OCT4-free reprogramming of human fibroblasts into pluripotent stem cells

Replacing the transcription factor OCT4, one of the master pluripotency regulators, by small molecules has been a long standing challenge to establish small molecule based reprogramming for the generation of human chemically induced pluripotent stem cells (hciPSCs). Using a cell-based high throughput screen, we have previously identified a new series of OCT4-inducing compounds (O4Is). In this paper, we prepared metabolically stable analogues, including O4I4, which strongly activate pluripotency-associated signaling. In combination with a transcription factor cocktail of SOX2, KLF4, MYC, and LIN28 (collectively referred to as CSKML) we achieved to reprogram human fibroblasts into a stable and authentic pluripotent state independent of exogenous OCT4. Transcriptomic analysis of fibroblasts reprogrammed by this approach revealed that O4I4 activated bone morphogenetic protein (BMP)/SMAD/ID signaling at the early stage of reprogramming and subsequent expression of the chromatin modifier, high mobility group A1 (HMGA1), resulting in re-activation of endogenous OCT4 to initiate the reprogramming process. Consistently, chemical or genetic inhibition of BMP/SMAD/ID or HMGA1 was found to block cellular reprogramming. In C.elegans and Drosophila, O4I4 expanded life spans in a BMP-signaling pathway-dependent manner. Given limitations of OCT4-based reprogramming, our findings provide an alternative to OSKM-mediated iPSC generation, and importantly unravel previously-unrecognized molecular mechanisms of pluripotency in the context of regenerative medicine and rejuvenation therapy. RNA was obtained from treated and non-treated human fibroblast and fibroblast-derived induced Pluripotent Stem Cells and treated with an episomal constrcuts of Oct4, Sox2, Klf4 and c-Myc in addition to O4I3