Altered protein metabolism in arrested populations of aging human diploid fibroblasts

Protein synthesis and turnover were measured in human diploid fibroblasts which were arrested in an essentially nonmitotic state by reducing the serum concentration in the incubation medium to 0.5%. Through the first 4 days of the arrested period both early and late passage cells lost about 20% of their cellular protein. There was a reduction in the rate of protein synthesis at both passage levels during this period, but there was no significant age-related difference in the synthetic rate or the rate of protein turnover. After day 4 both early and late passage cells maintained a constant protein content, but late passage cells did this while processing more protein through faster rates of both synthesis and turnover than did early passage cells. These results support those theories of cellular senescence which predict altered protein metabolism as a major consequence of the aging process.