Neuroprotective and neurorestorative strategies for Parkinson's disease

Liver X receptor α contribution to neuroinflammation and glial cells activation induced by MPTP: Implications for Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder whose etiology remains unknown. The immune system has been implicated in hallmarks of PD including aggregation of α-synuclein and death of dopaminergic neurons in the substantia nigra. As a core regulator of immune response and inflammation, liver X receptors (LXRs) have been shown to have protective effects in a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced mouse model of PD. With two isoforms of LXRs (LXRα and LXRβ) expressed in the brain, their roles and distributions in this tissue remain largely unexplored. Here, we used MPTP to mimic symptoms and biomedical changes seen in PD in LXRα-/- and wild-type mice to investigate the role of LXRα in the etiology and progression of PD. We found that MPTP is unable to induce motor deficits, anxiety-like behavior in LXRα-/- mice, which has been seen in WT mice. Gene ontology analysis of RNA sequencing revealed that knockout of LXRα led to enrichment of the process, including immune response and inflammation in the midbrain. In addition, MPTP did not lead to dopaminergic neuron death in the striatum and substantia nigra in LXRα-/- mice, the basal GFAP protein level, and pro-inflammatory cytokines were elevated in LXRα-/- mice. Lastly, the microglia activation and astrogliosis caused by MPTP intoxication we found in WT mice were abolished in LXRα-/- mice. To sum up, we conclude that LXRα is a critical regulator in MPTP intoxication and may play a unique role in astrogliosis seen in the neuroinflammation of PD.

Neural stimulation and modulation with sub-cellular precision by optomechanical bio-dart

Neural stimulation and modulation at high spatial resolution are crucial for mediating neuronal signaling and plasticity, aiding in a better understanding of neuronal dysfunction and neurodegenerative diseases. However, developing a biocompatible and precisely controllable technique for accurate and effective stimulation and modulation of neurons at the subcellular level is highly challenging. Here, we report an optomechanical method for neural stimulation and modulation with subcellular precision using optically controlled bio-darts. The bio-dart is obtained from the tip of sunflower pollen grain and can generate transient pressure on the cell membrane with submicrometer spatial resolution when propelled by optical scattering force controlled with an optical fiber probe, which results in precision neural stimulation via precisely activation of membrane mechanosensitive ion channel. Importantly, controllable modulation of a single neuronal cell, even down to subcellular neuronal structures such as dendrites, axons, and soma, can be achieved. This bio-dart can also serve as a drug delivery tool for multifunctional neural stimulation and modulation. Remarkably, our optomechanical bio-darts can also be used for in vivo neural stimulation in larval zebrafish. This strategy provides a novel approach for neural stimulation and modulation with sub-cellular precision, paving the way for high-precision neuronal plasticity and neuromodulation.

Ablation of Shank1 Protects against 6-OHDA-induced Cytotoxicity via PRDX3-mediated Inhibition of ER Stress in SN4741 Cells

BACKGROUND

Postsynaptic density (PSD) is an electron-dense structure that contains various scaffolding and signaling proteins. Shank1 is a master regulator of the synaptic scaffold located at glutamatergic synapses, and has been proposed to be involved in multiple neurological disorders.

METHODS

In this study, we investigated the role of shank1 in an in vitro Parkinson's disease (PD) model mimicked by 6-OHDA treatment in neuronal SN4741 cells. The expression of related molecules was detected by western blot and immunostaining.

RESULTS

We found that 6-OHDA significantly increased the mRNA and protein levels of shank1 in SN4741 cells, but the subcellular distribution was not altered. Knockdown of shank1 via small interfering RNA (siRNA) protected against 6-OHDA treatment, as evidenced by reduced lactate dehydrogenase (LDH) release and decreased apoptosis. The results of RT-PCR and western blot showed that knockdown of shank1 markedly inhibited the activation of endoplasmic reticulum (ER) stress associated factors after 6-OHDA exposure. In addition, the downregulation of shank1 obviously increased the expression of PRDX3, which was accompanied by the preservation of mitochondrial function. Mechanically, downregulation of PRDX3 via siRNA partially prevented the shank1 knockdowninduced protection against 6-OHDA in SN4741 cells.

CONCLUSION

In summary, the present study has provided the first evidence that the knockdown of shank1 protects against 6-OHDA-induced ER stress and mitochondrial dysfunction through activating the PRDX3 pathway.

Functional nanoparticle-enabled non-genetic neuromodulation

Stimulating ion channels targeting in neuromodulation by external signals with the help of functionalized nanoparticles, which integrates the pioneering achievements in the fields of neurosciences and nanomaterials, has involved into a novel interdisciplinary field. The emerging technique developed in this field enable simple, remote, non-invasive, and spatiotemporally precise nerve regulations and disease therapeutics, beyond traditional treatment methods. In this paper, we define this emerging field as nano-neuromodulation and summarize the most recent developments of non-genetic nano-neuromodulation (non-genetic NNM) over the past decade based on the innovative design concepts of neuromodulation nanoparticle systems. These nanosystems, which feature diverse compositions, structures and synthesis approaches, could absorb certain exogenous stimuli like light, sound, electric or magnetic signals, and subsequently mediate mutual transformations between above signals, or chemical reactions, to regulate stimuli-sensitive ion channels and ion migrations which play vital roles in the nervous system. We will also discuss the obstacles and challenges in the future development of non-genetic NNM, and propose its future developments, to add the further progress of this promising field.

Functional nanoparticle-enabled non-genetic neuromodulation

Stimulating ion channels targeting in neuromodulation by external signals with the help of functionalized nanoparticles, which integrates the pioneering achievements in the fields of neurosciences and nanomaterials, has involved into a novel interdisciplinary field. The emerging technique developed in this field enable simple, remote, non-invasive, and spatiotemporally precise nerve regulations and disease therapeutics, beyond traditional treatment methods. In this paper, we define this emerging field as nano-neuromodulation and summarize the most recent developments of non-genetic nano-neuromodulation (non-genetic NNM) over the past decade based on the innovative design concepts of neuromodulation nanoparticle systems. These nanosystems, which feature diverse compositions, structures and synthesis approaches, could absorb certain exogenous stimuli like light, sound, electric or magnetic signals, and subsequently mediate mutual transformations between above signals, or chemical reactions, to regulate stimuli-sensitive ion channels and ion migrations which play vital roles in the nervous system. We will also discuss the obstacles and challenges in the future development of non-genetic NNM, and propose its future developments, to add the further progress of this promising field.

Graphical Abstract

Identification of novel glucocerebrosidase chaperone for potential treatment of Parkinson's disease: An approach using in silico virtual screening, molecular docking and molecular dynamics, and in vitro studies

Glucocerebrosidase (GCase), a GBA1 gene-encoded lysosomal enzyme, is a risk factor for Parkinson's disease (PD). Chaperones that increase GCase activity can potentially be disease-modifying agents in PD. To date, none of the registered treatments has demonstrated disease-modifying effects. Thus, chaperones for GCase were identified using in-silico virtual screening, molecular property filtering, and molecular dynamics and validated by circular dichroism, FT-IR, and Raman spectroscopies. In-vitro enzyme kinetics, thermal denaturation assay (TDA), and cell-line model were used to test their potential for GCase In-silico investigation revealed four compounds as candidate chaperones with adequate brain penetrability and binding energy (BE). Of them, GC466 showed ideal chaperoning characteristics, including potent BE -8.92 ± 0.68 Kcal/mol and binding affinity (K_i) 0.64 ± 0.12 μM against rGCase (Asp146, Phe265, and His329 residues) at pH 7.0 than at 4.5 (BE: -5.06 Kcal/mol, K_i: not found). Spectroscopic results confirmed the stability of GCase by GC466. TDA determined its chaperoning behavior, signified by improved rGCase thermal stabilization with stabilization ratio of 10.20 at 10 μM. In addition, it demonstrated GCase restorative, neurorestorative, and ROS scavenging activity in 6-OHDA treated cell-line model. Therefore, the present study may offer a novel chaperone with the potential to be a disease-modifying agent for PD.

Efficient Entrapment of Alpha-Synuclein Biotinylated Antibody in KCC-1-NH-CS2 and Application for the Sensitive Diagnosis of Parkinson's Using Recognition of Biomarker: An Innovative Electrochemical Label-Free Immunosensor for the Biomedical Analysis of Neurodegenerative Diseases

The early detection of Parkinson's disease (PD) is a critical issue in terms of efficiency. Alpha-synuclein (α-Syn) is a biomarker in PD checks. Alpha-synuclein (α-syn) is the major constituent of Lewy bodies and a pathogenic hallmark of all synucleinopathies, including PDs, dementia with Lewy bodies, and multiple system atrophy. In this study, KCC-1-NH-CS₂ was conjugated with biotinylated Ab and entrapped in P(β-CD) polymer cavities. Using this approach, a novel electrochemical label-free immunosensor was designed for the quantification of α-syn in real human samples. For this purpose, the glassy carbon electrode electropolymerized with P(β-CD) biopolymer provided an excellent matrix for entrapping of KCC-1-NH-CS₂ loaded with the biotinylated antibody of α-syn. Using the chronoamperometric technique, the proposed immunosensor shows a suitable range of 0.02 to 64 ng/mL for the determination of α-syn. Additionally, a low limit of quantification of the engineered biosensor was obtained at 0.02 ng/mL. The developed immunosensor's adequate stability, sensitivity, and selectivity, together with its ease of manufacture, make it a promising diagnostic technique for further research. This study also will pave the way for further applications of the synergetic effect of β-CD and KCC-1-NH-CS₂ for biomedical analysis in the near future.

Aza-Flavanone Diminishes Parkinsonism in the Drosophila melanogaster Parkin Mutant

Parkinson's disease is a chronic and progressive neurodegenerative disease, induced by slow and progressive death of the dopaminergic (DA) neurons from the midbrain region called substantia nigra (SNc) leading to difficulty in locomotion. At present, very few potential therapeutic drugs are available for treatment, necessitating an urgent need for development. In the current study, the parkin transgenic Drosophila melanogaster model that induces selective loss in dopaminergic neurons and impairment of locomotory functions has been used to see the effect of the aza-flavanone molecule. D. melanogaster serves as an amazing in vivo model making valuable contribution in the development of promising treatment strategies. Our in-silico study showed spontaneous binding of this molecule to the D2 receptor making it a potential dopamine agonist. PARKIN protein is well conserved, and it has been reported that Drosophila PARKIN is 42% identical to human PARKIN. Interestingly, this molecule enhances the motor coordination and survivability rate of the transgenic flies along with an increase in expression of the master regulator of Dopamine synthesis, that is, tyrosine hydroxylase (TH), in the substantia nigra region of the fly brain. Moreover, it plays a significant effect on mitochondrial health and biogenesis via modulation of a conserved mitochondrial protein PHB2. Therefore, this molecule could lead to the development of an effective therapeutic approach for the treatment of PD.

Quercetin exhibits potent antioxidant activity, restores motor and non-motor deficits induced by rotenone toxicity

The rotenone-induced animal model of Parkinson's disease (PD) has been used to investigate the pathogenesis of PD. Oxidative stress is one of the main contributors of neurodegeneration in PD. Flavonoids have the potential to modulate neuronal function and combat various neurodegenerative diseases. The pre- and post-supplementation of quercetin (50 mg/kg, p.o) was done in rats injected with rotenone (1.5 mg/kg, s.c). After the treatment, behavioral activities were monitored for motor activity, depression-like behavior, and cognitive changes. Rats were decapitated after behavioral analysis and the brain samples were dissected out for neurochemical and biochemical estimation. Results showed that supplementation of quercetin significantly (p<0.01) restored rotenone-induced motor and non-motor deficits (depression and cognitive impairments), enhanced antioxidant enzyme activities (p<0.01), and attenuated neurotransmitter alterations (p<0.01). It is suggested that quercetin supplementation improves neurotransmitter levels by mitigating oxidative stress via increasing antioxidant enzyme activity and hence improves motor activity, cognitive functions, and reduces depressive behavior. The results of the present study showed that quercetin pre-supplementation produced more significant results as compared to post-supplementation. These findings show that quercetin can be a potential therapeutic agent to reduce the risk and progression of PD.

Biosensors in Parkinson's disease

Parkinson's disease (PD) is one of the most critical disorders of the elderly and strongly associated with increased disability, and reduced quality of life. PD is a progressive neurodegenerative disease affecting more than six million people worldwide. Evaluation of clinical manifestations, as well as movement disorders by a neurologist and some routine laboratory tests are the most important diagnostic methods for PD. However, routine and old methods have several disadvantages and limitations such as low sensitivity and selectivity, high cost, and need for advanced equipment. Biosensors technology opens up new diagnoses approach for PD with the use of a new platform that allows reliable, repeatable, and multidimensional identification to be made with minimal problem and discomfort for patients. For instance, biosensing systems can provide promising tools for PD treatment and monitoring. Amongst biosensor technology, electrochemical techniques have been at the frontline of this progress, thanks to the developments in material science, such as gold nanoparticles (AuNPs), quantum dots (QDs), and carbon nanotubes (CNTs). This paper evaluates the latest progress in electrochemical and optical biosensors for PD diagnosis.

Neuroprotective and Neurorestorative Effects of Holothuria scabra Extract in the MPTP/MPP+-Induced Mouse and Cellular Models of Parkinson's Disease

Extracts from Holothuria scabra (HS) have been shown to possess anti-inflammation, anti-oxidant and anti-cancer activities. More recently, it was shown to have neuroprotective potential in Caenorhabditis elegans PD model. Here, we assessed whether HS has neuroprotective and neurorestorative effects on dopaminergic neurons in both mouse and cellular models of PD. We found that both pre-treatment and post-treatment with HS improved motor deficits in PD mouse model induced with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) as determined by grid walk test. This was likely mediated by HS protective and restorative effects on maintaining the numbers of dopaminergic neurons and fibers in both substantia nigra pars compacta (SNpc) and striatum. In a cellular model of PD, HS significantly attenuated 1-methyl-4-phenylpyridinium (MPP⁺)-induced apoptosis of DAergic-like neurons differentiated from SH-SY5Y cells by enhancing the expression of Bcl-2, suppressing the expression of cleaved Caspase 3 and preventing depolarization of mitochondrial membrane. In addition, HS could stimulate the expression of tyrosine hydroxylase (TH) and suppressed the formation of α-synuclein protein. Taken together, our in vivo and in vitro findings suggested that HS is an attractive candidate for the neuroprotection rather than neurorestoration in PD.

Hepcidin Decreases Rotenone-Induced α-Synuclein Accumulation via Autophagy in SH-SY5Y Cells

Parkinson’s disease (PD) is a neurodegenerative disorder, and the hallmarks of this disease include iron deposition and α-synuclein (α-syn) aggregation. Hepcidin could reduce iron in the central and peripheral nervous systems. Here, we hypothesized that hepcidin could further decrease α-syn accumulation via reducing iron. Therefore, rotenone or α-syn was introduced into human neuroblastoma SH-SY5Y cells to imitate the pathological progress of PD in vitro. This study investigated the clearance effects of hepcidin on α-syn induced by a relatively low concentration of rotenone exposure or α-syn overexpression to elucidate the potential clearance pathway involved in this process. We demonstrated that SH-SY5Y cell viability was impaired after rotenone treatment in a dose-dependent manner. α-syn expression and iron content increased under a low concentration rotenone (25 nM for 3 days) treatment in SH-SY5Y cells. Pre-treatment with hepcidin peptide suppressed the abovementioned effects of rotenone. However, hepcidin did not affect treatment with rotenone under high iron conditions. Hepcidin also played a role in reducing α-syn accumulation in rotenone and α-syn overexpression conditions. We identified that the probable clearance effect of hepcidin on α-syn was mediated by the autophagy pathway using pretreatment with autophagy inhibitors (3-MA and CQ) and detection of autophagy protein markers (LC3II/I and p62). In conclusion, hepcidin eliminated α-syn expression via the autophagy pathway in rotenone-treated and α-syn overexpression SH-SY5Y cells. This study highlights that hepcidin may offer a potential therapeutic perspective in α-syn accumulation diseases.

Electromagnetized-Nanoparticle-Modulated Neural Plasticity and Recovery of Degenerative Dopaminergic Neurons in the Mid-Brain

The degeneration of dopaminergic neurons is a major contributor to the pathogenesis of mid-brain disorders. Clinically, cell therapeutic solutions, by increasing the neurotransmitter dopamine levels in the patients, are hindered by low efficiency and/or side effects. Here, a strategy using electromagnetized nanoparticles to modulate neural plasticity and recover degenerative dopamine neurons in vivo is reported. Remarkably, electromagnetic fields generated by the nanoparticles under ultrasound stimulation modulate intracellular calcium signaling to influence synaptic plasticity and control neural behavior. Dopaminergic neuronal functions are reversed by upregulating the expression tyrosine hydroxylase, thus resulting in ameliorating the neural behavioral disorders in zebrafish. This wireless tool can serve as a viable and safe strategy for the regenerative therapy of the neurodegenerative disorders.

Regulation of microglia by glutamate and its signal pathway in neurodegenerative diseases

Microglia are an essential component of the central nervous system (CNS) and are involved in the primary response to microorganisms, neuroinflammation, homeostasis, and tissue regeneration, as well as contributing to the pathogenesis of neurodegenerative diseases. Research has shown that microglial diversity, multifunctionality, and their relationship with glutamate are crucial to determining their roles in these diseases. In this review, we focus on recent progress in determining microglial characteristics and the role of glutamate and its receptors in microglia regulation, which could be a novel therapeutic strategy for neurodegenerative diseases.

Dopamine, a key factor of mitochondrial damage and neuronal toxicity on rotenone exposure and also parkinsonic motor dysfunction-Impact of asiaticoside with a probable vesicular involvement

Persuasive evidence propose that the toxicity of dopamine in parkinsonism and the loss of dopaminergic neurons are the earliest events during the pathogenesis of Parkinson's disease (PD). In our earlier study, Asiaticoside (AS), a triterpenoid saponin isolated from Centella asiatica was shown to exert a neuroprotective effect against hemiparkinsonism, purportedly due to phosphoinositides (PI)-assisted cytodynamics and synaptic function. Here, we evaluate AS in the modulation of dopamine (DA), mitochondrial integrity and neurite variations in vitro and motor dysfunctions in vivo. PC12 cells challenged with rotenone-(ROT) (0.1 μM/mL) were exposed to AS and l-DOPA (10 mM and 20 μM/mL respectively). The protein expressions of Bax and Bcl-2 that regulate cell death were assessed following neurite length assays. Rats were distributed into 6 groups (6 rats/group): Sham, Vehicle controls, ROT-infused (6 μg/μl/kg), AS- treated (50 mg/kg/day), Drug control, and ROT + L-DOPA-treated (6 mg/kg/day) groups. At the end of the experimental period, the rats were sacrificed after performing motor behavioral analysis, and the striatum was dissected out. The contents of synaptic vesicular and cytosolic DA were analyzed. Further, the levels of striatal PI were also measured. ROT had caused significant reduction in the neurite outgrowth in the exposed PC12 cells while the tested concentrations of AS and l-DOPA can exert their protective effect on the stunted neurite growth. The levels of Bax, Bcl-2, and cytochrome c which were significantly disturbed by ROT, could also be affected by AS thereby suggesting its effect on neurons. AS treatment caused an improved motor performance, vesicular and cytosolic DA, and striatal PI. These pre-clinical findings force us to speculate that AS could be a potential drug candidate in combating ROT-induced variations that are possibly precipitated by varied vesicular trafficking of DA.

Absence of a synergic nigral proapoptotic effect triggered by REM sleep deprivation in the rotenone model of Parkinson´s disease

Excitotoxicity has been related to play a crucial role in Parkinson's disease (PD) pathogenesis. Pedunculopontine tegmental nucleus (PPT) represents one of the major sources of glutamatergic afferences to nigrostriatal pathway and putative reciprocal connectivity between these structures may exert a potential influence on rapid eye movement (REM) sleep control. Also, PPT could be overactive in PD, it seems that dopaminergic neurons are under abnormally high levels of glutamate and consequently might be more vulnerable to neurodegeneration. We decided to investigate the neuroprotective effect of riluzole administration, a N-methyl-D-aspartate (NMDA) receptor antagonist, in rats submitted simultaneously to nigrostrial rotenone and 24h of REM sleep deprivation (REMSD). Our findings showed that blocking NMDA glutamatergic receptors in the SNpc, after REMSD challenge, protected the dopaminergic neurons from rotenone lesion. Concerning rotenone-induced hypolocomotion, riluzole reversed this impairment in the control groups. Also, REMSD prevented the occurrence of rotenone-induced motor impairment as a result of dopaminergic supersensitivity. In addition, higher Fluoro Jade C (FJC) staining within the SNpc was associated with decreased cognitive performance observed in rotenone groups. Such effect was counteracted by riluzole suggesting the occurrence of an antiapoptotic effect. Moreover, riluzole did not rescue cognitive impairment impinged by rotenone, REMSD or their combination. These data indicated that reductions of excitotoxicity, by riluzole, partially protected dopamine neurons from neuronal death and appeared to be effective in relieve specific rotenone-induce motor disabilities.

Impaired dopamine metabolism in Parkinson's disease pathogenesis

A full understanding of Parkinson's Disease etiopathogenesis and of the causes of the preferential vulnerability of nigrostriatal dopaminergic neurons is still an unsolved puzzle. A multiple-hit hypothesis has been proposed, which may explain the convergence of familial, environmental and idiopathic forms of the disease. Among the various determinants of the degeneration of the neurons in Substantia Nigra pars compacta, in this review we will focus on the endotoxicity associated to dopamine dyshomeostasis. In particular, we will discuss the relevance of the reactive dopamine metabolite 3,4-dihydroxyphenylacetaldehyde (DOPAL) in the catechol-induced neurotoxicity. Indeed, the synergy between the catechol and the aldehyde moieties of DOPAL exacerbates its reactivity, resulting in modification of functional protein residues, protein aggregation, oxidative stress and cell death. Interestingly, αSynuclein, whose altered proteostasis is a recurrent element in Parkinson's Disease pathology, is considered a preferential target of DOPAL modification. DOPAL triggers αSynuclein oligomerization leading to synapse physiology impairment. Several factors can be responsible for DOPAL accumulation at the pre-synaptic terminals, i.e. dopamine leakage from synaptic vesicles, increased rate of dopamine conversion to DOPAL by upregulated monoamine oxidase and decreased DOPAL degradation by aldehyde dehydrogenases. Various studies report the decreased expression and activity of aldehyde dehydrogenases in parkinsonian brains, as well as genetic variants associated to increased risk in developing the pathology. Thus, we discuss how the deregulation of these enzymes might be considered a contributing element in the pathogenesis of Parkinson's Disease or a down-stream effect. Finally, we propose that a better understanding of the impaired dopamine metabolism in Parkinson's Disease would allow a more refined patients stratification and the design of more targeted and successful therapeutic strategies.

GRK5 - A Functional Bridge Between Cardiovascular and Neurodegenerative Disorders

Complex aging-triggered disorders are multifactorial programs that comprise a myriad of alterations in interconnected protein networks over a broad range of tissues. It is evident that rather than being randomly organized events, pathophysiologies that possess a strong aging component such as cardiovascular diseases (hypertensions, atherosclerosis, and vascular stiffening) and neurodegenerative conditions (dementia, Alzheimer's disease, mild cognitive impairment, Parkinson's disease), in essence represent a subtly modified version of the intricate molecular programs already in place for normal aging. To control such multidimensional activities there are layers of trophic protein control across these networks mediated by so-called "keystone" proteins. We propose that these "keystones" coordinate and interconnect multiple signaling pathways to control whole somatic activities such as aging-related disease etiology. Given its ability to control multiple receptor sensitivities and its broad protein-protein interactomic nature, we propose that G protein coupled receptor kinase 5 (GRK5) represents one of these key network controllers. Considerable data has emerged, suggesting that GRK5 acts as a bridging factor, allowing signaling regulation in pathophysiological settings to control the connectivity between both the cardiovascular and neurophysiological complications of aging.

Gold nanoclusters for Parkinson's disease treatment

Drug discovery for Parkinson's disease (PD) is challenging. Here we report that gold nanoclusters (AuNCs) can serve as a novel candidate for the design of anti-PD drugs. With N-isobutyryl-l-cysteine (L-NIBC) protected AuNCs as an example, we show that AuNCs effectively prevent α-Synuclein (α-Syn) fibrillation in in vitro experiments. Cell experiments demonstrate good neuroprotective effects in PD cell models. More significantly, experiments of mouse PD model further show that AuNCs largely ameliorate the behavioral disorders of sick mice. In addition, immunohistochemical and western blot (WB) analyses indicate that AuNCs can significantly reverse dopaminergic (DA) neuron loss in substantia nigra and striatum of sick mice. This study opens up a novel avenue to develop anti-PD drugs and points a new direction for AuNCs in medicinal applications.

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.

Astrocytic JWA deletion exacerbates dopaminergic neurodegeneration by decreasing glutamate transporters in mice

Astrocytic JWA exerts neuroprotective roles by alleviating oxidative stress and inhibiting inflammation. However, the molecular mechanisms of how astrocytic JWA is involved in dopaminergic neurodegeneration in Parkinson's disease (PD) remain largely unknown. In this study, we found that astrocyte-specific JWA knockout mice (JWA CKO) exacerbated dopamine (DA) neuronal loss and motor dysfunction, and reduced the levels of DA and its metabolites in a 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine/probenecid (MPTP/p)-induced PD model. Astrocytic JWA deficiency repressed expression of excitatory amino-acid transporter 2 (GLT-1) and glutamate uptake both in vivo and in vitro. Further, the regulation of GLT-1 expression was involved in JWA-triggered activation of the MAPK and PI3K signaling pathways. JWA-increased GLT-1 expression was abolished by inhibitors of MEK and PI3K. Silencing CREB also abrogated JWA-increased GLT-1 expression and glutamate uptake. Additionally, JWA deficiency activated glial fibrillary acidic protein (GFAP), and increased the expression of STAT3. Similarly to the MPTP model, paraquat (PQ) exposure produced PD-like phenotypes in JWA CKO mice. Taken together, our findings provide novel insights into astrocytic JWA function in the pathogenesis of neurotoxin mouse models of PD.

Sorbus alnifolia protects dopaminergic neurodegeneration in Caenorhabditis elegans

CONTEXT

The twigs of Sorbus alnifolia (Sieb. et Zucc.) K. Koch (Rosaceae) have been used to treat neurological disorders as a traditional medicine in Korea. However, there are limited data describing the efficacy of S. alnifolia in Parkinson's disease (PD).

OBJECTIVE

This study was conducted to identify the protective effects of the methanol extracts of S. alnifolia (MESA) on the dopaminergic (DA) neurodegeneration in Caenorhabditis elegans.

MATERIALS AND METHODS

To test the neuroprotective action of MESA, viability assay was performed after 48 h exposure to 1-methyl-4-phenylpyridine (MMP+) in PC12 cells and C. elegans (400 μM and 2 mM of MMP+, respectively). Fluorescence intensity was quantified using transgenic mutants such as BZ555 (Pdat-1::GFP) and and UA57 (Pdat-1::GFP and Pdat-1::CAT-2) to determine MESA's effects on DA neurodegeneration in C. elegans. Aggregation of α-synuclein was observed using NL5901 strain (unc-54p::α-synuclein::YFP). MESA's protective effects on the DA neuronal functions were examined by food-sensing assay. Lifespan assay was conducted to test the effects of MESA on the longevity.

RESULTS

MESA restored MPP+-induced loss of viability in both PC12 cells and C. elegans (85.8% and 54.9%, respectively). In C. elegans, MESA provided protection against chemically and genetically-induced DA neurodegeneration, respectively. Moreover, food-sensing functions were increased 58.4% by MESA in the DA neuron degraded worms. MESA also prolonged the average lifespan by 25.6%. However, MESA failed to alter α-synuclein aggregation.

DISCUSSION AND CONCLUSIONS

These results revealed that MESA protects DA neurodegeneration and recovers diminished DA neuronal functions, thereby can be a valuable candidate for the treatment of PD.

Low Levels of Prohibitin in Substantia Nigra Makes Dopaminergic Neurons Vulnerable in Parkinson's Disease

Since substantia nigra (SN) and ventral tegmental area (VTA) dopaminergic neurons are, respectively, susceptible or largely unaffected in Parkinson's disease (PD), we searched for protein(s) that regulates this differential sensitivity. Differentially, expressed proteins in SN and VTA were investigated employing two-directional gel electrophoresis- matrix-assisted laser desorption ionization time of flight (MALDI-TOF-TOF) analyses. Prohibitin, which is involved in mitochondrial integrity, was validated using immunoblot, qRT-PCR, and immunohistochemistry in normal mice as well as 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-model, PD postmortem human brains, and PD cybrids. In prohibitin over-expression, differentiated SH-SY5Y neurons were investigated for their susceptibility to PD neurotoxin, 1-methyl-4-phenyl-pyridnium (MPP⁺). Prohibitin, Hsc73, and Cu-Zn superoxide dismutase (Cu-Zn SOD) were highly expressed in VTA, whereas heat shock protein A8 (HSPA8) and 14-3-3ζ/δ were 2-fold more in SN. Prohibitin level was transiently increased in SN but unaltered in VTA on the third day of MPTP-induced mice, whereas in PD human brains, prohibitin was depleted in both these regions. Parallel to mouse SN, an enhanced prohibitin expression was found in human PD cybrids. In MPP⁺-induced cellular model of PD, reduction in prohibitin level was found to be associated with a loss in its binding with Ndufs3, a mitochondrial complex I protein partner. Prohibitin over-expression resisted MPP⁺-induced neuronal death by restoring mitochondrial membrane potential, preventing reactive oxygen species generation and cytochrome c release into cytosol. These protective phenomena exerted by prohibitin over-expression altogether hinder caspase 3 activation induced by MPP⁺. These results imply that prohibitin is an important negotiator protein that regulates dopaminergic cell death in SN and their protection in VTA in PD.

MPP+-Lesioned Mice: an Experimental Model of Motor, Emotional, Memory/Learning, and Striatal Neurochemical Dysfunctions

The neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induces motor and nonmotor dysfunctions resembling Parkinson's disease (PD); however, studies investigating the effects of 1-methyl-4-phenylpyridinium (MPP⁺), an active oxidative product of MPTP, are scarce. This study investigated the behavioral and striatal neurochemical changes (related to oxidative damage, glial markers, and neurotrophic factors) 24 h after intracerebroventricular administration of MPP⁺ (1.8-18 μg/mouse) in C57BL6 mice. MPP⁺ administration at high dose (18 μg/mouse) altered motor parameters, since it increased the latency to leave the first quadrant and reduced crossing, rearing, and grooming responses in the open-field test and decreased rotarod latency time. MPP⁺ administration at low dose (1.8 μg/mouse) caused specific nonmotor dysfunctions as it produced a depressive-like effect in the forced swim test and tail suspension test, loss of motivational and self-care behavior in the splash test, anxiety-like effect in the elevated plus maze test, and short-term memory deficit in the step-down inhibitory avoidance task, without altering ambulation. MPP⁺ at doses of 1.8-18 μg/mouse increased tyrosine hydroxylase (TH) immunocontent and at 18 μg/mouse increased α-synuclein and decreased parkin immunocontent. The astrocytic calcium-binding protein S100B and glial fibrillary acidic protein (GFAP)/S100B ratio was decreased following MPP⁺ administration (18 μg/mouse). At this highest dose, MPP⁺ increased the ionized calcium-binding adapter molecule 1 (Iba-1) immunocontent, suggesting microglial activation. Also, MPP⁺ at a dose of 18 μg/mouse increased thiobarbituric acid reactive substances (TBARS) and glutathione (GSH) levels and increased glutathione peroxidase (GPx) and hemeoxygenase-1 (HO-1) immunocontent, suggesting a significant role for oxidative stress in the MPP⁺-induced striatal damage. MPP⁺ (18 μg/mouse) also increased striatal fibroblast growth factor 2 (FGF-2) and brain-derived neurotrophic factor (BDNF) levels. Moreover, MPP⁺ decreased tropomyosin receptor kinase B (TrkB) immunocontent. Finally, MPP⁺ (1.8-18 μg/mouse) increased serum corticosterone levels and did not alter acetylcholinesterase (AChE) activity in the striatum but increased it in cerebral cortex and hippocampus. Collectively, these results indicate that MPP⁺ administration at low doses may be used as a model of emotional and memory/learning behavioral deficit related to PD and that MPP⁺ administration at high dose could be useful for analysis of striatal dysfunctions associated with motor deficits in PD.

Protective Mechanisms of Flavonoids in Parkinson's Disease

Parkinson's disease is a chronic, debilitating neurodegenerative movement disorder characterized by progressive degeneration of dopaminergic neurons in the substantia nigra pars compacta region in human midbrain. To date, oxidative stress is the well accepted concept in the etiology and progression of Parkinson's disease. Hence, the therapeutic agent is targeted against suppressing and alleviating the oxidative stress-induced cellular damage. Within the past decades, an explosion of research discoveries has reported on the protective mechanisms of flavonoids, which are plant-based polyphenols, in the treatment of neurodegenerative disease using both in vitro and in vivo models. In this paper, we have reviewed the literature on the neuroprotective mechanisms of flavonoids in protecting the dopaminergic neurons hence reducing the symptoms of this movement disorder. The mechanism reviewed includes effect of flavonoids in activation of endogenous antioxidant enzymes, suppressing the lipid peroxidation, inhibition of inflammatory mediators, flavonoids as a mitochondrial target therapy, and modulation of gene expression in neuronal cells.

Chemical biology of compounds obtained from screening using disease models

Bioactive compounds are extremely powerful tools for studying biological systems because they can rapidly, conditionally, often reversibly, and dose-dependently modulate the biological function of living cells. Moreover, they are expected to be drug seeds for chemotherapy of several diseases. Two approaches are used to find and obtain bioactive compounds, namely, molecular-target-based screening and phenotypic screening. Through phenotypic screening that mimics tumor metastasis, multi-drug resistance, and Parkinson's disease, we identified several compounds that inhibit cancer cell migration, anti-apoptotic function of Bcl-2/Bcl-xL, and neuronal cell death. By using MEK inhibitor that was developed by target-based screening, we discovered that MEK inhibitor selectively induces apoptosis in tumor cells with β-catenin mutation. Using target-based screening, we identified arabilin, a novel androgen antagonist. In this review, we introduce our recent studies on the identification of bioactive compounds by phenotypic screening and by target-based screening for drug-seed discovery.

Aging decreases L-type calcium channel currents and pacemaker firing fidelity in substantia nigra dopamine neurons

Substantia nigra dopamine neurons are involved in behavioral processes that include cognition, reward learning, and voluntary movement. Selective deterioration of these neurons is responsible for the motor deficits associated with Parkinson's disease (PD). Aging is the leading risk factor for PD, suggesting that adaptations occurring in dopamine neurons during normal aging may predispose individuals to the development of PD. Previous studies suggest that the unique set of ion conductances that drive spontaneous, rhythmic firing of action potentials could predispose substantia nigra dopamine neurons to selective neurodegeneration. Here we show, using patch-clamp electrophysiological recordings in brain slices, that substantia nigra dopamine neurons from mice 25-30 months of age (old) have comparable membrane capacitance and input resistance to neurons from mice 2-7 months of age (young). However, neurons from old mice exhibit slower firing rates, narrower spike widths, and more variable interspike intervals compared with neurons from young mice. Dopamine neurons from old mice also exhibit smaller L-type calcium channel currents, providing a plausible mechanism that likely contributes to the changes in impulse activity. Age-related decrements in the physiological function of dopamine neurons could contribute to the decrease in voluntary movement and other dopamine-mediated behaviors observed in aging populations. Furthermore, as pharmacological antagonism of L-type calcium channels has been proposed as a potential treatment for the early stages of PD, our results could point to a limited temporal window of opportunity for this therapeutic intervention.

Role of aldehyde dehydrogenase 2 in 1-methy-4-phenylpyridinium ion-induced aldehyde stress and cytotoxicity in PC12 cells

Aldehyde stress contributes to molecular mechanisms of cell death and the pathogenesis of Parkinson's disease (PD). The neurotoxin 1-Methy-4-Phenylpyridinium Ion (MPP(+)) is commonly used to model PD. Aldehyde dehydrogenase 2 (ALDH2) is an important enzyme detoxifying aldehydes. The aim of this study is to evaluate whether MPP(+)-induced neurotoxicity is involved in aldehyde stress by modulation of ALDH2. Our results demonstrated that treatment of PC12 cells with MPP(+) leads to aldehyde stress by increasing in loads of malondialdehyde and 4-hydroxynonenal, which indicated that MPP(+)-induced aldehyde stress contributes to its cytotoxicity in PC12 cells. We also showed that MPP(+) up-regulates the expression and activity of ALDH2 in PC12 cells and that inhibition of ALDH2 by its specific inhibitor daidzin prevents MPP(+)-induced decrease in cell viability and increases in apoptosis, oxidative stress and aldehyde stress in PC12 cells. These findings suggest that aldehyde stress contributes to MPP(+)-induced toxicity in PC12 cells by upregulation of ALDH2. This study provides a novel insight into the role of ALDH2 in the neurotoxicity of MPP(+).

Intracellular methamphetamine prevents the dopamine-induced enhancement of neuronal firing

The dysregulation of the dopaminergic system is implicated in multiple neurological and neuropsychiatric disorders such as Parkinson disease and drug addiction. The primary target of psychostimulants such as amphetamine and methamphetamine is the dopamine transporter (DAT), the major regulator of extracellular dopamine levels in the brain. However, the behavioral and neurophysiological correlates of methamphetamine and amphetamine administration are unique from one another, thereby suggesting these two compounds impact dopaminergic neurotransmission differentially. We further examined the unique mechanisms by which amphetamine and methamphetamine regulate DAT function and dopamine neurotransmission; in the present study we examined the impact of extracellular and intracellular amphetamine and methamphetamine on the spontaneous firing of cultured midbrain dopaminergic neurons and isolated DAT-mediated current. In dopaminergic neurons the spontaneous firing rate was enhanced by extracellular application of amphetamine > dopamine > methamphetamine and was DAT-dependent. Amphetamine > methamphetamine similarly enhanced DAT-mediated inward current, which was sensitive to isosmotic substitution of Na(+) or Cl(-) ion. Although isosmotic substitution of extracellular Na(+) ions blocked amphetamine and methamphetamine-induced DAT-mediated inward current similarly, the removal of extracellular Cl(-) ions preferentially blocked amphetamine-induced inward current. The intracellular application of methamphetamine, but not amphetamine, prevented the dopamine-induced increase in the spontaneous firing of dopaminergic neurons and the corresponding DAT-mediated inward current. The results reveal a new mechanism for methamphetamine-induced dysregulation of dopaminergic neurons.

Identification of licopyranocoumarin and glycyrurol from herbal medicines as neuroprotective compounds for Parkinson's disease

In the course of screening for the anti-Parkinsonian drugs from a library of traditional herbal medicines, we found that the extracts of choi-joki-to and daio-kanzo-to protected cells from MPP⁺-induced cell death. Because choi-joki-to and daio-kanzo-to commonly contain the genus Glycyrrhiza, we isolated licopyranocoumarin (LPC) and glycyrurol (GCR) as potent neuroprotective principals from Glycyrrhiza. LPC and GCR markedly blocked MPP⁺-induced neuronal PC12D cell death and disappearance of mitochondrial membrane potential, which were mediated by JNK. LPC and GCR inhibited MPP⁺-induced JNK activation through the suppression of reactive oxygen species (ROS) generation, thereby inhibiting MPP⁺-induced neuronal PC12D cell death. These results indicated that LPC and GCR derived from choi-joki-to and daio-kanzo-to would be promising drug leads for PD treatment in the future.

Ubiquinone-quantum dot bioconjugates for in vitro and intracellular complex I sensing

Quantum dots (QDs) have attracted increasing interest in bioimaging and sensing. Here, we report a biosensor of complex I using ubiquinone-terminated disulphides with different alkyl spacers (QnNS, n = 2, 5 and 10) as surface-capping ligands to functionalise CdSe/ZnS QDs. The enhancement or quenching of the QD bioconjugates fluorescence changes as a function of the redox state of QnNS, since QDs are highly sensitive to the electron-transfer processes. The bioconjugated QnNS-QDs emission could be modulated by complex I in the presence of NADH, which simulates an electron-transfer system part of the mitochondrial respiratory chain, providing an in vitro and intracellular complex I sensor. Epidemiological studies suggest that Parkinson's patients have the impaired activity of complex I in the electron-transfer chain of mitochondria. We have demonstrated that the QnNS-QDs system could aid in early stage Parkinson's disease diagnosis and progression monitoring by following different complex I levels in SH-SY5Y cells.

Opportunities and challenges of pluripotent stem cell neurodegenerative disease models

Human neurodegenerative disorders are among the most difficult to study. In particular, the inability to readily obtain the faulty cell types most relevant to these diseases has impeded progress for decades. Recent advances in pluripotent stem cell technology now grant access to substantial quantities of disease-pertinent neurons both with and without predisposing mutations. While this suite of technologies has revolutionized the field of 'in vitro disease modeling', great care must be taken in their deployment if robust, durable discoveries are to be made. Here we review what we perceive to be several of the stumbling blocks in the use of stem cells for the study of neurological disease and offer strategies to overcome them.

Isolation, characterization, and neuroprotective activities of sesquiterpenes from Petasites japonicus

Neuroprotective reagents to protect the nerve cells against oxidative stress and other damages are potentially effective for the medical treatment of Parkinson's disease. Petasites japonicus, a wild vegetable, belongs to the family Compositae and its extract has shown the neuroprotective effects. A further phytochemical investigation of P. japonicus for neuroprotective substances led to the isolation of eight new (1-8) and two known (9 and 10) sesquiterpenes. Their structures were elucidated on the basis of extensive 1D and 2D NMR (HMQC, HMBC, (1)H-(1)H COSY, and NOESY) spectroscopic data analyses, and the structure of 1 was confirmed by X-ray crystallography. The neuroprotective activities of these sesquiterpenes were evaluated against cobalt chloride (CoCl2)-induced neuronal cell death in human dopaminergic SH-SY5Y cells. Five compounds showed a neuroprotective activity.

SF-6 attenuates 6-hydroxydopamine-induced neurotoxicity: an in vitro and in vivo investigation in experimental models of Parkinson's disease

ETHNOPHARMACOLOGICAL RELEVANCE

Indigofera tinctoria Linn. (I. tinctoria, Fabaceae) has been widely used for several years in the traditional Indian and Chinese system of Medicine for the treatment of epilepsy, nervous and brain disorders.

AIM OF THE STUDY

The effect of SF-6, a compound isolated from I. tinctoria to exhibit neuroprotection in in vitro and in vivo models of Parkinson's disease (PD), was investigated.

MATERIALS AND METHODS

Using human neuroblastoma SH-SY5Y cells, the effect of SF-6 on α-synuclein- or 6-hydroxydopamine (6-OHDA)-, hydrogen peroxide (H(2)O(2))-induced cytotoxicity in vitro was investigated. In in vivo studies SF-6 was challenged against 6-OHDA-induced neuronal damage and behavioral deficits in mice.

RESULTS

SF-6 (1, 5 and 10 μg/mL) significantly inhibited α-synuclein- or 6-OHDA-, H(2)O(2)-induced cytotoxicity and decreased the reactive oxygen species production in SH-SY5Y cells. SF-6 also scavenged hydroxyl free radicals. In in vivo evaluation, SF-6 attenuated the contralateral rotational asymmetry observed by apomorphine challenge in 6-OHDA-lesioned mice. Further, the behavioral deficits evaluated by rotarod test, Y-maze and passive avoidance tasks were reversed by SF-6 and was found more potent compared with standard compound deprenyl.

CONCLUSION

Data suggest that SF-6 showed neuroprotection in experimental models of PD due to its potent antioxidant action supporting the traditional claim for its use in nervous and brain disorders.

Parkin promotes degradation of the mitochondrial pro-apoptotic ARTS protein

Parkinson's disease (PD) is associated with excessive cell death causing selective loss of dopaminergic neurons. Dysfunction of the Ubiquitin Proteasome System (UPS) is associated with the pathophysiology of PD. Mutations in Parkin which impair its E3-ligase activity play a major role in the pathogenesis of inherited PD. ARTS (Sept4_i2) is a mitochondrial protein, which initiates caspase activation upstream of cytochrome c release in the mitochondrial apoptotic pathway. Here we show that Parkin serves as an E3-ubiquitin ligase to restrict the levels of ARTS through UPS-mediated degradation. Though Parkin binds equally to ARTS and Sept4_i1 (H5/PNUTL2), the non-apoptotic splice variant of Sept4, Parkin ubiquitinates and degrades only ARTS. Thus, the effect of Parkin on ARTS is specific and probably related to its pro-apoptotic function. High levels of ARTS are sufficient to promote apoptosis in cultured neuronal cells, and rat brains treated with 6-OHDA reveal high levels of ARTS. However, over-expression of Parkin can protect cells from ARTS-induced apoptosis. Furthermore, Parkin loss-of-function experiments reveal that reduction of Parkin causes increased levels of ARTS and apoptosis. We propose that in brain cells in which the E3-ligase activity of Parkin is compromised, ARTS levels increase and facilitate apoptosis. Thus, ARTS is a novel substrate of Parkin. These observations link Parkin directly to a pro-apoptotic protein and reveal a novel connection between Parkin, apoptosis, and PD.

Animal models of Parkinson's disease: limits and relevance to neuroprotection studies

Over the last two decades, significant strides has been made toward acquiring a better knowledge of both the etiology and pathogenesis of Parkinson's disease (PD). Experimental models are of paramount importance to obtain greater insights into the pathogenesis of the disease. Thus far, neurotoxin-based animal models have been the most popular tools employed to produce selective neuronal death in both in vitro and in vivo systems. These models have been commonly referred to as the pathogenic models. The current trend in modeling PD revolves around what can be called the disease gene-based models or etiologic models. The value of utilizing multiple models with a different mechanism of insult rests on the premise that dopamine-producing neurons die by stereotyped cascades that can be activated by a range of insults, from neurotoxins to downregulation and overexpression of disease-related genes. In this position article, we present the relevance of both pathogenic and etiologic models as well as the concept of clinically relevant designs that, we argue, should be utilized in the preclinical development phase of new neuroprotective therapies before embarking into clinical trials.

Lithium and valproate prevent olfactory discrimination and short-term memory impairments in the intranasal 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) rat model of Parkinson's disease

We have recently demonstrated that rodents treated intranasally with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) display time-dependent impairments in olfactory, emotional, cognitive and motor functions associated with disruption of dopaminergic neurotransmission in different brain structures conceivably analogous to those observed during different stages of Parkinson's disease (PD). On the other hand, lithium (Li) and valproate (VPA) are two primary drugs used to treat bipolar mood disorder that have recently emerged as promising neuroprotective agents. The present data indicates that the pretreatment with Li (47.5 mg/kg) or VPA (200 mg/kg) by intraperitoneal route during 7 consecutive days was able to prevent olfactory discrimination and short-term memory impairments evaluated in the social recognition and step-down inhibitory avoidance tasks in rats infused with a single intranasal (i.n.) administration of MPTP (0.1 mg/nostril). Despite the absence of clear depressive-like responses following the current MPTP dose, Li and VPA treatment presented an antidepressant profile reducing the immobility time in the forced swimming test. Importantly, at this time no significant alterations on the locomotor activity of the animals were observed in the open field test. Moreover, Li and VPA prevented dopamine depletion in the olfactory bulb and striatum of MPTP-infused rats. These results provide new insights in experimental models of PD, indicating that Li and VPA may represent new therapeutic tools for the management of olfactory and cognitive symptoms associated to early preclinical phases of PD, together with their neuroprotective potential demonstrated in previous research.

α-synuclein regulation of dopamine transporter

The development of effective therapeutic interventions for neurodegeneration requires a better understanding of the early events that precede neuronal loss. Recent work in various disease models has begun to emphasize the significance of presynaptic dysfunction as an early event that occurs before manifestation of neurological disorders. Dysregulation of dopamine (DA) homeostasis is implicated in neurodegenerative diseases, drug addiction, and neuropsychiatric disorders. The neuronal plasma membrane dopamine transporter (DAT) is essential for the maintenance of DA homeostasis in the brain. α-synuclein is a 140-amino acid protein that forms a stable complex with DAT and is linked to the pathogenesis of neurodegenerative disease. In this review we will examine the prevailing hypotheses for α-synuclein-regulation of DAT biology.

Lonicera japonica THUNB. protects 6-hydroxydopamine-induced neurotoxicity by inhibiting activation of MAPKs, PI3K/Akt, and NF-κB in SH-SY5Y cells

In this study, we investigated the neuroprotective effects of Lonicera japonica THUNB. extract (LJ) on 6-hydroxydopamine (6-OHDA)-induced neurotoxicity in SH-SY5Y cells. We found that LJ significantly increased cell viability decrease, lactate dehydrogenase release (LDH), morphological changes, nuclear condensation, fragmentation, and reactive oxygen species (ROS) production induced by 6-OHDA in SH-SY5Y cells. The cytoprotection afforded by pretreatment with LJ was associated with increases of the glutathione (GSH) level, superoxide dismutase (SOD) activity, and catalase (CAT) activity in 6-OHDA-induced SH-SY5Y cells. In addition, LJ strikingly inhibited 6-OHDA-induced mitochondrial dysfunctions including reduction of mitochondria membrane potential (MMP) and activation of cleaved poly-ADP-ribose polymerase (PARP), cleaved caspase-3, cleaved caspase-9, increased Bax, as well as decreased Bcl-2 and Bcl-xL. Additionally, LJ dramatically attenuated 6-OHDA-induced phosphorylation of c-Jun N-terminal kinase (JNK), p38 mitogen-activated protein kinase (MAPK), extracellular signal-regulated kinase 1/2 (ERK 1/2), and phosphoinositide 3-kinase (PI3K)/Akt. Meanwhile, LJ counteracted nuclear factor-κB (NF-κB) activation by blocking its translocation to the nucleus. These findings suggest that LJ has a potent anti-parkinsonism; this effect was mediated, at least in part, by inhibition of neurotoxicity, apoptotic cascade events, and oxidative stress via activation of MAPKs, PI3K/Akt, and NF-κB.

Leaf extract of Rhus verniciflua Stokes protects dopaminergic neuronal cells in a rotenone model of Parkinson's disease

Objectives

The present study investigated the neuroprotective effects of Rhus verniciflua Stokes (RVS) leaf extract on rotenone-induced apoptosis in human dopaminergic cells, SH-SY5Y.

Methods

Cells were pretreated with RVS extract for 1 h then treated with vehicle or rotenone for 24 h. Cell viability, cell cytotoxicity, cell morphology and nuclear morphology were examined by MTT assay, lactate dehydrogenase release assay, phase contrast microscopy and staining with Hoechast 33342, respectively. Reactive oxygen species were measured by 2′7′-dichlorofluorescein diacetate and fragmented DNA was observed by TUNEL assay. Mitochondrial membrane potential was determined by Rhodamine 123. Pro-apoptotic and anti-apoptotic proteins and tyrosine hydroxylase were analysed by Western blotting.

Key findings

Results showed that RVS suppressed rotenone-induced reactive oxygen species generation, cellular injury and apoptotic cell death. RVS also prevented rotenone-mediated changes in Bax/Bcl-2 levels, mitochondrial membrane potential dissipation and Caspase 3 activation. Moreover, RVS pretreatment increased the tyrosine hydroxylase levels in SH-SY5Y cells.

Conclusions

These findings demonstrate that RVS protects SH-SY5Y cells against rotenone-induced injury and suggest that RVS may have potential therapeutic value for neurodegenerative disease associated with oxidative stress.

PI3-K/Akt and ERK pathways activated by VEGF play opposite roles in MPP+-induced neuronal apoptosis

Vascular endothelial growth factor (VEGF), a specific pro-angiogenic peptide, has shown neuroprotective effects in the Parkinson's disease (PD) models, but the underlying mechanisms remain elusive. In this study, the neuroprotective properties of VEGF on 1-methyl-4-phenylpyridinium ion (MPP(+))-induced neurotoxicity in primary cerebellar granule neurons were investigated. Pretreatment of VEGF prevented MPP(+)-induced neuronal apoptosis in a concentration- and time-dependent manner. And this prevention was blocked by PTK787/ZK222584, a VEGF receptor-2 specific inhibitor. Both inhibition of the Akt pathway and activation of the extracellular signal-regulated kinase (ERK) pathway contribute to MPP(+)-induced neuronal apoptosis. VEGF reversed the inhibition of phosphoinositide 3-kinase (PI3-K)/Akt pathway caused by MPP(+), but further enhanced the activation of ERK induced by MPP(+). Interestingly, VEGF and PD98059 (an ERK kinase inhibitor) play a synergistic role in protecting neurons from MPP(+)-induced toxicity. Collectively, these findings suggest that the PI3-K/Akt and ERK pathways activated by VEGF play opposite roles in MPP(+)-induced neuronal apoptosis. This finding offers not only a new and clinically significant modality as to how VEGF exerts its neuroprotective effects but also a novel therapeutic strategy for PD by differentially regulating PD-associated signaling pathways.