Mice Doubly-Deficient in Lysosomal Hexosaminidase A and Neuraminidase 4 Show Epileptic Crises and Rapid Neuronal Loss

Abstract

Tay-Sachs disease is a severe lysosomal disorder caused by mutations in the HexA gene coding for the α-subunit of lysosomal β-hexosaminidase A, which converts GM2 to GM3 ganglioside. Hexa−/− mice, depleted of β-hexosaminidase A, remain asymptomatic to 1 year of age, because they catabolise GM2 ganglioside via a lysosomal sialidase into glycolipid GA2, which is further processed by β-hexosaminidase B to lactosyl-ceramide, thereby bypassing the β-hexosaminidase A defect. Since this bypass is not effective in humans, infantile Tay-Sachs disease is fatal in the first years of life. Previously, we identified a novel ganglioside metabolizing sialidase, Neu4, abundantly expressed in mouse brain neurons. Now we demonstrate that mice with targeted disruption of both Neu4 and Hexa genes (Neu4 −/−;Hexa −/−) show epileptic seizures with 40% penetrance correlating with polyspike discharges on the cortical electrodes of the electroencephalogram. Single knockout Hexa −/− or Neu4 −/− siblings do not show such symptoms. Further, double-knockout but not single-knockout mice have multiple degenerating neurons in the cortex and hippocampus and multiple layers of cortical neurons accumulating GM2 ganglioside. Together, our data suggest that the Neu4 block exacerbates the disease in Hexa−/− mice, indicating that Neu4 is a modifier gene in the mouse model of Tay-Sachs disease, reducing the disease severity through the metabolic bypass. However, while disease severity in the double mutant is increased, it is not profound suggesting that Neu4 is not the only sialidase contributing to the metabolic bypass in Hexa −/− mice.

Neuraminidases 3 and 4 regulate neuronal function by catabolizing brain gangliosides

“…9A–D). The inclusions were membrane‐bound structures containing whorls of membranes, typical of lysosomes with sphingolipid storage disorders (25). The number of affected neurons was lower in the brains of neu4 ‒ / ‒ mice [0.37 ± 0.17 (SEM) per frame] and higher in the brains of the neu3 ‒ / ‒ (2.0 ± 0.28 per frame] and neu3 ‒ / ‒ neu4 ‒ / ‒ mice (2.46 ± 0.29 per frame).…”

Sialidase NEU4 Hydrolyzes Polysialic Acids of Neural Cell Adhesion Molecules and Negatively Regulates Neurite Formation by Hippocampal Neurons

“…In mouse, sialidase NEU4 is dominantly expressed in the brain (25,26), and whereas NEU4-deficient mice lack apparent pathological changes or behavioral deficits reflective of neuronal abnormalities, their ganglioside pattern in the brain features increased GD1a and decreased GM1 (41). In addition, mice with a double deficiency of NEU4 and ␤-hexosaminidase A exhibit epileptic seizures and rapid neuronal loss accompanied by GM2 accumulation (42). Although only a lack of NEU4 does not seem to apparently lead to abnormal expression of polySia-NCAM, the detailed observations on this point would be necessary in future.…”

Mice with Catalytically Inactive Cathepsin A Display Neurobehavioral Alterations

“…The test was conducted as previously described [13]. Mice first received a 3-day habituation period requiring them to swim (60 s) to a visible platform located in a circular tank (diameter, 140 cm; depth, 45 cm) filled with water (22°C) made opaque with powdered milk.…”