The link between the GBA gene and parkinsonism

Parkinson's Clustering in Families of Non-Neuronopathic N370S GBA Mutation Carriers Indicates the Presence of Genetic Modifiers

Low penetrance of Parkinson's disease (PD) associated with GBA pathogenic variants indicates the presence of modifiers genes. Clusters of PD cases in certain families with GBA variants would serve as a strong evidence for the clinical relevance of such modifiers. We studied eight family trees of non-Parkinsonian, GBA-N370S homozygote, Gaucher probands, with multiple cases of PD. Differences in PD risk associated with different GBA variants were balanced by variant homozygosity. In these families, all PD cases stemmed from only one of the proband's parents. This observation provides a direct epidemiological evidence for genetic modifiers determining PD risk in GBA variant carriers.

Complement cascade functions during brain development and neurodegeneration

The complement system, an essential tightly regulated innate immune system, is a key regulator of normal central nervous system (CNS) development and function. However, aberrant complement component expression and activation in the brain may culminate into marked neuroinflammatory response, neurodegenerative processes and cognitive impairment. Over the years, complement-mediated neuroinflammatory responses and complement-driven neurodegeneration have been increasingly implicated in the pathogenesis of a wide spectrum of CNS disorders. This review describes how complement system contributes to normal brain development and function. We also discuss how pathologic insults such as misfolded proteins, lipid droplet/lipid droplet-associated protein or glycosaminoglycan accumulation could trigger complement-mediated neuroinflammatory responses and neurodegenerative process in neurodegenerative proteinopathies, age-related macular degeneration and neurodegenerative lysosomal storage disorders.

Therapeutic Potential of αS Evolvability for Neuropathic Gaucher Disease

Gaucher disease (GD), the most common lysosomal storage disorder (LSD), is caused by autosomal recessive mutations of the glucocerebrosidase gene, GBA1. In the majority of cases, GD has a non-neuropathic chronic form with adult onset (GD1), while other cases are more acute and severer neuropathic forms with early onset (GD2/3). Currently, no radical therapies are established for GD2/3. Notably, GD1, but not GD2/3, is associated with increased risk of Parkinson's disease (PD), the elucidation of which might provide a clue for novel therapeutic strategies. In this context, the objective of the present study is to discuss that the evolvability of α-synuclein (αS) might be differentially involved in GD subtypes. Hypothetically, aging-associated PD features with accumulation of αS, and the autophagy-lysosomal dysfunction might be an antagonistic pleiotropy phenomenon derived from αS evolvability in the development in GD1, without which neuropathies like GD2/3 might be manifested due to the autophagy-lysosomal dysfunction. Supposing that the increased severity of GD2/3 might be attributed to the decreased activity of αS evolvability, suppressing the expression of β-synuclein (βS), a potential buffer against αS evolvability, might be therapeutically efficient. Of interest, a similar view might be applicable to Niemann-Pick type C (NPC), another LSD, given that the adult type of NPC, which is comorbid with Alzheimer's disease, exhibits milder medical symptoms compared with those of infantile NPC. Thus, it is predicted that the evolvability of amyloid β and tau, might be beneficial for the adult type of NPC. Collectively, a better understanding of amyloidogenic evolvability in the pathogenesis of LSD may inform rational therapy development.

Advances of Mechanisms-Related Metabolomics in Parkinson's Disease

Parkinson's disease (PD) is a multifactorial disorder characterized by progressively debilitating dopaminergic neurodegeneration in the substantia nigra and the striatum, along with various metabolic dysfunctions and molecular abnormalities. Metabolomics is an emerging study and has been demonstrated to play important roles in describing complex human diseases by integrating endogenous and exogenous sources of alterations. Recently, an increasing amount of research has shown that metabolomics profiling holds great promise in providing unique insights into molecular pathogenesis and could be helpful in identifying candidate biomarkers for clinical detection and therapies of PD. In this review, we briefly summarize recent findings and analyze the application of molecular metabolomics in familial and sporadic PD from genetic mutations, mitochondrial dysfunction, and dysbacteriosis. We also review metabolic biomarkers to assess the functional stage and improve therapeutic strategies to postpone or hinder the disease progression.

Cross-talks among GBA mutations, glucocerebrosidase, and α-synuclein in GBA-associated Parkinson's disease and their targeted therapeutic approaches: a comprehensive review

Current therapies for Parkinson's disease (PD) are palliative, of which the levodopa/carbidopa therapy remains the primary choice but is unable to modulate the progression of neurodegeneration. Due to the complication of such a multifactorial disorder and significant limitations of the therapy, numerous genetic approaches have been proved effective in finding out genes and mechanisms implicated in this disease. Following the observation of a higher frequency of PD in Gaucher's disease (GD), a lysosomal storage condition, mutations of glycosylceramidase beta (GBA) encoding glucocerebrosidase (GCase) have been shown to be involved and have been explored in the context of PD. GBA mutations are the most common genetic risk factor of PD. Various studies have revealed the relationships between PD and GBA gene mutations, facilitating a better understanding of this disorder. Various hypotheses delineate that the pathological mutations of GBA minimize the enzymatic activity of GCase, which affects the proliferation and clearance of α-synuclein; this affects the lysosomal homeostasis, exacerbating the endoplasmic reticulum stress or encouraging the mitochondrial dysfunction. Identification of the pathological mechanisms underlying the GBA-associated parkinsonism (GBA + PD) advances our understanding of PD. This review based on current literature aims to elucidate various genetic and clinical characteristics correlated with GBA mutations and to identify the numerous pathological processes underlying GBA + PD. We also delineate the therapeutic strategies to interfere with the mutant GCase function for further improvement of the related α-synuclein-GCase crosstalks. Moreover, the various therapeutic approaches such as gene therapy, chaperone proteins, and histone deacetylase inhibitors for the treatment of GBA + PD are discussed.

Cross-talks among GBA mutations, glucocerebrosidase, and α-synuclein in GBA-associated Parkinson’s disease and their targeted therapeutic approaches: a comprehensive review

Current therapies for Parkinson’s disease (PD) are palliative, of which the levodopa/carbidopa therapy remains the primary choice but is unable to modulate the progression of neurodegeneration. Due to the complication of such a multifactorial disorder and significant limitations of the therapy, numerous genetic approaches have been proved effective in finding out genes and mechanisms implicated in this disease. Following the observation of a higher frequency of PD in Gaucher’s disease (GD), a lysosomal storage condition, mutations of glycosylceramidase beta (GBA) encoding glucocerebrosidase (GCase) have been shown to be involved and have been explored in the context of PD. GBA mutations are the most common genetic risk factor of PD. Various studies have revealed the relationships between PD and GBA gene mutations, facilitating a better understanding of this disorder. Various hypotheses delineate that the pathological mutations of GBA minimize the enzymatic activity of GCase, which affects the proliferation and clearance of α-synuclein; this affects the lysosomal homeostasis, exacerbating the endoplasmic reticulum stress or encouraging the mitochondrial dysfunction. Identification of the pathological mechanisms underlying the GBA-associated parkinsonism (GBA + PD) advances our understanding of PD. This review based on current literature aims to elucidate various genetic and clinical characteristics correlated with GBA mutations and to identify the numerous pathological processes underlying GBA + PD. We also delineate the therapeutic strategies to interfere with the mutant GCase function for further improvement of the related α-synuclein–GCase crosstalks. Moreover, the various therapeutic approaches such as gene therapy, chaperone proteins, and histone deacetylase inhibitors for the treatment of GBA + PD are discussed.

Glycosphingolipids

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

Research on developing drugs for Parkinson's disease

Current treatments for Parkinson's disease (PD) are mainly dopaminergic drugs. However, dopaminergic drugs are only symptomatic treatments and limited by several side effects. Recent studies into drug development focused on emerging new molecular mechanisms, including nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, nuclear receptor-related 1 (Nurr1), adenosine receptor A2, nicotine receptor, metabotropic glutamate receptors (mGluRs), and glucocerebrosidase (GCase). Also, immunotherapy and common pathological mechanisms shared with Alzheimer's Disease (AD) and diabetes have attracted much attention. In this review, we summarized the development of preclinical and clinical studies of novel drugs and the improvement of dopaminergic drugs to provide a prospect for PD treatment.

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.

Impulse control behavior in GBA-mutated parkinsonian patients

OBJECTIVE

To assess the prevalence and phenomenology of Impulse control behavior (ICB) in Parkinson's disease (PD) patients carrying mutations in the β-glucocerebrosidase (GBA) gene.

BACKGROUND

GBA mutations are a common genetic factor predisposing to PD. ICB is among the most disabling non-motor complications of PD. The occurrence of ICB in PD patients carrying GBA gene mutations (GBA-PD) has not been yet established.

METHODS

Forty-six patients with clinically definite PD (23 GBA-PD and 23 non-mutated patients, NM-PD) were screened for ICB. Diagnosis was clinically and rating based on a specific questionnaire (QUIP-RS). Other demographic and clinical variables did not differ between groups.

RESULTS

ICB occurred more frequently in GBA-PD patients (52.2%) compared to NM-PD (13%) and the total QUIP-RS score was higher in the GBA-PD group. Hypersexuality and compulsive shopping were the most prevalent ICB types occurring in GBA patients. ICB occurred only in one GBA-PD patient on levodopa monotherapy and in 11 patients taking dopamine agonists, either monotherapy or combined with levodopa (the corresponding figures in NM-PD patients were 0 and 3). Most GBA-PD patients were heterozygous for two common genetic variants, without appreciable difference in their ICB profile.

CONCLUSION

ICB is more common in GBA-PD patients compared to NM-PD. Dopamine agonist therapy may be synergic to GBA carrier status for ICB occurrence.

Association of GBA Genotype With Motor and Functional Decline in Patients With Newly Diagnosed Parkinson Disease

Objective

To establish the significance of glucocerebrosidase gene (GBA) carrier status on motor impairment in a large cohort of patients with incident Parkinson disease (PD).

Methods

Three European population-based studies followed 528 patients with PD from diagnosis. A total of 440 with genomic DNA from baseline were assessed for GBA variants. We evaluated motor and functional impairment annually using the Unified Parkinson’s Disease Rating Scale (UPDRS) motor and activities of daily living (ADL) sections. Differential effects of classes of GBA variants on disease progression were evaluated using mixed random and fixed effects models.

Results

A total of 387 patients with idiopathic disease (age at baseline 70.3 ± 9.5 years; 60.2% male) and 53 GBA carriers (age at baseline 66.8 ± 10.1 years; 64.2% male) were included. The motor profile of the groups was clinically indistinguishable at diagnosis. GBA carriers showed faster annual increase in UPDRS scores measuring ADL (1.5 point per year, 95% confidence interval [CI] 1.1–2.0) and motor symptoms (2.2 points per year, 95% CI 1.3–3.1) compared to noncarriers (ADL, 1.0 point per year, 95% CI 0.9–1.1, p = 0.003; motor, 1.3 point per year, 95% CI 1.1–1.6, p = 0.007). Simulations of clinical trial designs showed that recruiting only GBA carriers can reduce trial size by up to 65% compared to a trial recruiting all patients with PD.

Conclusion

GBA variants are linked to a more aggressive motor disease course over 7 years from diagnosis in patients with PD. A better understanding of PD progression in genetic subpopulations may improve disease management and has direct implications for improving the design of clinical trials.

Gut-Brain axis in Parkinson's disease etiology: The role of lipopolysaccharide

Recent studies highlight the initiation of Parkinson's disease (PD) in the gastrointestinal tract, decades before the manifestations in the central nervous system (CNS). This gut-brain axis of neurodegenerative diseases defines the critical role played by the unique microbial composition of the "second brain" formed by the enteric nervous system (ENS). Compromise in the enteric wall can result in the translocation of gut-microbiota along with their metabolites into the system that can affect the homeostatic machinery. The released metabolites can associate with protein substrates affecting several biological pathways. Among these, the bacterial endotoxin from Gram-negative bacteria, i.e., Lipopolysaccharide (LPS), has been implicated to play a definite role in progressive neurodegeneration. The molecular interaction of the lipid metabolites can have a direct neuro-modulatory effect on homeostatic protein components that can be transported to the CNS via the vagus nerve. α-synuclein (α-syn) is one such partner protein, the molecular interactions with which modulate its overall fibrillation propensity in the system. LPS interaction has been shown to affect the protein's aggregation kinetics in an alternative inflammatory pathway of PD pathogenesis. Several other lipid contents from the bacterial membranes could also be responsible for the initiation of α-syn amyloidogenesis. The present review will focus on the intermolecular interactions of α-syn with bacterial lipid components, particularly LPS, with a definite clinical manifestation in PD pathogenesis. However, deconvolution of the sequence of interaction events from the ENS to its propagation in the CNS is not easy or obvious. Nevertheless, the characterization of these lipid-mediated structures is a step towards realizing the novel targets in the pre-emptive diagnoses of PD. This comprehensive description should prompt the correlation of potential risk of amyloidogenesis upon detection of specific paradigm shifts in the microbial composition of the gut.

From beta amyloid to altered proteostasis in Alzheimer's disease

Alzheimer's disease (AD) is an age related neurodegenerative disorder causing severe disability and important socio-economic burden, but with no cure available to date. To disentangle this puzzling disease genetic studies represented an important way for the comprehension of pathogenic mechanisms. Abnormal processing and accumulation of amyloid-β peptide (Aβ) has been considered the main cause and trigger factor of the disease. The amyloid cascade theory has fallen into crisis because the failure of several anti-amyloid drugs trials and because of the simple equation AD = abnormal Aβ deposition is not always the case. We now know that multiple neurodegenerative diseases share common pathogenic mechanisms leading to accumulation of misfolded protein species. Genome Wide Association studies (GWAS) led to the identification of large numbers of DNA common variants (SNPs) distributed on different chromosomes and modulating the Alzheimer's risk. GWAS genes fall into several common pathways such as immune system and neuroinflammation, lipid metabolism, synaptic dysfunction and endocytosis, all of them addressing to novel routes for different pathogenic mechanisms. Other hints could be derived from epidemiological and experimental studies showing some lifestyles may have a major role in the pathogenesis of many age-associated diseases by modifying cell metabolism, proteostasis and microglia mediated neuroinflammation.

When Friendship Turns Sour: Effective Communication Between Mitochondria and Intracellular Organelles in Parkinson's Disease

Parkinson's disease (PD) is a complex neurodegenerative disease with pathological hallmarks including progressive neuronal loss from the substantia nigra pars compacta and α-synuclein intraneuronal inclusions, known as Lewy bodies. Although the etiology of PD remains elusive, mitochondrial damage has been established to take center stage in the pathogenesis of PD. Mitochondria are critical to cellular energy production, metabolism, homeostasis, and stress responses; the association with PD emphasizes the importance of maintenance of mitochondrial network integrity. To accomplish the pleiotropic functions, mitochondria are dynamic not only within their own network but also in orchestrated coordination with other organelles in the cellular community. Through physical contact sites, signal transduction, and vesicle transport, mitochondria and intracellular organelles achieve the goals of calcium homeostasis, redox homeostasis, protein homeostasis, autophagy, and apoptosis. Herein, we review the finely tuned interactions between mitochondria and surrounding intracellular organelles, with focus on the nucleus, endoplasmic reticulum, Golgi apparatus, peroxisomes, and lysosomes. Participants that may contribute to the pathogenic mechanisms of PD will be highlighted in this review.

Genetic parkinsonisms and cancer: a systematic review and meta-analysis

Genes associated with parkinsonism may also be implicated in carcinogenesis, but their interplay remains unclear. We systematically reviewed studies (PubMed 1967-2019) reporting gene variants associated with both parkinsonism and cancer. Somatic variants were examined in cancer samples, whereas germline variants were examined in cancer patients with both symptomatic and asymptomatic (carriers) genetic parkinsonisms. Pooled proportions were calculated with random-effects meta-analyses. Out of 9,967 eligible articles, 60 were included. Of the 28 genetic variants associated with parkinsonism, six were also associated with cancer. In cancer samples, SNCA was predominantly associated with gastrointestinal cancers, UCHL1 with breast cancer, and PRKN with head-and-neck cancers. In asymptomatic carriers, LRRK2 was predominantly associated with gastrointestinal and prostate cancers, PRKN with prostate and genitourinary tract cancers, GBA with sarcoma, and 22q11.2 deletion with leukemia. In symptomatic genetic parkinsonism, LRRK2 was associated with nonmelanoma skin cancers and breast cancers, and PRKN with head-and-neck cancers. Cancer was more often manifested in genetic parkinsonisms compared to asymptomatic carriers. These results suggest that intraindividual genetic contributions may modify the co-occurrence of cancer and neurodegeneration.

Sphingolipids metabolism alteration in the central nervous system: Amyotrophic lateral sclerosis (ALS) and other neurodegenerative diseases

Sphingolipids are complex lipids. They play a structural role in neurons, but are also involved in regulating cellular communication, and neuronal differentiation and maturation. There is increasing evidence to suggest that dysregulated metabolism of sphingolipids is linked to neurodegenerative processes in amyotrophic lateral sclerosis (ALS), Parkinson's disease and Gaucher's disease. In this review, we provide an overview of the role of sphingolipids in the development and maintenance of the nervous system. We describe the implications of altered metabolism of sphingolipids in the pathophysiology of certain neurodegenerative diseases, with a primary focus on ALS. Finally, we provide an update of potential treatments that could be used to target the metabolism of sphingolipids in neurodegenerative diseases.

Loss-of-Function NUBPL Mutation May Link Parkinson's Disease to Recessive Complex I Deficiency

In an unbiased genome-wide screen for copy number variants (CNVs) on a cohort of Parkinson's disease (PD) patients, we identified in one patient a complex chromosomal rearrangement involving the nucleotide binding protein-like (NUBPL) gene on chromosome 14q12. We noted that mutations in the NUBPL gene had been reported as causing autosomal recessive (AR) mitochondrial Complex I (CI) deficiency in children. The precise breakpoints of the rearrangement in our PD case were found to be identical to those described in a patient with AR CI deficiency who also harbored a second pathogenic mutation in NUBPL. Mitochondrial dysfunction has long been considered a strong contributor to PD, and there is substantial evidence that decreased CI activity plays a central role in PD pathogenesis. We hypothesize that pathogenic NUBPL variants may increase the risk for PD analogous to variants in the glucosylceramidase beta (GBA) gene that increase the risk of developing PD in heterozygous carriers.

Toxic Metamorphosis-How Changes from Lysosomal to Cytosolic pH Modify the Alpha-Synuclein Aggregation Pattern

Alpha-synuclein (aSyn) is a cytosolic, aggregation-prone protein that is associated with neurodegenerative disorders like Parkinson's disease. Interestingly, the protein can appear in different conformations, including monomeric and oligomeric forms as well as amyloid fibrils. Its individual structural constituents seem to be dependent on various factors and the composition of the respective cellular surroundings. Although under physiological conditions, most aSyn is found in the cytosol and synapses of neurons, aSyn can also be found in lysosomal compartments, where it gets degraded. We here compare the assembly speed, morphology, folding state, and spreading of aSyn at cytosolic pH (pH 7.4) and lysosomal pH (pH 5) using Thioflavin T, transmission electron microscopy, circular dichroism, and Fourier transform infrared spectroscopy. Interestingly, we found substantial differences between aSyn aggregation under neutral and acidic pH conditions, like those present in cytosolic and lysosomal cellular compartments. Also, lysosomal aSyn enriched from an aSyn-overexpressing cell line was able to seed aggregation in a concentration-dependent manner. Moreover, we observed that aSyn aggregates formed under in vitro lysosomal pH (pH 5) conditions were not stable at neutral pH and collapsed into partly soluble aggregates with changed structural characteristics. Our findings have meaningful implications in intracellular toxicity events as well as in lysis procedures for molecular and structural characterization of intracellular aSyn conformers.

Lyso-glycosphingolipids: presence and consequences

Lyso-glycosphingolipids are generated in excess in glycosphingolipid storage disorders. In the course of these pathologies glycosylated sphingolipid species accumulate within lysosomes due to flaws in the respective lipid degrading machinery. Deacylation of accumulating glycosphingolipids drives the formation of lyso-glycosphingolipids. In lysosomal storage diseases such as Gaucher Disease, Fabry Disease, Krabbe disease, GM1 -and GM2 gangliosidosis, Niemann Pick type C and Metachromatic leukodystrophy massive intra-lysosomal glycosphingolipid accumulation occurs. The lysosomal enzyme acid ceramidase generates the deacylated lyso-glycosphingolipid species. This review discusses how the various lyso-glycosphingolipids are synthesized, how they may contribute to abnormal immunity in glycosphingolipid storing lysosomal diseases and what therapeutic opportunities exist.

Metabolic alterations in Parkinson's disease astrocytes

In Parkinson`s disease (PD), the loss of dopaminergic (DA) neurons in the substantia nigra pars compacta is associated with Lewy bodies arising from the accumulation of alpha-synuclein protein which leads ultimately to movement impairment. While PD has been considered a disease of the DA neurons, a glial contribution, in particular that of astrocytes, in PD pathogenesis is starting to be uncovered. Here, we report findings from astrocytes derived from induced pluripotent stem cells of LRRK2 G2019S mutant patients, with one patient also carrying a GBA N370S mutation, as well as healthy individuals. The PD patient astrocytes manifest the hallmarks of the disease pathology including increased expression of alpha-synuclein. This has detrimental consequences, resulting in altered metabolism, disturbed Ca2+ homeostasis and increased release of cytokines upon inflammatory stimulation. Furthermore, PD astroglial cells manifest increased levels of polyamines and polyamine precursors while lysophosphatidylethanolamine levels are decreased, both of these changes have been reported also in PD brain. Collectively, these data reveal an important role for astrocytes in PD pathology and highlight the potential of iPSC-derived cells in disease modeling and drug discovery.

Enhancing the Activity of Glucocerebrosidase as a Treatment for Parkinson Disease

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

GBA Variants in Parkinson's Disease: Clinical, Metabolomic, and Multimodal Neuroimaging Phenotypes

BACKGROUND

Alterations in the GBA gene (NM_000157.3) are the most important genetic risk factor for Parkinson's disease (PD). Biallelic GBA mutations cause the lysosomal storage disorder Gaucher's disease. The GBA variants p.E365K and p.T408M are associated with PD but not with Gaucher's disease. The pathophysiological role of these variants needs to be further explored.

OBJECTIVE

This study analyzed clinical, neuropsychological, metabolic, and neuroimaging phenotypes of patients with PD carrying the GBA variants p.E365K and p.T408M.

METHODS

GBA was sequenced in 56 patients with mid-stage PD. Carriers of GBA variants were compared with noncarriers regarding clinical history and symptoms, neuropsychological features, metabolomics, and multimodal neuroimaging. Blood plasma gas chromatography coupled to mass spectrometry, 6-[¹⁸ F]fluoro-L-Dopa positron emission tomography (PET), [¹⁸ F]fluorodeoxyglucose PET, and resting-state functional magnetic resonance imaging were performed.

RESULTS

Sequence analysis detected 13 heterozygous GBA variant carriers (7 with p.E365K, 6 with p.T408M). One patient carried a GBA mutation (p.N409S) and was excluded. Clinical history and symptoms were not significantly different between groups. Global cognitive performance was lower in variant carriers. Metabolomic group differences were suggestive of more severe PD-related alterations in carriers versus noncarriers. Both PET scans showed signs of a more advanced disease; [¹⁸ F]fluorodeoxyglucose PET and functional magnetic resonance imaging showed similarities with Lewy body dementia and PD dementia in carriers.

CONCLUSIONS

This is the first study to comprehensively assess (neuro-)biological phenotypes of GBA variants in PD. Metabolomics and neuroimaging detected more significant group differences than clinical and behavioral evaluation. These alterations could be promising to monitor effects of disease-modifying treatments targeting glucocerebrosidase metabolism. © 2020 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Protective effect of club cell secretory protein (CC-16) on COPD risk and progression: a Mendelian randomisation study

BACKGROUND

The anti-inflammatory pneumoprotein club cell secretory protein-16 (CC-16) is associated with the clinical expression of chronic obstructive pulmonary disease (COPD). We aimed to determine if there is a causal effect of serum CC-16 level on the risk of having COPD and/or its progression using Mendelian randomisation (MR) analysis.

METHODS

We performed a genome-wide association meta-analysis for serum CC-16 in two COPD cohorts (Lung Health Study (LHS), n=3850 and ECLIPSE, n=1702). We then used the CC-16-associated single-nucleotide polymorphisms (SNPs) as instrumental variables in MR analysis to identify a causal effect of serum CC-16 on 'COPD risk' (ie, case status in the International COPD Genetics Consortium/UK-Biobank dataset; n=35 735 COPD cases, n=222 076 controls) and 'COPD progression' (ie, annual change in forced expiratory volume in 1 s in LHS and ECLIPSE). We also determined the associations between SNPs associated with CC-16 and gene expression using n=1111 lung tissue samples from the Lung Expression Quantitative Trait Locus Study.

RESULTS

We identified seven SNPs independently associated (p<5×10^-8) with serum CC-16 levels; six of these were novel. MR analysis suggested a protective causal effect of increased serum CC-16 on COPD risk (MR estimate (SE) -0.11 (0.04), p=0.008) and progression (LHS only, MR estimate (SE) 7.40 (3.28), p=0.02). Five of the SNPs were also associated with gene expression in lung tissue (at false discovery rate <0.1) of several genes, including the CC-16-encoding gene SCGB1A1.

CONCLUSION

We have identified several novel genetic variants associated with serum CC-16 level in COPD cohorts. These genetic associations suggest a potential causal effect of serum CC-16 on the risk of having COPD and its progression, the biological basis of which warrants further investigation.

β-Glucocerebrosidase activity in GBA-linked Parkinson disease: The type of mutation matters

OBJECTIVE

To test the relationship between clinically relevant types of GBA mutations (none, risk variants, mild mutations, severe mutations) and β-glucocerebrosidase activity in patients with Parkinson disease (PD) in cross-sectional and longitudinal case-control studies.

METHODS

A total of 481 participants from the Harvard Biomarkers Study (HBS) and the NIH Parkinson's Disease Biomarkers Program (PDBP) were analyzed, including 47 patients with PD carrying GBA variants (GBA-PD), 247 without a GBA variant (idiopathic PD), and 187 healthy controls. Longitudinal analysis comprised 195 participants with 548 longitudinal measurements over a median follow-up period of 2.0 years (interquartile range, 1-2 years).

RESULTS

β-Glucocerebrosidase activity was low in blood of patients with GBA-PD compared to healthy controls and patients with idiopathic PD, respectively, in HBS (p < 0.001) and PDBP (p < 0.05) in multivariate analyses adjusting for age, sex, blood storage time, and batch. Enzyme activity in patients with idiopathic PD was unchanged. Innovative enzymatic quantitative trait locus (xQTL) analysis revealed a negative linear association between residual β-glucocerebrosidase activity and mutation type with p < 0.0001. For each increment in the severity of mutation type, a reduction of mean β-glucocerebrosidase activity by 0.85 μmol/L/h (95% confidence interval, -1.17, -0.54) was predicted. In a first longitudinal analysis, increasing mutation severity types were prospectively associated with steeper declines in β-glucocerebrosidase activity during a median 2 years of follow-up (p = 0.02).

CONCLUSIONS

Residual activity of the β-glucocerebrosidase enzyme measured in blood inversely correlates with clinical severity types of GBA mutations in PD. β-Glucocerebrosidase activity is a quantitative endophenotype that can be monitored noninvasively and targeted therapeutically.

Progress in the molecular pathogenesis and nucleic acid therapeutics for Parkinson's disease in the precision medicine era

Parkinson's disease (PD) is one of the most common neurodegenerative disorders that manifest various motor and nonmotor symptoms. Although currently available therapies can alleviate some of the symptoms, the disease continues to progress, leading eventually to severe motor and cognitive decline and reduced life expectancy. The past two decades have witnessed rapid progress in our understanding of the molecular and genetic pathogenesis of the disease, paving the way for the development of new therapeutic approaches to arrest or delay the neurodegenerative process. As a result of these advances, biomarker‐driven subtyping is making it possible to stratify PD patients into more homogeneous subgroups that may better respond to potential genetic‐molecular pathway targeted disease‐modifying therapies. Therapeutic nucleic acid oligomers can bind to target gene sequences with very high specificity in a base‐pairing manner and precisely modulate downstream molecular events. Recently, nucleic acid therapeutics have proven effective in the treatment of a number of severe neurological and neuromuscular disorders, drawing increasing attention to the possibility of developing novel molecular therapies for PD. In this review, we update the molecular pathogenesis of PD and discuss progress in the use of antisense oligonucleotides, small interfering RNAs, short hairpin RNAs, aptamers, and microRNA‐based therapeutics to target critical elements in the pathogenesis of PD that could have the potential to modify disease progression. In addition, recent advances in the delivery of nucleic acid compounds across the blood–brain barrier and challenges facing PD clinical trials are also reviewed.

The sirtuin inhibitor cambinol reduces intracellular glucosylceramide with ceramide accumulation by inhibiting glucosylceramide synthase

The accumulation of glucosylceramide (GlcCer), which is synthesized by UDP-glucose ceramide glucosyltransferase (UGCG), is associated with several diseases, including Gaucher disease and Parkinson's disease. Since the inhibition of UGCG can be used to treat diseases caused by GlcCer accumulation, several UGCG inhibitors have been developed. In this study, we report on the inhibition of UGCG activity by cambinol, a sirtuin inhibitor. Unlike conventional UGCG inhibitors, cambinol has no structural similarity to GlcCer. LC-ESI MS/MS analysis revealed that the cellular GlcCer levels were reduced by cambinol with an increase in ceramide, the GlcCer precursor. Histidine 193 plays an important role in the inhibition of UGCG via a known UGCG inhibitor, D-PDMP. However, cambinol was found to inhibit UGCG activity in a histidine 193-independent manner. This study provides insights into the mechanism of inhibition of UGCG activity by cambinol, and provides a basis for the development of a cambinol-based novel UGCG inhibitor.

Longitudinal Monitoring of Parkinson's Disease in Different Ethnic Cohorts: The DodoNA and LONG-PD Study

Background: Different factors influence severity, progression, and outcomes in Parkinson's disease (PD). Lack of standardized clinical assessment limits comparison of outcomes and availability of well-characterized cohorts for collaborative studies. Methods: Structured clinical documentation support (SCDS) was developed within the DNA Predictions to Improve Neurological Health (DodoNA) project to standardize clinical assessment and identify molecular predictors of disease progression. The Longitudinal Clinical and Genetic Study of Parkinson's Disease (LONG-PD) was launched within the Genetic Epidemiology of Parkinson's disease (GEoPD) consortium using a Research Electronic Data Capture (REDCap) format mirroring the DodoNA SCDS. Demographics, education, exposures, age at onset (AAO), Unified Parkinson's Disease Rating Scale (UPDRS) parts I-VI or Movement Disorders Society (MDS)-UPDRS, Montreal Cognitive Assessment (MoCA)/Short Test of Mental Status (STMS)/Mini Mental State Examination (MMSE), Geriatric Depression Scale (GDS), Epworth Sleepiness Scale (ESS), dopaminergic therapy, family history, nursing home placement, death and blood samples were collected. DodoNA participants (396) with 6 years of follow-up and 346 LONG-PD participants with up to 3 years of follow-up were analyzed using group-based trajectory modeling (GBTM) focused on: AAO, education, family history, MMSE/MoCA/STMS, UPDRS II-II, UPDRS-III tremor and bradykinesia sub-scores, Hoehn and Yahr staging (H&Y) stage, disease subtype, dopaminergic therapy, and presence of autonomic symptoms. The analysis was performed with either cohort as the training/test set. Results: Patients are classified into slowly and rapidly progressing courses by AAO, MMSE score, H &Y stage, UPDRS-III tremor and bradykinesia sub-scores relatively early in the disease course. Late AAO and male sex assigned patients to the rapidly progressing group, whereas tremor to the slower progressing group. Classification is independent of which cohort serves as the training set. Frequencies of disease-causing variants in LRRK2 and GBA were 1.89 and 2.96%, respectively. Conclusions: Standardized clinical assessment provides accurate phenotypic characterization in pragmatic clinical settings. Trajectory analysis identified two different trajectories of disease progression and determinants of classification. Accurate phenotypic characterization is essential in interpreting genomic information that is generated within consortia, such as the GEoPD, formed to understand the genetic epidemiology of PD. Furthermore, the LONGPD study protocol has served as the prototype for collecting standardized phenotypic information at GEoPD sites. With genomic analysis, this will elucidate disease etiology and lead to targeted therapies that can improve disease outcomes.

Studying the Pathophysiology of Parkinson's Disease Using Zebrafish

Parkinson's disease is a common neurodegenerative disorder leading to severe disability. The clinical features reflect progressive neuronal loss, especially involving the dopaminergic system. The causes of Parkinson's disease are slowly being uncovered and include both genetic and environmental insults. Zebrafish have been a valuable tool in modeling various aspects of human disease. Here, we review studies utilizing zebrafish to investigate both genetic and toxin causes of Parkinson's disease. They have provided important insights into disease mechanisms and will be of great value in the search for disease-modifying therapies.

Association Between Glucocerebrosidase Mutations and Parkinson's Disease in Ireland

Multiple studies implicate heterozygous GBA mutations as a major genetic risk factor for Parkinson's disease (PD); however, the frequency of mutations has never been examined in PD patients from the Irish population. We prospectively recruited 314 unrelated Irish PD patients (UK Brain Bank Criteria) and 96 Irish healthy controls (without any signs or family history of parkinsonism) attending. The Dublin Neurological Institute (DNI). Complete exon GBA Sanger sequencing analysis with flanking intronic regions was performed. The GBA carrier frequency was 8.3% in PD and 3.1% in controls. We identified a number of potentially pathogenic mutations including a p.G195E substitution and a p.G377C variant, previously described in a case study of Gaucher's disease in Ireland. On genotype-phenotype assessment hallucinations, dyskinesia, and dystonia were more prevalent in GBA-PD. The genetic etiology of PD in Ireland differs from the continental Europe as seen with the lower LRRK2 and higher than in most European countries GBA mutation frequency. Determining genetic risk factors in different ethnicities will be critical for future personalized therapeutic approach.

The S1P-S1PR Axis in Neurological Disorders-Insights into Current and Future Therapeutic Perspectives

Sphingosine 1-phosphate (S1P), derived from membrane sphingolipids, is a pleiotropic bioactive lipid mediator capable of evoking complex immune phenomena. Studies have highlighted its importance regarding intracellular signaling cascades as well as membrane-bound S1P receptor (S1PR) engagement in various clinical conditions. In neurological disorders, the S1P–S1PR axis is acknowledged in neurodegenerative, neuroinflammatory, and cerebrovascular disorders. Modulators of S1P signaling have enabled an immense insight into fundamental pathological pathways, which were pivotal in identifying and improving the treatment of human diseases. However, its intricate molecular signaling pathways initiated upon receptor ligation are still poorly elucidated. In this review, the authors highlight the current evidence for S1P signaling in neurodegenerative and neuroinflammatory disorders as well as stroke and present an array of drugs targeting the S1P signaling pathway, which are being tested in clinical trials. Further insights on how the S1P–S1PR axis orchestrates disease initiation, progression, and recovery may hold a remarkable potential regarding therapeutic options in these neurological disorders.

The Future of Targeted Gene-Based Treatment Strategies and Biomarkers in Parkinson's Disease

Biomarkers and disease-modifying therapies are both urgent unmet medical needs in the treatment of Parkinson's disease (PD) and must be developed concurrently because of their interdependent relationship: biomarkers for the early detection of disease (i.e., prior to overt neurodegeneration) are necessary in order for patients to receive maximal therapeutic benefit and vice versa; disease-modifying therapies must become available for patients whose potential for disease diagnosis and prognosis can be predicted with biomarkers. This review provides an overview of the milestones achieved to date in the therapeutic strategy development of disease-modifying therapies and biomarkers for PD, with a focus on the most common and advanced genetically linked targets alpha-synuclein (SNCA), leucine-rich repeat kinase-2 (LRRK2) and glucocerebrosidase (GBA1). Furthermore, we discuss the convergence of the different pathways and the importance of patient stratification and how these advances may apply more broadly to idiopathic PD. The heterogeneity of PD poses a challenge for therapeutic and biomarker development, however, the one gene- one target approach has brought us closer than ever before to an unprecedented number of clinical trials and biomarker advancements.

Early cognitive decline after bilateral subthalamic deep brain stimulation in Parkinson's disease patients with GBA mutations

BACKGROUND

Subthalamic nucleus deep brain stimulation (STN-DBS) has demonstrated its efficacy on motor complications in advanced Parkinson's disease (PD) but does not modify disease progression. Genetic forms of PD have been associated with different cognitive progression profiles.

OBJECTIVE

To assess the effect of PD-related genetic mutations on cognitive outcome after STN-DBS.

METHODS

Patients with STN-DBS were screened for LRRK2, GBA, and PRKN mutations at the Pitié-Salpêtrière Hospital between 1997 and 2009. Patients with known monogenetic forms of PD from six other centers were also included. The Mattis Dementia Rating Scale (MDRS) was used to evaluate cognition at baseline and one-year post-surgery. The standardized Unified PD Rating Scale (UPDRS) evaluation On and Off medication/DBS was also administered. A generalized linear model adjusted for sex, ethnicity, age at onset, and disease duration was used to evaluate the effect of genetic factors on MDRS changes.

RESULTS

We analyzed 208 patients (131 males, 77 females, 54.3 ± 8.8 years) including 25 GBA, 18 LRRK2, 22 PRKN, and 143 PD patients without mutations. PRKN patients were younger and had a longer disease duration at baseline. A GBA mutation was the only significant genetic factor associated with MDRS change (β = -2.51, p = 0.009). GBA mutation carriers had a more pronounced post-operative MDRS decline (3.2 ± 5.1) than patients with LRRK2 (0.9 ± 4.8), PRKN (0.5 ± 2.7) or controls (1.4 ± 4.4). The motor response to DBS was similar between groups.

CONCLUSION

GBA mutations are associated with early cognitive decline following STN-DBS. Neuropsychological assessment and discussions on the benefit/risk ratio of DBS are particularly important for this population.

Long-Term Outcomes of Genetic Parkinson's Disease

Parkinson’s disease (PD) is a progressive neurodegenerative disorder that affects 1–2% of people by the age of 70 years. Age is the most important risk factor, and most cases are sporadic without any known environmental or genetic causes. Since the late 1990s, mutations in the genes SNCA, PRKN, LRRK2, PINK1, DJ-1, VPS35, and GBA have been shown to be important risk factors for PD. In addition, common variants with small effect sizes are now recognized to modulate the risk for PD. Most studies in genetic PD have focused on finding new genes, but few have studied the long-term outcome of patients with the specific genetic PD forms. Patients with known genetic PD have now been followed for more than 20 years, and we see that they may have distinct and different prognoses. New therapeutic possibilities are emerging based on the genetic cause underlying the disease. Future medication may be based on the pathophysiology individualized to the patient’s genetic background. The challenge is to find the biological consequences of different genetic variants. In this review, the clinical patterns and long-term prognoses of the most common genetic PD variants are presented.

Small Molecule Chaperones for the Treatment of Gaucher Disease and GBA1-Associated Parkinson Disease

Parkinson disease, the second most common movement disorder, is a complex neurodegenerative disorder hallmarked by the accumulation of alpha-synuclein, a neural-specific small protein associated with neuronal synapses. Mutations in the glucocerebrosidase gene (GBA1), implicated in the rare, autosomal recessive lysosomal disorder Gaucher disease, are the most common known genetic risk factor for Parkinson disease. Insights into the inverse relationship between glucocerebrosidase and alpha-synuclein have led to new therapeutic approaches for the treatment of Gaucher disease and GBA1-associated Parkinson disease. Unlike the current drugs used to treat Gaucher disease, which are highly expensive and do not cross the blood-brain-barrier, new small molecules therapies, including competitive and non-competitive chaperones that enhance glucocerebrosidase levels are being developed to overcome these limitations. Some of these include iminosugars, ambroxol, other competitive glucocerebrosidase inhibitors, and non-inhibitory chaperones or activators that do not compete for the active site. These drugs, which have been shown in different disease models to increase glucocerebrosidase activity, could have potential as a therapy for Gaucher disease and GBA1- associated Parkinson disease. Some have been demonstrated to reduce α-synuclein levels in pre-clinical studies using cell-based or animal models of GBA1-associated Parkinson disease, and may also have utility for idiopathic Parkinson disease.

Epigenetic regulation in the pathophysiology of Lewy body dementia

Lewy body dementia encompasses both dementia with Lewy bodies and Parkinson's disease dementia. Although both are common causes of dementia, they remain relatively understudied. The review summarises the clinico-pathologic characteristics of Lewy Body dementia and discusses the genetic and environmental evidence contributing to the risk of developing the condition. Considering that the pathophysiology of Lewy body dementia is not yet fully understood, here we focus on the role of epigenetic mechanisms as potential key mediators of gene-environment interactions in the development of the disease. We examine available important data on genomics, epigenomics, gene expression and proteomic studies in Lewy body dementia on human post-mortem brain and peripheral tissues. Genetic variation and epigenetic modifications in key genes involved in the disorder, such as apolipoprotein E (APOE), α-synuclein (SNCA) and glucocerobrosidase (GBA), suggest a central involvement of epigenetics in DLB but conclusive evidence is scarce. This is due to limitations of existing literature, such as small sample sizes, lack of replication and lack of studies interrogating cell-type specific epigenetic modifications in the brain. Future research in the field can improve the understanding of this common but complex and rapidly progressing type of dementia and potentially open early diagnostic and effective therapeutic targets.

HOTAIR drives autophagy in midbrain dopaminergic neurons in the substantia nigra compacta in a mouse model of Parkinson's disease by elevating NPTX2 via miR-221-3p binding

Parkinson’s disease (PD) is a neurodegenerative disorder characterized by progressive cell loss, largely confined to mesencephalic dopamine neurons of the substantia nigra. This study investigated the functional relevance of the HOX transcript antisense intergenic RNA (HOTAIR)/microRNA-221-3 (miR-221-3p)/neuronal pentraxin II (NPTX2) axis in the process of dopaminergic neuron autophagy using PD mouse models. The PD mouse models were established by intraperitoneal injection of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyrindine (MPTP), while PD cell model was constructed by pretreatment with 1-methyl-4-phenylpyridinium (MPP⁺). The expression of HOTAIR was then examined using RT-qPCR. In addition, the interactions between HOTAIR, miR-221-3p, and NPTX2 were detected through RIP and dual-luciferase reporter gene assays. CCK-8 assay was performed to measure cell viability, and the expression of autophagy-related genes was determined using Western blot analysis. HOTAIR was found to be significantly expressed in the substantia nigra compact tissues and MN9D cells following PD modeling. HOTAIR could bind to miR-221-3p and elevate the NPTX2 expression, which resulted in diminished cell viability and enhanced autophagy of dopaminergic neurons both in vitro and in vivo. In summary, down-regulation of HOTAIR could potentially inhibit the autophagy of dopaminergic neurons in the substantia nigra compacta in a mouse model of PD, thus saving the demise of dopaminergic neurons.

Autophagy in Neurodegenerative Diseases: A Hunter for Aggregates

Cells have developed elaborate quality-control mechanisms for proteins and organelles to maintain cellular homeostasis. Such quality-control mechanisms are maintained by conformational folding via molecular chaperones and by degradation through the ubiquitin-proteasome or autophagy-lysosome system. Accumulating evidence suggests that impaired autophagy contributes to the accumulation of intracellular inclusion bodies consisting of misfolded proteins, which is a hallmark of most neurodegenerative diseases. In addition, genetic mutations in core autophagy-related genes have been reported to be linked to neurodegenerative diseases, such as Alzheimer’s disease, Parkinson’s disease, and Huntington’s disease. Conversely, the pathogenic proteins, such as amyloid β and α-synuclein, are detrimental to the autophagy pathway. Here, we review the recent advances in understanding the relationship between autophagic defects and the pathogenesis of neurodegenerative diseases and suggest autophagy induction as a promising strategy for the treatment of these conditions.

CRISPR/Cas9 Editing for Gaucher Disease Modelling

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

Systematic review of genetic association studies in people with Lewy body dementia

OBJECTIVES

Lewy body dementia (LBD) causes more morbidity, disability, and earlier mortality than Alzheimer disease. Molecular mechanisms underlying neurodegeneration in LBD are poorly understood. We aimed to do a systematic review of all genetic association studies that investigated people with LBD for improving our understanding of LBD molecular genetics and for facilitating discovery of novel biomarkers and therapeutic targets for LBD.

METHODS

We systematically reviewed five online databases (PROSPERO protocol: CRD42018087114) and completed the quality assessment using the quality of genetic association studies tool.

RESULTS

Eight thousand five hundred twenty-one articles were screened, and 75 articles were eligible to be included. Genetic associations of LBD with APOE, GBA, and SNCA variants have been replicated by two or more good quality studies. Our meta-analyses confirmed that APOE-ε4 is significantly associated with dementia with Lewy bodies (pooled odds ratio [POR] = 2.70; 95% CI, 2.37-3.07; P < .001) and Parkinson's disease dementia (POR = 1.60; 95% CI, 1.21-2.11; P = .001). Other reported genetic associations that need further replication include variants in A2M, BCHE-K, BCL7C, CHRFAM7A, CNTN1, ESR1, GABRB3, MAPT, mitochondrial DNA (mtDNA) haplogroup H, NOS2A, PSEN1, SCARB2, TFAM, TREM2, and UCHL1.

CONCLUSIONS

The reported genetic associations and their potential interactions indicate the importance of α-synuclein, amyloid, and tau pathology, autophagy lysosomal pathway, ubiquitin proteasome system, oxidative stress, and mitochondrial dysfunction in LBD. There is a need for larger genome-wide association study (GWAS) for identifying more LBD-associated genes. Future hypothesis-driven studies should aim to replicate reported genetic associations of LBD and to explore their functional implications.

Genetic variability and potential effects on clinical trial outcomes: perspectives in Parkinson's disease

BACKGROUND

Classical randomisation of clinical trial patients creates a source of genetic variance that may be contributing to the high failure rate seen in neurodegenerative disease trials. Our objective was to quantify genetic difference between randomised trial arms and determine how imbalance can affect trial outcomes.

METHODS

5851 patients with Parkinson's disease of European ancestry data and two simulated virtual cohorts based on public data were used. Data were resampled at different sizes for 1000 iterations and randomly assigned to the two arms of a simulated trial. False-negative and false-positive rates were estimated using simulated clinical trials, and per cent difference in genetic risk score (GRS) and allele frequency was calculated to quantify variance between arms.

RESULTS

5851 patients with Parkinson's disease (mean (SD) age, 61.02 (12.61) years; 2095 women (35.81%)) as well as simulated patients from virtually created cohorts were used in the study. Approximately 90% of the iterations had at least one statistically significant difference in individual risk SNPs between each trial arm. Approximately 5%-6% of iterations had a statistically significant difference between trial arms in mean GRS. For significant iterations, the average per cent difference for mean GRS between trial arms was 130.87%, 95% CI 120.89 to 140.85 (n=200). Glucocerebrocidase (GBA) gene-only simulations see an average 18.86%, 95% CI 18.01 to 19.71 difference in GRS scores between trial arms (n=50). When adding a drug effect of -0.5 points in MDS-UPDRS per year at n=50, 33.9% of trials resulted in false negatives.

CONCLUSIONS

Our data support the hypothesis that within genetically unmatched clinical trials, genetic heterogeneity could confound true therapeutic effects as expected. Clinical trials should undergo pretrial genetic adjustment or, at the minimum, post-trial adjustment and analysis for failed trials.

Genetic predispositions of Parkinson's disease revealed in patient-derived brain cells

Parkinson's disease (PD) is the second most prevalent neurological disorder and has been the focus of intense investigations to understand its etiology and progression, but it still lacks a cure. Modeling diseases of the central nervous system in vitro with human induced pluripotent stem cells (hiPSC) is still in its infancy but has the potential to expedite the discovery and validation of new treatments. Here, we discuss the interplay between genetic predispositions and midbrain neuronal impairments in people living with PD. We first summarize the prevalence of causal Parkinson's genes and risk factors reported in 74 epidemiological and genomic studies. We then present a meta-analysis of 385 hiPSC-derived neuronal lines from 67 recent independent original research articles, which point towards specific impairments in neurons from Parkinson's patients, within the context of genetic predispositions. Despite the heterogeneous nature of the disease, current iPSC models reveal converging molecular pathways underlying neurodegeneration in a range of familial and sporadic forms of Parkinson's disease. Altogether, consolidating our understanding of robust cellular phenotypes across genetic cohorts of Parkinson's patients may guide future personalized drug screens in preclinical research.

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

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

Rare Variants in Specific Lysosomal Genes Are Associated With Parkinson's Disease

OBJECTIVE

Impaired lysosomal degradation of α-synuclein and other cellular constituents may play an important role in Parkinson's disease (PD). Rare genetic variants in the glucocerebrosidase (GBA) gene were consistently associated with PD. Here we examine the association between rare variants in lysosomal candidate genes and PD.

METHODS

We investigated the association between PD and rare genetic variants in 23 lysosomal candidate genes in 4096 patients with PD and an equal number of controls using pooled targeted next-generation DNA sequencing. Genewise association of rare variants in cases or controls was analyzed using the optimized sequence kernel association test with Bonferroni correction for the 23 tested genes.

RESULTS

We confirm the association of rare variants in GBA with PD and report novel associations for rare variants in ATP13A2, LAMP1, TMEM175, and VPS13C.

CONCLUSION

Rare variants in selected lysosomal genes, first and foremost GBA, are associated with PD. Rare variants in ATP13A2 and VPC13C previously linked to monogenic PD and more common variants in TMEM175 and VPS13C previously linked to sporadic PD in genome-wide association studies are associated with PD. © 2020 International Parkinson and Movement Disorder Society.

Flow Cytometry Measurement of Glucocerebrosidase Activity in Human Monocytes

Glucocerebrosidase (GCase) is an important enzyme for the metabolism of glycolipids. GCase enzyme deficiency is implicated in human disease and the efficient measurement of GCase activity is important for evaluating the efficacy of therapeutics targeting this enzyme. Existing approaches to measure GCase activity include whole blood mass spectrometry-based assays, where an internal standard is used to measure the accumulation of ceramide following metabolism of the synthetic substrate C12-glucocerebroside, and the utilisation of fluorescent probes that bind active GCase and/or release fluorescent metabolites upon cleavage by GCase. Here, we describe the application of a fluorescence-activated cell sorter-based assay to efficiently quantitate GCase enzyme activity in the monocyte population of human peripheral blood mononuclear cells. The cell-permeable GCase substrate 5-(Pentafluorobenzoylamino) Fluorescein Di-beta-D-Glucopyranoside (PFB-FDGlu) provides a means to measure GCase activity, whereby enzymatic cleavage yields the green-fluorescent PFB-F dye, detectable in the FL-1 channel of a flow cytometer. An inhibitor of lysosomal GCase activity, conduritol B-epoxide, is employed to ensure specificity. This protocol provides an advantageous approach for measuring GCase activity in living individual cells.

Advances in elucidating the function of leucine-rich repeat protein kinase-2 in normal cells and Parkinson's disease

Autosomal dominant missense mutations that hyperactivate the leucine-rich repeat protein kinase-2 (LRRK2) are a common cause of inherited Parkinson's disease and therapeutic efficacy of LRRK2 inhibitors is being tested in clinical trials. In this review, we discuss the nuts and bolts of our current understanding of how the LRRK2 is misregulated by mutations and how pathway activity is affected by LRRK2 binding to membrane, microtubule filaments, and 14-3-3, as well as by upstream components such as Rab29 and VPS35. We discuss recent work that points toward a subset of Rab proteins comprising key physiological substrates that bind new sets of effectors, such as RILPL1/2, JIP3 and JIP4 after phosphorylation by LRRK2. We explore what is known about how LRRK2 regulates ciliogenesis, the endosomal-lysosomal system, immune responses and interplay with alpha-synuclein and tau and how this might be linked to Parkinson's' disease.