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 alt eration of interactions between the plasma membrane and the underlying cytoskeleton. The blebbing formation remains poorly understood but th e involvement of cytosolic Ca2+ and the production of free radicals ma y contribute to this cellular phenomenom. The amyloid precursor protei n (APP), is a transmembrane protein that can be cleaved to produce the beta amyloid peptide (A beta) which accumulates in brain senile plaqu es of Alzheimer's disease. Our study reveals that the exposure of rat and human (hNT) neuronal cultures to a mild concentration of the excit otoxin 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 memb rane blebs are also associated with a redistribution and an accumulati on 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 neuro nal degeneration induced by slow excitotoxicity, is associated with th e presence of APP-accumulating blebs, that can be secondly released in the extracellular region.