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Regulation of Extracellular Matrix Remodeling and Bone Morphology by Discoidin Domain Receptors

Blissett, Angela Rae

Abstract Details

2011, Doctor of Philosophy, Ohio State University, Biophysics.
Bone remodeling impacts the material and structural composition of bone, both which are determinants of tissue strength. The underlying mechanisms involved in bone remodeling are not fully understood. Collagen type 1 is the major component of bone; therefore, processes that regulate collagen deposition and ultrastructure will likely impact bone quality. Discoidin domain receptors (DDR1 and DDR2) are ubiquitously expressed transmembrane proteins that bind to and get activated by collagens, including collagen type I. DDR receptor activation is known to regulate numerous cellular functions including differentiation, migration, cell cycle control and extracellular matrix (ECM) remodeling. This thesis explores the role of DDR1 and DDR2 in bone formation and remodeling. We hypothesize that the expression of DDR extracellular domain (ECD) inhibits collagen fibrillogenesis and alters collagen matrix mineralization. Our aim was to understand how DDR ECD expression impacts the morphology of collagen matrices assembled by osteoblasts in cell culture. To address this, we created stably transfected pre-osteoblast cell lines which express various ECD-containing isoforms of DDRs. Cells were cultured in the presence of ascorbic acid to facilitate production of matrix proteins and prepared for assessment by transmission electron microscopy (TEM). We found that samples over-expressing DDR ECD exhibit collagen matrices with smaller fiber diameters, disrupted banded structures, reduced matrix deposition, delayed fibrillogenesis and increased matrix mineralization as compared to nontransfected controls. Based on our findings, we conclude that DDR ECDs are inhibitors of collagen fibrillogenesis and promote matrix mineralization. In addition, we hypothesized that DDR1 regulates the differentiation and function of bone cells such as osteoblasts and osteoclasts. Utilizing TEM we observed the abundance of osteoblasts and osteocytes (bone forming cells) and the ultrastructure of the collagen matrix in cortical bone from wildtype and DDR1 knockout (KO) mice. We found that cortical bone from DDR1 KO mice contained far fewer osteoblastic cells and collagen fibers with increased fiber diameters as compared to wildtype. To assess osteoclast differentiation, we isolate primary monocytes from wildtype and DDR1 KO mice. Isolated cells were cultured in media containing M-CSF and RANKL to determine rate of osteoclast differentiation. Further, we seeded multinucleated wildtype and DDR1-/- osteoclasts onto ivory substrates (which mimics bone) to observe resorption efficiency. We found that DDR1-/- pre-osteoclasts exhibited a slower rate of differentiation and that DDR1-/- osteoclasts resorb at a slower rate as compared to wildtype cells. Lastly, we hypothesized that DDR1 expression regulates bone microarchitecture. We employed μ-CT analysis on femurs isolated from wildtype and DDR1 KO mice in order to quantitatively assess various parameters for cortical and trabecular bone. We find that DDR1 KO mice exhibited femurs with reduced mass indicative of bone more likely to fracture as compared to wildtype. Taken together, our results demonstrate an important role of DDRs in bone remodeling.
Gunjan Agarwal (Committee Chair)
Anthony Brown (Committee Member)
Beth Lee (Committee Member)
Heather Powell (Committee Member)
142 p.

Recommended Citations

Citations

  • Blissett, A. R. (2011). Regulation of Extracellular Matrix Remodeling and Bone Morphology by Discoidin Domain Receptors [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1305900854

    APA Style (7th edition)

  • Blissett, Angela. Regulation of Extracellular Matrix Remodeling and Bone Morphology by Discoidin Domain Receptors. 2011. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1305900854.

    MLA Style (8th edition)

  • Blissett, Angela. "Regulation of Extracellular Matrix Remodeling and Bone Morphology by Discoidin Domain Receptors." Doctoral dissertation, Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1305900854

    Chicago Manual of Style (17th edition)