No abstract

Although the urinary tract is constantly challenged by microbial invasion, it remains free from colonization. Although little is known about how the urinary tract maintains sterility, the presence of antimicrobial peptides (AMPs) in the urine suggests that they may play a role in its protection from infection. Ribonuclease 7 (RNase 7) is a potent AMP that was first identified in the skin. Here, we characterize the expression and relevance of RNase 7 in the human kidney and urinary tract. Using RNA isolated from healthy human tissue, we performed quantitative real-time PCR and found basal RNASE7 expression in kidney and bladder tissue. Immunohistochemical and immunofluorescent analysis localized RNase 7 to the urothelium of the bladder, ureter, and the intercalated cells of the collecting tubules. In control urine samples from healthy individuals, the concentration of RNase 7 was found to be in the low micromolar range; very abundant for an AMP. Antibacterial neutralization assays showed that urinary RNase 7 has potent antimicrobial properties against Gram-negative and Gram-positive uropathogenic bacteria. Thus, RNase 7 is expressed in the human kidney and urinary tract and it may have an important antimicrobial role in maintaining tract sterility.

The mechanisms that maintain sterility in the urinary tract are incompletely understood; however, recent studies stress the importance of antimicrobial peptides in protecting the urinary tract from infection. Ribonuclease 7 (RNase 7), a potent antimicrobial peptide contributing to urinary tract sterility, is expressed by intercalated cells in the renal collecting tubules and is present in the urine at levels sufficient to kill bacteria at baseline. Here, we characterize the expression and function of RNase 7 in the human urinary tract during infection. Both quantitative real-time PCR and ELISA assays demonstrated increases in RNASE7 expression in the kidney along with kidney and urinary RNase 7 peptide concentrations with infection. While immunostaining localized RNase 7 production to the intercalated cells of the collecting tubule during sterility, its expression during pyelonephritis was found to increase throughout the nephron but not in glomeruli or the interstitium. Recombinant RNase 7 exhibited antimicrobial activity against uropathogens at low micromolar concentrations by disrupting the microbial membrane as determined by atomic force microscopy. Thus, RNase 7 expression is increased in the urinary tract with infection, and has antibacterial activity against uropathogens at micromolar concentrations.