Structure of human Nav1.5 reveals the fast inactivation-related segments as a mutational hotspot for the long QT syndrome

Nav1.5 is the primary voltage-gated Na+ (Nav) channel in the heart. Mutations of Nav1.5 are associated with various cardiac disorders exemplified by the type 3 long QT syndrome (LQT3) and Brugada syndrome (BrS). E1784K is a common mutation that has been found in both LQT3 and BrS patients. Here we present the cryo-EM structure of the human Nav1.5-E1784K variant at an overall resolution of 3.3 Å. The structure is nearly identical to that of the wild-type human Nav1.5 bound to quinidine. Structural mapping of 91- and 178-point mutations that are respectively associated with LQT3 and BrS reveals a unique distribution pattern for LQT3 mutations. Whereas the BrS mutations spread evenly on the structure, LQT3 mutations are clustered mainly to the segments in repeats III and IV that are involved in gating, voltage-sensing, and particularly inactivation. A mutational hotspot involving the fast inactivation segments is identified and can be mechanistically interpreted by our “door wedge” model for fast inactivation. The structural analysis presented here, with a focus on the impact of mutations on inactivation and late sodium current, establishes a structure-function relationship for the mechanistic understanding of Nav1.5 channelopathies.

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Structure of human Nav1.5 reveals the fast inactivation-related segments as a mutational hotspot for the Long QT Syndrome

10.1101/2021.02.06.430010 ◽

2021 ◽

Author(s):

Zhangqiang Li ◽

Xueqin Jin ◽

Tong Wu ◽

Xin Zhao ◽

Weipeng Wang ◽

...

Keyword(s):

Long Qt Syndrome ◽

Sodium Current ◽

Point Mutations ◽

Common Mutation ◽

Fast Inactivation ◽

Long Qt ◽

Qt Syndrome ◽

Function Relationship ◽

Type 3 ◽

The Impact

AbstractNav1.5 is the primary voltage-gated Na+ (Nav) channel in the heart. Mutations of Nav1.5 are associated with various cardiac disorders exemplified by the type 3 long QT syndrome (LQT3) and Brugada syndrome (BrS). E1784K is a common mutation that has been found in both LQT3 and BrS patients. Here we present the cryo-EM structure of the human Nav1.5-E1784K variant at an overall resolution of 3.3 Å. Structural mapping of 91 and 178 point mutations that are respectively associated with LQT3 and BrS reveals a unique distribution pattern for LQT3 mutations. Whereas the BrS mutations spread evenly on the structure, LQT3 mutations are mainly clustered to the segments in repeats III and IV that are involved in gating, voltage-sensing, and particularly inactivation. A mutational hotspot involving the fast inactivation segments is identified and can be mechanistically interpreted by our “door wedge” model for fast inactivation. The structural analysis presented here, with a focus on the impact of disease mutations on inactivation and late sodium current, establishes a structure-function relationship for the mechanistic understanding of Nav1.5 channelopathies.

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Ranolazine as an Alternative Therapy to Flecainide for SCN5A V411M Long QT Syndrome Type 3 Patients

Frontiers in Pharmacology ◽

10.3389/fphar.2020.580481 ◽

2020 ◽

Vol 11 ◽

Author(s):

Jordi Cano ◽

Esther Zorio ◽

Andrea Mazzanti ◽

Miguel Ángel Arnau ◽

Beatriz Trenor ◽

...

Keyword(s):

Clinical Data ◽

Long Qt Syndrome ◽

Qt Interval ◽

Sodium Current ◽

Long Qt ◽

One Dimensional ◽

Qt Interval Prolongation ◽

Number Of Patients ◽

Qt Syndrome ◽

Type 3

The prolongation of the QT interval represents the main feature of the long QT syndrome (LQTS), a life-threatening genetic disease. The heterozygous SCN5A V411M mutation of the human sodium channel leads to a LQTS type 3 with severe proarrhythmic effects due to an increase in the late component of the sodium current (INaL). The two sodium blockers flecainide and ranolazine are equally recommended by the current 2015 ESC guidelines to treat patients with LQTS type 3 and persistently prolonged QT intervals. However, awareness of pro-arrhythmic effects of flecainide in LQTS type 3 patients arose upon the study of the SCN5A E1784K mutation. Regarding SCN5A V411M individuals, flecainide showed good results albeit in a reduced number of patients and no evidence supporting the use of ranolazine has ever been released. Therefore, we ought to compare the effect of ranolazine and flecainide in a SCN5A V411M model using an in-silico modeling and simulation approach. We collected clinical data of four patients. Then, we fitted four Markovian models of the human sodium current (INa) to experimental and clinical data. Two of them correspond to the wild type and the heterozygous SCN5A V411M scenarios, and the other two mimic the effects of flecainide and ranolazine on INa. Next, we inserted them into three isolated cell action potential (AP) models for endocardial, midmyocardial and epicardial cells and in a one-dimensional tissue model. The SCN5A V411M mutation produced a 15.9% APD90 prolongation in the isolated endocardial cell model, which corresponded to a 14.3% of the QT interval prolongation in a one-dimensional strand model, in keeping with clinical observations. Although with different underlying mechanisms, flecainide and ranolazine partially countered this prolongation at the isolated endocardial model by reducing the APD90 by 8.7 and 4.3%, and the QT interval by 7.2 and 3.2%, respectively. While flecainide specifically targeted the mutation-induced increase in peak INaL, ranolazine reduced it during the entire AP. Our simulations also suggest that ranolazine could prevent early afterdepolarizations triggered by the SCN5A V411M mutation during bradycardia, as flecainide. We conclude that ranolazine could be used to treat SCN5A V411M patients, specifically when flecainide is contraindicated.

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Abstract 13191: Increased Extracellular Sodium and Intercellular Cleft Separation Synergistically Prolong Repolarization in the Long-qt Syndrome Type 3

Circulation ◽

10.1161/circ.142.suppl_3.13191 ◽

2020 ◽

Vol 142 (Suppl_3) ◽

Author(s):

Xiaobo Wu ◽

Gregory HOEKER ◽

David Ryan King ◽

Robert G Gourdie ◽

Seth Weinberg ◽

...

Keyword(s):

Long Qt Syndrome ◽

Sodium Current ◽

Syndrome Type ◽

Long Qt ◽

Late Sodium Current ◽

Individual Effects ◽

Qt Syndrome ◽

The Individual ◽

Extracellular Sodium ◽

Type 3

Introduction: Long-QT syndrome type 3 (LQT3) is caused by a gain-of-function mutation in the cardiac sodium channel that increases the late sodium current and prolongs repolarization. We previously suggested that narrowing the perinexus which is adjacent gap junction conceals the LQT3 phenotype by depleting extracellular sodium ([Na]) within this nanodomain and curtails the late current and repolarization. However, it is unknown if elevating bulk [Na] alone modulates action potential duration (APD) in widened perinexi to unmask LQT3. Hypothesis: Elevated [Na] and widened perinexi synergistically prolong APD in LQT3. Methods: The dependence of APD on [Na] and perinexal width was explored with a computational model and in Langendorff-perfused guinea pig hearts. The late sodium current was induced with ATXII (7nM). Perfusate [Na] changed from 145 (145Na) to 160 mM (160Na). Perinexal expansion was induced with βadp1 (1uM). APD was quantified from whole-heart optical maps. Perinexal width was quantified by transmission electron microscopy. Results: A computational model, including preferential sodium channel location at the intercalated disk, predicts that combination of elevated [Na] and widened perinexus prolongs APD greater than summing the effect of the individual interventions alone. Therefore, the combination is synergistic and not additive. Isolated heart experiments are consistent with the model. Specifically, ATXII+βadp1 significantly widens perinexal width from 27.8±4.1 to 49.7±9.3 nm and prolongs APD by 18.1±5.1ms with 600ms pacing relative to ATXII alone. In the presence of ATXII, 160Na significantly prolongs APD by 12.0±5.8ms relative to 145Na. Furthermore, the combination of both interventions is synergistic. Specifically, in the presence of ATXII, 160Na+βadp1 significantly prolongs APD more than the sum of the individual effects (49.9±7.5ms vs. 30.2±5.4ms). Conclusions: The data demonstrate that in LQT3, enhancing sodium and perinexal width concurrently prolong APD more than the individual effects alone. This synergistic effect suggests that maintaining reduced plasma sodium level can be a simple and effective method to conceal LQT3, even in the presence of perinexal expansion associated with osmotically induced stress.

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Functional modulation of atrio-ventricular conduction by enhanced late sodium current and calcium-dependent mechanisms in Scn5a1798insD/+ mice

EP Europace ◽

10.1093/europace/euaa127 ◽

2020 ◽

Vol 22 (10) ◽

pp. 1579-1589

Author(s):

Mathilde R Rivaud ◽

Gerard A Marchal ◽

Rianne Wolswinkel ◽

John A Jansen ◽

Ingeborg van der Made ◽

...

Keyword(s):

Long Qt Syndrome ◽

Sodium Current ◽

Mrna Levels ◽

Syndrome Type ◽

Long Qt ◽

Late Sodium Current ◽

Conduction Abnormalities ◽

Av Conduction ◽

Qt Syndrome ◽

Type 3

Abstract Aims SCN5A mutations are associated with arrhythmia syndromes, including Brugada syndrome, long QT syndrome type 3 (LQT3), and cardiac conduction disease. Long QT syndrome type 3 patients display atrio-ventricular (AV) conduction slowing which may contribute to arrhythmogenesis. We here investigated the as yet unknown underlying mechanisms. Methods and results We assessed electrophysiological and molecular alterations underlying AV-conduction abnormalities in mice carrying the Scn5a1798insD/+ mutation. Langendorff-perfused Scn5a1798insD/+ hearts showed prolonged AV-conduction compared to wild type (WT) without changes in atrial and His-ventricular (HV) conduction. The late sodium current (INa,L) inhibitor ranolazine (RAN) normalized AV-conduction in Scn5a1798insD/+ mice, likely by preventing the mutation-induced increase in intracellular sodium ([Na+]i) and calcium ([Ca2+]i) concentrations. Indeed, further enhancement of [Na+]i and [Ca2+]i by the Na+/K+-ATPase inhibitor ouabain caused excessive increase in AV-conduction time in Scn5a1798insD/+ hearts. Scn5a1798insD/+ mice from the 129P2 strain displayed more severe AV-conduction abnormalities than FVB/N-Scn5a1798insD/+ mice, in line with their larger mutation-induced INa,L. Transverse aortic constriction (TAC) caused excessive prolongation of AV-conduction in FVB/N-Scn5a1798insD/+ mice (while HV-intervals remained unchanged), which was prevented by chronic RAN treatment. Scn5a1798insD/+-TAC hearts showed decreased mRNA levels of conduction genes in the AV-nodal region, but no structural changes in the AV-node or His bundle. In Scn5a1798insD/+-TAC mice deficient for the transcription factor Nfatc2 (effector of the calcium-calcineurin pathway), AV-conduction and conduction gene expression were restored to WT levels. Conclusions Our findings indicate a detrimental role for enhanced INa,L and consequent calcium dysregulation on AV-conduction in Scn5a1798insD/+ mice, providing evidence for a functional mechanism underlying AV-conduction disturbances secondary to gain-of-function SCN5A mutations.

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Ranolazine Shortens Repolarization in Patients with Sustained Inward Sodium Current Due to Type-3 Long-QT Syndrome

Journal of Cardiovascular Electrophysiology ◽

10.1111/j.1540-8167.2008.01246.x ◽

2008 ◽

Vol 19 (12) ◽

pp. 1289-1293 ◽

Cited By ~ 197

Author(s):

ARTHUR J. MOSS ◽

WOJCIECH ZAREBA ◽

KARL Q. SCHWARZ ◽

SPENCER ROSERO ◽

SCOTT MCNITT ◽

...

Keyword(s):

Long Qt Syndrome ◽

Sodium Current ◽

Long Qt ◽

Qt Syndrome ◽

Type 3

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E1784K, the most common Brugada syndrome and long-QT syndrome type 3 mutant, disrupts sodium channel inactivation through two separate mechanisms

The Journal of General Physiology ◽

10.1085/jgp.202012595 ◽

2020 ◽

Vol 152 (9) ◽

Author(s):

Colin H. Peters ◽

Abeline R. Watkins ◽

Olivia L. Poirier ◽

Peter C. Ruben

Keyword(s):

Long Qt Syndrome ◽

Brugada Syndrome ◽

Double Mutant ◽

Voltage Dependence ◽

Syndrome Type ◽

Fast Inactivation ◽

Long Qt ◽

Qt Syndrome ◽

Type 3 ◽

Dependent Interaction

Inheritable and de novo variants in the cardiac voltage-gated sodium channel, Nav1.5, are responsible for both long-QT syndrome type 3 (LQT3) and Brugada syndrome type 1 (BrS1). Interestingly, a subset of Nav1.5 variants can cause both LQT3 and BrS1. Many of these variants are found in channel structures that form the channel fast inactivation machinery, altering the rate, voltage dependence, and completeness of the fast inactivation process. We used a series of mutants at position 1784 to show that the most common inheritable Nav1.5 variant, E1784K, alters fast inactivation through two separable mechanisms: (1) a charge-dependent interaction that increases the noninactivating current characteristic of E1784K; and (2) a hyperpolarized voltage dependence and accelerated rate of fast inactivation that decreases the peak sodium current. Using a homology model built on the NavPaS structure, we find that the charge-dependent interaction is between E1784 and K1493 in the DIII–DIV linker of the channel, five residues downstream of the putative inactivation gate. This interaction can be disrupted by a positive charge at position 1784 and rescued with the K1493E/E1784K double mutant that abolishes the noninactivating current. However, the double mutant does not restore either the voltage dependence or rates of fast inactivation. Conversely, a mutant at the bottom of DIVS4, K1641D, causes a hyperpolarizing shift in the voltage dependence of fast inactivation and accelerates the rate of fast inactivation without causing an increase in noninactivating current. These findings provide novel mechanistic insights into how the most common inheritable arrhythmogenic mixed syndrome variant, E1784K, simultaneously decreases transient sodium currents and increases noninactivating currents, leading to both BrS1 and LQT3.

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