Calpain inhibitors protect against axonal degeneration in a model of anti-ganglioside antibody-mediated motor nerve terminal injury

Abstract

Miller Fisher syndrome-associated anti-GQ1b ganglioside antibodies produce an acute complement-dependent neuroexocytic effect at the mouse neuromuscular junction (NMJ) that closely resembles the effect of alpha-latrotoxin (LTx). This pathophysiological effect is accompanied by morphological disruption of the nerve terminal involving the loss of major cytoskeletal components, including neurofilament. Both LTx and the membrane attack complex of complement form membrane pores that allow free ionic movement and we have previously hypothesized that Ca2+ ingress and the subsequent activation of Ca2+-dependent proteases, calpains, may lead to substrate degradation resulting in structural disorganization of the terminal. Here, we treated mouse NMJs in hemidiaphragm preparations with anti-GQ1b antibodies and complement, or with LTx in the presence and absence of extracellular Ca2+, and studied possible neuroprotective effects of the calpain inhibitors calpeptin and calpain inhibitor V. Both Ca2+ depletion and calpain inhibition protected the cytoskeleton from degradation, as assessed by immunohistological and ultrastructural analysis. Calpain inhibitors may therefore be useful therapeutically in limiting nerve terminal and axonal injury in autoimmune peripheral neuropathy and in human latrodectism.

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

“…In this study and previous mouse models of acute axonal neuropathy and Fisher syndrome, nerve terminal injury is dependent upon MAC pore formation and is attenuated by terminal complement inhibitors (5,(47)(48)(49). Once any MAC-mediated membrane injury has occurred, thereby allowing uncontrolled calcium influx and calpain activation (50), the ability of the endosomal machinery to actively endocytose additional AGAb will be severely compromised, and the pathological cascade would thus accelerate. In our studies, nerve terminals were pulsed with a high concentration of AGAb at a single time point, whereas in human disease, chronic exposure to smaller amounts of Ab over longer time frames occurs; thus, further consideration of the kinetics and saturation dynamics would need to be introduced to this model to predict the implications of these effects in humans.…”

The Membrane Attack Complex of the Complement System Is Essential for Rapid Wallerian Degeneration

“…Complement blockade (Halstead et al, 2005), calcium depletion, and calpain inhibition (O'Hanlon et al, 2003) have been shown previously to limit nerve terminal and axonal injury in a model of acquired peripheral neuropathy. We propose that complement inhibition could directly prevent axonal damage and indirectly inhibit macrophage accumulation in the nerve, ameliorating the disease outcome.…”

Overexpression of GD1a Ganglioside Sensitizes Motor Nerve Terminals to Anti-GD1a Antibody-Mediated Injury in a Model of Acute Motor Axonal Neuropathy

“…Our studies on antidisialosyl ganglioside Ab binding to presynaptic NMJ gangliosides indicate that uncontrolled calcium influx through MAC pores triggers massive neurotransmitter release with electrophysiological failure and calpain-mediated disintegration of the presynaptic axon Bullens et al, 2000;O'Hanlon et al, 2001O'Hanlon et al, , 2003Halstead et al, 2004).…”