Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Anatomy and Cell Biology

Supervisor

Dr. Douglas W. Hamilton

Abstract

Successful wound healing involves tightly controlled regulation of extracellular matrix (ECM) deposition and remodeling, and myofibroblast-mediated wound contraction, to restore normal tissue function. However, these events involved in healing are also associated with development of tissue fibrosis, which is characterized by excessive deposition of ECM and the presence of myofibroblasts. Increasing evidence suggests that periostin is a critical player in regulating skin healing and fibrosis. In contrast to most adult tissues, gingival connective tissue is known to heal more rapidly and with less scarring, yet is still associated with fibrosis, such as drug-induced gingival enlargement. The aim of this study is to understand the mechanism of gingival healing and fibrosis, and to describe the role of periostin. Chapter 2 demonstrates that during wound healing of rat gingiva, periostin upregulation coincides with collagen and fibronectin deposition, while only few myofibroblasts are evident. Although periostin has no influence over myofibroblast differentiation of human gingival fibroblasts (HGFs), it induces synthesis of collagen and fibronectin proteins. Chapters 3-4 and Appendix 4 show that periostin is highly upregulated by nifedipine and phenytoin in gingiva, and the drugs increase periostin through TGF-b signaling in HGFs. Such increase of periostin also coincides with greater ECM deposition, while myofibroblasts are absent. As adhesive signaling is critical in myofibroblast differentiation, Chapter 5 demonstrates that HGFs cultured on smooth titanium topography have more mature focal adhesions and greater phosphorylated-focal adhesion kinase, compared to HGFs on rough substratum. HGFs cultured on smooth titanium are also associated with greater gene expressions of periostin and CCN2, fibronectin deposition, and more myofibroblast differentiation, compared to HGFs on rough topography. The overall findings from this thesis are that periostin is a pro-fibrotic protein in gingiva, where it increases matrix synthesis, but not myofibroblast differentiation of gingival fibroblasts, to regulate healing as well as contributing to fibrosis. While seemingly not normally active in gingival fibroblasts, adhesive signaling can be induced resulting in the cells assuming a fibrotic phenotype. Furthermore, this study shows that increased stiffness of the culture substratum does not induce myofibroblast differentiation if cell attachment sites are physically restricted.


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