RESUMEN
Misfolding and aggregation of amyloid-ß (Aß) is an important early event in the pathogenesis of Alzheimer's disease. Aß is produced by sequential proteolysis of the amyloid-ß protein precursor (AßPP) by ß- and γ-secretases. A third protease, α-secretase, cleaves AßPP in the middle of the Aß sequence precluding formation of Aß. The levels of Aß generated from AßPP can therefore be controlled by tailoring activity of these proteases toward AßPP. We previously showed that ß-secretase proteolysis of AßPP could be selectively inhibited using the single chain antibody fragment (scFv) iBSEC1, which blocks the cleavage site on AßPP, and α-secretase proteolysis of AßPP could be selectively enhanced using a proteolytic scFv (Asec1A) engineered to have α-secretase-like activity. Here we show that DIA10D, a novel tandem bispecific scFv combining iBSEC1 with the ASec1A can control amyloidogenic processing of AßPP by simultaneously inhibiting ß-secretase and increasing α-secretase processing of AßPP. When expressed in H4 (neuroglioma) cells overexpressing AßPP, DIA10D potently reduces levels of extracellular Aß by around 50% while also increasing levels of neuroprotective sAßPPα. DIA10D activity has been designed to selectively target AßPP, so this modulation of AßPP processing should not affect endogenous activity of α-and ß-secretases towards other substrates.