BACE1 blocking peptide

Background Synaptic degeneration and accumulation of amyloid beta-peptides (A beta) are hallmarks of the Alzheimer diseased brain. A beta is synaptotoxic and produced by sequential cleavage of the amyloid precursor protein (APP) by the beta-secretase BACE1 and by gamma-secretase. If APP is instead cleaved by the alpha-secretase ADAM10, A beta will not be generated. Although BACE1 is considered to be a presynaptic protein and ADAM10 has been reported to mainly localize to the postsynaptic density, we have previously shown that both ADAM10 and BACE1 are highly enriched in synaptic vesicles of rat brain and mouse primary hippocampal neurons. Results Here, using brightfield proximity ligation assay, we expanded our previous result in primary neurons and investigated the in situ synaptic localization of ADAM10 and BACE1 in rat and human adult brain using both pre- and postsynaptic markers. We found that ADAM10 and BACE1 were in close proximity with both the presynaptic marker synaptophysin and the postsynaptic marker PSD-95. The substrate APP was also detected both pre- and postsynaptically. Subcellular fractionation confirmed that ADAM10 and BACE1 are enriched to a similar degree in synaptic vesicles and as well as in the postsynaptic density. Conclusions We show that the alpha-secretase ADAM10 and the beta-secretase BACE1 are located in both the pre- and postsynaptic compartments in intact brain sections. These findings increase our understanding of the regulation of APP processing, thereby facilitating development of more specific treatment strategies.

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by abnormal deposition of ?-amyloid (A?) peptides. A? is a cleavage product of the amyloid precursor protein (APP), and aberrant posttranslational modifications of APP can alter APP processing and increase A? generation. In the AD brain, seven different residues, including Ser-675 (APP(695) numbering) in the APP cytoplasmic domain has been found to be phosphorylated. Here, we show that expression of a phosphomimetic variant of Ser-675 in APP (APP-S675E), in human neuroblastoma SK-N-AS cells, reduces secretion of the soluble APP ectodomain (sAPP?), even though the total plasma membrane level of APP was unchanged compared with APP levels in cells expressing APPwt or APP-S675A. Moreover, the level of an alternative larger C-terminal fragment (CTF) increased in the APP-S675E cells, whereas the CTF form that was most abundant in cells expressing APPwt or APP-S675A decreased in the APP-S675E cells. Upon siRNA-mediated knockdown of the astacin metalloprotease meprin ?, the levels of the alternative CTF decreased and the CTF ratio was restored back to APPwt levels. Our findings suggest that APP?Ser-675 phosphorylation alters the balance of APP processing, increasing meprin ??mediated and decreasing ?-secretase?mediated processing of APP at the plasma membrane. As meprin ? cleavage of APP has been shown to result in formation of highly aggregation-prone, truncated A?2?40/42 peptides, enhanced APP processing by this enzyme could contribute to AD pathology. We propose that it would be of interest to clarify in future studies how APP?Ser-675 phosphorylation promotes meprin ??mediated APP cleavage.