EXPRESSION OF BONE-RELATED PROTEIN MESSENGER-RNA IN HUMAN MENINGIOMAS - POSSIBLE INVOLVEMENT OF OSTEOPONTIN IN DEVELOPMENT OF PSAMMOMA BODIES

Meningiomas often contain concentric calcified foci, referred to as psammoma bodies. Since calcium phosphate deposits in both psammoma bodies and bone tissues, we examined whether messenger (m) RNA of bone-related extracellular matrix proteins and bone morphogenetic proteins (BMP) were expressed in human meningioma tissues. Northern blotting demonstrated the expression of osteopontin (OPN), matrix Gla protein (MGP), osteonectin (ON) and BMP-4 mRNA but not bone sialoprotein, osteocalcin and BMP-2 mRNA. In situ hybridization revealed that most OPN mRNA-expressing cells were located around the psammoma bodies in meningothelial whorls. Moreover, combination of in situ hybridization and immunohistochemistry on serial sections showed that the OPN mRNA-expressing cells were CD68-positive, suggesting they were macrophages. Immunohistochemistry with anti-OPN antibody and von Kossa staining on the adjacent section showed that the deposition site of OPN protein was consistent with that of calcium phosphate. Neither MGP nor ON mRNA expression appeared to correlate with the calcification. The present result suggests that OPN produced by CD68-positive macrophages may play a significant role for development of psammoma bodies in meningiomas.