Effects of the number of cell divisions and of added isologous nucleic acids on ageing of normal human fibroblasts in vitro.

Abstract

It is a matter of debate if the life span of a normal cell strain in vitro depends on the number of cell divisions passed or simply on metabolic time in culture. We have cultured sub-strains of the same normal human foetal fibroblast strain, separated but in a common dish with a common medium. One sub-strain was forced by infrequent transfers to grow slowly, the other was transferred frequently and grew freely. At intervals, cell kinetics of the strains was registered by time-lapse photography. The results indicate that ageing in vitro, manifested by changes of cell kinetics, and the total life span in vitro for normal human fibroblasts are dependent on the number of passed cell divisions, supporting the idea of a progressive decay of the transcription mechanism. A trial to postpone ageing of normal human foetal fibroblasts in vitro was made by adding nucleic acids, extracted from other organs of the same ovum, to the medium for 7 to 14 transfers. Four to 18 transfers after the end of the treatment, the cells still revealed a kinetic pattern typical of much younger normal strains, pointing to an influence on the genes. The effect is probably due to the DNA of the nucleic acid extract.