Intracellular sAPP retention in response to Abeta is mapped to cytoskeleton-associated structures

Amyloid beta (Abeta) contributes to neurodegeneration in Alzheimer's disease and provides a close association between molecular events and pathology, although the underlying molecular mechanisms are unclear. In the work described here, Abeta did not induce amyloid precursor protein (APP) expression, but APP processing/trafficking was markedly affected. In COS-7 cells, Abeta provokes retention of intracellular sAPPalpha (isAPPalpha). Intracellular holo-APP levels remain unchanged, and extracellular total sAPP increases, although extracellular sAPPalpha alone was not altered significantly. In primary neuronal cultures and PC12 cells, isAPP also increased, but this was mirrored by a decrease in extracellular total sAPP. The isAPP retention was particularly associated with the cytoskeletal fraction. The retention "per se" occurred in vesicular-like densities, negative for a C-terminal antibody and strongly positive for the 6E10 antibody, clearly showing abnormal intracellular accumulation of sAPPalpha in response to Abeta. Our data support a dynamic model for intracellular retention of sAPPalpha as an early response to Abeta exposure. Particularly noteworthy was the observation that removal of Abeta reversed the isAPP accumulation. Mechanistically, these findings disclose an attractive physiological response, revealing the capacity of cells to deal with adverse effects induced by Abeta.