Development of whole brain organotypic slice culture to investigate in vitro seeding of amyloid plaques
Ireland2017 Adult male J20 seizure.MTS (58.71Mb)
Ireland, Kirsty Anne
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A feature of prion disease and other protein misfolding neurodegenerative disease is the formation of amyloid plaques. Amyloid is commonly found in the brain of individuals who have died from prion disease and Alzheimer’s disease. The formation and purpose of amyloid in such diseases is poorly understood and it is not currently known whether the material is neurotoxic, neuroprotective or an artefact. Several methods are used to investigate the formation of amyloid both in vitro and in vivo. A cell free protein conversion assay has been optimised to gain insight into the protein misfolding pathway and prion infection has been introduced to a newly characterised whole brain organotypic slice culture model. Fibrillar, but not oligomeric, recombinant PrP species induce a seeding effect on amyloid formation in the protein conversion assay. Brain homogenate containing amyloid from a β-amyloid aggregation mouse model is demonstrated to have a similar effect to recombinant fibril seeds with a PrP substrate indicating a cross-seeding effect. A whole brain organotypic slice culture (BOSC) model has been developed and slices maintained in culture for up to 8 months. During this time slices remain viable with low levels of stress and thin down from 400μm to 30-50μm with morphological consequences. A prominent glial scar forms on the surface of the slice as a result of astrocyte activation and proliferation. The neuronal population decreases while the microglia have a consistent presence throughout time in culture. Replication of misfolded prion protein has been successfully demonstrated within whole BOSC following prion infection after 2 months in culture. The BOSC model represents an accessible short term in vitro model of the brain which can offer insights into protein misfolding in a complex multicellular context. Amyloid formation has been investigated in vivo using a β-amyloid misfolding mouse model following seeding with a range of recombinant protein and brain homogenate seeds. No seeding effect was observed in animals which had received intracerebral inoculations compared to control animals within the time frame of the experiment. A lack of overall amyloid within all animals at the final time point investigated suggests later time points are required for observation of seeding. The functional role of amyloid in protein misfolding neurodegenerative diseases remains unclear. From the cell free protein conversion assay oligomers do not form on the direct pathway towards amyloid in prion misfolding. BOSC provide an accessible and useful short term in vitro model which retains multiple characteristics of the brain. BOSC support replication of misfolded protein and amyloid formation therefore this model can now be utilised to investigate plaque growth and the effect of amyloid formation on surrounding cells. Results from these assays provide important information to guide future in vivo studies and aid the search for therapeutic intervention in these devastating diseases.