Sodium channel current loss of function in induced pluripotent stem cell-derived cardiomyocytes from a Brugada syndrome patient

Abstract

Brugada syndrome predisposes to sudden death due to disruption of normal cardiac ion channel function, yet our understanding of the underlying cellular mechanisms is incomplete. Commonly used heterologous expression models lack many characteristics of native cardiomyocytes and, in particular, the individual genetic background of a patient. Patient-specific induced pluripotent stem (iPS) cell-derived cardiomyocytes (iPS-CM) may uncover cellular phenotypical characteristics not observed in heterologous models. Our objective was to determine the properties of the sodium current in iPS-CM with a mutation in SCN5A associated with Brugada syndrome.Dermal fibroblasts from a Brugada syndrome patient with a mutation in SCN5A (c.1100G > A, leading to Nav1.5_p.R367H) were reprogrammed to iPS cells. Clones were characterized and differentiated to form beating clusters and sheets. Patient and control iPS-CM were structurally indistinguishable. Sodium current properties of patient and control iPS-CM were compared. These results were contrasted with those obtained in tsA201 cells heterologously expressing sodium channels with the same mutation.Patient-derived iPS-CM showed a 33.1–45.5% reduction in INa density, a shift in both activation and inactivation voltage-dependence curves, and faster recovery from inactivation. Co-expression of wild-type and mutant channels in tsA201 cells did not compromise channel trafficking to the membrane, but resulted in a reduction of 49.8% in sodium current density without affecting any other parameters.Cardiomyocytes derived from iPS cells from a Brugada syndrome patient with a mutation in SCN5A recapitulate the loss of function of sodium channel current associated with this syndrome; including pro-arrhythmic changes in channel function not detected using conventional heterologous expression systems.

Mechanisms of Arrhythmias in the Brugada Syndrome

“…While some studies reported no clear electrophysiological abnormalities in Brugada syndrome patient-derived iPSC-derived cardiomyocyte lines compared to controls [ 147 , 148 ], other reports contrarily showed evidence of significant alterations in action potential duration [ 65 , 144 ], decreased I Na density [ 65 , 144 , 145 , 149 , 150 , 151 ], decreased action potential upstroke velocity [ 65 , 144 , 145 , 150 , 151 ], or irregular calcium handling [ 65 , 145 ]. Ma and colleagues found that pacing at a frequency of 0.1 Hz led to a small subgroup (25%) of Brugada syndrome patient-derived iPSC-derived cardiomyocytes presenting with action potentials which were by the authors claimed to resemble the loss of action potential dome configuration as postulated by the repolarization hypothesis, albeit the pacing frequency exceeding human physiological range [ 71 , 144 ].…”

Calcium in Brugada Syndrome: Questions for Future Research

“…Indeed, a few groups have already generated and used iCMs to perform electrophysiological studies at the cellular level to characterize BrS ion current alterations. In particular, iCMs obtained from fibroblasts from BrS patients carrying an SCN5A mutation exhibited BrS features, including a reduction in inward sodium current, a shift in voltage-dependence curves and abnormal calcium handling ( Liang et al, 2016 ; Selga et al, 2018 ). Remarkably, iCMs generated from BrS patients without SCN5A mutations showed no significant functional difference when compared to iCMs generated from healthy controls ( Miller et al, 2017 ; Koivumaki et al, 2018 ).…”

Human Induced Pluripotent Stem Cells Derived from a Cardiac Somatic Source: Insights for an In-Vitro Cardiomyocyte Platform

“…To date, it has been widely described how hiPSC-CMs are able to recapitulate molecular and functional aspects of human heart pathophysiology, thus providing a good tool for disease modelling and development of personalized therapy that involves a pharmacological treatment. A wide range of genetic cardiomyopathies has been modelled using hiPSC-CMs [131], for example familiar long QT (LQT) syndromes [4,[85][86][87]132,133], Brugada syndrome [134,135], Catecholaminergic polymorphic tachycardia (CPVT) [136,137] and atrial fibrillation [138,139].…”