Leslie Crews

Inclusion formation and neuronal cell death through neuron-to-neuron transmission of alpha-synuclein.

Neuronal accumulation of α-synuclein and Lewy body formation are characteristic to many neurodegenerative diseases, including Parkinsons disease (PD). This Lewy pathology appears to spread throughout the brain as the disease progresses. Furthermore, recent studies showed the occurrence of Lewy pathology in neurons grafted into the brains of PD patients, suggesting the spread of pathology from the host tissues to the grafts. The mechanism underlying this propagation is unknown. Here, we show that α-synuclein is transmitted via endocytosis to neighboring neurons and neuronal precursor cells, forming Lewy-like inclusions. Moreover, α-synuclein was transmitted from the affected neurons to engrafted neuronal precursor cells in a transgenic model of PD-like pathology. Failure of the protein quality control systems, especially lysosomes, promoted the accumulation of transmitted α-synuclein and inclusion formation. Cells exposed to neuron-derived α-synuclein showed signs of apoptosis, such as nuclear fragmentation and caspase 3 activation, both in vitro and in vivo. These findings demonstrate the cell-to-cell transmission of α-synuclein aggregates and provide critical insights into the mechanism of pathological progression in PD and other proteinopathies.

Effects of α-Synuclein Immunization in a Mouse Model of Parkinson’s Disease

Abnormal folding of alpha-synuclein (alpha-syn) is thought to lead to neurodegeneration and the characteristic symptoms of Lewy body disease (LBD). Since previous studies suggest that immunization might be a potential therapy for Alzheimers disease, we hypothesized that immunization with human (h)alpha-syn might have therapeutic effects in LBD. For this purpose, halpha-syn transgenic (tg) mice were vaccinated with halpha-syn. In mice that produced high relative affinity antibodies, there was decreased accumulation of aggregated halpha-syn in neuronal cell bodies and synapses that was associated with reduced neurodegeneration. Furthermore, antibodies produced by immunized mice recognized abnormal halpha-syn associated with the neuronal membrane and promoted the degradation of halpha-syn aggregates, probably via lysosomal pathways. Similar effects were observed with an exogenously applied FITC-tagged halpha-syn antibody. These results suggest that vaccination is effective in reducing neuronal accumulation of halpha-syn aggregates and that further development of this approach might have a potential role in the treatment of LBD.

Targeting BACE1 with siRNAs ameliorates Alzheimer disease neuropathology in a transgenic model

In Alzheimer disease, increased β-secretase (BACE1) activity has been associated with neurodegeneration and accumulation of amyloid precursor protein (APP) products. Thus, inactivation of BACE1 could be important in the treatment of Alzheimer disease. In this study, we found that lowering BACE1 levels using lentiviral vectors expressing siRNAs targeting BACE1 reduced amyloid production and the neurodegenerative and behavioral deficits in APP transgenic mice, a model of Alzheimer disease. Our results suggest that lentiviral vector delivery of BACE1 siRNA can specifically reduce the cleavage of APP and neurodegeneration in vivo and indicate that this approach could have potential therapeutic value for treatment of Alzheimer disease.

Aβ vaccination effects on plaque pathology in the absence of encephalitis in Alzheimer disease

The authors report a patient with Alzheimer disease (AD) without encephalitis who was immunized with AN-1792 (an adjuvanted formulation of Aβ-42). There were no amyloid plaques in the frontal cortex and abundant Aβ-immunoreactive macrophages, but tangles and amyloid angiopathy were present. The white matter appeared normal and minimal lymphocytic infiltration in the leptomeninges was observed. This case illustrates the effects of an Aβ-based immunization on AD pathogenesis in the absence of overt meningoencephalitis and leukoencephalopathy.

Role of Protein Aggregation in Mitochondrial Dysfunction and Neurodegeneration in Alzheimer's and Parkinson's Diseases

Abnormal interactions and misfolding of synaptic proteins in the nervous system are being extensively explored as important pathogenic events resulting in neurodegeneration in various neurological disorders. These include Alzheimer’s disease (AD), Parkinson’s disease (PD), and dementia with Lewy bodies (DLB). In AD, misfolded amyloid β peptide 1–42 (Aβ), a proteolytic product of amyloid precursor protein metabolism, accumulates in the neuronal endoplasmic reticulum and extracellularly as plaques. In contrast, in PD and DLB cases there is abnormal accumulation of α-synuclein in neuronal cell bodies, axons, and synapses. Furthermore, in DLB, Aβ 1–42 may promote α-synuclein accumulation and neurodegeneration. The central event leading to synaptic and neuronal loss in these diseases is not completely clear yet; however, recent advances in the field suggest that nerve damage might result from the conversion of nontoxic monomers to toxic oligomers and protofibrils. The mechanisms by which misfolded Aβ peptide and α-synuclein might lead to synapse loss are currently under investigation. Several lines of evidence support the possibility that Aβ peptide and α-synuclein might interact to cause mitochondrial and plasma membrane damage upon translocation of protofibrils to the membranes. Accumulation of Aβ and α-synuclein oligomers in the mitochondrial membrane might result in the release of cytochrome C with the subsequent activation of the apoptosis cascade. Conversely, the oxidative stress and mitochondrial dysfunction associated with AD and PD may also lead to increased membrane permeability and cytochrome C release, which promotes Aβ and α-synuclein oligomerization and neurodegeneration. Together, these studies suggest that the translocation of misfolded proteins to the mitochondrial membrane might play an important role in either triggering or perpetuating neurodegeneration. The insights obtained from the characterization of this process may be applied to the role of mitochondrial dysfunction in other neurodegenerative disorders, including AD. New evidence may also provide a rationale for the mitochondrial membrane as a target for therapy in a variety of neurodegenerative diseases.

Molecular Mechanisms of Neurodegeneration in Alzheimer’s Disease

Alzheimers disease (AD) is characterized by cognitive impairment, progressive neurodegeneration and formation of amyloid-beta (Abeta)-containing plaques and neurofibrillary tangles composed of hyperphosphorylated tau. The neurodegenerative process in AD is initially characterized by synaptic damage accompanied by neuronal loss. In addition, recent evidence suggests that alterations in adult neurogenesis in the hippocampus might play a role. Synaptic loss is one of the strongest correlates to the cognitive impairment in patients with AD. Several lines of investigation support the notion that the synaptic pathology and defective neurogenesis in AD are related to progressive accumulation of Abeta oligomers rather than fibrils. Abnormal accumulation of Abeta resulting in the formation of toxic oligomers is the result of an imbalance between the levels of Abeta production, aggregation and clearance. Abeta oligomers might lead to synaptic damage by forming pore-like structures with channel activity; alterations in glutamate receptors; circuitry hyper-excitability; mitochondrial dysfunction; lysosomal failure and alterations in signaling pathways related to synaptic plasticity, neuronal cell and neurogenesis. A number of signaling proteins, including fyn kinase; glycogen synthase kinase-3beta (GSK3beta) and cyclin-dependent kinase-5 (CDK5), are involved in the neurodegenerative progression of AD. Therapies for AD might require the development of anti-aggregation compounds, pro-clearance pathways and blockers of hyperactive signaling pathways.

Passive Immunization Reduces Behavioral and Neuropathological Deficits in an Alpha-Synuclein Transgenic Model of Lewy Body Disease

Dementia with Lewy bodies (DLB) and Parkinsons 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.

Neuroprotective Effects of Regulators of the Glycogen Synthase Kinase-3β Signaling Pathway in a Transgenic Model of Alzheimer's Disease Are Associated with Reduced Amyloid Precursor Protein Phosphorylation

The glycogen synthase kinase-3β (GSK3β) pathway plays an important role in mediating neuronal fate and synaptic plasticity. In Alzheimers disease (AD), abnormal activation of this pathway might play an important role in neurodegeneration, and compounds such as lithium that modulate GSK3β activity have been shown to reduce amyloid production and tau phosphorylation in amyloid precursor protein (APP) transgenic (tg) mice. However, it is unclear whether regulation of GSK3β is neuroprotective in APP tg mice. In this context, the main objective of the present study was to determine whether pharmacological or genetic manipulations that block the GSK3β pathway might ameliorate the neurodegenerative alterations in APP tg mice and to better understand the mechanisms involved. For this purpose, two sets of experiments were performed. First, tg mice expressing mutant human APP under the Thy1 promoter (hAPP tg) were treated with either lithium chloride or saline alone. Second, hAPP tg mice were crossed with GSK3β tg mice, in which overexpression of this signaling molecule results in a dominant-negative (DN) effect with inhibition of activity. hAPP tg mice that were treated with lithium or that were crossed with DN–GSK3β tg mice displayed improved performance in the water maze, preservation of the dendritic structure in the frontal cortex and hippocampus, and decreased tau phosphorylation. Moreover, reduced activation of GSK3β was associated with decreased levels of APP phosphorylation that resulted in decreased amyloid-β production. In conclusion, the present study showed that modulation of the GSK3β signaling pathway might also have neuroprotective effects in tg mice by regulating APP maturation and processing and further supports the notion that GSK3β might be a suitable target for the treatment of AD.

Selective Molecular Alterations in the Autophagy Pathway in Patients with Lewy Body Disease and in Models of α-Synucleinopathy

Background Lewy body disease is a heterogeneous group of neurodegenerative disorders characterized by α-synuclein accumulation that includes dementia with Lewy bodies (DLB) and Parkinsons Disease (PD). Recent evidence suggests that impairment of lysosomal pathways (i.e. autophagy) involved in α-synuclein clearance might play an important role. For this reason, we sought to examine the expression levels of members of the autophagy pathway in brains of patients with DLB and Alzheimers Disease (AD) and in α-synuclein transgenic mice. Methodology/Principal Findings By immunoblot analysis, compared to controls and AD, in DLB cases levels of mTor were elevated and Atg7 were reduced. Levels of other components of the autophagy pathway such as Atg5, Atg10, Atg12 and Beclin-1 were not different in DLB compared to controls. In DLB brains, mTor was more abundant in neurons displaying α-synuclein accumulation. These neurons also showed abnormal expression of lysosomal markers such as LC3, and ultrastructural analysis revealed the presence of abundant and abnormal autophagosomes. Similar alterations were observed in the brains of α-synuclein transgenic mice. Intra-cerebral infusion of rapamycin, an inhibitor of mTor, or injection of a lentiviral vector expressing Atg7 resulted in reduced accumulation of α-synuclein in transgenic mice and amelioration of associated neurodegenerative alterations. Conclusions/Significance This study supports the notion that defects in the autophagy pathway and more specifically in mTor and Atg7 are associated with neurodegeneration in DLB cases and α-synuclein transgenic models and supports the possibility that modulators of the autophagy pathway might have potential therapeutic effects.

Deficiency in neuronal TGF-β signaling promotes neurodegeneration and Alzheimer's pathology

Alzheimers disease (AD) is characterized by progressive neurodegeneration and cerebral accumulation of the beta-amyloid peptide (Abeta), but it is unknown what makes neurons susceptible to degeneration. We report that the TGF-beta type II receptor (TbetaRII) is mainly expressed by neurons, and that TbetaRII levels are reduced in human AD brain and correlate with pathological hallmarks of the disease. Reducing neuronal TGF-beta signaling in mice resulted in age-dependent neurodegeneration and promoted Abeta accumulation and dendritic loss in a mouse model of AD. In cultured cells, reduced TGF-beta signaling caused neuronal degeneration and resulted in increased levels of secreted Abeta and beta-secretase-cleaved soluble amyloid precursor protein. These results show that reduced neuronal TGF-beta signaling increases age-dependent neurodegeneration and AD-like disease in vivo. Increasing neuronal TGF-beta signaling may thus reduce neurodegeneration and be beneficial in AD.