Aβ42 Double Mutant Inhibits Aβ42-Induced Plasma and Mitochondrial Membrane Disruption in Artificial Membranes, Isolated Organs, and Intact Cells

Destabilization of plasma and inner mitochondrial membranes by extra- and intracellular amyloid beta peptide (A beta 42) aggregates may lead to dysregulated calcium flux through the plasma membrane, mitochondrial-mediated apoptosis, and neuronal cell death in patients with Alzheimer's disease. In the current study, experiments performed with artificial membranes, isolated mitochondria, and neuronal cells allowed us to understand the mechanism by which a nonaggregating A beta 42 double mutant (designated A beta 42(DM)) exerts its neuroprotective effects. Specifically, we showed that A beta 42(DM) protected neuronal cells from A beta 42-induced accumulation of toxic intracellular levels of calcium and from apoptosis. A beta 42(DM) also inhibited A beta 42-induced mitochondrial membrane potential depolarization in the cells and abolished the A beta 42-mediated decrease in cytochrome c oxidase activity in purified mitochondrial particles. These results can be explained in terms of the amelioration by A beta 42(DM) of A beta 42-mediated changes in membrane fluidity in DOPC and cardiolipin/DOPC phospholipid vesicles, mimicking plasma and mitochondrial membranes, respectively. These observations are also in agreement with the inhibition by A beta 42(DM) of phospholipid-induced conformational changes in A beta 42 and with the fact that, unlike A beta 42, the A beta 42-A beta 42(DM) complex could not permeate into cells but instead remained attached to the cell membrane. Although most of the A beta 42(DM) molecules were localized on the cell membrane, some penetrated into the cytosol in an A beta 42-independent process, and, unlike A beta 42, did not form intracellular inclusion bodies. Overall, we provide a mechanistic explanation for the inhibitory activity of A beta 42(DM) against A beta 42-induced membrane permeability and cell toxicity and provide confirmatory evidence for its protective function in neuronal cells.