Normal human urine contains large numbers of exosomes, which are 40- to 100-nm 
vesicles that originate as the internal vesicles in multivesicular bodies from 
every renal epithelial cell type facing the urinary space. Here, we used 
LC-MS/MS to profile the proteome of human urinary exosomes. Overall, the 
analysis identified 1132 proteins unambiguously, including 177 that are 
represented on the Online Mendelian Inheritance in Man database of 
disease-related genes, suggesting that exosome analysis is a potential approach 
to discover urinary biomarkers. We extended the proteomic analysis to 
phosphoproteomic profiling using neutral loss scanning, and this yielded 
multiple novel phosphorylation sites, including serine-811 in the 
thiazide-sensitive Na-Cl co-transporter, NCC. To demonstrate the potential use 
of exosome analysis to identify a genetic renal disease, we carried out 
immunoblotting of exosomes from urine samples of patients with a clinical 
diagnosis of Bartter syndrome type I, showing an absence of the 
sodium-potassium-chloride co-transporter 2, NKCC2. The proteomic data are 
publicly accessible at http://dir.nhlbi.nih.gov/papers/lkem/exosome/.