Intracellular amyloid formation in muscle cells of Abeta-transgenic Caenorhabditis elegans: determinants and physiological role in copper detoxification.

BACKGROUND: The amyloid beta-peptide is a ubiquitous peptide, which is prone to aggregate forming soluble toxic oligomers and insoluble less-toxic aggregates. The intrinsic and external/environmental factors that determine Abeta aggregation in vivo are poorly understood, as well as the cellular meaning of this process itself. Genetic data as well as cell biological and biochemical evidence strongly support the hypothesis that Abeta is a major player in the onset and development of Alzheimer's disease. In addition, it is also known that Abeta is involved in Inclusion Body Myositis, a common myopathy of the elderly in which the peptide accumulates intracellularly. RESULTS: In the present work, we found that intracellular Abeta aggregation in muscle cells of Caenorhabditis elegans overexpressing Abeta peptide is affected by two single amino acid substitutions, E22G (Arctic) and V18A (NIC). Both variations show decrease intracellular amyloidogenesis compared to wild type Abeta. We show that intracellular amyloid aggregation of wild type Abeta is accelerated by Cu2+ and diminished by copper chelators. Moreover, we demonstrate through toxicity and behavioral assays that Abeta-transgenic worms display a higher tolerance to Cu2+ toxic effects and that this resistance may be linked to the formation of amyloid aggregates. CONCLUSION: Our data show that intracellular Abeta amyloid aggregates may trap excess of free Cu2+ buffering its cytotoxic effects and that accelerated intracellular Abeta aggregation may be part of a cell protective mechanism.

Metalloenzyme-like activity of Alzheimer's disease beta-amyloid. Cu-dependent catalytic conversion of dopamine, cholesterol, and biological reducing agents to neurotoxic H(2)O(2).

Beta-amyloid (Abeta) 1-42, implicated in the pathogenesis of Alzheimer's disease, forms an oligomeric complex that binds copper at a CuZn superoxide dismutase-like binding site. Abeta.Cu complexes generate neurotoxic H(2)O(2) from O(2) through Cu(2+) reduction, but the reaction mechanism has been unclear. We now report that Abeta1-42, when binding up to 2 eq of Cu(2+), generates the H(2)O(2) catalytically by recruiting biological reducing agents as substrates under conditions where the Cu(2+) or reducing agents will not form H(2)O(2) themselves. Cholesterol is an important substrate for this activity, as are vitamin C, L-DOPA, and dopamine (V(max) for dopamine = 34.5 nm/min, K(m) = 8.9 microm). The activity was inhibited by anti-Abeta antibodies, Cu(2+) chelators, and Zn(2+). Toxicity of Abeta in neuronal culture was consistent with catalytic H(2)O(2) production. Abeta was not toxic in cell cultures in the absence of Cu(2+), and dopamine (5 microm) markedly exaggerated the neurotoxicity of 200 nm Abeta1-42.Cu. Therefore, microregional catalytic H(2)O(2) production, combined with the exhaustion of reducing agents, may mediate the neurotoxicity of Abeta in Alzheimer's disease, and inhibitors of this novel activity may be of therapeutic value.