Co‐clustering of galactosylceramide and membrane proteins in oligodendrocyte membranes on interaction with polyvalent carbohydrate and prevention by an intact cytoskeleton

Abstract

We have shown previously that addition of liposomes containing the two major glycosphingolipids of myelin, galactosylceramide (GalC) and cerebroside sulfate (CBS), to cultured oligodendrocytes (OLs) caused clustering of GalC on the extracellular surface and myelin basic protein (MBP) on the cytosolic surface to the same membrane domains. It also caused depolymerization of actin microfilaments and microtubules, indicating that interaction of the liposomes with the OL surface induces transmembrane signal transmission. We show that a multivalent form of galactose conjugated to bovine serum albumin has a similar effect as the multivalent GalC/CBS-containing liposomes. Because GalC and CBS can interact with each other across apposed membranes and because anti-GalC and anti-CBS antibodies also cause redistribution of GalC/CBS and depolymerization of microtubules, we believe that the multivalent carbohydrate interacts with GalC and CBS in the OL membrane. Several myelin-specific transmembrane proteins could be involved in this transmembrane signal transmission from GalC/CBS. We looked at co-clustering of several myelin constituents by confocal microscopy to determine if they are located in or redistribute to GalC/MBP-containing domains. Myelin oligodendrocyte glycoprotein (MOG), proteolipid protein (PLP), MAPK, and some phosphotyrosine-containing proteins were found to co-cluster with GalC and MBP, but myelin-associated glycoprotein (MAG) and phosphatidylinositol-4,5-bisphosphate (PIP(2)) did not. These results suggest that MOG and PLP, but probably not MAG, are possible candidates for transmembrane transmission of the signal received by GalC/CBS. To determine if depolymerization of actin microfilaments was required for co-clustering, or was secondary to clustering, we stabilized F-actin with jasplakinolide. This also prevented depolymerization of the microtubules and prevented clustering of all constituents, including GalC. The prevention of clustering or redistribution of these glycolipids and proteins by an intact cytoskeleton is consistent with the picket fence model.

Myelin basic protein: a multifunctional protein

“…Addition of GalC/sulfatide-containing liposomes to cultured OLs to interact with GalC and sulfatide in the OL membrane by these Ca 2+ -mediated trans carbohydrate-carbohydrate interactions across apposed membranes had similar effects on lipid and protein distribution and depolymerization of the cytoskeleton as anti-GalC antibody [192]. Stabilization of the actin cytoskeleton with jasplakinolide prevented all effects of the liposomes including GalC and MBP redistribution and microtubule depolymerization, suggesting that the stability of microtubules in OLs depends on the integrity of the actin cytoskeleton [193]. The MBP redistribution caused by depolymerization of the actin cytoskeleton suggests that actin is linked directly or indirectly to MBP in OLs.…”

CLN3p Impacts Galactosylceramide Transport, Raft Morphology, and Lipid Content

“…ER comes into close proximity with mitochondria/PM/trans-Golgi network/endosomes/lysosomes and phagosomes (33). Contact sites are bridgeable by a single protein forming intracellular communication facilitating rapid/ energy-efficient trafficking of lipids/other small molecules in/ out of the ER (34).…”

“…GalCer/ sulfatide are major components of myelin/oligodendrocyte PM (36) and of neuronal axons. GalCer is involved in Schwann cell-axon interactions, oligodendrocyte differentiation, and transduction of signals across the myelin membrane (34,36).…”

Challenges in drug delivery to the brain: Nature is against us

“…Another but more uncommon NP effect on membranes was described by Boggs and Wang [108]. They studied a specific type of multilamellar vesicles consisting of the same compounds like the myelin sheath, the polyvalent carbohydrate, galactosylceramide and negatively charged cerebroside sulfate.…”