Mitochondrial dysfunction in Parkinson's disease

Activation of Ca2+ phosphatase Calcineurin regulates Parkin translocation to mitochondria and mitophagy in flies

Selective removal of dysfunctional mitochondria via autophagy is crucial for the maintenance of cellular homeostasis. This event is initiated by the translocation of the E3 ubiquitin ligase Parkin to damaged mitochondria, and it requires the Serine/Threonine-protein kinase PINK1. In a coordinated set of events, PINK1 operates upstream of Parkin in a linear pathway that leads to the phosphorylation of Parkin, Ubiquitin, and Parkin mitochondrial substrates, to promote ubiquitination of outer mitochondrial membrane proteins. Ubiquitin-decorated mitochondria are selectively recruiting autophagy receptors, which are required to terminate the organelle via autophagy. In this work, we show a previously uncharacterized molecular pathway that correlates the activation of the Ca2+-dependent phosphatase Calcineurin to Parkin translocation and Parkin-dependent mitophagy. Calcineurin downregulation or genetic inhibition prevents Parkin translocation to CCCP-treated mitochondria and impairs stress-induced mitophagy, whereas Calcineurin activation promotes Parkin mitochondrial recruitment and basal mitophagy. Calcineurin interacts with Parkin, and promotes Parkin translocation in the absence of PINK1, but requires PINK1 expression to execute mitophagy in MEF cells. Genetic activation of Calcineurin in vivo boosts basal mitophagy in neurons and corrects locomotor dysfunction and mitochondrial respiratory defects of a Drosophila model of impaired mitochondrial functions. Our study identifies Calcineurin as a novel key player in the regulation of Parkin translocation and mitophagy.

Embryonic exposure to benzo[a]pyrene causes age-dependent behavioral alterations and long-term metabolic dysfunction in zebrafish

Polycyclic aromatic hydrocarbons (PAH) are products of incomplete combustion which are ubiquitous pollutants and constituents of harmful mixtures such as tobacco smoke, petroleum and creosote. Animal studies have shown that these compounds exert developmental toxicity in multiple organ systems, including the nervous system. The relative persistence of or recovery from these effects across the lifespan remain poorly characterized. These studies tested for persistence of neurobehavioral effects in AB* zebrafish exposed 5-120 h post-fertilization to a typical PAH, benzo[a]pyrene (BAP). Study 1 evaluated the neurobehavioral effects of a wide concentration range of BAP (0.02-10 μM) exposures from 5 to 120 hpf during larval (6 days) and adult (6 months) stages of development, while study 2 evaluated neurobehavioral effects of BAP (0.3-3 μM) from 5 to 120 hpf across four stages of development: larval (6 days), adolescence (2.5 months), adulthood (8 months) and late adulthood (14 months). Embryonic BAP exposure caused minimal effects on larval motility, but did cause neurobehavioral changes at later points in life. Embryonic BAP exposure led to nonmonotonic effects on adolescent activity (0.3 μM hyperactive, Study 2), which attenuated with age, as well as startle responses (0.2 μM enhanced, Study 1) at 6 months of age. Similar startle changes were also detected in Study 2 (1.0 μM), though it was observed that the phenotype shifted from reduced pretap activity to enhanced posttap activity from 8 to 14 months of age. Changes in the avoidance (0.02-10 μM, Study 1) and approach (reduced, 0.3 μM, Study 2) of aversive/social cues were also detected, with the latter attenuating from 8 to 14 months of age. Fish from study 2 were maintained into aging (18 months) and evaluated for overall and tissue-specific oxygen consumption to determine whether metabolic processes in the brain and other target organs show altered function in late life based on embryonic PAH toxicity. BAP reduced whole animal oxygen consumption, and overall reductions in total basal, mitochondrial basal, and mitochondrial maximum respiration in target organs, including the brain, liver and heart. The present data show that embryonic BAP exposure can lead to neurobehavioral impairment across the life-span, but that these long-term risks differentially emerge or attenuate as development progresses.

Human gingival mesenchymal stem cells improve movement disorders and tyrosine hydroxylase neuronal damage in Parkinson disease rats

BACKGROUND AIMS

Gingival mesenchymal stem cells (GMSCs) demonstrate high proliferation, trilineage differentiation and immunomodulatory properties. Parkinson disease (PD) is the second most common type of neurodegenerative disease. This study aimed to explore the effect and mechanism of GMSC-based therapy in 6-hydroxydopamine-induced PD rats.

METHODS

RNA sequencing and quantitative proteomics technology was used to validate the neuroprotective role of GMSCs therapeutic in 6-Hydroxydopamine -induced PD model in vitro and in vivo. Western blotting, immunofluorescence and real-time quantitative PCR verified the molecular mechanism of GMSCs treatment.

RESULTS

Intravenous injection of GMSCs improved rotation and forelimb misalignment behavior, enhanced the anti-apoptotic B-cell lymphoma 2/B-cell lymphoma 2-associated X axis, protected tyrosine hydroxylase neurons, decreased the activation of astrocytes and reduced the astrocyte marker glial fibrillary acidic protein and microglia marker ionized calcium-binding adaptor molecule 1 in the substantia nigra and striatum of PD rats. The authors found that GMSCs upregulated nerve regeneration-related molecules and inhibited metabolic disorders and the activation of signal transducer and activator of transcription 3. GMSCs showed a strong ability to protect neurons and reduce mitochondrial membrane potential damage and reactive oxygen species accumulation. The safety of GMSC transplantation was confirmed by the lack of tumor formation following subcutaneous transplantation into nude mice for up to 8 weeks.

CONCLUSIONS

The authors' research helps to explain the mechanism of GMSC-based therapeutic strategies and promote potential clinical application in Parkinson disease.

Dopamine and Methamphetamine Differentially Affect Electron Transport Chain Complexes and Parkin in Rat Striatum: New Insight into Methamphetamine Neurotoxicity

Methamphetamine (METH) is a highly abused psychostimulant that is neurotoxic to dopaminergic (DAergic) nerve terminals in the striatum and increases the risk of developing Parkinson’s disease (PD). In vivo, METH-mediated DA release, followed by DA-mediated oxidative stress and mitochondrial dysfunction in pre- and postsynaptic neurons, mediates METH neurotoxicity. METH-triggered oxidative stress damages parkin, a neuroprotective protein involved in PD etiology via its involvement in the maintenance of mitochondria. It is not known whether METH itself contributes to mitochondrial dysfunction and whether parkin regulates complex I, an enzymatic complex downregulated in PD. To determine this, we separately assessed the effects of METH or DA alone on electron transport chain (ETC) complexes and the protein parkin in isolated striatal mitochondria. We show that METH decreases the levels of selected complex I, II, and III subunits (NDUFS3, SDHA, and UQCRC2, respectively), whereas DA decreases the levels only of the NDUFS3 subunit in our preparations. We also show that the selected subunits are not decreased in synaptosomal mitochondria under similar experimental conditions. Finally, we found that parkin overexpression does not influence the levels of the NDUFS3 subunit in rat striatum. The presented results indicate that METH itself is a factor promoting dysfunction of striatal mitochondria; therefore, it is a potential drug target against METH neurotoxicity. The observed decreases in ETC complex subunits suggest that DA and METH decrease activities of the ETC complexes via oxidative damage to their subunits and that synaptosomal mitochondria may be somewhat “resistant” to DA- and METH-induced disruption in mitochondrial ETC complexes than perikaryal mitochondria. The results also suggest that parkin does not regulate NDUFS3 turnover in rat striatum.

Resveratrol in Rodent Models of Parkinson's Disease: A Systematic Review of Experimental Studies

Parkinson’s disease (PD) is a common neurodegenerative disease featured by progressive degeneration of nigrostriatal dopaminergic neurons (DA) accompanied with motor function impairment. Accumulating evidence has demonstrated that natural compounds from herbs have potent anti-PD efficacy in PD models. Among those compounds, resveratrol, a polyphenol found in many common plants and fruits, is more effective against PD. Resveratrol has displayed a potent neuroprotective efficacy in several PD animal models. However, there is still no systematic analysis of the quality of methodological design of these studies, nor of their results. In this review, we retrieved and analyzed 18 studies describing the therapeutic effect of resveratrol on PD animal models. There are 5 main kinds of PD rodent models involved in the 18 articles, including chemical-induced (MPTP, rotenone, 6-OHDA, paraquat, and maneb) and transgenic PD models. The neuroprotective mechanisms of resveratrol were mainly concentrated on the antioxidation, anti-inflammation, ameliorating mitochondrial dysfunction, and motor function. We discussed the disadvantages of different PD animal models, and we used meta-analysis approach to evaluate the results of the selected studies and used SYRCLE’s risk of bias tool to evaluate the methodological quality. Our analytical approach minimized the bias of different studies. We have also summarized the pharmacological mechanisms of resveratrol on PD models as reported by the researchers. The results of this study support the notion that resveratrol has significant neuroprotective effects on different PD models quantified using qualitative and quantitative methods. The collective information in our review can guide researchers to further plan their future experiments without any hassle regarding preclinical and clinical studies. In addition, this collective assessment of animal studies can provide a qualitative analysis of different PD animal models, either to guide further testing of these models or to avoid unnecessary duplication in their future research.

Protection from α-Synuclein induced dopaminergic neurodegeneration by overexpression of the mitochondrial import receptor TOM20

Dopaminergic neurons of the substantia nigra are selectively vulnerable to mitochondrial dysfunction, which is hypothesized to be an early and fundamental pathogenic mechanism in Parkinson's disease (PD). Mitochondrial function depends on the successful import of nuclear-encoded proteins, many of which are transported through the TOM20-TOM22 outer mitochondrial membrane import receptor machinery. Recent data suggests that post-translational modifications of α-synuclein promote its interaction with TOM20 at the outer mitochondrial membrane and thereby inhibit normal protein import, leading to dysfunction, and death of dopaminergic neurons. As such, preservation of mitochondrial import in the face of α-synuclein accumulation might be a strategy to prevent dopaminergic neurodegeneration, however, this is difficult to assess using current in vivo models of PD. To this end, we established an exogenous co-expression system, utilizing AAV2 vectors to overexpress human α-synuclein and TOM20, individually or together, in the adult Lewis rat substantia nigra to assess whether TOM20 overexpression attenuates α-synuclein-induced dopaminergic neurodegeneration. Twelve weeks after viral injection, we observed that AAV2-TOM20 expression was sufficient to prevent loss of nigral dopaminergic neurons caused by AAV2-αSyn overexpression. The observed TOM20-mediated dopaminergic neuron preservation appeared to be due, in part, to the rescued expression (and presumed import) of nuclear-encoded mitochondrial electron transport chain proteins that were inhibited by α-synuclein overexpression. In addition, TOM20 overexpression rescued the expression of the chaperone protein GRP75/mtHSP70/mortalin, a stress-response protein involved in α-synuclein-induced injury. Collectively, these data indicate that TOM20 expression prevents α-synuclein-induced mitochondrial dysfunction, which is sufficient to rescue dopaminergic neurons in the adult rat brain.

Anti-inflammatory and Anti-oxidant Activity of Hidrox® in Rotenone-Induced Parkinson's Disease in Mice

BACKGROUND

In developed countries, the extension of human life is increasingly accompanied by a progressive increase in neurodegenerative diseases, most of which do not yet have effective therapy but only symptomatic treatments. In recent years, plant polyphenols have aroused considerable interest in the scientific community. The mechanisms currently hypothesized for the pathogenesis of Parkinson's disease (PD) are neuroinflammation, oxidative stress and apoptosis. Hydroxytyrosol (HT), the main component of Hidrox^® (HD), has been shown to have some of the highest free radical evacuation and anti-inflammatory activities. Here we wanted to study the role of HD on the neurobiological and behavioral alterations induced by rotenone.

METHODS

A study was conducted in which mice received HD (10 mg/kg, i.p.) concomitantly with rotenone (5 mg/kg, o.s.) for 28 days.

RESULTS

Locomotor activity, catalepsy, histological damage and several characteristic markers of the PD, such as the dopamine transporter (DAT) content, tyrosine hydroxylase (TH) and accumulation of α-synuclein, have been evaluated. Moreover, we observed the effects of HD on oxidative stress, neuroinflammation, apoptosis and inflammasomes. Taken together, the results obtained highlight HD's ability to reduce the loss of dopaminergic neurons and the damage associated with it by counteracting the three main mechanisms of PD pathogenesis.

CONCLUSION

HD is subject to fewer regulations than traditional drugs to improve patients' brain health and could represent a promising nutraceutical choice to prevent PD.

Teaching the basics of repurposing mitochondria-targeted drugs: From Parkinson's disease to cancer and back to Parkinson's disease

Parkinson's disease (PD) and cancer share common mutations in mitochondrial proteins: Parkin and PINK1. The overlapping of genes involved in PD and cancer implies that the two diseases might share a common pathogenic mechanism. There are other compelling rationales for a mechanistic link between these diseases. Mitochondria and autophagy/mitophagy are emerging as therapeutic targets in PD and cancer: Ongoing research in our laboratories has shown that, when administered early, mitochondria-targeted agents afford neuroprotection in preclinical mice models of PD. Also, we discovered that mitochondria-targeted drugs inhibit tumor cell proliferation. We propose that mitochondrial targeting stimulates conservation of cellular energy critical for neuronal cell survival, whereas the energy conservation mechanism inhibits proliferation of cancer cells by depriving the energy necessary for cancer cell growth. We propose a promising drug repurposing strategy involving mitochondria-targeted drugs synthesized from naturally occurring molecules and FDA-approved drugs that are relatively nontoxic in both PD and cancer. These compounds have been shown to induce various cellular signaling pathways for autophagy/mitophagy, anti-inflammatory, and immunomodulatory effects that are implicated as therapeutic mechanisms in PD and cancer.

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Targeting mitochondria in cancer and PD could be a useful drug repurposing strategy.

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Modification of natural compounds with TPP+targets mitochondria.

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Mitochondria-targeted agents induce multiple cell signaling mechanisms.

Fisetin Improved Rotenone-Induced Behavioral Deficits, Oxidative Changes, and Mitochondrial Dysfunctions in Rat Model of Parkinson's Disease

Oxidative stress plays an important role in the pathogenesis of Parkinson's disease (PD), particularly the inhibition of mitochondrial complex-I. This study aimed to evaluate the effect of fisetin in the rotenone-induced rat model of PD. Rotenone was administered (2   mg/kg s.c.) for 35   days to induce PD in animals. Fisetin was administered at two doses (10   mg/kg and 20   mg/kg p.o.) for 25   days to the animals that were given rotenone. Behavioral experiment, i.e. cylinder test, was performed to assess the motor asymmetry. Animals were euthanized, and mid brains were isolated for the estimation of tricarboxylic acid cycle enzymes, oxidative measures (lipid peroxidation (LPO), glutathione (GSH) and catalase) and complex-I activity. In addition, histopathological studies were conducted. Fisetin treatment improved motor function in the cylinder test and reversed the rotenone-induced changes in mitochondrial enzymes, striatal dopamine levels, antioxidant enzyme levels and histological changes. An important finding of this study was both the doses of fisetin significantly (p   <   0.05) enhanced rotenone-induced behavioral and biochemical changes and the effects were found to be dose dependent. Based on the present results, we hypothesize that fisetin may improve the mitochondrial enzyme activity, thereby preventing the pathogenesis of PD.

4'-Phosphopantetheine corrects CoA, iron, and dopamine metabolic defects in mammalian models of PKAN

Pantothenate kinase-associated neurodegeneration (PKAN) is an inborn error of CoA metabolism causing dystonia, parkinsonism, and brain iron accumulation. Lack of a good mammalian model has impeded studies of pathogenesis and development of rational therapeutics. We took a new approach to investigating an existing mouse mutant of Pank2 and found that isolating the disease-vulnerable brain revealed regional perturbations in CoA metabolism, iron homeostasis, and dopamine metabolism and functional defects in complex I and pyruvate dehydrogenase. Feeding mice a CoA pathway intermediate, 4'-phosphopantetheine, normalized levels of the CoA-, iron-, and dopamine-related biomarkers as well as activities of mitochondrial enzymes. Human cell changes also were recovered by 4'-phosphopantetheine. We can mechanistically link a defect in CoA metabolism to these secondary effects via the activation of mitochondrial acyl carrier protein, which is essential to oxidative phosphorylation, iron-sulfur cluster biogenesis, and mitochondrial fatty acid synthesis. We demonstrate the fidelity of our model in recapitulating features of the human disease. Moreover, we identify pharmacodynamic biomarkers, provide insights into disease pathogenesis, and offer evidence for 4'-phosphopantetheine as a candidate therapeutic for PKAN.

Impaired metabolism of kynurenine and its metabolites in CSF of parkinson's disease

AIM

The kynurenine (KYN) pathway plays an important role in degrading molecules responsible for oxidative stress in the central nervous system (CNS), but can also have neurotoxic effects. Both 3-hydroxykynurenine (3-HK) and quinolinic acid are neurotoxic metabolites produced from this pathway. In Parkinson's disease (PD), oxidative stress is suspected to represent a key pathogenic mechanism. This study aimed to investigate the function of the KYN pathway and interactions between oxidative stress and neuroinflammation in PD.

METHODS

Participants comprised 20 patients with PD and 13 controls. Cerebrospinal fluid (CSF) levels of KYN and 3-HK were measured using high-performance liquid chromatography coupled with an electrochemical detector. CSF levels of tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6, and interferon (IFN)-γ were measured with an enzyme-linked immunosorbent assay, and results were statistically compared between PD patients and controls.

RESULTS

Median CSF levels of KYN and 3-HK were 49.0 nM and 4.25 nM in PD and 30.5 nM and 1.55 nM in controls, respectively, showing significantly higher levels in PD (p < 0.05). CSF levels of measured cytokines showed that TNF-α and IL-1β were significantly higher in PD patients than in controls. No positive correlation between 3-HK and TNF-α was seen in PD.

CONCLUSION

Dysfunction of the KYN pathway may induce oxidative stress in the CNS in PD, and may also induce cytokine-mediated neuroinflammation. Functional amelioration of the KYN pathway may facilitate modification of neurodegenerative processes in PD.

Evidence of Neurobiological Changes in the Presymptomatic PINK1 Knockout Rat

BACKGROUND

Genetic models of Parkinson's disease (PD) coupled with advanced imaging techniques can elucidate neurobiological disease progression, and can help identify early biomarkers before clinical signs emerge. PTEN-induced putative kinase 1 (PINK1) helps protect neurons from mitochondrial dysfunction, and a mutation in the associated gene is a risk factor for recessive familial PD. The PINK1 knockout (KO) rat is a novel model for familial PD that has not been neuroradiologically characterized for alterations in brain structure/function, alongside behavior, prior to 4 months of age.

OBJECTIVE

To identify biomarkers of presymptomatic PD in the PINK1 -/- rat at 3 months using magnetic resonance imaging techniques.

METHODS

At postnatal weeks 12-13; one month earlier than previously reported signs of motor and cognitive dysfunction, this study combined imaging modalities, including assessment of quantitative anisotropy across 171 individual brain areas using an annotated MRI rat brain atlas to identify sites of gray matter alteration between wild-type and PINK1 -/- rats.

RESULTS

The olfactory system, hypothalamus, thalamus, nucleus accumbens, and cerebellum showed differences in anisotropy between experimental groups. Molecular analyses revealed reduced levels of glutathione, ATP, and elevated oxidative stress in the substantia nigra, striatum and deep cerebellar nuclei. Mitochondrial genes encoding proteins in Complex IV, along with mRNA levels associated with mitochondrial function and genes involved in glutathione synthesis were reduced. Differences in brain structure did not align with any cognitive or motor impairment.

CONCLUSIONS

These data reveal early markers, and highlight novel brain regions involved in the pathology of PD in the PINK1 -/- rat before behavioral dysfunction occurs.

Parkinson's disease research: adopting a more human perspective to accelerate advances

Parkinson's disease (PD) affects 1% of the population over 60 years old and, with global increases in the aging population, presents huge economic and societal burdens. The etiology of PD remains unknown; most cases are idiopathic, presumed to result from genetic and environmental risk factors. Despite 200 years since the first description of PD, the mechanisms behind initiation and progression of the characteristic neurodegenerative processes are not known. Here, we review progress and limitations of the multiple PD animal models available and identify advances that could be implemented to better understand pathological processes, improve disease outcome, and reduce dependence on animal models. Lessons learned from reducing animal use in PD research could serve as guideposts for wider biomedical research.

Creatine Protects Against Cytosolic Calcium Dysregulation, Mitochondrial Depolarization and Increase of Reactive Oxygen Species Production in Rotenone-Induced Cell Death of Cerebellar Granule Neurons

Rotenone is a neurotoxin that is an active component of many pesticides which has been shown to induce Parkinsonism in animal models. We show that the cytotoxicity of exposure to nanomolar concentrations of rotenone in cultures of mature cerebellar granule neurons (CGN) in serum-free medium is not due to phagocytosis by glial contamination. A concentration as low as 5.65 ± 0.51 nM of rotenone was enough to trigger 50% cell death of mature CGN in culture after 12 h. The addition of serum proteins to the culture medium attenuated rotenone neurotoxicity, and this can account at least in part for the requirement of higher rotenone concentrations to elicit neuronal cytotoxicity reported in previous works. Creatine partial protection against CGN death promoted by 5 nM rotenone correlated with creatine protection against rotenone-induced mitochondrial depolarization and oxidative stress. Furthermore, creatine largely attenuated the early dysregulation of cytosolic Ca²⁺ concentration after acute rotenone treatment. Noteworthy, our results also revealed that the sustained alteration of Ca²⁺ homeostasis induced by rotenone takes place at the onset of the enhancement of intracellular oxidative stress and before mitochondrial depolarization, pointing out that cytosolic Ca²⁺ dysregulation is a very early event in the rotenone toxicity to CGN.

Sex differences in Parkinson's disease: Features on clinical symptoms, treatment outcome, sexual hormones and genetics

Parkinson's disease (PD) is the second most frequent age-related neurodegenerative disorder. Sex is an important factor in the development of PD, as reflected by the fact that it is more common in men than in women by an approximate ratio of 2:1. Our hypothesis is that differences in PD among men and women are highly determined by sex-dependent differences in the nigrostriatal dopaminergic system, which arise from environmental, hormonal and genetic influences. Sex hormones, specifically estrogens, influence PD pathogenesis and might play an important role in PD differences between men and women. The objective of this review was to discuss the PD physiopathology and point out sex differences in nigrostriatal degeneration, symptoms, genetics, responsiveness to treatments and biochemical and molecular mechanisms among patients suffering from this disease. Finally, we discuss the role estrogens may have on PD sex differences.

Intermittent Fasting Applied in Combination with Rotenone Treatment Exacerbates Dopamine Neurons Degeneration in Mice

Intermittent fasting (IF) was suggested to be a powerful nutritional strategy to prevent the onset of age-related neurodegenerative diseases associated with compromised brain bioenergetics. Whether the application of IF in combination with a mitochondrial insult could buffer the neurodegenerative process has never been explored yet. Herein, we defined the effects of IF in C57BL/6J mice treated once per 24 h with rotenone (Rot) for 28 days. Rot is a neurotoxin that inhibits the mitochondrial complex I and causes dopamine neurons degeneration, thus reproducing the neurodegenerative process observed in Parkinson's disease (PD). IF (24 h alternate-day fasting) was applied alone or in concomitance with Rot treatment (Rot/IF). IF and Rot/IF groups showed the same degree of weight loss when compared to control and Rot groups. An accelerating rotarod test revealed that only Rot/IF mice have a decreased ability to sustain the test at the higher speeds. Rot/IF group showed a more marked decrease of dopaminergic neurons and increase in alpha-synuclein (α-syn) accumulation with respect to Rot group in the substantia nigra (SN). Through lipidomics and metabolomics analyses, we found that in the SN of Rot/IF mice a significant elevation of excitatory amino acids, inflammatory lysophospholipids and sphingolipids occurred. Collectively, our data suggest that, when applied in combination with neurotoxin exposure, IF does not exert neuroprotective effects but rather exacerbate neuronal death by increasing the levels of excitatory amino acids and inflammatory lipids in association with altered brain membrane composition.

Identification of key genes and pathways in Parkinson's disease through integrated analysis

Parkinson's disease (PD) is a progressive, degene-rative neurological disease, typically characterized by tremors and muscle rigidity. The present study aimed to identify differe-ntially expressed genes (DEGs) between patients with PD and healthy patients, and clarify their association with additional biological processes that may regulate factors that lead to PD. An integrated analysis of publicly available Gene Expression Omnibus datasets of PD was performed. DEGs were identified between PD and normal blood samples. Gene Ontology enrichment and Kyoto Encyclopedia of Genes and Genomes pathway analyses, as well as protein‑protein interaction (PPI) networks were used to predict the functions of identified DEGs. Reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR) was performed to validate the predicted expression levels of identified DEGs in whole blood samples obtained from patients with PD and normal healthy controls. A total of 292DEGs were identified between the PD and normal blood samples. Of these, 156 genes were significantly upregulated and 136 genes were significantly downregulated in PD samples following integrated analysis of four PD expression datasets. The 10 most upregulated and downregulated genes were used to construct a PPI network, where ubiquitin C‑terminal hydrolase L1 (UCHL1), 3‑phosphoinositide dependent protein kinase 1 (PDPK1) and protein kinase cAMP‑activated catalytic subunit β (PRKACB) demonstrated the highest connectivity in the network. DEGs were significantly enriched in amoebiasis, vascular smooth muscle contraction, and the Wnt and calcium signaling pathways. The expression levels of significant DEGs, UCHL1, PDPK1 and PRKACB were validated using RT‑qPCR analysis. The findings revealed that UCHL1 and PDPK1 were upregulated and PRKACB was downregulated in patients with PD when compared with normal healthy controls. In conclusion, the results indicate that the significant DEGs, including UCHL1, PDPK1 and PRKACB may be associated with the development of PD. In addition, these factors may be involved in various signaling pathways, including amoebiasis, vascular smooth muscle contraction and the Wnt and calcium signaling pathways.

From the Cover: Manganese and Rotenone-Induced Oxidative Stress Signatures Differ in iPSC-Derived Human Dopamine Neurons

Parkinson's disease (PD) is the result of complex interactions between genetic and environmental factors. Two chemically distinct environmental stressors relevant to PD are the metal manganese and the pesticide rotenone. Both are thought to exert neurotoxicity at least in part via oxidative stress resulting from impaired mitochondrial activity. Identifying shared mechanism of action may reveal clues towards an understanding of the mechanisms underlying PD pathogenesis. Here we compare the effects of manganese and rotenone in human-induced pluripotent stem cells-derived postmitotic mesencephalic dopamine neurons by assessing several different oxidative stress endpoints. Manganese, but not rotenone caused a concentration and time-dependent increase in intracellular reactive oxygen/nitrogen species measured by quantifying the fluorescence of oxidized chloromethyl 2',7'-dichlorodihydrofluorescein diacetate (DCF) assay. In contrast, rotenone but not manganese caused an increase in cellular isoprostane levels, an indicator of lipid peroxidation. Manganese and rotenone both caused an initial decrease in cellular reduced glutathione; however, glutathione levels remained low in neurons treated with rotenone for 24 h but recovered in manganese-exposed cells. Neurite length, a sensitive indicator of overall neuronal health was adversely affected by rotenone, but not manganese. Thus, our observations suggest that the cellular oxidative stress evoked by these 2 agents is distinct yielding unique oxidative stress signatures across outcome measures. The protective effect of rasagiline, a compound used in the clinic for PD, had negligible impact on any of oxidative stress outcome measures except a subtle significant decrease in manganese-dependent production of reactive oxygen/nitrogen species detected by the DCF assay.

Neural Repair Strategies for Parkinson's Disease: Insights from Primate Models

Nonhuman primate models of Parkinson's disease (PD) have been invaluable to our understanding of the human disease and in the advancement of novel therapies for its treatment. In this review, we attempt to give a brief overview of the animal models of PD currently used, with a more comprehensive focus on the advantages and disadvantages presented by their use in the nonhuman primate. In particular, discussion addresses the 6-hydroxydopamine (6-OHDA), 1-methyl-1,2,3,6-tetrahydopyridine (MPTP), rotenone, paraquat, and maneb parkinsonian models. Additionally, the role of primate PD models in the development of novel therapies, such as trophic factor delivery, grafting, and deep brain stimulation, are described. Finally, the contribution of primate PD models to our understanding of the etiology and pathology of human PD is discussed.

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.

Mitophagy as a stress response in mammalian cells and in respiring S. cerevisiae

The degradation of malfunctioning or superfluous mitochondria in the lysosome/vacuole is an important housekeeping function in respiring eukaryotic cells. This clearance is thought to occur by a specific form of autophagic degradation called mitophagy, and plays a role in physiological homoeostasis as well as in the progression of late-onset diseases. Although the mechanism of bulk degradation by macroautophagy is relatively well established, the selective autophagic degradation of mitochondria has only recently begun to receive significant attention. In this mini-review, we introduce mitophagy as a form of mitochondrial quality control and proceed to provide specific examples from yeast and mammalian systems. We then discuss the relationship of mitophagy to mitochondrial stress, and provide a broad mechanistic overview of the process with an emphasis on evolutionarily conserved pathways.

Imipramine and amitriptyline ameliorate the rotenone model of Parkinson's disease in rats

Amitriptyline (AMI), a commonly prescribed tricyclic antidepressant (TCA) to parkinsonian patients, specifically showed a significant delay in dopaminergic therapy initiation and improvement in motor disability in parkinsonian patients. Moreover, it was recently shown that AMI has neuroprotective properties; however, the mechanisms underlying this effect in Parkinson's disease (PD) are not fully understood. The current study aimed to investigate the possible neuroprotective mechanisms afforded by AMI in the rotenone model of PD and to assess whether another TCA member, imipramine (IMI), shows a corresponding effect. Rats were allocated into seven groups. Four groups were given either saline, dimethyl sulfoxide, AMI or IMI. Three rotenone groups were either untreated or treated with AMI or IMI. Rats receiving rotenone exhibited motor impairment in open field and rotarod tests. Additionally, immunohistochemical examination revealed dopaminergic neuronal damage in substantia nigra. Besides, striatal monoamines and brain derived neurotrophic factor levels were declined. Furthermore, oxidative stress, microglial activation and inflammation were evident in the striata. Pretreatment of rotenone groups with AMI or IMI prevented rotenone-induced neuronal degeneration and increased striatal dopamine level with motor recovery. These effects were accompanied by restoring striatal monoamines and brain-derived neurotrophic factor levels, as well as reducing oxidative damage, microglial activation and expression of proinflammatory cytokines and inducible nitric oxide synthase. The present results suggest that modulation of noradrenaline and serotonin levels, up-regulation of neurotrophin, inhibition of glial activation, anti-oxidant and anti-inflammatory activities could serve as important mechanisms underlying the neuroprotective effects of the used drugs in the rotenone model of PD.

Lipopolysaccharide-induced functional and structural injury of the mitochondria in the nigrostriatal pathway

Accumulating evidence suggests that chronic inflammation plays a role in the progressive dopaminergic neurodegeneration that occurs in Parkinson's disease. It has been hypothesized that inflammation mediates neuronal damage via exacerbation of a vicious cycle of oxidative stress and mitochondrial dysfunction. The bacterial endotoxin, lipopolysaccharide (LPS), induces microglial activation and inflammation driven dopaminergic neurodegeneration. In order to test the hypothesis that LPS-induced inflammatory response might damage mitochondrial structure and function leading to nigral dopaminergic neuron loss, we injected LPS or saline into the striatum of rats. Here, we found that intrastriatal LPS induced deficit in mitochondrial respiration, damage to mitochondrial cristae, mitochondrial oxidation and nitration. Finally, we found significant loss of dopaminergic neurons in the substantia nigra one week after LPS injection. This study indicates that LPS-induced dopaminergic neurodegeneration might be exerted by mitochondrial injury.

Mitochondrial dysfunction in Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disease. About 2% of the population above the age of 60 is affected by the disease. The pathological hallmarks of the disease include the loss of dopaminergic neurons in the substantia nigra and the presence of Lewy bodies that are made of α-synuclein. Several theories have been suggested for the pathogenesis of PD, of which mitochondrial dysfunction plays a pivotal role in both sporadic and familial forms of the disease. Dysfunction of the mitochondria that is caused by bioenergetic defects, mutations in mitochondrial DNA, nuclear DNA gene mutations linked to mitochondria, and changes in dynamics of the mitochondria such fusion or fission, changes in size and morphology, alterations in trafficking or transport, altered movement of mitochondria, impairment of transcription, and the presence of mutated proteins associated with mitochondria are implicated in PD. In this review, we provide a detailed overview of the mechanisms that can cause mitochondrial dysfunction in PD. We bring to the forefront, new signaling pathways such as the retromer-trafficking pathway and its implication in the disease and also provide a brief overview of therapeutic strategies to improve mitochondrial defects in PD. Bioenergetic defects, mutations in mitochondrial DNA, nuclear DNA gene mutations, alterations in mitochondrial dynamics, alterations in trafficking/transport and mitochondrial movement, abnormal size and morphology, impairment of transcription and the presence of mutated proteins associated with mitochondria are implicated in PD. In this review, we focus on the mechanisms underlying mitochondrial dysfunction in PD and bring to the forefront new signaling pathways that may be involved in PD. We also provide an overview of therapeutic strategies to improve mitochondrial defects in PD. This article is part of a special issue on Parkinson disease.

Roles of mitophagy in cellular physiology and development

The autophagic degradation of mitochondria, or mitophagy, has been shown to occur in eukaryotic cells under various physiological conditions. Broadly, these fall into two categories: quality-control related mitophagy and developmentally induced mitophagy. Quality-control related mitophagy, which is the lysosomal/vacuolar degradation of malfunctioning or superfluous mitochondria, is an important housekeeping function in respiring eukaryotic cells. It plays an essential role in physiological homeostasis and its deregulation has been linked to the progression of late-onset diseases. On the other hand, developmental processes such as reticulocyte maturation have also been shown to involve mitophagy. Importantly, there are clear differences between these processes. Unlike our knowledge of the more general degradation of soluble cytosolic content during starvation-induced macroautophagy, the mechanisms involved in the selective autophagic degradation of mitochondria have only recently begun to receive significant attention. Here, we review the current literature on these topics and proceed to provide specific examples from yeast and mammalian systems. Finally, we cover experimental approaches, with a focus on proteomic methods dedicated to the study of mitophagy in different systems.

Parkinson's Disease: The Mitochondria-Iron Link

Mitochondrial dysfunction, iron accumulation, and oxidative damage are conditions often found in damaged brain areas of Parkinson's disease. We propose that a causal link exists between these three events. Mitochondrial dysfunction results not only in increased reactive oxygen species production but also in decreased iron-sulfur cluster synthesis and unorthodox activation of Iron Regulatory Protein 1 (IRP1), a key regulator of cell iron homeostasis. In turn, IRP1 activation results in iron accumulation and hydroxyl radical-mediated damage. These three occurrences-mitochondrial dysfunction, iron accumulation, and oxidative damage-generate a positive feedback loop of increased iron accumulation and oxidative stress. Here, we review the evidence that points to a link between mitochondrial dysfunction and iron accumulation as early events in the development of sporadic and genetic cases of Parkinson's disease. Finally, an attempt is done to contextualize the possible relationship between mitochondria dysfunction and iron dyshomeostasis. Based on published evidence, we propose that iron chelation-by decreasing iron-associated oxidative damage and by inducing cell survival and cell-rescue pathways-is a viable therapy for retarding this cycle.

Mitochondrial NADH Dehydrogenase Subunit 3 Polymorphism Associated with an Earlier Age at Onset in Male Machado-Joseph disease Patients

AIMS

To investigate the potential effect of six previously reported candidate single nucleotide polymorphisms on age at onset (AAO) among Chinese patients with Machado-Joseph disease (MJD).

METHODS

Three hundred and twenty-four unrelated molecular-confirmed MJD patients were recruited between January 2006 and December 2014. The screening of candidate polymorphisms was first performed in 173 subjects using the SNaPshot(®) Multiplex System. The mitochondrial NADH dehydrogenase subunit 3 (MT-ND3) polymorphism 10398A>G (rs2853826) was further verified with Sanger sequencing in additional 151 patients.

RESULTS

An inverse correlation was found between expanded CAG repeat length and AAO. The expanded CAG repeat length can explain 63% of AAO variance. The 10398A polymorphism was significantly associated with a 3-year earlier AAO in male patients with MJD (P = 0.001). Stepwise multiple regressions revealed that the 10398A polymorphism could account for nearly 2% of AAO variance in male patients.

CONCLUSION

Six candidate SNPs have been screened in Chinese patients with MJD. A remarkable earlier AAO was noted in male Chinese MJD patients with MT-ND3 gene 10398A polymorphism.

Neuroprotective effects of Eucommia ulmoides Oliv. and its bioactive constituent work via ameliorating the ubiquitin-proteasome system

BACKGROUND

Parkinson's disease (PD) is a chronic neurodegenerative disorder characterized by a loss of dopaminergic neurons in the substantia nigra, decreased striatal dopamine levels, and consequent extrapyramidal motor dysfunction. The purpose of this study was to investigate potential in vivo protective effects of Duzhong against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), as well as the bioactive constituents against 1-methyl-4-phenylpyridinium (MPP(+)) toxicity in vitro.

METHODS

Male C57BL/6 mice were intraperitoneally administrated five consecutive injections of MPTP every 24 h at a dose of 30 mg/kg to induce an in vivo PD model. Pole and traction tests were performed in mice to evaluate motor deficits and bradykinesia after the final MPTP administration. The striatal levels of dopamine and its metabolites, 3,4-dihydroxyphenylacetic acid and homovanilic acid, were measured using a High-performance liquid chromatography-electrical conductivity detector. To further explore the bioactive constituents and protective mechanisms of Duzhong, seven compounds from Duzhong were tested on MPP(+)-treated SH-SY5Y cell lines in vitro. A proteasome enzymatic assay and Cell Counting Kit-8 were performed to examine proteasomal activity and cell viability of Duzhong-treated cells, respectively, after exposure to MPP(+) and proteasome inhibitor MG132.

RESULTS

Duzhong antagonized the loss of striatal neurotransmitters and relieved the associated anomaly in ambulatory locomotor activity in PD mice after a 3-day pre-treatment of Duzhong crude extract. The five Duzhong compounds attenuated MPP(+)-induced dysfunction of protease activity and reduced MG132-induced cytotoxicity.

CONCLUSION

Duzhong could serve as a potential candidate for PD treatment, and its mechanism involves the amelioration of the ubiquitin-proteasome system.

Anti-oxidant polydatin (piceid) protects against substantia nigral motor degeneration in multiple rodent models of Parkinson's disease

Background

Compelling evidence suggests that inhibition of the complex I of the electron transport chain and elevated oxidative stress are the earliest events during the pathogenesis of Parkinson’s disease (PD). Therefore, anti-oxidants, especially those from natural sources, hold good promise in treating PD as demonstrated mostly by the studies in rodent models.

Results

Herein, we determined if polydatin (piceid), a natural polyphenol, could exert anti-oxidative activity and attenuate dopaminergic neurodegeneration in three commonly used rodent models of PD. Male Sprague Dawley rats given rotenone subcutaneously for 5 weeks developed all the essential features of PD, including a strong increase in catalepsy score and a decrease in motor coordination activity, starting at 4 weeks. Selective increase in oxidative damage was found in the striatal region as compared to the hippocampus and cortex, accompanied by massive degeneration of dopaminergic neurons in the substantia nigra (SNc). Co-administration of piceid orally was able to attenuate rotenone-induced motor defects in a dose dependent manner, with 80 mg/kg dosage showing even better effect than L-levodopa (L-dopa). Piceid treatment significantly prevented the rotenone-induced changes in the levels of glutathione, thioredoxin, ATP, malondialdehyde (MDA) and the manganese superoxide dismutases (SOD) in striatum. Furthermore, piceid treatment rescued rotenone-induced dopaminergic neurodegeneration in the SNc region. Similar protective effect of piceid was also observed in two additional models of PD, MPTP in mice and 6-OHDA in rats, showing corrected motor functions, SOD and MDA activities as well as p-Akt and activated caspase-3 levels.

Conclusion

In three rodent models of PD, piceid preserves and corrects several major anti-oxidant pathways/parameters selectively in the affected SNc region. This implies its potent anti-oxidant activity as one major underscoring mechanism for protecting the vulnerable SNc neurodegeneration in these models. Taken together, these findings strongly suggest a therapeutic potential of piceid in treating PD.

Electronic supplementary material

The online version of this article (doi:10.1186/1750-1326-10-4) contains supplementary material, which is available to authorized users.

The Genetic Link between Parkinson's Disease and the Kynurenine Pathway Is Still Missing

Background. There is substantial evidence that the kynurenine pathway (KP) plays a role in the normal physiology of the brain and is involved in the pathology of neurodegenerative disorders such as Huntington's disease and Parkinson's disease (PD). Objective. We set out to investigate the potential roles in PD of single nucleotide polymorphisms (SNPs) from one of the key enzymes of the KP, kynurenine 3-monooxygenase (KMO). Methods. 105 unrelated, clinically definitive PD patients and 131 healthy controls were enrolled to investigate the possible effects of the different alleles of KMO. Fluorescently labeled TaqMan probes were used for allele discrimination. Results. None of the four investigated SNPs proved to be associated with PD or influenced the age at onset of the disease. Conclusions. The genetic link between the KP and PD is still missing. The investigated SNPs presumably do not appear to influence the function of KMO and probably do not contain binding sites for regulatory proteins of relevance in PD. This is the first study to assess the genetic background behind the biochemical alterations of the kynurenine pathway in PD, directing the attention to this previously unexamined field.

NAD+ treatment can prevent rotenone-induced increases in DNA damage, Bax levels and nuclear translocation of apoptosis-inducing factor in differentiated PC12 cells

Nicotinamide adenine dinucleotide (NAD(+)) plays critical roles in energy metabolism, mitochondrial functions, calcium homeostasis and immunological functions. Our previous studies have found that NAD(+) administration can profoundly decrease ischemic brain injury and traumatic brain injury. Our recent study has also provided first direct evidence indicating that NAD(+) treatment can decrease cellular apoptosis, while the mechanisms underlying this protective effect remain unclear. In our current study, we determined the effects of NAD(+) treatment on several major factors in apoptosis and necrosis, including levels of Bax and nuclear translocation of apoptosis-inducing factor (AIF), as well as levels of DNA double-strand breaks (DSBs) and intracellular ATP in rotenone-treated differentiated PC12 cells. We found that NAD(+) treatment can markedly attenuate the rotenone-induced increases in the levels of Bax and nuclear translocation of AIF in the cells. We further found that NAD(+) treatment can significantly attenuate the rotenone-induced increase in the levels of DSBs and decrease in the intracellular ATP levels. Collectively, our study has suggested mechanisms underlying the preventive effects of NAD(+) on apoptosis, which has highlighted the therapeutic potential of NAD(+) for decreasing apoptotic changes in multiple major diseases.

Gender-specific brain regional variation of neurons, endogenous estrogen, neuroinflammation and glial cells during rotenone-induced mouse model of Parkinson's disease

Rotenone (RT) produces reactive oxygen species (ROS) by inhibiting the mitochondrial electron transport chain; causing dopaminergic (DA) cell death in the substantia nigra (SN) and simulates other models of induced Parkinson's disease (PD). There is a sincere dearth of knowledge regarding the status of glial cells, neuroprotective estrogen and the status of neuroinflammatory TNF-α in the different brain regions in either sex during healthy, as well as during PD conditions. In the present study of RT-induced mouse model of PD, we have selected the frontal cortex (FC), hippocampus (HC) and SN from either sex of Swiss albino mice as these are the major regions involved during PD pathogenesis. During non pathogenic conditions, the ROS-scavenging enzyme activity varied among the brain regions and also in between genders. The number of DOPA decarboxylase-positive cells, astrocytes and microglia was similar in the respective regions of the brain in both the sexes. The level of proinflammatory cytokine TNF-α was same in the respective FC and HC in either sex except that of SN. The expression level of estrogen and its receptors varied among the three brain regions. During RT treatment, ROS-scavenging enzyme activities increased, DOPA decarboxylase-positive neurons and fibers in DA as well as in norepinephrinergic (NE) systems become degenerated, number of astrocytes decreased and microglial cells increased in those specific brain regions in either of the sexes except in the SN region of males where astrocyte number remained unaltered and microglial cell percentage decreased. TNF-α increased in the FC and SN but remained unaltered in the HC of both sexes. Estradiol level decreased in the HC and SN but the level unevenly varied in the FC. Similarly, the estrogen bound and nuclear-cytosolic receptor α and β also varied differentially among the brain regions of the two sexes. Therefore our present study depicts that there exists a clear variation of neuronal and astroglial cell population, estrogen and its receptor levels in different brain regions of both the sexes during control and RT-treated pathogenic condition and these variations have major implication in PD pathogenesis and progression.

Therapeutic effects of fucoidan in 6-hydroxydopamine-lesioned rat model of Parkinson's disease: Role of NADPH oxidase-1

AIMS

To explore the effect of fucoidan treatment on oxidative stress-mediated dopaminergic neuronal damage and its potential mechanisms.

METHODS

The effect of fucoidan was investigated in a 6-hydroxydopamine (6-OHDA) rat model of PD, an animal model considered appropriate for preclinical studies of PD therapy. The effects of fucoidan treatment on animal behavior and the survival ratio of dopaminergic neurons were investigated. We further observed the effect of fucoidan on microglia and the NADPH oxidases-1 (Nox1), a family of enzymes generating reactive oxygen species (ROS).

RESULTS

We found that chronic fucoidan administration mitigated the motor dysfunction induced by 6-OHDA. Similarly, fucoidan reduced the loss of DA neurons in the SNc and DA fibers in the striatum in 6-OHDA-lesioned rats. Moreover, we found that fucoidan inhibited the 6-OHDA-stimulating expression of Nox1 in both tyrosine hydroxylase (TH)-positive neurons and non-TH-positive neurons, prevented Nox1-sensitive oxidative stress and cell damage in SNc neurons. Fucoidan also effectively inhibited nigral microglial activation.

CONCLUSION

These results support the beneficial effect of fucoidan in 6-OHDA-lesioned rat model of PD. Fucoidan may suppress the Nox1-triggered oxidative stress in the SNc to protect DA neurons from 6-OHDA-induced toxicity and achieve its beneficial effect.

Mitochondria and NMDA receptor-dependent toxicity of berberine sensitizes neurons to glutamate and rotenone injury

The global incidence of metabolic and age-related diseases, including type 2 diabetes and Alzheimer's disease, is on the rise. In addition to traditional pharmacotherapy, drug candidates from complementary and alternative medicine are actively being pursued for further drug development. Berberine, a nutraceutical traditionally used as an antibiotic, has recently been proposed to act as a multi-target protective agent against type 2 diabetes, dyslipidemias, ischemic brain injury and neurodegenerative diseases, such as Parkinson's and Alzheimer's disease. However, the safety profile of berberine remains controversial, as isolated reports suggest risks with acute toxicity, bradycardia and exacerbation of neurodegeneration. We report that low micromolar berberine causes rapid mitochondria-dependent toxicity in primary neurons characterized by mitochondrial swelling, increased oxidative stress, decreased mitochondrial membrane potential and depletion of ATP content. Berberine does not induce caspase-3 activation and the resulting neurotoxicity remains unaffected by pan-caspase inhibitor treatment. Interestingly, inhibition of NMDA receptors by memantine and MK-801 completely blocked berberine-induced neurotoxicity. Additionally, subtoxic nanomolar concentrations of berberine were sufficient to sensitize neurons to glutamate excitotoxicity and rotenone injury. Our study highlights the need for further safety assessment of berberine, especially due to its tendency to accumulate in the CNS and the risk of potential neurotoxicity as a consequence of increasing bioavailability of berberine.

MPP(+) -dependent inhibition of Ih reduces spontaneous activity and enhances EPSP summation in nigral dopamine neurons

BACKGROUND AND PURPOSE

1-Methyl-4-phenylpyridinium (MPP(+) ), a potent parkinsonizing agent in primates and rodents, is a blocker of mitochondrial complex I, therefore MPP(+) -induced parkinsonism is believed to depend largely on mitochondrial impairment. However, it has recently been proposed that other mechanisms may participate in MPP(+) -induced toxicity. We tackled this issue by probing the effects of an acute application of MPP(+) on substantia nigra pars compacta (SNc) dopamine (DA) neurons.

EXPERIMENTAL APPROACH

The effects of MPP(+) on SNc DA neurons in acute midbrain slices were investigated with electrophysiology techniques.

KEY RESULTS

MPP(+) (50 μM) was able to (i) hyperpolarize SNc DA neurons by ∼6 mV; (ii) cause an abrupt and marked (over 50%) reduction of the spontaneous activity; and (iii) inhibit the hyperpolarization-activated inward current (Ih ). MPP(+) shifted Ih activation curve towards negative potentials by ∼11 mV both in Wistar rats and in C57/BL6 mice. Inhibition was voltage- and concentration-dependent (Imax = 47%, IC50 = 7.74 μM). MPP(+) slowed Ih activation kinetics at all potentials. These effects were not dependent on (i) block of mitochondrial complex I/fall of ATP levels; (ii) activation of type 2 DA receptor; and (iii) alteration of cAMP metabolism. Finally, MPP(+) -dependent inhibition of Ih facilitated temporal summation of evoked EPSPs in SNc DA, but not in CA1 hippocampal neurons.

CONCLUSION AND IMPLICATIONS

Reduced functionality of Ih in SNc DA neurons, via increased responsiveness towards synaptic excitation, might play a role in MPP(+) -induced parkinsonism and, possibly, in the pathogenesis of human Parkinson's.

Targeting heat shock proteins to modulate α-synuclein toxicity

Parkinson's disease is a slowly progressive neurodegenerative disorder typically characterized by the loss of dopaminergic neurons within the substantia nigra pars compacta, and the intraneuronal deposition of insoluble protein aggregates chiefly comprised of α-synuclein. Patients experience debilitating symptoms including bradykinesia, rigidity and postural instability. No curative treatment currently exists and therapeutic strategies are restricted to symptomatic treatment only. Over the past decade a class of molecular chaperones called the heat shock proteins has emerged as a potentially promising therapeutic target. Heat shock proteins aid in the folding and refolding of proteins, and target denatured proteins to degradation systems. By targeting heat shock proteins through various means including overexpression and pharmacological enhancement, researchers have shown that α-synuclein aggregation and its associated cytotoxicity can be therapeutically modulated in an array of cell and animal models. This review highlights the relevant progress in this field and discusses the relevance of heat shock proteins as therapeutic modulators of α-synuclein toxicity to the rapidly evolving understanding of Parkinson's disease pathogenesis.

Changes in mitochondrial function are pivotal in neurodegenerative and psychiatric disorders: how important is BDNF?

The brain is at the very limit of its energy supply and has evolved specific means of adapting function to energy supply, of which mitochondria form a crucial link. Neurotrophic and inflammatory processes may not only have opposite effects on neuroplasticity, but also involve opposite effects on mitochondrial oxidative phosphorylation and glycolytic processes, respectively, modulated by stress and glucocorticoids, which also have marked effects on mood. Neurodegenerative processes show marked disorders in oxidative metabolism in key brain areas, sometimes decades before symptoms appear (Parkinson's and Alzheimer's diseases). We argue that brain-derived neurotrophic factor couples activity to changes in respiratory efficiency and these effects may be opposed by inflammatory cytokines, a key factor in neurodegenerative processes.

Mitochondrial dysfunction, oxidative stress, and neurodegeneration elicited by a bacterial metabolite in a C. elegans Parkinson's model

Genetic and idiopathic forms of Parkinson's disease (PD) are characterized by loss of dopamine (DA) neurons and typically the formation of protein inclusions containing the alpha-synuclein (α-syn) protein. Environmental contributors to PD remain largely unresolved but toxins, such as paraquat or rotenone, represent well-studied enhancers of susceptibility. Previously, we reported that a bacterial metabolite produced by Streptomyces venezuelae caused age- and dose-dependent DA neurodegeneration in Caenorhabditis elegans and human SH-SY5Y neurons. We hypothesized that this metabolite from a common soil bacterium could enhance neurodegeneration in combination with PD susceptibility gene mutations or toxicants. Here, we report that exposure to the metabolite in C. elegans DA neurons expressing human α-syn or LRRK2 G2019S exacerbates neurodegeneration. Using the PD toxin models 6-hydroxydopamine and rotenone, we demonstrate that exposure to more than one environmental risk factor has an additive effect in eliciting DA neurodegeneration. Evidence suggests that PD-related toxicants cause mitochondrial dysfunction, thus we examined the impact of the metabolite on mitochondrial activity and oxidative stress. An ex vivo assay of C. elegans extracts revealed that this metabolite causes excessive production of reactive oxygen species. Likewise, enhanced expression of a superoxide dismutase reporter was observed in vivo. The anti-oxidant probucol fully rescued metabolite-induced DA neurodegeneration, as well. Interestingly, the stress-responsive FOXO transcription factor DAF-16 was activated following exposure to the metabolite. Through further mechanistic analysis, we discerned the mitochondrial defects associated with metabolite exposure included adenosine triphosphate impairment and upregulation of the mitochondrial unfolded protein response. Metabolite-induced toxicity in DA neurons was rescued by complex I activators. RNA interference (RNAi) knockdown of mitochondrial complex I subunits resulted in rescue of metabolite-induced toxicity in DA neurons. Taken together, our characterization of cellular responses to the S. venezuelae metabolite indicates that this putative environmental trigger of neurotoxicity may cause cell death, in part, through mitochondrial dysfunction and oxidative stress.

Pinocembrin protects SH-SY5Y cells against MPP+-induced neurotoxicity through the mitochondrial apoptotic pathway

Pinocembrin (PB), the most abundant flavonoid in propolis, has been proven to have neuroprotective property against neurotoxicity in vivo and in vitro. Our recent study demonstrated the neuroprotective effect of PB against Aβ25-35-induced SH-SY5Y neurotoxicity. However, the mechanism as how PB can induce neuroprotection is not known. In the present study, we demonstrate here that PB abrogates the effects of the neurotoxin 1-methyl-4-phenylpyridinium (MPP(+)) which mimics Parkinson's disease (PD) with elevation of intracellular reactive oxygen species (ROS) level and apoptotic death. We found that pretreatment of SH-SY5Y cells with PB significantly reduced the MPP(+)-induced loss of cell viability, the generation of intracellular ROS, apoptotic rate, and the cleavage of caspase-3. PB strikingly inhibited MPP(+)-induced mitochondrial dysfunctions, including lowered membrane potential, decreased Bcl-2/Bax ratio, and the release of cytochrome c. Overall, these results suggest that PB is intimately involved in inhibiting MPP(+)-induced loss of mitochondrial function and induction of apoptosis that contributes toward neuronal survival. These data indicated that PB might provide a valuable therapeutic strategy for the treatment of PD.

Co-administration of betulinic acid and methamphetamine causes toxicity to dopaminergic and serotonergic nerve terminals in the striatum of late adolescent rats

Psychostimulant methamphetamine (METH) is toxic to striatal dopaminergic and serotonergic nerve terminals in adult, but not in the adolescent, brain. Betulinic acid (BA) and its derivatives are promising anti-HIV agents with some toxic properties. Many METH users, particularly young men, are HIV-positive; therefore, they might be treated with BA or its derivative for HIV infection. It is not known whether BA, or any of its derivatives, are neurotoxic in combination with METH in the adolescent brain. The present study investigated the effects of BA and binge METH in the striatum of late adolescent rats. BA or METH alone did not decrease the levels of dopaminergic or serotonergic markers in the striatum whereas BA and METH together decreased these markers in a BA dose-dependent manner. BA+METH also caused decreases in the levels of mitochondrial complex I in the same manner; BA alone only slightly decreased the levels of this enzyme in striatal synaptosomes. BA or METH alone increased cytochrome c. METH alone decreased parkin, increased complex II and striatal BA levels. These results suggest that METH in combination with BA can be neurotoxic to striatal dopaminergic and serotonergic nerve terminals in the late adolescent brain via mitochondrial dysfunction and parkin deficit. We report a synergistic neurotoxicity of betulinic acid (BA) and methamphetamine (METH) to monoaminergic terminals in the striatum of male late adolescent rats. BA contribution to the neurotoxicity is decreasing mitochondrial complex I whereas METH contribution is decreasing parkin and increasing brain concentration of BA. We propose that clinical use of BA in young male METH users can be neurotoxic.

NAD(+) treatment prevents rotenone-induced apoptosis and necrosis of differentiated PC12 cells

Nicotinamide adenine dinucleotide (NAD(+)) plays critical roles in not only energy metabolism and mitochondrial functions, but also calcium homeostasis and immunological functions. It has been reported that NAD(+) administration can reduce ischemic brain damage. However, the mechanisms underlying the protective effects remain unclear. Because mitochondrial impairments play a key role in the cell death in cerebral ischemia, in this study we tested our hypothesis that NAD(+) can decrease mitochondrial damage-induced cell death using differentiated PC12 cells as a cellular model. We found that NAD(+) can decrease both early-stage and late-stage apoptosis, as well as necrosis of rotenone-treated PC12 cells, as assessed by FACS-based Annexin V/AAD assay. We also found that NAD(+) treatment can restore the intracellular NAD(+) levels of the rotenone-treated cells. Moreover, NAD(+) treatment can prevent rotenone-induced mitochondria depolarization. In summary, our study has provided first direct evidence that NAD(+) treatment can prevent rotenone-induced apoptosis and necrosis. Our study has also indicated that NAD(+) treatment can prevent mitochondrial damage-induced cell death, which may at least partially result from its protective effects on rotenone-induced mitochondrial depolarization. Because both mitochondrial damage and apoptosis play key roles in multiple neurological disorders, our study has highlighted the therapeutic potential of NAD(+) for brain ischemia and other neurological diseases.

Rotenone induces neuronal death by microglial phagocytosis of neurons

Rotenone, a common pesticide and inhibitor of mitochondrial complex I, induces microglial activation and loss of dopaminergic neurons in models of Parkinson's disease. However, the mechanisms of rotenone neurotoxicity are still poorly defined. Here, we used primary neuronal/glial cultures prepared from rat cerebella to investigate the contribution of microglia to neuronal cell death induced by low concentrations of rotenone. Rotenone at 2.5 nm induced neuronal loss over several days without increasing the numbers of necrotic or apoptotic neurons, and neuronal loss/death could be prevented by selective removal of microglia. Rotenone increased microglial proliferation and phagocytic activity, without increasing tumour necrosis factor-α release. Rotenone-induced neuronal loss/death could be prevented by inhibition of phagocytic signalling between neurons and microglia with: cyclo(Arg-Gly-Asp-d-Phe-Val) (to block the microglial vitronectin receptor); MRS2578 (to block the microglial P2Y6 receptor); or either annexin V or an antibody against phosphatidylserine (to block exposed phosphatidylserine, a well-characterized neuronal 'eat-me' signal). As inhibition of phagocytosis by five different means prevented neuronal loss without increasing neuronal death, these data indicate that rotenone neurotoxicity is at least partially mediated by microglial phagocytosis of otherwise viable neurons (phagoptosis). Thus, neuronal loss in Parkinson's disease and other neurological diseases might be prevented by blocking phagocytic signalling.

A phenotypic model recapitulating the neuropathology of Parkinson's disease

This study was undertaken to develop a phenotypic model recapitulating the neuropathology of Parkinson's disease (PD). Such a model would show loss of dopamine in the basal ganglia, appearance of Lewy bodies, and the early stages of motor dysfunction. The model was developed by subcutaneously injecting biodegradable microspheres of rotenone, a complex I inhibitor in 8-9 month old, ovariectomized Long-Evans rats. Animals were observed for changes in body weight and motor activity. At the end of 11-12 weeks animals were euthanized and the brains examined for histopathological changes. Rotenone treated animals gain weight and appear normal and healthy as compared to controls but showed modest hypokinesia around 5-6 weeks posttreatment. Animals showed loss of dopaminergic (DA) neurons and the appearance of putative Lewy bodies in the substantia nigra. Neuroinflammation and oxidative stress were evidenced by the appearance of activated microglia, iron precipitates, and 8-oxo-2'-deoxyguanosine a major product of DNA oxidation. The dorsal striatum, the projection site of midbrain DA neurons, showed a significant reduction in tyrosine hydroxylase immunostaining, together with an increase in reactive astrocytes, an early sign of DA nerve terminal damage. Levels of vesicular monoamine transporter 2 (VMAT2) were significantly reduced in the dorsal striatum; however, there was an unexpected increase in dopamine transporter (DAT) levels. Old, ovariectomized females treated with rotenone microspheres present with normal weight gain and good health but a modest hypokinesia. Accompanying this behavioral phenotype are a constellation of neuropathologies characteristic of PD that include loss of DA neurons, microglia activation, oxidative damage to nuclear DNA, iron deposition, and appearance of putative Lewy bodies. This phenotypic model recapitulating the neuropathology of Parkinson's disease could provide insight into early mechanisms of pathogenesis and could aid in the identification of biomarkers to identify patients in early stage, PD.

Transcriptomic and proteomic responses of sweetpotato whitefly, Bemisia tabaci, to thiamethoxam

BACKGROUND

The sweetpotato whitefly, Bemisia tabaci (Hemiptera: Aleyrodidae), is one of the most widely distributed agricultural pests. Although it has developed resistance to many registered insecticides including the neonicotinoid insecticide thiamethoxam, the mechanisms that regulate the resistance are poorly understood. To understand the molecular basis of thiamethoxam resistance, "omics" analyses were carried out to examine differences between resistant and susceptible B. tabaci at both transcriptional and translational levels.

RESULTS

A total of 1,338 mRNAs and 52 proteins were differentially expressed between resistant and susceptible B. tabaci. Among them, 11 transcripts had concurrent transcription and translation profiles. KEGG analysis mapped 318 and 35 differentially expressed genes and proteins, respectively, to 160 and 59 pathways (p<0.05). Thiamethoxam treatment activated metabolic pathways (e.g., drug metabolism), in which 118 transcripts were putatively linked to insecticide resistance, including up-regulated glutathione-S-transferase, UDP glucuronosyltransferase, glucosyl/glucuronosyl transferase, and cytochrome P450. Gene Ontology analysis placed these genes and proteins into protein complex, metabolic process, cellular process, signaling, and response to stimulus categories. Quantitative real-time PCR analysis validated "omics" response, and suggested a highly overexpressed P450, CYP6CX1, as a candidate molecular basis for the mechanistic study of thiamethoxam resistance in whiteflies. Finally, enzymatic activity assays showed elevated detoxification activities in the resistant B. tabaci.

CONCLUSIONS

This study demonstrates the applicability of high-throughput omics tools for identifying molecular candidates related to thiamethoxam resistance in an agricultural important insect pest. In addition, transcriptomic and proteomic analyses provide a solid foundation for future functional investigations into the complex molecular mechanisms governing the neonicotinoid resistance in whiteflies.

Neuroprotective and behavioural assessments of an imidazolium compound (DBZIM) in a rat model of Parkinson's disease induced by 6-OHDA

The neuroprotective effect of DBZIM, a novel imidazolium compound, has previously been documented to slow down neurodegeneration in a mouse model of Parkinson's disease. In this study, we conducted behavioural studies and further investigated the neuroprotection in a rat Parkinsonian model induced by 6-hydroxydopamine (6-OHDA). DBZIM was found to significantly reduce the 6-OHDA-induced asymmetrical rotation and preferential usage of contralateral forelimbs. Furthermore, the degeneration of tyrosine hydroxylase immunopositive (TH+) dopaminergic neurones in the substantia nigra par compacta (SNc) was illustrated by immunohistochemistry. The significant loss of TH+ neurones by 6-OHDA administration was ameliorated by three different doses of DBZIM treatment in a bell-shape manner. Such neuroprotection was also observed in the 6-OHDA-lesioned striata. High-performance liquid chromatography (HPLC) analysis of the striatal tissues revealed that DBZIM beneficially maintained the dopamine level by slowing down its metabolism. In addition, DBZIM attenuated the activation of astrocytes and microglia. This suggests that anti-inflammation may be an additional mechanism underlying the DBZIM-mediated neuroprotection. These findings warrant further investigation of DBZIM as a promising and potent agent for the future treatment of Parkinson's disease.