Neurotrophic properties of gm1 oligosaccharide: evidence on the development of primary neurons in culture

Gangliosides are sialic-acid containing glycosphingolipids, mostly abundant in the nervous tissues. Among these, the monosialo-ganglioside GM1 plays a pivotal role during neuronal development and its neuroprotective and neurotrophic properties have been largely reported both in vitro and in vivo. In cultured neurons, the GM1 enrichment in plasma membrane (PM) microdomains crucially contributes to the activation of neurotrophins receptors belonging to Trk family. This event triggers a specific signaling cascade resulting in actin depolymerization, axon protrusion and elongation. Despite this evidence, the mechanism of action of GM1 is still unknown. In neuroblastoma cells we demonstrated that GM1 oligosaccharide (OligoGM1) was able to induce cell differentiation and also protect cells against neurotoxins. This effect was due to a direct OligoGM1 binding to NGF receptor TrkA, resulting in the TrkA-MAPK pathway activation. Here, we characterize OligoGM1 effect on the developmental process of mouse primary neurons. Time-lapse recordings of plated neurons showed that exogenously administered OligoGM1 enhances neuron clustering, arborization and networking. Accordingly, in the presence of OligoGM1 neurons shows a higher phosphorylation rate of FAK and Src proteins, the intracellular key regulators of neuronal motility. Moreover, treated cells express increased level of specific neuronal markers, suggesting an advanced stage of maturation compared to controls. Moreover, in the presence of OligoGM1, neurons anticipate the expression of more complex ganglioside and reduce the level of simpler ones, displaying the typical ganglioside pathway of mature neurons. Concerning its mechanism of action, OligoGM1 interacts with cell surface without entering the cells, suggesting the presence of a biological target on neuronal PM. Interestingly, we observed the TrkA-MAPK pathway activation as an early event underlying OligoGM1 effects in neurons. Our data reveal that the specific role of GM1 in neuronal differentiation and maturation, described in the past, is determined by its oligosaccharide portion which, by interacting with the cell surface, triggers the activation of intracellular biochemical pathways responsible for neuronal migration, dendrites emission and axon growth.