Foxd1-Dependent and Independent Pathways for Reprogramming from Fibroblasts to Induced Pluripotent Stem Cells or Cardiomyocytes

Induced Pluripotent Stem Cells (iPSCs) can differentiate into any cell type. Cardiomyogenesis from iPSCs is useful for clinical application in myocardial regeneration. However, the efficiency and duration of producing iPSCs and iPSC-derived cardiomyocytes must be improved. We previously demonstrated that a surface marker profile of Sca1-CD34- or Foxd1+ during the reprogramming process is a predictor of successful iPSC formation. Here, we examine the correlation of feasibility as iPSC predictors between Sca1-CD34- and Foxd1+ cell populations, and their possibility as predictors for cardiomyocyte transdifferentiation. The fate-tracing analysis revealed that most iPSC colonies were formed from GFP-positive cells in which Foxd1 was transactivated in the middle-to-late phase of the reprogramming process. In addition, GFP expression was observed mainly in the Sca1-CD34- cell population. Thus, Foxd1+ could be an indicator of successful reprogramming to iPSCs mainly derived from Sca1-CD34- cells. As for cardiac transdifferentiation, reprogramming cells were sorted based on the expression pattern of Sca1 and CD34, resulting in a higher incidence of beating cell aggregates derived from theSca1+CD34+ population, which expresses less Foxd1 promoter-driven GFP and contained very few undifferentiated iPSCs. Moreover, the cardiomyocyte marker α-actinin only partially co-localized with GFP expression in the aggregates derived from Sca1+CD34+ or Sca1-CD34- cells. Therefore,Sca1+CD34+ could be a better cell source for Foxd1-independent cardiomyocyte creation despite the failed reprogramming cell population.