Expression of acyl-CoA synthetase 5 in human epidermis.

The human epidermis is characterized by a constant renewal of keratinocytes embedded in a matrix enriched with lipids. Numerous proteins involved in lipid metabolism are found in human epidermis, especially in keratinocytes. Long-chain acyl-CoA derivatives, which are catalyzed by human ACSL5, are important metabolites in several biochemical pathways, including ceramide de novo synthesis. The aim of the present study was to investigate expression of acyl-CoA synthetase isoform 5 (ACSL5) in human epidermis by an in situ, as well as a molecular approach. We show that ACSL5 mRNA and protein are found in human epidermis, as well as in non-differentiated and differentiated HaCaT cells. Keratinocytes of stratum spinosum are the main source for ACSL5 expression in both meshed facial or abdominal skin and ridged skin of upper or lower extremities including TUNEL-positive cells in upper cellular layers. Single keratinocytes of chronic solar-exposed meshed facial epidermis occasionally display a stronger ACSL5 immunostaining. In conclusion, our study indicates that epidermal ACSL5 expression might be involved in differentiation and the stress response of keratinocytes.