The telomeric length and heterogeneity decrease with age in normal human oral keratinocytes

We have examined the telomere length in NHOK explanted from 28 donors between the ages of 21 and 84 years. Genomic DNA was isolated from exponentially replicating NHOK and digested with HinFI to yield terminal restriction fragments (TRF). The TRF length ranged from 4.1 to 7.0 kbp with a mean of 5.3 +/- 0.8 kbp, which was significantly shorter than that (8.9 +/- 1.0 kbp) of normal human oral fibroblasts (NHOF). The TRF length was inversely correlated to the increase of donor age in NHOK (m=-23 bp per year; r=-0.60; P<0.001). Also, the heterogeneity of TRF length in cultured NHOK decreased with increased donor age (r=-0.38, P<0.05). These data indicated that clonogenic NHOK cells had replicated in situ and showed a progressive shortening of TRF length. The short telomere length and decreased telomeric length heterogeneity in immortalized cells suggested that there is a critical minimum for cell survival.