Senile plaques in Alzheimer’s disease arise from Aβ and Cathepsin D-enriched amyloidogenic mixtures out of intravascular hemolysis and Charcot-Bouchard aneurysm-related vascular degeneration

The mechanism governing senile plaque generation in Alzheimer’s disease (AD) remains intensively debated. We analyzed AD brain tissues with histochemistry, immunohistochemistry and fluorescence imaging. We found little co-expression between neural markers and plaque Aβ while abundant co-expression between blood or plasma markers such as HBA, HbA1C, Hemin, ApoE and plaque Aβ. The cores of dense-core plaques were structured with vascular proteins and glial processes at the periphery and blood metabolites in the center. Senile plaques additionally co-localized with a characteristic Hoechst-staining-independent blue autofluorescence, likely also derived from red blood cells. Aβ interacts with hemoglobin in an in vitro assay and also at single cell levels in red blood cells in vivo , showing as dots, stripes or diffusive patterns with its intensity correlated with coagulation, the elevation of calcium and blue autofluorescence. Interaction between Aβ and ApoE in the blood stream forms vascular amyloid plaques that restrict red blood cell passage. The interaction of Aβ and red blood cells associates with multiple blood and vascular defects besides CAA, including increased perivascular space, microaneurysm, intravascular hemolysis and vascular calcification. Senile plaque formation was intrinsically linked to vascular degeneration as shown by LRP1, ColIV and ACTA2 immunostaining. Aβ staining also overlapped with Cathepsin D expression in intravascular hemolysis, CAA, microaneurysm and senile plaques in AD brain tissues. Microaneurysms with chronic hemolysis were identified as important sites of amyloid formation besides CAA and intravascular hemolysis. In summary, our data suggested that senile plaques arise from Aβ and Cathepsin D-enriched amyloid mixtures out of intravascular hemolysis and Charcot-Bouchard aneurysm-related vascular degeneration. In addition, hemoglobin could be a primary physiological target of Aβ.