Regulation of Sulfoglucuronyl Glycolipid Synthesis in the Developing Rat Sciatic Nerve

Sulfoglucuronyl glycolipids (SGGLs) have been considered as target antigens in demyelinating peripheral neuropathies associated with IgM monoclonal gammopathy. The regulation of expression of SGGLs in the rat sciatic nerve during development was studied by assaying the levels of SGGLs and activities of four glycosyltransferases sequentially involved in their synthesis from lactosylceramide. The levels of SGGLs in the sciatic nerve increased with development and reached a maximum at sixty days after birth. The rate of increase in the level of SGGLs between day 5 to 20 was similar to rate of deposition of myelin in the nerve. Analysis of the activities of the glycosyltransferases showed that only lactotriosylceramide galactosyltransferase (LcOse₃Cer-GalTr) increased in parallel with the levels of SGGLs during development. The other three enzymes were not co-relative with the synthesis of SGGLs. The product of LcOse₃Cer-GalTr reaction, nLcOse₄Cer is the key intermediate for all neolactoglycolipids, particularly NeuAc2-3nLcOse₄Cer or nLM1, which is the major ganglioside (60%) of myelin in rat sciatic nerve. The results suggest that in the sciatic nerve SGGLs are mostly associated with Schwann cell myelin and their synthesis is regulated by LcOse₃Cer-GalTr, unlike in the cerebral cortex and cerebellum where SGGLs are associated with the neuronal membranes and their synthesis is regulated by lactosylceramide N-acetylglucosaminyltransferase (LcOse₂Cer-GlcNAcTr).