抗PLA2R1 IgG介导的足细胞PLA2R1胞外域切割驱动膜性肾病中肾小球上皮下免疫复合物沉积

Introduction: In membranous nephropathy (MN), subepithelial immune deposits and glomerular basement membrane (GBM) thickening are defining lesions, yet how circulating anti-phospholipase A2 receptor 1 (PLA2R1) IgG generates GBM-anchored complexes from podocyte antigen remains unclear. Methods: To clarify this, human podocytes stably expressing PLA2R1 and HEK293 cells expressing full-length or antibody-binding-deficient PLA2R1 (ΔN1-9) were stimulated with PLA2R1-positive MN [MN(P+)] serum or purified IgG or the metalloproteinase activator phorbol 12-myristate 13-acetate (PMA). Metalloprotease/γ-secretase dependence was tested with pharmacologic inhibitors; specificity controls included soluble ectodomain (ECD) blockade, IgG depletion, purified anti-PLA2R1 IgG, and THSD7A as unrelated antigen. Kidney biopsies underwent dual immunofluorescence and dual label immunogold electron microscopy. Recombinant ECD binding to collagen IV/laminin was assayed in vitro. Results: MN(P+) serum or purified anti-PLA2R1 IgG increased the PLA2R1 C-terminal fragment and soluble ECD. These effects were blocked by metalloproteinase ADAM10/17 inhibitors and by preincubating IgG/serum with soluble ECD and were complement-independent (heat-inactivation). MN(P+) IgG enhanced shedding of full-length PLA2R1 but not ΔN1-9, whereas PMA increased shedding of both, indicating epitope-dependent, antibody-triggered cleavage. MN(P+) IgG did not cleave THSD7A. In biopsies, PLA2R1-ECD was enriched within GBM deposits in MN(P+) only while PLA2R1-intracellular domain remained podocyte-restricted across groups. Quantitative electron microscopy confirmed GBM-biased ECD distribution in MN(P+). In vitro, PLA2R1-ECD bound collagen IV/laminin and selectively captured MN(P+) IgG. Early MN showed focal GBM thickening at deposit sites. Conclusions: Anti-PLA2R1 IgG accelerates ADAM10/17-dependent shedding of podocyte PLA2R1 releasing ECD anchors to GBM constituents. This mechanism reconciles the serum antibody glomerular antigen match and the preferential localization of deposits.