O06 Naïve human keratinocytes initiate a chromatin-protective mechanism in response to ultraviolet radiation through the upregulation of histone deacetylase 5

Abstract

Abstract Introduction and aims During normal development and throughout life, epigenetic changes arise in response to an individuals’ behaviour and environmental exposures. Histone deacetylases (HDACs) are chromatin-modifying enzymes that regulate gene expression and their activity and expression in primary human keratinocytes alters with increasing age. Solar ultraviolet radiation (UVR) is a major causative factor of skin ageing, but how this factor affects HDAC expression and activity is largely unknown. We aimed to determine how UVR exposure affects HDAC expression and activity in primary human keratinocytes. Methods Normal human epidermal keratinocytes (NHEKs) from juvenile (aged 1–6 years; n = 3), middle-aged (56–61 years; n = 3) and aged (83–85 years; n = 3) donors were exposed to solar-simulated radiation (SSR) and HDAC abundance and activity were assayed. Results Exposure to SSR significantly increased HDAC activity in primary NHEKs irrespective of donor age (P < 0.05). However, Western blotting for HDAC abundance revealed that there was a differential response to SSR exposure across age groups; juvenile NHEKs expressed significantly more HDAC5 in response to SSR (P < 0.05) than cells from middle-aged or aged donors. Furthermore, following SSR exposure of juvenile NHEKs, the cellular localization of HDAC5 was redistributed to the nucleus from the cytoplasm. Dual immunofluorescence staining revealed that those NHEKs with nuclear HDAC5 expression were also positive for p16INK4a, a robust marker of cellular senescence (P < 0.01). Conclusions Our Results suggest that naïve human keratinocytes are responsive to UVR exposure and appear to initiate a chromatin-protective mechanism through the upregulation of HDAC5 to prevent gene expression of damaged DNA.