Ganglioside GM1 binding toxins and human neuropathy-associated IgM antibodies differentially promote neuritogenesis in a PC12 assay.

PC12 cells undergo neuritogenesis upon nerve growth factor (NGF) activation of the TrkA receptor, an effect mimicked by the ganglioside GM1 binding B-subunit of cholera toxin (CTB). Modulation of neuritogenesis by a GM1 ligand indicates a possible pathway for pathophysiological actions of neuropathy-associated anti-GM1 antibodies. Here we examine the ability of GM1 binding toxins and antibodies to induce neuritogenesis, using a PC12 neurite outgrowth assay. Cholera toxin (CT) and commercially prepared CTB (sCTB, contaminated with traces of the adenyl cyclase activating CT A-subunit) were highly neuritogenic. Recombinant cholera toxin B-subunit (rCTB, free from CTA) induced a much smaller effect, suggesting that the potent effects of sCTB are largely due to contaminating CTA. The recombinant GM1 binding B-subunit of Escherichia coli heat-labile enterotoxin (rETxB) exhibited no neuritogenic activity, whilst rETx holotoxin, which activates adenyl cyclase, was highly neuritogenic. Monoclonal anti-GM1 IgM antibodies from human neuropathy subjects induced small neuritogenic effects. These data indicate that GM1/ligand interaction does not necessarily lead to neuritogenesis and suggest that a specialisation of CTB, not shared by anti-GM1 antibodies or rETxB, is required to activate TrkA. Our data also indicate that antibodies are unlikely to exert major modulatory effects on TrkA activity in patients with anti-GM1 antibody-associated peripheral neuropathies.