BackgroundPrevious studies have extensively documented antimicrobial and chemotactic activities of beta-defensins. Human beta-defensin-2 (hBD-2) is strongly expressed in lesional psoriatic epidermis, and recently we have shown that high beta-defensin genomic copy number is associated with psoriasis susceptibility. It is not known, however, if biologically and pathophysiologically relevant concentrations of hBD-2 protein are present in vivo, which could support an antimicrobial and proinflammatory role of beta-defensins in lesional psoriatic epidermis.Methodology/Principal FindingsWe found that systemic levels of hBD-2 showed a weak but significant correlation with beta defensin copy number in healthy controls but not in psoriasis patients with active disease. In psoriasis patients but not in atopic dermatitis patients, we found high systemic hBD-2 levels that strongly correlated with disease activity as assessed by the PASI score. Our findings suggest that systemic levels in psoriasis are largely determined by secretion from involved skin and not by genomic copy number. Modelling of the in vivo epidermal hBD-2 concentration based on the secretion rate in a reconstructed skin model for psoriatic epidermis provides evidence that epidermal hBD-2 levels in vivo are probably well above the concentrations required for in vitro antimicrobial and chemokine-like effects.Conclusions/SignificanceSerum hBD-2 appears to be a useful surrogate marker for disease activity in psoriasis. The discrepancy between hBD-2 levels in psoriasis and atopic dermatitis could explain the well known differences in infection rate between these two diseases.

Psoriasis is an inflammatory skin disease driven by aberrant interactions between the epithelium and the immune system. Anti-psoriatic drugs can therefore target either the keratinocytes or the immunocytes. Here we sought to develop an in vitro reconstructed skin model that would display the molecular characteristics of psoriatic epidermis in a controlled manner, allowing the screening of anti-psoriatic drugs and providing a model in which to study the biology of this disease. Human skin equivalents generated from normal human adult keratinocytes after air exposure and stimulation by keratinocyte growth factor and epidermal growth factor displayed the correct morphological and molecular characteristics of normal human epidermis whereas the psoriasis-associated proteins, hBD-2, SKALP/elafin, and CK16, were absent. Skin equivalents generated from foreskin keratinocytes were clearly abnormal both morphologically and with respect to gene expression. When normal skin equivalents derived from adult keratinocytes were stimulated with psoriasis-associated cytokines

Activated leukocyte cell adhesion molecule (ALCAM/CD166/ MEMD) could function as a cell surface sensor for cell density, controlling the transition between local cell proliferation and tissue invasion in melanoma progression. We have tested the hypothesis that progressive cell clustering controls the proteolytic cascade for activation of gelatinase A/matrix metalloproteinase-2 (MMP-2), which involves formation of an intermediate ternary complex of membrane type 1 MMP (MT1-MMP/MMP-14), tissue inhibitor of metalloproteinase-2 (TIMP-2), and pro-MMP-2 at the cell surface. Surprisingly, truncation of ALCAM severely impaired MMP-2 activation in a nude mouse xenograft model, in which we previously observed diminished primary tumor growth and enhanced melanoma metastasis. Comparative studies of twodimensional monolayer and three-dimensional collagen-gel cultures revealed that extensive cell-to-cell contacts, wildtype ALCAM, and cell-to-matrix interactions were all indispensable for efficient conversion of pro-MMP-2 to its active form in metastatic melanoma cells. Truncated, dominantnegative ALCAM diminished MMP-2 activation via reduced transcript levels and decreased processing of MT1-MMP. Failure of the proteolytic cascade after selective ALCAM depletion by RNA interference was mainly due to incomplete MT1-MMP processing, which was otherwise promoted by extensive cell-to-cell contacts. These data attribute a novel signaling role to ALCAM in regulation of proteolysis and support its previously postulated sensor function in invasive growth. (Cancer Res 2005; 65(19): 8801-8)

Both the immune system and the epidermis likely have an important role in the pathogenesis of atopic dermatitis (AD). The objective of the present study was to develop a human skin equivalent model exhibiting morphologic and molecular characteristics of AD in a controlled manner. Skin equivalents generated from normal adult human keratinocytes were stimulated with type 2 T-helper cell (Th2) cytokines IL-4 and IL-13, and morphologic features and gene expression of the epidermis were studied. Th2 cytokines induced intercellular edema similar to spongiotic changes observed in lesional AD as assessed at histopathologic analysis and electron microscopy. Furthermore, genes known to be specifically expressed in epidermis of patients with AD such as CAII and NELL2 were induced. In contrast, expression of psoriasis-associated genes such as elafin and hBD2 was not changed. Th2 cytokines caused DNA fragmentation in the keratinocytes, which could be inhibited by the caspase inhibitor Z-VAD, which suggests that apoptosis was induced. In addition, up-regulation of the death receptor Fas was observed in keratinocytes after Th2 cytokine stimulation. IL-4 and IL-13 induced phosphorylation of the signaling molecule STAT6. It was concluded that the skin equivalent model described herein may be useful in investigation of the epidermal aspects of AD and for study of drugs that act at the level of keratinocyte biology.

I In adult human skin, the expression of the extracellular matrix glycoprotein tenascin is limited. Under hyperproliferative conditions such as psoriasis and epidermal tumours, dermal tenascin expression is strongly upregulated. The aim of this study was to investigate the pattern and kinetics of tenascin expression in human skin during wound healing and to address the question of whether keratinocytes can directly interact with tenascin during re-epithelialization. Tenascin expression was investigated in excisional wounds in normal human skin, in explants of normal human skin, and in chronic venous ulcers, using immunohistochemistry. No tenascin staining was found directly underneath the leading edge of the sheet of migrating keratinocytes in the excisional wounds and explants. In the excisional wounds and the ulcers, dermal tcnascin was strongly upregulated in areas adjacent to hyperproliferative epidermis. These hyperproliferative areas are located approximately 10-50 cells behind the leading edge, as assessed by staining for the Ki-67 antigen and the proliferating cell nuclear antigen (PCNA). At the later stages of normal wound healing and in the chronic ulcers, tenascin was also detected in the wound bed. In these areas, the dermal-epidermal junction stained positive for laminin but was negative for heparan sulphate. The absence of the latter basement membrane component suggests that the formation of a new basement membrane is not completed in these wounds. These findings suggest that tenascin is not a substrate for migrating keratinocytes; that the rapid induction of tenascin expression in the papillary dermis during wound healing results from interaction with the hyperproliferative epidermis; and that in the later stages of wound healing, keratinocytes can potentially interact with tenascin in the wound bed, because the basement membrane of the neo-epidermis is incomplete.