Date of Award
Doctor of Philosophy (PhD)
Urinary tract infections (UTIs) are among the most common infectious diseases and are primarily caused by uropathogenic E. coli (UPEC). Given the greater incidence of antibiotic resistance among UPEC isolates, it is vital to determine factors and pathways important for an effective host response to UPEC in order to improve therapeutic options for combating UTIs. Autophagy is a cellular degradation pathway that plays important roles in pathogen control and modulation of innate immunity. One essential autophagy protein, ATG16L1, has been further implicated in controlling inflammation due to a common variant of ATG16L1 being associated with increased risk of Crohns disease, a disease of continuous excessive inflammation in the gut. Autophagy and ATG16L1 had been shown to play anti-pathogenic roles in response to a number of infections, yet little was known about their role in response to UPEC. In this thesis, I examined the role of ATG16L1 in response to UPEC pathogenesis.
We found ATG16L1-deficient mice clear bacteriuria faster, recruit more monocytes/macrophages, and recover their epithelial barrier faster than WT mice in a well-established mouse model of UPEC induced UTI. ATG16L1 deficiency in the urothelium led to altered urothelial cell architecture, with accumulations of lysosomes and multivesicular bodies, and fewer UPEC quiescent intracellular reservoirs that can seed recurrent infections. Additionally, we found that immune cells lacking ATG16L1 were better able to clear their infection. Furthermore, ATG16L1 deficient macrophages were particularly adept at clearing their bacteria load. My work has revealed that ATG16L1-deficiency in fact improves the ability of macrophages derived from the bones of mice to take up more UPEC and enhances their secretion of IL-1, a key pro-inflammatory cytokine, in response to UPEC. This increased IL-1 secretion by ATG16L1-deficient macrophages in response to UPEC was dependent on enhanced cleavage of pro-IL-1 to its active form by activated caspase-1 and the NLRP3 inflammasome. Finally, to confirm that enhanced IL-1 secretion was the key mechanism for UTI clearance in ATG16L1-deficient mice, I determined that the mutant mice secreted more IL-1 in their urine in response to UPEC infection, and inhibition of IL-1 signaling abrogated the ATG16L1-deficiency dependent protection from UTIs. Together, my work suggests that ATG16L1 dampens what is otherwise a protective increase in macrophage recruitment and IL-1 production in response to UPEC infection. Thus, ATG16L1 deficiency improved the host response to UPEC infection, challenging the paradigm that deficiency in autophagy proteins is detrimental to the host. Furthermore, the detrimental ATG16L1-deficiency induced inflammation against commensal bacteria that is associated with Crohns disease may be the trade off for enhanced protection against acute infection and reservoir formation by UPEC and possibly other common infections.
Chair and Committee
Indira U. Mysorekar
David Hunstad, Jason Mills, Joel Schilling, David Sibley,
Symington, Jane, "Role of ATG16L1 in Uropathogenic E. Coli Pathogenesis" (2016). Arts & Sciences Electronic Theses and Dissertations. 764.