Author ORCID Identifier
https://orcid.org/0000-0002-0498-3871
Date of Graduation
5-2023
Document Type
Dissertation (PhD)
Program Affiliation
Immunology
Degree Name
Doctor of Philosophy (PhD)
Advisor/Committee Chair
Scott Evans,MD
Committee Member
Jeffrey K. Actor, Ph.D.
Committee Member
Hesham Amin, MD.
Committee Member
Rick Wetsel, Ph.D.
Committee Member
Jichao Chen, Ph.D.
Abstract
Investigating the roles of lung epithelial STAT3 in therapeutically inducible resistance to acute bacterial pneumonia.
Vikram Vitthal Kulkarni, M.S.
Advisory Professor: Scott Evans, MD.
The lung epithelium is a dynamic tissue capable of displaying structural and functional plasticity in response to pathogenic challenges. Our lab has demonstrated that it is possible to therapeutically exploit the lung epithelium’s versatility by inducing resistance to lethal pneumonias caused by viruses, bacteria and fungi. An inhaled combination of a TLR2/6 agonist and a TLR9 agonist (Pam2ODN) results in robust protection against otherwise lethal pneumonia caused by Pseudomonas aeruginosa. Pam2ODN-mediated protection requires key signaling components of the TLR pathway and generation of multisource reactive oxygen species (ROS). However, a complete understanding of this unique synergistic protection offered by Pam2ODN is lacking. To investigate the mechanisms underlying inducible resistance, we performed reverse phase protein array analysis and identified STAT3 phosphorylation as a potential mediator of synergy. There was a robust activation of epithelial STAT3 by Pam2ODN treatment and we demonstrated that it was independent of IL-6 signaling. While IL-6 knockout mice exhibited epithelial STAT3 activation and strong protection against Pseudomonas aeruginosa pneumonia after Pam2ODN treatment, we found that deletion of lung epithelial STAT3 completely abrogated the protection induced by Pam2ODN. Further studies revealed that inhibiting DUOX enzymes or chemically scavenging ROS significantly decreased Pam2ODN-induced STAT3 activation in cultured lung epithelial cells, alluding to a signaling role for Pam2ODN induced ROS upstream of STAT3. Dissecting these mechanisms, we analyzed the contributions of redox-sensitive kinases and found that Pam2ODN activated EGFR in a ROS-dependent manner that is required for therapeutically-inducible STAT3 activation. Taken together, we demonstrate that epithelial STAT3 is imperative for Pam2ODN’s function and describe a novel, redox based mechanism for its activation. These key mechanistic insights may facilitate strategies to leverage inducible epithelial resistance to protect susceptible patients during periods of peak vulnerability.
Keywords
Inducible resistance, epithelium, innate immunity, bacterial pneumonia, redox-signaling