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Corneodesmosin (CDSN), desmoglein 1 (DSG1), and desmocollin 1 (DSC1) are adhesive proteins of the extracellular part of the corneodesmosomes, the junctional structures that mediate corneocyte cohesion. The degradation of these proteins at the epidermis surface is necessary for desquamation. Two serine proteases of the kallikrein family synthesized as inactive precursors have been implicated in this process: the stratum corneum chymotryptic enzyme (SCCE/KLK7/hK7) and the stratum corneum tryptic enzyme (SCTE/KLK5/hK5). Here, we analyzed the capacity of these enzymes to cleave DSG1, DSC1, and epidermal or recombinant forms of CDSN, at an acidic pH close to that of the stratum corneum. SCCE directly cleaved CDSN and DSC1 but was unable to degrade DSG1. But incubation with SCTE induced degradation of the three corneodesmosomal components. Using the recombinant form of CDSN, either with its N-glycan chain or enzymatically deglycosylated, we also demonstrated that oligosaccharide residues do not protect CDSN against proteolysis by SCCE. Moreover, our results suggest that SCTE is able to activate the proform of SCCE. These results strongly suggest that the two kalikreins are involved in desquamation. A model is proposed for desquamation that could be regulated by a precisely controlled protease-protease inhibitor balance.

Corneodesmosin, defined as the protein recognized by the monoclonal antibody G36-19, is a recently described late differentiation protein of human cornified epithelium. In the stratum corneum it is localized in the extracellular parts of modified desmosomes (corneodesmosomes) and adjacent parts of the cornified cell envelope. The aim of the present study was to investigate whether corneodesmosin undergoes changes in the stratum corneum which can be related to the cohesive state of the tissue and to desquamation. Extracts of plantar stratum corneum from various tissue levels and tape-stripped non-palmoplantar stratum corneum were analysed by immunoblotting with G36-19. In addition, the fate of corneodesmosin during shedding of surface cells in a recently described in vitro model of desquamation in plantar stratum corneum was investigated and compared with the degradation of the desmosomal protein desmoglein I in this system. The apparent molecular weights of the major G36-19-positive components in plantar stratum corneum ranged between 33 and 48 kDa. The components with the highest molecular weights were predominant in the deepest tissue layers. In the intermediate tissue layers G36-19-positive components of molecular weight 33-36, 39 and 44-48 kDa were found. There seemed to be a further degradation of the 33 to 36-kDa components in the most superficial parts of the tissue. In surface cells dissociated in vivo as well as in vitro no G36-19-positive components with molecular weights above 36 kDa were detected. Results from analyses of nonpalmoplantar stratum corneum suggested that corneodesmosin is degraded in this tissue in a way that may be similar to that in plantar stratum corneum.(ABSTRACT TRUNCATED AT 250 WORDS)

Plantar stratum corneum was examined by means of transmission electron microscopy after conventional osmium fixation and after fixation with ruthenium tetroxide. The latter fixative was used in order to reveal the possible existence of lamelarly ordered lipids in the intercellular space, as has previously been demonstrated for non-palmo-plantar stratum corneum. A major part of the plantar stratum corneum intercellular space was occupied by extracellular parts of desmosomes. In specimens fixed with ruthenium tetroxide the intercellular space not occupied by desmosomes was found to contain multiple alternating electron dense and electron lucid bands, suggestive of membraneous structures. This pattern appeared to be similar to that previously described for non-palmo-plantar stratum corneum. It is suggested that the intercellular lipids of palmo-plantar stratum corneum may be qualitatively similar to the intercellular lipids of non-palmo-plantar stratum corneum. The lower lipid content, expressed as weight per unit weight of tissue, in palmo-plantar stratum corneum as compared to non-palmo-plantar stratum corneum may be related to the fact that a larger portion of the intercellular space of the former tissue is occupied by desmosomes. The relatively high water permeability of palmo-plantar stratum corneum implies that desmosomes, i.e. non-lipid regions of the intercellular space, may have a high water permeability and hence could establish a hydrophilic route through the stratum corneum.

Pieces of plantar stratum corneum were incubated with trypsin. This resulted in cell dissociation. The only observable ultrastructural change caused by trypsin was a degradation of desmosomal plates between dissociating cells. This suggests that desmosomes are of primary importance in plantar stratum corneum cell adhesion.