FRET-Based Calcium Imaging

Perturbed intracellular store calcium homeostasis is suggested to play a major role in the pathophysiology of Alzheimer disease (AD). A number of mechanisms have been suggested to underlie the impairment of endoplasmic reticulum calcium homeostasis associated with familial AD-linked presenilin 1 mutations (FAD-PS1). Without aiming at specifically targeting any of those pathophysiological mechanisms in particular, we rather performed a high-throughput phenotypic screen to identify compounds that can reverse the exaggerated agonist-evoked endoplasmic reticulum calcium release phenotype in HEK293 cells expressing FAD-PS1. For that purpose, we developed a fully automated high-throughput calcium imaging assay using a fluorescence resonance energy transfer–based calcium indicator at single-cell resolution. This novel robust assay offers a number of advantages compared with the conventional calcium measurement screening technologies. The assay was employed in a large-scale screen with a library of diverse compounds comprising 20,000 low-molecular-weight molecules, which resulted in the identification of 52 primary hits and 4 lead structures. In a secondary assay, several hits were found to alter the amyloid β (Aβ) production. In view of the recent failure of AD drug candidates identified by target-based approaches, such a phenotypic drug discovery paradigm may present an attractive alternative for the identification of novel AD therapeutics.