Amyloid-Beta peptide (Abeta) is considered to be of central importance in the pathogenesis of Alzheimer's disease (AD); it is known to be neurotoxic, very probably after engagement to cellular receptors. Such cellular binding sites mediating Abeta effects on neurons have not hitherto been defined. The applicants have purified to homogeneity an approximately 55 kDa polypeptide, which interacts with synthetic Abeta(residues 1-40), and have shown it to be identified to RAGE, an immunoglobulin superfamily receptor previously found to bind nonenzymatically glycated adducts of proteins termed advanced glycation endproducts. Recombinant RAGE bound 125 I-Abeta(1-40 and 25-35), but not binding to immobilized synthetic Abeta(1-40 or 1-42) or Abeta derived from AD brain. Binding of 125 I-Abeta to cultured cortical neurons was prevented by anti-RAGE IgG or excess soluble receptor; in parallel, blocking access to RAGE prevented Abeta-induced cellular oxidant stress and cytotoxicity. Increased expression of RAGE in neurons, as well as microglia, near senile plaques in AD brain underscored the probable relevance of RAGE-Abeta interaction to AD. The investigators hypothesize that Abeta-induced perturbation of cellular targets, especially neurons and microglia, is mediated, at least in part, via interaction with RAGE; initially, this is a protective mechanism, in which engagement of RAGE by Abeta activates cellular defenses and, potentially, promotes cellular uptake and degradation of the peptide. Later, after extensive aggregates of Abeta have formed, Abeta-RAGE interaction eventuates in cytotoxicity. They propose that blockage of Abeta-RAGE interaction will attenuate Abeta-induced cellular oxidant stress and its consequences, including induction of cytokines and release of toxic mediators, thus, ultimately protecting neurons form cytotoxicity.
The specific aims are (1) to characterize the interaction of Abeta with RAGE using purified recombinant RAGE and RAGE- bearing cells, cortical neurons and microglia; and to compare binding of Abeta microglia RAGE and the macrophage scavenger receptor, the latter a receptor on microglia shown to interact with Abeta; and (2) to assess if expression of Macrophage-Colony Stimulating Factor, which they have found to be increased in cerebrospinal fluid from AD patients, is a consequence of Abeta-RAGE-mediated neuronal oxidant stress and can be exploited as a dynamic index of neuronal perturbation and microglial activation in AD. These studies have the goal of determining if RAGE expressed by neurons and microglia represents an important cellular target of Abeta in the pathogenesis of AD.
