Proteolytic stress: a unifying concept for the etiopathogenesis of Parkinson's disease

Accurate identification of genes associated with brain disorders by integrating heterogeneous genomic data into a Bayesian framework

BACKGROUND

Genome-wide association studies (GWAS) have revealed many brain disorder-associated SNPs residing in the noncoding genome, rendering it a challenge to decipher the underlying pathogenic mechanisms.

METHODS

Here, we present an unsupervised Bayesian framework to identify disease-associated genes by integrating risk SNPs with long-range chromatin interactions (iGOAT), including SNP-SNP interactions extracted from ∼500,000 patients and controls from the UK Biobank, and enhancer-promoter interactions derived from multiple brain cell types at different developmental stages.

FINDINGS

The application of iGOAT to three psychiatric disorders and three neurodegenerative/neurological diseases predicted sets of high-risk (HRGs) and low-risk (LRGs) genes for each disorder. The HRGs were enriched in drug targets, and exhibited higher expression during prenatal brain developmental stages than postnatal stages, indicating their potential to affect brain development at an early stage. The HRGs associated with Alzheimer's disease were found to share genetic architecture with schizophrenia, bipolar disorder and major depressive disorder according to gene co-expression module analysis and rare variants analysis. Comparisons of this method to the eQTL-based method, the TWAS-based method, and the gene-level GWAS method indicated that the genes identified by our method are more enriched in known brain disorder-related genes, and exhibited higher precision. Finally, the method predicted 205 risk genes not previously reported to be associated with any brain disorder, of which one top-risk gene, MLH1, was experimentally validated as being schizophrenia-associated.

INTERPRETATION

iGOAT can successfully leverage epigenomic data, phenotype-genotype associations, and protein-protein interactions to advance our understanding of brain disorders, thereby facilitating the development of new therapeutic approaches.

FUNDING

The work was funded by the National Key Research and Development Program of China (2024YFF1204902), the Natural Science Foundation of China (82371482), Guangzhou Science and Technology Research Plan (2023A03J0659) and Natural Science Foundation of Guangdong (2024A1515011363).

Dynamic Metabolic and Transcriptional Responses of Proteasome-Inhibited Neurons

Proteasome inhibition is associated with parkinsonian pathology in vivo and degeneration of dopaminergic neurons in vitro. We explored here the metabolome (386 metabolites) and transcriptome (3257 transcripts) regulations of human LUHMES neurons, following exposure to MG-132 [100 nM]. This proteasome inhibitor killed cells within 24 h but did not reduce viability for 12 h. Overall, 206 metabolites were changed in live neurons. The early (3 h) metabolome changes suggested a compromised energy metabolism. For instance, AMP, NADH and lactate were up-regulated, while glycolytic and citric acid cycle intermediates were down-regulated. At later time points, glutathione-related metabolites were up-regulated, most likely by an early oxidative stress response and activation of NRF2/ATF4 target genes. The transcriptome pattern confirmed proteostatic stress (fast up-regulation of proteasome subunits) and also suggested the progressive activation of additional stress response pathways. The early ones (e.g., HIF-1, NF-kB, HSF-1) can be considered a cytoprotective cellular counter-regulation, which maintained cell viability. For instance, a very strong up-regulation of AIFM2 (=FSP1) may have prevented fast ferroptotic death. For most of the initial period, a definite life-death decision was not taken, as neurons could be rescued for at least 10 h after the start of proteasome inhibition. Late responses involved p53 activation and catabolic processes such as a loss of pyrimidine synthesis intermediates. We interpret this as a phase of co-occurrence of protective and maladaptive cellular changes. Altogether, this combined metabolomics-transcriptomics analysis informs on responses triggered in neurons by proteasome dysfunction that may be targeted by novel therapeutic intervention in Parkinson's disease.

Elucidating the Neuroprotective Role of PPARs in Parkinson's Disease: A Neoteric and Prospective Target

One of the utmost frequently emerging neurodegenerative diseases, Parkinson's disease (PD) must be comprehended through the forfeit of dopamine (DA)-generating nerve cells in the substantia nigra pars compacta (SN-PC). The etiology and pathogenesis underlying the emergence of PD is still obscure. However, expanding corroboration encourages the involvement of genetic and environmental factors in the etiology of PD. The destruction of numerous cellular components, namely oxidative stress, ubiquitin-proteasome system (UPS) dysfunction, autophagy-lysosome system dysfunction, neuroinflammation and programmed cell death, and mitochondrial dysfunction partake in the pathogenesis of PD. Present-day pharmacotherapy can alleviate the manifestations, but no therapy has been demonstrated to cease disease progression. Peroxisome proliferator-activated receptors (PPARs) are ligand-directed transcription factors pertaining to the class of nuclear hormone receptors (NHR), and are implicated in the modulation of mitochondrial operation, inflammation, wound healing, redox equilibrium, and metabolism of blood sugar and lipids. Numerous PPAR agonists have been recognized to safeguard nerve cells from oxidative destruction, inflammation, and programmed cell death in PD and other neurodegenerative diseases. Additionally, various investigations suggest that regular administration of PPAR-activating non-steroidal anti-inflammatory drugs (NSAIDs) (ibuprofen, indomethacin), and leukotriene receptor antagonists (montelukast) were related to the de-escalated evolution of neurodegenerative diseases. The present review elucidates the emerging evidence enlightening the neuroprotective outcomes of PPAR agonists in in vivo and in vitro models experiencing PD. Existing articles up to the present were procured through PubMed, MEDLINE, etc., utilizing specific keywords spotlighted in this review. Furthermore, the authors aim to provide insight into the neuroprotective actions of PPAR agonists by outlining the pharmacological mechanism. As a conclusion, PPAR agonists exhibit neuroprotection through modulating the expression of a group of genes implicated in cellular survival pathways, and may be a propitious target in the therapy of incapacitating neurodegenerative diseases like PD.

Connecting the dots between mitochondrial dysfunction and Parkinson's disorder: focus mitochondria-targeting therapeutic paradigm in mitigating the disease severity

Mitochondria are unique cell organelles, which exhibit multifactorial roles in numerous cell physiological processes, significantly preserving the integrity of neural synaptic interconnections, mediating ATP production, and regulating apoptotic signaling pathways and calcium homeostasis. Multiple neurological disorders occur as a consequence of impaired mitochondrial functioning, with greater sensitivity of dopaminergic (DA) neurons to mitochondrial dysfunction, due to oxidative nature and low mitochondrial mass, thus supporting the contribution of mitochondrial impairment in Parkinson's disorder (neuronal damage due to curbed dopamine levels). The pathophysiology of the second most common disorder, PD, is potentiated by various mitochondrial homeostasis regulating genes, as discussed in the review. The PD symptoms are known to be aggravated by multiple mitochondria-linked alterations, like reactive oxygen species (ROS) production, Ca2+ buffering, imbalanced mitochondrial dynamics (fission, fusion, mitophagy), biogenetic dysfunctions, disrupted mitochondrial membrane potential (MMP), protein aggregation, neurotoxins, and genetic mutations, which manifest the central involvement of unhealthy mitochondria in neurodegeneration, resulting in retarded DA neurons in region of substantia nigra pars compacta (SNpc), causing PD. Furthermore, the review tends to target altered mitochondrial components, like oxidative stress, inflammation, biogenetic alterations, impaired dynamics, uncontrolled homeostasis, and genetic mutations, to provide a sustainable and reliable alternative in PD therapeutics and to overcome the pitfalls of conventional therapeutic agents. Therefore, the authors elaborate the relationship between PD pathogenesis and mitochondrial dysfunctions, followed by a suitable mitochondria-targeting therapeutic portfolio, as well as future considerations, aiding the researchers to investigate novel strategies to mitigate the severity of the disease.

Integrative genomics analysis identifies five promising genes implicated in insomnia risk based on multiple omics datasets

In recent decades, many genome-wide association studies on insomnia have reported numerous genes harboring multiple risk variants. Nevertheless, the molecular functions of these risk variants conveying risk to insomnia are still ill-studied. In the present study, we integrated GWAS summary statistics (N=386,533) with two independent brain expression quantitative trait loci (eQTL) datasets (N=329) to determine whether expression-associated SNPs convey risk to insomnia. Furthermore, we applied numerous bioinformatics analyses to highlight promising genes associated with insomnia risk. By using Sherlock integrative analysis, we detected 449 significant insomnia-associated genes in the discovery stage. These identified genes were significantly overrepresented in six biological pathways including Huntington’s disease (P=5.58 × 10⁻⁵), Alzheimer’s disease (P=5.58 × 10⁻⁵), Parkinson’s disease (P=6.34 × 10⁻⁵), spliceosome (P=1.17 × 10⁻⁴), oxidative phosphorylation (P=1.09 × 10⁻⁴), and wnt signaling pathways (P=2.07 × 10⁻⁴). Further, five of these identified genes were replicated in an independent brain eQTL dataset. Through a PPI network analysis, we found that there existed highly functional interactions among these five identified genes. Three genes of LDHA (P=0.044), DALRD3 (P=5.0 × 10⁻⁵), and HEBP2 (P=0.032) showed significantly lower expression level in brain tissues of insomnic patients than that in controls. In addition, the expression levels of these five genes showed prominently dynamic changes across different time points between behavioral states of sleep and sleep deprivation in mice brain cortex. Together, the evidence of the present study strongly suggested that these five identified genes may represent candidate genes and contributed risk to the etiology of insomnia.

Increased telomerase improves motor function and alpha-synuclein pathology in a transgenic mouse model of Parkinson's disease associated with enhanced autophagy

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Telomerase activators (TA) increase Tert expression in brains of a PD mouse model.

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Activator treatment improves PD motor symptoms: gait and balance.

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Activators reduce different forms of alpha-synuclein in brains of transgenic mice.

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Decreased autophagy markers LC3 and p62 suggest a better protein degradation.

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Our preclinical data suggest a use of TA to ameliorate PD-like symptoms.

Protective effects of the telomerase protein TERT have been shown in neurons and brain. We previously demonstrated that TERT protein can accumulate in mitochondria of Alzheimer’s disease (AD) brains and protect from pathological tau in primary mouse neurons. This prompted us to employ telomerase activators in order to boost telomerase expression in a mouse model of Parkinson’s disease (PD) overexpressing human wild type α-synuclein. Our aim was to test whether increased Tert expression levels were able to ameliorate PD symptoms and to activate protein degradation.

We found increased Tert expression in brain for both activators which correlated with a substantial improvement of motor functions such as gait and motor coordination while telomere length in the analysed region was not changed. Interestingly, only one activator (TA-65) resulted in a decrease of reactive oxygen species from brain mitochondria. Importantly, we demonstrate that total, phosphorylated and aggregated α-synuclein were significantly decreased in the hippocampus and neocortex of activator-treated mice corresponding to enhanced markers of autophagy suggesting an improved degradation of toxic alpha-synuclein. We conclude that increased Tert expression caused by telomerase activators is associated with decreased α-synuclein protein levels either by activating autophagy or by preventing or delaying impairment of degradation mechanisms during disease progression. This encouraging preclinical data could be translated into novel therapeutic options for neurodegenerative disorders such as PD.

Degradation of Tyrosine Hydroxylase by the Ubiquitin-Proteasome System in the Pathogenesis of Parkinson's Disease and Dopa-Responsive Dystonia

Nigrostriatal dopaminergic systems govern physiological functions related to locomotion, and their dysfunction leads to movement disorders, such as Parkinson’s disease and dopa-responsive dystonia (Segawa disease). Previous studies revealed that expression of the gene encoding nigrostriatal tyrosine hydroxylase (TH), a rate-limiting enzyme of dopamine biosynthesis, is reduced in Parkinson’s disease and dopa-responsive dystonia; however, the mechanism of TH depletion in these disorders remains unclear. In this article, we review the molecular mechanism underlying the neurodegeneration process in dopamine-containing neurons and focus on the novel degradation pathway of TH through the ubiquitin-proteasome system to advance our understanding of the etiology of Parkinson’s disease and dopa-responsive dystonia. We also introduce the relation of α-synuclein propagation with the loss of TH protein in Parkinson’s disease as well as anticipate therapeutic targets and early diagnosis of these diseases.

Clinical Features of Parkinson's Disease: The Evolution of Critical Symptoms

Parkinson’s disease (PD) is a multi-attribute neurodegenerative disorder combining motor and nonmotor symptoms without well-defined diagnostic clinical markers. The presence of primary motor features (bradykinesia, rest tremor, rigidity and loss of postural reflexes) are the most characteristic signs of PD that are also utilized to identify patients in current clinical practice. The successful implementation of levodopa treatment revealed that nonmotor features are the main contributors of patient disability in PD, and their occurrence might be earlier than motor symptoms during disease progression. Targeted detection of prodromal PD symptoms can open up new possibilities in the identification of PD patients and provide potential patient populations for developing novel neuroprotective therapies. In this review, the evolution of critical features in PD diagnosis is described with special attention to nonmotor symptoms and their possible detection.

Effect of Curcumin on Protein Damage Induced by Rotenone in Dopaminergic PC12 Cells

Oxidative stress is considered to be a key factor of the pathogenesis of Parkinson's disease, a multifactorial neurodegenerative disorder characterized by reduced dopaminergic neurons in the substantia nigra pars compacta and accumulated protein aggregates. Rotenone is a worldwide-used pesticide that induces the most common features of Parkinson's by direct inhibition of the mitochondrial complex I. Rotenone-induced Parkinson's models, as well as brain tissues from Parkinson's patients, are characterized by the presence of both lipid peroxidation and protein oxidation markers resulting from the increased level of free radical species. Oxidation introduces several modifications in protein structure, including carbonylation and nitrotyrosine formation, which severely compromise cell function. Due to the link existing between oxidative stress and Parkinson's disease, antioxidant molecules could represent possible therapeutic tools for this disease. In this study, we evaluated the effect of curcumin, a natural compound known for its antioxidant properties, in dopaminergic PC12 cells treated with rotenone, a cell model of Parkinsonism. Our results demonstrate that the treatment of PC12 cells with rotenone causes severe protein damage, with formation of both carbonylated and nitrotyrosine-derived proteins, whereas curcumin (10 µM) co-exposure exerts protective effects by reducing the levels of oxidized proteins. Curcumin also promotes proteasome activation, abolishing the inhibitory effect exerted by rotenone on this degradative system.

Adhesion Molecule L1 Agonist Mimetics Protect Against the Pesticide Paraquat-Induced Locomotor Deficits and Biochemical Alterations in Zebrafish

Besides several endogenous elements, exogenous factors, including exposure to pesticides, have been recognized as putative factors contributing to the onset and development of neurodegenerative diseases, including Parkinson's disease (PD). Considering the availability, success rate, and limitations associated with the current arsenals to fight PD, there is an unmet need for novel therapeutic interventions. Therefore, based on the previously reported beneficial functions of the L1 cell adhesion molecule, we hypothesized that L1 mimetic compounds may serve to neutralize neurotoxicity triggered by the pesticide paraquat (PQ). In this study, we attempt to use PQ for inducing PD-like pathology and the L1 mimetic compounds phenelzine sulfate (PS) and tacrine (TC) as potential candidates for the amelioration of PD symptoms using zebrafish as a model system. Administration of PQ together with the L1 mimetic compounds PS or TC (250 nM) improved survival of zebrafish larvae, protected them from locomotor deficits, and increased their sensorimotor reflexes. Moreover, application of PQ together with PS (500 nM) or TC (1000 nM) in adult zebrafish counteracted PQ-induced toxicity, maintaining normal locomotor functions and spatial memory in an open field and T-maze task, respectively. Both L1 mimetic compounds prevented reduction in tyrosine hydroxylase and dopamine levels, reduced reactive oxygen species (ROS) generation, protected against impairment of mitochondrial viability, improved the antioxidant enzyme system, and prevented a decrease in ATP levels. Altogether, our findings highlight the beneficial functions of the agonistic L1 mimetics PS and TC by improving several vital cell functions against PQ-triggered neurotoxicity.

Adhesion Molecule L1 Agonist Mimetics Protect Against the Pesticide Paraquat-Induced Locomotor Deficits and Biochemical Alterations in Zebrafish

Besides several endogenous elements, exogenous factors, including exposure to pesticides, have been recognized as putative factors contributing to the onset and development of neurodegenerative diseases, including Parkinson's disease (PD). Considering the availability, success rate, and limitations associated with the current arsenals to fight PD, there is an unmet need for novel therapeutic interventions. Therefore, based on the previously reported beneficial functions of the L1 cell adhesion molecule, we hypothesized that L1 mimetic compounds may serve to neutralize neurotoxicity triggered by the pesticide paraquat (PQ). In this study, we attempt to use PQ for inducing PD-like pathology and the L1 mimetic compounds phenelzine sulfate (PS) and tacrine (TC) as potential candidates for the amelioration of PD symptoms using zebrafish as a model system. Administration of PQ together with the L1 mimetic compounds PS or TC (250 nM) improved survival of zebrafish larvae, protected them from locomotor deficits, and increased their sensorimotor reflexes. Moreover, application of PQ together with PS (500 nM) or TC (1000 nM) in adult zebrafish counteracted PQ-induced toxicity, maintaining normal locomotor functions and spatial memory in an open field and T-maze task, respectively. Both L1 mimetic compounds prevented reduction in tyrosine hydroxylase and dopamine levels, reduced reactive oxygen species (ROS) generation, protected against impairment of mitochondrial viability, improved the antioxidant enzyme system, and prevented a decrease in ATP levels. Altogether, our findings highlight the beneficial functions of the agonistic L1 mimetics PS and TC by improving several vital cell functions against PQ-triggered neurotoxicity.

Rosmarinic acid protects against MPTP-induced toxicity and inhibits iron-induced α-synuclein aggregation

Rosmarinic acid (RA) is a naturally occurring polyphenolic compound. In this study, we demonstrated that RA could protect against the degeneration of the nigrostriatal dopaminergic system in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced mouse model of Parkinson's disease (PD). In addition, RA could inhibit MPTP-induced decrease of superoxide dismutase (SOD) and tyrosine hydroxylase (TH) and increase in nigral iron content. Further studies elucidated the effects of RA on iron-induced neurotoxicity and the possible underlying mechanisms in the SK-N-SH cells. Results showed that iron could induce a decrease in the mitochondrial transmembrane potential and result in α-synuclein aggregation in the SK-N-SH cells, which could be restored by RA pretreatment. Further results showed RA pretreatment could inhibit iron-induced α-synuclein aggregation by up-regulating hemeoxygenase-1 (HO-1). In addition, iron could increase the mRNA levels of α-synuclein via iron responsive element/iron regulatory protein (IRE/IRP) system. RA pretreatment could decrease the mRNA levels of α-synuclein by decreasing the protein levels of IRP1. These results indicated that RA protected against iron-induced α-synuclein aggregation by up-regulating HO-1 and inhibiting α-synuclein expression.

Differential protein expression of hippocampal cells associated with heavy metals (Pb, As, and MeHg) neurotoxicity: Deepening into the molecular mechanism of neurodegenerative diseases

Chronic exposure to heavy metals such as Pb, As, and MeHg can be associated with an increased risk of developing neurodegenerative diseases. Our in vitro bioassays results showed the potency of heavy metals in the order of Pb < As < MeHg on hippocampal cells. The main objective of this study was combining in vitro label free proteomics and systems biology approach for elucidating patterns of biological response, discovering underlying mechanisms of Pb, As, and MeHg toxicity in hippocampal cells. The omics data was refined by using different filters and normalization and multilevel analysis tools were employed to explore the data visualization. The functional and pathway visualization was performed by using Gene ontology and PathVisio tools. Using these all integrated approaches, we identified significant proteins across treatments within the mitochondrial dysfunction, oxidative stress, ubiquitin proteome dysfunction, and mRNA splicing related to neurodegenerative diseases. The systems biology analysis revealed significant alterations in proteins implicated in Parkinson's disease (PD) and Alzheimer's disease (AD). The current proteomics analysis of three metals support the insight into the proteins involved in neurodegeneration and the altered proteins can be useful for metal-specific biomarkers of exposure and its adverse effects.

SIGNIFICANCE

The proteomics techniques have been claimed to be more sensitive than the conventional toxicological assays, facilitating the measurement of responses to heavy metals (Pb, As, and MeHg) exposure before obvious harm has occurred demonstrating their predictive value. Also, proteomics allows for the comparison of responses between Pb, As, and MeHg metals, permitting the evaluation of potency differences hippocampal cells of the brain. Hereby, the molecular information provided by pathway and gene functional analysis can be used to develop a more thorough understanding of each metal mechanism at the protein level for different neurological adverse outcomes (e.g. Parkinson's disease, Alzheimer's diseases). Efforts are put into developing proteomics based toxicity testing methods using in vitro models for improving human risk assessment. Some of the key proteins identified can also potentially be used as biomarkers in epidemiologic studies. These heavy metal response patterns shed new light on the mechanisms of mRNA splicing, ubiquitin pathway role in neurodegeneration, and can be useful for the development of molecular biomarkers of heavy metals exposure.

The Neuroprotective Effect of Dimethyl Fumarate in an MPTP-Mouse Model of Parkinson's Disease: Involvement of Reactive Oxygen Species/Nuclear Factor-κB/Nuclear Transcription Factor Related to NF-E2

AIM

Oxidative stress plays a key role in Parkinson disease (PD), and nuclear transcription factor related to NF-E2 (Nrf-2) is involved in neuroprotection against PD. The aim of the present study was to investigate a role for nuclear factor-κB (NF-κB)/Nrf-2 in the neurotherapeutic action of dimethyl fumarate (DMF) in a mouse model of PD and in vitro in SHSY-5Y cells.

RESULTS

Daily oral gavage of DMF (10, 30, and 100 mg/kg) significantly reduced neuronal cell degeneration of the dopaminergic tract and behavioral impairments induced by four injections of the dopaminergic neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. Moreover, treatment with DMF prevented dopamine depletion, increased tyrosine hydroxylase and dopamine transporter activities, and also reduced the number of α-synuclein-positive neurons. Furthermore, DMF treatment upregulated the Nrf-2 pathway, increased NeuN⁺/Nrf-2⁺ cell number in the striatum, induced activation of manganese superoxide dismutase and heme oxygenase-1, and regulated glutathione levels. Moreover, DMF reduced interleukin 1 levels, cyclooxygenase 2 activity, and nitrotyrosine neuronal nitrite oxide synthase expression. This treatment also modulated microglia activation, restored nerve growth factor levels, and preserved microtubule-associated protein 2 alterations. The protective effects of DMF treatment, via Nrf-2, were confirmed in in vitro studies, through inhibition of Nrf-2 by trigonelline.

INNOVATION

These findings demonstrate that DMF, both in a mouse model of PD and in vitro, provides, via regulation of the NF-κB/Nrf-2 pathway, novel cytoprotective modalities that further augment the natural antioxidant response in neurodegenerative and inflammatory disease models.

CONCLUSION

These results support the thesis that DMF may constitute a promising therapeutic target for the treatment of PD. Antioxid. Redox Signal. 27, 453-471.

Adverse outcome pathways: Application to enhance mechanistic understanding of neurotoxicity

Recent developments have prompted the transition of empirically based testing of late stage toxicity in animals for a range of different endpoints including neurotoxicity to more efficient and predictive mechanistically based approaches with greater emphasis on measurable key events early in the progression of disease. The adverse outcome pathway (AOP) has been proposed as a simplified organizational construct to contribute to this transition by linking molecular initiating events and earlier (more predictive) key events at lower levels of biological organization to disease outcomes. As such, AOPs are anticipated to facilitate the compilation of information to increase mechanistic understanding of pathophysiological pathways that are responsible for human disease.

In this review, the sequence of key events resulting in adverse outcome (AO) defined as parkinsonian motor impairment and learning and memory deficit in children, triggered by exposure to environmental chemicals has been briefly described using the AOP framework. These AOPs follow convention adopted in an Organization for Economic Cooperation and Development (OECD) AOP development program, publically available, to permit tailored application of AOPs for a range of different purposes.

Due to the complexity of disease pathways, including neurodegenerative disorders, a specific symptom of the disease (e.g. parkinsonian motor deficit) is considered as the AO in a developed AOP. Though the description is necessarily limited by the extent of current knowledge, additional characterization of involved pathways through description of related AOPs interlinked into networks for the same disease has potential to contribute to more holistic and mechanistic understanding of the pathophysiological pathways involved, possibly leading to the mechanism-based reclassification of diseases, thus facilitating more personalized treatment.

Paraquat and Parkinson's disease: a systematic review protocol according to the OHAT approach for hazard identification

BACKGROUND

Parkinson's disease (PD) is a progressive neurodegenerative condition that has genetic susceptibility, aging, and exposure to certain chemicals as risk factors. In recent decades, epidemiological and experimental studies have investigated the role of pesticides in the development of PD, in particular that of the herbicide paraquat. Here, we, therefore, aim to systematically review the association between paraquat exposure and PD.

METHODS

Observational studies (cohort, case-control, and cross-sectional) eligible for this systematic review will enroll any participant who was occupationally and/or environmentally exposed to paraquat. Experimental studies, including in vivo and in vitro assays designed to assess neurotoxicological endpoints or mechanisms of paraquat neurotoxicity, will also be eligible. Outcomes of interest include the following: PD diagnosis; neurobehavioral, biochemical, and/or morphological alterations; and cellular, biochemical, and/or molecular pathways to oxidative stress. Using terms to include all forms of paraquat combined with PD, the following electronic databases will be searched: PubMed, EMBASE, LILACS, Toxnet, and Web of Science, without restrictions as to language, year, or status of publication. A team of reviewers will independently select potential titles and abstracts, extract data, assess risk of bias, and determine the overall quality of evidence for each outcome using the Office of Health Assessment and Translation (OHAT) approach for systematic reviews and evidence integration. Dichotomous data will be summarized as odds ratios, and continuous data will be given as mean differences, both with their respective 95% confidence intervals.

DISCUSSION

This is the first time that the OHAT systematic review protocol will be applied to investigate a possible causal association between exposure to paraquat and PD. Results from this study could serve as basis for regulatory agencies to define paraquat levels of concern, supporting its risk assessment process.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42016050861.

Role of Chaperone-Mediated Autophagy Dysfunctions in the Pathogenesis of Parkinson's Disease

Chaperone-mediated autophagy (CMA) represents a selective form of autophagy involved in the degradation of specific soluble proteins containing a pentapeptide motif that is recognized by a cytosolic chaperone able to deliver proteins to the lysosomes for degradation. Physiologically, CMA contributes to maintain crucial cellular functions including energetic balance and protein quality control. Dysfunctions in CMA have been associated to the pathogenesis of several neurodegenerative diseases characterized by accumulation and aggregation of proteins identified as CMA substrates. In particular, increasing evidence highlights the existence of a strong relationship between CMA defects and Parkinson’s disease (PD). Several mutations associated with familial forms of PD (SNCA, LRRK2, UCHL1 and DJ-1) have been demonstrated to block or reduce the activity of CMA, the main catabolic pathway for alpha-synuclein (asyn). CMA dysfunctions also leads to a mislocalization and inactivation of the transcription factor MEF2D that plays a key-role in the survival of dopaminergic neurons. Furthermore, reduced levels of CMA markers have been observed in post mortem brain samples from PD patients. The aim of this review article is to provide an organic revision of evidence for the involvement of CMA dysfunctions in the pathogenesis of PD. Updated findings obtained in patient’s specimens will be resumed, and results deriving from in vivo and in vitro studies will be discussed to evidence the current knowledge on the molecular mechanisms underlying CMA alterations in PD. Finally, the possibility of up-regulating CMA pathway as promising neuroprotective strategy will be considered.

Disease-Toxicant Interactions in Parkinson's Disease Neuropathology

Human disease commonly manifests as a result of complex genetic and environmental interactions. In the case of neurodegenerative diseases, such as Parkinson's disease (PD), understanding how environmental exposures collude with genetic polymorphisms in the central nervous system to cause dysfunction is critical in order to develop better treatment strategies, therapies, and a more cohesive paradigm for future research. The intersection of genetics and the environment in disease etiology is particularly relevant in the context of their shared pathophysiological mechanisms. This review offers an integrated view of disease-toxicant interactions in PD. Particular attention is dedicated to how mutations in the genes SNCA, parkin, leucine-rich repeat kinase 2 (LRRK2) and DJ-1, as well as dysfunction of the ubiquitin proteasome system, may contribute to PD and how exposure to heavy metals, pesticides and illicit drugs may further the consequences of these mutations to exacerbate PD and PD-like disorders. Although the toxic effects induced by exposure to these environmental factors may not be the primary causes of PD, their mechanisms of action are critical for our current understanding of the neuropathologies driving PD. Elucidating how environment and genetics collude to cause pathogenesis of PD will facilitate the development of more effective treatments for the disease. Additionally, we discuss the neuroprotection exerted by estrogen and other compounds that may prevent PD and provide an overview of current treatment strategies and therapies.

Redox Modulations, Antioxidants, and Neuropsychiatric Disorders

Although antioxidants, redox modulations, and neuropsychiatric disorders have been widely studied for many years, the field would benefit from an integrative and corroborative review. Our primary objective is to delineate the biological significance of compounds that modulate our redox status (i.e., reactive species and antioxidants) as well as outline their current role in brain health and the impact of redox modulations on the severity of illnesses. Therefore, this review will not enter into the debate regarding the perceived medical legitimacy of antioxidants but rather seek to clarify their abilities and limitations. With this in mind, antioxidants may be interpreted as natural products with significant pharmacological actions in the body. A renewed understanding of these often overlooked compounds will allow us to critically appraise the current literature and provide an informed, novel perspective on an important healthcare issue. In this review, we will introduce the complex topics of redox modulations and their role in the development of select neuropsychiatric disorders.

Neuroprotective effect of modified Chungsimyeolda-tang, a traditional Korean herbal formula, via autophagy induction in models of Parkinson's disease

AIM OF THE STUDY

Previous studies in our laboratory revealed the neuroprotective effect of modified Yeoldahanso-tang (MYH) in models of Parkinson׳s disease (PD). In this study, we investigated another traditional Korean herbal formula, modified Chungsimyeolda-tang (termed DG), as a potential treatment for PD. Chungsimyeolda-tang has been used in Korea to treat cerebrovascular diseases, such as stroke. Here, we verify the neuroprotective and autophagy-inducing effects of DG to evaluate any potential anti-parkinsonian properties.

MATERIALS AND METHODS

1-Methyl-4-phenylpyridinium (MPP(+)) and rotenone were used to induce cytotoxicity in nerve growth factor (NGF)-differentiated rat pheochromocytoma (PC12) cells. Cell viability was measured using an MTT assay. Induction of autophagy by DG in NGF-differentiated PC12 cells was measured using an immunoblotting assay with an LC3 antibody. The proteasomal inhibitor lactacystin was used to induce ubiquitin-proteasome system (UPS) dysfunction in NGF-differentiated PC12 cells. DG-mediated clearance of aggregated proteins was measured using an immunoblotting assay with a ubiquitin antibody.

RESULTS AND CONCLUSIONS

Our findings indicate that DG robustly protects NGF-differentiated PC12 cells against the neurotoxic effects of MPP(+) and rotenone in an in vitro model. Furthermore, DG protects NGF-differentiated PC12 cells against lactacystin-induced cell death. This effect is partially mediated by an increased autophagy associated with the enhanced degradation of aggregated proteins. This study suggests that DG is an attractive candidate drug for inducing autophagy and, therefore, may represent a promising strategy to prevent diseases associated with misfolded/aggregated proteins in various neurodegenerative disorders, including Parkinson׳s disease.

Proteasome Inhibitor Lactacystin Induces Cholinergic Degeneration

Objective:

Ubiquitin proteasome system dysfunction is believed to play an important role in the development of Parkinson's disease (PD), and almost all studies till now have mainly focused on the susceptibility of dopaminergic neurons to proteasome inhibition. However, in fact, there are many other types of neurons such as cholinergic ones involved in PD. In our present study, we attempt to figure out what effect the failure of ubiquitin proteasome function would execute on cholinergic cells in culture.

Methods:

We treated cholinergic cells in culture with various doses of lactacystin. Then MTT assay was used to evaluate the cellular viability and the Annexin V-PI method was used to detect apoptosis. Both cellular soluble and insoluble polyubiquitinated proteins were detected by western blot. Furthermore, the mitochondrial membrane potential was analyzed using JC-1 and the intracellular production of reactive oxygen species (ROS) was determined using the fluorescent probe CM-H2DCFDA.

Results:

We found that low doses of lactacystin were enough to induce significant apoptotic cell death, disturb the mitochondrial membrane potential, and cause oxidative stress. We also found that the amounts of polyubiquitinated proteins dramatically increased with high doses, although the loss of cells did not increase accordingly.

Conclusions:

Our results suggest that cholinergic cells are sensitive to ubiquitin proteasome system dysfunction, which exerts its toxic effect by causing mitochondrial dysfunction and subsequent oxidative stress, not through polyubiquitinated proteins accumulation.

Quinone-induced protein handling changes: implications for major protein handling systems in quinone-mediated toxicity

Para-quinones such as 1,4-Benzoquinone (BQ) and menadione (MD) and ortho-quinones including the oxidation products of catecholamines, are derived from xenobiotics as well as endogenous molecules. The effects of quinones on major protein handling systems in cells; the 20/26S proteasome, the ER stress response, autophagy, chaperone proteins and aggresome formation, have not been investigated in a systematic manner. Both BQ and aminochrome (AC) inhibited proteasomal activity and activated the ER stress response and autophagy in rat dopaminergic N27 cells. AC also induced aggresome formation while MD had little effect on any protein handling systems in N27 cells. The effect of NQO1 on quinone induced protein handling changes and toxicity was examined using N27 cells stably transfected with NQO1 to generate an isogenic NQO1-overexpressing line. NQO1 protected against BQ-induced apoptosis but led to a potentiation of AC- and MD-induced apoptosis. Modulation of quinone-induced apoptosis in N27 and NQO1-overexpressing cells correlated only with changes in the ER stress response and not with changes in other protein handling systems. These data suggested that NQO1 modulated the ER stress response to potentiate toxicity of AC and MD, but protected against BQ toxicity. We further demonstrated that NQO1 mediated reduction to unstable hydroquinones and subsequent redox cycling was important for the activation of the ER stress response and toxicity for both AC and MD. In summary, our data demonstrate that quinone-specific changes in protein handling are evident in N27 cells and the induction of the ER stress response is associated with quinone-mediated toxicity.

Alteration of striatal tetrahydrobiopterin in iron-induced unilateral model of Parkinson's disease

It has been suggested that transition metal ions such as iron can produce an oxidative injuries to nigrostriatal dopaminergic neurons, like Parkinson's disease (PD) and subsequent compensative increase of tetrahydrobiopterin (BH₄) during the disease progression induces the aggravation of dopaminergic neurodegeneration in striatum. It had been established that the direct administration of BH₄ into neuron would induce the neuronal toxicity in vitro. To elucidate a role of BH₄ in pathogenesis in the PD in vivo, we assessed the changes of dopamine (DA) and BH₄ at striatum in unilateral intranigral iron infused PD rat model. The ipsistriatal DA and BH₄ levels were significantly increased at 0.5 to 1 d and were continually depleting during 2 to 7 d after intranigral iron infusion. The turnover rate of BH₄ was higher than that of DA in early phase. However, the expression level of GTP-cyclohydrolase I mRNA in striatum was steadily increased after iron administration. These results suggest that the accumulation of intranigral iron leads to generation of oxidative stress which damage to dopaminergic neurons and causes increased release of BH₄ in the dopaminergic neuron. The degenerating dopaminergic neurons decrease the synthesis and release of both BH4 and DA in vivo that are relevance to the progression of PD. Based on these data, we propose that the increase of BH₄ can deteriorate the disease progression in early phase of PD, and the inhibition of BH4 increase could be a strategy for PD treatment.

NAC1, A POZ/BTB protein interacts with Parkin and may contribute to Parkinson's disease

Loss-of-function in the Parkin protein is thought to play a part in causing neuronal cell death in patients with Parkinson's disease. This study explores the effect of Parkin degradation, via the overexpression of nucleus accumbens 1 (NAC1), on cell viability. It was found that NAC1 and Parkin are co-localized within the cell and interact with one another, leading to a decrease in Parkin levels. Moreover, NAC1 down-regulates Parkin by presenting it for ubiquitin-dependent proteasome degradation, which causes a decrease in proteasomal activity in neuronal cells. Consequently, this decrease in proteasomal activity leads to an increase in the cells' susceptibility to proteasome inhibition-induced toxicity. It was also found that Parkin and NAC1 are key proteins found to be present mainly in the cytoplasm and are co-localized in neurons of Parkinson's disease patients. Interestingly, mutation in the POZ/BTB domain (Q23L) of NAC1 disrupts the co-localization and interaction of NAC1 with Parkin and it further abrogates the proteasome inhibition-induced toxicity. We further observed that co-transfection of the mutant form of NAC1 with Parkin reversed the proteasome activity and 20S proteasome protein levels. These results indicate a novel interaction between NAC1 and Parkin that leads to neuronal cell death, a main characteristic in Parkinson's disease.

The innate and adaptive immunological aspects in neurodegenerative diseases

Neurodegenerative diseases affect a considerable percentage of the elderly population. New therapeutic approaches are warranted, aiming to at least delay and possibly reverse disease progression. Strategies to elaborate such approaches require knowledge of specific immune system involvement in disease pathogenesis. In this review, innate and adaptive immunological aspects of neurodegenerative disorders, in particular Parkinson's disease, Alzheimer's disease, and amyotrophic lateral sclerosis (ALS), are discussed. Initiating disease factors, as well as common mechanistic pathways, are detailed and potential immunological therapeutic targets are identified.

The activation sequence of cellular protein handling systems after proteasomal inhibition in dopaminergic cells

Dysfunction of protein handling has been implicated in many neurodegenerative diseases and inhibition of the ubiquitin-proteasome system (UPS) has been linked to the formation of protein aggregates and proteinopathies in such diseases. While proteasomal inhibition could trigger an array of downstream protein handling changes including up-regulation of heat shock proteins (HSPs), induction of molecular chaperones, activation of the ER stress/unfolded protein response (UPR), autophagy and aggresome formation, little is known of the relationship of proteasomal inhibition to the sequence of activation of these diverse protein handling systems. In this study we utilized the reversible proteasome inhibitor MG132 and examined the activity of several major protein handling systems in the immortalized dopaminergic neuronal N27 cell line. In the early phase (up to 6h after proteasomal inhibition), MG132 induced time-dependent proteasomal inhibition which resulted in stimulation of the UPR, increased autophagic flux and stimulated heat shock protein response as determined by increased levels of phosphorylation of the eukaryotic translation initiation factor 2 alpha (eIF2α), C/EBP homologous protein (CHOP)/GADD153, turnover of autophagy related microtubule-associated protein 1 light chain 3 (LC3) and increased levels of Hsp70 respectively. After prolonged proteasomal inhibition induced by MG132, we observed the formation of vimentin-caged aggresome-like inclusion bodies. A recovery study after MG132-induced proteasomal inhibition indicated that the autophagy-lysosomal pathway participated in the clearance of aggresomes. Our data characterizes the relationship between proteasome inhibition and activation of other protein handling systems. These data also indicated that the induction of alternate protein handling systems and their temporal relationships may be important factors that determine the extent of accumulation of misfolded proteins in cells as a result of proteasome inhibition.

Retinoic acid protects against proteasome inhibition associated cell death in SH-SY5Y cells via the AKT pathway

Inhibition of proteasome activity and the resulting protein accumulation are now known to be important events in the development of many neurological disorders, including Alzheimer's and Parkinson's diseases. Abnormal or over expressed proteins cause endoplasmic reticulum and oxidative stress leading to cell death, thus, normal proteasome function is critical for their removal. We have shown previously, with cultured SH-SY5Y neuroblastoma cells, that proteasome inhibition by the drug epoxomicin results in accumulation of ubiquitinated proteins. This causes obligatory loading of the mitochondria with calcium (Ca(2+)), resulting in mitochondrial damage and cytochrome c release, followed by programmed cell death (PCD). In the present study, we demonstrate that all-trans-retinoic acid (RA) pretreatment of SH-SY5Y cells protects them from PCD death after subsequent epoxomicin treatment which causes proteasome inhibition. Even though ubiquitinated protein aggregates are present, there is no evidence to suggest that autophagy is involved. We conclude that protection by RA is likely by mechanisms that interfere with cell stress-PCD pathway that otherwise would result from protein accumulation after proteasome inhibition. In addition, although RA activates both the AKT and ERK phosphorylation signaling pathways, only pretreatment with LY294002, an inhibitor of PI3-kinase in the AKT pathway, removed the protective effect of RA from the cells. This finding implies that RA activation of the AKT signaling cascade takes precedence over its activation of ERK1/2 phosphorylation, and that this selective effect of RA is key to its protection of epoxomicin-treated cells. Taken together, these findings suggest that RA treatment of cultured neuroblastoma cells sets up conditions under which proteasome inhibition, and the resultant accumulation of ubiquitinated proteins, loses its ability to kill the cells and may likely play a therapeutic role in neurodegenerative diseases.

Biology of Parkinson's disease: pathogenesis and pathophysiology of a multisystem neurodegenerative disorder

Parkinson's disease (PD) is the second most common movement disorder. The characteristic motor impairments - bradykinesia, rigidity, and resting tremor - result from degenerative loss of midbrain dopamine (DA) neurons in the substantia nigra, and are responsive to symptomatic treatment with dopaminergic medications and functional neurosurgery. PD is also the second most common neurodegenerative disorder. Viewed from this perspective, PD is a disorder of multiple functional systems, not simply the motor system, and of multiple neurotransmitter systems, not merely that of DA. The characteristic pathology - intraneuronal Lewy body inclusions and reduced numbers of surviving neurons - is similar in each of the targeted neuron groups, suggesting a common neurodegenerative process. Pathological and experimental studies indicate that oxidative stress, proteolytic stress, and inflammation figure prominently in the pathogenesis of PD. Yet, whether any of these mechanisms plays a causal role in human PD is unknown, because to date we have no proven neuroprotective therapies that slow or reverse disease progression in patients with PD. We are beginning to understand the pathophysiology of motor dysfunction in PD, but its etiopathogenesis as a neurodegenerative disorder remains poorly understood.

Excess α-synuclein worsens disease in mice lacking ubiquitin carboxy-terminal hydrolase L1

Mutations in α-synuclein (αSN) and ubiquitin carboxy-terminal hydrolase L1 (UCH-L1) have been linked to familial Parkinson's disease (PD). Physical and functional interactions between these two proteins have been described. Whether they act additively in vivo to influence disease has remained controversial. αSN is a presynaptic protein and the major constituent of Lewy inclusions, histopathological hallmarks of PD. UCH-L1 regulates ubiquitin stability in the nervous system and its loss results in neurodegeneration in peripheral and central neurons. Here, we used genetics to show that UCH-L1-deficiency together with excess αSN worsen disease. Double mutant mice show earlier-onset motor deficits, a shorter lifespan and forebrain astrogliosis but the additive disease-worsening effects of UCH-L1-deficiency and excess αSN are not accompanied by microgliosis, ubiquitin pathology or changes in pathological αSN protein levels and species.

A Wnt1 regulated Frizzled-1/β-Catenin signaling pathway as a candidate regulatory circuit controlling mesencephalic dopaminergic neuron-astrocyte crosstalk: Therapeutical relevance for neuron survival and neuroprotection

BACKGROUND

Dopamine-synthesizing (dopaminergic, DA) neurons in the ventral midbrain (VM) constitute a pivotal neuronal population controlling motor behaviors, cognitive and affective brain functions, which generation critically relies on the activation of Wingless-type MMTV integration site (Wnt)/β-catenin pathway in their progenitors. In Parkinson's disease, DA cell bodies within the substantia nigra pars compacta (SNpc) progressively degenerate, with causes and mechanisms poorly understood. Emerging evidence suggests that Wnt signaling via Frizzled (Fzd) receptors may play a role in different degenerative states, but little is known about Wnt signaling in the adult midbrain. Using in vitro and in vivo model systems of DA degeneration, along with functional studies in both intact and SN lesioned mice, we herein highlight an intrinsic Wnt1/Fzd-1/β-catenin tone critically contributing to the survival and protection of adult midbrain DA neurons.

RESULTS

In vitro experiments identifie Fzd-1 receptor expression at a mRNA and protein levels in dopamine transporter (DAT) expressing neurons, and demonstrate the ability of exogenous Wnt1 to exert robust neuroprotective effects against Caspase-3 activation, the loss of tyrosine hydroxylase-positive (TH+) neurons and [3H] dopamine uptake induced by different DA-specific insults, including serum and growth factor deprivation, 6-hydroxydopamine and MPTP/MPP+. Co-culture of DA neurons with midbrain astrocytes phenocopies Wnt1 neuroprotective effects, whereas RNA interference-mediated knockdown of Wnt1 in midbrain astrocytes markedly reduces astrocyte-induced TH+ neuroprotection. Likewise, silencing β-catenin mRNA or knocking down Fzd-1 receptor expression in mesencephalic neurons counteract astrocyte-induced TH+ neuroprotection. In vivo experiments document Fzd-1 co-localization with TH+ neurons within the intact SNpc and blockade of Fzd/β-catenin signaling by unilateral infusion of a Fzd/β-catenin antagonist within the SN induces reactive astrocytosis and acutely inhibits TH+ neuron survival in ipsilateral SNpc, an effect efficiently prevented by pharmacological activation of β-catenin signaling within the SNpc.

CONCLUSION

These results defining a novel Wnt1/Fzd-1/β-catenin astrocyte-DA autoprotective loop provide a new mechanistic inside into the regulation of pro-survival processes, with potentially relevant consequences for drug design or drug action in Parkinson's disease.

Proteasome inhibition induces α-synuclein SUMOylation and aggregate formation

Parkinson's disease (PD) and Dementia with Lewy Bodies (DLB) are characterized pathologically by intraneuronal inclusions called Lewy bodies (LBs) and Lewy neurites. A major component of these inclusions is the protein α-synuclein, which is natively unfolded but forms oligomers and insoluble fibrillar aggregates under pathological conditions. Although α-synuclein is known to undergo several posttranslational modifications, the contribution of SUMOylation to α-synuclein aggregation and the pathogenesis of α-synucleinopathies have not been elucidated. Here, we provide evidence that aggregates and inclusions formed as a result of impaired proteasome activity contain SUMOylated α-synuclein. Additionally, SUMO1 is present in the halo of LBs colocalizing with α-synuclein in the brains of PD and DLB patients. Interestingly, SUMOylation does not affect the ubiquitination of α-synuclein. These findings suggest that proteasomal dysfunction results in the accumulation of SUMOylated α-synuclein and subsequently its aggregation, pointing to the contribution of this posttranslational modification to the pathogenesis of inclusion formation in α-synucleinopathies.

Epidemiology and etiology of Parkinson's disease: a review of the evidence

The etiology of Parkinson's disease (PD) is not well understood but likely to involve both genetic and environmental factors. Incidence and prevalence estimates vary to a large extent-at least partly due to methodological differences between studies-but are consistently higher in men than in women. Several genes that cause familial as well as sporadic PD have been identified and familial aggregation studies support a genetic component. Despite a vast literature on lifestyle and environmental possible risk or protection factors, consistent findings are few. There is compelling evidence for protective effects of smoking and coffee, but the biologic mechanisms for these possibly causal relations are poorly understood. Uric acid also seems to be associated with lower PD risk. Evidence that one or several pesticides increase PD risk is suggestive but further research is needed to identify specific compounds that may play a causal role. Evidence is limited on the role of metals, other chemicals and magnetic fields. Important methodological limitations include crude classification of exposure, low frequency and intensity of exposure, inadequate sample size, potential for confounding, retrospective study designs and lack of consistent diagnostic criteria for PD. Studies that assessed possible shared etiological components between PD and other diseases show that REM sleep behavior disorder and mental illness increase PD risk and that PD patients have lower cancer risk, but methodological concerns exist. Future epidemiologic studies of PD should be large, include detailed quantifications of exposure, and collect information on environmental exposures as well as genetic polymorphisms.

Insulin-like growth factor-I mediates neuroprotection in proteasome inhibition-induced cytotoxicity in SH-SY5Y cells

The proteasome is an enzyme complex responsible for targeted intracellular proteolysis. Alterations in proteasome-mediated protein clearance have been implicated in the pathogenesis of aging, Alzheimer's disease (AD) and Parkinson's disease (PD). In such diseases, proteasome inhibition may contribute to formation of abnormal protein aggregates, which in turn activate intracellular unfolded protein responses that cause oxidative stress and apoptosis. In this study, we investigated the protective effect of Insulin-like Growth Factor-I (IGF-1) for neural SH-SY5Y cells treated with the proteasomal inhibitor, Epoxomicin. In SH-SY5Y cells, Epoxomicin treatment results in accumulation of intracellular ubiquitinated proteins and cytochrome c release from damaged mitochondria, leading to cell death, in Epoxomicin time- and dose-dependent manner. In cells treated with small amounts of IGF-1, the same dosages of Epoxomicin reduced both mitochondrial damage (cytochrome c release) and reduced caspase-3 activation and PARP cleavage, both of which are markers of apoptosis. Notably, however, IGF-1-treated SH-SY5Y cells still contained ubiquitinated protein aggregates. This result indicates that IGF-1 blocks the downstream apoptotic consequences of Epoxomicin treatment leading to decreased proteasome function. Clues as to the mechanism for this protective effect come from (a) increased AKT phosphorylation observed in IGF-1-protected cells, vs. cells exposed to Epoxomicin without IGF-1, and (b) reduction of IGF-1 protection by pretreatment of the cells with LY294002 (an inhibitor of PI3-kinase). Together these findings suggest that activation of PI3/AKT pathways by IGF-1 is involved in IGF-1 neuroprotection against apoptosis following proteasome inhibition.

The neuroprotective effect of modified Yeoldahanso-tang via autophagy enhancement in models of Parkinson's disease

AIM OF STUDY

Modified Yeoldahanso-tang (MYH) is a Korean herbal formula, containing 10 herbs: Pueraria lobata (Willd.) Ohwi, Angelica tenuissima Nakai, Scutellaria baicalensis Georgi, Platycodon grandiflorum (Jacq), Angelicae Dahurica, Cimicifuga heracleifolia Kom, Raphanus sativa L., Polygala tenuifolia (Willd.), Acorus gramineus Soland. and Dimocarpus longan Lour. The constitutive ratio of the ten herbs is at 6:4:2:1:2:2:2:4:6:6 in dry weight. MYH has been used to treat amnesia, hypochondria and dementia in Korea. In this study, we explored the possibility of using MYH in the prevention and treatment of Parkinson's disease (PD). Specifically, we made an effort to demonstrate the neuroprotective effects of MYH using experimental methods similar to those used in a recent study of PD.

MATERIALS AND METHODS

1-Methyl-4-phenylpyridinium (MPP+) (400μM) was used to induce cytotoxicity in NGF (nerve growth factor)-differentiated PC12 cells. Cell viability was measured using a MTT assay. Induction of autophagy by MYH in NGF-differentiated PC12 cells was measured using an immunoblotting assay with LC3 and beclin 1 antibodies. The proteasomal inhibitor lactacystin (10μM) was used to cause UPS dysfunction in NGF-differentiated PC12 cells. Clearance of aggregated proteins by MYH was measured using an immunoblotting assay with an ubiquitin antibody. 1-Methyl-4-phenyl-1,2,3,6-tetrahydrophenylpyridine (MPTP) (20mg/kg, 4 times i.p.) caused substantia nigra injuries in C57BL/6 mice. Dopamine (DA) neurons were identified using a tyrosine hydroxylase-immunohistochemistry (TH-IHC) assay with a rabbit anti-TH antibody.

RESULTS

Our findings indicate that MYH provides protection against MPP+-induced injury in NGF-differentiated PC12 cell. And MYH provides neuroprotection against lactacystin-induced NGF-differentiated PC12 cell death, which effect is partially mediated by autophagy enhancement through enhanced degradation of aggregated proteins. Additionally, in a C57BL/6 mice model with MPTP-induced substantia nigra injuries, MYH inhibits both the loss of TH-positive neurons in the substantia nigra pars compacta (SNpc) and the reduction of the optical density of TH-IR fibers in the striatum (ST).

CONCLUSIONS

All of our results indicate that MYH treatment has neuroprotective effects that are partially mediated by autophagy enhancement. MYH may be a promising herbal formula for the prevention and treatment of neurodegenerative diseases, especially PD.

Mitochondrial dysfunction in Parkinson's disease

Parkinson's disease (PD) is a progressive, neurodegenerative condition that has increasingly been linked with mitochondrial dysfunction and inhibition of the electron transport chain. This inhibition leads to the generation of reactive oxygen species and depletion of cellular energy levels, which can consequently cause cellular damage and death mediated by oxidative stress and excitotoxicity. A number of genes that have been shown to have links with inherited forms of PD encode mitochondrial proteins or proteins implicated in mitochondrial dysfunction, supporting the central involvement of mitochondria in PD. This involvement is corroborated by reports that environmental toxins that inhibit the mitochondrial respiratory chain have been shown to be associated with PD. This paper aims to illustrate the considerable body of evidence linking mitochondrial dysfunction with neuronal cell death in the substantia nigra pars compacta (SNpc) of PD patients and to highlight the important need for further research in this area.

Proteomic insights into the protective mechanisms of an in vitro oxidative stress model of early stage Parkinson's disease

Previous studies in Parkinson's disease (PD) models suggest that early events along the path to neurodegeneration involve activation of the ubiquitin-proteasome system (UPS), endoplasmic reticulum-associated degradation (ERAD), and the unfolded protein response (UPR) pathways, in both the sporadic and familial forms of the disease, and thus ER stress may be a common feature. Furthermore, impairments in protein degradation have been linked to oxidative stress as well as pathways associated with ER stress. We hypothesize that oxidative stress is a primary initiator in a multi-factorial cascade driving dopaminergic (DA) neurons towards death in the early stages of the disease. We now report results from proteomic analysis of a rotenone-induced oxidative stress model of PD in the human neuroblastoma cell line, SH-SY5Y. Cells were exposed to sub-micromolar concentrations of rotenone for 48h prior to whole cell protein extraction and shotgun proteomic analysis. Evidence for activation of the UPR comes from our observation of up-regulated binding immunoglobulin protein (BiP), heat shock proteins, and foldases. We also observed up-regulation of proteins that contribute to the degradation of misfolded or unfolded proteins controlled by the UPS and ERAD pathways. Activation of the UPR may allow neurons to maintain protein homeostasis in the cytosol and ER despite an increase in reactive oxygen species due to oxidative stress, and activation of the UPS and ERAD may further augment clean-up and quality control in the cell.

Parkin directly modulates 26S proteasome activity

Parkinson's disease (PD) is a common neurodegenerative disease that involves the deterioration of dopaminergic neurons in the substantia nigra pars compacta. Although the etiology of PD remains poorly understood, recent genetic, postmortem, and experimental evidence shows that abnormal protein accumulation and subsequent aggregate formation are prominent features of both sporadic and familial PD. While proteasome dysfunction is observed in PD, diverse mutations in the parkin gene are linked to early-onset autosomal-recessive forms of familial PD. We demonstrate that parkin, an E3 ubiquitin ligase, activates the 26S proteasome in an E3 ligase activity-independent manner. Furthermore, an N-terminal ubiquitin-like domain within parkin is critical for the activation of the 26S proteasome through enhancing the interaction between 19S proteasomal subunits, whereas the PD-linked R42P mutant abolishes this action. The current findings point to a novel role for parkin for 26S proteasome assembly and suggest that parkin mutations contribute to the proteasomal dysfunction in PD.

Neuroprotective effect of Rosmarinus officinalis extract on human dopaminergic cell line, SH-SY5Y

Hydrogen peroxide (H2O2) is a major Reactive Oxygen Species (ROS), which has been implicated in many neurodegenerative conditions including Parkinson's disease (PD). Rosmarinus officinalis (R. officinalis) has been reported to have various pharmacological properties including anti-oxidant activity. In this study, we investigated the neuroprotective effects of R. officinalis extract on H2O2-induced apoptosis in human dopaminergic cells, SH-SY5Y. Our results showed that H2O2-induced cytotoxicity in SH-SY5Y cells was suppressed by treatment with R. officinalis. Moreover, R. officinalis was very effective in attenuating the disruption of mitochondrial membrane potential and apoptotic cell death induced by H2O2. R. officinalis extract effectively suppressed the up-regulation of Bax, Bak, Caspase-3 and -9, and down-regulation of Bcl-2. Pretreatment with R. officinalis significantly attenuated the down-regulation of tyrosine hydroxylase (TH), and aromatic amino acid decarboxylase (AADC) gene in SH-SY5Y cells. These findings indicate that R. officinalis is able to protect the neuronal cells against H2O2-induced injury and suggest that R. officinalis might potentially serve as an agent for prevention of several human neurodegenerative diseases caused by oxidative stress and apoptosis.

Review: the ubiquitin-proteasome system: contributions to cell death or survival in neurodegeneration

The significance of the accumulation of ubiquitin-positive intraneuronal inclusions in the brains of those affected with different neurodegenerative diseases is currently unclear. While one interpretation is that the disease mechanism(s) involves dysfunction of an ubiquitin-mediated process, such as the ubiquitin-proteasome system, the inclusions are also found in surviving neurones, suggesting a possible neuroprotective role. Here we review recent evidence in support of these seemingly opposing notions gleaned from cell and animal models as well as investigations of patient samples, with particular emphasis on studies relevant to Parkinson's disease.

Coenzyme Q10 and its effects in the treatment of neurodegenerative diseases

According to clinical and pre-clinical studies, oxidative stress and its consequences may be the cause or, at least, a contributing factor, to a large number of neurodegenerative diseases. These diseases include common and debilitating disorders, characterized by progressive and irreversible loss of neurons in specific regions of the brain. The most common neurodegenerative diseases are Parkinson's disease, Huntington's disease, Alzheimer's disease and amyotrophic lateral sclerosis. Coenzyme Q10 (CoQ10) has been extensively studied since its discovery in 1957. It is a component of the electron transportation chain and participates in aerobic cellular respiration, generating energy in the form of adenosine triphosphate (ATP). The property of CoQ10 to act as an antioxidant or a pro-oxidant, suggests that it also plays an important role in the modulation of redox cellular status under physiological and pathological conditions, also performing a role in the ageing process. In several animal models of neurodegenerative diseases, CoQ10 has shown beneficial effects in reducing disease progression. However, further studies are needed to assess the outcome and effectiveness of CoQ10 before exposing patients to unnecessary health risks at significant costs.

Potential neuroprotection mechanisms in PD: focus on dopamine agonist pramipexole

BACKGROUND

The death of dopaminergic neurons in Parkinson's disease (PD) appears to have various causes, including oxidative stress, excitotoxicity, mitochondrial dysfunction (and associated apoptosis), ubiquitin/proteasomal dysfunction, and inflammation, any of which could in principle be the therapeutic target of a neuroprotective drug. The biology of dopaminergic neurons offers further potential targets, involving neurotrophic factors, dopamine-neuron genes, and even neurogenesis.

OBJECTIVE

To outline each hypothetical neuroprotective mechanism, the evidence suggesting its relevance to PD, and the research on pharmacologic intervention.

METHODS

A PubMed search was conducted to identify relevant preclinical and clinical literature published between 1989 and 2009. Additional articles were identified by reviewing the reference lists of papers selected in the original search. To circumscribe the survey and facilitate consideration of the conditions required for a neuroprotective effect, emphasis was placed on a single drug class, dopamine agonists, and in particular pramipexole. REVIEW OF THE FIELD: In a variety of in vitro and in vivo PD models, pramipexole exhibited preclinical evidence of neuroprotective actions of all hypothesized types, and in human neuroimaging studies it slowed the rate of loss of markers of dopaminergic function, consistent with drug-conferred neuroprotection in PD itself. Interpretation of the preclinical data was hampered by differences among models and by uncertainties concerning each model's mimicry of PD. Overall, the identified neuroprotection almost always required pretreatment (i.e., before insult) and high drug concentration. Interpretation of the clinical data was hampered by absence of placebo control and of a direct measure of neuroprotection.

CONCLUSIONS

Although the evidence is promising, neuroprotection in PD remains an elusive goal. In whatever form it emerges, neuroprotective therapy would be a strong argument against deferring PD treatment until symptoms are a significant life impediment, and thus would add urgency to early PD identification.

Accumulation of phosphorylated tyrosine hydroxylase into insoluble protein aggregates by inhibition of an ubiquitin-proteasome system in PC12D cells

Tyrosine hydroxylase (TH) is a rate-limiting enzyme for the biosynthesis of catecholamines including dopamine. The relationship between proteasomal dysfunction and the etiology of Parkinson's disease has been suggested, but it is unknown if TH protein is affected by proteasomal dysfunctions. Here, we examined the effect of inhibition of ubiquitin-proteasomal pathway on biochemical characteristics of TH protein in the neuronal cells. Inhibition of 20S or 26S proteasome by proteasome inhibitor I, or MG-132 in NGF-differentiated PC12D cells induced dot-like immunoreactivities with the anti-(40)Ser-phosphorylated TH (p40-TH) antibody. These dots were tightly co-localized with ubiquitin and positive to Thioflavine-S staining. These dot-like immunoreactivities were not obvious when immunostaining was performed against total-TH or choline acetyltransferase. Western blotting analysis showed time-dependent increase of p40-TH in the Triton-insoluble fractions. We also examined the effect of okadaic acid, an inhibitor of protein phosphatase 2A, which is a phosphatase acting on p40-TH. Okadaic acid increased the amount of insoluble p40-TH. These data suggest that p40-TH is prone to be insolubilized and aggregated by dysfunction of an ubiquitin-proteasome system in PC12D cells.