Suppression by gangliosides of polymerization of glial cytoskeletons prepared from rat astrocytes: a role of sialic acid moiety.

This study investigated in vitro the effects of gangliosides on polymerization of either the depolymerized microfilament preparation (MF) or depolymerized glia filament preparation (GF) extracted separately from the crude cytoskeletal fraction of rat astrocytes. Gangliosides GM1, GM2 and GM3 markedly suppressed polymerization of both MF and GF. The concentration of GM1, GM2 or GM3 required to induce 50% inhibition of the polymerization of 7.5 micrograms MF protein/200 microliters (IC50 of GM1, GM2, or GM3) was 3.2, 2.8 or 5.6 micrograms/200 microliters, respectively. The IC50 of each ganglioside for the polymerization of 7.5 micrograms/200 microliters of GF, furthermore, was 3.3, 3.5 or 7.4 micrograms/200 microliters, respectively, suggesting that the inhibitory activities of GM1 and GM2 on polymerization of both MF and GF were greater than those of GM3. GM1, GM2 and GM3 also suppressed dose-dependently the polymerization of both actin and vimentin. The inhibitory activities of GM1 and GM2 on the polymerization of actin or vimentin were greater than GM3, as in the case of polymerization of MF or GF. The IC50S of GD1a and GT1b for MF polymerization at the same concentration were 2.2 and 1.2 micrograms/200 microliters, respectively, and those for GF polymerization were 2.7 and 1.7 micrograms/200 microliters, respectively. The IC50 of GD3 for MF polymerization was 3.9 micrograms/200 microliters, and that for GF polymerization 4.0 micrograms/200 microliters, implying that the inhibitory activities of GD3 on polymerization of both MF and GF were greater than those of GM3. The findings suggested that the inhibitory activities of gangliosides on MF or GF polymerization became greater with increasing number of sialic acid residues. AsialoGM1 suppressed neither MF nor GF polymerization, and inhibited dose-dependently the ability of GM1 to suppress MF polymerization.

Promotion of microfilament polymerization by depolymerized glia filament preparation through interaction of vimentin with actin.

We investigated the in vitro interaction between microfilaments and glia filaments in the presence of alpha-sialosylcholesterol (SC). The depolymerized glia filament preparation (GF) that had been extracted from a crude cytoskeletal fraction of cultured rat astrocytes promoted markedly the polymerization of the depolymerized microfilament preparation (MF) in the presence of SC. The ability of GF to promote the MF polymerization was highest in the concentration range 7.5-15 microM SC. The polymerization of MF at the concentration of 10 micrograms protein/200 microliters was enhanced to the highest level by 4 micrograms protein/200 microliters of GF in the presence of 15 microM SC. The MF polymerization was promoted more efficiently by GF than by MF: for example, the polymerization of actin in MF (7.5 micrograms/200 microliters) was enhanced by the addition of 5 micrograms GF protein/200 microliters to a twice greater extent than by the addition of 5 micrograms MF protein/200 microliters in the presence of 15 microM SC. GF enhanced the MF polymerization by over three-fold at 4-37 degrees C, and the GF activity became greater with an increase in incubation temperature. Vimentin promoted the G-actin polymerization in the presence of 11.3 microM alpha-SC. The finding suggested that the interaction between vimentin and actin was one of the factors to cause GF to promote the MF polymerization.