Histamine suppresses epidermal keratinocyte differentiation and impairs skin barrier function in a human skin model.

BACKGROUND: Defects in keratinocyte differentiation and skin barrier are important features of inflammatory skin diseases like atopic dermatitis. Mast cells and their main mediator histamine are abundant in inflamed skin and thus may contribute to disease pathogenesis. METHODS: Human primary keratinocytes were cultured under differentiation-promoting conditions in the presence and absence of histamine, histamine receptor agonists and antagonists. The expression of differentiation-associated genes and epidermal junction proteins was quantified by real-time PCR, Western blot, and immunofluorescence labeling. The barrier function of human skin models was tested by the application of biotin as tracer molecule. RESULTS: The addition of histamine to human keratinocyte cultures and organotypic skin models reduced the expression of the differentiation-associated proteins keratin 1/10, filaggrin, and loricrin by 80-95%. Moreover, the addition of histamine to skin models resulted in the loss of the granular layer and thinning of the epidermis and stratum corneum by 50%. The histamine receptor H1R agonist, 2-pyridylethylamine, suppressed keratinocyte differentiation to the same extent as did histamine. Correspondingly, cetirizine, an antagonist of H1R, virtually abrogated the effect of histamine. The expression of tight junction proteins zona occludens-1, occludin, claudin-1, and claudin-4, as well as that of desmosomal junction proteins corneodesmosin and desmoglein-1, was down-regulated by histamine. The tracer molecule biotin readily penetrated the tight junction barrier of skin cultures grown in the presence of histamine, while their diffusion was completely blocked in nontreated controls. CONCLUSIONS: Our findings suggest a new mechanism by which mast cell activation and histamine release contribute to skin barrier defects in inflammatory skin diseases.

Impact of filaggrin mutations on Raman spectra and biophysical properties of the stratum corneum in mild to moderate atopic dermatitis.

BACKGROUND: Atopic dermatitis (AD) is associated with null mutations in the filaggrin (FLG) gene. OBJECTIVE: To assess the impact of FLG null mutations on biophysical properties and the molecular composition of the stratum corneum (SC) in healthy individuals and AD patients. METHODS: A total of 196 French adults, including 97 with a history of mild to moderate AD, were genotyped for the three major European FLG mutations. Components of the natural moisturizing factor (NMF), lipids and water content in the SC were determined using Raman spectroscopy. In addition, trans-epidermal water loss, capacitance and pH of the SC were measured. RESULTS: Stratum corneum concentrations of total NMF, water, ornithine and urocanic acid (UCA) were significantly lower in AD patients than in healthy controls. Null mutations of FLG were detected in 4% of controls and 10% of AD patients. FLG mutations were associated with increased SC levels of lactate, reduced concentrations of most other NMF components and higher disease severity in AD patients. In AD patients without FLG mutations, the content of NMF constituents decreased with increasing disease severity. The concomittant presence of low concentrations of histidine, alanine and either glycine or pyrrolidone-5-carboxylic acid (PCA) in the SC was associated with FLG mutations with 92% specificity. CONCLUSIONS: Our findings suggest a low prevalence of FLG mutations in mild AD and support an important role for filaggrin in determining the physicochemical parameters of the SC. The combined measurement of several filaggrin breakdown products in the SC may be useful to specifically predict the presence of FLG mutations.

Immunolocalization of scaffoldin, a trichohyalin-like protein, in the epidermis of the chicken embryo.

Recent comparative genomic studies have identified a chicken gene that codes for a trichohyalin-like protein rich in arginine and glutamic acid termed scaffoldin. Immunocytochemistry and immunoelectron microscopy show that this protein is predominantly localized in periderm granules, subcellular structures present in the periderm of the embryonic epidermis of chick scales, beak, claw, and in the sheath of developing and regenerating feathers. This suggests that scaffoldin contributes to the formation of periderm granules and to the soft cornification of the embryonic epidermis before the definitive epidermis is formed. Scaffoldin is absent from the definitive and adult epidermis generated underneath the periderm in scales and in inter-follicular regions. Scaffoldin mixes with corneous beta-proteins (beta-keratins) synthesized in keratinocytes of the transitional layers formed beneath the periderm in the subunguis of the developing claws. Immunoreactivity for scaffoldin is absent in keratinocytes that accumulate corneous beta-proteins such as those of scales, claws, and barbule-barb cells of feathers. Corneous beta-proteins represent the prevalent type of proteins present in adult epidermis of claws, scales, and feathers. These observations indicate that scaffoldin is a protein of transitional epidermal cells of the avian integument and might represent an important component of periderm granules.

Psoriasin (S100A7) is a major Escherichia coli-cidal factor of the female genital tract.

The female urogenital tract requires an efficient defense against bacteria, potentially derived from the adjacent intestinal tract. We have thus sought to identify the factors that protect against Escherichia coli (E. coli) in the female genital tract. Vaginal fluid from healthy human donors consistently killed E. coli in vitro and vaginal epithelium strongly expressed and secreted psoriasin. Psoriasin was constitutively produced in an organotypic vaginal epithelium model, and exposure of these cells to supernatants of E. coli cultures led to an enhanced psoriasin expression. Secreted psoriasin in vaginal fluids accounted for approximately 2.5-3% of total protein. Fractionation of vaginal fluids by high performance liquid chromatography (HPLC) showed that psoriasin co-eluted with a peak of E. coli killing activity. Our data show that normal vaginal fluid contains a powerful intrinsic antimicrobial defense against E. coli and that psoriasin contributes to the innate immune response of the female genital tract.