Interplay between ?-, ?-, and ?-secretases determines biphasic amyloid-? protein level in the presence of a ?-secretase inhibitor.

ABSTRACT: Amyloid-? (A?) is produced by the consecutive cleavage of amyloid precursor protein (APP) first by ?-secretase, generating C99, and then by ?-secretase. APP is also cleaved by ?-secretase. It is hypothesized that reducing the production of A? in the brain may slow the progression of Alzheimer disease. Therefore, different ?-secretase inhibitors have been developed to reduce A? production. Paradoxically, it has been shown that low to moderate inhibitor concentrations cause a rise in A? production in different cell lines, in different animal models, and also in humans. A mechanistic understanding of the A? rise remains elusive. Here, a minimal mathematical model has been developed that quantitatively describes the A? dynamics in cell lines that exhibit the rise as well as in cell lines that do not. The model includes steps of APP processing through both the so-called amyloidogenic pathway and the so-called non-amyloidogenic pathway. It is shown that the cross-talk between these two pathways accounts for the increase in A? production in response to inhibitor, i.e. an increase in C99 will inhibit the non-amyloidogenic pathway, redirecting APP to be cleaved by ?-secretase, leading to an additional increase in C99 that overcomes the loss in ?-secretase activity. With a minor extension, the model also describes plasma A? profiles observed in humans upon dosing with a ?-secretase inhibitor. In conclusion, this mechanistic model rationalizes a series of experimental results that spans from in vitro to in vivo and to humans. This has important implications for the development of drugs targeting A? production in Alzheimer disease.

SUBMITTER: Ortega F 

PROVIDER: S-EPMC3543028 | biostudies-literature | 2013 Jan

REPOSITORIES: biostudies-literature