SCN5A mRNA Research Articles

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.

Abstract Mo054: Long Noncoding RNA LINC00667 Downregulation Leads to SCN5A Alternative Splicing and Arrhythmogenesis

Background: The voltage-gated sodium channel SCN5A, which encodes the Nav1.5 protein, is integral to the propagation of electrical signals in cardiac tissue. SCN5A expression is diminished in cardiomyopathy, significantly increasing the susceptibility to arrhythmias. This reduction in channel activity can be attributed to decreased mRNA stability coupled with aberrant mRNA splicing. The underlying mechanisms driving the dysregulation of mRNA splicing under pathophysiological conditions remain poorly understood. Objective: This study explores the role of long noncoding RNA LINC00667 in the abnormal alternative splicing of SCN5A mRNA. Methods: LINC00667 expression was analyzed using public databases, human heart tissue, iPSC-derived cardiomyocytes (iPSCMs), and cell lines. The impact of SCN5A on action potentials and sodium currents was studied in iPSCMs. LINC00667 and SCN5A expressions were measured using qRT-PCR, while Nav1.5 protein levels were assessed through Western blot. Alternative splicing of SCN5A mRNA was examined using PCR with exon-specific primers. Gene ontology and in silico analysis identified RNA binding proteins (RBPs) potentially interacting with LINC00667. RNA immunoprecipitation (RIP) assays confirmed direct binding with key splice factors. Group differences were assessed using 2-tailed Student’s t-tests, with P < 0.05 indicating significance. Results: LINC00667, found at chromosome 18p11.31, is expressed in the human heart and associated cells, including cardiomyocytes. Its levels are inversely related to arrhythmic risk, decreasing in heart failure and ischemic cardiomyopathy as well as under hypoxic conditions. Gene ontology linked RBPs to SCN5A mRNA splicing, with RBM25, RBM5, and TIA1 identified as LINC00667 interactors. LINC00667 reduction affected regions of SCN5A mRNA encompassing Exons 6, 24, and 28, which could potentially be linked to decreased function/expression or increased unfolded protein response (UPR). Abnormal RNA splicing decreased SCN5A-encoded sodium current, reduced action potential upstroke velocity, and shortened AP duration without altering resting membrane potential. Conclusion: Decreased LINC00667 releases splicing factors that result in abnormal SCN5A mRNA splicing and reduced sodium current. Since LINC00667 is reduced in cardiomyopathy, overexpression may be antiarrhythmic by preventing sodium channel downregulation.

14-3-3ε/YWHAE regulates the transcriptional expression of cardiac sodium channel NaV1.5

BackgroundCardiac voltage-gated sodium channel alpha subunit 5 (NaV1.5) encoded by SCN5A is associated with arrhythmia disorders. However, the molecular mechanism underlying NaV1.5 expression remains to be fully elucidated. Previous studies have reported that the 14-3-3 family acts as an adaptor involved in regulating kinetic characteristics of cardiac ion channels. ObjectiveThe purpose of this study was to establish 14-3-3ε/YWHAE, a member of the 14-3-3 family, as a crucial regulator of NaV1.5 and to explore the potential role of 14-3-3ε in the heart. MethodsWestern blotting, patch clamping, real-time reverse transcription–polymerase chain reaction, RNA immunoprecipitation, electrocardiogram recording, echocardiography, and histologic analysis were performed. ResultsYWHAE overexpression significantly reduced the expression level of SCN5A mRNA and sodium current density, whereas YWHAE knockdown significantly increased SCN5A mRNA expression and sodium current density in HEK293/NaV1.5 and H9c2 cells. Similar results were observed in mice injected with adeno-associated virus serotype 9–mediated YWHAE knockdown. The effect of 14-3-3ε on NaV1.5 expression was abrogated by knockdown of TBX5, a transcription factor of NaV1.5. An interaction between 14-3-3ε protein and TBX5 mRNA was identified, and YWHAE overexpression significantly decreased TBX5 mRNA stability without affecting SCN5A mRNA stability. In addition, mice subjected to adeno-associated virus serotype 9–mediated YWHAE knockdown exhibited shorter R-R intervals and higher prevalence of premature ventricular contractions. ConclusionOur data unveil a novel regulatory mechanism of NaV1.5 by 14-3-3ε and highlight the significance of 14-3-3ε in transcriptional regulation of NaV1.5 expression and cardiac arrhythmias.

Chronic Testosterone Deficiency Increases Late Inward Sodium Current and Promotes Triggered Activity in Ventricular Myocytes from Aging Male Mice.

Clinical studies suggest low testosterone levels are associated with cardiac arrhythmias, especially in later life. We investigated whether chronic exposure to low circulating testosterone promoted maladaptive electrical remodeling in ventricular myocytes from aging male mice and determined the role of late inward sodium current (INa-L) in this remodeling. C57BL/6 mice had a gonadectomy (GDX) or sham surgery (1-month) and were aged to 22-28-months. Ventricular myocytes were isolated; transmembrane voltage and currents were recorded (37°C). Action potential duration at 70 and 90% repolarization (APD70 and APD90) was prolonged in GDX compared to sham myocytes (APD90: 96.9±3.2 vs 55.4±2.0 ms; p<0.001). INa-L was also larger in GDX than sham (-2.4±0.4 vs -1.2±0.2 pA/pF; p=0.002). When cells were exposed to the INa-L antagonist ranolazine (10 µM), INa-L declined in GDX cells (-1.9±0.5 vs -0.4±0.2 pA/pF; p<0.001) and APD90 was reduced (96.3±14.8 vs 49.2±9.4 ms; p=0.001). GDX cells had more triggered activity (early/delayed afterdepolarizations, EADs/DADs) and spontaneous activity than sham. EADs were inhibited by ranolazine in GDX cells. The selective NaV1.8 blocker A-803467 (30 nM) also reduced INa-L, decreased APD and abolished triggered activity in GDX cells. Scn5a (NaV1.5) and Scn10a (NaV1.8) mRNA was increased in GDX ventricles, but only NaV1.8 protein abundance was increased in GDX compared to sham. In vivo studies showed QT prolongation and more arrhythmias in GDX mice. Thus, triggered activity in ventricular myocytes from aging male mice with long-term testosterone deficiency arises from APD prolongation mediated by larger NaV1.8- and NaV1.5-associated currents, which may explain the increase in arrhythmias.

Inhibition of Wnt/β-catenin signaling upregulates Nav 1.5 channels in Brugada syndrome iPSC-derived cardiomyocytes.

The voltage-gated Nav 1.5 channels mediate the fast Na+ current (INa ) in cardiomyocytes initiating action potentials and cardiac contraction. Downregulation of INa , as occurs in Brugada syndrome (BrS), causes ventricular arrhythmias. The present study investigated whether the Wnt/β-catenin signaling regulates Nav 1.5 in human-induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs). In healthy male and female iPSC-CMs, activation of Wnt/β-catenin signaling by CHIR-99021 reduced (p < 0.01) both Nav 1.5 protein and SCN5A mRNA. In iPSC-CMs from a BrS patient, both Nav 1.5 protein and peak INa were reduced compared to those in healthy iPSC-CMs. Treatment of BrS iPSC-CMs with Wnt-C59, a small-molecule Wnt inhibitor, led to a 2.1-fold increase in Nav 1.5 protein (p = 0.0005) but surprisingly did not affect SCN5A mRNA (p = 0.146). Similarly, inhibition of Wnt signaling using shRNA-mediated β-catenin knockdown in BrS iPSC-CMs led to a 4.0-fold increase in Nav 1.5, which was associated with a 4.9-fold increase in peak INa but only a 2.1-fold increase in SCN5A mRNA. The upregulation of Nav 1.5 by β-catenin knockdown was verified in iPSC-CMs from a second BrS patient. This study demonstrated that Wnt/β-catenin signaling inhibits Nav 1.5 expression in both male and female human iPSC-CMs, and inhibition of Wnt/β-catenin signaling upregulates Nav 1.5 in BrS iPSC-CMs through both transcriptional and posttranscriptional mechanisms.

Life Cycle of the Cardiac Voltage-Gated Sodium Channel NaV1.5.

Cardiac voltage-gated sodium channel NaV1.5, encoded by SCN5A, is crucial for the upstroke of action potential and excitation of cardiomyocytes. NaV1.5 undergoes complex processes before it reaches the target membrane microdomains and performs normal functions. A variety of protein partners are needed to achieve the balance between SCN5A transcription and mRNA decay, endoplasmic reticulum retention and export, Golgi apparatus retention and export, selective anchoring and degradation, activation, and inactivation of sodium currents. Subtle alterations can impair NaV1.5 in terms of expression or function, eventually leading to NaV1.5-associated diseases such as lethal arrhythmias and cardiomyopathy.

MicroRNA overexpression in slow transit constipation leads to reduced NaV1.5 current and altered smooth muscle contractility

ObjectiveThis study was designed to evaluate the roles of microRNAs (miRNAs) in slow transit constipation (STC).DesignAll human tissue samples were from the muscularis externa of the colon. Expression of 372...

Direct and Indirect Suppression of Scn5a Gene Expression Mediates Cardiac Na+ Channel Inhibition by Wnt Signalling

BackgroundMyocardial infarction and heart failure are associated with reduced voltage-gated Na+ current (INa) that promotes arrhythmias and sudden deaths. We have previously shown that the Wnt/β-catenin signalling (Wnt signalling), which is active in heart disease, reduces cardiac INa, suggesting that Wnt signalling may be a potential therapeutic target. However, because Wnt signalling is required for the homeostasis of many noncardiac tissues, administration of Wnt inhibitors to heart patients would cause significant side effects. The present study aims to elucidate the molecular mechanisms of cardiac INa inhibition by Wnt, which would identify cardiac-specific therapeutic targets. MethodsWnt signalling was activated in neonatal rat ventricular myocytes by Wnt3a protein. Adenovirus expressing Wnt3a was injected into the adult rat ventricle. CRISPR/Cas9 and chromatin immunoprecipitation were used for mechanistic studies. ResultsWnt signalling activation in neonatal rat ventricular myocytes reduced Nav1.5 protein and Scn5a mRNA, but increased Tbx3, a known suppressor of Scn5a. Chromatin immunoprecipitation showed that Wnt signalling inhibits Scn5a expression through downstream mediator (TCF4) binding to both Tbx3 and Scn5a promoters. Overexpression or knockdown of Tbx3 directly modified Nav1.5 and INa, whereas CRISPR/Cas9-induced mutations at TCF4 binding sites within the Scn5a promoter attenuated Wnt inhibition of Scn5a and Nav1.5. In adult rat hearts, adenovirus expressing Wnt3a reduced Nav1.5, increased QRS duration in electrocardiogram, and increased the susceptibility to ventricular tachycardia. ConclusionsWnt signalling inhibits the Na+ channel by direct and indirect (via Tbx3) suppression of Scn5a transcription. Strategies to block TCF4 binding to the Tbx3 and Scn5a promoters would represent novel strategies for cardiac-specific inhibition of the Wnt pathway to rescue INa and prevent sudden cardiac deaths.

Abstract 893: MicroRNA-448 Regulates the Cardiac Sodium Channel During Ischemia

Background: The cardiac voltage-gated sodium channel ( SCN5A ; encoding Na v 1.5) plays a key role in cardiac conduction. The sodium channel is downregulated in cardiomyopathy, contributing to arrhythmic risk. In part, this downregulation is because of abnormal mRNA splicing and reduced mRNA stability. The reason for decreased mRNA stability is unclear, however. Objective: Here, we examined whether microRNA-448 (miR-448)can contribute to SCN5A mRNA instability. Methods: Datasets from the Gene Expression Omnibus database were utilized to screen miR-448 in human and mouse heart tissues. The relationship between SCN5A and miR-448 was predicted by three independent prediction tools. The expressions of SCN5A and miR-448 were determined by quantitative real time polymerase chain reaction. Protein levels of Na v 1.5 were determined by Western blot. The effect of miR-448 mimic on sodium current was determined in induced pluripotent stem cells-derived cardiomyocytes. Mouse myocardial infarction was created by left anterior descending coronary artery ligation. Results: The expression of miR-448 is increased in stressed heart after myocardial infarction. The binding sequence for miR-448 is well-conserved in 3’-UTR of SCN5A and miR-448 directly bound to a consensus cis element, suppressing SCN5A expression and sodium currents. miR-448 expression wass increased by hypoxia. Activated by hypoxia, HIF1α and NF-κB activated were major transcriptional regulator for MIR448 . Conclusion: These results indicated that miR-448 contributed to post-transcriptional modification of SCN5A . miR-448 is likely one cause of sodium channel downregulation during ischemia and may represent a target for antagomir therapy to reduce arrhythmic risk associated with cardiomyopathy.. Keywords: SCN5A, miR-448, Cardiomyocyte, Hypoxia, NF-κB, HIF1α

Expression of Nav1.5 in the pathogenesis of temporal lobe epilepsy

To investigate the expressions of Nav1.5 mRNA at different time points in a rat model of temporal lobe epilepsy (TLE), and to assess the potential contribution of Nav1.5 to epileptogenesis. Male Sprague-Dawley rats (72) weighing 230 to 250 g were used for this study. They were randomly assigned to six groups (12 rats/group): control and five TLE groups. The TLE groups were day 1 (acute period), days 7 and 14 (latent period), and days 30 and 60 (chronic period). With the exception of control, epilepsy was induced in the rats with an intraperitoneal (i.p.) injection of aqueous solution of lithium chloride 18 h prior to pilocarpine injection (i.p.) at a dose of 125 mg/kg body weight (b.wt). Rats in the control group were injected i.p. with 0.9 % sodium chloride (125 mg/kg b.wt.) in place of pilocarpine. A total of 84 out of 112 rats developed status epilepticus (SE). The expression of Nav1.5 in the brains of rats was assessed using quantitative real-time polymerase chain reaction (qRT-PCR), immunohistochemistry and Western blot analysis. The expressions of Scn5a mRNA in the hippocampus during the latent and chronic periods were significantly higher than in the control group (p &lt; 0.05), but there were no significant differences in the corresponding expressions between the two different time points in the latent and chronic period groups (p &gt; 0.05). The expression peaked 30 days post-SE, and was sustained for 60 days. There was no significant difference in the expression of Scn5a mRNA in the acute group, when compared to control. Immunohistochemical staining showed that expression levels of Nav1.5 in the CA3 region during latent and chronic periods were significantly higher than those in control group (p &lt; 0.05), and the expressions peaked at day 30. However, there was no significant difference in the expression of Nav1.5 in the latent group, relative to the chronic period group. These results show that Nav1.5 might be involved in the pathogenesis of TLE.

Nucleoporin 107 facilitates the nuclear export of Scn5a mRNA to regulate cardiac bioelectricity.

Nucleoporins (Nups) are known to be functional in nucleo‐cytoplasmic transport, but the roles of nucleoporins in nonproliferating cells, such as cardiac myocytes, are still poorly understood. In this study, we report that Nup107 regulates cardiac bioelectricity by controlling the nucleo‐cytoplasmic trafficking of Scn5a mRNA. Overexpression of Nup107 induced the protein expression of Scn5a rather than that of other ion channels, with no effects of their mRNA levels. The analysis for the protein production demonstrated Nup107‐facilitated transport of Scn5a mRNA. Using RIP‐PCR and luciferase assay, we found that the 5′‐UTR of Scn5a mRNA was not involved in the interaction, whereas the spatial interaction between Nup107 protein and Scn5a mRNA was formed when Scn5a mRNA passing through the nuclear pore. Functionally, Nup107 overexpression in neonatal rat ventricle myocytes significantly increased the currents of Scn5a‐encoded INa channel. Moreover, the close correlation between Nup107 and Nav1.5 protein expression was observed in cardiomycytes and heart tissues subjected to hypoxia and ischaemic insults, suggesting a fast regulation of Nup107 on Nav1.5 channel in cardiac myocytes in a posttranscriptional manner. These findings may provide insights into the emergent control of cardiac electrophysiology through Nup‐mediated modulation of ion channels.

Pathophysiology of R222Q mutant SCN5a channels

Consistent with the role of sodium channels in initiating action potentials throughout myocardial tissue, mutations in SCN5a are associated with arrhythmias and cardiomyopathy. The present studies aim to advance understanding of the mechanism underlying the arrhythmias and dilated cardiomyopathy (DCM) observed in patents with an SCN5a mutation (c.665G>A/R222Q) located in one of the voltage sensor regions. Induced pluripotent stem cells (iPSCs) were generated from a patient heterozygous for the R222Q mutation. Isogenic controls were generated by corrected the mutation. Directed differentiation techniques were used to produce ventricular CMs characterized by the expression of cTnT (Control: 85.10±2.90%, Mutant: 83.14±4.46%) and ventricular-specific MLC2v (Control: 45.62±7.02%, Mutant: 43.92±3.86%). The SCN5a gene undergoes extensive alternative splicing, which is developmentally regulated, resulting in the R222Q loci being expressed exclusively in adult SCN5a mRNA. Consistent with an immature phenotype in our iPSC-derived CMs, about half of the SCN5a mRNA is the adult isoform (Control: 54.40±9.29%, Mutant: 48.45±6.21%, n=4), indicating that ~25% of the SCN5a channels expressed in mutant CMs contain the R222Q mutation. Optical mapping of our 2-dimentional tissue model (monolayers) reveal slower conduction velocities in mutant compared to control monolayers (13.14±0.74cm/s, n=10, vs. 25.09±1.99cm/s, n=7, p<0.05). Treatment with flecainide (10 μM), a sodium channel blocker associated with arrhythmia reduction and DCM reversal in R222Q patients results in conduction slowing (Control: 25.09±1.99cm/s to 18.47±3.20cm/s, n=7, p<0.05, Mutant: 13.14±0.74cm/s to 8.92±0.64cm/s, n=10, p<0.05) and a reduction in maximum capture rates (Control: 3.22±0.14Hz to 1.42±0.13Hz, n=5, p<0.05, Mutant: 3.43±0.18 to 2.38±0.22Hz, n=10, p<0.05). We are currently performing electrophysiological studies to further assess the mechanisms underlying R222Q-associated cardiomyopathy and arrhythmias and advancement of therapeutic options for R222Q patients.

HuR-mediated SCN5A messenger RNA stability reduces arrhythmic risk in heart failure

Downregulated sodium currents in heart failure (HF) have been linked to increased arrhythmic risk. Reduced expression of the messenger RNA (mRNA)-stabilizing protein HuR (also known as ELAVL1) may be responsible for the downregulation of sodium channel gene SCN5A mRNA. The purpose of this article was to investigate whether HuR regulates SCN5A mRNA expression and whether manipulation of HuR benefits arrhythmia control in HF. Quantitative real-time reverse-transcriptase polymerase chain reaction was used to investigate the expression of SCN5A. Optical mapping of the intact heart was adopted to study the effects of HuR on the conduction velocity and action potential upstroke in mice with myocardial infarct and HF after injection of AAV9 viral particles carrying HuR. HuR was associated with SCN5A mRNA in cardiomyocytes, and expression of HuR was downregulated in failing hearts. The association of HuR and SCN5A mRNA protected SCN5A mRNA from decay. Injection of AAV9 viral particles carrying HuR increased SCN5A expression in mouse heart tissues after MI. Optical mapping of the intact heart demonstrated that overexpression of HuR improved action potential upstroke and conduction velocity in the infarct border zone, which reduced the risk of reentrant arrhythmia after MI. Our data indicate that HuR is an important RNA-binding protein in maintaining SCN5A mRNA abundance in cardiomyocytes. Reduced expression of HuR may be at least partially responsible for the downregulation of SCN5A mRNA expression in ischemic HF. Overexpression of HuR may rescue decreased SCN5A expression and reduce arrhythmic risk in HF. Increasing mRNA stability to increase ion channel currents may correct a fundamental defect in HF and represent a new paradigm in antiarrhythmic therapy.

Abnormal sodium channel mRNA splicing in hypertrophic cardiomyopathy

BackgroundOur previous studies showed that in ischemic and nonischemic heart failure (HF), the voltage-gated cardiac Na+ channel α subunit (SCN5A) mRNA is abnormally spliced to produce two truncated transcript variants (E28C and D) that activate the unfolded protein response (UPR). We tested whether SCN5A post-transcriptional regulation was abnormal in hypertrophic cardiomyopathy (HCM). Material and methodsHuman heart tissue was obtained from HCM patients. The changes in relative abundances of SCN5A, its variants, splicing factors RBM25 and LUC7A, and PERK, a major effector of the UPR, were analyzed by real time RT-PCR and the expression changes were confirmed by Western Blot. ResultsWe found reduced full-length transcript, increased SCN5A truncation variants and activation of UPR in HCM when compared to control hearts. In these patients, real time RT-PCR revealed that HCM patients had decreased SCN5A mRNA to 27.8±4.07% of control (P<0.01) and an increased abundance of E28C and E28D (3.4±0.3 and 2.8±0.3-fold, respectively, P<0.05). PERK mRNA increased 8.2±3.1 fold (P<0.01) in HCM patients. Western blot confirmed a significant increase of PERK. ConclusionsThese data suggested that the full-length SCN5A was reduced in patients with HCM. This reduction was accompanied by abnormal SCN5A pre-mRNA splicing and UPR activation. These changes may contribute to the arrhythmic risk in HCM.

Abstract 13939: Cardiac Resynchronization Improves Cardiac Sodium Channel mRNA Splicing Most in Patients With Severe Heart Failure

Introduction: Heart failure (HF) downregulates full-length cardiac sodium channel (SCN5A) mRNA and upregulates the splicing variant D (VD), which encodes a prematurely truncated, nonfunctional channel. Recently, we have shown that the ratio of circulating VD to full-length mRNA can predict the risk of sudden death. Cardiac resynchronization therapy (CRT) improves heart function and decreases arrhythmic events. Nevertheless, the mechanisms are unclear. Hypothesis: We tested whether CRT altered circulating full-length SCN5A mRNA and VD and further investigated its correlation with clinical parameters in HF. Methods: HF patients with new implantable cardioverter-defibrillators (ICDs) for primary prevention were enrolled. Circulating SCN5A and VD levels at baseline and at a follow-up visit were measured and compared using the ratio of VD to total SCN5A transcripts. The change of VD was expressed as the difference between the proportion of VD levels at baseline and at a follow-up visit. Results: A total of 81 HF patients were enrolled. At enrollment, patients with lower ejection fraction (EF) (≤30%) had higher circulating VD levels (0.80±0.11 vs. 0.73±0.07, P&lt;0.05). After a median follow-up of 235 days, the VD ratio significantly improved (0.84±0.08 vs. 0.74±0.10, P&lt;0.01) in patients receiving CRT. In patients without CRT, the VD ratio had significantly increased (0.77±0.07 vs 0.84±0.05, P&lt;0.05). In patients with CRT, the change of the VD ratio significantly correlated with left ventricular end systolic diameter (r=0.853, p&lt;0.01), EF (r=-0.643, p&lt;0.05) and ischemic cardiomyopathy (r=0.645, p&lt;0.05). Conclusions: CRT decreased the proportion of nonfunctional sodium channels, which may explain the lower arrhythmic risk with CRT therapy. Furthermore, the improvement was more prominent in patients with left ventricular dilation, lower EF and ischemic cardiomyopathy.

The water extract of Veratrilla baillonii could attenuate the subacute toxicity induced by Aconitum brachypodum

BackgroundAconitum brachypodum Diels (Family Ranunculaceae) is a Chinese ethnodrug and is well known for both its therapeutic application and high toxicity. However, no detoxication strategy is available for the complete elimination of the toxicity of Aconitum plants.Veratrilla baillonii Franch is believed to possess antitoxic effects on the toxicity induced by Aconitum plants and has been clinically used for hundreds of time by Naxi and Lisu nationalities in Yunnan Province of China.To further address the mechanism of the detoxication of Veratrilla baillonii, the effect of water decoction of Veratrilla baillonii (WVBF) on subacute toxicology of SD rats induced by Aconitum brachypodum (CFA), a genus Aconitum, was determined and studied in the present work. MethodsThe clinical behavior and number of survivors for different dosage of WVBF (25, 50, 100mg/kg) on CFA (4mg/kg) induced rats were observed until day 28. Histological changes and haematological parameters were evaluated. Moreover, Na+-K+-ATPase pathway in heart as well as key enzymes in liver were determined to further discuss the mechanism. ResultsThe results showed that the exposure of CFA led to some subacute toxicity to rats, especially male ones, accompanied with abnormality of serum biochemical index in rats’ serum. The toxicological target organs of CFA may be the heart, liver, kidney and brain. It is demonstrated that WVBF could attenuate the toxicity induced by Aconitum brachypodum via promoting the metabolic enzymes CYP3A1 and CYP3A2 in liver, downregulating the expression of Sodium/Calcium exchanger 1 (NCX1) and SCN5A sodium channal mRNA, and inducing Na+/K+-ATPase activity in heart. This study provides insights into detoxifying measures of Aconitum plants. ConclusionsAconitum brachypodum may lead to subacute toxicity of rats after long term of administration, and the toxicity could be attenuated by Veratrilla baillonii via promoting the metabolic enzymes in liver, downregulating the expression of NCX1 and SCN5A mRNA, and inducing Na+/K+-ATPase activity in heart.

Changes in cardiac Nav1.5 expression, function, and acetylation by pan-histone deacetylase inhibitors.

Histone deacetylase (HDAC) inhibitors are small molecule anticancer therapeutics that exhibit limiting cardiotoxicities including QT interval prolongation and life-threatening cardiac arrhythmias. Because the molecular mechanisms for HDAC inhibitor-induced cardiotoxicity are poorly understood, we performed whole cell patch voltage-clamp experiments to measure cardiac sodium currents (INa) from wild-type neonatal mouse ventricular or human-induced pluripotent stem cell-derived cardiomyocytes treated with trichostatin A (TSA), vorinostat (VOR), or romidepsin (FK228). All three pan-HDAC inhibitors dose dependently decreased peak INa density and shifted the voltage activation curve 3- to 8-mV positive. Increases in late INa were not observed despite a moderate slowing of the inactivation rate at low activating potentials (<-40 mV). Scn5a mRNA levels were not significantly altered but NaV1.5 protein levels were significantly reduced. Immunoprecipitation with anti-NaV1.5 and Western blotting with anti-acetyl-lysine antibodies indicated that NaV1.5 acetylation is increased in vivo after HDAC inhibition. FK228 inhibited total cardiac HDAC activity with two apparent IC50s of 5 nM and 1.75 μM, consistent with previous findings with TSA and VOR. FK228 also decreased ventricular gap junction conductance (gj), again consistent with previous findings. We conclude that pan-HDAC inhibition reduces cardiac INa density and NaV1.5 protein levels without affecting late INa amplitude and, thus, probably does not contribute to the reported QT interval prolongation and arrhythmias associated with pan-HDAC inhibitor therapies. Conversely, reductions in gj may enhance the occurrence of triggered activity by limiting electrotonic inhibition and, combined with reduced INa, slow myocardial conduction and increase vulnerability to reentrant arrhythmias.

Splicing misregulation of SCN5A contributes to cardiac-conduction delay and heart arrhythmia in myotonic dystrophy.

Myotonic dystrophy (DM) is caused by the expression of mutant RNAs containing expanded CUG repeats that sequester muscleblind-like (MBNL) proteins, leading to alternative splicing changes. Cardiac alterations, characterized by conduction delays and arrhythmia, are the second most common cause of death in DM. Using RNA sequencing, here we identify novel splicing alterations in DM heart samples, including a switch from adult exon 6B towards fetal exon 6A in the cardiac sodium channel, SCN5A. We find that MBNL1 regulates alternative splicing of SCN5A mRNA and that the splicing variant of SCN5A produced in DM presents a reduced excitability compared with the control adult isoform. Importantly, reproducing splicing alteration of Scn5a in mice is sufficient to promote heart arrhythmia and cardiac-conduction delay, two predominant features of myotonic dystrophy. In conclusion, misregulation of the alternative splicing of SCN5A may contribute to a subset of the cardiac dysfunctions observed in myotonic dystrophy.

Abstract 14356: Blood Tests That Improve the Accuracy of a Brugada Syndrome Diagnosis

Objectives: To discover the role of altered gene expression regulation in Brugada Syndrome (BrS) and to find biomarkers for BrS diagnosis. Methods: Twenty-five control patients (Control), 25 BrS patients without SCN5A mutation (SCN5A(-)) and 20 BrS patients with SCN5A mutation (SCN5A(+)) were included in this study. Specified gene expression of white blood cells (WBC) were measured by RT-qPCR using TaqMan® Gene Expression assay. Results: MEF2C and MESP1 are the two major cardiac specific transcription factors expressed in WBC. The mRNA expression levels of SCN5A, MEF2C and HuR, one of mRNA stabilizers, were decreased in the SCN5A (+) group (P=0.047, 0.02, 0.000 vs. control group, respectively). The mRNA expression of MESP1 in WBCs was significantly lower in both SCN5A(-) (P=0.012 vs. control) and SCN5A(+) (P=0.000 vs. control) groups. There was no difference between the two BrS groups in MESP1 expression (P=0.215). The area under the Receiver Operating Characteristics (ROC) analysis curve for prediction of BrS using MESP1 levels was 0.775 (95% CI 0.668, 0.882, asymptotic Sig.=0.000). At the optimal cutoff, the corresponding maximum sensitivity and specificity were 0.62 (95% CI: 0.47, 0.76) and 0.88 (0.69, 0.97), respectively. The diagnostic odds ratio (DOR) of MESP1 for BrS diagnosis was 11.96 (95% CI: 5.79, 24.73). The assessment of the mRNA levels in blood SCN5A, MEF2C and HuR were useful for predicting BrS patients with an SCN5A mutation. The area under the ROC analysis curve for prediction of BrS with an SCN5A mutation using SCN5A, MEF2C and HuR mRNA levels in WBCs was 0.847 (95% CI 0.752, 0.942, asymptotic Sig.=0.000), 0.685 (95% CI 0.542, 0.828, asymptotic Sig.=0.016) and 0.777 (95% CI 0.652, 0.902, asymptotic Sig.=0.000), respectively. At the optimal cutoff, the DOR of SCN5A, MEF2C and HuR for SCN5A(+) BrS diagnosis was 17.5 (95% CI: 8.06, 37.86), 4.9 (95% CI: 2.61, 9.17) and 23.5 (95% CI: 9.39, 58.80), respectively. Conclusions: Our results suggest that assessment of circulating MESP1 may be used as a biomarker for BrS diagnosis while decreased SCN5A, MEF2C and HuR mRNA in WBCs is associated with BrS patients with an SCN5A mutation. Our results also suggest that decreased expression of SCN5A, MEF2C, MESP1, and HuR may be pathophysiologically related to BrS.

Expression and function of the Scn5a-encoded voltage-gated sodium channel NaV 1.5 in the rat jejunum.

The SCN5A-encoded voltage-gated sodium channel NaV 1.5 is expressed in human jejunum and colon. Mutations in NaV 1.5 are associated with gastrointestinal motility disorders. The rat gastrointestinal tract expresses voltage-gated sodium channels, but their molecular identity and role in rat gastrointestinal electrophysiology are unknown. The presence and distribution of Scn5a-encoded NaV 1.5 was examined by PCR, Western blotting and immunohistochemistry in rat jejunum. Freshly dissociated smooth muscle cells were examined by whole cell electrophysiology. Zinc finger nuclease was used to target Scn5a in rats. Lentiviral-mediated transduction with shRNA was used to target Scn5a in rat jejunum smooth muscle organotypic cultures. Organotypic cultures were examined by sharp electrode electrophysiology and RT-PCR. We found NaV 1.5 in rat jejunum and colon smooth muscle by Western blot. Immunohistochemistry using two other antibodies of different portions of NaV 1.5 revealed the presence of the ion channel in rat jejunum. Whole cell voltage-clamp in dissociated smooth muscle cells from rat jejunum showed fast activating and inactivating voltage-dependent inward current that was eliminated by Na(+) replacement by NMDG(+) . Constitutive rat Scn5a knockout resulted in death in utero. NaV 1.5 shRNA delivered by lentivirus into rat jejunum smooth muscle organotypic culture resulted in 57% loss of Scn5a mRNA and several significant changes in slow waves, namely 40% decrease in peak amplitude, 30% decrease in half-width, and 7 mV hyperpolarization of the membrane potential at peak amplitude. Scn5a-encoded NaV 1.5 is expressed in rat gastrointestinal smooth muscle and it contributes to smooth muscle electrophysiology.