Fig. 3.

Pre-existing plaques locally potentiate formation of new plaques. a BACE1 immunostainings 10 weeks after treatment initiation. The green line depicts the outer plaque border as defined by Methoxy-X04 fluorescence, and white lines indicate 5 µm spaced distance rings from the plaque border. Scale bar represents 10 μm. b Fraction of BACE1 immuno positive brain volume at varying distances to the closest plaque border. c Mean fraction of BACE1 immuno positive brain volume within 1 µm distance from plaque border for plaques of different radii (TWA: F_int[4] = 0.63, p = 0.643; F_treatment[1] = 0.01, p = 0.912; F_radius[4] = 5.90, p < 0.001). d In all parts of the imaged brain volume, the distance to the closest plaque was determined via 3D distance transformation. In this simplified illustrative image, the distance representation is demonstrated only for plaques positioned on one Z-layer. Black concentric rings indicate distance to closest plaque border with 10 µm interval. Red lines outline sectors of the image stack closest to one individual plaque. e Representative images of 3D rendered plaques before and 8 weeks after treatment. White plaques were already present at treatment start while colored plaques appeared during the treatment period. The colormap indicates the distance of each newly formed plaque to the closest border of a pre-existing plaque at the respective timepoint of formation. Since plaques are scattered in 3D over a depth of 200 µm, the inter-plaque-distance in these 2D representations occasionally seems smaller than inferred from the color code. Scale bar represents 50 µm. f Mean rate of plaque formation after treatment initiation at varying distances to already existing plaques (TWA: F_int[4] = 2.20, p = 0.089; F_treatment[1] = 8.17, p = 0.019; F_distance[4] = 6.17, p < 0.001). Data presented as mean ± SEM. b, c n = 5–6 mice (mean plaque number analyzed per mouse = 44). d–f n = 5–6 mice, (mean number of newly formed plaques analyzed per mouse = 15)