Arrhythmogenic cardiomyopathy (ACM) is an inherited progressive cardiac disease. Many patients with ACM harbor mutations in desmosomal genes, predominantly in plakophilin-2 ( PKP2 ). Although the genetic basis of ACM is well characterized, the underlying disease-driving mechanisms remain unresolved. Explanted hearts from patients with ACM had less PKP2 compared with healthy hearts, which correlated with reduced expression of desmosomal and adherens junction (AJ) proteins. These proteins were also disorganized in areas of fibrotic remodeling. In vitro data from human-induced pluripotent stem cell–derived cardiomyocytes and microtissues carrying the heterozygous PKP2 c.2013delC pathogenic mutation also displayed impaired contractility. Knockin mice carrying the equivalent heterozygous Pkp2 c.1755delA mutation recapitulated changes in desmosomal and AJ proteins and displayed cardiac dysfunction and fibrosis with age. Global proteomics analysis of 4-month-old heterozygous Pkp2 c.1755delA hearts indicated involvement of the ubiquitin-proteasome system (UPS) in ACM pathogenesis. Inhibition of the UPS in mutant mice increased area composita proteins and improved calcium dynamics in isolated cardiomyocytes. Additional proteomics analyses identified lysine ubiquitination sites on the desmosomal proteins, which were more ubiquitinated in mutant mice. In summary, we show that a plakophilin-2 mutation can lead to decreased desmosomal and AJ protein expression through a UPS-dependent mechanism, which preceded cardiac remodeling. These findings suggest that targeting protein degradation and improving desmosomal protein stability may be a potential therapeutic strategy for the treatment of ACM.

Chronic kidney disease (CKD) and cardiovascular disease (CVD) have an estimated 700–800 and 523 million cases worldwide, respectively, with CVD being the leading cause of death in CKD patients. The pathophysiological interplay between the heart and kidneys is defined as the cardiorenal syndrome (CRS), in which worsening of kidney function is represented by increased plasma concentrations of uremic toxins (UTs), culminating in dialysis patients. As there is a high incidence of CVD in CKD patients, accompanied by arrhythmias and sudden cardiac death, knowledge on electrophysiological remodeling would be instrumental for understanding the CRS. While the interplay between both organs is clearly of importance in CRS, the involvement of UTs in pro‐arrhythmic remodeling is only poorly investigated, especially regarding the mechanistic background. Currently, the clinical approach against potential arrhythmic events is mainly restricted to symptom treatment, stressing the need for fundamental research on UT in relation to electrophysiology. This review addresses the existing knowledge of UTs and cardiac electrophysiology, and the experimental research gap between fundamental research and clinical research of the CRS. Clinically, mainly absorbents like ibuprofen and AST‐120 are studied, which show limited safe and efficient usability. Experimental research shows disturbances in cardiac electrical activation and conduction after inducing CKD or exposure to UTs, but are scarcely present or focus solely on already well‐investigated UTs. Based on UTs data derived from CKD patient cohort studies, a clinically relevant overview of physiological and pathological UTs concentrations is created. Using this, future experimental research is stimulated to involve electrophysiologically translatable animals, such as rabbits, or in vitro engineered heart tissues.

Background and Purpose: The increasing number of cancer survivors has caused growing concern over chemotherapy‐induced cardiotoxicity. This study aimed to investigate a novel human model of cardiotoxicity and explore cardioprotection.Experimental Approach: Living myocardial slices (LMS) were obtained from explanted end‐stage heart failure hearts, then exposed to doxorubicin (Dox) to investigate cardiotoxic effects and to dexrazoxane (Dex) to explore cardioprotection. We assessed contractile function and glucose consumption, followed by evaluation of calcium transients, structural integrity and transcriptomic changes. Additionally, electrocardiogram (ECG) alterations were analysed in patients treated with anthracyclines to corroborate the cardiotoxicity findings from LMS.Key Results: We observed distinct functional responses to Dox, with LMS derived from some patients exhibiting high susceptibility to Dox‐induced cardiotoxicity. LMS from susceptible patients displayed reduced contractile function and excitability, myofibre dyssynchrony, structural damage and decreased metabolic activity. Dex pretreatment partially mitigated these effects, preserving contractile function and preventing structural damage. Consistent with ex vivo findings, patients treated with anthracyclines exhibited acute and chronic alterations in T‐, P‐ and R‐wave morphology of the ECG, confirming variable susceptibility at the clinical level.Conclusions and Implications: We highlight the value of human LMS in studying Dox‐induced cardiotoxicity and the cardioprotective potential of Dex, even when sourced from end‐stage heart failure patients. Susceptible patients harboured cardiomyopathy‐associated genetic mutations, suggesting that genetic screening including cardiomyopathy‐associated genes, prior to anthracycline treatment, could enable improved patient risk stratification. We demonstrate the potential utility of ECG changes for early detection of subclinical cardiotoxicity.

Kv11.1 (hERG) channels play a critical role in repolarization of cardiomyocytes during the cardiac action potential (AP). Drug mediated Kv11.1 blockade results in AP prolongation, which poses an increased risk of sudden cardiac death. Many drugs, like pentamidine, interfere with normal Kv11.1 forward trafficking and thus reduce functional Kv11.1 channel densities. Although class III antiarrhythmics, e.g. dofetilide, rescue congenital and acquired forward trafficking defects, this is of little use due to their simultaneous acute channel blocking effect. We aimed to test the ability of a combination of dofetilide plus LUF7244, a Kv11.1 allosteric modulator/activator, to rescue Kv11.1 trafficking and produce functional Kv11.1 current. LUF7244 treatment by itself did not disturb or rescue WT or G601S Kv11.1 trafficking as shown by western blot and immunofluorescence microcopy analysis. Pentamidine-decreased maturation of WT Kv11.1 levels was rescued by 10 μM dofetilide or 10 μM dofetilide + 5 μM LUF7244. In trafficking defective G601S Kv11.1 cells, dofetilide (10 μM) or dofetilide+LUF7244 (10+5 μM) restored Kv11.1 trafficking also, as demonstrated by western blot and immunofluorescence microscopy. LUF7244 (10 μM) increased IKv11.1 despite the presence of dofetilide (1 μM) in WT Kv11.1 cells. In G601S expressing cells, long-term treatment (24-48 h) with LUF7244 (10 μM) and dofetilide (1 μM) increased IKv11.1 compared to non-treated, or acutely treated cells. We conclude that dofetilide plus LUF7244 rescues Kv11.1 trafficking and produces functional IKv11.1. Thus, combined administration of LUF7244 and an IKV11.1 trafficking corrector could serve as a new pharmacological therapy of both congenital and drug-induced Kv11.1 trafficking defects. SIGNIFICANCE STATEMENT LUF7244, a negative allosteric modulator/activator, in combination with dofetilide corrected both congenital and acquired Kv11.1 trafficking defects resulting in functional Kv11.1 current.

Chronic kidney disease (CKD) is represented by a diminished filtration capacity of the kidneys. End-stage renal disease patients need dialysis treatment to remove waste and toxins from the circulation. However, endogenously produced uremic toxins (UTs) cannot always be filtered during dialysis. UTs are among the CKD-related factors that have been linked to maladaptive and pathophysiological remodeling of the heart. Importantly, 50% of the deaths in dialysis patients are cardiovascular related, with sudden cardiac death predominating. However, the mechanisms responsible remain poorly understood. The current study aimed to assess the vulnerability of action potential repolarization caused by exposure to pre-identified UTs at clinically relevant concentrations. We exposed human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) and HEK293 chronically (48 h) to the UTs indoxyl sulfate, kynurenine, or kynurenic acid. We used optical and manual electrophysiological techniques to assess action potential duration (APD) in the hiPSC-CMs and recorded I_Kr currents in stably transfected HEK293 cells (HEK-hERG). Molecular analysis of K_V11.1, the ion channel responsible for I_Kr, was performed to further understand the potential mechanism underlying the effects of the UTs. Chronic exposure to the UTs resulted in significant APD prolongation. Subsequent assessment of the repolarization current I_Kr, often most sensitive and responsible for APD alterations, showed decreased current densities after chronic exposure to the UTs. This outcome was supported by lowered protein levels of K_V11.1. Finally, treatment with an activator of the I_Kr current, LUF7244, could reverse the APD prolongation, indicating the potential modulation of electrophysiological effects caused by these UTs. This study highlights the pro-arrhythmogenic potential of UTs and reveals a mode of action by which they affect cardiac repolarization.

Background and Purposes: Reduced inward rectifier potassium channel (K_ir2.1) functioning is associated with heart failure and may cause Andersen‐Tawil Syndrome, among others characterized by ventricular arrhythmias. Most heart failure or Andersen–Tawil Syndrome patients are treated with β‐adrenoceptor antagonists (β‐blockers) or sodium channel blockers; however, these do not specifically address the inward rectifier current (I_K1) nor aim to improve resting membrane potential stability. Consequently, additional pharmacotherapy for heart failure and Andersen–Tawil Syndrome treatment would be highly desirable. Acute propafenone treatment at low concentrations enhances I_K1 current, but it also exerts many off‐target effects. Therefore, discovering and exploring new I_K1‐channel openers is necessary.Experimental Approach: Effects of propafenone and 10 additional propafenone analogues were analysed. Currents were measured by single‐cell patch‐clamp electrophysiology. K_ir2.1 protein expression levels were determined by western blot analysis and action potential characteristics were further validated in human‐induced pluripotent stem cells–derived cardiomyocytes (hiPSC‐CMCs). Molecular docking was performed to obtain detailed information on drug‐channel interactions.Key Results: Analogues GPV0019, GPV0057 and GPV0576 strongly increased the outward component of I_K1 while not affecting the K_ir2.1 channel expression levels. GPV0057 did not block I_Kr at concentrations below 0.5 μmol L⁻¹ nor Na_V1.5 current below 1 μmol L⁻¹. Moreover, hiPSC‐CMC action potential duration was also not affected by GPV0057 at 0.5 and 1 μmol L⁻¹. Structure analysis indicates a mechanism by which GPV0057 might enhance K_ir2.1 channel activation.Conclusion and Implications: GPV0057 has a strong efficiency towards increasing I_K1, which makes it a good candidate to address I_K1 deficiency‐associated diseases.