Glycoproteins in brain tissue of the O-variant of GM2 gangliosidosis

Anderson-Fabry's disease: neuropathological and neurochemical investigation

A clinical, neuropathological and neurochemical study of a case of Anderson-Fabry's disease is described. The clinical course mainly consisted of repeated ictus with major involvement of the CNS. The neuropathological examination is dominated by severe alterations in the cerebral vessels due to glycolipid deposits on the walls, with reduction or occlusion of the lumen. This is correlated with secondary ischaemic foci scattered throughout the cortex as well as through the white matter. In addition, the cells of the cerebral cortex, thalamus, basal ganglia, amygdala, cerebellar and olivary nuclei show a marked accumulation of lipofuscin. Biochemical examination reveals a threefold increase in galactolipids due to the specific alpha-galactosidase deficiency. Cholesterol is reduced secondarily to ischaemic myelin damage. Glycosaminoglycans uronic acid is increased in cytosol and membrane-bound fractions which could be related to reactive gliosis. Glycoprotein sugars show a decrease in N-acetyl-neuraminic acid and fucose as well as an increase in hexosamines and hexoses in membrane-bound fraction, while in cytosol fraction all sugars are increased. This suggests that the alpha-galactosidase deficiency can alter not only the glycolipid but also the glycoprotein metabolism, resulting in a higher presence of hexosamines and hexoses-rich glycoproteins.

Cleavage of the (1 goes to 3)-2-acetamido-2-deoxy-beta-D-glucopyranosyl linkage present in keratan sulfate. The A and B isoenzymes of human liver hexosaminidase (EC 3.2.1.30)

The disaccharide 2-acetamido-2-deoxy-beta-D-glucopyranosyl-(1 goes to 3)-D-[1-3H]-galactitol, prepared from keratan sulfate, was rapidly hydrolyzed by the A and B isoenzymes of normal human liver hexosaminidase (EC 3.2.1.30), and by the B isoenzyme prepared from the liver of a patient who had died of Tay-Sachs disease. The disaccharide substrate was also hydrolyzed by extracts of normal, cultured-skin fibroblasts, and fibroblasts of patients with Tay-Sachs disease, whereas it was not hydrolyzed by fibroblast extracts of patients with Sandhoff disease. Thus, effective degradation of keratan sulfate, secondary to a defect of the beta subunits present in the A and B isoenzymes of hexosaminidase, may contribute to the appearance of skeletal lesions in patients affected by Sandhoff disease.

Incorporation of intrastriatally injected[3H]fucose into electrophoretically separated synaptosomal glycoproteins. I. Turnover and molecular weight estimations

The radioactivity profiles of electrophoresed neostriatal P2 fraction glycoproteins were examined at a series of times (2.5, 3 and 4 h; 1, 5 and 10 days) following intracranial injections of [3H]fucose into the neostriatum. Ten major fucosylglycoprotein peaks were discerned in these profiles and certain aspects of their metabolism were characterized. The half-life of fucosylglycoproteins in the P2 fraction was estimated to be 9.7 days. The half-lives of the individual glycoprotein peaks ranged from 4.9 to 17.9 days. The apparent molecular weights of the glycoprotein peaks obtained by our procedures ranged from 32,000 to 180,000 daltons. One peak (peak VIII) incorporated radioactivity primarily at short intervals following the injection. The time course of [3H] fucose incorporation into this peak suggests involvement in the transport, activation and/or incorporation of fucose in brain. Since intracranial injections of [3H]fucose are incorporated into proteins in the cell body, synaptosomal fractions from caudate neurons alone are labeled by this technique. This may be useful in separating pre- and postsynaptic glycoprotein biochemistry. Finally, we tentatively propose that the glycoprotein peaks observed in neostriatum may be identical to previously isolated glycoproteins of known function or subcellular location.

Biochemistry and genetics of gangliosidoses

The gangliosidoses comprise an-ever increasing number of biochemically and phenotypically variant diseases. In most of them an autosomal recessive inherited deficiency of a lysosomal hydrolase results in the fatal accumulation of glucolipids (predominantly in the nervous tissue) and of oligosaccharides. The structure, substrate specificity, immunological properties of and genetic studies on the relevant glycosidases, ganglioside GM1 beta-galactosidase and beta-hexosaminidase isoenzymes, are reviewed in this paper. Contrary to general expectation, only a poor correlation is observed between the severity of the disease and residual activity of the defective enzyme when measured with synthetic or natural substrates in the presence of detergents. For the understanding of variant diseases and for their pre- and postnatal diagnosis, the necessity of studying the substrate specificity of normal and mutated enzymes under conditions similar to the in vivo situation, e.g., with natural substrates in the presence of appropriate activator proteins, is stressed. The possibility that detergents may have adverse affects on the substrate specificity of the enzymes is discussed for the beta-hexosaminidases. The significance of activator proteins for the proper interaction of lipid substrates and water-soluble hydrolases is illustrated by the fatal glycolipid storage resulting from an activator protein deficiency in the AB variant of GM2-gangliosidosis. Recent somatic complementation studies have revealed the existence of a presumably post-translational modification factor necessary for the expression of ganglioside GM1 beta-galactosidase activity. This factor is deficient in a group of variants of GM1-glangliosidosis. Among the possible reasons for the variability of enzyme activity levels in heterozygotes and patients, allelic mutations, formation of hybrid enzymes, and the existence of patients as compound heterozygotes are discussed. All these may result in the production of mutant enzymes with an altered specificity for a variety of natural substrates.

The gangliosidoses

The gangliosidoses are hereditary diseases with a recessive mode of inheritance and are caused by a genetically induced enzymatic block, which results in the accumulation of gangliosides in various tissues of the body, mainly in the brain. Although Tay-Sachs disease, the most commonly occurring of the gangliosidoses, has been known for nearly 100 years, additional variants of ganglioside "storage" disorders have been discovered during the past 15 years. Considerable progress in the knowledge of these disorders has been made with the advent of electron microscopy and with the elaboration of new biochemical and enzyme-chemical techniques. At the present the gangliosidoses are not amenable to therapy. Therefore the foreseeable future the pragmatic approach involves identification of the high-risk pregnancy and antenatal diagnosis.