Cellular senescence induces replication stress with almost no affect on DNA replication timing

Abstract

Organismal aging entails a gradual decline of normal physiological functions and a major contributor to this decline is withdrawal of the cell cycle, known as senescence. Senescence can result from telomere diminution leading to a finite number of population doublings, known as replicative senescence (RS), or from oncogene overexpression, as a protective mechanism against cancer. Senescence is associated with large-scale chromatin re-organization and changes in gene expression. Replication stress is a complex phenomenon, defined as the slowing or stalling of replication fork progression and/or DNA synthesis, which has serious implications for genome stability, and consequently in human diseases. Aberrant replication fork structures activate the replication stress response leading to the activation of dormant origins, which is thought to be a safeguard mechanism to complete DNA replication on time. However, the relationship between replicative stress and the changes in the spatiotemporal program of DNA replication in senescence progression remains unclear. Here, we studied the DNA replication program during senescence progression in proliferative and pre-senescent cells from donors of various ages by single DNA fiber combing of replicated DNA, origin mapping by sequencing short nascent strands and genome-wide profiling of replication timing (TRT). We demonstrate that, progression into RS leads to reduced replication fork rates and activation of dormant origins, which are the hallmarks of replication stress. However, with the exception of a delay in RT of the CREB5 gene in all pre-senescent cells, RT was globally unaffected by replication stress during entry into either oncogene-induced or RS. Consequently, we conclude that RT alterations associated with physiological and accelerated aging, do not result from senescence progression. Our results clarify the interplay between senescence, aging and replication programs and demonstrate that RT is largely resistant to replication stress.

Cellular aging beyond cellular senescence: Markers of senescence prior to cell cycle arrest in vitro and in vivo

“…Increase in cell cycle duration as well as the abovementioned changes in metabolism of primary cells is among the main inducers of replication stress (Magdalou et al, 2014). Consistently, hallmarks of replication stress have been shown for primary cells approaching Hayflick limit (Rivera‐Mulia et al, 2018).…”

Replication timing networks reveal a link between transcription regulatory circuits and replication timing control

“…In this study, we introduced a new approach to construct gene regulatory networks, exploiting the dynamic changes in DNA RT during lineage specification. RT is cell-type-specific Ryba et al 2011;Rivera-Mulia et al 2015); regulation of RT is critical to maintain genome stability (Donley et al 2013;Neelsen et al 2013;Alver et al 2014); and abnormal RT is observed in disease (Ryba et al 2012;Gerhardt et al 2014;Rivera-Mulia et al 2017, 2018bSasaki et al 2017). RT is closely related to the spatiotemporal organization of the genome with early and late replicating domains segregating to distinct nuclear compartments (Pope et al 2014;Rivera-Mulia and Gilbert 2016b).…”

DNA methylation in genes of longevity-regulating pathways: association with obesity and metabolic complications

“…A second differentially methylated site is cg11301281, which exhibits a negative association with age and is located in the 5´ UTR of CREB5 gene. CREB5 encodes cyclic AMP-responsive element binding protein 5, a key factor in cell growth, proliferation, differentiation and cell cycle control [53]. Up-regulation of CREB5 is associated with metastatic process [54], inflammatory response genes and modulation of immune responses [55–57].…”