Prolongation Of Action Potential Duration Research Articles

Atrial hiPSC-CM as a Pharmacologic Model to Evaluate Anti-AF Drugs: Some Lessons From I Kur.

Human induced pluripotent stem cells (hiPSC) and atrial hiPSC-derived cardiomyocytes (hiPSC-CM) have entered the arena of preclinical atrial fibrillation research. A central question is whether they reproduce the physiologic contribution of atrial selective potassium currents (such as the ultrarapid potassium current, I Kur ) to repolarization. Of note, 2 studies in single atrial hiPSC-CM reported prolongation of action potential duration by I Kur block indicating that I Kur might in fact represent a valuable target for the treatment of human atrial fibrillation. However, the results and interpretation are at odds with the literature on I Kur block in human atria and the results of clinical studies. We believe that the discrepancies indicate that experiments in single atrial CM (both adult atrial CM and atrial hiPSC-CM) might be misleading. Under particular experimental conditions, atrial hiPSC-CMs may not closely resemble the electrophysiology of the human atrium. Therefore, we recapitulate here methodological issues evaluating potential value of the I Kur as an antiarrhythmic target when investigated in animal models, in human atrial tissues, and finally in atrial hiPSC-CM.

The endocannabinoid ARA-S facilitates the activation of cardiac Kv7.1/KCNE1 channels from different species

ABSTRACT The endogenous endocannabinoid-like compound N-arachidonoyl-L-serine (ARA-S) facilitates activation of the human Kv7.1/KCNE1 channel and shortens a prolonged action potential duration and QT interval in guinea pig hearts. Hence, ARA-S is interesting to study further in cardiac models to explore the functional impact of such Kv7.1/KCNE1-mediated effects. To guide which animal models would be suitable for assessing ARA-S effects, and to aid interpretation of findings in different experimental models, it is useful to know whether Kv7.1/KCNE1 channels from relevant species respond similarly to ARA-S. To this end, we used the two-electrode voltage clamp technique to compare the effects of ARA-S on Kv7.1/KCNE1 channels from guinea pig, rabbit, and human Kv7.1/KCNE1, when expressed in Xenopus laevis oocytes. We found that the activation of Kv7.1/KCNE1 channels from all tested species was facilitated by ARA-S, seen as a concentration-dependent shift in the voltage-dependence of channel opening and increase in current amplitude and conductance over a broad voltage range. The rabbit channel displayed quantitatively similar effects as the human channel, whereas the guinea pig channel responded with more prominent increase in current amplitude and maximal conductance. This study suggests that rabbit and guinea pig models are both suitable for studying ARA-S effects mediated via Kv7.1/KCNE1.

Effects of SZV-2649, a new multiple ion channel inhibitor mexiletine analogue

The antiarrhythmic and cardiac electrophysiological effects of SZV-2649 that contains a 2,6-diiodophenoxy moiety but lacks the benzofuran ring system present in amiodarone, were studied in mammalian cell line, rat and dog cardiac preparations. SZV-2649 exerted antiarrhythmic effects against coronary artery occlusion/reperfusion induced ventricular arrhythmias in rats and in acetylcholine- and burst stimulation induced atrial fibrillation in dogs. SZV-2649 inhibited hERG and GIRK currents in HEK cells (IC50: 342 and 529 nM, respectively). In canine ventricular myocytes, SZV-2649 (10 µM) decreased the densities of IKr, and Ito outward and INaL and ICaL inward currents. The compound (2.5–10 µM) elicited Class IB type Vmax reducing and Class III type action potential duration prolonging effects in dog right ventricular muscle preparations. In canine atrial muscle, SZV-2629 (2.5–10 µM) moderately prolonged action potential duration and this effect was greatly augmented in preparations pretreated with 1 µM carbachol. In conclusion, SZV-2649, has antiarrhythmic effects based on its multiple ion channel blocking properties. Since its chemical structure substantially differs from that of amiodarone, it is expected that SZV-2649 would exhibit fewer adverse effects than the currently used most effective multichannel inhibitor drug amiodarone and may be a promising molecule for further development.

The interaction between neutrophils and atrial myocytes in the occurrence and development of atrial fibrillation

BackgroundAtrial fibrillation (AF) is one of the most prevalent sustained cardiac arrhythmias, strongly associated with neutrophils. However, the underlying mechanism remain unclear. This study aims to explore the interaction between neutrophils and atrial myocytes in the pathogenesis of AF.MethodsPatch-clamp was employed to record the action potential duration (APD) and ion channels in HL-1 cells. Flow cytometry was used to assess the differentiation of neutrophils. The mRNA and protein levels of CACNA1C, CACNA2D, and CACNB2 in HL-1 cells were detected.ResultsHigh-frequency electrical stimulation resulted in a shortening of the APD in HL-1 cells. Flow cytometry demonstrated that neutrophils were polarized into N1 phenotype when cultured with stimulated HL-1 cells medium. Compared to control neutrophils conditioned medium (CM), cocultured with TNF-α knockout neutrophils CM prolonged APD and the L-type Ca (2+) channel (LTCC) of HL-1 cells. Additionally, the expression of CACNA2D, CACNB2 and CACNA1C in HL-1 cells were upregulated. Compared with CACNA1C siRNA-transfected HL-1 cells treated with TNF-α siRNA-transfected neutrophils CM, the APD and LTCC of CACNA1C siRNA-transfected HL-1 cells were shortened in control N1 neutrophil CM. The APD and LTCC of control HL-1 cells were also shortened in control N1 neutrophil CM, but prolonged in TNF-α siRNA-transfected neutrophils CM.ConclusionThese findings suggest that neutrophils were polarized into N1 phenotype in AF, TNF-α released from N1 neutrophils contributes to the pathogenesis of AF, via decreasing the APD and LTCC in atrial myocytes through down-regulation of CACNA1C expression.

PDE8 Inhibition and Its Impact on ICa,L in Persistent Atrial Fibrillation: Evaluation of PDE8 as a Potential Drug Target.

Atrial fibrillation (AF) poses a significant therapeutic challenge with drug interventions showing only limited success. Phosphodiesterases (PDE) regulate cardiac electrical stability and may represent an interesting target. Recently, PDE8 inhibition was proposed as an antiarrhythmic intervention by increasing L-type Ca2+ current (ICa,L) and action potential duration (APD). However, the effect size of PDE8 inhibition on ICa,L and APD seems discrepant and effects on force are unknown. We investigated the impact of PDE8 inhibition on force using PF-04957325 in right atrial appendages, obtained from patients in sinus rhythm (SR) and with persistent AF (peAF) undergoing cardiac surgery. A computational model was employed to predict the effects of PDE8 inhibition on APD in SR and peAF. Results showed no increase in force after exposure to increasing concentrations of the PDE8 inhibitor PF-04957325 in either SR or peAF tissues. Furthermore, PDE8 inhibition did not affect the potency or efficacy of norepinephrine-induced inotropic effects in either group. Arrhythmic events triggered by norepinephrine were observed in both SR and peAF, but their frequency remained unaffected by PF-04957325 treatment. Computational modeling predicted that the reported increase in ICa,L induced by PDE8 inhibition would lead to substantial APD prolongation at all repolarization states, particularly in peAF. Our findings indicate that PDE8 inhibition does not significantly impact force or arrhythmogenicity in human atrial tissue.

C-Src Is Responsible for Mitochondria-Mediated Arrhythmic Risk in Ischemic Cardiomyopathy.

Increased mitochondrial Ca2+ uptake has been implicated in the QT prolongation and lethal arrhythmias associated with nonischemic cardiomyopathy. We attempted to define the role of mitochondria in ischemic arrhythmic risk and to identify upstream regulators. Myocardial infarction (MI) was induced in wild-type FVB/NJ mice by ligation of the left anterior descending coronary artery. Western blot, immunoprecipitation, ECG telemetry, and patch-clamp techniques were used. After MI, c-Src (proto-oncogene tyrosine-protein kinase Src) and its active form (p-Src Y416) were increased. The activation of c-Src was associated with increased diastolic Ca2+ sparks, action potential duration prolongation, and arrhythmia in MI mice. c-Src upregulation and arrhythmia could be reversed by treatment of mice with the Src inhibitor PP1 but not with the inactive analogue PP3. Tyrosine phosphorylated mitochondrial Ca2+ uniporter (MCU) was upregulated in the heart tissues of MI mice and patients with ischemic cardiomyopathy. In a heterologous expression system, c-Src could bind MCU and phosphorylate MCU tyrosines. Overexpression of wild-type c-Src significantly increased the mitochondrial Ca2+ transient while overexpression of dominant-negative c-Src significantly decreased the mitochondrial Ca2+ transient. c-Src inhibition by PP1, MCU inhibition by Ru360, or MCU knockdown could reduce the action potential duration, Ca2+ sparks, and arrhythmia after MI. The human heart tissue showed that patients with ischemic cardiomyopathy had significantly increased c-Src active form associated with increased MCU tyrosine phosphorylation and ventricular arrhythmia. MI leads to increased c-Src active form that results in MCU tyrosine phosphorylation, increased mitochondrial Ca2+ uptake, QT prolongation, and arrhythmia, suggesting c-Src or MCU may represent novel antiarrhythmic targets.

The Kv4 potassium channel modulator NS5806 attenuates cardiac hypertrophy in vivo and in vitro

The compound NS5806 is a Kv4 channel modulator. This study investigated the chronic effects of NS5806 on cardiac hypertrophy induced by transverse aortic constriction (TAC) in mice in vivo and on neonatal rat ventricular cardiomyocyte hypertrophy induced by endothelin-1 (ET-1) in vitro. Four weeks after TAC, NS5806 was administered by gavage for 4 weeks. Echocardiograms revealed pronounced left ventricular (LV) hypertrophy in TAC-treated mice compared with sham mice. NS5806 attenuated LV hypertrophy, as manifested by the restoration of LV wall thickness and weight and the reversal of contractile dysfunction in TAC-treated mice. NS5806 also blunted the TAC-induced increases in the expression of cardiac hypertrophic and fibrotic genes, including ANP, BNP and TGF-β. Electrophysiological recordings revealed a significant prolongation of action potential duration and QT intervals, accompanied by an increase in susceptibility to ventricular arrhythmias in mice with cardiac hypertrophy. However, NS5806 restored these alterations in electrical parameters and thus reduced the incidence of mouse sudden death. Furthermore, NS5806 abrogated the downregulation of the Kv4 protein in the hypertrophic myocardium but did not influence the reduction in Kv4 mRNA expression. In addition, NS5806 suppressed in vitro cardiomyocyte hypertrophy. The results provide novel insight for further ion channel modulator development as a potential treatment option for cardiac hypertrophy.

Abstract Mo021: Role of Estrogen and Testosterone in promoting Sex Dimorphism in Doxorubicin Cardiotoxicity.

Background: Doxorubicin (DOX), a cancer chemotherapeutic agent, causes sex-specific cardiotoxicity. Lower cardiotoxicity in females compared to males is typically attributed to the cardioprotective effects of estrogen (E2). However, the role of the sex hormones, E2 and testosterone (T), in modulating DOX induced cardiac dysfunction and its underlying mechanisms are not known. Methods: C57BL/6J mice were divided into four groups, 1) Control, 2) DOX (5 mg/kg/week for 6 weeks), 3) Reverse hormone profile (RevH, castrated males+E2 and ovariectomized females+T), and 4) RevH + DOX. Mouse morbidity was tracked daily. Total body weight and cardiac function was assessed biweekly for 6 weeks by echocardiography, ECG and optical mapping. Dependence on fatty acid versus glucose for metabolism was measured by seahorse analysis. Results: DOX treatment reduced total body weight (11%) in males, and increased morbidity in males and females. This was associated with reduced mechanical function (15% decrease in stroke volume) in males and electrical remodeling (29% action potential duration prolongation) in females. In RevH mice, no changes in morbidity or cardiac function were observed compared to Control. In RevH+DOX males, the onset of morbidity was delayed by two weeks compared to DOX males. This cardioprotective effect was associated with preserved mechanical and electrical function. On the other hand, in RevH+DOX females, morbidity was increased, and this correlated with mechanical (20% reduction in cardiac output) and electrical remodeling (22% increase in action potential duration). Comparing RevH+DOX males to females, males had greater fatty acid dependency while females had greater glucose dependency for metabolism. Conclusions: These results suggest that sex hormones play a significant role in modulating specific aspects of DOX cardiotoxicity. While E2 has a critical role in preserving cardiac mechanics during DOX therapy, high T levels were associated with mechanical dysfunction in both males and RevH females. Switching of metabolic substrates with greater preference for fatty acid metabolism in mice with higher E2 could underlie cardiac mechanics preservation. Finally, DOX induced electrical remodeling was not altered by sex hormones.

Abstract Mo092: Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes as an In Vitro Model to Evaluate the Efficacy of a Gene Replacement Therapy for Plakophilin-2- Associated Arrhythmogenic Right Ventricular Cardiomyopathy

Background: Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a genetic cardiac disorder characterized by severe arrhythmias and heart dysfunction. Mutations in desmosome gene Plakophilin-2 ( PKP2 ) account for 40% of ARVC cases, with current palliative therapies failing to address the genetic cause. Herein, we generated an in vitro ARVC model using human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CM) harboring a pathogenic PKP2 variant (c.2146G>C), as a platform to test a PKP2 -gene replacement approach developed at Tenaya Therapeutics for the treatment of PKP2 -associated ARVC patients. Methods: Three isogenic human iPSC lines (wild-type, heterozygous and homozygous PKP2 mutant) were differentiated to iPSC-CM; and monolayers and engineered heart tissues (EHTs) were generated. Gene and protein expression were assessed by RNA-Seq/RT-qPCR, and immunocytochemistry, respectively. Contractility, electrophysiology and calcium handling were measured. A proprietary adeno-associated virus gene therapy (AAV9: PKP2 ) was used to transduce human iPSC-CM, and changes in gene and protein expression, and contractile function were evaluated. Results: A human iPSC-CM beating monolayer was achieved for all three lines. PKP2 expression was depleted in a genotype-dependent manner, and desmosome structure was disrupted in the mutant lines. Functional assessment of human iPSC-CM monolayers showed impaired contractile properties and abnormal electrophysiological and calcium transients in the mutant lines, such as decreased contraction amplitude and prolonged field and action potential duration. Transcriptional analysis revealed changes in desmosome, gap junctions, sarcomere, ion channels, metabolic and apoptosis gene expression. Characterization of EHTs displayed a deficit in contractility, slower action and field potential kinetics and irregular calcium homeostasis in the mutant lines. The administration of AAV9: PKP2 to the mutant lines restored ion channel and desmosome gene and protein expression, and contractile function. Conclusions: Our PKP2 human iPSC-CM disease model recapitulated the main hallmarks of ARVC phenotype. Administration of AAV9: PKP2 restored desmosome protein expression and contractility. This model lays a foundation for the understanding of the underlying molecular pathophysiological mechanisms of PKP2 -ARVC, and the potential for AAV9: PKP2 as a one-time dose to correct the genetic cause of disease in individuals with PKP2 -associated ARVC.

Compound Muscle Action Potential and Myosin-Loss Pathology in Patients With Critical Illness Myopathy: Correlation and Prognostication.

Prolonged compound muscle action potential (CMAP) duration and preferential loss of myosin are considered the diagnostic hallmarks of critical illness myopathy (CIM); however, their correlation and prognostic values have not been studied. We aimed to investigate the correlation between CMAP duration and myosin loss and their effect on mortality by comparing between patients with CIM with and without myosin loss. We searched the Mayo Clinic Electromyography Laboratory databases (1986-2021) for patients diagnosed with CIM on the basis of prolonged distal CMAP durations (>15 msec in fibular motor nerve studies recording over the tibialis anterior or >8 msec in other motor nerves) and needle EMG findings compatible with myopathy. Electrodiagnostic studies were generally performed within 24 hours after weakness became noticeable. We included only patients who underwent muscle biopsy. Clinical, electrophysiologic, and myopathologic data were reviewed. We conducted myosin/actin ratio analysis when muscle tissue was available. We used the Fisher exact test for categorical data comparisons and the Mann-Whitney 2-tailed test for continuous data. We applied the Kaplan-Meier technique to analyze survival rates. Twenty patients (13 female patients) were identified [median age at diagnosis of 62.5 years (range: 19-80 years)]. The median onset of weakness was 24 days (range: 1-128) from the first day of intensive care unit admission. Muscle biopsy showed myosin loss in 14 patients, 9 of whom had >50% of myofibers affected (high grade). Type 2 fiber atrophy was observed in 19 patients, 13 of whom also had myosin loss. Patients with myosin loss had higher frequency of steroid exposure (14 vs 3; p = 0.004); higher median number of necrotic fibers per low-power field (2.5 vs 1, p = 0.04); and longer median CMAP duration (msec) of fibular (13.4 vs 8.75, p = 0.02), tibial (10 vs 7.8, p = 0.01), and ulnar (11.1 vs 7.95, p = 0.002) nerves compared with those without. Only patients with high-grade myosin loss had reduced myosin/actin ratios (<1.7). Ten patients died during median follow-up of 3 months. The mortality rate was similar between patients with and without myosin loss. Patients with high-grade myosin loss had a lower overall survival rate than those with low-grade or no myosin loss, but this was not statistically significant (p = 0.05). Myosin loss occurred in 70% of the patients with CIM with prolonged CMAP duration. Longer CMAP duration predicts myosin-loss pathology. The extent of myosin loss marginally correlates with the mortality rate. Our findings highlight the potential prognostic values of CMAP duration and myosin loss severity in predicting disease outcome.

Male and female atria exhibit distinct acute electrophysiological responses to sex steroids

The electrophysiological properties of the hearts of women and men are different. These differences are at least partly mediated by the actions of circulating estrogens and androgens on the cardiomyocytes. Experimentally, much of our understanding in this field is based on studies focusing on ventricular tissue, with considerably less known in the context of atrial electrophysiology. The aim of this investigation was to compare the electrophysiological properties of male and female atria and assess responses to acute sex steroid exposure. Age-matched adult male and female C57BL/6 mice were anesthetized (4 % isoflurane) and left atria isolated. Atria were loaded with Di-4-ANEPPS voltage sensitive dye and optical mapping performed to assess action potential duration (APD; at 10 %, 20 %, 30 %, 50 %, and 70 % repolarization) and conduction velocity in the presence of 1 nM and 100 nM 17β-estradiol or testosterone. Male and female left atria demonstrated similar baseline action potential duration and conduction velocity, with significantly greater APD70 spatial heterogeneity evident in females. 17β-estradiol prolonged action potential duration in both sexes – an effect that was augmented in females. Atrial conduction was slowed in the presence of 100 nM 17β-estradiol in both males and females. Testosterone prolonged action potential duration in males only and did not modulate conduction velocity in either sex. This study provides novel insights into male and female atrial electrophysiology and its regulation by sex steroids. As systemic sex steroid levels change and intra-cardiac estrogen synthesis capacity increases with aging, these actions may have an increasingly important role in determining atrial arrhythmia vulnerability.

Dapagliflozin: A sodium–glucose cotransporter 2 inhibitor, attenuates angiotensin II-induced atrial fibrillation by regulating atrial electrical and structural remodeling

AimAtrial fibrillation (AF), the most common arrhythmia, is characterized by atrial electrical and structural remodeling. Previous studies have found that sodium–glucose cotransporter 2 inhibitor (SGLT2i) can protect myocardium in a glucose independent mechanism. But the role of SGLT2i in regulating AF remains largely unknown. This study, we aimed to investigate the effect of Dapagliflozin (DAPA) in reducing AF susceptibility via inhibiting electrical and structural remodeling. MethodThe mouse model was established by Angiotensin II (2000 ng/kg/min) infusion for 3 weeks, and an in vitro model was generated by stimulating HL-1 and primary mouse fibroblast with Ang II (1 μM) for 24 h. Programmed electrical stimulation, ECG and whole-cell patch clamp were used to detect DAPA effect on atrial electrical remodeling induced by Ang II. To observe DAPA effect on atrial structural remodeling induced by Ang II, we used echocardiographic, H&E and Masson staining to evaluate atrial dilation. To further explore the protective mechanism of DAPA, we adopt in silico molecular docking approaches to investigate the binding affinity of Ang II and CaMKII at Met-281 site. Western blot was to detect expression level of CaMKII, ox-CaMKII, Nav1.5, Kv4.3, Kv4.2, Kchip2, Kir2.1 and Cx40. ResultsAng II induced AF, atrial dilatation and fibrosis, led to atrial electrical and structural remodeling. However, these effects were markedly abrogated by DAPA treatment, a specific SGLT2i. Our observation of atrial electrical activity in mice revealed that DAPA could rescue the prolonged action potential duration (APD) and the abnormal currents of IK1, Ito and INaL triggered by Ang II infusion. DAPA could reduce the binding affinity of Ang II and CaMKII at Met-281 site, which indicated that DAPA may directly alleviate the activation of CaMKII caused by Ang II. DAPA could reduce the upregulation of ox-CaMKII caused by Ang II infusion in atrial tissues. Moreover, DAPA also ameliorated the aberrant expression levels of electrical activity related proteins (Nav1.5, Kv4.3, Kv4.2, Kchip2, Kir2.1 and Cx40) and fibrosis related signal pathways (TGF-β1, p-smad/smad) caused by Ang II. Furthermore, we confirmed that DAPA, as well as other SGLT2i (EMPA, CANA), could reverse these abnormalities caused by Ang II incubation in HL-1 cells and primary mouse fibroblasts, respectively. ConclusionOverall, our study identifies DAPA, a widely used SGLT2i, contributes to inhibiting Ang II-induced ox-CaMKII upregulation and electrical and structural remodeling to reduce AF susceptibility, suggesting that DAPA may be a potential therapy of treating AF.

2-Aminoethoxydiphenyl borate prolongs atrial and shortens ventricular action potential duration through modulation of ion channels in the sarcolemma

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): PPP allowance, Health holland ZonmW Background 2-Aminoethoxydiphenyl Borate (2-APB) has been shown to prevent atrial fibrillation in animal models, supposedly through its inhibitory action on the intracellular IP3 receptor and subsequent calcium regulation. However, 2-APB may modulate other ion channels or transporters and the cellular mechanisms associated with the prevention of atrial fibrillation are not well established. We aimed at unravelling the cellular effects of 2-APB on atrial and ventricular action potential and currents. Methods Rabbit (New Zealand White) left atrial and ventricular cardiomyocytes were isolated from Langendorff-perfused hearts by enzymatic dissociation. Adult human atrial cardiomyocytes were obtained by enzymatic dissociation from left atrial appendages (LAA) routinely removed from AF patients undergoing minimally invasive surgical pulmonary vein isolation. Action potentials (APs) and K+ currents were recorded at 36.5 °C with the amphotericin-B-perforated or whole cell patch clamp technique. RNA was isolated from left atrial and ventricular tissue and sequenced on an Illumina HiSeq4000 platform. Results In rabbit atrial cardiomyocytes, extracellular application of 5 uM 2-APB had no effect on action potential duration (APD), but extracellular application of 50 uM 2-APB prolonged the APD by 40% and inhibited an outward K+-current. Inversely, extracellular application of 5 uM 2-APB shortened the APD of rabbit left ventricular cardiomyocytes by 20% while extracellular application 50 uM 2-APB did not prolong the APD. Additionally, 2-APB did not modulate K+ currents in ventricular rabbit cardiomyocytes. Intracellular application (in the patch pipet) of 50 uM 2-APB did not have any effects on atrial APD, suggesting that IP3 receptor inhibition is not involved. However, subsequent application of 50 uM 2-APB in the bath prolonged the APD by 40% indicating that 2-APB prolongs atrial APD by inhibiting one or more K+ channel types in the sarcolemmal membrane from the extracellular site. RNA sequencing analysis revealed potential targets channel including TRP and Kv channels differentially expressed in atria versus ventricle. In human atrial cardiomyocytes from AF patients, application of 50 uM 2-APB prolonged APD by 25%. Conclusions 2-APB prolongs rabbit and human atrial APD and shortens rabbit ventricular APD in a concentration dependent manner, most likely due to modulation of sarcolemmal K+ channels, differentially expressed in the two cell types. Pharmacological studies with 2-APB may reveal novel cellular mechanisms identifying potential new targets for the treatment of atrial fibrillation.

SGK1 inhibition normalizes action potential duration in transgenic LQT2 rabbits but not in LQT1, suggesting a novel gene-specific therapeutic approach in long QT syndrome

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): SNSF (Swiss National Science Fundation) Background Increasing evidence suggests that secondary remodeling in Na+ and Ca2+ homeostasis may further enhance the propensity to develop arrhythmias in K-channelopathies LQT1 and LQT2 syndrome. In this context, the Serum and Glucocorticoid regulated Kinase-1 (SGK-1) was recently identified as a major regulator of sodium channels in cardiomyocytes. It is mainly activated in pathological conditions, leading to increased INaLate, prolongation of action potential duration (APD) and increased susceptibility to ventricular arrhythmias, recapitulating LQTS phenotype. SGK1 inhibition might hence be a novel therapeutic target also in genetic LQTS subtypes. Methods In cardiomyocytes (CM) isolated from wild type (WT), LQT1 and LQT2 adult rabbits patch-clamp experiments were performed to record AP with SGK1-inhibitor(SGK1-inh, 3 µM) or DMSO vehicle control. Results In the perforated patch configuration at 37°C, 3 μM of SGK1-inh shortened APD90 in LQT2 CMs at 1 Hz (DMSO-control [ms]: 477.3 vs treated cells[ms]: 362.8 p &amp;lt; 0.0001) and at 2 Hz (DMSO-cells: 325.7 vs treated cells:295.4,p &amp;lt;0.05). In contrast, in WT and LQT1 CMs, no effect on APD90 was observed neither at 1 Hz (WT, DMSO-cells: 329.2 vs treated cells: 301.6 p=ns; LQT1, DMSO-cells: 429.8 vs treated cells: 431.6, p=ns) nor at 2 Hz (WT, DMSO-cells:256.8 vs treated cells:242 p=ns; LQT1,DMSO cells:310.4 vs treated cells: 315.8,p=ns). Importantly, the SGK1-inhibitor effect in LQT2 rabbit CMs was so pronounced that it normalized APD to the wildtype level (LQT2+SGK1-Inh: 362.8 vs WT:329.2, ps=ns). Furthermore, short-term-variability in APD was markedly reduced by SGK1-Inh in LQT2, indicating an antiarrhythmic effect. Conclusions SGK1-inhibition exerts a beneficial APD-shortening effect only in LQT2, indicating a gene-specific efficacy. The underlying mechanism is still unclear. We hypothesize that the SGK1 pathway/INaLate activation in LQT1 might not be as active as in LQT2. We are currently conducting more experiments on potential genotype differences in SGK1 activity and SGK1-mediated INaLate inhibition to further elucidate the differences.Effects of SGK1-inh on AP characteristic

Maturing hiPSC-cardiomyocytes in cardiac microtissues for accurate preclinical in vitro modelling of long-QT syndrome type 1

Abstract Funding Acknowledgements Type of funding sources: Foundation. Main funding source(s): reNEW - Novo Nordisk Foundation Center for Stem Cell Medicine Background Long-QT syndrome type 1 (LQT1), a cardiac arrhythmia often leading to sudden cardiac death, is due to mutations in KCNQ1 gene. Human iPSC-derived cardiomyocytes (hiPSC-CMs) have been widely used to model LQT1, promoting the concept of their use in preclinical studies. However, KCNQ1 locus is subjected to developmentally regulated genomic imprinting in the heart: in fetal cardiomyocytes the paternal allele is repressed, while both alleles become expressed after birth. Since hiPSC-CMs are typically immature fetal-like cells, residual imprinting may affect evaluation of KCNQ1 mutations in this system. Purpose This study wants to address the imprinting status of KCNQ1 in hiPSC-CMs and propose maturing hiPSC-CMs as a solution for reliable LQT1 modelling. Methods We derived hiPSC-CMs from a LQT1 patient carrying a heterozygous KCNQ1 mutation on the paternal allele and compared their electrical properties with the isogenic corrected hiPSC-CMs by patch clamp. We analysed KCNQ1 expression by ddPCR and DNA methylation. We used three-dimensional cardiac microtissues (MTs) composed by hiPSC-CMs, hiPSC-derived cardiac fibroblasts and endothelial cells to induce cardiomyocte maturation. Results LQT1 and isogenic corrected hiPSC-CMs showed no difference in action potential duration (APD). We hypothesized that residual KCNQ1 imprinting in hiPSC-CMs due to their immaturity was masking the phenotype. When we analyzed different hiPSC-CM lines, we found in all an unbalanced KCNQ1 allelic expression, with paternal allele accounting for 5-15% of the total. We then investigated whether maturing hiPSC-CMs could remove KCNQ1 imprinting. We included hiPSC-CMs in MTs, as this system previously showed to promote functional maturation and upregulation of KCNQ1. Here, we observed a substantial increased expression of the paternal allele and a reduction in the expression of KCNQ1OT1, the long non-coding RNA inducing paternal allele repression. LQT1 hiPSC-CMs dissociated from MTs showed prolonged APD compared to the corrected line. We also demonstrated that this was due to the reduction of the ionic current mediated by KCNQ1 (IKs) in LQT1 hiPSC-CMs compared to the corrected controls, thus revealing the mutation causative effect. Conclusions Our findings show that residual KCNQ1 imprinting in immature hiPSC-CMs can lead to underestimate (or overestimate) functional effects of pathological variants based on the parental allele that carries the mutation. This is overcome by maturation of hiPSC-CMs in tri-cellular cardiac microtissue which promotes KCNQ1 bi-allelic expression and allow dissecting mutation mechanisms. This study brings attention to the epigenetic regulation of hiPSC models and demonstrates the utility of using matured hiPSC-CMs as in vitro preclinical model for cardiac arrhythmias.

Striatin knock out induces a gain of function of INa and impaired Ca2+ handling in mESC-derived cardiomyocytes.

Striatin (Strn) is a scaffold protein expressed in cardiomyocytes (CMs) and alteration of its expression are described in various cardiac diseases. However, the alteration underlying its pathogenicity have been poorly investigated. We studied the role(s) of cardiac Strn gene (STRN) by comparing the functional properties of CMs, generated from Strn-KO and isogenic WT mouse embryonic stem cell lines. The spontaneous beating rate of Strn-KO CMs was faster than WT cells, and this correlated with a larger fast INa conductance and no changes in If. Paced (2-8 Hz) Strn-KO CMs showed prolonged action potential (AP) duration in comparison with WT CMs and this was not associated with changes in ICaL and IKr. Motion video tracking analysis highlighted an altered contraction in Strn-KO CMs; this was associated with a global increase in intracellular Ca2+, caused by an enhanced late Na+ current density (INaL) and a reduced Na+/Ca2+ exchanger (NCX) activity and expression. Immunofluorescence analysis confirmed the higher Na+ channel expression and a more dynamic microtubule network in Strn-KO CMs than in WT. Indeed, incubation of Strn-KO CMs with the microtubule stabilizer taxol, induced a rescue (downregulation) of INa conductance toward WT levels. Loss of STRN alters CMs electrical and contractile profiles and affects cell functionality by a disarrangement of Strn-related multi-protein complexes. This leads to impaired microtubules dynamics and Na+ channels trafficking to the plasma membrane, causing a global Na+ and Ca2+ enhancement.

Dexmedetomidine inhibited arrhythmia susceptibility to adrenergic stress in RyR2R2474S mice through regulating the coupling of membrane potential and intracellular calcium

BackgroundDexmedetomidine (DEX), a highly selective α2-adrenoceptor agonist, can decrease the incidence of arrhythmias, such as catecholaminergic polymorphic ventricular tachycardia (CPVT). However, the underlying mechanisms by which DEX affects cardiac electrophysiological function remain unclear. MethodsRyanodine receptor (RyR2) heterozygous R2474S mice were used as a model for CPVT. WT and RyR2R2474S/+ mice were treated with isoproterenol (ISO) and DEX, and electrocardiograms were continuously monitored during both in vivo and ex vivo experiments. Dual-dye optical mapping was used to explore the anti-arrhythmic mechanism of DEX. ResultsDEX significantly reduced the occurrence and duration of ISO-induced of VT/VF in RyR2R2474S/+ mice in vivo and ex vivo. DEX remarkably prolonged action potential duration (APD80) and calcium transient duration (CaTD80) in both RyR2R2474S/+ and WT hearts, whereas it reduced APD heterogeneity and CaT alternans in RyR2R2474S/+ hearts. DEX inhibited ectopy and reentry formation, and stabilized voltage-calcium latency. ConclusionDEX exhibited an antiarrhythmic effect through stabilizing membrane voltage and intracellular Ca2+. DEX can be used as a beneficial perioperative anesthetic for patients with CPVT or other tachy-arrhythmias.

Moderate Endurance Exercise Increases Arrhythmia Susceptibility and Modulates Cardiac Structure and Function in a Sexually Dimorphic Manner.

Although moderate endurance exercise has been reported to improve cardiovascular health, its effects on cardiac structure and function are not fully characterized, especially with respect to sexual dimorphism. We aimed to assess the effects of moderate endurance exercise on cardiac physiology in male versus female mice. C57BL/6J mice of both sexes were run on a treadmill for 6 weeks. ECG and echocardiography were performed every 2 weeks. After 6 weeks of exercise, mice were euthanized, and triple parametric optical mapping was performed on Langendorff perfused hearts to assess cardiac electrophysiology. Arrhythmia inducibility was tested by programmed electrical stimulation. Left ventricular tissue was fixed, and RNA sequencing was performed to determine exercise-induced transcriptional changes. Exercise-induced left ventricular dilatation was observed in female mice alone, as evidenced by increased left ventricular diameter and reduced left ventricular wall thickness. Increased cardiac output was also observed in female exercised mice but not males. Optical mapping revealed further sexual dimorphism in exercise-induced modulation of cardiac electrophysiology. In female mice, exercise prolonged action potential duration and reduced voltage-calcium influx delay. In male mice, exercise reduced the calcium decay constant, suggesting faster calcium reuptake. Exercise increased arrhythmia inducibility in both male and female mice; however, arrhythmia duration was increased only in females. Lastly, exercise-induced transcriptional changes were sex dependent: females and males exhibited the most significant changes in contractile versus metabolism-related genes, respectively. Our data suggest that moderate endurance exercise can significantly alter multiple aspects of cardiac physiology in a sex-dependent manner. Although some of these effects are beneficial, like improved cardiac mechanical function, others are potentially proarrhythmic.

Differential sex-dependent susceptibility to diastolic dysfunction and arrhythmia in cardiomyocytes from obese diabetic HFpEF model.

Sex-differences in heart failure with preserved ejection fraction (HFpEF) are important, but key mechanisms involved are incompletely understood. While animal models can inform about sex-dependent cellular and molecular changes, many previous preclinical HFpEF models have failed to recapitulate sex-dependent characteristics of human HFpEF. We tested for sex-differences in HFpEF using a two-hit mouse model (leptin receptor-deficient db/db mice plus aldosterone infusion for 4 weeks; db/db+Aldo). We performed echocardiography, electrophysiology, intracellular Ca2+ imaging, and protein analysis. Female HFpEF mice exhibited more severe diastolic dysfunction in line with increased titin N2B isoform expression and PEVK element phosphorylation, and reduced troponin-I phosphorylation. Female HFpEF mice had lower BNP levels than males despite similar comorbidity burden (obesity, diabetes) and cardiac hypertrophy in both sexes. Male HFpEF mice were more susceptible to cardiac alternans. Male HFpEF cardiomyocytes (versus female) exhibited higher diastolic [Ca2+], slower Ca2+ transient decay, reduced L-type Ca2+ current, more pronounced enhancement of the late Na+ current, and increased short-term variability of action potential duration (APD). However, male and female HFpEF myocytes showed similar downregulation of inward rectifier and transient outward K+ currents, APD prolongation, and frequency of delayed afterdepolarizations. Inhibition of Ca2+/calmodulin-dependent protein kinase II (CaMKII) reversed all pathological APD changes in HFpEF in both sexes, and empagliflozin pretreatment mimicked these effects of CaMKII inhibition. Vericiguat had only slight benefits, and these effects were larger in HFpEF females. We conclude that the db/db+Aldo preclinical HFpEF murine model recapitulates key sex-specific mechanisms in HFpEF and provides mechanistic insights into impaired excitation-contraction coupling and sex-dependent differential arrhythmia susceptibility in HFpEF with potential therapeutic implications. In male HFpEF myocytes, altered Ca2+ handling and electrophysiology aligned with diastolic dysfunction and arrhythmias, while worse diastolic dysfunction in females may depend more on altered myofilaments properties.

Vericiguat suppresses ventricular tachyarrhythmias inducibility in a rabbit myocardial infarction model.

The VICTORIA trial demonstrated a significant decrease in cardiovascular events through vericiguat therapy. This study aimed to assess the potential mechanisms responsible for the reduction of cardiovascular events with vericiguat therapy in a rabbit model of myocardial infarction (MI). A chronic MI rabbit model was created through coronary artery ligation. Following 4 weeks, the hearts were harvested and Langendorff perfused. Subsequently, electrophysiological examinations and dual voltage-calcium optical mapping studies were conducted at baseline and after administration of vericiguat at a dose of 5 μmol/L. Acute vericiguat therapy demonstrated a significant reduction in premature ventricular beat burden and effectively suppressed ventricular arrhythmic inducibility. The electrophysiological influences of vericiguat therapy included an increased ventricular effective refractory period, prolonged action potential duration, and accelerated intracellular calcium (Cai) homeostasis, leading to the suppression of action potential and Cai alternans. The pacing-induced ventricular arrhythmias exhibited a reentrant pattern, attributed to fixed or functional conduction block in the peri-infarct zone. Vericiguat therapy effectively mitigated the formation of cardiac alternans as well as the development of reentrant impulses, providing additional anti-arrhythmic benefits. In the MI rabbit model, vericiguat therapy demonstrates anti-ventricular arrhythmia effects. The vericiguat therapy reduces ventricular ectopic beats, inhibiting the initiation of ventricular arrhythmias. Furthermore, the therapy successfully suppresses cardiac alternans, preventing conduction block and, consequently, the formation of reentry circuits.