968. Co-Expression of FGE Is Essential for Gene Therapy of MLD Based on Cross-Correction of ASA Deficiency

Metachromatic leukodystrophy (MLD) is a lysosomal storage disorder with inherited deficiency of arylsulfatase A (ASA). The disease is characterized by progressive demyelination and widespread deposition of sulfatide in both central and peripheral nervous systems. Direct injection of viral vector through the blood brain barrier is a possible approach of gene therapy for MLD. However, to treat a wide area of brain, it is essential to efficiently secrete functional ASA from limited numbers of transduced cells. In this study, we tested the utility of FGE (formylglycine generating enzyme) for over-expression of functional ASA. FGE is a recently identified post-translational modifying enzyme which converts cystein common in the active site of all sulfatases to formylglycine and is thought to be essential for all sulfatases including ASA. COS-7 cells were transfected with the ASA and FGE expression plasmids. ASA activity was increased up to 20 folds in cell lysates and 70 folds in conditioned media by co-expression of FGE. When the expression plasmids were injected into the MLD knock-out mice by the hydrodynamics-based procedure, a striking synergistic increase of ASA activity was also observed in both liver and serum. Blot hybridization analysis of FGE mRNA demonstrated that expression of endogenous FGE is particularly low in human brain. These results suggest that co-expression of FGE and ASA should be essential for gene therapy of MLD targeted whole brain.