Sex-dimorphic neuroprotective effect of CD163 in an α-synuclein mouse model of Parkinson's disease

Alpha-synuclein (α-syn) aggregation and immune activation represent hallmark pathological events in Parkinson's disease (PD). The PD-associated immune response encompasses both brain and peripheral immune cells, although little is known about the immune proteins relevant for such a response. We propose that the upregulation of CD163 observed in blood monocytes and in the responsive microglia in PD patients is a protective mechanism in the disease. To investigate this, we used the PD model based on intrastriatal injections of murine α-syn pre-formed fibrils in CD163 knockout (KO) mice and wild-type littermates. CD163KO females revealed an impaired and differential early immune response to α-syn pathology as revealed by immunohistochemical and transcriptomic analysis. After 6 months, CD163KO females showed an exacerbated immune response and α-syn pathology, which ultimately led to dopaminergic neurodegeneration of greater magnitude. These findings support a sex-dimorphic neuroprotective role for CD163 during α-syn-induced neurodegeneration.

α-Synuclein pathology in Parkinson disease activates homeostatic NRF2 anti-oxidant response

Circumstantial evidence points to a pathological role of alpha-synuclein (aSyn; gene symbol SNCA), conferred by aSyn misfolding and aggregation, in Parkinson disease (PD) and related synucleinopathies. Several findings in experimental models implicate perturbations in the tissue homeostatic mechanisms triggered by pathological aSyn accumulation, including impaired redox homeostasis, as significant contributors in the pathogenesis of PD. The nuclear factor erythroid 2-related factor (NRF2/Nrf2) is recognized as ‘the master regulator of cellular anti-oxidant response’, both under physiological as well as in pathological conditions. Using immunohistochemical analyses, we show a robust nuclear NRF2 accumulation in post-mortem PD midbrain, detected by NRF2 phosphorylation on the serine residue 40 (nuclear active p-NRF2, S40). Curated gene expression analyses of four independent publicly available microarray datasets revealed considerable alterations in NRF2-responsive genes in the disease affected regions in PD, including substantia nigra, dorsal motor nucleus of vagus, locus coeruleus and globus pallidus. To further examine the putative role of pathological aSyn accumulation on nuclear NRF2 response, we employed a transgenic mouse model of synucleionopathy (M83 line, expressing the mutant human A53T aSyn), which manifests widespread aSyn pathology (phosphorylated aSyn; S129) in the nervous system following intramuscular inoculation of exogenous fibrillar aSyn. We observed strong immunodetection of nuclear NRF2 in neuronal populations harboring p-aSyn (S129), and found an aberrant anti-oxidant and inflammatory gene response in the affected neuraxis. Taken together, our data support the notion that pathological aSyn accumulation impairs the redox homeostasis in nervous system, and boosting neuronal anti-oxidant response is potentially a promising approach to mitigate neurodegeneration in PD and related diseases.

Prodromal neuroinvasion of pathological α-synuclein in brainstem reticular nuclei and white matter lesions in a model of α-synucleinopathy

Neuropathological observations in neurodegenerative synucleinopathies, including Parkinson disease, implicate a pathological role of α-synuclein accumulation in extranigral sites during the prodromal phase of the disease. In a transgenic mouse model of peripheral-to-central neuroinvasion and propagation of α-synuclein pathology (via hindlimb intramuscular inoculation with exogenous fibrillar α-synuclein: the M83 line, expressing the mutant human Ala53Thr α-synuclein), we studied the development and early-stage progression of α-synuclein pathology in the CNS of non-symptomatic (i.e. freely mobile) mice. By immunohistochemical analyses of phosphroylated α-synuclein on serine residue 129 (p-S129), our data indicate that the incipient stage of pathological α-synuclein propagation could be categorized in distinct phases: (i) initiation phase, whereby α-synuclein fibrillar inoculum induced pathological lesions in pools of premotor and motor neurons of the lumbar spinal cord, as early as 14 days post-inoculation; (ii) early central phase, whereby incipient α-synuclein pathology was predominantly detected in the reticular nuclei of the brainstem; and (iii) late central phase, characterized by additional sites of lesions in the brain including vestibular nuclei, deep cerebellar nuclei and primary motor cortex, with coincidental emergence of a sensorimotor deficit (mild degree of hindlimb clasping). Intriguingly, we also detected progressive α-synuclein pathology in premotor and motor neurons in the thoracic spinal cord, which does not directly innervate the hindlimb, as well as in the oligodendroglia within the white matter tracts of the CNS during this prodromal phase. Collectively, our data provide crucial insights into the spatiotemporal propagation of α-synuclein pathology in the nervous system of this rodent model of α-synucleinopathy following origin in periphery, and present a neuropathological context for the progression from pre-symptomatic stage to an early deficit in sensorimotor coordination. These findings also hint towards a therapeutic window for targeting the early stages of α-synuclein pathology progression in this model, and potentially facilitate the discovery of mechanisms relevant to α-synuclein proteinopathies. In a rodent model of synucleinopathy, Ferreira et al., delineate the spatiotemporal progression of incipient α-synuclein pathology (of peripheral origin) in the CNS. The authors show early affection of brainstem reticular nuclei in non-paralyzed mice, and pathological white matter lesions in relation to the neuronal pathology.

PET imaging reveals early and progressive dopaminergic deficits after intra-striatal injection of preformed alpha-synuclein fibrils in rats

Alpha-synuclein (a-syn) can aggregate and form toxic oligomers and insoluble fibrils which are the main component of Lewy bodies. Intra-neuronal Lewy bodies are a major pathological characteristic of Parkinson's disease (PD). These fibrillar structures can act as seeds and accelerate the aggregation of monomeric a-syn. Indeed, recent studies show that injection of preformed a-syn fibrils (PFF) into the rodent brain can induce aggregation of the endogenous monomeric a-syn resulting in neuronal dysfunction and eventual cell death. We injected 8 μg of murine a-syn PFF, or soluble monomeric a-syn into the right striatum of rats. The animals were monitored behaviourally using the cylinder test, which measures paw asymmetry, and the corridor task that measures lateralized sensorimotor response to sugar treats. In vivo PET imaging was performed after 6, 13 and 22 weeks using [¹¹C]DTBZ, a marker of the vesicular monoamine 2 transporter (VMAT2), and after 15 and 22 weeks using [¹¹C]UCB-J, a marker of synaptic SV2A protein in nerve terminals. Histology was performed at the three time points using antibodies against dopaminergic markers, aggregated a-syn, and MHCII to evaluate the immune response. While the a-syn PFF injection caused only mild behavioural changes, [¹¹C]DTBZ PET showed a significant and progressive decrease of VMAT2 binding in the ipsilateral striatum. This was accompanied by a small progressive decrease in [¹¹C]UCB-J binding in the same area. In addition, our histological analysis revealed a gradual spread of misfolded a-syn pathology in areas anatomically connected to striatum that became bilateral with time. The striatal a-syn PFF injection resulted in a progressive unilateral degeneration of dopamine terminals, and an early and sustained presence of MHCII positive ramified microglia in the ipsilateral striatum and substantia nigra. Our study shows that striatal injections of a-syn fibrils induce progressive pathological synaptic dysfunction prior to cell death that can be detected in vivo with PET. We confirm that intrastriatal injection of a-syn PFFs provides a model of progressive a-syn pathology with loss of dopaminergic and synaptic function accompanied by neuroinflammation, as found in human PD.

Gene Transfer in Rodent Nervous Tissue Following Hindlimb Intramuscular Delivery of Recombinant Adeno-Associated Virus Serotypes AAV2/6, AAV2/8, and AAV2/9

Recombinant adeno-associated virus (rAAV) vectors have emerged as the safe vehicles of choice for long-term gene transfer in mammalian nervous system. Recombinant adeno-associated virus–mediated localized gene transfer in adult nervous system following direct inoculation, that is, intracerebral or intrathecal, is well documented. However, recombinant adeno-associated virus delivery in defined neuronal populations in adult animals using less-invasive methods as well as avoiding ectopic gene expression following systemic inoculation remain challenging. Harnessing the capability of some recombinant adeno-associated virus serotypes for retrograde transduction may potentially address such limitations (Note: The term retrograde transduction in this manuscript refers to the uptake of injected recombinant adeno-associated virus particles at nerve terminals, retrograde transport, and subsequent transduction of nerve cell soma). In some studies, recombinant adeno-associated virus serotypes 2/6, 2/8, and 2/9 have been shown to exhibit transduction of connected neuroanatomical tracts in adult animals following lower limb intramuscular recombinant adeno-associated virus delivery in a pattern suggestive of retrograde transduction. However, an extensive side-by-side comparison of these serotypes following intramuscular delivery regarding tissue viral load, and the effect of promoter on transgene expression, has not been performed. Hence, we delivered recombinant adeno-associated virus serotypes 2/6, 2/8, or 2/9 encoding enhanced green fluorescent protein (eGFP), under the control of either cytomegalovirus (CMV) or human synapsin (hSyn) promoter, via a single unilateral hindlimb intramuscular injection in the bicep femoris of adult C57BL/6J mice. Four weeks post injection, we quantified viral load and transgene (enhanced green fluorescent protein) expression in muscle and related nervous tissues. Our data show that the select recombinant adeno-associated virus serotypes transduce sciatic nerve and groups of neurons in the dorsal root ganglia on the injected side, indicating that the intramuscular recombinant adeno-associated virus delivery is useful for achieving gene transfer in local neuroanatomical tracts. We also observed sparse recombinant adeno-associated virus viral delivery or eGFP transduction in lumbar spinal cord and a noticeable lack thereof in brain. Therefore, further improvements in recombinant adeno-associated virus design are warranted to achieve efficient widespread retrograde transduction following intramuscular and possibly other peripheral routes of delivery.

Reductions in COQ2 Expression Relate to Reduced ATP Levels in Multiple System Atrophy Brain

Multiple system atrophy (MSA) is a progressive neurodegenerative disease clinically characterized by parkinsonism and cerebellar ataxia, and pathologically by oligodendrocyte α-synuclein inclusions. Genetic variants of COQ2 are associated with an increased risk for MSA in certain populations. Also, deficits in the level of coenzyme Q10 and its biosynthetic enzymes are associated with MSA. Here, we measured ATP levels and expression of biosynthetic enzymes for coenzyme Q10, including COQ2, in multiple regions of MSA and control brains. We found a reduction in ATP levels in disease-affected regions of MSA brain that associated with reduced expression of COQ2 and COQ7, supporting the concept that abnormalities in the biosynthesis of coenzyme Q10 play an important role in the pathogenesis of MSA.

A Longitudinal Study of Total and Phosphorylated α-Synuclein with Other Biomarkers in Cerebrospinal Fluid of Alzheimer's Disease and Mild Cognitive Impairment

Alzheimer's disease (AD) features a dynamic sequence of amyloid deposition, neurodegeneration, and cognitive impairment. A significant fraction of AD brains also displays Lewy body pathology, suggesting that addition of classically Parkinson's disease-related proteins to the AD biomarker panel may be of value. To determine whether addition of cerebrospinal fluid (CSF) total α-synuclein and its form phosphorylated at S129 (pS129) to the AD biomarker panel [Amyloid-β1-42 (Aβ42), tau, and phosphorylated tau (p-tau181)] improves its performance, we examined CSF samples collected longitudinally up to 7 years as part of the Alzheimer's Disease Neuroimaging Initiative. From 87 AD, 177 mild cognitive impairment (MCI), and 104 age-matched healthy controls, 792 baseline and longitudinal CSF samples were tested for total α-synuclein, pS129, Aβ42, tau, and p-tau181. pS129, but not total α-synuclein, was weakly associated with diagnosis at baseline when t-tau/Aβ42 was included in the statistical model (β= 0.0026, p = 0.041, 95% CI [(0.0001)-(0.005)]). CSF α-synuclein predicted Alzheimer's Disease Assessment Scale-Cognitive (β= -0.59, p = 0.0015, 95% CI [(-0.96)-(-0.23)]), memory (β= 0.4, p = 0.00025, 95% CI [(0.16)-(0.59)]), and executive (0.62,<0.0001, 95% CI [(0.31)-(0.93)]) function composite scores, and progression from MCI to AD (β= 0.019, p = 0.0011, 95% CI [(0.002)-(0.20)]). pS129 was associated with executive function (β= -2.55, p = 0.0085, 95% CI [(-4.45)-(-0.66)]). Lower values in the mismatch between α-synuclein and p-tau181 predicted faster cognitive decline (β= 0.64, p = 0.0012, 95% CI [(0.48)-(0.84)]). Longitudinal biomarker changes did not differ between groups, and may not reflect AD progression. The α-synuclein-p-tau181-Mismatch could better predict longitudinal cognitive changes than classical AD markers alone, and its pathological correlates should be investigated further.

Activity of translation regulator eukaryotic elongation factor-2 kinase is increased in Parkinson disease brain and its inhibition reduces alpha synuclein toxicity

Parkinson disease (PD) is the second most common neurodegenerative disorder and the leading neurodegenerative cause of motor disability. Pathologic accumulation of aggregated alpha synuclein (AS) protein in brain, and imbalance in the nigrostriatal system due to the loss of dopaminergic neurons in the substantia nigra- pars compacta, are hallmark features in PD. AS aggregation and propagation are considered to trigger neurotoxic mechanisms in PD, including mitochondrial deficits and oxidative stress. The eukaryotic elongation factor-2 kinase (eEF2K) mediates critical regulation of dendritic mRNA translation and is a crucial molecule in diverse forms of synaptic plasticity. Here we show that eEF2K activity, assessed by immuonohistochemical detection of eEF2 phosphorylation on serine residue 56, is increased in postmortem PD midbrain and hippocampus. Induction of aggressive, AS-related motor phenotypes in a transgenic PD M83 mouse model also increased brain eEF2K expression and activity. In cultures of dopaminergic N2A cells, overexpression of wild-type human AS or the A53T mutant increased eEF2K activity. eEF2K inhibition prevented the cytotoxicity associated with AS overexpression in N2A cells by improving mitochondrial function and reduced oxidative stress. Furthermore, genetic deletion of the eEF2K ortholog efk-1 in C. elegans attenuated human A53T AS induced defects in behavioural assays reliant on dopaminergic neuron function. These data suggest a role for eEF2K activity in AS toxicity, and support eEF2K inhibition as a potential target in reducing AS-induced oxidative stress in PD.

Investigation of RNA Synthesis Using 5-Bromouridine Labelling and Immunoprecipitation

When steady state RNA levels are compared between two conditions, it is not possible to distinguish whether changes are caused by alterations in production or degradation of RNA. This protocol describes a method for measurement of RNA production, using 5-Bromouridine labelling of RNA followed by immunoprecipitation, which enables investigation of RNA synthesized within a short timeframe (e.g., 1 h). The advantage of 5-Bromouridine-labelling and immunoprecipitation over the use of toxic transcriptional inhibitors, such as α-amanitin and actinomycin D, is that there are no or very low effects on cell viability during short-term use. However, because 5-Bromouridine-immunoprecipitation only captures RNA produced within the short labelling time, slowly produced as well as rapidly degraded RNA can be difficult to measure by this method. The 5-Bromouridine-labelled RNA captured by 5-Bromouridine-immunoprecipitation can be analyzed by reverse transcription, quantitative polymerase chain reaction, and next generation sequencing. All types of RNA can be investigated, and the method is not limited to measuring mRNA as is presented in this example.

Cerebrospinal fluid α-synuclein contributes to the differential diagnosis of Alzheimer's disease

INTRODUCTION

The ability of Alzheimer's disease (AD) cerebrospinal fluid (CSF) biomarkers (amyloid β peptide 1-42, total tau, and phosphorylated tau) to discriminate AD from related disorders is limited. Biomarkers for other concomitant pathologies (e.g., CSF α-synuclein [α-syn] for Lewy body pathology) may be needed to further improve the differential diagnosis.

METHODS

CSF total α-syn, phosphorylated α-syn at Ser129, and AD CSF biomarkers were evaluated with Luminex immunoassays in 367 participants, followed by validation in 74 different neuropathologically confirmed cases.

RESULTS

CSF total α-syn, when combined with amyloid β peptide 1-42 and either total tau or phosphorylated tau, improved the differential diagnosis of AD versus frontotemporal dementia, Lewy body disorders, or other neurological disorders. The diagnostic accuracy of the combined models attained clinical relevance (area under curve ∼0.9) and was largely validated in neuropathologically confirmed cases.

DISCUSSION

Combining CSF biomarkers representing AD and Lewy body pathologies may have clinical value in the differential diagnosis of AD.

Recommendations of the Global Multiple System Atrophy Research Roadmap Meeting

Multiple system atrophy (MSA) is a rare neurodegenerative disorder with substantial knowledge gaps despite recent gains in basic and clinical research. In order to make further advances, concerted international collaboration is vital. In 2014, an international meeting involving leaders in the field and MSA advocacy groups was convened in Las Vegas, Nevada, to identify critical research areas where consensus and progress was needed to improve understanding, diagnosis, and treatment of the disease. Eight topic areas were defined: pathogenesis, preclinical modeling, target identification, endophenotyping, clinical measures, imaging biomarkers, nonimaging biomarkers, treatments/trial designs, and patient advocacy. For each topic area, an expert served as a working group chair and each working group developed priority-ranked research recommendations with associated timelines and pathways to reach the intended goals. In this report, each groups' recommendations are provided.

Polo-like kinase 2 modulates α-synuclein protein levels by regulating its mRNA production

Variations in the α-synuclein-encoding SNCA gene represent the greatest genetic risk factor for Parkinson's disease (PD), and duplications/triplications of SNCA cause autosomal dominant familial PD. These facts closely link brain levels of α-synuclein with the risk of PD, and make lowering α-synuclein levels a therapeutic strategy for the treatment of PD and related synucleinopathies. In this paper, we corroborate previous findings on the ability of overexpressed Polo-like kinase 2 (PLK-2) to decrease cellular α-synuclein, but demonstrate that the process is independent of PLK-2 phosphorylating S129 in α-synuclein because a similar reduction is achieved with the non-phosphorable S129A mutant α-synuclein. Using a specific PLK-2 inhibitor (compound 37), we demonstrate that endogenous PLK-2 phosphorylates S129 only in some cells, but increases α-synuclein protein levels in all tested cell cultures and brain slices. PLK-2 is found to regulate the transcription of α-synuclein mRNA from both the endogenous mouse SNCA gene and transgenic vectors that only contain the open reading frame. Moreover, we are the first to show that regulation of α-synuclein by PLK-2 is of physiological importance since 10days' inhibition of endogenous PLK-2 in wt C57BL/6 mice increases endogenous α-synuclein protein levels. Our findings collectively demonstrate that PLK-2 regulates α-synuclein levels by a previously undescribed transcription-based mechanism. This mechanism is active in cells and brain tissue, opening up for alternative strategies for modulating α-synuclein levels and thereby for the possibility of modifying disease progression in synucleinopaties.

DJ-1 interactions with α-synuclein attenuate aggregation and cellular toxicity in models of Parkinson's disease

Parkinson's disease (PD) is a devastating neurodegenerative disorder characterized by the loss of neurons in the substantia nigra pars compacta and the presence of Lewy bodies in surviving neurons. These intracellular protein inclusions are primarily composed of misfolded α-synuclein (aSyn), which has also been genetically linked to familial and sporadic forms of PD. DJ-1 is a small ubiquitously expressed protein implicated in several pathways associated with PD pathogenesis. Although mutations in the gene encoding DJ-1 lead to familial early-onset PD, the exact mechanisms responsible for its role in PD pathogenesis are still elusive. Previous work has found that DJ-1--which has protein chaperone-like activity--modulates aSyn aggregation. Here, we investigated possible physical interactions between aSyn and DJ-1 and any consequent functional and pathological relevance. We found that DJ-1 interacts directly with aSyn monomers and oligomers in vitro, and that this also occurs in living cells. Notably, several PD-causing mutations in DJ-1 constrain this interaction. In addition, we found that overexpression of DJ-1 reduces aSyn dimerization, whereas mutant forms of DJ-1 impair this process. Finally, we found that human DJ-1 as well as yeast orthologs of DJ-1 reversed aSyn-dependent cellular toxicity in Saccharomyces cerevisiae. Taken together, these data suggest that direct interactions between DJ-1 and aSyn constitute the basis for a neuroprotective mechanism and that familial mutations in DJ-1 may contribute to PD by disrupting these interactions.

Accumulation of oligomer-prone α-synuclein exacerbates synaptic and neuronal degeneration in vivo

In Parkinson's disease and dementia with Lewy bodies, α-synuclein aggregates to form oligomers and fibrils; however, the precise nature of the toxic α-synuclein species remains unclear. A number of synthetic α-synuclein mutations were recently created (E57K and E35K) that produce species of α-synuclein that preferentially form oligomers and increase α-synuclein-mediated toxicity. We have shown that acute lentiviral expression of α-synuclein E57K leads to the degeneration of dopaminergic neurons; however, the effects of chronic expression of oligomer-prone α-synuclein in synapses throughout the brain have not been investigated. Such a study could provide insight into the possible mechanism(s) through which accumulation of α-synuclein oligomers in the synapse leads to neurodegeneration. For this purpose, we compared the patterns of neurodegeneration and synaptic damage between a newly generated mThy-1 α-synuclein E57K transgenic mouse model that is prone to forming oligomers and the mThy-1 α-synuclein wild-type mouse model (Line 61), which accumulates various forms of α-synuclein. Three lines of α-synuclein E57K (Lines 9, 16 and 54) were generated and compared with the wild-type. The α-synuclein E57K Lines 9 and 16 were higher expressings of α-synuclein, similar to α-synuclein wild-type Line 61, and Line 54 was a low expressing of α-synuclein compared to Line 61. By immunoblot analysis, the higher-expressing α-synuclein E57K transgenic mice showed abundant oligomeric, but not fibrillar, α-synuclein whereas lower-expressing mice accumulated monomeric α-synuclein. Monomers, oligomers, and fibrils were present in α-synuclein wild-type Line 61. Immunohistochemical and ultrastructural analyses demonstrated that α-synuclein accumulated in the synapses but not in the neuronal cells bodies, which was different from the α-synuclein wild-type Line 61, which accumulates α-synuclein in the soma. Compared to non-transgenic and lower-expressing mice, the higher-expressing α-synuclein E57K mice displayed synaptic and dendritic loss, reduced levels of synapsin 1 and synaptic vesicles, and behavioural deficits. Similar alterations, but to a lesser extent, were seen in the α-synuclein wild-type mice. Moreover, although the oligomer-prone α-synuclein mice displayed neurodegeneration in the frontal cortex and hippocampus, the α-synuclein wild-type only displayed neuronal loss in the hippocampus. These results support the hypothesis that accumulating oligomeric α-synuclein may mediate early synaptic pathology in Parkinson's disease and dementia with Lewy bodies by disrupting synaptic vesicles. This oligomer-prone model might be useful for evaluating therapies directed at oligomer reduction.

Characterizing the dynamics of α-synuclein oligomers using hydrogen/deuterium exchange monitored by mass spectrometry

Soluble oligomers formed by α-synuclein (αSN) are suspected to play a central role in neuronal cell death during Parkinson's disease. While studies have probed the surface structure of these oligomers, little is known about the backbone dynamics of αSN when they form soluble oligomers. Using hydrogen/deuterium exchange monitored by mass spectrometry (HDX-MS), we have analyzed the structural dynamics of soluble αSN oligomers. The analyzed oligomers were metastable, slowly dissociating to monomers over a period of 21 days, after excess monomer had been removed. The C-terminal region of αSN (residues 94-140) underwent isotopic exchange very rapidly, demonstrating a highly dynamic region in the oligomeric state. Three regions (residues 4-17, 39-54, and 70-89) were strongly protected against isotopic exchange in the oligomers, indicating the presence of a stable hydrogen-bonded or solvent-shielded structure. The protected regions were interspersed by two somewhat more dynamic regions (residues 18-38 and 55-70). In the oligomeric state, the isotopic exchange pattern of the region of residues 35-95 of αSN corresponded well with previous nuclear magnetic resonance and electron paramagnetic resonance analyses performed on αSN fibrils and indicated a possible zipperlike maturation mechanism for αSN aggregates. We find the protected N-terminus (residues 4-17) to be of particular interest, as this region has previously been observed to be highly dynamic for both monomeric and fibrillar αSN. This region has mainly been described in relation to membrane binding of αSN, and structuring may be important in relation to disease.

A progressive dopaminergic phenotype associated with neurotoxic conversion of α-synuclein in BAC-transgenic rats

Conversion of soluble α-synuclein into insoluble and fibrillar inclusions is a hallmark of Parkinson's disease and other synucleinopathies. Accumulating evidence points towards a relationship between its generation at nerve terminals and structural synaptic pathology. Little is known about the pathogenic impact of α-synuclein conversion and deposition at nigrostriatal dopaminergic synapses in transgenic mice, mainly owing to expression limitations of the α-synuclein construct. Here, we explore whether both the rat as a model and expression of the bacterial artificial chromosome construct consisting of human full-length wild-type α-synuclein could exert dopaminergic neuropathological effects. We found that the human promoter induced a pan-neuronal expression, matching the rodent α-synuclein expression pattern, however, with prominent C-terminally truncated fragments. Ageing promoted conversion of both full-length and C-terminally truncated α-synuclein species into insolube and proteinase K-resistant fibres, with strongest accumulation in the striatum, resembling biochemical changes seen in human Parkinson's disease. Transgenic rats develop early changes in novelty-seeking, avoidance and smell before the progressive motor deficit. Importantly, the observed pathological changes were associated with severe loss of the dopaminergic integrity, thus resembling more closely the human pathology.

FAS-dependent cell death in α-synuclein transgenic oligodendrocyte models of multiple system atrophy

Multiple system atrophy is a parkinsonian neurodegenerative disorder. It is cytopathologically characterized by accumulation of the protein p25α in cell bodies of oligodendrocytes followed by accumulation of aggregated α-synuclein in so-called glial cytoplasmic inclusions. p25α is a stimulator of α-synuclein aggregation, and coexpression of α-synuclein and p25α in the oligodendroglial OLN-t40-AS cell line causes α-synuclein aggregate-dependent toxicity. In this study, we investigated whether the FAS system is involved in α-synuclein aggregate dependent degeneration in oligodendrocytes and may play a role in multiple system atrophy. Using rat oligodendroglial OLN-t40-AS cells we demonstrate that the cytotoxicity caused by coexpressing α-synuclein and p25α relies on stimulation of the death domain receptor FAS and caspase-8 activation. Using primary oligodendrocytes derived from PLP-α-synuclein transgenic mice we demonstrate that they exist in a sensitized state expressing pro-apoptotic FAS receptor, which makes them sensitive to FAS ligand-mediated apoptosis. Immunoblot analysis shows an increase in FAS in brain extracts from multiple system atrophy cases. Immunohistochemical analysis demonstrated enhanced FAS expression in multiple system atrophy brains notably in oligodendrocytes harboring the earliest stages of glial cytoplasmic inclusion formation. Oligodendroglial FAS expression is an early hallmark of oligodendroglial pathology in multiple system atrophy that mechanistically may be coupled to α-synuclein dependent degeneration and thus represent a potential target for protective intervention.

Loss of DJ-1 protein stability and cytoprotective function by Parkinson's disease-associated proline-158 deletion

DJ-1 is a ubiquitous protein regulating cellular viability. Recessive mutations in the PARK7/DJ-1 gene are linked to Parkinson's disease (PD). Although the most dramatic L166P point mutation practically eliminates DJ-1 protein and function, the effects of other PD-linked mutations are subtler. Here, we investigated two recently described PD-associated DJ-1 point mutations, the A179T substitution and the P158Δ in-frame deletion. [A179T]DJ-1 protein was as stable as wild-type [wt]DJ-1, but the P158Δ mutant protein was less stable. In accord with the notion that dimer formation is essential for DJ-1 protein stability, [P158Δ]DJ-1 was impaired in dimer formation. Similar to our previous findings for [M26I]DJ-1, [P158Δ]DJ-1 bound aberrantly to apoptosis signal-regulating kinase 1. Thus, the PD-associated P158Δ mutation destabilizes DJ-1 protein and function. As there is also evidence for an involvement of DJ-1 in multiple system atrophy, a PD-related α-synucleinopathy characterized by oligodendroglial cytoplasmic inclusions, we studied an oligodendroglial cell line stably expressing α-synuclein. α-Synuclein aggregate dependent microtubule retraction upon co-transfection with tubulin polymerization-promoting protein p25α was ameliorated by [wt]DJ-1. In contrast, DJ-1 mutants including P158Δ failed to protect in this system, where we found evidence of apoptosis signal-regulating kinase 1 (ASK1) involvement. In conclusion, the P158Δ point mutation may contribute to neurodegeneration by protein destabilization and hence loss of DJ-1 function.

Abstract 4319: Effects of chemotherapeutics on organotypic corticostriatal slice cultures identified by a new panel of fluorescent and immunohistochemical markers

Effects of chemotherapeutics on glioma cell lines and spheroids are usually investigated without evaluating the effects of even very high concentrations of chemotherapeutics on normal brain tissue. To perform such investigations, the aim of the present study was to establish a panel of markers for detection of general cell death and more specific neuronal and glial degeneration induced by chemotherapeutics in organotypic rat corticostriatal slice cultures. Organotypic rat corticostriatal slice cultures were exposed to the alkylating agents temozolomide and nimustine, the tyrosine kinase inhibitor imatinib mesylate and the microtubule destabilizing agent vincristine. Densitometric measurements of uptake of the fluorescent dye propidium iodide were used for quantifying cellular degeneration. Moreover, paraffin sections were HE stained and immunohistochemically stained for the neuronal marker MAP2, the astroglial marker GFAP, and the oligodendrocyte marker p25α. The results showed that clinical drug concentrations were non-toxic. However, a time dependent increase in PI uptake was observed for supratherapeutic concentrations of the drugs, except for temozolomide, where no toxicity was observed at all. Corresponding immunostaining showed loss of MAP2 staining and increased expression of GFAP and p25α for cultures exposed to 1000 nM vincristine. Cultures exposed to supratherapeutic concentrations of nimustine and imatinib mesylate disintegrated, leaving no tissue for histology.

In conclusion, corticostriatal slice cultures and the established panel of markers represent an excellent tool for detecting toxicity by chemotherapeutics. Toxicity was not detected at clinical concentrations, but high concentrations with toxic effects were identified suggesting that some of the earlier identified anti-cancer effects in the literature are general cytotoxic effects and not specific anti-cancer effects.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4319. doi:10.1158/1538-7445.AM2011-4319

P25α / TPPP expression increases plasma membrane presentation of the dopamine transporter and enhances cellular sensitivity to dopamine toxicity

Parkinson's disease is characterized by preferential degeneration of the dopamine-producing neurons of the brain stem substantia nigra. Imbalances between mechanisms governing dopamine transport across the plasma membrane and cellular storage vesicles increase the level of toxic pro-oxidative cytosolic dopamine. The microtubule-stabilizing protein p25α accumulates in dopaminergic neurons in Parkinson's disease. We hypothesized that p25α modulates the subcellular localization of the dopamine transporter via effects on sorting vesicles, and thereby indirectly affects its cellular activity. Here we show that co-expression of the dopamine transporter with p25α in HEK-293-MSR cells increases dopamine uptake via increased plasma membrane presentation of the transporter. No direct interaction between p25α and the dopamine transporter was demonstrated, but they co-fractionated during subcellular fractionation of brain tissue from striatum, and direct binding of p25α peptides to brain vesicles was demonstrated. Truncations of the p25α peptide revealed that the requirement for stimulating dopamine uptake is located in the central core and were similar to those required for vesicle binding. Co-expression of p25α and the dopamine transporter in HEK-293-MSR cells sensitized them to the toxicity of extracellular dopamine. Neuronal expression of p25α thus holds the potential to sensitize the cells toward dopamine and toxins carried by the dopamine transporter.

Co-expression of C-terminal truncated alpha-synuclein enhances full-length alpha-synuclein-induced pathology

Lewy bodies, which are a pathological hallmark of Parkinson's disease, contain insoluble polymers of alpha-synuclein (alphasyn). Among the different modifications that can promote the formation of toxic alphasyn species, C-terminal truncation is among the most abundant alterations in patients with Parkinson's disease. In vitro, C-terminal truncated alphasyn aggregates faster and sub-stoichiometric amounts of C-terminal truncated alphasyn promote aggregation of the full-length alphasyn (alphasynFL) and induce neuronal toxicity. To address in vivo the putative stimulation of alphasyn-induced pathology by the presence of truncated alphasyn, we used recombinant adeno-associated virus to express either alphasynFL or a C-terminal truncated alphasyn (1-110) in rats. We adjusted the recombinant adeno-associated virus vector concentrations so that either protein alone led to only mild to moderate axonal pathology in the terminals of nigrostriatal dopamine neurons without frank cell loss. When these two forms of alphasyn were co-expressed at these pre-determined levels, it resulted in a more aggressive pathology in fiber terminals as well as dopaminergic cell loss in the substantia nigra. Using an antibody that did not detect the C-terminal truncated alphasyn (1-110) but only alphasynFL, we demonstrated that the co-expressed truncated protein promoted the progressive accumulation of alphasynFL and formation of larger pathological accumulations. Moreover, in the co-expression group, three of the eight animals showed apomorphine-induced turning, suggesting prominent post-synaptic alterations due to impairments in the dopamine release, whereas the mild pathology induced by either form alone did not cause motor abnormalities. Taken together these data suggest that C-terminal truncated alphasyn can interact with and exacerbate the formation of pathological accumulations containing alphasynFL in vivo.

DJ-1 and alpha-synuclein in human cerebrospinal fluid as biomarkers of Parkinson's disease

Biomarkers are urgently needed for the diagnosis and monitoring of disease progression in Parkinson's disease. Both DJ-1 and alpha-synuclein, two proteins critically involved in Parkinson's disease pathogenesis, have been tested as disease biomarkers in several recent studies with inconsistent results. These have been largely due to variation in the protein species detected by different antibodies, limited numbers of patients in some studies, or inadequate control of several important variables. In this study, the nature of DJ-1 and alpha-synuclein in human cerebrospinal fluid was studied by a combination of western blotting, gel filtration and mass spectrometry. Sensitive and quantitative Luminex assays detecting most, if not all, species of DJ-1 and alpha-synuclein in human cerebrospinal fluid were established. Cerebrospinal fluid concentrations of DJ-1 and alpha-synuclein from 117 patients with Parkinson's disease, 132 healthy individuals and 50 patients with Alzheimer's disease were analysed using newly developed, highly sensitive Luminex technology while controlling for several major confounders. A total of 299 individuals and 389 samples were analysed. The results showed that cerebrospinal fluid DJ-1 and alpha-synuclein levels were dependent on age and influenced by the extent of blood contamination in cerebrospinal fluid. Both DJ-1 and alpha-synuclein levels were decreased in Parkinson's patients versus controls or Alzheimer's patients when blood contamination was controlled for. In the population aged > or = 65 years, when cut-off values of 40 and 0.5 ng/ml were chosen for DJ-1 and alpha-synuclein, respectively, the sensitivity and specificity for patients with Parkinson's disease versus controls were 90 and 70% for DJ-1, and 92 and 58% for alpha-synuclein. A combination of the two markers did not enhance the test performance. There was no association between DJ-1 or alpha-synuclein and the severity of Parkinson's disease. Taken together, this represents the largest scale study for DJ-1 or alpha-synuclein in human cerebrospinal fluid so far, while using newly established sensitive Luminex assays, with controls for multiple variables. We have demonstrated that total DJ-1 and alpha-synuclein in human cerebrospinal fluid are helpful diagnostic markers for Parkinson's disease, if variables such as blood contamination and age are taken into consideration.

Detection of elevated levels of soluble alpha-synuclein oligomers in post-mortem brain extracts from patients with dementia with Lewy bodies

A number of neurodegenerative diseases including Parkinson's disease, dementia with Lewy bodies (DLB) and multiple system atrophy are characterized by the formation and intraneuronal accumulation of fibrillar aggregates of alpha-synuclein (alpha-syn) protein in affected brain regions. These and other findings suggest that the accumulation of alpha-syn in the brain plays an important role in the pathogenesis of these diseases. However, more recently it has been reported that early amyloid aggregates or 'soluble oligomers' are the pathogenic species that lead to neurodegeneration and neuronal cell death rather than the later 'mature fibrils'. In this study, we investigated the presence of alpha-syn oligomers in brain lysates prepared from frozen post-mortem brains of normal, Alzheimer's disease and DLB patients. The brain extracts were subjected to high speed centrifugation, to remove insoluble alpha-syn aggregates, followed by specific detection of soluble oligomers in the supernatants by employing FILA-1, an antibody that specifically binds to alpha-syn aggregates, but not to alpha-syn monomers, or to tau or beta-amyloid aggregates. Using this novel enzyme-linked immunosorbent assay (ELISA) method to quantify the amounts of alpha-syn oligomers in the brain extracts, our data clearly show an increase in the levels of soluble oligomers of alpha-syn in the DLB brains compared to those with Alzheimer's disease and the controls (P < 0.0001). Our findings provide strong evidence to support the contention that elevated soluble oligomers of alpha-syn are involved in the pathogenesis of DLB. Furthermore, these findings establish FILA-1 as a very sensitive tool for the detection of oligomeric forms of alpha-syn in human brain lysates.

Peroxiredoxin 6 in human brain: molecular forms, cellular distribution and association with Alzheimer's disease pathology

Peroxiredoxin 6 is an antioxidant enzyme and is the 1-cys member of the peroxiredoxin family. Using two-dimensional electrophoresis and Western blotting, we have shown for the first time that, in human control and brain tissue of patient’s with Alzheimer’s disease (AD), this enzyme exists as three major and five minor forms with pIs from 5.3 to 6.1. Using specific cellular markers, we have shown that peroxiredoxin 6 is present in astrocytes with very low levels in neurons, but not detectable in microglia or oligodendrocytes. In control brains, there was a very low level of peroxiredoxin 6 staining in astrocytes that was confined to a “halo” around the nucleus. In AD, there were marked increases in the number and staining intensity of peroxiredoxin 6 positive astrocytes in both gray and white matter in the midfrontal cortex, cingulate, hippocampus and amygdala. Confocal microscopy using antibodies to Aβ peptide, tau and peroxiredoxin 6 showed that peroxiredoxin 6 positive astrocytes are closely involved with diffuse plaques and to a lesser extent with neuritic plaques, suggesting that plaques are producing reactive oxygen species. There appeared to be little astrocytic response to tau containing neurons. Although peroxiredoxin 6 positive astrocytes were seen to make multiple contacts with tau positive neurons, there was no intraneuronal colocalization. In brain tissue of patients with AD, many blood vessels exhibited peroxiredoxin 6 staining that appeared to be due to the astrocytic foot processes. These results suggest that oxidative stress conditions exist in AD and that peroxiredoxin 6 is an important antioxidant enzyme in human brain defenses.

p25alpha relocalizes in oligodendroglia from myelin to cytoplasmic inclusions in multiple system atrophy

p25alpha is an oligodendroglial protein that can induce aggregation of alpha-synuclein and accumulates in oligodendroglial cell bodies containing fibrillized alpha-synuclein in the neurodegenerative disease multiple system atrophy (MSA). We demonstrate biochemically that p25alpha is a constituent of myelin and a high-affinity ligand for myelin basic protein (MBP), and in situ immunohistochemistry revealed that MBP and p25alpha colocalize in myelin in normal human brains. Analysis of MSA cases reveals dramatic changes in p25alpha and MBP throughout the course of the disease. In situ immunohistochemistry revealed a cellular redistribution of p25alpha immunoreactivity from the myelin to the oligodendroglial cell soma, with no overall change in p25alpha protein concentration using immunoblotting. Concomitantly, an approximately 80% reduction in the concentration of full-length MBP protein was revealed by immunoblotting along with the presence of immunoreactivity for MBP degradation products in oligodendroglia. The oligodendroglial cell bodies in MSA displayed an enlargement along with the relocalization of p25alpha, and this was enhanced after the deposition of alpha-synuclein in the glial cytoplasmic inclusions. Overall, the data indicate that changes in the cellular interactions between MBP and p25alpha occur early in MSA and contribute to abnormalities in myelin and subsequent alpha-synuclein aggregation and the ensuing neuronal degeneration that characterizes this disease.

P25?/Tubulin polymerization promoting protein expression by myelinating oligodendrocytes of the developing rat brain

P25alpha/tubulin polymerization promoting protein (TPPP) is a brain specific phosphoprotein that displays microtubule bundling activity. In the mature brain, p25alpha/TPPP distributes to oligodendrocytes and choroid plexus epithelium. We mapped the spatial and temporal distribution of p25alpha/TPPP in the developing rat brain. Having localized its expression to neuronal tissue by Western blot analyses, the distribution of p25alpha/TPPP to developing oligodendrocytes was confirmed using a specific antibody. In the pre-natal and post-natal brain, p25alpha/TPPP was localized to the perinuclear cytoplasm of myelinating oligodendrocytes from embryonic (E) day E20 as verified from cellular co-localization with 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP). Oligodendrocyte progenitor cells and pre-myelinating oligodendrocytes identified by the expression of NG2 proteoglycan and CD9, respectively, both failed to contain p25alpha/TPPP. In contrast, P25alpha/TPPP co-localized with beta(IV)-tubulin from post-natal (p) day P10 suggesting that p25alpha/TPPP plays an important role for tubulin-related transport in developing, myelinating oligodendrocytes.

Cellular parkin mutants are soluble under non-stress conditions

The parkin gene encodes an E3 ubiquitin ligase and loss of function mutations herein are the most frequent cause of early-onset Parkinson's disease. Reports have suggested that aggregation of mutant protein is the cause of the loss of function. We established stably transfected SH-SY5Y dopaminergic cell lines expressing wild-type and mutant parkin proteins. All the mutant proteins were soluble but could be rendered insoluble by subjecting the cellsto stress by proteasomal inhibition, treatment with oxidants and upon transient expression of the mutant proteins. A functional assay demonstrated that the R42P mutant retained functional activity in contrast to the W453stop mutant. Accordingly, the functional impairment by the mutations is not simply caused by turning the proteins insoluble.

Association of alpha-synuclein and mutants with lipid membranes: spin-label ESR and polarized IR

Alpha-synuclein is a presynaptic protein, the A53T and A30P mutants of which are linked independently to early-onset familial Parkinson's disease. The association of wild-type alpha-synuclein with lipid membranes was characterized previously by electron spin resonance (ESR) spectroscopy with spin-labeled lipids [Ramakrishnan, M., Jensen, P. H., and Marsh, D. (2003) Biochemistry 42, 12919-12926]. Here, we study the interaction of the A53T and A30P alpha-synuclein mutants and a truncated form that lacks the acidic C-terminal domain with phosphatidylglycerol bilayer membranes, using anionic phospholipid spin labels. The strength of the interaction with phosphatidylglycerol membranes lies in the order: wild type approximately truncated > A53T > A30P > fibrils approximately 0, and only the truncated form interacts with phosphatidylcholine membranes. The selectivity of the interaction of the mutant alpha-synucleins with different spin-labeled lipid species is reduced considerably, relative to the wild-type protein, whereas that of the truncated protein is increased. Polarized infrared (IR) spectroscopy is used to study the interactions of the wild-type and truncated proteins with aligned lipid membranes and additionally to characterize the fibrillar form. Wild-type alpha-synuclein is natively unfolded in solution and acquires secondary structure upon binding to membranes containing phosphatidylglycerol. Up to 30-40% of the amide I band intensity of the membrane-bound wild-type and truncated proteins is attributable to beta-sheet structure, at the surface densities used for IR spectroscopy. The remainder is alpha-helix and residual unordered structure. Fibrillar alpha-synuclein contains 62% antiparallel beta-sheet and is oriented on the substrate surface but does not interact with deposited lipid membranes. The beta-sheet secondary-structural elements of the wild-type and truncated proteins are partially oriented on the surface of membranes with which they interact.

Oligodendrocytes within astrocytes ("emperipolesis") in the cerebral white matter in hepatic and hypoglycemic encephalopathy

We report the occurrence of oligodendrocytes within astrocytes ("emperipolesis") in two autopsy cases of metabolic encephalopathy: one patient with hepatic encephalopathy due to citrullinemia who suffered recurrent unconsciousness (clinical duration, 32 months) and another with hypoglycemic encephalopathy who lapsed into a persistent vegetative state (clinical duration, 22 months). In both cases, hypertrophic astrocytes were found to have engulfed one to several oligodendrocytes in the devastated cerebral white matter. Previous studies have reported that emperipolesis occurs in various CNS diseases showing destruction of myelin or inflammation of the white matter, including multiple sclerosis, cerebral infarct and CJD. The present findings suggest that emperipolesis can occur even in chronic metabolic disorders that extensively involve the cerebral white matter.

α-Synuclein redistributes to neuromelanin lipid in the substantia nigra early in Parkinson's disease

The distribution and tempo of neuronal loss in Parkinson's disease correlates poorly with the characteristic and more widely spread intracellular changes associated with the disease process (Lewy bodies and Lewy neurites). To determine early intracellular changes in regions where cell loss is most marked (dopaminergic A9 substantia nigra) versus regions with Lewy bodies but where cell loss is limited, we assessed 13 patients with definite Parkinson's disease at various disease stages in comparison with controls. Using immunohistochemistry for alpha-synuclein, we confirmed the concentration of this protein in the soma of normal A9 neurons and in Lewy body pathology in brainstem catecholamine neurons in Parkinson's disease. Analysis of the degree of cell loss in brainstem catecholamine cell groups revealed that only the A9 substantia nigra had consistent significant cell loss early in the disease course with greater A9 cell loss correlating with increasing disease duration. To assess the earliest intracellular changes differentiating neurons more likely to degenerate, pigmented A9 and A10 neurons with and without obvious pathology were targeted, cell size and pigment density measured, and intracellular changes in alpha-synuclein location and lipid components analysed at both the light and electron microscope levels. There were no changes observed in healthy A10 neurons in Parkinson's disease compared with controls. Pigmented A9 neurons in later stages of degeneration with obvious Lewy body formation had a significant reduction in intracellular pigment, as previously described. In contrast, A9 neurons of normal morphological appearance and no characteristic pathology in Parkinson's disease exhibited significantly increased pigment density associated with a concentration of alpha-synuclein to the lipid component of the pigment and a loss of associated cholesterol. These changes in vulnerable but apparently healthy A9 neurons occurred without any change in cell size or in the amount of intracellular pigment compared with controls. The increase in pigment density is consistent with previously reported increases associated with oxidation and iron loading, reactions known to precipitate alpha-synuclein. The selectivity of the changes observed in A9 nigral neurons suggests that these early intracellular changes predispose these neurons to more rapid cell loss in Parkinson's disease. The increased concentration of neuronal alpha-synuclein and pigment in normal A9 neurons may already predispose these neurons to precipitate alpha-synuclein around pigment-associated lipid under oxidative conditions. Overall, these changes may trigger a cascade of events leading to larger intracellular aggregates of alpha-synuclein and the dispersement of protective pigment to precipitate cell death in Parkinson's disease.

p25alpha is flexible but natively folded and binds tubulin with oligomeric stoichiometry

p25alpha is a 219-residue protein which stimulates aberrant tubulin polymerization and is implicated in a variety of other functions. The protein has unusual secondary structure involving significant amounts of random coil, and binding to microtubules is accompanied by a large structural change, suggesting a high degree of plasticity. p25alpha has been proposed to be natively unfolded, so that folding is coupled to interaction with its physiological partners. Here we show that recombinant human p25alpha is folded under physiological conditions, since it has a well structured and solvent-sequestered aromatic environment and considerable chemical shift dispersion of amide and aliphatic protons. With increasing urea concentrations, p25alpha undergoes clear spectral changes suggesting significant loss of structure. p25alpha unfolds cooperatively in urea according to a simple two-state transition with a stability in water of approximately 5 kcal/mol. The protein behaves as a monomer and refolds with a transient on-pathway folding intermediate. However, high sensitivity to proteolytic attack and abnormal gel filtration migration behavior suggests a relatively extended structure, possibly organized in distinct domains. A deletion mutant of p25alpha lacking residues 3-43 also unfolds cooperatively and with similar stability, suggesting that the N-terminal region is largely unstructured. Both proteins undergo significant loss of structure when bound to monomeric tubulin. The stoichiometry of binding is estimated to be 3-4 molecules of tubulin per p25alpha and is not significantly affected by the deletion of residues 3-43. In conclusion, we dismiss the proposal that p25alpha is natively unfolded, although the protein is relatively flexible. This flexibility may be linked to its tubulin-binding properties.

Alpha-synuclein association with phosphatidylglycerol probed by lipid spin labels

Alpha-synuclein is a small presynaptic protein, which is linked to the development of Parkinson's disease. Alpha-synuclein partitions between cytosolic and vesicle-bound states, where membrane binding is accompanied by the formation of an amphipathic helix in the N-terminal section of the otherwise unstructured protein. The impact on alpha-synuclein of binding to vesicle-like liposomes has been studied extensively, but far less is known about the impact of alpha-synuclein on the membrane. The interactions of alpha-synuclein with phosphatidylglycerol membranes are studied here by using spin-labeled lipid species and electron spin resonance (ESR) spectroscopy to allow a detailed analysis of the effect on the membrane lipids. Membrane association of alpha-synuclein perturbs the ESR spectra of spin-labeled lipids in bilayers of phosphatidylglycerol but not of phosphatidylcholine. The interaction is inhibited at high ionic strength. The segmental motion is hindered at all positions of spin labeling in the phosphatidylglycerol sn-2 chain, while still preserving the chain flexibility gradient characteristic of fluid phospholipid membranes. Direct motional restriction of the lipid chains, resulting from penetration of the protein into the hydrophobic interior of the membrane, is not observed. Saturation occurs at a protein/lipid ratio corresponding to approximately 36 lipids/protein added. Alpha-synuclein exhibits a selectivity of interaction with different phospholipid spin labels when bound to phosphatidylglycerol membranes in the following order: stearic acid > cardiolipin > phosphatidylcholine > phosphatidylglycerol approximately phosphatidylethanolamine > phosphatidic acid approximately phosphatidylserine > N-acyl phosphatidylethanolamine > diglyceride. Accordingly, membrane-bound alpha-synuclein associates at the interfacial region of the bilayer where it may favor a local concentration of certain phospholipids.

Proteasomal inhibition by alpha-synuclein filaments and oligomers

A unifying feature of many neurodegenerative disorders is the accumulation of polyubiquitinated protein inclusions in dystrophic neurons, e.g. containing alpha-synuclein, which is suggestive of an insufficient proteasomal activity. We demonstrate that alpha-synuclein and 20 S proteasome components co-localize in Lewy bodies and show that subunits from 20 S proteasome particles, in contrast to subunits of the 19 S regulatory complex, bind efficiently to aggregated filamentous but not monomeric alpha-synuclein. Proteasome binding to insoluble alpha-synuclein filaments and soluble alpha-synuclein oligomers results in marked inhibition of its chymotrypsin-like hydrolytic activity through a non-competitive mechanism that is mimicked by model amyloid-Abeta peptide aggregates. Endogenous ligands of aggregated alpha-synuclein like heat shock protein 70 and glyceraldehyde-6-phosphate dehydrogenase bind filaments and inhibit their anti-proteasomal activity. The inhibitory effect of amyloid aggregates may thus be amenable to modulation by endogenous chaperones and possibly accessible for therapeutic intervention.

Absence of prostate apoptosis response-4 protein in substantia nigra of Parkinson's disease autopsies

The morphological evidence for apoptosis of dopaminergic neurons in Parkinson's disease (PD) remains a conflicting issue. The present study examined autopsy material containing substantia nigra and putamen of PD ( n=7) and control subjects ( n=5) for the expression of prostate apoptosis response-4 (Par-4) protein, a protein expressed by apoptotic cells. Par-4 was not detected in the substantia nigra pars compacta. By contrast, duodenal enterocytes, which served as positive controls and are known to be apoptotic, profoundly expressed Par-4. The present study is in agreement with previous studies of the substantia nigra pars compacta in PD, which failed to detect molecules expressed by apoptotic cells. The absence of Par-4 immunoreactivity suggests that death of dopaminergic neurons in PD follows a degenerative pathway that circumvents the induction of Par-4.

Parkin is recruited into aggresomes in a stress-specific manner: over-expression of parkin reduces aggresome formation but can be dissociated from parkin's effect on neuronal survival

Parkinson's disease (PD) is characterized by loss of dopamine neurons in the substantia nigra and the presence of cytoplasmic inclusions known as Lewy bodies (LBs). Mutations in parkin cause autosomal recessive juvenile parkinsonism (AR-JP) that is distinct from sporadic PD by the general absence of LBs. Several studies have reported that parkin is present in LBs of sporadic PD but the role of parkin in LB formation is unclear. Aggresomes are perinuclear aggregates representing intracellular deposition of misfolded protein. LBs and aggresomes have been reported to share a common biogenesis. We have investigated the role of parkin in aggresome formation. In human SH-SY5Y neuroblastoma cells we observe that endogenous parkin is present in aggresomes induced by a variety of stresses including dopamine, proteosome inhibition and a pro-apoptopic stimulus. We show that vimentin is invariably collapsed around the aggresome but that the detection of ubiquitin is variable depending on the stress. We show that cells that stably over-express human wild-type parkin form fewer aggresomes upon stress compared to cells that express vector alone whereas over-expression of AR-JP causing mutants of parkin have no effect on stress-induced aggresome formation. Finally, we show that the prevention of aggresome formation by over-expression of wild-type parkin is not always associated with a beneficial effect on neuronal survival. Our findings suggest that parkin is important for aggresome formation in human neuronal cells and may lead to a better understanding of the biogenesis of LBs in sporadic PD.

Recombinant mannan-binding lectin (MBL) for therapy

Mannan-binding lectin (MBL) is a plasma protein involved in the innate immune response. It binds to a number of micro-organisms and promotes killing of these through complement activation either directly or through opsonization. Clinical evidence indicates that in a variety of situations genetically determined low MBL levels are associated with increased susceptibility to infections. Infusions of plasma-derived MBL into MBL-deficient individuals was found to be safe in preliminary trials, but we considered that sufficient production and product safety could only be achieved through synthesis of recombinant MBL. A transfected human cell line produces MBL showing the same biological activity as plasma-derived MBL, and an essentially identical profile on MS. The production has been scaled up and clinical trials will start this year.

alpha-Synuclein fibrils constitute the central core of oligodendroglial inclusion filaments in multiple system atrophy

Multiple system atrophy (MSA) belongs to synucleinopathies and is characterized pathologically by oligodendroglial inclusions (GCIs) composed of 20- to 30-nm tubular filaments. alpha-Synuclein fibrils formed in vitro, however, range between 10 and 12 nm in diameter. To understand the relationship between alpha-synuclein and GCI filaments, we conducted structural analyses of GCIs in fixed brain sections and isolated from fresh-frozen MSA brains. In fixed brain sections, GCIs were composed of amorphous material-coated filaments up to 30 nm in size. The filaments were often organized in parallel bundles extending into oligodendroglial processes. In freshly isolated GCIs, progressive buffer washes removed amorphous material and revealed that GCI filaments consisted of 10-nm-sized central core fibrils that were strongly alpha-synuclein immunoreactive. Image analysis revealed that each core fibril was made of two subfibrils, and each subfibril was made of a string of 3- to 6-nm-sized particles probably alpha-synuclein oligomers. Immunogold labeling demonstrated that epitopes encompassing entire alpha-synuclein molecule were represented in the core fibrils, with the N-terminal 11-26 and C-terminal 108-131 amino acid residues most accessible to antibodies, probably exposed on the surface of the fibril. Our study indicates that GCI filaments are multilayered in structure, with alpha-synuclein oligomers forming the central core fibrils of the filaments.

Down-regulation of parkin protein in transient focal cerebral ischemia: A link between stroke and degenerative disease?

Ubiquitylated protein aggregates are characteristic features of neurodegenerative disorders that are also found in acute pathological states of the brain such as stroke. Many of the proteins connected to neurodegenerative diseases play a role in the ubiquitin-proteasomal pathway. Mutation of one of these proteins, the E3 ubiquitin ligase parkin, is the cause of autosomal recessive juvenile Parkinson's disease. Here we show that transient focal cerebral ischemia of 1-h duration induces marked depletion of parkin protein levels, to 60%, 36%, 33%, and 25% of controls after 1, 3, 6, and 24 h of reperfusion, but that ischemia does not cause lower protein levels of E2 ubiquitin-conjugating enzymes Ubc6, Ubc7, or Ubc9. After 3 h of reperfusion, when parkin protein levels were already reduced to <40% of control, ATP levels were almost completely recovered from ischemia and we did not observe DNA fragmentation, suggesting that parkin depletion preceded development of neuronal cell death. Up-regulation of the expression of parkin has been shown to protect cells from injury induced by endoplasmic reticulum (ER) dysfunction, and this form of cellular stress is also triggered by transient cerebral ischemia. However, in contrast to observations in neuroblastoma cells, we saw no up-regulation of parkin expression in primary neuronal cell cultures after induction of ER dysfunction. Our data thus suggest that ischemia-induced depletion of parkin protein may contribute to the pathological process resulting in cell injury by increasing the sensitivity of neurons to ER dysfunction and the aggregation of ubiquitylated proteins during the reperfusion period.

The glycan structure of albumin Redhill, a glycosylated variant of human serum albumin

Although human serum albumin is synthesized without carbohydrate, glycosylated variants of the protein can be found. We have determined the structure of the glycan bound to the double-mutant albumin Redhill (-1 Arg, 320 Ala-->Thr). The oligosaccharide was released from the protein using anhydrous hydrazine, and its structure was investigated using neuraminidase and a reagent array analysis method, which is based on the use of specific exoglycosidases. The glycan was shown to be a disialylated biantennary complex type oligosaccharide N-linked to 318 Asn. However, a minor part (11 mol%) of the glycan was without sialic acid. The structure is principally the same as that of glycans bound to two other types of glycosylated albumin variants. Glycosylation can affect, for example, the fatty acid binding properties of albumin. Taking the present information into account, it is apparent that different effects on binding are caused not by different glycan structures but by different locations of attachment, with the possible addition of local conformational changes in the protein molecule.

Ca2+ binding to alpha-synuclein regulates ligand binding and oligomerization

alpha-Synuclein is a protein normally involved in presynaptic vesicle homeostasis. It participates in the development of Parkinson's disease, in which the nerve cell lesions, Lewy bodies, accumulate alpha-synuclein filaments. The synaptic neurotransmitter release is primarily dependent on Ca(2+)-regulated processes. A microdialysis technique was applied showing that alpha-synuclein binds Ca(2+) with an IC(50) of about 2-300 microm and in a reaction uninhibited by a 50-fold excess of Mg(2+). The Ca(2+)-binding site consists of a novel C-terminally localized acidic 32-amino acid domain also present in the homologue beta-synuclein, as shown by Ca(2+) binding to truncated recombinant and synthetic alpha-synuclein peptides. Ca(2+) binding affects the functional properties of alpha-synuclein. First, the ligand binding of (125)I-labeled bovine microtubule-associated protein 1A is stimulated by Ca(2+) ions in the 1-500 microm range and is dependent on an intact Ca(2+) binding site in alpha-synuclein. Second, the Ca(2+) binding stimulates the proportion of (125)I-alpha-synuclein-containing oligomers. This suggests that Ca(2+) ions may both participate in normal alpha-synuclein functions in the nerve terminal and exercise pathological effects involved in the formation of Lewy bodies.

Evaluation and ranking of restoration strategies for radioactively contaminated sites

An international project, whose aim was the development of a transparent and robust method for evaluating and ranking restoration strategies for radioactively contaminated sites (RESTRAT), was carried out under the Fourth Framework of the Nuclear Fission Safety Programme of the EU. The evaluation and ranking procedure used was based on the principles of justification and optimisation for radiation protection. A multi-attribute utility analysis was applied to allow for the inclusion of radiological health effects, economic costs and social factors. Values of these attributes were converted into utility values by applying linear utility functions and weighting factors, derived from scaling constants and expert judgement. The uncertainties and variabilities associated with these utility functions and weighting factors were dealt with by a probabilistic approach which utilised a Latin Hypercube Sampling technique. Potentially relevant restoration techniques were identified and their characteristics determined through a literature review. The methodology developed by this project has been illustrated by application to representative examples of different categories of contaminated sites; a waste disposal site, a uranium tailing site and a contaminated freshwater river.

In situ and in vitro study of colocalization and segregation of alpha-synuclein, ubiquitin, and lipids in Lewy bodies

alpha-Synuclein and ubiquitin are two Lewy body protein components that may play antagonistic roles in the pathogenesis of Lewy bodies. We examined the relationship between alpha-synuclein, ubiquitin, and lipids in Lewy bodies of fixed brain sections or isolated from cortical tissues of dementia with Lewy bodies. Lewy bodies exhibited a range of labeling patterns for alpha-synuclein and ubiquitin, from a homogeneous pattern in which alpha-synuclein and ubiquitin were evenly distributed and overlapped across the inclusion body to a concentric pattern in which alpha-synuclein and ubiquitin were partially segregated, with alpha-synuclein labeling concentrated in the peripheral domain and ubiquitin in the central domain of the Lewy body. Lipids represented a significant component in both homogeneous and concentric Lewy bodies. These results suggest that Lewy bodies are heterogeneous in their subregional composition. The segregation of alpha-synuclein to Lewy body peripheral domain is consistent with the hypothesis that alpha-synuclein is continually deposited onto Lewy bodies.

Are public dose limits necessary?

The distinction between practices and interventions in the System of Radiation Protection has created a lot of confusion in the population and amongst decision-makers, especially with regards to the concepts of dose limits and intervention levels. The experience gained after the Chernobyl accident indicated that many actions taken led to an unnecessarily large expenditure of national resources and many instances occurred of contradictory national responses. A major reason was the mixture of dose limits for the population, which apply only to exposures from practices, and intervention levels, which apply only to protective measures in de-facto exposure situations. The existing System of Radiation Protection is revisited and it is suggested that the System can be revised with no dose limits for the public without causing a lower degree of protection of the population. With the widespread use of source-related dose constraints and practical restrictions on the sources of public exposure from practices, generally applicable dose limits are rarely limiting in any practical situation, even if dose constraints might, at least in principle, fail to take adequate account of the exposures from other practices. Constraints can be expressed as operational protection quantities, e.g., nuclide-specific release rates, dose rate at the fence of a facility, or nuclide-specific surface contamination density in the environment. A revised System of Radiation Protection without public dose limits would not cause any reduced protection of the public compared to the existing System, and it has a potential for removing much of the confusion with regards to application of intervention/action levels. It would also have the potential for improving public perception of radiation protection and radiation risks as well as for saving vast resources in intervention situations for better application in general health care of the public.