Abstract
Intracellular accumulation of oligomeric forms of β amyloid (Aβ) are now believed to play a key role in the earliest phase of Alzheimer's disease (AD) as their rise correlates well with the early symptoms of the disease. Extensive evidence points to impaired neuronal Ca(2+) homeostasis as a direct consequence of the intracellular Aβ oligomers. However, little is known about the downstream effects of the resulting Ca(2+) rise on the many intracellular Ca(2+)-dependent pathways. Here we use multiscale modeling in conjunction with patch-clamp electrophysiology of single inositol 1,4,5-trisphosphate (IP(3)) receptor (IP(3)R) and fluorescence imaging of whole-cell Ca(2+) response, induced by exogenously applied intracellular Aβ(42) oligomers to show that Aβ(42) inflicts cytotoxicity by impairing mitochondrial function. Driven by patch-clamp experiments, we first model the kinetics of IP(3)R, which is then extended to build a model for the whole-cell Ca(2+) signals. The whole-cell model is then fitted to fluorescence signals to quantify the overall Ca(2+) release from the endoplasmic reticulum by intracellular Aβ(42) oligomers through G-protein-mediated stimulation of IP(3) production. The estimated IP(3) concentration as a function of intracellular Aβ(42) content together with the whole-cell model allows us to show that Aβ(42) oligomers impair mitochondrial function through pathological Ca(2+) uptake and the resulting reduced mitochondrial inner membrane potential, leading to an overall lower ATP and increased production of reactive oxygen species and H(2)O(2). We further show that mitochondrial function can be restored by the addition of Ca(2+) buffer EGTA, in accordance with the observed abrogation of Aβ(42) cytotoxicity by EGTA in our live cells experiments.