Canine fucosidosis: a model for retroviral gene transfer into haematopoietic stem cells

Fucosidosis-Clinical Manifestation, Long-Term Outcomes, and Genetic Profile-Review and Case Series

Fucosidosis is a neurodegenerative disorder which progresses inexorably. Clinical features include coarse facial features, growth retardation, recurrent upper respiratory infections, dysostosis multiplex, and angiokeratoma corporis diffusum. Fucosidosis is caused by mutations in the FUCA1 gene resulting in α-L-fucosidase deficiency. Only 36 pathogenic variants in the FUCA1 gene are related to fucosidosis. Most of them are missense/nonsense substitutions; six missense and 11 nonsense mutations. Among deletions there were eight small and five gross changes. So far, only three splice site variants have been described—one small deletion, one complete deletion and one stop-loss mutation. The disease has a significant clinical variability, the cause of which is not well understood. The genotype–phenotype correlation has not been well defined. This review describes the genetic profile and clinical manifestations of fucosidosis in pediatric and adult cases.

Sensorimotor and Neurocognitive Dysfunctions Parallel Early Telencephalic Neuropathology in Fucosidosis Mice

Fucosidosis is a lysosomal storage disorder (LSD) caused by lysosomal α-L-fucosidase deficiency. Insufficient α-L-fucosidase activity triggers accumulation of undegraded, fucosylated glycoproteins and glycolipids in various tissues. The human phenotype is heterogeneous, but progressive motor and cognitive impairments represent the most characteristic symptoms. Recently, Fuca1-deficient mice were generated by gene targeting techniques, constituting a novel animal model for human fucosidosis. These mice display widespread LSD pathology, accumulation of secondary storage material and neuroinflammation throughout the brain, as well as progressive loss of Purkinje cells. Fuca1-deficient mice and control littermates were subjected to a battery of tests detailing different aspects of motor, emotional and cognitive function. At an early stage of disease, we observed reduced exploratory activity, sensorimotor disintegration as well as impaired spatial learning and fear memory. These early markers of neurological deterioration were related to the respective stage of neuropathology using molecular genetic and immunochemical procedures. Increased expression of the lysosomal marker Lamp1 and neuroinflammation markers was observed throughout the brain, but appeared more prominent in cerebral areas in comparison to cerebellum of Fuca1-deficient mice. This is consistent with impaired behaviors putatively related to early disruptions of motor and cognitive circuits particularly involving cerebral cortex, basal ganglia, and hippocampus. Thus, Fuca1-deficient mice represent a practical and promising fucosidosis model, which can be utilized for pathogenetic and therapeutic studies.

Associations between neurologic dysfunction and lesions in canine fucosidosis

Canine fucosidosis in English Springer spaniels is the only animal model of the neurovisceral lysosomal storage disease fucosidosis available for preclinical therapeutic trials. For this reason, it is crucial to identify critical time points in disease progression, and if there are particular lesions associated with specific aspects of neurologic dysfunction. Historical records of 53 canine fucosidosis cases from 1979 to 2009 containing a neurologic dysfunction score assessing motor, behavioral and sensory dysfunction were interrogated by statistical analysis. Motor and behavioral dysfunction scores assessing gait deficits and apprehensive behavior first significantly increased at 12-17 months, and increased at each 6-month interval thereafter. Sensory dysfunction scores, assessing hearing loss, balance and vision deterioration, did not significantly increase until 18-23 months, and coincided with a rapid decline in neurologic function. Regression analysis incorporating published neuropathology data, measured by image analysis, identified neuroinflammation and apoptotic cell death as significant informative predictors of increasing neurologic dysfunction. These findings indicate that the level of neuropathology required to induce consistent and conspicuous clinical signs in canine fucosidosis is reached by approximately 12 months of age in the absence of other disease processes. Significant association between neuroinflammation and apoptotic cell death also suggests that specifically targeting these lesions combined with enzyme replacement in future studies may reduce disease burden in fucosidosis. Overall, examining this historical clinical data to identify associations between the extent of neuropathology and degree of clinical dysfunction provides a useful reference tool for monitoring disease and evaluating therapeutic trials conducted in canine fucosidosis.

Advances and pitfalls of cell therapy in metabolic leukodystrophies

Leukodystrophies are a group of disorders characterized by myelin dysfunction, either at the level of myelin formation or maintenance, that affect the central nervous system (CNS) and also in some cases, to a lesser extent, the peripheral nervous system (PNS). Although these genetic-based disorders are generally rare, all together they have a significant impact in the society, with an estimated overall incidence of 1 in 7,663 live births. Currently, there is no cure for leukodystrophies, and the development of effective treatments remains challenging. Not only leukodystrophies generally progress very fast, but also most are multifocal needing the simultaneous targeting at multiple sites. Moreover, as the CNS is affected, the blood-brain barrier (BBB) limits the efficacy of treatment. Recently, interest on cell therapy has increased, and the leukodystrophies for which metabolic correction is needed have become first-choice candidates for cell-based clinical trials. In this review, we present and discuss the available cell transplantation therapies in metabolic leukodystrophies including fucosidosis, X-linked adrenoleukodystrophy, metachromatic leukodystrophy, Canavan disease, and Krabbe's disease. We will discuss the latest advances of cell therapy and its pitfalls in this group of disorders, taking into account, among others, the limitations imposed by reduced cell migration in multifocal conditions, the need to achieve corrective enzyme threshold levels, and the growing awareness that not only myelin but also the associated axonopathy needs to be targeted in some leukodystrophies.

Treatment of canine fucosidosis by intracisternal enzyme infusion

The blood brain barrier is the major obstacle to treating lysosomal storage disorders of the central nervous system such as canine fucosidosis. This barrier was overcome by three, monthly injections of recombinant canine α-l-fucosidase enzyme were given intracisternally. In dogs treated from 8 weeks of age enzyme reached all areas of central nervous system as well as the cervical lymph node, bone marrow and liver. Brainstem and spinal cord samples from regions adjacent to the injection site had highest enzyme levels (39-73% of normal). Substantial enzyme activity (8.5-20% of normal controls) was found in the superficial brain compared to deeper regions (2.6-5.5% of normal). Treatment significantly reduced the fucosyl-linked oligosaccharide accumulation in most areas of CNS, liver and lymph node. In the surface and deep areas of lumbar spinal cord, oligosaccharide accumulation was corrected (79-80% reduction) to near normal levels (p<0.05). In the spinal meninges (thoracic and lumbar) enzyme activity (35-39% of normal control) and substrate reduction (58-63% affected vehicle treated samples) reached levels similar to those seen in phenotypically normal carriers (p<0.05).The procedure was safe and well-tolerated, treated (average 16%) dogs gained more weight (p<0.05) and there was no antibody formation or inflammatory reaction in plasma and CSF following treatments. The capacity of early ERT to modify progression of biochemical storage in fucosidosis is promising as this disease is currently only amenable to treatment by bone marrow transplantation which entails unacceptably high risks for many patients.

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.

Gene therapy for lysosomal storage diseases

The lysosomal storage diseases are a family of inherited disorders usually caused by a deficiency in a single lysosomal enzyme, and are characterised by progressive intralysosomal storage in multiple cell types. Although individual syndromes can be uncommon, as a whole this family of diseases affects approximately 1 in 3,000 live births. The severity of disease can be variable, ranging from minimal evidence of lysosomal storage to widespread multi-system involvement and early mortality. Although the enzymatic defects responsible for most of these diseases are known, treatment options for the majority of these disorders are limited to supportive care and genetic counselling. Knowledge of the genetic defects underlying these diseases, coupled with advances in the fields of gene transfer and expression, provide an opportunity to utilise gene therapy strategies in order to treat these disorders. Here we provide a description of the biochemical and molecular basis of gene therapy for lysosomal storage diseases, as well as an overview of some of the in vitro and in vivo studies that have been performed.

Gene transfer strategies for correction of lysosomal storage disorders

Lysosomal storage diseases (LSDs) represent a large group of monogenic disorders of metabolism, which affect approximately 1 in 5000 live births. LSDs result from a single or multiple deficiency of specific lysosomal hydrolases, the enzymes responsible for the luminal catabolization of macromolecular substrates. The consequent accumulation of undigested metabolites in lysosomes leads to polysystemic dysfunction, including progressive neurologic deterioration, mental retardation, visceromegaly, blindness, and early death. In general, the residual amount of functional enzyme in lysosomes determines the severity and age at onset of the clinical symptoms, implying that even modest increases in enzyme activity might affect a cure. A key feature on which therapy for LSDs is based is the ability of soluble enzyme precursors to be secreted by one cell type and reinternalize by neighboring cells via receptor-mediated endocytosis and routed to lysosomes, where they function normally. In principle, somatic gene therapy could be the preferred treatment for LSDs if the patient's own cells could be genetically modified in vitro or in vivo to constitutively express high levels of the correcting enzyme and become the source of the enzyme in the patient. Both ex vivo and in vivo gene transfer methods have been experimented with for gene therapy of lysosomal disorders. Several of these methods have proved efficient for the transfer of genetic material into deficient cells in culture and reconstitution of enzyme activity. However, the same methods applied to humans or animal models have been giving inconsistent results, the bases of which are not fully understood. A broader knowledge of disease pathogenesis, facilitated by available, faithful animal models of LSDs, coupled to the development of better gene transfer systems as well as the understanding of vector host interactions will make somatic gene therapy for these devastating and complex diseases the most suitable therapeutic approach.

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.

Gene transfer into canine myoblasts

We have developed and characterized cultures of healthy and dystrophic canine myoblasts for the evaluation of various gene transfer protocols. The number of desmin-positive myoblasts was elevated (>>80%) in cultures of myoblasts obtained from different muscle territories, the diaphragm muscle giving rise to the purest cultures. Myoblasts from dogs turned out to be a very convenient source of well transfectable and transducible cells. Transfection with plasmid DNA allowed efficient transgene expression (50% of beta-galactosidase positive cells and about 375 ng luciferase/mg protein after transfection with a calcium phosphate-precipitated plasmid). Infection with high concentrations of adenoviral and retroviral vectors allowed transgene (beta-galactosidase or mini-dystrophin) detection in about 75 to 90% of the canine cells. Therefore, primary dog myoblast cultures represent a useful in vitro model for viral and non-viral gene delivery, as well as for functional evaluation and cell grafting with applications in genetic diseases, vaccination or production of circulating therapeutic proteins.

Determination of cell origin after marrow transplantation in canines by polymerase chain reaction and quantitation of the ZFY/ZFX genes

BACKGROUND

In order to follow the course of bone marrow engraftment in dogs, and to determine the presence, and percentage, of donor-derived cells in other canine tissues, a simple and fast method of determining cell origin after sex-mismatched bone marrow transplantation was developed.

METHODS

Using universal primers, fragments from genomic DNA corresponding to ZFX and ZFY genes were amplified by polymerase chain reaction. A restriction fragment length polymorphism, combined with densitometric analysis, was then used to distinguish and quantitate ZFY and ZFX sequences. Unknown samples were analyzed against standards of known mixtures of male and female DNA.

RESULTS

Canine ZFY and ZFX genes were clearly resolved after amplification, digestion with HaeIII, and denaturing polyacrylamide gel electrophoresis. Microchimerism could be detected in male and female dog DNA samples derived from a range of fresh and frozen tissues including spleen, testicle, and the central nervous system. The levels of chimerism determined using this method were in either agreement with results obtained by karyotyping or more sensitive, with a detection limit of 0.4% compared with 1-2%.

CONCLUSIONS

Polymerase chain reaction/restriction fragment length polymorphism detection of the ZFY and ZFX genes was found to be simple, accurate, and reliable for assessing engraftment in dogs. When compared with cytogenetic analysis, this method was found to be faster to perform, more capable of detecting lower levels of microchimerism, and useful for detecting donor-derived cells in stored specimens and in tissues other than peripheral blood or bone marrow.