α-Synuclein: Normal Function and Role in Neurodegenerative Diseases

Dynein dysfunction induces endocytic pathology accompanied by an increase in Rab GTPases: a potential mechanism underlying age-dependent endocytic dysfunction

Growing evidence suggests that endocytic dysfunction is intimately involved in early stage Alzheimer disease pathology, such as the accumulation of beta-amyloid precursor protein in enlarged early endosomes. However, it remains unclear how endocytic dysfunction is induced in an age-dependent manner. Cytoplasmic dynein, a microtubule-based motor protein, interacts with another microtubule-associated protein, dynactin. The resulting dynein-dynactin complex mediates minus end-directed vesicle transport, including endosome trafficking. We have previously shown that the interaction between dynein-dynactin complexes is clearly attenuated in aged monkey brains, suggesting that dynein-mediated transport dysfunction exists in aged brains. Our immunohistochemical analyses revealed that age-dependent endocytic pathology was accompanied by an increase in Rab GTPases in aged monkey brains. Here, we demonstrated that siRNA-induced dynein dysfunction reproduced the endocytic pathology accompanied by increased Rab GTPases seen in aged monkey brains and significantly disrupted exosome release. Moreover, it also resulted in endosomal beta-amyloid precursor protein accumulation characterized by increased beta-site cleavage. These findings suggest that dynein dysfunction may underlie age-dependent endocytic dysfunction via the up-regulation of Rab GTPases. In addition, this vicious circle may worsen endocytic dysfunction, ultimately leading to Alzheimer disease pathology.

Pre-fibrillar alpha-synuclein variants with impaired beta-structure increase neurotoxicity in Parkinson's disease models

The relation of alpha-synuclein (alphaS) aggregation to Parkinson's disease (PD) has long been recognized, but the mechanism of toxicity, the pathogenic species and its molecular properties are yet to be identified. To obtain insight into the function different aggregated alphaS species have in neurotoxicity in vivo, we generated alphaS variants by a structure-based rational design. Biophysical analysis revealed that the alphaS mutants have a reduced fibrillization propensity, but form increased amounts of soluble oligomers. To assess their biological response in vivo, we studied the effects of the biophysically defined pre-fibrillar alphaS mutants after expression in tissue culture cells, in mammalian neurons and in PD model organisms, such as Caenorhabditis elegans and Drosophila melanogaster. The results show a striking correlation between alphaS aggregates with impaired beta-structure, neuronal toxicity and behavioural defects, and they establish a tight link between the biophysical properties of multimeric alphaS species and their in vivo function.

Valproic acid is neuroprotective in the rotenone rat model of Parkinson's disease: involvement of alpha-synuclein

Valproic acid (VPA), an established antiepileptic and antimanic drug, has recently emerged as a promising neuroprotective agent. Among its many cellular targets, VPA has been recently demonstrated to be an effective inhibitor of histone deacetylases. Accordingly, we have adopted a schedule of dietary administration (2% VPA added to the chow) that results in a significant inhibition of histone deacetylase activity and in an increase of histone H3 acetylation in brain tissues of 4 weeks-treated rats. We have tested this schedule of VPA treatment in an animal model of Parkinson's disease (PD), in which degeneration of nigro-striatal dopaminergic neurons is obtained through sub-chronic administration of the mitochondrial toxin, rotenone, via osmotic mini pumps implanted to rats. The decrease of the dopaminergic marker tyrosine hydroxylase in substantia nigra and striatum caused by 7 days toxin administration was prevented in VPA-fed rats. VPA treatment also significantly counteracted the death of nigral neurons and the 50% drop of striatal dopamine levels caused by rotenone administration. The PD-marker protein alpha-synuclein decreased, in its native form, in substantia nigra and striatum of rotenone-treated rats, while monoubiquitinated alpha-synuclein increased in the same regions. VPA treatment counteracted both these alpha-synuclein alterations. Furthermore, monoubiquitinated alpha-synuclein increased its localization in nuclei isolated from substantia nigra of rotenone-treated rats, an effect also prevented by VPA treatment. Nuclear localization of alpha-synuclein has been recently described in some models of PD and its neurodegenerative effect has been ascribed to histone acetylation inhibition. Thus, the ability of VPA to increase histone acetylation is a novel candidate mechanism for its neuroprotective action.

Lewy body/alpha-synucleinopathy in schizophrenia and depression: a preliminary neuropathological study

The role of alpha-synuclein (alphaSyn) in schizophrenia is unknown, whereas in a recent animal model of depression, alpha- and gamma-synuclein have been related to its pathophysiology. Previous biochemical studies in Brodmann area 9 showed significant reduction of alphaSyn in both chronic schizophrenia and bipolar disorder. Here, prevalence and cerebral distribution of alphaSyn were examined in 80 autopsy cases of elderly subjects (41 chronic schizophrenia, 12 late live depression/LLD and bipolar disorder/BD, and 27 age-matched controls without neuropsychiatric disorders). Using immunohistochemistry, alphaSyn-positive lesions (Lewy bodies and neurites) were assessed semiquantitatively. Among 41 chronic schizophrenics, all except one showing low neuritic Braak stages (mean 1.46), three brains (7.3%) revealed only few alphaSyn-positive inclusions restricted to medullary nuclei. Among 12 LLD and BD patients with mean Braak stage 2.25, alphaSyn-positive pathology was seen in two cases (16.7%) with clinical LLD, but none in BD. Among 27 controls, showing mean neuritic Braak stage 2.6, seven brains (26%) with higher mean age showed alphaSyn-positive lesions, either isolated in substantia nigra and nucleus basalis of Meynert (n = 2 each), in medullary nuclei, locus ceruleus and substantia nigra (n = 2), with additional involvement of nucleus basalis (n = 1). This first preliminary study in non-demented psychiatric disorders indicates that alphaSyn/Lewy pathology in chronic schizophrenia is significantly less frequent than in clinically healthy elderly people (P < 0.01), showing 10-30% of so-called incidental Lewy body disease. Among chronic affective disorders, according to our small cohort, the incidence of Lewy-pathology in LLD appears to be comparable to a healthy elderly population, whereas its occurence in BD is to be elucidated.

Small molecule protein-protein interaction inhibitors as CNS therapeutic agents: current progress and future hurdles

Protein-protein interactions are a crucial element in cellular function. The wealth of information currently available on intracellular-signaling pathways has led many to appreciate the untapped pool of potential drug targets that reside downstream of the commonly targeted receptors. Over the last two decades, there has been significant interest in developing therapeutics and chemical probes that inhibit specific protein-protein interactions. Although it has been a challenge to develop small molecules that are capable of occluding the large, often relatively featureless protein-protein interaction interface, there are increasing numbers of examples of small molecules that function in this manner with reasonable potency. This article will highlight the current progress in the development of small molecule protein-protein interaction inhibitors that have applications in the treatment or study of central nervous system function and disease. In particular, we will focus upon recent work towards developing small molecule inhibitors of amyloid-beta and alpha-synuclein aggregation, inhibitors of critical components of G-protein-signaling pathways, and PDZ domain inhibitors.

Microglial phagocytosis is enhanced by monomeric alpha-synuclein, not aggregated alpha-synuclein: implications for Parkinson's disease

Gathering evidence has associated activation of microglia with the pathogenesis of numerous neurodegenerative diseases of the central nervous system (CNS) such as Alzheimer's disease and Parkinson's disease. Microglia are the resident macrophages of the CNS whose functions include chemotaxis, phagocytosis, and secretion of a variety of cytokines and proteases. In this study, we examined the possibility that alpha-synuclein (alpha-syn), which is associated with the pathogenesis of Parkinson's disease, may affect the phagocytic function of microglia. We found that extracellular monomeric alpha-syn enhanced microglial phagocytosis in both a dose- and time-dependent manner, but beta- and gamma- syn did not. We also found that the N-terminal and NAC region of alpha-syn, especially the NAC region, might be responsible for the effect of alpha-syn on microglial phagocytosis. In contrast to monomeric alpha-syn, aggregated alpha-syn actually inhibited microglial phagocytosis. The different effects of monomeric and aggregated alpha-syn on phagocytosis might be related to their localization in cells. This study indicates that alpha-syn can modulate the function of microglia and influence inflammatory changes such as those seen in neurodegenerative disorders.

Common key-signals in learning and neurodegeneration: focus on excito-amino acids, beta-amyloid peptides and alpha-synuclein

In this paper a hypothesis that some special signals ("key-signals" excito-amino acids, beta-amyloid peptides and alpha-synuclein) are not only involved in information handling by the neuronal circuits, but also trigger out substantial structural and/or functional changes in the Central Nervous System (CNS) is introduced. This forces the neuronal circuits to move from one stable state towards a new state, but in doing so these signals became potentially dangerous. Several mechanisms are put in action to protect neurons and glial cells from these potentially harmful signals. However, in agreement with the Red Queen Theory of Ageing (Agnati et al. in Acta Physiol Scand 145:301-309, 1992), it is proposed that during ageing these neuroprotective processes become less effective while, in the meantime, a shortage of brain plasticity occurs together with an increased need of plasticity for repairing the wear and tear of the CNS. The paper presents findings supporting the concept that such key-signals in instances such as ageing may favour neurodegenerative processes in an attempt of maximizing neuronal plasticity.

Aging and alpha-synuclein affect synaptic plasticity in the dentate gyrus

Although intracellular accumulation of alpha-synuclein (alpha-syn) is a characteristic pathological change in Parkinson's disease, Lewy body dementia and Alzheimer's disease, the normal function of this presynaptic protein is still unknown. To assess the contribution of alpha-syn to synaptic plasticity as well as to age-related synaptic degeneration in mice, we compared adult and aged mice overexpressing mutated (A30P) human alpha-syn with their nontransgenic littermates using behavioral tests and electrophysiological measures in the dentate gyrus. We found decreased basal synaptic transmission and paired-pulse facilitation in the perforant path-dentate granule cell synapses of aged mice. In addition, alpha-syn accumulation in aged A30P mice but not in aged wild-type mice led to long-term depression of synaptic transmission after a stimulation protocol that normally induces long-term potentiation. These findings suggest that overexpression of mutated alpha-syn exacerbates the aging process and leads to impaired synaptic plasticity.

Molecular mechanisms of alpha-synuclein neurodegeneration

alpha-Synuclein is an abundant highly charged protein that is normally predominantly localized around synaptic vesicles in presynaptic terminals. Although the function of this protein is still ill-defined, genetic studies have demonstrated that point mutations or genetic alteration (duplications or triplications) that increase the number of copies of the alpha-synuclein (SCNA) gene can cause Parkinson's disease or the related disorder dementia with Lewy bodies. alpha-Synuclein can aberrantly polymerize into fibrils with typical amyloid properties, and these fibrils are the major component of many types of pathological inclusions, including Lewy bodies, which are associated with neurodegenerative diseases, such as Parkinson's disease. Although there is substantial evidence supporting the toxic nature of alpha-synuclein inclusions, other modes of toxicity such as oligomers have been proposed. In this review, some of the evidence for the different mechanisms of alpha-synuclein toxicity is presented and discussed.

Neuroinflammation and oxidation/nitration of alpha-synuclein linked to dopaminergic neurodegeneration

alpha-Synuclein (SYN) is the major component of Lewy bodies, the neuropathological hallmarks of Parkinson's disease (PD). Missense mutations and multiplications of the SYN gene cause autosomal dominant inherited PD. Thus, SYN is implicated in the pathogenesis of PD. However, the mechanism whereby SYN promotes neurodegeneration remains unclear. Familial PD with SYN gene mutations are rare because the majority of PD is sporadic and emerging evidence indicates that sporadic PD may result from genetic and environmental risk factors including neuroinflammation. Hence, we examined the relationship between SYN dysfunction and neuroinflammation in mediating dopaminergic neurodegeneration in mice and dopaminergic neuronal cultures derived from wild-type SYN and mutant A53T SYN transgenic mice in a murine SYN-null (SYNKO) background (M7KO and M83KO, respectively). Stereotaxic injection of an inflammagen, lipopolysaccharide, into substantia nigra of these SYN genetically engineered mice induced similar inflammatory reactions. In M7KO and M83KO, but not in SYNKO mice, the neuroinflammation was associated with dopaminergic neuronal death and the accumulation of insoluble aggregated SYN as cytoplasmic inclusions in nigral neurons. Nitrated/oxidized SYN was detected in these inclusions and abatement of microglia-derived nitric oxide and superoxide provided significant neuroprotection in neuron-glia cultures from M7KO mice. These data suggest that nitric oxide and superoxide released by activated microglia may be mediators that link inflammation and abnormal SYN in mechanisms of PD neurodegeneration. This study advances understanding of the role of neuroinflammation and abnormal SYN in the pathogenesis of PD and opens new avenues for the discovery of more effective therapies for PD.

Amyloidogenesis of natively unfolded proteins

Aggregation and subsequent development of protein deposition diseases originate from conformational changes in corresponding amyloidogenic proteins. The accumulated data support the model where protein fibrillogenesis proceeds via the formation of a relatively unfolded amyloidogenic conformation, which shares many structural properties with the pre-molten globule state, a partially folded intermediate first found during the equilibrium and kinetic (un)folding studies of several globular proteins and later described as one of the structural forms of natively unfolded proteins. The flexibility of this structural form is essential for the conformational rearrangements driving the formation of the core cross-beta structure of the amyloid fibril. Obviously, molecular mechanisms describing amyloidogenesis of ordered and natively unfolded proteins are different. For ordered protein to fibrillate, its unique and rigid structure has to be destabilized and partially unfolded. On the other hand, fibrillogenesis of a natively unfolded protein involves the formation of partially folded conformation; i.e., partial folding rather than unfolding. In this review recent findings are surveyed to illustrate some unique features of the natively unfolded proteins amyloidogenesis.

The fold of alpha-synuclein fibrils

The aggregation of proteins into amyloid fibrils is associated with several neurodegenerative diseases. In Parkinson's disease it is believed that the aggregation of alpha-synuclein (alpha-syn) from monomers by intermediates into amyloid fibrils is the toxic disease-causative mechanism. Here, we studied the structure of alpha-syn in its amyloid state by using various biophysical approaches. Quenched hydrogen/deuterium exchange NMR spectroscopy identified five beta-strands within the fibril core comprising residues 35-96 and solid-state NMR data from amyloid fibrils comprising the fibril core residues 30-110 confirmed the presence of beta-sheet secondary structure. The data suggest that beta1-strand interacts with beta2, beta2 with beta3, beta3 with beta4, and beta4 with beta5. High-resolution cryoelectron microscopy revealed the protofilament boundaries of approximately 2 x 3.5 nm. Based on the combination of these data and published structural studies, a fold of alpha-syn in the fibrils is proposed and discussed.

Alpha-synuclein-immunopositive myenteric neurons and vagal preganglionic terminals: autonomic pathway implicated in Parkinson's disease?

The protein alpha-synuclein is implicated in the development of Parkinson's disease. The molecule forms Lewy body aggregates that are hallmarks of the disease, has been associated with the spread of neuropathology from the peripheral to the CNS, and appears to be involved with the autonomic disorders responsible for the gastrointestinal (GI) symptoms of individuals afflicted with Parkinson's. To characterize the normative expression of alpha-synuclein in the innervation of the GI tract, we examined both the postganglionic neurons and the preganglionic projections by which the disease is postulated to retrogradely invade the CNS. Specifically, in Fischer 344 and Sprague-Dawley rats, immunohistochemistry in conjunction with injections of the tracer Dextran-Texas Red was used to determine, respectively, the expression of alpha-synuclein in the myenteric plexus and in the vagal terminals. Alpha-synuclein is expressed in a subpopulation of myenteric neurons, with the proportion of positive somata increasing from the stomach (approximately 3%) through duodenum (proximal, approximately 6%; distal, approximately 13%) to jejunum (approximately 22%). Alpha-synuclein is co-expressed with the nitrergic enzyme nitric oxide synthase (NOS) or the cholinergic markers calbindin and calretinin in regionally specific patterns: approximately 90% of forestomach neurons positive for alpha-synuclein express NOS, whereas approximately 92% of corpus-antrum neurons positive for alpha-synuclein express cholinergic markers. Vagal afferent endings in the myenteric plexus and the GI smooth muscle do not express alpha-synuclein, whereas, virtually all vagal preganglionic projections to the gut express alpha-synuclein, both in axons and in terminal varicosities in apposition with myenteric neurons. Vagotomy eliminates most, but not all, alpha-synuclein-positive neurites in the plexus. Some vagal preganglionic efferents expressing alpha-synuclein form varicose terminal rings around myenteric plexus neurons that are also positive for the protein, thus providing a candidate alpha-synuclein-expressing pathway for the retrograde transport of putative Parkinson's pathogens or toxins from the ENS to the CNS.

Differential expression of alpha-synuclein, parkin, and synphilin-1 isoforms in Lewy body disease

Alpha-synuclein, parkin, and synphilin-1 are proteins mainly involved in the pathogenesis of Lewy body (LB) diseases. mRNAs of all three undergo alternative splicing, so that the existence of various isoforms has been described. Since increasing evidence supports the importance of differential isoform-expression changes in disease development, we have established isoform-expression profiles in frontal cortices of LB disease brains in comparison with those of Alzheimer disease (AD) and control frontal cortices. The differential expression of four alpha-synuclein, seven parkin, and four synphilin-1 isoforms was ascertained by the use of isoform-specific primers and relative expression analysis with SybrGreen and beta-actin as an internal standard. The establishment of isoform-expression profiles revealed that these are disease specific. Moreover, isoform-expression deregulation of mainly one gene in each disease could be observed. All four alpha-synuclein isoforms were affected in the case of the pure form of dementia with LB, most parkin transcript variants in common LB disease, and all synphilin-1 isoforms in Parkinson disease. Only minor involvement was detected in AD. Finally, the existence of a proprietary isoform-expression profile in common LB disease indicates that this disease develops as a result of its own molecular mechanisms, and so, at the molecular level, it does not exactly share changes found in pure dementia with LB and AD. In conclusion, isoform-expression profiles in LB diseases represent additional evidence for the direct involvement of isoform-expression deregulation in the development of neurodegenerative disorders.

Elevated alpha-synuclein mRNA levels in individual UV-laser-microdissected dopaminergic substantia nigra neurons in idiopathic Parkinson's disease

The presynaptic protein α-synuclein is involved in several neurodegenerative diseases, including Parkinson's disease (PD). In rare familial forms of PD, causal mutations (PARK1) as well as multiplications (PARK4) of the α-synuclein gene have been identified. In sporadic, idiopathic PD, abnormal accumulation and deposition of α-synuclein might also cause degeneration of dopaminergic midbrain neurons, the clinically most relevant neuronal population in PD. Thus, cell-specific quantification of α-synuclein expression-levels in dopaminergic neurons from idiopathic PD patients in comparison to controls would provide essential information about contributions of α-synuclein to the etiology of PD. However, a number of previous studies addressing this question at the tissue-level yielded varying results regarding α-synuclein expression. To increase specificity, we developed a cell-specific approach for mRNA quantification that also took into account the important issue of variable RNA integrities of the individual human postmortem brain samples. We demonstrate that PCR –amplicon size can confound quantitative gene-expression analysis, in particular of partly degraded RNA. By combining optimized UV-laser microdissection- and quantitative RT–PCR-techniques with suitable PCR assays, we detected significantly elevated α-synuclein mRNA levels in individual, surviving neuromelanin- and tyrosine hydroxylase-positive substantia nigra dopaminergic neurons from idiopathic PD brains compared to controls. These results strengthen the pathophysiologic role of transcriptional dysregulation of the α-synuclein gene in sporadic PD.

Multiple system atrophy: alpha-synuclein and neuronal degeneration

Multiple system atrophy (MSA) is a sporadic neurodegenerative disorder that encompasses olivopontocerebellar atrophy (OPCA), striatonigral degeneration (SND) and Shy-Drager syndrome (SDS). The histopathological hallmark is the formation of alpha-synuclein-positive glial cytoplasmic inclusions (GCIs) in oligodendroglia. alpha-synuclein aggregation is also found in glial nuclear inclusions, neuronal cytoplasmic inclusions (NCIs), neuronal nuclear inclusions (NNIs) and dystrophic neurites. We evaluated the pathological features of 102 MSA cases, and presented the pathological spectrum of MSA and initial features of alpha-synuclein accumulation. We found that 39% of the 102 cases showed equivalent SND and OPCA pathologies, 33% showed OPCA- and 22% showed SND-predominant pathology, whereas 6% showed extremely mild changes. Our pathological analysis indicated that OPCA-type was relatively more frequent and SND-type was less frequent in Japanese MSA cases, compared to the relatively high frequency of SND-type in Western countries, suggesting that different phenotypic patterns of MSA may exist between races. In the early stage, in addition to GCIs, NNIs and diffuse homogenous alpha-synuclein staining in neuronal nuclei and cytoplasm were observed in lesions in the pontine nuclei, putamen, substantia nigra, locus ceruleus, inferior olivary nucleus, intermediolateral column of thoracic spinal cord, lower motor neurons and cortical pyramidal neurons. A subgroup of MSA cases with severe temporal atrophy showed numerous NCIs, particularly in the limbic system. These findings suggest that primary non-fibrillar and fibrillar alpha-synuclein aggregation also occur in neurons. The oligo-myelin-axon-neuron complex mechanism, along with the direct involvement of neurons themselves, may synergistically accelerate the degenerative process of MSA.

The microtubule-associated protein tau is phosphorylated by Syk

Aberrant phosphorylation of tau protein on serine and threonine residues has been shown to be critical in neurodegenerative disorders called tauopathies. An increasing amount of data suggest that tyrosine phosphorylation of tau might play an equally important role in pathology, with at least three putative tyrosine kinases of tau identified to date. It was recently shown that the tyrosine kinase Syk could efficiently phosphorylate α-synuclein, the aggregated protein found in Parkinson's disease and other synucleinopathies. We report herein that Syk is also a tau kinase, phosphorylating tau in vitro and in CHO cells when both proteins are expressed exogenously. In CHO cells, we have also demonstrated by co-immunoprecipitation that Syk binds to tau. Finally, by site-directed mutagenesis substituting the tyrosine residues of tau with phenylalanine, we established that tyrosine 18 was the primary residue in tau phosphorylated by Syk. The identification of Syk as a common tyrosine kinase of both tau and α-synuclein may be of potential significance in neurodegenerative disorders and also in neuronal physiology. These results bring another clue to the intriguing overlaps between tauopathies and synucleinopathies and provide new insights into the role of Syk in neuronal physiology.

Identification and characterization of a new alpha-synuclein isoform and its role in Lewy body diseases

Alternative splicing is an important mechanism to generate a large number of mRNAs, thus increasing proteome diversity and tissue specificity. Three transcript variants of alpha-synuclein, a neuronal protein mainly involved in synapses, have been described so far. Whereas alpha-synuclein 140 is the whole and main transcript, alpha-synuclein 112 and 126 are short proteins that result from in-frame deletions of exons 3 and 5, respectively. Because the aforesaid alpha-synuclein isoforms show differential expression changes in Lewy body diseases (LBDs), in the present work, we searched for a fourth alpha-synuclein isoform and studied its expression levels in LBD brains. By using isoform-specific primers, isoform co-amplification and direct sequencing, we identified alpha-synuclein 98, which lacks exons 3 and 5. mRNA expression analyses in non-neuronal tissue revealed that alpha-synuclein 98 is a brain-specific splice variant with varying expression levels in different areas of fetal and adult brain. Additionally, we studied alpha-synuclein 98 expression levels by real-time semi-quantitative RT-PCR in the frontal cortices of LBD patients and compared them with those of Alzheimer disease (AD) patients and control subjects. Overexpression of alpha-synuclein 98 in LBD and AD brains would indicate its specific involvement in the pathogenesis of these neurodegenerative disorders.

Pial arteriolar vasomotion changes during cortical activation in rats

The oscillatory pattern of pial arterioles, i.e. vasomotion, has been described since early 1980s, but the impact of neural activation on such oscillations has never been formally examined. Sciatic nerve stimulation, a well characterized model for studying neurovascular coupling (NVC), leads to a neural activity-related increase of pial arteriolar diameter in the contralateral hindlimb somatosensory cortex. Exploiting such an experimental model, the aim of the present study was to explore vasomotion and its changes during NVC with a novel analytical approach. Indeed, to characterize oscillations, we evaluated the total spectral power in the range 0.02-2.00 Hz and subdivided this frequency interval into seven 50% overlapping frequency bands. Results indicated that only arterioles overlying the stimulated hindlimb cortex showed a significant increase of total power, unlike arterioles overlaying the whisker barrel cortex, used as control for the vascular response specificity. The total power increase was sustained mainly by marked increments in the low frequency range, with two peaks at 0.03 and 0.08 Hz, and by a wide increase in the high frequency range (0.60-2.00 Hz) in the averaged spectrum. These activity-related spectral changes suggest: (i) that it is possible to assess the vascular responses by using total power; (ii) the existence of at least three distinct mechanisms involved in the control of NVC, two with a feedback frequency loop in the low frequency range and another one in the high range; (iii) a potential involvement of vasomotion in NVC. Moreover, these findings highlight the oscillatory nature of the mechanisms controlling NVC.

Alpha-synuclein involvement in hippocampal synaptic plasticity: role of NO, cGMP, cGK and CaMKII

Synaptic plasticity involves a series of coordinate changes occurring both pre- and postsynaptically, of which alpha-synuclein is an integral part. We have investigated on mouse primary hippocampal neurons in culture whether redistribution of alpha-synuclein during plasticity involves retrograde signaling activation through nitric oxide (NO), cGMP, cGMP-dependent protein kinase (cGK) and calmodulin-dependent protein kinase II. We have found that deletion of the alpha-synuclein gene blocks both the long-lasting enhancement of evoked and miniature transmitter release and the increase in the number of functional presynaptic boutons evoked through the NO donor, DEA/NO, and the cGMP analog, 8-Br-cGMP. In agreement with these findings both DEA/NO and 8-Br-cGMP were capable of producing a long-lasting increase in number of clusters for alpha-synuclein through activation of soluble guanylyl cyclase, cGK and calcium/calmodulin-dependent protein kinase IIalpha. Thus, our results suggest that NO, cGMP, GMP-dependent protein kinase and calmodulin-dependent protein kinase II play a key role in the redistribution of alpha-synuclein during plasticity.

Alpha-synuclein protects cerebellar granule neurons against 6-hydroxydopamine-induced death

The physiological role of alpha-synuclein, a protein found enriched in intraneuronal deposits characterizing Parkinson's disease, is debated. While its aggregation is usually considered linked to neuropathology, its normal function may be related to fundamental processes of synaptic transmission and plasticity. By using antisense oligonucleotide strategy, we report in this study that alpha-synuclein silencing in cultured cerebellar granule cells results in widespread death of these neurons, thus demonstrating an essential pro-survival role of the protein towards primary neurons. To study alpha-synuclein expression and processing in a Parkinson's disease model of neurotoxicity, we exposed differentiated cultures of cerebellar granule neurons to toxic concentrations of 6-hydroxydopamine (6-OHDA). This resulted in neuronal death accompanied by a decrease of the monomeric form of alpha-synuclein, which was due to both decreased synthesis of the protein and its increased mono-ubiquitination accompanied by nuclear translocation. The essential neuroprotective role of alpha-synuclein was confirmed by the fact that subchronic valproate treatment, which increases alpha-synuclein expression and prevents its nuclear translocation in cerebellar granule cells exposed to 6-OHDA, significantly protected these neurons from 6-OHDA insult. In agreement with the pro-survival role of alpha-synuclein in this model, subtoxic concentrations of alpha-synuclein antisense oligonucleotides, aggravated 6-OHDA toxicity towards granule neurons. Our results demonstrate that normal alpha-synuclein expression is essential for the viability of primary neurons and that its pro-survival role is abolished in 6-OHDA neurotoxic challenge. These results are relevant to more precisely define the role of alpha-synuclein in neuronal cells and to better understand its putative involvement in neurodegeneration.

Multiple proteins implicated in neurodegenerative diseases accumulate in axons after brain trauma in humans

Studies in animal models have shown that traumatic brain injury (TBI) induces the rapid accumulation of many of the same key proteins that form pathologic aggregates in neurodegenerative diseases. Here, we examined whether this rapid process also occurs in humans after TBI. Brain tissue from 18 cases who died after TBI and from 6 control cases was examined using immunohistochemistry. Following TBI, widespread axonal injury was persistently identified by the accumulation of neurofilament protein and amyloid precursor protein (APP) in axonal bulbs and varicosities. Axonal APP was found to co-accumulate with its cleavage enzymes, beta-site APP cleaving enzyme (BACE), presenilin-1 (PS1) and their product, amyloid-beta (Abeta). In addition, extensive accumulation of alpha-synuclein (alpha-syn) was found in swollen axons and tau protein was found to accumulate in both axons and neuronal cell bodies. These data show rapid axonal accumulation of proteins implicated in neurodegenerative diseases including Alzheimer's disease and the synucleinopathies. The cause of axonal pathology can be attributed to disruption of axons due to trauma, or as a secondary effect of raised intracranial pressure or hypoxia. Such axonal pathology in humans may provide a unique environment whereby co-accumulation of APP, BACE, and PS1 leads to intra-axonal production of Abeta as well as accumulation of alpha-syn and tau. This process may have important implications for survivors of TBI who have been shown to be at greater risk of developing neurodegenerative diseases.

Investigation of alpha-synuclein fibril structure by site-directed spin labeling

The misfolding and fibril formation of alpha-synuclein plays an important role in neurodegenerative diseases such as Parkinson disease. Here we used electron paramagnetic resonance spectroscopy, together with site-directed spin labeling, to investigate the structural features of alpha-synuclein fibrils. We generated fibrils from a total of 83 different spin-labeled derivatives and observed single-line, exchange-narrowed EPR spectra for the majority of all sites located within the core region of alpha-synuclein fibrils. Such exchange narrowing requires the orbital overlap between multiple spin labels in close contact. The core region of alpha-synuclein fibrils must therefore be arranged in a parallel, in-register structure wherein same residues from different molecules are stacked on top of each other. This parallel, in-register core region extends from residue 36 to residue 98 and is tightly packed. Only a few sites within the core region, such as residues 62-67 located at the beginning of the NAC region, as well as the N- and C-terminal regions outside the core region, are significantly less ordered. Together with the accessibility measurements that suggest the location of potential beta-sheet regions within the fibril, the data provide significant structural constraints for generating three-dimensional models. Furthermore, the data support the emerging view that parallel, in-register structure is a common feature shared by a number of naturally occurring amyloid fibrils.

Role of mitochondrial dysfunction in Parkinson's disease: Implications for treatment

The role of mitochondrial dysfunction as a possible cause of parkinsonism became apparent in the mid-1980s with the discovery of a group of individuals with chronic parkinsonism who had been exposed to the chemical 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and the subsequent elucidation of the mode of action of this toxin as a mitochondrial complex I inhibitor. Thereafter, a defect in mitochondrial complex I was supported by biochemical studies in patients with sporadic Parkinson's disease. Recently, striking genetic findings and biological studies have further substantiated that mitochondrial dysfunction is likely an important disease mechanism in a significant percentage, if not the majority, of patients with Parkinson's disease. These findings have defined novel biochemical pathways that can directly or indirectly affect mitochondrial function and/or integrity. Although various primary insults (genetic or environmental factors) are involved in the aetiology of Parkinson's disease, emerging evidence supports the notion that attempting to prevent or compensate for mitochondrial dysfunction could have therapeutic benefits for a majority of patients with Parkinson's disease.

Pesticide exposure exacerbates alpha-synucleinopathy in an A53T transgenic mouse model

The factors initiating or contributing to the pathogenesis of Parkinson's disease and related neurodegenerative synucleinopathies are still largely unclear, but environmental factors such as pesticides have been implicated. In this study, A53T mutant human alpha-synuclein transgenic mice (M83), which develop alpha-synuclein neuropathology, were treated with the pesticides paraquat and maneb (either singly or together), and their effects were analyzed. Immunohistochemical and biochemical analyses showed that chronic treatment of M83 transgenic mice with both pesticides (but not with either pesticide alone) drastically increased neuronal alpha-synuclein pathology throughout the central nervous system including the hippocampus, cerebellum, and sensory and auditory cortices. alpha-Synuclein-associated mitochondrial degeneration was observed in M83 but not in wild-type alpha-synuclein transgenic mice. Because alpha-synuclein inclusions accumulated in pesticide-exposed M83 transgenic mice without a motor phenotype, we conclude that alpha-synuclein aggregate formation precedes disease onset. These studies support the notion that environmental factors causing nitrative damage are closely linked to mechanisms underlying the formation of alpha-synuclein pathologies and the onset of Parkinson's-like neurodegeneration.

Aging of the rat mesostriatal system: Differences between the nigrostriatal and the mesolimbic compartments

The impairment of the mesostriatal dopaminergic system has been considered responsible for motor and affective disturbances associated with aging and a risk factor for Parkinson's disease. However, the basic mechanisms underlying this phenomenon are still unknown. Here we used biochemical, molecular and morphological techniques directed at detecting flaws in the dopamine synthesis route and signs of dopaminergic degeneration in the rat mesostriatal system during normal aging. We found two different age-related processes. One is characterized by a dopa decarboxylase decrease, and involves both the nigrostriatal and mesolimbic compartments, and is responsible for a moderate dopamine loss in the dorsal striatum, where other parameters of dopamine synthesis are not affected. The other is characterized by axonal degeneration with aggregation of phosphorylated forms of tyrosine hydroxylase (TH) and amyloid precursor protein in degenerate terminals, and alpha-synuclein in their original somata. This process is restricted to mesolimbic regions and is responsible for the decline of TH activity and l-dopa levels and the greater decrease in dopamine levels in this compartment. These findings suggest that both the nigrostriatal and the mesolimbic systems are vulnerable to aging, but in contrast to what occurs in Parkinson's disease, the mesolimbic system is more vulnerable to aging than the nigrostriatal one.

Alpha-synuclein activates stress signaling protein kinases in THP-1 cells and microglia

Here we show that alpha-synuclein, a major constituent of Lewy bodies, induces inflammation in human microglial and human THP-1 cells. Secretions from such stimulated THP-1 cells contain increased levels of IL-1beta and TNF-alpha. When stimulated by alpha-synuclein in combination with IFN-gamma, secretions from the cells also become toxic towards SH-SY5Y neuroblastoma cells. The A30P, E46K and A53T alpha-synuclein mutations, which induce Parkinson's disease, are more potent than normal alpha-synuclein in the induction of such cytotoxicity. To investigate the signaling mechanisms evoked, protein phosphorylation profiling was applied. At least 81 target phospho-sites were identified. Large increases were induced in the three major mitogen-activated protein (MAP) kinase pathways: p38 MAP kinase, extracellular regulated protein-serine kinase (ERK)1/2 and c-Jun-N-terminal kinase (JNK). Upregulation occurred within minutes following exposure to alpha-synuclein, which is consistent with a receptor-mediated effect. These findings demonstrate that alpha-synuclein acts as a potent inflammatory stimulator of microglial cells, and that inhibitors of such stimulation might be beneficial in the treatment of Parkinson's disease and other synucleinopathies.

Alpha-synuclein and its disease-causing mutants induce ICAM-1 and IL-6 in human astrocytes and astrocytoma cells

Autosomal dominant Parkinson disease (PD) is caused by duplication or triplication of the alpha-synuclein gene as well as by the A30P, E46K, and A53T mutations. The mechanisms are unknown. Reactive astrocytes in the substantia nigra of PD and MPTP-treated monkeys display high levels of the inflammatory mediator intercellular adhesion molecule-1 (ICAM-1), indicating that chronic inflammation contributes to the degeneration. Here we report that alpha-synuclein strongly stimulates human astrocytes as well as human U-373 MG astrocytoma cells to up-regulate both interleukin (IL)-6 and ICAM-1 (ED50=5 microg ml(-1)). The mutated forms are more potent stimulators than wild-type (WT) alpha-synuclein in these assays. We demonstrate by immunoblotting analysis that this up-regulation is associated with activation of the major mitogen-activated protein kinase (MAPK) pathways. It is also attenuated by PD 98059, an inhibitor of the MAPK/extracellular-regulated kinase kinase MEK1/2, SP 600125, an inhibitor of c-Jun N-terminal kinase (JNK), and SB 202190, an inhibitor of p38 MAPK. The inhibitory effects on human astrocytes have IC50 values of 2, 5, and 1.5 microM respectively. We hypothesize that the neuroinflammation stimulated by release of an excess of normal alpha-synuclein or by release of its mutated forms can be involved in the pathobiology of PD.

Interactions of volatile anesthetics with neurodegenerative-disease-associated proteins

The prevalence of the neurodegenerative disorders is increasing as life expectancy lengthens, and there exists concern that environmental influences may contribute to this increase. These disorders are varied in their clinical presentation, but appear to have a common biophysical initiation. At this level, it is both plausible and now proven that anesthetics can enhance aggregation of some disease-causing proteins. Although data in support of an interaction in animal models are still lacking, data from clinical studies indicate an association, which provides further cause for concern. Many opportunities exist for rapid progress at all levels on defining whether anesthetics do indeed contribute to the pathogenesis of these progressive, debilitating disorders.

gamma-synuclein has a dynamic intracellular localization

gamma-Synuclein is a member of the synuclein family consisting of three proteins. Within the last several years increasing attention has focused on these proteins because of their role in human diseases. alpha-Synuclein relevance to Parkinson's disease is based on mutations found in familial cases of the disease and its presence in filaments and inclusion bodies in sporadic cases. gamma-Synuclein is implicated in some forms of cancer and ocular diseases, while beta-synuclein may antagonize their pathological functions. In this paper we present data on the localization and properties of gamma-synuclein in several neuronal and nonneuronal cell cultures. We show that contrary to the current opinion, gamma-synuclein is not an exclusively cytoplasmic protein, but has a dynamic localization and can associate with subcellular structures. It is present in the perinuclear area and may be associated to centrosomes. On late steps of mitosis gamma-synuclein is not found in the centrosomes, and redistributes to the midbody in telophase. Under stress conditions a translocation of gamma-synuclein from the perinuclear area to the nucleus occurs exhibiting nucleocytoplasmic shuttling. gamma-Synuclein overexpression reduces neurite outgrowth in a greater extent then alpha-synuclein overexpression. These data support the view that gamma-synuclein may change its intracellular localization and associate with subcellular structures in response to intracellular signaling or stress.

Endogenous alpha-synuclein is induced by valproic acid through histone deacetylase inhibition and participates in neuroprotection against glutamate-induced excitotoxicity

Emerging evidence suggests that alpha-synuclein (alpha-syn), which is traditionally thought to have a pathophysiological role in neurodegenerative diseases, can have neuroprotective effects. This study aimed to investigate whether endogenous alpha-syn in neurons can be induced by valproic acid (VPA), a mood-stabilizer, anticonvulsant and histone deacetylase (HDAC) inhibitor, and if so, whether the alpha-syn induction is neuroprotective. VPA treatment of rat cerebellar granule cells caused a robust dose- and time-dependent increase in levels of alpha-syn protein and mRNA and in the intensity of alpha-syn immunostaining. Knockdown of VPA-induced alpha-syn overexpression with alpha-syn antisense oligonucleotides or siRNA completely blocked VPA-induced neuroprotection. alpha-Syn knockdown also exacerbated glutamate neurotoxicity, stimulated the expression of the proapoptotic gene ubiquitin-conjugating enzyme E2N, and downregulated the expression of the anti-apoptotic gene Bcl-2. Induction of alpha-syn by VPA was associated with inhibition of HDAC activity, resulting in hyperacetylation of histone H3 in the alpha-syn promoter and a marked increase in alpha-syn promoter activity. Moreover, VPA-induced alpha-syn induction and neuroprotection were mimicked by HDAC inhibitors sodium 4-phenylbutyrate and trichostatin A (TSA). alpha-syn was also induced by VPA in rat cerebral cortical neurons. Additionally, treatment of rats with VPA, sodium butyrate, or TSA markedly increased alpha-syn protein levels in the cortex and cerebellum. Together, our results demonstrate for the first time that VPA induces alpha-syn in neurons through inhibition of HDAC and that this alpha-syn induction is critically involved in neuroprotection against glutamate excitotoxicity. Clinically, VPA may represent a suitable treatment for excitotoxicity-related neurodegenerative diseases.

Cellular and molecular mechanisms of Parkinson's disease: neurotoxins, causative genes, and inflammatory cytokines

1. Parkinson's disease (PD) is considered to be an aging-related neurodegeneration of catecholamine (CA) systems [typically A9 dopamine (DA) neurons in the substantia nigra and A6 noradrenaline (NA) neurons in the locus coeruleus]. The main symptom is movement disorder caused by a DA deficiency at the nerve terminals of fibers that project from the substantia nigra to the striatum. Most PD is sporadic (sPD) without any hereditary history. sPD is speculated to be caused by some exogenous or endogenous substances that are neurotoxic toward CA neurons, which toxicity leads to mitochondrial dysfunction and subsequent oxidative stress resulting in the programmed cell death (apoptosis or autophagy) of DA neurons. 2. Recent studies on the causative genes of rare familial PD (fPD) cases, such as alpha-synuclein and parkin, suggest that dysfunction of the ubiquitin-proteasome system (UPS) and the resultant accumulation of misfolded proteins and endoplasmic reticulum stress may cause the death of DA neurons. 3. Activated microglia, which accompany an inflammatory process, are present in the nigro-striatum of the PD brain; and they produce protective or toxic substances, such as cytokines, neurotrophins, and reactive oxygen or nitrogen species. These activated microglia may be neuroprotective at first in the initial stage, and later may become neurotoxic owing to toxic change to promote the progression toward the death of CA neurons.4. All of these accumulating evidences on sPD and fPD points to a hypothesis that multiple primary causes of PD may be ultimately linked to a final common signal-transduction pathway leading to programmed cell death, i.e., apoptosis or autophagy, of the CA neurons.

Increased lifespan in transgenic Caenorhabditis elegans overexpressing human alpha-synuclein

alpha-Synuclein is a short 14-kDa protein found in pathological lesions of age-related neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, and multiple system atrophy. Its overexpression in transgenic mice, rats, Drosophila melanogaster, and Caenorhabditis elegans recapitulates many of the pathologic features observed in human Parkinson's disease including loss of dopaminergic neurons and motor deficits. Integrated transgenic C. elegans lines were generated that overexpress either human wildtype (WT) or mutant (A53T) forms. These transgenic lines demonstrated approximately 25% increase in lifespan (p<0.0001) compared to controls. When the transgenes were crossed into long-lived daf-2 (m577) or daf-2 (e1370) genetic backgrounds, the lifespan increase was also approximately 25% in comparison to the corresponding daf-2 strains (p<0.05). Pharyngeal pumping and egg laying were significantly decreased in the overexpressing transgenic lines, and lifespan increases were attenuated when lines were grown on thick bacterial lawns, suggesting that caloric restriction may explain some of the effects on lifespan. These studies provide initial evidence for a beneficial role of human alpha-synuclein in influencing lifespan.

Importin-mediated nuclear transport in neurons

The polarized morphology of neurons poses a particular challenge to intracellular signal transduction. Local signals generated at distal sites must be retrogradely transported to the nucleus to produce persistent changes in neuronal function. Such communication of signals between distal neuronal compartments and the nucleus occurs during axon guidance, synapse formation, synaptic plasticity and following neuronal injury. Recent studies have begun to delineate a role for the active nuclear import pathway in transporting signals from axons and dendrites to the nucleus. In this pathway, soluble cargo proteins are recognized by nuclear transport carriers, called importins, which mediate their translocation from the cytoplasm into the nucleus. In neurons, importins might serve an additional function by carrying signals from distal sites to the soma.

Low concentrations of paraquat induces early activation of extracellular signal-regulated kinase 1/2, protein kinase B, and c-Jun N-terminal kinase 1/2 pathways: role of c-Jun N-terminal kinase in paraquat-induced cell death

Paraquat is a herbicide with a potential risk to induce parkinsonism due to its demonstrated neurotoxicity and its strong structural similarity to 1-methyl-4-phenylpyridinium (MPP(+)), a well-known neurotoxin which causes a clinical syndrome similar to Parkinson's disease (PD). However, at present very little is known about the signaling pathways activated by paraquat in any cell system. In this study, we have investigated the effect of paraquat on extracellular signal-regulated kinases 1 and 2 (ERK1/2), c-Jun N-terminal kinase (JNK), and protein kinase B (PKB) activation in E18 cells. Low concentrations of paraquat stimulated very early increases in ERK1/2, JNK1/2, and PKB phosphorylation. The phosphatidylinositol 3-kinase (PI-3K) inhibitors wortmannin and LY 294002 (2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one) inhibited early paraquat-induced increases in PKB phosphorylation. Furthermore, early paraquat-mediated increases in ERK1/2 activation were sensitive to the mitogen-activated protein kinase kinase 1 (MEK1) inhibitor PD 98059 (2'-amino-3'-methoxyflavone), whereas JNK1/2 responses were blocked by the JNK1/2 inhibitor SP 600125 (anthra[1-9-cd]pyrazol-6(2H)-one). Pretreatment with wortmannin, LY 294002, or PD 98059 had no effect on paraquat cell death in E18 cells. In contrast, SP 600125 significantly decreased paraquat-induced cell death in E18 cells. In conclusion, we have shown that low concentrations of paraquat stimulate robust very early increases in ERK1/2, JNK1/2, and PKB phosphorylation in E18 cells. Furthermore, the data presented clearly suggest that inhibition of the JNK1/2 pathway protects E18 cells from paraquat-induced cell death and support the fact that inhibition of early activation of JNK1/2 can constitute a potential strategy in PD treatment.

Protein aggregation in the pathogenesis of familial and sporadic Parkinson's disease

Parkinson's disease (PD) is a slowly progressive, age-related, neurodegenerative disorder. The cause and mechanism of neuronal death have been elusive. However, recent genetic, postmortem and experimental evidence show that protein accumulation and aggregation are prominent occurrences in both sporadic and familial PD. The relevance of these events to other cellular and biochemical changes, and to the neurodegenerative process, is being unraveled. It is increasingly evident that one or a combination of defects, including mutations, oxidative stress, mitochondrial impairment and dysfunction of the ubiquitin-proteasome system, lead to an excess production and aggregation of abnormal proteins in PD. In this respect, altered protein handling appears to be a central factor in the pathogenic process occurring in the various hereditary and sporadic forms of PD. This suggests that manipulation of proteolytic systems is a rational approach in the development of neuroprotective therapies that could modify the pathological course of PD.

Fine epitope mapping of monoclonal antibodies specific to human α-synuclein

The neuronal phosphoprotein alpha-synuclein has been increasingly implicated in the pathogenesis of Parkinson's disease (PD) and other neurodegenerative diseases; however, the exact function of alpha-synuclein still remains illusive. Suitable antibodies (Abs) specific for the gene of interest are indispensable for studying biological and immunological properties of the target gene. Here, we report not only the generation and characterization of monoclonal Abs, Syn-1 and Syn-17, against human alpha-synuclein, but also the epitope mapping by using recombinant synuclein family proteins and various GST fusion proteins of human alpha-synuclein domains. Syn-17 recognizes human and rodent alpha-synuclein, and its epitope is localized within residues 97-99 and 101 of alpha-synuclein. In contrast, the Syn-1 epitope is localized in residues 121 and 122 of human alpha-synuclein, and Syn-1 recognizes only human but not rodent alpha-synuclein, indicating that it can be utilized as a useful reagent for studying human alpha-synuclein transgenic mouse and zebrafish lines.

Robust dysregulation of gene expression in substantia nigra and striatum in Parkinson's disease

Large-scale genomics approaches are now widely utilized to study a myriad of human diseases. These powerful techniques, when combined with data analysis tools, detect changes in transcript abundance in diseased tissue relative to control. We hypothesize that specific differential gene expression underlies important pathogenic processes in Parkinson's disease, which is characterized by the gradual loss of dopaminergic neurons in the substantia nigra and consequent loss of dopamine in the striatum. We have therefore examined gene expression levels in the human parkinsonian nigrostriatal pathway, and compared them with those of neurologically normal controls. Using unsupervised clustering methods, we demonstrate that relatively few genes' expression levels can effectively distinguish between disease and control brains. Further, we identify several interesting patterns of gene expression that illuminate pathogenic cascades in Parkinson's disease. In particular is the robust loss of synaptic gene expression in diseased substantia nigra and striatum.

Lewy bodies

Lewy bodies (LB) in the substantia nigra are a cardinal pathological feature of Parkinson's disease, but they occur in a number of neurodegenerative diseases and can be widespread in the nervous system. The characteristics, locations, and composition of LB are reviewed, with particular attention to alpha-synuclein (alpha-SYN), which appears to be the major component of LB. The propensity for alpha-SYN, a presynaptic protein widely expressed in the brain, to aggregate is because of an amyloidogenic central region. The factors that favor the aggregation of alpha-SYN and mechanisms of toxicity are examined, and a mechanism through which aggregates of alpha-SYN could induce mitochondrial dysfunction and/or release of proapoptotic molecules is proposed.

Copper(ii) binding by fragments of α-synuclein containing M1-D2- and -H50-residues; a combined potentiometric and spectroscopic study

Stability constants and ligand donor sets of the copper(II) complexes of the NH2-29-56(L1)(AA30GKTKEGVLYV40GSKTKEGVVH50GVATVA56-NH2), NH2-M29-D30-56(L2) and Ac-M29-D30-56(L3) fragments of alpha-synuclein were determined in aqueous solution for 1 : 1 metal-to-ligand molar ratio in the pH range 2.5-10.5. The tyrosine residue in the 39th position of the alpha-synuclein fragments does not take part in the coordination of the metal ion. The potentiometric and spectroscopic data (UV-Vis, CD, EPR) show that acetylation of the amino terminal group induces significant changes in the coordination properties of the L3 fragment compared to that of the L2 peptide. When the amino group is blocked (L3) the imidazole nitrogen of the histidine residue acts as an anchoring site and at higher pH the 3N {N(Im),2N-} and 4N {N(Im),3N-} complexes are formed. The L1 peptide at physiological pH forms in equilibrium 3N {NH2,N-,CO,N(Im)} and 4N {NH2,2N-,N(Im)} complexes. For the L2 peptide the coordination of the copper(II) ions starts from the N-terminal Met residue and with increasing of pH the Asp residue in second position of amino acid sequence coordinates and stabilizes significantly the 2N complex as a result of chelation through the beta-carboxylate group. At physiological pH the 3N {NH2,N-,beta-COO-,N(Im)} coordination mode dominates. At pH above 6 the results for the L2 fragment suggest the formation of 3N and 4N complexes (in equatorial plane) and the involvement of the lateral NH2 group of Lys residue in the axial coordination of Cu(II) ion. In CD spectra sigma (epsilon-NH2-Lys) --> Cu(II) charge transfer transition is observed. The stability constants for the L2 fragment of alpha-synuclein of the 4N {NH2,2N-,N(Im)} and {NH2,3N-} complexes are higher about 1.5 and 0.7 orders of magnitude, respectively, by comparison to those of the L1 peptide. This increase may be explained by the involvement of the epsilon-NH2 group of Lys residue in the coordination sphere of metal ion.

Alpha-synuclein cooperates with CSPalpha in preventing neurodegeneration

Alpha-synuclein and cysteine-string protein-alpha (CSPalpha) are abundant synaptic vesicle proteins independently linked to neurodegeneration. Dominantly inherited mutations in alpha-synuclein cause Parkinson's disease, but the physiological role of alpha-synuclein remains unknown. Deletion of CSPalpha produces rapidly progressive neurodegeneration in mice, presumably because the cochaperone function of CSPalpha is essential for neuronal survival. Here, we report the surprising finding that transgenic expression of alpha-synuclein abolishes the lethality and neurodegeneration caused by deletion of CSPalpha. Conversely, ablation of endogenous synucleins exacerbates these phenotypes. Deletion of CSPalpha inhibits SNARE complex assembly; transgenic alpha-synuclein ameliorates this inhibition. In preventing neurodegeneration in CSPalpha-deficient mice, alpha-synuclein does not simply substitute for CSPalpha but acts by a downstream mechanism that requires phospholipid binding by alpha-synuclein. These observations reveal a powerful in vivo activity of alpha-synuclein in protecting nerve terminals against injury and suggest that this activity operates in conjunction with CSPalpha and SNARE proteins on the presynaptic membrane interface.

Cocaine abuse elevates alpha-synuclein and dopamine transporter levels in the human striatum

Direct protein interactions between the dopamine transporter and alpha-synuclein demonstrate that dopamine uptake function is modulated by alpha-synuclein. We report here that chronic cocaine abuse results in an increase in alpha-synuclein expression in the human striatum. Immunoblot analysis in the ventral putamen showed that alpha-synuclein protein was increased in striatal synaptosomes from cocaine users compared with age-matched drug-free controls. [H]-Dopamine transporter uptake was increased in parallel with 2beta-carbomethoxy-3beta-(4-fluorophenyl)tropane binding to the dopamine transporter. The increase in alpha-synuclein protein was more marked in the ventromedial sectors of the striatum than in the dorsal caudate nucleus. These results demonstrate concomitant regulation of alpha-synuclein and dopamine transporter binding and function in human striatal synaptic terminals isolated from cocaine abusers. Overexpression of alpha-synuclein may play a role in cocaine-induced plasticity and regulation of dopamine synaptic tone.

Structure and properties of alpha-synuclein and other amyloids determined at the amino acid level

The structure of alpha-synuclein (alpha-syn) amyloid was studied by hydrogen-deuterium exchange by using a fragment separation-MS analysis. The conditions used made it possible to distinguish the exchange of unprotected and protected amide hydrogens and to define the order/disorder boundaries at close to amino acid resolution. The soluble alpha-syn monomer exchanges its amide hydrogens with water hydrogens at random coil rates, consistent with its natively unstructured condition. In assembled amyloid, long N-terminal and C-terminal segments remain unprotected (residues 1- approximately 38 and 102-140), although the N-terminal segment shows some heterogeneity. A continuous middle segment (residues approximately 39-101) is strongly protected by systematically H-bonded cross-beta structure. This segment is much too long to fit the amyloid ribbon width, but non-H-bonded amides expected for direction-changing loops are not apparent. These results and other known constraints specify that alpha-syn amyloid adopts a chain fold like that suggested before for amyloid-beta [Petkova et al. (2002) Proc. Natl. Acad Sci. USA 99, 16742-16747] but with a short, H-bonded interlamina turn. More generally, we suggest that the prevalence of accidental amyloid formation derives mainly from the exceptional ability of the main chain in a structurally relaxed beta-conformation to adapt to and energy-minimize side-chain mismatching. Seeding specificity, strain variability, and species barriers then arise because newly added parallel in-register chains must faithfully reproduce the same set of adaptations.

Comparison of structure and dynamics of micelle-bound human alpha-synuclein and Parkinson disease variants

Three point mutations (A30P, E46K, and A53T) as well as gene triplication genetically link the 140-residue protein alpha-synuclein (aS) to the development of Parkinson disease. Here, the structure and dynamics of micelle-bound aS(A30P) and aS(A53T) are described and compared with wild-type aS, in addition to describing the aS-micelle interaction. A53T is sensed only by directly adjacent residues and leaves the backbone structure and dynamics indistinguishable from the wild type. A30P interrupts one helix turn (Val26-Ala29) and destabilizes the preceding one. A shift in helix register following A30P disturbs the canonical succession of polar and hydrophobic residues for at least two turns. The shortened helix-N adopts a slightly higher helical content and is less bent, indicating that strain was present in the micelle-bound helix. In the vicinity of the A30P-induced perturbations, the underlying micelle environment has rearranged, but nevertheless all aS variants maintain similar interrelationships with the micelle. Moreover, aS-micelle immersion correlates well with fast and slow aS backbone dynamics, allowing a rare insight into protein-micelle interplay.

Alpha-synuclein expression in the substantia nigra of MPTP-lesioned non-human primates

Changes in the expression of alpha-synuclein are likely to underlie its normal function as well as its role in pathological processes. The relationship between toxic injury and alpha-synuclein expression was assessed in the substantia nigra of squirrel monkeys treated with a single injection of MPTP and sacrificed 1 week or 1 month later. At 1 week, when stereological cell counting revealed only a small decrease (-10%) in the number of dopaminergic neurons, alpha-synuclein mRNA and protein were markedly enhanced. Increased alpha-synuclein immunoreactivity was evident at the level of neuronal fibers whereas nigral cell bodies were devoid of detectable protein. At 1 month post-MPTP, neuronal loss rose to 40%. Both alpha-synuclein mRNA and protein remained elevated but, noticeably, a robust alpha-synuclein immunoreactivity characterized a significant number of cell bodies. Neuromelanin granules are hallmarks of dopaminergic neurons in primates. Therefore, the number of alpha-synuclein-positive cells that also contained neuromelanin was counted throughout the substantia nigra. At 1 month, the vast majority of alpha-synuclein-immunoreactive neurons contained neuromelanin, and approximately 80% of the dopaminergic cell bodies that survived MPTP toxicity stained positive for alpha-synuclein. The results indicate that a single toxic insult is capable of inducing a sustained alpha-synuclein up-regulation in the primate brain. They support a direct relationship between neuronal injury and enhanced alpha-synuclein expression, and suggest that protein elevation within cell bodies may be a late feature of neurons that have endured a toxic stress.

Mutations in the pantothenate kinase gene PANK2 are not associated with Parkinson disease

Pantothenate kinase-associated neurodegeneration (PKAN) may serve as a model for Parkinson disease (PD) since many PKAN patients suffer from parkinsonism and both conditions lead to iron accumulation in the basal ganglia. We screened the gene coding for pantothenate kinase 2 (PANK2) for sequence variants in PD. We found no mutations in 67 PD patients with affected sibs or early-onset disease. Moreover, PANK2 polymorphisms were not associated with late-onset idiopathic PD in 339 patients. We conclude that PANK2 variants exert, if any, only a very small effect in the genetic risk of PD.

Axonal transport defects: a common theme in neurodegenerative diseases

A core pathology central to most neurodegenerative diseases is the misfolding, fibrillization and aggregation of disease proteins to form the hallmark lesions of specific disorders. The mechanisms underlying these brain-specific neurodegenerative amyloidoses are the focus of intense investigation and defective axonal transport has been hypothesized to play a mechanistic role in several neurodegenerative disorders; however, this hypothesis has not been extensively examined. Discoveries of mutations in human genes encoding motor proteins responsible for axonal transport do provide direct evidence for the involvement of axonal transport in neurodegenerative diseases, and this evidence is supported by studies of animal models of neurodegeneration. In this review, we summarize recent findings related to axonal transport and neurodegeneration. Focusing on specific neurodegenerative diseases from a neuropathologic perspective, we highlight discoveries of human motor protein mutations in some of these diseases, as well as illustrate new insights from animal models of neurodegenerative disorders. We also review the current understanding of the biology of axonal transport including major recent findings related to slow axonal transport.

Calcium(II) selectively induces alpha-synuclein annular oligomers via interaction with the C-terminal domain

Alpha-synuclein filaments are the major component of intracytoplasmic inclusion bodies characteristic of Parkinson's disease and related disorders. The process of alpha-synuclein filament formation proceeds via intermediate or protofibrillar species, each of which may be cytotoxic. Because high levels of calcium(II) and other metal ions may play a role in disease pathogenesis, we investigated the influence of calcium and other metals on alpha-synuclein speciation. Here we report that calcium(II) and cobalt(II) selectively induce the rapid formation of discrete annular alpha-synuclein oligomeric species. We used atomic force microscopy to monitor the aggregation state of alpha-synuclein after 1 d at 4 degrees C in the presence of a range of metal ions compared with the filament formation pathway in the absence of metal ions. Three classes of effect were observed with different groups of metal ions: (1) Copper(II), iron(III), and nickel(II) yielded 0.8-4 nm spherical particles, similar to alpha-synuclein incubated without metal ions; (2) magnesium(II), cadmium(II), and zinc(II) gave larger, 5-8 nm spherical oligomers; and, (3) cobalt(II) and calcium(II) gave frequent annular oligomers, 70-90 nm in diameter with calcium(II) and 22-30 nm in diameter with cobalt(II). In the absence of metal ions, annular oligomers ranging 45-90 nm in diameter were observed after 10 d incubation, short branched structures appeared after a further 3 wk and extended filaments after 2-3 mo. Previous studies have shown that alpha-synuclein calcium binding is mediated by the acidic C terminus. We found that truncated alpha-synuclein (1-125), lacking the C-terminal 15 amino acids, did not form annular oligomers upon calcium addition, indicating the involvement of the calcium-binding domain.