Sean Waugh

Topic

Investigating the Impact of Treponema pallidum Exposure on Human Brain Microvascular Endothelial Cells

Department of Biochemistry and Microbiology

Date & location

• Friday, September 12, 2025
• 11:30 A.M.
• Clearihue Building, Room B017

Examining Committee

Supervisory Committee

• Dr. Caroline Cameron, Department of Biochemistry & Microbiology, University of Victoria (Supervisor)
• Dr. David Goodlett, Department of Biochemistry & Microbiology, UVic (Member)
• Dr. Lisa Reynolds, Department of Biochemistry & Microbiology, UVic (Member)
• Dr. Leigh Anne Swayne, School of Medical Sciences, UVic (Outside Member)

External Examiner

• Dr. David Haake, David Geffen School of Medicine, University of California, Los Angeles

Chair of Oral Examination

• Dr. Sandra Gibbons, School of Exercise Science, Physical and Health Education, UVic

Abstract

Syphilis, caused by Treponema pallidum subspecies pallidum, is a growing global health concern. The molecular mechanisms underlying T. pallidum vascular dissemination and the host endothelial response remain incompletely understood. Notably, while T. pallidum traverses the endothelium to establish systemic infection, no systems-level characterization of endothelial responses to T. pallidum has previously been reported. This dissertation addresses this knowledge gap by investigating the molecular and immunological responses of human brain microvascular endothelial cells to T. pallidum using proteomic, transcriptomic, and cytokine profiling approaches.

The findings of this dissertation demonstrate that T. pallidum exposure markedly alters endothelial signaling, with consistent results across proteomic, transcriptomic, and cytokine profiling methods. Key proteomics and cytokine findings include modulation of extracellular matrix composition (ECM), and activation of signaling pathways associated with cytoskeletal reorganization and endothelial barrier disruption. Inflammatory signaling was consistently induced, including secretion of IL-6 and TNF, while macrophage-recruiting cytokines were reduced. These cytokine profiles were amplified in co-cultures with macrophages, suggesting coordinated innate immune signaling during infection. At the transcriptional level, T. pallidum exposure resulted in activation of pathways involving ECM dysregulation and signaling, growth factor signaling, and integrin activation.

Importantly, the endothelial response was consistent with endothelial to mesenchymal transition (EndMT) – a transformation associated with fibrosis, vascular remodeling, and inflammation. EndMT induction was further supported by the activation of TGF-β, NF-κB, and MAPK-associated pathways, and identification of Snail as a central transcriptional regulator during infection. Additionally, pathway analyses identified the modulation of programmed cell death pathways, including necroptosis, suggesting a molecular basis for the tissue necrosis observed in syphilis. Collectively, these findings support a model in which T. pallidum takes advantage of both non-inflammatory and inflammatory mechanisms of endothelial traversal. In the non-inflammatory route, T. pallidum binds host ECM proteins and triggers cytoskeletal rearrangements to cross the endothelium without triggering significant immune activation. In contrast, during sustained exposure, inflammatory signaling promotes EndMT, ECM remodeling, and endothelial dysfunction. Collectively, this dissertation presents the first systems-level characterization of host endothelial responses to T. pallidum, identifying molecular pathways involved in bacterial dissemination and vascular dysfunction. These findings advance our understanding of T. pallidum-host interactions, bacterial dissemination, and disease progression.