P3–270: Metal ion–induced gene expression patterns in aging human brain cells in primary culture; implications for neurodegeneration and Alzheimer's disease

Alterations in metal–ion induced catalysis, oxidative stress, homeostasis and trace metal overload are implicated in neurodegenerative disorders such as Alzheimer's disease (AD). The mechanisms of metal–induced disruption of gene expression and genetic signaling function in primary human brain cells, termed genotoxicity, are not well understood. These studies examined the effects of physiologically relevant, non–apoptotic concentrations of magnesium–, iron–, zinc– and aluminum–sulfate on gene expression patterns in untransformed human neural (HN) cells in primary culture. To simulate environmental exposure against a background of brain cell aging, HN cells were exposed to low micromolar concentrations of metal sulfates for 7 and 14 days, representing trace metal exposure from one–third to two–thirds of their in vitro lifespan. High density DNA array technologies (Affymetrix, Santa Clara, CA) were used that simultaneously analyzed the expression of every human gene. Changes in micro RNA, messenger RNA and protein abundance were independently assayed using Northern blotting, RT–PCR and/or Western immunoassay. Oxidative stress was measured by using a modified 2',7'–dichlorofluorescein diacetate assay. Bioinformatics analyses employed GeneSpring algorithms (Silicon Genetics, Redwood City, CA). Metal sulfates induced general decreases in both micro RNA and messenger RNA abundance while up–regulating a family of potentially pathogenic genes. Changes in gene expression profiles were preceded by the evolution of reactive oxygen intermediates. While magnesium sulfate exposure showed negligible effects, iron–, zinc– and aluminum–sulfate exposure each showed time–specific alterations in HN cell gene expression patterns. Interestingly, combinations of iron– and aluminum–sulfate together were found to significantly induce the expression of cyclooxygenase–2, β–amyloid precursor protein, DAXX protein and heat shock proteins. Similarly up–regulated gene expression profiles for these stress–sensing, pro–inflammatory and pro–apoptotic elements have been observed in AD brain. Zinc–, iron– and aluminum–sulfate, and in particular the combination of iron– and aluminum–sulfate together, were found to up–regulate the expression of a pro–apoptotic, pro–inflammatory and/or pathogenic gene family. The data also indicate that physiologically relevant amounts of iron and aluminum in combination are especially capable of inducing Fenton chemistry–triggered, pre–apoptotic gene expression programs that may support downstream pathogenic responses, brain cell dysfunction and AD–type change.