Paradoxical Mitophagy Regulation by PINK1 and TUFm.

Aberrant mitophagy has been implicated in a broad spectrum of disorders. PINK1, Parkin, and ubiquitin have pivotal roles in priming mitophagy. However, the entire regulatory landscape and the precise control mechanisms of mitophagy remain to be elucidated. Here, we uncover fundamental mitophagy regulation involving PINK1 and a non-canonical role of the mitochondrial Tu translation elongation factor (TUFm). The mitochondrion-cytosol dual-localized TUFm interacts with PINK1 biochemically and genetically, which is an evolutionarily conserved Parkin-independent route toward mitophagy. A PINK1-dependent TUFm phosphoswitch at Ser222 determines conversion from activating to suppressing mitophagy. PINK1 modulates differential translocation of TUFm because p-S222-TUFm is restricted predominantly to the cytosol, where it inhibits mitophagy by impeding Atg5-Atg12 formation. The self-antagonizing feature of PINK1/TUFm is critical for the robustness of mitophagy regulation, achieved by the unique kinetic parameters of p-S222-TUFm, p-S65-ubiquitin, and their common kinase PINK1. Our findings provide new mechanistic insights into mitophagy and mitophagy-associated disorders.

Parkinson's Disease: Exploring Different Animal Model Systems.

Disease modeling in non-human subjects is an essential part of any clinical research. To gain proper understanding of the etiology and pathophysiology of any disease, experimental models are required to replicate the disease process. Due to the huge diversity in pathophysiology and prognosis in different diseases, animal modeling is customized and specific accordingly. As in other neurodegenerative diseases, Parkinson's disease is a progressive disorder coupled with varying forms of physical and mental disabilities. The pathological hallmarks of Parkinson's disease are associated with the accumulation of misfolded protein called α-synuclein as Lewy body, and degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNc) area affecting the patient's motor activity. Extensive research has already been conducted regarding animal modeling of Parkinson's diseases. These include animal systems with induction of Parkinson's, either pharmacologically or via genetic manipulation. In this review, we will be summarizing and discussing some of the commonly employed Parkinson's disease animal model systems and their applications and limitations.

History of Parkinson's Disease-Associated Gene, Parkin: Research over a Quarter Century in Quest of Finding the Physiological Substrate.

Parkin, the gene responsible for hereditary Parkinson's disease (PD) called "Autosomal Recessive Juvenile Parkinsonism (AR-JP)" was discovered a quarter of a century ago. Owing to its huge gene structure and unique protein functions, parkin has become a subject of interest to those involved in PD research and researchers and clinicians in various fields and is being vigorously studied worldwide in relation to its nature and disease. The gene structure was registered under the gene name "parkin" in the GenBank in 1997. In 1998, deletion and point mutations in the parkin gene were reported, thereby demonstrating parkin is the causative gene for hereditary PD. Although 25 years have passed since the gene's discovery and many researchers have worked tirelessly to elucidate the function of the Parkin protein and the mechanism of its role against neuronal cell death and pathogenesis remain unknown, which raises a major question concerning the current leading hypothesis. In this review, we present the results of related research on the parkin gene in chronological order and discuss unresolved problems concerning its function and pathology as well as new trends in the research conducted to solve them. The relationship between parkin and tumorigenesis has also been addressed from the perspective of Parkin's redox molecule.

ATP13A2 Gene Silencing in Drosophila Affects Autophagic Degradation of A53T Mutant α-Synuclein.

Mutations in ATP13A2 (PARK9), an autophagy-related protein, cause Kufor-Rakeb syndrome, an autosomal recessive, juvenile-onset form of parkinsonism. α-Synuclein (α-syn) is a presynaptic neuronal protein that forms toxic aggregates in Parkinson's disease (PD). We studied α-syn aggregation and autophagic flux in ATP13A2-knockdown Drosophila expressing either wild-type (WT) or mutant α-syn. Dopaminergic (DA) neuron loss was studied by confocal microscopy. Sleep and circadian activity were evaluated in young and old flies using a Drosophila activity monitor. Thirty-day-old ATP13A2-RNAi A53T-α-syn flies had increased Triton-insoluble α-syn levels, compared to control A53T-α-syn flies without ATP13A2-RNAi. Whole-brain staining revealed significantly fewer dopaminergic (DA) neurons in the PPL2 cluster of 30-day-old ATP13A2-RNAi flies expressing WT-, A30P-, and A53T-α-syn than in that of controls. In ATP13A2-RNAi A53T-α-syn flies, autophagic flux was decreased, as indicated by increased accumulation of Ref(2)P, the Drosophila p62 homologue. ATP13A2 silencing decreased total locomotor activity in young, and enhanced sleep features, similar to PD (decreasing bout length), in old flies expressing A53T-α-syn. ATP13A2 silencing also altered the circadian locomotor activity of A30P- and A53T-α-syn flies. Thus, ATP13A2 may play a role in the autophagic degradation of A53T-α-syn.

Parkin Precipitates on Mitochondria via Aggregation and Autoubiquitination.

The loss of the E3 ligase Parkin, in a familial form of Parkinson's disease, is thought to cause the failure of both the polyubiquitination of abnormal mitochondria and the consequent induction of mitophagy, resulting in abnormal mitochondrial accumulation. However, this has not been confirmed in patient autopsy cases or animal models. More recently, the function of Parkin as a redox molecule that directly scavenges hydrogen peroxide has attracted much attention. To determine the role of Parkin as a redox molecule in the mitochondria, we overexpressed various combinations of Parkin, along with its substrates FAF1, PINK1, and ubiquitin in cell culture systems. Here, we observed that the E3 Parkin monomer was surprisingly not recruited to abnormal mitochondria but self-aggregated with or without self-ubiquitination into the inner and outer membranes, becoming insoluble. Parkin overexpression alone generated aggregates without self-ubiquitination, but it activated autophagy. These results suggest that for damaged mitochondria, the polyubiquitination of Parkin substrates on the mitochondria is not indispensable for mitophagy.

Ellagic Acid Prevents α-Synuclein Aggregation and Protects SH-SY5Y Cells from Aggregated α-Synuclein-Induced Toxicity via Suppression of Apoptosis and Activation of Autophagy.

Parkinson's disease (PD) is a neurodegenerative disease characterized by the loss of dopamine neurons and the deposition of misfolded proteins known as Lewy bodies (LBs), which contain α-synuclein (α-syn). The causes and molecular mechanisms of PD are not clearly understood to date. However, misfolded proteins, oxidative stress, and impaired autophagy are believed to play important roles in the pathogenesis of PD. Importantly, α-syn is considered a key player in the development of PD. The present study aimed to assess the role of Ellagic acid (EA), a polyphenol found in many fruits, on α-syn aggregation and toxicity. Using thioflavin and seeding polymerization assays, in addition to electron microscopy, we found that EA could dramatically reduce α-syn aggregation. Moreover, EA significantly mitigated the aggregated α-syn-induced toxicity in SH-SY5Y cells and thus enhanced their viability. Mechanistically, these cytoprotective effects of EA are mediated by the suppression of apoptotic proteins BAX and p53 and a concomitant increase in the anti-apoptotic protein, BCL-2. Interestingly, EA was able to activate autophagy in SH-SY5Y cells, as evidenced by normalized/enhanced expression of LC3-II, p62, and pAKT. Together, our findings suggest that EA may attenuate α-syn toxicity by preventing aggregation and improving viability by restoring autophagy and suppressing apoptosis.

LRRK2(I2020T) functional genetic interactors that modify eye degeneration and dopaminergic cell loss in Drosophila.

Progressive degeneration of dopaminergic neurons in the substantia nigra pars compacta is the primary cause for motor symptoms observed in Parkinson's disease (PD). Mutations in leucine-rich repeat kinase 2 (LRRK2) are the most commonly linked contributor to familial PD. LRRK2 is suggested to be involved in a wide variety of cellular processes, but deciphering its role in the pathogenesis of PD has been difficult. Modelling PD in rodents has been a persistent challenge for the field. However, the fruit fly has been exploited to recapitulate PD gene related dopaminergic cell loss. Using the GAL4-UAS system and established models of hLRRK2 induced eye degeneration in Drosophila, we conducted an unbiased suppressor/enhancer screen to uncover genetic modifiers of LRRK2. We have identified 36 candidate interactors that modify LRRK2 induced toxicity in the Drosophila eye. Importantly, we determined that a subset of these interactors also modified hLRRK2(I2020T) induced dopaminergic neuronal loss in the fly brain and uncovered 16 candidates that modify dopaminergic cell loss. Our results suggest LRRK2 may be involved in a wide variety of cellular processes and the results from this screen provide an important genetic resource for further evaluation of LRRK2 function.

Development of Nonviral Vectors Targeting the Brain as a Therapeutic Approach For Parkinson's Disease and Other Brain Disorders.

Parkinson's disease (PD) is a debilitating neurodegenerative disease characterized by tremor, rigidity, bradykinesia, and postural instability, for which there is no effective treatment available till date. Here, we report the development of nonviral vectors specific for neuronal cells that can deliver short interfering RNA (siRNA) against the α-synuclein gene (SNCA), and prevent PD-like symptoms both in vitro and in vivo. These vectors not only help siRNA duplexes cross the blood-brain barrier in mice, but also stabilize these siRNAs leading to a sustainable 60-90% knockdown of α-synuclein protein. Mice treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine rapidly develop PD-like symptoms which were significantly alleviated when SNCA was knocked down using our vectors. Together, our data not only confirm the central role of α-synuclein in the onset of PD, but also provide a proof of principle that these nonviral vectors can be used as novel tools to design effective strategies to combat central nervous system diseases.

Neuroprotective effect of nerolidol against neuroinflammation and oxidative stress induced by rotenone.

BACKGROUND: Parkinson disease (PD) is a movement disorder affecting 1 % of people over the age of 60. The etiology of the disease is unknown; however, accumulating evidence suggests that mitochondrial defects, oxidative stress, and neuroinflammation play important roles in developing the disease. Current medications for PD can only improve its symptoms, but are unable to halt its progressive nature. Although many therapeutic approaches are available, new drugs are urgently needed for the treatment of PD. Thus, the present study was undertaken to investigate the neuroprotective potential of nerolidol, a sesquiterpene alcohol, on a rotenone-induced experimental model of PD, where male Wistar rats intraperitoneally received rotenone (ROT) at a dose of 2.5 mg/kg of body weight once daily for 4 weeks. RESULTS: Nerolidol, which has antioxidant and anti-inflammatory properties, was injected intraperitoneally at 50 mg/kg of body weight, once daily for 4 weeks, and at 30 min prior to ROT administration. ROT administration significantly reduced the activities of antioxidant enzymes superoxide dismutase (SOD) and catalase (CAT), and the level of the antioxidant tripeptide glutathione (GSH). Moreover, ROT increased the levels of the lipid peroxidation product malondialdehyde (MDA), proinflammatory cytokines (IL-1ß, IL-6, and TNF-α), and inflammatory mediators (COX-2 and iNOS) in rat brain tissues. Immunostaining of brain tissue sections revealed a significant increase in the number of activated astrocytes (GFAP) and microglia (Iba-1), along with the concomitant loss of dopamine (DA) neurons in the substantia nigra pars compacta and dopaminergic nerve fibers in the striatum of ROT-treated rats. As expected, nerolidol supplementation to ROT-injected rats significantly increased the level of SOD, CAT, and GSH, and decreased the level of MDA. Nerolidol also inhibited the release of proinflammatory cytokines and inflammatory mediators. Finally, nerolidol treatment prevented ROT-induced glial cell activation and the loss of dopaminergic neurons and nerve fibers, and ultimately attenuated ROT-induced dopaminergic neurodegeneration. CONCLUSION: Our findings are the first to show that the neuroprotective effect of nerolidol is mediated through its anti-oxidant and anti-inflammatory activities, which strongly supports its therapeutic potential for the treatment of PD.

Longitudinal changes in CSF alpha-synuclein species reflect Parkinson's disease progression.

BACKGROUND: Parkinson's disease (PD) diagnosis is mainly based on clinical criteria, with a high risk of misdiagnosis. The identification of reliable biomarkers for disease diagnosis and progression has a key role for developing disease-modifying therapies. In this article, we investigated the longitudinal changes of CSF α-synuclein species in early PD patients and explored the potential use of these species as surrogate biomarkers for PD progression. METHODS: We used our newly developed enzyme-linked immunosorbent assay systems for measuring different forms of α-synuclein, such as oligomeric-α-synuclein, phosphorylated-α-synuclein at serine 129, or total-α-synuclein in CSF from the longitudinal Deprenyl and Tocopherol Antioxidative Therapy for Parkinsonism study cohort (n = 121). CSF Alzheimer's disease biomarkers (total-tau, phosphorylated-tau, Aß40 , and Aß42 ) were also measured for this cohort. RESULTS: Interestingly, total-α-synuclein and oligomeric-α-synuclein levels significantly increased during the 2-year Deprenyl and Tocopherol Antioxidative Therapy for Parkinsonism study follow-up period, whereas phosphorylated-α-synuclein at serine 129 levels showed a longitudinal decrease. We have also noted an association between a change of the oligomeric-α-synuclein/total-α-synuclein ratio and a worsening of motor signs, in particular in the postural-instability and gait-difficulty dominant PD group. A strong positive correlation between the changes in CSF total-α-synuclein and oligomeric-α-synuclein during the 2-year Deprenyl and Tocopherol Antioxidative Therapy for Parkinsonism study was also noted (r = 0.84, P < .001). CONCLUSION: Our data show that CSF α-synuclein species have a dynamic pattern along the course of the disease, supporting their possible role as progression biomarkers for PD and their link with PD clinical phenotypes. © 2016 International Parkinson and Movement Disorder Society.

ß-Caryophyllene, a phytocannabinoid attenuates oxidative stress, neuroinflammation, glial activation, and salvages dopaminergic neurons in a rat model of Parkinson disease.

Parkinson disease (PD) is a neurodegenerative disease characterized by progressive dopaminergic neurodegeneration in the substantia nigra pars compacta (SNc) area. The present study was undertaken to evaluate the neuroprotective effect of ß-caryophyllene (BCP) against rotenone-induced oxidative stress and neuroinflammation in a rat model of PD. In the present study, BCP was administered once daily for 4 weeks at a dose of 50 mg/kg body weight prior to a rotenone (2.5 mg/kg body weight) challenge to mimic the progressive neurodegenerative nature of PD. Rotenone administration results in oxidative stress as evidenced by decreased activities of superoxide dismutase, catalase, and depletion of glutathione with a concomitant rise in lipid peroxidation product, malondialdehyde. Rotenone also significantly increased pro-inflammatory cytokines in the midbrain region and elevated the inflammatory mediators such as cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) in the striatum. Further, immunohistochemical analysis revealed loss of dopaminergic neurons in the SNc area and enhanced expression of ionized calcium-binding adaptor molecule-1 (Iba-1) and glial fibrillary acidic protein (GFAP), indicators of microglia activation, and astrocyte hypertrophy, respectively, as an index of inflammation. However, treatment with BCP rescued dopaminergic neurons and decreased microglia and astrocyte activation evidenced by reduced Iba-1 and GFAP expression. BCP in addition to attenuation of pro-inflammatory cytokines and inflammatory mediators such as COX-2 and iNOS, also restored antioxidant enzymes and inhibited lipid peroxidation as well as glutathione depletion. The findings demonstrate that BCP provides neuroprotection against rotenone-induced PD and the neuroprotective effects can be ascribed to its potent antioxidant and anti-inflammatory activities.

Mitochondrial processing peptidase regulates PINK1 processing, import and Parkin recruitment.

Mutations in phosphatase and tensin homologue-induced kinase 1 (PINK1) cause recessively inherited Parkinson's disease (PD), a neurodegenerative disorder linked to mitochondrial dysfunction. In healthy mitochondria, PINK1 is rapidly degraded in a process involving both mitochondrial proteases and the proteasome. However, when mitochondrial import is compromised by depolarization, PINK1 accumulates on the mitochondrial surface where it recruits the PD-linked E3 ubiquitin ligase Parkin from the cytosol, which in turn mediates the autophagic destruction of the dysfunctional organelles. Using an unbiased RNA-mediated interference (RNAi)-based screen, we identified four mitochondrial proteases, mitochondrial processing peptidase (MPP), presenilin-associated rhomboid-like protease (PARL), m-AAA and ClpXP, involved in PINK1 degradation. We find that PINK1 turnover is particularly sensitive to even modest reductions in MPP levels. Moreover, PINK1 cleavage by MPP is coupled to import such that reducing MPP activity induces PINK1 accumulation at the mitochondrial surface, leading to Parkin recruitment and mitophagy. These results highlight a new role for MPP in PINK1 import and mitochondrial quality control via the PINK1­Parkin pathway.

Inactivation of Pink1 gene in vivo sensitizes dopamine-producing neurons to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and can be rescued by autosomal recessive Parkinson disease genes, Parkin or DJ-1.

Mutations in the mitochondrial PTEN-induced kinase 1 (Pink1) gene have been linked to Parkinson disease (PD). Recent reports including our own indicated that ectopic Pink1 expression is protective against toxic insult in vitro, suggesting a potential role for endogenous Pink1 in mediating survival. However, the role of endogenous Pink1 in survival, particularly in vivo, is unclear. To address this critical question, we examined whether down-regulation of Pink1 affects dopaminergic neuron loss following 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in the adult mouse. Two model systems were utilized: virally delivered shRNA-mediated knockdown of Pink1 and germ line-deficient mice. In both instances, loss of Pink1 generated significant sensitivity to damage induced by systemic MPTP treatment. This sensitivity was associated with greater loss of dopaminergic neurons in the Substantia Nigra pars compacta and terminal dopamine fiber density in the striatum region. Importantly, we also show that viral mediated expression of two other recessive PD-linked familial genes, DJ-1 and Parkin, can protect dopaminergic neurons even in the absence of Pink1. This evidence not only provides strong evidence for the role of endogenous Pink1 in neuronal survival, but also supports a role of DJ-1 and Parkin acting parallel or downstream of endogenous Pink1 to mediate survival in a mammalian in vivo context.

Ellagic Acid Prevents α-Synuclein Spread and Mitigates Toxicity by Enhancing Autophagic Flux in an Animal Model of Parkinson's Disease.

Parkinson's disease (PD) is the second most common neurological disorder, pathologically characterized by loss of dopaminergic neurons in the substantia nigra pars compacta (SNc) as well as the formation of Lewy bodies composed mainly of α-synuclein (α-syn) aggregates. It has been documented that abnormal aggregation of α-syn is one of the major causes of developing PD. In the current study, administration of ellagic acid (EA), a polyphenolic compound (10 mg/kg bodyweight), significantly decreased α-syn spreading and preserved dopaminergic neurons in a male C57BL/6 mouse model of PD. Moreover, EA altered the autophagic flux, suggesting the involvement of a restorative mechanism meditated by EA treatment. Our data support that EA could play a major role in the clearing of toxic α-syn from spreading, in addition to the canonical antioxidative role, and thus preventing dopaminergic neuronal death.

Leucine-Rich Repeat Kinase 2 interacts with Parkin, DJ-1 and PINK-1 in a Drosophila melanogaster model of Parkinson's disease.

Mutations in the LRRK2 gene are the most common genetic cause of familial Parkinson's disease (PD). However, its physiological and pathological functions are unknown. Therefore, we generated several independent Drosophila lines carrying WT or mutant human LRRK2 (mutations in kinase, COR or LRR domains, resp.). Ectopic expression of WT or mutant LRRK2 in dopaminergic neurons caused their significant loss accompanied by complex age-dependent changes in locomotor activity. Overall, the ubiquitous expression of LRRK2 increased lifespan and fertility of the flies. However, these flies were more sensitive to rotenone. LRRK2 expression in the eye exacerbated retinal degeneration. Importantly, in double transgenic flies, various indices of the eye and dopaminergic survival were modified in a complex fashion by a concomitant expression of PINK1, DJ-1 or Parkin. This evidence suggests a genetic interaction between these PD-relevant genes.

Cytoplasmic Pink1 activity protects neurons from dopaminergic neurotoxin MPTP.

PTEN-induced putative kinase 1 (Pink1) is a recently identified gene linked to a recessive form of familial Parkinson's disease (PD). The kinase contains a mitochondrial localization sequence and is reported to reside, at least in part, in mitochondria. However, neither the manner by which the loss of Pink1 contributes to dopamine neuron loss nor its impact on mitochondrial function and relevance to death is clear. Here, we report that depletion of Pink1 by RNAi increased neuronal toxicity induced by MPP(+). Moreover, wild-type Pink1, but not the G309D mutant linked to familial PD or an engineered kinase-dead mutant K219M, protects neurons against MPTP both in vitro and in vivo. Intriguingly, a mutant that contains a deletion of the putative mitochondrial-targeting motif was targeted to the cytoplasm but still provided protection against 1-methyl-4-phenylpyridine (MPP(+))/1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced toxicity. In addition, we also show that endogenous Pink1 is localized to cytosolic as well as mitochondrial fractions. Thus, our findings indicate that Pink1 plays a functional role in the survival of neurons and that cytoplasmic targets, in addition to its other actions in the mitochondria, may be important for this protective effect.

The use of phosphorescence oxygen analyzer to measure the effects of rotenone and 1-methyl-4-phenylpyridinium on striatal cellular respiration in C57BL6 mice.

BACKGROUND: We have previously reported on the use of the phosphorescence oxygen analyzer for measuring spinal cord cellular respiration. This analytical tool is used here to investigate the effects of two inhibitors of NADH:ubiquinone oxidoreductase, rotenone and 1-methyl-4-phenylpyridinium, on cellular respiration in striatal tissue. Both neurotoxins can induce Parkinson's disease-like symptoms, and have been used to study this disease in animals. Our hypothesis is that striatal cellular respiration is a sensitive biomarker for the adverse effects of toxins, and the phosphorescence oxygen analyzer can be used as a screening tool for this purpose. METHODS: Striatal fragments were collected from C57BL6 mice and immersed in Pd phosphor solution [phosphate-buffered saline, 3.0 µM 'Pd(II)-meso-tetra (sulfophenyl) tetrabenzoporphyrin' and 0.5% fat-free albumin, with and without 5.0 mM glucose]. The sample was transferred to a glass vial containing 2-mL Pd phosphor solution. The vial was sealed from air and placed in the instrument that measures dissolved oxygen as function of time. Immunoblots of the studied tissue were positive for the dopamine neuronal cell biomarker tyrosine hydroxylase. RESULTS: Striatal oxygen consumption was linear with time, exhibiting zero-order kinetics of oxygen reduction by cytochrome oxidase. Cyanide sensitive respiration was ≥90%, confirming oxygen was reduced by cytochrome oxidase. The rate of respiration increased by ~2-fold in the presence of glucose. Striatal oxygen consumption in the presence of rotenone or 1-methyl-4-phenylpyridinium was exponential, demonstrating impaired respiration. CONCLUSION: Striatal cellular mitochondrial oxygen consumption was impaired by the studied inhibitors of complex I of the respiratory chain. This effect is expected to deplete NAD+ (oxidized nicotinamide adenine dinucleotide), a principle driver of glycolysis. In vivo studies are required to determine if these toxin-induced metabolic derangements contribute to the development of sporadic Parkinson's disease. This analytic tool can be used to screen environmental toxins for their in vitro effects on the striatum.

Dose-related biphasic effect of the Parkinson's disease neurotoxin MPTP, on the spread, accumulation, and toxicity of α-synuclein.

BACKGROUND: Parkinson's disease (PD), the second most common progressive neurodegenerative disorder, is characterized by the abnormal accumulation of intraneuronal inclusions enriched in aggregated α-synuclein (α-syn), known as Lewy bodies (LBs) and Lewy neurites (LNs), and significant loss of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNpc) of the brain. Recent evidence suggests that the intrastriatal inoculation of α-syn preformed fibrils (PFF) in mice brain triggers endogenous α-syn in interconnected brain regions. 1-methyl, 4-phenyl, 1,2,3,6 tetrahydropyridine (MPTP), a mitochondrial neurotoxin, has been used previously to generate a PD mouse model. However, the common methods of MPTP exposure do not induce LB or α-syn aggregation in mice. In the present study, we evaluated the effect of different doses of MPTP (10 mg/kg.b.wt and/or 25 mg/kg.b.wt) on the spread, accumulation, and toxicity of endogenous α-syn in mice administered an intrastriatal injection of human α-syn PFF. METHODS: We inoculated human WT α-syn PFF in mouse striatum. At 6 weeks post PFF injection, we challenged the animal with two different doses of MPTP (10 mg/kg.b.wt and 25 mg/kg.b.wt) once daily for five consecutive days. At 2 weeks from the start of the MPTP regimen, we collected the mice brain and performed immunohistochemical analysis, and Rotarod test to assess motor coordination and muscle strength before and after MPTP injection. RESULTS: A single injection of human WT α-syn PFF in the mice striatum induced the propagation of α-syn, occurring as phosphorylated α-synuclein (pS129), towards the SNpc, within a very short time. Injection of a low dose of MPTP (10 mg/kg.b.wt) at 6 weeks post α-syn PFF inoculation further enhanced the spread, whereas a high dose of MPTP (25 mg/kg.b.wt.) reduced the spread. Majority of the accumulated α-syn were proteinase K resistant, as recognized using a conformation-specific α-syn antibody. Injection of α-syn PFF alone caused 12 % reduction in the number of tyrosine hydroxylase positive neurons while α-syn PFF + a low dose of MPTP caused 33 % reduction (loss), compared to the control mice injected with saline. This combination also reduced the motor coordination. Interestingly, a low dose of MPTP alone did not cause any significant reduction in the number of tyrosine hydroxylase positive neurons compared to saline treatment. Animals that received α-syn PFF and a high dose of MPTP showed massive activation of glial cells and decreased spread of α-syn, majority of which were detected in the nucleus. CONCLUSION: Our results suggest that a combination of human WT α-syn PFF and a low dose of MPTP increases the pathological conversion and propagation of endogenous α-syn, and neurodegeneration, within a very short time. Our model can be used to study the mechanisms of α-syn propagation and screen for potential drugs against PD.