Analysis of gene expression during the macrophage to foam cell transformation using cDNA arrays

Coronary heart disease (CHD) is the leading cause of death in most industrialised countries. Atherosclerosis is the major underlying cause of CHD. Atherosclerosis is a disease process in which monocyte derived macrophages enter the subendothelial space, accumulate excess amounts of cholesterol to form lipid filled foam cells. These foam cells have been found contribute significantly to the aetiology of the fatty streak and subsequent lesions involved in atherosclerosis. The aim of this study was to gain a further understanding of the foam cell formation process by studying gene expression during the macrophage to foam cell transformation. Human THP-1 monocytic cells were differentiated into macrophages using a phorbol ester. Macrophages were subsequently exposed to either acetylated LDL or oxidised LDL to induce foam cell formation. Foam cell formation was assessed using the techniques of flow cytometry, Oil Red о staining, fluorescence microscopy and cholesteryl oleate loading. Gene expression was examined using high density cDNA array technology. RNA was isolated from cells exposed to native or modified LDL. First strand cDNA probes were subsequently generated and applied to high-density cDNA arrays. Two different arrays were probed; an array representative of the Human I M A G E collection and a custom array containing known genes thought to be involved in the cardiovascular disease process. The results of this study showed increased expression in CD36, a known receptor for OxLDL. In addition other genes were also identified including IL Iß and fíbronectin. Cluster analysis of a time series experiment showed the existence of nine distinct clusters of genes with different expression patterns. In particular two genes IL-1 β and TIMP-1 were shown to have a highly correlated pattern of expression.