How Vibrio cholerae Type VI Secretion System Blocks Intestinal Epithelial Repair
Creators: Xu, Xinyue
Publisher: name: University of Alberta Library
Year: 2024

<p>To maintain an effective barrier, intestinal epithelial progenitor cells must divide at a rate that matches the loss of dead and dying cells. Epithelial damage during most enteric infection accelerates cell proliferation and tissue repair via multiple stress responses. However, infection with the causative agent of cholera, Vibrio cholerae, blocks the proliferation of intestinal progenitor cells in a Type VI Secretion System (T6SS)-dependent manner and therefore arrests epithelial repair in the Drosophila infection model, which exacerbates diarrheal disease symptoms and shortens host lifespan. It is unknown how V. cholerae circumvents such a critical antibacterial defense. Previously, our lab found that V. cholerae T6SS enhances transcriptional expression of multiple Bone Morphogenetic Protein (BMP) pathway components in the fly progenitor compartment. We consider this discovery noteworthy, as BMP members of the Transforming Growth Factor-β (TGF-β) cytokine family regulate intestinal homeostasis in flies and vertebrates. In both systems, BMPs act in a paracrine manner to inhibit progenitor proliferation and promote intestinal epithelial cell differentiation. At present, molecular mechanisms of how V. cholerae T6SS arrest host tissue repair remain unclear. We consider this an important question, as failure to repair damage in intestinal epithelium exposes the host to lumenal microbes, increasing the risk of systemic infection and chronic inflammation. <br>
Using Drosophila, I demonstrated that V. cholerae infection activates the BMP signaling specifically in intestinal progenitors in a T6SS-dependent manner. As the T6SS mediates interactions with gut-resident bacteria, I examined the contribution of gut commensals to T6SS-responsive BMP activation. In germ-free flies without gut microbiome, V. cholerae infection failed to induce BMP response in progenitors or block progenitor growth, indicating that BMP activation requires pathogen-commensal interactions. Next, I asked if host innate immune response is involved in regulating BMP activity during V. cholerae infection. Loss of the immune deficiency (IMD) protein ablated progenitor-specific BMP response. Furthermore, the enterocyte-specific Relish, an NF-κB family transcription factor in the IMD pathway,  is essential for BMP activation during V. cholerae infection. Then, I tested if progenitor-specific BMP activation is necessary to block epithelial repair upon infection. Without BMP activity, V. cholerae infection could no longer limit progenitor proliferation. Mechanistically, BMP in enteroblasts of the progenitor compartment suppresses intestinal stem cell proliferation non cell autonomously. Finally, I asked if the impacts of V. cholerae T6SS on intestinal epithelial renewal apply to vertebrate hosts. Using the zebrafish model, I found that V. cholerae T6SS promotes damage, blocks proliferation, and induces TGF-β/BMP activation in the intestine, indicating an evolutionarily conserved link between infection, BMP, and failure in tissue repair. Combined, the findings in this thesis highlight how pathogen-commensal interactions engage host immune response and growth regulatory pathways to disrupt intestinal epithelial repair.</p>