Axonal regulation of Schwann cell glycolipid biosynthesis.

Schwann cell biosynthesis of glycolipids was studied by in vitro incorporation of [3H]galactose into neonatal rat sciatic nerves before and after endoneurial explant culture and in culture of purified Schwann cells. In neonatal nerves prior to culture, [3H]galactose was actively incorporated into galactocerebrosides (GalCe), monogalactosyl diacylglycerol (MGDG), and the sulfatides (Su). In contrast, the incorporation of [3H]galactose into MGDG, GalCe, and Su was nearly undetected in endoneurial explants after 4 days in vitro (div). Instead, there was increased 3H-labeling of glucocerebrosides (GlcCe) and its homologues, with tetrahexosylceramides (GL-4) being a major product, which continued through 8 div. This shift in glycolipid biosynthesis was further demonstrated in the purified Schwann cell cultures. These observations, together with our early findings in the permanent transection paradigm support a direct role of axons in specifying Schwann cell biosynthesis of the GalCe, MGDG, and Su and that the absence of this Schwann cell-axon interaction results in the phenotypic expression of glucocerebroside homologues by the Schwann cell.