A Key Role for Telomerase Reverse Transcriptase Unit in Modulating Human Embryonic Stem Cell Proliferation, Cell Cycle Dynamics, and In Vitro Differentiation

Abstract

Embryonic stem cells (ESC) are a unique cell population with the ability to self-renew and differentiate into all three germ layers. Human ESC express the telomerase reverse transcriptase (TERT) gene and the telomerase RNA (TR) and show telomerase activity, but TERT, TR, and telomerase are all downregulated during the differentiation process. To examine the role of telomerase in human ESC self-renewal and differentiation, we modulated the expression of TERT. Upregulation of TERT and increased telomerase activity enhanced the proliferation and colony-forming ability of human ESC, as well as increasing the S phase of the cell cycle at the expense of a reduced G1 phase. Upregulation of TERT expression was associated with increases in CYCLIN D1 and CDC6 expression, as well as hyperphosphorylation of RB. The differentiated progeny of control ESC showed shortening of telomeric DNA as a result of loss of telomerase activity. In contrast, the differentiated cells from TERToverexpressing ESC maintained high telomerase activity and accumulated lower concentrations of peroxides than wild-type cells, implying greater resistance to oxidative stress. Although the TERT-overexpressing human ESC are able to form teratoma composed of three germ layers in vivo, their in vitro differentiation to all primitive and embryonic lineages was suppressed. In contrast, downregulation of TERT resulted in reduced ESC proliferation, increased G1, and reduced S phase. Most importantly, downregulation of TERT caused loss of pluripotency and human ESC differentiation to extraembryonic and embryonic lineages. Our results indicate for the first time an important role for TERT in the maintenance of human ESC pluripotency, cell cycle regulation, and in vitro differentiation capacity.

Downregulation of Multiple Stress Defense Mechanisms During Differentiation of Human Embryonic Stem Cells

“…Thus, downregulation of telomerase during differentiation, as well as nuclear exclusion during stress and senescence, might have a causal effect on mitochondrial ROS production. In fact, overexpression of TERT in mESC [11] and hESC [48] decreased ROS production during differentiation, thus suggesting an intrinsic link between these two maintenance functions [11]. Also, both telomerase expression and ROS levels do influence DNA damage repair activities, as shown by global gene expression and functional studies [23,34].…”

Association of telomere length with authentic pluripotency of ES/iPS cells

“…The telomere length of human chromosomes, typically 5-15 kb [36], is much shorter than that of mouse chromosomes, and human ESCs are more sensitive than mouse ESCs to telomerase deficiency and telomere shortening [48]. Prematurely aged (shortened) telomeres are a common feature of human iPSCs created by current pluripotency protocols [24].…”

Physiological and molecular characterisation of cadmium stress in Schmidtea mediterranea

“…erase activity of stem cells can protect these cells to the effects of oxidative stress, one of the most important cadmium-induced effects (Yang et al, 2008). As a trigger of both (uncontrolled) cell proliferation and repair, the redox status of the organisms was evaluated to further elucidate this ambiguity .…”