Non-invasive gene therapy for inherited neurodegenerative disorders (How to cross the BBB?)

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The feasibility of non-invasive gene therapy for inherited neurodegenerative disorders like metachromatic leuko dystrophy (MLD) has been investigated. Mannose-6-phosphate receptor (M6PR) plays important roles in both corss-correction and transcytosis across the blood brain barrier of lysosomal enzymes. M6PR is a multifunctional cell surface receptor which also interacts with insulin-like growth factor II (IGF-II) and is composed of 15 repeated domains. We have cloned 7.6kb M6PR cDNA and constructed a series of minigenes. The 4.8kb minigene containing domain 1 to 9 was shown to bind M6P but not IGF-II. Using a lentiviral vector containing the 4.8kb minigene, M6PR can be expressed in various cell lines and tissues of animal models. M6PR expression vector should be useful for studying subcellular localization and trafficking of lysosomal enzymes and for enhancing the efficacy of enzyme replacement therapy for lysosomal disorders. In an alternative approach, we examined the feasibility of intrathecal (IT) injection of adeno-associated viral vector serotype 1 (AAV1) to treat MLD. AAV1 vector expressing arylsulfatase A (ASA) or green fluorescence protein (GFP) was intrathecally injected into ASA knockout MLD model mice. Broad distribution of GFP expression was seen throughout the brain. In addition, a large number of nerve fibers in the dorsal spinal cord and many neural cell bodies in the dorsal root ganglia were efficiently transduced. Widespread distribution of ASA activity and significant reduction of sulfatide content were confirmed in treated MLD model mice. IT injection of AAV1 vector is a useful and noninvasive method for widespread gene delivery to the brain and dorsal root ganglia.