Gene expression profiling of amyloid beta peptide-stimulated human post-mortem brain microglia

Activation of microglia is a central part of the chronic inflammatory processes in Alzheimer’s disease (AD). In the brains of AD patients, activated microglia are associated with amyloid beta (Aβ) peptide plaques. A number of previous studies have shown that aggregated synthetic Aβ peptide activates cultured microglia to produce a range inflammatory products. The full extent of the inflammatory response still remains to be determined. In this study, gene array technology was employed to investigate in a more extensive manner the consequences of microglial activation by Aβ peptide. RNA was prepared from pooled samples of cortical human microglia isolated from post-mortem cases and incubated with a low dose (2.5 μM) of Aβ1–42 (or peptide solvent) for 24 h. This material was used to prepare cDNA probes, which were used to detect the differential pattern of expressed genes on a 1,176 Clontech membrane gene array. Results obtained showed that 104 genes were either upregulated or downregulated by 1.67 fold or greater. The most highly induced genes belonged to the chemokine family with interleukin-8 (IL-8) expression being increased by 11.7 fold. Interestingly, many of the highly induced genes had been identified as being responsive to activation by the transcription factor NF-κB. A number of genes were downregulated. Thymosin beta, prothymosin alpha and parathymosin, all belonging to the same gene family, were downregulated. To validate these semi-quantitative results, the expression of intercellular adhesion molecule-1 (ICAM-1) and rhoB were measured by RT-PCR in samples of cDNA derived from Aβ and control stimulated human cortical microglia. These results confirm the usefulness of the gene array approach for studying Aβ-mediated inflammatory processes.