Effects of huperzine A on amyloid precursor protein processing and beta-amyloid generation in human embryonic kidney 293 APP Swedish mutant cells.

The amyloid precursor protein (APP) is cleaved enzymatically by nonamyloidogenic and amyloidogenic pathways. alpha-Secretase (alpha-secretase), cleaves APP within the beta-amyloid (A beta) sequence, resulting in the release of a secreted fragment of APP (alpha APPs) and precluding A beta generation. In this study, we investigated the effects of an acetylcholinesterase inhibitor, huperzine A (Hup A), on APP processing and A beta generation in human embryonic kidney 293 cells transfected with human APP bearing the Swedish mutation (HEK293 APPsw). Hup A dose dependently (0-10 mu M) increased alpha APPs release and membrane-coupled APP CTF-C83, suggesting increased APP metabolism toward the nonamyloidogenic alpha-secretase pathway. The metalloprotease inhibitor TAPI-2 inhibited the Hup A-induced increase in alpha APPs release, further suggesting a modulatory effect of Hup A on alpha-secretase activity. The synthesis of full-length APP and cell viability were unchanged after Hup A incubation, whereas the level of A beta(Total) was significantly decreased, suggesting an inhibitory effect of Hup A on A beta production. Hup A-induced alpha APPs release was significantly reduced by the protein kinase C (PKC) inhibitors GF109203X and Calphostin C. These data, together with the finding that the PKC alpha level was enhanced prior to the increase of alpha APPs secretion, indicate that PKC may be involved in Hup A-induced alpha APPs secretion by HEK293 APPsw cells. Our data suggest alternative pharmacological mechanisms of Hup A relevant to the treatment of Alzheimer's disease. (c) 2006 Wiley-Liss, Inc.