Fatty acid 2-hydroxylase, encoded by FA2H, accounts for differentiation-associated increase in 2-OH ceramides during keratinocyte differentiation

J Biol Chem. 2007 May 4;282(18):13211-9. doi: 10.1074/jbc.M611562200. Epub 2007 Mar 12.


Ceramides in mammalian stratum corneum comprise a heterogeneous mixture of molecular species that subserve the epidermal permeability barrier, an essential function for survival in a terrestrial environment. In addition to a variation of sphingol species, hydroxylation of the amide-linked fatty acids contributes to the diversity of epidermal ceramides. Fatty acid 2-hydroxylase, encoded by the gene FA2H, the mammalian homologue of FAH1 in yeast, catalyzes the synthesis of 2-hydroxy fatty acid-containing sphingolipids. We assessed here whether FA2H accounts for 2-hydroxyceramide/2-hydroxyglucosylceramide synthesis in epidermis. Reverse transcription-PCR and Western immunoblots demonstrated that FA2H is expressed in cultured human keratinocytes and human epidermis, with FA2H expression and fatty acid 2-hydroxylase activity increased with differentiation. FA2H-siRNA suppressed 2-hydroxylase activity and decreased 2-hydroxyceramide/2-hydroxyglucosylceramide levels, demonstrating that FA2H accounts for synthesis of these sphingolipids in keratinocytes. Whereas FA2H expression and 2-hydroxy free fatty acid production increased early in keratinocyte differentiation, production of 2-hydroxyceramides/2-hydroxyglucosylceramides with longer chain amide-linked fatty acids (> or =C24) increased later. Keratinocytes transduced with FA2H-siRNA contained abnormal epidermal lamellar bodies and did not form the normal extracellular lamellar membranes required for the epidermal permeability barrier. These results reveal that 1) differentiation-dependent up-regulation of ceramide synthesis and fatty acid elongation is accompanied by up-regulation of FA2H; 2) 2-hydroxylation of fatty acid by FA2H occurs prior to generation of ceramides/glucosylceramides; and 3) 2-hydroxyceramides/2-hydroxyglucosylceramides are required for epidermal lamellar membrane formation. Thus, late differentiation-linked increases in FA2H expression are essential for epidermal permeability barrier homeostasis.

Publication types

  • Clinical Trial
  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Cell Differentiation* / genetics
  • Cell Membrane / genetics
  • Cell Membrane / metabolism*
  • Cell Membrane / ultrastructure
  • Cells, Cultured
  • Fatty Acids / metabolism
  • Gene Expression Regulation, Enzymologic* / genetics
  • Glucosylceramides / biosynthesis*
  • Homeostasis / genetics
  • Humans
  • Keratinocytes / enzymology*
  • Keratinocytes / ultrastructure
  • Mixed Function Oxygenases / antagonists & inhibitors
  • Mixed Function Oxygenases / biosynthesis*
  • Mixed Function Oxygenases / genetics
  • Permeability
  • RNA, Small Interfering / genetics


  • Fatty Acids
  • Glucosylceramides
  • RNA, Small Interfering
  • Mixed Function Oxygenases
  • fatty acid alpha-hydroxylase