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Astrocytes in Alzheimer’s disease: Exploring the impact of amyloid-β pathology on neurotoxicity, metabolism and inflammation.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Public Health and Caring Sciences. (Molecular geriatrics)ORCID iD: 0000-0002-5817-9547
2024 (English)Doctoral thesis, comprehensive summary (Other academic)
Description
Abstract [en]

Astrocytes play a central role in brain homeostasis, but are also tightly connected to the pathogenesis of Alzheimer’s disease (AD). Yet, their exact role in amyloid-beta (Aβ) pathology and chronic neuroinflammation is unclear. The aim of this thesis was to elucidate the impact of astrocytes in AD progression. For this purpose, astrocytes in different culture set-ups were exposed to soluble Aβ aggregates. The astrocytes engulf and process, but fail to fully degrade the Aβ aggregates, which are instead stored as large intracellular deposits. In Paper I, we show that extracellular vesicles (EVs), secreted from the Aβ-containing cells induce synaptic loss, axonal swelling and vacuolization of primary neurons, which consequently leads to apoptosis. 

Astrocytes play a central role in the brain’s energy metabolism and we were therefore interested in how Aβ pathology affects their metabolism. In Paper II, we report that Aβ accumulation in astrocytes disrupts mitochondrial fission/fusion homeostasis, resulting in decreased mitochondrial respiration and altered glycolysis. Interestingly, the astrocytes switch to fatty acid β oxidation with the aid of peroxisomes to maintain stable energy production. 

Another important task is to understand how astrocytes modify the ingested Aβ.  In Paper III, we characterized the astrocytic Aβ inclusions by isolating them with magnetic beads. Our analysis showed that the astrocytes truncate and pack together the Aβ aggregates. Moreover, we found that astrocytes release specifically truncated forms of Aβ via different routes.

Astrocytes’ involvement in lipid metabolism and inflammation has recently gained much interest, but many questions remain about the connection between these processes. In Paper IV, we show that Aβ pathology causes lipid droplet (LD) accumulation in astrocytes. Moreover, we could show that astrocytes frequently transfer LDs to neighboring cells, both through direct cell-to-cell contacts and via secretion. Astrocytes have previously been reported to express major histocompatibility complex II (MHCII) and have the capacity to perform as professional antigen presenting cells. Interestingly, our results demonstrate that LDs contain MHCII, identifying a link between LDs and inflammation in astrocytes.

Taken together, this thesis contributes with important knowledge of the role of astrocytes in AD pathology. 

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2024. , p. 66
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 2041
Keywords [en]
Alzheimer’s disease, astrocytes, amyloid-beta, extracellular vesicles, mitochondria, lipid droplets, lipid metabolism, inflammation
National Category
Neurosciences
Research subject
Molecular Medicine
Identifiers
URN: urn:nbn:se:uu:diva-525110ISBN: 978-91-513-2089-2 (print)OAI: oai:DiVA.org:uu-525110DiVA, id: diva2:1847161
Public defence
2024-05-17, Rudbecksalen, Rudbeck Laboratory, Dag Hammarskjölds Väg 20, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2024-04-25 Created: 2024-03-26 Last updated: 2024-04-25
List of papers
1. Extracellular vesicles from amyloid-beta exposed cell cultures induce severe dysfunction in cortical neurons
Open this publication in new window or tab >>Extracellular vesicles from amyloid-beta exposed cell cultures induce severe dysfunction in cortical neurons
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2020 (English)In: Scientific Reports, E-ISSN 2045-2322, Vol. 10, article id 19656Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
NATURE RESEARCH, 2020
National Category
Neurosciences
Identifiers
urn:nbn:se:uu:diva-428933 (URN)10.1038/s41598-020-72355-2 (DOI)000595255700049 ()33184307 (PubMedID)
Funder
Swedish Research CouncilThe Swedish Brain FoundationGun och Bertil Stohnes StiftelseStiftelsen Gamla Tjänarinnor
Available from: 2020-12-18 Created: 2020-12-18 Last updated: 2024-03-26Bibliographically approved
2. Amyloid-beta accumulation in human astrocytes induces mitochondrial disruption and changed energy metabolism
Open this publication in new window or tab >>Amyloid-beta accumulation in human astrocytes induces mitochondrial disruption and changed energy metabolism
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2023 (English)In: Journal of Neuroinflammation, ISSN 1742-2094, E-ISSN 1742-2094, Vol. 20, article id 43Article in journal (Refereed) Published
Abstract [en]

Background: Astrocytes play a central role in maintaining brain energy metabolism, but are also tightly connected to the pathogenesis of Alzheimer's disease (AD). Our previous studies demonstrate that inflammatory astrocytes accumulate large amounts of aggregated amyloid-beta (A beta). However, in which way these A beta deposits influence their energy production remain unclear.

Methods: The aim of the present study was to investigate how A beta pathology in astrocytes affects their mitochondria functionality and overall energy metabolism. For this purpose, human induced pluripotent cell (hiPSC)-derived astrocytes were exposed to sonicated A beta(42) fibrils for 7 days and analyzed over time using different experimental approaches.

Results: Our results show that to maintain stable energy production, the astrocytes initially increased their mitochondrial fusion, but eventually the A beta-mediated stress led to abnormal mitochondrial swelling and excessive fission. Moreover, we detected increased levels of phosphorylated DRP-1 in the A beta-exposed astrocytes, which co-localized with lipid droplets. Analysis of ATP levels, when blocking certain stages of the energy pathways, indicated a metabolic shift to peroxisomal-based fatty acid beta-oxidation and glycolysis.

Conclusions: Taken together, our data conclude that A beta pathology profoundly affects human astrocytes and changes their entire energy metabolism, which could result in disturbed brain homeostasis and aggravated disease progression.

Place, publisher, year, edition, pages
BioMed Central (BMC), 2023
Keywords
Alzheimer's disease, Glia, Lipid droplets, Mitochondria dynamics, DRP-1
National Category
Neurology Cell Biology
Identifiers
urn:nbn:se:uu:diva-498551 (URN)10.1186/s12974-023-02722-z (DOI)000935963900001 ()36803838 (PubMedID)
Funder
Swedish Research Council, 2021-02563Uppsala UniversityAlzheimerfonden, AF-968209Åhlén-stiftelsen, 213021The Swedish Brain Foundation, FO2021-0174Stiftelsen Gamla Tjänarinnor, 2021-01171O.E. och Edla Johanssons vetenskapliga stiftelseOlle Engkvists stiftelse, 215-0399Bertil and Ebon Norlin Foundation for Medical ResearchGun och Bertil Stohnes Stiftelse
Note

De två första författarna delar förstaförfattarskapet.

Available from: 2023-03-17 Created: 2023-03-17 Last updated: 2024-03-26Bibliographically approved
3. Amyloid-β deposits in human astrocytes contain truncated and highly resistant proteoforms
Open this publication in new window or tab >>Amyloid-β deposits in human astrocytes contain truncated and highly resistant proteoforms
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2024 (English)In: Molecular and Cellular Neuroscience, ISSN 1044-7431, E-ISSN 1095-9327, Vol. 128, article id 103916Article in journal (Refereed) Published
Abstract [en]

Alzheimer's disease (AD) is a neurodegenerative disorder that develops over decades. Glial cells, including astrocytes are tightly connected to the AD pathogenesis, but their impact on disease progression is still unclear. Our previous data show that astrocytes take up large amounts of aggregated amyloid-beta (Aβ) but are unable to successfully degrade the material, which is instead stored intracellularly. The aim of the present study was to analyze the astrocytic Aβ deposits composition in detail in order to understand their role in AD propagation. For this purpose, human induced pluripotent cell (hiPSC)-derived astrocytes were exposed to sonicated Aβ42 fibrils and magnetic beads. Live cell imaging and immunocytochemistry confirmed that the ingested Aβ aggregates and beads were transported to the same lysosomal compartments in the perinuclear region, which allowed us to successfully isolate the Aβ deposits from the astrocytes. Using a battery of experimental techniques, including mass spectrometry, western blot, ELISA and electron microscopy we demonstrate that human astrocytes truncate and pack the Aβ aggregates in a way that makes them highly resistant. Moreover, the astrocytes release specifically truncated forms of Aβ via different routes and thereby expose neighboring cells to pathogenic proteins. Taken together, our study establishes a role for astrocytes in mediating Aβ pathology, which could be of relevance for identifying novel treatment targets for AD.

Place, publisher, year, edition, pages
Elsevier, 2024
Keywords
Alzheimer's disease, Amyloid β, Astrocytes, Aggregate
National Category
Other Medical Sciences not elsewhere specified Other Biological Topics Neurosciences
Identifiers
urn:nbn:se:uu:diva-525108 (URN)10.1016/j.mcn.2024.103916 (DOI)001175074700001 ()
Funder
Uppsala UniversitySwedish Research Council, 2021-02563Alzheimerfonden, AF-980656Åhlén-stiftelsen, 223037The Swedish Brain Foundation, FO2022-0083Stiftelsen Gamla Tjänarinnor, 2021-01171O.E. och Edla Johanssons vetenskapliga stiftelseOlle Engkvists stiftelse, 215-0399Bertil and Ebon Norlin Foundation for Medical ResearchGun och Bertil Stohnes Stiftelse
Available from: 2024-03-15 Created: 2024-03-15 Last updated: 2024-04-09Bibliographically approved
4. Astrocytes with Alzheimer’s disease pathology provoke lipid droplet mediated cell-to-cell propagation of MHC II complexes
Open this publication in new window or tab >>Astrocytes with Alzheimer’s disease pathology provoke lipid droplet mediated cell-to-cell propagation of MHC II complexes
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Background. Astrocytes are critical for maintaining brain homeostasis, but are also highly involved in neuroinflammation. In the Alzheimer disease (AD) brain, reactive, inflammatory astrocytes are situated closely around amyloid β (Aβ) plaques. We have previously shown that reactive astrocytes ingest large quantities of soluble Aβ aggregates, but are unable to degrade the material, which leads to intracellular Aβ accumulation and severe cellular stress. A common response to cellular stress is the formation of lipid droplets (LDs). Novel data indicate that LDs play an important role in inflammatory processes. However, the involvement of LDs in AD inflammation and progression remains unclear.

Methods. The aim of this study was to investigate how astrocytic Aβ pathology affects lipid metabolism and antigen presentation. For this purpose, human induced pluripotent stem cell (iPSC) derived astrocytes were exposed to soluble Aβ42 aggregates and analyzed over time, using a battery of experimental approaches.

Results. Our results show that Aβ exposure induces LD accumulation in astrocytes, although the overall lipid composition remains unchanged. Moreover, astrocytes transfer LDs to neighboring cells via tunneling nanotubes (TNTs) and extracellular vesicle (EVs). Interestingly, we found that the antigen presenting protein major histocompatibility complex II (MHCII) is present inside LDs, suggesting an active role of LDs in astrocytic antigen presentation. Immunohistochemical analysis of human brain tissue verified the presence of LD-loaded MHCII+ astrocytes in AD individuals. Moreover, we found infiltrated CD4+ T cells to be in close contact with astrocytes, confirming an astrocyte T cell cross-talk in the AD brain

Conclusions. Taken together, our data show that Aβ pathology drastically affects lipid storage in astrocytes, which in turn modulates the astrocytic antigen presentation, indicating a role for astrocytic LDs in T cell responses in the AD brain.

Keywords
Alzheimer’s disease, Aβ, astrocytes, lipid droplets, inflammation, MHCII, T cells
National Category
Neurosciences
Research subject
Molecular Medicine
Identifiers
urn:nbn:se:uu:diva-525161 (URN)
Available from: 2024-03-26 Created: 2024-03-26 Last updated: 2024-03-26

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Beretta, Chiara

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