855 Histone deacetylase activity and expression alters with increasing age in primary human keratinocytes

During normal development and throughout life, epigenetic changes arise in response to an individuals’ behavior and environment. Histone deacetylases (HDACs) are chromatin-modifying enzymes that remove acetyl groups from histones, inducing conformational DNA changes, so regulating gene expression. To date, four classes of HDACs have been identified: class I (HDACs-1, -2, -3 & -8); class II (HDACs-4, -5, -6, -7, -9 & -10); class III (SIRT1-7) and class IV (HDAC11), but their role in keratinocyte biology is largely unknown. In this study, we investigated the activity and abundance of HDACs in both immortalized human keratinocytes (HaCaT) and in primary normal human epidermal keratinocytes (NHEK) from juvenile (n=3, mean age: 6yrs), middle-aged (n=3, mean age: 51yrs) and elderly (n=3, mean age: 80yrs) donors. We found that HaCaT cells expressed high HDAC activity when compared to juvenile (P<0.05) and elderly (P<0.05) NHEKs; however, activity was comparable between HaCaTs and NHEKs derived from middle-aged donors. Western blot analysis revealed that HDACs-1, -2, -3 & -5 were expressed at significantly higher levels in HaCaTs as compared to NHEKs derived from juvenile, middle-aged or elderly NHEK (P<0.05). HaCaTs further expressed significantly lower levels of HDACs-4 & -6 than NHEKs derived from middle-aged donors (P<0.05); expression of HDACs-7, -8, -9, -10 and -11 were invariant between HaCaT and NHEK cells. Immunocytochemistry confirmed Western blot findings. Taken together, these data suggest that HDAC is cell type-specific and that in primary cells, expression and activity significantly alters throughout the life course. Further studies exploring the consequences of such changes in primary keratinocytes are warranted at both the transcriptional and translational level to better understand the contribution of HDACs to epidermal aging.