Targeted disruption of the lysosomal alpha-mannosidase gene results in mice resembling a mild form of human alpha-mannosidosis.
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Alpha-mannosidosis is a lysosomal storage disease with autosomal recessive inheritance caused by a deficiency of the lysosomal alpha-mannosidase, which is involved in the degradation of asparagine-linked carbohydrate cores of glycoproteins. An alpha-mannosidosis mouse model was generated by targeted disruption of the gene for lysosomal alpha-mannosidase. Homozygous mutant animals exhibit alpha-mannosidase enzyme deficiency and elevated urinary secretion of mannose-containing oligosaccharides. Thin-layer chromatography revealed an accumulation of oligosaccharides in liver, kidney, spleen, testis and brain. The cellular alterations were characterized by multiple membrane-limited cytoplasmic vacuoles as seen for instance in liver, exocrine pancreas, kidney, thyroid gland, smooth muscle cells, osteocytes and in various neurons of the central and peripheral nervous systems. The morphological lesions and their topographical distribution, as well as the biochemical alterations, closely resemble those reported for human alpha-mannosidosis. This mouse model will be a valuable tool for studying the pathogenesis of inherited alpha-mannosidosis and may help to evaluate therapeutic approaches for lysosomal storage diseases. (+info)
Glycoprotein lysosomal storage disorders: alpha- and beta-mannosidosis, fucosidosis and alpha-N-acetylgalactosaminidase deficiency.
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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. (+info)
Lysosomal storage disease caused by Sida carpinifolia poisoning in goats.
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A neurologic disease characterized by ataxia, hypermetria, hyperesthesia, and muscle tremors of the head and neck was observed for 2 years in a flock of 28 Anglo-Nubian and Saanen goats on a farm with 5 ha of pasture. Six newborns died during the first week of life, and five abortions were recorded. The predominant plant in the pasture was Sida carpinifolia. The disease was reproduced experimentally in two goats by administration of this plant. Three goats with spontaneous disease and the two experimental animals were euthanatized and necropsied. No significant gross lesions were observed. Fragments of several organs, including the central nervous system, were processed for histopathology. Small fragments of the cerebellar cortex, liver, and pancreas of two spontaneously poisoned goats and two experimentally poisoned goats were processed for electron microscopy. Multiple cytoplasm vacuoles in hepatocytes, acinar pancreatic cells, and neurons, especially Purkinje cells, were the most striking microscopic lesions in the five animals. Ultrastructural changes included membrane-bound vacuoles in hepatocytes, Kupffer cells, acinar pancreatic cells, Purkinje cells, and the small neurons of the granular cell layer of the cerebellum. Paraffin-embedded sections of the cerebellum and pancreas were submitted for lectin histochemical analysis. The vacuoles in different cerebellar and acinar pancreatic cells reacted strongly to the following lectins: Concanavalia ensiformis, Triticum vulgaris, and succinylated Triticum vulgaris. The pattern of staining, analyzed in Purkinje cells and acinar pancreatic cells coincides with results reported for both swainsonine toxicosis and inherited mannosidosis. (+info)
Recent progress in lysosomal alpha-mannosidase and its deficiency.
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Lysosomal alpha-mannosidase (EC 3.2.1.24) is a major exoglycosidase in the glycoprotein degradation pathway. A deficiency of this enzyme causes the lysosomal storage disease, alpha-mannosidosis, which has been described in humans, cattle, domestic cats and guinea pigs. Recently, great progress has been made in studying the enzyme and its deficiency. This includes cloning of the gene encoding the enzyme, characterization of mutations related to the disease, establishment of valuable animal models, and encouraging results from bone marrow transplantation experiments. (+info)
alpha-Mannosidosis in the guinea pig: cloning of the lysosomal alpha-mannosidase cDNA and identification of a missense mutation causing alpha-mannosidosis.
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alpha-Mannosidosis is a lysosomal storage disorder caused by deficient activity of the lysosomal alpha-mannosidase. We report here the sequencing and expression of the lysosomal alpha-mannosidase cDNA from normal and alpha-mannosidosis guinea pigs. The amino acid sequence of the guinea pig enzyme displayed 82-85% identity to the lysosomal alpha-mannosidase in other mammals. The cDNA of the alpha-mannosidosis guinea pig contained a missense mutation, 679C>T, leading to substitution of arginine by tryptophan at amino acid position 227 (R227W). The R227W allele segregated with the alpha-mannosidosis genotype in the guinea pig colony and introduction of R227W into the wild-type sequence eliminated the production of recombinant alpha-mannosidase activity in heterologous expression studies. Furthermore, the guinea pig mutation has been found in human patients. Our results strongly indicate that the 679C>T mutation causes alpha-mannosidosis and suggest that the guinea pig will be an excellent model for investigation of pathogenesis and evaluation of therapeutic strategies for human alpha-mannosidosis. (+info)
Alpha-mannosidosis and mutational analysis in a Turkish patient.
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We present a case of alpha-mannosidosis with its mutational analysis. She was referred to our hospital with the provisional diagnosis of mucolipidosis. She was the first child of second-degree relative parents. She had a coarse face with flat and wide nasal bridge, hepatosplenomegaly, umbilical hernia, lumbar gibbus, motor and mental retardation and deafness. On peripheral blood smear, lymphocytes revealed vacuoles and neutrophils contained some granules resembling Reilly bodies seen in mucopolysaccharidosis (MPS). Based on these findings, the diagnosis of alpha-mannosidosis was suspected. Her urine oligosaccharide chromatography showed an abnormal pattern with a heavy trisaccharide band. Enzyme studies on white cells confirmed a deficiency of alpha-mannosidase activity, which was 2.6 micromol/g/hr. Her DNA analysis showed a S453Y mutation. (+info)
Bovine plasma beta-mannosidase activity and its potential use for beta-mannosidosis carrier detection.
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Plasma beta-mannosidase activities were determined for Salers cattle from 8 herds as an evaluation of this method for detection of beta-mannosidosis heterozygotes. Several biological factors, such as age, gender, herd, and risk of being a beta-mannosidosis carrier, were considered in this study. The mean enzyme activity for obligate heterozygotes (n = 8) was 55 U/ml (range = 43-65 U/ml), which was 59% of the mean enzyme activity for cattle that were low risk for being a carrier. These data indicate that bovine beta-mannosidosis is characterized by a gene dosage effect. The analytical and biological variation of plasma beta-mannosidase activity that was observed necessitates limiting the test to adult fullblood/purebred Salers cattle within a herd. Plasma beta-mannosidase analysis provides important information for intraherd selection of Salers cattle that are heterozygous for beta-mannosidosis. (+info)
Intracellular transport of human lysosomal alpha-mannosidase and alpha-mannosidosis-related mutants.
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Human LAMAN (lysosomal a-mannosidase) was synthesized as a 120 kDa precursor in transfected COS cells [African-green-monkey kidney cells], which was partly secreted as a single-chain form and partly sorted to the lysosomes being subsequently cleaved into three peptides of 70, 40 and 15 kDa respectively. Both the secreted and the lysosomal forms contained endo H (endoglucosidase H)-resistant glycans, suggesting a common pathway through the trans-Golgi network. A fraction of LAMAN was retained intracellularly as a single-chain endo H-sensitive form, probably in the ER (endoplasmic reticulum). The inherited lack of LAMAN causes the autosomal recessive storage disease a-mannosidosis. To understand the biochemical consequences of the disease-causing mutations, 11 missense mutations and two in-frame deletions were introduced into human LAMAN cDNA by in vitro mutagenesis and the resulting proteins were expressed in COS cells. Some selected mutants were also expressed in Chinese-hamster ovary cells. T355P (Thr355Pro), P356R, W714R, R750W and L809P LAMANs as well as both deletion mutants were misfolded and arrested in the ER as inactive single-chain forms. Six of the mutants were transported to the lysosomes, either with less than 5% of normal specific activity (H72L, D196E/N and R220H LAMANs) or with more than 30% of normal specific activity (E402K LAMAN). F320L LAMAN resulted in much lower activity in Chinese-hamster ovary cells when compared with COS cells. Modelling into the three-dimensional structure revealed that the mutants with highly reduced specific activities contained substitutions of amino acids involved in the catalysis, either co-ordinating Zn2+ (His72 and Asp196), stabilizing the active-site nucleophile (Arg220) or positioning the active-site residue Asp319 (Phe320). (+info)