Tandem mass spectrometric enzyme assay for simultaneous detection of Tay-Sachs and Sandhoff diseases in dried blood spots for newborn screening.

GM2 gangliosidosis is a group of rare lysosomal storage disorders (LSDs) including Tay-Sachs disease (TSD) and Sandhoff disease (SD), caused by deficiency in activity of either ß-hexosaminidase A (HexA) or both ß-hexosaminidase A and ß-hexosaminidase B (HexB). Methods for screening and diagnosis of TSD and SD include measurement and comparison of the activity of these two enzymes. Here we report a novel method for duplex screening of dried blood spots (DBS) for TSD and SD by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The method requires incubation of a single 3 mm DBS punch with the assay cocktail followed by the injection into the LC-MS/MS. The performance of the method was evaluated by comparing the confirmed TSD and SD patient DBS to random healthy newborn DBS which showed easy discrimination between the three cohorts. The method is multiplexable with other LSD MS/MS enzyme assays which is critical to the continued expansion of the NBS panels.

A case of Sandhoff disease caused by a novel ß-hexosaminidase B (HEXB) mutation c.118delG (p.A40fs*24): A case report from China.

BACKGROUND: Sandhoff disease (SD, Online Mendelian Inheritance in Man: 268800) is an autosomal recessive lysosomal storage disorder caused by variants of the ß-hexosaminidase B (HEXB) gene (Online Mendelian Inheritance in Man: 606873). The HEXB gene has been mapped to chromosome 5q13 and contains 14 exons. The symptoms of SD include progressive weakness, intellectual disability, visual and hearing impairment, exaggerated startle response, and seizures; the patients usually die before the age of 3 years.[1]. CASE SUMMARY: We present a case of SD caused by a homozygous frameshift mutation in the HEXB gene, c.118delG (p.A40fs*24). The male child, aged 2 years 7 months, showed movement retrogression with orbital hypertelorism at age 2 years, accompanied by seizures. Magnetic resonance imaging of the head showed cerebral atrophy and delayed myelination of the white matter of the brain. CONCLUSION: A novel homozygous frameshift c.118delG (p.A40fs*24) variant of HEXB has caused SD in the child. The major symptoms are intellectual disability, visual and hearing impairment, and seizures. Investigation will be continued in the future to comprehensively describe the genotype/phenotype and gain information on other associated features to understand the variable expressivity of this condition.

Saposin C, Key Regulator in the Alpha-Synuclein Degradation Mediated by Lysosome.

Lysosomal dysfunction has been proposed as one of the most important pathogenic molecular mechanisms in Parkinson disease (PD). The most significant evidence lies in the GBA gene, which encodes for the lysosomal enzyme ß-glucocerebrosidase (ß-GCase), considered the main genetic risk factor for sporadic PD. The loss of ß-GCase activity results in the formation of α-synuclein deposits. The present study was aimed to determine the activity of the main lysosomal enzymes and the cofactors Prosaposin (PSAP) and Saposin C in PD and healthy controls, and their contribution to α-synuclein (α-Syn) aggregation. 42 PD patients and 37 age-matched healthy controls were included in the study. We first analyzed the ß-GCase, ß-galactosidase (ß-gal), ß-hexosaminidase (Hex B) and Cathepsin D (CatD) activities in white blood cells. We also measured the GBA, ß-GAL, ß-HEX, CTSD, PSAP, Saposin C and α-Syn protein levels by Western-blot. We found a 20% reduced ß-GCase and ß-gal activities in PD patients compared to controls. PSAP and Saposin C protein levels were significantly lower in PD patients and correlated with increased levels of α-synuclein. CatD, in contrast, showed significantly increased activity and protein levels in PD patients compared to controls. Increased CTSD protein levels in PD patients correlated, intriguingly, with a higher concentration of α-Syn. Our findings suggest that lysosomal dysfunction in sporadic PD is due, at least in part, to an alteration in Saposin C derived from reduced PSAP levels. That would lead to a significant decrease in the ß-GCase activity, resulting in the accumulation of α-syn. The accumulation of monohexosylceramides might act in favor of CTSD activation and, therefore, increase its enzymatic activity. The evaluation of lysosomal activity in the peripheral blood of patients is expected to be a promising approach to investigate pathological mechanisms and novel therapies aimed to restore the lysosomal function in sporadic PD.

[Clinical characteristics and genetic analysis of a child with infantile Sandhoff disease and eosinophilia].

OBJECTIVE: To explore the genetic basis for a girl featuring epilepsy, developmental delay and regression. METHODS: Clinical data of the patient was collected. Activities of hexosaminidase A (Hex A) and hexosaminidase A&B (Hex A&B) in blood leukocytes were determined by using a fluorometric assay. Peripheral blood samples were collected from the proband and six members from her pedigree. Following extraction of genomic DNA, whole exome sequencing was carried out. Candidate variants were verified by Sanger sequencing. RESULTS: Enzymatic studies of the proband have shown reduced plasma Hex A and Hex A&B activities. Genetic testing revealed that she has carried c.1260_1263del and c.1601G>C heterozygous compound variants of the HEXB gene. Her mother, brother and sister were heterozygous carriers of c.1260_1263del, while her father, mother, three brothers and sister did not carry the c.1601G>C variant, suggesting that it has a de novo origin. Increased eosinophils were discovered upon cytological examination of peripheral blood and bone marrow samples. CONCLUSION: The compound heterozygous variants of c.1260_1263del and c.1601G>C of the HEXB gene probably underlay the Sandhoff disease in this child. Eosinophilia may be noted in infantile Sandhoff disease.

N-acetyl-ß-D-hexosaminidases mediate the generation of paucimannosidic proteins via a putative noncanonical truncation pathway in human neutrophils.

We recently discovered that human neutrophils express immunomodulatory glycoproteins carrying unusual and highly truncated paucimannosidic N-glycans (Man1-3GlcNAc2Fuc0-1), but their biosynthesis remains elusive. Guided by the well-characterized truncation pathway in invertebrates and plants in which the N-acetyl-ß-D-hexosaminidase (Hex) isoenzymes catalyze paucimannosidic protein (PMP) formation, we here set out to test if the homologous human Hex α and ß subunits encoded by HEXA and HEXB drive a similar truncation pathway in human neutrophils. To this end, we performed quantitative glycomics and glycoproteomics of several CRISPR-Cas9-edited Hex-disrupted neutrophil-like HL-60 mutants (HEXA-KO and HEXB-KO) and matching unedited cell lines. Hex disruption was validated using next-generation sequencing, enzyme-linked immunosorbent assay (ELISA), quantitative proteomics and Hex activity assays. Excitingly, all Hex-disrupted mutants displayed significantly reduced levels of paucimannosylation, particularly Man2-3GlcNAc2Fuc1, relative to unedited HL-60 suggesting that both HEXA and HEXB contribute to PMP formation via a hitherto unexplored truncation pathway in neutrophils. Quantitative N-glycomics indeed demonstrated reduced utilization of a putative noncanonical truncation pathway in favor of the canonical elongation pathway in all Hex-disrupted mutants relative to unedited controls. Quantitative glycoproteomics recapitulated the truncation-to-elongation switch in all Hex-disrupted mutants and showed a greater switch for N-glycoproteins cotrafficking with Hex to the azurophilic granules of neutrophils such as myeloperoxidase. Finally, we supported the Hex-PMP relationship by documenting that primary neutrophils isolated from an early-onset Sandhoff disease patient (HEXB-/-) displayed dramatically reduced paucimannosylation relative to neutrophils from an age-matched unaffected donor. We conclude that both human Hex α and ß mediate PMP formation via a putative noncanonical truncation pathway in neutrophils.

Atypical presentation of late-onset Sandhoff disease: a case report.

BACKGROUND AND PURPOSE: Sandhoff disease is a rare type of hereditary (autosomal recessive) GM2-gangliosidosis, which is caused by mutation of the HEXB gene. Disruption of the ß subunit of the hexosaminidase (Hex) enzyme affects the function of both the Hex-A and Hex-B isoforms. The severity and the age of onset of the disease (infantile or classic; juvenile; adult) depends on the residual activity of the enzyme. The late-onset form is characterized by diverse symptomatology, comprising motor neuron disease, ataxia, tremor, dystonia, psychiatric symptoms and neuropathy. METHODS: A 36-year-old female patient has been presenting progressive, symmetrical lower limb weakness for 9 years. Detailed neurological examination revealed mild symmetrical weakness in the hip flexors without the involvement of other muscle groups. The patellar reflex was decreased on both sides. Laboratory tests showed no relevant alteration and routine electroencephalography and brain MRI were normal. Nerve conduction studies and electromyography revealed alterations corresponding to sensory neuropathy. Muscle biopsy demonstrated signs of mild neurogenic lesion. Her younger brother (32-year-old) was observed with similar symptoms. RESULTS: Detailed genetic study detected a known pathogenic missense mutation and a 15,088 base pair long known pathogenic deletion in the HEXB gene (NM_000521.4:c.1417G>A; NM_000521:c.-376-5836_669+1473del; double heterozygous state). Segregation analysis and hexosaminidase enzyme assay of the family further confirmed the diagnosis of late-onset Sandhoff disease. CONCLUSION: The purpose of this case report is to draw attention to the significance of late-onset Sandhoff disease amongst disorders presenting with proximal predominant symmetric lower limb muscle weakness in adulthood.

L-Arginine Ameliorates Defective Autophagy in GM2 Gangliosidoses by mTOR Modulation.

AIMS: Tay-Sachs and Sandhoff diseases (GM2 gangliosidosis) are autosomal recessive disorders of lysosomal function that cause progressive neurodegeneration in infants and young children. Impaired hydrolysis catalysed by ß-hexosaminidase A (HexA) leads to the accumulation of GM2 ganglioside in neuronal lysosomes. Despite the storage phenotype, the role of autophagy and its regulation by mTOR has yet to be explored in the neuropathogenesis. Accordingly, we investigated the effects on autophagy and lysosomal integrity using skin fibroblasts obtained from patients with Tay-Sachs and Sandhoff diseases. RESULTS: Pathological autophagosomes with impaired autophagic flux, an abnormality confirmed by electron microscopy and biochemical studies revealing the accelerated release of mature cathepsins and HexA into the cytosol, indicating increased lysosomal permeability. GM2 fibroblasts showed diminished mTOR signalling with reduced basal mTOR activity. Accordingly, provision of a positive nutrient signal by L-arginine supplementation partially restored mTOR activity and ameliorated the cytopathological abnormalities. INNOVATION: Our data provide a novel molecular mechanism underlying GM2 gangliosidosis. Impaired autophagy caused by insufficient lysosomal function might represent a new therapeutic target for these diseases. CONCLUSIONS: We contend that the expression of autophagy/lysosome/mTOR-associated molecules may prove useful peripheral biomarkers for facile monitoring of treatment of GM2 gangliosidosis and neurodegenerative disorders that affect the lysosomal function and disrupt autophagy.

[Glial cells and pharmacological targets in Sandhoff disease].

Sandhoff disease (SD) is a genetic disorder caused by a mutation in the ß-hexosaminidase B (HexB) gene in humans. This results in the massive accumulation of GM2 gangliosides in the nervous system, causing progressive neurodegeneration. The symptoms of SD include muscle weakness, seizures, and mental illness;along with loss of muscle coordination, vision, and hearing. In the most severe form, the onset begins during early infancy, and death usually occurs within 3-5 years of age. The established animal model, Hexb-deficient (Hexb-/-) mouse, shows abnormalities that resemble the severe phenotype found in human infants. We have previously reported that activated microglia causes astrogliosis in Hexb-/- mouse at the early stage of development that can be ameliorated via immunosuppression. Moreover, within the cerebral cortices of Hexb-/- mouse, reactive astrocytes were found to express adenosine A2A receptors in later inflammatory phases. Inhibiting this receptor with istradefylline decreases the number of activated microglial cells and inflammatory cytokines/chemokines. Thus, we underline the importance of the astrocytic A2A receptor as a sensor, in regulating microglial activation in the late phase of inflammation.

Infantile onset Sandhoff disease: clinical manifestation and a novel common mutation in Thai patients.

BACKGROUND: Sandhoff disease (SD) is an autosomal recessive lysosomal storage disorder, resulting in accumulation of GM2 ganglioside, particular in neuronal cells. The disorder is caused by deficiency of ß-hexosaminidase B (HEX-B), due to pathogenic variant of human HEXB gene. METHOD: This study describes clinical features, biochemical, and genetic defects among Thai patients with infantile SD during 2008-2019. RESULTS: Five unrelated Thai patients presenting with developmental regression, axial hypotonia, seizures, exaggerated startle response to noise, and macular cherry red spot were confirmed to have infantile SD based on deficient HEX enzyme activities and biallelic variants of the HEXB gene. In addition, an uncommon presenting feature, cardiac defect, was observed in one patient. All the patients died in their early childhood. Plasma total HEX and HEX-B activities were severely deficient. Sequencing analysis of HEXB gene identified two variants including c.1652G>A (p.Cys551Tyr) and a novel variant of c.761T>C (p.Leu254Ser), in 90 and 10% of the mutant alleles found, respectively. The results from in silico analysis using multiple bioinformatics tools were in agreement that the p.Cys551Tyr and the p.Leu254Ser are likely pathogenic variants. Molecular modelling suggested that the Cys551Tyr disrupt disulfide bond, leading to protein destabilization while the Leu254Ser resulted in change of secondary structure from helix to coil and disturbing conformation of the active site of the enzyme. Genome-wide SNP array analysis showed no significant relatedness between the five affected individuals. These two variants were not present in control individuals. The prevalence of infantile SD in Thai population is estimated 1 in 1,458,521 and carrier frequency at 1 in 604. CONCLUSION: The study suggests that SD likely represents the most common subtype of rare infantile GM2 gangliosidosis identified among Thai patients. We firstly described a potential common variant in HEXB in Thai patients with infantile onset SD. The data can aid a rapid molecular confirmation of infantile SD starting with the hotspot variant and the use of expanded carrier testing.

Identification and characterization of a residual host cell protein hexosaminidase B associated with N-glycan degradation during the stability study of a therapeutic recombinant monoclonal antibody product.

Host cell proteins (HCPs) are process-related impurities derived from host organisms, which need to be controlled to ensure adequate product quality and safety. In this study, product quality attributes were tracked for several monoclonal antibodies (mAbs) under the intended storage and accelerated stability conditions. One product quality attribute not expected to be stability indicating is the N-glycan heterogeneity profile. However, significant N-glycan degradation was observed for one mAb under accelerated and stressed stability conditions. The root cause for this instability was attributed to hexosaminidase B (HEXB), an enzyme known to remove terminal N-acetylglucosamine (GlcNAc). HEXB was identified by liquid chromatography-mass spectrometry (LC-MS)-based proteomics approach to be enriched in the impacted stability batches from mAb-1. Subsequently, enzymatic and targeted multiple reaction monitoring (MRM) MS assays were developed to support process and product characterization. A potential interaction between HEXB and mAb-1 was initially observed from the analysis of process intermediates by proteomics among several mAbs and later supported by computational modeling. An improved bioprocess was developed to significantly reduce HEXB levels in the final drug substance. A risk assessment was conducted by evaluating the in silico immunogenicity risk and the impact on product quality. To the best of our knowledge, HEXB is the first residual HCP reported to have impact on the glycan profile of a formulated drug product. The combination of different analytical tools, mass spectrometry, and computational modeling provides a general strategy on how to study residual HCP for biotherapeutics development.

Patient and caregiver perspectives on burden of disease manifestations in late-onset Tay-Sachs and Sandhoff diseases.

BACKGROUND: The GM2 gangliosidoses (GM2), Tay-Sachs and Sandhoff diseases, are rare, autosomal recessive genetic disorders caused by mutations in the lysosomal enzyme ß-hexosaminidase A (HEXA) or ß-hexosaminidase B (HEXB) genes, respectively. A minority of patients have a late-onset form of disease that presents from late-childhood to adulthood and has a slowly progressive course with prolonged survival. Little research has been published documenting patient experiences with late-onset Tay-Sachs and Sandhoff diseases and how the disease impacts their daily lives and functioning. This study explored the most frequent symptoms and functional impacts experienced by patients with late-onset GM2 gangliosidosis through interviews with patients and caregivers. METHODS: A qualitative research study design was employed, using three focus groups and 18 one-on-one interviews with patients who were recruited at the National Tay-Sachs and Allied Diseases Annual Family Conference. Transcripts were generated from the discussions, and patient quotes were analyzed using a content analysis approach. Concepts were aggregated into symptom and functional impacts, and the frequency of mention in the focus groups and individual interviews was calculated. KEY FINDINGS: Many of the frequently described symptoms [muscle weakness (n = 19, 95%), "clumsy" gait (n = 12, 60%), fatigue (n = 10, 50%)] and impacts [difficulty walking (n = 19, 95%), falling (n = 17, 85%), and climbing stairs (n = 16, 80%)] disclosed by patients and caregivers were similar to those previously reported in the literature. However, less frequently described symptoms such as gastrointestinal issues (n = 4, 20%) and coughing fits (n = 5, 25%) have been expanded upon. This study evaluated the immediate impact of these symptoms on the patients' lives to highlight the burden of these symptoms and the functional limitations on daily living activities, independence, and emotional well-being. The findings were used to develop a conceptual disease model that could serve as a foundation for patient-centered outcomes in clinical trials and provide insights to the medical community that may benefit patient care. CONCLUSIONS: This study contributes to the current understanding of symptoms associated with late-onset GM2 gangliosidosis, and further identifies the many consequences and impacts of the disease. These symptoms and impacts could be measured in clinical trials to examine the effects of novel treatments from the patient perspective.

Purification and biochemical/biophysical characterization of two hexosaminidases from the fresh water mussel, Lamellidens corrianus.

Two thermostable isoforms of a hexosaminidase were purified to homogeneity from the soluble extract of fresh water mussel Lamellidens corrianus, employing a variety of chromatographic techniques. Hexosaminidase A (HexA) is a heterodimer with subunit masses of ~80 and 55 kDa. Hexosaminidase B (HexB) is a homodimer with a subunit mass of 55-60 kDa. Circular dichroism spectroscopic studies indicated that both HexA and HexB contain ß-sheet as the major secondary structural component with considerably lower content of α-helix. The temperature and pH optima of both the isoforms were found to be 60 °C and 4.0, respectively. The IC50 values for HexA with N-acetyl-d-galactosamine, N-acetyl-d-glucosamine, d-galactosamine, d-glucosamine, methyl α-d-mannopyranoside and d-mannose are 3.7, 72.8, 307, 216, 244 and 128 mM, respectively, whereas the corresponding IC50 values for HexB were estimated as 5.1, 61, 68, 190, 92 and 133 mM, respectively. Kinetic parameters KM and Vmax for HexA and B with p-nitrophenyl N-acetyl-ß-d-glucosaminide are 4 mM, 0.23 µmol·min-1·mL-1 and 2.86 mM, 0.29 µmol·min-1·mL-1, respectively, and with p-nitrophenyl N-acetyl-ß-d-galactosaminide are 4.5 mM, 0.054 µmol·min-1·mL-1 and 1.4 mM, 0.14 µmol·min-1·mL-1, respectively. GalNAc inhibited both isoforms in a non-competitive manner, whereas a mixed mode of inhibition was observed with GlcNAc with both forms.

Abnormal organization during neurodevelopment in a mouse model of Sandhoff disease.

Sandhoff disease (SD) is a genetic disorder caused by a mutation of HEXB, which is the ß-subunit gene of ß-hexosaminidase A and B (HexA and HexB) in humans. HEXB mutation reduces HexA and HexB enzymatic activities, and results in the massive accumulation of ganglioside GM2 in the nervous system. Severe phenotypes of SD show progressive neurodegeneration in human infants, and lysosomal dysfunction that may affect the early development of the nervous system. In a previous study, neural stem cells (NSCs) and induced pluripotent stem cells derived from SD model mice, which are Hexb-deficient (Hexb-/-), demonstrated impaired neuronal differentiation. This study investigated early neurodevelopment in vivo using Hexb-/- mice. The structure of adult cerebral cortices of Hexb-/- mice was normal. However, the expression of Sox2, an NSC-related gene, was reduced in the embryonic cerebral cortices of Hexb-/- mice. Moreover, a reduction of early neuronal migration and differentiation was observed in the embryonic cerebral cortices of Hexb-/- mice. In addition, we showed that the production of layer-specific neurons was delayed in somatosensory cerebral cortices of Hexb-/- mice. These findings suggest that the alterations observed in embryonic Hexb-/- mice may contribute to deficits in neurodevelopment of SD.

Screening anaphylactoid components of Shuang Huang Lian Injection by analyzing spectrum-effect relationships coupled with UPLC-TOF-MS.

Shuang Huang Lian Injection (SHLI) has been used in China for over 30 years as an effective and widely used Chinese herbal prescription to treat acute respiratory infectious. SHLI has, however, caused many severe anaphylactoid reactions. It is important to identify the potential anaphylactoid components of SHLI. Spectrum-effect relationships were used to explore potentially anaphylactoid components. Based on the original herbal formula, honeysuckle, Fructus Forsythiae and Radix Scutellariae extracts were prepared and combined in appropriate proportions. The preparations were then injected into the caudal vein of rats to obtain in vivo serum samples for pharmacological evaluation and fingerprint analysis. The release rate of ß-hexosaminidase from RBL-2H3 cells and plasma histamine level was used as the pharmacological index. Chromatographic fingerprint analysis identified 22 common peaks. Regression analysis and correlation analysis were used to calculate the relationships between the peaks and the pharmacological effects and identified peaks 5, 6, 11, 12 and 17 as likely anaphylactoid agents. The correlated peaks were identified by comparing the fingerprints with in vitro samples and reference standard samples and the structure was identified by UPLC-TOF-MS. This study established a prospective method to clarify the anaphylactoid components in SHLI, which would provide guidances for screening anaphylactoid components in other traditional Chinese medicine injections.

Improvement in dysmyelination by the inhibition of microglial activation in a mouse model of Sandhoff disease.

Sandhoff disease (SD) is a genetic disorder caused by a mutation of the ß-subunit gene ß-hexosaminidase B (HexB) in humans, which results in the massive accumulation of the ganglioside GM2 and related glycosphingolipids in the nervous system. SD causes progressive neurodegeneration and changes in white matter in human infants. An animal model of SD has been established, Hexb-deficient (Hexb) mice, which shows abnormalities resembling the severe phenotype found in human infants. Previously, we reported that the activation state of microglia caused astrogliosis in the early stage of Hexb mouse development. To study how the symptoms of SD develop, we explored the difference in gene expression between 4-week-old Hexb and Hexb mouse cerebral cortices by microarray analysis. The data indicated not only the upregulation of immune system-related genes but also the downregulation of myelin-related genes in the 4-week-old Hexb mouse cerebral cortices. To test the correlation between inflammation and dysmyelination, we generated double-knockout mice of Hexb and the Fc receptor γ gene (Fcrγ), which is a regulator of autoimmune responses. Dysmyelination recovered in these double-knockout mice. The number of oligodendrocyte progenitors, which expressed platelet-derived growth factor receptor-α, did not change in the 2-week-old mouse brain. These results indicate that microglial activation plays an important role in the myelination process, without influencing the number of oligodendrocyte progenitors, in the development of Hexb mice.

Intravenous administration of scAAV9-Hexb normalizes lifespan and prevents pathology in Sandhoff disease mice.

Sandhoff disease (SD) is a rare inherited disorder caused by a deficiency of ß-hexosaminidase activity which is fatal because no effective treatment is available. A mouse model of Hexb deficiency reproduces the key pathognomonic features of SD patients with severe ubiquitous lysosomal dysfunction, GM2 accumulation, neuroinflammation and neurodegeneration, culminating in death at 4 months. Here, we show that a single intravenous neonatal administration of a self-complementary adeno-associated virus 9 vector (scAAV9) expressing the Hexb cDNA in SD mice is safe and sufficient to prevent disease development. Importantly, we demonstrate for the first time that this treatment results in a normal lifespan (over 700 days) and normalizes motor function assessed by a battery of behavioral tests, with scAAV9-treated SD mice being indistinguishable from wild-type littermates. Biochemical analyses in multiple tissues showed a significant increase in hexosaminidase A activity, which reached 10-15% of normal levels. AAV9 treatment was sufficient to prevent GM2 and GA2 storage almost completely in the cerebrum (less so in the cerebellum), as well as thalamic reactive gliosis and thalamocortical neuron loss in treated Hexb-/- mice. In summary, this study demonstrated a widespread protective effect throughout the entire CNS after a single intravenous administration of the scAAV9-Hexb vector to neonatal SD mice.

Murine Sialidase Neu3 facilitates GM2 degradation and bypass in mouse model of Tay-Sachs disease.

Tay-Sachs disease is a severe lysosomal storage disorder caused by mutations in Hexa, the gene that encodes for the α subunit of lysosomal ß-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 ß-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 Hexa-/-Neu3-/- 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 Hexa-/-Neu3-/- 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 Hexa-/-Neu3-/- 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 Hexa-/-Neu3-/- mice. Thus, the Hexa-/-Neu3-/- 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.

Canine GM2-Gangliosidosis Sandhoff Disease Associated with a 3-Base Pair Deletion in the HEXB Gene.

BACKGROUND: GM2-gangliosidosis is a fatal neurodegenerative lysosomal storage disease (LSD) caused by deficiency of either ß-hexosaminidase A (Hex-A) and ß-hexosaminidase B (Hex-B) together, or the GM2 activator protein. Clinical signs can be variable and are not pathognomonic for the specific, causal deficiency. OBJECTIVES: To characterize the phenotype and genotype of GM2-gangliosidosis disease in an affected dog. ANIMALS: One affected Shiba Inu and a clinically healthy dog. METHODS: Clinical and neurologic evaluation, brain magnetic resonance imaging (MRI), assays of lysosomal enzyme activities, and sequencing of all coding regions of HEXA, HEXB, and GM2A genes. RESULTS: A 14-month-old, female Shiba Inu presented with clinical signs resembling GM2-gangliosidosis in humans and GM1-gangliosidosis in the Shiba Inu. Magnetic resonance imaging (MRI) of the dog's brain indicated neurodegenerative disease, and evaluation of cerebrospinal fluid (CSF) identified storage granules in leukocytes. Lysosomal enzyme assays of plasma and leukocytes showed deficiencies of Hex-A and Hex-B activities in both tissues. Genetic analysis identified a homozygous, 3-base pair deletion in the HEXB gene (c.618-620delCCT). CONCLUSIONS AND CLINICAL IMPORTANCE: Clinical, biochemical, and molecular features are characterized in a Shiba Inu with GM2-gangliosidosis. The deletion of 3 adjacent base pairs in HEXB predicts the loss of a leucine residue at amino acid position 207 (p.Leu207del) supporting the hypothesis that GM2-gangliosidosis seen in this dog is the Sandhoff type. Because GM1-gangliosidosis also exists in this breed with almost identical clinical signs, genetic testing for both GM1- and GM2-gangliosidosis should be considered to make a definitive diagnosis.

Suppression of NK and CD8+ T cells reduces astrogliosis but accelerates cerebellar dysfunction and shortens life span in a mouse model of Sandhoff disease.

Sandhoff disease is an inherited lysosomal storage disease, resulting from the deficiency of lysosomal ß-hexosaminidase A and B enzyme activity. The Hexb-/- mouse model recapitulates human disease and leads to fatal neurodegeneration and neuroinflammation. IL-15 is important for the proliferation of NK, NK T, and CD8+ cytotoxic/memory T cells. In order to determine how changes to IL-15-dependent immune cell populations would alter the course of Sandhoff disease in mice, we generated a Hexb-/-Il-15-/- double knockout mouse and used motor behaviour tests, analyzed peripheral blood and brain leukocyte immunophenotypes, cytokine secretion, as well as examined markers of microgliosis, astrogliosis and apoptosis. Hexb-/-Il-15-/- mice had an accelerated neurodegenerative phenotype, and reached the humane endpoint at 118±3.5d, compared to Hexb-/- mice (127±2.2d). The performance of Hexb-/-Il-15-/- mice declined earlier than Hexb-/- mice on the rotarod and righting reflex motor behaviour tests. Hexb-/- mice had a significantly higher prevalence of pro-inflammatory monocytes in the blood relative to C57BL/6 mice, but this was unaltered by IL-15 deficiency. The prevalence of NK cells and CD8+ T cells in Il-15-/- and Hexb-/-Il-15-/- mice was decreased compared to wild type and Hexb-/- mice. While Hexb-/- mice displayed an increase in the prevalence of CD4+ and CD8+ T cells in brain leukocytes compared to C57BL/6 mice, there was a decrease in CD8+ T cells in Hexb-/-Il-15-/- compared to Hexb-/- mice. In addition, circulating IL-17 and IL-10 levels were significantly higher in Hexb-/-Il-15-/- mice, suggesting heightened inflammation compared to Hexb-/- mice. Interestingly, astrogliosis levels were significantly reduced in the cerebellum of Hexb-/-Il-15-/- mice compared to Hexb-/- mice while microgliosis was not affected in brains of Hexb-/-Il-15-/- mice. Our study demonstrated that IL-15 depletion dramatically reduced numbers of NK and CD8+ T cells as well as astrocytes but accelerated disease progression in Sandhoff mice. These results pointed to interactions between NK/CD8+ T cells and astrogliosis and potentially a protective role for NK/CD8+ T cells and/or astrocytes during disease progression. This observation supports the notion that expanding the IL-15-dependent NK and CD8+ T cells populations with IL-15 therapy may have therapeutic benefits for Sandhoff disease.

Lysosomal Proteins as a Therapeutic Target in Neurodegeneration.

Several proteins that are mutated in lysosomal storage diseases are linked to neurodegenerative disease. This review focuses on some of these lysosomal enzymes and transporters, as well as current therapies that have emerged from the lysosomal storage disease field. Given the deeper genetic understanding of lysosomal defects in neurodegeneration, we explore why some of these orphan disease drug candidates are also attractive targets in subpopulations of individuals with neurodegenerative disease.