PNPLA1 has a crucial role in skin barrier function by directing acylceramide biosynthesis.

Mutations in patatin-like phospholipase domain-containing 1 (PNPLA1) cause autosomal recessive congenital ichthyosis, but the mechanism involved remains unclear. Here we show that PNPLA1, an enzyme expressed in differentiated keratinocytes, plays a crucial role in the biosynthesis of ω-O-acylceramide, a lipid component essential for skin barrier. Global or keratinocyte-specific Pnpla1-deficient neonates die due to epidermal permeability barrier defects with severe transepidermal water loss, decreased intercellular lipid lamellae in the stratum corneum, and aberrant keratinocyte differentiation. In Pnpla1-/- epidermis, unique linoleate-containing lipids including acylceramides, acylglucosylceramides and (O-acyl)-ω-hydroxy fatty acids are almost absent with reciprocal increases in their putative precursors, indicating that PNPLA1 catalyses the ω-O-esterification with linoleic acid to form acylceramides. Moreover, acylceramide supplementation partially rescues the altered differentiation of Pnpla1-/- keratinocytes. Our findings provide valuable insight into the skin barrier formation and ichthyosis development, and may contribute to novel therapeutic strategies for treatment of epidermal barrier defects.

Synergistic effects of flavonoids and ascorbate on enhancement in DNA degradation induced by a bleomycin-Fe complex.

Flavonoids were examined for synergistic effects with ascorbate on enhancement of DNA degradation induced by a bleomycin(BLM)-Fe complex. The synergistic effects of flavonoids and ascorbate on DNA degradation induced by the BLM-Fe complex were observed to be greater with flavonoids such as isorhamnetin, kaempferol and morin, which accelerated oxidation more markedly in the presence, than in the absence of BLM. Conversely, myricetin and fisetin, which showed oxidation barely accelerated by the addition of BLM, inhibited DNA degradation promoted by ascorbate. Consequently, there was a good correlation between oxidation of flavonoids accelerated by BLM and the extent of DNA degradation promoted synergistically with ascorbate. Our previous studies indicated that oxidation of flavonoids accelerated by BLM and DNA degradation promoted by flavonoids were not correlated with Fe(III)-reducing activity of flavonoids. Those results suggest that Fe(III)-reducing activity of flavonoids is not the only factor determining DNA degradation-promoting activity induced by the BLM-Fe complex. On the other hand, in a Fenton reaction, degradation of 2-deoxy-d-ribose promoted by flavonoids was correlated to the Fe(III)-reducing activity of flavonoids. However, there was not a synergistic interaction between flavonoids and ascorbate in the degradation of 2-deoxy-d-ribose. Therefore, it is suggested that the synergistic DNA degradation caused by flavonoids and ascorbate in the BLM-Fe redox cycle arose from the difference in the reductive processes in which flavonoids and ascorbate mainly act.

Oxidation of flavonoids which promote DNA degradation induced by bleomycin-Fe complex.

Sixteen flavonoids including quercetin and kaempferol and their relatives were examined for their ability to promote DNA degradation induced by the bleomycin (BLM)-Fe complex. Three hydroxyl groups in the flavonoidal nucleus were proposed as a crucial structural requirement for effectively promoting DNA degradation: 1). the C7-hydroxyl substitution in the A-ring; 2). the C4'-hydroxyl substitution in the B-ring; and 3). the C3-hydroxyl substitution in the C-ring. Flavonoids, which lack even one of these hydroxyl substitutions, showed remarkably diminished activity. There was a good correlation (r=0.920, p<0.001) between activity to promote DNA degradation and oxidizability, which was measured following the Fe(III)-induced oxidation of flavonoids themselves, among the 16 flavonoids. The oxidizability of flavonoids which have the crucial hydroxyl substitutions, was remarkably enhanced in the presence compared with the absence of BLM. On the other hand, the extent of oxidation of flavonoids lacking these substitutions was enhanced little or not at all by BLM. No correlation between the Fe(III)-reducing activity and DNA degradation-promoting activity was found among flavonoids satisfying the crucial structural requirements. Furthermore, the correlation between the extent of oxidation of flavonoids and the Fe(III)-reducing activity was not confirmed among these flavonoids. Therefore, it was suggested that Fe(III)-reducing activity was not the only factor determining DNA degradation-promoting activity in flavonoids having the three hydroxyl groups necessary for effectively promoting DNA degradation induced by BLM-Fe complex.