Three-dimensional and fractal analyses of assemblies of amyloid beta protein subtypes [Abeta40 and Abeta42(43)] in canine senile plaques.

The three-dimensional (3D) distribution of amyloid beta protein (Abeta) subtypes [Abeta40 and Abeta42(43)] in canine senile plaques (SP) was observed using a confocal laser scanning microscope. In diffuse plaques (DP), Abeta42(43) alone was deposited as an uneven nebula-like assembly of fine granules. The border of the Abeta42(43) assembly was unclear and diffusely merged to the surrounding area. Mature plaques (MP), on the other hand, showed two patterns of Abeta deposition. In some MP, only Abeta40 was deposited as a defined assembly of very short fibrillary structures. Other MP consisted of both Abeta40 and Abeta42(43), and the deposition patterns of the two Abeta species were the same as those in single-positive plaques; fine granular with unclear margin for Abeta42(43), and short fibrillary structures for Abeta40. Additionally, we calculated the fractal dimensions (FD) of both Abeta40 and Abeta42(43) assemblies, and examined the serial change of FD in each SP. The FD of Abeta42(43)-positive DP ranged from 1.05 to 1.27, and those of Abeta40-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 Abeta42(43) and from 1.01 to 1.51 for Abeta40. These results showed that the FD of canine Abeta40 assemblies was higher than that of Abeta42(43) assemblies, and the spatial changes of FD values for Abeta40 and Abeta42(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.