Evidence for a relationship between longevity of mammalian species and life spans of normal fibroblasts in vitro and erythrocytes in vivo

Cellular theories of aging as related to the liver

The age-associated decline in function of several organs, including the liver, may be caused by mechanisms operating on the cellular level. Fibroblasts and several other cell types derived from normal individuals have limited lifespans in culture, and several abnormalities described for senescent cultured fibroblasts also apply to hepatocytes and other cell types obtained from aged organisms. Cellular theories of aging can be divided into two broad and overlapping categories: (a) those that view cell death as an actively programmed developmental process, and (b) those that consider cellular aging to result from a passive accumulation of errors in macromolecules. These theories are not necessarily mutually exclusive, and many of the phenotypic changes in senescent hepatocytes, fibroblasts and other cells are compatible with several different theories. The challenge for the future is to distinguish primary causes from secondary consequences of cellular aging so that rational attempts to intervene in the aging process are possible.

Gamma-radiation induced ADP-ribosyl transferase activity and mammalian longevity

The levels of ADP-ribosyl transferase (ADPRT) activity following a standardized dose of 100 Gy gamma-radiation have been determined in leukocytes from 12 different mammalian species. Here, we report that the 100 Gy-induced levels of ADPRT correlated in a highly significant manner to the line spans of the mammals.

Increased DNA topoisomerase I activity in aging human cell chromatin

Chromatin-associated DNA topoisomerase I activity was measured in human diploid fibroblasts during in vitro aging. No difference was detected as a function of cell age in the nicking and the closing activities of the DNA-unwinding enzyme. The capacity of type-I topoisomerase to relax superhelical DNA molecules was, however, increased in aged cells. An age-related increase in nucleoprotein content was also observed.

A quantitative analysis of the aging of human glial cells in culture

The kinetics of aging of normal human diploid brain cells in culture have been determined using the miniclone technique in which cells are cloned in the presence of a large number of other cells. The miniclone technique records the behaviour of every viable cell in the sample, not merely those cells capable of forming visible clones. This technique permits the direct measurement of the reproductive potential of individual cells growing in bulk culture and of the dispersion of the sizes of colonies generated by dividing cells. The fraction of cells that are able to divide declines smoothly and continuously from the beginning of in vitro cultures of human glial cells. There is a broad distribution of colony sizes; even at the earliest passages there are significant numbers of small colonies. With increasing age of the culture there is a shift in the distribution, so that fewer large colonies and more small colonies occur. The distribution of intermitotic times is almost identical in young and middle-aged cultures. Our data seem to exclude quite positively any description in terms of a catastrophe or any abrupt change in the population. On the contrary, the decline in reproductive potential may be described adequately either as a linear change with time, or as predicted by the mortality theory of Shall and Stein (1979), in which the single constant, gamma, describes the change in reproductive potential over the entire lifetime.

Comparative rates of decline in the primary cloning efficiencies of smooth muscle cells from the aging thoracic aorta of two murine species of contrasting maximum life span potentials

Primary cloning assays of thoracic aortic smooth muscle cells from an F1 hybrid strain of Mus musculus demonstrated linear regressions of replicative potentials as functions of donor age (6-30 months), with regression coefficients, in two independent cohorts, of -1.69 +/- 0.27 (SE) and -1.88 +/- 0.19 (SE) clones per milligram wet weight of intima-media per month and correlation coefficients of -0.83 and -0.92 (P less than 0.001). Secondary cloning (dilute plating from first passages) also demonstrated a high negative correlation (r = -0.90) between donor age and cloning efficiency, thus implicating intrinsic differences in cell populations. Comparable primary cloning assays on the aortas of aging cohorts of Peromyscus leucopus, a murine species with a maximum life span potential approximately twice that of Mus musculus, yielded about twice the number of clonable smooth muscle cells per unit weight; the rate of decline with age was slightly but significantly greater (P less than 0.01). Electron-microscopic studies revealed cellular alterations confined to the first subintimal layer of aortas from mice (Mus musculus) 18 months and older.