Epigenetic modification in congenital heart diseases by using stem cell technologies

Congenital heart diseases are the most common birth defects, occurring in more than 1% of newborns. The gene regulatory network of cardiac development has been revealed and some cases of congenital heart diseases have been shown to be associated with cardiac-specific gene mutations or related chromosomal abnormalities; however, almost all cases of congenital heart diseases are sporadic and the pathogenesis of heart malformations still remains unknown. Recently, studies of epigenetic regulation have been making progress in the field of cardiac development and the accumulated knowledge helps us understand more about cardiogenesis and congenital heart diseases. Interestingly, pluripotent stem cells such as embryonic stem (ES) cells and induced pluripotent stem (iPS) cells have attracted attention as tools to dissect epigenetic regulation during differentiation. Reprogramming and differentiation of ES cells and iPS cells can be induced by changes of gene expression patterns and epigenetic regulation, not by changing DNA sequences. We can also modify histone patterns and chromatin structures using chemical reagents. Hence, pluripotent stem cells enable us to dissect and modify epigenetic regulation during cardiogenesis in vitro. Moreover, in terms of iPS cells, they have become disease models because they can be generated from the somatic cells of patients. In this review, we summarize the recent findings of epigenetic regulation in cardiac development and congenital heart diseases. We also review the epigenetic modification during the reprogramming and cardiac differentiation of ES cells and iPS cells, and introduce our study showing that the disease-specific iPS cells of hypoplastic left heart syndrome, one of the severest congenital heart diseases with single ventricular circulation, exhibit unique epigenetic regulation during differentiation. Furthermore, we briefly focus on modifications of epigenetic regulation in cardiac development using chemical reagents, which suggest the possibility of treating congenital heart diseases using drugs. Lastly, we discuss the epigenetic memory of iPS cells, a specific feature that often complicates or prevents study of the differentiation of iPS cells.