Neuronal APP accumulates in toxic membrane blebbings.

The occurence of plasma membrane blebbings is an early cytotoxic event, associated with the reorganization of cytoskeletal proteins, the alteration of interactions between the plasma membrane and the underlying cytoskeleton. The blebbing formation remains poorly understood but the involvement of cytosolic Ca2+ and the production of free radicals may contribute to this cellular phenomenom. The amyloid precursor protein (APP), is a transmembrane protein that can be cleaved to produce the beta amyloid peptide (Abeta) which accumulates in brain senile plaques of Alzheimer's disease. Our study reveals that the exposure of rat and human (hNT) neuronal cultures to a mild concentration of the excitotoxin NMDA slowly induces perturbations of the neuronal cytoskeleton and the occurence of plasma membrane blebbings. An immunocytochemical study using four different APP antibodies demonstrates that these membrane blebs are also associated with a redistribution and an accumulation of cellular APP. This phenomenon is linked to a Ca2+-influx through NMDA-receptors since it is prevented by the NMDA antagonist MK801 or by Ca2+-depleted conditions. In conclusion this study shows that neuronal degeneration induced by slow excitotoxicity, is associated with the presence of APP-accumulating blebs, that can be secondly released in the extracellular region.