Biology subjects

London, B.

Publications and source records attributed to London, B..

8 recordsLinked to original sources

bioRxiv2026

Post-daunorubicin treatment effects on cardiovascular function in the Ts65Dn mouse model of Down syndrome

Adults with Down syndrome (DS) are two times more likely to be diagnosed with chronic heart failure post-anthracycline chemotherapy compared to age and sex-matched adults without DS. They have an elevated lifetime risk of cardiovascular diseases, increasing their likelihood of anthracycline-induced chronic cardiovascular toxicity. We investigated the chronic effects of daunorubicin on the cardiovascular system of the adult Ts65Dn mouse model of DS compared to wild type euploid mice (WT). WT and Ts65Dn mice received two doses of 2mg/kg or 4mg/kg of daunorubicin or saline and were monitored for up to 117 days. Cardiac and vascular function were evaluated using left ventricular catheterization, histology, pulse wave velocity, and cardiac troponin tests. Survival significantly decreased in the Ts65Dn 4mg/kg group compared to saline controls (p<0.001). Further experiments were carried out with the saline and 2mg/kg groups, which exhibited lower mortality, more consistent with chronic toxicity. Body weight (p=0.001), end-diastolic pressure (p=0.016), and left ventricular mass (p=0.021) decreased in treated mice. The effect of treatment differed significantly between strains for ejection fraction (p=0.029). Pulse wave velocity increased over time (p<0.001). A significant interaction between treatment and strain was observed for collagen in both the left ventricles and thoracic aorta (p=0.002 and p<0.001, respectively). There was a strain difference for cardiac troponin I, indicating an increase in Ts65Dn mice (p=0.020). Daunorubicin treatment results in a distinct cardiovascular remodeling phenotype in Ts65Dn mice. More mechanistic studies are warranted to outline the pathophysiology of anthracycline cardiovascular toxicity in DS.

cancer biology↗

bioRxiv2025

Non-canonical Sodium Channel Isoforms Underlie Chamber Specific Cardiac Excitability

Voltage-gated sodium (NaV) channels drive cardiac excitability. While NaV1.5 is the primary cardiac isoform, the composition and functional contributions of non-NaV1.5 isoforms in the heart remain unclear. Here, we developed a chemical-genetic mouse model (NaV1.5-GX) in which NaV1.5 can be selectively and reversibly inhibited by acyl- and aryl-sulfonamide compounds (GX drugs). NaV1.5-GX mice exhibited normal cardiac function at baseline, but acute GX drug administration caused profound conduction defects and arrhythmias. Whole-heart optical mapping revealed dose-dependent chamber-specific sensitivity to NaV1.5 inhibition, with the right ventricle (RV) being the most sensitive, followed by the left ventricle (LV), left atrium (LA), and right atrium (RA). Patch-clamp recordings of isolated cardiomyocytes with application of NaV isoform-selective inhibitors showed that NaV1.5 contributed 93% of sodium current in the LV, 81% in the RV and 78% in the LA. Non-NaV1.5 isoforms were differentially enriched across chambers: NaV1.8 in the LV, NaV1.1/1.3 in the RV, and NaV1.2/1.6/1.7 in the atria. These results reveal a surprising chamber-specific isoform landscape of cardiac sodium currents which may underlie the right ventricular predominant phenotype of Brugada syndrome and highlight non-NaV1.5 isoforms as potential mediators of chamber-specific cardiac pathologies and as pharmacological targets.

physiology↗

bioRxiv2024

Identification of In Vivo Internalizing Cardiac-Specific RNA Aptamers

BackgroundThe pursuit of selective therapeutic delivery to target tissue types represents a key goal in the treatment of a range of adverse health issues, including diseases afflicting the heart. The development of new cardiac-specific ligands is a crucial step towards effectively targeting therapeutics to the heart. MethodsUtilizing an ex vivo and in vivo SELEX approaches, we enriched a library of 2-fluoro modified aptamers for ventricular cardiomyocyte specificity. Lead candidates were identified from this library, and their binding and internalization into cardiomyocytes was evaluated in both ex vivo and in vivo mouse studies. ResultsThe ex vivo and in vivo SELEX processes generated an aptamer library with significant cardiac specificity over non-cardiac tissues such as liver and skeletal muscle. Our lead candidate aptamer from this library, CA1, demonstrates selective in vivo targeting and delivery of a fluorophore cargo to ventricular cardiomyocytes within the murine heart, while minimizing off-target localization to non-cardiac tissues, including the liver. By employing a novel RNase-based assay to evaluate aptamer interactions with cardiomyocytes, we discovered that CA1 predominantly internalizes into ventricular cardiomyocytes; conversely, another candidate CA41 primarily binds to the cardiomyocyte cell surface. ConclusionsThese findings suggest that CA1 and CA41 have the potential to be promising candidates for targeted drug delivery and imaging applications in cardiac diseases.

bioengineering↗

bioRxiv2024

Upstream alternative polyadenylation in SCN5A produces a short transcript isoform encoding a mitochondria-localized NaV1.5 N-terminal fragment that influences cardiomyocyte respiration

SCN5A encodes the cardiac voltage-gated Na+ channel, NaV1.5, that initiates action potentials. SCN5A gene variants cause arrhythmias and increased heart failure risk. Mechanisms controlling NaV1.5 expression and activity are not fully understood. We recently found a well-conserved alternative polyadenylation (APA) signal downstream of the first SCN5A coding exon. This yields a SCN5A-short transcript isoform expressed in several species (e.g. human, pig, and cat), though rodents lack this upstream APA. Reanalysis of transcriptome-wide cardiac APA-seq and mRNA-seq data shows reductions in both upstream APA usage and short/full-length SCN5A mRNA ratios in failing hearts. Knock-in of the human SCN5A APA sequence into mice is sufficient to enable expression of SCN5A-short transcript, while significantly decreasing expression of full-length SCN5A mRNA. Notably, SCN5A-short transcript encodes a novel protein (NaV1.5-NT), composed of an N-terminus identical to NaV1.5 and a unique C-terminus derived from intronic sequence. AAV9 constructs were able to achieve stable NaV1.5-NT expression in mouse hearts, and western blot of human heart tissues showed bands co-migrating with NaV1.5-NT transgene-derived bands. NaV1.5-NT is predicted to contain a mitochondrial targeting sequence and localizes to mitochondria in cultured cardiomyocytes and in mouse hearts. NaV1.5-NT expression in cardiomyocytes led to elevations in basal oxygen consumption rate, ATP production, and mitochondrial ROS, while depleting NADH supply. Native PAGE analyses of mitochondria lysates revealed that NaV1.5-NT expression resulted in increased levels of disassembled complex V subunits and accumulation of complex I-containing supercomplexes. Overall, we discovered that APA-mediated regulation of SCN5A produces a short transcript encoding NaV1.5-NT. Our data support that NaV1.5-NT plays a multifaceted role in influencing mitochondrial physiology: 1) by increasing basal respiration likely through promoting complex V conformations that enhance proton leak, and 2) by increasing overall respiratory efficiency and NADH consumption by enhancing formation and/or stability of complex I-containing respiratory supercomplexes, though the specific molecular mechanisms underlying each of these remain unresolved.

physiology↗

bioRxiv2022

SUMOylation of the Cardiac Sodium Channel NaV1.5 Modifies Inward Current and Cardiac Excitability

BackgroundDecreased peak sodium current (INa) and increased late sodium current (INa,L), through the cardiac sodium channel NaV1.5 encoded by SCN5A, cause arrhythmias. Many NaV1.5 post-translational modifications have been reported by us and others. A recent report concluded that acute hypoxia increases INa,L by increasing a Small Ubiquitin-like MOdifier (SUMOylation) at K442-NaV1.5. ObjectiveTo determine whether and by what mechanisms SUMOylation alters INa, INa,L and cardiac electrophysiology. MethodsSUMOylation of NaV1.5 was detected by immunoprecipitation and immunoblotting. INa was measured by patch clamp with/without SUMO1 overexpression in HEK293 cells expressing wild type (WT) or K442R-NaV1.5 and in neonatal rat cardiac myocytes (NRCMs). SUMOylation effects were studied in vivo by electrocardiograms and ambulatory telemetry using Scn5a heterozygous knockout (SCN5A+/-) mice and the de-SUMOylating protein SENP2 (AAV9-SENP2) or the SUMOylation inhibitor anacardic acid. NaV1.5 trafficking was detected by immunofluorescence. ResultsNaV1.5 was SUMOylated in HEK293 cells, NRCMs and human heart tissue. HyperSUMOylation at NaV1.5-K442 increased INa in NRCMs and in HEK cells overexpressing WT but not K442R-Nav1.5. SUMOylation did not alter other channel properties including INa,L. AAV9-SENP2 or anacardic acid treatment of SCN5A+/- mice decreased INa, prolonged QRS duration, and produced heart block and ventricular arrhythmias. SUMO1 overexpression enhanced membrane localization of NaV1.5. ConclusionSUMOylation of K442-Nav1.5 increases peak INa without changing INa,L, at least in part by altering membrane abundance. Our findings do not support SUMOylation as a mechanism for changes in INa,L. Nav1.5 SUMOylation may modify arrhythmic risk in disease states and represents a potential target for pharmacological manipulation.

physiology↗

bioRxiv2022

Knockout of Sorbs2 in Cardiomyocytes Leads to Dilated Cardiomyopathy in Mice

2.RationaleSorbs2 is a cardiomyocyte-enriched, cytoskeletal adaptor protein, and given some evidence for its dysregulated expression in failing hearts, there is growing interest in understanding its roles in cardiac biology and disease. While Sorbs2 global knockout mice display lethal cardiomyopathy with severe arrhythmias, the underlying mechanisms remain unclear, and whether this results from intrinsic loss of Sorbs2 in cardiomyocytes is unknown, as Sorbs2 is also well-expressed in the nervous system and vasculature. In addition, the potential relevance of Sorbs2 in human cardiomyopathy remains underexplored. ObjectiveTo characterize the effects and potential underlying mechanisms of cardiomyocyte- specific deletion of Sorbs2 on cardiac structure and function in mice, and to further examine Sorbs2 dysregulation in failing hearts and explore potential links between Sorbs2 genetic variations and human cardiovascular disease phenotypes. Methods and ResultsWe report that myocardial Sorbs2 expression is consistently upregulated in humans with ischemic and idiopathic cardiomyopathies, and in experimental animal models of heart failure (HF). We generated mice with cardiomyocyte-specific loss of Sorbs2 (Sorbs2-cKO) and found early atrial and ventricular conduction abnormalities, despite unaltered expression of primary action potential ion channels and gap junction proteins. At mid-life, Sorbs2-cKO mice exhibit impaired cardiac contractility with cardiomyofibers failing to maintain adequate mechanical tension. As a result, these mice develop progressive diastolic and systolic dysfunction, enlarged cardiac chambers, and die with congestive HF at approximately one year of age. Comprehensive survey of potential underlying mechanisms revealed that Sorbs2-cKO hearts exhibit defective microtubule polymerization and compensatory upregulation of structural proteins desmin, vinculin, and tubulins. Finally, consistent with our observations in mice, we identified suggestive links between Sorbs2 genetic variants and related human cardiac phenotypes, including conduction abnormalities, atrial enlargement, and dilated cardiomyopathy. ConclusionsOur studies show that Sorbs2 is essential for maintaining cytoskeletal structural integrity in cardiomyocytes likely through strengthening the interactions between microtubules and other structural proteins at crosslink sites. Overall, this study provides key insights into the critical role for Sorbs2 in cardiomyocytes and likely other cell types in maintaining normal cardiac structure and function and highlights its potential clinical relevance.

physiology↗

bioRxiv2022

Metabolic rescue ameliorates mitochondrial encephalo-cardiomyopathy in murine and human iPSC models of Leigh syndrome

Mice with deletion of complex I subunit Ndufs4 develop mitochondrial encephalomyopathy resembling Leigh syndrome (LS). We report that LS mice also develop severe cardiac bradyarrhythmia and diastolic dysfunction. Human induced pluripotent stem cell-derived cardiomyocytes (iPS-CMs) with Ndufs4 deletion recapitulate LS cardiomyopathy. Mechanistically, we demonstrate a direct link between complex I deficiency, decreased intracellular NAD+/ NADH and bradyarrhythmia, mediated by hyperacetylation of the cardiac sodium channel NaV1.5, particularly at K1479 site. Neuronal apoptosis in the cerebellar and midbrain regions in LS mice was associated with hyperacetylation of p53 and activation of microglia. Targeted metabolomics revealed increases in several amino acids and citric acid cycle intermediates, likely due to impairment of NAD+-dependent dehydrogenases, and a substantial decrease in reduced Glutathione (GSH). Metabolic rescue by nicotinamide riboside (NR) supplementation increased intracellular NAD+/ NADH, restored metabolic derangement, reversed protein hyperacetylation through NAD+-dependent Sirtuin deacetylase, and ameliorated cardiomyopathic phenotypes, concomitant with improvement of NaV1.5 current and SERCA2a function measured by Ca2+- transients. NR also attenuated neuronal apoptosis and microglial activation in the LS brain and human iPS-derived neurons with Ndufs4 deletion. Our study reveals direct mechanistic explanations of the observed cardiac bradyarrhythmia, diastolic dysfunction and neuronal apoptosis in mouse and human iPSC models of LS.

pathology↗

bioRxiv2020

Modulation of the Cardiac Sodium Channel Nav1.5 Peak and Late Currents by NAD+ Precursors

RationaleThe cardiac sodium channel NaV1.5, encoded by SCN5A, produces the rapidly inactivating depolarizing current INa that is responsible for the initiation and propagation of the cardiac action potential. Acquired and inherited dysfunction of NaV1.5 results in either decreased peak INa or increased residual late INa (INa,L), leading to tachy/bradyarrhythmias and sudden cardiac death. Previous studies have shown that increased cellular NAD+ and NAD+/NADH ratio increase INa through suppression of mitochondrial reactive oxygen species and PKC-mediated NaV1.5 phosphorylation. In addition, NAD+-dependent deacetylation of NaV1.5 at K1479 by Sirtuin 1 increases NaV1.5 membrane trafficking and INa. The role of NAD+ precursors in modulating INa remains unknown. ObjectiveTo determine whether and by which mechanisms the NAD+ precursors nicotinamide riboside (NR) and nicotinamide (NAM) affect peak INa and INa,L in vitro and cardiac electrophysiology in vivo. Methods and ResultsThe effects of NAD+ precursors on the NAD+ metabolome and electrophysiology were studied using HEK293 cells expressing wild-type and mutant NaV1.5, rat neonatal cardiomyocytes (RNCMs), and mice. NR increased INa in HEK293 cells expressing NaV1.5 (500 M: 51 {+/-} 18%, p=0.02, 5 mM: 59 {+/-} 22%, p=0.03) and RNCMs (500 {micro}M: 60 {+/-} 26%, p=0.02, 5 mM: 75 {+/-} 39%, p=0.03) while reducing INa,L at the higher concentration (RNCMs, 5 mM: -45 {+/-} 11%, p=0.04). NR (5 mM) decreased NaV1.5 K1479 acetylation but increased INa in HEK293 cells expressing a mutant form of NaV1.5 with disruption of the acetylation site (NaV1.5-K1479A). Disruption of the PKC phosphorylation site abolished the effect of NR on INa. Furthermore, NAM (5 mM) had no effect on INa in RNCMs or in HEK293 cells expressing wild-type NaV1.5, but increased INa in HEK293 cells expressing NaV1.5-K1479A. Dietary supplementation with NR for 10-12 weeks decreased QTc in C57BL/6J mice (0.35% NR: -4.9 {+/-} 2.0%, p=0.26; 1.0% NR: -9.5 {+/-} 2.8%, p=0.01). ConclusionsNAD+ precursors differentially regulate NaV1.5 via multiple mechanisms. NR increases INa, decreases INa,L, and warrants further investigation as a potential therapy for arrhythmic disorders caused by NaV1.5 deficiency and/or dysfunction.

physiology↗