Autoantibody of NRIP, a novel AChR-interacting protein, plays a detrimental role in myasthenia gravis
Journal
Journal of Cachexia, Sarcopenia and Muscle
Journal Volume
12
Journal Issue
3
Pages
665-676
Date Issued
2021
Author(s)
Chen I.-H.
Chen H.-H.
Huang Y.-H.
Weng R.-W.
Lai T.-Y.
Tsai Y.-C.
Tsao Y.-P.
Abstract
Background: Nuclear receptor interaction protein (NRIP) co-localizes with acetylcholine receptor (AChR) at the neuromuscular junction (NMJ), and NRIP deficiency causes aberrant NMJ architecture. However, the normal physiological and pathophysiological roles of NRIP in NMJ are still unclear. Methods: We investigated the co-localization and interaction of NRIP with AChR-associated proteins using immunofluorescence and immunoprecipitation assay, respectively. The binding affinity of AChR-associated proteins was analysed in muscle-restricted NRIP knockout mice and NRIP knockout muscle cells (C2C12). We further collected the sera from 43 patients with myasthenia gravis (MG), an NMJ disorder. The existence and features of anti-NRIP autoantibody in sera were studied using Western blot and epitope mapping. Results: NRIP co-localized with AChR, rapsyn and α-actinin 2 (ACTN2) in gastrocnemius muscles of mice; and α-bungarotoxin (BTX) pull-down assay revealed NRIP with rapsyn and ACTN2 in complexes from muscle tissues and cells. NRIP directly binds with α subunit of AChR (AChRα) in vitro and in vivo to affect the binding affinity of AChR with rapsyn and rapsyn with ACTN2. In 43 patients with MG (age, 58.4?±?14.5?years; female, 55.8%), we detected six of them (14.0%) having anti-NRIP autoantibody. The presence of anti-NRIP autoantibody correlated with a more severe type of MG when AChR autoantibody existed (P?=?0.011). The higher the titre of anti-NRIP autoantibody, the more severe MG severity (P?=?0.032). The main immunogenic region is likely on the IQ motif of NRIP. We also showed the IgG subclass of anti-NRIP autoantibody mainly to be IgG1. Conclusions: NRIP is a novel AChRα binding protein and involves structural NMJ formation, which acts as a scaffold to stabilize AChR–rapsyn–ACTN2 complexes. Anti-NRIP autoantibody is a novel autoantibody in MG and plays a detrimental role in MG with the coexistence of anti-AChR autoantibody. ? 2021 The Authors. Journal of Cachexia, Sarcopenia and Muscle published by John Wiley & Sons Ltd on behalf of Society on Sarcopenia, Cachexia and Wasting Disorders
SDGs
Other Subjects
alpha actinin 2; alpha bungarotoxin; autoantibody; cell nucleus receptor; cholinergic receptor; cholinergic receptor antibody; immunoglobulin G1; multiprotein complex; muscle relaxant agent; nuclear receptor interaction protein; rapsyn; receptor antibody; unclassified drug; acetylcholine; cholinergic receptor; adult; animal cell; animal experiment; animal tissue; antibody detection; antibody titer; Article; assisted ventilation; binding affinity; cell structure; clinical article; clinical classification; controlled study; disease association; disease severity; drug dose titration; epitope mapping; eye disease; female; gastrocnemius muscle; hospitalization; human; immunofluorescence; immunoprecipitation; in vitro study; in vivo study; knockout mouse; male; middle aged; molecular pathology; molecular stability; mouse; muscle cell; myasthenia gravis; neuromuscular junction; nonhuman; protein domain; protein localization; protein protein interaction; pull-down assay; receptor binding; Western blotting; animal; myasthenia gravis; skeletal muscle; Acetylcholine; Animals; Female; Humans; Mice; Muscle, Skeletal; Myasthenia Gravis; Neuromuscular Junction; Receptors, Cholinergic
Type
journal article