scholarly journals Targeting the Microtubule EB1-CLASP2 Complex Modulates Na V 1.5 at Intercalated Discs

2021 ◽  
Author(s):  
Gerard A Marchal ◽  
Mariam Jouni ◽  
David Y Chiang ◽  
Marta Pérez-Hernández Duran ◽  
Svitlana Podliesna ◽  
...  
Keyword(s):  
Sodium Current ◽  
Induced Pluripotent Stem Cell ◽  
Loss Of Function ◽  
Whole Cell ◽  
Intercalated Discs ◽  
Cardiac Sodium Channel ◽  
Optical Reconstruction ◽  
Induced Pluripotent ◽  
And Function

Rationale: Loss-of-function of the cardiac sodium channel Na V 1.5 causes conduction slowing and arrhythmias. Na V 1.5 is differentially distributed within subcellular domains of cardiomyocytes, with sodium current (I Na ) being enriched at the intercalated discs (ID). Various pathophysiological conditions associated with lethal arrhythmias display ID-specific I Na reduction, but the mechanisms underlying microdomain-specific targeting of Na V 1.5 remain largely unknown. Objective: To investigate the role of the microtubule (MT) plus-end tracking proteins end binding protein 1 (EB1) and CLIP-associated protein 2 (CLASP2) in mediating Na V 1.5 trafficking and subcellular distribution in cardiomyocytes. Methods and Results: EB1 overexpression in human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) resulted in enhanced whole-cell I Na , increased action potential (AP) upstroke velocity (V max ), and enhanced Na V 1.5 localization at the plasma membrane as detected by multi-color stochastic optical reconstruction microscopy (STORM). Fluorescence recovery after photobleaching (FRAP) experiments in HEK293A cells demonstrated that EB1 overexpression promoted Na V 1.5 forward trafficking. Knockout of MAPRE1 in hiPSC-CMs led to reduced whole-cell I Na , decreased V max and AP duration (APD) prolongation. Similarly, acute knockout of the MAPRE1 homolog in zebrafish (mapre1b) resulted in decreased ventricular conduction velocity and V max as well as increased APD. STORM imaging and macropatch I Na measurements showed that subacute treatment (2-3 hours) with SB216763 (SB2), a GSK3β inhibitor known to modulate CLASP2-EB1 interaction, reduced GSK3β localization and increased Na V 1.5 and I Na preferentially at the ID region of wild type murine ventricular cardiomyocytes. By contrast, SB2 did not affect whole cell I Na or Na V 1.5 localization in cardiomyocytes from Clasp2-deficient mice, uncovering the crucial role of CLASP2 in SB2-mediated modulation of NaV1.5 at the ID. Conclusions: Our findings demonstrate the modulatory effect of the MT plus-end tracking protein EB1 on Na V 1.5 trafficking and function, and identify the EB1-CLASP2 complex as a target for preferential modulation of I Na within the ID region of cardiomyocytes.

Common Ancestry-specific Ion Channel Variants Predispose to Drug-induced Arrhythmias

Circulation ◽  
2022 ◽  
Author(s):  
Yuko Wada ◽  
Tao Yang ◽  
Christian M. Shaffer ◽  
Laura L. Daniel ◽  
Andrew M. Glazer ◽  
...  
Keyword(s):  
Sodium Current ◽  
Common Ancestry ◽  
Drug Induced ◽  
Reference Allele ◽  
Qt Intervals ◽  
Cardiac Sodium Channel ◽  
Induced Pluripotent ◽  
Type 3 ◽  
Congenital Long Qt Syndrome

Background: Multiple reports associate the cardiac sodium channel gene ( SCN5A ) variants S1103Y and R1193Q with type 3 congenital long QT syndrome (LQTS) and drug-induced LQTS. These variants are, however, too common in ancestral populations to be highly arrhythmogenic at baseline: S1103Y allele frequency is 8.1% in Africans and R1193Q 6.1% in East Asians. R1193Q is known to increase late sodium current (I Na-L ) in cardiomyocytes derived from induced pluripotent stem cells (iPSC-CMs) but the role of these variants in modulating repolarization remains poorly-understood. Methods: We determined the effect of S1103Y on QT intervals among Africans in a large electronic health record. Using iPSC-CMs carrying naturally occurring or genome-edited variants, we studied action potential durations (APDs) at baseline and after challenge with the repolarizing potassium current (I Kr ) blocker dofetilide, and I Na-L and I Kr at baseline. Results: In 1479 African subjects with no confounding medications or diagnoses of heart disease, QT in S1103Y carriers was no different from that in non-carriers. Similarly, baseline APD was no different in cells expressing the Y allele (SY, YY cells) compared to isogenic cells with the reference allele (SS cells). However, I Na-L was increased in SY and YY cells and the I Na-L blocker GS967 shortened APD in SY/YY but not SS cells (p<0.001). I Kr was increased almost 2-fold in SY/YY cells compared to SS cells (tail current: 0.66±0.1 vs 1.2±0.1 pA/pF, p<0.001). Dofetilide challenge prolonged APD at much lower concentrations in SY (4.1 nM [IQR 1.5-9.3], n=11) and YY (4.2 nM [1.7- 5.0], n=5) than in SS cells (249 nM [22.3-2905], n=14, p<0.001 and p<0.01, respectively) and elicited afterdepolarizations in 8/16 SY/YY cells but only in 1/14 SS cells. R1193Q cells similarly displayed no difference in baseline APD but increased I Kr and increased dofetilide sensitivity. Conclusions: These common ancestry-specific variants do not affect baseline repolarization, despite generating increased I Na-L . We propose that increased I Kr serves to maintain normal repolarization but increases the risk of manifest QT prolongation with I Kr block in variant carriers. Our findings further emphasize the need for inclusion of diverse populations in the study of adverse drug reactions.

scholarly journals Lysosomal perturbations in dopaminergic neurons derived from induced pluripotent stem cells with PARK2 mutation

2019 ◽  
Author(s):  
Justyna Okarmus ◽  
Helle Bogetofte ◽  
Sissel Ida Schmidt ◽  
Matias Ryding ◽  
Silvia Garcia Lopez ◽  
...  
Keyword(s):  
Dopaminergic Neurons ◽  
Induced Pluripotent Stem Cell ◽  
Autophagic Flux ◽  
Compensatory Mechanism ◽  
Loss Of Function ◽  
Gene Encoding ◽  
Tem Analysis ◽  
Induced Pluripotent ◽  
And Function ◽  
The Impact

AbstractMutations in the PARK2 gene encoding parkin, an E3 ubiquitin ligase, are associated with autosomal recessive early-onset Parkinson’s disease (PD). While parkin has been implicated in the regulation of mitophagy and proteasomal degradation, the precise mechanism leading to neurodegeneration in both sporadic and familial PD upon parkin loss-of-function mutations remains unknown. Cultures of isogenic induced pluripotent stem cell (iPSC) lines with and without PARK2 knockout (KO) enable mechanistic studies of the effect of parkin deficiency in human dopaminergic neurons. In the present study, we used such cells to investigate the impact of PARK2 KO on the lysosomal compartment combining different approaches, such as mass spectrometry-based proteomics, electron microscopy (TEM) analysis and functional assays. We discovered a clear link between parkin deficiency and lysosomal alterations. PARK2 KO neurons exhibited a perturbed lysosomal morphology, displaying significantly enlarged and electron-lucent lysosomes as well as an increased total lysosomal content, which was exacerbated by mitochondrial stress. In addition, we found perturbed autophagic flux and decreased lysosomal enzyme activity suggesting an impairment of the autophagy-lysosomal pathway in parkin-deficient cells. Interestingly, activity of the GBA-encoded enzyme, β-glucocerebrosidase, was significantly increased suggesting the existence of a compensatory mechanism. In conclusion, our data provide a unique characterization of the morphology, content, and function of lysosomes in PARK2 KO neurons, thus revealing a new important connection between mitochondrial dysfunction and lysosomal dysregulation in PD pathogenesis.

scholarly journals 4346 Potential Sudden Unexpected Death in Epilepsy (SUDEP) Biomarkers in Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes with DEPDC5 Loss-of-Function

2020 ◽  
Vol 4 (s1) ◽  
pp. 100-100
Author(s):  
Yanting Zhao ◽  
Helen Zhang ◽  
Jack M. Parent ◽  
Lori L. Isom
Keyword(s):  
Stem Cell ◽  
Voltage Clamp ◽  
Cardiac Arrhythmias ◽  
Pluripotent Stem Cell ◽  
Induced Pluripotent Stem Cell ◽  
Loss Of Function ◽  
Current Clamp ◽  
Unexpected Death ◽  
Whole Cell ◽  
Induced Pluripotent

OBJECTIVES/GOALS: Sudden Unexpected Death in Epilepsy (SUDEP) is a leading cause of death in epilepsy patients. This study aims to determine whether cardiac mechanisms contribute to SUDEP in epilepsy patients with variants in DEPDC5, a gene encoding a member of the mTOR GATOR complex, to identify SUDEP biomarkers. METHODS/STUDY POPULATION: SUDEP has been reported in 10% of epilepsy patients with DEPDC5 loss-of-function variants. We used human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) to measure changes in cellular excitability that are known to be substrates for cardiac arrhythmias. CRISPR-derived isogenic DEPDC5 iPSC-CMs and DEPDC5 patient-derived iPSC-CMs were used in this study. Whole-cell patch-clamp was used to measure voltage-gated sodium current (INa) and calcium current (I>Ca) in single iPSC-CMs in voltage-clamp mode; and to measure action potentials (APs) in 3-dimentional iPSC-CM-derived micro-tissues in current-clamp mode. RESULTS/ANTICIPATED RESULTS: CRISPR generated heterozygous deletion of 1 base-pair in the first coding exon of DEPDC5 gene, resulting in a premature stop codon, simulated the variants identified in DEPDC5 epilepsy patients. In CRISPR generated heterozygousDEPDC5 iPSC-CMs, whole-cell voltage-clamp recordings revealed that INa was increased and ICa was reduced compared with isogenic control iPSC-CMs. Whole-cell current-clamp recordings revealed that AP duration at 80% and 90% of repolarization, APD80 and APD90, respectively, were prolonged compared to isogenic control iPSC-CMs. Similar measurements will be performed for iPSC-CMs derived from DEPDC5 patients. DISCUSSION/SIGNIFICANCE OF IMPACT: This study shows that epilepsy patients with non-ion channel gene variants in DEPDC5 have altered CM excitability, which may serve as a substrate for cardiac arrhythmias in DEPDC5 patients. Importantly, this work may allow us to identify biomarkers for SUDEP risk in these patients in the future. CONFLICT OF INTEREST DESCRIPTION: L.L.I. is the recipient of a collaborative research grant from Stoke Therapeutics.

scholarly journals Calmodulin binds to the N-terminal domain of the cardiac sodium channel Nav1.5

2020 ◽  
Author(s):  
Zizun Wang ◽  
Sarah H. Vermij ◽  
Valentin Sottas ◽  
Anna Shestak ◽  
Daniela Ross-Kaschitza ◽  
...  
Keyword(s):  
Sodium Channel ◽  
Sodium Current ◽  
Dominant Negative ◽  
Dominant Negative Effect ◽  
Loss Of Function ◽  
Whole Cell ◽  
Calmodulin Binding ◽  
Neonatal Cardiomyocytes ◽  
Terminal Domain ◽  
Cardiac Sodium Channel

ABSTRACTThe cardiac voltage-gated sodium channel Nav1.5 conducts the rapid inward sodium current crucial for cardiomyocyte excitability. Loss-of-function mutations in its gene SCN5A are linked to cardiac arrhythmias such as Brugada Syndrome (BrS). Several BrS-associated mutations in the Nav1.5 N-terminal domain exert a dominant-negative effect (DNE) on wild-type channel function, for which mechanisms remain poorly understood. We aim to contribute to the understanding of BrS pathophysiology by characterizing three mutations in the Nav1.5 N-terminal domain (NTD): Y87C–here newly identified–, R104W and R121W. In addition, we hypothesize that the calcium sensor protein calmodulin is a new NTD binding partner.Recordings of whole-cell sodium currents in TsA-201 cells expressing WT and variant Nav1.5 showed that Y87C and R104W but not R121W exert a DNE on WT channels. Biotinylation assays revealed reduction in fully glycosylated Nav1.5 at the cell surface and in whole-cell lysates. Localization of Nav1.5 WT channel with the ER however did not change in the presence of variants, shown by transfected and stained rat neonatal cardiomyocytes. We next demonstrated that calmodulin binds Nav1.5 N-terminus using in silico modeling, SPOTS, pull-down and proximity ligation assays. This binding is impaired in the R121W variant and in a Nav1.5 construct missing residues 80-105, a predicted calmodulin binding site.In conclusion, we present the first evidence that calmodulin binds to the Nav1.5 NTD, which seems to be a determinant for the DNE.

scholarly journals Thioester-Containing Protein-4 Regulates the Drosophila Immune Signaling and Function against the Pathogen Photorhabdus

2016 ◽  
Vol 9 (1) ◽  
pp. 83-93 ◽  
Author(s):  
Upasana Shokal ◽  
Ioannis Eleftherianos
Keyword(s):  
Immune Response ◽  
Photorhabdus Luminescens ◽  
Human Pathogen ◽  
Loss Of Function ◽  
Phenoloxidase Activity ◽  
Microbial Infections ◽  
Immune Pathways ◽  
And Function ◽  
Important Progress

Despite important progress in identifying the molecules that participate in the immune response of Drosophila melanogaster to microbial infections, the involvement of thioester-containing proteins (TEPs) in the antibacterial immunity of the fly is not fully clarified. Previous studies mostly focused on identifying the function of TEP2, TEP3 and TEP6 molecules in the D. melanogaster immune system. Here, we investigated the role of TEP4 in the regulation and function of D. melanogaster host defense against 2 virulent pathogens from the genus Photorhabdus, i.e. the insect pathogenic bacterium Photorhabdus luminescens and the emerging human pathogen P. asymbiotica. We demonstrate that Tep4 is strongly upregulated in adult flies following the injection of Photorhabdus bacteria. We also show that Tep4 loss-of-function mutants are resistant to P. luminescens but not to P. asymbiotica infection. In addition, we find that inactivation of Tep4 results in the upregulation of the Toll and Imd immune pathways, and the downregulation of the Jak/Stat and Jnk pathways upon Photorhabdus infection. We document that loss of Tep4 promotes melanization and phenoloxidase activity in the mutant flies infected with Photorhabdus. Together, these findings generate novel insights into the immune role of TEP4 as a regulator and effector of the D. melanogaster antibacterial immune response.

PIN-FORMED 1 regulates cell fate at the periphery of the shoot apical meristem

Development ◽  
2000 ◽  
Vol 127 (23) ◽  
pp. 5157-5165 ◽  
Author(s):  
T. Vernoux ◽  
J. Kronenberger ◽  
O. Grandjean ◽  
P. Laufs ◽  
J. Traas
Keyword(s):  
Cell Fate ◽  
Apical Meristem ◽  
Transmembrane Protein ◽  
Loss Of Function ◽  
Hybrid Identity ◽  
Hormone Transport ◽  
Early Markers ◽  
Ideal Tool ◽  
And Function

The process of organ positioning has been addressed, using the pin-formed 1 (pin1) mutant as a tool. PIN1 is a transmembrane protein involved in auxin transport in Arabidopsis. Loss of function severely affects organ initiation, and pin1 mutants are characterised by an inflorescence meristem that does not initiate any flowers, resulting in the formation of a naked inflorescence stem. This phenotype, combined with the proposed role of PIN1 in hormone transport, makes the mutant an ideal tool to study organ formation and phyllotaxis, and here we present a detailed analysis of the molecular modifications at the shoot apex caused by the mutation. We show that meristem structure and function are not severely affected in the mutant. Major alterations, however, are observed at the periphery of the pin1 meristem, where organ initiation should occur. Although two very early markers of organ initiation, LEAFY and AINTEGUMENTA, are expressed at the periphery of the mutant meristem, the cells are not recruited into distinct primordia. Instead a ring-like domain expressing those primordium specific genes is observed around the meristem. This ring-like domain also expresses a boundary marker, CUP-SHAPED COTYLEDON 2, involved in organ separation, showing that the zone at the meristem periphery has a hybrid identity. This implies that PIN1 is not only involved in organ outgrowth, but that it is also necessary for organ separation and positioning. A model is presented in which PIN1 and the local distribution of auxin control phyllotaxis.

Role of Mcl-1 in regulation of cell death in human induced pluripotent stem cell-derived cardiomyocytes in vitro

2018 ◽  
Vol 360 ◽  
pp. 88-98 ◽  
Author(s):  
Liang Guo ◽  
Sandy Eldridge ◽  
Michael Furniss ◽  
Jodie Mussio ◽  
Myrtle Davis
Keyword(s):  
Cell Death ◽  
Stem Cell ◽  
Pluripotent Stem Cell ◽  
Induced Pluripotent Stem Cell ◽  
Induced Pluripotent
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