Increase of brain Aβ peptides and secretase activity during normal aging in rodent and human

Age increases of brain amyloid plaques may be mediated by prior increase of soluble Aβ42. Here, we show that frontal cortex samples from brains of cognitively normal aging humans had progressively increased levels of soluble amyloid peptide Aβ40 throughout the lifespan. Aggregated amyloid fraction was subsequently obtained by formic acid, where Aβ42 showed increases only in humans over 90 years old when compared to those younger than 50. Similarly, aging wild-type mice without amyloid plaques had increases of both soluble Aβ40 and Aβ42, as previously shown in normal aging rats. Aging also alters secretase enzymes and processing of amyloid precursor protein (APP). Here, we isolate membrane domains known as lipid rafts, a site of APP cleavage. We found that lipid rafts isolated from mouse and human cerebral cortex showed age increases of β-secretase enzyme activity, while amyloidogenic secretase proteins levels BACE1 and PS1 decreased with age in mouse. Lipid rafts merit further study in aging and neurodegeneration.