Midbrain Dopaminergic Neurons Research Articles

Overexpression of tyrosine hydroxylase in dopaminergic neurons increased sensitivity to methamphetamine

Drug abuse is one of the great social problems in the world and a major healthcare challenge. It is supposed that sensitivity and reactivity to abuse drugs may vary from person to person, while its molecular basis is largely unknown. Dopaminergic neurons are deeply involved in addiction, and tyrosine hydroxylase (TH) catalyzes the first and rate-limiting step of the biosynthesis of dopamine (DA). We investigated the effects of increased TH expression on the metabolism of DA and reactivity to methamphetamine (METH), a drug of abuse, in mice. Wild-type TH (WT-TH) or the S40E mutant of TH (S40E-TH), which is an active form of TH mimicking phosphorylated TH at the 40th serine, was expressed in midbrain dopaminergic neurons using an adeno-associated virus (AAV) vector. The biochemical analysis showed that the turnover rates of DA in the nerve terminals were increased by the expression of WT-TH and S40E-TH, while there were few changes in the DA contents. Next, we administered METH to TH-overexpressing mice. We found that the S40E-TH-expressing mice responded to lower doses of METH than the control mice and WT-TH mice. The stereotyped behaviors appeared first in S40E-TH mice and then in WT-TH and control mice in this order. These data showed that the TH activity and expression level differentially affect DA metabolism in the nerve terminals from that in the cell bodies and that the TH activity and expression level are one of the determining factors for sensitivity and reactivity to METH. We suggest that TH may be a drug target for ameliorating sensitivity to drugs of abuse.

Nicotine-Mediated Recruitment of GABAergic Neurons to a Dopaminergic Phenotype Attenuates Motor Deficits in an Alpha-Synuclein Parkinson's Model.

Previous work revealed an inverse correlation between tobacco smoking and Parkinson's disease (PD) that is associated with nicotine-induced neuroprotection of dopaminergic (DA) neurons against nigrostriatal damage in PD primates and rodent models. Nicotine, a neuroactive component of tobacco, can directly alter the activity of midbrain DA neurons and induce non-DA neurons in the substantia nigra (SN) to acquire a DA phenotype. Here, we investigated the recruitment mechanism of nigrostriatal GABAergic neurons to express DA phenotypes, such as transcription factor Nurr1 and DA-synthesizing enzyme tyrosine hydroxylase (TH), and the concomitant effects on motor function. Wild-type and α-syn-overexpressing (PD) mice treated with chronic nicotine were assessed by behavioral pattern monitor (BPM) and immunohistochemistry/in situ hybridization to measure behavior and the translational/transcriptional regulation of neurotransmitter phenotype following selective Nurr1 overexpression or DREADD-mediated chemogenetic activation. We found that nicotine treatment led to a transcriptional TH and translational Nurr1 upregulation within a pool of SN GABAergic neurons in wild-type animals. In PD mice, nicotine increased Nurr1 expression, reduced the number of α-syn-expressing neurons, and simultaneously rescued motor deficits. Hyperactivation of GABA neurons alone was sufficient to elicit de novo translational upregulation of Nurr1. Retrograde labeling revealed that a fraction of these GABAergic neurons projects to the dorsal striatum. Finally, concomitant depolarization and Nurr1 overexpression within GABA neurons were sufficient to mimic nicotine-mediated dopamine plasticity. Revealing the mechanism of nicotine-induced DA plasticity protecting SN neurons against nigrostriatal damage could contribute to developing new strategies for neurotransmitter replacement in PD.

TGFβ3, dibutyryl cAMP and a notch inhibitor modulate phenotype late in stem cell-derived dopaminergic neuron maturation.

The generation of midbrain dopaminergic neurons (mDAs) from pluripotent stem cells (hPSC) holds much promise for both disease modelling studies and as a cell therapy for Parkinson's disease (PD). Generally, dopaminergic neuron differentiation paradigms rely on inhibition of smad signalling for neural induction followed by hedgehog signalling and an elevation of β-catenin to drive dopaminergic differentiation. Post-patterning, differentiating dopaminergic neuron cultures are permitted time for maturation after which the success of these differentiation paradigms is usually defined by expression of tyrosine hydroxylase (TH), the rate limiting enzyme in the synthesis of dopamine. However, during maturation, culture media is often supplemented with additives to promote neuron survival and or promote cell differentiation. These additives include dibutyryl cyclic adenosine monophosphate (dbcAMP), transforming growth factor β3 (TGFβ3) and or the γ-secretase inhibitor (DAPT). While these factors are routinely added to cultures, their impact upon pluripotent stem cell-derived mDA phenotype is largely unclear. In this study, we differentiate pluripotent stem cells toward a dopaminergic phenotype and investigate how the omission of dbcAMP, TGFβ3 or DAPT, late in maturation, affects the regulation of multiple dopaminergic neuron phenotype markers. We now show that the removal of dbcAMP or TGFβ3 significantly and distinctly impacts multiple markers of the mDA phenotype (FOXA2, EN1, EN2, FOXA2, SOX6), while commonly increasing both MSX2 and NEUROD1 and reducing expression of both tyrosine hydroxylase and WNT5A. Removing DAPT significantly impacted MSX2, OTX2, EN1, and KCNJ6. In the absence of any stressful stimuli, we suggest that these culture additives should be viewed as mDA phenotype-modifying, rather than neuroprotective. We also suggest that their addition to cultures is likely to confound the interpretation of both transplantation and disease modelling studies.

From 2D to 3D: Development of Monolayer Dopaminergic Neuronal and Midbrain Organoid Cultures for Parkinson's Disease Modeling and Regenerative Therapy.

Parkinson's Disease (PD) is a prevalent neurodegenerative disorder that is characterized pathologically by the loss of A9-specific dopaminergic (DA) neurons in the substantia nigra pars compacta (SNpc) of the midbrain. Despite intensive research, the etiology of PD is currently unresolved, and the disease remains incurable. This, in part, is due to the lack of an experimental disease model that could faithfully recapitulate the features of human PD. However, the recent advent of induced pluripotent stem cell (iPSC) technology has allowed PD models to be created from patient-derived cells. Indeed, DA neurons from PD patients are now routinely established in many laboratories as monolayers as well as 3D organoid cultures that serve as useful toolboxes for understanding the mechanism underlying PD and also for drug discovery. At the same time, the iPSC technology also provides unprecedented opportunity for autologous cell-based therapy for the PD patient to be performed using the patient's own cells as starting materials. In this review, we provide an update on the molecular processes underpinning the development and differentiation of human pluripotent stem cells (PSCs) into midbrain DA neurons in both 2D and 3D cultures, as well as the latest advancements in using these cells for drug discovery and regenerative medicine. For the novice entering the field, the cornucopia of differentiation protocols reported for the generation of midbrain DA neurons may seem daunting. Here, we have distilled the essence of the different approaches and summarized the main factors driving DA neuronal differentiation, with the view to provide a useful guide to newcomers who are interested in developing iPSC-based models of PD.

Genome-wide analyses of ADHD identify 27 risk loci, refine the genetic architecture and implicate several cognitive domains.

Attention-deficit hyperactivity disorder (ADHD) is a prevalent neurodevelopmental disorder with a major genetic component. Here, we present a genome-wide association study meta-analysis of ADHD comprising 38,691 individuals with ADHD and 186,843 controls. We identified 27 genome-wide significant loci, highlighting 76 potential risk genes enriched among genes expressed particularly in early brain development. Overall, ADHD genetic risk was associated with several brain-specific neuronal subtypes and midbrain dopaminergic neurons. In exome-sequencing data from 17,896 individuals, we identified an increased load of rare protein-truncating variants in ADHD for a set of risk genes enriched with probable causal common variants, potentially implicating SORCS3 in ADHD by both common and rare variants. Bivariate Gaussian mixture modeling estimated that 84-98% of ADHD-influencing variants are shared with other psychiatric disorders. In addition, common-variant ADHD risk was associated with impaired complex cognition such as verbal reasoning and a range of executive functions, including attention.

Glial Cultures Differentiated from iPSCs of Patients with PARK2-Associated Parkinson's Disease Demonstrate a Pro-Inflammatory Shift and Reduced Response to TNFα Stimulation.

Parkinson's disease (PD) is the second most common neurodegenerative diseases characterized by progressive loss of midbrain dopaminergic neurons in the substantia nigra. Mutations in the PARK2 gene are a frequent cause of familial forms of PD. Sustained chronic neuroinflammation in the central nervous system makes a significant contribution to neurodegeneration events. In response to inflammatory factors produced by activated microglia, astrocytes change their transcriptional programs and secretion profiles, thus acting as immunocompetent cells. Here, we investigated iPSC-derived glial cell cultures obtained from healthy donors (HD) and from PD patients with PARK2 mutations in resting state and upon stimulation by TNFα. The non-stimulated glia of PD patients demonstrated higher IL1B and IL6 expression levels and increased IL6 protein synthesis, while BDNF and GDNF expression was down-regulated when compared to that of the glial cells of HDs. In the presence of TNFα, all of the glial cultures displayed a multiplied expression of genes encoding inflammatory cytokines: TNFA, IL1B, and IL6, as well as IL6 protein synthesis, although PD glia responded to TNFα stimulation less strongly than HD glia. Our results demonstrated a pro-inflammatory shift, a suppression of the neuroprotective gene program, and some depletion of reactivity to TNFα in PARK2-deficient glia compared to glial cells of HDs.

Role of midbrain dopaminergic neurones in post-anaesthetic cognitive recovery in rats

Dopaminergic ventral tegmental area (VTA) neurones are critically involved in restoring consciousness after general anaesthesia.1, 2 Whether these circuits contribute to cognitive recovery after emergence is unknown. Previous work using touchscreen-based neurocognitive tasks in rats has shown that after conscious recovery, cognitive recovery trajectories are highly anaesthetic-dependent. Notably, rats have delayed cognitive recovery after dexmedetomidine- and ketamine-induced loss of consciousness (LOC).3 To assess whether circuits known to be involved in re-establishing consciousness can be similarly exploited to hasten cognitive recovery, we used chemogenetic techniques to activate midbrain dopaminergic neurones in rats after dexmedetomidine- and ketamine-induced LOC and measured performance on a sustained attention task. As previous investigations have shown that pharmacologic activation of dopaminergic pathways hastens emergence from dexmedetomidine-, but not ketamine-induced LOC, we hypothesised that activating dopaminergic midbrain neurones would differentially affect cognitive recovery after dexmedetomidine and ketamine exposure.

The humanised CYP2C19 transgenic mouse exhibits cerebellar atrophy and movement impairment reminiscent of ataxia.

CYP2C19 transgenic mouse expresses the human CYP2C19 gene in the liver and developing brain, and it exhibits altered neurodevelopment associated with impairments in emotionality and locomotion. Because the validation of new animal models is essential for the understanding of the aetiology and pathophysiology of movement disorders, the objective was to characterise motoric phenotype in CYP2C19 transgenic mice and to investigate its validity as a new animal model of ataxia. The rotarod, paw-print and beam-walking tests were utilised to characterise the motoric phenotype. The volumes of 20 brain regions in CYP2C19 transgenic and wild-type mice were quantified by 9.4T gadolinium-enhanced post-mortem structural neuroimaging. Antioxidative enzymatic activity was quantified biochemically. Dopaminergic alterations were characterised by chromatographic quantification of concentrations of dopamine and its metabolites and by subsequent immunohistochemical analyses. The beam-walking test was repeated after the treatment with dopamine receptor antagonists ecopipam and raclopride. CYP2C19 transgenic mice exhibit abnormal, unilateral ataxia-like gait, clasping reflex and 5.6-fold more paw-slips in the beam-walking test; the motoric phenotype was more pronounced in youth. Transgenic mice exhibited a profound reduction of 12% in cerebellar volume and a moderate reduction of 4% in hippocampal volume; both regions exhibited an increased antioxidative enzyme activity. CYP2C19 mice were hyperdopaminergic; however, the motoric impairment was not ameliorated by dopamine receptor antagonists, and there was no alteration in the number of midbrain dopaminergic neurons in CYP2C19 mice. Humanised CYP2C19 transgenic mice exhibit altered gait and functional motoric impairments; this phenotype is likely caused by an aberrant cerebellar development.

Brain-enriched miR-128: Reduced in exosomes from Parkinson's patient plasma, improves synaptic integrity, and prevents 6-OHDA mediated neuronal apoptosis.

Parkinson's disease (PD) is a progressive neurodegenerative disorder associated with the death of mid-brain dopaminergic neurons. Unfortunately, no effective cure or diagnostic biomarkers for PD are available yet. To address this, the present study focuses on brain-enriched small non-coding regulatory RNAs called microRNAs (miRNAs) that are released into the circulation packaged inside small extracellular vesicles called exosomes. We collected blood samples from PD patients and isolated exosomes from the plasma. qPCR-based detection revealed a particular neuron-enriched miR-128 to be significantly decreased in the patient-derived exosomes. Interestingly, a concomitant decreased expression of miR-128 was observed in the cellular models of PD. Fluorescent live cell imaging and flow-cytometry revealed that over-expression of miR-128 can prevent 6-OHDA-mediated mitochondrial superoxide production and induction of neuronal death respectively. This neuroprotective effect was found to be induced by miR-128-mediated inhibition of FoxO3a activation, a transcription factor involved in apoptosis. miR-128 over-expression also resulted in down-regulation of pro-apoptotic FoxO3a targets- FasL and PUMA, at both transcript and protein levels. Further downstream, miR-128 over-expression inhibited activation of caspases-8, -9 and -3, preventing both the intrinsic and extrinsic pathways of apoptosis. Additionally, over expression of miR-128 prevented down-regulation of synaptic proteins- Synaptophysin and PSD-95 and attenuated neurite shortening, thereby maintaining overall neuronal integrity. Thus, our study depicts the intracellular role of miR-128 in neuronal apoptosis and neurodegeneration and its implications as a biomarker being detectable in the circulating exosomes of PD patient blood. Thus, characterization of such exosomal brain-enriched miRNAs hold promise for effective detection and diagnosis of PD.

D2/3 Agonist during Learning Potentiates Cued Risky Choice.

Impulse control and/or gambling disorders can be triggered by dopamine agonist therapies used to treat Parkinson's disease, but the cognitive and neurobiological mechanisms underlying these adverse effects are unknown. Recent data show that adding win-paired sound and light cues to the rat gambling task (rGT) potentiates risky decision-making and impulsivity via the dopamine system, and that changing dopaminergic tone has a greater influence on behavior while subjects are learning task contingencies. Dopamine agonist therapy may therefore be potentiating risk-taking by amplifying the behavioral impact of gambling-related cues on novel behavior. Here, we show that ropinirole treatment in male rats transiently increased motor impulsivity but robustly and progressively increased choice of the high-risk/high-reward options when administered during acquisition of the cued but not uncued rGT. Early in training, ropinirole increased win-stay behavior after large unlikely wins on the cued rGT, indicative of enhanced model-free learning, which mediated the drug's effect on later risk preference. Ex vivo cFos imaging showed that both chronic ropinirole and the addition of win-paired cues suppressed the activity of dopaminergic midbrain neurons. The ratio of midbrain:prefrontal cFos+ neurons was lower in animals with suboptimal choice patterns and tended to predict risk preference across all rats. Network analyses further suggested that ropinirole induced decoupling of the dopaminergic cells of the VTA and nucleus accumbens but only when win-paired cues were present. Frontostriatal activity uninformed by the endogenous dopaminergic teaching signal therefore appeared to perpetuate risky choice, and ropinirole exaggerated this disconnect in synergy with reward-paired cues.SIGNIFICANCE STATEMENT D2/3 receptor agonists, used to treat Parkinson's disease, can cause gambling disorder through an unknown mechanism. Ropinirole increased risky decision-making in rats, but only when wins were paired with casino-inspired sounds and lights. This was mediated by increased win-stay behavior after large unlikely wins early in learning, indicating enhanced model-free learning. cFos imaging showed that ropinirole suppressed activity of midbrain dopamine neurons, an effect that was mimicked by the addition of win-paired cues. The degree of risky choice rats exhibited was uniquely predicted by the ratio of midbrain dopamine:PFC activity. Depriving the PFC of the endogenous dopaminergic teaching signal may therefore drive risky decision-making on-task, and ropinirole acts synergistically with win-paired cues to amplify this.

Methodologies for Detecting Quantal Exocytosis in Adrenal Chromaffin Cells Through Diamond-Based MEAs.

Diamond-based multiarray sensors are suitable to detect in real-time exocytosis and action potentials from cultured, spontaneously firing chromaffin cells, primary hippocampal neurons, and midbrain dopaminergic neurons. Here, we focus on how amperometric measurements of catecholamine release are performed on micrographitic diamond multiarrays (μG-D-MEAs) with high temporal and spatial resolution by 16 electrodes simultaneously.

Single-cell transcriptomics reveals correct developmental dynamics and high-quality midbrain cell types by improved hESC differentiation.

Stem cell technologies provide new opportunities for modeling cells in health and disease and for regenerative medicine. In both cases, developmental knowledge and defining the molecular properties and quality of the cell types is essential. In this study, we identify developmental factors important for the differentiation of human embryonic stem cells (hESCs) into functional midbrain dopaminergic (mDA) neurons. We found that laminin-511, and dual canonical and non-canonical WNT activation followed by GSK3β inhibition plus FGF8b, improved midbrain patterning. In addition, neurogenesis and differentiation were enhanced by activation of liver X receptors and inhibition of fibroblast growth factor signaling. Moreover, single-cell RNA-sequencing analysis revealed a developmental dynamics similar to that of the endogenous human ventral midbrain and the emergence of high-quality molecularly defined midbrain cell types, including mDA neurons. Our study identifies novel factors important for human midbrain development and opens the door for a future application of molecularly defined hESC-derived cell types in Parkinson disease.

Bioinformatic Analysis of Genetic Factors from Human Blood Samples and Postmortem Brains in Parkinson's Disease.

Parkinson's disease (PD) is one of the most prevalent neurodegenerative disorders characterized by motor and nonmotor symptoms due to the selective loss of midbrain dopaminergic neurons. Pharmacological and surgical interventions have not been possible to cure PD; however, the cause of neurodegeneration remains unclear. Here, we performed and tested a multitiered bioinformatic analysis using the GEO and Proteinexchange database to investigate the gene expression involved in the pathogenesis of PD. Then we further validated individual differences in gene expression in whole blood samples that we collected in the clinic. We also made an interaction analysis and prediction for these genetic factors. There were in all 1045 genes expressing differently in PD compared with the healthy control group. Protein-protein interaction (PPI) networks showed 10 top hub genes: ACO2, MDH2, SDHA, ATP5A1, UQCRC2, PDHB, SUCLG1, NDUFS3, UQCRC1, and ATP5C1. We validated the ten hub gene expression in clinical PD patients and showed the expression of MDH2 was significantly different compared with healthy control. Besides, we also identified the expression of G6PD, GRID2, RIPK2, CUL4B, BCL6, MRPS31, GPI, and MAP 2 K1 were all significantly increased, and levels of MAPK, ELAVL1, RAB14, KLF9, ARF1, ARFGAP1, ATG7, ABCA7, SFT2D2, E2F2, MAPK7, and UHRF1 were all significantly decreased in PD. Among them, to our knowledge, we presently have the most recent and conclusive evidence that GRID2, RIPK2, CUL4B, E2F2, and ABCA7 are possible PD indicators. We confirmed several genetic factors which may be involved in the pathogenesis of PD. They could be promising markers for discriminating the PD and potential factors that may affect PD development.

Developmental pathways linked to the vulnerability of adult midbrain dopaminergic neurons to neurodegeneration.

The degeneration of dopaminergic and other neurons in the aging brain is considered a process starting well beyond the infantile and juvenile period. In contrast to other dopamine-associated neuropsychiatric disorders, such as schizophrenia and drug addiction, typically diagnosed during adolescence or young adulthood and, thus, thought to be rooted in the developing brain, Parkinson's Disease (PD) is rarely viewed as such. However, evidences have accumulated suggesting that several factors might contribute to an increased vulnerability to death of the dopaminergic neurons at an already very early (developmental) phase in life. Despite the remarkable ability of the brain to compensate such dopamine deficits, the early loss or dysfunction of these neurons might predispose an individual to suffer from PD because the critical threshold of dopamine function will be reached much earlier in life, even if the time-course and strength of naturally occurring and age-dependent dopaminergic cell death is not markedly altered in this individual. Several signaling and transcriptional pathways required for the proper embryonic development of the midbrain dopaminergic neurons, which are the most affected in PD, either continue to be active in the adult mammalian midbrain or are reactivated at the transition to adulthood and under neurotoxic conditions. The persistent activity of these pathways often has neuroprotective functions in adult midbrain dopaminergic neurons, whereas the reactivation of silenced pathways under pathological conditions can promote the survival and even regeneration of these neurons in the lesioned or aging brain. This article summarizes our current knowledge about signaling and transcription factors involved in midbrain dopaminergic neuron development, whose reduced gene dosage or signaling activity are implicated in a lower survival rate of these neurons in the postnatal or aging brain. It also discusses the evidences supporting the neuroprotection of the midbrain dopaminergic system after the external supply or ectopic expression of some of these secreted and nuclear factors in the adult and aging brain. Altogether, the timely monitoring and/or correction of these signaling and transcriptional pathways might be a promising approach to a much earlier diagnosis and/or prevention of PD.

Right vagus nerve stimulation improves motor behavior by exerting neuroprotective effects in Parkinson's disease rats.

Parkinson's disease (PD) is a common movement disorder disease. Left vagus nerve stimulation (LVNS) is a potential treatment option for PD. Compared with the left vagus nerve, the right vagus nerve is more closely connected with the midbrain dopaminergic neurons, which are the lesion locations of PD. However, whether right vagus nerve stimulation (RVNS) has a therapeutic effect on PD has not yet been studied. Therefore, in this study, we studied the therapeutic effect and underlying mechanism of RVNS using a PD rat model. To establish the PD rat model, 8-week-old male Sprague-Dawley rats were intraperitoneally injected with rotenone for 21 days. The cuff electrodes were implanted into the right cervical vagal carotid sheaths of the rats. The right vagus nerve was continuously stimulated for 14 days using a radio stimulation system. Behavioral tests were performed before and after stimulation. Finally, tyrosine hydroxylase (TH), vesicular monoamine transporter 2 (VMAT2), and α-synuclein in the midbrain, including the substantia nigra (SN) and ventral tegmental area (VTA), were detected by immunofluorescence. A markedly lower distance traveled and rearing number was observed in the rotenone, rotenone + sham, and rotenone + RVNS groups compared to the vehicle group. After the stimulation days, the distance traveled and rearing number were both higher in the rotenone + RVNS group compared to the rotenone and rotenone + sham groups (P<0.01, P<0.0001). A remarkable increase in distance traveled and rearing number was observed in the rotenone + RVNS group after stimulation. TH expression in the vehicle group was significantly up-regulated than the other groups. RVNS markedly up-regulated TH expression level. A significantly higher expression of α-synuclein was observed in the rotenone, rotenone + sham, and rotenone + RVNS groups compared to the vehicle group. The expression of α-synuclein was lower in the rotenone + RVNS group compared to the rotenone and rotenone + sham groups. A markedly higher VMAT2 expression was observed in the vehicle group compared to other groups. RVNS significantly up-regulated VMAT2 expression. The improved motor behavior and neuroprotective effects on the midbrain dopaminergic neurons in the PD rat model suggest that RVNS could be used as a potential treatment for PD.

Human Embryonic Stem Cells-derived Immature Midbrain Dopaminergic Neurons Transplanted in Parkinsonian Monkeys Recover Dopamine Levels and Motor Behavior

Human Embryonic Stem Cells-derived Immature Midbrain Dopaminergic Neurons Transplanted in Parkinsonian Monkeys Recover Dopamine Levels and Motor Behavior

Protein aggregation and calcium dysregulation are hallmarks of familial Parkinson’s disease in midbrain dopaminergic neurons

Mutations in the SNCA gene cause autosomal dominant Parkinson’s disease (PD), with loss of dopaminergic neurons in the substantia nigra, and aggregation of α-synuclein. The sequence of molecular events that proceed from an SNCA mutation during development, to end-stage pathology is unknown. Utilising human-induced pluripotent stem cells (hiPSCs), we resolved the temporal sequence of SNCA-induced pathophysiological events in order to discover early, and likely causative, events. Our small molecule-based protocol generates highly enriched midbrain dopaminergic (mDA) neurons: molecular identity was confirmed using single-cell RNA sequencing and proteomics, and functional identity was established through dopamine synthesis, and measures of electrophysiological activity. At the earliest stage of differentiation, prior to maturation to mDA neurons, we demonstrate the formation of small β-sheet-rich oligomeric aggregates, in SNCA-mutant cultures. Aggregation persists and progresses, ultimately resulting in the accumulation of phosphorylated α-synuclein aggregates. Impaired intracellular calcium signalling, increased basal calcium, and impairments in mitochondrial calcium handling occurred early at day 34–41 post differentiation. Once midbrain identity fully developed, at day 48–62 post differentiation, SNCA-mutant neurons exhibited mitochondrial dysfunction, oxidative stress, lysosomal swelling and increased autophagy. Ultimately these multiple cellular stresses lead to abnormal excitability, altered neuronal activity, and cell death. Our differentiation paradigm generates an efficient model for studying disease mechanisms in PD and highlights that protein misfolding to generate intraneuronal oligomers is one of the earliest critical events driving disease in human neurons, rather than a late-stage hallmark of the disease.

Neuroprotective effects of a lead compound from coral via modulation of the orphan nuclear receptor Nurr1.

To screen coral-derived compounds with neuroprotective activity and clarify the potential mechanism of lead compounds. The lead compounds with neuroprotective effects were screened by H2 O2 and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPP+ )-induced cell damage models in SH-SY5Y cells. CCK8 and LDH assays were used to detect cell viability. The anti-apoptosis of lead compounds was evaluated by flow cytometry. JC-1 and MitoSox assays were performed to examine the changes in mitochondrial membrane potential and mitochondrial ROS level. Survival of primary cortical and dopaminergic midbrain neurons was measured by MAP2 and TH immunoreactivities. The Caenorhabditis elegans (C. elegans) model was established to determine the effect of lead compounds on dopaminergic neurons and behavior changes. Three compounds (No. 63, 68, and 74), derived from marine corals, could markedly alleviate the cell damage and notably reverse the loss of worm dopaminergic neurons. Further investigation indicated that compound 63 could promote the expression of Nurr1 and inhibit neuronal apoptosis signaling pathways. Lead compounds from marine corals exerted significant neuroprotective effects， which indicated that coral might be a new and potential resource for screening and isolating novel natural compounds with neuroprotective effects. Furthermore, this study also provided a new strategy for the clinical treatment of neurodegenerative diseases such as Parkinson's disease.

Chronobiology of Parkinson's disease: Past, present and future.

Parkinson's disease is a neurodegenerative disorder predominately affecting midbrain dopaminergic neurons that results in a broad range of motor and non-motor symptoms. Sleep complaints are among the most common non-motor symptoms, even in the prodromal period. Sleep alterations in Parkinson's disease patients may be associated with dysregulation of circadian rhythms, intrinsic 24-h cycles that control essential physiological functions, or with side effects from levodopa medication and physical and mental health challenges. The impact of circadian dysregulation on sleep disturbances in Parkinson's disease is not fully understood; as such, we review the systems, cellular and molecular mechanisms that may underlie circadian perturbations in Parkinson's disease. We also discuss the potential benefits of chronobiology-based personalized medicine in the management of Parkinson's disease both in terms of behavioural and pharmacological interventions. We propose that a fuller understanding of circadian clock function may shed important new light on the aetiology and symptomatology of the disease and may allow for improvements in the quality of life for the millions of people with Parkinson's disease.

Melanin and Neuromelanin: Linking Skin Pigmentation and Parkinson's Disease.

Neuromelanin-containing dopaminergic neurons in the substantia nigra pars compacta (SNpc) are the most vulnerable neurons in Parkinson's disease (PD). Recent work suggests that the accumulation of oxidized dopamine and neuromelanin mediate the convergence of mitochondrial and lysosomal dysfunction in patient-derived neurons. In addition, the expression of human tyrosinase in mouse SNpc led to the formation of neuromelanin resulting in the degeneration of nigral dopaminergic neurons, further highlighting the importance of neuromelanin in PD. The potential role of neuromelanin in PD pathogenesis has been supported by epidemiological observations, whereby individuals with lighter pigmentation or cutaneous malignant melanoma exhibit higher incidence of PD. Because neuromelanin and melanin share many functional characteristics and overlapping biosynthetic pathways, it has been postulated that genes involved in skin pigmentation and melanin formation may play a role in the susceptibility of vulnerable midbrain dopaminergic neurons to neurodegeneration. Here, we highlight potential mechanisms that may explain the link between skin pigmentation and PD, focusing on the role of skin pigmentation genes in the pathogenesis of PD. We also discuss the importance of genetic ancestry in assessing the contribution of pigmentation-related genes to risk of PD. © 2022 International Parkinson and Movement Disorder Society.