Myelin sulfatides

Ishibashi, T., Dupree, J. L., Ikenaka, K. et al. A myelin galac-tolipid, sulfatide, is essential for maintenance of channels on myelinated axons but not essential for initial cluster formation. /. Neurosci. 22 6507-6514, 2002. 

Peripheral and central nervous system myelin lipids are qualitatively similar. However, there are quantitative differences. PNS myelin has less cerebroside and sulfatide and considerably more sphingomyelin than CNS myelin. Of interest is the presence of the LM1 ganglioside, sialosyl-lactoneotetraosylceramide, as a characteristic component of myelin in the PNS of some species. These differences in lipid composition between CNS and PNS myelin are not, however, as dramatic as the differences in protein composition discussed below. 

Myelin components exhibit great heterogeneity of metabolic turnover. One of the novel characteristics of myelin demonstrated in early biochemical studies was that its overall rate of metabolic turnover is substantially slower than that of other neural membranes [1]. A standard type of experiment was to evaluate lipid or protein turnover by injecting rat brains with a radioactive metabolic precursor and then follow loss of radioactivity from individual components as a function of time. Structural lipid components of myelin, notably cholesterol, cerebro-side and sulfatide, as well as proteins of compact myelin, are relatively stable, with half-lives of the order of many months. One complication in interpreting these studies is that the metabolic turnover of individual myelin components is multiphasic - consisting of an initial rapid loss of radioactivity followed by a much longer slower loss. 

Familial demyelinative/dysmyelinative and axonal neuropathies may also be caused by impaired lysosomal lipid metabolism. Metachromatic leukodystrophy (sulfatide lipidosis) results from mutations of the arylsulfatase A gene, which encodes a lysosomal enzyme required for sulfatide turnover. Myelin is affected in both CNS and PNS, though dysfunction is restricted to the PNS in some patients, and the onset of symptoms can occur at any time between infancy and adulthood. Bone marrow transplantation can slow disease progression and improve nerve conduction velocities [57]. (See in Ch. 41.)... 

Glycolipids are important constituents of the plasma membranes, of the endoplasmic reticulum, and of chloroplasts. The cerebrosides and their sulfate esters, the sulfatides, are especially abundant in myelin. In plant membranes, the predominant lipids are the galactosyl diglycerides.29 74 The previously described ether phospholipids (archaebacteria), ceramide arnino-ethylphosphonate (invertebrates), and sulfolipid (chloroplasts) are also important membrane components. 

In this manuscript, we will first describe the newly developed high performance liquid chromatography of cerebroside, sulfatide, and other minor galactolipids. This method allows complete analysis of a very small amount of these glycolipids in cell or membrane preparations. This will be followed by a description of our new method of determining surface galactolipids and its application to myelin cerebrosides. 

Figure 1. TLC of myelin lipids after treatment with perbenzoylation-desulfa-tion. Line S, standard line M, derivatized myelin lipids. Spots 1 through 6 are ben-zoylated-desulfated derivatives of (I) glucocerebroside, (2) nonhydroxycere-broside, (3) monogalactosyl diglyceride, (4) hydroxycerebroside, (5) nonhydroxy-sulfatide, and (6) hydroxysulfatide, respectively. See text for details of TLC conditions.

Figure 2. Silica HPLC of myelin lipids. NC, nonhydroxycerebroside HC, hydroxycerebroside NS, nonhydroxysulfatide HS, hydroxy sulfatide and GD, monogalactosyl diglyceride. See text for details of TLC conditions.

Using the new procedure, attempts were made to quantitate the cerebrosides located on the surface of myelin. Myelin is composed of multilamellar bilayers of membrane of approximately 70% lipid and 30% protein (16). About 20% of the total lipid consists of cerebroside and sulfatide. Because of the lipophilic nature of the ceramide moiety and the hydrophilic nature of galactose, it has been postulated that the galactose moiety of myelin cerebrosides is facing the surface while the ceramide moiety is buried within the bilayer. Even considering the multilamellar structure of myelin, at least several percent of the cerebrosides should be present on the myelin surface. The method described in this manuscript should allow us to determine surface cerebrosides to as little as 0.5% of the total cerebrosides. 

Sulfogalactosylceramide (Sulfatide) synthesis and degradation in CNS and PNS. Regional and cellular abnormalities may also be related to defects in the synthesis of sulfatides. Sulfatides, coded by the galactosylceramide sulfotransferase gene, are essential for maintenance of Na" ion channels on myelinated axons but are not required for initial clusto formation (Ishibashi et al., 2002). Mice deficient for this gene are unable to synthesize sulfatides. They display abnormal paranodal junctions in the CNS and PNS, whereas their compact myelin is preserved (Honke et al.,... 

Lopate G, Pestronk A, Evans S, Li L, Clifford D (2005) Anti-sulfatide antibodies in HIV-infected individuals with sensory neuropathy. Neurology 64 1632-1634 Lubetzki C, Demerens C, Anglade P, Villarroya H, Frankfurter A, Lee VM, Zalc B (1993) Even in culture, oligodendrocytes myelinate solely axons. Proc Natl Acad Sci U S A 90 6820-6824... 

Popko B. Myelination in the absence of galactocerebroside and 95. sulfatide normal structure with abnormal function and regional instability. Cell 1996 86 209-219. 

Dupree JL, Coetzee T, Suzuki K, Popko B. Myelin abnormalities in mice deficient in galactocerebroside and sulfatide. J. Neuro-... 

Other abundant lipids in myelin are galactosylcerebrosides (Gal-C) and their sulfated derivatives (sulfatides). GalC represent 20% lipid dry weight in mature myelin. Immunological and chemical perturbation studies indicate that these lipids are involved in oligodendrocyte differentiation, myelin formation and myelin stability. These galactolipid-deficient animals exhibit severe tremor, hindlimb paralysis and display electro-physiological deficits in both CNS and PNS (Baumann and Pham-Dinh, 2001). 

Myelin is approximately 75% lipid and 25% protein. Carbohydrate residues are associated with both the lipid and the protein components of myelin. High proportions of cholesterol, phospholipid, and glycolipid are found in the lipid fractions. Phospholipids include ethanolamine phosphatides, phosphatidylserine, and phosphatidylinositol glycolipids include both neutral (cerebroside, sulfatide, galactosyldiglyceride) and polar (gangliosides, especially GMj and GMJ lipids. A classification and discussion of the metabolism of brain lipids is beyond the scope of this article readers are referred to Lajtha (1969), Davison (1968), Awasthi and Srivastava (1980), and Suzuki (1981). 

Estimates of the rate of myelin synthesis can be obtained in vitro from the measurement of cerebroside synthesis, which increases fourfold from day 10 to day 20 in the rat and then slowly decreases along with the overall rate of myelin synthesis. In vivo studies employing radiolabeled precursors of specific myelin components, such as sulfate into sulfatide, yield results similar to those obtained in vitro. In situ studies with tissue slices confirm in vitro and in vivo experiments. These studies also indicate that the appearance of... 

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