Nicotine Promotes AβPP Nonamyloidogenic Processing via RACK1-Dependent Activation of PKC in SH-SY5Y-AβPP695 Cells.

Background: Accumulation of amyloid-beta (A beta) peptides, generated from amyloid-beta precursor protein (A beta PP) amyloidogenic processing, is one of the most salient disease hallmarks of Alzheimer's disease (AD). Nicotine is able to promote alpha-secretase-mediated A beta PP nonamyloidogenic processing and increase the release of sA beta PP alpha and C-terminal fragment of 83 amino acids (C83). However, the potential molecular mechanism remains elusive. Objective: The aim of the present study was to investigate the effect of nicotine on A beta PP processing in SH-SY5Y cells that stably express human Swedish mutant A beta PP695 (SH-SY5Y-A beta PP695). Methods: The expression of A beta PP and its C-terminal fragments including C99, C89, and C83, was measured in SH-SY5YA beta PP695 cells treated with nicotine for 6 h. Protein kinase C (PKC) antagonist Ro30-8220 or agonist PMA was used to determine the role of PKC in A beta PP processing. Lentivirus-mediated shRNA targeting receptor for activated C-kinase 1 (RACK1) gene was added into the media to knockdown RACK1 expression, and then A beta PP processing was examined. Results: The results showed that 6 h of nicotine exposure increased the expression of alpha-secretase (ADAM10) and C83 in a dose dependent manner. While the beta-secretase (BACE1), A beta PP amyloidogenic processing products C89 and C99 as well as A beta peptides (including A beta(40) and A beta(42)) remained unchanged. We also found that nicotine elevated the expression of phosphorylated PKC (P-PKC) and RACK1 on the cytomembrane. PKC antagonist Ro30-8220 treatment prevented the increase of ADAM10 and C83 by nicotine. Genetic knockdown RACK1 significantly inhibited P-PKC, and consequently abolished the increase of ADAM10 and C83 by nicotine. Conclusion: Taken together, these results indicate that nicotine effectively promotes A beta PP nonamyloidogenic processing via RACK1-dependent activation of PKC in SH-SY5Y-A beta PP695 cells and could be a potential molecule for AD treatment.