Expression of amyloid precursor protein in human astrocytes in vitro: Isoform-specific increases following heat shock

The beta-amyloid protein deposited in senile plaques and cerebral blood ves sels in the Alzheimer's disease brain is derived from the larger transmembr ane spanning amyloid precursor protein. The present study investigates the effects of heat shock on the expression and processing of amyloid precursor protein in a normal human fetal astrocytic cell line CC2565 using reverse transcription-polymerase chain reaction, in situ hybridization histochemist ry and western blot analysis. Hear shock led to an increase in the messenge r RNA encoding Kunitz protease inhibitor isoforms of amyloid precursor prot ein, which peaked at 4 h post-heat shock. This increase was confined to the messenger RNA encoding amyloid precursor protein-751, with a decrease in a myloid precursor protein-770 and no change in amyloid precursor protein-695 . This shift in splicing was accompanied by a significant decrease in secre ted amyloid precursor protein and an increase in beta-secretase processing within the cell. These findings demonstrate that astrocytes in vitro demonstrate a striking response to heat shock. This is unlikely to be due to a direct action on th e promoter region of the gene, since the response is specific for one splic e variant; amyloid precursor protein-751 messenger RNA. This increase in ex pression is further accompanied by a decrease in secretion of amyloid precu rsor protein, implying a shift in processing towards an intracellular route , possibly via the actions of the beta-secretase enzyme, which is known to be potentially amyloidogenic. Such a mechanism may contribute to amyloidosi s in the intact brain in response to cellular stress, such as head injury. (C) 2000 IBRO. published by Elsevier Science Ltd. All rights reserved.