Senescence impairs successful reprogramming to pluripotent stem cells

Abstract

Somatic cells can be reprogrammed into induced pluripotent stem (iPS) cells by overexpressing combinations of factors such as Oct4, Sox2, Klf4, and c-Myc. Reprogramming is slow and stochastic, suggesting the existence of barriers limiting its efficiency. Here we identify senescence as one such barrier. Expression of the four reprogramming factors triggers senescence by up-regulating p53, p16INK4a , and p21 CIP1. Induction of DNA damage response and chromatin remodeling of the INK4a/ARF locus are two of the mechanisms behind senescence induction. Crucially, ablation of different senescence effectors improves the efficiency of reprogramming, suggesting novel strategies for maximizing the generation of iPS cells.Supplemental material is available at http://www.genesdev.org.

The emerging role of p53 in stem cells

“…At least two of the four reprogramming genes (c-myc and klf-4) are very well-known oncogenes that are able to activate a checkpoint response. Expression of the reprogramming genes, inserted either in combination or alone, induces a complex response involving upregulation of gH2AX, p53, p21, p16 and p15 and leads to a senescent phenotype, characterized by low BrdU incorporation, representative of low levels of DNA replication, and high bGal staining, indicating senescence [21,22]. Importantly, one of the first events occurring during reprogramming seems to be the epigenetic silencing of the ink4a locus, which encodes p16 and p19arf.…”

“…These proteins are positive regulators of the pRb and p53 tumor suppressor pathways, respectively. However, the p53 pathway seems more relevant to the reprogramming of mouse cells, whereas pRb is more important in human cells [21,22]. Notably, telomere shortening, which is known to induce a p53 response, is also able to counteract the reprogramming process [23].…”

Mechanism and methods to induce pluripotency

“…Only a few cells can overcome this barrier and become iPSCs. A number of studies demonstrated that when key components (such as p53 and p21) of the DNA damage pathway were deleted, the percentage of iPS cell generation significantly increased (Zhao et al, 2008a;Banito et al, 2009;Hong et al, 2009;Kawamura et al, 2009;Li et al, 2009;Marión et al, 2009;Utikal et al, 2009b). Suppression of the p53 pathway may compromise a cell's genome stability.…”

“…As the DNA damage pathway poses a major barrier towards regaining pluripotency (Zhao et al, 2008b;Banito et al, 2009;Hong et al, 2009;Kawamura et al, 2009;Li et al, 2009;Marión et al, 2009;Utikal et al, 2009b), chemical compounds that alleviate the stress of DNA damage response may help cells to overcome this barrier. To this end, Vitamin C has been shown to significantly increase the formation of both mouse and human iPSC by suppressing p53 induced cell senescence (Esteban et al, 2010).…”

Reprogramming and Carcinogenesis—Parallels and Distinctions

“…They indicate that GSK3-inhibitor can replace the reprogramming-related effects of Sox2 transcription factor (Banito et al, 2009). …”