EVALUATION OF THE GM1 OLIGOSACCHARIDE ROLE IN NEURONAL DIFFERENTIATION

GM1 is a mono-sialo ganglioside with amphiphilic character due to the presence of a hydrophobic group, ceramide, and a hydrophilic head (oligosaccharide chain). GM1 represents one of the most important modulator in the nervous system where it is involve in maturations of neurons, differentiation, increase responses to neurotrophic factors, protection against neuronal death and reduction brain damage. The effects of GM1 are known in vitro and in vivo, but the molecular mechanism of action underlying the GM1 properties is unknown. The present work aims to analyze the mechanism of action of GM1, and in particular to demonstrate that the effects of this ganglioside are attributable to the action of its oligosaccharide portion (OligoGM1) and not to the entire molecule. To reach our purpose we used mouse neuroblastoma cell line Neuro2a (N2a). Like GM1, OligoGM1 promotes neurodifferentiation by increasing both neurite elongation and the expression of neurofilament proteins in N2a cell. A similar effect was obtained with the use of fucosyl-OligoGM1 but not with the administration of asialo-OligoGM1, OligoGM2, OligoGM3, sialic acid or galactose (single components of Oligo GM1). OligoGM1, in N2a cells, activates ERK1/2 pathway binding to the NGF specific receptor TrkA present on the cell surface. To study this mechanism of action we used tritium labeled derivative of OligoGM1. The activator for GM1 mediated functions (differentiation and protection) is the interaction between OligoGM1 and TrkA. This was established with the use of a TrkA inhibition. With a bioinformatics study it was established that OligoGM1 inserts in a pocket of the TrkA-NGF complex. An increase in energy associated to the complex TrkA-NGF-OligoGM1 indicates greater stability of intermolecular interactions. All the results lead to the conclusion that the bioactive portion of GM1, in neuronal differentiation and protection, is represented by its hydrophilic chain (OligoGM1). These conclusions open up new perspectives on the therapeutic use of gangliosides.