Publications

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

  Uchida Y., Hama H., Alderson N.L., Douangpanya S., Wang Y., Crumrine D.A., Elias P.M., Holleran W.M.

  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 ac ... >> More

  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. << Less

  J. Biol. Chem. 282:13211-13219(2007) [PubMed] [EuropePMC]

• Stereospecificity of fatty acid 2-hydroxylase and differential functions of 2-hydroxy fatty acid enantiomers.

  Guo L., Zhang X., Zhou D., Okunade A.L., Su X.

  FA 2-hydroxylase (FA2H) is an NAD(P)H-dependent enzyme that initiates FA α oxidation and is also responsible for the biosynthesis of 2-hydroxy FA (2-OH FA)-containing sphingolipids in mammalian cells. The 2-OH FA is chiral due to the asymmetric carbon bearing the hydroxyl group. Our current study ... >> More

  FA 2-hydroxylase (FA2H) is an NAD(P)H-dependent enzyme that initiates FA α oxidation and is also responsible for the biosynthesis of 2-hydroxy FA (2-OH FA)-containing sphingolipids in mammalian cells. The 2-OH FA is chiral due to the asymmetric carbon bearing the hydroxyl group. Our current study performed stereochemistry investigation and showed that FA2H is stereospecific for the production of (R)-enantiomers. FA2H knockdown in adipocytes increases diffusional mobility of raft-associated lipids, leading to reduced GLUT4 protein level, glucose uptake, and lipogenesis. The effects caused by FA2H knockdown were reversed by treatment with exogenous (R)-2-hydroxy palmitic acid, but not with the (S)-enantiomer. Further analysis of sphingolipids demonstrated that the (R)-enantiomer is enriched in hexosylceramide whereas the (S)-enantiomer is preferentially incorporated into ceramide, suggesting that the observed differential effects are in part due to synthesis of sphingolipids containing different 2-OH FA enantiomers. These results may help clarify the mechanisms underlying the recently identified diseases associated with FA2H mutations in humans and may lead to potential pharmaceutical and dietary treatments. This study also provides critical information to help study functions of 2-OH FA enantiomers in FA α oxidation and possibly other sphingolipid-independent pathways. << Less

  J. Lipid Res. 53:1327-1335(2012) [PubMed] [EuropePMC]

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