Application of a GM1 ganglioside beta-galactosidase microassay method to diagnosis of GM1 gangliosidosis

Abnormal cross-talk between mutant presenilin 1 (I143T, G384A) and glycosphingolipid biosynthesis

Mutations in the presenilin 1 (PS1) gene are associated with early onset familial Alzheimer's disease (FAD). In this study, we found that the expression of mutant-PS1 in stable transfectants of SH-SY5Y neuroblastoma cells results in a reduction of the biosynthesis and steady-state levels of glucosylceramide. As an in vivo corroboration of these data, there was a significant reduction of brain glucosylceramide and gangliosides in an animal model of FAD. In mutant-PS1-transfectants (I143T, G384A), immunocytochemistry disclosed a remarkable reduction of glucosylceramide synthase (GlcT-1)-like immunoreactivity in the cells when compared with those of mock- and wild-PS1 transfectants. Immunoprecipitation of GlcT-1 protein from mutant-PS1 transfectants demonstrated a marked reduction in GlcT-1 protein, but there was no reduction in the levels of GlcT-1 mRNA. Both coprecipitation and γ-secretase inhibition experiments suggest that mutant-PS1 seems to form a complex with GlcT-1 protein and to be involved in GlcT-1 degradation, which was never found in other cell types. Thus, mutations in the PS1 gene result in profound glycosphingolipids abnormalities by abnormal molecular interaction with GlcT-1.

Effect of collection, transport, processing and storage of blood specimens on the activity of lysosomal enzymes in plasma and leukocytes

This study was designed to evaluate the effect of different conditions of collection, transport and storage on the quality of blood samples from normal individuals in terms of the activity of the enzymes ss-glucuronidase, total hexosaminidase, hexosaminidase A, arylsulfatase A and ss-galactosidase. The enzyme activities were not affected by the different materials used for collection (plastic syringes or vacuum glass tubes). In the evaluation of different heparin concentrations (10% heparin, 5% heparin, and heparinized syringe) in the syringes, it was observed that higher doses resulted in an increase of at least 1-fold in the activities of ss-galactosidase, total hexosaminidase and hexosaminidase A in leukocytes, and ss-glucuronidase in plasma. When the effects of time and means of transportation were studied, samples that had been kept at room temperature showed higher deterioration with time (72 and 96 h) before processing, and in this case it was impossible to isolate leukocytes from most samples. Comparison of heparin and acid citrate-dextrose (ACD) as anticoagulants revealed that ss-glucuronidase and hexosaminidase activities in plasma reached levels near the lower normal limits when ACD was used. In conclusion, we observed that heparin should be used as the preferable anticoagulant when measuring these lysosomal enzyme activities, and we recommend that, when transport time is more than 24 h, samples should be shipped by air in a styrofoam box containing wet ice.

Purification and characterization of human liver beta-galactosidase from a patient with the adult form of GM1 gangliosidosis and a normal control

beta-Galactosidases were purified to homogeneity from livers of a normal control and a patient with the adult form of GM1 gangliosidosis. The purification was achieved by chromatography on DEAE-Sepharose fast flow, Con A-Sepharose, p-aminophenyl-1-thio-beta-D-galactopyranoside-Sepharose, and QAE-Mono Q. The normal and mutant enzymes were purified about 5000-fold with a yield of 10% and 1800-fold with a yield of 34%, respectively, and could hydrolyze 4-methylumbelliferyl-beta-D-galactoside, GM1 ganglioside, and asialofetuin. The purified normal enzyme was eluted from a TSK gel G-4000SW column as three symmetrical peaks of protein which were coincident with the three peaks of enzyme activity. The enzyme in these three peaks had apparent molecular weights of 800,000 (polymer), 140,000 (dimer), and 65,000 (monomer), whereas the mutant enzyme was eluted as two symmetrical peaks of protein and enzyme activity. The apparent molecular weight of a major monomeric form of the enzyme (beta-galactosidase A) was 60,000, and no dimeric form of the enzyme existed. Normal and mutant purified enzyme preparations migrated as a single major protein band with apparent molecular weights of 65,000 or 60,000, respectively, by SDS-polyacrylamide gel electrophoresis after treatment with mercaptoethanol. On isoelectric focussing, the mutant enzyme migrated more anodally than the normal enzyme. The mutant enzyme also had altered enzyme properties, such as pH optimum, Km values, substrate specificity and heat-stability. These data on the characteristics of the purified enzyme preparations provide the first direct evidence that patients with the adult form of GM1 gangliosidosis have a structurally altered beta-galactosidase.

A microassay for acid beta-galactosidase activity toward asialofetuin

To study the enzymatic properties of beta-galactosidase from the patients with a beta-galactosidase deficiency such as GM1 gangliosidosis, determination of enzymatic activity with naturally occurring substrates, asialofetuin in addition to another natural substrate, GM1 ganglioside, is essentially required. With a previously reported, simple and sensitive fluorometric assay for GM1 ganglioside beta-galactosidase using high performance liquid chromatography (HPLC), optimal reaction conditions were determined for the assay of acid beta-galactosidase activity toward asialofetuin in skin fibroblast homogenates. Under these conditions, reduced enzymatic activities could be detected in cultured skin fibroblasts from patients with type 1 and 3 GM1 gangliosidoses and mucopolysaccharidosis IV-B (Morquio B syndrome). This method was applicable to study of the enzymatic properties of the mutant beta-galactosidase and provided an alternative to assays employing radioactive or artificial substrates.