Correction of murine mucopolysaccharidosis VII by a human beta-glucuronidase transgene

THAP1 modulates oligodendrocyte maturation by regulating ECM degradation in lysosomes

Mechanisms controlling myelination during central nervous system (CNS) maturation play a pivotal role in the development and refinement of CNS circuits. The transcription factor THAP1 is essential for timing the inception of myelination during CNS maturation through a cell-autonomous role in the oligodendrocyte lineage. Here, we demonstrate that THAP1 modulates the extracellular matrix (ECM) composition by regulating glycosaminoglycan (GAG) catabolism within oligodendrocyte progenitor cells (OPCs). Thap1 ^-/- OPCs accumulate and secrete excess GAGs, inhibiting their maturation through an autoinhibitory mechanism. THAP1 controls GAG metabolism by binding to and regulating the GusB gene encoding β-glucuronidase, a GAG-catabolic lysosomal enzyme. Applying GAG-degrading enzymes or overexpressing β-glucuronidase rescues Thap1 ^-/- OL maturation deficits in vitro and in vivo. Our studies establish lysosomal GAG catabolism within OPCs as a critical mechanism regulating oligodendrocyte development.

The beta-glucuronidase intracisternal A particle insertion model results in similar overall MPSVII phenotype as the single base deletion model when on the same C57BL/6J mouse background

Two unique gene mutations in the enzyme beta-glucuronidase (GUSB) that result in the lysosomal storage disease Mucopolysaccharidosis (MPS) type VII had previously been reported to have differing disease phenotype severities when compared on differing mouse strains. The MPSVII mouse has proven to be a highly efficacious model to study mucopolysaccharidoses and for evaluating potential gene or stem cell therapies for lysosomal storage diseases. We examined the single base pair deletion (MPSVII) and the intracisternal A particle element insertion (MPSVII2J) in GUSB compared with control animals by skeletal measures, electroretinography, auditory-evoked brainstem response and life span on a C57BL/6J background strain. In all measures, both mutations result in either a trend toward or significant changes from the background strain control. In all measures, there is no significant phenotypic difference between the two mutations. The 2J variant is a more easily genotyped and equally affected phenotype, which holds promise for further studies of chimerism and stem cell therapy approaches.

Engineering mesenchymal stem cells for regenerative medicine and drug delivery

Researchers have applied mesenchymal stem cells (MSC) to a variety of therapeutic scenarios by harnessing their multipotent, regenerative, and immunosuppressive properties with tropisms toward inflamed, hypoxic, and cancerous sites. Although MSC-based therapies have been shown to be safe and effective to a certain degree, the efficacy remains low in most cases when MSC are applied alone. To enhance their therapeutic efficacy, researchers have equipped MSC with targeted delivery functions using genetic engineering, therapeutic agent incorporation, and cell surface modification. MSC can be genetically modified virally or non-virally to overexpress therapeutic proteins that complement their innate properties. MSC can also be primed with non-peptidic drugs or magnetic nanoparticles for enhanced efficacy and externally regulated targeting, respectively. Furthermore, MSC can be functionalized with targeting moieties to augment their homing toward therapeutic sites using enzymatic modification, chemical conjugation, or non-covalent interactions. These engineering techniques are still works in progress, requiring optimization to improve the therapeutic efficacy and targeting effectiveness while minimizing any loss of MSC function. In this review, we will highlight the advanced techniques of engineering MSC, describe their promise and the challenges of translation into clinical settings, and suggest future perspectives on realizing their full potential for MSC-based therapy.

Effect of Culture Conditions on Reference Genes Expression in Placenta-derived Stem Cells

BACKGROUND AND OBJECTIVES

Normalization with valid reference genes is crucial for gene expression analysis with quantitative real-time reverse transcription PCR (qRT-PCR). This is especially relevant when stem cells are investigated with respect to gene expression in the differentiation process. Due to the plasticity of the stem cells, the variation of reference gene expression may cause misinterpretation of the target gene expression.

METHODS AND RESULTS

In this study, we investigated the gene expression stability of commonly used 32 reference genes in placenta-derived stem cells, which were cultured with or without exogenous epidermal growth factor. The influence of unstable reference gene expression on the data interpretation was also demonstrated with stem cell marker gene expressions on the placenta-derived stem cells. Statistical validation analysis of reference genes revealed the stability of each gene. Commonly used β-actin, 18S and GAPDH expression were relatively instable. The cell cycle relating house keeping genes, PPIA, POLR2A, and POP4 were most stable in the compared culture conditions. Reference genes were divided into the following three groups and statistically analyzed; 1) unstable genes, 2) stable genes, and 3) commonly used genes. The results indicate that the interpretation of the experiments was significantly different depending on the stability of the reference genes.

CONCLUSIONS

In the stem cell experiments, even minor differences in the culture conditions influenced the expression of reference genes. Thus, the identification of valid reference genes must be determined at each experimental setting. We recommend performing a stepwise screening process to determine valid reference genes.

Comparison of ventricular and intravenous lentiviral-mediated gene therapy for murine MPS VII

Mucopolysaccharidosis type VII (MPS VII) is caused by the deficiency of the lysosomal hydrolase β-glucuronidase. Symptoms include intellectual impairment, growth retardation, visual and hearing deficits and organ malfunction. The MPS VII mouse displays most of the symptoms variously associated with the MPS disorders, and has been widely used as a developmental paradigm for gene therapy. In this study, a lentiviral vector expressing murine β-glucuronidase was delivered to 6-week-old MPS VII affected mice, either by intravenous injection, or by ventricular infusion. Therapeutic outcomes were assessed 7 months after gene transfer. Intravenous vector delivery restored liver β-glucuronidase to normal levels. Consequently, most somatic pathology was corrected, and brain pathology was reduced. In mice that received ventricular vector most brain regions appeared biochemically and histologically normal. These animals showed significantly improved behavioural performance within the open-field test. An additional positive outcome of ventricular vector delivery was the significant reduction of lysosomal storage within the eye. The blood-brain barrier is not completely impervious to lysosomal enzymes, therefore, therapeutic enzyme can be distributed widely throughout the brain via the extensive cerebral vasculature. However, improvements in somatic gene delivery and expression are required for this to be completely successful. Ventricular vector delivery cleared lysosomal storage within the CNS making this a reasonable, albeit more challenging, therapeutic option for the MPS. The best therapeutic outcomes, with possible synergistic effects within the CNS, might be expected to occur when vector delivery to the brain is used in combination with somatic gene transfer.

Mesenchymal stem cells for the sustained in vivo delivery of bioactive factors

Mesenchymal stem cells (MSC) are a promising tool for cell therapy, either through direct contribution to the repair of bone, tendon and cartilage or as an adjunct therapy through protein production and immune mediation. They are an attractive vehicle for cellular therapies due to a variety of cell intrinsic and environmentally responsive properties. Following transplantation, MSC are capable of systemic migration, are not prone to tumor formation, and appear to tolerize the immune response across donor mismatch. These attributes combine to allow MSC to reside in many different tissue types without disrupting the local microenvironment and, in some cases, responding to the local environment with appropriate protein secretion. We describe work done by our group and others in using human MSC for the sustained in vivo production of supraphysiological levels of cytokines for the support of cotransplanted hematopoietic stem cells and enzymes that are deficient in animal models of lysosomal storage disorders such as MPSVII. In addition, the use of MSC engineered to secrete protein products has been reviewed in several fields of tissue injury repair, including but not limited to revascularization after myocardial infarction, regeneration of intervertebral disc defects and spine therapy, repair of stroke, therapy for epilepsy, skeletal tissue repair, chondrogenesis/knee and joint repair, and neurodegenerative diseases. Genetically engineered MSC have thus proven safe and efficacious in numerous animal models of disease modification and tissue repair and are poised to be tested in human clinical trials. The potential for these interesting cells to secrete endogenous or transgene products in a sustained and long-term manner is highly promising and is discussed in the current review.

Biopharmaceutical drug targeting to the brain

Biopharmaceuticals are large molecule drugs that do not cross the blood-brain barrier (BBB). The limiting factor in the drug development of biopharmaceuticals as new drugs for the human brain is the engineering of effective brain drug targeting technology platforms. Recombinant proteins, enzymes, and monoclonal antibodies can be re-engineered for transport across the human BBB with the molecular Trojan horse technology. The most active BBB molecular Trojan horse is a monoclonal antibody to the human insulin receptor. The genetic engineering of IgG fusion proteins has been demonstrated for neurotrophic factors, decoy receptors, therapeutic enzymes, single chain Fv antibodies, and avidin. The IgG fusion proteins are not toxic on repeated administration in high doses to primates and do not interfere with glycemic control in plasma or brain. IgG fusion proteins contain amino acid sequences that induce immune tolerance, and show low immunogenicity in primates. The IgG fusion proteins are new bifunctional biopharmaceuticals that are both targeted to brain via transport on endogenous BBB receptors, and exert pharmacological effects in brain at the cognate receptor, ligand, or enzyme substrate.

Long-term AAV vector gene and protein expression in mouse brain from a small pan-cellular promoter is similar to neural cell promoters

The neurogenetic, lysosomal enzyme (LSE) deficiency diseases are characterized by storage lesions throughout the brain; therefore, gene transfer needs to provide widespread distribution of the normal enzyme. Adeno-associated virus (AAV) vectors can be effective in the brain despite limited transduction because LSEs are exported to neighboring cells (cross-correction) to reverse the metabolic deficit. The extent of correction is determined by a combination of the total amount of LSE produced by a vector and the spatial distribution of the vector within the brain. Neuron-specific promoters have been used in the brain because AAV predominantly transduces neurons. However, these promoters are large, using up a substantial amount of the limited cloning capacity of AAV vector genomes. A small promoter that is active in all cells, from the LSE beta-glucuronidase (GUSB), has been used for long-term expression in AAV vectors in the brain but the natural promoter is expressed at very low levels. The amount of LSE exported from a cell is proportional to the level of transcription, thus more active promoters would export more LSE for cross-correction, but direct comparisons have not been reported. In this study, we show that in long-term experiments (>6 months) the GUSB minimal promoter (hGBp) expresses the hGUSB enzyme in brain at similar levels as the neuron-specific enolase promoter or the promoter from the latency-associated transcript of herpes simplex virus. The hGBp minimal promoter thus may be useful for long-term expression in the central nervous system of large cDNAs, bicitronic transcription units, self-complimentary or other designs with size constraints in the AAV vector system.

Magnetic resonance imaging detects differences in migration between primary and immortalized neural stem cells

RATIONALE AND OBJECTIVES

The study was performed to evaluate the effect of magnetic resonance imaging (MRI) contrast agent (super paramagnetic iron oxide [SPIO]) on differentiation and migration of primary murine neural stem cells (NSCs) in comparison to a neural stem cell line (C17.2). Because detection of labeled cells depends on the concentration of SPIO particles per imaging voxel, the study was performed at various concentrations of SPIO particles to determine the concentration that could be used for in vivo detection of small clusters of grafted cells.

MATERIALS AND METHODS

Murine primary NSCs or C17.2 cells were labeled with different concentrations of SPIO particles (0, 25, 100, and 250 microg Fe/mL) and in vitro assays were performed to assess cell differentiation. In vivo MRI was performed 7 weeks after neonatal transplantation of labeled cells to evaluate the difference in migration capability of the two cell populations.

RESULTS

Both the primary NSCs and the C17.2 cells differentiated to similar number of neurons (Map2ab-positive cells). Similar patterns of engraftment of C17.2 cells were seen in transplanted mice regardless of the SPIO concentration used. In vivo MRI detection of grafted primary and C17.2 cells was only possible when cells were incubated with 100 microg/mL or higher concentration of SPIO. Extensive migration of C17.2 cells throughout the brain was observed, whereas the migration of the primary NSCs was more restricted.

CONCLUSIONS

Engraftment of primary NSCs can be detected noninvasively by in vivo MRI, and the presence of SPIO particles do not affect the viability, differentiation, or engraftment pattern of the donor cells.

Lysosomal Enzyme Replacement of the Brain with Intravenous Non-Viral Gene Transfer

PURPOSE

The delivery of non-viral plasmid DNA to brain across the blood-brain barrier (BBB) with intravenous administration of non-viral plasmid DNA encoding a lysosomal enzyme, beta-glucuronidase (GUSB), was examined in GUSB null mice, a model of type VII mucopolysaccharidosis.

METHODS

The plasmid, designated pCMV-GUSB, is encapsulated in Trojan horse liposomes, which are targeted across the BBB, and the brain cell membrane, with a monoclonal antibody to the mouse transferrin receptor.

RESULTS

The GUSB enzyme activity was increased >50-fold in cell culture of fibroblasts obtained from GUSB null mice, following application of the antibody-targeted liposomes carrying the pCMV-GUSB, and enzyme activity remained high for >2 weeks. Adult GUSB null mice were treated with a single intravenous administration of 0.2 ml of Trojan horse liposomes carrying the pCMV-GUSB at a dose of 10 mug/mouse of plasmid DNA. The GUSB enzyme activity was increased greater than tenfold in brain, liver, spleen, lung, and kidney, but not in heart.

CONCLUSIONS

Intravenous Trojan horse liposome administration increased brain GUSB enzyme activity to the therapeutic range of brain GUSB enzyme activity. These studies show it is possible to deliver non-viral plasmid DNA encoding lysosomal enzymes to the brain following intravenous administration of receptor-specific Trojan horse liposomes.

Α genetic fusion construct between the tetanus toxin C fragment and the lysosomal acid hydrolase β-glucuronidase expresses a bifunctional protein with enhanced secretion and neuronal uptake

The neurotropic atoxic fragment of tetanus toxin has been used as a carrier for transporting macromolecules into neurons but all studies to date have tested cytosolic proteins. In this study we investigated the effect of a genetic addition of the tetanus toxin C fragment sequence to a lysosomal enzyme which contains a signal sequence for insertion into the membrane-bound compartment and must be extensively modified in the endoplasmic reticulum (ER) and Golgi to attain functionality. In-frame fusion constructs between the atoxic C fragment and beta-glucuronidase were compared with the wild-type enzyme for: (i) enzymatic activity; (ii) heat stability; (iii) pH dependence; (iv) specific activity; (v) apparent molecular mass and (vi) receptor-mediated uptake by fibroblasts and neurons. The modified proteins had biochemical properties similar to wild-type enzyme but exhibited different enzyme secretion profiles. Addition of the secreted fusion enzyme to cultures of primary neurons showed significantly increased neuronal uptake of the modified protein compared with the wild-type, demonstrating the bifunctionality of the chimeric molecule.

Exocytosis of storage material in a lysosomal disorder

Lysosomal exocytosis is a ubiquitously occurring process, which has a physiological role in repair of wounds of the plasma membrane. Lysosomal storage disorders are a group of more than 40 different diseases, which are characterized by intralysosomal storage of various substances. Metachromatic leukodystrophy is a lysosomal disease caused by the deficiency of arylsulfatase A, which results in the storage of the sphingolipid 3-O-sulfogalactosylceramide (sulfatide) in, e.g., oligodendrocytes and distal tubule kidney cells. Here we show that sulfatide storing cultured primary kidney cells of arylsulfatase A deficient mice can undergo calcium induced lysosomal exocytosis and that this results in the delivery of storage material to the culture medium. In metachromatic leukodystrophy extracellular sulfatide has been found in urine and cerebrospinal fluid. Lysosomal exocytosis may explain the presence of sulfatide in these body fluids.

AAV-mediated intravitreal gene therapy reduces lysosomal storage in the retinal pigmented epithelium and improves retinal function in adult MPS VII mice

The beta-glucuronidase-deficient mucopolysaccharidosis type VII (MPS VII) mouse accumulates partially degraded glycosaminoglycans in many cell types, including retinal pigmented epithelial (RPE) cells in the eye. This lysosomal storage in RPE cells leads to progressive retinal degeneration and reduced function as measured by flash electroretinography (ERG). The impact of AAV-mediated intraocular gene therapy on pathology and retinal function was examined in normal and MPS VII mice treated at 4 weeks of age, when lysosomal storage is evident but functional impairment is minimal in affected animals. At 16 weeks, an age at which untreated MPS VII mice have advanced histologic lesions and significantly reduced ERG amplitudes, treated eyes had nearly normal levels of beta-glucuronidase activity, preservation of cells in the outer nuclear layer of the retina, and decreased lysosomal storage within the RPE. The AAV-treated MPS VII mice also had significantly increased dark-adapted ERG amplitudes compared to untreated MPS VII mice. Although retinal function was improved, the efficacy of the treatment depended heavily on parameters related to the injection procedure, such as the injection volume, injection site, and vector dose. These data suggest that intraocular AAV-mediated therapy may be efficacious for treating the retinal disease associated with certain lysosomal storage diseases.

Viable mouse models of acid beta-glucosidase deficiency: the defect in Gaucher disease

Gaucher disease is an autosomal recessively inherited disease caused by mutations at the acid beta-glucosidase (GCase) locus (GBA). To develop viable models of Gaucher disease, point mutations (pmuts), encoding N370S, V394L, D409H, or D409V were introduced into the mouse GCase (gba) locus. DNA sequencing verified each unique pmut. Mutant GCase mRNAs were near wild-type (WT) levels. GCase activities were reduced to 2 to 25% of WT in liver, lung, spleen, and cultured fibroblasts from pmut/pmut or pmut/null mice. The corresponding brain GCase activities were approximately 25% of WT. N370S homozygosity was lethal in the neonatal period. For the other pmut mice, a few storage cells appeared in the spleen at > or =7 months (D409H or D409V homozygotes) or > or =1 year (V394L homozygotes). V394L/null, D409H/null, or D409V/null mice showed scattered storage cells in spleen at approximately 3 to 4 months. Occasional storage cells (sinusoidal cells) were present in liver. In D409V/null mice, large numbers of Mac-3-positive storage cells (ie, macrophages) accumulated in the lung. Glycosphingolipid analyses showed varying rates of progressive glucosylceramide accumulation in visceral organs of pmut/pmut or pmut/null mice, but not in brain. These GCase-deficient mice provide tools for gaining insight into the pathophysiology of Gaucher disease and developing improved therapies.

Transgene produces massive overexpression of human beta -glucuronidase in mice, lysosomal storage of enzyme, and strain-dependent tumors

beta-Glucuronidase (GUSB) is a lysosomal enzyme important in the normal step-wise degradation of glycosaminoglycans. Deficiency of GUSB causes the lysosomal storage disease mucopolysaccharidosis VII (MPS VII, Sly disease). Affected patients have widespread progressive accumulation of beta-glucuronide-containing glycosaminoglycans in lysosomes. Enzyme replacement, bone marrow transplantation, and gene therapy can correct lysosomal storage in the MPS VII mouse model. Gene therapy in MPS VII patients and animals may result in massive overexpression of GUSB in individual tissues, and the toxicity of such overexpression is incompletely investigated. To gain insight into the effect of massive overexpression of GUSB, we established 19 transgenic mouse lines, two of which expressed very high levels of human GUSB in many tissues. The founder overexpressing mice had from >100- to several thousand-fold increases in tissue and serum GUSB. The enzyme expression in most tissues decreased in subsequent generations in one line, and expression in liver and marrow fell in subsequent generations of the other. Both lines had morphologically similar widespread lysosomal storage of GUSB and secondary elevations of other lysosomal enzymes, a finding characteristic of lysosomal storage disease. One line developed tumors, and one did not. These transgenic models show that massive overexpression of a lysosomal enzyme can be associated with dramatic morphological alterations, which, at least in one of the two lines, had little clinical consequence. For the other transgenic line, the high frequency of tumor development in F(2) FVB progeny suggests that the vector used to generate the transgenic lines has an integration site-dependent potential to be oncogenic, at least in this strain background.

Biodistribution and efficacy of donor T lymphocytes in a murine model of lysosomal storage disease

Lymphocyte-directed gene transfer has been proposed as potential therapy to treat certain congenital immunological deficiencies as well as other genetic diseases such as lysosomal storage diseases (LSDs). To understand better the extent to which adoptively transferred peripheral T lymphocytes (PTLs) are able to ameliorate LSDs we utilized the beta-glucuronidase-deficient mouse as a model system. PTLs (1 x 10(7)) isolated from the spleen of syngeneic mice overexpressing ( approximately 8-fold) human beta-glucuronidase (GUSB) were injected intravenously into young adult beta-glucuronidase-deficient mice without myeloablative conditioning. Using biochemical and histochemical assays, we were able to track the donor lymphocytes in vivo. Donor lymphocytes were detected in relatively high numbers in liver, spleen, small intestine, mesenteric lymph node, and thymus for at least 5 months, the last time point of analysis. Although liver and spleen had the highest total GUSB activity, histopathologic analysis demonstrated minimal to no correction of lysosomal distention at all time points studied. By contrast, we have shown in earlier studies that administration of similar numbers of macrophages reduced lysosomal storage in several organs, including liver and spleen. To understand this difference in efficacy, we compared the relative level of GUSB released into the medium by nonactivated and activated PTLs as well as by macrophages. Macrophages released >50-fold excess enzyme compared to either activated or nonactivated PTLs. These data suggest that a LSD can be more effectively treated by directing a gene therapy approach to a hematopoietic lineage other than T lymphocytes.

Distribution of a lysosomal enzyme in the adult brain by axonal transport and by cells of the rostral migratory stream

A portion of the lysosomal enzymes produced by cells is secreted, diffuses through extracellular spaces, and can be taken up by distal cells via mannose-6-phosphate receptor-mediated endocytosis. This provides the basis for treating lysosomal storage diseases, many of which affect the CNS. Normal enzyme secreted from a cluster of genetically corrected cells has been shown to reverse storage lesions in a zone of surrounding brain tissue in mouse disease models. However, low levels of enzyme activity and reduction of storage lesions also have been observed at sites in the brain that may not be explained by a contiguous gradient of secreted enzyme diffusing away from the genetically corrected cells. No direct evidence for alternative mechanisms of enzyme transport has been shown, and little is understood about the intracellular movement of lysosomal enzymes in neurons. We investigated whether axonal transport could occur, by expressing an eukaryotic lysosomal enzyme that can be visualized in tissue sections (beta-glucuronidase) in brain structures that have defined axonal connections to other structures. This resulted in the transfer of enzyme to, and a reversal of storage lesions in, neurons that project to the gene expression site, but not in nearby structures that would have been corrected if the effect had been mediated by diffusion. In addition, transduction of cells in the subventricular zone resulted in the uptake of beta-glucuronidase by cells entering the rostral migratory stream. Gene transfer to specific neuronal circuits or cells in migratory pathways may facilitate delivery to the global brain lesions found in these disorders.

The role of sphingolipids in neuronal development: lessons from models of sphingolipid storage diseases

The study of sphingolipids has undergone a renaissance over the past decade due to the realization that these lipids are involved in a variety a biological processes, such as differentiation, apoptosis, cell growth, and cell migration. In the nervous system, sphingolipids, particularly gangliosides, have attracted particular attention as they occur at high levels and their levels change in a developmentally regulated program. Despite the fact that a large body of data has accumulated on the expression and metabolism of individual gangliosides within specific brain regions, the role of individual gangliosides in neuronal development is still poorly understood, and their specific functions are only now beginning to be elucidated. In the present article, we discuss various aspects of our current knowledge concerning the involvement of sphingolipids and gangliosides in neuronal development, and then discuss some recent findings that shed light on the role of sphingolipids and gangliosides obtained with animal models of sphingolipid and other lysosomal storage diseases.

Enhanced secretion and uptake of beta-glucuronidase improves adeno-associated viral-mediated gene therapy of mucopolysaccharidosis type VII mice

Previous treatment of mucopolysaccharidosis type VII mice (Sly syndrome) with AAV vectors has resulted in increased levels of beta-glucuronidase (GUS) enzyme in some tissues with reduction of glycosaminoglycan storage granules and improved health. By adding coding sequences for secretion (Igkappa) and uptake (HIV-1 TAT) signals to the GUS gene delivered by AAV, and treating mice both intrathecally and intravenously as newborns, we have increased the GUS enzyme levels in more tissues and have improved the health of the mice so much that they are able to breed. The levels of GUS in the serum were above normal in some mice, which caused reduction of storage in the spleen, a nontransduced tissue. The heart and aorta showed therapeutic levels of GUS enzyme. AAV GUS DNA was found in brain and liver, which showed no storage. Phenotypically the treated mice were more active and showed less stunted skeletal growth. The pups born to these mice were not affected by the gene therapy, as shown by mutant levels of GUS enzyme in their tissues and the absence of AAV GUS DNA. However, they were resistant to intravenous treatment with AAV GUS due to the mother's antibodies, but not to intrathecal treatment.

Widespread gene delivery and structure-specific patterns of expression in the brain after intraventricular injections of neonatal mice with an adeno-associated virus vector

Developing a system for widespread somatic gene transfer in the central nervous system (CNS) would be beneficial for understanding the global influence of exogenous genes on animal models. We injected an adeno-associated virus serotype 2 (AAV2) vector into the cerebral lateral ventricles at birth and mapped its distribution and transduction pattern from a promoter capable of expression in multiple targets. The injections resulted in structure-specific patterns of expression that were maintained for at least 1 year in most regions, with efficient targeting of some of the major principal neuron layers. The patterns of transduction were explained by circulation of the viral vector in the subarachnoid space via CSF flow, followed by transduction of underlying structures, rather than by progenitor cell infection and subsequent migration. This study demonstrates that gene transfer throughout the CNS can be achieved without germ line transmission and establishes an experimental strategy for introducing genes to somatic cells in a highly predictable manner.

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.

In utero transplantation of fetal liver cells in the mucopolysaccharidosis type VII mouse results in low-level chimerism, but overexpression of beta-glucuronidase can delay onset of clinical signs

Mice with the lysosomal storage disease mucopolysaccharidosis (MPS) VII, caused by a deficiency of beta-glucuronidase (GUSB), have signs of disease present at birth. Bone marrow transplantation (BMT) or retroviral vector-mediated gene transfer into hematopoietic stem cells can partially correct the disease in adult mice, and BMT performed at birth results in a better clinical outcome. Thus, treatment in utero may result in further improvement. However, this must be done without cyto-ablation, and the donor cells do not have a competitive repopulating advantage over host cells. Transplantation in utero of either syngeneic fetal liver hematopoietic stem cells marked with a retroviral vector, or allogeneic donor cells that constitutively express high levels of human GUSB from a transgene, resulted in only about 0.1% engraftment in the adult. Immuno-affinity enrichment of stem and progenitor cells of 5- to 10-fold resulted in significantly higher GUSB activities at 2 months of age, but by 6 months engraftment was about 0.1%. Attempts to further increase the number of stem and progenitor cells were deleterious to the recipients. Nevertheless, GUSB expressed during the first 2 months of life in MPS VII fetuses could delay the onset of overt signs of disease. This suggests that the expression of some normal enzyme activity beginning in fetal life may offer the possibility of slowing the progression of the disease until more definitive postnatal transplantation or gene transfer to stem cells could be accomplished.

Intracranial injection of recombinant adeno-associated virus improves cognitive function in a murine model of mucopolysaccharidosis type VII

Mucopolysaccharidosis type VII (MPS VII) is a lysosomal storage disease caused by the lack of beta-glucuronidase (GUSB) activity. GUSB deficiency leads to the progressive accumulation of undegraded glycosaminoglycans (GAGs) in cells of most tissues, including the brain, and is associated with mental retardation. Reduction of lysosomal storage in the central nervous system and prevention of cognitive dysfunction may require intracranial delivery of a therapeutic agent during the newborn period that provides a continuous source of GUSB. Therefore, we injected recombinant adeno-associated virus encoding human GUSB into both the anterior cortex and the hippocampus of newborn MPS VII mice. Total GUSB activity in the brain approached normal levels by 18 weeks. Although GUSB activity was concentrated near the injection sites, lysosomal distension was reduced in most areas of the brain. In addition to histopathologic evidence of GAG reduction, the previously undescribed accumulation of GM2 and GM3 gangliosides in the brain was also prevented. Furthermore, GUSB expression and reduced lysosomal distension correlated with improvements in cognitive function as measured in the Morris Water Maze test. These findings indicate that localized overexpression of GUSB has positive effects on the pathology and cognitive function and does not have overt toxicity.

Active site mutant transgene confers tolerance to human beta-glucuronidase without affecting the phenotype of MPS VII mice

Mucopolysaccharidosis type VII (MPS VII; Sly syndrome) is an autosomal recessive lysosomal storage disorder due to an inherited deficiency of beta-glucuronidase. A naturally occurring mouse model for this disease was discovered at The Jackson Laboratory and shown to be due to homozygosity for a 1-bp deletion in exon 10 of the gus gene. The murine model MPS VII (gus(mps/mps)) has been very well characterized and used extensively to evaluate experimental strategies for lysosomal storage diseases, including bone marrow transplantation, enzyme replacement therapy, and gene therapy. To enhance the value of this model for enzyme and gene therapy, we produced a transgenic mouse expressing the human beta-glucuronidase cDNA with an amino acid substitution at the active site nucleophile (E540A) and bred it onto the MPS VII (gus(mps/mps)) background. We demonstrate here that the mutant mice bearing the active site mutant human transgene retain the clinical, morphological, biochemical, and histopathological characteristics of the original MPS VII (gus(mps/mps)) mouse. However, they are now tolerant to immune challenge with human beta-glucuronidase. This "tolerant MPS VII mouse model" should be useful for preclinical trials evaluating the effectiveness of enzyme and/or gene therapy with the human gene products likely to be administered to human patients with MPS VII.

Accumulation of abnormal amounts of glycosaminoglycans in murine mucopolysaccharidosis type VII neural progenitor cells does not alter the growth rate or efficiency of differentiation into neurons

Mucopolysaccharidosis type VII (MPS VII) results from deficiencies in the gene encoding the lysosomal enzyme beta-glucuronidase (GUSB). To study how the genetic and biochemical defects of MPS disease affect neural cell populations, neural progenitor cells (NPCs) were isolated from MPS VII mice and normal littermates. After growth in culture, approximately 90% of cells from both genotypes were nestin positive, a marker for NPCs, and lacked markers associated with lineage commitment. The mutant NPCs contained elevated levels of undegraded glycosaminoglycans (GAGs), the substrate for GUSB. Transduction with a retrovirus-vector expressing normal GUSB resulted in correction of the biochemical defects. Because of the demonstrated roles that GAGs and proteoglycans have in NPC biology and neural development, we tested whether the alterations in GAG metabolism affected MPS VII NPC properties regulated by GAG-containing molecules. MPS VII NPC cultures had growth rates in response to FGF-2 that were similar to normal cultures and the efficiency of differentiation into neurons was the same as with normal cells. Thus, even though isolated NPCs accumulate abnormally high levels of GAGs, these two key developmental properties were not altered when the cells were examined outside the milieu of the diseased brain.

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.

Animal models of lysosomal disease: an overview

The relative rarity of human lysosomal disorders, extremely heterogeneous genetic background and ethical restrictions make well-controlled studies difficult with human patients. Genetically authentic animal models complement human patients with their ready availability, homogeneous genetic background and the relatively flexible experimental designs. Spontaneous animal models of human lysosomal disorders are rare, particularly among small laboratory animals. However, the homologous recombination and embryonic stem cell technology has so far enabled us to duplicate almost all known human sphingolipidoses, two mucopolysaccharidoses and aspartylgly-cosaminuria in mice and more disorders are expected in the near future. This technology also allows generation of mouse mutants that are not known or are highly unlikely to exist in humans, such as 'double-knockouts'. Studies of lysosomal disease have come to the half-way turning point of the marathon race from clincopathological descriptions, identification of affected compounds, enzymology, to the present gene-level inquiries. The animal models will play an important role in our long journey from nucleic acids back to biology. While the utility of these mouse models is obvious, species differences in the brain development and metabolic pathways must be always remembered if the ultimate goal of the study is application to human patients. After all, the mouse is not human.

Enzyme replacement therapy for murine mucopolysaccharidosis type VII leads to improvements in behavior and auditory function

Mucopolysaccharidosis type VII (MPS VII; Sly syndrome) is one of a group of lysosomal storage diseases that share many clinical features, including mental retardation and hearing loss. Lysosomal storage in neurons of the brain and the associated behavioral abnormalities characteristic of a murine model of MPS VII have not been shown to be corrected by either bone marrow transplantation or gene therapy. However, intravenous injections of recombinant beta-glucuronidase initiated at birth reduce the pathological evidence of disease in MPS VII mice. In this study we present evidence that enzyme replacement initiated at birth improved the behavioral performance and reduced hearing loss in MPS VII mice. Enzyme-treated MPS VII mice performed similarly to normal mice and significantly better than mock- treated MPS VII mice in every phase of the Morris Water Maze test. In addition, the auditory function of treated MPS VII mice was dramatically improved, and was indistinguishable from normal mice. These data indicate that some of the learning, memory, and hearing deficits can be prevented in MPS VII mice if enzyme replacement therapy is initiated early in life. These data also provide functional correlates to the biochemical and histopathological improvements observed after enzyme replacement therapy.

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.

Decreased lysosomal storage in the adult MPS VII mouse brain in the vicinity of grafts of retroviral vector-corrected fibroblasts secreting high levels of beta-glucuronidase

A deficiency of beta-glucuronidase (GUSB) causes the multisystem progressive degenerative syndrome, mucopolysaccharidosis (MPS) type VII (Sly disease), which includes mental retardation. Animal homologues of MPS VII (ref. 3, 4) are models for testing somatic gene transfer approaches to treat the central nervous system in this and other lysosomal storage disorders. Previous attempts to correct murine MPS VII by gene therapy have successfully treated lesions in some organs but not in the brain. Other experimental modalities have forestalled some disease progression in the brain, but only if done at birth, before the onset of severe lesions, when the animals are phenotypically normal. We tested whether therapeutic amounts of GUSB could be delivered to the diseased adult brain by transplanting cells engineered to super-secrete the normal enzyme for export to surrounding neural tissues. Lysosomal distention was cleared from neurons and glial cells in the vicinity of the grafts, showing that the secreted enzyme could reach the diseased cells and reverse lesions in the severely diseased brain. The ability to correct established lesions will be important for the treatment of many lysosomal storage diseases affecting the brain, because most patients are not diagnosed until lesions are advanced enough to affect phenotype or developmental milestones in early childhood, and some forms of the diseases do not become apparent until later in life.

Morphological alterations in dental and periodontal tissues in murine mucopolysaccharidosis type VII

Mucopolysaccharidoses (MPSs) in humans are frequently associated with tooth and periodontal aberrations. Although the cause is known, namely, enzyme deficiency, the pathophysiology of these alterations is not well defined. A murine MPS VII (beta-glucuronidase deficiency) model has earlier been identified with morphological, genetic, and biochemical characteristics that closely mimic those of human MPS VII. The present investigation describes the histopathological alterations in dental and periodontal tissues from such mutant mice. Homozygous animals were identified by external phenotypical features and as being beta-glucuronidase deficient by a fluorometric assay of liver samples. In the incisor and the periodontium, abnormalities were evident in both cells and the extracellular matrices. Mesenchyme-derived cells were more aberrant than epithelial cells. Moreover, undifferentiated cells appeared unaffected, whereas actively synthesizing and resorbing cells were distended by virtually empty or granular material-containing vacuoles, the content presumably being glycosaminoglycans. The cells most affected were those in which macromolecular turnover is normally the highest, namely, odontoblasts, postsecretory ameloblasts, and periodontal ligament fibroblasts. Extracellularly, predentin displayed abnormal collagen fibrils, whereas mineralization defects occurred in both dentin and enamel. This murine model of MPS VII provides a good tool for understanding the pathophysiology of this disease in bone, periodontium, and teeth.

Phenotype correction in retinal pigment epithelium in murine mucopolysaccharidosis VII by adenovirus-mediated gene transfer

We have studied the use of adenovirus-mediated gene transfer to reverse the pathologic changes of lysosomal storage disease caused by beta-glucuronidase deficiency in the eyes of mice with mucopolysaccharidosis VII. A recombinant adenovirus carrying the human beta-glucuronidase cDNA coding region under the control of a non-tissue-specific promoter was injected intravitreally or subretinally into the eyes of mice with mucopolysaccharidosis VII. At 1-3 weeks after injection, the treated and control eyes were examined histochemically for beta-glucuronidase expression and histologically for phenotypic correction of the lysosomal storage defect. Enzymatic expression was detected 1-3 weeks after injection. Storage vacuoles in the retinal pigment epithelium (RPE) were still present 1 week after gene transfer but were reduced to undetectable levels by 3 weeks in both intravitreally and subretinally injected eyes. There was minimal evidence of ocular pathology associated with the viral injection. These data indicate that adenovirus-mediated gene transfer to the eye may provide for adjunctive therapy for lysosomal storage diseases affecting the RPE in conjunction with enzyme replacement and/or gene therapies for correction of systemic disease manifestations. The data also support the view that recombinant adenovirus may be useful as a gene therapy vector for retinal degenerations that result from a primary genetic defect in the RPE cells.

The twitcher mouse: a model for Krabbe disease and for experimental therapies

The twitcher is a naturally-occurring mouse mutant caused by an abnormality in the gene coded for galactosylceramidase. It is therefore genetically equivalent to human globoid cell leukodystrophy (Krabbe disease). Affected mice develop clinical symptoms at the onset of the active myelination period and, if untreated, die by 35 +/- days. The pathology is very similar to that in human disease. Toxicity of galactosylsphingosine (psychosine) that accumulates abnormally in the nervous system is considered to be primarily responsible for the pathogenesis. Transplantation of bone marrow cells from normal donors is partially effective and triples the life span of affected mice to 100 +/- days with evidence of remyelination in the CNS. The mutation responsible for the twitcher mutant has recently been identified. It is expected that this model will be useful for basic studies on treatment of this group of genetic disorders affecting the brain through transgenic and/or gene therapy approaches.

Neural progenitor cell engraftment corrects lysosomal storage throughout the MPS VII mouse brain

Many metabolic diseases affecting the central nervous system are refractory to treatment because the blood-brain barrier restricts entry of therapeutic molecules. It may be possible to deliver therapeutic gene products directly to the brain by transplantation of neural progenitor cells, which can integrate into the murine central nervous system in a cytoarchitecturally appropriate manner. We tested this approach in mucopolysaccharidosis VII (Sly disease), a lysosomal storage disorder of humans, dogs and mice caused by an inherited deficiency of beta-glucuronidase. Lysosomal accumulation of glycosaminoglycans occurs in the brain and other tissues, causing a fatal progressive degenerative disorder, including mental retardation. Treatments are designed to provide a source of normal enzyme for uptake by diseased cells. We report here that by transplanting beta-glucuronidase-expressing neural progenitors into the cerebral ventricles of newborn mice, donor cells engrafted throughout the neuraxis. At maturity, donor-derived cells were present as normal constituents of diverse brain regions. beta-Glucuronidase activity was expressed along the entire neuraxis, resulting in widespread correction of lysosomal storage in neurons and glia in affected mice.

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.

Germ-line gene modification and disease prevention: some medical and ethical perspectives

There has been considerable debate about the ethics of human germ-line gene modification. As a result of recent advances in the micromanipulation of embryos and the laboratory development of transgenic mice, a lively discussion has begun concerning both the technical feasibility and the ethical acceptability of human germ-line modification for the prevention of serious disease. This article summarizes some of the recent research on germ-line gene modification in animal models. Certain monogenic deficiency diseases that ultimately might be candidates for correction by germ-line intervention are identified. Several of the most frequently considered ethical issues relative to human germ-line gene modification are considered in the context of professional ethics, parental responsibility, and public policy. Finally, it is suggested that there is merit in continuing the discussion about human germ-line intervention, so that this technique can be carefully compared with alternative strategies for preventing genetic disease.

A single-base-pair deletion in the beta-glucuronidase gene accounts for the phenotype of murine mucopolysaccharidosis type VII

Murine mucopolysaccharidosis type VII is a heritable disease caused by a spontaneous mutation, gus(mps), closely linked to the beta-glucuronidase structural gene on chromosome 5. Mice homozygous for the mutation have a > 200-fold decrease in beta-glucuronidase mRNA levels and virtually no enzyme activity detectable by a sensitive fluorometric assay. Approximately 20 kb of genomic DNA containing the beta-glucuronidase gene Gus and > 2 kb of 5' and 3' flanking sequences were cloned from both a gus(mps)/gus(mps) mouse and a +/+ mouse of the progenitor strain. Restriction enzyme digests containing DNA fragments 20-400 bp in length were generated from each of the two Gus alleles and then compared by using nondenaturing polyacrylamide DNA-sequencing gels. This method rapidly identified a large number of restriction sites and was sensitive enough to detect a restriction fragment length variation resulting from a 1-bp deletion in the gus(mps) allele. DNA-sequence analysis of the mutant genomic fragment showed that the 1-bp deletion created a frameshift mutation within exon 10. Insertion of the deleted nucleotide by oligonucleotide site-directed mutagenesis restored function to the corrected mutant gene when transfected into gus(mps)/gus(mps) fibroblasts. We concluded that the frameshift mutation, which introduces a premature stop codon at codon 497 in exon 10, accounts for the molecular, biochemical, and pathological abnormalities associated with the gus(mps) phenotype.

Suramin-induced mucopolysaccharidosis in rat incisor

Two weeks after a single injection of suramin, the secretory and post-secretory ameloblasts of the rat incisor were filled with large lysosome-like vacuoles. At the light-microscope level, these vacuoles were positively stained with Alcian blue when MgCl2 was used at a critical electrolyte concentration varying between 0.1 and 0.3 M, whereas no staining appeared when MgCl2 varied between 0.7 and 0.9 M. Hyaluronidase digestion markedly reduced but did not totally abolish the staining, indicating that glycosaminoglycans were accumulated inside these vacuoles. Examination of these cells with the electron microscope revealed a polymorphic population of large vesicles, filled to various degrees with cetylpyridinium chloride (CPC)-positive and malachite green aldehyde (MGA)-positive material. The same pattern was observed in secretory odontoblasts but to a lesser extent. In the extracellular matrix, suramin-induced alterations appeared as large defects occurring during enamel formation. In predentin and dentin, the number and/or size of electron-dense aggregates resulting from CPC and MGA fixation, were enhanced in the suramin-injected rats. These aggregates were largely reduced or suppressed respectively by hyaluronidase digestion and chloroform/methanol treatment of the sections. The accumulation of glycosaminoglycans and phospholipids reported here inside ameloblasts and odontoblasts and in predentin and dentin supports the occurrence of suramin-induced mucopolysaccharidosis and lipidosis in this experimental animal model.

Exploring pathogenetic mechanisms using transgenic animals

Molecular technologies for the permanent germ-line transformation of animals are now well established and routine. These new strains of animals, called transgenic, offer an unprecedented opportunity to gain a basic understanding of human genetic disorders. In this brief review we discuss the role of transgenic animals in the creation of new models of human disease and their experimental use in biomedical research. Models are now available for the study of the genetic processes involved in the pathogenesis of neoplasia, diabetes, atherosclerosis, and developmental abnormalities. Many others are available and new ones are being produced at a great rate. Principles of gene replacement therapy are amenable to analysis with transgenic animals and the information gained will be important for the development of rational therapy.

Treatment of inherited neurometabolic diseases: the future

The past 10 years' experience with bone marrow transplantation from normal, immunologically compatible donors indicates its possible use in various neurometabolic diseases, particularly in a patient who has not suffered irreparable brain damage. This experience may be a prelude to treatment by somatic gene therapy. This can be applied as an autologous bone marrow transplant, grafting the patient's own stem cells inserted with the normal gene. Although somatic gene therapy will be relatively easy for tissues with dividing cells, its application to target tissues with little or no cell division may pose difficulties. Meanwhile, techniques for the preservation, culture, and grafting of fetal neurons in humans have been developed and have been used in the treatment of Parkinson's disease. These procedures could readily be transferred to the treatment of other neurodegenerative diseases that cause significant morbidity, but ethical, legal, and religious considerations must be taken into account. All these efforts promise novel and improved management of inborn neurometabolic errors.

Germ-line gene therapy: a new stage of debate

Ethical debate on human germ-line gene therapy is in a new stage. After an era when only individual convictions could be examined, technology is on a threshold of real possibilities. Germ-line gene therapy can conceivably be carried out in either of two practical ways: 1) insertion of a gene into a pre-embryo, which is the subject of this paper, or 2) insertion of a gene into the germ cells of an individual.

Transgenic animal research and pre-implantation embryo diagnosis have implications for human embryonic germ-line experiments to correct single gene disorders. When would such experiments be feasible and ethically acceptable? If further animal research supports it, we argue for a moral obligation to learn if human germ-line experiments are feasible and safe to attempt. The obligation is grounded in several social-ethical principles that lead society and researchers to set gods for studies that promisc to relieve and to prevent human suffering and premature death. These principles also shape the practices and restrictions of biomedical research.