Andrew L. Schwaderer

Ribonuclease 7 is a potent antimicrobial peptide within the human urinary tract

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.

Ribonuclease 7, an antimicrobial peptide upregulated during infection, contributes to microbial defense of the human urinary tract

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.

Human Alpha Defensin 5 Expression in the Human Kidney and Urinary Tract

Background The mechanisms that maintain sterility in the urinary tract are incompletely understood. Recent studies have implicated the importance of antimicrobial peptides (AMP) in protecting the urinary tract from infection. Here, we characterize the expression and relevance of the AMP human alpha-defensin 5 (HD5) in the human kidney and urinary tract in normal and infected subjects. Methodology/Principal Findings Using RNA isolated from human kidney, ureter, and bladder tissue, we performed quantitative real-time PCR to show that DEFA5, the gene encoding HD5, is constitutively expressed throughout the urinary tract. With pyelonephritis, DEFA5 expression significantly increased in the kidney. Using immunoblot analysis, HD5 production also increased with pyelonephritis. Immunostaining localized HD5 to the urothelium of the bladder and ureter. In the kidney, HD5 was primarily produced in the distal nephron and collecting tubules. Using immunoblot and ELISA assays, HD5 was not routinely detected in non-infected human urine samples while mean urinary HD5 production increased with E.coli urinary tract infection. Conclusions/Significance DEFA5 is expressed throughout the urinary tract in non-infected subjects. Specifically, HD5 is expressed throughout the urothelium of the lower urinary tract and in the collecting tubules of the kidney. With infection, HD5 expression increases in the kidney and levels become detectable in the urine. To our knowledge, our findings represent the first to quantitate HD5 expression and production in the human kidney. Moreover, this is the first report to detect the presence of HD5 in infected urine samples. Our results suggest that HD5 may have an important role in maintaining urinary tract sterility.

The innate immune response during urinary tract infection and pyelonephritis.

Despite its proximity to the fecal flora, the urinary tract is considered sterile. The precise mechanisms by which the urinary tract maintains sterility are not well understood. Host immune responses are critically important in the antimicrobial defense of the urinary tract. During recent years, considerable advances have been made in our understanding of the mechanisms underlying immune homeostasis of the kidney and urinary tract. Dysfunctions in these immune mechanisms may result in acute disease, tissue destruction and overwhelming infection. The objective of this review is to provide an overview of the innate immune response in the urinary tract in response to microbial assault. In doing so, we focus on the role of antimicrobial peptides—a ubiquitous component of the innate immune response.

Low bone density in children with hypercalciuria and/or nephrolithiasis

The objective of this study was to identify how many children with hypercalciuria and/or nephrolithiasis have a low bone density and whether the risk of low bone density can be identified by 24-h urine stone-risk profiles and/or growth parameters. A retrospective chart review was performed on 110 idiopathic hypercalciuria and/or kidney stone patients who received both a 24-h urine for stone-risk profile and a dual-energy X-ray densitometry scan. Patients were divided into low bone density vs. normal bone density groups and hypercalcuria verus nephrolithiasis groups and analyzed for differences in growth parameters, urine stone-risk profiles, and bone densities. Overall, 47% had a bone density z score < −1, and 26% had a bone density z score < −2. Patients with a low bone density had a higher body mass index and lower urine creatinine and ammonium than those with a normal bone density. Patients with nephrolithiasis had a lower bone density z score than patients with hypercalcuria and no nephrolithiasis. Clinicians should be aware of the increased incidence of low bone density in children with hypercalciuria and nephrolithiasis. The effect of hypercalciuria and nephrolithiasis treatment on bone density and the natural progression of the bone density in the studied patient population warrants further investigation.

Expression and antimicrobial function of beta-defensin 1 in the lower urinary tract.

Beta defensins (BDs) are cationic peptides with antimicrobial activity that defend epithelial surfaces including the skin, gastrointestinal, and respiratory tracts. However, BD expression and function in the urinary tract are incompletely characterized. The purpose of this study was to describe Beta Defensin-1 (BD-1) expression in the lower urinary tract, regulation by cystitis, and antimicrobial activity toward uropathogenic Escherichia coli (UPEC) in vivo. Human DEFB1 and orthologous mouse Defb1 mRNA are detectable in bladder and ureter homogenates, and human BD-1 protein localizes to the urothelium. To determine the relevance of BD-1 to lower urinary tract defense in vivo, we evaluated clearance of UPEC by Defb1 knockout (Defb1 -/-) mice. At 6, 18, and 48 hours following transurethral UPEC inoculation, no significant differences were observed in bacterial burden in bladders or kidneys of Defb1 -/- and wild type C57BL/6 mice. In wild type mice, bladder Defb1 mRNA levels decreased as early as two hours post-infection and reached a nadir by six hours. RT-PCR profiling of BDs identified expression of Defb3 and Defb14 mRNA in murine bladder and ureter, which encode for mBD-3 and mBD-14 protein, respectively. MBD-14 protein expression was observed in bladder urothelium following UPEC infection, and both mBD-3 and mBD-14 displayed dose-dependent bactericidal activity toward UPEC in vitro. Thus, whereas mBD-1 deficiency does not alter bladder UPEC burden in vivo, we have identified mBD-3 and mBD-14 as potential mediators of mucosal immunity in the lower urinary tract.

An endogenous ribonuclease inhibitor regulates the antimicrobial activity of ribonuclease 7 in the human urinary tract

Recent studies stress the importance of antimicrobial peptides in protecting the urinary tract from infection. Previously, we have shown that ribonuclease 7 (RNase 7) is a potent antimicrobial peptide that has broad-spectrum antimicrobial activity against uropathogenic bacteria. The urothelium of the lower urinary tract and intercalated cells of the kidney produce RNase 7 but regulation of its antimicrobial activity has not been well defined. Here we characterize the expression of an endogenous inhibitor, ribonuclease inhibitor (RI), in the urinary tract and evaluate its effect on RNase 7’s antimicrobial activity. Using RNA isolated from non-infected human bladder and kidney tissue, quantitative real-time PCR showed that RNH1, the gene encoding RI, is constitutively expressed throughout the urinary tract. With pyelonephritis, RNH1 expression and RI peptide production significantly decrease. Immunostaining localized RI production to the umbrella cells of the bladder and intercalated cells of the renal collecting tubule. In vitro assays showed that RI bound to RNase 7 and suppressed its antimicrobial activity by blocking its ability to bind the cell wall of uropathogenic bacteria. Thus, these results demonstrate a new immunomodulatory role for RI and identified a unique regulatory pathway that may affect how RNase 7 maintains urinary tract sterility.

Contribution of Structural Domains to the Activity of Ribonuclease 7 against Uropathogenic Bacteria

ABSTRACT Ribonuclease 7 (RNase 7) is a 14.5-kDa peptide that possesses potent antimicrobial properties against Gram-negative and Gram-positive bacteria and is expressed in a variety of epithelial tissues. Little is known about its mechanisms of action and the determinants of its antimicrobial properties. The objective of this study was to identify the intrinsic functional domains of RNase 7 that influence its activity against uropathogenic bacteria. A series of RNase 7 fragments were generated that contained different components of its secondary motifs starting from both the N terminus and the C terminus of RNase 7. We determined the antimicrobial properties of each fragment against both Gram-positive Staphylococcus saprophyticus and Gram-negative Escherichia coli and Proteus mirabilis. RNase 7 fragments displayed significant differences in their antimicrobial activity profiles. Compared to N-terminal fragments, C-terminal fragments showed uniformly decreased activity against Gram-negative E. coli and P. mirabilis and Gram-positive S. saprophyticus. Fragments that lack β-sheets 1, 3, and 4 also demonstrated significantly decreased activities. We have also identified one fragment with at least 4-fold increased potency against both E. coli and Staphylococcus compared to full-length peptide. We identified distinct regions of the peptide that are independently responsible for Gram-negative and Gram-positive activity. Our results suggest that distinct mechanisms are responsible for RNase 7s antimicrobial activity against various uropathogens.

Urinary Stone Disease: Advancing Knowledge, Patient Care, and Population Health

Expanding epidemiologic and physiologic data suggest that urinary stone disease is best conceptualized as a chronic metabolic condition punctuated by symptomatic, preventable stone events. These acute events herald substantial future chronic morbidity, including decreased bone mineral density, cardiovascular disease, and CKD. Urinary stone disease imposes a large and growing public health burden. In the United States, 1 in 11 individuals will experience a urinary stone in their lifetime. Given this high incidence and prevalence, urinary stone disease is one of the most expensive urologic conditions, with health care charges exceeding

Amplifying renal immunity: the role of antimicrobial peptides in pyelonephritis

10 billion annually. Patient care focuses on management of symptomatic stones rather than prevention; after three decades of innovation, procedural interventions are almost exclusively minimally invasive or noninvasive, and mortality is rare. Despite these advances, the prevalence of stone disease has nearly doubled over the past 15 years, likely secondary to dietary and health trends. The NIDDK recently convened a symposium to assess knowledge and treatment gaps to inform future urinary stone disease research. Reducing the public health burden of urinary stone disease will require key advances in understanding environmental, genetic, and other individual disease determinants; improving secondary prevention; and optimal population health strategies in an increasingly cost-conscious care environment.