PNPLA1 is a transacylase essential for the generation of the skin barrier lipid ω-O-acylceramide

Lipids are the primary components of the skin permeability barrier, which is the body’s most powerful defensive mechanism against pathogens. Acylceramide ( ω - O -acylceramide) is a specialized lipid essential for skin barrier formation. Here, we identify PNPLA1 as the long-sought gene involved in the final step of acylceramide synthesis, esterification of ω -hydroxyceramide with linoleic acid, by cell-based assays. We show that increasing triglyceride levels by overproduction of the diacylglycerol acyltransferase DGAT2 stimulates acylceramide production, suggesting that triglyceride may act as a linoleic acid donor. Indeed, the in vitro analyses confirm that PNPLA1 catalyses acylceramide synthesis using triglyceride as a substrate. Mutant forms of PNPLA1 found in patients with ichthyosis exhibit reduced or no enzyme activity in either cell-based or in vitro assays. Altogether, our results indicate that PNPLA1 is directly involved in acylceramide synthesis as a transacylase, and provide important insights into the molecular mechanisms of skin barrier formation and of ichthyosis pathogenesis. Loss-of-function mutations in an enzyme of unknown function, PNPLA1, cause dry and scaling skin in humans. Here Ohno et al . show that PNPLA1 is a transacylase that acts in the final step of acylceramide production- esterification between ω -hydroxyceramide and linoleic acid acylceramide, yielding a lipid essential for skin barrier function.