Reversal of non-hydroxy : α-hydroxy galactosylceramide ratio and unstable myelin in transgenic mice overexpressing UDP-galactose : ceramide galactosyltransferase (original) (raw)
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Journal of Neurochemistry, 2002
Oligodendrocytes and Schwann cell-specific proteins are assembled with a highly ordered membrane lipid bilayer to the myelin sheath of axons, which functions as an insulator and allows rapid saltatory conduction. We approached the question of the function of the CNS and PNS myelin-specific galactospingolipids cerebrosides and sulfatides by generating a ceramide galactosyltransferase null allelic mouse line (cgt~).Galactocerebroside-and sulfatide-deficient myelin loses its insulating properties and causes a severe dysmyelinosis that is incompatible with life. Here, we describe the biochemical and biophysical analysis of the myelin lipid bilayer of cgt~mice. The lipid composition of CNS and PNS myel m of cgt~mice is seriously perturbed and the sphingolipid biosynthetic pathway altered. Nonhydroxy and hydroxy fatty acid-substituted glycosylceramides (GIcC) are synthesized by oligodendrocytes and sulfated GIcC in addition in Schwann cells. The monogalactosyldiglyceride fraction is missing in the cgt~mouse. This new lipid composition can be correlated with the biophysical properties of the myelin sheath. The deficiency of galactocerebrosides and sulfatides leads to an increased fluidity, permeability, and impaired packing of the myelin lipid bilayer of the internodal membrane system. The loss of the two glycosphingolipid classes causes the breakdown of saltatory conductance of myelinated axons in the cgt' mouse. KeyWords: Myelin lipid bilayer-Packing of acyl chains-Polar head group-Insulation and conductance-Ceramide galactosyltransferase deficiency.
Myelin galactolipids are essential for proper node of Ranvier formation in the CNS
The Journal of neuroscience : the official journal of the Society for Neuroscience, 1998
The vertebrate myelin sheath is greatly enriched in the galactolipids galactocerebroside (GalC) and sulfatide. Mice with a disruption in the gene that encodes the biosynthetic enzyme UDP-galactose:ceramide galactosyl transferase (CGT) are incapable of synthesizing these lipids yet form myelin sheaths that exhibit major and minor dense lines with spacing comparable to controls. These CGT mutant mice exhibit a severe tremor that is accompanied by hindlimb paralysis. Furthermore, electrophysiological studies reveal nerve conduction deficits in the spinal cord of these mutants. Here, using electron microscopic techniques, we demonstrate ultrastructural myelin abnormalities in the CNS that are consistent with the electrophysiological deficits. These abnormalities include altered nodal lengths, an abundance of heminodes, an absence of transverse bands, and the presence of reversed lateral loops. In contrast to the CNS, no ultrastructural abnormalities and only modest electrophysiological ...
Proceedings of the National Academy of Sciences, 2005
Globoid cell leukodystrophy (GLD) is a lysosomal storage disease caused by genetic deficiency of galactocerebrosidase (GALC) activity. Failure in catalyzing the degradation of its major substrate, galactocerebroside, in oligodendrocytes (OLs) and Schwann cells leads to death of these myelinating cells, progressive demyelination, and early demise of GLD patients. Transplantation of bone marrow cells and umbilical cord blood have been attempted as a means of enzyme replacement and have shown limited success. It remains unknown whether or how these therapies support survival of GALC-deficient OLs and myelin maintenance. We report that, upon transplantation, GALC-deficient OLs from the twitcher mouse, a model of GLD, achieved widespread myelination in the brain and spinal cord of the myelin-deficient shiverer mouse, which was preserved for the life of the host. GALC immunohistochemistry showed direct evidence for GALC transfer from the shiverer environment to the engrafted mutant OLs in...
Myelin glycolipids and their functions
Current Opinion in Neurobiology, 1997
During myelination, oligodendrocytes in the CNS and Schwann cells in the PNS synthesise myelin-specific proteins and lipids for the assembly of the axon myelin sheath. A dominant class of lipids in the myelin bilayer are the glycolipids, which include galactocerebroside (GalC), galactosulfatide (sGalC) and galactodiglyceride (GalDG). A promising approach for unravelling the roles played by various lipids in the myelin membrane involves knocking out the genes encoding important enzymes in lipid biosynthesis. The recent ablation of the ceramide galactosyltransferase (cgt) gene in mice is the first example. The cgt gene encodes a key enzyme in glycolipid biosynthesis. Its absence causes glycolipid deficiency in the lipid bilayer, breakdown of axon insulation and loss of saltatory conduction. Additional knock-out studies should provide important insights into the various functions of glycolipids in myelinogenesis and myelin structure.
Biochemical Journal, 2005
Hydroxylation is an abundant modification of the ceramides in brain, skin, intestinal tract and kidney. Hydroxylation occurs at the sphingosine base at C-4 or within the amide-linked fatty acid. In myelin, hydroxylation of ceramide is exclusively found at the α-C atom of the fatty acid moiety. α-Hydroxylated cerebrosides are the most abundant lipids in the myelin sheath. The functional role of this modification, however, is not known. On the basis of sequence similarity to a yeast C26 fatty acid hydroxylase, we have identified a murine cDNA encoding FA2H (fatty acid 2-hydroxylase). Transfection of FA2H cDNA in CHO cells (Chinese-hamster ovary cells) led to the formation of α-hydroxylated fatty acid containing hexosylceramide. An EGFP (enhanced green fluorescent protein)–FA2H fusion protein co-localized with calnexin, indicating that the enzyme resides in the endoplasmic reticulum. FA2H is expressed in brain, stomach, skin, kidney and testis, i.e. in tissues known to synthesize fatty...
Journal of Neurochemistry, 1985
Galactolipid metabolism was investigated as a function of development in primary cultures initiated from 19-21-day-old dissociated fetal rat brain. Significant amounts of galactocerebrosides, sulfatides, and monogalactosylglycerides were synthesized and accumulated by 8 days in culture. Thereafter the synthetic rates and levels of these galactolipids increased rapidly, reaching maximal values -22-29 days in culture. Galactolipids containing nonhydroxy or 2-hydroxy fatty acid were both synthesized at approximately equal rates. The initial rates of synthesis, investigated at 15, 29, and 50 days in culture, were three-to fivefold higher for galactocerebrosides than for sulfatides and two-to threefold higher than for monogalactosylglycerides. The total number of cells staining with antisera against galactocerebroside of sulfatide also increased very rapidly between 8 and 22 days in culture, reaching levels of 4-5 million cells per seeded fetal brain. The amount of galactocerebroside or sulfatide per cell stained with the corresponding antiserum increased sev-~ Abbreviations used: BBSS, basic balanced salt solution; CNP, 2',3'-cyclic nucleotide 3'-phosphohydrolase; DEAE, diethylaminoethyl; DIC, days in culture; GC, galactocerebroside; GC + , cells staining in imrnunofluorescence microscopy with anti-GC; HFA, 2-hydroxy fatty acid; MBP, myelin basic protein; MG, monogalactosylglyceride; NFA, nonhydroxy fatty acid; NGS, normal goat serum; SGG, monogalactosylglycende sulfate; SUL + , cells staining in immunofluorescence microscopy with anti-sulfatide.