Proteomic Signatures of Podocyte Injury Are Reflected in Urinary Extracellular Vesicles in Pediatric Nephrotic Syndrome.

Idiopathic nephrotic syndrome (NS) is a common glomerulopathy in children and presents with significant proteinuria. There are no reliable clinical or biochemical markers of disease relapse, or prognosis. Extracellular vesicles (EVs) are small, membrane-bound biological effectors released from stressed cells. We previously showed increases in podocyte-specific urinary EVs from children with disease relapse in NS, with numbers returning to near-zero in remission. Herein, we have expanded this work to evaluate puromycin aminonucleoside (PAN) injury by characterizing proteomic signatures of podocytes and their EVs in vitro. In addition, we performed data-independent proteomic analysis (DIA) to characterize changes in signatures of EVs from pediatric patients with active NS versus remission. Our key findings reveal PAN-injured podocytes increase large EV (LEV) secretion in vitro; moreover, DIA uncovered changes in cellular and LEV proteomes that were also observed in urinary LEVs from patients with active disease. Urinary LEV proteomes from children with active NS were significantly different than those in remission, highlighted by 645 and 240 unique proteins associated with disease or remission, respectively. This foundational work provides the impetus for a larger, prospective biomarker study aimed at identifying EV-specific proteins associated with relapse versus remission.