MODIFICATIONS OF PROTEOGLYCANS PRODUCED BY HUMAN SKIN FIBROBLAST-CULTURES DURING REPLICATIVE SENESCENCE

The properties of proteoglycans (PGs) produced by normal human skin fi broblasts were investigated with increasing passage. The increase of s ubculture number was associated with a constant increase in PG molecul ar size, which was particularly evident in cell layer extracts. In the cell layer, the ratio of DS-PGs/HS-PGs was markedly higher in early p assage cultures. Moreover, the cell layer from young cells contained l ower amounts of radioactivity incorporated into the most hydrophobic P G populations, suggesting that the PG core protein might also undergo significant modification with increasing subcultures. There was no sig nificant difference in energy charge value between early and late pass age cultures, whereas the NAD/NADH ratio was found to decrease markedl y in senescent cells.