Inhibition of glutaminyl cyclase prevents pGlu-Aβ formation after intracortical/hippocampal microinjection in vivo/in situ

Modified amyloid beta (A beta) peptides represent major constituents of the amyloid deposits in Alzheimer's disease and Down's syndrome. In particular, N-terminal pyroglutamate (pGlu) following truncation renders A beta more stable, increases hydrophobicity and the aggregation velocity. Recent evidence based on in vitro studies suggests that the cyclization of glutamic acid, leading to pGlu-A beta, is catalyzed by the enzyme glutaminyl cyclase (QC) following limited proteolysis of A beta at the N-terminus. Here, we studied the pGlu-formation by rat QC in vitro as well as after microinjection of A beta(1-40) and A beta(3-40) into the rat cortex in vivo/in situ with and without pharmacological QC inhibition. Significant pGlu-A beta formation was observed following injection of A beta(3-40) after 24 h, indicating a catalyzed process. The generation of pGlu-A beta from A beta(3-40) was significantly inhibited by intracortical microinjection of a QC inhibitor. The study provides first evidence that generation of pGlu-A beta is a QC-catalyzed process in vivo. The approach per se offers a strategy for a rapid evaluation of compounds targeting a reduction of pGlu formation at the N-terminus of amyloid peptides.