Grant: Project Grant

Bones and teeth undergo a process called mineralization where small calcium- and phosphate-containing crystals are deposited into a scaffolding of proteins called the extracellular matrix. Protein-mineral interactions define properties of the mineral phase making the tissues strong and hard. Our work is relevant to understanding the decreased mineralization that occurs in the osteomalacia and odontomalacia diseases where bones and teeth are incompletely mineralized, soft and deformable, and prone to buckling called pseudofracturing. The research is also relevant to calcification diseases of normally "soft" tissues (such as the mineralization of blood vessels and heart valves). Compelling evidence indicates that a protein called osteopontin (OPN) controls mineralization in most tissues. Also important is that processing of OPN by enzymes leads to mineralization-inhibiting protein fragments (peptides) with different inhibitory potencies. We investigate how processing of OPN defines a control mechanism affecting biomineralization. Here we propose to examine this possible regulation, guided by the general hypothesis that OPN in bones and teeth, and peptides derived from enzymatic processing of OPN, control mineralization by binding to mineral precursor phases and crystal surfaces in a way that influences the hardening process. We will investigate these mechanisms in cell-free systems in which calcium-phosphate crystals are grown in the presence of OPN/peptides, in cell culture and mouse models of disease, and in humans from small bone biopsy samples and extracted teeth. We will use biochemical measurements, bioimaging microscopies including high-resolution electron and atomic force microscopy and X-ray approaches, and various biophysical methods to characterize tissues, mineral and mineral-protein complexes. Such work should provide insight into keeping bones and teeth strong and healthy, and may suggest ways to treat patients where these tissues are defective.