Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Anatomy and Cell Biology

Supervisor

Hamilton, Douglas W.

Abstract

The oral tissues, including gingiva and buccal mucosa, heal rapidly with minimal scar formation. Although in the oral cavity, the palatal mucosa is associated with excessive scarring in response to injury. In this thesis, first, I investigated the complex relationship between cells and their microenvironment using wound healing models in which extracellular matrix composition and mechanical stiffness affect cellular responses during acute wound repair. I also determined how intrinsic differences of cells recruited during healing contribute to wound resolution.

In Chapter 2, I first investigated cell-extrinsic factors, specifically the influence of the pro-fibrotic matricellular protein periostin on palatal healing. Using a genetic deletion strategy, it was determined that in the palate periostin modulates myofibroblast differentiation and fibronectin synthesis in a manner dependent on the stiffness of the microenvironment surrounding the cells.

In chapter 3, I focused on the role of extracellular periostin on periodontal ligament (PDL) fibroblast phenotype using in vitro assays and gene-expression analyses. These findings suggest that the influence of periostin is context dependent; matrix-bound periostin does not promote or inhibit mineralization of the PDL, but the addition of exogenous periostin to isolated PDL fibroblasts resulted in increased mineralization concomitant with changes in gene expression.

In chapter 4, to explore cell-intrinsic differences, a lineage tracing approach was used to trace populations of cells derived from embryonic Foxd1- and NG2- expressing progenitors during development, homeostasis, and excisional wound healing. I show in the palate that Foxd1-lineage progeny associate with blood vessels in development and adult tissues, after injury, they expand but remain associated with neovascular structures. In contrast, NG2-lineage progeny associate with fibroblasts in healthy adult tissues and post-injury contribute to myofibroblast populations.

In conclusion, the studies in this thesis have further defined the complex interactions that exist between resident cells and their micro-environment using the palate as a model system. The data from this thesis provides important information for the design of future therapeutics for oral wounds, and also contributes to a growing understanding of fibroblast heterogeneity and how divergent populations contribute to different processes during wound repair.

Summary for Lay Audience

In Canada, approximately 400-500 babies are born each year with cleft palate (1 in 790 live births, among the highest in the world). This condition occurs when tissues in the baby's face and mouth do not fuse properly during pregnancy, leaving an opening (cleft) in the roof of the mouth (palate). Surgery is required during infancy or childhood in order to close the opening. Due to the specific characteristics of the palate, healing after surgery typically results in the formation of a scar. This scar is very rigid and prevents proper development of the face and mouth, which can dramatically affect a child’s appearance, speech, teeth, eating, and the ability to develop socially. My research focuses on periostin, a protein playing a prominent role during scar formation in human skin and in skin wound repair. I found that this protein, as well as the stiffness of the hard palate, play a significant role in the function of cells that participate in the healing process. This protein is also found in the supporting structures around the tooth. Here, I showed that the role of periostin in the periodontium is to support the maintenance of these structures. Lastly, I investigated what types of cells are recruited during palatal healing and I found two distinct populations that they have unique roles: one population is primarily involved in the formation of new vessels in the wound, and the other is involved in the formation of matrix that supports the growing cells. In conclusion, studies in this thesis have further defined the complex interactions that exist between cells and their environment using the palate as a model system. The data from this thesis provides important information for the design of future therapeutics for oral wounds, cleft palate reconstruction, and also contributes to a growing understanding of fibroblast heterogeneity and how divergent populations contribute to different processes during wound repair.

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