Effect of KCNJ2 overexpression on gene expression profile in human iPS cell-derived cardiomyocytes

Drug-induced cardiac arrhythmia characterized by QT prolongation and torsade de pointes has been a major reason for drug withdrawal at the late stage of clinical trials. Current preclinical testing is still insufficient to identify drugs with pro-arrhythmic risks. Human induced pluripotent stem cell-derived cardiomyocytes are a promising development in safety screening as a reproducible human model. Using the patch-clamp technique, we showed that human induced pluripotent stem cell-derived cardiomyocytes exhibited spontaneous action potentials, which represent relatively immature forms of cardiac cells. Furthermore, in some spontaneously beating cells, a hERG blocker, E4031, depolarized membrane potentials and stopped spontaneous firing, resulting in failure to evaluate drug effects on electrophysiological parameters that reflect repolarization processes. Here we show that human stem cell-derived cardiomyocytes with transduced KCNJ2 encoding the inward-rectifier potassium channel have characteristics similar to mature cardiomyocytes including responsiveness to rate changes and potassium channel blockers. Our novel strategy could allow implementation of human induced pluripotent stem cell-derived cardiomyocytes in drug safety assessment for cardiac toxicity. As a commercially available differentiated cardiac cell line derived from hiPS cells, iCell-CMs (Cellular Dynamics International; CDI, Madison, WI, USA) were purchased from iPS Academia Japan Inc. (Kyoto, Japan), and were thawed and cultured according to the manual provided from the company (CDI) before adenoviral infections. After pre-culture for 4-days, cells are replated to the culture substrate (collagen-coated 24-well plate). Initial plating cell numbers were 2.5 X 10^5 / well. At replating, Ad-EGFP or Ad-KCNJ2-EGFP at 100 MOI (final) were applied to the cells for 24 h to achieve adenoviral infection. The cells were then cultured for 4 days after replating, and were collected for total RNA preparation.