Biochemical studies on a case of feline mannosidosis

A Homozygous MAN2B1 Missense Mutation in a Doberman Pinscher Dog with Neurodegeneration, Cytoplasmic Vacuoles, Autofluorescent Storage Granules, and an α-Mannosidase Deficiency

A 7-month-old Doberman Pinscher dog presented with progressive neurological signs and brain atrophy suggestive of a hereditary neurodegenerative disorder. The dog was euthanized due to the progression of disease signs. Microscopic examination of tissues collected at the time of euthanasia revealed massive accumulations of vacuolar inclusions in cells throughout the central nervous system, suggestive of a lysosomal storage disorder. A whole genome sequence generated with DNA from the affected dog contained a likely causal, homozygous missense variant in MAN2B1 that predicted an Asp104Gly amino acid substitution that was unique among whole genome sequences from over 4000 dogs. A lack of detectable α-mannosidase enzyme activity confirmed a diagnosis of a-mannosidosis. In addition to the vacuolar inclusions characteristic of α-mannosidosis, the dog exhibited accumulations of autofluorescent intracellular inclusions in some of the same tissues. The autofluorescence was similar to that which occurs in a group of lysosomal storage disorders called neuronal ceroid lipofuscinoses (NCLs). As in many of the NCLs, some of the storage bodies immunostained strongly for mitochondrial ATP synthase subunit c protein. This protein is not a substrate for α-mannosidase, so its accumulation and the development of storage body autofluorescence were likely due to a generalized impairment of lysosomal function secondary to the accumulation of α-mannosidase substrates. Thus, it appears that storage body autofluorescence and subunit c accumulation are not unique to the NCLs. Consistent with generalized lysosomal impairment, the affected dog exhibited accumulations of intracellular inclusions with varied and complex ultrastructural features characteristic of autophagolysosomes. Impaired autophagic flux may be a general feature of this class of disorders that contributes to disease pathology and could be a target for therapeutic intervention. In addition to storage body accumulation, glial activation indicative of neuroinflammation was observed in the brain and spinal cord of the proband.

Alpha-Mannosidosis: Therapeutic Strategies

Alpha-mannosidosis (α-mannosidosis) is a rare lysosomal storage disorder with an autosomal recessive inheritance caused by mutations in the gene encoding for the lysosomal α-d-mannosidase. So far, 155 variants from 191 patients have been identified and in part characterized at the biochemical level. Similarly to other lysosomal storage diseases, there is no relationship between genotype and phenotype in alpha-mannosidosis. Enzyme replacement therapy is at the moment the most effective therapy for lysosomal storage disease, including alpha-mannosidosis. In this review, the genetic of alpha-mannosidosis has been described together with the results so far obtained by two different therapeutic strategies: bone marrow transplantation and enzyme replacement therapy. The primary indication to offer hematopoietic stem cell transplantation in patients affected by alpha-mannosidosis is preservation of neurocognitive function and prevention of early death. The results obtained from a Phase I⁻II study and a Phase III study provide evidence of the positive clinical effect of the recombinant enzyme on patients with alpha-mannosidosis.

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.

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.

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.

Impaired lysosomal trimming of N-linked oligosaccharides leads to hyperglycosylation of native lysosomal proteins in mice with alpha-mannosidosis

Alpha-mannosidosis is caused by the genetic defect of the lysosomal alpha-d-mannosidase (LAMAN), which is involved in the breakdown of free alpha-linked mannose-containing oligosaccharides originating from glycoproteins with N-linked glycans, and thus manifests itself in an extensive storage of mannose-containing oligosaccharides. Here we demonstrate in a model of mice with alpha-mannosidosis that native lysosomal proteins exhibit elongated N-linked oligosaccharides as shown by two-dimensional difference gel electrophoresis, deglycosylation assays, and mass spectrometry. The analysis of cathepsin B-derived oligosaccharides revealed a hypermannosylation of glycoproteins in mice with alpha-mannosidosis as indicated by the predominance of extended Man3GlcNAc2 oligosaccharides. Treatment with recombinant human alpha-mannosidase partially corrected the hyperglycosylation of lysosomal proteins in vivo and in vitro. These data clearly demonstrate that LAMAN is involved not only in the lysosomal catabolism of free oligosaccharides but also in the trimming of asparagine-linked oligosaccharides on native lysosomal proteins.

In utero transplantation of monocytic cells in cats with alpha-mannosidosis

BACKGROUND

Lysosomal storage diseases are devastating illnesses, in large part because of their neurologic consequences. Because significant morbidity occurs prenatally, in utero (IU) therapy is an attractive therapeutic approach.

METHODS

We studied the feasibility and efficacy of IU injections of monocytic cells (derived from normal marrow) in feline alpha-mannosidosis. Heterozygous cats were interbred to produce affected (homozygous) and control (heterozygous and wild-type) offspring. Thirty-seven pregnancies were studied in which fetuses were transplanted intraperitoneally (1x10 cells/kg recipient) at gestational days 27 to 33 and then each week for 2 weeks (term=63 days). After birth, affected kittens were evaluated clinically and pathologically, tissue alpha-mannosidase levels were assayed, and in many studies, the numbers of alpha-mannosidase-containing cells were enumerated. When male donor cells were transplanted into female recipients, engraftment was also quantified using polymerase chain reaction to amplify a Y chromosome-specific sequence.

RESULTS

We establish methods to transplant cats intraperitoneally while IU using ultrasound guidance, thus, describing a new large animal model for prenatal therapy. We show that the donor monocytic cells engraft and persist (for up to 125 days) in the brain, liver, and spleen, albeit at levels below those needed to alter the clinical or pathological progression of the alpha-mannosidosis.

CONCLUSIONS

This is the first study of monocyte transplantation in a large animal model of a lysosomal storage disorder and demonstrates its feasibility, safety, and promise. Delivering cells IU may be a useful strategy to prevent morbidities before a definitive therapy, such as hematopoietic stem-cell transplantation, can be administered after birth.

Large animal models of neurological disorders for gene therapy

he development of therapeutic interventions for genetic disorders and diseases that affect the central nervous system (CNS) has proven challenging. There has been significant progress in the development of gene therapy strategies in murine models of human disease, but gene therapy outcomes in these models do not always translate to the human setting. Therefore, large animal models are crucial to the development of diagnostics, treatments, and eventual cures for debilitating neurological disorders. This review focuses on the description of large animal models of neurological diseases such as lysosomal storage diseases, Parkinsons disease, Huntingtons disease, and neuroAIDS. The review also describes the contributions of these models to progress in gene therapy research.

Spontaneous Lysosomal Storage Disease Caused by Sida carpinifolia (Malvaceae) Poisoning in Cattle

Clinical and pathologic findings for the spontaneous poisoning by Sida carpinifolia in cattle are described in this study. A survey on field cases of S. carpinifolia in cattle was carried out on farms of Alto Vale do Itajai, State of Santa Catarina, southern Brazil. Sixteen affected animals were clinically evaluated and 9 were subjected to postmortem examination. The main clinical signs consisted of marching gait, alert gaze, head tremors, and poor growth. Histologic and ultrastructural lesions consisted of vacuolization and distension of neuronal perikarya, mainly from Purkinje cells, and of the cytoplasm of acinar pancreatic and thyroid follicular cells. Clinical signs and lesions varied from mild to severe. Improvement of the clinical signs was observed in cattle after a period of up to 90 days without consuming the plant; however, residual lesions, mainly characterized by axonal spheroids and absence of Purkinje neurons in some areas of the cerebellum, were observed in these cases. It is concluded that the natural chronic consumption of S. carpinifolia was the etiologic cause of storage disease in cattle in this study.

Apparent diffusion coefficient reveals gray and white matter disease, and T2 mapping detects white matter disease in the brain in feline alpha-mannosidosis

BACKGROUND AND PURPOSE

Methods to locate and identify brain pathology are critical for monitoring disease progression and for evaluating the efficacy of therapeutic intervention. The purpose of this study was to detect cell swelling, abnormal myelin, and astrogliosis in the feline model of the lysosomal storage disease alpha-mannosidosis (AMD) by using diffusion and T2 mapping.

MATERIALS AND METHODS

Average apparent diffusion coefficient (ADC(av)) and T2 were measured by imaging the brains of five 16-week-old cats with feline AMD on a 4.7T magnet. ADC(av) and T2 data from affected cats were compared with data from age-matched normal cats. Brains were collected from both affected and normal cats following imaging, and histology was compared with quantitative imaging data.

RESULTS

Gray matter from AMD cats demonstrated a 13%-15% decrease in ADC(av) compared with that in normal cats. White matter from AMD cats exhibited an 11%-16% decrease in ADC(av) and a 5%-12% increase in T2 values compared with those in normal control cats. Histologic evidence of neuronal and glial swelling, abnormal myelin, and astrogliosis was consistent with changes in ADC(av) and T2.

CONCLUSION

ADC(av) and T2 data can be used to quantify differences in the gray and white matter in the feline AMD brain and may serve as surrogate markers of neuronal swelling, abnormal myelin, and astrogliosis associated with this disease. These studies may be helpful in assessing the efficacy of experimental therapies for central nervous system disease associated with lysosomal storage diseases.

Intoxicação experimental por Sida carpinifolia (Malvaceae) em bovinos

Descrevem-se os achados clínicos e patológicos da intoxicação experimental por Sida carpinifolia em bovinos. Para a reprodução experimental da doença, folhas verdes da planta foram coletadas semanalmente na região do Alto Vale do Itajaí e fornecidas in natura diariamente para cinco bovinos nas doses de 10 e 20g/kg por 120 dias, 40g/kg por 30 dias, e 30 e 40g/kg de peso animal por 150 dias. Um bovino morreu e os outros foram eutanasiados ao final do período de consumo da planta. Os principais sinais clínicos consistiam de andar em marcha, olhar atento e tremores de cabeça e foram de intensidade leve a acentuado conforme a dose de planta e tempo de consumo. A lesão histológica predominante caracterizava-se por vacuolização e tumefação de neurônios (principalmente os de Purkinje), das células acinares pancreáticas e células foliculares da tireóide. Ultra-estruturalmente verificou-se vacúolos, por vezes, contendo material finamente granular em neurônios, células acinares pancreáticas e células foliculares da tireóide. S. carpinifolia causa doença de depósito lisossomal em bovinos quando consumida por período prolongado, mesmo em pequenas doses.

Multivariate neurocognitive and emotional profile of a mannosidosis murine model for therapy assessment

alpha-Mannosidosis is a lysosomal storage disorder caused by lysosomal alpha-mannosidase (LAMAN) deficiency that leads to neurocognitive dysfunctions, psychotic symptoms and emotional changes in human patients. A murine mannosidosis model, LAMAN-deficient mice, was examined on a behavioral task battery that included test for neuromotor, exploratory and neurocognitive (spatial learning and memory) abilities, and multivariate statistical analyses were used to identify behavioral and neurocognitive domains that are most heavily affected by LAMAN deficiency. In addition, we further investigated synaptic plasticity recordings on hippocampal slices that may relate to these behavioral alterations. Correlation analysis revealed significant intra- and intertask correlations and factor analysis that included all 21 behavioral variables identified three main factors (exploration/emotionality, locomotion and learning/memory abilities). Significant correlations were observed between genotype, and factor 1 (exploration/emotionality) and factor 3 (learning/memory abilities). Discriminant function analysis showed that "path length in the open field test" and "time spent in the target quadrant during the water maze probe trial" were the most decisive variables to distinguish between the genotypes. We therefore suggest that these variables would be especially important in forthcoming therapy assessment experiments using this murine mannosidosis model. LAMAN-deficient mice displayed severe changes in synaptic plasticity, which may have contributed to the neurocognitive impairments observed. The present report further shows that targeted deletion of the LAMAN gene in mice mimics many aspects of human alpha-mannosidosis, and these data provide a basis for future therapeutic experiments.

Neurocognitive and psychotiform behavioral alterations and enhanced hippocampal long-term potentiation in transgenic mice displaying neuropathological features of human alpha-mannosidosis

Mice with alpha-mannosidase gene inactivation provide an experimental model for alpha-mannosidosis, a lysosomal storage disease with severe neuropsychological and psychopathological complications. Neurohistological alterations in these mice were similar to those in patients and included vacuolations and axonal spheroids in the CNS and peripheral nervous system. Vacuolation was most prominent and evenly distributed in neuronal perikarya of the hippocampal CA2 and CA3 regions, whereas CA1 and dentate gyrus were weakly or not affected. Field potential recordings from CA1 region in hippocampal slices showed enhanced theta burst-induced long-term potentiation (LTP) in alpha-mannosidase-deficient mice. Longitudinal assessment in age-matched alpha-mannosidase-deficient and wild-type littermates, using an extended test battery, demonstrated a neurocognitive and psychotiform profile that may relate to the psychopathological alterations in clinical alpha-mannosidosis. Brainstem auditory-evoked potentials and basic neuromotor abilities were not impaired and did not deteriorate with age. Exploratory and conflict tests revealed consistent decreases in exploratory activity and emotional blunting in the knock-out group. alpha-Mannosidosis mice were also impaired in aversively motivated learning and acquisition of signal-shock associations. Acquisition and reversal learning in the water maze task, passive avoidance learning in the step-through procedure, as well as emotional response conditioning in an operant procedure were all impaired. Acquisition or shaping of an appetitive instrumental conditioning task was unchanged. Appetitive odor discrimination learning was only marginally impaired during shaping, whereas both the discrimination and reversal subtasks were normal. We propose that prominent storage and enhanced LTP in hippocampus have contributed to these specific behavioral alterations in alpha-mannosidase-deficient mice.

Characterization of a human core-specific lysosomal {alpha}1,6-mannosidase involved in N-glycan catabolism

In humans and rodents, the lysosomal catabolism of core Man(3)GlcNAc(2) N-glycan structures is catalyzed by the concerted action of several exoglycosidases, including a broad specificity lysosomal alpha-mannosidase (LysMan), core-specific alpha1,6-mannosidase, beta-mannosidase, and cleavage at the reducing terminus by a di-N-acetylchitobiase. We describe here the first cloning, expression, purification, and characterization of a novel human glycosylhydrolase family 38 alpha-mannosidase with catalytic characteristics similar to those established previously for the core-specific alpha1,6-mannosidase (acidic pH optimum, inhibition by swainsonine and 1,4-dideoxy-1,4-imino-d-mannitol, and stimulation by Co(2+) and Zn(2+)). Substrate specificity studies comparing the novel human alpha-mannosidase with human LysMan revealed that the former enzyme efficiently cleaved only the alpha1-6mannose residue from Man(3)GlcNAc but not Man(3)GlcNAc(2) or other larger high mannose oligosaccharides, indicating a requirement for chitobiase action before alpha1,6-mannosidase activity. In contrast, LysMan cleaved all of the alpha-linked mannose residues from high mannose oligosaccharides except the core alpha1-6mannose residue. alpha1,6-Mannosidase transcripts were ubiquitously expressed in human tissues, and expressed sequence tag searches identified homologous sequences in murine, porcine, and canine databases. No expressed sequence tags were identified for bovine alpha1,6-mannosidase, despite the identification of two sequence homologs in the bovine genome. The lack of conservation in 5'-flanking sequences for the bovine alpha1,6-mannosidase genes may lead to defective transcription similar to transcription defects in the bovine chitobiase gene. These results suggest that the chitobiase and alpha1,6-mannosidase function in tandem for mammalian lysosomal N-glycan catabolism.

Ocular manifestations of systemic disease in cats

Systemic feline diseases (parasitic, bacterial, fungal, viral, neoplastic, metabolic, vascular, and immune-mediated) are often associated with ocular symptoms. An ocular examination is an important diagnostic tool and should be part of any physical examination. Conversely, cats afflicted with systemic disease require periodic ocular examinations for prognostic information and to prevent vision threatening complications. Typical feline systemic diseases encountered by the practicing clinician are presented with their commonly associated ocular signs.

Effective gene therapy for an inherited CNS disease in a large animal model

Genetic diseases affecting the brain typically have widespread lesions that require global correction. Lysosomal storage diseases are good candidates for central nervous system gene therapy, because active enzyme from genetically corrected cells can be secreted and taken up by surrounding diseased cells, and only small amounts of enzyme (<5% of normal) are required to reverse storage lesions. Injection of gene transfer vectors into multiple sites in the mouse brain has been shown to mediate widespread reversal of storage lesions in several disease models. To study a brain closer in size to the human brain, we evaluated the extent of storage correction mediated by a limited number of adeno-associated virus vector injections in the cat model of human alpha-mannosidosis. The treated cats showed remarkable improvements in clinical neurological signs and in brain myelination assessed by quantitative magnetic resonance imaging. Postmortem examination showed that storage lesions were greatly reduced throughout the brain, even though gene transfer was limited to the areas surrounding the injection tracks. The data demonstrate that widespread improvement of neuropathology in a large mammalian brain can be achieved using multiple injection sites during one operation and suggest that this could be an effective treatment for the central nervous system component of human lysosomal enzyme deficiencies.

The Feline Genome Project

The compilation of a dense gene map and eventually a whole genome sequence (WGS) of the domestic cat holds considerable value for human genome annotation, for veterinary medicine, and for insight into the evolution of genome organization among mammals. Human association and veterinary studies of the cat, its domestic breeds, and its charismatic wild relatives of the family Felidae have rendered the species a powerful model for human hereditary diseases, for infectious disease agents, for adaptive evolutionary divergence, for conservation genetics, and for forensic applications. Here we review the advantages, rationale, and present strategy of a feline genome project, and we describe the disease models, comparative genomics, and biological applications posed by the full resolution of the cat's genome.

Animal models for mucopolysaccharidoses and their clinical relevance

The mucopolysaccharidoses (MPS) are characterized by the accumulation of glycosaminoglycans (GAG) and result from the impaired function of one of 11 enzymes required for normal GAG degradation. MPS II was the first MPS to be defined clinically in humans and is caused by deficient activity of the enzyme iduronate-2-sulphatase. MPS VI was the first MPS recognized in an animal; since then, all but MPS IIIC and IX have been described as naturally occurring in animals or made by knock-out technology. As in humans, all are inherited as autosomal recessive traits, except for MPS II, which is X-linked. Most animal colonies have been established from single related heterozygous animals, making the affected offspring homozygous for the same mutant allele. Importantly, these models have disease pathology that is similar to that seen in humans, making the animals extremely valuable for the investigation of disease pathogenesis and the testing of therapies. Large animal homologues are similar to humans in natural genetic diversity, approaches to therapy and care, and the possibility of evaluating long-term effects of treatment. Therapeutic strategies for MPS include enzyme replacement therapy, heterologous bone marrow transplantation, and somatic cell gene transfer, all of which have been tested in animals with some success.

alpha-Mannosidosis in the guinea pig: cloning of the lysosomal alpha-mannosidase cDNA and identification of a missense mutation causing alpha-mannosidosis

alpha-Mannosidosis is a lysosomal storage disorder caused by deficient activity of the lysosomal alpha-mannosidase. We report here the sequencing and expression of the lysosomal alpha-mannosidase cDNA from normal and alpha-mannosidosis guinea pigs. The amino acid sequence of the guinea pig enzyme displayed 82-85% identity to the lysosomal alpha-mannosidase in other mammals. The cDNA of the alpha-mannosidosis guinea pig contained a missense mutation, 679C>T, leading to substitution of arginine by tryptophan at amino acid position 227 (R227W). The R227W allele segregated with the alpha-mannosidosis genotype in the guinea pig colony and introduction of R227W into the wild-type sequence eliminated the production of recombinant alpha-mannosidase activity in heterologous expression studies. Furthermore, the guinea pig mutation has been found in human patients. Our results strongly indicate that the 679C>T mutation causes alpha-mannosidosis and suggest that the guinea pig will be an excellent model for investigation of pathogenesis and evaluation of therapeutic strategies for human alpha-mannosidosis.

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.

Histopathology, electrodiagnostic testing, and magnetic resonance imaging show significant peripheral and central nervous system myelin abnormalities in the cat model of alpha-mannosidosis

Alpha-mannosidosis is a disease caused by the deficient activity of alpha-mannosidase, a lysosomal hydrolase involved in the degradation of glycoproteins. The disease is characterized by the accumulation of mannose-rich oligosaccharides within lysosomes. The purpose of this study was to characterize the peripheral nervous system (PNS) and central nervous system (CNS) myelin abnormalities in cats from a breeding colony with a uniform mutation in the gene encoding alpha-mannosidase. Three affected cats and 3 normal cats from 2 litters were examined weekly from 4 to 18 wk of age. Progressively worsening neurological signs developed in affected cats that included tremors, loss of balance, and nystagmus. In the PNS, affected cats showed slow motor nerve conduction velocity and increased F-wave latency. Single nerve fiber teasing revealed significant demyelination/remyelination in affected cats. Mean G-ratios of nerves showed a significant increase in affected cats compared to normal cats. Magnetic resonance imaging of the CNS revealed diffuse white matter signal abnormalities throughout the brain of affected cats. Quantitative magnetization transfer imaging showed a 8%-16% decrease in the magnetization transfer ratio in brain white matter of affected cats compared to normal cats, consistent with myelin abnormalities. Histology confirmed myelin loss throughout the cerebrum and cerebellum. Thus, histology, electrodiagnostic testing, and magnetic resonance imaging identified significant myelination abnormalities in both the PNS and CNS that have not been described previously in alpha-mannosidosis.

Polyhydroxylated alkaloids -- natural occurrence and therapeutic applications

Over one hundred polyhydroxylated alkaloids have been isolated from plants and micro-organisms. These alkaloids can be potent and highly selective glycosidase inhibitors and are arousing great interest as tools to study cellular recognition and as potential therapeutic agents. However, only three of the natural products so far have been widely studied for therapeutic potential due largely to the limited commercial availability of the other compounds.

Are there useful biochemical markers of disease activity in lysosomal storage diseases?

The primary biochemical consequence of a defect in a gene encoding a functional component of the lysosomal system is disruption of the catabolism or processing of macromolecules in the lumen of the lysosome. Transport of the resulting digestion products through the lysosomal membrane may also be affected. This leads to the accumulation of specific metabolites within the lysosomes of affected cells. The nature of these storage products depends upon the functional protein affected and the cell type. The accumulation of storage products is progressive and leads to hypertrophy of the lysosomal system, the hallmark of lysosomal storage diseases (LSDs). Subsequent cell necrosis or, possibly, exocytosis results in the appearance in body fluids of the storage products and components of the lysosomes at much higher concentrations than seen in normal unaffected individuals. Measurement of these increased levels of metabolites and proteins provides disease-specific and generic biochemical markers for LSDs. Secondary changes in metabolism and cellular function may also produce characteristic changes in the levels of metabolites or proteins, which can also be used as markers of the disease process. Although the rate of appearance of these biochemical markers in an individual will depend upon the underlying mutation in the gene and on other genetic and environmental factors, it provides a good indicator of the progression of the disease. As the novel forms of treatment being developed may reverse the hypertrophy of the lysosomal system, biochemical markers could also be used to monitor the reversal of pathology and the efficacy of treatment.

Identification of Asp197 as the catalytic nucleophile in the family 38 alpha-mannosidase from bovine kidney lysosomes

Bovine kidney lysosomal alpha-mannosidase is a family 38 alpha-mannosidase involved in the degradation of glycoproteins. The mechanism-based reagent, 5-fluoro-beta-L-gulosyl fluoride, was used to trap a glycosyl-enzyme intermediate, thereby labelling the catalytic nucleophile of this enzyme. After proteolytic digestion and high performance liquid chromatography/tandem mass spectrometry (MS) analysis, a labelled peptide was localised, and the sequence: HIDPFGHSRE determined by fragmentation tandem MS analysis. Taking into consideration sequence alignments of this region with those of other alpha-mannosidases of the same family, this result strongly suggests that the catalytic nucleophile in this enzyme is Asp197.

Alpha-mannosidosis in the guinea pig: a new animal model for lysosomal storage disorders

Alpha-mannosidosis is a lysosomal storage disorder resulting from deficient activity of lysosomal alpha-mannosidase. It has been described previously in humans, cattle, and cats, and is characterized in all of these species principally by neuronal storage leading to progressive mental deterioration. Two guinea pigs with stunted growth, progressive mental dullness, behavioral abnormalities, and abnormal posture and gait, showed a deficiency of acidic alpha-mannosidase activity in leukocytes, plasma, fibroblasts, and whole liver extracts. Fractionation of liver demonstrated a deficiency of lysosomal (acidic) alpha-mannosidase activity. Thin layer chromatography of urine and tissue extracts confirmed the diagnosis by demonstrating a pattern of excreted and stored oligosaccharides almost identical to that of urine from a human alpha-mannosidosis patient. Widespread neuronal vacuolation was observed throughout the CNS, including the cerebral cortex, hippocampus, thalamus, cerebellum, midbrain, pons, medulla, and the dorsal and ventral horns of the spinal cord. Lysosomal vacuolation also occurred in many other visceral tissues and was particularly severe in pancreas, thyroid, epididymis, and peripheral ganglion. Axonal spheroids were observed in some brain regions, but gliosis and demyelination were not observed. Ultrastructurally, most vacuoles in both the CNS and visceral tissues were lucent or contained fine fibrillar or flocculent material. Rare large neurons in the cerebral cortex contained fine membranous structures. Skeletal abnormalities were very mild. Alpha-mannosidosis in the guinea pig closely resembles the human disease and will provide a convenient model for investigation of new therapeutic strategies for neuronal storage diseases, such as enzyme replacement and gene replacement therapies.

Glycoprotein lysosomal storage disorders: alpha- and beta-mannosidosis, fucosidosis and alpha-N-acetylgalactosaminidase deficiency

Glycoproteinoses belong to the lysosomal storage disorders group. The common feature of these diseases is the deficiency of a lysosomal protein that is part of glycan catabolism. Most of the lysosomal enzymes involved in the hydrolysis of glycoprotein carbohydrate chains are exo-glycosidases, which stepwise remove terminal monosaccharides. Thus, the deficiency of a single enzyme causes the blockage of the entire pathway and induces a storage of incompletely degraded substances inside the lysosome. Different mutations may be observed in a single disease and in all cases account for the nonexpression of lysosomal glycosidase activity. Different clinical phenotypes generally characterize a specific disorder, which rather must be described as a continuum in severity, suggesting that other biochemical or environmental factors influence the course of the disease. This review provides details on clinical features, genotype-phenotype correlations, enzymology and biochemical storage of four human glycoprotein lysosomal storage disorders, respectively alpha- and beta-mannosidosis, fucosidosis and alpha-N-acetylgalactosaminidase deficiency. Moreover, several animal disorders of glycoprotein metabolism have been found and constitute valuable models for the understanding of their human counterparts.

Targeted disruption of the Cln3 gene provides a mouse model for Batten disease. The Batten Mouse Model Consortium [corrected]

Batten disease, a degenerative neurological disorder with juvenile onset, is the most common form of the neuronal ceroid lipofuscinoses. Mutations in the CLN3 gene cause Batten disease. To facilitate studies of Batten disease pathogenesis and treatment, a murine model was created by targeted disruption of the Cln3 gene. Mice homozygous for the disrupted Cln3 allele had a neuronal storage disorder resembling that seen in Batten disease patients: there was widespread and progressive intracellular accumulation of autofluorescent material that by EM displayed a multilamellar rectilinear/fingerprint appearance. Inclusions contained subunit c of mitochondrial ATP synthase. Mutant animals also showed neuropathological abnormalities with loss of certain cortical interneurons and hypertrophy of many interneuron populations in the hippocampus. Finally, as is true in Batten disease patients, there was increased activity in the brain of the lysosomal protease Cln2/TPP-1. Our findings are evidence that the Cln3-deficient mouse provides a valuable model for studying Batten disease.

Targeted disruption of the lysosomal alpha-mannosidase gene results in mice resembling a mild form of human alpha-mannosidosis

Alpha-mannosidosis is a lysosomal storage disease with autosomal recessive inheritance caused by a deficiency of the lysosomal alpha-mannosidase, which is involved in the degradation of asparagine-linked carbohydrate cores of glycoproteins. An alpha-mannosidosis mouse model was generated by targeted disruption of the gene for lysosomal alpha-mannosidase. Homozygous mutant animals exhibit alpha-mannosidase enzyme deficiency and elevated urinary secretion of mannose-containing oligosaccharides. Thin-layer chromatography revealed an accumulation of oligosaccharides in liver, kidney, spleen, testis and brain. The cellular alterations were characterized by multiple membrane-limited cytoplasmic vacuoles as seen for instance in liver, exocrine pancreas, kidney, thyroid gland, smooth muscle cells, osteocytes and in various neurons of the central and peripheral nervous systems. The morphological lesions and their topographical distribution, as well as the biochemical alterations, closely resemble those reported for human alpha-mannosidosis. This mouse model will be a valuable tool for studying the pathogenesis of inherited alpha-mannosidosis and may help to evaluate therapeutic approaches for lysosomal storage diseases.

Retrovirus vector-mediated correction and cross-correction of lysosomal alpha-mannosidase deficiency in human and feline fibroblasts

Lysosomal alpha-mannosidase (EC 3.2.1.24) is an exoglycosidase in the glycoprotein degradation pathway. A deficiency of this enzyme causes the lysosomal storage disease alpha-mannosidosis. Retrovirus vector transfer of a new human alpha-mannosidase cDNA resulted in high-level expression of alpha-mannosidase enzymatic activity in deficient human and feline fibroblasts. The expressed alpha-mannosidase had the same biochemical properties (thermal stability, pH profile, inhibitor/activator sensitivity) as the native enzyme expressed in normal cells. The transferred enzyme colocalized with a control lysosomal hydrolase in cell fractionation experiments. The vector-encoded enzyme also was released at high levels from the corrected cells, and was taken up by untreated mutant cells via the mannose 6-phosphate receptor-mediated endocytic pathway (cross-correction). It is envisioned that genetic correction of a subset of cells (e.g., hematopoietic stem cells) in patients will provide a source of corrective enzyme for other affected tissues in this multisystem disease. Development of a vector expressing high levels of alpha-mannosidase that cross-corrects mutant cells will enable somatic gene transfer experiments in the cat model of human alpha-mannosidosis.

Isolation and characterization of the gene encoding the mouse broad specificity lysosomal alpha-mannosidase1

A genomic clone encoding the mouse lysosomal alpha-mannosidases was isolated and the gene was found to be encoded by 24 exons spanning approximately 14.5 kb of genomic DNA. The intron-exon boundaries were conserved between the mouse, human, and bovine lysosomal alpha-mannosidase genes as well as being partially conserved in several other species. In order to define the promoter of the mouse mannosidase gene, >1 kb of DNA sequence was obtained upstream from the respective initiation codon. The transcription start site was identified by a 5'-RACE procedure and putative promoter elements were identified by expression of promoter/reporter constructs. Fluorescence in situ hybridization analysis using the mouse and human mannosidase genomic clones as probes, localized the mouse gene to chromosome 8, at band position 8C2, and the human gene to chromosome 19p13.2, a region syntenic to the lysosomal mannosidase gene on mouse chromosome 8.

Spectrum of mutations in alpha-mannosidosis

alpha-Mannosidosis is an autosomal recessive disorder caused by deficiency of lysosomal alpha-mannosidase (LAMAN). The resulting intracellular accumulation of mannose-containing oligosaccharides leads to mental retardation, hearing impairment, skeletal changes, and immunodeficiency. Recently, we reported the first alpha-mannosidosis-causing mutation affecting two Palestinian siblings. In the present study 21 novel mutations and four polymorphic amino acid positions were identified by the screening of 43 patients, from 39 families, mainly of European origin. Disease-causing mutations were identified in 72% of the alleles and included eight splicing, six missense, and three nonsense mutations, as well as two small insertions and two small deletions. In addition, Southern blot analysis indicated rearrangements in some alleles. Most mutations were private or occurred in two or three families, except for a missense mutation resulting in an R750W substitution. This mutation was found in 13 patients, from different European countries, and accounted for 21% of the disease alleles. Although there were clinical variations among the patients, no significant LAMAN activity could be detected in any of the fibroblast cultures. In addition, no correlation between the types of mutations and the clinical manifestations was evident.

alpha-Mannosidase from Trichoderma reesei participates in the postsecretory deglycosylation of glycoproteins

The 160 kDa alpha-mannosidase (E.C. 3.2.1.24) isolated from culture filtrate of Trichoderma reesei has wide aglycon specificity but cleaves the alpha1 --> 2 and alpha1 --> 3 mannosidic bonds with higher rate than alpha1 --> 6 bond and slowly hydrolyses yeast mannan and 1,6-alpha-mannan. The specific activity of the enzyme and rate constant in the reaction with p-nitrophenyl-alpha-D-mannopyranoside were 0.15 U/mg and 1.62 x 10(-4) microM/min/microg, respectively, at optimal pH 6.5. We have found that in vitro enzyme is able to cleave off 30% of total alpha-mannopyranosyl residues from N- and O-linked glycans of secreted glycoproteins. The activity of the alpha-mannosidase toward glycoproteins in vivo was studied comparing the structures of O- and N-linked glycans of glycoproteins isolated from the cultures growing with and without 1-deoxymannojirimycin, an inhibitor of alpha-mannosidases. Difference in structures of these glycans may be explained by postsecretory deglycosylation catalysed by the alpha-mannosidase.

Purification of feline lysosomal alpha-mannosidase, determination of its cDNA sequence and identification of a mutation causing alpha-mannosidosis in Persian cats

alpha-Mannosidosis is a lysosomal storage disorder that is caused by the deficiency of lysosomal alpha-mannosidase. Feline alpha-mannosidosis is a well-characterized animal model used for studying pathological and therapeutic aspects of lysosomal storage disorders. We here report the purification of feline liver lysosomal alpha-mannosidase and determination of its cDNA sequence. The active enzyme consisted of three polypeptides, with molecular masses of 72, 41 and 12 kDa, joined by non-covalent forces. The cDNA sequence of feline lysosomal alpha-mannosidase was determined from reverse transcriptase PCR products obtained from skin fibroblast mRNA. The deduced amino acid sequence contained the N-terminal sequences of the 72 and 41 kDa peptides. This indicated that the enzyme is synthesized as a single-chain precursor with a putative signal peptide of 50 amino acids followed by a polypeptide chain of 957 amino acids, which is cleaved into the three polypeptides of the mature enzyme. The deduced amino acid sequence was 81.1 and 83.2% identical with the human and bovine lysosomal alpha-mannosidases sequences respectively. A 4 bp deletion was identified in an alpha-mannosidosis-affected Persian cat by DNA sequencing of reverse transcriptase PCR products. The deletion resulted in a frame shift from codon 583 and premature termination at codon 645. No lysosomal alpha-mannosidase activity could be detected in the liver of this cat. A domestic long-haired cat expressing a milder alpha-mannosidosis phenotype than the Persian cat had a lysosomal alpha-mannosidase activity of 2% of normal. This domestic long-haired cat did not possess the 4 bp deletion, proving molecular heterogeneity for feline alpha-mannosidosis.

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.

Cloning, expression, purification, and characterization of the murine lysosomal acid alpha-mannosidase

Catabolism of alpha-linked mannose residues on eukaryotic glycoproteins is accomplished by a broad specificity lysosomal alpha-mannosidase (EC 3.2.1.24). Based on regions of protein sequence conservation between the lysosomal alpha-mannosidase from Dictyostelium discoideum and the murine Golgi glycoprotein processing alpha 1,3/1,6-mannosidase, alpha-mannosidase II, we have cloned a cDNA encoding the murine lysosomal alpha-mannosidase. The longest of the clones was 3.1 kb in length and encoded a polypeptide of 992 amino acids containing a putative NH2-terminal signal sequence and 11 potential N-glycosylation sites. The deduced amino acid sequence was 76.5% identical to the human lysosomal alpha-mannosidase and 38.1% identical to the lysosomal alpha-mannosidase from D. discoideum. Expression of the cDNA in Pichia pastoris resulted in the secretion of an alpha-mannosidase activity into the culture medium. This recombinant expression product was purified and was shown to have enzymatic characteristics highly similar to the enzyme purified from mammalian sources and to the human lysosomal alpha-mannosidase cDNA expressed in Pichia. These characteristics include a similar pH optimum, Km, Vmax, inhibition by swainsonine, and activity toward natural substrates. Northern blots identified a major 3.5 kb RNA transcript in all murine tissues tested. A minor transcript of 5.4 kb was also detected in some murine tissues similar to the alternatively spliced transcripts that have been previously identified in human tissues.

Genomic structure of the human lysosomal alpha-mannosidase gene (MANB)

Lysosomal alpha-mannosidase (LAMAN) (EC 3.2.1.24) is an exoglycosidase involved in the ordered degradation of N-linked oligosaccharides. Lack of LAMAN activity leads to the lysosomal storage disorder alpha-mannosidosis (MIM No. 248500). We determined the genomic organization of the human lysosomal alpha-mannosidase gene (laman; HGMW-approved symbol MANB) by using oligonucleotide primers designed from the human laman cDNA sequence as part of a PCR-based strategy. The gene spanned 21.5 kb and contained 24 exons. By primer extension analysis, the major transcription initiation sites were mapped to positions -309, -196, and -191 relative to the first in-frame ATG. No CAAT or TATA sequences could be identified within 134 bp upstream of the transcription initiation sites, but the 5' flanking region contained several GC-rich regions with putative binding sites for the transcription factors SP-1, AP-2, and ETF.

Purification of bovine lysosomal alpha-mannosidase, characterization of its gene and determination of two mutations that cause alpha-mannosidosis

Bovine kidney lysosomal alpha-mannosidase was purified to homogeneity and the gene was cloned. The gene was organized in 24 exons that spanned 16 kb and its corresponding cDNA contained an open reading frame of 2997 bp beginning from a putative ATG start codon. The deduced amino acid sequence contained a signal peptide of 50 amino acids adjacent to a protein sequence of 949 amino acids that was cleaved into five peptides in the mature enzyme; starting with the peptide derived from the N-terminal part of this precursor, their molecular masses were 35/38 (peptide a), 11/13 (peptide b), 22 (peptide c), 38 (peptide d) and 13/15 kDa (peptide e). Variation in the degree of N-glycosylation accounts for molecular mass heterogeneities of peptides a, b and e. Peptides a, b and c were disulphide-linked. A T961-->C transition, resulting in Phe321-->Leu substitution, was identified in the cDNA of alpha-mannosidosis-affected Angus cattle. In affected Galloway cattle, a G662-->A transition that causes Arg221-->His substitution was identified. Phe321 and Arg221 are conserved among the alpha-mannosidase class-2 family, indicating that the substitutions resulted from disease-causing mutations in these breeds.

alpha-Mannosidosis: functional cloning of the lysosomal alpha-mannosidase cDNA and identification of a mutation in two affected siblings

a-Mannosidosis (MIM 248500) is an autosomal recessive lysosomal storage disorder resulting from deficient activity of lysosomal alpha-mannosidase (LAMAN) (EC 3.2.1.24). The disease is characterized by massive intracellular accumulation of mannose-rich oligosaccharides with resulting mental retardation, hearing loss, immune deficiency and skeletal changes. We report here the purification and characterization of human placenta LAMAN. The enzyme is synthesized as a single-chain precursor which is processed into three glycopeptides of 70, 42 and 15 kDa. The 70 kDa peptide is further partially proteolysed into three more peptides that are joined by disulfide bridges. The laman cDNA sequence was assembled from overlapping fragments obtained by PCR on human fibroblast and human lung cDNA. The deduced amino acid sequence contains a putative signal peptide of 48 amino acids followed by a polypeptide sequence of 962 amino acids. Northern blot analyses revealed a single transcript of approximately 3.5 kb present in all tissues examined but at varying levels. Two affected siblings of Palestinian origin were homozygous for a mutation that causes a His-->Leu replacement at a position which is conserved among class 2 alpha-mannosidases from several species.

A new form of ovine GM1-gangliosidosis

Neurological signs were observed in 3 lambs at approximately 1 month of age, in a flock of 1 ram and 29 ewes with 43 lambs. Deterioration occurred such that the lambs had either died or been killed by 4 months of age. Necropsies of two of these lambs revealed a diffuse encephalopathy in which the most prominent feature was ballooned neurons. Sections of frozen brain showed PAS-positive, oil red O-negative, and weak Sudan Black-positive material in the swollen neuronal cytoplasm. The ultrastructure of the neuronal inclusions showed characteristic whorled membranes, suggesting diagnosis of a gangliosidosis. The underlying enzymic defect was investigated by assaying 11 lysosomal enzymes in extracts of kidney from an affected lamb and from normal lambs. A deficiency (90%) of acidic beta-D-galactosidase was found in the affected lamb. All other activities, including N-acetylneuraminidase, were normal. A specific deficiency of lysosomal beta-D-galactosidase was demonstrated by separating the lysosomal and cytosolic beta-D-galactosidase by chromatography on concanavalin A-Sepharose. Diagnosis of GM1-gangliosidosis, analogous to the severe infantile form of the human disease, was made on the basis of the pathology and enzymology. The beta-D-galactosidase activity in the white blood cells of the ram and several of the ewes was consistent with their being heterozygotes. This disorder is different from a previously described lipidosis in sheep, in which there was a combined deficiency of beta-D-galactosidase and alpha-neuraminidase.

Substrate specificity of the bovine and feline neutral alpha-mannosidases

Neutral alpha-mannosidases were prepared from bovine and cat liver. The activities were distinguished from lysosomal and Golgi alpha-mannosidases by their neutral pH optima, relatively low Km for their synthetic substrate p-nitrophenyl alpha-D-mannoside, inhibition by Zn2+ and absence of inhibition by Co2+, EDTA, low concentrations of swainsonine, or deoxymannojirimycin. The cytosolic alpha-mannosidases were not retained by concanavalin A-Sepharose. They were able to degrade efficiently a variety of oligosaccharides with structures corresponding to certain high-mannose glycans or the oligomannosyl parts of hybrid and complex glycans. However, unlike lysosomal alpha-mannosidases from the same species these enzymes were not able to degrade Man9GlcNAc2 efficiently, and the bovine neutral alpha-mannosidase was not able to degrade a hexasaccharide with a structure analogous to Man5GlcNAc2-PP-dolichol. Sharp differences were noted for the bovine and cat enzymes with regard to the specificity of degradation. The bovine neutral alpha-mannosidase degraded the substrates by defined pathways, but the cat neutral alpha-mannosidase often produced complex mixtures of products, especially from the larger oligosaccharides. Therefore the bovine enzyme resembled the rat and human cytosolic alpha-mannosidases, but the cat enzyme did not. The bovine and cat neutral alpha-mannosidases, unlike the corresponding lysosomal activities, did not show specificity for the hydrolysis of the (1----3)- and (1----6)-linked mannose residues in the N-linked glycan pentasaccharide core.

Ectopic dendrites occur only on cortical pyramidal cells containing elevated GM2 ganglioside in alpha-mannosidosis

In a variety of neuronal storage diseases, cortical pyramidal cells elaborate ectopic dendrites at the axon hillock. A feature common to all the diseases characterized by ectopic dendrites is an elevated level of GM2 ganglioside in cerebral cortex. In cats with one such disease, alpha-mannosidosis, the number of pyramidal cells bearing ectopic dendrites is small; the present study shows that GM2 ganglioside is stored only in those pyramidal neurons exhibiting ectopic dendrites. Using a Golgi-electron microscopy method with periodic acid-Schiff (PAS) staining, we first established that pyramidal cells bearing ectopic dendrites contained PAS+ membranous inclusions, consistent with storage of glycolipids. In contrast, those with smooth axon hillocks accumulated PAS- floccular inclusions, consistent with storage of oligosaccharides. Next, application of a monoclonal antibody against GM2 ganglioside revealed that subsets of both pyramidal and intrinsic neurons contained GM2-like immunoreactivity. Every GM2+ cell contained PAS+ membranous inclusions, indicating that pyramidal cells bearing ectopic dendrites stored GM2 ganglioside. In cats with alpha-mannosidosis induced by swainsonine, some pyramidal neurons showed GM2-like immunoreactivity after 4 weeks of treatment, whereas ectopic dendrites only became evident after 7 weeks of treatment. Thus, GM2 ganglioside accumulated in pyramidal neurons before ectopic dendrites emerged from the axon hillock. We propose that the reinitiation of dendrite growth on mature pyramidal cells is brought about by accumulated GM2 ganglioside.

The substrate-specificity of human lysosomal alpha-D-mannosidase in relation to genetic alpha-mannosidosis

The specificity of human liver lysosomal alpha-mannosidase (EC 3.2.1.24) towards a series of oligosaccharide substrates derived from high-mannose, complex and hybrid asparagine-linked glycans and from the storage products in alpha-mannosidosis was investigated. The enzyme hydrolyses all alpha(1-2)-, alpha(1-3)- and alpha(1-6)-mannosidic linkages in these glycans without a requirement for added Zn2+, albeit at different rates. A major finding of this study is that all the substrates are hydrolysed by non-random pathways. These pathways were established by determining the structures of intermediates in the digestion mixtures by a combination of h.p.t.l.c. and h.p.l.c. before and after acetolysis. The catabolic pathway for a particular substrate appears to be determined by its structure, raising the possibility that degradation occurs by an uninterrupted sequence of steps within one active site. The structures of the digestion intermediates are compared with the published structures of the storage products in mannosidosis and of intact asparagine-linked glycans. Most but not all of the digestion intermediates derived from high-mannose glycans have structures found in intact asparagine-linked glycans of human glycoproteins or among the storage products in the urine of patients with mannosidosis. However, the relative abundances of these structures suggests that the catabolic pathway is not the same as the processing pathway. In contrast, the intermediates formed from the digestion of oligosaccharides derived from hybrid and complex N-glycans are completely different from any processing intermediates and also from the oligosaccharides of composition Man2-4GlcNAc that account for 80-90% of the storage products in alpha-mannosidosis. It is postulated that the structures of these major storage products arise from the action of an exo/endo-alpha(1-6)-mannosidase on the partially catabolized oligomannosides that accumulate in the absence of the main lysosomal alpha-mannosidase.

Different oligosaccharides accumulate in the brain and urine of a cat with alpha-mannosidosis: structure determination of five brain-derived and seventeen urinary oligosaccharides

Five brain-derived and 17 urinary oligomannose-type oligosaccharides were isolated by ion-exchange chromatography on Mono Q or Dowex, followed by HPLC on Lichrosorb-NH2 from a Persian cat suffering from alpha-mannosidosis. The structures of the carbohydrate chains were determined by 500- or 600-MHz 1H-NMR spectroscopy. Different oligosaccharide patterns were found in brain and urine. 99% of the urinary oligosaccharides possess an alpha(1-6)-linked mannose residue attached to beta-mannose, whereas only 5% of the brain-derived oligosaccharides contain such a residue. Furthermore, of the urinary carbohydrate chains 71% end with Man beta 1-4GlcNAc beta 1-4GlcNAc and 29% end with Man beta 1-4GlcNAc, whereas the corresponding amounts are 23% and 77%, respectively, for the brain-derived oligosaccharides.