Date of Award

Spring 2010

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Graduate Group

Bioengineering

First Advisor

Christopher Chen

Abstract

Angiogenesis, the sprouting of new capillaries from existing blood vessels, is essential for the survival of tissues and normally occurs during development and wound healing. Successful vascularization of engineered tissues is currently a major challenge, as it is critical for the survival and incorporation of implanted tissue replacements. While the role of soluble factors in regulating angiogenesis is well established, there is significant interest in uncovering the contributions of cellular interactions with the extracellular matrix (ECM). We chose to study the role of cell-ECM adhesion in regulating angiogenesis, with the hypothesis that quantitative changes in the degree of cell-ECM adhesion can regulate endothelial cell behaviors important for angiogenesis. We also hypothesized that we could employ our basic knowledge of angiogenesis to develop a synthetic material system to support vascularization for potential applications in tissue engineering.

We first examined whether quantitative changes in cell-ECM adhesion regulate angiogenesis and observed increased angiogenic sprouting in three-dimensional fibrin gels with progressively decreasing densities of fibrin. Examining changes in global gene expression, we demonstrated a vascular endothelial growth factor (VEGF)-induced upregulation of genes associated with vascular invasion and remodeling when cell adhesion was limited, whereas cells on highly adhesive surfaces upregulated genes associated with proliferation. We showed that proline-rich tyrosine kinase 2 (Pyk2) regulates both gene expression and endothelial sprouting through its enhanced activation by VEGF in limited adhesion contexts. These results suggest that limited cell adhesion can enhance endothelial responsiveness to VEGF and demonstrate a novel role for Pyk2 in the adhesive regulation of angiogenesis.

Finally, we have developed poly(ethylene glycol) (PEG)-based hydrogels that support three-dimensional angiogenic sprouting. By tuning the mechanical, adhesive, and degradable parameters of these wholly synthetic materials, we have begun to identify conditions optimal for vascularization, as well as provided a tool to isolate the effects of single ECM parameters. We have demonstrated control of angiogenic sprouting by the MMP sensitivity of the hydrogels, as well as an interplay between ECM stiffness and adhesive ligand density in regulating sprouting.

Together, these studies highlight the importance of cellular interactions with the ECM in regulating angiogenesis and demonstrate a path by which we can apply basic understanding toward vascularization of engineered tissues for tissue regeneration and repair.

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