Protein oxidative modifications and replicative senescence of WI-38 human embryonic fibroblasts.

The age-related accumulation of oxidized proteins is dependent on the balance between the generation of oxidatively modified proteins and their elimination by protein degradation and repair systems. Previous studies have demonstrated that replicative senescence represents a valid model of in vitro aging and that senescent cells do accumulate oxidized proteins while both proteasome, which is the major intracellular proteolytic system implicated in the removal of abnormal and oxidized proteins, and the oxidized protein-repair enzymes, methionine sulfoxide reductases, are being impaired. Declining proteasome activity with age has been attributed to decreased proteasome subunits expression and/or inactivation upon alteration of proteasome subunits, as well as accumulation of endogeneous inhibitors, such as highly oxidized and cross-linked proteins.