PARATHYROID HORMONE-RELATED PROTEIN EXPRESSION AND SECRETION IN A SKIN ORGANOTYPIC CULTURE SYSTEM

Parathyroid hormone-related protein (PTHrP), an important factor in th e pathogenesis of humoral hypercalcemia of malignancy, is produced by many normal tissues, including the epidermis, where it is thought to p lay a role in the regulation of keratinocyte growth and differentiatio n. Most in vitro studies of normal keratinocytes use monolayer cell cu ltures, which have limitations, including the inability to reproduce t he stratified structure of the epidermis. The objective of this study was to investigate PTHrP production and secretion, and mRNA expression in skin organotypic cultures. The cultures consisted of an artificial dermis with differentiating keratinocytes grown at the air-liquid int erface. Immunohistochemical assessment of cytokeratins 14 and 10/13, i nvolucrin, and proliferative cell nuclear antigen (PCNA) demonstrated that keratinocytes differentiated in a manner similar to keratinocytes in normal epidermis. PTHrP expression was demonstrated in all viable layers of the epidermis, as well as in some fibroblasts of the collage n lattice by immunohistochemistry and in situ hybridization. Since mos t fibroblasts expressed alpha-smooth muscle actin, these cells were in terpreted to be consistent with myofibroblasts, PTHrP expression by my ofibroblasts suggests a possible role for PTHrP in the regulation of c ontractibility of these cells, PTHrP was also detected in conditioned media for 50 days. In conclusion, because of its superior tissue morph ology and ability to induce organized keratinocyte differentiation, th is culture system will be an excellent model to study the role of PTHr P in pathologic and physiologic processes involving the epidermis in v itro.