Ceramide biosynthesis in mouse brain microsomes: comparison between C57-BL controls and quaking mutants

Lack of in vitro ceramide formation in the PNS of trembler mice

The amidification of sphingosine by acyl donors has been investigated in a microsomal fraction prepared from sciatic nerves of normal and Trembler mice. In the control, a ceramide synthesis is observed in the presence of acyl-CoAs and not with free fatty acids. The synthesis increases as a function of the protein amount and the time and is dependent on acyl-CoA concentration. The level of synthesis is highly similar to that observed in vivo after palmitate injection into the sciatic nerves of normal mice. In the mutant, there is a major abnormality because a weak synthesis (20% of the control) is observed only with high acyl-CoA concentration (greater than 200 microM), whereas in the range of the physiological acyl-CoA concentrations (less than 20 microM), there is no ceramide formation from stearoyl-CoA or lignoceroyl-CoA.

Sphingomyelin and derivatives as cellular signals

This comprehensive review was necessitated by recent observations suggesting that sphingomyelin and derivatives may serve second messenger functions. It has attempted to remain true to the theme of cellular signalling. Hence, it has focussed on the lipids involved primarily with respect to their metabolism and properties in mammalian systems. The enzymology involved has been emphasized. An attempt was made to define directions in which signals may be flowing. However, the evidence presented to date is insufficient to conclusively designate the mechanisms of stimulated lipid metabolism. Hence, the proposed pathways must be viewed as preliminary. Further, the biologic functions of these lipids is for the most part uncertain. Thus, it is difficult to presently integrate this sphingomyelin pathway into the greater realm of cell biology. Nevertheless, the present evidence appears to suggest that a sphingomyelin pathway is likely to possess important bioregulatory functions. Hopefully, interest in this novel pathway will grow and allow a more complete understanding of the roles of these sphingolipids in physiology and pathology.

Biochemical and physicochemical determinations in a premyelin fraction obtained by zonal centrifugation in normal mouse and in dysmyelinating mutants (quaking, shiverer, and myelin-deficient)

Myelin and premyelin material denser than myelin were obtained from quaking (Qk), shiverer (Shi), and myelin-deficient (mld) mutant and control mice, using zonal centrifugation on zonal rotor. On these fractions, we performed biochemical analysis (lipids and fatty acid), and, in parallel, we determined the physical structure of membranes by the spin-label method. The hyperfine splitting constant (2 Tll) was used to determine the order of membranes and their rigidity, and frequency of rotation (Vc) was used to measure fluidity. In control mice, the premyelin material contained a lesser amount of sphingolipids than pure myelin, but the relative proportions between hydroxy- and nonhydroxy-cerebroside and sulfatides were similar in the premyelin material and in pure myelin. The premyelin material contained half the alkanes found in the pure myelin and much less very-long-chain fatty acids. The (2 Tll) was lower in the premyelin material, but the (Vc) was similar in myelin and premyelin material. In mutants, the amount of material recovered in the premyelin fraction was reduced in qk, and increased in both shi and mld. The relative amount of sphingolipids were normal in mld, but not in shi mutants, especially in cerebrosides formed with alpha-hydroxylated fatty acids and sulfatides formed with unsubstituted fatty acids. The absolute amounts of sphingolipids were nearly normal in both shi and mld. In the premyelin fraction from qk mutants, both relative and absolute amounts of sphingolipids were drastically altered. In percentage, cerebrosides and sulfatides formed with nonhydroxyfatty acids were dramatically reduced, and, conversely, cerebrosides and sulfatides formed with hydroxyfatty acids were increased. In terms of absolute amount, only cerebrosides and sulfatides formed with nonhydroxyfatty acids were dramatically reduced. In the premyelin fraction, polyunsaturated fatty acids were increased in shi and mld, but decreased in qk. In this mutant, lignoceric (24:0) and nervonic (24:1) acids were drastically reduced. The amount of alkanes in the premylin material from qk and mld was reduced by 50%. The shi fraction was nearly free of alkanes. The maximal apparent coupling constant (hyperfine splitting constant, 2 Tll) was not affected in the mld and qk mutant, but was reduced in the shi mutant premyelin fraction. The Vc was dramatically increased in the qk, slightly decreased in the shi, and close to control in the mld. This work provides additional data on premyelin material prepared in various neurological mutants using continuous gradients in zonal rotor.(ABSTRACT TRUNCATED AT 400 WORDS)

Brain-specific ceramide synthesis activity: change during brain maturation and in jimpy mouse brain

The synthesis of ceramide from lignoceric acid was studied in normally developing rat brain and jimpy mouse brain. The developmental pattern of the synthesis of both non-hydroxy and hydroxyceramide from free lignoceric acid in a brain-specific pathway requiring NADPH and cytosolic factors was similar to the synthesis from lignoceroyl CoA and both showed increasing activity during myelination. There were no differences in non-hydroxyceramide synthesis between jimpy and normal littermate control mouse brains by both pathways. HPLC analysis showed the same non-hydroxyceramide level in both types of brains.

Immunohistochemical localization of galactosyl and sulfogalactosyl ceramide in the brain of the 30-day-old mouse

We have used purified antibodies against galactosylceramide (galCb) and sulfogalactosylceramide (sulf) to study the topographical distribution of these two lipid haptens in the brain of the 30-day-old mouse. This study has been conducted, using the indirect immunofluorescence method, on cerebellum, brain stem and hemispherical tissue sections. Both haptens are present in the myelin sheaths and in the oligodendrocytes within the myelinated bundles. Cortical oligodendrocytes as well as some of the subependymal cells are also galCb-positive but sulf-negative. On the contrary, ciliated ependymal cells and subpial astrocytic processes (especially the Bergmann glia fibers in the cerebellum) are sulf-positive and galCb-negative. Astrocyte cell bodies and other astrocytic cell processes are devoid of both haptens. Lastly, some-sulf positive galCb-negative processes, as yet unidentified, were also found in the periaqueductal gray matter and in the nucleus interpeduncularis.

Developmental dissociation of myelin synthesis and "myelin-associated" enzyme activities in the shiverer mouse

Developmental changes in three enzymes associated with myelin lipids were studied in the shiverer mouse, a murine mutant showing a severe deficiency of CNS myelin. Age-related changes in cerebroside sulfotransferase (measured in brain) and arylsulfatase A and cerebroside B-galactosidase (measured in brain and liver) were the same for shiverer and control mice. The shiverer mouse, therefore, demonstrates a dissociation between the genetic mechanisms regulating myelination in the CNS and developmental changes in enzyme activities thought to be closely related to the synthesis of myelin. In addition, we found no defect in the shiverer mouse in the incorporation of glycine-labeled basic protein into CNS myelin, indicating an important metabolic difference between the morphologically similar shiverer and quaking mutants.

Brain nucleic acids and protein in various neurological mutant mice

A study was made to compare alterations in the cerebral contents of nucleic acids and protein of several mouse strains affected by different neurological mutations: jimpy, msd, quaking, reeler, weaver, and dwarf. In normal and affected jimpy and msd mice the brain components analyzed were very similar. On the other hand, the cerebral hemispheres of quaking mice showed significant decreases in total RNA and DNA, when compared with those of normal littermates. In the affected reeler and weaver mice, total protein, RNA, and DNA in the cerebellum differed markedly from controls. Protein decreased slightly, whereas nucleic acids showed no significant variation in the cerebral hemispheres of the same mutants. The cerebella and cerebral hemispheres of affected dwarf mice had wet weights and total protein contents that were about 20% lower than those of their controls; DNA did not vary significantly in the various brain regions analyzed. The decrease of DNA we report in reeler and weaver mutant cerebellum in toto quantifies the lack of cell number, in contrast to histological studies which give only semiquantitative information.