α-Synuclein in synaptic function and dysfunction

α-Synuclein is a neuronal protein that is enriched in presynaptic terminals. Under physiological conditions, it binds to synaptic vesicle membranes and functions in neurotransmitter release, although the molecular details remain unclear, and it is controversial whether α-synuclein inhibits or facilitates neurotransmitter release. Pathologically, in synucleinopathies including Parkinson’s disease (PD), α-synuclein forms aggregates that recruit monomeric α-synuclein and spread throughout the brain, which triggers neuronal dysfunction at molecular, cellular, and organ levels. Here, we present an overview of the effects of α-synuclein on SNARE-complex assembly, neurotransmitter release, and synaptic vesicle pool homeostasis, and discuss how the observed divergent effects of α-synuclein on neurotransmitter release can be reconciled. We also discuss how gain-of-function versus loss-of-function of α-synuclein may contribute to pathogenesis in synucleinopathies.     

α-Synuclein immunoreactivity in dementia with Lewy bodies: morphological staging and comparison with ubiquitin immunostaining

α-Synuclein is a presynaptic protein recently identified as a specific component of Lewy bodies (LB) and Lewy neurites. The aim of this study was to assess the morphology and distribution of α-synuclein immunoreactivity in cases of dementia with LB (DLB), and to compare α-synuclein with ubiquitin immunostaining. We examined substantia nigra, paralimbic regions (entorhinal cortex, cingulate gyrus, insula and hippocampus), and neocortex (frontal and occipital association cortices) with double α-synuclein and ubiquitin immunostaining in 25 cases meeting neuropathological criteria for DLB. α-Synuclein immunostaining was more specific than ubiquitin immunostaining in that it differentiated LB from globose tangles. It was also slightly more sensitive, staining 4–5% more intracytoplasmic structures, especially diffuse α-synuclein deposits that were ubiquitin negative. In addition to LB, α-synuclein staining showed filiform and globose neurites in the substantia nigra, CA2–3 regions of the hippocampus, and entorhinal cortex. A spectrum of α-synuclein staining was seen in substantia nigra: from diffuse “cloud-like” inclusions to aggregated intracytoplasmic inclusions with variable ubiquitin staining to classic LB. We hypothesize that these represent different stages in LB formation. Received: 18 May 1999 / Revised: 28 July 1999 / Accepted: 30 July 1999     

α-Synuclein pathology affecting Bergmann glia of the cerebellum in patients with α-synucleinopathies

We carried out immunohistochemical examinations of the brains (cerebella) of patients who had suffered from Parkinson's disease (PD), diffuse Lewy body disease (DLBD) or multiple system atrophy (MSA), using antibodies specific for alpha-synuclein. Alpha-synuclein-positive doughnut-shaped structures were found occasionally in the cerebellar molecular layer in some of these patients. Double-labeling immunofluorescence and immunoelectron microscopy studies revealed that these alpha-synuclein-positive doughnut-shaped structures were located in the glial fibrillary acidic protein-positive radial processes of Bergmann glia, corresponding to the outer area of Lewy body-like inclusions, and consisted of granulo-filamentous structures. These findings indicate that, although not frequently, Bergmann glia of the cerebellum are also the targets of alpha-synuclein pathology in alpha-synucleinopathies such as PD, DLBD and MSA.     

α-Synuclein and Mitochondria: Partners in Crime?

Increased α-synuclein levels and mutations in mitochondria-associated proteins both cause familial Parkinson’s disease (PD), and synuclein and mitochondria also play central, but poorly understood, roles in the pathogenesis of idiopathic PD. A fraction of synuclein interacts with mitochondria, and synuclein can produce mitochondrial fragmentation and impair mitochondrial complex I activity. However, the consequences of these mitochondrial changes for bioenergetic and other mitochondrial functions remain poorly defined, as does the role of synuclein–mitochondria interactions in the normal and pathologic effects of synuclein. Understanding the functional consequences of synuclein’s interactions with mitochondria is likely to provide important insights into disease pathophysiology, and may also reveal therapeutic strategies.     

α-Synuclein multiplication analysis in Italian familial Parkinson disease

The α-synuclein gene (SNCA) multiplication causes autosomal dominant Parkinson Disease (PD): triplication is associated with early-onset rapidly progressing parkinsonism with a strong likelihood of developing dementia, while duplication is associated with a less severe phenotype similar to idiopathic PD.We tested for SNCA multiplication 144 unrelated PD patients with a dominant family history. We identified one patient with SNCA duplication (0.7%).The SNCA-duplicated patient was a woman of 45 years of age with PD onset at 41 years of age. She experienced a rapidly progressive disease with early motor complications (on/off fluctuations and dyskinesias). Medical records confirmed that the proband's mother developed PD at 47 years of age and died at 63 with dementia. She experienced rapid progression in both motor and cognitive symptoms: development of dementia at 54 years of age, 7 years after onset.Although SNCA duplication is an unusual cause of familial PD testing for it is worthwhile. The clinical presentation of duplicated cases may be more aggressive than usual.     

α-Synuclein oligomers and fibrils:partners in crime in synucleinopathies

The misfolding and aggregation of a-synuclein is the general hallmark of a group of devastating neurodegenerative pathologies referred to as synucleinopathies,such as Parkinson’s disease,dementia with Lewy bodies,and multiple system atrophy.In such conditions,a range of different misfolded aggregates,including oligomers,protofibrils,and fibrils,are present both in neurons and glial cells.Growing expe rimental evidence supports the proposition that solu ble oligomeric assemblies,formed during the...     

α-Synuclein pathology in the neostriatum in Parkinson’s disease

We immunohistochemically examined the neostriatum from 25 patients with symptomatic and presymptomatic Parkinson’s disease (PD) with various degrees of Lewy body pathology, using anti-phosphorylated α-synuclein (αS) antibody. These patients were classified according to the PD staging proposed by Braak et al. (Neurobiol Aging 24:197–211, 2003): stage II (αS pathology confined to the medulla oblongata and pontine tegmentum), stage III (αS pathology confined to the brainstem), stage IV (limbic stage), and stages V and VI (neocortical stage). αS immunohistochemistry revealed neuronal and glial cytoplasmic inclusions and neuritic changes in the neostriatum. αS inclusions were found in the medium-sized neurons (GABAergic neurons that project to the globus pallidus) and large neurons (cholinergic interneurons); the former began to appear at stage III and the latter was noted at stages V and VI. Neuritic changes and glial inclusions also began to appear at stage III. The numbers of neuronal and glial inclusions, and the extent of neuritic changes, correlated with the PD stage (P < 0.001). These findings suggest that intrinsic neostriatal neurons degenerate through αS aggregation during PD progression.     

α-Synuclein phosphorylation as a therapeutic target in Parkinson's disease

Phosphorylation is a key post-translational modification necessary for normal cellular signaling and, therefore, lies at the heart of cellular function. In neurodegenerative disorders, abnormal hyperphosphorylation of pathogenic proteins is a common phenomenon that contributes in important ways to the disease process. A prototypical protein that is hyperphosphorylated in the brain is α-synuclein (α-syn) - found in Lewy bodies and Lewy neurites - the pathological hallmarks of Parkinson's disease (PD) and other α-synucleinopathies. The genetic linkage of α-syn to PD as well as its pathological association in both genetic and sporadic cases have made it the primary protein of interest. In understanding how α-syn dysfunction occurs, increasing focus is being placed on its abnormal aggregation and the contribution of phosphorylation to this process. Studies of both the kinases and phosphatases that regulate α-syn phosphorylation are beginning to reveal the roles of this post-translational modification in disease pathogenesis. Modulation of α-syn phosphorylation may ultimately prove to be a viable strategy for disease-modifying therapeutic interventions. In this review, we explore mechanisms related to α-syn phosphorylation, its biophysical and functional consequences, and its role in neurodegeneration.     

α-Synuclein in motor neuron disease: an immunohistologic study

-Synuclein (ASN) has been implicated in neurodegenerative disorders characterized by Lewy body inclusions such as Parkinsons disease and dementia with Lewy bodies. Lewy body-like inclusions have also been observed in spinal neurons of patients with amyotrophic lateral sclerosis (ALS) and reports suggest possible ASN abnormalities in ALS patients. We assessed ASN immunoreactivity in spinal and brain tissues of subjects who had died of progressive motor neuron disorders (MND). Clinical records of subjects with MND and a comparison group were reviewed to determine the diagnosis according to El-Escariol Criteria of ALS. Cervical, thoracic and lumbar cord sections were stained with an antibody to ASN. A blinded, semiquantitative review of sections from both groups included examination for evidence of spheroids, neuronal staining, cytoplasmic inclusions, anterior horn granules, white and gray matter glial staining, corticospinal tract axonal fiber and myelin changes. MND cases, including ALS and progressive muscular atrophy, displayed significantly increased ASN staining of spheroids (P0.001), and glial staining in gray and white matter (P0.05). Significant abnormal staining of corticospinal axon tract fibers and myelin was also observed (P0.05 and 0.01). Detection of possible ASN-positive neuronal inclusions did not differ between groups. Significant ASN abnormalities were observed in MND. These findings suggest a possible role for ASN in MND; however, the precise nature of this association is unclear.     

α-Synuclein immunopositive Parkinson's disease-related inclusion bodies in lower brain stem nuclei

Advanced silver stains and immunohistochemical reactions against alpha-synuclein were used to detect Parkinson's disease-related cytoskeletal abnormalities in select lower brain stem nuclei. Various types of inclusion bodies including inconspicuous and heretofore unnoted granular particles and thread-like Lewy neurites were visualized. Of the nuclei investigated (gigantocellular reticular nucleus, bulbar raphe nuclei, coeruleus-subcoeruleus area), only lipofuscin- or neuromelanin-laden neuronal types showed a propensity to develop the pathological changes. Neuronal types devoid of pigment deposits remained free of the cytoskeletal abnormalities. Fine, dust-like particles and small globular Lewy bodies were encountered solely within the limits of intraneuronal lipofuscin or neuromelanin deposits.     

α-Synuclein is colocalized with 14-3-3 and synphilin-1 in A53T transgenic mice

α-Synuclein is a major constituent of Lewy bodies, the neuropathological hallmark of Parkinson’s disease (PD). Three types of α-synuclein mutations, A53T, A30P, and E46K, have been reported in familial PD. Wild-type α-synuclein accumulates at high concentrations in Lewy bodies, and this process is accelerated with mutated A53T α-synuclein. The accumulation of α-synuclein is thought to be toxic, and causes neuronal death when α-synuclein aggregates into protofibrils and fibrils. Lewy bodies contain not only α-synuclein, but also other proteins including 14-3-3 proteins and synphilin-1. 14-3-3 Proteins exist mainly as dimers and are related to intracellular signal transduction pathways. Synphilin-1 is known to interact with α-synuclein, promoting the formation of cytoplasmic inclusions like Lewy bodies in vitro. To investigate the colocalization of α-synuclein, synphilin-1, and 14-3-3 proteins, we performed immunohistochemical studies on α-synuclein, 14-3-3 proteins, and synphilin-1 in the brain and spinal cord of A53T transgenic mice. In homozygous mouse brains, α-synuclein immunoreactivity was observed in the neuronal somata and processes in the medial part of the brainstem, deep cerebellar nuclei, and spinal cord. The distribution of 14-3-3 proteins and synphilin-1 immunoreactivity was similar to that of α-synuclein in the homozygous mice. Double immunofluorescent staining showed that α-synuclein and synphilin-1 or 14-3-3 proteins were colocalized in the pons and spinal cord. These results indicate that the accumulation of mutant α-synuclein occurs in association with 14-3-3 proteins and synphilin-1, and may cause the sequestration of important proteins including 14-3-3 proteins and synphilin-1. The sequestration and subsequent decrease in 14-3-3 proteins and synphilin-1 levels may account for neuronal cell death.     

α-Synuclein knockout mice have cognitive impairments

α-Synuclein is a member of the synuclein family of cytoplasmic, predominantly neuron-specific proteins. Considerable amount of α-synuclein is found in axons and presynaptic terminals of neurons located in brain areas responsible for emotions and memory. In the present study we have carried out behavioral evaluation of spatial and working long-term memory of α-synuclein knockout mice. Our data shows that α-synuclein knockout mice have reduced learning ability in tests requiring both working and spatial memory. For the first time we have demonstrated that α-synuclein is necessary for these types of learning.     

α-Synuclein is expressed in a variety of brain tumors showing neuronal differentiation

α-Synuclein is presynaptic nerve terminal protein and its immunoreactivity has been observed in such neurodegenerative structures as senile plaques of Alzheimer’s disease or Lewy bodies of Parkinson’s disease. The physiological role of α-synuclein is still unknown. It is speculated that α-synuclein may be expressed in brain tumors, especially in those showing neuronal differentiation. We examined the immunohistochemical localization of α-synuclein in 77 human brain tumors. α-Synuclein was widely distributed in the brain tumors showing neuronal differentiation. As a result, positive immunostaining for α-synuclein was observed in ganglioglioma, medulloblastoma, neuroblastoma, primitive neuroectodermal tumor, pineocytoma/pineoblastoma, and central neurocytoma. Compared with other neuronal markers, the positive ratio of α-synuclein was not as high as synaptophysin, microtubule-associacted protein 2, neuron-specific enolase and tau, but it was higher than neurofilament and chromogranin A. The expression of synaptophysin was diffusely observed in the cytoplasm, cellular processes and nucleus in tumors showing neuronal differentiation; however, the expression of α-synuclein was predominantly observed in the cytoplasm of the tumors as well as in the cellular processes. On the other hand, non-neuronal brain tumors such as astrocytic tumors or meningiomas were totally negative for α-synuclein. In conclusion, the appearance of an α-synuclein-positive structure was not limited to neurodegenerative diseases, but could also be detected in neoplastic cells showing neuronal differentiation. Received: 22 March 1999 / Revised, accepted: 1 June 1999     

α-Synuclein pathology in the spinal cord autonomic nuclei associates with α-synuclein pathology in the brain: a population-based Vantaa 85+ study

In most subjects with Parkinson’s disease and dementia with Lewy bodies, α-synuclein (αS) immunoreactive pathology is found not only in the brain but also in the autonomic nuclei of the spinal cord. However, neither has the temporal course of αS pathology in the spinal cord in relation to the brain progression been established, nor has the extent of αS pathology in the spinal cord been analyzed in population-based studies. Using immunohistochemistry, the frequency and distribution of αS pathology were assessed semiquantitatively in the brains and spinal cord nuclei of 304 subjects who were aged at least 85 in the population-based Vantaa 85+ study. αS pathology was common in the spinal cord; 102 (34%) subjects had classic αS pathology in the thoracic and/or sacral autonomic nuclei. Moreover, 134 (44%) subjects showed grain- or dot-like immunoreactivity in neuropil (mini-aggregates) without classic Lewy neurites or Lewy bodies (LBs). The latter type of αS accumulation is associated with age, but also the classic αS pathology was found more often in the oldest compared to the youngest age group. The severity of αS pathology in the spinal cord autonomic nuclei is significantly associated with the extent and severity of αS pathology in the brain. Of the subjects, 60% with moderate to severe thoracic αS pathology and up to 89% with moderate to severe sacral αS pathology had diffuse neocortical type of LB pathology in the brain. αS pathology exclusively in the spinal cord was rare. Our study indicates that in general αS pathology in the spinal cord autonomic nuclei is associated with similar pathology in the brain.     

Plasma β-Amyloids and Tau Proteins in Patients with Vascular Cognitive Impairment

Increases in plasma of β-amyloids (Aβ) and tau proteins have been noted in patients with Alzheimer’s dementia (AD). Our study investigated the associations of plasma Aβ and tau proteins with dementia in stroke patients. This cross-sectional study recruited 24 controls (mean age: 67.4?±?7.5 years, 33.3% male), 27 stroke patients without dementia (mean age: 70.7?±?6.9 years, 60.7% male), 34 stroke patients with dementia (mean age: 78.3?±?5.3 years, 45.5% male, Clinical Dementia Ranking (CDR): 1.46?±?0.63), and 21 AD patients (mean age: 77.1?±?9.1 years, 42.9% male, CDR: 1.43?±?0.60) from a medical center. Dementia was defined as a CDR scale score of ≥?1. The plasma levels of Aβ-40, Aβ-42, and tau were analyzed using immunomagnetic reduction. One-way analysis of variance was used to compare the differences in measured protein levels between the groups. The results indicated that plasma levels of tau and Aβ-42, but not Aβ-40, in stroke patients were significantly higher than in the controls. After adjustment for age, sex, diabetes mellitus, hypertension, and hyperlipidemia, only plasma level of Aβ-42 remained significantly higher in stroke patients with dementia than in those without dementia (OR 1.85, 1.25–2.75, p?=?0.002). In summary, our results suggest that plasma Aβ-42 is a potential biomarker for dementia in stroke patients.