Because existing mouse models of UTI have historically been restricted to female hosts due to technical issues, we developed new models of cystitis and pyelonephritis that encompass male and female mice, allowing direct identification and study of sex differences in the pathogenesis of these infections. Our initial studies in these models implicated androgens as a driver of severe UTI outcomes in both female and male hosts. Our Infant and Childhood UTI Project (ICUP) enrolled patients under 2 years of age, with or without UTI, to gain valuable information about the pathogenesis of, and host responses to, UTIs in both male and female children. We are now embarking on bacterial RNAseq and host single-nucleus RNAseq to define sex-specific host responses and host-sex-specific bacterial virulence requirements in upper-tract UTI.
Our new models of experimental UTI in male and androgenized female hosts demonstrate severe kidney infection, nucleated by kidney bacterial communities arising in the renal tubules near the corticomedullary junction. Between 5 and 7 days post infection, these KBCs evolve into renal abscesses. We have also modeled the abrogation of abscess formation with timely antibiotic administration, as well as the development of renal scarring even after achieving microbiologic cure. These processes recapitulate the renal scars that often follow pyelonephritis in children, a risk factor for hypertension and possibly chronic kidney disease later in life. We used this model to demonstrate the importance of TGFβ signaling in post-infection scar formation, and our ongoing studies aim to understand these injury, repair, and fibrosis processes at a cellular and molecular level so that these long-term sequelae of pyelonephritis can be averted.
Neutrophils arriving in the bladder in response to chemokines interact directly with E. coli bacteria and with IBC-containing superficial bladder epithelial cells to control initial infection in the murine cystitis model. Despite the arrival of neutrophils, UPEC can multiply to high titers in the mouse bladder by 48 hours after infection. Our findings demonstrate that UPEC, in contrast to nonpathogenic E. coli, employ strategies to resist phagocytosis, survive within phagocytes, and attenuate the production of reactive oxygen species by neutrophils. We have detailed this host-pathogen crosstalk by simultaneous profiling of bacterial and eukaryotic gene expression during phagocytosis of UPEC by human neutrophils. These transcriptional profiles have provided new leads for investigation of bacterial effector proteins and the host pathways that they modulate, such as the mammalian indoleamine 2,3-dioxygenase pathway. In addition, we have identified new bacterial effectors such as YbcL that are liberated from dying UPEC and suppress neutrophil migration to the infected bladder. Our ongoing work has specified the host cellular binding target of this UPEC effector.
We aim to leverage recent discoveries about the pathogenic cascade of cystitis in developing novel therapeutic interventions for acute and recurrent UTI, as typical oral antibiotic therapy fails to eradicate the intraepithelial reservoir which can serve as a seed for repeated UTIs. We have identified small-molecule bladder epithelial renewal agents in collaboration with the research group of Wiley Youngs, PhD, a distinguished chemist at the University of Akron, and we are collaborating with Karen Wooley, PhD, an accomplished polymer chemist at Texas A&M University, to develop functionalized nanostructures for delivery of bioactive cargo to the uroepithelium. We aim to demonstrate that these optimized constructs, when applied intravesically, can eradicate chronically resident E. coli from the bladder tissue, breaking the cycle of recurrent UTI that plagues many otherwise healthy women.
Work in the Hunstad lab is supported by the NIH (NIDDK and NIAID). We acknowledge past support from the NIH Office of Research on Women’s Health, the March of Dimes, and the Mallinckrodt Foundation.