Telomere shortening and decline in replicative potential as a function of donor age in human adrenocortical cells

Telomere shortening is the cause of replicative senescence of mammalian cel ls in culture and may be a cause of cellular aging in vivo. Some tissues cl early show telomere shortening during aging in humans, but the relationship between replication history and telomere length is obscured by complex rel ationships between stem cells and more differentiated cell types. Previous experiments on the adrenal cortex and human adrenocortical cells in culture indicate that the proliferative biology of this tissue is relatively simpl e; cell division occurs continuously throughout life, without evidence for a distinct stem cell compartment. In this tissue we investigated the relati onship between telomere biology and replicative senescence by measuring rep licative capacity and telomere length as a function of donor age. Cells cul tured from adrenal tissue from donors of different ages showed a strong age -related decline in total replicative capacity, falling from about 50 popul ation doublings for fetal cells to an almost total lack of division in cult ure for cells from older donors. Telomere restriction fragment (TRF) length was analyzed in the same sets of cells and decreased from a value of about 12 kb in fetal cells to approximately 7 kb in cells from older donors. The latter value is consistent with that in fibroblasts which have reached rep licative senescence. Furthermore, there was a good correlation in individua l donor samples between TRF length and replicative capacity in culture. To confirm the relationship between telomere length, telomerase, and replicati ve capacity, we measured telomere length in cells before and after infectio n with a retrovirus encoding hTERT, the catalytic component of human telome rase. The adult adrenal cortex does not have telomerase activity; cells aft er transduction with the hTERT retrovirus had high telomerase activity. Whe reas control cells underwent a replication-dependent shortening in telomere s during long-term growth in culture, hTERT-modified cells maintained telom ere length and are probably immortalized. Symmetric cell division in human adrenocortical cells, occurring slowly over the life span, is associated wi th progressive telomere shortening and may result in proliferative defects in vivo in old age, which could partly account for the age-related changes in the structure and function of the human adrenal cortex. (C) 2001 Elsevie r Science Ireland Ltd. All rights reserved.