Development of human skin equivalents with inducible ceramide depletion for in vitro modelling of lipid deficiency

The lipid composition of the epidermis plays a critical role in the skins barrier function, and defects in lipid synthesis or assembly can cause a spectrum of skin diseases, ranging from dry skin to severe ichthyoses. The aim of this study was to develop an in vitro model of human skin with tuneable lipid deficiency. Human N/TERT keratinocytes were engineered to express doxycycline-inducible short hairpin RNAs targeting ceramide synthase 3 (CerS3), which is essential for synthesis of ultra long chain ceramides and skin barrier function. We show that 3D human skin equivalents (HSEs) with induced knockdown of CerS3 display normal stratification and terminal differentiation but have reduced Nile Red staining for polar lipids. Further analysis of the lipidome by mass spectrometry confirmed a significant reduction in specific classes of ceramides and ceramide chain length in the CerS3 depleted HSEs. We also show that CerS3 knockdown is reversible upon removal of doxycycline and can be used to study recovery and repair of epidermal lipids. Together, these findings provide an overall strategy for genetically tuning the lipid composition within human skin models and establish a new in vitro model of ceramide deficiency.