The Non-Amyloid-β Component of Alzheimer’s Disease Plaque Amyloid: Comparative Analysis Suggests a Normal Function as a Synaptic Plasticizer

Abstract

A second intrinsic peptide component of Alzheimer’s Disease amyloid has recently been identified and called the “Non-Amyloid-β Component” (NAC)¹. The peptide’s precursor (NACP) is the homologue of a brain-specific presynaptic protein of unknown function, identified independently in at least four other laboratories. The first report of this protein was in 1988 by Maroteaux et al.², who identified it as a component enriched in a biochemical preparation of synaptic vesicles from the electric organ of Torpedo. Later, they cloned related sequences from the rat, and showed them to be enriched in telencephalic regions of the rat brain³. They originally termed this protein “synuclein,” although early evidence for nuclear localization² has yet to be corroborated. Nakajo and colleagues identified a closely-related protein, first in bovine brain⁴ and then from rats⁵. They showed this protein to be phosphorylated on serine residues, and have suggested it is also phosphorylated on tyrosine⁶; they named the protein Phosphoneuroprotein-14-kDa (PNP-14). More recently, Jakes et al.⁷, using an antibody originally raised against paired helical filaments, detected two forms of the same human protein, one more closely related to PNP-14 and the other more related to the original synuclein. Consistent among all these reports has been the observation that the protein(s) is especially abundant in the telencephalon (especially the hippocampus) where it is distinctly enriched in presynaptic elements^{2, 7–10}.