Sebum is a lipid mixture produced and delivered to the skin surface by appendages called sebaceous glands (SGs) in a holocrine secretion process. Sebum contributes to the skin barrier, lubricates hair and skin, provides antimicrobial protection, and has pheromone functions. During the terminal differentiation of SG cells (sebocytes), macroautophagy, an intracellular process for major metabolic reconfiguration, is activated. Deletion of autophagy affects the hair sebum composition in mice. This study aimed to investigate lipid composition and localization within SG and the epidermis in Atg7 (autophagy related 7)-knockout (atg7ΔKC) and autophagy-competent mouse ears in situ using mass spectrometry imaging. Spatial lipidomics revealed lipid distribution with high spatial accuracy and identified lipid species with altered intensities in autophagy-deficient tissue. In SG regions of interest, signals putatively annotated as ceramide phosphate species (including ceramide phosphate 44:2;O2) showed higher signal intensities in atg7ΔKC mice. In contrast, selected sphingomyelin-associated signals showed lower intensities in the whole-tissue profile but not exclusively in SG regions of interest. It is also demonstrated that spatially resolved ion mass signatures are suitable for identifying the epidermis and SG in tissue ion images, a step toward "chemical analytical histology" of the skin.
