Specific Population of Urinary Extracellular Vesicles Distinguishes Pediatric Patients with ADPKD from Controls

Background: There is an urgent need for specific cellular and molecular biomarkers to predict ADPKD progression in children. Emerging studies show that renal cell-derived urinary extracellular vesicles (EVs) are stable biomarkers of kidney pathophysiology. Animal studies suggested that certain EVs promote cyst growth. However, the excretion of EVs from specific renal tubular segments and interstitial pro-and anti-inflammatory immune cells in children with ADPKD is unknown. Thus, we quantified urinary excretion of EVs from renal tubular and interstitial immune cells in children with and without ADPKD using an established and published method of digital flow cytometer. Methods: We collected 24-hour urine from children (9-18 years old; median 14) with genetically defined ADPKD (n=21; 12F/9M) and age-/sex-matched controls (n=18; 7F/11M). Data are presented as median (25th, 75th percentile) and analyzed by the Mann-Whitney test to identify significant (P<0.05) differences between groups. Results: Excretion of EVs from papillary epithelium (cytokeratin 20 (CK20) positive/24hr urine or mg creatinine) was significantly greater in ADPKD patients compared to controls (Fig.1). Excretion of EVs from M2 macrophages (Mφ’s; anti-inflammatory; CD206 positive/24hr urine) was significantly increased in ADPKD patients (Fig.1). Excretion of urinary EVs from the proximal tubule, thin and thick limb, distal and collecting tubules, monocytes, M1-Mφ’s, other M2-Mφ’s markers, T-cells, B-cells, NK-cells, and plasma cells did not different between groups. There was a trend toward increased excretion of phosphatidylserine and CD63-positive urinary EVs in ADPKD patients. Number of CK20 positive EVs correlated (Pearson (r) =0.57; P=0.032) with height-adjusted total kidney volume (ml/m) in ADPKD patients. Conclusion: These results suggest that pediatric ADPKD patients have increased excretion of CK20-carrying urinary EVs, as well as EVs derived from M2-Mφ’s. The potential role and pathophysiological significance of these urinary EV biomarkers requires further study. Funding: NIDDK Support - NIDDK Support, NIDDK Support