Systemic Hyperosmolality Improves β-Glucuronidase Distribution and Pathology in Murine MPS VII Brain Following Intraventricular Gene Transfer

Abstract

Mucopolysaccharidosis VII, a classical lysosomal storage disease, is caused by deficiency of the enzyme β-glucuronidase. Central nervous system (CNS) manifestations are severe with accumulations of storage vacuoles in all cell types. Intraventricular gene transfer can lead to transduction of the ependyma, with production and secretion of β-glucuronidase into the cerebral spinal fluid and underlying cortex resulting in reversal of disease pathology restricted to the periventricular areas. We tested if systemic hyperosmolality would increase the distribution of β-glucuronidase in brain parenchyma after intraventricular virus injection. Mice were administered mannitol, intraperitoneally, 20 days after gene transfer and 1 day prior to sacrifice. Mannitol-induced systemic hyperosmolality caused a marked penetration of β-glucuronidase into the brain parenchyma. If mannitol was administered at the time of the intraventricular injection of virus, there was penetration of vector across the ependymal cell layer, with infection of cells in the subependymal region. This also resulted in increased β-glucuronidase activity throughout the brain. Sections of brains from β-glucuronidase-deficient mice showed correction of cellular pathology in the subependymal region plus cortical structures away from the ventricular wall. These data indicate that virus-mediated gene transfer to the brain via the ventricles, coupled with systemic mannitol administration, can lead to extensive CNS distribution of β-glucuronidase with concomitant correction of the storage defect. Our findings have positive therapeutic implications for the treatment of CNS disorders with gene transfer vectors and recombinant proteins.