Glomerular Endothelial Cell-Derived microRNA-192 Regulates Nephronectin Expression in Idiopathic Membranous Glomerulonephritis

Significance Statement MicroRNA-192-5p (miR-192-5p) is upregulated in the glomeruli and urine of patients with idiopathic membranous glomerulonephritis (iMGN). It derives from glomerular endothelial cells, is packed into exosomes, and decreases podocyte nephronectin (NPNT) in the glomerular basement membrane (GBM) by paracrine signaling. Patients with iMGN have reduced glomerular NPNT expression. Whole-body knockdown of npnt in zebrafish and podocyte-specific knockout of Npnt in mice damage the GBM, increasing lucidity of the lamina rara interna, which admits high molecular weight proteins. Reduced NPNT leading to GBM leakiness might be an important part of iMGN pathophysiology, initiating podocyte antigen presentation, and admitting autoantibodies into the subepithelial space. NPNT might be a prognostic parameter and noninvasive marker for iMGN. Monitoring and targeting this miR could be a promising diagnostic and therapeutic approach for iMGN. Background Autoantibodies binding to podocyte antigens cause idiopathic membranous glomerulonephritis (iMGN). However, it remains elusive how autoantibodies reach the subepithelial space because the glomerular filtration barrier (GFB) is size selective and almost impermeable for antibodies. Methods Kidney biopsies from patients with iMGN, cell culture, zebrafish, and mouse models were used to investigate the role of nephronectin (NPNT) regulating microRNAs (miRs) for the GFB. Results Glomerular endothelial cell (GEC)-derived miR-192-5p and podocyte-derived miR-378a-3p are upregulated in urine and glomeruli of patients with iMGN, whereas glomerular NPNT is reduced. Overexpression of miR-192-5p and morpholino-mediated npnt knockdown induced edema, proteinuria, and podocyte effacement similar to podocyte-derived miR-378a-3p in zebrafish. Structural changes of the glomerular basement membrane (GBM) with increased lucidity, splitting, and lamellation, especially of the lamina rara interna, similar to ultrastructural findings seen in advanced stages of iMGN, were found. IgG-size nanoparticles accumulated in lucidity areas of the lamina rara interna and lamina densa of the GBM in npnt-knockdown zebrafish models. Loss of slit diaphragm proteins and severe structural impairment of the GBM were further confirmed in podocyte-specific Npnt knockout mice. GECs downregulate podocyte NPNT by transfer of miR-192-5p–containing exosomes in a paracrine manner. Conclusions Podocyte NPNT is important for proper glomerular filter function and GBM structure and is regulated by GEC-derived miR-192-5p and podocyte-derived miR-378a-3p. We hypothesize that loss of NPNT in the GBM is an important part of the initial pathophysiology of iMGN and enables autoantigenicity of podocyte antigens and subepithelial immune complex deposition in iMGN.