Low-density plating is sufficient to induce cardiac hypertrophy and electrical remodeling in highly purified human iPS cell-derived cardiomyocytes

Introduction: Cardiac hypertrophy is a leading cause of many cardiovascular diseases, including heart failure, but its pathological mechanism is not fully understood. This study used highly purified human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes to produce an in vitro hypertrophy model and characterize its gene expression and electrophysiological properties. Methods: For 7 days we cultured hiPSC-derived cardiomyocytes plated at high (2800-4800 cells/mm(2)) or low (500-1200 cells/mm(2)) cell density and assessed their cell size with confocal and fluorescence microscopy, their electrophysiological and pharmacological responses with multi-electrode array systems, and their gene expression patterns by using DNA microarray technology and quantitative PCR. We used quantitative PCR and Western blotting to compare the expression of potassium-channel genes between the hiPSC-derived cardiomyocytes and human fetal and adult hearts. Results: The hiPSC-derived cardiomyocytes showed spontaneous beating and similar pattern of a-actinin molecules regardless of plating density. However, cells plated at low density had the following characteristics compared with those at high density: 1) significant enlargement in size; 2) significant increase or decrease in expression of the cardiac hypertrophy-characteristic genes NPPA, ATP2A2, ANKRD1 and MYL2 in accordance with the progression of hypertrophy; 3) significant reduction in responses to the inhibitors of cardiac slow delayed-rectifier K+ current (I-Ks), chromanol 293B and HMR1556, in a cell-density-dependent manner; and 4) significant reduction in the expression of the KCNQ1 and KCNJ2 genes coding the K+ ion channels conducting each IKs and cardiac inward rectifier outward K+ current (I-K1). Discussion: The enlargement, hypertrophy-characteristic and potassium ion channels gene expression of hiPSC-derived cardiomyocytes suggest that low-density plating was sufficient to induce cardiac hypertrophy. This model may be useful in elucidating mechanisms underlying the onset and progress of cardiac hypertrophy, because these cells can be cultured for several weeks. (C) 2013 Elsevier Inc. All rights reserved.