Proteomic profiling in MPTP monkey model for early Parkinson disease biomarker discovery

Protein kinase R dependent phosphorylation of α-synuclein regulates its membrane binding and aggregation

Aggregated α-synuclein (α-syn) accumulates in the neuronal Lewy body (LB) inclusions in Parkinson's disease (PD) and LB dementia. Yet, under nonpathological conditions, monomeric α-syn is hypothesized to exist in an equilibrium between disordered cytosolic- and partially α-helical lipid-bound states: a feature presumably important in synaptic vesicle release machinery. The exact underlying role of α-syn in these processes, and the mechanisms regulating membrane-binding of α-syn remains poorly understood. Herein we demonstrate that Protein kinase R (PKR) can phosphorylate α-syn at several Ser/Thr residues located in the membrane-binding region that is essential for α-syn's vesicle-interactions. α-Syn phosphorylated by PKR or α-syn isolated from PKR overexpressing cells, exhibit decreased binding to lipid membranes. Phosphorylation of Thr64 and Thr72 appears as the major contributor to this effect, as the phosphomimetic Thr64Glu/Thr72Glu-α-syn mutant displays reduced overall attachment to brain vesicles due to a decrease in vesicle-affinity of the last two thirds of α-syn's membrane binding region. This allows enhancement of the "double-anchor" vesicle-binding mechanism that tethers two vesicles and thus promote the clustering of presynaptic vesicles in vitro. Furthermore, phosphomimetic Thr64Glu/Thr72Glu-α-syn inhibits α-syn oligomerization and completely abolishes nucleation, elongation, and seeding of α-syn fibrillation in vitro and in cells, and prevents trans-synaptic spreading of aggregated α-syn pathology in organotypic hippocampal slice cultures. Overall, our findings demonstrate that normal and abnormal functions of α-syn, like membrane-binding, synaptic vesicle clustering and aggregation can be regulated by phosphorylation, e.g., via PKR. Mechanisms that could potentially be modulated for the benefit of patients suffering from α-syn aggregate-related diseases.

Cortical Serotonergic and Catecholaminergic Denervation in MPTP-Treated Parkinsonian Monkeys

Decreased cortical serotonergic and catecholaminergic innervation of the frontal cortex has been reported at early stages of Parkinson's disease (PD). However, the limited availability of animal models that exhibit these pathological features has hampered our understanding of the functional significance of these changes during the course of the disease. In the present study, we assessed longitudinal changes in cortical serotonin and catecholamine innervation in motor-symptomatic and asymptomatic monkeys chronically treated with low doses of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Densitometry and unbiased stereological techniques were used to quantify changes in serotonin and tyrosine hydroxylase (TH) immunoreactivity in frontal cortices of 3 control monkeys and 3 groups of MPTP-treated monkeys (motor-asymptomatic [N = 2], mild parkinsonian [N = 3], and moderate parkinsonian [N = 3]). Our findings revealed a significant decrease (P < 0.001) in serotonin innervation of motor (Areas 4 and 6), dorsolateral prefrontal (Areas 9 and 46), and limbic (Areas 24 and 25) cortical areas in motor-asymptomatic MPTP-treated monkeys. Both groups of symptomatic MPTP-treated animals displayed further serotonin denervation in these cortical regions (P < 0.0001). A significant loss of serotonin-positive dorsal raphe neurons was found in the moderate parkinsonian group. On the other hand, the intensity of cortical TH immunostaining was not significantly affected in motor asymptomatic MPTP-treated monkeys, but underwent a significant reduction in the moderate symptomatic group (P < 0.05). Our results indicate that chronic intoxication with MPTP induces early pathology in the corticopetal serotonergic system, which may contribute to early non-motor symptoms in PD.

Complement and Coagulation Cascades are Potentially Involved in Dopaminergic Neurodegeneration in α-Synuclein-Based Mouse Models of Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder that results in motor dysfunction and, eventually, cognitive impairment. α-Synuclein protein is known as a central protein to the pathophysiology of PD, but the underlying pathological mechanism still remains to be elucidated. In an effort to understand how α-synuclein underlies the pathology of PD, various PD mouse models with α-synuclein overexpression have been developed. However, systemic analysis of the brain proteome of those mouse models is lacking. In this study, we established two mouse models of PD by injecting α-synuclein preformed fibrils (PFF) or by inducing overexpression of human A53T α-synuclein to investigate common pathways in the two different types of the PD mouse models. For more accurate quantification of mouse brain proteome, the proteins were quantified using the method of stable isotope labeling with amino acids in mammals . We identified a total of 8355 proteins from the two mouse models; ∼6800 and ∼7200 proteins from α-synuclein PFF-injected mice and human A53T α-synuclein transgenic mice, respectively. Through pathway analysis of the differentially expressed proteins common to both PD mouse models, it was discovered that the complement and coagulation cascade pathways were enriched in the PD mice compared to control animals. Notably, a validation study demonstrated that complement component 3 (C3)-positive astrocytes were increased in the ventral midbrain of the intrastriatal α-synuclein PFF-injected mice and C3 secreted from astrocytes could induce the degeneration of dopaminergic neurons. This is the first study that highlights the significance of the complement and coagulation pathways in the pathogenesis of PD through proteome analyses with two sophisticated mouse models of PD.

A novel phosphodiesterase 1 inhibitor reverses L-dopa-induced dyskinesia, but not motivation deficits, in monkeys

The enzyme phosphodiesterase 1 (PDE1) is highly expressed in the striatum and cortex. However, its role in corticostriatal function has not been fully investigated. The present study was aimed at evaluating the therapeutic potential of PDE1 inhibitors in treating motivation deficits and 3,4-dihydroxy-L-phenylalanine (L-dopa)-induced dyskinesia, which are pathological conditions of the corticostriatal system. We used a novel PDE1 inhibitor 3-ethyl-2-{[trans-4-(methoxymethyl)cyclohexyl]oxy}-7-(tetrahydro-2H-pyran-4-yl)-imidazo[5,1-f][1,2,4]triazin-4(3H)-one (DSR-143136), which was identified in our drug discovery program. Motivation in monkeys was measured using a progressive ratio task. L-Dopa-induced dyskinesia and disability scores were measured in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated monkeys. DSR-143136 had a high selectivity for PDE1 over other PDE families and 67 other biologic targets. A dopamine D₁ receptor antagonist SCH-39166 at 0.01, 0.03 and 0.1 mg/kg potently decreased motivation in monkeys. However, DSR-143136 at 0.3 and 3 mg/kg did not affect motivation deficits induced by low-dose SCH-39166 (0.01 mg/kg). On the other hand, DSR-143136 at 3 mg/kg potently decreased L-dopa-induced dyskinesia in the Parkinsonian monkey model. Importantly, this antidyskinesic efficacy was NOT accompanied by detrimental effects on motor function. Further, this compound decreased on-time with marked or severe dyskinesia, without affecting on-time itself. These findings suggest that PDE1 inhibitor could be a therapeutic candidate for treating L-dopa-induced dyskinesia in Parkinson's disease, but not for motivation deficits.

Mitochondrial Dysfunction in Parkinson's Disease: Focus on Mitochondrial DNA

Mitochondria, the energy stations of the cell, are the only extranuclear organelles, containing their own (mitochondrial) DNA (mtDNA) and the protein synthesizing machinery. The location of mtDNA in close proximity to the oxidative phosphorylation system of the inner mitochondrial membrane, the main source of reactive oxygen species (ROS), is an important factor responsible for its much higher mutation rate than nuclear DNA. Being more vulnerable to damage than nuclear DNA, mtDNA accumulates mutations, crucial for the development of mitochondrial dysfunction playing a key role in the pathogenesis of various diseases. Good evidence exists that some mtDNA mutations are associated with increased risk of Parkinson’s disease (PD), the movement disorder resulted from the degenerative loss of dopaminergic neurons of substantia nigra. Although their direct impact on mitochondrial function/dysfunction needs further investigation, results of various studies performed using cells isolated from PD patients or their mitochondria (cybrids) suggest their functional importance. Studies involving mtDNA mutator mice also demonstrated the importance of mtDNA deletions, which could also originate from abnormalities induced by mutations in nuclear encoded proteins needed for mtDNA replication (e.g., polymerase γ). However, proteomic studies revealed only a few mitochondrial proteins encoded by mtDNA which were downregulated in various PD models. This suggests nuclear suppression of the mitochondrial defects, which obviously involve cross-talk between nuclear and mitochondrial genomes for maintenance of mitochondrial functioning.

Opicapone enhances the reversal of MPTP-induced Parkinson-like syndrome by levodopa in cynomolgus monkeys

Opicapone is a third generation nitrocatechol catechol-O-methyltransferase inhibitor that has received regional market approval for use as adjunctive therapy to levodopa in Parkinson's disease patients with motor fluctuations. This study evaluated the effects of opicapone as adjunct to levodopa in reversing a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induced Parkinson's-like syndrome in cynomolgus monkeys in during opicapone preclinical development program. A Parkinson's-like syndrome was induced in cynomolgus monkeys by daily administrations of MPTP. Evaluation of the animals included scoring with the Primate Parkinsonism Motor Rating Scale (PPMRS) and assessment of locomotor activity. MPTP produced a stable Parkinson's-like behavioural syndrome as evidenced by tremor, postural changes, rigidity, impaired movements and balance, (PPMRS scores of 10-15) and decreased locomotor activity (13% of pre-MPTP values). Opicapone treatment alone, for 14 days, did not change Parkinson's-like symptoms nor decreased subject's locomotor behaviour. Ascending combinations of levodopa/benserazide dose-dependently decreased PPMRS and improved locomotor behaviour reaching statistical significance for levodopa/benserazide doses of 18/4.5 mg/kg and those effects were enhanced in opicapone treated subjects. Opicapone treated subjects as compared vehicle-treated, had markedly reduced erythrocyte catechol-O-methyltransferase activity, significantly increased plasma levodopa levels (1.8-fold higher AUC) with no statistically significant changes in C_max and significantly reduced 3-OMD AUC and C_max values (7.8- and 6.8-fold respectively). Opicapone potentiated the improvements in Parkinson's-like symptoms produced by levodopa/benserazide combinations with concomitant increase in plasma levodopa exposure, reduction of plasma 3-O-methyldopa levels and erythrocyte catechol-O-methyltransferase activity, results that were later demonstrated in 2 large Phase 3 studies in Parkinson's disease patients.

[The effect of neurotoxin MPTP administration to mice on the proteomic profile of brain isatin-binding proteins]

Isatin (indole-2,3-dione) is an endogenous indole found in the mammalian brain, peripheral organs and body fluids. It acts as a neuroprotector, which decreases manifestation of locomotor impairments in animal models of Parkinson's disease. A wide range of biological activity of isatin is associated with interaction of this regulator with numerous isatin-binding proteins. The aim of this study was to investigate the profile of brain isatin-binding proteins in mice with MPTP-induced Parkinsonism (90 min and seven days after administration of this neurotoxin). A single dose administration of MPTP (30 mg/kg, ip.) was accompanied by locomotor impairments in the open field test 90 min after administration; seven days after MPTP administration locomotor activity of mice significantly improved but did not reach the control level. Five independent experiments on proteomic profiling of isatin-binding proteins resulted in confident identification of 96±12 proteins. Development of MPTP-induced locomotor impairments was accompanied by a significant decrease in the number of isatin-binding proteins (63±6; n=5; p<0.01). Seven days after MPTP administration the total number of identified proteins increased and reached the control level (132±34; n=4). The profiles of isatin-binding proteins were rather specific for each group of mice: in the control group these proteins (which were not found in both groups of MPTP-treated mice) represented more than 70% of total proteins. In the case of MPTP treated mice this parameter was 60% (90 min after MPTP administration) and >82% (seven days after MPTP administration). The major changes were found in the groups of isatin-binding proteins involved into cytoskeleton formation and exocytosis, regulation of gene expression, cell division and differentiation and also proteins involved in signal transduction.

A non-human primate model for stable chronic Parkinson's disease induced by MPTP administration based on individual behavioral quantification

BACKGROUND

The guidelines for applying individual adjustments to macaques according to the severity of behavioral symptoms during 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treatment were provided to reproduce stable chronic Parkinsonism in a recent study (Potts et al., 2014). But, since there are insufficient guidelines regarding objective severity criteria of individual symptoms for adjustments of MPTP treatment, it is difficult to develop MPTP-induced chronic non-human primate (NHP) models with stable symptoms.

NEW METHOD

The individual adjustments of MPTP administration based on results of automatic quantification of global activity (GA) using a video-based tracking system were applied to develop MPTP-PD model. Low-dose (0.2 mg/kg) intramuscular injection was repeated continuously until GA was lower than 8% of baseline Parkinsonian behavior scores. The positron emission tomography imaging were used to follow the longitudinal course of Parkinson's disease (PD).

RESULTS

Significant reductions in GA and dopamine transporter activity, along with significant increases in Parkinsonian behavior scores were found from 4 to 48 weeks following the first administration. GA was correlated with the Parkinsonian behavior score. The dopamine transporter activity was correlated with GA and the Parkinsonian behavior score. However, it was not correlated with the total dose of MPTP. Damage of dopaminergic neuronal systems in the basal ganglia was confirmed by immunohistochemistry and Western blot.

COMPARISON WITH EXISTING METHOD

This study reinforces previous guidelines regarding production of NHP models with stable Parkinsonian symptoms.

CONCLUSIONS

This novel strategy of MPTP administration based on global activity evaluations provides an important conceptual advance for the development of chronic NHP Parkinsonian models.

Animal models of early-stage Parkinson's disease and acute dopamine deficiency to study compensatory neurodegenerative mechanisms

Parkinson's disease is a common neurodegenerative disease characterized by a widely variety of motor and non-motor symptoms. While the motor deficits are only visible following a severe dopamine depletion, neurodegenerative process and some non-motor symptoms are manifested years before the motor deficits. Importantly, chronic degeneration of dopaminergic neurons leads to the development of compensatory mechanisms that play roles in the progression of the disease and the response to anti-parkinsonian therapies. The identification of these mechanisms will be of great importance for improving our understanding of factors with important contributions to the disease course and the underlying adaptive process. To date, most of the data obtained from animal models reflect the late, chronic, dopamine-depleted states, when compensatory mechanisms have already been established. Thus, adequate animal models with which researchers are able to dissect early- and late-phase mechanisms are necessary. Here, we reviewed the literature related to animal models of early-stage PD and pharmacological treatments capable of inducing acute dopamine impairments and/or depletion, such as reserpine, haloperidol and tetrodotoxin. We highlighted the advantages, limitations and the future prospective uses of these models, as well as their applications in the identification of novel agents for treating this neurological disorder.

Systematically integrated metabonomic-proteomic studies of Escherichia coli under ciprofloxacin stress

Many antibiotics are used to kill pathogenic Escherichia coli each year, resulting in an increase in the number of antibiotic-resistant strains. In this study, an integrated metabonomic-proteomic method was performed to systematically compare the profiles of metabolites and proteins with or without ciprofloxacin (CFLX) treatment. Proteomics identified 290 altered proteins including 143 with decreased and 147 increased expression, respectively. Metabonomics identified 65 altered metabolites including 58 and 7 with decreased and increased expression, respectively. The integrated analysis showed that the CFLX inhibited the DNA replication and increased the expression of DNA gyrase and DNA topoisomerase 1, while causing a sharp decrease in metabolic activity such as the alanine, aspartate and glutamate metabolism. Moreover, CFLX affected the biosynthesis of aminoacyl- transfer RNAs (tRNAs), leading to an increase in aminoacyl-tRNAs ligases, but limited the aminoacyl-tRNAs-mediated-biosynthesis of related amino acids. In this study, we identified the metabolite and protein profiles under CFLX stress, indicating the mode of action of antibiotics in E. coli. Furthermore, the decreasing metabolic activity in E. coli may be an effective strategy to escape killing by antimicrobials or toxic compounds. The results of this study will advance our understanding of the mechanisms underlying the resistance of bacteria to antibiotics.

BIOLOGICAL SIGNIFICANCE

To investigate the biological impact of antibiotics stress on Escherichia coli, we applied an integrated metabonomic-proteomic method to systematically compare the profiles of metabolites and proteins between with and without antibiotics ciprofloxacin (CFLX) treatment. Following bioinformatics analysis showed that CFLX inhibited the DNA replication and increased the expression of DNA gyrase and DNA topoisomerase, while causing a sharp increase in the alanine, aspartate and glutamate metabolism. Moreover, CFLX affected the biosynthesis of tRNAs and limited the generation of related amino acids metabolites. In a summary, our results will provide the metabolite and protein profiles under CFLX stress, indicating the mode of action of antibiotics in E. coli. The results of this study will advance our understanding of the mechanisms underlying the resistance of bacteria to antibiotics.

Kinome and phosphoproteome of high-grade meningiomas reveal AKAP12 as a central regulator of aggressiveness and its possible role in progression

There is a need to better understand meningioma oncogenesis for biomarker discovery and development of targeted therapies. Histological or genetic criteria do not accurately predict aggressiveness. Post-translational studies in meningioma progression are lacking. In the present work, we introduce a combination of mass spectrometry-based phosphoproteomics and peptide array kinomics to profile atypical and anaplastic (high-grade) meningiomas. In the discovery set of fresh-frozen tissue specimens (14), the A-kinase anchor protein 12 (AKAP12) protein was found downregulated across the grades. AKAP12 knockdown in benign meningioma cells SF4433 increases proliferation, cell cycle, migration, invasion, and confers an anaplastic profile. Differentially regulated pathways were characteristic of high-grade meningiomas. Low AKAP12 expression in a larger cohort of patients (75) characterized tumor invasiveness, recurrence, and progression, indicating its potential as a prognostic biomarker. These results demonstrate AKAP12 as a central regulator of meningioma aggressiveness with a possible role in progression.

Chronic MPTP administration regimen in monkeys: a model of dopaminergic and non-dopaminergic cell loss in Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disorder clinically characterized by cardinal motor deficits including bradykinesia, tremor, rigidity and postural instability. Over the past decades, it has become clear that PD symptoms extend far beyond motor signs to include cognitive, autonomic and psychiatric impairments, most likely resulting from cortical and subcortical lesions of non-dopaminergic systems. In addition to nigrostriatal dopaminergic degeneration, pathological examination of PD brains, indeed, reveals widespread distribution of intracytoplasmic inclusions (Lewy bodies) and death of non-dopaminergic neurons in the brainstem and thalamus. For that past three decades, the MPTP-treated monkey has been recognized as the gold standard PD model because it displays some of the key behavioral and pathophysiological changes seen in PD patients. However, a common criticism raised by some authors about this model, and other neurotoxin-based models of PD, is the lack of neuronal loss beyond the nigrostriatal dopaminergic system. In this review, we argue that this assumption is largely incorrect and solely based on data from monkeys intoxicated with acute administration of MPTP. Work achieved in our laboratory and others strongly suggest that long-term chronic administration of MPTP leads to brain pathology beyond the dopaminergic system that displays close similarities to that seen in PD patients. This review critically examines these data and suggests that the chronically MPTP-treated nonhuman primate model may be suitable to study the pathophysiology and therapeutics of some non-motor features of PD.

Quantitative proteomics in A30P*A53T α-synuclein transgenic mice reveals upregulation of Sel1l

α-Synuclein is an abundantly expressed neuronal protein that is at the center of focus in understanding a group of neurodegenerative disorders called synucleinopathies, which are characterized by the intracellular presence of aggregated α-synuclein. However, the mechanism of α-synuclein biology in synucleinopathies pathogenesis is not fully understood. In this study, mice overexpressing human A30P*A53T α-synuclein were evaluated by a motor behavior test and count of TH-positive neurons, and then two-dimensional liquid chromatography-tandem mass spectrometry coupled with tandem mass tags (TMTs) labeling was employed to quantitatively identify the differentially expressed proteins of substantia nigra pars compacta (SNpc) tissue samples that were obtained from the α-synuclein transgenic mice and wild type controls. The number of SNpc dopaminergic neurons and the motor behavior were unchanged in A30P*A53T transgenic mice at the age of 6 months. Of the 4,715 proteins identified by proteomic techniques, 271 were differentially expressed, including 249 upregulated and 22 downregulated proteins. These alterations were primarily associated with mitochondrial dysfunction, oxidative stress, ubiquitin-proteasome system impairment, and endoplasmic reticulum (ER) stress. Some obviously changed proteins, which were validated by western blotting and immunofluorescence staining, including Sel1l and Sdhc, may be involved in the α-synuclein pathologies of synucleinopathies. A biological pathway analysis of common related proteins showed that the proteins were linked to a total of 31 KEGG pathways. Our findings suggest that these identified proteins may serve as novel therapeutic targets for synucleinopathies.

Proteomic studies associated with Parkinson's disease

INTRODUCTION

Parkinson's disease (PD) is an insidious disorder affecting more than 1-2% of the population over the age of 65. Understanding the etiology of PD may create opportunities for developing new treatments. Genomic and transcriptomic studies are useful, but do not provide evidence for the actual status of the disease. Conversely, proteomic studies deal with proteins, which are real time players, and can hence provide information on the dynamic nature of the affected cells. The number of publications relating to the proteomics of PD is vast. Therefore, there is a need to evaluate the current proteomics literature and establish the connections between the past and the present to foresee the future. Areas covered: PubMed and Web of Science were used to retrieve the literature associated with PD proteomics. Studies using human samples, model organisms and cell lines were selected and reviewed to highlight their contributions to PD. Expert commentary: The proteomic studies associated with PD achieved only limited success in facilitating disease diagnosis, monitoring and progression. A global system biology approach using new models is needed. Future research should integrate the findings of proteomics with other omics data to facilitate both early diagnosis and the treatment of PD.

Combining Diffusion Tensor Imaging and Susceptibility Weighted Imaging on the Substantia Nigra of 1-Methyl-4-Phenyl-1, 2, 3, 6-Tetrahydropyridine (MPTP)-induced Rhesus Monkey Model of Parkinson's Disease

Objective

The aim of this study was to evaluate whether combining diffusion tensor magnetic resonance imaging (DTI) and susceptibility weighted imaging (SWI) techniques would provide a sensitive method for differentiating between 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced rhesus monkey model of Parkinson's disease (PD) and wild-type controls.

Subjects and Methods

Seventeen rhesus monkeys were divided into two groups. A series of intramuscular injections of either saline (control group, n = 8) or MPTP (0.2 mg/kg body weight; PD group, n = 9) were given to the monkeys, twice a week. Then, SWI and DTI scans were obtained from the monkeys with Siemens Magnetom Verio 3.0T superconductive MRI system. Region of interest analysis was performed on substantia nigra pars compacta (SNc) and substantia nigra pars reticulata (SNr). In addition, immunohistochemical staining of tyrosine hydroxylase was applied to assess degeneration of SN dopaminergic neurons.

Results

Monkeys in the PD group displayed mild to moderate motor symptoms assessed using Kurlan's scale. With SWI scans, decreased width of SNc but increased width of SNr was found in PD group monkeys compared to controls. Calculation of the ratios of widths of SNc and SNr to the anterior and posterior mesencephalic diameter also reflected narrower SNc but wider SNr than controls. Decreased SWI signal intensity of SNc and SNr suggested iron deposition in both subregions of SN. The DTI scans showed lower fractional anisotropy (FA) values in SNc of the PD group monkeys, while no change of FA values in SNr was detected. Immunohistochemical test displayed generalized loss of dopaminergic neurons in SN of PD group monkeys.

Conclusion

Combining the use of DTI and SWI can provide a sensitive method for differentiating between MPTP-induced rhesus monkey model of PD and wild-type controls. This effective imaging modality might provide additional information for characteristic identification of PD at early stages, thus enhancing the ability to make early diagnosis, and monitor progression of the natural history and treatment effects.