Analyses of variant acid beta-glucosidases: effects of Gaucher disease mutations

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.

Variant-specific effects of GBA1 mutations on dopaminergic neuron proteostasis

Glucocerebrosidase 1 (GBA1) mutations are the most important genetic risk factors for Parkinson's disease (PD). Clinically, mild (e.g., p.N370S) and severe (e.g., p.L444P and p.D409H) GBA1 mutations have different PD phenotypes, with differences in age at disease onset, progression, and the severity of motor and non-motor symptoms. We hypothesize that GBA1 mutations cause the accumulation of α-synuclein by affecting the cross-talk between cellular protein degradation mechanisms, leading to neurodegeneration. Accordingly, we tested whether mild and severe GBA1 mutations differentially affect the degradation of α-synuclein via the ubiquitin-proteasome system (UPS), chaperone-mediated autophagy (CMA), and macroautophagy and differentially cause accumulation and/or release of α-synuclein. Our results demonstrate that endoplasmic reticulum (ER) stress and total ubiquitination rates were significantly increased in cells with severe GBA1 mutations. CMA was found to be defective in induced pluripotent stem cell (iPSC)-derived dopaminergic neurons with mild GBA1 mutations, but not in those with severe GBA1 mutations. When examining macroautophagy, we observed reduced formation of autophagosomes in cells with the N370S and D409H GBA1 mutations and impairments in autophagosome-lysosome fusion in cells with the L444P GBA1 mutation. Accordingly, severe GBA1 mutations were found to trigger the accumulation and release of oligomeric α-synuclein in iPSC-derived dopaminergic neurons, primarily as a result of increased ER stress and defective macroautophagy, while mild GBA1 mutations affected CMA, which is mainly responsible for the degradation of the monomeric form of α-synuclein. Overall, our findings provide new insight into the molecular basis of the clinical variability in PD associated with different GBA1 mutations.

The GBA1 K198E Variant Is Associated with Suppression of Glucocerebrosidase Activity, Autophagy Impairment, Oxidative Stress, Mitochondrial Damage, and Apoptosis in Skin Fibroblasts

Parkinson's disease (PD) is a multifactorial, chronic, and progressive neurodegenerative disorder inducing movement alterations as a result of the loss of dopaminergic (DAergic) neurons of the pars compacta in the substantia nigra and protein aggregates of alpha synuclein (α-Syn). Although its etiopathology agent has not yet been clearly established, environmental and genetic factors have been suggested as the major contributors to the disease. Mutations in the glucosidase beta acid 1 (GBA1) gene, which encodes the lysosomal glucosylceramidase (GCase) enzyme, are one of the major genetic risks for PD. We found that the GBA1 K198E fibroblasts but not WT fibroblasts showed reduced catalytic activity of heterozygous mutant GCase by -70% but its expression levels increased by 3.68-fold; increased the acidification of autophagy vacuoles (e.g., autophagosomes, lysosomes, and autolysosomes) by +1600%; augmented the expression of autophagosome protein Beclin-1 (+133%) and LC3-II (+750%), and lysosomal-autophagosome fusion protein LAMP-2 (+107%); increased the accumulation of lysosomes (+400%); decreased the mitochondrial membrane potential (∆Ψm) by -19% but the expression of Parkin protein remained unperturbed; increased the oxidized DJ-1Cys106-SOH by +900%, as evidence of oxidative stress; increased phosphorylated LRRK2 at Ser935 (+1050%) along with phosphorylated α-synuclein (α-Syn) at pathological residue Ser129 (+1200%); increased the executer apoptotic protein caspase 3 (cleaved caspase 3) by +733%. Although exposure of WT fibroblasts to environmental neutoxin rotenone (ROT, 1 μM) exacerbated the autophagy-lysosomal system, oxidative stress, and apoptosis markers, ROT moderately increased those markers in GBA1 K198E fibroblasts. We concluded that the K198E mutation endogenously primes skin fibroblasts toward autophagy dysfunction, OS, and apoptosis. Our findings suggest that the GBA1 K198E fibroblasts are biochemically and molecularly equivalent to the response of WT GBA1 fibroblasts exposed to ROT.

Expanding the Spectrum of GBA1-Associated Neurodegenerative Diseases in an Italian Family

BACKGROUND

Heterozygous mutations in GBA1 gene are known as most common genetic risk factor for Parkinson's disease (PD). However, role of GBA1 mutations in non-α-synuclein disorders is unclear.

CASES

Case index, 76 year-old woman referred to our movement disorders outpatient clinic for 2-year history of gait impairment, falls and motor slowness, with partial response to levodopa. Clinical and instrumental examinations were consistent with Progressive Supranuclear Palsy-Corticobasal Syndrome (PSP-CBS). Case 2 is older sister reporting depressive symptoms; however, she had dementia (MMSE 18/30), gait apraxia and vertical supranuclear gaze palsy (VSNGP). Case 3 is her deceased older sister who had been diagnosed with Corticobasal Syndrome (CBS). Case 4, older brother had been diagnosed with Parkinson's disease-dementia (PDD) with good response to levodopa. Two affected living siblings harboring same genetic variant.

CONCLUSIONS

To our knowledge, this is the first family showing such intrafamilial variability ranging from CBS to PDD to dementia.

Activation and Purification of ß-Glucocerebrosidase by Exploiting its Transporter LIMP-2 - Implications for Novel Treatment Strategies in Gaucher's and Parkinson's Disease

Genetic variants of GBA1 can cause the lysosomal storage disorder Gaucher disease and are among the highest genetic risk factors for Parkinson's disease (PD). GBA1 encodes the lysosomal enzyme beta-glucocerebrosidase (GCase), which orchestrates the degradation of glucosylceramide (GluCer) in the lysosome. Recent studies have shown that GluCer accelerates α-synuclein aggregation, exposing GCase deficiency as a major risk factor in PD pathology and as a promising target for treatment. This study investigates the interaction of GCase and three disease-associated variants (p.E326K, p.N370S, p.L444P) with their transporter, the lysosomal integral membrane protein 2 (LIMP-2). Overexpression of LIMP-2 in HEK 293T cells boosts lysosomal abundance of wt, E326K, and N370S GCase and increases/rescues enzymatic activity of the wt and E326K variant. Using a novel purification approach, co-purification of untagged wt, E326K, and N370S GCase in complex with His-tagged LIMP-2 from cell supernatant of HEK 293F cells is achieved, confirming functional binding and trafficking for these variants. Furthermore, a single helix in the LIMP-2 ectodomain is exploited to design a lysosome-targeted peptide that enhances lysosomal GCase activity in PD patient-derived and control fibroblasts. These findings reveal LIMP-2 as an allosteric activator of GCase, suggesting a possible therapeutic potential of targeting this interaction.

Neuronopathic Gaucher disease: Rare in the West, common in the East

Gaucher disease (GD) stands as one of the most prevalent lysosomal disorders, yet neuronopathic GD (nGD) is an uncommon subset characterized by a wide array of clinical manifestations that complicate diagnosis, particularly when neurological symptoms are understated. nGD may manifest as the acute neuronopathic type, or GD type 2 (GD2), either prenatally or within the first weeks to months of life, whereas GD type 3 (GD3) symptoms may emerge at any point during childhood or occasionally in adolescence. The clinical presentation encompasses severe systemic involvement to mild visceral disease, often coupled with a spectrum of progressive neurological signs and symptoms such as cognitive impairment, ataxia, seizures, myoclonus, varying degrees of brainstem dysfunction presenting with stridor, apneic episodes, and/or impaired swallowing. This manuscript aims to provide a comprehensive review of the incidence, distinctive presentations, and diverse clinical phenotypes of nGD across various countries and regions. It will explore the natural history of the neurodegenerative process in GD, shedding light on its various manifestations during infancy and childhood, and offer insights into the diagnostic journey, the challenges faced in the clinical management, and current and investigative therapeutic approaches for GD's neurological variants.

Mutations in Glycosyltransferases and Glycosidases: Implications for Associated Diseases

Glycosylation, a crucial and the most common post-translational modification, coordinates a multitude of biological functions through the attachment of glycans to proteins and lipids. This process, predominantly governed by glycosyltransferases (GTs) and glycoside hydrolases (GHs), decides not only biomolecular functionality but also protein stability and solubility. Mutations in these enzymes have been implicated in a spectrum of diseases, prompting critical research into the structural and functional consequences of such genetic variations. This study compiles an extensive dataset from ClinVar and UniProt, providing a nuanced analysis of 2603 variants within 343 GT and GH genes. We conduct thorough MTR score analyses for the proteins with the most documented variants using MTR3D-AF2 via AlphaFold2 (AlphaFold v2.2.4) predicted protein structure, with the analyses indicating that pathogenic mutations frequently correlate with Beta Bridge secondary structures. Further, the calculation of the solvent accessibility score and variant visualisation show that pathogenic mutations exhibit reduced solvent accessibility, suggesting the mutated residues are likely buried and their localisation is within protein cores. We also find that pathogenic variants are often found proximal to active and binding sites, which may interfere with substrate interactions. We also incorporate computational predictions to assess the impact of these mutations on protein function, utilising tools such as mCSM to predict the destabilisation effect of variants. By identifying these critical regions that are prone to disease-associated mutations, our study opens avenues for designing small molecules or biologics that can modulate enzyme function or compensate for the loss of stability due to these mutations.

Inhibition of cysteine protease cathepsin L increases the level and activity of lysosomal glucocerebrosidase

The glucocerebrosidase (GCase) encoded by the GBA1 gene hydrolyzes glucosylceramide (GluCer) to ceramide and glucose in lysosomes. Homozygous or compound heterozygous GBA1 mutations cause the lysosomal storage disease Gaucher disease (GD) due to severe loss of GCase activity. Loss-of-function variants in the GBA1 gene are also the most common genetic risk factor for Parkinson's disease (PD) and dementia with Lewy bodies (DLB). Restoring lysosomal GCase activity represents an important therapeutic approach for GBA1-associated diseases. We hypothesized that increasing the stability of lysosomal GCase protein could correct deficient GCase activity in these conditions. However, it remains unknown how GCase stability is regulated in the lysosome. We found that cathepsin L, a lysosomal cysteine protease, cleaves GCase and regulates its stability. In support of these data, GCase protein was elevated in the brain of cathepsin L-KO mice. Chemical inhibition of cathepsin L increased both GCase levels and activity in fibroblasts from patients with GD. Importantly, inhibition of cathepsin L in dopaminergic neurons from a patient GBA1-PD led to increased GCase levels and activity as well as reduced phosphorylated α-synuclein. These results suggest that targeting cathepsin L-mediated GCase degradation represents a potential therapeutic strategy for GCase deficiency in PD and related disorders that exhibit decreased GCase activity.

iPSC-derived neural precursor cells engineering GBA1 recovers acid β-glucosidase deficiency and diminishes α-synuclein and neuropathology

Mutations in GBA1, encoding the lysosomal acid β-glucosidase (GCase), cause neuronopathic Gaucher disease (nGD) and promote Parkinson disease (PD). The mutations on GBA1 include deletion and missense mutations that are pathological and lead to GCase deficiency in Gaucher disease. Both nGD and PD lack disease-modifying treatments and are critical unmet medical needs. In this study, we evaluated a cell therapy treatment using mouse iPSC-derived neural precursor cells (NPCs) engineered to overexpress GCase (termed hGBA1-NPCs). The hGBA1-NPCs secreted GCase that was taken up by adjacent mouse Gba -/- neurons and improved GCase activity, reduced GCase substrate accumulation, and improved mitochondrial function. Short-term in vivo effects were evaluated in 9H/PS-NA mice, an nGD mouse model exhibiting neuropathology and α-synuclein aggregation, the typical PD phenotypes. Intravenously administrated hGBA1-NPCs were engrafted throughout the brain and differentiated into neural lineages. GCase activity was increased in various brain regions of treated 9H/PS-NA mice. Compared with vehicle, hGBA1-NPC-transplanted mice showed ∼50% reduction of α-synuclein aggregates in the substantia nigra, significant reduction of neuroinflammation and neurodegeneration in the regions of NPC migration, and increased expression of neurotrophic factors that support neural cell function. Together, these results support the therapeutic benefit of intravenous delivery of iPSC-derived NPCs overexpressing GCase in mitigating nGD and PD phenotypes and establish the feasibility of combined cell and gene therapy for GBA1-associated PD.

Targeting the GBA1 pathway to slow Parkinson disease: Insights into clinical aspects, pathogenic mechanisms and new therapeutic avenues

The GBA1 gene encodes the lysosomal enzyme glucocerebrosidase (GCase), which is involved in sphingolipid metabolism. Biallelic variants in GBA1 cause Gaucher disease (GD), a lysosomal storage disorder characterised by loss of GCase activity and aberrant intracellular accumulation of GCase substrates. Carriers of GBA1 variants have an increased risk of developing Parkinson disease (PD), with odds ratio ranging from 2.2 to 30 according to variant severity. GBA1 variants which do not cause GD in homozygosis can also increase PD risk. Patients with PD carrying GBA1 variants show a more rapidly progressive phenotype compared to non-carriers, emphasising the need for disease modifying treatments targeting the GBA1 pathway. Several mechanisms secondary to GCase dysfunction are potentially responsible for the pathological changes leading to PD. Misfolded GCase proteins induce endoplasmic reticulum stress and subsequent unfolded protein response and impair the autophagy-lysosomal pathway. This results in α-synuclein accumulation and spread, and promotes neurodegenerative changes. Preclinical evidence also shows that products of GCase activity can promote accumulation of α-synuclein, however there is no convincing evidence of substrate accumulation in GBA1-PD brains. Altered lipid homeostasis secondary to loss of GCase activity could also contribute to PD pathology. Treatments that target the GBA1 pathway could reverse these pathological processes and halt/slow the progression of PD. These range from augmentation of GCase activity via GBA1 gene therapy, restoration of normal intracellular GCase trafficking via molecular chaperones, and substrate reduction therapy. This review discusses the pathways associated with GBA1-PD and related novel GBA1-targeted interventions for PD treatment.

The molecular mechanism of Gaucher disease caused by compound heterozygous mutations in GBA1 gene

Gaucher disease (GD, ORPHA355) is a rare autosomal recessive genetic disease caused by mutations in GBA1, which encodes the lysosomal enzyme glucocerebrosidase (GCase). Here, we report a patient with GD who carried the heterozygous c.1240G > C (p.Val414Leu) mutation and the heterozygous pathogenic c.1342G > C (p.Asp448His) mutation in GBA1. Bioinformatics analysis suggested that the two mutations are pathogenic. Functional studies showed that GBA1 mRNA and GCase protein levels of mutant types were significantly less than the wild-type. In the cell lysates, the two mutations of GBA1 c.1240G > C and c.1342G > C caused a decreased GCase concentration, while the two mutations did not change the distribution in the cell. The pathogenicity of the compound heterozygous mutations was verified. Early diagnosis and treatment can improve the quality of life and prevent unnecessary procedures in patients with GD.

Compound heterozygous p.L483P and p.S310G mutations in GBA1 cause type 1 adult Gaucher disease: A case report

BACKGROUND

Gaucher disease (GD) is caused by a GBA1 gene mutation that leads to decreased acid β-glucosidase activity [glucocerebrosidase (GCase)]. This study aimed to identify and characterise compound heterozygous mutations in GBA1 in a patient with type 1 GD.

CASE SUMMARY

Here, we report a rare adult-onset type 1 GD in a 46-year-old female patient with clinical manifestations of giant spleen, thrombocytopenia, and bone pain, diagnosed by enzymatic and genetic testing. Enzymology and whole exome sequencing revealed heterozygous missense mutations in exon 10 c.1448T>C (p.L483P) and exon 7 c.928A>G (p.S310G) of GBA1. The latter was first reported in patients with GD. Structural modelling showed that p.S310G and p.L483P were distant from the GCase active site. The p.S310G mutation in domain 1 may decrease stability between the α2 and α3 helices of GBA1. The p.L483P mutation in domain 2 reduced the van der Waals force of the side chain and disrupted the C-terminal β-sheet. The patient was treated with imiglucerase replacement therapy, and her condition was stable.

CONCLUSION

The p.L483P/p.S310G novel compound heterozygous mutation underlies type 1 GD and likely affects GCase protein function. This is the first description of p.S310G being associated with mild type 1 GD in the context of a coinherited p.L483P mutation.

Gaucher disease in North Macedonia: Unexpected prevalence of the N370S GBA1 allele with attenuated disease expression

The majority of Gaucher Disease (GD) cases result from pathologic mutations in the GBA1 gene. A rich mutational spectrum of about 500 identified variants has been recognized. The disease is characterized by phenotypic diversity. Data regarding the genotype-phenotype correlation are scanty and inconclusive. Here, we summarize the genetic and phenotypic “portraits” of 14 patients with GD type 1 in the Republic of North Macedonia, 4 of Macedonian and 10 of Albanian origin. Altogether, 6 variants were detected, compounding 6 different genotypes. All genotypes contained the N370S variant, which was detected with an overall prevalence of 60.7%. Other frequent variants included the 1263del55 deletion and the double mutant allele D409H;H255Q, each with a prevalence of 14.2%. We detected two rare mutations: W92* - a pathogenic nonsense mutation and D399N – a single nucleotide variant of uncertain pathogenicity. The most common genotypes were N370S/1263del55 and H255Q;D409H/N370S, both present in 4/14 patients, followed by N370S homozygosity (3/14). Splenomegaly was the most common clinical manifestation, identified in all patients. Hepatomegaly was less frequent and was present in 50% of cases. Thrombocytopenia was present in 9/14, while half of the patients had anemia. Bone pathology was demonstrated in 8 patients. Patients with different genotypes displayed a high degree of phenotypic heterogeneity, suggesting that the other allele determines the onset and severity of the disease in patients with the N370S mutation. Longer follow-up, bigger cohorts of patients and multicentric studies should be conducted to further define the association between the genotypic and phenotypic expression in GD.

Genetic variations in GBA1 and LRRK2 genes: Biochemical and clinical consequences in Parkinson disease

Variants in the GBA1 and LRRK2 genes are the most common genetic risk factors associated with Parkinson disease (PD). Both genes are associated with lysosomal and autophagic pathways, with the GBA1 gene encoding for the lysosomal enzyme, glucocerebrosidase (GCase) and the LRRK2 gene encoding for the leucine-rich repeat kinase 2 enzyme. GBA1-associated PD is characterized by earlier age at onset and more severe non-motor symptoms compared to sporadic PD. Mutations in the GBA1 gene can be stratified into severe, mild and risk variants depending on the clinical presentation of disease. Both a loss- and gain- of function hypothesis has been proposed for GBA1 variants and the functional consequences associated with each variant is often linked to mutation severity. On the other hand, LRRK2-associated PD is similar to sporadic PD, but with a more benign disease course. Mutations in the LRRK2 gene occur in several structural domains and affect phosphorylation of GTPases. Biochemical studies suggest a possible convergence of GBA1 and LRRK2 pathways, with double mutant carriers showing a milder phenotype compared to GBA1-associated PD. This review compares GBA1 and LRRK2-associated PD, and highlights possible genotype-phenotype associations for GBA1 and LRRK2 separately, based on biochemical consequences of single variants.

GBA Variants and Parkinson Disease: Mechanisms and Treatments

The GBA gene encodes for the lysosomal enzyme glucocerebrosidase (GCase), which maintains glycosphingolipid homeostasis. Approximately 5–15% of PD patients have mutations in the GBA gene, making it numerically the most important genetic risk factor for Parkinson disease (PD). Clinically, GBA-associated PD is identical to sporadic PD, aside from the earlier age at onset (AAO), more frequent cognitive impairment and more rapid progression. Mutations in GBA can be associated with loss- and gain-of-function mechanisms. A key hallmark of PD is the presence of intraneuronal proteinaceous inclusions named Lewy bodies, which are made up primarily of alpha-synuclein. Mutations in the GBA gene may lead to loss of GCase activity and lysosomal dysfunction, which may impair alpha-synuclein metabolism. Models of GCase deficiency demonstrate dysfunction of the autophagic-lysosomal pathway and subsequent accumulation of alpha-synuclein. This dysfunction can also lead to aberrant lipid metabolism, including the accumulation of glycosphingolipids, glucosylceramide and glucosylsphingosine. Certain mutations cause GCase to be misfolded and retained in the endoplasmic reticulum (ER), activating stress responses including the unfolded protein response (UPR), which may contribute to neurodegeneration. In addition to these mechanisms, a GCase deficiency has also been associated with mitochondrial dysfunction and neuroinflammation, which have been implicated in the pathogenesis of PD. This review discusses the pathways associated with GBA-PD and highlights potential treatments which may act to target GCase and prevent neurodegeneration.

Dynamic coupling of residues within proteins as a mechanistic foundation of many enigmatic pathogenic missense variants

Many pathogenic missense mutations are found in protein positions that are neither well-conserved nor fall in any known functional domains. Consequently, we lack any mechanistic underpinning of dysfunction caused by such mutations. We explored the disruption of allosteric dynamic coupling between these positions and the known functional sites as a possible mechanism for pathogenesis. In this study, we present an analysis of 591 pathogenic missense variants in 144 human enzymes that suggests that allosteric dynamic coupling of mutated positions with known active sites is a plausible biophysical mechanism and evidence of their functional importance. We illustrate this mechanism in a case study of β-Glucocerebrosidase (GCase) in which a vast majority of 94 sites harboring Gaucher disease-associated missense variants are located some distance away from the active site. An analysis of the conformational dynamics of GCase suggests that mutations on these distal sites cause changes in the flexibility of active site residues despite their distance, indicating a dynamic communication network throughout the protein. The disruption of the long-distance dynamic coupling caused by missense mutations may provide a plausible general mechanistic explanation for biological dysfunction and disease.

Glucocerebrosidase Gene Therapy Induces Alpha-Synuclein Clearance and Neuroprotection of Midbrain Dopaminergic Neurons in Mice and Macaques

Mutations in the GBA1 gene coding for glucocerebrosidase (GCase) are the main genetic risk factor for Parkinson’s disease (PD). Indeed, identifying reduced GCase activity as a common feature underlying the typical neuropathological signatures of PD—even when considering idiopathic forms of PD—has recently paved the way for designing novel strategies focused on enhancing GCase activity to reduce alpha-synuclein burden and preventing dopaminergic cell death. Here we have performed bilateral injections of a viral vector coding for the mutated form of alpha-synuclein (rAAV9-SynA53T) for disease modeling purposes, both in mice as well as in nonhuman primates (NHPs), further inducing a progressive neuronal death in the substantia nigra pars compacta (SNpc). Next, another vector coding for the GBA1 gene (rAAV9-GBA1) was unilaterally delivered in the SNpc of mice and NHPs one month after the initial insult, together with the contralateral delivery of an empty/null rAAV9 for control purposes. Obtained results showed that GCase enhancement reduced alpha-synuclein burden, leading to improved survival of dopaminergic neurons. Data reported here support using GCase gene therapy as a disease-modifying treatment for PD and related synucleinopathies, including idiopathic forms of these disorders.

Glucocerebrosidase Gene Therapy Induces Alpha-Synuclein Clearance and Neuroprotection of Midbrain Dopaminergic Neurons in Mice and Macaques

Mutations in the GBA1 gene coding for glucocerebrosidase (GCase) are the main genetic risk factor for Parkinson's disease (PD). Indeed, identifying reduced GCase activity as a common feature underlying the typical neuropathological signatures of PD-even when considering idiopathic forms of PD-has recently paved the way for designing novel strategies focused on enhancing GCase activity to reduce alpha-synuclein burden and preventing dopaminergic cell death. Here we have performed bilateral injections of a viral vector coding for the mutated form of alpha-synuclein (rAAV9-SynA53T) for disease modeling purposes, both in mice as well as in nonhuman primates (NHPs), further inducing a progressive neuronal death in the substantia nigra pars compacta (SNpc). Next, another vector coding for the GBA1 gene (rAAV9-GBA1) was unilaterally delivered in the SNpc of mice and NHPs one month after the initial insult, together with the contralateral delivery of an empty/null rAAV9 for control purposes. Obtained results showed that GCase enhancement reduced alpha-synuclein burden, leading to improved survival of dopaminergic neurons. Data reported here support using GCase gene therapy as a disease-modifying treatment for PD and related synucleinopathies, including idiopathic forms of these disorders.

Glucocerebrosidase Gene Therapy Induces Alpha-Synuclein Clearance and Neuroprotection of Midbrain Dopaminergic Neurons in Mice and Macaques

Mutations in the GBA1 gene coding for glucocerebrosidase (GCase) are the main genetic risk factor for Parkinson’s disease (PD). Indeed, identifying reduced GCase activity as a common feature underlying the typical neuropathological signatures of PD—even when considering idiopathic forms of PD—has recently paved the way for designing novel strategies focused on enhancing GCase activity to reduce alpha-synuclein burden and preventing dopaminergic cell death. Here we have performed bilateral injections of a viral vector coding for the mutated form of alpha-synuclein (rAAV9-SynA53T) for disease modeling purposes, both in mice as well as in nonhuman primates (NHPs), further inducing a progressive neuronal death in the substantia nigra pars compacta (SNpc). Next, another vector coding for the GBA1 gene (rAAV9-GBA1) was unilaterally delivered in the SNpc of mice and NHPs one month after the initial insult, together with the contralateral delivery of an empty/null rAAV9 for control purposes. Obtained results showed that GCase enhancement reduced alpha-synuclein burden, leading to improved survival of dopaminergic neurons. Data reported here support using GCase gene therapy as a disease-modifying treatment for PD and related synucleinopathies, including idiopathic forms of these disorders.

Ambroxol increases glucocerebrosidase (GCase) activity and restores GCase translocation in primary patient-derived macrophages in Gaucher disease and Parkinsonism

Mutations in the glucocerebrosidase gene (GBA) encoding the lysosomal enzyme glucocerebrosidase (GCase) cause Gaucher disease (GD) and are the most commonly known genetic risk factor for Parkinson disease (PD). Ambroxol is one of the most effective pharmacological chaperones of GCase. Fourteen GD patients, six PD patients with mutations in the GBA gene (GBA-PD), and thirty controls were enrolled. GCase activity and hexosylsphingosine (HexSph) concentration were measured in dried blood and macrophage spots using liquid chromatography coupled with tandem mass spectrometry. The effect of ambroxol on GCase translocation to lysosomes was assessed using confocal microscopy. The results showed that ambroxol treatment significantly increased GCase activity in cultured macrophages derived from patient blood monocytic cell (PBMC) of GD (by 3.3-fold) and GBA-PD patients (by 3.5-fold) compared to untreated cells (p < 0.0001 and p < 0.0001, respectively) four days after cultivation. Ambroxol treatment significantly reduced HexSph concentration in GD (by 2.1-fold) and GBA-PD patients (by 1.6-fold) (p < 0.0001 and p < 0.0001, respectively). GD macrophage treatment resulted in increased GCase level and increased enzyme colocalization with the lysosomal marker LAMP2. The possible binding modes of ambroxol to mutant GCase carrying N370S amino acid substitution at pH 4.7 were examined using molecular docking and molecular dynamics simulations. The ambroxol position characterized by minimal binding free energy was observed in close vicinity to the residue, at position 370. Taken together, these data showed that PBMC-derived macrophages could be used for assessing ambroxol therapy response for GD patients and also for GBA-PD patients.

The interplay between Glucocerebrosidase, α-synuclein and lipids in human models of Parkinson's disease

Mutations in the gene GBA, encoding glucocerebrosidase (GCase), are the highest genetic risk factor for Parkinson's disease (PD). GCase is a lysosomal glycoprotein responsible for the hydrolysis of glucosylceramide into glucose and ceramide. Mutations in GBA cause a decrease in GCase activity, stability and protein levels which in turn lead to the accumulation of GCase lipid substrates as well as α-synuclein (αS) in vitro and in vivo. αS is the main constituent of Lewy bodies found in the brain of PD patients and an increase in its levels was found to be associated with a decrease in GCase activity/protein levels in vitro and in vivo. In this review, we describe the reported biophysical and biochemical changes that GBA mutations can induce in GCase activity and stability as well as the current overview of the levels of GCase protein/activity, αS and lipids measured in patient-derived samples including post-mortem brains, stem cell-derived neurons, cerebrospinal fluid, blood and fibroblasts as well as in SH-SY5Y cells. In particular, we report how the levels of αS and lipids are affected by/correlated to significant changes in GCase activity/protein levels and which cellular pathways are activated or disrupted by these changes in each model. Finally, we review the current strategies used to revert the changes in the levels of GCase activity/protein, αS and lipids in the context of PD.

Clinical phenotype features and genetic etiologies of 38 children with progressive myoclonic epilepsy

Background

Progressive myoclonic epilepsy (PME) is a group of neurodegenerative diseases with genetic heterogeneity and phenotypic similarities, and many cases remain unknown of the genetic causes. This study is aim to summarize the clinical features and study the genetic causes of PME patients.

Methods

Sanger sequencing of the target gene, Next Generation Sequencing (NGS) panels of epilepsy, trio-based Whole Exome Sequencing (WES) and detection of cytosine-adenine-guanine (CAG) repeat number were used to investigate the genetic causes of PME patients.

Results

Thirty-eight children with PME whose seizure onset age ranged from 3 months to 12 years were collected from February 2012 to November 2019 in three hospitals in Beijing, China. The seizure types included myoclonic seizures (n = 38), focal seizures (n = 19), generalized tonic-clonie seizure (GTCS) (n = 13), absence seizures (n = 4), atonic seizures (n = 3), epileptic spasms (n = 2) and tonic seizures (n = 1). Twenty-seven cases were sporadic and 11 had family members affected. Established PME-related genes were identified in 30 out of 38 (78.9%) patients who had either recessively inherited or de novo heterozygous mutations. Among these 30 cases, there were 12 cases (31.6%) of neuronal ceroid lipofuscinoses (the causing gene contains TPP1, PPT1, CLN5, CLN6 and MFSD8), two cases of sialidosis (the causing gene is NEU1), two cases of neuronopathic Gaucher disease (the causing gene is GBA), one case of spinal muscular atrophy-progressive myoclonic epilepsy (the causing gene is ASAH1), four cases of KCNC1 mutation-related PME, four cases of KCTD7 mutation-related PME, two cases of TBC1D24 mutation-related PME, one case of GOSR2 related PME, and two of dentatorubral-pallidoluysian atrophy (the causing gene is ATN1). In total, 13 PME genes were identified in our cohort. The etiology was not clear in eight patients.

Conclusion

PME is a group of clinically and genetically heterogeneous diseases. Genetic diagnosis was clear in 78.9% of PME patients. Various of genetic testing methods could increase the rate of genetic diagnosis. Neuronal ceroid lipofuscinoses (NCL) is the most common etiology of PME in children. Nearly one third PME children were diagnosed with NCL. GOSR2 related PME was in our cohort in Asia for the first time.

A baculoviral system for the production of human β-glucocerebrosidase enables atomic resolution analysis

The lysosomal glycoside hydrolase β-glucocerebrosidase (GBA; sometimes called GBA1 or GCase) catalyses the hydrolysis of glycosphingolipids. Inherited deficiencies in GBA cause the lysosomal storage disorder Gaucher disease (GD). Consequently, GBA is of considerable medical interest, with continuous advances in the development of inhibitors, chaperones and activity-based probes. The development of new GBA inhibitors requires a source of active protein; however, the majority of structural and mechanistic studies of GBA today rely on clinical enzyme-replacement therapy (ERT) formulations, which are incredibly costly and are often difficult to obtain in adequate supply. Here, the production of active crystallizable GBA in insect cells using a baculovirus expression system is reported, providing a nonclinical source of recombinant GBA with comparable activity and biophysical properties to ERT preparations. Furthermore, a novel crystal form of GBA is described which diffracts to give a 0.98 Å resolution unliganded structure. A structure in complex with the inactivator 2,4-dinitrophenyl-2-deoxy-2-fluoro-β-D-glucopyranoside was also obtained, demonstrating the ability of this GBA formulation to be used in ligand-binding studies. In light of its purity, stability and activity, the GBA production protocol described here should circumvent the need for ERT formulations for structural and biochemical studies and serve to support GD research.

Systemic enzyme delivery by blood-brain barrier-penetrating SapC-DOPS nanovesicles for treatment of neuronopathic Gaucher disease

Background

Enzyme replacement therapy (ERT) can positively affect the visceral manifestations of lysosomal storage diseases (LSDs). However, the exclusion of the intravenous ERT agents from the central nervous system (CNS) prevents direct therapeutic effects.

Methods

Using a neuronopathic Gaucher disease (nGD) mouse model, CNS-ERT was created using a systemic, non-invasive, and CNS-selective delivery system based on nanovesicles of saposin C (SapC) and dioleoylphosphatidylserine (DOPS) to deliver to CNS cells and tissues the corrective, functional acid β-glucosidase (GCase).

Findings

Compared to free GCase, human GCase formulated with SapC-DOPS nanovesicles (SapC-DOPS-GCase) was more stable in serum, taken up into cells, mostly by a mannose receptor-independent pathway, and resulted in higher activity in GCase-deficient cells. In contrast to free GCase, SapC-DOPS-GCase nanovesicles penetrated through the blood-brain barrier into the CNS. The CNS targeting was mediated by surface phosphatidylserine (PS) of blood vessel and brain cells. Increased GCase activity and reduced GCase substrate levels were found in the CNS of SapC-DOPS-GCase-treated nGD mice, which showed profound improvement in brain inflammation and neurological phenotypes.

Interpretation

This first-in-class CNS-ERT approach provides considerable promise of therapeutic benefits for neurodegenerative diseases.

Funding

This study was supported by the National Institutes of Health grants R21NS 095047 to XQ and YS, R01NS 086134 and UH2NS092981 in part to YS; Cincinnati Children's Hospital Medical Center Research Innovation/Pilot award to YS and XQ; Gardner Neuroscience Institute/Neurobiology Research Center Pilot award to XQ and YS, Hematology-Oncology Programmatic Support from University of Cincinnati and New Drug State Key Project grant 009ZX09102-205 to XQ.

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.

Decreased Penetrance of Parkinson's Disease in Elderly Carriers of Glucocerebrosidase Gene L444P/R Mutations: A Community-Based 10-Year Longitudinal Study

BACKGROUND

Heterozygous mutations in the glucocerebrosidase gene (GBA) have been shown to be an important genetic risk factor for Parkinson's disease (PD) worldwide. However, the penetrance of GBA heterozygote for L444P, the common mutation for Asian population, is not known in older Chinese people.

OBJECTIVES

To assess the conversion rate to PD in identified carriers of GBA L444P/R mutations in Chinese community-dwelling older adults.

METHODS

The GBA gene was sequenced for mutations at position 444 in 8405 people older than 55 years who participated in the Beijing Longitudinal Study on Aging II cohort. Nine subjects were identified as heterozygous carriers of GBA L444P or L444R mutations at baseline and clinically followed up from 2009 to 2019 to investigate their PD conversion, motor and nonmotor symptoms, and change of vesicular monoamine transporter type 2 using tracer of [¹⁸ F]9-fluoropropyl-(+)-dihydrotetrabenazine (¹⁸ F-DTBZ, also known as ¹⁸ F-AV-133).

RESULTS

Eight heterozygous GBA L444P and 1 L444R mutation carriers were identified without PD at baseline, and none of them developed clinical parkinsonism after a 10-year follow-up.

CONCLUSIONS

Although GBA mutations may lead to an earlier onset PD, the majority of GBA L444P heterozygotes in older adults may not convert to PD. Further studies are warranted to identify factors that modify the risk of conversion. © 2020 International Parkinson and Movement Disorder Society.

Rare GBA1 genotype associated with severe bone disease in Gaucher disease type 1

Introduction

Gaucher disease (GD) type 1 is a lysosomal disease characterised by hepatosplenomegaly, anemia, thrombocytopenia, bone changes, and bone marrow infiltration. The disease is caused by biallelic pathogenic variants in GBA1 which codes for glucocerebrosidase, an enzyme involved in the catabolic pathway of complex lipids.

Aims

To report on the case of two sisters with GD type 1 who bear a genotype never reported in the literature.

Case report

Patient 1 is a 47-year-old female diagnosed at 42 years of age with chronic lumbar pain, mild splenomegaly, slightly reduced platelets and normal hemoglobin values, severe Bone Marrow Burden (BMB) score, high chitotriosidase activity, and low glucocerebrosidase. Patient 2 is a 50-year-old female, sister of patient 1, who was diagnosed after familial screening. At 45 years of age, she had osteonecrosis of the left femur and a total hysterectomy because of uncontrollable bleeding. At first evaluation, she had bone pain with a high BMB score, mild splenomegaly, normal hemoglobin, normal platelets count, elevated chitotriosidase activity, and low glucocerebrosidase activity. Both patients were found to be compound heterozygotes for the p.Glu388Lys and the p.Ser405Asn variants in GBA1.

Conclusions

This is the first family with GD and this combination of variants which causes a phenotype remarkable for severe bone disease with no or mild hematological manifestations.

Intravenous infusion of iPSC-derived neural precursor cells increases acid β-glucosidase function in the brain and lessens the neuronopathic phenotype in a mouse model of Gaucher disease

Gaucher disease (GD) is caused by GBA1 mutations leading to functional deficiency of acid-β-glucosidase (GCase). No effective treatment is available for neuronopathic GD (nGD). A subclass of neural stem and precursor cells (NPCs) expresses VLA4 (integrin α4β1, very late antigen-4) that facilitates NPC entry into the brain following intravenous (IV) infusion. Here, the therapeutic potential of IV VLA4+NPCs was assessed for nGD using wild-type mouse green fluorescent protein (GFP)-positive multipotent induced pluripotent stem cell (iPSC)-derived VLA4+NPCs. VLA4+NPCs successfully engrafted in the nGD (4L;C*) mouse brain. GFP-positive cells differentiated into neurons, astrocytes and oligodendrocytes in the brainstem, midbrain and thalamus of the transplanted mice and significantly improved sensorimotor function and prolonged life span compared to vehicle-treated 4L;C* mice. VLA4+NPC transplantation significantly decreased levels of CD68 and glial fibrillary acidic protein, as well as TNFα mRNA levels in the brain, indicating reduced neuroinflammation. Furthermore, decreased Fluoro-Jade C and NeuroSilver staining suggested inhibition of neurodegeneration. VLA4+NPC-engrafted 4L;C* midbrains showed 35% increased GCase activity, reduced substrate [glucosylceramide (GC, -34%) and glucosylsphingosine (GS, -11%)] levels and improved mitochondrial oxygen consumption rates in comparison to vehicle-4L;C* mice. VLA4+NPC engraftment in 4L;C* brain also led to enhanced expression of neurotrophic factors that have roles in neuronal survival and the promotion of neurogenesis. This study provides evidence that iPSC-derived NPC transplantation has efficacy in an nGD mouse model and provides proof of concept for autologous NPC therapy in nGD.

Combination of acid β-glucosidase mutation and Saposin C deficiency in mice reveals Gba1 mutation dependent and tissue-specific disease phenotype

Gaucher disease is caused by mutations in GBA1 encoding acid β-glucosidase (GCase). Saposin C enhances GCase activity and protects GCase from intracellular proteolysis. Structure simulations indicated that the mutant GCases, N370S (0 S), V394L (4L) and D409V(9V)/H(9H), had altered function. To investigate the in vivo function of Gba1 mutants, mouse models were generated by backcrossing the above homozygous mutant GCase mice into Saposin C deficient (C*) mice. Without saposin C, the mutant GCase activities in the resultant mouse tissues were reduced by ~50% compared with those in the presence of Saposin C. In contrast to 9H and 4L mice that have normal histology and life span, the 9H;C* and 4L;C* mice had shorter life spans. 9H;C* mice developed significant visceral glucosylceramide (GC) and glucosylsphingosine (GS) accumulation (GC»GS) and storage macrophages, but lesser GC in the brain, compared to 4L;C* mice that presents with a severe neuronopathic phenotype and accumulated GC and GS primarily in the brain. Unlike 9V mice that developed normally for over a year, 9V;C* pups had a lethal skin defect as did 0S;C* mice resembled that of 0S mice. These variant Gaucher disease mouse models presented a mutation specific phenotype and underscored the in vivo role of Saposin C in the modulation of Gaucher disease.

Distinguishing the differences in β-glycosylceramidase folds, dynamics, and actions informs therapeutic uses

Glycosyl hydrolases (GHs) are carbohydrate-active enzymes that hydrolyze a specific β-glycosidic bond in glycoconjugate substrates; β-glucosidases degrade glucosylceramide, a ubiquitous glycosphingolipid. GHs are grouped into structurally similar families that themselves can be grouped into clans. GH1, GH5, and GH30 glycosidases belong to clan A hydrolases with a catalytic (β/α)8 TIM barrel domain, whereas GH116 belongs to clan O with a catalytic (α/α)6 domain. In humans, GH abnormalities underlie metabolic diseases. The lysosomal enzyme glucocerebrosidase (family GH30), deficient in Gaucher disease and implicated in Parkinson disease etiology, and the cytosol-facing membrane-bound glucosylceramidase (family GH116) remove the terminal glucose from the ceramide lipid moiety. Here, we compare enzyme differences in fold, action, dynamics, and catalytic domain stabilization by binding site occupancy. We also explore other glycosidases with reported glycosylceramidase activity, including human cytosolic β-glucosidase, intestinal lactase-phlorizin hydrolase, and lysosomal galactosylceramidase. Last, we describe the successful translation of research to practice: recombinant glycosidases and glucosylceramide metabolism modulators are approved drug products (enzyme replacement therapies). Activity-based probes now facilitate the diagnosis of enzyme deficiency and screening for compounds that interact with the catalytic pocket of glycosidases. Future research may deepen the understanding of the functional variety of these enzymes and their therapeutic potential.

In Silico Analysis of Missense Mutations as a First Step in Functional Studies: Examples from Two Sphingolipidoses

In order to delineate a better approach to functional studies, we have selected 23 missense mutations distributed in different domains of two lysosomal enzymes, to be studied by in silico analysis. In silico analysis of mutations relies on computational modeling to predict their effects. Various computational platforms are currently available to check the probable causality of mutations encountered in patients at the protein and at the RNA levels. In this work we used four different platforms freely available online (Protein Variation Effect Analyzer- PROVEAN, PolyPhen-2, Swiss-model Expert Protein Analysis System—ExPASy, and SNAP2) to check amino acid substitutions and their effect at the protein level. The existence of functional studies, regarding the amino acid substitutions, led to the selection of the distinct protein mutants. Functional data were used to compare the results obtained with different bioinformatics tools. With the advent of next-generation sequencing, it is not feasible to carry out functional tests in all the variants detected. In silico analysis seems to be useful for the delineation of which mutants are worth studying through functional studies. Therefore, prediction of the mutation impact at the protein level, applying computational analysis, confers the means to rapidly provide a prognosis value to genotyping results, making it potentially valuable for patient care as well as research purposes. The present work points to the need to carry out functional studies in mutations that might look neutral. Moreover, it should be noted that single nucleotide polymorphisms (SNPs), occurring in coding and non-coding regions, may lead to RNA alterations and should be systematically verified. Functional studies can gain from a preliminary multi-step approach, such as the one proposed here.

Design of a New α-1-C-Alkyl-DAB Derivative Acting as a Pharmacological Chaperone for β-Glucocerebrosidase Using Ligand Docking and Molecular Dynamics Simulation

Some point mutations in β-glucocerebrosidase cause either improper folding or instability of this protein, resulting in Gaucher disease. Pharmacological chaperones bind to the mutant enzyme and stabilize this enzyme; thus, pharmacological chaperone therapy was proposed as a potential treatment for Gaucher disease. The binding affinities of α-1-C-alkyl 1,4-dideoxy-1,4-imino-d-arabinitol (DAB) derivatives, which act as pharmacological chaperones for β-glucocerebrosidase, abruptly increased upon elongation of their alkyl chain. In this study, the primary causes of such an increase in binding affinity were analyzed using protein–ligand docking and molecular dynamics simulations. We found that the activity cliff between α-1-C-heptyl-DAB and α-1-C-octyl-DAB was due to the shape and size of the hydrophobic binding site accommodating the alkyl chains, and that the interaction with this hydrophobic site controlled the binding affinity of the ligands well. Furthermore, based on the aromatic/hydrophobic properties of the binding site, a 7-(tetralin-2-yl)-heptyl-DAB compound was designed and synthesized. This compound had significantly enhanced activity. The design strategy in consideration of aromatic interactions in the hydrophobic pocket was useful for generating effective pharmacological chaperones for the treatment of Gaucher disease.

GBA-Associated Parkinson's Disease and Other Synucleinopathies

PURPOSE OF REVIEW

GBA mutations are the most common known genetic cause of Parkinson's disease (PD). Its biological pathway may be important in idiopathic PD, since activity of the enzyme encoded by GBA, glucocerebrosidase, is reduced even among PD patients without GBA mutations. This article describes the structure and function of GBA, reviews recent literature on the clinical phenotype of GBA PD, and suggests future directions for research, counseling, and treatment.

RECENT FINDINGS

Several longitudinal studies have shown that GBA PD has faster motor and cognitive progression than idiopathic PD and that this effect is dose dependent. New evidence suggests that GBA mutations may be important in multiple system atrophy. Further, new interventional studies focusing on GBA PD are described. These studies may increase the interest of PD patients and caregivers in genetic counseling. GBA mutation status may help clinicians estimate PD progression, though mechanisms underlying GBA and synucleinopathy require further understanding.

Chitinase-3-like Protein 1: A Progranulin Downstream Molecule and Potential Biomarker for Gaucher Disease

We recently reported that progranulin (PGRN) is a novel regulator of glucocerebrosidase and its deficiency associates with Gaucher Diseases (GD) (Jian et al., 2016a; Jian et al., 2018). To isolate the relevant downstream molecules, we performed a whole genome microarray and mass spectrometry analysis, which led to the isolation of Chitinase-3-like-1 (CHI3L1) as one of the up-regulated genes in PGRN null mice. Elevated levels of CHI3L1 were confirmed by immunoblotting and immunohistochemistry. In contrast, treatment with recombinant Pcgin, a derivative of PGRN, as well as imigluerase, significantly reduced the expressions of CHI3L1 in both PGRN null GD model and the fibroblasts from GD patients. Serum levels of CHIT1, a clinical biomarker for GD, were significantly higher in GD patients than healthy controls (51.16±2.824ng/ml vs 35.07±2.099ng/ml, p<0.001). Similar to CHIT1, serum CHI3L1 was also significantly increased in GD patients compared with healthy controls (1736±152.1pg/ml vs 684.7±68.20pg/ml, p<0.001). Whereas the PGRN level is significantly reduced in GD patients as compared to the healthy control (91.56±3.986ng/ml vs 150.6±4.501, p<0.001). Collectively, these results indicate that CHI3L1 may be a previously unrecognized biomarker for diagnosing GD and for evaluating the therapeutic effects of new GD drug(s).

Insights into the structural biology of Gaucher disease

Gaucher disease, the most common lysosomal storage disorder, is caused by mutations in the gene encoding the acid-β-glucosidase lysosomal hydrolase enzyme that cleaves glucocerebroside into glucose and ceramide. Reduced enzyme activity and impaired structural stability arise due to >300 known disease-causing mutations. Several of these mutations have also been associated with an increased risk of Parkinson disease (PD). Since the discovery of the acid-β-glucosidase X-ray structure, there have been major advances in our understanding of the structural properties of the protein. Analysis of specific residues has provided insight into their functional and structural importance and provided insight into the pathogenesis of Gaucher disease and the contribution to PD. Disease-causing mutations are positioned throughout the acid-β-glucosidase structure, with many located far from the active site and thus retaining some enzymatic activity however, thus far no clear relationship between mutation location and disease severity has been established. Here, we review the crystal structure of acid-β-glucosidase, while highlighting important structural aspects of the protein in detail. This review discusses the structural stability of acid-β-glucosidase, which can be altered by pH and glycosylation, and explores the relationship between known Gaucher disease and PD mutations, structural stability and disease severity.

Modulating ryanodine receptors with dantrolene attenuates neuronopathic phenotype in Gaucher disease mice

Neuronopathic Gaucher disease (nGD) manifests as severe neurological symptoms in patients with no effective treatment available. Ryanodine receptors (Ryrs) are a family of calcium release channels on intracellular stores. The goal of this study is to determine if Ryrs are potential targets for nGD treatment. A nGD cell model (CBE-N2a) was created by inhibiting acid β-glucosidase (GCase) in N2a cells with conduritol B epoxide (CBE). Enhanced cytosolic calcium in CBE-N2a cells was blocked by either ryanodine or dantrolene, antagonists of Ryrs and by Genz-161, a glucosylceramide synthase inhibitor, suggesting substrate-mediated ER-calcium efflux occurs through ryanodine receptors. In the brain of a nGD (4L;C*) mouse model, expression of Ryrs was normal at 13 days of age, but significantly decreased below the wild type level in end-stage 4L;C* brains at 40 days. Treatment with dantrolene in 4L;C* mice starting at postnatal day 5 delayed neurological pathology and prolonged survival. Compared to untreated 4L;C* mice, dantrolene treatment significantly improved gait, reduced LC3-II levels, improved mitochondrial ATP production and reduced inflammation in the brain. Dantrolene treatment partially normalized Ryr expression and its potential regulators, CAMK IV and calmodulin. Furthermore, dantrolene treatment increased residual mutant GCase activity in 4L;C* brains. These data demonstrate that modulating Ryrs has neuroprotective effects in nGD through mechanisms that protect the mitochondria, autophagy, Ryr expression and enhance GCase activity. This study suggests that calcium signalling stabilization, e.g. with dantrolene, could be a potential disease modifying therapy for nGD.

Stabilization of Glucocerebrosidase by Active Site Occupancy

Glucocerebrosidase (GBA) is a lysosomal β-glucosidase that degrades glucosylceramide. Its deficiency results in Gaucher disease (GD). We examined the effects of active site occupancy of GBA on its structural stability. For this, we made use of cyclophellitol-derived activity-based probes (ABPs) that bind irreversibly to the catalytic nucleophile (E340), and for comparison, we used the potent reversible inhibitor isofagomine. We demonstrate that cyclophellitol ABPs improve the stability of GBA in vitro, as revealed by thermodynamic measurements (T_m increase by 21 °C), and introduce resistance to tryptic digestion. The stabilizing effect of cell-permeable cyclophellitol ABPs is also observed in intact cultured cells containing wild-type GBA, N370S GBA (labile in lysosomes), and L444P GBA (exhibits impaired ER folding): all show marked increases in lysosomal forms of GBA molecules upon exposure to ABPs. The same stabilization effect is observed for endogenous GBA in the liver of wild-type mice injected with cyclophellitol ABPs. Stabilization effects similar to those observed with ABPs were also noted at high concentrations of the reversible inhibitor isofagomine. In conclusion, we provide evidence that the increase in cellular levels of GBA by ABPs and by the reversible inhibitor is in part caused by their ability to stabilize GBA folding, which increases the resistance of GBA against breakdown by lysosomal proteases. These effects are more pronounced in the case of the amphiphilic ABPs, presumably due to their high lipophilic potential, which may promote further structural compactness of GBA through hydrophobic interactions. Our study provides further rationale for the design of chaperones for GBA to ameliorate Gaucher disease.

Fluorinated Chaperone-β-Cyclodextrin Formulations for β-Glucocerebrosidase Activity Enhancement in Neuronopathic Gaucher Disease

Amphiphilic glycomimetics encompassing a rigid, undistortable nortropane skeleton based on 1,6-anhydro-l-idonojirimycin and a polyfluorinated antenna, when formulated as the corresponding inclusion complexes with β-cyclodextrin (βCD), have been shown to behave as pharmacological chaperones (PCs) that efficiently rescue lysosomal β-glucocerebrosidase mutants associated with the neuronopathic variants of Gaucher disease (GD), including the highly refractory L444P/L444P and L444P/P415R single nucleotide polymorphs, in patient fibroblasts. The body of work here presented includes the design criteria for the PC prototype, the synthesis of a series of candidates, the characterization of the PC:βCD complexes, the determination of the selectivity profiles toward a panel of commercial and human lysosomal glycosidases, the evaluation of the chaperoning activity in type 1 (non-neuronopathic), type 2 (acute neuronopathic), and type 3 (adult neuronopathic) GD fibroblasts, the confirmation of the rescuing mechanism by immunolabeling, and the analysis of the PC:GCase binding mode by docking experiments.

The metabolism of glucocerebrosides - From 1965 to the present

Gaucher disease is caused by the defective catabolism of the simple glycosphingolipid, glucosylceramide (GlcCer), due to mutations in the GBA1 gene which encodes for acid β-glucosidase (GCase), the lysosomal enzyme that degrades GlcCer. Today, Gaucher disease patients are routinely treated with recombinant GCase, in a treatment regimen known as enzyme replacement therapy (ERT). We now review the biochemical basis of ERT and discuss how this treatment has advanced since it was first pioneered by Dr. Roscoe Brady in the 1960s. We will place particular emphasis on the three dimensional structure of GCase, and subsequently discuss a relatively new treatment paradigm, substrate reduction therapy (SRT), in which GlcCer synthesis is partially inhibited, thus reducing its accumulation. Both of these approaches are based on studies and concepts developed by Dr. Brady over his remarkable research career spanning six decades.

Association Between Progranulin and Gaucher Disease

BACKGROUND

Gaucher disease (GD) is a genetic disease caused by mutations in the GBA1 gene which result in reduced enzymatic activity of β-glucocerebrosidase (GCase). This study identified the progranulin (PGRN) gene (GRN) as another gene associated with GD.

METHODS

Serum levels of PGRN were measured from 115 GD patients and 99 healthy controls, whole GRN gene from 40 GD patients was sequenced, and the genotyping of 4 SNPs identified in GD patients was performed in 161 GD and 142 healthy control samples. Development of GD in PGRN-deficient mice was characterized, and the therapeutic effect of rPGRN on GD analyzed.

FINDINGS

Serum PGRN levels were significantly lower in GD patients (96.65±53.45ng/ml) than those in healthy controls of the general population (164.99±43.16ng/ml, p<0.0001) and of Ashkenazi Jews (150.64±33.99ng/ml, p<0.0001). Four GRN gene SNPs, including rs4792937, rs78403836, rs850713, and rs5848, and three point mutations, were identified in a full-length GRN gene sequencing in 40 GD patients. Large scale SNP genotyping in 161 GD and 142 healthy controls was conducted and the four SNP sites have significantly higher frequency in GD patients. In addition, "aged" and challenged adult PGRN null mice develop GD-like phenotypes, including typical Gaucher-like cells in lung, spleen, and bone marrow. Moreover, lysosomes in PGRN KO mice exhibit a tubular-like appearance. PGRN is required for the lysosomal appearance of GCase and its deficiency leads to GCase accumulation in the cytoplasm. More importantly, recombinant PGRN is therapeutic in various animal models of GD and human fibroblasts from GD patients.

INTERPRETATION

Our data demonstrates an unknown association between PGRN and GD and identifies PGRN as an essential factor for GCase's lysosomal localization. These findings not only provide new insight into the pathogenesis of GD, but may also have implications for diagnosis and alternative targeted therapies for GD.

A Novel Functional Missense Mutation p.T219A in Type 1 Gaucher's Disease

Background:

Gaucher's disease (GD) is an autosomal recessive disorder caused by a deficiency of acid β-glucosidase (glucocerebrosidase [GBA]) that results in the accumulation of glucocerebroside within macrophages. Many mutations have been reported to be associated with this disorder. This study aimed to discover more mutations and provide data for the genetic pattern of the gene, which will help the development of quick and accurate genetic diagnostic tools for this disease.

Methods:

Genomic DNA was obtained from peripheral blood leukocytes of the patient and Sanger sequencing is used to sequence GBA gene. Sequence alignments of mammalian β-GBA (GCase) and three-dimensional protein structure prediction of the mutation were made. A construct of this mutant and its compound heterozygous counterpart were used to measure GCase in vitro.

Results:

GCase is relatively conserved at p.T219A. This novel mutation differs from its wild-type in structure. Moreover, it also causes a reduction in GCase enzyme activity.

Conclusion:

This novel mutation (c.655A>G, p.T219A) is a pathogenic missense mutation, which contributes to GD.

Characterization of the complex formed by β-glucocerebrosidase and the lysosomal integral membrane protein type-2

The lysosomal integral membrane protein type-2 (LIMP-2) plays a pivotal role in the delivery of β-glucocerebrosidase (GC) to lysosomes. Mutations in GC result in Gaucher's disease (GD) and are the major genetic risk factor for the development of Parkinson's disease (PD). Variants in the LIMP-2 gene cause action myoclonus-renal failure syndrome and also have been linked to PD. Given the importance of GC and LIMP-2 in disease pathogenesis, we studied their interaction sites in more detail. Our previous data demonstrated that the crystal structure of LIMP-2 displays a hydrophobic three-helix bundle composed of helices 4, 5, and 7, of which helix 5 and 7 are important for ligand binding. Here, we identified a similar helical motif in GC through surface potential analysis. Coimmunoprecipitation and immunofluorescence studies revealed a triple-helical interface region within GC as critical for LIMP-2 binding and lysosomal transport. Based on these findings, we generated a LIMP-2 helix 5-derived peptide that precipitated and activated recombinant wild-type and GD-associated N370S mutant GC in vitro. The helix 5 peptide fused to a cell-penetrating peptide also activated endogenous lysosomal GC and reduced α-synuclein levels, suggesting that LIMP-2-derived peptides can be used to activate endogenous as well as recombinant wild-type or mutant GC efficiently. Our data also provide a structural model of the LIMP-2/GC complex that will facilitate the development of GC chaperones and activators as potential therapeutics for GD, PD, and related synucleinopathies.