Effect of cellular cholesterol content on monocyte biophysical response
Background: Cholesterol content alters cell membrane stiffness and lateral lipid and protein diffusion. It is an important risk factor in diseases like atherosclerosis, due to its active uptake by monocytes/macrophages. In fact, monocyte recruitment from flowing blood to atherosclerotic foci is a key step in the development of atherosclerosis. We hypothesized that cholesterol content governs the biophysical response of monocytes and thereby alters the overall immune response. Methods: We depleted or enriched cholesterol levels in either human monocytic cell line THP-1 cells or primary human monocytes freshly isolated from whole blood. We investigated the effect of these changes on dynamics of monocyte rolling on E-selectin surfaces at 1 dyn/sq.cm. in micro-channels. We also assessed the effect of cholesterol modification on monocyte chemotaxis towards the chemokine MCP-1. Using a plethora of engineering and biological techniques, we characterized changes induced by cholesterol on the plasma membrane as well as in the cytoskeleton, in order to obtain an understanding of the detected changes. Results: We observed that cholesterol enriched monocytes exhibited faster, non-uniform rolling on the E-selectin-coated surfaces, for longer distances. They also demonstrated a significantly higher chemotactic response towards MCP-1. Cholesterol enrichment reduced the plasma membrane fluidity. We also identified significant changes in the expression and distribution of specific receptors implicated in rolling and chemotaxis. Cholesterol content also significantly regulated cell deformability and spreading behavior. Significance: This work provides an understanding of the cholesterol influenced biomechanical changes in monocytes and paves the path towards better understanding of the mechanistic aspects of diseases like atherosclerosis and hypercholesterolemia.