Senescence impairs successful reprogramming to pluripotent stem cells
Author(s)
Banito, Ana Cristina Tome Moita
Type
Thesis
Abstract
Somatic cells can be reprogrammed into induced pluripotent stem (iPS) cells
by overexpression of combinations of transcription factors such as Oct4, Sox2, Klf4
and c-Myc. However, reprogramming is slow and stochastic, suggesting the
existence of mechanisms that limit its efficiency. Senescence is an irreversible G1
cell cycle arrest elicited by replicative exhaustion or in response to stresses such as
DNA damage, or aberrant expression of oncogenes. The arrest observed during
senescence is implemented mainly through activation of p53 and the upregulation of
the cyclin-dependent kinase (CDK) inhibitors, p16INK4a and p21Cip1.
In this work the relation between the process of reprogramming to iPS cells
and senescence was investigated. The expression of the 4 reprogramming factors
from a polycistronic vector in human fibroblasts (IMR90) was shown to induce cell
cycle arrest and upregulation of p53, p16INK4a and p21Cip1. Reprogramming-induced
senescence (RIS) results from the activation of a DNA damage response, and
chromatin remodeling of the INK4a/ARF locus, as shown by a decrease in the levels
of the H3K27me3 modification following expression of the reprogramming factors.
RIS resembles a stress response, which parallels oncogene-induced senescence,
however context-dependent differences may also contribute as shown by the fact
that ES cells-specific miRNAs can partially bypass RIS. Additionally when
expressed individually, each reprogramming factor was shown to have a negative
effect over the proliferation of somatic cells.
Since reprogramming initially triggers a stress response with characteristics
of senescence it may act as an initial barrier limiting the efficiency of the process.
Indeed, ablation of different senescence effectors improved the efficiency of
reprogramming, both in mouse and human cells. Additionally, the polycomb protein
CBX7 was also shown to increase reprogramming efficiency in a process that may
partially dependent on repression of the INK4a/ARF locus. The senescence
response to expression of reprogramming factors uncovers an important barrier to
induced pluripotency but also highlights the importance of tumour suppressor
pathways in preventing dedifferentiation during tumorigenesis. Identification of RIS
mediators may help to understand this connection and provide safer approaches to
increase reprogramming efficiency.
by overexpression of combinations of transcription factors such as Oct4, Sox2, Klf4
and c-Myc. However, reprogramming is slow and stochastic, suggesting the
existence of mechanisms that limit its efficiency. Senescence is an irreversible G1
cell cycle arrest elicited by replicative exhaustion or in response to stresses such as
DNA damage, or aberrant expression of oncogenes. The arrest observed during
senescence is implemented mainly through activation of p53 and the upregulation of
the cyclin-dependent kinase (CDK) inhibitors, p16INK4a and p21Cip1.
In this work the relation between the process of reprogramming to iPS cells
and senescence was investigated. The expression of the 4 reprogramming factors
from a polycistronic vector in human fibroblasts (IMR90) was shown to induce cell
cycle arrest and upregulation of p53, p16INK4a and p21Cip1. Reprogramming-induced
senescence (RIS) results from the activation of a DNA damage response, and
chromatin remodeling of the INK4a/ARF locus, as shown by a decrease in the levels
of the H3K27me3 modification following expression of the reprogramming factors.
RIS resembles a stress response, which parallels oncogene-induced senescence,
however context-dependent differences may also contribute as shown by the fact
that ES cells-specific miRNAs can partially bypass RIS. Additionally when
expressed individually, each reprogramming factor was shown to have a negative
effect over the proliferation of somatic cells.
Since reprogramming initially triggers a stress response with characteristics
of senescence it may act as an initial barrier limiting the efficiency of the process.
Indeed, ablation of different senescence effectors improved the efficiency of
reprogramming, both in mouse and human cells. Additionally, the polycomb protein
CBX7 was also shown to increase reprogramming efficiency in a process that may
partially dependent on repression of the INK4a/ARF locus. The senescence
response to expression of reprogramming factors uncovers an important barrier to
induced pluripotency but also highlights the importance of tumour suppressor
pathways in preventing dedifferentiation during tumorigenesis. Identification of RIS
mediators may help to understand this connection and provide safer approaches to
increase reprogramming efficiency.
Date Issued
2011-03
Date Awarded
2011-05
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
Advisor
Gil, Jesus
Sponsor
Fundação para a Ciência e a Tecnologia
Creator
Banito, Ana Cristina Tome Moita
Publisher Department
Medcine
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)