Bone marrow transplantation prolongs life span and ameliorates neurologic manifestations in Sandhoff disease mice

Gene Therapy Targeting GD3 Synthase Protects Against MPTP-Induced Parkinsonism and Executive Dysfunction

More than half of Parkinson's patients exhibit fronto-striatally mediated executive dysfunction, including deficits in sustained attention, judgment, and impulse control. We have previously shown that modification of brain gangliosides by targeted deletion of GD3 synthase (GD3S) is neuroprotective in vivo and in vitro. The objective of the present study was to determine whether GD3S knockdown will protect neurons and prevent executive dysfunction following a subchronic regimen of 25-mg/kg 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). C57BL/6N wild-type mice were assessed on a battery of sensorimotor tasks and a reaction-time task that included measures of sustained attention and impulse control. Sustained attention was measured by response accuracy and reaction time; impulsivity was measured by premature responding in the response holes or the food well during the precue period. After reaching stable performance, mice received intrastriatal injections of a recombinant adeno-associated viral (AAV) vector expressing a short-hairpin RNA (shRNA) construct targeting St8sia1, the gene that codes for GD3S, or a scrambled-sequence control (scrRNA). After 4 weeks, mice received MPTP or saline injections. MPTP-lesioned mice in the scrRNA control group exhibited loss of impulse control in the sessions following MPTP injections, compared to the other three groups. These deficits abated with extended training but re-emerged on challenge sessions with shorter cue durations or longer precue durations. GD3S knockdown partially protected nigrostriatal neurons from MPTP neurotoxicity and prevented the motor impairments (coordination, bradykinesia, fine motor skills) and loss of impulse control. Our data suggest that inhibition of GD3S warrants further investigation as a novel therapeutic strategy for Parkinson's disease.

Myeloid-derived β-hexosaminidase is essential for neuronal health and lysosome function: implications for Sandhoff disease

Lysosomal storage disorders (LSDs) are a large disease class involving lysosomal dysfunction, often resulting in neurodegeneration. Sandhoff disease (SD) is an LSD caused by a deficiency in the β subunit of the β-hexosaminidase enzyme (Hexb). Although Hexb expression in the brain is specific to microglia, SD primarily affects neurons. To understand how a microglial gene is involved in maintaining neuronal homeostasis, we demonstrated that β-hexosaminidase is secreted by microglia and integrated into the neuronal lysosomal compartment. To assess therapeutic relevance, we treated SD mice with bone marrow transplant and colony stimulating factor 1 receptor inhibition, which broadly replaced Hexb -/- microglia with Hexb-sufficient cells. This intervention reversed apoptotic gene signatures, improved behavior, restored enzymatic activity and Hexb expression, ameliorated substrate accumulation, and normalized neuronal lysosomal phenotypes. These results underscore the critical role of myeloid-derived β-hexosaminidase in neuronal lysosomal function and establish microglial replacement as a potential LSD therapy.

Gene and Cellular Therapies for Leukodystrophies

Leukodystrophies are a heterogenous group of inherited, degenerative encephalopathies, that if left untreated, are often lethal at an early age. Although some of the leukodystrophies can be treated with allogeneic hematopoietic stem cell transplantation, not all patients have suitable donors, and new treatment strategies, such as gene therapy, are rapidly being developed. Recent developments in the field of gene therapy for severe combined immune deficiencies, Leber's amaurosis, epidermolysis bullosa, Duchenne's muscular dystrophy and spinal muscular atrophy, have paved the way for the treatment of leukodystrophies, revealing some of the pitfalls, but overall showing promising results. Gene therapy offers the possibility for overexpression of secretable enzymes that can be released and through uptake, allow cross-correction of affected cells. Here, we discuss some of the leukodystrophies that have demonstrated strong potential for gene therapy interventions, such as X-linked adrenoleukodystrophy (X-ALD), and metachromatic leukodystrophy (MLD), which have reached clinical application. We further discuss the advantages and disadvantages of ex vivo lentiviral hematopoietic stem cell gene therapy, an approach for targeting microglia-like cells or rendering cross-correction. In addition, we summarize ongoing developments in the field of in vivo administration of recombinant adeno-associated viral (rAAV) vectors, which can be used for direct targeting of affected cells, and other recently developed molecular technologies that may be applicable to treating leukodystrophies in the future.

Efficacy and safety of miglustat in the treatment of GM2 gangliosidosis: A systematic review

BACKGROUND

Since the results of previous studies regarding the safety and efficacy of miglustat in GM2 gangliosidosis (GM2g) were inconsistent, we aimed to assess miglustat therapy in GM2g patients.

METHODS

This study followed the latest version of PRISMA. We included the observational or interventional studies reporting GM2g patients under miglustat therapy by searching PubMed, Web of Science, and Scopus. Data extracted included the natural history of individual patient data, as well as the safety and efficacy of miglustat in GM2g patients. The quality assessment was performed using the Joanna Briggs Institute Critical Appraisal checklist.

RESULTS

A total of 1023 records were identified and reduced to 621 after removing duplicates. After screening and applying the eligibility criteria, 10 articles and 2 abstracts met the inclusion criteria. Overall, the studies represented 54 patients with GM2g under treatment with miglustat and 22 patients with GM2g in the control group. Among patients with available data, 14 and 54 have been diagnosed with Sandhoff disease and Tay-Sachs disease, respectively. Patients included in this review consisted of 23 infantile, 4 late-infantile, 18 juvenile, and 31 adult-onset GM2g.

CONCLUSIONS

Although miglustat should not be considered a definite treatment for GM2g, it appears that patients, particularly those with infantile or late-infantile GM2g, could benefit from miglustat therapy to some extent. We also make some suggestions regarding future studies presenting their findings in a standard format to facilitate pooling the available data in such rare diseases for a more comprehensive conclusion.

Glb1 knockout mouse model shares natural history with type II GM1 gangliosidosis patients

GM1 gangliosidosis is a rare lysosomal storage disorder affecting multiple organ systems, primarily the central nervous system, and is caused by functional deficiency of β-galactosidase (GLB1). Using CRISPR/Cas9 genome editing, we generated a mouse model to evaluate characteristics of the disease in comparison to GM1 gangliosidosis patients. Our Glb1-/- mice contain small deletions in exons 2 and 6, producing a null allele. Longevity is approximately 50 weeks and studies demonstrated that female Glb1-/- mice die six weeks earlier than male Glb1-/- mice. Gait analyses showed progressive abnormalities including abnormal foot placement, decreased stride length and increased stance width, comparable with what is observed in type II GM1 gangliosidosis patients. Furthermore, Glb1-/- mice show loss of motor skills by 20 weeks assessed by adhesive dot, hanging wire, and inverted grid tests, and deterioration of motor coordination by 32 weeks of age when evaluated by rotarod testing. Brain MRI showed progressive cerebellar atrophy in Glb1-/- mice as seen in some patients. In addition, Glb1-/- mice also show significantly increased levels of a novel pentasaccharide biomarker in urine and plasma which we also observed in GM1 gangliosidosis patients. Glb1-/- mice also exhibit accumulation of glycosphingolipids in the brain with increases in GM1 and GA1 beginning by 8 weeks. Surprisingly, despite being a null variant, this Glb1-/- mouse most closely models the less severe type II disease and will guide the development of new therapies for patients with the disorder.

Therapeutic Strategies For Tay-Sachs Disease

Tay-Sachs disease (TSD) is an autosomal recessive disease that features progressive neurodegenerative presentations. It affects one in 100,000 live births. Currently, there is no approved therapy or cure. This review summarizes multiple drug development strategies for TSD, including enzyme replacement therapy, pharmaceutical chaperone therapy, substrate reduction therapy, gene therapy, and hematopoietic stem cell replacement therapy. In vitro and in vivo systems are described to assess the efficacy of the aforementioned therapeutic strategies. Furthermore, we discuss using MALDI mass spectrometry to perform a high throughput screen of compound libraries. This enables discovery of compounds that reduce GM2 and can lead to further development of a TSD therapy.

Therapeutic advantages of combined gene/cell therapy strategies in a murine model of GM2 gangliosidosis

Genetic deficiency of β-N-acetylhexosaminidase (Hex) functionality leads to accumulation of GM2 ganglioside in Tay-Sachs disease and Sandhoff disease (SD), which presently lack approved therapies. Current experimental gene therapy (GT) approaches with adeno-associated viral vectors (AAVs) still pose safety and efficacy issues, supporting the search for alternative therapeutic strategies. Here we leveraged the lentiviral vector (LV)-mediated intracerebral (IC) GT platform to deliver Hex genes to the CNS and combined this strategy with bone marrow transplantation (BMT) to provide a timely, pervasive, and long-lasting source of the Hex enzyme in the CNS and periphery of SD mice. Combined therapy outperformed individual treatments in terms of lifespan extension and normalization of the neuroinflammatory/neurodegenerative phenotypes of SD mice. These benefits correlated with a time-dependent increase in Hex activity and a remarkable reduction in GM2 storage in brain tissues that single treatments failed to achieve. Our results highlight the synergic mode of action of LV-mediated IC GT and BMT, clarify the contribution of treatments to the therapeutic outcome, and inform on the realistic threshold of corrective enzymatic activity. These results have important implications for interpretation of ongoing experimental therapies and for design of more effective treatment strategies for GM2 gangliosidosis.

Paradoxical immunodeficiencies-When failures of innate immunity cause immunopathology

Innate immunity facilitates immediate defense against invading pathogens throughout all organs and tissues but also mediates tissue homeostasis and repair, thereby playing a key role in health and development. Recognition of pathogens is mediated by germline-encoded PRRs. Depending on the specific PRRs triggered, ligand binding leads to phagocytosis and pathogen killing and the controlled release of immune-modulatory factors such as IFNs, cytokines, or chemokines. PRR-mediated and other innate immune responses do not only prevent uncontrolled replication of intruding pathogens but also contribute to the tailoring of an effective adaptive immune response. Therefore, hereditary or acquired immunodeficiencies impairing innate responses may paradoxically cause severe immunopathology in patients. This can occur in the context of, but also independently of an increased microbial burden. It can include pathogen-dependent organ damage, autoinflammatory syndromes, and neurodevelopmental or neurodegenerative diseases. Here, we discuss the current state of research of several different such immune paradoxes. Understanding the underlying mechanisms causing immunopathology as a consequence of failures of innate immunity may help to prevent life-threatening disease.

Lysosphingolipid urine screening test using mass spectrometry for the early detection of lysosomal storage disorders

Background: Sphingolipidoses are caused by a defective sphingolipid catabolism, leading to an accumulation of several glycolipid species in tissues and resulting in neurotoxicity and severe systemic manifestations. Methods & results: Urine samples from controls and patients were purified by solid-phase extraction prior to the analysis by ultra-high-performance liquid chromatography (UPLC) combined with MS/MS. A UPLC-MS/MS method for the analysis of 21 urinary creatinine-normalized biomarkers for eight diseases was developed and validated. Conclusion: Considering the growing demand to identify patients with different sphingolipidoses early and reliably, this methodology will be applied for high-risk screening to target efficiently patients with various sphingolipidoses.

[Glial cells and pharmacological targets in Sandhoff disease]

Sandhoff disease (SD) is a genetic disorder caused by a mutation in the β-hexosaminidase B (HexB) gene in humans. This results in the massive accumulation of GM2 gangliosides in the nervous system, causing progressive neurodegeneration. The symptoms of SD include muscle weakness, seizures, and mental illness;along with loss of muscle coordination, vision, and hearing. In the most severe form, the onset begins during early infancy, and death usually occurs within 3-5 years of age. The established animal model, Hexb-deficient (Hexb^-/-) mouse, shows abnormalities that resemble the severe phenotype found in human infants. We have previously reported that activated microglia causes astrogliosis in Hexb^-/- mouse at the early stage of development that can be ameliorated via immunosuppression. Moreover, within the cerebral cortices of Hexb^-/- mouse, reactive astrocytes were found to express adenosine A_2A receptors in later inflammatory phases. Inhibiting this receptor with istradefylline decreases the number of activated microglial cells and inflammatory cytokines/chemokines. Thus, we underline the importance of the astrocytic A_2A receptor as a sensor, in regulating microglial activation in the late phase of inflammation.

Motility Profile of Captive-Bred Marmosets Revealed by a Long-Term In-Cage Monitoring System

A quantitative evaluation of motility is crucial for studies employing experimental animals. Here, we describe the development of an in-cage motility monitoring method for new world monkeys using off-the-shelf components, and demonstrate its capability for long-term operation (e.g., a year). Based on this novel system, we characterized the motility of the common marmoset over different time scales (seconds, hours, days, and weeks). Monitoring of seven young animals belonging to two different age groups (sub-adult and young-adult) over a 231-day period revealed: (1) strictly diurnal activity (97.3% of movement during daytime), (2) short-cycle (∼20 s) transition in activity, and (3) bimodal diurnal activity including a "siesta" break. Additionally, while the mean duration of short-cycle activity, net daily activity, and diurnal activity changed over the course of development, 24-h periodicity remained constant. Finally, the method allowed for detection of progressive motility deterioration in a transgenic marmoset. Motility measurement offers a convenient way to characterize developmental and pathological changes in animals, as well as an economical and labor-free means for long-term evaluation in a wide range of basic and translational studies.

Genetic defects in the sphingolipid degradation pathway and their effects on microglia in neurodegenerative disease

Sphingolipids, which function as plasma membrane lipids and signaling molecules, are highly enriched in neuronal and myelin membranes in the nervous system. They are degraded in lysosomes by a defined sequence of enzymatic steps. In the related group of disorders, the sphingolipidoses, mutations in the genes that encode the individual degradative enzymes cause lysosomal accumulation of sphingolipids and often result in severe neurodegenerative disease. Here we review the information indicating that microglia, which actively clear sphingolipid-rich membranes in the brain during development and homeostasis, are directly affected by these mutations and promote neurodegeneration in the sphingolipidoses. We also identify parallels between the sphingolipidoses and more common forms of neurodegeneration, which both exhibit evidence of defective sphingolipid clearance in the nervous system.

Pre-clinical Mouse Models of Neurodegenerative Lysosomal Storage Diseases

There are over 50 lysosomal hydrolase deficiencies, many of which cause neurodegeneration, cognitive decline and death. In recent years, a number of broad innovative therapies have been proposed and investigated for lysosomal storage diseases (LSDs), such as enzyme replacement, substrate reduction, pharmacologic chaperones, stem cell transplantation, and various forms of gene therapy. Murine models that accurately reflect the phenotypes observed in human LSDs are critical for the development, assessment and implementation of novel translational therapies. The goal of this review is to summarize the neurodegenerative murine LSD models available that recapitulate human disease, and the pre-clinical studies previously conducted. We also describe some limitations and difficulties in working with mouse models of neurodegenerative LSDs.

Novel bicistronic lentiviral vectors correct β-Hexosaminidase deficiency in neural and hematopoietic stem cells and progeny: implications for in vivo and ex vivo gene therapy of GM2 gangliosidosis

The favorable outcome of in vivo and ex vivo gene therapy approaches in several Lysosomal Storage Diseases suggests that these treatment strategies might equally benefit GM2 gangliosidosis. Tay-Sachs and Sandhoff disease (the main forms of GM2 gangliosidosis) result from mutations in either the HEXA or HEXB genes encoding, respectively, the α- or β-subunits of the lysosomal β-Hexosaminidase enzyme. In physiological conditions, α- and β-subunits combine to generate β-Hexosaminidase A (HexA, αβ) and β-Hexosaminidase B (HexB, ββ). A major impairment to establishing in vivo or ex vivo gene therapy for GM2 gangliosidosis is the need to synthesize the α- and β-subunits at high levels and with the correct stoichiometric ratio, and to safely deliver the therapeutic products to all affected tissues/organs. Here, we report the generation and in vitro validation of novel bicistronic lentiviral vectors (LVs) encoding for both the murine and human codon optimized Hexa and Hexb genes. We show that these LVs drive the safe and coordinate expression of the α- and β-subunits, leading to supranormal levels of β-Hexosaminidase activity with prevalent formation of a functional HexA in SD murine neurons and glia, murine bone marrow-derived hematopoietic stem/progenitor cells (HSPCs), and human SD fibroblasts. The restoration/overexpression of β-Hexosaminidase leads to the reduction of intracellular GM2 ganglioside storage in transduced and in cross-corrected SD murine neural progeny, indicating that the transgenic enzyme is secreted and functional. Importantly, bicistronic LVs safely and efficiently transduce human neurons/glia and CD34+ HSPCs, which are target and effector cells, respectively, in prospective in vivo and ex vivo GT approaches. We anticipate that these bicistronic LVs may overcome the current requirement of two vectors co-delivering the α- or β-subunits genes. Careful assessment of the safety and therapeutic potential of these bicistronic LVs in the SD murine model will pave the way to the clinical development of LV-based gene therapy for GM2 gangliosidosis.

Substrate Reduction Therapy for Sandhoff Disease through Inhibition of Glucosylceramide Synthase Activity

Neuronopathic glycosphingolipidoses are a sub-group of lysosomal storage disorders for which there are presently no effective therapies. Here, we evaluated the potential of substrate reduction therapy (SRT) using an inhibitor of glucosylceramide synthase (GCS) to decrease the synthesis of glucosylceramide (GL1) and related glycosphingolipids. The substrates that accumulate in Sandhoff disease (e.g., ganglioside GM2 and its nonacylated derivative, lyso-GM2) are distal to the drug target, GCS. Treatment of Sandhoff mice with a GCS inhibitor that has demonstrated CNS access (Genz-682452) reduced the accumulation of GL1 and GM2, as well as a variety of disease-associated substrates in the liver and brain. Concomitant with these effects was a significant decrease in the expression of CD68 and glycoprotein non-metastatic melanoma B protein (Gpnmb) in the brain, indicating a reduction in microgliosis in the treated mice. Moreover, using in vivo imaging, we showed that the monocytic biomarker translocator protein (TSPO), which was elevated in Sandhoff mice, was normalized following Genz-682452 treatment. These positive effects translated in turn into a delay (∼28 days) in loss of motor function and coordination, as measured by rotarod latency, and a significant increase in longevity (∼17.5%). Together, these results support the development of SRT for the treatment of gangliosidoses, particularly in patients with residual enzyme activity.

Improvement in dysmyelination by the inhibition of microglial activation in a mouse model of Sandhoff disease

Sandhoff disease (SD) is a genetic disorder caused by a mutation of the β-subunit gene β-hexosaminidase B (HexB) in humans, which results in the massive accumulation of the ganglioside GM2 and related glycosphingolipids in the nervous system. SD causes progressive neurodegeneration and changes in white matter in human infants. An animal model of SD has been established, Hexb-deficient (Hexb) mice, which shows abnormalities resembling the severe phenotype found in human infants. Previously, we reported that the activation state of microglia caused astrogliosis in the early stage of Hexb mouse development. To study how the symptoms of SD develop, we explored the difference in gene expression between 4-week-old Hexb and Hexb mouse cerebral cortices by microarray analysis. The data indicated not only the upregulation of immune system-related genes but also the downregulation of myelin-related genes in the 4-week-old Hexb mouse cerebral cortices. To test the correlation between inflammation and dysmyelination, we generated double-knockout mice of Hexb and the Fc receptor γ gene (Fcrγ), which is a regulator of autoimmune responses. Dysmyelination recovered in these double-knockout mice. The number of oligodendrocyte progenitors, which expressed platelet-derived growth factor receptor-α, did not change in the 2-week-old mouse brain. These results indicate that microglial activation plays an important role in the myelination process, without influencing the number of oligodendrocyte progenitors, in the development of Hexb mice.

New Approaches to Tay-Sachs Disease Therapy

Tay-Sachs disease belongs to the group of autosomal-recessive lysosomal storage metabolic disorders. This disease is caused by β-hexosaminidase A (HexA) enzyme deficiency due to various mutations in α-subunit gene of this enzyme, resulting in GM2 ganglioside accumulation predominantly in lysosomes of nerve cells. Tay-Sachs disease is characterized by acute neurodegeneration preceded by activated microglia expansion, macrophage and astrocyte activation along with inflammatory mediator production. In most cases, the disease manifests itself during infancy, the “infantile form,” which characterizes the most severe disorders of the nervous system. The juvenile form, the symptoms of which appear in adolescence, and the most rare form with late onset of symptoms in adulthood are also described. The typical features of Tay-Sachs disease are muscle weakness, ataxia, speech, and mental disorders. Clinical symptom severity depends on residual HexA enzymatic activity associated with some mutations. Currently, Tay-Sachs disease treatment is based on symptom relief and, in case of the late-onset form, on the delay of progression. There are also clinical reports of substrate reduction therapy using miglustat and bone marrow or hematopoietic stem cell transplantation. At the development stage there are methods of Tay-Sachs disease gene therapy using adeno- or adeno-associated viruses as vectors for the delivery of cDNA encoding α and β HexA subunit genes. Effectiveness of this approach is evaluated in α or β HexA subunit defective model mice or Jacob sheep, in which Tay-Sachs disease arises spontaneously and is characterized by the same pathological features as in humans. This review discusses the possibilities of new therapeutic strategies in Tay-Sachs disease therapy aimed at preventing neurodegeneration and neuroinflammation.

Cerebral organoids derived from Sandhoff disease-induced pluripotent stem cells exhibit impaired neurodifferentiation

Sandhoff disease, one of the GM2 gangliosidoses, is a lysosomal storage disorder characterized by the absence of β-hexosaminidase A and B activity and the concomitant lysosomal accumulation of its substrate, GM2 ganglioside. It features catastrophic neurodegeneration and death in early childhood. How the lysosomal accumulation of ganglioside might affect the early development of the nervous system is not understood. Recently, cerebral organoids derived from induced pluripotent stem (iPS) cells have illuminated early developmental events altered by disease processes. To develop an early neurodevelopmental model of Sandhoff disease, we first generated iPS cells from the fibroblasts of an infantile Sandhoff disease patient, then corrected one of the mutant HEXB alleles in those iPS cells using CRISPR/Cas9 genome-editing technology, thereby creating isogenic controls. Next, we used the parental Sandhoff disease iPS cells and isogenic HEXB-corrected iPS cell clones to generate cerebral organoids that modeled the first trimester of neurodevelopment. The Sandhoff disease organoids, but not the HEXB-corrected organoids, accumulated GM2 ganglioside and exhibited increased size and cellular proliferation compared with the HEXB-corrected organoids. Whole-transcriptome analysis demonstrated that development was impaired in the Sandhoff disease organoids, suggesting that alterations in neuronal differentiation may occur during early development in the GM2 gangliosidoses.

Genetics and Therapies for GM2 Gangliosidosis

Tay-Sachs disease, caused by impaired β-N-acetylhexosaminidase activity, was the first GM2 gangliosidosis to be studied and one of the most severe and earliest lysosomal diseases to be described. The condition, associated with the pathological build-up of GM2 ganglioside, has acquired almost iconic status and serves as a paradigm in the study of lysosomal storage diseases. Inherited as a classical autosomal recessive disorder, this global disease of the nervous system induces developmental arrest with regression of attained milestones; neurodegeneration progresses rapidly to cause premature death in young children. There is no effective treatment beyond palliative care, and while the genetic basis of GM2 gangliosidosis is well established, the molecular and cellular events, from diseasecausing mutations and glycosphingolipid storage to disease manifestations, remain to be fully delineated. Several therapeutic approaches have been attempted in patients, including enzymatic augmentation, bone marrow transplantation, enzyme enhancement, and substrate reduction therapy. Hitherto, none of these stratagems has materially altered the course of the disease. Authentic animal models of GM2 gangliodidosis have facilitated in-depth evaluation of innovative applications such as gene transfer, which in contrast to other interventions, shows great promise. This review outlines current knowledge pertaining the pathobiology as well as potential innovative treatments for the GM2 gangliosidoses.

Haematopoietic Stem Cell Transplantation Arrests the Progression of Neurodegenerative Disease in Late-Onset Tay-Sachs Disease

Tay-Sachs disease is a rare metabolic disease caused by a deficiency of hexosaminidase A that leads to accumulation of GM2 gangliosides predominantly in neural tissue. Late-onset Tay-Sachs disease variant is associated with a higher level of residual HexA activity. Treatment options are limited, and there are a few described cases who have undergone haematopoietic stem cell transplantation (HSCT) with variable outcome.We describe a case of a 23-year-old male patient who presented with a long-standing tremor since 7 years of age. He had gait ataxia, a speech stammer and swallowing problems. His condition had had a static course apart from his tremor that had been gradually deteriorating. Because of the deterioration in his neurological function, the patient had an uneventful, matched-sibling donor bone marrow transplant at the age of 15 years. Eight years post-HSCT, at the age of 23, he retains full donor engraftment, and his white cell beta-HexA of 191 nmol/mg/h is comparable to normal controls (in-assay control = 187). He continues to experience some intentional tremor that is tolerable for daily life and nonprogressive since HSCT.

CONCLUSION

HSCT is a potential treatment option which might arrest neurodegeneration in patients with LOTS.

Targeted deletion of GD3 synthase protects against MPTP-induced neurodegeneration

Parkinson's disease is a debilitating neurodegenerative condition for which there is no cure. Converging evidence implicates gangliosides in the pathogenesis of several neurodegenerative diseases, suggesting a potential new class of therapeutic targets. We have shown that interventions that simultaneously increase the neuroprotective GM1 ganglioside and decrease the pro-apoptotic GD3 ganglioside - such as inhibition of GD3 synthase (GD3S) or administration of sialidase - are neuroprotective in vitro and in a number of preclinical models. In this study, we investigated the effects of GD3S deletion on parkinsonism induced by 1-methyl-4phenyl-1,2,3,6-tetrahydropyridine (MPTP). MPTP was administered to GD3S-/- mice or controls using a subchronic regimen consisting of three series of low-dose injections (11 mg/kg/day × 5 days each, 3 weeks apart), and motor function was assessed after each. The typical battery of tests used to assess parkinsonism failed to detect deficits in MPTP-treated mice. More sensitive measures - such as the force-plate actimeter and treadmill gait parameters - detected subtle effects of MPTP, some of which were absent in mice lacking GD3S. In wild-type mice, MPTP destroyed 53% of the tyrosine-hydroxylase (TH)-positive neurons in the substantia nigra pars compacta (SNc) and reduced striatal dopamine 60.7%. In contrast, lesion size was only 22.5% in GD3S-/- mice and striatal dopamine was reduced by 37.2%. Stereological counts of Nissl-positive SNc neurons that did not express TH suggest that neuroprotection was complete but TH expression was suppressed in some cells. These results show that inhibition of GD3S has neuroprotective properties in the MPTP model and may warrant further investigation as a therapeutic target.

Lysosomal Disorders Drive Susceptibility to Tuberculosis by Compromising Macrophage Migration

A zebrafish genetic screen for determinants of susceptibility to Mycobacterium marinum identified a hypersusceptible mutant deficient in lysosomal cysteine cathepsins that manifests hallmarks of human lysosomal storage diseases. Under homeostatic conditions, mutant macrophages accumulate undigested lysosomal material, which disrupts endocytic recycling and impairs their migration to, and thus engulfment of, dying cells. This causes a buildup of unengulfed cell debris. During mycobacterial infection, macrophages with lysosomal storage cannot migrate toward infected macrophages undergoing apoptosis in the tuberculous granuloma. The unengulfed apoptotic macrophages undergo secondary necrosis, causing granuloma breakdown and increased mycobacterial growth. Macrophage lysosomal storage similarly impairs migration to newly infecting mycobacteria. This phenotype is recapitulated in human smokers, who are at increased risk for tuberculosis. A majority of their alveolar macrophages exhibit lysosomal accumulations of tobacco smoke particulates and do not migrate to Mycobacterium tuberculosis. The incapacitation of highly microbicidal first-responding macrophages may contribute to smokers’ susceptibility to tuberculosis.

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Lysosomal storage diseases reduce macrophage endocytic recycling and migration

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Reduced macrophage migration increases tuberculosis severity via granuloma breakdown

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Tobacco smoke particles accumulate in lysosomes of smokers’ alveolar macrophages

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Lysosomal particles reduce smokers’ macrophage migration to infecting mycobacteria

Accumulated α-synuclein affects the progression of GM2 gangliosidoses

The accumulation of α-synuclein (ASyn) has been observed in several lysosomal storage diseases (LSDs) but it remains unclear if ASyn accumulation contributes to LSD pathology. ASyn also accumulates in the neurons of Sandhoff disease (SD) patients and SD model mice (Hexb-/- ASyn+/+ mice). SD is a lysosomal storage disorder caused by the absence of a functional β-subunit on the β-hexosaminidase A and B enzymes, which leads to the accumulation of ganglioside in the central nervous system. Here, we explored the role of accumulated ASyn in the progression of Hexb-/- mice by creating a Hexb-/- ASyn-/- double-knockout mice. Our results show that Hexb-/- ASyn-/- mice demonstrated active microglia levels and less dopaminergic neuron loss, without altering the neuronal storage of ganglioside. The autophagy and ubiquitin proteasome pathways are defective in the neurons of Hexb-/- ASyn+/+ mice. In ultrastructural physiological studies, the mitochondria structures look degenerated and dysfunctional. As a result, expression of manganese superoxide dismutase 2 are reduced, and reactive oxygen species-mediated oxidative damage in the neurons of Hexb-/- ASyn+/+ mice. Interestingly, these dysfunctions improved in Hexb-/- ASyn-/- mice. But any clinical improvement were hardly observed in Hexb-/- ASyn-/- mice. Taken together, these findings suggest that ASyn accumulation plays an important role in the pathogenesis of neuropathy in SD and other LSDs, and is therefore a target for novel therapies.

Suppression of the motor deficit in a mucolipidosis type IV mouse model by bone marrow transplantation

Mucolipidosis IV (MLIV) is a severe lysosomal storage disorder, which results from loss of the TRPML1 channel. MLIV causes multiple impairments in young children, including severe motor deficits. Currently, there is no effective treatment. Using a Drosophila MLIV model, we showed previously that introduction of trpml⁺ in phagocytic glia rescued the locomotor deficit by removing early dying neurons, thereby preventing amplification of neuronal death from cytotoxicity. Because microglia, which are phagocytic cells in the mammalian brain, are bone marrow derived, and cross the blood-brain barrier, we used a mouse MLIV model to test the efficacy of bone marrow transplantation (BMT). We found that BMT suppressed the reduced myelination and the increased caspase-3 activity due to loss of TRPML1. Using a rotarod test, we demonstrated that early BMT greatly delayed the motor impairment in the mutant mice. These data offer the possibility that BMT might provide the first therapy for MLIV.

The GM1 and GM2 Gangliosidoses: Natural History and Progress toward Therapy

The gangliosidoses are lysosomal storage disorders caused by accumulation of GM1 or GM2 gangliosides. GM1 gangliosidosis has both central nervous system and systemic findings; while, GM2 gangliosidosis is restricted primarily to the central nervous system. Both disorders have autosomal recessive modes of inheritance and a continuum of clinical presentations from a severe infantile form to a milder, chronic adult form. Both are devastating diseases without cure or specific treatment however, with the use of supportive aggressive medical management, the lifespan and quality of life has been extended for both diseases. Naturally occurring and engineered animal models that mimic the human diseases have enhanced our understanding of the pathogenesis of disease progression. Some models have shown significant improvement in symptoms and lifespan with enzyme replacement, substrate reduction, and anti-inflammatory treatments alone or in combination. More recently gene therapy has shown impressive results in large and small animal models. Treatment with FDA-approved glucose analogs to reduce the amount of ganglioside substrate is used as off-label treatments for some patients. Therapies also under clinical development include small molecule chaperones and gene therapy.

Enhancement by Uridine Diphosphate of Macrophage Inflammatory Protein-1 Alpha Production in Microglia Derived from Sandhoff Disease Model Mice

Sandhoff disease (SD) is a lysosomal β-hexosaminidase (Hex) deficiency involving excessive accumulation of undegraded substrates, including GM2 ganglioside, and progressive neurodegeneration. Macrophage inflammatory protein-1α (MIP-1α) is a crucial factor for microglia-mediated neuroinflammation in the onset or progression of SD. However, the transmitter-mediated production of MIP-1α in SD is still poorly understood.Extracellular nucleotides, including uridine diphosphate (UDP), leaked by either injured or damaged neuronal cells activate microglia to trigger chemotaxis, phagocytosis, macropinocytosis, and cytokine production.In this study, we demonstrated that UDP enhanced the production of MIP-1α by microglia derived from SD mice (SD-Mg), but not that from wild-type mice (WT-Mg). The UDP-induced MIP-1α production was mediated by the activation of P2Y6 receptor, ERK, and JNK. We also found the amount of dimeric P2Y6 receptor protein to have increased in SD-Mg in comparison to WT-Mg. In addition, we demonstrated that the disruption of lipid rafts enhanced the effect of UDP on MIP-1α production and the disordered maintenance of the lipid rafts in SD-Mg. Thus, the accumulation of undegraded substrates might cause the enhanced effect of UDP in SD-Mg through the increased expression of the dimeric P2Y6 receptors and the disordered maintenance of the lipid rafts. These findings provide new insights into the pathogenic mechanism and therapeutic strategies for SD.

AAV-mediated gene delivery in a feline model of Sandhoff disease corrects lysosomal storage in the central nervous system

Sandhoff disease (SD) is an autosomal recessive neurodegenerative disease caused by a mutation in the gene for the β-subunit of β-N-acetylhexosaminidase (Hex), resulting in the inability to catabolize ganglioside GM2 within the lysosomes. SD presents with an accumulation of GM2 and its asialo derivative GA2, primarily in the central nervous system. Myelin-enriched glycolipids, cerebrosides and sulfatides, are also decreased in SD corresponding with dysmyelination. At present, no treatment exists for SD. Previous studies have shown the therapeutic benefit of adeno-associated virus (AAV) vector-mediated gene therapy in the treatment of SD in murine and feline models. In this study, we treated presymptomatic SD cats with AAVrh8 vectors expressing feline Hex in the thalamus combined with intracerebroventricular (Thal/ICV) injections. Treated animals showed clearly improved neurologic function and quality of life, manifested in part by prevention or attenuation of whole-body tremors characteristic of untreated animals. Hex activity was significantly elevated, whereas storage of GM2 and GA2 was significantly decreased in tissue samples taken from the cortex, cerebellum, thalamus, and cervical spinal cord. Treatment also increased levels of myelin-enriched cerebrosides and sulfatides in the cortex and thalamus. This study demonstrates the therapeutic potential of AAV for feline SD and suggests a similar potential for human SD patients.

Delivering drugs to the central nervous system: an overview

Developing therapies for the brain is perhaps the greatest challenge facing modern medicine today. While a great many potential therapies show promise in animal models, precious few make it to approval or are even studied in human patients. The particular challenges to the translation of neurotherapeutics to the clinic are many, but a major barrier is difficulty in delivering therapeutics into the brain. The goal of this workshop was to present ways to deliver therapeutics to the brain, including the limitations of each method, and describe ways to track their delivery, safety, and efficacy. Solving the problem of delivery will aid translation of therapeutics for patients suffering from neurodegeneration and other disorders of the brain.

Widespread correction of central nervous system disease after intracranial gene therapy in a feline model of Sandhoff disease

Sandhoff disease (SD) is caused by deficiency of N-acetyl-β-hexosaminidase (Hex) resulting in pathological accumulation of GM2 ganglioside in lysosomes of the central nervous system (CNS) and progressive neurodegeneration. Currently, there is no treatment for SD, which often results in death by the age of five years. Adeno-associated virus (AAV) gene therapy achieved global CNS Hex restoration and widespread normalization of storage in the SD mouse model. Using a similar treatment approach, we sought to translate the outcome in mice to the feline SD model as an important step toward human clinical trials. Sixteen weeks after four intracranial injections of AAVrh8 vectors, Hex activity was restored to above normal levels throughout the entire CNS and in cerebrospinal fluid, despite a humoral immune response to the vector. In accordance with significant normalization of a secondary lysosomal biomarker, ganglioside storage was substantially improved, but not completely cleared. At the study endpoint, 5-month-old AAV-treated SD cats had preserved neurological function and gait compared with untreated animals (humane endpoint, 4.4±0.6 months) demonstrating clinical benefit from AAV treatment. Translation of widespread biochemical disease correction from the mouse to the feline SD model provides optimism for treatment of the larger human CNS with minimal modification of approach.

Ganglioside storage diseases: on the road to management

Although the biochemical and genetic basis for the GM1 and GM2 gangliosidoses has been known for decades, effective therapies for these diseases remain in early stages of development. The difficulty with many therapeutic strategies for treating the gangliosidoses comes largely from their inability to remove stored ganglioside once it accumulates in central nervous system (CNS) neurons and glia. This chapter highlights advances made using substrate reduction therapy and gene therapy in reducing CNS ganglioside storage. Information obtained from mouse and feline models provides insight on therapeutic strategies that could be effective in human clinical trials. In addition, information is presented showing how a calorie-restricted diet might facilitate therapeutic drug delivery to the CNS. The development of multiple new therapeutic approaches offers hope that longer-term management of these diseases can be achieved. It is also clear that multiple therapeutic strategies will likely be needed to provide the most complete management.

Impaired neural differentiation of induced pluripotent stem cells generated from a mouse model of Sandhoff disease

Sandhoff disease (SD) is a glycosphingolipid storage disease that arises from mutations in the Hexb gene and the resultant deficiency in β-hexosaminidase activity. This deficiency results in aberrant lysosomal accumulation of the ganglioside GM2 and related glycolipids, and progressive deterioration of the central nervous system. Dysfunctional glycolipid storage causes severe neurodegeneration through a poorly understood pathogenic mechanism. Induced pluripotent stem cell (iPSC) technology offers new opportunities for both elucidation of the pathogenesis of diseases and the development of stem cell-based therapies. Here, we report the generation of disease-specific iPSCs from a mouse model of SD. These mouse model-derived iPSCs (SD-iPSCs) exhibited pluripotent stem cell properties and significant accumulation of GM2 ganglioside. In lineage-directed differentiation studies using the stromal cell-derived inducing activity method, SD-iPSCs showed an impaired ability to differentiate into early stage neural precursors. Moreover, fewer neurons differentiated from neural precursors in SD-iPSCs than in the case of the wild type. Recovery of the Hexb gene in SD-iPSCs improved this impairment of neuronal differentiation. These results provide new insights as to understanding the complex pathogenic mechanisms of SD.

Ganglioside biochemistry

Gangliosides are sialic acid-containing glycosphingolipids. They occur especially on the cellular surfaces of neuronal cells, where they form a complex pattern, but are also found in many other cell types. The paper provides a general overview on their structures, occurrence, and metabolism. Key functional, biochemical, and pathobiochemical aspects are summarized.

A single intramuscular injection of rAAV-mediated mutant erythropoietin protects against MPTP-induced parkinsonism

Erythropoietin (Epo) is neuroprotective in a number of preparations, but can lead to unacceptably high and even lethal hematocrit levels. Recent reports show that modified Epo variants confer neuroprotection in models of glaucoma and retinal degeneration without raising hematocrit. In this study, neuroprotective effects of two Epo variants (EpoR76E and EpoS71E) were assessed in a model of Parkinson's disease. The constructs were packaged in recombinant adeno-associated viral (rAAV) vectors and injected intramuscularly. After 3 weeks, mice received five daily injections of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and were killed 5 weeks later. The MPTP-lesioned mice pretreated with rAAV.eGFP (negative control) exhibited a 7- to 9-Hz tremor and slower latencies to move on a grid test (akinesia). Both of these symptomatic features were absent in mice pretreated with either modified Epo construct. The rAAV.eGFP-treated mice lesioned with MPTP exhibited a 41% reduction in tyrosine hydroxylase (TH)-positive neurons in the substantia nigra. The rAAV.EpoS71E construct did not protect nigral neurons, but neuronal loss in mice pretreated with rAAV.EpoR76E was only half that of rAAV.eGFP controls. Although dopamine levels were normal in all groups, 3,4-dihydroxyphenylacetic acid (DOPAC) was significantly reduced only in MPTP-lesioned mice pretreated with rAAV.eGFP, indicating reduced dopamine turnover. Analysis of TH-positive fibers in the striatum showed normalized density in MPTP-lesioned mice pretreated with rAAV.EpoS71E, suggesting that enhanced sprouting induced by EpoS71E may have been responsible for normal behavior and dopaminergic tone in these mice. These results show that systemically administered rAAV-generated non-erythropoietic Epo may protect against MPTP-induced parkinsonism by a combination of neuroprotection and enhanced axonal sprouting.

Conditional expression of human β-hexosaminidase in the neurons of Sandhoff disease rescues mice from neurodegeneration but not neuroinflammation

This study evaluated whether GM₂ ganglioside storage is necessary for neurodegeneration and neuroinflammation by performing β-hexosaminidase rescue experiments in neurons of HexB^−/− mice. We developed a novel mouse model, whereby the expression of the human HEXB gene was targeted to neurons of HexB^−/− mice by the Thy1 promoter. Despite β-hexosaminidase restoration in neurons was sufficient in rescuing HexB^−/− mice from GM₂ neuronal storage and neurodegeneration, brain inflammation persisted, including the presence of large numbers of reactive microglia/macrophages due to persisting GM₂ presence in this cell type. In conclusion, our results suggest that neuroinflammation is not sufficient to elicit neurodegeneration as long as neuronal function is restored.

The cellular pathology of lysosomal diseases

With a constitutive recycling function and the capacity to digest exogenous material as well as endogenous organelles in the process of autophagy, lysosomes are at the heart of the living cell. Dynamic interactions with other cellular components ensure that the lysosomal compartment is a central point of convergence in countless diverse diseases. Inborn lysosomal (storage) diseases represent about 70 genetically distinct conditions, with a combined birth frequency of about 1 in 7500. Many are associated with macromolecular storage, causing physical disruption of the organelle and cognate structures; in neurons, ectopic dendritogenesis and axonal swelling due to distension with membraneous tubules and autophagic vacuoles are observed. Disordered autophagy is almost universal in lysosomal diseases but biochemical injury due to toxic metabolites such as lysosphingolipid molecules, abnormal calcium homeostasis and endoplasmic reticulum stress responses and immune-inflammatory processes occur. However, in no case have the mechanistic links between individual clinico-pathological manifestations and the underlying molecular defect been precisely defined. With access to the external fluid-phase and intracellular trafficking pathways, the lysosome and its diseases are a focus of pioneering investment in biotechnology; this has generated innovative orphan drugs and, in the case of Gaucher's disease, effective treatment for the haematological and visceral manifestations. Given that two-thirds of lysosomal diseases have potentially devastating consequences in the nervous system, future therapeutic research will require an integrative understanding of the unitary steps in their neuro pathogenesis. Informative genetic variants illustrated by patients with primary defects in this organelle offer unique insights into the central role of lysosomes in human health and disease. We provide a conspectus of inborn lysosomal diseases and their pathobiology; the cryptic evolution of events leading to irreversible changes may be dissociated from the cellular storage phenotype, as revealed by the outcome of therapeutic gene transfer undertaken at different stages of disease.

Intracranial V. cholerae sialidase protects against excitotoxic neurodegeneration

Converging evidence shows that GD3 ganglioside is a critical effector in a number of apoptotic pathways, and GM1 ganglioside has neuroprotective and noötropic properties. Targeted deletion of GD3 synthase (GD3S) eliminates GD3 and increases GM1 levels. Primary neurons from GD3S−/− mice are resistant to neurotoxicity induced by amyloid-β or hyperhomocysteinemia, and when GD3S is eliminated in the APP/PSEN1 double-transgenic model of Alzheimer's disease the plaque-associated oxidative stress and inflammatory response are absent. To date, no small-molecule inhibitor of GD3S exists. In the present study we used sialidase from Vibrio cholerae (VCS) to produce a brain ganglioside profile that approximates that of GD3S deletion. VCS hydrolyzes GD1a and complex b-series gangliosides to GM1, and the apoptogenic GD3 is degraded. VCS was infused by osmotic minipump into the dorsal third ventricle in mice over a 4-week period. Sensorimotor behaviors, anxiety, and cognition were unaffected in VCS-treated mice. To determine whether VCS was neuroprotective in vivo, we injected kainic acid on the 25th day of infusion to induce status epilepticus. Kainic acid induced a robust lesion of the CA3 hippocampal subfield in aCSF-treated controls. In contrast, all hippocampal regions in VCS-treated mice were largely intact. VCS did not protect against seizures. These results demonstrate that strategic degradation of complex gangliosides and GD3 can be used to achieve neuroprotection without adversely affecting behavior.

Thymic involution and corticosterone level in Sandhoff disease model mice: new aspects the pathogenesis of GM2 gangliosidosis

Sandhoff disease (SD) is a lysosomal disease caused by a mutation of the HEXB gene associated with excessive accumulation of GM2 ganglioside (GM2) in lysosomes and neurological manifestations. Production of autoantibodies against the accumulated gangliosides has been reported to be involved in the progressive pathogenesis of GM2 gangliosidosis, although the underlying mechanism has not been fully elucidated. The thymus is the key organ in the acquired immune system including the development of autoantibodies. We showed here that thymic involution and an increase in cell death in the organ occur in SD model mice at a late stage of the pathogenesis. Dramatic increases in the populations of Annexin-V(+) cells and terminal deoxynucletidyl transferase dUTP nick end labeling (TUNEL) (+) cells were observed throughout the thymuses of 15-week old SD mice. Enhanced caspase-3/7 activation, but not that of caspase-1/4, -6 ,-8, or -9, was also demonstrated. Furthermore, the serum level of corticosterone, a potent inducer of apoptosis of thymocytes, was elevated during the same period of apoptosis. Our studies suggested that an increase in endocrine corticosterone may be one of the causes that accelerate the apoptosis of thymocytes leading to thymic involution in GM2 gangliosidosis, and thus can be used as a disease marker for evaluation of the thymic condition and disease progression.

Adeno-associated virus-mediated expression of β-hexosaminidase prevents neuronal loss in the Sandhoff mouse brain

Sandhoff disease, a GM2 gangliosidosis caused by a deficiency in β-hexosaminidase, is characterized by progressive neurodegeneration. Although loss of neurons in association with lysosomal storage of glycosphingolipids occurs in patients with this disease, the molecular pathways that lead to the accompanying neurological defects are unclear. Using an authentic murine model of GM2 gangliosidosis, we examined the pattern of neuronal loss in the central nervous system and investigated the effects of gene transfer using recombinant adeno-associated viral vectors expressing β-hexosaminidase subunits (rAAV2/1-Hex). In 4-month-old Sandhoff mice with neurological deficits, cells staining positively for the apoptotic signature in the TUNEL reaction were found in the ventroposterior medial and ventroposterior lateral (VPM/VPL) nuclei of the thalamus. There was progressive loss of neuronal density in this region with age. Comparable loss of neuronal density was identified in the lateral vestibular nucleus of the brainstem and a small but statistically significant loss was present in the ventral spinal cord. Loss of neurons was not detected in other regions that were analysed. Administration of rAAV2/1-Hex into the brain of Sandhoff mice prevented the decline in neuronal density in the VPM/VPL. Preservation of neurons in the VPM/VPL was variable at the humane endpoint in treated animals, but correlated directly with increased lifespan. Loss of neurons was localized to only a few regions in the Sandhoff brain and was prevented by rAAV-mediated transfer of β-hexosaminidase gene function at considerable distances from the site of vector administration.

Iminosugar-based inhibitors of glucosylceramide synthase increase brain glycosphingolipids and survival in a mouse model of Sandhoff disease

The neuropathic glycosphingolipidoses are a subgroup of lysosomal storage disorders for which there are no effective therapies. A potential approach is substrate reduction therapy using inhibitors of glucosylceramide synthase (GCS) to decrease the synthesis of glucosylceramide and related glycosphingolipids that accumulate in the lysosomes. Genz-529468, a blood-brain barrier-permeant iminosugar-based GCS inhibitor, was used to evaluate this concept in a mouse model of Sandhoff disease, which accumulates the glycosphingolipid GM2 in the visceral organs and CNS. As expected, oral administration of the drug inhibited hepatic GM2 accumulation. Paradoxically, in the brain, treatment resulted in a slight increase in GM2 levels and a 20-fold increase in glucosylceramide levels. The increase in brain glucosylceramide levels might be due to concurrent inhibition of the non-lysosomal glucosylceramidase, Gba2. Similar results were observed with NB-DNJ, another iminosugar-based GCS inhibitor. Despite these unanticipated increases in glycosphingolipids in the CNS, treatment nevertheless delayed the loss of motor function and coordination and extended the lifespan of the Sandhoff mice. These results suggest that the CNS benefits observed in the Sandhoff mice might not necessarily be due to substrate reduction therapy but rather to off-target effects.

Gene therapy for lysosomal storage disorders

INTRODUCTION

Lysosomal storage disorders (LSDs) encompass more than 50 distinct diseases, caused by defects in various aspects of lysosomal function. Neurodegeneration and/or dysmyelination are the hallmark of roughly 70% of LSDs. Gene therapy represents a promising approach for the treatment of CNS manifestations in LSDs, as it has the potential to provide a permanent source of the deficient enzyme, either by direct injection of vectors or by transplantation of gene-corrected cells. In this latter approach, the biology of neural stem/progenitor cells and hematopoietic cells might be exploited.

AREAS COVERED

Based on an extensive literature search up until March 2011, the author reviews and discusses the progress, the crucial aspects and the major challenges towards the development of novel gene therapy strategies aimed to target the CNS, with particular attention to direct intracerebral gene delivery and transplantation of neural stem/progenitor cells.

EXPERT OPINION

The implementation of viral vector delivery systems with specific tropism, regulated transgene expression, low immunogenicity and low genotoxic risk and the improvement in isolation and manipulation of relevant cell types to be transplanted, are fundamental challenges to the field. Also, combinatorial strategies might be required to achieve full correction in LSDs with neurological involvement.

Prostaglandin E2 reverses aberrant production of an inflammatory chemokine by microglia from Sandhoff disease model mice through the cAMP-PKA pathway

Background

Sandhoff disease (SD) is a neurodegenerative lysosomal β-hexosaminidase (Hex) deficiency involving excessive accumulation of undegraded substrates, including terminal GlcNAc-oligosaccharides and GM2 ganglioside. Microglia-mediated neuroinflammation contributes to the pathogenesis and progression of SD. Our previous study demonstrated that MIP-1α, a putative pathogenic factor for SD, is up-regulated in microglial cells derived from SD model mice (SD-Mg) through activation of Akt and JNK.

Methodology/Principal Findings

In this study, we first demonstrated that prostaglandin E2 (PGE2), which is one of the lipid mediators derived from arachidonic acid and is known to suppress activation of microglia, reduced the aberrant MIP-1α production by SD-Mg to the same level as by WT-Mg. PGE2 also attenuated the activation of Akt and JNK. The inhibition of MIP-1α production and the activation of Akt and JNK occurred through the EP2 and 4/cAMP/PKA signaling pathway in the murine microglia derived from SD model mice.

Conclusions/Significance

We propose that PGE2 plays a role as a negative regulator of MIP-1α production in the pathogenesis of SD, and that PGE2-EP2 and 4/cAMP/PKA signaling could be a target pathway for therapy for SD.

Mouse mutagenesis and disease models for neuropsychiatric disorders

In this chapter, mutant mouse resources which have been developed by classical genetics as well as by modern large-scale mutagenesis projects are summarized. Various spontaneous and induced mouse mutations have been archived since the rediscovery of Mendel's genetics in 1900. Moreover, genome-wide, large-scale mutagenesis efforts have recently been expanding the available mutant mouse resources. Forward genetics projects using ENU mutagenesis in the mouse were started in the mid-1990s. The widespread adoption of reverse genetics, using knockouts and conditional mutagenesis based on gene-targeting technology, followed. ENU mutagenesis has now evolved to provide a further resource for reverse genetics, with multiple point mutations in a single gene and this new approach is described. Researchers now have various options to obtain mutant mice: point mutations, transgenic mouse strains, and constitutional or conditional knockout mice. The established mutant strains have already contributed to modeling human diseases by elucidating the underlying molecular mechanisms as well as by providing preclinical applications. Examples of mutant mice, focusing on neurological and behavioral models for human diseases, are reviewed. Human diseases caused by a single gene or a small number of major genes have been well modeled by corresponding mutant mice. Current evidence suggests that quantitative traits based on polygenes are likely to be associated with a range of psychiatric diseases, and these are now coming within the range of modeling by mouse mutagenesis.

Thymic alterations in GM2 gangliosidoses model mice

Background

Sandhoff disease is a lysosomal storage disorder characterized by the absence of β-hexosaminidase and storage of GM2 ganglioside and related glycolipids. We have previously found that the progressive neurologic disease induced in Hexb^−/− mice, an animal model for Sandhoff disease, is associated with the production of pathogenic anti-glycolipid autoantibodies.

Methodology/Principal Findings

In our current study, we report on the alterations in the thymus during the development of mild to severe progressive neurologic disease. The thymus from Hexb^−/− mice of greater than 15 weeks of age showed a marked decrease in the percentage of immature CD4⁺/CD8⁺ T cells and a significantly increased number of CD4⁺/CD8⁻ T cells. During involution, the levels of both apoptotic thymic cells and IgG deposits to T cells were found to have increased, whilst swollen macrophages were prominently observed, particularly in the cortex. We employed cDNA microarray analysis to monitor gene expression during the involution process and found that genes associated with the immune responses were upregulated, particularly those expressed in macrophages. CXCL13 was one of these upregulated genes and is expressed specifically in the thymus. B1 cells were also found to have increased in the thy mus. It is significant that these alterations in the thymus were reduced in FcRγ additionally disrupted Hexb^−/− mice.

Conclusions/Significance

These results suggest that the FcRγ chain may render the usually poorly immunogenic thymus into an organ prone to autoimmune responses, including the chemotaxis of B1 cells toward CXCL13.

Microglia and neuroprotection: from in vitro studies to therapeutic applications

Microglia are the main immune cells in the brain, playing a role in both physiological and pathological conditions. Microglial involvement in neurodegenerative diseases is well-established, being microglial activation and neuroinflammation common features of these neuropathologies. Microglial activation has been considered harmful for neurons, but inflammatory state is not only associated with neurotoxic consequences, but also with neuroprotective effects, such as phagocytosis of dead neurons and clearance of debris. This brought to the idea of protective autoimmunity in the brain and to devise immunomodulatory therapies, aimed to specifically increase neuroprotective aspects of microglia. During the last years, several data supported the intrinsic neuroprotective function of microglia through the release of neuroprotective molecules. These data led to change the traditional view of microglia in neurodegenerative diseases: from the idea that these cells play an detrimental role for neurons due to a gain of their inflammatory function, to the proposal of a loss of microglial neuroprotective function as a causing factor in neuropathologies. This "microglial dysfunction hypothesis" points at the importance of understanding the mechanisms of microglial-mediated neuroprotection to develop new therapies for neurodegenerative diseases. In vitro models are very important to clarify the basic mechanisms of microglial-mediated neuroprotection, mainly for the identification of potentially effective neuroprotective molecules, and to design new approaches in a gene therapy set-up. Microglia could act as both a target and a vehicle for CNS gene delivery of neuroprotective factors, endogenously produced by microglia in physiological conditions, thus strengthening the microglial neuroprotective phenotype, even in a pathological situation.

Glycosphingolipid storage leads to the enhanced degradation of the B cell receptor in Sandhoff disease mice

Glycosphingolipid storage diseases are a group of inherited metabolic diseases in which glycosphingolipids accumulate due to their impaired lysosomal breakdown. Splenic B cells isolated from NPC1, Sandhoff, GM1-gangliosidosis and Fabry disease mouse models showed large (20- to 30-fold) increases in disease specific glycosphingolipids and up to a 4-fold increase in cholesterol. The magnitude of glycosphingolipid storage was in the order NPC1 > Sandhoff approximately GM1 gangliosidosis > Fabry. Except for Fabry disease, glycosphingolipid storage led to an increase in the lysosomal compartment and altered glycosphingolipid trafficking. In order to investigate the consequences of storage on B cell function, the levels of surface expression of B cell IgM receptor and its associated components were quantitated in Sandhoff B cells, since they are all raft-associated on activation. Both the B cell receptor, CD21 and CD19 had decreased cell surface expression. In contrast, CD40 and MHC II, surface receptors that do not associate with lipid rafts, were unchanged. Using a pulse chase biotinylation procedure, surface B cell receptors on a Sandhoff lymphoblast cell line were found to have a significantly decreased half-life. Increased co-localization of fluorescently conjugated cholera toxin and lysosomes was also observed in Sandhoff B cells. Glycosphingolipid storage leads to the enhanced formation of lysosomal lipid rafts, altered endocytic trafficking and increased degradation of the B cell receptor.

Proteolytic processing of the gamma-subunit is associated with the failure to form GlcNAc-1-phosphotransferase complexes and mannose 6-phosphate residues on lysosomal enzymes in human macrophages

GlcNAc-1-phosphotransferase is a Golgi-resident 540-kDa complex of three subunits, alpha(2)beta(2)gamma(2), that catalyze the first step in the formation of the mannose 6-phosphate (M6P) recognition marker on lysosomal enzymes. Anti-M6P antibody analysis shows that human primary macrophages fail to generate M6P residues. Here we have explored the sorting and intracellular targeting of cathepsin D as a model, and the expression of the GlcNAc-1-phosphotransferase complex in macrophages. Newly synthesized cathepsin D is transported to lysosomes in an M6P-independent manner in association with membranes whereas the majority is secreted. Realtime PCR analysis revealed a 3-10-fold higher GlcNAc-1-phosphotransferase subunit mRNA levels in macrophages than in fibroblasts or HeLa cells. At the protein level, the gamma-subunit but not the beta-subunit was found to be proteolytically cleaved into three fragments which form irregular 97-kDa disulfide-linked oligomers in macrophages. Size exclusion chromatography showed that the gamma-subunit fragments lost the capability to assemble with other GlcNAc-1-phosphotransferase subunits to higher molecular complexes. These findings demonstrate that proteolytic processing of the gamma-subunit represents a novel mechanism to regulate GlcNAc-1-phosphotransferase activity and the subsequent sorting of lysosomal enzymes.