Functional Failures of Cultured Human Diploid Fibroblasts After Continued Population Doublings 1

Conclusions and Summary

Cell populations which were karyologically normal and which were capable of a normal rate of cell division apparently lost much of their ability to synthesize collagen and to induce col-lagenolytic activity after approximately 37 to 39 doublings. This loss of at least two fibroblastic functions prior to either the loss of the ability to divide or to the appearance of significant changes in the karyology of these cells suggest that other cell functions might also be altered as human diploid cells near the end of their in vitro life time (Phase III). Fewer cell doublings can be expected from fibroblasts derived from adult tissue (6). Consequently caution should be exercised when interpreting the results of metabolic studies on embryonic cells that have doubled many times or cells grown out of explants from adult tissues which had been allowed to double even a relatively small number of times.