Aβ Oligomers and Fibrillar Aggregates Induce Different Apoptotic Pathways in LAN5 Neuroblastoma Cell Cultures

Fibril deposit formation of amyloid beta-protein (A beta) in the brain is a hallmark of Alzheimer's disease (AD). Increasing evidence suggests that toxicity is linked to diffusible A beta oligomers, which have been found in soluble brain extracts of AD patients, rather than to insoluble fibers. Here we report a study of the toxicity of two distinct forms of recombinant A beta small oligomers and fibrillar aggregates to simulate the action of diffusible A beta oligomers and amyloid plaques on neuronal cells. Different techniques, including dynamic light scattering, fluorescence, and scanning electron microscopy, have been used to characterize the two forms of A beta. Under similar conditions and comparable incubation times in neuroblastoma LAN5 cell cultures, oligomeric species obtained from A beta peptide are more toxic than fibrillar aggregates. Both oligomers and aggregates are able to induce neurodegeneration by apoptosis activation, as demonstrated by TUNEL assay and Hoechst staining assays. Moreover, we show that aggregates induce apoptosis by caspase 8 activation (extrinsic pathway), whereas oligomers induce apoptosis principally by caspase 9 activation (intrinsic pathway). These results are confirmed by cytochrome c release, almost exclusively detected in the cytosolic fraction of LAN5 cells treated with oligomers. These findings indicate an active and direct interaction between oligomers and the cellular membrane, and are consistent with internalization of the oligomeric species into the cytosol.