BM-40 (OSTEONECTIN, SPARC) IS EXPRESSED BOTH IN THE EPIDERMAL AND IN THE DERMAL COMPARTMENT OF ADULT HUMAN SKIN

BM-40 (Osteonectin, SPARC) is the most abundant glycoprotein secreted by human osteoblasts. hybridization studies on the expression of BM-40 mRNA in murine tissues have demonstrated the highest. levels of trans cripts in bone, but expression was also observed in several other mese nchymal tissues. In contrast, little is known about the expression of BM-40 in human tissues, especially in situ. Total RNA obtained from no rmal human skin was analyzed by northern blotting and revealed a marke d expression of BM-40, To analyze its expression in vivo, in situ hybr idization was performed, demonstrating that BM-40 is expressed in fibr oblasts, smooth muscle, and endothelial cells in the dermis, Interesti ngly, BM-40 mRNA was also detected throughout the basal, spinous, and granular layers in the epidermis of adult human skin. Further analysis by immunohistochemistry revealed a marked deposition in the dermis th at was most intense-directly below the basement membrane in the papill ary dermis and around vascular as well as glandular structures, In the epidermis, BM-40 protein could be detected intercellularly in supraba sal layers, This finding is further supported by the intercellular dep osition of BM40 detected by immunofluorescence in cultured keratinocyt es. This study demonstrates that BM-40 that has previously been though t to be exclusively expressed in extracellular matrix producing cells may in fact play a role in differentiation and maintenance of the epid ermis.