IMMUNOHISTOLOGICAL ANALYSIS OF AMYLOID-β OLIGOMER DEPOSITS IN APP KNOCK-IN MICE

Abstract

Growing evidences indicate that amyloid-β (Aβ) oligomer plays an important role in the pathophysiological process of Alzheimer's disease (AD). Recently, the knock-in AD model mouse (APPNL-F-G mouse) has been reported to show typical AD pathology1), with appearance of Aβ deposition at the age of 2 months, and its behavioral disorder started at 7 months of age. The aim of this study is to clarify the relationship over time between Aβ oligomer depositions and amyloid plaques in this model mouse. We examined paraffin embedded brain sections from 2-, 4-, 7- and 12-month-old APPNL-F-G mice. Aβ oligomer and Aβ were immunostained with Aβ oligomer specific antibody2), m6H4, and 6E10 respectively. We measured diameters of those amyloid depositions, and compared the differences of deposition patterns and diameters over time, and also these parameters between Aβ oligomer and Aβ. Immunoreactive depositions for those antibodies were detected in the mouse brains as following. At 2 months of age, there were a few small diffuse plaque-like depositions with having diameters of 10–20μm, and there was no difference in diameters between Aβ oligomer and Aβ. At 4 months of age, diameters of these plaques became significantly enlarged to 30–60μm, and m6H4-positive depositions were significantly wider in diameter than 6E10-positive depositions. At the same time, some 6E10-positive plaques had a very small core-like structure. At 7- and 12-month of age, numerous larger depositions were observed with diameters of 40–90μm. There was no difference in the diameters of depositions immunostained with each antibody. The plaque core became clearly stained with 6E10 antibody, but not with m6H4 antibody. The diameters tended to increase over time until 7 months of age in 6E10-positive depositions, and until 4months of age in m6H4-positive depositions (P<0.05). Comparing staining patterns of the depositions, 6E10-positive depositions were observed torus-like shapes with having relatively strongly immunoreactive cores, and m6H4-positive depositions existed inhomogeneous granular shapes. Aβ oligomer depositions possibly grow according to the increase of Aβ depositions, but its immunoreactivity was different from those of senile plaques.