Natural history study of glycan accumulation in large animal models of GM2 gangliosidoses

beta-hexosaminidase is an enzyme responsible for the degradation of gangliosides, glycans, and other glycoconjugates containing beta-linked hexosamines that enter the lysosome. GM2 gangliosidoses, such as Tay-Sachs and Sandhoff, are lysosomal storage disorders characterized by beta-hexosaminidase deficiency and subsequent lysosomal accumulation of its substrate metabolites. These two diseases result in neurodegeneration and early mortality in children. A significant difference between these two disorders is the accumulation in Sandhoff disease of soluble oligosaccharide metabolites that derive from N- and O-linked glycans. In this paper we describe our results from a longitudinal biochemical study of a feline model of Sandhoff disease and an ovine model of Tay-Sachs disease to investigate the accumulation of GM2/GA2 gangliosides, a secondary biomarker for phospholipidosis, bis-(monoacylglycero)-phosphate, and soluble glycan metabolites in both tissue and fluid samples from both animal models. While both Sandhoff cats and Tay-Sachs sheep accumulated significant amounts of GM2 and GA2 gangliosides compared to age-matched unaffected controls, the Sandhoff cats having the more severe disease, accumulated larger amounts of gangliosides compared to Tay-Sachs sheep in their occipital lobes. For monitoring glycan metabolites, we developed a quantitative LC/MS assay for one of these free glycans in order to perform longitudinal analysis. The Sandhoff cats showed significant disease-related increases in this glycan in brain and in other matrices including urine which may provide a useful clinical tool for measuring disease severity and therapeutic efficacy. Finally, we observed age-dependent increasing accumulation for a number of analytes, especially in Sandhoff cats where glycosphingolipid, phospholipid, and glycan levels showed incremental increases at later time points without signs of peaking. This large animal natural history study for Sandhoff and Tay-Sachs is the first of its kind, providing insight into disease progression at the biochemical level. This report may help in the development and testing of new therapies to treat these disorders

GM2 Gangliosidosis Natural History Study: Sandhoff Feline and Tay-Sachs Sheep And Evaluation of different bead coupling chemistries for immobilizing GAG chains to produce affinity resins to discover GAG-binding proteins important for neuroregeneration after central nervous system injury

β-N-acetylhexosaminidase B, or just β-hexosaminidase, is an enzyme responsible for the degradation of gangliosides, glycans and other glycoconjugates in the lysosome. The gene HEXA encodes the α-subunit and HEXB encodes the β-subunit of the β-hexosaminidase enzyme which functions as a dimer pair either as a heterodimer, Hex A (αβ), or homodimer, Hex B (ββ) or Hex S (αα). GM2 gangliosidoses, like Tay-Sachs and Sandhoff, are lysosomal storage diseases characterized by a disruption in the β-hexosaminidase genes. The loss of β-hexosaminidase activity results in the toxic accumulation of substrate metabolites. Tay-Sachs is caused by a disruption in the HEXA gene causing a deficiency in the Hex A enzyme. Sandhoff, is due to a disruption in the HEXB gene causing a deficiency in the Hex A and Hex B enzymes. Both diseases accumulate GM2 gangliosides, but Sandhoff accumulates free oligosaccharides as well because the β-subunit is required for their degradation. Ganglioside and glycan levels in both tissues and biological fluids from two large animal models, Sandhoff feline and Tay-Sachs sheep, were longitudinally examined for a natural history study. Sandhoff cats accumulated the same amount of gangliosides as the Tay-Sachs sheep, but at a much quicker rate, and accumulated glycan metabolites. This large animal natural history for Sandhoff and Tay-Sachs gives more insight into the progression of these diseases at the biochemical level. These results are more relevant to humans compared to other animal models because of their similarities to human pathology and thus, may help in the development of new therapeutics to treat these and similar disorders