Cellular responses to amyloid-beta protofibrils : Focus on astrocytes, extracellular vesicles and antibody treatment

Knowledge about the cellular mechanisms behind the initiation and propagation of Alzheimer’s disease (AD) is limited. Decades of research have focused on neuronal abnormalities in AD, but recently more attention has been given to the glial cells. Being the most numerous glial cell type in the brain, astrocytes are important for many functions, but their role in AD is poorly understood. The aim with this thesis was to clarify the involvement of astrocytes in AD by using a co-culture system of primary neurons and glia. The co-cultures were exposed to soluble amyloid-beta (Aβ) aggregates, i.e. protofibrils that are known to be particularly harmful. In Paper I, the capacity of astrocytes to ingest and degrade Aβ protofibrils was investigated. We found that astrocytes effectively ingested Aβ, but were ineffective in degrading the material. The intracellular accumulation of Aβ in astrocytes resulted in lysosomal dysfunction, high intracellular load of partly N-terminally truncated Aβ and extracellular vesicle (EV) mediated neuronal cell death. Cells can communicate by releasing cargo into EVs, but the role of EVs in the spreading of Aβ pathology is unclear. In Paper II, the protein content of EVs released specifically following Aβ protofibril exposure was analyzed. We found markedly increased levels of apolipoprotein E (apoE) in EVs from Aβ protofibril exposed co-cultures, suggesting a role for intercellular transfer of apoE in Aβ pathology. Passive immunotherapy has been suggested as a promising therapeutic strategy for AD. In Paper III, we investigated if the Aβ protofibril-selective antibody mAb158 could affect Aβ clearance in the co-culture. The mAb158 treatment reduced Aβ accumulation in astrocytes and rescued neurons from Aβ-induced cell death. In Paper IV, we explored the effect of EVs, isolated from Aβ protofibril exposed co-cultures on cultured neurons. In addition to increased cell death, we found that such EVs had a strong negative impact on the synapses, dendrites and mitochondria of the neurons. Taken together, this thesis contributes with important knowledge about the role of astrocytes in Aβ pathology, the vesicle-mediated spreading of Aβ and the effects of anti-Aβ antibody treatment

Cellular responses to amyloid-beta protofibrils : Focus on astrocytes, extracellular vesicles and antibody treatment

Knowledge about the cellular mechanisms behind the initiation and propagation of Alzheimer’s disease (AD) is limited. Decades of research have focused on neuronal abnormalities in AD, but recently more attention has been given to the glial cells. Being the most numerous glial cell type in the brain, astrocytes are important for many functions, but their role in AD is poorly understood. The aim with this thesis was to clarify the involvement of astrocytes in AD by using a co-culture system of primary neurons and glia. The co-cultures were exposed to soluble amyloid-beta (Aβ) aggregates, i.e. protofibrils that are known to be particularly harmful. In Paper I, the capacity of astrocytes to ingest and degrade Aβ protofibrils was investigated. We found that astrocytes effectively ingested Aβ, but were ineffective in degrading the material. The intracellular accumulation of Aβ in astrocytes resulted in lysosomal dysfunction, high intracellular load of partly N-terminally truncated Aβ and extracellular vesicle (EV) mediated neuronal cell death. Cells can communicate by releasing cargo into EVs, but the role of EVs in the spreading of Aβ pathology is unclear. In Paper II, the protein content of EVs released specifically following Aβ protofibril exposure was analyzed. We found markedly increased levels of apolipoprotein E (apoE) in EVs from Aβ protofibril exposed co-cultures, suggesting a role for intercellular transfer of apoE in Aβ pathology. Passive immunotherapy has been suggested as a promising therapeutic strategy for AD. In Paper III, we investigated if the Aβ protofibril-selective antibody mAb158 could affect Aβ clearance in the co-culture. The mAb158 treatment reduced Aβ accumulation in astrocytes and rescued neurons from Aβ-induced cell death. In Paper IV, we explored the effect of EVs, isolated from Aβ protofibril exposed co-cultures on cultured neurons. In addition to increased cell death, we found that such EVs had a strong negative impact on the synapses, dendrites and mitochondria of the neurons. Taken together, this thesis contributes with important knowledge about the role of astrocytes in Aβ pathology, the vesicle-mediated spreading of Aβ and the effects of anti-Aβ antibody treatment

Cellular responses to amyloid-beta protofibrils : Focus on astrocytes, extracellular vesicles and antibody treatment

Knowledge about the cellular mechanisms behind the initiation and propagation of Alzheimer’s disease (AD) is limited. Decades of research have focused on neuronal abnormalities in AD, but recently more attention has been given to the glial cells. Being the most numerous glial cell type in the brain, astrocytes are important for many functions, but their role in AD is poorly understood. The aim with this thesis was to clarify the involvement of astrocytes in AD by using a co-culture system of primary neurons and glia. The co-cultures were exposed to soluble amyloid-beta (Aβ) aggregates, i.e. protofibrils that are known to be particularly harmful. In Paper I, the capacity of astrocytes to ingest and degrade Aβ protofibrils was investigated. We found that astrocytes effectively ingested Aβ, but were ineffective in degrading the material. The intracellular accumulation of Aβ in astrocytes resulted in lysosomal dysfunction, high intracellular load of partly N-terminally truncated Aβ and extracellular vesicle (EV) mediated neuronal cell death. Cells can communicate by releasing cargo into EVs, but the role of EVs in the spreading of Aβ pathology is unclear. In Paper II, the protein content of EVs released specifically following Aβ protofibril exposure was analyzed. We found markedly increased levels of apolipoprotein E (apoE) in EVs from Aβ protofibril exposed co-cultures, suggesting a role for intercellular transfer of apoE in Aβ pathology. Passive immunotherapy has been suggested as a promising therapeutic strategy for AD. In Paper III, we investigated if the Aβ protofibril-selective antibody mAb158 could affect Aβ clearance in the co-culture. The mAb158 treatment reduced Aβ accumulation in astrocytes and rescued neurons from Aβ-induced cell death. In Paper IV, we explored the effect of EVs, isolated from Aβ protofibril exposed co-cultures on cultured neurons. In addition to increased cell death, we found that such EVs had a strong negative impact on the synapses, dendrites and mitochondria of the neurons. Taken together, this thesis contributes with important knowledge about the role of astrocytes in Aβ pathology, the vesicle-mediated spreading of Aβ and the effects of anti-Aβ antibody treatment

Extracellular vesicles from amyloid-beta exposed cell cultures induce severe dysfunction in cortical neurons

Alzheimer's disease (AD) is characterized by a substantial loss of neurons and synapses throughout the brain. The exact mechanism behind the neurodegeneration is still unclear, but recent data suggests that spreading of amyloid-beta (A beta) pathology via extracellular vesicles (EVs) may contribute to disease progression. We have previously shown that an incomplete degradation of A beta (42) protofibrils by astrocytes results in the release of EVs containing neurotoxic A beta. Here, we describe the cellular mechanisms behind EV-associated neurotoxicity in detail. EVs were isolated from untreated and A beta (42) protofibril exposed neuroglial co-cultures, consisting mainly of astrocytes. The EVs were added to cortical neurons for 2 or 4 days and the neurodegenerative processes were followed with immunocytochemistry, time-lapse imaging and transmission electron microscopy (TEM). Addition of EVs from A beta (42) protofibril exposed co-cultures resulted in synaptic loss, severe mitochondrial impairment and apoptosis. TEM analysis demonstrated that the EVs induced axonal swelling and vacuolization of the neuronal cell bodies. Interestingly, EV exposed neurons also displayed pathological lamellar bodies of cholesterol deposits in lysosomal compartments. Taken together, our data show that the secretion of EVs from A beta exposed cells induces neuronal dysfunction in several ways, indicating a central role for EVs in the progression of A beta -induced pathology

Increased Release of Apolipoprotein E in Extracellular Vesicles Following Amyloid-β Protofibril Exposure of Neuroglial Co-Cultures

Extracellular vesicles (EVs), including exosomes and larger microvesicles, have been implicated to play a role in several conditions, including Alzheimer's disease (AD). Since the EV content mirrors the intracellular environment, it could contribute with important information about ongoing pathological processes and may be a useful source for biomarkers, reflecting the disease progression. The aim of the present study was to analyze the protein content of EVs specifically released from a mixed co-culture of primary astrocytes, neurons, and oligodendrocytes treated with synthetic amyloid-beta (A beta(42)) protofibrils. The EV isolation was performed by ultracentrifugation and validated by transmission electron microscopy. Mass spectrometry analysis of the EV content revealed a total of 807 unique proteins, of which five displayed altered levels in A beta(42) protofibril exposed cultures. The most prominent protein was apolipoprotein E (apoE), and by western blot analysis we could confirm a threefold increase of apoE in EVs from A beta(42) protofibril exposed cells, compared to unexposed cells. Moreover, immunoprecipitation studies demonstrated that apoE was primarily situated inside the EVs, whereas immunocytochemistry indicated that the EVs most likely derived from the astrocytes and the neurons in the culture. The identified A beta-induced sorting of apoE into EVs from cultured neuroglial cells suggests a possible role for intercellular transfer of apoE in AD pathology and encourage future studies to fully elucidate the clinical relevance of this event

Accumulation of amyloid-beta by astrocytes result in enlarged endosomes and microvesicle-induced apoptosis of neurons

Background: Despite the clear physical association between activated astrocytes and amyloid-beta (A beta) plaques, the importance of astrocytes and their therapeutic potential in Alzheimer's disease remain elusive. Soluble A beta aggregates, such as protofibrils, have been suggested to be responsible for the widespread neuronal cell death in Alzheimer's disease, but the mechanisms behind this remain unclear. Moreover, ineffective degradation is of great interest when it comes to the development and progression of neurodegeneration. Based on our previous results that astrocytes are extremely slow in degrading phagocytosed material, we hypothesized that astrocytes may be an important player in these processes. Hence, the aim of this study was to clarify the role of astrocytes in clearance, spreading and neuronal toxicity of A beta. Results: To examine the role of astrocytes in A beta pathology, we added A beta protofibrils to a co-culture system of primary neurons and glia. Our data demonstrates that astrocytes rapidly engulf large amounts of A beta protofibrils, but then store, rather than degrade the ingested material. The incomplete digestion results in a high intracellular load of toxic, partly N-terminally truncated A beta and severe lysosomal dysfunction. Moreover, secretion of microvesicles containing N-terminally truncated A beta, induce apoptosis of cortical neurons. Conclusions: Taken together, our results suggest that astrocytes play a central role in the progression of Alzheimer's disease, by accumulating and spreading toxic A beta species

The A beta protofibril selective antibody mAb158 prevents accumulation of A beta in astrocytes and rescues neurons from A beta-induced cell death

Background: Currently, several amyloid beta (A beta) antibodies, including the protofibril selective antibody BAN2401, are in clinical trials. The murine version of BAN2401, mAb158, has previously been shown to lower the levels of pathogenic A beta and prevent A beta deposition in animal models of Alzheimer's disease (AD). However, the cellular mechanisms of the antibody's action remain unknown. We have recently shown that astrocytes effectively engulf A beta(42) protofibrils, but store rather than degrade the ingested A beta aggregates. In a co-culture set-up, the incomplete degradation of A beta(42) protofibrils by astrocytes results in increased neuronal cell death, due to the release of extracellular vesicles, containing N-truncated, neurotoxic A beta. Methods: The aim of the present study was to investigate if the accumulation of A beta in astrocytes can be affected by the A beta protofibril selective antibody mAb158. Co-cultures of astrocytes, neurons, and oligodendrocytes, derived from embryonic mouse cortex, were exposed to A beta(42) protofibrils in the presence or absence of mAb158. Results: Our results demonstrate that the presence of mAb158 almost abolished A beta accumulation in astrocytes. Consequently, mAb158 treatment rescued neurons from A beta-induced cell death. Conclusion: Based on these findings, we conclude that astrocytes may play a central mechanistic role in anti-A beta immunotherapy

Continuous DOPA synthesis from a single AAV: dosing and efficacy in models of Parkinson's disease.

We used a single adeno-associated viral (AAV) vector co-expressing tyrosine hydroxylase (TH) and GTP cyclohydrolase 1 (GCH1) to investigate the relationship between vector dose, and the magnitude and rate of recovery in hemi-parkinsonian rats. Intrastriatal injections of >1E10 genomic copies (gc) of TH-GCH1 vector resulted in complete recovery in drug-naïve behavior tests. Lower vector dose gave partial to no functional improvement. Stereological quantification revealed no striatal NeuN+ cell loss in any of the groups, whereas a TH-GCH1 dose of >1E11 gc resulted in cell loss in globus pallidus. Thus, a TH-GCH1 dose of 1E10 gc gave complete recovery without causing neuronal loss. Safety and efficacy was also studied in non-human primates where the control vector resulted in co-expression of the transgenes in caudate-putamen. In the TH-GCH1 group, GCH1 expression was robust but TH was not detectable. Moreover, TH-GCH1 treatment did not result in functional improvement in non-human primates

Additional file 13: of Accumulation of amyloid-β by astrocytes result in enlarged endosomes and microvesicle-induced apoptosis of neurons

Aβ42 protofibril characterization. No considerable difference is noticed comparing serially diluted Aβ42 protofibrils and Aβ42-555 protofibrils with the Aβ protofibril selective mAb158 ELISA. (TIF 149 kb