Innate Immune Roles of Alpha-Defensin 1-3 in Neutralizing Uropathogenic Escherichia Coli

Abstract

Urinary tract infections (UTIs) are characterized by microbial colonization of the bladder, ureters or/and kidneys. Host-pathogen interactions compound to drive UTI susceptibility. The host innate immune system is composed of physio-chemical barriers and broad-spectrum potent effector responses that prevent pathogenic host colonization and bystander damage. Uropathogenic Escherichia coli (UPEC) isolates account for the majority of reported UTI cases. Virulence factors that are expressed by CFT073/UPEC heighten pathogenesis by permitting preferential invasion towards kidneys (pyelonephritis). During the acute invasion of the urinary tract tissues, pathogen molecular patterns and host-damage signals represent triggers that lead to host-defense responses. The release of antimicrobial peptides (AMPs) prevents microbial attachment to the epithelium. α-Defensin 1-3 are host-defense AMPs that work by eliciting microbial membrane interactions and inducing immunomodulatory effects. In humans, the DEFA1A3 locus encodes for three α-Defensin peptides (1-3). Chromosome 8 can harbor copy number polymorphism of the DEFA1A3 locus that range from 3-16 copies per diploid genome. Low copy numbers of DEFA1A3 have been associated with increased UTI risk in children (< 5 copies). On the other hand, patients with > 8 per copies per diploid genome have improved antibiotic therapy outcomes. In this thesis, we establish a pipeline to characterize α-Defensin 1-3 mechanisms of action, dissect contributors of expression at the cellular level, and protective DEFA1A3 gene-dose-dependent effects in the pyelonephritis setting. Using a manipulable mouse model expressing transgenic human DEFA1A3 gene copies, we explored dynamics of inducible α-Defensin 1-3 expression in the UPEC-infected kidney. Additionally, in vitro combinations of α-Defensin 1-3 and other host-defense AMPs work in concert to drive diverse cooperative action effects against UPEC. Methods and findings from my research in this thesis improve the current biomedical approaches to study AMP functions. Collectively, my results expand the understanding of DEFA1A3 polymorphic locus as a stratification UTI biomarker and exploration for the pre-clinical evaluation of kidney α-Defensin 1-3 expression as a potential therapeutic target for UTIs and other infectious diseases.