Telomeres Acquire Embryonic Stem Cell Characteristics in Induced Pluripotent Stem Cells

Abstract

Telomere shortening is associated with organismal aging. iPS cells have been recently derived from old patients; however, it is not known whether telomere chromatin acquires the same characteristics as in ES cells. We show here that telomeres are elongated in iPS cells compared to the parental differentiated cells both when using four (Oct3/4, Sox2, Klf4, cMyc) or three (Oct3/4, Sox2, Klf4) reprogramming factors and both from young and aged individuals. We demonstrate genetically that, during reprogramming, telomere elongation is usually mediated by telomerase and that iPS telomeres acquire the epigenetic marks of ES cells, including a low density of trimethylated histones H3K9 and H4K20 and increased abundance of telomere transcripts. Finally, reprogramming efficiency of cells derived from increasing generations of telomerase-deficient mice shows a dramatic decrease in iPS cell efficiency, a defect that is restored by telomerase reintroduction. Together, these results highlight the importance of telomere biology for iPS cell generation and functionality.

Zscan4 promotes genomic stability during reprogramming and dramatically improves the quality of iPS cells as demonstrated by tetraploid complementation

“…These findings may also partially explain why NT can faithfully reprogram somatic cells into ES cells [5,8,20,21,42]. In contrast, during somatic reprogramming induced by the Yamanaka factors, telomere elongation is primarily mediated by telomerase [59,60]. Endogenous Zscan4 is not activated during the early stages of reprogramming induced by OKSM or OSK, as shown in our study (Supplementary information, Figure S1F) and in other report [38], further supporting the hypothesis that telomerase activity is the primary mechanism of telomere re-elongation regulation during OSKM-or OSK-mediated reprogramming.…”

“…Endogenous Zscan4 is not activated during the early stages of reprogramming induced by OKSM or OSK, as shown in our study (Supplementary information, Figure S1F) and in other report [38], further supporting the hypothesis that telomerase activity is the primary mechanism of telomere re-elongation regulation during OSKM-or OSK-mediated reprogramming. However, telomere extension by telomerase is a slow process and requires a number of cell divisions to restore a normal average telomere length [59,61]. The delay in telomere extension by telomerase alone may not properly protect the genome, especially during the early stages of reprogramming when most epigenetic reprogramming events occur.…”

Blockade of senescence‐associated micro RNA ‐195 in aged skeletal muscle cells facilitates reprogramming to produce induced pluripotent stem cells.

“…For example, reprogramming can trigger an increase in telomere length in cells of both old mice and humans, reversing the erosion characteristics of aged and senescent cells. However, whether the resulting iPSCs can maintain their telomere length over long‐term passages is still subject to debate (Marion et al ., 2009; Vaziri et al ., 2010). The epigenetic state of iPSCs derived from old donors is another aspect of reprogramming‐induced rejuvenation that has not been investigated thoroughly.…”

“…TERT is required for elongating telomeres during the reprogramming process, and telomere shortening represents a potent barrier against iPSCs generation in telomerase‐deficient mice (Marion et al ., 2009). Donor cells that are difficult to be reprogrammed can be more efficiently induced into the pluripotent state by including TERT and SV40 large T antigen with the four Yamanaka factors, highlighting the critical role of TERT in period of iPSC generation (Park et al ., 2008).…”

Transcriptional regulation of telomeric non-coding RNA: Implications on telomere biology, replicative senescence and cancer

“…9 Induced pluripotent stem cells produced by MEF reprogramming have shown telomerase-dependent telomere elongation together with increased amount of TERRA. 15 Furthermore, in telomerase (TERC)-knockout MEFs at second and fifth generation, the progressive telomere shortening has led to a reduction in TERRA levels despite an open chromatin conformation as a result of a reduced density of H3K9 and H4K20 trimethylation and elevated levels of H3 and H4 acetylation. 9,16 In human diploid fibroblasts (HDFs) undergoing replicative senescence, the telomere shortening was also found to correlate directly with decreasing levels of TERRA and H3K4 by telomeres on reporter genes inserted at subtelomeric loci, a phenomenon known as telomere position effect (TPE), led to the idea that telomeres were devoid of any transcriptional activity.…”