Nigrostriatal Dopamine Neurons Research Articles

Alpha-synuclein inclusion responsive microglia are resistant to CSF1R inhibition

BackgroundParkinson’s disease (PD) is a neurodegenerative disorder that is characterized by the presence of proteinaceous alpha-synuclein (α-syn) inclusions (Lewy bodies), markers of neuroinflammation and the progressive loss of nigrostriatal dopamine (DA) neurons. These pathological features can be recapitulated in vivo using the α-syn preformed fibril (PFF) model of synucleinopathy. We have previously determined that microglia proximal to PFF-induced nigral α-syn inclusions increase in soma size, upregulate major-histocompatibility complex-II (MHC-II) expression, and increase expression of a suite of inflammation-associated transcripts. This microglial response is observed months prior to degeneration, suggesting that microglia reacting to α-syn inclusion may contribute to neurodegeneration and could represent a potential target for novel therapeutics. The goal of this study was to determine whether colony stimulating factor-1 receptor (CSF1R)-mediated microglial depletion impacts the magnitude of α-syn aggregation, nigrostriatal degeneration, or the response of microglial in the context of the α-syn PFF model.MethodsMale Fischer 344 rats were injected intrastriatally with either α-syn PFFs or saline. Rats were continuously administered Pexidartinib (PLX3397B, 600 mg/kg), a CSF1R inhibitor, to deplete microglia for a period of either 2 or 6 months.ResultsCSF1R inhibition resulted in significant depletion (~ 43%) of ionized calcium-binding adapter molecule 1 immunoreactive (Iba-1ir) microglia within the SNpc. However, CSF1R inhibition did not impact the increase in microglial number, soma size, number of MHC-II immunoreactive microglia or microglial expression of Cd74, Cxcl10, Rt-1a2, Grn, Csf1r, Tyrobp, and Fcer1g associated with phosphorylated α-syn (pSyn) nigral inclusions. Further, accumulation of pSyn and degeneration of nigral neurons was not impacted by CSF1R inhibition. Paradoxically, long term CSF1R inhibition resulted in increased soma size of remaining Iba-1ir microglia in both control and PFF rats, as well as expression of MHC-II in extranigral regions.ConclusionsCollectively, our results suggest that CSF1R inhibition does not impact the microglial response to nigral pSyn inclusions and that CSF1R inhibition is not a viable disease-modifying strategy for PD.

Dysfunction of synaptic endocytic trafficking in Parkinson's disease.

Parkinson's disease is characterized by the selective degeneration of dopamine neurons in the nigrostriatal pathway and dopamine deficiency in the striatum. The precise reasons behind the specific degeneration of these dopamine neurons remain largely elusive. Genetic investigations have identified over 20 causative PARK genes and 90 genomic risk loci associated with both familial and sporadic Parkinson's disease. Notably, several of these genes are linked to the synaptic vesicle recycling process, particularly the clathrin-mediated endocytosis pathway. This suggests that impaired synaptic vesicle recycling might represent an early feature of Parkinson's disease, followed by axonal degeneration and the eventual loss of dopamine cell bodies in the midbrain via a "dying back" mechanism. Recently, several new animal and cellular models with Parkinson's disease-linked mutations affecting the endocytic pathway have been created and extensively characterized. These models faithfully recapitulate certain Parkinson's disease-like features at the animal, circuit, and cellular levels, and exhibit defects in synaptic membrane trafficking, further supporting the findings from human genetics and clinical studies. In this review, we will first summarize the cellular and molecular findings from the models of two Parkinson's disease-linked clathrin uncoating proteins: auxilin (DNAJC6/PARK19) and synaptojanin 1 (SYNJ1/PARK20). The mouse models carrying these two PARK gene mutations phenocopy each other with specific dopamine terminal pathology and display a potent synergistic effect. Subsequently, we will delve into the involvement of several clathrin-mediated endocytosis-related proteins (GAK, endophilin A1, SAC2/INPP5F, synaptotagmin-11), identified as Parkinson's disease risk factors through genome-wide association studies, in Parkinson's disease pathogenesis. We will also explore the direct or indirect roles of some common Parkinson's disease-linked proteins (alpha-synuclein (PARK1/4), Parkin (PARK2), and LRRK2 (PARK8)) in synaptic endocytic trafficking. Additionally, we will discuss the emerging novel functions of these endocytic proteins in downstream membrane traffic pathways, particularly autophagy. Given that synaptic dysfunction is considered as an early event in Parkinson's disease, a deeper understanding of the cellular mechanisms underlying synaptic vesicle endocytic trafficking may unveil novel targets for early diagnosis and the development of interventional therapies for Parkinson's disease. Future research should aim to elucidate why generalized synaptic endocytic dysfunction leads to the selective degeneration of nigrostriatal dopamine neurons in Parkinson's disease.

Interhemispheric reactivity of the subthalamic nucleus sustains progressive dopamine neuron loss in asymmetrical parkinsonism

Parkinson's disease (PD) is characterized by the progressive and asymmetrical degeneration of the nigrostriatal dopamine neurons and the unilateral presentation of the motor symptoms at onset, contralateral to the most impaired hemisphere. We previously developed a rat PD model that mimics these typical features, based on unilateral injection of a substrate inhibitor of excitatory amino acid transporters, L-trans-pyrrolidine-2,4-dicarboxylate (PDC), in the substantia nigra (SN). Here, we used this progressive model in a multilevel study (behavioral testing, in vivo 1H-magnetic resonance spectroscopy, slice electrophysiology, immunocytochemistry and in situ hybridization) to characterize the functional changes occurring in the cortico-basal ganglia-cortical network in an evolving asymmetrical neurodegeneration context and their possible contribution to the cell death progression. We focused on the corticostriatal input and the subthalamic nucleus (STN), two glutamate components with major implications in PD pathophysiology. In the striatum, glutamate and glutamine levels increased from presymptomatic stages in the PDC-injected hemisphere only, which also showed enhanced glutamatergic transmission and loss of plasticity at corticostriatal synapses assessed at symptomatic stage. Surprisingly, the contralateral STN showed earlier and stronger reactivity than the ipsilateral side (increased intraneuronal cytochrome oxidase subunit I mRNA levels; enhanced glutamate and glutamine concentrations). Moreover, its lesion at early presymptomatic stage halted the ongoing neurodegeneration in the PDC-injected SN and prevented the expression of motor asymmetry. These findings reveal the existence of endogenous interhemispheric processes linking the primary injured SN and the contralateral STN that could sustain progressive dopamine neuron loss, opening new perspectives for disease-modifying treatment of PD.

Current Review of the Function and Regulation of Tuberoinfundibular Dopamine Neurons.

Tuberoinfundibular dopamine (TIDA) neurons have cell bodies located in the arcuate nucleus of the mediobasal hypothalamus. They project to the external zone of the median eminence, and the dopamine (DA) released there is carried by the hypophysial portal vasculature to the anterior pituitary. The DA then activates D2 receptors to inhibit prolactin (PRL) secretion from lactotrophs. The TIDA neuronal population is the principal regulatory factor controlling PRL secretion. The neuroendocrine role subserved by TIDA neurons sets them apart from other dopaminergic populations like the nigrostriatal and mesolimbic DA neurons. TIDA neurons exhibit intrinsic oscillatory fluctuations in their membrane potential that give rise to phasic firing and bursting activity. TIDA neuronal activity is sexually differentiated and modulated by gonadal hormones and PRL, as well as an array of small molecule and peptide neurotransmitters. This review covers these characteristics.

Inhibition of striatal dopamine release by the L-type calcium channel inhibitor isradipine co-varies with risk factors for Parkinson's.

Ca2+ entry into nigrostriatal dopamine (DA) neurons and axons via L-type voltage-gated Ca2+ channels (LTCCs) contributes, respectively, to pacemaker activity and DA release and has long been thought to contribute to vulnerability to degeneration in Parkinson's disease. LTCC function is greater in DA axons and neurons from substantia nigra pars compacta than from ventral tegmental area, but this is not explained by channel expression level. We tested the hypothesis that LTCC control of DA release is governed rather by local mechanisms, focussing on candidate biological factors known to operate differently between types of DA neurons and/or be associated with their differing vulnerability to parkinsonism, including biological sex, α-synuclein, DA transporters (DATs) and calbindin-D28k (Calb1). We detected evoked DA release ex vivo in mouse striatal slices using fast-scan cyclic voltammetry and assessed LTCC support of DA release by detecting the inhibition of DA release by the LTCC inhibitors isradipine or CP8. Using genetic knockouts or pharmacological manipulations, we identified that striatal LTCC support of DA release depended on multiple intersecting factors, in a regionally and sexually divergent manner. LTCC function was promoted by factors associated with Parkinsonian risk, including male sex, α-synuclein, DAT and a dorsolateral co-ordinate, but limited by factors associated with protection, that is, female sex, glucocerebrosidase activity, Calb1 and ventromedial co-ordinate. Together, these data show that LTCC function in DA axons and isradipine effect are locally governed and suggest they vary in a manner that in turn might impact on, or reflect, the cellular stress that leads to parkinsonian degeneration.

Feasibility of combining alpha-synuclein aggregation and 6-OHDA in embryonic midbrain culture for modeling dopamine neuron degeneration

Parkinson’s disease (PD) is characterized by the loss of nigrostriatal dopamine (DA) neurons and the presence of alpha-synuclein (αSyn)-positive Lewy body (LB) pathology. In this study, we attempted to recapitulate both these features in a novel in vitro model for PD. To achieve this, we combined the αSyn pre-formed fibril (PFF)-seeded LB-like pathology with 6-hydroxydopamine (6-OHDA)-induced mitochondrial toxicity in mouse embryonic midbrain cultures. To pilot the model for therapeutics testing, we assessed the effects of cerebral dopamine neurotrophic factor (CDNF) on αSyn aggregation and neuron survival. PFF-seeded pathology did not lead to DA neuron loss even with the highest dose of PFFs. The combination of PFFs and 6-OHDA did not trigger additional neurodegeneration or LB–like pathology and instead presented DA neuron loss to a similar extent as with 6-OHDA only. CDNF did not affect the PFF-seeded αSyn pathology or the DA neuron survival in the combination model but showed a trend toward neuroprotection in the 6-OHDA-only cultures.

Modeling Parkinson's disease in LRRK2 rodents.

Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene are associated with familial and sporadic forms of Parkinson's disease (PD). Sporadic PD and LRRK2 PD share main clinical and neuropathological features, namely hypokinesia, degeneration of nigro-striatal dopamine neurons and α-synuclein aggregates in the form of Lewy bodies. Animals harboring the most common LRRK2 mutations, i.e. p.G2019S and p.R1441C/G, have been generated to replicate the parkinsonian phenotype and investigate the underlying pathogenic mechanisms. Disappointingly, however, LRRK2 rodents did not consistently phenocopy hypokinesia and nigro-striatal degeneration, or showed Lewy body-like aggregates. Instead, LRRK2 rodents manifested non-motor signs and dysregulated transmission at dopaminergic and non-dopaminergic synapses that are reminiscent of behavioral and functional network changes observed in the prodromal phase of the disease. LRRK2 rodents also manifested greater susceptibility to different parkinsonian toxins or stressors when subjected to dual-hit or multiple-hit protocols, confirming LRRK2 mutations as genetic risk factors. In conclusion, LRRK2 rodents represent a unique tool to identify the molecular mechanisms through which LRRK2 modulates the course and clinical presentations of PD and to study the interplay between genetic, intrinsic and environmental protective/risk factors in PD pathogenesis.

Sex and Age Differences in a Progressive Synucleinopathy Mouse Model.

The mutation and overexpression of the alpha-synuclein protein (αSyn), described as synucleinopathy, is associated with Parkinson's disease (PD)-like pathologies. A higher prevalence of PD is documented for men versus women, suggesting female hormones' implication in slowing PD progression. The nigrostriatal dopamine (DA) neurons in rodent males are more vulnerable to toxins than those in females. The effect of biological sex on synucleinopathy remains poorly described and was investigated using mice knocked out for murine αSyn (SNCA-/-) and also overexpressing human αSyn (SNCA-OVX) compared to wildtype (WT) mice. All the mice showed decreased locomotor activity with age, and more abruptly in the male than in the female SNCA-OVX mice; anxiety-like behavior increased with age. The SNCA-OVX mice had an age-dependent accumulation of αSyn. Older age was associated with the loss of nigral DA neurons and decreased striatal DA contents. The astrogliosis, microgliosis, and cytokine concentrations increased with aging. More abrupt nigrostriatal DA decreases and increased microgliosis were observed in the male SNCA-OVX mice. Human αSyn overexpression and murine αSyn knockout resulted in behavioral dysfunctions, while only human αSyn overexpression was toxic to DA neurons. At 18 months, neuroprotection was lost in the female SNCA-OVX mice, with a likely loss of estrus cycles. In conclusion, sex-dependent αSyn toxicity was observed, affecting the male mice more significantly.

FGF2 activity regulates operant alcohol self-administration and mesolimbic dopamine transmission

Fibroblast growth factor 2 (FGF2) is involved in the development and maintenance of the brain dopamine system. We previously showed that alcohol exposure alters the expression of FGF2 and its receptor, FGF receptor 1 (FGFR1) in mesolimbic and nigrostriatal brain regions, and that FGF2 is a positive regulator of alcohol drinking. Here, we determined the effects of FGF2 and of FGFR1 inhibition on alcohol consumption, seeking and relapse, using a rat operant self-administration paradigm. In addition, we characterized the effects of FGF2-FGFR1 activation and inhibition on mesolimbic and nigrostriatal dopamine neuron activation using in vivo electrophysiology. We found that recombinant FGF2 (rFGF2) increased the firing rate and burst firing activity of dopaminergic neurons in the mesolimbic and nigrostriatal systems and led to increased operant alcohol self-administration. In contrast, the FGFR1 inhibitor PD173074 suppressed the firing rate of these dopaminergic neurons, and reduced operant alcohol self-administration. Alcohol seeking behavior was not affected by PD173074, but this FGFR1 inhibitor reduced post-abstinence relapse to alcohol consumption, albeit only in male rats. The latter was paralleled by the increased potency and efficacy of PD173074 in inhibiting dopamine neuron firing. Together, our findings suggest that targeting the FGF2-FGFR1 pathway can reduce alcohol consumption, possibly via altering mesolimbic and nigrostriatal neuronal activity.

Midbrain Dopamine Neurons Derived from Induced Pluripotent Stem Cells from Patients with Lesch Nyhan Disease and Gene-Edited Knock-In HPRT1 Mutations (P10-9.007)

<h3>Objective:</h3> To create a novel in-vitro model to study molecular pathogenesis of midbrain dopamine abnormalities during neuronal development in Lesch Nyhan disease (LND). <h3>Background:</h3> LND is a neurodevelopmental disease which manifests with neurobehavior abnormalities starting in early childhood. It is linked to abnormal development of nigrostriatal dopamine neurons. However, the molecular pathogenesis of impaired development is not well understood. One of the main reasons has been lack of a good model to study midbrain development. <h3>Design/Methods:</h3> We generated 24 induced pluripotent stem cell (iPSC) lines; 12 from 4 individuals with LND, and another 12 from 4 normal individuals. We also generated 12 gene-edited lines, all containing a c.C508&gt;T stop codon in the <i>HPRT1</i> gene. All 24 lines were assessed for pluripotency markers and several of the lines were differentiated into midbrain dopamine neurons using a floor-plate induction protocol. Differentiation was assessed at 3 stages of development in vitro: day 11 (neuroprogenitor), day 25 (early neuron) and day 60 (late neuron). The percentages of dopamine neurons were determined by tyrosine hydroxylase (TH) immunostaining with flow cytometry. The expression of FOXA2, TH and DAT were also measured by quantitative qPCR. Dopamine and its derivatives were measured using HPLC. <h3>Results:</h3> The differentiation protocol yielded a high percentage of TH-positive neurons (50–80%) that produced a high quantity of dopamine and its metabolites across all cell lines. TH and related markers all varied significantly among the different cell lines, and during differentiation. Results are being interrogated to identify any systematic changes between the LND and control lines. <h3>Conclusions:</h3> We have generated a large bank of iPSCs from individuals with LND, <i>HPRT1</i> gene-edited lines, and parallel control lines. We have shown that these lines can be used to generate developing dopamine neurons, providing a new model to investigate the molecular pathogenesis of LND. <b>Disclosure:</b> Ms. Seifar has nothing to disclose. Ms. Sutcliffe has nothing to disclose. Dr. Jinnah has received personal compensation in the range of $500-$4,999 for serving as a Consultant for Takaha/Ene. Dr. Jinnah has received personal compensation in the range of $5,000-$9,999 for serving as a Consultant for Ipsen. Dr. Jinnah has received personal compensation in the range of $500-$4,999 for serving on a Scientific Advisory or Data Safety Monitoring board for Ipsen. Dr. Jinnah has received personal compensation in the range of $500-$4,999 for serving on a Scientific Advisory or Data Safety Monitoring board for Abbvie. The institution of Dr. Jinnah has received research support from Addex. The institution of Dr. Jinnah has received research support from Aeon. The institution of Dr. Jinnah has received research support from Revance. The institution of Dr. Jinnah has received research support from Jazz.

Curcumin Regulates Gut Microbiota and Exerts a Neuroprotective Effect in the MPTP Model of Parkinson's Disease.

The experiment aimed to explore the effects of curcumin on motor impairment, dopamine neurons, and gut microbiota in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mice model. Mice were randomly assigned to six groups: normal control group, solvent control group, MPTP group, curcumin-low-dose group (40 mg/kg), curcumin-medium-dose group (80 mg/kg), and curcumin-high-dose group (160 mg/kg). After 14 days, each group of mice was subjected to the pole text, the hanging test, and the open-field test. Tyrosine hydroxylase (TH) immunohistochemistry was used to observe the survival of nigrostriatal dopamine neurons. Moreover, ultrastructural changes were observed with a transmission electron microscope in mice striatal tissue cells. Then, 16S rRNA was used to assess changes in the gut microbiota. (1) Each dose of curcumin reduced pole climbing time and increased suspension score and total distance moved dose-dependently. (2) All curcumin groups improved cell wrinkling and vacuolar degeneration, increased the number of TH positives, improved cell survival, and the higher the dose of curcumin, the better the effect. (3) There were differences in microbiota composition and a relative abundance among the groups. The relative abundance of Patescibacteria, Proteobacteria, and Verrucomicrobia was higher in the MPTP group. The relative abundance of Patescibacteria, Enterobacteriaceae, Enterococcaceae all decreased in all curcumin groups. In addition, the Kyoto Encyclopedia of Genes and Genomes pathways showed a reduction in the superpathway of N-acetylneuraminate degradation after medium- and high-dose curcumin administration. Curcumin regulates gut microbiota and exerts a neuroprotective effect in the MPTP mice model. This preliminary study demonstrates the therapeutic potential of curcumin for Parkinson's disease, providing clues for microbially targeted therapies for Parkinson's disease.

Feruloylated oligosaccharides ameliorate MPTP-induced neurotoxicity in mice by activating ERK/CREB/BDNF/TrkB signalling pathway

BackgroundFeruloylated oligosaccharides (FOs) are natural esterification products of ferulic acid and oligosaccharides. Study DesignIn this study, we examined whether FOs contribute to the ensured survival of nigrostriatal dopamine neurons and inhibition of neuroinflammation in Parkinson's disease (PD). Methods1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP, 30 mg/kg) was injected intraperitoneally into mice to establish a Parkinson's disease (PD) mouse model. FOs (15 and 30 mg/kg) were orally administered daily to the MPTP-treated mice. The rotarod test, balance beam test, immunofluorescence, enzyme-linked immunosorbent assay (ELISA), quantitative PCR (qPCR), and western blot analyses were performed to examine the neuroprotective effects of FOs on MPTP-treated mice. ResultsOur study indicated that FOs increased the survival of dopamine neurons in the substantia nigra pars compacta (SNc) of the MPTP-treated mice. The neuroprotective effects of FOs were accompanied by inhibited glial activation and reduced inflammatory cytokine production. The mechanistic experiments revealed that the neuroprotective effects of FOs might be mediated through the activation of the ERK/CREB/BDNF/TrkB signalling pathway. ConclusionThis study provides new insights into the mechanism underlying the anti-neuroinflammatory effect of phytochemicals and may facilitate the development of dietary supplements for PD patients. Our results indicate that FOs can be used as potential modulators for the prevention and treatment of PD.

Effects of Early Life Exposure to Sex Hormones on Neurochemical and Behavioral Responses to Psychostimulants in Adulthood: Implications in Drug Addiction.

Early life exposure to sex hormones affects several brain areas involved in regulating locomotor and motivation behaviors. Our group has shown that neonatal exposure to testosterone propionate (TP) or estradiol valerate (EV) affected the brain dopamine (DA) system in adulthood. Here, we studied the long-lasting effects of neonatal exposure to sex hormones on behavioral and neurochemical responses to amphetamine (AMPH) and methylphenidate (MPD). Our results show that AMPH-induced locomotor activity was higher in female than male control rats. The conditioned place preference (CPP) to AMPH was only observed in EV male rats. In EV female rats, AMPH did not increase locomotor activity, but MPD-induced CPP was observed in control, EV and TP female rats. Using in vivo brain microdialysis, we observed that AMPH-induced extracellular DA levels were lower in nucleus accumbens (NAcc) of EV and TP female rats than control rats. In addition, MPD did not increase NAcc extracellular DA levels in EV rats. Using in vivo fast-scan cyclic voltammetry in striatum, MPD-induced DA reuptake was higher in EV than control rats. In summary, our results show that early life exposure to sex hormones modulates mesolimbic and nigrostriatal DA neurons producing opposite neurochemical effects induced by psychostimulant drugs in NAcc or striatum.

The multimodal serotonin compound Vilazodone alone, but not combined with the glutamate antagonist Amantadine, reduces l-DOPA-induced dyskinesia in hemiparkinsonian rats

Parkinson's disease (PD) is a progressive, neurodegenerative movement disorder caused by loss of nigrostriatal dopamine (DA) neurons. DA replacement therapy using L-3,4-dihydroxyphenylalanine (l-DOPA) improves motor function but often results in l-DOPA-induced dyskinesia (LID) typified by abnormal involuntary movements (AIMs). In states of DA depletion, striatal serotonin (5-HT) hyperinnervation and glutamate overactivity are implicated in LID. To target these co-mechanisms, this study investigated the potential anti-dyskinetic effects of FDA-approved Vilazodone (VZD), a 5-HT transport blocker and partial 5-HT1A agonist, and Amantadine (AMAT), a purported NMDA glutamate antagonist, in 6-hydroxydopamine-lesioned hemiparkinsonian Sprague-Dawley rats. Dose-response curves for each drug against l-DOPA-induced AIMs were determined to identify effective threshold doses. A second cohort of rats was tested using the threshold doses of VZD (1, 2.5 mg/kg, s.c.) and/or AMAT (40 mg/kg, s.c.) to examine their combined, acute effects on LID. In a third cohort, VZD and/or AMAT were administered daily with l-DOPA for 14 days to determine prophylactic effects on LID development. In a final cohort, rats with established LID received VZD and/or AMAT injections for 2 weeks to examine their interventional properties. Throughout experiments, AIMs were rated for dyskinesia severity and forepaw adjusting steps (FAS) were monitored l-DOPA motor efficacy. Results revealed that acute and chronic VZD + l-DOPA treatment significantly decreased AIMs and maintained FAS compared to l-DOPA alone. AMAT + l-DOPA co-administration did not exert any significant effects on AIMs or FAS, while the co-administration of VZD and AMAT with l-DOPA demonstrated intermediate effects. These results suggest that co-administration of low-dose VZD and AMAT with l-DOPA does not synergistically reduce LID in hemiparkinsonian rats. Importantly, low doses of VZD (2.5, 5 mg/kg) did reduce the development and expression of LID while maintaining l-DOPA efficacy, supporting its potential therapeutic utility for PD patients.

Neuromelanin in Parkinson's Disease: Tyrosine Hydroxylase and Tyrosinase.

Parkinson’s disease (PD) is an aging-related disease and the second most common neurodegenerative disease after Alzheimer’s disease. The main symptoms of PD are movement disorders accompanied with deficiency of neurotransmitter dopamine (DA) in the striatum due to cell death of the nigrostriatal DA neurons. Two main histopathological hallmarks exist in PD: cytosolic inclusion bodies termed Lewy bodies that mainly consist of α-synuclein protein, the oligomers of which produced by misfolding are regarded to be neurotoxic, causing DA cell death; and black pigments termed neuromelanin (NM) that are contained in DA neurons and markedly decrease in PD. The synthesis of human NM is regarded to be similar to that of melanin in melanocytes; melanin synthesis in skin is via DOPAquinone (DQ) by tyrosinase, whereas NM synthesis in DA neurons is via DAquinone (DAQ) by tyrosine hydroxylase (TH) and aromatic L-amino acid decarboxylase (AADC). DA in cytoplasm is highly reactive and is assumed to be oxidized spontaneously or by an unidentified tyrosinase to DAQ and then, synthesized to NM. Intracellular NM accumulation above a specific threshold has been reported to be associated with DA neuron death and PD phenotypes. This review reports recent progress in the biosynthesis and pathophysiology of NM in PD.

Neuroprotective Effects of the DPP4 Inhibitor Vildagliptin in In Vivo and In Vitro Models of Parkinson's Disease.

Parkinson’s disease (PD) is characterized by loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc) of the midbrain. Restoration of nigrostriatal dopamine neurons has been proposed as a potential therapeutic strategy for PD. Because currently used PD therapeutics only help relieve motor symptoms and do not treat the cause of the disease, highly effective drugs are needed. Vildagliptin, a dipeptidyl peptidase 4 (DPP4) inhibitor, is an anti-diabetic drug with various pharmacological properties including neuroprotective effects. However, the detailed effects of vildagliptin against PD are not fully understood. We investigated the effects of vildagliptin on PD and its underlying molecular mechanisms using a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced mouse model and a 1-methyl-4-phenylpyridium (MPP+)-induced cytotoxicity model. Vildagliptin (50 mg/kg) administration significantly attenuated MPTP-induced motor deficits as evidenced by rotarod, pole, and nest building tests. Immunohistochemistry and Western blot analysis revealed that vildagliptin increased tyrosine hydroxylase-positive cells in the SNpc and striatum, which was reduced by MPTP treatment. Furthermore, vildagliptin activated MPTP-decreased PI3k/Akt and mitigated MPTP-increased ERK and JNK signaling pathways in the striatum. Consistent with signaling transduction in the mouse striatum, vildagliptin reversed MPP+-induced dephosphorylation of PI3K/Akt and phosphorylation of ERK and JNK in SH-SY5Y cells. Moreover, vildagliptin attenuated MPP+-induced conversion of LC3B-II in SH-SY5Y cells, suggesting its role in autophagy inhibition. Taken together, these findings indicate that vildagliptin has protective effects against MPTP-induced motor dysfunction by inhibiting dopaminergic neuronal apoptosis, which is associated with regulation of PI3k/Akt, ERK, and JNK signaling transduction. Our findings suggest vildagliptin as a promising repurposing drug to treat PD.

PBX1 attenuates 6-OHDA-induced oxidative stress and apoptosis and affects PINK1/PARKIN expression in dopaminergic neurons via FOXA1.

PBX1 expression has been found to be significantly reduced in nigrostriatal neurons of PD patients, but the effect of PBX1 on ROS and apoptosis in nigrostriatal dopamine neurons is not yet known. This paper aimed to explore whether PBX1 could be involved in the development of PD. The construction of the in vitro PD model was followed by the determination of PBX1 expression. Then, PBX1 was overexpressed to observe the changes in the cell viability, TH expression, oxidative stress and apoptosis of the model. The mitochondrial membrane potential analysis and detection of PINK1/parkin expression were also conducted. To observe whether FOXA1 was involved in the mechanism, its expression was measured, and its association with PBX1 was determined. Subsequently, FOXA1 was silenced to observe whether PBX1 did effects on dopaminergic neuron via FOXA1. PBX1 attenuates 6-OHDA-induced dopaminergic neuronal cell injury and oxidative stress, and apoptosis. Its overexpression ameliorates mitochondrial dysfunction in dopaminergic neurons and upregulates the expression of PINK1/parkin. PBX1 could combine with FOXA1 and affects 6-OHDA-induced dopaminergic neuronal damage and regulates PINK1/PARKIN expression via FOXA1. To conclude, PBX1 attenuates 6-OHDA-induced oxidative stress and apoptosis in dopaminergic neurons, and affected PINK1/PARKIN expression via FOXA1, which indicates the great potential of the PBX1 in prevention against PD.

Chemogenetic activation of nigrostriatal dopamine neurons in freely moving common marmosets

SummaryTo interrogate particular neuronal pathways in nonhuman primates under natural and stress-free conditions, we applied designer receptors exclusively activated by designer drugs (DREADDs) technology to common marmosets. We injected adeno-associated virus vectors expressing the excitatory DREADD hM3Dq into the unilateral substantia nigra (SN) in four marmosets. Using multi-tracer positron emission tomography imaging, we detected DREADD expression in vivo, which was confirmed in nigrostriatal dopamine neurons by immunohistochemistry, as well as by assessed activation of the SN following agonist administration. The marmosets rotated in a contralateral direction relative to the activated side 30–90 min after consuming food containing the highly potent DREADD agonist deschloroclozapine (DCZ) but not on the following days without DCZ. These results indicate that non-invasive and reversible DREADD manipulation will extend the utility of marmosets as a primate model for linking neuronal activity and natural behavior in various contexts.

Low-dose oral pyrethroid exposure induces gastrointestinal dysfunction and alters nigrostriatal dopamine signaling pathways in mice

BACKGROUND AND AIM: Insecticide exposure is associated with greater risk for developing Parkinson’s disease (PD). PD is characterized by motor impairments due to loss of nigrostriatal dopamine (DA) neurons in the midbrain, and patients commonly experience gastrointestinal (GI) dysfunction long before the onset of motor symptoms. Pyrethroids, synthetic insecticides commonly used around the world, disrupt DA signaling pathways. One of the most common routes of pyrethroid exposure is ingestion, so it is plausible that oral exposure acts locally within the GI tract and facilitates PD pathogenesis via the gut-brain axis. Here, we sought to determine the functional and molecular consequences of oral pyrethroid exposure in the adult mouse gut and brain in the context of idiopathic PD. METHODS: Adult mice were orally gavaged with 3 mg/kg deltamethrin weekly for 3 weeks. Intestinal behaviors were assessed to determine constipation phenotypes. Gut microbiome composition was determined by 16S rRNA sequencing. Intestinal and brain tissues were collected following the final dose to assess changes in gene expression and protein production pathways related to DA and other monoamine signaling, as determined by qPCR and western blot. RESULTS:Oral deltamethrin exposure significantly impaired GI function compared to vehicle controls. We observed reduced fecal output, changed gene and protein levels important for normal gut function, and altered gut microbial composition in deltamethrin-exposed mice, all of which are reflective of changes observed in PD patients. In the brain, oral deltamethrin exposure significantly altered production of proteins important for DA synthesis and reuptake compared to controls. CONCLUSIONS:Low-dose oral pyrethroid exposure induces GI dysfunction and alters DA pathways in the brain. These findings support the idea that pyrethroids induce functional and molecular changes relevant to PD pathology from within the gut, and further investigation is warranted to fully understand this phenomenon as a potential trigger in the etiology of PD. KEYWORDS: Pesticides, Chemical exposures, Neurodegenerative outcomes, Microbes/Microbiome

Effects of bromelain on striatal neuroinflammation in rat model of Parkinsonism

Background: Neuroinflammation alters the microenvironment in certain areas of the brain resulting in the development of Parkinson's disease (PD). Mechanisms involving cytokine and non-cytokine induced pathways are activated in the inflammatory response following injury. The proteolytic activity of bromelain appears to eliminate receptors on immune cells that respond to pro-inflammatory signals. This raises the question of whether manipulation of the inflammatory response pathways could lead to a beneficial intervention for PD. In this study, we investigated the effect of bromelain exposure on pro-inflammatory cytokine concentration and microglial activation in a parkinsonian rat model. Methods: Nigrostriatal dopamine neurons were lesioned by stereotaxic injection of the neurotoxin, 6-OHDA, into the medial forebrain bundle (MFB) of male Sprague-Dawley rats with weight ranging from 230- 250 g. The anti-inflammatory drug bromelain was used to treat a subset of the rats before or 24 h post 6-OHDA lesion. The systemic blood concentration of neutrophils and platelets was measured along with plasma and striatal concentrations of pro-inflammatory cytokines IL-1β, IL-6 and TNF-α. In addition, the densities of CD11b and CD86 cells were differently quantified as a measure of glial cell activation. ResultsPre-treatment with bromelain decreased the plasma concentration of neutrophils and platelets in 6-OHDA lesioned rats. The bromelain treatments (Pre and Post) decreased the plasma concentration of TNF-α and IL-1β. Pre-treatment with bromelain further resulted in the suppression of both systemic pro-inflammatory cytokines and microgliosis. Post-surgical bromelain treatment significantly resulted in the alleviation of systemic pro-inflammatory cytokines. ConclusionEarly treatment with bromelain may slow the progression of PD by attenuating the inflammatory response associated with the disease. The present results suggest that bromelain may be considered for further clinical study and perhaps use as prophylactic treatment for patients with PD.