Neuronal GM1 gangliosidosis in a Siamese cat with beta-galactosidase deficiency

Polymer-based drug delivery systems under investigation for enzyme replacement and other therapies of lysosomal storage disorders

Lysosomes play a central role in cellular homeostasis and alterations in this compartment associate with many diseases. The most studied example is that of lysosomal storage disorders (LSDs), a group of 60 + maladies due to genetic mutations affecting lysosomal components, mostly enzymes. This leads to aberrant intracellular storage of macromolecules, altering normal cell function and causing multiorgan syndromes, often fatal within the first years of life. Several treatment modalities are available for a dozen LSDs, mostly consisting of enzyme replacement therapy (ERT) strategies. Yet, poor biodistribution to main targets such as the central nervous system, musculoskeletal tissue, and others, as well as generation of blocking antibodies and adverse effects hinder effective LSD treatment. Drug delivery systems are being studied to surmount these obstacles, including polymeric constructs and nanoparticles that constitute the focus of this article. We provide an overview of the formulations being tested, the diseases they aim to treat, and the results observed from respective in vitro and in vivo studies. We also discuss the advantages and disadvantages of these strategies, the remaining gaps of knowledge regarding their performance, and important items to consider for their clinical translation. Overall, polymeric nanoconstructs hold considerable promise to advance treatment for LSDs.

Intravenous delivery of adeno-associated viral gene therapy in feline GM1 gangliosidosis

GM1 gangliosidosis is a fatal neurodegenerative disease caused by a deficiency of lysosomal β-galactosidase. In its most severe form, GM1 gangliosidosis causes death by 4 years of age, and no effective treatments exist. Previous work has shown that injection of the brain parenchyma with an adeno-associated viral vector provides pronounced therapeutic benefit in a feline GM1 model. To develop a less invasive treatment for the brain and increase systemic biodistribution, intravenous injection of AAV9 was evaluated. AAV9 expressing feline β-galactosidase was intravenously administered at 1.5x1013 vector genomes/kilogram body weight to six GM1 cats at approximately 1 month of age. The animals were divided into two cohorts: 1) a long-term group, which was followed to humane endpoint, and 2) a short-term group, which was analyzed 16-weeks post treatment. Clinical assessments included neurological exams, cerebrospinal fluid and urine biomarkers, and 7-Telsa magnetic resonance imaging and spectroscopy. Postmortem analysis included β-galactosidase and virus distribution, histological analysis, and ganglioside content. Untreated GM1 animals survived 8.0 ± 0.6 months while intravenous treatment increased survival to an average of 3.5 years (n = 2) with substantial improvements in quality of life and neurologic function. Neurological abnormalities, which in untreated animals progress to the inability to stand and debilitating neurological disease by 8 months of age, were mild in all treated animals. Cerebrospinal fluid biomarkers were normalized, indicating decreased central nervous system cell damage in the treated animals. Urinary glycosaminoglycans decreased to normal levels in the long-term cohort. Magnetic resonance imaging and spectroscopy showed partial preservation of the brain in treated animals, which was supported by postmortem histological evaluation. β-galactosidase activity was increased throughout the central nervous system, reaching carrier levels in much of the cerebrum and normal levels in the cerebellum, spinal cord and cerebrospinal fluid. Ganglioside accumulation was significantly reduced by treatment. Peripheral tissues such as heart, skeletal muscle, and sciatic nerve also had normal β-galactosidase activity in treated GM1 cats. GM1 histopathology was largely corrected with treatment. There was no evidence of tumorigenesis or toxicity. Restoration of β-galactosidase activity in the central nervous system and peripheral organs by intravenous gene therapy led to profound increases in lifespan and quality of life in GM1 cats. This data supports the promise of intravenous gene therapy as a safe, effective treatment for GM1 gangliosidosis.

7T MRI Predicts Amelioration of Neurodegeneration in the Brain after AAV Gene Therapy

GM1 gangliosidosis (GM1) is a fatal neurodegenerative lysosomal storage disease that occurs most commonly in young children, with no effective treatment available. Long-term follow-up of GM1 cats treated by bilateral thalamic and deep cerebellar nuclei (DCN) injection of adeno-associated virus (AAV)-mediated gene therapy has increased lifespan to 8 years of age, compared with an untreated lifespan of ~8 months. Due to risks associated with cerebellar injection in humans, the lateral ventricle was tested as a replacement route to deliver an AAVrh8 vector expressing feline β-galactosidase (β-gal), the defective enzyme in GM1. Treatment via the thalamus and lateral ventricle corrected storage, myelination, astrogliosis, and neuronal morphology in areas where β-gal was effectively delivered. Oligodendrocyte number increased, but only in areas where myelination was corrected. Reduced AAV and β-gal distribution were noted in the cerebellum with subsequent increases in storage, demyelination, astrogliosis, and neuronal degeneration. These postmortem findings were correlated with endpoint MRI and magnetic resonance spectroscopy (MRS). Compared with the moderate dose with which most cats were treated, a higher AAV dose produced superior survival, currently 6.5 years. Thus, MRI and MRS can predict therapeutic efficacy of AAV gene therapy and non-invasively monitor cellular events within the GM1 brain.

Axonopathy and Reduction of Membrane Resistance: Key Features in a New Murine Model of Human GM1-Gangliosidosis

G_M1-gangliosidosis is caused by a reduced activity of β-galactosidase (Glb1), resulting in intralysosomal accumulations of G_M1. The aim of this study was to reveal the pathogenic mechanisms of G_M1-gangliosidosis in a new Glb1 knockout mouse model. Glb1^−/− mice were analyzed clinically, histologically, immunohistochemically, electrophysiologically and biochemically. Morphological lesions in the central nervous system were already observed in two-month-old mice, whereas functional deficits, including ataxia and tremor, did not start before 3.5-months of age. This was most likely due to a reduced membrane resistance as a compensatory mechanism. Swollen neurons exhibited intralysosomal storage of lipids extending into axons and amyloid precursor protein positive spheroids. Additionally, axons showed a higher kinesin and lower dynein immunoreactivity compared to wildtype controls. Glb1^−/− mice also demonstrated loss of phosphorylated neurofilament positive axons and a mild increase in non-phosphorylated neurofilament positive axons. Moreover, marked astrogliosis and microgliosis were found, but no demyelination. In addition to the main storage material G_M1, G_A1, sphingomyelin, phosphatidylcholine and phosphatidylserine were elevated in the brain. In summary, the current Glb1^−/− mice exhibit a so far undescribed axonopathy and a reduced membrane resistance to compensate the functional effects of structural changes. They can be used for detailed examinations of axon–glial interactions and therapy trials of lysosomal storage diseases.

Human GLB1 knockout cerebral organoids: A model system for testing AAV9-mediated GLB1 gene therapy for reducing GM1 ganglioside storage in GM1 gangliosidosis

GM1 gangliosidosis is an autosomal recessive neurodegenerative disorder caused by the deficiency of lysosomal β-galactosidase (β-gal) and resulting in accumulation of GM1 ganglioside. The disease spectrum ranges from infantile to late onset and is uniformly fatal, with no effective therapy currently available. Although animal models have been useful for understanding disease pathogenesis and exploring therapeutic targets, no relevant human central nervous system (CNS) model system has been available to study its early pathogenic events or test therapies. To develop a model of human GM1 gangliosidosis in the CNS, we employed CRISPR/Cas9 genome editing to target GLB1 exons 2 and 6, common sites for mutations in patients, to create isogenic induced pluripotent stem (iPS) cell lines with lysosomal β-gal deficiency. We screened for clones with <5% of parental cell line β-gal enzyme activity and confirmed GLB1 knockout clones using DNA sequencing. We then generated GLB1 knockout cerebral organoids from one of these GLB1 knockout iPS cell clones. Analysis of GLB1 knockout organoids in culture revealed progressive accumulation of GM1 ganglioside. GLB1 knockout organoids microinjected with AAV9-GLB1 vector showed a significant increase in β-gal activity and a significant reduction in GM1 ganglioside content compared with AAV9-GFP-injected organoids, demonstrating the efficacy of an AAV9 gene therapy-based approach in GM1 gangliosidosis. This proof-of-concept in a human cerebral organoid model completes the pre-clinical studies to advance to clinical trials using the AAV9-GLB1 vector.

2-Hydroxyglutaric aciduria as a cause for seizure-like episodes in a domestic shorthair cat

Case summary

A 14-month-old male castrated domestic shorthair cat, which 2 months prior to presentation underwent hindlimb amputation following a road traffic accident, presented for investigation of four suspected generalised tonic–clonic seizures. Neurological examination was unremarkable. Routine blood work (haematology, biochemistry, ammonia, preprandial bile acids) was unremarkable. MRI of the brain identified marked symmetrical T2-weighted hyperintensities of the cerebellum and brainstem, mainly affecting the grey matter. Urine amino acid and mucopolysaccharide levels were unremarkable. Urine organic acids on two separate samples, 35 days apart, identified highly increased excretion of 2-hydroxyglutaric acid, indicative of 2-hydroxyglutaric aciduria. The cat was started on anticonvulsant therapy with phenobarbitone, which, at the point of writing, has improved seizure control, although the cat has not achieved seizure freedom.

Relevance and novel information

This case report describes the first reported case of a 2-hydroxyglutaric aciduria, an inherited neurometabolic disorder, as a cause for seizure-like episodes in a cat.

Lysosomal enzyme replacement therapies: Historical development, clinical outcomes, and future perspectives

Lysosomes and lysosomal enzymes play a central role in numerous cellular processes, including cellular nutrition, recycling, signaling, defense, and cell death. Genetic deficiencies of lysosomal components, most commonly enzymes, are known as "lysosomal storage disorders" or "lysosomal diseases" (LDs) and lead to lysosomal dysfunction. LDs broadly affect peripheral organs and the central nervous system (CNS), debilitating patients and frequently causing fatality. Among other approaches, enzyme replacement therapy (ERT) has advanced to the clinic and represents a beneficial strategy for 8 out of the 50-60 known LDs. However, despite its value, current ERT suffers from several shortcomings, including various side effects, development of "resistance", and suboptimal delivery throughout the body, particularly to the CNS, lowering the therapeutic outcome and precluding the use of this strategy for a majority of LDs. This review offers an overview of the biomedical causes of LDs, their socio-medical relevance, treatment modalities and caveats, experimental alternatives, and future treatment perspectives.

Lipidomic Evaluation of Feline Neurologic Disease after AAV Gene Therapy

GM1 gangliosidosis is a fatal lysosomal disorder, for which there is no effective treatment. Adeno-associated virus (AAV) gene therapy in GM1 cats has resulted in a greater than 6-fold increase in lifespan, with many cats remaining alive at >5.7 years of age, with minimal clinical signs. Glycolipids are the principal storage product in GM1 gangliosidosis whose pathogenic mechanism is not completely understood. Targeted lipidomics analysis was performed to better define disease mechanisms and identify markers of disease progression for upcoming clinical trials in humans. 36 sphingolipids and subspecies associated with ganglioside biosynthesis were tested in the cerebrospinal fluid of untreated GM1 cats at a humane endpoint (∼8 months), AAV-treated GM1 cats (∼5 years old), and normal adult controls. In untreated GM1 cats, significant alterations were noted in 16 sphingolipid species, including gangliosides (GM1 and GM3), lactosylceramides, ceramides, sphingomyelins, monohexosylceramides, and sulfatides. Variable degrees of correction in many lipid metabolites reflected the efficacy of AAV gene therapy. Sphingolipid levels were highly predictive of neurologic disease progression, with 11 metabolites having a coefficient of determination (R²) > 0.75. Also, a specific detergent additive significantly increased the recovery of certain lipid species in cerebrospinal fluid samples. This report demonstrates the methodology and utility of targeted lipidomics to examine the pathophysiology of lipid storage disorders.

Novel Biomarkers of Human GM1 Gangliosidosis Reflect the Clinical Efficacy of Gene Therapy in a Feline Model

GM1 gangliosidosis is a fatal neurodegenerative disease that affects individuals of all ages. Favorable outcomes using adeno-associated viral (AAV) gene therapy in GM1 mice and cats have prompted consideration of human clinical trials, yet there remains a paucity of objective biomarkers to track disease status. We developed a panel of biomarkers using blood, urine, cerebrospinal fluid (CSF), electrodiagnostics, 7 T MRI, and magnetic resonance spectroscopy in GM1 cats-either untreated or AAV treated for more than 5 years-and compared them to markers in human GM1 patients where possible. Significant alterations were noted in CSF and blood of GM1 humans and cats, with partial or full normalization after gene therapy in cats. Gene therapy improved the rhythmic slowing of electroencephalograms (EEGs) in GM1 cats, a phenomenon present also in GM1 patients, but nonetheless the epileptiform activity persisted. After gene therapy, MR-based analyses revealed remarkable preservation of brain architecture and correction of brain metabolites associated with microgliosis, neuroaxonal loss, and demyelination. Therapeutic benefit of AAV gene therapy in GM1 cats, many of which maintain near-normal function >5 years post-treatment, supports the strong consideration of human clinical trials, for which the biomarkers described herein will be essential for outcome assessment.

In situ detection of GM1 and GM2 gangliosides using immunohistochemical and immunofluorescent techniques for auxiliary diagnosis of canine and feline gangliosidoses

Background

GM1 and GM2 gangliosidoses are progressive neurodegenerative lysosomal storage diseases resulting from the excessive accumulation of GM1 and GM2 gangliosides in the lysosomes, respectively. The diagnosis of gangliosidosis is carried out based on comprehensive findings using various types of specimens for histological, ultrastructural, biochemical and genetic analyses. Therefore, the partial absence or lack of specimens might have resulted in many undiagnosed cases. The aim of the present study was to establish immunohistochemical and immunofluorescent techniques for the auxiliary diagnosis of canine and feline gangliosidoses, using paraffin-embedded brain specimens stored for a long period.

Results

Using hematoxylin and eosin staining, cytoplasmic accumulation of pale to eosinophilic granular materials in swollen neurons was observed in animals previously diagnosed with GM1 or GM2 gangliosidosis. The immunohistochemical and immunofluorescent techniques developed in this study clearly demonstrated the accumulated material to be either GM1 or GM2 ganglioside.

Conclusions

Immunohistochemical and immunofluorescent techniques using stored paraffin-embedded brain specimens are useful for the retrospective diagnosis of GM1 and GM2 gangliosidoses in dogs and cats.

GM1 gangliosidosis in a Japanese domestic cat: a new variant identified in Hokkaido, Japan

A male Japanese domestic cat with retarded growth in Hokkaido, Japan, showed progressive motor dysfunction, such as ataxia starting at 3 months of age and tremors, visual disorder and seizure after 4 months of age. Finally, the cat died of neurological deterioration at 9 months of age. Approximately half of the peripheral blood lymphocytes had multiple abnormal vacuoles. Magnetic resonance imaging showed bisymmetrical hyperintensity in the white matter of the parietal and occipital lobes in the forebrain on T2-weighted and fluid-attenuated inversion recovery images, and mild encephalatrophy of the olfactory bulbs and temporal lobes. The activity of lysosomal acid β-galactosidase in leukocytes was negligible, resulting in the biochemical diagnosis of GM1 gangliosidosis. Histologically, swollen neurons characterized by accumulation of pale, slightly granular cytoplasmic materials were observed throughout the central nervous system. Dysmyelination or demyelination and gemistocytic astrocytosis were observed in the white matter. Ultrastructually, membranous cytoplasmic bodies were detected in the lysosomes of neurons. However, genetic analysis did not identify the c.1448G>C mutation, which is the single known mutation of feline GM1 gangliosidosis, suggesting that the cat was affected with a new variant of the feline disease.

Bis(monoacylglycero)phosphate: a secondary storage lipid in the gangliosidoses

Bis(monoacylglycero)phosphate (BMP) is a negatively charged glycerophospholipid with an unusual sn-1;sn-1' structural configuration. BMP is primarily enriched in endosomal/lysosomal membranes. BMP is thought to play a role in glycosphingolipid degradation and cholesterol transport. Elevated BMP levels have been found in many lysosomal storage diseases (LSDs), suggesting an association with lysosomal storage material. The gangliosidoses are a group of neurodegenerative LSDs involving the accumulation of either GM1 or GM2 gangliosides resulting from inherited deficiencies in β-galactosidase or β-hexosaminidase, respectively. Little information is available on BMP levels in gangliosidosis brain tissue. Our results showed that the content of BMP in brain was significantly greater in humans and in animals (mice, cats, American black bears) with either GM1 or GM2 ganglioside storage diseases, than in brains of normal subjects. The storage of BMP and ganglioside GM2 in brain were reduced similarly following adeno-associated viral-mediated gene therapy in Sandhoff disease mice. We also found that C22:6, C18:0, and C18:1 were the predominant BMP fatty acid species in gangliosidosis brains. The results show that BMP accumulates as a secondary storage material in the brain of a broad range of mammals with gangliosidoses.

A review of gene therapy in canine and feline models of lysosomal storage disorders

Lysosomal storage disorders (LSDs) are inherited diseases that result from the intracellular accumulation of incompletely degraded macromolecules. The majority of LSDs affect both the peripheral and central nervous systems and are not effectively treated by enzyme replacement therapy, substrate reduction therapy, or bone marrow transplantation. Advances in adeno-associated virus and retroviral vector development over the past decade have resurged gene therapy as a promising therapeutic intervention for these monogenic diseases. Animal models of LSDs provide a necessary intermediate to optimize gene therapy protocols and assess the safety and efficacy of treatment prior to initiating human clinical trials. Numerous LSDs are naturally occurring in large animal models and closely reiterate the lesions, biochemical defect, and clinical phenotype observed in human patients, and whose lifetime is sufficiently long to assess the effect on symptoms that develop later in life. Herein, we review that gene therapy in large animal models (dogs and cats) of LSDs improved many manifestations of disease, and may be used in patients in the near future.

Biomarkers for disease progression and AAV therapeutic efficacy in feline Sandhoff disease

The GM2 gangliosidoses, Tay-Sachs disease (TSD) and Sandhoff disease (SD), are progressive neurodegenerative disorders that are caused by a mutation in the enzyme β-N-acetylhexosaminidase (Hex). Due to the recent emergence of novel experimental treatments, biomarker development has become particularly relevant in GM2 gangliosidosis as an objective means to measure therapeutic efficacy. Here we describe blood, cerebrospinal fluid (CSF), magnetic resonance imaging (MRI), and electrodiagnostic methods for evaluating disease progression in the feline SD model and application of these approaches to assess AAV-mediated gene therapy. SD cats were treated by intracranial injections of the thalami combined with either the deep cerebellar nuclei or a single lateral ventricle using AAVrh8 vectors encoding feline Hex. Significantly altered in untreated SD cats, blood and CSF based biomarkers were largely normalized after AAV gene therapy. Also reduced after treatment were expansion of the lysosomal compartment in peripheral blood mononuclear cells and elevated activity of secondary lysosomal enzymes. MRI changes characteristic of the gangliosidoses were documented in SD cats and normalized after AAV gene therapy. The minimally invasive biomarkers reported herein should be useful to assess disease progression of untreated SD patients and those in future clinical trials.

Polycystic kidneys and GM2 gangliosidosis-like disease in neonatal springboks (Antidorcas marsupialis)

Clinical, gross, histopathologic, electron microscopic findings and enzymatic analysis of 4 captive, juvenile springboks (Antidorcas marsupialis) showing both polycystic kidneys and a storage disease are described. Springbok offspring (4 of 34; 12%) were affected by either one or both disorders in a German zoo within a period of 5 years (2008-2013). Macroscopic findings included bilaterally severely enlarged kidneys displaying numerous cysts in 4 animals and superior brachygnathism in 2 animals. Histopathologically, kidneys of 4 animals displayed cystic dilation of the renal tubules. In addition, abundant cytoplasmic vacuoles with a diameter ranging from 2 to 10 μm in neurons of the central and peripheral nervous system, hepatocytes, thyroid follicular epithelial cells, pancreatic islets of Langerhans and renal tubular cells were found in 2 springbok neonates indicative of an additional storage disease. Ultrastructurally, round electron-lucent vacuoles, up to 4 μm in diameter, were present in neurons. Enzymatic analysis of liver and kidney tissue of 1 affected springbok revealed a reduced activity of total hexosaminidase (Hex) with relatively increased HexA activity at the same level of total Hex, suggesting a hexosaminidase defect. Pedigree analysis suggested a monogenic autosomal recessive inheritance for both diseases. In summary, related springboks showed 2 different changes resembling both polycystic kidney and a GM2 gangliosidosis similar to the human Sandhoff disease. Whether the simultaneous occurrence of these 2 entities represents an incidental finding or has a genetic link needs to be investigated in future studies.

Sustained normalization of neurological disease after intracranial gene therapy in a feline model

Progressive debilitating neurological defects characterize feline G(M1) gangliosidosis, a lysosomal storage disease caused by deficiency of lysosomal β-galactosidase. No effective therapy exists for affected children, who often die before age 5 years. An adeno-associated viral vector carrying the therapeutic gene was injected bilaterally into two brain targets (thalamus and deep cerebellar nuclei) of a feline model of G(M1) gangliosidosis. Gene therapy normalized β-galactosidase activity and storage throughout the brain and spinal cord. The mean survival of 12 treated G(M1) animals was >38 months, compared to 8 months for untreated animals. Seven of the eight treated animals remaining alive demonstrated normalization of disease, with abrogation of many symptoms including gait deficits and postural imbalance. Sustained correction of the G(M1) gangliosidosis disease phenotype after limited intracranial targeting by gene therapy in a large animal model suggests that this approach may be useful for treating the human version of this lysosomal storage disorder.

High resolution MRI anatomy of the cat brain at 3 Tesla

BACKGROUND

Feline models of neurologic diseases, such as lysosomal storage diseases, leukodystrophies, Parkinson's disease, stroke and NeuroAIDS, accurately recreate many aspects of human disease allowing for comparative study of neuropathology and the testing of novel therapeutics. Here we describe in vivo visualization of fine structures within the feline brain that were previously only visible post mortem.

NEW METHOD

3Tesla MR images were acquired using T1-weighted (T1w) 3D magnetization-prepared rapid gradient echo (MPRAGE) sequence (0.4mm isotropic resolution) and T2-weighted (T2w) turbo spin echo (TSE) images (0.3mm×0.3mm×1mm resolution). Anatomic structures were identified based on feline and canine histology.

RESULTS

T2w high resolution MR images with detailed structural identification are provided in transverse, sagittal and dorsal planes. T1w MR images are provided electronically in three dimensions for unrestricted spatial evaluation.

COMPARISON WITH EXISTING METHODS

Many areas of the feline brain previously unresolvable on MRI are clearly visible in three orientations, including the dentate, interpositus and fastigial cerebellar nuclei, cranial nerves, lateral geniculate nucleus, optic radiation, cochlea, caudal colliculus, temporal lobe, precuneus, spinocerebellar tract, vestibular nuclei, reticular formation, pyramids and rostral and middle cerebral arteries. Additionally, the feline brain is represented in three dimensions for the first time.

CONCLUSIONS

These data establish normal appearance of detailed anatomical structures of the feline brain, which provide reference when evaluating neurologic disease or testing efficacy of novel therapeutics in animal models.

Ganglioside storage diseases: on the road to management

Although the biochemical and genetic basis for the GM1 and GM2 gangliosidoses has been known for decades, effective therapies for these diseases remain in early stages of development. The difficulty with many therapeutic strategies for treating the gangliosidoses comes largely from their inability to remove stored ganglioside once it accumulates in central nervous system (CNS) neurons and glia. This chapter highlights advances made using substrate reduction therapy and gene therapy in reducing CNS ganglioside storage. Information obtained from mouse and feline models provides insight on therapeutic strategies that could be effective in human clinical trials. In addition, information is presented showing how a calorie-restricted diet might facilitate therapeutic drug delivery to the CNS. The development of multiple new therapeutic approaches offers hope that longer-term management of these diseases can be achieved. It is also clear that multiple therapeutic strategies will likely be needed to provide the most complete management.

Cats: a gold mine for ophthalmology

Over 200 hereditary diseases have been identified and reported in the cat, several of which affect the eye, with homology to human hereditary disease. Compared with traditional murine models, the cat demonstrates more features in common with humans, including many anatomic and physiologic similarities, longer life span, increased size, and a genetically more heterogeneous background. The development of genomic resources in the cat has facilitated mapping and further characterization of feline models. During recent years, the wealth of knowledge in feline ophthalmology and neurophysiology has been extended to include new diseases of significant interest for comparative ophthalmology. This makes the cat an extremely valuable animal species to utilize for further research into disease processes affecting both cats and humans. This is especially true in the advancement and study of new treatment regimens and for extended therapeutic trials. Groups of feline eye diseases reviewed in the following are lysosomal storage disorders, congenital glaucoma, and neuroretinal degenerations. Each has important implications for human ophthalmic research.

Identification of Bangladeshi domestic cats with GM1 gangliosidosis caused by the c.1448G>C mutation of the feline GLB1 gene: case study

GM1 gangliosidosis is a fatal, progressive neurodegenerative lysosomal storage disease caused by mutations in the β-galactosidase (GLB1) gene. In feline GM1 gangliosidosis, a pathogenic mutation (c.1448G>C) in the feline GLB1 gene was identified in Siamese cats in the United States and Japan and in Korat cats in Western countries. The present study found the homozygous c.1448G>C mutation in 2 apparent littermate native kittens in Bangladesh that were exhibiting neurological signs. This is the first identification of GM1 gangliosidosis in native domestic cats in Southeast Asia. This pathogenic mutation seems to have been present in the domestic cat population in the Siamese region and may have been transferred to pure breeds such as Siamese and Korat cats originating in this region.

Evaluation of N-nonyl-deoxygalactonojirimycin as a pharmacological chaperone for human GM1 gangliosidosis leads to identification of a feline model suitable for testing enzyme enhancement therapy

Deficiencies of lysosomal β-D-galactosidase can result in GM1 gangliosidosis, a severe neurodegenerative disease characterized by massive neuronal storage of GM1 ganglioside in the brain. Currently there are no available therapies that can even slow the progression of this disease. Enzyme enhancement therapy utilizes small molecules that can often cross the blood brain barrier, but are also often competitive inhibitors of their target enzyme. It is a promising new approach for treating diseases, often caused by missense mutations, associated with dramatically reduced levels of functionally folded enzyme. Despite a number of positive reports based on assays performed with patient cells, skepticism persists that an inhibitor-based treatment can increase mutant enzyme activity in vivo. To date no appropriate animal model, i.e., one that recapitulates a responsive human genotype and clinical phenotype, has been reported that could be used to validate enzyme enhancement therapy. In this report, we identify a novel enzyme enhancement-agent, N-nonyl-deoxygalactonojirimycin, that enhances the mutant β-galactosidase activity in the lysosomes of a number of patient cell lines containing a variety of missense mutations. We then demonstrate that treatment of cells from a previously described, naturally occurring feline model (that biochemically, clinically and molecularly closely mimics GM1 gangliosidosis in humans) with this molecule, results in a robust enhancement of their mutant lysosomal β-galactosidase activity. These data indicate that the feline model could be used to validate this therapeutic approach and determine the relationship between the disease stage at which this therapy is initiated and the maximum clinical benefits obtainable.

Mutation analysis of GM1 gangliosidosis in a Siamese cat from Japan in the 1960s

GM1 gangliosidosis is a fatal, progressive neurodegenerative lysosomal storage disease caused by mutations of the β-galactosidase ( GLB1) gene. In feline GM1 gangliosidosis, a pathogenic mutation (c.1448G>C) of the feline GLB1 gene was identified in Siamese and Korat cats previously diagnosed with the disease in the USA and Italy, respectively. The present study demonstrated the same mutation in a Siamese cat that had been diagnosed with GM1 gangliosidosis in Japan in the 1960s. The mutation was confirmed using DNA extracted from stored paraffin-embedded brain tissue by a direct sequencing method and a polymerase chain reaction–restriction fragment length polymorphism assay. This pathogenic mutation seems to have been distributed around the world.

Rapid detection of GM1 ganglioside in cerebrospinal fluid in dogs with GM1 gangliosidosis using matrix-assisted laser desorption ionization time-of-flight mass spectrometry

The concentration of GM1 (monosialotetrahexosyl ganglioside) in cerebrospinal fluid (CSF) is markedly increased in dogs with GM1 gangliosidosis due to GM1 accumulation in the central nervous system and leakage to the CSF. The present study established a rapid and simple method for detection of accumulated GM1 in the CSF in dogs with GM1 gangliosidosis using matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI TOF MS) and discusses the usefulness of this method for the rapid diagnosis and/or high-risk screening of this disease in domestic animals. Cerebrospinal fluid was collected from normal dogs and 4- to 11-month-old Shiba dogs with GM1 gangliosidosis. The MALDI TOF MS analysis was carried out in combination with a special sample plate and a simple desalting step on the plate. Specific signs of GM1 could be detected in the standard GM1 solutions at concentrations of 50 nmol/l or more. The signs were also clearly detected in CSF (131–618 nmol/l) in affected dogs, but not in normal canine CSF (12 ± 5 nmol/l, mean ± standard deviation). The results demonstrated that MALDI TOF MS can detect GM1 accumulated in canine CSF even in the early stage of the disease. In conclusion, the rapid detection of increased CSF GM1 using MALDI TOF MS is a useful method for diagnosis and/or screening for canine GM1 gangliosidosis.

Lessons learnt from animal models: pathophysiology of neuropathic lysosomal storage disorders

Approximately 50 inborn errors of metabolism known as lysosomal storage disorders have been discovered to date, most of which are due to a single mutation in a gene encoding a soluble lysosomal enzyme. Consequently, inadequate enzyme activity results in the accumulation of substrates for that enzyme, invariably accompanied by a wide variety of secondary pathological changes. Many of these conditions remain untreatable, and therefore, research into pathogenic processes and potential treatment strategies is intense. A key tool for researchers in this area is the availability of clinically relevant animal models in which to study disease manifestation and evaluate therapeutic outcomes. Large numbers of both naturally occurring and genetically modified animal models of neurodegenerative lysosomal storage disorders are in existence, with spontaneous models occurring in both large domestic (e.g., cat, dog, sheep) and small (e.g., mouse) animal species. Many have undergone rigorous phenotypic characterization and are now providing us with insights into neurological disease processes. The purpose of this review is to highlight some of the major lessons learnt from these studies.

Gene therapy for lysosomal storage diseases (LSDs) in large animal models

Lysosomal storage diseases (LSDs) are inherited metabolic disorders caused by deficient activity of a single lysosomal enzyme or other defects resulting in deficient catabolism of large substrates in lysosomes. There are more than 40 forms of inherited LSDs known to occur in humans, with an aggregate incidence estimated at 1 in 7,000 live births. Clinical signs result from the inability of lysosomes to degrade large substrates; because most lysosomal enzymes are ubiquitously expressed, a deficiency in a single enzyme can affect multiple organ systems. Thus LSDs are associated with high morbidity and mortality and represent a significant burden on patients, their families, the health care system, and society. Because lysosomal enzymes are trafficked by a mannose 6-phosphate receptor mechanism, normal enzyme provided to deficient cells can be localized to the lysosome to reduce and prevent storage. However, many LSDs remain untreatable, and gene therapy holds the promise for effective therapy. Other therapies for some LSDs do exist, or are under evaluation, including heterologous bone marrow or cord blood transplantation (BMT), enzyme replacement therapy (ERT), and substrate reduction therapy (SRT), but these treatments are associated with significant concerns, including high morbidity and mortality (BMT), limited positive outcomes (BMT), incomplete response to therapy (BMT, ERT, and SRT), life-long therapy (ERT, SRT), and cost (BMT, ERT, SRT). Gene therapy represents a potential alternative, albeit with its own attendant concerns, including levels and persistence of expression and insertional mutagenesis resulting in neoplasia. Naturally occurring animal homologues of LSDs have been described in all common domestic animals (and in some that are less common) and these animal models play a critical role in evaluating the efficacy and safety of therapy.

Neurodegenerative lysosomal storage disease in European Burmese cats with hexosaminidase beta-subunit deficiency

GM2 gangliosidosis is a fatal, progressive neuronopathic lysosomal storage disease resulting from a deficiency of beta-N-acetylhexosaminidase (EC 3.2.1.52) activity. GM2 gangliosidosis occurs with varying degrees of severity in humans and in a variety of animals, including cats. In the current research, European Burmese cats presented with clinical neurological signs and histopathological features typical of a lysosomal storage disease. Thin layer chromatography revealed substantial storage of GM2 ganglioside in brain tissue of affected cats, and assays with a synthetic fluorogenic substrate confirmed the absence of hexosaminidase activity. When the hexosaminidase beta-subunit cDNA was sequenced from affected cats, a 91 base pair deletion constituting the entirety of exon 12 was documented. Subsequent sequencing of introns 11 and 12 revealed a 15 base pair deletion at the 3' end of intron 11 that included the preferred splice acceptor site, generating two minor transcripts from cryptic splice acceptor sites in affected Burmese cats. In the cerebral cortex of affected cats, hexosaminidase beta-subunit mRNA levels were approximately 1.5 times higher than normal (P<0.001), while beta-subunit protein levels were substantially reduced on Western blots.

Molecular consequences of the pathogenic mutation in feline GM1 gangliosidosis

G(M1) gangliosidosis is an inherited, fatal neurodegenerative disease caused by deficiency of lysosomal beta-d-galactosidase (EC 3.2.1.23) and consequent storage of undegraded G(M1) ganglioside. To characterize the genetic mutation responsible for feline G(M1) gangliosidosis, the normal sequence of feline beta-galactosidase cDNA first was defined. The feline beta-galactosidase open reading frame is 2010 base pairs, producing a protein of 669 amino acids. The putative signal sequence consists of amino acids 1-24 of the beta-galactosidase precursor protein, which contains seven potential N-linked glycosylation sites, as in the human protein. Overall sequence homology between feline and human beta-galactosidase is 74% for the open reading frame and 82% for the amino acid sequence. After normal beta-galactosidase was sequenced, the mutation responsible for feline G(M1) gangliosidosis was defined as a G to C substitution at position 1448 of the open reading frame, resulting in an amino acid substitution at arginine 483, known to cause G(M1) gangliosidosis in humans. Feline beta-galactosidase messenger RNA levels were normal in cerebral cortex, as determined by quantitative RT-PCR assays. Although enzymatic activity is severely reduced by the mutation, a full-length feline beta-galactosidase cDNA restored activity in transfected G(M1) fibroblasts to 18-times normal. beta-Galactosidase protein levels in G(M1) tissues were normal on Western blots, but immunofluorescence analysis demonstrated that the majority of mutant beta-galactosidase protein did not reach the lysosome. Additionally, G(M1) cat fibroblasts demonstrated increased expression of glucose-related protein 78/BiP and protein disulfide isomerase, suggesting that the unfolded protein response plays a role in pathogenesis of feline G(M1) gangliosidosis.

Generation and characterization of recombinant feline beta-galactosidase for preclinical enzyme replacement therapy studies in GM1 gangliosidosis

Lysosomal beta-galactosidase is required for the degradation of GM1 ganglioside and other glycolipids and glycoproteins with a terminal galactose moiety. Deficiency of this enzyme leads to the lysosomal storage disorder, GM1 gangliosidosis, marked by severe neurodegeneration resulting in premature death. As a step towards preclinical studies for enzyme replacement therapy in an animal model of GM1 gangliosidosis, a feline beta-galactosidase cDNA was cloned into a mammalian expression vector and subsequently expressed in Chinese hamster ovary (CHO-K1) cells. The enzyme secreted into culture medium exhibited specific activity on two synthetic substrates as well as on the native beta-galactosidase substrate, GM1 ganglioside. The enzyme was purified from transfected CHO-K1 cell culture medium by chromatography on PATG-agarose. The affinity-purified enzyme preparation consisted mainly of the protein with approximate molecular weight of 94 kDa and displayed immunoreactivity with antibodies raised against a 16-mer synthetic peptide corresponding to C-terminal amino acid sequence deduced from the feline beta-galactosidase cDNA.

Inherited metabolic disease in companion animals: searching for nature's mistakes

Inborn errors of metabolism are caused by genetic defects in intermediary metabolic pathways. Although long considered to be the domain of human paediatric medicine, they are also recognised with increasing frequency in companion animals. The diagnosis of diseased animals can be achieved by searching for abnormal metabolites in body fluids, although such screening programmes have, until now, not been widely available to the small animal clinician. A comprehensive battery of analytical tools exists for screening for inborn metabolic diseases in humans which can be applied to animals and serve not only for the diagnosis of affected patients but also to detect asymptomatic carriers and further our understanding of metabolic pathways in dogs and cats. Moreover, naturally occurring animal models of inherited metabolic diseases provide a unique opportunity to study the biochemical and molecular pathogenesis of these disorders and to investigate possible therapeutic options.

Neural progenitor cell transplantation and imaging in a large animal model

To evaluate neural stem/progenitor cell (NPC) transplantation therapy in cat models of neurodegenerative diseases, we have isolated, expanded and characterized feline NPCs (fNPCs) from normal fetal cat brain. Feline NPCs responsive to both human epidermal growth factor (hEGF) and human fibroblast growth factor 2 (hFGF2) proliferated as neurospheres, which were able to differentiate to neurons and glial cells. The analysis of growth factors indicated that both hEGF and hFGF2 were required for proliferation of fNPCs. In contrast to the effect on human NPCs, human leukemia inhibitory factor (hLIF) enhanced differentiation of fNPCs. Expanded fNPCs were injected into the brains of normal adult cats. Immunohistochemical analysis showed that the majority of transplanted cells were located adjacent to the injection site and some fNPCs differentiated into neurons. The survival of transplanted fNPCs over time was monitored using non-invasive bioluminescent imaging technology. This study provided the first evidence of allotransplantation of fNPCs into feline CNS. Cats have heterogeneous genetic backgrounds and possess neurological diseases that closely resemble analogous human diseases. The characterization of fNPCs and exploration of non-invasive bioluminescent imaging to track transplanted cells in this study will allow evaluation of NPC transplantation therapy using feline models of human neurological diseases.

Development of quantitative polymerase chain reaction assays for allelic discrimination of gangliosidoses in cats

OBJECTIVE

To develop quantitative PCR (qPCR) assays with allele-specific primers to provide a rapid and accurate diagnostic and screening test for the 3 mutations identified as causes of gangliosidoses in domestic cats.

SAMPLE POPULATION

DNA samples obtained from archived feline blood samples submitted for GM1 and GM2 testing.

PROCEDURES

A qPCR assay was developed for each mutation to monitor the efficiency of PCR amplification. Results were determined on the basis of the fluorescent intensity of DNA staining.

RESULTS

Samples from 60 cats were screened by use of the 3 qPCR assays. Of these, 59 qPCR results agreed with the sequence-derived genotypes. The phenotype (affected) for the other cat agreed with results for the qPCR assay, which indicated that interpretation of the sequence-based result was incorrect.

CONCLUSIONS AND CLINICAL RELEVANCE

The qPCR assays offer a sensitive, rapid, and reproducible technique for allelic discrimination without the need for complicated processing steps, such as hybridization or sequencing, after PCR procedures. These assays may prove beneficial for a rapid diagnosis of gangliosidoses in cats and could also provide a means for reliable large-scale screening for the carrier state, thereby accelerating the eradication of these debilitating diseases from feline populations.

Animal models for mucopolysaccharidosis disorders and their clinical relevance

Progress in understanding how a particular genotype produces the phenotype of an inborn error of metabolism, such as a mucopolysaccharidosis, in human patients has been facilitated by the study of animals with mutations in the orthologous genes. These are not just animal models, but true orthologues of the human genetic disease, with defects involving the same evolutionarily conserved genes and the same molecular, biochemical, and anatomic lesions as in human patients. These animals are often domestic species because of the individual medical attention paid to them, particularly dogs and cats. In addition, naturally occurring mouse models have also been found in breeding colonies. Within the last several decades, advances in molecular biology have allowed the production of knockout mouse models of human genetic disease, including the lysosomal storage diseases. The ability to use both inbred strains of a small, prolific species together with larger out-bred animals found because of their disease phenotype provides a powerful combination with which to investigate pathogenesis, develop approaches to therapy, and define biomarkers to evaluate therapeutic success. This has been true for the inborn errors of metabolism and, in particular, the mucopolysaccharidoses.

CONCLUSION

Animal models of human genetic disease continue to play an important role in understanding the molecular and physiological consequences of lysosomal storage diseases and to provide an opportunity to evaluate the efficacy and safety of therapeutic interventions.

Mutation of the GM2 activator protein in a feline model of GM2 gangliosidosis

The G(M2) activator protein is required for successful degradation of G(M2) ganglioside by the A isozyme of lysosomal beta-N-acetylhexosaminidase (EC 3.2.1.52). Deficiency of the G(M2) activator protein leads to a relentlessly progressive accumulation of G(M2) ganglioside in neuronal lysosomes and subsequent fatal deterioration of central nervous system function. G(M2) activator deficiency has been described in humans, dogs and mice. This manuscript reports the discovery and characterization of a feline model of G(M2) activator deficiency that exhibits many disease traits typical of the disorder in other species. Cats deficient in the G(M2) activator protein develop clinical signs at approximately 14 months of age, including motor incoordination and exaggerated startle response to sharp sounds. Affected cats exhibit central nervous system abnormalities such as swollen neurons, membranous cytoplasmic bodies, increased sialic acid content and elevated levels of G(M2) ganglioside. As is typical of G(M2) activator deficiency, hexosaminidase A activity in tissue homogenates appears normal when assayed with a commonly used synthetic substrate. When the G(M2) activator cDNA was sequenced from normal and affected cats, a deletion of 4 base pairs was identified as the causative mutation, resulting in alteration of 21 amino acids at the C terminus of the G(M2) activator protein.

An inversion of 25 base pairs causes feline GM2 gangliosidosis variant

In G(M2) gangliosidosis variant 0, a defect in the beta-subunit of lysosomal beta-N-acetylhexosaminidase (EC 3.2.1.52) causes abnormal accumulation of G(M2) ganglioside and severe neurodegeneration. Distinct feline models of G(M2) gangliosidosis variant 0 have been described in both domestic shorthair and Korat cats. In this study, we determined that the causative mutation of G(M2) gangliosidosis in the domestic shorthair cat is a 25-base-pair inversion at the extreme 3' end of the beta-subunit (HEXB) coding sequence, which introduces three amino acid substitutions at the carboxyl terminus of the protein and a translational stop that is eight amino acids premature. Cats homozygous for the 25-base-pair inversion express levels of beta-subunit mRNA approximately 190% of normal and protein levels only 10-20% of normal. Because the 25-base-pair inversion is similar to mutations in the terminal exon of human HEXB, the domestic shorthair cat should serve as an appropriate model to study the molecular pathogenesis of human G(M2) gangliosidosis variant 0 (Sandhoff disease).

Isolation and characterization of multipotential mesenchymal stem cells from feline bone marrow

OBJECTIVE

Although several types of stem cells have been isolated from rodent and human tissues, very few data exist on stem cell isolation from nonrodent animals, which seriously limits the advancement of stem cell biology and its ultimate translation to human clinical applications. Domestic cats are used frequently in biomedical research and are the preferred species for studies of normal physiology and disease, particularly in neuroscience. Therefore, the objective of this study was to characterize mesenchymal stem cells (MSC) from feline bone marrow for use in research on the application of stem cells to human health problems for which cats are the preferred model.

METHODS

Mesenchymal stem cells from feline bone marrow were isolated by standard methodology developed for other species and characterized according to morphology, growth traits, cell-surface antigen profile, and differentiation repertoire in vitro.

RESULTS

Feline mesenchymal stem cells exhibit a fibroblast-like morphology with bipolar or polygonal cell bodies and possess a cell-surface antigen profile similar to their rodent and human counterparts. Feline MSC exist at a frequency of 1 in 3.8 x 10(5) bone marrow mononuclear cells and are capable of differentiation to adipocytic, osteocytic, and neuronal phenotypes when exposed to appropriate induction media.

CONCLUSIONS

Mesenchymal stem cells isolated from feline bone marrow possess several traits typical of MSC from other species. Characterization of feline mesenchymal stem cells will facilitate future studies of stem cell biology and therapeutics for which the domestic cat is an indispensable model.

Adult-onset cerebellar cortical abiotrophy and retinal degeneration in a domestic shorthair cat

A 4-year-old, neutered male domestic shorthair cat presented for evaluation of ataxia and visual deficits. Neurological examination revealed severe cerebellar ataxia with symmetrical hypermetria and spasticity, a coarse whole-body tremor, positional vertical nystagmus, and frequent loss of balance. A menace response was absent bilaterally, and the pupils were widely dilated in room light. A funduscopic examination revealed markedly attenuated to absent retinal vessels and pronounced tapetal hyperreflectivity, findings consistent with end-stage retinal degeneration. Blood work evaluation included retroviral testing, a complete blood count, serum biochemistry analysis, taurine levels, and toxoplasma immunoglobulin G and immunoglobulin M titers. All were within reference ranges. The patient was euthanized, and a necropsy was performed. Microscopically, lesions of the nervous system were confined to the cerebellum and were consistent with cerebellar cortical abiotrophy. Selective photoreceptor degeneration was seen on histopathological examination of the retina with a reduction in the number of rods and cones. The combination of clinical findings and histopathological lesions seen here has not been previously reported in the cat.

GM1-gangliosidosis in Alaskan huskies: clinical and pathologic findings

Three Alaskan Huskies, two females and one male, were diagnosed with GM1-gangliosidosis. Clinically, diseased animals exhibited proportional dwarfism and developed progressive neurologic impairment with signs of cerebellar dysfunction at the age of 5-7 months. Skeletal lesions characterized by retarded enchondral ossification of vertebral epiphyses were revealed by radiographs of the male dog at 5.5 months of age. Histologic examination of the central nervous system (CNS) revealed that most neurons were enlarged with a foamy to granular cytoplasm due to tightly packed vacuoles that displaced the Nissl substance. Vacuoles in paraffin-embedded sections stained positively with Luxol fast blue and Grocott's method, and in frozen sections vacuoles were periodic acid-Schiff positive. Foamy vacuolation also occurred within neurons of the autonomic ganglia. Extracerebral cells such as macrophages and peripheral lymphocytes also displayed foamy cytoplasm and vacuolation. In the CNS of diseased animals, a mild demyelination and axonal degeneration was accompanied by a significant astrogliosis (P < 0.05) in the gray matter as compared with age- and sex-matched control dogs. There was also a significant loss (P < 0.05) of oligodendrocytes in the gray and white matter of affected animals as compared with controls. Ultrastructurally, the neuronal storage material consisted of numerous circular to concentric whorls of lamellated membranes or stacks of membranes in parallel arrays. GM1-gangliosidosis in Alaskan Huskies resembles beta-galactosidase deficiency in other canine breeds, and these CNS disorders may be a consequence of neuronal storage and disturbed myelin processing.

GM1 gangliosidosis in shiba dogs

A six-month-old shiba dog with a one-month history of progressive motor dysfunction showed clinical signs of a cerebellar disorder, including ataxia, dysmetria and intention tremor of the head. Histopathological and ultrastructural studies revealed distended neurons packed with membranous cytoplasmic bodies throughout the central nervous system. The activities of lysosomal acid beta-galactosidase in its leucocytes and liver were less than 2 per cent of the control levels, and the compound accumulated in the brain was identified as GM1 ganglioside. A sibling which died immediately after birth was shown to have a beta-galactosidase deficiency in the brain and visceral organs. A family study revealed that the sire and dam of the probands were heterozygotes with approximately half of the normal level of beta-galactosidase activity, suggesting an autosomal recessive pattern of inheritance.

Alterations in the growth hormone/insulin-like growth factor I pathways in feline GM1 gangliosidosis

Cats affected with feline GM1 gangliosidosis, an autosomal, recessively inherited, lysosomal enzymopathy, have progressive neurological dysfunction, premature thymic involution, stunted growth, and premature death. Although increased membrane GM1 gangliosides can result in increased apoptosis of thymocytes, there is not a direct correlation between thymocyte surface GM1 and thymic apoptosis in vivo, suggesting that other factors may be important to the pathogenesis of thymic involution in affected cats. Because GH and insulin-like growth factor I (IGF-I) are important hormonal peptides supporting thymic function and affecting growth throughout the body, particularly in the prepubescent period, several components of the GH/IGF-I pathway were compared in GM1 mutant and normal age-matched cats. GM1 mutant cat serum IGF-I concentrations were reduced significantly compared with those in normal cats by 150 days of age, and GM1 mutant cats had no peripubertal increase in serum IGF-I. Additionally, IGF-binding protein-3 was reduced, and IGF-binding protein-2 was elevated significantly in GM1 mutant cats more than 200 days of age. Liver IGF-I messenger RNA and pituitary GH messenger RNA both were reduced significantly in GM1 mutant cats. After stimulation by exogenous recombinant canine GH, serum IGF-I levels increased significantly in GM1 mutant cats, indicating that GH/IGF-I signaling pathways within the liver remain intact and suggesting that alterations are external to the liver.

Lysosomal storage diseases of animals: an essay in comparative pathology

A wide variety of inherited lysosomal hydrolase deficiencies have been reported in animals and are characterized by accumulation of sphingolipids, glycolipids, oligosaccharides, or mucopolysaccharides within lysosomes. Inhibitors of a lysosomal hydrolase, e.g., swainsonine, may also induce storage disease. Another group of lysosomal storage diseases, the ceroid-lipofuscinoses, involve the accumulation of hydrophobic proteins, but their pathogenesis is unclear. Some of these diseases are of veterinary importance, and those caused by a hydrolase deficiency can be controlled by detection of heterozygotes through the gene dosage phenomenon or by molecular genetic techniques. Other of these diseases are important to biomedical research either as models of the analogous human disease and/or through their ability to help elucidate specific aspects of cell biology. Some of these models have been used to explore possible therapeutic strategies and to define their limitations and expectations.

Beta-galactosidase-deficient mouse as an animal model for GM1-gangliosidosis

GM1-gangliosidosis is a progressive neurological disease in humans caused by deficiency of lysosomal acid beta-galactosidase, which hydrolyses the terminal beta-galactosidic residue from ganglioside GM1 and other glycoconjugates. In this study, we generated a mouse model for GM1-gangliosidosis by gene targeting in embryonic stem cells. The mouse homozygous for the disrupted beta-galactosidase gene showed beta-galactosidase deficiency, presented with progressive spastic diplegia, and died of emaciation at 7-10 months of age. Pathologically, PAS-positive intracytoplasmic storage was observed in neuronal cells of various areas in the brain. Biochemical analysis revealed a marked accumulation of ganglioside GM1 and asialo GM1 in brain tissue. This animal model will be useful for pathogenetic analysis and therapeutic trial of human GM1-gangliosidosis.

Neurological manifestations of knockout mice with beta-galactosidase deficiency

We succeeded in producing the beta-galactosidase-deficient knockout mouse by gene targeting in embryonic stem cells. The mutant mice developed progressive spastic diplegia within a few months after birth, and died of emaciation at 7-10 months of age. This is an authentic murine model of human GMI-gangliosidosis, and is useful for studies of its pathogenesis and treatment.

Mucolipidosis type II in a domestic shorthair cat

A seven-month-old, female domestic shorthair cat was presented to the Veterinary Teaching Hospital, University of Zurich, with abnormal facial features, retarded growth and progressive hindlimb paresis. On physical examination the cat had a flat, broad face with hypertelorism, frontal bossing, small ears and thickened upper and lower eyelids. The corneas of both eyes were clear and the pupils were dilated. The skin was generally thickened, most prominently on the dorsal aspect of the neck. Radiography of the entire skeleton revealed a severely deformed spinal column, bilateral hip luxation with hip dysplasia, an abnormally shaped skull and generalised decreased bone opacity. The clinical features and radiographic changes were suggestive of mucopolysaccharidosis. The toluidine blue spot test on a urine sample, however, was negative for glycosaminoglycans. Further biochemical investigations revealed a deficiency of the enzyme N-acetylglucosamine-1-phosphotransferase (GlcNAc-phosphotransferase, EC 2.7.8.17) in peripheral leukocytes and an elevation of many lysosomal enzymes in the serum of the cat which is diagnostic for mucolipidosis type II. Histology and electron microscopy of different tissues are briefly summarised. The findings of this cat, the first reported case of mucolipidosis type II are compared with other similar storage diseases described in the cat.

Pyramidal neurons with ectopic dendrites in storage diseases exhibit increased GM2 ganglioside immunoreactivity

Cortical pyramidal neurons in several types of neuronal storage diseases have been shown by Golgi staining to sprout axon hillock-associated dendritic processes. Based on the relative incidence of this ectopic dendritogenesis, and on quantitative analyses of gangliosides in these same tissues, it has been proposed that abnormal accumulation of a specific metabolic product, GM2 ganglioside, is the pivotal event leading to re-initiation of dendritic sprouting [Siegel D. A. Walkley S.U. (1994) J. Neurochem. 62, 1852-1862]. In the present study, a monoclonal antibody was used to determine the cellular location of this ganglioside within the cerebral cortex of animal models of storage diseases with and without ectopic dendrite growth. Diseases exhibiting ectopic dendritogenesis included inherited and swainsonine-induced (juvenile-onset) alpha-mannosidosis, mucopolysaccharidosis type I, Niemann-Pick disease type C, and GM1 and GM2 gangliosidosis. Conditions lacking ectopic dendrite growth included adult-onset swainsonine-induced alpha-mannosidosis, fucosidosis, neuronal ceroid lipofuscinosis (Batten disease) and normal, mature brain. Immunocytochemical staining for GM2 ganglioside indicated that diseases exhibiting new dendritic sprouting with the exception of GM1 gangliosidosis, exhibited abundant GM2-like immunoreactivity within the cortical pyramidal cell population, whereas diseases without dendritic sprouting had GM2-like immunoreactivity limited to glia and/or to non-pyramidal neurons. Cortical tissues from normal animals at comparable ages and processed by similar procedures exhibited occasional glial cell staining but little or no neuronal labelling. Mechanisms by which normal cortical pyramidal regulate dendritic initiation are poorly understood. However, it is known that this event is developmentally restricted, occurring only during early brain development.(ABSTRACT TRUNCATED AT 250 WORDS)

Growth of ectopic dendrites on cortical pyramidal neurons in neuronal storage diseases correlates with abnormal accumulation of GM2 ganglioside

Ganglioside analysis and quantitative Golgi studies of the cerebral cortex of cats with ganglioside and nonganglioside lysosomal storage diseases reveal a correlation between the amount of accumulated GM2 ganglioside and the extent of ectopic dendrite growth on cortical pyramidal neurons. This correlation was not observed with any of the other gangliosides assayed for, including GM1 ganglioside. These results suggest a specific role for GM2 ganglioside in the initiation of ectopic neurites on pyramidal cells in vivo and are consistent with the developing hypothesis that different gangliosides have specific roles in different cell types dependent upon the receptor or other effector molecules with which they may interact.