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 associat ed with Alzheimer's disease (AD) is due to proteolytic fragments of the amy loid 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-term inal 105 amino acid fragment (CT 105) of APP induced strong nonselective in ward currents in Xenopus oocyte; it also revealed neurotoxicity in PC12 cel ls and primary cortical neurons, blocked later phase of long-term potentiat ion in rat hippocampus ill vivo, and induced memory deficits and neuropatho logical changes in mice. We report here that the pretreatment with CT 105 f or 24 h at a 10 mu M concentration increases intracellular calcium concentr ation by about twofold in SK-N-SH and PC 12 cells, but not in U251 cells, o riginated from human glioblastoma. In addition, the calcium increase and to xicity 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 nif edipine and verapamil. CT 105 rendered SK-N-SH cells and rat primary cortic al neurons more vulnerable to glutamate-induced excitotoxicity, Also, confo rmational studies using circular dichroism experiments showed that CT 105 h as similar to 15% of beta-sheet content in phosphate buffer and aqueous 2,2 ,2-trifluoroethanol solutions. However, the content of beta-sheet conformat ion in dodecyl phosphocholine micelle or in the negatively charged vesicles , is increased to 22%-23%. The results of this study showed that CT 105 dis rupts calcium homeostasis and renders neuronal cells more vulnerable to glu tamate-induced excitotoxicity, and that some portion of CT 105 has partial beta-sheet conformation in various environments, which may be related to th e self-aggregation and toxicity. This may be significantly possibly involve d in inducing the neurotoxicity characteristic of AD.