Neurons In Parkinson's Disease Research Articles

DNA Methylation Signature of Aging: Potential Impact on the Pathogenesis of Parkinson's Disease.

Regulation of gene expression by epigenetic modifications means lasting and heritable changes in the function of genes without alterations in the DNA sequence. Of all epigenetic mechanisms identified thus far, DNA methylation has been of particular interest in both aging and age-related disease research over the last decade given the consistency of site-specific DNA methylation changes during aging that can predict future health and lifespan. An increasing line of evidence has implied the dynamic nature of DNA (de)methylation events that occur throughout the lifespan has a role in the pathophysiology of aging and age-associated neurodegenerative conditions, including Parkinson's disease (PD). In this regard, PD methylome shows, to some extent, similar genome-wide changes observed in the methylome of healthy individuals of matching age. In this review, we start by providing a brief overview of studies outlining global patterns of DNA methylation, then its mechanisms and regulation, within the context of aging and PD. Considering diverging lines of evidence from different experimental and animal models of neurodegeneration and how they combine to shape our current understanding of tissue-specific changes in DNA methylome in health and disease, we report a high-level comparison of the genomic methylation landscapes of brain, with an emphasis on dopaminergic neurons in PD and in natural aging. We believe this will be particularly useful for systematically dissecting overlapping genome-wide alterations in DNA methylation during PD and healthy aging, and for improving our knowledge of PD-specific changes in methylation patterns independent of aging process.

Tat-GSTpi Inhibits Dopaminergic Cells against MPP+-Induced Cellular Damage via the Reduction of Oxidative Stress and MAPK Activation

Glutathione S-transferase pi (GSTpi) is a member of the GST family and plays many critical roles in cellular processes, including anti-oxidative and signal transduction. However, the role of anti-oxidant enzyme GSTpi against dopaminergic neuronal cell death has not been fully investigated. In the present study, we investigated the roles of cell permeable Tat-GSTpi fusion protein in a SH-SY5Y cell and a Parkinson's disease (PD) mouse model. In the 1-methyl-4-phenylpyridinium (MPP+)-exposed cells, Tat-GSTpi protein decreased DNA damage and reactive oxygen species (ROS) generation. Furthermore, this fusion protein increased cell viability by regulating MAPKs, Bcl-2, and Bax signaling. In addition, Tat-GSTpi protein delivered into the substantia nigra (SN) of mice brains protected dopaminergic neuronal cell death in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD animal model. Our results indicate that the Tat-GSTpi protein inhibited cell death from MPP+- and MPTP-induced damage, suggesting that it plays a protective role during the loss of dopaminergic neurons in PD and that it could help to identify the mechanism responsible for neurodegenerative diseases, including PD.

The Pedunculopontine Tegmental Nucleus is not Important for Breathing Impairments Observed in a Parkinson’s Disease Model

Parkinson’s disease (PD) is a motor disorder resulting from degeneration of dopaminergic neurons of substantia nigra pars compacta (SNpc), with classical and non-classical symptoms such as respiratory instability. An important region for breathing control, the Pedunculopontine Tegmental Nucleus (PPTg), is composed of cholinergic, glutamatergic, and GABAergic neurons. We hypothesize that degenerated PPTg neurons in a PD model contribute to the blunted respiratory activity. Adult mice (40 males and 29 females) that express the fluorescent green protein in cholinergic, glutamatergic or GABAergic cells were used (Chat-cre Ai6, Vglut2-cre Ai6 and Vgat-cre Ai6) and received bilateral intrastriatal injections of vehicle or 6-hydroxydopamine (6-OHDA). Ten days later, the animals were exposed to hypercapnia or hypoxia to activate PPTg neurons. Vglut2-cre Ai6 animals also received retrograde tracer injections (cholera toxin b) into the retrotrapezoid nucleus (RTN) or preBötzinger Complex (preBötC) and anterograde tracer injections (AAV-mCherry) into the SNpc. In 6-OHDA-injected mice, there is a 77% reduction in the number of dopaminergic neurons in SNpc without changing the number of neurons in the PPTg. Hypercapnia activated fewer Vglut2 neurons in PD, and hypoxia did not activate PPTg neurons. PPTg neurons do not input RTN or preBötC regions but receive projections from SNpc. Although our results did not show a reduction in the number of glutamatergic neurons in PPTg, we observed a reduction in the number of neurons activated by hypercapnia in the PD animal model, suggesting that PPTg may participate in the hypercapnia ventilatory response.

In vivooverexpression of synaptogyrin-3 promotes striatal synapticdopamineuptakein LRRK2R1441G mutant mouse model of Parkinson's disease.

Leucine-rich repeat kinase 2 (LRRK2) mutation is a common genetic risk factor of Parkinson's disease (PD). Presynaptic dysfunction is an early pathogenic event associated with dopamine (DA) dysregulation in striatum of the brain. DA uptake activity of DA uptake transporter (DAT) affects synaptic plasticity andmotorand non-motorbehavior. Synaptogyrin-3(SYNGR3)is part of the synaptogyrin family, especially abundant in brain. Previousin vitrostudies demonstrated interaction between SYNGR3 and DAT.Reduced SYNGR3 expression was observed inhuman PD brainswith unclear reasons. Here, wefurtherexplored whether inducing SYNGR3 expression can influence(i) cellular DA uptake using differentiated humanSH-SY5Yneuronalcells, (ii) striatal synaptosomalDA uptakein amutant LRRK2R1441G knockin mouse modelof PD, and (iii) innate rodentbehaviorusing the marble burying test. Young LRRK2 mutant mice exhibited significantly lower SYNGR3 levels in striatum compared to age-matched wild-type (WT) controls, resembling level in aged WT mice. SYNGR3 is spatially co-localized with DAT at striatal presynaptic terminals, visualized by immuno-gold transmission electron microscopyand immunohistochemistry. Their protein-protein interaction was confirmed by co-immunoprecipitation. Transient overexpression of SYNGR3 in differentiated SH-SY5Y cellsincreasedcellular DA uptake activity without affecting total DAT levels. Inducing SYNGR3 overexpression by adeno-associated virus-7 (AAV7) injectionin vivointo striatum increasedex vivosynaptosomal DA uptakein LRRK2 mutant mice and improved theirinnatemarble buryingbehavior. Brain SYNGR3expressionmay be an important determinant to striatal DA homeostasisand synaptic function.Ourpreliminarybehavioraltest showed improved innatebehaviorafter SYNGR3 overexpression in LRRK2 mutant mice, advocating further studies to determine the influence of SYNGR3 in thepathophysiology of DA neuronsin PD.

Altered transcriptome-proteome coupling indicates aberrant proteostasis in Parkinson’s disease

Aberrant proteostasis is thought to be implicated in Parkinson's disease (PD), but patient-derived evidence is scant. We hypothesized that impaired proteostasis is reflected as altered transcriptome-proteome correlation in the PD brain. We integrated transcriptomic and proteomic data from prefrontal cortex of PD patients and young and aged controls to assess RNA-protein correlations across samples. The aged brain showed a genome-wide decrease in mRNA-protein correlation. Genes encoding synaptic vesicle proteins showed negative correlations, likely reflecting spatial separation of mRNA and protein into soma and synapses. PD showed a broader transcriptome-proteome decoupling, consistent with a proteome-wide decline in proteostasis. Genes showing negative correlation in PD were enriched for proteasome subunits, indicating accentuated spatial separation of transcript and protein in PD neurons. In addition, PD showed positive correlations for mitochondrial respiratory chain genes, suggesting a tighter regulation in the face of mitochondrial dysfunction. Our results support the hypothesis that aberrant proteasomal function is implicated in PD pathogenesis.

Implications of p53 in mitochondrial dysfunction and Parkinson’s disease

Purpose: To study the underlying molecular mechanisms of p53 in the mitochondrial dysfunction and the pathogenesis of Parkinson’s disease (PD), and provide a potential therapeutic target for PD treatment. Methods: We review the contributions of p53 to mitochondrial changes leading to apoptosis and the subsequent degeneration of dopaminergic neurons in PD. Results: P53 is a multifunctional protein implicated in the regulation of diverse cellular processes via transcription-dependent and transcription-independent mechanisms. Mitochondria are vital subcellular organelles for that maintain cellular function, and mitochondrial defect and impairment are primary causes of dopaminergic neuron degeneration in PD. Increasing evidence has revealed that mitochondrial dysfunction-associated dopaminergic neuron degeneration is tightly regulated by p53 in PD pathogenesis. Neurodegenerative stress triggers p53 activation, which induces mitochondrial changes, including transmembrane permeability, reactive oxygen species production, Ca2+ overload, electron transport chain defects and other dynamic alterations, and these changes contribute to neurodegeneration and are linked closely with PD occurrence and development. P53 inhibition has been shown to attenuate mitochondrial dysfunction and protect dopaminergic neurons from degeneration under conditions of neurodegenerative stress. Conclusions: p53 appears to be a potential target for neuroprotective therapy of PD.

Ketone Body β-Hydroxybutyric Acid Ameliorates Dopaminergic Neuron Injury Through Modulating Zinc Finger Protein 36/Acyl-CoA Synthetase Long-Chain Family Member Four Signaling Axis-Mediated Ferroptosis

β-hydroxybutyrate (BHB) is one of main component of ketone body, which plays an important protective role in various tissues and organs. Whereas, its exact regulatory roles and mechanisms in Parkinson's disease (PD) have not been full elucidated. In this study, SN4741 cells and C57BL/6 mice were treated with 1-methyl-4-phenylpyridinium ion (MPP+)/1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to establish the PD model in vitro and in vivo. Cell viability and damage to dopaminergic neurons were measured by cell counting kit 8, Calcein-AM/PI staining, terminal dexynucleotidyl transferase (TdT)-mediated dUTP nick end labeling and hematoxylin & eosin staining. Corresponding assay kits and BODIPY 581/591 C11 probe evaluated oxidative stress and intracellular iron levels. Western blot examined the ferroptosis-related proteins. MPTP/MPP+-treatment reduced cell viability but triggered oxidative stress and ferroptosis in SNA4741 cells and brain tissues of mice. However, these effects were dramatically reversed by BHB and Fer-1 treatment. Mechanistically, Zinc finger protein 36 (ZFP36) was a target of BHB, and its depletion could reverse the anti-oxidative stress and anti-ferroptosis roles of BHB. Moreover, ZFP36 could directly bound to acyl-CoA synthetase long-chain family member 4 (ACSL4) mRNA to decay its expression, thus negatively modulating ACSL4-mediated oxidative stress and ferroptosis. Summary, BHB alleviated oxidative stress and ferroptosis of dopaminergic neurons in PD via modulating ZFP36/ACSL4 axis, which provided some new understanding for PD prevention and treatment.

Dexmedetomidine alleviates pain in MPTP-treated mice by activating the AMPK/mTOR/NF-κB pathways in astrocytes

Pain is a major non-motor symptom that contributes to impaired quality of life in Parkinson's disease (PD). However, the mechanisms and treatment of pain in PD have not been well studied. Dexmedetomidine (Dex) is used for analgesia and sedation during deep brain stimulation (DBS) and may reverse the progression of PD. Here, we explored the effect of Dex on Parkinson’s pain and the underlying mechanism. C57BL/6 mice were intraperitoneally injected with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP, 30 mg/kg) to establish a PD model. Then, the mice were treated with Dex (50 µg/kg) or Compound C (CC, 10 mg/kg, AMPK inhibitor). A motor behavioral test was used to validate the PD model, and a plantar test was conducted to assess mechanical and thermal stimulation thresholds. Immunofluorescence and western blotting were used to analyze the level of tyrosine hydroxylase (TH) in the substantia nigra (SN) and the expression of c-Fos, GFAP, p-AMPK, mTOR, NF-κB, TNFα, and IL-6 in the dorsal horn of the spinal cord (DHSC). We found that mice exhibited motor dysfunction and mechanical allodynia and thermal hyperalgesia after MPTP injection, and these changes were partially reversed by Dex. Dex also reduced MPTP-induced astrocyte activation and TNFα and IL-6 expression, increased p-AMPK and reduced mTOR and NF-κB expression in DHSC. Moreover, the effects of Dex were partially reversed by the AMPK inhibitor Compound C. Conclusions: These findings reveal that Dex protects dopaminergic neurons in PD and alleviates pain by reducing the activation of DHSC astrocytes through the AMPK/mTOR/NF-κB pathway. Therefore, Dex may be a potential drug for treating Parkinson’s pain.

Axonal Domain Structure as a Putative Identifier of Neuron-Specific Vulnerability to Oxidative Stress in Cultured Neurons.

Several populations of neurons are purported to degenerate in Parkinson's disease (PD). One current hypothesis suggests that vulnerable neurons in PD share common characteristics including projecting to voluminous territories and having extremely long and branched axonal domains with large numbers of neurotransmitter release sites. In this study, we used a mouse in vitro culture system to compare the axonal domain of neuronal populations suspected to be vulnerable in PD to that of neuronal populations considered at a lesser risk. In the first category, we included dopamine (DA) neurons of the substantia nigra, noradrenergic neurons of the locus coeruleus (LC), serotonin neurons of the raphe nuclei (R), and cholinergic neurons of the dorsal motor nucleus of the vagus (DMV). In the second category, we included DA neurons of the ventral tegmental area, cholinergic neurons of the hypoglossal nucleus, and cholinergic interneurons of the dorsal striatum. Validating their differential vulnerability, we find that, when compared with neurons presumed to be resilient in PD, a larger proportion of neurons presumed to be vulnerable in PD degenerate in response to cell stress induced by hydrogen peroxide. We also find that they are endowed with larger axonal domains, that are more complex, have more axonal varicosities with a higher proportion of varicosities that are positive for synaptotagmin 1 (Syt-1). Notwithstanding the obvious limitations related to the dissection of small brain nuclei and to the growth of these neurons in vitro, these findings support the hypothesis that axonal domain structure is a key characteristic of neuronal vulnerability to oxidative stress.

The APP intracellular domain promotes LRRK2 expression to enable feed-forward neurodegenerative mechanisms in Parkinson's disease.

Gain-of-function mutations in the leucine-rich repeat kinase 2 (LRRK2) gene are common in familial forms of Parkinson's disease (PD), which is characterized by progressive neurodegeneration that impairs motor and cognitive function. We previously demonstrated that LRRK2-mediated phosphorylation of β-amyloid precursor protein (APP) triggers the production and nuclear translocation of the APP intracellular domain (AICD). Here, we connected LRRK2 to AICD in a feed-forward cycle that enhanced LRRK2-mediated neurotoxicity. In cooperation with the transcription factor FOXO3a, AICD promoted LRRK2 expression, thus increasing the abundance of LRRK2 that promotes AICD activation. APP deficiency in LRRK2G2019S mice suppressed LRRK2 expression, LRRK2-mediated mitochondrial dysfunction, α-synuclein accumulation, and tyrosine hydroxylase (TH) loss in the brain, phenotypes associated with toxicity and loss of dopaminergic neurons in PD. Conversely, AICD overexpression increased LRRK2 expression and LRRK2-mediated neurotoxicity in LRRK2G2019S mice. In LRRK2G2019S mice or cultured dopaminergic neurons from LRRK2G2019S patients, treatment with itanapraced reduced LRRK2 expression and was neuroprotective. Itanapraced showed similar effects in a neurotoxin-induced PD mouse model, suggesting that inhibiting the AICD may also have therapeutic benefits in idiopathic PD. Our findings reveal a therapeutically targetable, feed-forward mechanism through which AICD promotes LRRK2-mediated neurotoxicity in PD.

Pilot Study for Correlation of Heart Rate Variability and Dopamine Transporter Brain Imaging in Patients with Parkinsonian Syndrome.

Background: Parkinsonian syndrome (PS) is a broad category of neurodegenerative movement disorders that includes Parkinson disease, multiple system atrophy (MSA), progressive supranuclear palsy, and corticobasal degeneration. Parkinson disease (PD) is the second most common neurodegenerative disorder with loss of dopaminergic neurons of the substantia nigra and, thus, dysfunction of the nigrostriatal pathway. In addition to the motor symptoms of bradykinesia, rigidity, tremors, and postural instability, nonmotor symptoms such as autonomic dysregulation (AutD) can also occur. Heart rate variability (HRV) has been used as a measure of AutD and has shown to be prognostic in diseases such as diabetes mellitus and cirrhosis, as well as PD. I-123 ioflupane, a gamma ray-emitting radiopharmaceutical used in single-photon emission computed tomography (SPECT), is used to measure the loss of dopaminergic neurons in PD. Through the combination of SPECT and HRV, we tested the hypothesis that asymmetrically worse left-sided neuronal loss would cause greater AutD. Methods: 51 patients were enrolled on the day of their standard of care I-123 ioflupane scan for the work-up of possible Parkinsonian syndrome. Demographic information, medical and medication history, and ECG data were collected. HRV metrics were extracted from the ECG data. I-123 ioflupane scans were interpreted by a board-certified nuclear radiologist and quantified by automated software to generate striatal binding ratios (SBRs). Statistical analyses were performed to find correlations between the HRV and SPECT parameters. Results: 32 patients were excluded from the final analysis because of normal scans, prior strokes, cardiac disorders and procedures, or cancer. Abnormal I-123 ioflupane scans were clustered using T-SNE, and one-way ANOVA was performed to compare HRV and SBR parameters. The analysis was repeated after the exclusion of patients taking angiotensin-converting enzyme inhibitors, given the known mechanism on autonomic function. Subsequent analysis showed a significant difference between the high-frequency domains of heart rate variability, asymmetry of the caudate SBR, and putamen-to-caudate SBR. Conclusion: Our results support the hypothesis that more imbalanced (specifically worse left-sided) neuronal loss results in greater AutD.

Age-Related Midbrain Inflammation and Senescence in Parkinson's Disease.

Immune responses are arising as a common feature of several neurodegenerative diseases, such as Parkinson’s disease (PD), Alzheimer’s disease (AD), and Amyotrophic Lateral Sclerosis (ALS), but their role as either causative or consequential remains debated. It is evident that there is local inflammation in the midbrain in PD patients even before symptom onset, but the underlying mechanisms remain elusive. In this mini-review, we discuss this midbrain inflammation in the context of PD and argue that cellular senescence may be the cause for this immune response. We postulate that to unravel the relationship between inflammation and senescence in PD, it is crucial to first understand the potential causative roles of various cell types of the midbrain and determine how the possible paracrine spreading of senescence between them may lead to observed local immune responses. We hypothesize that secretion of pro-inflammatory factors by senescent cells in the midbrain triggers neuroinflammation resulting in immune cell-mediated killing of midbrain dopaminergic (DA) neurons in PD.

Effects of hCG on DA neuronal death of Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disease worldwide, with the incidence in men being about twice as compared to women. Gender differences may provide clues for finding key targets that mediate the death of dopaminergic (DA) neurons in PD. Luteinizing hormone (LH), analog of human chorionic gonadotropin (hCG), and their receptor, luteinizing hormone/choriogonadotropin receptor (LHCGR), are associated with the pathogenesis of PD. Movement-related symptoms are partially improved by hCG in PD patients. However, the relationship between hCG and PD, as well as its roles in mediating DA neuronal death, has not been elucidated. In this study, we investigated the potential of hCG as a treatment during PD progression. After establishment of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD mouse models, we found that hCG restored the decrease of LHCGR activity caused by down-regulation of LH in the substantia nigra. Furthermore, the reduction of LHCGR activity led to DA neuronal death through knocking down the LHCGR in DA neurons by AAV-mTH-shRNA. Treatment with hCG alleviated the DA neuronal death induced by MPTP. Finally, hCG exerted neuroprotective effects by inhibiting the activation of glycogen synthase kinase 3 beta (GSK3β) in our MPTP-induced PD mouse and MPP+-treated SH-SY5Y cell models. Together, these results demonstrate that hCG exerts neuroprotective effects for PD through LHCGR, and the inhibition of GSK3β activation is involved in this protective effect, suggesting that hCG can be taken as a potential therapeutic for the treatment of PD.

CREB Inactivation by HDAC1/PP1γ Contributes to Dopaminergic Neurodegeneration in Parkinson's Disease.

Understanding the pathogenesis of nigral dopaminergic neurodegeneration is critical for developing mechanism-based treatments for Parkinson's disease (PD). In the nigral dopaminergic neurons of postmortem human PD brains, we found that CREB, a well-recognized pro-survival transcription factor in neurons, was inactivated by dephosphorylation at Ser133. CREB dephosphorylation correlated with decreased expression of NURR1, one of its target genes crucial for dopaminergic neuron survival, confirming that CREB function was impaired in nigral dopaminergic neurons in PD. An MPTP mouse model was used to further elucidate the mechanism underlying CREB dephosphorylation. Protein phosphatase 1γ (PP1γ), which dephosphorylates CREB, was constitutively associated with histone deacetylase 1 (HDAC1). HDAC1 promotes CREB Ser133 dephosphorylation via a stable interaction with PP1γ. We found that CREB interacted with the HDAC1/PP1γ complex during dopaminergic neurodegeneration. Importantly, increased CREB/HDAC1 interaction occurred in the nigral dopaminergic neurons of PD patients as demonstrated using a proximity ligation assay. Disrupting CREB/HDAC1 interaction via either overexpression of GAL4 M1, a CREB mutant, or administration of trichostatin A, a pan-HDAC inhibitor, restored the expression levels of phospho-CREB (Ser133) and NURR1, and protected nigral dopaminergic neurons in the MPTP-treated mouse brain. Collectively, our results demonstrated that HDAC1/PP1γ-mediated CREB inactivation contributed to dopaminergic neuronal degeneration. Disruption of CREB/HDAC1 interaction has the potential to be a new approach for PD therapy.SIGNIFICANCE STATEMENT Parkinson's disease (PD) is the most common movement disorder attributed to the progressive loss of dopaminergic neurons in the substantia nigra. Understanding the pathogenesis of nigral dopaminergic neurodegeneration is critical for developing mechanism-based treatments for PD. We found in nigral dopaminergic neurons of postmortem human PD brains that CREB, a well-recognized pro-survival transcription factor in neurons, was inactivated by dephosphorylation at Ser133. HDAC1, constitutively associated with PP1γ, interacted with CREB to mediate its dephosphorylation during dopaminergic neurodegeneration. Disrupting CREB/HDAC1 interaction restored CREB activity and protected nigral dopaminergic neurons in the MPTP mouse brains. This work suggests that disruption of the CREB/HDAC1 interaction to restore CREB activity may be a potential therapeutic approach in PD.

Exploring the focal role of LRRK2 kinase in Parkinson's disease.

The major breakthroughs in our knowledge of how biology plays a role in Parkinson's disease (PD) have opened up fresh avenues designed to know the pathogenesis of disease and identify possible therapeutic targets. Mitochondrial abnormal functioning is a key cellular feature in the pathogenesis of PD. An enzyme, leucine-rich repeat kinase 2 (LRRK2), involved in both the idiopathic and familial PD risk, is a therapeutic target. LRRK2 has a link to the endolysosomal activity. Enhanced activity of the LRRK2 kinase, endolysosomal abnormalities and aggregation of autophagic vesicles with imperfectly depleted substrates, such as α-synuclein, are all seen in the substantia nigra dopaminergic neurons in PD. Despite the fact that LRRK2 is involved in endolysosomal and autophagic activity, it is undefined if inhibiting LRRK2 kinase activity will prevent endolysosomal dysfunction or minimise the degeneration of dopaminergic neurons. The inhibitor's capability of LRRK2 kinase to inhibit endolysosomal and neuropathological alterations in human PD indicates that LRRK2 inhibitors could have significant therapeutic usefulness in PD. G2019S is perhaps the maximum common mutation in PD subjects. Even though LRRK2's well-defined structure has still not been established, numerous LRRK2 inhibitors have been discovered. This review summarises the role of LRRK2 kinase in Parkinson's disease.

Aminochrome Induces Neuroinflammation and Dopaminergic Neuronal Loss: A New Preclinical Model to Find Anti-inflammatory and Neuroprotective Drugs for Parkinson's Disease.

Studies have suggested aminochrome as an endogenous neurotoxin responsible for the dopaminergic neuron degeneration in Parkinson's disease (PD). However, neuroinflammation, an important alteration in PD pathogenesis, has been strictly induced in vitro by aminochrome. The aim of this study was to characterize the neuroinflammation induced in vivo by aminochrome. Wistar rats (male, 250-270g) received a unilateral single dose by stereotaxic injection of saline into three sites in the striatum in the negative control group, or 32nmol 6-hydroxydopamine (6-OHDA) in the positive control, or 6nmol aminochrome. After 14 days, histological and molecular analyses were performed. We observed by immunofluorescence that aminochrome, as well as 6-OHDA, induced an increase in the number of Iba-1+ cells and in the number of activated (Iba-1+/ CD68+) microglia. An increase in the number of S100b+ cells and in the GFAP expression were also evidenced in the striatum and the SNpc of animals from aminochrome and positive control group. Dopaminergic neuronal loss was marked by reduction of TH+ cells and confirmed with reduction in the number of Nissl-stained neurons in the SNpc of rats from aminochrome and positive control groups. In addition, we observed by qPCR that aminocrhome induced an increase in the levels of IL-1β, TNF-α, NLRP3, CCL5 and CCR2 mRNA in the SNpc. This work provides the first evidence of microgliosis, astrogliosis and neuroinflammation induced by aminochrome in an in vivo model. Since aminochrome is an endogenous molecule derived from dopamine oxidation present in the targeted neurons in PD, these results reinforce the potential of aminochrome as a useful preclinical model to find anti-inflammatory and neuroprotective drugs for PD. Aminochrome induced dopaminergic neuronal loss, microglial activation, astroglial activation and neuroinflammation marked by an increase in NLRP3, IL1β, TNF-α, CCL2, CCL5 and CCR2.

Association between cigarette smoking and Parkinson’s disease: a neuroimaging study

Background:Mounting evidence has revealed an inverse association between cigarette smoking and the risk of Parkinson’s disease (PD). Meanwhile, cigarette smoking has been found to be associated with cognitive impairment in PD patients. However, the neural mechanisms of the association between cigarette smoking and PD are not fully understood.Objective:The aim of this study is to explore the neural mechanisms of the association between cigarette smoking and PD.Methods:A total of 129 PD patients and 69 controls were recruited from the Parkinson’s Progression Markers Initiative (PPMI) cohort, including 39 PD patients with regular smoking history (PD-S), 90 PD patients without regular smoking history (PD-NS), 26 healthy controls with regular smoking history (HC-S), and 43 healthy controls without regular smoking history (HC-NS). Striatal dopamine transporter (DAT) binding and gray matter (GM) volume of the whole brain were compared among the four groups.Results:PD patients showed significantly reduced striatal DAT binding compared with healthy controls, and HC-S showed significantly reduced striatal DAT binding compared with HC-NS. Moreover, smoking and PD showed a significant interaction effect in the left medial prefrontal cortex (mPFC). PD-S showed reduced GM volume in the left mPFC compared with PD-NS.Conclusion:The degeneration of dopaminergic neurons in PD results in a substantial reduction of the DAT and dopamine levels. Nicotine may act as a stimulant to inhibit the action of striatal DAT, increasing dopamine levels in the synaptic gap. The inverse alteration of dopamine levels between PD and nicotine addiction may be the reason for the inverse association between smoking and the risk of PD. In addition, the mPFC atrophy in PD-S may be associated with cognitive impairment.

Upregulated hexokinase 2 expression induces the apoptosis of dopaminergic neurons by promoting lactate production in Parkinson's disease

Parkinson's disease (PD) is characterized by impaired mitochondrial function and decreased ATP levels. Aerobic glycolysis and lactate production have been shown to be upregulated in dopaminergic neurons to sustain ATP levels, but the effect of upregulated glycolysis on dopaminergic neurons remains unknown. Since lactate promotes apoptosis and α-synuclein accumulation in neurons, we hypothesized that the lactate produced upon upregulated glycolysis is involved in the apoptosis of dopaminergic neurons in PD. In this study, we examined the expression of hexokinase 2 (HK2) and lactate dehydrogenase (LDH), the key enzymes in glycolysis, and lactate levels in the substantia nigra pars compacta (SNpc) of a MPTP-induced mouse model of PD and in MPP+-treated SH-SY5Y cells. We found that the expression of HK2 and LDHA and the lactate levels were markedly increased in the SNpc of MPTP-treated mice and in MPP+-treated SH-SY5Y cells. Exogenous lactate treatment led to the apoptosis of SH-SY5Y cells. Intriguingly, lactate production and the apoptosis of dopaminergic neurons were suppressed by the application of 3-bromopyruvic acid (3-Brpa), a HK2 inhibitor, or siRNA both in vivo and in vitro. 3-Brpa treatment markedly improved the motor behaviour of MPTP-treated mice in pole test and rotarod test. Mechanistically, lactate increases the activity of adenosine monophosphate-activated protein kinase (AMPK) and suppresses the phosphorylation of serine/threonine kinase 1 (Akt) and mammalian target of rapamycin (mTOR). Together, our data suggest that upregulated HK2 and LDHA and increased lactate levels prompt the apoptosis of dopaminergic neurons in PD. Inhibition of HK2 expression attenuated the apoptosis of dopaminergic neurons by downregulating lactate production and AMPK/Akt/mTOR pathway in PD.

Tocotrienols protect differentiated SH-SY5Y human neuroblastoma cells against 6-hydroxydopamine-induced cytotoxicity by ameliorating dopamine biosynthesis and dopamine receptor D2 gene expression

Oxidative stress is a critical factor that triggers a “domino” cascade of events leading to the degeneration of dopaminergic neurons in Parkinson disease. Tocotrienols (T3) have antioxidant effects and can protect neuronal cells against oxidative damage. In the present study, we investigated the neuroprotective effects of different forms of T3 (alpha, delta, gamma) or tocotrienol-rich fraction (TRF) against 6-hydroxydopamine (6-OHDA)-induced oxidative damage in differentiated SH-SY5Y human neural cells. Differentiating the SH-SY5Y cells with retinoic acid and a low-serum culture medium for 6 days allowed development of human dopamine-like neural cells. Subsequently, the differentiated SH-SY5Y neural cells were pretreated with different forms of T3 for 24 hours before these cells were exposed to 6-OHDA. The T3 analogues and TRF displayed neuroprotective effects (P < .05) via restoration of cell viability and activation of antioxidant enzymes (e.g., superoxide dismutase, catalase). Notably, TRF was highly efficient in scavenging reactive oxygen species and upregulating dopamine and tyrosine hydroxylase levels in the differentiated SH-SY5Y cells. Gamma-T3 exhibited the most potent effects in attenuating apoptosis, whereas alpha-T3 was most effective in preventing 6-OHDA-induced leakage of α-Synuclein. Delta-T3 displayed a noticeable effect in upregulating the dopamine receptor D2 gene expression compared with controls. These findings suggest T3 isoforms and TRF demonstrate significant neuroprotective effects in protecting differentiated neural cells against 6-OHDA-mediated oxidative stress.

Mitochondrial Phenotypes in Parkinson’s Diseases—A Focus on Human iPSC-Derived Dopaminergic Neurons

Established disease models have helped unravel the mechanistic underpinnings of pathological phenotypes in Parkinson’s disease (PD), the second most common neurodegenerative disorder. However, these discoveries have been limited to relatively simple cellular systems and animal models, which typically manifest with incomplete or imperfect recapitulation of disease phenotypes. The advent of induced pluripotent stem cells (iPSCs) has provided a powerful scientific tool for investigating the underlying molecular mechanisms of both familial and sporadic PD within disease-relevant cell types and patient-specific genetic backgrounds. Overwhelming evidence supports mitochondrial dysfunction as a central feature in PD pathophysiology, and iPSC-based neuronal models have expanded our understanding of mitochondrial dynamics in the development and progression of this devastating disorder. The present review provides a comprehensive assessment of mitochondrial phenotypes reported in iPSC-derived neurons generated from PD patients’ somatic cells, with an emphasis on the role of mitochondrial respiration, morphology, and trafficking, as well as mitophagy and calcium handling in health and disease. Furthermore, we summarize the distinguishing characteristics of vulnerable midbrain dopaminergic neurons in PD and report the unique advantages and challenges of iPSC disease modeling at present, and for future mechanistic and therapeutic applications.