Carboxyl-terminal fragment of Alzheimer's APP destabilizes calcium homeostasis and renders neuronal cells vulnerable to excitotoxicity

Numerous lines of evidence indicate that some of the neurotoxicity associated with Alzheimer's disease (AD) is due to proteolytic fragments of the amyloid precursor protein (APP). Most research has focused on the amyloid beta peptide (A beta). However, the possible role of other cleaved products of APP is less clear. We have previously shown that a recombinant carboxy-terminal 105 amino acid fragment (CT 105) of APP induced strong nonselective inward currents in Xenopus oocyte; it also revealed neurotoxicity in PC12 cells and primary cortical neurons, blocked later phase of long-term potentiation in rat hippocampus in vivo, and induced memory deficits and neuropathological changes in mice. We report here that the pretreatment with CT 105 for 24 h at a 10 mu M concentration increases intracellular calcium concentration by about twofold in SK-N-SH and PC 12 cells, but not in U251 cells, originated from human glioblastoma. In addition, the calcium increase and toxicity induced by CT 105 were reduced by cholesterol and MK 801 in SK-N-SH and PC 12 cells, whereas the toxicity of A beta(1-42) was attenuated by nifedipine and verapamil. CT 105 rendered SK-N-SH cells and rat primary cortical neurons more vulnerable to glutamate-induced excitotoxicity, Also, conformational studies using circular dichroism experiments showed that CT 105 has similar to 15% of beta-sheet content in phosphate buffer and aqueous 2,2,2-trifluoroethanol solutions. However, the content of beta-sheet conformation in dodecyl phosphocholine micelle or in the negatively charged vesicles, is increased to 22%-23%. The results of this study showed that CT 105 disrupts calcium homeostasis and renders neuronal cells more vulnerable to glutamate-induced excitotoxicity, and that some portion of CT 105 has partial beta-sheet conformation in various environments, which may be related to the self-aggregation and toxicity. This may be significantly possibly involved in inducing the neurotoxicity characteristic of AD.