RNAseq from normal human epidermal keratinocytes treated with C. acnes 6919 conditioned media and propionic acid

Lipid synthesis is necessary for formation of epithelial barriers and
homeostasis with external microbes. An analysis of the response of human
keratinocytes to several different commensal bacteria on the skin revealed
that Cutibacterium acnes induced a large increase in essential lipids
including triglycerides, ceramides, cholesterol, and free fatty acids. A
similar response occurred in mouse epidermis and in human skin affected
with acne. Further analysis showed that this increase in lipids was
mediated by short-chain fatty acids produced by Cutibacterium acnes and
was dependent on increased expression of several lipid synthesis genes
including glycerol3-phosphate-acyltransferase-3. Inhibition or RNA
silencing of peroxisome proliferator–activated receptor–α (PPARα), but not
PPARβ and PPARγ, blocked this response. The increase in keratinocyte lipid
content improved innate barrier functions including antimicrobial
activity, paracellular diffusion, and transepidermal water loss. These
results reveal that metabolites from a common commensal bacterium have a
previously unappreciated influence on the composition of epidermal lipids.