| 1. |
- Näsström, Thomas
(författare)
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Characterization of α-synuclein oligomers : Implications for Lewy Body Disorders
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Parkinson’s disease, dementia with Lewy bodies and multiple system atrophy are disorders featuring accumulation of Lewy bodies in brain. The main component of these large insoluble intracellular inclusions is the presynaptic protein alpha-synuclein (α-synuclein). It is generally believed that α-synuclein monomers adopt an abnormal conformation that favors the formation of soluble oligomers or protofibrils and, eventually, insoluble fibrils depositing as Lewy bodies. Notably, the intermediately sized oligomers/protofibrils seem to have particular neurotoxic effects. Several factors may influence the formation of α-synuclein oligomers/protofibrils, e.g. the reactive aldehydes 4-hydroxy-2-nonenal (HNE) and 4-oxo-2-nonenal (ONE) formed during oxidative stress. The overall aims of this thesis were to investigate biophysical and biochemical properties of in vitro generated α-synuclein oligomers, characterize their functional effects on cell and animal disease models as well as to explore whether their formation could be prevented in a cell culture model for oligomerization. Here, it was found that α-synuclein rapidly formed oligomers after incubation with both ONE and HNE. The resulting oligomers were stable and did not continue to form insoluble fibrils. By comparing HNE- and ONE induced α-synuclein oligomers biochemically they were both found to exhibit extensive β-beta sheet structure and had a molecular size of ~2000 kDa. However, they differed in morphology; the ONE induced α-synuclein oligomers described round amorphous species whereas the HNE induced α-synuclein oligomers appeared as elongated protofibril-like structures. Both these oligomers were cell internalized to varying degrees and induced toxicity in neuroblastoma cells. In addition, the ONE induced α-synuclein oligomers seemed to initiate aggregation of monomeric α-synuclein in vitro, but failed to do so in vivo. Finally, treatment of α-synuclein overexpressing cells with monoclonal antibodies specific for α-synuclein significantly reduced aggregation and lowered levels of the protein, suggesting increased turnover in these cells. To conclude, this thesis has characterized different oligomeric α-synuclein species, which may have properties similar to soluble species central to the pathogenesis of Parkinson’s disease and other disorders with α-synuclein pathology. For therapeutic strategies it is important to selectively target such harmful protein species and avoid interaction with other forms of α-synuclein, which may have vital physiological cellular functions.
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| 2. |
- Mothes, Tobias
(författare)
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A stargazer's guide to neurodegeneration : Astrocytes' role in the propagation of pathological proteins
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Alzheimer’s disease (AD) and Parkinson’s disease (PD) are characterized by brain accumulation of pathogenic protein aggregates. In the AD brain, amyloid-β (Aβ) and tau form plaques respective tangles, while in the PD brain α-synuclein (α-syn) form Lewy bodies and Lewy neurites. In addition, deposits of Aβ, tau and α-syn are frequently present in glial cells, including astrocytes. Historically, the focus was on neuronal dysfunction, leaving the involvement of glia largely understudied. The overall aim of this thesis was to investigate the role of glial cells in the disease progression, primarily focusing on astrocytes and the role they play in tau pathology.Paper I focuses on the crosstalk between astrocytes and microglia in respects to degradation of α-syn and Aβ fibrils. Our results show that mono-cultured microglia are more effective than astrocytes at degrading exogenously added fibrils. However, when cultured together, microglia and astrocytes work synergistically, leading to an overall increase in the degradation.In Paper II, we show that astrocytic tau inclusions are not benign, but in fact act as a reservoir for seeding competent tau species. The astrocytes engulf and process, but fail to fully degrade internalized material. Instead, seeding competent pathogenic tau spreads to nearby cells via secretion and tunneling nanotube mediated transfer. Furthermore, we show that tau and debris burdened astrocytes negatively affected the health of nearby neurons.In Paper III, we investigated the cellular effects following astrocytic engulfment of human brain-derived tau. Our results show that astrocytes internalize and accumulate both AD and control tau fibrils. However, fibrils from AD brains were more neurotoxic and induced a stronger immune response in astrocytes, compared to fibrils derived from control brains.In Paper IV, we studied the effects of APOE-genotype on astrocytic processing of tau by comparing astrocytes homozygous for APOEε2 and APOEε4. Our results showed that APOE2/2 astrocytes contained more and larger tau aggregates. Moreover, APOE 2/2 astrocytes excreted higher levels of pro-inflammatory cytokines, including IL-8, CCL2 and CXCL10 compared to APOE 4/4 astrocytes.Paper V aimed to establish a cortical organoid model for studies of AD and PD. Exposure to α-syn especially led to internalisation by the organoid cells and active spreading throughout the tissue.Our results demonstrate that astrocytes work closely with microglia to degrade internalised material. Furthermore, astrocytes actively contribute to neurodegeneration and disease propagation by affecting the health of neurons and by spreading seeding competent tau species.
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| 3. |
- Skoglund, Lena, 1980-
(författare)
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Molecular Mechanisms of Frontotemporal Lobar Degeneration
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this thesis was to identify genetic factors involved in frontotemporal lobar degeneration (FTLD), a neurodegenerative disorder clinically characterised by a progressive change in personality, behaviour and language. FTLD is a genetically complex disorder and a positive family history is found in up to 40% of the cases.In 10-20% of the familial cases the disease can be explained by mutations in the gene encoding the microtubule associated protein tau (MAPT). In the first study we describe the clinical and neuropathological features of a Finnish family with FTLD caused by a mutation in MAPT. We also provide evidence that the pathogenic mechanism of this mutation is through altered splicing of MAPT transcripts.Recently, mutations in the gene encoding progranulin (PGRN) were identified as a major cause of FTLD. In the second study we describe a Swedish family with FTLD caused by a frameshift mutation in PGRN. We provide a clinical and neuropathological description of the family, as well as evidence that the pathogenicity of this mutation is through nonsense-mediated decay of the mutant mRNA transcripts and PGRN haploinsufficiency.In the third study we describe a novel PGRN splice site mutation and a previously described PGRN frameshift mutation, found in a mutation screen of 51 FTLD patients. We describe the clinical and neuropathological characteristics of the mutation carriers and demonstrate that haploinsufficiency is the pathogenic mechanism of the two mutations.In the fourth study we investigate the prevalence of PGRN and MAPT gene dosage alterations in 39 patients with FTLD. No gene dosage alterations were identified, indicating that variations in copy number of the PGRN and MAPT genes are not a common cause of disease, at least not in this FTLD patient collection.
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| 4. |
- Blom, Elin, 1979-
(författare)
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Genetic Studies of Alzheimer's Disease
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Patients with Alzheimer's disease (AD) often have a family history of the disease, implicating genetics as a major risk factor. Three genes are currently known to cause familial early-onset AD (<65 years): the amyloid precursor protein (APP) and the presenilins (PSEN1 and PSEN2). For the much more common late-onset disease (>65 years), only the APOE gene has repeatedly been associated to AD, where the ε4 allele increases disease risk and decreases age at onset. As APOE ε4 only explains part of the total estimated disease risk, more genes are expected to contribute to AD.This thesis has focused on the study of genetic risk factors involved in AD. In the first study, we conducted a linkage analysis of six chromosomes previously implicated in AD in a collection of affected relative pairs from Sweden, the UK and the USA. An earlier described linkage peak on chromosome 10q21 could not be replicated in the current sample, while significant linkage was demonstrated to chromosome 19q13 where the APOE gene is located. The linkage to 19q13 was further analyzed in the second study, demonstrating no significant evidence of genes other than APOE contributing to this peak. In the third study, the prevalence of APP duplications, a recently reported cause of early-onset AD, was investigated. No APP duplications were identified in 141 Swedish and Finnish early-onset AD patients, implying that this is not a common disease mechanism in the Scandinavian population. In the fourth study, genes with altered mRNA levels in the brain of a transgenic AD mouse model (tgAPP-ArcSwe) were identified using microarray analysis. Differentially expressed genes were further analyzed in AD brain. Two genes from the Wnt signaling pathway, TCF7L2 and MYC, had significantly increased mRNA levels in both transgenic mice and in AD brains, implicating cell differentiation and possibly neurogenesis in AD.
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