First name
Francesca
Last name
Rossiello
Year of Study
Thesis Title
Persistent DNA damage at telomeres, caused by trf2-mediated DNA repair inhibition, Triggers cellular senescence and is associated with primates ageing
Thesis Abstract
The DNA damage response (DDR) coordinates DNA repair events and transiently arrests cell-cycle progression until DNA damage has been removed. If the damage is not resolved, cells can enter an irreversible cell cycle arrest called cellular senescence.
In irradiation-induced senescent cells a large fraction of persistent DDR markers are associated with telomeric DNA, both in cultured cells and in in vivo tissues. The aim of my PhD project was to investigate the mechanism underlying this phenomenon. I showed that persistent DDR activation has a causative role for the senescence-associated cell cycle exit and that a double-strand break (DSB) within telomeric repeats is inducing a more protracted DDR activation compared with a nontelomeric one in human cells. The DDR persistency at telomeres is neither dependent on their heterochromatic state nor on TRF2 loss from telomeres during senescence establishment. Rather, TRF2 recruitment next to a DSB, in the absence of telomeric DNA, is sufficient to induce a more protracted site-specific DDR focus and to impair DSB repair in mouse cells. Ageing is associated with accumulation of markers of DDR activation. In terminally differentiated brain neurons from old primates, I observed DDR activation at telomeres that were not critically short. Taken together, these results strongly suggest that TRF2 inhibits DNA repair at broken telomeres, contributing to the accumulation of unrepaired, DDR-positive telomeres during ageing. This can in turn trigger cellular senescence and impair tissue homeostasis providing a mechanism for ageing also in non-proliferating tissues.
In irradiation-induced senescent cells a large fraction of persistent DDR markers are associated with telomeric DNA, both in cultured cells and in in vivo tissues. The aim of my PhD project was to investigate the mechanism underlying this phenomenon. I showed that persistent DDR activation has a causative role for the senescence-associated cell cycle exit and that a double-strand break (DSB) within telomeric repeats is inducing a more protracted DDR activation compared with a nontelomeric one in human cells. The DDR persistency at telomeres is neither dependent on their heterochromatic state nor on TRF2 loss from telomeres during senescence establishment. Rather, TRF2 recruitment next to a DSB, in the absence of telomeric DNA, is sufficient to induce a more protracted site-specific DDR focus and to impair DSB repair in mouse cells. Ageing is associated with accumulation of markers of DDR activation. In terminally differentiated brain neurons from old primates, I observed DDR activation at telomeres that were not critically short. Taken together, these results strongly suggest that TRF2 inhibits DNA repair at broken telomeres, contributing to the accumulation of unrepaired, DDR-positive telomeres during ageing. This can in turn trigger cellular senescence and impair tissue homeostasis providing a mechanism for ageing also in non-proliferating tissues.
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