Signaling sphingolipids are biomarkers for atopic dermatitis prone to disseminated viral infections.

BACKGROUND: Life-threatening viral diseases such as eczema herpeticum (EH) and eczema vaccinatum (EV) occur in <5% of individuals with atopic dermatitis (AD). The diagnosis of AD, however, excludes all individuals with AD from smallpox vaccination. OBJECTIVES: We sought to identify circulatory and skin lipid biomarkers associated with EH and EV. METHODS: Stratum corneum and plasma samples from 15 subjects with AD and a history of EH, 13 age- and gender-matched subjects with AD and without EH history, and 13 healthy nonatopic (NA) controls were analyzed by liquid chromatography tandem mass spectrometry for sphingolipid content. Sphingosine-1-phosphate (S1P) and ceramide levels were validated in plasma samples from the Atopic Dermatitis Vaccinia Network/Atopic Dermatitis Research Network repository (12 NA, 12 AD, 23 EH) and plasma from 7 subjects with EV and 7 matched subjects with AD. S1P lyase was downregulated in human primary keratinocytes to evaluate its effect on herpes simplex virus 1 (HSV-1) replication in vitro. RESULTS: The stratum corneum of patients with EH demonstrated significantly higher levels of free sphingoid bases than those in patients who were NA, indicating enhanced sphingolipid turnover in keratinocytes (P < .05). Plasma from 2 independent cohorts of patients with EH had a significantly increased S1P/ceramide ratio in subjects with EH versus those with AD and or who were NA (P < .01). The S1P level in plasma from subjects with EV was twice the level in plasma from subjects with AD (mean = 1,533 vs 732 pmol/mL; P < .001). Downregulation of S1P lyase expression with silencing RNA led to an increased S1P level and doubled HSV-1 titer in keratinocytes. CONCLUSIONS: Our data point to long-term abnormalities in the S1P signaling system as a biomarker for previous disseminated viral diseases and a potential treatment target in recurring infections.

Particulate matter causes skin barrier dysfunction.

The molecular mechanisms that underlie the detrimental effects of particulate matter (PM) on skin barrier function are poorly understood. In this study, the effects of PM2.5 on filaggrin (FLG) and skin barrier function were investigated in vitro and in vivo. The levels of FLG degradation products, including pyrrolidone carboxylic acid, urocanic acid (UCA), and cis/trans-UCA, were significantly decreased in skin tape stripping samples of study subjects when they moved from Denver, an area with low PM2.5, to Seoul, an area with high PM2.5 count. Experimentally, PM2.5 collected in Seoul inhibited FLG, loricrin, keratin-1, desmocollin-1, and corneodesmosin but did not modulate involucrin or claudin-1 in keratinocyte cultures. Moreover, FLG protein expression was inhibited in human skin equivalents and murine skin treated with PM2.5. We demonstrate that this process was mediated by PM2.5-induced TNF-α and was aryl hydrocarbon receptor dependent. PM2.5 exposure compromised skin barrier function, resulting in increased transepidermal water loss, and enhanced the penetration of FITC-dextran in organotypic and mouse skin. PM2.5-induced TNF-α caused FLG deficiency in the skin and subsequently induced skin barrier dysfunction. Compromised skin barrier due to PM2.5 exposure may contribute to the development and the exacerbation of allergic diseases such as atopic dermatitis.

SMOC1 and IL-4 and IL-13 Cytokines Interfere with Ca2+ Mobilization in Primary Human Keratinocytes.

Immunoregulatory effects of IL-4 and IL-13 and alterations of keratinocyte (KC) differentiation are important factors in the pathogenesis of atopic dermatitis. This study investigated the role of IL-4 and IL-13 in KC responses to changes in extracellular calcium (Ca2+) and analyzed differentiation signals elicited via a Ca2+ sensor, SMOC1. Real-time dynamics of transmembrane Ca2+ influx were assessed in live KCs by flow cytometry and microscopy. Exposure of KCs to a high Ca2+ environment (1.3 mM) triggered a rapid intracellular Ca2+ influx, whereas IL-4- and IL-13-treated cells exhibited a significant decrease in the peak amplitude of Ca2+ influx (P < 0.01). IL-17A and IL-22 did not elicit such responses. Evaluation of intracellular Ca2+ dynamics by microscopy confirmed these observations and revealed heterogeneity of individual KC responses. IL-4 and IL-13 significantly inhibited the expression of Ca2+-binding protein SMOC1 (P < 0.001). Inhibition of epidermal differentiation markers were also observed in SMOC1 small interfering RNA-transfected KCs. Concurrently, the deletion of SMOC1 increased the amplitude of Ca2+ peak response (P < 0.05). In conclusion, our results provide innovative data that IL-4 and IL-13 regulate KC sensitivity to microenvironmental Ca2+ changes and inhibit Ca2+-induced KC differentiation signals. SMOC1 inhibition by IL-4 and IL-13 alters Ca2+ transport in KCs and inhibits differentiation, suggesting a new target for treatment of atopic dermatitis.