Glycolipids and transmembrane signaling: antibodies to galactocerebroside cause an influx of calcium in oligodendrocytes.

Abstract

Abstract. This is the first study to provide evidence that one function for the surface glycolipid galactocerebroside (GalC) is participation in the opening of Ca 2+ channels in oligodendroglia in culture. This glycolipid is a unique differentiation marker for myelin-producing cells; antibodies to GalC have been shown to markedly alter oligodendroglial morphology via disruption of microtubules (Dyer, C. A., and J. A. Benjamins. 1988. J. Neurosci. 8:4307--4318). This study demonstrates that extracellular EGTA blocks anti-GalC-induced disassembly of microtubules in oligodendroglial membrane sheets, demonstrating that an influx of extracellular Ca 2÷ mediates the cytoskeletal changes. The Ca 2÷ influx was examined directly by loading oligodendroglia with the fluorescent dye Indo-1 in defined medium, and measuring changes in Ca 2÷ in individual cells with a laser cytometer. Upon addition of anti-GalC IgG, a marked sustained increase in intracellular Ca 2÷ occurred in 80% of the oligodendroglia observed. EGTA blocked the increase, indicating the increase is due to an influx of extracellular Ca 2+, and not due to release from intracellular stores. The effect is specific, since Ca 2+ levels remain normal in oligodendroglia treated with nonimmune IgG; astrocytes do not respond to the anti-GalC. The Ca 2+ response in oligodendrocytes is dependent on concentration of antibody and GalC on the oligodendroglial membrane surface. The Ca 2+ influx is not mediated by voltage-sensitive Ca 2÷ channels: it is not blocked by cadmium, and depolarization with K ÷ does not mimic the response. The kinetics of the response suggest that second messenger-mediated opening of Ca 2÷ channels is involved. lvms have received increasing attention for their role in receptor-mediated signaling across cell membranes. In particular, glycolipids presumably associated with transmembrane proteins have been reported to participate in ligand binding and signaling; for example, cholera toxin binds to GMI ganglioside leading to activation of adenylate cyclase (see Fishman, 1982, for review). Glycolipids are involved in initiating such events as mitogenesis, morphogenesis, and cell recognition (Sharom and Grant, 1978;Grant and Peters, 1979;Hakomori, 1981;Spiegel and Wilchek, 1981;Thompson and Tillack, 1985;Facci et al., 1988;Curatolo, 1987;Bansal and Pfeiffer, 1989). However, little is known about the mechanisms underlying these effects.We have focused on the function of galactocerebroside (GalC), a glycolipid highly enriched on the surface of myelin-producing cells. Oligodendrocytes are the only cells in the central nervous system that express this lipid; although it is used widely as a unique marker for differentiation of oligodendrocytes, its role in the specialized membrane produced by these cells is not known. Several studies over the last decade indicate that antibodies to GalC can alter oligodendroglial morphology and myelination, providing indirect evidence that this glycolipid is involved in signal transduction (Diaz et al., 1978;Dorfman et al., ...

Probing the influence of myelin and glia on the tensile properties of the spinal cord

“…Unlike EB, αGalC causes demyelination without damage to astrocytes or axons (Carroll et al 1987;Dyer and Benjamins 1990). Galactocerebroside is a major sphingolipid constituent of myelin (Sergott et al 1984;Mastaglia et al 1989).…”

Human monoclonal antibodies reactive to oligodendrocytes promote remyelination in a model of multiple sclerosis

“…Because many of the remyelination-promoting mAbs bind to OLs and͞or myelin, it is reasonable to hypothesize a direct effect on the recognized cells. There are examples of mAbs binding to and altering the biology of OLs in culture (46)(47)(48). However, because the mAbs that promote remyelination have varying specificities (23,26) it is unlikely that each mAb functions directly through a common antigen or receptor.…”

Cyclic GMP-Dependent Pathways Protect Differentiated Oligodendrocytes from Multiple Types of Injury

“…Enriched OL cultures were prepared from brains of 1-2 day-old Balb/C mice or Sprague Dawley rats by a modification [6,7] of the shakeoff method of McCarthy and de Vellis [8]. The OLs were removed from the primary astroglial bed layer by rapping the flasks sharply multiple times on the bench top.…”

“…The OLs were removed from the primary astroglial bed layer by rapping the flasks sharply multiple times on the bench top. Detached cells were placed in plastic dishes to remove microglia and other cells by adherence; the remaining cells, primarily OL precursors, were plated on glass coverslips (Bellco) coated with poly-D-lysine [5,6]. Cultures were grown overnight in chemically defined medium [9].…”