Human Cells and the Finite Lifespan Theory
Cultures of human diploid fibroblasts are characterized by: i) finite lifespan, ii) marked heterogeneity in the growth potential of individual cells within the culture, iii) considerable variation in lifespans of parallel cultures of the same cell strain. To explain these properties, we have proposed a commitment theory of cellular aging. Cells are assumed initially to be uncommitted (potentially immortal) but, at each cell division, each daughter cell is assumed to have some fixed probability of becoming irreversibly committed to senesce and die after a specific number of cell generations. During the period between commitment and senescence, cells are assumed to multiply normally, so the uncommitted cells are diluted by committed ones and may be lost in subculturing. The theory explains features i) - iii) above and, in particular, suggests why diploid cultures have finite lifespans while transformed or permanent lines grow indefinitely. It also validly predicts the behaviour of mixed cultures of distinguishable but otherwise similar cell types, and that culture lifespan may be significantly decreased by drastic reduction of population size. The important converse prediction that culture lifespan may be extended indefinitely by growing sufficiently large cultures or by selectively isolating uncommitted cells remains to be tested.
KeywordsCellular Aging Diploid Fibroblast Human Diploid Fibroblast Cell Cycle Time Human Diploid Cell
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- 9.Holliday, R. Growth and death of diploid and transformed human fibroblasts. Fed. Proc. Fed. Am. Soc. Exp. Biol. 34:51–55, 1974.Google Scholar
- 10.Kirkwood, T.B.L., Holliday R. Commitment to senescence. A model for the finite and infinite growth of diploid and transformed human fibroblasts in culture. J. Theoret Biol. 53:481–496, 1975.Google Scholar
- 12.Kirkwood, T.B.L., Holliday, R. A stochastic model for the commitment of human cells to senescence. Biomathematics and Cell Kinetics. Edited by A.J. Valleron, P.D.M. Macdonald. Elsevier/North-Holland, Biomedical Press, 1978, pp. 161–172.Google Scholar