Dementia with Lewy bodies (DLB) and Parkinson's Disease (PD) are common causes of motor and cognitive deficits and are associated with the abnormal accumulation of alpha-synuclein (α-syn). This study investigated whether passive immunization with a novel monoclonal α-syn antibody (9E4) against the C-terminus (CT) of α-syn was able to cross into the CNS and ameliorate the deficits associated with α-syn accumulation. In this study we demonstrate that 9E4 was effective at reducing behavioral deficits in the water maze, moreover, immunization with 9E4 reduced the accumulation of calpain-cleaved α-syn in axons and synapses and the associated neurodegenerative deficits. In vivo studies demonstrated that 9E4 traffics into the CNS, binds to cells that display α-syn accumulation and promotes α-syn clearance via the lysosomal pathway. These results suggest that passive immunization with monoclonal antibodies against the CT of α-syn may be of therapeutic relevance in patients with PD and DLB.

Parkinson's disease (PD) and dementia with Lewy bodies (DLB) are common neurodegenerative disorders of the aging population, characterized by progressive and abnormal accumulation of ␣-synuclein (␣-syn). Recent studies have shown that C-terminus (CT) truncation and propagation of ␣-syn play a role in the pathogenesis of PD/DLB. Therefore, we explored the effect of passive immunization against the CT of ␣-syn in the mThy1-␣-syn transgenic (tg) mouse model, which resembles the striato-nigral and motor deficits of PD. Mice were immunized with the new monoclonal antibodies 1H7, 5C1, or 5D12, all directed against the CT of ␣-syn. CT ␣-syn antibodies attenuated synaptic and axonal pathology, reduced the accumulation of CT-truncated ␣-syn (CT-␣-syn) in axons, rescued the loss of tyrosine hydroxylase fibers in striatum, and improved motor and memory deficits. Among them, 1H7 and 5C1 were most effective at decreasing levels of CT-␣-syn and higher-molecular-weight aggregates. Furthermore, in vitro studies showed that preincubation of recombinant ␣-syn with 1H7 and 5C1 prevented CT cleavage of ␣-syn. In a cell-based system, CT antibodies reduced cell-to-cell propagation of full-length ␣-syn, but not of the CT-␣-syn that lacked the 118 -126 aa recognition site needed for antibody binding. Furthermore, the results obtained after lentiviral expression of ␣-syn suggest that antibodies might be blocking the extracellular truncation of ␣-syn by calpain-1. Together, these results demonstrate that antibodies against the CT of ␣-syn reduce levels of CT-truncated fragments of the protein and its propagation, thus ameliorating PD-like pathology and improving behavioral and motor functions in a mouse model of this disease.

The cognitive impairment in patients with Alzheimer's disease is closely associated with synaptic loss in the neocortex and limbic system. Although the neurotoxic effects of aggregated amyloid-b oligomers in Alzheimer's disease have been studied extensively in experimental models, less is known about the characteristics of these aggregates across the spectrum of Alzheimer's disease. In this study, postmortem frontal cortex samples from controls and patients with Alzheimer's disease were fractionated and analyzed for levels of oligomers and synaptic proteins. We found that the levels of oligomers correlated with the severity of cognitive impairment (blessed information-memory-concentration score and mini-mental state examination) and with the loss of synaptic markers. Reduced levels of the synaptic vesicle protein, vesicle-associated membrane protein-2, and the postsynaptic protein, postsynaptic density-95, correlated with the levels of oligomers in the various fractions analyzed. The strongest associations were found with amyloid-b dimers and pentamers. Co-immunoprecipitation and doublelabeling experiments supported the possibility that amyloid-b and postsynaptic density-95 interact at synaptic sites. Similarly, in transgenic mice expressing high levels of neuronal amyloid precursor protein, amyloid-b co-immunoprecipitated with postsynaptic density-95. This was accompanied by a decrease in the levels of the postsynaptic proteins Shank1 and Shank3 in patients with Alzheimer's disease and in the brains of amyloid precursor protein transgenic mice. In conclusion, this study suggests that the presence of a subpopulation of amyloid-b oligomers in the brains of patients with Alzheimer's disease might be related to alterations in selected synaptic proteins and cognitive impairment.

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.

Multiple system atrophy (MSA) is a neurodegenerative disorder characterized by striatonigral degeneration and olivo-pontocerebellar atrophy. Neuronal degeneration is accompanied by primarily oligodendrocytic accumulation of ␣-synuclein (␣syn) as opposed to the neuronal inclusions more commonly found in other ␣-synucleinopathies such as Parkinson's disease. It is unclear how ␣syn accumulation in oligodendrocytes may lead to the extensive neurodegeneration observed in MSA; we hypothesize that the altered expression of oligodendrocyte-derived neurotrophic factors by ␣syn may be involved. In this context, the expression of a number neurotrophic factors reportedly expressed by oligodendrocytes [glial-derived neurotrophic factor (GDNF), brain-derived neurotrophic factor (BDNF), and insulin-like growth factor 1 (IGF-1), as well as basic fibroblast growth factor 2 (bFGF2), reportedly astrocyte derived] were examined in transgenic mouse models expressing human ␣syn (h␣syn) under the control of either neuronal (PDGF␤ or mThy1) or oligodendrocytic (MBP) promoters. Although protein levels of BDNF and IGF-1 were altered in all the ␣syn transgenic mice regardless of promoter type, a specific decrease in GDNF protein expression was observed in the MBP-h␣syn transgenic mice. Intracerebroventricular infusion of GDNF improved behavioral deficits and ameliorated neurodegenerative pathology in the MBP-h␣syn transgenic mice. Consistent with the studies in the MBP-h␣syn transgenic mice, analysis of GDNF expression levels in human MSA samples demonstrated a decrease in the white frontal cortex and to a lesser degree in the cerebellum compared with controls. These results suggest a mechanism in which ␣syn expression in oligodendrocytes impacts on the trophic support provided by these cells for neurons, perhaps contributing to neurodegeneration.