Bone is continually remodeled and must maintain homeostasis of both the collagen and mineral components. Collagen is the primary matrix protein found in bone; it provides the structural organization and is a determinant of whole bone mechanical properties. Collagen is post-translationally modified by the lysyl oxidase (LOX) enzyme family to produce a distinct profile of mature and immature cross-links. The composition of cross-links is thought to alter the collagen fibril diameter and D-spacing, and altered fibril geometry may lead to altered mineralization. In experimental models of perturbed collagen cross-links, the mechanical strength and toughness directly correlate to the cross-link profile. Therefore, it is possible that compositional changes are contributing to the altered structure and function in patients suffering from a variety of systemic conditions that also exhibit reduced bone quality. The mechanisms controlling collagen cross-linking and mineralization in homeostasis and healing are understudied in the axial skeleton and craniofacial bones. Collagen content and relative cross-link maturity differ between the axial and craniofacial bones, and therefore may respond differently to altered LOX activity. My preliminary data suggests that altered collagen-cross-link profiles may be associated with an increase in the relative mineralization in the axial skeleton, but a decrease in the craniofacial bone. My central hypothesis is that collagen cross-linking dictates mineralization by controlling fibril diameter and collagen D-spacing and that inhibition of cross-linking compromises bone quality and healing in osseous wound sites.
Two aims are proposed: 1) Define the role of collagen cross-links in craniofacial and axial bone mineralization, i2) Determine the effect of impaired collagen cross-links on craniofacial bone quality during healing after molar extraction. These studies will be accomplished using an established mouse model, where LOX-family enzymes are inhibited by treatment with a pharmacological agent, beta-aminoproprionitrile (BAPN). This model reduces the amount and alters the profile of cross-links in a dose dependent fashion. I will determine the fibril diameter and D-spacing via atomic force microscopy, mineral and collagen changes via Raman spectroscopy, and compare the response of craniofacial bone to axial bone. A molar extraction model will then be used to determine the effect of partial LOX-family enzyme inhibition on healing in craniofacial bone. Histology and histomorphometry will be used to determine the overarching effects on osteoblasts and osteoclasts. The outcomes of the proposed experiments will gain insight into the role of collagen cross-links in mineral composition, mechanical properties, and healing processes of axial and craniofacial bone for application in a variety of systemic conditions. Collagen cross-links are relatively easily manipulated via the LOX-family enzymes and therefore may serve as a target for disease therapy or for controlled use in tissue engineering.
Mineralized tissues are composed of both an organic component and mineral component which give a tissue both toughness and stiffness, respectively. Bone collagen cross-links within the organic component alone can contribute significantly to its mechanical properties, deficiencies in formation of these cross-links are observed in a variety of diseases which manifest in the oral cavity that correlate with poor osseous healing following extraction. Understanding the key cross-link drivers for compromised quality and healing will allow for better prediction of surgical expectations and outcomes, as well as therapies for systemic diseases involving collagen composition.
