Chapter 02, Bone Matrix and Mineralization

By Francis Glorieux

Academic Press
Publication date: September 2011

ISBN: 9780124094079

Digital Book format: ePub (Adobe DRM)

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This chapter provides an overview on the composition of the extracellular matrix of bone and discusses the matrix mineralization, and how proteins in the matrix are thought to regulate the process. The organic matrix constitutes approximately 20%-30% by weight of bone. The organic matrix contains approximately 90% collagen (by weight) and 10% non-collagenous proteins, proteoglycans, and lipids. Plasma proteins are also present in the organic matrix. Many plasma proteins permeate bone deriving from its rich vasculature, but have little or no affinity for bone, whereas others such as ?2-HS glycoprotein (fetuin A) have a higher affinity for the matrix and/or mineral of bone. The mineralization of vertebrate bone is a remarkable melding of geological and biological processes. The location of mineral within bone extracellular matrix clearly resides both within, and between, the collagen fibrils. These distinct ultra structural compartments for the mineral phase invariably provide different spatial and chemical environments for crystal growth, affecting crystal size and orientation. Beyond the initiation of mineralization in bone, crystal growth is regulated by a subcategory of the secreted, calcium-binding phosphoprotein (SCPP) family called the small, integrin-binding ligand, N-linked glycoproteins (SIBLINGs) that includes: OPN, MEPE, BSP, DMP1 and DSPP. The need for crystal growth inhibitors in tissues destined for mineralization may not at first glance be readily apparent but the massive mineralization events that occur in bones and teeth require a significant level of SIBLING protein regulation at the organic-inorganic interface as crystals must attain tissue-specific size, shape, and orientation with the extracellular matrix.