Biglycan Modulation of Bone Morphogenetic Protein-2 Functions

Patricia A. Miguez Biglycan Modulation of Bone Morphogenetic Protein-2 Functions (Under the direction of Professor Mitsuo Yamauchi) Biglycan (BGN) is a proteoglycan found in high abundance in mineralized tissues. Study of its functions has unveiled roles in collagen organization (i.e. type VI), osteoblast differentiation, matrix mineralization, inflammatory processes, etc. Recently, we have reported that BGN promotion of osteoblast differentiation is due in part to its ability to positively modulate bone morphogenetic protein (BMP) functions. In the studies that follow, we (1) investigated the role of glycosaminoglycans (GAGs) of BGN on BGN-assisted BMP-2 function in vitro by utilizing a C2C12 cell system and in vivo by using a critical-sized mandible defect model in the Sprague-Dawley rat; (2) characterized by microcomputed tomography and histology the newly formed bone (NFB) in BGN-assisted BMP-2-induced osteogenesis; and (3) investigated which domain of the core protein of BGN is most effective in promoting BMP-2 function in vitro and applied it in vivo. We found that BGN devoid of GAGs is most effective in assisting BMP function in vitro and in vivo and that this positive modulation in vitro occurs through increased phosphorylation of Smad 1/5/8. In the animal model, rats treated with a low dose of BMP-2 in conjunction with appropriate dose of BGN formed a less porous and more mature type of bone than a high dose of BMP-2 alone. High iii dose BMP-2 formed an ectopic type of NFB and presented characteristics of a high turnover bone as per presence of osteoclast-like cells and yellow/orange picrosirius red staining. The BMP-2 and BMP-2 + BGN rats showed strong β-catenin immunoreactivity at 2 weeks post-surgery. The rats that did not form significant amounts of bone did not show this pattern of staining. Finally, the effector domain of the core protein appears to reside between the N terminus and leucine rich repeat (LRR) 6, possibly in the LRR1~3. LRR1~3 was as effective as BGN full core protein in assisting BMP-2-induced osteogenesis in vivo. We conclude that the use of BGN or its effective domain combined with low concentrations of BMP-2 may be a more predictable, controllable and cost-effective approach than the use of high dose BMP-2. iv To my mom and dad that have so deeply supported my dream of going this far with my education. To my husband and daughter that have sacrificed their time with me for this to happen.