Antimicrobial Peptides as Novel Treatments for Urinary Tract Infection

Urinary tract infections (UTIs) are one of the most common bacterial infections, impacting more than 150 million individuals annually. Left untreated, UTIs can result in serious complications, including kidney injury, bacteremia, urosepsis, and, in severe cases, death.

A range of pathogens are known to cause UTIs, but uropathogenic Escherichia coli (UPEC) is the primary culprit accounting for over 80% of diagnosed cases. The primary target of infection is usually the epithelial cells lining the urinary tract, including the bladder and urethra.

Currently, the standard treatment for UTIs is antibiotics. However, the overuse of antibiotics has contributed to the emergence and global spread of antibiotic-resistant bacteria, limiting the effectiveness of these treatments. Consequently, there is an urgent need for new UTI prevention and treatment approaches that are not solely reliant on antibiotics.

An area of active research is the use of host defense antimicrobial peptides, such as ribonucleases, in UTI prevention and treatment. They are naturally produced by the kidney and bladder cells and exhibit bactericidal activity that can protect against uropathogenic bacteria, making them a promising non-antibiotic approach to UTI treatment.

Cultured Kidney Cells for In Vitro Research

Researchers frequently turn to cultured renal or kidney cells as predictive models because they offer a practical and ethical approach to better understand renal physiology and pathology, particularly in the context of kidney-related conditions such as UTIs.

Renal cells make up the tissues of the kidney and include a variety of cell types such as renal tubular epithelial cells, and glomerular endothelial cells, among others, each with specific functions in the kidney. Cultivating these cells in a laboratory setting enables researchers to maintain control over experimental conditions to conduct in vitro studies in a scientifically rigorous manner.

In the upcoming section, we will summarize several recent publications that leverage Lifeline Cell Technology’s cultured Human Renal Medullary Epithelial Cells and RenaLife™ Epithelial Media. These high-quality cells played a critical role in experiments conducted to understand the function of peptides in the ribonuclease (RNase) A superfamily in mitigating UPEC and to explore their potential as alternative treatments for UTIs.

Expression and function of human ribonuclease 4 in the kidney and urinary tract

In this first publication, Bender et al evaluate the role of ribonuclease 4 (RNase 4) in the human urinary tract and its potential as a host defense mechanism against urinary tract infections (UTIs). Previous work by this group identified other members of the RNAse A superfamily, including RNAse 6 and 7, which are expressed by immune cells such as monocytes, macrophages, and neutrophils recruited to the kidneys and bladder during UTIs. These peptides are known to exhibit potent antibacterial activity against uropathogens like UPEC; however, the expression and function of RNase 4 in the human urinary tract had not been defined.

The study first explores the antimicrobial properties of RNase 4 in the human urinary tract. Both the full-length recombinant RNase 4 peptide and a synthetic amino-terminal RNase 4 peptide fragment exhibited antibacterial activity against UPEC and multidrug-resistant UPEC.

RNASE4 transcript expression was detected in kidney and bladder through quantitative real-time PCR. Immunostaining and in situ hybridization techniques localized RNase 4 expression to the proximal tubules, principal cells, intercalated cells in the kidney’s collecting duct, and the bladder urothelium.

RNase 4 expression was knocked down in vitro using siRNA in bladder cells and Lifeline’s primary human kidney medullary cells to confirm that reduced expression leads to a higher susceptibility to UPEC infection. Silencing RNase 4 resulted in a significant increase in the percentage of UPEC replication, attachment to, and invasion of urothelial and kidney medullary cells.

Collectively, the data suggests that RNase 4 is a promising candidate for the development of endogenous UTI therapies due to its effectiveness in preventing invasive UPEC infections.

Repurposing HDAC inhibitors to enhance ribonuclease 4 and 7 expression and reduce urinary tract infection

In this next publication, Schwartz et al conducted a high-throughput screening of FDA-approved medications that can be repurposed as new therapeutics for UTIs. Their objective was to identify compounds that can boost the expression of antimicrobial peptides RNase 4 and RNase 7 as antibiotic-conserving UTI therapies to treat antibiotic-resistant uropathogens.

The screen identified histone deacetylase inhibitors (HDACi) as a class of drugs that can enhance RNase 4 and RNase 7 expression. Validation studies in primary human kidney (Lifeline Cell Technology) and bladder cells confirmed that pan-HDAC inhibitors, as well as the HDAC class I inhibitor MS-275, induced RNase 4 and RNase 7 expression, which effectively protected human kidney and bladder cells from UPEC infection.

The study showed that MS-275 treatment increased acetylated histone H3 binding to the RNASE4 and RNASE7 promoters. Furthermore, overexpression and knockdown experiments pinpointed HDAC3 as a primary regulator of RNase 4 and 7. The results demonstrated the protective effects of enhancing RNase 4 and RNase 7 expression, providing insight into new mechanisms that offer a novel approach to UTI treatment.

Lifeline Cell Technology Renal & Bladder Cells

Lifeline Cell Technology’s primary kidney and bladder cells are sourced from multiple donors and directly isolated and cultured from their source tissues, which maintains the cells in their natural, unaltered state. This makes them ideal culture models for a wide range of applications from fundamental research to drug screening, to preserve the integrity of experimental outcomes and ensure the validity of research findings.

If you are interested in renal or bladder cells for your own research, please see the Lifeline catalog for more information:

• Human Renal Medullary Epithelial Cells
• Human Renal Proximal Tubule Epithelial Cells
• Human Renal Cortical Epithelial Cells
• Human Renal Mixed Epithelial Cells
• Human Bladder Apex Epithelial Cells
• Human Bladder Dome Epithelial Cells
• Human Bladder Smooth Muscle Cells
• Human Bladder Fibroblasts

Visit us here at our blog to learn how researchers around the world are utilizing our portfolio of human cells and culture media, to answer their scientific questions.

Have you used our products to power your research? We’d love to hear from you!