Distribution of noncollagenous proteins in the matrix of adult human bone: Evidence of anatomic and functional heterogeneity

The microanatomic distribution of several noncollagenous proteins (NCPs) in bone matrix was examined by immunohistochemical analysis of glycol‐methyl methacrylate‐embedded normal adult human bone biopsies. Osteopontin and bone sialoprotein stained throughout the lamellae of both trabecular and cortical bone. Cement lines (cortical and trabecular) and the mineralized matrix immediately adjacent to each Haversian canal were intensely stained. Osteocalcin was detected in cement lines; however, lamellar staining varied depending on the location within the individual unit of bone. In cortical bone, the inner concentric lamellae of osteons were often unstained but the outer lamellae were heavily stained for osteocalcin. Osteonectin was not detected in cement lines and in most specimens revealed a pattern similar to that of osteocalcin with respect to the absence of immunostaining within the inner concentric lamellae. Decorin was prominent in the perilacunar matrix, the canaliculi of osteocytes, and the matrix immediately adjacent to quiescent Haversian canals. Biglycan appeared evenly distributed throughout cortical and trabecular bone matrix. These results suggest that the incorporation of NCPs into matrix may vary depending on the stage of formation of individual bone units. The specific distribution and spatial relationship of these NCPs may be related to the function of each protein during bone resorption and formation. The distinct patterns of NCP localization in bone support the hypothesis that in addition to their structural and mineral‐inducing properties, these proteins may influence the events associated with bone remodeling, such as recruitment, attachment, differentiation, and activity of bone cells.