Extracellular Galectin-3 Induces Accelerated Oligodendroglial Differentiation Through Changes in Signaling Pathways and Cytoskeleton Dynamics.

Galectin-3 (Gal-3) is a chimeric protein structurally composed of unusual tandem repeats of proline and short glycine-rich segments fused onto a carbohydrate recognition domain. Our studies have previously demonstrated that Gal-3 drives oligodendrocyte (OLG) differentiation to control myelin integrity and function. The cytoskeleton plays a key role in OLG maturation: the initial stage of OLG process extension requires dynamic actin filament assembly, while subsequent myelin wrapping coincides with the upregulation of actin disassembly proteins which are dependent on myelin basic protein (MPB) expression. In this context, the aim of the present work was to elucidate the mechanism by which recombinant Gal-3 (rGal-3) induces OLG maturation, giving special attention to the actin cytoskeleton. Our results show that rGal-3 induced early actin filament assembly accompanied by Erk signaling deactivation, which led to a decrease in the number of platelet-derived growth factor receptor α (PDGFRα)+ cells concomitantly with an increase in the number of 2',3'-cyclic-nucleotide 3'-phosphodiesterase (CNPase)+ cells at 1 day of treatment (TD1), and Akt signaling activation at TD1 and TD3. Strikingly, rGal-3 induced an accelerated shift from polymerized to depolymerized actin between TD3 and TD5, accompanied by a significant increase in MBP, gelsolin, Rac1, Rac1-GTP, and β-catenin expression at TD5. These results were strongly supported by assays using Erk 1/2 and Akt inhibitors, indicating that both pathways are key to rGal-3-mediated effects. Erk 1/2 inhibition in control-treated cells resembled an rGal-3 like state characterized by an increase in MBP, β-catenin, and gelsolin expression. In contrast, Akt inhibition in rGal-3-treated cells reduced MBP, β-catenin, and gelsolin expression, indicating a blockade of rGal-3 effects. Taken together, these results indicate that rGal-3 accelerates OLG maturation by modulating signaling pathways and protein expression which lead to changes in actin cytoskeleton dynamics.