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In pathological intimal proliferations cells of various origins can be present. Next to the smooth muscle cells from the tunica media also adventitial fibroblasts, macrophages and bone marrow-derived progenitor cells contribute to the formation and differentiation of the neointima. A contribution of mature endothelial cells to the mesenchymal intimal population has been suggested as embryonic endothelial cells appeared to transdifferentiate into smooth muscle cells during the initial phases of media formation. In the present study we have studied the changes in the endothelial monolayer in cuff-induced neointima. A non-constrictive cuff was placed around the femoral artery in a transgenic Tie2LacZ reporter mouse strain. The animals were studied after 1, 2, 3, 7, 10, 14 and 21 days. Changes in the endothelial phenotype was investigated with (immuno)histochemistry (Ki67, vWF, ICAM, VCAM, CD31, CD34, AIA31240, elastin, sm-actin) in combination with β-galactosidase (beta-gal) staining (both light and electron microscopy). After cuff placement a rapid upregulation of mRNA expression of several inflammation related genes (TNFalpha, MCP1, GM-CSF, TLR-4) could be observed within the first two days. At three days the first morphological signs of remodeling were visible. The endothelial cells became activated, protruded into the lumen and detached at many places from the intact internal elastic lamel. The number of proliferating endothelial nuclei per mm2 increased significantly (0.0045 vs 0.00021 (control); p<0.005). Beta-gal expression (membrane bound and cytoplasmic) was solely confined to the endothelium. From day 5 the first subendothelial intimal cells were present. In these intimal cells a membrane bound β-gal precipitate was still detected. After 1.5 week these precipitates had disappeared. Tie2lacZ bone marrow transplantations to wild type mice and immunohistochemistry did not prove bone marrow contribution to the neo-intima. After 14 days the first signs of fragmentation of the internal elastic lamel were seen and medial smooth muscle cells started to migrate into the neointima. These data demonstrate that the endothelial monolayer is activated by the presence of perivascular granulocytes within the cuff area. It supports the idea that endothelial cells can contribute to the earliest fase of intimal formation. The role of these endothelial-derived intimal cells has to be elucidated.
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J. Vasc. Biol. 42, Sup:2 (2005) p69