Role of Intestinal Epithelial Cells in Controlling Local and Systemic Yersinia Infection through IL-1 Signaling

PROJECT SUMMARY/ABSTRACT
Bacterial infections that become systemic are significant public health threats and can result in life-threatening
conditions such as sepsis. While the importance of various immune signals and processes in protecting against
infectious agents is appreciated, how immune responses regulate pathogen tissue infection, replication, and
dissemination throughout the organism is poorly understood. Insights into these infection dynamics will lead to
new targets for host-directed therapeutics to combat disseminated infections. To this end, our labs study the host
response to infection by Yersinia pseudotuberculosis (Yp). Despite the virulence and systemic spread of Yp, we
and others have found that immune-competent mice successfully control and clear oral Yp infection, providing a
robust host-pathogen model to dissect infection dynamics and successful immune control of intestinal bacterial
pathogens. Recently, we reported on the formation of pyogranulomas (PGs, granulomas enriched in neutrophils
and monocytes that encapsulate Yp) throughout the gastrointestinal tract of Yp-infected mice. Interleukin-1 (IL-
1) signaling is required for control of bacterial replication within PGs and in distal organs. Mice lacking IL-1
signaling form PGs with necrotic cores and contain fewer activated neutrophils that fail to contain Yp. However,
we critically lack an understanding of the identity of IL-1 responsive cells, how IL-1 signaling promotes protective
PG formation, and how protective PG formation impacts systemic infection control. My novel preliminary data
demonstrate that IL-1 signaling is required on intestinal epithelial cells (IECs) to control bacterial burdens in PGs
and systemic tissues. Also, preliminary single-cell RNA sequencing studies reveal a subset of IECs activate
antimicrobial and inflammatory genes in response to Yp infection. In parallel studies, I utilized a novel barcoded
Yersinia library of isogenic bacteria that contains nearly 70,000 unique genetic barcodes to study infection
dynamics. I found that, in immune-competent mice, the Yp in systemic organs do not share barcodes with the
Yp in PGs, suggesting that PGs could be restricting systemic spread. Therefore, we hypothesize that IL-1R
signaling in IECs limits systemic dissemination of intestinal Yp through neutrophil recruitment and
activation to PGs and production of antimicrobial defenses. In Aim 1, we will mechanistically dissect the
contribution of IL-1 signaling in IECs to the recruitment and activation of neutrophils in PGs, the containment of
Yp within PGs, and the expression of antimicrobial and inflammatory response genes by IECs. In Aim 2, we will
determine how IL-1 signaling in IECs contributes to restricting Yp dissemination and controlling systemic bacterial
burdens using the barcoded Yersinia library. The scientific goal of this work is to uncover how infection dynamics
are regulated by host responses. The tools and models developed during this project will provide a solid
foundation and enable more detailed studies of epithelial cells and infection dynamics in the future. The careful
guidance of Dr. Sunny Shin and Dr. Igor Brodsky and the exceptional research environment at Penn will help me
develop as a scientist and prepare me for a career in leading my own independent research program.

Grant Number: 1F32AI186538-01A1
NIH Institute/Center: NIH
Principal Investigator: Suhas Bobba