Biomineralization allows craniofacial bones, long bones and teeth to exert their normal function in the adult. However, despite its obvious importance, the mechanisms of regulation of mineralization are still poorly understood. Matrix vesicles, cell-derived microstructures, appear to play a critical role in this process, but the mechanisms of their control is still not understood. In the preliminary studies from this investigator, there are original data to show that interactions between matrix proteins, collagen type II and X collagens, and matrix vesicles lead to a stimulation of their calcification. Evidence is also presented that these interactions are mediated by annexin V, a major component of matrix vesicles. Annexin V belongs to a family of proteins that bind to acidic phospholipids in the presence of calcium. In addition, annexin V forms calcium channels when inserted into phospholipid bilayer membranes. Therefore, it seems that the binding of type II and X collagens to annexin V stimulates its calcium channel properties, thereby controlling calcium influx into matrix vesicles and initiation of calcification. The hypothesis of this proposal is that the collagen-annexin V interactions play a critical role in the regulation of tissue mineralization. This hypothesis will be tested directly by the use of diverse experimental strategies, including binding assays, site-directed mutagenesis, calcium channel studies, cell culture, photochemical studies and overexpression of mutated annexin molecules. The results are intended to shed light on fundamental mechanisms involved in annexin V calcium channel formation and modulation by binding to collagens, and provide insights into the function of these interactions in tissue calcification. The applicant suggests that this information should contribute greatly to the current understanding of biomineralization, and could suggest direct ways to prevent uncontrolled mineralization in tissues during pathological conditions.
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