BME PhD Defense: Candace Gildner

Effect of Vitronectin on the Deposition, Conformation, and Physiologic Properties of Extracellular Matrix Fibronectin

Supervised by Professor Denise Hocking

Abstract

Interactions of cells with extracellular matrix (ECM) fibronectin direct many activities necessary for tissue regeneration. Factors that regulate fibronectin matrix assembly and the cellular responses to ECM fibronectin during regenerative processes are not completely understood. Evidence indicates that other ECM proteins, including collagen and vitronectin, affect the deposition of fibronectin into the ECM, suggesting that these proteins may regulate fibronectin-mediated effects on cell behavior. In this study, we examined the effects of collagen- and vitronectin-coated adhesive substrates on fibronectin matrix assembly and the functional properties of ECM fibronectin.

Cells adherent to collagen or vitronectin-coated substrates produced fibrillar, detergent-insoluble fibronectin matrices. However, fibronectin was 10-fold less effective at enhancing proliferation of vitronectin-adherent cells than collagen-adherent cells. The reduced response to fibronectin was not due to an overall decrease in the proliferative capacity of vitronectin-adherent cells, but instead appeared to be a unique property of vitronectin-cell interactions. Conformational differences in the I-9/III-1 region of the fibronectin matrix produced by vitronectin- or collagen-adherent cells were detected by immunofluorescence microscopy. At early time points, differences in the rate of fibronectin matrix assembly by vitronectin- and collagen-adherent cells were also observed. Fragments of fibronectin derived from the III1 region inhibited vitronectin-mediated fibronectin matrix assembly, but not collagen-mediated fibronectin matrix assembly, providing evidence that different mechanisms are utilized by collagen- and vitronectin-adherent cells to assemble fibronectin fibrils. Together, these data indicate that the interaction of cells with different adhesive substrates defines the mechanism of fibronectin matrix assembly and in turn, determines the structural and functional properties of ECM fibronectin.