Immunohistology of bone proteins, bone quality, and bone turnover

The role played by noncollagenous proteins in bone metabolism, originally conceived as mainly related to the promotion and regulation of matrix mineralization, probably involves a number of regulatory functions. Local composition of the bone matrix may affect cell responses to regulatory agents in different ways, which include binding of growth factors within the pericellular environment, and integrins on the cell surface. The focus of studies on the expression and localization of bone proteins in intact tissues should therefore move towards a detailed dissection of heterogeneity of matrix locales throughout bone development, growth, and postnatal remodeling. So far, such studies have provided valuable information on the diverse phenotypic profiles of maturational stages of bone cells, and more recently, on actual differences in secretory output of cells otherwise comprised in the 'mature' osteoblastic compartment. Still, a main gap in current information is represented by the paucity of data on bone protein expression and deposition during post-natal remodeling and its diseases. Filling this gap will require a more focused interest in post-natal (trabecular) bone, and the development of appropriate protocols of tissue preparation (noncollagenous) proteins in bone physiology.