Possible Role of Osteopontin in Deposition of Calcium Phosphate in Human Pilomatricomas

Abstract

Human pilomatricomas are benign epidermal appendage tumors composed of hair matrix-like basaloid cells and keratinized remnant cells referred to as shadow cells. Deposition of calcium phosphate usually occurs in the shadow cell nests. Because osteopontin is believed to be involved in the deposition of calcium phosphate in bones, we asked whether osteopontin messenger RNA also is expressed in pilomatricomas. Using Northern blotting and in situ hybridization we detected osteopontin messenger RNA in pilomatricoma tissues but not in normal skin tissue. By the combination of in situ hybridization and immunohistochemistry, osteopontin messenger RNA-expressing cells were identified as CD68-positive macrophages surrounding the shadow cell nests. Immunohistochemistry of anti-human osteopontin antibodies revealed that the localization of osteopontin protein was consistent with that of calcium phosphate. The present results suggest that osteopontin produced by macrophages may play a significant role in the deposition of calcium phosphate in the shadow cell nests of pilomatricomas.