The Whey Acidic Protein WFDC12 Is Specifically Expressed in Terminally Differentiated Keratinocytes and Regulates Epidermal Serine Protease Activity.

WFDC proteins such as peptidase inhibitor 3 and SLPI inhibit proteases in the epidermis and other tissues. In this study, we tested the hypothesis that further WFDC protein family members might contribute to epidermal homeostasis. We found that in addition to peptidase inhibitor 3 and SLPI, WFDC5 and WFDC12 were expressed in human epidermis. In contrast to WFDC5, the expression of WFDC12 was induced during the late differentiation of keratinocytes and was restricted to the outermost layer of live cells. Single-cell RNA sequencing demonstrated that WFDC12-positive keratinocytes were characterized by the upregulation of LCE mRNA expression and downregulated the expression of keratins and claudins. Immunogold-electron microscopy revealed the colocalization of WFDC12 with corneodesmosomes in the lower stratum corneum. WFDC12 was elevated in the affected skin of patients with psoriasis, atopic dermatitis, and Darier disease. By contrast, WFDC12 expression was strongly upregulated not only in the affected but even more so in clinically normal-appearing skin of patients with Netherton syndrome. Finally, functional analysis showed distinct inhibitory activity of WFDC12 on neutrophil elastase and epidermal kallikrein‒related peptidase. Altogether, our study identified WFDC12 as a marker of the last stage of epidermal keratinocyte differentiation and suggests that WFDC12 contributes to the control of protease activity in the stratum corneum.

Impact of infrared radiation on UVB-induced skin tumourigenesis in wild type C57BL/6 mice.

Although infrared radiation (IR) represents more than 50% of the solar radiation reaching the Earth's surface, this waveband has been hardly investigated in terms of tumourigenesis. The objective of the present study was to investigate the influence of IR on ultraviolet B (UVB)-induced carcinogenesis in male and female wild type mice. For this purpose, male and female C57BL/6N mice were subjected to a long-term irradiation protocol. Mice were irradiated once neonatally and from the age of eight weeks for 36 weeks with a cumulative dose of 576 kJ m-2 UVB and/or 78 895 kJ m-2 IR. In order to resemble natural sun irradiation, exposure to physiological doses of UVB and IR was performed simultaneously. Mice were screened for arising lesions twice a week. Lesions were excised and histologically diagnosed. Kaplan-Meier analyses were carried out and lesion counts and cumulated hazard rates for the development of lesions in the UVB and IR + UVB-exposed groups in male and female mice were compared. We found that IR-exposure did not change the number of epithelial malignant tumours in UVB-exposed wild type mice. In combination with IR there was a tendency of more tumours with increased malignancy: 23 vs. seven spindle cell shaped sarcomas and seven vs. two MelanA+/S100+ tumours in groups of 35 C57BL/6 mice. IR did not influence UVB-induced carcinogenesis differently in male and female mice. However, comparing UVB and sham irradiated animals irrespective of IR exposure, UVB-induced non-epithelial tumours arose significantly earlier in male mice than in female mice.

Ultraviolet radiation induces Melan-A-expressing cells in interfollicular epidermis in wild-type mice.

Adult wild-type mice are not supposed to be proper models for ultraviolet radiation (UVR)-induced melanoma since melanocytes are confined to hair follicles and cannot be sufficiently reached by UVR. On the other hand, in mutated mouse models used for melanoma research limitations, including an altered immune system and selection of affected pathways, lead to tumors phenotypically quite different from naturally occurring melanomas. We compared the distribution of epidermal melanocytes in UVR and not-UVR-exposed wild-type C57BL/6 mice. Starting at the age of 8 weeks, mice were exposed to physiologic doses of UVR three times weekly over 16 weeks. Back skin biopsies were taken 4, 8, 12 and 16 weeks after initiation of exposure, and stained for Melan-A, representing a highly selective marker for melanocytes. Surprisingly, after exposure to UVR, Melan-A positive cells were detected also in the interfollicular epidermis of C57BL/6 mice. We conclude that UVR is capable of inducing interfollicular epidermal melanocytes in wild-type mice.

Knockdown of filaggrin impairs diffusion barrier function and increases UV sensitivity in a human skin model.

Loss-of-function mutations in the filaggrin gene are associated with ichthyosis vulgaris and atopic dermatitis. To investigate the impact of filaggrin deficiency on the skin barrier, filaggrin expression was knocked down by small interfering RNA (siRNA) technology in an organotypic skin model in vitro. Three different siRNAs each efficiently suppressed the expression of profilaggrin and the formation of mature filaggrin. Electron microscopy revealed that keratohyalin granules were reduced in number and size and lamellar body formation was disturbed. Expression of keratinocyte differentiation markers and the composition of lipids appeared normal in filaggrin-deficient models. The absence of filaggrin did not render keratins 1, 2, and 10 more susceptible to extraction by urea, arguing against a defect in aggregation. Despite grossly normal stratum corneum morphology, filaggrin-deficient skin models showed a disturbed diffusion barrier function in a dye penetration assay. Moreover, lack of filaggrin led to a reduction in the concentration of urocanic acid, and sensitized the organotypic skin to UVB-induced apoptosis. This study thus demonstrates that knockdown of filaggrin expression in an organotypic skin model reproduces epidermal alterations caused by filaggrin mutations in vivo. In addition, our results challenge the role of filaggrin in intermediate filament aggregation and establish a link between filaggrin and endogenous UVB protection.

Unusual clinical manifestation of linear IgA dermatosis: a report of two cases.

Linear IgA dermatosis is a rare autoimmune bullous skin disease with subepidermal blister formation and linear IgA deposits along the basement membrane zone. We describe two female patients showing erythematous annular plaques with scaling at the margin, strictly localized to the palms in one patient, and also found on the soles and buttocks in the second patient. Histology showed numerous neutrophils in the dermis with an admixture of eosinophils, some subepidermal clefting, and occasional papillary microabscesses. Direct immunofluorescence and immunoelectron microscopy revealed in vivo IgA deposition along the basement membrane zone. One patient cleared after treatment with dapsone. The second patient did not respond to dapsone alone and various immunosuppressive treatment regimens. Considerable improvement was achieved with intravenous immunoglobulin therapy combined with corticosteroid and dapsone.