Restoration of arylsulphatase B activity in human mucopolysaccharidosis-type-VI fibroblasts by retroviral-vector-mediated gene transfer

Secondary storage of dermatan sulfate in Sanfilippo disease

Mucopolysaccharidoses are a group of genetically inherited disorders that result from the defective activity of lysosomal enzymes involved in glycosaminoglycan catabolism, causing their intralysosomal accumulation. Sanfilippo disease describes a subset of mucopolysaccharidoses resulting from defects in heparan sulfate catabolism. Sanfilippo disorders cause severe neuropathology in affected children. The reason for such extensive central nervous system dysfunction is unresolved, but it may be associated with the secondary accumulation of metabolites such as gangliosides. In this article, we describe the accumulation of dermatan sulfate as a novel secondary metabolite in Sanfilippo. Based on chondroitinase ABC digestion, chondroitin/dermatan sulfate levels in fibroblasts from Sanfilippo patients were elevated 2-5-fold above wild-type dermal fibroblasts. Lysosomal turnover of chondroitin/dermatan sulfate in these cell lines was significantly impaired but could be normalized by reducing heparan sulfate storage using enzyme replacement therapy. Examination of chondroitin/dermatan sulfate catabolic enzymes showed that heparan sulfate and heparin can inhibit iduronate 2-sulfatase. Analysis of the chondroitin/dermatan sulfate fraction by chondroitinase ACII digestion showed dermatan sulfate storage, consistent with inhibition of iduronate 2-sulfatase. The discovery of a novel storage metabolite in Sanfilippo patients may have important implications for diagnosis and understanding disease pathology.

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.

Neurological correction of lysosomal storage in a mucopolysaccharidosis IIIB mouse model by adeno-associated virus-mediated gene delivery

Mucopolysaccharidosis (MPS) IIIB is characterized by mild somatic features and severe neurological diseases leading to premature death. No definite treatment is available for MPS IIIB patients. We constructed two recombinant adeno-associated virus (rAAV) vectors containing the human alpha-N-acetylglucosaminidase (NaGlu) cDNA driven by either a CMV or a neuron-specific enolase (NSE) promoter. In vitro, these rAAV vectors mediated efficient expression of recombinant NaGlu in human MPS IIIB fibroblasts and mouse MPS IIIB somatic and brain primary cell cultures. The secreted rNaGlu was taken up by both human and mouse MPS IIIB cells in culture and degraded the accumulated glycosaminoglycans (GAG). A direct microinjection (10(7) viral particles, 1 microl/10 minutes per injection) of vectors containing the NSE promoter resulted in long-term (6 months, the duration of the experiments) expression of rNaGlu in multiple brain structures/areas of adult MPS IIIB mice. Consistent with previous studies, the main target cells were neurons. However, while vector typically transduced an area of 400-500 microm surrounding the infusion sites, the correction of GAG storage involved neurons of a much broader area (1.5 mm) in a 6-month duration of experiments. These results provide a basis for the development of a treatment for neurological disease in MPS IIIB patients using AAV vectors.

Non-viral, integrin-mediated gene transfer into fibroblasts from patients with lysosomal storage diseases

BACKGROUND

Non-viral vectors consisting of Lipofectin/integrin-targeting peptide/DNA (LID) complexes have great potential for gene therapy, as they are safe, simple, and able to package large DNA molecules. In this study, these vectors were evaluated in vitro for the therapy of lysosomal storage disorders.

METHODS

Non-viral vectors were designed to deliver therapeutic genes by integrin-mediated uptake into fibroblasts from patients with the lysosomal storage disorders fucosidosis and Fabry disease, which result from deficiencies of alpha-L-fucosidase and alpha-galactosidase A, respectively. The vectors consisted of a complex (LID) of Lipofectin and a peptide containing an integrin-targeting domain and a poly-lysine domain to which was bound plasmid DNA, containing alpha-L-fucosidase (LID-alpha-Fuc) or alpha-galactosidase A (LID-alpha-Gal).

RESULTS

Patients' fibroblasts transfected with LID-alpha-Fuc and LID-alpha-Gal produced the corresponding enzyme at levels which were 10-40% of the total activity in cultures of normal fibroblasts. However, 95-98% of this activity was secreted. Transfection of endothelial cells, the main target cells in Fabry disease, with an LID-alpha-Gal produced a total alpha-galactosidase activity 65% higher than that in untransfected cultures after 6 days, 67% of the activity being secreted. Although transfection of fibroblasts with LID complexes also caused small changes in the distribution of endogenous lysosomal enzymes, it did not appear to affect the viability of the cells.

CONCLUSIONS

The integrin-mediated transfer of genes encoding lysosomal enzymes into cells results in the secretion of large amounts of normal enzyme that could be taken up by other cells. This could be a useful strategy for enzyme-replacement therapy.

Correction of acid beta-galactosidase deficiency in GM1 gangliosidosis human fibroblasts by retrovirus vector-mediated gene transfer: higher efficiency of release and cross-correction by the murine enzyme

Mutations in the lysosomal acid beta-galactosidase (EC 3.2.1.23) underlie two different disorders: GM1 gangliosidosis, which involves the nervous system and visceral organs to varying extents, and Morquio's syndrome type B (Morquio B disease), which is a skeletal-connective tissue disease without any CNS symptoms. This article shows that transduction of human GM1 gangliosidosis fibroblasts with retrovirus vectors encoding the human acid beta-galactosidase cDNA leads to complete correction of the enzymatic deficiency. The newly synthesized enzyme is correctly processed and targeted to the lysosomes in transduced cells. Cross-correction experiments using retrovirus-modified cells as enzyme donors showed, however, that the human enzyme is transferred at low efficiencies. Experiments using a different retrovirus vector carrying the human cDNA confirmed this observation. Transduction of human GM1 fibroblasts and mouse NIH 3T3 cells with a retrovirus vector encoding the mouse beta-galactosidase cDNA resulted in high levels of enzymatic activity. Furthermore, the mouse enzyme was found to be transferred to human cells at high efficiency. Enzyme activity measurements in medium conditioned by genetically modified cells suggest that the human beta-galactosidase enzyme is less efficiently released to the extracellular space than its mouse counterpart. This study suggests that lysosomal enzymes, contrary to the generalized perception in the field of gene therapy, may differ significantly in their properties and provides insights for design of future gene therapy interventions in acid beta-galactosidase deficiency.

A genetic linkage map of microsatellites in the domestic cat (Felis catus)

Of the nonprimate mammalian species with developing comparative gene maps, the feline gene map (Felis catus, Order Carnivora, 2N = 38) displays the highest level of syntenic conservation with humans, with as few as 10 translocation exchanges discriminating the human and feline genome organization. To extend this model, a genetic linkage map of microsatellite loci in the feline genome has been constructed including 246 autosomal and 7 X-linked loci. Two hundred thirty-five dinucleotide (dC. dA)n. (dG. dT)n and 18 tetranucleotide repeat loci were identified and genotyped in a two-family, 108-member multigeneration interspecies backcross pedigree between the domestic cat (F. catus) and the Asian leopard cat (Prionailurus bengalensis). Two hundred twenty-nine loci were linked to at least one other marker with a lod score >/=3.0, identifying 34 linkage groups. Representative markers from each linkage group were assigned to specific cat chromosomes by somatic cell hybrid analysis, resulting in chromosomal assignments to 16 of the 19 feline chromosomes. Genome coverage spans approximately 2900 cM, and we estimate a genetic length for the sex-averaged map as 3300 cM. The map has an average intragroup intermarker spacing of 11 cM and provides a valuable resource for mapping phenotypic variation in the species and relating it to gene maps of other mammals, including human.

Arylsulfatase B activities and glycosaminoglycan levels in retrovirally transduced mucopolysaccharidosis type VI cells. Prospects for gene therapy

Mucopolysacchariodosis type VI (MPS VI) is the lysosomal storage disorder caused by the deficient activity of arylsulfatase B (ASB; N-acetylgalactosamine 4-sulfatase) and the subsequent accumulation of the glycosaminoglycan (GAG), dermatan sulfate. In this study, a retroviral vector containing the full-length human ASB cDNA was constructed and used to transduce skin fibroblasts, chondrocytes, and bone marrow cells from human patients, cats, or rats with MPS VI. The ASB vector expressed high levels of enzymatic activity in each of the cell types tested and, in the case of cat and rat cells, enzymatic expression led to complete normalization of 35SO4 incorporation. In contrast, overexpression of ASB in human MPS VI skin fibroblasts did not lead to metabolic correction. High-level ASB expression was detected for up to eight weeks in transduced MPS VI cat and rat bone marrow cultures, and PCR analysis demonstrated retroviral-mediated gene transfer to approximately 30-50% of the CFU GM-derived colonies. Notably, overexpression of ASB in bone marrow cells led to release of the enzyme into the media and uptake by MPS VI cat and rat skin fibroblasts and/or chondrocytes via the mannose-6-phosphate receptor system, leading to metabolic correction. Thus, these studies provide important rationale for the development of gene therapy for this disorder and lay the frame-work for future in vivo studies in the animal model systems.

Correction of deficient enzyme activity in a lysosomal storage disease, aspartylglucosaminuria, by enzyme replacement and retroviral gene transfer

The ability of lysosomal enzymes to be secreted and subsequently captured by adjacent cells provides an excellent basis for investigating different therapy strategies in lysosomal storage disorders. Aspartylglucosaminuria (AGU) is caused by deficiency of aspartylglucosaminidase (AGA) leading to interruption of the ordered breakdown of glycoproteins in lysosomes. As a consequence of the disturbed glycoprotein catabolism, patients with AGU exhibit severe cell dysfunction especially in the central nervous system (CNS). The uniform phenotype observed in these patients will make effective evaluation of treatment trials feasible in future. Here we have used fibroblasts and lymphoblasts from AGU patients and murine neural cell lines as targets to evaluate in vitro the feasibility of enzyme replacement and gene therapy in the treatment of this disorder. Complete correction of the enzyme deficiency was obtained both with recombinant AGA enzyme purified from CHO-K1 cells and with retrovirus-mediated transfer of the AGA gene. Furthermore, we were able to demonstrate enzyme correction by cell-to-cell interaction of transduced and nontransduced cells.

Metabolic correction and cross-correction of mucopolysaccharidosis type II (Hunter syndrome) by retroviral-mediated gene transfer and expression of human iduronate-2-sulfatase

To explore the possibility of using gene transfer to provide iduronate-2-sulfatase (IDS; EC 3.1.6.13) enzyme activity for treatment of Hunter syndrome, an amphotropic retroviral vector, L2SN, containing the human IDS coding sequence was constructed and studied for gene expression in vitro. Lymphoblastoid cell lines (LCLs) from patients with Hunter syndrome were transduced with L2SN and expressed high levels of IDS enzyme activity, 10- to 70-fold higher than normal human peripheral blood leukocytes or LCLs. Such L2SN-transduced LCLs failed to show accumulation of 35SO4 into glycosaminoglycan (35SO4-GAG), indicating that recombinant IDS enzyme participated in GAG metabolism. Coculture of L2SN-transduced LCLs with fibroblasts from patients with Hunter syndrome reduced the accumulation of 35SO4-GAG. These results demonstrated retroviral-mediated IDS gene transfer into lymphoid cells and the ability of such cells to provide recombinant enzyme for intercellular metabolic cross-correction.

Metabolic correction and cross-correction of mucopolysaccharidosis type II (Hunter syndrome) by retroviral-mediated gene transfer and expression of human iduronate-2-sulfatase

To explore the possibility of using gene transfer to provide iduronate-2-sulfatase (IDS; EC 3.1.6.13) enzyme activity for treatment of Hunter syndrome, an amphotropic retroviral vector, L2SN, containing the human IDS coding sequence was constructed and studied for gene expression in vitro. Lymphoblastoid cell lines (LCLs) from patients with Hunter syndrome were transduced with L2SN and expressed high levels of IDS enzyme activity, 10- to 70-fold higher than normal human peripheral blood leukocytes or LCLs. Such L2SN-transduced LCLs failed to show accumulation of 35SO4 into glycosaminoglycan (35SO4-GAG), indicating that recombinant IDS enzyme participated in GAG metabolism. Coculture of L2SN-transduced LCLs with fibroblasts from patients with Hunter syndrome reduced the accumulation of 35SO4-GAG. These results demonstrated retroviral-mediated IDS gene transfer into lymphoid cells and the ability of such cells to provide recombinant enzyme for intercellular metabolic cross-correction.

Overexpression of N-acetylgalactosamine-4-sulphatase induces a multiple sulphatase deficiency in mucopolysaccharidosis-type-VI fibroblasts

High-titre stocks of an amphotropic retrovirus, constructed so as to express a full-length cDNA encoding the human lysosomal enzyme N-acetylgalactosamine-4-sulphatase (4-sulphatase) from the cytomegalovirus immediate early promoter, were used to infect skin fibroblasts from a clinically severe mucopolysaccharidosis type VI (MPS VI) patient. The infected MPS VI cells showed correction of the enzymic defect with the enzyme being expressed at high levels and in the correct subcellular compartment. Surprisingly this did not result in correction of glycosaminoglycan turnover as measured by accumulation of 35S in metabolically labelled cells. We demonstrate that this is apparently caused by an induced reduction of the activities of other lysosomal sulphatases, presumably due to competition for a sulphatase-specific processing mechanism by the over-expressed 4-sulphatase. The level of steroid sulphatase, which is a microsomal sulphatase, was also reduced. Infection of skin fibroblasts from a second, clinically mildly affected, MPS VI patient with the same virus also resulted in no significant change in the level of glycosaminoglycan storage. However, in this case the cause of the observed phenomenon was less clear. These results are of obvious practical importance when considering gene therapy for a sulphatase deficiency such as MPS VI and also provide possible new avenues for exploration of the processes involved in sulphatase synthesis and genetically determined multiple sulphatase deficiency.

Multiple sulfatase deficiency: catalytically inactive sulfatases are expressed from retrovirally introduced sulfatase cDNAs

Multiple sulfatase deficiency (MSD) is an inherited lysosomal storage disease characterized by the deficiency of at least seven sulfatases. The basic defect in MSD is thought to be in a post-translational modification common to all sulfatases. In accordance with this concept, RNAs of normal size and amount were detected in MSD fibroblasts for three sulfatases tested. cDNAs encoding arylsulfatase A, arylsulfatase B, or steroid sulfatase were introduced into MSD fibroblasts and fibroblasts with a single sulfatase deficiency by retroviral gene transfer. Infected fibroblasts overexpressed the respective sulfatase polypeptides. While in single-sulfatase-deficiency fibroblasts a concomitant increase of sulfatase activities was observed, MSD fibroblasts expressed sulfatase polypeptides with a severely diminished catalytic activity. From these results we conclude that the mutation in MSD severely decreases the capacity of a co- or post-translational process that renders sulfatases enzymatically active or prevents their premature inactivation.

Restoration of arylsulphatase A activity in human-metachromatic-leucodystrophy fibroblasts via retroviral-vector-mediated gene transfer

Metachromatic leukodystrophy is a lysosomal storage disease caused by the deficiency of arylsulphatase A (ASA). A human ASA cDNA was subcloned into the retroviral vector pXT1. Replication-defective retrovirus was generated by transfection of the vector into the amphotropic packaging cell line PA317. Human fibroblasts from a patient suffering from metachromatic leucodystrophy was infected with the recombinant retrovirus. Infected fibroblasts expressed ten times more ASA compared with control fibroblasts from a normal individual. The ASA encoded by the integrated provirus was shown to be correctly transported into the lysosomes and to normalize the impaired degradation of cerebroside sulphate.