PATTERNS OF ENDOGENOUS GANGLIOSIDES AND METABOLIC PROCESSING OF EXOGENOUS GANGLIOSIDES IN CEREBELLAR GRANULE CELLS DURING DIFFERENTIATION IN CULTURE

The qualitative and quantitative pattern of endogenous gangliosides and the routes of metabolic processing of exogenous GM1, H-3 labeled in the sphingosine moiety (Sph-H-3 GM1) were studied in cerebellar granule cells during differentiation in vitro. During the first 7-8 days in culture the ganglioside content markedly increased, and the qualitative pattern showed, in percentage terms, a drastic decrease of GD3 and a marked increase of GD2, O-Ac-GT1b, O-Ac-GQ1b and GQ1b. After pulse with (Sph-H-3) GM1, at all the investigated days in culture, different radiolabelled lipids were formed indicating that taken up exogenous GM1 was degraded and that its catabolic fragments, and partly GM1 itself, were used for biosynthetic purposes; moreover radioactive water was measured in the culture medium during chase indicating that labelled sphingosine underwent also degradation. The uptake of exogenous GM1 and the extent of its metabolic processing per cell unit increased during differentiation: a) GM2 was the major metabolic product and was relatively more abundant at 2 than 7 days in culture; b) the percentage of metabolites of biosynthetic origin over total metabolites increased during differentiation, especially at the short pulse times; c) among the metabolities of anabolic origin sphingomyelin equalled gangliosides at 2 days, whereas it was largely overcome by gangliosides at 7 days in culture; d) at 4 and 7 days in culture a radioactive substance, not yet identified, was present, whereas no trace of it was found at 2 days. In conclusion, cerebellar granule cells in culture feature a different pattern of endogenous gangliosides and display different ability to metabolically process exogenous GM1 ganglioside in the undifferentiated and fully differentiated stage.