Intracerebroventricular enzyme replacement therapy with Beta-Galactosidase reverses brain pathologies due to GM1 gangliosidosis in mice

: Autosomal recessive mutations in the galactosidase beta 1 (GLB1) gene cause lysosomal β-galactosidase (Beta-Gal) deficiency, resulting in accumulation of galactose-containing substrates and onset of the progressive and fatal neurodegenerative lysosomal storage disease, GM1 gangliosidosis. Here, an enzyme replacement therapy (ERT) approach in fibroblasts from GM1 gangliosidosis patients with recombinant human Beta-Gal (rhBeta-Gal) produced in Chinese hamster ovary cells enabled direct and precise rhBeta-Gal delivery to acidified lysosomes. A single, low dose (3 nM) of rhBeta-Gal was sufficient for normalizing Beta-Gal activity and mediating substrate clearance for several weeks. We found that rhBeta-Gal uptake by the fibroblasts is dose dependent and saturable, and can be competitively inhibited by mannose-6-phophate, suggesting cation-independent, mannose-6-phophate receptor-mediated endocytosis from the cell-surface. A single intracerebroventricular (ICV)-administered dose of rhBeta-Gal (100 micrograms) resulted in broad bilateral biodistribution of rhBeta-Gal to critical regions of pathology in a mouse model of GM1 gangliosidosis. Weekly ICV dosing of rhBeta-Gal for 8 weeks substantially reduced brain levels of ganglioside and oligosaccharide substrates and reversed well-established secondary neuropathology. Of note, unlike with the ERT approach, chronic lentiviral-mediated GLB1 overexpression in the GM1 gangliosidosis patient fibroblasts caused accumulation of a prelysosomal pool of Beta-Gal, resulting in activation of the unfolded protein response and endoplasmic reticulum stress. This outcome was unsurprising in light of our in vitro biophysical findings for rhBeta-Gal, which include pH-dependent and concentration-dependent stability and dynamic self-association. Collectively, our results highlight that ICV-ERT is an effective therapeutic intervention for managing GM1 gangliosidosis potentially more safely than with gene therapy approaches.