Graduation Year

2024

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Medical Sciences

Major Professor

George E. Davis, M.D., Ph.D.

Committee Member

Jerome Breslin, Ph.D.

Committee Member

Saulius Sumanas, Ph.D.

Committee Member

Yao Yao, Ph.D.

Keywords

Pericyte, Basement Membrane, Vasculogenic 3D Model, TIMP-3, TBX2

Abstract

Capillaries, the smallest blood vascular networks, are formed by narrow and elongated endothelial cell (EC)-lined tubes with associated pericytes anchored to the abluminal tube surface. Our laboratory demonstrated that dynamic interactions between ECs and pericytes during capillary tube network assembly are required for basement membrane matrix deposition and maturation. We have also shown that key EC-derived factors promote pericyte recruitment, proliferation, and pericyte-induced basement membrane formation during capillary assembly. In the first section, we aim to identify if vascular smooth muscle cells (VSMCs) respond to the same factors and have the same invasive ability as pericytes since they are both mural cells. We investigate functional differences between pericytes and VSMCs using serum-free defined systems in 3D collagen matrices. By studying how these two mural cells differ, we highlight the importance of studying pericyte biology and function and suggest that the undifferentiated pericyte might be the progenitor of VSMCs.

Next, we identify a novel pericyte-derived molecular factor, tissue inhibitor of metalloproteinase (TIMP)-3, as an enhancer of capillary tube assembly and maturation. We show capillary tube widths dramatically narrowed to an average of 8 µm (physiologic capillary tube width), tube lengths and branching increased, and basement membrane matrix assembly robustly stimulated in induced pericyte-TIMP-3 and EC cocultures. These results could lead to the development of an effective therapeutic approach against vascular malformations where capillaries have marked widening and shortening of tubes.

Lastly, we investigate the role of T-box transcription factor 2 (TBX2) in pericyte function using 3D models of human capillaries. The function of pericyte-derived transcription factors (TFs) in capillary assembly is poorly understood. Using RNA-seq analysis, we discovered genes that were expressed differently in human pericytes compared to ECs, and among these genes, we detected the selective expression of TBX2 in pericytes. Our findings indicate that TBX2 downregulation impairs pericyte function in the formation and maturation of capillaries in vitro. Understanding vascular development and disease states where capillary malfunction is a major pathogenic characteristic will be made possible by our results, which provide light on the physiological and behavioral roles played by pericytes in capillary formation.

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