Correction of AB Variant GM2 Gangliosidoses Using AAV9 Viral Vector Gene Therapy in a Mouse Model
GM2 Gangliosidoses are a group of neurodegenerative diseases affecting the brain. In humans, these diseases are characterized by rapid neurological deterioration and death before 4-years of age. GM2 gangliosides are normally degraded in a cell’s lysosomes through the action of three gene products, HEXA, HEXB, and GM2A. A defect in any one of these genes can result in a deficiency of Hexosaminidase A (HexA) enzyme activity, which then cannot breakdown GM2 gangliosides. The rarest form of these diseases, the AB-variant (AB- GM2), is characterized by a mutation in the GM2A gene encoding the GM2-activator protein (GM2AP), which is a required co-factor for the HexA protein. The aim of this study is to give a one-time treatment of single stranded (ss) AAV9/GM2A viral vector therapy at a dose of 1 x 1014 vector genomes per kilogram of mouse and to see at least biochemical reduction in GM2 ganglioside storage in both the short- and long-term treated cohorts. ssAAV9/GM2A plasmid was created and tested in vitro on a GM2AP-deficient patient cell line to confirm the expression of the protein using Western Blot analysis. Later, treatments were given to 1-day old pups via the superficial temporal vein, as well as 6-week old adult mice via tail vein, to correct AB- GM2. These mice underwent monthly behavioural testing, as well as biochemical and molecular analysis performed at 20- and 60-week end-points. We hypothesized that an optimized ssAAV9/GM2A treatment can correct the gene mutation as well as phenotype of AB- GM2 in mice. Biochemical data for both end-points showed reduction in GM2 gangliosides storage in the treated cohorts compared to the vehicle cohorts for both the neonatal and adult treated cohorts. Behavioural data for the 20- and 60-week end-points, as well as the neonatal treated and adult treated mice, showed the treated cohorts inconsistently outperformed the vehicle cohorts. Almost uniform biodistribution of the hGM2AP vector was also seen across the rostral section, caudal section, mid-section and liver. This proof of concept study is a step forward towards the development of a therapeutic approach for AB-GM2 and towards our goal of human clinical gene therapy trials.