Low oxygen delays fibroblast senescence despite shorter telomeres

Abstract

It has been widely accepted that telomere shortening acts as a cell division counting mechanism that beyond a set critical length signals cells to enter replicative senescence. In this study, we demonstrate that by simply lowering the oxygen content of the cell culture environment 10-fold (20-2%) extends the replicative lifespan of fetal bovine fibroblasts at least five-times (30-150 days). Although, low oxygen fibroblasts display a slightly slower rate (P > 0.05) of telomere attrition than their high oxygen counterparts (171 bp versus 182 bp/PD), late passage fibroblasts (>50 PD) that have extended their replicative capacity under low oxygen conditions exhibited significantly (P < 0.05) shorter telomere lengths (11,135 +/- 467 bp) compared to senescent cells (25-34 PD) cultured under high oxygen conditions (14,827 +/- 1173 bp). There was a significant increase (P < 0.05) in chromosomal abnormalities with continual cell division under both high and low oxygen environments, however, fibroblasts displayed a significant reduction (P < 0.001) in chromosomal abnormalities at low oxygen tensions compared to those under 20% oxygen. These apparent protective effects on telomere shortening, delayed senescence and reduced chromosomal aberrations may be attributed to the up-regulation of telomerase activity observed for fibroblasts cultured under low oxygen. These results are consistent with the idea that a critically short telomere length may not be the sole trigger of replicative senescence, but may be regulated by the integrity of telomere structure itself and/or the amount of oxidative DNA damage in the cell.

Cancers and the concept of cell senescence

“…Maintenance of human fibroblasts in 1.5 or 3% O 2 concentration delayed the appearance of replicative senescence compared to cells grown in 20% and resulted in reduced expression levels of the cell cycle modulators p21 and p16 (Poulios et al 2007). Late passage fibroblasts have extended replicative capacity under 3% as compared to 20% O 2 , but have significantly shorter telomere lengths (Betts et al 2008). These results are consistent with the idea that critically short telomere length may not be the sole trigger of replicative senescence.…”

A comparative analysis of the cell biology of senescence and aging

“…The work of Jendrach et al [148] showed that, in senescent HUVEC cells, large aggregates of mitochondria with low membrane potential were frequently observed, and the fission and fusion activities as scored by number of filmed events were substantially lower in late-passage cells. Fibroblasts cultured at low oxygen (1-5% instead of 20% O 2 ) proliferate with significantly extended population doubling capacity [149][150][151], and it would be interesting to determine the status of mitochondrial fusion and fission dynamics in these cells. Mitochondrial fission and fusion in mammals are mediated by a family of proteins, Drp1 and Fis1 for fission, Mfn1, Mfn2 and Opa1 for fusion [152], and it is of importance to determine whether the levels of these proteins and their activities are regulated during cellular senescence and in aged tissues.…”

Our NIH Years: A Confluence of Beginnings

“…Furthermore, they grow faster and maintain steady growth for a substantially higher number of passages, i.e. the cellular senescence that commonly occurs after 50 population passages for fibroblasts (the "Hayflick limit") is readily surpassed (80,99,100).…”