3D Microscopic profiling of pathological tau spreading in optically cleared brains

Abstract

Event Abstract Back to Event 3D Microscopic profiling of pathological tau spreading in optically cleared brains Jan R. Detrez1*, Hervé Maurin2, Kristof Van Kolen2, Roland Willems2, Julien Colombelli3, Benoit Lechat4, Bart Roucourt5, Fred Van Leuven4, Sarah Baatout6, Peter Larsen2, Rony Nuydens2, Jean-Pierre Timmermans1 and Winnok H. De Vos1 1 University of Antwerp, Belgium 2 Janssen Research & Development, Belgium 3 Institute for Research in Biomedicine, Spain 4 Laboratory for Experimental Mouse Genetics, Belgium 5 reMYND NV, Belgium 6 Belgian Nuclear Research Centre, Belgium Layman Abstract Converging evidence suggest that the progression of Alzheimer’s disease is characterized by the accumulation and spreading of pathological proteins throughout the brain. Investigating this 3D spreading process in mouse models is however limited to 2D tissue sections with conventional microscopic methods. We have developed an innovative approach that is able to render a mouse brain transparent, allowing us to capture this spreading process in intact mouse brains. We have used this technology to acquire a detailed description of the disease progression in 3 mouse models, and showed that we can inhibit the spreading process using therapeutic antibodies. Abstract Alzheimer’s disease (AD) is characterised by the progressive deposition of beta-amyloid plaques and hyperphosphorylated tau in the brain. Both tau, and to a lesser extent amyloid, oligomers progressively spread via defined patterns throughout the brain and are proposed to act as seeds for ensuing protein aggregation. However, transgenic mouse models for tauopathies show tau spreading patterns that do not resemble those observed in human patients. Moreover, previous histological examination was done based on brain sections, which is labour-intensive and complicates downstream procedures, such as brain atlas mapping. To study the development of tau pathology in a controlled manner, we inoculated pathogenic tau fibrils – either synthetically produced (K18) or isolated from AD patient brains (ePHF) - in the CA1 region of a tauopathy mouse model (Tau.P301L) and after set time points we monitored the distribution of hyperphosphorylated tau in toto using iDISCO+ clearing and light sheet microscopy [1]. While the pathological tau load in non-inoculated Tau.P301L mice only became detectable at 6 months of age, we found that inoculation of 3 months-old Tau-P301L mice with K18 fibrils significantly expedited tau pathology, with hyperphosphorylated tau-positive neurons emerging as early as 7 days post injection (DPI), in both the ispi- and contralateral hemisphere. With a strong enrichment in the hippocampus, cortex and thalamus, the tauopathy pattern also vastly differed from that of the non-inoculated counterparts, where hyperphosphorylated tau predominantly accumulated in the brainstem. The K18-inoculation induced spreading pattern followed anatomical connections that directly emanated from the injection site, feeding the theory of cellular transmission through anatomically connected networks. Inoculation with ePHF resulted in a slower progression, with negligible somatic tau pathology at 28 DPI, but a pronounced hyperphosphorylated tau load at 84 DPI that spatially resembled the K18 inoculation pattern. We further demonstrate that tau pathology can be lowered after intracranial and systemic administration of a microtubule-binding domain targeted antibody in combination with K18 seeding. The combination of targeted seeding and in toto staging of hyperphosphorylated tau offers a unique approach to assess regional vulnerability and connectivity. This in turn will contribute to a better understanding of pathological progression and will allow evaluating the potential of therapeutic interventions aimed at halting or reversing the spreading process. Figure 1: In toto Imaging of hyperphosphorylated tau in P301L mice after K18 inoculation. A. Workflow for microscopic interrogation of hyperphospho-rylated tau in intact mouse brain. B. 3D rendering of AT8 pathology in K18-injected Tau.P301L mouse brains over time. C. Heatmap plots are used to visualise the AT8 load in brain subregions over time. P-Values within the tiles indicate significant increases compared to buffer-injected controls. Figure 1