Inflammasome inhibition protects dopaminergic neurons from α-synuclein pathology in a model of progressive Parkinson's disease.

Neuroinflammation has been suggested as a pathogenetic mechanism contributing to Parkinson's disease (PD). However, anti-inflammatory treatment strategies have not yet been established as a therapeutic option for PD patients. We have used a human α-synuclein mouse model of progressive PD to examine the anti-inflammatory and neuroprotective effects of inflammasome inhibition on dopaminergic (DA) neurons in the substantia nigra (SN). As the NLRP3 (NOD-, LRR- and pyrin domain-containing 3)-inflammasome is a core interface for both adaptive and innate inflammation and is also highly druggable, we investigated the implications of its inhibition. Repeat administration of MCC950, an inhibitor of NLRP3, in a PD model with ongoing pathology reduced CD4+ and CD8+ T cell infiltration into the SN. Furthermore, the anti-inflammasome treatment mitigated microglial activation and modified the aggregation of α-synuclein protein in DA neurons. MCC950-treated mice showed significantly less neurodegeneration of DA neurons and a reduction in PD-related motor behavior. In summary, early inflammasome inhibition can reduce neuroinflammation and prevent DA cell death in an α-synuclein mouse model for progressive PD.

Expansion of regulatory T cells by CD28 superagonistic antibodies attenuates neurodegeneration in A53T-α-synuclein Parkinson's disease mice.

BACKGROUND: Regulatory CD4+CD25+FoxP3+ T cells (Treg) are a subgroup of T lymphocytes involved in maintaining immune balance. Disturbance of Treg number and impaired suppressive function of Treg correlate with Parkinson's disease severity. Superagonistic anti-CD28 monoclonal antibodies (CD28SA) activate Treg and cause their expansion to create an anti-inflammatory environment. METHODS: Using the AAV1/2-A53T-α-synuclein Parkinson's disease mouse model that overexpresses the pathogenic human A53T-α-synuclein (hαSyn) variant in dopaminergic neurons of the substantia nigra, we assessed the neuroprotective and disease-modifying efficacy of a single intraperitoneal dose of CD28SA given at an early disease stage. RESULTS: CD28SA led to Treg expansion 3 days after delivery in hαSyn Parkinson's disease mice. At this timepoint, an early pro-inflammation was observed in vehicle-treated hαSyn Parkinson's disease mice with elevated percentages of CD8+CD69+ T cells in brain and increased levels of interleukin-2 (IL-2) in the cervical lymph nodes and spleen. These immune responses were suppressed in CD28SA-treated hαSyn Parkinson's disease mice. Early treatment with CD28SA attenuated dopaminergic neurodegeneration in the SN of hαSyn Parkinson's disease mice accompanied with reduced brain numbers of activated CD4+, CD8+ T cells and CD11b+ microglia observed at the late disease-stage 10 weeks after AAV injection. In contrast, a later treatment 4 weeks after AAV delivery failed to reduce dopaminergic neurodegeneration. CONCLUSIONS: Our data indicate that immune modulation by Treg expansion at a timepoint of overt inflammation is effective for treatment of hαSyn Parkinson's disease mice and suggest that the concept of early immune therapy could pose a disease-modifying option for Parkinson's disease patients.

Animal models of α-synucleinopathy for Parkinson disease drug development.

A major challenge in Parkinson disease (PD) will be to turn an emerging and expanding pipeline of novel disease-modifying candidate compounds into therapeutics. Novel targets need in vivo validation, and candidate therapeutics require appropriate preclinical platforms on which to define potential efficacy and target engagement before advancement to clinical development. We propose that α-synuclein (α-syn)-based mammalian models will be crucial for this process. Here, we review α-syn transgenic mouse models, viral vector models of α-syn overexpression and models of 'prion-like' spread of α-syn, and describe how each of these model types may contribute to PD drug discovery. We conclude by presenting our opinion on how to use a combination of these models through the late-stage preclinical, proof-of-principle investigation of novel therapeutics.

Neurodegeneration by α-synuclein-specific T cells in AAV-A53T-α-synuclein Parkinson's disease mice.

BACKGROUND: Antigen-specific neuroinflammation and neurodegeneration are characteristic for neuroimmunological diseases. In Parkinson's disease (PD) pathogenesis, α-synuclein is a known culprit. Evidence for α-synuclein-specific T cell responses was recently obtained in PD. Still, a causative link between these α-synuclein responses and dopaminergic neurodegeneration had been lacking. We thus addressed the functional relevance of α-synuclein-specific immune responses in PD in a mouse model. METHODS: We utilized a mouse model of PD in which an Adeno-associated Vector 1/2 serotype (AAV1/2) expressing human mutated A53T-α-Synuclein was stereotactically injected into the substantia nigra (SN) of either wildtype C57BL/6 or Recombination-activating gene 1 (RAG1)-/- mice. Brain, spleen, and lymph node tissues from different time points following injection were then analyzed via FACS, cytokine bead assay, immunohistochemistry and RNA-sequencing to determine the role of T cells and inflammation in this model. Bone marrow transfer from either CD4+/CD8-, CD4-/CD8+, or CD4+/CD8+ (JHD-/-) mice into the RAG-1-/- mice was also employed. In addition to the in vivo studies, a newly developed A53T-α-synuclein-expressing neuronal cell culture/immune cell assay was utilized. RESULTS: AAV-based overexpression of pathogenic human A53T-α-synuclein in dopaminergic neurons of the SN stimulated T cell infiltration. RNA-sequencing of immune cells from PD mouse brains confirmed a pro-inflammatory gene profile. T cell responses were directed against A53T-α-synuclein-peptides in the vicinity of position 53 (68-78) and surrounding the pathogenically relevant S129 (120-134). T cells were required for α-synuclein-induced neurodegeneration in vivo and in vitro, while B cell deficiency did not protect from dopaminergic neurodegeneration. CONCLUSIONS: Using T cell and/or B cell deficient mice and a newly developed A53T-α-synuclein-expressing neuronal cell culture/immune cell assay, we confirmed in vivo and in vitro that pathogenic α-synuclein peptide-specific T cell responses can cause dopaminergic neurodegeneration and thereby contribute to PD-like pathology.

Propagated α-synucleinopathy recapitulates REM sleep behaviour disorder followed by parkinsonian phenotypes in mice.

Idiopathic rapid eye movement sleep behaviour disorder (RBD) is now recognized as an early manifestation of α-synucleinopathies. Increasing experimental studies demonstrate that manipulative lesion or inactivation of the neurons within the sublaterodorsal tegmental nucleus (also known as the subcoeruleus nucleus in humans) can induce RBD-like behaviours in animals. As current RBD animal models are not established on the basis of α-synucleinopathy, they do not represent the pathological substrate of idiopathic RBD and thus cannot model the phenoconversion to Parkinson's disease. The purpose of this study was therefore to establish an α-synucleinopathy-based RBD animal model with the potential to convert to parkinsonian disorder. To this end, we first determined the functional neuroanatomical location of the sublaterodorsal tegmental nucleus in wild-type C57BL/6J mice and then validated its function by recapitulating RBD-like behaviours based on this determined nucleus. Next, we injected preformed α-synuclein fibrils into the sublaterodorsal tegmental nucleus and performed regular polysomnographic recordings and parkinsonian behavioural and histopathological studies in these mice. As a result, we recapitulated RBD-like behaviours in the mice and further showed that the α-synucleinopathy and neuron degeneration identified within the sublaterodorsal tegmental nucleus acted as the neuropathological substrates. Subsequent parkinsonian behavioural studies indicated that the α-synucleinopathy-based RBD mouse model were not stationary, but could further progress to display parkinsonian locomotor dysfunction, depression-like disorder, olfactory dysfunction and gastrointestinal dysmotility. Corresponding to that, we determined α-synuclein pathology in the substantia nigra pars compacta, olfactory bulb, enteral neuroplexus and dorsal motor nucleus of vagus nerve, which could underlie the parkinsonian manifestations in mice. In conclusion, we established a novel α-synucleinopathy-based RBD mouse model and further demonstrated the phenoconversion of RBD to Parkinson's disease in this animal model.

Beneficial Effects of Trehalose on Striatal Dopaminergic Deficits in Rodent and Primate Models of Synucleinopathy in Parkinson's Disease.

Disease modification in Parkinson's disease (PD) is an unmet medical need. In the current study, we evaluated trehalose, a safe and well-tolerated disaccharide that has previously demonstrated efficacy in rodent models of neurodegenerative diseases, including PD. In a rat model of PD, based on delivery of adeno-associated virus serotype 1/2 containing the mutated human A53T α-synuclein gene (AAV1/2-hourA53T-aSyn) to the substantia nigra (SN), we showed that rats administered trehalose (2.67 g/kg per day, by mouth) for 6 weeks had less forelimb asymmetry (93% reduction) and higher striatal dopamine (54% increase) compared with rats receiving vehicle. In a pharmacokinetic study, we determined that efficacy was associated with plasma C max of 8900 ng/ml and area under the curve from time 0 to infinity (AUC0-inf) of 11,136 hour⋅ng/ml. We then showed, in macaques, that oral administration of trehalose (2.67 g/kg per day) produced plasma exposures of similar magnitude, with plasma C max of 10,918 ng/ml and AUC0-inf of 27,445 hour⋅ng/ml. In a macaque model of PD, also based on delivery of AAV1/2-hourA53T-aSyn to the SN, trehalose (2.67 g/kg per day, by mouth), administered for 142 days, produced higher striatal dopamine (by 39%) and dopamine transporter levels (by 50%), compared with macaques receiving vehicle. In neither model did trehalose treatment prevent loss of tyrosine hydroxylase (TH) positive (TH+ve) cells in the SN or alter α-synuclein levels in the striatum. These studies demonstrated that trehalose reduces striatal dopaminergic deficits in a rodent and macaque model of synucleinopathy in PD. Furthermore, we have determined the pharmacokinetic parameters associated with efficacy, and thus defined exposures to target in future clinical trials.

Subthalamic nucleus deep brain stimulation is neuroprotective in the A53T α-synuclein Parkinson's disease rat model.

OBJECTIVE: Deep brain stimulation (DBS) of the subthalamic nucleus (STN) is a highly effective symptomatic therapy for motor deficits in Parkinson's disease (PD). An additional, disease-modifying effect has been suspected from studies in toxin-based PD animal models, but these models do not reflect the molecular pathology and progressive nature of PD that would be required to evaluate a disease-modifying action. Defining a disease-modifying effect could radically change the way in which DBS is used in PD. METHODS: We applied STN-DBS in an adeno-associated virus (AAV) 1/2-driven human mutated A53T α-synuclein (aSyn)-overexpressing PD rat model (AAV1/2-A53T-aSyn). Rats were injected unilaterally, in the substantia nigra (SN), with AAV1/2-A53T-aSyn or control vector. Three weeks later, after behavioral and nigrostriatal dopaminergic deficits had developed, rats underwent STN-DBS electrode implantation ipsilateral to the vector-injected SN. Stimulation lasted for 3 weeks. Control groups remained OFF stimulation. Animals were sacrificed at 6 weeks. RESULTS: Motor performance in the single pellet reaching task was impaired in the AAV1/2-A53T-aSyn-injected stim-OFF group, 6 weeks after AAV1/2-A53T-aSyn injection, compared to preoperative levels (-82%; p < 0.01). Deficits were reversed in AAV1/2-A53T-aSyn, stim-ON rats after 3 weeks of active stimulation, compared to the AAV1/2-A53T-aSyn stim-OFF rats (an increase of ∼400%; p < 0.05), demonstrating a beneficial effect of DBS. This motor improvement was maintained when the stimulation was turned off and was accompanied by a higher number of tyrosine hydroxylase+ SN neurons (increase of ∼29%), compared to AAV1/2-A53T-aSyn stim-OFF rats (p < 0.05). INTERPRETATION: Our data support the putative neuroprotective and disease-modifying effect of STN-DBS in a mechanistically relevant model of PD. Ann Neurol 2017;81:825-836.

Sirtuin 3 rescues neurons through the stabilisation of mitochondrial biogenetics in the virally-expressing mutant α-synuclein rat model of parkinsonism.

Parkinson's disease (PD) is a neurodegenerative movement disorder, which affects approximately 1-2% of the population over 60years of age. Current treatments for PD are symptomatic, and the pathology of the disease continues to progresses over time until palliative care is required. Mitochondria are key players in the pathology of PD. Genetic and post mortem studies have shown a large number of mitochondrial abnormalities in the substantia nigra pars compacta (SNc) of the parkinsonian brain. Furthermore, physiologically, mitochondria of nigral neurons are constantly under unusually high levels of metabolic stress because of the excitatory properties and architecture of these neurons. The protein deacetylase, Sirtuin 3 (SIRT3) reduces the impact subcellular stresses on mitochondria, by stabilising the electron transport chain (ETC), and reducing oxidative stress. We hypothesised that viral overexpression of myc-tagged SIRT3 (SIRT3-myc) would slow the progression of PD pathology, by enhancing the functional capacity of mitochondria. For this study, SIRT3-myc was administered both before and after viral induction of parkinsonism with the AAV-expressing mutant (A53T) α-synuclein. SIRT3-myc corrected behavioural abnormalities, as well as changes in striatal dopamine turnover. SIRT3-myc also prevented degeneration of dopaminergic neurons in the SNc. These effects were apparent, even when SIRT3-myc was transduced after the induction of parkinsonism, at a time point when cell stress and behavioural abnormalities are already observed. Furthermore, in an isolated mitochondria nigral homogenate prepared from parkinsonian SIRT3-myc infected animals, SIRT3 targeted the mitochondria, to reduce protein acetylation levels. Our results demonstrate that transduction of SIRT3 has the potential to be an effective disease-modifying strategy for patients with PD. This study also provides potential mechanisms for the protective effects of SIRT3-myc.

The pharmacology of L-DOPA-induced dyskinesia in Parkinson's disease.

L-3,4-Dihydroxyphenylalanine (L-DOPA) remains the most effective symptomatic treatment of Parkinson's disease (PD). However, long-term administration of L-DOPA is marred by the emergence of abnormal involuntary movements, i.e., L-DOPA-induced dyskinesia (LID). Years of intensive research have yielded significant progress in the quest to elucidate the mechanisms leading to the development and expression of dyskinesia and maintenance of the dyskinetic state, but the search for a complete understanding is still ongoing. Herein, we summarize the current knowledge of the pharmacology of LID in PD. Specifically, we review evidence gathered from postmortem and pharmacological studies, both preclinical and clinical, and discuss the involvement of dopaminergic and nondopaminergic systems, including glutamatergic, opioid, serotonergic, γ-aminobutyric acid (GABA)-ergic, adenosine, cannabinoid, adrenergic, histaminergic, and cholinergic systems. Moreover, we discuss changes occurring in transcription factors, intracellular signaling, and gene expression in the dyskinetic phenotype. Inasmuch as a multitude of neurotransmitters and receptors play a role in the etiology of dyskinesia, we propose that to optimally alleviate this motor complication, it may be necessary to develop combined treatment approaches that will target simultaneously more than one neurotransmitter system. This could be achieved via three ways as follows: 1) by developing compounds that will interact simultaneously to a multitude of receptors with the required agonist/antagonist effect at each target, 2) by targeting intracellular signaling cascades where the signals mediated by multiple receptors converge, and/or 3) to regulate gene expression in a manner that has effects on signaling by multiple pathways.

Reproducibility of a Parkinsonism-related metabolic brain network in non-human primates: A descriptive pilot study with FDG PET.

BACKGROUND: We have previously defined a parkinsonism-related metabolic brain network in rhesus macaques using a high-resolution research positron emission tomography camera. This brief article reports a descriptive pilot study to assess the reproducibility of network activity and regional glucose metabolism in independent parkinsonian macaques using a clinical positron emission tomography/CT camera. METHODS: [(18)F]fluorodeoxyglucose PET scans were acquired longitudinally over 3 months in three drug-naïve parkinsonian and three healthy control cynomolgus macaques. Group difference and test-retest stability in network activity and regional glucose metabolism were evaluated graphically, using all brain images from these macaques. RESULTS: Comparing the parkinsonian macaques with the controls, network activity was elevated and remained stable over 3 months. Normalized glucose metabolism increased in putamen/globus pallidus and sensorimotor regions but decreased in posterior parietal cortices. CONCLUSIONS: Parkinsonism-related network activity can be reliably quantified in different macaques with a clinical positron emission tomography/CT scanner and is reproducible over a period typically employed in preclinical intervention studies. This measure can be a useful biomarker of disease process or drug effects in primate models of Parkinson's disease.

L-745,870 reduces the expression of abnormal involuntary movements in the 6-OHDA-lesioned rat.

L-3,4-Dihydroxyphenylalanine (L-DOPA) is the most effective treatment for Parkinson's disease, but chronic administration is complicated by the development of dyskinesia. We have previously demonstrated that the dopamine D4 receptor antagonist L-745,870 reduces the severity of L-DOPA-induced dyskinesia in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned macaque without compromising L-DOPA antiparkinsonian benefits. In the current study, we have addressed the effects of L-745,870 on the expression of L-DOPA-induced abnormal involuntary movements (AIMs) in the 6-hydroxydopamine-lesioned rat. Rats were primed with repeated L-DOPA administration, after which acute challenges of L-DOPA/L-745,870 (vehicle, 0.1, 0.3 and 1 mg/kg) were administered, and AIMs were assessed. Rotarod performance and AIMs were assessed. In L-DOPA-primed rats, L-745,870 (1 mg/kg, but not lower doses) alleviated previously established AIMs (by 84%, P<0.001). Whereas rotarod performance was significantly improved by L-DOPA/vehicle treatment, L-DOPA/L-745,870 failed to improve rotarod performance (P>0.05), suggesting that, in contrast to the MPTP-lesioned macaque, L-745,870 reduces L-DOPA antiparkinsonian benefit in the rat model. Overall, these data suggest that L-745,870 may have a narrow therapeutic window as an antidyskinetic agent in advanced Parkinson's disease.

Use of catechol-O-methyltransferase inhibition to minimize L-3,4-dihydroxyphenylalanine-induced dyskinesia in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-lesioned macaque.

L-3,4-dihydroxyphenylalanine (L-DOPA)-induced dyskinesia is a complication of dopaminergic treatment in Parkinson's disease. Lowering the L-DOPA dose reduces dyskinesia but also reduces the antiparkinsonian benefit. A therapy that could enhance the antiparkinsonian action of low-dose L-DOPA (LDl) without exacerbating dyskinesia would thus be of considerable therapeutic benefit. This study assessed whether catechol-O-methyltransferase (COMT) inhibition, as an add-on to LDl, might be a means to achieve this goal. Cynomolgus macaques were administered 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. Dyskinesia was established by chronic treatment with L-DOPA. Two doses of L-DOPA were identified - high-dose L-DOPA (LDh), which provided good antiparkinsonian benefit but was compromised by disabling dyskinesia, and LDl, which was sub-threshold for providing significant antiparkinsonian benefit, without dyskinesia. LDh and LDl were administered in acute challenges in combination with vehicle and, for LDl, with the COMT inhibitor entacapone (5, 15 and 45 mg/kg). The duration of antiparkinsonian benefit (ON-time), parkinsonism and dyskinesia were determined. The ON-time after LDh was ∼170 min and the ON-time after LDl alone (∼98 min) was not significantly different to vehicle (∼37 min). In combination with LDl, entacapone significantly increased the ON-time (5, 15 and 45 mg/kg being ∼123, ∼148 and ∼180 min, respectively). The ON-time after LDl/entacapone 45 mg/kg was not different to that after LDh. However, whereas the percentage ON-time that was compromised by disabling dyskinesia was ∼56% with LDh, it was only ∼31% with LDl/entacapone 45 mg/kg. In addition to the well-recognized action of COMT inhibition to reduce wearing-OFF, the data presented suggest that COMT inhibition in combination with low doses of L-DOPA has potential as a strategy to alleviate dyskinesia.

Brain-to-gut trafficking of alpha-synuclein by CD11c+ cells in a mouse model of Parkinson's disease.

Inflammation in the brain and gut is a critical component of several neurological diseases, such as Parkinson's disease (PD). One trigger of the immune system in PD is aggregation of the pre-synaptic protein, α-synuclein (αSyn). Understanding the mechanism of propagation of αSyn aggregates is essential to developing disease-modifying therapeutics. Using a brain-first mouse model of PD, we demonstrate αSyn trafficking from the brain to the ileum of male mice. Immunohistochemistry revealed that the ileal αSyn aggregations are contained within CD11c+ cells. Using single-cell RNA sequencing, we demonstrate that ileal CD11c+ cells are microglia-like and the same subtype of cells is activated in the brain and ileum of PD mice. Moreover, by utilizing mice expressing the photo-convertible protein, Dendra2, we show that CD11c+ cells traffic from the brain to the ileum. Together these data provide a mechanism of αSyn trafficking between the brain and gut.

Characterization of 3,4-methylenedioxymethamphetamine (MDMA) enantiomers in vitro and in the MPTP-lesioned primate: R-MDMA reduces severity of dyskinesia, whereas S-MDMA extends duration of ON-time.

l-3,4-dihydroxyphenylalanine (l-DOPA) is the most effective treatment for Parkinson's disease, but long-term l-DOPA administration is marred by the emergence of motor complications, namely, dyskinesia and a shortening of antiparkinsonian benefit (wearing-OFF). 3,4-methylenedioxymethamphetamine (MDMA) is unique in that it exerts antidyskinetic effects and may enhance antiparkinsonian actions of l-DOPA. MDMA is composed of two enantiomers with different pharmacological profiles; here, we describe a novel enantiospecific synthesis of the two enantiomers and expand on the previous characterization of their pharmacology. R-MDMA (rectus-MDMA) is relatively selective for 5-HT(2A) receptors, whereas S-MDMA (sinister-MDMA) inhibits both serotonin (SERT) and dopamine transporters (DAT; SERT/DAT ratio of 10 to 1). R- or S-MDMA (1, 3, and 10 mg/kg, s.c.) was administered in combination with l-DOPA (15 mg/kg, s.c.) to six female common marmosets (Callithrix jacchus) rendered parkinsonian by MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) administration. Motor disability, including parkinsonism and dyskinesia, and duration of antiparkinsonian benefit (ON-time) were evaluated. After the administration of R-MDMA (3 and 10 mg/kg), the severity of peak-dose dyskinesia was decreased (by 33 and 46%, respectively; p < 0.05); although total ON-time was unchanged (approximately 220 min), the duration of ON-time with disabling dyskinesia was decreased by 90 min when compared to l-DOPA alone (69% reduction; p < 0.05). S-MDMA (1 mg/kg) increased the total ON-time by 88 min compared to l-DOPA alone (34% increase; p < 0.05), though dyskinesia were exacerbated. These data suggest that racemic MDMA exerts simultaneous effects, reducing dyskinesia and extending ON-time, by 5-HT(2A) antagonism and SERT-selective mixed monoamine uptake inhibition, which arise from its R and S enantiomers, respectively.

L-745,870 reduces L-DOPA-induced dyskinesia in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-lesioned macaque model of Parkinson's disease.

L-DOPA-induced dyskinesia remains an unmet challenge in the treatment of Parkinson's disease (PD). Here, we investigate the potential antidyskinetic efficacy of 3-([4-(4-chlorophenyl)piperazin-1-yl]methyl)-1H-pyrrolo[2,3-b]pyridine (L-745,870), a potent and selective dopamine D(4) receptor antagonist with a good toxicology profile and an excellent safety and tolerability record in phase I/II clinical studies, for non-PD indications. Six macaques were rendered parkinsonian by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine administration. After induction of stable and marked dyskinesia, animals were administered acute challenges of L-745,870 in combination with L-DOPA. To guarantee D(4) selectivity at the doses used in the study, we determined the plasma, cerebrospinal fluid, and brain levels of L-745,870. Coadministration of L-745,870 (1 mg/kg) and L-DOPA significantly reduced the severity of dyskinesia, by up to 59%, in comparison with L-DOPA alone (P < 0.01). L-745,870 had no effect on the duration of antiparkinsonian benefit (ON-time) (P > 0.05). However, L-745,870 (1 mg/kg) significantly increased the duration of ON-time without disabling dyskinesia (+204%; P < 0.001) and decreased duration of ON-time with disabling dyskinesia compared with L-DOPA alone (-56%; P < 0.01). Brain levels of L-745,870 (∼600 ng/g) were within the range at which L-745,870 provides selective D(4) receptor antagonism. Plasma levels were comparable with those demonstrated to be well tolerated in human studies. These data suggest that selective D(4) receptor antagonists represent a potential therapeutic approach for L-DOPA-induced dyskinesia. It is noteworthy that L-745,870 has already undergone significant clinical development, has an excellent profile for a therapeutic candidate, and could be advanced rapidly to phase IIa clinical studies for dyskinesia in PD.

Functional enhancement and protection of dopaminergic terminals by RAB3B overexpression.

In Parkinson's disease (PD), dopaminergic (DA) neurons in the substantia nigra (SN, A9) are particularly vulnerable, compared to adjacent DA neurons within the ventral tegmental area (VTA, A10). Here, we show that in rat and human, one RAB3 isoform, RAB3B, has higher expression levels in A10 compared to A9 neurons. RAB3 is a monomeric GTPase protein that is highly enriched in synaptic vesicles and is involved in synaptic vesicle trafficking and synaptic transmission, disturbances of which have been implicated in several neurodegenerative diseases, including PD. These findings prompted us to further investigate the biology and neuroprotective capacity of RAB3B both in vitro and in vivo. RAB3B overexpression in human dopaminergic BE (2)-M17 cells increased neurotransmitter content, [(3)H] dopamine uptake, and levels of presynaptic proteins. AAV-mediated RAB3B overexpression in A9 DA neurons of the rat SN increased striatal dopamine content, number and size of synaptic vesicles, and levels of the presynaptic proteins, confirming in vitro findings. Measurement of extracellular DOPAC, a dopamine metabolite, following l-DOPA injection supported a role for RAB3B in enhancing the dopamine storage capacity of synaptic terminals. RAB3B overexpression in BE (2)-M17 cells was protective against toxins that simulate aspects of PD in vitro, including an oxidative stressor 6-hydroxydopamine (6-OHDA) and a proteasome inhibitor MG-132. Furthermore, RAB3B overexpression in rat SN both protected A9 DA neurons and resulted in behavioral improvement in a 6-OHDA retrograde lesion model of PD. These results suggest that RAB3B improves dopamine handling and storage capacity at presynaptic terminals, and confers protection to vulnerable DA neurons.

Temporal, spatial and molecular pattern of dopaminergic neurodegeneration in the AAV-A53T α-synuclein rat model of Parkinson's disease.

Degeneration of the nigrostriatal tract is a neuropathological hallmark of Parkinson's disease (PD). A differential intraneuronal vulnerability of dopaminergic neurons within the substantia nigra (SN) has been suggested, starting as an axonopathy followed by neuronal cell loss that is accompanied with motor deficits. To date, there is no therapy available to delay or halt this neurodegeneration. Nuclear factor (erythroid-derived 2)-like-2 factor (Nrf2) and histone deacetylase 1 (HDAC1) are crucial molecular regulators that undergo nucleo-cytoplasmic shuttling and are involved in regulation of axonal and perikarya degeneration of neurons under various pathologic conditions. We here aimed to analyze the time course of dopaminergic neurodegeneration in an AAV PD rat model overexpressing human mutated A53T α-synuclein (haSyn), differentially correlate striatal terminal and SN perikarya loss with behavioral deficits and investigate if nucleo-cytoplasmic Nrf2 and HDAC1 expression are altered in dopaminergic perikarya of the haSyn PD rat model. We observed impaired motor performance in haSyn PD rats assessed by the single pellet reaching task at four- and six-weeks post AAV injection (P < 0.05 each). However, only striatal terminal loss correlated significantly with motor deficits in haSyn PD rats, indicating that parkinsonian motor features reflect the striatal dopaminergic denervation, but cannot be taken as an indirect measure of neurodegeneration per se. Immunofluorescence staining demonstrated an upregulation of HDAC1 in the dopaminergic cell nucleus (P < 0.05) while no changes were observed for Nrf2. These data suggest a critical functional role of the axonopathy on motor behavior in haSyn PD rats and mechanistically point towards an impaired nucleo-cytoplasmic translocation of HDAC1 and thus a potential role of disturbed histone acetylation in neurodegeneration.

Enhanced firing of locus coeruleus neurons and SK channel dysfunction are conserved in distinct models of prodromal Parkinson's disease.

Parkinson's disease (PD) is clinically defined by the presence of the cardinal motor symptoms, which are associated with a loss of dopaminergic nigrostriatal neurons in the substantia nigra pars compacta (SNpc). While SNpc neurons serve as the prototypical cell-type to study cellular vulnerability in PD, there is an unmet need to extent our efforts to other neurons at risk. The noradrenergic locus coeruleus (LC) represents one of the first brain structures affected in Parkinson's disease (PD) and plays not only a crucial role for the evolving non-motor symptomatology, but it is also believed to contribute to disease progression by efferent noradrenergic deficiency. Therefore, we sought to characterize the electrophysiological properties of LC neurons in two distinct PD models: (1) in an in vivo mouse model of focal α-synuclein overexpression; and (2) in an in vitro rotenone-induced PD model. Despite the fundamental differences of these two PD models, α-synuclein overexpression as well as rotenone exposure led to an accelerated autonomous pacemaker frequency of LC neurons, accompanied by severe alterations of the afterhyperpolarization amplitude. On the mechanistic side, we suggest that Ca2+-activated K+ (SK) channels are mediators of the increased LC neuronal excitability, as pharmacological activation of these channels is sufficient to prevent increased LC pacemaking and subsequent neuronal loss in the LC following in vitro rotenone exposure. These findings suggest a role of SK channels in PD by linking α-synuclein- and rotenone-induced changes in LC firing rate to SK channel dysfunction.