Hepatic storage of glycosaminoglycans in feline and canine models of mucopolysaccharidoses I, VI, and VII

Reduction of lysosome abundance and GAG accumulation after odiparcil treatment in MPS I and MPS VI models

Deficiencies of lysosomal enzymes responsible for the degradation of glycosaminoglycans (GAG) cause pathologies commonly known as the mucopolysaccharidoses (MPS). Each type of MPS is caused by a deficiency in a specific GAG-degrading enzyme and is characterized by an accumulation of disease-specific GAG species. Previously, we have shown the potential of the beta-D-xyloside, odiparcil, as an oral GAG clearance therapy for Maroteaux-Lamy syndrome (MPS VI), an MPS characterized by an accumulation of chondroitin sulphate (CS) and dermatan sulphate (DS). This work suggested that odiparcil acts via diverting the synthesis of CS and DS into odiparcil-bound excretable GAG. Here, we investigated the effect of odiparcil on lysosomal abundance in fibroblasts from patients with MPS I and MPS VI. In MPS VI fibroblasts, odiparcil reduced the accumulation of a lysosomal-specific lysotracker dye. Interestingly, a reduction of the lysotracker dye was also observed in odiparcil-treated fibroblasts from patients with MPS I, a disorder characterized by an accumulation of DS and heparan sulphate (HS). Furthermore, odiparcil was shown to be effective in reducing CS, DS, and HS concentrations in liver and eye, as representative organs, in MPS VI and MPS I mice treated with 3 doses of odiparcil over 3 and 9 months, respectively. In conclusion, our data demonstrates odiparcil efficiently reduced lysosome abundance and tissue GAG concentrations in in vitro and in vivo models of MPS VI and MPS I and has potential as a treatment for these disorders.

The Interplay of Glycosaminoglycans and Cysteine Cathepsins in Mucopolysaccharidosis

Mucopolysaccharidosis (MPS) consists of a group of inherited lysosomal storage disorders that are caused by a defect of certain enzymes that participate in the metabolism of glycosaminoglycans (GAGs). The abnormal accumulation of GAGs leads to progressive dysfunctions in various tissues and organs during childhood, contributing to premature death. As the current therapies are limited and inefficient, exploring the molecular mechanisms of the pathology is thus required to address the unmet needs of MPS patients to improve their quality of life. Lysosomal cysteine cathepsins are a family of proteases that play key roles in numerous physiological processes. Dysregulation of cysteine cathepsins expression and activity can be frequently observed in many human diseases, including MPS. This review summarizes the basic knowledge on MPS disorders and their current management and focuses on GAGs and cysteine cathepsins expression in MPS, as well their interplay, which may lead to the development of MPS-associated disorders.

The abnormal accumulation of heparan sulfate in patients with mucopolysaccharidosis prevents the elastolytic activity of cathepsin V

Mucopolysaccharidosis (MPS) are rare inherited diseases characterized by accumulation of lysosomal glycosaminoglycans, including heparan sulfate (HS). Patients exhibit progressive multi-visceral dysfunction and shortened lifespan mainly due to a severe cardiac/respiratory decline. Cathepsin V (CatV) is a potent elastolytic protease implicated in extracellular matrix (ECM) remodeling. Whether CatV is inactivated by HS in lungs from MPS patients remained unknown. Herein, CatV colocalized with HS in MPS bronchial epithelial cells. HS level correlated positively with the severity of respiratory symptoms and negatively to the overall endopeptidase activity of cysteine cathepsins. HS bound tightly to CatV and impaired its activity. Withdrawal of HS by glycosidases preserved exogenous CatV activity, while addition of Surfen, a HS antagonist, restored elastolytic CatV-like activity in MPS samples. Our data suggest that the pathophysiological accumulation of HS may be deleterious for CatV-mediated ECM remodeling and for lung tissue homeostasis, thus contributing to respiratory disorders associated to MPS diseases.

Mucopolysaccharidosis VI in cats - clarification regarding genetic testing

The release of new DNA-based diagnostic tools has increased tremendously in companion animals. Over 70 different DNA variants are now known for the cat, including DNA variants in disease-associated genes and genes causing aesthetically interesting traits. The impact genetic tests have on animal breeding and health management is significant because of the ability to control the breeding of domestic cats, especially breed cats. If used properly, genetic testing can prevent the production of diseased animals, causing the reduction of the frequency of the causal variant in the population, and, potentially, the eventual eradication of the disease. However, testing of some identified DNA variants may be unwarranted and cause undo strife within the cat breeding community and unnecessary reduction of gene pools and availability of breeding animals. Testing for mucopolysaccharidosis Type VI (MPS VI) in cats, specifically the genetic testing of the L476P (c.1427T>C) and the D520N (c.1558G>A) variants in arylsulfatase B (ARSB), has come under scrutiny. No health problems are associated with the D520N (c.1558G>A) variant, however, breeders that obtain positive results for this variant are speculating as to possible correlation with health concerns. Birman cats already have a markedly reduced gene pool and have a high frequency of the MPS VI D520N variant. Further reduction of the gene pool by eliminating cats that are heterozygous or homozygous for only the MPS VI D520N variant could lead to more inbreeding depression effects on the breed population. Herein is debated the genetic testing of the MPS VI D520N variant in cats. Surveys from different laboratories suggest the L476P (c.1427T>C) disease-associated variant should be monitored in the cat breed populations, particularly breeds with Siamese derivations and outcrosses. However, the D520N has no evidence of association with disease in cats and testing is not recommended in the absence of L476P genotyping. Selection against the D520N is not warranted in cat populations. More rigorous guidelines may be required to support the genetic testing of DNA variants in all animal species.

Glycosaminoglycan-mediated loss of cathepsin K collagenolytic activity in MPS I contributes to osteoclast and growth plate abnormalities

Mucopolysaccharidoses are a group of lysosomal storage diseases characterized by the build-up of glycosaminoglycans (GAGs) and severe skeletal abnormalities. As GAGs can regulate the collagenolytic activity of the major osteoclastic protease cathepsin K, we investigated the presence and activity of cathepsin K and its co-localization with GAGs in mucopolysaccharidosis (MPS) type I bone. The most dramatic difference between MPS I and wild-type mice was an increase in the amount of cartilage in the growth plates in MPS I bones. Though the number of cathepsin K-expressing osteoclasts was increased in MPS I mice, these mice revealed a significant reduction in cathepsin K-mediated cartilage degradation. As excess heparan and dermatan sulfates inhibit type II collagen degradation by cathepsin K and the spatial overlap between cathepsin K and heparan sulfate strongly increased in MPS I mice, the build up of subepiphyseal cartilage is speculated to be a direct consequence of cathepsin K inhibition by MPS I-associated GAGs. Moreover, isolated MPS I and Ctsk(-/-) osteoclasts displayed fewer actin rings and formed fewer resorption pits on dentine disks, as compared with wild-type cells. These results suggest that the accumulation of GAGs in murine MPS I bone has an inhibitory effect on cathepsin K activity, resulting in impaired osteoclast activity and decreased cartilage resorption, which may contribute to the bone pathology seen in MPS diseases.

Bone marrow transplantation for feline mucopolysaccharidosis I

Severe mucopolysaccharidosis type I (MPS I) is a fatal neuropathic lysosomal storage disorder with significant skeletal involvement. Treatment involves bone marrow transplantation (BMT), and although effective, is suboptimal, due to treatment sequelae and residual disease. Improved approaches will need to be tested in animal models and compared to BMT. Herein we report on bone marrow transplantation to treat feline mucopolysaccharidosis I (MPS I). Five MPS I stably engrafted kittens, transplanted with unfractionated bone marrow (6.3x10(7)-1.1x10(9) nucleated bone marrow cells per kilogram) were monitored for 13-37 months post-engraftment. The tissue total glycosaminoglycan (GAG) content was reduced to normal levels in liver, spleen, kidney, heart muscle, lung, and thyroid. Aorta GAG content was between normal and affected levels. Treated cats had a significant decrease in the brain GAG levels relative to untreated MPS I cats and a paradoxical decrease relative to normal cats. The alpha-l-iduronidase (IDUA) activity in the livers and spleens of transplanted MPS I cats approached heterozygote levels. In kidney cortex, aorta, heart muscle, and cerebrum, there were decreases in GAG without significant increases in detectable IDUA activity. Treated animals had improved mobility and decreased radiographic signs of disease. However, significant pathology remained, especially in the cervical spine. Corneal clouding appeared improved in some animals. Immunohistochemical and biochemical analysis documented decreased central nervous system ganglioside storage. This large animal MPS I study will serve as a benchmark of future therapies designed to improve on BMT.

Mucopolysaccharidosis type VII in a German Shepherd Dog

A 12-week-old male German Shepherd Dog was evaluated because of a 3-week history of a progressive inability to ambulate. Clinical and laboratory findings included skeletal deformities, corneal cloudiness, cytoplasmic granules in the neutrophils and lymphocytes of blood and CSF and glycosaminoglycans in a urine sample (detected via a toluidine blue spot test). Enzyme activity and DNA analyses confirmed mucopolysaccharidosis type VII as a result of severe beta-glucuronidase deficiency; this condition had been identified in a mixed-breed dog (likely of German Shepherd Dog descent) that was reported 20 years earlier and caused by the same missense mutation. Because of the progressive nature of this disease, the puppy was euthanatized and all tissues examined contained evidence of lysosomal storage leading to marked cellular distention. Mucopolysaccharidosis type VII is only one of many hereditary lysosomal storage diseases identified in companion animals. It is important that clinicians recognize the typical signs of lysosomal storage diseases and are aware of the cytologic and urinary screening tests for mucopolysaccharidosis disorders. Furthermore, there are specific blood enzyme and DNA-based tests to distinguish the forms of mucopolysaccharidosis in affected and carrier animals.

Mucopolysaccharidosis VI in a Siamese/short-haired European cat

A 3-year-old Siamese/short-haired European cat was referred for clinical disease characterized by dwarfism, facial dysmorphia, paralysis, small and curled ears, corneal clouding and large areas of alopecia. X-ray examination showed multiple bone dysplasia. On the basis of clinical features a form of mucopolysaccharidosis was suspected. The cat, killed at the owner's request, presented several severe skeletal deformities such as long caudal limbs, enlarged thorax with sunken breastbone, vertebral ankylosis in many spinal segments and visceral involvement. Histologically, the cat showed diffuse vacuolization and enlargement of cells in cartilage, bone and visceral organs. Ultrastructurally, membrane-bound vacuoles were filled with fibrillar and fluffy-material or concentrically whorled lamellae. Arylsulphatase B activity was 3.24 nm/mg/h in the affected cat and 30.6 in a normal age-matched control (NC). The L-iduronidase activity was slightly increased. Quantitation of total glycosaminoglycans (GAGs) revealed a 4.5-fold increase in the affected cat as compared with NC, while electrophoretic run of specific GAGs [chondroitin sulphate (CA); hyaluronan (HA); heparan sulphate (HS); dermatan sulphate (DS); keratan sulphate (KS)] performed on a cellulose acetate sheet, showed a striking increase in the DS band. On densitometric analysis of the electrophoretic run stained with Alcian Blue 8GX, the absorption of DS was eight-fold increased as compared with NC. The clinical and morphological features, and the biochemical findings, were consistent with the diagnosis of feline mucopolysaccharidosis VI.

Prevention of systemic clinical disease in MPS VII mice following AAV-mediated neonatal gene transfer

For many inborn errors of metabolism, early treatment is critical to prevent long-term developmental sequelae. We have previously shown that systemic treatment of neonatal mucopolysaccharidosis type VII (MPS VII) mice with recombinant adeno-associated virus (AAV) vectors results in relatively long-term expression of beta-glucuronidase (GUSB) in multiple tissues, and a reduction in lysosomal storage. Here, we demonstrate that therapeutic levels of enzyme persist for at least 1 year following a single intravenous injection of virus in neonatal MPS VII mice. The level and distribution of GUSB expression achieved is sufficient to prevent the development of many aspects of clinical disease over the life of the animal. Following treatment, bone lengths, weights and retinal function were maintained at nearly normal levels throughout the life of the animal. In addition, significant improvements in survival and auditory function were seen in AAV-treated MPS VII mice when compared with untreated mutant siblings. These data suggest that AAV-mediated gene transfer in the neonatal period can lead to prevention of many of the clinical symptoms associated with MPS VII in the murine model of this disease.

Forelimb lameness in the young patient

Forelimb lameness is a common problem in young dogs and can be caused by a wide variety of problems. Accurate and comprehensive diagnosis and treatment must be provided for these patients. Differential diagnoses for forelimb lameness in the young patient fall into the categories of congenital abnormalities; developmental disorders; trauma; and infectious, nutritional, metabolic, and neoplastic causes. The etiopathogeneses of many of these disorders are still unknown, and treatment options and prognoses vary tremendously. Until definitive causes are determined, it is the responsibility of veterinarians to address the factors that contribute to the development and progression of these disorders. These areas primarily involve weight and nutritional management as well as breeding programs.

Gene transfer of low levels of beta-glucuronidase corrects hepatic lysosomal storage in a large animal model of mucopolysaccharidosis VII

Gene therapy has been at least partially effective in several mouse disease models, but treatment of large mammals has been more difficult to achieve. One major limitation is that only low levels of expression of the corrective gene are often maintained in vivo. In a mouse model of the lysosomal storage disease mucopolysaccharidosis (MPS) type VII (Sly disease) with a null mutation in beta-glucuronidase, gene transfer experiments have shown that only 1-2% of normal beta-glucuronidase can correct the storage in some major organs. In contrast, MPS VII dogs, cats, and humans that have residual beta-glucuronidase activity levels in this range are affected. Thus, higher levels of transferred gene expression may be needed to achieve a therapeutic effect in large animals and humans. We tested this by examining liver pathology in MPS VII dogs after intraperitoneal transplantation of neo-organs containing retrovirus vector-corrected autologous fibroblasts that expressed low levels of beta-glucuronidase. The enzyme secreted from the neo-organs was taken up by the liver and significantly reduced the substrate content compared with untreated dogs. This suggests that small amounts of normal enzyme, when delivered to target tissues, may be therapeutically effective in human MPS VII patients.

Mucopolysaccharidosis VII in a cat

Mucopolysaccharidosis VII was diagnosed in a domestic shorthair cat from California. The cat was small and had multiple abnormalities, including a small body disproportionate to the size of the skull, angular deformities of the ribs, abnormally short forelimbs, luxating patellas, generalized epiphyseal dysplasia involving the vertebrae and long bones, cuboidal vertebrae, pectus excavatum, subluxation of both hips, osteosclerosis of the tentorium cerebelli and left petrous temporal bone, tracheal hypoplasia, and corneal clouding. Beta-glucuronidase activity was markedly decreased in peripheral blood leukocytes. The cat died at 21 months of age, and a complete necropsy was performed. Tissues were examined by light and transmission electron microscopy. Large clear, round vacuoles representing distended lysosomes were present in many epithelial and connective tissue cells, including fibrocytes, chondrocytes, smooth muscle cells, hepatocytes, astrocytes, and macrophages.

Enzyme replacement in murine mucopolysaccharidosis type VII: neuronal and glial response to beta-glucuronidase requires early initiation of enzyme replacement therapy

We have previously shown that mucopolysaccharidosis type VII (MPS VII) mice receiving six weekly injections of recombinant beta-glucuronidase from birth had improved cognitive ability and reduced central nervous system lysosomal storage. However, a single beta-glucuronidase injection at 5 wk of age did not correct neuronal storage. We define the age at which central nervous system storage in MPS VII mice becomes resistant to beta-glucuronidase therapy and determine the effect of enzyme on other tissues by comparing the histology of mice begun on therapy at various times after birth. MPS VII mice received injections on the day of birth and then weekly for 5 wk with 16,000U/g beta-glucuronidase had reduced lysosomal storage in brain. The same therapy begun on d 14 of life or thereafter failed to correct neuronal storage, even when treatment was continued for six doses. Glial responsiveness or accessibility to enzyme also depended on early treatment. In contrast, leptomeningeal, osteoblast, and retinal pigment epithelial storage reduction depended on enzyme dose rather than age at initiation of therapy. Fixed tissue macrophage storage was reduced in all treated MPS VII mice, even those receiving a single dose. These observations indicate that fixed tissue macrophages in MPS VII mice remain sensitive to enzyme replacement therapy well into adulthood although neurons are responsive or accessible to enzyme therapy early in life. Because early initiation of enzyme replacement is important to achieve a central nervous system response, these studies emphasize the importance of newborn screening for lysosomal storage diseases so that early treatment can maximize the likelihood of a favorable therapeutic response.

Sulfamidase deficiency in a family of Dachshunds: a canine model of mucopolysaccharidosis IIIA (Sanfilippo A)

Mucopolysaccharidosis IIIA (MPS IIIA or Sanfilippo A, McKusick 25290) was diagnosed in two adult wire-haired Dachshund littermates. Clinical and pathologic features paralleled the human disorder; both dogs exhibited progressive neurologic disease without apparent somatic involvement. Pelvic limb ataxia was observed when the dogs were 3 y old and progressed gradually within 1-2 y to severe generalized spinocerebellar ataxia. Mentation remained normal throughout the course of the disease. A mucopolysaccharide storage disorder was indicated in both dogs by positive toluidine blue spot tests of urine. The diagnosis of MPS IIIA was confirmed by documentation of urinary excretion and tissue accumulation of heparan sulfate and decreased sulfamidase activity in fibroblasts and hepatic tissue. Mild cerebral cortical atrophy and dilation of the lateral ventricles were grossly evident in both dogs. Light microscopically, fibroblasts, hepatocytes, and renal tubular epithelial cells were vacuolated. Within the nervous system, cerebellar Purkinje cells, neurons of brainstem nuclei, ventral and dorsal horns, and dorsal ganglia were distended with brightly autofluorescent, periodic acid-Schiff-positive, sudanophilic material. Ultrastructurally, visceral storage presented as membrane-bound vacuoles with finely granular, variably electron-lucent contents. Neuronal storage appeared as membranous concentric whorls, lamellated parallel membrane stacks, or electron-dense lipid-like globules. This represents the first reported animal disease homolog of the human Sanfilippo A syndrome.

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.

Diagnosis of lysosomal storage disorders: evaluation of lysosome-associated membrane protein LAMP-1 as a diagnostic marker

Early diagnosis of lysosomal storage disorders (LSDs), before the onset of irreversible pathologies, will be a key factor in the development of effective therapies for many of these disorders. Newborn screening offers a potential mechanism for the early detection of these disorders. From studies of both normal and LSD-affected human skin fibroblasts we identified the lysosome-associated membrane protein LAMP-1 as a potential diagnostic marker. We have developed a sensitive method for the quantification of this protein with a time-resolved fluorescence immunoassay. A soluble form of LAMP-1 was observed in plasma samples, and determination of 152 unaffected individuals gave a median value of 303 μg/L with the 5th and 95th percentile at 175 and 448 μg/L respectively. Plasma samples from 320 LSD-affected individuals representing 25 different disorders were assayed. We observed that 17 of the 25 disorder groups tested had >88% of individuals above the 95th percentile of the control population, with 12 groups having 100% above the 95th percentile. Overall, 72% of patients had LAMP-1 concentrations above the 95th percentile of the unpartitioned control population. We suggest that LAMP-1 may be a useful marker in newborn screening for LSDs.

Feline mucopolysaccharidosis VII due to beta-glucuronidase deficiency

A male cat 12-14 weeks old had walking difficulties and an enlarged abdomen. Facial dysmorphism, plump paws, corneal clouding, granulation of neutrophils, vacuolated lymphocytes, and a positive urine test for sulfated glycosaminoglycans suggested mucopolysaccharidosis. Cultured fibroblasts incorporated 35SO4 into mucopolysaccharides more actively than did fibroblasts of a feline control, and degradation was far inferior. Activity of beta-glucuronidase was absent in leukocytes and markedly reduced in fibroblasts, thus establishing the diagnosis of mucopolysaccharidosis VII, a disorder previously described in humans, dogs, and mice. Light microscopic examination revealed foam cells in virtually all organs examined, and electron microscopic examination showed pancytic storage of floccular material characteristic of mucopolysaccharides. Stored sphingolipids in the form of zebra bodies were seen in ganglion cells of the central nervous system and in smooth muscle cells of blood vessels. This case represents another animal model of mucopolysaccharidosis VII with the full disease characteristics known in human patients.

Pathological characteristics of mucopolysaccharidosis VI in the rat

The histological and electron microscopical characteristics of the pathology of rats with arylsulphatase B-deficient mucopolysaccharidosis (mucopolysaccharidosis VI; MPS VI) were investigated. In affected animals, intracytoplasmic vacuoles were prominent in chondrocytes, the macrophage system, cardiac valve fibroblasts, cornea, connective tissues, vascular smooth muscle cells and uterine stromal cells. Tissues containing glucosaminoglycans stored in lysosomes were positive to Mowry's colloidal iron and alcian blue stains. By electron microscopy, the lysosomes were seen to be distended by electron lucent or fine fibrillary storage material, and lysosomal storage was also detected in the endothelial cells of the arteries and cornea. In the central and peripheral nervous system abnormalities were restricted to the connective tissue. Lesions in the affected rats resembled those described in human and feline mucopolysaccharidosis VI. These results indicate that MPS VI of the rat may be a useful animal model for human MPS VI (Maroteaux-Lamy syndrome).

Arylsulfatase B-deficient mucopolysaccharidosis in rats

A rat colony with mucopolysaccharidosis VI was established and the clinical, pathological, and biochemical features were characterized. Affected rats had facial dysmorphia, dysostosis multiplex, and increased urinary excretion of glucosaminoglycans (GAGs). Ultrastructural studies revealed storage of GAGs throughout the reticuloendothelial cells, cartilage, and other connective tissues, but no deposition was observed in the nervous system. Biochemical analyses demonstrated that the excreted GAG was dermatan sulfate and the activity of hepatic arylsulfatase B was < 5% of the normal mean value. Pedigree analysis showed that the phenotype was inherited as an autosomal recessive single trait. The availability of a rat model of human mucopolysaccharidosis VI should permit the development and evaluation of various strategies to treat the human disease.