Relation between replicative senescence of human fibroblasts and life history characteristics

Abstract

Replicative ageing of fibroblasts in vitro has often been used as a model for organismal ageing. The general assumption that the ageing process is mirrored by cellular senescence in vitro is based on lower replicative capacity of human fibroblasts from patients with accelerated ageing syndromes, patients with age related diseases such as diabetes mellitus, and donors of higher chronological age, but these inverse relations have not been reported unequivocally. Therefore, we have performed a formal review on the replicative capacity of fibroblasts from patients suffering from accelerated ageing syndromes, age related diseases and donor age. Some 13 studies including 79 patients with accelerated ageing syndromes showed replicative capacity of fibroblasts to be consistently lower when compared to fibroblasts obtained from age-matched controls. Some 12 studies reported on a total of 160 patients with various age related diseases, but compared to age-matched controls no consistent difference in replicative capacity was reported. Finally, in the period from 1964 to 2006 a total of 23 studies, including some 1115 individuals, reported on the relation between chronological age and replicative capacity of human fibroblasts. Earlier studies preferentially described an inverse relation between replicative capacity and chronological age that was absent in studies including higher numbers of subjects and were published more recently. There was marked heterogeneity between the studies (Egger test: p = 0.018) indicating that publication bias is at play. We conclude that, except for premature ageing syndromes, replicative capacity of fibroblasts in vitro does not mirror key characteristics of human life histories.

Introduction

It is not unreasonable to assume that life history characteristics such as maximal life span should be reflected in properties of isolated cells in culture. However, despite the general assumption that differences in maximal life span result from cellular defects, only few cellular characteristics have yet been identified that could be relevant to life span determination, among which there the is maximal replicative capacity of fibroblasts in vitro. Under laboratory conditions, cells gradually and irreversibly lose their ability to proliferate upon subsequent subculturing. This process of ‘cellular senescence’ has often been taken as a read out for the critical processes that underline the ageing process of organisms (Hayflick, 1965). This notion is supported by the in vivo observation, using distinct markers such as p16, p53, and beta-galactosidase, that in tissues of various species the number of senescent cells accumulates proportional with the age of the organism (Dimri et al., 1995, Herbig et al., 2006, Pendergrass et al., 1999, Ressler et al., 2006).

The outgrowth of fibroblasts from skin biopsies has been related to the chronological age of the donor, i.e. the number of small, spindle-shaped fibroblasts is lower in biopsies from older donors (Bayreuther et al., 1992). Replicative capacity of fibroblasts in vitro has also been positively correlated with life span of species (Hayflick, 1975, Roehme, 1981), whereas a lower replicative capacity has been reported in fibroblasts obtained from patients who suffer accelerated ageing syndromes (Martin et al., 1970), or age related diseases (Goldstein et al., 1969). In line with these observations, studies (Goldstein et al., 1969, Martin et al., 1970) have also demonstrated an inverse relationship between donor age and replicative capacity of fibroblasts in vitro which suggests that the progenitor cells in renewable tissues may progressively lose their ability to divide and may thus explain for tissue atrophy and dysfunction.

More recently Cristofalo et al. have determined the replicative capacity of a large number of fibroblast strains established from healthy donors within a wide age range and were unable to confirm the correlation between replicative capacity and donor age (Cristofalo et al., 1998). This finding questions the validity of the relation between the replicative capacity of cells in mixed culture and the life span of organisms. As the debate continues, we set out to perform a formal review of studies on the replicative capacity of fibroblasts in vitro obtained from patients with accelerated ageing syndromes, patients who suffer age related diseases, and donor age.