Extensive beta-glucuronidase activity in murine central nervous system after adenovirus-mediated gene transfer to brain

Mucopolysaccharidosis type VII (MPS VII), caused by beta-glucuronidase deficiency, is a classic lysosomal storage disease. In the central nervous system (CNS), there is widespread pathology with distention of vacuoles in neurons and glia. An approach to therapy for MPS VII would require extensive delivery of enzyme to the CNS and subsequent uptake by the affected cells. In this study we show that intrastriatal injection of recombinant adenovirus encoding beta-glucuronidase (Ad betagluc) to MPS VII or wild-type mice results in focal, intense beta-glucuronidase mRNA expression near the injection site. Further, histochemical staining for enzyme activity showed that beta-glucuronidase activity extended well beyond transduced cells. Activity was detected throughout the ipsilateral striatum as well as in the corpus callosum, ventricles, and bilateral neocortex. Similarly, after injection into the right lateral ventricle or cisterna magna, enzyme activity was present in the ependymal cells of the ventricles, in the subarachnoid spaces, and also in the underlying cortex (150-500 microm from ependyma). The distribution of enzyme was most extensive 21 days after gene transfer to normal mouse brain, with more than 50% of the hemisphere positive for beta-glucuronidase activity. Eighty-four days after adenovirus injection a substantial level of enzyme expression remained (>40% of hemisphere positive for beta-glucuronidase activity). Histological sections from striatum of beta-glucuronidase-deficient mice injected with Ad betagluc showed a marked reduction in the number of distended vacuoles in both neurons and glia, as compared with uninjected striatum. Importantly, correction was noted in both hemispheres. Our finding that a relatively small number of transduced cells produce enzyme that reaches a large proportion of the CNS has favorable implications in developing direct gene transfer therapies for lysosomal storage disorders.