Telomere Length Differences upon Keratinization and its Variations in Normal Human Epidermal Keratinocytes

Abstract

Telomeres are the physical ends of chromosomes, and are cleaved with each cell division. Telomere loss results from not only incomplete DNA replication (“end replication problem”), followed by the processing of chromosome, but also exposure to various DNA damaging agents. Human epidermis is constantly replaced through replication at the basal layer, followed by upward movement and terminal differentiation at the suprabasal layer. The objective of this study was to assess differences in telomere length between basal and suprabasal keratinocytes, and variations of telomere lengths among basal cells. We investigated terminal restriction fragment (TRF) length in fractions of epidermal cells by Southern blot analysis. Time-dependent trypsin treatment to epidermis divided into basal cell rich and suprabasal cell rich fractions. In the five skin samples from various sites of the body, the mean TRF length were 5,932 ± 470 (range 5,182-6,630) bp in basal cell rich fraction showing 21.5% ± 5.8% (range 12.6-28.6%) of keratin 10 (K10)-positivity, which is marker of keratinizing suprabasal cell, and 5,320 ± 640 (range 4,495-6,212) bp in suprabasal cell rich fraction showing 78.8% ± 4.0% (range 72.8-83.0%) of K10-positivity. It was calculated that K10 positive cells have 1,091 ± 963 (range 248-2,650) bp shorter telomeres compared to K10 negative cells. In addition, fluorescence in situ hybridization (FISH) study showed that columnar groups of keratinocytes with statistically longer telomere in each nucleus than the other epidermal cells in the vicinity occupied occasionally between the tip of dermal papilla and the bottom of rete ridge. The present study showed that the keratinizing suprabasal cells have shorter telomeres compared to basal cells. FISH study showed that some groups of epidermal cells having different replicative histories among the groups of epidermal cells in the vicinity.