scholarly journals Fatty acid analogue N-arachidonoyl taurine restores function of IKs channels with diverse long QT mutations

eLife ◽  
2016 ◽  
Vol 5 ◽  
Author(s):  
Sara I Liin ◽  
Johan E Larsson ◽  
Rene Barro-Soria ◽  
Bo Hjorth Bentzen ◽  
H Peter Larsson
Keyword(s):  
Fatty Acid ◽  
Long Qt Syndrome ◽  
Molecular Mechanisms ◽  
Loss Of Function ◽  
Long Qt ◽  
Acid Analogue ◽  
Fatty Acid Analogue ◽  
Qt Syndrome ◽  
Channel Currents ◽  
Iks Channel

About 300 loss-of-function mutations in the IKs channel have been identified in patients with Long QT syndrome and cardiac arrhythmia. How specific mutations cause arrhythmia is largely unknown and there are no approved IKs channel activators for treatment of these arrhythmias. We find that several Long QT syndrome-associated IKs channel mutations shift channel voltage dependence and accelerate channel closing. Voltage-clamp fluorometry experiments and kinetic modeling suggest that similar mutation-induced alterations in IKs channel currents may be caused by different molecular mechanisms. Finally, we find that the fatty acid analogue N-arachidonoyl taurine restores channel gating of many different mutant channels, even though the mutations are in different domains of the IKs channel and affect the channel by different molecular mechanisms. N-arachidonoyl taurine is therefore an interesting prototype compound that may inspire development of future IKs channel activators to treat Long QT syndrome caused by diverse IKs channel mutations.

scholarly journals Mechanisms of KCNQ1 Channel Dysfunction in Long QT Syndrome Involving Voltage Sensor Domain Mutations

2017 ◽  
Author(s):  
Hui Huang ◽  
Georg Kuenze ◽  
Jarrod A. Smith ◽  
Keenan C. Taylor ◽  
Amanda M. Duran ◽  
...  
Keyword(s):  
Long Qt Syndrome ◽  
Molecular Mechanisms ◽  
Critical Role ◽  
Voltage Sensor ◽  
Cell Surface Expression ◽  
Loss Of Function ◽  
Long Qt ◽  
Qt Syndrome ◽  
The Impact ◽  
Voltage Sensor Domain

AbstractLoss-of-function (LOF) mutations in human KCNQ1 are responsible for susceptibility to a life-threatening heart rhythm disorder, the congenital long-QT syndrome (LQTS). Hundreds of KCNQ1 mutations have been identified, but the molecular mechanisms responsible for impaired function are poorly understood. Here, we investigated the impact of 51 KCNQ1 variants located within the voltage sensor domain (VSD), with an emphasis on elucidating effects on cell surface expression, protein folding and structure. For each variant, the efficiency of trafficking to the plasma membrane, the impact of proteasome inhibition, and protein stability were assayed. The results of these experiments, combined with channel functional data, provided the basis for classifying each mutation into one of 6 mechanistic categories. More than half of the KCNQ1 LOF mutations destabilize the structure of the VSD, resulting in mistrafficking and degradation by the proteasome, an observation that underscores the growing appreciation that mutation-induced destabilization of membrane proteins may be a common human disease mechanism. Finally, we observed that 5 of the folding-defective LQTS mutants are located in the VSD S0 helix, where they interact with a number of other LOF mutation sites in other segments of the VSD. These observations reveal a critical role for the S0 helix as a central scaffold to help organize and stabilize the KCNQ1 VSD and, most likely, the corresponding domain of many other ion channels.One Sentence SummaryLong QT syndrome-associated mutations in KCNQ1 most often destabilize the protein, leading to mistrafficking and degradation.

scholarly journals Molecular Mechanism of Autosomal Recessive Long QT-Syndrome 1 without Deafness

2021 ◽  
Vol 22 (3) ◽  
pp. 1112
Author(s):  
Annemarie Oertli ◽  
Susanne Rinné ◽  
Robin Moss ◽  
Stefan Kääb ◽  
Gunnar Seemann ◽  
...  
Keyword(s):  
Action Potential ◽  
Molecular Mechanism ◽  
Long Qt Syndrome ◽  
Autosomal Recessive ◽  
Delayed Rectifier ◽  
Loss Of Function ◽  
Wild Type ◽  
Long Qt ◽  
Qt Syndrome ◽  
Iks Channel

KCNQ1 encodes the voltage-gated potassium (Kv) channel KCNQ1, also known as KvLQT1 or Kv7.1. Together with its ß-subunit KCNE1, also denoted as minK, this channel generates the slowly activating cardiac delayed rectifier current IKs, which is a key regulator of the heart rate dependent adaptation of the cardiac action potential duration (APD). Loss-of-function mutations in KCNQ1 cause congenital long QT1 (LQT1) syndrome, characterized by a delayed cardiac repolarization and a prolonged QT interval in the surface electrocardiogram. Autosomal dominant loss-of-function mutations in KCNQ1 result in long QT syndrome, called Romano–Ward Syndrome (RWS), while autosomal recessive mutations lead to Jervell and Lange-Nielsen syndrome (JLNS), associated with deafness. Here, we identified a homozygous KCNQ1 mutation, c.1892_1893insC (p.P631fs*20), in a patient with an isolated LQT syndrome (LQTS) without hearing loss. Nevertheless, the inheritance trait is autosomal recessive, with heterozygous family members being asymptomatic. The results of the electrophysiological characterization of the mutant, using voltage-clamp recordings in Xenopus laevis oocytes, are in agreement with an autosomal recessive disorder, since the IKs reduction was only observed in homomeric mutants, but not in heteromeric IKs channel complexes containing wild-type channel subunits. We found that KCNE1 rescues the KCNQ1 loss-of-function in mutant IKs channel complexes when they contain wild-type KCNQ1 subunits, as found in the heterozygous state. Action potential modellings confirmed that the recessive c.1892_1893insC LQT1 mutation only affects the APD of homozygous mutation carriers. Thus, our study provides the molecular mechanism for an atypical autosomal recessive LQT trait that lacks hearing impairment.

scholarly journals Long QT Syndrome Type 2: Emerging Strategies for Correcting Class 2 KCNH2 (hERG) Mutations and Identifying New Patients

Biomolecules ◽  
2020 ◽  
Vol 10 (8) ◽  
pp. 1144
Author(s):  
Makoto Ono ◽  
Don E. Burgess ◽  
Elizabeth A. Schroder ◽  
Claude S. Elayi ◽  
Corey L. Anderson ◽  
...  
Keyword(s):  
Cell Surface ◽  
Long Qt Syndrome ◽  
Molecular Mechanisms ◽  
Surface Membrane ◽  
Long Qt ◽  
Cell Surface Membrane ◽  
Channel Protein ◽  
Channel Proteins ◽  
Qt Syndrome

Significant advances in our understanding of the molecular mechanisms that cause congenital long QT syndrome (LQTS) have been made. A wide variety of experimental approaches, including heterologous expression of mutant ion channel proteins and the use of inducible pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) from LQTS patients offer insights into etiology and new therapeutic strategies. This review briefly discusses the major molecular mechanisms underlying LQTS type 2 (LQT2), which is caused by loss-of-function (LOF) mutations in the KCNH2 gene (also known as the human ether-à-go-go-related gene or hERG). Almost half of suspected LQT2-causing mutations are missense mutations, and functional studies suggest that about 90% of these mutations disrupt the intracellular transport, or trafficking, of the KCNH2-encoded Kv11.1 channel protein to the cell surface membrane. In this review, we discuss emerging strategies that improve the trafficking and functional expression of trafficking-deficient LQT2 Kv11.1 channel proteins to the cell surface membrane and how new insights into the structure of the Kv11.1 channel protein will lead to computational approaches that identify which KCNH2 missense variants confer a high-risk for LQT2.

scholarly journals Overlapping LQT1 and LQT2 phenotype in a patient with long QT syndrome associated with loss-of-function variations in KCNQ1 and KCNH2

2010 ◽  
Vol 88 (12) ◽  
pp. 1181-1190 ◽  
Author(s):  
Jonathan M. Cordeiro ◽  
Guillermo J. Perez ◽  
Nicole Schmitt ◽  
Ryan Pfeiffer ◽  
Vladislav V. Nesterenko ◽  
...  
Keyword(s):  
Patch Clamp ◽  
Long Qt Syndrome ◽  
Loss Of Function ◽  
Long Qt ◽  
Tail Current ◽  
Qt Intervals ◽  
Ventricular Extrasystoles ◽  
Current Voltage ◽  
Life Threatening ◽  
Qt Syndrome

Long QT syndrome (LQTS) is an inherited disorder characterized by prolonged QT intervals and potentially life-threatening arrhythmias. Mutations in 12 different genes have been associated with LQTS. Here we describe a patient with LQTS who has a mutation in KCNQ1 as well as a polymorphism in KCNH2. The proband (MMRL0362), a 32-year-old female, exhibited multiple ventricular extrasystoles and one syncope. Her ECG (QT interval corrected for heart rate (QTc) = 518ms) showed an LQT2 morphology in leads V4–V6 and LQT1 morphology in leads V1–V2. Genomic DNA was isolated from lymphocytes. All exons and intron borders of 7 LQTS susceptibility genes were amplified and sequenced. Variations were detected predicting a novel missense mutation (V110I) in KCNQ1, as well as a common polymorphism in KCNH2 (K897T). We expressed wild-type (WT) or V110I Kv7.1 channels in CHO-K1 cells cotransfected with KCNE1 and performed patch-clamp analysis. In addition, WT or K897T Kv11.1 were also studied by patch clamp. Current–voltage (I-V) relations for V110I showed a significant reduction in both developing and tail current densities compared with WT at potentials >+20 mV (p < 0.05; n = 8 cells, each group), suggesting a reduction in IKs currents. K897T- Kv11.1 channels displayed a significantly reduced tail current density compared with WT-Kv11.1 at potentials >+10 mV. Interestingly, channel availability assessed using a triple-pulse protocol was slightly greater for K897T compared with WT (V0.5 = –53.1 ± 1.13 mV and –60.7 ± 1.15 mV for K897T and WT, respectively; p < 0.05). Comparison of the fully activated I-V revealed no difference in the rectification properties between WT and K897T channels. We report a patient with a loss-of-function mutation in KCNQ1 and a loss-of-function polymorphism in KCNH2. Our results suggest that a reduction of both IKr and IKs underlies the combined LQT1 and LQT2 phenotype observed in this patient.

scholarly journals A de novo missense mutation of human cardiac Na+ channel exhibiting novel molecular mechanisms of long QT syndrome

FEBS Letters ◽  
1998 ◽  
Vol 423 (1) ◽  
pp. 5-9 ◽  
Author(s):  
Naomasa Makita ◽  
Nobumasa Shirai ◽  
Masato Nagashima ◽  
Rumiko Matsuoka ◽  
Yoichi Yamada ◽  
...  
Keyword(s):  
Missense Mutation ◽  
Long Qt Syndrome ◽  
Molecular Mechanisms ◽  
De Novo ◽  
Na Channel ◽  
Long Qt ◽  
Qt Syndrome

scholarly journals ML277 specifically enhances the fully activated open state of KCNQ1 by modulating VSD-pore coupling

eLife ◽  
2019 ◽  
Vol 8 ◽  
Author(s):  
Panpan Hou ◽  
Jingyi Shi ◽  
Kelli McFarland White ◽  
Yuan Gao ◽  
Jianmin Cui
Keyword(s):  
Long Qt Syndrome ◽  
Xenopus Oocytes ◽  
Heart Rhythm ◽  
Long Qt ◽  
Gating Mechanism ◽  
New Strategy ◽  
Pore Opening ◽  
Qt Syndrome ◽  
Voltage Sensing Domain ◽  
Iks Channel

Upon membrane depolarization, the KCNQ1 potassium channel opens at the intermediate (IO) and activated (AO) states of the stepwise voltage-sensing domain (VSD) activation. In the heart, KCNQ1 associates with KCNE1 subunits to form IKs channels that regulate heart rhythm. KCNE1 suppresses the IO state so that the IKs channel opens only to the AO state. Here, we tested modulations of human KCNQ1 channels by an activator ML277 in Xenopus oocytes. It exclusively changes the pore opening properties of the AO state without altering the IO state, but does not affect VSD activation. These observations support a distinctive mechanism responsible for the VSD-pore coupling at the AO state that is sensitive to ML277 modulation. ML277 provides insights and a tool to investigate the gating mechanism of KCNQ1 channels, and our study reveals a new strategy for treating long QT syndrome by specifically enhancing the AO state of native IKs currents.

scholarly journals Clinical, genetic and functional analysis of R562S-Kv7.1 mutation associated with long QT syndrome type 1

EP Europace ◽  
2021 ◽  
Vol 23 (Supplement_3) ◽  
Author(s):  
O Svecova ◽  
R Kula ◽  
L Chmelikova ◽  
J Hosek ◽  
I Synkova ◽  
...  
Keyword(s):  
Long Qt Syndrome ◽  
Adrenergic Stimulation ◽  
Long Qt ◽  
Beta Adrenergic ◽  
The Czech Republic ◽  
Whole Cell Patch Clamp ◽  
Life Threatening ◽  
Qt Syndrome ◽  
Iks Channel

Abstract Funding Acknowledgements Type of funding sources: Public Institution(s). Main funding source(s): Ministry of Education, Youth and Sports of the Czech Republic Introduction Loss-of-function variants of the KCNQ1 gene are associated with life-threatening arrhythmogenic long QT syndrome type 1 (LQT1). This gene encodes structure of the slow delayed rectifier potassium channel (IKs). Some functional characteristics of the C-terminal KCNQ1 variant c.1686G &gt; C (p.R562S) have been recently described [1]. However, accumulation of the current under beta-adrenergic stimulation, essential for shortening the action potential duration during exercise, have not been tested. Purpose The aim of this study was to analyse clinical and genetic characteristics of the R562S variant in our patients and to investigate impact of the variant on IKs channel function with a special focus on reactivity of the channels on beta-adrenergic stimulation. Methods The clinical diagnosis was established according to ESC Guidelines including QTc analysis at rest and after exercise. The molecular genetics diagnostics followed according to current practices (the massive parallel sequencing since 2016). The biophysical analysis was performed on Chinese hamster ovary cells (CHO) by the whole cell patch clamp technique at 37 °C. CHO cells were transiently transfected with wild type (WT) and/or R562S human IKs channels (KCNQ1/KCNE1/Yotiao, 1:2:4). Cyclic adenosine monophosphate (cAMP, 200 µM) and okadaic acid (OA, 0.2 µM) in the pipette solution were used to simulate the beta-adrenergic stimulation. In the confocal microscopy experiments, expression of Yotiao was omitted and GFP-tagged KCNQ1 was used. Results The variant R562S-Kv7.1 has been identified in 7 heterozygous carriers from 3 putatively unrelated families in the Czech Republic. The genotype was associated with long QT syndrome phenotype (prolonged QTc, symptoms including syncopes and aborted cardiac arrest) in some of the carriers. The basic functional analysis proved that both homozygous and heterozygous R562S channels are expressed on the cell membrane (confocal microscopy) and carry IKs (whole cell patch clamp) which agrees with the recently published data on this variant. Importantly, reactivity on beta-adrenergic stimulation was absent in both homozygous and heterozygous R562S channels (n = 14 and 8, respectively), but present in the wild-type channels (increase by 51.4 ± 11.1 % at 120-s cAMP/OA diffusion; n = 12). Conclusions The R562S-Kv7.1 variant may be a founder LQT1 variant in our region which will be further investigated in the future. This variant impairs response of IKs channel to beta-adrenergic stimulation. Absence of this essential regulation may considerably aggravate the channel dysfunction and, thus, may result in life-threatening arrhythmias in R562S carriers during exercise.

Abstract 17137: Unmasking Pathological Mechanisms of Long QT Syndrome KCNH2 H70R Variant Using Human iPSC-Cardiomyocytes

Circulation ◽  
2018 ◽  
Vol 138 (Suppl_1) ◽  
Author(s):  
Li Feng ◽  
Gina Kim ◽  
Catherine A Eichel ◽  
Fang Liu ◽  
Evi Lim ◽  
...  
Keyword(s):  
Long Qt Syndrome ◽  
Herg Channel ◽  
Patient Specific ◽  
Delayed Rectifier ◽  
Pas Domain ◽  
Loss Of Function ◽  
Long Qt ◽  
Unrelated Control ◽  
Qt Syndrome ◽  
Human Ipsc

Introduction: Inherited long QT syndrome type 2 (LQT2) results from loss-of-function mutations in the KCNH2 gene encoding the hERG channel, which conducts I Kr , the rapid component of the delayed rectifier K + current. The N-terminal Per-Arnt-Sim (PAS) domain present on the hERG1a subunit, but not the hERG1b subunit, is the site of multiple LQT2-linked missense variants. The mechanism of loss of function by many of these missense PAS variants is unclear given conflicting results from different heterologous expression systems expressing hERG1a. Hypothesis: Patient-specific LQT2 human iPSC-cardiomyocytes (hiPSC-CMs) which naturally express hERG1a/1b carrying the KCNH2 H70R variant in the PAS domain will exhibit loss of I Kr associated with APD prolongation due to impaired channel protein trafficking. Methods and Results: Human iPSCs were derived from a patient carrying the LQT2-associated PAS domain mutation KCNH2 H70R, which has been reported to cause impaired hERG channel trafficking without effects on channel gating when expressed in HEK 293 cells but accelerated deactivation kinetics of I hERG when expressed in Xenopus laevis oocytes. Two clones of KCNH2 H70R and unrelated control hiPSCs (DF19-9-11T) were differentiated using monolayer-base, small molecule protocol to CMs, evaluated with whole-cell patch clamp. Action potentials from single hiPSC-CMs paced at 1Hz were prolonged in the hERG-H70R group compared to control (APD 90 439.9 ± 15.3 ms vs. 363.7 ± 29.0ms, p =0.003, H70R: n=11, control: n=9, Temp 36 ± 1°C). Voltage clamp studies showed hERG-H70R hiPSC-CMs had a significantly smaller peak tail I Kr current density (1.1 ± 0.3 vs. 2.9 ± 0.5 pA/pF, p <0.001, H70R: n=11, control: n=7, Temp 36 ± 1°C). The voltage dependence of I Kr activation (V½ and k) were not affected by the mutation; however, the fast (τf) and slow (τs) deactivation time constants were significantly decreased in hERG-H70R hiPSC-CMs. Further, Western blot characterization revealed impaired trafficking of hERG-H70R channels relative to control. Conclusions: The LQT2 PAS domain variant hERG-H70R results in loss of function of I Kr by both reduced membrane trafficking and accelerated deactivation of hERG in a hiPSC-CMs model which informs therapeutic approaches.

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