Cytokines, neurotrophins, and oxidative stress in brain disease from mucopolysaccharidosis IIIB

Evidence of epigenetic landscape shifts in mucopolysaccharidosis IIIB and IVA

Lysosomal storage diseases (LSDs) are a group of monogenic diseases characterized by mutations in genes coding for proteins associated with the lysosomal function. Despite the monogenic nature, LSDs patients exhibit variable and heterogeneous clinical manifestations, prompting investigations into epigenetic factors underlying this phenotypic diversity. In this study, we focused on the potential role of epigenetic mechanisms in the pathogenesis of mucopolysaccharidosis IIIB (MPS IIIB) and mucopolysaccharidosis IVA (MPS IVA). We analyzed DNA methylation (5mC) and histone modifications (H3K14 acetylation and H3K9 trimethylation) in MPS IIIB and MPS IVA patients' fibroblasts and healthy controls. The findings revealed that global DNA hypomethylation is present in cell lines for both diseases. At the same time, histone acetylation was increased in MPS IIIB and MPS IVA cells in a donor-dependent way, further indicating a shift towards relaxed open chromatin in these MPS. Finally, the constitutive heterochromatin marker, histone H3K9 trimethylation, only showed reduced clustering in MPS IIIB cells, suggesting limited alterations in heterochromatin organization. These findings collectively emphasize the significance of epigenetic mechanisms in modulating the phenotypic variations observed in LSDs. While global DNA hypomethylation could contribute to the MPS pathogenesis, the study also highlights individual-specific epigenetic responses that might contribute to phenotypic heterogeneity. Further research into the specific genes and pathways affected by these epigenetic changes could provide insights into potential therapeutic interventions for these MPS and other LSDs.

Intracerebroventricular enzyme replacement therapy in patients with neuronopathic mucopolysaccharidosis type II: Final report of 5-year results from a Japanese open-label phase 1/2 study

Intravenous idursulfase is standard treatment for mucopolysaccharidosis II (MPS II) in Japan. In the interim analysis of this open-label, phase 1/2 study (Center for Clinical Trials, Japan Medical Association: JMA-IIA00350), intracerebroventricular (ICV) idursulfase beta was well tolerated, suppressed cerebrospinal fluid (CSF) heparan sulfate (HS) levels, and stabilized developmental decline over 100 weeks in Japanese children with MPS II. Here, we report the final study results, representing 5 years of ICV idursulfase beta treatment. Six male patients with MPS II and developmental delay were enrolled starting in June 2016 and followed until March 2021. Patients received up to 30 mg ICV idursulfase beta every 4 weeks. Outcomes included CSF HS levels, developmental age (DA) (assessed by the Kyoto Scale of Psychological Development), and safety (adverse events). Monitoring by laboratory biochemistry tests, urinary uronic tests, immunogenicity tests, and head computed tomography or magnetic resonance imaging were also conducted regularly. Following ICV idursulfase beta administration, mean CSF HS concentrations decreased from 7.75 μg/mL at baseline to 2.15 μg/mL at final injection (72.3% reduction). Mean DA increased from 23.2 months at screening to 36.0 months at final observation. In five patients with null mutations, mean DA at the final observation was higher than or did not regress compared with that of historical controls receiving intravenous idursulfase only, and the change in DA was greater in patients who started administration aged ≤3 years than in those aged >3 years (+28.7 vs -6.5 months). The difference in DA change versus historical controls in individual patients was +39.5, +40.8, +17.8, +10.5, +7.6 and - 4.5 (mean + 18.6). Common ICV idursulfase beta-related adverse events were vomiting, pyrexia, gastroenteritis, and upper respiratory tract infection (most mild/moderate). These results suggest that long-term ICV idursulfase beta treatment improved neurological symptoms in Japanese children with neuronopathic MPS II.

Enhanced Efficiency of the Basal and Induced Apoptosis Process in Mucopolysaccharidosis IVA and IVB Human Fibroblasts

Morquio disease, also called mucopolysaccharidosis IV (MPS IV), belongs to the group of lysosomal storage diseases (LSD). Due to deficiencies in the activities of galactose-6-sulfate sulfatase (in type A) or β-galactosidase (in type B), arising from mutations in GALNS or GLB1, respectively, keratan sulfate (one of glycosaminoglycans, GAGs) cannot be degraded efficiently and accumulates in lysosomes. This primary defect leads to many cellular dysfunctions which then cause specific disease symptoms. Recent works have indicated that different secondary effects of GAG accumulation might significantly contribute to the pathomechanisms of MPS. Apoptosis is among the cellular processes that were discovered to be affected in MPS cells on the basis of transcriptomic studies and some cell biology experiments. However, Morquio disease is the MPS type which is the least studied in light of apoptosis dysregulation, while RNA-seq analyses suggested considerable changes in the expression of genes involved in apoptosis in MPS IVA and IVB fibroblasts. Here we demonstrate that cytochrome c release from mitochondria is more efficient in MPS IVA and IVB fibroblasts relative to control cells, both under the standard cultivation conditions and after treatment with staurosporine, an apoptosis inducer. This indication of apoptosis stimulation was corroborated by measurements of the levels of caspases 9, 3, 6, and 7, as well as PARP, cleaved at specific sites, in Morquio disease and control fibroblasts. The more detailed analyses of the transcriptomic data revealed which genes related to apoptosis are down- and up-regulated in MPS IVA and IVB fibroblasts. We conclude that apoptosis is stimulated in Morquio disease under both standard cell culture conditions and after induction with staurosporine which may contribute to the pathomechanism of this disorder. Dysregulation of apoptosis in other MPS types is discussed.

Alterations of Plasmatic Biomarkers of Neurodegeneration in Mucopolysaccharidosis Type II Patients Under Enzyme Replacement Therapy

Mucopolysaccharidosis type II (MPS II) is a disorder caused by a deficient activity of iduronate-2-sulfatase, a lysosomal enzyme responsible for degrading glycosaminoglycans (GAGs). The abnormal storage of GAGs within lysosomes disrupts cellular homeostasis and leads to a severe symptomatology. Patients present neuropsychiatric impairment characterized by mental retardation and impaired cognition. The aim of this study was to quantify four neurodegeneration biomarkers in plasma: brain-derived neurotrophic factor (BDNF), platelet-derived growth factor (PDGF-AA), neural cell adhesion molecule (NCAM) and cathepsin-D, as well as to identify possible correlations with urinary GAGs in seven patients undergoing treatment with ERT (Elaprase® 0.5 mg/kg of body weight). Patients with both severe and attenuated forms of MPS II showed signs of neurodegeneration in neuroimaging exams. Patients have a decrease in BDNF and PDGF-AA concentrations, and an increase in NCAM level compared to controls. No alterations in cathepsin-D concentration were seen. GAGs levels were higher in patients than in controls, but no significant correlations between GAGs and biomarkers were observed. These results evidence that patients have neurodegeneration and that monitoring these biomarkers might be useful for assessing this process. To this date, this is the first work to analyze these plasmatic markers of neurodegeneration in patients.

A zebrafish model of combined saposin deficiency identifies acid sphingomyelinase as a potential therapeutic target

Sphingolipidoses are a subcategory of lysosomal storage diseases (LSDs) caused by mutations in enzymes of the sphingolipid catabolic pathway. Like many LSDs, neurological involvement in sphingolipidoses leads to early mortality with limited treatment options. Given the role of myelin loss as a major contributor toward LSD-associated neurodegeneration, we investigated the pathways contributing to demyelination in a CRISPR-Cas9-generated zebrafish model of combined saposin (psap) deficiency. psap knockout (KO) zebrafish recapitulated major LSD pathologies, including reduced lifespan, reduced lipid storage, impaired locomotion and severe myelin loss; loss of myelin basic protein a (mbpa) mRNA was progressive, with no changes in additional markers of oligodendrocyte differentiation. Brain transcriptomics revealed dysregulated mTORC1 signaling and elevated neuroinflammation, where increased proinflammatory cytokine expression preceded and mTORC1 signaling changes followed mbpa loss. We examined pharmacological and genetic rescue strategies via water tank administration of the multiple sclerosis drug monomethylfumarate (MMF), and crossing the psap KO line into an acid sphingomyelinase (smpd1) deficiency model. smpd1 mutagenesis, but not MMF treatment, prolonged lifespan in psap KO zebrafish, highlighting the modulation of acid sphingomyelinase activity as a potential path toward sphingolipidosis treatment.

Redox Imbalance in Neurological Disorders in Adults and Children

Oxygen is a central molecule for numerous metabolic and cytophysiological processes, and, indeed, its imbalance can lead to numerous pathological consequences. In the human body, the brain is an aerobic organ and for this reason, it is very sensitive to oxygen equilibrium. The consequences of oxygen imbalance are especially devastating when occurring in this organ. Indeed, oxygen imbalance can lead to hypoxia, hyperoxia, protein misfolding, mitochondria dysfunction, alterations in heme metabolism and neuroinflammation. Consequently, these dysfunctions can cause numerous neurological alterations, both in the pediatric life and in the adult ages. These disorders share numerous common pathways, most of which are consequent to redox imbalance. In this review, we will focus on the dysfunctions present in neurodegenerative disorders (specifically Alzheimer's disease, Parkinson's disease and amyotrophic lateral sclerosis) and pediatric neurological disorders (X-adrenoleukodystrophies, spinal muscular atrophy, mucopolysaccharidoses and Pelizaeus-Merzbacher Disease), highlighting their underlining dysfunction in redox and identifying potential therapeutic strategies.

Mucopolysaccharidoses: Cellular Consequences of Glycosaminoglycans Accumulation and Potential Targets

Mucopolysaccharidoses (MPSs) constitute a heterogeneous group of lysosomal storage disorders characterized by the lysosomal accumulation of glycosaminoglycans (GAGs). Although lysosomal dysfunction is mainly affected, several cellular organelles such as mitochondria, endoplasmic reticulum, Golgi apparatus, and their related process are also impaired, leading to the activation of pathophysiological cascades. While supplying missing enzymes is the mainstream for the treatment of MPS, including enzyme replacement therapy (ERT), hematopoietic stem cell transplantation (HSCT), or gene therapy (GT), the use of modulators available to restore affected organelles for recovering cell homeostasis may be a simultaneous approach. This review summarizes the current knowledge about the cellular consequences of the lysosomal GAGs accumulation and discusses the use of potential modulators that can reestablish normal cell function beyond ERT-, HSCT-, or GT-based alternatives.

The Inflammation in the Cytopathology of Patients With Mucopolysaccharidoses- Immunomodulatory Drugs as an Approach to Therapy

Mucopolysaccharidoses (MPS) are a group of lysosomal storage diseases (LSDs), characterized by the accumulation of glycosaminoglycans (GAGs). GAG storage-induced inflammatory processes are a driver of cytopathology in MPS and pharmacological immunomodulation can bring improvements in brain, cartilage and bone pathology in rodent models. This manuscript reviews current knowledge with regard to inflammation in MPS patients and provides hypotheses for the therapeutic use of immunomodulators in MPS. Thus, we aim to set the foundation for a rational repurposing of the discussed molecules to minimize the clinical unmet needs still remaining despite enzyme replacement therapy (ERT) and hematopoietic stem cell transplantation (HSCT).

Blood-brain barrier delivery for lysosomal storage disorders with IgG-lysosomal enzyme fusion proteins

The majority of lysosomal storage diseases affect the brain. Treatment of the brain with intravenous enzyme replacement therapy is not successful, because the recombinant lysosomal enzymes do not cross the blood-brain barrier (BBB). Biologic drugs, including lysosomal enzymes, can be re-engineered for BBB delivery as IgG-enzyme fusion proteins. The IgG domain of the fusion protein is a monoclonal antibody directed against an endogenous receptor-mediated transporter at the BBB, such as the insulin receptor or the transferrin receptor. This receptor transports the IgG across the BBB, in parallel with the endogenous receptor ligand, and the IgG acts as a molecular Trojan horse to ferry into brain the lysosomal enzyme genetically fused to the IgG. The IgG-enzyme fusion protein is bi-functional and retains both high affinity binding for the BBB receptor, and high lysosomal enzyme activity. IgG-lysosomal enzymes are presently in clinical trials for treatment of the brain in Mucopolysaccharidosis.

Heparan Sulfate, Mucopolysaccharidosis IIIB and Sulfur Metabolism Disorders

Mucopolysaccharidosis, type IIIB (MPS IIIB) is a rare disease caused by mutations in the N-alpha-acetylglucosaminidase (NAGLU) gene resulting in decreased or absent enzyme activity. On the cellular level, the disorder is characterized by the massive lysosomal storage of heparan sulfate (HS)—one species of glycosaminoglycans. HS is a sulfur-rich macromolecule, and its accumulation should affect the turnover of total sulfur in cells; according to the studies presented here, it, indeed, does. The lysosomal degradation of HS in cells produces monosaccharides and inorganic sulfate (SO₄²⁻). Sulfate is a product of L-cysteine metabolism, and any disruption of its levels affects the entire L-cysteine catabolism pathway, which was first reported in 2019. It is known that L-cysteine level is elevated in cells with the Naglu^−/− gene mutation and in selected tissues of individuals with MPS IIIB. The level of glutathione and the Naglu^−/− cells’ antioxidant potential are significantly reduced, as well as the activity of 3-mercaptopyruvate sulfurtransferase (MPST, EC 2.8.1.2) and the level of sulfane sulfur-containing compounds. The direct reason is not yet known. This paper attempts to identify some of cause-and-effect correlations that may lead to this condition and identifies research directions that should be explored.

Computational strategies to identify new drug candidates against neuroinflammation

The even more increasing application of computational approaches in these last decades has deeply modified the process of discovery and commercialization of new therapeutic entities. This is especially true in the field of neuroinflammation, in which both the peculiar anatomical localization and the presence of the blood-brain barrier makeit mandatory to finely tune the candidates' physicochemical properties from the early stages of the discovery pipeline. The aim of this review is therefore to provide a general overview to the readers about the topic of neuroinflammation, together with the most common computational strategies that can be exploited to discover and design small molecules controlling neuroinflammation, especially those based on the knowledge of the three-dimensional structure of the biological targets of therapeutic interest. The techniques used to describe the molecular recognition mechanisms, such as molecular docking and molecular dynamics, will therefore be eviscerated, highlighting their advantages and their limitations. Finally, we report several case studies in which computational methods have been applied in drug discovery on neuroinflammation, focusing on the last decade's research.

Oxidative Stress in Mucopolysaccharidoses: Pharmacological Implications

Although mucopolysaccharidoses (MPS) are caused by mutations in genes coding for enzymes responsible for degradation of glycosaminoglycans, storage of these compounds is crucial but is not the only pathomechanism of these severe, inherited metabolic diseases. Among various factors and processes influencing the course of MPS, oxidative stress appears to be a major one. Oxidative imbalance, occurring in MPS and resulting in increased levels of reactive oxidative species, causes damage of various biomolecules, leading to worsening of symptoms, especially in the central nervous system (but not restricted to this system). A few therapeutic options are available for some types of MPS, including enzyme replacement therapy and hematopoietic stem cell transplantation, however, none of them are fully effective in reducing all symptoms. A possibility that molecules with antioxidative activities might be useful accompanying drugs, administered together with other therapies, is discussed in light of the potential efficacy of MPS treatment.

Long-term effect of hematopoietic cell transplantation on systemic inflammation in patients with mucopolysaccharidoses

Mucopolysaccharidoses (MPS) are devastating inherited diseases treated with hematopoietic cell transplantation (HCT). However, disease progression, especially skeletal, still occurs in all patients. Secondary inflammation has been hypothesized to be a cause. To investigate whether systemic inflammation is present in untreated patients and to evaluate the effect of HCT on systemic inflammation, dried blood spots (n = 66) of patients with MPS (n = 33) treated with HCT between 2003 and 2019 were included. Time points consisted of pre-HCT and, for patients with MPS type I (MPS I), also at 1, 3, and 10 years of follow-up. Ninety-two markers of the OLINK inflammation panel were measured and compared with those of age-matched control subjects (n = 31) by using principal component analysis and Wilcoxon rank sum tests with correction. Median age at transplantation was 1.3 years (range, 0.2-4.8 years), and median time of pre-HCT sample to transplantation was 0.1 year. Normal leukocyte enzyme activity levels were achieved in 93% of patients post-HCT. Pretransplant samples showed clear separation of patients and control subjects. Markers that differentiated pre-HCT between control subjects and patients were mainly pro-inflammatory (50%) or related to bone homeostasis and extracellular matrix degradation (33%). After 10 years' follow-up, only 5 markers (receptor activator of nuclear factor kappa-Β ligand, osteoprotegerin, axis inhibition protein 1 [AXIN1], stem cell factor, and Fms-related tyrosine kinase 3 ligand) remained significantly increased, with a large fold change difference between patients with MPS I and control subjects. In conclusion, systemic inflammation is present in untreated MPS patients and is reduced upon treatment with HCT. Markers related to bone homeostasis remain elevated up to 10 years after HCT and possibly reflect the ongoing skeletal disease, making them potential biomarkers for the evaluation of new therapies.

Impact of intracerebroventricular enzyme replacement therapy in patients with neuronopathic mucopolysaccharidosis type II

This open-label, phase 1/2 study (JMACCT CTR JMA-IIA00350) evaluated the efficacy and safety of intracerebroventricular idursulfase beta in patients with mucopolysaccharidosis II (MPS II). Herein, we report the 100-week results. Six patients with severe MPS II aged 23-65 months were enrolled. Idursulfase beta (increasing from 1 to 30 mg between weeks 0 and 24, followed by a 30-mg final dose) was administered intracerebroventricularly once every 4 weeks using an implanted cerebrospinal fluid (CSF) reservoir; intravenous administration of idursulfase was also continued throughout the study. Efficacy endpoints included developmental age by the Kyoto Scale of Psychological Development 2001 and heparan sulfate (HS) concentration in CSF (primary outcome). In all six patients, HS concentrations decreased (40%-80%) from baseline to week 100. For overall developmental age, the difference in change from baseline to week 100 in each patient compared with patients treated by intravenous idursulfase administration (n = 13) was +8.0, +14.5, +4.5, +3.7, +8.2, and -8.3 months (mean, +5.1 months). Idursulfase beta was well tolerated. The most common adverse events were pyrexia, upper respiratory tract infection, and vomiting. The results suggest that intracerebroventricular idursulfase beta is well tolerated and can be effective at preventing and stabilizing developmental decline in patients with neuronopathic MPS II.

GM2 ganglioside accumulation causes neuroinflammation and behavioral alterations in a mouse model of early onset Tay-Sachs disease

Background

Tay-Sachs disease (TSD), a type of GM2-gangliosidosis, is a progressive neurodegenerative lysosomal storage disorder caused by mutations in the α subunit of the lysosomal β-hexosaminidase enzyme. This disease is characterized by excessive accumulation of GM2 ganglioside, predominantly in the central nervous system. Although Tay-Sachs patients appear normal at birth, the progressive accumulation of undegraded GM2 gangliosides in neurons leads to death. Recently, an early onset Tay-Sachs disease mouse model, with genotype Hexa−/−Neu3−/−, was generated. Progressive accumulation of GM2 led to premature death of the double KO mice. Importantly, this double-deficient mouse model displays typical features of Tay-Sachs patients, such as cytoplasmic vacuolization of nerve cells, deterioration of Purkinje cells, neuronal death, deceleration in movement, ataxia, and tremors. GM2-gangliosidosis is characterized by acute neurodegeneration preceded by activated microglia expansion, macrophage, and astrocyte activation, along with the production of inflammatory mediators. However, the mechanism of disease progression in Hexa−/−Neu3−/− mice, relevant to neuroinflammation is poorly understood.

Method

In this study, we investigated the onset and progression of neuroinflammatory changes in the cortex, cerebellum, and retina of Hexa−/−Neu3−/− mice and control littermates by using a combination of molecular genetics and immunochemical procedures.

Results

We found elevated levels of pro-inflammatory cytokine and chemokine transcripts, such as Ccl2, Ccl3, Ccl4, and Cxcl10 and also extensive microglial and astrocyte activation and proliferation, accompanied by peripheral blood mononuclear cell infiltration in the vicinity of neurons and oligodendrocytes. Behavioral tests demonstrated a high level of anxiety, and age-dependent loss in both spatial learning and fear memory in Hexa−/−Neu3−/− mice compared with that in the controls.

Conclusion

Altogether, our data suggest that Hexa−/−Neu3−/− mice display a phenotype similar to Tay-Sachs patients suffering from chronic neuroinflammation triggered by GM2 accumulation. Furthermore, our work contributes to better understanding of the neuropathology in a mouse model of early onset Tay-Sachs disease.

Intravenous Enzyme Replacement Therapy in Mucopolysaccharidoses: Clinical Effectiveness and Limitations

The aim of this review is to summarize the evidence on efficacy, effectiveness and safety of intravenous enzyme replacement therapy (ERT) available for mucopolysaccharidoses (MPSs) I, II, IVA, VI and VII, gained in phase III clinical trials and in observational post-approval studies. Post-marketing data are sometimes conflicting or controversial, possibly depending on disease severity, differently involved organs, age at starting treatment, and development of anti-drug antibodies (ADAs). There is general agreement that ERT is effective in reducing urinary glycosaminoglycans and liver and spleen volume, while heart and joints outcomes are variable in different studies. Effectiveness on cardiac valves, trachea and bronchi, hearing and eyes is definitely poor, probably due to limited penetration in the specific tissues. ERT does not cross the blood–brain barrier, with the consequence that the central nervous system is not cured by intravenously injected ERT. All patients develop ADAs but their role in ERT tolerance and effectiveness has not been well defined yet. Lack of reliable biomarkers contributes to the uncertainties about effectiveness. The data obtained from affected siblings strongly indicates the need of neonatal screening for treatable MPSs. Currently, other treatments are under evaluation and will surely help improve the prognosis of MPS patients.

Elevated LysoGb3 Concentration in the Neuronopathic Forms of Mucopolysaccharidoses

Mucopolysaccharidoses (MPSs) are a group of lysosomal storage disorders associated with impaired glycosaminoglycans (GAGs) catabolism. In MPS I, II, III, and VII, heparan sulfate (HS) cannot be degraded because of the lack of sufficient activity of the respective enzymes, and its accumulation in the brain causes neurological symptoms. Globotriaosylsphingosine (LysoGb3), the deacylated form of globotriaosylceramide (Gb3), is described as a highly sensitive biomarker for another lysosomal storage disease—Fabry disease. The connection between MPSs and LysoGb3 has not yet been established. This study included 36—MPS I, 15—MPS II, 25—MPS III, 26—MPS IV, and 14—MPS VI patients who were diagnosed by biochemical and molecular methods and a control group of 250 males and 250 females. The concentration of lysosphingolipids (LysoSLs) was measured in dried blood spots by high pressure liquid chromatography—tandem mass spectrometry. We have demonstrated that LysoGb3 concentration was significantly elevated (p < 0.0001) in untreated MPS I (3.07 + 1.55 ng/mL), MPS II (5.24 + 2.13 ng/mL), and MPS III (6.82 + 3.69 ng/mL) patients, compared to the control group (0.87 + 0.55 ng/mL). LysoGb3 level was normal in MPS VI and MPS IVA (1.26 + 0.39 and 0.99 + 0.38 ng/mL, respectively). Activity of α-galactosidase A (α-Gal A), an enzyme deficient in Fabry disease, was not, however, inhibited by heparan sulfate in vitro, indicating that an increase of LysoGb3 level in MPS I, MPS II, and MPS III is an indirect effect of stored MPSs rather than a direct result of impairment of degradation of this compound by HS. Our findings indicate some association of elevated LysoGb3 concentration with the neuronopathic forms of MPSs. The pathological mechanism of which is still to be studied.

Expression of genes involved in apoptosis is dysregulated in mucopolysaccharidoses as revealed by pilot transcriptomic analyses

Mucopolysaccharidoses (MPS), a group of lysosomal storage diseases (LSD), are inherited disorders caused by mutations in genes coding for enzymes involved in the degradation of glycosaminoglycans (GAGs). Therefore, accumulated GAGs in lysosomes lead to severe symptoms in patients and significantly shortened life span. Although GAG accumulation in cells is the primary cellular defect in MPS, recent reports indicated that severe changes in cellular processes occur there as secondary or tertiary effects, which may contribute significantly to the disease pathomechanism. Apoptosis is one of such process, while mechanisms leading to dysregulation of this process in MPS remain largely unknown. To learn about these mechanisms, we have performed transcriptomic studies using cultures of fibroblasts derived from patients suffering from all types and subtypes of MPS, and assessed genes related to apoptosis. We found that there are significant changes in expression levels of many such genes relative to control fibroblasts (Human Dermal Fibroblasts-adult cell line), and the number of down- or up-regulated transcripts was between 19 and 73 in different MPS types. We have identified apoptosis-related genes, which were considerably dysregulated in many MPS types, as well as those in which expression was significantly changed in specific MPS types. BNIP3, C1D, CLU, GPER1, KREMEN1, and PRKCD genes displayed the most changed expression profiles in most MPS types relative to control cells. Caspase 3/7 activity was increased in MPS IVA and IX. These results indicate that changes in apoptosis, observed in MPS, may arise, at least partially, from dysregulation of genes coding for proteins involved in this process.

Molecular Bases of Neurodegeneration and Cognitive Decline, the Major Burden of Sanfilippo Disease

The mucopolysaccharidoses (MPS) are a group of diseases caused by the lysosomal accumulation of glycosaminoglycans, due to genetic deficiencies of enzymes involved in their degradation. MPS III or Sanfilippo disease, in particular, is characterized by early-onset severe, progressive neurodegeneration but mild somatic involvement, with patients losing milestones and previously acquired skills as the disease progresses. Despite being the focus of extensive research over the past years, the links between accumulation of the primary molecule, the glycosaminoglycan heparan sulfate, and the neurodegeneration seen in patients have yet to be fully elucidated. This review summarizes the current knowledge on the molecular bases of neurological decline in Sanfilippo disease. It emerges that this deterioration results from the dysregulation of multiple cellular pathways, leading to neuroinflammation, oxidative stress, impaired autophagy and defects in cellular signaling. However, many important questions about the neuropathological mechanisms of the disease remain unanswered, highlighting the need for further research in this area.

Changes in cellular processes occurring in mucopolysaccharidoses as underestimated pathomechanisms of these diseases

Mucopolysaccharidoses (MPS) are a group of genetic disorders belonging to lysosomal storage diseases. They are caused by genetic defects leading to a lack or severe deficiency of activity of one of lysosomal hydrolases involved in degradation of glycosaminoglycans (GAGs). Partially degraded GAGs accumulate in lysosomes, which results in dysfunctions of cells, tissues, and organs. Until recently, it was assumed that GAG accumulation in cells is the major, if not the only, mechanism of pathogenesis in MPS, as GAGs may be a physical ballast for lysosomes causing inefficiency of cells due to a large amount of a stored material. However, recent reports suggest that in MPS cells there are changes in many different processes, which might be even more important for pathogenesis than lysosomal accumulation of GAGs per se. Moreover, there are many recently published results indicating that lysosomes not only are responsible for degradation of various macromolecules, but also play crucial roles in the regulation of cellular metabolism. Therefore, it appears plausible that previous failures in treatment of MPS (i.e., possibility to correct only some symptoms and slowing down of the disease rather than fully effective management of MPS) might be caused by underestimation of changes in cellular processes and concentration solely on decreasing GAG levels in cells.

Brain-targeted stem cell gene therapy corrects mucopolysaccharidosis type II via multiple mechanisms

The pediatric lysosomal storage disorder mucopolysaccharidosis type II is caused by mutations in IDS, resulting in accumulation of heparan and dermatan sulfate, causing severe neurodegeneration, skeletal disease, and cardiorespiratory disease. Most patients manifest with cognitive symptoms, which cannot be treated with enzyme replacement therapy, as native IDS does not cross the blood-brain barrier. We tested a brain-targeted hematopoietic stem cell gene therapy approach using lentiviral IDS fused to ApoEII (IDS.ApoEII) compared to a lentivirus expressing normal IDS or a normal bone marrow transplant. In mucopolysaccharidosis II mice, all treatments corrected peripheral disease, but only IDS.ApoEII mediated complete normalization of brain pathology and behavior, providing significantly enhanced correction compared to IDS. A normal bone marrow transplant achieved no brain correction. Whilst corrected macrophages traffic to the brain, secreting IDS/IDS.ApoEII enzyme for cross-correction, IDS.ApoEII was additionally more active in plasma and was taken up and transcytosed across brain endothelia significantly better than IDS via both heparan sulfate/ApoE-dependent receptors and mannose-6-phosphate receptors. Brain-targeted hematopoietic stem cell gene therapy provides a promising therapy for MPS II patients.

The role of innate immunity in mucopolysaccharide diseases

Mucopolysaccharidoses are lysosomal storage disorders characterised by accumulation of abnormal pathological glycosaminoglycans, cellular dysfunction and widespread inflammation, resulting in progressive cognitive and motor decline. Lysosomes are important mediators of immune cell function, and therefore accumulation of glycosaminoglycans (GAGs) and other abnormal substrates could affect immune function and directly impact on disease pathogenesis. This review summarises current knowledge with regard to inflammation in mucopolysaccharidosis, with an emphasis on the brain and outlines a potential role for GAGs in induction of inflammation. We propose a model by which the accumulation of GAGs and other factors may impact on innate immune signalling with particular focus on the Toll‐like receptor 4 pathway. Innate immunity appears to have a dominating role in mucopolysaccharidosis; however, furthering understanding of innate immune signalling would have significant impact on highlighting novel anti‐inflammatory therapeutics for use in mucopolysaccharide diseases.

This article is part of the Special Issue “Lysosomal Storage Disorders”.

Anatomical changes and pathophysiology of the brain in mucopolysaccharidosis disorders

Mucopolysaccharidosis (MPS) disorders are caused by deficiencies in lysosomal enzymes, leading to impaired glycosaminoglycan (GAG) degradation. The resulting GAG accumulation in cells and connective tissues ultimately results in widespread tissue and organ dysfunction. The seven MPS types currently described are heterogeneous and progressive disorders, with somatic and neurological manifestations depending on the type of accumulating GAG. Heparan sulfate (HS) is one of the GAGs stored in patients with MPS I, II, and VII and the main GAG stored in patients with MPS III. These disorders are associated with significant central nervous system (CNS) abnormalities that can manifest as impaired cognition, hyperactive and/or aggressive behavior, epilepsy, hydrocephalus, and sleeping problems. This review discusses the anatomical and pathophysiological CNS changes accompanying HS accumulation as well as the mechanisms believed to cause CNS abnormalities in MPS patients. The content of this review is based on presentations and discussions on these topics during a meeting on the brain in MPS attended by an international group of MPS experts.

Neurobehavioral phenotypes of neuronopathic mucopolysaccharidoses

Mucopolysaccharidoses (MPS) are a group of lysosomal multisystemic, chronic, and progressive diseases characterized by the storage of glycosaminoglycans (GAGs) that may affect the central nervous system. Neuronopathic MPS such as MPS IH, MPS II, MPS IIIA–D, and MPS VII are characterized by neurocognitive regression. In severe MPS I (MPS IH, or Hurler syndrome) initial developmental trajectory is usually unremarkable but cognitive development shows a plateau by 2 to 4 years of age and then progressively regresses with aging. Patients with neuronopathic MPS II have a plateau of cognitive and adaptive development on average by 4 to 4.5 years of age, although there is significant variability, followed by progressive neurocognitive decline. In patients with classic MPS III, developmental trajectory reaches a plateau around 3 years of age, followed by regression. Sleep disturbances and behavioral problems occur early in MPS II and III with features of externalizing disorders. Acquired autism-like behavior is often observed in children with MPS III after 4–6 years of age. Impaired social and communication abilities do occur, but MPS III children do not have restricted and repetitive interests such as in autism spectrum disorder. MPS type VII is an ultra-rare neuronopathic MPS with a wide clinical spectrum from very severe with early mortality to milder phenotypes with longer survival into adolescence and adulthood. Most patients with MPS VII have intellectual disability and severely delayed speech development, usually associated with hearing impairment. Cognitive regression in neuronopathic MPS runs parallel to a significant decrease in brain tissue volume. Assessment of the developmental profile is challenging because of low cognitive abilities, physical impairment, and behavioral disturbances. Early diagnosis is crucial as different promising treatment approaches have been extensively studied in animal MPS models and are currently being applied in clinical trials.

Neuromelanin organelles are specialized autolysosomes that accumulate undegraded proteins and lipids in aging human brain and are likely involved in Parkinson's disease

During aging, neuronal organelles filled with neuromelanin (a dark-brown pigment) and lipid bodies accumulate in the brain, particularly in the substantia nigra, a region targeted in Parkinson's disease. We have investigated protein and lipid systems involved in the formation of these organelles and in the synthesis of the neuromelanin of human substantia nigra. Membrane and matrix proteins characteristic of lysosomes were found in neuromelanin-containing organelles at a lower number than in typical lysosomes, indicating a reduced enzymatic activity and likely impaired capacity for lysosomal and autophagosomal fusion. The presence of proteins involved in lipid transport may explain the accumulation of lipid bodies in the organelle and the lipid component in neuromelanin structure. The major lipids observed in lipid bodies of the organelle are dolichols with lower amounts of other lipids. Proteins of aggregation and degradation pathways were present, suggesting a role for accumulation by this organelle when the ubiquitin-proteasome system is inadequate. The presence of proteins associated with aging and storage diseases may reflect impaired autophagic degradation or impaired function of lysosomal enzymes. The identification of typical autophagy proteins and double membranes demonstrates the organelle's autophagic nature and indicates that it has engulfed neuromelanin precursors from the cytosol. Based on these data, it appears that the neuromelanin-containing organelle has a very slow turnover during the life of a neuron and represents an intracellular compartment of final destination for numerous molecules not degraded by other systems.

Serum global metabolomics profiling reveals profound metabolic impairments in patients with MPS IIIA and MPS IIIB

The monogenic defects in specific lysosomal enzymes in mucopolysaccharidosis (MPS) III lead to lysosomal storage of glycosaminoglycans and complex CNS and somatic pathology, for which the detailed mechanisms remain unclear. In this study, serum samples from patients with MPS IIIA (age 2-9 yr) and MPS IIIB (2-13 yr) and healthy controls (age 2-9 yr) were assayed by global metabolomics profiling of 658 metabolites using mass spectrometry. Significant alterations were detected in 423 metabolites in all MPS III patients, of which 366 (86.5%) decreased and 57 (13.5%) increased. Similar profiles were observed when analyzing data from MPS IIIA and MPS IIIB samples separately, with only limited age variations in 36 metabolites. The observed metabolic disturbances in MPS III patients involve virtually all major pathways of amino acid (101/150), peptide (17/21), carbohydrate (19/23), lipid (221/325), nucleotide (15/25), energy (8/9), vitamins and co-factors (8/21), and xenobiotics (34/84) metabolism. Notably, detected serum metabolite decreases involved all key amino acids, all major neurotransmitter pathways, and broad neuroprotective compounds. The elevated metabolites are predominantly lipid derivatives, and also include cysteine metabolites and a fibrinogen peptide fragment, consistent with the status of oxidative stress and inflammation in MPS III. This study demonstrates that the lysosomal glycosaminoglycans storage triggers profound metabolic disturbances in patients with MPS III disorders, leading to severe functional depression of virtually all metabolic pathways, which emerge early during the disease progression. Serum global metabolomics profiling may provide an important and minimally invasive tool for better understanding the disease mechanisms and identification of potential biomarkers for MPS III.

A novel conditional Sgsh knockout mouse model recapitulates phenotypic and neuropathic deficits of Sanfilippo syndrome

Mucopolysaccharidosis (MPS) type IIIA, or Sanfilippo syndrome, is a neurodegenerative lysosomal storage disorder caused by a deficiency of the lysosomal enzyme N-sulfoglucosamine sulfohydrolase (SGSH), involved in the catabolism of heparan sulfate. The clinical spectrum is broad and the age of symptom onset and the degree of preservation of cognitive and motor functions appears greatly influenced by genotype. To explore this further, we generated a conditional knockout (Sgsh ^KO ) mouse model with ubiquitous Sgsh deletion, and compared the clinical and pathological phenotype with that of the spontaneous Sgsh ^D31N MPS-IIIA mouse model. Phenotypic deficits were noted in Sgsh ^KO mice prior to Sgsh ^D31N mice, however these outcomes did not correlate with any shift in the time of appearance nor rate of accumulation of primary (heparan sulfate) or secondary substrates (GM2/GM3 gangliosides). Other disease lesions (elevations in lysosomal integral membrane protein-II expression, reactive astrocytosis and appearance of ubiquitin-positive inclusions) were also comparable between affected mouse strains. This suggests that gross substrate storage and these neuropathological markers are neither primary determinants, nor good biomarkers/indicators of symptom generation, confirming similar observations made recently in MPS-IIIA patients. The Sgsh ^KO mouse will be a useful tool for elucidation of the neurological basis of disease and assessment of the clinical efficacy of new treatments for Sanfilippo syndrome.

Near-Complete Correction of Profound Metabolomic Impairments Corresponding to Functional Benefit in MPS IIIB Mice after IV rAAV9-hNAGLU Gene Delivery

Mucopolysaccharidosis (MPS) IIIB is a lysosomal storage disease with complex CNS and somatic pathology due to a deficiency in α-N-acetylglucosaminidase (NAGLU). Using global metabolic profiling by mass spectrometry targeting 361 metabolites, this study detected significant decreases in 225 and increases in six metabolites in serum samples from 7-month-old MPS IIIB mice, compared to wild-type (WT) mice. The metabolic disturbances involve virtually all major pathways of amino acid, peptide (58/102), carbohydrate (18/28), lipid (111/139), nucleotide (12/24), energy (2/9), vitamin and cofactor (11/16), and xenobiotic (11/28) metabolism. Notably, the reduced metabolites included eight essential amino acids, vitamins (C, E, B2, and B6), and neurotransmitters (serotonin, glutamate, aspartate, tryptophan, and N-acetyltyrosine). The metabolic impairments appear to emerge early during disease progression before the age of 2 months. Importantly, the restoration of NAGLU activity with an intravenous (i.v.) injection of rAAV9-hNAGLU vector led to near-complete correction of all serum metabolite abnormalities, with 201 (87%) metabolites normalized and 30 (13%) over-corrected. While the mechanisms are unclear, our data demonstrate that the lack of NAGLU activity triggers profound functional metabolic disturbances in MPS IIIB. These metabolic impairments respond well to a systemic rAAV9-hNAGLU gene delivery, supporting the surrogate biomarker potential of serum metabolomic profiles for MPS IIIB therapies.

A GLP-Compliant Toxicology and Biodistribution Study: Systemic Delivery of an rAAV9 Vector for the Treatment of Mucopolysaccharidosis IIIB

No treatment is currently available for mucopolysaccharidosis (MPS) IIIB, a neuropathic lysosomal storage disease due to defect in α-N-acetylglucosaminidase (NAGLU). In preparation for a clinical trial, we performed an IND-enabling GLP-toxicology study to assess systemic rAAV9-CMV-hNAGLU gene delivery in WT C57BL/6 mice at 1 × 10(14) vg/kg and 2 × 10(14) vg/kg (n = 30/group, M:F = 1:1), and non-GLP testing in MPS IIIB mice at 2 × 10(14) vg/kg. Importantly, no adverse clinical signs or chronic toxicity were observed through the 6 month study duration. The rAAV9-mediated rNAGLU expression was rapid and persistent in virtually all tested CNS and somatic tissues. However, acute liver toxicity occurred in 33% (5/15) WT males in the 2 × 10(14) vg/kg cohort, which was dose-dependent, sex-associated, and genotype-specific, likely due to hepatic rNAGLU overexpression. Interestingly, a significant dose response was observed only in the brain and spinal cord, whereas in the liver at 24 weeks postinfection (pi), NAGLU activity was reduced to endogenous levels in the high dose cohort but remained at supranormal levels in the low dose group. The possibility of rAAV9 germline transmission appears to be minimal. The vector delivery resulted in transient T-cell responses and characteristic acute antibody responses to both AAV9 and rNAGLU in all rAAV9-treated animals, with no detectable impacts on tissue transgene expression. This study demonstrates a generally safe and effective profile, and may have identified the upper dosing limit of rAAV9-CMV-hNAGLU via systemic delivery for the treatment of MPS IIIB.

Progressive neurologic and somatic disease in a novel mouse model of human mucopolysaccharidosis type IIIC

Mucopolysaccharidosis type IIIC (MPSIIIC) is a severe lysosomal storage disease caused by deficiency in activity of the transmembrane enzyme heparan-α-glucosaminide N-acetyltransferase (HGSNAT) that catalyses the N-acetylation of α-glucosamine residues of heparan sulfate. Enzyme deficiency causes abnormal substrate accumulation in lysosomes, leading to progressive and severe neurodegeneration, somatic pathology and early death. There is no cure for MPSIIIC, and development of new therapies is challenging because of the unfeasibility of cross-correction. In this study, we generated a new mouse model of MPSIIIC by targeted disruption of the Hgsnat gene. Successful targeting left LacZ expression under control of the Hgsnat promoter, allowing investigation into sites of endogenous expression, which was particularly prominent in the CNS, but was also detectable in peripheral organs. Signs of CNS storage pathology, including glycosaminoglycan accumulation, lysosomal distension, lysosomal dysfunction and neuroinflammation were detected in 2-month-old animals and progressed with age. Glycosaminoglycan accumulation and ultrastructural changes were also observed in most somatic organs, but lysosomal pathology seemed most severe in liver. Furthermore, HGSNAT-deficient mice had altered locomotor and exploratory activity and shortened lifespan. Hence, this animal model recapitulates human MPSIIIC and provides a useful tool for the study of disease physiopathology and the development of new therapeutic approaches.

N-butyldeoxynojirimycin treatment restores the innate fear response and improves learning in mucopolysaccharidosis IIIA mice

Mucopolysaccharidosis IIIA is a heritable neurodegenerative disorder resulting from the dysfunction of the lysosomal hydrolase sulphamidase. This leads to the primary accumulation of the complex carbohydrate heparan sulphate in a wide range of tissues and the secondary neuronal storage of gangliosides GM2 and GM3 in the brain. GM2 storage is associated with CNS deterioration in the GM2 gangliosidosis group of lysosomal storage disorders and may also contribute to MPS CNS disease. N-butyldeoxynojirimycin, an inhibitor of ceramide glucosyltransferase activity and therefore of ganglioside synthesis, was administered to MPS IIIA mice both prior to maximal GM2 and GM3 accumulation (early treatment) and after the maximum level of ganglioside had accumulated in the brain (late treatment) to determine if behaviour was altered by ganglioside level. Ceramide glucosyltransferase activity was decreased in both treatment groups; however, brain ganglioside levels were only decreased in the late treatment group. Learning in the water cross maze was improved in both groups and the innate fear response was also restored in both groups. A reduction in the expression of inflammatory gene Ccl3 was observed in the early treatment group, while IL1β expression was reduced in both treatment groups. Thus, it appears that NB-DNJ elicits a transient decrease in brain ganglioside levels, some modulation of inflammatory cytokines and a functional improvement in behaviour that can be elicited both before and after overt neurological changes manifest.

SYNOPSIS

NB-DNJ improves learning and restores the innate fear response in MPS IIIA mice by decreasing ceramide glucosyltransferase activity and transiently reducing ganglioside storage and/or modulating inflammatory signals.

Oxidative and nitrative stress and pro-inflammatory cytokines in Mucopolysaccharidosis type II patients: effect of long-term enzyme replacement therapy and relation with glycosaminoglycan accumulation

Mucopolysaccharidosis type II (MPS II) is a lysosomal storage disease caused by a deficient activity of iduronate-2-sulfatase, leading to abnormal accumulation of glycosaminoglycans (GAG). The main treatment for MPS II is enzyme replacement therapy (ERT). Previous studies described potential benefits of six months of ERT against oxidative stress in patients. Thus, the aim of this study was to investigate oxidative, nitrative and inflammatory biomarkers in MPS II patients submitted to long term ERT. It were analyzed urine and blood samples from patients on ERT (mean time: 5.2years) and healthy controls. Patients presented increased levels of lipid peroxidation, assessed by urinary 15-F2t-isoprostane and plasmatic thiobarbituric acid-reactive substances. Concerning to protein damage, urinary di-tyrosine (di-Tyr) was increased in patients; however, sulfhydryl and carbonyl groups in plasma were not altered. It were also verified increased levels of urinary nitrate+nitrite and plasmatic nitric oxide (NO) in MPS II patients. Pro-inflammatory cytokines IL-1β and TNF-α were increased in treated patients. GAG levels were correlated to di-Tyr and nitrate+nitrite. Furthermore, IL-1β was positively correlated with TNF-α and NO. Contrastingly, we did not observed alterations in erythrocyte superoxide dismutase, catalase, glutathione peroxidase and glutathione reductase activities, in reduced glutathione content and in the plasmatic antioxidant capacity. Although some parameters were still altered in MPS II patients, these results may suggest a protective role of long-term ERT against oxidative stress, especially upon oxidative damage to protein and enzymatic and non-enzymatic defenses. Moreover, the redox imbalance observed in treated patients seems to be GAG- and pro-inflammatory cytokine-related.

Novel grooved substrata stimulate macrophage fusion, CCL2 and MMP-9 secretion

Rough surface topographies on implants attract macrophages but the influence of topography on macrophage fusion to produce multinucleated giant cells (MGC) and foreign body giant cells (FBGC) is unclear. Two rough novel grooved substrata, G1 and G2, fabricated by anisotropic etching of Silicon <110> crystals without the use of photolithographic patterning, and a control smooth surface (Pol) were produced and replicated in epoxy. The surfaces were compared for their effects on RAW264.7 macrophage morphology, gene expression, cyto/chemokine secretion, and fusion for one and five days. Macrophages on grooved surfaces exhibited an elongated morphology similar to M2 macrophages and increased cell alignment with surface directionality, roughness and cell culture time. Up-regulated expression of macrophage chemoattractants at gene and protein level was observed on both grooved surfaces relative to Pol. Grooved surfaces showed time-dependent increase in soluble mediators involved in cell fusion, CCL2 and MMP-9, and an increased proportion of multinucleated cells at Day 5. Collectively, this study demonstrated that a rough surface with surface directionality produced changes in macrophage shape and macrophage attractant chemokines and soluble mediators involved in cell fusion. These in vitro results suggest a possible explanation for the observed accumulation of macrophages and MGCs on rough surfaced implants in vivo. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 2243-2254, 2016.

Immune-Mediated Inflammation May Contribute to the Pathogenesis of Cardiovascular Disease in Mucopolysaccharidosis Type I

Background

Cardiovascular disease, a progressive manifestation of α-L-iduronidase deficiency or mucopolysaccharidosis type I, continues in patients both untreated and treated with hematopoietic stem cell transplantation or intravenous enzyme replacement. Few studies have examined the effects of α-L-iduronidase deficiency and subsequent glycosaminoglycan storage upon arterial gene expression to understand the pathogenesis of cardiovascular disease.

Methods

Gene expression in carotid artery, ascending, and descending aortas from four non-tolerized, non-enzyme treated 19 month-old mucopolysaccharidosis type I dogs was compared with expression in corresponding vascular segments from three normal, age-matched dogs. Data were analyzed using R and whole genome network correlation analysis, a bias-free method of categorizing expression level and significance into discrete modules. Genes were further categorized based on module-trait relationships. Expression of clusterin, a protein implicated in other etiologies of cardiovascular disease, was assessed in canine and murine mucopolysaccharidosis type I aortas via Western blot and in situ immunohistochemistry.

Results

Gene families with more than two-fold, significant increased expression involved lysosomal function, proteasome function, and immune regulation. Significantly downregulated genes were related to cellular adhesion, cytoskeletal elements, and calcium regulation. Clusterin gene overexpression (9-fold) and protein overexpression (1.3 to 1.62-fold) was confirmed and located specifically in arterial plaques of mucopolysaccharidosis-affected dogs and mice.

Conclusions

Overexpression of lysosomal and proteasomal-related genes are expected responses to cellular stress induced by lysosomal storage in mucopolysaccharidosis type I. Upregulation of immunity-related genes implicates the potential involvement of glycosaminoglycan-induced inflammation in the pathogenesis of mucopolysaccharidosis-related arterial disease, for which clusterin represents a potential biomarker.

Electrophysiological and Histological Characterization of Rod-Cone Retinal Degeneration and Microglia Activation in a Mouse Model of Mucopolysaccharidosis Type IIIB

Sanfilippo syndrome Type B or Mucopolysaccharidosis IIIB (MPS IIIB) is a neurodegenerative autosomal recessive lysosomal storage disorder in which patients suffer severe vision loss from associated retinopathy. Here we sought to study the underlying retinal functional and morphological changes associated with MPS IIIB disease progression using the established model of MPS IIIB, the B6.129S6-Naglu(tm1Efn)/J mouse line. Electroretinogram (ERG) was recorded from MPS IIIB and wild-type (WT) mice at the age of 28 and 46 weeks, and retinal tissues were subsequently collected for immunohistochemistry analysis. At the 28th week, rod a- and b-wave amplitudes were significantly diminished in MPS IIIB compared to WT mice. The cone a- and b-waves of MPS IIIB mice were not significantly different from those of the control at the 28th week but were significantly diminished at the 46 th week, when MPS IIIB mice showed a major loss of rods and rod bipolar cells in both central and peripheral regions and a minor loss of cones in the periphery. Activation of microglia and neovascularization were also detected in the MPS IIIB retina. The new findings that cones and rod bipolar cells also undergo degeneration, and that retinal microglia are activated, will inform future development of therapeutic strategies.

Neuroinflammatory paradigms in lysosomal storage diseases

Lysosomal storage diseases (LSDs) include approximately 70 distinct disorders that collectively account for 14% of all inherited metabolic diseases. LSDs are caused by mutations in various enzymes/proteins that disrupt lysosomal function, which impairs macromolecule degradation following endosome-lysosome and phagosome-lysosome fusion and autophagy, ultimately disrupting cellular homeostasis. LSDs are pathologically typified by lysosomal inclusions composed of a heterogeneous mixture of various proteins and lipids that can be found throughout the body. However, in many cases the CNS is dramatically affected, which may result from heightened neuronal vulnerability based on their post-mitotic state. Besides intrinsic neuronal defects, another emerging factor common to many LSDs is neuroinflammation, which may negatively impact neuronal survival and contribute to neurodegeneration. Microglial and astrocyte activation is a hallmark of many LSDs that affect the CNS, which often precedes and predicts regions where eventual neuron loss will occur. However, the timing, intensity, and duration of neuroinflammation may ultimately dictate the impact on CNS homeostasis. For example, a transient inflammatory response following CNS insult/injury can be neuroprotective, as glial cells attempt to remove the insult and provide trophic support to neurons. However, chronic inflammation, as seen in several LSDs, can promote neurodegeneration by creating a neurotoxic environment due to elevated levels of cytokines, chemokines, and pro-apoptotic molecules. Although neuroinflammation has been reported in several LSDs, the cellular basis and mechanisms responsible for eliciting neuroinflammatory pathways are just beginning to be defined. This review highlights the role of neuroinflammation in select LSDs and its potential contribution to neuron loss.

Oxidative stress and inflammation in mucopolysaccharidosis type IVA patients treated with enzyme replacement therapy

Mucopolysaccharidosis type IVA (MPS IVA) is an inborn error of glycosaminoglycan (GAG) catabolism due to the deficient activity of N-acetylgalactosamine-6-sulfate sulfatase that leads to accumulation of the keratan sulfate and chondroitin 6-sulfate in body fluids and in lysosomes. The pathophysiology of this lysosomal storage disorder is not completely understood. The aim of this study was to investigate oxidative stress parameters, pro-inflammatory cytokine and GAG levels in MPS IVA patients. We analyzed urine and blood samples from patients under ERT (n=17) and healthy age-matched controls (n=10-15). Patients presented a reduction of antioxidant defense levels, assessed by a decrease in glutathione content and by an increase in superoxide dismutase activity in erythrocytes. Concerning lipid and protein damage, it was verified increased urine isoprostanes and di-tyrosine levels and decreased plasma sulfhydryl groups in MPS IVA patients compared to controls. MPS IVA patients showed higher DNA damage than control group and this damage had an oxidative origin in both pyrimidine and purine bases. Interleukin 6 was increased in patients and presented an inverse correlation with GSH levels, showing a possible link between inflammation and oxidative stress in MPS IVA disease. The data presented suggest that pro-inflammatory and pro-oxidant states occur in MPS IVA patients even under ERT. Taking these results into account, supplementation of antioxidants in combination with ERT can be a tentative therapeutic approach with the purpose of improving the patient's quality of life. To the best of our knowledge, this is the first study relating MPS IVA patients with oxidative stress.

Neuroinflammation, mitochondrial defects and neurodegeneration in mucopolysaccharidosis III type C mouse model

Severe progressive neurological paediatric disease mucopolysaccharidosis III type C is caused by mutations in the HGSNAT gene leading to deficiency of acetyl-CoA: α-glucosaminide N-acetyltransferase involved in the lysosomal catabolism of heparan sulphate. To understand the pathophysiology of the disease we generated a mouse model of mucopolysaccharidosis III type C by germline inactivation of the Hgsnat gene. At 6-8 months mice showed hyperactivity, and reduced anxiety. Cognitive memory decline was detected at 10 months and at 12-13 months mice showed signs of unbalanced hesitant walk and urinary retention. Lysosomal accumulation of heparan sulphate was observed in hepatocytes, splenic sinus endothelium, cerebral microglia, liver Kupffer cells, fibroblasts and pericytes. Starting from 5 months, brain neurons showed enlarged, structurally abnormal mitochondria, impaired mitochondrial energy metabolism, and storage of densely packed autofluorescent material, gangliosides, lysozyme, phosphorylated tau, and amyloid-β. Taken together, our data demonstrate for the first time that deficiency of acetyl-CoA: α-glucosaminide N-acetyltransferase causes lysosomal accumulation of heparan sulphate in microglial cells followed by their activation and cytokine release. They also show mitochondrial dysfunction in the neurons and neuronal loss explaining why mucopolysaccharidosis III type C manifests primarily as a neurodegenerative disease.

Biochemical, histological and functional correction of mucopolysaccharidosis type IIIB by intra-cerebrospinal fluid gene therapy

Gene therapy is an attractive tool for the treatment of monogenic disorders, in particular for lysosomal storage diseases (LSD) caused by deficiencies in secretable lysosomal enzymes in which neither full restoration of normal enzymatic activity nor transduction of all affected cells are necessary. However, some LSD such as Mucopolysaccharidosis Type IIIB (MPSIIIB) are challenging because the disease's main target organ is the brain and enzymes do not efficiently cross the blood-brain barrier even if present at very high concentration in circulation. To overcome these limitations, we delivered AAV9 vectors encoding for α-N-acetylglucosaminidase (NAGLU) to the Cerebrospinal Fluid (CSF) of MPSIIIB mice with the disease already detectable at biochemical, histological and functional level. Restoration of enzymatic activity in Central Nervous System (CNS) resulted in normalization of glycosaminoglycan content and lysosomal physiology, resolved neuroinflammation and restored the pattern of gene expression in brain similar to that of healthy animals. Additionally, transduction of the liver due to passage of vectors to the circulation led to whole-body disease correction. Treated animals also showed reversal of behavioural deficits and extended lifespan. Importantly, when the levels of enzymatic activity were monitored in the CSF of dogs following administration of canine NAGLU-coding vectors to animals that were either naïve or had pre-existing immunity against AAV9, similar levels of activity were achieved, suggesting that CNS efficacy would not be compromised in patients seropositive for AAV9. Our studies provide a strong rationale for the clinical development of this novel therapeutic approach as the treatment for MPSIIIB.

Repeated Administrations of Human Umbilical Cord Blood Cells Improve Disease Outcomes in a Mouse Model of Sanfilippo Syndrome Type III B

Sanfilippo syndrome type III B (MPS III B) is an inherited disorder characterized by a deficiency of α- N-acetylglucosaminidase (Naglu) enzyme leading to accumulation of heparan sulfate in lysosomes and severe neurological deficits. We have previously shown that a single administration of human umbilical cord mononuclear cells (hUCB MNCs) into Naglu knockout mice decreased behavioral abnormalities and tissue pathology. In this study, we tested whether repeated doses of hUCB MNCs would be more beneficial than a single dose of cells. Naglu mice at 3 months of age were randomly assigned to either a Media-only group or one of three hUCB MNC treatment groups-single low dose (3 × 106 cells), single high dose (1.8 × 107 cells), or multiple doses (3 × 106 cells monthly for 6 months) delivered intravenously; cyclosporine was injected intraperitoneally to immune suppress the mice for the duration of the study. An additional control group of wild-type mice was also used. We measured anxiety in an open field test and cognition in an active avoidance test prior to treatment and then at monthly intervals for 6 months. hUCB MNCs restored normal anxiety-like behavior in these mice ( p< 0.001). The repeated cell administrations also restored hippocampal cytoarchitecture, protected the dendritic tree, decreased GM3 ganglioside accumulation, and decreased microglial activation, particularly in the hippocampus and cortex. These data suggest that the neuroprotective effect of hUCB MNCs can be enhanced by repeated cell administrations.

Feasibility and safety of systemic rAAV9-hNAGLU delivery for treating mucopolysaccharidosis IIIB: toxicology, biodistribution, and immunological assessments in primates

No treatment is currently available for mucopolysaccharidosis (MPS) IIIB, a neuropathic lysosomal storage disease caused by autosomal recessive defect in α-N-acetylglucosaminidase (NAGLU). In anticipation of a clinical gene therapy treatment for MPS IIIB in humans, we tested the rAAV9-CMV-hNAGLU vector administration to cynomolgus monkeys (n=8) at 1E13 vg/kg or 2E13 vg/kg via intravenous injection. No adverse events or detectable toxicity occurred over a 6-month period. Gene delivery resulted in persistent global central nervous system and broad somatic transduction, with NAGLU activity detected at 2.9-12-fold above endogenous levels in somatic tissues and 1.3-3-fold above endogenous levels in the brain. Secreted rNAGLU was detected in serum. Low levels of preexisting anti-AAV9 antibodies (Abs) did not diminish vector transduction. Importantly, high-level preexisting anti-AAV9 Abs lead to reduced transduction in liver and other somatic tissues, but had no detectable impact on transgene expression in the brain. Enzyme-linked immunoabsorbent assay showed Ab responses to both AAV9 and rNAGLU in treated animals. Serum anti-hNAGLU Abs, but not anti-AAV9 Abs, correlated with the loss of circulating rNAGLU enzyme. However, serum Abs did not affect tissue rNAGLU activity levels. Weekly or monthly peripheral blood interferon-γ enzyme-linked immunospot assays detected a CD4(+) T-cell (Th-1) response to rNAGLU only at 4 weeks postinjection in one treated subject, without observable correlation to tissue transduction levels. The treatment did not result in detectable CTL responses to either AAV9 or rNAGLU. Our data demonstrate an effective and safe profile for systemic rAAV9-hNAGLU vector delivery in nonhuman primates, supporting its clinical potential in humans.

Pathological and biochemical studies of mucopolysaccharidosis type IIIB (Sanfilippo syndrome type B) in juvenile emus (Dromaius novaehollandiae)

Mucopolysaccharidosis (MPS) type IIIB was diagnosed in 14 juvenile emus (Dromaius novaehollandiae), ages 3 weeks to 6 months, based on pathological and biochemical analyses. The animals had a history of neurological signs or sudden death; one of the birds with neurological signs and 3 others experienced acute hemoabdomen. Histopathologically, neuronal swelling and vacuolation in the cerebrum, cerebellum, brainstem, and spinal cord (80%-92%); retina (100%); autonomic ganglia of the intestine (71%); gizzard (50%); adrenal gland (27%); and ear (50%) were noted in affected but not healthy emus. Cytoplasmic vacuoles were also observed in the pancreas, liver, intestine, adrenal glands, and kidneys. The intracytoplasmic inclusions were periodic acid-Schiff and Luxol Fast Blue positive, consistent with a storage disease. Foamy macrophages infiltrated the liver, intestine, tunica media of the aorta, and spleen. By transmission electron microscopy, typical lamellated cytoplasmic bodies were detected in neurons of the brain and retina, while electron-dense bodies consistent with glycosaminoglycan inclusions were observed in hepatocytes and/or hepatic macrophages. The livers of the 2 affected emus studied contained large amounts of heparan sulfate, which is suggestive of MPS type III. Compared with normal controls, hepatic and serum α-N-acetylglucosaminidase activity was very low (<8% of control), while other enzyme activities were normal to increased in the 2 affected emus studied. Moreover, affected emus were homozygous for a 2-bp deletion in the NAGLU gene. This study characterizes the pathology of MPS type IIIB in emus, which is one of the rare inborn errors in birds, showing the homology of this condition to Sanfilippo syndrome in humans.

Mucopolysaccharide diseases: a complex interplay between neuroinflammation, microglial activation and adaptive immunity

Mucopolysaccharide (MPS) diseases are lysosomal storage disorders (LSDs) caused by deficiencies in enzymes required for glycosaminoglycan (GAG) catabolism. Mucopolysaccharidosis I (MPS I), MPS IIIA, MPS IIIB and MPS VII are deficient in the enzymes α-L-Iduronidase, Heparan-N-Sulphatase, N-Acetylglucosaminidase and Beta-Glucuronidase, respectively. Enzyme deficiency leads to the progressive multi-systemic build-up of heparan sulphate (HS) and dermatan sulphate (DS) within cellular lysosomes, followed by cell, tissue and organ damage and in particular neurodegeneration. Clinical manifestations of MPS are well established; however as lysosomes represent vital components of immune cells, it follows that lysosomal accumulation of GAGs could affect diverse immune functions and therefore influence disease pathogenesis. Theoretically, MPS neurodegeneration and GAGs could be substantiating a threat of danger and damage to alert the immune system for cellular clearance, which due to the progressive nature of MPS storage would propagate disease pathogenesis. Innate immunity appears to have a key role in MPS; however the extent of adaptive immune involvement remains to be elucidated. The current literature suggests a complex interplay between neuroinflammation, microglial activation and adaptive immunity in MPS disease.

Amyloidosis, synucleinopathy, and prion encephalopathy in a neuropathic lysosomal storage disease: the CNS-biomarker potential of peripheral blood

Mucopolysaccharidosis (MPS) IIIB is a devastating neuropathic lysosomal storage disease with complex pathology. This study identifies molecular signatures in peripheral blood that may be relevant to MPS IIIB pathogenesis using a mouse model. Genome-wide gene expression microarrays on pooled RNAs showed dysregulation of 2,802 transcripts in blood from MPS IIIB mice, reflecting pathological complexity of MPS IIIB, encompassing virtually all previously reported and as yet unexplored disease aspects. Importantly, many of the dysregulated genes are reported to be tissue-specific. Further analyses of multiple genes linked to major pathways of neurodegeneration demonstrated a strong brain-blood correlation in amyloidosis and synucleinopathy in MPS IIIB. We also detected prion protein (Prnp) deposition in the CNS and Prnp dysregulation in the blood in MPS IIIB mice, suggesting the involvement of Prnp aggregation in neuropathology. Systemic delivery of trans-BBB-neurotropic rAAV9-hNAGLU vector mediated not only efficient restoration of functional α-N-acetylglucosaminidase and clearance of lysosomal storage pathology in the central nervous system (CNS) and periphery, but also the correction of impaired neurodegenerative molecular pathways in the brain and blood. Our data suggest that molecular changes in blood may reflect pathological status in the CNS and provide a useful tool for identifying potential CNS-specific biomarkers for MPS IIIB and possibly other neurological diseases.