Date of Award

January 2026

Document Type

Open Access Thesis

Degree Name

Medical Doctor (MD)

Department

Medicine

First Advisor

Alan Dardik

Abstract

Background/Scientific Premise Mature arteriovenous fistulae (AVF) are the gold standard vascular access allowing hemodialysis for patients with end-stage kidney disease. The rate of AVF failure remains high, reflecting an incomplete understanding of the biology of AVF maturation and failure. Sox17 is a transcription factor indispensable for the acquisition and maintenance of endothelial arterial identity. Because endothelial cells (EC) acquire dual arteriovenous identity after AVF creation, we determined whether Sox17 mediates venous remodeling in AVF. Research Aims This study aims to characterize the degree of Sox17 expression within the venous outflow tract after AVF creation in humans and in a mouse model and to understand the impact of Sox17 expression on venous remodeling after AVF creation. Our specific aims include to determine the relative expression of Sox17 in each cell type within the vascular wall in human veins, to use a mouse model of AVF to quantify Sox17 expression in the venous outflow tract and characterize the impact of decreased Sox17 expression on venous remodeling after AVF creation. We hypothesize that Sox17 expression is increased in the venous outflow following AVF creation and regulates venous remodeling in AVF. Methods Human preaccess vein, failed AVF, and mature AVF from second stage basilic vein transpositions were collected. AVF were determined to be patent at the time of second stage procedure, with failed AVF being defined clinically as AVF that never obtained a luminal diameter of 6 mm or greater or an AVF that require further surgical intervention rather than a standard second stage transposition. AVF and control veins were analyzed using immunofluorescence and single cell sequencing to determine Sox17 expression. Bioinformatic analysis was performed on single-cell RNA sequencing data from 70,281 cells derived from human veins and AVF collected from patients requiring two-stage AVF creation. For the. Mouse model of AVF creation, Aortocaval fistulae created in 9 to 11-week-old C57BL/6J mice were harvested on day 7 or 21 for analysis with Western blot, quantitative polymerase chain reaction, histology, or immunofluorescence to assess Sox17 immunoreactivity in EC. Doppler ultrasound examination confirmed AVF patency and measured inferior vena cava and aortic flow velocity and diameter. Relative diameter was the ratio of the diameter at a specified time point relative to the day 0 diameter. Velocities were obtained at the same anatomical location using pulse wave mode to measure waveforms. The average of the waveform was taken to calculate a mean velocity for the aorta and IVC. Sox17 knockdown was performed using short hairpin RNA lentivirus dissolved in Pluronic gel delivered perivascularly immediately after AVF creation. Analysis of variance and t tests were used for statistical analyses. Results Sox17 was significantly elevated in mature human AVF compared with control veins (p = .02) and in mature human AVF compared with failed human AVF (p = .04). In the mouse AVF, Sox17 expression was also significantly upregulated compared with sham-operated mice (p = .0012 in male mice; p = .0062 in female mice). Sox17 immunoreactivity was highest on days 7 and 21 and returned to near sham levels at day 42. In both human and mouse AVF, Sox17 expression was localized to the nucleus of EC. Sox17 knockdown mice had impaired venous remodeling, characterized by a smaller inferior vena cava diameter (p = .001) and thinner intima-media layers relative to control AVF (p = .015). However, despite the small change in AVF diameter, there was no difference in shear stress in the IVC between mice treated with control and knockdown lentivirus. Since AVF with reduced Sox17 expression had less outward remodeling and thinner walls, we determined whether there was altered cell turnover in the remodeling venous outflow tract after AVF creation. Sox17 knockdown mice had decreased JAG1 expression (p = .008) and decreased smooth muscle cell proliferation (p = .03) on day 7. Statement of scientific impact or relevance In this work, we show that Sox17 expression is elevated in human AVF and in a murine aortocaval fistula model. In a mouse model of AVF maturation, topical knockdown of Sox17 impairs AVF maturation, evidenced by reduced outward remodeling and attenuated wall thickening. We also show that Sox17 knockdown disrupts early SMC proliferation during AVF maturation. Overall, these findings suggest that Sox17-mediated transcriptional regulation is needed for venous adaptation to altered hemodynamic forces. Thus, transcriptional regulation of vascular identity by Sox17 may represent a translationally relevant target to enhance AVF maturation for patients undergoing hemodialysis.

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