Transient expression of human telomerase extends the life span of normal human fibroblasts

We utilized the Cre/lox recombination system to transiently express the cat alytic subunit of telomerase (hTERT) in normal diploid foreskin fibroblasts (BJ cells). A retroviral construct containing an hTERT cDNA, flanked by lo xP-sites was introduced into near senescent BJ cells (population doubling 8 5). At population doubling (PD) 92, which exceeds the typical life span of these cells, we excised the gene via Cre-mediated recombination. All clones lost telomerase activity and showed telomere shortening over an additional 50 PDs. Interestingly, the average telomere length in these cells became s horter than in untreated BJ cells at senescence, This may be due to hTERT p referentially elongating the shortest telomeres, leading to greater length uniformity, In summary, transient telomerase expression and only a very sma ll average telomere elongation by hTERT resulted in a 50% increase in life span of human fibroblasts. This suggests a potentially safe use of hTERT in tissue engineering. (C) 2000 Academic Press.