Dopamine promotes formation and secretion of non-fibrillar alpha-synuclein oligomers.
ABSTRACT: Parkinson's disease (PD) is characterized by selective and progressive degeneration of dopamine (DA)-producing neurons in the substantia nigra pars compacta (SNpc) and by abnormal aggregation of ?-synuclein. Previous studies have suggested that DA can interact with ?-synuclein, thus modulating the aggregation process of this protein; this interaction may account for the selective vulnerability of DA neurons in patients with PD. However, the relationship between DA and ?-synuclein, and the role in progressive degeneration of DA neurons remains elusive. We have shown that in the presence of DA, recombinant human ?-synuclein produces non-fibrillar, SDS-resistant oligomers, while ?-sheet-rich fibril formation is inhibited. Pharmacologic elevation of the cytoplasmic DA level increased the formation of SDS-resistant oligomers in DA-producing neuronal cells. DA promoted ?-synuclein oligomerization in intracellular vesicles, but not in the cytosol. Furthermore, elevation of DA levels increased secretion of ?-synuclein oligomers to the extracellular space, but the secretion of monomers was not changed. DA-induced secretion of ?-synuclein oligomers may contribute to the progressive loss of the dopaminergic neuronal population and the pronounced neuroinflammation observed in the SNpc in patients with PD.
Project description:Subpopulations of dopaminergic (DA) neurons within the substantia nigra pars compacta (SNpc) display a differential vulnerability to loss in Parkinson's disease (PD); however, it is not clear why these subsets are preferentially selected in PD-associated neurodegeneration. In rodent SNpc, DA neurons can be divided into two subpopulations based on the expression of aldehyde dehydrogenase 1 (ALDH1A1). Here, we have shown that, in ?-synuclein transgenic mice, a murine model of PD-related disease, DA neurodegeneration occurs mainly in a dorsomedial ALDH1A1-negative subpopulation that is also prone to cytotoxic aggregation of ?-synuclein. Notably, the topographic ALDH1A1 pattern observed in ?-synuclein transgenic mice was conserved in human SNpc. Postmortem evaluation of brains of patients with PD revealed a severe reduction of ALDH1A1 expression and neurodegeneration in the ventral ALDH1A1-positive DA subpopulations. ALDH1A1 expression was also suppressed in ?-synuclein transgenic mice. Deletion of Aldh1a1 exacerbated ?-synuclein-mediated DA neurodegeneration and ?-synuclein aggregation, whereas Aldh1a1-null and control DA neurons were comparably susceptible to 1-methyl-4-phenylpyridinium-, glutamate-, or camptothecin-induced cell death. ALDH1A1 overexpression appeared to preferentially protect against ?-synuclein-mediated DA neurodegeneration but did not rescue ?-synuclein-induced loss of cortical neurons. Together, our findings suggest that ALDH1A1 protects subpopulations of SNpc DA neurons by preventing the accumulation of dopamine aldehyde intermediates and formation of cytotoxic ?-synuclein oligomers.
Project description:Parkinson's disease (PD) is associated with progressive degeneration of dopaminergic (DA) neurons. We report for the first time that the Drosophila histone deacetylase 6 (dHDAC6) plays a critical role in the protection of DA neurons and the formation of alpha-synuclein inclusions by using a Drosophila PD model constructed by ectopic expression of human alpha-synuclein. Depletion of dHDAC6 significantly enhances the effects caused by ectopic expression of alpha-synuclein, namely, loss of DA neurons, retinal degeneration, and locomotor dysfunction. Expression of alpha-synuclein in the DA neurons leads to fewer inclusions in the brains of dHDAC6 mutant flies than in wild-type flies. Conversely, overexpression of dHDAC6 is able to suppress the alpha-synuclein-induced DA neuron loss and retinal degeneration and promote inclusion formation. Furthermore, mutation of dHDAC6 reinforces the accumulation of oligomers that are suggested to be a toxic form of alpha-synuclein. We propose that alpha-synuclein inclusion formation in the presence of dHDAC6 protects DA neurons from being damaged by oligomers, which may uncover a common mechanism for synucleinopathies.
Project description:The accumulation of aggregated ?-synuclein (?Syn) is a hallmark of Parkinson's disease (PD). Current evidence indicates that small soluble ?Syn oligomers (?SynOs) are the most toxic species among the forms of ?Syn aggregates, and that size and topological structural properties are crucial factors for ?SynOs-mediated toxicity, involving the interaction with either neurons or glial cells. We previously characterized a human ?SynO (H-?SynO) with specific structural properties promoting toxicity against neuronal membranes. Here, we tested the neurotoxic potential of these H-?SynOs in vivo, in relation to the neuropathological and symptomatic features of PD. The H-?SynOs were unilaterally infused into the rat substantia nigra pars compacta (SNpc). Phosphorylated ?Syn (p129-?Syn), reactive microglia, and cytokine levels were measured at progressive time points. Additionally, a phagocytosis assay in vitro was performed after microglia pre-exposure to ?synOs. Dopaminergic loss, motor, and cognitive performances were assessed. H-?SynOs triggered p129-?Syn deposition in SNpc neurons and microglia and spread to the striatum. Early and persistent neuroinflammatory responses were induced in the SNpc. In vitro, H-?SynOs inhibited the phagocytic function of microglia. H-?synOs-infused rats displayed early mitochondrial loss and abnormalities in SNpc neurons, followed by a gradual nigrostriatal dopaminergic loss, associated with motor and cognitive impairment. The intracerebral inoculation of structurally characterized H-?SynOs provides a model of progressive PD neuropathology in rats, which will be helpful for testing neuroprotective therapies.
Project description:Parkinson's disease (PD) is a chronic progressive neurodegenerative disorder. Recent studies have implicated a role for peroxisome proliferator-activated receptor ? coactivator protein-1? (PGC-1?) in PD and in animal or cellular models of PD. The role of PGC-1? in the function and survival of substantia nigra pars compacta (SNpc) dopamine neurons is not clear. Here we find that there are four different PGC-1? isoforms expressed in SH-SY5Y cells, and these four isoforms are expressed across subregions of mouse brain. Adult conditional PGC-1? knock-out mice show a significant loss of dopaminergic neurons that is accompanied by a reduction of dopamine in the striatum. In human PD postmortem tissue from the SNpc, there is a reduction of PGC-1? isoforms and mitochondria markers. Our findings suggest that all four isoforms of PGC-1? are required for the proper expression of mitochondrial proteins in SNpc DA neurons and that PGC-1? is essential for SNpc DA neuronal survival, possibly through the maintenance of mitochondrial function.
Project description:Parkinson's disease (PD) is a progressive neurodegenerative disorder typified by the loss of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNpc). Recent evidence indicates that neuroinflammation may play a critical role in the pathogenesis of PD, particularly tumor necrosis factor (TNF). We have previously shown that soluble TNF (solTNF) is required to mediate robust degeneration induced by 6-hydroxydopamine (6-OHDA) or lipopolysaccharide. What remains unknown is whether TNF inhibition can attenuate the delayed and progressive phase of neurodegeneration. To test this, rats were injected in the SNpc with lentivirus encoding dominant-negative TNF (lenti-DN-TNF) 2 weeks after receiving a 6-OHDA lesion. Remarkably, when examined 5 weeks after the initial 6-OHDA lesion, no further loss of nigral DA neurons was observed. Lenti-DN-TNF also attenuated microglial activation. Together, these data suggest that TNF is likely a critical mediator of nigral DA neuron death during the delayed and progressive phase of neurodegeneration, and that microglia may be the principal cell type involved. These promising findings provide compelling reasons to perform DN-TNF gene transfer studies in nonhuman primates with the long-term goal of using it in the clinic to prevent the delayed and progressive degeneration of DA neurons that gives rise to motor symptoms in PD.
Project description:Parkinson's disease (PD) is defined by the loss of dopaminergic neurons in the substantia nigra and the formation of Lewy body inclusions containing aggregated ?-synuclein. Efforts to explain dopamine neuron vulnerability are hindered by the lack of dopaminergic cell death in ?-synuclein transgenic mice. To address this, we manipulated both dopamine levels and ?-synuclein expression. Nigrally targeted expression of mutant tyrosine hydroxylase with enhanced catalytic activity increased dopamine levels without damaging neurons in non-transgenic mice. In contrast, raising dopamine levels in mice expressing human A53T mutant ?-synuclein induced progressive nigrostriatal degeneration and reduced locomotion. Dopamine elevation in A53T mice increased levels of potentially toxic ?-synuclein oligomers, resulting in conformationally and functionally modified species. Moreover, in genetically tractable Caenorhabditis elegans models, expression of ?-synuclein mutated at the site of interaction with dopamine prevented dopamine-induced toxicity. These data suggest that a unique mechanism links two cardinal features of PD: dopaminergic cell death and ?-synuclein aggregation.
Project description:Progressive loss of substantia nigra dopamine neurons (SN DA) is a hallmark of aging and of Parkinson's disease (PD). Mutations in PARK genes cause familial PD forms. Increased expression of alpha-synuclein (PARK4) is a disease-triggering event in familial PD and also observed in SN DA neurons in sporadic PD but related transcriptional changes are unknown. With optimized single-cell quantitative real-time polymerase chain reaction analysis, we compared messenger RNA and microRNA levels in SN DA neurons from sporadic PD patients and controls. Non-optimally matched donor ages and RNA integrities are common problems when analyzing human samples. We dissected the influence of distinct ages and RNA integrities of our samples by applying a specifically-optimized, linear-mixed-effects model to quantitative real-time polymerase chain reaction-data. We identified that elevated alpha-synuclein messenger RNA levels in SN DA neurons of human PD brains were positively correlated with corresponding elevated levels of mRNAs for functional compensation of progressive SN DA loss and for enhanced proteasomal (PARK5/UCHL1) and lysosomal (PARK9/ATPase13A2) function, possibly counteracting alpha-synuclein toxicity. In contrast, microRNA miR-133b levels, previously implicated in transcriptional dysregulation in PD, were not altered in SN DA neurons in PD.
Project description:Parkinson's disease (PD) is characterised pathologically by degeneration of the dopaminergic (DA) neurones of the substantia nigra pars compacta (SNpc) and the presence of ?-synuclein containing Lewy body inclusions. Trichloroethylene (TCE) has been suggested as a potential environmental chemical that may contribute to the development of PD, via conversion to the neurotoxin, 1-Trichloromethyl-1,2,3,4-tetrahydro-?-carboline (TaClo). We investigated the effect of an 8 week exposure to TCE or TaClo on wild type and, as an experimental model of PD, A30P mutant ?-synuclein overexpressing mice using a combination of behaviour and pathology. TCE or TaClo exposure caused significant DA neuronal loss within the SNpc in both wild type and transgenic mice. Cell numbers were lower in A30P animals than wild type, however, no additive effect of TCE or TaClo exposure and A30P overexpression was found. TCE or TaClo did not appear to lead to acceleration of motor or cognitive deficits in either wild type or A30P mutant mice, potentially because of the modest reductions of DA neuronal number in the SNpc. Our results do however suggest that TCE exposure could be a possible factor in development of PD like changes following exposure.
Project description:Parkinson's disease (PD), clinically characterized by motor and nonmotor symptoms, is a common progressive and multisystem neurodegenerative disorder, which is caused by both genetic and environmental risk factors. The main pathological features of PD are the loss of dopaminergic (DA) neurons and the accumulation of alpha-synuclein (?-syn) in the residual DA neurons in the substantia nigra pars compacta (SNpc). In recent years, substantial progress has been made in discovering the genetic factors of PD. In particular, a total of 19 PD-causing genes have been unraveled, among which some members have been regarded to be related to mitochondrial dysfunction. Mitochondria are key regulators of cellular metabolic activity and are critical for many important cellular processes including energy metabolism and even cell death. Their normal function is basically maintained by the mitochondrial quality control (MQC) mechanism. Accordingly, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a kind of neurotoxin, exerts its neurotoxic effects at least partially by producing its toxic metabolite, namely, 1-methyl-4-phenylpyridine (MPP+), which in turn causes mitochondrial dysfunction by inhibiting complex I and mimicking the key features of PD pathogenesis. This review focused on three main aspects of the MQC signaling pathways, that is, mitochondrial biogenesis, mitochondrial dynamics, and mitochondrial autophagy; hence, it demonstrates in detail how genetic and environmental factors result in PD pathogenesis by interfering with MQC pathways, thereby hopefully contributing to the discovery of novel potential therapeutic targets for PD.
Project description:BACKGROUND:Parkinson's disease (PD) is a neurodegenerative disorder characterized by progressive death of dopaminergic neurons in the substantia nigra pars compacta (SNpc). AIMS:To study if tenuigenin (TEN), the main active component of Polygala tenuifolia, can protect dopaminergic neurons from inflammation-mediated damage in vivo. METHODS:We observed the effects of TEN on lipopolysaccharide (LPS) induced PD model by behavioral analysis, high-performance liquid chromatography, immunohistochemistry and enzyme-linked immunoadsorbent assay, etc. RESULTS:We showed that a single intranigral dose of LPSs (10 ?g) induced microglial activation, reduced the survival ratio of tyrosine hydroxylase-immunoreactive (TH-ir) neurons in the SNpc and reduced dopamine (DA) content in the striatum. Treatment with 300 mg/kg TEN once per day over 14 weeks improved the survival rate of TH-ir neurons in the SNpc to 75%, on the non-injected side. Treatment with 200 or 300 mg/kg TEN once per day over 14 weeks significantly improved DA levels in the striatum to 73% and 81% on the non-injected side, respectively. The excessive production of cytokines, such as tumor necrosis factor (TNF)-? and interleukin (IL)-1?, was abolished by TEN administration. CONCLUSION:Our results suggest that TEN may play a role in protecting dopaminergic neurons against inflammatory challenge.