Ascension and Adhesion of Uropathogenic Escherichia coli during Pyelonephritis

The ability of uropathogenic Escherichia coli (UPEC) to successfully establish an infection within the urinary tract relies on the pathogen to be able to navigate the complex interactions between pathogen and host. During a urinary tract infection (UTI), UPEC must ascend, adhere, and form bacterial communities in various infection niches, from the bladder (cystitis) to the kidneys (pyelonephritis). Each of these steps is critical for bacterial survival, and host and pathogen factors required at each stage can vary depending on host sex and anatomic niche. Preclinical modeling of pyelonephritis and sex effects on UTI has been limited due to the propensity for kidney infections in standard female murine catheterization models to resolve spontaneously, and technical barriers to infection of male mice via catheter. As a result, host and bacterial factors involved in pyelonephritis and male UTI remain incompletely defined.Here, we employed newly developed in vivo and in vitro models to begin addressing this gap in our understanding of UTI pathogenesis. In these models, we found that male and androgenized murine hosts with vesicoureteral reflux develop severe pyelonephritis, leading to the formation of penetrant renal abscesses. We also demonstrated the presence and localization of kidney bacterial communities (KBCs) that nucleate renal abscess formation, and identified KBC formation as a key pathogenic stage in pyelonephritis. We sought to define UPEC community behavior during abscess formation, as ascension into the kidney has been thought to impose a severe population bottleneck. Using a set of “barcoded” isogenic UPEC isolates and confocal microscopy, we defined the spatial and temporal dynamics of UPEC populations during experimental ascending pyelonephritis in mice. Further, we found that KBCs were clonal, and thus ascension into the nephron is a relatively uncommon event accomplished by single bacteria within a nephron unit. Once UPEC arrives within a nephron, it must adhere in order to withstand the shear force of urine flow and to enable replication and ultimately KBC formation. Type 1 pili and the tip adhesin FimH have long been recognized to be critical for UPEC adhesion to bladder epithelium. However, we demonstrated an essential role for type 1 pili in colonizing the kidney during pyelonephritis and showed that mannosides (novel small-molecule inhibitors of FimH) can limit the severity of experimental pyelonephritis. Further, by performing a lentiviral CRISPR screen in cultured renal collecting duct epithelial cells, we identified desmoglein-2, a mannosylated, surface-expressed tight junctional protein, as the first known kidney receptor for FimH. Using cellular assays and biochemical approaches, we confirmed that desmoglein-2 binds FimH and that this interaction is critical for UPEC binding to collecting duct cells. Effective and personalized future treatment of UTIs will rely on a deep mechanistic understanding of host-pathogen interactions mediating each step of the virulence cascade, in all urinary tract niches and in both host sexes. The present work suggests that androgen modulation may represent a new therapeutic or preventive strategy for UTI in selected males and in women with hyperandrogenic conditions, such as polycystic ovary syndrome. Further, identification of the FimH-Dsg2 interaction in the kidney indicates that mannosides and vaccines that target FimH binding can be further developed as non-antibiotic approaches to pyelonephritis