Ceramide Analysis in Combination With Genetic Testing May Provide a Precise Diagnosis for Self-Healing Collodion Babies

Self-healing collodion baby (SHCB), also called "self-improving collodion baby", is a rare mild variant of autosomal recessive congenital ichthyosis and is defined as a collodion baby who shows the nearly complete resolution of scaling within the first 3 months to 1 year of life. However, during the neonatal period, it is not easy to distinguish SHCB from other inflammatory forms of autosomal recessive congenital ichthyosis, such as congenital ichthyosiform erythroderma. Here, we report a case study of two Japanese SHCB patients with compound heterozygous mutations, c.235G>T (p.(Glu79∗))/ c.1189C>T (p.(Arg397Cys)) and c.1295A>G (p.(Tyr432Cys))/ c.1138delG (p.(Asp380Thrfs∗3)), in CYP4F22, which encodes cytochrome P450, family 4, subfamily F, polypeptide 22 (CYP4F22). Immunohistochemically, inflammation with the strong expression of IL-17C, IL-36γ, and TNF-α was seen in the skin at birth. CYP4F22 is an ultra-long-chain FA ω-hydroxylase responsible for ω-O-acylceramide (acylceramide) production. Among the epidermal ceramides, acylceramide is a key lipid in maintaining the epidermal permeability barrier function. We found that the levels of ceramides with ω-hydroxy FAs including acylceramides and the levels of protein-bound ceramides were much lower in stratum corneum samples obtained by tape stripping from SHCB patients than in those from their unaffected parents and individuals without SHCB. Additionally, our cell-based enzyme assay revealed that two mutants, p.(Glu79∗) and p.(Arg397Cys), had no enzyme activity. Our findings suggest that genetic testing coupled with noninvasive ceramide analyses using tape-stripped stratum corneum samples might be useful for the early and precise diagnosis of congenital ichthyoses, including SHCB.

A promiscuous fatty acid ω-hydroxylase CYP94A90 is likely to be involved in biosynthesis of a floral nitro compound in loquat (Eriobotrya japonica)

Nitro groups are often associated with synthetically manufactured compounds such as medicines and explosives, and rarely with natural products. Loquat emits a nitro compound, (2-nitroethyl)benzene, as a flower scent. The nitro compound exhibits fungistatic activity and is biosynthesised from l-phenylalanine via (E/Z)-phenylacetaldoxime. Although aldoxime-producing CYP79s have been intensively studied, it is unclear what enzymes form nitro groups from aldoximes either in plants or in other organisms. Here, we report the identification of two cytochrome P450s that are likely to be involved in (2-nitroethyl)benzene biosynthesis in loquat through differential gene expression analysis using RNA-seq and functional identification using yeast and tobacco. CYP79D80 and CYP94A90 catalysed the formation of (E/Z)-phenylacetaldoxime from l-phenylalanine and (2-nitroethyl)benzene from the aldoxime, respectively. Expression profiles of CYP79D80 and CYP94A90 were correlated with the emission of (2-nitroethyl)benzene from loquat flowers. CYP94A90 also functioned as a fatty acid ω-hydroxylase as do other CYP94A fatty acid ω-hydroxylases. The CYP94As tested from other plants were all found to catalyse the formation of (2-nitroethyl)benzene from (E/Z)-phenylacetaldoxime. CYP79D80 and CYP94A90 are likely to operate in concert to biosynthesise (2-nitroethyl)benzene in loquat. CYP94A90 and other CYP94As are 'promiscuous fatty acid ω-hydroxylases', catalysing the formation of nitro groups from aldoximes, and are widely distributed in dicot plants.

Lipid polarity gradient formed by ω-hydroxy lipids in tear film prevents dry eye disease

Meibum lipids form a lipid layer on the outermost side of the tear film and function to prevent water evaporation and reduce surface tension. (O-Acyl)-ω-hydroxy fatty acids (OAHFAs), a subclass of these lipids, are thought to be involved in connecting the lipid and aqueous layers in tears, although their actual function and synthesis pathway have to date remained unclear. Here, we reveal that the fatty acid ω-hydroxylase Cyp4f39 is involved in OAHFA production. Cyp4f39-deficient mice exhibited damaged corneal epithelium and shortening of tear film break-up time, both indicative of dry eye disease. In addition, tears accumulated on the lower eyelid side, indicating increased tear surface tension. In Cyp4f39-deficient mice, the production of wax diesters (type 1ω and 2ω) and cholesteryl OAHFAs was also impaired. These OAHFA derivatives show intermediate polarity among meibum lipids, suggesting that OAHFAs and their derivatives contribute to lipid polarity gradient formation for tear film stabilization.