Membrane assembly of aquaporin-4 autoantibodies regulates classical complement activation in neuromyelitis optica
John Soltys, … , Gregory P. Owens, Jeffrey L. Bennett
John Soltys, … , Gregory P. Owens, Jeffrey L. Bennett
Published April 8, 2019
Citation Information: J Clin Invest. 2019;129(5):2000-2013. https://doi.org/10.1172/JCI122942.
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Research Article Inflammation Neuroscience

Membrane assembly of aquaporin-4 autoantibodies regulates classical complement activation in neuromyelitis optica

Abstract

Neuromyelitis optica (NMO) is an autoimmune CNS disorder mediated by pathogenic aquaporin-4 (AQP4) water channel autoantibodies (AQP4-IgG). Although AQP4-IgG–driven complement-dependent cytotoxicity (CDC) is critical for the formation of NMO lesions, the molecular mechanisms governing optimal classical pathway activation are unknown. We investigated the molecular determinants driving CDC in NMO using recombinant AQP4–specific autoantibodies (AQP4 rAbs) derived from affected patients. We identified a group of AQP4 rAbs targeting a distinct extracellular loop C epitope that demonstrated enhanced CDC on target cells. Targeted mutations of AQP4 rAb Fc domains that enhance or diminish C1q binding or antibody Fc-Fc interactions showed that optimal CDC was driven by the assembly of multimeric rAb platforms that increase multivalent C1q binding and facilitate C1q activation. A peptide that blocks antibody Fc-Fc interaction inhibited CDC induced by AQP4 rAbs and polyclonal NMO patient sera. Super-resolution microscopy revealed that AQP4 rAbs with enhanced CDC preferentially formed organized clusters on supramolecular AQP4 orthogonal arrays, linking epitope-dependent multimeric assembly with enhanced C1q binding and activation. The resulting model of AQP4-IgG CDC provides a framework for understanding classical complement activation in human autoantibody–mediated disorders and identifies a potential new therapeutic avenue for treating NMO.

Authors

John Soltys, Yiting Liu, Alanna Ritchie, Scott Wemlinger, Kristin Schaller, Hannah Schumann, Gregory P. Owens, Jeffrey L. Bennett

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Figure 3

AQP4 rAb CDC and C1q binding on M1-AQP4.

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AQP4 rAb CDC and C1q binding on M1-AQP4. (A) Space-filling and ribbon mo...
(A) Space-filling and ribbon models of C1q, AQP4 rAb, and M1-AQP4 tetramers illustrating interactions potentially driving C1q–AQP4 rAb–M1-AQP4 multivalent complex assembly. C1q globular heads bind to the CH2 domain of AQP4 rAb (green), while neighboring AQP4 rAbs interact via CH3 hydrophobic patches (blue). Fab variable regions and AQP4 extracellular loops are colored brown. (B) CDC (left graphs; mean ± SEM; n = 4) and C1q binding (right graphs; mean ± SD; n = 3) was measured on M1-AQP4–expressing CHO cells using His151/Leu154-independent (B–D) and His151/Leu154-dependent (E–H) AQP4 rAbs. CDC activity for the native IgG1 AQP4 rAb on M23-AQP4 is plotted as the dotted black line. Some Fc domain mutations were introduced only into selected rAbs, as indicated in the key.