HindIII/EcoRI polymorphism in the GAA gene.
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Chromosomes, Human, Pair 17↗
Biomedical subjects
A J Reuser
Publications and source records attributed to A J Reuser.
Rat heart perfusion as model system for enzyme replacement therapy in glycogenosis type II.
Cardiac failure and skeletal muscle weakness are the main clinical features of glycogenosis type II, a lysosomal storage disorder caused by acid alpha-glucosidase deficiency. In our study, we have investigated in a rat heart perfusion-recirculation system whether acid alpha-glucosidase can be taken up from the vascular system into cardiomyocytes. When rat hearts were perfused with mannose 6-phosphate-containing acid alpha-glucosidase purified from bovine testis, a 3- to 4-fold increase of enzyme activity was obtained. Perfusion with human placental acid alpha-glucosidase not containing the mannose 6-phosphate recognition marker did not have such an effect. The presence of bovine testis acid alpha-glucosidase in heart tissue was demonstrated by immunoblotting. Immunocytochemistry provides evidence for uptake of the exogenous enzyme in lysosomes of the cardiomyocytes. The relevance of these findings for enzyme therapy in glycogenosis type II is discussed.
Animals↗
Adult and infantile glycogenosis type II in one family, explained by allelic diversity.
To define the cause of clinical heterogeneity in glycogenosis type II we have studied the inheritance and molecular nature of acid alpha-glucosidase deficiency in a rare family with severe infantile as well as mild late-onset variants of this disease. The (mutant) acid alpha-glucosidase alleles of crucial family members were segregated in human-mouse somatic cell hybrids to investigate their individual function. Two types of mutant alleles were identified. The first leads to complete deficiency of acid alpha-glucosidase. Homozygosity of this allele is demonstrated in three cases of severe infantile glycogenosis type II in the family under study. The second mutant allele is characterized by a reduced net production of catalytically active acid alpha-glucosidase, resulting in partial enzyme deficiency. The eldest patient in the family, with very mild clinical symptoms, is shown to be a compound heterozygote having both types of mutant alleles. These studies emphasize the effect of allelic diversity on the level of residual acid alpha-glucosidase activity and on the clinical course of glycogenosis type II.
Adult↗
Effects of N-hydroxyethyl-1-deoxynojirimycin (BAY m 1099) on the activity of neutral- and acid alpha-glucosidases in human fibroblasts and HepG2 cells.
The effect of the glucose analogue N-hydroxyethyl-1-deoxynojirimycin (BAY m 1099) on the activity of alpha-glucosidases was studied in human fibroblasts and HepG2 cells. BAY m 1099 inhibits neutral and acid alpha-glucosidase activities of both cell types in a dosage-dependent and reversible manner. Inhibition of endoplasmic reticulum glucosidases I and/or II is suggested by delayed processing of lysosomal (acid) alpha-glucosidase. Competitive inhibition of mature acid alpha-glucosidase leads to lysosomal accumulation of glycogen as in glycogenosis type II. There seems to be little risk, however, of inducing this storage disorder when using the drug in a dose of 50 mg per os for treatment of type II diabetes. In high doses, the drug may prove useful for studying the pathogenesis of glycogenosis type II in vitro or in animal models.
1-Deoxynojirimycin↗
An investigation of the properties and possible clinical significance of the lysosomal alpha-glucosidase GAA*2 allele.
Properties of the acid alpha-glucosidase, GAA2, the product of the GAA*2 allele have been compared with those of the common allele product GAA1, GAA2 has an altered affinity for glycogen but resembles GAA1 in its affinity for low molecular weight substrates, and also in its processing, as judged by immunoblot analysis of the denatured polypeptides. Starch gel electrophoretic analysis of fibroblasts from 15 patients with late onset glycogen storage disease type II (GSDII) failed to reveal either homozygotes or heterozygotes for the GAA*2 allele (GAA2-2 or GAA2-0) providing evidence that neither of these genotypes lead to late onset GSDII despite the impaired activity of the enzyme towards glycogen.
Alleles↗
An investigation of the possible influence of neutral alpha-glucosidases on the clinical heterogeneity of glycogenosis type II.
The lysosomal storage disorder glycogenosis type II, caused by a deficiency of lysosomal alpha-glucosidase, is very heterogeneous in its clinical presentation. It has been suggested that this heterogeneity may be due to differential expression of neutral alpha-glucosidases. We have therefore analysed the activity of the major neutral alpha-glucosidases in cultured fibroblasts or muscle cells from 26 patients with glycogenosis type II. The results indicate that there is no correlation between the expression of neutral alpha-glucosidase isoenzymes and the clinical phenotype of this disease.
Cells, Cultured↗
Isolation and structural characterization of twenty-one sialyloligosaccharides from galactosialidosis urine. An intact N,N'-diacetylchitobiose unit at the reducing end of a diantennary structure.
Galactosialidosis urine was fractionated by gel-permeation chromatography on Bio-Gel P-6. The obtained sialic acid-containing carbohydrate fractions were purified by reversed-phase chromatography and separated according to charge by medium-pressure anion-exchange chromatography on Mono Q. The Mono Q fractions, being mixtures of sialyloligosaccharides differing mainly in sialic acid-linkage type (alpha 2-3/alpha 2-6), were subfractionated by high-performance liquid chromatography on Lichrosorb-NH2. The purified compounds were analysed by 500-MHz 1H-NMR spectroscopy. Twenty-one fully and partially sialylated N-acetyllactosamine-type compounds include mono-, di-, tri- and tetra-antennary structures. All structures have the sequence Man beta 1-4Glc-NAc at the reducing terminus in common, except one diantennary structure bearing an intact N,N'-diacetylchitobiose unit at the reducing end, which is a new feature in human glycoproteinosis urine.
Chromatography, Gel↗
Glycogenosis type II: protein and DNA analysis in five South African families from various ethnic origins.
The molecular nature of lysosomal alpha-glucosidase deficiency was studied in five South African families with glycogenosis type II. Distinct ethnic origins were represented. Two new mutant acid alpha-glucosidase alleles were discovered. In two infantile patients from a consanguineous Indian family we found for the first time an acid alpha-glucosidase precursor of reduced size. The mutant precursor appeared normally glycosylated and phosphorylated but was not processed to mature enzyme. Abnormalities of the mRNA were not obvious, but digestion of genomic DNA with HindIII, BglII, and StuI revealed for each enzyme a fragment of increased length. Heterozygosity was demonstrated in the parents. Complete lack of acid alpha-glucosidase mRNA, as well as deficiency of precursor synthesis, was observed in two black baby girls from unrelated families. In these cases the length of all restriction-enzyme fragments was normal. Reduced enzyme synthesis but normal processing was registered in juvenile and young adult Cape colored patients. The extensive heterogeneity of glycogenosis type II is emphasized in these studies on various ethnic groups. The newly discovered mutants are valuable for the understanding of clinical diversity as a result of allelic variation.
Adolescent↗
Primary structure and processing of lysosomal alpha-glucosidase; homology with the intestinal sucrase-isomaltase complex.
Lysosomal alpha-glucosidase (acid maltase) is essential for degradation of glycogen in lysosomes. Enzyme deficiency results in glycogenosis type II. The amino acid sequence of the entire enzyme was derived from the nucleotide sequence of cloned cDNA. The cDNA comprises 3636 nt, and hybridizes with a messenger RNA of approximately 3.6 kb, which is absent in fibroblasts of two patients with glycogenosis type II. The encoded protein has a molecular mass of 104.645 kd and starts with a signal peptide. Sites of proteolytic processing are established by identification of N-terminal amino acid sequences of the 110-kd precursor, and the 76-kd and 70-kd mature forms of the enzyme encoded by the cDNA. Interestingly, both amino-terminal and carboxy-terminal processing occurs. Sites of sugar-chain attachment are proposed. A remarkable homology is observed between this soluble lysosomal alpha-glucosidase and the membrane-bound intestinal brush border sucrase-isomaltase enzyme complex. It is proposed that these enzymes are derived from the same ancestral gene. Around the putative active site of sucrase and isomaltase, 10 out of 13 amino acids are identical to the corresponding amino acids of lysosomal alpha-glucosidase. This strongly suggests that the aspartic acid residue at this position is essential for catalytic function of lysosomal alpha-glucosidase.
Amino Acid Sequence↗
Prospect for enzyme therapy in glycogenosis II variants: a study on cultured muscle cells.
Impairment of skeletal muscle function is the common feature of distinct clinical forms of glycogenosis type II. In the present study, muscle cultures from different patients were used to investigate the cause of clinical heterogeneity and the feasibility of enzyme replacement therapy. The activity of acid alpha-glucosidase appears to be the primary factor in determining the extent of lysosomal glycogen storage in muscle, and thereby the clinical severity of the disease. Neutral alpha-glucosidases do not seem influential. Correction of the enzymatic defect was achieved in skeletal muscle cultures from patients by administration of a "high-uptake" form of acid alpha-glucosidase, purified from human urine. The enzyme reaches the lysosomes, including the glycogen storage vacuoles, and the lysosomal glycogen content is reduced to control level. In normal muscle cells 20% of the total cellular glycogen pool is segregated in lysosomal compartments. This percentage is higher than in fibroblasts, which may partly explain why muscles are more prone to store glycogen. The relevance of this study for enzyme therapy is discussed.
Cells, Cultured↗
Ultrastructural localization of steroid sulphatase in cultured human fibroblasts by immunocytochemistry: a comparative study with lysosomal enzymes and the mannose 6-phosphate receptor.
Immunocytochemistry was used to study the subcellular localization of steroid sulphatase in cultured human fibroblasts. Ultra-thin cryosections were incubated with antibodies raised against steroid sulphatase purified from human placenta and immune complexes were visualized with gold probes as electron dense markers. Steroid sulphatase was found in rough endoplasmic reticulum, Golgi cisternae and in the trans-Golgi reticulum, where it co-distributes with lysosomal enzymes and the mannose 6-phosphate receptor. The enzyme was not detected in lysosomes. Steroid sulphatase was also found at the plasma membrane and in the endocytic pathway (i.e. coated pits, endosomes and multivesicular endosomes). These may be the sites where sulphated oestrogen precursors are hydrolysed. Also here, it co-localizes with lysosomal enzymes and the mannose 6-phosphate receptor. It is concluded that microsomal steroid sulphatase and lysosomal enzymes share several cellular compartments.
Carrier Proteins↗
Km mutant of acid alpha-glucosidase in a case of cardiomyopathy without signs of skeletal muscle involvement.
A male patient is reported with a mutation of acid alpha-glucosidase causing an altered Km toward natural substrates. Cardiac arrhythmia was found at 12 years of age, and he died of heart failure at 15 years. No skeletal muscle involvement was observed either clinically or histologically. Acid alpha-glucosidase activity in fibroblasts was moderately low (43% of the control mean) with normal Km for 4-methylumbelliferyl alpha-D-glucoside. The hydrolysis of glycogen was markedly decreased (14% of the control mean), and the Km for maltose was increased 4-fold and for glycogen 5-fold. The biosynthesis and the posttranslational processing of the mutant enzyme appeared normal, but the total amount of the enzyme was lower than normal. This mutant enzyme comigrated with normal acid alpha-glucosidase on starch gel electrophoresis, and not with the rare isozyme, acid alpha-glucosidase 2. A possible role of this mutant enzyme in the pathogenesis of this disease and the relationship to glycogenesis II are discussed.
Adolescent↗
Receptor-mediated uptake of acid alpha-glucosidase corrects lysosomal glycogen storage in cultured skeletal muscle.
Attempts at treatment of glycogenosis type II and other lysosomal storage disorders by enzyme replacement have been reported. Parenteral enzyme administration has been ineffectual. Treatment by bone marrow transplantation is currently under investigation. We have used cultured skeletal muscle cells from a patient with infantile glycogenosis type II to study fundamental aspects of enzyme replacement therapy. Efficient uptake of acid alpha-glucosidase was achieved by using the mannose-6-phosphate receptor on the cell surface as a target for an enzyme precursor with phosphorylated high-mannose types carbohydrate chains purified from human urine. We found that the enzyme was channeled to the lysosomes and converted to mature acid alpha-glucosidase. Glycogen storage was reversed. The results are discussed in relation to treatment of glycogenosis type II.
Carrier Proteins↗
Cell-free translation of human lysosomal alpha-glucosidase: evidence for reduced precursor synthesis in an adult patient with glycogenosis type II.
Early events in the biosynthesis of alpha-glucosidase (EC 3.2.1.20) were studied in a wheat-germ cell-free translation system, using control and mutant RNA. In vitro, the primary translation product of the alpha-glucosidase mRNA is a 100 kDa protein. When canine microsomal membranes are added to the translation system, the nascent alpha-glucosidase precursor is cotranslationally transported across the microsomal membranes, yielding a 110 kDa glycosylated form. This protein has the same electrophoretic characteristics as the alpha-glucosidase precursor observed after in vivo labeling of control fibroblasts. Inhibition of glycosylation in vivo by tunicamycin or deglycosylation of the in vivo synthesized alpha-glucosidase precursor by glycopeptidase F reveals a core protein similar in molecular mass to the primary translation product. Total RNA from a patient with the adult form of glycogenosis type II is not able to direct the synthesis of normal amounts of alpha-glucosidase in vitro. Northern blot analysis of the RNA, using cloned alpha-glucosidase cDNA sequences as a probe, demonstrates that in this patient the amount of the 3.4 kb alpha-glucosidase mRNA is highly reduced. The results indicate that the synthesis or stability of the mRNA is affected.
Cell-Free System↗
Determination of the structure of the carbohydrate chains of acid alpha-glucosidase from human placenta.
Acid alpha-glucosidase (alpha-D-glucoside glucohydrolase, EC 3.2.1.20) from human placenta (70 and 76 kDa) was found to contain 4 N-glycosidic carbohydrate chains per molecule. Sugar analysis of purified enzyme revealed the presence of mannose, N-acetylglucosamine and fucose at a molar ratio of 5.0:2.0:0.6. In addition, trace amounts of galactose and N-acetylneuraminic acid were detected. The sugar chains were liberated from the polypeptides by the hydrazinolysis procedure and subsequently fractionated by gel filtration and HPLC. Purified compounds were investigated by 500-MHz 1H-NMR spectroscopy. Oligomannoside-type chains of intermediate size, e.g., Man5GlcNAcGlcNAc-ol and Man7GlcNAcGlcNAc-ol, and N-type chains of smaller size e.g., Man2-3GlcNAc[Fuc]0-1GlcNAc-ol, were demonstrated to be present at a ratio of 2:3. In addition, a small amount of sialylated N-acetyllactosamine-type chains has been found. The possible biosynthetic route of the fucose-containing small-size chains is discussed.
Carbohydrate Sequence↗
Ultrastructural localization of glucocerebrosidase in cultured Gaucher's disease fibroblasts by immunocytochemistry.
The subcellular localization of glucocerebrosidase was studied in cultured skin fibroblasts from eight patients with Gaucher's disease. The enzyme, in situ, was visualized under the electron microscope by incubating ultrathin frozen sections of fibroblasts with antibodies against glucocerebrosidase, followed by a second incubation with goat anti- (rabbit IgG) coupled to colloidal gold. In control cells, most of the gold label was found in lysosomes, associated with the membrane. Labelling of the rough endoplasmic reticulum (RER) and Golgi complex was also observed. In fibroblasts from three Gaucher's disease patients without neurological symptoms (type 1 disease), a near normal amount of cross-reactive material (CRM) was detected in lysosomes, but in a fourth such patient, the lysosomal CRM was reduced. Little lysosomal glucocerebrosidase was detected in cells from patients with the acute neuronopathic form (type 2) or the subacute neuronopathic form (type 3) of Gaucher's disease. CRM in lysosomes correlates with amount of mature, 59 kDA glucocerebrosidase which is undetectable in type 2 and type 3 Gaucher's disease cell lines. These findings demonstrate that different mutations in the gene for glucocerebrosidase result in mutant proteins that have different intracellular localizations. They also suggest that there is a relationship between the amount of cross-reactive material in the lysosomes and the phenotypic expression of the disease.
Cell Line↗
Breakdown of lysosomal glycogen in cultured fibroblasts from glycogenosis type II patients after uptake of acid alpha-glucosidase.
Fibroblast cultures from patients with different clinical subtypes of glycogenosis type II were compared with respect to residual acid alpha-glucosidase activity and lysosomal glycogen content. Lysosomal glycogen storage was most pronounced in fibroblasts from patients with the rapidly progressive infantile form of the disease, and the most severe enzyme deficiency. In fibroblasts from adult patients with more than 10% of the control activity storage did not occur, and 15% of the total cellular glycogen was found in the lysosomes as in control cells. The strict correlation between residual acid alpha-glucosidase activity and lysosomal glycogen accumulation was further illustrated in two adult Pompe patients with an unusually low enzyme activity. The mild clinical course is unexplained in these particular cases. The enzyme deficiency in all the different mutant cell lines was corrected by the uptake of bovine testis acid alpha-glucosidase from the culture medium. As a result of this, the lysosomal glycogen storage disappeared, and the balance between lysosomal and cytoplasmic glycogen was restored to normal. The implications of this study as a model for enzyme replacement therapy are discussed.
Cell Fractionation↗
Clinical diversity in glycogenosis type II. Biosynthesis and in situ localization of acid alpha-glucosidase in mutant fibroblasts.
The molecular basis of clinical diversity in glycogenosis type II (Pompe's disease) was investigated by comparing the nature of acid alpha-glucosidase deficiency in cultured fibroblasts from 30 patients. Biosynthetic forms of acid alpha-glucosidase with different molecular mass were separated electrophoretically and identified by immunoblotting. Immuno-electron microscopy was employed to determine the intracellular localization of mutant enzyme. Our studies illustrate that maturation of acid alpha-glucosidase is associated with transport to the lysosomes. Deficiency of catalytically active mature enzyme in lysosomes is common to all clinical phenotypes but, in the majority of cases, is more profound in early onset than in late onset forms of the disease. Thus, the results suggest that the clinical course of glycogenosis type II is primarily determined by the amount of functional acid alpha-glucosidase. The role of secondary factors can, however, not be excluded because three adult patients were identified with very low activity and little enzyme in the lysosomes.
Adult↗