Telomere erosion varies during in vitro aging of normal human fibroblasts from young and adult donors

The life span of normal fibroblasts in vitro (Hayflick limit) depends on do nor age, and telomere shortening has been proposed as a potential mechanism , By quantitative fluorescence irt situ hybridization and Southern blot ana lysis, we show progressive telomere loss to about 5 kb mean telomere restri ction fragment length in fibroblasts from two adult donors within 40 popula tion doublings, whereas in fibroblasts from two infant donors, telomere ero sion is reduced, leaving a mean telomere restriction fragment length of sim ilar to 7 kb at senescence (after similar to 60 population doublings). Agin g of fibroblasts from both infant and adult donors was not accompanied by c hromosomal abnormalities but was correlated with increased telomere repeat- binding factor 2 expression at both the protein and transcriptional level.