Involvement of beta-site APP cleaving enzyme 1 (BACE1) in amyloid precursor protein-mediated enhancement of memory and activity-dependent synaptic plasticity.

The amyloid precursor protein (APP) undergoes sequential cleavages to generate various polypeptides, including the amyloid-beta protein (Abeta), which forms amyloid plaques in Alzheimer's disease (AD), secreted APPalpha (sAPPalpha) which enhances memory, and the APP intracellular domain (AICD), which has been implicated in the regulation of gene transcription and calcium signaling. The beta-site APP cleaving enzyme 1 (BACE1) cleaves APP in an activity-dependent manner to form Abeta, AICD, and secreted APPbeta. Because this neural activity was shown to diminish synaptic transmission in vitro [Kamenetz F, Tomita T, Hsieh H, Seabrook G, Borchelt D, Iwatsubo T, Sisodia S, Malinow R (2003) Neuron 37:925-937], the prevailing notion has been that this pathway diminishes synaptic function. Here we investigated the role of this pathway in vivo. We studied transgenic mice overproducing APP that do not develop AD pathology or memory deficits but instead exhibit enhanced spatial memory. We showed enhanced synaptic plasticity in the hippocampus that depends on prior synaptic activity. We found that the enhanced memory and synaptic plasticity are abolished by the ablation of one or both copies of the BACE1 gene, leading to a significant decrease in AICD but not of any other APP cleavage products. In contrast to the previously described negative effect of BACE1-mediated cleavage of APP on synaptic function in vitro, our in vivo work indicates that BACE1-mediated cleavage of APP can facilitate learning, memory, and synaptic plasticity.