Long Term Correction of GM2 Gangliosidoses in Sandhoff Mice Through Intravenous Neonatal Gene Therapy, Using a Recombinant Adeno-Associated Viral Vector Expressing a New Hexosaminidase Variant
Sandhoff Disease , GM2 Gangliosidoses , Tay-Sachs Disease , Hexosaminidase , Gene Therapy , AAV Adeno-Associated Virus
GM2 gangliosidoses are a group of neurodegenerative disorders, characterized by the malfunctioning β-Hexosaminidase A (HexA) enzyme, for which there is no current treatment. HexA is composed of two similar, non-identical subunits, the alpha and the beta, which must interact with the GM2 activator protein, a substrate-specific co-factor, to hydrolyze GM2 gangliosides. Mutations in either subunit (or the activator) result in the development of GM2 gangliosidoses due to the toxic accumulation of GM2 gangliosides, within the neurons of the central nervous system. The resulting neuronal death induces the primary symptoms of the disease; motor and sensory impairments, and seizures. The aim of this study was to observe the long-term in vivo effects of an innovative gene therapy treatment method in a Sandhoff (β-subunit deficient) mouse model. The treatment utilized a new engineered variant of Hexosaminidase isoenzyme, HexM, which is formed by the homodimerization of a modified human Hex α-subunit called Hex µ, which contains critical beta-components that allow it to form stable homodimers and interact with the GM2 activator protein to reduce substrate storage. We tested this scAAV vector expressing HexM through intravenous injections of the neonatal mice. Previous work on a systemic gene therapy treatment saw drastic increases in lifespan to approximately 43 weeks in the Sandhoff mice using a beta-subunit treatment. We monitored one cohort for 8 weeks and another cohort long-term (>40 weeks) for biochemical, behavioural and molecular analyses. Through the enzymatic and GM2 ganglioside lipid analyses, we observed that with a slight non-significant increase in enzyme activity, there is a significant decrease in the storage of GM2 gangliosides. On behavioural tests, the treated mice outperform their knockout age matched controls and perform similarly to the heterozygous controls. While the untreated controls were humanely euthanized by 16 weeks, the treated animals have survived significantly longer, to an average of 41 weeks. The molecular analyses revealed a slightly variable distribution of the vector between brain and spinal cord regions. In conclusion, the neonatal delivery of our newly synthesized viral vector expressing HexM to the Sandhoff mice provided long-term correction of the disease. This study will have implications not only for treatment of Sandhoff disease, but also Tay-Sachs disease (α- subunit deficiency).