Three-dimensional and fractal analyses of assemblies of amyloid β protein subtypes [Aβ40 and Aβ42(43)] in canine senile plaques

The three-dimensional (3D) distribution of amyloid β protein (Aβ) subtypes [Aβ40 and Aβ42(43)] in canine senile plaques (SP) was observed using a confocal laser scanning microscope. In diffuse plaques (DP), Aβ42(43) alone was deposited as an uneven nebula-like assembly of fine granules. The border of the Aβ42(43) assembly was unclear and diffusely merged to the surrounding area. Mature plaques (MP), on the other hand, showed two patterns of Aβ deposition. In some MP, only Aβ40 was deposited as a defined assembly of very short fibrillary structures. Other MP consisted of both Aβ40 and Aβ42(43), and the deposition patterns of the two Aβ species were the same as those in single-positive plaques; fine granular with unclear margin for Aβ42(43), and short fibrillary structures for Aβ40. Additionally, we calculated the fractal dimensions (FD) of both Aβ40 and Aβ42(43) assemblies, and examined the serial change of FD in each SP. The FD of Aβ42(43)-positive DP ranged from 1.05 to 1.27, and those of Aβ40-positive MP ranged from 1.13 to 1.54 in single-positive plaques. In one double-positive MP, FD ranged from 1.02 to 1.36 for Aβ42(43) and from 1.01 to 1.51 for Aβ40. These results showed that the FD of canine Aβ40 assemblies was higher than that of Aβ42(43) assemblies, and the spatial changes of FD values for Aβ40 and Aβ42(43) in double-positive plaques were quite different. These morphological analyses clearly showed that canine DP and MP have completely different 3D structures, suggesting that their processes of formation are different.