Construction of Drug Screening Cell Model and Application to New Compounds Interfering Production and Accumulation of Beta-Amyloid by Inhibiting Gamma-Secretase

Alzheimer’s disease (AD) is a tenacious neurodegenerative dementia, characterized clinically by progressive loss of memory, cognitive dysfunction, and behavioral abnormalities, accompanied by the accumulation of intracellular neurofibrillary tangles (NFTs), neuropil threads, as well as extracellular amyloid-beta containing senile plaques, cerebrovascular amyloid-beta deposits, and selective nerve cell and synapse loss (Kelliher et al, 1999; Tanzi, 1999; Solertea et al, 2000). The last two decades have witnessed an expanding body of research that elucidated the central role of amyloid precursor protein (APP) processing and amyloid beta (Abeta) production in the risk, onset, and progression of AD (Findeis, 2007). The accumulation of insoluble aggregates of Abeta peptide 1–42 (Abeta42) derived from APP is believed to play an important role in AD (Hardy, 1997; Kelliher et al, 1999). The generation of Abeta peptides requires two sequential proteolytical cleavages of APP by beta-secretase (BACE1) (Roßner et al, 2006) and gamma-secretase, composed of four integral membrane proteins, presenilins (PS1/2), APH-1 (anterior pharynx-defective 1), PEN-2 (presenilin enhancer 2) and nicastrin (NCT) (Kaether et al, 2006; Zhang & Koo, 2006). Previous evidence points to the involvement of the endoplasmic reticulum (ER) in AD pathogenesis owing to the fact that it is an important site for generating Abeta42 in neurons (Hartmann et al, 1998) and that presenilins are predominantly localized in this cellular compartment (Kovacs et al, 1996; Cook et al, 1996). Cleavage of the APP ectodomain by beta-secretase at the amino-terminus of Abeta is followed by cleavage of the beta-secretasegenerated carboxyl-terminal fragment (beta-CTF, C99) at the carboxyl terminus of Abeta  by gamma-secretase. A third activity, referred to as alpha-secretase, cleaves otherwise the APP ectodomain within the Abeta sequence, and subsequent cleavage of the alpha-secretasederived APP CTF (alpha-CTF, C83) by gamma-secretase results in production of P3