Human Atrial Cardiomyocytes Research Articles

Postnatal development of human atrial cardiomyocytes: linking atrial gene expression profiles and atrial electrophysiology.

Postnatal development of human atrial cardiomyocytes: linking atrial gene expression profiles and atrial electrophysiology.

Impact of glucose fluctuation on the paracrine secretome profile of human epicardial adipocyte

Abstract Background Glucose fluctuations (GF) is known to be the significant factor related to poor cardiovascular outcome in the diabetic patients. We investigated the potential impact of GF on paracrine effect of human epicardial adipocyte on cardiomyocyte. Methods Human EAT biopsies obtained during surgery and isolated preadipocyte/adipocytes were used to evaluate the direct impact of GF on the adipocytes. Matured adipocytes were exposed to the media containing normal glucose (100 mg/dl, NG), high glucose (300 mg/dl, HG), or high-low glucose (75-300 mg/dl, GF) for 1 week. Transcriptomic profiling of the cultured matured adipocyte was performed using microarray analysis. The impact of GF on the paracrine effect of adipocyte was evaluated using a co-culture with human iPS-derived atrial cardiomyocytes and the adipocytes. Clinical association study verified the validity of the findings. Results GF for 1 week altered the expression of 595 differentially expressed genes (up-regulated or down-regulated) with an effect size of >50% or `−50% and a significant statistical difference (P < 0.05) in human epicardial adipocytes, while the continuous HG for 1 week altered the expression of only 182 differentially expressed genes. Of the genes affected by GF, top 3 most affected genes included IL1β, IL33, IL8. Regarding the other major pro-inflammatory cytokines, IL1α, CCL2 and IL6 were also significantly increased in the adipocyte treated with GF, however these were not increased in the adipocyte treated with HG. Co-culture of human iPS cell-derived atrial cardiomyocytes and adipocytes treated with NG, HG and GF revealed that GF-treated adipocyte strikingly increased oxidative stress in the cardiomyocyte through the paracrine effect. In the real-world clinical association study, IL1β mRNA expression in human epicardial adipose tissue showed significant positive correlation with the severity of GF during hospitalization and oxidative stress in the left atrial myocardium. Conclusions GF adversely affect the paracrine secretome profile of human epicardial adipocyte. IL1β may be a critical epicardial adipocyte-derived adipokine that is enhanced by GF.

Novel role of human epicardial adipocyte-derived SPARCL1 in suppression of postoperative atrial fibrillation in patients undergoing cardiovascular surgery

Abstract Background Postoperative atrial fibrillation (POAF) occurs in 20-50% after cardiovascular surgery and is associated with the short and long-term morbidity/mortality. The epicardial adipose tissue (EAT) may have a potential role to regulate the incidence of POAF. Purpose We explored the possible role of human epicardial adipocyte-derived adipokines in the regulation of the myocardial redox state and POAF. Methods We prospectively evaluated 149 patients without known AF who underwent scheduled open-heart cardiovascular surgery between May 2020 and November 2022. They were divided into POAF or Non-POAF group and followed up after discharge (476.6 ± 290.0 days). POAF was defined as AF lasting more than 30 seconds after the surgery. Human EAT samples were obtained from these patients during surgery and the preadipocytes were isolated. Preadipocytes were terminally differentiated to mature adipocytes and mRNAs were extracted. Genome-wide expression profiling of 6 vs. 6 matched samples of the POAF and Non-POAF groups was performed using Microarray analysis, and the results were validated with qPCR in all the cohort samples. The effects of secreted adipokines on the cardiomyocytes were assessed in terms of oxidative stress. Superoxide and whole reactive oxygen species (ROS) were evaluated with luminometry and live-cell fluorescent probes respectively. As the oxidative stress associated signalling, the phosphorylation of ERK and p38-MAPK were evaluated with western blotting. Angiotensin II (Ang-II) was used to induce oxidative stress and phosphorylation of MAPK. Results POAF was observed in 53 patients (36%). Microarray analysis (n = 6) revealed that there were 132 down- or up-regulated cording genes in epicardial adipocytes of the POAF group compared to the Non-POAF group. Of these genes, 11 genes cording secretable molecules were validated by qPCR (n = 69), showing that only SPARCL1 had significantly downregulated in the POAF group compared to the Non-POAF group (P = 0.005). Superoxide and ROS were induced by Ang II (P < 0.01) and attenuated by SPARCL1 dose-dependent manner (P < 0.01) in neonatal rat cardiomyocytes. The phosphorylation of ERK and p38-MAPK were induced by Ang II (P < 0.01) and attenuated by SPARCL1 (P < 0.01) dose-dependently. Co-culture of human induced pluripotent stem cell-derived atrial cardiomyocytes (iPS-ACM) and human epicardial adipocytes revealed that the adipocytes derived from Non-POAF group suppressed the superoxide (P = 0.002) and ROS (P = 0.02) in iPS-ACM compared to POAF group. Kaplan-Meier survival analysis revealed that the POAF group (P = 0.01) and low SPARCL1 expression in epicardial adipocytes (P = 0.018) were associated with a higher incidence of long-term adverse cardiovascular events after surgery. Conclusion: SPARCL1 derived from epicardial adipocytes may play an important role in the suppression of POAF and long-term cardiovascular events via improving the myocardial redox state.

Serum exosomal long non-coding RNA H19 as a theragnostic target for atrial fibrillation

Abstract Background/Introduction Exosomes are membrane vesicles of 30- to 150-nm secreted by most cell types that can mediate intercellular communication by transmitting various forms of RNAs. Long non-coding RNAs (lncRNAs, ≥ 200 nucleotides length) have been reported to play important roles in the pathophysiological processes that promote the development and progression of many diseases. Interestingly, recent studies have shown that exosomal lncRNAs exhibit different expression profiles in various diseases and are being extensively studied in the medical field as an ideal target for the diagnosis and treatment. However, there is still little known about their role in atrial fibrillation (AF). Purpose The aim of this study was to identify a novel theragnostic target exosomal lncRNA for AF. Methods First, serum exosomes from controls and patients with persistent AF were isolated and characterized by transmission electron microscopy, nanoparticle tracking analysis, and western blot. Next, serum exosomal lncRNA expression profiles were explored using RNA-sequencing analysis. In addition, the expression levels of candidate exosomal lncRNAs were confirmed using qRT-PCR (n = 50 per group). Finally, AF-related pathophysiological mechanisms of exosomal lncRNA were investigated in angiotensin II (Ang II)-treated human induced pluripotent stem cell-derived atrial cardiomyocytes (iPSC-atrial CMs). Results After RNA-sequencing analysis, we identified 27 differentially expressed lncRNAs (i.e., 4 upregulated and 23 downregulated lncRNAs with a |fold change| ≥ 2 and p < 0.05) in serum exosomes from patients with persistent AF compared with the controls. In fact, qRT-PCR reveled that exosomal lncRNA H19 was consistently downregulated in the serum of patients with persistent AF compared with the controls (p < 0.01). In addition, exosomal lncRNA H19 exhibited significant diagnostic validity for AF. Notably, we confirmed that exosomal lncRNA H19 was involved in AF-related pathophysiological mechanisms. In Ang II-treated iPSC-atrial CMs, inhibition of lncRNA H19 significantly aggravated Ang II-induced increases in levels of hypertrophic markers (ANP, BNP and β-MHC), cell surface area and inflammation (p < 0.05). Mechanistically, we found that loss of lncRNA H19 weakens the inhibition of its direct target microRNAs, miR-141-3p and miR-200a-3p, leading to downregulation of their target PTEN, thereby promoting the atrial remodeling and the consequent AF. Conclusion In conclusion, serum-derived exosomal lncRNA H19 could serve as a potential target for the diagnosis and treatment of AF.

Combined class I and class III antiarrhythmic effects of sotagliflozin - insights from heterologous expressions systems and atrial cardiomyocytes

Abstract Background The demand for more effective treatment options for atrial fibrillation (AF), the most common sustained arrhythmia, is driven by its direct impact on morbidity and mortality. Current therapies, such as antiarrhythmic drugs and catheter ablation, are limited by suboptimal efficacy and adverse effects or periinterventional complications. Therefore, safe and effective treatment of AF remains a major unmet clinical need. Sodium-glucose cotransporter (SGLT) inhibitors have shown promise in reducing the incidence of AF in large cardiovascular endpoint trials. However, the exact mechanisms of action remain unclear. While only two SGLT2 inhibitors are approved and clinically used in Europe, sotagliflozin, which inhibits both SGLT1 and SGLT2, might also have potential for the treatment of AF. Purpose This study aims to elucidate the effects of sotagliflozin on cardiac action potential formation. This understanding could optimise its clinical use, identify new targets for the treatment of atrial fibrillation and ultimately improve the quality of life of patients suffering from AF. Methods The effects of sotagliflozin on cardiac ionic currents were assessed using two-electrode voltage clamp measurements of several sodium and potassium channels heterologously expressed in Xenopus laevis oocytes. Subsequently, ascending concentrations of sotagliflozin were administered to isolated human atrial cardiomyocytes during patch-clamp measurements to investigate its effect on atrial action potential morphology. Results At a concentration of 100 µM, sotagliflozin showed significant inhibitory effects on three out of ten ion channels tested: NaV1.5 sodium channel current was reduced by 22,3 % %, hERG and KV4.3 potassium currents were reduced by 30,4 % and 22,5 % respectively. Patch-clamp experiments, performed on isolated human atrial cardiomyocytes showed a dose-dependent reduction in upstroke velocity and action potential amplitude by 20,8 % and 13,8 % at a concentration of 20 µM, reflecting class-I-antiarrhythmic effects. Furthermore, a prolongation of AP duration measured at 50 % (APD50) and 90 % (APD90) of repolarization by 57,7 % and 27,9 % at a sotagliflozin concentration of 20 µM was noted, implying additional class-III-antiarrhythmic action. Conclusions Sotagliflozin exerts direct inhibitory effects on heterologously expressed NaV1.5, hERG and KV4.3 channels, resulting in a reduction in upstroke velocity and action potential amplitude, as well as a prolongation of APD50 and APD90 levels in isolated human atrial cardiomyocytes. These results extend the pharmacological profile of sotagliflozin and suggest a potential role for the clinical use of combined SGLT1/SGLT2 inhibitors in the treatment of AF.

Senescent CD8+ T cells: a novel risk factor in atrial fibrillation.

Immune cell alterations may play a role in the development of atrial fibrillation (AF). Our objective was to comprehensively characterize immune cells in AF, and investigate the potential mechanisms. Single-cell RNA sequencing and multicolor flow cytometry revealed that T cells constituted the most significant subset alterations in AF, and senescent CD8+ T cells were AF-associated subset. Senescent CD8+ T cells increased in both peripheral veins (p < 0.0001) and the left atria (p < 0.05) in patients with AF compared to non-AF control. Senescent CD8+ T cells were independently associated with AF prevalence (odds ratio = 2.876, p < 0.05) and postprocedural recurrence (hazard ratio = 22.955, p < 0.0001) using a cross-sectional study and a subsequent prospective cohort study. Senescent CD8+ T cells secreted an increased amount of interferon (IFN)-γ, which induces Ca2+ handling abnormalities in human induced pluripotent stem cell-derived atrial cardiomyocytes, and translated into an increased susceptibility to AF assessed by heart optical mapping. An increased amount of senescent CD8+ T cells may be a hallmark of the immune senescence phenotype in AF and potentially serve as a valid biomarker for assessing prevalence and postprocedural recurrence of AF. By connecting immune senescence with electrophysiological disturbances in AF, this research provides a potential mechanism for the involvement of senescent CD8+ T cells in proarrhythmic calcium disorders and suggests novel avenues for developing new immune-modulatory and senolytic therapies for AF.

Enhanced Ca2+-Driven Arrhythmogenic Events in Female Patients With AtrialFibrillation: Insights From Computational Modeling.

Substantial sex-based differences have been reported in atrial fibrillation (AF), but the underlying mechanisms are poorly understood. This study sought to gain a mechanistic understanding of Ca2+-handling disturbances and Ca2+-driven arrhythmogenic events in male vs female atrial cardiomyocytes and establish their responses to Ca2+-targeted interventions. We integrated reported sex differences and AF-associated changes (ie, expression and phosphorylation of Ca2+-handling proteins, cardiomyocyte ultrastructural characteristics, and dimensions) into our human atrial cardiomyocyte model that couples electrophysiology with spatially detailed Ca2+-handling processes. Sex-specific responses of atrial cardiomyocytes to arrhythmia-provoking protocols and Ca2+-targeted interventions were evaluated. Simulated quiescent cardiomyocytes showed increased incidence of Ca2+ sparks in female vs male myocytes inAF, in agreement with previous experimental reports. Additionally, our female model exhibited elevated propensity to develop pacing-induced spontaneous Ca2+ releases (SCRs) and augmented beat-to-beat variability in action potential (AP)-elicited Ca2+ transients compared with the male model. Sensitivity analysis uncovered distinct arrhythmogenic contributions of each component involved in sex and/or AF alterations. Specifically, increased ryanodine receptor phosphorylation emerged as the major SCR contributor in female AF cardiomyocytes, whereas reduced L-type Ca2+ current was protective against SCRs for male AF cardiomyocytes. Furthermore, simulated Ca2+-targeted interventions identified potential strategies (eg, t-tubule restoration, and inhibition of ryanodine receptor and sarcoplasmic/endoplasmic reticulum Ca2⁺-ATPase) to attenuate Ca2+-driven arrhythmogenic events in women, and revealed enhanced efficacy when applied in combination. Sex-specific modeling uncovers increased Ca2+-driven arrhythmogenic events in female vs male atria inAF, and suggests combined Ca2+-targeted interventions are promising therapeutic approaches in women.

Modulation of NOX2 causes obesity-mediated atrial fibrillation.

Obesity is linked to an increased risk of atrial fibrillation (AF) via increased oxidative stress. While NADPH oxidase 2 (NOX2), a major source of oxidative stress and reactive oxygen species (ROS) in the heart, predisposes to AF, the underlying mechanisms remain unclear. Here, we studied NOX2-mediated ROS production in obesity-mediated AF using Nox2-knockout mice and mature human induced pluripotent stem cell-derived atrial cardiomyocytes (hiPSC-aCMs). Diet-induced obesity (DIO) mice and hiPSC-aCMs treated with palmitic acid (PA) were infused with a NOX blocker (apocynin) and a NOX2-specific inhibitor, respectively. We showed that NOX2 inhibition normalized atrial action potential duration and abrogated obesity-mediated ion channel remodeling with reduced AF burden. Unbiased transcriptomics analysis revealed that NOX2 mediates atrial remodeling in obesity-mediated AF in DIO mice, PA-treated hiPSC-aCMs, and human atrial tissue from obese individuals by upregulation of paired-like homeodomain transcription factor 2 (PITX2). Furthermore, hiPSC-aCMs treated with hydrogen peroxide, a NOX2 surrogate, displayed increased PITX2 expression, establishing a mechanistic link between increased NOX2-mediated ROS production and modulation of PITX2. Our findings offer insights into possible mechanisms through which obesity triggers AF and support NOX2 inhibition as a potential novel prophylactic or adjunctive therapy for patients with obesity-mediated AF.

PITX2 deficiency leads to atrial mitochondrial dysfunction.

Reduced left atrial PITX2 is associated with atrial cardiomyopathy and atrial fibrillation. PITX2 is restricted to left atrial cardiomyocytes in the adult heart. The links between PITX2 deficiency, atrial cardiomyopathy and atrial fibrillation are not fully understood. To identify mechanisms linking PITX2 deficiency to atrial fibrillation, we generated and characterized PITX2-deficient human atrial cardiomyocytes derived from human induced pluripotent stem cells (hiPSC) and their controls. PITX2-deficient hiPSC-derived atrial cardiomyocytes showed shorter and disorganised sarcomeres and increased mononucleation. Electron microscopy found an increased number of smaller mitochondria compared to the control. Mitochondrial protein expression was altered in PITX2-deficient hiPSC-derived atrial cardiomyocytes. Single-nuclear RNA-sequencing found differences in cellular respiration pathways and differentially expressed mitochondrial and ion channel genes in PITX2-deficient hiPSC-derived atrial cardiomyocytes. PITX2 repression in hiPSC-derived atrial cardiomyocytes replicated dysregulation of cellular respiration. Mitochondrial respiration was shifted to increased glycolysis in PITX2-deficient hiPSC-derived atrial cardiomyocytes. PITX2-deficient human hiPSC-derived atrial cardiomyocytes showed higher spontaneous beating rates. Action potential duration was more variable with an overall prolongation of early repolarization, consistent with metabolic defects. Gene expression analyses confirmed changes in mitochondrial genes in left atria from 42 patients with atrial fibrillation compared to 43 patients in sinus rhythm. Dysregulation of left atrial mitochondrial (COX7C) and metabolic (FOXO1) genes was associated with PITX2 expression in human left atria. In summary, PITX2 deficiency causes mitochondrial dysfunction and a metabolic shift to glycolysis in human atrial cardiomyocytes. PITX2-dependent metabolic changes can contribute to the structural and functional defects found in PITX2-deficient atria.

Polycystin-1 loss of function increases susceptibility to atrial fibrillation through impaired DNA damage response.

The increasing prevalence of atrial fibrillation (AF) and chronic kidney diseases highlights the need for a deeper comprehension of the molecular mechanisms linking them. Mutations in PKD1, the gene encoding Polycystin-1 (PKD1 or PC1), account for 85% of autosomal dominant polycystic kidney disease (ADPKD) cases. This disease often includes cardiac complications such as AF. In cardiomyocytes, PC1 deletion reduces hypertrophic response to pressure overload but promotes baseline ventricular dysfunction, while deletion in fibroblasts ameliorates post-myocardial infarction fibrosis. Despite its known cardiac impact, the role of PC1 in atrial cardiomyocytes and arrhythmias is less understood. Here, we sought to investigate the role of PC1 in AF. We used intracardiac programmed stimulation and optical mapping to evaluate AF inducibility in two mouse models, Pkd1 R3277C, which recapitulates human ADPKD progression, and cardiomyocyte-specific Pkd1 deletion, and their respective controls. Isolated adult mouse atrial cardiomyocytes, human iPSC-derived atrial cardiomyocytes (hiPSC-aCM), and HL-1 cells served as in vitro cellular models. Molecular mechanisms were evaluated using optical mapping and molecular and biochemical approaches. Loss-of-function PC1 mutations significantly increased AF susceptibility in vivo and facilitated local reentry in ex vivo left atrial appendages. Comprehensive in vitro experiments supported a direct effect of PC1 in atrial cardiomyocytes. PC1-deficient monolayers exhibited increased arrhythmic events, escalating into reentrant spiral waves post-tachypacing. Transcriptomics analysis revealed PC1-dependent regulation of DNA repair, with PC1 deficiency leading to increased DNA damage under stress. PARP1 inhibitors or nicotinamide riboside, which counteract DNA damage-related metabolic consequences, reduced in vitro arrhythmias PC1-deficient monolayers. Overexpression of the C-terminus of PC1 had the opposite effects in DNA repair genes, suggesting its regulatory effects in atrial cardiomyocytes through retinoblastoma/E2F. Analyses of human atrial tissue from non-ADPKD patients showed reduced levels of mature PC1, suggesting a broader relevance of impaired PC1 in AF. Impaired PC1 increases in vivo AF inducibility under programmed electrical stimulation and promotes in vitro arrhythmias in hiPSC-aCM and HL-1 cells. Our findings indicate that PC1 protects against DNA damage to reduce AF susceptibility.

NaV1.8 as Proarrhythmic Target in a Ventricular Cardiac Stem Cell Model.

The sodium channel NaV1.8, encoded by the SCN10A gene, has recently emerged as a potential regulator of cardiac electrophysiology. We have previously shown that NaV1.8 contributes to arrhythmogenesis by inducing a persistent Na+ current (late Na+ current, INaL) in human atrial and ventricular cardiomyocytes (CM). We now aim to further investigate the contribution of NaV1.8 to human ventricular arrhythmogenesis at the CM-specific level using pharmacological inhibition as well as a genetic knockout (KO) of SCN10A in induced pluripotent stem cell CM (iPSC-CM). In functional voltage-clamp experiments, we demonstrate that INaL was significantly reduced in ventricular SCN10A-KO iPSC-CM and in control CM after a specific pharmacological inhibition of NaV1.8. In contrast, we did not find any effects on ventricular APD90. The frequency of spontaneous sarcoplasmic reticulum Ca2+ sparks and waves were reduced in SCN10A-KO iPSC-CM and control cells following the pharmacological inhibition of NaV1.8. We further analyzed potential triggers of arrhythmias and found reduced delayed afterdepolarizations (DAD) in SCN10A-KO iPSC-CM and after the specific inhibition of NaV1.8 in control cells. In conclusion, we show that NaV1.8-induced INaL primarily impacts arrhythmogenesis at a subcellular level, with minimal effects on systolic cellular Ca2+ release. The inhibition or knockout of NaV1.8 diminishes proarrhythmic triggers in ventricular CM. In conjunction with our previously published results, this work confirms NaV1.8 as a proarrhythmic target that may be useful in an anti-arrhythmic therapeutic strategy.

Activation of Exchange Proteins directly Activated by cAMP (EPAC) promotes electrophysiological remodeling and arrhythmogenic activity in human atrial cardiomyocytes

Activation of Exchange Proteins directly Activated by cAMP (EPAC) promotes electrophysiological remodeling and arrhythmogenic activity in human atrial cardiomyocytes

A detailed mathematical model of the human atrial cardiomyocyte: Integration of electrophysiology and cardiomechanics

A detailed mathematical model of the human atrial cardiomyocyte: Integration of electrophysiology and cardiomechanics

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.

Human induced pluripotent stem cell-derived atrial cardiomyocytes recapitulate contribution of the slowly activating delayed rectifier currents IKs to repolarization in the human atrium.

Human induced pluripotent stem cell-derived atrial cardiomyocytes (hiPSC-aCM) could be a helpful tool to study the physiology and diseases of the human atrium. To fulfil this expectation, the electrophysiology of hiPSC-aCM should closely resemble the situation in the human atrium. Data on the contribution of the slowly activating delayed rectifier currents (IKs) to repolarization are lacking for both human atrium and hiPSC-aCM. Human atrial tissues were obtained from patients with sinus rhythm (SR) or atrial fibrillation (AF). Currents were measured in human atrial cardiomyocytes (aCM) and compared with hiPSC-aCM and used to model IKs contribution to action potential (AP) shape. Action potential was recorded by sharp microelectrodes. HMR-1556 (1 µM) was used to identify IKs and to estimate IKs contribution to repolarization. Less than 50% of hiPSC-aCM and aCM possessed IKs. Frequency of occurrence, current densities, activation/deactivation kinetics, and voltage dependency of IKs did not differ significantly between hiPSC-aCM and aCM, neither in SR nor AF. β-Adrenoceptor stimulation with isoprenaline did not increase IKs neither in aCM nor in hiPSC-aCM. In tissue from SR, block of IKs with HMR-1556 did not lengthen the action potential duration, even when repolarization reserve was reduced by block of the ultra-rapid repolarizing current with 4-aminopyridine or the rapidly activating delayed rectifier potassium outward current with E-4031. I Ks exists in hiPSC-aCM with biophysics not different from aCM. As in adult human atrium (SR and AF), IKs does not appear to relevantly contribute to repolarization in hiPSC-aCM.

Empagliflozin inhibits increased Na influx in atrial cardiomyocytes of patients with HFpEF.

Heart failure with preserved ejection fraction (HFpEF) causes substantial morbidity and mortality. Importantly, atrial remodelling and atrial fibrillation are frequently observed in HFpEF. Sodium-glucose cotransporter 2 inhibitors (SGLT2i) have recently been shown to improve clinical outcomes in HFpEF, and post-hoc analyses suggest atrial anti-arrhythmic effects. We tested if isolated human atrial cardiomyocytes from patients with HFpEF exhibit an increased Na influx, which is known to cause atrial arrhythmias, and if that is responsive to treatment with the SGTL2i empagliflozin. Cardiomyocytes were isolated from atrial biopsies of 124 patients (82 with HFpEF) undergoing elective cardiac surgery. Na influx was measured with the Na-dye Asante Natrium Green-2 AM (ANG-2). Compared to patients without heart failure (NF), Na influx was doubled in HFpEF patients (NF vs. HFpEF: 0.21 ± 0.02 vs. 0.38 ± 0.04 mmol/L/min (N = 7 vs. 18); P = 0.0078). Moreover, late INa (measured via whole-cell patch clamp) was significantly increased in HFpEF compared to NF. Western blot and HDAC4 pulldown assay indicated a significant increase in CaMKII expression, CaMKII autophosphorylation, CaMKII activity, and CaMKII-dependent NaV1.5 phosphorylation in HFpEF compared to NF, whereas NaV1.5 protein and mRNA abundance remained unchanged. Consistently, increased Na influx was significantly reduced by treatment not only with the CaMKII inhibitor autocamtide-2-related inhibitory peptide (AIP), late INa inhibitor tetrodotoxin (TTX) but also with sodium/hydrogen exchanger 1 (NHE1) inhibitor cariporide. Importantly, empagliflozin abolished both increased Na influx and late INa in HFpEF. Multivariate linear regression analysis, adjusting for important clinical confounders, revealed HFpEF to be an independent predictor for changes in Na handling in atrial cardiomyocytes. We show for the first time increased Na influx in human atrial cardiomyocytes from HFpEF patients, partly due to increased late INa and enhanced NHE1-mediated Na influx. Empagliflozin inhibits Na influx and late INa, which could contribute to anti-arrhythmic effects in patients with HFpEF.

HiPSC-derived cardiomyocytes as a model to study the role of small-conductance Ca2+-activated K+ (SK) ion channel variants associated with atrial fibrillation.

Atrial fibrillation (AF), the most common arrhythmia, has been associated with different electrophysiological, molecular, and structural alterations in atrial cardiomyocytes. Therefore, more studies are required to elucidate the genetic and molecular basis of AF. Various genome-wide association studies (GWAS) have strongly associated different single nucleotide polymorphisms (SNPs) with AF. One of these GWAS identified the rs13376333 risk SNP as the most significant one from the 1q21 chromosomal region. The rs13376333 risk SNP is intronic to the KCNN3 gene that encodes for small conductance calcium-activated potassium channels type 3 (SK3). However, the functional electrophysiological effects of this variant are not known. SK channels represent a unique family of K+ channels, primarily regulated by cytosolic Ca2+ concentration, and different studies support their critical role in the regulation of atrial excitability and consequently in the development of arrhythmias like AF. Since different studies have shown that both upregulation and downregulation of SK3 channels can lead to arrhythmias by different mechanisms, an important goal is to elucidate whether the rs13376333 risk SNP is a gain-of-function (GoF) or a loss-of-function (LoF) variant. A better understanding of the functional consequences associated with these SNPs could influence clinical practice guidelines by improving genotype-based risk stratification and personalized treatment. Although research using native human atrial cardiomyocytes and animal models has provided useful insights, each model has its limitations. Therefore, there is a critical need to develop a human-derived model that represents human physiology more accurately than existing animal models. In this context, research with human induced pluripotent stem cells (hiPSC) and subsequent generation of cardiomyocytes derived from hiPSC (hiPSC-CMs) has revealed the underlying causes of various cardiovascular diseases and identified treatment opportunities that were not possible using in vitro or in vivo studies with animal models. Thus, the ability to generate atrial cardiomyocytes and atrial tissue derived from hiPSCs from human/patients with specific genetic diseases, incorporating novel genetic editing tools to generate isogenic controls and organelle-specific reporters, and 3D bioprinting of atrial tissue could be essential to study AF pathophysiological mechanisms. In this review, we will first give an overview of SK-channel function, its role in atrial fibrillation and outline pathophysiological mechanisms of KCNN3 risk SNPs. We will then highlight the advantages of using the hiPSC-CM model to investigate SNPs associated with AF, while addressing limitations and best practices for rigorous hiPSC studies.

Acute antiarrhythmic effects of SGLT2 inhibitors–dapagliflozin lowers the excitability of atrial cardiomyocytes

In recent years, SGLT2 inhibitors have become an integral part of heart failure therapy, and several mechanisms contributing to cardiorenal protection have been identified. In this study, we place special emphasis on the atria and investigate acute electrophysiological effects of dapagliflozin to assess the antiarrhythmic potential of SGLT2 inhibitors. Direct electrophysiological effects of dapagliflozin were investigated in patch clamp experiments on isolated atrial cardiomyocytes. Acute treatment with elevated-dose dapagliflozin caused a significant reduction of the action potential inducibility, the amplitude and maximum upstroke velocity. The inhibitory effects were reproduced in human induced pluripotent stem cell-derived cardiomyocytes, and were more pronounced in atrial compared to ventricular cells. Hypothesizing that dapagliflozin directly affects the depolarization phase of atrial action potentials, we examined fast inward sodium currents in human atrial cardiomyocytes and found a significant decrease of peak sodium current densities by dapagliflozin, accompanied by a moderate inhibition of the transient outward potassium current. Translating these findings into a porcine large animal model, acute elevated-dose dapagliflozin treatment caused an atrial-dominant reduction of myocardial conduction velocity in vivo. This could be utilized for both, acute cardioversion of paroxysmal atrial fibrillation episodes and rhythm control of persistent atrial fibrillation. In this study, we show that dapagliflozin alters the excitability of atrial cardiomyocytes by direct inhibition of peak sodium currents. In vivo, dapagliflozin exerts antiarrhythmic effects, revealing a potential new additional role of SGLT2 inhibitors in the treatment of atrial arrhythmias.

Selective and brain-penetrant HCN1 inhibitors reveal links between synaptic integration, cortical function, and working memory

Hyperpolarization-activated and cyclic-nucleotide-gated 1 (HCN1) ion channels are proposed to be critical for cognitive function through regulation of synaptic integration. However, resolving the precise role of HCN1 in neurophysiology and exploiting its therapeutic potential has been hampered by minimally selective antagonists with poor potency and limited invivo efficiency. Using automated electrophysiology in a small-molecule library screen and chemical optimization, we identified a primary carboxamide series of potent and selective HCN1 inhibitors with a distinct mode of action. In cognition-relevant brain circuits, selective inhibition of native HCN1 produced on-target effects, including enhanced excitatory postsynaptic potential summation, while administration of a selective HCN1 inhibitor to rats recovered decrement working memory. Unlike prior non-selective HCN antagonists, selective HCN1 inhibition did not alter cardiac physiology in human atrial cardiomyocytes or in rats. Collectively, selective HCN1 inhibitors described herein unmask HCN1 as a potential target for the treatment of cognitive dysfunction in brain disorders.

Empagliflozin suppresses the differentiation/maturation of human epicardial preadipocytes and improves paracrine secretome profile

Abstract Aims Sodium-glucose cotransporter 2 (SGLT2) inhibitors reduce the epicardial adipose tissue (EAT) in human, which could enhance the cardioprotective effect in heart failure and atrial fibrillation. However, the precise mechanism of EAT reduction remains unclear. We investigated the direct effect of SGLT2 inhibitor, empagliflozin, on human primary epicardial adipocyte and preadipocyte. Methods and Results In Arm1, human EAT biopsies obtained during surgery and isolated preadipocyte/adipocytes were used for evaluating SGLT2 expression. In Arm2 and Arm3, we investigated the direct effect of empagliflozin on the differentiation/maturation and secretome profile of human preadipocyte/adipocyte. We validated the effect of empagliflozin on paracrine effect of EAT using co-culture with human iPS-derived atrial cardiomyocytes and empagliflozin-treated human epicardial adipocyte in Arm4. The validity of findings obtained from Arm1-4 were verified in view of clinical perspective in Arm5 and Arm6. SGLT2 was mainly expressed in the human pre-adipocyte in EAT. The expression levels of SGLT2 significantly diminished when the pre-adipocyte terminally differentiated. The formation of lipid droplets and fatty acid binding protein 4 (FABP4) expression in adipocyte were attenuated by empagliflozin treatment without affecting cell proliferation. mRNA levels of IL1α, IL1β, IL6, TGFβ and MCP1 in empagliflozin-treated adipocyte were significantly decreased. Of these, secreted protein levels of IL6 and MCP1 were significantly downregulated in supernatant of empagliflozin-treated cells. Co-culture of human iPS-derived atrial cardiomyocytes and adipocyte pre-treated with or without empagliflozin revealed that empagliflozin had striking suppressive effects on myocardial oxidative stress. Only IL6 mRNA expression in human EAT showed the clinically relevant association in terms of the difference of AF prevalence, anti-diabetic drug and N-terminal pro-brain natriuretic peptide. Conclusions We demonstrated that empagliflozin suppresses human epicardial pre-adipocyte differentiation/maturation, possibly leading to the reduction of EAT volume, and improves paracrine secretome profile of EAT. IL6 might be a key adipokine regulated by SGLT2 inhibitors.