Lipidome of narrow-band ultraviolet B irradiated keratinocytes shows apoptotic hallmarks

P>Background: UV light triggers a variety of biological responses in irradiated keratinocytes that might be associated with global perturbation of their lipidome. However, lipids that are specifically affected and the exact molecular mechanisms involved remain poorly understood. Objectives: To characterize time-dependent changes of the lipidome of cultured keratinocytes induced by narrow-band ultraviolet B (NB-UVB) irradiation. Methods: Immortalized human keratinocytes (HaCaT) were cultured under standard conditions, irradiated with NB-UVB light (311 nm) at 400 and 800 mJ/cm2 and collected 1, 2, 3, 6, 12 and 24 h later for lipid extraction. Lipid extracts were separated on silica plates in chloroform/ethanol/water/triethylamine (35:40:9:35) and in n-hexane/ethylacetate (5:1) followed by quantitative shotgun lipidomics analysis. Results: Irradiation with 800 mJ/cm2 of NB-UVB altered morphology and lipidome composition of HaCaT cells. Ceramide content increased two-fold 6- and 12-h postirradiation with 800 mJ/cm2, followed by threefold increase in triacylglycerols (TAGs) that peaked at 24 h. In addition, we observed marked increase of various phosphatidylcholine and phosphatidylethanolamine ethers, whereas phosphatidylcholine-species with short-chain fatty acid moieties decreased. The abundance of other lipid species was altered to lesser extent or remained unchanged. Conclusions: NB-UVB affected the cellular lipidome of keratinocytes in strictly apoptosis-specific manner.