VITAMIN D RECEPTOR mRNA IS EXPRESSED IN OSTEOCLAST-LIKE CELLS OF HUMAN GIANT CELL TUMOR OF BONE (OSTEOCLASTOMA)

The conventional view of the effects of 1,25- (OH)2D3on osteoclastogenesis and bone resorption are thought to be mediated by stromal cells or osteoblastic cell. Giant cell tumor of bone (GCT) is characterized by multinuclear giant cells (osteoclast-like cells) distributed among a mass of mononuclear cells. Because it is very difficult to obtain normal human osteoclasts, many investigators, including ourselves, have used GCT as a source of human osteoclasts to enhance the understanding of normal skeletal remodeling and especially the hormone regulation of osteoclast functions. In this report, expression of human vitamin D receptor (VDR) mRNA was examined in the various components of GCT using the fluorescence in situ hybridization (FISH) technique. The results showed that VDR gene transcripts were expressed in both multinuclear cells (osteoclast-like cells) and mononuclear macrophage-like cells but not in stromal-like tumor cells in two cases of GCT examined. Measurement of VDR gene transcripts in situ by confocal microscopy showed that the level of VDR mRNA in osteoclast-like giant cells is greater than that in macrophage-like cells (p < 0.05). These findings suggest that 1,25- (OH)2D3mediated osteoclastic bone resorption or osteoclastogenesis could at least, in part, occur by direct action on osteoclasts/their precursor cells.