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Title: Evaluating the relationship between alpha-synuclein phosphorylation and amyloid-beta in Lewy body diseases
Author: Swirski, Marta Izabella Hope
ISNI:       0000 0004 5917 1066
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2015
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Introduction: Lewy body and Alzheimer-type pathologies often co-exist. Several studies suggest a synergistic relationship between amyloid-β (Aβ) and a-synuclein (α-syn) accumulation. This thesis describes a series of studies exploring the relationship between Aβ accumulation and the phosphorylation of α-syn at serine-129 (pSer129 α-syn) and at serine-87 (pSer87 α-synL in postmortem human brain tissue and in SH-SYSY neuroblastoma cells transfected to overexpress human α-syn. Methods: Formalin-fixed paraffin-embedded sections of cingulate and parahippocampal gyri from dementia with Lewy bodies (DLB), Parkinson's disease (PD) with dementia (PDD), Parkinson's disease without dementia (PDND) and control brains were immunolabelled for Aβ40, Aβ42, α-syn, pSer129 α-syn, and pSer87 α-syn. Levels of Aβ40, Aβ42, α-syn, and pSer129 α-syn, were also measured by sandwich ELlSA, in soluble and insoluble fractions of midfrontal, cingulate and para hippocampal cortex and thalamus, from cases of PDD, PDND, DLB and age-matched controls. The relationship of these measurements to cognitive decline was measured by time-to-dementia and the last available mini-mental state examination (MMSE) score in the PD patients with and without dementia, and to Braak tangle stage. Levels of α-syn, pSer129 α-syn and pSer87 α-syn were measured by sandwich ELlSA in SHSY-SY cells that had been stably transfected to over-express α-syn and were exposed to aggregated or soluble Aβ42 or Aβ40, at 1 or 10 μM. Results: Immunohistochemical data showed that Aβ42 and pSer129 α-syn antigen loads in the cingulate and parahippocampal cortex were higher in disease groups than controls, as measured by field fraction analysis. Significant positive correlations were observed between Aβ42 and pSer129 α-syn in both regions. In the cingulate cortex, the pSer87 α-syn field fraction was significantly lower in DLB than PDND, PDD or control brains. In the para hippocampal cortex, the pSer87 a-syn field fraction was significantly higher in PDD than PDND and DLB. Only in the midfrontal cortex was there a (positive) correlation between the pSer87 α-syn and Aβ42 field fractions. Data from sandwich ELlSAs showed that in most brain regions, the concentration of insoluble pSer129 α-syn correlated positively, and soluble pSer129 α-syn negatively, with the levels of soluble and insoluble Aβ. Insoluble pSer129 α-syn also correlated positively with Braak tangle stage. In most regions, the levels of insoluble and soluble Aβ and the proportion of insoluble α-syn that was phosphorylated at Ser129 were significantly higher in the PD and DLB groups than the controls, and higher in the PDD and DLB groups than the PDND brains. In PD, the MMSE score correlated negatively with the level of insoluble pSer129 α-syn. Exposure of SH-SYSY cells to aggregated Aβ42 significantly increased the proportion of α-syn that was phosphorylated at Ser129 (aggregated Aβ40 exposure had a smaller, non-significant effect). Exposure of cells to 10 μM soluble or aggregated Aβ42 increased the percentage of insoluble α-syn that was phosphorylated at Ser87 but was not affected by treatment with Aβ40. Conclusions: Together these data show that the concentration of pSer129 α-syn in brain tissue homogenates is directly related to the level of Aβ and the Braak tangle stage, and predicts cognitive status in Lewy body diseases. In vitro, in the presence of Aβ42, phosphorylation of α-syn is also induced at Ser87. Phosphorylation at this latter site may be an initial protective response to increased Aβ42 in the human brain but, if so, it seems that the protective response fails as disease progresses
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available