Stimulatory effect of gangliosides on phagocytosis, phagosome–lysosome fusion, and intracellular signal transduction system by human polymorphonuclear leukocytes

Abstract

Gangliosides are known to be differentiation-inducing molecules in mammalian stem cells. We studied the interaction between the molecular structure of glycosphingolipids (GSLs) and their promoting mechanisms of the phagocytic processes in human polymorphonuclear leukocytes (PMN). The effect of various gangliosides from mammalian tissues on adhesion, phagocytosis, phagosome–lysosome (P–L) fusion and superoxide anion production was examined by human PMN using heat-killed cells of Staphylococcus aureus coated with GSLs. Gangliosides GM3, GD1a, GD3 and GT1b showed a marked stimulatory effect on the phagocytosis and P–L fusion in a dose-dependent manner, while ganglioside GM1, asialo GM1 and neutral GSLs did not. The relative phagocytic rate of ganglioside GM3-coated S. aureus was the highest among the tested GSLs. Both P–L fusion rate and phagocytosis of S. aureus were elevated significantly when coated with ganglioside GD1a, GD3 or GT1b, and GT1b gave a five times higher rate than that of the non-coated control. These results suggest that the terminal sialic acid moiety is essential for the enhancement of phagocytosis and that the number of sialic acid molecules in the ganglioside is related to the enhancement of the P–L fusion process. On the other hand, the superoxide anion release from PMN was not affected by ganglioside GM2, GM3, GD1a or GT1b. Furthermore, to clarify the trigger or the signal transduction mechanism of phagocytic processes, we examined the effect of protein kinase inhibitors such as H-7, staurosporine (protein kinase C inhibitor), H-89 (protein kinase A inhibitor), genistein (tyrosine kinase inhibitor), ML-7 (myosin light chain kinase inhibitor), and KN-62 (Ca2+/calmodulin-dependent protein kinase II inhibitor) on ganglioside-induced phagocytosis. H-7, staurosporine and KN-62 inhibited ganglioside-induced phagocytosis in the range of concentration without cell damage, while H-89, genistein and ML-7 did not. Moreover, H-7 and KN-62 inhibited ganglioside-induced P–L fusion. These results suggest that protein kinase C and Ca2+/calmodulin-dependent protein kinase II may be involved in the induction of phagocytosis and P–L fusion stimulated by gangliosides.