are tightly linked to cardiac pathologies, including myopathies, aortopathies, and dystrophies. Conversely, the link between cytoskeletal protein dysfunction and cardiac electric activity is not well understood and often overlooked in the cardiac arrhythmia field.Here, we uncover a new mechanism for the regulation of cardiac membrane excitability. We report that Î²II spectrin, an actin-associated molecule, is essential for the posttranslational targeting and localization of critical membrane proteins in heart. Î²II spectrin recruits ankyrin-B to the cardiac dyad, and a novel human mutation in the ankyrin-B gene disrupts the ankyrin-B/Î²II spectrin interaction, leading to severe human arrhythmia phenotypes. Mice lacking cardiac Î²II spectrin display lethal arrhythmias, aberrant electric and calcium handling phenotypes, and abnormal expression/localization of cardiac membrane proteins. Mechanistically, Î²II spectrin regulates the localization of cytoskeletal and plasma membrane/sarcoplasmic reticulum protein complexes, including the Na/Ca exchanger, ryanodine receptor 2, ankyrin-B, actin, and Î±II spectrin. Finally, we observe accelerated heart failure phenotypes in Î²II spectrin-deficient mice.Our findings identify Î²II spectrin as critical for normal myocyte electric activity, link this molecule to human disease, and provide new insight into the mechanisms underlying cardiac myocyte biology.Â© 2015 American Heart Association, Inc.
Isolation of single Chlamydia-infected cells using laser microdissection. - Journal of microbiological methods
Chlamydia are obligate intracellular parasites of humans and animals that cause a wide range of acute and chronic infections. To elucidate the genetic basis of chlamydial parasitism, several approaches for making genetic modifications to Chlamydia have recently been reported. However, the lack of the available methods for the fast and effective selection of genetically modified bacteria restricts the application of genetic tools. We suggest the use of laser microdissection to isolate of single live Chlamydia-infected cells for the re-cultivation and whole-genome sequencing of single inclusion-derived Chlamydia. To visualise individual infected cells, we made use of the vital labelling of inclusions with the fluorescent Golgi-specific dye BODIPYÂ® FL C5-ceramide. We demonstrated that single Chlamydia-infected cells isolated by laser microdissection and placed onto a host cell monolayer resulted in new cycles of infection. We also demonstrated the successful use of whole-genome sequencing to study the genomic variability of Chlamydia derived from a single inclusion. Our work provides the first evidence of the successful use of laser microdissection for the isolation of single live Chlamydia-infected cells, thus demonstrating that this method can help overcome the barriers to the fast and effective selection of Chlamydia.Copyright Â© 2014 Elsevier B.V. All rights reserved.
Ankyrin-G coordinates intercalated disc signaling platform to regulate cardiac excitability in vivo. - Circulation research
Nav1.5 (SCN5A) is the primary cardiac voltage-gated Nav channel. Nav1.5 is critical for cardiac excitability and conduction, and human SCN5A mutations cause sinus node dysfunction, atrial fibrillation, conductional abnormalities, and ventricular arrhythmias. Further, defects in Nav1.5 regulation are linked with malignant arrhythmias associated with human heart failure. Consequently, therapies to target select Nav1.5 properties have remained at the forefront of cardiovascular medicine. However, despite years of investigation, the fundamental pathways governing Nav1.5 membrane targeting, assembly, and regulation are still largely undefined.Define the in vivo mechanisms underlying Nav1.5 membrane regulation.Here, we define the molecular basis of an Nav channel regulatory platform in heart. Using new cardiac-selective ankyrin-G(-/-) mice (conditional knock-out mouse), we report that ankyrin-G targets Nav1.5 and its regulatory protein calcium/calmodulin-dependent kinase II to the intercalated disc. Mechanistically, Î²IV-spectrin is requisite for ankyrin-dependent targeting of calcium/calmodulin-dependent kinase II-Î´; however, Î²IV-spectrin is not essential for ankyrin-G expression. Ankyrin-G conditional knock-out mouse myocytes display decreased Nav1.5 expression/membrane localization and reduced INa associated with pronounced bradycardia, conduction abnormalities, and ventricular arrhythmia in response to Nav channel antagonists. Moreover, we report that ankyrin-G links Nav channels with broader intercalated disc signaling/structural nodes, as ankyrin-G loss results in reorganization of plakophilin-2 and lethal arrhythmias in response to Î²-adrenergic stimulation.Our findings provide the first in vivo data for the molecular pathway required for intercalated disc Nav1.5 targeting/regulation in heart. Further, these new data identify the basis of an in vivo cellular platform critical for membrane recruitment and regulation of Nav1.5.Â© 2014 American Heart Association, Inc.
EHD3-dependent endosome pathway regulates cardiac membrane excitability and physiology. - Circulation research
Cardiac function is dependent on the coordinate activities of membrane ion channels, transporters, pumps, and hormone receptors to tune the membrane electrochemical gradient dynamically in response to acute and chronic stress. Although our knowledge of membrane proteins has rapidly advanced during the past decade, our understanding of the subcellular pathways governing the trafficking and localization of integral membrane proteins is limited and essentially unstudied in vivo. In the heart, to our knowledge, there are no in vivo mechanistic studies that directly link endosome-based machinery with cardiac physiology.To define the in vivo roles of endosome-based cellular machinery for cardiac membrane protein trafficking, myocyte excitability, and cardiac physiology.We identify the endosome-based Eps15 homology domain 3 (EHD3) pathway as essential for cardiac physiology. EHD3-deficient hearts display structural and functional defects including bradycardia and rate variability, conduction block, and blunted response to adrenergic stimulation. Mechanistically, EHD3 is critical for membrane protein trafficking, because EHD3-deficient myocytes display reduced expression/localization of Na/Ca exchanger and L-type Ca channel type 1.2 with a parallel reduction in Na/Ca exchanger-mediated membrane current and Cav1.2-mediated membrane current. Functionally, EHD3-deficient myocytes show increased sarcoplasmic reticulum [Ca], increased spark frequency, and reduced expression/localization of ankyrin-B, a binding partner for EHD3 and Na/Ca exchanger. Finally, we show that in vivo EHD3-deficient defects are attributable to cardiac-specific roles of EHD3 because mice with cardiac-selective EHD3 deficiency demonstrate both structural and electric phenotypes.These data provide new insight into the critical role of endosome-based pathways in membrane protein targeting and cardiac physiology. EHD3 is a critical component of protein trafficking in heart and is essential for the proper membrane targeting of select cellular proteins that maintain excitability.Â© 2014 American Heart Association, Inc.
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