AAV2-mediated ocular gene therapy for infantile neuronal ceroid lipofuscinosis

Abstract

Infantile neuronal ceroid lipofuscinosis (INCL) is a neurodegenerative disorder caused by mutations in the gene encoding the lysosomal enzyme palmitoyl protein thioesterase-1 (PPT1). The earliest clinical sign in INCL is blindness, followed by seizures, cognitive deficits, and early death. Little is known about the progression of the visual deficits in INCL. Here we characterize the progressive retinal dysfunction and examine the efficacy of AAV2-mediated ocular gene therapy in the murine model of INCL. Significant decreases in both mixed rod/cone and pure cone electroretinographic amplitudes were observed at as early as 2 months of age. Intravitreal injection of AAV2-PPT1 increased enzyme levels in the eye to greater than normal levels. The increased PPT1 activity correlated with improvements in the histological abnormalities as well as both mixed rod/cone and pure cone functions. We also demonstrated that palmitoyl protein thioesterase-1 activity was detected in the brain following intravitreal injection. The brain activity is likely due to anterograde axonal transport along the optic tracts. Interestingly, the degree of neurodegeneration throughout the visual pathways of the brain was greatly reduced in AAV-treated INCL mice. Therefore, intravitreal AAV-mediated gene therapy has direct benefits to the eye and to distal sites in the brain along the visual pathways.

Intracranial Delivery of CLN2 Reduces Brain Pathology in a Mouse Model of Classical Late Infantile Neuronal Ceroid Lipofuscinosis

“…Ecoptic distribution of TPP1 to dendritic structures may be attributable to overabundance of expressed protein in transduced cells. Similarly, viral vector-mediated expression of other lysosomal enzymes resulted in labeling of dendrites and, in some cases, labeling of axonal tracts (Passini et al, 2002;Haskell et al, 2003;Hennig et al, 2003;Griffey et al, 2005;Luca et al, 2005). Consistent with the enzyme activity data (Fig.…”

“…Time points that exceeded 8 months resulted in higher enzyme activity and detection of TPP1 in areas of the brain with synaptic connections to the injection site (Sondhi et al, 2005). Similarly, widespread distribution of palmitoyl protein thioesterase (PPT) in a mouse model of INCL occurred at 7 months after injection (Griffey et al, 2005). These data suggest that distribution of TPP1 (and other NCL enzymes) may be achieved at longer time points but cannot be measured directly in the CLN2 Ϫ/Ϫ mouse model because of the shorter lifespan.…”

“…However, despite these disruptions, many lysosomal enzymes undergo axonal transport to distal locations in disease brain, such as ␤-glucuronidase (Passini et al, 2002;Hennig et al, 2003), arylsulfatase A (Luca et al, 2005), and acid sphingomyelinase Passini et al, 2005). PPT1 is also widely distributed in the INCL mouse, demonstrating that disease-compromised neurons of the Batten brain support axonal transport (Griffey et al, 2005). Although these data provide optimism that axonal transport may be a general property of lysosomal enzymes in affected brain, it still remains to be verified that TPP1 can become distributed through axons of the cLINCL brain.…”

Successive neuron loss in the thalamus and cortex in a mouse model of infantile neuronal ceroid lipofuscinosis

“…To analyze the progression of pathological changes in the Ppt1 −/− deficient CNS, the brains of Ppt1 −/− mice and C57BL/6 controls were harvested at 1, 3, 5 and 7 months of age (n=3 Ppt1 −/− and C57BL/6 control mice at each age). These brains were immersion fixed for at least one week in 4% paraformaldehyde in 0.1 M phosphate-buffered saline, cryoprotected in a solution of 30% sucrose in Tris buffered saline (TBS: 50mM Tris, pH 7.6, 150 mM NaCl) and 40μm frozen coronal sections cut through the rostrocaudal extent of the cortical mantle Griffey et al, 2004Griffey et al, , 2005. Sections were collected one per well into 96 well plates containing a cryoprotectant solution (TBS/ 30% ethylene glycol/ 15% sucrose/ 0.05% sodium azide) and stored at −40°C prior to histological processing.…”

“…However, the precise role of PPT1 in the CNS is uncertain and the mechanisms by which PPT1 deficiency leads to the devastating clinical profile of INCL remains poorly understood. Ppt1 null mutant mice (Ppt1 −/− ) are a valuable tool for investigating these issues and display an INCL-like phenotype with marked neurodegeneration and glial responses, visual, motor and cognitive deficits and the development of spontaneous seizures (Gupta et al, 2001;Griffey et al, 2005Griffey et al, , 2006). …”