Background: Sarcoplasmic reticulum Ca²⁺ leak and post-translational modifications under stress have been implicated in catecholaminergic polymorphic ventricular tachycardia (CPVT), a highly lethal inherited arrhythmogenic disorder. Human induced pluripotent stem cells (hiPSCs) offer a unique opportunity for disease modeling. Objective: The aims were to obtain functional hiPSC-derived cardiomyocytes from a CPVT patient harboring a novel ryanodine receptor (RyR2) mutation and model the syndrome, drug responses and investigate the molecular mechanisms associated to the CPVT syndrome. Methods: Patient-specific cardiomyocytes were generated from a young athletic female diagnosed with CPVT. The contractile, intracellular Ca²⁺ handling and electrophysiological properties as well as the RyR2 macromolecular remodeling were studied. Results: Exercise stress electrocardiography revealed polymorphic ventricular tachycardia when treated with metoprolol and marked improvement with flecainide alone. We found abnormal stress-induced contractile and electrophysiological properties associated with sarcoplasmic reticulum Ca²⁺ leak in CPVT hiPSC-derived cardiomyocytes. We found inadequate response to metoprolol and a potent response of flecainide. Stabilizing RyR2 with a Rycal compound prevents those abnormalities specifically in CPVT hiPSC-derived cardiomyocytes. The RyR2-D3638A mutation is located in the conformational change inducing-central core domain and leads to RyR2 macromolecular remodeling including depletion of PP2A and Calstabin2. Conclusion: We identified a novel RyR2-D3638A mutation causing 3D conformational defects and aberrant biophysical properties associated to RyR2 macromolecular complex post-translational remodeling. The molecular remodeling is for the first time revealed using patient-specific hiPSC-derived cardiomyocytes which may explain the CPVT proband’s resistance. Our study promotes hiPSC-derived cardiomyocytes as a suitable model for disease modeling, testing new therapeutic compounds, personalized medicine and deciphering underlying molecular mechanisms.

While mutations in the cardiac type 2 ryanodine receptor (RyR2) have been linked to exercise-induced or catecholaminergic polymorphic ventricular tachycardia (CPVT), its association with polymorphic ventricular tachycardia (PMVT) occurring at rest is unclear. We aimed at constructing a patient-specific human-induced pluripotent stem cell (hiPSC) model of PMVT occurring at rest linked to a single point mutation in RyR2. Blood samples were obtained from a patient with PMVT at rest due to a heterozygous RyR2-H29D mutation. Patient-specific hiPSCs were generated from the blood samples, and the hiPSC-derived cardiomyocytes (CMs) were generated via directed differentiation. Using CRIPSR/Cas9 technology, isogenic controls were generated by correcting the RyR2-H29D mutation. Using patch-clamp, fluorescent confocal microscopy and video-image-based analysis, the molecular and functional properties of RyR2-H29D hiPSC—CMs and control hiPSC—CMs were compared. RyR2-H29D hiPSC—CMs exhibit intracellular sarcoplasmic reticulum (SR) Ca2+ leak through RyR2 under physiological pacing. RyR2-H29D enhances the contribution of inositol 1,4,5-trisphosphate receptors to excitation-contraction coupling (ECC) that exacerbates abnormal Ca2+ release in RyR2-H29D hiPSC—CMs. RyR2-H29D hiPSC—CMs exhibit shorter action potentials, delayed afterdepolarizations, arrhythmias and aberrant contractile properties compared to isogenic controls. The RyR2-H29D mutation causes post-translational remodeling that is fully reversed with isogenic controls. To conclude, in a model based on a RyR2 point mutation that is associated with short-coupled PMVT at rest, RyR2-H29D hiPSC—CMs exhibited aberrant intracellular Ca2+ homeostasis, shortened action potentials, arrhythmias and abnormal contractile properties. French Muscular Dystrophy Association (AFM; project 16,073, MNM2 2012 and 20,225), “Fondation de la Recherche Médicale” (FRM; SPF20130526710), “Institut National pour la Santé et la Recherche Médicale” (INSERM), National Institutes of Health (ARM; R01 HL145473) and New York State Department of Health (NYSTEM C029156).

Numerous protocols of cardiac differentiation have been established by essentially focusing on specific growth factors on human pluripotent stem cell (hPSC) differentiation efficiency. However, the optimal environmental factors to obtain cardiac myocytes in network are still unclear. The mesoderm germ layer differentiation is known to be enhanced by low oxygen exposure. Here, we hypothesized that low oxygen exposure enhances the molecular and functional maturity of the cardiomyocytes. We aimed at comparing the molecular and functional consequences of low (5% O₂ or LOE) and high oxygen exposure (21% O₂ or HOE) on cardiac differentiation of hPSCs in 2D- and 3D-based protocols. hPSC-CMs were differentiated through both the 2D (monolayer) and 3D (embryoid body) protocols using several lines. Cardiac marker expression and cell morphology were assessed. The mitochondrial localization and metabolic properties were evaluated. The intracellular Ca²⁺ handling and contractile properties were also monitored. The 2D cardiac monolayer can only be differentiated in HOE. The 3D cardiac spheroids containing hPSC-CMs in LOE further exhibited cardiac markers, hypertrophy, steadier SR Ca²⁺ release properties revealing a better SR Ca²⁺ handling, and enhanced contractile force. Preserved distribution of mitochondria and similar oxygen consumption by the mitochondrial respiratory chain complexes were also observed. Our results brought evidences that LOE is moderately beneficial for the 3D cardiac spheroids with hPSC-CMs exhibiting further maturity. In contrast, the 2D cardiac monolayers strictly require HOE.

Montivipera bornmuelleri is an endangered viper that has been described as endemic to the Lebanese mountains. The lethal dose 50% (LD50) of M. bornmuelleri venom has been determined by performing intravenous, intraperitoneal (IP), and subcutaneous injections. However, to date, intramuscular injection has not been performed to determine LD50, nor have the minimum hemorrhagic (MHD) or the minimum necrotic doses (MND) been evaluated. Thus, this study was conducted to complete the characterization of the M. bornmuelleri venom. Our results showed that intramuscularly injected LD50 is around 5.39 mg/kg, and IP LD50 is around 1.93 mg/kg. After intradermal injection, our findings showed significant necrotic and medium hemorrhagic activities, and MHD was around 250 µg/kg. By comparing with other local venomous snakes, these results indicate that the lethality of M. bornmuelleri venom is similar to that of Daboia palaestinae venom (IP LD50=1.9 mg/kg) and is higher than that of Macrovipera lebetina venom (...

Arrhythmogenic cardiomyopathy (ACM) is a rare genetic disease associated with ventricular arrhythmias in patients. The occurrence of these arrhythmias is due to direct electrophysiological remodeling of the cardiomyocytes, namely a reduction in the action potential duration (APD) and a disturbance of Ca²⁺ homeostasis. Interestingly, spironolactone (SP), a mineralocorticoid receptor antagonist, is known to block K⁺ channels and may reduce arrhythmias. Here, we assess the direct effect of SP and its metabolite canrenoic acid (CA) in cardiomyocytes derived from human-induced pluripotent stem cells (hiPSC-CMs) of a patient bearing a missense mutation (c.394C>T) in the DSC2 gene coding for desmocollin 2 and for the amino acid replacement of arginine by cysteine at position 132 (R132C). SP and CA corrected the APD in the muted cells (vs. the control) in linking to a normalization of the hERG and KCNQ1 K⁺ channel currents. In addition, SP and CA had a direct cellular effect on Ca²⁺ homeostasis. They reduced the amplitude and aberrant Ca²⁺ events. In conclusion, we show the direct beneficial effects of SP on the AP and Ca²⁺ homeostasis of DSC2-specific hiPSC-CMs. These results provide a rationale for a new therapeutical approach to tackle mechanical and electrical burdens in patients suffering from ACM.

The intricate brain–heart interaction, essential for physiological balance, is largely governed by the autonomic nervous system (ANS). This bidirectional communication, involving both the sympathetic and parasympathetic branches of the ANS, is critical for maintaining cardiac homeostasis. Dysregulation of the ANS is a significant factor in cardiovascular diseases. Beyond the ANS, higher brain functions, particularly through interoceptive prediction, contribute to this dynamic interplay. The Cav1.3 L-type calcium channel, expressed in both the central nervous system (CNS) and the heart, is crucial for this interaction. Cav1.3, a key regulator of cellular excitability, exhibits genetic variations that are linked to both neurological and cardiac disorders, highlighting its pivotal role in the brain–heart axis. This review aims to delve into the under-explored role of Cav1.3 in brain–heart interaction, specifically examining how it modulates ANS activity and, consequently, the cardiac function. This will illuminate its significant role in the broader context of brain–heart interactions.