Expression of corneodesmosin in the granular layer and stratum corneum of normal and diseased epidermis.
The stratum corneum (SC) has long been considered as a sort of inert membrane destined to be shed at the surface of the epidermis. During the last two decades, however, several lines of evidence have been reported, suggesting that active physical and chemical changes take place in the horny layer despite the absence of intracytoplasmic organelles. In particular, processing of filaggrin, replacement of the plasma membrane by a ceramide envelope and constant, progressive modification of extracellular lipid multilayers have been put forward. Recently, attention has focused on the intercellular junctions, which may be involved in the regulation of SC desquamation. Corneodesmosin, a newly discovered protein of s.c. desmosomes (corneodesmosomes), is synthesized at the latest stages of keratinocyte differentiation and persists between the horny cells until desquamation occurs. In the present study, we performed immunohistochemical and immuno-ultrastructural investigations on corneodesmosin expression in various skin lesions characterized by abnormal production and/or retention of the horny layer. Our results suggest that corneodesmosin expression is independent from profilaggrin synthesis. We found corneodesmosin in almost all morphologically recognizable corneodesmosomal structures and specifically those which persisted up to the SC surface. Hyperkeratotic lesions which are characterized by an increased number of junctions showed intense immunoreactivity with anticorneodesmosin antibody. A complete absence of corneodesmosin was not observed in any disease. This finding, together with our previous biochemical studies, suggests that corneodesmosin may exert a protective function against proteolytic degradation of corneodesmosomes both in normal skin and in the pathological horny layer.