Protein variations associated with in vitro aging of human fibroblasts and quantitative limits on the error...

Two-dimensional electrophoresis was used to examine protein alterations associated with in vitro cellular aging. Patterns of cellular proteins from early and late passage human fibroblasts of two strains (normal and trisomy 21) were analyzed in silver-stained gels and autoradiograms with computerized microdensitometry. Four proteins were significantly altered in density in both cell strains. In late passage cells, these proteins were from 6 to 66% the density in early passage cells. The error catastrophe hypothesis predicts that random amino acid substitutions accumulate with cellular aging. No new proteins or satellite spots due to such substitutions, however, were detected in late passage cells. An upper bound of 2.5% was set by high resolution densitometry for the fraction of abnormal protein that could be present but undetected by these methods.