Exposure of Human Diploid Fibroblasts to Hypoxia Extends Proliferative Life Span

Abstract

Normal human mitotic cells do not proliferate indefinitely in culture but undergo a limited number of divisions and progressively reach a state of irreversible growth arrest, a process termed replicative senescence. Hypoxia is a situation of reduced oxygen concentration that relates to many physiological and pathophysiological conditions. In the current study we investigated the effects of oxygen concentration, in both normoxic and hypoxic conditions, on the proliferative capacity, cell viability, oxidative status, and protein expression of human embryonic diploid fibroblasts. Maintenance of WI38 and IMR90 cells in 1.5% or 3% O(2) concentration significantly delayed the appearance of replicative senescence compared to cells grown in 20% O(2), induced the hypoxia-inducible factor-1alpha, and resulted in reduced expression levels of the key cell cycle modulators, namely p21 and p16. Moreover, cell exposure to short-term hypoxia affected their response to several cytotoxic agents, whereas adaptation to the hypoxic environment prior to the treatment had no impact on cell viability. These findings clearly identify that oxygen concentration plays a crucial role in regulating cellular life span of normal human cells.

COOH-Terminal Binding Protein Regulates Expression of the p16INK4A Tumor Suppressor and Senescence in Primary Human Cells

“…Our findings that CtBP knockdown diminishes this mark, increases p16 expression, and accelerates senescence make CtBP a candidate for mediating the effects of culture stress; in particular, the effects of oxygen on CtBP-mediated repression ( Fig. 4B and C) could mediate stress from atmospheric oxygen (14). This mechanism might also help explain the long-appreciated excess of p16 defects in tumor cell lines versus their primary tumors of origin (15).…”

Reactive oxygen species control senescence‐associated matrix metalloproteinase‐1 through c‐Jun‐N‐terminal kinase

“…Analysis of late passage cells also revealed a striking increase in the levels of secreted MMP-1 relative to the young cells both at the level of protein and RNA (Fig 1B and C). Senescence can be delayed by maintaining cells under low oxygen conditions (3%) relative to ambient air (21%) (Chen et al, 1995;Poulios et al, 2007;Poulios et al, 2006). IMR-90 cells maintained at 3% O 2 showed a reduced level expression of both p16 and p21 senescent markers (Fig 1B) and also an extended replicative lifespan (data not shown).…”

Hypoxic reprograming of H3K27me3 and H3K4me3 at the INK4A locus

“…Mild hypoxia (1.5% and 3% O 2 ) prevented cellular senescence in mouse embryonic fibroblasts, human mesenchymal stem cells, and human fibroblasts but enhanced cell proliferation [31][32][33]. However, the correlation between hypoxia and senescence is controversial.…”