Urinary extracellular vesicles as reservoirs of altered proteins during the pathogenesis of polycystic kidney disease

Purpose: Recent findings indicate that urinary extracellular vesicles (EVs) might reflect the pathophysiological state of urinary system; and that EVs-induced ciliary signaling is a possible mechanism of intercellular communication within the tract. Here, we aimed to analyze the protein expression of urinary EVs during autosomal dominant polycystic kidney disease (ADPKD). Experimental design: EVs were isolated from pooled urine samples of healthy control and ADPKD patients at two different stages of the disease and under tolvaptan treatment using the double-cushion ultracentrifugation method. Proteins were isolated and identified using iTRAQ and MudPIT. Results: Quantitative analyses identified 83 differentially expressed EVs proteins. Many of these have apical membrane origin and are involved in signal transduction pathways of primary cilia, Ca2+-activated signaling, cell-cycle regulation, and cell differentiation. Conclusions and clinical relevance: The reduced AQP-2 and the increased APO-A1levels observed in all ADPKD-affected groups may reflects the impaired renal concentrating capability of these patients and correlated with eGRF decline. The levels of some up-regulated proteins involved in Ca2+-activated signaling declined upon tolvaptan treatment. The results obtained suggest that the quantitative proteomics of urinary EVs might be useful to monitor proteins difficult to access non-invasively, and thus advance our understanding of urinary tract physiology and pathology.