002 – The neuroprotective effects of calpastatin on axonal integrity in a murine model of Guillian-Barre_ Syndrome
Hannah Bialic (1) – Rhona McGonigal (1) – Hugh Willison (1)
University of Glasgow, Institute of Infection, Immunity, and Inflammation, Glasgow, United Kingdom (1)
In the Guillian-Barre_ Syndrome (GBS) variant acute motor axonal neuropathy (AMAN) the nodes of Ranvier are key sites of complement-mediated degradation. AMAN is characteristically preceded by an infection of Campylobacter jejuni, to which the body generates antibodies against lipo-oligosaccharides in the bacterial outer membrane. These molecules are molecular mimics of neuronal gangliosides, such as GD1b, which are highly expressed along the axon and exposed at the nodes. Auto-reactive antibodies generated in the infection bind gangliosides and activate the complement cascade, triggering an influx of calcium through the membrane attack complex (MAC). Calcium proceeds to activate calpain, a cysteine protease which degrades axonal structural proteins such as spectrin. A marker of degradation in AMAN is the delocalization and degradation of nodal proteins such as Nav1.6 channels and contactin associated protein 1 (CASPR), which is anchored to spectrin at the axo-glial junction. In this study, calpain inhibition was investigated in an ex vivo and in vivo AMAN model via transgenic overexpression of the human calpain inhibitor calpastatin. Mice either highly overexpressed human calpastatin (hCAST) or presented normal calpain inhibition via mouse calpastatin (wild type). In ex vivo TS muscle preparations, CASPR expression was significantly better preserved in the hCAST mice when compared against the wild type, as was the general nodal architecture. Analysis of diaphragm preparations from the in vivo model showed that hCAST mice showed better CASPR expression, total protein conservation and preservation of nodal architecture when compared against wild type mice. The node of Ranvier is especially targeted during peripheral nerve damage and this protection at the node by calpain inhibition indicates a stronger rescue phenotype after instigation of AMAN. We have thus identified a promising avenue for attenuation of the nodal degradation characteristic of AMAN via the inhibition of the protease calpain. The consequences of these findings pave the way for further investigation in vivo using synthetic calpain inhibitors.