α-Helix targeting reduces amyloid-β peptide toxicity

Abstract

The amyloid-␤ peptide (A␤) can generate cytotoxic oligomers, and their accumulation is thought to underlie the neuropathologic changes found in Alzheimer's disease. Known inhibitors of A␤ polymerization bind to undefined structures and can work as nonspecific aggregators, and inhibitors that target conformations that also occur in larger A␤ assemblies may even increase oligomerderived toxicity. Here we report on an alternative approach whereby ligands are designed to bind and stabilize the 13-26 region of A␤ in an ␣-helical conformation, inspired by the postulated A␤ native structure. This is achieved with 2 different classes of compounds that also reduce A␤ toxicity to cells in culture and to hippocampal slice preparations, and that do not show any nonspecific aggregatory properties. In addition, when these inhibitors are administered to Drosophila melanogaster expressing human A␤ 1-42 in the central nervous system, a prolonged lifespan, increased locomotor activity, and reduced neurodegeneration is observed. We conclude that stabilization of the central A␤ ␣-helix counteracts polymerization into toxic assemblies and provides a strategy for development of specific inhibitors of A␤ polymerization.amyloid fibrils ͉ neurodegenerative disease ͉ protein misfolding ͉ Alzheimer's disease A lzheimer's disease is a progressive neurodegenerative disorder that is characterized by cerebral extracellular amyloid plaques and intracellular neurofibrillary tangles (1). Classically, the amyloid cascade hypothesis (2) states that Alzheimer's disease is caused by fibril and plaque formation of amyloid-␤ peptide (A␤) in the central nervous system. More recently, the hypothesis has been modified to include A␤ assemblies of sizes intermediate to monomeric and fibrillar forms, which today are considered to be the main source of cytotoxicity (3). Such A␤ assemblies include low-number oligomers and larger assemblies known as protofibrils, globulomers, Alzheimer's disease diffusible ligands, or A␤*56 (4-7). A␤ is cleaved from an integral membrane protein, the amyloid ␤ precursor protein (A␤PP), predominantly as a 40-residue peptide (A␤ 1-40 ). In addition, a C-terminally elongated 42-residue version can be excised (A␤ 1-42 ); it is this longer variant that is the main constituent of parenchymal amyloid deposits (8).The link between A␤ aggregation and Alzheimer's disease implies that inhibitors of this process should be able to slow down disease progression. A number of low-molecular-mass A␤ aggregation inhibitors have been identified by use of screens of compound libraries as well as rational design strategies. The resulting inhibitors include such chemically diverse compounds as curcumin, inositol, and nicotine (9, 10). The screens have identified inhibitors of fibril formation that similarly to the rationally designed inhibitors are predicted to bind to A␤ in an elongated, ␤-strand-like conformation and prevent its polymerization. A potential problem with this strategy is that blocking the later stages of fibril formation will favor t...

Converting the Highly Amyloidogenic Human Calcitonin into a Powerful Fibril Inhibitor by Three-dimensional Structure Homology with a Non-amyloidogenic Analogue

“…Most likely an efficient stabilization should lock the molecule in the socalled "␣-basin" (a free energy surface dominated by ␣-helical structures with minima of comparable free energies separated by low barriers (72)), avoiding the migration toward the "␤-basin." Such ␣-helix 3 ␤-sheet conversion going through progressively looser helical segments can be hampered by targeting either the intact ␣-helix with ligand molecules (73) or the structurally independent folding units (turnlike structures) present in the peptide (72,74). The presence of SDS, used as a helix stabilizer, does lengthen the fibrillation time (the lag time of the onset of fibrillation) but does not abolish hCT aggregation.…”

Molecular basis of β-amyloid oligomer recognition with a conformational antibody fragment

“…For example, the ability of KW1AP to discriminate between different types of Aβ oligomers (Fig. 2F) could give rise to highly targeted applications to ascertain the contribution of specific Aβ assemblies to pathogenicity using in vivo systems that facilitate analysis of protein modifiers of aggregation (42,43).…”

Biochemistry of Amyloid -Protein and Amyloid Deposits in Alzheimer Disease

“…The structure of the carboxyl terminus may involve novel metastable conformations (b-hairpin at 35 -37), but these remain to be confirmed by crystallographic methods . Synthetic oligomers are also being used in attempts to discover small molecules which are able to target these specific assemblies (Davis and Berkowitz 2009a;Davis et al 2009;Feng et al 2009;Liu et al 2009a;Nerelius et al 2009;Pitt et al 2009;Riviere et al 2009;Smith et al 2009;Sun et al 2009;Yamin et al 2009;Hawkes et al 2010;Ladiwala et al 2010). …”