Dysfunction Of Dopaminergic Neurons Research Articles

Sinapic Acid Protects SH-SY5Y Human Neuroblastoma Cells against 6-Hydroxydopamine-Induced Neurotoxicity.

Parkinson’s disease (PD) is characterized by progressive dopaminergic neuron loss or dysfunction and is the second most prevalent neurodegenerative disorder after Alzheimer’s disease. However, current therapeutic strategies for PD are limited to treating the outcomes of this disease rather than preventing it. Sinapic acid (SA) is a phenolic compound with potential antioxidant properties, which reportedly acts as a therapeutic agent against many diseases including cancer, as well as cardiac and liver diseases. However, little is known about the effects of SA against neurodegenerative disorders. Therefore, our study sought to evaluate the neuroprotective effects of non-cytotoxic concentrations of SA against 6-hydroxydopamine (6-OHDA)-induced neurotoxicity in SH-SY5Y human neuroblastoma cells, which we used as an in vitro PD model. SA increased cell viability and rescued the cells from 6-OHDA-induced apoptotic cell death. Additionally, oxidative stress responses were significantly blocked by SA, including reactive oxygen species (ROS) overproduction and decreased expression levels of antioxidant proteins. Notably, SA also attenuated mitochondrial dysfunction and endoplasmic reticulum (ER) stress. Moreover, SA dramatically inhibited the activation of mitogen-activated protein kinase (MAPK) proteins. Taken together, our findings highlight the potential PD prevention effects of SA, as well as its underlying mechanisms, making this compound a promising prevention and treatment agent for PD.

Perspective: Low Risk of Parkinson's Disease in Quasi-Vegan Cultures May Reflect GCN2-Mediated Upregulation of Parkin

Mitochondrial dysfunction in dopaminergic neurons of the substantia nigra (SN) appears to be a key mediating feature of Parkinson's disease (PD), a complex neurodegenerative disorder of still unknown etiology. Parkin is an E3 ubiquitin ligase that promotes mitophagy of damaged depolarized mitochondria while also boosting mitochondrial biogenesis-thereby helping to maintain efficient mitochondrial function. Boosting Parkin expression in the SN with viral vectors is protective in multiple rodent models of PD. Conversely, homozygosity for inactivating mutations of Parkin results in early-onset PD. Moderate protein plant-based diets relatively low in certain essential amino acids have the potential to boost Parkin expression by activating the kinase GCN2, which in turn boosts the expression of ATF4, a factor that drives transcription of the Parkin gene. Protein-restricted diets also upregulate the expression of PINK1, a protein that binds to the outer membrane of depolarized mitochondria and then recruits and activates Parkin. This effect of protein restriction is mediated by the downregulation of the kinase activity of mammalian target of rapamycin complex 1; the latter suppresses PINK1 expression at the transcriptional level. During the 20th century, cultures in East Asia and sub-Sahara Africa consuming quasi-vegan diets were found to be at notably decreased risk of PD compared with the USA or Europe. It is proposed that such diets may provide protection from PD by boosting Parkin and PINK1 expression in the SN. Other measures that might be expected to upregulate protective mitophagy include supplemental N-acetylcysteine (precursor for hydrogen sulfide) and a diet rich in spermidine-a polyamine notably high in corn.

REST Protects Dopaminergic Neurons from Mitochondrial and α-Synuclein Oligomer Pathology in an Alpha Synuclein Overexpressing BAC-Transgenic Mouse Model.

Alpha-synuclein pathology is associated with dopaminergic neuronal loss in the substantia nigra (SN) of Parkinson's patients. Working across human and mouse models, we investigated mechanisms by which the accumulation of soluble α-synuclein oligomers leads to neurodegeneration. Biochemical analysis of the midbrain of α-synuclein overexpressing BAC-transgenic male and female mice revealed age- and region-dependent mitochondrial dysfunction and accumulation of damaged proteins downstream of the RE1 Silencing Transcription Factor (REST). Vulnerable SN dopaminergic neurons displayed low REST levels compared with neighboring protected SN GABAergic neurons, which correlated with the accumulation of α-synuclein oligomers and disrupted mitochondrial morphology. Consistent with a protective role, REST levels were reduced in patient induced pluripotent stem cell-derived dopaminergic neurons carrying the SNCA-Triplication mutation, which accumulated α-synuclein oligomers and mitochondrial damage, and displayed REST target gene dysregulation. Furthermore, CRISPR-mediated REST KO induced mitochondrial dysfunction and impaired mitophagy in vitro Conversely, REST overexpression attenuated mitochondrial toxicity and mitochondrial morphology disruption through the transcription factor PGC-1α. Finally, decreased α-synuclein oligomer accumulation and mitochondrial dysfunction in mice correlated with nuclear REST and PGC-1α in protected SN GABAergic neurons compared with vulnerable dopaminergic neurons. Our findings show that increased levels of α-synuclein oligomers cause dopaminergic neuronal-specific dysfunction through mitochondrial toxicity, which can be attenuated by REST in an early model of Parkinsonian pathology. These findings highlight REST as a mediator of dopaminergic vulnerability in PD.SIGNIFICANCE STATEMENT Understanding early Parkinsonian pathophysiology through studies of advanced preclinical models is fundamental to the translation of disease-modifying therapies. Here we show disease-relevant levels of α-synuclein expression in mice leads to accumulation of α-synuclein oligomers in the absence of overt aggregation, and mitochondrial dysfunction in dopaminergic neurons lacking the RE1 Silencing Transcription Factor. Our findings identify the mechanism of action of RE1 Silencing Transcription Factor and PGC-1α as mediators of dopaminergic vulnerability in α-synuclein BAC-transgenic mice and induced pluripotent stem cell-derived dopaminergic cultures, highlighting their potential as therapeutic targets.

Nmnat1 Modulates Mitochondrial Oxidative Stress by Inhibiting Caspase-3 Signaling in Alzheimer's Disease.

Nigrostriatal pathway disturbance is one of the major pathogenic factors in Alzheimer's disease (AD). Dopaminergic neuron dysfunction results in bradykinesia and akinesia (inability to initiate movement), indicating a significant risk factor for substantia nigra pars compacta lesions. Furthermore, the nicotinamide adenine dinucleotide (NAD+) is associated with Aβ toxicity decline in AD therapy. Nicotinamide mononucleotide adenylyltransferase 1 (Nmnat1) is an essential enzyme that preserves normal neuronal function and protects neurons from insult. This study aimed to investigate the potential therapeutic effects of Nmnat1 and its underlying mechanisms in a triple-transgenic mouse model of AD (3xTgAD). Results showed that Nmnat1 improved the substantial behavioral measures of cognitive impairments compared with the 3xTgAD control. Additionally, Nmnat1 overexpression significantly increased tyrosine hydroxylase-positive neurons and anti-apoptotic protein Bcl2 and caspase-3 expression levels in 3xTgAD mice. Nmnat1 also effectively controlled SOD1 activation. In conclusion, Nmnat1 substantially decreases multiple AD-associated pathological characteristics at least partially by the increase of caspase-3 activation.

Analysis of Dopaminergic Functions in Drosophila.

Dopaminergic (DA) neurons regulate various physiological functions, including motor function, emotion, learning, sleep, and arousal. Degeneration of DA neurons in the substantia nigra of the midbrain causes motor disturbance in Parkinson's disease (PD). Studies on familial PD have revealed that a subset of PD genes encode proteins that regulate mitochondrial function and synaptic dynamics. Drosophila is a powerful model of PD, whereby genetic interactions of PD genes with well-conserved cellular signaling can be evaluated. Morphological changes in mitochondria, along with dysfunction and degeneration of DA neurons, have been reported in many studies using Drosophila PD models. In this chapter, we will describe imaging methods to visualize mitochondria in DA neurons and to evaluate spontaneous neural activity of DA neurons in the Drosophila brain.

Teaghrelin Protects SH-SY5Y Cells against MPP+-Induced Neurotoxicity through Activation of AMPK/SIRT1/PGC-1α and ERK1/2 Pathways

The prevalence and incidence of Parkinson’s disease (PD), an age-related neurodegenerative disease, are higher among elderly people. Independent of etiology, dysfunction and loss of dopaminergic neurons are common pathophysiological changes in PD patients with impaired motor and non-motor function. Currently, preventive or therapeutic treatment for combating PD is limited. The ghrelin axis and ghrelin receptor have been implicated in the preservation of dopaminergic neurons and have potential implications in PD treatment. Teaghrelin, a compound originating from Chin-Shin Oolong tea, exhibits ghrelin agonist activity. In this study, the neuroprotective potential of teaghrelin against PD was explored in a cell model in which human neuroblastoma SH-SY5Y cells were treated with the mitochondrial toxin 1-methyl-4-phenylpyridinium (MPP+). Upon MPP+ exposure, SH-SY5Y cells exhibited decreased mitochondrial complex I activity and apoptotic cell death. Teaghrelin activated AMP-activated protein kinase (AMPK)/sirtuin 1(SIRT1)/peroxisome proliferator-activated receptor gamma (PPARγ) coactivator-1α (PGC-1α) and extracellular signal–regulated kinases 1 and 2 (ERK1/2) pathways to antagonize MPP+-induced cell death. Herein, we propose that teaghrelin is a potential candidate for the therapeutic treatment of PD.

Preventive role of regular low-intensity exercise during adolescence in schizophrenia model mice with abnormal behaviors

Schizophrenia is probably ascribed to perinatal neurodevelopmental deficits, and its onset might be affected by environmental factors. Hypofrontality with glutamatergic and dopaminergic neuronal dysfunction are known factors, but a way to mitigate abnormalities remains unfound. An early enriched environment such as a wheel running in rodents may contribute to the prevention, but its clinical applicability is very limited. From our studies, low-intensity exercise training (LET) based on physiological indices, such as lactate threshold, easily translates to humans and positively affects the brains. Hence, LET during adolescence may ameliorate abnormalities in neurodevelopment and prevent the development of schizophrenia. In the current study, LET prevented sensitization to phencyclidine (PCP) treatment, impairment of cognition, and affective behavioral abnormalities in an animal model of schizophrenia induced by prenatal PCP treatment. Further, LET increased dopamine turnover and attenuated the impairment of phosphorylation of ERK1/2 after exposure to a novel object in the prenatal PCP-treated mice. These results suggest that LET during adolescence completely improves schizophrenia-like abnormal behaviors associated with improved glutamate uptake and the dopamine-induced ERK1/2 signaling pathway in the PFC.

Pharmacocorrection of mitochondrial dysfunction and energy imbalance of substantia nigra neurons in experimental Parkinson's disease in rats

Parkinson's disease (PD) is a progressive disease and the incidence increases markedly with age, treatment has significantly improved the quality of life of patients with PD, but statistics show that these patients continue to show shorter life expectancies compared to the general population.Aim of the study. To investigate the features of changes in energy balance and mitochondrial dysfunction on the basis of experimental studies in rats in the modeling of PD and justify the development of possible treatment regimens with specific neuroprotective effects on the dopaminergic system.Materials and methods. The study was carried out on 90 Wistar rats at the age of 6 months weighing 220-290 grams. Parkinsonism was induced by the administration of the neurotoxin MPTP (N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) to experimental rats with neuroprotective treatment: I – Intact (passive control); II – animals with experimental Parkinson's disease (PD, active control); III – PD + Amantadine (AM) IV – PD + AM + Cerebrocurin; V – PD + AM + Pramistar; VI – PD + AM + Gliatilin; VII – PD + AM + Noofen; VIII – PD + AM + Pronoran; IX – PD + AM + Melatonin.Results. Under conditions of formation of experimental PD in rats develops energy deficiency of neuronal cells and dysfunction of the Krebs cycle with a predominance of anaerobic oxidation of the substrate, as well as the development of mitochondrial dysfunction. Prescribed neuroprotective drugs significantly improved energy metabolism in the brain of rats with PD within statistical significance, increased levels of ATP and ADP, enzymatic activity of mCPK and ATPase, decreased levels of AMP, especially pronounced drugs melatonin, cerebrocurin, gliatilin and pronoran. Neuroprotective therapy of experimental PD in rats contributed to a statistically significant increase in the values of pyruvate, malate, LDH and MDG, and also led to a decrease in the values of lactate and lactic acidosis in brain tissues. The appointment of neuroprotective therapy with basic amantadine therapy led to an increase in energy charge, energy potential, phosphorylation index and thermodynamic control of respiration in the mitochondria of neurons, especially in the groups of melatonin, cerebrocurin, gliatilin and pronoran.Conclusions. Pharmacocorrection of mitochondrial dysfunction and energy imbalance of dopaminergic neurons in experimental PD in rats may indirectly or directly inhibite to the progression of pathology in PD.

Gut Microbiota Approach-A New Strategy to Treat Parkinson's Disease.

Parkinson’s disease (PD) is a progressive neurodegenerative disorder characterized by neuronal loss and dysfunction of dopaminergic neurons located in the substantia nigra, which contain a variety of misfolded α-synuclein (α-syn). Medications that increase or substitute for dopamine can be used for the treatment of PD. Recently, numerous studies have shown gut microbiota plays a crucial role in regulating and maintaining multiple aspects of host physiology including host metabolism and neurodevelopment. In this review article, the role of gut microbiota in the etiological mechanism of PD will be reviewed. Furthermore, we discussed current pharmaceutical medicine-based methods to prevent and treat PD, followed by describing specific strains that affect the host brain function through the gut-brain axis. We explained in detail how gut microbiota directly produces neurotransmitters or regulate the host biosynthesis of neurotransmitters. The neurotransmitters secreted by the intestinal lumen bacteria may induce epithelial cells to release molecules that, in turn, can regulate neural signaling in the enteric nervous system and subsequently control brain function and behavior through the brain-gut axis. Finally, we proved that the microbial regulation of the host neuronal system. Endogenous α-syn can be transmitted long distance and bidirectional between ENS and brain through the circulatory system which gives us a new option that the possibility of altering the community of gut microbiota in completely new medication option for treating PD.

α-Synuclein amplifies cytoplasmic peroxide flux and oxidative stress provoked by mitochondrial inhibitors in CNS dopaminergic neurons in vivo

Convergent evidence implicates impaired mitochondrial function and α-Synuclein accumulation as critical upstream events in the pathogenesis of Parkinson's disease, but comparatively little is known about how these factors interact to provoke neurodegeneration. We previously showed that α-Synuclein knockdown protected rat substantia nigra dopaminergic neurons from systemic exposure to the mitochondrial complex I inhibitor rotenone. Here we show that motor abnormalities prior to neuronal loss in this model are associated with extensive α-Synuclein-dependent cellular thiol oxidation. In order to elucidate the underlying events in vivo we constructed novel transgenic zebrafish that co-express, in dopaminergic neurons: (i) human α-Synuclein at levels insufficient to provoke neurodegeneration or neurobehavioral abnormalities; and (ii) genetically-encoded ratiometric fluorescent biosensors to detect cytoplasmic peroxide flux and glutathione oxidation. Live intravital imaging of the intact zebrafish CNS at cellular resolution showed unequivocally that α-Synuclein amplified dynamic cytoplasmic peroxide flux in dopaminergic neurons following exposure to the mitochondrial complex I inhibitors MPP+ or rotenone. This effect was robust and clearly evident following either acute or prolonged exposure to each inhibitor. In addition, disturbance of the resting glutathione redox potential following exogenous hydrogen peroxide challenge was augmented by α-Synuclein. Together these data show that α-Synuclein is a critical determinant of the redox consequences of mitochondrial dysfunction in dopaminergic neurons. The findings are important because the mechanisms underlying α-Synuclein-dependent reactive oxygen species fluxes and antioxidant suppression might provide a pharmacological target in Parkinson's disease to prevent progression from mitochondrial dysfunction and oxidative stress to cell death.

PET imaging with [18F]FP-(+)-DTBZ in 6-OHDA-induced partial and full unilaterally-lesioned model rats of Parkinson's disease and the correlations to the biological data

ObjectiveThe deficit of dopaminergic neurons in the nigrostriatal pathway is one of the pathological features of Parkinson's disease (PD). The decline of vesicular monoamine transporter type 2 (VMAT2) has been verified to relate with the severity of PD. The purpose of this study was to evaluate the ability of [18F]fluoropropyl-(+)-dihydrotetrabenazine ([18F]FP-(+)-DTBZ) to detect dopaminergic neuron dysfunction in a standard rat model of PD using PET imaging. Specifically, two different doses of 6-hydroxydopamine (6-OHDA) were injected unilaterally into the medial forebrain bundle (MFB) to create the models with two different severities. MethodsMale Sprague-Dawley rats were intracranially injected with 8 μg 6-OHDA (partial lesion group), 16 μg 6-OHDA (full lesion group) and vehicle (sham group) into MFB, respectively. Thirty minutes static [18F]FP-(+)-DTBZ microPET scanning was performed to determine the dopaminergic neuron integrity on the 28th day post-injection and the behavioral tests were carried out in the next two days. Then, the rats were decapitated, and the brains were collected for biogenic amines content analysis or dissected for autoradiography and immunohistochemical (IHC) staining. The correlations of PET results to the behavioral, biological, histological, autoradiography results were analyzed, respectively. ResultsThe standardized uptake value ratio (ST to CB) of [18F]FP-(+)-DTBZ in the ipsilateral striata decreased significantly in partial lesion group and full lesion group. Compared with the sham group, the ratio of the standardized uptake value in ipsilateral striatum to that in contralateral striatum decreased by 57.09 ± 2.30% (full lesion group) and 25.31 ± 5.70% (partial lesion group), respectively. The dopaminergic neuronal dysfunction was corroborated by in vitro autoradiography, IHC, and quantitative analysis of DA as well as its metabolites concentration tests. The motor function impairments of 6-OHDA-treated animals were manifested by a series of behavioral tests. The results of microPET imaging were linearly correlated with behavioral, biological, histological, and autoradiography results, respectively. ConclusionOur data suggest that [18F]FP-(+)-DTBZ may be useful for detecting different degrees of dopaminergic neuronal lesions by PET imaging in PD models induced by 6-OHDA.

Novel Drosophila model for parkinsonism by targeting phosphoglycerate kinase

Patients with Parkinson's disease (PD) show a common progressive neurodegenerative movement disorder characterized by rigidity, tremors, postural instability, and bradykinesia due to the loss of dopaminergic neurons in the substantia nigra, and is often accompanied by several non-motor symptoms, called parkinsonism. Several lines of recent evidence support the hypothesis that mutations in the gene encoding phosphoglycerate kinase (PGK) play an important role in the PD mechanism. PGK is a key enzyme in the glycolytic pathway that catalyzes the reaction from 1,3-diphosphoglycerate to 3-phosphoglycerate. We herein established a parkinsonism model targeting Drosophila Pgk. Dopaminergic (DA) neuron-specific Pgk knockdown lead to locomotive defects in both young and aged adult flies and was accompanied by progressive DA neuron loss with aging. Pgk knockdown in DA neurons decreased dopamine levels in the central nervous system (CNS) of both young and aged adult flies. These phenotypes are similar to the defects observed in human PD patients, suggesting that the Pgk knockdown flies established herein are a promising model for parkinsonism. Furthermore, pan-neuron-specific Pgk knockdown induced low ATP levels and the accumulation of reactive oxygen species (ROS) in the CNS of third instar larvae. Collectively, these results indicate that a failure in the energy production system of Pgk knockdown flies causes locomotive defects accompanied by neuronal dysfunction and degeneration in DA neurons.

Low dopamine transporter binding in the nucleus accumbens in geriatric patients with severe depression.

Dysfunction of dopaminergic neurons in the central nervous system is considered to be related to major depressive disorder (MDD). Especially, MDD in geriatric patients is characterized by anhedonia, which is assumed to be associated with reduced dopamine neurotransmission in the reward system. Dopamine transporter (DAT) is considered to reflect the function of the dopamine nerve system. However, previous DAT imaging studies using single photon emission computed tomography or positron emission tomography (PET) have shown inconsistent results. The radioligand [18 F]FE-PE2I for PET enables more precise evaluation of DAT availability. Hence, we aimed to evaluate the DAT availability in geriatric patients with MDD using [18 F]FE-PE2I. Eleven geriatric patients with severe MDD and 27 healthy controls underwent PET with [18 F]FE-PE2I, which has high affinity and selectivity for DAT. Binding potentials (BPND ) in the striatum (caudate and putamen), nucleus accumbens (NAc), and substantia nigra were calculated. BPND values were compared between MDD patients and healthy controls. MDD patients showed significantly lower DAT BPND in the NAc (P = 0.009), and there was a trend of lower BPND in the putamen (P = 0.032) compared to controls. We found low DAT in the NAc and putamen in geriatric patients with severe MDD, which could be related to dysregulation of the reward system.

Shati/Nat8l deficiency disrupts adult neurogenesis and causes attentional impairment through dopaminergic neuronal dysfunction in the dentate gyrus.

Successful completion of daily activities relies on the ability to select the relevant features of the environment for memory and recall. Disruption to these processes can lead to various disorders, such as attention-deficit hyperactivity disorder (ADHD). Dopamine is a neurotransmitter implicated in the regulation of several processes, including attention. In addition to the higher-order brain function, dopamine is implicated in the regulation of adult neurogenesis. Previously, we generated mice lacking Shati, an N-acetyltransferase-8-like protein on a C57BL/6J genetic background (Shati/Nat8l-/- ). These mice showed a series of changes in the dopamine system and ADHD-like behavioral phenotypes. Therefore, we hypothesized that deficiency of Shati/Nat8l would affect neurogenesis and attentional behavior in mice. We found aberrant morphology of neurons and impaired neurogenesis in the dentate gyrus of Shati/Nat8l-/- mice. Additionally, research has suggested that impaired neurogenesis might be because of the reduction of dopamine in the hippocampus. Galantamine (GAL) attenuated the attentional impairment observed in the object-based attention test via increasing the dopamine release in the hippocampus of Shati/Nat8l-/- mice. The α7 nicotinic acetylcholine receptor antagonist, methyllycaconitine, and dopamine D1 receptor antagonist, SCH23390, blocked the ameliorating effect of GAL on attentional impairment in Shati/Nat8l-/- mice. These results suggest that the ameliorating effect of GAL on Shati/Nat8l-/- attentional impairment is associated with activation of D1 receptors following increased dopamine release in the hippocampus via α7 nicotinic acetylcholine receptor. In summary, Shati/Nat8l is important in both morphogenesis and neurogenesis in the dentate gyrus and attention, possible via modulation of dopaminergic transmission. Cover Image for this issue: https://doi.org/10.1111/jnc.15061.

Fatty-acid-binding protein 3 is critical for α-Synuclein uptake and MPP<sup>+</sup>-induced mitochondrial dysfunction in dopaminergic neurons

Fatty-acid-binding protein 3 is critical for α-Synuclein uptake and MPP<sup>+</sup>-induced mitochondrial dysfunction in dopaminergic neurons

Pathogenic Pathways in Early-Onset Autosomal Recessive Parkinson's Disease Discovered Using Isogenic Human Dopaminergic Neurons.

SummaryParkinson's disease (PD) is a complex and highly variable neurodegenerative disease. Familial PD is caused by mutations in several genes with diverse and mostly unknown functions. It is unclear how dysregulation of these genes results in the relatively selective death of nigral dopaminergic neurons (DNs). To address this question, we modeled PD by knocking out the PD genes PARKIN (PRKN), DJ-1 (PARK7), and ATP13A2 (PARK9) in independent isogenic human pluripotent stem cell (hPSC) lines. We found increased levels of oxidative stress in all PD lines. Increased death of DNs upon differentiation was found only in the PARKIN knockout line. Using quantitative proteomics, we observed dysregulation of mitochondrial and lysosomal function in all of the lines, as well as common and distinct molecular defects caused by the different PD genes. Our results suggest that precise delineation of PD subtypes will require evaluation of molecular and clinical data.

Homogenous generation of dopaminergic neurons from multiple hiPSC lines by transient expression of transcription factors

A major hallmark of Parkinson's disease is loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc). The pathophysiological mechanisms causing this relatively selective neurodegeneration are poorly understood, and thus experimental systems allowing to study dopaminergic neuron dysfunction are needed. Induced pluripotent stem cells (iPSCs) differentiated toward a dopaminergic neuronal phenotype offer a valuable source to generate human dopaminergic neurons. However, currently available protocols result in a highly variable yield of dopaminergic neurons depending on the source of hiPSCs. We have now developed a protocol based on HBA promoter-driven transient expression of transcription factors by means of adeno-associated viral (AAV) vectors, that allowed to generate very consistent numbers of dopaminergic neurons from four different human iPSC lines. We also demonstrate that AAV vectors expressing reporter genes from a neuron-specific hSyn1 promoter can serve as surrogate markers for maturation of hiPSC-derived dopaminergic neurons. Dopaminergic neurons differentiated by transcription factor expression showed aggravated neurodegeneration through α-synuclein overexpression, but were not sensitive to γ-synuclein overexpression, suggesting that these neurons are well suited to study neurodegeneration in the context of Parkinson’s disease.

Mitochondrial damage by \u03b1-synuclein causes cell death in human dopaminergic neurons

Evolving concepts on Parkinson’s disease (PD) pathology suggest that α-synuclein (aSYN) promote dopaminergic neuron dysfunction and death through accumulating in the mitochondria. However, the consequence of mitochondrial aSYN localisation on mitochondrial structure and bioenergetic functions in neuronal cells are poorly understood. Therefore, we investigated deleterious effects of mitochondria-targeted aSYN in differentiated human dopaminergic neurons in comparison with wild-type (WT) aSYN overexpression and corresponding EGFP (enhanced green fluorescent protein)-expressing controls. Mitochondria-targeted aSYN enhanced mitochondrial reactive oxygen species (ROS) formation, reduced ATP levels and showed severely disrupted structure and function of the dendritic neural network, preceding neuronal death. Transmission electron microscopy illustrated distorted cristae and many fragmented mitochondria in response to WT-aSYN overexpression, and a complete loss of cristae structure and massively swollen mitochondria in neurons expressing mitochondria-targeted aSYN. Further, the analysis of mitochondrial bioenergetics in differentiated dopaminergic neurons, expressing WT or mitochondria-targeted aSYN, elicited a pronounced impairment of mitochondrial respiration. In a pharmacological compound screening, we found that the pan-caspase inhibitors QVD and zVAD-FMK, and a specific caspase-1 inhibitor significantly prevented aSYN-induced cell death. In addition, the caspase inhibitor QVD preserved mitochondrial function and neuronal network activity in the human dopaminergic neurons overexpressing aSYN. Overall, our findings indicated therapeutic effects by caspase-1 inhibition despite aSYN-mediated alterations in mitochondrial morphology and function.

The neuroprotective effect of schisandrol A on 6-OHDA-induced PD mice may be related to PI3K/AKT and IKK/IκBα/NF-κB pathway.

Parkinson's disease is the second most common neurodegenerative disease. Its main pathological feature is the substantial nigra-striatum dopaminergic neuronal dysfunction, which causes insufficient release of DA, induces motor symptoms, and is accompanied by nonmotor symptoms. Schisandrol A belongs to lignan components and has anti-inflammatory, antioxidant and neuroprotective effects. In this experiment, we injected 6-OHDA into medial forebrain bundle of C57BL/6J male mice to establish the model. The motor function of mice was examined by open field test and pole test, the depression-like behavior of mice was examined by sucrose preference test and the memory function was examined by Y maze. We found that schisandrol A (20 mg/kg/d) could significantly improve the motor symptoms, and alleviate the depression-like symptoms and memory dysfunction of PD mice induced by 6-OHDA. Then we studied the neuroprotective mechanism of schisandrol A by H.E., ELISA assay kits and Western blot. Results showed that schisandrol A may enhance the PI3K/AKT pathway, inhibit the IKK/IκBα/NF-κB pathway, reduce neuronal inflammation and oxidative stress, and enhance the survival of DA neurons in the brain of mice. These results indicate that schisandrol A is expected to be a potential drug for improving Parkinson's disease.

Recuperative effect of metformin loaded polydopamine nanoformulation promoting EZH2 mediated proteasomal degradation of phospho-α-synuclein in Parkinson’s disease model

Posttranslational modification and agglomeration of α-synuclein (α-Syn), mitochondrial dysfunction, oxidative stress and loss of dopaminergic neurons are hallmark of Parkinson’s disease (PD). This paper evaluates neuroprotection efficacy of nature inspired biocompatible polydopamine nanocarrier for metformin delivery (Met encapsulated PDANPs) by crossing blood brain barrier in in vitro, 3D and in vivo experimental PD models. The neuroprotective potential was arbitrated by downregulation of phospho-serine 129 (pSer129) α-Syn, with reduction in oxidative stress, prevention of apoptosis and anti-inflammatory activities. The neuroprotective mechanism proved novel interaction of epigenetic regulator EZH2 mediated ubiquitination and proteasomal degradation of aggregated pSer129 α-Syn. In summary, this study divulges the neuroprotective role of Met loaded PDANPs by reversing the neurochemical deficits by confirming an epigenetic mediated nanotherapeutic approach for the PD prevention.