Massive accumulation of Man2GlcNAc2-Asn in nonneuronal tissues of glycosylasparaginase-deficient mice and its removal by enzyme replacement therapy.

Aspartylglycosaminuria (AGU) is caused by deficient enzymatic activity of glycosylasparaginase (GA). The disease is characterized by accumulation of aspartylglucosamine (GlcNAc-Asn) and other glycoasparagines in tissues and body fluids of AGU patients and in an AGU mouse model. In the current study, we characterized a glycoasparagine carrying the tetrasaccharide moiety of alpha-D-Man-(1-->6)-beta-D-Man-(1-->4)-beta-D-GlcNAc-(1-->4)-beta-D-GlcNAc-(1-->N)-Asn (Man2GlcNAc2-Asn) in urine of an AGU patient and also in the tissues of the AGU mouse model. Quantitative analysis demonstrated a massive accumulation of the compound especially in nonneuronal tissues of the AGU mice, in which the levels of Man2GlcNAc2-Asn were typically 30-87% of those of GlcNAc-Asn. The highest level of Man2GlcNAc2-Asn was found in the liver, spleen, and heart tissues of the AGU mice, the respective amounts being 87%, 76%, and 57% of the GlcNAc-Asn levels. In the brain tissue of AGU mice the Man2GlcNAc2-Asn storage was only 9% of that of GlcNAc-Asn. In contrast to GlcNAc-Asn, the storage of Man2GlcNAc2-Asn markedly increased in the liver and spleen tissues of AGU mice as they grew older. Enzyme replacement therapy with glycosylasparaginase for 3.5 weeks reduced the amount of Man2GlcNAc2-Asn by 66-97% in nonneuronal tissues, but only by 13% in the brain tissue of the AGU mice. In conclusion, there is evidence for a role for storage of glycoasparagines other than aspartylglucosamine in the pathogenesis of AGU, and this possibility should be taken into consideration in the treatment of the disease.

Enzyme replacement therapy in a mouse model of aspartylglycosaminuria.

Aspartylglycosaminuria (AGU), the most common lysosomal disorder of glycoprotein degradation, is caused by deficient activity of glycosylasparaginase (AGA). AGA-deficient mice share most of the clinical, biochemical and histopathologic characteristics of human AGU disease. In the current study, recombinant human AGA administered i.v. to adult AGU mice disappeared from the systemic circulation of the animals in two phases predominantly into non-neuronal tissues, which were rapidly cleared from storage compound aspartylglucosamine. Even a single AGA injection reduced the amount of aspartylglucosamine in the liver and spleen of AGU mice by 90% and 80%, respectively. Quantitative biochemical analyses along with histological and immunohistochemical studies demonstrated that the pathophysiologic characteristics of AGU were effectively corrected in non-neuronal tissues of AGU mice during 2 wk of AGA therapy. At the same time, AGA activity increased to 10% of that in normal brain tissue and the accumulation of aspartylglucosamine was reduced by 20% in total brain of the treated animals. Immunohistochemical studies suggested that the corrective enzyme was widely distributed within the brain tissue. These findings suggest that AGU may be correctable by enzyme therapy.-Dunder, U., Kaartinen, V., Valtonen, P., Väänänen, E., Kosma, V.-M., Heisterkamp, N., Groffen, J., Mononen, I. Enzyme replacement therapy in a mouse model of aspartylglycosaminuria.

Recombinant glycosylasparaginase and in vitro correction of aspartylglycosaminuria.

Aspartylglycosaminuria (AGU) is the most common disorder of glycoprotein degradation. AGU patients are deficient in glycosylasparaginase (GA), which results in accumulation of aspartylglucosamine in body fluids and tissues. Human glycosylasparaginase was stably overexpressed in NIH-3T3 mouse fibroblasts, in which the unusual posttranslational processing and maturation of the enzyme occurred in a high degree. The recombinant enzyme was isolated as two isoforms, which were both phosphorylated, and actively transported into AGU fibroblasts and lymphoblasts through mannose-6-phosphate receptor-mediated endocytosis. The rate of uptake into fibroblasts was half-maximal when the concentration of GA in the medium was 5 x 10(-8) M. Immunofluorescence microscopy suggested compartmentalization of the recombinant enzyme in the lysosomes. Supplementation of culture medium with either isoform cleared AGU lymphoblasts of stored aspartylglucosamine when glycosylasparaginase activity in the cells reached 3-4% of that in normal lymphoblasts. A relatively small amount of recombinant GA in the culture medium was sufficient to reverse pathology in the target cells, indicating high corrective quality of the enzyme preparations. The combined evidence indicates that enzyme replacement therapy with the present recombinant glycosylasparaginase might reverse pathology at least in somatic cells of AGU patients.