Role of Subsrate Stiffness on Macrophage and Foam Cell Function in Atherosclerosis

Cardiovascular disease is the number one cause of mortality in developed countries with atherosclerosis being the major underlying cause. It is characterized by the accumulation of cholesterol in the arterial walls which leads to partial or full occlusion of the artery due to the development of plaque. The disease manifests over several years and the clinical consequences at chronic stages of the pathology can lead to myocardial infarction or stroke. Plaques in the artery are detected using methods like cholesterol screening, ultrasound, CT scanning and MRI. These technologies are able to detect the mechanical and biological variation within advanced stages of atherosclerosis. Thus, it is important to understand how mechanical heterogeneity at these stages ranging from lipoprotein accumulation in the artery intima to formation of calcified plaque influence the function of mechanosensitive cells. Primary cells involved in atherosclerosis, macrophages, have been shown to be mechanosensitive but the role of biochemical and mechanical activation of these cells in the uptake of modified lipoproteins and foam cell formation is yet to be fully discovered. The goal of this research is to investigate the processes of native and oxidized low-density lipoprotein uptake by macrophages at the site of artery inflammation to form foam cells and understand the role of matrix stiffness in the process of uptake. In this study, we developed an in vitro model leveraging peripheral blood derived human primary macrophages and physiologically relevant stiffness range of 1-8 kPa to study macrophage and foam cell function. First, we characterized our cell-based model and demonstrated the efficiency of our system to form foam cells. Next, we characterized the cell viability of macrophages and foam cells cultured on polyacrylamide gels. Additionally, we conducted a morphological characterization of macrophages and foam cells. After characterizing our model, we applied the model to answer questions about the effect of substrate stiffness and inflammation on macrophage and foam cell proliferation, traction forces and uptake of oxLDL by macrophages. Lastly, we performed pathway studies using pharmacological inhibitors of oxLDL uptake to elucidate which pathways are predominant in oxLDL internalization in macrophages.