Morphologic changes accompanying senescence of cultured human diploid cells.

The lysosomes of serially propagated human fibroblasts gradually transform to residual bodies which increase in number and size, and show progressive degenerative changes. There is an accompanying, and less regular, decrease in the number of cytoplasmic polyribosomes and an increased number of glycogen particles. The onset of these morphologic alterations occurs shortly after culture initiation and precedes any marked decrease in the rate of cellular growth; however, in their extreme form these changes may be related to the ultimate cessation of cellular multiplication ("senescence"). The lysosomal changes were seen only in those cell strains which eventually showed senescence, and were absent or minimal either in cell lines which can be propagated indefinitely ("spontaneous" and viral transformants, cancer cells), or in skin sections from aging subjects.