CNS gene therapy for lysosomal storage diseases

Lysosomal storage diseases (LSDs) are a group of inherited metabolic disorders due to deficiency of one or more lysosomal enzymes. Over 40 LSDs have been identified and 65% of them have central nervous system (CNS) involvements. In this study, we investigated the feasibility of Adeno-associated virus (AAV) type 4 and 5 in mediating functional CNS therapy using a murine model of LSDs, Mucopolysaccharidosis type VII (MPS VII) which is caused by beta-glucuronidase deficiency.; We show that AAV4 had unique ependymal tropism independent of delivery route. However, AAV4 did not target endogenous neuroprogenitor cells (NPCs), which made AAV4 mediated stem cell therapy unlikely. Activity of beta-glucuronidase following intraventricular injection of AAV4beta-gluc distributed well beyond the transduced ependyma and was sufficient for global correction of lysosomal storage. Our evidence suggests that circulating CSF in the ventricular system and perivascular spaces delivered secreted beta-glucuronidase throughout the brain. Pathological improvement due to improved enzyme levels was pervasive as early as 4 weeks after AAv4beta-gluc treatment and persisted for at least 8 months post-injection. We also examined the beta-glucuronidase distribution pattern following bilateral intrastriatal injection of AAV5beta-gluc. Robust enzyme activity was detected in various brain regions including the hippocampus and cerebral cortex at 8 weeks after gene transfer. Accordingly, resolution of lysosomal storage was observed in those structures. Furthermore, the impaired hippocampus-dependent spatial learning in MPS VII mice, measured by repeated acquisition and performance chamber (RAPC), was reversed upon delivery of AAV5beta-gluc.; MPS VII mice have severe systemic disease, which prevents adult mice from performing in some behavioral assays and complicated data interpretation. We established context fear conditioning as a measurement for CNS dysfunction in adult MPS VII mice and provide a practical behavioral paradigm for monitoring long-term therapies. Importantly, context fear conditioning deficits in MPS VII mice were corrected at 6 weeks after a single intraventricular injection of AAV4beta-gluc.; In summary, both AAV4 and AAV5 mediated efficient correction of CNS phenotypes in MPS VII mice. Our data suggest that AAV4 and AAV5 are suitable vectors to mediate CNS gene therapy in LSDs.