Ortega2013 - Interplay between secretases determines biphasic amyloid-beta level

Ortega2013 - Interplay between secretases
determines biphasic amyloid-beta level

This model is described in the article:

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

Ortega F, Stott J, Visser SA,
Bendtsen C.
J. Biol. Chem. 2013 Jan; 288(2):
785-792
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.

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