Endothelial-to-mesenchymal transition shapes the atherosclerotic plaque and modulates macrophage function

Endothelial cells can acquire a mesenchymal phenotype upon irritation [endothelial-to-mesenchymal transition (EndMT)]. Macrophages accumulate in the atherosclerotic plaque. This study addressed whether macrophages modulate EndMT and delineated a reciprocal effect of EndMT on macrophage functions in atherosclerosis. In atherosclerotic murine and human aortas, endothelial cells with mesenchymal markers were elevated by confocal microscopy and flow cytometric analysis. Increased EndMT master transcription factor Snai1 expression and extracellular matrix are consistent with enhanced EndMT in this condition. Hypoxia was detected in individual aortic EndMT cells in vivo and rapidly induced a similar EndMT phenotype in vitro. As a novel inducer of EndMT, macrophages, which are abundant in the atherosclerotic lesions, enhance mesothelial marker expression during coculture in vitro. In the reverse relationship, EndMT altered endothelial colony-stimulating factor expression. Functionally, EndMT cell-conditioned media attenuated macrophage proliferation, antigen-presenting cell marker expression, and TNF-α production in response to oxidized LDL but increased oxidized LDL uptake and scavenger receptor expression. These experiments demonstrate that macrophages promote partial EndMT. In turn, EndMT cells modulate macrophage phenotype and lipid uptake. Our data suggest that EndMT shapes macrophage and endothelial cell phenotypes, thus affecting internal atherosclerotic plaque in addition to surface structure.-Helmke, A., Casper, J., Nordlohne, J., David, S., Haller, H., Zeisberg, E. M., von Vietinghoff, S. Endothelial-to-mesenchymal transition shapes the atherosclerotic plaque and modulates macrophage function.