Human macrophage pro-inflammatory polarization in response to free cholesterol and cholesterol remnants

Atherosclerosis is a chronic inflammatory disease of the blood vessels caused by elevated levels of lipoproteins. The hyperlipoproteinemia triggers a series of cellular changes, particularly the activation of the macrophages, which play a crucial role in the development and progression of atherosclerosis. The presence of free cholesterol (FC) in lipoproteins may contribute to macrophage stimulation. However, the mechanisms linking the accumulation of FC in macrophages to their pro-inflammatory activation remain poorly understood. Our research found a positive correlation between the number of pro-inflammatory macrophages (CD14 + CD16 + CD36^high) in visceral adipose tissue and the levels of LDL-C and cholesterol remnant particles in 56 healthy people. In contrast, the proportion of anti-inflammatory, alternatively activated macrophages (CD14 + CD16-CD163+) correlated negatively with HDL-C. Additionally, our in vitro study demonstrated that macrophages accumulating FC promoted a pro-inflammatory response, activating the TNF-α and chemokine CCL3 genes. Furthermore, the accumulation of FC in macrophages alters the surface receptors on macrophages (CD206 and CD16) and increases cellular granularity. Notably, the CD36 surface receptor and the ACAT and CD36 genes did not show a response. These results suggest a link between excessive FC accumulation and systemic inflammation to underlie the development of atherosclerosis.