Lysosomal sulfatide storage in the brain of arylsulfatase A-deficient mice: cellular alterations and topographic distribution

Dose-response evaluation of intravenous gene therapy in a symptomatic mouse model of metachromatic leukodystrophy

Metachromatic leukodystrophy (MLD) is a rare, autosomal recessive neurodegenerative disease caused by deficient activity of the lysosomal enzyme arylsulfatase A (ARSA), resulting in sulfatide accumulation and subsequent demyelination and neuronal damage within the central and peripheral nervous systems. Three clinical forms of MLD have been described, based on age at symptom onset. The most frequent and severe forms have an early onset, with the disease progressing rapidly toward severe motor and cognitive regression and ultimately premature death. There are currently no approved therapies for most of these early-onset patients once symptoms are present. Thus, it is crucial to develop new approaches to treat symptomatic patients. Here, we proposed a gene therapy approach based on the intravenous delivery of AAVPHP.eB encoding ARSA. MLD mice were treated at 6 months for a dose-response study and at 9 months to assess late-treatment efficacy. Therapeutic efficacy was evaluated 3 or 6 months after injection. We demonstrated a broad transduction in the central nervous system, a complete correction of sulfatide storage, and a significant improvement in neuroinflammation at low dose and late treatment. Taken together, this work establishes a strong rationale for proposing a phase I/II clinical trial in MLD patients.

Deciphering Oligodendrocyte Lineages in the Human Fetal Central Nervous System Using Single-Cell RNA Sequencing

Oligodendrocytes form myelin sheaths and wrap axons of neurons to facilitate various crucial neurological functions. Oligodendrocyte progenitor cells (OPCs) persist in the embryonic, postnatal, and adult central nervous system (CNS). OPCs and mature oligodendrocytes are involved in a variety of biological processes such as memory, learning, and diseases. How oligodendrocytes are specified in different regions in the CNS, in particular in humans, remains obscure. We here explored oligodendrocyte development in three CNS regions, subpallium, brainstem, and spinal cord, in human fetuses from gestational week 8 (GW8) to GW12 using single-cell RNA sequencing. We detected multiple lineages of OPCs and illustrated distinct developmental trajectories of oligodendrocyte differentiation in three CNS regions. We also identified major genes, particularly transcription factors, which maintain status of OPC proliferation and promote generation of mature oligodendrocytes. Moreover, we discovered new marker genes that might be crucial for oligodendrocyte specification in humans, and detected common and distinct genes expressed in oligodendrocyte lineages in three CNS regions. Our study has demonstrated molecular heterogeneity of oligodendrocyte lineages in different CNS regions and provided references for further investigation of roles of important genes in oligodendrocyte development in humans.

A bidirectional link between sulfatide and Alzheimer's disease

Reduced sulfatide level is found in Alzheimer's disease (AD) patients. Here, we demonstrate that amyloid precursor protein (APP) processing regulates sulfatide synthesis and vice versa. Different cell culture models and transgenic mice models devoid of APP processing or in particular the APP intracellular domain (AICD) reveal that AICD decreases Gal3st1/CST expression and subsequently sulfatide synthesis. In return, sulfatide supplementation decreases Aβ generation by reducing β-secretase (BACE1) and γ-secretase processing of APP. Increased BACE1 lysosomal degradation leads to reduced BACE1 protein level in endosomes. Reduced γ-secretase activity is caused by a direct effect on γ-secretase activity and reduced amounts of γ-secretase components in lipid rafts. Similar changes were observed by analyzing cells and mice brain samples deficient of arylsulfatase A responsible for sulfatide degradation or knocked down in Gal3st1/CST. In line with these findings, addition of sulfatides to brain homogenates of AD patients resulted in reduced γ-secretase activity. Human brain APP level shows a significant negative correlation with GAL3ST1/CST expression underlining the in vivo relevance of sulfatide homeostasis in AD.

Single Systemic Administration of a Gene Therapy Leading to Disease Treatment in Metachromatic Leukodystrophy Arsa Knock-Out Mice

Metachromatic leukodystrophy (MLD) is a rare, inherited, demyelinating lysosomal storage disorder caused by mutations in the arylsulfatase-A gene (ARSA). In patients, levels of functional ARSA enzyme are diminished and lead to deleterious accumulation of sulfatides. Herein, we demonstrate that intravenous administration of HSC15/ARSA restored the endogenous murine biodistribution of the corresponding enzyme, and overexpression of ARSA corrected disease biomarkers and ameliorated motor deficits in Arsa KO mice of either sex. In treated Arsa KO mice, when compared with intravenously administered AAV9/ARSA, significant increases in brain ARSA activity, transcript levels, and vector genomes were observed with HSC15/ARSA Durability of transgene expression was established in neonate and adult mice out to 12 and 52 weeks, respectively. Levels and correlation between changes in biomarkers and ARSA activity required to achieve functional motor benefit was also defined. Finally, we demonstrated blood-nerve, blood-spinal and blood-brain barrier crossing as well as the presence of circulating ARSA enzyme activity in the serum of healthy nonhuman primates of either sex. Together, these findings support the use of intravenous delivery of HSC15/ARSA-mediated gene therapy for the treatment of MLD.SIGNIFICANCE STATEMENT Herein, we describe the method of gene therapy adeno-associated virus (AAV) capsid and route of administration selection leading to an efficacious gene therapy in a mouse model of metachromatic leukodystrophy. We demonstrate the therapeutic outcome of a new naturally derived clade F AAV capsid (AAVHSC15) in a disease model and the importance of triangulating multiple end points to increase the translation into higher species via ARSA enzyme activity and biodistribution profile (with a focus on the CNS) with that of a key clinically relevant biomarker.

Treatment of adult metachromatic leukodystrophy model mice using intrathecal administration of type 9 AAV vector encoding arylsulfatase A

Metachromatic leukodystrophy (MLD) is a lysosomal storage disease caused by an arylsulfatase A (ARSA) deficiency and characterized by severe neurological symptoms resulting from demyelination within the central and peripheral nervous systems. We investigated the feasibility and efficacy of intrathecal administration of a type 9 adeno-associated viral vector encoding ARSA (AAV9/ARSA) for the treatment of 6-week-old MLD model mice, which are presymptomatic, and 1-year-old mice, which exhibit neurological abnormalities. Immunohistochemical analysis following AAV9/ARSA administration showed ARSA expression within the brain, with highest activities in the cerebellum and olfactory bulbs. In mice treated at 1 year, alcian blue staining and quantitative analysis revealed significant decreases in stored sulfatide. Behaviorally, mice treated at 1 year showed no improvement in their ability to traverse narrow balance beams as compared to untreated mice. By contrast, MLD mice treated at 6 weeks showed significant decreases in stored sulfatide throughout the entire brain and improved ability to traverse narrow balance beams. These findings suggest intrathecal administration of an AAV9/ARSA vector is a promising approach to treating genetic diseases of the central nervous system, including MLD, though it may be essential to begin therapy before the onset of neurological symptoms.

Complete Correction of Brain and Spinal Cord Pathology in Metachromatic Leukodystrophy Mice

Metachromatic leukodystrophy (MLD) is a lysosomal storage disorder characterized by accumulation of sulfatides in both glial cells and neurons. MLD results from an inherited deficiency of arylsulfatase A (ARSA) and myelin degeneration in the central and peripheral nervous systems. Currently, no effective treatment is available for the most frequent late infantile (LI) form of MLD after symptom onset. The LI form results in rapid neurological degradation and early death. ARSA enzyme must be rapidly and efficiently delivered to brain and spinal cord oligodendrocytes of patients with LI MLD in order to potentially stop the progression of the disease. We previously showed that brain gene therapy with adeno-associated virus serotype rh10 (AAVrh10) driving the expression of human ARSA cDNA alleviated most long-term disease manifestations in MLD mice but was not sufficient in MLD patient to improve disease progression. Herein, we evaluated the short-term effects of intravenous AAVPHP.eB delivery driving the expression of human ARSA cDNA under the control of the cytomegalovirus/b-actin hybrid (CAG) promoter in 6-month-old MLD mice that already show marked sulfatide accumulation and brain pathology. Within 3 months, a single intravenous injection of AAVPHP.eB-hARSA-HA resulted in correction of brain and spinal cord sulfatide storage, and improvement of astrogliosis and microgliosis in brain and spinal cord of treated animals. These results strongly support to consider the use of AAVPHP.eB-hARSA vector for intravenous gene therapy in symptomatic rapidly progressing forms of MLD.

Safety of Direct Intraparenchymal AAVrh.10-Mediated Central Nervous System Gene Therapy for Metachromatic Leukodystrophy

Metachromatic leukodystrophy, a fatal pediatric neurodegenerative lysosomal storage disease caused by mutations in the arylsulfatase A (ARSA) gene, is characterized by intracellular accumulation of sulfatides in the lysosomes of cells of the central nervous system (CNS). In previous studies, we have demonstrated efficacy of AAVrh.10hARSA, an adeno-associated virus (AAV) serotype rh.10 vector coding for the human ARSA gene to the CNS of a mouse model of the disease, and that catheter-based intraparenchymal administration of AAVrh.10hARSA to the CNS of nonhuman primates (NHPs) white matter results in widespread expression of ARSA. As a formal dose-escalating safety/toxicology study, we assessed the safety of intraparenchymal delivery of AAVrh.10hARSA vector to 12 sites in the white matter of the CNS of NHPs at 2.85 × 10¹⁰ (total low dose, 2.4 × 10⁹ genome copies [gc]/site) and 1.5 × 10¹² (total high dose, 1.3 × 10¹¹ gc/site) gc, compared to AAVrh.10Null (1.5 × 10¹² gc total, 1.3 × 10¹¹ gc/site) as a vector control, and phosphate buffered saline for a sham surgical control. No significant adverse effects were observed in animals treated with low dose AAVrh.10hARSA. However, animals treated with the high dose AAVrh.10ARSA and the high dose Null vector had highly localized CNS abnormalities on magnetic resonance imaging scans at the sites of catheter infusions, and histopathology demonstrated that these sites were associated with infiltrates of T cells, B cells, microglial cells, and/or macrophages. Although these findings had no clinical consequences, these safety data contribute to understanding the dose limits for CNS white matter direct intraparenchymal administration of AAVrh.10 vectors for treatment of CNS disorders.

Brain cell type-specific endocytosis of arylsulfatase A identifies limitations of enzyme-based therapies for metachromatic leukodystrophy

Enzyme replacement therapies, allogeneic bone marrow transplantation and gene therapies are treatment options for lysosomal storage diseases caused by inherited deficiencies of soluble lysosomal enzymes. Independent from the approach, the enzyme must be delivered to lysosomes of deficient patient cells. Little is known about the dissemination of enzyme within a tissue where cells compete for uptake via different receptor systems, binding affinities and endocytic rates. To evaluate dissemination and lysosomal targeting of a lysosomal enzyme in the CNS, we analysed receptor-mediated endocytosis of arylsulfatase A (ASA) by different types of brain-derived cell lines and primary murine brain cells. For ASA expressed by chinese hamster ovary cells for enzyme replacement therapy of metachromatic leukodystrophy, endocytic rates decline from microglia to neurons and astrocytes and to oligodendrocytes. Only immature oligodendrocytes endocytose significant amounts of enzyme. Uptake by non-microglial cells is due to mannose 6-phosphate receptors, whereas several receptor systems participate in endocytosis by microglial cells. Interestingly, ASA expressed by microglial cells cannot be taken up in a mannose 6-phosphate dependent manner. The resulting failure to correct non-microglial cells corroborates in vivo data and indicates that therapeutic effects of allogeneic bone marrow transplantation and hematopoietic stem cell gene therapy on metachromatic leukodystrophy are independent of metabolic cross-correction of neurons, astrocytes and oligodendrocytes by receptor-mediated endocytosis.

Arylsulfatase A (ASA) in Parkinson's Disease: From Pathogenesis to Biomarker Potential

Parkinson's disease (PD), the second most common neurodegenerative disorder after Alzheimer's disease, is a clinically heterogeneous disorder, with obscure etiology and no disease-modifying therapy to date. Currently, there is no available biomarker for PD endophenotypes or disease progression. Accumulating evidence suggests that mutations in genes related to lysosomal function or lysosomal storage disorders may affect the risk of PD development, such as GBA1 gene mutations. In this context, recent studies have revealed the emerging role of arylsulfatase A (ASA), a lysosomal hydrolase encoded by the ARSA gene causing metachromatic leukodystrophy (MLD) in PD pathogenesis. In particular, altered ASA levels have been detected during disease progression, and reduced enzymatic activity of ASA has been associated with an atypical PD clinical phenotype, including early cognitive impairment and essential-like tremor. Clinical evidence further reveals that specific ARSA gene variants may act as genetic modifiers in PD. Recent in vitro and in vivo studies indicate that ASA may function as a molecular chaperone interacting with α-synuclein (SNCA) in the cytoplasm, preventing its aggregation, secretion and cell-to-cell propagation. In this review, we summarize the results of recent preclinical and clinical studies on the role of ASA in PD, aiming to shed more light on the potential implication of ASA in PD pathogenesis and highlight its biomarker potential.

Lipids in the Physiopathology of Hereditary Spastic Paraplegias

Hereditary spastic paraplegias (HSP) are a group of neurodegenerative diseases sharing spasticity in lower limbs as common symptom. There is a large clinical variability in the presentation of patients, partly underlined by the large genetic heterogeneity, with more than 60 genes responsible for HSP. Despite this large heterogeneity, the proteins with known function are supposed to be involved in a limited number of cellular compartments such as shaping of the endoplasmic reticulum or endolysosomal function. Yet, it is difficult to understand why alteration of such different cellular compartments can lead to degeneration of the axons of cortical motor neurons. A common feature that has emerged over the last decade is the alteration of lipid metabolism in this group of pathologies. This was first revealed by the identification of mutations in genes encoding proteins that have or are supposed to have enzymatic activities on lipid substrates. However, it also appears that mutations in genes affecting endoplasmic reticulum, mitochondria, or endolysosome function can lead to changes in lipid distribution or metabolism. The aim of this review is to discuss the role of lipid metabolism alterations in the physiopathology of HSP, to evaluate how such alterations contribute to neurodegenerative phenotypes, and to understand how this knowledge can help develop therapeutic strategy for HSP.

Microglia damage precedes major myelin breakdown in X-linked adrenoleukodystrophy and metachromatic leukodystrophy

X-linked adrenoleukodystrophy (X-ALD) and metachromatic leukodystrophy (MLD) are two relatively common examples of hereditary demyelinating diseases caused by a dysfunction of peroxisomal or lysosomal lipid degradation. In both conditions, accumulation of nondegraded lipids leads to the destruction of cerebral white matter. Because of their high lipid content, oligodendrocytes are considered key to the pathophysiology of these leukodystrophies. However, the response to allogeneic stem cell transplantation points to the relevance of cells related to the hematopoietic lineage. In the present study, we aimed to better characterize the pathogenetic role of microglia in the above-mentioned diseases. Applying recently established microglia markers to human autopsy cases of X-ALD and MLD we were able to delineate distinct lesion stages in evolving demyelinating lesions. The immune-phenotype of microglia was altered already early in lesion evolution, and microglia loss preceded full-blown myelin degeneration both in X-ALD and MLD. DNA fragmentation indicating phagocyte death was observed in areas showing microglia loss. The morphology and dynamics of phagocyte decay differed between the diseases and between lesion stages, hinting at distinct pathways of programmed cell death. In summary, the present study shows an early and severe damage to microglia in the pathogenesis of X-ALD and MLD. This hints at a central pathophysiologic role of these cells in the diseases and provides evidence for an ongoing transfer of toxic substrates primarily enriched in myelinating cells to microglia.

Human iPSC-based models highlight defective glial and neuronal differentiation from neural progenitor cells in metachromatic leukodystrophy

The pathological cascade leading from primary storage to neural cell dysfunction and death in metachromatic leukodystrophy (MLD) has been poorly elucidated in human-derived neural cell systems. In the present study, we have modeled the progression of pathological events during the differentiation of patient-specific iPSCs to neuroepithelial progenitor cells (iPSC-NPCs) and mature neurons, astrocytes, and oligodendrocytes at the morphological, molecular, and biochemical level. We showed significant sulfatide accumulation and altered sulfatide composition during the differentiation of MLD iPSC-NPCs into neuronal and glial cells. Changes in sulfatide levels and composition were accompanied by the expansion of the lysosomal compartment, oxidative stress, and apoptosis. The neuronal and glial differentiation capacity of MLD iPSC-NPCs was significantly impaired. We showed delayed appearance and/or reduced levels of oligodendroglial and astroglial markers as well as reduced number of neurons and disorganized neuronal network. Restoration of a functional Arylsulfatase A (ARSA) enzyme in MLD cells using lentiviral-mediated gene transfer normalized sulfatide levels and composition, globally rescuing the pathological phenotype. Our study points to MLD iPSC-derived neural progeny as a useful in vitro model to assess the impact of ARSA deficiency along NPC differentiation into neurons and glial cells. In addition, iPSC-derived neural cultures allowed testing the impact of ARSA reconstitution/overexpression on disease correction and, importantly, on the biology and functional features of human NPCs, with important therapeutic implications.

Nonclinical comparability studies of recombinant human arylsulfatase A addressing manufacturing process changes

Recombinant human arylsulfatase A (rhASA) is in clinical development for the treatment of patients with metachromatic leukodystrophy (MLD). Manufacturing process changes were introduced to improve robustness and efficiency, resulting in higher levels of mannose-6-phosphate and sialic acid in post-change (process B) compared with pre-change (process A) rhASA. A nonclinical comparability program was conducted to compare process A and process B rhASA. All doses were administered intrathecally. Pharmacodynamic comparability was evaluated in immunotolerant MLD mice, using immunohistochemical staining of lysosomal-associated membrane protein-1 (LAMP-1). Pharmacokinetic comparability was assessed in juvenile cynomolgus monkeys dosed once with 6.0 mg (equivalent to 100 mg/kg of brain weight) process A or process B rhASA. Biodistribution was compared by quantitative whole-body autoradiography in rats. Potential toxicity of process B rhASA was evaluated by repeated rhASA administration at doses of 18.6 mg in juvenile cynomolgus monkeys. The specific activities for process A and process B rhASA were 89 U/mg and 106 U/mg, respectively, which were both well within the target range for the assay. Pharmacodynamic assessments showed no statistically significant differences in LAMP-1 immunohistochemical staining in the spinal cord and in most of the brain areas assessed between process A and B rhASA-dosed mice. LAMP-1 staining was reduced with both process A and B rhASA compared with vehicle, supporting its activity. Concentration–time curves in cerebrospinal fluid and serum of cynomolgus monkeys were similar with process A and B rhASA. Process A and B rhASA were similar in terms of their pharmacokinetic parameters and biodistribution data. No process B rhASA-related toxicity was detected. In conclusion, manufacturing process changes did not affect the pharmacodynamic, pharmacokinetic or safety profiles of process B rhASA relative to process A rhASA.

Gene therapy for metachromatic leukodystrophy

Leukodystrophies (LDs) are rare, often devastating genetic disorders with neurologic symptoms. There are currently no disease-specific therapeutic approaches for these diseases. In this review we use metachromatic leukodystrophy as an example to outline in the brief the therapeutic approaches to MLD that have been tested in animal models and in clinical trials, such as enzyme-replacement therapy, bone marrow/umbilical cord blood transplants, ex vivo transplantation of genetically modified hematopoietic stem cells, and gene therapy. These studies suggest that to be successful the ideal therapy for MLD must provide persistent and high level expression of the deficient gene, arylsulfatase A in the CNS. Gene therapy using adeno-associated viruses is therefore the ideal choice for clinical development as it provides the best balance of potential for efficacy with reduced safety risk. Here we have summarized the published preclinical data from our group and from others that support the use of a gene therapy with AAVrh.10 serotype for clinical development as a treatment for MLD, and as an example of the potential of gene therapy for LDs especially for Krabbe disease, which is the focus of this special issue. © 2016 Wiley Periodicals, Inc.

Sulfatides Primarily Exist in the Substantia Nigra Region of Mouse Brain Tissue

Lipid distribution in the brain is important for many biological functions and has been associated with some brain diseases. The aim of this study was to investigate lipid distribution in different regions of brain tissue in mice. To this end, substantia nigra (SN), caudate putamen (CPu), hippocampus (Hip), hypothalamus (Hyp), and cortex (Cx) tissues of mice were analyzed using direct infusion nanoelectrospray-ion trap mass spectrometry and multivariate analyses. The SN, CPu, Hip, Hyp, and Cx groups showed clear differences in lipid distribution using principal component analysis and a partial least-squares discriminant analysis score plot, and lipid levels were significantly different in different brain regions. In particular, sulfatides were mainly distributed in the SN region. Our results could be used to help understand the functions and mechanisms of lipids in various brain diseases.

Generation of Human Induced Pluripotent Stem Cell-Derived Bona Fide Neural Stem Cells for Ex Vivo Gene Therapy of Metachromatic Leukodystrophy

Allogeneic fetal‐derived human neural stem cells (hfNSCs) that are under clinical evaluation for several neurodegenerative diseases display a favorable safety profile, but require immunosuppression upon transplantation in patients. Neural progenitors derived from patient‐specific induced pluripotent stem cells (iPSCs) may be relevant for autologous ex vivo gene‐therapy applications to treat genetic diseases with unmet medical need. In this scenario, obtaining iPSC‐derived neural stem cells (NSCs) showing a reliable “NSC signature” is mandatory. Here, we generated human iPSC (hiPSC) clones via reprogramming of skin fibroblasts derived from normal donors and patients affected by metachromatic leukodystrophy (MLD), a fatal neurodegenerative lysosomal storage disease caused by genetic defects of the arylsulfatase A (ARSA) enzyme. We differentiated hiPSCs into NSCs (hiPS‐NSCs) sharing molecular, phenotypic, and functional identity with hfNSCs, which we used as a “gold standard” in a side‐by‐side comparison when validating the phenotype of hiPS‐NSCs and predicting their performance after intracerebral transplantation. Using lentiviral vectors, we efficiently transduced MLD hiPSCs, achieving supraphysiological ARSA activity that further increased upon neural differentiation. Intracerebral transplantation of hiPS‐NSCs into neonatal and adult immunodeficient MLD mice stably restored ARSA activity in the whole central nervous system. Importantly, we observed a significant decrease of sulfatide storage when ARSA‐overexpressing cells were used, with a clear advantage in those mice receiving neonatal as compared with adult intervention. Thus, we generated a renewable source of ARSA‐overexpressing iPSC‐derived bona fide hNSCs with improved features compared with clinically approved hfNSCs. Patient‐specific ARSA‐overexpressing hiPS‐NSCs may be used in autologous ex vivo gene therapy protocols to provide long‐lasting enzymatic supply in MLD‐affected brains. Stem Cells Translational Medicine2017;6:352–368

Intracerebral Gene Therapy Using AAVrh.10-hARSA Recombinant Vector to Treat Patients with Early-Onset Forms of Metachromatic Leukodystrophy: Preclinical Feasibility and Safety Assessments in Nonhuman Primates

No treatment is available for early-onset forms of metachromatic leukodystrophy (MLD), a lysosomal storage disease caused by autosomal recessive defect in arylsulfatase A (ARSA) gene causing severe demyelination in central and peripheral nervous systems. We have developed a gene therapy approach, based on intracerebral administration of AAVrh.10-hARSA vector, coding for human ARSA enzyme. We have previously demonstrated potency of this approach in MLD mice lacking ARSA expression. We describe herein the preclinical efficacy, safety, and biodistribution profile of intracerebral administration of AAVrh.10-hARSA to nonhuman primates (NHPs). NHPs received either the dose planned for patients adjusted to the brain volume ratio between child and NHP (1×dose, 1.1×10(11) vg/hemisphere, unilateral or bilateral injection) or 5-fold this dose (5×dose, 5.5×10(11) vg/hemisphere, bilateral injection). NHPs were subjected to clinical, biological, and brain imaging observations and were euthanized 7 or 90 days after injection. There was no toxicity based on clinical and biological parameters, nor treatment-related histological findings in peripheral organs. A neuroinflammatory process correlating with brain MRI T2 hypersignals was observed in the brain 90 days after administration of the 5×dose, but was absent or minimal after administration of the 1×dose. Antibody response to AAVrh.10 and hARSA was detected, without correlation with brain lesions. After injection of the 1×dose, AAVrh.10-hARSA vector was detected in a large part of the injected hemisphere, while ARSA activity exceeded the normal endogenous activity level by 14-31%. Consistently with other reports, vector genome was detected in off-target organs such as liver, spleen, lymph nodes, or blood, but not in gonads. Importantly, AAVrh.10-hARSA vector was no longer detectable in urine at day 7. Our data demonstrate requisite safe and effective profile for intracerebral AAVrh.10-hARSA delivery in NHPs, supporting its clinical use in children affected with MLD.

Anti-inflammatory Therapy With Simvastatin Improves Neuroinflammation and CNS Function in a Mouse Model of Metachromatic Leukodystrophy

Metachromatic leukodystrophy (MLD) is a lysosomal storage disease caused by a functional deficiency of the lysosomal enzyme arylsulfatase A. The prevailing late-infantile variant of MLD is characterized by widespread and progressive demyelination of the central nervous system (CNS) causing death during childhood. In order to gain insight into the pathomechanism of the disease and to identify novel therapeutic targets, we analyzed neuroinflammation in two mouse models reproducing a mild, nondemyelinating, and a more severe, demyelinating, variant of MLD, respectively. Microgliosis and upregulation of cytokine/chemokine levels were clearly more pronounced in the demyelinating model. The analysis of the temporal cytokine/chemokine profiles revealed that the onset of demyelination is preceded by a sustained elevation of the macrophage inflammatory protein (MIP)-1α followed by an upregulation of MIP-1β, monocyte chemotactic protein (MCP)-1, and several interleukins. The tumor necrosis factor (TNF)-α remains unchanged. Treatment of the demyelinating mouse model with the nonsteroidal anti-inflammatory drug simvastatin reduced neuroinflammation, improved the swimming performance and ataxic gait, and retarded demyelination of the spinal cord. Our data suggest that neuroinflammation is causative for demyelination in MLD mice and that anti-inflammatory treatment might be a novel therapeutic option to improve the CNS function of MLD patients.

Quantification of sulfatides and lysosulfatides in tissues and body fluids by liquid chromatography-tandem mass spectrometry

Sulfatides are found in brain as components of myelin, oligodendrocytes, and neurons but are also present in various visceral tissues. Metachromatic leukodystrophy (MLD) is an inherited lysosomal storage disorder caused by a deficiency of arylsulfatase A, leading to severe white matter disease due to the accumulation of sulfatides and lysosulfatides. To study the physiological role of sulfatides, accessible and sensitive quantitative methods are required. We developed a sensitive LC/MS/MS method to quantify total sulfatide and lysosulfatide content as well as individual molecular species in urine and plasma from MLD patients and plasma and tissues from an MLD mouse model. Our results demonstrate that the method can quantify a wide range of sulfatide concentrations and can be used to quantify total sulfatide content and levels of individual molecular species of sulfatides in tissues, cells, and body fluids. Even though plasma sulfatides and lysosulfatides would seem attractive candidate biomarkers that could possibly correlate with the severity of MLD and be of use to monitor the effects of therapeutic intervention, our results indicate that it is unlikely that the determination of these storage products in plasma will be useful in this respect.

Distribution of C16:0, C18:0, C24:1, and C24:0 sulfatides in central nervous system lipid rafts by quantitative ultra-high-pressure liquid chromatography tandem mass spectrometry

Sulfated galactosylceramides (sulfatides) are glycosphingolipids associated with cholesterol- and sphingolipid-enriched membrane microdomains (lipid rafts) and are highly expressed in brain tissue. Although it is known that sulfatide species show heterogeneity in their fatty acid acyl group composition throughout brain development, their lipid raft distribution and biological relevance is poorly understood. We validated a fast and sensitive ultra-high-pressure liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) method to measure developmentally regulated sulfatide species (C16:0, C18:0, C24:1, and C24:0) in central nervous system (CNS) lipid rafts isolated without using detergent. Our UHPLC-MS/MS assay showed good accuracy and precision with a linear range of 5 to 1,000 nM for C18:0 and C24:1 sulfatides and 10 to 1,000 nM for C16:0 and C24:0 sulfatides. We applied this quantitative analysis to detergent-free lipid rafts isolated from wild-type mice and arylsulfatase A-deficient (ASA knockout) mice that accumulate sulfatides. All four sulfatide species were more abundant in raft membranes than in non-raft membranes, with a significant increase in lipid rafts isolated from ASA knockout mice. This is the first description of an analytical method to study these sulfatide species in raft and non-raft membranes and has the potential to be applied to preparations from other tissues.

Comparative efficacy and safety of multiple routes of direct CNS administration of adeno-associated virus gene transfer vector serotype rh.10 expressing the human arylsulfatase A cDNA to nonhuman primates

Metachromatic leukodystrophy (MLD), a fatal disorder caused by deficiency of the lysosomal enzyme arylsulfatase A (ARSA), is associated with an accumulation of sulfatides, causing widespread demyelination in both central and peripheral nervous systems. On the basis of prior studies demonstrating that adeno-associated virus AAVrh.10 can mediate widespread distribution in the CNS of a secreted lysosomal transgene, and as a prelude to human trials, we comparatively assessed the optimal CNS delivery route of an AAVrh.10 vector encoding human ARSA in a large animal model for broadest distribution of ARSA enzyme. Five routes were tested (each total dose, 1.5 × 10(12) genome copies of AAVrh.10hARSA-FLAG): (1) delivery to white matter centrum ovale; (2) deep gray matter delivery (putamen, thalamus, and caudate) plus overlying white matter; (3) convection-enhanced delivery to same deep gray matter locations; (4) lateral cerebral ventricle; and (5) intraarterial delivery with hyperosmotic mannitol to the middle cerebral artery. After 13 weeks, the distribution of ARSA activity subsequent to each of the three direct intraparenchymal administration routes was significantly higher than in phosphate-buffered saline-administered controls, but administration by the intraventricular and intraarterial routes failed to demonstrate measurable levels above controls. Immunohistochemical staining in the cortex, white matter, deep gray matter of the striatum, thalamus, choroid plexus, and spinal cord dorsal root ganglions confirmed these results. Of the five routes studied, administration to the white matter generated the broadest distribution of ARSA, with 80% of the brain displaying more than a therapeutic (10%) increase in ARSA activity above PBS controls. No significant toxicity was observed with any delivery route as measured by safety parameters, although some inflammatory changes were seen by histopathology. We conclude that AAVrh.10-mediated delivery of ARSA via CNS administration into the white matter is likely to be safe and yields the widest distribution of ARSA, making it the most suitable route of vector delivery.

Factors and processes modulating phenotypes in neuronopathic lysosomal storage diseases

Lysosomal storage diseases are inherited metabolic disorders caused by genetic defects causing deficiency of various lysosomal proteins, and resultant accumulation of non-degraded compounds. They are multisystemic diseases, and in most of them (>70%) severe brain dysfunctions are evident. However, expression of various phenotypes in particular diseases is extremely variable, from non-neuronopathic to severely neurodegenerative in the deficiency of the same enzyme. Although all lysosomal storage diseases are monogenic, clear genotype-phenotype correlations occur only in some cases. In this article, we present an overview on various factors and processes, both general and specific for certain disorders, that can significantly modulate expression of phenotypes in these diseases. On the basis of recent reports describing studies on both animal models and clinical data, we propose a hypothesis that efficiency of production of compounds that cannot be degraded due to enzyme deficiency might be especially important in modulation of phenotypes of patients suffering from lysosomal storage diseases.

Long-term correction of biochemical and neurological abnormalities in MLD mice model by neonatal systemic injection of an AAV serotype 9 vector

As both the immune system and the blood-brain barrier (BBB) are likely to be developmentally immature in the perinatal period, neonatal gene transfer may be useful for the treatment of lysosomal storage disease (LSD) with neurological involvements such as metachromatic leukodystrophy (MLD). In this experiment, we examined the feasibility of single-strand adeno-associated viral serotype-9 (ssAAV9)-mediated systemic neonatal gene therapy of MLD mice. ssAAV9 vector expressing human arylsulfatase A (ASA) and green fluorescent protein (GFP) (ssAAV9/ASA) was injected into the jugular vein of newborn MLD mice. High levels of ASA expression were observed in the muscle and heart for at least 15 months. ASA was continuously secreted into plasma without development of antibodies against ASA. Global gene transfer into the brain and spinal cord (SC), across the BBB, and long-term ASA expression in the central nervous system were detected in treated mice. Significant inhibition of the accumulation of sulfatide (Sulf) in the brain and cervical SC was confirmed by Alcian blue staining and biochemical analysis of the Sulf content. In a behavior test, treated mice showed a greater ability to traverse narrow balance beams than untreated mice. These data clearly demonstrate that MLD mice model can be effectively treated through neonatal systemic injection of ssAAV9/ASA.

Developing therapeutic approaches for metachromatic leukodystrophy

Metachromatic leukodystrophy (MLD) is an autosomal recessive lysosomal disorder caused by the deficiency of arylsulfatase A (ASA), resulting in impaired degradation of sulfatide, an essential sphingolipid of myelin. The clinical manifestations of MLD are characterized by progressive demyelination and subsequent neurological symptoms resulting in severe debilitation. The availability of therapeutic options for treating MLD is limited but expanding with a number of early stage clinical trials already in progress. In the development of therapeutic approaches for MLD, scientists have been facing a number of challenges including blood–brain barrier (BBB) penetration, safety issues concerning therapies targeting the central nervous system, uncertainty regarding the ideal timing for intervention in the disease course, and the lack of more in-depth understanding of the molecular pathogenesis of MLD. Here, we discuss the current status of the different approaches to developing therapies for MLD. Hematopoietic stem cell transplantation has been used to treat MLD patients, utilizing both umbilical cord blood and bone marrow sources. Intrathecal enzyme replacement therapy and gene therapies, administered locally into the brain or by generating genetically modified hematopoietic stem cells, are emerging as novel strategies. In pre-clinical studies, different cell delivery systems including microencapsulated cells or selectively neural cells have shown encouraging results. Small molecules that are more likely to cross the BBB can be used as enzyme enhancers of diverse ASA mutants, either as pharmacological chaperones, or proteostasis regulators. Specific small molecules may also be used to reduce the biosynthesis of sulfatides, or target different affected downstream pathways secondary to the primary ASA deficiency. Given the progressive neurodegenerative aspects of MLD, also seen in other lysosomal diseases, current and future therapeutic strategies will be complementary, whether used in combination or separately at specific stages of the disease course, to produce better outcomes for patients afflicted with this devastating inherited disorder.

Correction of brain oligodendrocytes by AAVrh.10 intracerebral gene therapy in metachromatic leukodystrophy mice

Metachromatic leukodystrophy (MLD) is a lysosomal storage disorder characterized by accumulation of sulfatides in glial cells and neurons, the result of an inherited deficiency of arylsulfatase A (ARSA; EC 3.1.6.8) and myelin degeneration in the central and peripheral nervous systems. No effective treatment is currently available for the most frequent late infantile (LI) form of MLD, which results in rapid neurological degradation and early death after the onset of clinical manifestations. To potentially arrest or reverse disease progression, ARSA enzyme must be rapidly delivered to brain oligodendrocytes of patients with LI MLD. We previously showed that brain gene therapy with adeno-associated virus serotype 5 (AAV5) driving the expression of human ARSA cDNA under the control of the murine phosphoglycerate kinase (PGK) promoter alleviated most long-term disease manifestations in MLD mice. Herein, we evaluated the short-term effects of AAVrh.10 driving the expression of human ARSA cDNA under the control of the cytomegalovirus/β-actin hybrid (CAG/cu) promoter in 8-month-old MLD mice that already show marked sulfatide accumulation and brain pathology. Within 2 months, and in contrast to results with the AAV5-PGK-ARSA vector, a single intrastriatal injection of AAVrh.10cuARSA resulted in correction of brain sulfatide storage, accumulation of specific sulfatide species in oligodendrocytes, and associated brain pathology in the injected hemisphere. Better potency of the AAVrh.10cuARSA vector was mediated by higher neuronal and oligodendrocyte transduction, axonal transport of the AAVrh.10 vector and ARSA enzyme, as well as higher CAG/cu promoter driven expression of ARSA enzyme. These results strongly support the use of AAVrh.10cuARSA vector for intracerebral gene therapy in rapidly progressing early-onset forms of MLD.

Toward a better understanding of brain lesions during metachromatic leukodystrophy evolution

BACKGROUND AND PURPOSE

The prospect of new therapies in MLD stresses the need to refine the indications for treatment. The aim of this study was, therefore, to perform a detailed analysis of MRI brain lesions at diagnosis and follow-up, to better understand the natural history of MLD.

MATERIAL AND METHODS

This retrospective case-control study (2005-2010) looked at 13 patients with MLD (2-5 years of age) with 28 MRIs (mean follow-up, 2 years), compared with 39 age- and sex-matched controls. All MRIs were evaluated qualitatively and semiquantitatively. The Student t test, Wilcoxon signed rank test, and Pearson correlation were used for statistical analysis (P < .05).

RESULTS

In addition to diffuse symmetric supratentorial WM T2 hyperintensities with a tigroid pattern (70%) and T2 hyperintensities in the CC (100%) and internal capsules (46%), we found significant GM abnormalities such as thalamic T2 hypointensity (92%), thalamic (23%, P < .05, EJ) and caudate nuclei (23%, P < .05, EJ) atrophy, and cerebellar atrophy without WM involvement (15%). The pattern of splenium involvement progression was misleading, with initially diffuse high signal intensity, which later became curvilinear before finally progressing to atrophy (23%, P < .05; EJ). This should not be mistaken for a disease regression. Spectroscopy confirmed a decrease in the NAA/Cr ratio, an increase in the Cho/Cr ratio and in myo-inositol, and a lactate resonance.

CONCLUSIONS

Thalamic changes may be a common finding in MLD, raising the prospect of primary GM lesions. This may prove important when evaluating the efficacy of new treatments.

Developing treatment options for metachromatic leukodystrophy

Metachromatic leukodystrophy (MLD) represents a devastating lysosomal storage disease characterized by intralysosomal accumulation of the sphingolipid sulfatide in various tissues. Three types of the disease are currently distinguished: the late-infantile, which is the most commonly observed, the juvenile and the adult type. Demyelination represents the main histopathological feature of the disorder, leading to neurological impairment with no curative treatment currently available. Nevertheless, the increased scientific interest on the disease has led to the experimental use of innovative therapeutic approaches in animal models, aiming to provide an effective therapeutic regimen for human patients, as well. This paper provides an overview of developing treatment options among patients with MLD. Apart from hematopoietic stem cell transplantation, already in use for decades, other recent data discussed includes umbilical cord blood and stem cell transplantation, enzyme replacement therapy, gene therapy and autologous hematopoietic transplantation of genetically modified stem cells. Gene therapy with oligodedroglial, neural progenitor, embryonic and microencapsulated recombinant cells represents add-on treatment options still on experimental level.

Intracerebroventricular enzyme infusion corrects central nervous system pathology and dysfunction in a mouse model of metachromatic leukodystrophy

Arylsulfatase A (ASA) catalyzes the desulfation of sulfatide, a major lipid component of myelin. Inherited functional deficiencies of ASA cause the lysosomal storage disease (LSD) metachromatic leukodystrophy (MLD), which is characterized by intralysosomal accumulation of sulfatide, progressive neurological symptoms and early death. Enzyme replacement therapy (ERT) using intravenous injection of active enzyme is a treatment option for many LSDs as exogenous lysosomal enzymes are delivered to lysosomes of patient's cells via receptor-mediated endocytosis. Efficient treatment of MLD and other LSDs with central nervous system (CNS) involvement is, however, hampered by the blood-brain barrier (BBB), which limits transfer of therapeutic enzymes from the circulation to the brain parenchyma. To bypass the BBB, we infused recombinant human ASA (rhASA) by implanted miniature pumps into the cerebrospinal fluid (CSF) of a conventional and a novel, genetically aggravated ASA knockout mouse model of MLD. rhASA continuously delivered to the lateral ventricle for 4 weeks penetrated the brain parenchyma and was targeted to the lysosomes of brain cells. Histological analysis revealed complete reversal of lysosomal storage in the infused hemisphere. rhASA concentrations and sulfatide clearance declined with increasing distance from the infusion site. Correction of the ataxic gait indicated reversal of central nervous system dysfunctions. The profound histopathological and functional improvements, the requirement of low enzyme doses and the absence of immunological side effects suggest intracerebroventricular ERT to be a promising treatment option for MLD and other LSDs with prevailing CNS disease.

Pathology and current treatment of neurodegenerative sphingolipidoses

Sphingolipidoses constitute a large subgroup of lysosomal storage disorders (LSDs). Many of them are associated with a progressive neurodegeneration. As is the case for LSDs in general, most sphingolipidoses are caused by deficiencies in lysosomal hydrolases. However, accumulation of sphingolipids can also result from deficiencies in proteins involved in the transport or posttranslational modification of lysosomal enzymes, transport of lipids, or lysosomal membrane proteins required for transport of lysosomal degradation end products. The accumulation of sphingolipids in the lysosome together with secondary changes in the concentration and localization of other lipids may cause trafficking defects of membrane lipids and proteins, affect calcium homeostasis, induce the unfolded protein response, activate apoptotic cascades, and affect various signal transduction pathways. To what extent, however, these changes contribute to the pathogenesis of the diseases is not fully understood. Currently, there is no cure for sphingolipidoses. Therapies like enzyme replacement, pharmacological chaperone, and substrate reduction therapy, which have been shown to be efficient in non-neuronopathic LSDs, are currently evaluated in clinical trials of neuronopathic sphingolipidoses. In the future, neural stem cell therapy and gene therapy may become an option for these disorders.

Successful treatment of metachromatic leukodystrophy using bone marrow transplantation of HoxB4 overexpressing cells

To evaluate the contribution of bone marrow (BM) cells to treat neurological disorders, we examined the effectiveness of BM cells expressing the homeobox B4 (HoxB4) gene to cure mice with metachromatic leukodystrophy (MLD) through transplantation. Increased number of donor cells was observed in brains of the MLD mice transplanted with HoxB4-transduced BM cells (B4MLD) in contrast to those transplanted with control green fluorescent protein (GFP)-transduced BM cells (MIGMLD). Immunohistochemical staining showed that most of the GFP(+) cells were Iba1(+) microglia. In addition, O4(+) oligodendrocytes were identified only in the B4MLD brains but not in the MIGMLD brain. Alcian blue staining showed that accumulation of sulfatide was dramatically reduced in brain tissue from B4MLD mice, and there was a corresponding improvement in the animals' ability to walk a balance beam 8 months after transplantation. Thus transplantation of BM cells overexpressing HoxB4 appears to effectively prevent the progression of MLD in this mouse model. These findings support the idea that hematopoietic stem cells (HSCs) transduced with a HoxB4 expression vector could be the useful carriers of therapeutic proteins into the brain for regeneration of oligodendrocytes to treat such demyelinating disorders as MLD, Krabbe disease, and multiple sclerosis.

Animal models of human cerebellar ataxias: a cornerstone for the therapies of the twenty-first century

Cerebellar ataxias represent a group of disabling neurological disorders. Our understanding of the pathogenesis of cerebellar ataxias is continuously expanding. A considerable number of laboratory animals with neurological mutations have been reported and numerous relevant animal models mimicking the phenotype of cerebellar ataxias are becoming available. These models greatly help dissecting the numerous mechanisms of cerebellar dysfunction, a major step for the assessment of therapeutics targeting a given deleterious pathway and for the screening of old or newly synthesized chemical compounds. Nevertheless, differences between animal models and human disorders should not be overlooked and difficulties in terms of characterization should not be occulted. The identification of the mutations of many hereditary ataxias, the development of valuable animal models, and the recent identifications of the molecular mechanisms underlying cerebellar disorders represent a combination of key factors for the development of anti-ataxic innovative therapies. It is anticipated that the twenty-first century will be the century of effective therapies in the field of cerebellar ataxias. The animal models are a cornerstone to reach this goal.

Enzyme replacement improves ataxic gait and central nervous system histopathology in a mouse model of metachromatic leukodystrophy

Inherited deficiencies of lysosomal hydrolases cause lysosomal storage diseases (LSDs) that are characterized by a progressive multisystemic pathology and premature death. Repeated intravenous injection of the active counterpart of the deficient enzyme, a treatment strategy called enzyme replacement therapy (ERT), evolved as a clinical option for several LSDs without central nervous system (CNS) involvement. To assess the efficacy of long-term ERT in metachromatic leukodystrophy (MLD), an LSD with prevailing nervous system disease, we treated immunotolerant arylsulfatase A (ASA) knockout mice with 52 doses of either 4 or 50 mg/kg recombinant human ASA (rhASA). ERT was tolerated without side effects and improved disease manifestations in a dose-dependent manner. Dosing of 4 mg/kg diminished sulfatide storage in kidney and peripheral nervous system (PNS) but not the CNS, whereas treatment with 50 mg/kg was also effective in the CNS in reducing storage in brain and spinal cord by 34 and 45%, respectively. Histological analyses revealed regional differences in sulfatide clearance. While 70% less storage profiles were detectable, for example, in the hippocampal fimbria, the histopathology of the brain stem was unchanged. Both enzyme doses normalized the ataxic gait of ASA knockout mice, demonstrating prevention of nervous system dysfunctions that dominate early stages of MLD.

In vitro correction of ARSA deficiency in human skin fibroblasts from metachromatic leukodystrophy patients after treatment with microencapsulated recombinant cells

Metachromatic leukodystrophy (MLD) is an autosomal recessive disorder due to arylsulfatase A (ARSA) deficiency that affects primarily the central nervous system. Ongoing treatments include enzyme replacement therapy and bone marrow transplantation, both limited in their effects due to the blood-brain barrier. An alternative approach would be the in situ implantation of encapsulated cells over expressing ARSA. Based on that, we tested the ability of encapsulated BHK cells over expressing ARSA to correct the enzyme deficiency in MLD patients' fibroblasts. Three groups were analyzed: fibroblasts treated with ARSA-over expressing BHK cells (rBHK) trapped in alginate capsules (capsules group), fibroblasts treated with supernatant of non-encapsulated rBHK (uptake control) and fibroblasts treated with empty capsules (empty group). Untreated and normal fibroblasts were used as controls. rBHK obtained by clone selection after non-viral transfection with pTARSA-CMV2. ARSA activity was measured after 1, 2, 3 and 4 weeks of treatment and beta-gal was used as reference enzyme. Statistical analysis was performed using ANOVA and Tukey's test. Normal fibroblasts showed ARSA activity of 23.9 + /- 2.01 nmol/h/mg of protein, whereas untreated MLD fibroblasts had the low ARSA activity (2.22 + /- 0.17). In the empty group, ARSA activity was equal to that of untreated fibroblasts (2.71 + /- 0.34). Capsules and uptake control groups showed higher enzymatic activity levels, compared to MLD untreated, 23.42 + /- 6.39 and 42.35 + /- 5.20, respectively (p < 0.01 for all groups). Encapsulated rBHK clones show potential as a new therapeutic strategy for the treatment of MLD, reaching normal enzyme levels in human MLD fibroblasts.

Metachromatic leukodystrophy: genetics, pathogenesis and therapeutic options

Metachromatic leukodystrophy is a lysosomal storage disease caused by the deficiency of arylsulphatase A (ASA). This leads to storage of the membrane lipid sulphatide, which is abundant in myelin. A pathological hallmark of the disease is demyelination, causing various and ultimately lethal neurological symptoms. Today more than 110 mutations in the ASA gene have been identified, of which only three are frequent. Patients homozygous for alleles, which do not allow for the synthesis of functional ASA always suffer from the severe form of the disease, whereas alleles allowing the expression of residual enzyme activity are associated with the later onset juvenile or adult forms of metachromatic leukodystrophy. In addition, there are other as yet unknown genetic or epigenetic factors modifying the phenotype substantially. ASA-deficient mice have been generated as a model of metachromatic leukodystrophy. These mice store sulphatide and show progressive neurological symptoms, but do not demyelinate. This animal model was recently improved using a transgenic approach, which generated mice in which sulphatide synthesis in myelin-producing cells is enhanced. This new animal model reflects the pathological characteristics of the human disease. ASA-deficient mice have been used in various therapeutic trials involving enzyme replacement, haematopoietic stem-cell-based gene therapy and direct injections of ASA-expressing viral vectors into the brain. These animal studies have paved the way for future clinical studies of enzyme replacement and gene therapy.

CONCLUSION

For many years this devastating disorder was considered untreatable and the outlook for patients was poor. Within a comparatively short period of time since the ASA gene was cloned in 1989, genetic and biochemical studies and data generated from newly developed animal models have led to the first clinical trials. It is hoped that these developments will prove beneficial for patients.

Early signs of neurolipidosis-related behavioural alterations in a murine model of metachromatic leukodystrophy

Arylsulfatase A (ASA)-deficient mice represent an animal model for the lysosomal storage disorder metachromatic leukodystrophy (MLD). Although the model has been applied in pathophysiological and therapeutic studies, the behavioural phenotype of ASA(-/-) mice is only partially characterized, and the most decisive outcome measures for therapy evaluation only emerge beyond 1 year of age. Presently, ASA(-/-) mice and ASA(+/-) control mice were studied at 6 and 12 months of age on an extensive battery including tests of neuromotor ability, exploratory behaviour, and learning and memory. Overt signs of ataxia were not observed in 6-month-old ASA(-/-) mice, but quantitative gait analysis during open-field exploration revealed that ASA(-/-) mice displayed increased hind base width and increased stride lengths for all paws. Their covert motor incoordination was evident in a correlation analysis which unveiled decreased harmonisation of concurrent gait parameters. For example, while ASA(+/-) controls demonstrated substantial convergence of front and hind base width (r=0.54), these variables actually diverged in ASA(-/-) mice (r=-0.37). Furthermore, various behavioural observations indicated emotional alterations in ASA(-/-) mice. Six-month-old ASA(-/-) mice also showed decreased response rates in scheduled operant responding. The present findings could provide relevant behavioural outcome measures for further use of this murine MLD model in preclinical studies.

Induction of tolerance to human arylsulfatase A in a mouse model of metachromatic leukodystrophy

A deficiency of arylsulfatase A (ASA) causes metachromatic leukodystrophy (MLD), a lysosomal storage disorder characterized by accumulation of sulfatide, a severe neurological phenotype and early death. The efficacy of enzyme replacement therapy (ERT) has previously been determined in ASA knockout (ASA-/-) mice representing the only available animal model for MLD. Repeated intravenous injection of human ASA (hASA) improved the nervous system pathology and function, but also elicited a progressive humoral immune response leading to treatment resistance, anaphylactic reactions, and high mortality. In contrast to ASA-/- mice, most MLD patients express mutant hASA which may entail immunological tolerance to substituted wildtype hASA and thus protect from immunological complications. To test this notion, a cysteine-to-serine substitution was introduced into the active site of the hASA and the resulting inactive hASA-C69S variant was constitutively expressed in ASA-/- mice. Mice with sub-to supranormal levels of mutant hASA expression were analyzed. All mice, including those showing transgene expression below the limit of detection, were immunologically unresponsive to injected hASA. More than 100-fold overexpression did not induce an overt new phenotype except occasional intralysosomal deposition of minor amounts of glycogen in hepatocytes. Furthermore, long-term, low-dose ERT reduced sulfatide storage in peripheral tissues and the central nervous system indicating that high levels of extracellular mutant hASA do not prevent cellular uptake and lysosomal targeting of substituted wildtype hASA. Due to the tolerance to hASA and maintenance of the MLD-like phenotype, the novel transgenic strain may be particularly advantageous to assess the benefit and risk of long-term ERT.

Increasing sulfatide synthesis in myelin-forming cells of arylsulfatase A-deficient mice causes demyelination and neurological symptoms reminiscent of human metachromatic leukodystrophy

Metachromatic leukodystrophy (MLD) is a lysosomal storage disorder caused by the deficiency of arylsulfatase A (ASA). This results in accumulation of sulfated glycosphingolipids, mainly 3-O-sulfogalactosylceramide (sulfatide), in the nervous system and various other organs. In patients, lipid storage causes a progressive loss of myelin leading to various neurological symptoms. The sulfatide storage pattern in ASA-deficient [ASA(-/-)] mice is comparable to humans, but regrettably, the mice do not mimic the myelin pathology. We reasoned that increasing sulfatide storage in this animal model might provoke demyelination. Therefore, we generated transgenic ASA(-/-) [tg/ASA(-/-)] mice overexpressing the sulfatide-synthesizing enzyme galactose-3-O-sulfotransferase-1 in myelinating cells. Indeed, these tg/ASA(-/-) mice displayed a significant increase in sulfatide storage in brain and peripheral nerves. Mice older than 1 year developed severe neurological symptoms. Nerve conduction velocity was significantly reduced in tg/ASA(-/-) mice because of a peripheral neuropathy characterized by hypomyelinated and demyelinated axons. Inhomogeneous myelin thickness in the corpus callosum, increased frequency of hypomyelinated and demyelinated axons in corpus callosum and optic nerve, and substantially reduced myelin basic protein levels are in accordance with loss of myelin in the CNS. Thus, increasing sulfatide storage in ASA(-/-) mice leads to neurological symptoms and morphological alterations that are reminiscent of human MLD. The approach described here may also be applicable to improve other mouse models of lysosomal as well as nonlysosomal disorders.

Sulfatide storage in neurons causes hyperexcitability and axonal degeneration in a mouse model of metachromatic leukodystrophy

Metachromatic leukodystrophy is a lysosomal storage disorder caused by deficiency in the sulfolipid degrading enzyme arylsulfatase A (ASA). In the absence of a functional ASA gene, 3-O-sulfogalactosylceramide (sulfatide; SGalCer) and other sulfolipids accumulate. The storage is associated with progressive demyelination and various finally lethal neurological symptoms. Lipid storage, however, is not restricted to myelin-producing cells but also occurs in neurons. It is unclear whether neuronal storage contributes to symptoms of the patients. Therefore, we have generated transgenic ASA-deficient [ASA(-/-)] mice overexpressing the sulfatide synthesizing enzymes UDP-galactose:ceramide galactosyltransferase (CGT) and cerebroside sulfotransferase (CST) in neurons to provoke neuronal lipid storage. CGT-transgenic ASA(-/-) [CGT/ASA(-/-)] mice showed an accumulation of C18:0 fatty acid-containing SGalCer in the brain. Histochemically, an increase in sulfolipid storage could be detected in central and peripheral neurons of both CGT/ASA(-/-) and CST/ASA(-/-) mice compared with ASA(-/-) mice. CGT/ASA(-/-) mice developed severe neuromotor coordination deficits and weakness of hindlimbs and forelimbs. Light and electron microscopic analyses demonstrated nerve fiber degeneration in the spinal cord of CGT/ASA(-/-) mice. CGT/ASA(-/-) and, to a lesser extent, young ASA(-/-) mice exhibited cortical hyperexcitability, with recurrent spontaneous cortical EEG discharges lasting 5-15 s. These observations suggest that SGalCer accumulation in neurons contributes to disease phenotype.

Enzyme, cell and gene-based therapies for metachromatic leukodystrophy

Metachromatic leukodystrophy (MLD) is a demyelinating storage disease caused by deficiency of the lysosomal enzyme arylsulfatase A (ARSA). Lack of ARSA activity leads to the accumulation of galactosylceramide-3-O-sulfate (sulfatide) in the central and peripheral nervous systems. Based on the age at onset, the disease is usually classified into three forms: the late-infantile form, which manifests in the second year of life; the juvenile variants (onset between 4 and 12 years), which are subdivided into early-juvenile (EJ, onset before 6 years) and late-juvenile (LJ, onset after 6 years); and the adult form (onset after 12 years of age). Currently, there is no efficient therapy for the late-infantile form of MLD (50% of the patients), death occurring within a few years after onset of neurological symptoms. Allogeneic haematopoietic cell transplantation (HCT), when performed at a very early stage of the disease, may improve selected patients with juvenile or adult forms of MLD. As with other lysosomal storage diseases, the physiopathology of MLD is poorly understood. Demyelination is the main pathological finding, but substantial storage of sulfatides in neurons also occurs, and may contribute to the clinical phenotype. The physiopathological process leading to neuronal and glial cell degeneration and apoptosis involves accumulation of undegraded sulfatides but also secondary abnormalities (storage/mislocalization of unrelated lipids, inflammatory processes). This review summarizes the recent advances in the understanding of the physiopathology of MLD and the new therapeutic perspectives currently under preclinical investigation, including enzyme replacement therapy, gene therapy and cell therapy.

A spontaneously immortalized Schwann cell line to study the molecular aspects of metachromatic leukodystrophy

The arylsulfatase A (ASA)-deficient mouse is a murine model of human metachromatic leukodystrophy (MLD) caused by a genetic defect in the ASA gene. Deficiency of ASA causes accumulation of cerebroside-3-sulfate (sulfatide) in visceral organs and in the central and peripheral nervous system, which subsequently causes demyelination in these areas. To investigate further the cellular pathomechanism of MLD, we established spontaneously immortalized Schwann cell lines from ASA-deficient mice. Cells showed marked sulfatide storage in the late endosomal/lysosomal compartment. This sulfatide accumulation can be further increased by external treatment with sulfatide using a lipid based transfection reagent as a cargo. The accumulated sulfatide was degraded in response to ASA treatment and first examination revealed that alteration on the molecular level found in ASA-deficient mice can also be observed in the presented cell culture model. Hence, these cells could be a suitable model to study MLD at a molecular level.

AAV1 Mediated Co-expression of Formylglycine-Generating Enzyme and Arylsulfatase A Efficiently Corrects Sulfatide Storage in a Mouse Model of Metachromatic Leukodystrophy

Metachromatic leukodystrophy (MLD) is a lysosomal storage disorder caused by a deficiency of arylsulfatase A (ASA) and is characterized by deposition of sulfatide in all organs, particularly the nervous system. Recently, formylglycine-generating enzyme (FGE) was found to be essential for activation of sulfatases. This study examined the utility of FGE co-expression in AAV type 1 vector (AAV1)-mediated gene therapy of ASA knockout (MLD) mice. AAV1-ASA alone or AAV1-ASA and AAV1-FGE were co-injected into a single site of the hippocampus. Enzyme assay and immunohistochemical analysis showed that ASA was detected not only in the injected hemisphere but also in the non-injected hemisphere by 7 months after injection. Level of ASA activity and extent of ASA distribution were significantly enhanced by co-introduction of AAV1-FGE. Marked reductions in sulfatide levels were observed throughout the entire brain. The unexpectedly widespread distribution of ASA may be due to a combination of diffusion in extracellular spaces, transport through axons, and circulation in cerebrospinal fluid. The rotarod test revealed improvement of neurological functions. These results demonstrate that direct injection of AAV1 vectors expressing ASA and FGE represents a highly promising approach with significant implications for the development of clinical protocols for MLD gene therapy.

Modest phenotypic improvements in ASA-deficient mice with only one UDP-galactose:ceramide-galactosyltransferase gene

Background

Arylsulfatase A (ASA)-deficient mice are a model for the lysosomal storage disorder metachromatic leukodystrophy. This lipidosis is characterised by the lysosomal accumulation of the sphingolipid sulfatide. Storage of this lipid is associated with progressive demyelination. We have mated ASA-deficient mice with mice heterozygous for a non-functional allele of UDP-galactose:ceramide-galactosyltransferase (CGT). This deficiency is known to lead to a decreased synthesis of galactosylceramide and sulfatide, which should reduce sulfatide storage and improve pathology in ASA-deficient mice.

Results

ASA-/- CGT+/- mice, however, showed no detectable decrease in sulfatide storage. Neuronal degeneration of cells in the spiral ganglion of the inner ear, however, was decreased. Behavioural tests showed small but clear improvements of the phenotype in ASA-/- CGT+/- mice.

Conclusion

Thus the reduction of galactosylceramide and sulfatide biosynthesis by genetic means overall causes modest improvements of pathology.

Sulfatide with short fatty acid dominates in astrocytes and neurons

Glycosphingolipids are located in cell membranes and the brain is especially enriched. We speculated that the subcellular location of glycosphingolipids depends on their fatty acid chain length because their sugar residues are constant, whereas fatty acid chain length can vary within the same molecule. To test this hypothesis we analysed the glycosphingolipid sulfatide, which is highly abundant in myelin and has mostly long fatty acids. We used a negative ion electrospray tandem mass spectrometry precursor ion scan to analyse the molecular species of sulfatide in cultured astrocytes and a mouse model of the human disease metachromatic leukodystrophy. In these arylsulfatase A (ASA)-deficient mice sulfatide accumulates intracellularly in neurons and astrocytes. Immunocytochemistry was also performed on cultured astrocytes and analysed using confocal laser scanning microscopy. Analyses of the molecular species showed that cultured astrocytes contained sulfatide with a predominance of stearic acid (C18), which was located in large intracellular vesicles throughout the cell body and along the processes. The same was seen in ASA-deficient mice, which accumulated a higher proportion (15 mol% compared with 8 mol% in control mice) of sulfatide with stearic acid. We conclude that the major fatty acid composition of sulfatide differs between white and grey matter, with neurons and astrocytes containing mostly short-chain fatty acids with an emphasis on stearic acid. Based on our results, we speculate that the fatty acid chain length of sulfatide might determine its intracellular (short chain) or extracellular (long chain) location and thereby its functions.

Reduced brain cholesterol content in arylsulfatase A-deficient mice

Metachromatic leukodystrophy (MLD) is a lysosomal storage disorder caused by deficiency in arylsulfatase A (ASA). Concentrations of cholesterol and its metabolites were determined in ASA deficient [ASA(-/-)] mice which serve as an animal model of MLD. We observed a significant reduction in cholesterol content in the brain of adult ASA(-/-) mice when compared to wild-type controls. This was not due to loss of myelin, because ASA(-/-) mice do not demyelinate. Other cholesterol metabolites were not changed significantly in ASA(-/-) mice, except for an increase in lathosterol. Moreover, reduced cholesterol levels were also found in tissue samples from two juvenile MLD cases. Since high cholesterol levels are important for myelination, and various cellular processes, like vesicular trafficking and signal transduction, reduced cholesterol levels might be an important factor in the molecular pathology of MLD.