Degeneration Of Nigral Dopaminergic Neurons Research Articles

Inflammatory bowel disease induces pathological α-synuclein aggregation in the human gut and brain.

According to Braak's hypothesis, it is plausible that Parkinson's disease (PD) originates in the enteric nervous system (ENS) and spreads to the brain through the vagus nerve. In this work, we studied whether inflammatory bowel diseases (IBDs) in humans can progress with the emergence of pathogenic α-synuclein (α-syn) in the gastrointestinal tract and midbrain dopaminergic neurons. We have analysed the gut and the ventral midbrain from subjects previously diagnosed with IBD and form a DSS-based rat model of gut inflammation in terms of α-syn pathology. Our data support the existence of pathogenic α-syn in both the gut and the brain, thus reinforcing the potential role of the ENS as a contributing factor in PD aetiology. Additionally, we have analysed the effect of a DSS-based rat model of gut inflammation to demonstrate (i) the appearance of P-α-syn inclusions in both Auerbach's and Meissner's plexuses (gut), (ii) an increase in α-syn expression in the ventral mesencephalon (brain) and (iii) the degeneration of nigral dopaminergic neurons, which all are considered classical hallmarks in PD. These results strongly support the plausibility of Braak's hypothesis and emphasise the significance of peripheral inflammation and the gut-brain axis in initiating α-syn aggregation and transport to the substantia nigra, resulting in neurodegeneration.

GGC expansions in NOTCH2NLC contribute to Parkinson disease and dopaminergic neuron degeneration.

The role of GGC repeat expansions within NOTCH2NLC in Parkinson's disease (PD) and the substantia nigra (SN) dopaminergic neuron remains unclear. Here, we profile the NOTCH2NLC GGC repeat expansions in a large cohort of patients with PD. We also investigate the role of GGC repeat expansions within NOTCH2NLC in the dopaminergic neurodegeneration of SN. A total of 2,522 patients diagnosed with PD and 1,085 health controls were analyzed for the repeat expansions of NOTCH2NLC by repeat-primed PCR and GC-rich PCR assay. Furthermore, the effects of GGC repeat expansions in NOTCH2NLC on dopaminergic neurons were investigated by using recombinant adeno-associated virus (AAV)-mediated overexpression of NOTCH2NLC with 98 GGC repeats in the SN of mice by stereotactic injection. Four PD pedigrees (4/333, 1.2%) and three sporadic PD patients (3/2189, 0.14%) were identified with pathogenic GGC repeat expansions (larger than 60 GGC repeats) in the NOTCH2NLC gene, while eight PD patients and one healthy control were identified with intermediate GGC repeat expansions ranging from 41 to 60 repeats. No significant difference was observed in the distribution of intermediate NOTCH2NLC GGC repeat expansions between PD cases and controls (Fisher's exact test p-value = 0.29). Skin biopsy showed P62-positive intranuclear NOTCH2NLC-polyGlycine (polyG) inclusions in the skin nerve fibers of patient. Expanded GGC repeats in NOTCH2NLC produced widespread intranuclear and perinuclear polyG inclusions, which led to a severe loss of dopaminergic neurons in the SN. Consistently, polyG inclusions were presented in the SN of EIIa-NOTCH2NLC-(GGC)98 transgenic mice and also led to dopaminergic neuron loss in the SN. Overall, our findings provide strong evidence that GGC repeat expansions within NOTCH2NLC contribute to the pathogenesis of PD and cause degeneration of nigral dopaminergic neurons.

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.

Pathophysiological Features of Nigral Dopaminergic Neurons in Animal Models of Parkinson's Disease.

The degeneration of nigral dopaminergic neurons is considered the hallmark of Parkinson’s disease (PD), and it is triggered by different factors, including mitochondrial dysfunction, Lewy body accumulation, neuroinflammation, excitotoxicity and metal accumulation. Despite the extensive literature devoted to unravelling the signalling pathways involved in neuronal degeneration, little is known about the functional impairments occurring in these cells during illness progression. Of course, it is not possible to obtain direct information on the properties of the dopaminergic cells in patients. However, several data are available in the literature reporting changes in the function of these cells in PD animal models. In the present manuscript, we focus on dopaminergic neuron functional properties and summarize shared or peculiar features of neuronal dysfunction in different PD animal models at different stages of the disease in an attempt to design a picture of the functional modifications occurring in nigral dopaminergic neurons during disease progression preceding their eventual death.

Aged xCT-Deficient Mice Are Less Susceptible for Lactacystin-, but Not 1-Methyl-4-Phenyl-1,2,3,6- Tetrahydropyridine-, Induced Degeneration of the Nigrostriatal Pathway.

The astrocytic cystine/glutamate antiporter system xc– (with xCT as the specific subunit) imports cystine in exchange for glutamate and has been shown to interact with multiple pathways in the brain that are dysregulated in age-related neurological disorders, including glutamate homeostasis, redox balance, and neuroinflammation. In the current study, we investigated the effect of genetic xCT deletion on lactacystin (LAC)- and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced degeneration of the nigrostriatal pathway, as models for Parkinson’s disease (PD). Dopaminergic neurons of adult xCT knock-out mice (xCT–/–) demonstrated an equal susceptibility to intranigral injection of the proteasome inhibitor LAC, as their wild-type (xCT+/+) littermates. Contrary to adult mice, aged xCT–/– mice showed a significant decrease in LAC-induced degeneration of nigral dopaminergic neurons, depletion of striatal dopamine (DA) and neuroinflammatory reaction, compared to age-matched xCT+/+ littermates. Given this age-related protection, we further investigated the sensitivity of aged xCT–/– mice to chronic and progressive MPTP treatment. However, in accordance with our previous observations in adult mice (Bentea et al., 2015a), xCT deletion did not confer protection against MPTP-induced nigrostriatal degeneration in aged mice. We observed an increased loss of nigral dopaminergic neurons, but equal striatal DA denervation, in MPTP-treated aged xCT–/– mice when compared to age-matched xCT+/+ littermates. To conclude, we reveal age-related protection against proteasome inhibition-induced nigrostriatal degeneration in xCT–/– mice, while xCT deletion failed to protect nigral dopaminergic neurons of aged mice against MPTP-induced toxicity. Our findings thereby provide new insights into the role of system xc– in mechanisms of dopaminergic cell loss and its interaction with aging.

Neuroprotective effect of NXP031 in the MPTP-induced Parkinson's disease model

Parkinson’s disease (PD) is a neurodegenerative disease characterized by the progressive degeneration of dopaminergic neurons in the substantia nigra (SN). Oxidative stress has been identified as one of the major causes of nigrostriatal degeneration in PD. Ascorbic acid plays a role as an efficient antioxidant to protect cells from free radical damage, but it is easily oxidized and loses its antioxidant activity. To overcome this limitation, we have recently developed NXP031, a single-stranded DNA aptamer that binds to ascorbic acid with excellent specificity, reducing its oxidation and increasing its efficacy. This study investigated the neuroprotective effects of NXP031 in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD model. Acute degeneration of nigral dopaminergic neurons was induced by four consecutive treatments of MPTP (20 mg/kg) in male C57BL/6 J mice. NXP031 (Vitamin C/Aptamin C 200 mg/4 mg/kg) was administered intraperitoneally for 5 days following MPTP. We observed that the administration of NXP031 ameliorated MPTP-induced loss of dopaminergic neurons in the SN and exhibited improvement of MPTP-mediated motor impairment. We further found that NXP031 increased plasma ascorbic acid levels and inhibited microglia activation-induced neuroinflammation in the SN, which might contribute to the protective effects of NXP031 on nigrostriatal degeneration. Our findings suggest that NXP031 could be a potential therapeutic intervention in PD.

Dopamine promotes the neurodegenerative potential of β‐synuclein

A contribution of α-Synuclein (α-Syn) to etiology of Parkinson´s disease (PD) and Dementia with Lewy bodies (DLB) is currently undisputed, while the impact of the closely related β-Synuclein (β-Syn) on these disorders remains enigmatic. β-Syn has long been considered to be an attenuator of the neurotoxic effects of α-Syn, but in a rodent model of PD β-Syn induced robust neurodegeneration in dopaminergic neurons of the substantia nigra. Given that dopaminergic nigral neurons are selectively vulnerable to neurodegeneration in PD, we now investigated if dopamine can promote the neurodegenerative potential of β-Syn. We show that in cultured rodent and human neurons a dopaminergic neurotransmitter phenotype substantially enhanced β-Syn-induced neurodegeneration, irrespective if dopamine is synthesized within neurons or up-taken from extracellular space. Nuclear magnetic resonance interaction and thioflavin-T incorporation studies demonstrated that dopamine and its oxidized metabolites 3,4-dihydroxyphenylacetaldehyde (DOPAL) and dopaminochrome (DCH) directly interact with β-Syn, thereby enabling structural and functional modifications. Interaction of DCH with β-Syn inhibits its aggregation, which might result in increased levels of neurotoxic oligomeric β-Syn. Since protection of outer mitochondrial membrane integrity prevented the additive neurodegenerative effect of dopamine and β-Syn, such oligomers might act at a mitochondrial level similar to what is suggested for α-Syn. In conclusion, our results suggest that β-Syn can play a significant pathophysiological role in etiology of PD through its interaction with dopamine metabolites and thus should be re-considered as a disease-relevant factor, at least for those symptoms of PD that depend on degeneration of nigral dopaminergic neurons.

Baicalein Attenuates Neuroinflammation by Inhibiting NLRP3/caspase-1/GSDMD Pathway in MPTP Induced Mice Model of Parkinson's Disease.

BackgroundInflammasome-induced neuroinflammation is a major pathogenic mechanism underlying the degeneration of nigral dopaminergic neurons in Parkinson’s disease (PD). Baicalein is a flavonoid isolated from the traditional Chinese medicinal herbal Scutellaria baicalensis Georgi with known anti-inflammatory and neuroprotective efficacy in models of neurodegenerative diseases, including PD. However, its effects on inflammasome-induced neuroinflammation during PD remain unclear.MethodsWe used N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to induce PD-like pathology in mice. Behavioral assessments including the pole test, rotarod test, and open field test were conducted to evaluate the effects of baicalein on MPTP-induced motor dysfunction. The efficacies of baicalein against MPTP-induced dopaminergic neuron loss and glial cell activation in the substantia nigra compact were examined by immunohistochemistry, effects on proinflammatory cytokines by quantitative real-time PCR and enzyme-linked immunosorbent assay, and effects on inflammasome pathway activation by immunoblotting and flow cytometry.ResultsAdministration of baicalein reversed MPTP-induced motor dysfunction, loss of dopaminergic neurons, and pro-inflammatory cytokine elevation. Baicalein also inhibited NLRP3 and caspase-1 activation and suppressed gasdermin D-dependent pyroptosis. Additionally, baicalein inhibited the activation and proliferation of disease-associated proinflammatory microglia.ConclusionsThese findings suggest that baicalein can reverse MPTP-induced neuroinflammation in mice by suppressing NLRP3/caspase-1/gasdermin D pathway. Our study provides potential insight into the use of baicalein in PD therapy.

Gender Differences in Neurodegeneration, Neuroinflammation and Na+-Ca2+ Exchangers in the Female A53T Transgenic Mouse Model of Parkinson's Disease.

Twelve-month-old male mice expressing the human A53T variant of α-synuclein (A53T) develop dopamine neuron degeneration, neuroinflammation, and motor deficits, along with dysfunctions of the mitochondrial Na+-Ca2+ exchanger (NCX) isoforms 1 (NCX1) and 3 (NCX3) in the nigrostriatal system. Since gender is thought to play a role in the etiology of Parkinson’s disease (PD), we characterized neurochemical and behavioral alterations in 12-month-old female A53T transgenic mice. We investigated the presence of dopaminergic degeneration, astrogliosis and microgliosis using immunohistochemistry for tyrosine hydroxylase (TH), glial fibrillary acidic protein (GFAP) and ionized calcium-binding adaptor molecule-1 (IBA-1) in both the substantia nigra pars compacta (SNc) and striatum. In the same regions, we also evaluated the co-localization of NCX1 in cells positive for IBA-1 and the co-localization of NCX3 in TH-positive neurons and fibers. Furthermore, in both male and female mice, we performed motor (beam walking and pole tests) and memory [novel object recognition (NOR) and spontaneous alternation] tasks, together with tests to evaluate peripheral deficits (olfactory and stool collection tests). Female A53T transgenic mice displayed degeneration of nigral dopaminergic neurons, but neither microgliosis nor astrogliosis in the SNc and striatum. Moreover, female A53T transgenic mice displayed co-localization between NCX1 and IBA-1 positive cells in the striatum but not SNc, whereas NCX3 did not co-localize with either TH-positive terminals or neuronal bodies in the nigrostriatal system. Furthermore, female A53T transgenic mice showed increased crossing time in the beam walking test, but no impairments in the pole or memory tests, and in tests that evaluated peripheral deficits, whereas male A53T transgenic mice displayed motor, memory and peripheral deficits. Immunohistochemical and behavioral results obtained here in the female mice differ from those previously observed in males, and suggest a dissimilar influence of NCX1 and NCX3 on dopaminergic function in female and male A53T transgenic mice, strengthening the validity of these mice as a model for studying the etiological factors of PD.

BRUP-1, an intracellular bilirubin modulator, exerts neuroprotective activity in a cellular Parkinson's disease model.

Bilirubin, the end product of heme redox metabolism, has cytoprotective properties and is an essential metabolite associated with cardiovascular disease, inflammatory bowel disease, type 2 diabetes, and neurodegenerative diseases including Parkinson's disease (PD). PD is characterized by progressive degeneration of nigral dopaminergic neurons and is associated with elevated oxidative stress due to mitochondrial dysfunction. In this study, using a ratiometric bilirubin probe, we revealed that the mitochondrial inhibitor, rotenone, which is widely used to create a PD model, significantly decreased intracellular bilirubin levels in HepG2 cells. Chemical screening showed that BRUP-1 was a top hit that restored cellular bilirubin levels that were lowered by rotenone. We found that BRUP-1 up-regulated the expression level of heme oxygenase-1 (HO-1), one of the rate-limiting enzyme of bilirubin production via nuclear factor erythroid 2-related factor 2 (Nrf2) activation. In addition, we demonstrated that this Nrf2 activation was due to a direct inhibition of the interaction between Nrf2 and Kelch-like ECH-associated protein 1 (Keap1) by BRUP-1. Both HO-1 up-regulation and bilirubin restoration by BRUP-1 treatment were significantly abrogated by Nrf2 silencing. In neuronal PC12D cells, BRUP-1 also activated the Nrf2-HO-1 axis and increased bilirubin production, resulted in the suppression of neurotoxin-induced cell death, reactive oxygen species production, and protein aggregation, which are hallmarks of PD. Furthermore, BRUP-1 showed neuroprotective activity against rotenone-treated neurons derived from induced pluripotent stem cells. These findings provide a new member of Keap1-Nrf2 direct inhibitors and suggest that chemical modulation of heme metabolism using BRUP-1 may be beneficial for PD treatment.

G2019S LRRK2 mutation facilitates α-synuclein neuropathology in aged mice

Fibrillization of α-synuclein is instrumental for the development of Parkinson's disease (PD), thus modulating this process can have profound impact on disease initiation/progression. Here, the impact of the p.G2019S mutation of leucine-rich repeat kinase 2 (LRRK2), which is most frequently associated with familial and sporadic PD, on α-synuclein pathology was investigated. G2019S knock-in mice and wild-type controls were injected with a recombinant adeno-associated viral vector serotype 2/9 (AAV2/9) overexpressing human mutant p.A53T α-synuclein (AAV2/9-hα-syn). Control animals were injected with AAV2/9 carrying green fluorescent protein. Motor behavior, transgene expression, α-syn and pSer129 α-syn load, number of nigral dopamine neurons and density of striatal dopaminergic terminals were evaluated. To investigate the effect of aging, experiments were performed in 3- and 12-month-old mice, evaluated 20 and 12 weeks after virus injection, respectively. hα-syn overexpression induced progressive motor deficits, loss of nigral dopaminergic neurons and striatal terminals, and appearance of proteinase K-resistant aggregates of pSer129 α-syn in both young and old mice. Although no genotype difference was observed in 3-month-old mice, degeneration of nigral dopaminergic neurons was higher in 12-month-old G2019S knock-in mice compared with age-matched wild-type controls (−55% vs −39%, respectively). Consistently, a two-fold higher load of pSer129 α-syn aggregates was found in 12-month-old G2019S knock-in mice. We conclude that G2019S LRRK2 facilitates α-synucleinopathy and degeneration of nigral dopaminergic neurons, and that aging is a major determinant of this effect.

AAV1/2-induced overexpression of A53T-\u03b1-synuclein in the substantia nigra results in degeneration of the nigrostriatal system with Lewy-like pathology and motor impairment: a new mouse model for Parkinson\u2019s disease

α-Synuclein is a protein implicated in the etiopathogenesis of Parkinson’s disease (PD). AAV1/2-driven overexpression of human mutated A53T-α-synuclein in rat and monkey substantia nigra (SN) induces degeneration of nigral dopaminergic neurons and decreases striatal dopamine and tyrosine hydroxylase (TH). Given certain advantages of the mouse, especially it being amendable to genetic manipulation, translating the AAV1/2-A53T α-synuclein model to mice would be of significant value. AAV1/2-A53T α-synuclein or AAV1/2 empty vector (EV) at a concentration of 5.16 x 1012 gp/ml were unilaterally injected into the right SN of male adult C57BL/6 mice. Post-mortem examinations included immunohistochemistry to analyze nigral α-synuclein, Ser129 phosphorylated α-synuclein and TH expression, striatal dopamine transporter (DAT) levels by autoradiography and dopamine levels by high performance liquid chromatography. At 10 weeks, in AAV1/2-A53T α-synuclein mice there was a 33% reduction in TH+ dopaminergic nigral neurons (P < 0.001), 29% deficit in striatal DAT binding (P < 0.05), 38% and 33% reductions in dopamine (P < 0.001) and DOPAC (P < 0.01) levels and a 60% increase in dopamine turnover (homovanilic acid/dopamine ratio; P < 0.001). Immunofluorescence showed that the AAV1/2-A53T α-synuclein injected mice had widespread nigral and striatal expression of vector-delivered A53T-α-synuclein. Concurrent staining with human PD SN samples using gold standard histological methodology for Lewy pathology detection by proteinase K digestion and application of specific antibody raised against human Lewy body α-synuclein (LB509) and Ser129 phosphorylated α-synuclein (81A) revealed insoluble α-synuclein aggregates in AAV1/2-A53T α-synuclein mice resembling Lewy-like neurites and bodies. In the cylinder test, we observed significant paw use asymmetry in the AAV1/2-A53T α-synuclein group when compared to EV controls at 5 and 9 weeks post injection (P < 0.001; P < 0.05). These data show that unilateral injection of AAV1/2-A53T α-synuclein into the mouse SN leads to persistent motor deficits, neurodegeneration of the nigrostriatal dopaminergic system and development of Lewy-like pathology, thereby reflecting clinical and pathological hallmarks of human PD.

Neurometabolic profiles of the substantia nigra and striatum of MPTP-intoxicated common marmosets: An in vivo proton MRS study at 9.4T.

Given the strong coupling between the substantia nigra (SN) and striatum (STR) in the early stage of Parkinson's disease (PD), yet only a few studies reported to date that have simultaneously investigated the neurochemistry of these two brain regions in vivo, we performed longitudinal metabolic profiling in the SN and STR of 1-methyl-1,2,3,6-tetrahydropyridine (MPTP)-intoxicated common marmoset monkey models of PD (n=10) by using proton MRS (1 H-MRS) at 9.4T. T2 relaxometry was also performed in the SN by using MRI. Data were classified into control, MPTP_2weeks, and MPTP_6-10weeks groups according to the treatment duration. In the SN, T2 of the MPTP_6-10weeks group was lower than that of the control group (44.33±1.75 versus 47.21±2.47ms, p<0.05). The N-acetylaspartate to total creatine ratio (NAA/tCr) and γ-aminobutyric acid to tCr ratio (GABA/tCr) of the MPTP_6-10weeks group were lower than those of the control group (0.41±0.04 versus 0.54±0.08 (p<0.01) and 0.19±0.03 versus 0.30±0.09 (p<0.05), respectively). The glutathione to tCr ratio (GSH/tCr) was correlated with T2 for the MPTP_6-10weeks group (r=0.83, p=0.04). In the STR, however, GABA/tCr of the MPTP_6-10weeks group was higher than that of the control group (0.25±0.10 versus 0.16±0.05, p<0.05). These findings may be an in vivo depiction of the altered basal ganglion circuit in PD brain resulting from the degeneration of nigral dopaminergic neurons and disruption of nigrostriatal dopaminergic projections. Given the important role of non-human primates in translational studies, our findings provide better understanding of the complicated evolution of PD.

Early synaptic dysfunction in Parkinson's disease: Insights from animal models.

The appearance of motor manifestations in Parkinson's disease (PD) is invariably linked to degeneration of nigral dopaminergic neurons of the substantia nigra pars compacta. Traditional views on PD neuropathology have been grounded in the assumption that the prime event of neurodegeneration involves neuronal cell bodies with the accumulation of metabolic products. However, this view has recently been challenged by both clinical and experimental evidence. Neuropathological studies in human brain samples and both in vivo and in vitro models support the hypothesis that nigrostriatal synapses may indeed be affected at the earliest stages of the neurodegenerative process. The mechanisms leading to either structural or functional synaptic dysfunction are starting to be elucidated and include dysregulation of axonal transport, impairment of the exocytosis and endocytosis machinery, altered intracellular trafficking, and loss of corticostriatal synaptic plasticity. The aim of this review is to try to integrate different lines of evidence from both pathogenic and genetic animal models that, to different extents, suggest that early synaptic impairment may represent the key event in PD pathogenesis. Understanding the molecular and cellular events underlying such synaptopathy is a fundamental step toward developing specific biomarkers of early dopaminergic dysfunction and, more importantly, designing novel therapies targeting the synaptic apparatus of selective, vulnerable synapses. © 2016 International Parkinson and Movement Disorder Society.

Alpha-Synuclein Produces Early Behavioral Alterations via Striatal Cholinergic Synaptic Dysfunction by Interacting With GluN2D N-Methyl-D-Aspartate Receptor Subunit

BackgroundAdvanced Parkinson’s disease (PD) is characterized by massive degeneration of nigral dopaminergic neurons, dramatic motor and cognitive alterations, and presence of nigral Lewy bodies, whose main constituent is α-synuclein (α-syn). However, the synaptic mechanisms underlying behavioral and motor effects induced by early selective overexpression of nigral α-syn are still a matter of debate. MethodsWe performed behavioral, molecular, and immunohistochemical analyses in two transgenic models of PD, mice transgenic for truncated human α-synuclein 1-120 and rats injected with the adeno-associated viral vector carrying wild-type human α-synuclein. We also investigated striatal synaptic plasticity by electrophysiological recordings from spiny projection neurons and cholinergic interneurons. ResultsWe found that overexpression of truncated or wild-type human α-syn causes partial reduction of striatal dopamine levels and selectively blocks the induction of long-term potentiation in striatal cholinergic interneurons, producing early memory and motor alterations. These effects were dependent on α-syn modulation of the GluN2D-expressing N-methyl-D-aspartate receptors in cholinergic interneurons. Acute in vitro application of human α-syn oligomers mimicked the synaptic effects observed ex vivo in PD models. ConclusionsWe suggest that striatal cholinergic dysfunction, induced by a direct interaction between α-syn and GluN2D-expressing N-methyl-D-aspartate receptors, represents a precocious biological marker of the disease.

ShRNA targeting α-synuclein prevents neurodegeneration in a Parkinson's disease model.

Multiple convergent lines of evidence implicate both α-synuclein (encoded by SCNA) and mitochondrial dysfunction in the pathogenesis of sporadic Parkinson's disease (PD). Occupational exposure to the mitochondrial complex I inhibitor rotenone increases PD risk; rotenone-exposed rats show systemic mitochondrial defects but develop specific neuropathology, including α-synuclein aggregation and degeneration of substantia nigra dopaminergic neurons. Here, we inhibited expression of endogenous α-synuclein in the adult rat substantia nigra by adeno-associated virus-mediated delivery of a short hairpin RNA (shRNA) targeting the endogenous rat Snca transcript. Knockdown of α-synuclein by ~35% did not affect motor function or cause degeneration of nigral dopaminergic neurons in control rats. However, in rotenone-exposed rats, progressive motor deficits were substantially attenuated contralateral to α-synuclein knockdown. Correspondingly, rotenone-induced degeneration of nigral dopaminergic neurons, their dendrites, and their striatal terminals was decreased ipsilateral to α-synuclein knockdown. These data show that α-synuclein knockdown is neuroprotective in the rotenone model of PD and indicate that endogenous α-synuclein contributes to the specific vulnerability of dopaminergic neurons to systemic mitochondrial inhibition. Our findings are consistent with a model in which genetic variants influencing α-synuclein expression modulate cellular susceptibility to environmental exposures in PD patients. shRNA targeting the SNCA transcript should be further evaluated as a possible neuroprotective therapy in PD.

Rotenone impairs autophagic flux and lysosomal functions in Parkinson’s disease

BackgroundRotenone is an environmental neurotoxin that induces accumulation of α-synuclein and degeneration of dopaminergic neurons in substantia nigra pars compacta (SNpc), but the molecular mechanisms are not fully understood. We investigated whether rotenone induced impairment of autophagic flux and lysosomal functions. MethodsAutophagy flux, accumulation of α-synuclein, lysosomal membrane integrity and neurodegeneration were assessed in the rotenone-treated rat model and PC12 cells, and the effects of the autophagy inducer trehalose on rotenone’s cytotoxicity were also studied. ResultsRotenone administration significantly reduced motor activity and caused a loss of tyrosine hydroxylase in SNpc of Lewis rats. The degeneration of nigral dopaminergic neurons was accompanied by the deposition of α-synuclein aggregates, autophagosomes and redistribution of cathepsin D from lysosomes to the cytosol. In cultured PC12 cells, rotenone also induced increases in protein levels of α-synuclein, microtubule-associated protein 1 light chain 3-II, Beclin 1, and p62. Rotenone increased lysosomal membrane permeability as evidenced by leakage of N-acetyl-beta-d-glucosaminidase and cathepsin D, the effects were blocked by reactive oxygen species scavenger tiron. Autophagy inducer trehalose enhanced the nuclear translocation of transcription factor EB, accelerated the clearance of autophagosomes and α-synuclein and attenuated rotenone-induced cell death of PC12 cells. Meanwhile, administration of trehalose to rats in drinking water (2%) decreased rotenone-induced dopaminergic neurons loss in SNpc. ConclusionsThese studies indicate that the lysosomal dysfunction contributes to rotenone’s neurotoxicity and restoration of lysosomal function could be a new therapeutic strategy for Parkinson’s disease.

Overview of mouse models of Parkinson's disease.

Parkinson's disease is a neurodegenerative disorder characterized by the loss of neurons in specific regions of the nervous system, notably in the substantia nigra pars compacta and, in most cases, by the deposition of intraneuronal inclusions named Lewy bodies. These pathological alterations have profound effects on the brain function, leading to the progressive development of various symptoms, the most prominent being the impaired initiation of voluntary movements caused by the loss of dopamine signaling in the basal ganglia. Here, we provide an overview of the mouse models of Parkinson's disease, with the goal of guiding selection of the most appropriate model for studying the question at hand. Pharmacological approaches targeting dopamine signaling and toxins leading to selective degeneration of nigral neurons are used to validate symptomatic treatments that aim at restoring effective dopaminergic function for motor control. Alternative mouse models are based on genetic modifications that are meant to reproduce the inherited alterations associated with familial forms of Parkinson's disease. Although genetic models have most often failed to induce overt degeneration of nigral dopaminergic neurons, they provide essential tools to explore the multifactorial etiology of this complex neurodegenerative disorder.

Harnessing neurogenesis for the possible treatment of Parkinson's disease

The discovery of neurogenesis in the adult brain has created new possibilities for therapeutics in neurodegenerative diseases. Neural precursor cells, which have been found in various parts of the brain, e.g., the subventricular zone (SVZ) and substantia nigra (SN), have promising potential to replace the extensive loss of neurons occurring in neurodegenerative disorders. In Parkinson's disease (PD) the degeneration of nigral dopaminergic neurons and consequently the nigrostriatal pathway, which has been found to innervate proximally to the SVZ, causes motor and cognitive impairments. There is strong evidence that neurogenesis is impaired in PD, which has been related to the nonmotor symptoms of the disease. Recent evidence supports that this impairment in neurogenesis is partially caused by the lack of dopamine in one of the adult neurogenic niches, the SVZ. Thus, restoring the dopaminergic pathway in PD patients may have implications not only for motor function improvement, but for other cognitive and autonomic symptoms. Currently, there are no effective treatments that can stop or reverse the neurodegeneration process in the brain. Here we review the neurogenic process and observed alterations found in PD animal models and postmortem brains of PD patients. Finally, we review several attempts to stimulate the neurogenic process for nigral and/or striatal dopaminergic restoration by transgenic expression, exercise, or cell therapy.

Cypermethrin-induced nigrostriatal dopaminergic neurodegeneration alters the mitochondrial function: a proteomics study.

Cypermethrin induces the slow and progressive degeneration of the nigrostriatal dopaminergic neurons in rats. Postnatal preexposure with low doses of cypermethrin is known to enhance the susceptibility of animals upon adulthood reexposure. The study was undertaken to delineate the role of mitochondria in cypermethrin-induced neurodegeneration. Indexes of dopaminergic neurodegeneration, microglial activation, and mitochondrial dysfunction and its proteome profile were assessed in controls and cypermethrin-treated rats. Cypermethrin increased nigral dopaminergic neurodegeneration and microglial activation while reduced mitochondrial membrane potential and complex I activity. Cypermethrin attenuated striatal dopamine content and differentially regulated the expressions of the nine striatal and ten nigral proteins. Western blot analyses showed that cypermethrin also increased c-Jun N-terminal kinase (JNK), caspase-3, tumor suppressor protein (p53), tumor necrosis factor-α (TNF-α), p38 mitogen-activated protein kinase (p38 MAPK), and heme oxygenase-1 (HO-1) expressions and reduced B cell lymphoma-2 protein (Bcl-2) expression. Syndopa and minocycline rescued from cypermethrin induced augmentation in microglial activation and reductions in mitochondrial membrane potential and complex I activity, striatal dopamine content, and degeneration of nigral dopaminergic neurons. Syndopa and minocycline, respectively, modulated the expressions of four and six striatal and four and seven nigral proteins. Furthermore, they reinstated the expressions of JNK, caspase-3, Bcl-2, p53, p38 MAPK, TNF-α, and HO-1. The study demonstrates that cypermethrin induces mitochondrial dysfunction and alters mitochondrial proteome leading to oxidative stress and apoptosis, which regulate the nigrostriatal dopaminergic neurodegeneration.