Differential brain expression of the Alzheimer's amyloid precursor protein.

The expression of the Alzheimer amyloid protein precursor (AAPP) was examined in human, monkey, dog and rat brains. Two proteins, one identified as AAPP695 and the other as AAPP751, were immunoprecipitated from the in vitro translation of human, dog and rat brain polysomes. The AAPP751 to AAPP695 ratio was highest in human, intermediate in dog and lowest in rat brain polysomes. Human cerebral cortex contained higher levels of the AAPP751 mRNA than either dog or rat cortex. AAPP695 was detected in both cerebral cortex and cerebellum of all species examined. In contrast, AAPP751 was detected predominantly in the cortex of human, monkey and to a lesser extent dog brains while it was not detected in rat brain. These findings indicate that the amyloid precursors are differentially expressed in different mammalian brains and suggest that AAPP751 is mainly expressed in the brain regions involved in plaque formation.