Glycosphingolipid-high density lipoprotein 3 interactions. II. Characterization of the glycosphingolipid component of modified high density lipoprotein

Absence of oligodendroglial glucosylceramide synthesis does not result in CNS myelin abnormalities or alter the dysmyelinating phenotype of CGT-deficient mice

To examine the function of glycosphingolipids (GSLs) in oligodendrocytes, the myelinating cells of the central nervous system (CNS), mice were generated that lack oligodendroglial expression of UDP-glucose ceramide glucosyltransferase (encoded by Ugcg). These mice (Ugcg(flox/flox);Cnp/Cre) did not show any apparent clinical phenotype, their total brain and myelin extracts had normal GSL content, including ganglioside composition, and myelin abnormalities were not detected in their CNS. These data indicate that the elimination of gangliosides from oligodendrocytes is not detrimental to myelination. These mice were also used to asses the potential compensatory effect of hydroxyl fatty acid glucosylceramide (HFA-GlcCer) accumulation in UDP-galactose:ceramide galactosyltransferase (encoded by Cgt, also known as Ugt8a) deficient mice. At postnatal day 18, the phenotypic characteristics of the Ugcg(flox/flox);Cnp/Cre;Cgt(-/-) mutants, including the degree of hypomyelination, were surprisingly similar to that of Cgt(-/-) mice, suggesting that the accumulation of HFA-GlcCer in Cgt(-/-) mice does not modify their phenotype. These studies demonstrate that abundant, structurally intact myelin can form in the absence of glycolipids, which normally represent over 20% of the dry weight of myelin.

Membrane properties of cultured glial cells obtained mechanically or by enzymatic dissociation: differential alterations by gangliosides

Rat astroglial cells were obtained either mechanically or by enzymatic dissociation and some properties of the primary and secondary cultures were studied. Differences in the ganglioside amount, taurine uptake, membrane fluorescence anisotropy, or their respective modulation by total brain gangliosides confirmed that although the two types of cultures are morphologically similar, they are biochemically distinct.

Spontaneous transfer of ganglioside GM1 between phospholipid vesicles

The transfer kinetics of the negatively charged glycosphingolipid II3-N-acetylneuraminosyl-gangliotetraosylceramide (GM1) were investigated by monitoring tritiated GM1 movement between donor and acceptor vesicles. After appropriate incubation times at 45 degrees C, donor and acceptor vesicles were separated by molecular sieve chromatography. Donors were small unilamellar vesicles produced by sonication, whereas acceptors were large unilamellar vesicles produced by either fusion or ethanol injection. Initial GM1 transfer to acceptors followed first-order kinetics with a half-time of about 40 h assuming that GM1 is present in equal mole fractions in the exterior and interior surfaces of the donor vesicle bilayer and that no glycolipid flip-flop occurs. GM1 net transfer was calculated relative to that of [14C]cholesteryl oleate, which served as a nontransferable marker in the donor vesicles. Factors affecting the GM1 interbilayer transfer rate included phospholipid matrix composition, initial GM1 concentration in donor vesicles, and the GM1 distribution in donor vesicles with respect to total lipid symmetry. The findings provide evidence that GM1 is molecularly dispersed at low concentrations within liquid-crystalline phospholipid bilayers.

Spontaneous and plasma factor-mediated transfer of pyrenyl cerebrosides between model and native lipoproteins

A series of pyrenyl glucocerebrosides was synthesized by reacylation of psychosine with pyrene-labeled fatty acids having 3-11 methylene units. When incorporated into model high-density lipoproteins consisting of dimyristoylphosphatidylcholine-apolipoprotein A-II complexes and incubated with unlabeled complexes, these lipids exhibited spontaneous transfer. Half times of transfer varied from 1.5 min to 365 min at 37 degrees C. The logarithm of the rate of transfer was linearly related to the number of fatty acyl methylene units and HPLC retention time. Transfer occurred by passage of lipid monomers through the aqueous phase. Spontaneous transfer of the glycolipids also occurred when they were incorporated into native high-density lipoproteins. Rates of transfer between native high-density lipoprotein particles were higher than those observed between model high-density lipoprotein particles. A partially purified lipid exchange protein from plasma, as well as unfractionated lipoprotein-deficient serum, stimulated the transfer of fluorescent glycolipid between model high-density lipoprotein or native high-density lipoprotein and low-density lipoprotein 2-24 fold. The protein also stimulated the transfer of tritiated ganglioside GM3 between native low-density lipoprotein and high-density lipoprotein. This protein may play a role in glycolipid exchange in vivo.