Comparison by autoradiography of macromolecular biosynthesis in "young" and "old" human diploid fibroblast cultures....

The biosynthetic abilities of WI-38 fibroblasts from early and late population-doubling-level cultures were compared by autoradiography of cells grown with labeled precursors of DNA, RNA, protein and lipids. Incorporation of radioactive thymidine, uridine, protein-hydrolysate, acetate, oleic acid and cholesterol, as measured by the number of grains per cell surface, decreased with the progressive aging of the culture. However, the decrease in the incorporation of acetate, oleic acid and cholesterol was much smaller than that of the other precursors, indicating that lipid synthesis is affected to a lesser degree than protein and nucleic acid synthesis on aging. This result is in accord with the higher lipid content and proliferation of intracellular membranes in cells of "old" WI-38 cultures reported by others.