A Mechanism For The Inhibition Of Tau Neurotoxicity: Studies With Artificial Membranes, Isolated Mitochondria, And Intact Cells

It is currently believed that molecular agents that specifically bind to and neutralize the toxic proteins/peptides, amyloid beta (A beta 42), tau, and the tau-derived peptide PHF6, hold the key to attenuating the progression of Alzheimer's disease (AD). We thus tested our previously developed nonaggregating A beta 42 double mutant (A beta 42(DM)) as a multispecific binder for three AD-associated molecules, wild-type A beta 42, the tau(K174Q) mutant, and a synthetic PHF6 peptide. A beta 42(DM) acted as a functional inhibitor of these molecules in in vitro assays and in neuronal cell-based models of AD. The double mutant bound both cytotoxic tau(K174Q) and synthetic PHF6 and protected neuronal cells from the accumulation of tau in cell lysates and mitochondria. A beta 42(DM) also reduced toxic intracellular levels of calcium and the overall cell toxicity induced by overexpressed tau, synthetic PHF6, A beta 42, or a combination of PHF6 and A beta 42. A beta 42(DM) inhibited PHF6-induced overall mitochondrial dysfunction: In particular, A beta 42(DM) inhibited PHF6-induced damage to submitochondrial particles (SMPs) and suppressed PHF6-induced elevation of the zeta-potential of inverted SMPs (proxy for the inner mitochondrial membrane, IMM). PHF6 reduced the lipid fluidity of cardiolipin/DOPC vesicles (that mimic the IMM) but not DOPC (which mimics the outer mitochondrial membrane), and this effect was inhibited by A beta 42(DM). This inhibition may be explained by the conformational changes in PHF6 induced by A beta 42(DM) in solution and in membrane mimetics. On this basis, the paper presents a mechanistic explanation for the inhibitory activity of A beta 42(DM) against A beta 42- and tau- induced membrane permeability and cell toxicity and provides confirmatory evidence for its protective function in neuronal cells.