# Porphyromonas gingivalis Type 9 Secretion System Promotes Dysregulation of Vascular Smooth Muscle Cell Plasticity With Perturbed TGF‐β/Smad Signaling

## TL;DR

This paper shows how a bacterial secretion system disrupts muscle cell behavior and signaling, contributing to disease.

## Contribution

The study identifies a new virulence function of the T9SS in manipulating host cell signaling.

## Key findings

- T9SS is necessary for P. gingivalis-induced dysregulation of AoSMC plasticity.
- T9SS promotes Smad3 phosphorylation, affecting TGF-β/Smad signaling in infected cells.
- PorU deletion attenuates microbial effects on AoSMC proliferation and migration.

## Abstract

The Porphyromonas gingivalis type 9 secretion system (T9SS) is known for secreting and anchoring protein cargos to the outer surface of the bacterium, which are then selectively packaged into outer membrane vesicles. We previously identified a link between P. gingivalis‐mediated dysregulated aortic smooth muscle cell (AoSMC) plasticity with binding of T9SS outer protein, PorU and select T9SS cargos to AoSMC proteins. To assess the role of T9SS in dysregulated AoSMC plasticity, a PorU‐deficient mutant was constructed in P. gingivalis strain A7UF. AoSMC was inoculated with sterile vehicle, wild‐type A7UF, or A7UFΔPorU and evaluated for proliferation, migration, and changes in the TGF‐β/Smad2/3 signaling axis. Deletion of PorU disrupted T9SS function in P. gingivalis A7UF. Loss of T9SS function impaired P. gingivalis invasion and persistence in AoSMC as well as attenuated microbial‐induced effects on AoSMC plasticity. Specifically, direct T9SS/AoSMC interactions were necessary for P. gingivalis‐induced AoSMC proliferation. Clarified supernatant from A7UF impaired the migration of infected AoSMC. P. gingivalis T9SS function was perturbed AoSMC TGF‐β/Smad3 signaling. Specifically, A7UF‐inoculated cells had increased linker and carboxy‐terminal phosphorylation of Smad3 that was attenuated in AoSMC inoculated with A7UFΔPorU. In summary, PorU and/or T9SS cargo play a role in P. gingivalis‐induced dysregulation of AoSMC plasticity as well as TGF‐β/Smad signaling. Microbial manipulation of host cell signaling events is important for cell differentiation and tissue remodeling and would constitute a new virulence function for T9SS.

An intact type 9 secretion system (T9SS) is required for Porphyromonas gingivalis‐mediated dysregulation of aortic smooth muscle cell migration and proliferation. During infection, T9SS also enhanced phosphorylation of multiple sites on transcription factor Smad3 that is implicated in pathologic cell responses to TGF‐β/Smad signaling.