Glucocerebrosidase deficiency in dopaminergic neurons induces microglial activation without neurodegeneration

Metal-Organic Framework Based Nanozyme System for NLRP3 Inflammasome-Mediated Neuroinflammatory Regulation in Parkinson's Disease

Neuroinflammation is associated with a series of pathological symptoms in Parkinson's disease (PD), including α-synuclein aggregation and dopaminergic neuronal death. The NOD-like receptor protein 3 (NLRP3) inflammasome plays a crucial role in neuroinflammation at the lesion site and is a promising target for PD treatment. In this study, a nanoscale metal-organic framework (Zr-FeP MOF) based nanozyme is fabricated using Fe-5,10,15,20-tetra (4-carboxyphenyl) porphyrin (Fe-TCPP) and Zr6 cluster as ligands. The Zr-FeP MOF is subsequently encapsulated with mannitol (Man)-liposome, resulting in the formation of Zr-FeP MOF@Man liposome (MOF@Man Liposome) nanozyme system. The in vitro studies show that this nanozyme system is effective in relieving the formation of NLRP3 inflammasome and mitochondrial dysfunction. In mouse models of PD, the nanozyme system demonstrates a significant blood-brain barrier-crossing capability attributed to the Man-mediated brain targeting. Additionally, transcriptomic and biochemical studies show that the nanozyme system effectively inhibits the formation and assembly of inflammasome components, mitigating the activation of glial cells and neuroinflammatory response, and ultimately regulating the pathological symptoms of PD effectively.

GBA1 inactivation in oligodendrocytes affects myelination and induces neurodegenerative hallmarks and lipid dyshomeostasis in mice

BACKGROUND

Mutations in the β-glucocerebrosidase (GBA1) gene do cause the lysosomal storage Gaucher disease (GD) and are among the most frequent genetic risk factors for Parkinson's disease (PD). So far, studies on both neuronopathic GD and PD primarily focused on neuronal manifestations, besides the evaluation of microglial and astrocyte implication. White matter alterations were described in the central nervous system of paediatric type 1 GD patients and were suggested to sustain or even play a role in the PD process, although the contribution of oligodendrocytes has been so far scarcely investigated.

METHODS

We exploited a system to study the induction of central myelination in vitro, consisting of Oli-neu cells treated with dibutyryl-cAMP, in order to evaluate the expression levels and function of β-glucocerebrosidase during oligodendrocyte differentiation. Conduritol-B-epoxide, a β-glucocerebrosidase irreversible inhibitor was used to dissect the impact of β-glucocerebrosidase inactivation in the process of myelination, lysosomal degradation and α-synuclein accumulation in vitro. Moreover, to study the role of β-glucocerebrosidase in the white matter in vivo, we developed a novel mouse transgenic line in which β-glucocerebrosidase function is abolished in myelinating glia, by crossing the Cnp1-cre mouse line with a line bearing loxP sequences flanking Gba1 exons 9-11, encoding for β-glucocerebrosidase catalytic domain. Immunofluorescence, western blot and lipidomic analyses were performed in brain samples from wild-type and knockout animals in order to assess the impact of genetic inactivation of β-glucocerebrosidase on myelination and on the onset of early neurodegenerative hallmarks, together with differentiation analysis in primary oligodendrocyte cultures.

RESULTS

Here we show that β-glucocerebrosidase inactivation in oligodendrocytes induces lysosomal dysfunction and inhibits myelination in vitro. Moreover, oligodendrocyte-specific β-glucocerebrosidase loss-of-function was sufficient to induce in vivo demyelination and early neurodegenerative hallmarks, including axonal degeneration, α-synuclein accumulation and astrogliosis, together with brain lipid dyshomeostasis and functional impairment.

CONCLUSIONS

Our study sheds light on the contribution of oligodendrocytes in GBA1-related diseases and supports the need for better characterizing oligodendrocytes as actors playing a role in neurodegenerative diseases, also pointing at them as potential novel targets to set a brake to disease progression.

Tau seeds from Alzheimer's disease brains trigger tau spread in macaques while oligomeric-Aβ mediates pathology maturation

INTRODUCTION

The "prion-like" features of Alzheimer's disease (AD) tauopathy and its relationship with amyloid-β (Aβ) have never been experimentally studied in primates phylogenetically close to humans.

METHODS

We injected 17 macaques in the entorhinal cortex with nanograms of seeding-competent tau aggregates purified from AD brains or control extracts from aged-matched healthy brains, with or without intracerebroventricular co-injections of oligomeric-Aβ.

RESULTS

Pathological tau injection increased cerebrospinal fluid (CSF) p-tau181 concentration after 18 months. Tau pathology spreads from the entorhinal cortex to the hippocampal trisynaptic loop and the cingulate cortex, resuming the experimental progression of Braak stage I to IV. Many AD-related molecular networks were impacted by tau seeds injections regardless of Aβ injections in proteomic analyses. However, we found mature neurofibrillary tangles, increased CSF total-tau concentration, and pre- and postsynaptic degeneration only in Aβ co-injected macaques.

DISCUSSION

Oligomeric-Aβ mediates the maturation of tau pathology and its neuronal toxicity in macaques but not its initial spreading.

HIGHLIGHTS

This study supports the "prion-like" properties of misfolded tau extracted from AD brains. This study empirically validates the Braak staging in an anthropomorphic brain. This study highlights the role of oligomeric Aβ in driving the maturation and toxicity of tau pathology. This work establishes a novel animal model of early sporadic AD that is closer to the human pathology.

Qiji Shujiang granules alleviates dopaminergic neuronal injury of parkinson's disease by inhibiting NLRP3/Caspase-1 pathway mediated pyroptosis

BACKGROUND

The Qiji Shujiang granule (QJG) is a traditional Chinese drug widely used in treating PD patients. However, the potential mechanism of QJG in PD therapy is still unclear.

PURPOSE

This study aims to examine the neuroprotective effects of QJG and the specific mechanism by which QJG alleviates MPTP/Probenecid-induced pyroptosis and offers an alternative for PD treatment.

STUDY DESIGN AND METHODS

We first employed network pharmacology along with molecular docking to identify potential molecular targets and pathways. Subsequently, we validated our findings of RNA-sequencing (RNA-seq) analysis and experiments in vivo and vitro. Lentiviral systems and inhibitors were used for experiments.

RESULTS

The protein-protein interactions (PPI) core genes network consists of NLRP3, CASP1 (caspase-1), TP53, and MAPK8. Pathway enrichment analysis revealed that inflammatory responses related to pyroptosis were significantly enriched. The molecular docking findings showed the highest degree of centrality regarding the top three bioactive compounds following the online database. RNA-seq analysis identified that NLRP3 inflammasome was significantly downregulated in the QJG group while it was significantly upregulated in the model group. Our findings revealed that QJG dose-dependently increased the total traveled distances, enhanced the dopaminergic neurons, and accelerated the restoration of the TH protein level, showing a good antioxidant capacity through increasing the SOD levels and decreasing MDA levels. QJG significantly reduced the expression levels of NLRP3, GSDMD-N, IL-1β, and caspase-1 in striatum tissue. Furthermore, the group treated with OE-NLRP3 decreased cell viability, increased ROS and MDA levels, and promoted NLRP3, GSDMD-N, and caspase-1, in addition to IL-1β expression levels. Furthermore, OE-NLRP3+QJG treatment significantly reversed the effect. In vivo experiments, QJG dose-dependently alleviated motor impairment by increasing the total traveled distances, rescued dopaminergic neurons, inhibited oxidative stress through increasing the SOD levels and decreasing MDA levels and suppressed NLRP3-mediated pyroptosis by reducing the expression levels of NLRP3, GSDMD-N, IL-1β, and caspase-1 in MPTP induced PD Mice. Moreover, in vitro experiments, the OE-NLRP3 treated group decreased cell viability, increased ROS and MDA levels, and promoted NLRP3, GSDMD-N, caspase-1, in addition to IL-1β expression levels. Furthermore, OE-NLRP3+QJG treatment significantly reversed the effect.

CONCLUSIONS

This study provides pharmacological support for the use of QJG in the treatment of PD. Herein, we concluded that QJG induced the alleviation of pyroptosis by inhibiting the NLRP3/caspase-1 pathway to exert a neuroprotective effect.

Axonal Transport of Lysosomes Is Unaffected in Glucocerebrosidase-Inhibited iPSC-Derived Forebrain Neurons

Lysosomes are acidic organelles that traffic throughout neurons delivering catabolic enzymes to distal regions of the cell and maintaining degradative demands. Loss of function mutations in the gene GBA encoding the lysosomal enzyme glucocerebrosidase (GCase) cause the lysosomal storage disorder Gaucher's disease (GD) and are the most common genetic risk factor for synucleinopathies like Parkinson's disease (PD) and dementia with Lewy bodies (DLB). GCase degrades the membrane lipid glucosylceramide (GlcCer) and mutations in GBA, or inhibiting its activity, results in the accumulation of GlcCer and disturbs the composition of the lysosomal membrane. The lysosomal membrane serves as the platform to which intracellular trafficking complexes are recruited and activated. Here, we investigated whether lysosomal trafficking in axons was altered by inhibition of GCase with the pharmacological agent Conduritol B Epoxide (CBE). Using live cell imaging in human male induced pluripotent human stem cell (iPSC)-derived forebrain neurons, we demonstrated that lysosomal transport was similar in both control and CBE-treated neurons. Furthermore, we tested whether lysosomal rupture, a process implicated in various neurodegenerative disorders, was affected by inhibition of GCase. Using L-leucyl-L-leucine methyl ester (LLoME) to induce lysosomal membrane damage and immunocytochemical staining for markers of lysosomal rupture, we found no difference in susceptibility to rupture between control and CBE-treated neurons. These results suggest the loss of GCase activity does not contribute to neurodegenerative disease by disrupting either lysosomal transport or rupture.

Cortical Lewy body injections induce long-distance pathogenic alterations in the non-human primate brain

Aggregation of α-synuclein (α-syn) is the cornerstone of neurodegenerative diseases termed synucleinopathies, which include Parkinson's Disease (PD), Dementia with Lewy Bodies (DLB), and Multiple System Atrophy (MSA). These synucleinopathies are characterized by the deposit of aggregated α-syn in intracellular inclusions observable in neurons and glial cells. In PD and DLB, these aggregates, predominantly located in neurons, are called Lewy Bodies (LBs). These LBs are one of the pathological hallmarks of PD and DLB, alongside dopaminergic neuron loss in the substantia nigra. Previous studies have demonstrated the ability of PD patient-derived LB fractions to induce nigrostriatal neurodegeneration and α-syn pathology when injected into the striatum or the enteric nervous system of non-human primates. Here, we report the pathological consequences of injecting these LB fractions into the cortex of non-human primates. To this end, we inoculated mesencephalic PD patient-derived LB fractions into the prefrontal cortex of baboon monkeys terminated one year later. Extensive analyses were performed to evaluate pathological markers known to be affected in LB pathologies. We first assessed the hypothesized presence of phosphorylated α-syn at S129 (pSyn) in the prefrontal cortices. Second, we quantified the neuronal, microglial, and astrocytic cell survival in the same cortices. Third, we characterized these cortical LB injections' putative impact on the integrity of the nigrostriatal system. Overall, we observed pSyn accumulation around the injection site in the dorsal prefrontal cortex, in connected cortical regions, and further towards the striatum, suggesting α-syn pathological propagation. The pathology was also accompanied by neuronal loss in these prefrontal cortical regions and the caudate nucleus, without, however, loss of nigral dopamine neurons. In conclusion, this pilot study provides novel data demonstrating the toxicity of patient-derived extracts, their potential to propagate from the cortex to the striatum in non-human primates, and a possible primate model of DLB.

Mechanisms of Glucocerebrosidase Dysfunction in Parkinson's Disease

Beta-glucocerebrosidase is a lysosomal hydrolase, encoded by GBA1 that represents the most common risk gene associated with Parkinson's disease (PD) and Lewy Body Dementia. Glucocerebrosidase dysfunction has been also observed in the absence of GBA1 mutations across different genetic and sporadic forms of PD and related disorders, suggesting a broader role of glucocerebrosidase in neurodegeneration. In this review, we highlight recent advances in mechanistic characterization of glucocerebrosidase function as the foundation for development of novel therapeutics targeting glucocerebrosidase in PD and related disorders.

Neuronal activity induces glucosylceramide that is secreted via exosomes for lysosomal degradation in glia

Recessive variants in GBA1 cause Gaucher disease, a prevalent form of lysosome storage disease. GBA1 encodes a lysosomal enzyme that hydrolyzes glucosylceramide (GlcCer) into glucose and ceramide. Its loss causes lysosomal dysfunction and increased levels of GlcCer. We generated a null allele of the Drosophila ortholog Gba1b by inserting the Gal4 using CRISPR-Cas9. Here, we show that Gba1b is expressed in glia but not in neurons. Glial-specific knockdown recapitulates the defects found in Gba1b mutants, and these can be rescued by glial expression of human GBA1. We show that GlcCer is synthesized upon neuronal activity, and it is transported from neurons to glia through exosomes. Furthermore, we found that glial TGF-β/BMP induces the transfer of GlcCer from neurons to glia and that the White protein, an ABCG transporter, promotes GlcCer trafficking to glial lysosomes for degradation.

Imaging and genetics in Parkinson's disease: assessment of the GBA1 mutation

INTRODUCTION

Several genetic variants are associated with an increased risk for developing Parkinson's Disease (PD) and limited genotype/phenotype correlation. Specifically, mutations in GBA1, the gene coding for the lysosomal enzyme glucocerebrosidase, are associated with an earlier age of onset and faster disease progression. Given these phenotypic differences associated with GBA1 variants, we explored whether cortical thickness and other biomarkers of neurodegeneration differed in healthy controls and PD patients with and without GBA1 variants.

METHODS

To understand how different GBA1 variants influence PD phenotype early in the disease, we retrieved neuroimaging and biospecimen data from the Parkinson's Progression Markers Initiative database. Using FreeSurfer, we compared T1-weighted MRI images from healthy controls (N = 47) to PD patients with heterozygous N370S (N = 21), heterozygous E326K (N = 18) or heterozygous T369M (N = 8) variants, and GBA1 non-mutation carriers (N = 47).

RESULTS

Cortical thickness in PD patients differed from controls in the parietal cortex, with E365K, T369M variants, and GBA1 non-mutation carriers showing more cortical thinning than N370S variants. Patients with N370S variants had significantly higher serum neurofilament light levels among all groups.

CONCLUSION

Our results demonstrate significant cortical thinning in PD patients independent of genotype in superior parietal and postcentral regions when compared to the controls. They highlight the impact of GBA1 variants on cortical thickness in the parietal cortex. Finally, they suggest that recently diagnosed PD patients with N370S variants have a higher cortical thickness and increased active neurodegeneration when compared to PD patients without GBA1 mutations and PD patients with E326K or T369M variants.

Consequences of excessive glucosylsphingosine in glucocerebrosidase-deficient zebrafish

In Gaucher disease (GD), the deficiency of glucocerebrosidase causes lysosomal accumulation of glucosylceramide (GlcCer), which is partly converted by acid ceramidase to glucosylsphingosine (GlcSph) in the lysosome. Chronically elevated blood and tissue GlcSph is thought to contribute to symptoms in GD patients as well as to increased risk for Parkinson’s disease. On the other hand, formation of GlcSph may be beneficial since the water soluble sphingoid base is excreted via urine and bile. To study the role of excessive GlcSph formation during glucocerebrosidase deficiency, we studied zebrafish that have two orthologs of acid ceramidase, Asah1a and Asah1b. Only the latter is involved in the formation of GlcSph in glucocerebrosidase-deficient zebrafish as revealed by knockouts of Asah1a or Asah1b with glucocerebrosidase deficiency (either pharmacologically induced or genetic). Comparison of zebrafish with excessive GlcSph (gba1^-/- fish) and without GlcSph (gba1^-/-:asah1b^-/- fish) allowed us to study the consequences of chronic high levels of GlcSph. Prevention of excessive GlcSph in gba1^-/-:asah1b^-/- fish did not restrict storage cells, GlcCer accumulation, or neuroinflammation. However, GD fish lacking excessive GlcSph show an ameliorated course of disease reflected by significantly increased lifespan, delayed locomotor abnormality, and delayed development of an abnormal curved back posture. The loss of tyrosine hydroxylase 1 (th1) mRNA, a marker of dopaminergic neurons, is slowed down in brain of GD fish lacking excessive GlcSph. In conclusion, in the zebrafish GD model, excess GlcSph has little impact on (neuro)inflammation or the presence of GlcCer-laden macrophages but rather seems harmful to th1-positive dopaminergic neurons.

The neuroinflammatory role of glucocerebrosidase in Parkinson's disease

The lysosomal enzyme glucocerebrosidase (GCase), encoded by the GBA1 gene, is a membrane-associated protein catalyzing the cleavage of glucosylceramide (GlcCer) and glucosylsphingosine (GlcSph). Homologous GBA1 mutations cause Gaucher disease (GD) and heterologous mutations cause Parkinson's disease (PD). Importantly, heterologous GBA1 mutations are recognized as the second risk factor of PD. The pathological features of PD are Lewy neurites (LNs) and Lewy bodies (LBs) composed of pathological α-synuclein. Oxidative stress, inflammatory response, autophagic impairment, and α-synuclein accumulation play critical roles in PD pathogenic cascades, but the pathogenesis of PD has not yet been fully elucidated. What's more, PD treatment drugs can only relieve symptoms to a certain extent, but cannot alleviate neurodegenerative progression. Therefore, it's urgent to explore new targets that can alleviate the neurodegenerative process. Deficient GCase can cause lysosomal dysfunction, obstructing the metabolism of α-synuclein. Meanwhile, GCase dysfunction causes accumulation of its substrates, leading to lipid metabolism disorders. Subsequently, astrocytes and microglia are activated, releasing amounts of pro-inflammatory mediators and causing extensive neuroinflammation. All these cascades can induce neuron damage and death, eventually promoting PD pathology. This review aims to summarize these points and the potential of GCase as an original target to provide some ideas for elucidating the pathogenesis of PD.

Neuroinflammation in aucher disease, neuronal ceroid lipofuscinosis, and commonalities with Parkinson’s disease

Lysosomal storage diseases (LSDs) are rare genetic disorders caused by a disruption in cellular clearance, resulting in pathological storage of undegraded lysosomal substrates. Recent clinical and genetic studies have uncovered links between multiple LSDs and common neurodegenerative diseases such as Parkinson's disease (PD). Here, we review recent literature describing the role of glia cells and neuroinflammation in PD and LSDs, including Gaucher disease (GD) and neuronal ceroid lipofuscinosis (NCL), and highlight converging inflammation pathways that lead to neuron loss. Recent data indicates that lysosomal dysfunction and accumulation of storage materials can initiate the activation of glial cells, through interaction with cell surface or cytosolic pattern recognition receptors that detect pathogenic aggregates of cellular debris. Activated glia cells could act to protect neurons through the elimination of toxic protein or lipid aggregates early in the disease process. However prolonged glial activation that occurs over several decades in chronic-age related neurodegeneration could induce the inappropriate elimination of synapses, leading to neuron loss. These studies provide mechanistic insight into the relationship between lysosomal dysfunction and glial activation, and offer novel therapeutic pathways for the treatment of PD and LSDs focused on reducing neuroinflammation and mitigating cell loss.

Role of NLRP3 Inflammasome in Parkinson's Disease and Therapeutic Considerations

Parkinson's disease (PD) is the second most common neurodegenerative disease, with two main pathological features: misfolded α-synuclein protein accumulation and neurodegeneration. Inflammation has recently been identified as a contributor to a cascade of events that may aggravate PD pathology. Inflammasomes, a group of intracellular protein complexes, play an important role in innate immune responses to various diseases, including infection. In PD research, accumulating evidence suggests that α-synuclein aggregations may activate inflammasomes, particularly the nucleotide-binding oligomerization domain-leucine-rich repeat-pyrin domain-containing 3 (NLRP3) type, which exacerbates inflammation in the central nervous system by secreting proinflammatory cytokines like interleukin (IL)-18 and IL-1β. Afterward, activated NLRP3 triggers local microglia and astrocytes to release additional IL-1β. In turn, the activated inflammatory process may contribute to additional α-synuclein aggregation and cell loss. This review summarizes current research evidence on how the NLRP3 inflammasome contributes to PD pathogenesis, as well as potential therapeutic strategies targeting the NLRP3 inflammasome in PD.

Proteomic analysis capsule synthesis and redox mechanisms in the intracellular survival of group B Streptococcus in fish microglia

Group B Streptococcus (GBS) causes meningitis in neonates and Nile tilapia (Oreochromis niloticus). The molecular mechanisms regulating the intracellular survival of this pathogen in the host cell are complex and crucial for the progression of infection. Thus, we propose the use of GBS-infected Nile tilapia microglia as an in vitro model system simulating infection caused by homologous bacteria in humans. We used this model to evaluate the phagocytic activity, as well as the functional aspects of the capsular proteins A, B, C, and D and the major redox enzymes, and the synergistic role of mechanisms/proteins involved in blocking phagocytic process. We observed that in the intracellular phase, GBS showed enhanced synthesis of the polysaccharide capsule and used superoxide dismutase, thioredoxin, NADH oxidase, and alkyl hydroperoxide reductase to scavenge reactive oxygen species and reactive nitrogen species produced by the host cell. Furthermore, although these virulence mechanisms were effective during the initial hours of infection, they were not able to subvert microglial responses, which partially neutralized the infection. Altogether, our findings provided important information regarding the intracellular survival mechanisms of GBS and perspectives for the production of new drugs and vaccines, through the druggability analysis of specific proteins. In conclusion, tilapia microglia serve as a potent in vitro experimental model for the study of meningitis.

Astrocyte dysfunction in Parkinson's disease: from the perspectives of transmitted α-synuclein and genetic modulation

Parkinson's disease (PD) is a common neurodegenerative disorder that primarily affects the elderly. While the etiology of PD is likely multifactorial with the involvement of genetic, environmental, aging and other factors, α-synuclein (α-syn) pathology is a pivotal mechanism underlying the development of PD. In recent years, astrocytes have attracted considerable attention in the field. Although astrocytes perform a variety of physiological functions in the brain, they are pivotal mediators of α-syn toxicity since they internalize α-syn released from damaged neurons, and this triggers an inflammatory response, protein degradation dysfunction, mitochondrial dysfunction and endoplasmic reticulum stress. Astrocytes are indispensable coordinators in the background of several genetic mutations, including PARK7, GBA1, LRRK2, ATP13A2, PINK1, PRKN and PLA2G6. As the most abundant glial cells in the brain, functional astrocytes can be replenished and even converted to functional neurons. In this review, we discuss astrocyte dysfunction in PD with an emphasis on α-syn toxicity and genetic modulation and conclude that astrocyte replenishment is a valuable therapeutic approach in PD.

Inhibition of microglial β-glucocerebrosidase hampers the microglia-mediated antioxidant and protective response in neurons

BACKGROUND

Homozygotic mutations in the GBA gene cause Gaucher's disease; moreover, both patients and heterozygotic carriers have been associated with 20- to 30-fold increased risk of developing Parkinson's disease. In homozygosis, these mutations impair the activity of β-glucocerebrosidase, the enzyme encoded by GBA, and generate a lysosomal disorder in macrophages, which changes morphology towards an engorged phenotype, considered the hallmark of Gaucher's disease. Notwithstanding the key role of macrophages in this disease, most of the effects in the brain have been attributed to the β-glucocerebrosidase deficit in neurons, while a microglial phenotype for these mutations has never been reported.

METHODS

We applied the bioluminescence imaging technology, immunohistochemistry and gene expression analysis to investigate the consequences of microglial β-glucocerebrosidase inhibition in the brain of reporter mice, in primary neuron/microglia cocultures and in cell lines. The use of primary cells from reporter mice allowed for the first time, to discriminate in cocultures neuronal from microglial responses consequent to the β-glucocerebrosidase inhibition; results were finally confirmed by pharmacological depletion of microglia from the brain of mice.

RESULTS

Our data demonstrate the existence of a novel neuroprotective mechanism mediated by a direct microglia-to-neuron contact supported by functional actin structures. This cellular contact stimulates the nuclear factor erythroid 2-related factor 2 activity in neurons, a key signal involved in drug detoxification, redox balance, metabolism, autophagy, lysosomal biogenesis, mitochondrial dysfunctions, and neuroinflammation. The central role played by microglia in this neuronal response in vivo was proven by depletion of the lineage in the brain of reporter mice. Pharmacological inhibition of microglial β-glucocerebrosidase was proven to induce morphological changes, to turn on an anti-inflammatory/repairing pathway, and to hinder the microglia ability to activate the nuclear factor erythroid 2-related factor 2 response, thus increasing the neuronal susceptibility to neurotoxins.

CONCLUSION

This mechanism provides a possible explanation for the increased risk of neurodegeneration observed in carriers of GBA mutations and suggest novel therapeutic strategies designed to revert the microglial phenotype associated with β-glucocerebrosidase inhibition, aimed at resetting the protective microglia-to-neuron communication.

Targeting of Lysosomal Pathway Genes for Parkinson's Disease Modification: Insights From Cellular and Animal Models

Previous genetic studies on hereditary Parkinson's disease (PD) have identified a set of pathogenic gene mutations that have strong impacts on the pathogenicity of PD. In addition, genome-wide association studies (GWAS) targeted to sporadic PD have nominated an increasing number of genetic variants that influence PD susceptibility. Although the clinical and pathological characteristics in hereditary PD are not identical to those in sporadic PD, α-synuclein, and LRRK2 are definitely associated with both types of PD, with LRRK2 mutations being the most frequent cause of autosomal-dominant PD. On the other hand, a significant portion of risk genes identified from GWAS have been associated with lysosomal functions, pointing to a critical role of lysosomes in PD pathogenesis. Experimental studies have suggested that the maintenance or upregulation of lysosomal activity may protect against neuronal dysfunction or degeneration. Here we focus on the roles of representative PD gene products that are implicated in lysosomal pathway, namely LRRK2, VPS35, ATP13A2, and glucocerebrosidase, and provide an overview of their disease-associated functions as well as their cooperative actions in the pathogenesis of PD, based on the evidence from cellular and animal models. We also discuss future perspectives of targeting lysosomal activation as a possible strategy to treat neurodegeneration.

Aerts J, Moratalla R. The Role of Cholesterol in α-Synuclein and Lewy Body Pathology in GBA1 Parkinson's Disease

Parkinson's disease (PD) is a progressive neurodegenerative disease where dopaminergic neurons in the substantia nigra are lost, resulting in a decrease in striatal dopamine and, consequently, motor control. Dopaminergic degeneration is associated with the appearance of Lewy bodies, which contain membrane structures and proteins, including α-synuclein (α-Syn), in surviving neurons. PD displays a multifactorial pathology and develops from interactions between multiple elements, such as age, environmental conditions, and genetics. Mutations in the GBA1 gene represent one of the major genetic risk factors for PD. This gene encodes an essential lysosomal enzyme called β-glucocerebrosidase (GCase), which is responsible for degrading the glycolipid glucocerebroside into glucose and ceramide. GCase can generate glucosylated cholesterol via transglucosylation and can also degrade the sterol glucoside. Although the molecular mechanisms that predispose an individual to neurodegeneration remain unknown, the role of cholesterol in PD pathology deserves consideration. Disturbed cellular cholesterol metabolism, as reflected by accumulation of lysosomal cholesterol in GBA1-associated PD cellular models, could contribute to changes in lipid rafts, which are necessary for synaptic localization and vesicle cycling and modulation of synaptic integrity. α-Syn has been implicated in the regulation of neuronal cholesterol, and cholesterol facilitates interactions between α-Syn oligomers. In this review, we integrate the results of previous studies and describe the cholesterol landscape in cellular homeostasis and neuronal function. We discuss its implication in α-Syn and Lewy body pathophysiological mechanisms underlying PD, focusing on the role of GCase and cholesterol. © 2020 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Comparison of the expression and toxicity of AAV2/9 carrying the human A53T α-synuclein gene in presence or absence of WPRE

Woodchuck Hepatitis Virus Post-transcriptional Regulatory Element (WPRE) is thought to enhance transgene expression of target genes delivered by adeno-associated viral (AAV) vectors. This study assessed the protein expression of α-synuclein, phosphorylated α-synuclein at Serine 129, extent of nigrostriatal degeneration as well as subsequent behavioral deficits induced by unilateral intranigral stereotactic injection in male adult C57BL/6J mice of an AAV2/9 expressing A53T human α-synuclein under the control of the synapsin promoter in presence or absence of the WPRE. The presence of WPRE enabled to achieve greater nigrostriatal degeneration and synucleinopathy which was concomitant with worsened forelimb use asymmetry. This work refines a mouse Parkinson's disease model in which anatomo-pathology is related to behavioral deficits.

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.

Identification of distinct pathological signatures induced by patient-derived α-synuclein structures in nonhuman primates

Dopaminergic neuronal cell death, associated with intracellular α-synuclein (α-syn)-rich protein aggregates [termed "Lewy bodies" (LBs)], is a well-established characteristic of Parkinson's disease (PD). Much evidence, accumulated from multiple experimental models, has suggested that α-syn plays a role in PD pathogenesis, not only as a trigger of pathology but also as a mediator of disease progression through pathological spreading. Here, we have used a machine learning-based approach to identify unique signatures of neurodegeneration in monkeys induced by distinct α-syn pathogenic structures derived from patients with PD. Unexpectedly, our results show that, in nonhuman primates, a small amount of singular α-syn aggregates is as toxic as larger amyloid fibrils present in the LBs, thus reinforcing the need for preclinical research in this species. Furthermore, our results provide evidence supporting the true multifactorial nature of PD, as multiple causes can induce a similar outcome regarding dopaminergic neurodegeneration.

Glucocerebrosidase Defects as a Major Risk Factor for Parkinson's Disease

Heterozygous mutations of the GBA1 gene, encoding for lysosomal enzyme glucocerebrosidase (GCase), occur in a considerable percentage of all patients with sporadic Parkinson's disease (PD), varying between 8% and 12% across the world. Genome wide association studies have confirmed the strong correlation between PD and GBA1 mutations, pointing to this element as a major risk factor for PD, possibly the most important one after age. The pathobiological mechanisms underlying the link between a defective function of GCase and the development of PD are still unknown and are currently the focus of intense investigation in the community of pre-clinical and clinical researchers in the PD field. A major controversy regards the fact that, despite the unequivocal correlation between the presence of GBA1 mutations and the risk of developing PD, only a minority of asymptomatic carriers with GBA1 mutations convert to PD in their lifetime. GBA1 mutations reduce the enzymatic function of GCase, impairing lysosomal efficiency and the cellular ability to dispose of pathological alpha-synuclein. Changes in the cellular lipidic content resulting from the accumulation of glycosphingolipids, triggered by lysosomal dysfunction, may contribute to the pathological modification of alpha-synuclein, due to its ability to interact with cell membrane lipids. Mutant GCase can impair mitochondrial function and cause endoplasmic reticulum stress, thereby impacting on cellular energy production and proteostasis. Importantly, reduced GCase activity is associated with clear activation of microglia, a major mediator of neuroinflammatory response within the brain parenchyma, which points to neuroinflammation as a major consequence of GCase dysfunction. In this present review article, we summarize the current knowledge on the role of GBA1 mutations in PD development and their phenotypic correlations. We also discuss the potential role of the GCase pathway in the search for PD biomarkers that may enable the development of disease modifying therapies. Answering these questions will aid clinicians in offering more appropriate counseling to the patients and their caregivers and provide future directions for PD preclinical research.

The biochemical basis of interactions between Glucocerebrosidase and alpha-synuclein in GBA1 mutation carriers

The discovery of genes involved in familial as well as sporadic forms of Parkinson disease (PD) constitutes an important milestone in understanding this disorder's pathophysiology and potential treatment. Among these genes, GBA1 is one of the most common and well-studied, but it is still unclear how mutations in GBA1 translate into an increased risk for developing PD. In this review, we provide an overview of the biochemical and structural relationship between GBA1 and PD to help understand the recent advances in the development of PD therapies intended to target this pathway.

Glucocerebrosidase Activity Modulates Neuronal Susceptibility to Pathological α-Synuclein Insult

Mutations in the GBA1 gene are the most common genetic risk factor for Parkinson's disease (PD) and dementia with Lewy bodies (DLB). GBA1 encodes the lysosomal lipid hydrolase glucocerebrosidase (GCase), and its activity has been linked to accumulation of α-synuclein. The current study systematically examines the relationship between GCase activity and both pathogenic and non-pathogenic forms of α-synuclein in primary hippocampal, cortical, and midbrain neuron and astrocyte cultures, as well as in transgenic mice and a non-transgenic mouse model of PD. We find that reduced GCase activity does not result in aggregation of α-synuclein. However, in the context of extant misfolded α-synuclein, GCase activity modulates neuronal susceptibility to pathology. Furthermore, this modulation does not depend on neuron type but rather is driven by the level of pathological α-synuclein seeds. This study has implications for understanding how GBA1 mutations influence PD pathogenesis and provides a platform for testing novel therapeutics.

Inflammasome inhibition prevents α-synuclein pathology and dopaminergic neurodegeneration in mice

Parkinson's disease (PD) is characterized by a profound loss of dopaminergic neurons in the substantia nigra, accompanied by chronic neuroinflammation, mitochondrial dysfunction, and widespread accumulation of α-synuclein-rich protein aggregates in the form of Lewy bodies. However, the mechanisms linking α-synuclein pathology and dopaminergic neuronal death to chronic microglial neuroinflammation have not been completely elucidated. We show that activation of the microglial NLR family pyrin domain containing 3 (NLRP3) inflammasome is a common pathway triggered by both fibrillar α-synuclein and dopaminergic degeneration in the absence of α-synuclein aggregates. Cleaved caspase-1 and the inflammasome adaptor protein apoptosis-associated speck-like protein containing a C-terminal caspase recruitment domain (ASC) were elevated in the substantia nigra of the brains of patients with PD and in multiple preclinical PD models. NLRP3 activation by fibrillar α-synuclein in mouse microglia resulted in a delayed but robust activation of the NLRP3 inflammasome leading to extracellular interleukin-1β and ASC release in the absence of pyroptosis. Nanomolar doses of a small-molecule NLRP3 inhibitor, MCC950, abolished fibrillar α-synuclein-mediated inflammasome activation in mouse microglial cells and extracellular ASC release. Furthermore, oral administration of MCC950 in multiple rodent PD models inhibited inflammasome activation and effectively mitigated motor deficits, nigrostriatal dopaminergic degeneration, and accumulation of α-synuclein aggregates. These findings suggest that microglial NLRP3 may be a sustained source of neuroinflammation that could drive progressive dopaminergic neuropathology and highlight NLRP3 as a potential target for disease-modifying treatments for PD.

Age-related neurochemical and behavioural changes in D409V/WT GBA1 mouse: Relevance to lewy body dementia

Heterozygous mutations in GBA1, the gene which encodes the lysosomal enzyme glucocerebrosidase (GCase), are a strong genetic risk factor for the development of Lewy body dementia (LBD). Until this point however, recapitulation of the symptoms and pathology of LBD has been limited to a homozygous GBA1 mouse model which genetically and enzymatically reflects the lysosomal storage disorder Gaucher's disease. This study reports for the first time cognitive impairment by two independent behavioural tests in heterozygous GBA1 mutant mice (D409V/WT) which demonstrate significant cognitive impairment by the age of 12 months. Furthermore, reductions in GBA1 GCase enzyme activity within the brain reflects levels seen in sporadic and GBA1 mutant LBD patients. While there is no overt deposition of Lewy bodies within the hippocampus, alterations to cholinergic machinery and glial proliferation are evident, both pathological features of LBD. Interestingly, we also describe the novel finding of significantly reduced GBA2 GCase enzyme activity specifically within the hippocampus. This suggests that reduced GBA1 GCase enzyme activity dis-equilibrates the finely balanced glycosphingolipid metabolism pathway and that reductions in GBA2 GCase enzyme could contribute to the pathological and behavioural effects seen. Overall, this study presents evidence to suggest that pathological hallmarks associated with LBD specifically affecting brain regions intrinsically linked with cognition are present in the D409V/WT mice. In the absence of Lewy body deposition, the D409V/WT mice could be considered an early pre-clinical model of LBD with potential for drug discovery. Since few robust pre-clinical models of LBD currently exist, with further characterization, the mouse model described here may contribute significantly to developments in the LBD field.

Can GBA1-Associated Parkinson Disease Be Modeled in the Mouse?

Homozygous and heterozygous mutations in GBA1, the gene implicated in Gaucher disease, increase the risk and severity of Parkinson disease (PD). We evaluated the design, phenotype, strengths, and limitations of current GBA1-associated PD mouse models. Although faithful modeling of a genetic risk factor poses many challenges, the different approaches taken were successful in revealing predisposing abnormalities in heterozygotes for GBA1 mutations and demonstrating the deleterious effects of GBA1 impairment on the PD course in PD models. GBA1-PD models differ in key parameters, with no single model recapitulating all aspects of the GBA1-PD puzzle, emphasizing the importance of selecting the proper in vivo model depending on the specific molecular mechanism or potential therapy being studied.

α-Synuclein pathology in Parkinson's disease and related α-synucleinopathies

Over 20 years ago, the synaptic protein α-synuclein was identified as the primary component of the Lewy bodies (LBs) that are a sine qua non of Parkinson's disease (PD). Since that time, extensive research has demonstrated that α-synuclein pathology is not only a hallmark of PD, but can also cause neuronal dysfunction and death. Detailed staging of α-synuclein pathology in the brains of patients has revealed a progressive pattern of pathology that correlates with the symptoms of disease. Early in the disease course, PD patients exhibit motor dysfunction, and α-synuclein pathology at this stage is primarily found in regions controlling motor function. At later stages of disease as patients' cognitive function deteriorates, α-synuclein pathology can be found in cortical structures responsible for higher cognitive processing. The stereotypical progression of α-synuclein pathology through the brain over time suggests that there may be a physical transmission of pathological α-synuclein from one area of the brain to another. The transmission hypothesis posits that an initial seed of pathological α-synuclein in one neuron may be released and taken up by another vulnerable neuron and thereby initiate pathological misfolding of α-synuclein in the recipient neuron. In recent years, convergent evidence from various studies has indicated that pathological protein transmission can occur in the human brain. Cell and animal models based on the transmission hypothesis have shown not only that pathological α-synuclein can be transmitted from cell-to-cell, but that this pathology can lead to neuronal dysfunction and degeneration. The α-synuclein transmission hypothesis has profound implications for treatment of what is currently an intractable neurodegenerative disease. In this review, we explore the evidence for cell-to-cell transmission of pathological α-synuclein, the current understanding of how pathological α-synuclein can move to a new cell and template misfolding, and the therapeutic implications of α-synuclein transmission.

Selective autophagy as a potential therapeutic target for neurodegenerative disorders

Cells rely on surveillance systems such as autophagy to handle protein alterations and organelle damage. Dysfunctional autophagy, an evolutionarily conserved cellular mechanism for degradation of intracellular components in lysosomes, frequently leads to neurodegeneration. The neuroprotective effect of autophagy stems from its ability to eliminate pathogenic forms of proteins such as α-synuclein or tau. However, the same pathogenic proteins often affect different types and steps of the autophagic process. Furthermore, genetic studies have shown that some proteins related to neurodegeneration, such as huntingtin, participate in autophagy as one of their physiological functions. This complex interplay between autophagy and neurodegeneration suggests that targeting autophagy as a whole might have limited applicability in neurodegenerative diseases, and that future efforts should focus instead on targeting specific types and steps of the autophagic process. This change of strategy in the modulation of autophagy might hold promise for future disease-modifying therapies for patients with neurodegenerative disorders.

Sex-dependent behavioral deficits and neuropathology in a maternal immune activation model of autism

Infections during gestation and the consequent maternal immune activation (MIA) increase the risk of developing neuropsychiatric disorders in infants and throughout life, including autism spectrum disorders (ASD). ASD is a neurodevelopmental disorder that affects three times more males than females and is mainly characterized by deficits in social communication and restricted interests. Consistent findings also indicate that ASD patients suffer from movement disorders, although these symptoms are not yet considered as diagnosis criteria. Here we used the double-stranded RNA analog polyinosinic:polycytidylic acid (poly I:C) MIA animal model of ASD in mice and explored its effects in males and females on social and motor behavior. We then investigated brain areas implicated in controlling and coordinating movements, namely the nigro-striatal pathway, motor cortex and cerebellum. We show that male mice are more affected by this treatment than females as they show reduced social interactions as well as motor development and coordination deficits. Reduced numbers of Purkinje cells in the cerebellum was found more widespread and within distinct lobules in males than in females. Moreover, a reduced number of neurons was found in the motor cortex of males only. These results suggest that females are better protected against developmental insults leading to ASD symptoms in mice. They also point to brain areas that may be targeted to better manage social and motor consequences of ASD.

Glucocerebrosidase haploinsufficiency in A53T α-synuclein mice impacts disease onset and course

Mutations in GBA1 encountered in Gaucher disease are a leading risk factor for Parkinson disease and associated Lewy body disorders. Many GBA1 mutation carriers, especially those with severe or null GBA1 alleles, have earlier and more progressive parkinsonism. To model the effect of partial glucocerebrosidase deficiency on neurological progression in vivo, mice with a human A53T α-synuclein (SNCA^A53T) transgene were crossed with heterozygous null gba mice (gba^+/-). Survival analysis of 84 mice showed that in gba^+/-//SNCA^A53T hemizygotes and homozygotes, the symptom onset was significantly earlier than in gba^+/+//SNCA^A53T mice (p-values 0.023-0.0030), with exacerbated disease progression (p-value <0.0001). Over-expression of SNCA^A53T had no effect on glucocerebrosidase levels or activity. Immunoblotting demonstrated that gba haploinsufficiency did not lead to increased levels of either monomeric SNCA or insoluble high molecular weight SNCA in this model. Immunohistochemical analyses demonstrated that the abundance and distribution of SNCA pathology was also unaltered by gba haploinsufficiency. Thus, while the underlying mechanism is not clear, this model shows that gba deficiency impacts the age of onset and disease duration in aged SNCA^A53T mice, providing a valuable resource to identify modifiers, pathways and possible moonlighting roles of glucocerebrosidase in Parkinson pathogenesis.

Altered Differentiation Potential of Gaucher's Disease iPSC Neuronal Progenitors due to Wnt/β-Catenin Downregulation

Gaucher’s disease (GD) is an autosomal recessive disorder caused by mutations in the GBA1 gene, which encodes acid β-glucocerebrosidase (GCase). Severe GBA1 mutations cause neuropathology that manifests soon after birth, suggesting that GCase deficiency interferes with neuronal development. We found that neuronopathic GD induced pluripotent stem cell (iPSC)-derived neuronal progenitor cells (NPCs) exhibit developmental defects due to downregulation of canonical Wnt/β-catenin signaling and that GD iPSCs’ ability to differentiate to dopaminergic (DA) neurons was strikingly reduced due to early loss of DA progenitors. Incubation of the mutant cells with the Wnt activator CHIR99021 (CHIR) or with recombinant GCase restored Wnt/β-catenin signaling and rescued DA differentiation. We also found that GD NPCs exhibit lysosomal dysfunction, which may be involved in Wnt downregulation by mutant GCase. We conclude that neuronopathic mutations in GCase lead to neurodevelopmental abnormalities due to a critical requirement of this enzyme for canonical Wnt/β-catenin signaling at early stages of neurogenesis.

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Neuronopathic GBA1 mutations attenuate canonical Wnt signaling in iPSC-derived NPCs

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GD NPC differentiation to DA neurons impaired due to early loss of DA progenitors

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GBA1-mediated lysosomal alterations may be involved in Wnt signal downregulation

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The Wnt pathway may be a potential new therapeutic target for neuronopathic GD