Alteration of the 4-sphingenine scaffolds of ceramides in keratinocyte-specific Arnt-deficient mice affects skin barrier function

Abstract

Aryl hydrocarbon receptor nuclear translocator (ARNT), a transcription factor of the Per/AHR/ ARNT/Sim family, regulates gene expression in response to environmental stimuli including xenobiotics and hypoxia. To examine its role in the epidermis, the Cre-loxP system was used to disrupt the Arnt gene in a keratinocyte-specific manner. Gene-targeted, newborn mice with almost normal appearance died neonatally of severe dehydration caused by water loss. Histology showed small changes in the architecture of cornified layers, with apparently preserved intercorneocyte lamellar structures responsible for the skin barrier function. In contrast, HPLC/ion-trap mass spectrometry revealed significant alterations in the compositions of ceramides, the major components of the lamellae. The murine epidermal ceramides normally contain 4-sphingenine and 4-hydroxysphinganine. In Arnt-null epidermis, 4-sphingenine was largely replaced by sphinganine and the amounts of ceramides with 4-hydroxysphinganine were greatly decreased, suggesting deficiency of dihydroceramide desaturases that catalyze the formation of both 4-sphingenyl and 4-hydroxysphinganyl moieties. A desaturase isoenzyme, DES-1, prefers desaturation, but DES-2 catalyzes both reactions to a similar extent. Transcript levels of Des-2, but not Des-1, were considerably decreased in cultured keratinocytes from Arntnull epidermis. These results indicate that proper ceramide compositions through 4-desaturation regulated by ARNT are crucial for maintaining the epidermal barrier function. .jp. Conflict of interest:The authors have declared that no conflict of interest exists. Nonstandard abbreviations used: aryl hydrocarbon receptor nuclear translocator (ARNT); basic helix-loop-helix (bHLH); aryl hydrocarbon receptor (AHR); Per/AHR/ARNT/Sim (PAS); hypoxia-inducible factor 1α (HIF1α); stratum corneum (SC); high-performance TLC (HPTLC); tandem mass spectrometry (MS/MS); embryonic day (E); electrospray ionization (ESI).

EGF receptor signaling blocks aryl hydrocarbon receptor-mediated transcription and cell differentiation in human epidermal keratinocytes

“…Two independent studies have shown that targeted ablation of Arnt in the mouse epidermis results in early postnatal death associated with a failure of epidermal permeability barrier function (18,19). In each study, histology showed small changes in the architecture of the cornified layers.…”

“…In each study, histology showed small changes in the architecture of the cornified layers. Biochemical analyses revealed changes in lipid metabolism affecting permeability, specifically alterations of the 4-sphingenine scaffolds of ceramides (18), and ceramide metabolism, including downregulation of the UGCG pathway in the Arnt null epidermis (19). In one study, microarray analysis revealed that the expression of FLG was regulated by ARNT (19).…”

“…4 E-G). These genes included filaggrin (FLG), ceramide glucosyltransferase (UGCG), and sphingolipid C4-hydroxylase/ delta 4-desaturase (DEGS2), all known to be regulated by ARNT during cornification (late differentiation) and to contribute to epidermal barrier function (18,19). Also, treatment with EGF markedly inhibited both the cell density-dependent and TCDDmediated expression of each of these 3 genes (Fig.…”

Targeted ablation of Arnt in mouse epidermis results in profound defects in desquamation and epidermal barrier function

“…Ceramide composition in the interfollicular epidermis of Arnt ⌬/⌬ mice On the basis of previous data (Takagi et al, 2003), and the downregulation of Asah3 and Ugt8a genes revealed by our microarray studies, we assumed that deregulation of lipid turnover may be one of the mechanisms causing epidermal barrier failure in our Arnt ⌬/⌬ mouse model. …”

“…According to the current dogma, the stratum corneum is not simply a protective mechanical cover, but also a 'biosensor' that employs sophisticated mechanisms inducing proteolysis, DNA/lipid synthesis, and inflammation in response to the subtle changes of the environment (Elias et al, 2004). The pivotal role of Arnt in sensory pathways in brain, liver and reproductive organs (Gu et al, 2000;Xu et al, 2005;Hombach-Klonisch et al, 2005), as well as the striking skin symptoms in dioxin toxicity (Kuratsune, 1980;Crow, 1983;Poskitt et al, 1994;Geusau et al, 2000), led us to hypothesize that Arnt is a potential key element of skin-environment communication, yet the role of Arnt in skin functioning is just beginning to be unraveled (Takagi et al, 2003).…”