Dynamics of Telomere Rejuvenation During Chemical Induction to Pluripotent Stem Cells

Chemical induced pluripotent stem cells (CiPSCs) have been successfully achieved and may provide an alternative and attractive source for stem cell-based therapy. Sufficient telomere lengths are critical for unlimited self-renewal and genomic stability of pluripotent stem cells. Dynamics of telomere reprogramming and whether and how telomeres are sufficiently elongated in the CiPSCs have remained to be understood. We show that CiPSCs acquire telomere lengthening with increasing passages after clonal formation. Both telomerase activity and recombination-based mechanisms are involved in the telomere elongation. Telomere lengths strongly indicate the degree of reprogramming, pluripotency and differentiation capacity of CiPSCs. Nevertheless, telomere damage and shortening occur at late stage of lengthy induction, limiting CiPSC formation. Recombination mechanism is not activated during induction until CiPSC clonal formation and passages. We find that histone crotonylation induced by crotonic acid can activate two-cell genes including Zscan4, alleviate telomere damage and shortening during induction and promote CiPSC generation. Moreover, crotonylation decreases abundance of heterochromatic H3K9me3 and HP1a at subtelomeres and Zscan4 loci. Taken together, telomere rejuvenation links to reprogramming and pluripotency of CiPSCs. Crotonylation facilitates telomere maintenance and enhances chemical induced reprogramming to pluripotency.