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Abstract
Atherosclerosis is driven by the accumulation of monocyte-derived cells in the arterial wall and the formation of cholesterol-loaded macrophage foam cells . A proportion of lesion foam cells migrate out of the lesion site inducing regression. Some lesion cells bear dendritic rather than macrophage markers. This is significant because dendritic cells (DCs) are known to be migratory. Little is known of the influence of circulating lipids and cellular cholesterol levels on the ability of these cells to migrate out of atherosclerotic lesions.
The aim of this thesis was to investigate the extent to which cellular cholesterol controls the phenotype and migratory abilities of monocyte-derived cells both in vitro and in vivo.
Bone marrow isolated from C57Bl6/J mice was differentiated into either bone marrow derived macrophages (BMM) or bone marrow derived dendritic cells (BMDC). The phenotype of the resulting cells was confirmed by flow cytometry and mRNA expression. BMM and BMDC were enriched with cholesterol to generate foam cells . These resulting cellular phenotypes were again examined by flow cytometry. Cellular function was investigated using transwell migration assays, co-culturing with T-cells to determine immunostimulatory ability and cytokine secretion.
Migration of both macrophages and dendritic cells was impaired by elevated cholesterol. In addition, cholesterol reduced the expression of classic dendritic cell markers and MHCII levels on BMDC. However, cholesterol-enriched BMDC demonstrated an increased ability to stimulate T cell proliferation, due to increased secretion of inflammatory cytokines.
The role of CCR7, a protein involved in dendritic cell migration, and its involvement in atherosclerotic lesion regression, was investigated by transferring bone marrow from either a WT or CCR7 KO mouse into an LDLr KO mouse. The mice were then fed different diets (normal chow, HFD or HFD followed by chow) and aortic lesions were analysed.
Placing mice on a HFD caused an increase in plasma cholesterol and lesion development. Reverting their diet back to chow reduced plasma cholesterol levels and enabled lesion regression in mice with WT BMT. However, lesions in mice that received a CCR7 KO BMT did not regress, indicating the importance of CCR7 in lesion regression.