Free fatty acids stimulate the polymerization of tau and amyloid beta peptides. In vitro evidence for a common effector of pathogenesis in Alzheimer's disease

Alzheimer's disease is a degenerative disorder of the central nervous system, characterized by the concomitant deposition of extracellular filaments composed of beta-amyloid peptides and intracellular filaments composed of the microtubule-associated protein tau. We have discovered that free fatty acids (FFAs) stimulate the assembly of both amyloid and tau filaments in vitro. The minimal concentration of arachidonic acid observed to stimulate tau assembly ranged from 10 to 20 mumol/L, depending on the source of the purified tau. Tau preparations that do not exhibit spontaneous assembly were among those induced to polymerize by arachidonic acid. All long-chain FFAs tested enhanced assembly to some extent, although greater stimulation was usually associated with unsaturated forms. Utilizing fluorescence spectroscopy, unsaturated FFAs were also demonstrated to induce beta-amyloid assembly. The minimal concentration of oleic or linoleic acid observed to stimulate the assembly of amyloid was 40 mumol/L. The filamentous nature of these thioflavin-binding amyloid polymers was verified by electron microscopy. These data define a new set of tools for examining the polymerization of amyloid and tau proteins and suggest that cortical elevations of FFAs may constitute a unifying stimulatory event driving the formation of two of the obvious pathogenetic lesions in Alzheimer's disease.