Date of Award

January 2012

Document Type

Open Access Thesis

Degree Name

Medical Doctor (MD)

Department

Medicine

First Advisor

Christopher K. Breuer

Subject Area(s)

Medicine, Biomedical engineering

Abstract

The development of an autologous tissue engineered vascular graft (TEVG) holds great promise for improving outcomes in congenital heart surgery. The first clinical trial showed that this approach is safe and effective but that the primary mode of failure is stenosis. In a C57BL/6 mouse model of unseeded TEVGs implanted as inferior vena cava interposition grafts, neovessels form in 2 weeks and patent grafts show endothelial and smooth muscle cell (SMC) layers, but occluded grafts show accumulation of SMCs. This suggests stenosis results from abnormal SMC in-growth in the neointima. Studies on fibrosis have shown that resident endothelial cells (EC) contribute to fibroblast accumulation through endothelial-mesenchymal transition (EMT). We utilized transgenic EC lineage-tracing mouse models to track the occurrence of EMT in our TEVG and found an increased percentage of cells co-expressing LacZ and smooth muscle actin in occluded grafts, suggesting that EMT contributes to occlusion in our TEVG. We hypothesized that ECs in our TEVG undergo EMT driven by TGF-B to contribute to stenosis. Immunohistochemistry and qRT-PCR showed higher expression of TGF-B in occluded compared to patent grafts. In vivo expression of a soluble FGF trap virus to increase TGF-B signaling and thus increase EMT was found to result in a significantly increased stenosis rate in our TEVG. We next modulated this pathway by intraperitoneal administration of a small molecule inhibitor of TGF-B receptor type 1 (SB431542). Grafts from treated mice had significantly increased patency rates and internal diameters at 2 weeks compared to controls while maintaining normal neovessel architecture. We then designed a novel local delivery system for this TGF-B R1 inhibitor in our grafts and showed that local drug delivery inhibits stenosis without cell seeding and maintains normal neovessel formation. These results suggest that EMT under the control of TGF-B is a significant mediator of stenosis and that modulation of this pathway by local drug delivery might be useful in next generation TEVGs.

Comments

This is an Open Access Thesis.

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