Background:The oligomeric state of ␣-syn in vivo remains unknown. Results: ␣-syn in the CNS and produced by erythrocytes, mammalian cells, and Escherichia coli exists predominantly as a disordered monomer. Conclusion: Native ␣-syn from various sources behaves as unstructured and monomeric. Significance: Stabilizing monomeric ␣-syn, lowering its levels, and/or inhibiting its fibrillization remain viable therapeutic strategies for Parkinson disease.

Our results demonstrate that levels of α-synuclein oligomers in CSF and the oligomers/total-α-synuclein ratio can be useful biomarkers for diagnosis and early detection of PD.

BackgroundDespite decades of intensive research, to date, there is no accepted diagnosis for Parkinson’s disease (PD) based on biochemical analysis of blood or CSF. However, neurodegeneration in the brains of PD patients begins several years before the manifestation of the clinical symptoms, pointing to serious flaw/limitations in this approach.ResultsTo explore the potential use of alpha-synuclein (α-syn) species as candidate biomarkers for PD, we generated specific antibodies directed against wide array of α-syn species, namely total-, oligomeric- and phosphorylated-Ser129-α-syn (t-, o- and p-S129-α-syn). Next we sought to employ our antibodies to develop highly specific ELISA assays to quantify α-syn species in biological samples. Finally we verified the usefulness of our assays in CSF samples from 46 PD patients and 48 age-matched healthy controls. We also assessed the discriminating power of combining multiple CSF α-syn species with classical Alzheimer’s disease biomarkers. The combination of CSF o-/t-α-syn, p-S129-α-syn and p-tau provided the best fitting predictive model for discriminating PD patients from controls. Moreover, CSF o-α-syn levels correlated significantly with the severity of PD motor symptoms (r = -0.37).ConclusionOur new ELISA assays can serve as research tools to address the unmet need for reliable CSF biomarkers for PD and related disorders.Electronic supplementary materialThe online version of this article (doi:10.1186/s13024-016-0072-9) contains supplementary material, which is available to authorized users.

Although alpha-synuclein is the main constituent of Lewy bodies, cerebrospinal fluid determination on its own does not seem fundamental for the diagnosis of synucleinopathies. We evaluated whether the combination of classical biomarkers, Aβ(1-42) , total tau, phosphorylated tau, and α-synuclein can improve discrimination of Parkinson's disease, dementia with Lewy bodies, Alzheimer's disease, and frontotemporal dementia. Aβ(1-42) , total tau, phosphorylated tau, and α-synuclein were measured in a series of patients with Parkinson's disease (n = 38), dementia with Lewy bodies (n = 32), Alzheimer's disease (n = 48), frontotemporal dementia (n = 31), and age-matched control patients with other neurological diseases (n = 32). Mean α-synuclein levels in cerebrospinal fluid were significantly lower in the pathological groups than in cognitively healthy subjects. An inverse correlation of α-synuclein with total tau (r = -0.196, P < .01) was observed. In the group of patients with Parkinson's disease, Aβ(1-42) , total tau, and phosphorylated tau values were similar to controls, whereas total tau/α-synuclein and phosphorylated tau/α-synuclein ratios showed the lowest values. Cerebrospinal fluid α-synuclein alone did not provide relevant information for Parkinson's disease diagnosis, showing low specificity (area under the curve, 0.662; sensitivity, 94%; specificity, 25%). Instead, a better performance was obtained with the total tau/α-syn ratio (area under the curve, 0.765; sensitivity, 89%; specificity, 61%). Combined determination of α-synuclein and classical biomarkers in cerebrospinal fluid shows differential patterns in neurodegenerative disorders. In particular, total tau/α-synuclein and phosphorylated tau/α-synuclein ratios can contribute to the discrimination of Parkinson's disease. © 2011 Movement Disorder Society.

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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.

The aggregation of α-synuclein (α-syn) is considered the key pathogenic event in many neurological disorders such as Parkinson's disease (PD), dementia with Lewy bodies and multiple system atrophy, giving rise to a whole category of neurodegenerative diseases known as synucleinopathies. Although the molecular basis of α-syn toxicity has not been precisely elucidated, a great deal of effort has been put into identifying compounds that could inhibit or even reverse the aggregation process. Previous reports indicated that many phenolic compounds are potent inhibitors of α-syn aggregation. The aim of the present study was to assess the anti-aggregating effect of gallic acid (GA) (3,4,5-trihydroxybenzoic acid), a benzoic acid derivative that belongs to a group of phenolic compounds known as phenolic acids. By employing an array of biophysical and biochemical techniques and a cell-viability assay, GA was shown not only to inhibit α-syn fibrillation and toxicity but also to disaggregate preformed α-syn amyloid fibrils. Interestingly, GA was found to bind to soluble, non-toxic oligomers with no β-sheet content, and to stabilize their structure. The binding of GA to the oligomers may represent a potential mechanism of action. Additionally, by using structure activity relationship data obtained from fourteen structurally similar benzoic acid derivatives, it was determined that the inhibition of α-syn fibrillation by GA is related to the number of hydroxyl moieties and their position on the phenyl ring. GA may represent the starting point for designing new molecules that could be used for the treatment of PD and related disorders.

α-Synuclein (α-syn) is a presynaptic protein present at most nerve terminals, but its function remains largely unknown. The familial forms of Parkinson's disease associated with multiplications of the α-syn gene locus indicate that overabundance of this protein might have a detrimental effect on dopaminergic transmission. To investigate this hypothesis, we use adeno-associated viral (AAV) vectors to overexpress human α-syn in the rat substantia nigra. Moderate overexpression of either wild-type (WT) or A30P α-syn differs in the motor phenotypes induced, with only the WT form generating hemiparkinsonian impairments. Wild-type α-syn causes a reduction of dopamine release in the striatum that exceeds the loss of dopaminergic neurons, axonal fibers, and the reduction in total dopamine. At the ultrastructural level, the reduced dopamine release corresponds to a decreased density of dopaminergic vesicles and synaptic contacts in striatal terminals. Interestingly, the membrane-binding-deficient A30P mutant does neither notably reduce dopamine release nor it cause ultrastructural changes in dopaminergic axons, showing that α-syn's membrane-binding properties are critically involved in the presynaptic defects. To further determine if the affinity of the protein for membranes determines the extent of motor defects, we compare three forms of α-syn in conditions leading to pronounced degeneration. While membrane-binding α-syns (wild-type and A53T) induce severe motor impairments, an N-terminal deleted form with attenuated affinity for membranes is inefficient in inducing motor defects. Overall, these results demonstrate that α-syn overabundance is detrimental to dopamine neurotransmission at early stages of the degeneration of nigrostriatal dopaminergic axons.