Gating mechanisms underlying deactivation slowing by two KCNQ1 atrial fibrillation mutations.
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ABSTRACT:
SUBMITTER: Peng G
PROVIDER: S-EPMC5382920 | biostudies-literature | 2017 Apr
REPOSITORIES: biostudies-literature
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Gating mechanisms underlying deactivation slowing by two KCNQ1 atrial fibrillation mutations.
Peng Gary G Barro-Soria Rene R Sampson Kevin J KJ Larsson H Peter HP Kass Robert S RS
Scientific reports 20170406
KCNQ1 is a voltage-gated potassium channel that is modulated by the beta-subunit KCNE1 to generate I<sub>Ks</sub>, the slow delayed rectifier current, which plays a critical role in repolarizing the cardiac action potential. Two KCNQ1 gain-of-function mutations that cause a genetic form of atrial fibrillation, S140G and V141M, drastically slow I<sub>Ks</sub> deactivation. However, the underlying gating alterations remain unknown. Voltage clamp fluorometry (VCF) allows simultaneous measurement of ...[more]
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Project description:BACKGROUND:Atrial fibrillation is the most common sustained cardiac arrhythmia in adults. We hypothesized that gain-of-function KCNQ1 mutations previously associated with familial atrial fibrillation have distinct pharmacological properties that may enable targeted inhibition. METHODS AND RESULTS:Wild-type (WT) KCNQ1 or the familial atrial fibrillation mutation KCNQ1-S140G was heterologously coexpressed with KCNE1 to enable electrophysiological recording of the slow delayed rectifier current (IKs) and investigation of pharmacological effects of the IKs selective blocker HMR-1556. Coexpression of KCNQ1-S140G with KCNE1 generated potassium currents (S140G-IKs) that exhibited greater sensitivity to HMR-1556 than WT-IKs. Enhanced HMR-1556 sensitivity was also observed for another gain-of-function atrial fibrillation mutation, KCNQ1-V141M. Heteromeric expression of KCNE1 with both KCNQ1-WT and KCNQ1-S140G generated currents (HET-IKs) with gain-of-function features, including larger amplitude, a constitutively active component, hyperpolarized voltage dependence of activation, and extremely slow deactivation. A low concentration of HMR-1556, which had little effect on WT-IKs but was capable of inhibiting the mutant channel, reduced both instantaneous and steady state HET-IKs to levels that were not significantly different from WT-IKs and attenuated use-dependent accumulation of the current. In cultured adult rabbit left atrial myocytes, expression of S140G-IKs shortened action potential duration compared with WT-IKs. Application of HMR-1556 mitigated S140G-IKs-induced action potential duration shortening and did not alter action potential duration in cells expressing WT-IKs. CONCLUSIONS:The enhanced sensitivity of KCNQ1 gain-of-function mutations for HMR-1556 suggests the possibility of selective therapeutic targeting, and, therefore, our data illustrate a potential proof of principle for genotype-specific treatment of this heritable arrhythmia.
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Project description:BackgroundRecent studies suggest that mutation of the slow delayed rectifier potassium channel (IKs) contributes to familial atrial fibrillation (FAF). In the current study, we identified common genetic variants of KCNQ1 and explored the potential association between KCNQ1 polymorphism with lone AF (LAF).MethodsClinical data and blood samples were collected from 190 Han Chinese patients with sporadic AF and matched healthy controls. Variants of the KCNQ1 gene were identified using single-strand conformational polymorphism (SSCP) analysis. A case-control association study in KCNQ1 identified six known single-nucleotide polymorphisms (SNPs) during SSCP screening of the 190 LAF patients and 190 healthy controls.ResultsOne of the SNPs in KCNQ1 was strongly associated with LAF; significant allelic association was detected rs59233444 (P = 0.013, OR = 1.469, 95% confidence interval (CI): 1.083-1.993). A multiple regression analysis indicated that rs59233444 is an independent risk factor for LAF. Twelve new variants were identified in KCNQ1, including one in the 5'-UTR, two in the 3'-UTR, six in introns, two synonymous substitutions, and one missense substitution. Variants c.1009C>T, c.1860C>T, and c.+2285C>T were not present in the 190 controls, and the others were identified in controls at various frequencies.Conclusionsrs59233444, a common SNP but not mutation in the coding regions of the KCNQ1 gene, is a risk factor for LAF in Chinese Han population.
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Project description:Genome-wide association studies have uncovered over a 100 genetic loci associated with atrial fibrillation (AF), the most common arrhythmia. Many of the top AF-associated loci harbor key cardiac transcription factors, including PITX2, TBX5, PRRX1, and ZFHX3. Moreover, the vast majority of the AF-associated variants lie within noncoding regions of the genome where causal variants affect gene expression by altering the activity of transcription factors and the epigenetic state of chromatin. In this review, we discuss a transcriptional regulatory network model for AF defined by effector genes in Genome-wide association studies loci. We describe the current state of the field regarding the identification and function of AF-relevant gene regulatory networks, including variant regulatory elements, dose-sensitive transcription factor functionality, target genes, and epigenetic states. We illustrate how altered transcriptional networks may impact cardiomyocyte function and ionic currents that impact AF risk. Last, we identify the need for improved tools to identify and functionally test transcriptional components to define the links between genetic variation, epigenetic gene regulation, and atrial function.
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Project description:The IKs channel complex is formed by the co-assembly of Kv7.1 (KCNQ1), a voltage-gated potassium channel, with its β-subunit, KCNE1 and the association of numerous accessory regulatory molecules such as PIP2, calmodulin, and yotiao. As a result, the IKs potassium current shows kinetic and regulatory flexibility, which not only allows IKs to fulfill physiological roles as disparate as cardiac repolarization and the maintenance of endolymph K+ homeostasis, but also to cause significant disease when it malfunctions. Here, we review new areas of understanding in the assembly, kinetics of activation and inactivation, voltage-sensor pore coupling, unitary events and regulation of this important ion channel complex, all of which have been given further impetus by the recent solution of cryo-EM structural representations of KCNQ1 alone and KCNQ1+KCNE3. Recently, the stoichiometric ratio of KCNE1 to KCNQ1 subunits has been confirmed to be variable up to a ratio of 4:4, rather than fixed at 2:4, and we will review the results and new methodologies that support this conclusion. Significant advances have been made in understanding differences between KCNQ1 and IKs gating using voltage clamp fluorimetry and mutational analysis to illuminate voltage sensor activation and inactivation, and the relationship between voltage sensor translation and pore domain opening. We now understand that the KCNQ1 pore can open with different permeabilities and conductance when the voltage sensor is in partially or fully activated positions, and the ability to make robust single channel recordings from IKs channels has also revealed the complicated pore subconductance architecture during these opening steps, during inactivation, and regulation by 1-4 associated KCNE1 subunits. Experiments placing mutations into individual voltage sensors to drastically change voltage dependence or prevent their movement altogether have demonstrated that the activation of KCNQ1 alone and IKs can best be explained using allosteric models of channel gating. Finally, we discuss how the intrinsic gating properties of KCNQ1 and IKs are highly modulated through the impact of intracellular signaling molecules and co-factors such as PIP2, protein kinase A, calmodulin and ATP, all of which modulate IKs current kinetics and contribute to diverse IKs channel complex function.
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