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Background: Epidermal homeostasis is maintained through the balance between keratinocyte proliferation, differentiation and desquamation; however, human skin equivalent (HSE) models are known to differentiate excessively. In native tissue, proteases such as kallikrein-related peptidase (KLK) 5 and KLK7 cleave the extracellular components of corneodesmosomes; proteins corneodesmosin, desmocollin 1 and desmoglein 1, loosening the cellular connections and enabling desquamation. The actions of KLK7 are tightly controlled by protease inhibitors, skin-derived antileucoproteinase (SKALP) and lymphoepithelial Kazal-type-related inhibitor (LEKTI), which also inhibits KLK5, localizing protease activity to the stratum corneum., Objectives: To investigate the mechanisms that inhibit the desquamation cascade in HSE models., Methods: Human skin tissue and HSE models were investigated using gene microarray, real-time polymerase chain reaction (PCR), immunohistochemistry and Western blot analysis to examine key components of the desquamation pathway. To elucidate proteolytic activity in HSEs and native skin, in situ and gel zymography was performed., Results: Histological analysis indicated that HSE models form a well-organized epidermis, yet develop an excessively thick and compact stratum corneum. Gene microarray analysis revealed that the desquamation cascade was dysregulated in HSE models and this was confirmed using real-time PCR and immunohistochemistry. Immunohistochemistry and Western blot indicated overexpression of LEKTI and SKALP in HSEs. Although KLK7 was also highly expressed in HSEs, zymography indicated that protease activation and activity was lower than in native skin., Conclusions: These findings demonstrate that stratum corneum thickening is due to inhibited KLK5 and KLK7 activation and a subsequent lack of corneodesmosome degradation in the HSE model epidermis., (© 2016 British Association of Dermatologists.)

Background: Epidermogenesis and epidermal wound healing are tightly regulated processes during which keratinocytes must migrate, proliferate and differentiate. Cell-to-cell adhesion is crucial to the initiation and regulation of these processes. CUB-domain-containing protein (CDCP)1 is a transmembrane glycoprotein that is differentially tyrosine phosphorylated during changes in cell adhesion and survival signalling, and is expressed by keratinocytes in native human skin, as well as in primary cultures., Objectives: To investigate the expression of CDCP1 during epidermogenesis and its role in keratinocyte migration., Methods: We examined both human skin tissue and an in vitro three-dimensional human skin equivalent model to examine the expression of CDCP1 during epidermogenesis. To examine the role of CDCP1 in keratinocyte migration we used a function-blocking anti-CDCP1 antibody and a real-time Transwell™ cell migration assay., Results: Immunohistochemical analysis indicated that in native human skin CDCP1 is expressed in the stratum basale and stratum spinosum. In contrast, during epidermogenesis in a three-dimensional human skin equivalent model, CDCP1 was expressed only in the stratum basale, with localization restricted to the cell-cell membrane. No expression was detected in basal keratinocytes that were in contact with the basement membrane. Furthermore, an anti-CDCP1 function-blocking antibody was shown to disrupt keratinocyte chemotactic migration in vitro., Conclusions: These findings delineate the expression of CDCP1 in human epidermal keratinocytes during epidermogenesis and demonstrate that CDCP1 is involved in keratinocyte migration., (© 2012 The Authors. BJD © 2012 British Association of Dermatologists.)