The neuropathic potential of anti-GM1 autoantibodies is regulated by the local glycolipid environment in mice

Abstract

Anti-GM1 ganglioside autoantibodies are used as diagnostic markers for motor axonal peripheral neuropathies and are believed to be the primary mediators of such diseases. However, their ability to bind and exert pathogenic effects at neuronal membranes is highly inconsistent. Using human and mouse monoclonal anti-GM1 antibodies to probe the GM1-rich motor nerve terminal membrane in mice, we here show that the antigenic oligosaccharide of GM1 in the live plasma membrane is cryptic, hidden on surface domains that become buried for a proportion of anti-GM1 antibodies due to a masking effect of neighboring gangliosides. The cryptic GM1 binding domain was exposed by sialidase treatment that liberated sialic acid from masking gangliosides including GD1a or by disruption of the live membrane by freezing or fixation. This cryptic behavior was also recapitulated in solid-phase immunoassays. These data show that certain anti-GM1 antibodies exert potent complement activation-mediated neuropathogenic effects, including morphological damage at living terminal motor axons, leading to a block of synaptic transmission. This occurred only when GM1 was topologically available for antibody binding, but not when GM1 was cryptic. This revised understanding of the complexities in ganglioside membrane topology provides a mechanistic account for wide variations in the neuropathic potential of anti-GM1 antibodies.

Anti-ganglioside antibody internalization attenuates motor nerve terminal injury in a mouse model of acute motor axonal neuropathy

“…At hemidiaphragm NMJs sensitized by anti-GM1 Ab, but prior to exposure with NHS, MEPP frequency was normal, at approximately 1.5/s, as expected ( Figure 5, A and B) (22). When these preparations were immediately exposed to NHS, a large elevation in the MEPP frequency - to a level of 56.6 ± 9.6/s (n = 51 NMJs from 2 muscles) - occurred, as expected from earlier studies with this Ab (23). When anti-GM1 Ab-sensitized preparations were incubated for 1 hour at 37°C prior to exposure to NHS, the increase in MEPP frequency was significantly attenuated, by approximately 75% (13.1 ± 3.5/s; n = 46 NMJs; P < 0.001).…”

“…Two signals were considered as strongly colocalizing if the Manders coefficient was equal to or greater than 0.7 (56,57). For quantitative assessment of Ab and complement levels in all ex vivo TS preparations, images were collected using confocal microscopy (Zeiss LMS 5 Pascal) under constant acquisition settings and quantified using ImageJ software (http://rsbweb.nih.gov/ij/) as previously described (23). For illustrations, all images were collected using a Zeiss AxioImager equipped with an Apotome and AxioVision software.…”

Anti-ganglioside complex IgM antibodies in multifocal motor neuropathy and chronic immune-mediated neuropathies

“…If we suppose indeed that variable proportions and contiguities of individual gangliosides may be expressed in different neural membrane, it is tempting to speculate that this may lead to the formation of new antigens but also to the different expressions or hiding of reactive epitopes in different neural membranes. A brilliant support to this hypothesis was recently given by Greeshields et al (2009) who showed that the GM1 binding epitope may be often hidden in mice membranes by contiguous gangliosides and particularly by GD1a, so that the pathogenic effect of anti-GM1 antibodies may vary depending on recognition of exposed or cryptic antigens. This may theoretically help in explaining the different pathogenic effects of apparently similarly reacting antiganglioside antibodies.…”

Guillain–Barré syndrome: a century of progress

“…Numerous investigators over several decades and several continents have attempted to determine whether these antibodies are pathogenetic and how they mediate damage. In summary, many collaborative efforts have demonstrated that anti-GM1 and anti-GQ1b antibodies bind to peripheral nerve and neuromuscular junctions 64,65 , and anti-GD1a antibodies bind to the nodes of Ranvier, paranodal myelin and neuromuscular junction 66,67,68 . Upon binding, the antibodies activate the complement cascade, resulting in formation of the membrane attack complex, disruption of sodium channel clusters at the node of Ranvier with disruption of nodal architecture 69 , and calcium influx and calpain-dependent neuronal and glial injury at the neuromuscular junction 70,71 .This injury can be ameliorated with complement inhibitors 72,73 .…”