METABOLISM OF EXOGENOUS GANGLIOSIDE GM1 IN CULTURED CEREBELLAR GRANULE CELLS - THE FATTY-ACID AND SPHINGOSINE MOIETIES FORMED DURING DEGRADATION ARE RE-USED FOR LIPID BIOSYNTHESIS

Cerebellar granule cells, differentiated in vitro, were parallelly fed with [Sph-H-3]GM1 and [stearoyl-C-14]GM1, under identical conditions (10(-6) M ganglioside; pulse, from 1-4 h; chase, up to 24 h after 4 h pulse) and the salvage pathways of sphingosine and stearic acid were investigated. It was observed that both sphingosine and stearic acid, liberated during the intralysosomal degradation of ganglioside, are metabolically recycled, along distinct pathways. Sphingosine is used for the biosynthesis of a number of sphingolipids, particularly ceramide, glucosyl-ceramide, gangliosides and sphingomyelin; stearic acid is utilized for the biosynthesis of sphingolipids, and to a greater extent, glycero-phospholipids, especially those endogenously richer in stearic acid (phosphatidyl-ethanolamine and phosphatidyl-choline). No evidence was provided for a salvage pathway for ceramide.