Early Inhibition of Retinoic Acid Signaling Rapidly Generates Cardiomyocytes Expressing Ventricular Markers from Human Induced Pluripotent Stem Cells

SUMMARY Current protocols for the differentiation of cardiomyocytes from human induced pluripotent stem cells (iPSCs) generally require prolonged time in culture and result in heterogeneous cellular populations. We present a method for the generation of beating cardiomyocytes expressing specific ventricular markers after just 14 days. Addition of the pan-retinoic acid receptor inverse agonist BMS 493 to human iPSCs for the first 8 days of differentiation resulted in increased protein expression of the ventricular isoform of myosin regulatory light chain (MLC2V) from 18.7% ± 1.72% to 55.8% ± 11.4% (p <0.0001) in cells co-expressing the cardiac muscle protein troponin T (TNNT2). Increased MLC2V expression was also accompanied by a slower beating rate (49.4 ± 1.53 vs. 93.0 ± 2.81 beats per minute, p <0.0001) and increased contraction amplitude (201% ± 8.33% vs. 100% ± 10.85%, p <0.0001) compared to untreated cells. Improved directed differentiation will improve in vitro cardiac modeling.