Aβ-aggregation-generated blue autofluorescence illuminates senile plaques, complex blood and vascular pathologies in the Alzheimer’s disease

Senile plaque blue autofluorescence in the Alzheimer’s disease (AD) was discovered around 40 years ago, however, its impact on AD pathology is not fully examined. We analyzed senile plaques with immunohistochemistry and fluorescence imaging on AD brain pathological sections and also the Aβ aggregation process in vitro in test tubes. In DAPI or Hoechst staining experiments, the data showed that the nuclear blue fluorescence could only be correctly assigned after subtracting the blue autofluorescence background. The plaque cores have very strong blue autofluorescence which is roughly 2.09 times of average DAPI nuclear staining and roughly 1.78 times of average Hoechst nuclear staining. The composite flower-like structures formed by Cathepsin D lysosomal staining wrapping dense core blue fluorescence should not be considered as central-nucleated neurons filled with defective lysosomes since there was no nuclear staining in the plaque core when the blue autofluorescence was subtracted. Furthermore, the dense cores were shown to be completely lack of nuclear signals by PI staining. The Aβ aggregation assay indicated that both Aβ self-oligomers and Aβ/Hemoglobin (Hb) heterocomplexes had significant blue autofluorescence. However, the blue autofluorescence intensity was not always proportional to the intensity of Aβ immunostaining. The majority of aggregates in the Aβ/Hb incubations were sensitive to Proteinase K (PK) digestion while the rest were PK resistant. The blue autofluorescence of Aβ aggregates not only labels senile plaques but also illustrates red blood cell aggregation, hemolysis, CAA, vascular amyloid plaques, vascular adhesion and microaneurysm. In summary, we conclude that Aβ-aggregation-generated blue autofluorescence is an excellent amyloid pathology marker in the senile plaques, blood and vascular pathologies in the Alzheimer’s disease. ### Competing Interest Statement The authors have declared no competing interest.