Harmful effects of anti-GalNAc-GD1a antibodies and TNF-alpha on rat dorsal root ganglia

Blockade of Rho-associated kinase prevents inhibition of axon regeneration of peripheral nerves induced by anti-ganglioside antibodies

Anti-ganglioside antibodies are associated with delayed/poor clinical recovery in Guillain-Barrè syndrome, mostly related to halted axon regeneration. Cross-linking of cell surface gangliosides by anti-ganglioside antibodies triggers inhibition of nerve repair in in vitro and in vivo paradigms of axon regeneration. These effects involve the activation of the small GTPase RhoA/ROCK signaling pathways, which negatively modulate growth cone cytoskeleton, similarly to well stablished inhibitors of axon regeneration described so far. The aim of this work was to perform a proof of concept study to demonstrate the effectiveness of Y-27632, a selective pharmacological inhibitor of ROCK, in a mouse model of axon regeneration of peripheral nerves, where the passive immunization with a monoclonal antibody targeting gangliosides GD1a and GT1b was previously reported to exert a potent inhibitory effect on regeneration of both myelinated and unmyelinated fibers. Our results demonstrate a differential sensitivity of myelinated and unmyelinated axons to the pro-regenerative effect of Y-27632. Treatment with a total dosage of 9 mg/kg of Y-27632 resulted in a complete prevention of anti-GD1a/GT1b monoclonal antibody-mediated inhibition of axon regeneration of unmyelinated fibers to skin and the functional recovery of mechanical cutaneous sensitivity. In contrast, the same dose showed toxic effects on the regeneration of myelinated fibers. Interestingly, scale down of the dosage of Y-27632 to 5 mg/kg resulted in a significant although not complete recovery of regenerated myelinated axons exposed to anti-GD1a/GT1b monoclonal antibody in the absence of toxicity in animals exposed to only Y-27632. Overall, these findings confirm the in vivo participation of RhoA/ROCK signaling pathways in the molecular mechanisms associated with the inhibition of axon regeneration induced by anti-GD1a/GT1b monoclonal antibody. Our findings open the possibility of therapeutic pharmacological intervention targeting RhoA/Rock pathway in immune neuropathies associated with the presence of anti-ganglioside antibodies and delayed or incomplete clinical recovery after injury in the peripheral nervous system.

Myelin-Associated Glycoprotein Inhibits Schwann Cell Migration and Induces Their Death

Remyelination of CNS axons by Schwann cells (SCs) is not efficient, in part due to the poor migration of SCs into the adult CNS. Although it is known that migrating SCs avoid white matter tracts, the molecular mechanisms underlying this exclusion have never been elucidated. We now demonstrate that myelin-associated glycoprotein (MAG), a well known inhibitor of neurite outgrowth, inhibits rat SC migration and induces their death via γ-secretase-dependent regulated intramembrane proteolysis of the p75 neurotrophin receptor (also known as p75 cleavage). Blocking p75 cleavage using inhibitor X (Inh X), a compound that inhibits γ-secretase activity before exposing to MAG or CNS myelin improves SC migration and survival in vitro Furthermore, mouse SCs pretreated with Inh X migrate extensively in the demyelinated mouse spinal cord and remyelinate axons. These results suggest a novel role for MAG/myelin in poor SC-myelin interaction and identify p75 cleavage as a mechanism that can be therapeutically targeted to enhance SC-mediated axon remyelination in the adult CNS.SIGNIFICANCE STATEMENT Numerous studies have used Schwann cells, the myelin-making cells of the peripheral nervous system to remyelinate adult CNS axons. Indeed, these transplanted cells successfully remyelinate axons, but unfortunately they do not migrate far and so remyelinate only a few axons in the vicinity of the transplant site. It is believed that if Schwann cells could be induced to migrate further and survive better, they may represent a valid therapy for remyelination. We show that myelin-associated glycoprotein or CNS myelin, in general, inhibit rodent Schwann cell migration and induce their death via cleavage of the neurotrophin receptor p75. Blockade of p75 cleavage using a specific inhibitor significantly improves migration and survival of the transplanted Schwann cells in vivo.

The Pathogenesis of the Demyelinating Form of Guillain-Barre Syndrome (GBS): Proteo-peptidomic and Immunological Profiling of Physiological Fluids

Acute inflammatory demyelinating polyneuropathy (AIDP) - the main form of Guillain-Barre syndrome-is a rare and severe disorder of the peripheral nervous system with an unknown etiology. One of the hallmarks of the AIDP pathogenesis is a significantly elevated cerebrospinal fluid (CSF) protein level. In this paper CSF peptidome and proteome in AIDP were analyzed and compared with multiple sclerosis and control patients. A total protein concentration increase was shown to be because of even changes in all proteins rather than some specific response, supporting the hypothesis of protein leakage from blood through the blood-nerve barrier. The elevated CSF protein level in AIDP was complemented by activization of protein degradation and much higher peptidome diversity. Because of the studies of the acute motor axonal form, Guillain-Barre syndrome as a whole is thought to be associated with autoimmune response against neurospecific molecules. Thus, in AIDP, autoantibodies against cell adhesion proteins localized at Ranvier's nodes were suggested as possible targets in AIDP. Indeed, AIDP CSF peptidome analysis revealed cell adhesion proteins degradation, however no reliable dependence on the corresponding autoantibodies levels was found. Proteome analysis revealed overrepresentation of Gene Ontology groups related to responses to bacteria and virus infections, which were earlier suggested as possible AIDP triggers. Immunoglobulin blood serum analysis against most common neuronal viruses did not reveal any specific pathogen; however, AIDP patients were more immunopositive in average and often had polyinfections. Cytokine analysis of both AIDP CSF and blood did not show a systemic adaptive immune response or general inflammation, whereas innate immunity cytokines were up-regulated. To supplement the widely-accepted though still unproven autoimmunity-based AIDP mechanism we propose a hypothesis of the primary peripheral nervous system damaging initiated as an innate immunity-associated local inflammation following neurotropic viruses egress, whereas the autoantibody production might be an optional complementary secondary process.

Ambiguous value of anti-ganglioside IgM autoantibodies in Guillain-Barré syndrome and its variants

Anti-ganglioside autoantibodies of the IgG type are detected in a half of patients with Guillain-Barré syndrome (GBS), and their detection strongly supports the diagnosis of GBS. In contrast, anti-ganglioside IgM antibodies are also often detected in GBS patients, but it remains unclear whether IgM antibodies indicate a diagnosis of GBS. We identified four GBS patients (3.3%) who tested positive for IgM antibodies but negative for IgG antibodies among 122 patients with GBS and its variants. These four patients were all adolescents or young adults (age 13-22 years), experienced preceding gastrointestinal symptoms, and had serological and/or bacterial evidence of recent Campylobacter jejuni enteritis. Serum IgG reacted strongly with the lipo-oligosaccharide (LOS) of the C. jejuni isolates from these patients' stool specimens. Thin-layer chromatography with immunostaining showed that their serum IgG reacted with resorcinol-positive portion of LOS, suggesting that these patients had IgG autoantibodies against sialic acid-containing epitopes, probably unrecognized ganglioside-like structures on the bacterial LOS. We also examined anti-ganglioside autoantibodies in 22 patients with C. jejuni enteritis without subsequent neurological disorders and detected IgM antibodies in seven (32%) patients. Our data indicate that anti-ganglioside IgM antibodies can be detected in C. jejuni enteritis without complication of GBS, and that the detection of anti-ganglioside IgM antibodies does not always support a diagnosis of GBS. IgG autoantibodies against unrecognized gangliosides might play a role in the development of disease in patients with GBS in whom only anti-ganglioside IgM antibodies are detected by routine clinical testing.

A reliable in vitro model for studying peripheral nerve myelination in mouse

The rat dorsal root ganglia (DRG) model is a long-standing in vitro model for analysis of myelination in the peripheral nervous system. For performing systematic, high throughput analysis with transgenic animals, a simplified BL6 mouse protocol is indispensable. Here we present a stable and reliable protocol for myelinating co-cultures producing a high myelin ratio using cells from C57BL/6 mice. As an easy accessible and operable method, Sudan staining proved to be efficient in myelin detection for fixed cultures. Green fatty acid stain turned out to be highly reliable for analysis of the dynamic biological processes of myelination in vital cultures. Once myelinated we were able to induce demyelination by the addition of forskolin into the model system. In addition, we provide an optimised rat DRG protocol with significantly improved myelin ratio and a comparison of the protocols presented. Our results strengthen the value of ex vivo myelination models in neurobiology.