Presentation Authors: Laura Schwartz, Tad Eichler, Kristin Bender, Matthew Murtha, John Spencer*, Columbus, OH
Introduction: Urinary tract infection (UTI) is more common and has worse outcomes in people with diabetes mellitus (DM). The mechanisms that predispose diabetics to UTI are not defined. Uropathogens are rapidly developing antibiotic resistance. Thus, a greater understanding of host defenses that protect the urinary tract from microbial insult are needed to develop new UTI treatment options that will improve care provided to people with DM. This project was designed to investigate how insulin signaling affects urothelial antibacterial defenses and UTI susceptibility, independent of hyperglycemia and glucosuria.
Methods: To investigate the impact of insulin signaling on bladder innate defenses, we genetically deleted the insulin receptor (IR) in the urothelium. Urothelial-specific IR knock-out mice (IRKO) were generated by breeding homozygous mice for the floxed Insr gene with mice that express a tamoxifen-inducible Cre recombinase under the Uroplakin 2 (Upk2) promoter. Littermates lacking the Upk2-Cre transgene served as controls (IRflox). To determine if urothelial-specific IR deletion impacts host defense, female mice were transurethrally infected with uropathogenic E. coli (UPEC). UPEC burden was enumerated in urine, bladder, and kidney post infection. To assess how IR deletion increases UTI risk, antibacterial peptide (AMP) expression and urothelial barrier formation were assessed.
Results: Compared to controls, IRKO mice exhibit normal development, normal bladder histology, and no evidence of hyperglycemia/glucosuria. IRKO mice were more susceptible to experimental UTI compared to controls, as significantly greater UPEC titers were enumerated in their urine, bladder, and kidneys. This was accompanied by increased bladder edema and inflammatory scores. IR deletion suppressed urothelial AMP mRNA expression and increased urothelial permeability in vivo. To confirm that suppressed AMP expression increases UPEC susceptibility, AMPs were silenced in 5637 urothelial cells in vitro. siRNA-mediated AMP silencing increased UPEC cellular invasion. Similarly, siRNA-mediated INSR knock-down decreased urothelial barrier formation and increased urothelial permeability.
Conclusions: These results suggest that defective insulin signaling impairs urothelial innate defenses. Also, they indicate that hyperglycemia alone does not explain increased UTI risk. In part, increased UPEC susceptibility may be due to decreased expression of AMPs or disrupted urothelial barrier formation, indicating potential targets for mitigating UTI risk in insulin-resistant individuals.
Source of Funding: National Institutes of Health (NIDDK R01 DK114035).