DNA damage response activation in mouse embryonic fibroblasts undergoing replicative senescence and following...

Area of Science:

• Molecular Biology
• Cell Biology
• Genetics

Background:

• Primary mouse embryonic fibroblasts (MEFs) are widely used in research but undergo replicative senescence, limiting their utility.
• The precise molecular mechanisms driving cell cycle arrest and senescence in MEFs remain incompletely understood.

Purpose of the Study:

• To elucidate the molecular mechanisms underlying replicative cellular senescence in primary mouse embryonic fibroblasts (MEFs).
• To investigate the role of the DNA damage response (DDR) and ATM kinase in MEF senescence.

Main Methods:

• Analysis of DNA damage response (DDR) markers, including ATM, phosphorylated substrates, and gammaH2AX, in senescent MEFs.
• Comparison of MEF proliferation and senescence under standard versus low oxygen (3% O2) conditions.
• Assessment of senescence escape and cell cycle progression following ATM inactivation in senescent MEFs.

Main Results:

• A robust DNA damage response (DDR) is activated during replicative senescence in MEFs, characterized by senescence-associated DDR foci (SDFs).
• DDR markers do not specifically localize to telomeres in senescent MEFs.
• Culturing MEFs at low oxygen tension (3% O2) inhibits DDR activation and prevents senescence.
• Inactivation of ATM kinase in senescent MEFs permits escape from senescence and allows S-phase progression.
• Spontaneously immortalized MEFs exhibit markers of activated DDR, indicating underlying chromosomal DNA damage.

Conclusions:

• Replicative cellular senescence in MEFs is driven by an ATM kinase-mediated DNA damage checkpoint.
• ATM activation and subsequent DDR are critical for inducing proliferation arrest in senescent MEFs.
• Chromosomal DNA damage may be a common feature in both senescent and spontaneously immortalized MEFs.