Neuronal lysosomal enzyme replacement using fragment C of tetanus toxin.

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Abstract
Development of a strategy for efficient delivery of exogenous enzyme to neuronal lysosomes is essential to achieve enzyme replacement in neurodegenerative lysosomal storage diseases. We tested whether effective lysosomal targeting of the human enzyme beta-N-acetylhexosaminidase A (Hex A; beta-N-acetyl-D-hexosaminide N-acetylhexosaminohydrolase, EC 3.2.1.52) can be obtained by coupling it via disulfide linkage to the atoxic fragment C of tetanus toxin (TTC) that is bound avidly by neuronal membrane. TTC-Hex A conjugation resulted in neuronal surface binding and enhanced endocytosis of enzyme as observed in immunofluorescence studies with rat brain cultures. In immunoelectrophoretic quantitative uptake studies, rat neuronal cell cultures contained 16- and 40-fold greater amounts of enzyme after incubation with TTC-Hex A than with nonderivatized Hex A. In cerebral cortex cell cultures from a feline model of human GM2 gangliosidosis (Tay-Sachs and Sandhoff diseases), binding and uptake patterns of the enzymes were similar to those in the rat brain cell cultures. After exposure to extracellular concentrations of enzyme attainable in vivo, lysosomal storage of immunodetectable GM2 ganglioside was virtually eliminated in neurons exposed to TTC-Hex A, whereas a minimal effect was observed with Hex A. These findings demonstrate the usefulness of TTC adducts for effective neuronal lysosomal enzyme replacement.