Essential role of the cytochrome P450 CYP4F22 in the production of acylceramide, the key lipid for skin permeability barrier formation

A skin permeability barrier is essential for terrestrial animals, and its impairment causes several cutaneous disorders such as ichthyosis and atopic dermatitis. Although acylceramide is an important lipid for the skin permeability barrier, details of its production have yet to be determined, leaving the molecular mechanism of skin permeability barrier formation unclear. Here we identified the cytochrome P450 gene CYP4F22 as the long-sought fatty acid ω- hydroxylase gene required for acylceramide production. CYP4F22 has been identified as one of the autosomal recessive congenital ichthyosis-causative genes. Ichthyosis mutant proteins exhibited reduced enzyme activity, indicating correlation between activity and pathology. Furthermore, lipid analysis of an ichthyosis patient showed a drastic decrease in acylceramide production. We determined that CYP4F22 was a type I membrane protein that locates in the endoplasmic reticulum (ER), suggesting that the ω-hydroxylation occurs on the cytoplasmic side of the ER. The preferred substrate of the CYP4F22 was ?C28 fatty acids. In conclusion, our findings demonstrated that CYP4F22 is an ultra long-chain fatty acid ω-hydroxylase responsible for acylceramide production and provides important new insights into the molecular mechanisms of skin permeability barrier formation. Furthermore, based on the results obtained here, we proposed a detailed reaction series for acylceramide production

Properties of Skin in Chinese Infants: Developmental Changes in Ceramides and in Protein Secondary Structure of the Stratum Corneum

The properties of infant skin regarding its structure and stratum corneum (SC) properties during development compared to adult skin have been reported only for a few races and body sites. The aim of this study was to understand the developmental changes of skin properties in Chinese infants, focusing on SC ceramides and protein secondary structure, which are important for skin barrier function. Three body sites with distinct characteristics (cheeks, inner upper arms, and buttocks) were assessed. Sixty pairs of Chinese infants and their mothers were measured for SC hydration, transepidermal water loss, ceramide levels, sebum with an ester bond, and protein secondary structure of superficial SC. Skin hydration decreased with age at all body sites. TEWL was similar between the 2–12- and 13–24-month-old groups but was higher than the adult group at the buttocks and inner upper arms and was equal to the adult group at the cheeks. These differences coincided with differences in protein secondary structure. Ceramide and sebum levels were lower in the infant groups. We conclude that both the SC functions and the components of infant skin are still developing and are not fully adapted as in adult skin at each body site examined