The Expression and Function of Human Ribonuclease 4 in the Kidney and Urinary Tract.

Antimicrobial peptides are essential host defense mechanisms that prevent urinary tract infections. Recent studies demonstrate that peptides in the Ribonuclease A Superfamily have antimicrobial activity against uropathogens and protect the urinary tract from uropathogenic Escherichia coli (UPEC). Little is known is about the antibacterial function or expression of Ribonuclease 4 in the human urinary tract. Here, we show that full-length recombinant Ribonuclease 4 peptide and synthetic amino-terminal Ribonuclease 4 peptide fragment have antibacterial activity against UPEC and multi-drug resistant UPEC. RNASE4 transcript expression was detected in human kidney and bladder tissue using quantitative real-time polymerase chain reaction. Immunostaining or in situ hybridization localized Ribonuclease 4 expression to proximal tubules, principal and intercalated cells in the kidney's collecting duct, and the bladder urothelium. Urinary Ribonuclease 4 concentrations were quantified in healthy controls and females with a urinary tract infection history. Compared to controls, urinary RNase 4 concentrations were significantly lower in females with a urinary tract infection history. When Ribonuclease 4 was neutralized in human urine or silenced in vitro using small interfering RNA, urinary UPEC replication or attachment to and invasion of urothelial and kidney medullary cells increased. These data show that Ribonuclease 4 has antibacterial activity against UPEC, is expressed in the human urinary tract, and can contribute to host defense against urinary tract infections.