AAV-Mediated Gene Delivery in a Feline Model of Sandhoff Disease Corrects Lysosomal Storage in the Central Nervous System

Abstract

Sandhoff disease (SD) is an autosomal recessive neurodegenerative disease caused by a mutation in the gene for the β-subunit of β-N-acetylhexosaminidase (Hex), resulting in the inability to catabolize ganglioside GM2 within the lysosomes. SD presents with an accumulation of GM2 and its asialo derivative GA2, primarily in the central nervous system. Myelin-enriched glycolipids, cerebrosides and sulfatides, are also decreased in SD corresponding with dysmyelination. At present, no treatment exists for SD. Previous studies have shown the therapeutic benefit of adeno-associated virus (AAV) vector-mediated gene therapy in the treatment of SD in murine and feline models. In this study, we treated presymptomatic SD cats with AAVrh8 vectors expressing feline Hex in the thalamus combined with intracerebroventricular (Thal/ICV) injections. Treated animals showed clearly improved neurologic function and quality of life, manifested in part by prevention or attenuation of whole-body tremors characteristic of untreated animals. Hex activity was significantly elevated, whereas storage of GM2 and GA2 was significantly decreased in tissue samples taken from the cortex, cerebellum, thalamus, and cervical spinal cord. Treatment also increased levels of myelin-enriched cerebrosides and sulfatides in the cortex and thalamus. This study demonstrates the therapeutic potential of AAV for feline SD and suggests a similar potential for human SD patients.

AAV-mediated gene delivery attenuates neuroinflammation in feline Sandhoff disease

“…Previous reports showed that all treated cats had clearly preserved neurologic function and improved disease phenotype, though mild symptoms such as fine tremors and slight hind limb weakness were present. Also, previously published postmortem analysis revealed above-normal levels of Hex activity throughout the brain and spinal cord, with clearance of GM2 ganglioside storage (McCurdy et al, 2015, Rockwell et al, 2015). Microglia from treated cats retained a ramified morphology and lacked expression of MHC-II in regions of cleared storage such as the thalamus (Fig.…”

“…Seven SD cats were treated with monocistronic AAVrh8 vectors encoding feline HEX α and β subunits between 4-7 weeks of age, prior to symptom onset. Two treatment cohorts were based on injection route: bilateral thalamic and DCN injection (n=3) (McCurdy et al, 2015) or bilateral thalamic and unilateral ICV injection (n=4) (Rockwell et al, 2015) (Table 1). Treated SD cats were euthanized 16 weeks after injection, an age comparable to the humane endpoint of untreated SD cats.…”

“…Treatment dramatically ameliorated clinical signs of disease, with cats demonstrating slight hind limb weakness and whole-body tremors that were mild (Thal+ICV) (Rockwell et al, 2015) or nonexistent (Thal+DCN) (McCurdy et al, 2015). The current report extends previous findings by showing that SD cats treated with AAV had marked attenuation of microglia activation, with a ramified morphology and lack of MHC-II expression, in areas of GM2 ganglioside clearance.…”

“…AAV vectors encoding feline α and β Hex subunits were injected bilaterally into the thalamus of SD cats, which reduced the immune response and increased survival to 10.4 ± 3.7 months of age, or > 2 times that of untreated cats (Bradbury et al, 2013). Further studies were conducted combining thalamic infusion with additional delivery routes such as bilateral injection into the deep cerebellar nuclei (DCN) (McCurdy et al, 2015), or intracerebroventricular (ICV) injection (Rockwell et al, 2015). Restoration of Hex activity, clearance of storage material, and a panel of biomarkers from combined delivery routes have been reported elsewhere (Bradbury et al, 2015, McCurdy et al, 2015, Rockwell et al, 2015).…”

“…Further studies were conducted combining thalamic infusion with additional delivery routes such as bilateral injection into the deep cerebellar nuclei (DCN) (McCurdy et al, 2015), or intracerebroventricular (ICV) injection (Rockwell et al, 2015). Restoration of Hex activity, clearance of storage material, and a panel of biomarkers from combined delivery routes have been reported elsewhere (Bradbury et al, 2015, McCurdy et al, 2015, Rockwell et al, 2015). In the current study, we analyze the effect of intracranial gene therapy with thalamus + DCN and thalamus + ICV injection routes on the neuroinflammatory response in SD.…”