Martin Kral

Alzheimer’s disease (AD) is a neurodegenerative disorder characterised by progressive dementia, brain atrophy, and ultimately death. Using cerebral organoids derived from human-induced pluripotent stem cells (hiPSCs) carrying the familial PSEN1 A246E variant, we investigated the temporal relationship between amyloid-β (Aβ) dysregulation and spontaneous neuronal activity. Multielectrode array recordings from the differentiation day 60 (DD60) to at least DD130 revealed that AD organoids exhibited transient hyperexcitability and hypersynchrony compared with wild-type (WT) controls, followed by a gradual decline in activity. During the enhanced excitability stage, both elevated Aβ42/40 and Aβ aggregate size showed positive correlations with the percentage of active electrodes and the global synchrony index (GSI) in AD organoids. These findings indicate that Aβ dysregulation might contribute to transient network hyperexcitability in early AD. The results also suggest that patient-derived cerebral organoids may serve as a translational model to examine early network dysfunction and inform future investigations of potential Aβ-induced changes in excitability during the preclinical stages of AD.

Aims: Kv7.1 variants, associated with long QT syndrome type 1 (LQT1) and altering the function of the slow delayed rectifier K+ (IKs) channel, may result in arrhythmias, especially during exercise. This study focused on complex analysis of the R562S-Kv7.1 variant located in helix C of the Kv7.1 C terminus, which was identified in four putatively unrelated families in the Czech Republic. Methods and results: The clinical and genetic investigation was followed by functional analysis (whole-cell patch clamp, confocal microscopy, computational simulations) and structural modelling. The genetic analysis suggested that R562S-Kv7.1 might be a founder LQT1 variant in Central Europe. R562S carriers showed a significantly prolonged corrected QT (QTc) interval at rest and a significantly higher QTc prolongation after exercise vs. healthy relatives. The functional analysis of R562S channels demonstrated their preserved membrane localization, a significant decrease in IKs with a rightward shift of the voltage dependence of activation, and, importantly, a lack of responsiveness to β-adrenergic stimulation. The latter seems to be related to a modified interaction of the modulatory KCNE1 subunit with Kv7.1. The pro-arrhythmic potential of R562S dysfunction, mediated by delayed afterdepolarizations during β-adrenergic stimulation, could be effectively prevented by mild (5%) inhibition of L-type Ca2+ current (ICa). Conclusion: R562S-Kv7.1 is the first variant in helix C causing an impaired response of IKs channel to β-adrenergic stimulation, likely due to altered interactions between channel subunits, namely Kv7.1 and KCNE1. Mild ICa inhibition was suggested as a new treatment option.

Alzheimer’s disease (AD) is a neurodegenerative disorder characterised by progressive dementia, brain atrophy, and ultimately death. Using cerebral organoids derived from human induced pluripotent stem cells (hiPSCs) carrying the familial PSEN1 A246E variant, we investigated the temporal relationship between amyloid-β (Aβ) dysregulation and spontaneous neuronal activity. Multielectrode array recordings from the differentiation day 60 (DD60) to at least DD130 revealed that AD organoids exhibited transient hyperexcitability and hypersynchrony compared with wild-type (WT) controls, followed by a gradual decline in activity. During the enhanced excitability stage, both elevated Aβ42/40 and Aβ aggregate size showed positive correlations with the percentage of active electrodes and the global synchrony index (GSI) in AD organoids. These findings indicate that Aβ dysregulation might contribute to transient network hyperexcitability in early AD. The results also suggest that patient-derived cerebral organoids may serve as a translational model to examine early network dysfunction and inform future investigations of potential Aβ-induced changes in excitability during the preclinical stages of AD.

Background and Aims: The KCNH2 (hERG) gene encodes the Kv11.1 protein, the pore-forming subunit of the rapid delayed rectifier potassium channel, which plays a key role in cardiac repolarization. We aimed to investigate the function of two Kv11.1 variants in trans, S1021Qfs*98 and A228V, identified in a patient suffering from idiopathic ventricular fibrillation (VF). Methods: A detailed clinical and genetic investigation was followed by functional analysis using the whole-cell patch clamp technique, western blot, and mathematical simulations in a human ventricular cell model. Results: In comparison with wild type, the current was decreased by 69.5 and 69.2% in S1021Qfs*98 and S1021Qfs*98/A228V, respectively, which agreed well with a significant decrease in the expression of S1021Qfs*98 channels, but no differences were observed in A228V. The voltage dependence of activation and inactivation and the time course of activation and deactivation remained unchanged. Minor changes were observed in the time course of inactivation and recovery from inactivation in S1021Qfs*98 and S1021Qfs*98/A228V. Arrhythmogenesis based on early afterdepolarizations (EADs) at rest, provoked by hypokalemia, and during β-adrenergic stimulation was suggested by simulations in a human ventricular cell model. Conclusion: To conclude, A228V is a benign variant, whereas S1021Qfs*98 exhibits a loss-of-function defect and dominant negativity. EADs-related arrhythmogenesis was predicted, which explains the pathogenic phenotype of the proband carrying both these variants and experiencing repetitive VF episodes. Based on the findings, we reclassify S1021Qfs*98 as a pathogenic, LQT2-associated variant. The data highlight the importance of functional analysis for the correct management of patients with idiopathic VF and genetic variants.