Background Syphilis is a chronic, multi-stage and systemic infection caused by the extracellular bacterium Treponema pallidum ssp. pallidum (Tp). Treponema pallidum causes widespread infection by disseminating through the vasculature, crossing endothelial, blood-brain, and placental barriers. Although the ability of Tp to engage and traverse the endothelium is well-described, the response of endothelial cells to Tp, and the contribution of the host response to Tp endothelial traversal, is unclear. Our study aims to understand the mechanisms underlying Tp infection and dissemination by performing multi-omic analyses of host microvascular brain endothelial cells (HBMECs) exposed to Tp.
Methods In this study, we perform a time-course assay profiling transcriptomics (RNA-seq), proteomics (2-dimensional liquid chromatography tandem mass-spectrometry), and cytokine secretome (cytometric bead arrays and flow cytometry) of HBMECs exposed to Tp or a background control to characterize the cellular response of HBMECs during Tp exposure. These studies allow us to measure changes in endothelial cellular function in response to Tp engagement by comparing HBMECs exposed to Tp versus a background control lacking the pathogen.
Results Transcriptomic and cytokine secretion analyses revealed that exposure to Tp significantly modifies HBMEC gene expression and cytokine secretion, with longer exposures times causing more gene expression patterns to be modified. The host pathways that were most significantly altered included those involved in cytoskeletal and extracellular matrix organization, cell viability and programmed cell death, monocyte recruitment, and inflammatory signaling associated with endothelial permeability. Importantly, these altered cellular pathways support clinical observations of syphilis disease manifestations.
Conclusion Our investigations provide novel insight into the cellular consequences of Tp-endothelial interactions, enhance our understanding of the host mechanisms enabling Tp dissemination throughout the body, and contribute to our molecular understanding of syphilis symptoms. Our research is the most comprehensive molecular investigation of host cellular responses to Tp to date, and will inform syphilis vaccine design by identifying, for the first time, host cellular pathways that are manipulated by Tp and are essential for establishment and maintenance of Tp infection.
