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

Abstract

BackgroundAutoantibodies 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.MethodsKidney 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.ResultsGlomerular 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.ConclusionsPodocyte 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.

A Tight Control of Non-Canonical TGF-β Pathways and MicroRNAs Downregulates Nephronectin in Podocytes

“…As TGF-β and NPNT are dysregulated in different glomerular diseases [ 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 19 , 20 , 21 , 22 , 23 ], our results of a TGF-β-mediated NPNT regulation, facilitated mainly by non-canonical pathways and post-transcriptional mechanisms, might have important impact for the development of novel therapeutic strategies in the future.…”

“…We could previously show that podocytes express NPNT mRNA and protein [ 10 , 11 ]. Cell fractionation of human podocytes could only detect intracellular NPNT protein in the cytosolic fraction but not in the membrane or nucleus ( Figure S1a ).…”

“…In addition to collagens and laminins, nephronectin (NPNT) is another ECM protein of the GBM. We previously described that podocyte-derived miR-378a-3p and endothelial-cell-derived miR-192-5p downregulate NPNT in podocytes [ 10 , 11 ]. Furthermore, TGF-β upregulated miR-378a-3p and downregulated NPNT, suggesting a TGF-β-mediated miR-378a-3p–NPNT axis [ 10 , 12 ].…”

“…In our previous study, we observed that the knockdown of NPNT caused podocyte effacement, whereas glomerular endothelial cells were not affected [ 10 , 11 ]. Transgenic mice with increased plasma levels of TGF-β developed glomerular disease [ 20 ].…”

Extracellular Vesicles Released from Stem Cells as a New Therapeutic Strategy for Primary and Secondary Glomerulonephritis

“…Some of these may be considered as potential diagnostic biomarkers of IMN and represent future therapeutic targets. Of interest, glomerular endothelial cell-derived miR-192 and podocyte-derived miR-378a-3p are both upregulated in IMN and impair expression of Nephronectin in glomerular basement membrane (GBM), possibly contributing to disease pathogenesis [ 99 ]. On the contrary, other types of miRNA may exert protective actions.…”