Aspartylglucosaminidase (AGA) is efficiently produced and endocytosed by glial cells: implication for the therapy of a lysosomal storage disorder.

Abstract

Aspartylglucosaminuria (AGU) represents diseases affecting the central nervous system and is caused by a deficiency of a lysosomal enzyme, aspartylglucosaminidase (AGA). AGA, like lysosomal enzymes in general, are good targets for gene therapy since they move from cell to cell using the mannose-6-phosphate receptor. Consequently, only a minority of target cells need to be corrected. Here, we wanted to determine which cell type, neurons or glia would better produce AGA to be transported to adjacent cells for use in possible treatment strategies. Adenoviruses containing tissue-specific glial fibrillary acidic protein (GFAP) promoter and neuron-specific enolase (NSE) promoter were generated to target expression of AGA in Aga-deficient mouse primary glial and neuronal cell cultures. In addition an endogenous AGA promoter was used. The experimental design was planned to measure the enzymatic activities in the cells and media of neurons and glia infected with each specific virus. The endocytosis of AGA was analyzed by incubating neuronal and glial cells with media produced by each virus-cell combination. AGA promoter was shown to be a very powerful glia promoter producing 32 times higher specific AGA activity in glia than in neurons. GFAP and NSE promoters also produced a clear overexpression of AGA in glia and neurons, respectively. Interestingly, both the NSE and GFAP promoters were not cell-specific in our system. The amount of exocytosed AGA was significantly higher in glial cells than neurons and glial cells were also found to have a greater capacity to endocytose AGA. These data indicate the importance of glial cells in the expression and transport of AGA. Subsequently, new approaches can be developed for therapeutic intervention.