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.
View: Text | PDF
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

×

Figure 2

Degradation of synaptopodin and NEPH1 depends on the lectin pathway.

Options: View larger image (or click on image) Download as PowerPoint
Degradation of synaptopodin and NEPH1 depends on the lectin pathway. (A)...
(A) Podocytes expressing PLA2R1 were treated for 60 minutes with 5% NHS after preincubation for 30 minutes with 2.5% high-titer (1:1000, 2138 RU/mL) anti-PLA2R1–positive patient serum in incomplete RPMI1640 medium (second lane) or various gelatin veronal buffers (GVB). EDTA (GVBE) inhibits all complement pathways by depleting calcium and magnesium; addition of recombinant MBL in the presence of calcium and magnesium further facilitates activation of the lectin pathway, and calcium depletion with EGTA in the presence of magnesium (GVBMg) inhibits the classical and the lectin pathway but allows for activation of the alternative complement pathway. S = serum, C = complement. (B) The same experiment was performed in the presence of SGMI1 and SGMI2, specific inhibitors of the 2 proteases required for activation of the lectin pathway, MASP1 and MASP2, respectively. Bars represent mean ± SEM of 3 independent experiments, *P < 0.05 by 1-way ANOVA and Tukey’s post hoc test for the comparison with control (A) or with S + C (B).