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Biogenic monoamines—vital transmitters orchestrating neurological, endocrinal and immunological functions 1 – 5 —are stored in secretory vesicles by vesicular monoamine transporters (VMATs) for controlled quantal release 6 , 7 . Harnessing proton antiport, VMATs enrich monoamines around 10,000-fold and sequester neurotoxicants to protect neurons 8 – 10 . VMATs are targeted by an arsenal of therapeutic drugs and imaging agents to treat and monitor neurodegenerative disorders, hypertension and drug addiction 1 , 8 , 11 – 16 . However, the structural mechanisms underlying these actions remain unclear. Here we report eight cryo-electron microscopy structures of human VMAT1 in unbound form and in complex with four monoamines (dopamine, noradrenaline, serotonin and histamine), the Parkinsonism-inducing MPP + , the psychostimulant amphetamine and the antihypertensive drug reserpine. Reserpine binding captures a cytoplasmic-open conformation, whereas the other structures show a lumenal-open conformation stabilized by extensive gating interactions. The favoured transition to this lumenal-open state contributes to monoamine accumulation, while protonation facilitates the cytoplasmic-open transition and concurrently prevents monoamine binding to avoid unintended depletion. Monoamines and neurotoxicants share a binding pocket that possesses polar sites for specificity and a wrist-and-fist shape for versatility. Variations in this pocket explain substrate preferences across the SLC18 family. Overall, these structural insights and supporting functional studies elucidate the mechanism of vesicular monoamine transport and provide the basis to develop therapeutics for neurodegenerative diseases and substance abuse. Monoamines and neurotoxicants share a binding pocket in VMAT1 featuring polar sites for specificity and a wrist-and-fist shape for versatility, and monoamine enrichment in storage vesicles arises from dominant import via favoured lumenal-open transition of VMAT1 and protonation-precluded binding during its cytoplasmic-open transition.

DJ-1 plays an important role in antioxidant defenses, and a reactive cysteine at position 106 (Cys106) of DJ-1, a critical residue of its biological function, is oxidized under oxidative stress. DJ-1 oxidation has been reported in patients with Parkinson’s disease (PD), but the relationship between DJ-1 oxidation and PD is still unclear. In the present study using specific antibody for Cys106-oxidized DJ-1 (oxDJ-1), we analyzed oxDJ-1 levels in the brain and peripheral tissues in young and aged mice and in a mouse model of PD induced using 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). OxDJ-1 levels in the brain, heart, and skeletal muscle were high compared with other tissues. In the brain, oxDJ-1 was detected in PD-related brain sites such as the substantia nigra (SN) of the midbrain, olfactory bulb (OB), and striatum. In aged wild-type mice, oxDJ-1 levels in the OB, striatum, and heart tended to decrease, while those in the skeletal muscle increased significantly. Expression of dopamine-metabolizing enzymes significantly increased in the SN and OB of aged DJ-1 −/− mice, accompanied by a complementary increase in glutathione peroxidase 1. MPTP treatment concordantly changed oxDJ-1 levels in PD-related brain sites and heart. These results indicate that the effects of physiological metabolism, aging, and neurotoxin change oxDJ-1 levels in PD-related brain sites, heart, and skeletal muscle where mitochondrial load is high, suggesting a substantial role of DJ-1 in antioxidant defenses and/or dopamine metabolism in these tissues.

Astrocytes release exosomes that regulate neuronal cell function. 1-methyl-4-phenylpyridinium (MPP + ) is a well-known neurotoxin used to induce cell death in in vitro Parkinson’s disease models, and microRNA (miRNA) transferred by released exosomes can regulate its mechanisms. Here, we demonstrated that exosomes released from normal astrocytes (ADEXs), but not exosomes derived from MPP + -stimulated astrocytes (MPP + -ADEXs), significantly attenuate MPP + -induced cell death in SH-SY5Y cells and primary mesencephalic dopaminergic neuron cultures, and reduce expression of mitogen-activated protein kinase kinase 4 (MKK4), an important upstream kinase in the c-Jun N-terminal kinase cell death pathway. Similar neuroprotective results were obtained from primary hippocampal neuron cultures, an in vitro glutamate excitotoxicity model. Through small-RNA sequencing of exosomal miRNA, we identified miR-200a-3p as the most down-regulated miRNA expressed in MPP + -ADEXs. miRNA target analysis and reporter assay confirmed that miR-200a-3p targets MKK4 through binding to two independent sites on the 3′-UTR of Map2k4 /MKK4 mRNA. Treatment with miR-200a-3p mimic suppressed both MKK4 mRNA and protein expressions, and attenuated cell death in MPP + -treated SH-SY5Y cells and glutamate-treated hippocampal neuron cultures. Our results suggest that normal astrocytes release miR-200a-3p which exhibits a neuroprotective effect through down-regulation of MKK4.

Human MATE1 (multidrug and toxin extrusion protein 1) is highly expressed in the kidney and liver, where it mediates the final step in the excretion of a broad range of cationic drugs, including the antidiabetic drug metformin, into the urine and bile. This transport process is essential for drug clearance and also affects therapeutic efficacy. To understand the molecular basis of drug recognition by hMATE1, we determined cryo-electron microscopy structures of the transporter in complex with the substrates 1-methyl-4-phenylpyridinium (MPP) and metformin and with the inhibitor cimetidine. The structures reveal a shared binding site located in a negatively charged pocket in the C-lobe of the protein. We functionally validated key interactions using radioactivity-based cellular uptake assays using hMATE1 mutants. Molecular dynamics simulations provide insights into the different binding modes and dynamic behaviour of the ligands within the pocket. Collectively, these findings define the structural basis of hMATE1 substrate specificity and shed light on its role in drug transport and drug-drug interactions. Human MATE1 is a key transporter in kidney and liver drug clearance. Here, authors present cryo-EM structures of MATE1 in complex with substrates and an inhibitor, revealing the structural basis of drug recognition.

Parkinson’s disease (PD) is characterized by the progressive degeneration of dopaminergic neurons. The cause of PD is still unclear. Oxidative stress and mitochondrial dysfunction have been linked to the development of PD. Luteolin, a non-toxic flavonoid, has become interested in an alternative medicine, according to its effects on anti-oxidative stress and anti-apoptosis, although the underlying mechanism of luteolin on PD has not been fully elucidated. This study aims to investigate whether luteolin prevents neurotoxicity induction by 1-methyl-4-phenylpyridinium iodide (MPP+), a neurotoxin in neuroblastoma SH-SY5Y cells. The results reveal that luteolin significantly improved cell viability and reduced apoptosis in MPP+-treated cells. Increasing lipid peroxidation and superoxide anion (O2−), including mitochondrial membrane potential (Δψm) disruption, is ameliorated by luteolin treatment. In addition, luteolin attenuated MPP+-induced neurite damage via GAP43 and synapsin-1. Furthermore, Cdk5 is found to be overactivated and correlated with elevation of cleaved caspase-3 activity in MPP+-exposed cells, while phosphorylation of Erk1/2, Drp1, Fak, Akt and GSK3β are inhibited. In contrast, luteolin attenuated Cdk5 overactivation and supported phosphorylated level of Erk1/2, Drp1, Fak, Akt and GSK3β with reducing in cleaved caspase-3 activity. Results indicate that luteolin exerts neuroprotective effects via Cdk5-mediated Erk1/2/Drp1 and Fak/Akt/GSK3β pathways, possibly representing a potential preventive agent for neuronal disorder.

Parkinson’s disease (PD) is one of the most common neurodegenerative diseases and affects approximately 6.3 million people worldwide. To date, the treatment of PD remains a challenge, as available treatment options are known to be associated with serious side effects; hence, the search for new treatment strategies is critical. Extracts from the Amaryllidaceae plant family as well as their alkaloids have been reported to have neuroprotective potentials. This study, therefore, investigated the biological activities of Crossyne flava and its isolated alkaloids in an in vitro MPP+ (1-methyl-4-phenylpyridinium) PD model using SH-SY5Y cells. The effects of the total extract as well as the four compounds isolated from Crossyne flava (i.e., pancratinine B (1), bufanidrine (2), buphanisine (3), and epibuphanisine (4)) were evaluated for cell viability, neuroprotection, levels of reactive oxygen species (ROS), adenosine triphosphate activity (ATP), and caspase 3/7 activity in SH-SY5Y cells. The results obtained showed that pre-treatment with both the extract and the isolated compounds was effective in protecting the SH-SY5Y cells from MPP+-induced neurotoxicity and inhibited ROS generation, ATP depletion as well as apoptosis induction in the SH-SY5Y cells. The results of this study show that the Amaryllidaceae plant family may be a source of novel compounds for the treatment of neurodegenerative diseases, which validates the reported traditional uses.

α-Synuclein is an abundant neuronal protein that accumulates in insoluble inclusions in Parkinson′s disease and other synucleinopathies. Fatty acids partially regulate α-Synuclein accumulation, and mesencephalic dopaminergic neurons highly express fatty acid-binding protein 3 (FABP3). We previously demonstrated that FABP3 knockout mice show decreased α-Synuclein oligomerization and neuronal degeneration of tyrosine hydroxylase (TH)-positive neurons in vivo. In this study, we newly investigated the importance of FABP3 in α-Synuclein uptake, 1-methyl-4-phenylpyridinium (MPP+)-induced axodendritic retraction, and mitochondrial dysfunction. To disclose the issues, we employed cultured mesencephalic neurons derived from wild type or FABP3−/− C57BL6 mice and performed immunocytochemical analysis. We demonstrated that TH+ neurons from FABP3+/+ mice take up α-Synuclein monomers while FABP3−/− TH+ neurons do not. The formation of filamentous α-Synuclein inclusions following treatment with MPP+ was observed only in FABP3+/+, and not in FABP3−/− neurons. Notably, detailed morphological analysis revealed that FABP−/− neurons did not exhibit MPP+-induced axodendritic retraction. Moreover, FABP3 was also critical for MPP+-induced reduction of mitochondrial activity and the production of reactive oxygen species. These data indicate that FABP3 is critical for α-Synuclein uptake in dopaminergic neurons, thereby preventing synucleinopathies, including Parkinson′s disease.

The pathogenesis of Parkinson’s disease (PD) consists of the apoptosis of dopaminergic neurons in the substantia nigra pars compacta (SNpc) due to oxidative stress. The present study aimed to evaluate the potential antioxidant activity of whey protein isolate (WPI) in PD models, using neurotoxin-exposed SH-SY5Y cells differentiated into dopaminergic-like neurons. Our research shows that WPI’s high glutamic acid, aspartic acid, and leucine contribute to its antioxidant and neuroprotective effects, with glutamic acid crucial for glutathione synthesis. In vitro studies found that WPI, at concentrations of 5–1000 µg/mL, is non-toxic to differentiated SH-SY5Y cells. Notably, the lowest con-centration of WPI (5 µg/mL) significantly decreased intracellular reactive oxygen species (ROS) levels in these cells following a 24 h co-treatment with 1-methyl-4-phenylpyridinium (MPP+). The antioxidant effects of WPI were also confirmed by the increased expression of HO1 and GPx antioxidant enzymes, which are Nrf2 pathway target genes and were evaluated by real-time PCR. Furthermore, Nrf2 nuclear translocation in the differentiated SH-SY5Y cells was also increased when the cells were exposed to 5 µg/mL of WPI with MPP+. These results together suggest that WPI has antioxidant effects on dopaminergic-like neurons in a Parkinson’s disease model.

Background Mitochondria play crucial roles in cellular metabolism, and metabolite compartmentalization significantly impacts mitochondrial function and disease pathophysiology. MPP + accumulation in mitochondria, a key factor in MPTP-induced neurodegeneration, leads to mitochondrial dysfunction, such as respiratory chain inhibition, ultimately leading to neuronal death. However, the mechanisms underlying mitochondrial MPP + accumulation remain poorly understood. Organic cation transporter 3 (OCT3), a passive transporter mediating MPP + transport, has been observed on the mitochondrial membrane, but it remains unclear whether mitochondrial OCT3 is involved in MPP + accumulation in mitochondria. Results OCT3 was detected in the mitochondria fraction of SH-SY5Y cells, located on both the inner membrane and outer membrane. Following MPP + incubation, there was a significant increase in mitochondrial uptake of MPP + , which was mitigated by OCT3 inhibition. Knockdown of the translocase of inner mitochondrial membrane 22 (TIMM22), an important component of the mitochondrial protein import apparatus, successfully reduced OCT3 levels on mitochondria without impairing mitochondrial morphology or mitochondrial membrane potential. TIMM22 knockdown reduced mitochondrial MPP + uptake, which in turn rescued MPP + -induced mitochondrial fragmentation, complex I inhibition, and mitochondrial membrane potential reduction. Furthermore, TIMM22 knockdown suppressed caspase-9 and caspase-3 activation and reversed the alterations of BAX and BCL-xL induced by mitochondrial MPP + accumulation. Conclusions Here we found that OCT3 on neuronal mitochondria serves as an effective MPP + transporter, crucial for mitochondrial MPP + uptake and MPP + -induced neurotoxicity. Furthermore, TIMM22 downregulation can selectively reduce mitochondrial OCT3 and reverse MPP + -induced mitochondrial dysfunction and neurotoxicity, highlighting TIMM22 and OCT3 as potential therapeutic targets for MPP + -associated neurodegeneration and diseases.

Neuroinflammation is closely associated with the pathophysiology of neurodegenerative diseases including Parkinson's disease (PD). Recent evidence indicates that astrocytes also play pro-inflammatory roles in the central nervous system (CNS) by activation with toll-like receptor (TLR) ligands. Therefore, targeting anti-inflammation may provide a promising therapeutic strategy for PD. Curcumin, a polyphenolic compound isolated from Curcuma longa root, has been commonly used for the treatment of neurodegenerative diseases. However, the details of how curcumin exerts neuroprotection remain uncertain. Here, we investigated the protective effect of curcumin on 1-methyl-4-phenylpyridinium ion-(MPP⁺-) stimulated primary astrocytes. Our results showed that MPP⁺ stimulation resulted in significant production of tumor necrosis factor (TNF)-α, interleukin (IL-6), and reactive oxygen species (ROS) in primary mesencephalic astrocytes. Curcumin pretreatment decreased the levels of these pro-inflammatory cytokines while increased IL-10 expression in MPP⁺-stimulated astrocytes. In addition, curcumin increased the levels of antioxidant glutathione (GSH) and reduced ROS production. Our results further showed that curcumin decreased the levels of TLR4 and its downstream effectors including NF-κ, IRF3, MyD88, and TIRF that are induced by MPP⁺ as well as inhibited the immunoreactivity of TLR4 and morphological activation in MPP⁺-stimulated astrocytes. Together, data suggest that curcumin might exert a beneficial effect on neuroinflammation in the pathophysiology of PD.