Ubiquitin-proteasome system and Parkinson's disease.

Increasing genetic, pathological, and experimental evidence suggest that neurodegeneration in both familial and sporadic forms of Parkinson's disease (PD) may be related to a defect in the capacity of the ubiquitin-proteasome system (UPS) to clear unwanted proteins, resulting in protein accumulation, aggregation, and cytotoxicity. This concept is supported by in vitro and in vivo laboratory experiments which show that inhibition of UPS function can cause neurodegeneration coupled with the formation of Lewy body-like inclusions. This hypothesis could account for the presence of protein aggregates and Lewy bodies in PD, the other biochemical features seen in the disorder, and the age-related vulnerability of the substantia nigra pars compacta. It also suggests novel targets for putative neuroprotective therapies for PD.     

Animal models of Parkinson's disease: Similarities and differences between the disease and models

Parkinson's disease (PD) is a progressive movement disorder characterized by resting tremor, rigidity, akinesia, and postural instability. In addition, PD is characterized by the appearance of Lewy bodies in the remaining neurons. The exact etiology for this disease is still unknown. However, genetic–environmental interaction could contribute to the pathomechanisms of PD. Indeed, seven causative genes responsible for familial PD have been identified. Since discovery of familial PD (FPD), genetic PD models have been developed. Moreover, new PD models using neurotoxins have been reported. In this review, the similarities between human PD and PD models such as genetic mice and Drosophila models are reviewed.     

Overcoming obstacles in Parkinson's disease

Improved symptomatic and disease‐modifying treatments are needed for Parkinson's disease (PD). Although significant advances have been made in the understanding of PD etiology, the translation of these discoveries into novel transformative therapies has been limited as a result of systemic challenges in PD drug development. Preclinical testing lacks clear standards and prioritization criteria for advancing therapies to the clinic. Clinical testing is marked by expensive, long, and uninformative studies. In parallel to these scientific challenges, funding of late‐stage drug development has become increasingly scarce and risk averse. In this context, novel models of collaboration and funding are opening up new avenues for pursuing treatments. This review will discuss the most critical challenges in PD drug development and the innovative approaches being developed to overcome these hurdles. © 2012 Movement Disorder Society     

Functional ryanodine receptors are expressed by human microglia and THP-1 cells: Their possible involvement in modulation of neurotoxicity

Ryanodine receptors (RyRs) are intracellular Ca(2+) channels that mediate the release of calcium from internal stores and therefore play an important role in Ca(2+) signaling and homeostasis. Three RyR isoforms have been described thus far, and various areas of brain are known to express each of them. It is well established that neurons can express different RyR isoforms, but it is not known whether microglial cells do so. In the present study we showed that cultured human microglia from both fetal and adult brain specimens express mRNA for RyR1 and RyR2, whereas RyR3 mRNA can be detected only in fetal microglial cells. Calcium spectrofluorometry showed that high levels of the RyR agonist 4-chloro-m-cresol (4-CmC, 1-5 mM) induced elevation of intracellular Ca(2+) concentration ([Ca(2+)](i)) in both types of cultured human microglial cells. This effect was attenuated by the RyR antagonist 1,1'-diheptyl-4,4'-bipyridinium dibromide (DHBP, 10 microM). Neurotoxicity of conditioned medium from human microglia and THP-1 monocytic cells stimulated with a combination of interferon-gamma (IFN-gamma) with either lipopolysaccharide (LPS) or alpha-synuclein was diminished by DHBP. It was also diminished by 4-CmC at concentrations approximately 100-fold lower than those used to stimulate intracellular Ca(2+) release. These data indicate that human microglial cells express functional RyRs and that selective RyR ligands exert antineurotoxic action on this cell type. Therefore, RyR ligands may represent a novel class of compounds that have utility in reducing microglial-mediated inflammation, which is believed to contribute to the pathogenesis of a number of neurodegenerative disorders including Alzheimer's disease and Parkinson's disease.     

Alpha-synuclein mRNA expression in sporadic Parkinson's disease.

The expression of alpha-synuclein gene can be influenced by the genomic load and/or epigenetic factors. By using quantitative real-time polymerase chain reaction techniques, we demonstrated that the alpha-synuclein gene mRNA expression in sporadic PD did not differ from healthy controls (median [range] 0.110 ]0.012-0.628] vs. 0.120 [0.028-0.447]; P = 0.15). There was no difference in the alpha-synuclein gene dosage between PD patients with high and low mRNA expression. Multivariate analysis did not reveal age, gender, or cigarette smoking as confounding variables. Our study suggests that there was no significant alteration of alpha-synuclein mRNA expression in our sporadic PD patients compared to controls. However, the role of alpha-synuclein mRNA expression in select groups of sporadic PD patients and its interaction with environmental agents need to be further determined.     

Alpha‐synuclein polymorphisms are associated with Parkinson's disease in a Saskatchewan population

Alpha‐synuclein gene (SNCA) mutations cause familial Parkinsonism but the role of SNCA variability in idiopathic Parkinson's disease (PD) remains incompletely defined. We report a study of SNCA genetic variation in 452 idiopathic PD cases and 245 controls. SNCA copy number mutations were not associated with early‐onset disease in this population. The minor allele “G” at rs356165 was associated with increased odds of PD (P = 0.013) and genetic variation in D4S3481 (Rep1) was associated with age of disease onset (P = 0.007). There was a trend toward association between variation at rs2583988 and rapid PD progression. © 2009 Movement Disorder Society     

Alpha‐synuclein and familial Parkinson's disease

Whole gene duplications and triplications of alpha‐synuclein (SNCA) can cause Parkinson's disease (PD), and variation in the promoter region (Rep1) and 3' region of SNCA has been reported to increase disease susceptibility. Within our cohort, one affected individual from each of 92 multiplex PD families showing the greatest evidence of linkage to the region around SNCA was screened for dosage alterations and sequence changes; no dosage or non‐synonymous sequence changes were found. In addition, 737 individuals (from 450 multiplex PD families) that met strict diagnostic criteria for PD and did not harbor a known causative mutation, as well as 359 neurologically normal controls, were genotyped for the Rep1 polymorphism and four SNPs in the 3′ region of SNCA. The four SNPs were in high LD (r² > 0.95) and were analyzed as a haplotype. The effects of the Rep1 genotype and the 3′ haplotype were evaluated using regression models employing only one individual per family. Cases had a 3% higher frequency of the Rep1 263 bp allele compared with controls (OR = 1.54; empirical P‐value = 0.02). There was an inverse linear relationship between the number of 263 bp alleles and age of onset (empirical P‐value = 0.0004). The 3′ haplotype was also associated with disease (OR = 1.29; empirical P‐value = 0.01), but not age of onset (P = 0.40). These data suggest that dosage and sequence changes are a rare cause of PD, but variation in the promoter and 3′ region of SNCA convey an increased risk for PD. © 2009 Movement Disorder Society     

Glial reactions in Parkinson's disease

Dopaminergic neurons of the substantia nigra are particularly vulnerable to oxidative and inflammatory attack. Such processes may play a crucial role in the etiology of Parkinson disease (PD). Since glia are the main generators of these processes, the possibility that PD may be caused by glial dysfunction needs to be considered. This review concentrates on glial reactions in PD. Reactive astrocytes and reactive microglia are abundant in the substantia nigra (SN) of PD cases indicating a robust inflammatory state. Glia normally serve neuroprotective roles but, given adverse stimulation, they may contribute to damaging chronic inflammation. Microglia, the phagocytes of brain, may be the main contributors since they can produce large numbers of superoxide anions and other neurotoxins. Their toxicity towards dopaminergic neurons has been demonstrated in tissue culture and various animal models of PD. The MPTP and α‐synuclein models are of particular interest. Years after exposure to MPTP, inflammation has been observed in the SN. This has established that an acute insult to the SN can result in a sustained local inflammation. The α‐synuclein model indicates that an endogenous protein can induce inflammation, and, when overexpressed, can lead to autosomal dominant PD. Less is known about the role of astrocytes than microglia, but they are known to secrete both inflammatory and anti‐inflammatory molecules and may play a role in modulating microglial activity. Oligodendrocytes do not seem to play a role in promoting inflammation although, like neurons, they may be damaged by inflammatory processes. Further research concerning glial reactions in PD may lead to disease‐modifying therapeutic approaches. © 2007 Movement Disorder Society     

Glucocerebrosidase in Parkinson's disease: Insights into pathogenesis and prospects for treatment

PD involves several converging pathogenetic pathways to neurodegeneration; highlighted in specific cases by genetic mutations causing familial PD. Numerically, the most important genetic mutations associated with PD are those of the glucocerebrosidase gene. Approximately 10% of PD patients carry glucocerebrosidase mutations. This observation has enhanced focus on the autophagy‐lysosome system as important in pathogenesis. The relationship of the glucocerebrosidase pathway to the cause and progression of PD highlights the potential to use abnormalities identified as biomarkers and modify glucocerebrosidase activity or substrate accumulation as neuroprotection. Biomarkers relevant to the glucocerebrosidase pathway, for example, enzyme activity and substrate levels, may be identified in blood, urine, and CSF. These may be combined with clinical features to help identify mutation carriers that are at increased risk of PD. The molecular mechanisms by which glucocerebrosidase mutations may result in PD are not fully understood. There is evidence accumulating that there is a reciprocal interaction between glucocerebrosidase and alpha‐synuclein levels. This interaction may potentially be used to increase glucocerebrosidase enzyme activities and therefore reduce alpha‐synuclein levels to modify the course of PD. Substrate reduction therapy may be an alternative strategy, particularly if membrane abnormalities underlie the organellar dysfunction in PD neurodegeneration. © 2016 International Parkinson and Movement Disorder Society     

Progressive supranuclear palsy and Parkinson's disease overlap: A clinicopathological case report

We describe a woman with a 13‐year history of postural instability, vertical gaze palsy and dopa‐responsive parkinsonism ‐ a clinical profile that corresponds to progressive supranuclear palsy (PSP) and Parkinson's disease (PD). The patient died at the age of 82 years. Neuropathological features included neuronal loss and gliosis in the substantia nigra, locus ceruleus, dorsal motor nucleus of the vagus, thoracic intermediolateral nucleus and nucleus basalis of Meynert, in addition to the typical pathology of PSP. Immunohistochemical studies demonstrated that PSP‐tau pathology was localized in the central nervous system, but Lewy body‐related α‐synucleinopathy was extensive in the central and peripheral nervous systems. Although PSP and PD may represent independent processes, this case could provide insight into a common defect in either protein phosphorylation or the proteinase surveillance system that contributes to human aging.     

Alpha-synuclein and Parkinson's disease: implications from the screening of more than 1,900 patients.

Data on the frequency of alpha-synuclein mutations in Parkinson's disease (PD) are limited. Screening the entire coding region in 1,921 PD patients with denaturing high performance liquid chromatography and subsequent sequencing we only detected silent mutations (g.2654A>G, g.10151G>A, and g.15986A>T) and the c.209G>A substitution corresponding to the p.A53T mutation. These results demonstrate that mutations in the alpha-synuclein gene are rare and suggest that other factors contribute to alpha-synuclein aggregation in the majority of PD patients.     

Somatic alpha‐synuclein mutations in Parkinson's disease: Hypothesis and preliminary data

Alpha‐synuclein (SNCA) is crucial in the pathogenesis of Parkinson's disease (PD), yet mutations in the SNCA gene are rare. Evidence for somatic genetic variation in normal humans, also involving the brain, is increasing, but its role in disease is unknown. Somatic SNCA mutations, arising in early development and leading to mosaicism, could contribute to PD pathogenesis and yet be absent or undetectable in DNA derived from peripheral lymphocytes. Such mutations could underlie the widespread pathology in PD, with the precise clinical outcome dependent on their type and the timing and location of their occurrence. We recently reported a novel SNCA mutation (c.150T>G, p.H50Q) in PD brain‐derived DNA. To determine if there was mosaicism for this, a PCR and cloning strategy was used to take advantage of a nearby heterozygous intronic polymorphism. No evidence of mosaicism was found. High‐resolution melting curve analysis of SNCA coding exons, which was shown to be sensitive enough to detect low proportions of 2 known mutations, did not reveal any further mutations in DNA from 28 PD brain‐derived samples. We outline the grounds that make the somatic SNCA mutation hypothesis consistent with genetic, embryological, and pathological data. Further studies of brain‐derived DNA are warranted and should include DNA from multiple regions and methods for detecting other types of genomic variation. © 2013 The Authors. International Parkinson and Movement Disorder Society published by Wiley Periodicals, Inc.     

Cerebrospinal fluid,plasma, and saliva in the BioFIND study: Relationships among biomarkers and Parkinson's disease Features

Objective: Examine relationships among neurodegenerative biomarkers and PD motor and nonmotor symptoms. Background: CSF alpha‐synuclein is decreased in PD versus healthy controls, but whether plasma and saliva alpha‐synuclein differentiate these groups is controversial. Correlations of alpha‐synuclein among biofluids (CSF, plasma, saliva) or biomarkers (eg, beta‐amyloid, tau [total, phosphorylated]) are not fully understood. The relationships of these biomarkers with PD clinical features remain unclear. Methods: BioFIND, a cross‐sectional, observational study, examines clinical and biomarker characteristics in moderate‐advanced PD and matched healthy controls. We compared alpha‐synuclein concentrations across diagnosis, biofluids, and CSF biomarkers. Correlations of CSF biomarkers and MDS‐UPDRS, motor phenotype, MoCA, and rapid eye movement sleep behavior disorder questionnaire scores in PD were examined. Results: CSF alpha‐synuclein was lower in PD versus controls (P = .01), controlling for age, gender, and education. Plasma and saliva alpha‐synuclein did not differ between PD and controls, and alpha‐synuclein did not significantly correlate among biofluids. CSF beta‐amyloid_1‐42 was lower in PD versus controls (P < .01), and correlated weakly with MoCA recall scores (r = 0.23, P = .02). CSF alpha‐synuclein was lower in the postural instability/gait difficulty phenotype than other motor phenotypes (P < .01). No CSF biomarkers predicted or correlated with total motor or rapid eye movement sleep behavior disorder scores. CSF alpha‐synuclein correlated with beta‐amyloid_1‐42, total‐tau, and phosphorylated‐tau (r = 0.41, 0.81, 0.43, respectively; Ps < .001). Conclusion: Lower CSF alpha‐synuclein is associated with diagnosis and motor phenotype in moderate‐advanced PD. Plasma and saliva alpha‐synuclein neither correlate with CSF alpha‐synuclein, nor distinguish PD from controls. CSF beta‐amyloid_1‐42 remains a potential biomarker for cognitive impairment in PD. © 2017 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.     

Stem cell therapy for Parkinson's disease: safety and modeling

For decades,clinicians have developed medications and therapies to alleviate the symptoms of Parkinson’s disease,but no treatment currently can slow or even stop the progression of this localized neurodegeneration.Fortunately,sparked by the genetic revolution,stem cell reprogramming research and the advancing capabilities of personalization in medicine enable forward-thinking to unprecedented patient-specific modeling and cell therapies for Parkinson’s disease using induced pluripotent stem cells(iPSCs).In addition to modeling Parkinson’s disease more accurately than chemically-induced animal models,patient-specific stem cell lines can be created,elucidating the effects of genetic susceptibility and sub-populations’differing responses to in vitro treatments.Sourcing cell therapy with iPSC lines provides ethical advantages because these stem cell lines do not require the sacrifice of human zygotes and genetically-specific drug trails can be tested in vitro without lasting damage to patients.In hopes of finally slowing the progression of Parkinson’s disease or re-establishing function,iPSC lines can ultimately be corrected with gene therapy and used as cell sources for neural transplantation for Parkinson’s disease.With relatively localized neural degeneration,similar to spinal column injury,Parkinson’s disease presents a better candidacy for cell therapy when compared to other diffuse degeneration found in Alzheimer’s or Huntington’s Disease.Neurosurgical implantation of pluripotent cells poses the risk of an innate immune response and tumorigenesis.Precautions,therefore,must be taken to ensure cell line quality before transplantation.While cell quality can be quantified using a number of assays,a yielding a high percentage of therapeutically relevant dopaminergic neurons,minimal de novo genetic mutations,and standard chromosomal structure is of the utmost importance.Current techniques focus on iPSCs because they can be matched with donors using human leukocyte antigens,thereby reducing the severity and risk of immune rejection.In August of 2018,researchers in Kyoto,Japan embarked on the first human clinical trial using iPSC cell therapy transplantation for patients with moderate Parkinson’s disease.Transplantation of many cell sources has already proven to reduce Parkinson’s disease symptoms in mouse and primate models.Here we discuss the history and implications for cell therapy for Parkinson’s disease,as well as the necessary safety standards needed for using iPSC transplantation to slow or halt the progression of Parkinson’s disease.     

Parkinson's disease,cortical dysfunction,and alpha‐synuclein

The ability to understand how Parkinson's disease neurodegeneration leads to cortical dysfunction will be critical for developing therapeutic advances in Parkinson's disease dementia. The overall purpose of this project was to study the small‐amplitude cortical myoclonus in Parkinson's disease as an in vivo model of focal cortical dysfunction secondary to Parkinson's disease neurodegeneration. The objectives were to test the hypothesis that cortical myoclonus in Parkinson's disease is linked to abnormal levels of α‐synuclein in the primary motor cortex and to define its relationship to various biochemical, clinical, and pathological measures. The primary motor cortex was evaluated for 11 Parkinson's disease subjects with and 8 without electrophysiologically confirmed cortical myoclonus (the Parkinson's disease + myoclonus group and the Parkinson's disease group, respectively) who had premortem movement and cognitive testing. Similarly assessed 9 controls were used for comparison. Measurements for α‐synuclein, Aβ‐42 peptide, and other biochemical measures were made in the primary motor cortex. A 36% increase in α‐synuclein was found in the motor cortex of Parkinson's disease + myoclonus cases when compared with Parkinson's disease without myoclonus. This occurred without significant differences in insoluble α‐synuclein, phosphorylated to total α‐synuclein ratio, or Aβ‐42 peptide levels. Higher total motor cortex α‐synuclein levels significantly correlated with the presence of cortical myoclonus but did not correlate with multiple clinical or pathological findings. These results suggest an association between elevated α‐synuclein and the dysfunctional physiology arising from the motor cortex in Parkinson's disease + myoclonus cases. Alzheimer's disease pathology was not associated with cortical myoclonus in Parkinson's disease. Cortical myoclonus arising from the motor cortex is a model to study cortical dysfunction in Parkinson's disease. © 2011 Movement Disorder Society     

Cerebrospinal fluid lysosomal enzymes and alpha‐synuclein in Parkinson's disease

To assess the discriminating power of multiple cerebrospinal fluid (CSF) biomarkers for Parkinson's disease (PD), we measured several proteins playing an important role in the disease pathogenesis. The activities of β‐glucocerebrosidase and other lysosomal enzymes, together with total and oligomeric α‐synuclein, and total and phosphorylated tau, were thus assessed in CSF of 71 PD patients and compared to 45 neurological controls. Activities of β‐glucocerebrosidase, β‐mannosidase, β‐hexosaminidase, and β‐galactosidase were measured with established enzymatic assays, while α‐synuclein and tau biomarkers were evaluated with immunoassays. A subset of PD patients (n = 44) was also screened for mutations in the β‐glucocerebrosidase‐encoding gene (GBA1). In the PD group, β‐glucocerebrosidase activity was reduced (P < 0.05) and patients at earlier stages showed lower enzymatic activity (P < 0.05); conversely, β‐hexosaminidase activity was significantly increased (P < 0.05). Eight PD patients (18%) presented GBA1 sequence variations; 3 of them were heterozygous for the N370S mutation. Levels of total α‐synuclein were significantly reduced (P < 0.05) in PD, in contrast to increased levels of α‐synuclein oligomers, with a higher oligomeric/total α‐synuclein ratio in PD patients when compared with controls (P < 0.001). A combination of β‐glucocerebrosidase activity, oligomeric/total α‐synuclein ratio, and age gave the best performance in discriminating PD from neurological controls (sensitivity 82%; specificity 71%, area under the receiver operating characteristic curve = 0.87). These results demonstrate the possibility of detecting lysosomal dysfunction in CSF and further support the need to combine different biomarkers for improving the diagnostic accuracy of PD. © 2014 International Parkinson and Movement Disorder Society     

Multiple alpha-synuclein gene polymorphisms are associated with Parkinson's disease in a Norwegian population

Objectives – Previous studies have found associations between Parkinson’s disease (PD) and polymorphisms located within both the alpha‐synuclein gene (SNCA) promoter and other gene regions. Our aim was to study SNCA gene markers in a closely matched Norwegian PD population to examine the genetic relationship between different polymorphisms associated with the disease. Methods – We genotyped seven single nucleotide polymorphisms (SNPs) located in the SNCA promoter and two SNPs in the 3′ gene region and seven microsatellite markers located across the gene in a closely matched series of 236 PD patients and 236 controls. Linkage disequilibrium (LD) structure was examined, and association of single markers and gene haplotypes analyzed. Results – Several markers located across the SNCA gene were associated with PD, including marker alleles associated with disease in previous studies (Rep1 263‐bp allele, rs356165 and rs356219). Conclusion – LD between associated marker alleles located across the SNCA gene suggests that a single genetic effect might explain the previous reported association in the promoter and 3′ regions.