Monocyte-derived macrophages play a central role in the pathogenesis of atherosclerosis. They actively promote oxidation of LDL, express scavenger receptors, and secrete cytokines and growth factors which influence the migration, growth and function of arterial cells. They may also contribute to plaque instability b secretion of metalloproteinases. Our laboratory characterized transcriptional control elements of the scavenger receptor A (SR-A) gene that are required for macrophage-specific expression of this gene. We also demonstrated that regulatory elements of the SR-A gene can be used to specifically target reporter reporter gene expression in macrophage foam cells of murine atherosclerotic lesions. A major aim of this unit is to fully develop and validate a variety of vector systems for the overexpression or disruption of genes in a macrophage-specific manor. Vector based on the SR-A promoter and other macrophage-specific promoters will be developed to allow targeting of cDNAs to mature macrophages and macrophage progenitor cells. These vectors will also be used to direct expression of Cre-recombinase or a doxycycline-inducible transcriptional activator in transgenic mice. The ability of these vectors to direct efficient macrophage-specific expression of genes in forms cells of atherosclerotic lesions will be assessed in apo E- deficient, or LDL receptor-deficient (LDLR) mice, utilizing reporter genes, such as human growth hormone.
A second aim will be to utilize this information to determine the impact on atherogenesis of macrophage specific overexperssion of genes that could influence atherogenesis. Overexpression of 15-lipoxygenase will serve as an example of a gene that can enhance the oxidation of LDL, and overexpression of phospholipid-hydroperoxide glutathione peroxidase as an example of a gene that should decrease oxidation of LDL. In a similar manner we will determine the consequences to the integrity of the artery wall of macrophage-specific overexpression of metalloproteinases, including the 92 kDa gelatisase, interstitial collagenase, and stromelysin, expressed individually and in combination. The effects of overexpression of these genes on the atherosclerotic process will be tested in appropriate murine models. Finally, we will determine the consequences for atherogenesis of macrophage-specific disruption of the c-jun gene. C-jun appears to regulate transcription of several important macrophase genes, including SR-A, cytokines, and metalloproteinases. Because a global disruption of c-jun results in embryonic lethality, macrophage-specific disruption will serve as a paradigm for the evaluation of gene required for normal development but which may contribute to atherogenesis. The information gained from these studies should yield fundamental insights into the role that macrophages play in atherogenesis and could be used to develop novel and effective therapeutic strategies.
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