Organotypic hippocampal slices as an ex-vivo model to study tauopathy and related microglial morphology Jasmeet Virdee1, Jessica Brown1, Jim McCarthy1, Suchira Bose1, Annalisa Cavallini1, Michael O'Neill1, Hugh Nuthall1 1Lilly Research Centre, Eli Lilly and Company, Surrey, UK
Organotypic hippocampal slice cultures (OHCs) are explants from hippocampal tissue that can be maintained in culture for several months, maintaining their synaptic connections and multicellular 3D architecture. They can be manipulated over time, permitting direct control of their environment and allowing access for various readouts, including imaging and biochemical assays. We have used this model to investigate the presence and propagation of aggregated tau.
OHCs prepared from P301S mice were inoculated with brain homogenate from terminally ill P301S mice and then examined for viability and the production and localization of insoluble phosphorylated tau. We observed high levels of tau aggregates in the CA1 region and, to a lesser extent in the CA3 region. The levels of tau aggregation correlated with the concentration of applied P301S seed and this accumulated over time in culture, shown via immunohistochemistry and biochemical quantification. Inoculation of slices with the P310S seed had no significant effects on slice viability visualized by a propidium iodide (PI) uptake assay. This model has now been used to test a number of compounds, including anti-tau antibodies for their ability to reduce tau pathology. Here we show that pre-incubation of P301S seed with anti-tau antibodies blocks tau aggregation in OHCs in a concentration-dependent manner, shown by a reduction of AT100 labelled tau inclusions.
OHCs provide an invaluable insight into the functional and morphological behavior of microglia in an intact system. Microglia at 14 days in vitro (DIV) display numerous fine processes and have a ramified appearance suggestive of a down-regulated resting state. Microglia post incubation with LPS for 24 hours exhibit features of an active state; spherical and macrophage-like. We see a heterogeneous morphology of microglia in those OHCs seeded with P301S seed and around visible tau aggregates. Notably, our preliminary data suggests a decrease in the number of microglia around tau inclusions, microglial quantity appearing inversely correlated with the concentration of P301S seed. We are further investigating the relationship between tau pathology and microglial quantity and morphology.