Repository logo
 

Investigation of the ABI3 protein in microglia and its association with Alzheimer’s disease in TgCRND8 mouse model


Change log

Authors

Ghaffari, Seyedeh Deniz 

Abstract

Recent genome wide-association studies (GWAS) have identified several disease-related genetic variants among Alzheimer’s disease (AD) patients. A cluster of these genes, including TREM2, PLCG2 and ABI3, are highly expressed in microglia and their exact function in these cells is poorly understood. Since microglial dysfunction is thought to play an important role in AD pathogenesis, this thesis was aimed at analysing the expression and cellular function of ABI3 in microglia within the context of AD pathology in the CRND8 transgenic mouse model. Initially, commercial ABI3 antibodies were tested for their specificity in detecting endogenous ABI3 protein, using ABI3 knock-out (KO) mice as the negative control. These studies showed a punctate-like ABI3 expression across the cytoplasm in microglia. The following in vitro studies then focused on ABI3 cellular localization and showed limited co-localization between ABI3 and filamentous actin in rat microglia. On the other hand, ABI3 was localized to the cellular regions with lower F-actin expression. The functional role of ABI3 in microglia was studied by performing migration and phagocytosis assays in microglia. A significant increase in migration was seen after knocking down ABI3 in BV2 cells and similar results were observed in ABI3 KO primary microglia. The consequences of ABI3 KO could also be seen in several aspects of amyloid-beta plaques properties since the number of the plaques as well as average plaque size were significantly lower in ABI3 KO x TgCRND8 mice. ABI3 KO microglia also showed significant changes in cell morphology and the expression levels of several actin cytoskeleton components. Furthermore, ABI3 immunoreactivity in microglia was significantly higher in TgCRND8 mouse brains compared to age-matched controls; especially in the microglia surrounding the amyloid-beta plaques. Finally, the consequences of ABI3 S209F mutation were investigated in transfected U2OS cells, purified ABI3 proteins and in S212F microglia by Western blotting, immunoprecipitation and immunofluorescence. Significant changes in ABI3 cellular expression pattern and posttranslational modifications, i.e., phosphorylation, were observed following S209F/S212F mutation in ABI3. The findings of this thesis highlight the ABI3 expression pattern in microglia, the significant changes in its expression during AD pathogenesis and the possible role of ABI3 in regulating microglial functions. These results will provide an insight into underlying mechanisms in which, ABI3 mutation may increase the risk of developing LOAD by altering microglial functions.

Description

Date

2021-02-27

Advisors

St George-Hyslop, Peter
Brown, Guy

Keywords

Alzheimer's Disease, Microglia, ABI3, actin cytoskeleton, cell migration, TgCRND8 mouse model

Qualification

Doctor of Philosophy (PhD)

Awarding Institution

University of Cambridge