The Role of Kidney Intercalated Cells in the Immune Response Against UTIs

Abstract

Introduction: Urinary tract infections (UTIs) are among the most prevalent infections. About 3 in 5 women will experience UTIs in their lifetime, resulting from a bacterial infection caused by uropathogenic E. coli (UPEC). Ascending UPEC first adhere to the collecting ducts, where intercalated cells (ICs) are essential for raising an innate immune response activated by UPEC-outer membrane lipopolysaccharide (LPS). Interestingly, individuals with distal renal tubular acidosis (dRTA) who have a mutation on the gene encoding the kidney anion exchanger 1 (kAE1) have a decreased abundance of IC and are at a higher risk for UTIs. The cellular mechanisms contributing to this higher vulnerability to UTIs remain unclear. Objective and Hypothesis: To enhance our understanding of the immune response mechanisms of collecting duct cells in dRTA patients during UTIs, we hypothesize that the loss of intercalated cells (ICs) in dRTA results in an inadequate immune response against UPEC. Methods: Mouse inner medullary collecting duct cells (mIMCD3) and a mouse strain with a knock-in mutation for kAE1 dRTA (specifically, R607H, equivalent to human R589H) were utilized in the study. We identified and quantified innate immunity markers in mIMCD3 cells exposed to vehicle, UPEC or LPS using qRT-PCR and immunoblot. Primary IC were prepared by magnetic-activated cell sorting (MACS). Various incubation conditions, including exposure to vehicle, LPS, control K12 bacteria, and UPEC for different time intervals were assessed to determine the best experimental conditions. Transurethral UPEC inoculation procedures were also performed to validate results obtained in the in vitro approaches. Results: Experiments on mIMCD3 cells showed a significant increase in the innate immunity marker adrenomedullin (ADM) following exposure to UPEC or LPS, compared to the control group. After 17 h, exposing the primary MACS-enriched ICs to UPEC significantly increased the adrenomedullin protein abundance. UPEC transurethral infections in dRTA mice resulted in a higher bacterial load and increased IL-1β, IL-6, and TNF-α mRNA and protein levels compared to WT mice at 24 post-UTI. In the transgenic mice, ADM gene expression was not up-regulated to the same extent as in WT mice, but LCN2/NGAL gene expression was significantly higher. Conclusions: Our study suggests that the loss of IC in a dRTA mouse model results in higher inflammation and reduced immunity against UPEC exposure. Our research will unravel new therapeutic leads on the intracellular signaling pathway(s) and cellular changes that result in IC-mediated renal protection. The findings may contribute to the development of novel therapeutics for UTIs. Natural Sciences and Engineering Research Council of Canada (NSERC), the Canadian Institutes of Health Research (CIHR), University of Alberta Graduate Recruitment Scholarship (2023). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.