The potential action of galactose as a "chemical chaperone": increase of beta galactosidase activity in fibroblasts from an adult GM1-gangliosidosis patient.

BACKGROUND: The glycosphingolipid storage disorder GM1-gangliosidosis is a severe neurodegenerative condition for which no therapy is currently available. Protein misfolding in lysosomal defects may have the potential to be corrected by chemical chaperones: in vitro and clinical approaches are being investigated.

AIMS: We investigated the in vitro effect of galactose on some lysosomal hydrolases, and its in vitro efficacy as a chemical chaperone in GM1-gangliosidosis.

METHODS: Galactose was added to the culture medium of fibroblasts from patients, controls and transfected COS-1 cells. Enzyme assays of lysosomal hydrolases, beta galactosidase in particular, were performed.

RESULTS: Our data show that galactose alters selectively alpha and beta galactosidases. A significant increase (2,5 fold) in beta galactosidase activity occurred when galactose was added to the cultured fibroblasts of an adult patient. Chemical chaperone therapy requires the presence of residual enzyme activity. The adult patient here reported is heterozygous for the p.T329A mutation that showed no beta galactosidase activity, and for the p.R442Q mutation with residual enzyme activity. The p.R442Q mutation was therefore selected as a potential target for the galactose chaperone; after the addition of galactose, COS-1 cells transfected with this mutation showed an increase in beta galactosidase activity from 6.9% to 12% of control values.

CONCLUSIONS: These results suggest that galactose or its derivatives with potential chaperone properties could be used in the development of non-invasive therapies for GM1-gangliosidosis.