Mutations in the lysosomal
acid beta-galactosidase (EC 3.2.1.23) underlie two different disorders:
GM1 gangliosidosis, which involves the nervous system and visceral organs to varying extents, and
Morquio's syndrome type B (
Morquio B disease), which is a skeletal-
connective tissue disease without any CNS symptoms. This article shows that transduction of human
GM1 gangliosidosis fibroblasts with retrovirus vectors encoding the human
acid beta-galactosidase cDNA leads to complete correction of the enzymatic deficiency. The newly synthesized
enzyme is correctly processed and targeted to the lysosomes in transduced cells. Cross-correction experiments using retrovirus-modified cells as
enzyme donors showed, however, that the human
enzyme is transferred at low efficiencies. Experiments using a different retrovirus vector carrying the human
cDNA confirmed this observation. Transduction of human GM1 fibroblasts and mouse NIH 3T3 cells with a retrovirus vector encoding the mouse
beta-galactosidase cDNA resulted in high levels of enzymatic activity. Furthermore, the mouse
enzyme was found to be transferred to human cells at high efficiency.
Enzyme activity measurements in
medium conditioned by genetically modified cells suggest that the human
beta-galactosidase enzyme is less efficiently released to the extracellular space than its mouse counterpart. This study suggests that lysosomal
enzymes, contrary to the generalized perception in the field of gene therapy, may differ significantly in their properties and provides insights for design of future gene therapy interventions in
acid beta-galactosidase deficiency.