Background/Objectives
Membranous nephropathy (MN) is an autoimmune glomerulonephritis of kidney podocytes caused by circulating autoantibodies against podocyte foot process proteins. The morphological hallmark is glomerular antigen–autoantibody deposition. The underlying mechanisms and clinical significance of glomerular aggregate formation and release in MN remain unclear. This study analyzed podocyte-derived urinary extracellular vesicle (EV) formation in human nephrotic patients and experimental murine MN, identifying exopher-like vesicles (ELVs) as the pathobiological correlate of glomerular urinary space antigen/autoantibody aggregates.
Methods
EVs were isolated from mouse and human urine by differential ultracentrifugation, followed by ultrafiltration (human urine) or dialysis (mouse urine). EVs were quantified by nanoparticle tracking analysis, characterized by electron microscopy, ImageStream, and immunoblotting. Proteostatic content of human urinary EVs was assessed by mass spectrometry. Immunohistology was performed on biopsies from human nephrotic patients.
Results
Podocyte ELVs were identified as biological correlates of glomerular urinary space aggregates in MN. These large, stalked vesicles form by translocating THSD7A and bound autoantibodies from the subepithelial to the urinary side of the podocyte plasma membrane. ELVs in MN patients contained antigen/autoantibody complexes and disease-associated proteins such as complement. ELV release, enhanced by proteotoxic stress, reduced aggregate burden in experimental MN. Monitoring urinary ELV abundance and autoantibodies was particularly valuable when serum autoantibody titers were negative. The proteostatic content of podocyte-derived urinary EVs varied with disease status, reflecting the proteostatic state of podocytes.
Conclusion
Exopher-like vesicle genesis appears to be a protective pathomechanism in MN. Tracking autoantibodies from the serum to the urinary ELV-bound state can assess the podocytes’ ability to manage disease-initiating autoantibodies. This approach may offer a non-invasive diagnostic tool with prognostic potential in MN.
Keywords
Membranous nephropathy, podocytes, extracellular vesicles, exopher-like vesicles, autoantibodies
