A genomic approach to atherosclerotic plaque vulnerability

Abstract

BACKGROUND: Macrophages in atherosclerotic plaques are believed to play a central role in plaque instability. However, the cell-specific molecular mechanisms involved are incompletely characterized. To address this, we performed genome-wide gene expression analyses using microarrays on RNA extracted from macrophage-rich regions of stable and unstable human atheromatous plaques. METHODS AND RESULTS: Plaques derived from carotid endarterectomy specimens (n=118) were designated as stable or unstable according to clinical, radiological and histopathological criteria. Macrophage-rich regions were excised from unstable and stable plaques by laser microdissection. Transcriptional profiling of extracted RNA was carried out using Affymetrix U133plus2 microarrays. The expression profiles were characteristic of activated macrophages. Expression profiles from stable and unstable samples clustered into distinct groups. Nine hundred and fourteen genes differentially expressed between stable and unstable sample groups were identified at a false discovery rate of 10%. The findings were confirmed by real-time PCR for eleven of the twelve genes with the highest fold expression difference (p<0.05). The analysis of the gene expression of the twelve highest fold expression genes by their principal components demonstrated a distribution of the samples along an axis of stability-instability in gene expression space. More specifically, components of the PPAR/Adipocytokine signalling pathway were significantly differentially expressed (p=5.4x10-7) between stable and unstable plaques with greater expression in unstable plaques. Key components of the pathway, fatty acid binding protein 4 (FABP4) and leptin, showed nine-fold (p=0.0086) and five-fold (p=0.0012) greater expression in unstable plaques respectively. The immunohistochemistry of the protein products for FABP4 and Leptin confirmed their co-localisation with the macrophages in the plaque. CONCLUSION: Differences in gene expression signatures are present between macrophages isolated from stable and unstable human atheromatous plaques. Components of the PPAR/adipocytokine signalling pathway, specifically FABP4 and Leptin, are expressed at higher levels in macrophages from unstable plaques. These findings suggest that down-regulation of PPAR/adipocytokine signalling within plaques may have therapeutic potential.