Effect of cellular factors on the generation of beta-amyloid.

There is considerable interest in the role of aggregated protein in the underlying pathology of human neurodegenerative conditions including Alzheimer's disease (AD), light chain amyloidosis, spongiform encephalopathies, Huntingdon's disease, Parkinson's disease, etc. AD is a progressive neurodegenerative condition responsible for dementia in the elderly. An early onset, familial genetic basis (FAD) for the disease has been established in kindreds, where mutations in the amyloid precursor protein (APP) and the presenilin proteins (PS) cause cerebral deposition and aggregation of the beta-amyloid (Abeta) peptide responsible for the clinical and pathological features of the disease.In order to investigate the cell biology of presenilinl and the effect of AD-causing mutations on intracellular dynamics, constructs of enhanced green fluorescent protein fused to wild type or mutant N-terminal fragment and full-length PS1 were prepared. Immunocytochemical analysis reveals that the fusion proteins display four distinct phenotypes: ER, Golgi, vesicular and 'blob-like aggregates'. Furthermore, removal of the EGFP moiety had no effect on the phenotype. The 'blob-like aggregates', are high copy number, ubiquitinated structures that originate from the nuclear/ER interface, and are not dependent on microtubules for their formation nor are they contained by the intermediate filament vimentin, indicating that they are neither aggresomes nor inclusion bodies. Moderate to high levels of the fusion protein disrupt the endoplasmic reticulum and Golgi compartments, suggesting that the normal trafficking of materials within the cell may be disturbed. Additionally, the N-terminal construct sensitises cells to staurosporine-induced apoptosis. TEM images from cells expressing the fusion protein reveals numerous phagosomes and mutilaminar bodies that fit the profile seen for the blob-like aggregates in terms of dimension, number and general morphology. These data suggest that the blob-like aggregates might be novel membrane-bound structures. These fusion proteins provide a convenient means for studying the consequences of protein aggregation on the ubiquitin-proteasome system (UPS), apoptosis and phagocytosis within the cell.