Accumulation of single-strand breaks is the major cause of telomere shortening in human fibroblasts

Free Radic Biol Med. 2000 Jan 1;28(1):64-74. doi: 10.1016/s0891-5849(99)00207-5.


Telomere shortening triggers replicative senescence in human fibroblasts. The inability of DNA polymerases to replicate a linear DNA molecule completely (the end replication problem) is one cause of telomere shortening. Other possible causes are the formation of single-stranded overhangs at the end of telomeres and the preferential vulnerability of telomeres to oxidative stress. To elucidate the relative importance of these possibilities, amount and distribution of telomeric single-strand breaks, length of the G-rich overhang, and telomere shortening rate in human MRC-5 fibroblasts were measured. Treatment of nonproliferating cells with hydrogen peroxide increases the sensitivity to S1 nuclease in telomeres preferentially and accelerates their shortening by a corresponding amount as soon as the cells proliferate. A reduction of the activity of intracellular peroxides using the spin trap alpha-phenyl-t-butyl-nitrone reduces the telomere shortening rate and increases the replicative life span. The length of the telomeric single-stranded overhang is independent of DNA damaging stresses, but single-strand breaks accumulate randomly all along the telomere after alkylation. The telomere shortening rate and the rate of replicative aging can be either accelerated or decelerated by a modification of the amount of oxidative stress. Quantitatively, stress-mediated telomere damage contributes most to telomere shortening under standard conditions.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alkylation
  • Cell Cycle
  • Cells, Cultured
  • Cellular Senescence / physiology*
  • DNA Damage*
  • DNA Replication
  • DNA, Single-Stranded / metabolism*
  • Fibroblasts / drug effects
  • Fibroblasts / metabolism
  • Fibroblasts / ultrastructure*
  • Humans
  • Hydrogen Peroxide / toxicity*
  • Oxidants / toxicity*
  • Oxidative Stress
  • Reactive Oxygen Species / metabolism
  • Spin Labels
  • Telomere / metabolism
  • Telomere / ultrastructure*


  • DNA, Single-Stranded
  • Oxidants
  • Reactive Oxygen Species
  • Spin Labels
  • Hydrogen Peroxide