AMYLOID BETA AND BIOENERGETICS

A relationship between mitochondrial function and amyloid beta (Aβ) is well established. The exact mechanism of this relationship and its effects on amyloid precursor protein (APP) processing homeostasis and secretase enzyme function is not understood. Our goal is to elucidate the relationship between bioenergetics, mitochondrial function, and the molecular machinery of APP processing. SH-SY5Y cells were transfected with either wild-type APP or Swedish/Indiana mutant APP. After treatment with FCCP (uncoupler), oligomycin (ATP synthase inhibitor), DNP (uncoupler), or starvation (Hank's balanced salt solution for 6 hours) APP processing was measured (full length APP protein, soluble APPα, Aβ40, and Aβ42). β-secretase (BACE) activity was measured using a fluorescent assay. Mitochondrial-localized full-length APP was also measured. All parameters listed were measured in ρ0 cells on an SH-SY5Y background (cells lacking mitochondrial DNA and thus mitochondrial respiration). All manipulations lowered the ATP/ADP ratio. Cells treated with FCCP (or DNP) and ρ0 cells had depolarized mitochondrial membrane potential. Under conditions of depolarized mitochondrial membrane potential, mitochondrial-localized APP was increased while Aβ40 and Aβ42 were reduced (no change in Aβ40/Aβ42 ratio for FCCP treated cells, this ratio was reduced in the ρ0 model). Oligomycin treated cells had hyperpolarized mitochondrial membrane potential, decreased mitochondrial-localized full-length APP, higher Aβ42 and lower Aβ40 (lower Aβ40/Aβ42 ratio). Cells which were starved had no change in mitochondrial membrane potential but had higher Aβ42 and Aβ40 (no change in Aβ40/Aβ42 ratio). BACE activity was reduced when cells were treated with oligomycin or FCCP, but starvation had no effect on BACE activity. Mitochondrial membrane potential is an important factor for secretase activity and APP localization. Mitochondrial membrane potential likely influences pH balance (in a compartmentalized manner) and could alter autophagy, endosome function, lipid raft formation, and APP processing homeostasis. Further studies will focus on the effects of mitochondrial membrane potential on APP processing and secretase function in induced pluripotent stem cell derived neurons.