A bacteria-fighting peptide previously identified in skin cells, hair follicles and the mouth has been identified in the urinary tract and may be partly responsible for protecting it from infection. These are the findings from a Nationwide Children’s study appearing in Kidney International.
“The urinary tract is constantly challenged by microbial invasion,” said David Hains, MD, principal investigator in the Center for Clinical and Translational Research at The Research Institute at Nationwide Children’s. “Yet, it often remains free from colonization. It’s not clear how the urinary tract maintains sterility.”
Components of the innate immune response known as antimicrobial peptides have been shown to kill bacteria, including strains that are antibiotic resistant. Several antimicrobial peptides are found in urine.
“The presence of antimicrobial peptides in the urine suggests that they may play a role in protecting the urinary tract from infection,” said Dr. Hains.
Upon examining human kidney, ureter and bladder tissue samples and urine samples from 20 health individuals, Nationwide Children’s investigators identified a novel antimicrobial peptide expressed in the human urinary tract, RNase 7. Ribonuclease 7 (RNase 7) is a potent antimicrobial peptide that was first identified in the skin.
The study revealed that RNase 7 is expressed in high levels throughout the urinary tract and its concentration in the urine is very abundant for an antimicrobial peptide. “We found that when expressed at these concentrations, RNase 7 greatly affects bacterial growth of several bacteria often found in the urinary tract,” said John David Spencer, MD, Nephrology fellow at Nationwide Children’s and lead study author.
They also found that RNase 7’s expression pattern differs from the expression of other antimicrobial peptides that have been described in the kidney, suggesting that it may be particularly critical in a healthy urinary tract. In addition, RNase 7 is present in locations where microbial exposure occurs most frequently.
“Overall, these data suggest that RNase 7 is involved in maintaining urine sterility,” said Dr. Spencer. “This brings us one step closer to understanding how a healthy urinary tract functions.”
Dr. Hains says this is especially important as urinary-tract-infection-causing bacteria such as E. coli become resistant to standard antibiotics. “Further evaluation of human antimicrobial peptides like RNase 7 may lead to the development of new treatment strategies for antibiotic-resistant urinary tract infections,” he said.
Spencer JD, Schwaderer AL, Dirosario JD, McHugh KM, McGillivary G, Justice SS, Carpenter AR, Baker PB, Harder J, Hains DS.Ribonuclease 7 is a potent antimicrobial peptide within the human urinary tract. Kidney Int. 2011 Apr 27. [Epub ahead of print]