Altered glycosylation of IgG4 promotes lectin complement pathway activation in anti-PLA2R1–associated membranous nephropathy
George Haddad, … , Gérard Lambeau, Andreas D. Kistler
George Haddad, … , Gérard Lambeau, Andreas D. Kistler
Published December 22, 2020
Citation Information: J Clin Invest. 2021;131(5):e140453. https://doi.org/10.1172/JCI140453.
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Research Article Immunology Nephrology

Altered glycosylation of IgG4 promotes lectin complement pathway activation in anti-PLA2R1–associated membranous nephropathy

Abstract

Primary membranous nephropathy (pMN) is a leading cause of nephrotic syndrome in adults. In most cases, this autoimmune kidney disease is associated with autoantibodies against the M-type phospholipase A2 receptor (PLA2R1) expressed on kidney podocytes, but the mechanisms leading to glomerular damage remain elusive. Here, we developed a cell culture model using human podocytes and found that anti-PLA2R1–positive pMN patient sera or isolated IgG4, but not IgG4-depleted sera, induced proteolysis of the 2 essential podocyte proteins synaptopodin and NEPH1 in the presence of complement, resulting in perturbations of the podocyte cytoskeleton. Specific blockade of the lectin pathway prevented degradation of synaptopodin and NEPH1. Anti-PLA2R1 IgG4 directly bound mannose-binding lectin in a glycosylation-dependent manner. In a cohort of pMN patients, we identified increased levels of galactose-deficient IgG4, which correlated with anti-PLA2R1 titers and podocyte damage induced by patient sera. Assembly of the terminal C5b-9 complement complex and activation of the complement receptors C3aR1 or C5aR1 were required to induce proteolysis of synaptopodin and NEPH1 by 2 distinct proteolytic pathways mediated by cysteine and aspartic proteinases, respectively. Together, these results demonstrated a mechanism by which aberrantly glycosylated IgG4 activated the lectin pathway and induced podocyte injury in primary membranous nephropathy.

Authors

George Haddad, Johan M. Lorenzen, Hong Ma, Noortje de Haan, Harald Seeger, Christelle Zaghrini, Simone Brandt, Malte Kölling, Urs Wegmann, Bence Kiss, Gábor Pál, Péter Gál, Rudolf P. Wüthrich, Manfred Wuhrer, Laurence H. Beck, David J. Salant, Gérard Lambeau, Andreas D. Kistler

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Figure 5

Anti-PLA2R1–specific IgG4 directly binds MBL and triggers lectin pathway activation.

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Anti-PLA2R1–specific IgG4 directly binds MBL and triggers lectin pathway...
(A) Affinity-purified anti-PLA2R1–specific IgG4 from a patient with pMN was resolved by SDS-PAGE under nonreducing and reducing conditions, blotted, and stained for human IgG or MBL with or without prior incubation with recombinant MBL, as indicated. (B) MBL binding was confirmed using anti-PLA2R1–specific IgG4 from 4 additional pMN patients and total IgG4 from healthy controls. (C) The experiment was repeated with anti-PLA2R1–specific IgG4 with or without prior deglycosylation. The densitometric ratio of MBL to IgG staining was reduced by 64% through deglycosylation. (D) An ELISA plate was coated with anti-PLA2R1–specific or control IgG4, followed by the addition of NHS as a source of MBL and MASPs, human C4, and anti-C4b antibody either in the presence of 10 mM calcium or 1 mM EDTA. C4 deposition was calculated as the difference in OD in the presence versus absence of calcium divided by the amount of IgG4. The bars represent mean ± SEM for triplicate measurements in samples from 4 pMN patients and 4 controls; *P < 0.05 by Mann-Whitney U test.