Cardiac mesenchymal progenitors differentiate into adipocytes via Klf4 and c-Myc

Direct reprogramming of differentiated cells to pluripotent stem cells has great potential to improve our understanding of developmental biology and disorders such as cancers, and has implications for regenerative medicine. In general, the effects of transcription factors (TFs) that are transduced into cells can be influenced by pre-existing transcriptional networks and epigenetic modifications. However, previous work has identified four key TFs, Oct4, Sox2, Klf4 and c-Myc, which can reprogram various differentiated cells to generate induced pluripotent stem cells. Here, we show that in the heart, the transduction of cardiac mesenchymal progenitors (CMPs) with Klf4 and c-Myc (KM) was sufficient to drive the differentiation of these cells into adipocytes without the use of adipogenic stimulation cocktail, that is, insulin, 3-isobutyl-1-methylxanthine (IBMX) and dexamethasone. KM-transduced CMPs exhibited a gradually increased expression of adipogenic-related genes, such as C/Ebpα, Pparγ and Fabp4, activation of the peroxisome proliferator-activated receptor (PPAR) signaling pathway, inactivation of the cell cycle-related pathway and formation of cytoplasmic lipid droplets within 10 days. In contrast, NIH3T3 fibroblasts, 3T3-L1 preadipocytes, and bone marrow-derived mesenchymal stem cells transduced with KM did not differentiate into adipocytes. Both in vitro and in vivo cardiac ischemia reperfusion injury models demonstrated that the expression of KM genes sharply increased following a reperfusion insult. These results suggest that ectopic adipose tissue formation in the heart following myocardial infarction results from CMPs that express KM following a stress response.