Effects of sulindac sulfide on the membrane architecture and the activity of γ-secretase

γ-Secretase is a membrane-embedded multi-protein complex that catalyzes the final cut of the Alzheimer's disease-related amyloid precursor protein (APP) to amyloid-β peptides of variable length (37–43 amino acids) via an unusual intramembrane cleavage. Recent findings propose that some commonly used non-steroidal anti-inflammatory drugs (NSAIDs) have the ability to modulate specifically γ-secretase activity without inhibiting the enzyme as a whole. These drugs may shift the processing of APP from the longer amyloid-β 42 peptide towards shorter, less fibrillogenic and less toxic amyloid-β species. We hypothesize that γ-secretase activity, as an enzyme that is strictly associated with cellular membranes, is sensitive to alterations of the hydrophobic membrane environment. Here, we show that the γ-secretase modulator and amyloid-β 42-lowering drug sulindac sulfide alters the physical state of the membrane and strongly decreases fluidity of cellular membranes. Furthermore, sulindac sulfide changed the protein composition of membrane microdomains, the so-called lipid rafts. Most significantly, APP C-terminal fragments (CTFs) were redistributed from rafts towards non-raft membrane domains. This could be demonstrated also in cell-free assays, where in addition presenilin-1, the catalytic subunit of the γ-secretase complex, was shifted out of lipid rafts. Together, these findings suggest that sulindac sulfide directly alters the membrane architecture and shifts the γ-secretase-mediated cleavage of APP towards a hydrophobic environment where the enzyme–substrate complex is in a conformation for processing preferentially shorter amyloid-β peptides.