Role of theGM1 ganglioside oligosaccharide portion in the TrkA‐dependent neurite sprouting in neuroblastoma cells

GM 1 ganglioside ( II 3 NeuAc‐Gg 4 Cer) is known to promote neurite formation in neuroblastoma cells by activating TrkA‐ MAPK pathway. The molecular mechanism by which GM 1 is involved in the neurodifferentiation process is still unknown, however, in vitro and in vivo evidences have suggested that the oligosaccharide portion of this ganglioside could be involved. Here, we report that, similarly to the entire GM 1 molecule, its oligosaccharide II 3 NeuAc‐Gg 4, rather than its ceramide (Cer) portion is responsible for the neurodifferentiation process by augmenting neurite elongation and increasing the neurofilament protein expression in murine neuroblastoma cells, Neuro2a. Conversely, asialo‐ GM 1, GM 2 and GM 3 oligosaccharides are not effective in neurite elongation on Neuro2a cells, whereas the effect exerted by the Fuc‐ GM 1 oligosaccharide ( IV 2 αFuc II 3 Neu5Ac‐Gg 4 ) is similar to that exerted by GM 1 oligosaccharide. The neurotrophic properties of GM 1 oligosaccharide are exerted by activating the TrkA receptor and the following phosphorylation cascade. By photolabeling experiments performed with a nitrophenylazide containing GM 1 oligosaccharide, labeled with tritium, we showed a direct interaction between the GM 1 oligosaccharide and the extracellular domain of TrkA receptor. Moreover, molecular docking analyses confirmed that GM 1 oligosaccharide binds the TrkA‐nerve growth factor complex leading to a binding free energy of approx. −11.5 kcal/mol, acting as a bridge able to increase and stabilize the TrkA‐nerve growth factor molecular interactions.