High expression level of bone degrading proteins as a possible inducer of osteolytic features in pigmented villonodular synovitis

Protein expression of osteopontin (OPN), osteoprotegerin (OPG), bone sialoprotein (BSP), osteocalcin (OC), RANKL and PTHrP was determined by use of immunohistochemical analysis on tissue arrays (48 cases of PVNS, 20 cases of active (a-RA), non-active rheumatoid arthritis (na-RA), and osteoarthritis (OA)). Additionally, gene expression was analysed using complimentary DNA (cDNA) microarrays. NS cases showed a higher level of both protein and gene expression of RANKL, OPN and BSP in comparison with OA cases. Expression of OPG was not significantly different in PVNS compared to OA. The RANKL/OPG expression ratio was significantly higher in PVNS than in OA. High expressions level of proteins involved in bone degradation in PVNS may promote an intra-osseous propagation of the lesion. This evidence suggests that PVNS might respond to treatment using specific inhibitors of RANKL, OPN and BSP.