Dermatofibroma: upregulation of syndecan-1 expression in mesenchymal tissue.

Cell surface proteoglycans play a prominent role in tissue remodeling and homeostasis. Syndecans, their most prominent members, act by binding to growth factors and interstitial matrix molecules. They, thereby, modulate the effect of the primary ligand-receptor interaction at the cell membrane by increasing the affinity of cell-ligand interactions. Additionally, they influence the strength of cell-cell and cell-matrix interactions. Syndecan-1 is the prototypical member of this family of proteins. Under physiological conditions, its expression is restricted to the epidermis, the outer root sheath of the anagen hair follicle, and the sweat gland epithelium. The dermal compartment-with the exception of the follicular papilla of the anagen hair follicle-physiologically does not express syndecan-1. Dermatofibromas are mesenchymal lesions, which often exhibit hyperplastic changes in the overlying epidermis. In analogy to the hair follicle, they, thereby, can be used as a model for studying epithelial-mesenchymal interactions. In the current study, we examined dermatofibromas immunohistochemically for syndecan-1 expression. We report immunoreactivity for syndecan-1 in dermatofibromas, which correlates mainly with the deposition of intercellular matrix material. Syndecan-1 is also noted in the stroma surrounding areas of basaloid hyperplasia overlying dermatofibromas and may be important in the pathogenesis of this inductive phenomenon. In analogy to the follicular papilla of the anagen hair follicle, the staining pattern for syndecan-1 in dermatofibromas indicates that this cell surface protein is produced by stromal cells and most likely serves an essential function in the growth of these common mesenchymal cutaneous lesions.