Human IMR-32 neuroblastoma cells as a model cell line in Alzheimer's disease research.

The present study investigated expression and processing of amyloid precursor protein by neuronally differentiated IMR-32 neuroblastoma cells. APP mRNA in these cells was found to consist of approximately 58% APP695, 38% APP751, and < 4% APP770. APP-immunoreactive bands detected in western blots of cellular protein extracts were only detected by anti-APP antibodies to peptides with strong homology to APLP2, suggesting that these bands represent APP-like proteins and not APP itself. This result suggests that previous studies claiming immunodetection of cellular forms of APP may have to be re-evaluated. Four main species of C-terminal truncated, secreted APP were detected in blots of protein extracts from medium conditioned by these cells. The immunoreactive profile of these bands suggested a cleavage site N-terminal to the Lys16-Leu17 bond of alpha-secretase. This, together with differences in number and molecular mass of APP-immunoreactive bands between secreted APP from IMR-32 cells and that from the commonly used PC-12 cells, suggests differences in APP processing between these two neuronally differentiated cell lines. In theory, IMR-32 cells being of human neuronal origin may be a more appropriate cell line to study APP-processing in relation to Alzheimer's disease than the rat phaeochromocytoma PC-12 cell line. Therefore, these detected differences warrant further investigation. Additionally IMR-32 cells under certain tissue culture conditions can form intracellular fibrillary material that reacts with anti-PHF specific antibodies. Neuronally differentiated IMR-32 cells could therefore be used as a model system to investigate possible interactions between APP-processing and PHF formation.