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

High-throughput screening for small-molecule stabilizers of misfolded glucocerebrosidase in Gaucher disease and Parkinson's disease

Glucocerebrosidase (GCase) is implicated in both a rare, monogenic disorder (Gaucher disease, GD) and a common, multifactorial condition (Parkinson's disease, PD); hence, it is an urgent therapeutic target. To identify correctors of severe protein misfolding and trafficking obstruction manifested by the pathogenic L444P-variant of GCase, we developed a suite of quantitative, high-throughput, cell-based assays. First, we labeled GCase with a small proluminescent HiBiT peptide reporter tag, enabling quantitation of protein stabilization in cells while faithfully maintaining target biology. TALEN-based gene editing allowed for stable integration of a single HiBiT-GBA1 transgene into an intragenic safe-harbor locus in GBA1-knockout H4 (neuroglioma) cells. This GD cell model was amenable to lead discovery via titration-based quantitative high-throughput screening and lead optimization via structure-activity relationships. A primary screen of 10,779 compounds from the NCATS bioactive collections identified 140 stabilizers of HiBiT-GCase-L444P, including both pharmacological chaperones (ambroxol and noninhibitory chaperone NCGC326) and proteostasis regulators (panobinostat, trans-ISRIB, and pladienolide B). Two complementary high-content imaging-based assays were deployed to triage hits: The fluorescence-quenched substrate LysoFix-GBA captured functional lysosomal GCase activity, while an immunofluorescence assay featuring antibody hGCase-1/23 directly visualized GCase lysosomal translocation. NCGC326 was active in both secondary assays and completely reversed pathological glucosylsphingosine accumulation. Finally, we tested the concept of combination therapy by demonstrating synergistic actions of NCGC326 with proteostasis regulators in enhancing GCase-L444P levels. Looking forward, these physiologically relevant assays can facilitate the identification, pharmacological validation, and medicinal chemistry optimization of small molecules targeting GCase, ultimately leading to a viable therapeutic for GD and PD.

Development of quantitative high-throughput screening assays to identify, validate, and optimize small-molecule stabilizers of misfolded β-glucocerebrosidase with therapeutic potential for Gaucher disease and Parkinson's disease

Glucocerebrosidase (GCase) is implicated in both a rare, monogenic disorder (Gaucher disease, GD) and a common, multifactorial condition (Parkinson's disease); hence, it is an urgent therapeutic target. To identify correctors of severe protein misfolding and trafficking obstruction manifested by the pathogenic L444P-variant of GCase, we developed a suite of quantitative, high-throughput, cell-based assays. First, we labeled GCase with a small pro-luminescent HiBiT peptide reporter tag, enabling quantitation of protein stabilization in cells while faithfully maintaining target biology. TALEN-based gene editing allowed for stable integration of a single HiBiT-GBA1 transgene into an intragenic safe-harbor locus in GBA1-knockout H4 (neuroglioma) cells. This GD cell model was amenable to lead discovery via titration-based quantitative high-throughput screening and lead optimization via structure-activity relationships. A primary screen of 10,779 compounds from the NCATS bioactive collections identified 140 stabilizers of HiBiT-GCase-L444P, including both pharmacological chaperones (ambroxol and non-inhibitory chaperone NCGC326) and proteostasis regulators (panobinostat, trans-ISRIB, and pladienolide B). Two complementary high-content imaging-based assays were deployed to triage hits: the fluorescence-quenched substrate LysoFix-GBA captured functional lysosomal GCase activity, while an immunofluorescence assay featuring antibody hGCase-1/23 provided direct visualization of GCase lysosomal translocation. NCGC326 was active in both secondary assays and completely reversed pathological glucosylsphingosine accumulation. Finally, we tested the concept of combination therapy, by demonstrating synergistic actions of NCGC326 with proteostasis regulators in enhancing GCase-L444P levels. Looking forward, these physiologically-relevant assays can facilitate the identification, pharmacological validation, and medicinal chemistry optimization of new chemical matter targeting GCase, ultimately leading to a viable therapeutic for two protein-misfolding diseases.

Strategies for dissecting the complexity of neurodevelopmental disorders

Neurodevelopmental disorders (NDDs) are associated with a wide range of clinical features, affecting multiple pathways involved in brain development and function. Recent advances in high-throughput sequencing have unveiled numerous genetic variants associated with NDDs, which further contribute to disease complexity and make it challenging to infer disease causation and underlying mechanisms. Herein, we review current strategies for dissecting the complexity of NDDs using model organisms, induced pluripotent stem cells, single-cell sequencing technologies, and massively parallel reporter assays. We further highlight single-cell CRISPR-based screening techniques that allow genomic investigation of cellular transcriptomes with high efficiency, accuracy, and throughput. Overall, we provide an integrated review of experimental approaches that can be applicable for investigating a broad range of complex disorders.

What Can Inflammation Tell Us about Therapeutic Strategies for Parkinson's Disease?

Parkinson's disease (PD) is a common neurodegenerative disorder with a complicated etiology and pathogenesis. α-Synuclein aggregation, dopaminergic (DA) neuron loss, mitochondrial injury, oxidative stress, and inflammation are involved in the process of PD. Neuroinflammation has been recognized as a key element in the initiation and progression of PD. In this review, we summarize the inflammatory response and pathogenic mechanisms of PD. Additionally, we describe the potential anti-inflammatory therapies, including nod-like receptor pyrin domain containing protein 3 (NLRP3) inflammasome inhibition, nuclear factor κB (NF-κB) inhibition, microglia inhibition, astrocyte inhibition, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibition, the peroxisome proliferator-activated receptor γ (PPARγ) agonist, targeting the mitogen-activated protein kinase (MAPK) pathway, targeting the adenosine monophosphate-activated protein kinase (AMPK)-dependent pathway, targeting α-synuclein, targeting miRNA, acupuncture, and exercise. The review focuses on inflammation and will help in designing new prevention strategies for PD.

Impaired neuron differentiation in GBA-associated Parkinson's disease is linked to cell cycle defects in organoids

The mechanisms underlying Parkinson's disease (PD) etiology are only partially understood despite intensive research conducted in the field. Recent evidence suggests that early neurodevelopmental defects might play a role in cellular susceptibility to neurodegeneration. To study the early developmental contribution of GBA mutations in PD we used patient-derived iPSCs carrying a heterozygous N370S mutation in the GBA gene. Patient-specific midbrain organoids displayed GBA-PD relevant phenotypes such as reduction of GCase activity, autophagy impairment, and mitochondrial dysfunction. Genome-scale metabolic (GEM) modeling predicted changes in lipid metabolism which were validated with lipidomics analysis, showing significant differences in the lipidome of GBA-PD. In addition, patient-specific midbrain organoids exhibited a decrease in the number and complexity of dopaminergic neurons. This was accompanied by an increase in the neural progenitor population showing signs of oxidative stress-induced damage and premature cellular senescence. These results provide insights into how GBA mutations may lead to neurodevelopmental defects thereby predisposing to PD pathology.

WNT-β Catenin Signaling as a Potential Therapeutic Target for Neurodegenerative Diseases: Current Status and Future Perspective

Wnt/β-catenin (WβC) signaling pathway is an important signaling pathway for the maintenance of cellular homeostasis from the embryonic developmental stages to adulthood. The canonical pathway of WβC signaling is essential for neurogenesis, cell proliferation, and neurogenesis, whereas the noncanonical pathway (WNT/Ca²⁺ and WNT/PCP) is responsible for cell polarity, calcium maintenance, and cell migration. Abnormal regulation of WβC signaling is involved in the pathogenesis of several neurodegenerative diseases such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), amyotrophic lateral sclerosis (ALS), multiple sclerosis (MS), and spinal muscular atrophy (SMA). Hence, the alteration of WβC signaling is considered a potential therapeutic target for the treatment of neurodegenerative disease. In the present review, we have used the bibliographical information from PubMed, Google Scholar, and Scopus to address the current prospects of WβC signaling role in the abovementioned neurodegenerative diseases.

Deregulation of mTORC1-TFEB axis in human iPSC model of GBA1-associated Parkinson's disease

Mutations in the GBA1 gene are the single most frequent genetic risk factor for Parkinson's disease (PD). Neurodegenerative changes in GBA1-associated PD have been linked to the defective lysosomal clearance of autophagic substrates and aggregate-prone proteins. To elucidate novel mechanisms contributing to proteinopathy in PD, we investigated the effect of GBA1 mutations on the transcription factor EB (TFEB), the master regulator of the autophagy-lysosomal pathway (ALP). Using PD patients' induced-pluripotent stem cells (iPSCs), we examined TFEB activity and regulation of the ALP in dopaminergic neuronal cultures generated from iPSC lines harboring heterozygous GBA1 mutations and the CRISPR/Cas9-corrected isogenic controls. Our data showed a significant decrease in TFEB transcriptional activity and attenuated expression of many genes in the CLEAR network in GBA1 mutant neurons, but not in the isogenic gene-corrected cells. In PD neurons, we also detected increased activity of the mammalian target of rapamycin complex1 (mTORC1), the main upstream negative regulator of TFEB. Increased mTORC1 activity resulted in excess TFEB phosphorylation and decreased nuclear translocation. Pharmacological mTOR inhibition restored TFEB activity, decreased ER stress and reduced α-synuclein accumulation, indicating improvement of neuronal protiostasis. Moreover, treatment with the lipid substrate reducing compound Genz-123346, decreased mTORC1 activity and increased TFEB expression in the mutant neurons, suggesting that mTORC1-TFEB alterations are linked to the lipid substrate accumulation. Our study unveils a new mechanism contributing to PD susceptibility by GBA1 mutations in which deregulation of the mTORC1-TFEB axis mediates ALP dysfunction and subsequent proteinopathy. It also indicates that pharmacological restoration of TFEB activity could be a promising therapeutic approach in GBA1-associated neurodegeneration.

Applications of Boolean modeling to study the dynamics of a complex disease and therapeutics responses

Computational modeling has emerged as a critical tool in investigating the complex molecular processes involved in biological systems and diseases. In this study, we apply Boolean modeling to uncover the molecular mechanisms underlying Parkinson's disease (PD), one of the most prevalent neurodegenerative disorders. Our approach is based on the PD-map, a comprehensive molecular interaction diagram that captures the key mechanisms involved in the initiation and progression of PD. Using Boolean modeling, we aim to gain a deeper understanding of the disease dynamics, identify potential drug targets, and simulate the response to treatments. Our analysis demonstrates the effectiveness of this approach in uncovering the intricacies of PD. Our results confirm existing knowledge about the disease and provide valuable insights into the underlying mechanisms, ultimately suggesting potential targets for therapeutic intervention. Moreover, our approach allows us to parametrize the models based on omics data for further disease stratification. Our study highlights the value of computational modeling in advancing our understanding of complex biological systems and diseases, emphasizing the importance of continued research in this field. Furthermore, our findings have potential implications for the development of novel therapies for PD, which is a pressing public health concern. Overall, this study represents a significant step forward in the application of computational modeling to the investigation of neurodegenerative diseases, and underscores the power of interdisciplinary approaches in tackling challenging biomedical problems.

Induction of dopaminergic neurons for neuronal subtype-specific modeling of psychiatric disease risk

Dopaminergic neurons are critical to movement, mood, addiction, and stress. Current techniques for generating dopaminergic neurons from human induced pluripotent stem cells (hiPSCs) yield heterogenous cell populations with variable purity and inconsistent reproducibility between donors, hiPSC clones, and experiments. Here, we report the rapid (5 weeks) and efficient (~90%) induction of induced dopaminergic neurons (iDANs) through transient overexpression of lineage-promoting transcription factors combined with stringent selection across five donors. We observe maturation-dependent increase in dopamine synthesis and electrophysiological properties consistent with midbrain dopaminergic neuron identity, such as slow-rising after- hyperpolarization potentials, an action potential duration of ~3 ms, tonic sub-threshold oscillatory activity, and spontaneous burst firing at a frequency of ~1.0-1.75 Hz. Transcriptome analysis reveals robust expression of genes involved in fetal midbrain dopaminergic neuron identity. Specifically expressed genes in iDANs, as well as those from isogenic induced GABAergic and glutamatergic neurons, were enriched in loci conferring heritability for cannabis use disorder, schizophrenia, and bipolar disorder; however, each neuronal subtype demonstrated subtype-specific heritability enrichments in biologically relevant pathways, and iDANs alone were uniquely enriched in autism spectrum disorder risk loci. Therefore, iDANs provide a critical tool for modeling midbrain dopaminergic neuron development and dysfunction in psychiatric disease.

Neuronopathic Gaucher disease models reveal defects in cell growth promoted by Hippo pathway activation

Gaucher Disease (GD), the most common lysosomal disorder, arises from mutations in the GBA1 gene and is characterized by a wide spectrum of phenotypes, ranging from mild hematological and visceral involvement to severe neurological disease. Neuronopathic patients display dramatic neuronal loss and increased neuroinflammation, whose molecular basis are still unclear. Using a combination of Drosophila dGBA1b loss-of-function models and GD patient-derived iPSCs differentiated towards neuronal precursors and mature neurons we showed that different GD- tissues and neuronal cells display an impairment of growth mechanisms with an increased cell death and reduced proliferation. These phenotypes are coupled with the downregulation of several Hippo transcriptional targets, mainly involved in cells and tissue growth, and YAP exclusion from nuclei. Interestingly, Hippo knock-down in the GBA-KO flies rescues the proliferative defect, suggesting that targeting the Hippo pathway can be a promising therapeutic approach to neuronopathic GD.

Neuronopathic Gaucher disease: Beyond lysosomal dysfunction

Gaucher disease (GD) is an inherited disorder caused by recessive mutations in the GBA1 gene that encodes the lysosomal enzyme β-glucocerebrosidase (β-GC). β-GC hydrolyzes glucosylceramide (GluCer) into glucose and ceramide in the lysosome, and the loss of its activity leads to GluCer accumulation in different tissues. In severe cases, enzymatic deficiency triggers inflammation, organomegaly, bone disease, and neurodegeneration. Neuronopathic Gaucher disease (nGD) encompasses two different forms of the disease, characterized by chronic or acute damage to the central nervous system (CNS). The cellular and molecular studies that uncover the pathological mechanisms of nGD mainly focus on lysosomal dysfunction since the lysosome is the key organelle affected in GD. However, new studies show alterations in other organelles that contribute to nGD pathology. For instance, abnormal accumulation of GluCer in lysosomes due to the loss of β-GC activity leads to excessive calcium release from the endoplasmic reticulum (ER), activating the ER-associated degradation pathway and the unfolded protein response. Recent evidence indicates mitophagy is altered in nGD, resulting in the accumulation of dysfunctional mitochondria, a critical factor in disease progression. Additionally, nGD patients present alterations in mitochondrial morphology, membrane potential, ATP production, and increased reactive oxygen species (ROS) levels. Little is known about potential dysfunction in other organelles of the secretory pathway, such as the Golgi apparatus and exosomes. This review focuses on collecting evidence regarding organelle dysfunction beyond lysosomes in nGD. We briefly describe cellular and animal models and signaling pathways relevant to uncovering the pathological mechanisms and new therapeutic targets in GD.

"Reframing" dopamine signaling at the intersection of glial networks in the aged Parkinsonian brain as innate Nrf2/Wnt driver: Therapeutical implications

Dopamine (DA) signaling via G protein-coupled receptors is a multifunctional neurotransmitter and neuroendocrine-immune modulator. The DA nigrostriatal pathway, which controls the motor coordination, progressively degenerates in Parkinson's disease (PD), a most common neurodegenerative disorder (ND) characterized by a selective, age-dependent loss of substantia nigra pars compacta (SNpc) neurons, where DA itself is a primary source of oxidative stress and mitochondrial impairment, intersecting astrocyte and microglial inflammatory networks. Importantly, glia acts as a preferential neuroendocrine-immune DA target, in turn, counter-modulating inflammatory processes. With a major focus on DA intersection within the astrocyte-microglial inflammatory network in PD vulnerability, we herein first summarize the characteristics of DA signaling systems, the propensity of DA neurons to oxidative stress, and glial inflammatory triggers dictating the vulnerability to PD. Reciprocally, DA modulation of astrocytes and microglial reactivity, coupled to the synergic impact of gene-environment interactions, then constitute a further level of control regulating midbrain DA neuron (mDAn) survival/death. Not surprisingly, within this circuitry, DA converges to modulate nuclear factor erythroid 2-like 2 (Nrf2), the master regulator of cellular defense against oxidative stress and inflammation, and Wingless (Wnt)/β-catenin signaling, a key pathway for mDAn neurogenesis, neuroprotection, and immunomodulation, adding to the already complex "signaling puzzle," a novel actor in mDAn-glial regulatory machinery. Here, we propose an autoregulatory feedback system allowing DA to act as an endogenous Nrf2/Wnt innate modulator and trace the importance of DA receptor agonists applied to the clinic as immune modifiers.

Electrophysiological Properties of Induced Pluripotent Stem Cell-Derived Midbrain Dopaminergic Neurons Correlate With Expression of Tyrosine Hydroxylase

Induced pluripotent stem cell (iPSC)-based generation of tyrosine hydroxylase-positive (TH+) dopaminergic neurons (DNs) is a powerful method for creating patient-specific in vitro models to elucidate mechanisms underlying Parkinson’s disease (PD) at the cellular and molecular level and to perform drug screening. However, currently available differentiation paradigms result in highly heterogeneous cell populations, often yielding a disappointing fraction (<50%) of the PD-relevant TH+ DNs. To facilitate the targeted analysis of this cell population and to characterize their electrophysiological properties, we employed CRISPR/Cas9 technology and generated an mCherry-based human TH reporter iPSC line. Subsequently, reporter iPSCs were subjected to dopaminergic differentiation using either a “floor plate protocol” generating DNs directly from iPSCs or an alternative method involving iPSC-derived neuronal precursors (NPC-derived DNs). To identify the strategy with the highest conversion efficiency to mature neurons, both cultures were examined for a period of 8 weeks after triggering neuronal differentiation by means of immunochemistry and single-cell electrophysiology. We confirmed that mCherry expression correlated with the expression of endogenous TH and that genetic editing did neither affect the differentiation process nor the endogenous TH expression in iPSC- and NPC-derived DNs. Although both cultures yielded identical proportions of TH+ cells (≈30%), whole-cell patch-clamp experiments revealed that iPSC-derived DNs gave rise to larger currents mediated by voltage-gated sodium and potassium channels, showed a higher degree of synaptic activity, and fired trains of mature spontaneous action potentials more frequently compared to NPC-derived DNs already after 2 weeks in differentiation. Moreover, spontaneous action potential firing was more frequently detected in TH+ neurons compared to the TH– cells, providing direct evidence that these two neuronal subpopulations exhibit different intrinsic electrophysiological properties. In summary, the data reveal substantial differences in the electrophysiological properties of iPSC-derived TH+ and TH– neuronal cell populations and that the “floor plate protocol” is particularly efficient in generating electrophysiologically mature TH+ DNs, which are the most vulnerable neuronal subtype in PD.

Actin Alpha 2 Downregulation Inhibits Neural Stem Cell Proliferation and Differentiation into Neurons through Canonical Wnt/β-Catenin Signaling Pathway

Our previous study has shown that actin alpha 2 (ACTA2) is expressed in NSC and ACTA2 downregulation inhibits NSC migration by increasing RhoA expression and decreasing the expression of Rac1 to curb actin filament polymerization. Given that proliferation and differentiation are the two main characteristics of NSC, the role of ACTA2 downregulation in the proliferation and differentiation of NSC remains elusive. Here, the results demonstrated that ACTA2 downregulation using ACTA2 siRNA held the potential of inhibiting NSC proliferation using cell counting kit-8 (CCK8) and immunostaining. Then, our data illustrated that ACTA2 downregulation attenuated NSC differentiation into neurons, while directing NSC into astrocytes and oligodendrocytes using immunostaining and immunoblotting. Thereafter, the results revealed that the canonical Wnt/β-catenin pathway was involved in the effect of ACTA2 downregulation on the proliferation and differentiation of NSC through upregulating p-β-catenin and decreasing β-catenin due to inactivating GSK-3β, while this effect could be partially abolished with administration of CHIR99012, a GSK-3 inhibitor. Collectively, these results indicate that ACTA2 downregulation inhibits NSC proliferation and differentiation into neurons through inactivation of the canonical Wnt/β-catenin pathway. The aim of the present study is to elucidate the role of ACTA2 in proliferation and differentiation of NSC and to provide an intervention target for promoting NSC proliferation and properly directing NSC differentiation.

Bioengineered models of Parkinson's disease using patient-derived dopaminergic neurons exhibit distinct biological profiles in a 3D microenvironment

Three-dimensional (3D) in vitro culture systems using human induced pluripotent stem cells (hiPSCs) are useful tools to model neurodegenerative disease biology in physiologically relevant microenvironments. Though many successful biomaterials-based 3D model systems have been established for other neurogenerative diseases, such as Alzheimer's disease, relatively few exist for Parkinson's disease (PD) research. We employed tissue engineering approaches to construct a 3D silk scaffold-based platform for the culture of hiPSC-dopaminergic (DA) neurons derived from healthy individuals and PD patients harboring LRRK2 G2019S or GBA N370S mutations. We then compared results from protein, gene expression, and metabolic analyses obtained from two-dimensional (2D) and 3D culture systems. The 3D platform enabled the formation of dense dopamine neuronal network architectures and developed biological profiles both similar and distinct from 2D culture systems in healthy and PD disease lines. PD cultures developed in 3D platforms showed elevated levels of α-synuclein and alterations in purine metabolite profiles. Furthermore, computational network analysis of transcriptomic networks nominated several novel molecular interactions occurring in neurons from patients with mutations in LRRK2 and GBA. We conclude that the brain-like 3D system presented here is a realistic platform to interrogate molecular mechanisms underlying PD biology.

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.

Wnt signaling pathway inhibitors, sclerostin and DKK-1, correlate with pain and bone pathology in patients with Gaucher disease

Patients with Gaucher disease (GD) have progressive bone involvement that clinically presents with debilitating bone pain, structural bone changes, bone marrow infiltration (BMI), Erlenmeyer (EM) flask deformity, and osteoporosis. Pain is referred by the majority of GD patients and continues to persist despite the type of therapy. The pain in GD is described as chronic deep penetrating pain; however, sometimes, patients experience severe acute pain. The source of bone pain is mainly debated as nociceptive pain secondary to bone pathology or neuropathic or inflammatory origins. Osteocytes constitute a significant source of secreted molecules that coordinate bone remodeling. Osteocyte markers, sclerostin (SOST) and Dickkopf-1 (DKK-1), inactivate the canonical Wnt signaling pathway and lead to the inhibition of bone formation. Thus, circulated sclerostin and DKK-1 are potential biomarkers of skeletal abnormalities. This study aimed to assess the circulating levels of sclerostin and DKK-1 in patients with GD and their correlation with clinical bone pathology parameters: pain, bone mineral density (BMD), and EM deformity. Thirty-nine patients with GD were classified into cohorts based on the presence and severity of bone manifestations. The serum levels of sclerostin and DKK-1 were quantified by enzyme-linked immunosorbent assays. The highest level of sclerostin was measured in GD patients with pain, BMI, and EM deformity. The multiparameter analysis demonstrated that 95% of GD patients with pain, BMI, and EM deformity had increased levels of sclerostin. The majority of patients with elevated sclerostin also have osteopenia or osteoporosis. Moreover, circulating sclerostin level increase with age, and GD patients have elevated sclerostin levels when compared with healthy control from the same age group. Pearson's linear correlation analysis showed a positive correlation between serum DKK-1 and sclerostin in healthy controls and GD patients with normal bone mineral density. However, the balance between sclerostin and DKK-1 waned in GD patients with osteopenia or osteoporosis. In conclusion, the osteocyte marker, sclerostin, when elevated, is associated with bone pain, BMI, and EM flask deformity in GD patients. The altered sclerostin/DKK-1 ratio correlates with the reduction of bone mineral density. These data confirm that the Wnt signaling pathway plays a role in GD-associated bone disease. Sclerostin and bone pain could be used as biomarkers to assess patients with a high risk of BMI and EM flask deformities.

Chronic lithium administration in a mouse model for Krabbe disease

Krabbe disease (KD; or globoid cell leukodystrophy) is an autosomal recessive lysosomal storage disorder caused by deficiency of the galactosylceramidase (GALC) enzyme. No cure is currently available for KD. Clinical applied treatments are supportive only. Recently, we demonstrated that two differently acting autophagy inducers (lithium and rapamycin) can improve some KD hallmarks in-vitro, laying the foundation for their in-vivo pre-clinical testing. Here, we test lithium carbonate in-vivo, in the spontaneous mouse model for KD, the Twitcher (TWI) mouse. The drug is administered ad libitum via drinking water (600 mg/L) starting from post natal day 20. We longitudinally monitor the mouse motor performance through the grip strength, the hanging wire and the rotarod tests, and a set of biochemical parameters related to the KD pathogenesis [i.e., GALC enzymatic activity, psychosine (PSY) accumulation and astrogliosis]. Additionally, we investigate the expression of some crucial markers related to the two pathways that could be altered by lithium: the autophagy and the β-catenin-dependent pathways. Results demonstrate that lithium has not a significant rescue effect on the TWI phenotype, although it can slightly and transiently improves muscle strength. We also show that lithium, with this administration protocol, is unable to stimulate autophagy in the TWI mice central nervous system, whereas results suggest that it can restore the β-catenin activation status in the TWI sciatic nerve. Overall, these data provide intriguing inputs for further evaluations of lithium treatment in TWI mice.

C5a Activates a Pro-Inflammatory Gene Expression Profile in Human Gaucher iPSC-Derived Macrophages

Gaucher disease (GD) is an autosomal recessive disorder caused by bi-allelic GBA1 mutations that reduce the activity of the lysosomal enzyme β-glucocerebrosidase (GCase). GCase catalyzes the conversion of glucosylceramide (GluCer), a ubiquitous glycosphingolipid, to glucose and ceramide. GCase deficiency causes the accumulation of GluCer and its metabolite glucosylsphingosine (GluSph) in a number of tissues and organs. In the immune system, GCase deficiency deregulates signal transduction events, resulting in an inflammatory environment. It is known that the complement system promotes inflammation, and complement inhibitors are currently being considered as a novel therapy for GD; however, the mechanism by which complement drives systemic macrophage-mediated inflammation remains incompletely understood. To help understand the mechanisms involved, we used human GD-induced pluripotent stem cell (iPSC)-derived macrophages. We found that GD macrophages exhibit exacerbated production of inflammatory cytokines via an innate immune response mediated by receptor 1 for complement component C5a (C5aR1). Quantitative RT-PCR and ELISA assays showed that in the presence of recombinant C5a (rC5a), GD macrophages secreted 8-10-fold higher levels of TNF-α compared to rC5a-stimulated control macrophages. PMX53, a C5aR1 blocker, reversed the enhanced GD macrophage TNF-α production, indicating that the observed effect was predominantly C5aR1-mediated. To further analyze the extent of changes induced by rC5a stimulation, we performed gene array analysis of the rC5a-treated macrophage transcriptomes. We found that rC5a-stimulated GD macrophages exhibit increased expression of genes involved in TNF-α inflammatory responses compared to rC5a-stimulated controls. Our results suggest that rC5a-induced inflammation in GD macrophages activates a unique immune response, supporting the potential use of inhibitors of the C5a-C5aR1 receptor axis to mitigate the chronic inflammatory abnormalities associated with GD.

Reconstruction of the Cytokine Signaling in Lysosomal Storage Diseases by Literature Mining and Network Analysis

Lysosomal storage diseases (LSDs) are characterized by the abnormal accumulation of substrates in tissues due to the deficiency of lysosomal proteins. Among the numerous clinical manifestations, chronic inflammation has been consistently reported for several LSDs. However, the molecular mechanisms involved in the inflammatory response are still not completely understood. In this study, we performed text-mining and systems biology analyses to investigate the inflammatory signals in three LSDs characterized by sphingolipid accumulation: Gaucher disease, Acid Sphingomyelinase Deficiency (ASMD), and Fabry Disease. We first identified the cytokines linked to the LSDs, and then built on the extracted knowledge to investigate the inflammatory signals. We found numerous transcription factors that are putative regulators of cytokine expression in a cell-specific context, such as the signaling axes controlled by STAT2, JUN, and NR4A2 as candidate regulators of the monocyte Gaucher disease cytokine network. Overall, our results suggest the presence of a complex inflammatory signaling in LSDs involving many cellular and molecular players that could be further investigated as putative targets of anti-inflammatory therapies.

Current State-of-the-Art and Unresolved Problems in Using Human Induced Pluripotent Stem Cell-Derived Dopamine Neurons for Parkinson's Disease Drug Development

Human induced pluripotent stem (iPS) cells have the potential to give rise to a new era in Parkinson's disease (PD) research. As a unique source of midbrain dopaminergic (DA) neurons, iPS cells provide unparalleled capabilities for investigating the pathogenesis of PD, the development of novel anti-parkinsonian drugs, and personalized therapy design. Significant progress in developmental biology of midbrain DA neurons laid the foundation for their efficient derivation from iPS cells. The introduction of 3D culture methods to mimic the brain microenvironment further expanded the vast opportunities of iPS cell-based research of the neurodegenerative diseases. However, while the benefits for basic and applied studies provided by iPS cells receive widespread coverage in the current literature, the drawbacks of this model in its current state, and in particular, the aspects of differentiation protocols requiring further refinement are commonly overlooked. This review summarizes the recent data on general and subtype-specific features of midbrain DA neurons and their development. Here, we review the current protocols for derivation of DA neurons from human iPS cells and outline their general weak spots. The associated gaps in the contemporary knowledge are considered and the possible directions for future research that may assist in improving the differentiation conditions and increase the efficiency of using iPS cell-derived neurons for PD drug development are discussed.

Ambroxol Upregulates Glucocerebrosidase Expression to Promote Neural Stem Cells Differentiation Into Neurons Through Wnt/β-Catenin Pathway After Ischemic Stroke

Ischemic stroke has been becoming one of the leading causes resulting in mortality and adult long-term disability worldwide. Post-stroke pneumonia is a common complication in patients with ischemic stroke and always associated with 1-year mortality. Though ambroxol therapy often serves as a supplementary treatment for post-stroke pneumonia in ischemic stroke patients, its effect on functional recovery and potential mechanism after ischemic stroke remain elusive. In the present study, the results indicated that administration of 70 mg/kg and 100 mg/kg enhanced functional recovery by virtue of decreasing infarct volume. The potential mechanism, to some extent, was due to promoting NSCs differentiation into neurons and interfering NSCs differentiation into astrocytes through increasing GCase expression to activate Wnt/β-catenin signaling pathway in penumbra after ischemic stroke, which advanced basic knowledge of ambroxol in regulating NSCs differentiation and provided a feasible therapy for ischemic stroke treatment, even in other brain disorders in clinic.

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.

Deregulation of signalling in genetic conditions affecting the lysosomal metabolism of cholesterol and galactosyl-sphingolipids

The role of lipids in neuroglial function is gaining momentum in part due to a better understanding of how many lipid species contribute to key cellular signalling pathways at the membrane level. The description of lipid rafts as membrane domains composed by defined classes of lipids such as cholesterol and sphingolipids has greatly helped in our understanding of how cellular signalling can be regulated and compartmentalized in neurons and glial cells. Genetic conditions affecting the metabolism of these lipids greatly impact on how some of these signalling pathways work, providing a context to understand the biological function of the lipid. Expectedly, abnormal metabolism of several lipids such as cholesterol and galactosyl-sphingolipids observed in several metabolic conditions involving lysosomal dysfunction are often accompanied by neuronal and myelin dysfunction. This review will discuss the role of lysosomal biology in the context of deficiencies in the metabolism of cholesterol and galactosyl-sphingolipids and their impact on neural function in three genetic disorders: Niemann-Pick type C, Metachromatic leukodystrophy and Krabbe's disease.

Nrf2/Wnt resilience orchestrates rejuvenation of glia-neuron dialogue in Parkinson's disease

Oxidative stress and inflammation have long been recognized to contribute to Parkinson's disease (PD), a common movement disorder characterized by the selective loss of midbrain dopaminergic neurons (mDAn) of the substantia nigra pars compacta (SNpc). The causes and mechanisms still remain elusive, but a complex interplay between several genes and a number of interconnected environmental factors, are chiefly involved in mDAn demise, as they intersect the key cellular functions affected in PD, such as the inflammatory response, mitochondrial, lysosomal, proteosomal and autophagic functions. Nuclear factor erythroid 2 -like 2 (NFE2L2/Nrf2), the master regulator of cellular defense against oxidative stress and inflammation, and Wingless (Wnt)/β-catenin signaling cascade, a vital pathway for mDAn neurogenesis and neuroprotection, emerge as critical intertwinned actors in mDAn physiopathology, as a decline of an Nrf2/Wnt/β-catenin prosurvival axis with age underlying PD mutations and a variety of noxious environmental exposures drive PD neurodegeneration. Unexpectedly, astrocytes, the so-called "star-shaped" cells, harbouring an arsenal of "beneficial" and "harmful" molecules represent the turning point in the physiopathological and therapeutical scenario of PD. Fascinatingly, "astrocyte's fil rouge" brings back to Nrf2/Wnt resilience, as boosting the Nrf2/Wnt resilience program rejuvenates astrocytes, in turn (i) mitigating nigrostriatal degeneration of aged mice, (ii) reactivating neural stem progenitor cell proliferation and neuron differentiation in the brain and (iii) promoting a beneficial immunomodulation via bidirectional communication with mDAns. Then, through resilience of Nrf2/Wnt/β-catenin anti-ageing, prosurvival and proregenerative molecular programs, it seems possible to boost the inherent endogenous self-repair mechanisms. Here, the cellular and molecular aspects as well as the therapeutical options for rejuvenating glia-neuron dialogue will be discussed together with major glial-derived mechanisms and therapies that will be fundamental to the identification of novel diagnostic tools and treatments for neurodegenerative diseases (NDs), to fight ageing and nigrostriatal DAergic degeneration and promote functional recovery.

Wnt/β-Catenin Signaling in Neural Stem Cell Homeostasis and Neurological Diseases

Neural stem/progenitor cells (NSCs) maintain the ability of self-renewal and differentiation and compose the complex nervous system. Wnt signaling is thought to control the balance of NSC proliferation and differentiation via the transcriptional coactivator β-catenin during brain development and adult tissue homeostasis. Disruption of Wnt signaling may result in developmental defects and neurological diseases. Here, we summarize recent findings of the roles of Wnt/β-catenin signaling components in NSC homeostasis for the regulation of functional brain circuits. We also suggest that the potential role of Wnt/β-catenin signaling might lead to new therapeutic strategies for neurological diseases, including, but not limited to, spinal cord injury, Alzheimer's disease, Parkinson's disease, and depression.

Parkinson's disease, aging and adult neurogenesis: Wnt/β-catenin signalling as the key to unlock the mystery of endogenous brain repair

A common hallmark of age-dependent neurodegenerative diseases is an impairment of adult neurogenesis. Wingless-type mouse mammary tumor virus integration site (Wnt)/β-catenin (WβC) signalling is a vital pathway for dopaminergic (DAergic) neurogenesis and an essential signalling system during embryonic development and aging, the most critical risk factor for Parkinson's disease (PD). To date, there is no known cause or cure for PD. Here we focus on the potential to reawaken the impaired neurogenic niches to rejuvenate and repair the aged PD brain. Specifically, we highlight WβC-signalling in the plasticity of the subventricular zone (SVZ), the largest germinal region in the mature brain innervated by nigrostriatal DAergic terminals, and the mesencephalic aqueduct-periventricular region (Aq-PVR) Wnt-sensitive niche, which is in proximity to the SNpc and harbors neural stem progenitor cells (NSCs) with DAergic potential. The hallmark of the WβC pathway is the cytosolic accumulation of β-catenin, which enters the nucleus and associates with T cell factor/lymphoid enhancer binding factor (TCF/LEF) transcription factors, leading to the transcription of Wnt target genes. Here, we underscore the dynamic interplay between DAergic innervation and astroglial-derived factors regulating WβC-dependent transcription of key genes orchestrating NSC proliferation, survival, migration and differentiation. Aging, inflammation and oxidative stress synergize with neurotoxin exposure in "turning off" the WβC neurogenic switch via down-regulation of the nuclear factor erythroid-2-related factor 2/Wnt-regulated signalosome, a key player in the maintenance of antioxidant self-defense mechanisms and NSC homeostasis. Harnessing WβC-signalling in the aged PD brain can thus restore neurogenesis, rejuvenate the microenvironment, and promote neurorescue and regeneration.

A transcriptional and post-transcriptional dysregulation of Dishevelled 1 and 2 underlies the Wnt signaling impairment in type I Gaucher disease experimental models

Bone differentiation defects have been recently tied to Wnt signaling alterations occurring in vitro and in vivo Gaucher disease (GD) models. In this work, we provide evidence that the Wnt signaling multi-domain intracellular transducers Dishevelled 1 and 2 (DVL1 and DVL2) may be potential upstream targets of impaired beta glucosidase (GBA1) activity by showing their misexpression in different type 1 GD in vitro models. We also show that in Gba mutant fish a miR-221 upregulation is associated with reduced dvl2 expression levels and that in type I Gaucher patients single-nucleotide variants in the DVL2 3′ untranslated region are related to variable canonical Wnt pathway activity. Thus, we strengthen the recently outlined relation between bone differentiation defects and Wnt/β-catenin dysregulation in type I GD and further propose novel mechanistic insights of the Wnt pathway impairment caused by glucocerebrosidase loss of function.

Homogenous generation of dopaminergic neurons from multiple hiPSC lines by transient expression of transcription factors

A major hallmark of Parkinson's disease is loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc). The pathophysiological mechanisms causing this relatively selective neurodegeneration are poorly understood, and thus experimental systems allowing to study dopaminergic neuron dysfunction are needed. Induced pluripotent stem cells (iPSCs) differentiated toward a dopaminergic neuronal phenotype offer a valuable source to generate human dopaminergic neurons. However, currently available protocols result in a highly variable yield of dopaminergic neurons depending on the source of hiPSCs. We have now developed a protocol based on HBA promoter-driven transient expression of transcription factors by means of adeno-associated viral (AAV) vectors, that allowed to generate very consistent numbers of dopaminergic neurons from four different human iPSC lines. We also demonstrate that AAV vectors expressing reporter genes from a neuron-specific hSyn1 promoter can serve as surrogate markers for maturation of hiPSC-derived dopaminergic neurons. Dopaminergic neurons differentiated by transcription factor expression showed aggravated neurodegeneration through α-synuclein overexpression, but were not sensitive to γ-synuclein overexpression, suggesting that these neurons are well suited to study neurodegeneration in the context of Parkinson’s disease.

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.

High lithium levels in tobacco may account for reduced incidences of both Parkinson's disease and melanoma in smokers through enhanced β-catenin-mediated activity

Parkinson's disease (PD) patients have higher rates of melanoma and vice versa, observations suggesting that the two conditions may share common pathogenic pathways. β-Catenin is a transcriptional cofactor that, when concentrated in the nucleus, upregulates the expression of canonical Wnt target genes, such as Nurr1, many of which are important for neuronal survival. β-Catenin-mediated activity is decreased in sporadic PD as well as in leucine-rich repeat kinase 2 (LRRK2) and β-glucosidase (GBA) mutation cellular models of PD, which is the most common genetic cause of and risk for PD, respectively. In addition, β-catenin expression is significantly decreased in more aggressive and metastatic melanoma. Multiple observational studies have shown smokers to have significantly lower rates of PD as well as melanoma implying that tobacco may contain one or more elements that protect against both conditions. In support, smoker's brains have significantly reduced levels of α-synuclein, a pathological intracellular protein found in PD brain and melanoma cells. Tobacco contains very high lithium levels compared to other plants. Lithium has a broad array of neuroprotective actions, including enhancing autophagy and reducing intracellular α-synuclein levels, and is effective in both neurotoxin and transgenic preclinical PD models. One of lithium's neuroprotective actions is enhancement of β-catenin-mediated activity leading to increased Nurr1 expression through its ability to inhibit glycogen synthase kinase-3 β (GSK-3β). Lithium also has anti-proliferative effects on melanoma cells and the clinical use of lithium is associated with a reduced incidence of melanoma as well as reduced melanoma-associated mortality. This is the first known report hypothesizing that inhaled lithium from smoking may account for the associated reduced rates of both PD and melanoma and that this protection may be mediated, in part, through lithium-induced GSK-3β inhibition and consequent enhanced β-catenin-mediated activity. This hypothesis could be directly tested in clinical trials assessing lithium therapy's ability to affect β-catenin-mediated activity and slow disease progression in patients with PD or melanoma.

Glucocerebrosidase and its relevance to Parkinson disease

Mutations in GBA1, the gene encoding the lysosomal enzyme glucocerebrosidase, are among the most common known genetic risk factors for the development of Parkinson disease and related synucleinopathies. A great deal is known about GBA1, as mutations in GBA1 are causal for the rare autosomal storage disorder Gaucher disease. Over the past decades, significant progress has been made in understanding the genetics and cell biology of glucocerebrosidase. A least 495 different mutations, found throughout the 11 exons of the gene are reported, including both common and rare variants. Mutations in GBA1 may lead to degradation of the protein, disruptions in lysosomal targeting and diminished performance of the enzyme in the lysosome.

Gaucher disease is phenotypically diverse and has both neuronopathic and non-neuronopathic forms. Both patients with Gaucher disease and heterozygous carriers are at increased risk of developing Parkinson disease and Dementia with Lewy Bodies, although our understanding of the mechanism for this association remains incomplete. There appears to be an inverse relationship between glucocerebrosidase and α-synuclein levels, and even patients with sporadic Parkinson disease have decreased glucocerebrosidase. Glucocerebrosidase may interact with α-synuclein to maintain basic cellular functions, or impaired glucocerebrosidase could contribute to Parkinson pathogenesis by disrupting lysosomal homeostasis, enhancing endoplasmic reticulum stress or contributing to mitochondrial impairment. However, the majority of patients with GBA1 mutations never develop parkinsonism, so clearly other risk factors play a role. Treatments for Gaucher disease have been developed that increase visceral glucocerebrosidase levels and decrease lipid storage, although they have yet to properly address the neurological defects associated with impaired glucocerebrosidase. Mouse and induced pluripotent stem cell derived models have improved our understanding of glucocerebrosidase function and the consequences of its deficiency. These models have been used to test novel therapies including chaperone proteins, histone deacetylase inhibitors, and gene therapy approaches that enhance glucocerebrosidase levels and could prove efficacious in the treatment of forms of parkinsonism. Consequently, this rare monogenic disorder, Gaucher disease, provides unique insights directly applicable to our understanding and treatment of Parkinson disease, a common and complex neurodegenerative disorder.

Modeling neuronopathic storage diseases with patient-derived culture systems

Lysosomes are organelles involved in the degradation and recycling of macromolecules, and play a critical role in sensing metabolic information in the cell. A class of rare metabolic diseases called lysosomal storage disorders (LSD) are characterized by lysosomal dysfunction and the accumulation of macromolecular substrates. The central nervous system appears to be particularly vulnerable to lysosomal dysfunction, since many LSDs are characterized by severe, widespread neurodegeneration with pediatric onset. Furthermore, variants in lysosomal genes are strongly associated with some common neurodegenerative disorders such as Parkinson's disease (PD). To better understand disease pathology and develop novel treatment strategies, it is critical to study the fundamental molecular disease mechanisms in the affected cell types that harbor endogenously expressed mutations. The discovery of methods for reprogramming of patient-derived somatic cells into induced pluripotent stem cells (iPSCs), and their differentiation into distinct neuronal and glial cell types, have provided novel opportunities to study mechanisms of lysosomal dysfunction within the relevant, vulnerable cell types. These models also expand our ability to develop and test novel therapeutic targets. We discuss recently developed methods for iPSC differentiation into distinct neuronal and glial cell types, while addressing the need for meticulous experimental techniques and parameters that are essential to accurately identify inherent cellular pathologies. iPSC models for neuronopathic LSDs and their relationship to sporadic age-related neurodegeneration are also discussed. These models should facilitate the discovery and development of personalized therapies in the future.

Targeting kinases in Parkinson's disease: A mechanism shared by LRRK2, neurotrophins, exenatide, urate, nilotinib and lithium

Several kinases have been implicated in the pathogenesis of Parkinson's disease (PD), most notably leucine-rich repeat kinase 2 (LRRK2), as LRRK2 mutations are the most common genetic cause of a late-onset parkinsonism that is clinically indistinguishable from sporadic PD. More recently, several other kinases have emerged as promising disease-modifying targets in PD based on both preclinical studies and clinical reports on exenatide, the urate precursor inosine, nilotinib and lithium use in PD patients. These kinases include protein kinase B (Akt), glycogen synthase kinases-3β and -3α (GSK-3β and GSK-3α), c-Abelson kinase (c-Abl) and cyclin-dependent kinase 5 (cdk5). Activities of each of these kinases are involved either directly or indirectly in phosphorylating tau or increasing α-synuclein levels, intracellular proteins whose toxic oligomeric forms are strongly implicated in the pathogenesis of PD. GSK-3β, GSK-3α and cdk5 are the principle kinases involved in phosphorylating tau at sites critical for the formation of tau oligomers. Exenatide analogues, urate, nilotinib and lithium have been shown to affect one or more of the above kinases, actions that can decrease the formation and increase the clearance of intraneuronal phosphorylated tau and α-synuclein. Here we review the current preclinical and clinical evidence supporting kinase-targeting agents as potential disease-modifying therapies for PD patients enriched with these therapeutic targets and incorporate LRRK2 physiology into this novel model.

The PARK10 gene USP24 is a negative regulator of autophagy and ULK1 protein stability

Recent studies indicate a causative relationship between defects in autophagy and dopaminergic neuron degeneration in Parkinson disease (PD). However, it is not fully understood how autophagy is regulated in the context of PD. Here we identify USP24 (ubiquitin specific peptidase 24), a gene located in the PARK10 (Parkinson disease 10 [susceptibility]) locus associated with late onset PD, as a novel negative regulator of autophagy. Our data indicate that USP24 regulates autophagy by affecting ubiquitination and stability of the ULK1 protein. Knockdown of USP24 in cell lines and in human induced-pluripotent stem cells (iPSC) differentiated into dopaminergic neurons resulted in elevated ULK1 protein levels and increased autophagy flux in a manner independent of MTORC1 but dependent on the class III phosphatidylinositol 3-kinase (PtdIns3K) activity. Surprisingly, USP24 knockdown also improved neurite extension and/or maintenance in aged iPSC-derived dopaminergic neurons. Furthermore, we observed elevated levels of USP24 in the substantia nigra of a subpopulation of idiopathic PD patients, suggesting that USP24 may negatively regulate autophagy in PD.

Abbreviations: Bafilomycin/BafA: bafilomycin A₁; DUB: deubiquitinating enzyme; iPSC: induced pluripotent stem cells; MTOR: mechanistic target of rapamycin kinase; MTORC1: MTOR complex 1; nt: non-targeting; PD: Parkinson disease; p-ATG13: phospho-ATG13; PtdIns3P: phosphatidylinositol 3-phosphate; RPS6: ribosomal protein S6; SNPs: single nucleotide polymorphisms; TH: tyrosine hydroxylase; USP24: ubiquitin specific peptidase 24

Crosstalk of Intercellular Signaling Pathways in the Generation of Midbrain Dopaminergic Neurons In Vivo and from Stem Cells

Dopamine-synthesizing neurons located in the mammalian ventral midbrain are at the center stage of biomedical research due to their involvement in severe human neuropsychiatric and neurodegenerative disorders, most prominently Parkinson’s Disease (PD). The induction of midbrain dopaminergic (mDA) neurons depends on two important signaling centers of the mammalian embryo: the ventral midline or floor plate (FP) of the neural tube, and the isthmic organizer (IsO) at the mid-/hindbrain boundary (MHB). Cells located within and close to the FP secrete sonic hedgehog (SHH), and members of the wingless-type MMTV integration site family (WNT1/5A), as well as bone morphogenetic protein (BMP) family. The IsO cells secrete WNT1 and the fibroblast growth factor 8 (FGF8). Accordingly, the FGF8, SHH, WNT, and BMP signaling pathways play crucial roles during the development of the mDA neurons in the mammalian embryo. Moreover, these morphogens are essential for the generation of stem cell-derived mDA neurons, which are critical for the modeling, drug screening, and cell replacement therapy of PD. This review summarizes our current knowledge about the functions and crosstalk of these signaling pathways in mammalian mDA neuron development in vivo and their applications in stem cell-based paradigms for the efficient derivation of these neurons in vitro.

Gaucher disease iPSC-derived osteoblasts have developmental and lysosomal defects that impair bone matrix deposition

Gaucher disease (GD) is caused by bi-allelic mutations in GBA1, the gene that encodes acid β-glucocerebrosidase (GCase). Individuals affected by GD have hematologic, visceral and bone abnormalities, and in severe cases there is also neurodegeneration. To shed light on the mechanisms by which mutant GBA1 causes bone disease, we examined the ability of human induced pluripotent stem cells (iPSC) derived from patients with Types 1, 2 and 3 GD, to differentiate to osteoblasts and carry out bone deposition. Differentiation of GD iPSC to osteoblasts revealed that these cells had developmental defects and lysosomal abnormalities that interfered with bone matrix deposition. Compared with controls, GD iPSC-derived osteoblasts exhibited reduced expression of osteoblast differentiation markers, and bone matrix protein and mineral deposition were defective. Concomitantly, canonical Wnt/β catenin signaling in the mutant osteoblasts was downregulated, whereas pharmacological Wnt activation with the GSK3β inhibitor CHIR99021 rescued GD osteoblast differentiation and bone matrix deposition. Importantly, incubation with recombinant GCase (rGCase) rescued the differentiation and bone-forming ability of GD osteoblasts, demonstrating that the abnormal GD phenotype was caused by GCase deficiency. GD osteoblasts were also defective in their ability to carry out Ca2+-dependent exocytosis, a lysosomal function that is necessary for bone matrix deposition. We conclude that normal GCase enzymatic activity is required for the differentiation and bone-forming activity of osteoblasts. Furthermore, the rescue of bone matrix deposition by pharmacological activation of Wnt/β catenin in GD osteoblasts uncovers a new therapeutic target for the treatment of bone abnormalities in GD.

Wnt/β-Catenin Signaling Pathway Governs a Full Program for Dopaminergic Neuron Survival, Neurorescue and Regeneration in the MPTP Mouse Model of Parkinson's Disease

Wingless-type mouse mammary tumor virus (MMTV) integration site (Wnt) signaling is one of the most critical pathways in developing and adult tissues. In the brain, Wnt signaling contributes to different neurodevelopmental aspects ranging from differentiation to axonal extension, synapse formation, neurogenesis, and neuroprotection. Canonical Wnt signaling is mediated mainly by the multifunctional β-catenin protein which is a potent co-activator of transcription factors such as lymphoid enhancer factor (LEF) and T-cell factor (TCF). Accumulating evidence points to dysregulation of Wnt/β-catenin signaling in major neurodegenerative disorders. This review highlights a Wnt/β-catenin/glial connection in Parkinson's disease (PD), the most common movement disorder characterized by the selective death of midbrain dopaminergic (mDAergic) neuronal cell bodies in the subtantia nigra pars compacta (SNpc) and gliosis. Major findings of the last decade document that Wnt/β-catenin signaling in partnership with glial cells is critically involved in each step and at every level in the regulation of nigrostriatal DAergic neuronal health, protection, and regeneration in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD, focusing on Wnt/β-catenin signaling to boost a full neurorestorative program in PD.

An integrated biomanufacturing platform for the large-scale expansion and neuronal differentiation of human pluripotent stem cell-derived neural progenitor cells

Human pluripotent stem cell derived neural progenitor cells (hNPCs) have the unique properties of long-term in vitro expansion as well as differentiation into the various neurons and supporting cell types of the central nervous system (CNS). Because of these characteristics, hNPCs have tremendous potential in the modeling and treatment of various CNS diseases and disorders. However, expansion and neuronal differentiation of hNPCs in quantities necessary for these applications is not possible with current two dimensional (2-D) approaches. Here, we used a fully defined peptide substrate as the basis for a microcarrier (MC)-based suspension culture system. Several independently derived hNPC lines were cultured on MCs for multiple passages as well as efficiently differentiated to neurons. Finally, this MC-based system was used in conjunction with a low shear rotating wall vessel (RWV) bioreactor for the integrated, large-scale expansion and neuronal differentiation of hNPCs. Overall, this fully defined and scalable biomanufacturing system will facilitate the generation of hNPCs and their neuronal derivatives in quantities necessary for basic and translational applications.

STATEMENT OF SIGNIFICANCE

In this work, we developed a microcarrier (MC)-based culture system that allows for the expansion and neuronal differentiation of human pluripotent stem cell-derived neural progenitor cells (hNPCs) under defined conditions. In turn, this MC approach was implemented in a rotating wall vessel (RWV) bioreactor for the large-scale expansion and neuronal differentiation of hNPCs. This work is of significance as it overcomes current limitations of conventional two dimensional (2-D) culture systems to enable the generation of hNPCs and their neuronal derivatives in quantities required for downstream applications in disease modeling, drug screening, and regenerative medicine.