Tay-Sachs disease is a severe lysosomal storage disorder caused by mutations in Hexa, the gene that encodes for the α subunit of lysosomal β-hexosaminidase A (HEXA), which converts GM2 to GM3 ganglioside. Unexpectedly, Hexa mice have a normal lifespan and show no obvious neurological impairment until at least one year of age. These mice catabolize stored GM2 ganglioside using sialidase(s) to remove sialic acid and form the glycolipid GA2, which is further processed by β-hexosaminidase B. Therefore, the presence of the sialidase (s) allows the consequences of the Hexa defect to be bypassed. To determine if the sialidase NEU3 contributes to GM2 ganglioside degradation, we generated a mouse model with combined deficiencies of HEXA and NEU3. The HexaNeu3 mice were healthy at birth, but died at 1.5 to 4.5months of age. Thin-layer chromatography and mass spectrometric analysis of the brains of HexaNeu3 mice revealed the abnormal accumulation of GM2 ganglioside. Histological and immunohistochemical analysis demonstrated cytoplasmic vacuolation in the neurons. Electron microscopic examination of the brain, kidneys and testes revealed pleomorphic inclusions of many small vesicles and complex lamellar structures. The HexaNeu3 mice exhibited progressive neurodegeneration with neuronal loss, Purkinje cell depletion, and astrogliosis. Slow movement, ataxia, and tremors were the prominent neurological abnormalities observed in these mice. Furthermore, radiographs revealed abnormalities in the skeletal bones of the HexaNeu3 mice. Thus, the HexaNeu3 mice mimic the neuropathological and clinical abnormalities of the classical early-onset Tay-Sachs patients, and provide a suitable model for the future pre-clinical testing of potential treatments for this condition.

Lysosomal serine carboxypeptidase Cathepsin A (CTSA) is a multifunctional enzyme with distinct protective and catalytic function. CTSA present in the lysosomal multienzyme complex to facilitate the correct lysosomal routing, stability and activation of with beta–galactosidase and alpha-neuraminidase. Beside CTSA has role in inactivation of bioactive peptides including bradykinin, substances P, oxytocin, angiotensin I and endothelin-I by cleavage of 1 or 2 amino acid(s) from C-terminal ends. In this study, we aimed to elucidate the regulatory role of CTSA on bioactive peptides in knock-in mice model of CTSAS190A. We investigated the level of bradykinin, substances P, oxytocin, angiotensin I and endothelin-I in the kidney, liver, lung, brain and serum from CTSAS190A mouse model at 3- and 6-months of age. Our results suggest CTSA selectively contributes to processing of bioactive peptides in different tissues from CTSAS190A mice compared to age matched WT mice.

Background Tay-Sachs disease (TSD), a type of GM2-gangliosidosis, is a progressive neurodegenerative lysosomal storage disorder caused by mutations in the α subunit of the lysosomal β-hexosaminidase enzyme. This disease is characterized by excessive accumulation of GM2 ganglioside, predominantly in the central nervous system. Although Tay-Sachs patients appear normal at birth, the progressive accumulation of undegraded GM2 gangliosides in neurons leads to death. Recently, an early onset Tay-Sachs disease mouse model, with genotype Hexa−/−Neu3−/−, was generated. Progressive accumulation of GM2 led to premature death of the double KO mice. Importantly, this double-deficient mouse model displays typical features of Tay-Sachs patients, such as cytoplasmic vacuolization of nerve cells, deterioration of Purkinje cells, neuronal death, deceleration in movement, ataxia, and tremors. GM2-gangliosidosis is characterized by acute neurodegeneration preceded by activated microglia expansion, macrophage, and astrocyte activation, along with the production of inflammatory mediators. However, the mechanism of disease progression in Hexa−/−Neu3−/− mice, relevant to neuroinflammation is poorly understood. Method In this study, we investigated the onset and progression of neuroinflammatory changes in the cortex, cerebellum, and retina of Hexa−/−Neu3−/− mice and control littermates by using a combination of molecular genetics and immunochemical procedures. Results We found elevated levels of pro-inflammatory cytokine and chemokine transcripts, such as Ccl2, Ccl3, Ccl4, and Cxcl10 and also extensive microglial and astrocyte activation and proliferation, accompanied by peripheral blood mononuclear cell infiltration in the vicinity of neurons and oligodendrocytes. Behavioral tests demonstrated a high level of anxiety, and age-dependent loss in both spatial learning and fear memory in Hexa−/−Neu3−/− mice compared with that in the controls. Conclusion Altogether, our data suggest that Hexa−/−Neu3−/− mice display a phenotype similar to Tay-Sachs patients suffering from chronic neuroinflammation triggered by GM2 accumulation. Furthermore, our work contributes to better understanding of the neuropathology in a mouse model of early onset Tay-Sachs disease.

Tay–Sachs disease is a severe lysosomal storage disorder caused by mutations in the HEXA gene coding for α subunit of lysosomal β-Hexosaminidase A enzyme, which converts GM2 to GM3 ganglioside. HexA−/− mice, depleted of the β-Hexosaminidase A iso-enzyme, remain asymptomatic up to 1 year of age because of a metabolic bypass by neuraminidase(s). These enzymes remove a sialic acid residue converting GM2 to GA2, which is further degraded by the still intact β-Hexosaminidase B iso-enzyme into lactosylceramide. A previously identified ganglioside metabolizing neuraminidase, Neu4, is abundantly expressed in the mouse brain and has activity against gangliosides like GM2in vitro. Neu4−/− mice showed increased GD1a and decreased GM1 ganglioside in the brain suggesting the importance of the Neu4 in ganglioside catabolism. Mice with targeted disruption of both HexA and Neu4 genes showed accumulating GM2 ganglioside and epileptic seizures with 40% penetrance, indicating that the neuraminidase Neu4 is a modulatory gene, but may not be the only neuraminidase contributing to the metabolic bypass in HexA−/− mice. Therefore, we elucidated the biological role of neuraminidase-1 in ganglioside degradation in mouse. Analysis of HexA−/− Neu1−/− and HexA−/− Neu4−/− Neu1−/− mice models showed significant contribution of neuraminidase-1 on B-series ganglioside degradation in the brain. Therefore, we speculate that other neuraminidase/neuraminidases such as Neu2 and/or Neu3 might be also involved in the ganglioside degradation pathway in HexA−/− mice.

BackgroundTay-Sachs disease (TSD), a type of GM2-gangliosidosis, is a progressive neurodegenerative lysosomal storage disorder, caused by mutations in the a subunit of lysosomal β-hexosaminidase enzyme. This disease is characterized by excessive accumulation of GM2 ganglioside, predominantly in the central nervous system. Although Tay-Sachs patients appear normal at birth, the progressive accumulation of undegraded GM2 gangliosides in neurons leads to death. Recently, an early-onset Tay-Sachs disease mouse model with genotype Hexa-/-Neu3-/- was generated. Progressive accumulation of GM2 led to premature death of the double KO mice. Importantly, this double-deficient mouse model displays typical features of Tay-Sachs patients, such as cytoplasmic vacuolization of nerve cells, deterioration of Purkinje cells, neuronal death, deceleration in movement, ataxia and, tremors. GM2-gangliosidosis is characterized by acute neurodegeneration preceded by activated microglia expansion, macrophage and astrocyte activation, along with the production of inflammatory mediators. However, the mechanism of disease progression in Hexa-/-Neu3-/- mice relevant to neuroinflammation is poorly understood. MethodWe investigated the onset and progression of neuropathological and neuroinflammatory changes in the cortex, cerebellum and retina of Hexa-/-Neu3-/- mice and littermate wild-type as well as Hexa-/- and Neu3-/- mice by using a combination of expression, immunofluorescence and behavioral analyses. ResultsWe found elevated levels of pro-inflamatory pro-inflammatory cytokine and chemokine transcripts, such as Ccl2, Ccl3, Ccl4 and Cxcl10 and also extensive microglial and astrocyte activation and proliferation accompanied by in peripheral blood mononuclear cell infiltration in neurons and oligodendrocytes. Behavioral tests demonstrated high level of anxiety, and age dependent loss in both memory and muscle strength in Hexa-/-Neu3-/- mice compared with that in the controls. ConclusionAltogether, our data suggest that Hexa-/-Neu3-/- mice display a phenotype similar to human TSD patients suffering from chronic neuroinflammation triggered by GM2 accumulation. Our observations collectively suggest a hypothesis that modulation of Ccl2, Ccl3, Ccl4 and Cxcl10 or of their receptors, in combination with traditional drugs such as propagermanium, may provide a novel approach for the management of disease and better understanding of the neuropathology in a mouse model of early-onset Tay-Sachs disease.