Selective cytotoxicity of intracellular amyloid β peptide1–42 through p53 and Bax in cultured primary human neurons

Abstract

Extracellular amyloid β peptides (Aβs) have long been thought to be a primary cause of Alzheimer's disease (AD). Now, detection of intracellular neuronal Aβ1–42 accumulation before extracellular Aβ deposits questions the relevance of intracellular peptides in AD. In the present study, we directly address whether intracellular Aβ is toxic to human neurons. Microinjections of Aβ1–42 peptide or a cDNA-expressing cytosolic Aβ1–42 rapidly induces cell death of primary human neurons. In contrast, Aβ1–40, Aβ40–1, or Aβ42–1 peptides, and cDNAs expressing cytosolic Aβ1–40 or secreted Aβ1–42 and Aβ1–40, are not toxic. As little as a 1-pM concentration or 1500 molecules/cell of Aβ1–42 peptides is neurotoxic. The nonfibrillized and fibrillized Aβ1–42 peptides are equally toxic. In contrast, Aβ1–42 peptides are not toxic to human primary astrocytes, neuronal, and nonneuronal cell lines. Inhibition of de novo protein synthesis protects against Aβ1–42 toxicity, indicating that programmed cell death is involved. Bcl-2, Bax-neutralizing antibodies, cDNA expression of a p53R273H dominant negative mutant, and caspase inhibitors prevent Aβ1–42-mediated human neuronal cell death. Taken together, our data directly demonstrate that intracellular Aβ1–42 is selectively cytotoxic to human neurons through the p53–Bax cell death pathway.