DOI
https://doi.org/10.25772/Q4X7-CQ54
Defense Date
2018
Document Type
Dissertation
Degree Name
Doctor of Philosophy
Department
Biomedical Engineering
First Advisor
Dr. Christopher Lemmon
Second Advisor
Dr. Barbara Boyan
Third Advisor
Dr. John Ryan
Fourth Advisor
Dr. Lynne Elmore
Fifth Advisor
Dr. Daniel Conway
Sixth Advisor
Dr. Seth Weinberg
Abstract
Epithelial to Mesenchymal Transition (EMT) is a dynamic process by which a distinct change in the phenotype and function of epithelial cells render them as mesenchymal cells. Characteristics of mesenchymal cells include the ability to invade, increased migratory kinetics and heightened resistance to apoptosis. Therefore, there is a strong need to fully understand the mechanism for the induction of EMT in pathological conditions such as carcinoma progression. Recent advances highlight two pivotal contributors, soluble growth factor (gf) signals, and mechanical signals, in the process. However, to date, no clear mechanism exists linking the two in epithelial transdifferentiation. Transforming Growth Factor-β1 (TGF-β1), a gf known to induce EMT in breast cancer formation, induces EMT on rigid surfaces and apoptosis on compliant surfaces. It is our belief that a combination of mechanical signals, gf signals, and the type of extracellular matrix (ECM) proteins assembled by cells together drive the process of EMT. Here we investigated the role of the ECM protein fibronectin (FN) in EMT. Upon assembly into elastic, insoluble fibrils through cell-generated forces which become larger on stiffer surfaces, FN is able to serve as a gf delivery system. We examined the following hypothesis: Increased tissue stiffness drives FN assembly, which exposes cryptic binding sites for various gfs, such as TGF-β1, and creates a high concentration of these gfs at the cell surface, which in turn drives EMT. In this project we investigated three aims: (1) evaluate the effect of inhibiting FN fibrillogenesis and gf localization on TGF-β1-induced EMT, (2) assess the effect of TGF-β1 concentration on spatial patterning of ECM dynamics, cell phenotype and adherens junctional force, and (3) probe the role of the FN matrix in TGF-β1-induced spatial patterning of EMT. Results showed that both inhibition of FN fibril assembly and blocking the gf binding site on fibrils significantly attenuated the downstream effects of EMT. In microcontact patterns of epithelial colonies, increasing gf concentration led to spatial patterning of FN fibrils, cell phenotype and cell-cell junctional force. Elimination of FN fibrils effectively attenuated TGF-β1-induced spatial patterning. The knowledge acquired through these studies serves as an addition to an increasingly important body of work aimed at elucidating how physical changes within the microenvironment regulate physiology and pathology. By establishing a novel mechanism by which gf signaling induces EMT through interaction with the extracellular matrix, this research serves to combat the development and initiation of pathological phenomena, such as metastasis.
Rights
© Lauren A. Griggs
Is Part Of
VCU University Archives
Is Part Of
VCU Theses and Dissertations
Date of Submission
7-3-2018