Novel direct reprogramming technique for the generation of culture-expandable cardiac progenitor cells from fibroblasts
Since the tremendous discovery of induce-pluripotent stem cells (iPSCs) in 2006 (1,2), investigators have been trying to induce somatic cell reprogramming into certain lineage cells following the basic method, in which lineage-related critical genes are initially screened out of numerous candidates and several master genes are then selected by transduction of multiple genes with appropriate culture conditions in somatic cells confirming transdifferentiation of the transduced cells. The technique is called as “direct reprogramming” which can avoid generating iPSCs and previous studies have successfully demonstrated lineage reprogramming into a variety of differentiated cell types such as neuronal cells (3), hepatocytes (4), and cardiomyocytes (5). Despite of the achievement of direct lineage reprogramming, investigators next challenged the generation of progenitor cells rather than terminally differentiated cells by direct reprogramming, because progenitor cells are generally proliferative and have advantage of large scale expansion as a tool for regeneration therapy. Indeed, recent reports exhibited that reprogrammed progenitors of neuronal cells (3), hepatocytes (6), and cardiomyocytes (7) were capable of proliferation.