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ABSTRACT: α-Synuclein is an abundant presynaptic protein and a primary component of Lewy bodies in Parkinson disease. Although its pathogenic role remains unclear, in healthy nerve terminals α-synuclein undergoes a cycle of membrane binding and dissociation. An α-synuclein binding assay was used to screen for vesicle proteins involved in α-synuclein membrane interactions and showed that antibodies directed to Ras-related GTPase Rab3a and its chaperone RabGDI abrogated α-synuclein membrane binding. Biochemical analyses including density gradient sedimentation and co-immunoprecipitation suggested that α-synuclein interacts with membrane associated GTP-bound Rab3a, but not to cytosolic GDP-Rab3a. Accumulation of membrane-bound α-synuclein was induced by the expression of a GTPase-deficient Rab3a mutant, by a dominant-negative GDI mutant unable to recycle Rab3a off membranes, and by Hsp90 inhibitors, radicicol and geldanamycin, which are known to inhibit Rab3a dissociation from membranes. Thus, all treatments that inhibited Rab3a recycling also increased α-synuclein sequestration on intracellular membranes. Our results suggest that membrane-bound GTP-Rab3a stabilizes α-synuclein on synaptic vesicles and that the GDI/Hsp90 complex that controls Rab3a membrane dissociation also regulates α-synuclein dissociation during synaptic activity.
Journal of Biological Chemistry 01/2013; · 4.77 Impact Factor
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ABSTRACT: Visual hallucinations are common in advanced Parkinson's disease (PD). The pathophysiology of visual hallucinations may involve enhanced serotonergic neurotransmission. The atypical antipsychotics clozapine and quetiapine, which have affinity for 5-HT(2A) and 5-HT(1A) receptors, are effective against visual hallucinations in PD. 5-HT(2A) receptors are increased in ventral visual pathways in PD patients with visual hallucinations, and we hypothesized that 5-HT(1A) receptors were also involved in visual hallucinations in PD. Autoradiographic binding using [(3) H]-WAY-100,635 and NAN-190 was performed in brain sections from 6 PD patients with visual hallucinations, 6 PD patients without visual hallucinations, and 5 age-matched controls. All PD subjects had been treated with L-dopa. Brain areas studied were the orbitofrontal, inferolateral temporal, and motor cortices, as well as the striatum, globus pallidus, substantia nigra, and thalamus. 5-HT(1A) -binding levels were dramatically increased in the ventral visual pathways of all PD patients compared with controls (0 vs 11 and 0 vs 100 nmol/mg, respectively; both P < .05). There was no significant difference in 5-HT(1A) -binding levels in PD patients with visual hallucinations compared with PD patients without visual hallucinations or with controls in any of the brain areas studied (P > .05). Gross abnormalities in 5-HT(1A) levels in ventral visual areas occurred in all PD patients exposed to L-dopa. However, as there was no difference in 5-HT(1A) -binding levels between hallucinators and nonhallucinators, alterations in 5-HT(1A) receptor levels may not contribute specifically to visual hallucinations in PD. However, the discrete anatomical distribution of rises to the ventral visual areas suggests some role in predisposing to visual hallucinations.
Movement Disorders 03/2012; 27(6):735-42. · 4.51 Impact Factor
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ABSTRACT: In the healthy brain, less than 5% of α-synuclein (α-syn) is phosphorylated at serine 129 (Ser(P)-129). However, within Parkinson
disease (PD) Lewy bodies, 89% of α-syn is Ser(P)-129. The effects of Ser(P)-129 modification on α-syn distribution and solubility
are poorly understood. As α-syn normally exists in both membrane-bound and cytosolic compartments, we examined the binding
and dissociation of Ser(P)-129 α-syn and analyzed the effects of manipulating Ser(P)-129 levels on α-syn membrane interactions
using synaptosomal membranes and neural precursor cells from α-syn-deficient mice or transgenic mice expressing human α-syn.
We first evaluated the recovery of the Ser(P)-129 epitope following either α-syn membrane binding or dissociation. We demonstrate
a rapid turnover of Ser(P)-129 during both binding to and dissociation from synaptic membranes. Although the membrane binding
of WT α-syn was insensitive to modulation of Ser(P)-129 levels by multiple strategies (the use of phosphomimic S129D and nonphosphorylated
S129A α-syn mutants; by enzymatic dephosphorylation of Ser(P)-129 or proteasome inhibitor-induced elevation in Ser(P)-129;
or by inhibition or stable overexpression of PLK2), PD mutant Ser(P)-129 α-syn showed a preferential membrane association
compared with WT Ser(P)-129 α-syn. Collectively, these data suggest that phosphorylation at Ser-129 is dynamic and that the
subcellular distribution of α-syn bearing PD-linked mutations, A30P or A53T, is influenced by the phosphorylation state of
Ser-129.
Journal of Biological Chemistry 10/2011; 286(41):35863-35873. · 4.77 Impact Factor
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ABSTRACT: In the healthy brain, less than 5% of α-synuclein (α-syn) is phosphorylated at serine 129 (Ser(P)-129). However, within Parkinson disease (PD) Lewy bodies, 89% of α-syn is Ser(P)-129. The effects of Ser(P)-129 modification on α-syn distribution and solubility are poorly understood. As α-syn normally exists in both membrane-bound and cytosolic compartments, we examined the binding and dissociation of Ser(P)-129 α-syn and analyzed the effects of manipulating Ser(P)-129 levels on α-syn membrane interactions using synaptosomal membranes and neural precursor cells from α-syn-deficient mice or transgenic mice expressing human α-syn. We first evaluated the recovery of the Ser(P)-129 epitope following either α-syn membrane binding or dissociation. We demonstrate a rapid turnover of Ser(P)-129 during both binding to and dissociation from synaptic membranes. Although the membrane binding of WT α-syn was insensitive to modulation of Ser(P)-129 levels by multiple strategies (the use of phosphomimic S129D and nonphosphorylated S129A α-syn mutants; by enzymatic dephosphorylation of Ser(P)-129 or proteasome inhibitor-induced elevation in Ser(P)-129; or by inhibition or stable overexpression of PLK2), PD mutant Ser(P)-129 α-syn showed a preferential membrane association compared with WT Ser(P)-129 α-syn. Collectively, these data suggest that phosphorylation at Ser-129 is dynamic and that the subcellular distribution of α-syn bearing PD-linked mutations, A30P or A53T, is influenced by the phosphorylation state of Ser-129.
Journal of Biological Chemistry 08/2011; 286(41):35863-73. · 4.77 Impact Factor
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ABSTRACT: Well-formed visual hallucinations (VH) are common in patients with Parkinson's disease (PD). The pathophysiology of VH in PD is unknown but may involve structures mediating visual processing such as the inferior temporal cortex. Serotonergic type 2A (5-HT(2A)) receptors have been linked to many psychiatric disorders, including psychosis. We hypothesized that enhanced 5-HT(2A) receptor levels may be involved in VH in PD. Autoradiographic binding using [(3)H]-ketanserin and spiperone, to define 5-HT(2A) receptors, was performed in 6 PD patients with VH, 6 PD patients without VH, and 5 healthy, age-matched controls. The cerebral regions studied included the orbitofrontal cortex, inferolateral temporal cortex, motor cortex, striatum, and substantia nigra. There was a significant (45.6%) increase in the levels of [(3)H]-ketanserin binding in the inferolateral temporal cortex of PD patients with VH when compared with PD patients without VH (54.3 +/- 5.2 fmol/mg vs. 37.3 +/- 4.3 fmol/mg, P = 0.039). Additionally, there was a significant increase in the levels of 5-HT(2A) receptors in the motor cortex of all PD patients taken as a group when compared with controls (57.8 +/- 5.7 fmol/mg vs. 41.2 +/- 2.6 fmol/mg, P = 0.0297). These results suggest that enhanced 5-HT(2A)-mediated neurotransmission in the inferolateral temporal cortex, a critical structure in visual processing, might be associated with the development of VH in PD. Our results provide new insights into the pathophysiology of VH in PD and provide an anatomical basis to explain why compounds with 5-HT(2A) antagonist activity are effective at alleviating this debilitating complication.
Movement Disorders 07/2010; 25(10):1399-408. · 4.51 Impact Factor
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ABSTRACT: Development of L-DOPA-induced dyskinesia (LID) remains a major problem in the long-term treatment of Parkinson's disease (PD). Sensitization to L-DOPA correlates with ectopic expression of D3 dopamine receptors in the striatum, implicating D3 receptors in development of LID. We demonstrate that the selective D3 antagonist S33084 abolishes development of LID over 30 days in MPTP-lesioned marmosets without effecting the anti-parkinsonian actions of L-DOPA. Furthermore, following a 14 day washout, when challenged with L-DOPA in the absence of S33084, these animals continued to exhibit reduced LID. In the 6-OHDA-lesioned rat, S33084 similarly attenuated development of behavioural sensitization to L-DOPA. Additionally, L-DOPA-induced elevations in striatal pre-proenkephalin-A (PPE-A) (but not PPE-B, phospho[Thr(34)]DARPP-32, D1, and D2 receptor mRNA or D3 receptor levels) were reduced in S33084 treated animals. Our data suggest a role for D3 receptors in the development of LID and suggest that initiating L-DOPA treatment with a D3 antagonist may reduce the development of LID in PD.
Neurobiology of Disease 01/2009; 35(2):184-92. · 5.40 Impact Factor
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ABSTRACT: The anti-parkinsonian and levodopa-sparing potential of the nociceptin/orphanin FQ receptor (NOP) antagonist J-113397 has been demonstrated in rodent models of Parkinson's disease. Here, we describe the levodopa-sparing potential of J-113397 in MPTP-lesioned marmosets. Coadministration of J-113397 (30 mg/kg) with a sub-therapeutic dose of levodopa (12.5 mg/kg) produced an anti-parkinsonian action equivalent to that of a therapeutic dose of levodopa. However, these effects were accompanied by an equivalent level of dyskinesia. The actions of NOP antagonists seen in rodents translate to nonhuman primates. However, the present study raises the possibility that these levodopa-sparing benefits may be offset by a propensity to exacerbate dyskinesia.
Movement Disorders 09/2008; 23(13):1922-5. · 4.51 Impact Factor
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ABSTRACT: Many experimental data support the enhancement of neurotrophic factors as a means to modify neurodegeneration in Parkinson's disease. However, the translation of this to the clinic has proven problematic. This is likely due to the complex nature of the surgical gene delivery and cell-based approaches adopted to deliver proteinaceous neurotrophic factors to targets within the central nervous system. We investigated the ability of a novel, orally active, nonpeptide neurotrophic factor inducer, PYM50028 (Cogane), to restore dopaminergic function after 1-methyl-4-phenylpyridinium (MPP(+)) -induced damage to mesencephalic neurons in vitro and in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) -lesioned mice. In rat mesencephalic neurons, administration of PYM50028, either before or after MPP(+), significantly prevented and reversed both MPP(+)-induced neuronal atrophy and cell loss. These effects were potent and of a magnitude equivalent to those achieved by a combination of brain-derived neurotrophic factor (BDNF) and glial-derived neurotrophic factor (GDNF). Oral administration of PYM50028 (10 mg/kg/day for 60 days) to MPTP-lesioned mice, commencing after a striatal impairment was evident, resulted in a significant elevation of striatal GDNF (297%) and BDNF (511%), and attenuated the loss of striatal dopaminergic transporter levels and dopaminergic neurons in the substantia nigra. PYM50028 did not inhibit monoamine oxidase B in vitro, nor did it alter brain levels of MPP(+) in vivo. PYM50028 has neuroprotective and neurorestorative potential and is in clinical development for the treatment of neurodegenerative disorders, including Parkinson's disease.
The FASEB Journal 08/2008; 22(7):2488-97. · 5.71 Impact Factor
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ABSTRACT: Rett syndrome is an X-linked neurological condition affecting almost exclusively girls that is caused by mutations of the MECP2 gene. Recent studies have shown that transgenic delivery of MeCP2 function to Mecp2-deficient male mice can improve their Rett-like behavior. However, as the brain of a Rett girl contains a mosaic of MeCP2 expressing and non-expressing neurons, and the over-expression of MeCP2 in neurons can induce a severe progressive neurological phenotype, testing whether functional rescue can be achieved by gene re-introduction strategies in a female model of Rett syndrome is warranted. To address this, we generated transgenic mice expressing an epitope-tagged Mecp2 transgene in forebrain neurons. These mice over-express MeCP2 protein at about 1.6 times normal levels in cortex and develop impaired motor behavior by 9-12 months of age. To test whether forebrain-targeted MeCP2 restoration would improve behavior in female Mecp2(-/+) mice, we crossed these transgenics with Mecp2(-/+) mice and examined the behavioral properties of the female rescue mice for 1 year. These assessments revealed that the diminished rearing activity, impaired mobility and the diminished locomotive activity of female Mecp2(-/+) mice were restored to wild-type levels in the rescue mice. These results show that improvement of Rett-like behavior can be achieved in Mecp2(-/+) females by targeted gene re-introduction without inducing deficits relating to MeCP2 over-expression.
Human Molecular Genetics 06/2008; 17(10):1386-96. · 7.64 Impact Factor
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ABSTRACT: The role of D(3) receptors in the antiparkinsonian actions of l-DOPA and l-DOPA-induced dyskinesia (LID) remains unclear. The D(3) receptor partial agonist BP897 attenuates LID in primates without affecting the antiparkinsonian actions of l-DOPA, suggesting that "normalization" of D(3) activity is antidyskinetic [Bezard, E., Ferry, S., Mach, U., Stark, H., Leriche, L., Boraud, T., Gross, C., and Sokoloff, P., 2003. Attenuation of levodopa-induced dyskinesia by normalizing dopamine D(3) receptor function. Nat. Med. 9, 762-767]. However, subsequent studies have questioned these findings [Hsu, A., Togasaki, D.M., Bezard, E., Sokoloff, P., Langston, J.W., Di Monte, D.A., and Quik, M., 2004. Effect of the D(3) dopamine receptor partial agonist BP897 [N-[4-(4-(2-methoxyphenyl)piperazinyl)butyl]-2-naphthamide] on l-3,4-dihydroxyphenylalanine-induced dyskinesias and parkinsonism in squirrel monkeys. J. Pharmacol. Exp. Ther. 311, 770-777]. The D(3) receptor antagonist S33084 is not antidyskinetic yet enhances the antiparkinsonian actions of l-DOPA, suggesting that stimulation of D(3) receptors is not involved in LID. Here, we address the possibility that in vivo BP897 acts via mechanisms in addition to attenuation of D(3) signaling. l-DOPA (125 mg/kg) elicits hyperkinesia in reserpine-treated rats, the vertical component of which (rearing) is attenuated by agents with antidyskinetic actions in MPTP-lesioned primates and Parkinson's disease (PD) [Johnston, T.H., Lee, J., Gomez-Ramirez, J., Fox, S.H., and Brotchie, J.M., 2005. A simple rodent assay for the in vivo identification of agents with potential to reduce levodopa-induced dyskinesia in Parkinson's disease. Exp. Neurol. 191, 243-250]. BP897 (0.1, 0.3, 1.0 and 3 mg/kg) reduced l-DOPA-induced rearing by 0%, 44%, 86% and 57% respectively. In contrast, S33084 had no effect on l-DOPA-induced rearing (0.1 mg/kg, 115%; 0.3 mg/kg, 94%, 1 mg/kg, 134%; 3 mg/kg, 100%, of vehicle, all P > 0.05). Furthermore, S33084 failed to antagonize the effects of BP897 on l-DOPA-induced rearing. The influence of BP897 on l-DOPA-induced rearing was, however, mimicked by the selective D(2) antagonist L741,626. Finally, BP897 attenuated l-DOPA-induced horizontal activity, an action attenuated by S33084 and mimicked by L741,626. Thus, while BP897 may reduce LID, we raise the possibility that receptors other than D(3) receptors might be involved in this action.
Experimental Neurology 12/2006; 202(1):85-92. · 4.70 Impact Factor
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ABSTRACT: Investigation of the pathophysiology of psychosis in Parkinson's disease (PD), as well as the assessment of potential novel therapeutics, has been limited by the lack of a well-validated animal model. MPTP-lesioned primates exhibit abnormal behaviors that are distinct from dyskinesia and parkinsonism and may represent behavioral correlates of neural processes related to psychosis in PD. Here we assess four types of behavior--agitation, hallucinatory-like responses to nonapparent stimuli, obsessive grooming, and stereotypies that are termed "psychosis-like"--and define their pharmacology using a psychosis-like behavior rating scale. By assessing the actions of drugs known to enhance or attenuate psychosis in PD patients, we find that the pharmacology of these behaviors recapitulates, in several respects, the pharmacology of psychosis in PD. Thus, levodopa and apomorphine elicited psychosis-like behaviors. Amantadine significantly decreased levodopa-induced dyskinesia but exacerbated psychosis-like behaviors. Haloperidol reduced psychosis-like behaviors but at the expense of increased parkinsonian disability while the atypical neuroleptics clozapine and quetiapine reduced psychosis-like behaviors without significant effect on parkinsonian disability. The response of different components of the psychotomimetic behavior suggested the involvement of both dopaminergic and nondopaminergic mechanisms in their expression.
Movement Disorders 12/2006; 21(11):1879-91. · 4.51 Impact Factor
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Archives of Neurology 10/2006; 63(9):1343-4. · 7.58 Impact Factor
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ABSTRACT: L-dopa-induced dyskinesia (LID) remains a major complication of the treatment of Parkinson's disease. The neural mechanisms underlying LID are thought to involve overactivity of striatal glutamatergic neurotransmission, with resultant underactivation of the output regions of the basal ganglia. Histamine H3 heteroreceptors can reduce glutamate and gamma-aminobutyric acid (GABA) transmission in the striatum and substantia nigra reticulata, respectively. Thus, we tested whether the histamine H3 receptor agonists immepip and imetit can alleviate LID in the MPTP-lesioned marmoset model of Parkinson's disease. Coadministration of immepip (1 mg/kg) with L-dopa (15 mg/kg) was associated with significantly less total dyskinesia than L-dopa alone. When dyskinesia was separately rated as chorea and dystonia, coadministration of L-dopa with either immepip or imetit (both 10 mg/kg) significantly reduced chorea but had no effect on dystonia. The antidyskinetic actions of the H3 agonists were not accompanied by alteration of the antiparkinsonian actions of L-dopa. However, immepip (10 mg/kg), when administered as monotherapy, significantly increased parkinsonian disability compared to vehicle. Overall, the results obtained in this study suggest that histamine H3 receptors may be involved in the neural mechanisms underlying L-dopa-induced dyskinesia in Parkinson's disease.
Movement Disorders 07/2006; 21(6):839-46. · 4.51 Impact Factor
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ABSTRACT: The pro-toxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is widely used to create animal models of Parkinson's disease. This unit describes protocols for the production of stable and substantial lesions in the dopaminergic nigrostriatal pathway of mice and non-human primates. The models can be employed for assessing the neural mechanisms underlying the development of Parkinson's disease and for screening potential therapies for the treatment of this condition.
Current protocols in pharmacology 07/2005; Chapter 5:Unit5.42.
