Myelin abnormalities in the optic and sciatic nerves in mice with GM1-gangliosidosis

Abstract

GM1-gangliosidosis is a glycosphingolipid lysosomal storage disease involving accumulation of GM1 and its asialo form (GA1) primarily in the brain. Thin-layer chromatography and X-ray diffraction were used to analyze the lipid content/composition and the myelin structure of the optic and sciatic nerves from 7- and 10-month old β-galactosidase (β-gal) +/? and β-gal -/- mice, a model of GM1gangliosidosis. Optic nerve weight was lower in the β-gal -/- mice than in unaffected β-gal +/? mice, but no difference was seen in sciatic nerve weight. The levels of GM1 and GA1 were significantly increased in both the optic nerve and sciatic nerve of the β-gal -/- mice. The content of myelin-enriched cerebrosides, sulfatides, and plasmalogen ethanolamines was significantly lower in optic nerve of β-gal -/- mice than in β-gal +/? mice; however, cholesteryl esters were enriched in the β-gal -/- mice. No major abnormalities in these lipids were detected in the sciatic nerve of the β-gal -/- mice. The abnormalities in GM1 and myelin lipids in optic nerve of β-gal -/- mice correlated with a reduction in the relative amount of myelin and periodicity in fresh nerve. By contrast, the relative amount of myelin and periodicity in the sciatic nerves from control and β-gal -/- mice were indistinguishable, suggesting minimal pathological involvement in sciatic nerve. Our results indicate that the greater neurochemical pathology observed in the optic nerve than in the sciatic nerve of β-gal -/- mice is likely due to the greater glycolipid storage in optic nerve.

Keywords: X-ray diffraction; cerebrosides; gangliosides; lipids.

Figure 1.

High-performance thin-layer chromatograms of neutral lipids in the optic and sciatic nerves of β-gal −/− and +/? mice. Representative samples for each age group and tissue type are presented. The amount of total lipids spotted per lane was equivalent to approximately 80 µg nerve dry weight. The plate was developed and the lipid bands visualized as described in Materials and Methods section. Std indicates 4 µg of neutral lipid standards and 2µg of GA1 standard. CE = cholesterol ester; TG = triacylglycerol; IS = internal standard (oleoyl alcohol); C = cholesterol; CM = ceramide; CBU = cerebroside upper band; CBL = cerebroside lower band; PE = phosphatidylethanolamine; PC = phosphatidylcholine; SM = sphingomyelin; LPC = lysophosphatidylcholine; SF = solvent front. The arrows indicate the presence of GA1 in the specific samples. Optic nerve contained no visible TG and sciatic nerves contained no visible CE.

Figure 2.

High-performance thin-layer chromatogram of gangliosides in the optic and sciatic nerves of β-gal −/− and +/? mice. Representative samples for each age group and tissue type are presented. Approximately 1.5 µg of ganglioside sialic acid were spotted per lane. Std, ganglioside standards for the labeled gangliosides; gangliosides GM2 and GD3 were not visualized in the nerve lipids. The plate was developed and the lipid bands visualized as described in Materials and Methods section.

Figure 3.

High-performance thin-layer chromatogram of acidic lipids in the optic and sciatic nerves of β-gal −/− and +/? mice. Representative samples for each age group and tissue type are presented. The amount of total lipids spotted per lane was equivalent to approximately 230 µg nerve dry weight for the acidic lipids. The plate was developed and the lipid bands visualized as described in Materials and Methods section. Std, 4 µg acidic lipid standards. IS = internal standard (oleoyl alcohol); CL = cardiolipin; PA = phosphatidic acid; SFU = sulfatide upper band; SFL = sulfatide lower band; PS = phosphatidylserine; PI = phosphatidylinositol; SF = solvent front.

Figure 4.

X-ray diffraction from optic and sciatic nerves from β-gal mice. Representative examples of data for optic (left) and sciatic (right) nerves from β-gal +/? and β-gal −/− are shown. Myelin scatter was significantly weaker in optic nerves (p < .001) and marginally weaker in sciatic nerves (p < .03) of β-gal −/− mice compared to nerves from β-gal +/? mice. The Bragg orders for the X-ray peaks are indicated by 2–5.

Figure 5.

XRD analysis of myelin content and myelin periodicity in β-gal −/− and β-gal +/? mice. The fractional amount of scatter by compact myelin (M) compared with the relative amount of total X-ray scatter (M + B) is plotted against the myelin period, in Angstroms (Å). The mean value and standard deviations are indicated for each group of data (N = 12 nerves per group for β-gal +/?, and six nerves per group for β-gal −/−). The relative amount of myelin was significantly lower in the optic and sciatic nerves of β-gal −/− (○) mice compared to β-gal +/? (♦) mice. Myelin periodicity was significantly less in the optic nerves of β-gal −/− (○) mice than in β-gal +/? (♦) mice. The sciatic nerves of β-gal −/− (○) and β-gal +/? (♦) mice showed no significant differences in periodicity. Asterisks indicate statistical significance of p < .003, based on Student’s two-tailed unpaired t test.