Neuropathology provides clues to the pathophysiology of Gaucher disease

Impact of Gba2 on neuronopathic Gaucher's disease and α-synuclein accumulation in medaka (Oryzias latipes)

Homozygous mutations in the lysosomal glucocerebrosidase gene, GBA1, cause Gaucher’s disease (GD), while heterozygous mutations in GBA1 are a strong risk factor for Parkinson’s disease (PD), whose pathological hallmark is intraneuronal α-synuclein (asyn) aggregates. We previously reported that gba1 knockout (KO) medaka exhibited glucosylceramide accumulation and neuronopathic GD phenotypes, including short lifespan, the dopaminergic and noradrenergic neuronal cell loss, microglial activation, and swimming abnormality, with asyn accumulation in the brains. A recent study reported that deletion of GBA2, non-lysosomal glucocerebrosidase, in a non-neuronopathic GD mouse model rescued its phenotypes. In the present study, we generated gba2 KO medaka and examined the effect of Gba2 deletion on the phenotypes of gba1 KO medaka. The Gba2 deletion in gba1 KO medaka resulted in the exacerbation of glucosylceramide accumulation and no improvement in neuronopathic GD pathological changes, asyn accumulation, or swimming abnormalities. Meanwhile, though gba2 KO medaka did not show any apparent phenotypes, biochemical analysis revealed asyn accumulation in the brains. gba2 KO medaka showed a trend towards an increase in sphingolipids in the brains, which is one of the possible causes of asyn accumulation. In conclusion, this study demonstrated that the deletion of Gba2 does not rescue the pathological changes or behavioral abnormalities of gba1 KO medaka, and GBA2 represents a novel factor affecting asyn accumulation in the brains.

Murine Models of Lysosomal Storage Diseases Exhibit Differences in Brain Protein Aggregation and Neuroinflammation

Genetic, epidemiological and experimental evidence implicate lysosomal dysfunction in Parkinson’s disease (PD) and related synucleinopathies. Investigate several mouse models of lysosomal storage diseases (LSDs) and evaluate pathologies reminiscent of synucleinopathies. We obtained brain tissue from symptomatic mouse models of Gaucher, Fabry, Sandhoff, Niemann–Pick A (NPA), Hurler, Pompe and Niemann–Pick C (NPC) diseases and assessed for the presence of Lewy body-like pathology (proteinase K-resistant α-synuclein and tau aggregates) and neuroinflammation (microglial Iba1 and astrocytic GFAP) by immunofluorescence. All seven LSD models exhibited evidence of proteinopathy and/or inflammation in the central nervous system (CNS). However, these phenotypes were divergent. Gaucher and Fabry mouse models displayed proteinase K-resistant α-synuclein and tau aggregates but no neuroinflammation; whereas Sandhoff, NPA and NPC showed marked neuroinflammation and no overt proteinopathy. Pompe disease animals uniquely displayed widespread distribution of tau aggregates accompanied by moderate microglial activation. Hurler mice also demonstrated proteinopathy and microglial activation. The present study demonstrated additional links between LSDs and pathogenic phenotypes that are hallmarks of synucleinopathies. The data suggest that lysosomal dysregulation can contribute to brain region-specific protein aggregation and induce widespread neuroinflammation in the brain. However, only a few LSD models examined exhibited phenotypes consistent with synucleinopathies. While no model can recapitulate the complexity of PD, they can enable the study of specific pathways and mechanisms contributing to disease pathophysiology. The present study provides evidence that there are existing, previously unutilized mouse models that can be employed to study pathogenic mechanisms and gain insights into potential PD subtypes, helping to determine if they are amenable to pathway-specific therapeutic interventions.

Lipids, lysosomes and mitochondria: insights into Lewy body formation from rare monogenic disorders

Accumulation of the protein α-synuclein into insoluble intracellular deposits termed Lewy bodies (LBs) is the characteristic neuropathological feature of LB diseases, such as Parkinson's disease (PD), Parkinson's disease dementia (PDD) and dementia with LB (DLB). α-Synuclein aggregation is thought to be a critical pathogenic event in the aetiology of LB disease, based on genetic analyses, fundamental studies using model systems, and the observation of LB pathology in post-mortem tissue. However, some monogenic disorders not traditionally characterised as synucleinopathies, such as lysosomal storage disorders, iron storage disorders and mitochondrial diseases, appear disproportionately vulnerable to the deposition of LBs, perhaps suggesting the process of LB formation may be a result of processes perturbed as a result of these conditions. The present review discusses biological pathways common to monogenic disorders associated with LB formation, identifying catabolic processes, particularly related to lipid homeostasis, autophagy and mitochondrial function, as processes that could contribute to LB formation. These findings are discussed in the context of known mediators of α-synuclein aggregation, highlighting the potential influence of impairments to these processes in the aetiology of LB formation.

Brain Microglial Activation Increased in Glucocerebrosidase (GBA) Mutation Carriers without Parkinson's disease

BACKGROUND

Glucocerebrosidase gene mutations are a common genetic risk factor for Parkinson's disease. They exhibit incomplete penetrance. The objective of the present study was to measure microglial activation and dopamine integrity in glucocerebrosidase gene mutation carriers without Parkinson's disease compared to controls.

METHODS

We performed PET scans on 9 glucocerebrosidase gene mutation carriers without Parkinson's disease and 29 age-matched controls. We measured microglial activation as 11 C-(R)-PK11195 binding potentials, and dopamine terminal integrity with 18 F-dopa influx constants.

RESULTS

The 11 C-(R)-PK11195 binding potential was increased in the substantia nigra of glucocerebrosidase gene carriers compared with controls (Student t test; right, t = -4.45, P = 0.0001). Statistical parametric mapping also localized significantly increased 11 C-(R)-PK11195 binding potential in the occipital and temporal lobes, cerebellum, hippocampus, and mesencephalon. The degree of hyposmia correlated with nigral 11 C-(R)-PK11195 regional binding potentials (Spearman's rank, P = 0.0066). Mean striatal 18 F-dopa uptake was similar to healthy controls.

CONCLUSIONS

In vivo 11 C-(R)-PK11195 PET imaging detects neuroinflammation in brain regions susceptible to Lewy pathology in glucocerebrosidase gene mutation carriers without Parkinson's. © 2020 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Diseases and conditions that impact maternal and fetal health and the potential for nanomedicine therapies

Maternal mortality rates in the United States have steadily increased since 1987 to the current rate of over 16 deaths per 100,000 live births. Whereas most of these deaths are related to an underlying condition, such as cardiovascular disease, many pregnant women die from diseases that emerge as a consequence of pregnancy. Both pre-existing and emergent diseases and conditions are difficult to treat in pregnant women because of the potential harmful effects of the treatment on the developing fetus. Often the health of the woman and the health of the baby are at odds and must be weighed against each other when medical treatment is needed, frequently leading to iatrogenic preterm birth. However, the use of engineered nanomedicines has the potential to fill the treatment gap for pregnant women. This review describes several conditions that may afflict pregnant women and fetuses and introduces how engineered nanomedicines may be used to treat these illnesses. Although the field of maternal-fetal nanomedicine is in its infancy, with additional research and development, engineered nanotherapeutics may greatly improve outcomes for pregnant women and their offspring in the future.

c-Abl activates RIPK3 signaling in Gaucher disease

Gaucher disease (GD) is caused by homozygous mutations in the GBA1 gene, which encodes the lysosomal β-glucosidase (GBA) enzyme. GD affects several organs and tissues, including the brain in certain variants of the disease. Heterozygous GBA1 variants are a major genetic risk factor for developing Parkinson's disease. The RIPK3 kinase is relevant in GD and its deficiency improves the neurological and visceral symptoms in a murine GD model. RIPK3 mediates necroptotic-like cell death: it is unknown whether the role of RIPK3 in GD is the direct induction of necroptosis or if it has a more indirect function by mediating necrosis-independent. Also, the mechanisms that activate RIPK3 in GD are currently unknown. In this study, we show that c-Abl tyrosine kinase participates upstream of RIPK3 in GD. We found that the active, phosphorylated form of c-Abl is increased in several GD models, including patient's fibroblasts and GBA null mice. Furthermore, its pharmacological inhibition with the FDA-approved drug Imatinib decreased RIPK3 signaling. We found that c-Abl interacts with RIPK3, that RIPK3 is phosphorylated at a tyrosine site, and that this phosphorylation is reduced when c-Abl is inhibited. Genetic ablation of c-Abl in neuronal GD and GD mice models significantly reduced RIPK3 activation and MLKL downstream signaling. These results showed that c-Abl signaling is a new upstream pathway that activates RIPK3 and that its inhibition is an attractive therapeutic approach for the treatment of GD.

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

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

Glycosphingolipids

Glycosphingolipids are amphiphilic plasma membrane components formed by a glycan linked to a specific lipid moiety. In this chapter we report on these compounds, on their role played in our cells to maintain the correct cell biology.In detail, we report on their structure, on their metabolic processes, on their interaction with proteins and from this, their property to modulate positively in health and negatively in disease, the cell signaling and cell biology.

Eye movement biomarkers allow for the definition of phenotypes in Gaucher Disease

BACKGROUND

Neurological forms of Gaucher disease, the inherited disorder of β-Glucosylceramidase caused by bi-allelic variants in GBA1, is a progressive disorder which lacks a disease-modifying therapy. Systemic manifestations of disease are effectively treated with enzyme replacement therapy, however, molecules which cross the blood-brain barrier are still under investigation. Clinical trials of such therapeutics require robust, reproducible clinical endpoints to demonstrate efficacy and clear phenotypic definitions to identify suitable patients for inclusion in trials. The single consistent clinical feature in all patients with neuronopathic disease is the presence of a supranuclear saccadic gaze palsy, in the presence of Gaucher disease this finding serves as diagnostic of 'type 3' Gaucher disease.

METHODS

We undertook a study to evaluate saccadic eye movements in Gaucher patients and to assess the role of the EyeSeeCam in measuring saccades. The EyeSeeCam is a video-oculography device which was used to run a protocol of saccade measures. We studied 39 patients with non-neurological Gaucher disease (type 1), 21 patients with type 3 (neurological) disease and a series of 35 healthy controls. Mean saccade parameters were compared across disease subgroups.

RESULTS

We confirmed the saccadic abnormality in patients with type 3 Gaucher disease and identified an unexpected subgroup of patients with type 1 Gaucher disease who demonstrated significant saccade parameter abnormalities. These patients also showed subtle neurological findings and shared a GBA1 variant.

CONCLUSIONS

This striking novel finding of a potentially attenuated type 3 Gaucher phenotype associated with a specific GBA1 variant and detectable saccadic abnormality prompts review of current disease classification. Further, this finding highlights the broad spectrum of neuronopathic Gaucher phenotypes relevant when designing inclusion criteria for clinical trials.

The Convergence of Alpha-Synuclein, Mitochondrial, and Lysosomal Pathways in Vulnerability of Midbrain Dopaminergic Neurons in Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disease, characterized by progressive bradykinesia, rigidity, resting tremor, and gait impairment, as well as a spectrum of non-motor symptoms including autonomic and cognitive dysfunction. The cardinal motor symptoms of PD stem from the loss of substantia nigra (SN) dopaminergic (DAergic) neurons, and it remains unclear why SN DAergic neurons are preferentially lost in PD. However, recent identification of several genetic PD forms suggests that mitochondrial and lysosomal dysfunctions play important roles in the degeneration of midbrain dopamine (DA) neurons. In this review, we discuss the interplay of cell-autonomous mechanisms linked to DAergic neuron vulnerability and alpha-synuclein homeostasis. Emerging studies highlight a deleterious feedback cycle, with oxidative stress, altered DA metabolism, dysfunctional lysosomes, and pathological alpha-synuclein species representing key events in the pathogenesis of PD. We also discuss the interactions of alpha-synuclein with toxic DA metabolites, as well as the biochemical links between intracellular iron, calcium, and alpha-synuclein accumulation. We suggest that targeting multiple pathways, rather than individual processes, will be important for developing disease-modifying therapies. In this context, we focus on current translational efforts specifically targeting lysosomal function, as well as oxidative stress via calcium and iron modulation. These efforts could have therapeutic benefits for the broader population of sporadic PD and related synucleinopathies.

Elevated Dkk1 Mediates Downregulation of the Canonical Wnt Pathway and Lysosomal Loss in an iPSC Model of Neuronopathic Gaucher Disease

Gaucher Disease (GD), which is the most common lysosomal storage disorder, is caused by bi-allelic mutations in GBA1-a gene that encodes the lysosomal hydrolase β-glucocerebrosidase (GCase). The neuronopathic forms of GD (nGD) are characterized by severe neurological abnormalities that arise during gestation or early in infancy. Using GD-induced pluripotent stem cell (iPSC)-derived neuronal progenitor cells (NPCs), we have previously reported that neuronal cells have neurodevelopmental defects associated with the downregulation of canonical Wnt signaling. In this study, we report that GD NPCs display elevated levels of Dkk1, which is a secreted Wnt antagonist that prevents receptor activation. Dkk1 upregulation in mutant NPCs resulted in an increased degradation of β-catenin, and there was a concomitant reduction in lysosomal numbers. Consistent with these results, incubation of the mutant NPCs with recombinant Wnt3a (rWnt3a) was able to outcompete the excess Dkk1, increasing β-catenin levels and rescuing lysosomal numbers. Furthermore, the incubation of WT NPCs with recombinant Dkk1 (rDkk1) phenocopied the mutant phenotype, recapitulating the decrease in β-catenin levels and lysosomal depletion seen in nGD NPCs. This study provides evidence that downregulation of the Wnt/β-catenin pathway in nGD neuronal cells involves the upregulation of Dkk1. As Dkk1 is an extracellular Wnt antagonist, our results suggest that the deleterious effects of Wnt/β-catenin downregulation in nGD may be ameliorated by the prevention of Dkk1 binding to the Wnt co-receptor LRP6, pointing to Dkk1 as a potential therapeutic target for GBA1-associated neurodegeneration.

The Role of iPSC Modeling Toward Projection of Autophagy Pathway in Disease Pathogenesis: Leader or Follower

Autophagy is responsible for degradation of non-essential or damaged cellular constituents and damaged organelles. The autophagy pathway maintains efficient cellular metabolism and reduces cellular stress by removing additional and pathogenic components. Dysfunctional autophagy underlies several diseases. Thus, several research groups have worked toward elucidating key steps in this pathway. Autophagy can be studied by animal modeling, chemical modulators, and in vitro disease modeling with induced pluripotent stem cells (iPSC) as a loss-of-function platform. The introduction of iPSC technology, which has the capability to maintain the genetic background, has facilitated in vitro modeling of some diseases. Furthermore, iPSC technology can be used as a platform to study defective cellular and molecular pathways during development and unravel novel steps in signaling pathways of health and disease. Different studies have used iPSC technology to explore the role of autophagy in disease pathogenesis which could not have been addressed by animal modeling or chemical inducers/inhibitors. In this review, we discuss iPSC models of autophagy-associated disorders where the disease is caused due to mutations in autophagy-related genes. We classified this group as "primary autophagy induced defects (PAID)". There are iPSC models of diseases in which the primary cause is not dysfunctional autophagy, but autophagy is impaired secondary to disease phenotypes. We call this group "secondary autophagy induced defects (SAID)" and discuss them. Graphical abstract.

Fabry Disease With Concomitant Lewy Body Disease

Although Gaucher disease can be accompanied by Lewy pathology (LP) and extrapyramidal symptoms, it is unknown if LP exists in Fabry disease (FD), another progressive multisystem lysosomal storage disorder. We aimed to elucidate the distribution patterns of FD-related inclusions and LP in the brain of a 58-year-old cognitively unimpaired male FD patient suffering from predominant hypokinesia. Immunohistochemistry (CD77, α-synuclein, collagen IV) and neuropathological staging were performed on 100-µm sections. Tissue from the enteric or peripheral nervous system was unavailable. As controls, a second cognitively unimpaired 50-year-old male FD patient without LP or motor symptoms and 3 age-matched individuals were examined. Inclusion body pathology was semiquantitatively evaluated. Although Lewy neurites/bodies were not present in the 50-year-old individual or in controls, severe neuronal loss in the substantia nigra pars compacta and LP corresponding to neuropathological stage 4 of Parkinson disease was seen in the 58-year-old FD patient. Major cerebrovascular lesions and/or additional pathologies were absent in this individual. We conclude that Lewy body disease with parkinsonism can occur within the context of FD. Further studies determining the frequencies of both inclusion pathologies in large autopsy-controlled FD cohorts could help clarify the implications of both lesions for disease pathogenesis, potential spreading mechanisms, and therapeutic interventions.

Fronto-temporal dementia risk gene TMEM106B has opposing effects in different lysosomal storage disorders

TMEM106B is a transmembrane protein localized to the endo-lysosomal compartment. Genome-wide association studies have identified TMEM106B as a risk modifier of Alzheimer's disease and frontotemporal lobar degeneration, especially with progranulin haploinsufficiency. We recently demonstrated that TMEM106B loss rescues progranulin null mouse phenotypes including lysosomal enzyme dysregulation, neurodegeneration and behavioural alterations. However, the reason whether TMEM106B is involved in other neurodegenerative lysosomal diseases is unknown. Here, we evaluate the potential role of TMEM106B in modifying the progression of lysosomal storage disorders using progranulin-independent models of Gaucher disease and neuronal ceroid lipofuscinosis. To study Gaucher disease, we employ a pharmacological approach using the inhibitor conduritol B epoxide in wild-type and hypomorphic Tmem106b-/- mice. TMEM106B depletion ameliorates neuronal degeneration and some behavioural abnormalities in the pharmacological model of Gaucher disease, similar to its effect on certain progranulin null phenotypes. In order to examine the role of TMEM106B in neuronal ceroid lipofuscinosis, we crossbred Tmem106b-/- mice with Ppt1-/-, a genetic model of the disease. In contrast to its conduritol B epoxide-rescuing effect, TMEM106B loss exacerbates Purkinje cell degeneration and motor deficits in Ppt1-/- mice. Mechanistically, TMEM106B is known to interact with subunits of the vacuolar ATPase and influence lysosomal acidification. In the pharmacological Gaucher disease model, the acidified lysosomal compartment is enhanced and TMEM106B loss rescues in vivo phenotypes. In contrast, gene-edited neuronal loss of Ppt1 causes a reduction in vacuolar ATPase levels and impairment of the acidified lysosomal compartment, and TMEM106B deletion exacerbates the mouse Ppt1-/- phenotype. Our findings indicate that TMEM106B differentially modulates the progression of the lysosomal storage disorders Gaucher disease and neuronal ceroid lipofuscinosis. The effect of TMEM106B in neurodegeneration varies depending on vacuolar ATPase state and modulation of lysosomal pH. These data suggest TMEM106B as a target for correcting lysosomal pH alterations, and in particular for therapeutic intervention in Gaucher disease and neuronal ceroid lipofuscinosis.

Brain pathology and cerebellar purkinje cell loss in a mouse model of chronic neuronopathic Gaucher disease

Gaucher disease (GD) is currently the focus of considerable attention due primarily to the association between the gene that causes GD (GBA) and Parkinson's disease. Mouse models exist for the systemic (type 1) and for the acute neuronopathic forms (type 2) of GD. Here we report the generation of a mouse that phenotypically models chronic neuronopathic type 3 GD. Gba^-/-;Gba^tg mice, which contain a Gba transgene regulated by doxycycline, accumulate moderate levels of the offending substrate in GD, glucosylceramide, and live for up to 10 months, i.e. significantly longer than mice which model type 2 GD. Gba^-/-;Gba^tg mice display behavioral abnormalities at ∼4 months, which deteriorate with age, along with significant neuropathology including loss of Purkinje neurons. Gene expression is altered in the brain and in isolated microglia, although the changes in gene expression are less extensive than in mice modeling type 2 disease. Finally, bone deformities are consistent with the Gba^-/-;Gba^tg mice being a genuine type 3 GD model. Together, the Gba^-/-;Gba^tg mice share pathological pathways with acute neuronopathic GD mice but also display differences that might help understand the distinct disease course and progression of type 2 and 3 patients.

The Emerging Role of the Lysosome in Parkinson's Disease

Lysosomal function has a central role in maintaining neuronal homeostasis, and, accordingly, lysosomal dysfunction has been linked to neurodegeneration and particularly to Parkinson’s disease (PD). Lysosomes are the converging step where the substrates delivered by autophagy and endocytosis are degraded in order to recycle their primary components to rebuild new macromolecules. Genetic studies have revealed the important link between the lysosomal function and PD; several of the autosomal dominant and recessive genes associated with PD as well as several genetic risk factors encode for lysosomal, autophagic, and endosomal proteins. Mutations in these PD-associated genes can cause lysosomal dysfunction, and since α-synuclein degradation is mostly lysosomal-dependent, among other consequences, lysosomal impairment can affect α-synuclein turnover, contributing to increase its intracellular levels and therefore promoting its accumulation and aggregation. Recent studies have also highlighted the bidirectional link between Parkinson’s disease and lysosomal storage diseases (LSD); evidence includes the presence of α-synuclein inclusions in the brain regions of patients with LSD and the identification of several lysosomal genes involved in LSD as genetic risk factors to develop PD.

Trends in Glucocerebrosides Research: A Systematic Review

Glucocerebrosides are sphingolipid components of cell membranes that intervene in numerous cell biological processes and signaling pathways and that deregulation is implicated in human diseases such as Gaucher disease and Parkinson's disease. In the present study, we conducted a systematic review using document co-citation analysis, clustering and visualization tools to explore the trends and knowledge structure of glucocerebrosides research as indexed in the Science Citation Index Expanded database (1956-present). A co-citation network of 5,324 publications related to glucocerebrosides was constructed. The analysis of emerging categories and keywords suggested a growth of research related to neurosciences over the last decade. We identified ten major areas of research (e.g., clusters) that developed over time, from the oldest (i.e., on glucocerebrosidase protein or molecular analysis of the GBA gene) to the most recent ones (i.e., on drug resistance in cancer, pharmacological chaperones, or Parkinson's disease). We provided for each cluster the most cited publications and a description of their intellectual content. We moreover identified emerging trends in glucocerebrosides research by detecting the surges in the rate of publication citations in the most recent years. In conclusion, this study helps to apprehend the most significant lines of research on glucocerebrosides. This should strengthen the connections between scientific communities studying glycosphingolipids to facilitate advances, especially for the most recent researches on cancer drug resistance and Parkinson's disease.

Glycosphingolipids and neuroinflammation in Parkinson's disease

Parkinson's disease is a progressive neurodegenerative disease characterized by the loss of dopaminergic neurons of the nigrostriatal pathway and the formation of neuronal inclusions known as Lewy bodies. Chronic neuroinflammation, another hallmark of the disease, is thought to play an important role in the neurodegenerative process. Glycosphingolipids are a well-defined subclass of lipids that regulate crucial aspects of the brain function and recently emerged as potent regulators of the inflammatory process. Deregulation in glycosphingolipid metabolism has been reported in Parkinson's disease. However, the interrelationship between glycosphingolipids and neuroinflammation in Parkinson's disease is not well known. This review provides a thorough overview of the links between glycosphingolipid metabolism and immune-mediated mechanisms involved in neuroinflammation in Parkinson's disease. After a brief presentation of the metabolism and function of glycosphingolipids in the brain, it summarizes the evidences supporting that glycosphingolipids (i.e. glucosylceramides or specific gangliosides) are deregulated in Parkinson's disease. Then, the implications of these deregulations for neuroinflammation, based on data from human inherited lysosomal glycosphingolipid storage disorders and gene-engineered animal studies are outlined. Finally, the key molecular mechanisms by which glycosphingolipids could control neuroinflammation in Parkinson's disease are highlighted. These include inflammasome activation and secretion of pro-inflammatory cytokines, altered calcium homeostasis, changes in the blood-brain barrier permeability, recruitment of peripheral immune cells or production of autoantibodies.

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

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

Microglia and astrocyte dysfunction in parkinson's disease

While glia are essential for regulating the homeostasis in the normal brain, their dysfunction contributes to neurodegeneration in many brain diseases, including Parkinson's disease (PD). Recent studies have identified that PD-associated genes are expressed in glial cells as well as neurons and have crucial roles in microglia and astrocytes. Here, we discuss the role of microglia and astrocytes dysfunction in relation to PD-linked mutations and their implications in PD pathogenesis. A better understanding of microglia and astrocyte functions in PD may provide insights into neurodegeneration and novel therapeutic approaches for PD.

Macular Ganglion Cell Complex and Peripapillary Retinal Nerve Fiber Layer Thinning in Patients with Type-1 Gaucher Disease

Type-1 Gaucher disease (GD1) is considered to be non- neuronopathic however recent evidence of neurological involvement continues to accumulate. There is limited evidence of retinal abnormalities in GD1. The purpose of this study was to evaluate the retinal findings of patients with GD1. Thirty GD1 individuals and 30 healthy volunteers between the ages 40–75 years were prospectively enrolled. Macular and optic nerve optical coherence tomography (OCT) scans of both eyes of each patient were performed and thickness maps were compared between groups. Patients with a known neurodegenerative disease, glaucoma, high myopia and previous intraocular surgeries were excluded. It was shown that patients with GD1 presented with higher incidence of abnormal pRNFL OCT scan and showed significantly thinner areas of pRNFL and macular ganglion cell complex (GCC) when compared to a healthy control population. Changes in retinal thickness were not associated with GD1 genotype, treatment status, disease monitoring biomarker (lyso-Gb1) and severity score index (Zimran SSI). Further investigations are needed to determine whether these findings possess functional visual implications and if retinal thinning may serve as biomarker for the development of future neurodegenerative disease in this population.

Enhancing the Activity of Glucocerebrosidase as a Treatment for Parkinson Disease

Mutations in the glucocerebrosidase (GBA1) gene are the most common genetic risk factor for Parkinson disease (PD). Homozygous or compound heterozygous GBA1 mutations cause the lysosomal storage disorder Gaucher disease (GD), characterized by deficient activity of the glucocerebrosidase enzyme (GCase). Both individuals with GD type I and heterozygous carriers of pathogenic variants of GBA1 have an increased risk of developing PD, by approximately ten- to 20-fold compared to non-carriers. GCase activity is also reduced in PD patients without GBA1 mutations, suggesting that the GCase lysosomal pathway might be involved in PD pathogenesis. Available evidence indicates that GCase can affect α-synuclein pathology in different ways. Misfolded GCase proteins are retained in the endoplasmic reticulum, altering the lysosomal trafficking of the enzyme and disrupting protein trafficking. Also, deficient GCase leads to accumulation of substrates that in turn may bind α-synuclein and promote pathological formation of aggregates. Furthermore, α-synuclein itself can lower the enzymatic activity of GCase, indicating that a bidirectional interaction exists between GCase and α-synuclein. Targeted therapies aimed at enhancing GCase activity, augmenting the trafficking of misfolded GCase proteins by small molecule chaperones, or reducing substrate accumulation, have been tested in preclinical and clinical trials. This article reviews the molecular mechanisms linking GCase to α-synuclein and discusses the therapeutic drugs that by targeting the GCase pathway can influence PD progression.

Innate immune response in neuronopathic forms of Gaucher disease confers resistance against viral-induced encephalitis

Both monogenic diseases and viral infections can manifest in a broad spectrum of clinical phenotypes that range from asymptomatic to lethal, suggesting that other factors modulate disease severity. Here, we examine the interplay between the genetic neuronopathic Gaucher’s disease (nGD), and neuroinvasive Sindbis virus (SVNI) infection. Infection of nGD mice with SVNI had no influence on nGD severity. However, nGD mice were more resistant to SVNI infection. Significantly different inflammatory responses were seen in nGD brains when compared with SVNI brains: the inflammatory response in the nGD brains consisted of reactive astrocytes and microglia with no infiltrating macrophages, but the inflammatory response in the brains of SVNI-infected mice was characterized by infiltration of macrophages and altered activation of microglia and astrocytes. We suggest that the innate immune response activated in nGD confers resistance against viral infection of the CNS.

Parkinsonism in Patients with Neuronopathic (Type 3) Gaucher Disease: A Case Series

Background

The link between Parkinson's disease (PD), the second most common neurodegenerative disorder, and nonneuronopathic Gaucher disease (GD) is well established. Currently, PD is primarily associated with nonneuronopathic GD; however, with currently available treatments, patients with chronic neuronopathic GD, who historically had a shortened life span, are now living well into their 50s and beyond.

Cases

We highlight 4 patients with chronic neuronopathic GD with parkinsonian features, describing their GD genotype and phenotype as well as the presentation and progression of their parkinsonism. Symptoms presented in their fourth or fifth decade of life, and include unilateral bradykinesia and/or tremor. Of the patients, 3 had cognitive impairment. The fourth patient has not shown cognitive decline 6 years after PD onset.

Conclusion

This small series highlights that PD is not exclusively associated with nonneuronopathic GD and that as the chronic neuronopathic GD population ages, the clinical spectrum and heterogeneity of neurological manifestations may include parkinsonism.

Upregulating β-hexosaminidase activity in rodents prevents α-synuclein lipid associations and protects dopaminergic neurons from α-synuclein-mediated neurotoxicity

Sandhoff disease (SD) is a lysosomal storage disease, caused by loss of β-hexosaminidase (HEX) activity resulting in the accumulation of ganglioside GM2. There are shared features between SD and Parkinson's disease (PD). α-synuclein (aSYN) inclusions, the diagnostic hallmark sign of PD, are frequently found in the brain in SD patients and HEX knockout mice, and HEX activity is reduced in the substantia nigra in PD. In this study, we biochemically demonstrate that HEX deficiency in mice causes formation of high-molecular weight (HMW) aSYN and ubiquitin in the brain. As expected from HEX enzymatic function requirements, overexpression in vivo of HEXA and B combined, but not either of the subunits expressed alone, increased HEX activity as evidenced by histochemical assays. Biochemically, such HEX gene expression resulted in increased conversion of GM2 to its breakdown product GM3. In a neurodegenerative model of overexpression of aSYN in rats, increasing HEX activity by AAV6 gene transfer in the substantia nigra reduced aSYN embedding in lipid compartments and rescued dopaminergic neurons from degeneration. Overall, these data are consistent with a paradigm shift where lipid abnormalities are central to or preceding protein changes typically associated with PD.

Systemic AAV9 gene therapy using the synapsin I promoter rescues a mouse model of neuronopathic Gaucher disease but with limited cross-correction potential to astrocytes

Gaucher disease is caused by mutations in the GBA gene, which encodes for the lysosomal enzyme β-glucocerebrosidase (GCase), resulting in the accumulation of storage material in visceral organs and in some cases the brain of affected patients. While there is a commercially available treatment for the systemic manifestations, neuropathology still remains untreatable. We previously demonstrated that gene therapy represents a feasible therapeutic tool for the treatment of the neuronopathic forms of Gaucher disease (nGD). In order to further enhance the therapeutic affects to the central nervous system, we systemically delivered an adeno-associated virus (AAV) serotype 9 carrying the human GBA gene under control of a neuron-specific promoter to an nGD mouse model. Gene therapy increased the life span of treated animals, rescued the lethal neurodegeneration, normalized the locomotor behavioural defects and ameliorated the visceral pathology. Together, these results provided further indication of gene therapy as a possible effective treatment option for the neuropathic forms of Gaucher disease.

Finding pathogenic commonalities between Niemann-Pick type C and other lysosomal storage disorders: Opportunities for shared therapeutic interventions

Lysosomal storage disorders (LSDs) are diseases characterized by the accumulation of macromolecules in the late endocytic system and are caused by inherited defects in genes that encode mainly lysosomal enzymes or transmembrane lysosomal proteins. Niemann-Pick type C disease (NPCD), a LSD characterized by liver damage and progressive neurodegeneration that leads to early death, is caused by mutations in the genes encoding the NPC1 or NPC2 proteins. Both proteins are involved in the transport of cholesterol from the late endosomal compartment to the rest of the cell. Loss of function of these proteins causes primary cholesterol accumulation, and secondary accumulation of other lipids, such as sphingolipids, in lysosomes. Despite years of studying the genetic and molecular bases of NPCD and related-lysosomal disorders, the pathogenic mechanisms involved in these diseases are not fully understood. In this review we will summarize the pathogenic mechanisms described for NPCD and we will discuss their relevance for other LSDs with neurological components such as Niemann- Pick type A and Gaucher diseases. We will particularly focus on the activation of signaling pathways that may be common to these three pathologies with emphasis on how the intra-lysosomal accumulation of lipids leads to pathology, specifically to neurological impairments. We will show that although the primary lipid storage defect is different in these three LSDs, there is a similar secondary accumulation of metabolites and activation of signaling pathways that can lead to common pathogenic mechanisms. This analysis might help to delineate common pathological mechanisms and therapeutic targets for lysosomal storage diseases.

Arylsulfatase A, a genetic modifier of Parkinson's disease, is an α-synuclein chaperone

Mutations in lysosomal genes increase the risk of neurodegenerative diseases, as is the case for Parkinson's disease. Here, we found that pathogenic and protective mutations in arylsulfatase A (ARSA), a gene responsible for metachromatic leukodystrophy, a lysosomal storage disorder, are linked to Parkinson's disease. Plasma ARSA protein levels were changed in Parkinson's disease patients. ARSA deficiency caused increases in α-synuclein aggregation and secretion, and increases in α-synuclein propagation in cells and nematodes. Despite being a lysosomal protein, ARSA directly interacts with α-synuclein in the cytosol. The interaction was more extensive with protective ARSA variant and less with pathogenic ARSA variant than wild-type. ARSA inhibited the in vitro fibrillation of α-synuclein in a dose-dependent manner. Ectopic expression of ARSA reversed the α-synuclein phenotypes in both cell and fly models of synucleinopathy, the effects correlating with the extent of the physical interaction between these molecules. Collectively, these results suggest that ARSA is a genetic modifier of Parkinson's disease pathogenesis, acting as a molecular chaperone for α-synuclein.

Lipids: Key Players That Modulate α-Synuclein Toxicity and Neurodegeneration in Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disease; it is characterized by the loss of dopaminergic neurons in the midbrain and the accumulation of neuronal inclusions, mainly consisting of α-synuclein (α-syn) fibrils in the affected regions. The prion-like property of the pathological forms of α-syn transmitted via neuronal circuits has been considered inherent in the nature of PD. Thus, one of the potential targets in terms of PD prevention is the suppression of α-syn conversion from the functional form to pathological forms. Recent studies suggested that α-syn interacts with synaptic vesicle membranes and modulate the synaptic functions. A series of studies suggest that transient interaction of α-syn as multimers with synaptic vesicle membranes composed of phospholipids and other lipids is required for its physiological function, while an α-syn-lipid interaction imbalance is believed to cause α-syn aggregation and the resultant pathological α-syn conversion. Altered lipid metabolisms have also been implicated in the modulation of PD pathogenesis. This review focuses on the current literature reporting the role of lipids, especially phospholipids, and lipid metabolism in α-syn dynamics and aggregation processes.

CRISPR/Cas9 Editing for Gaucher Disease Modelling

Gaucher disease (GD) is an autosomal recessive lysosomal storage disorder caused by mutations in the acid β-glucosidase gene (GBA1). Besides causing GD, GBA1 mutations constitute the main genetic risk factor for developing Parkinson’s disease. The molecular basis of neurological manifestations in GD remain elusive. However, neuroinflammation has been proposed as a key player in this process. We exploited CRISPR/Cas9 technology to edit GBA1 in the human monocytic THP-1 cell line to develop an isogenic GD model of monocytes and in glioblastoma U87 cell lines to generate an isogenic GD model of glial cells. Both edited (GBA1 mutant) cell lines presented low levels of mutant acid β-glucosidase expression, less than 1% of residual activity and massive accumulation of substrate. Moreover, U87 GBA1 mutant cells showed that the mutant enzyme was retained in the ER and subjected to proteasomal degradation, triggering unfolded protein response (UPR). U87 GBA1 mutant cells displayed an increased production of interleukin-1β, both with and without inflammosome activation, α-syn accumulation and a higher rate of cell death in comparison with wild-type cells. In conclusion, we developed reliable, isogenic, and easy-to-handle cellular models of GD obtained from commercially accessible cells to be employed in GD pathophysiology studies and high-throughput drug screenings.

Neurochemical abnormalities in patients with type 1 Gaucher disease on standard of care therapy

Type 1 Gaucher disease (GD1), a glycosphingolipid storage disorder caused by deficient activity of lysosomal glucocerebrosidase, is classically considered non-neuronopathic. However, current evidence challenges this view. Multiple studies show that mutations in GBA1 gene and decreased glucocerebrosidase activity are associated with increased risk for Parkinson disease. We tested the hypothesis that subjects with GD1 will show neurochemical abnormalities consistent with cerebral involvement. We performed Magnetic Resonance Spectroscopy at 7 T to quantify neurochemical profiles in participants with GD1 (n = 12) who are on stable therapy. Age and gender matched healthy participants served as controls (n = 13). Neurochemical profiles were obtained from parietal white matter (PWM), posterior cingulate cortex (PCC), and putamen. Further, in the GD1 group, the neurochemical profiles were compared between individuals with and without a single L444P allele. We observed significantly lower levels of key neuronal markers, N-acetylaspartate, γ-aminobutyric acid, glutamate and glutamate-to-glutamine ratio in PCC of participants with GD1 compared to healthy controls (P < .015). Glutamate concentration was also lower in the putamen in GD1 (P = .01). Glucose + taurine concentration was significantly higher in PWM (P = .04). Interestingly, individuals without L444P had significantly lower aspartate and N-acetylaspartylglutamate in PCC (both P < .001), although this group was 7 years younger than those with an L444P allele. This study demonstrates neurochemical abnormalities in individuals with GD1, for which clinical and prognostic significance remains to be determined. Further studies in a larger cohort are required to confirm an association of neurochemical levels with mutation status and glucocerebrosidase structure and function. SYNOPSIS: Ultrahigh field magnetic resonance spectroscopy reveals abnormalities in neurochemical profiles in patients with GD1 compared to matched healthy controls.

Lysosomal Ceramide Metabolism Disorders: Implications in Parkinson's Disease

Ceramides are a family of bioactive lipids belonging to the class of sphingolipids. Sphingolipidoses are a group of inherited genetic diseases characterized by the unmetabolized sphingolipids and the consequent reduction of ceramide pool in lysosomes. Sphingolipidoses include several disorders as Sandhoff disease, Fabry disease, Gaucher disease, metachromatic leukodystrophy, Krabbe disease, Niemann Pick disease, Farber disease, and GM2 gangliosidosis. In sphingolipidosis, lysosomal lipid storage occurs in both the central nervous system and visceral tissues, and central nervous system pathology is a common hallmark for all of them. Parkinson’s disease, the most common neurodegenerative movement disorder, is characterized by the accumulation and aggregation of misfolded α-synuclein that seem associated to some lysosomal disorders, in particular Gaucher disease. This review provides evidence into the role of ceramide metabolism in the pathophysiology of lysosomes, highlighting the more recent findings on its involvement in Parkinson’s disease.

Role of endolysosomes and inter-organellar signaling in brain disease

Endosomes and lysosomes (endolysosomes) are membrane bounded organelles that play a key role in cell survival and cell death. These acidic intracellular organelles are the principal sites for intracellular hydrolytic activity required for the maintenance of cellular homeostasis. Endolysosomes are involved in the degradation of plasma membrane components, extracellular macromolecules as well as intracellular macromolecules and cellular fragments. Understanding the physiological significance and pathological relevance of endolysosomes is now complicated by relatively recent findings of physical and functional interactions between endolysosomes with other intracellular organelles including endoplasmic reticulum, mitochondria, plasma membranes, and peroxisomes. Indeed, evidence clearly indicates that endolysosome dysfunction and inter-organellar signaling occurs in different neurodegenerative diseases including Alzheimer's disease (AD), HIV-1 associated neurocognitive disease (HAND), Parkinson's disease (PD) as well as various forms of brain cancer such as glioblastoma multiforme (GBM). These findings open new areas of cell biology research focusing on understanding the physiological actions and pathophysiological consequences of inter-organellar communication. Here, we will review findings of others and us that endolysosome de-acidification and dysfunction coupled with impaired inter-organellar signaling is involved in the pathogenesis of AD, HAND, PD, and GBM. A more comprehensive appreciation of cell biology and inter-organellar signaling could lead to the development of new drugs to prevent or cure these diseases.

Characterization of the visceral and neuronal phenotype of 4L/PS-NA mice modeling Gaucher disease

Gaucher disease is caused by a deficiency in glucocerebrosidase that can result in non-neuronal as well as neuronal symptoms. Common visceral symptoms are an increased organ size, specifically of the spleen, and glucosylceramide as well as glucosylsphingosine substrate accumulations as a direct result of the glucocerebrosidase deficiency. Neuronal symptoms include motor deficits and strong alterations in the cerebellum. To evaluate the effect of new compounds for the treatment of this devastating disease, animal models are needed that closely mimic the human phenotype. The 4L/PS-NA mouse as model of Gaucher disease is shown to present reduced glucocerebrosidase activity similar to human cases but an in-depth characterization of the model was still not performed. We therefore analyzed 4L/PS-NA mice for visceral alterations, motor deficits and also neuronal changes like glucocerebrosidase activity, substrate levels and neuroinflammation. A special focus was set at pathological changes of the cerebellum. Our results show that 4L/PS-NA mice have strongly enlarged visceral organs that are infiltrated by enlarged leukocytes and macrophages. Furthermore, animals present strong motor deficits that are accompanied by increased glucosylceramide and glucosylsphingosine levels in the brain, astrocytosis and activated microglia in the cortex and hippocampus as well as reduced calbindin levels in the cerebellum. The latter was directly related to a strong Purkinje cell loss. Our results thus provide a detailed characterization of the 4L/PS-NA mouse model over age showing the translational value of the model and validating its usefulness for preclinical efficiency studies to evaluate new compounds against Gaucher disease.

A characterization of Gaucher iPS-derived astrocytes: Potential implications for Parkinson's disease

While astrocytes, the most abundant cells found in the brain, have many diverse functions, their role in the lysosomal storage disorder Gaucher disease (GD) has not been explored. GD, resulting from the inherited deficiency of the enzyme glucocerebrosidase and subsequent accumulation of glucosylceramide and its acylated derivative glucosylsphingosine, has both non-neuronopathic (GD1) and neuronopathic forms (GD2 and 3). Furthermore, mutations in GBA1, the gene mutated in GD, are an important risk factor for Parkinson's disease (PD). To elucidate the role of astrocytes in the disease pathogenesis, we generated iAstrocytes from induced pluripotent stem cells made from fibroblasts taken from controls and patients with GD1, with and without PD. We also made iAstrocytes from an infant with GD2, the most severe and progressive form, manifesting in infancy. Gaucher iAstrocytes appropriately showed deficient glucocerebrosidase activity and levels and substrate accumulation. These cells exhibited varying degrees of astrogliosis, Glial Fibrillary Acidic Protein (GFAP) up-regulation and cellular proliferation, depending on the level of residual glucocerebrosidase activity. Glutamte uptake assays demonstrated that the cells were functionally active, although the glutamine transporter EEAT2 was upregulated and EEAT1 downregulated in the GD2 samples. GD2 iAstrocytes were morphologically different, with severe cytoskeletal hypertrophy, overlapping of astrocyte processes, pronounced up-regulation of GFAP and S100β, and significant astrocyte proliferation, recapitulating the neuropathology observed in patients with GD2. Although astrocytes do not express α-synuclein, when the iAstrocytes were co-cultured with dopaminergic neurons generated from the same iPSC lines, excessive α-synuclein released from neurons was endocytosed by astrocytes, translocating into lysosomes. Levels of aggregated α-synuclein increased significantly when cells were treated with monomeric or fibrillar α-synuclein. GD1-PD and GD2 iAstrocytes also exhibited impaired Cathepsin D activity, leading to further α-synuclein accumulation. Cytokine and chemokine profiling of the iAstrocytes demonstrated an inflammatory response. Thus, in patients with GBA1-associated parkinsonism, astrocytes appear to play a role in α-synuclein accumulation and processing, contributing to neuroinflammation.

The Overcrowded Crossroads: Mitochondria, Alpha-Synuclein, and the Endo-Lysosomal System Interaction in Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder worldwide, mainly affecting the elderly. The disease progresses gradually, with core motor presentations and a multitude of non-motor manifestations. There are two neuropathological hallmarks of PD, the dopaminergic neuronal loss and the alpha-synuclein-containing Lewy body inclusions in the substantia nigra. While the exact pathomechanisms of PD remain unclear, genetic investigations have revealed evidence of the involvement of mitochondrial function, alpha-synuclein (α-syn) aggregation, and the endo-lysosomal system, in disease pathogenesis. Due to the high energy demand of dopaminergic neurons, mitochondria are of special importance acting as the cellular powerhouse. Mitochondrial dynamic fusion and fission, and autophagy quality control keep the mitochondrial network in a healthy state. Should defects of the organelle occur, a variety of reactions would ensue at the cellular level, including disrupted mitochondrial respiratory network and perturbed calcium homeostasis, possibly resulting in cellular death. Meanwhile, α-syn is a presynaptic protein that helps regulate synaptic vesicle transportation and endocytosis. Its misfolding into oligomeric sheets and fibrillation is toxic to the mitochondria and neurons. Increased cellular oxidative stress leads to α-syn accumulation, causing mitochondrial dysfunction. The proteasome and endo-lysosomal systems function to regulate damage and unwanted waste management within the cell while facilitating the quality control of mitochondria and α-syn. This review will analyze the biological functions and interactions between mitochondria, α-syn, and the endo-lysosomal system in the pathogenesis of PD.

Autophagic- and Lysosomal-Related Biomarkers for Parkinson's Disease: Lights and Shadows

Parkinson’s disease (PD) is a neurodegenerative disorder that currently affects 1% of the population over the age of 60 years, for which no disease-modifying treatments exist. This lack of effective treatments is related to the advanced stage of neurodegeneration existing at the time of diagnosis. Thus, the identification of early stage biomarkers is crucial. Biomarker discovery is often guided by the underlying molecular mechanisms leading to the pathology. One of the central pathways deregulated during PD, supported both by genetic and functional studies, is the autophagy-lysosomal pathway. Hence, this review presents different studies on the expression and activity of autophagic and lysosomal proteins, and their functional consequences, performed in peripheral human biospecimens. Although most biomarkers are inconsistent between studies, some of them, namely HSC70 levels in sporadic PD patients, and cathepsin D levels and glucocerebrosidase activity in PD patients carrying GBA mutations, seem to be consistent. Hence, evidence exists that the impairment of the autophagy-lysosomal pathway underlying PD pathophysiology can be detected in peripheral biosamples and further tested as potential biomarkers. However, longitudinal, stratified, and standardized analyses are needed to confirm their clinical validity and utility.

Pharmacologic properties of high-dose ambroxol in four patients with Gaucher disease and myoclonic epilepsy

Background

Ambroxol (ABX) has been suggested as an augmentative pharmacological agent for neuronopathic Gaucher disease (nGD). This study assessed the long-term safety and efficacy of combined therapy with high-dose ABX and enzyme replacement therapy (ERT) in nGD.

Methods

ABX+ERT therapy was administered for 4.5 years in four patients with nGD. ABX was initiated at a dose of 1.5 mg/kg/day, and the dose was escalated up to 27 mg/kg/day. The target plasma level was 10 µmol/L or less. The changes in glucocerebrosidase activity, biochemical, safety and neurocognitive findings were assessed.

Results

Enhanced residual GCcase activity was observed in all patients, as evidenced in both in vitro and in vivo studies. During the first 2 years of study with ABX (up to 21 mg/kg/day), mean seizure frequencies and neurocognitive function worsened. After ABX dosage was increased up to 27 mg/kg/day of ABX, its trough plasma concentration was 3.2–8.8 µmol/L. Drug-to-drug interaction, especially with antiepileptic drug significantly affected the pharmacokinetic parameters of ABX. Importantly, at 27 mg/kg/day of ABX, the seizure frequencies markedly decreased from the baseline, and the neurocognitive function was improved. In addition, Lyso-Gb1, a biomarker for the severity and progression of GD, was normalised in all patients. High-dose ABX was well-tolerated with no severe adverse events.

Conclusions

Long-term treatment with high-dose ABX+ERT was safe and might help to arrest the progression of the neurological manifestations in GD.

mTOR hyperactivity mediates lysosomal dysfunction in Gaucher's disease iPSC-neuronal cells

Bi-allelic GBA1 mutations cause Gaucher's disease (GD), the most common lysosomal storage disorder. Neuronopathic manifestations in GD include neurodegeneration, which can be severe and rapidly progressive. GBA1 mutations are also the most frequent genetic risk factors for Parkinson's disease. Dysfunction of the autophagy-lysosomal pathway represents a key pathogenic event in GBA1-associated neurodegeneration. Using an induced pluripotent stem cell (iPSC) model of GD, we previously demonstrated that lysosomal alterations in GD neurons are linked to dysfunction of the transcription factor EB (TFEB). TFEB controls the coordinated expression of autophagy and lysosomal genes and is negatively regulated by the mammalian target of rapamycin complex 1 (mTORC1). To further investigate the mechanism of autophagy-lysosomal pathway dysfunction in neuronopathic GD, we examined mTORC1 kinase activity in GD iPSC neuronal progenitors and differentiated neurons. We found that mTORC1 is hyperactive in GD cells as evidenced by increased phosphorylation of its downstream protein substrates. We also found that pharmacological inhibition of glucosylceramide synthase enzyme reversed mTORC1 hyperactivation, suggesting that increased mTORC1 activity is mediated by the abnormal accumulation of glycosphingolipids in the mutant cells. Treatment with the mTOR inhibitor Torin1 upregulated lysosomal biogenesis and enhanced autophagic clearance in GD neurons, confirming that lysosomal dysfunction is mediated by mTOR hyperactivation. Further analysis demonstrated that increased TFEB phosphorylation by mTORC1 results in decreased TFEB stability in GD cells. Our study uncovers a new mechanism contributing to autophagy-lysosomal pathway dysfunction in GD, and identifies the mTOR complex as a potential therapeutic target for treatment of GBA1-associated neurodegeneration.

Measuring disease activity and patient experience remotely using wearable technology and a mobile phone app: outcomes from a pilot study in Gaucher disease

Background

Gaucher disease is an inherited lysosomal storage disorder of which there are three subtypes. Type 1 disease has no neurological involvement and is treatable with enzyme replacement therapy. Type 2 disease results in infant death and type 3 disease is a heterogenous disorder characterised by progressive neurological decline throughout childhood and adult life. Endeavours to find a therapy to modify neurological disease are limited by a lack of meaningful clinical outcome measures which are acceptable to patients.

Results

We present results from a pilot study utilising wearable technology to monitor physical activity as a surrogate of disease activity/severity paired with a mobile phone app allowing patients to complete self-reported outcome measures in the real world as opposed to the hospital environment. We demonstrate feasibility of the approach and highlight areas for development with this study of 21 patients, both children and adults.

Conclusions

We illustrate, where patients engage in the methodology, a rich dataset is obtainable and useful for proactive clinical care and for clinical trial outcome development.

The interplay of aging, genetics and environmental factors in the pathogenesis of Parkinson's disease

BACKGROUND

Parkinson's disease (PD) is characterized by dopaminergic neuronal loss in the substantia nigra pars compacta and intracellular inclusions called Lewy bodies (LB). During the course of disease, misfolded α-synuclein, the major constituent of LB, spreads to different regions of the brain in a prion-like fashion, giving rise to successive non-motor and motor symptoms. Etiology is likely multifactorial, and involves interplay among aging, genetic susceptibility and environmental factors.

MAIN BODY

The prevalence of PD rises exponentially with age, and aging is associated with impairment of cellular pathways which increases susceptibility of dopaminergic neurons to cell death. However, the majority of those over the age of 80 do not have PD, thus other factors in addition to aging are needed to cause disease. Discovery of neurotoxins which can result in parkinsonism led to efforts in identifying environmental factors which may influence PD risk. Nevertheless, the causality of most environmental factors is not conclusively established, and alternative explanations such as reverse causality and recall bias cannot be excluded. The lack of geographic clusters and conjugal cases also go against environmental toxins as a major cause of PD. Rare mutations as well as common variants in genes such as SNCA, LRRK2 and GBA are associated with risk of PD, but Mendelian causes collectively only account for 5% of PD and common polymorphisms are associated with small increase in PD risk. Heritability of PD has been estimated to be around 30%. Thus, aging, genetics and environmental factors each alone is rarely sufficient to cause PD for most patients.

CONCLUSION

PD is a multifactorial disorder involving interplay of aging, genetics and environmental factors. This has implications on the development of appropriate animal models of PD which take all these factors into account. Common converging pathways likely include mitochondrial dysfunction, impaired autophagy, oxidative stress and neuroinflammation, which are associated with the accumulation and spread of misfolded α-synuclein and neurodegeneration. Understanding the mechanisms involved in the initiation and progression of PD may lead to potential therapeutic targets to prevent PD or modify its course.

Early disease course is unaltered in mucopolysaccharidosis type IIIA (MPS IIIA) mice lacking α-synuclein

BACKGROUND

Sanfilippo syndrome (mucopolysaccharidosis type IIIA; MPS IIIA) is an inherited paediatric-onset neurodegenerative disorder caused by the lysosomal deficiency of sulphamidase with subsequent accumulation of heparan sulphate. The pathological mechanisms responsible for clinical disease are unknown; however, intraneuronal accumulation of aggregation-prone proteins such as α-synuclein, phosphorylated tau and amyloid precursor protein suggests inefficient intracellular trafficking and lysosomal degradation.

AIM

To investigate the contribution the accumulating α-synuclein plays in early symptom emergence that is, impaired cognition, reduced anxiety and motor deficits, first detectable between 3-5 months of age.

METHODS

We have crossed congenic MPS IIIA mice with α-synuclein-deficient (Snca^tm1Rosl /J) mice and evaluated phenotype and brain disease lesions.

RESULTS

In a battery of behavioural tests performed on mice aged 12-22 weeks, we were unable to differentiate α-synuclein-deficient MPS IIIA mice from those with one or both copies of the α-synuclein gene; all three affected genotypes were significantly impaired in test performance when compared to wild-type littermates. Histological studies revealed that the rate, location and nature of deposition of other proteinaceous lesions, the disruption to endolysosomal protein expression and the inflammatory response seen in the brain of α-synuclein-deficient MPS IIIA mice reflected that seen in MPS IIIA mice homo- or heterozygous for α-synuclein.

CONCLUSION

Deletion and/or deficiency of α-synuclein does not influence clinical and neuropathological disease progression in murine MPS IIIA, demonstrating that in and of itself, this protein does not initiate the cognitive and motor symptoms that occur in the first 5 months of life in MPS IIIA mice.

Glial phagocytic clearance in Parkinson's disease

An emerging picture suggests that glial cells' loss of beneficial roles or gain of toxic functions can contribute to neurodegenerative conditions. Among glial cells, microglia and astrocytes have been shown to play phagocytic roles by engulfing synapses, apoptotic cells, cell debris, and released toxic proteins. As pathogenic protein accumulation is a key feature in Parkinson's disease (PD), compromised phagocytic clearance might participate in PD pathogenesis. In contrast, enhanced, uncontrolled and potentially toxic glial clearance capacity could contribute to synaptic degeneration. Here, we summarize the current knowledge of the molecular mechanisms underlying microglial and astrocytic phagocytosis, focusing on the possible implication of phagocytic dysfunction in neuronal degeneration. Several endo-lysosomal proteins displaying genetic variants in PD are highly expressed by microglia and astrocytes. We also present the evidence that lysosomal defects can affect phagocytic clearance and discuss the therapeutic relevance of restoring or enhancing lysosomal function in PD.

Cognitive impairments in inherited metabolic diseases: Promises and challenges

This is an introduction to the special issue on cognitive impairments in inherited metabolic diseases (IMD). It provides an overview of the studies included, focusing on the possibility of selective impairments which could provide unique evidence on the specificity of neural circuitries mediating cognitive functions. It will suggest that these circuitries have different metabolic properties which make them especially apt to carry out certain functions, but also particularly susceptible to certain forms of metabolic disruption. Knowledge of selective impairments is also crucial to properly evaluate the difficulties engendered by individual diseases and track treatment outcomes. IMR research holds the promise of a more complete understanding of cognition, from cellular functioning to behaviour and of further improvements in treatment. Advances, however, will require detailed assessments, comparisons across diseases, and the integration of different levels of explanation. This will be possible only through close collaborations between centres and types of professionals.

Lysosomal enzyme activities as possible CSF biomarkers of synucleinopathies

Mutations on the GBA gene, encoding for the lysosomal enzyme β-glucocerebrosidase (GCase), have been identified as the most common genetic risk factor involved in the development of Parkinson's disease (PD) and dementia with Lewy bodies (DLB), indicating a direct contribution of this enzyme to the pathogenesis of synucleinopathies. Decreased GCase activity has been observed repeatedly in brain tissues and biological fluids of both GBA mutation carrier and non-carrier PD and DLB patients, suggesting that lower GCase activity constitutes a typical feature of these disorders. Additional genetic, pathological and biochemical data on other lysosomal enzymes (e.g., Acid sphingomyelinase, Cathepsin D, α-galactosidase A and β-hexosaminidase) have further strengthened the evidence of a link between lysosomal dysfunction and synucleinopathies. A few studies have been performed for assessing the potential value of lysosomal enzyme activities in cerebrospinal fluid (CSF) as biomarkers for synucleinopathies. The reduction of GCase activity in the CSF of PD and DLB patients was validated in several of them, whereas the behaviour of other lysosomal enzyme activities was not consistently reliable among the studies. More in-depth investigations on larger cohorts, following stringent standard operating procedures should be committed to really understand the diagnostic utility of lysosomal enzymes as biomarkers for synucleinopathies. In this review, we reported the evidences of the association between the defective function of lysosomal proteins and the pathogenesis of synucleinopathies, and examined the role of lysosomal enzyme activities in CSF as reliable biomarkers for the diagnosis of PD and related neurodegenerative disorders.