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Slow and Sure Wins the iPSC Race?



Review of “Excessive Cellular Proliferation Negatively Impacts Reprogramming Efficiency of Human Fibroblasts” from Stem Cells Translational Medicine by Stuart P. Atkinson

Induced pluripotent stem cell (iPSC) technology represents one of the biggest scientific breakthroughs in recent times, with the promise of effective patient-specific treatments for a range of diseases and disorders. Obstacles to the progression of this technology do, unfortunately, still exist. Perhaps the most important of these is the low reprogramming efficiency which some labs have sought to remedy by boosting somatic cell proliferation [1-3]. However, the laboratory of Rohit N. Kulkarni (Harvard Medical School) has now reported a direct inverse correlation of high cell proliferation and reprogramming efficiency of primary human fibroblasts [4]. Do we need to slow things down to improve iPSC production?

The authors discovered this inverse correlation during their studies into the reprogramming of human patient-derived fibroblasts cultured using two different media formulations; normal, conventional Dulbecco’s modified Eagle’s medium (N) and AmnioMAX (Ax) media, a defined insulin-rich medium designed for the optimal growth of human amniotic fluid cells and fibroblasts. Ax media boosted proliferation and enhanced cell-cycle protein expression via activation of the activation of the PI-3 kinase pathway via insulin/IGF-1 signaling, and the authors hoped that this boost would enhance their reprogramming efforts.

However, fibroblasts grown in Ax media actually exhibited a reduced reprogramming efficiency as compared to fibroblasts grown with N media, although iPSCs produced under both conditions displayed similar characteristics regarding their pluripotent state. Therefore, the authors posited that enhanced proliferation and stimulation of the insulin/IGF-1 signaling pathway inhibits the number of cells which become reprogrammed but does not affect the quality of iPSCs produced. Mechanistically, the group found that Ax-treated cells had to increase their oxygen consumption as means to supply the energy required for the enhanced proliferation. This also led to a reduction in the level of glycolysis, the main source of energy production in pluripotent cells, and they point to this as the cause of the reduced numbers of reprogrammed cells. 

Although increasing the proliferation of fibroblasts seems like an intuitively positive means to improve reprogramming, this new study suggests that currents methods to boost efficiency come at an unwanted price (See figure for overview). The authors strengthen their argument by pointing to a plethora of small molecules used to enhance the reprogramming process (kenpaullone, trichostatin A, 5-azacytidine, and CHIR99021), even though they actually have a proven detrimental effect on fibroblast proliferation. 

The message seems clear for all you reprogrammers: don’t rush ahead, slow and sure wins the race!


  1. Esteban MA, Wang T, Qin B, et al. Vitamin C enhances the generation of mouse and human induced pluripotent stem cells. Cell Stem Cell 2010;6:71-79.
  2. Son MJ, Son MY, Seol B, et al. Nicotinamide overcomes pluripotency deficits and reprogramming barriers. Stem Cells 2013;31:1121-1135.
  3. Ruiz S, Panopoulos AD, Herrerias A, et al. A high proliferation rate is required for cell reprogramming and maintenance of human embryonic stem cell identity. Curr Biol 2011;21:45-52.
  4. Gupta MK, Teo AK, Rao TN, et al. Excessive Cellular Proliferation Negatively Impacts Reprogramming Efficiency of Human Fibroblasts. Stem Cells Transl Med 2015;4:1101-1108.