Paget's disease is associated with changes in the immunohistochemical distribution of noncollagenous matrix proteins...

Paget's disease of bone is characterized histologically by abnormal architecture of bone matrix. Extensive areas of woven bone and numerous scalloped cement lines occur as a result of increased irregular remodeling. Noncollagenous proteins (NCP) play an important role in the organization and mineralization of bone matrix and promote distinct cell-matrix interactions necessary for normal remodeling. To gain insight into the pathological changes in the biochemical composition of Pagetic bone, the distribution of NCPs in the calcified matrix of bone from patients with known Paget's disease was compared to that of bone from normal healthy volunteers. Undecalcified plastic-embedded sections of bone were stained immunohistochemically using antibodies generated against several NCPs. In Pagetic and normal bone a similar distribution of osteopontin was observed at cement (reversal) lines, whereas significant differences were observed in the distribution of osteopontin in the matrix immediately adjacent to Haversian canals, where initial osteoclast recruitment and attachment occur. The differences in osteopontin distribution appeared to be related to the state and severity of the disease. Site-specific differences in the distribution of osteonectin, osteocalcin, and decorin were also observed between normal bone and cortical and periosteal de novo Pagetic bone, whereas the distribution of other matrix proteins, such as biglycan, was unchanged. We conclude that these site-specific changes in the biochemical distribution of NCPs in Pagetic bone probably reflect abnormal production and/or incorporation during bone remodeling and may lead to disorganized matrix assembly and mineralization as well as have profound effects on bone cell functions.