2Department of Pathology, College of Medicine, University of Wales, Heath Park, Cardiff CF4 4XN, UK; fax: +44-1222-743-524; E-mail: KiplingD@cardiff.ac.uk
3Department of Biological Sciences, The University, Dundee DD1 4HN, UK; E-mail: email@example.com
4To whom correspondence should be addressed.
Submitted July 7, 1997.
Senescence, or replicative failure, has been reported for a wide variety of human cell types but has seldom been characterized in any detail. The senescence of human fibroblast cultures has been shown to be due to a steadily decreasing percentage of cells able to proliferate in standard media. This paper reports the serial subculture of a strain of adult retinal pigmented epithelial (RPE) cells until replicative failure after ~15 population doublings. Measurement of the growth fraction of the RPE cells at each passage using antibodies to the proliferation marker pKi67 demonstrated a rate of decline in the proliferating fraction of 3.66% per population doubling. Similar experiments carried out using a strain of human fibroblasts yielded a decline of approximately 0.88% per population doubling. Thus, individual RPE cells enter senescence significantly faster than control fibroblasts (p < 0.001). At growth arrest the RPE cells retained viability for extended periods but showed elevated endogenous autofluorescence, analogous to observations on post-mitotic human fibroblasts. Taken together these findings suggest that the process of senescence is a common feature of different cell lineages but that the specific rate can differ between them. The significance of these observations for the telomere hypothesis of senescence is discussed.
KEY WORDS: ageing, telomere, retinal pigmented epithelial cell, senescence, macular degeneration.