The induction of surface beta-amyloid binding proteins and enhanced cytotoxicity in cultured PC-12 and IMR-32 cells...

During aging the non-enzymatic glycation of proteins and other molecules increases significantly, leading to the accumulation of advanced glycation end-products (AGEs). These AGEs enhance inflammatory and autoimmune reactions with resultant cytotoxicity. We noted in an earlier study that individuals with Alzheimer's disease exhibit enhanced expression of the receptor for advanced glycation end-products (RAGE) on the surface of their leukocytes. In order to better understand the relationship between AGEs and the cell surface binding of amyloid-beta protein (Abeta) 42 we studied the effect of two AGEs: glycated bovine serum albumin (BSA), and epsilon-carboxymethyllysine-BSA (CML), a glycoxidation product, on the binding of Abeta42 to rat PC-12 and IMR-32 cells. We measured the expression of three potential cell surface receptors binding Abeta42: RAGE, beta-amyloid precursor protein (beta-APP), and the alpha7 subtype of the nicotinic acetylcholine receptor (alpha7nAChR) by using specific antibody probes. Incubation of PC-12 or IMR-32 cells with bovine serum albumin-advanced glycation end-product (BSA-AGE) or with CML induced small but significant concentration-dependent increases in the expression of beta-APP, RAGE, and alpha7nAChRs as measured by flow cytometry or by ELISA. Incubation of the cells with 48 microM of either of the AGEs combined with varying concentrations (138-1100 nM) of Abeta42 resulted in the enhanced binding of the Abeta42 to the cell surface as compared with cells not exposed to the AGE co-treatment. The combination of AGE and Abeta treatment also resulted in the heightened expression of all three potential Abeta binding sites as well as their gene precursors. Exposure of cells to the same regimen of AGE plus Abeta resulted in the production of reactive oxygen species and mitochondrial toxicity. These results are consistent with the ability of AGEs to enhance the cell surface expression of diverse Abeta42 binding sites, a factor that can lead to the enhanced binding of amyloid and subsequent cell death.