Blebbistatin protects iPSC-CMs from hypercontraction and facilitates automated patch-clamp based electrophysiological study.

Recently, there have been great advances in cardiovascular channelopathy modeling and drug safety pharmacology using human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs). The automated patch-clamp (APC) technique overcomes the disadvantages of the manual patch-clamp (MPC) technique, which is labor intensive and gives low output. However, the application of the APC platform is still limited in iPSC-CM based research, due to the difficulty in maintaining the high quality of single iPSC-CMs during dissociation and recording. In this study, we improved the method for single iPSC-CM preparation by applying 2.5 µM blebbistatin (BB, an excitation-contraction coupling uncoupler) throughout APC procedures (dissociation, filtration, storage, and recording). Under non-BB buffered condition, iPSC-CMs in suspension showed a severe bleb-like morphology. However, BB-supplement led to significant improvements in morphology and INa recording, and we even obtained several CMs that showed spontaneous action potentials with typical morphology. Furthermore, APC faithfully recapitulated the single-cell electrophysiological phenotypes of iPSC-CMs derived from Brugada syndrome patients, as detected with MPC. Our study indicates that APC is capable of replacing MPC in the modeling of cardiac channelopathies using human iPSC-CMs by providing high-quality data with higher throughput.

Generation of iPSC lines from CPVT patient carrying heterozygous mutation p.A2254V in the ryanodine receptor 2 gene.

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a severe inheritable cardiac disorder, which is characterized by life-threatening cardiac arrhythmias, syncope, seizures, or sudden cardiac death in response to physical exercise or emotional stress. This inherited disease is predominantly caused by mutations in the ryanodine receptor type 2 (RYR2). To minimize the cell line variations for disease modeling, we generated two induced pluripotency stem cell lines (hiPSCs: isCPVTA2254V1-2 and isCPVTA2254V1-3) from skin fibroblasts of one CPVT patient carrying the p.A2254V mutation using CytoTune2.0 Sendai virus cocktail for non-integration reprogramming. All generated iPSCs maintained pluripotency, normal karyotype, and spontaneous in vivo and in vitro differentiation capacity.

Electrophysiological Abnormalities in VLCAD Deficient hiPSC-Cardiomyocytes Can Be Improved by Lowering Accumulation of Fatty Acid Oxidation Intermediates.

Patients with very long-chain acyl-CoA dehydrogenase deficiency (VLCADD) can present with life-threatening cardiac arrhythmias. The pathophysiological mechanism is unknown. We reprogrammed fibroblasts from one mildly and one severely affected VLCADD patient, into human induced pluripotent stem cells (hiPSCs) and differentiated these into cardiomyocytes (VLCADD-CMs). VLCADD-CMs displayed shorter action potentials (APs), more delayed afterdepolarizations (DADs) and higher systolic and diastolic intracellular Ca2+ concentration ([Ca2+]i) than control CMs. The mitochondrial booster resveratrol mitigated the biochemical, electrophysiological and [Ca2+]i changes in the mild but not in the severe VLCADD-CMs. Accumulation of potentially toxic intermediates of fatty acid oxidation was blocked by substrate reduction with etomoxir. Incubation with etomoxir led to marked prolongation of AP duration and reduced DADs and [Ca2+]i in both VLCADD-CMs. These results provide compelling evidence that reduced accumulation of fatty acid oxidation intermediates, either by enhanced fatty acid oxidation flux through increased mitochondria biogenesis (resveratrol) or by inhibition of fatty acid transport into the mitochondria (etomoxir), rescues pro-arrhythmia defects in VLCADD-CMs and open doors for new treatments.

Establishment of an automated patch-clamp platform for electrophysiological and pharmacological evaluation of hiPSC-CMs.

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) have evolved into widely used and reliable cell sources for modeling cardiovascular channelopathies and for drug safety pharmacology. However, the electrophysiological and pharmacological applications of hiPSC-CMs are hampered by manual patch-clamp technique, which is labor-intensive and generates low output. The automated patch-clamp technique is showing potential to overcome this problem. Here, we describe a new dissociation method, with which we can harvest a vast number of single relaxed hiPSC-CMs with smooth membrane suited for automated patch-clamp. Using the automated whole-cell patch-clamp technology, we report a high success rate for cell capture and whole-cell access (around 70%). We are able to identify and record several currents and paced action potentials (APs) with different success rates, including Na+ current (INa), L-type Ca2+ current (ICaL), two specific K+ currents, the transient outward K+ current (Ito) and the inward rectifier K+ current (IK1). Moreover, we successfully applied dynamic current-clamp to virtually increase IK1 for AP recordings. Our study suggests that automated patch-clamp technology could be used to investigate the relevant ionic currents and APs in hiPSC-CMs. The combination of automated patch-clamp and hiPSC-CM technologies promises a wide range of applications in the future.