Large-Scale Proteomic Assessment of Urinary Extracellular Vesicles Highlights Their Reliability in Reflecting Protein Changes in the Kidney

Background Urinary extracellular vesicles (uEVs) are secreted into urine by cells from the kidneys and urinary tract. Although changes in uEV proteins are used for quantitative assessment of protein levels in the kidney or biomarker discovery, whether they faithfully reflect (patho)physiologic changes in the kidney is a matter of debate. Methods Mass spectrometry was used to compare in an unbiased manner the correlations between protein levels in uEVs and kidney tissue from the same animal. Studies were performed on rats fed a normal or high K+ diet. Results Absolute quantification determined a positive correlation (Pearson R=0.46 or 0.45, control or high K+ respectively, P<0.0001) between the approximately 1000 proteins identified in uEVs and corresponding kidney tissue. Transmembrane proteins had greater positive correlations relative to cytoplasmic proteins. Proteins with high correlations (R>0.9), included exosome markers Tsg101 and Alix. Relative quantification highlighted a monotonic relationship between altered transporter/channel abundances in uEVs and the kidney after dietary K+ manipulation. Analysis of genetic mouse models also revealed correlations between uEVs and kidney. Conclusion This large-scale unbiased analysis identifies uEV proteins that track the abundance of the parent proteins in the kidney. The data form a novel resource for the kidney community and support the reliability of using uEV protein changes to monitor specific physiologic responses and disease mechanisms.

Automated summary

This study utilized mass spectrometry to compare the correlations between protein levels in urinary extracellular vesicles (uEVs) and kidney tissue, finding a positive correlation between them; transmembrane proteins showed higher correlations than cytoplasmic proteins; the changes in various proteins had a monotonic relationship with alterations in the kidney after dietary K+ manipulation.