GM1 and GD1a gangliosides modulate toxic and inflammatory effects of E. coli lipopolysaccharide by preventing TLR4 translocation into lipid rafts

Exogenous gangliosides are known to inhibit the effects of Escherichia coli lipopolysaccharide (LPS) in different cells exhibiting anti-inflammatory and immunosuppressive activities. The mechanisms underlying ganglioside action are not fully understood. Because LPS recognition and receptor complex formation occur in lipid rafts, and gangliosides play a key role in their maintenance, we hypothesize that protective effects of exogenous gangliosides would depend on inhibition of LPS signaling via prevention of TLR4 translocation into lipid rafts. The effect of GM1 and GD1a gangliosides on LPS-induced toxic and inflammatory reactions in PC12 cells, and in epithelial cells isolated from the frog urinary bladder, was studied. In PC12 cells, GD1a and GM1 significantly reduced the effect of LPS on the decrease of cell survival and on stimulation of reactive oxygen species production. In epithelial cells, gangliosides decreased LPS-stimulated iNOS expression, NO, and PGE2 production. Subcellular fractionation, in combination with immunoblotting, showed that pretreatment of cells with GM1, GD1a, or methyl-β-cyclodextrin, completely eliminated the effect of LPS on translocation of TLR4 into lipid rafts. The results are consistent with the hypothesis that ganglioside-induced prevention of TLR4 translocation into lipid rafts could be a mechanism of protection against LPS in various cells.