Exchange Rate Dynamics and Central Bank Interventions: On the (De)Stabilizing Nature of Targeting Long-Run Fundamentals Interventions

We develop a foreign exchange market model in which a market maker adjusts the exchange rate with respect to the trading behavior of chartists, fundamentalists and a central bank. While chartists bet on the persistence of bull and bear markets, fundamentalists speculate on mean reversion. The central bank seeks to stabilize the foreign exchange market by placing buy (sell) orders when the undervaluation (overvaluation) of the exchange rate exceeds a certain threshold. Since a one-dimensional piecewise-linear discontinuous map with three branches determines the evolution of the exchange rate, we use a combination of analytical and numerical tools to explore the extent to which the central bank is able to tame the behavior of the foreign exchange market.

Study of High-Transverse-Momentum Higgs Boson Production in Association with a Vector Boson in the qqbb Final State with the ATLAS Detector

This Letter presents the first study of Higgs boson production in association with a vector boson (V=W or Z) in the fully hadronic qqbb final state using data recorded by the ATLAS detector at the LHC in proton-proton collisions at sqrt[s]=13  TeV and corresponding to an integrated luminosity of 137  fb^{-1}. The vector bosons and Higgs bosons are each reconstructed as large-radius jets and tagged using jet substructure techniques. Dedicated tagging algorithms exploiting b-tagging properties are used to identify jets consistent with Higgs bosons decaying into bb[over ¯]. Dominant backgrounds from multijet production are determined directly from the data, and a likelihood fit to the jet mass distribution of Higgs boson candidates is used to extract the number of signal events. The VH production cross section is measured inclusively and differentially in several ranges of Higgs boson transverse momentum: 250-450, 450-650, and greater than 650 GeV. The inclusive signal yield relative to the standard model expectation is observed to be μ=1.4_{-0.9}^{+1.0} and the corresponding cross section is 3.1±1.3(stat)_{-1.4}^{+1.8}(syst)  pb.

Measurement of the Centrality Dependence of the Dijet Yield in p+Pb Collisions at sqrt[s_{NN}]=8.16 TeV with the ATLAS Detector

ATLAS measured the centrality dependence of the dijet yield using 165  nb^{-1} of p+Pb data collected at sqrt[s_{NN}]=8.16  TeV in 2016. The event centrality, which reflects the p+Pb impact parameter, is characterized by the total transverse energy registered in the Pb-going side of the forward calorimeter. The central-to-peripheral ratio of the scaled dijet yields, R_{CP}, is evaluated, and the results are presented as a function of variables that reflect the kinematics of the initial hard parton scattering process. The R_{CP} shows a scaling with the Bjorken x of the parton originating from the proton, x_{p}, while no such trend is observed as a function of x_{Pb}. This analysis provides unique input to understanding the role of small proton spatial configurations in p+Pb collisions by covering parton momentum fractions from the valence region down to x_{p}∼10^{-3} and x_{Pb}∼4×10^{-4}.

CAGI, the Critical Assessment of Genome Interpretation, establishes progress and prospects for computational genetic variant interpretation methods

BACKGROUND

The Critical Assessment of Genome Interpretation (CAGI) aims to advance the state-of-the-art for computational prediction of genetic variant impact, particularly where relevant to disease. The five complete editions of the CAGI community experiment comprised 50 challenges, in which participants made blind predictions of phenotypes from genetic data, and these were evaluated by independent assessors.

RESULTS

Performance was particularly strong for clinical pathogenic variants, including some difficult-to-diagnose cases, and extends to interpretation of cancer-related variants. Missense variant interpretation methods were able to estimate biochemical effects with increasing accuracy. Assessment of methods for regulatory variants and complex trait disease risk was less definitive and indicates performance potentially suitable for auxiliary use in the clinic.

CONCLUSIONS

Results show that while current methods are imperfect, they have major utility for research and clinical applications. Emerging methods and increasingly large, robust datasets for training and assessment promise further progress ahead.

Combined Measurement of the Higgs Boson Mass from the H→γγ and H→ZZ^{*}→4ℓ Decay Channels with the ATLAS Detector Using sqrt[s]=7, 8, and 13 TeV pp Collision Data

A measurement of the mass of the Higgs boson combining the H→ZZ^{*}→4ℓ and H→γγ decay channels is presented. The result is based on 140  fb^{-1} of proton-proton collision data collected by the ATLAS detector during LHC run 2 at a center-of-mass energy of 13 TeV combined with the run 1 ATLAS mass measurement, performed at center-of-mass energies of 7 and 8 TeV, yielding a Higgs boson mass of 125.11±0.09(stat)±0.06(syst)=125.11±0.11  GeV. This corresponds to a 0.09% precision achieved on this fundamental parameter of the Standard Model of particle physics.

Material-Specific Roadmap Modes Can Improve the Visibility of Liquid Embolic Agents for Endovascular Embolization: A Systematic In Vitro Study

BACKGROUND AND PURPOSE

Endovascular embolization using liquid embolic agents is a safe and effective treatment option for AVMs and fistulas. Because reliable visibility of these liquid embolic agents is essential for intraprocedural visual control to prevent complications, novel angiographic systems are equipped with material-specific roadmap modes. The aim of this study was the systematic in vitro comparison of conventional and material-specific roadmap modes regarding the visibility of the most used liquid embolic agents.

MATERIALS AND METHODS

A recently introduced in vitro model, resembling cerebral vessels, was embolized with Onyx 18, Squid 18, PHIL 25%, and n-BCA mixed with iodized oil (n = 4 for each liquid embolic agent), as well as with contrast medium and saline, both serving as a reference. Imaging was performed in conventional and material-specific roadmap modes. The visibility of the liquid embolic agents in both modes was compared quantitatively and qualitatively.

RESULTS

Significant differences between conventional and material-specific roadmap modes regarding the visibility of the liquid embolic agents were observed for all study groups. All liquid embolic agents were better visible in the material-specific roadmap modes compared with the conventional mode in qualitative and quantitative analyses (eg, Onyx in conventional-versus-material-specific modes along the 1.0-mm sector: mean contrast-to-noise ratio, 5.69 [SD, 0.85] versus 47.18 [SD, 5.72]; P < .001, respectively).

CONCLUSIONS

In this in vitro study, we demonstrated a better visibility of all investigated liquid embolic agents by using material-specific roadmap modes compared with the conventional roadmap technique. Especially in complex anatomic situations, these novel roadmap modes could improve the visual control and thus the safety and efficacy of embolization procedures in clinical practice.

Whole-Exome Sequencing Implicates Neuronal Calcium Channel with Familial Atrial Fibrillation

Background: Atrial Fibrillation (AF) is the most prevalent sustained cardiac arrhythmia, responsible for considerable morbidity and mortality. The heterogenic and complex pathogenesis of AF remains poorly understood, which contributes to the current limitation in effective treatments. We aimed to identify rare genetic variants associated with AF in patients with familial AF.

Methods and results: We performed whole exome sequencing in a large family with familial AF and identified a rare variant in the gene CACNA1A c.5053G > A which co-segregated with AF. The gene encodes for the protein variants Ca_V2.1-V1686M, and is important in neuronal function. Functional characterization of the CACNA1A, using patch-clamp recordings on transiently transfected mammalian cells, revealed a modest loss-of-function of Ca_V2.1-V1686M.

Conclusion: We identified a rare loss-of-function variant associated with AF in a gene previously linked with neuronal function. The results allude to a novel link between dysfunction of an ion channel previously associated with neuronal functions and increased risk of developing AF.

The Tunicate Metabolite 2-(3,5-Diiodo-4-methoxyphenyl)ethan-1-amine Targets Ion Channels of Vertebrate Sensory Neurons

Marine tunicates produce defensive amino-acid-derived metabolites, including 2-(3,5-diiodo-4-methoxyphenyl)ethan-1-amine (DIMTA), but their mechanisms of action are rarely known. Using an assay-guided approach, we found that out of the many different sensory cells in the mouse dorsal root ganglion (DRG), DIMTA selectively affected low-threshold cold thermosensors. Whole-cell electrophysiology experiments using DRG cells, channels expressed in Xenopus oocytes, and human cell lines revealed that DIMTA blocks several potassium channels, reducing the magnitude of the afterhyperpolarization and increasing the baseline intracellular calcium concentration [Ca²⁺]_i of low-threshold cold thermosensors. When injected into mice, DIMTA increased the threshold of cold sensation by >3 °C. DIMTA may thus serve as a lead in the further design of compounds that inhibit problems in the cold-sensory system, such as cold allodynia and other neuropathic pain conditions.

Imaging Artifacts of Liquid Embolic Agents on Conventional CT in an Experimental in Vitro Model

BACKGROUND AND PURPOSE

Endovascular embolization using liquid embolic agents is a safe and effective treatment option for AVMs and dural arteriovenous fistulas. The aim of this study was to assess the degree of artifact inducement by the most frequently used liquid embolic agents in conventional CT in an experimental in vitro model.

MATERIALS AND METHODS

Dimethyl-sulfoxide-compatible tubes were filled with the following liquid embolic agents (n = 10, respectively): Onyx 18, all variants of Squid, PHIL 25%, PHIL LV, and n-BCA mixed with iodized oil. After inserting the tubes into a CT imaging phantom, we acquired images. Artifacts were graded quantitatively by the use of Hounsfield units in a donut-shaped ROI using a customized software application that was specifically designed for this study and were graded qualitatively using a 5-point scale.

RESULTS

Quantitative and qualitative analyses revealed the most artifacts for Onyx 18 and the least artifacts for n-BCA, PHIL 25%, and PHIL LV. Squid caused more artifacts compared with PHIL, both for the low-viscosity and for the extra-low-viscosity versions (eg, quantitative analysis, Squid 18: mean ± SD, 30.3 ± 9.7 HU versus PHIL 25%: mean ± SD, 10.6 ± 0.8 HU; P < .001). Differences between the standard and low-density variants of Squid were observed only quantitatively for Squid 12. There were no statistical differences between the different concentrations of Squid and PHIL.

CONCLUSIONS

In this systematic in vitro analysis investigating the most commonly used liquid embolic agents, relevant differences in CT imaging artifacts could be demonstrated. Ethylene-vinyl alcohol-based liquid embolic agents induced more artifacts compared with liquid embolic agents that use iodine as a radiopaque component.

Investigating gene-microRNA networks in atrial fibrillation patients with mitral valve regurgitation

BACKGROUND

Atrial fibrillation (AF) is predicted to affect around 17.9 million individuals in Europe by 2060. The disease is associated with severe electrical and structural remodelling of the heart, and increased the risk of stroke and heart failure. In order to improve treatment and find new drug targets, the field needs to better comprehend the exact molecular mechanisms in these remodelling processes.

OBJECTIVES

This study aims to identify gene and miRNA networks involved in the remodelling of AF hearts in AF patients with mitral valve regurgitation (MVR).

METHODS

Total RNA was extracted from right atrial biopsies from patients undergoing surgery for mitral valve replacement or repair with AF and without history of AF to test for differentially expressed genes and miRNAs using RNA-sequencing and miRNA microarray. In silico predictions were used to construct a mRNA-miRNA network including differentially expressed mRNAs and miRNAs. Gene and chromosome enrichment analysis were used to identify molecular pathways and high-density AF loci.

RESULTS

We found 644 genes and 43 miRNAs differentially expressed in AF patients compared to controls. From these lists, we identified 905 pairs of putative miRNA-mRNA interactions, including 37 miRNAs and 295 genes. Of particular note, AF-associated miR-130b-3p, miR-338-5p and miR-208a-3p were differentially expressed in our AF tissue samples. These miRNAs are predicted regulators of several differentially expressed genes associated with cardiac conduction and fibrosis. We identified two high-density AF loci in chromosomes 14q11.2 and 6p21.3.

CONCLUSIONS

AF in MVR patients is associated with down-regulation of ion channel genes and up-regulation of extracellular matrix genes. Other AF related genes are dysregulated and several are predicted to be targeted by miRNAs. Our novel miRNA-mRNA regulatory network provides new insights into the mechanisms of AF.

A Novel Loss-of-Function Variant in the Chloride Ion Channel Gene Clcn2 Associates with Atrial Fibrillation

Atrial Fibrillation (AF) is the most common cardiac arrhythmia. Its pathogenesis is complex and poorly understood. Whole exome sequencing of Danish families with AF revealed a novel four nucleotide deletion c.1041_1044del in CLCN2 shared by affected individuals. We aimed to investigate the role of genetic variation of CLCN2 encoding the inwardly rectifying chloride channel ClC-2 as a risk factor for the development of familiar AF. The effect of the CLCN2 variant was evaluated by electrophysiological recordings on transiently transfected cells. We used quantitative PCR to assess CLCN2 mRNA expression levels in human atrial and ventricular tissue samples. The nucleotide deletion CLCN2 c.1041_1044del results in a frame-shift and premature stop codon. The truncated ClC-2 p.V347fs channel does not conduct current. Co-expression with wild-type ClC-2, imitating the heterozygote state of the patients, resulted in a 50% reduction in macroscopic current, suggesting an inability of truncated ClC-2 protein to form channel complexes with wild type channel subunits. Quantitative PCR experiments using human heart tissue from healthy donors demonstrated that CLCN2 is expressed across all four heart chambers. Our genetic and functional data points to a possible link between loss of ClC-2 function and an increased risk of developing AF.

Neoadjuvant PD-1 Immune Checkpoint Blockade Reverses Functional Immunodominance among Tumor Antigen-Specific T Cells

PURPOSE

Surgical resection of primary tumor with regional lymphadenectomy remains the treatment of choice for patients with advanced human papillomavirus-negative head and neck squamous cell carcinoma. However, even when pathologic disease-free margins can be achieved, locoregional and/or distant disease relapse remains high. Perioperative immunotherapy may improve outcomes, but mechanistic data supporting the use of neoadjuvant or adjuvant treatment clinically are sparse.

EXPERIMENTAL DESIGN

Two syngeneic models of oral cavity carcinoma with defined T-cell antigens were treated with programmed death receptor 1 (PD-1) mAb before or after surgical resection of primary tumors, and antigen-specific T-cell responses were explored with functional and in vivo challenge assays.

RESULTS

We demonstrated that functional immunodominance developed among T cells targeting multiple independent tumor antigens. T cells specific for subdominant antigens expressed greater levels of PD-1. Neoadjuvant, but not adjuvant, PD-1 immune checkpoint blockade broke immunodominance and induced T-cell responses to dominant and subdominant antigens. Using tumors lacking the immunodominant antigen as a model of antigen escape, neoadjuvant PD-1 immune checkpoint blockade induced effector T-cell immunity against tumor cells lacking immunodominant but retaining subdominant antigen. When combined with complete surgical excision, neoadjuvant PD-1 immune checkpoint blockade led to formation of immunologic memory capable of preventing engraftment of tumors lacking the immunodominant but retaining subdominant antigen.

CONCLUSIONS

Together, these results implicate PD-1 expression by T cells in the mechanism of functional immunodominance among independent T-cell clones within a progressing tumor and support the use of neoadjuvant PD-1 immune checkpoint blockade in patients with surgically resectable carcinomas.

Reappraisal of variants previously linked with sudden infant death syndrome: results from three population-based cohorts

We aimed to investigate the pathogenicity of cardiac ion channel variants previously associated with SIDS. We reviewed SIDS-associated variants previously reported in databases and the literature in three large population-based cohorts; The ExAC database, the Inter99 study, and the UK Biobank (UKBB). Variants were classified according to the American College of Medical Genetics and Genomics (ACMG) guidelines. Of the 92 SIDS-associated variants, 59 (64%) were present in ExAC, 18 (20%) in Inter99, and 24 (26%) in UKBB. Using the Inter99 cohort, we found no difference in J-point amplitude and QTc-interval between carriers and non-carriers for 14/18 variants. There was no difference in the risk of syncope (P = 0.32), malignant ventricular arrhythmia (P = 0.96), and all-cause mortality (P = 0.59) between carriers and non-carriers. The ACMG guidelines reclassified 75% of all variants as variant-of-uncertain significance, likely benign, and benign. We identified ~2/3 of variants previously associated with SIDS and found no significant associations with electrocardiographic traits, syncope, malignant ventricular arrhythmia, or all-cause mortality. These data indicate that many of these variants are not highly penetrant, monogenic causes of SIDS and underline the importance of frequent reappraisal of genetic variants to avoid future misdiagnosis.

Deletion in mice of X-linked, Brugada syndrome- and atrial fibrillation-associated Kcne5 augments ventricular KV currents and predisposes to ventricular arrhythmia

KCNE5 is an X-linked gene encoding KCNE5, an ancillary subunit to voltage-gated potassium (K_V) channels. Human KCNE5 mutations are associated with atrial fibrillation (AF)- and Brugada syndrome (BrS)-induced cardiac arrhythmias that can arise from increased potassium current in cardiomyocytes. Seeking to establish underlying molecular mechanisms, we created and studied Kcne5 knockout ( Kcne5^-/0) mice. Intracardiac ECG revealed that Kcne5 deletion caused ventricular premature beats, increased susceptibility to induction of polymorphic ventricular tachycardia (60 vs. 24% in Kcne5^+/0 mice), and 10% shorter ventricular refractory period. Kcne5 deletion increased mean ventricular myocyte K_V current density in the apex and also in the subpopulation of septal myocytes that lack fast transient outward current ( I_to,f). The current increases arose from an apex-specific increase in slow transient outward current-1 ( I_Kslow,1) (conducted by K_V1.5) and I_to,f (conducted by K_V4) and an increase in I_Kslow,2 (conducted by K_V2.1) in both apex and septum. Kcne5 protein localized to the intercalated discs in ventricular myocytes, where K_V2.1 was also detected in both Kcne5^-/0 and Kcne5^+/0 mice. In HL-1 cardiac cells and human embryonic kidney cells, KCNE5 and K_V2.1 colocalized at the cell surface, but predominantly in intracellular vesicles, suggesting that Kcne5 deletion increases I_K,slow2 by reducing K_V2.1 intracellular sequestration. The human AF-associated mutation KCNE5-L65F negative shifted the voltage dependence of K_V2.1-KCNE5 channels, increasing their maximum current density >2-fold, whereas BrS-associated KCNE5 mutations produced more subtle negative shifts in K_V2.1 voltage dependence. The findings represent the first reported native role for Kcne5 and the first demonstrated Kcne regulation of K_V2.1 in mouse heart. Increased K_V current is a manifestation of KCNE5 disruption that is most likely common to both mouse and human hearts, providing a plausible mechanistic basis for human KCNE5-linked AF and BrS.-David, J.-P., Lisewski, U., Crump, S. M., Jepps, T. A., Bocksteins, E., Wilck, N., Lossie, J., Roepke, T. K., Schmitt, N., Abbott, G. W. Deletion in mice of X-linked, Brugada syndrome- and atrial fibrillation-associated Kcne5 augments ventricular K_V currents and predisposes to ventricular arrhythmia.

Spinal dorsal horn astrocytes release GABA in response to synaptic activation

KEY POINTS

GABA is an essential molecule for sensory information processing. It is usually assumed to be released by neurons. Here we show that in the dorsal horn of the spinal cord, astrocytes respond to glutamate by releasing GABA. Our findings suggest a novel role for astrocytes in somatosensory information processing.

ABSTRACT

Astrocytes participate in neuronal signalling by releasing gliotransmitters in response to neurotransmitters. We investigated if astrocytes from the dorsal horn of the spinal cord of adult red-eared turtles (Trachemys scripta elegans) release GABA in response to glutamatergic receptor activation. For this, we developed a GABA sensor consisting of HEK cells expressing GABA_A receptors. By positioning the sensor recorded in the whole-cell patch-clamp configuration within the dorsal horn of a spinal cord slice, we could detect GABA in the extracellular space. Puff application of glutamate induced GABA release events with time courses that exceeded the duration of inhibitory postsynaptic currents by one order of magnitude. Because the events were neither affected by extracellular addition of nickel, cadmium and tetrodotoxin nor by removal of Ca²⁺ , we concluded that they originated from non-neuronal cells. Immunohistochemical staining allowed the detection of GABA in a fraction of dorsal horn astrocytes. The selective stimulation of A∂ and C fibres in a dorsal root filament induced a Ca²⁺ increase in astrocytes loaded with Oregon Green BAPTA. Finally, chelating Ca²⁺ in a single astrocyte was sufficient to prevent the GABA release evoked by glutamate. Our results indicate that glutamate triggers the release of GABA from dorsal horn astrocytes with a time course compatible with the integration of sensory inputs.

PKD Phosphorylation as Novel Pathway of KV11.1 Regulation

BACKGROUND/AIMS

The voltage-gated potassium channel KV11.1 has been originally cloned from the brain and is expressed in a variety of tissues. The role of phosphorylation for channel function is a matter of debate. In this study, we aimed to elucidate the extent and role of protein kinase D mediated phosphorylation.

METHODS

We employed mass spectrometry, whole-cell patch clamp electrophysiology, confocal microscopy, site-directed mutagenesis, and western blotting.

RESULTS

Using brain tissue from rat and mouse, we mapped several phosphorylated KV11.1 residues by LC-MS mass spectrometry and identified protein kinase D (PKD1) as possible regulatory kinase. Co-expression of KV11.1 with PKD1 reduced current amplitudes without altering protein levels or surface expression of the channel. Based on LC-MS results from in vivo and HEK293 cell experiments we chose four KV11.1 mutant candidates for further functional analysis. Ablation of the putative PKD phosphorylation site in the mutant S284A increased the maximal current indicating S284 as a main PKD target in KV11.1.

CONCLUSIONS

Our data might help mitigating a long-standing controversy in the field regarding PKC regulation of KV11.1. We propose that PKD1 mediates the PKC effects on KV11.1 and we found that PKD targets S284 in the N-terminus of the channel.

Multiple genetic variations in sodium channel subunits in a case of sudden infant death syndrome

BACKGROUND

Dysfunction of Na_V 1.5 encoded by SCN5A accounts for approximately half of the channelopathic SIDS cases. We investigated the functional effect of two gene variants identified in the same patient, one in SCN5A and one in SCN1Bb. The aim of the study was to risk stratify the proband's family.

METHODS

The family was referred for cardiovascular genetic evaluation to assess familial risk of cardiac disease. Functional analysis of the identified variants was performed with patch-clamp electrophysiology in HEK293 cells.

RESULTS

A 16-month-old healthy boy died suddenly in the context of nonspecific illness and possible fever. Postmortem genetic testing revealed variants in the SCN5A and SCN1Bb genes. The proband's father carries the same variants but is asymptomatic. Electrophysiological analysis of the Na_V 1.5_1281X truncation revealed complete loss-of-function of the channel. Coexpression of Na_V 1.5 with Na_V β1b significantly increased I_Na density when compared to Na_V 1.5 alone. The Na_V β1b _V268I variant abolished this I_Na density increase. Moreover, it shifted the activation curve toward more depolarized potentials.

CONCLUSIONS

Genetic variation of both sodium channel and its modifiers may contribute to sudden unexplained death in childhood. However, the asymptomatic father suggests that genetic variation of these genes is not sufficient to cause sudden death or clinically detectable SCN5A phenotypes.

PD-1 Inhibition Minimally Affects Cisplatin-Induced Toxicities in a Murine Model

Immune checkpoint inhibition used in combination with standard cisplatin-based chemotherapy regimens is currently under evaluation in clinical trials for head and neck squamous cell carcinoma (HNSCC). The impact of anti-PD-1 therapy on cisplatin-induced ototoxicity and nephrotoxicity has not been established. Here we use a murine model of cisplatin-induced hearing loss to investigate the impact of anti-PD-1 immunotherapy on auditory brainstem responses (ABRs), distortion product otoacoustic emissions (DPOAEs), serum creatinine, and hair cell and renal histology. We demonstrate only mild worsening of DPOAEs at 14.4 and 16 kHz as well as a mild increase in serum creatinine. Renal and hair cell histology as well as ABR measures were unchanged by PD-1 inhibition. Thus, our data suggest that the use of PD-1 inhibition in conjunction with cisplatin results in toxicities that are similar to those of cisplatin alone.

SUMO co-expression modifies KV 11.1 channel activity

AIM

The voltage-gated potassium channel K_V 11.1 is the molecular basis for the I_Kr current, which plays an important role in cardiac physiology. Its malfunction is associated with both inherited and acquired cardiac arrhythmias. Native currents differ from those in experimental models, suggesting additional regulatory mechanisms. We hypothesized that the post-translational modification sumoylation fine-tunes channel activity.

METHODS

The functional effects of sumoylation on K_V 11.1 were addressed by employing two-electrode voltage-clamp (TEVC) experiments in Xenopus laevis oocytes. Site-directed mutagenesis enabled a further analysis of the SUMO-target amino acids. We assessed protein expression levels and used confocal imaging for localization studies.

RESULTS

Co-expression with Ubc9 and SUMO alters the electrophysiological properties of K_V 11.1 leading to a decrease in steady-state current amplitude largely due to faster inactivation and alteration of deactivation kinetics. We identified three lysines (K21, K93 and K116) in the PAS domain as the putative SUMO-targets.

CONCLUSION

This study indicates K_V 11.1 as a sumoylation target and offers three main targets: K21, K93, and K116. Furthermore, it proposes an underlying mechanism for the observed kinetic impact of the PAS domain.

Functional consequences of genetic variation in sodium channel modifiers in early onset lone atrial fibrillation

Aim: We investigated the effect of variants in genes encoding sodium channel modifiers SNTA1 and GPD1L found in early onset atrial fibrillation (AF) patients. Patients & methods: Genetic screening in patients with early onset lone AF revealed three variants in GPD1L and SNTA1 in three AF patients. Functional analysis was performed by patch-clamp electrophysiology. Results: Co-expression of GPD1L or its p.A326E variant with NaV1.5 did not alter INa density or current kinetics. SNTA1 shifted the peak-current by -5 mV. The SNTA1-p.A257G variant significantly increased INa. SNTA1-p.P74L did not produce functional changes. Conclusion: Although genetic variation of sodium channel modifiers may contribute to development of AF at a molecular level, it is unlikely a monogenic cause of the disease.

In silico assessment of genetic variation in KCNA5 reveals multiple mechanisms of human atrial arrhythmogenesis

A recent experimental study investigating patients with lone atrial fibrillation identified six novel mutations in the KCNA5 gene. The mutants exhibited both gain- and loss-of-function of the atrial specific ultra-rapid delayed rectifier K⁺ current, I_Kur. The aim of this study is to elucidate and quantify the functional impact of these KCNA5 mutations on atrial electrical activity. A multi-scale model of the human atria was updated to incorporate detailed experimental data on I_Kur from both wild-type and mutants. The effects of the mutations on human atrial action potential and rate dependence were investigated at the cellular level. In tissue, we assessed the effects of the mutations on the vulnerability to unidirectional conduction patterns and dynamics of re-entrant excitation waves. Gain-of-function mutations shortened the action potential duration in single cells, and stabilised and accelerated re-entrant excitation in tissue. Loss-of-function mutations had heterogeneous effects on action potential duration and promoted early-after-depolarisations following beta-adrenergic stimulation. In the tissue model, loss-of-function mutations facilitated breakdown of excitation waves at more physiological excitation rates than the wild-type, and the generation of early-after-depolarisations promoted unidirectional patterns of excitation. Gain- and loss-of-function I_Kur mutations produced multiple mechanisms of atrial arrhythmogenesis, with significant differences between the two groups of mutations. This study provides new insights into understanding the mechanisms by which mutant I_Kur contributes to atrial arrhythmias. In addition, as I_Kur is an atrial-specific channel and a number of I_Kur-selective blockers have been developed as anti-AF agents, this study also helps to understand some contradictory results on both pro- and anti-arrhythmic effects of blocking I_Kur.

In a recent study, six mutations resulting in either gain-of-function or loss-of-function in the ultra-rapid delayed rectifier potassium current I_Kur, were identified to be associated with atrial fibrillation (AF). However, the causative link between the mutant I_Kur (either gain- or loss-of-function) and AF genesis, especially the difference and similarity between the two mutant groups, has not been elucidated. In our study, we used multiscale computational models to investigate the mechanism of arrhythmogenesis mediated by the two groups of mutations. The results suggest that the gain-of-function mutations shortened atrial action potential duration, stabilised and accelerated re-entrant excitation waves in tissue; the loss-of-function mutation promoted early-after-depolarisations following beta-adrenergic stimulation and thus wave breaks in tissue. We show these two groups of mutants carrying I_Kur produced multiple mechanisms of atrial arrhythmogenesis, with significant differences between the two groups. Our study provides new insights into understanding the mechanisms by which mutant I_Kur contributes to atrial arrhythmias. In addition, as I_Kur is an atrial-specific channel and a number of I_Kur-selective blockers have been developed as anti-AF agents, this study also helps to understand some contradictory results on both pro- and anti-arrhythmic effects of blocking I_Kur.

Deep sequencing of atrial fibrillation patients with mitral valve regurgitation shows no evidence of mosaicism but reveals novel rare germline variants

BACKGROUND

Atrial fibrillation (AF) is the most common cardiac arrhythmia. Valvular heart disease is a strong predictor, yet the underlying molecular mechanisms are unknown.

OBJECTIVE

The purpose of this study was to investigate the prevalence of somatic variants in AF candidate genes in an AF patient population undergoing surgery for mitral valve regurgitation (MVR) to determine whether these patients are genetically predisposed to AF.

METHODS

DNA was extracted from blood and left atrial tissue from 44 AF patients with MVR. Using next-generation sequencing, we investigated 110 genes using the HaloPlex Target Enrichment System. MuTect software was used for identification of somatic point variants. We functionally characterized selected variants using electrophysiologic techniques.

RESULTS

No somatic variants were identified in the cardiac tissue. Thirty-three patients (75%) had a rare germline variation in ≥1 candidate genes. Fourteen variants were novel. Fifteen variants were predicted damaging or likely damaging in ≥6 in silico predictions. We identified rare variants in genes never directly associated with AF: KCNE4, SCN4B, NEURL1, and CAND2. Interestingly, 7 patients (16%) had variants in genes involved in cellular potassium handling. The variants KCNQ1 (p.G272S) and KCNH2 (p.A913V) resulted in gain of function due to faster activation (KCNQ1) and slowed deactivation kinetics (KCNQ1, KCNH2).

CONCLUSION

We did not find any somatic variants in patients with AF and MVR. Surprisingly, we found that our cohort of non-lone AF patients might, like lone AF patients, be predisposed to AF by rare germline variants. Our findings emphasize the extent of still unknown factors in the pathogenesis of AF.

Adaptive resistance to anti-PD1 therapy by Tim-3 upregulation is mediated by the PI3K-Akt pathway in head and neck cancer

Programmed Death 1 (PD-1) and T cell Ig and mucin domain-3 protein (Tim-3) are immune checkpoint receptors that are expressed on tumor-infiltrating lymphocytes (TIL) in tumor-bearing mice and humans. As anti-PD-1 single agent response rates are only <20% in head and neck squamous cell carcinoma (HNSCC) patients, it is important to understand how multiple inhibitory checkpoint receptors maintain suppressed cellular immunity. One such receptor, Tim-3, activates downstream proliferative pathways through Akt/S6, and is highly expressed in dysfunctional TIL. We observed that PD-1 and Tim-3 co-expression was associated with a more exhausted phenotype, with the highest PD-1 levels on TIL co-expressing Tim-3. Dampened Akt/S6 phosphorylation in these PD-1⁺Tim-3⁺ TIL, when the PD-1 pathway was ligated, suggested that signaling cross-talk could lead to escape through Tim-3 expression. Indeed, PD-1 blockade of human HNSCC TIL led to further Tim-3 upregulation, supporting a circuit of compensatory signaling and potentially permitting escape from anti-PD-1 blockade in the tumor microenvironment. Also, in a murine HNC tumor model that is partially responsive to anti-PD-1 therapy, Tim-3 was upregulated in TIL from persistently growing tumors. Significant antitumor activity was observed after sequential addition of anti-Tim-3 mAb to overcome adaptive resistance to anti-PD-1 mAb. This increased Tim-3-mediated escape of exhausted TIL from PD-1 inhibition that was mediated by phospho-inositol-3 kinase (PI3K)/Akt complex downstream of TCR signaling but not cytokine-mediated pathways. Taken together, we conclude that during PD-1 blockade, TIL upregulate Tim-3 in a PI3K/Akt-dependent manner, providing further support for dual targeting of these molecules for more effective cancer immunotherapy.

The anticonvulsant retigabine suppresses neuronal KV2-mediated currents

Enhancement of neuronal M-currents, generated through K_V7.2-K_V7.5 channels, has gained much interest for its potential in developing treatments for hyperexcitability-related disorders such as epilepsy. Retigabine, a K_V7 channel opener, has proven to be an effective anticonvulsant and has recently also gained attention due to its neuroprotective properties. In the present study, we found that the auxiliary KCNE2 subunit reduced the K_V7.2-K_V7.3 retigabine sensitivity approximately 5-fold. In addition, using both mammalian expression systems and cultured hippocampal neurons we determined that low μM retigabine concentrations had ‘off-target’ effects on K_V2.1 channels which have recently been implicated in apoptosis. Clinical retigabine concentrations (0.3–3 μM) inhibited K_V2.1 channel function upon prolonged exposure. The suppression of the K_V2.1 conductance was only partially reversible. Our results identified K_V2.1 as a new molecular target for retigabine, thus giving a potential explanation for retigabine’s neuroprotective properties.

Tumor-infiltrating Tim-3+ T cells proliferate avidly except when PD-1 is co-expressed: Evidence for intracellular cross talk

Programmed Death 1 (PD-1) and T cell Ig and mucin domain-3 protein (Tim-3) are immune checkpoint receptors highly expressed on tumor infiltrating T lymphocytes (TIL). PD-1 inhibits T cell activation and type-1 T cell responses, while Tim-3 is proposed to mark more extensively exhausted cells, although the mechanisms underlying Tim-3 function are not clear. Trials of anti-PD-1 therapy have identified a large subset of non-responder patients, likely due to expression of alternative checkpoint molecules like Tim-3. We investigated the phenotypic and functional characteristics of T cells with differential expression of PD-1 (high/low) and Tim-3 (positive/negative), using TIL directly isolated from head and neck squamous cell carcinomas (HNSCC). Unexpectedly, we found that expression of Tim-3 alone does not necessarily mark TIL as dysfunctional/exhausted. In Tim-3-TIL, PD-1 levels correlate with T cell dysfunction, with a PD-1^low/intermed phenotype identifying recently activated and still functional cells, whereas PD-1^hiTim-3^- T cells are actually exhausted. Nonetheless, PD-1^intermed cells are still potently suppressed by PD-L1. PD-1 expression was associated with reduced phosphorylation of ribosomal protein S6 (pS6), whereas Tim-3 expression was associated with increased pS6. Using a novel mouse model for inducible Tim-3 expression, we confirmed that expression of Tim-3 does not necessarily render T cells refractory to further activation. These results suggest the existence of PD-1 and Tim-3 crosstalk in regulating antitumor T cell responses, with important implications for anti-PD-1 immunotherapy.

Polyunsaturated fatty acids are potent openers of human M-channels expressed in Xenopus laevis oocytes

AIM

Polyunsaturated fatty acids have been reported to reduce neuronal excitability, in part by promoting inactivation of voltage-gated sodium and calcium channels. Effects on neuronal potassium channels are less explored and experimental data ambiguous. The aim of this study was to investigate anti-excitable effects of polyunsaturated fatty acids on the neuronal M-channel, important for setting the resting membrane potential in hippocampal and dorsal root ganglion neurones.

METHODS

Effects of fatty acids and fatty acid analogues on mouse dorsal root ganglion neurones and on the human KV 7.2/3 channel expressed in Xenopus laevis oocytes were studied using electrophysiology.

RESULTS

Extracellular application of physiologically relevant concentrations of the polyunsaturated fatty acid docosahexaenoic acid hyperpolarized the resting membrane potential (-2.4 mV by 30 μm) and increased the threshold current to evoke action potentials in dorsal root ganglion neurones. The polyunsaturated fatty acids docosahexaenoic acid, α-linolenic acid and eicosapentaenoic acid facilitated opening of the human M-channel, comprised of the heteromeric human KV 7.2/3 channel expressed in Xenopus oocytes, by shifting the conductance-vs.-voltage curve towards more negative voltages (by -7.4 to -11.3 mV by 70 μm). Uncharged docosahexaenoic acid methyl ester and monounsaturated oleic acid did not facilitate opening of the human KV 7.2/3 channel.

CONCLUSIONS

These findings suggest that circulating polyunsaturated fatty acids, with a minimum requirement of multiple double bonds and a charged carboxyl group, dampen excitability by opening neuronal M-channels. Collectively, our data bring light to the molecular targets of polyunsaturated fatty acids and thus a possible mechanism by which polyunsaturated fatty acids reduce neuronal excitability.

The two-pore domain potassium channel, TWIK-1, has a role in the regulation of heart rate and atrial size

The two-pore domain potassium (K(+)) channel TWIK-1 (or K2P1.1) contributes to background K(+) conductance in diverse cell types. TWIK-1, encoded by the KCNK1 gene, is present in the human heart with robust expression in the atria, however its physiological significance is unknown. To evaluate the cardiac effects of TWIK-1 deficiency, we studied zebrafish embryos after knockdown of the two KCNK1 orthologues, kcnk1a and kcnk1b. Knockdown of kcnk1a or kcnk1b individually caused bradycardia and atrial dilation (p<0.001 vs. controls), while ventricular stroke volume was preserved. Combined knockdown of both kcnk1a and kcnk1b resulted in a more severe phenotype, which was partially reversed by co-injection of wild-type human KCNK1 mRNA, but not by a dominant negative variant of human KCNK1 mRNA. To determine whether genetic variants in KCNK1 might cause atrial fibrillation (AF), we sequenced protein-coding regions in two independent cohorts of patients (373 subjects) and identified three non-synonymous variants, p.R171H, p.I198M and p.G236S, that were all located in highly conserved amino acid residues. In transfected mammalian cells, zebrafish and wild-type human TWIK-1 channels had a similar cellular distribution with predominant localization in the endosomal compartment. Two-electrode voltage-clamp experiments using Xenopus oocytes showed that both zebrafish and wild-type human TWIK-1 channels produced K(+) currents that are sensitive to external K(+) concentration as well as acidic pH. There were no effects of the three KCNK1 variants on cellular localization, current amplitude or reversal potential at pH7.4 or pH6. Our data indicate that TWIK-1 has a highly conserved role in cardiac function and is required for normal heart rate and atrial morphology. Despite the functional importance of TWIK-1 in the atrium, genetic variation in KCNK1 is not a common primary cause of human AF.

Iron Overload Leading to Torsades de Pointes in β-Thalassemia and Long QT Syndrome

The authors present a unique case of torsades de pointes in a β-thalassemia patient with early iron overload in the absence of any structural abnormalities as seen in hemochromatosis. Genetic testing showed a novel KCNQ1 gene mutation 1591C>T [Gln531Ter(X)]. Testing of the gene mutation in Xenopus laevis oocytes showed loss of function of the IKs current. The authors hypothesize that iron overload combined with the KCNQ1 gene mutation leads to prolongation of QTc and torsades de pointes.

pH-dependent inhibition of K₂P3.1 prolongs atrial refractoriness in whole hearts

In isolated human atrial cardiomyocytes, inhibition of K2P3.1 K(+) channels results in action potential (action potential duration (APD)) prolongation. It has therefore been postulated that K2P3.1 (KCNK3), together with K2P9.1 (KCNK9), could represent novel drug targets for the treatment of atrial fibrillation (AF). However, it is unknown whether these findings in isolated cells translate to the whole heart. The purposes of this study were to investigate the expression levels of KCNK3 and KCNK9 in human hearts and two relevant rodent models and determine the antiarrhythmic potential of K2P3.1 inhibition in isolated whole-heart preparations. By quantitative PCR, we found that KCNK3 is predominantly expressed in human atria whereas KCNK9 was not detectable in heart human tissue. No differences were found between patients in AF or sinus rhythm. The expression in guinea pig heart resembled humans whereas rats displayed a more uniform expression of KCNK3 between atria and ventricle. In voltage-clamp experiments, ML365 and A293 were found to be potent and selective inhibitors of K2P3.1, but at pH 7.4, they failed to prolong atrial APD and refractory period (effective refractory period (ERP)) in isolated perfused rat and guinea pig hearts. At pH 7.8, which augments K2P3.1 currents, pharmacological channel inhibition produced a significant prolongation of atrial ERP (11.6 %, p = 0.004) without prolonging ventricular APD but did not display a significant antiarrhythmic effect in our guinea pig AF model (3/8 hearts converted on A293 vs 0/7 hearts in time-matched controls). These results suggest that when K2P3.1 current is augmented, K2P3.1 inhibition leads to atrial-specific prolongation of ERP; however, this ERP prolongation did not translate into significant antiarrhythmic effects in our AF model.

Protein kinase A stimulates Kv7.1 surface expression by regulating Nedd4-2-dependent endocytic trafficking

The potassium channel Kv7.1 plays critical physiological roles in both heart and epithelial tissues. In heart, Kv7.1 and the accessory subunit KCNE1 forms the slowly activating delayed-rectifier potassium current current, which is enhanced by protein kinase A (PKA)-mediated phosphorylation. The observed current increase requires both phosphorylation of Kv7.1 and the presence of KCNE1. However, PKA also stimulates Kv7.1 currents in epithelial tissues, such as colon, where the channel does not coassemble with KCNE1. Here, we demonstrate that PKA activity significantly impacts the subcellular localization of Kv7.1 in Madin-Darby canine kidney cells. While PKA inhibition reduced the fraction of channels at the cell surface, PKA activation increased it. We show that PKA inhibition led to intracellular accumulation of Kv7.1 in late endosomes/lysosomes. By mass spectroscopy we identified eight phosphorylated residues on Kv7.1, however, none appeared to play a role in the observed response. Instead, we found that PKA acted by regulating endocytic trafficking involving the ubiquitin ligase Nedd4-2. We show that a Nedd4-2-resistant Kv7.1-mutant displayed significantly reduced intracellular accumulation upon PKA inhibition. Similar effects were observed upon siRNA knockdown of Nedd4-2. However, although Nedd4-2 is known to regulate Kv7.1 by ubiquitylation, biochemical analyses demonstrated that PKA did not influence the amount of Nedd4-2 bound to Kv7.1 or the ubiquitylation level of the channel. This suggests that PKA influences Nedd4-2-dependent Kv7.1 transport though a different molecular mechanism. In summary, we identify a novel mechanism whereby PKA can increase Kv7.1 current levels, namely by regulating Nedd4-2-dependent Kv7.1 transport.

Analysis of the Antitumor Activity of Clotrimazole on A375 Human Melanoma Cells

AIM

The current study was designed to characterize the anticancer effects of clotrimazole on human cutaneous melanoma cells.

MATERIALS AND METHODS

The v-raf murine sarcoma viral oncogene homolog B1 V600E mutant melanoma cell line A375 was used as an in vitro model. Characterization tools included analyses of cell viability, gene expression, cell-cycle progression, annexin V reactivity and internucleosomal DNA fragmentation.

RESULTS

Clotrimazole induced cytotoxicity in A375 human melanoma cells without significant changes of human keratinocyte cell viability. Clotrimazole, at a concentration that approximates the inhibitory concentration 50% (IC50) value (i.e. 10 μM), reduced the expression of hexokinase type-II, induced cell-cycle arrest at G1-S phase transition, altered annexin V reactivity and induced DNA fragmentation without evidence of necrosis.

CONCLUSION

The current study provides evidence of a remarkable pro-apoptotic effect by clotrimazole against human melanoma cells, with a different mechanism of action and timeline of the apoptosis-related events when compared to cisplatin.

IKs Gain- and Loss-of-Function in Early-Onset Lone Atrial Fibrillation

INTRODUCTION

Atrial fibrillation (AF) is the most frequent cardiac arrhythmia. The potassium current IKs is essential for cardiac repolarization. Gain-of-function mutation in KCNQ1, the gene encoding the pore-forming α-subunit of the IKs channel (KV 7.1), was the first ion channel dysfunction to be associated with familial AF. We hypothesized that early-onset lone AF is associated with a high prevalence of mutations in KCNQ1.

METHODS AND RESULTS

We bidirectionally sequenced the entire coding sequence of KCNQ1 in 209 unrelated patients with early-onset lone AF (<40 years) and investigated the identified mutations functionally in a heterologous expression system. We found 4 nonsynonymous KCNQ1 mutations (A46T, R195W, A302V, and R670K) in 4 unrelated patients (38, 31, 39, and 36 years, respectively). None of the mutations were present in the control group (n = 416 alleles). No other mutations were found in genes previously associated with AF. The mutations A46T, R195W, and A302V have previously been associated with long-QT syndrome. In line with previous reports, we found A302V to display a pronounced loss-of-function of the IKs current, while the other mutants exhibited a gain-of-function phenotype.

CONCLUSIONS

Mutations in the IKs channel leading to gain-of-function have previously been described in familial AF, yet this is the first time a loss-of-function mutation in KCNQ1 is associated with early-onset lone AF. These findings suggest that both gain-of-function and loss-of-function of cardiac potassium currents enhance the susceptibility to AF.

Gain-of-function mutations in potassium channel subunit KCNE2 associated with early-onset lone atrial fibrillation

AIMS

Atrial fibrillation (AF) is the most common cardiac arrhythmia. Disturbances in cardiac potassium conductance are considered as one of the disease mechanisms in AF. We aimed to investigate if mutations in potassium-channel β-subunits KCNE2 and KCNE3 are associated with early-onset lone AF.

METHODS & RESULTS

The coding regions of KCNE2 and KCNE3 were bidirectionally sequenced in 192 unrelated patients diagnosed with early-onset lone AF (<40 years). Two nonsynonymous missense mutations were identified in KCNE2 (M23L and I57T). Both mutations were absent in a healthy control group (n=1500 alleles). Electrophysiological investigations were performed for both mutations in combination with candidate pore-forming α-subunits KV7.1, KV11.1, KV4.3 and KV1.5. A significant gain-of-function effect was observed upon coexpression with KV7.1 and KV7.1+KCNE1. Confocal imaging found no differences in subcellular localization. No disease-suspected mutations were identified in KCNE3.

CONCLUSION

We identified two KCNE2 gain-of-function missense mutations that seem to increase the susceptibility of early-onset lone AF. These results confirm previous findings indicating that gain-of-function in the slow delayed rectifier potassium current might be involved in the pathogenesis of AF.

From pan-reactive KV7 channel opener to subtype selective opener/inhibitor by addition of a methyl group

The voltage-gated potassium channels of the K_V7 family (K_V7.1–5) play important roles in controlling neuronal excitability and are therefore attractive targets for treatment of CNS disorders linked to hyperexcitability. One of the main challenges in developing K_V7 channel active drugs has been to identify compounds capable of discriminating between the neuronally expressed subtypes (K_V7.2–5), aiding the identification of the subunit composition of K_V7 currents in various tissues, and possessing better therapeutic potential for particular indications. By taking advantage of the structure-activity relationship of acrylamide K_V7 channel openers and the effects of these compounds on mutant K_V7 channels, we have designed and synthesized a novel K_V7 channel modulator with a unique profile. The compound, named SMB-1, is an inhibitor of K_V7.2 and an activator of K_V7.4. SMB-1 inhibits K_V7.2 by reducing the current amplitude and increasing the time constant for the slow component of the activation kinetics. The activation of K_V7.4 is seen as an increase in the current amplitude and a slowing of the deactivation kinetics. Experiments studying mutant channels with a compromised binding site for the K_V7.2–5 opener retigabine indicate that SMB-1 binds within the same pocket as retigabine for both inhibition of K_V7.2 and activation of K_V7.4. SMB-1 may serve as a valuable tool for K_V7 channel research and may be used as a template for further design of better subtype selective K_V7 channel modulators. A compound with this profile could hold novel therapeutic potential such as the treatment of both positive and cognitive symptoms in schizophrenia.

Novel Kv7.1-phosphatidylinositol 4,5-bisphosphate interaction sites uncovered by charge neutralization scanning

Kv7.1 to Kv7.5 α-subunits belong to the family of voltage-gated potassium channels (Kv). Assembled with the β-subunit KCNE1, Kv7.1 conducts the slowly activating potassium current IKs, which is one of the major currents underlying repolarization of the cardiac action potential. A known regulator of Kv7 channels is the lipid phosphatidylinositol 4,5-bisphosphate (PIP2). PIP2 increases the macroscopic current amplitude by stabilizing the open conformation of 7.1/KCNE1 channels. However, knowledge about the exact nature of the interaction is incomplete. The aim of this study was the identification of the amino acids responsible for the interaction between Kv7.1 and PIP2. We generated 13 charge neutralizing point mutations at the intracellular membrane border and characterized them electrophysiologically in complex with KCNE1 under the influence of diC8-PIP2. Electrophysiological analysis of corresponding long QT syndrome mutants suggested impaired PIP2 regulation as the cause for channel dysfunction. To clarify the underlying structural mechanism of PIP2 binding, molecular dynamics simulations of Kv7.1/KCNE1 complexes containing two PIP2 molecules in each subunit at specific sites were performed. Here, we identified a subset of nine residues participating in the interaction of PIP2 and Kv7.1/KCNE1. These residues may form at least two binding pockets per subunit, leading to the stabilization of channel conformations upon PIP2 binding.