Decline of poly(ADP-ribosyl)ation during in vitro senescence in human diploid fibroblasts

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Abstract
Poly(ADP‐ribose) polymerase activity was determined at various times during the in vitro life span of two human diploid fibroblast‐like cell lines of different donor ages. The cell lines differed in their ability to transfer ADP‐ribose, with cells from an embryonic donor exhibiting 2 to 3 times the activity found in cells obtained from a newborn donor. The activity in both cell lines decreased by 30–60% as the cells moved through their in vitro life spans. The decline could not be attributed to increases in glycohydrolase or the leakage of polymerase from older cell preparations. Enzyme activation with DNase I indicated that similar levels of enzyme were present in both cell lines at all in vitro ages. These results indicate that although poly(ADP‐ribosyl)ation is inversely related to donor age as well as in vitro age the decrease is in response to other factors which change with increasing age.