Changes in DNA Double Strand Break (DSB) Repair During Cellular Aging

Student Researcher:
Karolin Klement

Supervisor / Principle Investigator:
Dr. Susan Lees-Miller

Additional Authors:
Dr. Susan Lees-Miller
Dr. Karl Riabowol

MD Class of 2022


Cellular Senescence is a permanent cell cycle arrest induced by telomere shortening or prematurely due to severe stress. Exposure of cells to DNA damaging agents leads to the recognition of the DNA ends as double strand breaks (DSBs). Normally, cells have very efficient mechanisms to repair DSBs. However, an increased number of DSBs have been found in replicative senescent cells as well as prematurely aged cells. It is unclear whether these DSBs originated from endogenous or exogenous damage and why these DSBs persist.

Since some studies suggested that even one un-repaired break can trigger senescence, the goal of my project is to understand the underlying mechanisms of why and how DNA repair is altered in senescent cells.

To analyze the capability of senescent cells to repair exogenous DNA damage, DSB repair kinetics after ionizing radiation was investigated. Generally, DSBs induced by 1-4 Gray of ionizing radiation, such as γ-irradiation, are repaired within 48 hours. Young and senescent primary human fibroblasts were irradiated and repair kinetics monitored using the universal DSB marker γH2AX (H2AX phosphorylated at S139).

Preliminary results suggest that ~10-15% of induced DSB are not repaired after 48 hours in senescent cells, compared to ~1% in young or quiescent cells. These results indicate that despite repair proteins being abundant in senescent cells, the repair pathways might be compromised or certain key players downregulated or inactivated, which leads to the accumulation of un-repaired DSBs in senescent cells.