Disappearance of the telomere dysfunction-induced stress response in fully senescent cells

Area of Science:

• Cell Biology
• Molecular Biology
• Genetics

Background:

• Replicative senescence acts as a natural barrier to cellular proliferation.
• Telomere erosion and dysfunction are key triggers of senescence.
• ATM activation and H2AX-gamma foci are potential indicators of cellular stress.

Purpose of the Study:

• To investigate ATM activation and H2AX-gamma focus formation as markers of telomere dysfunction.
• To determine if telomere dysfunction is sufficient to induce ATM activation.
• To understand the role of constitutive signaling in maintaining senescence.

Main Methods:

• Primary human fibroblasts were cultured to early and late passages.
• Telomerase was ectopically expressed in late-passage cells.
• ATM activation and H2AX-gamma foci were assessed.
• TRF2 binding to telomeres was inhibited in quiescent fibroblasts.

Main Results:

• ATM activation and H2AX-gamma foci were significantly increased in late-passage fibroblasts compared to early-passage cells.
• Ectopic telomerase expression reduced ATM activation and H2AX-gamma foci in late-passage cells.
• Inhibition of TRF2 binding to telomeres induced ATM activation in quiescent fibroblasts.
• ATM activation and H2AX-gamma foci diminished in fully senescent cells.

Conclusions:

• ATM activation and H2AX-gamma foci are sensitive markers of telomere dysfunction in human fibroblasts.
• Telomere uncapping, not chromosome breakage, is sufficient to initiate the telomere signaling response.
• Constitutive signaling from dysfunctional telomeres is not required for the maintenance of replicative senescence.