Therapeutic potential of intracerebroventricular replacement of modified human β-hexosaminidase B for GM2 gangliosidosis

Aberrant autophagy in lysosomal storage disorders marked by a lysosomal SNARE protein shortage due to suppression of endocytosis

Lysosomal storage disorders (LSDs) are inherited metabolic diseases caused by genetic defects in lysosomal enzymes or related factors. LSDs are associated with excessive accumulation of natural substrates in lysosomes leading to central nervous system and peripheral tissue damage. Abnormal autophagy is also involved in pathogenesis, although the underlying mechanisms remain unclear. We demonstrated that impairment of lysosome-autophagosome fusion is due to suppressed endocytosis in LSDs. The fusion was reduced in several LSD cells and the brains of LSD model mice, suggesting that the completion of autophagy is suppressed by the accumulation of substrates. In this brain, the expression of the soluble N-ethylmaleimide sensitive factor attachment protein receptor (SNARE) proteins, VAMP8 and Syntaxin7, was decreased on the lysosomal surface but not intracellular. This aberrant autophagy preceded the development of pathological phenotypes in LSD-model mice. Furthermore, the enzyme deficiency leading to the substrate accumulation could suppress endocytosis, and the inhibited endocytosis decreased SNARE proteins localized on lysosomes. These findings suggest that the shortage of SNARE proteins on lysosomes is one of the reasons for the impairment of lysosome-autophagosome fusion in LSD cells. Defects in lysosomal enzyme activity suppress endocytosis and decrease the supply of intracellular SNARE proteins recruited to lysosomes. This shortage of lysosomal SNARE proteins impairs lysosome-autophagosome fusion in lysosomal storage disorders.

Drug delivery for neuronopathic lysosomal storage diseases: evolving roles of the blood brain barrier and cerebrospinal fluid

Whereas significant strides have been made in the treatment of lysosomal storage diseases (LSDs), the neuronopathy associated with these diseases remains impervious mainly because of the blood-brain barrier (BBB), which prevents delivery of large molecules to the brain. However, 100 years of research on the BBB since its conceptualization have clarified many of its functional and structural characteristics, spurring recent endeavors to deliver therapeutics across it to treat central nervous system (CNS) disorders, including neuronopathic LSDs. Along with the BBB, the cerebrospinal fluid (CSF) also functions to protect the microenvironment of the CNS, and it is therefore deeply involved in CNS disorders at large. Recent research aimed at developing therapeutics for neuronopathic LSDs has uncovered a number of critical roles played by the CSF that require further clarification. This review summarizes the most up-to-date understanding of the BBB and the CSF acquired during the development of therapeutics for neuronopathic LSDs, and highlights some of the associated challenges that require further research.

Current treatment options and novel nanotechnology-driven enzyme replacement strategies for lysosomal storage disorders

Lysosomal storage disorders (LSDs) are a vast group of more than 50 clinically identified metabolic diseases. They are singly rare, but they affect collectively 1 on 5,000 live births. They result in most of the cases from an enzymatic defect within lysosomes, which causes the subsequent augmentation of unwanted substrates. This accumulation process leads to plenty of clinical signs, determined by the specific substrate and accumulation area. The majority of LSDs present a broad organ and tissue engagement. Brain, connective tissues, viscera and bones are usually afflicted. Among them, brain disease is markedly frequent (two-thirds of LSDs). The most clinically employed approach to treat LSDs is enzyme replacement therapy (ERT), which is practiced by administering systemically the missed or defective enzyme. It represents a healthful strategy for 11 LSDs at the moment, but it solves the pathology only in the case of Gaucher disease. This approach, in fact, is not efficacious in the case of LSDs that have an effect on the central nervous system (CNS) due to the existence of the blood-brain barrier (BBB). Additionally, ERT suffers from several other weak points, such as low penetration of the exogenously administered enzyme to poorly vascularized areas, the development of immunogenicity and infusion-associated reactions (IARs), and, last but not least, the very high cost and lifelong needed. To ameliorate these weaknesses lot of efforts have been recently spent around the development of innovative nanotechnology-driven ERT strategies. They may boost the power of ERT and minimize adverse reactions by loading enzymes into biodegradable nanomaterials. Enzyme encapsulation into biocompatible liposomes, micelles, and polymeric nanoparticles, for example, can protect enzymatic activity, eliminating immunologic reactions and premature enzyme degradation. It can also permit a controlled release of the payload, ameliorating pharmacokinetics and pharmacodynamics of the drug. Additionally, the potential to functionalize the surface of the nanocarrier with targeting agents (antibodies or peptides), could promote the passage through biological barriers. In this review we examined the clinically applied ERTs, highlighting limitations that do not allow to completely cure the specific LSD. Later, we critically consider the nanotechnology-based ERT strategies that have beenin-vitroand/orin-vivotested to improve ERT efficacy.

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.

[Progressive psychomotor regression for 2.5 years in a boy aged 5 years]

A boy, aged 5 years, attended the hospital due to progressive psychomotor regression for 2.5 years. Motor function regression was the main manifestation in the early stage, and brain MRI and whole-exome sequencing (WES) of the family showed no abnormalities. After the age of 4 years and 9 months, the boy developed cognitive function regression, and brain MRI showed cerebellar atrophy. The reanalysis of WES results revealed a compound heterozygous mutation, [NM_000520, c.784C>T(p.His262Tyr]), c.1412C>T(p.Pro471Leu)], in the HEXA gene. The enzyme activity detection showed a significant reduction in the level of β-hexosaminidase encoded by this gene. The boy was diagnosed with juvenile Tay-Sachs disease (TSD). TSD has strong clinical heterogeneity, and cerebellar atrophy may be an important clue for the diagnosis of juvenile TSD. The reanalysis of genetic data when appropriate based on disease evolution may improve the positive rate of WES.

Treatment of Neuronopathic Mucopolysaccharidoses with Blood-Brain Barrier-Crossing Enzymes: Clinical Application of Receptor-Mediated Transcytosis

Enzyme replacement therapy (ERT) has paved the way for treating the somatic symptoms of lysosomal storage diseases (LSDs), but the inability of intravenously administered enzymes to cross the blood-brain barrier (BBB) has left the central nervous system (CNS)-related symptoms of LSDs largely impervious to the therapeutic benefits of ERT, although ERT via intrathecal and intracerebroventricular routes can be used for some neuronopathic LSDs (in particular, mucopolysaccharidoses). However, the considerable practical issues involved make these routes unsuitable for long-term treatment. Efforts have been made to modify enzymes (e.g., by fusing them with antibodies against innate receptors on the cerebrovascular endothelium) so that they can cross the BBB via receptor-mediated transcytosis (RMT) and address neuronopathy in the CNS. This review summarizes the various scientific and technological challenges of applying RMT to the development of safe and effective enzyme therapeutics for neuronopathic mucopolysaccharidoses; it then discusses the translational and methodological issues surrounding preclinical and clinical evaluation to establish RMT-applied ERT.

Reversal of neuroinflammation in novel GS model mice by single i.c.v. administration of CHO-derived rhCTSA precursor protein

Galactosialidosis (GS) is a lysosomal cathepsin A (CTSA) deficiency. It associates with a simultaneous decrease of neuraminidase 1 (NEU1) activity and sialylglycan storage. Central nervous system (CNS) symptoms reduce the quality of life of juvenile/adult-type GS patients, but there is no effective therapy. Here, we established a novel GS model mouse carrying homozygotic Ctsa IVS6+1g→a mutation causing partial exon 6 skipping with concomitant deficiency of Ctsa/Neu1. The GS mice developed juvenile/adult GS-like symptoms, such as gargoyle-like face, edema, proctoprosia due to sialylglycan accumulation, and neurovisceral inflammation, including activated microglia/macrophage appearance and increase of inflammatory chemokines. We produced human CTSA precursor proteins (proCTSA), a homodimer carrying terminal mannose 6-phosphate (M6P)-type N-glycans. The CHO-derived proCTSA was taken up by GS patient-derived fibroblasts via M6P receptors and delivered to lysosomes. Catalytically active mature CTSA showed a shorter half-life due to intralysosomal proteolytic degradation. Following single i.c.v. administration, proCTSA was widely distributed, restored the Neu1 activity, and reduced the sialylglycans accumulated in brain regions. Moreover, proCTSA suppressed neuroinflammation associated with reduction of activated microglia/macrophage and up-regulated Mip1α. The results show therapeutic effects of intracerebrospinal enzyme replacement utilizing CHO-derived proCTSA and suggest suppression of CNS symptoms.

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.

Functionality of a bicistronic construction containing HEXA and HEXB genes encoding β-hexosaminidase A for cell-mediated therapy of GM2 gangliosidoses

Tay-Sachs disease and Sandhoff disease are severe hereditary neurodegenerative disorders caused by a deficiency of β-hexosaminidase A (HexA) enzyme, which results in the accumulation of GM2 gangliosides in the nervous system cells. In this work, we analyzed the efficacy and safety of cell-mediated gene therapy for Sandhoff disease and Sandhoff disease using a bicistronic lentiviral vector encoding cDNA of HexA α- and β-subunit genes separated by the nucleotide sequence of a P2A peptide (HEXA-HEXB). The functionality of the bicistronic construct containing the HEXA-HEXB genetic cassette was analyzed in a culture of HEK293T cells and human umbilical cord blood mononuclear cells (hUCBMCs). Our results showed that the enzymatic activity of HexA in the conditioned medium harvested from genetically modified HEK293T-HEXA-HEXB and hUCBMCs-HEXA-HEXB was increased by 23 and 8 times, respectively, compared with the conditioned medium of native cells. Western blot analysis showed that hUCBMCs-HEXA-HEXB secreted both completely separated HEXA and HEXB proteins, and an uncleaved protein containing HEXA + HEXB linked by the P2A peptide. Intravenous injection of genetically modified hUCBMCs-HEXA-HEXB to laboratory Wistar rats was carried out, and the HexA enzymatic activity in the blood plasma of experimental animals, as well as the number of live cells of immune system organs (spleen, thymus, bone marrow, lymph nodes) were determined. A significant increase in the enzymatic activity of HexA in the blood plasma of laboratory rats on days 6 and 9 (by 2.5 and 3 times, respectively) after the administration of hUCBMCs-HEXA-HEXB was shown. At the same time, the number of live cells in the studied organs remained unchanged. Thus, the functionality of the bicistronic genetic construct encoding cDNA of the HEXA and HEXB genes separated by the nucleotide sequence of the P2A peptide was shown in vitro and in vivo. We hypothesize that due to the natural ability of hUCBMCs to overcome biological barriers, such a strategy can restore the activity of the missing enzyme in the central nervous system of patients with GM2 gangliosidoses. Based on the obtained data, it can be concluded that intravenous administration of hUCBMCs with HexA overexpression is a promising method of the therapy for GM2 gangliosidoses. The animal protocol was approved by the Animal Ethics Committee of the Kazan Federal University (No. 23) on June 30, 2020.

Novel HEXA variants in Korean children with Tay-Sachs disease with regression of neurodevelopment from infancy

Background

Tay–Sachs disease (TSD) is a lysosomal storage disease caused by mutations in the HEXA gene that encodes the HexosaminidaseA (HEXA) enzyme. As HEXA normally functions to degrade the protein GM2‐ganglioside in lysosomes, decreased levels of HEXAcauses an accumulation of the protein and leads to neurological toxicity. Typical clinical manifestations of TSD include neurodevelopmental regression, muscle weakness, hypotonia, hyperreflexia, ataxia, seizures, and other neurological symptoms. It is quite rare in Asian populations, wherein only two cases have been reported in Korea to date.

Methods

Clinical records, radiological assessments, and laboratory findings, such as plasma hexosaminidase assay and HEXA analysis, were extracted from the medical records of three (1 male and 2 female) independent Korean children with infantile form of Tay–Sachs disease.

Results

All three children presented with neurodevelopmental regression and strabismus at around 8 months of age. Presence of cherry‐red spots in the macula led to conduction of biochemical and genetic studies for TSD confirmation. The plasma hexosaminidase assay revealed decreased HEXA activity and low to normal total hexosaminidase activity. Similarly, genetic analysis revealed 4 variants from 6 alleles, including 2 previously reported and 2 novel variants, in the HEXA gene.

Conclusion

We presented three Korean children, who were recently diagnosed with infantile‐type TSDvia enzyme assay and genetic analysis. Furthermore, results showed that fundus examination can be helpful for early diagnosis of children with neurodevelopmental regression.

Iduronate-2-sulfatase fused with anti-hTfR antibody, pabinafusp alfa, for MPS-II: A phase 2 trial in Brazil

In Hunter syndrome (mucopolysaccharidosis II [MPS-II]), systemic accumulation of glycosaminoglycans (GAGs) due to a deficiency of iduronate-2-sulfatase (IDS), caused by mutations in the IDS gene, leads to multiple somatic manifestations and in patients with the severe (neuronopathic) phenotype, also to central nervous system (CNS) involvement. These symptoms cannot be effectively treated with current enzyme-replacement therapies, as they are unable to cross the blood-brain barrier (BBB). Pabinafusp alfa, a novel IDS fused with an anti-human transferrin receptor antibody, was shown to penetrate the BBB and to address neurodegeneration in preclinical studies. Subsequent phase 1/2 and 2/3 clinical studies in Japan have shown marked reduction of GAG accumulation in the cerebrospinal fluid (CSF), along with favorable clinical responses. A 26-week, open-label, randomized, parallel-group phase 2 study was conducted in Brazil to further evaluate the safety and efficacy of intravenously administered pabinafusp alfa at 1.0, 2.0, and 4.0 mg/kg/week in MPS-II patients. The safety profiles in the three dosage groups were similar. Neurodevelopmental evaluation suggested positive neurocognitive signals despite a relatively short study period. The 2.0-mg/kg group, which demonstrated marked reductions in substrate concentrations in the CSF, serum, and urine, was considered to provide the best combination regarding safety and efficacy signals.

Human recombinant lysosomal β-Hexosaminidases produced in Pichia pastoris efficiently reduced lipid accumulation in Tay-Sachs fibroblasts

GM2 gangliosidosis, Tay-Sachs and Sandhoff diseases, are lysosomal storage disorders characterized by the lysosomal accumulation of GM2 gangliosides. This accumulation is due to deficiency in the activity of the β-hexosaminidases Hex-A or Hex-B, which are dimeric hydrolases formed by αβ or ββ subunits, respectively. These disorders show similar clinical manifestations that range from mild systemic symptoms to neurological damage and premature death. There is still no effective therapy for GM2 gangliosidoses, but some therapeutic alternatives, as enzyme replacement therapy, have being evaluated. Previously, we reported the production of active human recombinant β-hexosaminidases (rhHex-A and rhHex-B) in the methylotrophic yeast Pichia pastoris. In this study, we evaluated in vitro the cellular uptake, intracellular delivery to lysosome, and reduction of stored substrates. Both enzymes were taken-up via endocytic pathway mediated by mannose and mannose-6-phosphate receptors and delivered to lysosomes. Noteworthy, rhHex-A diminished the levels of stored lipids and lysosome mass in fibroblasts from Tay-Sachs patients. Overall, these results confirm the potential of P. pastoris as host to produce recombinant β-hexosaminidases intended to be used in the treatment of GM2 gangliosidosis.

A Phase 2/3 Trial of Pabinafusp Alfa, IDS Fused with Anti-Human Transferrin Receptor Antibody, Targeting Neurodegeneration in MPS-II

Pabinafusp alfa (JR-141) is a novel enzyme drug that crosses the blood-brain barrier by transcytosis via transferrin receptors. In order to establish its efficacy and safety, a multicenter, single-arm, open-label phase 2/3 clinical trial was conducted in 28 Japanese patients with mucopolysaccharidosis II (MPS-II, Hunter syndrome) by intravenous administrations of 2.0 mg/kg of pabinafusp alfa for 52 weeks. The primary efficacy endpoint was changes in heparan sulfate (HS) concentrations in the cerebrospinal fluid (CSF). Secondary endpoints included assessments of neurocognitive development for central efficacy, and changes in plasma HS and dermatan sulfate (DS) concentrations for peripheral efficacy. HS concentrations in the CSF significantly decreased from baseline to week 52 (p < 0.001), suggesting continuous inhibition of substrate accumulations in the CNS, i.e., hitherto unaddressed progressive neurodegeneration. Evaluations of neurocognitive developments showed positive changes in 21 of the 28 patients. Serum HS and DS concentrations, liver and spleen volumes, and other assessments suggested the peripheral efficacy of pabinafusp alfa was comparable to that of idursulfase. Drug-related adverse events were mild or moderate in severity, transient, and manageable. The results establish delivery across the BBB of pabinafusp alfa as an effective therapeutic for treating both the CNS and peripheral symptoms of patients with MPS-II.

GM2 Gangliosidoses: Clinical Features, Pathophysiological Aspects, and Current Therapies

GM2 gangliosidoses are a group of pathologies characterized by GM2 ganglioside accumulation into the lysosome due to mutations on the genes encoding for the β-hexosaminidases subunits or the GM2 activator protein. Three GM2 gangliosidoses have been described: Tay-Sachs disease, Sandhoff disease, and the AB variant. Central nervous system dysfunction is the main characteristic of GM2 gangliosidoses patients that include neurodevelopment alterations, neuroinflammation, and neuronal apoptosis. Currently, there is not approved therapy for GM2 gangliosidoses, but different therapeutic strategies have been studied including hematopoietic stem cell transplantation, enzyme replacement therapy, substrate reduction therapy, pharmacological chaperones, and gene therapy. The blood-brain barrier represents a challenge for the development of therapeutic agents for these disorders. In this sense, alternative routes of administration (e.g., intrathecal or intracerebroventricular) have been evaluated, as well as the design of fusion peptides that allow the protein transport from the brain capillaries to the central nervous system. In this review, we outline the current knowledge about clinical and physiopathological findings of GM2 gangliosidoses, as well as the ongoing proposals to overcome some limitations of the traditional alternatives by using novel strategies such as molecular Trojan horses or advanced tools of genome editing.

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.

Intravenous administration of scAAV9-Hexb normalizes lifespan and prevents pathology in Sandhoff disease mice

Sandhoff disease (SD) is a rare inherited disorder caused by a deficiency of β-hexosaminidase activity which is fatal because no effective treatment is available. A mouse model of Hexb deficiency reproduces the key pathognomonic features of SD patients with severe ubiquitous lysosomal dysfunction, GM2 accumulation, neuroinflammation and neurodegeneration, culminating in death at 4 months. Here, we show that a single intravenous neonatal administration of a self-complementary adeno-associated virus 9 vector (scAAV9) expressing the Hexb cDNA in SD mice is safe and sufficient to prevent disease development. Importantly, we demonstrate for the first time that this treatment results in a normal lifespan (over 700 days) and normalizes motor function assessed by a battery of behavioral tests, with scAAV9-treated SD mice being indistinguishable from wild-type littermates. Biochemical analyses in multiple tissues showed a significant increase in hexosaminidase A activity, which reached 10-15% of normal levels. AAV9 treatment was sufficient to prevent GM2 and GA2 storage almost completely in the cerebrum (less so in the cerebellum), as well as thalamic reactive gliosis and thalamocortical neuron loss in treated Hexb-/- mice. In summary, this study demonstrated a widespread protective effect throughout the entire CNS after a single intravenous administration of the scAAV9-Hexb vector to neonatal SD mice.

Iduronate-2-Sulfatase with Anti-human Transferrin Receptor Antibody for Neuropathic Mucopolysaccharidosis II: A Phase 1/2 Trial

Hunter syndrome (mucopolysaccharidosis II [MPS II]), a deficiency of iduronate-2-sulfatase (IDS), causes an accumulation of glycosaminoglycans, giving rise to multiple systemic and CNS symptoms. The currently available therapies, idursulfase and idursulfase beta, are ineffective against the CNS symptoms because they cannot pass the blood-brain barrier (BBB). A novel IDS fused with anti-human transferrin receptor antibody (JR-141) has been shown to penetrate the BBB and ameliorate learning deficits in model mice. This first-in-human study evaluated the pharmacokinetics, safety, and potential efficacy of JR-141 in 14 patients with MPS II. In a dose-escalation study performed in two patients, JR-141 plasma concentrations were dose dependent and peaked at 3 hr after initiation of each infusion, and no or only mild adverse reactions were exhibited. In a subsequent 4-week evaluation at two dose levels, the plasma concentration profiles were similar between the first and final administration, indicating no drug accumulation. Levels of heparan sulfate (HS) and dermatan sulfate (DS) were suppressed in both plasma and urine and HS levels were significantly decreased in cerebrospinal fluid. Two patients experienced some amelioration of neurocognitive and motor symptoms. These results suggest that the drug successfully penetrates the BBB and could have CNS efficacy.

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.

Progranulin associates with hexosaminidase A and ameliorates GM2 ganglioside accumulation and lysosomal storage in Tay-Sachs disease

Tay-Sachs disease (TSD) is a lethal lysosomal storage disease (LSD) caused by mutations in the HexA gene, which can lead to deficiency of β-hexosaminidase A (HexA) activity and consequent accumulation of its substrate, GM2 ganglioside. Recent reports that progranulin (PGRN) functions as a chaperone of lysosomal enzymes and its deficiency is associated with LSDs, including Gaucher disease and neuronal ceroid lipofuscinosis, prompted us to screen the effects of recombinant PGRN on lysosomal storage in fibroblasts from 11 patients affected by various LSDs, which led to the isolation of TSD in which PGRN demonstrated the best effects in reducing lysosomal storage. Subsequent in vivo studies revealed significant GM2 accumulation and the existence of typical TSD cells containing zebra bodies in both aged and ovalbumin-challenged adult PGRN-deficient mice. In addition, HexA, but not HexB, was aggregated in PGRN-deficient cells. Furthermore, recombinant PGRN significantly reduced GM2 accumulation and lysosomal storage in these animal models. Mechanistic studies indicated that PGRN bound to HexA through granulins G and E domain and increased the enzymatic activity and lysosomal delivery of HexA. More importantly, Pcgin, an engineered PGRN derivative bearing the granulin E domain, also effectively bound to HexA and reduced the GM2 accumulation. Collectively, these studies not only provide new insights into the pathogenesis of TSD but may also have implications for developing PGRN-based therapy for this life-threatening disorder. KEY MESSAGES: GM2 accumulation and the existence of typical TSD cells containing zebra bodies are detected in both aged and ovalbumin-challenged adult PGRN deficient mice. Recombinant PGRN significantly reduces GM2 accumulation and lysosomal storage both in vivo and in vitro, which works through increasing the expression and lysosomal delivery of HexA. Pcgin, an engineered PGRN derivative bearing the granulin E domain, also effectively binds to to HexA and reduces GM2 accumulation.

Neural stem cells for disease modeling and evaluation of therapeutics for Tay-Sachs disease

Background

Tay-Sachs disease (TSD) is a rare neurodegenerative disorder caused by autosomal recessive mutations in the HEXA gene on chromosome 15 that encodes β-hexosaminidase. Deficiency in HEXA results in accumulation of GM2 ganglioside, a glycosphingolipid, in lysosomes. Currently, there is no effective treatment for TSD.

Results

We generated induced pluripotent stem cells (iPSCs) from two TSD patient dermal fibroblast lines and further differentiated them into neural stem cells (NSCs). The TSD neural stem cells exhibited a disease phenotype of lysosomal lipid accumulation. The Tay-Sachs disease NSCs were then used to evaluate the therapeutic effects of enzyme replacement therapy (ERT) with recombinant human Hex A protein and two small molecular compounds: hydroxypropyl-β-cyclodextrin (HPβCD) and δ-tocopherol. Using this disease model, we observed reduction of lipid accumulation by employing enzyme replacement therapy as well as by the use of HPβCD and δ-tocopherol.

Conclusion

Our results demonstrate that the Tay-Sachs disease NSCs possess the characteristic phenotype to serve as a cell-based disease model for study of the disease pathogenesis and evaluation of drug efficacy. The enzyme replacement therapy with recombinant Hex A protein and two small molecules (cyclodextrin and tocopherol) significantly ameliorated lipid accumulation in the Tay-Sachs disease cell model.

Electronic supplementary material

The online version of this article (10.1186/s13023-018-0886-3) contains supplementary material, which is available to authorized users.

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.

Novel Vector Design and Hexosaminidase Variant Enabling Self-Complementary Adeno-Associated Virus for the Treatment of Tay-Sachs Disease

GM2 gangliosidosis is a family of three genetic neurodegenerative disorders caused by the accumulation of GM2 ganglioside (GM2) in neuronal tissue. Two of these are due to the deficiency of the heterodimeric (α-β), "A" isoenzyme of lysosomal β-hexosaminidase (HexA). Mutations in the α-subunit (encoded by HEXA) lead to Tay-Sachs disease (TSD), whereas mutations in the β-subunit (encoded by HEXB) lead to Sandhoff disease (SD). The third form results from a deficiency of the GM2 activator protein (GM2AP), a substrate-specific cofactor for HexA. In their infantile, acute forms, these diseases rapidly progress with mental and psychomotor deterioration resulting in death by approximately 4 years of age. After gene transfer that overexpresses one of the deficient subunits, the amount of HexA heterodimer formed would empirically be limited by the availability of the other endogenous Hex subunit. The present study used a new variant of the human HexA α-subunit, μ, incorporating critical sequences from the β-subunit that produce a stable homodimer (HexM) and promote functional interactions with the GM2AP- GM2 complex. We report the design of a compact adeno-associated viral (AAV) genome using a synthetic promoter-intron combination to allow self-complementary (sc) packaging of the HEXM gene. Also, a previously published capsid mutant, AAV9.47, was used to deliver the gene to brain and spinal cord while having restricted biodistribution to the liver. The novel capsid and cassette design combination was characterized in vivo in TSD mice for its ability to efficiently transduce cells in the central nervous system when delivered intravenously in both adult and neonatal mice. This study demonstrates that the modified HexM is capable of degrading long-standing GM2 storage in mice, and it further demonstrates the potential of this novel scAAV vector design to facilitate widespread distribution of the HEXM gene or potentially other similar-sized genes to the nervous system.

Lysosomal storage diseases

Lysosomes are cytoplasmic organelles that contain a variety of different hydrolases. A genetic deficiency in the enzymatic activity of one of these hydrolases will lead to the accumulation of the material meant for lysosomal degradation. Examples include glycogen in the case of Pompe disease, glycosaminoglycans in the case of the mucopolysaccharidoses, glycoproteins in the cases of the oligosaccharidoses, and sphingolipids in the cases of Niemann-Pick disease types A and B, Gaucher disease, Tay-Sachs disease, Krabbe disease, and metachromatic leukodystrophy. Sometimes, the lysosomal storage can be caused not by the enzymatic deficiency of one of the hydrolases, but by the deficiency of an activator protein, as occurs in the AB variant of GM2 gangliosidosis. Still other times, the accumulated lysosomal material results from failed egress of a small molecule as a consequence of a deficient transporter, as in cystinosis or Salla disease. In the last couple of decades, enzyme replacement therapy has become available for a number of lysosomal storage diseases. Examples include imiglucerase, taliglucerase and velaglucerase for Gaucher disease, laronidase for Hurler disease, idursulfase for Hunter disease, elosulfase for Morquio disease, galsulfase for Maroteaux-Lamy disease, alglucosidase alfa for Pompe disease, and agalsidase alfa and beta for Fabry disease. In addition, substrate reduction therapy has been approved for certain disorders, such as eliglustat for Gaucher disease. The advent of treatment options for some of these disorders has led to newborn screening pilot studies, and ultimately to the addition of Pompe disease and Hurler disease to the Recommended Uniform Screening Panel (RUSP) in 2015 and 2016, respectively.

A Prospective Treatment Option for Lysosomal Storage Diseases: CRISPR/Cas9 Gene Editing Technology for Mutation Correction in Induced Pluripotent Stem Cells

Ease of design, relatively low cost and a multitude of gene-altering capabilities have all led to the adoption of the sophisticated and yet simple gene editing system: clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9 (CRISPR/Cas9). The CRISPR/Cas9 system holds promise for the correction of deleterious mutations by taking advantage of the homology directed repair pathway and by supplying a correction template to the affected patient's cells. Currently, this technique is being applied in vitro in human-induced pluripotent stem cells (iPSCs) to correct a variety of severe genetic diseases, but has not as of yet been used in iPSCs derived from patients affected with a lysosomal storage disease (LSD). If adopted into clinical practice, corrected iPSCs derived from cells that originate from the patient themselves could be used for therapeutic amelioration of LSD symptoms without the risks associated with allogeneic stem cell transplantation. CRISPR/Cas9 editing in a patient's cells would overcome the costly, lifelong process associated with currently available treatment methods, including enzyme replacement and substrate reduction therapies. In this review, the overall utility of the CRISPR/Cas9 gene editing technique for treatment of genetic diseases, the potential for the treatment of LSDs and methods currently employed to increase the efficiency of this re-engineered biological system will be discussed.

Tailored Synthesis of 162-Residue S-Monoglycosylated GM2-Activator Protein (GM2AP) Analogues that Allows Facile Access to a Protein Library

A synthetic protocol for the preparation of 162-residue S-monoglycosylated GM2-activator protein (GM2AP) analogues bearing various amino acid substitutions for Thr69 has been developed. The facile incorporation of the replacements into the protein was achieved by means of a one-pot/N-to-C-directed sequential ligation strategy using readily accessible middle N-sulfanylethylanilide (SEAlide) peptides each consisting of seven amino acid residues. A kinetically controlled ligation protocol was successfully applied to the assembly of three peptide segments covering the GM2AP. The native chemical ligation (NCL) reactivities of the SEAlide peptides can be tuned by the presence or absence of phosphate salts. Furthermore, NCL of the alkyl thioester fragment [GM2AP (1-31)] with the N-terminal cysteinyl prolyl thioester [GM2AP (32-67)] proceeded smoothly to yield the 67-residue prolyl thioester, with the prolyl thioester moiety remaining intact. This newly developed strategy enabled the facile synthesis of GM2AP analogues. Thus, we refer to this synthetic protocol as "tailored synthesis" for the construction of a GM2AP library.

Combined replacement effects of human modified β-hexosaminidase B and GM2 activator protein on GM2 gangliosidoses fibroblasts

GM2 gangliosidoses are autosomal recessive lysosomal storage diseases (LSDs) caused by mutations in the HEXA, HEXB and GM2A genes, which encode the human lysosomal β-hexosaminidase (Hex) α- and β-subunits, and GM2 activator protein (GM2A), respectively. These diseases are associated with excessive accumulation of GM2 ganglioside (GM2) in the brains of patients with neurological symptoms. Here we established a CHO cell line overexpressing human GM2A, and purified GM2A from the conditioned medium, which was taken up by fibroblasts derived from a patient with GM2A deficiency, and had the therapeutic effects of reducing the GM2 accumulated in fibroblasts when added to the culture medium. We also demonstrated for the first time that recombinant GM2A could enhance the replacement effect of human modified HexB (modB) with GM2-degrading activity, which is composed of homodimeric altered β-subunits containing a partial amino acid sequence of the α-subunit, including the GSEP loop necessary for binding to GM2A, on reduction of the GM2 accumulated in fibroblasts derived from a patient with Tay-Sachs disease, a HexA (αβ heterodimer) deficiency, caused by HEXA mutations. We predicted the same manner of binding of GM2A to the GSEP loop located in the modified HexB β-subunit to that in the native HexA α-subunit on the basis of the x-ray crystal structures. These findings suggest the effectiveness of combinational replacement therapy involving the human modified HexB and GM2A for GM2 gangliosidoses.

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Purification of recombinant human GM2A proteins by CHO cell line overexpressing GM2A.

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Reduction of GM2 accumulated in GM2A deficiency fibroblasts by GM2A replacement.

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Combined effects of modified HexB and GM2A for HexA deficiency fibroblasts.

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In silico prediction of molecular interaction between modified HexB and GM2A.

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.

Protease-resistant modified human β-hexosaminidase B ameliorates symptoms in GM2 gangliosidosis model

GM2 gangliosidoses, including Tay-Sachs and Sandhoff diseases, are neurodegenerative lysosomal storage diseases that are caused by deficiency of β-hexosaminidase A, which comprises an αβ heterodimer. There are no effective treatments for these diseases; however, various strategies aimed at restoring β-hexosaminidase A have been explored. Here, we produced a modified human hexosaminidase subunit β (HexB), which we have termed mod2B, composed of homodimeric β subunits that contain amino acid sequences from the α subunit that confer GM2 ganglioside-degrading activity and protease resistance. We also developed fluorescent probes that allow visualization of endocytosis of mod2B via mannose 6-phosphate receptors and delivery of mod2B to lysosomes in GM2 gangliosidosis models. In addition, we applied imaging mass spectrometry to monitor efficacy of this approach in Sandhoff disease model mice. Following i.c.v. administration, mod2B was widely distributed and reduced accumulation of GM2, asialo-GM2, and bis(monoacylglycero)phosphate in brain regions including the hypothalamus, hippocampus, and cerebellum. Moreover, mod2B administration markedly improved motor dysfunction and a prolonged lifespan in Sandhoff disease mice. Together, the results of our study indicate that mod2B has potential for intracerebrospinal fluid enzyme replacement therapy and should be further explored as a gene therapy for GM2 gangliosidoses.

Expression of human β-N-acetylhexosaminidase B in yeast eases the search for selective inhibitors

Human lysosomal β-N-acetylhexosaminidases from the family 20 of glycoside hydrolases are dimeric enzymes catalysing the cleavage of terminal β-N-acetylglucosamine and β-N-acetylgalactosamine residues from a broad spectrum of glycoconjugates. Here, we present a facile, robust, and cost-effective extracellular expression of human β-N-acetylhexosaminidase B in Pichia pastoris KM71H strain. The prepared Hex B was purified in a single step with 33% yield obtaining 10mg of the pure enzyme per 1L of the culture media. The enzyme was used in the inhibition assays with the known mechanism-based inhibitor NAG-thiazoline and a wide variety of its derivatives in the search for specific inhibitors of the human GH20 β-N-acetylhexosaminidases over the human GH84 β-N-acetylglucosaminidase, which was expressed, purified and used in the inhibition experiments as well. Moreover, enzyme-inhibitor complexes were analysed employing computational tools in order to reveal the structural basis of the results of the inhibition assays, showing the importance of water-mediated interactions between the enzyme and respective ligands. The presented method for the heterologous expression of human Hex B is robust, it significantly reduces the costs and equipment demands in comparison to the expression in mammalian cell lines. This will enhance accessibility of this human enzyme to the broad scientific community and may speed up the research of specific inhibitors of this physiologically important glycosidase family.

Construction of a hybrid β-hexosaminidase subunit capable of forming stable homodimers that hydrolyze GM2 ganglioside in vivo

Tay-Sachs or Sandhoff disease result from mutations in either the evolutionarily related HEXA or HEXB genes encoding respectively, the α- or β-subunits of β-hexosaminidase A (HexA). Of the three Hex isozymes, only HexA can interact with its cofactor, the GM2 activator protein (GM2AP), and hydrolyze GM2 ganglioside. A major impediment to establishing gene or enzyme replacement therapy based on HexA is the need to synthesize both subunits. Thus, we combined the critical features of both α- and β-subunits into a single hybrid µ-subunit that contains the α-subunit active site, the stable β-subunit interface and unique areas in each subunit needed to interact with GM2AP. To facilitate intracellular analysis and the purification of the µ-homodimer (HexM), CRISPR-based genome editing was used to disrupt the HEXA and HEXB genes in a Human Embryonic Kidney 293 cell line stably expressing the µ-subunit. In association with GM2AP, HexM was shown to hydrolyze a fluorescent GM2 ganglioside derivative both in cellulo and in vitro. Gene transfer studies in both Tay-Sachs and Sandhoff mouse models demonstrated that HexM expression reduced brain GM2 ganglioside levels.

Human recombinant lysosomal enzymes produced in microorganisms

Lysosomal storage diseases (LSDs) are caused by accumulation of partially degraded substrates within the lysosome, as a result of a function loss of a lysosomal protein. Recombinant lysosomal proteins are usually produced in mammalian cells, based on their capacity to carry out post-translational modifications similar to those observed in human native proteins. However, during the last years, a growing number of studies have shown the possibility to produce active forms of lysosomal proteins in other expression systems, such as plants and microorganisms. In this paper, we review the production and characterization of human lysosomal proteins, deficient in several LSDs, which have been produced in microorganisms. For this purpose, Escherichia coli, Saccharomyces cerevisiae, Pichia pastoris, Yarrowia lipolytica, and Ogataea minuta have been used as expression systems. The recombinant lysosomal proteins expressed in these hosts have shown similar substrate specificities, and temperature and pH stability profiles to those produced in mammalian cells. In addition, pre-clinical results have shown that recombinant lysosomal enzymes produced in microorganisms can be taken-up by cells and reduce the substrate accumulated within the lysosome. Recently, metabolic engineering in yeasts has allowed the production of lysosomal enzymes with tailored N-glycosylations, while progresses in E. coli N-glycosylations offer a potential platform to improve the production of these recombinant lysosomal enzymes. In summary, microorganisms represent convenient platform for the production of recombinant lysosomal proteins for biochemical and physicochemical characterization, as well as for the development of ERT for LSD.

Development of a Chemical Methodology for the Preparation of Peptide Thioesters Applicable to Naturally Occurring Peptides Using a Sequential Quadruple Acyl Transfer System

Peptide thioesters are very useful in protein chemistry, and chemistry- and biochemistry-based protocols are used for the preparation of thioesters. Among such protocols, only a few biochemistry-based approaches have been use for naturally occurring peptide sequences. The development of chemistry-based protocols applicable to natural sequences remains a challenge, and the development of such methods would be a major contribution to protein science. Here, we describe the preparation of peptide thioesters using innovative methodology that features nickel(II)-mediated alcoholysis of a naturally occurring peptide sequence, followed by O−N and N−S acyl transfers. This protocol involves sequential quadruple acyl transfer, termed SQAT. Notably, the SQAT system consists of sequential chemical reactions that allow naturally occurring peptide sequences to be converted to thioesters without requiring an artificial chemical unit.

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.

Disease stage determines the efficacy of treatment of a paediatric neurodegenerative disease

Lysosomal storage disorders are a large group of inherited metabolic conditions resulting from the deficiency of proteins involved in lysosomal catabolism, with resulting accumulation of substrates inside the cell. Two-thirds of these disorders are associated with a neurodegenerative phenotype and, although few therapeutic options are available to patients at present, clinical trials of several treatments including lysosomal enzyme replacement are underway. Although animal studies indicate the efficacy of presymptomatic treatment, it is largely unknown whether symptomatic disease-related pathology and functional deficits are reversible. To begin to address this, we used a naturally-occurring mouse model with Sanfilippo syndrome (mucopolysaccharidosis type IIIA) to examine the effectiveness of intracisternal cerebrospinal fluid enzyme replacement in early, mid- and symptomatic disease stage mice. We observed a disease-stage-dependent treatment effect, with the most significant reductions in primary and secondary substrate accumulation, astrogliosis and protein aggregate accumulation seen in mucopolysaccharidosis type IIIA mice treated very early in the disease course. Affected mice treated at a symptomatic age exhibited little change in these neuropathological markers in the time-frame of the study. Microgliosis was refractory to treatment regardless of the age at which treatment was instigated. Although longer-term studies are warranted, these findings indicate the importance of early intervention in this condition.

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.

Delivery of therapeutic protein for prevention of neurodegenerative changes: comparison of different CSF-delivery methods

Injection of lysosomal enzyme into cisternal or ventricular cerebrospinal fluid (CSF) has been carried out in 11 lysosomal storage disorder models, with each study demonstrating reductions in primary substrate and secondary neuropathological changes, and several reports of improved neurological function. Whilst acute studies in mucopolysaccharidosis (MPS) type II mice revealed that intrathecally-delivered enzyme (into thoraco-lumbar CSF) accesses the brain, the impact of longer-term treatment of affected subjects via this route is unknown. This approach is presently being utilized to treat children with MPS types I, II and III. Our aim was to determine the efficacy of repeated intrathecal injection of recombinant human sulfamidase (rhSGSH) on pathological changes in the MPS IIIA dog brain. The outcomes were compared with those in dogs treated via intra-cisternal or ventricular routes. Control dogs received buffer or no treatment. Significant reductions in primary/secondary substrate levels in brain were observed in dogs treated via all routes, although the extent of the reduction differed regionally. Treatment via all CSF access points resulted in large reductions in microgliosis in superficial cerebral cortex, but only ventricular injection enabled amelioration in deep cerebral cortex. Formation of glutamic acid decarboxylase-positive axonal spheroids in deep cerebellar nuclei was prevented by treatment delivered via any route. Anti-rhSGSH antibodies in the sera of some dogs did not reduce therapeutic efficacy. Our data indicates the capacity of intra-spinal CSF-injected rhSGSH to circulate within CSF-filled spaces, penetrate into brain and mediate a significant reduction in substrate accumulation and secondary pathology in the MPS IIIA dog brain.

Advances in understanding and treating dystrophic epidermolysis bullosa

Epidermolysis bullosa is a group of inherited disorders that can be both systemic and life-threatening. Standard treatments for the most severe forms of this disorder, typically limited to palliative care, are ineffective in reducing the morbidity and mortality due to complications of the disease. Emerging therapies—such as the use of allogeneic cellular therapy, gene therapy, and protein therapy—have all shown promise, but it is likely that several approaches will need to be combined to realize a cure. For recessive dystrophic epidermolysis bullosa, each particular therapeutic approach has added to our understanding of type VII collagen (C7) function and the basic biology surrounding the disease. The efficacy of these therapies and the mechanisms by which they function also give us insight into developing future strategies for treating this and other extracellular matrix disorders.

Liquid chromatography/electrospray ionisation-tandem mass spectrometry quantification of GM2 gangliosides in human peripheral cells and plasma

GM2 gangliosidosis is a group of inherited neurodegenerative disorders resulting primarily from the excessive accumulation of GM2 gangliosides (GM2) in neuronal cells. As biomarkers for categorising patients and monitoring the effectiveness of developing therapies are lacking for this group of disorders, we sought to develop methodology to quantify GM2 levels in more readily attainable patient samples such as plasma, leukocytes, and cultured skin fibroblasts. Following organic extraction, gangliosides were partitioned into the aqueous phase and isolated using C18 solid-phase extraction columns. Relative quantification of three species of GM2 was achieved using LC/ESI-MS/MS with d35GM1 18:1/18:0 as an internal standard. The assay was linear over the biological range, and all GM2 gangliosidosis patients were demarcated from controls by elevated GM2 in cultured skin fibroblast extracts. However, in leukocytes only some molecular species could be used for differentiation and in plasma only one was informative. A reduction in GM2 was easily detected in patient skin fibroblasts after a short treatment with media from normal cells enriched in secreted β-hexosaminidase. This method may show promise for measuring the effectiveness of experimental therapies for GM2 gangliosidosis by allowing quantification of a reduction in the primary storage burden.

[Molecular pathogenesis and therapeutic approach of GM2 gangliosidosis]

Tay-Sachs and Sandhoff diseases (GM2 gangliosidoses) are autosomal recessive lysosomal storage diseases caused by gene mutations in HEXA and HEXB, each encoding human lysosomal β-hexosaminidase α-subunits and β-subunits, respectively. In Tay-Sachs disease, excessive accumulation of GM2 ganglioside (GM2), mainly in the central nervous system, is caused by a deficiency of the HexA isozyme (αβ heterodimer), resulting in progressive neurologic disorders. In Sandhoff disease, combined deficiencies of HexA and HexB (ββ homodimer) cause not only the accumulation of GM2 but also of oligosaccharides carrying terminal N-acetylhexosamine residues (GlcNAc-oligosaccharides), resulting in systemic manifestations including hepatosplenomegaly as well as neurologic symptoms. Hence there is little clinically effective treatment for these GM2 gangliosidoses. Recent studies on the molecular pathogenesis in Sandhoff disease patients and disease model mice have shown the involvement of microglial activation and chemokine induction in neuroinflammation and neurodegeneration in this disease. Experimental and therapeutic approaches, including recombinant enzyme replacement, have been performed using Sandhoff disease model mice, suggesting the future application of novel techniques to treat GM2 gangliosidoses (Hex deficiencies), including Sandhoff disease as well as Tay-Sachs disease. In this study, we isolated astrocytes and microglia from the neonatal brain of Sandhoff disease model mice and demonstrated abnormalities of glial cells. Moreover, we demonstrated the therapeutic effect of an intracerebroventricular administration of novel recombinant human HexA carrying a high content of M6P residue in Sandhoff disease model mice.

Gangliosides and gangliosidoses: principles of molecular and metabolic pathogenesis

Gangliosides are the main glycolipids of neuronal plasma membranes. Their surface patterns are generated by coordinated processes, involving biosynthetic pathways of the secretory compartments, catabolic steps of the endolysosomal system, and intracellular trafficking. Inherited defects in ganglioside biosynthesis causing fatal neurodegenerative diseases have been described so far almost exclusively in mouse models, whereas inherited defects in ganglioside catabolism causing various clinical forms of GM1- and GM2-gangliosidoses have long been known. For digestion, gangliosides are endocytosed and reach intra-endosomal vesicles. At the level of late endosomes, they are depleted of membrane-stabilizing lipids like cholesterol and enriched with bis(monoacylglycero)phosphate (BMP). Lysosomal catabolism is catalyzed at acidic pH values by cationic sphingolipid activator proteins (SAPs), presenting lipids to their respective hydrolases, electrostatically attracted to the negatively charged surface of the luminal BMP-rich vesicles. Various inherited defects of ganglioside hydrolases, e.g., of β-galactosidase and β-hexosaminidases, and of GM2-activator protein, cause infantile (with tetraparesis, dementia, blindness) and different protracted clinical forms of GM1- and GM2-gangliosidoses. Mutations yielding proteins with small residual catabolic activities in the lysosome give rise to juvenile and adult clinical forms with a wide range of clinical symptomatology. Apart from patients' differences in their genetic background, clinical heterogeneity may be caused by rather diverse substrate specificities and functions of lysosomal hydrolases, multifunctional properties of SAPs, and the strong regulation of ganglioside catabolism by membrane lipids. Currently, there is no treatment available for neuronal ganglioside storage diseases. Therapeutic approaches in mouse models and patients with juvenile forms of gangliosidoses are discussed.

In cellulo examination of a beta-alpha hybrid construct of beta-hexosaminidase A subunits, reported to interact with the GM2 activator protein and hydrolyze GM2 ganglioside

The hydrolysis in lysosomes of GM2 ganglioside to GM3 ganglioside requires the correct synthesis, intracellular assembly and transport of three separate gene products; i.e., the alpha and beta subunits of heterodimeric beta-hexosaminidase A, E.C. # 3.2.1.52 (encoded by the HEXA and HEXB genes, respectively), and the GM2-activator protein (GM2AP, encoded by the GM2A gene). Mutations in any one of these genes can result in one of three neurodegenerative diseases collectively known as GM2 gangliosidosis (HEXA, Tay-Sachs disease, MIM # 272800; HEXB, Sandhoff disease, MIM # 268800; and GM2A, AB-variant form, MIM # 272750). Elements of both of the hexosaminidase A subunits are needed to productively interact with the GM2 ganglioside-GM2AP complex in the lysosome. Some of these elements have been predicted from the crystal structures of hexosaminidase and the activator. Recently a hybrid of the two subunits has been constructed and reported to be capable of forming homodimers that can perform this reaction in vivo, which could greatly simplify vector-mediated gene transfer approaches for Tay-Sachs or Sandhoff diseases. A cDNA encoding a hybrid hexosaminidase subunit capable of dimerizing and hydrolyzing GM2 ganglioside could be incorporated into a single vector, whereas packaging both subunits of hexosaminidase A into vectors, such as adeno-associated virus, would be impractical due to size constraints. In this report we examine the previously published hybrid construct (H1) and a new more extensive hybrid (H2), with our documented in cellulo (live cell- based) assay utilizing a fluorescent GM2 ganglioside derivative. Unfortunately when Tay-Sachs cells were transfected with either the H1 or H2 hybrid construct and then were fed the GM2 derivative, no significant increase in its turnover was detected. In vitro assays with the isolated H1 or H2 homodimers confirmed that neither was capable of human GM2AP-dependent hydrolysis of GM2 ganglioside.

Gangliosidoses

The gangliosidoses comprise a family of lysosomal storage diseases characterized by the accumulation of complex glycosphingolipids in the nervous system and other tissues, secondary to the deficient activity of lysosomal hydrolases or their associated activator proteins. GM1 and GM2 gangliosidosis are associated with deficiency of β-galactosidase and β-hexosaminidase respectively. All gangliosidoses are characterized by progressive neurodegeneration, the severity of which is proportional to the residual enzyme activity. The GM1 gangliosidoses are characterized by dysostosis, organomegaly and coarsening in their most severe forms, whereas children with classic infantile GM2 gangliosidosis (Tay-Sachs disease) are usually spared systemic involvement, except in the case of the Sandhoff variant, in which organomegaly may occur. Cherry-red macular spots occur in the early onset forms of the gangliosidoses, but are less frequently seen in the less severe, later onset phenotypes. Macrocephaly, an exaggerated startle response, cognitive decline, seizures, ataxia, and progressive muscular atrophy may occur in different forms of gangliosidosis. The diagnosis is made by assay of enzyme activity, and can be confirmed by mutation analysis. Carrier screening for Tay-Sachs disease has been remarkably successful in reducing the incidence of this disease in the at-risk Ashkenazi population. There are no proven disease-modifying therapies for the gangliosidoses.

Gene transfer corrects acute GM2 gangliosidosis--potential therapeutic contribution of perivascular enzyme flow

The GM2 gangliosidoses are fatal lysosomal storage diseases principally affecting the brain. Absence of β-hexosaminidase A and B activities in the Sandhoff mouse causes neurological dysfunction and recapitulates the acute Tay-Sachs (TSD) and Sandhoff diseases (SD) in infants. Intracranial coinjection of recombinant adeno-associated viral vectors (rAAV), serotype 2/1, expressing human β-hexosaminidase α (HEXA) and β (HEXB) subunits into 1-month-old Sandhoff mice gave unprecedented survival to 2 years and prevented disease throughout the brain and spinal cord. Classical manifestations of disease, including spasticity-as opposed to tremor-ataxia-were resolved by localized gene transfer to the striatum or cerebellum, respectively. Abundant biosynthesis of β-hexosaminidase isozymes and their global distribution via axonal, perivascular, and cerebrospinal fluid (CSF) spaces, as well as diffusion, account for the sustained phenotypic rescue-long-term protein expression by transduced brain parenchyma, choroid plexus epithelium, and dorsal root ganglia neurons supplies the corrective enzyme. Prolonged survival permitted expression of cryptic disease in organs not accessed by intracranial vector delivery. We contend that infusion of rAAV into CSF space and intraparenchymal administration by convection-enhanced delivery at a few strategic sites will optimally treat neurodegeneration in many diseases affecting the nervous system.

Lyso-GM2 ganglioside: a possible biomarker of Tay-Sachs disease and Sandhoff disease

To find a new biomarker of Tay-Sachs disease and Sandhoff disease. The lyso-GM2 ganglioside (lyso-GM2) levels in the brain and plasma in Sandhoff mice were measured by means of high performance liquid chromatography and the effect of a modified hexosaminidase (Hex) B exhibiting Hex A-like activity was examined. Then, the lyso-GM2 concentrations in human plasma samples were determined. The lyso-GM2 levels in the brain and plasma in Sandhoff mice were apparently increased compared with those in wild-type mice, and they decreased on intracerebroventricular administration of the modified Hex B. The lyso-GM2 levels in plasma of patients with Tay-Sachs disease and Sandhoff disease were increased, and the increase in lyso-GM2 was associated with a decrease in Hex A activity. Lyso-GM2 is expected to be a potential biomarker of Tay-Sachs disease and Sandhoff disease.

Knock-down of HEXA and HEXB genes correlate with the absence of the immunostimulatory function of HSC-derived dendritic cells

In an attempt to investigate whether the genetic defect in the HEXA and HEXB genes (which causes the absence of the lysosomal β-N-acetyl-hexosaminidase), are related to the wide inflammation in GM2 gangliosidoses (Tay-Sachs and Sandhoff disease), we have chosen the dendritic cells (DCs) as a study model. Using the RNA interference approach, we generated an in vitro model of HEXs knock-down immunogenic DCs (i-DCs) from CD34(+)-haemopoietic stem cells (CD34(+)-HSCs), thus mimicking the Tay-Sachs (HEXA-/-) and Sandhoff (HEXB-/-) cells. We showed that the absence of β-N-acetyl-hexosaminidase activity does not alter the differentiation of i-DCs from HSCs, but it is critical for the activation of CD4(+)T cells because knock-down of HEXA or HEXB gene causes a loss of function of i-DCs. Notably, the silencing of the HEXA gene had a stronger immune inhibitory effect, thereby indicating a major involvement of β-N-acetyl-hexosaminidase A isoenzyme within this mechanism.