The accumulation of oligosaccharides in tissues and body fluids of cats with alpha-mannosidosis

Alpha-mannosidosis in the guinea pig: a new animal model for lysosomal storage disorders

Alpha-mannosidosis is a lysosomal storage disorder resulting from deficient activity of lysosomal alpha-mannosidase. It has been described previously in humans, cattle, and cats, and is characterized in all of these species principally by neuronal storage leading to progressive mental deterioration. Two guinea pigs with stunted growth, progressive mental dullness, behavioral abnormalities, and abnormal posture and gait, showed a deficiency of acidic alpha-mannosidase activity in leukocytes, plasma, fibroblasts, and whole liver extracts. Fractionation of liver demonstrated a deficiency of lysosomal (acidic) alpha-mannosidase activity. Thin layer chromatography of urine and tissue extracts confirmed the diagnosis by demonstrating a pattern of excreted and stored oligosaccharides almost identical to that of urine from a human alpha-mannosidosis patient. Widespread neuronal vacuolation was observed throughout the CNS, including the cerebral cortex, hippocampus, thalamus, cerebellum, midbrain, pons, medulla, and the dorsal and ventral horns of the spinal cord. Lysosomal vacuolation also occurred in many other visceral tissues and was particularly severe in pancreas, thyroid, epididymis, and peripheral ganglion. Axonal spheroids were observed in some brain regions, but gliosis and demyelination were not observed. Ultrastructurally, most vacuoles in both the CNS and visceral tissues were lucent or contained fine fibrillar or flocculent material. Rare large neurons in the cerebral cortex contained fine membranous structures. Skeletal abnormalities were very mild. Alpha-mannosidosis in the guinea pig closely resembles the human disease and will provide a convenient model for investigation of new therapeutic strategies for neuronal storage diseases, such as enzyme replacement and gene replacement therapies.

Glycoprotein lysosomal storage disorders: alpha- and beta-mannosidosis, fucosidosis and alpha-N-acetylgalactosaminidase deficiency

Glycoproteinoses belong to the lysosomal storage disorders group. The common feature of these diseases is the deficiency of a lysosomal protein that is part of glycan catabolism. Most of the lysosomal enzymes involved in the hydrolysis of glycoprotein carbohydrate chains are exo-glycosidases, which stepwise remove terminal monosaccharides. Thus, the deficiency of a single enzyme causes the blockage of the entire pathway and induces a storage of incompletely degraded substances inside the lysosome. Different mutations may be observed in a single disease and in all cases account for the nonexpression of lysosomal glycosidase activity. Different clinical phenotypes generally characterize a specific disorder, which rather must be described as a continuum in severity, suggesting that other biochemical or environmental factors influence the course of the disease. This review provides details on clinical features, genotype-phenotype correlations, enzymology and biochemical storage of four human glycoprotein lysosomal storage disorders, respectively alpha- and beta-mannosidosis, fucosidosis and alpha-N-acetylgalactosaminidase deficiency. Moreover, several animal disorders of glycoprotein metabolism have been found and constitute valuable models for the understanding of their human counterparts.

Storage of glycoprotein in NCTR-Balb/C mouse. Lectin histochemistry, and biochemical studies

A strain of Balb/C mice carrying a lysosomal storage disorder exhibits metabolic and phenotypic abnormalities similar to patients with sphingomyelin-cholesterol lipidoses type II (i.e., Niemann-Pick C and D). Their foamy cells, which belong to the reticuloendothelial system, stained intensely by periodate-Schiff (PAS) reagent and were resistant to predigestion with diastase. To identify the chemical nature of the PAS-positive storage material, we applied lectin histochemistry and biochemical methods. Paraffin embedded sections, and delipidated frozen tissue sections, were treated with biotinylated lectins and localized with avidin-biotin-peroxidase complex. Araldite-embedded semithin sections were incubated with biotinylated lectins followed by avidin-gold and were enhanced with silver. By both histochemical methods the affected foamy cells stained positively as follows: Concanavalia ensiformis agglutinin, Datura stramonium agglutinin, Griffonia simplicifolia-I, Lens culinaris agglutinin, peanut agglutinin, Ricinus communis agglutinin-I, wheat germ agglutinin (WGA), and succinylated-WGA. Biochemical analysis of liver extracts complemented the histochemical data and demonstrated accumulation of glycoproteins containing polylactosaminoglycans in affected mice. Our findings indicate that the storage material in NCTR-Balb/C mice is heterogeneous. The lipids that are extracted by organic solvents during the histologic preparations mask the occurrence of polylactosaminoglycan containing glycoproteins in native frozen sections.

Substrate specificity of the bovine and feline neutral alpha-mannosidases

Neutral alpha-mannosidases were prepared from bovine and cat liver. The activities were distinguished from lysosomal and Golgi alpha-mannosidases by their neutral pH optima, relatively low Km for their synthetic substrate p-nitrophenyl alpha-D-mannoside, inhibition by Zn2+ and absence of inhibition by Co2+, EDTA, low concentrations of swainsonine, or deoxymannojirimycin. The cytosolic alpha-mannosidases were not retained by concanavalin A-Sepharose. They were able to degrade efficiently a variety of oligosaccharides with structures corresponding to certain high-mannose glycans or the oligomannosyl parts of hybrid and complex glycans. However, unlike lysosomal alpha-mannosidases from the same species these enzymes were not able to degrade Man9GlcNAc2 efficiently, and the bovine neutral alpha-mannosidase was not able to degrade a hexasaccharide with a structure analogous to Man5GlcNAc2-PP-dolichol. Sharp differences were noted for the bovine and cat enzymes with regard to the specificity of degradation. The bovine neutral alpha-mannosidase degraded the substrates by defined pathways, but the cat neutral alpha-mannosidase often produced complex mixtures of products, especially from the larger oligosaccharides. Therefore the bovine enzyme resembled the rat and human cytosolic alpha-mannosidases, but the cat enzyme did not. The bovine and cat neutral alpha-mannosidases, unlike the corresponding lysosomal activities, did not show specificity for the hydrolysis of the (1----3)- and (1----6)-linked mannose residues in the N-linked glycan pentasaccharide core.

Substrate specificity of human liver neutral alpha-mannosidase

The digestion of radiolabelled natural oligosaccharide substrates by human liver neutral alpha-mannosidase has been studied by h.p.l.c. and h.p.t.l.c. The high-mannose oligosaccharides Man9GlcNAc and Man8GlcNAc are hydrolysed by the enzyme by two distinct non-random routes to a common product of composition Man6GlcNAc, which is then slowly converted into a unique Man5GlcNAc oligosaccharide, Man alpha(1----2)Man alpha(1----2)Man alpha(1----3)[Man alpha (1----6)] Man beta(1----4)GlcNAc. These pathways are different from the processing and lysosomal catabolic pathways for these structures. In particular, the alpha(1----2)-linked mannose residues attached to the core alpha(1----3)-linked mannose residue are resistant to hydrolysis. The key processing intermediate, Man alpha(1----3)[Man alpha(1----6)]Man alpha(1----6)[Man alpha(1----3)] Man beta(1----4)GlcNAc, is not produced in the digestion of high-mannose glycans by the neutral alpha-mannosidase, but it is hydrolysed by the enzyme by a non-random route to Man beta(1----4)GlcNAc via the core structure Man alpha(1----3)[Man alpha(1----6)]Man beta(1----4)GlcNAc. In contrast with its ready hydrolysis by lysosomal alpha-mannosidase, the core alpha(1----3)-mannosidic linkage is quite resistant to hydrolysis by neutral alpha-mannosidase. The precise specificity of neutral alpha-mannosidase towards high-mannose oligosaccharides suggests that it has a role in the modification of such structures in the cytosol.

Clinical, neurophysiological, biochemical and morphological features of eyes in Persian cats with mannosidosis

The clinical, neurophysiological, morphological and biochemical manifestation of eyes from Persian kittens affected with alpha-mannosidosis were studied. Clinically the disease is characterized by progressive corneal and lenticular opacification. In addition there is asymmetry in shape and latency of signal conductions which were demonstrated by visual evoked potential studies. Morphological and histochemical studies revealed vacuolization of various ocular cell types which stained positively with Concanavalia ensiformis agglutinin (Con A) and wheat germ agglutinin (WGA). Biochemical studies illustrated low activity of acid alpha-mannosidase in cultured keratocytes and abnormal storage of partially degraded oligosaccharides in these cells, in vitreous humor and lens. This comprehensive study of ocular alpha-mannosidosis demonstrates enzyme deficiency which leads to abnormal storage of oligosaccharides in affected cells and is manifested by morphological alterations and functional impairment.

The substrate-specificity of human lysosomal alpha-D-mannosidase in relation to genetic alpha-mannosidosis

The specificity of human liver lysosomal alpha-mannosidase (EC 3.2.1.24) towards a series of oligosaccharide substrates derived from high-mannose, complex and hybrid asparagine-linked glycans and from the storage products in alpha-mannosidosis was investigated. The enzyme hydrolyses all alpha(1-2)-, alpha(1-3)- and alpha(1-6)-mannosidic linkages in these glycans without a requirement for added Zn2+, albeit at different rates. A major finding of this study is that all the substrates are hydrolysed by non-random pathways. These pathways were established by determining the structures of intermediates in the digestion mixtures by a combination of h.p.t.l.c. and h.p.l.c. before and after acetolysis. The catabolic pathway for a particular substrate appears to be determined by its structure, raising the possibility that degradation occurs by an uninterrupted sequence of steps within one active site. The structures of the digestion intermediates are compared with the published structures of the storage products in mannosidosis and of intact asparagine-linked glycans. Most but not all of the digestion intermediates derived from high-mannose glycans have structures found in intact asparagine-linked glycans of human glycoproteins or among the storage products in the urine of patients with mannosidosis. However, the relative abundances of these structures suggests that the catabolic pathway is not the same as the processing pathway. In contrast, the intermediates formed from the digestion of oligosaccharides derived from hybrid and complex N-glycans are completely different from any processing intermediates and also from the oligosaccharides of composition Man2-4GlcNAc that account for 80-90% of the storage products in alpha-mannosidosis. It is postulated that the structures of these major storage products arise from the action of an exo/endo-alpha(1-6)-mannosidase on the partially catabolized oligomannosides that accumulate in the absence of the main lysosomal alpha-mannosidase.

Application of lectin histochemistry and carbohydrate analysis to the characterization of lysosomal storage diseases

In lysosomal storage diseases that involve a defect in the catabolism of glycoconjugates, lectin histochemistry adds a new dimension to the characterization of stored carbohydrates as it identifies sugar residues in situ in the affected cells and, thus, determines which cell types are affected by storage. It may be combined with chemical and biochemical analysis by h.p.l.c. The present review summarizes recent results for a variety of storage diseases and presents new data for GM1-gangliosidosis.

Different oligosaccharides accumulate in the brain and urine of a cat with alpha-mannosidosis: structure determination of five brain-derived and seventeen urinary oligosaccharides

Five brain-derived and 17 urinary oligomannose-type oligosaccharides were isolated by ion-exchange chromatography on Mono Q or Dowex, followed by HPLC on Lichrosorb-NH2 from a Persian cat suffering from alpha-mannosidosis. The structures of the carbohydrate chains were determined by 500- or 600-MHz 1H-NMR spectroscopy. Different oligosaccharide patterns were found in brain and urine. 99% of the urinary oligosaccharides possess an alpha(1-6)-linked mannose residue attached to beta-mannose, whereas only 5% of the brain-derived oligosaccharides contain such a residue. Furthermore, of the urinary carbohydrate chains 71% end with Man beta 1-4GlcNAc beta 1-4GlcNAc and 29% end with Man beta 1-4GlcNAc, whereas the corresponding amounts are 23% and 77%, respectively, for the brain-derived oligosaccharides.

Morphology of leukocytes from cats affected with alpha-mannosidosis and mucopolysaccharidosis VI (MPS VI)

The morphology and ultrastructure of circulating white blood cells from six Persian and from five Russian Blue/Siamese cats deficient in lysosomal activity of alpha-mannosidase and arylsulfatase B, respectively, were studied and compared to cells from corresponding normal and carrier cats. In cats with mannosidosis, light microscopic examination revealed vacuoles in lymphocytes and monocytes, whereas electron microscopic studies demonstrated additional vacuoles in neutrophils, eosinophils, and basophils. In cats with mucopolysaccharidosis VI (MPS VI), vacuoles containing metachromatic granules were observed in lymphocytes, neutrophils, eosinophils, and monocytes. Ultrastructural studies of these cells identified the accumulation of fibrillar material, which often was associated with lamellated membrane structures.