Characterization of functional and molecular properties of circulating extracellular vesicles of childhood idiopathic nephrotic syndrome patients
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Nephrotic syndrome (NS) is one of the most common causes of glomerular disease in children and is characterized by the triad of proteinuria, hypoalbuminemia, and edema. The major molecular event in the pathogenesis of NS is the disruption of the glomerular filtration barrier, which is primarily driven by podocyte injury. The most common clinical presentation of NS in children is steroid-sensitive nephrotic syndrome (SSNS), characterized by complete remission within 4 weeks of steroid therapy and no apparent glomerular change in the light microscopic evaluation of kidney biopsies, thereby named as Minimal Change Disease (MCD). Since previous research suggests a role of a circulating factor in the pathogenesis of steroid-sensitive nephrotic syndrome (SSNS), we speculated that circulating plasma extracellular vesicles (EVs) are a candidate source of such a soluble mediator. Here, we aimed to characterize and try to delineate the effects of these EVs in vitro. Plasma EVs from 20 children with SSNS in relapse and remission, 10 healthy controls and 6 disease controls were obtained by serial ultracentrifugation. Characterization of these EVs was performed by electron microscopy, flow cytometry and western blotting. The major proteins from the plasma EVs were identified via mass spectrometry. A Gene Ontology classification analysis and ingenuity pathway analysis were performed on selectively expressed EV proteins during relapse. Immortalized human podocyte culture was used to detect the effects of EVs on podocytes. The protein content and the particle number of plasma EVs were significantly increased during NS relapse. Relapse NS EVs selectively express proteins which involved actin cytoskeleton rearrangement. Among these, the level of RAC-GTP was significantly increased in relapse EVs compared to remission and disease control EVs. Relapse EVs were efficiently internalized by podocytes and induced significantly enhanced motility and albumin permeability. Moreover, relapse EVs induced significantly higher levels of RAC-GTP and phospho p38 (p-p38) and decreased levels of synaptopodin in podocytes. Circulating relapse EVs are biologically active molecules that carry active RAC1 as cargo and induce recapitulation of the nephrotic syndrome phenotype in podocytes in vitro.