Yan Gong

Date of Award

8-2013

Level of Access Assigned by Author

Campus-Only Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biomedical Sciences

Advisor

Robert Friesel

Second Committee Member

Lucy Liaw

Third Committee Member

Thomas Gridley

Abstract

Angiogenesis is a normal and vital process in growth and development, as well as in wound healing and tumor growth. Angiogenesis may be a target for combating diseases characterized by either abnormal vasculature or formation of tumor blood vessels by either anti-angiogenic or pro-angiogenic therapies. Application of specific compounds that may inhibit or induce the creation of new blood vessels in the body may help combat such diseases. Vascular endothelial cells line the entire circulatory system, which have very distinct and unique functions that are paramount to vascular biology, especially angiogenesis.

The aim of my current study is to examine the effect of Sprouty genes in endothelial cells during angiogenesis. I compared the functions of different Sprouty isoforms in endothelial cells grown on various extracellular matrices. My results showed that endothelial cells favored vitronectin for their spreading and growth, and that Sprouty4 was the most potent isoform that regulated endothelial cell behaviors, such as adhesion, spreading and migration. Specifically overexpression or deletion of Sprouty4 also significantly regulates angiogenesis in vivo.

To further examine the mechanisms how Sprouty4 affects endothelial cell behaviors, I clarified that Sprouty4 modulated the crosstalk between vascular endothelial growth factor receptor-2 (VEGFR-2) and integrin aVp3, the receptors of vitronectin, via c-Src. I founded that Sprouty4 inhibited VEGFR-2-induced c-Src activation and tyrosine phosphorylation of integrin p3 in turn, and that the phosphorylation status of integrin β13 is crucial for its stability. Lack of integrin p3 impaired endothelial cell adhesion, spreading and migration.

Both my in vivo and in vitro studies also revealed that Sprouty4 regulated the permeability of endothelial cells, and this effect was c-Src-dependent as well. I found that Sprouty4 inhibited tyrosine phosphorylation of vascular endothelial cadherin (VE-cad) by c-Src, and that dephosphorylated VE-cad increased the interaction between VE-cad and P-catenin but decreased VE-cad internalization. On the other hand, Sprouty4 accelerated the degradation of VE-cad.

In summary, the results of my study will provide novel and important understanding of how Sprouty regulates endothelial cell functions during angiogenesis and also set the stage for future design of new therapeutic treatment for cardiovascular diseases and cancers.

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